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

Abstract

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)NiIH (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, N3─C1 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−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 (ΔG°‡ = 17.3 kcal mol−1). The final step of path 1 is metathesis between Ni─N3 bond of Int3 and Si─H bond of PhSiH3 to afford N‐silylated 1,2‐dihydroproduct and regenerate 1 (ΔG°‡ = 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 PhSiH3. Then, N‐silylated 1,2‐dihydroproduct is produced via hydride‐shuttle transition state TS5 (ΔG°‡ = 18.8 kcal mol−1). The absence of N‐coordination of substrate to NiI 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.

Computational Study of Photocatalytic CO2 Reduction by a Ni(II) Complex Bearing an S2N2-Type Ligand

“…Considering that the Ni hydride complex is an important intermediate in many Ni-catalyzed processes, we calculated the reaction of h-Int with CO 2 . As shown in Figure b, h-Int reacting with CO 2 to generate the intermediate i-Int1-1 (a precursor for the formation of HCOO – ) via the transition state i-TS1 requires overcoming a free energy barrier of 11.4 kcal/mol.…”

“…32,65 Since the concentration of protons is much lower than that of CO 2 in the reaction system, the formation of h-Int should be restrained, only generating a small amount of H 2 . Considering that the Ni hydride complex is an important intermediate in many Ni-catalyzed processes, 66 we calculated the reaction of h-Int with CO 2 . As shown in Figure 8b, h-Int reacting with CO 2 to generate the intermediate i-Int1-1 (a precursor for the formation of HCOO − ) via the transition state i-TS1 requires overcoming a free energy barrier of 11.4 kcal/ mol.…”

Insights into the Regioselectivity of Hydroheteroarylation of Allylbenzene with Pyridine Catalyzed by Ni/AlMe3 with N-Heterocyclic Carbene: The Concerted Hydrogen Transfer Mechanism

“…In combination with the experimental results, density functional calculations have been widely used to elucidate reaction mechanisms of Ni-catalyzed hydroelementation reactions. − In addition to the OA/MI and CMD mechanisms, recent density functional studies showed that hydroarylation and hydroalkenylation of alkenes and alkynes catalyzed by Ni complexes proceed via a ligand-to-ligand H-transfer (LLHT) pathway. − In the LLHT pathway, aromatic C–H bond activation occurs by direct H-transfer from the arene to alkene/alkyne; subsequently, the hydroarylation product is reductively eliminated. The alkene/alkyne plays the role of a hydrogen acceptor in the LLHT mechanism similar to what a Lewis base does in the CMD mechanism.…”

Ruthenium‐Catalyzed Regioselective 1,2‐Hydrosilylation of N‐Heteroarenes

“…In addition, when the reaction was performed by adding 5 mol% of 5 as catalyst, only 15 % NMR yield of the desired product was obtained in reactions proceeding for 18 h (Scheme 3, F ). This result suggests that the dihydrosilyl‐Ru species 5 is not an active (or off‐cycle) species in this reaction, [18,24] unless it proves to be an irreversibly formed off‐cycle species that is detrimental to catalytic progress.…”

“…This yields the N-silylated product 3 a with regeneration of the active catalyst I with an energy barrier of 30.2 kcal/mol (TS-IV). [17][18]24] In path B, complex II undergoes the six-member transition state TS-II' for the hydride transfer with a barrier of 33.6 kcal/ mol. Within TS-II' one H is transferred from Ru to silane and a H atom transfers from silane to carbon of the quinolone to form intermediate IV.…”