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

Abstract

Catalysts prepared in situ from 1,2-(But2PCH2)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-(MeBut2PCH2)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.