Detailed kinetic studies of the reaction of a model Ni 0 complex with a range of aryl electrophiles have been conducted. The reactions proceed via a fast ligand exchange preequilibrium, followed by oxidative addition to produce either [Ni I X(dppf)] (and biaryl) or [Ni II (Ar)X(dppf)]; the ortho substituent of the aryl halide determines selectivity between these possibilities. A reactivity scale is presented in which a range of substrates is quantitatively ranked in order of the rate at which they undergo oxidative addition. The rate of oxidative addition is loosely correlated to conversion in prototypical cross-coupling reactions. Substrates that lead to Ni I products in kinetic experiments produce more homocoupling products under catalytic conditions.

A new class of phosphorescent tris-heteroleptic iridium(III) complexes has been discovered. The addition of PhMeImAgI (PhMeIm = 1-phenyl-3-methylimidazolylidene) to the dimer [Ir(μ-Cl)(COD)] (1; COD = 1,5-cyclooctadiene) affords IrCl(COD)(PhMeIm) (2), which reacts with 1-phenylisoquinoline, 2-phenylpyridine, and 2-(2,4-difluorophenyl)pyridine to give the respective dimers [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}] (3), [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CH-py)}] (4), and [Ir(μ-Cl){κ- C, C-(CH-ImMe)}{κ- C, N-(CFH-py)}] (5), as a result of the N-heterocyclic carbene (NHC)- and N-heterocycle-supported o-CH bond activation of the aryl substituents and the hydrogenation of a C-C double bond of the coordinated diene. In solution, these dimers exist as a mixture of isomers a (Im trans to N) and b (Im trans to Cl), which lie in a dynamic equilibrium. The treatment of 3-5 with Kacac (acac = acetylacetonate) yields isomers a (Im trans to N) and b (Im trans to O) of Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}(κ- O, O-acac) (6a and 6b), Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-py)}(κ- O, O-acac) (7a and 7b), and Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CFH-py)}(κ- O, O-acac) (8a and 8b), which were separated by column chromatography. The treatment of 6a with HX in acetone-water produces the protonation of the acac ligand and the formation of the bis(aquo) complex [Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}(HO)]X [X = BF (9a[BF]), OTf (9a[OTf])]. The salt 9a[BF] reacts with 2-(2-pinacolborylphenyl)-5-methylpyridine in the presence of 40 equiv of KPO to afford Ir{κ- C, C-(CH-ImMe)}{κ- C, N-(CH-isoqui)}{κ- C, N-(CH-Mepy)} (10a). Complexes 6a, 6b, 7a, 7b, 8a, 8b, and 10a are phosphorescent emitters (λ = 465-655 nm), which display short lifetimes in the range of 0.2-5.6 μs. They show high quantum yields both in doped poly(methyl methacrylate) films (0.34-0.87) and in 2-methyltetrahydrofuran at room temperature (0.40-0.93). From the point of view of their applicability to the fabrication of organic-light-emitting-diode devices, a notable improvement with regard to those containing two cyclometalated C,N ligands is achieved. The introduction of the cyclometalated aryl-NHC group allows one to reach a brightness of 1000 cd/m at a lower voltage and appears to give rise to higher luminous efficacy and power efficacy.

Aldehydes and ketones can have beneficial or detrimental effects on nickel-catalysed reactions. When present on the aryl halide, excellent site-selectivity can be achieved; when present as additives, they inhibit the reaction.