Matrix isolation oxygen reactions

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). 

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. 

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. 

There have been numerous studies of low-temperature chemical reactions of matrix-isolated reactants (see, for example, the review by Perutz [1985]). Two of the most interesting from the standpoint of this volume are the reactions of NO with 02 and 03 studied by Smith and Guillory [1977] and Lucas and Pimentel [1979]. The cis dimer (NO)2 has been formed in solid oxygen at 13-29 K. Reaction of this species with the 02 matrix forms the product N204 in an electronically excited state. The transition state structure is reportedly of the form... 

Bicyclo[3.3.0]oct-l(5)-ene 178 (Scheme 4.55) is a stable compound with a flattened alkene fragment and exhibits a regular pattern of reactivity. Computational studies revealed, however, that installation of a short 3,7-bridge should lead to noticeable pyramidalization of the double bond. Compounds like 179-181 were synthesized to check this prediction. Tricyclic hydrocarbon 179, with the smallest possible bridge, was generated as a transient species from diiodide 182. The formation of 179 is implicated by the isolation of its cyclodimer 183 (or respective Diels-Alder adduct if the reaction is carried out in the presence of a 1,3-diene). The next member of this series, 180, is more stable. In fact, the formation of 180 was ascertained not only from the structure of the final products (as was done for 179), but also by its matrix isolation and analysis of spectral data. The selenium derivative 181 was found to be stable at ambient temperature in the absence of oxygen. X-ray data confirmed a noticeable pyramidalization of the double bond in 181 but the distortion was different [Pg.372]

Halogen-substituted silylenes Ic and Id are less reactive than alkyl-substituted silylenes. This is drastically shown by the matrix isolation of Ic and Id in solid oxygen up to 45 K, where O2 rapidly evaporates, no reaction is observed. However, irradiation at 365 nm and 575 nm for Ic and Id, respectively, rapidly yields dioxasiliranes 3c and 3d as the only products. Since there is no migratory aptitude of halogen from silicon to oxygen, these dioxasiliranes are photochemically stable even at 220 nm irradiation [3]. 

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