Amido, imido and carbene complexes of chromium

Article abstract of DOI:10.1016/S0277-5387(97)00221-0

Interaction of CrCl₂ with LiNHAr*, Ar* = 2,6-Prⁱ₂C₆H₃, in thf gave the homoleptic amide Cr^II (NHAr*)₄ [Li(thf)]₂ (1), which resisted further deprotonation by strong bases. Interaction of Cr(Nmes)₂ Cl₂,mes = 2,4,6-Me₃C₆H₂, with LiNHmes gave the mesitylimido complex [Cr^VI(Nmes)₃(NHmes)]Li(Et₂O)₂ (2), which also resisted further deprotonation. Pentamethylcyclopentadienyl chromium(V) complexes Cp*Cr(NAr′)X₂, X = SC₆H₅, Ar′ = 2-PrⁱC₆H₄, (3) ; 4-Me-C₆H₄ (4) ; 2-Bu′C₆H₄, (5), have been prepared by interaction of (Cp*CrBr₂)₂ with Li(Ar′NSPh). Reaction of (Cp*CrBr₂)₂ with mesitylnitrene, generated from mesN₃ in situ, gave the ionic Cr^III species [Cp*CrBr₃][mesNH₃], (6). (3) and (5) as well as the previously reported Cp*Cr(NBu^t)X₂ can be transformed to the corresponding chlorides (7)-(9), by reaction with BCl₃. Finally, interactions of Cr(mes)₂(thf)₃ with the carbene CN(Prⁱ)C₂Me₂NPrⁱ = L gave Cr(mes)₂L₂ (10). The X-ray crystal structures of compounds (1)-(3), (6), (7), (9) and (10) have been determined. (1) is a molecular cluster with square planar Cr^II and with two [Li(thf)]⁺ ions bridging the nitrogen atoms of pairs of amide ligands on opposite sides of the square. (2) has a distorted tetrahedral metal geometry with one [Li(Et₂O)₂]⁺ ion bridging the nitrogen atoms of two imido ligands. (3) has a monomeric pseudo tetrahedral structure, as do (7) and (9) and the anion in (6). (10) has a trans square planar structure in which the Cr - C distances to the mesityl and carbene ligands are equal within error.