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.