NMR and X-ray characterization of a platinum(II) complex with ()sparteine Francesco P. Intini, Concetta Pacifico, Raffaella Z. Pellicani, Virginia Roca, Giovanni Natile * Dipartimento Farmaco-Chimico, Universita ` di Bari, via E. Orabona 4, I-70125 Bari, Italy Received 4 January 2007; received in revised form 5 April 2007; accepted 15 April 2007 Available online 19 April 2007 Dedicated to Piero Zanello. Abstract A platinum(II) complex containing the diamine ()sparteine has been synthesized for the first time and fully characterized by 1 H and 13 C NMR spectroscopy and X-ray crystallography. ()Sparteine is an alkaloid containing four fused rings and four asymmetric centers of configurations 6R,7S,9S, and 11S at the four tertiary carbon atoms. In the cis conformation it can act as a chelating N-donor ligand toward a metal ion. The steric bulkiness of this ligand is such that the Pt–N bond lengths are greater than normal and the angle between the cis-chlorido ligands is well below the theoretical value of 90°. This sparteine complex of platinum appears to be an ideal substrate for investigating the stereochemistry of adducts with nucleotides and DNA. For instance the orientation of a coordinated nucleobase can be determined with precision by monitoring the strength of NOE cross peaks between the sparteine protons pointing toward the metal cen- ter and key protons of the coordinated nucleobase(s) (e.g. H8 protons of guanine or adenine). Ó 2007 Elsevier B.V. All rights reserved. Keywords: Platinum; Sparteine; NMR characterization; X-ray structure; Chiral diamines 1. Introduction In the past, many efforts have been devoted to the understanding of ()sparteine chemistry especially when it is complexed to a transition element such as Zn 2+ , Ni 2+ , Cu 2+ , Co 2+ [1,2], Fe 2+ ,V 3+ , and Cr 3+ [3], or as its own [4–6]. More recently, new interest in this chemistry was generated by the discovery of a Pd-complex with spar- teine proven to be a powerful catalyst of asymmetric syn- thesis [7–11], such as the enantioselective oxidation of alcohols to chetones in the presence of molecular oxygen [7]. Bulky diamine ligands (such as N,N 0 dimethyl-2,3- diaminebutane, Me 2 DAB, and 2,2 0 -bipiperidine, Bip) have extensively been used by us over about two decades to unravel the existence of multiple conformers in adducts of cisplatin [cis-diaminedichloridoplatinum(II)] with nucle- otides and DNA. The results of this extensive investigation have been recently reviewed [12]. A further extension of the latter investigation could be fostered by the use of platinum substrates with a carrier ligand like sparteine. A major dif- ference between sparteine and the previously used Me 2 DAB and Bip ligands is that, while the latter two ligands create steric hindrance mainly confined in the platinum coordina- tion plane, in contrast sparteine has steric hindrance extending above and below the coordination plane. As a consequence, in the adducts formation with nucleotides and DNA the platinum complex with sparteine could favor conformations different from those stabilized by platinum complexes with Me 2 DAB or Bip. In the present paper we report on the synthesis and spectroscopic characterization of the [PtCl 2 {()sparteine}] complex as well as its X-ray structure. Moreover the analogous Pd complex was pre- pared and its NMR spectrum compared to that of plati- num and fully assigned. 0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2007.04.008 * Corresponding author. Tel.: +39 080 544 2774; fax: +39 080 544 2230. E-mail address: natile@farmchim.uniba.it (G. Natile). www.elsevier.com/locate/ica Available online at www.sciencedirect.com Inorganica Chimica Acta 361 (2008) 1606–1615