Complexes isolation and characterization

SCHEME 2.12 o-QM metal complexes isolated and characterized by X-ray diffraction, which structures have been used as a validation for DFT calculations. 

Thiols like pyridine-2-thiol yield (carbene)gold thiolates, and onium salts give cationic (carbene)gold ylide complexes, isolated and characterized as the perchlorates.170 The reaction of dithiocatechol with (cyclohexylisocya-nide)gold chloride affords a carbene complex [(CyNC)AuC(NHCy)2]+Cl-, which co-crystallizes with a neutral tetranuclear complex [(CyNCAu)2Au2(S2C6H4)2].224... 

The intermediate formation of alkyl peroxide complexes has been postulated, and in several cases observed with spectroscopic and spectrometric techniques in several selective procedures based on metal catalyzed oxidation with hydroperoxides, Ti and V ions being among the transition metals most widely used for this purpose. However, to date the few examples of alkyl peroxide complexes isolated and characterized in the solid state refer to (dipic)V0(00Bu-f)(H20) 8, synthesized by Mimoun and coworkers in 1983, and to a dimeric Ti complex [((/7 -OOBu-f)titanatrane)2(CH2Cl2)3] 9, synthesized by Boche and coworkers. ... 

The modem era of biochemistry and molecular biology has been shaped not least by the isolation and characterization of individual molecules. Recently, however, more and more polyfunctional macromolecular complexes are being discovered, including nonrandomly codistributed membrane-bound proteins [41], These are made up of several individual proteins, which can assemble spontaneously, possibly in the presence of a lipid membrane or an element of the cytoskeleton [42] which are themselves supramolecular complexes. Some of these complexes, e.g. snail haemocyanin [4o], are merely assembled from a very large number of identical subunits vimses are much larger and more elaborate and we are still some way from understanding the processes controlling the assembly of the wonderfully intricate and beautiful stmctures responsible for the iridescent colours of butterflies and moths [44]. 

Several early interpretations of the polymerization mechanism have been proposed (1,17,29—31). Because of the complexity of this polymerization and insoluble character of the products, key intermediates have not ordinarily been isolated, nor have the products been characterized. Later work, however, on the resinification of furfural (32,33) has provided a new insight on the polymerization mechanism, particularly with respect to thermal reaction at 100—250°C in the absence of air. Based on the isolation and characterization of two intermediate products (9) and (10), stmcture (11) was proposed for the final resin. This work also explains the color produced during resinification, which always is a characteristic of the final polymer (33). The resinification chemistry is discussed in a recent review (5). 

Like mthenium, amines coordinated to osmium in higher oxidation states such as Os(IV) ate readily deprotonated, as in [Os(en) (NHCH2CH2NH2)] [111614-75-6], This complex is subject to oxidative dehydrogenation to form an imine complex (105). An unusual Os(IV) hydride, [OsH2(en)2] [57345-94-5] has been isolated and characterized. The complexes of aromatic heterocycHc amines such as pyridine, bipytidine, phenanthroline, and terpyridine ate similar to those of mthenium. Examples include [Os(bipy )3 [23648-06-8], [Os(bipy)2acac] [47691-08-7],... 

U(IV) nitrates have been obtained from aqueous solution, but a number of anionic complexes of general formula M2[U(N02)g], where M = NH Rb, Cs, and M[U(N02)g] 8H20, where M = Mg, Zn have been isolated and characterized. These soHds contain the 12 coordinate anionic U(IV) center shown in (2) (158). Neutral, U(IV) nitrate complexes of formula U(N02)4L2 (3) (L = OP(CgH )2, OP(NC4Hg)2) have also been isolated from aqueous solutions and stmcturaHy characterized (159). 

Syntheses, crystallization, structural identification, and chemical characterization of high nuclearity clusters can be exceedingly difficult. Usually, several different clusters are formed in any given synthetic procedure, and each compound must be extracted and identified. The problem may be compounded by the instabiUty of a particular molecule. In 1962 the stmcture of the first high nuclearity carbide complex formulated as Fe (CO) C [11087-47-1] was characterized (40,41) see stmcture (12). This complex was originally prepared in an extremely low yield of 0.5%. This molecule was the first carbide complex isolated and became the foremnner of a whole family of carbide complexes of square pyramidal stmcture and a total of 74-valence electrons (see also Carbides, survey). 

Similar halogeno complexes are produced in solution, and several salts of [HgXs]" have been isolated and characterized they display a variety of stereochemistries. In [HgCl3] the environment of the Hg is either distorted octahedral (with small cations such as NHj" "... 

Isolation and characterization of stereoisomers in di- and trinuclear complexes with N-heterocyclic ligands 98CSR185. 

The deprotonated flavin in the complex is readily attacked by molecular oxygen at C4a, giving 4a-hydroperoxide of the flavin-luciferase complex (intermediate A). This complex is an unusually stable intermediate, with a lifetime of tens of seconds at 20°C and hours at subzero temperatures, allowing its isolation and characterization (Hastings et al., 1973 Tu, 1979 Balny and Hastings, 1975 Vervoort et al., 1986 Kurfuerst et al., 1987 Lee et al., 1988). 

Much effort has been invested into the search for monomeric compounds [86-90]. One of the few reliable indications for a base-stabilized monomeric complex involved the use of spectroscopic methods. The complexes 1 and 2 could be isolated and characterized below —20 °C with spectroscopic methods [91],... 

Tezuka s group (Tezuka and Ando, 1985 Tezuka et al., 1986) was able to isolate and characterize the benzenediazo ether of 1-naphthol (6.10). They stirred a solid mixture of the molecular complex 6.9 formed between an a-azohydroperoxide acid and benzene with an excess of 1-naphthol at room temperature in the dark for several hours. The separation of this solid by thin layer chromatography (silica gel, with a benzene-ethyl acetate mixture [9 1] as eluent) afforded the diazo ether 6.10 as a yellow oil in 17 % yield, together with 4- and 2-phenylazo-l-naphthol (6.11 and 6.12, 4% and 42%, respectively), 4-phenylbenzaldehyde (32%), benzoic acid (23%), and traces of other compounds (Scheme 6-6). Higher yields of the diazo ether (up... 

The third area is the synthesis and characterization of aryldiazenido complexes of transition metals. In 1964 King and Bisnette isolated the first metal complex with an aryldiazenido ligand. The interest of organometallic chemists was concentrated mainly on the isolation and characterization of stable aryldiazenido complexes and not on potential metastable intermediates involved in metal-catalyzed dediazonia-tions. The situation is different, however, for metal complexes with alkyl-diazenido ligands. Complexes with aryl- and alkyldiazenido ligands are the subject of Chapter 10 in the forthcoming second book (Zollinger, 1995). 

Chaussepied, P. Kasprzak, A.A. (1989). Isolation and characterization of the G-actin-myosin head complex. Namre 342,950-953. 

Yields in the above reactions can often be improved by the addition of 1 mole of triphenylphosphine directly to the trifluoroacetic acid solution of the reactants immediately before final work-up. It would appear that the triphenylphosphine functions as a scavenger for TTFA released in the metal-metal exchange reaction, thus protecting the final phenol from further electrophilic thallation and/or oxidation. Validation of the metal-metal exchange mechanism was obtained indirectly by isolation and characterization of an ArTlX2/LTTFA complex directly from the reaction mixture. NMR analysis revealed that this complex still possessed an intact aryl-thallium bond, indicating that it was probably the precursor to the transmetallation products, an aryllead tristrifluoroacetate and TTFA. 

With sp bond angles calculated to be around 162°, macrocycle 131 would be highly strained and was therefore expected to be quite reactive [79]. The octa-cobalt complex 132, on the other hand, should be readily isolable. Indeed, 132 was prepared easily from 133 in five steps, and was isolated as stable, deep maroon crystals (Scheme 30). All spectroscopic data supported formation of the strain-free dimeric structure. Unfortunately, all attempts to liberate 132 from the cobalt units led only to insoluble materials. Diederich et al. observed similar problems when trying to prepare the cyclocarbons [5c]. Whether the failure to prepare these two classes of macrocycles is due to the extreme reactivity of the distorted polyyne moiety or to the lack of a viable synthetic route is not certain. Thus, isolation and characterization of smaller bent hexatriyne- and octatetrayne-containing systems is an important goal that should help answer these questions. 

Like the carbodiimide method, the mixed anhydride method results in an amide complex (Table 5, Figure 17). The acid-containing hapten is dissolved in a dry, inert, dipolar, aprotic solvent such as p-dioxane, and isobutyl chloroformate is added with an amine catalyst. The activated mixed anhydride is chemically stable and can be isolated and characterized. The aqueous protein solution is added to the activated acid and the pH is maintained at around 8.5. A low temperature (around 10 °C) is necessary during the reaction to minimize side reactions. 

Starting with (5) and (2), it was possible to isolate and characterize two stable unusnal complexes. This supports the premise of a bidentating structure. In comparison to monodentating complexes, (4a and 4b) those new complexes are expected to behave differently than that of catalysts mentioned in literature (1). 

Control of the onset of transcription. Cell 30 687—696 Robertson K, Hensey C, Gautier J 1999 Isolation and characterization of Xenopus ATM (X-ATM) expression, localization, and complex formation during oogenesis and early development. Oncogene 18 7070-7079... 

There are relatively few reports of trivalent Tp complexes by comparison with mono- and divalent systems. One interesting example involved transmetallation (from Sn to Co) in the reaction of TpSnCl3 with [Co(CO)4] to give a mixture of products from which [Co(Tp)2][/r[Pg.70]

Reduction of both nickel porphyrins and thiaporphyrins to Ni1 species has been studied by EPR and 2H NMR spectroscopy.179, 2 58 The Ni1 complex of 5,10,15,20-tetraphenyl-21-thiaporphyrin has been isolated and characterized. Reaction of this complex with sulfur dioxide produced a paramagnetic five-coordinated Ni1 S02 adduct, while reaction with nitrogenous base ligands (amines, pyridines, imidazoles) yielded five- and six-coordinate complexes. In addition, the crystal structure of Ni1 diphenyldi-p-tolyl-21-thiaporphyrin has been determined. The coordination geometry about the nickel center is essentially square planar with extremely short Ni—N and Ni—S bonds (Ni—N = 2.015(2) A, 2.014(12) A, and 1.910(14) A and Ni—S = 2.143(6) A).2359... 

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