Thomas Scheiring

Structures and spectroelectrochemistry (UV–vis, IR, EPR) of complexes [(OC)3ClRe]n(abpy), n=1, 2; abpy=2,2′-azobispyridine

Abstract 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 A 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) A. The azo bond lengths at 1.272(9) (1) and 1.304(10) A (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.

Cyclooctadienemethylplatinum complexes: synthesis, reactivity, molecular structure and spectroscopic properties of the organometallic hydroxoplatinum(II) complex ((COD)PtMe(OH))

Abstract Organometallic complexes of the type [(COD)PtMeL] (COD˚1,5-cyclooctadiene, L˚Cl, I, OH, Me, CH 2 C(O)CH 3 , C C Ph, pyridine, N -methyl pyrazinium) and the dinuclear complex [{(COD)PtMe} 2 (m-C C C C)] were prepared and charac-terised by 1 H-NMR spectroscopy. The crystal structures for the complexes with L˚Cl, OH and Me are reported. The complex[(COD)PtMe(OH)] is a unique example of a platinum complex containing an olefin and a hydroxy ligand on the same metalcentre. It reacts with C H acidic substrates to form Pt C bonds. Representative reactions with acetone, phenylacetylene and1,3-butadiyne and the corresponding products are reported.

The valence-localized decacyanodiruthenium(III,II) analogue of the Creutz–Taube ion. Completing the full d5/d6 triad [(NC)5M(μ-pz)M(CN)5]5−, M=Fe,Ru,Os; pz=pyrazine

Abstract The new ruthenium(II) complex ion [(NC) 5 Ru(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) 5 Ru(μ-pz)Ru(CN) 5 ] 5− is distinguished by less negative redox potentials, a smaller comproportionation constant K c of only 10 4.7 , a very broad (Δ ν 1/2 =4200 cm −1 ) symmetrical IVCT band at 1760 nm ( e =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.

Allylferrocenylselenide and the synthesis of the first seleno-substituted allenylidene complex: synthesis, spectroscopy, electrochemistry and the effect of electron transfer from the ferrocenylselenyl subunit

Abstract 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.

Electronic structure of radical anionic binuclear organoplatinum complexes. A multiple frequency EPR investigation

The dinuclear organoplatinum compounds RnPt(µ-BL)PtRn (R = Me = methyl, n = 2,4; R = Mes = mesityl, n = 2; µ-BL = the bridging ligands 2,2′-bipyrimidine (bpym), 2,5-bis(1-phenyliminoethyl)pyrazine (bpip) or 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) undergo reversible one-electron reductions to yield the corresponding radical anions [RnPt(µ-BL)PtRn]˙− The chemically or electrochemically reduced species were studied by continuous wave EPR spectroscopy at various microwave frequencies (4–34 GHz). With one exception, only a single broad line is observed in fluid solution at ambient temperatures and X-band. Measurements on glassy frozen solutions at 110 K at S-, X-, K- or Q-band reveal not only all the three g-values for the rhombic spectra but also most of the hyperfine coupling constants to the 195Pt nuclei and also to two 1H nuclei of the bridging ligand when µ-BL = bpym. Density functional–Hartree–Fock (DFT–HF) molecular orbital calculations show the singly occupied molecular orbital in each case to be predominantly bridging-ligand based, in good agreement with the magnitudes of the observed 195Pt hyperfine coupling constants. The molecular structure of the free ligand 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) was determined by X-ray crystallography to serve as a basis for the calculations.

Metallorganische Komplexkationen [(ηn-CnR′n M(RN=CH–CH=NR)Cl]+ von 1,4-Diazabutadienen (M = Os und n = 6 oder M = Rh, Ir und n = 5, R = 2,6-Dialkylphenyl). Strukturen und Reduktion zu den Neutralverbindungen [(ηn-CnR′n)M(RN–CH=CH–NR)]

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 fuhrt uber einen ECE-Prozess zu den teilweise auch praparativ isolierbaren Neutralverbindungen [(CnR′n)M(RN–CH=CH–NR)], deren Bestandigkeit trotz verringerter Koordinationszahl uber die axiale Abschirmung durch die 2,6-Dialkylphenylsubstituenten gewahrleistet ist und die sich als 16-Valenzelektronenspezies beschreiben lassen.

Geometrical and electronic structures of the acetyl complex Re(bpy)(CO)3(COCH3) and of [M(bpy)(CO)4](OTf), M=Mn,Re

The compound fac -Re(bpy)(CO) 3 (COCH 3 ) ( 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) A) and a long ReC(acetyl) bond (2.245(12) A) and an orientation of the ReC(O)CH 3 plane parallel to the C 2 axis of the coordinated bpy. The result is an orthogonal arrangement of d xz /π*(bpy) and d xy /π*(acetyl) orbitals. This situation stands in distinct contrast to the structure reported for the complex salt [Re(L)(CO) 3 (COCH 3 )](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.

Copper(I) and copper(II) complexes of the bidentate imidazole/thioether ligand 1-methyl-2-(methylthiomethyl)-1H-benzimidazole

Abstract The mixed imidazole/thioether chelate ligand 1-methyl-2-(methylthiomethyl)-1H-benzimidazole (mmb) which has been shown earlier to effect biomimicking valence tautomerism in copper/o-quinone systems forms crystallographically characterized chelate complexes [(η2-mmb)CuI(PPh3)2](BF4) (1) and [(η2-mmb)2CuII(η1-ClO4)](ClO4) (2). Compound 1 contains copper(I) in an approximately tetrahedral environment and complex 2, obtained as methanol solvate, exhibits an asymmetrically (trigonal bipyramidal/square pyramidal) coordinated CuII center. Whereas bidentate mmb forms shorter N–CuII (1.945 A) than N–CuI bonds (2.040 A), the S(thioether)–Cu bond lengths of about 2.43 A are independent of the metal oxidation state. Two relatively simple ligands mmb can effect similar spectroscopic responses as more complicated multidentate ligands.

Synthesis, Structures, Ligand Substitution Reactions, and Electrochemistry of the Nitrile Complexes cis‐[Ru(dppm)2Cl(NCR)]+ PF6– (dppm = Bis(diphenylphosphino)methane, R = CH3, C2H5, tBu, Ph)

Isomerically pure nitrile complexes cis-[Ru(dppm)2Cl(NCR)]+ (2 a–d) are formed upon chloride displacement from cis-[Ru(dppm)2Cl2] (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)2Cl(CNtBu)]+ slowly isomerizes to the trans from. The solid state structures of the CH3CN, C2H5CN and the trans-tBuNC complexes were established by X-ray crystallography. Electrochemical investigations of the nitrile complexes 2 a–d show in addition to a chemically reversible one-electron oxidation an irrversible reduction step. In CH2Cl2 solution, cis- and trans-[Ru(dppm)2Cl2] have been identified as the final products of the electrochemically induced reaction sequence. Synthese, Strukturen, Ligandenaustauschreaktionen und Elektrochemisches Verhalten der Nitrilkomplexe cis-[Ru(dppm)2Cl(NCR)]+ PF6– (dppm = Bis(diphenylphosphino)methan, R = CH3, C2H5, tBu, Ph) Isomerenreine Nitrilkomplexe cis-[Ru(dppm)2Cl(NCR)]+ (2 a–d) sind, ausgehend von cis-[Ru(dppm)2Cl2] (1), durch Chloridaustausch oder durch Substitution des Acetonitrilliganden von 2 a in einfacher Weise zuganglich. Die zweite Methode erlaubt auch die Einfuhrung von Pyridin- (3 a,b), Amin- (4) oder Isonitrilliganden (5), wobei die Substitutionsprodukte als konfigurationsstabile cis-Isomere erhalten werden. Lediglich im Falle von cis-[Ru(dppm)2Cl(CNtBu)]+ tritt Isomerisierung zur trans-Form ein. Die Strukturen der Komplexkationen im CH3CN-, C2H5CN- und im trans-tBuNC-Komplex wurden zusatzlich durch Rontgenbeugung bestimmt. Elektrochemische Untersuchungen an den Nitrilkomplexen 2 a–d zeigen neben einer chemisch reversiblen Einelektronenoxidation einen chemisch jeweils irreversiblen Reduktionsschritt. In CH2Cl2-Losung konnten cis- und trans-[Ru(dppm)2Cl2] als Folgeprodukte der elektrochemisch initiierten Reaktionssequenz identifiziert werden.

Structures and properties of complexes [MCl(C5Me5)(N∧S)](PF6), M=Rh, Ir, with N∧S=1-methyl-2-(alkylthiomethyl)-1H-benzimidazole ligands

Abstract 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 A) and shorter M–N bonds (ca. 2.09 A) 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.