Bis(cyclopentadienyl)niobium (niobocene) [Nb(h5-C5H5)2]2 (or NbCp2) is yellow diamagnetic solid (d3).
NbCp2 has dimeric structure: [NbCp2]2
Synthesis:
2 NbCl5 + 10 NaCp → [Nb(h5-Cp)2] + 10 NaCl
Nb(h5-C5H5)2 was reported to be applicable as precursor for Nb MOCVD