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 I 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 3 ─C 1 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 (Δ G ° ‡ ) of 21.8 kcal mol −1 . 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 (Δ G ° ‡ = 17.3 kcal mol −1 ). The final step of path 1 is metathesis between Ni─N 3 bond of Int3 and Si─H bond of PhSiH 3 to afford N ‐silylated 1,2‐dihydroproduct and regenerate 1 (Δ G ° ‡ = 4.5 kcal mol −1 ). 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 3 . Then, N ‐silylated 1,2‐dihydroproduct is produced via hydride‐shuttle transition state TS5 (Δ G ° ‡ = 18.8 kcal mol −1 ). The absence of N‐coordination of substrate to Ni I 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.