SYNTHESIS AND CHARACTERIZATION OF PSEUDOCLOSO IRIDIUM AND RUTHENIUM DIPHENYL CARBABORANES - MOLECULAR-STRUCTURES OF 1,2-PH(2)-3-(ETA-C6H6)-3,1,2-PSEUDOCLOSO-RUC2B9H9 AND 1,2-PH(2)-3-(CYM)-3,1,2-PSEUDOCLOSO-RUC2B9H9 (CYM EQUALS P-CYMENE) AND INDIVIDUAL GAUGE FOR LOCALIZED ORBITALS CALCULATIONS ON CARBAMETALLABORANES

The syntheses and characterisations of Ph(2)-3-(eta-C(5)Me(5))-3,1,2-p seudocloso-IrC2B9H9 1, 1,2-Ph(2)-3-(eta-C6H6)-3,1,2-pseudocloso-RuC2B9 H9 2, 1,2,-Ph(2)-3-(cym)-3,1,2-pseudocloso-RuC2B9H9 (cym = p-cymene) 3 and Ph(2)-3-(eta-C(6)Me(6))-3,1,2-pseudocloso-RuC2B9H9 4 are reported from the reactions between Tl-2[7,8-Ph(2)-nido-7,8-C2B9H9] and either [{IrCl2(C(5)Me(5))}(2)] or the appropiate [{RuCl2(arene)}(2)] species . By B-11 NMR spectroscopy all these compounds have pseudocloso geomet ries, in which the C(1)... C(2) connectivity is broken and an approxim ately square M(3)C(1)B(6)C(2) face is generated. Crystallographic stud ies on 2 and 3 confirm this suggestion. It is suggested that distortio n in these species arises from steric crowding between the C-phenyl su bstituents, forced to adopt conformations with high theta values by th e presence of the eta-bonded substituent at M(3). Individual gauge for localised orbitals calculations, reported for the first time on trans ition-metal heteroboranes, reasonably reproduce the (previously assign ed) B-11 NMR chemical shifts of 3-(eta-C(5)Me(5))-3,1,2-closo-RhC2B9H1 1, and allow a tentative assignment of those of h(2)-3-(eta-C(5)Me(5)) -3,1,2-pseudocloso-RhC2B9H9.