No abstract

Two new C 2 -symmetric diazaborinanes were prepared by diastereoselective intramolecular dihydroboration of bulky 1,3-diamines, the remarkably stable l-[HB(2,6-Pr i 2 -C 6 H 3 NCHMe) 2 CMe 2 ], from which it was not possible to isolate free diimine, and the less bulky l-[HB(2-Pr i -C 6 H 4 NCHMe) 2 CMe 2 ], which yielded l-(2-Pr i -C 6 H 4 NHCHMe) 2 CMe 2 on acid work up. The BH 3 reductions were highly diastereoselective for l-products (de > 95%). Use of AlCl 3 /LiAlH 4 mixtures in diethyl ether gave lower (de ≈ 75%) and opposite selectivity, yielding predominantly u-(2,6-Pr i 2 -C 6 H 3 NHCHMe) 2 CMe 2 upon work up, via a u-[H 2 Al(2,6-Pr i 2 -C 6 H 3 )NHCHMeCMe 2 CHMeN(2,6-Pr i 2 -C 6 H 3 )] intermediate in a two-step reduction. All products were characterized crystallographically.

The hemi‐solvated C2‐symmetric 1,3‐diamidolithium l‐[CMe2{CHMeN(R)}2Li2·OEt2] has been crystallographically characterized. It reacts with oxygen to form the N‐N ring‐closed pyrazolidine l‐[(RNCHMe)2CMe2]. The slightly bulkier Cs‐symmetric amidolithium u‐[CMe2{CHMeN(R′)}2·Li2] forms an unsolvated 1:2 heterocubane complex with nBuLi in the solid state and in solution, as determined by X‐ray crystallography and multinuclear NMR spectroscopy (R = 2‐iPr‐C6H4; R′ = 2,6‐iPr2‐C6H3). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The cover picture shows an Li2N2 unit which is prevented by the bulk of the aryl substituents from stacking with another to form a cubic cluster. The diethyl ether solvent traps this fragment of a molecule which, in the absence of diethyl ether, precipitates as a powder, possibly by lateral association of Li2N2 rings to form an infinite ladder in a manner first suggested by Ronald Snaith, whose memory is honoured in this special edition of EurJIC. Details are presented in the article by F. Mair et al. on p. 3464 ff.