The Structural Characteristics of Organozinc Complexes Incorporating N,N´-bidentate Ligands

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)]212a, that bridges two Zn[(p-Tol)N(2-C5H4N)]Me12b 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]e2NC{NiPr}{NHiPr}16 as a result of protonation at the guanidine ligand in addition to the Zn¿Me bond.