Diacetylplatinum(II) and -platinum(IV) Complexes Bearing κ2- and κ3-Coordinated Tris(pyrazolyl)methane Ligands: Investigations on the Synthesis, Fluxionality, and Reactivity in Relation to the Substitution Pattern of the Ligands



Reactions of the dinuclear platina-β-diketone [Pt2{(COMe)2H}2(μ-Cl)2] (1) with HC(pz)3 and HC(3,5-Me2pz)3 (pz = pyrazol-1-yl; 3,5-Me2pz = 3,5-dimethylpyrazol-1-yl) afforded cationic, thermally labile diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)2H{(pz)3CH}]Cl (3a) and [Pt(COMe)2H{(3,5-Me2pz)3CH}]Cl (3b) with κ3-coordinated tris(pyrazolyl)methane ligands, which were found to react with NaOH or NEt3 to yield neutral diacetylplatinum(II) complexes with κ2-coordinated tris(pyrazolyl)methane ligands {[Pt(COMe)2{(pz)3CH}] (4a); [Pt(COMe)2{(3,5-Me2pz)3CH}] (4b)}. In 4a/b, a molecular rearrangement (decoordination of a pyrazolyl ring and coordination of the originally pendant one) has been found that has been investigated by variable-temperature 1H NMR spectroscopic measurements (coalescence method) as well as by DFT calculations. Diacetylplatinum(II) complexes 4 were found to react in oxidative addition reactions with ROTf (R = H, Me; OTf = trifluoromethanesulfonate) and methyl iodide to yield cationic diacetylplatinum(IV) complexes of the type [Pt(COMe)2R{(pz)3CH}]X (R/X = H/OTf, 5a; Me/OTf, 6a; Me/I, 7a) and [Pt(COMe)2R{(3,5-Me2pz)3CH}]X [R/X = H/OTf (5b), Me/OTf (6b), Me/I (7b)] with κ3-bonded tris(pyrazolyl)methane ligands. Treatment of 4b with alkynyliodine(III) reagents of the type [IPh(C≡CR)]X (R/X = SiMe3/OTf, Ph/OTf, tBu/OTos, iPr/OTos; OTos = p-toluenesulfonate) led to the formation of cationic diacetyl(alkynyl)platinum(IV) complexes [Pt(COMe)2(C≡CR){(3,5-Me2pz)3CH}]X [R/X = SiMe3/OTf (8a), Ph/OTf (8b), tBu/OTos (8c), iPr/OTos (8d)]. The identities of all platinum complexes were unambiguously proven by high-resolution mass spectrometric investigations, by NMR (1H, 13C, 195Pt) and IR spectroscopy, as well as by single-crystal X-ray diffraction analyses (4a, 4b, 7a, 8a/d). The constitution of the thermally labile complexes 3a/b has been confirmed by low-temperature (–80 °C) NMR (1H, 13C) spectroscopic measurements. The electronic and steric influence of the additional methyl groups in HC(3,5-Me2pz)3 on reactivity, stability, and properties of the investigated compounds will be discussed.