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

Catalysts prepared in situ from 1,2-(Bu-t 2PCH2)(2)C6H4 (DTBPMB) and [RhCl(CO)(2)](2) catalyse the carbonylation of methanol in the presence of MeI at rates (4.12 and 8.90 x 10(-4) mol dm(-3) s(-1) at 150 and 180 degrees 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)I-2(CO)], but that methanol promotes decomposition to [RhI2(CO)(2)](-) and [1,2-(MeBut 2PCH2)(2)C6H4)][I-3](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.