om100961f_si_004.cif (107.67 kB)

Electronic Effects in the Oxidative Addition of Iodomethane with Mixed-Aryl β-Diketiminate Chromium Complexes

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posted on 14.02.2011, 00:00 by Wen Zhou, Liming Tang, Brian O. Patrick, Kevin M. Smith
The CrII complexes CpCr[DppNC(Me)CHC(Me)NC6H4Y] (1; Dpp = 2,6-(Me2CH)2C6H3) were used to prepare the corresponding CrIII iodo (2) and methyl (3) mixed-aryl β-diketiminate compounds with Y = OMe (a), CH3 (b), H (c), CF3 (d). Oxidation of the CrII precursors with iodine gave CpCr[DppNC(Me)CHC(Me)NC6H4Y](I) (2ad). The CrIII methyl compounds 3ad were prepared by reaction of the CrII complexes with iodomethane followed by MeMgI. The CrIII chloride complexes 4ad were synthesized by salt metathesis of isolated CpCrCl2(THF) with the appropriate deprotonated mixed-aryl β-diketiminate. The structures of the paramagnetic complexes 1b,c, 2a,b, 3ad, and 4ad were determined by single-crystal X-ray diffraction. The rate constants for the single-electron oxidative addition of iodomethane with 1ad were determined by monitoring the reaction by UV−vis spectroscopy. The rate constants correlated well with the electronic parameters of the Y substituents (ρ = −0.36). The rate constants for 1ad were an order of magnitude greater than those previously obtained for the same reaction with CpCr[(DppNCMe)2CH] and related ortho-disubstituted symmetric β-diketiminate complexes.