DOI: 10.1002/asia.201300599

Copolymerization of Isoprene and Nonconjugated a,w-Dienes by Half-Sandwich Scandium Catalysts with and without a Coordinative Side Arm

Fang Guo,[a, b] Masayoshi Nishiura,[b, c] Yang Li,[a] and Zhaomin Hou*[a, b, c]

Dedicated to Prof. Chunli Bai on the occasion of his 60th birthday

Introduction

The synthesis of novel polymer materials with desired struc-tures and properties relies significantly on the developmentof new generations of polymerization catalysts. The cycloco-polymerization of a nonconjugated a,w-diene such as 1,5-hexadiene (HD) or 1,6-heptadiene (HPD) with a conjugated1,3-diene such as isoprene (IP) is of much interest, becauseit can afford cycloolefin copolymers that contain cyclic unitsformed by the cyclization of the nonconjugated diene mono-mer and C=C double-bond units derived from the conjugat-ed diene monomer.[1,2] Further functionalization of the re-

maining C=C double bonds in the cycloolefin copolymerscould also be possible to afford a broad range of new func-tionalized polymers with improved properties. However, thecopolymerization of nonconjugated dienes with conjugateddienes is usually rather difficult, because these two classesof monomers show very different reactivity for a given cata-lyst and in some cases conjugated dienes could act asa poison to the catalysts designed for the polymerization ofhigher olefins including nonconjugated a,w-diene.[3,4] Previ-ously, the copolymerization of HD and 1,7-octadiene withIP by a Sm/Li bimetallic allyl complex [(Me2CC5H4)2Sm-ACHTUNGTRENNUNG(C3H5)2–LiACHTUNGTRENNUNG(dme)] (dme=1,2-dimethoxyethane) was report-ed, but only a small amount of nonconjugated dienes (4–10 mol %) was incorporated in the copolymers.[4]

We recently reported that half-sandwich scandium–dialkylcomplexes such as 1–3, in combination with an equivalent of[Ph3C][B ACHTUNGTRENNUNG(C6F5)4], can serve as excellent catalysts for thepolymerization and copolymerization of a wide range of ole-fins,[5,6] such as the syndiospecific copolymerization of sty-rene with ethylene,[6a] isoprene,[6e] or caprolactone,[6h] andthe cyclocopolymerization of HD or HPD with ethylene andstyrene.[6i,j] During these studies, we became interested in ex-amining the activity of such half-sandwich scandium cata-lysts toward the copolymerization of conjugated 1,3-dieneswith nonconjugated a,w-dienes. To see the possible influ-ence of the ancillary ligands, two new half-sandwich Sc com-plexes that bear an N-heterocyclic carbene (NHC) unit (4)

Abstract: A series of half-sandwichscandium–dialkyl complexes that bearvarious auxiliary ligands have been ex-amined for the copolymerization of iso-prene (IP) with nonconjugated a,w-dienes such as 1,5-hexadiene (HD) and1,6-heptadiene (HPD). Significantligand influence on the catalytic activi-ty and selectivity has been observed.The thf-coordinated complex[(C5Me4SiMe3)ScACHTUNGTRENNUNG(CH2SiMe3)2ACHTUNGTRENNUNG(thf)] (2)and the methoxy side arm containingthe half-sandwich complex[(C5Me4C6H4OMe-o)Sc ACHTUNGTRENNUNG(CH2SiMe3)2](3), in combination with an equivalentof [Ph3C][B ACHTUNGTRENNUNG(C6F5)4], can serve as excel-lent catalysts for the random cycloco-

polymerizations of IP with HD andHPD. The resulting random HD–IP co-polymers contain five-membered-ringmethylene-1,3-cyclopentane (MCP),3,4-polyisoprene (3,4-IP), and 1,4-poly-isoprene (1,4-IP) units with controlla-ble HD incorporation in a range of 17–82 mol%. The random HPD–IP co-polymers possess six-membered-ringmethylene-1,3-cyclohexane (MCH),1,4-IP, and 3,4-IP units with HPD in-corporation in a range of 11–55 mol%.

By use of a catalyst that bearsa phosphine oxide group[{C5Me4SiMe2CH2P(O)Ph2}Sc-ACHTUNGTRENNUNG(CH2SiMe3)2] (5), the alternating co-polymerizations of IP with HD andHPD have been achieved for the firsttime in which HD and HPD are com-pletely cyclized to the MCP and MCHunits, respectively. More remarkably, inthe alternating copolymerization ofHPD and IP by 5, the regio- and ste-reospecific cis-MCH selectivity reachedas high as 99 %. The microstructuresand compositions of these copolymersshowed significant influences on theirmechanical properties.

Keywords: dienes · ligand effects ·polymerization · sandwichcomplexes · scandium

[a] Dr. F. Guo, Prof. Y. Li, Prof. Z. HouThe State Key Laboratory of Fine ChemicalsSchool of Chemical EngineeringDalian University of TechnologyDalian 116012 (China)Fax: (+81) 48-462-4665houz@riken.jp

[b] Dr. F. Guo, Dr. M. Nishiura, Prof. Z. HouOrganometallic Chemistry Laboratory, RIKEN2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

[c] Dr. M. Nishiura, Prof. Z. HouAdvanced Catalysis Research GroupRIKEN Center for Sustainable Resource Science2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

Supporting information for this article is available on the WWWunder http://dx.doi.org/10.1002/asia.201300599.

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FULL PAPER

and a phosphine oxide unit (5) as a coordinative side armwere also synthesized and examined. In this article, wereport the copolymerization of IP with HD and HPD cata-lyzed by a series of half-sandwich scandium–alkyl complexesthat bear different ancillary ligands. By choosing an appro-priate catalyst, both random and alternating copolymeriza-tions of IP with HD and HPD have been achieved for thefirst time, thereby affording a new family of cyclocopoly-mers with a wide range of HD and HPD contents and vary-ing microstructures. The mechanical properties of the copo-lymer products are also described.

Results and Discussion

Synthesis and Structures of Half-Sandwich Scandium–Dialkyl Complexes with NHC and Phosphine Oxide Side

Arms

The acid–base reaction between the C5Me4H–NHC ligand,prepared in situ by treatment of the phenylethylene-linked tetramethylcyclopentadiene–imidazolium iodidesalt [C5Me4HCH2CH(Ph) ACHTUNGTRENNUNG{NCHCHN ACHTUNGTRENNUNG(CH3)CH}I] withLiCH2SiMe3, and the scandium trialkyl complex [Sc-ACHTUNGTRENNUNG(CH2SiMe3)3 ACHTUNGTRENNUNG(thf)2] afforded the corresponding half-sand-wich scandium–dialkyl complex [(C5Me4�NHC)Sc-ACHTUNGTRENNUNG(CH2SiMe3)2] (4) with an NHC side arm bonding to themetal center (Scheme 1, top). The analogous reaction of [Sc-ACHTUNGTRENNUNG(CH2SiMe3)3 ACHTUNGTRENNUNG(thf)2] with the cyclopentadiene derivative

[HC5Me4CH2SiMe2(O)PPh2] that contains the phosphineoxide side arm did not give an isolable product. Alternative-ly, the one-pot metathetical reaction of [ScACHTUNGTRENNUNG(CH2SiMe3)2ACHTUNGTRENNUNG(thf)x]ACHTUNGTRENNUNG[BPh4]

[7] with LiC5Me4CH2SiMe2(O)PPh2 (1 equiv)easily yielded the chelating half-sandwich scandium dialkylcomplex [{C5Me4CH2SiMe2(O)PPh2}Sc ACHTUNGTRENNUNG(CH2SiMe3)2] (5)(Scheme 1, bottom).

Both 4 and 5 were fully characterized by 1H and 13C NMRspectroscopy, X-ray, and microelemental analyses. In thesolid state, the two CH2SiMe3 groups in 5 (Figure 1, right)

adopt a prone fashion, similar to those in 2 and 3.[6f] In con-trast, one CH2SiMe3 group in 4 is in a prone fashion, where-as the other CH2SiMe3 group adopts a supine form probablybecause of the steric hindrance of the NHC unit (Figure 1,left). The bond length of Sc�NHC (C9) in 4 (2.355(5) �) isalmost the same as that in [(Ind–NHC)Sc ACHTUNGTRENNUNG(CH2SiMe3)2](2.350(3) �).[8] The Sc�O bond length in 5 (2.062(2) �) iscomparable with that in the nonchelation phosphine oxideSc complex [(C5Me5)ScMe2{OP ACHTUNGTRENNUNG(tBu3)}] (2.072(1) �),[9] butsignificantly shorter than those in 2 (2.158(1) �) and 3(2.208(1) �), thereby suggesting that the coordination of thephosphine oxide unit in 5 is stronger than that of the thfligand in 2 and the methoxyphenyl unit in 3. The averagebond length of Sc�Cp in 5 (2.528(2) �; Cp=cyclopentadien-yl) is somewhat longer than those in 2–4 (2.470(2)–2.499(4) �), probably owing to the stronger coordination ofthe phosphine oxide unit in 5.

Complexes 4 and 5 are soluble in common organic sol-vents such as THF, toluene, and hexane, and showed well-resolved 1H NMR spectra in C6D6. The two protons of themethylene unit attached to the Cp ligand in 4 showed twodoublets at d=3.01 and 2.70 ppm, thus indicating that theCp�NHC chelation is rather rigid. The four methyl groupson the Cp ring gave four singlets at d=2.31, 2.24, 2.14, and1.28 ppm, which shows that 4 possesses C1 symmetry. Themethylene protons of the CH2SiMe3 groups in 4 gave fourdoublets, which suggests that the rotation around the Sc�C

Scheme 1. Synthesis of half-sandwich scandium–dialkyl complexes withN-heterocyclic carbene and phosphine oxide side arms.

Figure 1. ORTEP drawings of 4 (left) and 5 (right) with thermal ellip-soids set at 30% probability. Hydrogen atoms have been omitted forclarity. Selected bond lengths [�] and angles [8] of 4 : Sc�C1 2.240(5),Sc�C5 2.227(4), Sc�C9 2.355(5), Sc�Cp (avg) 2.499(4); C9�Sc�C1101.0(2), C9�Sc�C5 106.7(2), C1�Sc�C5 105.4(2), Sc�C1�Si1 122.5(2),Sc�C5�Si2 131.7(3). Selected bond lengths [�] and angles [8] of 5 : Sc�C1 2.243(2), Sc�C5 2.256(2), Sc�O1 2.062(2), Sc�Cp (avg) 2.528(2); O1�Sc�C1 102.93(7), O1�Sc�C5 103.15(8), C1�Sc�C5 103.81(9), Sc�C1�Si1122.8(1), Sc�C5�Si2 126.8(1).

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(methylene) bond is restricted. The methylene unit bondingto the P atom in 5 showed a doublet signal at d= 1.51 ppmwith JACHTUNGTRENNUNG(P,H)=13.6 Hz. The methyl groups on the Cp ring in5 showed two singlets at d=2.30 and 2.13 ppm, thereby sug-gesting that this molecule has Cs symmetry. The methyleneprotons of the CH2SiMe3 groups in 5 gave two doublets,which suggests that a free rotation of these groups is not al-lowed. The 31P{H} NMR spectrum of 5 showed a singlet atd= 46.6 ppm, which is d= 19 ppm lower-field shifted thanthat of the free ligand C5HMe4CH2SiMe2(O)PPh2

(27.9 ppm), thereby suggesting that the P=O group in 5 iscoordinated to the scandium metal center as observed in thesolid state. Such a downfield shift was also observed ina scandium phosphine oxide complex [(C5Me5)ScMe2{OP-ACHTUNGTRENNUNG(tBu3)}].[9]

Homopolymerization of HD, HPD, and IP

At first, the homopolymerization of HD, HPD, and IP wasexamined by using the half-sandwich scandium–dialkyl com-plexes that bear different Cp ligands (1–5) in combinationwith [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] as a cocatalyst. Significant ligand in-fluences were observed in all of these polymerizations, asshown in Tables 1, 2, and 3.

The homopolymerization of HD by the thf-free, amino-benzyl–scandium catalyst 1 afforded a soluble cyclopolymerthat contained cis- and trans-methylene-1,3-cyclopentane(MCP) units (83 %) and vinyltetramethylene (VTM) units(17 %) (Table 1, run 1).[6j] In contrast, the scandium com-plexes with an extra Lewis base ligand such as thf (2) ora coordinating side arm attached to the Cp ring (3–5) yield-ed insoluble cross-linked polymers under the same condi-tions (Table 1, runs 2–5).

In the polymerization of HPD, all of these complexes (1–5) afforded the soluble cyclopolymers that contained thesix-membered-ring methylene-1,3-cyclohexane (MCH) unitsas a major component (80–91 %) with a smaller amount offive-membered-ring ethylene-1,2-cyclopentane (ECP) units(9–20 %) (Table 2).[6i] The activity of the Lewis base contain-ing complexes 2–5 is about 6–10 times higher than that ofthe thf-free complex 1. The molecular weights of the poly-ACHTUNGTRENNUNG(HPD)s prepared by the chelation complexes 3–5 (Mn =

15 000–27 000) are generally higher than those by the non-chelation complexes 1 and 2 (Mn =3000–4000), thereby sug-gesting that the chain-termination reaction (probably b-Helimination) in the case of the chelation complexes 3–5could be suppressed to a larger extent.

Table 1. Homopolymerization of 1,5-hexadiene (HD).[a]

Run Cat. t [min] Conv. [%] Activity[b] Composition [mol %][c] Mn[d] [� 104] Mw/Mn

[d] Tg[e] [8C]

MCP (trans/cis) VTM

1 1 80 91 28 83 (86/14) 17 1.6 2.56 �72 2 1 100 2463 cross-linked polymer n.d.[f] n.d. n.d.3 3 10 100 246 cross-linked polymer n.d. n.d. n.d.4 4 1 100 2463 cross-linked polymer n.d. n.d. n.d.5 5 1 100 2463 cross-linked polymer n.d. n.d. n.d.

[a] Conditions: [Sc] (19 mmol), [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (19 mmol), monomer (9.5 mmol), toluene (6 mL), T =25 8C. [b] Kilograms of polymer (mol of Sc)�1 h�1.[c] Determined by 1H NMR spectroscopy, trans/cis determined by 13C NMR spectroscopy. [d] Determined by GPC in THF at 40 8C relative to polystyrenestandard. [e] Determined by DSC. [f] n.d.=not determined.

Table 2. Homopolymerization of 1,6-heptadiene (HPD).[a]

Run Cat. t [min] Conv. [%] Activity[b] Composition [mol %][c] Mn[d] [� 104] Mw/Mn

[d] Tg[e] [8C]

MCH (cis/trans) ECP (cis/trans)

1 1 90 83 27 91 (86/14) 9 (34/66) 0.4 1.99 522 2 15 89 171 91 (88/12) 9 (39/61) 0.3 6.21 573 3 15 72 140 90 (81/19) 10 (53/47) 2.7 1.69 704 4 10 100 288 85 (85/15) 15 (36/64) 2.2 1.73 835 5 10 100 288 80 (90/10) 20 (28/72) 1.5 2.47 67

[a] Conditions: [Sc] (19 mmol), [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (19 mmol), monomer (9.5 mmol), toluene (6 mL), T =25 8C. [b] Kilograms of polymer (mol of Sc)�1 h�1.[c] Determined by 13C NMR spectroscopy. [d] Determined by GPC in THF at 40 8C relative to polystyrene standard. [e] Determined by DSC.

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The thf-free aminobenzyl complex 1 and the ether-con-taining complexes 2 and 3 are all active in the polymeri-zation of IP (Table 3, runs 1–3).[6e,f] Unexpectedly, the NHC-and phosphine oxide side-arm-containing complexes 4 and 5showed no activity in the polymerization of IP under thesame conditions (Table 3, runs 4 and 5), possibly owing tothe steric bulkiness of the whole molecules.[10]

Copolymerization of HD with IP

Although complex 1 showed good performance for the ho-mopolymerization of both HD and IP, the copolymerizationof these two monomers gave a mixture of the two homopol-ymers; formation of a copolymer was not observed (Table 4,run 1). In contrast, the copolymerization of HD with IP bythe thf-containing complex 2 afforded soluble copolymersunder appropriate conditions, although the homopolymeri-zation of HD by 2 yielded insoluble cross-linked products.When a sufficient amount of IP was used in the copolymeri-zation with HD (IP/HD molar ratio �1:1) by 2, the solublerandom IP–HD copolymers that contained the five-mem-bered-ring MCP units, 3,4-polyisoprene (3,4-IP), and 1,4-polyisoprene (trans- and cis-1,4-IP) units were obtained se-lectively (Table 4, runs 2–5). If an excess amount of HDover IP (HD/IP= 3:2) was used, insoluble cross-linked poly-mers were obtained (Table 4, run 6). The Cp–ether chelationcomplex 3 selectively catalyzed the copolymerization of HDand IP in a wide range of monomer-feed ratios (HD/IP=1:4to 4:1), thereby affording the random IP–HD copolymerswith the MCP content ranging from 23 to 82 mol %(Table 4, runs 7–12). The Cp�NHC chelation complex 4,which was inert for IP homopolymerization and yieldedcross-linked polymers in HD homopolymerization, showedalmost no activity for the copolymerization of HD and IP(Table 4, run 13). Surprisingly to us, the Cp–phosphine oxidechelation complex 5 showed high activity for the copolymer-ization of HD and IP to give soluble alternating HD–IP co-polymers that contained 3,4- and 1,4-IP units and MCPunits, although it was inactive for the homopolymerizationof IP and produced insoluble cross-linked polymers in the

homopolymerization of HD. The resulting copolymersalways showed alternating sequences with the MCP contentin a relatively narrow range of 50 to 59 mol %, irrespectiveof the HD/IP feed ratio (1:4 to 4:1) (Table 4, runs 14–19).These results suggest that alternating copolymerization ofHD and IP is much more favorable than the homopolymeri-zation of either monomer. Such preference of copolymeriza-tion to homopolymerization has also been observed previ-ously in other cases such as the copolymerization of ethyl-ene with norbornene[6b, 11] or dicyclopentadiene.[6c]

The gel permeation chromatography (GPC) analysesshowed that the HD–IP copolymers prepared by 2, 3, and 5all gave relatively narrow, unimodal molecular distributions,which suggests the predominance of a single-site catalystspecies. The glass transition temperature (Tg) values of thecopolymers varied in the range of �48 to �8 8C, dependingto some extent on the IP (or HD) content.

Because no NMR spectroscopic information on the HD–IP copolymers could be found in the literature, we then car-ried out a detailed characterization of our copolymer prod-ucts by means of 1H, 13C, DEPT-13C, HSQC (heteronuclearsingular quantum correlation), H2BC (heteronuclear two-bond correlation), and HMBC (heteronuclear multiple-bondcorrelation) NMR spectroscopic analyses (see the Support-ing Information) to establish the co-monomer incorporationand distribution in the copolymer chains. Relatively weaksignals were carefully assigned by comparison of the spectraldata with those of copolymers with different monomer con-tents and those of related polymers reported previously.[6f,i,j]

It was revealed that the HD–IP copolymers prepared by 2and 3 are random copolymers that contain IP–IP[6f] andMCP–MCP blocks[6j] and trans-1,4-IP–MCP sequences. Asa typical example, the aliphatic region of the 13C NMR spec-trum of a random HD–IP copolymer prepared by 2(Table 4, run 2) is shown in Figure 2. In contrast, the HD–IPcopolymers prepared by 5 gave much simpler 13C NMRspectra, which showed typical alternating features with dom-inant trans-1,4-IP–MCP and 3,4-IP–MCP sequences, a traceamount of HD–HD blocks; no IP–IP blocks were observed(see Figure 3).

Table 3. Homopolymerization of isoprene (IP).[a]

Run Cat. t [min] Conv. [%] Activity[b] Composition [mol %][c] Mn[d] [� 104] Mw/Mn

[d] Tg[e] [8C]

1,4-IP (trans/cis) 3,4-IP

1 1 50 88 36 30 (38/62) 70 4.3 1.17 �62 2 240 100 8 61 (94/6) 39 4.5 1.11 �353 3 60 95 32 88 (91/9) 12 7.9 1.35 �584 4 300 0 05 5 300 0 0

[a] Conditions: [Sc] (19 mmol), [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (19 mmol), monomer (9.5 mmol), toluene (6 mL), T =25 8C. [b] Kilograms of polymer (mol of Sc)�1 h�1.[c] Determined by 1H NMR spectroscopy, trans/cis determined by 13C NMR spectroscopy. [d] Determined by GPC in THF at 40 8C relative to polystyrenestandard. [e] Determined by DSC.

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Table 4. Copolymerization of 1,5-hexadiene (HD) with isoprene (IP).[a]

Run Cat. HD[b] IP[b] t [min] Yield [g] Activity[c] Composition [mol %][d] Mn[e] [� 104] Mw/Mn

[e] Tg[f] [8C]

1,4-IP (trans/cis) 3,4-IP MCP

1 1 250 250 25 0.550 69 –[g] n.d.[h] n.d. n.d.2 2 250 250 90 0.552 19 44 (95/5) 20 36 3.2 1.52 �303[i] 2 500 500 90 0.560 20 50 (90/10) 30 20 4.6 1.11 �314 2 100 400 90 0.158 6 48 (89/11) 35 17 1.7 1.09 �315 2 200 300 90 0.649 23 50 (89/11) 32 18 2.3 1.35 �296 2 300 200 90 0.629 22 cross-linked polymer n.d. n.d. n.d.7 3 250 250 60 0.590 31 44 (33/67) 17 39 4.7 1.44 �188[i] 3 500 500 60 1.264 66 37 (42/58) 10 53 7.7 1.21 �259 3 100 400 60 0.583 31 67 (85/15) 10 23 4.1 1.44 �4810 3 200 300 60 0.590 31 48 (38/67) 16 36 3.2 1.78 �2311 3 300 200 60 0.641 32 27 (51/49) 9 64 1.9 2.79 �1412 3 400 100 60 0.632 33 13 (52/48) 5 82 1.6 2.67 �813 4 250 250 300 trace 014 5 250 250 25 0.552 70 37 (99/1) 12 51 4.1 1.54 �1615[i] 5 500 500 25 0.854 108 36 (98/2) 12 52 5.2 1.94 �1316 5 100 400 25 0.172 22 44 (99/1) 6 50 1.2 1.69 �3017 5 200 300 25 0.464 59 40 (99/1) 6 54 3.1 1.68 �2518 5 300 200 25 0.474 60 34 (98/2) 7 59 3.8 1.64 �1919 5 400 100 25 0.201 25 31 (94/6) 10 59 2.2 1.66 �18

[a] Conditions: [Sc] (19 mmol), [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (19 mmol), toluene (6 mL), T =25 8C, unless otherwise noted. [b] Molar ratio to [Sc]. [c] Kilograms ofpolymer (mol of Sc)�1 h�1. [d] Determined by 1H NMR spectroscopy, trans/cis determined by 13C NMR spectroscopy. [e] Determined by GPC in THF at40 8C relative to polystyrene standard. [f] Determined by DSC. [g] A mixture of homopoly(HD) and homopoly(IP). [h] n.d.=not determined. [i] Toluene(12 mL).

Figure 2. Aliphatic part of the 13C NMR spectrum of a random HD–IPcopolymer obtained in run 2 of Table 4.

Figure 3. Aliphatic part of the 13C NMR spectrum of an alternating HD–IP copolymer obtained in run 14 of Table 4.

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Copolymerization of HPD and IP

Similar to the copolymerization of HD with IP, complexes1 and 4 are not effective for the copolymerization of HPDand IP (Table 5, runs 1 and 11). However, the thf-coordinat-ed complex 2 efficiently catalyzed the random copolymeri-zation of HPD and IP when a sufficient amount of IP (IP/HPD�1) was used (Table 5, run 2–5). The HPD monomerwas selectively transformed to the MCH unit, whereas theECP unit was not observed in the copolymerization with IP.The MCH content in the copolymers increased as the HPD/IP feed ratio was raised in the range of 1:4 to 1:1. The re-sulting HPD–IP copolymers showed relatively high molecu-lar weights (Mn = 2.2–4.2 � 104) and narrow molecular-weightdistributions (Mw/Mn =1.25–1.41) relative to the homopoly-ACHTUNGTRENNUNG(HPD) prepared by 2 under the similar conditions (Mn =3 �103, Mw/Mn =6.21). These results suggest that the presenceof IP could enhance the MCH selectivity and suppress theb-H elimination in the (co)polymerization of HPD.[6i] Whenan excess amount of HPD (HPD/IP =3:2) was used, a muchbroader molecular-weight distribution (Mw/Mn =4.05) wasobserved (Table 5, run 6). The copolymerization of HPDwith IP by the Cp–ether chelation complex 3 also affordedthe random HPD–IP copolymers with high MCH selectivityin the cyclization of HPD (Table 5, runs 7–10).

Although the Cp–phosphine oxide chelation complex 5was inert for the homopolymerization of IP, it showed highactivity for the copolymerization of IP with HPD in thepresence of both monomers to afford the alternating (ratherthan random) HPD–IP copolymers (Table 5, runs 12–15).More remarkably, the regio- and stereospecific cis-MCH for-mation could be achieved as high as 99 % when a sufficientamount of IP was present (Table 5, run 15). When an excessamount of HPD (HPD/IP=3:2) was used, the formation ofa small amount of the ECP units (5 mol %) in the copoly-mers was observed (Table 5, run 16). These results suggestthat the cyclization step of the HPD (co)polymerizationcould be influenced by the IP co-monomer. The GPC curvesof the HPD–IP copolymers are unimodal, with high molecu-lar weights (Mn = 1.9–9.1 � 104) and narrow molecular weightdistributions (Mw/Mn =1.42–1.60), thus indicating the pre-dominance of a single-site active catalyst species.

As in the case of the HD–IP copolymers, the HPD–IP co-polymers were also characterized by the 1H, 13C, DEPT-13C,HSQC, H2BC, and HMBC NMR spectroscopic analyses(see the Supporting Information). The 13C NMR spectra ofa typical random HPD–IP copolymer prepared by 2(Table 5, run 2) and a typical alternating HPD–IP copolymerprepared by 5 (Table 5, run 12) are shown in Figures 4 and5, respectively. The random HPD–IP copolymers contained

Table 5. Copolymerization of 1,6-heptadiene (HPD) with isoprene (IP).[a]

Run Cat. HPD[b] IP[b] t [min] Yield [g] Activity[c] Composition [mol %][d] Mn[e] ACHTUNGTRENNUNG[�104] Mw/Mn

[e] Tg[f] [8C]

3,4-IP 1,4-IP(cis/trans) MCH(cis/trans) ECP(cis/trans)

1 1 250 250 30 0.636 67 –[g] n.d.[h] n.d. n.d.2 2 250 250 60 0.294 15 21 44 (8/92) 35 (80/20) 0 2.2 1.41 �143[i] 2 500 500 60 0.457 24 22 53 (4/96) 25 (90/10) 0 4.2 1.25 �164 2 100 400 60 0.282 15 42 47 (9/91) 11 (95/15) 0 2.4 1.35 �215 2 200 300 60 0.260 14 25 53 (4/96) 22 (89/11) 0 2.3 1.36 �196 2 300 200 60 0.686 36 13 24 (5/95) 60 (85/15) 3 (45/55) 1.0 4.05 187 3 250 250 30 0.641 67 12 38 (66/34) 50 (92/8) 0 5.7 1.41 238 3 100 400 30 0.370 39 15 57 (71/29) 28 (91/9) 0 5.0 1.21 �179 3 200 300 30 0.463 49 17 44 (60/40) 39 (95/5) 0 4.0 1.24 310 3 300 200 30 0.698 73 13 39 (55/45) 35 (91/9) 12 (38/62) 3.0 1.75 2811 4 250 250 120 trace 012 5 250 250 30 0.710 75 10 36 (7/93) 54 (97/3) 0 4.9 1.50 2013[i] 5 500 500 30 1.379 145 16 29 (8/92) 55 (97/3) 0 9.1 1.60 3014 5 100 400 30 0.236 25 10 46 (3/97) 44 (98/1) 0 1.9 1.42 1515 5 200 300 30 0.601 63 18 33 (7/93) 49 (99/1) 0 3.9 1.50 3016 5 300 200 30 0.729 77 11 24 (7/93) 60 (88/12) 5 (38/62) 4.2 1.59 27

[a] Conditions: [Sc] (19 mmol), [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (19 mmol), toluene (6 mL), T=25 8C, unless otherwise noted. [b] Molar ratio to [Sc]. [c] Kilograms of poly-mer (mol of Sc)�1 h�1. [d] Determined by 1H NMR spectroscopy, trans/cis determined by 13C NMR spectroscopy. [e] Determined by GPC in THF at 40 8C rel-ative to polystyrene standard. [f] Determined by DSC. [g] A mixture of homopoly ACHTUNGTRENNUNG(HPD) and homopoly(IP). [h] n.d.=not determined. [i] Toluene (12 mL).

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the IP–IP[6f] and MCH–MCH blocks[6i] as well as trans-1,4-IP–MCH and cis-1,4-IP–MCH sequences (Figure 4). The al-ternating HD–IP copolymer possessed the trans-1,4-IP–MCH, cis-1,4-IP–MCH, and 3,4-IP–MCH sequences as maincomponents with a trace amount of HPD–HPD blocks; noIP–IP blocks were observed (Figure 5).

Polymerization Mechanism

The reaction mechanisms of the homopolymerization ofHD, HPD, and IP catalyzed by complexes 1–3 have been de-scribed in our previous studies.[6f,i,j] On the basis of previous

studies and the results described above, the possible scenar-ios of the HD–IP copolymerization and the HPD–IP copoly-merization are shown in Schemes 2 and 3, respectively. Ineach case, the polymerization might be initiated by the 3,4-insertion of an IP monomer into the Sc�alkyl bond to givean h3–s-allyl intermediate (a).[6f] The isomerization of the in-termediate (a) could give the syn-h3–p-allylic intermediate(b) or the anti-h3–p-allylic intermediate (c). The coordina-tion and 2,1-insertion of a C=C double bond of HD[6j] intothe Sc�IP bond in a, b, or c would yield d, e, or f, respective-ly (Scheme 2). The intramolecular 2,1-insertion of the re-maining C=C double bond of the HD unit into the Sc�Cs bond in d, e, or f followed by IP coordination shouldafford g, h, or i, which contain the 3,4-IP–MCP, trans-1,4-IP–MCP, or cis-1,4-IP–MCP sequence, respectively. If the coor-dination and insertion of IP take place at a, b, or c followedby HD insertion (random copolymerization), the 3,4-IP–IP–MCH, trans-1,4-IP–IP–MCH, or cis-1,4-IP–IP–MCH unitwould be formed, respectively. In the case of 5, because thesuccessive insertion of IP (IP homopolymerization) is diffi-cult, the alternating insertion of IP and HD could be pre-ferred even in the presence of an excess amount of IP.Moreover, the presence (or coordination) of IP around theactive metal site might prevent cross-linking reactions of theHD units.

The copolymerization of HPD with IP could proceed sim-ilarly via a, b, and c, but the insertion of HPD may takeplace in a 1,2-fashion to give D, E, and F, respectively (Sche-me 3).[6i] The subsequent intramolecular insertion (i.e. , cycli-zation) of the remaining C=C double bond of the HPD unitin D, E, and F followed by insertion of IP could afford thealternating 3,4-IP–MCH, trans-1,4-IP–MCH, and cis-1,4-IP–MCH sequences, respectively. The presence (or coordina-tion) of IP around the metal center might suppress the 2,1-insertion of HPD due to steric congestion, thus accountingfor the lack of the ECP units in the copolymers.[6i]

Mechanical Properties of the HD–IP and HPD–IPCopolymers

The tensile mechanical properties of some representativerandom and alternating HD–IP and HPD–IP copolymersprepared by 3 and 5, together with those of the homopoly-mers, are shown in Table 6. The homopolymers of IP, HD,and HPD generally showed poor tensile mechanical proper-ties. Poly(HD) and poly(IP) are too sticky to give a measura-ble value, and poly ACHTUNGTRENNUNG(HPD) is brittle and easy to break uponelongation (e= 3.7 %) (Table 6, run 2). The random HD–IPcopolymers are also too weak to carry out measurements,similar to poly(HD) and poly(IP). In contrast, the alternat-ing HD–IP copolymers showed good flexibility, albeit withpoor strength (Table 6, run 5). In the case of the HPD–IPcopolymers, both random and alternating copolymersshowed similarly good flexibility (elongation at break)(Table 6, runs 6 and 7), but the Young�s modulus of the al-ternating HPD–IP copolymer (2860 MPa) was much higherthan that of the random analogue (739 MPa). These results

Figure 4. Aliphatic part of the 13C NMR spectrum of a random HPD–IPcopolymer obtained in run 2 of Table 5.

Figure 5. Aliphatic part of the 13C NMR spectrum of an alternatingHPD–IP copolymer obtained in run 12 of Table 5.

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demonstrate that the mechanical properties of the copoly-mers are significantly influenced by their microstructuresand compositions.

Conclusion

We have demonstrated that half-sandwich scandium–dialkylcomplexes in combination with an equivalent of [Ph3C][B-ACHTUNGTRENNUNG(C6F5)4] can serve as excellent catalysts for the copolymeri-zation of nonconjugated a,w-dienes such as HD and HPDwith IP, with the activity and selectivity being significantlydependent on the ancillary ligands. The thf-containing com-plex 2 and the Cp–ether chelation complex 3 promoted therandom copolymerizations of IP with HD and HPD toafford the cyclopolymer materials that contain the five-membered-ring MCP units and the six-membered-ringMCH units, respectively. In contrast, the Cp–phosphineoxide chelation complex 5 selectively yielded the alternatingIP–HD and IP–HPD copolymers. The alternating copoly-mers generally showed better mechanical properties thanthe random analogues, and copolymers that had the six-membered-ring MCH units exhibited much higher stiffnessand strength than those with the five-membered-ring MCPunits, although both showed much better flexibility than thehomopolymers.

Scheme 2. Possible scenarios of 1,5-hexadiene–isoprene copolymerization catalyzed by cationic half-sandwich scandium species.

Table 6. Mechanical properties of HD–IP and HPD–IP copolymers.[a]

Run Sample Cat. Mn

[� 104]Mw/Mn

D/IP[b]

E[c]

[MPa]s[d]

[MPa]e[e]

[%]

1 poly(HD) 1 1.6 2.56 100/0 –[f] – –2 poly ACHTUNGTRENNUNG(HPD) 3 2.7 1.69 100/0 3750 109 3.73 poly(IP) 3 7.9 1.35 0/100 –[f] – –4 poly ACHTUNGTRENNUNG(HD-co-

IP)3 7.7 1.21 53/47 –[f] – –

5 poly(HD-alt-IP)

5 5.2 1.94 52/48 4.0 0.9 321

6 poly(HPD-co-IP)

3 5.7 1.41 55/45 739 19.6 461

7 poly(HPD-alt-IP)

5 9.1 1.60 54/46 2860 66.6 449

[a] Samples with approximately 200 mm thickness were measured at anextension rate of 20 mm min�1. [b] Molar ratio calculated from 1H NMRspectroscopy; D =HD or HPD. [c] Young�s modulus. [d] Tensile strength.[e] Elongation at break. [f] Samples were too sticky to give a measurablevalue.

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Experimental Section

General Procedures and Materials

All manipulations of air- and moisture-sensitive compounds were per-formed under a dry and oxygen-free nitrogen atmosphere by use of stan-dard Schlenk techniques or under a nitrogen atmosphere in a MBraunglovebox. Nitrogen (Takachiho Chemical Industrial Co., Ltd.) was puri-fied by being passed through a Dryclean column (4 A molecular sieves,Nikka Seiko Co.) and a Gasclean GC-XR column (Nikka Seiko Co.).The nitrogen in the glovebox was constantly circulated through a copper/molecular-sieve catalyst unit. The oxygen and moisture concentrations inthe glovebox atmosphere were monitored with an O2/H2O Combi-Ana-lyzer (MBraun) to ensure both were always below 1 ppm. All solventswere purified with a SPS-800 solvent purification system (MBraun) andstored over fresh Na chips in the glovebox. Samples of Sc complexes forNMR spectroscopic measurements were prepared in the glovebox with J.Young valve NMR spectroscopy tubes. The NMR (1H, 13C, 31P) spectrawere recorded with a JEOL JNM-EX 300 or JNM-EX 400 spectrometer.The 31P NMR spectra were referenced to external 85% H3PO4. Elemen-tal analyses were performed with a Micro Corder JM10 (J-Science LabCo.). Isoprene (IP) was purchased from TCI, dried by stirring with CaH2

for 24 h, vacuum-transferred, and degassed by two freeze–pump–thawcycles. HD and HPD were purchased from TCI, dried over Na chips andtripropylaluminum, vacuum-transferred, and degassed by two freeze–pump–thaw cycles. [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] was purchased from Tosoh FinechemCorporation and used without purification. Me3SiCH2Li (1.0 m in pen-tane) was purchased from Aldrich and used as a white solid after remov-al of the solvent. MethylACHTUNGTRENNUNG(diphenyl)phosphine oxide, nBuLi (2.27 m inhexane), and chlorodimethyl(2,3,4,5-tetramethylcyclopenta-2,4-dienyl)si-lane were purchased from TCI, Kanto Chemical Co., Inc., andAldrich, respectively, and used without purification.[(C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2] (1),[6d] [(C5Me4SiMe3)Sc-ACHTUNGTRENNUNG(CH2SiMe3)2 ACHTUNGTRENNUNG(thf)] (2),[6a] [(C5Me4C6H4OMe-o)Sc ACHTUNGTRENNUNG(CH2SiMe3)2] (3),[6f]

C5Me4NHCMeI (4 a),[12] and [Et3NH] ACHTUNGTRENNUNG[BPh4][13] were synthesized as de-

scribed previously. The deuterated solvents [D6]benzene (99.6 atom %D), [D8]THF (99.6 atom % D), CDCl3 (99.8 atom % D), and 1,1,2,2-[D2]tetrachloroethane (99.6 atom % D) were obtained from CambridgeIsotope.

The NMR spectroscopic data of the polymer products were obtainedwith a JEOL JNM-EX 300 and JNM-ECA 600 spectrometer in 1,1,2,2-[D2]tetrachloroethane at 80 8C. All 2D NMR spectroscopic experimentswere performed with a JEOL ECA 600 NMR spectrometer with a 5 mmgradient tunable broad-band double-resonance JEOL FGTH5 probe op-

Scheme 3. Possible scenarios of 1,6-heptadiene–isoprene copolymerization catalyzed by cationic half-sandwich scandium species.

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erating at 600.17 MHz for 1H and 150.91 MHz for 13C NMR spectroscopy.Heteronuclear 2D 1H–13C HSQC, H2BC, HMBC, and HSQC-TOCSYexperiments were measured by using standard NMR spectroscopic pulsesequence of Delta version 5.01; typical data matrix sizes were 256 and1 K points and were zero-filled to 512 points or linear predicted to 1 K inthe F1 domain prior to FT. The H2BC experiments were performed withthe constant time delay of 22 ms and low-pass J filters in the range of120–160 Hz. The HMBC experiments were measured using 50 or 62.5 msof the duration time for long-range coupling. The editing HSQC-TOCSYexperiments were measured using a mixing time of 5, 15, 30, or 45 ms.Typical conditions for 13C NMR spectroscopic experiments were as fol-lows: 458 pulse width, 4.57 ms; acquisition time, 0.72 s; sweep width45290 Hz; relaxation delay, 0.89 s; number of acquisitions, 6400; datasize, 32 K; line broadening 2.0 Hz. Methine and methylene carbon atomswere distinguished by the DEPT spectrum. Direct 1H–13C correlationswere established by HSQC spectral data. The H2BC and HMBC cross-peaks from vinyl protons were used to assign IP, IP–MCP, and IP–MCHunits.

The molecular weights and the molecular-weight distributions of thepolymers were determined at 40 8C by GPC with a HLC-8220 GPC appa-ratus (Tosoh Corporation). THF was employed as an eluent at a flowrate of 0.35 mL min�1. The calibration was made by polystyrene standard.The differential scanning calorimetry (DSC) measurements were per-formed with a DSC6220 (SII Co.) at a rate of 20 8C min�1. Any thermalhistory difference in the polymers was eliminated by first heating thespecimen to 200 8C, cooling at 20 8C min�1 to �100 8C, and then recordingthe second DSC scan.

X-ray Crystallographic Analysis

A crystal was selected and sealed in a thin-walled glass capillary undera microscope in a glovebox. Data collections were performed at �100 8Cwith a Bruker Smart Apex diffractometer with a CCD area detectorusing graphite-monochromated MoKa radiation (l=0.71069 �). The de-termination of crystal class and unit cells was carried out by using theSMART program package. The raw frame data were processed usingSAINT and SADABS to yield the reflection data file. The structureswere solved by using the SHELXTL program. Refinements were per-formed on F2 anisotropically for all the non-hydrogen atoms by the full-matrix least-squares method. The analytical scattering factors for neutralatoms were used throughout the analysis. The hydrogen atoms wereplaced at the calculated positions and were included in the structure cal-culation without further refinement of the parameters. The residual elec-tron densities were of no chemical significance.

CCDC 916490 (4) and 916491 (5) contain the supplementary crystallo-graphic data for this paper. These data can be obtained free of chargefrom The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-c.uk/data_request/cif.

Preparation of [{C5Me4ACHTUNGTRENNUNG(NHC)}Sc ACHTUNGTRENNUNG(CH2SiMe3)2] (4)

In a glovebox, a solution of Me3SiCH2Li (0.074 g, 0.50 mmol) in THF(2.0 mL) was added dropwise to a solution of C5Me4NHCMeI (4a)(0.341 g, 0.50 mmol) in hexane (6.0 mL), and the solution was stirred atroom temperature for 20 min. A solution of [Sc ACHTUNGTRENNUNG(CH2SiMe3)3ACHTUNGTRENNUNG(thf)2](0.353 g, 0.50 mmol) in THF (8.0 mL) was added dropwise to the solutionand stirred at room temperature for 2 h. The solvent was removed underreduced pressure. The residue was extracted with toluene. After reduc-tion of the solution volume (1 mL) under reduced pressure, the solutionwas cooled to �30 8C to give 4 as colorless crystals (0.200 g, 76 % yield).1H NMR (300 MHz, C6D6, RT): d=7.25–7.28 (m, 2 H; PhH), 7.09–7.12(m, 3H; PhH), 5.90 (d, J ACHTUNGTRENNUNG(H,H) =1.8 Hz, 1H; NCH), 5.62 (d, J ACHTUNGTRENNUNG(H,H) =

1.5 Hz, 1 H; NCH), 5.24 (dd, J ACHTUNGTRENNUNG(H,H) =11.5, J ACHTUNGTRENNUNG(H,H) =1.1 Hz, 1 H; Ph�CH(Im)�CH2�Cp), 3.27 (s, 3H; N�CH3), 3.01 (dd, J ACHTUNGTRENNUNG(H,H) = 14.3, J-ACHTUNGTRENNUNG(H,H) =1.6 Hz, 1 H; Ph�CH(Im)�CH2�Cp), 2.70 (dd, J ACHTUNGTRENNUNG(H,H) =14.3, J-ACHTUNGTRENNUNG(H,H) =11.7 Hz, 1H; Ph�CH(Im)�CH2�Cp), 2.31 (s, 3 H; Cp�CH3), 2.24(s, 3 H; Cp�CH3), 2.14 (s, 3 H; Cp�CH3), 1.28 (s, 3 H; Cp�CH3), 0.50 (s,9H; SiMe3), 0.25–0.27 (m, 10H; SiMe3 and Sc-CH2SiMe3), �0.01 (d, J-ACHTUNGTRENNUNG(H,H) =10.3 Hz, 1H; Sc�CH2SiMe3), �0.23 (d, J ACHTUNGTRENNUNG(H,H) =10.3 Hz, 1H;Sc�CH2SiMe3), �0.36 ppm (d, J ACHTUNGTRENNUNG(H,H) =11.7 Hz, 1H; Sc�CH2SiMe3);

13C NMR (75 MHz, C6D6, RT): d=4.52, 4.97 (s; SiCH3), 10.33, 11.46,12.90, 13.00 (s; CpMe), 21.39 (s; Ph�CH(Im)�CH2�Cp), 32.77, 38.03 (s;Sc�CH2SiMe3), 64.72 (s; Ph�CH(Im)�CH2�Cp), 116.93, 118.89, 119.05,120.53, 125.64 (Cp ring carbon atoms), 117.94, 119.75 (s; NCH), 128.50,129.02, 129.21, 129.27, 129.42 (aromatic carbon atoms), 137.91 ppm (Sc�CN); elemental analysis calcd (%) for C29H47N2ScSi2·0.2C7H8: C 67.27, H8.66, N 5.16; found: C 66.93, H 8.76, N 4.90.

Preparation of [{C5Me4SiMe2CH2P(O)Ph2}Sc ACHTUNGTRENNUNG(CH2SiMe3)2] (5)

A solution of nBuLi in hexane (3.61 mL, 2.77 mol L�1) was added drop-wise to a solution of methyl ACHTUNGTRENNUNG(diphenyl)phosphine oxide (2.162 g, 10 mmol)in THF (15 mL), and the solution was stirred at room temperature for30 min to give Ph2P(O)CH2Li. Ph2P(O)CH2Li in THF was added drop-wise to a solution of chlorodimethyl(2,3,4,5-tetramethylcyclopenta-2,4-di-enyl)silane (2.658 g, 12 mmol) in THF (15 mL) in a Schlenk tube withTeflon stopcock. This tube was taken outside and heated at 50 8C for 6 d.The solvent was removed under reduced pressure. The residue was dis-solved in toluene and filtered. The solvent of the filtrate was removedunder reduced pressure. The residue was washed with hexane to leave anorange solid, C5Me4H(SiMe2CH2POPh2) (5a ; 2.999 g, 76 % yield).1H NMR (300 MHz, C6D6, RT): d=7.92 (m, 4H; PhH), 7.06 (m, 6 H;PhH), 2.90 (s, 1 H; Cp�H) 1.83 (s, 6 H; Cp�CH3), 1.78 (s, 6 H; Cp�CH3),1.48, 1.43 (d, J ACHTUNGTRENNUNG(P,H)=13.6 Hz, 2 H; P�CH2�Si�Cp), 0.14 ppm (s, 6H; Si�CH3); 31P NMR (160 MHz, C6D6, RT): d =27.9 ppm.

A solution of Me3SiCH2Li (0.724 g, 7.7 mmol) in THF (10 mL) wasadded to a solution of C5Me4H(SiMe2CH2POPh2) (2.762 g, 7.0 mmol) inTHF (10 mL), and the solution was stirred at room temperature for 2 h.The solvent was removed under reduced pressure. The residue waswashed with hexane to leave an orange solid C5Me4(SiMe2CH2POPh2)Li(5b ; 2.747 g, 98% yield). 1H NMR (300 MHz, C6D6, RT): d=7.66 (m,4H; PhH), 7.38 (m, 6H; PhH), 1.98 (s, 6 H; Cp�CH3), 1.89 (s, 6H; Cp�CH3), 1.23, 0.84 (d, J ACHTUNGTRENNUNG(P,H)=13.6 Hz, 2H; P�CH2�Si�Cp), 0.01 ppm (s,6H; Si�CH3); 31P NMR (160 MHz, C6D6, RT): d=37.3 ppm.

A solution of [Et3NH] ACHTUNGTRENNUNG[BPh4] (2.528 g, 6.0 mmol) in THF (10 mL) wasadded to a solution of [Sc ACHTUNGTRENNUNG(CH2SiMe3)3 ACHTUNGTRENNUNG(thf)2] (2.702 g, 6.0 mmol) in THF(10 mL), and the solution was stirred at room temperature for 30 min. Asolution of C5Me4(SiMe2CH2POPh2)Li in THF (10 mL) was added to thesolution of [Sc ACHTUNGTRENNUNG(CH2SiMe3)2] ACHTUNGTRENNUNG[BPh4] and stirred at room temperature for30 min. After removal of the solvent, the residue was extracted withhexane. The solvent was removed under reduced pressure. Recrystalliza-tion from toluene solution at �30 8C gave 5 as colorless crystals (2.320 g,65% yield). 1H NMR (300 MHz, C6D6, RT): d =7.46–7.54 (m, 4 H; PhH),6.99–7.03 (m, 6H; PhH), 2.29 (s, 6H; Cp�CH3), 2.12 (s, 6 H; Cp�CH3),1.51 (d, J ACHTUNGTRENNUNG(P,H) =13.6 Hz, 2 H; P�CH2�Si�Cp), 0.35 (s, 18H; SiMe), 0 (s,6H; Si�CH3), �0.09 (d, J ACHTUNGTRENNUNG(H,H) =11.4 Hz, 2 H; Sc�CH2SiMe3),�0.30 ppm (d, J ACHTUNGTRENNUNG(H,H) = 11.4 Hz, 2 H; Sc�CH2SiMe3); 13C NMR (75 MHz,C6D6, RT): d=2.06 (s; SiMe2), 4.49 (s; SiMe3), 12.55 (s; CpMe), 15.35 (s;CpMe), 16.92 (s; CH2), 17.57 (s; CH2) 104.45 (s; Cp ring), 124.67 (s; Cpring), 125.50 (s; Cp ring), 128.97 (d, J ACHTUNGTRENNUNG(P,C)=13.1 Hz; ipso-Ph), 130.78 (d,J ACHTUNGTRENNUNG(P,C)=10.6 Hz; o-Ph), 131.89 (s; p-Ph), 132.95 ppm (s; m-Ph); 31P NMR(160 MHz, C6D6, RT): d= 46.6 ppm; elemental analysis calcd (%) forC32H52OPScSi3: C 62.70, H 8.55; found: C 62.79, H 8.47.

Typical Procedure for 1,5-Hexadiene Homopolymerization

For a typical polymerization (Table 1, run 1): In a glovebox, 1,5-hexa-diene (783 mg, 9.5 mmol) was added under vigorous stirring to a reactionmixture of 1 (10 mg, 19 mmol) and [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (18 mg, 19 mmol) intoluene (6 mL). Polymerization was terminated by the addition of metha-nol after 80 min. The resulting mixture was poured into a large amountof methanol to precipitate the polymer product, which was washed withmethanol and dried under vacuum at 60 8C to a constant weight. TheVTM and MCP contents of the HD homopolymer were calculated ac-cording to the formula [Eqs. (1) and (2)]:

VTM ðmol %Þ ¼ f0:5 I1=½0:5 I1 þ 0:1ðI2�3:5 I1Þ�g � 100 ð1Þ

MCP ðmol %Þ ¼ 100�VTM ðmol %Þ ð2Þ

in which I1 is the integration of the resonance at d=5.0 ppm (two vinyl

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protons of the VTM unit) and I2 is the integration of the resonance fromd=0.7–2.0 ppm (seven alkyl protons of the VTM unit and ten alkyl pro-tons of the MCP unit) in the 1H NMR spectrum of the HD homopoly-mer.

Typical Procedure for 1,6-Heptadiene Homopolymerization

For a typical polymerization (Table 2, run 1): In a glovebox, 1,6-hepta-diene (914 mg, 9.5 mmol) was added under vigorous stirring to a reactionmixture of 1 (10 mg, 19 mmol) and [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (18 mg, 19 mmol) intoluene (6 mL). The polymerization was terminated by the addition ofmethanol after 90 min. The resulting mixture was poured into a largeamount of methanol to precipitate the polymer product, which was thencollected by filtration, washed with methanol, and dried under vacuum at60 8C to a constant weight. The ratio of the MCH and ECP units in theHPD homopolymer was calculated according to the formula [Eq. (3)]:

cis-MCH=trans-MCH=cis-ECP=trans-ECP ¼ I1=I2=I3=I4 ð3Þ

in which I1 is the integration of the resonance at d=26.4 ppm (one meth-ylene carbon of the cis-MCH unit), I2 is the integration of the resonanceat d =21.1 ppm (one methylene carbon of the trans-MCH unit), I3 is theintegration of the resonance at d=22.5 ppm (one methylene carbon ofthe cis-ECP unit), and I4 is the integration of the resonance at d=

23.8 ppm (one methylene carbon of the trans-ECP unit) in the 13C NMRspectrum of the HPD homopolymer.

Typical Procedure for Isoprene Homopolymerization

For a typical polymerization (Table 3, run 1): In a glovebox, isoprene(648 mg, 9.5 mmol) was added under vigorous stirring to a reaction mix-ture of 1 (10 mg, 19 mmol) and [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (18 mg, 19 mmol) in tolu-ene (6 mL). The polymerization was terminated by the addition of meth-anol after 50 min. The resulting mixture was poured into a large amountof methanol to precipitate the polymer product, which was then collectedby filtration, washed with methanol, and dried under vacuum at 60 8C toa constant weight.

Typical Procedure for 1,5-Hexadiene and Isoprene Copolymerization

For a typical copolymerization (Table 4, run 14): In a glovebox, a mixtureof 1,5-hexadiene (390 mg, 4.75 mmol) and isoprene (324 mg, 4.75 mmol)was added under vigorous stirring to a reaction mixture of 5 (11 mg,19 mmol) and [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (18 mg, 19 mmol) in toluene (6 mL). Thepolymerization was terminated by the addition of methanol after 90 min.The resulting mixture was poured into a large amount of methanol toprecipitate the polymer product, which was then collected by filtration,washed with methanol, and dried under vacuum at 60 8C to a constantweight. The MCP, 3,4-IP, and 1,4-IP contents of the HD–IP copolymerwere calculated according to the formula [Eqs. (4), (5), and (6)]:

1,4-IP ðmol %Þ ¼ fI1=½I1 þ 0:5 I2 þ 0:1ðI3�7 I13�3 I2Þ�g � 100 ð4Þ

3,4-IP ðmol %Þ ¼ f0:5 I2=½I1 þ 0:5 I2 þ 0:1ðI33�7 I13�3 I2Þ�g � 100 ð5Þ

MCP ðmol %Þ ¼ f0:1ðI33�7 I13�3 I2Þ=½I1 þ 0:5 I2 þ 0:1

ðI33�7 I13�3 I2Þ�g � 100ð6Þ

in which I1 is the integration of the resonance d =5.1 ppm (one vinylproton of the 1,4-IP unit), I2 is the integration of the resonance d=

4.8 ppm (two vinyl protons of the 3,4-IP unit), and I3 is the integration ofthe resonance from d=0.5–2.5 ppm (seven alkyl protons of the 1,4-IPunit, six alkyl protons of the 3,4-IP unit, and ten alkyl protons of theMCP unit) in the 1H NMR spectrum of the HD–IP copolymer.

Typical Procedure for 1,6-Heptadiene and Isoprene Copolymerization

For a typical copolymerization (Table 5, run 12): In a glovebox, a mixtureof 1,6-heptadiene (457 mg, 4.75 mmol) and isoprene (324 mg, 4.75 mmol)was added under vigorous stirring to a reaction mixture of 5 (11 mg,19 mmol) and [Ph3C][B ACHTUNGTRENNUNG(C6F5)4] (18 mg, 19 mmol) in toluene (6 mL). Thepolymerization was terminated by the addition of methanol after 60 min.The resulting mixture was poured into a large amount of methanol to

precipitate the polymer product, which was then collected by filtration,washed with methanol, and dried under vacuum at 60 8C to a constantweight. The MCH, 3,4-IP, and 1,4-IP contents of the HPD–IP copolymerwere calculated according to the formula [Eqs. (7), (8), and (9)]:

1,4-IP ðmol %Þ ¼ fI1=½I1 þ 0:5 I2 þ 1=12ðI3�7 I1�3 I2Þ�g � 100 ð7Þ

3,4-IP ðmol %Þ ¼ f0:5 I2=½I1 þ 0:5 I2 þ 1=12ðI3�7 I1�3 I2Þ�g � 100 ð8Þ

MCH ðmol %Þ ¼ f1=12ðI3�7 I1�3 I2Þ=½I1 þ 0:5 I2 þ 1=12

ðI3�7 I1�3 I2Þ�g � 100ð9Þ

in which I1 is the integration of the resonance d =5.1 ppm (one vinylproton of the 1,4-IP unit), I2 is the integration of the resonance d=

4.8 ppm (two vinyl protons of the 3,4-IP unit), and I3 is the integration ofthe resonance from d=0.5–2.5 ppm (seven alkyl protons of the 1,4-IPunit, six alkyl protons of the 3,4-IP unit, and twelve alkyl protons of theMCH unit) in the 1H NMR spectrum of the HPD–IP copolymer.

Mechanical Property Study

Uniaxial tensile testing experiments were performed at room tempera-ture with an Instron 3342 Tensile Instrument molded according to ASTM882-09 at a crosshead speed of 20 mm min�1.

Acknowledgements

This work was supported by a Grant-in-aid for Scientific Research (B)(no. 24350030 to M.N.), a Grant-in-Aid for Scientific Research (S) (no.21225004 to Z.H.) from JSPS, the National Natural Science Foundationof China (no. 21204008), the China Postdoctoral Science Foundation (no.2012M520614), and the Thousand Talents Program of the Chinese gov-ernment (to Z.H.). We are grateful to Dr. Hiroyuki Koshino for NMRspectroscopic measurements of the copolymers.

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Received: April 30, 2013Published online: July 11, 2013

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