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

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(mu-Cl)(2)(dmpe)(2) (4a). Its analogue, Ti2Cl4(mu-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), (5). The cluster molecule consists of an equilateral triangle of Ti-II atoms with three coplanar mu-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) Angstrom. 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. (C) 1999 Published by Elsevier Science S.A. All rights reserved.