Palladium Goes First: A Neutral Asymmetric Heteroditopic N,P Ligand Forming Pd-3d Heterobimetallic Complexes.

A facile two-step synthesis of bis(1-methylhydrazinyl)pyrimidine from pyridine-2-carbaldehyde and 2-diphenylphosphanylbenzaldehyde gave access to the new asymmetric ligand 1. The phosphane selectively guides PdII into the softer tridentate N,N,P pocket, yielding monometallic complex 2. A second reaction with a 3d transition metal complex precursor (groups 7 to 12) fills the vacant N,N,N pocket and thus provides a variety of heterobimetallic complexes of the type PdII/MII (M = Mn (3), Fe (4), Co (5), Ni (6), Cu (7), Zn (8)). Single-crystal X-ray diffraction studies were performed for all complexes. The assembly of µ2-chlorido-bridged dimers was observed for complexes 5-7 in the solid state, while DOSY NMR experiments have shown that 5-7 are unbridged monomers in solution. As an exception, FeII prefers to form the homoleptic meridional complex [Fe{PdCl(1)}2](OTf)4 (4). The electrochemical behavior and the effective magnetic moment in solution were investigated for all complexes by cyclic voltammetry and Evans method, respectively. Experimental UV/vis results were interpreted by performing TD-DFT calculations on 1, 2, and 3.

The core of the matter - arene substitution determines the coordination and catalytic behaviour of tris(1-phosphanyl-1'-ferrocenylene)arene gold(I) complexes.

Changing the aromatic core of C3-symmetric tris(ferrocenyl)arene-based tris-phosphanes has profound effects on their coordination behaviour towards gold(i). Depending on the arene (s-triazine, benzene, or trifluorobenzene), four different coordination modes can be distinguished and their preference has been rationalised using computational methods. The corresponding 1 : 1 ligand-to-metal complexes, studied by variable-temperature NMR spectroscopy, revealed fluctional behaviour in solution. Given the presence of up to three or six ferrocenylene spacers per complex, their electrochemistry was investigated. The redox-responsive nature of the complexes can be advantageously exploited in the catalytic ring-closing isomerisation of N-(2-propyn-1-yl)benzamide, where the benzene-based 2 : 3 ligand-to-metal complex has been shown to display multiple activity states depending on the degree of (reversible) oxidation in a preliminary trial.

Tricoordinate Coinage Metal Complexes with a Redox-Active Tris-(Ferrocenyl)triazine Backbone Feature Triazine-Metal Interactions.

Invited for the cover of this issue is the group of Evamarie Hey-Hawkins at the University of Leipzig and colleagues at the University of Stuttgart and University of Regensburg. The image depicts the reported complexes as three similar flowers growing from one common branch representing the ligand. Read the full text of the article at 10.1002/chem.202000226.

Tricoordinate Coinage Metal Complexes with a Redox-Active Tris-(Ferrocenyl)triazine Backbone Feature Triazine-Metal Interactions.

2,4,6-Tris(1-diphenylphosphanyl-1'-ferrocenylene)-1,3,5-triazine (1) coordinates all three coinage metal(I) ions in a 1:1 tridentate coordination mode. The C3 -symmetric coordination in both solid state and solution is stabilised by an uncommon cation-π interaction between the triazine core and the metal cation. Intramolecular dynamic behaviour was observed by variable-temperature NMR spectroscopy. The borane adduct of 1, 1BH3 , displays four accessible oxidation states, suggesting complexes of 1 to be intriguing candidates for redox-switchable catalysis. Complexes 1Cu, 1Ag, and 1Au display a more complicated electrochemical behaviour, and the electrochemical mechanism was studied by temperature-resolved UV/Vis spectroelectrochemistry and chemical oxidation.

Triple the fun: tris(ferrocenyl)arene-based gold(i) complexes for redox-switchable catalysis.

The modular syntheses of C 3-symmetric tris(ferrocenyl)arene-based tris-phosphanes and their homotrinuclear gold(i) complexes are reported. Choosing the arene core allows fine-tuning of the exact oxidation potentials and thus tailoring of the electrochemical response. The tris[chloridogold(i)] complexes were investigated in the catalytic ring-closing isomerisation of N-(2-propyn-1-yl)benzamide, showing cooperative behaviour vs. a mononuclear chloridogold(i) complex. Adding one, two, or three equivalents of 1,1'-diacetylferrocenium[tetrakis(perfluoro-tert-butoxy)aluminate] as an oxidant during the catalytic reaction (in situ) resulted in a distinct, stepwise influence on the resulting catalytic rates. Isolation of the oxidised species is possible, and using them as (pre-)catalysts (ex situ oxidation) confirmed the activity trend. Proving the intactness of the P-Au-Cl motif during oxidation, the tri-oxidised benzene-based complex has been structurally characterised.

Rhodium(i) complexes with carborane-substituted P,N ligands: investigations of electronic structure and dynamic behaviour.

Two distorted square-planar RhI complexes (1 and 2) were obtained from [{RhCl(η4-cod)}2] and the respective P,N ligands. The metal-ligand interaction was probed with density functional theory (DFT) and ab initio (CASSCF-NEVPT2) calculations. NMR spectroscopy proved dynamic binding behaviour of the ligands in solution. The tetradenticity of the ligands also affects the electrochemical behaviour of complexes 1 and 2 significantly. Finally, preliminary catalytic studies, namely the dehydrocoupling of dimethylamine-borane, are presented.

Heterobimetallic complexes with highly flexible 1,1'-bis(phospholanoalkyl)ferrocene ligands.

The two highly flexible ligands 1,1'-bis(4-phospholanobutyl)ferrocene (5a) and 1,1'-bis(5-phospholanopentyl)ferrocene (5b) reacted with [PtCl2(cod)] (cod = 1,5-cyclooctadiene), [AuCl(tht)] (tht = tetrahydrothiophene) and [{RhCl(CO)2}2] to give the respective chelate complexes cis-[PtCl2(5a,b-κ(2)P,P')] (7a,b), [AuCl(5a,b-κ(2)P,P')] (8a,b) and trans-[RhCl(CO)(5b-κ(2)P,P')] (9b). Treatment of 5a,b with selenium gave the corresponding selenides 6a,b. All compounds have been fully characterised by NMR ((1)H, (13)C, (31)P) and IR spectroscopy and mass spectrometry. In addition, crystal structures of 6a, 7b, 8a,b and 9b were determined by X-ray crystallography. Furthermore, the rhodium-catalysed hydroformylation of 1-octene has been studied with ligand 5b.