scholarly journals Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

2015 ◽  
Vol 373 (2037) ◽  
pp. 20140189 ◽  
Author(s):  
David Milstein
Keyword(s):  
Bond Activation ◽  
Short Review ◽  
Catalytic Reactions ◽  
Pincer Complexes ◽  
Chemical Bonds ◽  
Single Bond ◽  
Metal Centre ◽  
Pincer Ligand ◽  
Mechanistic Insight ◽  
Metal Ligand

Metal–ligand cooperation (MLC) plays an important role in bond activation processes, enabling many chemical and biological catalytic reactions. A recent new mode of activation of chemical bonds involves ligand aromatization–dearomatization processes in pyridine-based pincer complexes in which chemical bonds are broken reversibly across the metal centre and the pincer-ligand arm, leading to new bond-making and -breaking processes, and new catalysis. In this short review, such processes are briefly exemplified in the activation of C–H, H–H, O–H, N–H and B–H bonds, and mechanistic insight is provided. This new bond activation mode has led to the development of various catalytic reactions, mainly based on alcohols and amines, and to a stepwise approach to thermal H 2 and light-induced O 2 liberation from water.

Challenging metal-based transformations. From single-bond activation to catalysis and metallaquinonoids

2003 ◽  
Vol 75 (4) ◽  
pp. 445-460 ◽  
Author(s):  
D. Milstein
Keyword(s):  
Bond Activation ◽  
Single Step ◽  
Catalytic Reactions ◽  
Single Bond ◽  
Quinone Methides ◽  
Pd Catalysts ◽  
Biologically Relevant ◽  
Aryl Chlorides ◽  
Metal Insertion ◽  
Aluminum Alkyls

Catalytic reactions resulting from our C–X (X = H, C, O, N, halide) bond activation studies are described. Aryl chlorides can react with aluminum alkyls in preference to bromides. Using PCP-type Pd catalysts, Heck reaction with aryl iodides and bromides can proceed without involvement of Pd(0). Ru-catalyzed oxidative coupling of arenes with alkenes using O2 was accomplished. Using specifically designed systems, the scope and mechanisms of C–C activation in solution was studied and compared to C–H activation. C–C activation by Rh(I), Ir(I), Ni(II),Pt(II), Ru(II), and Os(II) was observed. Metal insertion into a strong C–C bond can be kinetically and thermodynamically more favorable than the competing C–H activation. Selective, single-step oxidative addition of a strong C–C bond to a metal was observed and kinetically evaluated. Catalytic C–C hydrogenolysis was demonstrated. A combination of C–C activation and C–R formation (R = aryl, silyl) resulted in unusual methylene transfer chemistry. Selective activation of aryl–O and Me–O bonds was observed. New types of interactions between metals and arenes and unusual quinonoid complexes, including quinone methides, xylylenes, methylene arenium, and a metallaquinone, were discovered. C–H and C–C agostic complexes of cationic metals, proposed as intermediates in bond activation, were isolated. Stabilization and controlled release of biologically relevant, extremely unstable, simple quinone methides, was accomplished.

scholarly journals Synthesis & Xray structures of Rare Pentacoordinate Pincer Complexes of Ni(II)

2014 ◽  
Vol 70 (a1) ◽  
pp. C916-C916
Author(s):  
Berline Mougang-Soume ◽  
Davit Zargarian
Keyword(s):  
Organometallic Chemistry ◽  
Materials Science ◽  
Catalytic Reactions ◽  
Pincer Complexes ◽  
Substrate Uptake ◽  
Major Focus ◽  
Pincer Ligand ◽  
The Past ◽  
Coordination Site

Pincer complexes have been a major focus in organometallic chemistry over the past four decades due to their important potential in catalysis and materials science. In the case of pincer complexes of d8 metals, a growing number of charge-neutral and cationic derivatives featuring hydrides, alkyls, and other reactive moieties have been shown to catalyze important transformations. Regarding the mechanisms of these catalytic reactions, an important issue that remains unresolved concerns the type of intermediates formed upon substrate uptake, namely: A: Do substrates displace one or more hemi-labile donor moieties of the pincer ligand? Or B: Does the substrate occupy a fifth coordination site while the pincer ligand remains intact (Scheme 1)? In this presentation, Xray crystallography is used to describe the influence of the substitue on the 18-electron species based on POCN-Ni precursors. These new diamagnetic complexes are proposed as models for the intermediates that might be involved in catalytic reactions promoted by this family of complexes (Scheme 2).

scholarly journals Metal–Ligand Cooperation Facilitates Bond Activation and Catalytic Hydrogenation with Zinc Pincer Complexes

2020 ◽  
Vol 142 (34) ◽  
pp. 14513-14521 ◽  
Author(s):  
Michael Rauch ◽  
Sayan Kar ◽  
Amit Kumar ◽  
Liat Avram ◽  
Linda J. W. Shimon ◽  
...  
Keyword(s):  
Catalytic Hydrogenation ◽  
Bond Activation ◽  
Pincer Complexes ◽  
Metal Ligand

scholarly journals Charge Density and Chemical Bonding in Inorganic Materials

2014 ◽  
Vol 70 (a1) ◽  
pp. C8-C8
Author(s):  
Wolfgang Scherer
Keyword(s):  
Transition Metal Oxides ◽  
Bond Activation ◽  
Chemical Properties ◽  
Inorganic Materials ◽  
Catalytic Reactions ◽  
Valence Shell ◽  
Chemical Bonds ◽  
Complex Interplay ◽  
Main Group Elements ◽  
And Chemical Properties

Since the theoretical prediction and experimental verification of Charge Concentrations (CCs) in the valence shell of main group elements and transition metals several attempts have been undertaken to understand their origin and relevance in chemistry and physics. In pioneering studies we could demonstrate that these CCs not only influence the geometry of coordination compounds and solids but also serve as controlling parameters for important chemical reactions like the activation of chemical bonds in catalytic reactions [1]. Furthermore, in covalent solids such as transition metal oxides and carbides they appear to signal even subtle electron localization phenomena which might induce metal-to-insulator transitions or effect the onset of superconductivity [2]. The complex interplay between valence shell charge concentrations and chemical properties of molecules and solids will be the central topic of this contribution with the focus on (i) unusual bonding scenarios displayed by solid state compounds [3] and the (ii) control of geometry and bond activation processes in molecules.

Effect of Hydrated Metal Salts on the Coordination Product of Cobalt(II) halide and PNP Type Ligand, 2,6-bis(di-tertbutylphosphinomethyl) pyridine

2018 ◽  
Author(s):  
Tasneem Siddiquee ◽  
Abdul Goni
Keyword(s):  
Metal Salts ◽  
Molar Ratio ◽  
Pincer Complexes ◽  
Asymmetric Unit ◽  
X Ray Diffraction ◽  
Pincer Ligand ◽  
Tetrahedral Geometry ◽  
X Ray ◽  
Distorted Tetrahedral Geometry ◽  
Cobalt Center

Chemical treatment of CoX<sub>2</sub><b><sup>. </sup></b>6H<sub>2</sub>O (X = Cl, Br, I) with the potentially tridentate PNP pincer ligand 2,6-bis(di-<i>tert</i>-butylphosphinomethyl)pyridine in 1:1 molar ratio results in cobalt(II) halide-PNP pincer complexes. The effect of the hydrated metal source on molecular structure and geometry of the complexes was studied by single crystal X-ray diffraction analysis. The complexes are neutral and the cobalt center adopts a penta-coordinate system with potential atropisomerization. Within the unit cell there are two distinct molecules per asymmetric unit. One of the two phosphorus atoms in the PNP ligand was observed to be partially oxidized to phosphinoxide. Disorder in the structure reflects a mixture of square pyramidal and distorted tetrahedral geometry.

Pyridine-directed carbon-carbon single bond activation: rhodium-catalyzed decarbonylation of aryl and heteroaromatic ketones

2021 ◽  
pp. 153132
Author(s):  
Cole J. Wagner ◽  
Eric A. Salisbury ◽  
Erik J. Schoonover ◽  
Jacob P. VanderRoest ◽  
Jeffrey B. Johnson
Keyword(s):  
Bond Activation ◽  
Single Bond
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