Carsten D. Brandt

The first PdII complex of a non-heteroatom stabilised carbene ligand

Di(p-tolyl)diazomethane reacts with the tripyrrinate TrpyPdOAc(F) 1 after activation with NaBAr(F) to yield the first stable Pd(II) complex 2 of a non-Arduengo type carbene ligand, which could be characterised by X-ray crystallography.

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

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

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)

A five coordinate PdII complex stable in solution and in the solid state

The treatment of the strained complex TrpyPdOAcF1 with NaBArF, followed by the addition of trimethylphosphine, yields the stable cationic 16VE- or 18VE-complexes 3 and 4, depending on the amount of phosphane added.

Synthetic and structural studies on metal complexes of tripyrrin

A general two-step procedure for the synthesis of metallotripyrrinates TrpyMOAcf with M = Co(II), Cu(II), Zn(II) and Pd(II), and OAcf = trifluoroacetate, is described, starting from well-known monopyrrolic precursors and simple transition metal acetates. X-ray structural investigations were undertaken on four different complexes, and the results reveal, that the nature of the metal ion, rather than the ligand, determines the coordination geometry of these porphyrin fragment complexes. The finding of pseudotetrahedral and strained pseudoplanar coordination polyhedra at the metal centres makes a clear distinction between metalloporphyrins and metallotripyrrins and shows the latter to be related to some recently discovered metal chelates of macrocyclic porphyrin analogues.

Iodomanganesecorrole – a stable MnIV–I species

The first compound with a MnIV–I bond has successfully been prepared by oxidation of a manganese(III) corrole with molecular iodine and was structurally characterized by X-ray diffraction.

Monomeric and polymeric copper and zinc tripyrrins

Neutral transition metal complexes of different alpha,omega-dimethyltripyrrins TrpyMX with M = Cu(II) and Zn(II) have been prepared with a variety of anionic halogeno and pseudohalogeno ligands X, and have been studied with respect to coordination modes and structural distortion. Only four- and five-coordinate species have been observed throughout the series. All four-coordinate species display unstrained, but distorted tetrahedral or strained and distorted square-planar coordination environments for zinc(II) and copper(II) species, respectively, thus following the expectations from simple ligand field arguments. Five-coordinate species do not form easily and were observed either in donor solvents or in the solid as 1D coordination polymers with distorted trigonal-bipyramidal coordination and different topologies.

Superoxide induced cyclizations of metallo-2,2'-bidipyrrins

The reaction of the open-chain tetrapyrrolic ligand 2,2-bidipyrrin with molecular dioxygen in the presence of a catalytic amount of manganese(II)-acetate was found to produce 10,10-diformyl-2,2-bidipyrrin with a remarkable selectivity. To identify the active oxidant in this transformation, 2,2-bidipyrrin was treated with potassium superoxide, sodium peroxide and manganese(III) acetate, respectively, in dry DMF. While superoxide produces the dialdehyde in high yield, the treatment with peroxide or manganese(III) acetate leads to decomposition only. Nickel(II)-, palladium(II)- and copper(II)-2,2-bidipyrrin were found to undergo macrocyclization reactions when treated with potassium superoxide in dry DMF at room temperature. While the respective 10-oxocorrolates are formed from the nickel(II)- and palladium(II)-2,2-bidipyrrins, the copper(II) chelate reacts very slowly and yields copper(III) corrole in low yield. The results strongly point to superoxide as the active oxidant in a recently found new synthesis of corroles.

Tripyrrin—the missing link in the series of oligopyrrolic ligands

The first derivative of the hitherto elusive tripyrrin 2 was nprepared and characterized; the X-ray structural analysis of its ntrifluoracetato-palladium(II) complex 7 displays a highly nflexible N3 ligand.

One compound, two structures: synthesis, structures and reactivity of a novel (tripyrrinato)palladium(II) trifluoracetate complex TrpyPdOAcf

The novel (2,15-dimethyl-3,4,13,14-tetraethyltripyrrinato)palladium(II) trifluoroacetate (TrpyPdOAcf) 7 was found to exhibit two different geometries in the solid state. While in one crystal the tripyrrin ligand is helically distorted to ensure a square-planar coordination of the central palladium(II) ion, the bonding geometry of the metal centre of the other geometrical isomer found in a different crystal showed a pronounced tetrahedral deviation from planarity, accompanied with an almost planar tripyrrolic ligand. In solution, non-planar structures of 7 can not be detected, as judged by the results of variable temperature proton NMR spectroscopy. The energy stored in the strained complexes 6 and 7, however, becomes “visible” in fast ligand exchange processes, which nenable us to prepare a number of new TrpyPdX complexes with X = Cl, Br, I, N3, NCO, SCN and OAc, of which the latter two decompose in solution. As the X-ray crystallographic analysis of TrpyPdBr 9 demonstrates, complexes with a tilted fourth ligand are predominant in the solid state with donor atoms larger than oxygen.