Molecular and Electronic Structure of (2,2′-Bidipyrrinato)nickel(II) Complexes

Abstract

Nickel complexes of eight differently substituted 2,2′‐bidipyrrins have been prepared and fully characterized. The X‐ray analyses of three of these complexes revealed helical chiral molecules. Despite the tetrahedral deviation from the square‐planar coordination geometry at the metal centres, all compounds were found to be diamagnetic in nature. For (3,3′,4,4′,8,8′,9,9′‐octaethyl‐10,10′‐dimethyl‐6,6′‐diphenyl2,2′‐bidipyrrinato)nickel, a separation into the enantiomers by chiral MPLC could be achieved, and the first CD spectra of enantiomerically pure tetrapyrrole helicates are reported. An electrochemical study of the new complexes allowed a first insight into the electronic structure of (2,2′‐bidipyrrinato)nickel(II), disclosing a rather high energy HOMO and metal−ligand interaction similar to that observed in metalloporphyrins.

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

“…In both cases, two oneelectron transfer steps occurred upon oxidation or reduction, and all could be shown to be ligand centred. [4] The values detected for the potentials of (2,2Ј-bidipyrrinato)-nickel(II) complex oxidations and reductions, however, are more closely related to those of the chlorinato-and bacteriochlorinato complexes than to the metalloporphyrins themselves. [17,18] Cu II and Pd II complexes 6؊9 were studied in benzonitrile with 0.1 nBu 4 NPF 6 , and gave well-defined signals (FigFigure 4.…”

“…This finding, in particular, qualifies 2,2Ј-bidipyrrins as open-chain analogues of the porphyrins. [4] The higher flexibility of the 2,2Ј-bidipyrrin ligand with respect to the porphyrins, however, has tremendous impact on its coordination chemistry, as was recently shown by the X-ray crystallographic characterization of two non-porphyrinoid coordination modes (Scheme 1). [5,6] Therefore, a prediction of how this tetrapyrrole would interact with a given metal ion is not trivial.…”

Monohelical Metal Complexes of a Bis-Bidentate Schiff Base with a Short Rigid Spacer. The Spontaneous Resolution of P-[Ni(FTs)]·CH3CNDedicated to Professor Joachim Strähle in the Occasion of his 65th Birthday

“…These protons appear as two multiplet signals, each peak being the result of the overlapping of two doublets. Therefore, these protons are not more equivalent, and this observation could be a hint of a helical conformation of the complexes, as reported elsewhere [27], which is the only diastereoisomer present in solution. 4.…”

“…This result could indicate that a helical isomer of the ligand remains in solution, retaining the solid state structure [27]. However, when the solution is left to stand, a second diastereoisomer (b) exists as the major species in equilibrium with the first one (a).…”

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

“…So-called sitting-atop (SAT) intermediates [2] were proposed to be vital in this respect, and OgoshiÕs compounds were the first structurally characterized species, for which this particular feature was observed [3]. Later on rhodium(I) complexes of especially porphyrin and corrole derivatives were much studied with respect to the analogy with vitamin B 12 [4], the ability of anion sensing [5], and the finding of CH-activation processes [6].…”