1.2.3.4- Tetramethylcyclobutadiene dichloride

Tetramethylcyclobutadiene dichloride [76404-16-5] can be prepared by reaction of nickel carbonyl and 3,4-dichlorotetramethylcyclobutene (CBD) in polar solvents (103). The complex is black-violet, mp 185°C (dec). 

Tetramethylcyclobutadiene dication (43), has been prepared by Olah and co-workers by dissolving the dichloride (42) in a mixture of antimony penta-... 

CYDOADDITIONS Antimony(V) fluoride. Carbon disulfide. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone. Dimethyl acetylenedicarboxylate. Dimethylketene. Ethylaluminum dichloride. 2-Methoxyallyl bromide. Ninhydiin. Sodium cyclopentadienyldicarbonyl-ferrate. Sodium iodide-Coppet. Tetracyanoethylene. Tetramethylcyclobutadiene-Aluminum chloride complex. 

The first example of reaction of a half sandwich metallocene with a protein was reported a few years later. Tetramethylcyclobutadiene nickel(II) dichloride 2 was shown to react with the enzyme horse hver alcohol dehydrogenase to afford a modified enzyme devoid of zinc and enzymatic activity and containing 8 mol nickel per mol protein. The mode of binding of this organometallic complex had not been fully elucidated at that time but was thought to occur by substitution of the chloride ligands by nucleophilic residues [3],... 

Olefin Complexes Containing the ir- C M System. Cyclobutadiene is the simplest example of an olefin having a tt-(C4)M system. Complexes are known in which this ring system is believed to be present, for example, tetramethylcyclobutadiene-nickel dichloride 75a) or of nickel salts 129a). No magnetic resonance data are yet available for these compounds. 

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