Biphenylene has proven to have a rich chemistry with transition metals. In many cases, the aryl-aryl C-C bond is cleaved to give a metallocycle complex, which can go on to give a variety of reaction products. Insertion reactions with small molecules lead to the formation of new polycyclic aromatic derivatives with the incorporation of functional groups. In several cases, these reactions are selective and catalytic. (C) 2002 Elsevier Science B.V. All rights reserved.