Synthesis and M-Cγ hemilability of group 2 bis(phosphinimino)methanides

Shabana A. Ahmed, Michael S. Hill, Peter B. Hitchcock

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49 Citations (Scopus)

Abstract

The sterically demanding bis(phosphinimino)methanide [CH(Ph 2PNC6H2-2,4,6-Me3)2] -, formed by deprotonation of the bis(phosphinimino)methane [CH 2(Ph2PNC6H2-2,4,6-Me 3)2], has been employed in the synthesis of a variety of homo- and heteroleptic complexes of the group 2 metals Mg, Ca, Sr, and Ba. The crystallographically characterized magnesium complexes, the dimer [{CH(Ph 2PNC6H2-2,4,6-Me3) 2}MgCl]2 and the monomer [{CH(Ph2PNC 6H2-2,4,6-Me3)2}MgCl(THF)], were synthesized in a similar manner by deprotonation of the ligand precursor with MeMgCl but crystallized either without or in the presence of THF. The synthetically useful [{CH(Ph2PNC6H2-2,4,6- Me3)2}K], formed from [CH2(Ph 2-PNC6H2-2,4,6-Me3)2] and [KN(SiMe3)2] in toluene, was shown in the solid state to consist of dimeric species formed by K-mesityl multihapto interactions. Homoleptic [{CH(Ph2PNC6H2-2,4,6-Me 3)2}2Ae] (Ae = Ca and Ba) and heteroleptic [{CH(Ph2PNC6H2-2,4,6-Me3) 2}AeN(SiMe3)2(THF)] (Ae = Ca, Sr) complexes of the heavier alkaline earth metals Ca, Sr, and Ba were most readily provided by a "one-pot" procedure utilizing the appropriate AeI2 reagent and variation of [CH2(Ph2PNC6H 2-2,4,6-Me3)2] and [KN-(SiMe3) 2] stoichiometry in THF. The complexes were shown by 31P{1H} NMR to adopt variable and hemilabile (ΔG = ca. 50 kJ mol-1) coordination geometries involving, most likely, M-Cγ coordination and re-coordination. The ionic nature of the bonding was also implicated in our lack of success in the application of these complexes in reactivity studies with a variety of bulky protic reagents. This behavior was investigated by DFT (B3LYP/LANL2DZ) methods to highlight the differences in NBO charge distribution between model ionic bis(phosphinimino)methanide and β-diketiminato complexes.

Original languageEnglish
Pages (from-to)394-402
Number of pages9
JournalOrganometallics
Volume25
Issue number2
DOIs
Publication statusPublished - 16 Jan 2006

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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