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

Priya Saxena, Jisha Mary Thomas, Chinnappan Sivasankar, Natesan Thirupathi*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Six-membered palladacyclic complexes derived from N,N′,N′′-triarylguanidines, [Pd{κ2(C,N)}(μ-NCS)]2 (1-4), trans-[Pd{κ2(C,N)}(NCS)L] (L = nitrogen based planar Lewis bases, 5-7) and cis-[Pd{κ2(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(κ1C-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 (1H, 31P and 13C) spectroscopy and further the molecular structures of thirteen complexes were determined by single crystal X-ray diffraction. The Pd(ii) atom in 5·CH2Cl2 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 ← NCS (F) and Pd ← S-CN (H) resonance forms, respectively.

Original languageEnglish
Pages (from-to)2307-2327
Number of pages21
JournalNew Journal of Chemistry
Issue number5
StatePublished - 2019
Externally publishedYes


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