The ligand 1,4-di-2-pyridyl-5,6,7,8,9,10-hexahydrocycloocta[d]pyridazine (6-dppd) contains two potential chelate groups, but it coordinates to only one dimethylplatinum group in forming the complex [PtMe2(6-dppd)], 1. Complex 1 contains a free pyridyl and a free pyridazine nitrogen donor, but it fails to coordinate to ZnCl2 or to CuCl to give a bimetallic complex. Complex 1 reacted with mercury(II) salts HgX2 (X = Cl, Br, OAc), not by coordination but by oxidative addition to the dimethylplatinum(II) center to give the platinum(IV) complexes [PtX(HgX)Me2(6-dppd)]. Complex 1 reacted with bromine or iodine by trans oxidative addition to give [PtX2Me2(6-dppd)], X = Br or I, but, when X = I, a more complex sequence of reactions also gave rise to products of cis oxidative addition and to the products [PtIMe3(6-dppd)] and [PtI3Me(6-dppd)], which arise through a methyl group transfer reaction. Complex 1 reacted with alkyl halides RX by trans oxidative addition to give [PtXRMe2(6-dppd)], R = Me, X = I; R = CH2Ph,...