Calcium complexes with imino-phosphinanilido chalcogenide ligands for heterofunctionalisation catalysis

Abstract

The syntheses, characterisation and utilisation of the calcium complexes [{L^x}CaN(SiMe₃)₂·(THF)] supported by monoanionic, tridentate imino-phosphinanilido chalcogenide ligands {Ph₂P(E)–N–C₆H₄–CHN(Dipp)}⁻ (E = S, {L²}⁻; E = Se, {L³}⁻; Dipp = 2,6-diisopropylphenyl) as molecular precatalysts for the heterofunctionalisation of styrene are reported. The protio-ligand {L¹}H (for E = O) was obtained upon reaction of the aniline-iminophosphane {Ph₂PHN–C₆H₄–CHN(Dipp)} ({L⁰}H) and hydrogen peroxide at room temperature. The related sulphide and selenide compounds {L²}H and {L³}H were prepared by treatment of {L⁰}H with elemental sulphur and selenium. Beside, reaction of {L⁰}H with Me₂S·BH₃ yielded the corresponding imino-phosphinanilido borane protio-ligand {Ph₂P(BH₃)N–C₆H₄–CHN(Dipp)}H ({L⁴}H). The heteroleptic calcium complexes [{L^x}CaN(SiMe₃)₂·(THF)] (E = S, 2; E = Se, 3) were synthesised by one-pot reaction of {L²}H and {L³}H with 2 equiv of [KN(SiMe₃)₂] and CaI₂ at room temperature. The reaction of {L²}H with [KN(SiMe₃)₂] and CaI₂ in 2 : 2 : 1 proportions yielded the homoleptic complex [Ca{L²}₂] (5). The molecular structures of the protio-ligand {L³}H and complexes 3 and 5 were established by single crystal X-ray analysis. The heteroleptic complexes 2 and 3 constitute moderately efficient precatalysts for the intermolecular hydrophosphination and hydroamination of styrene with diphenylphosphine or pyrrolidine, respectively, to mediate the formation of C–P and C–N σ-bonds.