A novel [Mg2(μ-Cl)2](2+) cation complex, which is highly active for reversible Mg electrodeposition, was identified for the first time in this work. This complex was found to be present in electrolytes formulated in dimethoxyethane (DME) through dehalodimerization of non-nucleophilic MgCl2 by reacting with either Mg salts (such as Mg(TFSI)2, TFSI = bis(trifluoromethane)sulfonylimide) or Lewis acid salts (such as AlEtCl2 or AlCl3). The molecular structure of the cation complex was characterized by single crystal X-ray diffraction, Raman spectroscopy and NMR. The electrolyte synthesis process was studied and rational approaches for formulating highly active electrolytes were proposed. Through control of the anions, electrolytes with an efficiency close to 100%, a wide electrochemical window (up to 3.5 V) and a high ionic conductivity (>6 mS cm(-1)) were obtained. The understanding of electrolyte synthesis in DME developed in this work could bring significant opportunities for the rational formulation of electrolytes of the general formula [Mg2(μ-Cl)2][anion]x for practical Mg batteries.

A critically important process in catalysis is the formation of an active catalyst from the combination of a metal precursor and a ligand, as the efficacy of this reaction governs the amount of active catalyst. This Review is a comprehensive overview of reactions catalyzed by nickel and an added bidentate phosphine, focusing on the steps transforming the combination of precatalyst and ligand into an active catalyst and the potential effects of this transformation on nickel catalysis. Reactions covered include common cross-coupling reactions, such as Suzuki, Heck, Kumada, and Negishi couplings, addition reactions, cycloadditions, C−H functionalizations, polymerizations, hydrogenations, and reductive couplings, among others. Overall, the most widely used nickel precatalyst with free bidentate phosphines is Ni(cod) 2 , which accounts for ∼50% of the reports surveyed, distantly followed by Ni(acac) 2 and Ni(OAc) 2 , which account for ∼10% each. By compiling the reports of these reactions, we have calculated statistics of the usage and efficacy of each ligand with Ni(cod) 2 and other nickel sources. The most common bidentate phosphines are simple, relatively inexpensive ligands, such as DPPE, DCPE, DPPP, and DPPB, along with others with more complex backbones, such as DPPF and Xantphos. The use of expensive chiral phosphines is more scattered, but the most common ligands include BINAP, Me-Duphos, Josiphos, and related analogs.

We report solvent and electrolyte effects on the electrocatalytic oxidation of H2 using Ni(P(Cy)2N(R')2)2 (R = Bn, (t)Bu) complexes. A turnover frequency of 46 s(-1) for Ni(P(Cy)2N(Bn)2)2 was obtained using 0.2 M [(n)Bu4N][BF4] in THF. A turnover frequency of 51 s(-1) was observed for Ni(P(Cy)2N(tBu)2)2 using 0.2 M [(n)Bu4N][B(C6F5)4] in fluorobenzene. These observations, in conjunction with previous studies, indicate nitrile binding inhibits catalysis supported by Ni(P(Cy)2N(Bn)2)2.

A comprehensive study of the reactions of chelating phosphines with Ni(cod) 2 to form (phosphine)Ni(cod), (phosphine) 2 Ni, or mixtures thereof is presented. A series of (phosphine)Ni(cod) complexes were isolated and characterized. The structural differences between the (phosphine)Ni(cod) and (phosphine) 2 Ni complexes were examined using Xray crystallography and 1 H and 31 P NMR spectroscopy. In addition, the effects of ring size, rigidity, and bulk of the phosphine backbone on the formation of either (phosphine)Ni(cod) or (phosphine) 2 Ni were investigated. These studies show that the Ni−P bond lengths in both the (phosphine)-Ni(cod) and (phosphine) 2 Ni complexes and the size of the ring formed by the chelating phosphine and Ni are crucial in determining whether or not (phosphine)Ni(cod) complexes can be isolated. Other factors such as π-stacking interactions were found to have marginal influence.

A variety of bicyclic N,N-disubstituted 2-aminopyridines have been prepared from diynes and cyanamides by nickel-catalyzed [2+2+2] cycloaddition reactions. The reactions proceeded at room temperature with low catalyst loading to afford 2-aminopyridines in good to excellent yields. The method is amenable to both internal and terminal diynes and proceeds in a regioselective manner. A number of cyanamides with diverse functional group tolerance were used. The intermolecular version employing 3-hexyne and N-cyanopyrrolidine also afforded the desired N,N-disubstituted 2-aminopyridine in good yield.

A general synthetic route to the first Xantphos nickel alkyne and alkene complexes has been discovered. Various Ni complexes were prepared and characterized. NMR experiments indicate benzonitrile undergoes ligand exchange with a Xantphos ligand of (Xant)2Ni, a compound that was previously believed to be unreactive. The Ni π-complexes were also shown to be catalytically competent in cross coupling and cycloaddition reactions. (Xant)2Ni is also catalytically active for these reactions when activated by a nitrile or coordinating solvent.

The reaction of Ni(COD)2, IPr, and nitrile affords dimeric [Ni(IPr)RCN]2 in high yields. X-ray analysis revealed these species display simultaneous η1- and η2-nitrile binding modes. These dimers are catalytically competent in the formation of pyridines from the cycloaddition of diynes and nitriles. Kinetic analysis showed the reaction to be first order in [Ni(IPr)RCN]2, zeroth order in added IPr, zeroth order in nitrile, and zeroth order in diyne. Extensive stoichiometric competition studies were performed, and selective incorporation of the exogenous, not dimer bound, nitrile was observed. Post cycloaddition, the dimeric state was found to be largely preserved. Nitrile and ligand exchange experiments were performed and found to be inoperative in the catalytic cycle. These observations suggest a mechanism whereby the catalyst is activated by partial dimer-opening followed by binding of exogenous nitrile and subsequent oxidative heterocoupling.

A detailed mechanistic evaluation of the Ni(IPr)2-catalyzed [2+2+2]-cycloaddition of diynes and nitriles was 2 conducted. Through kinetic analysis of these reactions, observed regioselectivities of the products, and stoichiometric reactions, Ni(IPr)2-catalyzed cycloadditions of diynes and nitriles appear to proceed by a heterooxidative coupling mechanism, contrary to other common cycloaddition catalysts. Reaction profiles demonstrated strong dependence in nitrile, resulting in variable nitrile-dependent resting states. Strong coordination and considerable steric bulk of the carbene ligands facilitate selective initial binding of nitrile thereby forcing a heterocoupling pathway. In situ IR data suggests the initial binding of the nitrile resides in a rare, η1-bound conformation. Following nitrile coordination are a rate-determining hapticity shift of the nitrile and subsequent loss of carbene. Alkyne coordination then leads to heterooxidative coupling, insertion of the pendant alkyne, and reductive elimination to afford pyridine products.