The Best of Both Worlds: Combining the Power of MICs and WCAs to generate Stable and Crystalline Cr I -tetracarbonyl Complexes with π - ${{\bf \pi }-}$ 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(OR ) ] , R =C(CF ) and BAr =[B(Ar ) ] , Ar =3,5-(CF ) C H ). 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 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) ] complexes with a chelating accepting ligand, and the data presented here are of relevance for both the photochemical and the electrochemical properties of these classes of compounds.