Synthesis and Reactivity of Bis(cyclopentadienyl)titanacyclobutanes and Ketene Complexes of Bis(cyclopentadienyl)titanium and Bis(cyclopentadienyl)zirconium

Citation

Straus, Daniel Albert (1983) Synthesis and Reactivity of Bis(cyclopentadienyl)titanacyclobutanes and Ketene Complexes of Bis(cyclopentadienyl)titanium and Bis(cyclopentadienyl)zirconium. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1jtq-cj35. https://resolver.caltech.edu/CaltechTHESIS:11042019-122031306

Abstract

The synthesis of several titanacyclobutanes of the types [chemical formula; see abstract in scanned thesis for details] and [chemical formula; see abstract in scanned thesis for details] (Cp = η⁵-C₅H₅, R = alkyl) is described. The stability of several of these, as well as some metallacycles of the type [chemical formula; see abstract in scanned thesis for details], has been measured and is discussed in terms of the structure of these species. The reaction of some titanacyclobutanes with dimethylaluminum chloride in the presence of diethyl ether and tetrahydrofuran was investigated, and is discussed in terms of a scheme for olefin metathesis involving an aluminum co-catalyst. The thermolysis, acidolysis and reactions with bromine and iodine have been studied for a number of these metallacycles. The mechanism of the reaction with iodine is considered in some detail.

Titanacyclobutanes of the type [chemical formula; see abstract in scanned thesis for details] and [chemical formula; see abstract in scanned thesis for details] are known to catalyze degenerate metathesis of terminal olefins. The activity of the titanacyclobutanes in non-degenerate olefin metathesis has been investigated here. The titanacyclobutanes have been found to metathesize cis- and trans-2,8-decadiene with some stereospecificity. This process is very inefficient and the reasons for this are discussed in terms of the stability and reactivity of various titanacyclobutanes, which model presumed intermediates in this reaction.

The carbonylation of several titanacyclobutanes has been examined in detail and leads to insertion of two molecules of carbon monoxide to produce cyclic enediolate products in all cases when carbon monoxide is present in excess. Acidolysis and oxidation of these enediolates affords 2-hydroxycyclopentanones and 1,2-cyclopentanediones, respectively. Under conditions where the carbon monoxide concentration is limited, cyclobutanones and titanocene dicarbonyl are formed. A mechanism which explains these observations is presented. Carbon monoxide insertion has been found to proceed with retention of stereochemistry at migrating carbon.

Ketene complexes have been prepared by treatment of chloro and bromo acyl complexes of titanocene, zirconocene and decamethylzirconocene with strong bases. In this manner (Cp₂Ti(OCCH₂))_n (Cp₂Zr|OCCHC(CH₃)₃|)₂ and (η⁵-C₅Me₅)₂Zr(OCCH₂)(C₅H₅N) have been synthesized. The reactivity of these complexes with hydrochloric acid, hydrogen, ethylene and acetylene is discussed. Reaction of Cp₂Zr(COCH₃)CH₃ with CH₂PPh₃ gives the enolate complex Cp₂Zr(OC(CH₂)CH₃)CH₃ and PPh₃. Reaction of Cp₂Zr(COCH₃)CH₃ with NaN(TMS)₂ gives the anion Cp₂Zr(COCH₂)CH_3-, which is alkylated with methyl iodide to produce Cp₂Zr(COCH₂CH₃)CH₃.

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