Rhodium(I) carbonyl complexes of chalcogen functionalized tripodal phosphines, [CH3C(CH2P(X)Ph-2)(3)] {X = O, S, Se} and their reactivity

The reaction of dimeric rhodium precursor [Rh(CO)(2)Cl](2) with two molar equivalent of 1,1,1-tris(diphenylphosphinomethyl)ethane trichalcogenide ligands, [CH3C(CH2P(X)Ph-2)(3)](L), where X = O(a), S(b) and Se(c) affords the complexes of the type [Rh(CO)(2)Cl(L)] (1a-1c). The complexes 1a-1c have been characterized by elemental analyses, mass spectrometry. IR and NMR (H-1, P-13 and C-13) 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 CH3I, C2H5I and C6H5CH2Cl to give Rh(III) complexes of the types [Rh(CO)(COR)ClXL] {R = -CH3 (2a-2c), -C2H5 (3a-3c); X = I and R = -CH2C6H5 (4a-4c); X=Cl}. Kinetic data for the reaction of a-c with CH3I 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)(2)I-2](-) (TON = 1000) under the reaction conditions: temperature 130 +/- 2 degrees C, pressure 30 +/- 2 bar and time 1 h. (C) 2009 Elsevier B.V. All rights reserved.