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(CH2CH2PPri 2)2}2]

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.