The reaction mechanism of the gold(I)-phosphine-catalyzed hydroamination of 1,3-dienes was analyzed by means of density functional methods combined with polarizable continuum models. Several mechanistic pathways for the reaction were considered and evaluated. It was found that the most favorable series of reaction steps include the ligand substitution reaction in the catalytically active Ph3PAuOTf species between the triflate and the substrate, subsequent nucleophile attack of the N-nucleophile (benzyl carbamate) on the activated double bond, which is followed by proton transfer from the NH2 group to the unsaturated carbon atom. The latter step, the most striking one, was analyzed in detail, and a novel pathway involving tautomerization of benzyl carbamate nucleophile assisted by triflate anion acting as a proton shuttle was characterized by the lowest barrier, which is consistent with experimental findings.

The interaction of the ruthenium hydride complex CpRuH(CO)(PCy(3)) (1) with proton donors HOR of different strength was studied in hexane and compared with data in dichloromethane. The formation of dihydrogen-bonded complexes (2) and ion pairs stabilized by hydrogen bonds between the dihydrogen ligand and the anion (3) was observed. Kinetics of the interconversion from 2 to 3 was followed at different (CF(3))(3)COH concentrations between 200 and 240 K. The activation enthalpy and entropy values for proton transfer from the dihydrogen-bonded complex 2 to the (eta(2)-H(2))-complex 3 (DeltaH() = 11.0 +/- 0.5 kcal/mol and DeltaS() = -19 +/- 3 eu) were obtained for the first time. The results of the DFT study of the proton transfer process, taking CF(3)COOH and (CF(3))(3)COH as a proton donors and introducing solvent effects in the calculation with the PCM method, are presented. The role of homoconjugate pairs [ROHOR](-) in the protonation is analyzed by means of the inclusion of an additional ROH molecule in the calculations. The formation of the free cationic complex [CpRu(CO)(PCy(3))(eta(2)-H(2))](+) is driven by the formation of the homoconjugated anionic complex [ROHOR](-). Solvent polarity plays a significant role stabilizing the charged species formed in the process. The theoretical study also accounts for the dihydrogen release and production of CpRu(OR)(CO)(PCy(3)), observed at temperatures above 250 K.

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A series of bis-N-heterocyclic carbenes of rhodium and iridium have been obtained and characterized. The formation of the M-C bond has been studied according to experimental and theoretical data, showing that two different mechanisms are operative for the first (single proton deprotonation of the bisimidazolium salt, or oxidative addition followed by deprotonation of the metal hydride) and second (oxidative addition of the second bisimidazolium C-H bond, yielding a NHC-Ir III -H species) metalation processes. In the case of complexes with long linkers between the imidazolium rings, reductive elimination of HCl affords bisimidazolylidene complexes of Ir I . According to the theoretical studies we concluded that thermodynamic parameters would determine the formation of the NHC-Ir III -H species, while Ir I -NHC species would be kinetically favored in the case of complexes with long linkers between the azole rings. The crystal structures of a series of Ir-bis(NHC) complexes are described.

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.

Treatment of the complex (1) with HBF4·OEt2 in diethyl ether−acetone (2:1) affords the elongated dihydrogen derivative (2), which reacts with NaCl and CsF to give (X = Cl (3), F (4)). The X-ray diffraction studies on 2 and 4 and DFT calculations on the model complexes (1t), (2t), and (X = Cl (3t), F (4t)) suggest that one of the hydrogen atoms bonded to the osmium atom undergoes a cis electrostatic attraction with the L ligand (L = H (1, 1t), (CH3)2CO or H2O (2, 2t), Cl (3, 3t), F (4, 4t)), which increases in the sequence (CH3)2CO or H2O < Cl ≤ F < H. This interaction provokes a lengthening of the hydrogen−hydrogen bond and an increase in the rotation barrier of the elongated dihydrogen ligand. Thus, it is observed that the separation between the hydrogen atoms of the dihydrogen decreases in the sequence 1t (1.695 Å) > 4t (1.544 Å) > 3t (1.489 Å) > 2t (1.455 Å), whereas the rotation barrier of the dihydrogen increases in the sequence 2 (<9 kcal·mol-1) < 3 (≅9 kcal·mol-1) < 4 (10.1 ± 0.8 kcal·mol-1) < 1 (13.9 ± 0.3 kcal·mol-1).

The nucleophilicity of the [Pt(2)S(2)] core in [[Ph(2)P(CH(2))(n)PPh(2)]Pt(mu-S)(2)Pt[Ph(2)P(CH(2))(n)PPh(2)]] (n = 3, dppp (1); n = 2, dppe (2)) metalloligands toward the CH(2)Cl(2) solvent has been thoroughly studied. Complex 1, which has been obtained and characterized by X-ray diffraction, is structurally related to 2 and consists of dinuclear molecules with a hinged [Pt(2)S(2)] central ring. The reaction of 1 and 2 with CH(2)Cl(2) has been followed by means of (31)P, (1)H, and (13)C NMR, electrospray ionization mass spectrometry, and X-ray data. Although both reactions proceed at different rates, the first steps are common and lead to a mixture of the corresponding mononuclear complexes [Pt[Ph(2)P(CH(2))(n)PPh(2)](S(2)CH(2))], n = 3 (7), 2 (8), and [Pt[Ph(2)P(CH(2))(n)PPh(2)]Cl(2)], n = 3 (9), 2 (10). Theoretical calculations give support to the proposed pathway for the disintegration process of the [Pt(2)S(2)] ring. Only in the case of 1, the reaction proceeds further yielding [Pt(2)(dppp)(2)[mu-(SCH(2)SCH(2)S)-S,S']]Cl(2) (11). To confirm the sequence of the reactions leading from 1 and 2 to the final products 9 and 11 or 8 and 10, respectively, complexes 7, 8, and 11 have been synthesized and structurally characterized. Additional experiments have allowed elucidation of the reaction mechanism involved from 7 to 11, and thus, the origin of the CH(2) groups that participate in the expansion of the (SCH(2)S)(2-) ligand in 7 to afford the bridging (SCH(2)SCH(2)S)(2-) ligand in 11 has been established. The X-ray structure of 11 is totally unprecedented and consists of a hinged [(dppp)Pt(mu-S)(2)Pt(dppp)] core capped by a CH(2)SCH(2) fragment.

Density functional theory (DFT) Becke3LYP calculations including full and restricted geometry optimizations are carried out on the complex [Co(Cor)(Benz)(CH3)]+ (Cor = corrin, Benz = benzimidazole), which is a model of B 12 cofactors, and on the products of the two possible heterolytic cleavages of the Co−C bond, [Co(Cor)(Benz)(CH3)], CH3 +, [Co(Cor)(Benz)(CH3)]2 +, and CH3 -. The thermodynamics of the heterolytic processes are found to depend very significantly on the distance of the axial ligand from the cobalt. The results are explained through simple molecular orbital reasonings, and their possible implications for the biological reactivity of adenosylcobalamin and methylcobalamin are discussed.