Permethyltitanocene Derivatives with Naked Chalcogen Ligands: Synthesis of [(Cp*2Ti)2(μ‐E)] and [Cp*2Ti(μ2‐E2)] and the Role of the Terminal Chalcogenides [Cp*2Ti(E)] in Their Interconversion (E = Se, Te)

Abstract

AbstractPermethyltitanocene hydride, [Cp*2TiH], reacts with elemental selenium or tellurium to give the products [(Cp*2Ti)2(μ‐E)] (E = Se, 1a Te, 1b), [Cp*2Ti(μ2‐E2)] (E = Se, 2a; Te, 2b) and [Cp*2Ti(μ2‐Se3)] (3), depending on the equivalency of the chalcogen employed. Dinuclear compounds 1 are paramagnetic and have D2d (idealized) structures, as shown by X‐ray structural analysis of μ‐telluride 1b; they may be converted to diamagnetic dichalcogenides 2 through further reaction with the appropriate chalcogen. Derivatives 2 are monomeric in the solid state, as shown by X‐ray structural analysis of ditelluride 2b, and in solution, as demonstrated by multinuclear NMR spectroscopy. Combination of diselenide 2a and ditelluride 2b results in partial redistribution to the mixed species [Cp*2Ti(μ2‐SeTe)], suggesting dimeric structures of formula [Cp*2Ti(μ‐E‐E)2 TiCp*2] may be accessible in solution. The dichalcogenides and the triselenide may be converted back to complexes 1 by treatment with a chalcogen‐abstracting agent. The possible involvement of monomeric terminal chalcogenides [Cp*2Ti(E)] in the interconversion of 1 and 2 was probed experimentally and computationally by means of Density Functional Theory calculations on [Cp2M(E)] (M = Ti, E = O, S, Se, Te; M = Zr, E = O, Te). Several unsuccessful attempts to generate and trap [Cp*2Ti(Te)] are described. The results of these studies suggest that [Cp*2Ti(Te)] has a very weak Ti–Te bond and a readily accessible triplet excited state. These factors, along with the small size of titanium, render this member of the [Cp*2M(E)] family of complexes difficult to trap with Lewis bases, in contrast to many other congeners in the series of Group 4 terminal chalcogenides.