This thesis describes a study of dimethylplatinum(II) and dimethylplatinum(IV) complexes containing bidentate nitrogen donor ligands. This work deals with oxidative addition, and reductive elimination chemistry, and it focuses on synthesis, characterization, and reaction mechanisms in studies of these complexes. The compound [PtMe2(bpe)], bpe = 1,2-bis(2-pyridyl)ethane, is easily oxidized to give octahedral organoplatinum(IV) complexes and the subsequent chemistry is profoundly influenced by the accompanying strain induced in the 7-membered Pt(bpe) chelate ring. On reaction of [PtMe2(bpe)] with HCl, the initial product [PtHClMe2(bpe)] undergoes reductive elimination of methane to form [PtClMe(bpe)]. In contrast, methyl iodide reacts with [PtMe2(bpe)] to give [PtIMe3(bpe)], and this decomposes by loss of the bpe ligand to give the cubane [(PtIMe3)4] and not by reductive elimination. Finally, a new class of platinum(IV) double cubane clusters was obtained on oxidation of complex [PtMe2(bpe)] with either hydrogen peroxide to give [Pt4( -OH)4(3-OH)2Me10], as a mixed complex with [PtMe2(CO3)(bpe)], or with oxygen in methanol to give [Pt4( -OH)2( -OMe)2(3-OMe)2Me10]. The oxidation of the complex [PtMe2(bps)], bps = bis(2-pyridyl)-dimethylsilane, by oxygen, hydrogen peroxide or dibenzoyl peroxide in the presence of water or alcohol gives the complex cation, [PtMe3(k3-N, N, O-HOSiMe(2-C5H4N)2)]+, in a reaction involving easy cleavage of a methylsilicon bond. Treatment of the complex [PtMe2(bps)] with B(C6F5)3 in trifluoroethanol in air gives the complex [Me(bps)Pt-OSiMe(2-C5H4N)2PtMe3]+ [B(OCH2CF3)(C6F5)3]-. The unique binuclear platinum complex is formed via the competitive methyl platinum group cleavage from [PtMe2(bps)] by the acid H[B(OCH2CF3)(C6F5)3] to give the platinum(II) fragment and oxidation by air to give the platinum(IV) fragment. Combination of the two units then gives the binuclear complex which involves a very easy methylsilicon group cleavage reaction. The platinum(II) complexes containing five-membered heterocyclic imidazole ligands show high reactivity to a broad variety of alkyl halides, peroxides, and halogens forming stable platinum(IV) complexes. The dimethylplatinum(II) complex [PtMe2{(mim)2C=CH2}], (mim)2C=CH2 = 1,1-bis(1-methylimidazole-2-yl)ethene reacts with dichloromethane to give the dimethylplatinum(IV) complex [PtCl(CH2Cl)Me2{(mim)2C=CH2}]. The product exists as a mixture of two isomers, the cis isomer as the kinetic product and the trans isomer as the thermodynamic product. The dimethylplatinum(II) complex [PtMe2(DECBP)], DECBP = 4,4'-diethoxycarbonyl- 2-2'-bipyridine], undergoes easy oxidative addition to the corresponding platinum(IV) complexes. The reactions of the complex [PtMe2(DECBP)] with alkyl bromides RCH2Br, which have hydrogen bond donor or acceptor functional groups, result in the formation of stable platinum(IV) complexes. Those complexes self-assemble in the solid state to form supramolecular polymers via the intermolecular OH---O=C, N-H---Br, OH---BrPt, interactions, with other predicted interactions such as the -stacking, and the C(H)---BrPt secondary weak interactions.