Small ring metallocycles : V. Crystal and molecular structure of hydrido-1,3-(1,1,3,3-tetramethyldisiloxanediyl)carbonylbis(triphenylphosphine)iridium(III), Me2SiOSiMe2Ir(H)(CO)(PPh3)2 [middle dot] EtOH

Abstract

The structure of the cyclo-metalladisiloxane, Me2SiOSiMe2Ir(H)(CO)(PPh3)2, has been determined by single crystal X-ray diffraction using Mo-K[alpha] radiation. Data were collected to 20 = 45 [deg] giving 6060 unique reflections,of which 4582 had I [ges]3[sigma](I). The latter were used in the full-matrix refinement. Crystallographic data: space group, P; cell constants: 12.604(7),12.470(4), 15.821(6) A, 66.93(6)[deg], 105.34(7)[deg], 112.41(8)[deg];V 2095(3) A3; p(obs) 1.45 g/cm3; p(calc) 1.46g/cm3 (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, R1 0.034 and R2 0.042. The iridium metallocycle has approximate Cs 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 A, 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, P2Si2 plane toward the carbonyl by about 0.26 A. 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[deg] range. It is proposed that the strain in the ring is consistent with the catalytic activity of the metallocycle.