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

Abstract

AbstractReactions 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.