Alkaline‐Earth Metal Mediated Benzene‐to‐Biphenyl Coupling
Jonathan Mai, Michael Morasch, Dawid Jędrzkiewicz, Jens Langer, Bastian Rösch, Sjoerd Harder
Abstract
Abstract Complex [( DIPeP BDI)Ca] 2 (C 6 H 6 ), with a C 6 H 6 2− dianion bridging two Ca 2+ ions, reacts with benzene to yield [( DIPeP BDI)Ca] 2 (biphenyl) with a bridging biphenyl 2− dianion ( DIPeP BDI=HC[C(Me)N‐DIPeP] 2 ; DIPeP=2,6‐CH(Et) 2 ‐phenyl). The biphenyl complex was also prepared by reacting [( DIPeP BDI)Ca] 2 (C 6 H 6 ) with biphenyl or by reduction of [( DIPeP BDI)CaI] 2 with KC 8 in presence of biphenyl. Benzene‐benzene coupling was also observed when the deep purple product of ball‐milling [( DIPP BDI)CaI(THF)] 2 with K/KI was extracted with benzene (DIPP=2,6‐CH(Me) 2 ‐phenyl) giving crystalline [( DIPP BDI)Ca(THF)] 2 (biphenyl) (52 % yield). Reduction of [( DIPeP BDI)SrI] 2 with KC 8 gave highly labile [( DIPeP BDI)Sr] 2 (C 6 H 6 ) as a black powder (61 % yield) which reacts rapidly and selectively with benzene to [( DIPeP BDI)Sr] 2 (biphenyl). DFT calculations show that the most likely route for biphenyl formation is a pathway in which the C 6 H 6 2− dianion attacks neutral benzene. This is facilitated by metal‐benzene coordination.