Hydrogenation of α,β-Unsaturated Carbonyl Compounds over Covalently Heterogenized Ru(II) Diphosphine Complexes on AlPO4-Sepiolite Supports

In this work, the covalent immobilization of two ruthenium(II) complexes, i.e., [RuIICl (bpea){(S)(-)(BINAP)}](BF4), 1, and [RuIICl(bpea)(DPPE)](BF4), 2, where BINAP = 2,2’-bis(diphenylphosphino)-1,1’-binaphthyl and DPPE = 1,2-bis(diphenylphosphino)ethane, have been obtained (AlPO4-Sepiolite@1 and AlPO4-Sepiolite@2) by using a N-tridentate ligand N,N-bis-(2-pyridylmethyl)ethylamine (bpea), linked to an amorphous AlPO4-Sepiolite (20/80) inorganic support. This AlPO4-sepiolite support is able to immobilize the double amount of ruthenium complex (1.65%) than the amorphous AlPO4 (0.89%). Both heterogenized complexes have been assessed as catalysts in the liquid phase hydrogenation of several substrates with carbonyl and/or olefinic double bonds using methanol as solvent, attaining good catalytic activity and high enantioselectivity (99%). The highest Turn Over Number (TON) value (748.6) was obtained over the [RuII Cl (bpea)(DPPE)](BF4) 2 catalyst, although the [RuIICl(bpea){(S)(-)(BINAP)}](BF4) 1 exhibits better reusability. In fact, the [RuIICl(bpea){(S)(-)(BINAP)}](BF4) immobilized on AlPO4-Sepiolite maintained the activity throughout 14 successive runs. Furthermore, some findings on hydrogenation mechanisms of the α,β-unsaturated carbonyl compounds over Ru catalysts have been also obtained.

A broad view on the complexity involved in water oxidation catalysis based on Ru-bpn complexes

A new Ru complex with the formula [Ru(bpn)(pic)₂]Cl₂ (where bpn is 2,2'-bi(1,10-phenanthroline) and pic stands for 4-picoline) (1Cl₂) is synthesized to investigate the true nature of active species involved in the electrochemical and chemical water oxidation mediated by a class of N4 tetradentate equatorial ligands. Comprehensive electrochemical (by using cyclic voltammetry, differential pulse voltammetry, and controlled potential electrolysis), structural (X-ray diffraction analysis), spectroscopic (UV-vis, NMR, and resonance Raman), and kinetic studies are performed. 1²⁺ undergoes a substitution reaction when it is chemically (by using NaIO₄) or electrochemically oxidized to Ru^III, in which picoline is replaced by an hydroxido ligand to produce [Ru(bpn)(pic)(OH)]²⁺ (2²⁺). The former complex is in equilibrium with an oxo-bridged species {[Ru(bpn)(pic)]₂(μ-O)}⁴⁺ (3⁴⁺) which is the major form of the complex in the Ru^III oxidation state. The dimer formation is the rate determining step of the overall oxidation process (k_dimer = 1.35 M^-1 s^-1), which is in line with the electrochemical data at pH = 7 (k_dimer = 1.4 M^-1 s^-1). 3⁴⁺ can be reduced to [Ru(bpn)(pic)(OH₂)]²⁺ (4²⁺), showing a sort of square mechanism. All species generated in situ at pH 7 have been thoroughly characterized by NMR, mass spectrometry, UV-Vis and electrochemical techniques. 1²⁺ and 4²⁺ are also characterized by single crystal X-ray diffraction analysis. Chemical oxidation of 1²⁺ triggered by Ce^IV shows its capability to oxidize water to dioxygen.

A Heterogeneous Ruthenium dmso Complex Supported onto Silica Particles as a Recyclable Catalyst for the Efficient Hydration of Nitriles in Aqueous Medium

In the present work, we describe an efficient method for the covalent anchoring of a Ru-dmso complex onto two types of supports: mesoporous silica particles (SP) and silica coated magnetic particles (MSNP). First, we have prepared and characterized the molecular complexes containing the bidentate pyridylpyrazole ligands pypz-Me and pypz-CH₂COOEt, with the formula [Ru^IICl₂(pypz-R)(dmso)₂] (R = Me, 1; CH₂COOEt, 2). Complex 2 was anchored onto the silica supports, yielding the heterogeneous systems SP@2 and MSNP@2 which were fully characterized by IR, UV-vis, SEM, TEM, TGA, and XPS techniques. Hydration of representative nitriles has been tested with the molecular complexes and their SP@2 and MSNP@2 heterogeneous counterparts, in aqueous medium under neutral conditions. The heterogeneous catalysts display high yields and excellent selectivity values. Both systems can be reused throughout several cycles for benzonitrile and acrylonitrile substrates, without any significant loss in reactivity. The MSNP@2 material can be easily recovered by a magnet, facilitating its reusability.

Ru(ii)-dmso complexes containing azole-based ligands: synthesis, linkage isomerism and catalytic behaviour

Photochemical ligand substitution in acetonitrile and chloroform, together with the kinetics of dmso linkage isomerization, are investigated in new Ru(ii)-dmso complexes that are also active as nitrile hydration catalysts.

Crystal structure of cis,fac-{N,N-bis-[(pyridin-2-yl)meth-yl]methyl-amine-κ(3) N,N',N''}di-chlorido-(dimethyl sulfoxide-κS)ruthenium(II)

The reaction of di-chlorido-tetra-kis-(dimethyl sulfoxide)-ruthen-ium(II) with N,N-bis[(pyridin-2-yl)meth-yl]methyl-amine aff-ords the title complex, [RuCl2(C13H15N3)(C2H6OS)]. The asymmetric unit contains a well-ordered complex mol-ecule. The N,N-bis-[(pyridin-2-yl)meth-yl]methyl-amine (bpma) ligand binds the cation through its two pyridyl N atoms and one aliphatic N atom in a facial manner. The coordination sphere of the low-spin d (6) Ru(II) is distorted octahedral. The dimethyl sulfoxide (dmso) ligand coordinates to the cation through its S atom and is cis to the aliphatic N atom. The two chloride ligands occupy the remaining sites. The bpma ligand is folded with the dihedral angle between the mean planes passing through its two pyridine rings being 64.55 (8)°. The two N-Ru-N bite angles of the ligand at 81.70 (7) and 82.34 (8)° illustrate the distorted octa-hedral coordination geometry of the Ru(II) cation. Two neighboring molecules are weakly associated through mutual intermolecular hydrogen bonding involving the O atom and one of the methyl groups of the dmso ligand. One of the chloride ligands is also weakly hydrogen bonded to a pyridyl H atom of another molecule.

Oxo-bridge scenario behind single-site water-oxidation catalysts

High-oxidation-state decay of mononuclear complexes [RuTB(H2O)](2+) (X(2+), where B = 2,2'-bpy or bpy for X = 1; B = 5,5'-F2-bpy for X = 2; B = 6,6'-F2-bpy for X = 3; T = 2,2':6',2″-terpyridine) oxidized with a large excess of Ce(IV) generates a manifold of polynuclear oxo-bridged complexes. These include the following complexes: (a) dinuclear [TB-Ru(IV)-O-Ru(IV)-(T)(O)OH2](2+) (1-dn(4+)), [TB-Ru(III)-O-Ru(III)-T(MeCN)2](4+) (1-dn-N(4+)), and {[Ru(III)(trpy)(bpy)]2(μ-O)}(4+) (1-dm(4+)); (b) trinuclear {[Ru(III)(trpy)(bpy)(μ-O)]2Ru(IV)(trpy)(H2O)}(ClO4)5(6+) (1-tr(6+)) and {[Ru(III)(trpy)(bpy)(μ-O)]2Ru(IV)(pic)2}(ClO4)4 (1-tr-P(4+), where P is the 2-pyridinecarboxylate anion); and (c) tetranuclear [TB-Ru(III)-O-TRu(IV)(H2O)-O-TRu(IV)(H2O)-O-Ru(III)-TB](8+) (1-tn(8+)), [TB-Ru(III)-O-TRu(IV)(AcO)-O-TRu(IV)(AcO)-O-Ru(III)-TB](6+) (1-tn-Ac(6+)), and [TB-Ru(II)-O-TRu(IV)(MeCN)-O-TRu(IV)(MeCN)-O-Ru(II)-TB](6+) (1-tn-N(6+)). These complexes have been characterized structurally by single-crystal X-ray diffraction analysis, and their structural properties were correlated with their electronic structures. Dinuclear complex 1-dm(4+) has been further characterized by spectroscopic and electrochemical techniques. Addition of excess Ce(IV) to 1-dm(4+) generates dioxygen in a catalytic manner. However, resonance Raman spectroscopy points to the in situ formation of 1-dn(4+) as the active species.