## Electronic Theses and Dissertations

1996

Dissertation

Ph.D.

#### Department

Chemistry and Biochemistry

Stephan, Douglas W.,

#### Keywords

Chemistry, Inorganic.

CC BY-NC-ND 4.0

#### Abstract

Synthetic routes to terminal phosphinidene complexes of zirconium have been investigated. The attempted generation of (Cp$\sb2$Zr=PR) in the presence of polar organic unsaturates results in insertion of the organic molecule into the Zr-P single bond of the precursor. The stabilization of the Zr=P multiple bond requires a sterically demanding substituent on phosphorus. In the absence of the required steric demands, bimolecular reactions and C-H activation of the cyclopentadienyl rings occur. However, the supermesityl substituent allows for the trimethylphosphine trapping of (Cp$\sb2$Zr=PMes*) as the stable eighteen electron adduct. (Cp$\sb2$Zr=PMes*)(PMe$\sb3$) 84 is the first stable zirconium terminal phosphinidene complex. Initial reactivity studies of 84 were directed at exploring the nature of the Zr=P multiple bond. Organic reagents, as well as some of their lower congeners, react with 84 which acts as a source of the phosphinidene moiety. This group may be exchanged for an oxo, sulfido or two chloride groups to yield a variety of organophosphorus derivatives and the corresponding zirconocene oxide, sulfide or dichloride. 84 also undergoes 1,2-addition reactions of polar E-H bonds to afford complexes of the form Cp$\sb2$Zr(PHMes*)(ER) and Cp$\sb2$Zr(PHMes*)(EHR). Variable temperature NMR studies reveal that metal-mediated inversion of the pyramidal phosphide ligands can be stopped upon cooling. Zr-E $\pi$-interactions are generally weak, yet they have an influence over both the $\sp{31}$P NMR chemical shift and the inversion barrier of the phosphide ligand. (2+2) cycloaddition reactions of 84 with alkynes have furnished the first examples of phosphametallacyclobutenes. These complexes readily insert unsaturated polar organic molecules into the Zr-P bond, thus providing a family of four-, five- and six-membered metallacycles. Steric factors exert considerable influence over this entire group of complexes, causing reduced inversion barriers at phosphorus and (4+2) retrocycloadditions. The aforementioned phosphametallacycles provide a route to novel main group heterocycles via metallacycle transfer reactions with main group dihalides. These complexes offer several advantages as potential synthons for these phosphacycles, such as the possibility of substitution patterns that are not available by conventional syntheses. The chemistry described herein is distinguished by the reactive nature of Zr-P single and double bonds, a trait which provides intriguing and unparalleled chemistry.Dept. of Chemistry and Biochemistry. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1996 .B73. Source: Dissertation Abstracts International, Volume: 59-08, Section: B, page: 4100. Adviser: Douglas W. Stephan. Thesis (Ph.D.)--University of Windsor (Canada), 1996.

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