4 Au + 8 CN- + O2 + 2 H2O → 4 [Au(CN)2]- + 4 OH-
This is a complexation reaction: [Au(CN)2]- is the formed complex.
This is an oxidation-reduction (redox) reaction:
8 CII + 8 e- → 8 CI (reduction)
4 Au0 - 12 e- → 4 AuIII (oxidation)
2 O0 + 4 e- → 2 O-II (reduction)
CN- is an oxidizing agent, Au is a reducing agent, O2 is an oxidizing agent.