Synthesis of Intramolecular P/Al-Based Frustrated Lewis Pairs via Aluminum-Tin-Exchange and their Reactivity toward CO2.

Frustrated Lewis pairs (FLPs) composed of acidic alane and basic phosphane functions, separated by a xanthene linker, can be prepared through the corresponding Me3 Sn derivative and methyl aluminum compounds with elimination of Me4 Sn. This way MeClAl-, Cl2 Al- and (C6 F5 )2 Al- moieties could be introduced and the resulting FLPs are stabilized by a further equivalent of the alane precursors. In contact with the FLPs CO2 is bound via the C atom at the phosphane functions and the two O atoms at the Al centers. The residues at the latter determine the binding strength. Hence, in case of MeClAl CO2 capture occurs at higher pressure and under ambient conditions CO2 is released again, while for Cl2 Al and (C6 F5 )2 Al CO2 binding becomes irreversible. The results of DFT calculations rationalize these findings by the high thermodynamic stabilization in case of more electronegative residues, which concomitantly lead to higher barriers, and in case of (C6 F5 )2 Al further stabilization is achieved through a low reorganization energy.

Total Synthesis of Strigolactones via Palladium-Catalyzed Cascade Carbonylative Carbocyclization of Enallenes.

Here we report an efficient route for synthesizing strigolactones (SLs) and their derivatives. Our method relies on a palladium-catalyzed oxidative carbonylation/carbocyclization/carbonylation/alkoxylation cascade reaction, which involves the formation of three new C-C bonds and a new C-O bond while cleaving one C(sp3)-H bond in a single step. With our versatile synthetic strategy, both naturally occurring and artificial SLs were prepared.

A strained intramolecular P/Al-FLP and its reactivity toward allene.

FLPs featuring aluminum-phosphane interactions, spring-loaded by a rigid biphenylene linker, have been accessed through a route where trimethyltin units at phosphane-functionalized organic backbones are exchanged by an AlCl2 moiety. Upon contact with substrates like CO2 these are readily bound by the Al/P site with release of strain. The system could also be utilized for a unique reactivity, namely the activation of allene.

P-Protected Diphosphadibenzo[ a, e]pentalenes and Their Mono- and Dicationic P-Bridged Ladder Stilbenes.

The previously elusive diphosphadibenzo[ a, e]pentalene core skeleton was assembled via a surprisingly straightforward cyclization pathway starting from R2P-substituted 2,2'-diphosphinotolanes (R = Ph, iPr). The resulting P-protected diylidic compounds 4 (R = Ph, iPr) were converted to the corresponding P-bridged ladder stilbenes via two consecutive oxidation steps: upon selective one-electron oxidation, the persistent radical monocations 5 (R = Ph, iPr) were obtained and further oxidized to afford the respective fluorescent and air-stable dications 6 (R = Ph, iPr).