CHROMIUM(II) AMIDES - SYNTHESIS AND STRUCTURES

A novel class of mono- and di-meric chromium(II) amides has been prepared and characterized. Reaction of [CrCl2(thf)2] (thf = tetrahydrofuran) with 2 equivalents of M(NR2) (R = C6H11, Pr(i), Ph, or phenothiazinyl; M = Li or Na) allowed the formation of the homoleptic amides [{Cr(mu-NR2)(NR2)}2] (R = Ph 1a. C6H11 lb or Pr(i) 1c). The reaction is followed by co-ordination of a Lewis base which, although preserving the Cr2(NR2)2, core, remarkably elongated the Cr ... Cr distance forming [{Cr(mu-NR2)(NR2)L}2] (R = Ph, L = thf 2). Facile cleavage to give the square-planar monomeric species [Cr(NR2)L2] (R = Ph, L = pyridine 3a, thf 3b; NR2 = phenothiazinyl, L = thf 3c) occurred upon treatment with an excess of co-ordinating solvent. Reaction with an excess of M(NR2) led to the formation of anionic chromium(II) square-planar metalates [M2Cr(NR2)4L2] (R = Ph, M = Na, L = thf 4a; R = Et, M = Li, L = thf 4b or pyridine 4c). A dimeric species with a very short Cr ... Cr contact [{Cr[N(C5H4N-2)2]2}2].2dmf (dmf = dimethylformamide) 5b has been obtained involving a unique three-centre chelating geometry of the bridging amide ligand. The crystal structures of compounds 1 b, 2, 3a, 3c, 4c and 5b have been determined.