A Preference for Heterolepticity ‐ Schlenk Type Equilibria in Organometallic Beryllium Systems

Abstract

The reactions of beryllium halides with diphenyl beryllium were investigated in the N‐ and O‐donor solvents NEt3 and THF, as well as in benzene and dichloromethane in the presence of the Lewis basic ligands THF, NEt3 and N‐heterocyclic carbenes with various steric demand. In all cases the selective formation of heteroleptic beryllium Grignard compounds of the general formula [(L)1‐2BePhX]1‐2 (X = Cl, Br, I; L = C‐, N‐, O‐donor ligand) was observed. The stability of these complexes was investigated computationally, while the differences between homo‐ and heteroleptic systems were also evaluated NMR spectroscopically and with single crystal X‐ray diffraction. Mechanistic studies on the formation and speciation of these beryllium Grignard complexes in solution were performed.

An anionic beryllium hydride dimer with an exceedingly short Be⋯Be distance

“…16,17 Specifically, this 9 Be NMR shift for 2b is at the lower range for 4-coordainte Be systems, which are typically found from −1.5 ppm to lower field, with a peak width at half height ( ω 1/2 ) of 120 Hz, in agreement with heteroleptic beryllium organometallics reported earlier. 14–16 Calculated Be–H IR stretching frequencies (1542 and 1578 cm −1 ) align with broadened bands observed in the IR spectra of 2a (1530 cm −1 ) and 2b (1540 cm −1 ).…”

“…Structural aspects of 1 are in-keeping with previously reported monomeric heteroleptic beryllium halide complexes. 15…”

Tricoordinate Beryllium Radicals and Their Reactivity

“…The heteroleptic bromo­(duryl)beryllium complex, 1 , was synthesized by salt metathesis of CAAC-stabilized beryllium dibromide with duryllithium. It is noteworthy that unlike heteroleptic heavier Ae aryl Grignards (AeArX), which are highly susceptible to Schlenk-type disproportionation into AeAr 2 and AeX 2 , beryllium-based aryl Grignards, both base-free and base-stabilized, show a marked preference for heterolepticity and can be synthesized by comproportionation, in particular when using sterically demanding ligands. − In line with these observations, complex 1 does not disproportionate into [(CAAC)­BeDur] 2 (Dur = 2,3,5,6-triphenylmethyl = duryl) and [(CAAC)­BeBr 2 ] even after prolonged heating in toluene up to 100 °C.…”

Recent progress in beryllium organometallic chemistry

“…Furthermore, the addition of another NHC unit induces a certain steric congestion to the transfer of a hydride from a BeH 2 unit. Recent reports from the Buchner 52 and Jones 53 research groups disclose a Schlenk-type redistribution of Grignard-analogous aryl beryllium complexes, resulting preferentially in heteroleptic compounds rather than homoleptic ones. A monomeric beryllium hydride was synthesized by Hadlington et al from a dimeric beryllium hydride species which was then used to access a main-group metal formyl scaffold through CO-activation.…”