Synthesis and reactivity of Pd(II) imidoyl complexes obtained by insertion of isocyanoferrocene into the Pd-C bonds of orthopalladated precursors

While the multifaceted reactivity of organic isocyanides has been extensively demonstrated, that of their organometallic analogue, isocyanoferrocene (FcNC; Fc = ferrocenyl), has not yet been adequately explored. This contribution describes the syntheses of novel chelating Pd(II) imidoyl complexes, [(YCH2C6H4C(NFc)-κ2Y,C)PdCl(PR3)], by insertion of FcNC into the Pd-C bond of cyclopalladated precursors [(YCH2C6H4-κ2Y,C)PdCl(PR3)] (Y = Me2N, MeS, R = Ph, Me). The imidoyl complexes underwent facile alkylation with [Me3O][BF4] to produce the cationic aminocarbene complexes [{YCH2C6H4C(N(Me)Fc)-κ2Y,C}PdCl(PR3)][BF4]. All compounds were fully characterised using a combination of spectroscopic methods (NMR, FTIR and ESI MS), cyclic voltammetry and single-crystal X-ray crystallography. In addition, DFT calculations were used to describe the bonding in the two compound families. Analyses with intrinsic bond orbitals (IBOs) and the quantum theory of atoms in molecules (QTAIM) consistently pointed to the transformation of an X-type imidoyl C-ligand (σ-organyl) into an L-type carbene donor upon alkylation, which has only a minor structural consequence. Also reported is the unexpected conversion of the imidoyl complex [(Me2NCH2C6H4C(NFc)-κ2N,C)PdCl(PPh3)] into (Z)-2,2-dimethyl-1-(ferrocenylimino)isoindolin-2-ium tetrafluoroborate as a reductive elimination product, which was induced by Lewis and Brønsted acids.

Synthesis and Structure of Multinuclear Pd(II) Complexes Bridged by Phosphide or Azide Ligands

The synthesis and structure of phosphide- and azide-bridged multinuclear Pd(II) complexes bearing phosphine ligands [PdX(μ-X')(PR₃)] _n (X = Cl and N₃; X' = PR₂ ^' and N₃; n = 2 and 4) are reported. The oxidative addition of R₂ ^'PCl to Pd(PMe₃)₂ furnished the phosphide-bridged dinuclear Pd(II) complexes [PdCl(μ-PR₂ ^')(PMe₃)]₂ [R' = ⁱ Pr (1a) and Cy (1b)]. However, the oxidative addition of (o-tolyl)₂PCl to Pd(PMe₃)₂ produced a nonbridged mononuclear Pd(II) complex with the bis(o-tolyl)phosphinic ligand, trans-[Pd(PMe₃)₂{P(O)(o-tolyl)₂}] (2), via oxidation of the phosphinyl ligand. The reaction of the chloride-bridged dinuclear Pd(II) complexes [PdCl(μ-Cl)(PR₃)]₂ [PR₃ = PEt₃ (3a) and PPhMe₂ (3b)] with NaN₃ afforded the azide-bridged dinuclear and tetranuclear Pd(II) complexes [Pd(N₃)(μ-N₃)(PEt₃)]₂ (4) and [Pd(N₃)(μ-N₃)(PPhMe₂)]₄ (5). Comparisons of the X-ray structures of 4 and 5 show that the square-planar molecular geometry of the Pd(II) centers of 4 are more distorted than those of 5. Density functional theory calculations suggest that the tetranuclear eight-membered ring structure like 5 is more stable than the dinuclear four-membered ring structure like 4 in the gas phase in both PEt₃ and PPhMe₂ systems. However, because the relative energy difference between the four-membered and eight-membered ring structures is small in the PEt₃ system with smaller steric hindrance compared with PPhMe₂, it is assumed that this difference is compensated by the crystal packing energy, and the dinuclear four-membered ring complex 4 is actually obtained.

Hemilabile bonding of 1-oxa-4,7-dithiacyclononane in cyclometallated palladium(ii) complexes

The synthesis and characterization of a series of cyclometallated complexes of Pd(ii) incorporating the mixed donor ligand 1-oxa-4,7-dithiacyclononane ([9]aneS₂O) are presented in this study. Complexes of the form [Pd(C^N)([9]aneS₂O)](PF₆) (C^N = 2-phenylpyridine (ppy) 1b, 4-(2-pyridyl)benzaldehyde (ppyCHO) 2b, 7,8-benzoquinoline (bzq) 3b, 2-benzothienylpyridine (btp) 4b, 2-phenylbenzothiazole (pbt) 5b), were obtained in high-yield from a simple two-step synthetic scheme. All of these complexes were fully characterized by NMR, ESI-MS, IR, combustion analyses, and most (1b, 2b, 4b, 5b) by X-ray crystallography. Solution ¹H and ¹³C NMR studies of [Pd(C^N)([9]aneS₂O)](PF₆) complexes demonstrate complicated [9]aneS₂O behavior at room temperature. Variable temperature NMR reveals dynamic bonding of the [9]aneS₂O ligand consistent with the presence of both endodentate and exodentate bonding modes. This is in stark contrast to the related [9]aneS₃ (1,4,7-trithiacyclononane) cogeners that demonstrate fluxional endodentate bonding only in solution. X-ray structures reveal only exodenate [9]aneS₂O bonding in this series, unlike the related [9]aneS₃ complexes that show endodenate bonding with an axial PdS interaction. DFT calculations performed on endo and exo [9]aneS₂O bonding forms of 4b, as well as a transition state calculation for interconversion, suggest reasonable access to both bonding forms based on the energy barrier. Natural bond order calculations provide further evidence for a weak axial PdO interaction in the endo form of 4b.

Syntheses and structural aspects of six-membered palladacyclic complexes derived fromN,N′,N′′-triarylguanidines with N- or S-thiocyanate ligands

Linkage isomers8·2/3PhMe and9·MeOH were synthesized, isolated and structurally characterized by SCXRD and the role of solvent of crystallization in the formation of these linkage isomers identified.

Migratory insertion and hydrogenation of a bridging azide in a thiolate-bridged dicobalt reaction platform

A novel well-defined thiolate-bridged dicobalt azido complex is converted to a rare sulfilimide-bridged dicobalt complex via nitrogen atom migratory insertion into the Co-S bond upon thermolysis. Intriguingly, the homolytic cleavage of hydrogen is achieved by this azide under mild conditions to furnish a partially hydrogenated azido complex.

Stepwise cyclopalladation of 2-phenacylthiopyridine to give C,C,N-pincer complexes

The synthesis of a family of palladium C,C,N-pincer complexes derived from 2-phenacylthiopyridine, obtained by an unprecedented stepwise double cyclopalladation process, is reported. The pincer moiety behaves as a metallaligand.

Structure and properties of metal complexes of a pyridine based oxazolidinone synthesized by atmospheric CO2 fixation

Copper, platinum and palladium complexes of an oxazolidinone ligand show potential in catalysis or cytotoxicity, depending on the metal incorporated.

A highly efficient palladium-catalyzed decarboxylative ortho-acylation of azobenzenes with α-oxocarboxylic acids: direct access to acylated azo compounds

Avoiding additives: A highly efficient and mild Pd-catalyzed decarboxylative ortho-acylation of azobenzenes with α-oxocarboxylic acids was developed that provides an alternative route to acylated azo compounds. This decarboxylative acylation process was completed in the absence of any additives at ambient temperature, to afford the acylated azobenzenes in moderate to good yields.

Rollover cyclometalation with 2-(2'-pyridyl)quinoline

Rollover cyclometalation of 2-(2'-pyridyl)quinoline, L, allowed the synthesis of the family of complexes [Pt(L-H)(X)(L')] and [Pt(L*)(X)(L')][BF4] (X = Me, Cl; L' = neutral ligand), the former being the first examples of Pt(II) rollover complexes derived from the ligand L. The ligand L* is a C,N cyclometalated, N-protonated isomer of L, and can also be described as an abnormal-remote pyridylene. The corresponding [Pt(L-H)(Me)(L')]/[Pt(L*)(Me)(L')](+) complexes constitute an uncommon Brønsted-Lowry acid-base conjugated couple. The species obtained were investigated in depth through NMR and UV-vis spectroscopy, cyclic voltammetry, and density functional theory (DFT) methods to correlate different chemico-physical properties with the nature of the cyclometalated ligand (e.g., L vs bipy or L* vs L) and of the neutral ligand (DMSO, CO, PPh3). The crystal structures of [Pt(L-H)(Me)(PPh3)], [Pt(L-H)(Me)(CO)] and [Pt(L*)(Me)(CO)][BF4] were determined by X-ray powder diffraction methods, the latter being the first structure of a Pt(II)-based, protonated, rollover complex to be unraveled. The isomerization of [Pt(L*)(Me)(PPh3)](+) in solution proceeds through a retro-rollover process to give the corresponding adduct [Pt(L)(Me)(PPh3)](+), where L acts as a classical N,N chelating ligand. Notably, the retro-rollover reaction is the first process, among the plethora of Pt-C bond protonolysis reactions reported in the literature, where a Pt-C(heteroaryl) bond is cleaved rather than a Pt-C(alkyl) one.

Spin-labelled cyclometallated palladium complexes. EPR study of dynamic processes in coordination sphere

New four-, five- and six-coordinated cyclometallated o-semiquinonato palladium complexes were obtained and characterized in solution by EPR. Interaction of square-planar azaphenyl palladium semiquinonate with mono and bidentate phosphane donors leads to formation of five- and six-coordinated adducts. Typical values of HFC constants on apical and basal phosphorouses are observed for such compounds. In one case the reversible addition of tri-phenyl-phosphane was observed. The coordination mode of pincer ligand (bi- or tridentate) in o-semiquinonato pincer complexes depends on the nature of linker between coordinating group and pincer aryl ring. In the case of CH(2) linker five coordinated complexes are formed. The "swing" and "fan" oscillations are observed for these compounds. Complexes with -O- linker are the first examples of compounds with bidentate bonded phosphorous-based pincer ligand. Most of complexes are unstable and decompose during some hours. Only the application of o-semiquinones as spin labels and using the EPR technique made possible to observe and interpret their structure.