Diacetylplatinum(II) and ‐platinum(IV) Complexes Bearing κ 2 ‐ and κ 3 ‐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 [Pt 2 {(COMe) 2 H} 2 (μ‐Cl) 2 ] ( 1 ) with HC(pz) 3 and HC(3,5‐Me 2 pz) 3 (pz = pyrazol‐1‐yl; 3,5‐Me 2 pz = 3,5‐dimethylpyrazol‐1‐yl) afforded cationic, thermally labile diacetyl(hydrido)platinum(IV) complexes [Pt(COMe) 2 H{(pz) 3 CH}]Cl ( 3a ) and [Pt(COMe) 2 H{(3,5‐Me 2 pz) 3 CH}]Cl ( 3b ) with κ 3 ‐coordinated tris(pyrazolyl)methane ligands, which were found to react with NaOH or NEt 3 to yield neutral diacetylplatinum(II) complexes with κ 2 ‐coordinated tris(pyrazolyl)methane ligands {[Pt(COMe) 2 {(pz) 3 CH}] ( 4a ); [Pt(COMe) 2 {(3,5‐Me 2 pz) 3 CH}] ( 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 1 H 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) 2 R{(pz) 3 CH}]X (R/X = H/OTf, 5a ; Me/OTf, 6a ; Me/I, 7a ) and [Pt(COMe) 2 R{(3,5‐Me 2 pz) 3 CH}]X [R/X = H/OTf ( 5b ), Me/OTf ( 6b ), Me/I ( 7b )] with κ 3 ‐bonded tris(pyrazolyl)methane ligands. Treatment of 4b with alkynyliodine(III) reagents of the type [IPh(C≡CR)]X (R/X = SiMe 3 /OTf, Ph/OTf, t Bu/OTos, i Pr/OTos; OTos = p ‐toluenesulfonate) led to the formation of cationic diacetyl(alkynyl)platinum(IV) complexes [Pt(COMe) 2 (C≡CR){(3,5‐Me 2 pz) 3 CH}]X [R/X = SiMe 3 /OTf ( 8a ), Ph/OTf ( 8b ), t Bu/OTos ( 8c ), i Pr/OTos ( 8d )]. The identities of all platinum complexes were unambiguously proven by high‐resolution mass spectrometric investigations, by NMR ( 1 H, 13 C, 195 Pt) 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 ( 1 H, 13 C) spectroscopic measurements. The electronic and steric influence of the additional methyl groups in HC(3,5‐Me 2 pz) 3 on reactivity, stability, and properties of the investigated compounds will be discussed.