Synthesis and characterization of palladacyclopentadiene complexes with N-heterocyclic carbene ligands

Abstract

a b s t r a c tNew palladacyclopentadiene compounds containing different chelate NHC-thioether and NHC-pyridine ligands have been prepared by transfer of the functionalized carbenes from the respective silver complexes to the polymeric precursors [PdCeCOOR) 4 ] n (R ¼ Me, t-Bu). Their dynamic behaviour in solution was discussed and the solid-structure of 2c was determined by X-ray crystallography.The treatment of [Pd(CeCOOCH 3 ) 4 ] n with two equivalents of the carbene silver complexes led to the (NHC) 2 Pd(C 4 eCOOCH 3 ) 4 derivatives (3cei), a new class of compounds with only PdeC bonds. A serious limitation to this synthetic procedure is an excessive steric crowding around the metal centre.The complexes 3 are present in solution as a mixture of two atropoisomers, due to restricted rotation around the CarbeneePd bond. The kinetics of equilibration between the two configurational isomers was studied for complex 3c, which was also structurally defined by X-ray crystallography (anti isomer).Finally a synthetic protocol was set up for the synthesis of mixed NHC-Phosphine and NHC-Isocyanide palladacyclopentadiene complexes. In this procedure the order of addition of the reactants is of great importance.

Smart N-Heterocyclic Carbene Ligands in Catalysis

“…Since the publication of these two early examples of pyridine-NHC hemilabile ligands in 2000, , the number of complexes containing NHC ligands with nitrogen donor groups has increased enormously, and these include examples of coordination to palladium, − platinum, rhodium, ,− ,− iridium, ,− ,,,− ruthenium, ,,,− nickel, ,,− silver, − gold, copper, ,, and iron. , A s...…”

Mechanistic Study of Nickel-Catalyzed Reductive Coupling of Ynoates and Aldehydes

“…Unfortunately, our attempts to synthesize A independently were unsuccessful (see Supporting Information). Nickelacyclopentadienes have been previously proposed as intermediates in nickel-catalyzed cycloaddition reactions, although well-characterized ones often involve coordination of the nickelacyclopentadiene ring to another metal. − Reductive coupling of ynoates or their derivatives to form metallocyclopentadienes is, however, precedented with palladium − and iridium . Envisioning severe steric repulsions between the Me 3 Si groups and the i Pr groups of SIPr, we tentatively place the Me 3 Si groups at the β-positions of the nickelacyclopentadiene.…”

Platinum(0)-η2-1,2-(E)ditosylethene Complexes Bearing Phosphine, Isocyanide and N-Heterocyclic Carbene Ligands: Synthesis and Cytotoxicity towards Ovarian and Breast Cancer Cells

“…2-methyl-6-((phenylthio)methyl)pyridine, Pt(dba) 2 ( E )-1,2-ditosylethene and silver-NHC complexes 5a , b were synthetized according to the published procedures [ 21 , 22 , 23 , 24 , 25 ].…”