Metal-Induced Dimerisations of Cyclic Diacetylenes

At the beginning of our activities in the field of organometallic chemistry were spectroscopic and theoretical investigations concerned with π/σ interactions1. The comparison of the calculated energy levels of the highest occupied MO’s of hexadiyne-1,5 (1) and heptadiyne-1,6 (2) shows a remarkable influence on the chain length. The separation between the bonding (π+_i) and antibonding (π-_i) linear combination of the “in plane” π-MO’s of two acetylene moieties is diminished if we connect them with an ethano bridge as in 1 (see Figure 1 left).