Synthetic and Mechanistic Studies of Organoscandium Compounds. Dimerization and Branching of Alkenes Catalyzed by Scandocene Hydrides

Citation

Bunel, Emilio Enrique (1989) Synthetic and Mechanistic Studies of Organoscandium Compounds. Dimerization and Branching of Alkenes Catalyzed by Scandocene Hydrides. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3HDJ-ST65. https://resolver.caltech.edu/CaltechETD:etd-05242007-075254

Abstract

Mixed-ring scandocene alkyl and hydride derivatives of structure Cp*CpSc(CH₃)(PMe₃), Cp*CpSc(η¹-η⁵-C₅H₄(Cp*Sc(H), Cp*(η⁵-1,3,4-C₅Me₃H₂)Sc(CH₃)(PMe₃), and Cp*(η⁵-1,3,4-C₅Me₃H₂)Sc(H)(PMe₃) were prepared (Cp* = η⁵-C₅Me₅, Cp = η⁵-C₅H₅. Dimethylsilicon bridged scandocene alkyl and hydride derivatives Me₂Si(η⁵-C₅Me₄)₂ScCH(SiMe₃)₂, Me₂Si(η⁵-C₅Me₄)₂Sc(H)(PMe₃), meso-Me₂Si(η⁵-t-butylC₅H₃)₂ScCH₂SiMe₃, and (meso-Me₂Si(η⁵-t-butylC₅H₃)₂Sc(H))₂ were also prepared. The activation energy for phosphine dissociation in Cp*CpSc(CH₃)(PMe₃) and Cp*(η⁵-1,3,4-C₅Me₃H₂)Sc(H)(PMe₃) were measured. The crystal structures of Me₂Si(η⁵-C₅Me₄)₂ScCH(SiMe₃)₂ and Me₂Si(η⁵-C₅Me₄)₂Sc(H)(PMe₃) were determined.

The hydride derivatives, Me₂Si(η⁵-C₅Me₄)₂Sc(H)(PMe₃) and (meso-Me₂Si(η⁵-t-butylC₅H₃)₂Sc(H))₂ catalyze the following carbon-carbon bond forming reactions: (1) The catalytic dimerization of α-olefins to head-to-tail dimers, (2) The catalytic cyclization of α, ω-diolefins to methylenecycloalkanes with ring sizes between 5 and 9 carbon atoms, (3) The catalytic formation of six-membered ring nitrogen and sulfur heterocycles by catalytic cyclization of bisallyl amines and bisallyl sulfides respectively and (4) The catalytic formation of the spiro hydrocarbons 2-methylene spiro[4.4] nonane and 2-methylene dispiro [4.1.4.2] tridecane by catalytic cyclization of 5-methylene-1,8-nonadiene and 5,8-dimethylene-1,11-dodecadiene.

(meso-Me₂Si(η⁵-t-butylC₅H₃)₂Sc(H))₂ catalyzes the ring opening reaction of methylenecyclopropane to butadiene and methylenecyclobutane to 1,4-pentadiene. Labelling experiments show that intramolecular olefin insertion in ω-alkenyl scandium complexes and β-alkyl elimination in cycloalkylmethyl scandium complexes is reversible when rings containing 3 or 4 carbon atoms are involved. The hydride derivative (meso-Me₂Si(η⁵-t-butylC₅H₃)₂Sc(H))₂ also catalyzes the isomerization of 1,4-pentadiene to isoprene and 2-methyl-1,4-pentadiene to 2,3-dimethylbutadiene and the isomerization of 3-methyl-1,4-pentadiene to 1,5-hexadiene, which is then cyclized to methylenecyclopentane.

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