Oxygen matrix isolation

Oxychlorides are less prolific, apart from the red-brown OsOCl4 (m.p. 32°C). This probably has a molecular structure in the solid state as the IR spectra of the solid, matrix-isolated and gas-phase molecules are very similar, and the volatility is consonant with this [30]. Syntheses include heating osmium in a stream of oxygen/chlorine ( oxychlorination ) and by ... 

In the oxygen-potential model that was used for the U/0 system (l -2), two equilibria for the solid were considered. One of these equilibria is analogous to Eq. (11) and the other involved the U6+ ion. We are unaware of evidence for the existence of the Pu6+ ion in the oxide system. No PUO3 molecule was identified in the matrix-isolation studies (29) although, with similar experimental methods, the UO3 molecule was easily observed (30). 

Huber et al. 189) have investigated cocondensation (4.2—10 °K) reactions between Ni, Pd and Pt and molecular oxygen in pure O2 and Oj/Ar matrices. These reactions were studied by matrix isolation infra-red spectroscopy, including isotopic and diffusion controlled warm-up studies. They established that both M(02) and (0j)M(02) species were present. The 0-0 bond order suggested significant back-bonding, and this led them to reject the monodentate stmcture. Fig. 8 (b). 

Our interest in ketocarbenes originated from the aim to matrix-isolate oxirene (76) (Scheme 1), the oxygen-containing hetero analog of cyclobutadiene (1)... 

The carboxylic acid derivatives li-lm can only be matrix-isolated if the corresponding quinone diazides 2i-2m are irradiated with monochromatic blue light (k = 436 nm).81 91 92 UV or broad-band visible irradiation rapidly results in the decarboxylation of the carbenes. As expected, the IR and UV/vis spectra of the carbenes are very similar to that of la. Oxygen trapping results in the formation of the photolabile carbonyl oxides 7. Thus, the carbenes li-lm were identified both spectroscopically and by their characteristic reaction with molecular oxygen. 

The anthronylidenes lp-lr are easily matrix-isolated by photolysis of the corresponding diazo compounds 2 (Scheme 17).99 The reaction of the carbenes with molecular oxygen results in the formation of anthraquinone 0-oxides 7,... 

The matrix photochemistry of 2v proved to be fairly complicated.108 The primary product of the photolysis of 2v is carbene lv, which was identified by ESR spectroscopy. Under the conditions of matrix isolation the carbene showed the expected reactivity towards molecular oxygen (formation of carbonyl oxide 7v) and carbon monoxide (formation of ketene lOv) (Scheme 22). In contrast to the oxocyclohexadienylidenes (la and derivatives) carbene lv slowly reacted with CO2 to give an a-lactone with the characteristic C=0 stretching vibration at 1896 cm-1. The latter reaction indicates that lv is — as expected — more nucleophilic than la. 

Photochemistry of (2-nitrophenyl)diazomethane 70 has been studied by excitation at 350 nm in argon matrix isolation system54. That shows that at 10 K, 2-nitroso-benzaldehyde is formed by intramolecular oxygen migration from (2-nitrophenyl) carbene... 

Irradiation of matrix-isolated imidazole-2-carboxylic acid gave the 2,3-dihydro-imidazol-2-ylidene-C02 complex (31) characterized by IR spectroscopy and calculated to lie 15.9 kcal mol above the starting material. A series of non-aromatic nucleophilic carbenes (32) were prepared by desulfurization of the corresponding thiones by molten potassium in boiling THF. The most hindered of the series (32 R = Bu) is stable indefinitely under exclusion of air and water and can be distilled without decomposition. The less hindered carbenes slowly dimerize to the corresponding alkenes. Stable aminoxy- and aminothiocarbenes (33 X = O, S) were prepared by deprotonation of iminium salts with lithium amide bases. The carbene carbon resonance appears at 260-297 ppm in the NMR spectrum and an X-ray structure determination of an aminooxycarbene indicated that electron donation from the nitrogen is more important than that from oxygen. These carbenes do not dimerize. 

Vibrational spectroscopy (37, 55, 300) provided the best evidence for ClFsO possessing a pseudotrigonal bipyramidal structure of symmetry Cf, in which 2 fluorines occupy the axial and 1 fluorine, 1 oxygen, and a sterically active free valence electron pair occupy the equatorial positions (see structure III). At Rocketdyne (55), a thorough spectroscopic study was carried out including the infrared spectra of gaseous, solid, and matrix-isolated ClFsO and the Raman spectra of the gas and the liquid. 

Matrix isolated NH reacts with NO, an excellent nitrene trap, to form trans-HNNO, which was characterized by infrared (IR) spectroscopy. Triplet imidogen also reacts with oxygen in matrices. 

The EPR results discussed in this section are suggestive rather than definitive for the existence of O4 on oxide surfaces. However, it is clear from the preceding discussion that IR spectroscopy has proved to be a powerful technique to study O4 as a matrix-isolated species and the use of IR, Raman, and optical absorption together with EPR is likely to prove a very effective approach in elucidating the nature and properties of these complex oxygen ions on the surface. 

Thallium(I) oxide, T120, is a well-characterized compound and a useful source of Tl+ salts.1 Matrix isolation studies of the solid gave structural data in agreement with spectroscopic results.290,291 The so-called peroxide T102 is obtained electrochemically from aqueous T12S04, but the properties include insolubility in water, alkali and some dilute adds, and treatment with dilute HC1 yields oxygen. The stoichiometry suggests that the compound is in fact a superoxide, and this has been confirmed by spectroscopic studies on frozen matrices.292,293... 

Matrix isolation methods of synthesis have also been used to prepare and study coordination compounds. These involve the vaporization of a metal and a potential ligand, which are then rapidly carried in a stream of inert gas to a very cold surface, where the compound which has been formed is quickly trapped in the solid matrix. It is possible to determine the type of bonding, the structure and the thermodynamic properties of the compounds formed. Only small ligand molecules have been used thus far carbon monoxide, nitric oxide, nitrogen and oxygen, for example, but molecules of great interest have been formed. Some such are [Pd(C2H4)], [Pd(N2)3], [Ni(N2)202], [Ni(N2)4] and [Ni(CO)(N2)3].41... 

Carboxylate esters readily undergo photodecomposition with loss of carbon dioxide. Not surprisingly, lactones and related oxygen heterocycles undergo related transformations. A wide variety of lactones behave in this fashion443 for example, the cyclic dilactone (505) is converted on irradiation to the [2.2]paracyclophane (506).444 Of particular interest is the use of the /(-lactone (507) as a precursor of matrix-isolated cyclobutadiene (508).445... 

Photolysis of matrix-isolated (trimethoxysilyl)diazomethane at X > 305 nm produced carbene 3e (equation 1), which was characterized by IR and UV-Vis spectroscopy23. Under these conditions, no other species besides the carbene could be detected spectroscopically. In an 02-doped (1%) argon matrix, the carbene rapidly reacted with oxygen to give carbonyl oxide 4 which was further photoisomerized to formylsilane 5. Again, the fast reaction of 3e with 302 points to a triplet ground state of the carbene. 

Dimethylsilanone (97) is also formed in the oxygenation of 95 with oxygen atoms generated by a microwave discharge of an Ar/02 stream and subsequent matrix isolation of the reaction products101. 

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