Frontier transition metal reactions

During the past decade, NHCs have been coordinated to virtually all transition metals (TM) and studied in numerous catalytic transformations, pushing back the frontiers of catalysis. In this regard, the most salient examples are found in olefin metathesis and cross coupling reactions, and more recently in organocatalysis. 

Among the most exciting frontiers in boratabenzene chemistry is the development of transition metal-boratabenzene complexes as catalysts. As early as 1984, it had been demonstrated that these adducts can accelerate useful reactions— specifically, Bonnemann established that (C5H5B-Ph)Co(cod) serves as a catalyst for pyridine-forming cyclotrimerization reactions of alkynes and nitriles.39... 

The chemistry of atoms is dominated by the outermost atomic orbitals, which are, so to speak, their atomic frontier orbitals. This is not true, however, of transition metals, where the (n — l)d orbitals must also be taken into account because they lie very close in energy to the ns and np orbitals. The same kind of problem occurs in molecules. The subjacent or superjacent MOs may determine the outcome of a reaction if they lie close in energy to the frontier orbitals (p. 113) or if they are nonbonding orbitals (Exercise 3, p. 59). 

A reaction mechanism for the replacement of the endocyclic sulfur atom by the transition metal in these Tt-sulfuranes was given by Manabe et al. on the basis of frontier electron density analysis [282] (see Figure 4.95). Iwasaki explained the mechanism on the energetically less favourable isomer featuring S-S rather than S-N bonds. 

It has been proven that the chiral Pd(II) complexes as transition metal catalysts vs Lewis acid catalysts bring a breakthrough in the frontier of catalytic asymmetric organic synthesis. Here we discussed the key issues based on asymmetric carbon-carbon bond formations anomalous six-membered ring formation, ene-type cyclization leading to five-membered rings, spiro cycliza-tion, alkaloid and quinoline synthesis, Suzuki-Miyaura coupling, and C-H bond activation/C-C bond formation by transition metallic Pd(II) catalysts. On the other hand, the carbonyl-ene reaction, hetero Diels-Alder reaction, and... 

Understanding the role of orbital interactions can be beneficial from the practical perspective. For example, the symmetry of frontier molecular orbitals can explain why thermal [2+2] cycloaddition fails, whereas the analogous reaction of transition metal alkylidenes, compounds that can be described as having a metal-carbon double bond, proceeds efficiently under mild conditions (Figure 1.2). In this case, an extra orbital... 

Crystal structures of ethylmagnesium bromide Crystal structure of tetrameric phenyllithium etherate Representation of tt bonding in alkene-transition-metal complexes Mechanisms for addition of singlet and triplet carbenes to alkenes Frontier orbital interpretation of radical substituent effects Chain mechanism for radical addition reactions mediated by trialkylstannyl radicals... 

A collection of state of the art review articles on homogeneous catalysis could be found in Chem. Rev. 2011, 111, 2321 on the theme Frontiers in transition metal catalyzed reactions . 

Fukui, Kenichi (1918-98) Japanese physical and theoretical chemist. Fukui is best known for his work on frontier orbital theory, a theory which describes the changes in molecular orbitals during a chemical reaction. He was particularly interested in applying frontier orbital theory to the reactions of methyl radicals. He shared the 1981 Nobel Prize for chemistry with Roald HOFFMANN for his work on frontier orbital theory. He also studied the reaction between nitrogen molecules and transition metal complexes. 

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