Toward Transition‐Metal‐Templated Construction of Arylated B(4) Chains by Dihydroborane Dehydrocoupling

The reactivity of a diruthenium tetrahydride complex towards three selected dihydroboranes was investigated. The use of [DurBH(2)] (Dur=2,3,5,6‐Me(4)C(6)H) and [(Me(3)Si)(2)NBH(2)] led to the formation of bridging borylene complexes of the form [(Cp*RuH)(2)BR] (Cp*=C(5)Me(5); 1 a: R=Dur; 1 b: R=N(SiMe(3))(2)) through oxidative addition of the B−H bonds with concomitant hydrogen liberation. Employing the more electron‐deficient dihydroborane [3,5‐(CF(3))(2)‐C(6)H(3)BH(2)] led to the formation of an anionic complex bearing a tetraarylated chain of four boron atoms, namely Li(THF)(4)[(Cp*Ru)(2)B(4)H(5)(3,5‐(CF(3))(2)C(6)H(3))(4)] (4), through an unusual, incomplete threefold dehydrocoupling process. A comparative theoretical investigation of the bonding in a simplified model of 4 and the analogous complex nido‐[1,2(Cp*Ru)(2)(μ‐H)B(4)H(9)] (I) indicates that there appear to be no classical σ‐bonds between the boron atoms in complex I, whereas in the case of 4 the B(4) chain better resembles a network of three B−B σ bonds, the central bond being significantly weaker than the other two.