Structure and bonding of metallacyclocumulenes, radialenes, butadiyne complexes and their possible interconversion: a theoretical study

Density functional theory is used to study the dimerization of metallacyclocumulenes (1, 2 and 9) to metal substituted radialenes (3, 4 and 5). These were compared to the dimerization of ethylene to cyclobutane and cumulene to radialene. The bonding of the metallacyclocumulenes were discussed in the light of the Dewar–Chatt–Duncanson model. A possible mechanism for the formation of bis(butadiyne) complex of Ni (8) is also presented. Correlation diagrams constructed for the conversion of the radialene type structure to that of the bis(butadiyne) complex show that it is allowed for both Ti and Ni.