In-Depth Study on Chloride Abstractions from (NHC)Ir(COD)Cl Complexes

Bi- and trimetallic complexes with macrocyclic xanthene-4,5-diNHC ligands

Three different types of bimetallic NHC-metal complexes were synthesized, whose NHC units are attached at the 4,5-positions of xanthene. The NHC units are in close proximity and are designed such that each carbene coordinates one ML unit, while the chelation of one metal by two NHC is not possible. Several xanthene-((NHC)ML)₂ complexes with ML = RhCl(cod), IrCl(cod), RhCl(CO)₂, IrCl(CO)₂, AuCl, AgCl, CuCl and Pd(allyl)Cl were synthesized and investigated.

Structural Snapshots of π-Arene Bonding in a Gold Germylene Cation

Heavier group 14 element cations exhibit a remarkable reactivity that has typically hampered their isolation. For the few available examples, the role of π‐arene interactions is crucial to provide kinetic stabilization, but dynamic and structural information on those contacts is yet limited. In this study we have accessed the metalogermylenium cation [(PMe₂Ar^Dipp2)AuGe(Ar^Dipp2)Cl]⁺ (4⁺) (Ar^Dipp2=C₆H₃‐2,6‐(C₆H₃‐2,6‐iPr₂)₂) that has been structurally characterized with three different non‐coordinating counter anions. These studies provide for the first time dynamic information about the conformational rearrangement that characterizes π‐arene bonding thorough a series of X‐ray diffraction structural snapshots. Computational studies reveal the weak character of the π‐arene bonding (ca. 2 kcal mol⁻¹) that can be described as the donation from a π_C=C bond toward the empty p valence orbital of germanium.

Cooperative activation of X-H (X = H, C, O, N) bonds by a Pt(0)/Ag(i) metal-only Lewis pair

Metal-only Lewis pairs made of Pt(0)/Ag(i) combinations have been previously reported, but their cooperative reactivity remains unexplored. Here we demonstrate that these systems are capable of synergistically activating a wide variety of X-H (X = H, C, O, N) bonds, including those in dihydrogen, alkynes, water and ammonia.

On the interaction of N-heterocyclic carbene Ir+I complexes with His and Cys containing peptides

In the interaction of an [Ir(+i)(COD)(NHC)Cl] complex with model peptides a chelating motif with a particularly interesting bimetallic peptide-bridged Ir(+iii)–NHC motif was identified with loss of the COD and Cl ligands and oxidation of the metal.

A leap forward in iridium-NHC catalysis: new horizons and mechanistic insights

This review summarises the most recent advances in Ir-NHC catalysis while revisiting all the classical reactions in which this type of catalyst has proved to be active. The influence of the ligand system and, in particular, the impact of the NHC ligand on the activity and selectivity of the reaction have been analysed, accompanied by an examination of the great variety of catalytic cycles hitherto reported. The reaction mechanisms so far proposed are described and commented on for each individual process. Moreover, some general considerations that attempt to explain the influence of the NHC from a mechanistic viewpoint are presented at the end of the review. The first sections are dedicated to the most widely explored reactions that use Ir-NHCs, i.e., hydrogenation and transfer hydrogenation, for which a general overview that tries to compile all the Ir-NHC catalysts hitherto reported for these processes is provided. The next sections deal with hydrogen borrowing, hydrosilylation, water splitting, dehydrogenation (of alcohols, alkanes, aminoboranes and formic acid), hydrogen isotope exchange (HIE), signal amplification by reversible exchange and C-H bond functionalisation (silylation and borylation). The last section compiles a series of reactions somewhat less explored for Ir-NHC catalysts that include the hydroalkynylation of imines, hydroamination, diboration of olefins, hydrolysis and methanolysis of silanes, arylation of aldehydes with boronic acids, addition of aroyl chlorides to alkynes, visible light driven reactions, isomerisation of alkenes, asymmetric intramolecular allylic amination and reactions that employ heterometallic catalysts containing at least one Ir-NHC unit.

The Stepwise Reaction of Rhodium and Iridium Complexes of Formula [MCl2 (κ4 C,N,N',P-L)] with Silver Cations: A Case of trans-Influence and Chiral Self-Recognition

Acetonitrile suspensions of the dichlorido complexes [MCl₂ (κ⁴ C,N,N',P-L)] [M=Rh (1), Ir (2)] react with AgSbF₆ in a 1:2 molar ratio affording the bis-acetonitrile complexes [M(κ⁴ C,N,N',P-L)(NCMe)₂ ][SbF₆ ]₂ (3 and 4). The reaction takes place in a sequential manner and the intermediates can be isolated varying the M:Ag molar ratio. In a 2:1 molar ratio, it affords the dimetallic monochlorido-bridged compounds [{MCl(κ⁴ C,N,N',P-L)}₂ (μ-Cl)][SbF₆ ] (5 and 6). In a 1:1 molar ratio, the monosubstituted solvato-complexes [MCl(κ⁴ C,N,N',P-L)(Solv)][SbF₆ ] (Solv=H₂ O, MeCN, 7-10) were obtained. Finally, in a 2:3 molar ratio, it gives complexes 11 and 12 of formula [{M(κ⁴ C,N,N',P-L)(NCMe)(μ-Cl)}₂ Ag][SbF₆ ]₃ in which a silver cation joints two cationic monosubstituted acetonitrile-complexes [MCl(κ⁴ C,N,N',P-L)(NCMe)]⁺ through the remaining chlorido ligands and two Ag⋅⋅⋅C interactions with one of the phenyl rings of each PPh₂ group. In all the complexes, the aminic nitrogen and the central metal atom are stereogenic centers. In the trimetallic complexes 11 and 12, the silver atom is also a stereogenic center. The formation of the cation of the dimetallic complexes 5 and 6, as well as that of the trimetallic complexes 11 and 12, takes place with chiral molecular self-recognition. Experimental data and DFT calculations provide plausible explanations for the observed molecular recognition. The new complexes have been characterized by analytical, spectroscopic means and by X-ray diffraction methods.