Synthesis and characterisation of alkaline earth bis(diphenylphosphano)metallocene complexes and heterobimetallic alkaline earth metal/platinum(ii) complexes [Ae(thf)x(η5-C5H4PPh2)2Pt(Me)2] (Ae = Ca, Sr, Ba)

Abstract

A series of alkaline earth metallocene complexes carrying the diphenylphosphanocyclopentadienyl ligand, [Ae(L)_x(η⁵-C₅H₄PPh₂)₂] (Ae = Ca, L = thf, x = 1 (6a); Ae = Ca, L = dme, x = 1 (6b); Ae = Sr, L = thf, x = 1 (7); Ae = Ba, L = thf, x = 1 (8a); Ae = Ba, L = dme, x = 2 (8b)), were prepared by redox transmetallation/protolysis from the free metals, diphenylmercury and diphenylphosphanocyclopentadiene. These complexes were characterised using multinuclear NMR spectroscopy and two by single crystal X-ray diffraction. [Ca(dme)(η⁵-C₅H₄PPh₂)₂] (6b) is a discrete neutral monomeric eight coordinate molecule in which the phosphorus atoms are not coordinated to the calcium ion and the larger barium analogue, ten-coordinate [Ba(dme)₂(η⁵-C₅H₄PPh₂)₂] (8b), has an extremely bent sandwich structure due to the two dme ligands attached to the metal. Bimetallic complexes, [Ae(thf)_x(η⁵-C₅H₄PPh₂)₂Pt(Me)₂].(solv) (Ae = Ca, L = thf, x = 2, solv = 1.5thf (9); Ae = Sr, L = thf, x = 3, solv = 1.5thf (10); Ae = Ba, L = thf, x = 3, solv = thf (11)) were obtained by reaction of the homometallic complexes with [Pt(cod)(Me)₂]. The crystal structures of [Ca(thf)₂(η⁵-C₅H₄PPh₂)₂Pt(Me)₂].1.5thf (9), [Sr(thf)₃(η⁵-C₅H₄PPh₂)₂Pt(Me)₂].1.5thf (10) and [Ba(thf)₃(η⁵-C₅H₄PPh₂)₂Pt(Me)₂].thf (11) show the eight (calcium) and nine coordinate (strontium and barium) fragments acting as a chelating metalloligand attached to the square planar platinum through the phosphorus donor atoms. The solution chemistry of these bimetallic complexes has been investigated by NMR spectroscopy, electro-spray ionisation mass spectrometry and conductivity experiments which indicate that the bimetallic compounds persist in solution.