Synthesis and characterization of [Rh(PP)(PP)]X complexes (PP = DPPE or DPPP, X = Cl− or BF4-). Phosphine exchange and reactivity in transfer hydrogenation conditions

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.

Ni(II), Cu(II), Mn(II), and Fe(II) Metal Complexes Containing 1,3-Bis(diphenylphosphino)propane and Pyridine Derivative: Synthesis, Characterization, and Antimicrobial Activity

Four of the coordination compounds of the general formula, [M(DPPP)(APY)(H₂O) Cl₂].xH₂O, where M = Ni(II), Cu(II), Mn(II), and Fe(II) and x = 0, 1, or 2 molecules of H₂O, DPPP = 1,3-bis(diphenylphosphino)propane, and APY = 2-aminopyridine, have been prepared and characterized. The structure of the complexes has been confirmed by elemental analysis, FT-IR, and UV-Vis spectral data. Thermal analysis (thermogravimetry, derivative thermogravimetry, and differential thermal studies) has been used to study the thermal decomposition stages. Biological activity of all synthesized complexes was tested against five bacterial strains and three fungal strains. Bacteria and fungi strains are common contaminants of the environment in Saudi Arabia, some of which are frequently reported from contaminated water, soil, and food.

Transfer Hydrogenation from 2-propanol to Acetophenone Catalyzed by [RuCl2(η6-arene)P] (P = monophosphine) and [Rh(PP)2]X (PP = diphosphine, X = Cl−, BF4−) Complexes

The reduction of ketones through homogeneous transfer hydrogenation catalyzed by transition metals is one of the most important routes for obtaining alcohols from carbonyl compounds. The interest of this method increases when opportune catalytic precursors are able to perform the transformation in an asymmetric fashion, generating enantiomerically enriched chiral alcohols. This reaction has been extensively studied in terms of catalysts and variety of substrates. A large amount of information about the possible mechanisms is available nowadays, which has been of high importance for the development of systems with excellent outcomes in terms of conversion, enantioselectivity and Turn Over Frequency. On the other side, many mechanistic aspects are still unclear, especially for those catalytic precursors which have shown only moderate performances in transfer hydeogenation. This is the case of neutral [RuCl2(η6-arene)(P)] and cationic [Rh(PP)2]X (X = anion; P and PP = mono- and bidentate phosphine, respectively) complexes. Herein, a summary of the known information about the Transfer Hydrogenation catalyzed by these complexes is provided with a continuous focus on the more relevant mechanistic features.