The Platinum Center is a Stronger Nucleophile than the Free Nitrogen Donors in a Dimethylplatinum Complex with a Dipyridylpyridazine Ligand

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, X = Br; R = CH2-4-C6H4-CH2Br, X = Br. The cleavage of methyl groups
from complex 1 by DCl gave a mixture of all isotopomers
of methane, CH4–nDn, indicating ready equilibration between hydrido­(methyl)­platinum­(IV)
and methaneplatinum­(II) complex intermediates.