Becke, Frank; Wiegeleben, Peter; Rueffer, Tobias; Wagner, Christoph; Boese, Roland; Blaeser, Dieter; Steinborn, Dirk:

A Homoleptic [(Dimethylamino)methyl]chromium Complex with an Extremely Short Cr-Cr Bond, [{Li(THF)}2Cr2(CH2NMe2)6].

In: Organometallics, Jg. 17 (1998) ; Nr. 3, S. 475-478
ISSN: 0276-7333
Zeitschriftenaufsatz / Fach: Chemie
The homoleptic [(dimethylamino)methyl]chromate(II) complex [{Li(THF)}2Cr2(CH2NMe2)6] (1) was prepd. by the reaction of [CrCl2(THF)2] with LiCH2NMe2 in a 1:3 molar ratio. The thermally stable complex 1 (Tdec = 94-98 Deg) is diamagnetic (cg = -1.19 * 10-7 cm3 g-1 (295 K); meff = 0.67 mB/Cr), consistent with a Cr-Cr quadruple bond. The reaction of 1 with 1-bromopentane gave the paramagnetic (meff = 2.97 mB/Cr) Cr(III) deriv. [{Cr(h2-CH2NMe2)2(m-Br)}2] (2) with cleavage of the Cr-Cr quadruple bond. The structures of the dinuclear complexes 1 and 2 were detd. by x-ray crystallog. Complex 1 (Ci symmetry) exhibits a supershort Cr-Cr quadruple bond (1.884(1) .ANG.) that is not supported by bridging aminomethyl ligands. At each Cr, two CH2NMe2 ligands adopt an h1-coordination and one adopts an h2-coordination (d(Cr-C) = 2.124(4)-2.139(4) .ANG.). The primary donor set of Li is made up of two N atoms, one O atom (THF), and one methylene C atom. Complex 2 (Ci symmetry) has a planar central Cr(m-Br)2Cr unit. All aminomethyl ligands are h2-coordinated (d(Cr-C) = 2.030(5) and 2.043(5) .ANG.) to complete a distorted-octahedral coordination sphere at Cr.