COBALTOCENIUM METALLACARBORANIDE MIXED-SANDWICH SALTS, CP2CO+(ET2C2B4H4)2M- (M=CO(III),FE(III)) AND CP2CO+(ET2C2B3H4-X)CO(III)(ET2C2B4H4)- (X = H, ME)1,2

The first metallocenium metallacarboranide salts have been synthesized and isolated. The title compounds were prepared by reaction of cobaltocene and CoC12 or FeCl2 with the carborane anion Et2C2B4H5- in THF solution, in which the oxidation of two M(II) metal centers to M(III) is accompanied by reduction of two B-H-B bridging protons to H-2. Orange-red, air-stable, crystalline, diamagnetic Cp2Co+[(Et2C2BH4)2Co(III)]-(l) was characterized via NMR and UV-visible spectroscopy and an X-ray crystal structure determination, which revealed pairwise alignment of cobaltocenium and cobaltacarboranide sandwich units. Association of these units is also suggested in the FAB mass spectra of 1. Decapitation of 1 in acidic media gave the nido,closo-cobaltacarborane (EtC2B3H5)Co(Et2C2B4H4), which was converted to its B5-methyl derivative; reactions of the bridge-deprotonated anions of both compounds with cobaltocene afforded the corresponding red-brown diamagnetic cobaltocenium salts Cp2Co+(Et2C2B3H4-X)Co(III)(Et2C2B4H4)- (X = H, Me). The dark red, air-stable, crystalline, paramagnetic iron salt CP2Co+ [(Et2C2B4H4)2Fe(III)]- was synthesized in a procedure similar to that used for 1. The diamagnetic anion (Et2C2B4H4)2Fe(II)H-, detected in NMR spectra, was obtained as a minor product. Crystal data for 1: mol wt 506.9; space group P1BAR; Z = 4, a = 12.877 (4) angstrom, b = 16.554 (5) angstrom, c = 12.848 angstrom, alpha = 92.01 (3)-degrees, beta = 90.12 (2)-degrees, gamma = 98.56 (3)-degrees, V = 2707 angstrom3; R = 0.035 for 5051 reflections having I > 3sigma(l).