The Chemistry of Monoanionic Carbaborane Ligands . Synthesis and Structure of Compounds with Carbonyl and Cycloocta - I , 5 - diene Ligands Additionally bound to Metal

Reaction of [ (ML,CI),] with TI[9-SMe,-nido-7,8-C,B,H,,1 affords the new compounds [3,3-L2-4-SMe,closo-3.1 ,2-MC,B,Hl,]. Compounds 1 ( M = Rh, L = CO), 2 ( M = Rh, L2 = I12,T12-1,5-C8H12) and 3 (M = Pd, L, = qz,o-5-OMe-C8H,,) were characterised by microanalysis, multinuclear N M R spectroscopy and, in the case of 1 and 2, single-crystal X-ray diffraction studies. The experimentally determined conformations of the ML, fragments relative to the carbaborane ligands in 1 and 2 are in broad agreement with those predicted by analysis of the results of extended Huckel molecular orbital (EHMO) calculations on model compounds, especially in the case of 2. Reaction of 3 with HBF, in diethyl ether affords the cationic heteroborane [3(q2,qz-1 ,5-C,Hl,) -4-SMe2-c/oso-3,1 ,2-PdC,B,Hl,] + 4'. Crystallographic study of 4+BF,reveals a molecular conformation substantially influenced by H F inter-ion contacts. Comparative EHMO calculations on 2 and 4' imply that the majority of the additional positive charge in t he latter is not localised on the pendant sulfur atom alone, but rather is delocalised over the 12 cluster vertices and the atoms directly bonded to them.