COORDINATION OF SULFUR-DIOXIDE TO IRIDIUM(I) CENTERS - SULFUR-DIOXIDE INSERTION INTO A METHOXO-METAL BOND - CRYSTAL AND MOLECULAR-STRUCTURE OF CARBONYL(METHYL SULFITO)(SULFUR DIOXIDE)BIS(TRIPHENYLPHOSPHINE)IRIDIUM-HEMITOLUENE, THE 1ST STRUCTURALLY CHARACTERIZED EXAMPLE OF A TRANSITION-METAL COMPLEX CONTAINING AN O-COORDINATED METHYL SULFITO LIGAND

Reactions of SO2 with iridium(I) complexes have been examined. For trans-Ir(CO)L2X (L = PPh3, P(p-tolyl)3, PCy3; X = Cl, Br, Me), equilibrium constants for SO2 binding have been evaluated. The binding Of SO2 is as a Lewis acid and is enhanced by electron-donating groups on the iridium. Increasing the size of the phosphine reduces the equilibrium constant for SO2 binding. Reactions of SO2 with the hydroxo or alkoxo complexes Ir(CO)(OR)L2 (R = H, Me, t-Bu; L = PPh3, P(p-tolyl)3) result in insertion of the SO2 to form an oxygen-coordinated sulfite ligand. The sulfur center of the sulfite ligand is pyramidal and asymmetric, resulting in a second-order P-31 NMR spectrum at low temperature. A further rearrangement of the oxygen-coordinated sulfite ligand to the sulfur-coordinated occurs in solution. For R = H, further decomposition of the HSO3- ligand occurs. The products of each reaction are characterized by infrared and H-1 and P-31 NMR spectroscopy. The product of SO2 insertion into the iridium-methoxo bond, lr(CO)(OS(O)OMe)(SO2)(PPh3)2, is also characterized by X-ray crystallography. The complex Ir(CO)[OS(O)OMe](SO2)(PPh3)2 crystallizes from toluene as the hemitoluene solvate, Ir(CO)[OS(O)OMe](SO2)(PPh3)2.0.5(toluene), in the centrosymmetric triclinic space group P1BAR (No. 2) with a = 10.972(5) angstrom, b = 11.658(4) angstrom, c = 18.020(11) angstrom, a = 82.73(4)-degrees, beta = 77.76(4)-degrees, gamma = 63.25(3)-degrees, V = 2007.5(17) angstrom3, and Z = 2. The structure was solved and refined to R = 3.05 % and R(w) = 3.58 % for all 5280 reflections with 20 < 45-degrees (Mo Kalpha) and R = 2.31 % and R(w) = 3.23% for those 4502 reflections with \F(o)\ > 6sigma(F(o)). The iridium is in a square-pyramidal coordination environment with the SO2 ligand in the apical site. Iridium-ligand bond lengths are as follows: lr(1)-P(1) = 2.369(2) angstrom and Ir(l)-P(2) = 2.387(2) angstrom for the Ir-PPh3 groups, Ir(l)-S(1) = 2.451(2) angstrom for the SO2 ligand, Ir(1)-C(1) = 1.831(6) angstrom for the CO ligand, and Ir-O(23) = 2.080(4) angstrom for the OS(=O)OMe ligand. The trans-basal angles are P(1)-Ir-(1)-P(2) = 170.3(1)-degrees and C(1)-Ir(1)-O(23) = 176.7(2)-degrees; angles to the apical SO2 ligand are P(1)-Ir(1)-S(1) = 97.5(1)-degrees, P(2)-Ir(1)-S(1) = 92.2(1)-degrees, C(1)-Ir(1)-S(1) = 97.3(2)-degrees, and O(23)-Ir(1)-S(1) = 85.8(1)-degrees.