Trimethylsilyl, ligand structure

A variable-temperature Li, C, NMR spectroscopy study was carried out on the ligand structure and association behavior of [ Li, N]-enriched lithium bis(trimethylsilyl)-amide in hydrocarbon solntion. The system behaves as shown, for example, in equation 38, with the solnte adopting a dimeric form (209), which tnms to the monomeric 210 on... 

Snapper, Hoveyda and coworkers have used a ligand diversity approach for finding a catalyst for the addition of trimethylsilyl cyanide to epoxides. The basic ligand structure (12.130) was optimised using combinatorial techniques, which allowed for the parallel synthesis of over 20 ligands a day. Variation of the first amino... 

The reactions of 1-trimethylsilyl- or l-trimethylstannyl-2-butenyl-9-borabicyclo[3.3.1]-nonancs in the presence of pyridine are adequately explained by the usual transition structure 20 since the aldehyde should be capable of displacing pyridine as a ligand on boron. 

The bora-2,5-cyclohexadienes 25, 43, and 44 have been used in experimental studies. Photochemical reaction of 25 and 43 with Fe(CO)s produces the robust complexes 45 (29) and 46 (92) with 7)5-divinylborane structures (92), whereas thermally induced complex formation of 44 with Fe2(CO)9 is accompanied by ligand isomerization and affords complex 47 (67). We note in passing that S(UB) = 38.8 ppm for 47 is at rather low field. The only strictly comparable boraolefin known is l-methoxy-6-(trimethylsilyl)bora-2,4-cyclohexadiene [8(nB) = 47.1 ppm] (26). On this basis, the high field shift upon complexation (only 8.3 ppm) indicates weak Fe-B interaction. 

The tris(trimethylsilyl)silyl ligands can be easily modified by reactions with silyl chlorides, as shown with a series of phenylated species Mes Ph SiCl (n = 0-3). Furthermore, triisopropyl, thexyldimethylsilyl, or tert-butyldimethylsilyl substitution are all easily possible.190 The crystallographic characterization of some of the alkali metal derivatives indicates a direct correlation between ligand size and resulting structural parameters. 

The effect of structure and solvation on the Li quadrupolar interaction was studied for a relatively large number of cyclopentadienyllithium derivatives of known sohd state structure . As mentioned above, these complexes have been shown to form several types of structures (Scheme 3) . Again, the factors determining the structure are the steric requirements of the substituents and ligands. For solubility reasons, most of the complexes studied by X-ray crystallography are substituted, often with large trimethylsilyl substituents. 

---