Recent Development in the Synthesis and Catalytic Application of Iridacycles

Cyclometallated complexes are well-known and have found many applications. This article provides a short review on the progress made in the synthesis and application to catalysis of cyclometallated half-sandwich Cp*Ir(III) complexes (Cp*: pentamethylcyclopentadienyl) since 2017. Covered in the review are iridacycles featuring conventional C,N chelates and less common metallocene and carbene-derived C,N and C,C ligands. This is followed by an overview of the studies of their applications in catalysis ranging from asymmetric hydrogenation, transfer hydrogenation, hydrosilylation to dehydrogenation.

Making the unconventional μ2-P bridging binding mode more conventional in phosphinine complexes

As compared to the normal η¹-P σ-complexes or η⁶-phosphinine π-complexes, the rare μ²-P bridging binding mode of phosphinines can be tuned by employing electron donating substitute.

Phosphinines, as aromatic heterocycles, usually engage in coordination as η¹-P σ-complexes or η⁶-phosphinine π-complexes. The μ²-P bridging coordination mode is rarely observed. With the aim to study the effect of different electronic configurations of phosphinines on the coordination modes, a series of anionic phosphinin-2-olates and neutral phosphinin-2-ols were prepared with moderate to high yield. Then the coordination chemistry of these two series was studied in detail towards coinage metals (Au(i) and Cu(i)). It is observed that the anionic phosphinin-2-olates possess a higher tendency to take a bridging position between two metal centers compared to the neutral phosphinin-2-ols. Based on these experimental findings bolstered by DFT calculations, some insight is gained on how the unconventional μ²-P phosphinine bridging coordination mode can be made more conventional and used for the synthesis of polynuclear complexes.

Substituent effects in pyridyl-functionalized pyrylium salts, pyridines and λ3,σ2-phosphinines: a fundamental and systematic study

A series of pyridyl-functionalized O⁺–, N–, and P– containing heterocycles have been prepared and investigated for substituent effects.

Iridacycles for hydrogenation and dehydrogenation reactions

Iridacycles are a group of cyclometalated metal complexes, which have recently been shown to be versatile catalysts for a range of reactions. This Feature Article provides an account of the work carried out by our groups. We start with an introduction to the variety of iridacycles and how they entered into catalysis. The following sections provide an overview of the discovery and applications in catalysis of the iridacycles originated from our labs, including transfer hydrogenation with formic acid, hydrogenation with H₂, dehydrogenation and borrowing-hydrogen reactions. Where possible, mechanistic insight is also presented. A notable advantage of these iridacycles is their ease of preparation, stability to air and water and high modularity. With only one coordination site available for substrate activation, the iridacycles differ from most homogeneous catalysts structure-wise.

2-(2′-Pyridyl)-4,6-diphenylphosphinine versus 2-(2′-pyridyl)-4,6-diphenylpyridine: synthesis and characterization of novel Cr0, Mo0 and W0 carbonyl complexes containing chelating P,N and N,N ligands

Replacing nitrogen by phosphorus in otherwise similar structures changes the properties of the resulting compounds significantly due to the electronic differences that exist between these heteroatoms.

Cyclometalated [Cp*M(C^X)] (M = Ir, Rh; X = N, C, O, P) complexes

Isolated and well-defined cyclometalated iridium/rhodium complexes that contain a Cp*M–C (M = Ir, Rh) bond stabilised by the intramolecular coordination of neutral donor atoms (N, C, O or P), together with their applications, were summarized.

A theoretical study of the activity in Rh-catalysed hydroformylation: the origin of the enhanced activity of the π-acceptor phosphinine ligand

The factors governing the activity in Rh-catalyzed hydroformylation were investigated using DFT and QSAR methods.

An unprecedented cyclometallated platinum(ii) complex incorporating a phosphinine co-ligand: synthesis and photoluminescence behaviour

The first luminescent platinum(ii) complex bearing phosphinine co-ligands with a long-lived emission from a phosphinine-localised triplet excited state is reported.

2,4,6-Triarylphosphinines versus 2,4,6-triarylpyridines: an investigation of the differences in reactivity between structurally related aromatic phosphorus and nitrogen heterocycles

The novel atropisomeric pyridine derivative rac-10 has been synthesized and structurally characterized. In contrast to its phosphorus analogue 3, axially chiral 10 has a considerably lower rotational barrier as estimated by DFT calculations. However, the presence of the two enantiomers could be confirmed by means of chiral analytical HPLC analysis and by protonation experiments with a chiral acid. Compound rac-10 could be further dehydrogenated by treatment with DDQ to the benzo(h)quinoline derivative rac-12. This conversion failed for the phosphorus analogue rac-3. Interestingly, although 2,4,6-triarylphosphinines undergo facile CH activation with [Cp*IrCl2 ]2 in the presence of NaOAc, this reaction does not proceed with the corresponding pyridine derivatives. On the other hand, the latter ones can be selectively ortho-metalated with Pd(OAc)2 , leading to acetate-bridged dimeric species, which could be unambiguously confirmed by means of X-ray crystal structure analysis. The treatment of phosphinines with Pd(OAc)2 led instead to the formation of the unusual cofacial oxidative coupling products 16 and 17, which consist of a phosphorus-containing cage structure.