Phosphine complexes of aluminium(III) halides – preparation and structural and spectroscopic systematics

摘要

Six-coordinate pseudo-octahedral complexes trans-[AlX_2(L–L)_2][AlX_4] (X = Cl, Br or I; L–L = o-C_6H_4(PMe_2)_2, Me_2P(CH_2)_2PMe_2) are produced from reaction of AlX_3 with the diphosphine in CH_2Cl_2 (X = Cl) or toluene (X = Br or I) solution. Four-coordinate dimers [Cl_3Al(μ-L’–L’)AlCl_3] (L’–L’ = Me_2-P(CH_2)_2PMe_2, Cy_2P(CH_2)_2PCy_2), and the tetrahedral cation [AlCl_2{o-C_6H_4(PPh_2)_2}][AlCl_4] were also obtained. Both four- and five-coordinate complexes [AlX_3(PMe_3)] and [AlX_3(PMe_3)_2] could be isolated with PMe_3 depending upon the ratio of reagents used. These extremely moisture sensitive complexes have been characterised by microanalysis, IR and multinuclear NMR (~1H, ~(31)P{~1H} and ~(27)Al) spectroscopy. X-ray crystal structures are reported for [AlCl_2{o-C_6H_4(PMe_2)_2}_2][AlCl_4], [AlCl_2{Me_2P(CH_2)_2PMe_2}_2][AlCl_4], [Cl_3-Al{μ-Me_2P(CH_2)_2PMe_2}AlCl_3], [Cl_3Al{μ-Cy_2P(CH_2)_2PCy_2}AlCl_3], [AlCl_3(PMe_3)], [AlCl_3(PMe_3)_2], and for the six-coordinate cation complex [AlCl_2{o-C_6H_4(PPh_2)_2}_2][AlCl_4], although a bulk sample of the last could not be isolated. Tertiary arsines (AsPh_3 or AsEt_3) form only 1: 1 complexes even with excess arsine present. The unstable [AlCl_2{o-C_6H_4(AsMe_2)_2}][AlCl_4] is also described, and shown to decompose rapidly in CH_2Cl_2 solution to form the diquaternised diarsine cation [o-C_6H_4(AsMe_2)_2(CH_2)][AlCl_4]_2, which was fully characterised. Comparisons are drawn with the corresponding gallium(III) systems (Cheng et al., Inorg. Chem., 2007, 46, 7215–7223) and with AlX3 complexes of Group 16 ligands (George et al., Dalton Trans., 2014, 43, 3637–3648), and it is concluded that the differences between the Al and Ga systems reflect the higher Lewis acidity of aluminium(III) towards soft donor ligands.