Synthesis and Reactivity of Platinum(II) cis-Dialkyl, cis-Alkyl Chloro, and cis-Alkyl Hydrido Bis-N-heterocyclic Carbene Chelate Complexes

Abstract

Platinum(II) cis-dimethyl and cis-dineopentyl complexes bearing the alkyl-substituted bis-NHC ligands L t-Bu , L Me , and L i-Pr (L t-Bu = 1,1′-di-tert-butyl-3,3′-methylenediimidazolin-2,2′-diylidene, L Me = 1,1′-dimethyl-3,3′-methylenediimidazolin-2,2′-diylidene, L i-Pr = 1,1′-diisopropyl-3,3′methylenediimidazolin-2,2′-diylidene) as well as novel cisalkyl chloro and cis-alkyl hydrido compounds were synthesized. The reactivity of the dimethyl complexes toward dichloromethane and methanol was investigated. Reductive elimination of alkanes from cis-alkyl hydrido complexes requires much higher temperatures than in related bisphosphine systems, which limits their applicability for the generation of reactive, bent platinum(0) d 10 -ML 2 fragments for bond-activation chemistry. The platinum(II) complexes were characterized by NMR and IR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction in most cases.

Selectivity in Competitive Csp2–Csp3 versus Csp3–Csp3 Reductive Eliminations at Pt(IV) Complexes: Experimental and Computational Approaches

“…The stereochemistry of four-coordinated Pt­(II) complexes is usually square planar especially with strong-field ligands such as a Me group. Our calculations show that the geometry of [PtMe 2 (NHC)] ( 1a ) is square planar, in which bond distances and angles comply very well with the experimental finding, as shown in Figure S1 …”

“…The microanalyses were performed using a ThermoFinigan Flash EA-1112 CHNSO rapid elemental analyzer, and melting points were recorded on a Buchi 530 apparatus. The complexes [PtMe­(ppy)­(SMe 2 )] ( 1d ), [PtMe­(bhq)­(SMe 2 )] ( 1e ), [PtMeCl­(NHC)] ( P 2 aCl ), and [PtCl­(COMe)­Me 2 (phen)] ( P 1 c + P 4 c ) were prepared as previously reported.…”

“…Although the syntheses of bis-NHC chelate complexes of dimethylplatinum­(II) have been reported, their reactivity in oxidative addition and reductive elimination reactions has not been investigated. Hofmann et al synthesized platinum­(II) cis -dimethyl complexes bearing alkyl-substituted bis-NHC ligands, in which the bis-NHC ligands are 1,1′-di tert -butyl-3,3′-methylenediimidazolin-2,2′-diylidene, 1,1′-dimethyl-3,3′-methylenediimidazolin-2,2′-diylidene (NHC-L) and 1,1′-diisopropyl-3,3′-methylenediimidazolin-2,2′-diylidene, by the reaction of the [PtMe 2 (cod)] (cod = 1,5-cyclooctadiene) precursor with the corresponding bis-carbene . Subsequently they investigated the reactivity of these complexes toward dichloromethane, methanol, and acetyl chloride.…”

Boron‐Centered Scorpionate‐Type NHC‐Based Ligands and Their Metal Complexes

“…Bis‐carbene ligands have often been modeled on the analogous diphosphane ligands. Structural properties of chelating NHCs such as bite angle, steric hindrance, chirality, and fluxional behavior can be more finely tuned . Besides alkyl chains, the benzene ring could be a convenient choice as scaffolds for bis‐carbene ligands.…”

Methylpalladium complexes with pyrimidine-functionalized N-heterocyclic carbene ligands

“…It has the advantage that the formed ester can be separated and hydrolyzed, followed by recycling of the free acid which potentially can be reused in the process [ 24 – 30 ]. Contrary to the “Catalytica” bispyrimidine system, for the biscarbene system the palladium complexes turned out to be more stable than the corresponding platinum complexes under the reaction conditions [ 31 – 32 ], although Peter Hofmann had recently shown the stability and reactivity of the platinum-alkyl complexes with bis-NHC ligand [ 33 ]. To study the differences between both systems we synthesized palladium [ 34 ] and platinum [ 35 ] “hybrid complexes” with ligands combining both structural elements the pyrimidine as well as the NHC fragment.…”