Indian Joul'nal ol" Chemistry

Vol. 44A, January 2005, pp. 27-33

Dynamic processes of H-atom site exchange in trans dihydrogen hydride complex of ruthenium

V Sivak ulllar & 8alaji R Jag irdar*

Departmcnt of Inorganic & Phys ical Chem istry, I ndian ~l s t itule of Sc iencc, l3anga lore 5600 12. Ir~dia __

Hece il 'ed 25 Oerober 2004

A new dihydrogcn hydridc complex of ruthcnium of Ihe Iypc t/'{/II .1'- I(clppm)Ru (H)( ll '- I-I,)(PPh,h ll13F.,J ( I ) (dppm = Ph1PCH1PPh2) has bcen prcpared by prolonating Ihc precursor cli hydride complex ci.l'- I (d ppm)Ru ( H l2( PPh,)~ 1 usi ng HBF4.Et20. The fmmul ati on of ( 1) as a clihydroge n complex has heen hased upon the variahl e tempel'ature 1'1 measurements ('('I(min ) = 12.4 ms at 273 K, CICD2CD,CI, 400 MHz) and the observation 01' a substJn lial H-D coupl ing

constanl (.!(H,D) = 32 Hz, 243 K, ClCD,CD1Cl ) for the cOITesponding HD isotopol1ler t/'{{lIs- f(dppm)Ru(l-I)( 1l 2-

HD)(PPh,h IlI3F41. Thc '1'1 and Ihe H-D coupling constant measurements have been carried out in the lemperature range 243 - 2X3 K. The dihydrogen ,Ind the hydride l igands of (I ) show dynamic beha vior and undergo rapid H-atom site exchange;1I 343 K. At 273 K ( I ) shows a static structure. The dynamics of (I ) invol ving a trihydride intermediate has been stu died by vari ahle temperature NMR speclroscopy. The harrier to sile exchange of the H-atom bel ween the dihydrogen wi th the

hydride (t-.C1) has heen determined to be 14.4 kca l/mol al 303 K. Compound (I ) has been found to be stahl e up to 343 K in soluti on and no loss of the H, li gand has been ohserved at that temperature; in add ili on, the compound is stable in solution at room temperalure for a peri od of two days.

WC Code: Int CIJ C()7F 15/00

Introduction

Ever since the report of the first transition metal 111_H l complexes ' , the ques ti on of polyhydride complexes exh ibiting flu xional processes involving a dihydrogen ii gand has been ex tensively studied1. In addition, the dynamic processes in complexes containing a dihydrogen and a hydride li gand have also attracted enormous attention due primarily to their serving as prototypical examples of the polyhydride class of co mpounds. Depending upon the orientations of the dihydrogen and the hydride li gands with respect to one another in an octahedral complex, two poss ibiliti es arise, dihydrogen and the hydride ligands in: (a) cis conformat ions and (b) tmlls conformati ons. Thcre have been quile a few reports on the studies of the dynamic processes for situation (a/ as we ll as case (bt The tr({/IS dihydrogen hydride complexes usuall y exhib it high barriers for the dihydrogcn-hydride site exchange, whereas the cis compounds, relatively small er barriers". Maseras el

af.-' carried out theoretical studies to determine the relati ve stabilities of the six- and seven-coordinate isomers of IMH3L4t (M = Fe, Ru , Os; L = mono­dentate phosphine .Iiga nds) species. Berke and co-

workers(' followed up Museras ' theoretical work with certain experiments on the structural di versity and dynamics of [MH, L4t type complexes. Prior to these reports, Morri s and co-workers7 investigated besides other studies, dynamics of complexes of the type [(dppe)2MH (r{H1)f and determined the t'1C t for such derivatives. Morris proposed that the H-atom exchange in these derivatives in volves significant movement of the ditertiaryphosphine P atoms that would contribute to the hi gh barri ers to the site exchange (Scheme I).

We have been interested III preparing CI S

dihydrogen hydride complexes in order to study the dynamic processes of H-atom site exchange in such derivatives. Gusev e l rt/. o".h compil ed the dynami cs data for the known [MH1L4f complexes (M = Fe, Ru , Os) with respect to the type of L li gand, IZ.,

Illonodentate, bidentate, tridentate + Illonodenrate, or tetraclentate. In add i ti on to these, others have reponed sys tems such as [MI-I, P2(LX)t (P = monodentate phosphorus li gands, LX = bidentate, monoanioni c li gand/,e and [MH, P2(LL)t (P = monodentate phosphorus li gands, LL = bipyridyl)'a. Notably mi ss ing from these li stings is a case where L4 is a

28 INDIAN J CI-I EM, SEC A, JANUARY 2005

Schcmc I

combinati on of a bidentate and two mondentate li gands, all consisting of phosphoru s donors. In order to exa mine the effect of having two monodentate ligands and a bidentate li gand (a ll consisting of phosphorus donors) on the structure and dynamics, we have attempted to prepare one such derivative, cis­[(dppm)Ru(H)(rrH 2 )(p Ph,h][B F~] by protonating the prec ursor dihydride complex, CI.\'­

[(dppm)RuH2(PPh, )}]s using HBF~.E t20 . However, upon protonat ion, onl y the lJ'{JlIs-[(dppm)Ru(H)(r{ H2)( PPh,h][BF~] co mpl ex was reali zed. There are several exam ples of complexes ex hibiting the tran s stereochemistry for the hydride and dihydrogen ligands in the family of compounds of the type [MH, L~r (M = Ru ; L = monodentate ligand or two bidentate li gands) that are relevant to the current work~. In thi s paper, we report our in vestigati ons on the dynamic behaviour of the dihydrogen and the hydride li gands in IroIlS-[(dppm)Ru (H)(11 2-H2) (PPh' )2][BF4J.

Materials and Methods

General Procedure

All reacti ons were carried out under purified and dried N2 atmosphere except the ones involving the dihydrogen comBlex at room temperature using standard Schlenk 0 and inert atmosphere techniques unless otherwise stated. Reactions in volving the dihydrogen complexes were performed under H2 atmosphere and the solvents used for the preparation of the dihydrogen complexes were thoroughly saturated with H2 just before use,

The NMR spect ra were obtained usin g an Avancc Bruker 400 MH z spectrometer. The shirt or thc res idual protons of the deuterated solven t was uscd as an internal reference. Variabl e- tempcratu rc proton TI measurements were carried out at 400 MHz usin g thc in version recovery method". The .1I P1'H ) NMR spectra were recorded relati ve to 85% H,PO~

(aqueous so lution) as an ex ternal standard . Bi s(diphenylphosphino)methancI 2 and cis-I (dppm) s . RuH2(PPh,hl were prepared by literature methods.

Preparation of Iralls-f(dppm)Ru (H)(11 "-H z)( Pl'h.\)211 BF.d ( I)

To a suspension of c i.\· - [ (dppm)RuH ~ ( PPh')2 1 ( 15 mg, 0.014 11111101) in Et20 ( I mL) was added 54% HBF~ . E t20 (3 ~lL , 0.022 mmol). Immed iate reac ti on was ev ident and the product prec ipitated Oul. Thc product was washed wi th Et20 few ti mes to re l11 0vc the excess ac id and dried under a stream of H2 gas . For NMR characteri zati on, the dihydrogen complex was dissolved in CD2C12, whi ch was previoll sly freeze-pump-thaw degassed and sa turated with H2 and tran sferred to a 5 mm NMR tu be flushed with H2 gas. IH NMR (C D2C1}, 303 K): 8 -6.4 1 (br s, I H, Ru- H); - \.71 (br s, 2H, Yj 2-H2); 4.16 (m, 2H, PCN2P); 6.60-8.S0 (m, SOH , PP112, PPII .1) ' " P( ' H ) NM R (C D2CI2, 303 K): 84.2 (d, 2P, Ph2PCH2P Ph2, J (P,P","lS) = 186 Hz); 48.2 (d, 2P, PPh, ). The dihydrogen hyd ride complex (1) was prepared similarly in CIC D2CD2C1 solvent for va riable temperature NM R ex periments. ' H NMR (CICD2CD2C1, 303 K): 8 -6 37 (br s, I H, Ru-H); - 1.59 (br s, 2H, 11 2-N2); 4.27 (m, 2H, PCH2P); 6,60-S .40 (m, SOH , PPII2, PPII , ). " P( 'H ) NMR (CICD}CD}CI, 303 K): 8 3.4 (d, 2P, Ph 2PC H}PPh2,

J (P,P(r,"IS) = 188 Hz); 47,3 (d, 2P, PPh, ).

Observation of the H-D Isotopomer of Iralls-[(d ppm)Ru (H)

(11 2_ H2)(PPh.1h 1 r B F~ 1

The H-D isotopomer was obtaincd by purging HD gas (generated fro m D20 and NaH ) at a steady rate through a CICD}C D}CI soluti on of the dihydrogen complex for ca. 5 min. The HD isotopomer formed was observed by I H N M R spectroscopy.

Results and Discussion

Preparation and characterization of the dihyd ifOgen-h ydridc complex Iral1s-[ (dppm)Ru ( H)(11 2-H2)(PPh3h][IJ; F~1 ( 1)

The dihydrogen hydride complex (1) was prepared by protonating thc precursor dihydridc complex cis-[(dppm)RuH2(PPh, )2] using HBF~.Et}O

SIVAKUMAR & JACilRDA R: DYNAM IC PROCESSES or H-ATOM SITE EXCII ANGE 29

(Eq. I ) . The product was obtained as a cream-colored solid . The co mplex ( I ) was found to be stabl e in halogenated so lvents at room temperature for co. 2 days before i t decomposes into a spec ies that we ha ve not been ab le to identifyll; it is however, stabl e fo r much longer periods typi ca ll y I week or more at low temperatures (ca. - 5 to - 10 °C) .

The 11-1 N M R spec trum o f (l ) at room temperature in CD2Ci 2 shows two featureless broad signal s in the

hydri de reg ion at 8 - 1.7 1 and - 6.4 1 that integ rate to 2 to I number of protons respec ti ve ly indi cating th at the

down fi eld signal could be ass igned to the 112-1-1 2 and the upfield one to the hyd ride moiety . The broadness of bo th the hydride anci the dihydrogen signals in the room temperature spec trulll suggests that a dynamic process w:tS apparent. The :l Ip! 11-1) NMR spec trum

gave onl y two doublets at 0 4.2 and 48.2 w ith a .f(P,PI,a,,,) o f 186 I-I z indi cating thal the four P atoms were in pl ane w ith the two PPh, frall s to the two dppm phosphoru s atoms.

11-1 NM R TI measuremcnts

The variabl e-temperature spin -latti ce rela xati on

times CTI) for the 11 2-1-1 2 and the hydride hydrogen signals were determin ed in the temperature range 243-283 K in CiCD2CD2Ci solvent. The data are summari zed in Table I. As is evident, the TI data for the dihydrogen li gand shows a paraboli c beha viour w ith the TI(min ) (400 Ml-l z) o f 12.4 ms at 263/273 K whereas the T t values for the hydride moiety continuall y decrease from 243 to 283 K , thu s the hydride loses its identity at the high temperature limitl l, indi cating a flu x ional process in vo lving Ihe hydride ;lIlci the dihydrogen li gands. The 1-1 - 1-1 di stan ce has been cal culated from the TI minimum7h and found to be 1.03 and 0.82 A for th e slow and fas t rotati on regimes. At temperatures greater than 263 K , the TI values are we ighted averages for the rapidl y interconve rtin g tautomers invo lv ing the I-I -atom site

exchange (see la te r). I-I owever, from the line w idt hs o f the 1-1 2 and the hydride signal s in the 11-1 M R spectra as a functi on o f temperature, it is app:trent that the i nterconversion ac tu al I y sets in at temperat ures greater th an 273 K .

Variahle temperature III N i\ IR s pcctra or ( l ) in the hydrid e rc~i()n

T'he temperature-dependent 11-1 NMR spec tra of ( I ) in Ci CD2CD2Ci in the hydride reg ion is shown in Fi g. I . The temper:tture dependence o f the hydride and the dihydrogen signals is due to an intraillolecul ar I-I -atom site exchange process (see di scuss ion later). A t 273 K and below 400 MHz, the hydride resonance is a we ll-reso lved binomi al quintet ari sing from the I-I -Pc is couplings on the order o f 17 l-l z. T he hyd ride resonance broadens at temperatures greater than 273 K and goes into the base line at crt. 3 13 K. The broad

333K

323K

3LJK

293K

L ~ 283K

_Jl~ ~ 273K

J~ !L 263K

J~ l 253K

J~. Jl_ 243K

~,-.-" "" ' I " • • ',.,. , I" " '~~~n'n'~----r~" ~' n"l'

-1 -2 -3 -4 -5 -6 ppm

Fig. I - Variab le temperature .J OO MHz III NM R spect ra or lht: hydride region or 11'1111 .1'- 1 (d pplll ) R lI(I 'I )( ll ~ -1-1, )( PPh,h 11 13 r,ll in

ClCD,CD,CI

30 INDI AN J CHEM, SEC A, JANU ARY 2005

signal downfield to that of the hydride due to the dihydrogen moiety remains broad in the temperature range studied (243-3 13 K). The large line width of thi s resonance is due to the rapid dipolar relaxa tion of these nuclei lead ing to short T,I~ and T2 values I); the unresolved H2, P couplings are embedded in thi s signal. The broadening of the Hz signal below 273 K is caused by the ex pected decrease in To of the nuclei. The hyd ride and the dihydroge n signal s undergo broadeni ng above 273 K and at 323 K, coalesce into the base line. A broad resonance reappears at 8 -2.90 at 343 K indicating the fast exchange limit of the H­atom between the dihydrogen and the hydride ligands.

From the NMR spectral peaks, the Tz values were obtai ned and the rates of H-atom exchange (k) from the dihydrogen (Hz) to the hydride (H) site. The rate constant data is summarized in Table I. An Eyring plot of In (kiT) vs liT was found to be linear from which the acti vation parameters fo r the dynamic process were calculated to be t:..H+ = 19.6 kcallmol, t:..S+ = 17 .2 cal/mol, and t:..G" (303 K) = 14.4 kcallmol. The small t:..S + value indicates that the process is intramolecular. The t:..G+ obtained for complex (1) falls within the range observed for the H-atom site exchange processes for certain dihydrogen-hydride co~nplexes of the type trans-[(di phosphine)2RuH (,rr-H2)r as reported by Morri s et al.7h The t:..G+ values for similar processes in cis dihydrogen-hydride

Table 1- TI (400 MHz, CICD2CD2CI) va lues fo r the hydride and the dihydrogen ligands and rates of H-atom excha nge (k) trom the dihydrogen site to the hydride site in trallS-[(dppm)

Ru(H)(11 2- H2)(PPhJh l[BF41

T, K TI (ms), 112-H 2 TI (ms), H

243 17.3 288 .6

253 13.9 137.5

263 12.4 67 .7

273 12.4 37.5

283 15.2 24.5 22

293 110

303 305

3 13 577

333 4185

343 10291

complexes are much small er3-4. 16.

Variable temperature 31p{ I HI NMR spectra 0 (' (1)

In order to probe the rearrangements of the phosphorus ligands around the met~J center, we carried out the VT 3I p{ IH} NMR study of (1 ) in the temperature range 283-348 K in CICDoCDoCI. Fin. 2 shows the VT 3I p{ IH} NMR spectra illustrating "'the dynamics of the P atoms. The spin sys tem is expected to be AA'XX' at low temperatures, however, we observed on ly two doublets in the 3Ip (I H} NMR spectra. At temperatures of 303 K and hi gher, the coupling constants average out. Thus, there is movement of the phosphorus nuclei from one site to the other. Even at 348 K, the dynamic process involving rapid interchange of the axial :l.llcl equatori al p atoms (see di scussion of the mechani sm later) is not fast enough to render the two resonances into two singlets .

Preparation, properties, and variahle temperature 1/-1 NMR study of the H-D isotopomer

The H-D isotopomer trall s-L(dp pm )Ru(H)

348 K ~~_'-V"'Al~ mK~;l~,_JL

m.~I~ ~.~~_~~ ___ ~Jt~ 323 K

--L~Lm" L~ 3 0 3 K

293 K

2 83 K

ppm

Fig. 2 - Variable temperature 400 MHz Jl p{ 'H I NMR spectra of trallS-[(dppm)Ru(H)(112-H2)(PPhJhlfBF4] in CICD2CD2CI

SIYAKUMAR & JAGIRDAR DYNAMIC PROCESS ES OF H-ATOM SITE EXCHANGE 3 1

(11C-HD)( PPh3)2r was prepared by ex pos ing the 11 2- H2 complex to HD gas. Various isotopomers differing in the extent of deuterium incorporati on are poss ible. They are formed when the intramolecu lar H-atom exchange is slow. The first isotopomer formed upon exchange of H2 with HD is lralls-[(dppm)Ru (H) (rrHD)( PPh,ht which can transform into Ir([IIS­

[(dppm)Ru(D)(112-H2)( PPh,)2r; further reac ti on with more HD gas could result in HD2 species .

The 112-HD ligand of lralls-[(dppm)Ru(H) (112-HD)(PPh3)2r was observed in the IH NMR spectrum (Fi g. 3) at 243 K by nullifying the res idual 11"_H2 signal by an in vers ion recovery pulse

7h.1 7 A . I . h I I" sequence . signa Wit a most I: I: Intensity ratio was obta ined for the HD isotopomer with a J(H,D) of 32 Hz. The H- H di stance (dllH ) calcul ated from the in verse relati onship between d l-IH and J(H ,D)

• . 18 I I) . 0 • •

of the HD Isotopomer ' IS 0.88 A. ThiS va lue IS consistent with the H-H distance of 0.82 A obtained from TI meas urements assuming rapid rotation of the H2 li gand . In addition, each one of the three signals shows an approximate quintet pattern due to the coupling with the fo ur cis phosphorus atoms with a J (H2,PciJ = 5-7 Hz. At temperatures higher than 273 K, the onset of site exchange process causes line broadening and the H-D couplings are averaged out. We were able to resolve the H-D coupling at 263 and 253 K and found to be 28 and 31 Hz respectively . At temperatures higher than thi s, the resolution was poor circumventing the measurement of J(H,D). At the

I - 1. 4

I ' -1.5

, , I ' ,

- 1.6 ppm

Fig. 3 - I H NMR spectrum (hydride reg ion) of Irw/s-I (dppm) Ru(H)(r{HD)(PPh

')2lfBF4 1 (400 M Hz. 243 K) in CICD,CD,C1

wilh the residual signal due to 111_H1 ligand nullifie-d -

fast-exchange limit the J(H ,D ) would be expected to be small due to rapid intramolecular exc hange of HID atoms in the HOc isotopomer. Morri s sugges ted that three nuclei (H, 0 , D) need not retain bonds between themselves in order to give an averaged J (H,D) value7

". Small iso topic upfi eld shi fts of 3-8 ppb were noted in the HD isolopomers. Thi s upfi eld shirt is typ ical for dihydrogen complexes20.

Mechanism of the intramolecular H-atom exchange

Based on the VT IH NMR spectroscopic stu dies, we propose that the H-atom site exchange invo lves the homolytic cleavage of the H-H bond to give a flu xional trihydride intermed iate, which allows for the exchange of the H-atom. The barri ers for the H-atom site exc hange for lralls di sposition of the hydride and the dihydrogen li gands are usuall y higher compared to the sys tems that have the hydride and the H2 ligands in cis conformations'- Thus, the proposed mechani sm shown in Scheme 2 is consistent with a high value of 6.G 1 of 14.4 kcallmol. Signifi cant rearrangements have to take place in volving a fluxional seven coordinate pentagonal bipyramida l structure; the VT 31p NMR spectral data is consi stent with a site exchange of the axial and the equatori al r atoms as shown in the scheme. Another possible mechani sm involving the isomeri zation of the lrans

P* P'

H, I P H l"r ". Ru' ~ RU-H

/ I~H p~ l \ P H* ~p*H* L p*

if p

I P* H . " : RU-H

p~l\ ~p*H*

if P* p* p

H .p H_ :~H I-Ru'-' -H

~ Ru H* / ~ '1\ P~P* H* p'

P--1

Scheme 2

:n IN D IAN J C1-IEM. SEC A. JANUA RY 2005

clih ycl rogen hyd ride CO lllp leX to the cis isomer fo ll owed by the exchange o f the I-I -atom could be rul ed out hecau se no observabl e II -Plla", couplings were seen III the 1 1-1 NMR spectra at any

0 1 temperat ure- .

Interaction or 1-1 1 with the l1Ietall'l'llter

It is interes ting to note here that the chemical shift

of the l-i2 signal in (1) is quite downf ield (0 - 1.7 1 in

CD2C1 2; 8 - 1.59 in CIC D2CD2C1). In add iti on to our comp lex, there arc few other dihyd rogen co mplexes r~po rted in the literature th at show far c!ownfield

I .[. [. I 0 1-1 I ' I" (Jc d TI chem ical s 11 ts 0 t l e lr - 2 Igane --. ' . 1e appearance of the 11 2 at a signi f icantly down fi eld reg ion might suggest that the interaction o f 1-12 w ith the me tal is very weak and perh aps has properti es close to those of free 1-1 2. On the contrary , we found that despite heatin g the cO lllplex (I ) to ca. 343 K , no 1-1 2 loss was observed. M ore work is needed to understand thi s behav iour. Upon cooling the sample back to room temperature, the independent resonances for the hydride and the dihydrogen mo iet ies reappeared.

Conclusion

A new d ihydrogen hyd ri de complex Imll .\'­

l (dppm)Ru(l-I)(11 2-112)(PPI1 ])2J[BF.1l has been prepared and characteri zed. Thi s co mplex was found to be dy namic: I-I-atom undergoes exchange between the 1-1 2 and the hydride li gands. T he mechani sm in vo lves a

trihydride spec ies w ith a 6.C+ o f 14.4 kcal/mol at 303 K for the dynamic process.

Acknowledgement

We arc grateful to the Counc il o f Sc ientifi c and Industri al Research, India for the f inancial support. Acqui siti on of a 400 Ml-l z NMR spectrometer was supported by the Department of Sc ience and Technology, India under the ;'FIST" program . We also thank M r. Chandrashek har and Mr. G . Th iru illanavelan for help w ith acquiring the N MR spectral data.

References

Kubas Ci J, Ryan R R. Swanson 13 I. Vergailli ni R J & W;ISSC I'I11an II J • .J 11111 Chelll So!'. 106 ( 10X4) 45 1.

2 (a) Kuhas G J. M ct al Dih ydmgcn and (J-l3 ond CO lllplcxc:s: (Klu wc l' Acadell1 ic: Ncw York ). :WOO: (b) e,usev J) G. Kuh lman R L. Rcnkcma K B. Eiscnstcin 0 & Caulton KG. I ll o rg Chell /. ]5 ( I (06) 6775.

] (; 1) Heinckey 0 M. M ellmvs 1-1 & PI'atu lll T, .I / \ 111 CI/{' III

Sw, 122 (2000) 6,,) t)X -()..)0t) and refcl eil ces t herci n: (b) Kranen bu rg M. Kamer I' C J. van Lecu",'cil \V N M 8: Ch;llld rct n. Choll COIIIIIIllll. ( 1t)07) "7.

..) JessopI' Ci c' Morri s R II. Coord Chelll liel·. 12 1 ( 1002) 155.

5 (a) Maseras 1-'. Kog;1 N & Milrokuma K. Org lllllllll!' lltilics .

13 ( 100·1) ")OOX. (h) MasCl';ls r:. Duran M. Li ed(')s !\ & l3ert r;·11 .1 . .1 1\111 CIII' III

Sill . 11 4 ( I (02 ) 2<)22. (cl M asel'as F. Du r;ln M. Li cLi(ls i\ 8.: Ben r:1I1 J . .I / \ 111 CiII' II/

Soc. II ]( 190 1) 2X70.

6 (;1 ) Ciu sev D C. li lihener R. llul'ger 1'. Orailla () & Ik rkc I I. J 11111 ClICIII Sill' . I It) ( I ')<)7) 37 16. (h) euse v D e & Berke II. Cit !' II I /31'1'. 12<) ( 1')%) I I") ". (c) Chrisl M L. Sabo-Et ienllc S. Chung Ci & Ch;ludn:t Il. I llorg Cit I'll I. ]] ( 100,,) 5J 16.

7 (;1) Ea rl K A. Jia C. Ma lthy P A 8.: Morri s R 1-1 . J / \ 111 ClII' 1I1

Soc. I I] ( 19<)1 ) :1027. (h) 13auti sta M T . Cappell an i E 1'. Drouin S D, MOl'ris R II. Schwe it zer C T , Se l la A & Luhkowski J, J / \ 111 ClI(' 11I Soc.

I [] ( 199 1 ) 4876.

R Chaudre t n, Comillenges e & Po il blane R . .I ClII'1I1 Soc

D llllOll Trall.l . ( 10X4) 16]5.

o (a) Osakada K. Ohshi ro K & Yalll ;lllloto A . OrgallOlIlI' /(/l/in , 10 ( 100 I ) 40..). (b) Amendo la p, AnlOniu ll i S. Albenin Ci Lie l3ord igllon E. I llorg CItl'lll. 29 ( 1900) ] I X. (e) Tsuka hara T . Kawa no II, Ishi i Y, Takalwshi T. Sahul'i M , Uchida Y & Akutagawa S. Cllelll L ell. ( I <)R:) 20SS. (d) Sahuri M , Aoyag i K, Ta kahashi T & Uchi(L\ Y. Cli I'll I

LI'II . ( I <)00) 60 1. (e) Saburi M. Aoyagi K . Tak euchi H. Ta ka hashi T & Uchi da Y , CIt I'll I LI'II. ( 10<)0) 99 1. ( I,) Saburi M , Auyagi K , Kodama T . Takah ashi T . Uchida Y. Kozawa K & Uchida T . Clle/II t ('/{o ( 19<)0) 10()t). (g) Mezzeu i A. Del ZOllO A. Rigo P & Fa rill: II i E . .I ClWIII

Soc, Dal/()II TrailS. ( 1091 ) 1525. (h) Field L D. Hamb ley T W & Yau 13 C K. !lI l1 r~ ClII' II/. 3:1 ( 1<)04) 2009. ( i) Og;lsaw;.lI'a M & Saburi M. J Orgw/I)(:tc / ClII'II/. 4 :)2

( 1904) 7.

10 (a) Shl'ive l' D F & Drezdon M A. Tit!' Mlllliplilmioll o( /\ ir­

S('//.I'i/il'l' COll ljiOlilli/S. 2"d ed.: (W iley: New York ). 10R6. (b) Herzog S. Dchnen J & L uhder K. in Tee/Ill iI/II I' or I llorgallic Cllelliis/f)' Vol. V I I. cdited by I-I B Johnassen: ( Intersc ience: Ncw York ) 1069.

II Hami ltun DC & Crahtree R H . .I 11111 CItOIl S(}I' . 110 ( I 0XX) 4 126.

12 Ilcwcnson W & Wa tson II R • .I ClICIII Soc. ( I <)61) 1400.

13 T he decomposed product was obtained in a ve ry sillall amount after two days ;It ['()OI11 tCl11 pcralUrc . The so lutioll contained (I ) stil l as the l11ajor component.

14 Desros iers P J. Cai L . Lin Z. Rich;lI'(ls R & I-bl pern J . .I !l1I1

Cit I' ll I Soc, I I ] ( 190 I ) 417:>.

I S Yao W, r ai ler J W & Craht ree R H. I llorg ClIIIII /\ ('11/.15') ( 1<)07) 7 1.

SIVAKUMAR & JAGIRDAR: DYNAM IC PROCESSES OF H-ATOM SITE EXCHANGE :13

16 (a) Oldham W J. Jr.. Hinkle A S & Heinekey D M. J Alii

Clielll S(I('. I 19 ( 1997) I 102 8. (b) Jia G. Drouin S D. Jessop P G. Lough A J & M orri s R H. Orgflllolll(' l (ll/ics . 12 ( 1993) 906. (e) Bianchini C, Perez P J. Perru zini M . Zanohin i F & Vacca A. Illo rg Chelll, 30 ( 1991 ) 279. (d) Bampos & Ficld L D. Ill org Chelli . 29 ( 1990) SX7. (e) Bianchini C, Pcrru zzini M & Zanohini F . .I Orgw/olliel Clielll , 384 ( 198X) C 19-C22. (f) Crabtree R H. La vin M & Bonnev illl L. .I 11111 Chelll Soc. 108 ( 1986) 4023.

17 Chinn M S. Heinekey D M . Payne N G & Sorield C D. Orgll ll li lll elli l/ic.l. 8 ( 1989) 1824.

18 (a) Hei nekey D M & Luther T A, I llorg Chel ll, 35 ( 1996) 4396. (h) Maltby I' A. Schlar M , Stcinbcck M . Lough A J. Morri s R II , Kloostcr W T. Koetzlc T F & Srivasta va R C, .I 11111 CliI!III Soc. 11 8 ( 1996) 5396. (e) King W A. Luo X-L, Scott 13 L. Kubas G J & Z ilm K W . .I Alii CliOIl Soc. 11 8 ( 1996) 6782.

19 dllll (A ) = - O.0167[.I (H.D)(Hz) [+ 1.42.

20 (a) Maju mdar K K. Nan ishankar H V & Jagil'e1ar 13 R. Ellr .I IlI lirg Cheill. (200 I ) I 847. (b) Luthcr T A & Hcinckey D M. I llorg Chelli . 37 ( 1998) 127. (c) Hascgawa T F & Taubc H. J Alii Chl'lll Soc. 11 6 ( 1994) 4352.

(e1) M oreno 13, S:Jbo-Et ienne S. Ch:Judret 13 , Rodri!!uez­Fernandez A. Jal6n F & Trori mcnko S, .I Alii Chelll Soc~ I 16

( 1994 ) 2635. (e) Co llman J P. Wagenknecht P S. Hutchi son J E. Lcwis N S, Lopcz M A. Fuilard R. L'Her M , I3 othner- I3 y A A & Mishra P K, .I Alii ClI('III Soc, 11 4 ( 1992) 565-+. (I) Crabtree R H & Habib A. Illo rg Cliell/, 25 ( 1986) 3698.

2 1 J(H.PII·,,,,,) couplings are usually large and observah le in the IH NMR spectra. See ror example: . (a) M athew N, Jagirdal' 13 R & Ranganathan A. I llorg Clloll . 42 (20m) 187. (h) Mathew N, Jag irdar 13 R. Gopalan R S & Kulkarni G U. Org(lI/lJ/llel(ll/ics. 19 (2000) 4506. (c) Berger S. I3raun S & Kalinowsk i H- O. NMR

SjJe('/mscojJv of Ill e NOIl-Mellillic EiI'II 11'1 i1s: (Wiley. Ch ichester, U. K), 1996: pp 895-98 1 and rererences therein . (d) Guesmi S, T:l y lor N J, Di xneuf P H & Carty A. J. Orgall()flll'lIiilics. 5 ( 1986) 1964. (e) T:Ju K D & Meek D W . I llorg Clielll. 18 ( 1979) 357-+ . (I) GalTou P E & Hartwell G E. Ill org Chell!. 15 ( 1976) 646. (g) George T A & Sterner C D. i llorg Clielll, 15 ( 1976) 165.

22 (a) Cameron T M , Orti z C G, Ghiv ir iga I. Abboud K A & l30ncella J M , J 11111 Chelll Soc, 124 (2002) 922: M O- ll "-H" 0 3.59 (a stretched dihydrogen complex) . (b) l3akhmutov V I. I3ertran J. Esteruelas M A. Lled6s A . Maseras F, Modrego J, Oro L A & Sola E, Ch I'll I Ellr J. 2

( 1996) 815-825: OS-11"-H2 15 - 1. 8: thi s paper reports the dynamics or H-atom site exchange hetween the di hydrogcn and hydride ligands through a cis-hydride dihyelrogell i ntenneeliate. (e) Gusev D M . Vymenit s A 13 & Bakhmlltov V I. Illo rg

Clielll , 31 ( 1992) I : RU-1l 2-H2 15 - 0.8.