Recent Adventures in Beryllium Chemistry

Abstract

One of the least understood elements on the periodic table is beryllium, perhaps a result of the presumed toxicity of its complexes. Despite this limitation, beryllium exhibits a unique set of properties which sets it apart from its heavier alkaline earth congeners (Mg, Ca, Sr, Ba). Nevertheless, within the past five years, there have been a series of major advances in the field of organometallic beryllium chemistry. This article will highlight these advances by analyzing new oxidation states, reactivity, and bonding modes, targeting an audience of general synthetic chemists, including scientists at the undergraduate and graduate level.

Handling Beryllium, the Safe Way

“…Dubbed as the most toxic nonradioactive element, beryllium has been the focus of little fundamental research in the second half of the twentieth century . In the past two decades, however, beryllium chemistry has received significantly more interest. − This highly diverse field of research ranges from studies on fundamental compound classes like acido beryllates and amino and amido beryllium complexes − to investigations of the structure, properties, and reactivity of organo-beryllium compounds. − Researchers have developed efficient routes for the synthesis of beryllium halides and have found a new polymorph of BeBr 2 . Scientists have studied the influence on structure and reactivity of beryllium compounds − as well as their reactivity in substrate activation. − Furthermore, various novel Be–element single , and multiple bonds , have been prepared, and their bonding situation was evaluated in depth. − The groups of Braunschweig and Gilliard synthesized low-valent beryllium complexes and investigated their reactivity, − while the correct interpretation of the oxidation states in these compounds still receives attention. − …”

Ligand exchange at tetra-coordinated beryllium centres

“…Despite the considerable health hazards associated with beryllium and its compounds 1,2 the interest in the chemistry of this element has gained a lot of traction in the last two decades. [3][4][5] This ranges from the (re)investigation of fundamental compounds like Be[N(SiMe 3 ) 2 ] 2 , 6 diphenylberyllium 7 or acido beryllates 8 via beryllium-element multiple bonds 9,10 and novel Beelement bonds 11,12 to cluster chemistry. 13 Furthermore, the bonding situation in beryllium compounds has been examined more closely [14][15][16] and various compounds with beryllium in the formal oxidation states 0 and +1 have been isolated as well as applied for reductions; [17][18][19][20] how such oxidation states should be interpreted has been the subject of considerable discussion.…”

Beryllium-centred C–H activation of benzene

“…A C 6 D 6 solution of compound 8 displayed 1 H and 13 C NMR spectra diagnostic of a C 2 -symmetric structure. The incorporation of lithium in compound 8 was apparent from the corresponding 7 Li NMR spectrum (d Li À6.6 ppm) and a broad (o 1/2 = 314 Hz) 9 Be NMR signal was observed at d Be 8.2 ppm. While tetrahedrally coordinated Be centres have been shown to display chemical shifts in the range d Be = À2 to 8 ppm, this resonance lies to the far low field extreme and the breadth of the signal is more redolent of a lower symmetry environment.…”

“…Extension of this reduction chemistry to a reaction performed between 9 and 5 wt% Li/LiCl in C 6 D 6 heated at 100 1C for 5 days also yielded a mixture of products. The resultant 7 Li NMR spectrum presented a multiplicity of signals indicative of at least four well discriminated environments, and across a range of chemical shifts between d Li ca. À0.4 and À11.9 ppm.…”

“…1–3 More specifically, a flurry of reports have invigorated interest in the lower oxidation state chemistry of the lightest alkaline earth element. 4–7 Although the theoretical viability of Be( i )–Be( i )-bonded species analogous to Jones and co-workers’ landmark magnesium( i ) derivatives ( e.g. 1 ) 8,9 is yet to be realised, exploitation of neutral cyclic alkyl(amino)carbene (CAAC) ligands has led to the isolation of several compounds in which a formal oxidation state <+2 may be assigned to the Be atom.…”