The overall reductive elimination of RH from the ansa-molybdenocene and -tungstenocene complexes [Me(2)Si(C(5)Me(4))(2)]Mo(Ph)H and [Me(2)Si(C(5)Me(4))(2)]W(R)H (R = Me, Ph) is characterized by an inverse primary kinetic isotope effect (KIE) for the tungsten system but a normal KIE for the molybdenum system. Oxidative addition of PhH to [[Me(2)Si(C(5)Me(4))(2)]M] also differs for the two systems, with the molybdenum system exhibiting a substantial intermolecular KIE, while no effect is observed for the tungsten system. These differences in KIEs indicate a significant difference in the reactivity of the hydrocarbon adducts [Me(2)Si(C(5)Me(4))(2)]M(RH) for the molybdenum and tungsten systems. Specifically, oxidative cleavage of [Me(2)Si(C(5)Me(4))(2)]M(RH) is favored over RH dissociation for the tungsten system, whereas RH dissociation is favored for the molybdenum system. A kinetics analysis of the interconversion of [Me(2)Si(C(5)Me(4))(2)]W(CH(3))D and [Me(2)Si(C(5)Me(4))(2)]W(CH(2)D)H, accompanied by elimination of methane, provides evidence that the reductive coupling step in this system is characterized by a normal KIE. This observation demonstrates that the inverse KIE for overall reductive elimination is a result of an inverse equilibrium isotope effect (EIE) and is not a result of an inverse KIE for a single step. A previous report of an inverse kinetic isotope effect of 0.76 for C-H reductive coupling in the [Tp]Pt(CH(3))H(2) system is shown to be erroneous. Finally, a computational study provides evidence that the reductive coupling of [Me(2)Si(C(5)Me(4))(2)]W(Ph)H proceeds via the initial formation of a benzene sigma-complex, rather than an eta(2)-pi-benzene complex.

The zinc thiolate complex [Tm(Ph)]ZnSCH2C(O)N(H)Ph, which features a tetrahedral [ZnS4] motif analogous to that of the Ada DNA repair protein, may be obtained by the reaction of Zn(NO3)2 with [Tm(Ph)]Li and Li[SCH2C(O)N(H)Ph] ([Tm(Ph)] = tris(2-mercapto-1-phenylimidazolyl)hydroborato ligand). Structural characterization of [Tm(Ph)]ZnSCH2C(O)N(H)Ph by X-ray diffraction demonstrates that the molecule exhibits an intramolecular N-H...S hydrogen bond between the amide N-H group and thiolate sulfur atom, a structure that is reproduced by density functional theory (DFT) calculations. The thiolate ligand of [Tm(Ph)]ZnSCH2C(O)N(H)Ph is subject to alkylation, a reaction that is analogous to the function of the Ada DNA repair protein. Specifically, [Tm(Ph)]ZnSCH2C(O)N(H)Ph reacts with MeI to yield PhN(H)C(O)CH2SMe and [Tm(Ph)]ZnI, a reaction which is characterized by second-order kinetics that is consistent with either (i) an associative mechanism or (ii) a stepwise dissociative mechanism in which the alkylation step is rate determining. Although the kinetics studies are incapable of distinguishing between these possibilities, a small normal kinetic isotope effect of kH/kD = 1.16(1) at 0 degrees C for the reaction of [Tm(Ph)]ZnSCH2C(O)N(H*)Ph (H* = H, D) with MeI is suggestive of a dissociative mechanism on the basis of DFT calculations. In particular, DFT calculations demonstrate that a normal kinetic isotope effect requires thiolate dissociation because it results in the formation of [PhN(H)C(O)CH2S]- which, as an anion, exhibits a stronger N-H...S hydrogen bonding interaction than that in [Tm(Ph)]ZnSCH2C(O)N(H)Ph. Correspondingly, mechanisms that involve direct alkylation of coordinated thiolate are predicted to be characterized by kH/kD < or = 1 because the reaction involves a reduction of the negative charge on sulfur and hence a weakening of the N-H...S hydrogen bonding interaction.

In contrast to the benzene and naphthalene compounds (eta(6)-PhH)Mo(PMe(3))(3) and (eta(6)-NpH)Mo(PMe(3))(3), the anthracene complex (eta(6)-AnH)Mo(PMe(3))(3) reacts with H(2) to undergo a haptotropic shift and give the eta(4)-anthracene compound (eta(4)-AnH)Mo(PMe(3))(3)H(2). Density functional theory calculations indicate that the increased facility of naphthalene and anthracene to adopt eta(4)-coordination modes compared to that of benzene is a consequence of the fact that the Mo-(eta(4)-ArH) bonding interaction increases in the sequence benzene < naphthalene < anthracene, while the Mo-(eta(6)-ArH) bonding interaction follows the sequence benzene > naphthalene approximately anthracene.

The reactions of Mo(PMe3)6 towards a variety of five- and six-membered heterocyclic nitrogen compounds (namely, pyrrole, indole, carbazole, pyridine, quinoline, and acridine) have been studied to provide structural models for the coordination of these heterocycles to the molybdenum centers of hydrodenitrogenation catalysts. Pyrrole reacts with Mo(PMe3)6 to yield the eta5-pyrrolyl derivative (eta5-pyr)Mo(PMe3)3H, while indole gives sequentially (eta1-indolyl)Mo(PMe3)4H, (eta5-indolyl)Mo(PMe3)3H, and (eta6-indolyl)Mo(PMe3)3H, with the latter representing the first example of a structurally characterized complex with an eta6-indolyl ligand. Likewise, carbazole reacts with Mo(PMe3)6 to give (eta6-carbazolyl)Mo(PMe3)3H with an eta6-carbazolyl ligand. The reactions of Mo(PMe3)6 with six-membered heterocyclic nitrogen compounds display interesting differences in the nature of the products. Thus, Mo(PMe3)6 reacts with pyridine to give an eta2-pyridyl derivative [eta2-(C5H4N)]Mo(PMe3)4H as a result of alpha-C-H bond cleavage, whereas quinoline and acridine give products of the type (eta6-ArH)Mo(PMe3)3 in which both ligands coordinate in an eta6-manner. For the reaction with quinoline, products with both carbocyclic and heterocyclic coordination modes are observed, namely [eta6-(C6)-quinoline]Mo(PMe3)3 and [eta6-(C5N)-quinoline]Mo(PMe3)3, whereas only carbocyclic coordination is observed for acridine.

The rate constants for hydride transfer from CpRu(P−P)H (P−P = bis(diphenylphosphino)methane (dppm), bis(diphenylphosphino)ethane (dppe), bis(diphenylphosphino)benzene (dpbz), or bis(diphenylphosphino)propane (dppp)) to 1-(1-phenylethylidene)pyrrolidinium tetrafluoroborate have been measured. The bite angles of the hydride complexes CpRu(dppm)H, CpRu(dppe)H, CpRu(dpbz)H, and CpRu(dppb)H (dppb = bis(diphenylphosphino)butane) have been determined by X-ray diffraction. Hydride transfer is faster when the chelate ring of the diphosphine is smaller (i.e., CpRu(dppm)H > CpRu(dppe)H ≈ CpRu(dpbz)H > CpRu(dppp)H ≫ CpRu(dppb)H). Boiling CpRu(PPh3)2Cl with dpbz in benzene or toluene results in the formation of [CpRu(PPh3)(η2-dpbz)]Cl as well as CpRu(dpbz)Cl.