US EPA

1451696 

Journal Article 

Structural and dynamic NMR characterization of [Pd(bipy)(R-thiourea)(2)](2+) and [Pd(phen)(R-thiourea)(2)](2+) cations 

Rotondo, A; Barresi, S; Cusumano, M; Rotondo, E 

2012 

1 

Polyhedron
ISSN: 02775387 

45 

1 

23-29 

10.1016/j.poly.2012.07.064 

WOS:000309627000004 

The synthesis and characterization of 10 complexes, [Pd
(bipy)(R-TU)(2)]Cl-2 and [Pd(phen)(R-TU)(2)]Cl-2 (bipy = 2,2'-bipyridyl; phen = 1,10-
phenanthroline; R-TU = N-alkyl substituted thioureas), is presented. The conformational and
dynamic behavior in solution, analyzed by several NMR techniques, is compared to that of the free
thiourea ligands. Spectra at variable temperatures of the free thioureas are consistent with
hampered rotation around the C-N bonds. Mono-alkyl derivatives, in methanol, show equilibria
between syn and anti conformers, whereas di-alkyl thioureas show equilibria between the syn-anti
and syn-syn conformers (syn and anti indicate the position of the alkyl chain with respect to the
S atom over the two amino-branches). Syn protons of the alkyl-chains are converted into the
corresponding anti protons by C-N rotation, which also exchanges external (close to the S atom)
to internal N-H (on the opposite side with respect to the S atom) within the NMR timescale. This
is also observed for the corresponding Pd-II complexes, which, according to the enhancement of
the double C-N bond character, present slower syn/anti exchanges. Moreover, metal coordination
selects anti conformers for the mono-alkyl thioureas, and syn-anti conformers for the di-alkyl
thioureas. (C) 2012 Elsevier Ltd. All rights reserved. 

Palladium(II)-thiourea complexes; H-1, C-13, N-15 NMR; Dynamics; Conformational analysis