Synthesis of π-conjugated asymmetric aza-BODIPYs via nitrosobicyclopyrroles

Synthetic Exploration of Bis(phenolate) Aza-BODIPYs and Heavier Group 13 Chelates

“…Instead, the majority of HOMO and LUMO density resides on the aza-DIPY core, resulting in the expected π-π* transitions. Furthermore, little to no orbital density was found on the metal centers which agrees with numerous aza-DIPY studies performed previously [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 46 , 47 ]. Perhaps the greatest difference between the frontier molecular orbital plots of these compounds involves the LUMO+1 orbital as 1a-b has orbital density spread throughout the proximal rings and aza-DIPY core while 2a-b , 3a-b , and 4a-b have orbital density exclusively on the axially bound pyridines.…”

“…The synthesis of bis(phenolate) aza-MDIPYs 1a-b , 2a-b , 3a-b , and 4a-b follows the well-established procedures previously outlined by Burgess [ 18 ] and Nabeshima [ 23 ] as depicted in Scheme 1 . Bis(phenolate) aza-DIPY core structures 7a-b , containing para -functionalized methyl- and methoxyphenyl groups, were specifically chosen as they possess relatively similar electron donating capabilities and will likely exhibit the most bathochromically shifted absorption and emission spectra based on prior work by ourselves and others [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. The first step involves subjecting known chalcones 5a-b to a Henry reaction with nitromethane to give compounds 6a-b in excellent yields (>95%).…”

“…In conjunction with our prior work functionalizing aza-BODIPYs through the direct incorporation of nitro groups [ 11 ], we became interested with the bis(phenolate) aza-DIPY core structure ( C ), having ortho -functionalized phenolic groups present on the proximal rings. Motivation for this core structure stemmed from the previous work done by Burgess and others which demonstrated that bis(phenolate) aza-BODIPYs can achieve absorption and emission maxima upwards of 780 nm [ 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. Additionally, very recent work by Sauvé and coworkers detailed that the addition of phenylacetylene groups on the 2- and 6-positions of the bis(phenolate) aza-BODIPY core can further shift absorption and emission maxima past 820 nm [ 19 ].…”

A mild synthetic route to α-nitroso diaryl pyrroles

“…10 This method enables nitrosation of 2,5-diaryl substituted pyrroles, and tolerates the presence of electron-donating and electronwithdrawing groups on the aryl rings. [10][11][12][13] Given the highly acidic reaction conditions reported, and the acid-catalysed tendency of pyrroles to polymerise, we sought a mild approach that relied on pre-formed sources of nitrosonium ions. 14 Seeking inspiration from non-heterocyclic aromatic chemistry, an alternative nitrosation method was sought in order to diversify the scope of synthetically accessible nitroso pyrroles.…”

“…10 This method enables nitrosation of 2,5-diaryl substituted pyrroles, and tolerates the presence of electron-donating and electron-withdrawing groups on the aryl rings. 10–13 Given the highly acidic reaction conditions reported, and the acid-catalysed tendency of pyrroles to polymerise, we sought a mild approach that relied on pre-formed sources of nitrosonium ions. 14…”