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

Author: Meinhart, James Douglas

Year: 1987

Degree: Dissertation (Ph.D.)

Advisor: Grubbs, Robert H.

Committee Members: Dervan, Peter B.; Grubbs, Robert H.; Goddard, William A., III; Bercaw, John E.

Option: Chemistry

DOI: 10.7907/16dt-2465

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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