Photochemistry of Sulfilimine-Based Nitrene Precursors:  Generation of Both Singlet and Triplet Benzoylnitrene

Desikan, Vasumathi; Liu, Yonglin; Toscano, John P.; Jenks, William S.

doi:10.1021/jo071049r

Cited by 47 publications

(59 citation statements)

References 70 publications

(122 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Nanosecond time‐resolved infrared (TRIR) experiments with xanthone sensitization suggested that a singlet acyl azide excited state must be the precursor to the corresponding isocyanate . This was in agreement with the previous work of Schuster et al wherein they demonstrated that p ‐acetylbenzoyl azide (containing an internal triplet sensitizer) in the triplet ( n ,π*) state does not produce isocyanate.…”

Section: Introductionsupporting

confidence: 89%

An ultrafast time‐resolved infrared and UV–vis spectroscopic and computational study of the photochemistry of acyl azides

Vyas

Kubicki

Luk

et al. 2012

J of Physical Organic Chem

View full text Add to dashboard Cite

The photochemistry of pivaloyl, benzoyl, 4‐phenylbenzoyl, and 2‐anthroyl azides has been studied using femtosecond (fs) time‐resolved infrared (TRIR) and UV–vis spectroscopy and interpreted with the aid of computational chemistry. Density functional theory calculations revealed a significant difference in the nature of the lowest singlet excited state for these carbonyl azides. The lowest singlet excited states (S1) of p‐phenylbenzoyl and 2‐anthroyl azides are (π,π*) in nature, while the pivaloyl and benzoyl azides S1 states involve (n,π*) excitations. Nevertheless, for all acyl azides studied here, a similar, and intense, IR band at about 2100 cm−1 has been detected in the ultrafast TRIR experiments following 270 nm excitation. These bands were shifted to lower energy by about 100 cm−1 relative to the N3 stretching mode for the ground states of these azides. These 2100 cm−1 vibrational bands were assigned to the S1 states of acyl azides in agreement with density functional theory calculations. The decay of the acyl azide S1 states was described by bi‐exponential functions. The fast component was attributed to the decay of the hot S1 state and the longer component to the decay of the thermally relaxed S1 state. A strong and broad transient absorption in the 350–650 nm spectral range was observed in the fs UV–vis experiments for p‐phenylbenzoyl and 2‐anthroyl azides. The carrier of this absorption also decayed bi‐exponentially, and the time constants were in excellent agreement with those found in the fs TRIR experiments. The slow component of the S1 state decay was found to be dependent on the solvent polarity. When the lifetime of the acyl azide S1 state is substantially longer than the time constant for vibrational cooling of nascent (hot) isocyanate, the correlation between the S1 decay and isocyanate formation was clear. The 270 nm excitation populates the Sn (n ≥ 2) states of these acyl azides. It was established that a hot nitrene is produced more efficiently from both the Sn and hot S1 states than from the relaxed S1 state of these acyl azides. Thus, time‐resolved study provides direct experimental evidence that the S1 state is the precursor of nitrene only when the S1 state is pumped directly and when the S1 state lifetime is longer than the time constant of vibrational cooling of the newborn nitrene. All of these results are consistent with the data obtained recently for 2‐napththoyl azide. Copyright © 2012 John Wiley & Sons, Ltd.

show abstract

Section: Introductionsupporting

confidence: 89%

An ultrafast time‐resolved infrared and UV–vis spectroscopic and computational study of the photochemistry of acyl azides

Vyas

Kubicki

Luk

et al. 2012

J of Physical Organic Chem

View full text Add to dashboard Cite

show abstract

“…Although direct evidence for this mechanism in the form of spectroscopic detection of O( 3 P) is lacking, we have recently shown through time-resolved IR experiments that benzoyl nitrene is formed on photolysis of N-benzoyl dibenzothiophene sulfilimine. 19 These results, and our knowledge that the photochemistry of methyl phenyl sulfoxide is substantially more complex than that of dibenzothiophene-S-oxide, led us to predict that compounds 2 and 4 might be particularly attractive precursors. The photochemistry of benzothiophene-S-oxide is not dominated by deoxygenation, 20 but we believed that the bond dissociation enthalpy (BDE) for its S-O bond would be significantly higher than the corresponding S-C BDE for 3, 21 and that 3 might thus also be a reasonable carbene precursor.…”

mentioning

confidence: 98%

“…Photolysis of the structurally related N-benzoyl dibenzothiophene sulfilimine has been shown to yield both singlet and triplet benzoyl nitrene. 19 a Relative to sulfide formation or sulfide + 10. Φ+sulfide also includes 10 for precursor 2. b Overlapping absorption spectra made experiment impractical.…”

mentioning

confidence: 99%

S,C-Sulfonium Ylides from Thiophenes: Potential Carbene Precursors

2007

Self Cite

View full text Add to dashboard Cite

Carbenes remain important and intriguing reactive intermediates in organic chemistry despite years of study for many reasons, among them the access they provide to unusual product compounds, their differing chemistry depending on spin state, and their mechanistic complexity. Photochemical precursors to carbenes, such as diazo compounds and diazirines, are often favored, because they can yield carbenes by photolysis at low temperatures and can be used for laser flash photolysis experiments. However, because these nitrogenous precursors have been shown to undergo reactions in their excited states that mimic chemistry expected from the carbene itself, there is demand for alternative practical precursors. In this Communication, we report the use of S,C-sulfonium ylides 1-4 as photochemical carbene precursors, as illustrated in Scheme 1 for compound 4.The choice of compounds 1-4 as potential precursors to dicarbomethoxycarbene for this study was driven by two considerations. First S,C-ylides of malonates are known to be stable and easy to prepare, at least in part because of the electron withdrawing groups that delocalize the formal negative charge. Second, by generating dicarbomethoxycarbene 1-3 for the proof-of-concept work of showing carbene generation, we believed we could distinguish between reactions of the carbene and a potential excited state Wolfflike rearrangement that might yield a ketene derivative. Such 1,2shifts have been demonstrated repeatedly for nitrogenous carbene precursors that are subject to 1,2 hydrogen shifts or carbon shifts to relieve ring strain. [4][5][6][7][8][9][10]

show abstract

“…Kinetics of the reactions of singlet species 1 32b in solution at room temperature were studied using time -resolved IR spectroscopy (TRIR) 136,140 and nanosecond laser fl ash photolysis. 115,141 The absolute rate constants of bimolecular reactions of 1 32b with Figure 11.3 Difference electronic absorption spectra recorded upon irradiation of 31b at 254 nm for 2 min in argon matrix at 12 K (1) and the sample after further irradiation at 313 nm for 8 min (2).…”

Section: Photochemistry Of Carbonyl Azides and Azide Estersmentioning

confidence: 99%