Tricarbon carborane chemistry. 1. Syntheses and structural characterizations of monocage iron, manganese, and nickel metallatricarbaborane complexes

Article abstract of DOI:10.1021/om00040a042

Improvements in the route to the tricarbon carborane 6-CH₃-5,6,9-C₃B₇H₁₀ (1) and its corresponding monoanion, 6-CH₃-5,6,9-C₃B₇H₉^-, have enabled the syntheses of a series of monocage iron, manganese, and nickel tricarbaborane complexes that are analogues of the cyclopentadienyl complexes of these metals. Reaction of 6-CH₃-5,6,9-C₃B₇H₉^- with (η-C₅H₅)Fe(CO)₂I gave two isomeric products, 1-(η-C₅H₅)Fe-2-CH₃-2,3,4-C ₃B₇H₉ (2) and 1-(η-C₅H₅)Fe-4-CH₃-2,3,4-C ₃B₇H₉ (3), while reaction of the anion with Mn(CO)₅Br yielded 1-(CO)₃Mn-2-CH₃-2,3,4-C₃B₇H ₉ (4). Single-crystal X-ray structural determinations of 2 and 3 confirm that they are hybrid complexes in which an iron atom is sandwiched between cyclopentadienyl and tricarbon carborane ligands. The ferratricarbaborane cages in both 2 and 3 have closo-octadecahedral structures, consistent with their 24-skeletal-electron counts, with the iron atom in the six-coordinate position and two of the cage carbon atoms in four-coordinate positions adjacent to the iron. The two structures differ in the position of the exopolyhedral methyl group. In 2 the methyl group is bound to a four-coordinate carbon as in 1. In 3 the methyl group has rearranged to an adjacent five-coordinate cage carbon. The reaction of 6-CH₃-5,6,9-C₃B₇H₉^- with [(η-C₅H₅)NiCO]₂ yielded the compound 9-(η-C₅H₅)Ni-8-CH₃-7,8,10-C ₃B₇H₉ (5), which is proposed, on the basis of its skeletal-electron count and the spectroscopic data, to have a sandwich structure in which the nickelatricarbaborane cage has an open-cage geometry based on an icosahedron missing one vertex.