Theoretical prediction of Ni(I)-catalyst for hydrosilylation of pyridine and quinoline.

Catalytic synthesis of dihydropyridine by transition-metal complex is one of the important research targets, recently. Density functional theory calculations here demonstrate that nickel(I) hydride complex (bpy)Ni H (bpy = 2,2'-bipyridine) 1 is a good catalyst for hydrosilylation of both quinoline and pyridine. Two pathways are possible; in path 1, substrate reacts with 1 to form stable intermediate Int1. After that, N ─C bond of substrate inserts into Ni─H bond of 1 via TS1 to afford N-coordinated 1,2-dihydroquinoline Int2 with the Gibbs activation energy (ΔG° ) of 21.8 kcal mol . Then, Int2 reacts with hydrosilane to form hydrosilane σ-complex Int3; this is named path 1A. In the other route (path 1B), Int1 reacts with phenylsilane in a concerted manner via hydride-shuttle transition state TS2 to afford Int3. In TS2, Si atom takes hypervalent trigonal bipyramidal structure. Formation of hypervalent structure is crucial for stabilization of TS2 (ΔG° = 17.3 kcal mol ). The final step of path 1 is metathesis between Ni─N bond of Int3 and Si─H bond of PhSiH to afford N-silylated 1,2-dihydroproduct and regenerate 1 (ΔG° = 4.5 kcal mol ). In path 2, 1 reacts with hydrosilane to form Int5, which then forms adduct Int6 with substrate through Si-N interaction between substrate and PhSiH . Then, N-silylated 1,2-dihydroproduct is produced via hydride-shuttle transition state TS5 (ΔG° = 18.8 kcal mol ). The absence of N-coordination of substrate to Ni in TS5 is the reason why path 2 is less favorable than path 1B. Quinoline hydrosilylation occurs more easily than pyridine because quinoline has the lowest unoccupied molecular orbital at lower energy than that of pyridine. © 2019 Wiley Periodicals, Inc.