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 d_π(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.