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

Synthesis, isolation and crystal structures of the metalated ylides [Cy3P−C−SO2Tol]M[Cy_{3}P-C-SO_{2}Tol]M (M = Li, Na, K)

The preparation and isolation of the metalated ylides $[Cy_{3}PCSO_{2}Tol]M$ $(\bf {^{Cy}1-M)}$ (with M = Li, Na, K) are reported. In contrast to its triphenylphosphonium analogue the synthesis of $(\bf {^{Cy}1-M)}$ revealed to be less straight forward. Synthetic routes to the phosphonium salt precursor $(\bf {^{Cy}1-H_{2)}}$ via different methods revealed to be unsuccessful or low-yielding. However, nucleophilic attack of the ylide Cy3P = CH2 at toluenesulfonyl fluoride under basic conditions proved to be a high-yielding method directly leading to the ylide $(\bf {^{Cy}1-H)}$. Metalation to the yldiides was finally achieved with strong bases such as $\it {n}$BuLi, NaNH$_2$, or BnK. In the solid state, the lithium compound forms a tetrameric structure consisting of a (C–S–O–Li)$_4$ macrocycle, which incorporates an additional molecule of lithium iodide. The potassium compound forms a C$_4$-symmetric structure with a (K$_4$O$_4$)$_2$ octahedral prism as central structural motif. Upon deprotonation the P–C–S linkage undergoes a remarkable contraction typical for metalated ylides

Isolation of a diylide-stabilized stannylene and germylene

The preparation of the first stable diylide-substituted stannylene and germylene ( $\bf{Y_{2}E}$, with E=Ge, Sn and Y=PPh$_{3}$-C-SO$_{2}$Tol]$^{−}$) is reported. The synthesis is easily accomplished in one step from the sulfonyl-substituted metalated ylide $\bf{YNa}$ and the corresponding ECl$_{2}$ precursors. $\bf{Y_{2}Ge}$ and $\bf{Y_{2}Sn}$ exhibit unusual structures in the solid state and in solution, in which the three adjacent lone pairs in the C-E-C linkage are arranged coplanar to each other. As shown by DFT studies, this bonding situation is preferred over the typical π-donation from the ligands into the empty p-orbital at the metal due to the strong anion-stabilizing ability of the sulfonyl groups in the ylide backbone and their additional coordination to the metal. The alignment of the three lone pairs leads to a remarkable boost of the HOMO energy and thus of the donor strengths of the tetrylenes. Hence, $\bf{Y_{2}Ge}$ and $\bf{Y_{2}Sn}$ become stronger donors than their diamino or diaryl congeners and comparable to cyclic alkyl(amino)carbenes. First reactivity studies confirm the high reactivity of $\bf{Y_{2}Ge}$ and $\bf{Y_{2}Sn}$, which for example undergo an intramolecular C−H activation reaction via metal–ligand cooperation

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

Palladium complexes based on ylide-functionalized phosphines (YPhos)

Palladium allyl, cinnamyl, and indenyl complexes with the ylide‐substituted phosphines $Cy_{3}P^{+}−C^{−}(R)PCy_{2}$ (with R=Me ($\bf L1$) or Ph ($\bf L2$)) and $Cy_{3}P^{+}−C^{−}(Me)P$$\it t$Bu$_2$ ($\bf L3$) were prepared and applied as defined precatalysts in C−N coupling reactions. The complexes are highly active in the amination of 4‐chlorotoluene with a series of different amines. Higher yields were observed with the precatalysts in comparison to the in situ generated catalysts. Changes in the ligand structures allowed for improved selectivities by shutting down β‐hydride elimination or diarylation reactions. Particularly, the complexes based on $\bf L2$ (joYPhos) revealed to be universal precatalysts for various amines and aryl halides. Full conversions to the desired products are reached mostly within 1 h reaction time at room temperature, thus making $\bf L2$ to one of the most efficient ligands in C−N coupling reactions. The applicability of the catalysts was demonstrated for aryl chlorides, bromides and iodides together with primary and secondary aryl and alkyl amines, including gram‐scale applications also with low catalyst loadings of down to 0.05 mol %. Kinetic studies further demonstrated the outstanding activity of the precatalysts with TOF over 10.000 h$^{−1}$