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Cyclopentadienyldiphosphine complexes of zirconium and hafnium

University of British Columbia

The preparation of zirconium and hafnium complexes coordinated by a cyclopentadienyldiphosphine ligand are reported. Metal chloride complexes [P₂Cp]MCl₃ (P₂Cp= ɳ⁵-C₅H₃-l,3-(SiMe₂CH₂PPri₂)₂, M = Zr, Hf) are six-coordinate with an apical cyclopentadienyl donor tethered by two pendant chelating phosphines. Alkylating reactions give [P₂Cp]MClxR₃-x (R = Me, CH₂Ph, CH₂CMe₃, CH₂SiMe₃, x = 0, 2). The monoalkyl derivatives exhibit fluxional coordination of the side-arm phosphines, which generates an equilibrium mixture of isomers. A similar solution behaviour is noted for the trimethyl species [P₂Cp]M(CH₃)₃. In comparison, in the bulkier trialkyl complexes the side-arms remain dangling with no observation of phosphine coordination. The dialkyl complexes [P₂Cp]MClR₂ are not isolable, but instead yield a thermally sensitive equilibrium mixture of alkyl complexes, which upon thermolysis generates in high yield the first structurally characterized alkylidene complexes [P₂Cp]M=CH(R)Cl (R = CH₂Ph, CH₂CMe₃, CH₂SiMe₃). Kinetic studies indicate a composite reaction mechanism of a-abstraction from the dialkyl complex. Reaction of [P₂Cp]Zr=CH(R)Cl with ethylene yields an ethylene adduct [P₂Cp]Zr(ɳ²-CH₂=CH₂)C1. Kinetic studies show this reaction to be first order in both alkylidene and ethylene. Insertion reactions of alkylidenes with carbon monoxide generates ketene complexes [P₂Cp]M(ɳ²-C(0))=CH(R)Cl, while a reaction with tert-butyl isocyanide produces an analogous ketenimine. Reaction of the ketene complexes with ethylene gives metallacyclic complexes resulting from insertion of one ethylene unit. These species in turn react with carbon monoxide to produce acyl-ylide zwitterionic complexes. Methyl substituted phosphines give the zirconium chloride Me[P₂Cp]MCl₃ (Me[P₂C p] M C l ₃ = ɳ ⁵-C₅H₃-l,3-(SiMe₂CH₂PMe₂)₂)- Alkylation reactions yield Me[P₂Cp]ZrCl(CH₂Ph) ₂. Thermolysis of this complex produces a toluyne complex Me[P₂Cp]ZrCl(ɳ²-C₆H₃Me) instead of the anticipated alkylidene complex. Photolysis of the dibenzyl species generates a metal complex resulting from activation of a benzyl ligand. The ethylene complexes [ɳ⁵-C₅H₃-l,3-(SiMe₂CH₂PR₂)₂]Zr(ɳ²-CH₂=CH₂)Br (R = Me, Pri) can be prepared from the reaction of the starting trichloride with two equivalents of EtMgBr. Both of these ethylene derivatives react with carbon monoxide to give carbonyl complexes, and with dihydrogen to produce asymmetric dinuclear hydride complexes. Reaction of ethylene complexes with 1,2-diphenylacetylene eliminates the ethylene ligand to give an alkyne complex. Alkylating reagents permit the formation of the alkyl-ethylene complexes [ɳ⁵-C₅H₃-l,3- (SiMe₂CH₂PPri)₂]Zr(ɳ²-CH₂=CH₂)(R) (R = Me, Cp).

Thesis/Dissertation

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2009-06-19

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http://hdl.handle.net/2429/9468

Chemistry

University of British Columbia

UBCV

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