Martina Bubrin

Identifying Intermediates of Sequential Electron and Hydrogen Loss from a Dicarbonylcobalt Hydride Complex

Coordination compounds of cobalt have recently received special attention in the context of hydrogen production (“splitting water with cobalt”) and conversion. Within these studies the mechanistic sequence of electron and proton or hydrogen transfer has frequently been discussed. Although cobalt carbonyl hydrides, especially [Co(CO)4H] have been the subject of many studies since their development by Hieber and co-workers in the 1930s and since their use in hydroformylation processes, the hydrogen-producing reactions were mainly reported with non-organometallic cobalt complexes, involving ligands such as oligodentate imines, glyoximes, phosphanes, and macrocycles. Herein we describe the synthesis and characterization of the first dicarbonylhydridocobalt complex [Co(CO)2(dippf)H] = [(1)H] with a 1,1’-diphosphinoferrocene ligand (dippf = 1,1’-bis(diisopropylphosphino)ferrocene) and its chemical and (spectro)electrochemical oxidation via [(1)H] to the structurally characterized product [Co(CO)2(dippf)] + = [(1)], which has formally lost a hydrogen atom and can be reduced to a Co species [(1)] (Scheme 1). In contrast to the above-mentioned complexes, in our series the presence of CO ligands makes it possible to monitor several intermediates by IR spectroelectrochemistry. The family of 1,1’-bis(diorganophosphino)ferrocene ligands has been widely used in catalysis and for functional molecular materials; these ligands can also be considered as redox noninnocent due to the reversible oxidation of the ferrocene framework. For instance, it was shown that the assignment of the oxidation site in ambivalent [FeRu] heterobimetallic complexes involving 1,1’-bis(diorganophosphino)ferrocene ligands is not trivial. Reaction of [Co(CO)4H] with dippf leads to compound [(1)H]. In addition to the H and P NMR spectroscopy the crystal structure analysis (Figure 1A, Table 1) confirms the configuration with one metal–hydride bond (at a disordered position) pointing toward the inside—probably a result of the steric crowding from the PiPr2 groups at the outside. Both hydride positions (at half occupancy) were thus found crystallographically as capping the approximately tetrahedral CuP2C2 coordination core. DFT calculations confirm the experimental structure as a stable arrangement (Table 1, see also Figure S1 in the Supporting Information). Cyclic voltammetry at ambient temperature (Figure 2A) and at 50 8C in CH2Cl2 (Figure S2) showed an oxidation of

Electronic, charge and magnetic interactions in three-centre systems

Three-centre systems [QCuQ]n containing electron transfer-active and donor-substituted o-iminoquinone ligands were synthesised and studied as models for electronic, charge and magnetic coupling within materials involving coordinative bonding. The neutral precursors (n = 0) involve spin-bearing semiquinone radical ions, Q˙−, bridged by paramagnetic copper(II). Crystal structures and electron paramagnetic resonance (EPR) measurements reveal a delicate sensitivity of structures and of spin–spin coupling in these three-centre configurations, depending on weak secondary interactions involving substituents at the coordinatively ambivalent (hemilabile) ligands Q×. Stepwise electron loss or uptake by [QCuQ]n is accompanied by considerable redox potential splitting and by spectroelectrochemically monitored change of UV-Vis-NIR absorption. Whereas the monoanions exhibit long-wavelength ligand-to-ligand intervalence charge transfer bands around 2000 nm for π(Q2−) → π*(Q˙−) transitions, the monocations are formed in a reorganisation step, achieving coordinative saturation at the metal. Weak secondary interactions are thus shown to be sufficient to cause significant structural changes as well as qualitative differences in spin–spin interaction and in excited state structures.

Ruthenium(IV)–Bis(methallyl) Complexes as UV-Latent Initiators for Ring-Opening Metathesis Polymerization

The RuIV‐based transition metal catalysts [Ru(η3:η3‐C10H16)Cl2(PPh3)] (1), [Ru(η3:η3‐C10H16)Cl2(PCy3)] (2), and [Ru(η3:η3‐C10H16)(CF3COO)2(PPh3)] (3) have been synthesized and investigated for their use as initiators in the thermally and photo‐initiated ring‐opening metathesis polymerization (photo‐ROMP) of norborn‐2‐ene (NBE). Compounds 1 and 3 display significant photo‐ROMP activity with NBE whereas compound 2, although active in the ROMP of NBE, shows virtually no latency at all. The results are discussed with respect to the structural features of the novel catalysts.

Discovering More Non‐Innocence: Triazenido versus Triazenyl Radical Ligand Function, and a Comment on [NO2]n as a “Suspect” Ligand

The unusual suspects: Depending on co-ligands L(n) and the effects of substituents (R), the well-known triazenides [N(NR)2](-) may act as EPR detectable coordinated triazenyl ligands, [N(NR)2](·). They are thus new non-innocent ligands and are related to the hitherto unused non-innocent nitrogen dioxide ligand, [NO2](·).

Metal‐Induced Thiophene Ring Opening and CC Bond Formation To Produce Unique Hexa‐1,3,5‐trienediyl‐Coupled Non‐Innocent Ligand Chelates

Ring opening of thiophenes containing an azo function in 2-position and subsequent dimerization through C-C coupling were observed on reaction with [Ru(acac)2 (CH3 CN)2 ] (acac=acetylacetonate) to produce two 1,3,5-hexatriene-linked redox-active azothiocarbonyl chelate systems. Interaction of the non-innocent chelate ligands and of the metals at a nanoscale distance of 1.45 nm via the conjugated hexatriene bridge was studied by magnetic and electron spectroscopic measurements in conjunction with DFT calculations, revealing four-center magnetic interactions of this unique setting and weak intervalence coupling after reduction.

Near IR Absorbing Organometallic Diruthenium Complex Intermediates: Evidence for Bridging Anthrasemiquinone Formation and against Mixed Valency

The new redox-active complexes [RuH(CO)(EPh3 )2 (μ-Q2- )RuH(CO)(EPh3 )2 ], E=P (1) and E=As (2) with the bis-chelate bridging ligand Q2- =1,4-dioxido-9,10-anthraquinone were prepared and characterised. The related compound [RuCl(CO)(PPh3 )2 (μ-Qx2- )RuCl(CO)(PPh3 )2 ] (4) with E=P and Qx2- =5,8-dioxido-1,4-naphthoquinone 4 revealed trans-positioned PPh3 groups. The electrogenerated one-electron oxidised states 1+ and 2+ were examined using spectroelectrochemical techniques (EPR, IR and UV/Vis/NIR). In situ EPR studies gave spectra with 31 P or 75 As hyperfine splitting of about 16 Gauss, small 99, 101 Ru coupling and small g-anisotropy in the frozen solution state. The 31 P and 75 As hyperfine values reflect axial positioning of the four Ru-E bonds relative to the plane of an anthrasemiquinone bridge. Single CO stretching bands around 1910 cm-1 of the precursors 1 and 2 shift by about 25 cm-1 to higher energies on oxidation. The direction, uniformity and the extent of the shifts confirm ligand bridge-based oxidation. Absorbance by the cations in the near infrared region is thus assigned to intra-ligand transitions of ruthenium(II)-bonded anthrasemiquinones and not to intervalence charge transfer of mixed-valent species. Ruthenium(II) stabilisation by CO and EPh3 is made responsible for the anthrasemiquinone formation instead of metal-centered oxidation.

Metal carbonyl complexes of potentially ambidentate 2,1,3-benzothiadiazole and 2,1,3-benzoselenadiazole acceptors

Abstract The compounds [W(CO)5(btd)], [W(CO)5(bsd] and [Re(CO)3(bpy)(bsd)](BF4), btd=2,1,3-benzothiadiazole and bsd=2,1,3-benzoselenadiazole were isolated and characterized experimentally (crystal structure, spectroscopy, spectroelectrochemistry) and by density functional theory calculations. The results confirm single N-coordination in all cases, binding to Se was calculated to be less favorable. Studies of one-electron reduced forms indicate that the N-coordination is maintained during electron transfer.

New saccharinate complexes with 3,3′-azobispyridine ligand: synthesis, characterization, and spectroscopic properties

Abstract The new metal complexes with saccharinate (sac) and 3,3′-azobispyridine (3,3′-abpy), [Ni(H2O)4(3,3′-abpy)2](sac)2 (1), [Cu(sac)2(H2O)(μ-3,3′-abpy)]n (2), [Zn(H2O)4(3,3′-abpy)2](sac)2 (3), [Cd(sac)2(H2O)2(μ-3,3′-abpy)]n (4), and [Hg2(μ-sac)2(sac)2(μ-3,3′-abpy)(3,3′-abpy)2]n (5), were synthesized and characterized by IR spectra, elemental analysis, and single-crystal X-ray diffraction. Spectroscopic (UV–vis and photoluminescence) and thermal properties were also investigated. Single-crystal X-ray analysis reveals that Ni(II) and Zn(II) are coordinated by four aqua ligands and two nitrogens of 3,3′-abpy, while sac is a counter-ion in 1 and 3. In 2, Cu(II) and all ligands are linked by coordination bonds and 3,3′-abpy ligands connect the Cu(II) centers forming a 1-D coordination polymer. In 4, sac N-coordinated to Cd(II) and distorted octahedral geometry of Cd(II) ion is completed by two aqua and bridging 3,3′-abpy ligands. In 5, sac bridges two Hg(II) ions to generate dinuclear [Hg2(μ-sac)2] units. These dinuclear units are connected by 3,3′-abpy to form a 1-D coordination polymer. The photoluminescence spectra of 3 and 5 show blue fluorescent emission bands, and these emissions can probably be assigned to intraligand fluorescent emissions. Thermal decompositions of the compounds are also discussed. For all complexes, magnetic susceptibility measurements show expected magnetic behavior.

Tetra-μ3-iodido-tetra­kis­[(tri-n-butyl­phosphane-κP)copper(I)]

The title complex, [Cu4I4(C12H27P)4], crystallizes with six molecules in the unit cell and with three independent one-third molecule fragments, completed by application of the relevant symmetry operators, in the asymmetric unit. The tetranuclear copper core shows a tetrahedral geometry (site symmetry 3..). The I atoms also form a tetrahedron, with I⋯I distances of 4.471 (1) Å. Both tetrahedra show an orientation similar to that of a pair of self-dual platonic bodies. The edges of the I-tetrahedral structure are capped to the face centers of the Cu-tetrahedron and vice versa. The Cuface⋯I distances are 2.18 Å (averaged) and the Iface⋯Cu distances are 0.78 Å (averaged). As a geometric consequence of these properties there are eight distorted trigonal–bipyramidal polyhedra evident, wherein each trigonal face builds up the equatorial site and the opposite Cu⋯I positions form the axial site. As expected, the n-butyl moieties are highly flexible, resulting in large elongations of their anisotropic displacement parameters. Some C atoms of the n-butyl groups were needed to fix alternative discrete disordered positions.

Tetra-μ3-iodido-tetrakis[(tri-n-butylphosphane-κP)copper(I)]

Tetrameric phosphane complexes of copper(I) halides are extensively used as reagents for copper-mediated conjugate additions. Furthermore, theoretical interest stems from the fact that all group 11 elements in the oxidation state +1 are prone to form clusters with potential metal-metal distances. Thus, theoretical work on such complexes (XCuPR3)4 has been carried out to study structures and stabilities in detail. However, the plethora of structural information on these compounds came from X-ray crystal structure analyses. Although the known tri-n-butyl phosphane complex [n-Bu3PCuI]4 had already been characterized by using X-ray crystallography, no atomic coordinates, bond lengths or bond angles were reported. Thus, we reinvestigated the crystal structure of [n-Bu3PCuI]4. We were able to confirm the previously postulated tetrameric complex with a distorted heterocubane structure similar to the AsEt3 derivative.