Since the first reports in the late 1970s on transition metal complexes contain- ing pincer-type ligands—named after the particular coordination mode of these ligands—these systems have at- tracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typical- ly, such a ligand comprises an anionic aryl ring which is ortho,ortho-disubsti- tuted with heteroatom substituents, for example, CH2NR2 ,C H 2PR2 or CH2SR, which generally coordinate to the met- al center, and therefore support the MC s bond. This commonly results in a terdentate and meridional coordina- tion mode consisting of two metalla- cycles which share the MC bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental under- standing of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mecha- nistic elucidation of fundamental transformations (for example, CC bond activation), the construction of the first metallodendrimers for sustain- able homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous inves- tigations. This review discusses the synthetic methodologies that are cur- rently available for the preparation of platinum group metal complexes con- taining pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineer- ing of sensors, switches, and catalysts.

Platinum Group Organometallics Based on “Pincer” Complexes: Sensors, Switches, and Catalysts

Ammonia–borane, H3NBH3, is an intriguing molecule for chemical hydrogen storage applications. With both protic N–H and hydridic B–H bonds, three H atoms per main group element, and a low molecular weight, H3NBH3 has the potential to meet the stringent gravimetric and volumetric hydrogen storage capacity targets needed for transportation applications. Furthermore, devising an energy-efficient chemical process to regenerate H3NBH3 from dehydrogenated BNHx material is an important step towards realization of a sustainable transportation fuel. In this perspective we discuss current progress in catalysis research to control the rate and extent of hydrogen release and preliminary efforts at regeneration of H3NBH3.

Ammonia-borane: the hydrogen source par excellence?

The use of arynes in organic synthesis

o-(Pyrrolidinylmethyl)phenylboronic acid (4) and its complexes with bifunctional substrates such as catechol, alpha-hydroxyisobutyric acid, and hydrobenzoin have been studied in detail by X-ray crystallography, (11)B NMR, and computational analysis. The N-B interactions in analogous boronic acids and esters have been extensively cited in molecular recognition and chemosensing literature. The focal point of this study was to determine the factors that are pertinent to the formation of an intramolecular N-B dative bond. Our structural study predicts that the formation of an N-B dative bond, and/or solvent insertion to afford a tetrahedral boronate anion, depends on the solvent and the complexing substrate present. Specifically, from (11)B NMR studies, complexation of 4 with electron-withdrawing and/or vicinally bifunctionalized substrates promotes both the formation of N-B dative bonds and the solvation of sp(2) boron to a tetrahedral sp(3) boronate. In the solid state, the presence of an N-B dative bond in the complex of 4 and catechol (7) depends on the solvent from which it crystallizes. From chloroform, an N-B bond was observed, whereas from methanol, a methoxylated boronate was formed, where the methoxy group is hydrogen-bonded with the neighboring tertiary ammonium ion. The structural optimization of compounds 4 and 7 using density functional theory in a simulated water continuum also predicts that complexation of 4 and catechol promotes either the formation of an N-B bond or solvolysis if 1 equiv of water is present. The conclusion from this study will help in the design of future chemosensing technologies based on o-(N,N-dialkylaminomethyl)arylboronate scaffolds that are targeting physiologically important substances such as saccharides, alpha-hydroxycarboxylates, and catecholamines.

A structural investigation of the N-B interaction in an o-(N,N-dialkylaminomethyl)arylboronate system

Recent advances in atropisomerism

Experimental and Theoretical Evidence of an SN2-Type Mechanism for Dissociation of B−N Coordination Bonds in 2,6-Bis((dimethylamino)methyl)phenylborane Derivatives1

Cyclic Aminoacyloins and Aminoketones. IV. Dependence of Transannular Interaction Upon the Relative Location of N and CCO1

Facile exchange between the intramoleculariy coordinated and uncoordinated amine ligands in the title compounds is evidenced by NMR spectroscopy in solution, whereas the dynamic process is frozen in the solid phase as shown by X-ray crystallography.

Michinori Ōki

Papers

Experimental and Theoretical Evidence of an SN2-Type Mechanism for Dissociation of B−N Coordination Bonds in 2,6-Bis((dimethylamino)methyl)phenylborane Derivatives1

Cyclic Aminoacyloins and Aminoketones. IV. Dependence of Transannular Interaction Upon the Relative Location of N and CCO1

Switching of two amine ligands via an SN2-type mechanism in a coordinated form of 2,6-bis(N,N-dimethylaminomethyl)phenylboronates

The Influence of Steric Configuration on the Ultraviolet Absorption of “Fixed” Benzils1,2

Cyclic Aminoacyloins and Aminoketones. VII. N-Aryl Substitution and Transannular Interaction Between N and CCO1