Synthesis and Reactivity of Titanocene Methylene Complexes and Bis(η⁵-Cyclopentadienyl) Titanacyclobutenes

Citation

Meinhart, James Douglas (1987) Synthesis and Reactivity of Titanocene Methylene Complexes and Bis(η⁵-Cyclopentadienyl) Titanacyclobutenes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/16dt-2465. https://resolver.caltech.edu/CaltechTHESIS:10212019-165401033

Abstract

Syntheses of several bis(η⁵-cyclopentadienyl) titanium methylene phosphine complexes are reported. The titanium methylene phosphine complexes are generated from themolysis of titanacyclobutanes in the presence of excess phosphine. Spectral data and reactivity are consistent with a methylene phosphine complex rather than an ylide complex.

Bis(η⁵-cyclopentadienyl) titanacyclobutenes are readily synthesized by treatment of sources of "Cp₂TiCH₂" with disubstituted alkynes. A variety of stable titanacyclobutenes were synthesized containing aryl, alkyl, and etherial substituents. Titanacyclobutenes, unlike the related titanacyclobutanes, do not reform "Cp₂TiCH₂" thermally.

Titanacyclobutenes insert carbon monoxide, forming an acyl intermediate which rearranges to a titanocene vinyl ketene complex. A trimethylphosphine adduct of one of the ketene complexes was characterized by x-ray diffraction techniques. The carbonylation mechanism involves insertion of carbon monoxide into the more accessible titanium-carbon bond, followed by intra-molecular attack of the vinyl group to the acyl. Insertion of t-butyl isocyanide into a titanacyclobutene yields a cyclic imino-acyl complex, which was also characterized by x-ray diffraction. The vinyl ketene complexes react with many unsaturated substrates (alkynes, ethylene, and aldehydes) to form new organotitanium species.

Titanacyclobutenes react with ketones and aldehydes via 1,2-addition to yield titanium oxacyclohexenes. Aldehydes form both titanium-oxygen and titanium-carbon regioisomers. The organic ligand may be removed from the titanium to give homo-allylic alcohols in good yield. Nitriles also insert into titancyclobutenes to roduce titanium imidocyclohexenes.

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