Azide Chemistry – An Inorganic Perspective, Part I Metal ­Azides: Overview, General Trends and Recent Developments

Abstract

With Sharpless' and Meldal's discovery of the immensely supportive effect that metal catalysis has on Huisgen's classical 1, 3‐dipolar cycloaddition, azides (RN3) – long underappreciated in organic synthesis – suddenly got in the focus of attention as most crucial players in sensational ‘click chemistry'. Less noisy though with the same commitment and even a much broader scope of scientific topics and objectives, the inorganic azide chemistry has made just as great strides in the last few decades. This review (Part I) gives an introductory survey of the most important results, and informs about modern developments and general trends. Particular emphasis is placed on the recent successful approaches to highly unstable homoleptic azido metal complexes of the main group and early transition elements, as well as on the enormous structural versatility caused by the ‘flexidentate' N3– ligand with its unsurpassed bridging capacities. The presentation in this paper of selected compounds and reactions is meant, in a way, as a prelude to the [3+2]‐cycloadditions of metal azides and related species which will be covered in‐depths in Part II. A large part of the comments finally deals with applications in fields such as catalysis, high explosive performance or magnetism of metal compounds containing azide, today certainly one of the most attractive research areas world‐wide.

Synthesis of six-coordinate mono-, bis-, and tris(tetrazolato) complexes via [3 + 2] cycloadditions of nitriles to silicon-bound azido ligands

“…[53][54][55][56] In this paper we describe a convenient synthetic route to poly(tetrazolato) complexes based on the intriguing four reactive centres of the previously described N-rich, highly endothermic tetraazides of the type Si(N 3 ) 4 (L 2 ), 53 L 2 = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen); 51,52,57,58 see ref. 24 for recent reviews of azido complexes chemistry. The new method allows for the synthesis and isolation of unusual hyper-coordinate poly(tetrazolato) poly(azido) silicon complexes, where two types of N-rich ligands are combined on one centre and where the number of N 3 ligands engaging in cycloaddition with nitrile forming tetrazolato ligand can be varied from one to three by careful adjustment of reaction conditions.…”

“…These include Lewis base assisted HX elimination (i), 19,20,21 oxidative addition of tetrazole (ii), 22 Brønsted acid-base reaction (iii), 8,23 thermally activated [3+2] cycloaddition of mono(azido)silanes and aryl or alkyl nitriles (iv), [24][25][26] and silylation (v), 27 resulting in…”

Azide Chemistry – An Inorganic Perspective, Part II[‡][3+2]‐Cycloaddition Reactions of Metal Azides and Related Systems

“…[45a -d] Note that this and other reactions have also been mentioned in passing in the preceding paper "Part I -Metal Azides: Overview, General Trends and Recent Developments", [26] which, in a way, was designed as a prelude to and counterpart of the highly specialized Part II. According to that, a rather personal selection of azido transition metal complexes frequently employed in reactivity studies at this coordinated ligand has been made at the outset (Part I, Table 1) to which we refer in the following, time and again.…”

“…Today, azido complexes are known of almost any metal both in classical inorganic and organometallic type coordination chemistry. [26,27] Starting in the mid-1960s, a series of papers mainly coming from our Munich laboratory not only brought numerous new compounds into play, but also showed the azide ligand to be a centre of remarkable reactivity with a wide range of synthetic applications. [28][29][30][31][32][33][34][35][36][37] In a sense, this was the rise of what had recently been referred to as "the Inorganic Version of the Huisgen 1,3-Dipolar Cycloaddition", [20,21,38] exactly the subject of the present survey.…”

Self-assembled energetic coordination polymers based on multidentate pentazole cyclo-N5−

“…For a very long time, only the azide anion was used to produce energetic salts or simple CPs [14,15]. In 1999, a major breakthrough in poly-nitrogen area was achieved with the preparation of the N 5 + ion and its relative stable energetic salts were subsequently synthesized [16,17].…”