Nuclear magnetic resonance spectroscopic characterisation and the crystal and molecular structures of Ph3PSe·AlCl3and Ph3PSe·AlCl3: a classification of the co-ordinative bonding modes of the phosphine chalcogenides

Abstract

A series of compounds with the general formula R₃PE·AlCl₃(R = Ph or NMe₂, E = S or Se) has been examined by n.m.r. spectroscopy as a contribution toward the characterisation of the P–E bond and of the co-ordinate bond. Two derivatives, Ph₃PS·AlCl₃ and Ph₃PSe·AlCl₃, have been studied by X-ray crystallography. [Crystal data: C₁₈H₁₅AlCl₃PS, monoclinic, space group, P2₁/n, a= 9.710(2), b= 9.464(1), c= 21.893(5)Å, β= 95.15(2)°Z= 4, R= 0.042; C₁₈H₁₅AlCl₃PSe, triclinic, space group, Pa= 8.967(2), b= 12.626(4), c= 18.242(4)Å, α= 84.83(2), β= 89.02(2), γ= 85.67(2)°, Z= 4, R= 0.044.] In contrast to the oxygen analogues, the sulphur and selenium derivatives exhibit bent geometries [P–S–Al 109.62(8), P–Se–Al (mean)= 107.0(1)°]. The structures are maintained in solution, as demonstrated by the ²⁷Al n.m.r. spectra. The ³¹P and ¹³C n.m.r. spectra are informative of the changes associated with adduct formation, and show the oxygen derivatives (E = O) to be unique. Disruption of the P–E π interaction due to adduct formation is more dramatic for the sulphur and selenium than for the oxygen derivatives. The extensive information available in the literature is re-evaluated in the light of the present results, and a classification for the co-ordinative bonding modes of the phosphine chalcogenides is proposed.