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

Abstract

Treatment of N(2),N(6)-bis(6-acrylamidopyridin-2-yl)pyridine-2,6-dicarboxamide with benzimidazole gives the acyclic aza-Michael addition product N(2),N(6)-bis(6-(3-(1H-benzo[d]imidazol-1-yl)propanamido)pyridin-2-yl)pyridine-2,6-dicarboxamide (2). The macrocycle N(1),N(7)-pyridine-2,6-dimethyl-N(2),N(6)-bis(6-(3-(1H-benzo[d]imidazol-1-yl)propanamido)pyridin-2-yl)pyridine-2,6-dicarboxamide dibromide ([H(2)L(2)]Br(2)) is formed through the double alkylation of 2 with 2,6-bis(bromomethyl)pyridine. The imidazole analogues of 2 and [H(2)L(2)]Br(2) (1 and [H(2)L(1)]Br(2), respectively) have also been prepared. Mercuration of the two benzimidazolium groups in [H(2)L(2)]Br(2) with mercury(II) acetate in the presence of [N(CH(3))(4)](2)[HgBr(4)] proceeds to give [HgL(2)][HgBr(4)] in good yield. The ability of [HgL(2)][HgBr(4)] to readily partake in transmetallation reactions is demonstrated by the reaction that occurs with PdCl(2)(COD) to form [PdClL(2)][PF(6)]. The structures of 2, [HgL(2)][HgBr(4)] and [PdClL(2)][PF(6)] have been determined.

Synthesis, structure and dynamics of NHC-based palladium macrocycles

“…2) 18,19 or very large ring sizes (B and C; 28-38 membered). 20,21 Of these systems, tridentate coordination of the macrocycle was observed within B and C, although not in A; the smaller 15 membered ring adopting a bidentate cyclophane geometry 2,22 with no pyridine coordination as a consequence of the short butamethylene spacer. Although showing significantly lower catalytic activity than related non-macrocyclic variants, 7,10,13,14 both xylene and lutidine based B, promote C-C bond coupling reactions.…”

Controlled translocation of palladium(ii) within a 22 ring atom macrocyclic ligand

“…The vinyl groups in 2 are disposed towards aza-Michael additions 23,24 and on treatment with n-butylamine double addition occurs resulting in macrocyclization and formation of H 4 L. H 4 L has potential coordination pockets associated with the 2,6-dicarboxamide (head) and the butylamine (tail) regions of the macrocycle (Scheme 1). The amide NH protons of H 4 L appear as two singlets in the 1 H NMR spectrum at 10.91 and 10.45 ppm for the head and tail regions, respectively, indicating that the two NH protons in each of these regions are equivalent on the NMR timescale.…”

“…As might be expected, the head group pyridine and two associated transoid-carboxamide groups are essentially coplanar. 23,25 In the tail region of the macrocycle one of the amide groups (N7, C21, O4) also has transoid-geometry with the short distance between N7 and the tertiary amine N8 (2.890(4) Å) indicating an intramolecular hydrogen bonding interaction. In contrast, the other amide group in the tail region (N6, C18, O3) exhibits cisoid-geometry with two intermolecular short contacts (N6-N5′, 2.980(3) Å; O3-N1′, 2.962(3) Å) that are consistent with hydrogen bonds.…”

Synthesis, Structures, and Catalytic Properties of Dinuclear Iridium(I) Complexes with a Hexadentate Macrocyclic Diamine‐Tetracarbene Ligand

“…Since the isolation of the first stable N‐heterocyclic carbene (NHC) by Arduengo and co‐workers, NHCs have been extensively employed as ancillary ligands in organometallic chemistry due to the facile tuning of their electronic and steric effects through introduction of substituents on the heterocyclic rings In the past decades, metal complexes with various types of macrocyclic NHC‐containing ligands[2l] including bidentate, tridentate, and tetradentate ligands as well as high‐denticity ligands with more than four donors, have been reported, some of which have found potential applications as luminescent materials,[3a] medicines,[4a] and catalysts. [8c], [10c]…”