Azo-triazolide bis-cyclometalated Ir(iii) complexes via cyclization of 3-cyanodiarylformazanate ligands

Abstract

Sterically encumbered iridium-bound formazanate ligands undergo redox-neutral cyclization to form azo-triazolides, a new class of redox-active chelating ligand.

Dinuclear Complexes of Flexidentate Pyridine‐Substituted Formazanate Ligands

“…We note that complex 1, which contains an eutralf ormazan coordinated to iridium through the pyridine, is the most difficult to oxidize in the series, whereas in the rest of the compounds, with formally monoanionic metal-bound formazanate cores the oxidation waves are cathodically shifted. We have previously shown that the HOMO in platinum [29] and iridium [33] formazanate compounds is majority formazanate-centered with minor metal 5d contribution, thus we believe that the oxidation involves both the formazanate and the metal. Interestingly,t he oxidation wave in complex 1 has ah igherc urrent value than the reduction wave, suggesting that in this compound where the formazanatei snot chelated to the metal concurrent oxidation of the formazanate and the [Ir(F 2 ppy) 2 ] + fragment may be occurring.…”

“…Apart from intense peaks in the UV (l < 350 nm) attributed to localized p!p*t ransitions of the aryl substituents from both C^N and formazanate, an otable absorption between 460 nm and 700 nm stands out among all compounds,w hich is assigned as a p!p*t ransition within the formazanate framework with as mall amount of metal-to-ligand charge transfer (MLCT) character,o nt he basis of many other platinum and iridium formazanates previously studied experimentally and computationally. [29][30][31]33] The two free formazans have similar UV/Vis absorption wavelengths, with the low-energy transition occurring 482 nm in Fza and 466 nm in Fzb.C oordination through the 4-pyridyl substituent of Fza,a so bserved in complex 1,h as am inimal effect on the absorption wavelength, which occurs at nearly identicalw avelength (483 nm) in this complex. When the formazanate chelates the metal center, as observed in most other complexes,weo bserve as izeable red-shift of the p!p*t ransition, as we have previously noted in studying many other Pt and Ir formazanates.…”

“…[10] Our group has expanded the coordination chemistry of formazanatest ot hird-row transition metals with as eries of hetero-leptic cyclometalated platinumc omplexes and bis-cyclometalated iridium complexes, [29][30][31] and accessed homoleptic azo-iminate platinum complexes and azo-1,2,3-triazolide iridium complexesv ia hydrogenative cleavage or [3+ +2] cyclization of formazanates, respectively. [32,33] Compared to the numerous formazanate complexes where as ingle metal atom is chelated within the NNCNN framework, polynuclear compounds involving formazanates remain rare. Polynuclear coordination compounds with other ligand sets have ar ich history in the field of photochemistry and photocatalysis, providing platforms perfectly tailoredt os tudy fundamental aspects of excited-state chargea nd energy transfer processes, [34] and new multi-functional light harvester/catalyst arrays.…”

“…Havinge xtensively studied the coordination chemistry of formazanates with Ir III [31,33] and Pt II , [29,30] our initial effort presented herein includes as eries of complexes containing different combinations of these two metals bridged by pyridyl-substitutedf ormazanates.W ee laborate the coordination chemistry of formazans with either 4-and 2-pyridyl substituents as the central aryl ring. The pyridyl substituents offer one additional coordination site, and we showi nt his work the diversity of coordination modes possible with these ligands.…”

Dinuclear Complexes of Flexidentate Pyridine-Substituted Formazanate Ligands

“…10 Our group has expanded the coordination chemistry of formazanates to third-row transition metals with a series of heteroleptic cyclometalated platinum complexes and biscyclometalated iridium complexes, [29][30][31] and accessed homoleptic azo-iminate platinum complexes and azo-1,2,3triazolide iridium complexes via hydrogenative cleavage or [3+2] cyclization of formazanates, respectively. 32,33 Compared to the numerous formazanate complexes where a single metal atom is chelated within the NNCNN framework, polynuclear compounds involving formazanates remain rare. Access to complex polynuclear formazanate complexes is desirable for a number of reasons; in addition to greatly expanding the fundamental coordination chemistry of formazanates, there is the possibility of designing compounds with enhanced or unusual redox, magnetic, or photophysical properties, enabled by electronic communication between the building blocks mediated by the redox-active formazanate.…”