C–H Bond Activation by a Palladium(II) Thioether Complex: Formation of the Bis(nitromethanate) Complex [Pd(9S3)(CH₂NO₂)₂]

Abstract

Palladium(II) acetate reacts with 1 equiv of 1,4,7-trithiacyclononane (9S3) at room temperature to produce the neutral complex [Pd(9S3)(OAc)2] (1; OAc– = CH3COO–) as an analytically pure yellow solid, which has been characterized using 1H and 13C NMR spectroscopy and single-crystal X-ray diffraction. The crystal structure of 1 shows the first example of an exodentate third sulfur of the 9S3 ligand in a Pd(II) complex. Complex 1 reacts with nitromethane at room temperature in methanol to produce [Pd(9S3)(CH2NO2)2] (2) and acetic acid, as confirmed by 1H NMR and 13C NMR spectroscopy. Moreover, complex 2 has been characterized by single-crystal X-ray diffraction. Its crystal structure is the first example of any transition-metal complex containing two nitromethanate (anionic nitromethane) ligands. The complex shows the more typical elongated-square-pyramidal structure and [S2C2 + S1] coordination with one long Pd–S axial interaction at 2.823(2) Å and two C-bound nitromethanate ligands. Interestingly, each nitromethanate ligand is in a different coordination environment and varies in their trans-directing abilities. Reactivity studies suggest that the complexation behavior of the 9S3 ligand and the Pd(II) center as well as the σ-donor ability of the leaving group play key roles in the C–H activation of the nitromethane. Two related metal complexes, [Pd(dppe)(OAc)2] (dppe = 1,2-bis(diphenylphosphino)ethane) and [Pd(9S3)(CF3COO)2], were synthesized, but neither of these react in a similar fashion to form a nitromethanate complex. Also, the reaction of 1 with nitrobenzene and nitrocyclopentane was studied, but these nitro-organics do not undergo C–H bond activation like nitromethane.

Synthesis of mononuclear and dinuclear palladium (II) complexes containing oxadithioether ligands and their catalytic activities in norbornene polymerization

“…[4][5][6][7][8][9][10][11][12][13][14] These compounds have interesting properties, including the stabilization of rare mononuclear trivalent oxidation states, C-H bond activation, anion recognition, photophysical properties, intermolecular π-π stacking motifs, and axial ligand-metal interactions in square planar complexes. [8,9,[15][16][17][18][19][20][21][22][23][24][25] The last structural property for Pd (II) complexes are of theoretical interest, as these complexes may contain a weak bonding component and serve as important models in associative mechanisms for ligand substitution reactions in d 8 square planar complexes. [8,10] Sulfur species are poisons for many catalytic processes; therefore, sulfur-containing compounds are not usually employed as ligands in transition metal-catalyzed reactions.…”

Synthetic and structural studies of heteroleptic platinum(II) and palladium(II) complexes containing thiacrown and monodentate phosphane ligands

“…Our group and others have previously reported on Pt(II) and Pd(II) complexes with the thiacrown ligand, 1,4,7-trithiacyclononane ( [9]aneS 3 ) and related macrocyclic ligands [1][2][3]. The complexes show an interesting array of unusual properties including the stabilization of rare mononuclear trivalent oxidation states [4][5][6][7][8][9][10], C-H bond activation [12], anion recognition [13], photophysical properties [14,15], antimony-carbon bond activation [16], geometric distortions in five coordination [17], different intermolecular π-π stacking motifs [18], and uncommon metal-metal bond formation [19]. Heteroleptic Pt(II) and Pd(II) complexes with trithiacrowns form geometries best described as elongated square pyramids, with two of the three sulfur donors lying in the square plane while the third forms a long distance axial interaction.…”