Metal–Indolizine Zwitterion Complexes as a New Class of Organometallic Material: a Spectroscopic and Theoretical Investigation

Indolizine zwitterion coordinated
metal species have been commonly
proposed as intermediates in the mechanisms of metal-catalyzed cycloisomerization
of propargylic pyridines for indolizines. Yet, it is only recently
that the first metal–indolizine complexes have been isolated
by our group. Considering from the perspective of molecular materials,
the π-interaction between the dπ(M) and the
π-system of the indolizine skeleton in the electronic ground
or excited states may allow charge delocalization and offer functionalities
for optoelectronic applications. We herein report the synthesis and
spectroscopic and theoretical investigations on two classes of Ru–indolizine
zwitterion complexes. The synthetic strategy employed, i.e., cycloisomerization
of propargylic pyridines, represents a general preparation method
for stable metal–indolizine complexes. Indolizine zwitterions
in this work have been found to exhibit strong trans effect. Spectroscopic studies on these complexes reveals the tunability
of the π*­(indolizine) level and its impact on the luminophores
nearby. Overall, indolizine zwitterion represents a new class of organometallic
ligand with high potential in the design of functional molecular electronic/photonic
elements.