Bis(alkynyl)borane: A New Class of Acyclic Boron-Containing pi Ligands in eta(5)-Coordination Mode

Reactions between Rosenthal's zirconocene synthon, [Cp2Zr(py)Me3SiC CSiMe3] (py = pyridine), and two different types of bis(alkynyl) boranes, (Me3Si)(2)NB(C CSiMe3)(2) and MesB(CCSiMe3)(2) (Mes = 2,4,6-trimethylphenyl), both resulting in the formation of eta(5)-coordinated bis(alkynyl)borane zirconocene complexes. X-ray diffraction analysis revealed their six-membered cyclic structures featuring a boat conformation with considerable Zr-B interactions. The Zr-B bonding strength and conformational lability of the ZrC4B ring are dependent on the pi basicity of the exocyclic B substituent. These compounds represent the first examples of eta(5)-coordinated acyclic boron-containing pi ligands.