The structure of chlorocarbonyl(sulfur dioxide)bis(triphenylphosphine)rhodium, RhCl(CO)(SO₂)(P(C₆H₅)₃)₂

The structure of chlorocarbonyl (sulfur dioxide )bis(triphenylphosphine)rhodium, RhCl(CO)(SO₂)(P(C₆H₅)₃)₂, has been determined by single-crystal X-ray analysis. The compound crystallizes in the space group C_2h5-P2¹/c of the monoclinic system, with four monomeric molecules in a cell of dimensions a = 12.192 (3) Å, b = 17.020 (4) Å, c = 16.724 (5) Å, and β = 104.03 (2)°. The structure has been refined by least-squares methods to a conventional R factor of 5.0%, over 3716 counter-diffractometer data. The compound is isostructural with the analogous iridium compound. The coordination around the rhodium atom is that of a tetragonal pyramid, with CO, Cl, and trans P atoms in the basal plane and the S of the SO₂ group at the apex. The basal interatomic distances are normal. The Rh-S distance of 2.450 (2) Å is long. The bond angles about S are all within 5° of the tetrahedral angle, and the Rh-S vector makes an angle of 30.3 (3)° with the normal to the SO₂ plane. These results may be rationalized in terms of the formation of a Rh-S bond through the donation of a pair of electrons from the Rh to the weak Lewis acid SO₂. The bonding of SO₂ to the metal here is contrasted with that in [RuC1(NH₃)₄(SO₂)] Cl, where the Ru-S bond is much shorter and the Ru lies in the SO₂ plane.