Small ring metallocycles : V. Crystal and molecular structure of hydrido-1,3-(1,1,3,3-tetramethyldisiloxanediyl)carbonylbis(triphenylphosphine)iridium(III), Me 2SiOSiMe 2Ir(H)(CO)(PPh 3) 2 · EtOH

Abstract

The structure of the cyclo-metalladisiloxane, Me 2SiOSiMe 2Ir(H)(CO)(PPh 3) 2, has been determined by single crystal X-ray diffraction using Mo- K α radiation. Data were collected to 20 = 45 ° giving 6060 unique reflections,of which 4582 had I ⩾3σ( I). The latter were used in the full-matrix refinement. Crystallographic data: space group, P 1 ; cell constants: 12.604(7),12.470(4), 15.821(6) Å, 66.93(6)°, 105.34(7)°, 112.41(8)°; V 2095(3) Å 3; p(obs) 1.45 g/cm 3; p(calc) 1.46g/cm 3 (Z=2). The asymmetric unit consists of one iridium complex and one molecule of ethanol of salvation. The structure was solved by standard heavy atom methods and refined with all non-hydrogen atoms anisotrophic to final R factors, R 1 0.034 and R 2 0.042. The iridium metallocycle has approximate C s symmetry with the mirror plane passing through the four-membered IrSiOSi ring. The average IrP, IrSi and SiO bond lengths are 2.38, 2.41, and 1.68 Å, respectively. The IrCO and CO bond lengths are 1.903(8) and 1.133(8). The H atom bonded to Ir was not located.The Ir atom is raised out of the basal, P 2Si 2 plane toward the carbonyl by about 0.26 Å. The most striking feature of the structure is the strain apparent in the four-membered ring. The internal angels are: 64.7 (SiIrSi), 96.8 (IrSiO), 97.8 (IrSiO), and 99.8 (SiOSi). In an unstrained molecule, the SiOSi angle is normally in the 130–150° range. It is proposed that the strain in the ring is consistent with the catalytic activity of the metallocycle.