Tris derivative

Ir4(CO)ii(PPh3)149 The structures of the di- and tri-substituted iridium derivative are shown in Fig. 14. In all cases, the phosphines are around the basal plane. However, whereas the two phosphines are in relative trans-positions in the di-substituted compound, in the tris-derivative two of the phosphines are obliged to occupy relative c/s-position and, as a result, are involved in more steric interaction. 

It is probable that the compound described is not the tri-derivative but impure tetrapyridino-ferrous chloride, for Costacheseu and Spacu 4 claim to have isolated, in a pure state, a yellow crystalline body of composition [Fe(C5H5N)4]Cl2 by the interaction of ferrous chloride and excess of pyridine in an atmosphere of carbon dioxide at —15° C. The substance changes quickly on exposure to air and is decomposed by water. 

The tetrakis-phosphino and -arsino complexes reported in Table 3 have very different thermal and air stabilities. In general, complexes with alkyl-phosphines and -arsines are air-unstable or pyrophoric. The tetrakis(arylphosphino) complexes (but not the bis or tris derivatives) are moderately air- and heat-stable, and the tetrakis phosphites may be handled in the atmosphere. Ni(PF3)4 is a stable liquid compound, whereas Ni(PCl3)4 and Ni(PBr3)4 are solids and stable only in dry air. 

Metal-free catalysts for the hydrolysis of RNA derived from 2-aminobenzimidazoles were reported. The most active catalysts, tris derivatives (99 R = H, CC Me) built upon a framework of tris(2-aminoethyl)amine, were shown by fluorescence correlation spectroscopy to aggregate with oligonucleotides. However, at very low concentrations the compounds were still active in the non-aggregated state. Conjugates of the ester (99 CC Me) with antisense oligonucleotides or RNA binding peptides will, it was claimed, be promising candidates as site specific artificial ribonucleases.98... 

The tetra-derivative, which is described in Beilstein6 as easily soluble in water, in fact gives barely a 1% solution at 0°. At room temperature the solubility is higher but only about one-fourth that of mercury(II) chloride and one-sixth that of thiourea. The tri-derivative is still less soluble in water, giving a 0.2% solution at 0°, and the mono-derivative even less so. The least soluble is the di-derivative which is precipitated on mixing 0.1% solutions of mercury-(II) chloride and thiourea.2 It is also virtually insoluble in brine and alcohol2 and only sparingly soluble in hydrochloric acid.1... 

Thus the mono-derivative ionizes as a binary electrolyte and the tri-derivative as a ternary electrolyte in aqueous solution. The tetra-derivative does not exist at those dilutions, having completely dissociated, even at 0°, into the comparatively stable tri-derivative and free thiourea. 

The silylation of amino acids with BSTFA was studied in detail by Gehrke and coworkers [254—256]. BSTFA—acetonitrile (1 1) was applied first and fourteen amino acids were silylated at 135°C for 15 min. Glu, Arg, Lys, Trp, His and Cys, however, require up to 4 h, in order for measurable peaks to be obtained in the chromatogram. Despite such a long reaction, Gly and Glu gave two peaks and also it was difficult to separate the tris-TMS derivative of Gly from the derivatives of lie and Pro. The influence of polar and non-polar solvents was demonstrated later and was decisive mainly with respect to uniformity of the products. Only the bis-TMS derivative was produced in hexane, methylene chloride, chloroform and 1,2-dichloroethane bis- and tris-derivatives were produced in six more polar solvents. On the other hand, Arg did not provide any peak in the less polar solvents that were used and only one peak in the six more polar solvents. The best and most reproducible results were obtained when silylating seventeen amino acids with BSTFA—acetonitrile (1 1) at 150°C for 15 min 2.5 h at 150°C were necessary for the reproducible derivatization of Gly, Arg, and Glu. These reaction conditions were recommended for the analysis of all twenty amino acids. The TMS derivatives of amino acids were found to be stable on storing them in a sealed vial at room temperature for 8 days, with no decomposition. 

Applications of the method to w-amino acids were discussed and existing knowledge was summarized by Marik et al. [258]. Silylation was executed at 80°C for 1— 2 h or at 90°C for 0.5-1 h, with the use of BSA either alone or with the addition of triethylamine or acetonitrile. BSA alone was recommended as tris-TMS derivatives were produced in practically 100% yield. The presence of amine and solvent led to the formation of bisand tris-derivatives in various ratios, changing with time. However, these conclusions were valid only if the reaction was started with amino acid hydrochlorides. The presence of... 

The intramolecular Diels-Alder reactions of vinyl sulfoximines 270 (n = 1,2) have been studied by Craig.121,122 In all cases mixtures of four diastereomeric cycloadducts were formed. When n = 1 the major diastereoisomer was the transfused compound 271 (n = 1) while when n = 2 the major diastereoisomer was the cis-fused compound 273 (n = 2) The diastereoselectivity of these reactions when n = 1 were essentially independent of the nature of the N-substituent in 270, while when n = 2 thejV-2,4,6-triisopropylphenylsulfonyl (Tris) derivative gave the highest selectivity for 273. 

The distinction between the three groups is best made by the relations between the bi- and tri-substituted derivatives. The consecutive or ortho bisubstituted derivatives can produce by further substitution two tri-derivatives, one consecutive, the other unsymmetrical the urisyinmetrical, or meta, can produce three trisubstituted derivatives and the symmetrical, or para, can produce but one trisubstituted derivative, an unsymmetrical. 

The parameters that afTect the retention behaviour of volatile metal 3-diketonato-complexes in various g.l.c. systems have been investigated in some considerable detail. The vapour pressures and heats of vapourization have been determined for tris(hexafluoroacetylacetonato)- and tris(heptafluoro-dimethyloctanedionato)-chromium(ni), Cr(hfa)3 and Cr(fod)3, respectively, and those of the corresponding tris-derivatives of other metals. These results show that the hfa chelates are more volatile than the fod ones, the latter exhibiting a similar volatility to tris(trifluoroacetylacetonato) (tfa) complexes. 

In the bis-O-2-picolyl derivatives of calix[4]arene 26a-c, the two binding pendant functionalities can adopt syn-proximal (26a), syn-distal (26b) or flnh -distal (26c) relationships. On using lower proportions of NaH mainly st/n-proximal 26a and some syn-distal 26b products along with mono and tris derivatives were formed. 26a is a useful intermediate for further selective synthesis of tri and tetra alkylated cone conformers having the same or mixed pendants (92JOC2611). 

This is exactly what Kekule and his students were beginning to do, and what many of his colleagues soon started to do, as well. The theory provided hundreds or even thousands of specific predictions, and each prediction could only be tested by the accumulation of much laboratory evidence. Some of this evidence was of a positive character for instance, can one make the predicted third isomer of a given di-derivative of benzene—say, for example, bromobenzoic acid—only two isomers of which were currently known Some of the evidence was negative, which required even more empirical experience for instance, is the theory correct that it is in fact impossible to make an isomer of benzoic acid or phenol, or a fourth isomer of a di-derivative Is it impossible to make an aromatic compound with less than six carbons Are there always exactly three possible isomers of each tri-derivative ... 

The preparation of a variety of higher polysilanes using silylmetallic reagents has been described (4, 5, 14). More recently, silylmetallics have been successfully employed in the synthesis of branched polysilanes. Treatment of silicochloroform with either triphenyl- or dimethylphenyl-silyllithium gives the corresponding tris derivatives. 

The bis compound is obtained on reaction of the tris derivative with water or excess hydrogen halide. 

The halogen atom in dialkylaminophosphine chlorides or bromides can be replaced by fluorine on reaction with zinc of antimony fluoride (7.100). The same product is obtained from the tris derivative and boron trifluoride (7.101). 

Bromosilane can be used to obtain all three silyl phosphines. With lithium aluminium phosphide, monosilyl phosphine is obtained (9.170), while with potassium phosphide either the di or tri derivative can be made (9.171,9.172). 

The methylsilyl phosphines are obtainable in reasonable yields by reacting chloromethylsilanes with lithium or other alkali phosphides (9.190-9.192). The tris derivative is also obtained by reaction (9.193). 

Although the reaction of UCl with two equivalents of LiN(SiMe3>2 gave only the above tris derivative, the reaction with NaN(SiMe3)2 allowed the preparation of the bisamido complex (eq. 79) (95). All... 

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