Synthesis of η4-1,3-diphosphacyclobutadiene(η5-1,2-dicarbaborane)rhodium complexes; crystal structures of the compounds [NEt4][Rh(η4-But2C2P2)(η5-C2B9H11)], [Rh{η4-But2C2P2Au(PPh3)}(η5-C2B9H11)], and [Rh{η4-But2C2P2Co-(CO)2(η4-C4Me4)}(η5-C2B9H11)]

Abstract

Treatment of a thf (tetrahydrofuran) solution of K[Rh(PPh₃)₂(η⁵-C₂B₉H₁₁)] with Bu^tCP, followed by addition of NEt₄Cl, affords the salt [NEt₄][Rh(η⁴-Bu^t₂C₂P₂)(η⁵-C₂B₉H₁₁)](3), the structure of which has been established by X-ray diffraction. Compound (3) reacts with [AuCl(PPh₃)] and with [Co(CO)₂(NCMe)(η⁴-C₄Me₄)][PF₆] to afford, respectively, the complexes [Rh{η⁴-Bu^t₂C₂P₂Au-(PPh₃)}(η⁵-C₂B₉H₁₁)](4) and [Rh{η⁴-Bu^t₂C₂P₂Co(CO)₂(η⁴-C₄Me₄)}(η⁵-C₂B₉H₁₁)](5). The structures of the products (4) and (5) have also been determined by X-ray diffraction. In all three compounds the rhodium is η⁵ ligated by a nido-icosahedral C₂B₉H₁₁ fragment, and by a 1,3-diphosphacyclobutadiene group. Within the latter the P–C distances are equal, and the four-membered CPCP rings are close to planar. In the compounds (4) and (5) a phosphorus atom in the η⁴-Bu^t₂CP₂ group co-ordinates to the Au(PPh₃) and the Co(CO)₂(η⁴-C₄Me₄) groups, respectively. The n.m.r. data (¹H, ¹³C-{¹H}, ¹¹B-{¹H}, and ³¹P-{¹H}) are reported, and where appropriate discussed.