Syntheses and structural aspects of six-membered palladacyclic complexes derived from N, N′, N′′-triarylguanidines with N- or S-thiocyanate ligands. (16th January 2019)

• Record Type: Journal Article
• Authors: Saxena, Priya; Thomas, Jisha Mary; Sivasankar, Chinnappan; Thirupathi, Natesan
• Is Part Of: New journal of chemistry. Volume 43:Number 5(2019)
• Page Start: 2307
• Page End: 2327
• Publication Date: 2019-01-16
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/c8nj04167a
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : Linkage isomers 8 ·2/3PhMe and 9 ·MeOH were synthesized, isolated and structurally characterized by SCXRD and the role of solvent of crystallization in the formation of these linkage isomers identified. Abstract : 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)(PMe3 )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 ·CH2 Cl2 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.