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

Abstract

Reactions of the dinuclear platina-β-diketone [Pt2{(COR)2H}2(μ-Cl)2] (1) with K[(pz)3BH] and K[(3,5-Me2pz)3BH] (pz = pyrazolyl; 3,5-Me2pz = 3,5-dimethylpyrazolyl) afforded neutral diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)2H{(pz)3BH}] (4a) and [Pt(COMe)2H{(3,5-Me2pz)3BH}] (4b), bearing κ3-bonded tris(pyrazolyl)borate (scorpionate) ligands. These complexes were found to decompose in chloroform solution under formation of the respective chlorido complexes [Pt(COMe)2Cl{(pz)3BH}] (5a) and [Pt(COMe)2Cl{(3,5-Me2pz)3BH}] (5b) as the initial step. Diacetylplatinum(II) complexes with κ2-coordinated scorpionate ligands (K[Pt(COMe)2{(pz)3BH}], 6a; K[Pt(COMe)2{(3,5-Me2pz)3BH}], 6b; K[Pt(COMe)2{(pz)4B}], 7; K[{Pt(COMe)2}2{(pz)4B}], 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)2R{(pz)3BH)}] (R = Me, 9a; Et, 9b; Bn, 9c) and [Pt(COMe)2R{(pz)4B}] (R = Me, 10a; Et, 10b; Bn, 10c), respectively, with κ3-bonded scorpionate ligands. The identities of all platinum complexes were unambiguously proved by microanalyses or by high-resolution mass spectrometric investigations, by NMR (1H, 13C, 195Pt) 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.

Synthesis and characterization of diacetyl platinum(II) complexes with two primary and secondary amine ligands

“…Equilibrium between the precursor complexes 2 * /5 * and amine complexes 3 * , 6 * , 8 * , and 9 * . in reactions with tris-and tetrakis(pyrazolyl)borates yielding in new diacetyl platinum(II) and platinum(IV) complexes with hemilabile scorpionate ligands [15].…”

Activation of Acetyl Ligands through Hydrogen Bonds: A New Way to Platinum(II) Complexes Bearing Protonated Iminoacetyl Ligands

“…On the other hand, 2 J Pt,C couplings showed the opposite (155.3–159.0 Hz vs 246.4–249.0 Hz). The platinum shifts δ Pt (−3384 to −3391 ppm) are similar to those of the diacetyl platinum(II) complexes 4 and are in a range typical for organo platinum(II) complexes. ,, …”

“…In the three complexes, the platinum centers are square-planar coordinated (sum of angles around Pt: 360.0/360.1°, 4a ; 360.5°, 4b ; 359.9°, 4c ) by two nitrogen atoms of the bidentate 2-pyridyl oxime ligand and by two carbon atoms of the acetyl ligands in mutual cis position. As mostly found in acetyl platinum complexes, ,,, one of the two acetyl ligands is nearly perpendicular to the complex plane (interplanar angle: 86.7/86.1°, 4a ; 82.0°, 4b ; 85.9°, 4c ). In contrast, unusually, the other acetyl ligand lies in the complex plane (2.7/0.6°, 4a ; 16.0°, 4b ; 1.9°, 4c ), which is forced by the formation of an intramolecular O–H···O hydrogen bond to the oxime group (graph set: S (6)).…”

“…This assignment is in accord with the chemical shifts of the acetyl ligands in acetyl–iminoacetyl complexes 6a – d (vide infra, Table ). The platinum chemical shifts (−3411 to −3487 ppm, Table ) of the oxime–diacetyl complexes ( 4 / 5 ) are in the range of those of other diacetyl platinum(II) complexes with nitrogen coligands. ,, …”

“…Previous investigations showed that the amine ligands in complexes [Pt(COMe) 2 (NH 2 R′) 2 ] ( 3a – c ) are only weakly coordinated, and, thus, they are easily subject to ligand substitution reactions. , Unexpectedly, the bis(amine)–diacetyl platinum complexes 3a – c were found to react with pyridyl-functionalized monoximes not only under ligand substitution but, additionally, under conversion of one of the two acetyl ligands into a protonated iminoacetyl ligand (Pt–CMeO → Pt–CMeNHR′), thus yielding complexes of the type [Pt(COMe)(CMeNHR′)(2-pyCRNO)] ( 6a – e , Scheme , reaction path A). These complexes were isolated in moderate to good yields (35–80%).…”