TRIPLE-DECKER SANDWICH COMPLEXES OF COBALT, RHODIUM, AND RUTHENIUM BRIDGED BY C2B3 OR C3B2 RINGS - SYNTHESIS, STRUCTURE, AND ELECTROCHEMISTRY

The planned syntheses, structural characterization, and electrochemistry of new homo- and heterobimetallic triple-decker species bridged by C2B3 or C3B2 rings are described. Reactions of the carborane monoanions nido-R2C2B4H5- (1a-, 1b-) and the diborolyl monoanion CpCo(Et2MeC3B2Et2)- (2-) in cold THF produced the dicobalt diamagnetic 30-electron "hybrid" sandwiches (R2C2B4H4)Co(Et2MeC3B2Et2)CoCp (3a, R = Et; 3b, R = CH2Ph) as green crystalline solids. Decapitation (apex BH removal) of these complexes in TMEDA afforded yellow (R2C2B3H5)Co(Et2MeC3B2Et2) CoCp (4a, R = Et; 4b, R = CH2Ph). The reaction of the corresponding carborane dianion 1a2- with 2- and Rh3+ gave brown (Et2C2B4H4)Rh(Et2MeC3B2Et2)CoCp (5). The cobaltacarborane dianion (C5Me5)Co(Et2C2B3H3)2- (6(2-)) and ](C5Me5)RhCl2[2 reacted in THF to form the green triple-decker complexes (C5Me5)Co(2,3-Et2C2B3H2-4-R)Rh(C5Me5) (7a, R = H; 7b, Rr = Cl). In an alternative route to rhodium triple-deckers, the dianion 1a2- reacted with [(C5Me5)RhCl2]2 to generate the brown rhodacarborane (C5Me5)Rh(Et2C2B4H4) (8), which in turn was decapitated to give a nido-rhodacarborane complex (C5Me5)Rh(Et2C2B3H5) (9), isolated as a yellow oil. Deprotonation of 9 gave the dianion 9(2-), which reacted with [(C5Me5)RhCl2]2 to form the red crystalline dirhodium triple-decker (C5Me5)2Rh2-(Et2C2B3H3) (10a) and its orange 4-chloro derivative 10b. Treatment of the 9(2-) ion with (cymene)ruthenium(II) dichloride gave the red rhodium-ruthenium complex (C5Me5)Rh(Et2C2B3H3)Ru(MeC6H4CHMe2) (11), while 9(2-) and [(C5Me5)CoCl]2 reacted to form the cobalt-rhodium species 7a. The new compounds 3-11 were isolated via column and plate chromatography and characterized from their B-11 and H-1 NMR, IR, and mass spectra, supported by an X-ray diffraction study of 5. Most of the new complexes are stable indefinitely in air and undergo reversible electrochemical oxidation and reduction to give paramagnetic ions. Crystal data for 5: mol wt 543.4; space group Pbca; Z = 8; a = 17.322 (7), b = 19.698 (13), c = 15.619 (9) angstrom; V = 5327 (9) angstrom-3; R = 0.070 for 1714 reflections having F(o)2 > 2.5-sigma(F(o)2) > 2.5-sigma(F(o)2).