TETRADECKER LM(C3B2)CO(C2B3)COCP SANDWICH COMPLEXES [LM = CP-STAR-CO, CP-STAR-RH, OR (CYMENE)RU] - DESIGNED SYNTHESIS AND ELECTRONIC-PROPERTIES

A family of novel tetradecker transition-metal sandwich complexes, each incorporating four different ring ligands, was prepared via the addition of metal-ligand units to the open face of the (Et2C2B3H4)Co(Et2MeC3B2Et2)CoCp- anion. The "hybrid" complexes (containing both carborane and dihydrodiborole bridging rings) (C5Me5)Co(Et2C2B3H2R)Co(Et2MeC3B2Et2) CoCp (2a, R = H; 2b, R = Cl), (C5Me5)Rh(Et2C2B3H2R)Co(Et2MeC3B2Et2)cocp (3a, R = H; 3b, R = Cl), and (MeC6H4CHMe2)Ru-(ET2C2B3H3)Co(Et2MeC3B2Et2)CoCp (4) were isolated as air-stable solids and characterized from their B-11 and H-1 FT NMR, IR, and mass spectra and cyclic voltammetry measurements. The tetradecker geometry postulated from NMR data was confirmed by an X-ray crystallographic analysis of the Rh-Co-Co complex 3a, which showed the four rings to be not quite parallel with a 10.6-degrees tilt between the end rings and no significant slip-distortions in the stack. Each of the 42-electron neutral complexes exhibits a reversible oxidation and two reversible reductions, affording the respective monocation, monoanion, and dianion, respectively. crystal data for 3a: mol wt 727.6; space group P2(1)/c; Z = 4; a = 11.831 (6), b = 17.967 (8), c = 17.352 (8) angstrom; beta = 107.22 (4)degrees; V = 3523 (9) angstrom-3; R = 0.042 for 4294 reflections having F(o)2 > 2.0-sigma(F(o)2).