Re(CO)₃-Templated Synthesis of Semihemiporphyrazines

Abstract

Half-hemiporphyrazine macrocycles, which can be called "semihemiporphyrazines", were synthesized using the Re(CO) unit as a templating agent. The products of these template reactions are six-coordinate rhenium complexes, with a facial arrangement of carbonyls, a halide, and a bidentate semihemiporphyrazine chelate that tilts out of the plane of coordination. Three types of semihemiporphyrazines can be produced from these reactions, depending on the alternate heterocycle to the isoindoline unit; structures including pyridine, thiazole, and benzimidazole were formed. The electronic structures of these compounds were probed using spectroscopy as well as density functional theory methods.

Re(CO)3-Templated Synthesis of α-Amidinoazadi(benzopyrro)methenes

“…The terminal amine carbon-nitrogen bond lengths are ~1.31 Å which is longer than the carbon-nitrogen double bonds in the Re(CO) 3 -templated aza(dibenzopyrro)methenes and are comparable to the single bond terminal amine carbon-nitrogen bond lengths in the semihemiporphyrazines. 11,12 Additionally, the double bonds of the axial amidines are ~1.29 Å, whereas the single bonds of these groups are ~1.35 Å. The bond lengths of the amidines are consistent with those observed in the work of Marzilli et al .…”

“…7–10 Recently, we have used the Re(CO) 3 moiety as a template to produce isoindoline based chelates that can be considered as half of a phthalocyanine or a hemiporphyrazine (a “semihemiporphyrazine”). 11,12 The limited geometry options and inert nature of this metal unit in both cases prevent larger macrocycles or chelates from forming. In our continuing studies on the templating behavior of the Re(CO) 3 unit, we have uncovered a new nitrile-activating reaction that affords an α-amidino azadi(benzopyrro)methene (A 3 DBM) which is a tridentate complex that has similar connectivity to the “helmet” and bicyclic phthalocyanines.…”

“…32,33 The mean plane of the DII moieties in the A 3 DBM ligand tilts in relation to the C CO -Re-C CO plane by ~36 ° which is similar to the tilts seen in the semihemiporphyrazines and other transition metal containing azadipyrromethene complexes. 12,34–37 The terminal amine and carbonyl oxygen distances are ~3.5 Å or longer, indicating hydrogen bonding is not present and the tilt is due to other effects. The terminal amine carbon-nitrogen bond lengths are ~1.31 Å which is longer than the carbon-nitrogen double bonds in the Re(CO) 3 -templated aza(dibenzopyrro)methenes and are comparable to the single bond terminal amine carbon-nitrogen bond lengths in the semihemiporphyrazines.…”

Pyrazole and Indazole Semihemiporphyrazine Complexes of Rhenium Tricarbonyl: A Structure/Properties Study

“…These pyridine compounds were also fully characterized and show the expected 1 H resonances and stretching frequencies in their NMR and IR spectra respectively. [8,11] We were able to crystallographically characterize most of the semihemiporphyrazine complexes of Re(CO) 3 ; the only exceptions were the oxo terminated compounds 3 a and 3 b, which formed highly twinned crystals that were unsuitable for diffraction. The Re(CO) 3 X structures are shown in Figure 3, while the pyridine substituted Re(CO) 3 compounds are displayed in Figure 4.…”

“…We have recently investigated both halfphthalocyanine and half-hemiporphyrazine type ligands, [8][9][10] with the latter class of chelates known as semihemiporphyrazines. [11] Frequently, these types of bidentate chelates are not stable in the absence of a metal ion template designed to prevent macrocycle formation. However, recently we observed the stable formation of a family of bidentate chelates incorporating either a pyrazole or an indazole and an isoindoline unit.…”