Reduction of a Chelating Bis(NHC) Palladium(II) Complex to [{μ‐bis(NHC)}₂Pd₂H]⁺: A Terminal Hydride in a Binuclear Palladium(I) Species Formed under Catalytically Relevant Conditions

Abstract

Half‐way house: The first palladium(I) N‐heterocyclic carbene complex has been isolated in high yield by the base‐assisted reduction of a palladium(II) precursor. The location of the unique terminal hydride (see picture; PdI cyan, H white, N blue) was established by neutron crystal structure determination, and the solution fluxional behavior of the complex was explored.

Synthesis of palladium(0) and -(ii) complexes with chelating bis(N-heterocyclic carbene) ligands and their application in semihydrogenation

“…22,31 It has even been doubted whether chelated methylene linked bis-NHC ligands would be able to support a zero-valent palladium center. 32 However, we observed formation of only the chelate species for all wingtip substituents and for both linker lengths, as was concluded from the NMR-spectra. In the 1 H NMR spectra, the signals of the methylene linker hydrogens are split in two doublets with a geminal coupling of approximately 13 Hz (Table 1).…”

“…The decomposition of 3c in solution hampered the detection of the carbene signal in 13 C NMR spectroscopy. The complexes with the bulkier mesityl substituents, which have been used previously to ensure stability of palladium complexes bearing these ligands, 32,37,38 were stable in solution and resistant against air and moisture at room temperature for at least a week. In contrast to the findings of Riederer et al, 3 we did not observe a relation between stability and linker length.…”

Chelating Bis(N‐Heterocyclic Carbene) Palladium‐Catalyzed Reactions

“…Essentially,t he isolation of Pd I -NHC hydride by Gardiner and co-workersm ay be helpful in understanding the catalytically active speciesinc opolymerization. [82]…”

Molecular complexes and main-chain organometallic polymers based on Janus bis(carbenes) fused to metalloporphyrins

“…The chelating mode is when two NHCs bind one metal centre. [10][11][12][13] The bridging mode instead is when the two NHCs bind two different metal centres. [14][15][16][17][18] Many examples of bis(NHCs) acting as chelating ligands can be found in the literature since they have found useful applications in catalysis.…”