CH Activation of Benzene by a Photoactivated Ni^II(azide): Formation of a Transient Nickel Nitrido Complex

Abstract

Photochemical activation of nickel‐azido complex 2 [Ni(N3)(PNP)] (PNHP=2,2′‐di(isopropylphosphino)‐4,4′‐ditolylamine) in neat benzene produces diamagnetic complex 3 [Ni(Ph)(PNPNH)], which is crystallographically characterized. DFT calculations support photoinitiated N2‐loss of the azido complex to generate a rare, transient NiIV nitrido species, which bears significant nitridyl radical character. Subsequent trapping of this nitrido through insertion into the NiP bond generates a coordinatively unsaturated NiII imidophosphorane PN donor. This species shows unprecedented reactivity toward 1,2‐addition of a CH bond of benzene to form 3. The structurally characterized chlorido complex 4 [Ni(Cl)(PNPNH)] is generated by reaction of 3 with HCl or by direct photolysis of 2 in chlorobenzene. This is the first report of aromatic CH bond activation by a trapped transient nitrido species of a late transition metal.

Oxygen Atom Transfer to Cationic PCPNi(II) Complexes Using Amine-N-Oxides

“…In both cases, a color change from dark orange to red was noted and a small upfield shift in the 31 In contrast, attempted abstraction of bromide from the NMe 2 substituted 2 Br with silver salts resulted in an immediate color change from orange to dark blue, the formation of silver metal, and the complete loss of a 31 P{ 1 H} NMR spectral signature, suggesting a paramagnetic product. This is perhaps unsurprising, given the known propensity of silver salts to oxidize PNPNi(II) complexes, 29,46 and likely involves oxidation of the pendant NMe 2 group on the ligand. Attempted bromide abstractions using KOTf and NaOTf were unsuccessful but ion exchange was accomplished cleanly by using TlOTf (Scheme 2), resulting in a color change from orange to red, similar to 1 OTf , and an upfield shift in the 31 47 and more torsion between the ligand arene rings (55.67°vs 43.68°; throughout this discussion, these torsion values refer to the angle between the planes defined by the linking aryl rings of the pincer ligand arms).…”

“…While this strategy has met with modest success, leading to the isolation and structural characterization of iridium nitrido complexes, 22,23 and the isolation of a compound proposed to be a platinum-oxo complex, 24 for the most part, intermediary or transiently generated oxo and nitrido complexes have eluded explicit structural elucidation. 25−33 Spectroscopic observation has been noted in some cases, 25−27,30,34−36 but evidence for these species often hinges on the characterization of the products of trapping experiments with external reagents or isolation of "decomposition" products 28,29,31,32 resulting from the oxidation of one or both of the arms (usually phosphines) of the pincer ligand framework. Products arising from E-centered radical chemistry have also been observed, such as radical coupling of nitride ligands 22,27 or H atom abstraction.…”

“…24 In other systems, such as the PNPNi(IV) nitrido complex proposed by van der Vlugt and co-workers (Scheme 1b), the ligand oxidation is too rapid for observation of the transient Ni nitride; the resulting product of nitrido insertion rapidly activates the C−H bond of benzene. 29 This contrasts with a variety of group 9 systems where the primary decomposition pathway is ligand C−H bond activation, 28,32,34 or radical coupling of nitride ligands to yield dinitrogen adducts. 22,27 However, there are cobalt-based systems in which ligand oxidation is the primary mode of reactivity, such as Meyer's tripodal Co(IV) nitride complex, 30 and complexes arising from oxygen atom transfer to Caulton's PNPCo(I) complex (Scheme 1c).…”

Effect of Appended S-Block Metal Ion Crown Ethers on Redox Properties and Catalytic Activity of Mn–Nitride Schiff Base Complexes: Methane Activation

“…Transition metal nitride intermediates are key reactive intermediates in biological and industrial processes such as N 2 -to-NH 3 conversion (biologically through the action of the nitrogenase enzyme and industrially through Haber–Bosch process for ammonia synthesis) − and in catalytic applications. , Metal–nitrido complexes, L n MN, have gained interest for several reactions such as functionalization of inert C sp 3 –H (e.g., N-insertion into C–H bonds) and activation of aromatic C–H bonds. − For a complex to have a stable multiple bond between transition metals and nitrogen, there should be one or more empty metal d-orbitals of appropriate matching energy level and symmetry to accept the additional π-electron density. Hence, nitrido complexes with d n ( n ≥ 4) valence electron counts are rare and particularly unstable due to a bonding situation akin to the well-known “the oxo-wall dilemma” .…”

Tridentate NNN Ligand Associating Amidoquinoline and Iminophosphorane: Synthesis and Coordination to Pd and Ni Centers

“…The Ni1-C3 distance at 1.895 Å is comparable to that measured by van der Vlugt and coworkers on the only other example found in the CCDC database of a nickel-Ph complex with a pincer NNP ligand obtained via the photochemical CH activation of benzene by nitrido Ni complex. 23 The length of the P-N bond at 1.663(2) Å, is in the range of those measured for aminodiphenylphosphino nickel complexes (1.69 Å on average). This change in the nature of the phosphorous function induces also a slight elongation of the bonds within the aminoacetamide segment.…”