The new sterically encumbered facially coordinating N(3)-donor ligand cis,cis-1,3,5-tris(mesitylideneimino)cyclohexane (L1) has been synthesised. Reaction with [Cu(NCCH(3))(4)]PF(6) gives [Cu(L1)NCCH(3)]PF(6) (1), the bound acetonitrile being labile and readily replaced by CO to yield [Cu(L1)CO]PF(6) (2); both 1 and 2 have been structurally characterised. Complexes 1 and 2 do not undergo a substitution reaction with ethylene. This is in contrast to the related bidentate ligand complexes [Cu(L2)NCCH(3)]BF(4) (3) or [Cu(L2)CO]BF(4) (4) (L2= 1,2-bis(mesitylideneamino)cyclohexane) which rapidly form the ethylene complex under the same conditions.