Cationic NCN Palladium(II) Pincer Complexes of 5-tert-Butyl-1,3-bis(N‑substituted benzimidazol-2′-yl)benzenes: Synthesis, Structure, and Pd···Pd Metallophilic Interaction

• Published in: Organometallics Vol. 36; no. 24; pp. 4741 - 4752
• Main Authors: Rani, Varsha, Singh, Harkesh B, Butcher, Ray J
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 26.12.2017; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; MOLECULAR CALCULATIONS; PLATINUM(II) COMPLEXES; LIGANDS; EFFECTIVE CORE POTENTIALS; BUILDING-BLOCKS; PERFORMANCE; STRATEGY; BEARING; PHOTOPHYSICAL PROPERTIES; CATALYTIC-ACTIVITY
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.7b00620

The NCN palladium­(II) pincer complex [Benzoyl(N∧C∧N)­PdBr] (16) was synthesized by the oxidative addition of Benzoyl(N∧C∧N)Br to Pd­(dba)2 in 85% yield [(N∧C∧N) = 5-tert-butyl-1,3-bis­(N-substituted benzimidazol-2′-yl)­phenyl)]. Then treatment of complex 16 with KI yielded the iodopalladium complex [Benzoyl(N∧C∧N)­PdI] (17) in 92% yield. Furthermore, a series of cationic palladium­(II) complexes, including [Benzoyl(N∧C∧N)­Pd­(MeCN)]+[BF4]− (18), [Benzoyl(N∧C∧N)­Pd­(MeCN)]+[SbF6]− (19), and [Benzoyl(N∧C∧N)­Pd­(OTf)] (20), were prepared in 68–79% yields by the reaction of the neutral palladium­(II) complex (16) with AgBF4, AgSbF6, and AgOTf, respectively. Similarly, previously synthesized Tosyl(N∧C∧N)­PdBr [5-tert-butyl-1,3-bis­(N-tosylbenzimidazol-2′-yl)­phenyl]­palladium bromide (5b) was treated with AgSO3CF3 and AgSbF6 to afford cationic palladium­(II) complexes [Tosyl(N∧C∧N)­Pd­(OTf)] (21) and [Tosyl(N∧C∧N)­Pd­(MeCN)]+[SbF6]− (22) in 41 and 61% yields, respectively. 5-tert-Butyl-1,3-bis­[{(N-tosylbenzimidazol-2′-yl)­phenyl}­palladium­(II)] triflate (21) exhibited an unsupported metallophillic Pd···Pd interaction [3.166(8) Å] that is corroborated by X-ray crystallographic studies. Compared to other cationic palladium complexes, complex 21 was found to be less stable. In Atoms in Molecule (AIM) analysis, the bond critical point (ρ) between Pd and Pd atoms is 0.000865 au, supporting the presence of metallophillic interaction in complex 21. The bond strength of the Pd···Pd bond was also measured by density functional theory calculations that indicated that the calculated bond order was approximately one-fourth of the normal covalent Pd–Pd bond (natural atomic orbital bond order method). All eight complexes, two neutral and six cationic, were characterized by common spectroscopic techniques, and six complexes were corroborated by X-ray diffraction studies.