Arylimido complexes of chromium-(VI), -(V) and -(IV)

The first arylimido compounds of chromium(VI), CrCl2(NR)2(R = 2,4,6-Me3H2C6 or 2,6-Me2H3C6), have been made by interaction of CrCl2(NBut)2 with the aryl isocyanates. Similar interaction with 2,6-Pri2C6H3NCO gave a dimeric chromium(V) compound [CrCl(µ-NBut)(NC6H3Pri2-2,6)]2. The chloride CrCl2(NC6H2Me3-2,4,6)2 formed adducts with Lewis bases, e.g. CrCl2(NC6H2Me3-2,4,6)2(PMe3)2 and [Cr(NC6H2Me3-2,4,6)2(terpy)][BF4]2(terpy = 2,2′ : 6′,2″-terpyridine) was obtained with AgBF4. Substitution of Cl atoms occurred with NaR′(R′= OSiMe3, OC6H2Me3-2,4,6, SC6H2Me3-2,4,6, SC6F5 or SC6H2Pri3-2,4,6) and with Grignard reagents, MgR″Br (R″= CH2CMe3, CH2CMe2Ph or CH2Ph) giving in all cases compounds of the type Cr(NC6H2Me3-2,4,6)2R′2 or Cr(NC6H2Me3-2,4,6)2R″2. The alkyl compounds underwent insertion with ButNC, or 2,6-Me2H3C6NC to give η2-iminoacyl compounds or CrVI and reduction by PMe3 on heating to give the chromium(IV) dimer [Cr(µ-NC6H2Me3-2,4,6)(NC6H2Me3–2,4,6)(PMe3)]2. The interaction of CrCl2(NC6H2Me3-2,4,6)2 with the Grignard reagent derived from 4-tert-butylbenzyl chloride gave not a dialkyl but an amidochromium(IV) dimer {CrCl(µ-NC6H2Me3–2,4,6)[N(CH2C6H4But-4)(C6H2Me3-2,4,6)]}2, while on interaction with MgEtBr in the presence of PMe3 it gave the dichromium(V) compound (2,4,6-Me3H2C6N)BrCr(µ-NC6H2Me3-2,4,6)2CrBr(NC6H2Me3-2,4,6)(PMe3). The crystal structures of seven compounds have been determined, in six of which the Cr atoms have slightly distorted tetrahedral geometry, while in the remaining compound one atom is tetrahedral and the other five-co-ordinate. The geometries of the Cr2N2 rings in four of the compounds are indicative of some direct Cr Cr interaction