Diborylated Magnesium Anthracene as Precursor for B 2 H 5 − ‐Bridged 9,10‐Dihydroanthracene

9,10‐(Bpin) 2 ‐anthracene ( 3 , HBpin=pinacolborane) was synthesized from 9,10‐dibromoanthracene in a stepwise lithiation/borylation sequence. The reaction of 3 with highly activated magnesium furnished the diborylated magnesium anthracene 4 , which was quenched in situ with ethereal HCl to yield cis ‐9,10‐(Bpin) 2 ‐DHA ( cis ‐ 5 , DHA=9,10‐dihydroanthracene). Compound cis ‐ 5 , in turn, can be reduced with Li[AlH 4 ] in THF to give its diborate Li 2 [ cis ‐9,10‐(BH 3 ) 2 ‐DHA] (Li 2 [ cis ‐ 6 ]). In the crystal lattice, the THF solvate Li 2 [ cis ‐ 6 ] ⋅ 3 THF establishes a dimeric structure with Li‐(μ‐H)‐B coordination modes. Hydride abstraction from Li 2 [ cis ‐ 6 ] with Me 3 SiCl yields the BHB‐bridged DHA Li[ 7 ]. This product can also be viewed as a unique cyclic B 2 H 7 − derivative with a hydrocarbon backbone. Treatment of Li 2 [ cis ‐ 6 ] with the stronger hydride abstracting agent Me 3 SiOTf (HOTf=trifluoromethanesulfonic acid) in THF affords the THF diadduct of cis ‐9,10‐(BH(OTf)) 2 ‐DHA.