A Novel Cyclometalated Dimeric Iridium Complex, [(dfpbo)2Ir]2 [dfpbo = 2-(3,5-Difluorophenyl)benzoxazolato-N,C2′], Containing an Unsupported IrII−IrII Bond

Ligand effect of cyclometallated iridium(iii) complexes on N-alkylation of amines in hydrogen borrowing reactions

Dinuclear iridium complexes with the general formula (C^N)2Ir(μ-Cl)2Ir(C^N)2 (C^N = bidentate ligand with carbon and nitrogen donor atoms) were prepared and used in catalytic systems for N-alkylation of amines through the hydrogen borrowing pathway. Triphenylphosphine derivatives were used as auxiliary in catalytic systems to provide excellent conversion of amines to N-alkylation products in yields ranging from 57% to 100%. The catalytic ability of the catalyst depends on the structure of its coordination ligands, including bidentate ligands (C^N) and triphenylphosphine derivatives. These catalytic systems adopt an environmentally friendly and sustainable reaction process through a hydrogen self-transfer strategy, using readily available alcohols as alkylating agents without the need for bases, solvents, and other additives, showing potential in the synthetic and pharmaceutical industries.

Structure-property relationships of photofunctional diiridium(II) complexes with tetracationic charge and an unsupported Ir-Ir bond

In contrast to the extensively studied dirhodium(II) complexes and iridium(III) complexes, neutral or dicationic dinuclear iridium(II) complexes with an unsupported ligand are underdeveloped. Here, a series of tetracationic dinuclear iridium(II) complexes, featuring the unsupported Ir(II)-Ir(II) single bond with long bond distances (2.8942(4)-2.9731(4) Å), are synthesized and structurally characterized. Interestingly, compared to the previous unsupported neutral or dicationic diiridium(II) complexes, our DFT and high-level DLPNO-CCSD(T) results found the largest binding energy in these tetracationic complexes even with the long Ir(II)-Ir(II) bond. Our study further reveals that London dispersion interactions enhance the stability cooperatively and significantly to overcome the strong electrostatic repulsion between two half dicationic metal fragments. This class of complexes also exhibit photoluminescence in solution and solid states, which, to our knowledge, represents the first example of this unsupported dinuclear iridium(II) system. In addition, their photoreactivity involving the generation of iridium(II) radical monomer from homolytic cleavage was also explored. The experimental results of photophysical and photochemical behaviours were also correlated with computational studies.

Metal/Ligand Proton Tautomerism Facilitates Dinuclear H2 Reductive Elimination

Using the doubly protic bis-pyrazole-pyridine ligand (N(NN^H)₂), we have synthesized an octahedral Ir^III-H [HIr(κ³-N(NN^H)(NN^-))(CO)(^tBuPy)]⁺ ([1-MH]⁺) from an Ir^I starting material. This hydride was generated by adding sufficient electron density to the metal center such that it became the thermodynamically preferred site of protonation. It was observed via UV-vis spectroscopy that [1-MH]⁺ establishes a [^tBuPy] dependent equilibrium with a ligand protonated square-planar Ir^I [Ir(N(NN^H)₂)(CO)]⁺ ([2-LH]⁺). This example of metal/ligand proton tautomerism is unusual in that the position of the equilibrium can be controlled by the concentration of exogeneous ligand (i.e., ^tBuPy). This equilibrium was shown to be key to the reactivity of the Ir^III-H; 2 equiv of [1-MH]⁺ release H₂, converting to the Ir^II dimer [[Ir(N(NN^-)(NN^H))(CO)(^tBuPy)]₂]²⁺ ([7]²⁺) under mild conditions (observable at room temperature). Mechanistic evidence is presented to support that this dinuclear reductive elimination occurs by tautomerization of the metal hydride [1-MH]⁺ to a ligand protonated species [1-LH]⁺, from which ligand dissociation is facile, generating [2-LH]⁺. Subsequent reaction of [2-LH]⁺ with [1-MH]⁺ allows for production of H₂ and the Ir^II dimer [7]²⁺. The tautomerization between the metal-hydride and the ligand protonated species provides a low energy pathway for ligand dissociation, opening the needed coordination site. The ability to control the interconversion between a metal-hydride and a ligand-protonated congener using an exogeneous ligand introduces a new strategy for catalyst design with proton responsive ligands.

Graphene oxide-iridium nanocatalyst for the transformation of benzylic alcohols into carbonyl compounds

A catalyst constructed from graphene oxide and iridium chloride exhibited high activity and reliability for the selective transformation of benzylic alcohols into aromatic aldehydes or ketones. Instead of thermal reaction, the transformation was performed under ultrasonication, a green process with low byproduct, high atomic yield and high selectivity. Experimental data obtained from spherical-aberration corrected field emission TEM (ULTRA-HRTEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy and Raman spectra confirm the nanostructure of the title complex. Noticeably, the activity and selectivity for the transformation of benzylic alcohols remained unchanged within 25 catalytic cycles. The average turn over frequency is higher than 5000 h⁻¹, while the total turnover number (TON) is more than one hundred thousand, making it a high greenness and eco-friendly process for alcohol oxidation.

Graphene oxide–iridium nanostructure act as a robust catalyst exhibiting high activity and reliability for the selective transformation of benzylic alcohols into aromatic aldehydes or ketones.

Cyclometalated Iridium(III) Complexes Containing Benzoxazole Derivatives and Different Ancillary Ligands for Catalytic Oxidation of Toluene

A series of cyclometalated iridium(III) complexes that have the general formula [(C^N)2Ir(NR)(X)] (C^N = monoanionic bidentate cyclometalating ligands; NR = pyridine derivatives; X = Cl− or I−) are designed, prepared, and applied for the transformation of toluene to benzaldehyde using a clean, highly efficient, and environmentally-friendly process. The activation energies that are needed for the catalytic oxidation of toluene when using these complexes as catalysts are quite low: between 22.9 and 30.8 kcal mol−1. The catalytic frequencies (TOF) are fairly high (up to 7.0 × 102 h−1) with excellent reliability, and the turnover number (TON) can reach 4.2 × 103 after 6 h of processing time. Catalytic tests, X-ray absorption near-edge structure (XANES), and kinetic modeling are used to derive detailed insights into the characteristics of the catalysts and their effects on the reactions that are featured in the catalytic oxidation of toluene.

Diiridium Bimetallic Complexes Function as a Redox Switch To Directly Split Carbonate into Carbon Monoxide and Oxygen

A pair of diiridium bimetallic complexes exhibit a special type of oxidation-reduction reaction that could directly split carbonate into carbon monoxide and molecular oxygen via a low-energy pathway needing no sacrificial reagent. One of the bimetallic complexes, Ir(III)(μ-Cl)2Ir(III), can catch carbonato group from carbonate and reduce it to CO. The second complex, the rare bimetallic complex Ir(IV)(μ-oxo)2Ir(IV), can react with chlorine to release O2 by the oxidation of oxygen ions with synergistic oxidative effect of iridium ions and chlorine atoms. The activation energy needed for the key reaction is quite low (∼20 kJ/mol), which is far less than the dissociation energy of the C═O bond in CO2 (∼750 kJ/mol). These diiridium bimetallic complexes could be applied as a redox switch to split carbonate or combined with well-known processes in the chemical industry to build up a catalytic system to directly split CO2 into CO and O2.

Cadmium(ii) supramolecular complexes constructed from a phenylbenzoxazole-based ligand: self-assembly, structural features and nonlinear optical properties

Four novel Cd(ii) supramolecular complexes (1–4) have been prepared and their luminescent and nonlinear optical properties have been researched. Complexes 1 and 3 showed obvious nonlinear absorption when compared with to complexes 2 and 4.

μ-Oxido-bis-[hydridotris(tri-methyl-phosphane-κP)iridium(III)](Ir-Ir) bis-(tetra-fluorido-borate) dihydrate

The title compound, [Ir₂H₂O(C₃H₉P)₆](BF₄)₂·2H₂O, was isolated from the reaction between [Ir(COD)(PMe₃)₃]BF₄ and H₂ in water (COD is cyclo­octa-1,5-diene). The asymmetric unit consists of one Ir^III atom bonded to three PMe₃ groups, one hydride ligand and half an oxide ligand, in addition to a BF₄⁻ counter-ion and one water molecule of hydration. The single oxide ligand bridging two Ir^III atoms is disordered across an inversion center with each O atom having a 50% site occupancy. Each Ir^III atom has three PMe₃ groups occupying facial positions, with the half-occupancy O atoms, a hydride ligand and an Ir—Ir bond completing the coordination sphere. The Ir—Ir distance is 2.8614 (12) Å, comparable to other iridium(III) metal–metal bonds. Two water mol­ecules hydrogen bond to two BF₄⁻ anions in the unit cell.