Poly(1,4:2,2-butanetetrayl). A Novel Polyspirane via Metallocenium-Catalyzed Ring-Opening−Zipping-Up Polymerization of Methylenecyclopropane

Organolanthanide-Mediated Ring-Opening Ziegler Polymerization (ROZP) of Methylenecycloalkanes: A Theoretical Mechanistic Investigation of Alternative Mechanisms for Chain Initiation of the Samarocene-Promoted ROZP of 2-Phenyl-1-methylenecyclopropane

A detailed theoretical investigation of alternative mechanisms for chain initiation of the organolanthanide-promoted ring-opening polymerization of 2-phenyl-1-methylenecyclopropane (PhMCP) with an archetypical [Cp2SmH] model catalyst is presented. Several conceivable pathways for important elementary steps, which also included ring-opening isomerization of PhMCP to phenylbutadienes, were critically scrutinized for a tentative course of the catalytic reaction. The operative mechanism starts with the first exo-methylene C=C insertion into the Sm-H bond in a 1,2 fashion and is followed by shift-based beta-alkyl eliminative cyclopropyl ring opening by cleavage of a proximal bond, while the alternative mechanism that commences with 2,1-insertion and subsequent ring opening by distal bond scission is revealed to be almost entirely precluded. The facile and irreversible insertion process is not found to occur in a regioselective fashion. The ring-opening process is analyzed as the critical step that discriminates between the two conceivable mechanisms. Opening of the cyclopropyl ring is kinetically easy and proceeds readily for the 1,2-insertion species, while a prohibitively large barrier must be overcome for ring opening of 2,1-insertion species. The isomerization of PhMCP in a ring-opened fashion, which would afford phenylbutadienes as possible products, is predicted to be a less likely process, owing to both kinetic and thermodynamic factors. The phenyl functionality has been demonstrated to distinguish between the regioisomeric ring-opening pathways, both kinetically and thermodynamically, thereby rendering this process selective with regard to the regiochemistry. Overall, chain initiation of the samarocene-mediated ring-opening polymerization of PhMCP is predicted to be a smooth, kinetically facile process.

Pd-catalyzed ring-opening copolymerization of 2-aryl-1-methylenecyclopropanes with CO to afford polyketones via alternating insertion of the two monomers and C [bond] bond C activation of the three-membered ring

Pd-bpy complexes catalyze the ring-opening copolymerization of 2-aryl-1-methylenecyclopropanes with CO, affording the new polyketones composed of ring-opened structural units only. Kinetic and isotope-labeling studies revealed the mechanism of the reaction, which involves 1,2-insertion of the cyclic monomer followed by beta-alkyl elimination of the three-membered ring of the polymer chain.