The investigation of carbon-carbon nitride cleavage of allyl- and aryl-nitriles by [(dippe)nickel hydride]2 and [(dippe)platinum hydride]2.

摘要

The reaction of [(dippe)NiH]2 with 2-methyl-3-butenenitrile (2M3BN) in solvents spanning a wide range of polarities shows significant differences in the ratio of products derived from C--H and C--CN activation. This variation is attributed to the differential solvation of the transition states, which was further supported through the use of sterically-bulky solvents and weakly coordinating solvents. Variation of the temperature of reaction of [(dippe)NiH]2 with 2M3BN in decane and N,N-dimethylformamide (DMF) allowed for the calculation of Eyring activation parameters for the C--CN activation and C--H activation pathways.;Reactions of [(dippe)NiH]2 with benzonitrile and varying concentrations of Lewis acids (BPh3, BF3, and BEt3) have shown a dramatic variation of reaction rate compared to the same reaction without Lewis acids. When less than 1 equiv of Lewis acid is used, the reaction rate is as much as 100 times greater than without Lewis acid. Boron exchange was observed with less than one equiv of Lewis acid, allowing the formation of a Ni(0)-eta2-aryl complex (observed by low temperature NMR and DFT calculations) to which the Lewis acid is postulated to re-coordinate as the rate limiting step allowing the formation of a stable Ni(II) C-CN cleavage product. When 1 equiv or greater of Lewis acid is used, the reaction shows dramatic inhibition even compared to the reaction without Lewis acid due to the formation of (dippe)Ni(eta2-C,N-PhCNBPh3). Lewis acid dissociation can be considered to be the rate limiting step under these conditions.;Two different platinum complexes were evaluated for the potential to activate benzonitrile. [(dippe)PtH]2 was treated with LiBEt 3H to form the novel binuclear platinum-hydride complex [(dippe)PtH] 2·LiBEt3H. The reaction of [(dippe)PtH]2· LiBEt3H in neat benzonitrile was slower than the reaction of [(dippe)PtH] 2 with benzonitrile and was never fully consumed. A second complex, (dippe)Pt(nor)n was synthesized from the reaction of Pt(nor)3 and dippe. Reaction of (dippe)Pt(nor)n in neat benzonitrile also showed some activity; however this reaction showed a competition between benzonitrile and free norbornylene making neither complex as viable for the activation of benzonitrile as [(dippe)PtH]2.;The reaction of [(dippe)PtH]2 with benzonitrile at 140 °C produced two products, the C-H activated (dippe)Pt(H)(2-C6H 4) and the C-CN activated (dippe)Pt(Ph)(CN) with the kinetically favored C-H activation product forming in a significant majority (∼18:1). Further reaction showed beta-cyano elimination occurring in (dippe)Pt(H)(2-C 6H4CN) forming (dippe)Pt(H)(CN) and benzene, presumably via benzyne hydrogenation, as supported by deuterium experiments producing a series of deuterated benzene species. Following the elimination, a second C-H activation occurred forming three regioisomers of (dippe)Pt(CN)(C6H4 CN).