Influence of bulky substituents on the regioselective group-transfer reactions of diorganozinc compounds with N, N′-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene

Diorganozinc compounds R₂Zn (R=alkyl or aryl) react with N,N′-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene, (i-Pr₂Ph)N=CHCHp=N(i-Pr₂Ph) (i-Pr₂Ph-DAB) to give thermally unstable 1:1 coordination complexes R₂Zn(i-Pr2Ph-DAB), which subsequently undergo a slow regioselective alkyl or aryl group-transfer reaction from the zinc atom to an imine-nitrogen or a carbon atom of the NCCN system of the i-Pr₂Ph-DAB ligand. In the case of R=methyl, n-propyl, n-butyl, s-butyl, neopentyl and benzyl, C-alkylation occurs with a subsequent 1,2- hydrogen shift in the amino-imino skeleton affording RZn[(i-Pr₂Ph)N-CH₂-CR=N(i-Pr₂Ph)], whereas for R=t- butyl the C-alkylated product t-BuZn[(i-Pr₂Ph)N---CH(t-Bu)---CH=N(i-Pr₂Ph)] is stable. Surprisingly, diphenylzinc reacts with i-Pr₂Ph-DAB exclusively to give the N-arylated product PhZn[(i-Pr₂Ph)N=CHCH=N(Ph)(i-Pr₂Ph)].