Intramolecular C–H Functionalization Followed by a [2_σ + 2_π] Addition via an Intermediate Nickel–Nitridyl Complex

Abstract

Irradiation of a disphenoidal Ni(II) azido complex, [Cz tBu (Pyr iPr ) 2 NiN 3 ] (1), revealed an unprecedented nickel complex, [Cz tBu (Pyr iPr )(NH 2 −Pyr iPr )] (2), in >90% isolated yield. As evidenced by single-crystal Xray diffraction, 2 is produced by double intramolecular C−H activation of a putative nickel−nitridyl intermediate, [Cz tBu (Pyr iPr ) 2 Ni− ⃛ N • ]. Calculations support the generation of an intermediate with significant nitridyl radical character after the loss of N 2 , which, in turn, undergoes tandem C−H activations, leading to functionalized intermediates and products. This is an unprecedented example of transient Ni− ⃛ N • -promoted intramolecular C− H functionalization, followed by a [2 σ + 2 π ] addition, yielding bis-metallacyclic product 2. Complex 2 is also observed from the reaction of Ni(I) precursor Cz tBu (Pyr iPr ) 2 Ni (3) and Me 3 SiN 3 , suggesting a unique thermal route toward a masked nickel−nitridyl intermediate.

A platinum(ii) metallonitrene with a triplet ground state

“…H NMR (300 13. MHz, C 6 D 6 , 298 K): δ (ppm) 6.53 (A 18 XX′A′ 18 , N =| 3 J HP + 4 J HP | = 38.1 Hz,3 J H-H = 5.4 Hz,3 J PtH = 78.1 Hz, 2H, NCH), 3.91 (A 18 XX′A′ 18 , N =| 2 J HP + 4 J HP | = 9.3 Hz,3 J HH = 5.2 Hz,3 J PtH = 33.6 Hz, 2H, PCH), 1.33 (A 18 XX′A′ 18 , N =| 3 J HP + 5 J HP | = 14.4 Hz, 36H, CMe 3 ); 13 C{ 1 H} NMR (75.48 MHz, C 6 D 6 , 298 K): δ (ppm) 162.6 (t, 2 J PC = 7.4 Hz, 2 J PtC = 81.8 Hz, NCH), 82.8 (t, 1 J PC = 22.8 Hz, 2 J PtC = 53.2 Hz, CHP), 36.2 (t, 1 J PC = 13.0 Hz, PCMe 3 ), 29.1 (t, 2 J PC = 3.1 Hz, 3 J PtC = 12.8 Hz, PCMe 3 ); 31 P{ 1 H} NMR (121.49 MHz, C 6 D 6 , 298 K): δ (ppm) 66.8 (s, 1 J PtP = 2,686.5 Hz); 195Pt{ 1 H} NMR (107.14 MHz, toluene-d 8 , 298 K): δ (ppm) −3,917.4 (t, 1 J PtP = 2,719.7 Hz); IR (ATR): 2,052 (N 3 ), 1,530 (C = C) cm −1 ; UV-vis (THF): λ max (ε, M −1 cm −1 ) = 233 (17,160), 260 (7,760), 312 (19,980) nm; MS (LIFDI): m/z (%) 593.2 (100); analysis (calculated, found for C 20 H 40 N 4 P 2 Pt): C (40.47, 40.31%), H (6.79, 6.74%), N (9.44, 9.35%).…”

DFT and TDDFT Study of the Reaction Pathway for Double Intramolecular C–H Activation and Functionalization by Iron, Cobalt, and Nickel–Nitridyl Complexes

“…Such reactions may be driven by an external source of energy, photons that promote the ground states of these intermediates into excited electronic states that distort their bond lengths, bond orders, and vibrational modes to make them unstable/metastable enough for intermolecular reactions with inert alkanes. It was anticipated from earlier research that Co- and especially Fe nitrides may be more accessible by thermal as opposed to photochemical synthetic routes; however, by the same token, the generated nitridyl/nitride intermediates for these earlier 3d metals may be less reactive than the nickel congener.…”

“…Previous work by our group in collaboration with the experimental team of Lee reported the synthesis of nickel amine compound 2 via the irradiation of nickel–azido compound 1 , Figure , where M = Ni. Other groups have also synthesized pincer-like nickel nitrido species, , each generated by the photolysis of square planar (pincer)­NiN 3 , where the central metal may also be replaced with cobalt .…”

“…Synthetic scheme for the formation of the amine complex [Cz t Bu (Pyr i Pr )­M­(NH 2 –Pyr i Pr )] (2) from the azido complex [Cz t Bu (Pyr i Pr ) 2 MN 3 ] (1), where M represents the central metal (M = Ni, Co, or Fe). Adapted with permission from ref .…”

“…Results from research on Ni-nitrido intermediates , were considered promising for the study of intramolecular C–H functionalization, which could be extended to help design catalysts for this important transformation, in particular intermolecular C–H functionalization variants. Sun et al concluded that the Cz t Bu (Pyr i Pr ) 2 NiN intermediate is best described as [(L – )­(d 8 -Ni 2+ )­(N ••– )]albeit with significant multireference characterper density functional theory (DFT) and multiconfiguration self-consistent field (SCF) computations, with significant spin density on nitridyl nitrogen . Given such a precedent, the question arose as to the possibility of replacing nickel with earlier 3d metals such as Co and Fe.…”