Osmium complexes spectroscopy

NMR spectroscopy (continued) of nickel complexes, 12 305-311 of osmium complexes, 12 276-281... 

A variety of techniques are used to characterize organometallic osmium complexes. Particularly important are X-ray crystallography, for a three-dimensional picture of the placement of atoms within a molecule, NMR spectroscopy ( H, C, P, and Os), for information on the structure and symmetry of ligands in diamagnetic complexes, and IR spectroscopy, for the identification of multiple bonds between osmium and a ligand or within a ligand. Electrochemical studies and photoelectron spectroscopy provide information on the oxidation state of osmium and the relative electron density of the complex. 

The structures of anionic, triple-nuclear osmium and iron cluster catalysts supported on copolymers of styrene and divinylbenzene were analyzed by means of IR spectroscopy. Their catalytic activity during 1-hexene hydroformylation [250] and C5H5NO2 carbonylation [251] were investigated. It was found that isomerization proceeds simultaneously in the presence conventional catalysts. In the absence of moisture, a triple-nuclear osmium complex could be removed from a polymeric support after reaction. This suggests catalytic activity for this complex, particularly in the fixed state. Furthermore, a definite correlation was found to exist between polynuclearity and selectivity of heptanol formation. For iron, however, the cluster structure altered during the course of the reaction. 

Another promising technique based on Raman spectroscopy is SERS. In this technique the molecules to be studied are adsorbed on gold or silver colloidal particles, leading to an impressive amplification of the signal (typically by a factor of 100-1000). This technique was recently employed by Leong and coworkers to localize the osmium complex 55 (Scheme 11.10) adsorbed on gold nanoparticles [152]. This time the amplified t/(CO) peaks of the complex have an intensity sufficient to allow study at concentrations in the micromolar range. 

Unlike the above example, the majority of five-coordinate complexes appear to undergo oxidative-addition reactions in two separate steps. Additions to the bis phosphine complexes of ruthenium(O) (36) and osmium(O) (39) (XIV) are the most thoroughly studied examples of this generalization (see Section IV). The configurations of these complexes have been established by infrared spectroscopy and, in the case of the osmium complex, by X-ray diffraction (72), Addition of an electrophile A" " (for example H+, HgX+, or Br+ from Br2) to the five-coordinate complexes... 

The redox polymers, POs-EA, was polyvinylpyridine partially N-complexed with [osmium bis(bipyridine) chloride]+ 2+ and quaternized with bromoethylamine. The synthesis followed the published procedures (i). The structure and the composition of POs-EA is shown in Fig. 1. The elemental analysis and UV-VIS spectroscopy showed that the repeating unit of the POs-EA had 1.1 ethylamine pendant functions and 1.8 unsubstituted pyridine rings per osmium complexed pyridine. 

The structurally characterized octahedral tetracarbonyl complex m-[Os(GO)4(FSbF5)2] 3 is formed upon fluorination of [OS3GO12] with HF/SbFs. The oxidative fluorination of [M3(GO)i2] with XeF2 in anhydrous HF provides a route to m-[M(GO)4F2] (M = Ru 4a, Os 4b). Both the ruthenium and osmium complexes were characterized by multi-nuclear NMR spectroscopy, along with [M(GO)sF] (M = Ru 5a, Os 5b), mer- and < -[Ru(GO)3F3] 6 and 7, and a range of dinuclear complexes, which were formed as minor products. Removal of the HF solvent in vacuo results in conversion of [M(GO)4F2] to the tetrameric species [ Os(GO)3F2 4]- ... 

Diazoalkanes are u.seful is precursors to ruthenium and osmium alkylidene porphyrin complexes, and have also been investigated in iron porphyrin chemistry. In an attempt to prepare iron porphyrin carbene complexes containing an oxygen atom on the /(-carbon atom of the carbene, the reaction of the diazoketone PhC(0)C(Ni)CH3 with Fe(TpCIPP) was undertaken. A low spin, diamagnetic carbene complex formulated as Fe(TpCIPP)(=C(CH3)C(0)Ph) was identified by U V-visible and fI NMR spectroscopy and elemental analysis. Addition of CF3CO2H to this rapidly produced the protonated N-alkyl porphyrin, and Bit oxidation in the presence of sodium dithionitc gave the iron(II) N-alkyl porphyrin, both reactions evidence for Fe-to-N migration processes. ... 

A ruthenium porphyrin hydride complex was lirst prepared by protonation of the dianion, [Ru(TTP) in THF using benzoic acid or water as the proton source. The diamagnetic complex, formulated as the anionic Ru(If) hydride Ru(TTP)(H )(THF)l , showed by H NMR spectroscopy that the two faces of the porphyrin were not equivalent, and the hydride resonance appeared dramatically shifted upheld to —57.04 ppm. The hydride ligand in the osmium analogue resonates at —66.06 ppm. Reaction of [Ru(TTP)(H)(THF)j with excess benzoic-acid led to loss of the hydride ligand and formation of Ru(TTP)(THF)2. 

We do not know exactly where the hydrogen binds at the active site. We would not expect it to be detectable by X-ray diffraction, even at 0.1 nm resolution. EPR (Van der Zwaan et al. 1985), ENDOR (Fan et al. 1991b) and electron spin-echo envelope modulation (ESEEM) (Chapman et al. 1988) spectroscopy have detected hyperfine interactions with exchangeable hydrous in the NiC state of the [NiFe] hydrogenase, but have not so far located the hydron. It could bind to one or both metal ions, either as a hydride or H2 complex. Transition-metal chemistry provides many examples of hydrides and H2 complexes (see, for example. Bender et al. 1997). These are mostly with higher-mass elements such as osmium or ruthenium, but iron can form them too. In order to stabilize the compounds, carbonyl and phosphine ligands are commonly used (Section 6). 

Monooxo and cis- and trans-6ioxo complexes of ruthenium(VI) and osmium(VI) are known, with the trans-6ioxo species being most common. In general, these complexes are all diamagnetic and are characterized by vibrational spectroscopy and/or X-ray crystallography. One intense metal-0x0 stretch is usually observed for monooxo and trans-dioxo complexes while two metal-oxo stretches, j/s(M(0)2) and J/as(M(0)2), are found for the cw-dioxo species in the IR spectra. The structural and vibrational data are listed in Table 4. 

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