Synthesis and coordination chemistry of new asymmetric donor/acceptor pincer ligands, 1,3-C6H4(CH2PtBu(Rf))2 (Rf = CF3, C2F5)

Abstract

Syntheses of new asymmetric pincer precursors 1,3-C₆H₄{CH₂P(^tBu,X)}₂ (^tBu,XPCPH; X = Cl, SiMe₃, OPh) and a new class of hybrid donor/acceptor pincer ligands 1,3-C₆H₄{CH₂P(^tBu,R_f)}₂ (^tBu,RfPCPH; R_f = CF₃, C₂F₅) are reported. All ^tBu,XPCPH compounds are obtained as mixtures of meso and rac diastereomers in varying ratios (meso : rac ∼ 4 : 1 to 3 : 2) which were used without separation. Treatment of Ru(cot)(cod) with ^tBu,CF₃PCPH under 1 atm H₂ in acetone at 20 °C produced the hydride solvate (^tBu,CF₃PCP)Ru(acetone)_xH which was not isolated, but could be trapped as stable diene complexes (^tBu,CF₃PCP)Ru(L)₂H (L₂ = cod (), nbd ()). Catalytic cyclooctane dehydrogenation studies demonstrate that has ∼50% the activity of (^CF₃PCP)Ru(cod)(H), but significantly higher catalyst stability and is able to operate at higher catalyst loading concentrations without deactivation via bimolecular decomposition.