Triruthenium clusters containing mono and bidentate phosphines: Synthesis,structure, thermal reactivity and fluxional behavior

The syntheses, structures and thermal reactions of [Ru₃(CO)₉{P(C₄H₃E)₃}(μ-dppe)] (2, E = S; 3, E = O; dppe = 1,2-bis(diphenylphosphino)ethane) are described. These triphosphine-substituted clusters can be easily obtained in high yield from the Me₃NO initiated room temperature reaction between [Ru₃(CO)₁₀(μ-dppe)] (1) and P(C₄H₃E)₃. Both clusters have been structurally characterized which reveals that the functionalized phosphine P(C₄H₃E)₃ is coordinated to the remote ruthenium atom using the phosphorus atom, while the NMR spectroscopic data indicate that both clusters are fluxional in solution mainly due to the ring-flipping process involving the dppe ligand which has been probed by VT NMR spectroscopy. Thermolysis of 2 at 66 °C affords 1 via P(C₄H₃S)₃ dissociation, whilst that of 3 under similar experimental conditions also furnishes the diruthenium σ,π-furyl complex [Ru₂(CO)₆(μ,η²-C₄H₃O){μ-P(C₄H₃O)₂] (4) in addition to 1.     

Liquid Fluxional Ga Single Atom Catalysts for Efficient Electrochemical CO2 Reduction

Precise design and tuning of the micro-atomic structure of single atom catalysts (SACs) can help efficiently adapt complex catalytic systems. Herein, we inventively found that when the active center of the main group element gallium (Ga) is downsized to the atomic level, whose characteristic has significant differences from conventional bulk and rigid Ga catalysts. The Ga SACs with a P, S atomic coordination environment display specific flow properties, showing CO products with FE of ≈92 % at −0.3 V vs. RHE in electrochemical CO₂ reduction (CO₂RR). Theoretical simulations demonstrate that the adaptive dynamic transition of Ga optimizes the adsorption energy of the *COOH intermediate and renews the active sites in time, leading to excellent CO₂RR selectivity and stability. This liquid single atom catalysts system with dynamic interfaces lays the foundation for future exploration of synthesis and catalysis.     

Titanium imido complexes containing 1,3,5-triazacyclohexane ligands

The syntheses of the 1,3,5-trimethyl- and tri-tert-butyl-1,3,5-triazacyclohexane-supported imido complexes [M(NR)(R′₃tach)Cl₂] (M = Ti or Zr (NMR only); R = Bu^t or 2,6-C₆H₃Prⁱ₂; R′ = Me or Bu^t) are reported, along with that of the thermally robust dibenzyl derivative [Ti(NBu^t)(Me₃tach)(CH₂Ph)₂]. The tert-butylimido ligand in [Ti(NBu^t)(Me₃tach)Cl₂] undergoes exchange with ArNH₂ (Ar = 4-C₆H₄Me or 2,6-C₆H₄Me or 2,6-C₆H₃Prⁱ₂) to form the corresponding arylimides [Ti(NAr)(Me₃tach)Cl₂]. The Me₃tach ring in [Ti(NR)(Me₃tach)Cl₂] undergoes slow exchange with Bu^t₃tach or Me₃tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) to give the ring-exchanged products [Ti(NR)(Bu^t₃tach)Cl₂] and [Ti(NR)(Me₃tacn)Cl₂], respectively. The complexes [Ti(NR)(Me₃tach)X₂] (R = Bu^t or 2,6-C₆H₃Prⁱ₂; X = Cl or CH₂Ph) exhibit room-temperature dynamic NMR behaviour via an unusual trigonal twist of the facially coordinated Me₃tach ligand, and the activation parameters for these processes have been measured and are discussed. The X-ray structures of [Ti(NR)(Bu^t₃tach)Cl₂] (R = Bu^t or 2,6-C₆H₃Prⁱ₂) and [Ti(NBu^t)(Me₃tach)(X)₂] [X= Cl or CH₂Ph) are reported. Me₃tach and Bu^t₃tach = 1,3,5-trimethyl- and tri-tert-butyl-1,3,5-triazacyclohexane, respectively.     

Dichlorodinickel(I) Complexes with μ2-CO or μ2-CS Bridges and Trimethylphosphane Ligands: Homologous Composition,but Different Frameworks

High ligand mobility is shown by the coordinatively unsaturated nickel(I ) compound 1 with a short Ni–Ni distance and an asymmetric CO bridge. The thio homologue 2 contains the novel (thiocarbonyl)trimethylphosphorane bridging ligand, which sits like a “stork's nest” on top of the roof-shaped dinuclear complex. In contrast to 1 , complex 2 does not show fluctional behavior and can be methylated without decomposition. X=Cl, Me.     

Chiral memory effects in catalytic hydrogenations with dynamically chiral ligands

The low barrier for interconversion of chiral conformations of the dynamically chiral 2,2′-biphenyl ligand NMe₂C₆H₄C₆H₄PCy₂ is raised upon coordination. The individual enantiomers of the planar chiral arene-tethered complex Ru(η⁶:η¹- NMe₂C₆H₄C₆H₄PCy₂)Cl₂ (1), however, do not undergo racemization readily. A second source of chirality, such as a chiral diamine, can be included by conversion of 1 into a dicationic analogue [Ru(η⁶:η¹-NMe₂C₆H₄C₆H₄PCy₂)((1S,2S)-DPEN)](SbF₆)₂ (2), which is a catalyst precursor for the hydrogenation of aryl ketones. Two epimers of 2, R_Ar,S,S and S_Ar,S,S, are formed when starting from racemic 1; this 1:1 mixture of diastereomers catalyzed the asymmetric hydrogenation of acetophenone. The enantiomerically pure diastereomers were obtained from resolved 1 and used separately to catalyze the reaction. Each diastereomer showed different selectivity, with S_Ar,S,S-2 being the more selective (61% ee for the hydrogenation of acetophenone). Our studies suggest that ruthenium hydride formation is accompanied by a decrease in hapticity of the η⁶-arene and probable detachment of the ring from the metal. Nevertheless, the original conformational chirality of the biphenyl ligand appears to be at least partially retained during the catalysis.     

Ligand substitution in the heterometallic cluster Cp*IrOs3(μ-H)2(CO)10

The reactions of the heterometallic cluster Cp*IrOs₃(μ-H)₂(CO)₁₀ with phosphines, isonitriles and pyridine under TMNO activation afforded the substitution products Cp*IrOs₃(μ-H)₂(CO)_10−nL_n (n = 1, 2; L = PPh₃, P(OMe)₃, ^tBuNC, CyNC or py) in good yields. For the monosubstituted derivatives, the substitution site was exclusively at an osmium atom in an axial position for L = phosphine or phosphite. Spectroscopic evidence suggested the presence of isomers in solution for the PPh₃ derivative. In contrast, for L = isonitrile, the ligand occupied an equatorial site. In the disubstituted derivatives, the group 15 ligands were coordinated to two different osmium atoms, one each at an axial and an equatorial site. The isomerism and fluxional behaviour of some of these clusters have also been examined.     

Thermodynamic and kinetic parameters associated with the fluxional behavior of 2-methyl- and 2,6-dimethyltroponeiron tricarbonyl complexes

The kinetic and thermodynamic parameters for regioisomerisation of 2-methyl- and 2,6-dimethyl-derivatives of tricarbonyl[η⁴-tropone]iron complexes have been studied by ¹H NMR spectrometry over a range of 40 °C. Regioisomerisation of these complexes proceeds by an intramolecular first-order process and results in the almost complete conversion of the less stable complexes (4, 8) to more stable regioisomers (1, 5). The activation energies and half lifes for the conversion (4 → 1) and (8 → 5) were found to be ΔG^#=92 kJ mol⁻¹; τ_1/2=12.8 h, and ΔG^#=107 kJ mol⁻¹; τ_1/2=26.8 h, respectively, at 23 °C. Complex 1 reacts with (1R,2S,5R)-menthol in sulphuric acid solution, followed by neutralisation with sodium carbonate to give a separable mixture of diastereomeric tricarbonyl[(2,3,4,5-η)-(1R^′,2S^′,5R^′)-6-menthyloxy-2-methyltropone]iron complexes, 9 and 10. The corresponding dimethylated complex 5 fails to react under these conditions.     

Fluxional behavior of Al(Et)(q)2 (q=2-methyl-8-quinolinolato) studied by temperature dependent H NMR spectroscopy

Two α-CH₂ hydrogens of the Et group in Al(Et)(q^′)₂ (q^′=2-methyl-8-quinolinolato) show two ¹H NMR peaks at different positions with a separation of 0.19 ppm at 25 °C, due to the presence of a chiral center at Al. On raising the temperature, the two peaks collapsed, and coalesced above 100 °C. The ¹H NMR fluxional behavior is accounted for by simultaneous rotation of the q^′ ligands, and kinetic parameters of kJ mol⁻¹, kJ mol⁻¹, J K⁻¹ mol⁻¹ are evaluated.     

Reactions of Dienes with a Mo(0) Complex with Tetraphosphine Coligand [Mo(P4)(Ph2PCH2CH2PPh2)] (P4 = Meso‐o‐C6H4(PPhCH2CH2PPh2)2)

Reaction of tetraphosphine complex [Mo(κ⁴‐P4)(Ph₂PCH₂CH₂PPh₂)] (1; P4 = meso‐o‐C₆H₄‐(PPhCH₂CH₂PPh₂)₂) with E‐1,3‐pentadiene in toluene at 60 °C gave the η⁴‐diene complex [Mo(η⁴‐E‐1,3‐pentadiene)(κ⁴‐P4)] (2), which is present as a mixture of two isomers due to the orientation of the Me group in the diene ligand. Treatment of 1 with Z‐1,3‐pentadien also resulted in the formation of 2 as the sole product after heating the reaction mixture at 90 °C. Whereas the reaction of 1 with 1,3‐cyclohexadiene at 60 °C afforded the η⁴‐diene complex [Mo(η⁴‐cyclohexadiene)(κ⁴‐P4)] (6), that with cyclopentadiene led to the C‐H bond scission product [η⁵‐C₅H₅)MoH(κ³‐P4)] (7). Detailed structures were determined by X‐ray crystallography for 2, 6,and 7, and fluxional feature of 6 in solution was clarified based on the VT‐NMR studies.     

Syntheses, structures, and dynamic properties of M(CO)2(η-C3H5)(en)(X) (M = Mo, W; X = Br, N3, CN) and [(en)(η-C3H5)(CO)2M(μ-CN)M(CO)2(η-C3H5)(en)]Br (M = Mo, W)

Mononuclear compounds M(CO)₂(η³-C₃H₅)(en)(X) (X = Br, M = Mo(1), W(2); X = N₃, M = Mo(3), W(4); X = CN, M = Mo(5), W(6)) and cyanide-bridged bimetallic compounds [(en)(η³-C₃H₅)(CO)₂M(μ-CN)M(CO)₂(η³-C₃H₅)(en)]Br (M = Mo (7), W(8)) were prepared and characterized. These compounds are fluxional and display broad unresolved proton NMR signals at room temperature. Compounds 1-6 were characterized by NMR spectroscopy at −60 °C, which revealed isomers in solution. The major isomers of 1-4 adopt an asymmetric endo-conformation, while those of 5 and 6 were both found to possess a symmetric endo-conformation. The single crystal X-ray structures of 1-6 are consistent with the structures of the major isomer in solution at low temperature. In contrast to mononuclear terminal cyanide compounds 5 and 6, cyanide-bridged compounds 7 and 8 were found to adopt the asymmetric endo-conformation in the solid state.