Nitrene transfer catalyzed by copper complexes of ruthenium-thiolate molecular wheel and tripodal S-chelated ligands and C-H functionalization mediated by ruthenium phthalocyanine ketimido complex

Abstract

Metal-mediated nitrene transfer and C-H functionalization reactions have attracted tremendous attention. This thesis is focused on the development of new types of metal complexes that can mediate/catalyze nitrene transfer or C-H functionalization, leading to the findings of alkene aziridination catalyzed by copper molecular wheel (along with wheel-to-rhomboid isomerization), alkene aziridination, sulfide sulfimidation, and C-H amination catalyzed by metal tripodal S-chelated ligand complexes, and C-H functionalization of unactivated hydrocarbons mediated by metal-ketimido complex together with the corresponding catalytic reactions. Following literature reports on the treatment of M3(CO)12 (M = Ru, Os) with HSR to give [M(SR)2(CO)2]n (n = 6, 8) wheels, studies of the effect of temperature on the reaction resulted in formation of unprecedented molecular rhomboid ()-[M(SR)2(CO)2]8 (M = Ru, Os; R = 4-tBuC6H4) at higher temperature (160 C), with ()-[Ru(S(4-tBuC6H4))2(CO)2]8 isolated in pure form. ()-[Ru(S(4-tBuC6H4))2(CO)2]8 was also formed by heating ()-[Ru(S(4-tBuC6H4))2(CO)2]8 wheel in HS(4-tBuC6H4) at 160 C, providing a unique example of wheel-to-rhomboid isomerization. Extending ‘Ru3(CO)12/Os3(CO)12 + HSR’ reaction to rhenium led to formation of [Re(SR)(CO)3]4 (R = Ph, iPr). The application of molecular wheels in nitrene transfer was explored using structurally characterized [Ru(SR)2(CO)2]6 and [Cu{Ru(SR)2(CO)2]6}]+. [Cu{Ru(S(4-iPrC6H4))2(CO)2}6]PF6 catalyzed alkene aziridination with PhI=NSO2(4-RC6H4) (R = Me, H, NO2) to afford the aziridine products in up to 95% yield. High-resolution ESI-MS analysis suggested binding of NSO2(4-RC6H4) group by the molecular wheel. Reactions of [RuIV(Pc)(N=CR2)2] (H2Pc = phthalocyanine) with hydrocarbons, including ethyl benzene, cumene, toluene, fluorene, and xanthene, under aerobic conditions gave [RuII(Pc)(HN=CR2)2] and afforded benzylic C-H functionalization products in up to 84% yield. Based on this finding, and considering the preparation of [RuIV(Pc)(N=CR2)2] from [RuII(Pc)(HN=CR2)2] and PhI(OAc)2, a catalytic C-H functionalization system of ‘[RuII(Pc)(HN=CR2)2] + PhI(OAc)2’ was developed which provided a unique example of metal-catalyzed C-H functionalization via metal-ketimido intermediate. Mechanistic studies lent supports to the possible involvement of hydrogen-atom abstraction by [RuIV(Pc)(N=CR2)2]. Attempts to extend the C-H functionalization to ruthenium-amido system, via bis(secondary amine)ruthenium(II) phthalocyanine precursors [RuII(Pc)(HNR2)2], resulted in oxidative C-H functionalization of the coordinated secondary amines to give coordinated imines. To develop nitrene transfer catalyzed by a metal tripodal S-chelated ligand complex, a series of Cu(I) complexes bearing tris(thioimidazolyl) hydroborate ligands (RTmR or TmR), together with Ag(I) and Au(I) analogues, were synthesized and characterized. The structures of [Cu(TmPh)(PR3)] (R = Ph, Cy) have been determined by X-ray crystallography. These Cu(I) complexes are highly active catalysts for alkene aziridination and sulfide sulfimidation. [Cu(TmPh)(PCy3)] (1 mol%) catalyzed the aziridination of styrenes and 2-vinylnapthalene with PhI=NSO2(4-RC6H4) (R = Me, NO2) at room temperature to give the aziridine products in up to 99% yield (reaction time: 3 h). Sulfimidation of thioanisoles with PhI=NSO2(4-RC6H4) (R = Me, NO2) catalyzed by [Cu(TmPh)(PCy3)] under the same conditions except for a shorter reaction time (30 min) afforded the sulfimide products in up to 99% yield. Moreover, [Cu(TmPh)(PCy3)] was also found to be a highly selective catalyst for intramolecular aryl C-H amination of vinyl azides, producing indoles in up to 98% isolated yield. In addition, preliminary results about the formation of ruthenium complexes of cuboidal M3S4 (M = Fe, Mo) cluster ligands are described.