Synthesis and characterization of new RhI complexes bearing CO, PPh3 and chelating P,O- or Se,Se-ligands:: Application to hydroformylation of styrene

The complexes [Rh(CO)(PPh3){Ph2PNP(O)Ph-2-P,O}] (3), [Rh(CO)(2)(Ph2P(Se)NP(Se)Ph-2-Se,Se')] (5), and [Rh(CO)(PPh3){Ph2P (Se)NP(Se)Ph-2-Se,Se')] (6), were synthesised by stepwise reactions of CO and PPh3 with [Rh(cod){Ph2PNP(O)Ph-2-P,O)1 (2) and [Rh(cod)(Ph2P(Se)NP(Se)Ph-2-Se,Se')] (4), respectively. The complexes 3, 5 and 6 have been studied by IR, as well as H-1 and 3 1 P NMR spectroscopy. The v(CO) bands of complexes 3 and 6 appear at approximately 1960 cm(-1), indicating high electron density at the Rh-1 centre. The structure of complexes 3 and 6 has been determined by X-ray crystallography, and the P-31? NMR chemical shifts have been resolved via low temperature NMR experiments. Both complexes exhibit square planar geometry around the metal centre, with the five-membered ring of complex 3 being almost planar, and the six-membered ring of complex 6 adopting a slightly distorted boat conformation. The C-O bond of the carbonyl ligand is relatively weak in both complexes, due to strong R-back donation from the electron rich Rh-1 centre. The catalytic activity of the complexes 2, 3 and 6 in the hydroformylation of styrene has been investigated. Complexes 2 and 3 showed satisfactory catalytic properties, whereas complex 6 had effectively no catalytic activity. (c) 2007 Elsevier B.V. All rights reserved.