THE REACTION CHEMISTRY OF MULTIPLY BONDED DIMOLYBDENUM AND DITUNGSTEN COMPLEXES
Abstract
Halide exchange of Mo(,2)Cl(,4)(dppm)(,2) with I('-) affords the new quadruply bonded complex Mo(,2)I(,4)(dppm)(,2). The molecular structure of this compound determined on crystals grown from CH(,2)Cl(,2)/MeOH shows that molecules with both staggered and eclipsed rotational geometries are present in the same unit cell. This is the first report of such a case and suggests that crystal packing forces may have a greater effect on rotational geometry than hitherto suspected. Molecules of the type Mo(,2)X(,4)(dppm)(,2) (X = halide), undergo facile cleavage with alkyl isocyanides to give mononuclear products. Stoichiometric reactions in the presence of PF(,6)('-) allowed the isolation of several intermediates in this cleavage process. Thus, a reaction pathway for the cleavage of dinuclear multiply bonded compounds could be proposed. The new quadruply bonded compound Mo(,2)Cl(,4)(dmpm)(,2) was fully characterized. Its molecular structure is similar to that of Mo(,2)Cl(,4)(dppm)(,2), but with a shorter Mo-Mo quadruple bond length (2.12 (ANGSTROM)). In addition, the solution properties of the novel compound Re(,2)Cl(,4)(dmpm)(,3) are examined and discussed with respect to its molecular structure. This compound, which contains a Re(TBOND)Re bond is the first multiply bonded compound to be bridged by three bidentate phosphine ligands. The new compound of stoichiometry W(,2)((mu)-Cl)Cl(,4)(dppm)(,2) was synthesized and extended Huckel calculations were performed in order to describe the metal-metal bonding in this and related complexes. The possibility that this compound contains a bridging hydride is also discussed. The compound reacts with isocyanides, followed by oxidation, to give the air stable complexes W(,2)Cl(,5)(dppm)(,2)(CNR) PF(,6) (R = mesityl, xylyl or t-Bu). These M(,2)L(,10) complexes are inert to further reaction which provides an insight into the mechanism(s) available for metal bond cleavage. The substitution of the ethanol ligands in W(,2)Cl(,4)((mu)-OEt)(,2)(OEt)(,2)(HOEt)(,2) is proposed to be the first step in the reductive coupling of ketones by this reagent. The reaction of this compound with tertiary heterocyclic amines provides proof that such substituted complexes are stable.
Degree
Ph.D.
Subject Area
Chemistry
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