Benzene-Centered Tri- and Tetrametallacarborane Sandwich Complexes Organotransition-Metal Metallacarboranes, part 56. This work was supported in part by the National Science Foundation (grant CHE 9980708 to R.N.G.) and the Deutsche Forschungsgemeinschaft (SFB 247, to W.S. for M.B.). Part 55: T. Dodge, M. A. Curtis, J. M. Russell, M. Sabat, M. G. Finn, R. N. Grimes, J. Am. Chem. Soc. 2000, 122, 10 573.