William M. Maxwell

Structural consequences of electron hyperdeficiency. Synthesis and crystal structure of an iron-cobalt metallocarborane having two closed polyhedra fused along an edge

Abstract : A metallocarborane of novel structure, (CH3)4C4B8H8FeCo(Eta to the 5th power -C5H5), has been synthesized and structurally characterized from FTNMR, mass spectroscopic, infrared, and single crystal X-ray diffraction data. The dark green crystals are monoclinic, space group P2 sub 1, with two molecules per unit cell and a = 7.203(4) A, b = 14.77(2) A, c = 8.830(2) A, and beta = 99.7(1) degrees. (rho calcd = 1.38 g/cc, rho obsd = 1.38 g/cc). The structure was solved by the heavy-atom method and refined by full-matrix least-squares procedures to a final R value of 0.069 and R sub W = 0.081 for the 1657 reflectionions. The molecule contains a direct iron-cobalt bond and consists of two pentagonal bipyramidal units fused at a common iron atom with an additional BH group capping triangular faces on both polyhedra simultaneously. The structure is explained in terms of a shortage of two electrons in the cage framework, relative to the normal requirement for polyhedral clusters, which causes one BH group to adopt a capping location. These results are discussed in relation to the known structures of two osmium carbonyls and a diiron metallocarborane.

A mixed-metal trimetallic metallocarborane, [{(CO)3Fe}2(η5-C5H5) CoMe2C2B4H4]

The reaction of [1,2,3-(η5-C5H5) CoMe2C2B4H4] with [Fe(CO)5] produced [{(CO)3Fe}2(η5-C5H5) CoMe2C2-B4H4], which is a nine-vertex polyhedral cage system containing the highest ratio of metal to nonmetal cage atoms among known metallocarboranes and the first example of a mixed-metal trimetallocarborane.

Synthesis and X-ray crystal structures of two 14-vertex di-iron tetracarbon metallocarbaboranes

The reaction of Me4C4B8H8 with NaC10H8, NaC5H5, and FeCl2 produces at least four isomers of [(η5-C5H5)2Fe2Me4 C4B8H8], two of which have been structurally characterized from X-ray crystallographic studies and form 14-vertex polyhedra; neither compound has the closo-structure predicted from electron-counting rules, containing instead a 5-membered and a 4-membered open face respectively.