Silylene and Germylene Activation of Alkane, Ether and Amine C-H Bonds Mediated by an Aryl Halide. Observation of an Aryl Halide Kinetic Isotope Effect for the C-H Activation Reaction.

Two new types reactions capable of activation the C-H bond α to nitrogen are reported. The silylene [(CH)2tBu2N2]Si (1) was found to activate the weakest C-H bond of alkanes, ethers or amines when combined with an equivalent of an aryl halide. A competing reaction pathway to the C-H activation is oxidative addition of the aryl halide to 1, dilution techniques were used for reducing the percentage of oxidative addition product formed. Additionally, the germeylene [TMS2HC]2Ge (21) was also observed to C-H activate amines when combined with an aryl halide. Amine substrate with C(sp3)-H bonds α and β to the amine nitrogen atom demonstrate different reactivity with 1/Ph-I and 21/Ph-I. For example, reacting Et3N with 1/Ph-I forms the single C-H activation product [(CH)2tBu2N2]Si(I)[CH(CH3)NEt2] (7), a small percentage of [(CH)2tBu2N2]Si(I)(Ph) (2) and [(CH)2tBu2N2]Si(H)(NEt2) (8). In contrast, reacting Et3N with 21/Ph-I results in quantitative formation of [TMS2HC]2Ge(I)(H) (27). Independent synthesis of 8, or 27, was achieved by reacting 1, or 21, in Et3N with [Et3NH]I, implying in situ formation of [Et3NH]I. Deuterium labeled compounds were used for gaining a better understanding of the rate-determining step. The silylene C-H activation reaction of Et2O was found to have a KIE of 5.7 ± 0.1, a magnitude consistent with the C-H bond breaking at or before the rate-determining step. Additionally, the C-H activation of Et2O with 1/Ph-X or 21/Ph-X resulted in a KIE for the protons of the aryl halide. The KIEs of the aryl group range from a low of 1.1 ± 0.1 for 1/4-C6H4DI to high of 1.7 ± 0.1 for 21/C6D5Br. The aryl KIEs are consistent with the Ar-X bond breaking at or before the rate-determining step.Ph.D.ChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64636/1/rhwalker_1.pd