Rhodium(I) carbonyl complexes of chalcogen functionalized tripodal phosphines, [CH 3C(CH 2P(X)Ph 2) 3] {X = O, S, Se} and their reactivity

Abstract

The reaction of dimeric rhodium precursor [Rh(CO) 2Cl] 2 with two molar equivalent of 1,1,1-tris(diphenylphosphinomethyl)ethane trichalcogenide ligands, [CH 3C(CH 2P(X)Ph 2) 3](L), where X = O( a), S( b) and Se( c) affords the complexes of the type [Rh(CO) 2Cl(L)] ( 1a–1c). The complexes 1a–1c have been characterized by elemental analyses, mass spectrometry, IR and NMR ( 1H, 31P and 13C) spectroscopy and the ligands a–c are structurally determined by single crystal X-ray diffraction. 1a–1c undergo oxidative addition (OA) reactions with different electrophiles such as CH 3I, C 2H 5I and C 6H 5CH 2Cl to give Rh(III) complexes of the types [Rh(CO)(COR)ClXL] {R = –CH 3 ( 2a–2c), –C 2H 5 ( 3a–3c); X = I and R = –CH 2C 6H 5 ( 4a–4c); X = Cl}. Kinetic data for the reaction of a–c with CH 3I indicate a first-order reaction. The catalytic activity of 1a–1c for the carbonylation of methanol to acetic acid and its ester is evaluated and a higher turn over number (TON = 1564–1723) is obtained compared to that of the well-known commercial species [Rh(CO) 2I 2] − (TON = 1000) under the reaction conditions: temperature 130 ± 2 °C, pressure 30 ± 2 bar and time 1 h.