Structural Changes in the Carbon Sphere of a Dirhodium Complex Induced by Redox or Deprotonation Reactions.

A carbon-rich molecule is synthesized, which mainly contains conjugated sp2 and sp hybridized carbon centers. Alkenyl and alkynyl binding sites are arranged such that this compound serves as ligand to a binuclear metal unit with a RhI─RhI bond. Furthermore, CH units are placed in proximity to the metal centers. The dicationic complex [Rh2(bipy)2{Ph2Ptrop(C≡CCy)2}]2+(OTf-)2 allows to study possible responses of the carbon-framework to redox reactions as well as deprotonation reactions. All products are, whenever possible, characterized by X-ray diffraction (XRD) methods, NMR and EPR spectroscopy as well as electrochemical methods. It is shown that the carbon skeleton of the ligand framework undergoes C─C bond rearrangement reactions of remarkable diversity. In combination with DFT (density functional theory) studies, these results allow to gain insight into the electronic structure changes caused by metal sites in a carbon-rich environment, which may be of relevance for the properties of metal particles on carbon support materials when they are exposed to hydrogen, electrons, or protons.

Phosphonium-Substituted Diphosphaindenylide (PPI): Exploration of Biradical Character and Ligand Properties.

Invited for the cover of this issue is the group of Peter Coburger at the Technical University of Munich. The image, painted by Dr. Christoph Selg, depicts the bonding relationships in a biradicaloid chromium complex as a staircase, with the people symbolizing the two-way flow of electrons between the ligand and the metal. Read the full text of the article at 10.1002/chem.202302970.

Selective dehydrogenation of ammonia borane to polycondensated BN rings catalysed by ruthenium olefin complexes.

Dehydrogenation of ammonia borane to well-defined products is an important but challenging reaction. A dinuclear ruthenium complex with a Ru-Ru bond bearing a diazadiene (dad) unit and olefins as non-innocent ligands catalyzes the highly selective formation of conjugated polycondensed borazine oligomers (BxNxHy), predominantly B21N21H18, the BN analogue of superbenzene.

Phosphonium-substituted Diphosphaindenylide (PPI): Exploration of Biradical Character and Ligand Properties.

Starting from C6 H4 (PCl2 )2 and the TMS-substituted ylide (TMS)2 C=PR3 (TMS=trimethylsilyl, R=p-tolyl), the phosphonium-substituted diphosphaindenylide PPI was prepared in two steps. CASSCF calculations as well as the reactivity toward diphenyl acetylene suggest a notable biradical character in PPI. Reaction with [Cr(CO)3 (MeCN)3 ] affords the complex [Cr(CO)3 (η5 -PPI)] (5). This complex was employed to explore the ligand properties of PPI, which demonstrates considerable potential through the combination of strong metal-ligand interactions and the possibility of a pronounced indenyl effect.

Phosphine Oxide-Functionalized Terthiophene Redox Systems.

Main group systems capable of undergoing controlled redox events at extreme potentials are elusive yet highly desirable for a range of organic electronics applications including use as energy storage media. Herein we describe phosphine oxide-functionalized terthiophenes that exhibit two reversible 1e- reductions at potentials below -2 V vs Fc/Fc+ (Fc=ferrocene) while retaining high degrees of stability. A phosphine oxide-functionalized terthiophene radical anion was synthesized in which the redox-responsive nature of the platform was established using combined structural, spectroscopic, and computational characterization. Straightforward structural modification led to the identification of a derivative that exhibits exceptional stability during bulk 2 e- galvanostatic charge-discharge cycling and enabled characterization of a 2 e- redox series. A new multi-electron redox system class is hence disclosed that expands the electrochemical cell potential range achievable with main group electrolytes without compromising stability.

Reversible Single Electron Redox Steps Convert Polycycles with a C3 P3 Core to a Planar Triphosphinine.

Reaction of the imidazolium-stabilized diphosphete-diide IDP with trityl phosphaalkyne affords a mixture which contains the molecules 1 a and 1 b with a central C3 P3 core, which formally carries a two-fold negative charge. In order to avoid the formation of an antiaromatic 8π electron system within a conjugated dianionic six-membered [C3 P3 ]2- ring, 1 a adopts a bicyclic [3.1.0] and 1 b a tricyclic [2.2.0.0] structure which are in a dynamic equilibrium. 1 a, b can be reversibly oxidized to a triphosphinine dication [5]2+ with a central flat aromatic six-membered C3 P3 ring. This two-electron redox reaction occurs in two single-electron transfer steps via the 7π-radical cation [4]⋅+ , which could also be isolated and fully characterized. The profound reversible structural change observed for the two-electron redox couple [5]2+ /1 a, b is in sharp contrast to the C6 H6 /[C6 H6 ]2- couple, which undergoes only a modest structural deformation.

Bis(imidazolium)-1,3-diphosphete-diide: A Building Block for FeC2 P2 Complexes and Clusters.

Reaction of the 6π-electron aromatic four-membered heterocycle (IPr)2 C2 P2 (1) (IPr=1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) with [Fe2 CO9 ] gives the neutral iron tricarbonyl complex [Fe(CO)3 -η3 -{(IPr)2 C2 P2 }] (2). Oxidation with two equivalents of the ferrocenium salt, [Fe(Cp)2 ](BArF24 ), affords the dicationic tricarbonyl complex [Fe(CO)3 -η4 -{(IPr)2 C2 P2 }](BArF24 )2 (4). The one-electron oxidation proceeds under concomitant loss of one CO ligand to give the paramagnetic dicarbonyl radical cation complex [Fe(CO)2 -η4 -{(IPr)2 C2 P2 }](BArF24 ) (5). Reduction of 5 allows the preparation of the neutral dicarbonyl complex [Fe(CO)2 -η4 -{(IPr)2 C2 P2 }] (6). An analysis by various spectroscopic techniques (57 Fe Mössbauer, EPR) combined with DFT calculations gives insight into differences of the electronic structure within the members of this unique series of iron carbonyl complexes, which can be either described as electron precise or Wade-Mingos clusters.

A chromium tricarbonyl complex featuring the 4,6-bis(diphenylphosphinomethyl)dibenzothiophene (PSPPh) ligand.

ABSTRACT: The new PSP pincer ligand 4,6-bis(diphenylphosphinomethyl)dibenzothiophene (PSPPh) was prepared in 89 % yield. With this ligand, a solvothermal synthesis of a Cr complex of the type [Cr(κ3P,S,P-PSP)(CO)3] is described. The X-ray structure of this compound is presented. We demonstrate that the solvothermal synthesis technique provides a powerful, simple, and practical synthetic method resulting in a high isolated yield in a short reaction time.