Reactions of the η6-benzene(η5-ethyltetramethylcyclopentadienyl)-rhodium(III) cation and related species with nucleophiles; the crystal structure of [Rh(η5-C5Me4Et){η5-C6H6P(O)(OMe)2}][PF6]

Abstract

The salt [Rh(η⁵-C₅Me₄Et)(η⁶-C₆H₆)][PF₆]₂(1a) reacts with Li[AIH(OBu^t)₃] to give [Rh(η⁵-C₅Me₄Et)(η⁵-C₆H₇)][PF₆] which slowly loses hydride to regenerate the benzene complex; both hydride addition and hydride loss occur stereospecifically at the exo position. With TI[acac](acac = pentane-2,4-dionate) and phosphites P(OR)₃(R = Me or Et, not Ph), (1a) gives the substituted-hexadienyl compounds [Rh(C₅Me₄Et)(η⁵-C₆H₆X)][PF₆][X = CH(COMe)₂ or P(O)(OR)₂]; in both cases displacement of the co-ordinated benzene ligand is a competing reaction. An X-ray analysis of the dimethoxyphosphoryl derivative [X = P(O)(OMe)₂] has been carried out: the crystal is orthorhombic with a= 16.353, b= 21.847, c= 13.258 Å, Z= 8, and space group Pbca; the structure has been solved by the heavy-atom method from 903 observed reflections and refined to R 0.069 7. The cyclohexadienyl ring carries the phosphoryl group in an exo conformation. Phosphines (PBuⁿ₃ or PMe₂Ph, not PPh₃ or PPhH₂) and triethylamine react reversibly with [Rh (C₅Me₄Et)(C₆H₆)][BF₄]₂ to give the salts [Rh(C₅Me₄Et)(η⁵-C₆H₆L)][BF₄]₂(stability: L = PBu₃ > PMe₂Ph NEt₃). In contrast, pyridine attacked the metal atom of (1a) to give [Rh(C₅Me₄Et)(NC₅H₅)₃[PF₆]₂. The corresponding benzene compounds [M(η⁵-C₅Me₅)(η⁶-C₆H₆)] Y₂ react with tributylphosphine and methoxide ion to give [M(η⁵-C₅Me₅)(η⁵-C₆H₆L)]Y_n(M = Co, L = PBu₃, Y_n=[BF₄]₂; M = Ir, L = OMe, Y_n= PF₆). Infrared and ¹H, ¹³C, and ³¹P n.m.r. spectra are reported.