Isolation of (Aryl)-(Imino) Phosphide and (Aryl)-(Phosphaalkene) Amide Complexes of Alkali Metals from Carbene-Phosphinidenes under Reductive-Thermal Rearrangements

Graphical Abstract

Carbene-anchored chloro-phosphinidenes have undergone unprecedented rearrangements under reductive-thermal conditions in the presence of alkali metals to afford the corresponding (aryl)-(imino)phosphide and (phosphaalkene)amide complexes. The former proved to be an excellent precursor for a novel chelating ligand with dual PN-donor sites, which provided direct synthetic routes for Cu^I₄, Ag^I₈ clusters, and cyclic alkyl(aminoboryl) phoshaalkenes.

Abstract

Two-electron reduction of cyclic alkyl(amino) carbene (cAAC)-supported chloro-phosphinidene cAAC=P−Cl (1) followed by unprecedented thermal rearrangements afforded the alkali metal complexes of (aryl)-(cyclic alkyl(imino)) phosphides 3 a–3 c, 4 a–4 b through migration of the 2,6-diisopropylphenyl (dipp) group from N to the P centre, and the (aryl)-(cyclic alkyl(phosphaalkene)) amide 5 through cleavage of the CMe₂−N bond followed by energetically favoured 5-exo-tet ring-closure in the presence of the alkali metals Cs (3 a–3 c), K (4 a, 4 b), and Li (5). Compound 3 a was found to be photoluminescent (PL), emitting bright orange light under a laboratory UV lamp of wavelength 365 nm with PL quantum yield (ϕ_PL) of 2.6 % (λ_em=600 nm), and an average lifetime (τ) of 4.8 μs. Reaction of 3 a with CuCl and AgOTf afforded (aryl)-(cyclic alkyl(imino)) phosphide-stabilized tetra-nuclear Cu^I (6), and octa-nuclear Ag^I (7) clusters, respectively. Moreover, complexes 3 a–3 c provided a direct route for the stabilization of cyclic alkyl(aminoboryl) phosphaalkenes 8 a-8 c when treated with 1-bromo-N,N,N′,N′-tetraisopropylboranediamine.