Access to Stable Metalloradical Cations with Unsupported and Isomeric Metal–Metal Hemi‐Bonds

Abstract

Metalloradical species [Co2 Fv(CO)4 ](.+) (1(.+) , Fv=fulvalenediyl) and [Co2 Cp2 (CO)4 ](.+) (2(.+) , Cp=η(5) -C5 H5 ), formed by one-electron oxidations of piano-stool cobalt carbonyl complexes, can be stabilized with weakly coordinating polyfluoroaluminate anions in the solid state. They feature a supported and an unsupported (i.e. unbridged) cobalt-cobalt three-electron σ bond, respectively, each with a formal bond order of 0.5 (hemi-bond). When Cp is replaced by bulkier Cp* (Cp*=η(5) -C5 Me5 ), an interchange between an unsupported radical [Co2 Cp*2 (CO)4 ](.+) (anti-3(.+) ) and a supported radical [Co2 Cp*2 (μ-CO)2 (CO)2 ](.+) (trans-3(.+) ) is observed in solution, which cocrystallize and exist in the crystal phase. 2(.+) and anti-3(.+) are the first stable thus isolable examples that feature an unsupported metal-metal hemi-bond, and the coexistence of anti-3(.+) and trans-3(.+) in one crystal is unprecedented in the field of dinuclear metalloradical chemistry. The work suggests that more stable metalloradicals of metal-metal hemi-bonds may be accessible by using metal carbonyls together with large and weakly coordinating polyfluoroaluminate anions.

Organometallic Fe–Fe Interactions: Beyond Common Metal–Metal Bonds and Inverse Mixed‐Valent Charge Transfer

“…The back donation from the ferrocene iron to TCFe shown in Figure can be best described as a dative bond between the two metal centers. The complex [Cp*Co(CO) 2 ] 2 [Al(OC(CF 3 ) 3 ] 4 exhibits similar bonding, akin to three‐electron σ ‐bonds . Although the oxidation is calculated to occur at TCFe for 2 , it is clearly supported by interaction with the ferrocene‐iron as seen from the SOMO of 2 + (Figure ).…”

“…The complex [Cp*Co(CO) 2 ] 2 [Al(OC(CF 3 ) 3 ] 4 exhibits similarb onding, akin to three-electron s-bonds. [11] Although the oxidation is calculated to occur at TCFe for 2,i ti sc learly supported by interaction with the ferrocene-iron as seen from the SOMO of 2 + + ( Figure 5).…”

Metalloradicals Supported by a meta‐Carborane Ligand

“…[9] Just recently,as table metalloradical containing am etal-metal hemi-bond has been isolated by using metal carbonyls. [10] Herein, we have succeeded in stabilizing and isolating an ew stable pincer radical complex based on ac arborane backbone.Further studies indicate that hydrogen can induce the transformation of this radical complex. Interestingly, ap aramagnetic metal complex has also been synthesized as the mixed-valence Ir (III,IV) complex.…”

Zerovalent Rhodium and Iridium Silatranes Featuring Two‐Center, Three‐Electron Polar σ Bonds

“…Supported 2c/3e − bonds have also been the subject of many experimental and theoretical studies, leading to the expansion of this bonding scheme to the pnictogen and chalcogen families (Figure a) . With respect to 2c/3e − bonds featuring a transition metal (TM), bona fide examples of these bonds have been reported in a fascinating class of homobimetallic, mixed‐valence Ni 2 (II,III) and Pd 2 (II,III) paddlewheel complexes, as well as several Fe and Co piano‐stool dimers …”