The intramolecular carbene-carbonyl coupling has been investigated for the simple M(CH2)(CO)3 (M = Co, Rh, Ir) radical complexes at the DFT PBEPBE/TZVP level of theory. The coupling is predicted to be very fast for the cobalt-containing system, but it is still feasible for the systems based on the other two metals. The back-way reaction, that is, the conversion of the ketene complex into carbonyl-carbene complex, cannot be excluded from the Ir-containing system in CH2Cl2, and it is even favored in gas phase. The intermolecular ketene formation by the addition of external CO onto the CH2 moiety is the favored pathway for the Ir-complex. The Laplacian distribution, as well as the natural spin density distribution of all the species, being involved in the reaction, gives explanation for the significant difference between the nature of the Co-complex and the Rh- and Ir-systems. 1. Introduction Ketenes belong to the first generation of reactive intermediates [1], along with carbenes, radicals, carbocations, and carbanions [2], and are intensively studied members of the cumulene family, with a wide variety of synthetic applications [3–6]. The most common method to access ketenes is from acyl halides via dehalogenation promoted by bases. Therefore, carbonylation of metal carbene provides an alternative, straightforward approach to the generation of ketene species [7–10]. There are also many ketenes that cannot be synthetized by classical synthetic methods due to their high reactivity. The formation of ketenes from carbenes usually takes place via diamagnetic pathways; therefore less attention has been paid to the reaction of mononuclear radical carbene complexes. In particular, De Bruin and coworkers have reported various transition metal carbene radicals of the cobalt group, with catalytic applications, such as cyclopropanation [11, 12], carbonylation [13], and selective carbon-carbon bond formation by coupling of Ir-ethene complexes with Ir-carbenoid radicals [14]. The structure and the spin density distribution of mononuclear Rh(0) radical complexes were also examined experimentally and computationally [15]. The results have been reviewed as well [16, 17]. The main goal of this study is to further explore computationally the reactivity of simple carbonyl carbene radicals, which have already proven their applicability in the carbonylation of ethyl diazoacetate [8]. The second purpose is to scrutinize the vertical trends in the cobalt group of transition metals and to investigate the reaction profile for the rhodium and iridium analogues and to check whether
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