Dimeric porphyrins linked by conjugated groups containing triple bonds: the crystal structure of the nickel octaethylporphyrin dimer bridged by 2,5-diethynylthiophene

Abstract

The conjugated bridge and the attached meso-carbons in the title dimer are almost coplanar; the porphyrin rings are ruffled and distorted in this vicinity, indicating strong interporphyrin interaction via the n-orbitals of the diethynylthiophene unit.

Porphyrin Dimers Linked by Conjugated Butadiyne Bridges: Preparations, Spectra, Voltammetry and Reductive Spectroelectrochemistry of {[M(OEP)](μ-C4)[M(OEP)]}(M2≡H4, Co2, Ni2, Cu2, Zn2, Pd2, Pt2, Co/Ni, Ni

“…Configuration interaction (CI) leads to the transition to S 1 (the visible or Q band) being forbidden or weak and that to S 2 (the Soret or B band) being strongly allowed. The richer spectra of the dimers all exhibit the same gross features which were evident from the first description of the archetypal Ni 2 P 2 [17], and we now know that they are characteristic of bis(porphyrins) linked in the meso positions by conjugated ethyne and butadiyne bridges [17][18][19][21][22][23][24][25][26][27][28][29][30][31]. These features are (i) obvious red shifts of certain bands relative to the parent MOEP, (ii) multiple splitting of the Soret (B) band and (iii) intensification of Q relative to B.…”

“…Bis(4-nitrophenyl)butadiyne has orthogonal aryl groups, presumably to avoid electronic competition between the nitro groups, each of which is rigorously coplanar with its attached ring [48]. The only mesoalkynyl porphyrin dimer whose crystal structure is known is 2,5-bis(NiOEP C C)-thiophene, 1, prepared in our laboratory [21]. In this structure the mean planes of the porphyrin units are effectively parallel with each other and with the intervening heteroarene.…”

“…Our contribution in this area has concerned the introduction of triple bonds into the bridging groups used to link porphyrins into dimers [17][18][19][20][21][22][23][24]. This strategy has been taken up independently by several other groups and is now an active area of research [25][26][27][28][29][30][31][32][33][34].…”

“…This strategy has been taken up independently by several other groups and is now an active area of research [25][26][27][28][29][30][31][32][33][34]. It has become clear [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] that the linking of two or more porphyrins through conjugating moieties in which a carbon-carbon triple bond is attached directly to the meso positions causes unique modifications to the porphyrin electronic spectra. The general characteristics of these systems, when compared with monomeric porphyrins or with dimers with nonconjugated bridges, are (i) apparent red shifts of the spectra, (ii) substantial splittings of the Soret (B) bands and (iii) intensification of the visible (Q) bands relative to the Soret bands.…”

“…The first comprises the binuclear ligand [H 2 (OEP)](m-C 4 ) [H 2 (OEP)] ( H 4 P 2 ) (Scheme 1) and its complexes ( M 2 P 2 ) with many four-coordinate metal ions (M 2 Co 2 , Ni 2 , Cu 2 , Zn 2 , Pd 2 , Pt 2 , Co/Ni, Ni/Cu, Ni/Zn), which were introduced in our preliminary communication [19]. To date, the second series comprises a family of Ni 2 bis(porphyrins) linked in the meso positions by progressively extended bridges containing multiple alkyne units (up to C 8 ) or alkyne units in conjugation with arenes, heteroarenes and alkenes [20][21][22][23][24]. In both families we discovered by means of in situ spectroelectrochemical studies that the electrogenerated p-anions [M 2 P 2 ] 1À and [M 2 P 2 ] 2À of most systems exhibit remarkably intense near-IR absorption bands (e b 10 5 M À1 cm À1 ) [19,23,24].…”