Organometallics 1994, 13, 1911

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Organometallics 1994,13, 1911-1917 1911

Agostic Interaction and Intramolecular Hydrogen Exchangein Coordinatively Unsaturated Ruthenium Complexes:Effects of Chelate Ring Size on IntramolecularCarbon-Hydrogen Bond Activation of Diphosphine LigandsMasamichi Ogasawara and Masahiko S a b u r i *

D e p a r t m e n t of In d u s t r i a l Ch em i s t r y , F a cu l ty of E n g in eeri n g, Th e U n i ver s i t y of T o k y o ,H o ng o, B u n k y o - k u , T o k y o 1 13 , J a p a n

Received Augu s t 2 1993@Th e solution properties of formally five-coordinate ruthenium complexes [RuH(P-P)z]PFGP-P = 1,4-bis(diphenylphosphino)butane (dppb) la),2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane diop) lb),1,3-bis(diphenylphosphino)propanedppp) IC),1,2-bis(diphenylphosphino)ethane dppe) (Id))were examined by various NMR measurements.Variable temperature lH NMR measurements suggest th at the behaviors of la and l b a t lowtemperatures differ significantly from those a thigh temperature. The agostic interaction betweenan a-methylene CH moiety of the diphosphine ligand and the ruthenium cente r was detectedin la below-30 C and in l b below-60 C. In ICand Id no agostic interaction could be detected .The hydrogen exchanges among the terminal hydride, the agostic hydrogen, and a noncoordinatingmethylene hydrogen of dppb n la were proved on the basis of spin saturation ransfer phenomenain the 'H NMR measurements. Th e exchange rate between the agostic hydrogen and the terminalhydride was estimated in the temperature range -55 to -90 C by spin saturation transferstudies, o reveal that AG* or the hydrogen exchange is about 11kcal mol-'. At high temperaturesthe hydrogen scrambling between o r t h o hydrogens on the phenyl groups, all the methylenehydrogens, and the te rminal hydride in la was proved by employing the partially deuterizedligand PhzP(CDz)4PPhz.Upon the contact of la, IC, and Id with DZgas in solution, deuteriumincorporation takes place a t o r t h o and all methylene positions of diphosphines in these complexes.In the case of la, the deuterium content of each site is in the order P-CHZ> a-CHz > o-CH.In l b and IC, he H /D exchange at o-CH proceeded in preference t o those a t (u-CHZ r /3-CHz.

IntroductionThe activation of the carbon-hydrogen a bond is one ofthe most important target reactions in organo-transitionmetal chemistry.' In order to facilitate the cleavage of achemical bond with a metal complex, the interactionbetween the bonds and the metal center is necessary eitherin the transition state or in an intermediate. Organo-metallic moieties involving the coordination of a a bondto a transition metal center have attracted considerableattention as possible models for the intermediate of a abond dissociation.2It was proposed that M-H-C bonds, i.e. agosticinteractions, are similar in bonding character to the v2type coordination of a dihydrogen ligand to a transitionmetal (three-center two-electron bond).2c The fact that

some coordinatively unsaturated 16-electron complexes,which are the precursors of molecular hydrogen complexes,involve agostic interactions demonstrates the similarityin bonding between the agostic interaction and dihydrogenAbstract published in Advance ACS Abstracts, April 1,1994.(1)Gene ral reviews of C-H activation in a transition m etal complex:(a) Parshall, G. W. Acc. Chem. Res. 1975,8,113. b) Webster, D. E.Adu.Organomet. Chem. 1977,15,147. c) Bruce, M. I.Angew. Chem.,Int .Ed .Engl. 1977,16, 3. (d) Crabtree, R. H. Chem. Reu. 1985,85, 45. (e)Halpern, J. Inorg. Chim. Acta 1985,100, 1. 0 yabov, A. D. Chem.Reu; 1990, 0, 03.(2) (a) Brookhart, M.; Green, M. L. H.J.Organomet. Chem. 1983,250,395. (b) Brookha rt, M.; Green, M. L. H.; Wong, L.-L.rog. Inorg. Chem.1988,36,1. c) Crabtree, R. H.; Hamilton, D. G. Adv. Organomet. Chem.1988, 8, 299.

0276-733319412313-1911$04.50/0

c~ordination.~ue to the fact that the isolation of suchcoordinatively unsaturated complexes is often difficultbecause of their high reactivities, it is required on suchoccasions to generate them in situ by thermochemical4orphotochemical5 igand dissociation of saturated precursors.Although agostic interactions are regarded as intermedi-ates on the way to oxidative addition of carbon-hydrogenbonds, few cases are known as examples of actual C-Hbond activation, especially of aliphatic C-H groups.6We describe herein the solution behavior of the formallyfive-coordinate ruthenium complexes [RuH(P-P)zIPFsP-P= dppb (la),'diop (lb),8dppp 1 ~ 1 , ~nddppe (ldI7).It was disclosed by NMR measurements that, at lowtemperature, the interaction between an aliphatic C-H

(3) gasawara, M.; Aoyagi, K.; Saburi, M. Organometallics 1993,12,3393 and references therein.(4) a)Fendrick, C. M.; M arks, T. J.J.Am. Chem. SOC.984,106,2214.(b)Zeiher, E. . K.; DeWit, D. G.;Caulton, K. G. J.Am. Chem. SOC.984,106, 7006. (c) Buchanan, J.M.; Stryker, J. M.; Bergman, R. G. J . Am.Chem. SOC.986,108,1537.d) Desrosiers, P. .;Shinomoto, R. S.;Flood,T. C. J . Am. Chem. SOC.986,108,7964.(5) a) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. SOC.983,105,3929. (b) Wenzel, T. T.; Bergman, R. G. J . Am. Chem. SOC.986,108,4856. (c) Field,L .; George , A. V.; Messerle, B. A. J.Chem. SOC., hem.Commun. 991, 1339.(6) a) Calvert, R.B.; Shapley , J. R. J.Am. Chem. SOC.978,100,7726.(b) Cree-Uchiyama, M.; Shapley, J. R.; St. George, G. M. J. Am. Chem.SOC.986,108, 316.(7) a) Ashworth, T. V.; Singleton, E.J.Chem. SOC., hem. Commun .1976, 05. (b) Sabu ri, M.; Aoyagi, K.; Takahashi , T.;Uchida, Y. Chem.Let t . 1990,601.(8) a) Saburi, M.; Aoyagi, K.; Takeuchi, H.; Takahashi, T.; Uchida,Y. Chem. Lett . 1990,991. b) Saburi , M.; akeuchi, H.; Ogasawara, M.;Tsukahara, T.; Ishii, Y.; Ikariya, T.; Takahashi , T.; Uchida, Y. J .Organomet. Chem. 1992,428, 55.

1994 American Chemical Society


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1912moiety of the diphosphine ligand and the ruthenium centeris detected clearly for complexes la and lb and that theagostic hydrogen undergoes exchanges with the terminalhydride (Ru-H) at a considerable rate. Such an agosticinteraction could not be detected for analogous complexesIC and Id. The rate and thermodynamic parameters forthe exchange between the terminal hydride and the agostichydrogen in la were determined in the temperature range-55 to -90 C. At high temperatures, however, the ag-ostic interaction in lawasno longer observed, and instead,rapid hydrogen scrambling including the terminal hydride,all the methylene hydrogens, and the or tho hydrogens onthe phenyl groups of the ligands could be proved byemploying the partially deuterated ligand PhzP(CD&PPh2. It was demonstrated, further, that facile deuteriumincorporation takes place a t the diphosphines of the five-coordinate complexes la, IC, and Id) in solution underaD2 atmosphere. The mechanism for such H/D exchange,which could be promoted by a deuteride complex as [RuD-P-P)z]+,s proposed. The difference of the H/D exchangereactivity between complexes la, IC, and Id is alsodiscussed. Pa rt of this work has been reported in apreliminary communication.3

Organometallics, Vol. 13, No. 5, 1994 Ogasawara and SaburiTable 1. 31P{1HJ MR Data for [RuH(dppb)l]PFs (la) andIRuH(diop)2lPFs ( l b ) in CD2CIz at -90 C*

Results and DiscussionPreparationof [RuH diphosphine)2]PFs 1). Theformally five-coordinatecomplexes l a 4 re prepared from[RUH(CO~)(NH~NM~~)~IPF~~nd 2 equiv of respectivediphosphines according to the reported method7*tabwithslight modifications.

[RuH(cod)(NH2NMe2)31PF6 2P-P-[RuH(P-P),]PF, + COD + 3NH,NMe, 1)

In the previous papers,7a18bmethanol or ethanol was usedas a solvent for the synthesis of 1 (eq 1). These complexesare coordinativelyunsaturated and, therefore, tend toreactslowly with primary or secondary alcohols o give dihydridecomplexes (eq 2).7aJ0 The proton thus formed can reactwith 1,l-dimethylhydrazine, the salt of which remains ina reaction mixture as a byproduct.[RuH(P-P)J+ + RR'CHOH - uH,(P-P), +

RR'C=O +H+ 2)I twas found that the side reaction with alcoholic solventcan be avoided by employing tert-butyl alcohol or acetoneas a solvent.1H and 3lP NMR Characteristics of [RuH dppb)z]-PF6 la ) and [RuH diop)z]PFe ( l b ) . The high fieldregion of the variable temperature 'H NMR spectra of laand their spectroscopic features have been given in thepreliminary account.3 The intensity of the broad signalobserved in the 'H NMR spectra above 0 C correspondsto one hydrogen nucleus, and that of each resonancedetected below -30 C also corresponds to one proton,respectively. The 31P(1H} MR spectrum of la at -90 Cshowed the presence of four inequivalent phosphorus(9) Ashworth, T. V.; Singleton, E.; Hough, J. J. J. Chem. SOC. al ton(10)Meakin, P.; Muetter t ies , E. L.; Jesson, J. P. J. Am. Chem. SOC.Trans. 1977,1809.1973, 5, 5.

complex 6~~ 6~~ 6~~ 6xb JAM JBM JA X = BX1 d 37.9e -13.4 79.1 30 10lbd 30.4 31.1 -9.5 73.2 20 30Reco rdeda t 162 MH z. Relative toexternal 85 D,P04. Couplingconstants in hertz. JA Band J M Xwere not observed clearly. Observedas an unresolved multiplet.

nuclei (see Table 1).l1The possibility of the existence oftwo isomers or the formation of a polynuclear complex a tlow temperature was entirely denied by the 3lP(lHJNMRspectrum. Below -30 C, la seems to have two hydride-like nuclei in a molecule. The signal at 6 -10.6, whichreveals the couplings with phosphorus nuclei at -90 C,is ascribed to the terminal hydride (Ru-H), while the otherat 6 -7.0, showing no coupling with phosphorus a t thesame temperature, is assigned to the hydrogen in a C-Hmoiety interacting with the ruthenium center (agosticinteraction).2alb All these NMR characteristics wereobserved for the tetraphenylborate analogue [RuH-(dppb)~]BPh4 la-BPh4). This fact indicates that theanions, PF6- in la and BPh4- in la-BPh4, have nointeraction with the ruthenium center.

The diop complex1bexhibited 'H NMR features similarto those of la (Figure1). In the case of lb, two hydride-like resonances, a broad signal (ca. 6 -4.1), and a doubletof quartets (ca. 6 -10.21, were detected at and below -60C. The highest temperature where the agostic interactioncan be observed for lb is considerably lower than t hat forla. As we expected, lb shows an ABMX pattern in the31P{1HJNMR spectrum at -90 C (Table 1).Assignmentof the Agostic Hydrogen. As describedin the former communication,3 it is demonstrated that, onthe basis of the lH-lH COSY measurements, the complexesla and lb involve the coordination of an a-methylene C-Hmoiety, not an or tho phenyl proton, of dppb or diop at thesixth coordination site of the ruthenium center to give riseto the agostic interaction a t ow temperature, respectively.The 13C NMR spectrum of la at -90 C (Figure 2)showed eight resonances in the methylene region. Thisindicates that each methylene carbon in la differs fromthe remaining carbons, so that the structure of l a has noelements of molecular symmetry, in accord with the resultsof the 31P(1H}NMR data. On such an occasion, twohydrogens of each methylene group in dppb are inequiva-lent. The proton-coupled l3C NMR spectrum of la,however, appeared as eight pseudotriplets, instead of eightdoublets of doublets signals, in the methylene region. Thisis probably due to the broadening of the signals resultingfrom the coupling with 31Pnuclei and/or the similaritybetween the two geminalJCHvalues. Among the 13C NMRsignals of the CH2 groups of la, the resonance a t 6 27.9showed a JCHalue smaller than the others3 and wasassigned to the signal of the agostic carbon.2a,b This isconsistent with the coordination of a methylene C-H groupin la. Under selective decoupling at the agostic hydrogen(6 -7.0), only the resonance a t 6 27.9 turned into a simpledoublet. This observation confirms the above-mentionedassignment.A similar agostic interaction could not be detected foranalogous five-coordinate complexes of dppp (IC) ,dppe11)Ashworth,T. V.; Chalm ers, A. A.; S ingleton, E. Inorg. Chem. 1986,2 4 ,2 1 2 6 . In this paper , they reported th e lP NMR spectrum of la nacetone-& at -80 C as an A2MX pattern.


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H Exchange in Coordinatiuely Unsaturated Ru Complexes

40 C

Organometallics, Vol. 13,No. 5 1994 1913

i l l \ 30 C20 C[ 10C

P P H' '~ '~ ' l0 45 40 35 30 25 20Figure 2. 13C NMR (101-MHz)spectra of [RuH(dppb)zl-PF6 (la) in the methylene region at -90 c in CD2C12: (a)proton decoupled; (b)proton coupled (JCHvalue of eachsignalis shown in ref 3); (c) selective decoupled with the agostichydrogen 6 -7.0).(Id),dpbp,lzand binap.lZbJ3In the case of I Cand Id, thesmaller size of the chelate rings prevents a C-H bond ina methylene unit from coordinating to the rutheniumcenter, whereas dppb and diop ligands provide a flexibleseven-membered chelate upon coordination. As to thecomplexes of dpbp and binap, the ligands have no aliphatic

(12) a) dpbp =2,2'-bis(diphenylphosphino)-1,l'-biphenyl. (b) Ogasa-wara, M.; Saburi, M. J. Organomet. Chem., in press.(13) a) binap = 2,2'-bis(diphenylphosphino)-l,l'-binaphthyl. (b)Tsukah ara, T.; Kawano, H.; Ishii, Y.; Takahashi, T.;Saburi, M.; Uchida,Y.; Akutagawa, S. Chem. Lett . 1988, 2055.

C-H groups in themselves, although these diphosphinesform seven-membered chelate rings. The highest tem-perature, a t which the agostic interaction is recognized inthe lH N M R spectrum, is -30 C for la and -60 C orlb . The flexibility of the diop chelate ring should bereduced due to the presence of the dioxolane ring,compared to th at of the simple four-carbon chain in thedppb chelate. This makes the coordination of an a-methyl-ene hydrogen to the ruthenium center more difficult in l bthan in la. The difference in the chelate ring flexibilitybetween dppb and diop is reflected in the above-mentionedtemperature dependence of the agostic interaction.MM2 Calculation of la. In the 'H N M R spectra, thecoupling patterns (doublet of quarte ts) of the terminalhydride signals of la and l b at low temperature indicatethat the two chelating diphosphine ligands adopt a cisarrangement in these complexes. The terminal hydrideshould be located trans to one phosphorus nucleus, andcis to the other three. There are two candidates for themanner of coordination of an a-methylene hydrogen ofdppb to the ruthenium center in la at low temperatures( I and 11), both of which fill the other steric requirements

H H

I I1described above. We could not decide on the basis of thespectroscopic data alone which of these two structures isprobable for la. The molecular mechanics 2 (MM2)calculations suggest that structure I is more stable than11, he energy difference between I and I1being about 8.6kcal mol-'. Although electronic effects are completelyignored in the MM2 calculations, it is reasonable to supposethat the difference in the electronic properties between Iand I1 is small. Furthermore, the energy differenceobtained above is significantly large to suggest thatstructure I is a more possible structure of la.Intramolecular Hydrogen Exchange at Low Tem-per atu res . As we described pr ev i~ us ly ,~he rapid


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1914 Organometallics, Vol. 13 No. 5 1994Table 2. TI Values and Rate Constants, k for HydrogenExchange between the Agostic Hydrogen and the TerminalHydride in [RuH(dppb)*]PF6 ( l a )

Ogasawara and Saburi

Tl(agostic)/ Tl(hydride)/ AG'/T/'C T/K msa msa k/s-I kcal mol-]-55 218 102 120 32.6 11.1-60 213 141 147 17.1 11.1-65 208 174 171 12.9 11.0-70 203 242 182 8.9 10.8-75 198 284 193 4.5 10.8-80 193 335 287 1.5 11.0-85 188 395 389 0.6 11.0-90 183 483 513 0.3 11.0

The T Iexperiments were performed at 400 MH z with a 180-r-900pulse sequence by the inversion-recovery method. Calcu lated from therate constants k.hydrogen exchanges among the Ru-H, agostic C-H, andnoncoordinating methylene protons of the dppb ligandsin la were demonstrated by the 'H NMR spin saturationtransfer phenomena at -45 C.The exchange rate,k etween the agostic hydrogen andthe terminal hydride was estimated in the temperaturerange -55 to -90 C by the spin saturation transfertechnique.lP17 The rate constants and the T1 values ofeach signal are summarized in Table 2. The Eyring plot(In k/T vs 1/T) s linear, and the thermodynamic param-eters for the exchange between the agostic hydrogen andthe terminal hydride in la areAH 10.3 .5 kcal mol-'and AS*= -3.6 0.6 cal mol-' K-l. Interestingly, thesevalues lie in the range of those reported for the intramo-lecular hydrogen exchange between the hydride and thedihydrogen ligand in [R~H(q~-H2)(diphosphine)21+.'~Two intermediates are possible for the hydrogen ex-change; i.e., (A) a seven-coordinate dihydride, and B) asix-coordinate q2-H2 complex. Albkniz and co-workersrecently suggested the formation of the dihydrogen com-

H H:H

A Bplex as the intermediate for intramolecular hydrogenexchange-lg They also proposed the direct proton transferas a key step in the hydrogen exchange of the M-H-Csystem in a transition metal c0mp1ex.l~ As mentionedabove, complex la, which involves the agostic interactionbetween a-CH and the ruthenium center, exhibits thehydrogen exchange between the agostic hydrogen and theterminal hydride. The result of the 'H-lH COSY mea-

14) Campbell, I. D.; Dobson , C. M.; Ra tcliffe, R. G.; Williams, R. J.P. J. Magn. Reson. 1978, 29, 397.(15) a) ForsBn, S.; Hoffm an, R. A. J . Chem. Phys. 1963,39,2892. (b)F o r s h , S.; Hoffm an, R . A. J . Chem. Phys. 1964, 40, 1189.16) Sandstrhm,J.DynamicNM R Spectroscopy;Academic: NewYork,1982.17) In the preliminary account: we repo rted values for the rateconstants, k ifferent from those described here. In the course of furtherinvestigations, we found a technical mistake to obtain the differencespectra between the irradiated and the nonirradiated spectra.18) (a) Bautista, M. T.; Cappellani, E. P.; Drouin, S. D.; M orris, R.H.; S chweitzer, C. T.; Sella, A,; Zubkowski, J. J.Am. Chem. SOC. 991,113, 4876. (b) Bianchini, C.; Perez, P. J.; Peruzzini, M.; Zanobini, F.;Vacca, A. Inorg. Chem. 1991, 30, 279. (c) Jessop, P. G.; Morris, R. H.Coord. Chem. Reo. 1992,121, 155.19) AlbBniz,A. C.; Sch ulte, G.; Crabtre e, R. H. Organom etallics 1992,11 242.

11117nmlllllllll lilllillllilll/llilllTllllilillilll/ll10 9 7 6 5 4 3 2 1 -1 - 1 4 - 1 6Figure 3. 2D NMR (61-MHz) spectra at 30 C in CH2C12:(a)P ~ z P ( C D Z ) ~ P P ~ Zdppb-dd; (b) [RuH(dppb-d8)2lPF~la-d16).

surement demonstrates that this agostic hydrogen has acoupling with the neighboring methylene hydrogen^.^These observations suggest the possibility that thishydrogen exchange proceeds via direct proton transfer,rather than the successive process of oxidative additionand reductive el imi nat i0 n.2 ~~~ecently, Crabtree andco-workers reported either dissociative or nondissociativeinteraction of a C-H moiety in quinoline derivatives withiridium complexes and suggested the relationship betweenthese hydrogen exchanges and agostic interactions.24However, there has been no direct evidence of the agosticinteraction participating in C-H activation. Our resultsare the first example3 of the observation of the directintramolecular hydrogen exchange involving the agostichydrogen.Intramolecular Hydrogen Exchange at High Tem-peratures. A t higher temperatures, l a (above0 C) andl b (above -40 C) are highly fluxional in solution, so thatit is impossible to decide whether the hydrogen exchangebetween a-CH and Ru-H is still taking place or not.Judging from the variable temperature lH NMR spectra,3the high temperature behavior of la differs from the lowtemperature one. With a view to answer this problem, weprepared partially deuterated dppb Ph2P(CD2)4PPh2(dppb-d8). The lH NMR spectrum of the complex [RuH-(dppb-d&]PFs ladle),obtained by a reaction of dppb-d8 and [RuH(cod)(NH2NMe2)31PFs n ethanol, displaysthe signals assignable to the methylene protons ofcoordinating diphosphines. I t should be noted tha t theresonances not only of a-methylene but also of @-methyleneof dppb appear with practically equal intensities. The 2DNMR spectrum of lad16 revealed the resonance assignableto deuteriums incorporated into the phenyl group (6 7.1)and the Ru-D part (6 -14.7), in addition to the C-D signalsof the methylene groups (6 0.7 and2.4,Figure 3). Further,a detailed examination of the aromatic region in the 1HNMR spectrum showed that the intensity of the orthohydrogen resonance of lad16 is distinctly smaller thanthat of the meta hydrogens, and that the latter signalbroadens considerably as a result of H-D coupling withthe ortho deuterium (see Figure 4) . I t is demonstrated,therefore, that the protium source introduced into the

20) (a) Parshall, G. W.; Knoth, W. H.; Schunn, R. A. J.Am. Chem.SOC. 969,91,4990. (b) Parshall, G. W. Acc. Chem. Res. 1970,3,139. (c)Barefield, E. K.; Parshall, G. W. Inorg. Chem. 1972,5, 964.21) Chaudret, B. N.; Cole-Hamilton, D. J.; Wilkinson, G. J. Chem.SOC. al ton Trans . 1978, 1739.22) Rosete, R. 0.;ole-Ha milton, D. J.;Wilkinson, G. J . Chem. SOC.,Dalton Trans . 1984, 2067.23) Cheney, A. J.; Mann, B. E.; Shaw, B. L.; Slade, R. M. J.Chem.SOC. 1971, 3833.24) (a) Crabtree, R. H.; Ho lt, E. M.; Lavin, M.; Morehouse, S. M.Inorg. Chem. 1985,24,1986. (b) Lavin, M.; Holt, E. M.: Crabtree. R. H.Org&ometallics 1989,8, 99.


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H Exchange in Coordinatively Unsaturated Ru Complexes Organometallics,Vol 13, No. 5, 1994 1915m-

. PI I \ 0-

7.8 7 . 6 7 e 4 7 . 2 7 . 0 6 . 8 6 . 6Figure 4. 1H NMR spectra of la (left) and la-d16(right) in the phenyl region at 30 C in CD2Cl2 at 400 MHz.Scheme 1. Proposed Mechanism of the DeuteriumIncorporation and the Hydrogen Scrambling inComplex 1

(0methylene parts of dppb-da is the ortho C-H groups onthe phenyl moieties.lC.20821 I t is certain tha t the protiumsincorporated into the methylene groups do not originatefrom ethanol employed as a solvent, because the use ofC2DbOD in place of C2H50H causes no change in the 'HNMR spectrum of la-d16.25 he total protium amount oforthoand a- nd@-methylene ositions in la-dl6estimatedfrom the 'H NMR spectrum corresponds well to thehydrogens hat initially exist a t he orthopositions of dppb-da. These results indicate tha t this hydrogen exchangeproceeds via an intramolecular process.A t lower temperatures, only one of the a-methylenehydrogens of dppb exchanges with the terminal hydridevia the agostic interaction. In contrast, a t higher tem-peratures, not only the a-CH2 but also the @-CH2 nd theorthohydrogen on the phenyl groups of coordinating dppbcan be sufficiently activated, so that rapid hydrogenscrambling takes place among these hydrogens and theRu-H in la. The possible pathway of H-D scramblingamong a- nd @-CH2 arts and o-hydrogens of dppb-ds isillustrated in Scheme 1. Thus, according to the reactionsequence (i-, i-, ii- v), a deuterium a t the methylenegroups, not only of the a but also of the @-position, sreplaced with protium of Ru-H, while the Ru-H istransformed into Ru-D. The deuteration of the orthohydrogen on the phenyl group proceed via the sequenceiv- -. i-, . By uniting these sequences, a completecycle for H/D scrambling among a coordinating dppb-dawas obtained.We suppose that in the H /D scrambling in 1 a - d ~he@-CHand o-CH groups also take part in the agostic

(25) Kiffen, A. A.; Masters, C.; Raynand, L. J . Chem. SOC.DaltonTrans. 1975, 853.

interaction (ii, iii or v, vi) in a manner similar to that ofthe a-CH group. Although the agostic interactionsinvolving the @-CH r o-CH group have not been detectedin the 'H NMR spectra of la, the observed H/D scram-blings clearly indicate that these C-H bonds are sufficientlyactivated in a kinetic sense at higher temperatures.Deuterium Introduction nto Diphosphine LigandsbyTreatmentsof 1 with Da Gas. It is noteworthy thatall steps in the cycle shown in Scheme 1are reversible. Ifthe deuteride species [RuD(dppb),l+ were once obtained,the deuterium incorporation into the methylene moietiesand o-CH parts would be achieved via the sequences iv-

iii -, i - and iv -- v -,vi -, , respectively. Uponcontact with Dz gas, la is spontaneously converted intoamixture of [RuH(D2)(dppb)2l+and RuD(HD)(dppb)pl+,and the latter can afford [RuD(dppb)zl+by the dissociationof HD.7bJ8a It has been clarified, however, that under aH2 atmosphere, l a turned almost completely into [RuH-(Hz)(dppb)zl+and that the NMR measurements showedno detectable amount of the precursor remained.'b Despitethat, a trace amount of [RuD(dppb)21+could be generatedto promote the deuterium incorporation into the diphos-phine ligands.With a view to examine the above possibility, the 'HNMR change of la in tetrahydrofuran was followed undera D2 atmosphere. Indeed, a clear decrease of signalintensities in the methylene region could be observed afterkeeping a solution of la for several hours under D2. It wasfound to be somewhat difficult to determine the exactintensity ratio of CY-CH:@-CH:o-CHn the complex itselfby the 'H NMR measurements, presumably due to thebroadening of the signals resulting from th e presence ofconformers and isotopomers. Hence, the deuteratedcomplex was decomposed with H202 and the diphosphineligands were converted into the diphosphine dioxide. Thedioxide of dppb-d, was separated from the reaction mixture(dppb-d, refers to a mixture of partially deuterated dppb),and th e lH NMR spectrum was recorded for this dioxide(dppb02). Fortunately, a complete signal separation wasobtained between meta and para hydrogens and orthohydrogens of dppb02 in the IH NMR spectrum. Usingthe total signal intensity of meta and para hydrogens asthe internal standard , the intensities of o-CH, a-CH2, and@-CH2 ere evaluated with good accuracy. The results ofthe deuterium replacement after a 72-h treatment weregiven in Table 3. As shown in entry 1, deuteriumsubstitution occurred a t all possible sites of dppb. It isinteresting that the D content of each site in dppb is inthe order @-CH2> n-CH2 > o-CH. The deuteriumreplacement at @-CH2 roceeds faster than th at a t a-CH2groups, although @-CH onds are excluded from the agosticinteraction in complex l a at lower temperatures.This strongly suggests that similar H/D exchanges couldoccur in analogous complexes that exhibit no detectable


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1916 Organometal l ics , Vol. 13 No. 5, 1994Table 3. Ratio of Deuterium Incorporation into theDiphosphine Ligand.

Ogasawara and Sabur i( d p p e ) ~ l P F 6 ~ere prepared by literatur e methods, except thattert-butyl alcohol (for l a , IC, and Id) or acetone (for lb ) wasemployed as a solvent instead of ethanol. [RuH (dppb-d& lPF6was prepared by using dppb-de.NMR Studies. Th e preparation of sample solutions of th ecomplexes for NMR measurem ents was carried o ut under anargon (not dinitrogen) atmosphere using air free CDzClz as asolvent. lH NM R (400-MHz), 2D NMR (6l-M Hz) , l3C NMR(lOl-MHz), and 31PNMR (162-MHz) spectra were recorded ona JEO L JN M-G X 400 spectrometer. lH a nd 13C NMR chemicalshifts are reported in pp m dow nfield of tetram ethylsilan e. 2DNMR chemical shifts are relative to the solvent resonance,CHDClz 6 5.3), as an internal standard. 31PNMR chemicalshifts are reported in pp m downfield of external 85% D3P04.1HNMR T1 determinations were performed with a stan dard 180O-~ - 9 0 ~ulse sequence by the inversion-recovery method.Measurementsof the Exchange R ates between the Agos-tic Hydrogen and theTermina1Hydridein la. Determinationof th e exchange rates between th e two resonances was carriedout according to the ForsBn-Hoffman method.lSJ6 Spin satura-tion transfer ex periments were performed by irradiating the 1Hresonance of the agostic hydrogen. The exchange rates, k werecalculated from t he following equation:

entry comulex o-CD/% a -C D/ % 0-CD/%1 l absc 18 54 9 22 la-dI6 38 57 5sIbb 61 4s


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H Exchange in Coordinatively Unsaturated Ru Complexessolution was dried with MgS04. After the removal of th e solvent,residual diphosphine dioxide was purified by the appropriatemethods as follows. Th e dioxides of dp pb and d ppe wererecrystallized from acetone. Dp pp dioxide was purifie d with aHPLC equipped with a silica gel column (Merck R T 250-10)using isopropyl alcohol-n-hexane (3:7) as an eluent. Th e ratioof deuterium incorporation into the dipho sphine was determinedby the lH N MR m easurements of these diphosphine dioxides.Dppb Dioxide: lH NMR [CDCls, TMS] 6 1.65-1.78 (m,P-CHz), 2.16-2.29 (m , (r-CH z), 7.40-7.51 (m , m- and p- H) , 7.63-7.73 (m, - H ) . ~ n al. C alc d fo r C Z ~ H Z O . ~ D ~ . ~ O Z P Z :, 72.20; H+ D, 7.64. Fou nd: C, 72.63; H + D, 7.18.29

28) (a) Goda, K.; Yoshifuji, M.; Okazaki, R.; Inamoto, N. Bull. Chem.SOC. p n . 1975,48,2484. b)Aguiar, A. M.; Beisler, J.J . Org. Chem. 1964,29 1660.29) The disphosphine dioxides obtained here were mixtures ofisotopomers partially deuterated at all the methylene and the orthopositions. Th e formulas of the diphosphine dioxides (total amounts ofdeuterium atoms incorporated into the diphosphine dioxides) werecalculated from the results of lH NMR measurements see Table 3).

Organometallics, Vol. 13 No. 5 1994 1917Dppp Dioxide: 1H NMR [CDCla, TMS] 6 1.93-2.10 (m,

@ CH 2) , .46-2.59 (m , a-CHZ ), 7.39-7.53 (m , m- and p- H) , 7.64-7.74 (m, o-H ). Anal. C alcd for C Z , H ~ ~ . ~ D ~ . , O ~ P ~ :, 71.88; H +D, 7.30. Fou nd : C , 71.22; H + D, 7.63.29Dppe Dioxide: lH NM R [CDCls, TM S] 6 2.53 8, (r-CH2),7.41-7.55 (m, m- n d p - H ), 7.66-7.77 ( m, O - H ) . ~ ~ ~nal. Calcdfor C26H1g.5D4.502P2:, 71.80; H + D, 6.60. Fou nd: C, 71.83; H+ D, 6.21.29

Acknowledgment. We are grateful to Prof . AkiraMiyashita and Mr. Takeshi Chiba for their support andassistance in performing the MM2 calculations. We alsothank Dr. Makoto Koike for advice concerning NMR. Thiswork was supported by a Grant-in-Aid for ScientificResearch from the Ministry of Education, Science, andCulture, Japan (No. 03453098).OM9305273

Organometallics 1994, 13, 1911

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