Neutral Unsymmetrical Coordinated Cyclophane Polymerization Catalysts

Abstract

Cyclophane structures can control steric pressure in the otherwise open spaces of square‐planar d8‐metal catalysts. This elegant concept was so far limited to symmetrical coordinated metals. We report how a cyclophane motif can be generated in ligands that chelate via two different donors. An ancillary second imine in the versatile κ2‐N,O‐salicylaldiminato catalyst type enables ring closure via olefin metathesis and selective double bond hydrogenation to yield a 30‐membered ring efficiently. Experimental and theoretical analyses show the ancillary imine is directed away from the active site and inert for catalysis. In ethylene polymerization the cyclophane catalyst is more active and temperature stable vs. an open structure reference, notably also in polar solvents. Increased molecular weights and decreased degrees of branching can be traced to an increased energy of sterically demanding transition states by the encircling cyclophane while chain propagation remains highly efficient.

Origin of Suppressed Chain Transfer in Phosphinephenolato Ni(II)-Catalyzed Ethylene Polymerization

“…Ethylene dissociation takes place via a single-step ( TS-II Decoor ) process with a similar energy barrier for the two catalysts (16.2 and 16.7 kcal/mol for 1 and 2 , respectively). As a consequence, the ethylene decoordination step is not the decisive step , for the microstructure and molecular weights of the polyethylene obtained.…”

Suppression of Chain Transfer and Promotion of Chain Propagation in Neutral Anilinotropone Nickel Polymerization Catalysis

“…This is perhaps attributed to catalyst degradation and accelerated chain transfer, respectively. This phenomenon is common in salicylaldiminato Ni­(II) species. − …”

“…The 9-anthracenyl group has been proved to be crucial in salicylaldiminato Ni­(II) catalysts. − As a comparison, the isomer of anilinotropone Ni6 , namely, the salicylaldiminato Ni6-iso , is also synthesized (Scheme , see the Supporting Information). At 8 bar, raising the reaction temperature from 30 to 60 °C leads to the increase of TOF using the anilinotropone Ni­(II) catalyst Ni6 in ethylene polymerization (Table , entries 1–4), with the maximum TOF value being 1.6 × 10 5 h –1 .…”

“…α-Diimine cationic Ni­(II) and Pd­(II) catalysts, as a pioneer, overcome chain transfer and thus produce high-molecular-weight polymers in ethylene polymerization. − Significant efforts on modifying this type of catalyst advance the enhancement of TOF and MW. − Salicylaldiminato neutral Ni­(II) catalysts as another notable finding afford a more functional-group tolerant alternative relative to cationic analogues. ,,− Further neutral P,O-type catalysts predominantly including phosphine-sulfonate Ni­(II) and Pd­(II) catalysts and phosphine-phenolate Ni­(II) catalysts are a breakthrough to generate highly linear (functionalized) polyolefins. ,,,,− These above catalysts, along with other benchmark catalysts, − efficiently control fundamental steps in ethylene polymerization and even in copolymerization of ethylene with polar monomers.…”

Hydrogen-bonding and resonance stabilisation effects in cationic bis(iminium) phenoxide diacids

“…In these systems, one imine is permanently rotated away from the oxygen to relieve steric strain and enable stabilising imine-CHÁ Á ÁO interactions. 15,[25][26][27][28] Adoption of the unique conformation observed in the cationic conjugate diacid therefore implies that the typical steric constraint of the system is outweighed by alternative stabilising interactions. One such stabilising force is the enhanced delocalisation of electron density from the oxygen atom into the central p-ring and pendent iminium groups.…”