Yttrium-Mediated C–C Coupling of Sodium Acetylide Generates a Planar and Bridging Butatrienylidene Dianion

The reaction between (C5Me5)2Y(μ–Ph)2BPh2 and NaC≡CH
was explored to examine
the reactivity of an intermediate like “(C5Me5)2Y(C≡CH).” One of the products identified
from the reaction mixture is a bimetallic Y(III) complex that contains
a rare example of a planar and dianionic bridging butatrienylidene
ligand, namely (C5Me5)2Y(μ-η3:η1-CCCCH2)Y(C5Me5)2. The bridging butatrienylidene ligand is presumably
formed from the C–C coupling of two (C≡CH)1– moieties that also involve the migration of a hydrogen atom to form
the terminal methylidene group. Density functional theory (DFT) studies
were conducted to probe the electronic structure of the unsaturated
(C4H2)2– dianion.