Synthesis and Crystal Structure of Some Novel Titanocene Phosphido Compounds by P−H Activation in the Presence of Hydrosilanes

The reaction of dimethyltitanocene (Cp 2 TiMe 2 ) with PhSiH 3 in hexane in the presence of Cy 2 PH (Cy = cyclohexyl) is photoinitiated to give paramagnetic Cp 2 Ti(SiH 2 Ph)(PHCy 2 ), characterized in solution by EPR spectroscopy ( a (H) of phosphine = 4.8 G, a (P) = 26.9 G, g iso = 1.9950). Under the same conditions, a similar reaction with Ph 2 SiH 2 gives a crystalline solid, shown by an X-ray structure determination to be [(Cp 2 Ti) 2 (μ-H)(μ-PCy 2 )] ( 1 ). Under continuous photolysis Cp 2 TiMe 2 reacts with CyPH 2, in the presence of either PhSiH 3 or Ph 2 SiH 2, to give crystals of [Cp 2 Ti(μ-PHCy)] 2 ( 2 ). rac -[(EBTHI)Ti(μ-H)] 2 (EBTHI = ethylene-1,2-bis(η 5 -4,5,6,7-tetrahydro-1-indenyl)) reacts with PhPH 2 to give crystals of the complex (EBTHI)Ti(P 2 Ph 2 ) ( 4 ). In this reaction, excess PhPH 2 is polymerized by dehydrocoupling to a mixture of linear and cyclic oligophosphanes. The diphosphane is produced as an equal mixture of the two diastereoisomers. Due to precipitation of the highly insoluble 4, the catalytic reaction eventually ceases. The mechanisms of these reactions are discussed in terms of the oxidative addition of phosphines to Cp 2 Ti II, conproportionation of Cp 2 Ti II and Cp 2 Ti IV to Cp 2 Ti III, and σ-bond metathesis reactions of P−H, Ti−H, and Ti−P compounds.