Browsing by Author "Barkhuysen, Shani"

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    High resolution 195Pt and 119Sn NMR characterization of platinum(II)-tin(II) complexes
    (Stellenbosch : Stellenbosch University, 2011-12) Barkhuysen, Shani; Koch, Klaus R.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: See full text for abstract
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    High resolution multi-nuclear 1 and 2D NMR characterization of stannous halide complexes of Rh(I/III) in aqueous and non-aqueous solutions
    (Stellenbosch : Stellenbosch University, 2016-03) Barkhuysen, Shani; Koch, Klaus R.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: A detailed high-resolution multi-nuclear NMR study the stannous halide complexes of Rh(I/III) in aqueous and non-aqueous solutions has been undertaken. In this study the series of [RhIII(SnX3)nX6-n]3- (X = Cl-/Br-, n = 1 – 6) anions, the [RhI(SnX3)5]4- (X = Cl-/Br-) and the[RhIIIH(SnX3)5]3- (X = Cl-/Br-) complex anion have been synthesized and characterized bymeans of high-resolution 119Sn NMR spectroscopy in both aqueous and non-aqueous phases.It is shown in this work that, in contrast to the tacitly accepted kinetically labile nature of these Rh(III)-Sn(II) species, these do not undergo rapid inter- and intra-molecular exchange of the SnX3- ligands rapidly on the NMR time scale and are indeed kinetically inert. In aqueous HCl, the 119Sn NMR spectra display up to 9 (of an expected 10) main sets of 119Snresonances split into doublets due to 1J(103Rh-119Sn) (103Rh: I = ½, 100 %) in addition to2J(117/119Sn-119Sn) coupling satellites. A detailed investigation of the resonances at (119Sn) =-278.2 and -202.5 ppm reveals that the 2J(119Sn-119Sn) satellites are not symmetricallydistributed around the respective main signals. The set of resonances at -278.2 ppm was previously assigned to a kinetically labile cis-[RhIII(SnCl3)4Cl2]3- complex anion, whereas thesignal at -202.5 ppm was unassigned. We now find that the 119Sn NMR signals at -278.2 ppmand -202.5 ppm can be assigned to the equatorial and axial isotopomers of cis-RhIII(SnCl3)4Cl2]3-, respectively. This implies that the cis-RhIII(SnCl3)4Cl2]3- complex anion iskinetically inert and results in two resonances due to the observed 119SnCl3- ligand in theaxial (trans toSnCl3-) position not being magnetically equivalent to the 119SnCl3- ligand in theequatorial (trans to Cl-) position. This is supported by a detailed analysis of the 2J(119Sn-119Sn)cis,ax-eq coupling in the various possible isotopomers of this complex, as well as the good agreement between the simulated spectra generated by a computer program gNMR50 and the spectra experimentally recorded. Moreover, the experimental ratio of (νA – νB)/JAB  8.2 suggests second order 2J(119Sn-119Sn) coupling effects accounts for the asymmetrical 2J(119Sn-119Sn)cis,ax-eq satellites. Similarly the 119Sn NMR spectra of other [RhIII(SnCl3)nCl6-n]3- (n = 1 -5)species are consistent with kinetically inert complexes, including the [RhIII(SnCl3)6]3-species detected for the 1st time in solution. The 119Sn NMR signals of all the species in theseries of [RhIII(SnCl3)nCl6-n]3- (n = 1 - 6) complex anions, as well as [RhI(SnCl3)5]4- and the[RhIIIH(SnCl3)5]3- have been correctly assigned. The analogous series of [RhIII(SnBr3)nBr6-n]3- (n = 3 – 5) were prepared and characterized for thefirst time. Investigation of the stannous bromide complexes of rhodium(I/III) in HBr solutions furnished the assignment of 3 new [RhIII(SnBr3)nBr6-n]3- (n = 3 – 5) species. Moreover, thedistinctive isotopomer pairs of these complex anions were assigned. It is thus established that these species, as with the analogous chlorido species, are kinetically inert and do not undergo rapid intra- or inter-molecular exchange on the NMR time-scale. Comparison between the 119Sn NMR parameters of the stannous chlorido and stannous bromido species shows that the 1J(103Rh-119Sn) coupling constant is smaller for the [RhIII(SnBr3)nBr6-n]3- (n = 3 – 5) speciesthan the [RhIII(SnCl3)nCl6-n]3- species which suggests that the 103Rh-SnBr3- bond length islonger than the 103Rh-SnCl3- bond length. 119Sn NMR spectroscopy showed that the kinetically inert [RhIII(SnCl3)nCl6-n]3- (n = 1 - 6) and [RhIIIH(SnCl3)5]3- complex anions, together with the [RhI(SnCl3)5]4-, are extracted into non-aqueous solutions using methyl isobutyl ketone (MIBK) and methyltrioctylammonium chloride (AQ336) in chloroform. With a Rh:Sn mole ratio of more than 1:10, the [RhIIIH(SnCl3)5]3- complex anion predominates the non-aqueous solutions, howeveradditional signals are always observed. A detailed 1H and 119Sn NMR study of the isotopologues and isotopomers of the [RhIIIH(SnCl3)5]3- species extracted into MIBK wasundertaken. From the 119Sn NMR spectrum, and with the aid of gNMR50 to simulate thespectra, two isotopomers (axial 119SnCl3- and equatorial 119SnCl3-) and six isotopologues wereassigned and characterized. Twelve respective isotopologues and isotopomers were assigned in the 1H NMR spectrum of the [RhIIIH(SnCl3)5]3- complex anion. However, this was onlyachieved with the aid of a simulated 1H NMR spectrum with gNMR50, wherein the 1H NMRparameters were used to record a indirectly detected 103Rh,1H HMQC NMR spectrum for thisspecies and the δ(103Rh) was determined to be -1191 ppm. This is the first 103Rh chemicalshift value reported for these Rh(III)-Sn(II) species. Decreasing the stannous(II)chloride concentration, and thus the Rh:Sn mole ratio, in the aqueous phase results in the disappearance of the [RhIIIH(SnCl3)5]3- complex anion, accompanied by the formation ofmore 119Sn NMR signals upfield of the hydrido species. These species correspond well to thekinetically inert species in the aqueous phase and is assigned accordingly. A detailed isotopologue/isotopomer study of all the species observed in the non-aqueous phases resulted in the assignment of 7 possible species: [RhIII(SnCl3)nCl6-n]3- (n = 2 – 6), including the[RhIII(SnCl3)6]3- species not previously observed, [RhIIIH(SnCl3)5]3- and [RhI(SnCl3)5]4-. Moreover, 5 isotopomer pairs, as well as the respective isotopologues, for these species were identified and assigned for the first time.