Part I. Scandium Hydride and Alkyl Complexes with a Linked Monocyclopentadienyl-Amido Ligand-Framework: Single Component Catalysts for the Polymerization of α-Olefins. Part II. Hydrazido(1-) and 2,2-Dimethylhydrazido(1-) Derivatives of Permethylscandocene. Preparation and Structural Characterization of their Products from Reactions with Acetonitrile

Citation

Shapiro, Pamela Joy (1991) Part I. Scandium Hydride and Alkyl Complexes with a Linked Monocyclopentadienyl-Amido Ligand-Framework: Single Component Catalysts for the Polymerization of α-Olefins. Part II. Hydrazido(1-) and 2,2-Dimethylhydrazido(1-) Derivatives of Permethylscandocene. Preparation and Structural Characterization of their Products from Reactions with Acetonitrile. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/hmc3-gy25. https://resolver.caltech.edu/CaltechTHESIS:11042019-173308161

Abstract

Various monocyclopentadienyl scandium amido derivatives with the general formulas {(η⁵-C₅Me₄)SiMe₂(η¹-NCMe₃}ScR, (Cp*SiNR)ScR, and {(η⁵-C₅H₃CMe₃)SiMe₂(η¹-NCMe₃}ScR, (^tBuCpSiNR)ScR, have been prepared. [(Cp*SiNR)(PMe₃)ScH]₂ is prepared from the hydrogenation of (Cp*SiNR)ScCH(SiMe₃)₂ in the presence of PMe₃. The scandium hydride effects the multiple insertion of α-olefins in a controlled fashion to form low molecular weight polymers. β-H elimination appears to be a principal chain-transfer pathway in this catalyst system. The stoichiometric reaction between [(Cp*SINR)(PMe₃)ScH]₂ and two equivalents of ethylene produces the ethylene bridged dimer [(Cp*SiNR)(PMe₃)Sc]₂(µ, η², η²-C₂H₄) and an equivalent of ethane. The stoichiometric reaction between the scandium hydride and either propene or butene affords the PMe₃-free, alkyl-bridged scandium dimers [(Cp*SiNR)Sc]₂(µ-CH₂CH₂CH₃)₂ and [(Cp*SiNR)Sc]₂(µ-CH₂CH₂CH₂CH₃)₂. The absence of coordinating phosphine makes these complexes more active olefin polymerization catalysts. The complexes (Cp*SiNR)(PMe₃)ScCH₂CH(CH)₃CH₂CH₃ and (Cp*SiNR)(PMe₃)ScCH(C₆H₅)CH₂CH₂CH₂(C₆H₅) have also been prepared and spectroscopically characterized.

Kinetic analysis of the rate dependence of 1-pentene polymerization by [(Cp*SiNR)(PMe₃)ScH]₂ on added PMe₃ reveals a phosphine dissociation pre-equilibrium to form a PMe₃-free active intermediate. The monomeric nature of this intermediate is revealed by the kinetic analysis of 1-pentene polymerization by [(Cp*SiNR)Sc]₂(µ-CH₂CH₂CH₃)₂ as a function of scandium concentration.

(Cp*SiNR)ScR was found to be >99% head-to-tail regioselectfve in the polymerization of propene. Preliminary ¹³C NMR data indicate lower regioselectivity in propene polymerization by (^tBuCpSiNR)ScR. A slight syndiotactic preference is observed in the stereochemistry of the polypropene produced with [(Cp*SiNR)Sc]₂(µ-CH₂CH₂CH₃)₂. By contrast, [(^tBuCpSiNR)ScMe]_x displays no stereocontrol, producing an atactic polymer.

A rare example of an unsubstituted hydrazido(1-) complex, Cp*₂ScNHNH₂ (Cp* = (η⁵-C₅Me₅)), prepared by reaction of one equivalent of anhydrous hydrazine with Cp*₂ScCH₃, reacts with acetonitrile to form [chemical formula; see abstract in scanned thesis for details]. The crystal structure of [chemical formula; see abstract in scanned thesis for details] reveals a five-membered, nearly planar [chemical formula; see abstract in scanned thesis for details] ring. The results of a labeling study using ¹⁵N=CCH₃ are consistent with a mechanism involving insertion of acetonitrile into the Sc-N bond of Cp*₂ScNHNH₂, followed by tautomerization to form [chemical formula; see abstract in scanned thesis for details]. The closely related compounds Cp*₂ScNHNMe₂ and [chemical formula; see abstract in scanned thesis for details] have also been prepared, and the structure of the latter compound has been determined.

Thesis Files