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The development of catalysts for the oxidation of water using ligands with a non ‐ innocent character could potentially be employed for the rational design of efficient water ‐ oxidation catalysts. In their Full Paper on page 10039 ff., B. Åkermark, M. D. Kärkäs, R. ‐ Z. Liao and co ‐ workers explore the mechanistic details associated with a dinuclear Ru ‐ based water ‐ oxidation catalyst. Combining experimental studies and quantum chemical calculations provides insight into the fundamental principles controlling the reactivity of the catalyst, in which metal – ligand cooperation is a vital part. [ABSTRACT FROM AUTHOR]

The electronic structures within a series of square‐planar ruthenium(II) pincer complexes with dialkyl‐, vinyl alkyl‐, and divinyl amido pincer backbones is compared in an experimental and computational study. Although [RuCl{N(CH2CH2PtBu2)2}] exhibits a low‐spin (S=0) ground state and low‐lying triplet (S=1) excited state, [RuCl{N(CH2CH2PtBu2)(CHCHPtBu2)}] and [RuCl{N(CHCHPtBu2)2}] adopt intermediate‐spin (S=1) ground states with strong magnetic anisotropy due to large zero‐field splitting (D>+200cm–1). The change in ground‐state electronic configuration is attributed to tailored pincer ligand‐to‐metal π‐donation within the PNP ligand series. For more details, see the Full Paper by S. Schneider et al. on page 579 ff. [ABSTRACT FROM AUTHOR]

Functionalization of the PNP pincer ligand backbone allows for a comparison of the dialkyl amido, vinyl alkyl amido, and divinyl amido ruthenium(II) pincer complex series [RuCl{N(CH2CH2P tBu2)2}], [RuCl{N(CHCHP tBu2)(CH2CH2P tBu2)}], and [RuCl{N(CHCHP tBu2)2}], in which the ruthenium(II) ions are in the extremely rare square-planar coordination geometry. Whereas the dialkylamido complex adopts an electronic singlet ( S=0) ground state and energetically low-lying triplet ( S=1) state, the vinyl alkyl amido and the divinyl amido complexes exhibit unusual triplet ( S=1) ground states as confirmed by experimental and computational examination. However, essentially non-magnetic ground states arise for the two intermediate-spin complexes owing to unusually large zero-field splitting ( D>+200 cm−1). The change in ground state electronic configuration is attributed to tailored pincer ligand-to-metal π-donation within the PNP ligand series. [ABSTRACT FROM AUTHOR]

[RuCl(arene)(μ-Cl)]2 dimers were treated in a 1:2 molar ratio with sodium or thallium salts of bis- and tris(pyrazolyl)borate ligands [Na(Bp [ABSTRACT FROM AUTHOR]

The synthesis of a range of phosphine-diamine, phosphine-amino-alcohol, and phosphine-amino-amide ligands and their ruthenium(II) complexes are reported. Five of these were characterised by X-ray crystallography. The activities of this collection of catalysts were initially compared for the hydrogenation of two model ester hydrogenations. Catalyst turnover frequencies up to 2400 h−1 were observed at 85 °C. However, turnover is slow at near ambient temperatures. By using a phosphine-diamine RuII complex, identified as the most active catalyst, a range of aromatic esters were reduced in high yield. The hydrogenation of alkene-, diene-, and alkyne-functionalised esters was also studied. Substrates with a remote, but reactive terminal alkene substituent could be reduced chemoselectively in the presence of 4-dimethylaminopyridine (DMAP) co-catalyst. The chemoselective reduction of the ester function in conjugated dienoate ethyl sorbate could deliver (2 E,4 E)-hexa-2,4-dien-1-ol, a precursor to leaf alcohol. The monounsaturated alcohol ( E)-hex-4-en-1-ol was produced with reasonable selectivity, but complete chemoselectivity of CO over the diene is elusive. High chemoselectivity for the reduction of an ester over an alkyne group was observed in the hydrogenation of an alkynoate for the first time. The catalysts were also active in the depolymerisation reduction of samples of waste poly(ethylene terephthalate) (PET) to produce benzene dimethanol. These depolymerisations were found to be poisoned by the ethylene glycol side product, although good yields could still be achieved. [ABSTRACT FROM AUTHOR]

A series of Ru complexes containing lutidine-derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver-carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. In the presence of tBuOK, the Ru-CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand-assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru-CNC complex 5 e(BF4) is able to add aldimines to the metal-ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer-sphere stepwise hydrogen transfer to the CN bond assisted either by the pincer ligand or a second coordinated H2 molecule. [ABSTRACT FROM AUTHOR]

A series of tunable G0-G3 dendritic 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β-ketoesters, α-ketoesters, and α-ketoamides to reveal the effects of dendron size on the catalytic properties. The second- and third-generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first-generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second-generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity. [ABSTRACT FROM AUTHOR]

The synergy of push-pull substitution and enlarged ligand bite angles has been used in functionalized heteroleptic bis(tridentate) polypyridine complexes of ruthenium(II) to shift the 1MLCT absorption and the 3MLCT emission to lower energy, enhance the emission quantum yield, and to prolong the 3MLCT excited-state lifetime. In these complexes, that is, [Ru(ddpd)(EtOOC-tpy)][PF6]2, [Ru(ddpd-NH2)(EtOOC-tpy)][PF6]2, [Ru(ddpd){(MeOOC)3-tpy}][PF6]2, and [Ru(ddpd-NH2){(EtOOC)3-tpy}][PF6]2 the combination of the electron-accepting 2,2′;6′,2′′-terpyridine (tpy) ligand equipped with one or three COOR substituents with the electron-donating N, N′-dimethyl- N, N′-dipyridin-2-ylpyridine-2,6-diamine (ddpd) ligand decorated with none or one NH2 group enforces spatially separated and orthogonal frontier orbitals with a small HOMO-LUMO gap resulting in low-energy 1MLCT and 3MLCT states. The extended bite angle of the ddpd ligand increases the ligand field splitting and pushes the deactivating 3MC state to higher energy. The properties of the new isomerically pure mixed ligand complexes have been studied by using electrochemistry, UV/Vis absorption spectroscopy, static and time-resolved luminescence spectroscopy, and transient absorption spectroscopy. The experimental data were rationalized by using density functional calculations on differently charged species (charge n=0-4) and on triplet excited states (3MLCT and 3MC) as well as by time-dependent density functional calculations (excited singlet states). [ABSTRACT FROM AUTHOR]