Tetrakis volatility

The chemical and thermal stability of the fluorophosphine complexes is markedly increased in every case over the chlorophosphine complexes, none of the latter being volatile. The stability of the fluorophophine complexes as compared with the parent carbonyl is also noteworthy. While nickel carbonyl is distillable only with considerable decomposition, tetrakis(trifluorophosphine)nickel-(0) is far more stable on distillation at atmospheric pressure, and can also conveniently be handled in a high-vacuum system. 

Zirconium(IV) and hafnium(IV) tetrakis(tetrahydroborates) M(BH4)4 are of interest as extremely volatile, covalent complexes that contain tridentate BH ligands and exhibit rapid intramolecular exchange of bridging and terminal hydrogen atoms. 4,615 These compounds were prepared initially from NaMF5 (M = Zr or Hf) and excess A1(BH4)3 (equation 53),616 but they are obtained more conveniently from the reaction of the anhydrous metal tetrachloride with excess lithium tetrahydroborate (equation 54), either in the solid state617,618 or in the presence of a small amount of diethyl ether.619... 

Derivatives of simple amides are the volatile [Au N(SiMe3)2 (PMe3)] and the particularly significant tetrakis(triphenylphosphinegold)ammonium ion [N(AuPPh3)4].+ 174,297 There are also interesting cyclic derivatives, such as (26)-(28), prepared from pyrazoles, 2-pyridyllithium or isocyanide precursors respectively.298"301... 

The synthesis of several hydrogensulphate and tetrakis(hydrogensulphato)borate ionic liquids has been described by our group [29]. Mixtures of these ionic liquids with sulphuric acid were used as non-volatile acidic phases with tuneable solubility properties for catalytic applications such as e.g. the alkylation of benzene with 1-decene. 

High-coordination-number complexes of 0-keto-enolates continue to be obtained with the metals such as zirconium(IV),8 hafnium(IV),8 cerium(IV),9 and the lanthanons(III),10 the last being tetrakis anionic species. At least one example of a volatile tetrakis 0-keto-enolate salt has been reported,11 Cs[Y(CF3-COCHCOCF3)4]. The ionic charge on the 0-keto-enolate complex has been shown to produce12 a high field nuclear magnetic resonance for anions and low field shifts for cations, relative to the positions observed for the neutral species. 

A solution of [tetrakis(2,6-dichlorophenyl)porphyrinato]iron(III) perchlorate (0.005 mmol) in anhyd CH2C12 is added to 10 mL of the alkene under Ar. The resulting solution is transferred under Ar into a flask containing 0.1 mmol of C6H5I = NTs and molecular sieves. The mixture is then stirred for 30 min with a magnetic stirrer, then filtered. The solvent and excess alkene (if volatile) are removed under reduced pressure. The resulting solid is dissolved in CDCI, . and the composition of the mixture is determined by 1H-NMR spectroscopy. The yields of the aziridines are measured by using 1,1,2,2-tetrachloroethane as internal standard. 

Protodesilylation of allyl- or aryl-substituted trialkylsilanes with an acid partner is a cleaner method, producing propene or an aromatic hydrocarbon as a volatile inert byproduct. Although some methods of isolation have been reported, they can usually be prepared in situ in aprotic media and employed without further purification. Methods of preparation of representative organosilicon Lewis acids, la, trimethylsilyl bis(trifluoro-methanesulfone)imide (7) [9], trimethylsilyl perchlorate (6a) [10], iodotrimethylsilane, and trimethylsilyl tetrakis(trifluoromethanesulfonyl)borate [11] are described below. In principle, these analogs are also accessible in a similar manner (Table 1) [2d]. 

The apparent volatility of the triethylammonium tetrakis (hexaflu-oroacetylacetonato) europate (III) complex (21) (Figure 3) is especially interesting when compared with the nonvolatile tetramethylammonium analog. One could conceive of the following equilibrium... 

Four of the seven known metal tetrakis-borohydrides—Zr, Hf, Th, and U borohydrides (1,2)—were first synthesized about 30 years ago during the Manhattan project. They were found to be very volatile and reactive compounds. In recent years, much structural, spectroscopic, and chemical studies were done on these molecules. New tetrakis-borohydrides of the actinides Pa, Np, and Pu have recently been prepared by analogous reactions used in the syntheses of U and Th borohydrides (3). The Pa compound, Pa(BHi+K, is iso-morphous to and behaves like U(BHi+)i+ and Th(BHi+)i+ while x-ray studies on Np(BHi+)i+ and the isostructural Pu(BHi+)i+ have shown that they resemble the highly volatile Zr and Hf compounds both in structure and properties. All seven compounds contain triple hydrogen bridge bonds connecting the boron atom to the metal. 

Some of the physical properties of metal tetrakis-boro-hydrides, which are primarily determined by their solid-state structure, are listed in Table 1. The polymeric Th, Pa, and U borohydrides are of much lower volatility than the monomeric Zr, Hf, Np, and Pu compounds. The intermolecular bonds connecting molecules together decrease their volatility substantially since these bonds break when the solid vaporizes (12). A plot of log p(mmHg) vs 1/T yields the equation log p(mmHg) = -A/T + B, where T is in K. Values of A and B allow the calculation of the heats (AH) and entropies (AS) for phase-change processes as shown in Table 1. The actinide ions in the polymeric compounds are 14 coordinate however, in the gaseous state they are 12 coordinate (12). 

A number average degree of polymerization, n, as high as 8.4 has been obtained. Heating the initial polymers at 150°C/0.1 mm causes disproportionation to the volatile tetrakis compound and a nonvolatile more jiighly condensed polymer (73, 74). 

Polyphenolics and bisphenolics are higher in molecular weight than simple phenolics and both types are generally nonstaining. The increased molecular weight provides lower volatility, but is generally more costly. However, the loading of polyphenolics is much less than that of the simple phenolics. The most commonly used polyphenolic is tetrakis(methylene-(3,5-di- -butyl-4-hydroxyhydrocinnamate)... 

Although this transformation worked well enough in small reactions, it proved inefficient upon scale-up. A superior, scalable one-pot process (Scheme 3) from diazocinedione to HNFX was developed more recently [37]. Here, efficient protolytic N-denosylation is effected by trifiuoromethanesul-fonic acid added to the crude 3,3,7,7-tetrakis(difluoramino)octahydro-l,5-bis(4-nitrobenzenesulfonyl)-l,5-diazocine intermediate (4), still contained in the acid system used for difluoramination after expulsion of volatiles such as excess difluoramine and trichlorofluoromethane. The denosylated intermediate, a 3,3,7,7-tetrakis(difluoramino)octahydro-l,5-diazocinium salt (5), is straightforwardly nitrated to HNFX by added nitric acid. 

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