Understanding Ligand Effects on Bielectronic Transitions: Chemo- and Electroreduction of Rhodium Bis(Diphosphine) Complexes to Low Oxidation States

Rhodium complexes in the -I and 0 oxidation states are of great potential interest in catalytic applications. In contrast to their rhodium +I congeners, however, the structural and electronic parameters governing their access and stability are far less understood. Herein, we investigate the two-electron reduction of a parameterized series of bis(diphosphine) Rh complexes [Rh(dxpy)2]NTf2 (x=P-substituent, y=alkanediyl bridging P atoms). Through (electro)reductions from the RhI parents, Rh-I d10-complexes were obtained and characterized spectroscopically, including 103Rh NMR data. The reductive steps convolute with structural rearrangements from square planar to tetrahedral coordination. We found that the extent of these reorganisations defines whether the first E0(RhI/0) and second E0(Rh0/-I) reduction potentials are normally ordered, leading to monoelectronic stepwise transitions, or inverted, giving bielectronic events. Reductionist approaches based on Hammett parameters or the P-Rh-P bite angles provide only partial correlations with the redox potentials. However, we identified the C-O stretch of analogue diphosphine complexes as an expedient computational parameter that enables these correlations through both electronic and geometric features, even in a predictive manner. Gaining control over two-electron reduction behaviors through rationalized ligand effects has potential impact beyond Rh complexes, for molecular and enzymatic metal sites commonly exhibiting bielectronic transitions.

Phosphonium-Catalyzed Monoreduction of Bisphosphine Dioxides: Origin of Selectivity and Synthetic Applications

Controlling product selectivity in successive reactions of the same type is challenging owing to the comparable thermodynamic and kinetic properties of the reactions involved. Here, the synergistic interaction of the two phosphoryl groups in bisphosphine dioxides (BPDOs) with a bromo-phosphonium cation was studied experimentally to provide a practical tool for substrate-catalyst recognition. As the eventual result, we have developed a phosphonium-catalyzed monoreduction of chiral BPDOs to access an array of synthetically useful bisphosphine monoxides (BPMOs) with axial, spiro, and planar chirality, which are otherwise challenging to synthesize before. The reaction features excellent selectivity and impressive reactivity. It proceeds under mild conditions, avoiding the use of superstoichiometric amounts of additives and metal catalysts to simplify the synthetic procedure. The accessibility and scalability of the reaction allowed for the rapid construction of a ligand library for optimization of asymmetric Heck-type cyclization, laying the foundation for a broad range of applications of chiral BPMOs in catalysis.

Synthesis and Characterisation of Novel Bis(diphenylphosphane oxide)methanidoytterbium(III) Complexes

Reaction of [YbCp₂(dme)] (Cp = cyclopentadienyl, dme = 1,2 dimethoxyethane) with bis(diphenylphosphano)methane dioxide (H₂dppmO₂) leads to deprotonation of the ligand H₂dppmO₂ and oxidation of ytterbium, forming an extremely air-sensitive product, [Yb^III(HdppmO₂)₃] (1), a six-coordinate complex with three chelating (OPCHPO) HdppmO₂ ligands. Complex 1 was also obtained by a redox transmetallation/protolysis synthesis from metallic ytterbium, Hg(C₆F₅)_2, and H₂dppmO₂. In a further preparation, the reaction of [Yb(C₆F₅)₂] with H₂dppmO₂, not only yielded compound 1, but also gave a remarkable tetranuclear cage, [Yb₄(µ-HdppmO₂)₆(µ-F)₆] (2) containing two [Yb(µ-F)]₂ rhombic units linked by two fluoride ligands and the tetranuclear unit is encapsulated by six bridging HdppmO₂ donors. The fluoride ligands of the cage result from C-F activation of pentafluorobenzene and concomitant formation of p-H₂C₆F₄ and m-H₂C₆F₄, the last being an unexpected product.

Synthesis of Bis(phosphanyl)alkane Monosulfides by the Addition of Diphosphane Monosulfides to Alkenes under Light

Bis-phosphanated compounds are regarded as the most ubiquitous privileged ligand structures in transition-metal catalysis. The development of highly atom economical reactions is of great importance for their syntheses because less atom economical methods often require complicated purification procedures under inert atmospheres to remove excess starting materials and byproducts. Herein, the photoinduced addition reactions of diphosphane monosulfides bearing P^V (S)-P^III single bonds to alkenes is disclosed. These reactions require only equimolar amounts of the diphosphane monosulfide relative to the alkene and facilitate highly selective introduction of two different types of phosphorus-containing groups, such as thiophosphoryl and phosphanyl groups, into a variety of alkenes without any catalyst, base, or additive.

Chemoselective Activation of Diethyl Phosphonates: Modular Synthesis of Biologically Relevant Phosphonylated Scaffolds

Phosphonates have garnered considerable attention for years owing to both their singular biological properties and their synthetic potential. State-of-the-art methods for the preparation of mixed phosphonates, phosphonamidates, phosphonothioates, and phosphinates rely on harsh and poorly selective reaction conditions. We report herein a mild method for the modular preparation of phosphonylated derivatives, several of which exhibit interesting biological activities, that is based on chemoselective activation with triflic anhydride. This procedure enables flexible and even iterative substitution with a broad range of O, S, N, and C nucleophiles.

Mononuclear bis(dithiolene) Mo(iv) and W(iv) complexes with P,P; S,S; O,S and O,O donor ligands: a comparative reactivity study

Comparative redox reactions of eight Mo^IV/W^IVcomplexes with P,P; S,S; S,O and O,O donor ligands are presented.

Disilanes as oxygen scavengers and surrogates of hydrosilanes suitable for selective reduction of nitroarenes, phosphine oxides and other valuable substrates

In this report, we demonstrate that the reaction of nitroarenes with hexamethyldisilane under various conditions affords a different range of compounds with excellent selectivity.

Highly chemoselective metal-free reduction of phosphine oxides to phosphines

Unprecedented chemoselective reductions of phosphine oxides to phosphines proceed smoothly in the presence of catalytic amounts of specific Brønsted acids. By utilizing inexpensive silanes, e.g., PMHS or (EtO)(2)MeSiH, other reducible functional groups such as ketones, aldehydes, olefins, nitriles, and esters are well-tolerated under optimized conditions.