Two pathways of proton transfer reaction to (triphos)Cu(η1-BH4) via a dihydrogen bond [triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane]

The interaction of alcohols of variable strength with the copper(i) borohydride complex (triphos)Cu(η1-BH4) results in a great variety of DHB complexes which encompass different mechanisms involving M–H and E–H bond (E = B, O) activation steps

Exploring the Interaction of Pyridine-Based Chalcones with Trinuclear Silver(I) Pyrazolate Complex

The investigation of the interaction of cyclic trinuclear silver(I) pyrazolate [AgPz]3 (Pz = 3,5-bis(trifluoromethyl)pyrazolate) with pyridine-based chalcones (anthracen-9-yl and phenyl-substituted ones) has been performed by IR-, UV-vis, and NMR spectroscopies in the solution. The carbonyl group participates in coordination with metal ions in all complexes. However, the network of π-π/M-π non-covalent intermolecular interactions mainly influences complex formation. The spectral data suggest retaining the structures for all studied complexes in the solution and solid state. E-Z isomerization in the case of anthracene-containing compounds significantly influences the complexation. E-isomer of chalcones seeks the planar structure in the complexes with [AgPz]3. In contrast, the Z-isomer of chalcone demonstrates the chelating coordination of O- and N atoms to silver ions. The complexation of anthracene-containing chalcones allows the switching of the emission nature from charge transfer to ligand-centered at 77 K. In contrast, phenyl-substituted chalcone in complex with macrocycle demonstrates that the emission significantly shifted (Δ = ca. 155 nm) to the low-energy region compared to the free base

Catalytic redox isomerization of allylic alcohols with rhodium and iridium complexes with ferrocene phosphine-thioether ligands

International audienceComplexes [M(P,SR)(diene)X] where (P,SR) = CpFe[1,2-C 5 H 3 (PPh 2)(CH 2 SR)] (M = Ir, R = tBu or Bn diene = cod, X = Cl; M = Rh, diene = cod or nbd; X = BF 4 or Cl) were used as precatalysts for the redox isomerization of various allylic alcohols (7a-e) to the corresponding saturated ketones (8a-e) and or hydrogenation to the saturated alcohol (9a-e). In optimization studies using 1-phenyl-2-propen-1-ol (7a) in THF and in iPrOH/MeONa, the only observed product was the saturated alcohol 1-phenyl-1-propanol (9a) when working under a 30 bar H 2 pressure, but activation for only 1 min under H 2 pressure and then continuation under 1 bar of H 2 or Ar led to increasing amounts of the allylic isomerization product propiophenone (8a). Continued reaction under H 2 converted (8a) into (9a). The Rh precatalysts were more active than the Ir analogues. For the rhodium precatalysts (3) and (4), the redox isomerization reaction could be carried out after precatalyst activation in iPrOH/MeONa under Ar at 82°C (without H 2) with complete conversion in 1 h (1% catalyst loading). However, longer reaction times resulted in slow transfer hydrogenation of (8a) leading to (9a) with low enantiomeric excess. Extension of the H 2-free activation of the Rh precatalysts in iPrOH to other allylic alcohol substrates (7b-d) yielded the corresponding ketones with good to excellent yields and excellent chemoselectivities under appropriate conditions

Modeling the platinum-catalyzed intermolecular hydroamination of ethylene: The nucleophilic addition of HNEt2 to coordinated ethylene in trans-PtBr2(C2H4)(HNEt2)

International audienceCompound trans-PtBr2(C2H4)(NHEt2) (1) has been synthesized by Et2NH addition to K[PtBr3(C2H4)] and structurally characterized. Its isomer cis-PtBr2(C2H4)(NHEt2) (3) has been obtained from 1 by photolytic dissociation of ethylene, generating the dinuclear trans-[PtBr2(NHEt2)]2 intermediate (2), followed by thermal re-addition of C2H4, but only in low yields. The addition of further Et2NH to 1 in either dichloromethane or acetone yields the zwitterionic complex trans-Pt(−)Br2(NHEt2)(CH2CH2N(+)HEt2) (4) within the time of mixing in an equilibrated process, which shifts toward the product at lower temperatures (ΔH° = −6.8 ± 0.5 kcal/mol, ΔS° = 14.0 ± 2.0 e.u., from a variable temperature IR study). 1H NMR shows that free Et2NH exchanges rapidly with H-bonded amine in a 4·NHEt2 adduct, slowly with the coordinated Et2NH in 1, and not at all (on the NMR time scale) with Pt-NHEt2 or –CH2CH2N(+)HEt2 in 4. No evidence was obtained for deprotonation of 4 to yield an aminoethyl derivative trans-[PtBr2(NHEt2)(CH2CH2NEt2)]− (5), except as an intermediate in the averaging of the diasteretopic methylene protons of the CH2CH2N(+)HEt2 ligand of 4 in the higher polarity acetone solvent. Computational work by DFT attributes this phenomenon to more facile ion pair dissociation of 5·Et2NH2+, obtained from 4·Et2NH, facilitating inversion at the N atom. Complex 4 is the sole observable product initially but slow decomposition occurs in both solvents, though in different ways, without observable generation of NEt3. Addition of TfOH to equilibrated solutions of 4, 1 and excess Et2NH leads to partial protonolysis to yield NEt3 but also regenerates 1 through a shift of the equilibrium via protonation of free Et2NH. The DFT calculations reveal also a more favourable coordination (stronger Pt–N bond) of Et2NH relative to PhNH2 to the PtII center, but the barriers of the nucleophilic additions of Et2NH to the C2H4 ligand in 1 and of PhNH2 to trans-PtBr2(C2H4)(PhNH2) (1a) are predicted to be essentially identical for the two systems

Two active species from a single metal halide precursor: a case study of highly productive Mn-catalyzed dehydrogenation of amine-boranes via intermolecular bimetallic cooperation

International audienceMetal–metal cooperation for inert bond activation is a ubiquitous concept in coordination chemistry and catalysis. While the great majority of such transformations proceed via intramolecular mode in binuclear complexes, to date only a few examples of intermolecular small molecule activation using usually bimetallic frustrated Lewis pairs (Mδ+⋯M′δ−) have been reported. We introduce herein an alternative approach for the intermolecular bimetallic cooperativity observed in the catalytic dehydrogenation of amine-boranes, in which the concomitant activation of N–H and B–H bonds of the substrate via the synergetic action of Lewis acidic (M+) and basic hydride (M–H) metal species derived from the same mononuclear complex (M–Br). It was also demonstrated that this system generated in situ from the air-stable Mn(I) complex fac-[(CO)3(bis(NHC))MnBr] and NaBPh4 shows high activity for H2 production from several substrates (Me2NHBH3, tBuNH2BH3, MeNH2BH3, NH3BH3) at low catalyst loading (0.1% to 50 ppm), providing outstanding efficiency for Me2NHBH3 (TON up to 18 200) that is largely superior to all known 3d-, s-, p-, f-block metal derivatives and frustrated Lewis pairs (FLPs). These results represent a step forward towards more extensive use of intermolecular bimetallic cooperation concepts in modern homogeneous catalysis

Tetranuclear Copper(I) and Silver(I) Pyrazolate Adducts with 1,1′-Dimethyl-2,2’-bibenzimidazole: Influence of Structure on Photophysics

A reaction of a cyclic trinuclear copper(I) or silver(I) pyrazolate complex ([MPz]3, M = Cu, Ag) with 1,1′-dimethyl-2,2’-bibenzimidazole (L) leads to the formation of tetranuclear adducts decorated by one or two molecules of a diimine ligand, depending on the amount of the ligand added (0.75 or 1.5 equivalents). The coordination of two L molecules stabilizes the formation of a practically idealized tetrahedral four-metal core in the case of a copper-containing complex and a distorted tetrahedron in the case of a Ag analog. In contrast, complexes containing one molecule of diimine possess two types of metals, two- and three-coordinated, forming the significantly distorted central M4 cores. The diimine ligands are twisted in these complexes with dihedral angles of ca. 50–60°. A TD-DFT analysis demonstrated the preference of a triplet state for the twisted 1,1′-dimethyl-2,2’-bibenzimidazole and a singlet state for the planar geometry. All obtained complexes demonstrated, in a solution, the blue fluorescence of the ligand-centered (LC) nature typical for free diimine. In contrast, a temperature decrease to 77 K stabilized the structure close to that observed in the solid state and activated the triplet states, leading to green phosphorescence at ca. 500 nm. The silver-containing complex Ag4Pz4L exhibited dual emission from both the singlet and triplet states, even at room temperature

Thermodynamic Hydricity of Small Borane Clusters and Polyhedral closo-Boranes

Thermodynamic hydricity (HDAMeCN) determined as Gibbs free energy (ΔG°[H]−) of the H− detachment reaction in acetonitrile (MeCN) was assessed for 144 small borane clusters (up to 5 boron atoms), polyhedral closo-boranes dianions [BnHn]2−, and their lithium salts Li2[BnHn] (n = 5–17) by DFT method [M06/6-311++G(d,p)] taking into account non-specific solvent effect (SMD model). Thermodynamic hydricity values of diborane B2H6 (HDAMeCN = 82.1 kcal/mol) and its dianion [B2H6]2− (HDAMeCN = 40.9 kcal/mol for Li2[B2H6]) can be selected as border points for the range of borane clusters’ reactivity. Borane clusters with HDAMeCN below 41 kcal/mol are strong hydride donors capable of reducing CO2 (HDAMeCN = 44 kcal/mol for HCO2−), whereas those with HDAMeCN over 82 kcal/mol, predominately neutral boranes, are weak hydride donors and less prone to hydride transfer than to proton transfer (e.g., B2H6, B4H10, B5H11, etc.). The HDAMeCN values of closo-boranes are found to directly depend on the coordination number of the boron atom from which hydride detachment and stabilization of quasi-borinium cation takes place. In general, the larger the coordination number (CN) of a boron atom, the lower the value of HDAMeCN

Mononuclear Copper(I) 3-(2-pyridyl)pyrazole Complexes: The Crucial Role of Phosphine on Photoluminescence

A series of emissive Cu(I) cationic complexes with 3-(2-pyridyl)-5-phenyl-pyrazole and various phosphines: dppbz (1), Xantphos (2), DPEPhos (3), PPh3 (4), and BINAP (5) were designed and characterized. Complexes obtained exhibit bright yellow-green emission (ca. 520–650 nm) in the solid state with a wide range of QYs (1–78%) and lifetimes (19–119 µs) at 298 K. The photoluminescence efficiency dramatically depends on the phosphine ligand type. The theoretical calculations of buried volumes and excited states explained the emission behavior for 1–5 as well as their lifetimes. The bulky and rigid phosphines promote emission efficiency through the stabilization of singlet and triplet excited states