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

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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.

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