RESUMO
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(C6 F5 )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)Liâ 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)2 E2 , 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.
RESUMO
Coinage metal complexes of the N-heterocyclic carbene-phosphinidene adduct IPrâ 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 [(IPrâ PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPrâ PPh)(MCl)2 ] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPrâ PPh)(CuOTf)2 ] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPrâ PPh)(MCl)2 ] (M=Cu, Au) with Na(BAr(F) ) or AgSbF6 afforded the tetranuclear complexes [(IPrâ 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 Mâ â â M axes. Complete chloride abstraction from [(IPrâ PPh)(AuCl)2 ] was achieved with two equivalents of AgSbF6 in the presence of tetrahydrothiophene (THT) to form [(IPrâ PPh){Au(THT)}2 ][SbF6 ]2 . The cationic tetra- and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions.
RESUMO
A highly efficient NIS-promoted iodocarbocyclization reaction of various functionalized 1,5-enynes is described via a 5-endo diastereoselective process. The cyclizations are conducted in the presence of 1.2 equiv of N-iodosuccinimide in dichloromethane at room temperature. The reaction conditions are compatible with several functional groups and lead to original iodo-functionalized carbocycles in good to excellent yields.