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

Abstract

The dinuclear platina-β-diketone [Pt 2 {(COMe) 2 H} 2 (μ-Cl) 2 ] (1) reacted with 2-pyridyl-functionalized monoximes and with dioximes in the presence of NaOMe to yield oxime−diacetyl platinum(II) complexes [Pt(COMe) 2 (2-pyCRNOH)] (R = H, 4a; Me, 4b; Ph, 4c) and [Pt(COMe) 2 (HONCR−CRNOH)] (R/R = Me/Me, 5a; Ph/Ph, 5b; (CH 2 ) 4 , 5c; NH 2 /NH 2 , 5d), respectively. The strong intramolecular O−H•••O hydrogen bonds in these complexes give rise to an activation of the acetyl ligands for Schiff-base type reactions, thus forming with primary amines iminoacetyl platinum complexes [Pt(COMe)(CMeNHR′)(2-pyCRNO)] (R/R′ = H/ Bn, 6a; Me/Bn, 6b; Ph/Bn, 6c; H/CH 2 CH 2 Ph, 6d; H/CH 2 CHCH 2 , 6e; Bn = benzyl) and [{Pt(CMeNHR′) 2 (ONCR−CRNO)} 2 ] (R/R = Me/Me, 7a−d; Ph/Ph, 8a−d; (CH 2 ) 4 , 9a; R′ = Bn, a; CH 2 CH 2 Ph, b; CH 2 CHCH 2 , c; CH 2 CH 2 OH, d). The intramolecular N−H•••O hydrogen bonds in type 6−9 complexes make clear that protonated iminoacetyl ligands (i.e., aminocarbene ligands) and deprotoanted oxime ligands are present. These complexes could also be obtained in reactions of [Pt(COMe) 2 (NH 2 R′) 2 ] (3) with pyridyl-functionalized monoximes and with dioximes where type 4/5 complexes were found to be intermediates. In solution, the bis(iminoacetyl) complexes 7−9 were found to be present as dimers (as also 8a in the solid state) with smaller amounts of monomers. The importance of hydrogen bonds for activation of acetyl ligands was further evidenced by synthesis of complexes [Pt(COMe) 2 (2-pyCHNOMe)] ( 10) and [Pt(COMe) 2 (HONCMe−CMeNOMe)] (11) bearing O-methylated oxime ligands and their reactivty toward amines. The hydrogen-bond activated acetyl and iminoacetyl ligands in type 5, 7, and 8 complexes were found to undergo in CD 3 OD solutions facile H/D exchange reactions resulting in complexes bearing C(CD 3 )O/C(CD 3 )NDR′ ligands. The constitution of all complexes was unambiguously confirmed analytically, spectroscopically and in part by single-crystal X-ray diffraction analyses. Structural and NMR parameters as well as DFT calculations gave evidence for relatively strong intramolecular hydrogen bonds.

DFT Investigation of the Molecular Properties of the Dimethylglyoximato Complexes [M(Hdmg)2] (M = Ni, Pd, Pt)

“…On the other hand, some applications as the analytical photometric determination of traces of Ni, Pd or Pt [32,35,52] or their use in (medical) coordination chemistry [52][53][54][55][56] seem to make use of the properties of the molecular units and UV-vis absorption spectra of [Ni(Hdmg)2] in solution have been discussed as to stem from monomolecular units [15,16,46,57]. However, other spectroscopic data from species in solution is not reported and the frequently reported virtual insolubility of the materials sheds doubts on the question of the monomolecular species cause the absorptions of [Ni(Hdmg)2] [15,16,52,57] and are responsible for the biological effects of [Ni(Hdmg)2] [53] and [Pt(Hdmg)2] [54].…”

Acyliridium(III) Complexes with PCN Terdentate Ligands Including Imino‐ or Iminium‐Acyl Moieties or Formation of Hydrido from Hydroxyl

“…[7] Few examples of the imination reaction of transition-metal acyls have been reported and recently the reaction of diacetylplatinum(II) complexes bearing oxime ligands with intramolecular O-H···O hydrogen bonds has resulted in the formation of platinum(II) complexes bearing protonated iminoacetyl ligands. [8] More frequently, the migratory insertion of an isocyanide into a M-C bond has been used to obtain iminoacyl transition-metal complexes [9] that may undergo nitrogen protonation to afford aminocarbene complexes or the corresponding protonated zwitterionic molecules.…”

Versatile Coordination Modes in Silver-Imidazolecarbaldehyde Oxime Complexes: Structural and Computational Analysis

“…Oximes are a class of important functional ligands, which have been utilized, for example, in medicine, magnetism, , catalysis, and crystal engineering. − Oximes are versatile ligands, which can be easily tailored to yield materials with distinct characteristics. The synthesis, coordination, and reactivity of oximes have been reviewed, for instance, in the extensive paper by Milios et al, and also by Kukushkin and Pombeiro .…”

“…Oximes are a class of important functional ligands, which have been utilized, for example, in medicine, 1 magnetism, 2,3 catalysis, 4 and crystal engineering. 5−8 Oximes are versatile ligands, which can be easily tailored to yield materials with distinct characteristics.…”