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

• Published in: New journal of chemistry 2019, Vol.43 (5), p.2307-2327
• Main Authors: Saxena, Priya, Thomas, Jisha Mary, Sivasankar, Chinnappan, Thirupathi, Natesan
• Format: Article
• Language: English
• Subjects: Carbon 13; Configurations; Crystal lattices; Crystal structure; Crystallography; Dichloromethane; Dimers; Isomers; Lattice vibration; Methanol; Nitrogen; NMR; Nuclear magnetic resonance; Parameters; Single crystals; Spectrum analysis; Thiocyanates; X-ray diffraction
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/C8NJ04167A

Six-membered palladacyclic complexes derived from N , N ′, N ′′-triarylguanidines, [Pd{ κ 2 ( C , N )}(μ-NCS)] 2 ( 1–4 ), trans -[Pd{κ 2 ( C , N )}(NCS)L] (L = nitrogen based planar Lewis bases, 5–7 ) and cis -[Pd{κ 2 ( C , N )}(X)L] (L = phosphorus based conical Lewis bases, X = NCS or SCN) that contained N bound thiocyanate ( 8 and 10–16 ) and S bound thiocyanate ( 9 ) were isolated in good yields. trans -[Pd(κ 1 C -guanidine)(NCS)(PMe 3 ) 2 ] ( 17 and 18 ) were isolated in good yields in order to understand the factors that decide the thiocyanate coordination modes in 5–16 . The new complexes were characterized by analytical techniques, IR and multinuclear NMR ( 1 H, 31 P and 13 C) spectroscopy and further the molecular structures of thirteen complexes were determined by single crystal X-ray diffraction. The Pd( ii ) atom in 5 ·CH 2 Cl 2 and 6 ·PhMe revealed a trans configuration while that in the remaining structurally characterized monomeric palladacycles revealed a cis configuration. Palladacycles 8 ·2/3PhMe and 9 ·MeOH represent the first pair of structurally characterized linkage isomers of organopalladium complexes to be reported. The influence of solvents on thiocyanate coordination modes in 8 ·2/3PhMe and 9 ·MeOH is discussed. Theoretical studies were carried out on the 8 and 9 pair and on their model complexes, 8′ and 9′ , and in both cases an N bound isomer was found to be more stable than their S bound counterpart by 6.14 and 4.64 kcal mol −1 , respectively. In the case of methanol bridged dimers of 8′ and 9′ , namely 8′′ and 9′′ , the N bound isomer ( 8′′ ) is more stable by 8.11 kcal mol −1 suggesting the possible role of lattice methanol and its intermolecular interactions with 9 in the crystal lattice for the observance of a S bound thiocyanate coordination mode. The Wiberg bond index calculations were carried out on 8′ and 9′ which suggested the dominance of Pd ← NCS ( F ) and Pd ← S–CN ( H ) resonance forms, respectively.