The reaction of [Cp*CoClIz, Cp* = q5-C5Me5, with BHyTHF leads to the formation of nzdol-(q5-C5Me5)Co-2-( 4-C5Me5H)CoB3Hg, 1 (60%, monoclinic P21/n, a = 8.076(1), b = 20.359-(2), c = 13.880(2) 1, p = 91.23(1)", V = 2281.7(6) Hi3, d(ca1cd) = 1.251g/cm3, 2 = 4), and 5-C5Me5)CoB4Hl~, 2 (2-lo%, monoclinic P21/c, a = 13.954 (3), b = 14.185(4), c = arachno-(9, 29.383(7) , /? = 100.61(2)", V = 5717(2) A3, d(calcd) = 1.150 g/cm3, 2 = 16) via the metastable paramagnetic intermediate [{(q5-C5Me5)Co}(BH3Cl)l~, 9, with the coproduct BHzC1. Heating 1 leads to nido-2,4-{(q5-C5Me5)Co}2B3H7, 3 (80%, tetragonal P42/n, a = b = 23.440(4), c = 8.317(2) A, V = 4570(1) A3, d(ca1cd) = 1.244 g ~m -~, 2 = 8). The reaction of [Cp*CoClIz with LiBH4 leads to the formation of cZoso-2,3,4-{ (q5-C5Me5)Co}3B2H4, 4 (20%, rhombohedral, R3, a = 17.994 (1) A, c = 15.986 (1) A, V = 4477.3 A3, d(ca1cd) = 1.347 g ~m -~, 2 = 6) and lesser amounts of doso-1 2,3-{(q5-C5Me5)Co 3B3H5, 6 (triclinic, Pi, a = 8.461 (2) A, b = 10.718 (2) { (q5-C5Me5)Co}4B2H4, 6, via the sequential formation of the metastable intermediates [{(q5-C5Me5)Co}(BH4>In, 7 (paramagnetic), and { (q5-Cae5)Co}2B~H6, 8 (diamagnetic). These results demonstrate that a labile metal precursor permits control of the number of metal atoms in the metallaborane and the characterization of unusual and metastable cobaltaboranes. A kinetic study of the conversion of 1 to 3, which involves the intramolecular dehydrogenation of a q4-C5Me5H ligand and skeletal rearrangement, is reported and the mechanistic implications for the origin of 1 are discussed.A, c = 17.591 (4) A, V = 1511.0 (8) A 3, d(ca1cd) = 1.363 g ~m -~, 2 = 2), and closo-1,2,3,6-
