Synthesis of alkaline earth metal bis(2-phosphaethynolates)

Abstract

The reaction of dimethylcarbonate with magnesium bis(triisopropylsilyl phosphanide) or the alkaline earth metal bis[bis(trimethylsilyl)phosphanide] in 1,2-dimethoxyethane yields the corresponding bis(2-phosphaethynolate) of magnesium ( 1), calcium ( 2), strontium ( 3) and barium ( 4). These compounds decompose upon isolation and have to be stored in an etheral solution at low temperatures. The structure of (dme) 3Ca(OCP) 2 shows bent CaOC moieties and rather long CP triple bonds of 1.575 Å. In order to ensure a quantitative reaction an excess of dimethylcarbonate has to be used. For the strontium derivative a side reaction of a 1:3 stoichiometry of M[P(SiMe 3) 2] 2 to (MeO) 2CO gave a tridentate ligand which bridges two strontium atoms. The molecular structure of dimeric (dme) 2Sr{OC[PC(O)OMe] 2} ( 5) showed the delocalization of the anionic charge within the OCPCPCO fragment.