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Cp*Os(CO)2H is protonated by triflic acid (HOTf) in CD2Cl2 solution to give an equilibrium mixture (87:13) of the dihydride [Cp*Os(CO)2(H)2]+OTf− and the dihydrogen complex [Cp*Os(CO)2(η2-H2)]+OTf−. The acidity of these protonated species is roughly comparable to HOTf, since only partial protonation was observed, e.g., 36% protonation with 1.2 equiv of HOTf. In the absence of acid, the T 1 of the hydride ligand of Cp*Os(CO)2H is 5.9 s at −80 °C. When all of the Cp*Os(CO)2H is protonated by excess HOTf, the T 1 (−80 °C) of the terminal hydride ligands of [Cp*Os(CO)2(H)2]+OTf− is 2.8 s, while the T 1 of the dihydrogen ligand of [Cp*Os(CO)2(η2-H 2)]+OTf− is 19 ms (−80 °C). The observed T 1 values of the Os−H resonance of Cp*Os(CO)2H decreased significantly under conditions of partial protonation, indicating intermolecular proton transfer among [Cp*Os(CO)2(η2-H2)]+OTf−, [Cp*Os(CO)2(H)2]+OTf−, Cp*Os(CO)2H, and HOTf. IR spectra indicate that the two CO ligands of [Cp*Os(CO)2(H)2]+ (and hence the hydrides as well) are trans to each other in the four-legged piano stool geometry. Two resonances for HOTf are observed in the NMR spectra and are assigned as [HOTf] n (hydrogen bonded to itself) and TfOH···OTf− in which HOTf is hydrogen bonded to an OTf− counterion. [CpW(CO)3(H)2]+OTf− and [Cp*W(CO)3(H)2]+OTf− were formed by protonation of CpW(CO)3H and Cp*W(CO)3H. Protonation of the phosphine-substituted tungsten hydrides CpW(CO)2(PR3)H (R = Me, Cy, Ph) by HOTf or [H(Et2O)2]+ BAr‘4 − (Ar‘ = 3,5-bis(trifluoromethyl)phenyl) gives dihydrides [CpW(CO)2(PR3)(H)2]+ which were isolated and fully characterized. The structure of [CpW(CO)2(PMe3)(H)2]+OTf− was determined by single-crystal X-ray diffraction and reveals weak hydrogen bonds between one hydride on W and two of the fluorines on the triflate anion.

The reactivity of alkynes with the imido clusters Ru3(p3-NPh)2(CO)9, H2Ru3(g3-NPh)(CO)9, ß3(µ3-NPh)(CO)10, Fe3^3-NPh)2(CO)9, and H2Fe3(g3-NPh)(CO)9 has been examined. The cluster Fe3(¿¿3-NPh)(CO)10 reacts regiospecifically with a series of alkynes to form the binuclear ferrapyrrolinone complexes Fe2(M2-J73-RC=C(R')C(0)NPh)(C0)6, possessing a metallacycle formed by coupling of the alkyne with CO and the imido ligand. These same ferrapyrrolinone complexes also form when H2Fe3(¡u3-NPh)(CO)9 is allowed to react with PhC^sCPh, EtC=CEt, and PhC=CMe. The derivative formed from PhC^CMe was found to undergo subsequent substitution of one CO ligand by Bu'N=C to form Fe2^2-jj3-PhC=C(Me)C(0)-NPh)(CO)5(CNBu'), which was crystallographically characterized. The bis(imido) cluster Ru3(/i3-NPh)2(CO)9 reacts with PhC^CPh to form the tetranuclear cluster Ru4(g3-NPh) 2( 2-µ2-1 = 1 ) (CO) 10, which has been crystallographically shown to possess a butterfly arrangement of the four ruthenium atoms with the alkyne bridging the hinge of the butterfly in a perpendicular fashion and with the imido ligands bridging the open triangular faces of the butterfly. The analogous triiron cluster Fe3(g3-NPh)2(CO)9 reacts with PhC=CPh to give a mixture of products, from which the ferracyclopentadiene Fe2 (µ2-174 *-PhC=C (Ph) C -(Ph)=CPh)(CO)6 and the binuclear ferraazetine complex Fe2Gt2-7/3-PhC=C(Ph)NPh)(CO)6 were characterized. The latter compound possesses a four-membered metallacycle formed by coupling of the alkyne with the imido ligand. Treatment of H2Ru3U3-NPh)(CO)9 with PhC=CPh results in the formation of the cluster Ru4(M4-NPh)(M4-772-PhC=CPh)(CO)n, which has been crystallographically shown to possess a planar arrangement of the four ruthenium atoms bridged on one side by the M4-imido ligand and the other by the alkyne. The cluster Fe3(g3-NPh)(CO)10 has also been found to react with 1,3-cyclohexadiene and with aliene to respectively form the trinuclear clusters Fe3^3-NPh)(CO)8(7j4-l,3-cyclohexadiene) and Fe3(M3-NPh)(CO)8(M2-?;6-C6H8). Crystallographic characterization has shown that in the former the diene has replaced two CO's and is coordinated to a single iron atom whereas in the latter two alienes have coupled through their central carbon atoms to form a C6H8 ligand that bridges two iron atoms with each C3H4 unit of the ligand ?;3-bonded to a single iron.

Alkynes can be hydrogenated at room temperature by an ionic hydrogenation method using triflic acid (CF3SO3H) as the proton donor and a transition metal hydride (Cp(CO)aWH) as the hydride donor. Reaction of PhC^CH with HOTf and Cp(CO)3WH gives ethylbenzene as the final product in high yield. Intermediates observed in this reaction are the vinyl triflate CH2=C(Ph)(OTf) and the geminal ditriflate Ph(CH3)C(OTf)2, which result from the addition of 1 or 2 equiv of HOTf to the C=C triple bond of the alkyne. Hydrogenation of PhC=CMe by HOTf and Cp(CO)3WH similarly produces propylbenzene as the ultimate product. Along with vinyl triflates, additional intermediates observed in this reaction were the cis and trans isomers of the /3-methylstyrene complex [Cp(CO)3W-(?72-PhHC=CHCH3)]+[OTf]~. Hydrogenation of n-butylacetylene to n-hexane does occur upon reaction with HOTf7Cp(CO)3WH, but is very slow. In the absence of metal hydrides, 2-methyl-lbuten-3-yne reacts with HOTf to give the vinyl triflate CH2=CMeC(OTf)=CH2, but reaction with HOTf and Cp(CO)3WH gives Me2C=C(OTf)Me. The key characteristics required for the metal hydride used in these hydrogenations are the ability to donate hydride in the presence of strong acid, and the absence of rapid decomposition of the hydride through reaction with the strong acid. Cp(CO)3WH meets these requirements, but HSiEt3, while an effective hydride donor, is decomposed by HOTf on the time scale of these alkyne hydrogenation reactions.

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