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

Abstract

The reaction of dimethyltitanocene (Cp2TiMe2) with PhSiH3 in hexane in the presence of Cy2PH (Cy = cyclohexyl) is photoinitiated to give paramagnetic Cp2Ti(SiH2Ph)(PHCy2), characterized in solution by EPR spectroscopy (a(H) of phosphine = 4.8 G, a(P) = 26.9 G, giso = 1.9950). Under the same conditions, a similar reaction with Ph2SiH2 gives a crystalline solid, shown by an X-ray structure determination to be [(Cp2Ti)2(μ-H)(μ-PCy2)] (1). Under continuous photolysis Cp2TiMe2 reacts with CyPH2, in the presence of either PhSiH3 or Ph2SiH2, to give crystals of [Cp2Ti(μ-PHCy)]2 (2). rac-[(EBTHI)Ti(μ-H)]2 (EBTHI = ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl)) reacts with PhPH2 to give crystals of the complex (EBTHI)Ti(P2Ph2) (4). In this reaction, excess PhPH2 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 Cp2TiII, conproportionation of Cp2TiII and Cp2TiIV to Cp2TiIII, and σ-bond metathesis reactions of P−H, Ti−H, and Ti−P compounds.