Osmium complexes protonation

The preparation of two cyclo-octatetraene-gold complexes, (ct)AuCl and (cot)-AU2CI4, has been reported. The structures of biscyclo-octatetraenyl complexes of titanium, vanadium, thallium, and uranium, were deduced from their i.r. spectra. Protonation of (p-cyclo-octatetraene) (p-cyclopentadienyl) complexes has been studied. For the ruthenium and osmium complexes protonation occurs on the eight-membered ring to give CgH moiety co-ordinated to the metal atom via both an T -alkyl and an olefin-metal bond. For the cobalt and rhodium complexes a bicyclic cation (287) is produced which undergoes isomerization to the monocyclic (288). ... 

The infrared, NMR, and electronic absorption spectra of the two complexes H2FeRu2Os(CO)i3 and H2FeRuOs2(CO)13 have been taken to indicate a structure for these compounds similar to H2FeRu3(CO)13. However, the infrared and low-temperature proton NMR spectra of both compounds indicate that they exist as a mixture of isomers the two projected isomers for H2FeRu2Os(CO)13 are shown in Fig. 58 (247). The mixed manganese and rhenium-osmium complexes, H3MOs3(CO)13, have been prepared by acidification of the reaction mix-... 

Figure 2.5 Schematic representation of the Au/MPS/PAH-Os/solution interface modeled in Refs. [118-120] using the molecular theory for modified polyelectrolyte electrodes described in Section 2.5. The red arrows indicate the chemical equilibria considered by the theory. The redox polymer, PAH-Os (see Figure 2.4), is divided into the poly(allyl-amine) backbone (depicted as blue and light blue solid lines) and the pyridine-bipyridine osmium complexes. Each osmium complex is in redox equilibrium with the gold substrate and, dependingon its potential, can be in an oxidized Os(lll) (red spheres) or in a reduced Os(ll) (blue sphere) state. The allyl-amine units can be in a positively charged protonated state (plus signs on the polymer...

Proton nuclear magnetic resonance (NMR) is a widely used tool for researching biomolecules. Although much too detailed to report here, Zai-Wei La and Henry Taube (Stanford University) reported in 1992 that they have had success in analyzing for certain molecules by using a clihydrogen osmium complex on a versatile 1H NMR recognition probe. 

Comproportionation between cA-RuIV(bpy)2(py)02 + and cis- Run(bpy)2(py)(H20)2+ takes place by proton-coupled electron transfer (PCET) and exhibits a KIE of 16.1. Other PCET reactions of these and related ruthenium and osmium complexes also feature large KIEs. For example, oxidations of H202 by RuIV(bpy)2 (py)O2 + and by Ruin(bpy)2(py)OH2 + have KIEs of22.1 and 16.7, respectively. Oxidation of benzyl... 

The synthesis and chemistry of an 7] -selenophene osmium complex 50 has been studied <19990M1559>. Protonation and electrophilic substitution with acetaldehyde diethyl acetal occurred at C-2. Methylation of complex 50 with methyl triflate gave 51 which upon treatment with tetrabutylammonium borohydride (TBAB) led to the selenophene ring-opened complex 52 (Scheme 5). 

Friedel-Crafts reactions. The reaction of osmium-complexed anisoles with electrophiles such as enones is catalyzed by TfOH. Benzylation of arenes by a reductive alkylation with arenecarbaldehyde acetals involves an intramolecular redox process (hydride shift) after protonation of the benzylic ether intermediates. 

Although C4 addition occurs with phenol complexes even for cases where C4 is substituted, in many cases, ortho addition is thermodynamically favored. In this scenario, the regiochemistry can be effectively controlled by adjusting reaction variables such as temperature, time, and catalyst [44]. Under basic conditions, the active form of the phenol complex is the phenoxide species, which can undergo reversible Michael reactions at C4 and C2, provided that the resulting enolate is not protonated. For instance, the addition of MVK to the osmium complexes of para-cresol (31) or estradiol (27, Fig. 8) occurs at C4 to give the 4H-phenol product (28,32) at -40 °C with an amine base. However, if the reaction is carried out at 20 °C or is run in the presence of a Zn " co-catalyst, the initially formed enolate may undergo retroaddition, and ultimately, the reaction yields the orthoalkylated product (30,33 see Fig. 8). Electrophilic addition at the ortho... 

The pattern of chemical reactions observed for these compounds clearly sets them apart from "Fischer-type" carbyne complexes of GroupVI e.g., W(hCR)X(CO)4. Whereas the "Fischer-type" complexes typically react with nucleophiles at the carbyne carbon all of the reactions observed for the five coordinate mthenium and osmium complexes, including the cationic examples, are electrophilic additions to the MsC bond. The following sections deal individually with, protonation, addition of halides of the coinage metals, addition of chlorine and chalcogens, and finally an attempted nucleophilic addition where the nucleophile is directed to a remote site on the aryl ring of the carbyne substituent. 

Two lelH redox systems have been attached to SAMs, and full studies of the kinetics as a funchon of electrolyte pH have been performed [248-250]. The data were compared to the predictions of the stepwise mechanism. In this mechanism, electron and proton transfers are separate steps and proton transfer is treated as an equilibrium [251, 252]. With the inclusion of a potential-dependent transfer coefficient [253], two testable predictions can be made. A plot of logfA ) versus pH has a V shape, and a plot of afO) (the transfer coefficient at the formal potential) versus pH oscillates about 0.5. These predictions are consistent with kinetic data collected for a SAM with an attached galvi-nol (a phenol-hke redox molecule) at pHs greater than 8 [248, 249]. However, the data obtained for an osmium complex ([Os "/"(bpy)2(py)(L)], L = OH or H2O) deviate substantially from the predictions. The plot of hi(A ) versus pH is much less dependent on pH than expected, and the... 

The protonation of the iron-hydride complex [Fe Cp(PMe3)2(H)] leads to the H2 complex [Fe Cp(PMe3)2(H2)]+, because the iron atom in the starting complex is relatively electron poor, and the oxidation state Fe is much more favorable than Fe. On the other hand, the protonation of the osmium complex leads to the protonation of that is an electron-rich metal center, i.e. the oxidative addition occurs to yield the dihydride [Os Cp(PMe3)2(H)2], the oxidation state Os being much more common than Fe. ... 

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. ... 

The porphyrin ligands in the diamagnetic ruthenium and osmium carbene complexes generally exhibit four-fold symmetry by NMR, indicating that the barrier to rotation about the M=C bond is low. The carbenoid protons appear shifted down-field in the H NMR spectra, for example appearing for Ru(TTP)=CHC02Et and Ru(TTP)=CHSiMc3 at 13.43 and 19.44 ppm, respectively, and for the osmium... 

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. 

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