Alkene Assisted Homolysis of the Si‐H, Ge‐H, and Sn‐H Bond: New Examples of Molecule Assisted Homolysis (MAH)

Abstract

Radical hydrosilylation, hydrogermylation and hydrostannylation without any added initiator may be initiated by alkene‐assisted homolysis of the respective Si‐H, Ge‐H and Sn‐H bond, three more examples of molecule‐assisted homolysis (MAH). We studied the thermally initiated radical addition of tris(trimethylsilyl) silane 1a, tributylgermane 1b, and tributylstannane 1c to methyl 10‐undecenoate 2a and of 1a to 1‐decene 2b. Computed reaction enthalpies and pathways support the radical formation by MAH. These results give evidence that many respective radical reactions without any added initiator reported in literature may be initiated analogously by MAH.

Atmospheric Oxygen Mediated Radical Hydrothiolation of Alkenes

“…However, these processes typically involve solvent‐free conditions, high temperature (often >100 °C), or extended, multi‐day reaction times. The mechanism of initiation of such “dark” systems is intriguing and Metzger and co‐workers have postulated a Molecule‐Assisted Homolysis (MAH) initiation for the thermal generation of thiyl radicals in the absence of any other initiator in which the thiol and alkene form an electron‐donor/acceptor (EDA) complex, albeit these reactions were run in the absence of solvent at 118 °C [48, 49] . Though elegant, this approach is yet to see widespread use within the synthetic community.…”

“…The mechanism of initiation of such "dark" systems is intriguing and Metzger andc o-workersh ave postulated aM olecule-Assisted Homolysis (MAH) initiation for the thermal generation of thiyl radicals in the absence of any other initiator in which the thiol and alkene form an electron-donor/acceptor (EDA) complex, albeit these reactions were run in the absence of solventa t1 18 8C. [48,49] Thoughe legant, this approachi sy et to see widespread use within the synthetic community.W ith this in mind, we soughtt od evelop as implified protocol for thiyl radical initiation that is compatible with organics olvents, while maintaining efficient hydrothiolation applicable in the context of the thiol-ene reaction manifold. [50,51] We envisioned that molecularo xygen may function in the initial abstraction of ah ydrogen atom from thiols or thioacids, thereby generating at hiyl radicalw hich could undergo addition to an alkene furnishingathioether (sulfide) or thioester linkage (Figure 1c).…”

Role of thiol oxidation by air in the mechanism of the self-initiated thermal thiol–ene polymerization

“…24 The driving force is thus the formation of C-H bond at the olefin that reduces the endothermicity of S-H homolysis. 56 For this reason, it is referred to as "alkene-assisted homolysis", 57 or in a more general way as a MAH. The occurrence of a MAH of S-H as initiation mechanism was originally reported by the groups of Pryor 40 and Nuyken, 25 then more recently by Metzger et al…”