Reactions of TiCl4 with phosphines and alkylating reagents: An organometallic route to a titanium(II) cluster compound1

Article abstract of DOI:10.1016/S0022-328X(98)00655-X

Treatment of TiCl₄ with a stoichiometric amount of 1,2-bis(dimethylphosphino)ethane (dmpe) gives TiCl₄(dmpe) (1). This compound can be readily alkylated by 1 or 2 equivalents of PhCH₂MgCl affording TiCl₃(PhCH₂)(dmpe) (2) and TiCl₂(PhCH₂)₂(dmpe) (3), respectively. Syntheses and crystal structures of the three mononuclear titanium(IV) compounds 1-3 are presented. Decomposition of 'TiCl₃(Bu^t)(dmpe)' produces the dinuclear titanium(III) edge-sharing complex, Ti₂Cl₄(μ-Cl)₂(dmpe)₂ (4a). Its analogue, Ti₂Cl₄(μ-Cl)₂(depe)₂ (4b) has been obtained by direct reaction of TiCl₃(THF)₃ with the corresponding phosphine. Thermal decomposition of 'TiCl₂(Bu^t)₂(dmpe)' provides the first true, molecular metal atom cluster of titanium(II), Ti₃Cl₆(dmpe)₃ (5). The cluster molecule consists of an equilateral triangle of Ti^II atoms with three coplanar μ-Cl atoms bridging the edges. Each titanium atom is further coordinated by a chelating dmpe molecule and a chloride ion, with Ti-Ti distances of 2.872(3) A. The compound appears to be slightly paramagnetic but this is probably the result of a small amount of decomposition due to the difficulty of handling this pyrophoric complex. It is proposed that there are genuine Ti-Ti single bonds, and that this is a true metal atom cluster compound.