A HOMOLEPTIC [(DIMETHYLAMINO)METHYL]CHROMIUM COMPLEX WITH AN EXTREMELY SHORT CR-CR BOND, [(LI(THF))(2)CR-2(CH2NME2)(6)]

The homoleptic [(dimethylamino)methyl]chromate(II) complex [{Li(THF)}( 2)Cr-2(CH2NMe2)(6)] (1) has been prepared by the reaction of [CrCl2(TH F)(2)] with LiCH2NMe2 in a 1:3 molar ratio. The thermally stable compl ex 1 (T-dec = 94-98 degrees C) is diamagnetic (chi(g) = -1.19 x 10(-7) cm(3) g(-1) (295 K); mu(eff) = 0.67 mu(B)/Cr), consistent with a Cr-C r quadruple bond. The reaction of 1 with 1-bromopentane led to formati on of the paramagnetic (mu(eff) = 2.97 mu(B)/Cr) Cr(III) derivative [{ Cr(eta(2)-CH2NMe2)(2)(mu-Br)}(2)] (2) with cleavage of the Cr-Cr quadr uple bond. The structures of the dinuclear complexes 1 and 2 have been determined by X-ray crystallography. 1 (C-i symmetry) exhibits a supe rshort Cr-Cr quadruple bond (1.884(1) Angstrom) that is not supported by bridging aminomethyl ligands. At each chromium, two CH2NMe2 ligands adopt an eta(1)-coordination and one adopts an eta(2)-coordination (d (Cr-C) = 2.124(4)-2.139(4) Angstrom). The primary donor set of lithium is made up of two nitrogen atoms, one oxygen atom (THF), and one meth ylene carbon atom. Complex 2 (C-i symmetry) has a planar central Cr(mu -Br)(2)Cr unit. All aminomethyl ligands are eta(2)-coordinated (d(Cr-C ) = 2.030(5) and 2.043(5) Angstrom) to complete a distorted-octahedral coordination sphere at chromium.