DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 181–192 181 Synthesis and reactivity of [OsH{C6H4(CH] CHH)}(CO)(PPri 3)2] and the formato compounds [Os{(E)-CH] CHPh}(Á2-O2CH)- (CO)(PPri 3)2] and [OsH(Á2-O2CH)(CO)(PPri 3)2]* María J. Albéniz,a Miguel A. Esteruelas,a Agustí Lledós,b Feliu Maseras,b Enrique Oñate,a Luis A. Oro,a Eduardo Sola a and Bernd Zeier a a Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza, CSIC, 50009 Zaragoza, Spain b Departament de Química, Universitat Autónoma de Barcelona, 08193 Bellaterra, Barcelona, Spain The complex [OsH{C6H4(CH]] CHH)}(CO)(PPri 3)2] has been prepared by reaction of the five-co-ordinate [Os{(E)-CH]] CHPh}Cl(CO)(PPri 3)2] with LiBun in hexane.It reacts with P(OMe)3 and CO to give [OsH{(E)- CH]] CHPh}(CO){P(OMe)3}(PPri 3)2] and [OsH{(E)-CH]] CHPh}(CO)2(PPri 3)2], while under a CO2 atmosphere the formato derivative [Os{(E)-CH]] CHPh}(h2-O2CH)(CO)(PPri 3)2] is obtained.Carbonylation of the latter leads to the monodentate formato complex [Os{(E)-CH]] CHPh}{h1-OC(O)H}(CO)2(PPri 3)2] and under a hydrogen atmosphere it affords styrene and [OsH(h2-O2CH)(CO)(PPri 3)2], which can be also prepared by reaction of [OsH2(h2-CH2]] CHEt)(CO)(PPri 3)2] with CO2. The complex [OsH(h2-O2CH)(CO)(PPri 3)2] reacts with CO, P(OMe)3 and MeO2CC]] ] CCO2Me to give [OsH{h1-OC(O)H}(CO)L(PPri 3)2] [L = CO, P(OMe)3 or MeO2CC]] ] CCO2Me]; the carbon atom of its formate ligand is attacked by NEt2H leading to the carbamato compound [OsH(h2-O2CNEt2)(CO)(PPri 3)2] and molecular hydrogen.Similarly treatment of [Os{(E)-CH]] CHPh}- (h2-O2CH)(CO)(PPri 3)2] with NEt2H afforded [Os{(E)-CH]] CHPh}(h2-O2CNEt2)(CO)(PPri 3)2]. The former complex also reacts with HBF4?OEt2, giving two different derivatives depending upon the conditions: in diethyl ether as solvent and in the presence of acetonitrile the vinyl complex [Os{(E)-CH]] CHPh}(CO)(MeCN)2- (PPri 3)2]BF4 is formed, while the carbene derivative [Os(h2-O2CH)(]] CHCH2Ph)(CO)(PPri 3)2]BF4 is obtained in chloroform.The products formed by reaction of [OsH(h2-O2CH)(CO)(PPri 3)2] with HBF4?OEt2 also depend upon the reaction conditions: in diethyl ether and in the presence of MeCN the hydrido compound [OsH(CO)- (MeCN)2(PPri 3)2]BF4 is obtained; however a mixture of products, mainly dihydrogen derivatives, is formed in CDCl3. On the basis of theoretical calculations and T1 measurements, the nature and structure of these dihydrogen compounds are discussed. In the search for homogeneous transition-metal systems effective in the synthesis of functionalized organic molecules from basic hydrocarbons, we have recently observed that treatment of the alkenylosmium(II) complexes [Os{(E)-CH]] CHR}- Cl(CO)(PPri 3)2] (R = H or Ph) with main-group organometallic compounds leads to osmium(0) species containing olefin ligands.As shown in Scheme 1 for LiMe, these transformations involve replacement of the Cl2 anion by the organic fragments of the main-group organometallic compounds, and subsequent reductive carbon–carbon coupling of the h1-carbon ligands.†,1,2 For butadiene and phenylbutadiene the osmium(0) species are stable, and do not undergo subsequent transformation.1 However, for trans-stilbene and trans-methylstyrene, the metallic centre is capable of activating a C]H bond of the substituents of the co-ordinated olefin to afford hydridoosmium(II) derivatives.2 The C]H activation products depend upon the substituents present at the alkene ligand, and can be rationalized in the light of thermodynamic and kinetic considerations. Thus, when the alkene ligand is trans-methylstyrene, the activation of an ortho position of the phenyl ring is kinetically favoured.The product of this activation, which shows an agostic interaction between the osmium centre and one of the olefinic C]H bonds, evolves to the more favoured thermo- † Non-SI unit employed: cal = 4.184 J.dynamic product [OsH(h3-CH2CHCHPh)(CO)(PPri 3)2] (Scheme 1).2 Products from the oxidative addition of the olefinic C]H bonds of trans-methylstyrene were not observed. This does not necessarily imply that the olefinic C]H activation in [Os(h2-MeCH]] CHPh)(CO)(PPri 3)2] is kinetically disfavoured with regard to C]H activation of the phenyl ring. At first glance, low activation barriers should be expected for all the possible intramolecular C]H activations in osmium(0) intermediates like [Os(h2-MeCH]] CHPh)(CO)(PPri 3)2], in view of the mild isomerization conditions and the values of the activation enthalpies reported for this kind of reaction.3 So, the non-observation of hydridoalkenyl complexes could probably be a consequence of their lower thermodynamic stability compared to the hydridophenyl derivative [OsH{C6H4[(E)-CH]] CHMe]-2}(CO)(PPri 3)2].As a continuation of our work in this field, and with the idea of casting some light on olefinic C]H activation compared to C]H activation of the ortho position of the phenyl ring in osmium(0)–phenyl–olefin species, we have now studied the reaction of [Os{(E)-CH]] CHPh}Cl(CO)(PPri 3)2] with LiBun.In this paper, we also report the synthesis and characterization of [OsH{C6H4(CH]] CHH)}(CO)(PPri 3)2], [Os{(E)-CH]] CHPh}- (h2-O2CH)(CO)(PPri 3)2] and [OsH(h2-O2CH)(CO)(PPri 3)2], and the reactivity of the formato compounds towards CO, P(OMe)3, H2, NEt2H, alkynes and HBF4.On the basis of182 J. Chem. Soc., Dalton Trans., 1997, Pages 181–192 spectroscopic data and theoretical calculations, the nature of the compounds formed by addition of HBF4 to [OsH(h2-O2- CH)(CO)(PPri 3)2] is also discussed. Results and Discussion Reaction of [Os{(E)-CH]] CHPh}Cl(CO)(PPri 3)2] with LiBun Reaction of the five-co-ordinate alkenyl complex [Os{(E)- CH]] CHPh}Cl(CO)(PPri 3)2] 1 with LiBun in hexane at room temperature gives a yellow solution from which the hydridoaryl derivative [OsH{C6H4(CH]] CHH)}(CO)(PPri 3)2] 2 (Scheme 2) was isolated as a colourless oil in quantitative yield.In the presence of a trace of water this compound evolves into the previously reported [OsH2(h2-CH2]] CHPh)(CO)(PPri 3)2].4 Scheme 1 (i ) LiMe Scheme 2 The 1H NMR spectrum in C6D6 shows in the hydrido region a triplet at d 28.01 with a P]H coupling constant of 27.3 Hz. The low-field region contains the expected resonances for the 2- vinylphenyl ligand. The PhCH]] proton appears at d 4.95 as a doublet of doublets with H]H coupling constants of 9.0 and 7.7 Hz.The olefinic proton disposed cis to this appears at d 2.74 as a doublet while that disposed trans, consistent with the agostic interaction, displays a doublet of triplets with a P]H coupling constant of 5.7 Hz. In the 13C-{1H} NMR spectrum the olefinic carbon atoms gave rise to two broad signals at d 50.5 and 46.3.The aryl carbon atom linked to the metal is observed at d 138.6 as a triplet with a P]C coupling constant of 10.0 Hz. The 31P-{1H} NMR spectrum has a singlet at d 16.7 indicating that both phosphine ligands are equivalent and mutually trans disposed. These spectroscopic data agree well with those previously reported for the related complexes [OsH{C6H4[(E)-CH]] CHR]-2}(CO)(PPri 3)2] where a Os? ? ?H agostic interaction has been confirmed by X-ray diffraction.2 Complex 2 reacts with trimethyl phosphite and carbon monoxide in hexane at room temperature to give the six-co-ordinate hydridostyryl derivatives [OsH{(E)-CH]] CHPh}(CO)L(PPri 3)2] [L = P(OMe)3 3 or CO 4] (Scheme 3) which were isolated as white solids in good yields [85 (3), 72% (4)].The IR spectrum of 3 in Nujol shows two absorptions at 2050 and 1910 cm21, which were assigned to the n(Os]H) and n(CO) vibrations, respectively. The 31P-{1H} NMR spectrum contains a triplet at d 102.4 [P(OMe)3] and a doublet at d 17.5 (PPri 3) with a P]P coupling constant of 18.6 Hz, consistent with two equivalent PPri 3 ligands both cis disposed to the trimethyl phosphite group. The relative trans position of the hydride and phosphite ligands was inferred from the hydrido signal in the 1H NMR spectrum, which appears as a doublet (JP]H = 134.4 Hz) of triplets (JP]H = 24.5 Hz) of doublets (JH]H = 1.6 Hz) at d 28.94. In the low-field region the most noticeable resonances are those corresponding to the vinyl protons of the styryl ligand, which appear at d 8.78 (OsCH]] ) and 7.03 (]] CHPh).The trans stereochemistry of the two hydrogen atoms at the C]] C double bond is supported by the value of the H]H coupling constant (18.3 Hz), which is typical for this arrangement.5 In the 13C-{1H} NMR spectrum the Ca carbon atom of the styryl ligand appears at d 143.3 as a virtual quartet with a P]C coupling constant of 13.4 Hz, while the Cb carbon atom displays at d 144.4 a doublet of triplets with P]C coupling constants of 10.1 and 4.2 Hz.The spectroscopic data obtained for complex 4 also support the structure proposed in Scheme 3. The cis relative position of the carbonyl ligands was inferred from the IR spectrum in Nujol, which shows, together with the n(Os]H) band at 1990 cm21, two strong n(CO) absorptions at 1945 and 1865 cm21, typical for mononuclear cis-dicarbonyl complexes. The Scheme 3J. Chem. Soc., Dalton Trans., 1997, Pages 181–192 183 13C-{1H} NMR spectrum also supports this proposal, showing two triplets at d 190.4 (JP]C = 5.5) and 185.5 (JP]C = 7.8 Hz) attributable to the carbonyl ligands.It also contains the expected resonances for the vinylic carbon atoms of the styryl ligand, which appear at d 142.5 (Cb) and 135.2 (Ca) as triplets with P]C coupling constants of 3.7 and 12.9 Hz, respectively. The CH groups of the phosphine ligands give a virtual triplet at d 26.2 (N = 27.6 Hz), which is characteristic of the two equivalent phosphine ligands in a trans relative position.This is consistent with the singlet at d 19.0 found in the 31P-{1H} NMR spectrum. The 1H NMR spectrum shows the hydrido resonance at d 27.13 as a triplet (JP]H = 22.0 Hz) of doublets (JH]H = 5.0 Hz). The vinylic protons of the styryl ligand appear at d 8.34 (OsCH]] ) and 7.20 (]] CHPh). The value of the Ha]Hb coupling constant (16.1 Hz) is also in agreement with the proposed E stereochemistry at the C]] C double bond.On the basis of our previous reports1,2,6 the reactions shown in Schemes 2 and 3 can be rationalized according to Scheme 4. The reaction of 1 with LiBun to give 2 most probably involves replacement of the Cl2 anion by a butyl group to afford the intermediate 5, which by subsequent hydrogen b elimination could give 6. In this context, it should be mentioned that the reaction of the five-co-ordinate complex [OsH(Cl)(CO)- (PPri 3)2] with LiBun affords [OsH2(h2-CH2]] CHEt)(CO)- (PPri 3)2].6 The reductive elimination of styrene from 6 followed by the C]H activation of the o-aryl proton should lead to 2 via the styreneosmium(0) intermediate 7.In spite of the fact that 2 is the only species detected in solution, the formation of 3 and 4 from 2 (Scheme 3) suggests that in solution complex 2 is in equilibrium with no detectable concentrations of 6. This implies that 7 is easily accessible and can give rise to activation reactions at both the olefinic and the ortho phenyl C]H bonds of the co-ordinated styrene.Although 2 is more stable than 6, the latter is more substitution labile. In addition, it should be pointed out that the olefinic C]H activation is selective, thus Scheme 4 (i ) LiBun; (ii) P(OMe)3 only the C]H bond disposed trans to the phenyl group is activated. Consistent with the high selectivity observed for the olefinic C]H activation, the reaction of the deuteriated complex [Os{(E)-CH]] CDPh}Cl(CO)(PPri 3)2] 1a with LiBun leads to [OsH{C6H4(CD]] CHH)}(CO)(PPri 3)2] 2a, and the addition of trimethyl phosphite to 2a affords [OsH{(E)-CH]] CDPh}- (CO){P(OMe)3}(PPri 3)2] 3a containing the deuterium atom at the Cb carbon atom of the styryl ligand (Scheme 5).The position of the deuterium atoms in these compounds was inferred from the 2H NMR spectra, which contain resonances at d 5.03 (2a) and 7.01 (3a). The reaction of the Ca-deuteriated complex [Os{(E)-CD]] CHPh}Cl(CO)(PPri 3)2] (1b) with LiBun, in contrast to that of Cbdeuteriated 1a, produces a mixture of four deuteriated derivatives in approximately 1 : 1 : 1 : 1 molar ratio, as shown by the 2H NMR spectrum which contains four resonances with the same intensity at d 6.52, 3.68, 2.65 and 28.02.According to the 1H NMR spectrum of 2, these resonances were respectively assigned to the complexes 2b, 2c, 2d and 2e of Scheme 6. The presence of 2b, 2d and 2e in the mixture suggests that in 2 the terminal olefinic carbon atom interacts with the hydride ligand, thus the migration of the hydride onto the olefinic terminal carbon atom and subsequent hydrogen extraction from the resulting methyl group could explain the deuterium distribution.Direct migration of the hydride from the osmium atom onto the terminal olefinic carbon atom does not seem likely in view of the mutually trans disposition of the hydride and the agostic interaction. Hence it could be proposed that the exchange process proceeds by a five-co-cordinate aryl intermediate, resulting from cleavage of the agostic interaction.Although this intermediate has not been detected by NMR spectroscopy, even at 280 8C, one should assume it, giving that at high temperatures important amounts of the relative five-co-ordinate aryl derivatives [OsH{C6H4(CH]] CHR)}(CO)- (PPri 3)2] are in equilibrium with the six-co-ordinate complexes [OsH{C6H4(CH]] CHR)}(CO)(PPri 3)2] (R = Me or Ph).2 The 2H NMR spectrum of the solution formed by addition of ca. 1 equivalent of trimethyl phosphite to the mixture of Scheme 5 (i ) LiBun; (ii) P(OMe)3184 J. Chem. Soc., Dalton Trans., 1997, Pages 181–192 Scheme 6 (i ) LiBun; (ii) P(OMe)3 complexes 2b–2e in benzene shows two broad singlets at d 8.81 and 7.46 and a doublet at d 28.88, with a P]D coupling constant of 20.2 Hz. According to the 1H NMR spectrum of 3, the singlets correspond to complexes 3b and 3c of Scheme 6, respectively, while the doublet is due to the derivative 3d.The formation of these compounds is new evidence in favour of the equilibrium between 2 and 6 (Scheme 4). Thus complex 3b is the product of the reaction of 2c with P(OMe)3, 3c is formed from 2b and 2e in the presence of the phosphite, while 3d is a result of the addition of the ligand to 2d. Synthesis and reactivity of [Os{(E)-CH]] CHPh}(Á2-O2CH)- (CO)(PPri 3)2] and [OsH(Á2-O2CH)(CO)(PPri 3)2] Passing a slow stream of carbon dioxide through a hexane solution of complex 2 affords the formato complex [Os{(E)-CH]] CHPh}(h2-O2CH)(CO)(PPri 3)2] 8 (Scheme 7).This compound was isolated at 278 8C as a microcrystalline solid in 75% yield. The formation of 8 from the reaction of 2 with CO2 is consistent with the proposal that in solution 2 is in equilibrium with no detectable concentrations of 6 (Scheme 4). Thus, the reaction Scheme 7 can be easily rationalized as the transfer of the hydride ligand from 6 to the carbon atom of the CO2 molecule.The h2 co-ordination mode of the formate ligand in complex 8 is indicated by the IR spectrum in Nujol, which contains bands at 1300 and 1560 cm21 assignable to the symmetric and asymmetric (OCO) stretching frequencies, respectively.7 The value of the asymmetric n(OCO) stretching is very similar to that of 1565 cm21 for [RuH(h2-O2CH)(PPh3)3], which contains a chelating formate ligand as confirmed by X-ray diffraction.8 This value is also in agreement with those previously reported for the complexes [MoH(h2-O2CH)(dppe)2] (dppe = Ph2PCH2CH2PPh2; 1550 cm21) 9 and [RuH(h2-O2CH){PhP[CH2CH2- CH2P(C6H11)2]2}] (1575 cm21).10 Other characteristic bands are observed at 1900 and 1540 cm21 and were assigned to the n(CO) and n(C]] C) stretchings, respectively.The 1H NMR spectrum in C6D6 shows resonances due to the triisopropylphosphine ligands and the phenyl group, along with a doublet at d 9.09 (JH]H = 15.6 Hz), a triplet at d 8.63 (JP]H = 1.9 Hz) and a doublet of triplets at d 6.46 (JH]H = 15.6, JP]H < 1 Hz), which were assigned to the Os]CH]] , O2CH and ]] CHPh protons, respectively.The most noticeable signals in the 13C-{1H} NMR spectrum are three triplets at d 174.4 (JP]C = 1.4), 137.0 (JP]C = 9.7 Hz) and 132.8 (JP]C = 2.7 Hz). The triplet at d 174.4 was assigned to the carbon atom of the formato group by comparison of this spectrum with that previously reported for the complex [Re(h2- O2CH)(dppe)2] (d 171.9).11 The other two triplets were assigned to the Ca and Cb carbon atoms of the vinyl ligand.The 31P-{1H} NMR spectrum has a singlet at d 15.6, indicating that the two phosphine ligands are equivalent and are mutually trans disposed. Carbonylation of the bidentate formato complex 8 leads to formation of the monodentate formato derivative 9 (Scheme 8). The reaction was carried out in hexane, and complex 9 was isolated as a white solid in 83% yield.In agreement with the mutually cis disposition of the two carbonyl ligands, the IR spectrum in Nujol shows two n(CO) absorptions at 2020 and 1940 cm21. Furthermore, the carboxylato region reflects the conversion of the formato group from bi- to mono-dentate. Thus the symmetric and asymmetric n(OCO) stretchings appear at 1295 and 1625 cm21 in agreement with those of other monodentate formato species.12 In the 1H NMR spectrum theJ. Chem. Soc., Dalton Trans., 1997, Pages 181–192 185 formato proton gives a singlet at d 8.11.The a-vinyl proton appears at d 8.68 as a doublet of triplets with a H]H coupling constant of 17.0 Hz and a P]H coupling constant <1 Hz, whereas the proton in b position is masked by the C6D6 signal. In the 13C-{1H} NMR spectrum the carbon atom of the formate ligand appears at d 168.4 as a singlet, while the Cb and Ca carbon atoms of the styryl ligand display triplets, at d 143.2 (JP]C = 2.3) and 140.0 (JP]C = 4.6 Hz), respectively.The 31P-{1H} NMR spectrum shows a singlet at d 9.3. Under a hydrogen atmosphere complex 8 quantitatively yields styrene and the hydridoformato complex [OsH(h2-O2- CH)(CO)(PPri 3)2] 10,13 which can be also prepared in 82% yield by bubbling carbon dioxide through a hexane solution of the dihydrido complex [OsH2(h2-CH2]] CHEt)(CO)(PPri 3)2] 11 (Scheme 9). As for 8, the bidentate formate ligand of 10 is converted into a monodentate group by carbonylation. Thus, the reaction of 10 with carbon monoxide affords [OsH{h1-OC- (O)H}(CO)2(PPri 3)2] 12.Similarly, the addition of a stoichiometric amount of P(OMe)3 to a hexane solution of 10 yields [OsH{h1-OC(O)H}(CO)}(CO){P(OMe)3}(PPri 3)2] 13 (Scheme 10). The behaviour of 10 towards carbon monoxide contrasts to that previously reported for the related ruthenium compound [RuH(h2-O2CH)(PPh3)3], which reacts with CO to give [RuH2- (CO)(PPh3)3] and CO2.8 Complex 12 was isolated as a white solid in 82% yield.The monohapto nature of the formate ligand is supported by the values of the symmetric and asymmetric n(OCO) stretchings, in the IR spectrum in Nujol, which appear at 1370 and 1643 cm21 respectively. In the 2000 cm21 region the spectrum shows three Scheme 8 Scheme 9 bands, at 2050, 1975 and 1915 cm21. The first band was assigned to the n(Os]H) absorption, and the other two to n(CO) absorptions, in agreement with a cis arrangement of these ligands. In the 1H NMR spectrum in C6D6 the hydride ligand appears at d 24.29 as a triplet with a P]H coupling constant of 21.0 Hz. The chemical shift of this signal is very close to that previously reported for the hydride ligand disposed trans to a carbonyl group in the complex [OsH(Cl)(CO)2- (PPri 3)2] (d 24.70).14 The proton of the formato group gives rise to a singlet at d 7.88.The 31P-{1H} NMR spectrum shows a singlet at d 29.1. Complex 13 was isolated as a white solid in 80% yield. The IR spectrum in Nujol shows the symmetric and asymmetric n(OCO) stretchings at 1380 and 1650 cm21. The 31P-{1H} NMR contains a triplet at d 102.9 [P(OMe)3] and a doublet at d 20.8 (PPri 3).The value of the P]P coupling constant is 17.9 Hz. The proposed trans disposition of hydride and phosphite ligands is supported by the 1H NMR spectrum in C6D6, which contains a doublet of triplets at d 26.30, with P]H coupling constants of 149.0 and 23.8 Hz. The proton of the formato group appears at d 8.37 as a singlet.Attempts to prepare complex 8 by reaction of 10 with phenylacetylene were unsuccessful. Complex 10 is not only inert towards phenylacetylene but also towards cyclohexylacetylene and methyl propiolate. However, addition of the stoichiometric amount of methyl acetylenedicarboxylate to a hexane suspension of 10 leads to a white solid in 80% yield, which was characterized as the p-alkyne compound [OsH{h1-OC(O)H}(h2- MeO2CC]] ] CCO2Me)(CO)(PPri 3)2] 14. The p co-ordination of the alkyne is strongly supported by the IR spectrum of 14 in Nujol which shows a strong absorption at 1880 cm21, characteristic of a n(C]] ] C) vibration.15 Furthermore, the spectrum contains bands at 2040, 1955 and 1710 cm21, which were assigned to v(Os]H), n(CO) (carbonyl ligand) and n(CO) (CO2Me groups of the alkyne), along with the asymmetric and symmetric n(OCO) vibrations of the monodentate formate ligand, at 1620 and 1375 cm21 respectively.According to the 1H, 13C-{1H} and 31P-{1H} NMR spectra of complex 14, in solution, this compound partially dissociates the alkyne (Scheme 11). At room temperature in C6D6 the 14 : 10 molar ratio is 1 : 1.Characteristic signals for 14 in the 1H NMR spectrum are two singlets at d 7.63 and 3.74, and a triplet with a P]H coupling constant of 28.3 Hz at d 22.28. The singlets were assigned to the O2CH and CO2CH3 protons, respectively, and the triplet to the hydride ligand. The chemical shift of this ligand agrees well with that previously reported for the complex [OsH(Cl)(h2-MeO2CC]] ] CCO2Me)(CO)(PPri 3)2] (d 22.80), where a trans disposition of the hydride and p-alkyne ligands has also been proposed.16 In contrast to the behaviour of the related chloro-derivative, insertion of the alkyne into the osmium–hydride bond of 14 is not observed. In the 13C-{1H} Scheme 10186 J.Chem. Soc., Dalton Trans., 1997, Pages 181–192 NMR spectrum the acetylenic carbon atoms appear at d 107.3 as a triplet with a P]C coupling constant of 3.3 Hz.The resonance due to the carbon atom of the formato group is observed at d 166.2, as a triplet with a P]C coupling constant of 5.3 Hz. A singlet at d 30.8 in the 31P-{1H} NMR spectrum is also characteristic of 14. The carbon atom of the formate ligand of complex 10 is an electrophilic centre susceptible to attack by nucleophiles. Addition of 1 equivalent of diethylamine to a NMR tube containing a C6D6 solution of 10 yields, after 1 h at 60 8C, the carbamato derivative [OsH(h2-O2CNEt2)(CO)(PPri 3)2] 15 in quantitative yield, (Scheme 12).The 1H NMR spectrum of 15 exhibits two quartets at d 3.14 and 3.02 and two triplets at d 0.95 and 0.91, corresponding to two inequivalent ethyl groups. The inequivalence of the ethyl groups of the carbamate ligand indicates that the molecule has no mirror plane of symmetry containing the P]Os]P unit, in agreement with the structure shown. The hydride ligand appears at d 220.37 as a triplet with a P]H coupling constant of 16.2 Hz.In the 13C-{1H} NMR spectrum the ethyl groups display four singlets, two for the CH2 carbon atom at d 39.3 and 39.0 and two for the CH3 carbon atoms at d 14.2 and 14.2. The central carbon atom of the carbamato group appears at d 165.4. The chemical shift of this resonance compares well with those previously reported for related compounds (d 170–160).17 The 31P-{1H} NMR spectrum shows a singlet at d 38.4.The 1H, 13C-{1H} and 31P-{1H} NMR spectra of the solution formed by addition of ca. 1 equivalent of diethylamine to complex 8 in C6D6 show, after 3 h at room temperature, the presence of styrene and resonances that were assigned to the complexes 8(41), 10(10), 15(12) and the styrylcarbamato derivative [Os{(E)-CH]] CHPh}(h2-O2CNEt2)(CO)(PPri 3)2] 16 (37%), by comparison of these spectra with those recorded for 8, 10 Scheme 11 Scheme 12 and 15. After 24 h at room temperature the composition consists of only 15(60) and 16(40%).Bubbling molecular hydrogen through this solution does not affect the 15 : 16 molar ratio, even after 6 h. These results can be rationalized according to schemes 9, 12 and 13. As for 10, the carbon atom of the formate ligand of 8 is susceptible to attack by nucleophiles. Thus, the reaction of this complex with diethylamine leads to the styrylcarbamato derivative 16 (Scheme 13). The molecular hydrogen generated from the nucleophilic substitution reacts with 8 to give 10 and styrene (Scheme 9).Complex 10 then reacts further with the amine to afford 15 and molecular hydrogen (Scheme 12). In the 1H NMR spectrum the most noticeable signals for complex 16 are those corresponding to the styryl and carbamate ligands. The vinyl protons of the styryl ligand display a doublet at d 9.37 with a H]H coupling constants of 15.6 Hz, and a doublet of triplets at d 6.57 with a P]H coupling constant < 1 Hz, assigned to the a- and b-proton respectively.Similarly to 15, the ethyl protons of the carbamate ligand appear as two quartets at d 3.14 and 3.04 and two triplets at d 0.93 and 0.91. In the 13C-{1H} NMR spectrum the central carbon atom of the carbamato group appears as a singlet at d 165.0, the a-carbon atom of the styryl ligand appears at d 138.7 as a triplet with a P]C coupling constant of 7.7 Hz, and the b-carbon atom gives rise to a broad singlet at d 132.3. A singlet at d 16.1 in the 31P-{1H} NMR spectrum is also characteristic of 16.Protonation of complexes 8 and 10 Complex 8 also reacts with HBF4?OEt2, leading to different derivatives depending upon the conditions. In diethyl ether as solvent one of the two oxygen atoms of the formate ligand undergoes electrophilic attack of the proton of the acid to give the unsaturated [Os{(E)-CH]] CHPh}(CO)(PPri 3)2]+ fragment, which can be trapped as [Os{(E)-CH]] CHPh}(CO)(MeCN)2- (PPri 3)2]BF4 17 in the presence of acetonitrile.While, in chloroform as solvent, electrophilic attack of the proton takes place at the b-carbon atom of the styryl ligand. In this case the compound formed is the carbene derivative [Os(h2-O2CH)- (]] CHCH2Ph)(CO)(PPri 3)2]BF4 18 (Scheme 14). Complex 17 was isolated as a white solid in 80% yield. The IR spectrum in Nujol shows the absorption due to the [BF4]2 anion with Td symmetry, at about 1100 cm21 indicating that this anion is not co-ordinated to the metal.Consistent with the mutually cis disposition of the acetonitrile ligands, the 1H NMR spectrum shows two singlets for their protons, at d 2.68 and 2.57. The a-vinylic proton of the styryl group appears at d 8.28 as a doublet with a H]H coupling constant of 17.3 Hz, while the b-vinylic proton appears at d 6.42 as a doublet of triplets with a P]H coupling constant 1 Hz. In the 13C-{1H} NMR spectrum the acetonitrile ligands also give rise to two singlets at d 126.0 and 125.5.The Ca and Cb atoms of the vinyl Scheme 13J. Chem. Soc., Dalton Trans., 1997, Pages 181–192 187 ligand display triplets at d 132.7 and 136.2, with P]C coupling constants of 8.9 and 3.0 Hz, respectively. The 31P-{1H} NMR spectrum contains a singlet at d 3.1. Complex 18 was isolated as a green oil in quantitative yield, and was characterized in solution by IR, 1H, 13C-{1H} and 31P-{1H} NMR spectroscopy. The IR spectrum in dichloromethane shows two bands at 1560 and 1355 cm21, supporting the bidentate co-ordination of the formato group.The presence of a carbene ligand was inferred from the 1H and 13C-{1H} NMR spectra in CDCl3. The 1H NMR spectrum contains at d 17.63 a triplet with a H]H coupling constant of 6.1, and at d 3.52 a doublet with the same H]H coupling constant. These resonances were assigned to the Os]] CH and CH2Ph protons, respectively. The proton of the formato group appears at d 9.19, as a singlet. In the 13C-{1H} spectrum the Ca carbon atom of the carbene ligand appears at d 290.8 as a broad signal.The carbon atom of the formato group gives rise to a singlet at d 168.7. The 31P-{1H} NMR spectrum contains a singlet at d 38.3. The reaction of complex 10 with HBF4?OEt2 also leads to different derivatives depending upon the conditions. Similarly to 8, in diethyl ether as solvent, the reaction produces a very unsaturated [OsH(CO)(PPri 3)2]+ fragment, which can be trapped with acetonitrile to afford the previously reported compound [OsH(CO)(MeCN)2(PPri 3)2]BF4 19.18 However, in CDCl3 the electrophilic attack of the proton occurs at the Scheme 14 (i) HBF4, MeCN, Et2O; (ii) HBF4, CHCl3 Fig. 1 Proton NMR spectrum (CDCl3) of the mixture resulting from the reaction of [OsH(h2-O2CH)(CO)(PPri 3)2] 10 with HBF4?OEt2 in the hydrido region, at different reaction times hydride ligand and/or at the metal to give a mixture of products. Fig. 1 shows the high-field region of the 1H NMR spectrum at different reaction times.After 5 min the spectrum mainly contains four signals A–D. After 45 min signal D disappears, and the B:A intensity ratio increases. A variabletemperature 300 MHz T1 study of the peaks A–C gave T1(min) values of 17, 21 and 260 ms, respectively, suggesting that A and B correspond to dihydrogen compounds, while C is due to a dihydrido derivative. The correlation of the spectra shown in Fig. 1 with the 31P-{1H} NMR spectra registered at the same reaction times (5, 20 and 45 min) indicates that the signals A and B are related with singlets at d 25.6 and 41.8, respectively, while the D may be related with a broad resonance centred at d 35.6.The signal C could not be clearly correlated. In order to cast light on the nature and structure of the products of the reaction of complex 10 with HBF4?OEt2 in CDCl3, ab initio theoretical calculations have been carried out. They were performed at the Møller–Plesset Perturbatia (MP)2 and 4 levels using PH3 in place of the triisopropylphosphine ligand.The geometry optimizations were carried out at the MP2 level. Fig. 2 shows a plot of the optimized structure for the complex [OsH(h2-O2CH)(CO)(PH3)2] 10a. The most significant parameters are included in Table 1. As expected the co- Fig. 2 The MP2 optimized geometry of the reactant species [OsH(h2-O2CH)(CO)(PH3)2] 10a. Hydrogen atoms of phosphine ligands are omitted for clarity Table 1 Selected geometrical parameters (Å and 8) of the MP2 optimized structures.The atom numbering is that defined in Figs. 2 and 3; X corresponds to a point at the centre of the straight line between H(10) and H(11) Structure 10a 20a 21a 22a 23a Os(1)]P(2) 2.404 2.460 2.482 2.484 2.489 Os(1)]P(3) 2.404 2.460 2.476 2.502 2.495 Os(1)]C(4) 1.837 1.876 1.839 1.936 1.889 Os(1)]O(6) 2.419 2.156 1.979 1.987 2.000 Os(1)]O(8) 2.253 2.244 3.390 3.463 3.460 Os(1)]H(10) 1.588 1.688 1.728 1.594 1.603 Os(1)]H(11) — 1.688 1.729 1.594 1.592 Os(1)]X — 1.623 1.669 0.810 1.400 H(10)]H(11) — 0.930 0.894 2.745 1.534 P(2)]Os(1)]P(3) 172.4 169.3 170.1 170.3 165.2 P(2)]Os(1)]C(4) 93.6 93.0 90.8 103.6 98.2 P(2)]Os(1)]O(6) 89.9 84.9 89.9 93.9 90.6 P(2)]Os(1)]X — 94.5 93.8 53.3 96.7 C(4)]Os(1)]O(6) 114.1 104.8 110.6 162.5 150.9 C(4)]Os(1)]X — 94.5 93.8 53.3 96.7 C(4)]Os(1)]O(6) 114.1 104.8 110.6 162.5 150.9 C(4)]Os(1)]X — 89.0 88.2 50.3 81.9 O(6)]Os(1)]X — 166.2 160.8 147.2 127.0 H(10)]Os(1)]H(11) — 32.0 30.0 118.9 57.4188 J.Chem. Soc., Dalton Trans., 1997, Pages 181–192 ordination geometry around the metal is distorted octahedral. The distortion is due to the small angle of the bidentate formato group [O(6)]Os(1)]O(8) 57.98]. Since protonation of complex 10 leads a mixture of products containing dihydrogen and dihydride ligands, all the reasonable dihydrogen and dihydrido structures containing the formate ligand co-ordinated in mono- or di-hapto manner, and with the phosphine ligands mutually trans disposed, were considered.* The MP2 optimizations lead to the species 20a–23a, presented in Fig. 3. The most significant geometrical parameters are collected in Table 1, with MP2 and MP4 relative energies in Table 2. The theoretical calculations suggest that two dihydrogen and two dihydrido derivatives are possible. Thermodynamically, the most stable complex is the six-co-ordinated h2-formato (dihydrogen) 20a, where the two hydrogen atoms of the dihydrogen ligand are separated by 0.930 Å. Its stability is in agreement with its nature as a d6 ML6 complex.According to Fig. 1, the most stable species displays signal B, which shows a T1(min) value of 21 ms at 300 MHz. This value corresponds to a hydrogen–hydrogen distance of 0.94 Å (fast spinning).† So we propose that signal B is characteristic of the h2-formato (dihydrogen) cation [Os(h2-O2CH)(h2-H2)(CO)(PPri 3)2]+ 20. Signal A is also characteristic of a dihydrogen derivative, its T1(min) value (17 ms at 300 MHz) corresponding to a hydrogen– hydrogen distance of 0.90 Å (fast spinning).Species 21a has a square-pyramidal structure (Fig. 3) with a larger distortion corresponding to the C(4)]Os(1)]O(6) angle (110.68, Table 1). It is a dihydrogen complex [H(10)]H(11) 0.894 Å], and its nature as a monodentate formate compound is indisputable [Os(1) ? ? ? O(8) 3.390 Å]. Thus, at first glance, one could propose that signal A corresponds to a five-co-ordinate h1-formato (dihydrogen) derivative with the carbonyl group in the apical position.However, it should be noted that (i) 20a is 15.91 kcal mol21 more stable than 21a and (ii) a high kinetic barrier would not be expected for the h1-formato æÆ h2-formato transformation. Hence, we believe that this signal corresponds to a six-coordinate h1-formato (dihydrogen) species, stabilized by coordination of a diethyl ether molecule (21), originating from the HBF4?OEt2 solution used in the reaction.The co-ordination of the ether molecule cis to the dihydrogen ligand should increase the kinetic barrier for the h1-formato æÆ h2-formato transformation without affecting the metal–dihydrogen interaction and, therefore, the hydrogen–hydrogen separation. Signal C is characteristic of a dihydrido derivative containing non-equivalent phosphine ligands. The T1(min) value for this signal is 260 ms at 300 MHz. Complex 22a is not octahedral [H(10)]Os(1)]H(11) 118.98] but a bicapped tetrahedron, a coordination polyhedron characteristic for d4 ML6 complexes.21,22 The bicapped tetrahedron 22a contains non-equivalent phosphine ligands [Os(1)]P(2) 2.484, Os(1)]P(3) 2.502 Å], and they Table 2 The MP2 and MP4 relative energies (kcal mol21) of different isomers of [OsH2(O2CH)(CO)(PH3)2]+. Geometries are optimized at the MP2 level Geometry 20a 21a 22a 23a MP2 0.00 15.97 12.00 11.87 MP4 0.00 15.91 12.42 12.36 * The mutually trans disposition for the phosphine ligands is a reasonable assumption in the view of the steric demands of the PPri 3 ligand.Trigonal-bipyramidal geometries were not considered because they are not likely in d6 ML5 species like this one.19 † At the temperature of minimum T1, t = 0.62/2pn, and the equation for dipolar relaxation simplifies to rH]H = 4.611 (T1min/n)1-6 for rapid rotation (n/MHz, T1/s).20 cannot be interconverted through reorientation of the formate ligand. The hydrogen–hydrogen separation in 22a is 2.745 Å.For this distance a T1(min) value of 224 ms at 300 MHz‡ is expected. The experimental properties of signal C seem well suited to that inferred for 22a from the theoretical calculations. So, we correlate it to the derivative [OsH2{h1-OC(O)- Fig. 3 The MP2 optimized geometries of the dihydrogen complexes [Os(h2-O2CH)(h2-H2)(CO)(PH3)2]+ 20a and [Os{h1-OC(O)H}(h2-H2)- (CO)(PH3)2]+ 21a and of the dihydrido complexes [OsH2{h1-OC(O)H}- (CO)(PH3)2]+ 22a and 23a.Hydrogen atoms of phosphine ligands are omitted for clarity ‡ It has been recently shown that, for polyhydrido complexes, T1(min) can be calculated by using internuclear distances obtained from neutron, X-ray diffraction 23a and theoretical studies.23bJ. Chem. Soc., Dalton Trans., 1997, Pages 181–192 189 H}(CO)(PPri 3)2]+ 22, which may have the structure shown in Fig. 3. Signal D rapidly disappears, and it cannot be studied. It may be assigned to species 23a.The reactions of complex 10 with HBF4?OEt2 to give 19, and 20, and 21, as well as the protonations of 8 to afford 17 and 18, can be rationalized via the intermediates 24 and 25. The electrophilic attack of the proton could initially take place at one of the two oxygen atoms of the formate ligands of both 10 and 8. Thus, in the presence of acetonitrile the displacement of the resulting formic acid by the nitrogen-donor ligand should yield 19 and 17, while in the absence of this ligand the transfer of the proton from the oxygen atom to the hydride and vinyl ligands could afford the thermodynamically more stable compounds 21 and 18.Conclusion This study has shown that the reaction of the five-co-ordinate compound [Os{(E)-CH]] CHPh}Cl(CO)(PPri 3)2] 1 with LiBun leads to [OsH{C6H4(CH]] CHH)}(CO)(PPri 3)2] 2 in equilibrium with the co-ordinatively unsaturated complex [OsH{(E)-CH]] CHPh}(CO)(PPri 3)2] 6. Complexes 2 and 6 are connected by the osmium(0) intermediate [Os(h2-CH2]] CHPh)(CO)(PPri 3)2] 7, which gives rise to C]H activation reactions in the terminal olefinic and the ortho-phenyl C]H bonds of the co-ordinated styrene.Complex 6 cannot be detected in solution, most probably due to the higher stability of its 18-electron isomer 2. However, the reactivity of 2 can easily be understood as a result of the reactions of the more labile isomer 6. Thus, the formato complex [Os{(E)-CH]] CHPh}(h2-O2CH)(CO)(PPri 3)2] 8, formed by passing a slow stream of carbon dioxide through a hexane solution of 2, can be rationalized from the insertion of the CO2 molecule into the Os–H bond of 6.Hydrogenation of 8 gives styrene and the hydrido complex [OsH(h2-O2CH)(CO)- (PPri 3)2] 10. The reactivity of complexes 8 and 10 towards CO, NEt2H and HBF4 has been also studied. By carbonylation, the bidentate formate ligand of these compounds becomes monodentate. In the presence of diethylamine, the central carbon atoms of the bidentate formato groups undergo nucleophilic attack affording the carbamato derivatives [OsR(h2-O2CNEt2)(CO)- (PPri 3)2] (R = H 15 or CH]] CHPh 16).The reactions of 8 and 10 with HBF4 lead to different derivatives depending upon the conditions. In diethyl ether as solvent the formato groups of both compounds undergo electrophilic attack by protons to give fragments of the type [OsR(CO)(PPri 3)2]+ (R = H or CH]] CHPh), which can be trapped in the presence of acetonitrile.In chloroform, complex 8 leads to the carbene [Os(h2-O2CH)(]] CHCH2Ph)(CO)(PPri 3)2]+ 18, and 10 gives a mixture of products, mainly dihydrogen derivatives. On the basis of theoretical calculations and T1 measurements, we propose that these derivatives could be the cations [Os(h2-O2- CH)(h2-H2)(CO)(PPri 3)2]+ 20 and [Os{h1-OC(O)H}(h2-H2)- (Et2O)(CO)(PPri 3)2]+ 21. Experimental All reactions were carried out with rigorous exclusion of air by using Schlenk-tube techniques.Solvents were dried by known procedures and distilled under argon prior to use. Physical measurements Infrared spectra were recorded as Nujol mulls on polyethylene sheets or NaCl cell windows using a Perkin-Elmer 883 or a Nicolet 550 spectrometer, NMR spectra on a Varian UNITY 300 or Brucker 300 AXR spectrometer. Proton and 13C-{1H} chemical shifts were measured relative to partially deuteriated solvent peaks but are reported relative to tetramethylsilane, 31P-{1H} chemical shifts relative to external 85% H3PO4.Coupling constants J and N []] J(PH) + J(P9H) for 1H, J(PC) + J(P9C) for 13C] are given in Hz. The C, H and N analyses were carried out in a Perkin-Elmer 2400 CHNS/O analyser. The starting materials [Os{(E)-CH]] CHPh}Cl(CO)(PPri 3)2] 1 and [OsH2(h2-CH2]] CHEt)(CO)(PPri 3)2] 11 were prepared by published methods.5,6 The deuteriated complexes [Os{(E)-CH]] CDPh}Cl(CO)(PPri 3)2] 1a and [Os{(E)-CD]] CHPh}Cl(CO)- (PPri 3)2] 1b were prepared by reaction of [OsD(Cl)(CO)(PPri 3)2] with PhC]] ] CH and [OsH(Cl)(CO)(PPri 3)2] with PhC]] ] CD, respectively.Preparations [OsH{C6H4(CH]] CHH)}(CO)(PPri 3)2] 2. A solution of [Os{(E)-CH]] CHPh}Cl(CO)(PPri 3)2] 1 (100 mg, 0.15 mmol) in hexane (5 cm3) was treated with LiBun (0.01 cm3, 1.6 mol dm23 solution in hexane) and stirred during ca. 5 min at room temperature. The mixture changed from dark blue to pale yellow. The resulting suspension was filtered through Kieselguhr and the filtrate was dried in vacuo to give a colourless oil.NMR (C6D6, 20 8C): 1H, d 7.26 (d, JH]H = 7.1, 1 H, HPh), 7.03 (t, JH]H = 7.1, 1 H, HPh), 6.90 (t, JH]H = 7.1, 1 H, HPh), 6.56 (d, JH]H = 7.1, 1 H, HPh), 4.95 (dd, JH]H = 9.0, J 7.7, 1 H, CH]] ), 3.71 (dt, JH]H = 9.0, JP]H = 5.7, 1 H, ]] CH2), 2.74 (d, JH]H = 7.7, 1 H, ]] CH2), 2.15 (m, 6 H, PCHCH3), 1.05 (dvt, N = 13.5, JH]H = 6.3, 36 H, PCHCH3) and 28.01 (t, JP]H = 27.3, 1 H, OsH); 13C- {1H}, d 187.9 (t, JP]C = 8.0, CO), 152.2 (t, JP]C = 2.0, CPh), 138.6 (t, JP]C = 10.0, CPh), 135.8 (br, CHPh), 126.1 (br, CHPh), 122.9 (br, CHPh), 121.0 (br, CHPh), 50.5 (br, CH]] ), 46.3 (br, ]] CH2), 26.6 (vt, N = 26.4 Hz, PCHCH3), 20.1 (s, PCHCH3) and 20.0 (s, PCHCH3); 31P-{1H}, d 16.7 (s).[OsH{(E)-CH]] CHPh}(CO){P(OMe)3}(PPri 3)2] 3. A solution of complex 1 (100 mg, 0.15 mmol) in hexane (5 cm3) was treated with LiBun (0.01 cm3, 1.6 mol dm23 solution in hexane) and stirred during ca. 5 min at room temperature.The resulting suspension was filtered through Kieselguhr and treated with P(OMe)3 (17 ml, 0.15 mmol). After 30 min of reaction a white solid was formed, decanted, washed with hexane and dried in vacuo. Yield 95.7 mg (85%) (Found: C, 47.5; H, 8.2. Calc. for C30H59O4OsP3: C, 47.0; H, 7.75%). IR (Nujol, cm21): n(Os]H) 2050s, n(CO) 1910s, n(C]] C) 1540m. NMR (C6D6, 20 8C): 1H, d 8.78 (tq, JH]H = 18.3, JP]H = 18.3, JH]H 1.6 Hz, JH]H = 1.6, 1 H, OsCH]] CHPh), 7.46 (d, JH]H = 7.3, 2 H, o-H of Ph), 7.23 (t, JH]H = 7.3, 2 H, m-H of Ph), 7.03 (dt, JH]H = 18.3, JP]H = 2.5, 1 H, OsCH]] CHPh), 6.96 (t, JH]H = 7.3, 1 H, p-H of Ph, 3.39 (d, JP]H = 10.1, 9 H, POMe), 2.47 (m, 6 H, PCHCH3), 1.27 (dvt, N = 14.0, JH]H = 7.1 18 H, PCHCH3), 1.20 (dvt, N = 11.9,190 J.Chem. Soc., Dalton Trans., 1997, Pages 181–192 JH]H = 7.1 18 H, PCHCH3) and 28.94 (dtd, JP]H = 134.4, JP]H = 24.5, JH]H = 1.6, 1 H, OsH); 13C-{1H}, d 190.8 (vq, JP]C = 8.3 CO), 145.3 (t, JP]C = 2.3 ipso-C of Ph), 144.4 (dt, JP]C = 10.1, 4.2, OsCH]] CHPh), 143.3 (vq, JP]C = 13.4, OsCH]] CHPh), 128.6 (s, o-CH of Ph), 124.4 (s, m-CH of Ph), 124.0 (s, p-CH of Ph), 51.6 (d, JP]C = 8.8 POMe), 26.0 (vtd, N = 26.8, JP]C = 2.3, PCHCH3), 20.8 (s, PCHCH3) and 18.7 (s, PCHCH3); 31P-{1H}, d 102.4 (t, JP]P = 18.6 POMe) and 17.5 (d, JP]P = 18.6 Hz, PPri 3).[OsH{(E)-CH]] CHPh}(CO)2(PPri 3)2] 4. A solution of complex 1 (100 mg, 0.15 mmol) in hexane (5 cm3) was treated with LiBun (0.01 cm3, 1.6 mol dm23 solution in hexane) and stirred during ca. 5 min at room temperature. The resulting suspension was filtered through Kieselguhr and a slow stream of carbon monoxide was bubbled through it. After 30 min of reaction a white solid was formed, decanted, washed with hexane and dried in vacuo. Yield 74 mg (72%) (Found: C, 50.6; H, 8.4. Calc. for C28H50O2OsP2: C, 50.15; H, 7.55%). IR (Nujol, cm21): n(OsH) 1990s, n(CO) 1945s, 1865s, 1570m, n(C]] C). NMR (C6D6, 20 8C): 1H, d 8.34 (br d, JH]H = 16.1, 1 H, OsCH]] CHPh), 7.41 (d, JH]H = 7.3, 2 H, o-H of Ph), 7.23, (t, JH]H = 7.3, 2 H, m-H of Ph), 7.20 (d, JH]H = 16.1, 1 H, OsCH]] CHPh), 6.98 (t, JH]H = 7.3, 1 H, p-H of Ph), 2.24 (m, 6 H, PCHCH3), 1.16 (dvt, N = 13.5, JH]H = 6.9, 32 H, PCHCH3) and 27.13 (td, JP]H = 22.0, JH]H = 5.0, 1 H, OsH); 13C-{1H}, d 190.4 (t, JP]C = 5.5, CO), 185.5 (t, JP]C = 7.8, CO), 144.5 (t, JP]C = 1.9, ipso-C of Ph), 142.5 (t, JP]C = 3.7, OsCH]] CHPh), 135.2 (t, JP]C = 12.9, OsCH- ]] CHPh), 128.8 (s, o-C of Ph), 124.9 (s, m-C of Ph), 124.5 (s, p-C of Ph), 26.2 (vt, N = 27.6, JP]C = 2.3 Hz, PCHCH3) and 19.0 (s, PCHCH3); 31P-{1H}, d 19.0 (s).[OsH{C6H4(CD]] CHH)}(CO)(PPri 3)2] 2a. The complex was prepared using the procedure described for 2 (100 mg, 0.15 mmol), starting for [Os{(E)-CH]] CDPh}Cl(CO)(PPri 3)2]. NMR: 1H (C6D6, 20 8C), d 7.26 (d, JH]H = 7.1, 1 H, HPh), 7.03 (t, JH]H = 7.1, 1 H, HPh), 6.90 (t, JH]H = 7.1, 1 H, HPh), 6.56 (d, JH]H = 7.1, 1 H, HPh), 3.71 (t, JP]H = 5.7, 1 H, ]] CH2), 2.74 (s, ]] CH2), 2.15 (m, 6 H, PCHCH3), 1.05 (dvt, N = 13.5, JH]H = 6.3, 36 H, PCHCH3) and 28.01 (t, JP]H = 27.3 Hz, 1 H, OsH); 2H (C6H6, 20 8C), d 5.03 (s, CD]] ); 31P-{1H} (C6D6, 20 8C), d 17.1 (s).[OsH{(E)-CH]] CDPh}(CO){P(OMe)3}(PPri 3)2] 3a. The complex was prepared using the procedure described for 3 (100 mg, 0.15 mmol), starting for [Os{(E)-CH]] CDPh}Cl(CO)- (PPri 3)2]. NMR: 1H (C6D6, 20 8C), d 8.78 (d, JP]H = 18.3, 1 H, OsCH]] CHPh), 7.46 (d, JH]H = 7.3, 2 H, o-H of Ph), 7.23 (t, JH]H = 7.3, 2 H, m-H of Ph), 6.96 (t, JH]H = 7.3, 1 H, p-H of Ph), 3.39 (d, JP]H = 10.1, 9 H, POMe), 2.47 (m, 6 H, PCHCH3), 1.27 (dvt, N = 14.0, JH]H = 7.1, 18 H, PCHCH3), 1.20 (dvt, N = 11.9, JH]H = 7.1, 18 H, PCHCH3) and 28.94 (dt, JP]H = 134.4, 24.5, 1 H, OsH); 2H (C6H6, 20 8C), d 7.01 (s, OsCH]] CDPh); 31P-{1H} (C6D6, 20 8C), d 103.0 (t, JP]P = 18.6 POMe), 17.5 (d, JP]P = 18.6 Hz, PPri 3).[OsH{C6H3D(CH]] CHH)}(CO)(PPri 3)2] 2b, [OsH{C6H4(CH]] CDH)}(CO)(PPri 3)2] 2c, [OsH{C6H4(CH]] CHD)}(CO)(PPri 3)2] 2d and [OsD{C6H4(CH]] CHH)}(CO)(PPri 3)2] 2e.The complexes were prepared using the procedure described for 2 (100 mg, 0.15 mmol), starting from [Os{(E)-CD]] CHPh}Cl(CO)(PPri 3)2]. NMR: 1H (C6D6, 20 8C), d 7.26 (d, JH]H = 7.1, 1 H, HPh), 7.03 (t, JH]H = 7.1, 1 H, HPh), 6.90 (t, JH]H = 7.1, 1 H, HPh), 6.56 (d, JH]H = 7.1, HPh), 4.95 (br dd, JH]H = 9.0, J = 7.7, CH]] ), 3.71 (br dt, JH]H = 9.0, JP]H = 5.7, ]] CH2), 2.74 (br d, JH]H = 7.7, 1 H, ]] CH2), 2.15 (m, 6 H, PCHCH3), 1.05 (dvt, N = 13.5, JH]H = 6.3, 36 H, PCHCH3) and 28.01 (br t, JP]H = 27.3 Hz, 1 H, OsH); 2H (C6H6, 20 8C), d 6.52 (s, DPh), 3.68 (s, ]] CHD), 2.65 (s, ]] CHD) and 28.02 (s, OsD); 31P-{1H} (C6D6, 20 8C), d 17.1 (s). [OsH{(E)-CD]] CHPh}(CO){P(OMe)3}(PPri 3)2] 3b, [OsH- {(E)-CH]] CHC6H4D}(CO){P(OMe)3}(PPri 3)2] 3c and [OsD- {(E)-CH]] CHPh}(CO){P(OMe)3}(PPri 3)2 3d.The complexes were prepared using the procedure described for 3 (100 mg, 0.15 mmol), starting from [Os{(E)-CD]] CHPh}Cl(CO)(PPri 3)2].NMR: 1H (C6D6, 20 8C), d 8.78 (t, JH]H = 18.3, JP]H = 18.3, OsCH]] CHPh), 7.46 (d, JH]H = 7.3, o-H of Ph), 7.23 (t, JH]H = 7.3, 2 H, m-H of Ph), 7.03 (br d, JH]H = 18.3, OsCH]] CHPh), 6.96 (t, JH]H = 7.3, 1 H, p-H of Ph), 3.39 (d, JP]H = 10.1, 9 H, POMe), 2.47 (m, 6 H, PCHCH3), 1.27 (dvt, N = 14.0, JH]H = 7.1, 18 H, PCHCH3), 1.20 (dvt, N = 11.9, JH]H = 7.1, 18 H, PCHCH3) and 28.94 (dt, JP]H = 134.4, J 24.5, OsH); 2H (C6H6, 20 8C), d 8.81 (s, OsCD]] CHPh), 7.46 (s, o-D of Ph) and 28.88 (d, JP]D = 20.2, OsD); 31P-{1H} (C6D6, 20 8C), d 103.0 (dt, JP]D = 20.2, JP]P = 18.6, POMe) and 17.5 (d, JP]P = 18.6 Hz, PPri 3).[Os{(E)-CH]] CHPh}(Á2-O2CH)(CO)(PPri 3)2] 8. A solution of complex 1 (100 mg, 0.15 mmol) in hexane (5 cm3) was treated with LiBun (0.01 cm3, 1.6 mol dm23 solution in hexane) and stirred during ca. 5 min at room temperature.The resulting pale yellow suspension was filtered through Kieselguhr and a slow stream of carbon dioxide was bubbled through it for ca. 30 min. The solution was cooled at 278 8C, resulting in crystallization of a yellow solid. This was decanted and dried in vacuo. Yield 77.3 mg (75%) (Found: C, 48.89; H, 7.2. Calc. for C28H50O3OsP2: C, 48.95; H, 7.35%). IR (Nujol, cm21): n(CO) 1900s, nasym(OCO) 1560s, n(C]] C) 1540m, nsym(OCO) 1300s. NMR (C6D6, 20 8C): 1H, d 9.09 (d, JH]H = 15.6, 1 H, OsCH- ]] CHPh), 8.63 (t, JP]H = 1.9, 1 H, O2CH), 7.38 (d, JH]H = 7.4 Hz, 2 H, o-H of Ph), 7.24 (t, JH]H = 7.4, 2 H, m-H of Ph), 6.93 (t, JH]H = 7.4, 1 H, p-H of Ph), 6.46 (dt, JH]H = 15.6, JP]H < 1, 1 H, OsCH]] CHPh), 2.44 (m, 6 H, PCHCH3), 1.24 (dvt, N = 13.5, JH]H = 7.1, 18 H, PCHCH3) and 1.17 (dvt, N = 13.2, JH]H = 7.1, 18 H, PCHCH3). 13C-{1H}, d 185.9 (t, JP]C = 9.2, CO), 174.4 (t, JP]C = 1.4, O2CH), 142.6 (t, JP]C = 1.2, ipso-C of Ph), 137.0 (t, JP]C = 9.7, OsCH]] CHPh), 132.8 (t, JP]C = 2.7, OsCH]] CHPh), 128.8 (s, o-CH of Ph), 124.1 (s, m-CH of Ph), 123.7 (s, p-CH of Ph), 24.8 (vt, N = 24.0 Hz, PCHCH3), 19.7 (s, PCHCH3) and 19.6 (s, PCHCH3); 31P-{1H}, d 15.6 (s).[Os{(E)-CH]] CHPh}{Á1-OC(O)H}(CO)2(PPri 3)2] 9. A slow stream of carbon monoxide was bubbled through a hexane solution of complex 8 (100 mg, 0.15 mmol) during 5 min. The white solid obtained was decanted, washed with hexane and dried in vacuo. Yield 89.0 mg (83%) (Found: C, 48.75; H, 6.95.Calc. for C29H50O4OsP2: C, 48.75; H, 7.0%). IR (Nujol, cm21): n(CO) 2020s, 1940s, nasym(OCO) 1625s, n(C]] C) 1590m, nsym- (OCO) 1295s. NMR (C6D6, 20 8C): d 1H, 8.68 (dt, JH]H = 17.0, JP]H < 1, 1 H, OsCH]] CHPh), 8.11 [s, 1 H, OC(O)H)], 7.44 (d, JH]H = 7.7, 2 H, o-H of Ph), 7.44 (t, JH]H = 7.7, 2 H, m-H of Ph) (the OsCH]] CHPh signal is masked by the C6D6 signal), 6.69 (t, JH]H = 7.7, 1 H, p-H of Ph), 2.38 (m, 6 H, PCHCH3), 1.08 (dvt, N = 12.9, JH]H = 6.7, 18 H, PCHCH3) and 1.04 (dvt, N = 12.1, JH]H = 6.9, 18 H, PCHCH3); 13C-{1H}, d 186.8 (t, JP]C = 6.9, CO), 184.4 (t, JP]C = 7.8, CO), 168.4 [s, OC(O)H], 149.1 (t, JP]C = 12.9, ipso-C of Ph), 143.2 (t, JP]C = 2.3, OsCH]] CHPh), 140.0 (t, JP]C = 4.6, OsCH]] CHPh), 128.9 (s, CHo of Ph), 125.4 (s, CHm of Ph), 124.8 (s, p-CH of Ph), 25.3 (vt, N = 25.3 Hz, PCHCH3), 19.6 (s, PCHCH3) and 19.4 (s, PCHCH3); 31P-{1H}, d 9.3 (s).[OsH(Á2-O2CH)(CO)(PPri 3)2] 10. A slow stream of carbon dioxide was bubbled through a solution of [OsH2(h2-CH2]] CHEt)(CO)(PPri 3)2] 11 (93 mg, 0.16 mmol) in hexane (5 cm3) at room temperature. After ca. 20 min a yellow solid was formed. The solid was decanted, washed with hexane and driedJ. Chem. Soc., Dalton Trans., 1997, Pages 181–192 191 in vacuo. Yield 74.8 mg (82%) (Found: C, 41.6; H, 8.1. Calc. for C20H44O3OsP2: C, 41.1; H, 7.6%). IR (Nujol, cm21): n(Os]H) 2180m, n(CO) 1900s, nasym(OCO) 1565s, nsym(OCO) 1385m. NMR (CDCl3, 20 8C): 1H, d 8.81 (s, O2CH), 2.42 (m, 6 H, PCHCH3), 1.30 (dvt, N = 13.6, JH]H = 7.4, 18 H, PCHCH3), 1.26 (dvt, N = 13.0, JH]H = 7.2, 18 H, PCHCH3) and 221.58 (t, JP]H = 15.7, 1 H, OsH). 13C-{1H}, d 182.9 (t, JP]C = 9.1, CO), 173.3 (t, JP]C = 1.5, O2CH), 25.6 (vt, N = 24.8 Hz, PCHCH3), 20.1 (s, PCHCH3) and 19.4 (s, PCHCH3); 31P-{1H}, d 39.6 (s). Reaction of complex 8 with H2. A solution of complex 8 (25 mg, 0.04 mmol) in C6D6 placed in a NMR tube was saturated with H2 at room temperature and the tube sealed.The reaction was monitored by 1H and 31P-{1H} NMR spectroscopy. After 72 h the spectra showed signals corresponding to 10 and styrene. [OsH{Á1-OC(O)H}(CO)2(PPr3)2] 12. A slow stream of carbon monoxide was bubbled through a suspension of complex 10 (90 mg, 0.156 mmol) in dichroromethane (5 cm3) during 5 min. The solution was dried under vacuum, and the residue treated with hexane causing the precipitation of a white solid. The solid was washed with hexane and dried in vacuo.Yield 77.4 mg (82%) (Found: C, 41.15; H, 7.25. Calc. for C21H44O4OsP2: C, 40.6; H, 7.85%). IR (Nujol, cm21): n(Os]H) 2050m, n(CO) 1975s, 1915s, nasym(OCO) 1643s, nsym(OCO) 1370m. NMR (C6D6, 20 8C): 1H, d 7.88 [s, 1 H, OC(O)H], 2.10 (m, 6 H, PCHCH3), 1.14 (dvt, N = 14.1, JH]H = 7.5, 18 H, PCHCH3), 1.17 (dvt, N = 14.1, JH]H = 7.5, 18 H, PCHCH3) and 24.29 (t, JP]H = 21.0 Hz, 1 H, OsH); 31P-{1H}, d 29.1 (s). [OsH{Á1-OC(O)H}(CO){P(OMe)3}(PPri 3)2] 13. A suspension of complex 10 (65 mg, 0.11 mmol) in hexane (7 cm3) was treated with P(OMe)3 (19 ml, 0.16 mmol).After ca. 15 min at room temperature a white solid was formed. The solid was decanted, washed with hexane and dried in vacuo. Yield 60.7 mg (80%) (Found: C, 38.95; H, 7.55. Calc. for C23H53O6OsP3: C, 39.55; H, 8.45%). IR (Nujol, cm21): n(Os]H) 2030w, n(CO) 1920s, nasym(OCO) 1650s, nsym(OCO) 1380m. NMR (C6D6, 20 8C): d 1H, 8.37 [s, 1 H, OC(O)H], 3.43 (d, JP]H = 10.1, 9 H, POMe), 2.29 (m, 6 H, PCHCH3), 1.30 (dvt, N = 12.3, JH]H = 6.8, 18 H, PCHCH3), 1.10 (dvt, N = 12.3, JH]H = 6.8, 18 H, PCHCH3) and 26.30 (dt, JP]H = 149.0, 23.8, 1 H, OsH); 31P-{1H}, d 102.9 (t, JP]P = 17.9, POMe) and 20.8 (d, JP]P = 17.9 Hz, PPri 3).[OsH{Á1-OC(O)H}(Á2-MeO2CC]] ] CCO2Me)(CO)(PPri 3)2] 14. A suspension of complex 10 (65 mg, 0.11 mmol) in hexane (6 cm3) was treated with MeO2CC]] ] CCO2Me (14 ml, 0.11 mmol). After ca. 5 min at room temperature a white solid was formed.The solid was decanted, washed with hexane and dried in vacuo. Yield 60.7 mg (80%) (Found: C, 42.95; H, 6.95. Calc. for C26H50O7OsP2: C, 42.55; H, 7.2%). IR (Nujol, cm21): n(Os]H) 2040w, n(CO) 1955s, n(C]] ] C) 1880m, n(C]] O) 1710s, nasym(OCO) 1620s, nsym(OCO) 1375m. The 1H and 31P-{1H} NMR spectra of a solution of 14 (32 mg, 0.03 mmol) in C6D6 at room temperature showed signals corresponding to 14, 10 and MeO2- CC]] ] CCO2Me in ca. 1 : 1 : 1 molar ratio. Data for 14 (CDCl3, 20 8C): d 1H, 7.63 [s, 1 H, OC(O)H], 3.74 (s, 6 H, ]] ] CCO2Me), 2.64 (m, 6 H, PCHCH3), 1.27 (dvt, N = 12.7, JH]H = 6.7, 18 H, PCHCH3), 1.15 (dvt, N = 14.9, JH]H = 6.6, 18 H, PCHCH3) and 22.28 (dt, JP]H = 28.3, 1 H, OsH); 13C-{1H}, d 179.8 (t, JP]C = 9.1, CO), 167.4 (s, ]] ] CCO2Me), 166.2 [t, JP]C = 5.3, OC(O)H], 107.3 (t, JP]C = 3.3, ]] ] CCO2Me), 52.4 (s, ]] ] CCO2Me), 25.5 (vt, N = 28.0 Hz, PCHCH3), 20.8 (s, PCHCH3) and 18.8 (s, PCHCH3); 31P-{1H}, d 30.8 (s).[OsH(Á2-O2CNEt2)(CO)(PPri 3)2] 15.A solution of complex 9 (28 mg, 0.05 mmol) in C6D6 placed in a NMR tube was treated with NEt2H (5 ml, 0.05 mmol). The tube was sealed under Ar and heated at 60 8C for 1 h. Under these conditions complex 15 was the only detectable product. IR (CH2Cl2, cm21): n(CO) 1870s, n(OCO) 1525s. NMR (C6D6, 20 8C): 1H, d 3.14, 3.02 (both q, JH]H = 7.2, 2 H, NCH2), 2.37 (m, 6 H, PCHCH3), 1.38 (dvt, N = 13.5, JH]H = 6.9, 18 H, PCHCH3), 1.25 (dvt, N = 13.5, JH]H = 6.9, 18 H, PCHCH3), 0.95, 0.91 (both t, JH]H = 7.0, 3 H, NCH2CH2) and 220.37 (t, JP]H = 16.2, 1 H, Os]H); 13C-{1H}, d 184.5 (t, JP]C = 9.2, CO), 165.4 (s, O2C), 39.3, 39.0 (s, NCH2), 25.7 (vt, N = 24.8 Hz, PCHCH3), 20.4 (s, PCHCH3), 19.5 (s, PCHCH3), 14.2 (s, NCH2CH3); 31P-{1H}, d 38.4 (s).Reaction of complex 8 with NEt2H: preparation of [Os{(E)- CH]] CHPh}(Á2-O2CNEt2)(CO)(PPri 3)2] 16. A solution of complex 8 (25 mg, 0.04 mmol) in C6D6 placed in a NMR tube was treated with NEt2H (4 ml, 0.04 mmol).After 3 h at room temperature the 1H and 31P-{1H} NMR spectra of the solution showed a mixture of 8 (41), 10 (10), 15 (12) and 16 (37%). After 24 h at room temperature a mixture of complexes 15 (60) and 16 (40%) was obtained. NMR data for 16 (C6D6, 20 8C): 1H, d 9.37 (d, JH]H = 15.6, 1 H, OsCH]] CHPh), 7.43 (d, JH]H = 6.8 Hz, 2 H, o-H of Ph), 7.28 (t, JH]H = 6.8 Hz, 2 H, m-H of Ph, 7.09 (t, JH]H = 6.8 Hz, 1 H, p-H of Ph), 6.57 (dt, JH]H = 15.6 Hz, JP]H < 1 Hz, 1 H, OsCH]] CHPh), 3.14, 3.04 (q, JH]H = 7.0, 2 H, NCH2), 2.40 (m, 6 H, PCHCH3), 1.27 (dvt, N = 12.0, JH]H = 6.9, 18 H, PCHCH3), 1.17 (dvt, N = 12.0, JH]H = 6.9, 18 H, PCHCH3), 0.93, 0.91 (t, JH]H = 7.0, 3 H, NCH2CH3); 13C-{1H}, d 184.3 (t, JP]C = 9.1, CO), 165.0 (s, O2C), 143.2 (s, ipso-C of Ph), 138.7 (t, JP]C = 7.7, OsCH]] CHPh), 132.3 (br, OsCH]] CHPh), 128.6 (s, o-CH of Ph), 124.0 (s, m-CH of Ph), 123.2 (s, p-CH of Ph), 39.1, 38.7 (s, NCH2), 24.5 (vt, N = 23.7 Hz, PCHCH3), 19.8 (s, PCHCH3), 19.7 (s, PCHCH3), 16.7, 16.6 (s, NCH2CH3); 31P- {1H}, 16.1 (s).[Os{(E)-CH]] CHPh}(CO)(MeCN)2(PPri 3)2]BF4 17. A solution of complex 8 (100 mg, 0.15 mmol) was treated with HBF4?OEt2 (16 ml, 0.15 mmol) in diethyl ether. Addition of MeCN (8 ml, 0.15 mmol) caused the precipitatiion of a white solid, which was washed with ether and hexane and dried in vacuo. Yield 97.3 mg (80%) (Found: C, 45.4; H, 7.05; N, 3.15. Calc. for C31H55BF4N2OOsP2: C, 45.95; H, 6.8; N, 3.45%).IR (Nujol, cm21): n(C]] ] N) 2330w, 2300w, n(CO) 1930s, n(C]] C) 1550m, n([BF4]2) 1060 (br). NMR (CDCl3, 20 8C); 1H, d 8.28 (d, JH]H = 17.3, 1 H, OsCH]] CHPh), 7.20 (t, JH]H = 7.7, 2 H, m-H of Ph), 7.07 (d, JH]H = 7.7, 2 H, o-H of Ph), 6.99 (t, JH]H = 7.7, 1 H, p-H of Ph), 6.42 (d, JH]H = 17.3, 1 H, OsCH]] CHPh), 2.68 (s, 3 H, NCCH3), 2.58 (m, 6 H, PCHCH3), 2.57 (s, 3 H, NCCH3), 1.31 (dvt, N = 13.5, JH]H = 7.2, 18 H, PCHCH3) and 1.29 (dvt, N = 13.5, JH]H = 7.2, 18 H, PCHCH3); 13C-{1H}, d 185.0 (t, JP]C = 9.4, CO), 142.5 (br, ipso-C of Ph), 136.2 (t, JP]C = 3.0, OsCH]] CHPh), 132.7 (t, JP]C = 8.9, OsCH]] CHPh), 128.2 (br, o-CH of Ph), 126.0, 125.5 (both s, NCCH3), 124.0 (br, CHPh, m-CH of Ph), 24.4 (vt, N = 24.7 Hz, PCHCH3), 19.4 (s, PCHCH3), 19.0 (s, PCHCH3), 4.4, 3.7 (both s, NCCH3); 31P-{1H}, d 3.1 (s).[Os(Á2-O2CH)(]] CHCH2Ph)(CO)(PPri 3)2]BF4 18. A solution of complex 8 (100 mg, 0.15 mmol) in chloroform was treated with HBF4?OEt2 (16 ml, 0.15 mmol).The solution was dried in vacuo, yielding a green oil. IR (CH2Cl2, cm21): n(CO) 1980s, nasym(O2CH) 1560s, nsym(O2CH) 1355m. NMR (CDCl3, 20 8C): 1H, d 17.63 (t, JH]H = 6.1, 1 H, Os]] CH), 9.19 (s, O2CH), 7.35– 7.22 (m, 5 H, Ph), 3.52 (d, JH]H = 6.1, 2 H, ]] CHCH2Ph), 2.45 (m, 6 H, PCHCH3), 1.34 (dvt, N = 14.2, JH]H = 7.1, 18 H, PCHCH3) and 1.19 (dvt, N = 13.8, JH]H = 7.5, 18 H, PCHCH3); 13C, d 290.8 (br, Os]] C), 179.6 (t, JP]C = 8.3, CO), 168.7 (s, O2CH), 134.2 (s, ipso-C of Ph), 129.1 (s, o-CH of Ph), 127.8 (s, p-CH of Ph), 127.8 (s, m-CH of Ph), 65.3 (s, CH2Ph), 25.8 (vt, N = 25.9 Hz, PCHCH3), 19.3 (s, PCHCH3) and 19.1 (s, PCHCH3); 31P-{1H}, d 38.3 (s).192 J.Chem. Soc., Dalton Trans., 1997, Pages 181–192 [OsH(CO)(MeCN)2(PPri 3)2]BF4 19. A solution of complex 10 (65 mg, 0.11 mmol) in ether was treated with HBF4?OEt2 (11 ml, 0.11 mmol). The resulting suspension was treated with MeCN (6 ml, 0.11 mmol) causing the precipitation of a white solid.The solid was washed with ether and dried in vacuo. Yield 49.1 mg (75%) (Found: C, 39.3; H, 7.45; N, 3.8. Calc. for C23H49BF4- N2OOsP2: C, 39.0; H, 6.95; N, 3.95%). IR (Nujol, cm21): n(C]] ] N) 2330w, 2290w, n(Os]H) 2140w, n(CO) 2140s. NMR (CDCl3, 20 8C): 1H, d 2.53 (s, 3 H, NCCH3), 2.50 (s, 3 H, NCCH3), 2.40 (m, 6 H, PCHCH3), 1.30 (dvt, N = 13.5, JH]H = 7.0, 36 H, PCHCH3) and 214.87 (t, JP]H = 17.0 Hz, 1 H, OsH); 31P-{1H}, d 24.94 (s). Reaction of complex 10 with HBF4.A CDCl3 solution of complex 10 (8 mg, 0.01 mmol) placed in a NMR tube was treated with HBF4 (1.9 ml, 0.01 mmol) and the tube sealed under argon. After 5 min four products were mainly formed (Fig. 1). Significant NMR signals (CDCl3, 20 8C) are: A 1H, d 7.98 (br, 1 H, O2CH) and 26.80 (br, 2 H, h2-H2); 31P, d 25.6 (s); T1/ms [Os(h2-H2), 300 MHz, CDCl3] = 38 (293), 21 (253), 17 (233), 17 (218 K); B, 1H, d 8.14 [br, 1 H, OC(O)H] and 26.94 (br, 2 H, h2-H2); 31P, d 41.8 (s); T1/ms [Os(h2-H2), 300 MHz, CDCl3] = 36 (293), 21 (253 K); C, 1H, d 9.26 [br, 1 H, OC(O)H] and 29.04 (dd, JP]H = 28.6, 15.7 Hz, OsH); T1/ms (OsH, 300 MHz, CDCl3) = 740 (293), 305 (253), 290 (233), 260 (218 K); D, 1H, d 9.16 [br, 1 H, OC(O)H] and 29.70 (br, OsH); 31P, d 35.6 (br).Computation All calculations were performed with an ab initio molecular orbital method with introduction of correlation energy through the Møller–Plesset perturbational approach,24 excluding excitations concerning the lowest-energy electrons (frozen-core approach).Effective core potentials were used to represent the 60 innermost electrons (up to the 4d shell) of the osmium atom,25 as well as the 10-electron core of the phosphorus atoms.26 The basis set used for the osmium atom is that associated with the pseudo-potential,25 with a (541/41/111) contraction, 27 which is triple z for the 5d shell, double z for the 6s and single z for the 6p. For the phosphorus atoms a valence double z basis set 26 with a (21/21) contraction was used, while the standard 6-31G basis set was used for all the other atoms.28 Geometry optimizations were carried out at the second level of the Møller–Plesset theory (MP2). All geometrical parameters were optimized except the dihedral angle of one of the hydrogen atoms of each phosphine, which was fixed to be oriented towards the carbon of the carbonyl ligand, in order to avoid chemically meaningless rotations around the M]P axis.Single-point energy-only calculations were made at a higher computational level with the MP2 optimized geometries. This is the fourth level of the same perturbational theory (MP4), with consideration of single, double, triple and quadruple excitations. Acknowledgements We thank the Dirección General de Investigación Gentificay Técnica (Projects PB 92–0092 and PB 92–0621, Programa de Promoción General del Conocimiento) and EU (Project, Selective Processes and Catalysis Involving Small Molecules) for financial support. E.O. thanks the DGA (Diputación General de Aragón) for a grant. References 1 C. Bohanna, M. A. Esteruelas, F. J. Lahoz, E. Oñate and L. A. Oro, Organometallics, 1995, 14, 4825. 2 M. A. Esteruelas, F. J. Lahoz, E. Oñate, L. A. Oro and E. Sola, J. Am. Chem. Soc., 1996, 118, 89. 3 E. P. Wasserman, C. B. Moore and R. G. Bergman, Science, 1992, 255, 315. 4 J. Espuelas, M. A. Esteruelas, F. J. Lahoz, L. A. Oro and C. Valero, Organometallics, 1993, 12, 663. 5 H. Werner, M. A. Esteruelas and H. Otto, Organometallics, 1986, 5, 2295. 6 M. J. Albéniz, M. L. Buil, M. A. Esteruelas, A. M. López, L. A. Oro and B. Zeier, Organometallics, 1994, 13, 3746. 7 K. 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Chem., 1990, 14, 671. 23 (a) P. J. Desrosiers, L. Cai, Z. Lin, R. Richards and J. Halpern, J. Am. Chem. Soc., 1991, 113, 4173; (b) M. A. Esteruelas, Y. Jean, A. Lledós, L. A. Oro, N. Ruiz and F. Volatron, Inorg. Chem., 1994, 33, 3609. 24 C. Møller and M. S. Plesset, Phys. Rev., 1934, 46, 618. 25 P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299. 26 P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 284. 27 Z. Lin and M. B. Hall, J. Am. Chem. Soc., 1992, 114, 2928. 28 W. J. Hehre and R. Ditchfield, J. Chem. Phys., 1972, 56, 2257. Received 27th June 1996; Paper 6/04486G