Persistent Triplet Carbenes

Synthesis of azasilacyclopentenes and silanols via Huisgen cycloaddition-initiated C–H bond insertion cascades

“…Intramolecular cyclopropanations appear to be possible with silyl carbenes of either a triplet or singlet nature if pendant olefins are present ( 47 and 49 , respectively). On the other hand, the presence of a carbonyl induces more singlet-like reactivity, 28,30 including Wolff rearrangements and X–H insertion reactions. 31 Intramolecular C–H bond insertions may also occur for these cases, but the preference for insertion is typically at the β- or γ-position relative to silicon (see 60 ).…”

Examination of the Mode of Action of the Almiramide Family of Natural Products against the Kinetoplastid Parasite Trypanosoma brucei

“…Following incubation of 27 with the preclarified cell lysate, the photoaffinity probe was activated by irradiation with UV light (366 nm, 3 min) to generate a short-lived carbene species (1–2 µsec in benzene). 19 This highly reactive carbene will rapidly form a covalent attachment to neighboring proteins, creating a permanent bond between target proteins and the biotin reporter tag. The photoaffinity capture experiment was repeated twice (n = 2), and identified 73 proteins that were present in at least one replicate, but were not present in the streptavidin-only control lane.…”

Unusual solvation through both p-orbital lobes of a carbene carbon

“…[5][6][7][8][9][10] In general, the frontier orbitals of carbenes are highly located at the carbene carbon atom and consist in: (i) one orbital of σ type whose relevant part is disposed in the molecular R-C-R ′ plane with 2s and 2p carbon contribution (see the example (a) in Figure 1), and (ii) another orbital of higher energy and with the relevant part of almost pure carbon p type, disposed perpendicular to the R-C-R ′ plane (see the example (b) in Figure 1). 11 If the difference between the energies of these two orbitals is sufficiently large, then the 2 lone electrons are paired in the σ orbital, forming the overall singlet state, S o (σ 2 ), which leaves the almost pure p orbital empty. If the energy difference is small, then one electron will be in a σ orbital and the other in the p orbital, with an overall triplet minimum energy state, T 1 (σ 1 p 1 ).…”

“…If the energy difference is small, then one electron will be in a σ orbital and the other in the p orbital, with an overall triplet minimum energy state, T 1 (σ 1 p 1 ). 11 Either the singlet or the triplet situation will depend on the effect of the substituents and/or the type of solvent in which they are. [2][3][4]11 In this work, we are interested in singlet carbenes.…”

“…11 Either the singlet or the triplet situation will depend on the effect of the substituents and/or the type of solvent in which they are. [2][3][4]11 In this work, we are interested in singlet carbenes. These species are stabilized with substituents having electrons in orbitals that can interact with the almost p pure carbene carbon orbital (examples: -NR2, -OR, -SR. -F, -Cl, -Br, and -I).…”