BORON-NITROGEN COUPLING IN A RUTHENIUM-RICH RUTHENABORANE CLUSTER - SYNTHESIS, AND MOLECULAR AND ELECTRONIC-STRUCTURES OF [RU4H(CO)12BH(MU-NCHME)]

The photolysis of [Ru3(CO)9BH5] in acetonitrile in the presence of [M( CO)6] (M = Cr, Mo or W), with or without Me3NO, leads to the formation of [Ru4H(CO)12BH(mu-NCHMe)] 1 which is a butterfly cluster containing a semi-interstitial boron atom. The crystal structure of 1 has been d etermined: monoclinic, space group C2/c, a = 37.642(8), b = 9.340(2), c = 13.923(3) angstrom, beta = 111.19(2)-degrees, Z = 8, R = 0.0278, R ' = 0.0390. The formation of 1 represents an example of coupling betwe en a nitrogen atom and a boron atom in a metal-rich metallaborane clus ter, and is of interest because of the cluster expansion which accompa nies the B-N bond formation. The bonding in compound 1 has been invest igated by use of the Fenske-Hall approach. These quantum chemical resu lts are consistent with a picture of localized bonding in the region o f the B-N-Ru bridge, a conclusion that is also reached by a considerat ion of the requirements of the cluster valence electron count of 62.