Synthesis and Reactivity of Iridium(III) Dihydrido Aminocarbenes

Iridium complexes supported by the PNP amidophosphine scaffold (PNP = [N(2-PiPr2-4-Me-C6H3)2]−) perform the selective double C−H activation of methyl amines to produce iridium(III) dihydrido aminocarbenes. The reactivity of these complexes is presented and contrasted with that observed for the previously reported iridium(I) alkoxycarbenes

The development and use of novel iridium complexes as catalysts for ortho-directed hydrogen isotope exchange reactions

The preparation and application of groups of new iridium complexes are described. In particular, iridium complexes possessing phosphine ligands and a bulky N-heterocyclic carbene have been shown to be robust and readily handled species and have been applied in a range of directed hydrogen-deuterium and -tritium exchange processes and, in particular, with drug-like substrates or within ADMET-related studies. Overall, these new iridium(I) complexes are shown to be highly active catalysts and display catalytic activity far in excess of the industry standard, Crabtree's catalyst, with excellent levels of labelling being achieved over short reaction times and at low metal complex loadings, whilst tolerating a wide range of functional moieties. Furthermore and again in contrast to systems employing Crabtree's catalyst, the low catalyst loadings and short reaction times made possible by these emerging iridium carbene comple have delivered tritiated products with very good levels of labelling and without any appreciable by-product waste production

Iridium Complexes as Hydrosilylation Catalysts

Iridium complexes have been found to be active as catalysts for hydrosilylation reactions, especially for those involving 1,3-dienes and 1-alkynes. For ketones, iridium complexes show maximum activity if one molar equivalent (relative to iridium) of triphenylphosphine is added to the reaction mixture. Iridium complexes are also active catalysts for the hydrosilylation of a,ß-unsaturated ketones, although the regioselectivity differs from that obtained with rhodium complexes. Attempts at asymmetric hydrosilylation of keto compounds using iridium complexes resulted in extremely low enantiomeric excesses

Dipyrrinato‐Iridium(III) Complexes for Application in Photodynamic Therapy and Antimicrobial Photodynamic Inactivation

The generation of bio-targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo-)therapy. A synthetic strategy is presented in which chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N- and O-substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*-iridium(III) and ppy-iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl-eta(5)-cyclopentadienyl, ppy=2-phenylpyridyl). Similarly, electron-deficient [Ir-III(dipy)(ppy)(2)] complexes could be used for post-functionalization, forming alkenyl, alkynyl and glyco-appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the [Ir-III(Cl)(Cp*)(dipy)] complexes and the glyco-substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented

Dicarba-closo-dodecarborane-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium : biological relevance and synthetic strategies

This review describes how the incorporation of dicarba-closo-dodecarboranes into half-sandwich complexes of ruthenium, osmium, rhodium and iridium might lead to the development of a new class of compounds with applications in medicine. Such a combination not only has unexplored potential in traditional areas such as Boron Neutron Capture Therapy agents, but also as pharmacophores for the targeting of biologically important proteins and the development of targeted drugs. The synthetic pathways used for the syntheses of dicarba-closo-dodecarboranes-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium are also reviewed. Complexes with a wide variety of geometries and characteristics can be prepared. Examples of addition reactions on the metal centre, B–H activation, transmetalation reactions and/or direct formation of metal–metal bonds are discussed (103 references)

Protic NHC Iridium Complexes with beta-H Reactivity-Synthesis, Acetonitrile Insertion, and Oxidative Self-Activation

Protic NHC iridium complexes, obtained from the corresponding azido-phenylene-isocyanide precursor complexes, were investigated for ligand-based reactivity. Under redox-neutral conditions, acetonitrile inserts into the N-H bonds to provide kappa(2)-NHC-imidoyl ligand-based complexes, while under reductive conditions the complex also expels one N-H proton to provide the corresponding deprotonated analogues. Using zinc as a reductor activates the NHC-iridium complex to form an asymmetric bimetallic iridium hydrido complex, in which two anionic N-deprotonated NHCs bridge the bimetallic core. X-ray crystal structures are reported for the azido-phenylene-isocyanide precursor complex, the protic NHC complex, and the asymmetric bimetallic iridium hydride complex. Density functional computations and a QTAIM analysis of the bimetallic iridium hydrido complex are provided.Peer reviewe

Mixed-Valence Tetrametallic Iridium Chains

Neutral [X−{Ir2}−{Ir2}−X] (X=Cl, Br, SCN, I) and dicationic [L−{Ir2}−{Ir2}−L]2+ (L=MeCN, Me2CO) tetrametallic iridium chains made by connecting two dinuclear {Ir2} units ({Ir2}=[Ir2(μ‐OPy)2(CO)4], OPy=2‐pyridonate) by an iridium–iridium bond are described. The complexes exhibit fractional averaged oxidation states of +1.5 and electronic delocalization along the metallic chain. While the axial ligands do not significantly affect the metal–metal bond lengths, the metallic chain has a significant impact on the iridium–L/X bond distances. The complexes show free rotation around the unsupported iridium‐iridium bond in solution, with a low‐energy transition state for the chloride chain. The absorption spectra of these complexes show characteristic bands at 438–504 nm, which can be fine‐tuned by varying the terminal capping ligands

Transition metal complexes with P,N-ligands and silylenes : synthesis and catalytic studies

We were interested to extend our library of P,N-ligands, and to investigate the influence of a five-memebered ring-chelate, since most of the previously tested ligands form six-membered ring-chelates. In consequence, twelve new phosphinomethyl-oxazolines and their corresponding iridium-complexes were prepared and tested in the enantioselective hydrogenation of unfunctionalized and functionalized olefins. The tetrasubstituted olefin 2- (4’-methoxyphenyl)-3-methyl-2-butene was reduced with higher enantioselectivity than reported for other iridium catalysts. Another objective was to examine the effect of a strong π-accepting and planar phosphorusmoiety. Three chiral phosphininoxazolines were prepared by dehydration of a water-adduct, wherein the phosphorus atom is present as a secondary phosphine oxide. The corresponding cationic iridium-complexes were synthesized. One of these complexes was also tested in the iridium-catalyzed hydrogenation and transfer-hydrogenation showing good conversion, but low to moderate enantioselectivity. We were interested in the scope of iridium-PHOX complexes in other catalytic reactions. Initial studies towards the application of this system in asymmetric catalytic Pauson-Khand reaction were completed regarding pressure influence, reproducability and the influence of the counteranion on the enantioselectivity of the reaction. 3-Phenylsubstituted enynes undergo cycloaddition with good to very good yields and good enantioselectivities. Steric hindrance at the alkene moiety leads to a strong drop in yield. Among the tested counteranions, small and weakly-coordinating anions, such as triflate, tetrafluoroborate, hexafluorophosphate and hexafluoroantimonate proved to give the highest enantioselectivities. Inspired by the recent success of NHCs in the iridium catalyzed hydrogenation, we envisioned the synthesis of iridium- and rhodium-complexes containing N-heterocyclic silylenes. Two cationic rhodium(I)-silylene complexes 187 and 188 were prepared from [Rh(cod)2]BArF 185 and 1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazasilol-2-ylidene 171 and its saturated analogue 172, respectively (Figure 1). Only catalytically inactive complexes were formed. The corresponding iridium-complexes were not accessible by the same method

Highly active iridium(I) complexes for the selective hydrogenation of carbon-carbon multiple bonds

New iridium(I) complexes, bearing a bulky NHC/phosphine ligand combination, have been established as extremely efficient hydrogenation catalysts that can be used at low catalyst loadings, and are compatible with functional groups which are often sensitive to more routinely employed hydrogenation methods