The structure of hydridocarbonyl(fumaronitrile)bis(triphenylphosphine)iridium, an olefin-metal hydride complex

Abstract

The structure of the complex hydridocarbonyl(fumaronitrile)bis(triphenylphosphine)iridium, IrH(CO)( trans-NCCHCHCN)[P(C 6H 5) 3] 2, has been determined from a single crystal X-ray analysis. The complex crystallizes in a monoclinic cell of dimensions a = 21.289(14), b = 9.383(3), c = 21.650(10) Å, β= 123.87(2)°. The observed density is 1.53 g·cm −3, whereas the density calculated for four formula units per unit cell is 1.524 g·cm -3. On the basis of a successful structure analysis, the space group is C2/ c. The structure has been refined by least-squares methods to a conventional R-factor of 0.056 for the 2274 independent reflections whose intensities were above background, when measured by counter techniques. The molecules are monomeric; the configuration around the iridium atom is trigonal bipyramidal, with the olefin and phosphine ligands in the equatorial plane, which also contains a twofold axis of crystallographic symmetry. The fumaronitrile ligand is nonplanar, the dihedral angle between the two planes which contain a carbon atom of a cyanide group and both olefinic carbon atoms is 136(2)°. The IrP and IrC distances are respectively 2.317(3) and 2.110(9) Å, while the CC distance is 1.431 (20) Å. Assuming an IrH bonded distance of 1.6 Å, the nonbonded contact between the hydridic hydrogen atom and an olefin carbon atom is 2.6 Å. It is of interest that the hydridic hydrogen atom is cis to the olefin since complexes related to the present one are believed to play a role in the catalyzed hydrogenation reactions of olefins.