No abstract

Coinage metal complexes of the N-heterocyclic carbene-phosphinidene adduct IPr⋅PPh (IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by its reaction with CuCl, AgCl, and [(Me2 S)AuCl], which afforded the monometallic complexes [(IPr⋅PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPr⋅PPh)(MCl)2 ] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPr⋅PPh)(CuOTf)2 ] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPr⋅PPh)(MCl)2 ] (M=Cu, Au) with Na(BAr(F) ) or AgSbF6 afforded the tetranuclear complexes [(IPr⋅PPh)2 M4 Cl2 ]X2 (X=BAr(F) or SbF6 ), which contain unusual eight-membered M4 Cl2 P2 rings with short cuprophilic or aurophilic contacts along the chlorine-bridged M⋅⋅⋅M axes. Complete chloride abstraction from [(IPr⋅PPh)(AuCl)2 ] was achieved with two equivalents of AgSbF6 in the presence of tetrahydrothiophene (THT) to form [(IPr⋅PPh){Au(THT)}2 ][SbF6 ]2 . The cationic tetra- and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions.

Several pnictogen dihalide complexes of the type (WCA‐IDipp)EX2 (E=P, As, Sb; X=Cl, Br) that bear an anionic N‐heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA‐IDipp, WCA=B(C6F5)3, IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) were prepared by salt metathesis reactions between the respective pnictogen trihalides EX3 and the lithium salt (WCA‐IDipp)Li⋅toluene. Two‐electron reduction of the dihalides (WCA‐IDipp)EX2 with 1,3‐bis(trimethylsilyl)‐1,4‐dihydropyrazine or elemental magnesium afforded the dipnictenes (WCA‐IDipp)2E2, which display typical element‐element double bonds as observed in diaryldiphosphenes, ‐arsenes and ‐stibenes. To provide an insight into the factors contributing to the structural stability of the pnictogen dihalide and dipnictene compounds, quantum chemical calculations were performed at the domain‐based local pair natural orbital coupled‐cluster (DLPNO‐CCSD(T)) level. A local energy decomposition (LED) analysis of the interaction between the carbene and the pnictogen dihalide or dipnictene moiety demonstrates that London dispersion is an essential factor for the stabilization of these compounds.

A series of neutral iridium(I) complexes of the general type [(WCA−NHC)]IrL(COD)] (COD=1,5‐cyclooctadiene; L=phosphine, pyridine), bearing anionic N‐heterocyclic carbenes (WCA−NHC) with a weakly coordinating anionic (WCA) borate moiety, were prepared by addition of phosphines and pyridine to [(WCA−NHC)]Ir(COD)], in which the available coordination site is stabilized by intramolecular metal‐arene interaction (π‐face donation). The solvent and substrate scope of the neutral complexes as catalysts for H/D exchange was investigated, revealing their suitability for promoting efficient deuteration in nonpolar solvents such as cyclohexane.

Synthesis and structural analysis of half-titanocenes containing anionic N-heterocyclic carbenes with a weakly coordinating borate [B­(C6F5)3] moiety (WCA-NHC) of the type, [Cp′TiX2(WCA-NHC)] [Cp′ = C5H5, t BuC5H4; X = Cl, Me; NHC = 1,3-bis­(2,6-dimethylphenyl)­imidazolin-2-ylidene], have been explored. The Ti–C bond distances between titanium and the N-heterocyclic carbene carbon atoms [Ti–CNHC = 2.214(3)–2.246(3) Å] are longer than the Ti–methyl bond distances in the dimethyl complexes [2.063(5)–2.122(9) Å]; the WCA-NHC ligand coordinates to titanium as a conventional N-heterocyclic carbene ligand. [( t BuC5H4)­TiCl2(WCA-NHC)] exhibited high catalytic activity (e.g., 4590 kg-PE/mol-Ti·h) for ethylene polymerization in the presence of Al i Bu3–[Ph3C]­[B­(C6F5)4] cocatalyst, and the complex demonstrated high catalytic activity with efficient 1-hexene incorporation for the ethylene/1-hexene copolymerization in the presence of MAO cocatalyst.