Azides transition metal complexes

Numerous explosives are based on hydrazine and its derivatives, including the simple azide, nitrate, perchlorate, and diperchlorate salts. These are sometimes dissolved in anhydrous hydrazine for propeUant appUcations or in mixtures with other explosives (207). Hydrazine transition-metal complexes of nitrates, azides, and perchlorates are primary explosives (208). 

Copper catalyzes the decomposition of sulphonyl azides in benzene very slowly. When methanesulphonyl azide was boiled under reflux in benzene solution in the presence of an excess of freshly reduced copper powder, some decomposition occurred to give methanesulphonamide and azide was recovered 78>. Transition metal complexes have been found to exert a marked effect upon the yields of products and isomer ratios formed in the thermal decomposition of methanesulphonyl azide in methyl benzoate and in benzotrifluoride 36>. These results will be discussed in detail in the section on the properties of sulphonyl nitrenes and singlet and triplet behaviour. A sulphonyl nitrene-iron complex has recently been isolated 37> and more on this species will be reported soon. 

Jacobsen and coworkers discovered that chiral salicylimidato transition metal complexes activate epoxides in a stereoselective manner. The published mechanism indicates that one Cr° (salen)-N3 with (/ ,/ )-cyclohexyl backbone acts as Lewis acid and coordinates to the oxygen of PO, while a second catalyst molecule transfers the azide to the activated epoxide and thus opens the ring. The coplanar arrangement of the two chromium complexes prefers one enantiomer of PO and so induces stereochemical information [99,100, 121-129]. (cf. also Sect. 8.3) (Fig. 42). 

In contrast, tetrazadienes, RN=N—N=NR, which are unknown in the free state, are found in a growing number of transition metal complexes. The ligands can be generated in situ from organic azides or diazonium cations and, following the discovery of Fe(MeNNNNMeXCO)3 by Dekker and Knox in 1967 (59), an extensive range of transition metal tetrazadiene complexes has been synthesized. Finally, several papers report theoretical calculations on the stability and structure of N4 ligands bound to transition metals (196-198). 

Detailed crystal structures of only a few of the other heavy metal pseudohalides are available in the literature. Among them are, cuprous azide which has a relatively simple tetragonal lattice and cupric azide, mercuric fulminate and a-lead azide which have increasingly complex orthorhombic lattices. a-Lead azide has four types of anion sites of varying amounts of as5nnmetry (33) while cupric azide (35) and mercuric fulminate (72) have two such sites. The structure of cupric azide which is built up of distorted octahedra of asymmetric Ns ions about the central cupric ion is analogous to that of a transition metal complex. 

A related transformation to the previous carbene transfer reaction involves a nitrene ligand bonded to the metal center, in a metallonitrene intermediate in situ generated upon the appropriate selection of the catalyst and the nitrene precursor. As shown in Scheme 17, some transition metal complexes react with such a precursor to generate an unsaturated intermediate, generally electrophilic in nature, which might react with olefins or C—H bonds affording aziridines or amines in a catalytic manner. The most employed nitrene sources are hypervalent I(III) compounds such as PhI=NTs, chloramine-T or organic azides. 

There are many reports on azide-alkyne click polymerisation (a subject not discussed in the present chapter) but research on thiol-yne click polymerisation is in its early stages. New reaction types, novel catalyst systems other than those existing (i.e., photon, heat, organic base, transition-metal complexes) and new functionalities of the ensuing polymers are waiting to be developed [51]. 

If the metal site of a coordination compound is in a sterically and/or electronically saturated situation, coordination of an organo azide will be hindered and thus metal centred reactivity of the N3-fragment will not occur. If additionally the other ligands coordinated to the metal site are inert against an attack by the organoazide too, no reactivity will be observed at all. There must be a multitude of such intrinsically nonreactive combinations of organoazides and (transition) metal complexes which have not found their way into literature. 

Cenini S, Gallo E, Caselli A et al (2006) Coordination chemistry of organic azides and amination reactions catalyzed by transition metal complexes. Coord Chem Rev 250 1234—1253... 

Despite the volume of work concerned with metal-catalyzed decomposition of diazo compounds and carbenoid reactions 28>, relatively little work has been reported on the metal-catalyzed decomposition of sulphonyl azides. Some metal-aryl nitrene complexes have recently been isolated 29 31>. Nitro compounds have also been reduced to nitrene metal complexes with transition metal oxalates 32K... 

Azidorhodium complexes are of considerable structural interest, but limited applicability can be expected from the unusual triazole synthesis illustrated in Scheme 125.190 It is also difficult to envisage synthetic utility from reactions in which organic azides are decomposed by transition metal carbonyls. Thus 2-arylbenzotriazoles are formed in such reactions on... 

Reactions between 5-cyanotetrazole and transition metals, when performed in boiling acetone, lead to hydrolysis of the cyano group and formation of 5-carbamyl tetrazolate complexes (68). Complexes containing 1- or 5-substituted tetrazolate anions can also be obtained by 1,3-dipolar cycloaddition of organic isonitriles (RNC) (15) or nitriles (RCN) (61), respectively, to coordinated azide ligands [Eqs. (3) and (4)]. 

For example, oiganoimido complexes of Group VI transition metals have been shown to catalyze the ring cleavage of styrene oxide (48) by trimethylsilyl azide. The observed regio-... 

Among other convenient nitrene precursors are chloramine-T (A-chloro-A-sodio-p-toluenesulfonamide), bromamine-T, sulfonamides in the presence of (diacetoxyiodo)benzene and various transition metal catalysts, and sulfonyl azides in the presence of ruthenium complexes . 

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