Lithiumboryl — A Synthon for a Nucleophilic Boryl Anion

Braunschweig, Holger

doi:10.1002/chin.200722228

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“…The nucleophilicity of boryl ligands can be used to understand the regiochemistry of the insertion of alkenes into Cu−B bonds, as exemplified by styrene, which gives the Cu−CH(Ph)−CH 2 B(OR) 2 isomer kinetically. , The nucleophilicity of boryl ligands has also been demonstrated in various catalytic processes. − Recently, Segawa et al reported the isolation of the first structurally characterized lithium boryl compound, LiB(RNCHCHNR) (R = 2,6- i Pr 2 C 6 H 3 ) ( 4 ) in which the B−Li bond is highly polarized and the boron center has anionic character. − Reactivity studies of the lithium boryl compound indeed show that the boryl anion reacts with a variety of electrophiles …”

Section: Establishing Important Chemical Conceptsmentioning

confidence: 99%

“…[45][46][47] Recently, Segawa et al reported the isolation of the first structurally characterized lithium boryl compound, LiB(RNCHdCHNR) (R ) 2,6-i Pr 2 C 6 H 3 ) (4) in which the B-Li bond is highly polarized and the boron center has anionic character. [48][49][50] Reactivity studies of the lithium boryl compound indeed show that the boryl anion reacts with a variety of electrophiles. 51 On the basis of the above theoretical results, we considered the possible rearrangement of a species containing a Cu-O σ bond to the isomeric species containing a Cu-C σ bond (eq 3).…”

Section: Assisting Structure Determinationmentioning

confidence: 99%

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Interplay between Theory and Experiment: Computational Organometallic and Transition Metal Chemistry

Lin

2010

Acc. Chem. Res.

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Computational and theoretical chemistry provide fundamental insights into the structures, properties, and reactivities of molecules. As a result, theoretical calculations have become indispensable in various fields of chemical research and development. In this Account, we present our research in the area of computational transition metal chemistry, using examples to illustrate how theory impacts our understanding of experimental results and how close collaboration between theoreticians and experimental chemists can be mutually beneficial. We begin by examining the use of computational chemistry to elucidate the details of some unusual chemical bonds. We consider the three-center, two-electron bonding in titanocene sigma-borane complexes and the five-center, four-electron bonding in a rhodium-bismuth complex. The bonding in metallabenzene complexes is also examined. In each case, theoretical calculations provide particular insight into the electronic structure of the chemical bonds. We then give an example of how theoretical calculations aided the structural determination of a kappa(2)-N,N chelate ruthenium complex formed upon heating an intermediate benzonitrile-coordinated complex. An initial X-ray diffraction structure proposed on the basis of a reasonable mechanism appeared to fit well, with an apparently acceptable R value of 0.0478. But when DFT calculations were applied, the optimized geometry differed significantly from the experimental data. By combining experimental and theoretical outlooks, we posited a new structure. Remarkably, a re-refining of the X-ray diffraction data based on the new structure resulted in a slightly lower R value of 0.0453. We further examine the use of computational chemistry in providing new insight into C-H bond activation mechanisms and in understanding the reactivity properties of nucleophilic boryl ligands, addressing experimental difficulties with calculations and vice versa. Finally, we consider the impact of theoretical insights in three very specific experimental studies of chemical reactions, illustrating how theoretical results prompt further experimental studies: (i) diboration of aldehydes catalyzed by copper(I) boryl complexes, (ii) ruthenium-catalyzed C-H amination of arylazides, and (iii) zinc reduction of a vinylcarbyne complex. The concepts and examples presented here are intended for nonspecialists, particularly experimentalists. Together, they illustrate some of the achievements that are possible with a fruitful union of experiment and theory.

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