Bis(benzene)chromium. A Sandwich Complex Spin Trap As Revealed by ENDOR Spectroscopy

Abstract

Bis(benzene)chromium [(η6-C6H6)2Cr] (BBC) is shown to readily trap radical species R (R = H, D, isobutyronitrile (IBN)) to form complex paramagnetic adducts whose structure has been identified in frozen solution by ENDOR (electron nuclear double resonance spectroscopy). It is shown that radical attack yields the 17 valence electron species (η6-C6H6)(η5-C6H6R)Cr where R assumes the endo position of the η5-ring with respect to the metal in a dynamic interannular migration mediated by the central metal atom. It is further shown that PhSiH3 (Ph = phenyl) is an efficient source of hydrogen atoms in the presence of BBC as well as other conventional nitroxide spin traps.

A computational study of organic polyradicals stabilized by chromium atoms

“…A similarly bent benzene ring has been reported for the Bis(benzene)chromium (BBC) radical 62,63 obtained from addition of organic radicals to BBC. BBC is an efficient organometallic spin scavenger 62 and both theory and experiment assign the extra spin to the chromium atom. Fig.…”

Quantum coherence in a triangular Cu3complex

“…A fourth line left of the Larmor frequency is very weak, which is because of the low temperature, where according to the Boltzmann distribution the higher-energy levels are not populated. The dipolar contribution to the hyperfine tensor is given by [32] A(r) = g e μ B g n μ n hr 3…”

Radical Coordination Chemistry and Its Relevance to Metal‐Mediated Radical Polymerization

“…For example, the ketyl radical I 2 Sm–OCMe 2 · generated from acetone has been shown to add to the benzene ligand of [(C 6 H 6 )Cr(CO) 3 ] more than 10 5 times faster than to uncomplexed benzene 107. Radical additions to π‐bonded aromatic rings have mostly been studied for 18‐electron complexes, to arene ligands as in [(arene)Cr(CO) 3 ],107,108 [(arene)Mn(CO) 3 ] +[109] and [(C 6 H 6 ) 2 Cr],110 but also to the cyclopentadienyl ligand in ferrocene 111. Addition to Cp in 19‐electron [Cp 2 Co] leads to stable 18‐electron [CpCo(C 5 H 5 R)] products 112.…”