2,2′-Biphenyldiylbis(dimethylphosphan): Stereochemie, chirale Rhodiumkomplexe, cyclisierende Quartärsalz- und Ylidbildung sowie eine unerwartete Ylid-Ringkontraktion zum 9 λ5-Phosphaphenanthren

Straightforward Access to Multifunctional π‐Conjugated P‐Heterocycles Featuring an Internal Ylidic Bond**

We report the straightforward one‐pot synthesis of novel 5‐ or 6‐membered P‐heterocycles featuring an internal ylidic bond: P‐containing acenaphthylenes and phenanthrenes. The stability of the compounds tolerates post‐functionalization through direct arylation to introduce electron‐rich/poor substituents and the synthetic strategy is also compatible with the preparation of more elaborate polyaromatic scaffolds such as acenes and helicenes. Using a joint experimental (X‐ray analysis, optical and redox properties) and theoretical approach, we perform a full structure–property relationships study on these new platforms. In particular, we show that molecular engineering allows not only tuning their absorption/emission across the entire visible range but also endowing them with chiroptical or non‐linear optical properties, making them valuable dyes for a large panel of photonic or opto‐electronic applications.

Asymmetric Activation

While nonracemic catalysts can generate nonracemic products with or without the nonlinear relationship in enantiomeric excesses between catalysts and products, racemic catalysts inherently give only a racemic mixture of chiral products. Asymmetric catalysts, either in nonracemic or racemic form, can be further evolved into highly activated catalysts with association of chiral activators. This asymmetric activation process is particularly useful in racemic catalysis through selective activation of one enantiomer of the racemic catalyst. Recently, a strategy whereby a racemic catalyst is selectively deactivated by a chiral additive has been reported to yield nonracemic products. However, reported herein is an alternative and conceptually opposite strategy in which a chiral activator selectively activates, rather than deactivates, one enantiomer of a racemic chiral catalyst. The advantage of this activation strategy over the deactivation counterpart is that the activated catalyst can produce a greater enantiomeric excess in the products-even with the use of a catalytic amount of activator relative to chiral catalyst-than that attained by the enantiomerically pure catalyst on its own. Therefore, asymmetric activation could provide a general and powerful strategy for not only the use of atropisomeric, racemic ligands but also chirally flexible and proatropisomeric ligands without enantiomeric resolution!