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

Westra, Arjan Nicolaas (2005-12)

Thesis (PhD)--Stellenbosch University, 2005.

Thesis

ENGLISH ABSTRACT: Pt(JV) complexes with S, 0-donating aroylthioureas have been synthesized by oxidative addition of elemental halogens to the Pt(JJ) precursors, leading to the first-reported crystal structures of Pt(JV) with this class of ligand. The treatment of Pt(II) complexes of N,N-diethyi-N'-benzoylthiourea with 12, Br2 and Cl2 leads to facile oxidative addition of the halogens to the platinum center, yielding several geometric isomers, as determined by 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 structurally characterized. 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 compound trans-bis(N-benzoyl-N'-propylthiourea-kS)diiodoplatinum(II) diiodine, 28, was isolated. Short intermolecular I··· I interactions in crystals of compounds 26 and 28 lead to infinite chains of weakly linked molecules 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 : 2 trans-Pt(IV)-iodo metallamacrocycle, 35. The corresponding trans-Pt(IV)-X (X= Br, Cl) complexes were synthesized by oxidative addition in an electrolytic cell containing the 2 : 2 Pt(II) precursor and an appropriate halide salt in dichloromethane. The 2: 2 trans-Pt(IV)-X (X= I, Br, Cl) metallamacrocycles, 36 an 37, were isolated and structurally characterized. Intermolecular 1···1 interactions between molecules of 35, 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-aqueous solutions. The 195Pt NMR chemical shifts of the Pt~2 • (X = Cl, Br) anions in D20 and in various organic solvents have been determined, and are discussed with regard to solvent polarities and donor and acceptor properties. The non-linear variations of bp1•195 for the anions with changing bulk composition in aqueous binary mixtures with the organic solvents, suggest that the anions are preferentially solvated by the organic solvents relative to water. The anion solvation sphere compositions with changing bulk composition, as well 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 of PtXt (X = Cl, Br) ·with increasing NaCI04 concentrations indicate the occurrence of {Na+[PtX6 2_]}_ contact ion-pair formation in these solutions. By contrast, the variation of Dp1•195 for aqueous solutions of the halogenoplatinate anions with increasing sodium perchlorate concentration is slight, revealing that Na+···PtXe?- ion association is not favoured in the aqueous medium. The 195Pt chemical shift variations are used to estimate conditional ion-pair formation equilibrium quotients, Q (M"\ for {Na+[Ptxi·Jr contact ion-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 is in accordance with the solvent donor and acceptor properties.

AFRIKAANSE OPSOMMING: Pt(JV) komplekse met S, 0-donerende aroi"eltioiireum ligande is deur middel van die oksidatiewe addisie van halogene aan Pt(JJ) uitgangskomplekse gesintetiseer; die kristalstrukture van die Pt(IV) komplekse met hierdie tipe ligande word vir die eerste keer gerapporteer. Die behandeling van die Pt(II) komplekse van N,N-dietiel-N'-bensoieltioiireum met 12, Br2 en Cl2 gee geredelik aanleiding tot die oksidatiewe addisie van die halogene aan die platinum sentrum, en lei, volgens bepaling met 195Pt KMR, tot die vorming van verskeie geometriese isomere; die produkte cis-bis(N,Ndietiel- N' -bensoieltioiireato )di-jodoplatinum(IV), 26, en cis-bis(N,N-dietiel-N' -bensoieltioiireato )dibromoplatinum( IV), 27, is geisoleer en kristallografies gekarakteriseer. Reaksie van cis-/trans-bis(N-bensoiel-N'propieltioiireum- IGS)dibromoplatinum(II) met Br2, lei ooreenkomstiglik tot oksidatiewe addisie van die halogeen, met trans-bis(N-bensoiel-N' -propieltioiireum-IGS)tetrabromoplatinum(IV) as produk, 29. 12 ondergaan egter nie oksidatiewe addisie aan cis-ltrans-bis(N-bensolel-N' -propieltioiireum-IGS)dijodoplatinum( II) nie; 'n verbinding waarin h ingesluit word in 'n kristalstruktuur met trans-bis(N-bensoielN'- propieltioiireum-IGS)di-jodoplatinum(II), word geisoleer, 28. Kort intermolekulere 1···1 interaksies in die kristalstrukture van verbindings 26 en 28 lei tot die ontstaan van swak-gebonde molekuul-kettings in die kristalle. 195Pt KMR dui aan dat met behandeling van die 3 : 3 Pt(II) metallomakrosikliese kompleks van die 3,3,3' ,3 '-tetra(n-butiel)-1, 1 '-tereftaloielbis(tioiireum) ligand met 12 of Br2, daar stapsgewyse oksidatiewe addisie van die halogene aan die Pt(II) ione in die kompleks plaasvind. Behandeling van die 2 : 2 Pt(II) kompleks van 3,3,3' ,3 '-tetraetiel-1, 1 '-isoftaloielbis(tioiireum) met 12 gee ook aanleiding tot oksidatiewe addisie, met 'n 2 : 2 trans-Pt(IV)-jodo metallomakrosikliese kompleks as produk, 35. Die ooreenkomstige trans-Pt(IV)-X (X = Br, Cl) komplekse is gesintetiseer deur middel van oksidatiewe addisie in 'n elektrolitiese se! wat die 2 : 2 Pt(II) uitgangskompleks bevat tesame met 'n toepaslike haliedsout in dichlorometaan. Die 2 : 2 trans-Pt(IV)-X (X = I, Br, Cl) komplekse, 36 en 37, is geisoleer en kristallografies gekarakteriseer. lntermolekulere I··· I interaksies tussen molekule in kristalle van verbinding 35, gee aanleiding tot kettings van swak-gebonde molekule in die struktuur. 195 Pt KMR word gebruik om die hidraterings-/solvaterings-sfere van die PtX/" (X = Cl, Br) anione te ondersoek, asook om die voorkoms van {Na + [PtCIX/}F kontak-ioonparing in nie-waterige oplosmiddels te bestudeer. Die195Pt KMR chemise verskuiwing van die PtXl" (X= Cl, Br) anione in D20 en in verskeie organiese oplosmiddels is bepaal, en word bespreek met verwysing na die polariteite asook die donor- en akseptoreienskappe van die oplosmiddels. Die nie-lineere variasies van Op1_195 vir die anione met veranderende oplosmiddelsamestelling in waterige binere mengsels met die organiese oplosmiddels, dui aan dat die anione by voorkeur deur die organiese oplosmiddels gesolvateer word. Die solvateringssamestelling van die anione met veranderende oplosmiddelsamestelling, asook ewewigskonstantes vir die voorkeur-solvatering deur die organiese oplosmiddels, K11 ", word met behulp van die KMR data bepaal. Beduidende nie-lineere variasies van Op1_195 in metanol en asetonitriel oplossings van PtXl" (X = Cl, Br) met toenemende NaC104 konsentrasies, dui op die voorkoms van {Na +[PtClxl-]}- kontak-ioonparing in die oplossings. Die variasies van Op1_195 in waterige oplosings van die anione met toenemende NaC104 konsentrasies is egter minder beduidend, waaruit afgelei kan word dat ioonparing nie in die waterige medium bevoordeel word nie. Die 195Pt chemiese verskuiwings word gebruik om kondisionele ioonpaarvormings-ewewigskwosiente, Q (M-1 ), vir die vorming van {Na+[PtCIXtJr in water, metanol en asetonitriel af te lei. Die Q-waardes dui in ooreenstemming met die donor- en akseptoreienskappe van die onderskeie oplosmiddels aan dat die voorkoms van kontak-ioonparing toeneem vir die oplosmiddels in die volgorde water < metanol < asetonitriel.

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