The Best of Both Worlds: Combining the Power of MICs and WCAs to generate Stable and Crystalline Cr^I-tetracarbonyl Complexes with - ${{\bf \pi }-}$ Accepting Ligands

Here we present stable and crystalline chromium(I) tetracarbonyl complexes with pyridyl-MIC (MIC=mesoionic carbene) ligands and weakly coordinating anions (WCA=[Al(ORF)(4)](-), R-F=C(CF3)(3) and BArF=[B(Ar-F)(4)](-), Ar-F=3,5-(CF3)(2)C6H3). The complexes were fully characterized via crystallographic, spectroscopic and theoretical methods. The influence of counter anions on the IR and EPR spectroscopic properties of the Cr-I complexes was investigated, and the electronic innocence versus non-innocence of WCAs was probed. These are the first examples of stable and crystalline [Cr(CO)(4)](+) complexes with a chelating & pi;- ${\pi -}$ accepting ligand, and the data presented here are of relevance for both the photochemical and the electrochemical properties of these classes of compounds.