15.
Complex [(
DIPePBDI)Ca]
2(C
6H
6), with a C
6H
62− dianion bridging two Ca
2+ ions, reacts with benzene to yield [(
DIPePBDI)Ca]
2(biphenyl) with a bridging biphenyl
2− dianion (
DIPePBDI=HC[C(Me)N-DIPeP]
2; DIPeP=2,6-CH(Et)
2-phenyl). The biphenyl complex was also prepared by reacting [(
DIPePBDI)Ca]
2(C
6H
6) with biphenyl or by reduction of [(
DIPePBDI)CaI]
2 with KC
8 in presence of biphenyl. Benzene-benzene coupling was also observed when the deep purple product of ball-milling [(
DIPPBDI)CaI(THF)]
2 with K/KI was extracted with benzene (DIPP=2,6-CH(Me)
2-phenyl) giving crystalline [(
DIPPBDI)Ca(THF)]
2(biphenyl) (52 % yield). Reduction of [(
DIPePBDI)SrI]
2 with KC
8 gave highly labile [(
DIPePBDI)Sr]
2(C
6H
6) as a black powder (61 % yield) which reacts rapidly and selectively with benzene to [(
DIPePBDI)Sr]
2(biphenyl). DFT calculations show that the most likely route for biphenyl formation is a pathway in which the C
6H
62− dianion attacks neutral benzene. This is facilitated by metal-benzene coordination.
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