Coordination of a Triphosphine–Silane to Gold: Formation of a Trigonal Pyramidal Complex Featuring Au+→Si Interaction

Coordination and Electrochemical Switching on Paddle-Wheel Complexes Containing an As-Ru or a Sb-Ru Axis

Inspired by the known complex [PhP(μ-PyO)₄Ru(CO)] (PyO = 2-pyridyloxy), the family of group 15 paddle-wheel complexes has been expanded to [PhPn(μ-PyO)₄Ru(L)] (Pn = P, As, Sb; L = NCMe, CO). Solvent-dependent reversible switching between [PhAs(μ-PyO)₄Ru(NCMe)] and [PhAs(μ-PyO)₃Ru(κ²-PyO)] was detected. Electrochemical investigations of the [PhPn(μ-PyO)₄Ru(L)] complexes showed reversible oxidation of the complexes with L = NCMe and back-formation of the complexes with L = NCMe upon oxidation of the complexes with L = CO in NCMe. In the series of [PhPn(μ-PyO)₄Ru(L)] complexes, the Pn→Ru bonding mode is shifted from L-type Pn to X-type upon going from Pn = P and As to Pn = Sb, resulting in a pronounced electron-rich Ru site in the latter case. The easily accessible complex [PhSb(μ-PyO)₄RuCl] exhibits reversible electrochemical and coordinative exchange with its reduced analogue [PhSb(μ-PyO)₄Ru(NCMe)] under retention of the paddle-wheel motif and Sb-Ru bond properties.

Semi-bridging σ-silyls as Z-type ligands

The reactions of SiHPh(NCH₂PPh₂)₂C₆H₄-1,2 with zerovalent group 10 reagents afford the homoleptic bimetallic complexes [M₂{μ-κ³-Si,P,P′-SiPh(CH₂PPh₂)₂C₆H₄}₂] (M = Ni, Pd, Pt) in which the M–M bond is unsymmetrically bridged by two σ-silyl groups.

Ligand and counteranion enabled regiodivergent C-H bond functionalization of naphthols with α-aryl-α-diazoesters

Here, an unprecedented ligand and counteranion-controlled and site-selectivity switchable direct C-H bond functionalization of unprotected naphthols with α-aryl-α-diazoesters was developed. In this transformation, site selectivities are realized by turning on/off the coordination between metal complexes and hydroxy groups. The preliminary mechanism revealed that the interaction between the hydroxy group and gold catalyst plays a key role in switching the site-selectivity of gold-carbene. This protocol potentially provides a novel design for C-H bond functionalization.

(2-Pyridyloxy)silanes as Ligands in Transition Metal Coordination Chemistry

Proceeding our initial studies of compounds with formally dative TM→Si bonds (TM = Ni, Pd, Pt), which feature a paddlewheel arrangement of four (N,S) or (N,N) bridging ligands around the TM–Si axis, the current study shows that the (N,O)-bidentate ligand 2-pyridyloxy (pyO) is also capable of bridging systems with TM→Si bonds (shown for TM = Pd, Cu). Reactions of MeSi(pyO)3 with [PdCl2(NCMe)2] and CuCl afforded the compounds MeSi(µ-pyO)4PdCl (1) and MeSi(µ-pyO)3CuCl (2), respectively. In the latter case, some crystals of the Cu(II) compound MeSi(µ-pyO)4CuCl (3) were obtained as a byproduct. Analogous reactions of Si(pyO)4, in the presence of HpyO, with [PdCl2(NCMe)2] and CuCl2, afforded the compounds [(HpyO)Si(µ-pyO)4PdCl]Cl (4), (HpyO)2Si[(µ-pyO)2PdCl2]2 (5), and (HpyO)2Si[(µ-pyO)2CuCl2]2 (6), respectively. Compounds 1–6 and the starting silanes MeSi(pyO)3 and Si(pyO)4 were characterized by single-crystal X-ray diffraction analyses and, with exception of the paramagnetic compounds 3 and 6, with NMR spectroscopy. Compound 2 features a pentacoordinate Si atom, the Si atoms of the other complexes are hexacoordinate. Whereas compounds 1–4 feature a TM→Si bond each, the Si atoms of compounds 5 and 6 are situated in an O6 coordination sphere, while the TMCl2 groups are coordinated to pyridine moieties in the periphery of the molecule. The TM–Si interatomic distances in compounds 1–4 are close to the sum of the covalent radii (1 and 4) or at least significantly shorter than the sum of the van-der-Waals radii (2 and 3). The latter indicates a noticeably weaker interaction for TM = Cu. For the series 1, 2, and 3, all of which feature the Me–Si motif trans-disposed to the TM→Si bond, the dependence of the TM→Si interaction on the nature of TM (Pd(II), Cu(I), and Cu(II)) was analyzed using quantum chemical calculations, that is, the natural localized molecular orbitals (NLMO) analyses, the non-covalent interaction (NCI) descriptor, Wiberg bond order (WBO), and topological characteristics of the bond critical points using the atoms in molecules (AIM) approach.

Gold(I) Complexes of the Geminal Phosphinoborane tBu2PCH2BPh2

In this work, we explored the coordination properties of the geminal phosphinoborane tBu₂PCH₂BPh₂ (2) toward different gold(I) precursors. The reaction of 2 with an equimolar amount of the sulfur-based complex (Me₂S)AuCl resulted in displacement of the SMe₂ ligand and formation of linear phosphine gold(I) chloride 3. Using an excess of ligand 2, bisligated complex 4 was formed and showed dynamic behavior at room temperature. Changing the gold(I) metal precursor to the phosphorus-based complex, (Ph₃P)AuCl impacted the coordination behavior of ligand 2. Namely, the reaction of ligand 2 with (Ph₃P)AuCl led to the heterolytic cleavage of the gold-chloride bond, which is favored over PPh₃ ligand displacement. To the best of our knowledge, 2 is the first example of a P/B-ambiphilic ligand capable of cleaving the gold-chloride bond. The coordination chemistry of 2 was further analyzed by density functional theory calculations.

Tridentate Lewis-acids based on triphenylsilane

Triphenylsilanes are versatile propeller-shaped building blocks and have been used for the syntheses of several novel poly-Lewis-acids. The first solid-state structure of a bisma-silatriptycene as well as investigations in host–guest chemistry of a triple alane with a threefold amine are reported.

Utility of Ligand Effect in Homogenous Gold Catalysis: Enabling Regiodivergent π-Bond-Activated Cyclization

Comprehensive utilization of both electronic and steric properties of ligands in homogeneous gold catalysis is achieved in the regiodivergent intramolecular hydroarylation of alkynes. A flexible electron-deficient phosphite ligand, combined with the readily transformable directing group methoxyl amide, is attached to a cationic Au(I) center in three-coordinate mode, affording sterically hindered ortho-position cyclization. Meanwhile, para-position cyclization is exclusively achieved with the assistance of a rigid electron-abundant phosphine ligand-based Au(I) catalyst, in which ligands manifest the compensating effect for cyclization through steric hindrance and electronic properties. By combining gold with silver catalysts, tetrahydropyrroloquinolinones possessing a congested tricyclic structure are obtained via a proven Au/Ag relay catalytic process.

Experimental and theoretical studies of Si–Cl and Ge–Cl σ-bond activation reactions by iridium-hydride

We report the iridium hydride-mediated Si–Cl and Ge–Cl σ-bond activation in a low-polarity toluene solution owing to diphosphine-chelation, in which the Si–Cl and Ge–Cl σ-bonds are readily cleaved through an S_N2-type pathway via the formation of a free chloride anion.