Bis(adamantylimido) Complexes of Chromium (VI)

A series of complexes of chromium(VI) incorporating the adamantylimido ligand has been prepared. Reaction of the silylated amine AdNH(SiMe3) with CrO2Cl2 yields Cr(NAd)2(OSiMe3)2 (1), which is readily converted to the dichloride Cr(NAd)2Cl2 (2) upon treatment with excess BCl3. Compound 2 forms stable mono-adduct complexes of general formula Cr(NAd)2Cl2(L) (3, L=PMe3; 4, L=pyridine) and provides a synthetic entry into the dialkyl complexes Cr(NAd)2R2 upon treatment with 2 equivalents of RMgCl (5, R=CH2Ph; 6, R=CH2CMe2Ph; 7, R=CH2CMe3). The solid state NMR spectrum and a partial structure determination on 5 reveal ¿1 and ¿2 bonding arrangements for the two benzyl ligands. An X-ray structural analysis on 6 establishes a pseudo-tetrahedral coordination geometry with Cr¿N distances of 1.635(2) and 1.636(2) Å. Clos H contacts are present for one H-atom of each methylene unit indicating the possible presence of weak ¿-agostic type interactions. The difference in chemical shift (¿¿) between the ¿ and ß carbons of the adamantyl group can be used to give a qualitative indication of electron density at the adamantylimido nitrogen atom.