Details

Autor(en) / Beteiligte

• Korb, Marcus
• Schaarschmidt, Dieter
• Grumbt, Martin
• König, Matthias
• Lang, Heinrich

Titel

Evaluation of the Transferability of the “Flexible Steric Bulk” Concept from N‐Heterocyclic Carbenes to Planar‐Chiral Phosphinoferrocenes and their Electronic Modification

Ist Teil von

• European journal of inorganic chemistry, 2020-08, Vol.2020 (31), p.2968-2982

Ort / Verlag

Weinheim: Wiley Subscription Services, Inc

Erscheinungsjahr

2020

Quelle

Wiley Online Library

Beschreibungen/Notizen

• The concept of “flexible steric bulk” is discussed at 2‐phenylvinyl‐1‐phosphinoferrocenes. The introduction of freely rotatable 1'‐silyl groups increases the catalytic productivity within the synthesis of tri‐ortho‐substituted biaryls by Suzuki–Miyaura C,C cross‐coupling reactions, giving higher yields with 1/4 of catalyst concentration than for the non‐silylated derivatives. Electronic modification of the P and the vinyl donor functionalities was investigated by introducing substituents in the para positions of both groups. Therein, electron‐withdrawing phosphines increased the yield from 78 to 91 % for a given biaryl, by changing from a diphenylphosphino to the P(p‐CN‐C6H4)2 unit. Opposite results, obtained from electron‐donating and sterically demanding phosphines, were in accordance with the 1J(31P,77Se) values. However, the electron density of the ferrocenyl backbone, expressed by the redox potential of the first ferrocenyl‐related redox process, cannot be correlated with the donor‐properties at the P atom. Changing from a PPh2‐substituted ferrocene to a (RA)‐1,1'‐binaphthyl‐containing phosphonite, a complex interaction between the axial‐ and the planar‐chiral motifs occurs, resulting a change of the absolute biaryl configuration. Planar‐chiral vinyl‐phosphino ferrocenes were modified electronically to evaluate the role of each donor functionality within Pd‐catalyzed reactions. “Flexible steric bulk” was introduced to investigate its stabilization of the catalytically active species. The impact of additional asymmetry at the P‐donor towards the atroposelective synthesis of sterically hindered biaryls is demonstrated.