Preparation of Cyclobutadiene Complexes

The most important methods for the preparation of cyclobutadiene complexes are oxidative addition reactions of dihalogenocyclobutenes to low-valent transition metal compounds [equations (8.27) and (8.28)], as well as reactions of acetylenes with coordination compounds. 

Anionic carbonyl complexes of iron, ruthenium, chromium, molybdenum, tungsten, etc., also react with 3,4-dichlorocyclobutene or its derivatives. In order to obtain anionic derivatives, metal carbonyls are reduced by means of sodium amalgam [equations (8.29H8.31)]. 

The tetrahalogenocyclobutane derivatives may also undergo dehalogenation reactions [equation (8.32)]. Vinyl carbonate reacts with alkynes to give c -3,4-carbonyl- 

Acetylenes easily undergo dimerization to give cyclobutadiene compounds [equations (8.34)-(8.36)]. Cyclobutadiene coordination compounds may be obtained [equation (8.37)] by reductive decyclization reaction of metallacyclopentadiene, which is 

Acetylenes may form various organometallic compounds with metal complexes [equations (8.38)-(8-40)]. 

---