Cyclopalladation of dimesityl selenide: synthesis, reactivity, structural characterization, isolation of an intermediate complex with C–H⋯Pd intra-molecular interaction and computational studies

Abstract

The reaction of dimesityl selenide (Mes2Se) with either PdCl2(PhCN)2 in toluene or PdCl2 in toluene-acetonitrile yields a chloro-bridged binuclear palladium complex, [Pd2Cl2(μ-Cl)2(Mes2Se)2] (1), whereas with Na2PdCl4 in refluxing ethanol, a cyclometallated palladium complex, [Pd2(μ-Cl)2{MesSeC6H2(Me2)CH2}2] (2) is afforded. 2 can also be obtained when 1 is refluxed in ethanol. On treatment with Pb(Epy)2 in dichloromethane, 2 afforded the Epy-bridged binuclear complexes, [Pd2(μ-Epy)2{MesSeC6H2(Me2)CH2}2] (3; E = S (3a) or Se (3b)). Treatment of 2 with PPh3 yields a bridge-cleaved monomeric complex, [PdCl{MesSeC6H2(Me2)CH2}(PPh3)]. The molecular structures of 1-3 were established by X-ray diffraction analyses. All the complexes are dimeric, with the palladium atoms acquiring a distorted square planar configuration. There are intra-molecular C-H···Pd interactions (d(M-H): 2.75 Å and <C-H···Pd: 111.23°) in 1 which facilitate the activation of the C-H (sp(3)) bond leading to metallation. The optimized geometry of 1 obtained using the DFT(B3LYP) computational method identified a C-H···Pd contact distance of 2.78 Å. There are two independent molecules of 2 in the unit cell, which differ slightly in bond lengths, bond angles and torsion angles. The mechanism of formation of the dimeric species 2 is examined using DFT (B3LYP) computations.

Structural Variation in [PdX2{RE(CH2)nNMe2}] (E = Se, Te; X = Cl, OAc) Complexes: Experimental Results, Computational Analysis, and Catalytic Activity in Suzuki Coupling Reactions

“…2.37 Å) and Pd–Te (ca. 2.53 Å) bond lengths are in conformity with the values reported for palladium chalcogenoether complexes, such as [Pd 2 (μ‐Cl) 2 {MesSeC 6 H 2 (Me 2 )CH 2 } 2 ] [Pd–Se = 2.3438(8) Å],22a [PdCl{OC 6 H 4 C(Ph)=NCH 2 CH 2 SePh}] [Pd–Se = 2.3575(6) Å],32 [PdCl 2 {TeMe(C 4 H 3 O)} 2 ] [Pd–Te = 2.530(1) Å],33 and [Pd 2 (μ‐Cl) 2 Cl 2 (TeMes 2 ) 2 ] [Pd–Te = 2.5068(13) Å] 22b. The Pd–Se bond in [PdCl 2 {RSe(CH 2 ) n NMe 2 }] is slightly elongated either by replacing a phenyl group by mesityl with n = 2 {e.g., 2a [2.3611(11) Å] and 2b [2.3914(6) Å]} or increasing the alkyl chain length {e.g., 2a and 2d [Pd–Se = 2.3938(11) Å]}.…”

“…This difference is due to the difference in the trans influence of chalcogen and the chloride ligand. The observed distances are in good agreement with the values reported in palladium complexes 7,22a,29. The Pd–O and Pd–N (2.067–2.121 Å) distances are comparable to complexes of the composition [Pd(OAc){E(CH 2 ) n NMe 2 }] m ( n = 2 or 3; m = 3 or 2; E = S, Se, or Te) 17a,28b.…”

Cyclopalladation of telluro ether ligands: synthesis, reactivity and structural characterization

“…Such a large deshielding (69 ppm) from binuclear complex 2a to cyclopalladated complex 3 has also been noted by our group in the corresponding mesityl seleno ether derivatives (deshielded by 86 ppm in 77 Se resonance). 20 The effect of the bridging ligand as well as the nature of the R group on Te is also evident in cyclopalladated complexes. There is shielding of ∼90 ppm of the 125 Te NMR resonance on replacing the bridging chloride in 3 (δ 644.0 ppm) by the acetate group (5a) (δ 554.1 ppm).…”

“…Similar anisotropic behavior was also noted for analogous selenium complex, [Pd 2 (µ-Cl) 2 {CH 2 C 6 H 2 (4,6-Me 2 )SeMes} 2 ]. 20 The CH 2 protons in 4 were also anisotropic and appeared as an AX pattern at 3.55 ppm with significantly large chemical shift difference (2H, Δν AX = 169 Hz, J AX = 11 Hz). The 125 Te{ 1 H} NMR spectra of these complexes displayed a single resonance which appeared at higher frequency with respect to the free ligand (TeMes 2 , 125 Te δ = 260.8 ppm, Te(o-tol) 2 , 125 Te δ = 499.3 ppm, TePh 2 , 125 Te δ = 693.4 ppm, MesTe(o-tol) 125 Te δ = 336.8 ppm, MesTePh 125 Te δ = 427.2 ppm).…”

“…[Pd 2 (µ-Cl) 2 Cl 2 (SeMes 2 ) 2 ]. 20 Two telluro ether ligands are mutually trans, forming a sym-trans dimeric structure. The terminal Pd-Cl distances are marginally shorter (2.290(4) Å) than the bridging Pd-Cl distances (2.310(4), 2.403(4) Å).…”