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.