Synthesis and reactivity of rhodium(i) complexes containing keto-functionalised N-pyrrolyl phosphine ligands

Abstract

The reaction of [Rh(μ-Cl)(CO)₂]₂ with two equivalents of L [L = PR₂{NC₄H₃C(O)Me-2}; R = Ph, L¹; R = NC₄H₄, L²] gave the P,O-chelate complexes [RhCl(CO)(L-κ²P,O)] (1, L = L¹; 2, L = L²), whereas reaction with four equivalents of L gave [RhCl(CO)(L)₂] (3, L = L¹; 4, L = L²). Complexes 3 and 4 are fluxional in solution, and at low temperatures exist predominantly with one of the two keto groups coordinated. Complexes 3 and 4 undergo metal-promoted hydrolysis reactions with adventitious water leading to the diphosphoxane-bridged dimers [RhCl(CO)(μ-PR₂OPR₂)]₂ (5, R = Ph; 6, R = NC₄H₄), with the carbonyl and chloride ligands both terminal and semi-bridging in 5 but solely terminal in 6. Complexes 3 and 4 react with NH₄PF₆ or TlPF₆ to give cis-[Rh(L-κ²P,O)₂]PF₆ (7b, L = L¹; 8, L = L²). These complexes are also formed from the reaction of L with [Rh(μ-Cl)(cod)]₂ in the presence of NH₄PF₆. Complex 8 reacts with CO to give [Rh(CO)(L²)₂]PF₆9, with PMe₃ to give [Rh(PMe₃)₂(L²-κ²P,O)]PF₆10, and with [NEt₃Bz]Cl (Bz = CH₂Ph) to give [RhCl(L²-κ¹P)(L²-κ²P,O)] 11. Complexes 2, 5·CH₂Cl₂, 6·C₇H₈, 7b, 8 and 11 have been crystallographically characterised. The electron-withdrawing character of L¹ and L² has led to differences in reactivity from the β-ketophosphine PPh₂CH₂C(O)Ph and the ether-phosphine PPh₂CH₂CH₂OMe.