Experiments and Direct Dynamics Simulations That Probe η²-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

Abstract

Key steps in the functionalization of an unactivated arene often involve its dihaptocoordination by a transition metal followed by insertion into the C-H bond. However, rarely are the η 2 -arene and aryl hydride species in measurable equilibrium. In this study, the benzene/phenyl hydride equilibrium is explored for the {WTp(NO)(PBu 3 )} (Bu = n-butyl; Tp = trispyrazoylborate) system as a function of temperature, solvent, ancillary ligand, and arene substituent. Both face-flip and ring-walk isomerizations are identified through spin-saturation exchange measurements, which

Metathesis by Partner Interchange in σ‐Bond Ligands: Expanding Applications of the σ‐CAM Mechanism

“…There are numerous examples of isolable M(η 2 ‐ C,C ‐arenes) [128–129] and some of early metal M(κ 1 ‐ F,C ‐arene) coordination [130] . However, intermolecular coordination of arenes via M(η 1 ‐ H,C ‐arene) or M(η 2 ‐ H,C ‐arene) linkages is frequently postulated via DFT calculations, for example between TpW(PMe 3 )(NO)(η 2 ‐C 6 H 6 ) and TpW(PMe 3 )(NO)(Ph)(H) complexes [129a] . An intermolecular η 2 ‐Rh⋅⋅⋅H−C(aryl) σ‐interaction has been observed in the solid state [129b] .…”

Catalytic Cage BH Functionalization of Carboranes via “Cage Walking” Strategy

“…The cage-walking strategy can provide BH functionalization at positions different from those where initial bond activation occurs to achieve functionalized carboranes that are difficult to access by conventional methods. In comparison to the rich literature on chain-walking/ring-walking, − cage-walking remains a young, developing realm. We anticipate that our discussion herein can provide a better understanding of the catalytic selective carborane functionalization via the cage-walking strategy.…”

“…The “walking” process of a transition-metal catalyst along a carbon skeleton has inspired the development of remote functionalization at unfunctionalized sites which are otherwise difficult to access in an organic molecule. − In these “chain-walking” and “ring-walking” processes, the transition-metal catalyst migrates along the sp 3 carbon chain or the conjugated π-system of the substrate until a specific favorable reaction site is reached. In comparison to the extensively studied chain-/ring-walking processes on alkyl chain or aromatics, the “cage-walking” phenomenon is much less investigated.…”

“…According to the symmetry of the icosahedral carborane and the differences in electronegativity between carbon and boron elements, 10 B–H vertices can be divided into 4 regio groups for both o -carborane (B­(9,12), B­(8,10), B­(4,5,7,11), and B­(3,6)) and m -carborane (B­(9,10), B­(5,12), B­(4,6,8,11), and B­(2,3)) (Chart ). On consideration of the vertex charge of o -carborane (B­(9,12) > B­(8,10) > B­(4,5,7,11) > B­(3,6)), transition-metal complexes with different electronic natures were employed for catalytic site-selective cage B–H functionalization of o -carboranes: electron-rich transition-metal catalysts are used to activate electron-deficient cage B­(3,6)–H bonds; , electrophilic transition-metal catalysts are employed to activate electron-rich cage B­(8,9,10,12)–H bonds. , For the selective metalation of B­(4,5,7,11)–H bonds that lie between B­(3,6)–H and B­(8,9,10,12)–H vertices, a directing group is required to guide the electrophilic transition-metal catalysts. ,, On the other hand, such a charge distribution of carborane cages could promote the walking of the metal fragment on the cage from the viewpoint of intensely studied chain-walking and ring-walking processes.…”

Pathway Bifurcations in the Activation of Allylic Halides by Palladium and Their Influence on the Dynamics of η1 and η3 Allyl Intermediates

“…Furthermore, it is possible that more than two products may share a single transition state, which has been realized in a trifurcated cycloaddition process . Metal-catalyzed cases where a shallow intermediate is dynamically bypassed are also increasingly more common. − Recently, dynamics effects in the metal-catalyzed 1,4-hydride transfer have been explored in which an intermediate is dynamically bypassed between isomeric π-allyl intermediates …”