High resolution NMR studies concerning the solvation/hydration and coordination chemistry of Pt (II/IV) compounds

[摘要] ENGLISH ABSTRACT:Pt(JV) complexes with S, 0-donating aroylthioureas have been synthesized by oxidative addition ofelemental halogens to the Pt(JJ) precursors, leading to the first-reported crystal structures of Pt(JV) withthis class of ligand.The treatment of Pt(II) complexes of N,N-diethyi-N'-benzoylthiourea with 12, Br2 and Cl2 leads to facileoxidative addition of the halogens to the platinum center, yielding several geometric isomers, as determinedby 195Pt NMR; the products cis-bis(N ,N-diethyi-N' -benzoylthioureato )diiodoplatinum(IV), 26, and cisbis(N,N-diethyl-N'-benzoylthioureato)dibromo-platinum(IV), 27, have been isolated and structurallycharacterized. Reaction of cis-/trans-bis(N-benzoyi-N'-propylthiourea-kS)dibromoplatinum(II) with Br2,similarly results in oxidative addition of the dihalogen, yielding the product trans-bis(N-benzoyi-N'propylthiourea-kS)tetrabromoplatinum(IV), 29. lz, however, does not undergo oxidative addition to cis!trans-bis(N-benzoyi-N' -propylthiourea-kS)diiodoplatinum(II), instead the iodine inclusion compoundtrans-bis(N-benzoyl-N'-propylthiourea-kS)diiodoplatinum(II) diiodine, 28, was isolated. Shortintermolecular I··· I interactions in crystals of compounds 26 and 28 lead to infinite chains of weakly linkedmolecules in the respective solids.195Pt NMR reveals that the 3: 3 Pt(II) metallamacrocycle of 3,3,3',3'-tetra(n-butyl)-l,l'terephthaloylbis(thiourea) undergoes stepwise oxidative addition of 12 or Br2 to each of the Pt(II) centers,upon treatment with the dihalogens. Treatment of the 2: 2 Pt(II) complex of 3,3,3',3'-tetraethyl-1,1'isophthaloylbis(thiourea) with 12 also results in the oxidative addition of the halogen, yielding a 2 : 2trans-Pt(IV)-iodo metallamacrocycle, 35. The corresponding trans-Pt(IV)-X (X= Br, Cl) complexes weresynthesized by oxidative addition in an electrolytic cell containing the 2 : 2 Pt(II) precursor and anappropriate halide salt in dichloromethane. The 2: 2 trans-Pt(IV)-X (X= I, Br, Cl) metallamacrocycles, 36an 37, were isolated and structurally characterized. Intermolecular 1···1 interactions between molecules of35, in crystals of the compound, result in chains of weakly connectedmolecules in the lattice.195 Pt NMR is used as a sensitive probe for studying the hydration/solvation spheres of the PtX/ (X = Cl,Br) anions, and to investigate the occurrence of {Na + [PtCl/]} contact ion-pairing in non-aqueoussolutions.The 195Pt NMR chemical shifts of the Pt~2 • (X = Cl, Br) anions in D20 and in various organic solventshave been determined, and are discussed with regard to solvent polarities and donor and acceptorproperties. The non-linear variations of bp1•195 for the anions with changing bulk composition in aqueousbinary mixtures with the organic solvents, suggest that the anions are preferentially solvated by the organicsolvents relative to water. The anion solvation sphere compositions with changing bulk composition, aswell as preferential solvation equilibrium constants, K11, are determined from the NMR data.Significant non-linear variations of the 195Pt NMR chemical shift for methanol and acetonitrile solutions ofPtXt (X = Cl, Br) ·with increasing NaCI04 concentrations indicate the occurrence of {Na+[PtX62_]}_contact ion-pair formation in these solutions. By contrast, the variation of Dp1•195 for aqueous solutions of thehalogenoplatinate anions with increasing sodium perchlorate concentration is slight, revealing thatNa+···PtXe?- ion association is not favoured in the aqueous medium. The 195Pt chemical shift variations areused to estimate conditional ion-pair formation equilibrium quotients, Q (M\ for {Na+[Ptxi·Jr contaction-pair formation in water, methanol and acetonitrile. The estimated Q values illustrate that the extent of{Na+[Ptxi·Jr ion-pairing increases in these solvents in the order water< methanol< acetonitrile, which isin accordance with the solvent donor and acceptor properties.

[发布机构] Stellenbosch University