An N for Ir: The synthesis and X-ray crystal structure of a late-transition-metal complex with a terminal nitrido ligand and its hydrogenation to the related amido complex are reported (see scheme).

[Ni(P(R)(2)N(R')(2))(2)(CH(3)CN)](2+) complexes with R = Ph, R' = 4-MeOPh or R = Cy, R' = Ph , and a mixed-ligand [Ni(P(R)(2)N(R')(2))(P(R''(2))N(R'(2)))(CH(3)CN)](2+) with R = Cy, R' = Ph, R'' = Ph, have been synthesized and characterized by single-crystal X-ray crystallography. These and previously reported complexes are shown to be electrocatalysts for the oxidation of formate in solution to produce CO(2), protons, and electrons, with rates that are first-order in catalyst and formate at formate concentrations below ∼0.04 M (34 equiv). At concentrations above ∼0.06 M formate (52 equiv), catalytic rates become nearly independent of formate concentration. For the catalysts studied, maximum observed turnover frequencies vary from <1.1 to 15.8 s(-1) at room temperature, which are the highest rates yet reported for formate oxidation by homogeneous catalysts. These catalysts are the only base-metal electrocatalysts as well as the only homogeneous electrocatalysts reported to date for the oxidation of formate. An acetate complex demonstrating an η(1)-OC(O)CH(3) binding mode to nickel has also been synthesized and characterized by single-crystal X-ray crystallography. Based on this structure and the electrochemical and spectroscopic data, a mechanistic scheme for electrocatalytic formate oxidation is proposed which involves formate binding followed by a rate-limiting proton and two-electron transfer step accompanied by CO(2) liberation. The pendant amines have been demonstrated to be essential for electrocatalysis, as no activity toward formate oxidation was observed for the similar [Ni(depe)(2)](2+) (depe = 1,2-bis(diethylphosphino)ethane) complex.

The stability of (pyridinediimine)rhodium– and ‐iridium–azido complexes was studied by a combination of thermoanalytical methods (DTG/MS and DSC) and DFT calculations. On a preparative scale, the isolation and X‐ray crystallographic characterization of the thermolysis products confirmed intramolecular C–H activation processes with concomitant reorganisation of C–C, C–N, N–H and Ir–N bonds to yield tuck‐in complexes with a different constitution of the ligand framework for the Rh and Ir products. The tentatively formed (Rh) or initially present (Ir) nitrido unit was converted into either an amine (Rh) or amido (Ir) moiety. Furthermore, the dimerization of the nitrido complexes to the corresponding dinitrogen compounds, i.e. 2 LnM≡N → LnM–N2–MLn, was investigated. Experimental evidence for the relevance of this step was provided by the isolation and X‐ray crystallographic characterization of a related dinuclear N2‐bridged (pyridinediimine)dirhodium complex. DFT calculations revealed that the formation of dinitrogen complexes is thermodynamically strongly favourable and evidenced that the previous isolation of a terminal iridium–nitrido complex was possible due to a high barrier for the dimerization process and a sizeable barrier for the intramolecular C–H activation step.

Keywords: Charge transfer / NMR spectroscopy / Density functional calculations / Rhodium / IridiumOur recent results of the chemistry of group 9 Rh and Ir metal complexes bearing the ubiquitous pyridine, diimine (PDI) terdentate nitrogen donor are reviewed. Examples reflecting the special nature of the PDI ligand include a facile C-H activation process and the stabilization of a very rare late transition metal iridium nitrido compound, (PDI)IrϵN, and its direct hydrogenation to the corresponding amido complex according to (PDI)IrϵN + H 2 Ǟ (PDI)Ir-NH 2 . The amount of electron transfer to the PDI ligands in (PDI)Rh,Ir-R,X com-

Intramolecular activation processes of vulnerable ligand C-H bonds frequently limit the thermal stability and accessibility of late transition metal complexes with terminal metal nitrido units. In this study chloro substitution of the 2,6-ketimine N-aryl substituents (2,6-C(6)H(3)R(2), R = Cl) of the pyridine, diimine ligand is probed to increase the stability of square-planar iridium nitrido compounds. The thermal stability of iridium azido precursor and nitrido compounds was studied by a combination of thermoanalytical methods (DTG/MS and DSC) and were compared to the results for the related complexes with 2,6-dialkyl substituted N-aryl groups (R = Me, iPr). The investigations were complemented by DFT calculations, which allowed us to unravel details of the thermal decomposition pathways and provided mechanistic insights of further conversion steps and fluctional processes. The DTG/MS and DSC measurements revealed two different types of thermolysis pathways for the azido compounds. For the complexes with R = Cl and iPr substituents, two well-separated exothermic processes were observed. The first moderately exothermic loss of N(2) is followed by a second, strongly exothermic transformation. This contrasts the experimental results for the compound with 2,6-dimethyl substituents (R = Me), where both steps proceed concurrently in the same temperature range. The separation of the two thermal steps in the 2,6-dichloro substituted derivative allowed us to develop a protocol for the isolation of the highly insoluble nitrido complex, which was characterized by UV/vis, IR-spectroscopy and elemental analysis. Its constitution was further confirmed by reaction with silanes, which gave the corresponding silyl amido complexes.