Organometallic iridium complexes have been reported as water oxidation catalysts (WOCs) in the presence of ceric ammonium nitrate (CAN). One challenge for all WOCs regardless of the metal used is stability. Here we provide evidence for extensive modification of many Ir-based WOCs even after exposure to only 5 or 15 equiv of Ce(IV) (whereas typically 100-10000 equiv are employed during WOC testing). We also show formation of Ir-rich nanoparticles (likely IrO(x)) even in the first 20 min of reaction, associated with a Ce matrix. A combination of UV-vis and NMR spectroscopy, scanning transmission electron microscopy, and powder X-ray diffraction is used. Even simple IrCl(3) is an excellent catalyst. Our results point to the pitfalls of studying Ir WOCs using CAN.

A combined experimental and mechanistic study of the chemoselective hydroboration of carbonyls by the paramagnetic bis-amido Mn­[SMeNSMe]2 complex (1) is described. The catalyst allows for room-temperature hydroboration of carbonyls at low catalyst loadings (0.1 mol %) and reaction times (<30 min). A series of mechanistic studies highlight the significance of bifunctional amido bis­(thioether) ligand L to the success of the reaction, insight otherwise difficult to attain in paramagnetic systems. Kinetic studies using variable time normalization analysis revealed no unusual reaction kinetics, indicating the absence of side reactions. A borylated analogue of L was observed and characterized via mass spectrometry. Density functional theory (DFT) calculations showed that thioether hemilability of L is crucial during catalysis for providing the active coordinating site. Also, the frequently proposed Mn–H intermediate was found not to be the active species responsible for catalysis. Instead, an inner-sphere reaction pathway with carbonyl coordination to the metal center and amido-promoted B–H reactivity is proposed to be operative.

Nickel coordination chemistry with a biomimetic thiolate-imine-thioether SNSMe ligand is accompanied by diverse reactivity and multidentate ligand dynamics. Reaction of Ni­(acac)2 with 2 equiv of 2-(methylthio)-phenyl-benzothiazolidine (MPB) affords the bis­(arylimino-phenylene-thiolate) complex Ni­(κ2-SNSMe)2 (1; acac = acetylacetonate). Thermolysis of 1 in refluxing toluene is accompanied by imine C–C bond formation, yielding [Ni­(N2S2)] (2) with a redox-active ligand. Protonation of 1 with NHTf2 at a low temperature released 1 equiv of MPB, yielding crystals of the dimeric dication {[Ni­(μ-κ3-SNSMe)]2}­(NTf2)2 (3; Tf = SO2CF3) in high yield. In contrast, the same reaction at room temperature gave also paramagnetic complexes {Ni­[μ-Ni­(κ3-SNSMe)2]2}­(NTf2)2 (4) and {Ni­[μ-Ni­(κ3-SNSMe)2]3}­(NTf2)2 (5) that feature coordination of two or three pseudo-octahedral, paramagnetic Ni­(κ3-SNSMe)2 units to a central Ni­(II) dication via thiolate bridges. Remarkably, dissolution of 3 in a variety of solvents, including weakly coordinating CH2Cl2, rapidly generates a mixture of 4 and Ni­(NTf)2. Treatment of this mixture with Lewis bases L gave high yields of dimers {[Ni­(μ-κ3-SNSMe)­L]2}­(NTf2)2 for L = CNXylyl (6a) and {[Ni­(μ-κ3-SNSMe)]2(μ-dmpm)}­(NTf2)2 (6b; dmpm = bis­(dimethylphosphino)­methane) or monomers [Ni­(κ3-SNSMe)­L]­(NTf2) for L = PMe3 (7a) and P­(OMe)3 (7b). Addition of 2 equiv of the strong donor N-heterocyclic carbene ligand, IPr, to 3, however, led to thioether demethylation, affording neutral dithiolate complex Ni­(κ3-SNS)­(IPr) (8). Reaction products were characterized by NMR and mass spectrometry and complexes 1–5, 6a, 6b, 7a, and 8 by single-crystal X-ray diffraction.

Protic NHC (PNHC) complexes with N 1 H, N 2 -alkyl/aryl imidazolylidene ligands are relatively rare, and routes for their synthesis differ from what is used to make non-protic analogs. Prior work from our group and others showed that in the presence of a tethering ligand (phosphine or in one case, pyridine), CpM and Cp*M (M = Ir, Ru) PNHC complexes could be made by heating. Here, we find that the use of ionizing agents to activate [Cp*M III Cl(µ-Cl)] 2 (M = Ir, Rh) allows for what we believe is unprecedented ambient temperature formation of PNHC complexes from neutral imidazoles; the product complexes are able to perform transfer hydrogenation.