A series of Ni-based electrocatalysts, [Ni(7P(Ph)2N(C6H4X))2](BF4)2, featuring seven-membered cyclic diphosphine ligands incorporating a single amine base, 1-para-X-phenyl-3,6-triphenyl-1-aza-3,6-diphosphacycloheptane (7P(Ph)2N(C6H4X), where X = OMe, Me, Br, Cl, or CF3), have been synthesized and characterized. X-ray diffraction studies have established that the [Ni(7P(Ph)2N(C6H4X))2](2+) complexes have a square planar geometry, with bonds to four phosphorus atoms of the two bidentate diphosphine ligands. Each of the complexes is an efficient electrocatalyst for hydrogen production at the potential of the Ni(II/I) couple, with turnover frequencies ranging from 2400 to 27,000 s(-1) with [(DMF)H](+) in acetonitrile. Addition of water (up to 1.0 M) accelerates the catalysis, giving turnover frequencies ranging from 4100 to 96,000 s(-1). Computational studies carried out on the [Ni(7P(Ph)2N(C6H4X))2](2+) family indicate the catalytic rates reach a maximum when the electron-donating character of X results in the pKa of the Ni(I) protonated pendant amine matching that of the acid used for proton delivery. Additionally, the fast catalytic rates for hydrogen production by the [Ni(7P(Ph)2N(C6H4X))2](2+) family relative to the analogous [Ni(P(Ph)2N(C6H4X)2)2](2+) family are attributed to preferred formation of endo protonated isomers with respect to the metal center in the former, which is essential to attain suitable proximity to the reduced metal center to generate H2. The results of this work highlight the importance of precise pKa matching with the acid for proton delivery to obtain optimal rates of catalysis.

En route to catalysis: Two equivalents of the three‐coordinate copper(II) amide [(Cl2NN)Cu]‐NHAd participate in stoichiometric CH amination by a H‐atom abstraction/radical capture sequence. This active species may be generated through a copper(II) tert‐butoxide intermediate to allow for the unprecedented catalytic amination of sp3‐CH bonds with unactivated alkylamines. This method greatly expands the range of amines for catalytic CH amination since most protocols require N‐based electron‐withdrawing groups.

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A nickel(II) bis(diphosphine) complex, [Ni(PMe 2NPh 2)2](BF4)2 (PMe 2NPh 2 = 1,5-diphenyl-3,7-dimethyl-1,5-diaza-3,7-diphosphacyclooctane), has been synthesized and characterized. This complex, which contains pendant amines in the diphosphine ligand, is an electrocatalyst for hydrogen production by proton reduction. Using [(DMF)H]OTf as the acid, a turnover frequency of 1,540 s–1 was obtained with no added water, and a turnover frequency of 6,700 s–1 was found with 1.0 M water added. Thermochemical studies show that the hydride donor ability of [HNi(PMe 2NPh 2)2](BF4) is ΔG°H– = 54.0 kcal/mol, and we estimate a driving force for H2 elimination of 13.8 kcal/mol. [Ni(PMe 2NPh 2)2](BF4)2 is the fastest H2 production catalyst in the [Ni(PR 2NR′ 2)2](BF4)2 family of complexes.

A Ni-based electrocatalyst for H 2 production, [Ni(8P Ph 2 N C 6 H 4 Br ) 2 ](BF 4 ) 2 , featuring eight-membered cyclic diphosphine ligands incorporating a single amine base, 1-parabromophenyl-3,7-triphenyl-1-aza-3,7-diphosphacycloheptane (8P Ph 2 N C 6 H 4 Br ) has been synthesized and characterized. X-ray diffraction studies reveal that the cation of [Ni-(8P Ph 2 N C 6 H 4 Br ) 2 (CH 3 CN)](BF 4 ) 2 has a distorted trigonal bipyramidal geometry. In CH 3 CN, [Ni(8P Ph 2 N C 6 H 4 Br ) 2 ] 2+ is an electrocatalyst for reduction of protons, and it has a maximum turnover frequency for H 2 production of 800 s −1 with a 700 mV overpotential (at E cat/2 ) when using [(DMF)H]OTf as the acid. Addition of H 2 O to acidic CH 3 CN solutions of [Ni(8P Ph 2 N C 6 H 4 Br ) 2 ] 2+ results in an increase in the turnover frequency for H 2 production to a maximum of 3300 s −1 with an overpotential of 760 mV at E cat/2 . Computational studies carried out on [Ni(8P Ph 2 N C 6 H 4 Br ) 2 ] 2+ indicate the observed catalytic rate is limited by formation of nonproductive protonated isomers, diverting active catalyst from the catalytic cycle. The results of this research show that proton delivery from the exogenous acid to the correct position on the proton relay of the metal complex is essential for fast H 2 production.

Monovalent nickel and copper beta-diketiminato complexes react with ArN=O (Ar = 3,5-Me(2)C(6)H(3), Ph) to give C-nitroso adducts that exhibit three different modes of bonding with varying degrees of N-O bond activation. The addition of ArNO to 2 equiv of [Me(2)NN]Ni(2,4-lutidine) {[Me(2)NN](-) = 2,4-bis(2,6-dimethylphenylimido)pentyl} gives {[Me(2)NN]Ni}(2)(mu-eta(2):eta(2)-ONAr) (1a and 1b), which exhibit symmetrical bonding of the ArN=O moiety between two [Me(2)NN]Ni fragments, with a N-O bond distance of 1.440(4) A in 1a that is significantly longer than those in free C-organonitroso compounds (1.13-1.29 A). [Me(2)NN]Cu(NCMe) reacts with 0.5 equiv of ArNO in ether to give the dinuclear adducts {[Me(2)NN]Cu}(2)(mu-eta(2):eta(1)-ONAr) (2a and 2b), which exhibit eta(2) and eta(1) bonding of the ArN=O moiety with separate [Me(2)NN]Cu fragments possessing N-O distances of 1.375(6) A (2a) and 1.368(2) A (2b). In arene solvents, one beta-diketiminatocopper(I) fragment dissociates from 2 to give [Me(2)NN]Cu(eta(2)-ONAr) (3a and 3b), which may be isolated by the addition of 1 equiv of ArNO to [Me(2)NN]Cu(NCMe). The X-ray structures of 3a and 3b are similar to those of related Cu(I) alkene adducts, with N-O distances in the narrow range 1.333(4)-1.338(5) A. IR spectra of the nitrosobenzene adducts 1b, 2b, and 3b exhibit nu(NO) stretching frequencies at 915, 1040, and 1113 cm(-1), respectively, following the decreasing degree of N=O activation observed in the X-ray structures of species 1, 2, and 3. Both 1a and 3a react with anaerobic NO(g) to give the corresponding N-aryl-N-nitrosohydroxylaminato complexes [Me(2)NN]M(kappa(2)-O(2)N(2)Ar) [M = Ni (4), Cu (5)]. In the reaction of dinuclear 1a with NO, one [Me(2)NN]Ni fragment is trapped as the nickel nitrosyl [Me(2)NN]Ni(NO). Reaction of the monovalent complex [Me(2)NN]Cu(eta(2)-ONAr) with NO(g) to give divalent [Me(2)NN]Cu(kappa(2)-O(2)N(2)Ar) represents an example of oxidative nitrosylation.

Auf dem Weg zur Katalyse: Zwei Äquivalente des Kupfer(II)‐amids [(Cl2NN)]Cu‐NHAd nehmen über eine Sequenz aus H‐Abstraktion und Radikaleinfang an stöchiometrischen C‐H‐Aminierungen teil (siehe Schema). Diese aktive Spezies entsteht vermutlich über ein Kupfer(II)‐tert‐butoxid‐Zwischenprodukt und sorgt für eine beispiellose katalytische Aktivierung von sp3‐C‐H‐Bindungen mit nichtaktivierten Alkylaminen. Die Methode erweitert enorm die Bandbreite von Aminen für katalytische C‐H‐Aminierungen, da die meisten bisherigen Protokolle elektronenziehende N‐Substituenten erfordern.

The β-diketiminato nickel(I) species [Me 3 NN]Ni(2-picoline) (1) serves as an efficient catalyst for carbodiimide (RNCNR′) formation in the reactions of a range of organoazides N 3 R with isocyanides R′NC. [Me 3 NN]-Ni(CNR) 2 (R = t Bu, Ar (Ar = 2,6-Me 2 C 6 H 3 )) species provide carbodiimides RNCNAr′ upon reaction with Ar′N 3 (Ar′ = 3,5-Me 2 C 6 H 3 ). Nitrene transfer takes place via the intermediacy of nickel imides. Reaction of [Me x NN]Ni(2-picoline) (x = 2 or 3) with Ar′N 3 gives the new dinickel imides {[Me x NN]Ni} 2 (μ-NAr′) (4 (x = 3) and 5 (x = 2)) as deep purple, diamagnetic substances. The X-ray structure of {[Me 2 NN]Ni} 2 (μ-NAr′) (5) features short Ni−N imide distances of 1.747(2) and 1.755(2) Å along with a short Ni−Ni distance of 2.7210(3) Å. These dinickel imides 4 and 5 react stoichiometrically with t BuNC to provide the corresponding carbodiimides t BuNCNAr′ in good yield. Azide transfer takes place upon reaction of 1 with TMS-N 3 to give the square planar nickel(II) azide [Me 3 NN]Ni(N 3 )(2-picoline) (7). Stoichiometric reaction of dinickel dicarbonyl {[Me 3 NN]Ni} 2 (μ-CO) 2 with organoazides such as Ar′N 3 is sluggish, indicating that 1 is not an efficient catalyst for nitrene transfer from organoazides to CO to form isocyanates RNCO.