Synthesis and Reactivity of Electron-Rich Ruthenium and Iron Half-Sandwich Complexes

Citation

Paciello, Rocco Angelo (1987) Synthesis and Reactivity of Electron-Rich Ruthenium and Iron Half-Sandwich Complexes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/exhb-6f18. https://resolver.caltech.edu/CaltechTHESIS:10232019-091323168

Abstract

Late transition metal organometallic complexes, Cp*(PR₃)₂MX (Cp* = η⁵-C₅Me₅), with highly electron donating ligand sets have been synthesized and their reactivity studied. Synthetic routes which allow systematic variation of metal (Ru, Fe), phosphines (PMe₃, PEt₃, PⁿBu₃, PMe₂Ph, DMPE), and sigma-bonded ligands (halide, hydride, alkyl, heteroatom) have been developed.

Thermally and photochemically induced ligand loss from these complexes has been studied. Trapping and C-H bond activation chemistry have been observed for the transient [Cp*(PR₃)MX] complexes produced upon ligand loss. The reactivity of analogous ruthenium and iron complexes is compared and discussed.

The Ru(IV) complex, Cp*(PMe₃)RuH₃, has been prepared and isolated. This complex is found to catalyze H-D exchange, and hydrogenations of unsaturated organic species. The analogous Fe(IV) complex, Cp*(PMe₃)FeH₃, has been prepared and observed spectroscopically. Hydrogen bonding modes in these polyhydrides are discussed. Highly fluxional Cp*(PMe₃)FeH₃ is proposed to be in equilibrium with Cp*(PMe₃)Fe(η²-H₂)H.

An equilibrium method for the determination of relative Ru-X and Ru-Y bond strengths in Cp*(PMe₃)₂RuX has been developed. A linear correlation of Ru-X to H-X bond strengths has been found over a wide range of ligands, X. The relationship is found to be general for a number of metal centers.

A study of the kinetics of phosphine exchange for Cp*(PMe₃)₂RuX has been undertaken. The rate of phosphine loss can be abstracted from a treatment of the kinetics of approach to equilibrium. Lone pairs on X are found to promote ligand dissociation. Dative bond dissociation enthalpies are obtained if small, and constant, barriers for ligand recombination are assumed. The functional group approximation used in solution thermochemical studies is found to break down when large changes are made in the steric constraint at the metal center.

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