Many small cage hexaborane analogues have been synthesised using anionic or neutral polyborane
ligands or monoborane reagents (BH3·thf or LiBH4·thf) with the metal precursors [1]. Several electroncounting
rules in combination with the isolobal analogy permit to define such structural types. The nature
of hexaborane polyhedra depends upon the skeletal electron count as determined by Wade-Mingos rules
[2], ranging from 5 to 9. Going from early to late transition metal elements, (Cr to Ir), the structural motif
changes from oblato-nido to arachno, with increase in the sep by 1 unit (n-1 to n+3) (Chart 1). Interestingly,
some of the hexaborane analogues clusters [(Cp*M)2B4H8)] M = Cr(v), Re(vi), Ru(iv) and Ir(iii) are having
identical compound stoichiometries with different geometries [3]. Monometallic and bimetallic analogues
of hexaborane are well documented in the literature but trimetallic analogues are rather rare which
belongs to either closo, nido and pileo geometry. In this seminar, the synthesis, properties and
applications of various analogues of hexaborane as well as preliminary result of my research work in this
field will be discussed.
Chart 1. Different skeletal geometry for hexaboranes
References:
[1]. (a) N. N. Greenwood, I. M. Ward, Chem. Soc. Rev., 1974, 3, 231271; (b) T. P. Fehlner, Metallaboranes, Structural and
Electronic Paradigms in Cluster Chemistry, in: D. M. P. Mingos (Ed.), Springer-Verlag Berlin, Heidelberg, 1997, pp 111
135; (c) T. P. Fehlner, Organometallics, 2000, 19, 2643-2651; (d) T. P. Fehlner, PINSA, 2002, 68, 579-596.
[2]. (a) D. M. P. Mingos, D. J. Wales, Introduction to Cluster Chemistry, Prentice Hall, New York, 1990; (b) E. D. Jemmis, M.
M. Balakrishnarajan, P. D. Pancharatna, J. Am. Chem. Soc., 2001, 123, 4313-4323.
[3]. (a) K. J. Deck, Y. Nishihara, M. Shang, T. P. Fehlner, J. Am. Chem. Soc., 1994, 116, 8408-8409; (b) S. Ghosh, M. Shang,
T. P. Fehlner, J. Organomet. Chem., 2000, 614615, 92-98; (c) X. Lei, M. Shang, T. P. Fehlner, J. Am. Chem. Soc., 1999,
121, 1275-1287; (d) X. Lei, M. Shang, T. P. Fehlner, Chem. Eur. J., 2000, 6, 2653-2664.