This paper addresses a review of platinum-based hydrosilylation catalysts. The main field of application of these catalysts is the curing of silicone polymers. Since the 1960s, this area has developed rapidly in connection with the emergence of new polymer compositions and new areas of application. Here we describe general mechanisms of the catalyst activity and the structural effects of the ligands on activity and stability of the catalysts together with the methods for their synthesis.

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Palladium complexes of the novel unsymmetrical phosphine pyrazole-containing pincer ligands PCN H (PCN H = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole) and PCN Me (PCN Me = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-5-methyl-1H-pyrazole) have been prepared and characterized through single-crystal X-ray diffraction and multinuclear 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopy. In preparations of the monomeric hydroxide species (PCN H )Pd(OH), an unexpected N detachment followed by C−H activation on the heterocycle 5-position took place resulting in conversion of the monoanionic {P,C − ,N} framework into a dianionic {P,C − ,C − } ligand set. The dinuclear hydroxide-bridged species (PCN H )Pd(μ-OH)Pd(PCC) was the final product obtained under ambient conditions. The "rollover" activation was followed via 31 P{ 1 H} NMR spectroscopy, and dinuclear cationic μ-OH and monomeric Pd II hydroxide intermediates were identified. DFT computational analysis of the process (M06//6-31G*, THF) showed that the energy barriers for the pyrazolyl rollover and for C−H activation through a σ-bond metathesis reaction are low enough to be overcome under ambient-temperature conditions, in line with the experimental findings. In contrast to the PCN H system, no "rollover" reactivity was observed in the PCN Me system, and the terminal hydroxide complex (PCN Me )Pd(OH) could be readily isolated and fully characterized. ■ INTRODUCTIONThe use of pincer-ligated transition-metal complexes as catalysts for organic transformations has grown dramatically in recent years. 1 The robust tridentate binding motif coupled with the tunability of the steric and electronic parameters of pincer ligands has proven highly effective in stabilizing and allowing isolation of a variety of uncommon types of metal complexes. For example, pincer ligands have been very useful in the preparation of mononuclear late-metal complexes bearing M−OR and M−NR 2 bonds. Notably, there are significantly fewer mononuclear late-transition-metal hydroxide, alkoxide, and amide complexes relative to their metal alkyl (M−C) analogues. 2 However, such M−OR and M−NR 2 linkages are pertinent to catalysis, 3,4 and thus isolation and study of model metal hydroxide, alkoxide and amide complexes are of great value.The variety of available pincer ligands has increased in recent years. While early pincer ligands were symmetric with respect to ligand "arms" (e.g., PCP, PNP, POCOP, etc.), 5 pincer-type complexes bearing unsymmetrical arms have begun to appear in greater numbers (NCC, PNN, PCO, PCS, etc.). 6 PCN-type systems in particular are intriguing, because in (PCN)M(L) n complexes (M = transition metal; L = ancillary ligand) the tridentate hybrid ligand contains both hard (N) and soft (P) donor functions, thus leading to novel and unprecedented chemical properties. 7 In such species, there is a marked difference in the trans effect between the two different donor arms. This difference results in the group with the weaker trans effect (N) being more likely to dissociate fro...

Electrochemical methods have become important from the viewpoint of the development and creation of new ecologically safe and resource‐saving chemical processes. The use of electrons as a “universal” and “inexhaustible” reagent for chemical reactions is the main advantage of electrochemical tools. Although electrochemical processes have been already successfully applied in the preparation of different classes of practically important chemical compounds, a very limited number of industrially applicable electrochemical processes that involve elemental (white) phosphorus is currently known, except for some examples of the electrochemical production of phosphane PH3. These are mainly associated with the investigation of bulk reactions of the electrochemically activated P4 molecule and phosphorus intermediates derived therefrom; very limited attention has been paid to the electrode surface reactions as a key stage of the electrochemical process. In this Microreview we describe the electrode reactions of elemental (white) phosphorus and phosphane that accompany the electrochemical process of the preparation of some phosphorus compounds starting directly from P4. The important role of the nature of the electrode material, the reactivity of the formed phosphorus intermediates and the surface processes are discussed. Moreover, recently, we succeeded in discovering a new, previously unstable phosphorus compound, phosphane oxide H3PO, which can be easily produced using an electrochemical method by mild anodic oxidation of phosphane PH3 electrochemically formed from P4. In this respect, some attention has been paid to the electrochemically induced processes of PH3 oxidation that result in the selective formation of phosphane oxide, which is of high interest from the viewpoint of the investigation of its properties and reactivity.