Apart from the very bulky substituents, a η-coordination of diphosphene to a metal is also possible to stabilize the P-P double bond. In 1982, K. R. Dixon et al. synthesized platinum and palladium complexes  (with M=Pt or Pd and L=(PPh3) or ), which contained side-on coordination. Different from η coordination complex, where P-P still kept the double bond nature, P-P distance in side-on coordination complexes (2.121Å in ) was significantly longer than that in non-coordinated bis(2,4,6-tri-tert-butylphenyl)diphosphene.