Synthesis, Characterization, and Reactivity of Diacetylplatinum(II) and -platinum(IV) Complexes Bearing κ2- and κ3-Coordinated Scorpionate Ligands

Reactions of the dinuclear platina-beta-diketone [Pt-2{(COR)(2)H}(2)(mu-Cl)(2)] (1) with K[(pz)(3)BH] and K[(3,5-Me(2)pz)(3)BH] (pz = pyrazolyl; 3,5-Me(2)pz = 3,5-dimethylpyrazolyl) afforded neutral diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)(2)H{(pz)(3)BH}] (4a) and [Pt(COMe)(2)H{(3,5-Me(2)pz)(3)BH}] (4b), bearing kappa(3)-bonded tris(pyrazolyl)borate (scorpionate) ligands. These complexes were found to decompose in chloroform solution under formation of the respective chlorido complexes [Pt(COMe)(2)Cl{(pz)(3)BH}] (5a) and [Pt(COMe)(2)Cl{(3,5-Me(2)pz)(3)BH}] (5b) as the initial step. Diacetylplatinum(II) complexes with kappa(2)-coordinated scorpionate ligands (K[Pt(COMe)(2){(pz)(3)BH}], 6a; K[Pt(COMe)(2){(3,5-Me(2)pz)(3)BH}], 6b; K[Pt(COMe)(2){(pz)(4)B}], 7; K[{Pt(COMe)(2)}(2){(pz)(4)B}], 8) were obtained in ligand exchange reactions of [Pt(COMe)(2)(NH2Bn)(2)] (3; Bn = benzyl) with the respective potassium (pyrazolyl)borates. The deprotonation of the hydrido complexes 4 with potassium methoxide led also to the formation of 6. Diacetylplatinum(II) complexes 6a and 7 were found to react in oxidative addition reactions with alkyl halides to yield diacetylplatinum(IV) complexes of the type [Pt(COMe)(2)R{(pz)(3)BH))] (R = Me, 9a; Et, 9b; Bn, 9c) and [Pt(COMe)(2)R{(pz)(4)B}] (R = Me, 10a; Et, 10b; Bn, 10c), respectively, with kappa(3)-bonded scorpionate ligands. The identities of all platinum complexes were unambiguously proved by microanalyses or by high-resolution mass spectrometric investigations, by NMR (H-1, C-13, Pt-195) and IR spectroscopies, and by single-crystal X-ray diffraction analyses (4a, 5a, 7.(18C6), 9c; 18C6 = 18-crown-6). The reactivity of the complexes is discussed in terms of hemilability of the scorpionate ligands.