Carbodiimideinsertion reactions of homoleptic heavier alkaline earth amides and phosphides

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{ⁱPrNC(NPh₂)CNⁱPr}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)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-FC₆H₄)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.