Carbon-Rich Metallacarboranes. 15. Novel Metal-Promoted Cluster Fusion Reactions

Kent W. Piepgrass, Michael A. Curtis*, Xiaotai Wang, Xiangsheng Meng, Michal Sabat, Russell N. Grimes

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


In contrast to our recently reported syntheses2 of Co-M-Co tetradecker sandwich complexes (M = Co, Ni, Ru) via reactions of double-decker cobaltacarborane anions Cp*Co(Et2C2B3H3X) (1, X = H, Me, Cl, Br, acetyl) with metal halides, reactions of the anions having X = H, Me, Et, or Cl with FeCl2 did not produce the intended Co-Fe-Co tetradeckers. Instead, oxidative fusion of the CoC2B3 units occurred, generating tetracarbon metallacarboranes Cp*2Co2Et4C4B6H4X2 (3a–d), which have been characterized via NMR, IR, and mass spectroscopy, supported by X-ray crystallographic analyses of the parent (3a) and dichloro (3d) clusters. These compounds have an open Co2C4B6 12-vertex cage structure that is a fragment of a 16-vertex Td closo polyhedron, a geometry that was previously unknown in cluster chemistry and (in these species) is not consistent with the widely applied skeletal-electron counting rules. Moreover, it differs from the Co2C4B6 cage structures of several known cobaltacarboranes.4 An attempt to prepare a diiodo Co-Ni-Co tetradecker complex from 1 (X = I) with NiBr2 gave instead the dimer [Cp*Co(Et2C2B3H3)]2 (6), which was shown by X-ray crystallography to have an edge-fused structure in which the two C2B3 rings are mutually tilted. A centrosymmetric isomer of this dimer (8) having coplanar C2B3 rings with the Cp*Co units on opposite sides of the ring plane was isolated from a reaction of 1 (X = H) with CoCl2 and Cp2Co and characterized by X-ray diffraction. Also isolated from this reaction were a dimer of a different type (joined via a single B—B bond), [Cp*Co(Et2C2B3H4)]2 (9), together with previously reported2a Co-Co triple-decker and Co-Co-Co tetradecker products. The implications of the formation and structures of the fused and partially fused products found in this work are discussed in terms of multidecker stacking mechanisms and skeletal electron-counting theory.

Original languageEnglish
Pages (from-to)2156-2163
Number of pages8
JournalInorganic Chemistry
Issue number10
Publication statusPublished - 1993
Externally publishedYes


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