Amide-Stabilized, Diamagnetic Chromium(II) Nitrosyl Complexes1

Treatment of Cr(NO)(N i Pr 2 ) 3 with 2 equiv of PhCO 2 H affords Cr(NO)(N i Pr 2 )(O 2 CPh) 2 ( 1 ) in good yields. Reaction of CpNa·DME with 1 produces CpCr(NO)(N i Pr 2 )(OC(O)Ph) ( 2 ), which subsequently yields a series of 18-valence-electron (18e) complexes, CpCr(NO)(N i Pr 2 )(R) (R = η 1 -Cp ( 3 ), CH 2 SiMe 3 ( 4 ), η 1 -CH 2 Ph ( 5 ), Ph ( 6 ), CPh CH 2 ( 7 ), C⋮CCMe 3 ( 8 ), C⋮CPh ( 9 )) when treated with additional CpNa·DME or 1 equiv of the appropriate R 2 Mg· x (dioxane) reagent. 2 − 9 are low-spin ( S = 0) compounds, and their electronic stability is attributed to the strong, synergic π-bonding interactions present in the [Cr(NO)(N i Pr 2 )] 2+ core, as indicated both by the NMR and IR spectra of these complexes and by the solid-state molecular structures of 2 − 4 . The “strong-field” nitrosyl and amide ligands also enforce a diamagnetic configuration on the 14e bis(hydrocarbyl) complexes Cr(NO)(N i Pr 2 )R 2 (R = CH 2 SiMe 3 ( 10 ), CH 2 Ph ( 11 ), o -tolyl ( 12 )), which are obtained in good yields by reaction of 1 with 2 equiv of the corresponding R 2 Mg· x (dioxane) reactants. The solid-state molecular structures of 10 and 11 have also been established by single-crystal X-ray crystallographic analyses. Variable-temperature NMR spectroscopy was employed to study the fluxional processes occurring in 1, 10, and 11 .