Breath‐taking activation: Stereoregular carbene polymerization proceeds via cationic [(allyl)RhIII–polymeryl]+ species. These are most efficiently generated by oxygenation of the [(diene)RhI] precatalysts, which involves an unusual rearrangement of 2‐rhodaoxetane intermediates. This discovery gives detailed insight in the reaction mechanism.

Treatment of bis(2-picolyl)amine (bpa) with [{Rh(nbd)(mu-OMe)}2] leads to the unexpected and unique redox asymmetric dinuclear Rh-I,Rh+I complex [{Rh(nbd)}2(bpa-2H)] (2) with a pi-coordinating imine bound to a tetrahedral low valent rhodate(-I). Mono-oxygenation of the deprotonated bpa ligand in 2 by O2 leads to the mononuclear carboxamido complex [Rh(nbd)(bpam-H)] (3) (bpam = N-(2-picolyl)picolinamide). The second O atom of O2 ends up as a hydroxo fragment in [{Rh(nbd)(mu-OH)}2].

Replacement of the olefin in the complexes [{Rh(μ-RPz)(C2H4)2}2] (RPz = pyrazolate (Pz) (1), 3-methylpyrazolate (MePz) (2), 3,5-dimethylpyrazolate (Me2Pz) (3)) by tert-butyl isocyanide gives [{Rh(μ-RPz)(CNBut)2}2] (4, 5, 6) respectively. Complex 4 can alternatively be prepared from [{Rh(μ-Pz)(cod)}2] (cod = 1,5-cyclooctadiene) (7) leading to a chemical equilibrium between 4, 7, and the intermediate [(cod)Rh(μ-Pz)2Rh(CNBut)2] (8), which has been also isolated. Kinetic studies on this apparent ligand redistribution reaction, leading to 8, show that it follows a second order rate, giving the activation parameters ΔH ≠ = 21.8 kcal·mol-1, ΔS≠ = −7.4 eu, and ΔG ≠298 = 24.0 kcal·mol-1, suggesting that the dinuclear complexes are the active species, and no fragmentation seems to occur. The molecular structures of complexes 3, 4, 8, and [{Rh(μ-Pz)(CO)2}2] (9) determined by X-ray diffraction show discrete dinuclear complexes with the six-membered “Rh(μ-Pz)2Rh” ring showing a boatlike conformation. Complexes 3 and 4 present the shortest and the largest intermetallic nonbonding separations, 3.0961(2) and 3.8995(6) Å, respectively, so far reported in di-μ-pyrazolato-dirhodium(I) complexes. In addition, complex 3 shows the shortest olefinic CC distance found in ethylene rhodium complexes and accordingly a very low activation energy, 10.0 kcal·mol-1, for the rotation of the ethylene ligands. Complex 8 undergoes two independent intramolecular fluxional processes associated to the ring inversion of the six-membered “Rh(μ-Pz)2Rh” metallacycle and to a σ-1,2-metallotropic shift showing activation parameters ΔH ≠ = 15.0 kcal·mol-1, ΔS ≠ = −1.7 eu and ΔH ≠ = 19.7 kcal·mol-1, ΔS ≠ = 4.8 eu, respectively. The first movement is influenced by medium effects and may be restricted by the ancillary ligands and the substituents on the pyrazolate rings in other bis(μ-pyrazolato) complexes. Finally, the intermetallic distance in dinuclear pyrazolato complexes is analyzed in terms of steric and electronic factors.

Abstract:The binuclear iridium complex [(cod)(Cl)Ir(bpi)Ir(cod)]PF 6 (bpi = pyridine-2-ylmethylpyridine-2-ylmethyleneamine; cod = 1,5-cyclooctadiene) reveals a noteworthy asymmetric binuclear coordination geometry, wherein the bpi ligand acts as a heteroditopic ligand and shows an unusual -coordinated imine moiety. This species is an effective precatalyst for water oxidation. After a short incubation time the catalyst reveals a turnover frequency of 3400 mol mol 1 s 1 with overall turnover number >1000.

Complexes with terminal phosphanido (MÀPR 2 ) functionalities are believed to be crucial intermediates in new catalytic processes involving the formation of PÀP and PÀC bonds. We showcase here the isolation and characterization of mononuclear phosphanide rhodium complexes ([RhTp(H)-(PR 2 )L]) that result from the oxidative addition of secondary phosphanes, a reaction that was also explored computationally. These compounds are active catalysts for the dehydrocoupling of PHPh 2 to Ph 2 PÀPPh 2 . The hydrophosphination of dimethyl maleate and the unactivated olefin ethylene is also reported. Reliable evidence for the prominent role of mononuclear phosphanido rhodium species in these reactions is also provided.

Treatment of [Ir(bpa)(cod)](+) complex [1](+) with a strong base (e.g., tBuO(-)) led to unexpected double deprotonation to form the anionic [Ir(bpa-2H)(cod)](-) species [3](-), via the mono-deprotonated neutral amido complex [Ir(bpa-H)(cod)] as an isolable intermediate. A certain degree of aromaticity of the obtained metal-chelate ring may explain the favourable double deprotonation. The rhodium analogue [4](-) was prepared in situ. The new species [M(bpa-2H)(cod)](-) (M = Rh, Ir) are best described as two-electron reduced analogues of the cationic imine complexes [M(I)(cod)(Py-CH(2)-N=CH-Py)](+). One-electron oxidation of [3](-) and [4](-) produced the ligand radical complexes [3](*) and [4](*). Oxygenation of [3](-) with O(2) gave the neutral carboxamido complex [Ir(cod)(py-CH(2)-N-CO-py)] via the ligand radical complex [3](*) as a detectable intermediate.

A novel coordination mode of the hydroperoxido ligand in which each oxygen atom is bonded to a distinct metal center is present in a rare thermally stable example of this otherwise elusive family of complexes, which was obtained by protonating a bis‐peroxido‐bridged Rh2 complex. The OOH ligand is displaced by a chloride ion to give the corresponding chlorido‐bridged complex (see scheme, L3=tris(methylenediphenylphosphane)phenylborate).

Here we showcase the synthesis and catalytic response of the anionic iridium(III) complex [IrCl 3 (pic)(MeOH)] − ([1] − , pic = picolinate) toward the evolution of oxygen. Online electrochemical mass spectrometry experiments illustrate that an initial burst of CO 2 due to catalyst degradation is expelled before the oxygen evolution reaction commences. Electrochemical features and XPS analysis illustrate the presence of iridium oxide, which is the true active species.