Are there any elements or molecules that exchange greater than 4 electrons per bond? I just thought of something off the wall and have no idea what to even google.
I believe several Diatomic uranium complexes have quintuple bond.
A lot of metal-metal bonded complexes contain more than triple bond.
For example, F. A. Cotton's group reported complexes with Cr-Cr and Re-Re quadruple bond. I believe their group also reported sextuple bond as Ygggdrasil said.