Studies of the alkylation of niobium and tantalum halides containing 2,6-diarylphenoxide ancillary ligation

The mixed halo(aryloxide) compounds [Nb{OC6H(C6H4Me-4)(2)-2,6-Ph-2-3,5}(2)Cl-3], [Ta(OC6HPh4-2,3,5,6)(2)Br-3] and [Nb(OC6HPh4-2,3,5,6)(2)I-3] have been isolated and structurally characterized. Although the chloride and bromide compounds are square pyramidal with an axial aryloxide, the tris(iodide) compound was determined to adopt a trigonal bipyramidal geometry in the solid state with trans, axial aryloxides. The reaction of the tantalum tris(chlorides) [Ta(OC6H3Ph2-2,6)(2)Cl-3] or [Ta(OC6HPh4-2,3,5,6)(2)Cl-3] with RMgCl (R = CH2Ph or CH2SiMe3) forms the corresponding mono-, bis- and tris-(alkyls), all shown to adopt a trigonal bipyramidal geometry in the solidstate with trans, axial aryloxides. In contrast the mono(cycloalkyl) compounds [Ta(OC6H3Ph2-2,6)(2)(CnH2n+1)Cl] (n = 5, 6) were found to adopt square pyramidal structures in the solid state with the alkyl group axial (metal pseudo-equatorial) and mutually cis aryloxides. The alkylation of the corresponding niobium substrate [Nb(OC6HPh4-2,3,5,6)(2)Cl-3] with Me3SiCH2MgCl produced a complex mixture of products. Careful analysis including the use of Si-29 NMR identified the d(0)-alkyl products [Nb(OC6HPh4-2,3,5,6)(2)Cl-2(CH2SiMe3)], [Nb(OC6HPh4-2,3,5,6)(2)Cl(CH2SiMe3)(2)] and [Nb(OC6HPh4-2,3,5,6)(2)(CH2SiMe3)(3)],the alkylidene compounds [Nb(OC6HPh4-2,3,5,6)(2)Cl(=CHSiMe3)] and [Nb(OC6HPh4-2,3,5,6)(2)(CH2SiMe3)(=CHSiMe3)] and the d(1)-alkyl [Nb(OC6HPh4-2,3,5,6)(2)(CH2SiMe3)(2)]. Treating a benzene solution of [Nb(OC6HPh4-2,3,5,6)(2)(CH2SiMe3)(2)]/[Nb(OC6HPh4-2,3,5,6)(2)(CH2SiMe3)(=CHSiMe3)] and PMe3 at 85 degreesC under 1200 psi of H-2 produced deep-green crystals of the d(1)-di(hydride) [Nb(OC6HCy2-2,6-Ph-2-3,5)(2)(H)(2)(PMe3)(2)].