Structural and Spectroelectrochemical Studies on (2,2′-Bidipyrrinato)copper(II) and -palladium(II) Complexes

Abstract

Copper(II) and palladium(II) complexes of two 2,2′‐bidipyrrin ligands were prepared and examined, in comparison with the known nickel(II) complexes of these ligands, by means of X‐ray crystallography, cyclic voltammetry, and spectroelectrochemistry. All compounds are of helical geometry with coordination environments of the metal centres displaying very small tetrahedral distortions for palladium and very large ones for copper complexes. Porphyrinoid behaviour was found for the one‐ and two‐electron oxidations of all complexes studied, as well as for the reductions of the PdII species. On the other hand, the reduction of the CuII complexes shows some special features, which may be explained from the results of spectroelectrochemical studies as related to the particular non‐planarity of these compounds. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Helical Transition‐Metal Complexes of Constrained 2,2′‐Bidipyrrins

“…Isolation can be effected in good yields after chromatographic workup and recrystallization. As expected, the new complexes are of type A with a distorted square‐planar arrangement of the N donors and therefore analogous to known nonbridged nickel‐ and palladium‐2,2′‐bidipyrrins of, for example, 8 12c,12d. Results from high‐resolution mass spectrometry, NMR spectroscopy and UV/Vis measurements further support the assignments.…”

Electrochemical investigations of tripyrrin complexes

“…Especially the potential difference ΔE = E ox1 -E red1 is not constant for the studied series of complexes and spans a range from 1.63 to 1.79 V. The observed average value of 1.70 V is much smaller than for porphyrins (2.25 V) and close to bidipyrrins (1.60 V). Spectroelectrochemical studies clearly indicate that the stability of the electrogenerated species (radical cation and dianion) is much lower than for previously characterized complexes of porphyrins, or bidipyrrins [15,16]. The stability of the oxidized and reduced species is even lower for the palladium complex for which only irreversible electron transfers can be observed by cyclic voltammetry.…”

“…Chemical shifts (δ) are given in ppm relative to TMS. , tripyrrane complexes II [8], tripyrene complex III [1], tripyrrinone complexes IV [9,10], tripyrrin complexes V [11][12][13][14], bidipyrrin complexes VI [15,16], inverted porphyrin complex VII [22] and Nsubstituted porphyrin complex VIII [23] 5 V/s) or as a rotating disk electrode. The auxiliary electrode and the pseudo-reference electrode were platinum wires.…”

“…The aim of the present study is to obtain insights into the electrochemical behavior of this new class of complexes for which no data has been published before and to compare the observed electrochemical behavior to both previously studied tripyrroles and to open and closed tetrapyrroles like bidipyrrin complexes VI (Fig. 1) [15,16], bilindione [17][18][19], formylbiliverdin [20], porphyrin [21], inverted porphyrin VII [22] and Nsubstituted porphyrin complexes VIII [23] for which electrochemical data are available.…”

Conformational behaviour of dinuclear Rh(I) complexes of the open-chain tetrapyrrolic ligand 2,2′-bidipyrrin (H2BDP)

“…Besides the rather large number of macrocyclic compounds only one report about rhodium complexes of open-chain tetrapyrroles has been published so far [8]. This is surprising, since structural information on open-chain oligopyrroles is still rare, and, in addition, special reactivity schemes of these complexes can be deduced from the redox properties of open-chain oligopyrroles and group 9 cations [9].…”