A tritopic carbanionic N-heterocyclic dicarbene and its homo- and heterometallic coinage metal complexes.

Homo (Au3)- and heterotrinuclear coinage metal complexes (Au2Ag and Au2Cu) ligated by the first tritopic carbanionic N-heterocyclic carbene (NHC) have been prepared by deprotonation of ditopic NHC digold complexes and structurally characterized by single-crystal X-ray diffraction.

Ethylene tri-/tetramerization catalysts supported by diphosphinothiophene ligands.

Cr(iii) catalysts supported by a series of diphosphinothiophene ligands have been developed, all of which, upon activation with MMAO-3A, are active for ethylene tri-/tetramerization. The effect of ligand substitution on the catalytic performance has been examined. The Cr precatalyst supported by the diphosphinothiophene ligand containing one trimethylsilyl group at the C2 position achieved a high activity of up to 686 kg (g Cr h-1)-1 with a total selectivity of up to 69% toward 1-hexene (29.5%) and 1-octene (39.5%). Two representative Cr complexes bearing the diphosphinothiophene ligand were synthesized and structurally characterized by single-crystal X-ray diffraction. Comparison of the coordination structure data of the two Cr complexes with those of an analogous diphosphine Cr complex reveals a direct correlation between the bond length of two adjacent bridging carbon atoms and catalytic activity: a shorter bond length and hence smaller ligand bite angle lead to higher catalytic activity. These diphosphinothiophene ligands featuring a fine-tuned backbone provide a model for the precise understanding of the impact of ligand variations on the catalytic performance.

Facile Syntheses of N-Heterocyclic Carbene Precursors through I2 - or NIS-Promoted Amidiniumation of N-Alkenyl Formamidines.

We have developed I2 - or N-iodosuccinimide (NIS)-mediated amidiniumation of N-alkenyl formamidines for the syntheses of cyclic formamidinium salts, some of which could be directly used as N-heterocyclic carbene (NHC) precursors. Treatment of iodine-containing formamidinium salts with Al2 O3 led to the formation of cyclic formamidinium salts with an unsaturated backbone. A rhodium(I) complex ligated by a representative NHC was prepared by the reaction of [Rh(cod)Cl]2 (cod=1,5-cyclooctadiene) with the free carbene obtained in situ from deprotonation of the corresponding formamidinium salts. The NHCs prepared in situ can also react with S8 to afford the corresponding thiones.

Ruthenium-catalyzed olefin metathesis accelerated by the steric effect of the backbone substituent in cyclic (alkyl)(amino) carbenes.

Three ruthenium complexes bearing backbone-monosubstituted CAACs were prepared and displayed dramatic improvement in catalytic efficiency not only in RCM reaction but also in the ethenolysis of methyl oleate, compared to those bearing backbone-disubstituted CAACs.