Magnesium, tris salts structure

Excluding the a-P-, a-Si-substituted carbanions which are listed in Table 2, there exist relatively few simple a-P-substituted carbanions whose structures are known. References to the crystal structures of some tri (alkyl or aryl) substituted phosphines are listed in Table 4. Few if any of these compounds have been utilized as synthetic reagents. Only two synthetically useful phosphorus-stabilized carbanions of Group la or Ila metal cations have been examined by X-ray diffraction analysis. Hie lithium carbanion of 2-benzyl-2-oxo-l,3,2-diazaphosphorinane (198) crystallizes as a monomeric bis-THF solvate (199) with a tricoordinate lithium atom. The magnesium salt of diethoxyphosphinyl acetone (200) is cluirac-terized as an intramolecularly chelated trimer similar in structure to [Mg(acac)]3. The Cu salt of this 3-keto phosphorus-stabilized anion exists only as a monomer. 

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