Organozinc Coordination Chemistry and Catalytic Effects of Organozinc Coordination Compounds

A review of the present state of organozinc coordination chemistry. with special emphasis on compounds of the type RZnX is given. Their preparation as well as some factors determining their structure and stability are discussed. Certain organozinc coordination compounds have been found to be effective catalysts for cyclo-oligomerization and polymerization reactions. in particular of oxygen-containing monomers (isocyanates, aldehydes. lactones and epoxides). The present views on the mechanisms of these reactions are given. INTRODUCTION Organozinc chemistry is an old subject: it started around 1850 and contributed much to the early development of organometallic chemistry as a whole. Organozinc compounds. in particular the zinc dialkyls. for some decades found extensive laboratory use as alkylating agents. until their replacement around 1900 by the organomagnesium compounds. After having been somewhat dormant for about sixty years—one notable exception being the continuing and even extending use of the Reformatsky reaction— organozinc chemistry towards 1960 entered into its second stage. Partly this was caused by the general renascence of organometallic chemistry as a whole in the early fifties. but it also was due to the discovery by Simmons and Smith in 19581 of the extremely useful zinc-containing organometallic reagent for the generation of carbene. Our own interest in organozinc chemistry reaches back to 1962 when we were invited by the International Lead Zinc Research Organization at New York to start an exploratory programme of organozinc research. Since then we have been actively engaged at Utrecht in the synthesis of organozinc compounds and their use in organic synthesis. but in particular in the study of organozinc coordination chemistry and of the catalytic effects of organozinc coordination compounds. My lecture deals with the two latter aspects of this work. For bivalent zinc two basic types of organozinc compounds must be considered: R2Zn and RZnX. R being hydrocarbon groups or. more generally groups attached to zinc via a zinc—carbon bond. and X being a