The structural characteristics of organozinc complexes incorporating N,N′-bidentate ligands

Abstract

Dimethylzinc reacts with an excess of N-2-pyridylaniline 6 to give the homoleptic species, Zn[PhN(2-C₅H₄N)]₂8. Single crystal X-ray diffraction reveals a solid-state dimer based on an 8-membered (NCNZn)₂ core motif. Zn[CyN(2-C₅H₄N)]Me (Cy = c-C₆H₁₁) 10, prepared by the combination of ZnMe₂ with the corresponding cyclohexyl-substituted pyridylamine, is also dimeric in the solid state but reveals a central (ZnN)₂ metallacycle. Employment of (p-Tol)NH(2-C₅H₄N) (p-Tol = 4-MeC₆H₄) 11 yielded the tris(zinc) adduct Zn₃[(p-Tol)N(2-C₅H₄N)]₄Me₂12, which incorporates a central chiral molecule of ‘Zn[(p-Tol)N(2-C₅H₄N)]₂’ 12a, that bridges two ‘Zn[(p-Tol)N(2-C₅H₄N)]Me’ 12b units. A similar trimetallic structure is noted when the pyridylaniline substrate 11 is replaced with the bicyclic guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH), affording Zn₃(hpp)₄Me₂13. Spectroscopic studies point to retention of the solid-state structure of 13 in hydrocarbon solution. Reaction of 13 with dimesityl borinic acid, Mes₂BOH (Mes = mesityl), affords Zn₃(hpp)₄(OBMes₂)₂14 in which the trimetallic core is retained. This reactivity is in contrast to the closely related reaction of dimeric Zn[Me₂NC{NⁱPr}₂]Me 15 with Mes₂BOH, which yielded Zn[Me₂NC{NⁱPr}₂][OBMes₂]·Me₂NC{NⁱPr}{NHⁱPr} 16 as a result of protonation at the guanidine ligand in addition to the Zn–Me bond.