PLANAR TRICOORDINATE OXYGENS IN A MIXED AQUA(TETRAHYDROFURAN)IRIDIUM COMPLEX - X-RAY CRYSTAL AND MOLECULAR-STRUCTURE OF [IRH2(THF)(H2O)(PPH3)2]SBF6.THF

The hydrogenation of [(cod)Ir(PPh3)2]SbF6 in tetrahydrofuran (THF) gives [IrH2(THF)2(PPh3)2]SbF6 (1). [IrH2-(THF)(H2O)(PPh3)2]SbF6 (2) is formed on recrystallization of 1 from moist THF/hexane. The crystal structure of 2 THF has been determined by a single-crystal X-ray diffraction study. This is one of the rare crystallographically characterized examples of THF and of water binding to a late d-block transition metal. 2 THF crystallizes in the space group P21/n with a = 10.745 (4) Å, b = 18.793 (8) Å, c = 22.425 (8) Å, β = 96.42 (3)°, V = 4500 (6) Å3, Ζ = 4, and ρcaled = 1.64 g/cm3. The structure was refined by full-matrix least-squares techniques to a final R factor of 0.039 for 3666 reflections. One THF and one H2O molecule occupy two eis sites of the octahedron around the iridium(III) center. The phosphines are trans with Ir-P(av) of 2.298 (3) Å. The Ir-O bond distances are 2.305 (9) and 2.258 (9) Å, significantly longer than are expected in the absence of the trans influence of the hydride ligands. The coordinated THF ligand is reasonably well-defined and adopts an envelope conformation with C(3) on the flap atom; the tricoordinate oxygen atom is in a planar configuration, in contrast to the commonly observed pyramidal configuration. The aqua ligand is hydrogen-bonded to an F atom of the SbF6 counterion and to the oxygen of the lattice THF. The approximate positions of the H atoms constituting the Η-bonds were deduced from the heavy-atom positions by using the Ferraris-Franchini-Angela correlations. These are consistent with the H2O ligand also having a planar rather than a pyramidal oxygen. Arguments about π-bonding and 2-e vs 4-e donor character for ligands of the R2O type should therefore not be simply based on the distinction between planar and pyramidal geometries. © 1990, American Chemical Society. All rights reserved.