Carbenoid-mediated formation and activation of element-element and element–hydrogen bonds

The application of the silyl-substituted Li/Cl carbenoid RR'C(Li)Cl ($\bf 1$) [with R = Ph$_2$P(S), R' = SiMe$_3$] in the dehydrocoupling of group 14 element hydrides is reported. While silanes only yield product mixtures, selective E–E bond formation was observed for germanes and stannanes. In case of the tin compounds, also aliphatic stannanes could be successfully coupled to the corresponding distannanes. This reactivity is in contrast to that reported for BH$_3$, which preferentially undergoes B–H addition to the carbenoid carbon atom via borate formation. Formation of a borate intermediate is also assumed to be the initial step in the reaction of ($\bf 1$ with phosphinoborane CatB-PPh$_2$ (Cat = catecholato), which results in the generation of diphosphine Ph$_4$P$_2$ via chlorotrimethylsilane elimination and formation of a 1,1'-diborylated carbanion

Efficient Pd-catalyzed direct coupling of aryl chlorides with alkyllithium reagents

Organolithium compounds are amongst the most important organometallic reagents and frequently used in difficult metallation reactions. However, their direct use in the formation of C−C bonds is less established. Although remarkable advances in the coupling of aryllithium compounds have been achieved, Csp$^{2}$−Csp3 coupling reactions are very limited. Herein, we report the first general protocol for the coupling or aryl chlorides with alkyllithium reagents. Palladium catalysts based on ylide-substituted phosphines (YPhos) were found to be excellently suited for this transformation giving high selectivities at room temperature with a variety of aryl chlorides without the need for an additional transmetallation reagent. This is demonstrated in gram-scale synthesis including building blocks for materials chemistry and pharmaceutical industry. Furthermore, the direct coupling of aryllithiums as well as Grignard reagents with aryl chlorides was also easily accomplished at room temperature

Solvation effects on the structure and stability of alkali metal carbenoids

s-Block metal carbenoids are carbene synthons and applied in a myriad of organic transformations. They exhibit a strong structure–activity relationship, but this is only poorly understood due to the challenging high reactivity and sensitivity of these reagents. Here, we report on systematic VT and DOSY NMR studies, XRD analyses as well as DFT calculations on a sulfoximinoyl-substituted model system to explain the pronounced solvent dependency of the carbenoid stability. While the sodium and potassium chloride carbenoids showed high stabilities independent of the solvent, the lithium carbenoid was stable at room temperature in THF but decomposed at 108C in toluene. These divergent stabilities could be explained by the different structures formed in solution. In contrast to simple organolithium reagents, the monomeric THF-solvate was found to be more stable than the dimer in toluene, since the latter more readily forms direct Li/Cl interactions which facilitate decomposition via a-elimination