Mild sp2Carbon-Oxygen Bond Activation by an Isolable Ruthenium(II) bis(Dinitrogen) Complex: Experiment and Theory

The isolable ruthenium(II) bis(dinitrogen) complex [Ru(H)2(N2)2(PCy3)2] (1) reacts with aryl ethers (Ar–OR, R = Me and Ar) containing a ketone directing group to effect sp2C–O bond activation at temperatures below 40 °C. DFT studies support a low-energy Ru(II)/Ru(IV) pathway for C–O bond activation: oxidative addition of the C–O bond to Ru(II) occurs in an asynchronous manner with Ru–C bond formation preceding C–O bond breaking. Alternative pathways based on a Ru(0)/Ru(II) couple are competitive but less accessible due to the high energy of the Ru(0) precursors. Both experimentally and by DFT calculations, sp2C–H bond activation is shown to be more facile than sp2C–O bond activation. The kinetic preference for C–H bond activation over C–O activation is attributed to unfavorable approach of the C–O bond toward the metal in the selectivity determining step of the reaction pathway

Yttrium-Catalyzed Amine–Silane Dehydrocoupling: Extended Reaction Scope with a Phosphorus-Based Ligand

The scope of the catalytic dehydrocoupling of primary and secondary amines with phenylsilanes has been investigated using [Y­{N­(SiMe₃)₂}₃] and a four-coordinate analogue bearing a cyclometalated phosphonium methylide ligand. Inclusion of the phosphorus-based ligand on yttrium results in increased substrate scope in comparison to the tris­(amide) analogue. While reversible C–H bond activation of the cyclometalated ligand was observed in stoichiometric experiments, D-labeling experiments and DFT calculations suggest that reversible ligand activation is not involved in silazane formation under catalytic conditions. We suggest that the extended reaction scope with the four-coordinate yttrium phosphonium methylide complex relative to the three-coordinate yttrium (tris)­amide complex is a result of differences in the ease of amine inhibition of catalysis

Addition of carbon-fluorine bonds to a Mg(I)-Mg(I) bond: an equivalent of Grignard formation in solution

Addition of the carbon-fluorine bond of a series of perfluorinated and polyfluorinated arenes across the Mg-Mg bond of a simple coordination complex proceeds rapidly in solution. The reaction results in the formation of a new carbon-magnesium bond and a new fluorine-magnesium bond and is analogous to Grignard formation in homogeneous solution

Reversible Coordination of Boron–, Aluminum–, Zinc–, Magnesium–, and Calcium–Hydrogen Bonds to Bent {CuL₂} Fragments: Heavy σ Complexes of the Lightest Coinage Metal

A series of copper­(I) complexes bearing electron-deficient β-diketiminate ligands have been prepared. The study includes [{{ArNC­(CR₃)}₂CH}­Cu­(η²-toluene)_n] (Ar = Mes, R = F, <i>n</i> = 0.5, [<b>1</b>_<b>2</b><b>·tol</b>]; Ar = C₆F₅, R = Me, <i>n</i> = 1, [<b>2·tol</b>]; Ar = 2,6-Cl₂C₆H₃, R = H, <i>n</i> = 0.5, [<b>3</b>_<b>2</b><b>·tol</b>]). Reactions of [<b>1</b>–<b>3</b>_{<b><i>n</i></b>}<b>·tol</b>] with boranes, alanes, a zinc hydride, a magnesium hydride, and a calcium hydride generate the corresponding σ complexes ([<b>1–3·B</b>], <b>[3·B′</b>], [<b>3·Al</b>], [<b>3·Al′</b>], [<b>1–3·Zn</b>], [<b>1·Mg</b>], and [<b>1·Ca</b>]). These species all form reversibly, being in equilibrium with the arene solvates in solution. With the exception of the calcium complex, the complexes have all been characterized by single-crystal X-ray diffraction studies. In solution, the σ-hydride of the aluminum, zinc, magnesium, and calcium derivatives resonates between −0.12 and −1.77 ppm (C₆D₆ or toluene-<i>d</i>₈, 193–298 K). For the σ-borane complexes, the hydrides are observed as a single resonance between 2 and 3.5 ppm (C₆D₆, 298 K) and bridging and terminal hydrides rapidly exchange on the NMR time scale even at 193 K. Quantification of the solution dynamics by van’t Hoff analysis yields expectedly small values of Δ<i>H</i>° and negative values of Δ<i>S</i>° consistent with weak binding and a reversible process that does not involve aggregation of the copper species. The donor–acceptor complexes can be rationalized in terms of the Dewar–Chatt–Duncanson model. Density functional theory calculations show that the donation of σ-M–H (or E–H) electrons into the 4s-based orbital (LUMO or LUMO+1) of the copper fragment is accompanied by weak back-donation from a d_<i>xz</i>-based orbital (HOMO or HOMO–1) into the σ*-M–H (or E–H) orbital

Vinylic C–H Activation of Styrenes by an Iron–Aluminum Complex

The oxidative addition of sp2 C–H bonds of alkenes to single-site transition-metal complexes is complicated by the competing π-coordination of the CC double bond, limiting the examples of this type of reactivity and onward applications. Here, we report the C–H activation of styrenes by a well-defined bimetallic Fe–Al complex. These reactions are highly selective, resulting in the (E)-β-metalation of the alkene. For this bimetallic system, alkene binding appears to be essential for the reaction to occur. Experimental and computational insights suggest an unusual reaction pathway in which a (2 + 2) cycloaddition intermediate is directly converted into the hydrido vinyl product via an intramolecular sp2 C–H bond activation across the two metals. The key C–H cleavage step proceeds through a highly asynchronous transition state near the boundary between a concerted and a stepwise mechanism influenced by the resonance stabilization ability of the aryl substituent. The metalated alkenes can be further functionalized, which has been demonstrated by the (E)-selective phosphination of the employed styrenes