Synthesis and reactivity of metal-containing monomers. Part 59. Preparation and polymerization transformations of vinyl and isopropenyl derivatives of hafnocene dichloride

Abstract

Novel vinyl and isopropenyl substituted cyclopentadienyl complexes of hafnium(IV), [C 5 H 4 (CR=CH 2 )] 2 HfCl 2 [R = H (5), CH 3 (6)], were prepared and characterized. The organo metallic monomers obtained were shown to undergo radical or anionic homopolymerization. Copolymerization of these metallocenes with styrene was performed. The potential applica tions of the metal polymers in question were considered.Organometallic polymers obtained by polymerization or copolymerization of appropriate monomers are of con siderable interest as immobilized catalysts for various re actions and as precursors for the preparation of nano composite materials, ceramics, and so on.However, the range of organometallic monomers in which the group capable of polymerization is directly bound to a transition metal atom through a metal-car bon bond is very limited, as these molecules are unstable. On the one hand, the average dissociation energy of a metal-carbon bond D(M-C) is comparable 2,3 with the average metal-halogen bond energy, D(M-Cl) or D(M-Br), even for the least stable alkyl derivatives of transition metals, but on the other hand, this bond is much more reactive than the M-O, M-N, M-Hal, etc. bonds. This is especially clear in the polymerization of such monomers because in the majority of cases, the syn thesis of metal containing polymers is accompanied by elimination of metal hydride: 4The undesirable β hydride transfer can be prevented by using organometallic compounds devoid of hydrogen at the β carbon atom. For this purpose, Me or another group is introduced instead of the H atom.Procedures for the synthesis of organometallic mono mers in which the Cp rings contain a vinyl or an iso propenyl group have been developed in sufficient detail for a number of metals. This is a rather well studied field of chemistry of polymers based on vinylferrocene, which is among the first monomers containing a chemically bound metal. The polymerization of metal monomers of this type can be initiated by any type of initiation (radical, cationic, anionic, Ziegler-Natta catalysts). Their sus ceptibility to a particular initiation type can be changed crucially by introducing appropriate substituents into the vinyl group. As an example, one can mention cyclo pentadienyl complexes containing the isopropenyl group instead of vinyl, which are potential monomers for cat ionic polymerization. 5 The purpose of this study is to prepare bis(vinyl cyclopentadienyl) and bis(isopropenylcyclopentadi enyl)dichlorohafnium as potential metal monomers and to attempt the synthesis of polymers and copolymers based on these monomers. Results and DiscussionSynthesis of Hf IV containing monomers. As the start ing monomers for the subsequent polymerization, we prepared two new hafnocene dichlorides, * For Part 58, see Ref. 1.

Refractory Metal‐Containing Polymers and Nanocomposites: Preparation and Properties

“…Traditionally these materials have been prepared by high temperature powder techniques that are limited in their ability to generate homogeneous systems with controlled compositions and properties. We have elaborated a novel approach that employs metal‐containing monomer and metallopolymer precursor routes to such materials 1–5. It comprises; (i) thermal transformations of metal‐containing monomers (MCM); i.e., compounds comprising a metal equivalent and a polymerisable group containing multiple bonds, involving solid‐state (co)polymerization of the monomers (ii) thermolysis of the metallopolymers formed to generate nanoparticles stabilized with a polymer matrix.…”