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Recent studies have demonstrated that the incorporation of an ansa bridge may have a profound influence on the chemistry of a metallocene system. 1 We are particularly interested in delineating the origin of these effects by studying well-defined permethylated 2 ansa metallocene complexes, [A(C 5 Me 4 ) 2 ]MX n . For example, we recently demonstrated that the [Me 2 Si] ansa bridge in [Me 2 Si(C 5 Me 4 ) 2 ]ZrX 2 derivatives creates more electrophilic metal centers than those in Cp* 2 ZrX 2 counterparts. 3 In this paper, we report that incorporation of the [Me 2 Si] ansa bridge into the permethylmolybdenocene system promotes intermolecular C-H and C-C bond activation reactions.Access to the [Me 2 Si] ansa-bridged permethylmolybdenocene system is conveniently provided by the synthesis (1) For leading reports describing differences in the chemistry of ansa and non-ansa systems, see: (a) Conway, S. L. J.; Dijkstra, T.; Doerrer, L. H.; Green, J. C.; Green, M. L. H.; Stephens, M. L. H. Cook, J.; Green, M. L. H.; Labella, L.; Simpson, S. J.; Souter, J.; Stephens, A. H. H. J. Chem. Soc., Dalton Trans. 1997, 3225-3243 and references therein. (d) Wochner, F.; Brintzinger, H. H. J. Organomet. Chem. 1986, 309, 65-75. (e) Smith, J. A.; Brintzinger, H. H. J. Organomet. Chem. 1981, 218, 159-167. (f) Dorer, B.; Diebold, J.; Weyand, O.; Brintzinger, H. H. J. Organomet. Chem. 1992, 427, 245-255. (g) Fendrick, C. M.; Schertz, L. D.; Day, V. W.; Marks, T. J. Organometallics 1988, 7, 1828-1838 and references therein.(2) Our reason for studying permethylated ansa-metallocenes is associated with the fact that such substitution frequently allows isolation of complexes that have no counterparts in the corresponding unsubstituted cyclopentadienyl system. For reviews of heavily substituted cyclopentadienyl ligands, see: (a) Janiak, C.; Schumann, H. Adv. Organomet. Chem. 1991, 33, 291-393. (b) Okuda, J. Top. Curr. Chem. 1991 (3) Lee, H.; Desrosiers, P. J.; Guzei, I.; Rheingold, A. L.; Parkin, G. J. Am. Chem. Soc. 1998, 120, 3255-3256. (4) The diiodide [Me2Si(C5Me4)2]MoI2 may also be obtained by treatment of [Me2Si(C5Me4)2]MoH2 with (CH2I)2. (5) The molecular structures of [Me2Si(C5Me4)2]MoCl2, [Me2Si(C5-Me4)2]MoI2, [Me2Si(C5Me4)2]MoMe2, [Me2Si(C5Me4)2]MoH2, [Me2Si(C5-Me4)2]Mo(Ph)H, [Me2Si(C5Me4)2]Mo(η 2 -C2H4), [Me2Si(C5Me4)2]Mo(Me)-CN,[Me2Si(C5Me4)2]Mo(CO),[Me2Si(C5Me4)2]Mo(η 2 -Bu t CN),and[Me2Si(C5Me4)2]-Mo(η 2 -Bu t CP) have been determined by X-ray diffraction. See the Supporting Information.

The tripodal bis(thioimidazolyl)(pyrazolyl)hydroborato [NSS] donor ligand, [HB(timMe)2pz]-, has been synthesized by the sequential reaction of LiBH4 with methimazole and pyrazole. Importantly, the ligand binds to zinc in a manner which resembles the coordination of the histidine and cysteine residues at the active site of liver alcohol dehydrogenase.

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Salts of the ruthenocenylmethylium cation, 1 +, can be synthesized from the reaction of ruthenocenylmethanol with either Brønsted or Lewis acids. The X-ray crystal structures of the tetrakis{3,5-bis(trifluoromethyl)phenyl}borate and trifluoromethanesulfonate salts of 1 + reveal that the methylium carbon is bound to the ruthenium with Ru−C bond lengths in the range 2.251(9)−2.40(1) Å and confirm the description of the cation structure as η 5-cyclopentadienyl-η 6-fulvene-ruthenium(II). The UV−vis spectrum of 1 + shows a d−d transition at an energy similar to those of ruthenocene and the η 5-cyclopentadienyl-η 6-benzeneruthenium(II) cation, but with increased absorptivity. Cyclic voltammetry indicates that 1 + is reduced at considerably less negative potential than its isomer, the η 5-cyclopentadienyl-η 6-benzene-ruthenium(II) cation. Chemical reduction with sodium amalgam in tetrahydrofuran leads to the formation of methylruthenocene, 1,2-bis(ruthenocenyl)ethane, and bis(ruthenocenylmethyl)ether. Reaction of 1 + with triphenylphosphine affords the (ruthenocenylmethyl)triphenylphosphonium cation; the crystal structure of the dichloromethane solvate of its tetrafluoroborate salt has been determined. Density functional calculations closely reproduce the crystallographically determined geometry of 1 + and allow rationalization of some characteristics of its structure, spectroscopy, and reactivity. The calculations suggest that the ferrocenylmethylium cation, 3 +, has a geometry similar to 1 + with similar orbital structure, albeit with considerably more d-character to the occupied frontier orbitals.