Synthesis and structure of niobium and tantalum compounds containing 2,6-diphenyl-3,5-di-tert-butylphenoxide ligation

A series of mononuclear derivatives of niobium(V) and tantalum(V) containin g the new ligand 2,6-diphenyl-3,5-di-tert-butyl-phenoxide (OC6HPh2-2,6-Bu-t (2)-3,5) have been isolated. The addition of the parent phenol (2 equiv. pe r Nh) to a benzene solution of [Nb2Cl10] leads to formation of the trichlor ide [Nb(OC6HPh2-2,6-Bu-t(2)-3,5)(2)Cl-3] (1), while treatment of the tetra- chlorides [Cp*TaCl4] and [CpNbCl4] with [LiOC6HPh2-2,6-Bu-t(2)-3,5] leads t o the mixed cyclopentadienyl, aryloxides [Cp*Ta(OC6HPh2-2,6-Bu-t(2)-3,5)Cl- 3] (2) and [CpNb(OC6HPh2-2,6-Bu-t,-3,5)Cl-3] (3), respectively. Structural studies show a square pyramidal geometry for trichlorides 1-3 with a basal aryloxide in each case. An axial aryloxide, Cp* and Cp ligand are present f or 1, 2 and 3, respectively. The addition of HOC6HPh2-2,6-Bu-t(2)-3,5 to th e precursor [Ta(NMe2)(5)] results in formation of the mono-aryloxide [Ta(OC 6HPh2-2,6-Bu-t(2)-3,5)(NMe2)(4)] (4), which is also square pyramidal with a basal aryloxide ligand. Activation of a solution of 1 in benzene with 3 eq uiv. of (BuLi)-Bu-n, followed by treatment with H-2 (1200 psi, 100 degrees C) results in intramolecular hydrogenation of ortho-phenyl rings. Hydrolysi s of the reaction mixture leads to isolation of 2,6-dicyclohexyl-3,5-di-ter t-butylphenol (5), which has been structurally characterized. (C) 2000 Else vier Science S.A. All rights reserved.