18823-04-6Relevant articles and documents
The diethynylcyclobutadlene rearrangement: A degenerate ligand reorganization in the coordination sphere of (η5-Cyclopentadlenyl) cobalt
Fritch, Jonn R.,Volhardt, K. Peter C.
, p. 590 - 602 (2008/10/08)
Reaction of CpCo(CO)2 with bis(trimethylsilyl)butadiyne leads lo small amounts of silyleted 1,2- and 1,3-diethynylcyclobutadiene compleses 13 and 18 among other products. Alternatively, cocyclization of bis(trimethylsilyl)hexatriyne with bis(trimethylsilyl)acetylene furnishes 13 in 64.2% yield. These compounds may be protodesilylated with alcoholic KOH or fluoride. Flash vacuum thermolysis of the 1,2-diethynylcyclobutadiene complexes 9, 19, and 49 induces a clean rearrangement in which the four sp carbons of the ethynyl groups cyclize to form a new cyclobutadiene ring and the original cyclobutadiene ring retrocyclizes to generate two new alkyne groups. In this way 9 undergoes a degenerate rearrangement, whereas 19 converts to 30, and 49 equilibrates with 50. Mechanistic speculation is offered which suggests a CpCo-complexed cycloocta-3,7-diene-1,5-diyne (11) or cycloocta-1,2,3,5,6,7-hexaene (12) as a likely intermediate, A topologically equivalent alternnative, (η4-tricyclo[4,2.0.0 2,5]octs-1,3,5,7-tetraene)(η5-cyclopentadienyl)cobalt (10), appears less favored on theoretical grounds.
