Towards supported catalyst models: the synthesis, characterization, redox chemistry, and structures of the complexes Ti(OAr′)4 (Ar′ = C6H4(2-t-Bu), C6H(2,3,5,6-Me)4)

Abstract

Reaction of substituted phenoxides with TiCl4 affords the species Ti(OAr′)4 (Ar′ = C6H4(2-t-Bu), 1; Ar′ = C6H(2,3,5,6-Me)4, 2). The compound Ti(OC6H4(2-t-Bu))4, 1, crystallizes in the tetragonal space group [Formula: see text], with a = 15.203(4) Å, c = 8.026(3) Å, Z = 2, and V = 1855(2) Å3. The compound Ti(OC6H(2,3,5,6-Me)4)4, 2, crystallizes in the orthorhombic space group Pbcn, with a = 16.539(7) Å, b = 16.136(6) Å, c = 27.716(12) Å, Z = 8, and V = 7397(9) Å3. The geometry of the Ti coordination sphere in these complexes is best described as pseudo-tetrahedral. In the case of 1 strict crystallographic [Formula: see text] symmetry is imposed. The complex 2 exhibits reversible cyclic voltammetric behaviour consistent with a one electron reduction to the Ti(III) analogue. Chemical reduction of 2 employing sodium amalgam affords the quantitative formation of (C6H(2,3,5,6-Me)4O)2Ti(μ-OC6H(2,3,5,6-Me)4)2Na(THF)2, 3. The reaction of 3 with [(COD)Rh(μ-Cl)]2 does not afford the Ti(III)/Rh(I) early–late heterobimetallic (ELHB) complex (C6H(2,3,5,6-Me)4O)2Ti(μ-OC6H(2,3,5,6-Me)4)2Rh(COD). The nature of all products is not known; however, redox chemistry, in which electron transfer from Ti(III) to Rh(I) occurs is evidenced by the generation of 2 and Rh(0). In addition, ligand transfer reactions giving uncharacterized Rh-alkoxides are suggested by the spectral data. The implications and ramifications for the synthesis of alkoxide bridged ELHB models of bimetallic heterogeneous catalyst systems are discussed. Key words: titanium phenoxides, redox chemistry, structures.