The homologous series of parent octamethylcyclotetrasilazane (c‐NH‐SiMe2‐)4, (1), the lithium complex [(THF)2Li2(c‐N‐SiMe2‐NH‐SiMe2‐)2]2, (2), containing the cyclic dianion, and [(THF)2LiAl(c‐N‐SiMe2‐)4]2, (3), accommodating the unprecedented tetraanion [Me2SiN]4‐ was synthesized to investigate the nature of the covalent Si‐N single bond in the presence of various metals. These model compounds show a wide diversity of Si‐N(H), Si‐N(M), Si‐N(H, M) and M‐N bonds and serve as bench‐mark systems to study polar bonds by high‐resolution low‐temperature X‐ray structure analysis. Experimental charge density studies reveal highly polar Si‐N bonds with remarkable ionic contribution, even in the non‐metallated starting material 1. The Li‐N and Li‐O bonds have to be classified as almost purely ionic bonds with topological properties not far from those determined for NaCl.

No abstract

Calcium atoms react with +I-substituted benzene derivatives under cocondensation conditions to yield arylcalcium hydrides. With toluene, tert-butylbenzene, and trimethyl(phenyl)silane the reaction showed no selectivity for C−H activation, resulting in the formation of each of the three possible isomers, while with m-xylene the reaction resulted in selective activation of the bond meta to the CH 3 groups. Treatment of (tert-butylphenyl)calcium hydride with di-and trisubstituted phenols such as 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, and 2,4,6-tri-tert-butylphenol resulted in the formation of calcium aryloxides in yields Ͼ 95%.[Ca(2,4,6-tBu 3 C 6 H 2 O) 2 (THF) 3 ] crystallises from a THF solution as a distorted trigonal bipyramid, with two THF ligands in the trans-axial positions and the third THF ligand and both aryloxide groups in equatorial positions. The Ca−O Aryl bond

No abstract

Sulfurdiimides RN=S=NR react in donating solvents with two equivalents of lithiumalkyls to give the dimeric C,N-dilithium-methylenediimidosulfite solvent adducts [(Et2O)Li2{H2CS-(NSiMe3)(NtBu)}]2 (1) and [(thf)Li2{H8C4S(NtBu)2}]2 (2). Firstly, addition of a lithiumalkyl to sulfurdiimide gives the diimidosulfinates [RS(NR')2]- (1: R = Me, R′ = tBu, SiMe3; 2: R = nBu; R′ = tBu) while in a second step the α-carbon atom in R is metalated with one equivalent of lithiumalkyl to give the asymmetric S-ylides. The reaction of 3-bromothiophene with one equivalent of nBuLi and one of sulfurdiimide tBuN=S=NtBu resulted in the dilithium-3-thiophenylenediimidosulfite [(thf)Li2{(SC4H2)S(NtBu)2}]2 (3). It can be regardedas the first example of a dianionic S(IV)-β-ylide. This class of compounds can be rationalised as sulfite analogues, where two oxygen atoms are isoelectronically replaced by a NR group each and the remaining oxygen atom is replaced by a CR2 group. The rich coordination chemistry of the triimidosulfites is extended by the introduction of a hard carbanionic centre.