Bücherbesprechungen

Ohne Zusammenfassung     

Bücherbesprechungen

Ohne Zusammenfassung     

A new class of chiral organogermanes derived from C2-symmetric dithiols: synthesis,characterization and stereoselective free radical reactions

A new class of dithiostannanes and dithiogermanes have been prepared from 1,1'-binaphthyl-2,2'-dithiol and 3,3'-bis(trimethylsilyl)-1,1'-binaphtho-2,2'-dithiol. While reduction of 4-butyl-4-chloro-3,5-dithia-4-stanna-cyclohepta[2,1-a;3,4-a']dinaphthalene to the corresponding tin hydride was unsuccessful, 4-tert-butyl-3,5-dithia-4-germa-cyclohepta[2,1-a;3,4-a']dinaphthalene and 4-tert-butyl-2,6-bis(trimethylsilyl)-3,5-dithia-4-germa-cyclohepta[2,1-a;3,4-a']dinaphthalene were obtained by reduction of the parent germanium chlorides with NaBH(4) and LiBH(4), respectively. Kinetic constants for hydrogen transfer to a primary alkyl radical were measured for both germanium hydrides. Reduction of alpha-halo carbonyl compounds by these germanium hydrides occurs with moderate ee values (up to 42%), while hydrogermylation of methyl methacrylate occurs with low selectivity (<3/1) for the former hydride but high selectivity (>10/1) for the latter.     

2 + 2] cross coupling of benzene and tropylium ligands in reductively activated piano stool complexes of Mn,Cr, and W

We have established cation/anion coupling reactions between the tropylium ligand in [M(eta7-C7H7)(CO)3]+ (M = Cr, W) and the reductively activated eta4-benzene ligand in [Mn(eta4-C6H6)(CO)3]- (3-) to form [M(CO)3(mu2-eta6:eta5-C7H7-C6H6)Mn(CO)3]; [Cr(CO)3(mu2-eta6:eta5-C7H7-C6H6)Mn(CO)3] can be further reduced to [Cr(CO)3(mu2-eta5:eta4-C7H7-C6H6)Mn(CO)3]2-, in which the tropylium and benzene ligands have undergone a [2 + 2] cross coupling reaction.     

STUDIES OF ADHESION OF METAL PARTICLES TO SILICA PARTICLES BASED ON ZETA POTENTIAL MEASUREMENTS

The zeta-potentials of silica, copper, platinum and gold particles have been measured as a function of pH. The isoelectric points were found to be at pH 3.0, 5.8, 3.0 and 3.5, respectively. In the pH range 3.0 to 5.8 copper and silica particles are oppositely charged and accordingly the coating of silica with copper particles could be demonstrated. In the case of gold and platinum the sign of the charge is such that direct adhesion to silica particles cannot be expected and this was also demonstrated in the case of platinum.