UCL Discovery

Abstract

A series of homoleptic guanidinate-type complexes of the heavier alkaline earth (Ae) metals calcium and strontium have been prepared. The six-coordinate compounds [Ae{(PrNC)-Pr-i(NPh2)(CNPr)-Pr-i}(2)(THF)(2)] (Ae = Ca and Sr) were synthesised through reactions of the appropriate THF-solvated hexamethyldisilazide [Ae{N(SiMe3)(2)}(2)(THF)(2)] with two molar equivalents of diphenylamine and 1,3-di-iso-propylcarbodiimide. Both compounds were shown to crystallise with a cisoid arrangement of the two THF molecules at the metal centres. In contrast, the (Me3Si)(2)N-substituted calcium guanidinate, [Ca{CyNC{N(SiMe3)(2)}CNCy}(2)(THF)(2)], contains two coordinated THF molecules with a trans disposition. Further reactions of the free amidine [{(2-FC6H4)N}C((NHPr)-Pr-i)(2)] with either [Ca{N(SiMe3)(2)}(2)(THF)(2)] or its dimeric unsolvated analogue provided monomeric or dimeric derivatives respectively in which the ligands had tautomerised to an anisobidentate form. A further reaction of the phosphaguanidine [CyN=C(PPh2)N(H)Cy] with [Sr{N(SiMe3)(2)}(2)(THF)(2)] provided the first example of a phosphaguanidinate complex of this heavier alkaline earth metal. This compound has also been characterised in the solid state and shown to exist with a transoid configuration of the coordinated THF molecules.