Linear homobimetallic 4-thioacetyl-substituted NCN pincer palladium(II) and platinum(II) complexes with N-bidentate connecting units (NCN=[C6H2(CH2NMe2)2-2,6-R-4]−)

Computational Study of Bridge Splitting, Aryl Halide Oxidative Addition to PtII , and Reductive Elimination from PtIV : Route to Pincer-PtII Reagents with Chemical and Biological Applications

Density functional theory computation indicates that bridge splitting of [Pt^II R₂ (μ-SEt₂ )]₂ proceeds by partial dissociation to form R₂ Pt^a (μ-SEt₂ )Pt^b R₂ (SEt₂ ), followed by coordination of N-donor bromoarenes (L-Br) at Pt^a leading to release of Pt^b R₂ (SEt₂ ), which reacts with a second molecule of L-Br, providing two molecules of PtR₂ (SEt₂ )(L-Br-N). For R=4-tolyl (Tol), L-Br=2,6-(pzCH₂ )₂ C₆ H₃ Br (pz=pyrazol-1-yl) and 2,6-(Me₂ NCH₂ )₂ C₆ H₃ Br, subsequent oxidative addition assisted by intramolecular N-donor coordination via Pt^II Tol₂ (L-N,Br) and reductive elimination from Pt^IV intermediates gives mer-Pt^II (L-N,C,N)Br and Tol₂ . The strong σ-donor influence of Tol groups results in subtle differences in oxidative addition mechanisms when compared with related aryl halide oxidative addition to palladium(II) centres. For R=Me and L-Br=2,6-(pzCH₂ )₂ C₆ H₃ Br, a stable Pt^IV product, fac-Pt^IV Me₂ {2,6-(pzCH₂ )₂ C₆ H₃ -N,C,N)Br is predicted, as reported experimentally, acting as a model for undetected and unstable Pt^IV Tol₂ {L-N,C,N}Br undergoing facile Tol₂ reductive elimination. The mechanisms reported herein enable the synthesis of Pt^II pincer reagents with applications in materials and bio-organometallic chemistry.

Synthesis, characterization and solid-state photoluminescence studies of six alkoxy phenylene ethynylene dinuclear palladium(II) rods

A rare family of six discrete binuclear [PdCl(PEt3)2] phenylene ethynylene rods with alkoxy side chains (methoxy, ethoxy and heptoxy) have been developed, and their solid-state photoluminescence results have been presented and discussed. The shorter bridging ligands are of the general formula H-C≡C-C6H2(R)2-C≡C-H, where R = H, OCH3, OC2H5, and OC7H15, whereas the longer ones are based on H-C≡C-C6H4-C≡C-C6H2(R)2-C≡C-C6H4-C≡C-H, where R = OCH3, OC2H5. These ligands display increasing length in both the main dimension (backbone length) as well as the number of carbons in the side chains (R, alkoxide side chain) that stem from the central phenylene moiety. The X-ray crystal structures of two of the prepared complexes are reported: one corresponds to a shorter rod, 1,4-bis[trans-(PEt3)2ClPd-C≡C]-2,5-diethoxybenzene (6c), while the second one is associated with a longer rod, the binuclear complex 1,4-bis[trans-(PEt3)2ClPd-4-(-C≡C-C6H4-C≡C)]-2,5-diethoxybenzene (7c). All new compounds were characterized by NMR spectroscopy ((1)H, (13)C{(1)H} and (31)P{(1)H}) as well as ESI-MS(TOF), EA, FTIR, UV-Vis, cyclic voltammetry and solid-state photoluminescence. Our work shows the influence of the alkoxy side chains on the electronic structure of the family of binuclear Pd rods by lowering its oxidation potential. In addition to this, the increase of the length of the bridge results in a higher oxidation potential. Solid state photoluminescence results indicate that Pd complexes are characterized by a marked decrease in both the emission intensity and the fluorescence lifetime values as compared to their ligands. This behaviour could be due to some degree of ligand-to-metal charge transfer.