(Tetramethylcyclobutadiene)cobalt complexes with phosphacarborane ligands

Reactions of the 11-vertex phosphadicarbollide anions [10-R-7,8,9-PC 2B 8H 9] - (R = H (1a) and Cl (1b)) and [9-Cl-7,8,11-PC 2B 8H 9] - (7) with [Cb*Co(MeCN) 3]PF 6 or [Cb*Co(C 6H 6)]PF 6 (Cb* = C 4Me 4) give the expected cobaltaphosphadicarbollides 1-Cb*-5-R-1,2, 3,4-CoPC 2B 8H 9 (R = H (2a) and Cl (2b)) and 1-Cb*-4-Cl-1,2,3,6-CoPC 2B 8H 9 (5b), respectively. 2a rearranges to a mixture of 1-Cb*-1,2,4,5-CoPC 2B 8H 10 (4a) and 1-Cb*-1,2,3,6-CoPC 2B 8H 10 (5a) at 110°C and further to 1-Cb*-1,2,3,5-CoPC 2B 8H 10 (6a) at 160°C. Heating of the Cl-substituted derivative 2b at 65°C results in 1-Cb*-5-Cl-1,2,4,8-CoPC 2B 8H 9 (3b). Both 2b and 5b rearrange at 100°C, giving 1-Cb*-5-Cl-1,2,3,10-CoPC 2B 8H 9 (8b) as a main product. The observed rearrangement sequence of Cb*CoPC 2B 8H 10 isomers correlates well with the relative stabilities of their nonmethylated analogues estimated by DFT calculations. Reaction of the diphosphacarbollide anion [7,8,10-P 2CB 8H 9] - (11) with Cb*Co(CO) 2I at 160°C affords the nonrearranged complex 1-Cb°-1,2,3,5-CoP 2CB 8H 9 (12). The structures of 2a, 3b, and 4a were determined by X-ray diffraction. The electrochemical study revealed that phosphadicarbollide ligands are stronger acceptors compared with tricarbollide [C 3B 8H 11] - and charge-compensated dicarbollide [9-L-7,8-C 2B 9H 10] -. © 2006 American Chemical Society.