Functional Group Chemistry at the Group 4 Bent Metallocene Framework: [2+2] Cycloaddition of the Parent Bis(vinyl-Cp/vinyl-Ind)ZrCl₂ Systems

Abstract

Bis(vinyl-Cp)zirconium dichloride (6) undergoes a clean intramolecular photochemically induced [2þ2] cycloaddition reaction to yield the cyclobutylene-bridged ansa-zirconocene isomer (7) when irradiated with UV light (HPK 125, Pyrex filter) at ambient conditions. Both the open and the ansabridged isomers (6, 7) were characterized by X-ray diffraction. The corresponding bis(2-vinylindenyl)ZrCl 2 complex (12) also closes rapidly and completely to the ansa-metallocene (13) upon photolysis. The bis(2-butadienylindenyl)ZrCl 2 complex (20) undergoes a formal [4þ4] cycloaddition reaction upon photolysis to yield its ansa-metallocene isomer 21, exhibiting an eight-membered carbocyclic bridging unit. The metallocene complexes prepared and characterized in this study give very active ethene polymerization catalysts upon activation with excess methylalumoxane.

Facile Synthesis of 3-Arylindenes by HMPA-Promoted Direct Arylation of Indenes with Aryl Fluorides

“…1 Furthermore, they are also valuable ligand precursors in group IV metallocene complexes used in metallocene-catalyzed olefin polymerization. 2 Consequently, the efficient synthesis of structurally diverse substituted indenes continues to attract extensive attention from synthetic chemists. 3 To date, many synthetic approaches toward the construction of indene ring systems have been developed, such as the Ru-catalyzed C–H alkylation of indenes with alcohols, 4 the Au-mediated cyclodehydration of 1,1,3,3-tetraisopropyldisiloxane- and aryl-substituted allylic alcohols, 5 the iron-catalyzed domino reaction of benzylic compounds and alkynes, 6 and the iodonium-promoted 5-endo-dig carbocyclization of 2-substituted ethynylmalonates.…”

“…Substituted indene derivatives are very important carbocycles that are found in pharmaceuticals and agrochemicals (Figure ). Furthermore, they are also valuable ligand precursors in group IV metallocene complexes used in metallocene-catalyzed olefin polymerization . Consequently, the efficient synthesis of structurally diverse substituted indenes continues to attract extensive attention from synthetic chemists .…”

Bio-Organometallic Chemistry, ansa-Metallocenes, and Frustrated Lewis Pairs: Functional Group Chemistry at the Group 4 Bent Metallocenes

“…In these cases the nature of the α-substituents at the alkenyl groups is essential: small alkyl groups (CH 3 ) and hydrogen lead to practically complete conversion to the respective ansa -metallocenes, whereas larger groups (e.g., cyclohexyl and aryl) may result in unfavorable photostationary equilibria . Typical examples for complete conversion to the ansa -zirconocenes are the systems 27 → 28 depicted in Scheme and Figure …”