Transition metal alkylidene complexes via the ring-opening of cyclopropenes

• Main Author: Flatt, Brenton T.
• Format: Others
• Language: en
• Published: 1995
• Online Access: https://thesis.library.caltech.edu/4264/1/Flatt_bt_1995.pdf; Flatt, Brenton T. (1995) Transition metal alkylidene complexes via the ring-opening of cyclopropenes. Master's thesis, California Institute of Technology. doi:10.7907/9zd6-rr52. https://resolver.caltech.edu/CaltechETD:etd-10262007-082758 <https://resolver.caltech.edu/CaltechETD:etd-10262007-082758>

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The first chapter details the preparation and structural characterization of a rhenium (VII) oxo-vinylalkylidene complex and discusses its activity in olefin metathesis reactions. A substitution reaction affords the rhenium (V) oxo-trisalkoxide precursor, a species that surprisingly adopts a facial arrangement of three very bulky alkoxide ligands in its crystal structure. This complex reacts with 3,3-diphenylcyclopropene in a non-coordinating solvent to yield a mixture of two rhenium alkylidene isomers. Over time one species predominates and is isolated. An X-ray diffraction study of the isolated complex and [...] NMR studies of the isomerization process are described. Reactivity studies indicate that the isolated product demonstrates very limited olefin metathesis activity. However, the addition of Lewis acid cocatalysts to the rhenium alkylidene complex generates a much more active catalyst system, in particular, for the metathesis of cis-2-pentene. No propagating alkylidene species are observed during the metathesis reaction. The second chapter describes the synthesis and characterization of a dicyclopropene compound from which the preparation of ROMP diinitiators is reasoned to be possible. The starting material-1,4-di(1-phenylvinyl)benzene-is readily prepared via a Grignard reaction and subsequent dehydration. A series of three steps analogous to those of the 3,3 diphenylcyclopropene synthesis yield the desired roduct-1,4-di(1-phenylcycloprop-2-enyl)benzene. Alternate pathways to the product also are proposed and the investigations are detailed. In particular, a biphasic cyclopropanation reaction using either bromoform or chloroform as a carbene source affords the respective dicyclopropane intermediates. Ultimately the syntheses of bis(metal alkylidene) complexes from reactions of this dicyclo-propene with various transition metal precursors have implications for the formation of polymers which propagate in two directions and for the preparation of triblock copolymers.