Catalytic hydrodefluorination (HDF) of unactivated fluoroalkanes or CF -substituted aryl species is performed using the P Lewis acids, [(bipy)PPh] (1 ) and [(terpy)PPh] (2 ) under mild conditions (25 or 50 °C). Mechanistic studies indicate that activation of C-F bond by the P center is key. Particularly noteworthy is that the catalyst 2[B(C F ) ] is air-stable and readily accessible from bench-stable, commercially available reagents in one-step and can be used without isolation.

The capacity of transition metals to bind and transform carbon monoxide (CO) is critical to its use in many chemical processes as a sustainable, inexpensive C1 building block. By contrast, only few s- and p-block element compounds bind and activate CO, and conversion of CO into useful carbonyl-containing organic compounds in such cases remains elusive. We report that metalated phosphorus ylides provide facile access to ketenyl anions ([RC=C=O] – ) by phosphine displacement with CO. These anions are very stable and storable reagents with a distinctive electronic structure between that of the prototypical ketene (H 2 C=C=O) and that of ethynol (HC≡C–OH). Nonetheless, the ketenyl anions selectively react with a range of electrophiles at the carbon atom, thus offering high-yielding and versatile access to ketenes and related compounds.

On the occasion of the 60th birthday of Prof. Holger Braunschweig.

Owing to the strong electron-donating ability of ylide substituents, diylidyltetrylenes are usually highly nucleophilic species with strong donor capacities. Here, we demonstrate that their electronic properties are in fact highly flexible and can be effectively tuned through variation of the substituent in the ylide backbone. Initial density functional theory studies showed that cyano groups are particularly capable in lowering the LUMO energy of diylidyl germylenes thus turning these usually highly nucleophilic species into electrophilic compounds. This was confirmed by experimental studies. Attempts to synthesize the germylene (Y CN ) 2 Ge [with Y CN = Ph 3 P-(C)-CN] from the corresponding metalated ylide Y CN K selectively led to germanide [(Y CN ) 3 Ge)K] 2 thus reflecting the electrophilic nature of the intermediate formed germylene. XRD analysis of single crystals of (Y CN ) 2 Ge -serendipitously obtained through protonative cleavage of one ylide from the germanide -revealed a monomeric structure with rather long Ge-ylide linkages, which corroborates well with a pure single bond and no stabilization of the empty p π orbital at germanium through π bonding. The germanide exhibits methanide-like reactivity towards chalcogens but a likewise weak GeÀ C bond as demonstrated by the insertion of carbon dioxide.

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 tosyl-substituted metallated ylides (R3P=C(M)Ts) now reveal that carbonylation leads to either phosphine or metal salt (MTs) elimination. The selectivity of this reaction can be controlled by the nature of the phosphine and metal cation, the solvent and additional co-ligands, enabling full control of the selectivity and isolation of the ketenyl anion [Ts-CCO]M (2-M, M = Na, K) in high yields. Complexation of 2-Na by crown ether or cryptand allowed the structure elucidation of the first “naked” ketenyl anion [Ts-C=C=O]-, which showed only a slightly bent Ts-C-C linkage indicating pronounced ynolate character. However, DFT studies confirmed the high charge concentration at the ketenyl carbon, which is reflected in the selective carbon-centered reactivity of 2-M. In contrast to previously reported ketenyl anions, ketenes obtained from the tosyl-substituted anion 2-M reacted directly with the ketenyl anion to give convenient access to a range of cyclobutadiones. Overall, the present studies provide important information on the selectivity control of ketenyl anion formation which will be crucial for broader applications in the future.