Generation and Reactivity of Simple Chloro(aryl)carbenes within the Cavities of Nonacidic Zeolites

Abstract

A number of para-substituted chloro(aryl)carbenes are generated within the cavities of a series of dry alkali metal cation-exchanged zeolites (LiY, NaY, KY, RbY, and CsY) upon laser flash photolysis of the corresponding diazirine precursor. The absolute reactivity of the chloro(aryl)carbene is found to be strongly dependent on both the nature of the electron-donating and -withdrawing properties of the aryl substituent and the nature of the zeolite charge-balancing cations. The results strongly suggest that two opposing mechanisms for capture of the carbene can occur depending on whether the zeolite framework behaves as a nucleophilic reagent or an electrophilic reagent in its reaction with the carbene center. Hammett relationships for the decay of the carbene as a function of aryl substituent and zeolite counterion versus the sigma+ substituent parameter support a change in mechanism as the carbene center toggles between being electron poor and electron rich. For the electron-poor chloro(4-nitrophenyl)carbene, a framework adduct is proposed upon reaction of the nucleophilic [Si-O-Al]- bridge with the carbene center, and for the electron-rich chloro(4-methoxyphenyl)carbene, an adduct with the tight Li+ cation is proposed.

Carbon Atom Insertion into Pyrroles and Indoles Promoted by Chlorodiazirines

“…A limitation was observed in moving to electron-rich diazirines, which exclusively afforded the corresponding aldehydes. 66,67 Aliphatic diazirines were similarly poor coupling partners, either isomerizing to vinyl chlorides or undergoing competitive dimerization (see the experimental SI section IV). 68−71 Pyrroles (4) represent a more complex substrate class due to the potential for regioisomeric products derived from insertion into the two "olefinic" sites of the substrate (Figure 3).…”

“…A limitation was observed in moving to electron-rich diazirines, which exclusively afforded the corresponding aldehydes. 66 , 67 Aliphatic diazirines were similarly poor coupling partners, either isomerizing to vinyl chlorides or undergoing competitive dimerization (see the experimental SI section IV). 68 − 71 …”

“…NaOH, BnEt 3 NCl) followed by Suzuki coupling with 3-fluorophenylboronic acid afforded 3k in 22% yield over 2 steps, compared with 82% under the title conditions. A limitation was observed in moving to electron-rich diazirines, which exclusively afforded the corresponding aldehydes. , Aliphatic diazirines were similarly poor coupling partners, either isomerizing to vinyl chlorides or undergoing competitive dimerization (see the experimental SI section IV). − …”

Photophysics and Luminescence Spectroelectrochemistry of [Tc(dmpe)3]+/2+ (dmpe = 1,2-bis(dimethylphosphino)ethane)

“…The reduced POM can then be reoxidized by air or by proton reduction to complete the catalytic cycle. , An absorption threshold of about 400 nm, which is common for POMs, results in an ESP that is about 3 V more oxidizing than the GS reduction potential, which for most POMs shifts the oxidizing potential more positive than the 2.8 V (vs NHE) necessary to form OH radical. Because of their ideal GS and ES properties, POMs have successfully photocatalyzed the oxidation of a number of organic pollutants. ,, Uranyl ion (UO 2 2+ ) is another example of an oxygen containing transition metal ion that has a highly oxidizing excited state potential. The lowest energy transition in the uranyl ion is thought to involve excitation of an electron from the highest filled O π orbital to a nonbonding orbital on the uranium .…”

“…Because of their ideal GS and ES properties, POMs have successfully photocatalyzed the oxidation of a number of organic pollutants. 1,36,37 Uranyl ion (UO 2…”