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Synthesis and characterization of the homoleptic octahydrotriborate complex Cr(B3H8)2 and its Lewis base adducts.

Goedde DM, Windler GK, Girolami GS

School of Chemical Sciences, University of Illinois at Urbana Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.

Solvate-free sodium octahydrotriborate, NaB3H8, is prepared on a 20 gram scale from sodium amalgam and diborane in diethyl ether. This substance, which is chemically related to borohydride-based compounds being investigated as hydrogen storage materials, is also useful for the preparation of transition-metal complexes bearing B3H8 ligands. Treatment of CrCl3 with NaB3H8 affords a thermally unstable purple liquid thought to be a chromium(III) hydride of stoichiometry CrH(B3H8)2. This hydride converts rapidly at room temperature to the chromium(II) complex Cr(B3H8)2, which adopts a square-planar structure in which four hydrogen atoms form the coordination sphere of the chromium atom. This chromium(II) species forms six-coordinate Lewis base adducts Cr(B3H8)2L2, where L is Et2O, THF, or PMe3; the first two of these adopt trans geometries, whereas the latter is cis. Volatile Cr(B3H8)2 is the first homoleptic transition-metal complex of the octahydrotriborate anion, and it is an excellent single-source precursor for the chemical vapor deposition of thin films of CrB2 at temperatures as low as 200 degrees C. Crystal structures of the new complexes are reported.

Published 26 March 2007 in Inorg Chem, 46(7): 2814-23.
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