Synthesis, spectroscopic and structural properties of an unusual series of homoleptic phosphine oxide complexes of the alkaline earth dications

摘要

The distorted tetrahedral [M(OPPh3)(4)](SbCl6)(2) (M = Mg, Ca, Sr) are obtained from MCl2, OPPh3 and SbCl3 in suitable solvent conditions, while Ba2+ gives [Ba(OPPh3)(5)](SbCl6)(2). The chelating o-C6H4(P(O)Ph-2)(2) gives the tris complexes [M{o-C6H4(P(O)Ph-2)(2)}(3)](SbCl6)(2), while under similar conditions the stoichiometries of the products obtained using Ph2P(O)CH2P(O)Ph-2 vary, with M; and products include the five-coordinate [Mg{Ph2P(O)CH2P(O)Ph-2}(2)(H2O)](SbCl6)(2), the distorted octahedral [M{Ph2P(O)CH2P(O)Ph-2}(3)](SbCl6)(2) (M = Ca or Sr) and the seven-coordinate [Sr{Ph2P(O)CH2P(O)Ph-2}(3)(EtOH)](SbCl6)(2). Strontium is unusual in that both six- and seven-coordinate species are evident and may be isolated depending upon the reaction conditions. These are the first reported Group 2 complexes with bidentate phosphine oxides and there are no other phosphine oxide complexes with Sr or Ba. Crystal structures are reported for [Mg(OPPh3)(4)](SbCl6)(2).CH2Cl2 [Ca{Ph2P(O)CH2P(O)Ph-2}(3)] (SbCl6)(2).2CH(2)Cl(2) and [Sr{Ph2P(O)CH2P(O)Ph-2}(3)(EtOH)](SbCl6)(2).0.45CH(2)Cl(2). The compounds isolated show significant dependence upon the charge:radius ratio of the metal and the steric bulk and rigidity of the ligand. (C) 2004 Elsevier Ltd. All rights reserved.