Rhodium(I) carbonyl complexes of chalcogen functionalized tripodal phosphines, [CH3C(CH2P(X)Ph2)3] {X = O, S, Se} and their reactivity

The reaction of dimeric rhodium precursor [Rh(CO)2Cl]2 with two molar equivalent of 1,1,1-tris(diphenylphosphinomethyl)ethane trichalcogenide ligands, [CH3C(CH2P(X)Ph2)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 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)2I2]− (TON = 1000) under the reaction conditions: temperature 130 ± 2 °C, pressure 30 ± 2 bar and time 1 h.

Three newly synthesized rhodium(I) carbonyl complexes of 1,1,1-tris(diphenylphosphinomethyl)ethanetrichalcogenide ligands undergo oxidative addition reactions with different electrophiles such as CH3I, C2H5I and C6H5CH2Cl to generate a mixture of isomeric Rh(III) complexes, and exhibit higher catalytic activity (TON = 1564–1723) in carbonylation of methanol compared to well-known Monsanto's species [Rh(CO)2I2]− (TON = 1000).Figure optionsDownload as PowerPoint slide