Selective palladation of a large (32 ring atom) macrocyclic ligand at a bis(N-heterocyclic carbene) coordination pocket through transmetallation of the corresponding mercury(ii) derivative?

Dalton Transactions Pub Date: 2012-08-28 DOI: 10.1039/C2DT31818K

Abstract

Treatment of N2,N6-bis(6-acrylamidopyridin-2-yl)pyridine-2,6-dicarboxamide with benzimidazole gives the acyclic aza-Michael addition product N2,N6-bis(6-(3-(1H-benzo[d]imidazol-1-yl)propanamido)pyridin-2-yl)pyridine-2,6-dicarboxamide (2). The macrocycle N1,N7-pyridine-2,6-dimethyl-N2,N6-bis(6-(3-(1H-benzo[d]imidazol-1-yl)propanamido)pyridin-2-yl)pyridine-2,6-dicarboxamide dibromide ([H2L2]Br2) is formed through the double alkylation of 2 with 2,6-bis(bromomethyl)pyridine. The imidazole analogues of 2 and [H2L2]Br2 (1 and [H2L1]Br2, respectively) have also been prepared. Mercuration of the two benzimidazolium groups in [H2L2]Br2 with mercury(II) acetate in the presence of [N(CH3)4]2[HgBr4] proceeds to give [HgL2][HgBr4] in good yield. The ability of [HgL2][HgBr4] to readily partake in transmetallation reactions is demonstrated by the reaction that occurs with PdCl2(COD) to form [PdClL2][PF6]. The structures of 2, [HgL2][HgBr4] and [PdClL2][PF6] have been determined.

Graphical abstract: Selective palladation of a large (32 ring atom) macrocyclic ligand at a bis(N-heterocyclic carbene) coordination pocket through transmetallation of the corresponding mercury(ii) derivative
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