The interaction of [NbCp(2)H(3)] with fluorinated alcohols to give dihydrogen-bonded complexes was studied by a combination of IR, NMR and DFT methods. IR spectra were examined in the range from 200-295 K, affording a clear picture of dihydrogen-bond formation when [NbCp(2)H(3)]/HOR(f) mixtures (HOR(f) = hexafluoroisopropanol (HFIP) or perfluoro-tert-butanol (PFTB)) were quickly cooled to 200 K. Through examination of the OH region, the dihydrogen-bond energetics were determined to be 4.5+/-0.3 kcal mol(-1) for TFE (TFE = trifluoroethanol) and 5.7+/-0.3 kcal mol(-1) for HFIP. (1)H NMR studies of solutions of [NbCp(2)H(2)(B)H(A)] and HFIP in [D(8)]toluene revealed high-field shifts of the hydrides H(A) and H(B), characteristic of dihydrogen-bond formation, upon addition of alcohol. The magnitude of signal shifts and T(1) relaxation time measurements show preferential coordination of the alcohol to the central hydride H(A), but are also consistent with a bifurcated character of the dihydrogen bonding. Estimations of hydride-proton distances based on T(1) data are in good accord with the results of DFT calculations. DFT calculations for the interaction of [NbCp(2)H(3)] with a series of non-fluorinated (MeOH, CH(3)COOH) and fluorinated (CF(3)OH, TFE, HFIP, PFTB and CF(3)COOH) proton donors of different strengths showed dihydrogen-bond formation, with binding energies ranging from -5.7 to -12.3 kcal mol(-1), depending on the proton donor strength. Coordination of proton donors occurs both to the central and to the lateral hydrides of [NbCp(2)H(3)], the former interaction being of bifurcated type and energetically slightly more favourable. In the case of the strong acid H(3)O(+), the proton transfer occurs without any barrier, and no dihydrogen-bonded intermediates are found. Proton transfer to [NbCp(2)H(3)] gives bis(dihydrogen) [NbCp(2)(eta(2)-H(2))(2)](+) and dihydride(dihydrogen) complexes [NbCp(2)(H)(2)(eta(2)-H(2))](+) (with lateral hydrides and central dihydrogen), the former product being slightly more stable. When two molecules of TFA were included in the calculations, in addition to the dihydrogen-bonded adduct, an ionic pair formed by the cationic bis(dihydrogen) complex [NbCp(2)(eta(2)-H(2))(2)](+) and the homoconjugated anion pair (CF(3)COO...H...OOCCF(3))(-) was found as a minimum. It is very likely that these ionic pairs may be intermediates in the H/D exchange between the hydride ligands and the OD group observed with the more acidic alcohols in the NMR studies.

Treatment of OsH 6 (P i Pr 3 ) 2 (1) with benzophenone and acetophenone in toluene under reflux affords OsH 3 {C 6 H 4 C(O)R}(P i Pr 3 ) 2 (R ) Ph (2), CH 3 (3)), as a result of the ortho-CH activation of the aromatic group of the ketones. Complex 1 is also capable of activating ortho-CF bonds of fluorinated aromatic ketones. Thus, the reactions of this complex with pentafluoroacetophenone, decafluorobenzophenone, and 2,6-difluoroacetophenone give OsH 3 {C 6 F 4 C(O)R}-(PiPr 3 ) 2 (R ) CH 3 (4), C 6 F 5 (5)) and OsH 3 {C 6 H 3 FC(O)CH 3 }(P i Pr 3 ) 2 ( 6). The structure of 4 has been determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted pentagonal bipyramid with the phosphine ligands occupying axial positions. Complexes 4 and 6 can be also obtained by reaction of 1 with 2,3,4,5tetrafluoroacetophenone and 2-fluoroacetophenone, respectively. This selective C-H activation of the ortho-CH bond of the above-mentioned ketones is in contrast with the selective C-F activation observed for the reaction of 1 with 2,3,4,5,6-pentafluorobenzophenone, which affords OsH 3 {C 6 F 4 C(O)C 6 H 5 }(P i Pr 3 ) 2 ( 7). The structure of 7 has also been determined by X-ray diffraction. The geometry around the osmium is the same as that of 4. DFT calculations suggest that in fluorinated aromatic ketones the ortho-CF activation is thermodynamically favored over the ortho-CH activation and that the kinetically preferred ortho-CH activation of 2,3,4,5-tetrafluoroacetophenone and 2-fluoroacetophenone is in part due to the preferred anti arrangement of the F-C-C-CdO unit of the starting ketones. In solution, the hydride ligands of the OsH 3 unit of 2-7 undergo two different thermally activated exchange processes, which involve the central hydride with each hydride ligand situated close to the donor atoms of the chelate group. The exchange involving the hydride ligand disposed cis to the carbonyl group is faster than the other one in all the cases. For 2, 3, and 6, quantum exchange coupling is also observed between the hydride ligands involved in the faster thermally activated exchange process.

Reaction of GeH 4 and GeH 3 Ph with the agostic complex Mo(CO)(dppe) 2 (dppe ) Ph 2 PC 2 H 4 -PPh 2 ) provides germane σ complexes Mo(CO)(η 2 -GeH 4-n Ph n )(dppe) 2 (n ) 0, 1). The coordination in these complexes has been assigned as (η 2 -Ge-H) on the basis of NMR and IR spectroscopy and by comparison to the analogous complexes of silanes. When the more electron-rich phosphine depe (depe ) Et 2 PC 2 H 4 PEt 2 ) is used, oxidative addition (OA) products MoH(GeH 3 )(CO)(depe) 2 and MoH(GeH 2 Ph)(CO)(depe) 2 are isolated (NMR and X-ray evidence). However, when the secondary organogermane GeH 2 Ph 2 is used in the depe system, the η 2 -complex Mo(CO)(η 2 -GeH 2 Ph 2 )(depe) 2 is obtained. This complex was characterized by X-ray crystallography and NMR and IR spectroscopy. The Mo(CO)(η 2 -GeH 3 Ph)(dppe) 2 and Mo(CO)(η 2 -GeH 2 Ph 2 )(depe) 2 complexes were found to be in tautomeric equilibrium with their OA products in solution. Structure and bonding comparisons are made to the analogous silane complexes, e.g., Mo(CO)(η 2 -SiH 2 Ph 2 )(depe) 2 , the X-ray structure for which is also reported. The Ge-H bonds undergo OA much more easily than Si-H, and to obtain further insight into the activation processes, ab initio DFT calculations have been performed on Mo(CO)(EH 4-n vin n )(dhpe) 2 model complexes (E ) Si, Ge; n ) 0-3; dhpe ) H 2 PCH 2 CH 2 PH 2 ; vin ) CHdCH 2 ) and also the analogous H 2 complex. Because the ease of the whole OA process is a balance between the E-H bonding energy and Mo-E bonding energy, it can be concluded that the factor that makes OA of the Ge-H bond easier than that for Si-H is the relative weakness of the Ge-H bond, despite the fact that the Mo-Ge bond is also weaker. This competition between both factors is also seen for OA of H 2 , for which although the Mo-H bonding energy is much higher than Mo-Si and Mo-Ge bonding energies, the H-H bond is also significantly stronger than the Si-H and Ge-H bonds. In general, the ease of OA of molecular hydrogen is between that of germanes and silanes. Calculations show that for alkanes the OA is much more difficult because the loss of the high C-H bond energy (comparable to or greater than that for H-H) is not as well compensated for by the energy of formation of the Mo-C bond due to the weakness of the Mo-C bond.