Controlled Direct Synthesis of C-Mono- and C-Disubstituted Derivatives of [3,3-Co(1,2-C2B9H11)2]- with Organosilane Groups: Theoretical Calculations Compared with ACHTUNGTRENUNGExperimental Results

摘要

Mono- and dilithium salts of [3,3-Co(1,2-C2B9H11)2]-, (1-), react with different chlorosilanes (Me2SiHCl, Me2SiCl2, Me3SiCl and MeSiHCl2) with an accurate control of the temperature to give a set of novel Cc-mono- (Cc=Ccluster) and Cc-disubstituted cobaltabis(dicarbollide) derivatives with silyl functions: [1-SiMe2H-3,3-Co(1,2-C2B9H10)(1,2-C2B9H11)]- (3-); [1,1-m-SiMe2-3,3-Co(1,2-C2B9H10)2]- (4-); [1,1-m-SiMeH-3,3-Co(1,2-C2B9H10)2]-(5-); [1-SiMe3-3,3-Co(1,2-2B9H10)- (1,2-C2B9H11)]- (6-) and [1,1-(SiMe3)2-3,3-Co(1,2-C2B9H10)2]- (7-). In a similar way, the [8,8-m-(1,2-C6H4)-1,1-m-SiMe2-3,3-Co(1,2-C2B9H9)2]- (8-); [8,8-m-(1,2-C6H4)-1,1-m-SiMeH-3,3-Co(1,2-C2B9H9)2]- (9-) and [8,8-m-(1,2-C6H4)-1-SiMe3-3,3-Co(1,2-C2B9H9)(1,2-C2B9H10)]- (10-) ions have been prepared from [8,8-m-(1,2-C6H4)-3,3-Co(1,2-C2B9H10)2]- (2-). Thus, depending on the chlorosilane, the temperature and the stoichiometry of nBuLi used, it has been possible to control the number of substituents on the Cc atoms and the nature of the attached silyl function. All compounds were characterised by NMR and UV/Vis spectroscopy and MALDI-TOF mass spectrometry; [NMe4]-3, [NMe4]-4 and [NMe4]-7 were successfully isolated in crystalline forms suitable for X-ray diffraction analyses. The 4- and 8- ions, which contain one bridging -m-SiMe2 group between each of the dicarbollide clusters, were unexpectedly obtained from the reaction of the monolithium salts of 1- and 2-, respectively, with Me2SiHCl at -78 in 1,2-dimethoxyethane. This suggests that an intramolecular reaction has taken place, in which the acidic Cc-H proton reacts with the hydridic SiH, with subsequent loss of H2. Some aspects of this reaction have been studied by using DFT calculations and have been compared with experimental results. In addition, DFT theoretical studies at the B3LYP/6-311GACHTUNGTRENUNG(d,p) level of theory were applied to optimise the geometries of ions 1-C10- and calculate their relative energies. Results indicate that the racemic mixtures, rac form, are more stable than the meso isomers. A good concordance between theoretical studies and experimental results has been achieved.