Synthesis and Stereochemistry of the First Chiral (Imidazolinylidene)‐ and (Triazolinylidene)palladium(ii) Complexes

Abstract

The reaction of three equiv. of a chiral imidazolium or triazolium perchlorate with one equiv. of Pd(OAcj2, an excess of NaI and a base leads to the corresponding chiral dicarbenediiodopalladium(I1) complexes in chemical yields up to 98% and with the trons isomer as the major product (1, 2). If only one equiv. of the imidazolium or triazolium perchlorate is used, then dinuclear complexes with bridging iodine atoms are formed (3,4, chemical yield 92-94 %). The latter can add Lewis basic ligands, e.g. amines, phosphanes or other carbenes, to give mononuclear complexes with one carbene ligand coordinated to the PdI, fragment (5, 6). Preliminary test experiments with these Pd(I1) complexes as catalysts for an enantioselective Heck-type reaction have been carried out.

Synthesis and Crystal Structure of Bis(2,3-dihydro-3-methylbenzothiazole-2-ylidene)palladium(II) Diiodide: The First Palladium Complex with Benzothiazole Carbene Ligands Suitable for Homogeneous Catalysis

“…Besides the expected square-planar core geometry, a crystal structure analysis of 1 revealed that the two carbene ligands are in a trans arrangement and are coplanar with respect to the PdI 2 plane. The Pd-C bond lengths [2.01(4)/ 2.06(3) Å ] lie within the established range for Pd-C(alkyl) single bonds, [16] although the 13 C-NMR signal of the car-bene C appears further downfield (δ ϭ 210.5) than the corresponding signals of imidazole and triazole carbenes (δ ϭ 169-185); [3][4][5] this is in accordance with the values found for the stable N-diisopropylphenylthiazole carbene. [12] From an XPS analysis of 1, a binding energy of 337.2 eV was determined, which is very close to the value of 337.0 eV typical for Pd II .…”

Palladium Complexes of N‐Heterocyclic Carbenes as Catalysts for Cross‐Coupling Reactions—A Synthetic Chemist's Perspective

“…However, all attempts at developing catalytic enantioselective alkene carbopalladations or Heck-Mizoroki reactions with chiral Pd-NHC catalysts have not yet met with any success to date. [50,267,268,270] In addition, even though chiral Pd-NHC complexes [107,186,242] have been shown to achieve good conversions in arylations of acrylate or styrene (for example, 418, 419, Figure 10; 431, Scheme 81), neither of which generate any asymmetric centers, they have not been explored in asymmetric Heck-Mizoroki reactions.…”

Aus der Sicht des Synthetikers: Palladiumkomplexe N‐heterocyclischer Carbene als Katalysatoren für Kreuzkupplungen

“…[49,245,258,261,264] Die Gruppen um Andrus und Beller untersuchten auch weniger übliche Abgangsgruppen. Andrus et al zeigten, dass der in situ aus SIPr·HCl (13, Tabelle 1) und Pd(OAc) 2 [89] Unabhängig voneinander entwickelten die Gruppen um Mori [267,268] und Lautens [269] 2002 eine interessante intramolekulare Alken-Carbopalladierung (Schema 91 [50,267,268,270] Zwar konnten bei der Arylierung von Acrylaten oder Styrol (z. B.…”