Silicon‐Mediated Coupling of Carbon Monoxide, Ammonia, and Primary Amines to Form Acetamides

Abstract

Fort he first time,adirect transformation of CO, NH 3 ,a nd primary amines into acetamides,m ediated by am ain-group element (silicon), is reported. Starting point is the selective deoxygenative reductive homocoupling of two CO molecules by the Fc-bis(silylene) 1a (Fc = ferrocendiyl) as areducing agent, whichforms the ferrocendiyl-bridged disila-(1 bar,2 98 K) and benzylamine yields the Fc-disiloxanediamines [Fc(RHNSi-O-SiNHR)] 5a (R = H) and 5b (R = benzyl) under release of the respective acetamides H 3 CC-(O)NHR, as confirmed by 13 C-isotope-labelling experiments. IR and NMR studies of the reaction reveal af our-step mechanism involving an N-silylated carboxamidet hat can be isolated and fully characterized.T he striking reaction mechanism for this unprecedented transformation involves af acile SiÀCbond cleavage and ammonolysis of aSiÀObond, and has been demonstrated experimentally and by quantum-chemical calculations.

Where silylene–silicon centres matter in the activation of small molecules

“…In a related work, exposure of 16b to NH 3 and benzylamine yields Fc-disiloxanediamines and respective acetamides. 35 More recently, the same group reported another example of homocoupling of CO mediated by the bis-silylene 17 [(LSi:)C] 2 B 10 H 10 {L= PhC(tBuN) 2 } (Scheme 11). 23h Treatment of toluene solutions of 17 to CO atmosphere at À20 1C leads to a colour change from yellow to brown.…”

An Isolable Bis(Silanone–Borane) Adduct

“…[4,5] The silicon(II) atom in silylenes exhibits an ambiphilic character due to its vacant 3p orbital (LUMO) and the 3s-centered lone pair (HOMO). Owing to their interesting property and reactivity, stable N-heterocyclic silylenes (NHSis), the heaviera nalogues of NHCs, have been utilized successfully for the metal-free activation of small molecules [6] and as powerful steering ligandsi n homogeneous catalysis. [7] After the first isolation of an N-heter-ocyclic silylene in 1994 by Denk and West, the formation of a silylene-borane adduct was reported two years later,w hich, however,s lowly rearranges to as ilylborane through Si II insertion into the BÀCb ondo fB (C 6 F 5 ) 3 .…”

Metalation-induced denitrogenative reductive coupling of isocyanides on a silylene-bridged nickel cluster

“…In the IR spectrum of 4, one strong absorption band appeared at 2024 cm −1 ; this value is comparable to that observed for the disilylketenimine reported by Driess et al ( vide infra ). 9 …”

“…, silylenes, located adjacently through a xanthene or ferrocenyl linker promote deoxygenative homocoupling involving two molecules of CO or heterocoupling involving one molecule of CO and one molecule of CNXyl (Xyl = 2,6-dimethylphenyl) to form C C O or C C NXyl units via cleavage of the C O bond. 9 It is thus probable that the silylene “SiPh 2 ” moieties generated upon the insertion of the nickel species into the Si–Si bonds in 1c might play a crucial role to activate the inactive C N bond in CN t Bu. Ito et al reported another example of the scission of the C N bond of isocyanides assisted by organosilicon moieties, i.e.…”

“…In contrast, the development of deoxygenative reductive coupling reactions of CO on well-defined molecular compounds such as transition-metal complexes remains challenging, despite the fact that the development of homogeneous systems may facilitate the detailed investigation of the underlying reaction mechanism. 3–10 However, scientists have recently achieved coupling reactions of CO using several defined transition-metal and lanthanide complexes, which has led to a better understanding of the mechanisms of CO activation in each case. For instance, Agapie et al developed a deoxygenative reductive coupling of two molecules of CO at the single molybdenum center of a Mo( ii )–dicarbonyl complex with the aid of KC 8 and R 3 SiCl to form alkyne i Pr 3 SiO–CC–Si i Pr 3 or bis(silyl)ketene (SiMe 3 ) 2 CCO as the deoxygenative coupling products (Scheme 1).…”