Crystal structure of (η2-octahydropentaborano)bis(triphenylphosphine)-copper(I)

Abstract

The title compound, [Cu(η²-B₅H₈)(PPh₃)₂], crystallises as colourless needles in the monoclinic space group P2₁/c with a= 14.393(2), b= 12.291(2), c= 20.194(3)Å, β= 105.50(1)° and Z= 4. The structure was solved from diffractometer data on 1 998 independent reflections by use of Patterson and electron-density syntheses. Refinement by block-diagonal least-squares gave a final R of 0.0547. The molecular structure can be described as being derived from that of nido-B₅H₉ by replacing one of the basal bridging hydrogen atoms with a bridging Cu(PPh₃)₂ group such that B(2)–Cu 2.209(13) and B(3)–Cu 2.236(13)Å. The dihedral angle between the planes B(1), B(2), B(3) and Cu,B(2), B(3) is 178.4° the angle P(1)–Cu–P(2) is 123.4(1)°, and the mid-point between B(2) and B(3) is 0.20 Å from the CuP₂ plane. The copper atom is thus approximately trigonal planar and is formally 16-electron species, being bonded to the pentaborane unit only via a three-centre bond between Cu. B(2), and B(3). All the borane hydrogen atoms were located and their positions preclude the possibility of bonding via CU–H–B bonds.