TITANIUM MAGNESIUM COMPLEXES - INTERMEDIATES IN THE REDUCTION OF TITANOCENE DICHLORIDE BY MAGNESIUM

(Cp2Ti(mu-Cl)2)2Mg(THF)2 (1) and (Cp2Ti(mu-Cl)2Mg(THF)2(mu-Cl)2)2 (2) have been isolated from the reaction of Cp2TiCl2 with Mg in THF and in the presence of P donors. A more convenient synthesis of 1 is derived from the reaction of (Cp2Ti(mu-Cl))2 with anhydrous MgCl2. These species have been structurally characterized. Complex 1 crystallizes in the monoclinic space group P2(1)/c with a = 8.104 (2) angstrom, b = 11.371 (4) angstrom, c = 16.282 (9) angstrom, beta = 91.53 (3)-degrees, Z = 2, and V = 1500 (1) angstrom 3, while compound 2 crystallizes in the tetragonal space group I41/a with a = 24.018 (6) angstrom, c = 14.927 (7) angstrom, Z = 8, and V = 8611 (5) angstrom 3. These species react with PMe3 to yield the Ti(III) species Cp2Ti(PMe3)Cl (3) and MgCl2. The species 3 reacts further with Mg in the presence of PMe3 to give the ''stabilized titanocene'' Cp2Ti(PMe3)2. These observations support the notion that Ti(III)/Mg compounds such as 1 and 2 are intermediates in the reduction of Cp2TiCl2 to Ti(II).