Rhodium catalysed methanol carbonylation in the presence of bis(ditertiarybutylphosphinomethyl)benzene

Abstract

Catalysts prepared in situ from 1,2-(Bu^t₂PCH₂)₂C₆H₄ (DTBPMB) and [RhCl(CO)₂]₂ catalyse the carbonylation of methanol in the presence of MeI at rates (4.12 and 8.90 × 10⁻⁴ mol dm⁻³ s⁻¹ at 150 and 180 °C respectively) faster than those in the absence of added phosphine, although they decompose to [RhI₂(CO)₂]⁻ over time. HPIR studies suggest that MeI adds to [Rh(DTBPMB)X(CO)] (X = Cl or I), which have been isolated and fully characterised, to give [Rh(DTBPMB)MeI₂(CO)]. [Rh(DTBPMB)MeI₂(CO)] reacts with CO to give [Rh(DTBPMB)(C(O)Me)I₂(CO)], but that methanol promotes decomposition to [RhI₂(CO)₂]⁻ and [1,2-(MeBu^t₂PCH₂)₂C₆H₄)][I₃]₂, which has been isolated and characterised. HPNMR studies show that [Rh(DTBPMB)Cl(CO)] reacts with CO to give [Rh(DTBPMB)Cl(CO)₂], which is square pyramidal with an apical Cl.