Tridentate κ3-P,P,C iridium complexes: influence of ligand saturation on intramolecular C-H bond activation

Whereas κ3-P,C,P-based donor ligands are ubiquitous across synthetic chemistry, related unsymmetric systems having κ3-P,P,C-coordination are comparatively rare. In this contribution, we expose a new κ3-P,P,C ligand system, bearing a C3-anionic linker and its coordination chemistry with iridium. The title ligand has been coordinated in saturated and unsaturated forms. The degree of ligand saturation affected an onward (and unusual) oxidative rearrangement reaction.

Stable cyclopropenylvinyl ligands via insertion into a transient cyclopropenyl metal bond

Treatment of the rhodium pincer complexes [RhCl(RPm)] (RPm = N,N'-bis(di-R-phosphinomethyl)perimidinylidene, R = Ph, Cy) with triphenylcyclopropenium hexafluorophosphate affords rhodacyclobutadiene complexes. These in turn react with activated alkynes (RCCCO2Me, R = H, CO2Me) to afford unusually stable cyclopropenylvinyls, implicating the intermediacy of σ-cyclopropenyl isomers. In contrast, treatment of [RhCl{py(NHPtBu2)2-2,6}] with the same reagent instead results in double functionalisation (SEAr) at the pincer backbone.

2-(1H-Imidazol-2-yl)-2,3-dihydro-1H-perimidine

The novel compound 2-(1H-imidazol-2-yl)-2,3-dihydro-1H-perimidine was obtained in very good yield via a known eco-friendly protocol. The product was isolated in pure form as a solvate by simple filtration from the crude mixture. Its structure was assigned by 1D and 2D NMR experiments and was confirmed by high resolution MS and single crystal XRD. The temperature of methanol release was determined by DSC and the energy of the process theoretically estimated.

C-H activation in bimetallic rhodium complexes to afford N-heterocyclic carbene pincer complexes

The pro-ligands 1,8-bis(di-R-phosphinomethyl)-2,3-dihydroperimidine (RH₂Pm, R = phenyl, cyclohexyl) react with [RhCl(CE)(PPh₃)₂] (E = O, S) to afford the bimetallic complexes [RhCl(CE)(μ-RH₂Pm)]₂ (E = O, S). Upon heating, these species undergo double C-H activation to afford the N-heterocyclic carbene (NHC) pincer complexes [RhCl(RPm)]. Reduction of [RhCl(CO)(μ-PhH₂Pm)]₂ with KC₈ results in the bimetallic rhodium(0) complex, [Rh(μ-CO)(PhH₂Pm)]₂, with a formal Rh-Rh bond and a hydrogen-bonding interaction between rhodium and the central methylene group (C-H⋯Rh = 2.802 Å). Upon treatment with tritylium, ferrocenium or triphenylcyclopropenium tetrafluoroborates this species undergoes double C-H activation to afford a mononuclear NHC pincer complex salt, [Rh(CO)(PhPm)]BF₄. Treatment of [RhCl(CO)(PhH₂Pm)]₂ with lithium (trimethylsilyl)acetylide provides another bimetallic species, [Rh(CCSiMe₃)(CO)(PhH₂Pm)]₂, however heating this species does not proceed cleanly to the monomeric NHC complex, [Rh(CCSiMe₃)(CO)(PhPm)] which may however be obtained from [RhCl(RPm)] and LiCCSiMe₃.

Experimental and Theoretical Study of Ni II ‐ and Pd II ‐Promoted Double Geminal C(sp 3 )−H Bond Activation Providing Facile Access to NHC Pincer Complexes: Isolated Intermediates and Mechanism

We report the first examples of metal‐promoted double geminal activation of C(sp³)−H bonds of the N−CH₂−N moiety in an imidazole‐type heterocycle, leading to nickel and palladium N‐heterocyclic carbene complexes under mild conditions. Reaction of the new electron‐rich diphosphine 1,3‐bis((di‐tert‐butylphosphaneyl)methyl)‐2,3‐dihydro‐1H‐benzo[d]imidazole (1) with [PdCl₂(cod)] occurred in a stepwise fashion, first by single C−H bond activation yielding the alkyl pincer complex [PdCl(PCsp3^HP)] (3) with two trans phosphane donors and a covalent Pd−Csp3 bond. Activation of the C−H bond of the resulting α‐methine Csp3 H−M group occurred subsequently when 3 was treated with HCl to yield the NHC pincer complex [PdCl(PC^NHCP)]Cl (2). Treatment of 1 with [NiBr₂(dme)] also afforded a NHC pincer complex, [NiBr(PC^NHCP)]Br (6), but the reactions leading to the double geminal C−H bond activation of the N−CH₂−N group were too fast to allow identification or isolation of an intermediate analogous to 3. The determination of six crystal structures, the isolation of reaction intermediates and DFT calculations provided the basis for suggesting the mechanism of the stepwise transformation of a N−CH₂−N moiety in the N−C^NHC−N unit of NHC pincer complexes and explain the key differences observed between the Pd and Ni chemistries.

A Panchromatic Cyclometalated Iridium Dye Based on 2-Thienyl-Perimidine

Though 2-arylperimidines have never been used in iridium(III) chemistry, the present study on structural, electronic and optical properties of N-unsubstituted and N-methylated 2-(2-thienyl)perimidines, supported by DFT/TDDFT calculations, has shown that these ligands are promising candidates for construction of light-harvesting iridium(III) complexes. In contrast to N-H perimidine, the N-methylated ligand gave the expected cyclometalated μ-chloro-bridged iridium(III) dimer which was readily converted to a cationic heteroleptic complex with 4,4′-dicarboxy-2,2′-bipyridine. The resulting iridium(III) dye exhibited panchromatic absorption up to 1000 nm and was tested in a dye-sensitized solar cell.

Synthesis and comparative structural study of 2-(pyridin-2-yl)-1H-perimidine and its mono- and di-N-methyl-ated analogues

The title compounds, 2-(pyridin-2-yl)-1H-perimidine (C16H11N3; 1), 1-methyl-2-(pyridin-2-yl)-1H-perimidine (C17H13N3; 2), and 1,3-dimethyl-2-(pyridin-2-yl)-1H-perimidinium iodide (C18H16N3 +·I-; 3) were synthesized under mild conditions and their structures were determined by 1H NMR spectroscopy and single-crystal X-ray analysis. The N-methyl-ation of the nitro-gen atom(s) at the perimidine moiety results in a significant increase of the inter-plane angle between the pyridin-2-yl ring and the perimidine system. The unsubstituted perimidine (1) forms a weak intra-molecular N-H⋯N bond that consolidates the mol-ecular conformation. In the crystal structures of 1-3, the mol-ecular entities all are assembled through π-π and C-H⋯π inter-actions.

Recent Advances in the Synthesis of Perimidines and their Applications

Perimidines are versatile scaffolds and a fascinating class of N-heterocycles that have evolved significantly in recent years due to their immense applications in life sciences, medical sciences, and industrial chemistry. Their ability of molecular interaction with different proteins, complex formation with metals, and distinct behavior in various ranges of light makes them more appealing and challenging for future scientists. Various novel technologies have been developed for the selective synthesis of perimidines and their conjugated derivatives. These methods extend to the preparation of different bioactive and industrially applicable molecules. This review aims to present the most recent advancements in perimidine synthesis under varied conditions like MW radiation, ultrasound, and grinding using different catalysts such as ionic liquids, acid, metal, and nanocatalyst and also under green environments like catalyst and solvent-free synthesis. The applications of perimidine derivatives in drug discovery, polymer chemistry, photo sensors, dye industries, and catalytic activity in organic synthesis are discussed in this survey. This article is expected to be a systematic, authoritative, and critical review on the chemistry of perimidines that compiles most of the state-of-art innovation in this area.

Bis(diphenylphosphinyl)-functionalized dipyrido-annulated NHC towards copper(i) and silver(i)

Sterically rigid bis(phosphinyl)dipyrido-annulated NHC coordinates with Ag(i) and Cu(i) centres to form luminescent multinuclear complexes.

Facile synthesis of Pd(ii) and Ni(ii) pincer carbene complexes by the double C–H bond activation of a new hexahydropyrimidine-based bis(phosphine): catalysis of C–N couplings

A new hexahydropyrimidine-based NHC proligand undergoes facile double C–H bond activation to give Pd(ii) and Ni(ii) NHC pincer cationic complexes. The Pd complex catalyzes C–N cross couplings very efficiently.