cis-[RuCI2(depehl (1) (depe = Et2PC2H4PEt2) is obtained in excellent yield and high isomeric purity by the reaction of [RuCliDMSO)41 with two equivalents of depe in acetone 01" ethyl acetate under reflux conditions. One of the chloride ligands is labile and readily displaced by CH3CN to afford the cationic monosubstitution product cis-[RuCl(CH3CN)(depe)21 +(2), which was isolated as the PF 6 salt. The X-ray cl"ystal structure of 1 was determined. The redox properties of 1 and 2 as weil as the chloride displacement from 1 by CH3CN were studied by cyclic and square wave voltammetry KeYlVords: Ruthenium; Nitrile complexes; Electrochemistry; X-ray analysis

The widely used ligand 2,3-bppz = 2,3-bis(2-pyridyl)pyrazine and the complexes [(2,3-bppz){(C5Me5)ClM}(11)](PF6)(n), M = Rh or Ir and n = 1 or 2, were investigated by cyclic voltammetry and UV/VIS-spectroelectrochemistry. For both the mononuclear and, unusually, the dinuclear complexes we observed only chloride-dissociative two-electron reduction processes. One of the precursor complexes, [(2,3-bppz)(C5Me5)ClIr]Cl.2H(2)O, was structurally characterized and found to contain a considerably nonplanar 2,3-bppz ligand.

The title compounds are easily reduced to paramagnetic neutral species [(C5Me5)ClM(μ-L)Re(CO)3X] which were characterized as complexes of L−. On further electron addition the M-bound chloride is dissociated slowly to yield [(C5Me5)M(μ-L)Re(CO)3X], distinguished by intense low-energy charge transfer bands. Addition of a third electron causes this band to shift and diminish in intensity. Cyclic voltammetry, UV–Vis–NIR and IR spectroelectrochemistry as well as EPR at 9.5 and 285 GHz were used to establish the (E, EC, E) process sequence of electroreduction and to identify the products. The significance of these results for potential applications in catalysis is discussed.

Heterozweikernige Komplexverbindungen [(OC)3ClRe(μ-L)MCl(C5Me5)](PF6), M = Rh oder Ir und L = 2, 5-Bis(1-phenyliminoethyl)pyrazin (bpip), 3, 6-Bis(2-pyridyl)-1, 2, 4, 5-tetrazin (bptz) oder 2, 2′-Bipyrimidin (bpym) wurden ausgehend von einkernigen Rhenium-Komplexen (L)Re(CO)3Cl synthetisiert. Die stufenweise reduktive Aktivierung unter Chlorid-Dissoziation wurde durch cyclische Voltammetrie und Spektroelektrochemie im Bereich der CO-Streckschwingungen (IR), Charge-Transfer-Absorptionen (UV/Vis) und Elektronenspinresonanz (ESR) bei paramagnetischen Zwischenprodukten der ein- und zweikernigen Verbindungen untersucht. Wahrend fur Komplexe des bpip und bptz radikalische Einelektronenzwischenstufen [(OC)3ClRe(μ-L)MCl(C5Me5)]˙ nachgewiesen wurden, reagieren die Komplexe mit bpym unter MCl-dissoziativer Zweielektronenreduktion direkt zu den Verbindungen [(OC)3ClRe(μ-L)M(C5Me5)]. The Conjugative Bridging of Organometallic Reaction Centers in Heterodinuclear Complexes [(OC)3ClRe(μ-L)MCl(C5Me5)]+, M = Rh or Ir - Spectroscopic Consequences of Reductive Activation Heterodinuclear complexes [(OC)3ClRe(μ-L)MCl(C5Me5)](PF6), M = Rh or Ir and L = 2, 5-bis(1-phenyliminoethyl)pyrazine (bpip), 3, 6-bis(2-pyridyl)-1, 2, 4, 5-tetrazine (bptz) or 2, 2′-bipyrimidine (bpym), were synthesized via mononuclear rhenium compounds (L)Re(CO)3Cl. The stepwise reductive activation under chloride dissociation was studied through cyclic voltammetry and spectroelectrochemistry in the range of CO stretching vibrations (IR), charge transfer absorptions (UV/Vis) and electron spin resonance (ESR) for paramagnetic intermediates of the mono- and heterodinuclear compounds. While complexes of bpip and bptz form one-electron reduced radical intermediates [(OC)3ClRe(μ-L)MCl(C5Me5)]˙, the compounds with bpym react under MCl-dissociative two-electron reduction directly to [(OC)3ClRe(μ-L)M(C5Me5)].

The new complexes (RN=CH-CH=NR)Co(NO)(CO), R = isopropyl (1), 2,6-diisopropylphenyl (2) and p-tolyl (3), were synthesized and spectroscopically characterized. Compounds I and 2 could be crystallized for X-ray structure analysis, CO/NO disorder was observed for 1. The results indicate a negligible amount of charge transfer from the Co(NO)(CO) moiety to the 1,4-diaza-butadiene acceptor ligands in the ground state, in agreement with DFT calculations on I and as similarly reported for related 1,4-diaza-1,3-butadiene complexes of Ni(CO)(2) and Fe(NO)(2).

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Die Titelverbindungen mit d6-konfiguriertem Osmium(II), Rhodium(III) oder Iridium(III) wurden isoliert und UV/Vis- sowie 1H-NMR-spektroskopisch charakterisiert. Kristallstrukturanalysen von 1,4-Bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadien (Dipp-DAB) und den Komplexen [(η5-C5Me5)Ir(Dipp-DAB)Cl][PF6] und [(η6-C6Me6)Os(Xyl-DAB)Cl][PF6] (Xyl-DAB = 1,4-Bis(2,6dimethylphenyl)-1,4-diaza-1,3-butadien) werden vorgestellt. Elektrochemische Reduktion der Verbindungen führt über einen ECE-Prozess zu den teilweise auch präparativ isolierbaren Neutralverbindungen [(CnR′n)M(RN–CH=CH–NR)], deren Beständigkeit trotz verringerter Koordinationszahl über die axiale Abschirmung durch die 2,6-Dialkylphenylsubstituenten gewährleistet ist und die sich als 16-Valenzelektronenspezies beschreiben lassen. Organometallic Complex Cations [(ηn-CnR′n)M(RN=CH–CH=NR)Cl]+ of 1,4-Diazabutadienes (M = Os and n = 6 or M = Rh, Ir and n = 5, R = 2,6-Dialkylphenyl). Structures and Reduction to Neutral Compounds [(ηn-CnR′n)M(RN–CH=CH–NR)] The title compounds with d6 configurated osmium(II), rhodium(III), or iridium(III) were isolated and characterized by UV/Vis and 1H-NMR spectroscopy. Crystal structure analyses are presented for 1,4-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (Dipp-DAB) and for the complexes [(η5-C5Me5)Ir(Dipp-DAB)Cl][PF6] and [(η6-C6Me6)Os(Xyl-DAB)Cl][PF6] (Xyl-DAB = 1,4-bis(2,6-dimethylphenyl)-1,4-diaza-1,3-butadiene). The electrochemical reduction of the compounds proceeds via an ECE mechanism to neutral 16 valence electron species [(CnR′n)M(RN–CH=CH–NR)], some of which could be isolated despite coordinative unsaturation due to the stabilization through axial shielding by the 2,6-dialkylphenyl substituents.

The g factor components of [(NC)5M(NO)]3- were calculated by relativistic density functional calculations, including spin−orbit coupling. The calculated values are in good agreement with previous (M = Fe) and new experimental results (M = Ru, Os). Spin−orbit coupling effects are particularly strong for the osmium system. Whereas MII−NO• is the most appropriate formulation describing the spin distribution, there is substantial contribution (ca. 25%) from the metal to the singly occupied MO in each case.

Allylferrocenylselenide (2) is prepared from diferrocenyldiselenide (1Se) which was characterized along with its sulfur analog 1S by X-ray structure analysis. In the crystal lattice the packing is determined by 'point-to-face' CH⋯π interactions with close contacts between the CH π donors and cyclopentadienyl rings as the π acceptors. Compound 2 is then used in the trapping of the primary butatrienylidene intermediate trans-[ClRu(dppm)2CCCCH2]+. The isolated product, trans-[Cl(dppm)2RuCCC(SeFc)(C4H7)]+ (3) (Fc=ferrocenyl), represents the first seleno-substituted allenylidene complex to be reported to date. Compound 3 is formed in a sequence involving regioselective addition of the selenium nucleophile to Cγ followed by hetero-Cope-rearrangement of the allyl vinyl substituted SeR3+ cation. Its spectroscopic properties place 3 at an intermediate position between sulfur and arene substituted all-carbon allenylidene complexes of the same metal fragment. The selenoallenylidene complex 3 contains a redox active ferrocenyl substituent attached to the heteroatom giving rise to reversible electrochemistry. ESR spectroscopy proves that electron transfer occurs from this site and its effect on the spectroscopic properties of 3 is probed by combining electrochemistry and IR or UV–vis/NIR spectroscopy by in situ techniques. In contrast, the reversible reduction primarily involves the allenylidene ligand as ascertained by ESR spectroscopy. In situ spectro-electrochemical techniques reveal how the reduction affects the bonding within the unsaturated ligand.

The title compounds with d(6) configurated osmium(II), rhodium(III), or iridium(III) were isolated and characterized by UV/Vis and H-1-NMR spectroscopy. Crystal structure analyses are presented for 1,4-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (Dipp-DAB) and for the complexes [(eta (5)-C5Me5)Ir(Dipp-DAB)Cl] [PF6] and [(eta (6-) C6Me6)Os(Xyl-DAB) Cl] [PF6] (Xyl-DAB = 1,4-bis(2,6-di-methylphenyl)-1,4-diaza-1,3-butadiene). The electrochemical reduction of the compounds proceeds via an ECE mechanism to neutral 16 valence electron species [(CnRn' )M-(RN-CH=CH-NR)], some of which could be isolated despite coordinative unsaturation due to the stabilization through axial shielding by the 2,6-dialkylphenyl substituents.

The title complex contains two organometallic reaction centers which are known to engage in hydride transfer catalysis (Rh) or in CO2 activation (Re), each after reductive elimination of the respective chloride ligand. The bridged heterodinuclear compound has been structurally characterized in the form where the chloride ligands are in cis-configuration relative to the bptz plane. The complex was subjected to cyclic voltammetry and spectro electrochemical reduction to reveal an electrochemically reversible one-electron uptake by the bptz bridge, a rhodium chloride-dissociative second reduction to yield neutral [(eta (5)-C5Me5)Rh(mu -bptz)Re(CO)(3-)Cl], and a quasi-reversible third one-electron reduction.

The four complexes [MCl(C5Me5)(N∧S)](PF6), M=Rh, Ir; N∧S=1-methyl-2-(methylthiomethyl)-1H-benzimidazole (mmb) and 1-methyl-2-(tert-butylthiomethyl)-1H-benzimidazole (mtb) were synthesized and characterized by spectroscopy, electrochemistry and X-ray crystallography (as methanol solvates). The essential coordination features, viz., longer M–S (ca. 2.38 Å) and shorter M–N bonds (ca. 2.09 Å) in five-membered chelate rings are common to all four species. Cyclic voltammetry reveals irreversible two-electron reduction to MI complexes and partially reversible oxidation to IrIV species for [IrCl(C5Me5)(mtb)]+. The results are discussed in comparison with those obtained for α-diimine (N∧N) complexes of the [MCl(C5Me5)]+ fragments.

The compound fac-Re(bpy)(CO)3(COCH3) (1) (bpy=2,2′-bipyridine) with three different kinds of π-acceptor ligands coordinated to rhenium(I) has been investigated by infrared spectroelectrochemistry to reveal the occupation of the π*(bpy) MO on one-electron reduction to 1− with negligible participation of the π-accepting acetyl group. The results are discussed in relation to the spectroscopy (NMR, IR) and the crystal structure analysis of the neutral complex 1, which reveals a short CO(acetyl) (1.157(12) Å) and a long ReC(acetyl) bond (2.245(12) Å) and an orientation of the ReC(O)CH3 plane parallel to the C2 axis of the coordinated bpy. The result is an orthogonal arrangement of dxz/π*(bpy) and dxy/π*(acetyl) orbitals. This situation stands in distinct contrast to the structure reported for the complex salt [Re(L)(CO)3(COCH3)](PPN) (PPN+=bis(triphenylphosphoranylidene)ammonium) with a cyclometallated 2-phenylpyridine ligand L. The crystal structures of the related complexes [M(bpy)(CO)4](OTf), M=Re and Mn, were determined for comparison.

cis-[RuCl2(depe)2] (1) (depe=Et2PC2H4PEt2) is obtained in excellent yield and high isomeric purity by the reaction of [RuCl2(DMSO)4] with two equivalents of depe in acetone or ethyl acetate under reflux conditions. One of the chloride ligands is labile and readily displaced by CH3CN to afford the cationic monosubstitution product cis-[RuCl(CH3CN)(depe)2]+(2), which was isolated as the PF6− salt. The X-ray crystal structure of 1 was determined. The redox properties of 1 and 2 as well as the chloride displacement from 1 by CH3CN were studied by cyclic and square wave voltammetry.

The new ruthenium(II) complex ion [(NC)5Ru(μ-pz)Ru(CN)5]6− has been prepared and studied as the hexakis(tetraethylammonium) salt. Although spectroelectrochemical experiments in dichloromethane were affected by adsorption as they were in other solvents, the compound could be oxidized via two reversible one-electron steps with a mixed-valent pentaanionic intermediate. In comparison with the iron and osmium analogues, the system [(NC)5Ru(μ-pz)Ru(CN)5]5− is distinguished by less negative redox potentials, a smaller comproportionation constant Kc of only 104.7, a very broad (Δν1/2=4200 cm−1) symmetrical IVCT band at 1760 nm (ε=2600 M−1 cm−1) conforming with the Hush model for weakly coupled mixed-valent systems, the absence of an EPR signal even at 3.5 K and the appearance of infrared bands (CN, pyrazine ring vibrations) indicating localized valence on the time scale of 10−12 s. Together with the high MLCT energies these results suggest a weaker metal–pyrazine interaction for the ruthenium system in comparison with the Fe and Os analogues reported previously. In relation to the Creutz–Taube ion, the substitution of ammine ligands by non-innocent cyanide ions attenuates the metal–metal interaction across the π accepting pyrazine bridge.

The complexes (OC)3ClRe(abpy) (1) and [(OC)3ClRe]2(abpy) (2) with abpy=2,2′-azobispyridine were structurally characterized and studied by spectroelectrochemistry in the UV–vis and in the IR carbonyl stretching region. Compound 1 exhibits a s-cis/E/s-trans configurated abpy ligand with metal coordination to one pyridyl and one azo function and one non-bonding ReN interaction at 3.293 Å to the second pyridyl nitrogen atom. The dinuclear complex 2 with two azoimine-coordinated metal centers is distinguished by the trans arrangement of the chloride ligands with respect to the Re2(μ-abpy) plane, the ReRe distance is 5.033(7) Å. The azo bond lengths at 1.272(9) (1) and 1.304(10) Å (2) indicate substantial π back donation from the rhenium(I) centers into the π*(abpy) orbital. Spectroelectrochemistry reveals the successive occupation of the π*(abpy) orbital by electrons; metal-to-ligand charge transfer features are shifted to higher energies and carbonyl stretching bands to lower wavenumbers. The EPR spectra of both radical anion intermediates 1− and 2− are dominated by very similar 185,187Re hyperfine splitting, ruling out a mixed-valent formulation. The second electron uptake is followed by the rapid loss of one chloride, leading to an unsymmetrical species in the dinuclear system.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Isomerically pure nitrile complexes cis-[Ru(dppm)(2)Cl(NCR)](+) (2a-d) are formed upon chloride displacement from cis-[Ru(dppm)(2)Cl-2] (1) or, alternatively, by ligand substitution from the acetonitrile complex 2 a. This latter approach does also allow for the introduction of pyridine (3 a,b), heptamethyldisilazane (4) or isonitrile ligands (5). All complexes are obtained as the configurationally stable cis-isomers. Only cis-[Ru(dppm)(2)Cl((CNBu)-Bu-t)](+) slowly isomerizes to the trans from. The solid state structures of the CH3CN, C2H5CN and the trans-(BuNC)-Bu-t complexes were established by X-ray crystallography. Electrochemical investigations of the nitrile complexes 2a-d show in addition to a chemically reversible one-electron oxidation an irrversible reduction step. In CH2Cl2 solution, cis- and trans-[Ru(dppm)(2)Cl-2] have been identified as the final products of the electrochemically induced reaction sequence.