Syntheses, crystal structures and reactivity of organometallic tantalum(IV) phosphinidene complexes:: trans-[{Cp*TaCl(μ-PR)}2] (Cp* = C5Me5, R = Cy, tBu, Ph), cis- and trans-[{Cp*TaCl(μ-PMes)}2] (Mes=2,4,6-Me3C6H2) and cis-[{Cp′TaCl(μ-PMes)}2] (Cp′ = C5H4Me)

The reaction of [Cp.TaCl4] (CP. = C5Me5) with LiPHR (1: 1 or 1:2) gives the phosphinidene-bridged tantalum(IV) complexes trans-[{Cp.TaCl(mu-PR)}(2)] [R = Cy (1), tBu (2), Ph (3), 2,4,6-Me3C6H2 (Mes) (4b)]. When the reaction with LiPHMes is carried out in a 1:1 ratio, cis-[{Cp.TaCl(mu-PMes)}(2)] (4a) is also formed besides 4b. For comparison, cis-[JCp'TaCl(mu-PMes))21 (5) was prepared from [Cp'TaCl4] (CP' = C5MeH4) and LiPHMes (1: 1). 1-5 are diamagnetic and were characterised spectroscopically (IR, MS; H-1, P-31, C-13 NMR). Crystal structure determinations on 1-5 showed the presence of dimeric phosphinidene-bridged Ta-IV complexes. The phosphinidene-bridged complexes 1, 3 and 4b do not react with ace-tone, benzophenone, acetonitrile, CS2 (1, 3), acetaldehyde (4b), or ethylaluminum dichloride (3). 3 reacts with moist acetone in the presence of traces of air to give the trinuclear cluster [{Cp.TaCl(mu(2)-O)}(3)(mu(3)-O)(mu(2)-O2PHPh)] (6) in very low yield. With an excess of CyNC, 3 gives [Cp.TaCl(CNCy)(4)]Cl (7), which was characterised by H-1 and C-13 NMR spectroscopy and by crystal structure determination. As a minor product, [(Cp.TaCl2)(2)(mu(2)-O) (eta(2), mu(2)-P2Cy2)] (8) was also obtained in the reaction of [Cp.TaCl4] with LiPHCy. 6 and 8 were only characterised by crystal structure determination. ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).