Abstract
Homoleptic carbonyl radical cations are a textbook family of complexes hitherto unknown in the condensed phase, leaving their properties and applications fundamentally unexplored. Here we report on two stable 17-electron [Cr(CO)6]•+ salts that were synthesized by oxidation of Cr(CO)6 with [NO]+[Al(ORF)4]− (RF = C(CF3)3)) in CH2Cl2 and with removal of NO gas. Longer reaction times led to NO/CO ligand exchange and formation of the thermodynamically more stable 18-electron species [Cr(CO)5(NO)]+, which belongs to the family of heteroleptic chromium carbonyl/nitrosyl cations. All salts were fully characterized (IR, Raman, EPR, NMR, scXRD, pXRD, magnetics) and are stable at room temperature under inert conditions over months. The facile synthesis of these species enables the thorough investigation of their properties and applications to a broad scientific community.
Highlights
1234567890():,; Carbon monoxide is amongst the most important ligands in transition metal chemistry
By allowing the reaction to proceed for 7–14 days in a closed vessel at r.t. (Eq 2), the heteroleptic 18 valence electron (VE) complexes [Cr(CO)5(NO)]+[Al(ORF)4]− (3) and [Cr(CO)[5] (NO)]+[F-{Al(ORF)3}2]− (4) were obtained in near quantitative yield as orange solids
The right combination of [NO]+ as oxidant with the WCAs [Al(ORF)4]− and [F–{Al(ORF)3}2]− and the unique reactivity of Cr(CO)[6] gives facile access to the unexplored field of homoleptic VE radical carbonyl cations, as well as heteroleptic VE chromium carbonyl/nitrosyl cations. [Cr(CO)6]+[WCA]− shows surprising stability and is closely related to the isoelectronic and isostructural V(CO)[6] with the same D3d symmetric ground state, which is supported by experimental IR, Raman, and EPR spectroscopic investigations, as well as magnetic measurements and calculated DFT/full ab initio data
Summary
1234567890():,; Carbon monoxide is amongst the most important ligands in transition metal chemistry. The chromium hexacarbonyl cation, as a prototype example for such open-shell TMCC systems, was the subject of several electrochemical investigations[30,31,32,33], as well as gas phase and theoretical studies[34,35,36] In principle, these rather weakly bound TMCCs should be ideal starting materials for further substitution chemistry. The approach delineated here uses the weakly coordinating anions (WCAs) [Al(ORF)4]− and [F-{Al(ORF)3}2]− (RF = C(CF3)3)) that allow the use of regular organic solvents, as well as standard laboratory equipment In combination, this approach facilitates synthesis of the target TMCC salts—if desired, in multigram-scale—and enables a rich follow-up chemistry
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