A Polar Copper–Boron One-Electron σ‑Bond

Virtually all chemical bonds consist of one or several pairs of electrons shared by two atoms. Examples of σ-bonds made of a single electron delocalized over two neighboring atoms were until recently found only in gas-phase cations such as H₂⁺ and Li₂⁺ and in highly unstable species generated in solid matrices. Only in the past decade was bona fide one-electron bonding observed for molecules in fluid solution. Here we report the isolation and structural characterization of a thermally stable compound featuring a Cu–B one-electron bond, as well as its oxidized (nonbonded) and reduced (two-electrons-bonded) congeners. This triad provides an excellent opportunity to study the degree of σ-bonding in a metalloboratrane as a function of electron count

A Polar Copper–Boron One-Electron σ‑Bond

Virtually all chemical bonds consist of one or several pairs of electrons shared by two atoms. Examples of σ-bonds made of a single electron delocalized over two neighboring atoms were until recently found only in gas-phase cations such as H₂⁺ and Li₂⁺ and in highly unstable species generated in solid matrices. Only in the past decade was bona fide one-electron bonding observed for molecules in fluid solution. Here we report the isolation and structural characterization of a thermally stable compound featuring a Cu–B one-electron bond, as well as its oxidized (nonbonded) and reduced (two-electrons-bonded) congeners. This triad provides an excellent opportunity to study the degree of σ-bonding in a metalloboratrane as a function of electron count

Conversion of Fe–NH₂ to Fe–N₂ with release of NH₃

Tris­(phosphine)­borane ligated Fe­(I) centers featuring N₂H₄, NH₃, NH₂, and OH ligands are described. Conversion of Fe–NH₂ to Fe–NH₃⁺ by the addition of acid, and subsequent reductive release of NH₃ to generate Fe–N₂, is demonstrated. This sequence models the final steps of proposed Fe–mediated nitrogen fixation pathways. The five-coordinate trigonal bipyramidal complexes described are unusual in that they adopt <i>S</i> = 3/2 ground states and are prepared from a four-coordinate, <i>S</i> = 3/2 trigonal pyramidal precursor

Heterolytic H₂ Cleavage and Catalytic Hydrogenation by an Iron Metallaboratrane

Reversible, heterolytic addition of H₂ across an iron–boron bond in a ferraboratrane with formal hydride transfer to the boron gives iron-borohydrido-hydride complexes. These compounds catalyze the hydrogenation of alkenes and alkynes to the respective alkanes. Notably, the boron is capable of acting as a shuttle for hydride transfer to substrates. The results are interesting in the context of heterolytic substrate addition across metal–boron bonds in metallaboratranes and related systems, as well as metal–ligand bifunctional catalysis

Heterolytic H₂ Cleavage and Catalytic Hydrogenation by an Iron Metallaboratrane

Reversible, heterolytic addition of H₂ across an iron–boron bond in a ferraboratrane with formal hydride transfer to the boron gives iron-borohydrido-hydride complexes. These compounds catalyze the hydrogenation of alkenes and alkynes to the respective alkanes. Notably, the boron is capable of acting as a shuttle for hydride transfer to substrates. The results are interesting in the context of heterolytic substrate addition across metal–boron bonds in metallaboratranes and related systems, as well as metal–ligand bifunctional catalysis

Experimental Gas-Phase Thermochemistry for Alkane Reductive Elimination from Pt(IV)

The gas-phase reactivity of the [(<i>NN</i>)­Pt^IVMe₃]⁺ (<i>NN</i> = α-diimine) complex <b>1</b> and its acetonitrile adduct has been investigated by tandem mass spectrometry. The only observed reaction from the octahedral d⁶ complex <b>1</b>·MeCN is the simple dissociation of the coordinated solvent molecule with a binding energy of 24.5(6) kcal mol^–1 measured by energy-resolved collision-induced dissociation experiments. Further reactions of <b>1</b> are observed. In addition to the expected reductive elimination of ethane from <b>1</b>, competitive loss of methane occurs. Methane is generated from the initially formed ethane agostic complex via either C–H activation/bond formation or σ-bond metathesis with the third methyl group. Energy-resolved collision-induced dissociation experiments indicate that the initial reductive C–C coupling step is rate limiting for both ethane and methane elimination, and afford a gas-phase barrier of 22.6(7) kcal mol^–1 for this process. Density functional theory calculations confirm the reaction mechanisms, and a variety of functionals are benchmarked. The results at the M06-L/SDB-cc-pVTZ//mPW1K/SDD­(d,p) level of theory agree well with the experiments and suggest that the generation of [(<i>NN</i>)­PtH]⁺ at higher collision energy proceeds through sequential loss of methane and ethylene

Coordination of a Diphosphine–Ketone Ligand to Ni(0), Ni(I), and Ni(II): Reduction-Induced Coordination

The coordination chemistry of the diphosphine–ketone ligand 2,2′-bis­(diphenylphosphino)­benzophenone (^Phdpbp) with nickel is reported. The ketone moiety does not bind to Ni­(II) in the complex (^Phdpbp)­NiCl₂, whereas reduction to Ni­(I) or Ni(0) induces η²(C,O) coordination of the ketone to form the pseudotetrahedral complexes (^Phdpbp)­NiCl and (^Phdpbp)­Ni­(PPh₃). DFT calculations indicate that the metal–ketone bond is dominated by π back-donation; hence, ^Phdpbp functions as a hemilabile acceptor ligand in this series of complexes

Precursor Geometry Determines the Growth Mechanism in Graphene Nanoribbons

On-surface synthesis with molecular precursors has emerged as the de facto route to atomically well-defined graphene nanoribbons (GNRs) with controlled zigzag and armchair edges. On Au(111) and Ag(111) surfaces, the prototypical precursor 10,10′-dibromo-9,9′-bianthryl (DBBA) polymerizes through an Ullmann reaction to form straight GNRs with armchair edges. However, on Cu(111), irrespective of the bianthryl precursor (dibromo-, dichloro-, or halogen-free bianthryl), the Ullmann route is inactive, and instead, identical chiral GNRs are formed. Using atomically resolved noncontact atomic force microscopy (nc-AFM), we studied the growth mechanism in detail. In contrast to the nonplanar BA-derived precursors, planar dibromoperylene (DBP) molecules do form armchair GNRs by Ullmann coupling on Cu(111), as they do on Au(111). These results highlight the role of the substrate, precursor shape, and molecule–molecule interactions as decisive factors in determining the reaction pathway. Our findings establish a new design paradigm for molecular precursors and opens a route to the realization of previously unattainable covalently bonded nanostructures