Co-ordination behaviour of potentially tridentate diphosphinoamido ligands: synthesis and crystal structures of the complexes [CrCl{N(CH2CH2PMe2)2}2], [Cr2Cl3{N(CH2CH2PMe2)2}{CH2P(Me)CH2CH2NCH2CH2PMe2}] and [Cr2Cl4{N(CH2CH2PPri2)2}2]

Abstract

The reaction of CrCl₃·3tHf (thf = tetrahydrofuran) with bis(2-dialkylphosphinoethyl)amidolithium reagents, LiN(CH₂CH₂PR₂)_2′ resulted in the formation of the new compounds [CrCl{N(CH₂CH₂PMe₂)₂}₂]1, [Cr₂Cl₃{N(CH₂CH₂PMe₂)₂}{CH₂P(Me)CH₂CH₂NCH₂CH₂PMe₂}]2 and [Cr₂Cl₄{N(CH₂CH₂PPrⁱ₂)₂}₂]3 depending on reaction conditions and stoichiometry. Thus, if 2 equivalents (per Cr) of LiN(CH₂CH₂PMe₂)_2′are used 1 may be isolated where chromium is bound to two amido ligands each in different co-ordination modes (bi- and tri-dentate). With 1.5 equivalents of LiN(CH₂CH₂PMe₂)_2′2is formed which has a binuclear structure with bridging amido ligands and an unusual α-metallated PCH₂ group. With the more bulky LiN(CH₂CH₂PPrⁱ₂)_2′3 may be isolated in which a binuclear structure is bridged by both bi- and tri-dentate amido ligands. All complexes have been characterised by analysis, mass spectroscopy, and single-crystal X-ray crystallography.