Catalytic dimerization of norbornadiene and norbornene into hydrocarbons with multiple bridge rings for potential high-density fuels

• Review on NBD and NBE dimerization for the synthesis of high density fuels. • Typical metal-based catalysts and the key results have been summarized. • Dimerization mechanism on typical coordination catalysts has been illustrated. • The relationship between dimer structure and fuel properties has been discussed. High-density hydrocarbon fuels are essential for air craft to increase payload and expand flight distance. This review will summarize the synthesis of high-density hydrocarbon molecules through catalytic dimerization of norbornadiene and norbornene in the past few decades, which can be used as new fuels or high-energy additives for conventional fuels. Dimerization of norbornadiene including relationship between structural dimers and investigation on metal based homogeneous catalysts and heterogeneous catalysts as well as description of possible mechanisms are firstly introduced. Then synthesis of multi-cyclic compounds from norbornene is illustrated with a focus on efficient and greener routes. After that, physicochemical properties of partial norbornadiene and norbornene dimers and influence of the composition on fuel performance are reviewed. Finally, we will propose the problems in synthesis of high-energy-density fuel through dimerization of norbornene and norbornadiene. This review will be helpful to explore new approaches to synthesize more valuable high-density hydrocarbon fuels and predict possible directions of synthesizing new multi-cyclic hydrocarbon compounds with norbornadiene and norbornene.