Preparation of organocyanocobaltate(III) complexes

Catalytic hydrogen atom transfer to alkenes: a roadmap for metal hydrides and radicals

“…Several foundational studies on MHAT, particularly utilizing cobalt hydride complexes, have established that the formal addition of a hydrogen atom across an alkene proceeds stereospecifically to form the syn addition product (often observed as cage collapse to the organocobalt). 133 , 134 When cyclopentene- d 8 was treated with (tetraanisylporphyrinato)cobalt( iii )hydride ((TAP)Co–H), two diastereomers – the cis and trans organocobalt addition products – were formed, in which formation of trans product implied that a secondary process after radical-pair formation was occurring. At higher temperatures (60 °C), the cis / trans ratio was equal to 1.0, while at lower temperatures (6–23 °C), the cis / trans ratio increased to a relatively constant value of 2.8.…”

“… 135 Other studies have suggested that radical-pair collapse for organocobalt species is faster than molecular rotation; organocobalt formation could be highly dependent on the identity of the cobalt complex. 133 , 134 …”

“…135 Other studies have suggested that radical-pair collapse for organocobalt species is faster than molecular rotation; organocobalt formation could be highly dependent on the identity of the cobalt complex. 133,134 In related experiments, the racemization of organometallic complexes through carbon-metal bond homolysis was evaluated in two systems. Measuring the optical rotation of enantioenriched (alkyl)bis(dimethylglyoximato)cobalt(III) at a constant temperature over time led to a rst-order rate of racemization of the organocobalt.…”

Hydrogen Atom Transfer‐Mediated Cyclisations of Nitriles

“…In the early 1960s, Kwiatek and Seyler first reported the use of metal hydrides as catalysts in the hydrogenation of α,β‐unsaturated compounds . The discovery by Halpern, later elegantly developed by Norton, that metal‐hydride hydrogen atom transfer (HAT) proceeded by a free‐radical mechanism opened the door to a wide range of alkene hydrofunctionalisation reactions.…”

“…In the early 1960s, Kwiatek and Seyler first reported the use of metal hydrides as catalysts in the hydrogenation of a,b-unsaturated compounds. [1,2] The discoveryb yH alpern, [3] later elegantly developedb yN orton, [4] that metal-hydride hydrogen atom transfer (HAT) proceeded by af ree-radical mechanism opened the door to aw ide range of alkene hydrofunctionalisation reactions.H owever, it was the pioneering work by Mukaiyama [5] on the catalytic hydration of alkenes,u sing Co(acac) 2 and oxygen, that sparked wider interest in the field of alkene hydrofunctionalisation. As ar esult, there now exists an extensive "toolkit"f or the addition of hydrogen and af unctionalg roup to an alkene with Markovnikov selectivity and high chemo-selectivity using cobalt,m anganese and iron complexes.…”