Synthesis and Ethylene Reactivity of Dinuclear Iron and Cobalt Complexes Supported by Macrocyclic Bis(pyridine-diimine) Ligands Containing o-Terphenyl Linkers

Abstract

The synthesis and ethylene reactivity of a new family of dinuclear Co2Br4 and Fe2Br4 complexes supported by binucleating macrocyclic bis­(pyridine-diimine) (PDI) ligands that contain 4,4″-R2-3,3″-o-terphenyl linkers (1, R = H; 2, R = Me; 3, R = iPr) are described. In the solid state, (1–3)­M2Br4 (M = Zn, Fe, Co) adopt C s -skew-syn structures in which the (PDI)­M planes are skewed 49–82° relative to each other and both middle rings of the o-terphenyl bridges are on the same side of the molecule. The metal–metal distances range between 5.7600(8) and 6.232(1) Å. In solution, (1)­M2Br4 (M = Zn, Co, Fe) undergo a fluxional process that permutes the two inequivalent (PDI)­M units, while (2)­M2Br4 and (3)­M2Br4 are static and adopt C s -symmetric structures similar to those observed in the solid state. Activation of (2)­Fe2Br4 and (3)­Fe2Br4 with MMAO-12 or triisobutylaluminum (TIBA) in the presence of ethylene generates catalysts that produce solid polyethylene (M w = 4500–280000 Da), which contrasts with the reported production of α-olefins by analogous mononuclear (PDI)­FeCl2 catalysts. (3)­Fe2Br4/TIBA and (3)­Fe2Br4/MMAO-12 produce polyethylenes with broad molecular weight distributions (MWDs) due to chain transfer to Al. (3)­Co2Br4/1000 TIBA and (3)­Co2Br4/1000 MMAO-12 also produce polyethylenes with broad MWDs. However, in these cases chain transfer to Al is not operative and the broad MWDs result from multisite behavior.

Switch in Selectivities by Dinuclear Nickel Catalysis: 1,4-Hydroarylation of 1,3-Dienes to Z-Olefins

“…Transition metal complexes supported by redox-active pyridine-diimine ligands have attracted great attention in the field of earth-abundant metal catalysis . In this context, di- or multinuclear transition metal complexes supported by two or more PDI moieties have been developed by Li, Toti, Osakada, Sun, Jordan, and others, which have been studied in catalytic ethylene polymerization. In addition, Tomson and co-workers pioneered elegant studies on interesting structures of PDI-macrocyclic ligand-based binuclear metal complexes and their reactivities on small-molecule activation .…”

Dinuclear Cobalt Complex-Catalyzed Stereodivergent Semireduction of Alkynes: Switchable Selectivities Controlled by H2O

“…Remarkable advances in homogeneous catalysis have been achieved with systems comprising late transition metals and PDI ligands. − To date, several multinuclear transition-metal complexes supported by macrocyclic ligands bearing two or more PDI moieties have been developed, and they exhibited interesting reactivity differences in catalytic ethylene polymerization compared to analogous mononuclear complexes. − However, current uses of bis-PDI-based dinuclear complexes in the catalytic methodology are still in their infancy and further research efforts are warranted. In 2017, Tomson and co-workers reported an attractive work describing the dicobalt­(II) complexes bound by pyridyl diimine-containing macrocyclic ligands with flexible links. − Additionally, each cobalt atom was bonded by a PMe 3 ligand, which can further react with the dicobalt-bridging nitrides.…”

Coplanar binuclear group 4 post-metallocene complexes supported by chelating μ-(σ2-aryl) ligands: characterisation and olefin polymerisation catalysis

“…1,2 For multinuclear olefin polymerisation catalysts, proximal active sites can react complementarily and synergistically to achieve activity and selectivity that is superior to their mononuclear analogues. 3,4 Design strategies for bimetallic systems feature judiciously constructed bis-ligand assemblies, which can be (1) flexible, in order to adopt optimal structures to minimise activation energies [including constrained geometry catalysts of Zr 2 5 and Ti 2 6,7 (plus heteronuclear Ti–Cr 8 ), Cp*-amidinate-Zr 2 9 ], or (2) conformationally constrained (shape-persistent) or rigid, 10,11 to impart favourable entropic terms [including phenoxyimine-Ti 2 and -Zr 2 , 12,13 pyridylamide-Hf 2 , 14 amine-bis(phenolate)-Zr 2 , 15 μ-( cis -C 4 H 4 )-Ti 2 16 ].…”