Selectivity Control of the Ligand Exchange at Carbon in α-Metallated Ylides as a Route to Ketenyl Anions.

α-Metallated ylides have recently been reported to undergo phosphine by CO exchange at the ylidic carbon atom to form isolable ketenyl anions. Systematic studies on the tosyl-substituted yldiides, R3 P=C(M)Ts (M=Li, Na, K), now reveal that carbonylation may lead to a competing metal salt (MTs) elimination. This side-reaction can be controlled by the choice of phosphine, metal cation, solvent and co-ligands, thus enabling the selective isolation of the ketenyl anion [Ts-CCO]M (2-M). Complexation of 2-Na by crown ether or cryptand allowed structure elucidation of the first free ketenyl anion [Ts-CCO]- , which showed an almost linear Ts-C-C linkage indicative for a pronounced ynolate character. However, DFT studies support a high charge at the ketenyl carbon atom, which is reflected in the selective carbon-centered reactivity. Overall, the present study provides important information on the selectivity control of ketenyl anion formation which will be crucial for future applications.

Au⋠⋠⋠H-C Hydrogen Bonds as Design Principle in Gold(I) Catalysis.

Secondary ligand-metal interactions are decisive in many catalytic transformations. While arene-gold interactions have repeatedly been reported as critical structural feature in many high-performance gold catalysts, we herein report that these interactions can also be replaced by Au⋅⋅⋅H-C hydrogen bonds without suffering any reduction in catalytic performance. Systematic experimental and computational studies on a series of ylide-substituted phosphines featuring either a PPh3 (Ph YPhos) or PCy3 (Cy YPhos) moiety showed that the arene-gold interaction in the aryl-substituted compounds is efficiently compensated by the formation of Au⋅⋅⋅H-C hydrogen bonds. The strongest interaction is found with the C-H moiety next to the onium center, which due to the polarization results in remarkably strong interactions with the shortest Au⋅⋅⋅H-C hydrogen bonds reported to date. Calorimetric studies on the formation of the gold complexes further confirmed that the Ph YPhos and Cy YPhos ligands form similarly stable complexes. Consequently, both ligands showed the same catalytic performance in the hydroamination, hydrophenoxylation and hydrocarboxylation of alkynes, thus demonstrating that Au⋅⋅⋅H-C hydrogen bonds are equally suited for the generation of highly effective gold catalysts than gold-arene interactions. The generality of this observation was confirmed by a comparative study between a biaryl phosphine ligand and its cyclohexyl-substituted derivative, which again showed identical catalytic performance. These observations clearly support Au⋅⋅⋅H-C hydrogen bonds as fundamental secondary interactions in gold catalysts, thus further increasing the number of design elements that can be used for future catalyst construction.

Synthesis of Low-Valent Dinuclear Group†14 Compounds with Element-Element Bonds by Transylidation.

Dinuclear low-valent compounds of the heavy main group elements are rare species owing to their intrinsic reactivity. However, they represent desirable target molecules due to their unusual bonding situations as well as applications in bond activations and materials synthesis. The isolation of such compounds usually requires the use of substituents that provide sufficient stability and synthetic access. Herein, we report on the use of strongly donating ylide-substituents to access low-valent dinuclear group 14 compounds. The ylides not only impart steric and electronic stabilization, but also allow facile synthesis via transfer of an ylide from tetrylene precursors of type R Y2 E to ECl2 (E=Ge, Sn; R Y=TolSO2 (PR3 )C with R=Ph, Cy). This method allowed the isolation of dinuclear complexes amongst a germanium analogue of a vinyl cation, [(Ph Y)2 GeGe(Ph Y)]+ with an electronic structure best described as a germylene-stabilized GeII cation and a ylide(chloro)digermene [Cy Y(Cl)GeGe(Cl)Cy Y] with an unusually unsymmetrical structure.

A Size-Flexible Organometallic Box for the Encapsulation of Fullerenes.

A palladium-cornered molecular square with four pyrene-bis(imidazolylidene) bridging ligands is reported. This metallo-polygon can encapsulate C60 and C70 . The X-ray diffraction structures of the empty cage as well as the cages complexed with both fullerenes are described. The fullerene encapsulation produces perturbations in the structural parameters of the metallo-square, showing that it can adjust the shape of its cavity to the size of each fullerene.

Synthesis, Isolation and Crystal Structures of the Metalated Ylides [Cy3P-C-SO2Tol]M (M = Li, Na, K).

The preparation and isolation of the metalated ylides [Cy3PCSO2Tol]M ( Cy1-M) (with M = Li, Na, K) are reported. In contrast to its triphenylphosphonium analogue the synthesis of Cy1-M revealed to be less straight forward. Synthetic routes to the phosphonium salt precursor Cy1-H2 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 Cy1-H. Metalation to the yldiides was finally achieved with strong bases such as nBuLi, NaNH2, 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 (K4O4)2 octahedral prism as central structural motif. Upon deprotonation the P-C-S linkage undergoes a remarkable contraction typical for metalated ylides.