Carbodiimide insertion reactions of homoleptic heavier alkaline earth amides and phosphides

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{iPrNC(NPh2)CNiPr} 2(THF)2] (Ae = Ca and Sr) were synthesised through reactions of the appropriate THF-solvated hexamethyldisilazide [Ae{N(SiMe 3)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)2N-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-FC 6H4)N}C(NHiPr)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 [CyNC(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.