Cyclotriveratrylene-tethered trinuclear palladium(ii)–NHC complexes; reversal of site selectivity in Suzuki–Miyaura reactions. Issue 39 (20th September 2019)

• Record Type: Journal Article
• Authors: Fowler, Jonathan M.; Britton, Edward; Pask, Christopher M.; Willans, Charlotte E.; Hardie, Michaele J.
• Is Part Of: Dalton transactions. Volume 48:Issue 39(2019)
• Page Start: 14687
• Page End: 14695
• Publication Date: 2019-09-20
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c9dt03400e
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Trimetallic Pd–NHCs with a cyclotriguaiacylene scaffold display variable host–guest interactions and, along with monomeric analogues, catalyse cross-coupling reactions with a switch in the normal regioselectivity. Abstract : The trinuclear complexes [{PdI2 (pyCl)}3 (L1)] C1 and [{PdI2 (pyCl)}3 (L2)] C2, where pyCl = 3-chloropyridine, L1 = methyl(cyclotriguaiacylenyl)methylbenzimidazol-2-ylidene and L2 = benzyl(cyclotriguaiacylenyl)methylbenzimidazol-2-ylidene, each feature three palladium N-heterocyclic carbene (NHC) centres tethered onto a host-type cyclotriguaiacylene scaffold. Crystal structures of different solvates of complex C1 reveal different host–guest motifs including intra-cavity binding of dioxane guests concomitant with intramolecular halogen bonding interactions of C1 . Mononuclear NHC analogues of C1 and C2, namely [PdI2 (pyCl)(L3)] C3 and [PdI2 (pyCl)(L4)] C4, where L3 = (3-chloropyridyl)-1-(2-methoxyphenyoxy)methyl-3-methylbenzimidazol-2-ylidene and L4 = (3-chloropyridyl)-1-(2-methoxyphenyoxy)methyl-3-benzylbenzimidazol-2-ylidene, were also synthesised and their crystal structures determined. Complexes C1–C4 are competent catalysts for Suzuki Miyaura cross-coupling, and interestingly exhibit a switch in the normal regioselectivity observed for reactions of 2, 4-dibromopyridine with aryl boronic acids, usually C2-selective, yielding C4-arylated product preferentially over C2-arylated product.