1:1 and 2:1 Lithium Zincates with Intramolecular Coordination. Structures of Li(thf)Zn(C₆H₄CH₂NMe₂-2)₃ and Li₂Zn(C₆H₄CH₂NMe₂-2)₄

Abstract

Homoleptic lithium zincates with intramolecular Li−N coordination, i.e., Li(thf)nZn(C6H4CH2NMe2-2)3 (n = 0 (1); n = 1 (1(thf))) and Li2Zn(C6H4CH2NMe2-2)4 (2) have been prepared by reacting [Li(C6H4CH2NMe2-2)]4 with Zn(C6H4CH2NMe2-2)2. In the solid state 1(thf) is a monomer containing a distorted tetrahedral zinc atom. The zinc is surrounded by three monoanionic C6H4CH2NMe2-2 (dmba) ligands, which all show a different bonding mode: η1-C bonding to zinc and nitrogen coordination to lithium; η1,μ2-C bridge bonding to zinc and lithium with Li−N coordination; and C,N-chelate bonded to zinc. One thf coordinates to lithium. In the solid state, 2 is a monomeric dilithium tetraarylzincate complex containing a tetrahedral zinc atom. The four dmba ligands are all similarly η1,μ2-C bridge-bonded to zinc and lithium, and each lithium is four-coordinate by two additional Li−N bonds. The reaction of LiCH2SiMe3 and Zn(C6H4CH2NMe2-2)2 did not give a mixed zincate complex but the respective homoleptic zincate complexes instead. Both homoleptic and in situ prepared mixed zincate complexes react readily with 2-cyclohexen-1-one, but the product composition shows that the in situ prepared zincate disproportionates into the corresponding homoleptic zincates prior to reaction.