Alkaline‐Earth Metal Mediated Benzene‐to‐Biphenyl Coupling

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.