Ray Colton

Tin-119 NMR studies on diorganoyltin(IV)dihalides and triorganoyltin(IV)halides; Formation and stereochemistry of adducts

Abstract The reactions of R 2 SnX 2 (R = Ph, Me; X = Cl, Br) with excess halide, tributylphosphine, tricyclohexylphosphine and tributylphosphine oxide have been investigated in dichloromethane solution by tin-119 and phosphorus-31 NMR techniques. R 2 SnX 2 form five coordinate 1:1 adducts with halide and phosphine (phos) ligands whilst both 1:1 and 1:2 adducts are formed with tributylphosphine oxide (L). Tin-119 spectra imply that Ph 2 SnX 2 (phos) has the phosphine in the equatorial position of a trigonal bipyramid. At low temperature there is evidence for a slow intramolecular twist mechanism between octahedral isomers of Ph 2 SnCl 2 L 2 . The stereochemistry of the complexes Ph 2 SnX 2 L 2 differ between chloro and bromo compounds and no mixed halide complex is observed. In the case of the bromo system only, the 1:3 adduct [Ph 2 SnBrL 3 ] + Br − is formed. Ph 3 SnCl does not react with phosphines but it does give 1:1 adducts with Cl − , L and pyridine. All the adducts have similar tin-119 chemical shifts which is consistent with the phenyl groups being equatorial in the five coordinate trigonal bipyramidal adducts. Ph 4 Sn does not form adducts with X − , L or phosphine.

Phosphorus-31 and tin-119 NMR studies on tin(IV) halides and their adducts

Abstract Tin-119 NMR spectra have been recorded for SnX4 (X = Cl, Br, I) and mixtures thereof. All fifteen possible SnClxBryIz (x + y + z = 4) species were observed. Tin-119 NMR spectra were observed for SnX−5 and SnX2−6 (X = Cl, Br) and for an equimolar mixture of SnCl2−6 and SnBr2−6 which gave all ten possible isomers of [SnClxBr6−x]2− in the statistical distribution. Phosphorus-31 and tin-119 NMR spectra were observed for SnX4(PBu3)2 (X = Cl, Br) and a mixture gave all six possible trans phosphine isomers in the statistical distribution. [SnX5(PBu3)]− (X = Cl, Br) species show some disproportionation, although the [SnX5(PBu3)]− ion is the dominant species in solution. A mixture of [SnCl5(PBu3)]− and [SnBr5-(PBu3)]− gave a complex mixture in solution, but all twelve isomers of the [SnCl5Br5−x(PBu3)]− series were identified. The well known pairwise additivity model fits well within the tetrahalide or hexahalide anion series and it is shown that the chemical shift of tin both tetrahedral and octahedral environments may be predicted from a single set of interaction parameters if geometrical factors are taken into account. The same interaction parameters are of use in identifying the mixed tin halide-phosphine complexes.

Tin-119 NMR Studies on adduct formation and stereochemistry of organoyltin(IV)trihalides

Abstract qazTin-119 and phosphorus-31 NMR spectra have been recorded for a series of adducts of RSnX 3 (R  Me, Ph; X  Cl, Br) with halide, tributylphosphine (P) and tributylphosphine oxide (L). The adducts were either 1:1 five coordinate or 1:2 six coordinate complexes. The tin-ll9 NMR spectra of mixtures of corresponding chloro and bromo complexes reveal, in most cases, all possible mixed halide species but much additional structural information is obtained from these spectra which could not be extracted from the spectra of individual compounds themselves. Thus in some cases, in the five coordinate species the Berry pseudorotation between isomers within a particular stoichiometry could be slowed on the NMR timescale which allowed a determination of the molecular structure. An equimolar mixture of [PhSnCl 5 ] 2− and [PhSnBr 5 ] 2− shows eleven of the twelve geometries possible for [PhSnCl x Br 5− x ] 2− . In the six coordinate series [RSnX 4 P] − the tin-119 NMR spectra of the mixtures of [RSnCl 4 P] − and [RSnBr 4 P] − allow the geometry to be determined as trans . Application of the pairwise additivity model for calculation of the tin-119 chemical shift positions for the mixed halide systems are discussed.

Tin-119 NMR studies on some adducts of tin(IV) halides

Abstract Tin-119 and phosphorus-31 NMR spectra have been recorded for SnCI 4 L 2 , SnBr 4 L 2 (L = tributylphosphine oxide) and mixtures thereof. The compound SnCl 4 L 2 exists predominantly as the trans L 2 isomer with a small proportion of the cis L 2 isomer also present in solution whereas SnBr 4 L 2 appears to be present only as the trans L 2 isomer. In the mixed solution all the trans snCI x Br 4−x L 2 species are observed. The anionic complexes [SnCI 5- L] − and [SnBr 5 L] − both show slight dissociation in solution to SnX 4 L 2 and [SnX 6 ] 2− (X = CI, Br). The tin-199 NMR spectrum of an equimolar mixture of [SnCI 5 L] − and [SnBr 5 L] − shows ten of the possible twelve [SnCI x Br 5-x L] − species. In contrast, SnX 4 L 2 (L′ = acetone; X = CI, Br) exist predominantly as cis L′ 2 isomers. A 1:1 mixture of the complexes in dichloromethane solution at −50 °C shows average tin-119 resonances for each stoichiometry of mixed halo species cis SnCI x Br 4-x L′ 2 . Subsequent cooling to −100 °C slows intramolecular processes sufficiently to enable observation and identification of most of the individual geometric isomers of each stoichiometry. The anionic complexes [SnCI 5 L′ − and [SnBr 5 L′ − show no appreciable dissociation in dichloromethane solution and the tin-119 spectrum of a 1:1 mixture of these compounds at −100 °C shows only six resonances corresponding to various [SnCI x Br 5-x L′] − species without distinguishing between individual isomers of each stoichiometry. Cooling to −100 °C enables identification of some of these isomers. The pairwise additivity model, using previously established interaction parameters, was used to assign all isomers species observed in the tin-119 spectra of these systems.

Phosphorus-31, platinum-195 and lead-207 NMR studies on some platinum-lead bonded compounds

Abstract Phosphorus-31, platinum-195 and lead-207 nuclear magnetic resonance studies have been carried out on a series of complexes of the type cis -Pt(PPh 3 ) 2 (R)(PbR 2 R′) and trans -Pt(PBu 3 ) 2 (PbR 3 ) 2 (R  Ph, 4-MePh, 4-MeOPh, 4-ClPh, 4-FPh; R′  R, Br, I). Lead-platinum coupling constants, 1 J ( 207 Pb- 195 Pt), range between 14.5 kHz and 18.5 kHz with the trans compounds having the smaller coupling constants. Variation of the phenyl group substituents has only a small effect on the lead chemical shift and virtually no effect on the other NMR parameters. However, variation of the substituents directly bonded to the lead atom significantly effects the 207 Pb chemical shift and causes corresponding, but weaker, effects in the other spectral parameters. Second order heteronuclear coupling effects between platinum-195 and lead-207 are observed for all the complexes and this is the first time that second order coupling has been observed between different elements. Phosphorus-31, 195 Pt and 207 Pb NMR spectra have been used to confirm the identity of the intermediate cis -Pt(PPh 3 ) 2 (Ph)(Pb 2 Ph 5 ) observed during the preparation of cis -Pt(PPh 3 ) 2 (Ph)(PbPh 3 ).

Multinuclear (31P, 77Se, 195Pt) magnetic resonance studies on the interaction of platinum bis(n-propylxanthate) with potentially bidentate ligands

Abstract The reactions of platinum bis(n-propylxanthate), Pt(S 2 CO n Pr) 2 (Pt(xan) 2 ) with a number of potentially bidentate Group 15 and mixed Group 15/Group 16 donor ligands (L-L′) have been investigated in dichloromethane solution. The products of the reactions have been identified by multinuclear ( 31 P, 77 Se, 195 Pt) magnetic resonance, infrared and analytical studies. When reactions in 1:1 molar proportions are carried out at room temperature, one xanthate ligand is often displaced to give [(L-L′)Pt(xan)] + and further reaction occurs to give the dithiocarbonate complex (L-L′)Pt(S 2 CO) and the xanthate ester. If the reactions are carried out at low temperature this reaction is avoided and temperature dependent equilbria of the type (η 1 -L-L′)Pt(η 1 -xan)(η 2 -xan) ⇌ [(η 2 -L-L′)Pt(η 2 -xan)] + + xan − occur because of the similar donor powers of the various ligands. Dithiocarbonate is a much stronger ligand to platinum than xanthate, so these reactions do not occur with this ligand.

Platinum-195 NMR studies of Pt(LL)2 (LL = −S2PR2, −S2P(OR)2, −S2CNR2) and their derivatives with phosphorus containing ligands

Abstract Platinum-195 NMR spectra have been recorded for CH2Cl2 solutions of a range of Pt(LL)2 (LL = −S2PR2, −S2P(OR)2, −S2CNR2) and their derivatives with phosphorus containing ligands. Platinum chemical shifts cover a range of almost 2000 ppm.

Phosphorus-31, tin-119 and platinum-195 NMR studies on some platinum(II)-tin bonded compounds

Abstract Phosphorus-31, tin-119 and platinum-195 NMR spectra have been measured for three series of compounds; cis -Pt(PPh 3 ) 2 (Ph)(Z) where Z = SnPh 3 , SnPh 2 Cl, SnPhCl 2 , SnCl 3 , SnPh 2 Br, SnPhBr 2 , SnPh 2 I, SnPh 2 NCS, SnPh 2 SPh and SnPh 2 SCH 2 Ph; cis / trans -Pt(PPh 3 ) 2 (Cl)(Q) where Q = SnMe 2 Cl, SnBu 2 Cl, Sn(t-Bu) 2 Cl, SnMeCl 2 , SnBuCl 2 and SnPhCl 2 ; and cis / trans -Pt(PPh 3 ) 2 (Br)(Y) where Y = SnMe 2 Br, SnBu 2 Br, SnMeBr 2 , SnBuBr 2 , SnPhBr 2 . The 195 Pt resonances cover a range of 450 ppm and the 119 Sn resonances a range of 300 ppm, with 1 J (Pt- 119 Sn) varying between 7 and 20 kHz. Plots of 1 J (Pt-P trans ) against 1 J (Pt- 119 Sn) are approximately linear, indicating that the platinum-tin bond is predominantly σ in character.

Molecular weight and mercury-199 NMR studies on mercury-rich cations produced from mercury(II) dithiocarbamates

The mercury-rich dithiocarbamate cations [Hg3(R2dtc)4]2+ and [Hg4(pipdtc)6]2+ (R = Et, Bz; pip = piperidyl; dtc = dithiocarbamate) have been shown by a polarographic method to be partially dissociated at the \R~2 × 10−4 M concentration level in dichloromethane solution. However, for approximately 10−2 M solutions of [Hg3(R2dtc)4]2+ in dichloromethane, mercury-199 NMR studies over a wide temperature range are more consistent with the presence of higher oligomers such as [Hg6(R2dtc)8]4+.

Heteronuclear second-order coupling effects in platinum-lead-bonded compounds

As part of NMR investigations of chemical shifts and couplings of heavy nuclei bonded to each other we have been examining compounds with direct platinu ti nd platinum-lead bonds and now report second-order coupling effects betwee 19 and zo7Pb in platinum-lead compounds. This communication has bee prompted by the recent report (I) of isotopic heteronuclear second-order ~0~~1~~ between ‘17Sn and “‘Sn in (Ru(SnC1,),C1)4and (Os(SnC1,),C1)4-. As an example we take the compound cis-Pt(PPh,),(Ph)(PbPh3) for which the 31P NMR spectrum (2) in dichloromethane consists of two main doublets (6 24.85 ppm, 6 20.80 ppm) arising from the nonequivalent phosphines (2J(31P-3’ Hz). The doublet at higher frequency has satellites (‘J(‘95Pt-31P) = 2 2J(207Pb-31P) = 3460 Hz), which are consistent with a phosphorus tram to and the doublet at lower frequency has couplings (1J(g5Pt-31P) = 1965 Hz, 31P) = 260 Hz), which are consistent with a phosphorus cis to the lead atom. The “*Pt NMR spectrum at 21.3 1 MHz (Fig. 1) of cis-Pt(PPh3),(Ph)(PbFhs) has a central doublet of doublets resulting from coupling to the different phospbor~s atoms and two sets of *“Pb satellites (with the same phosphorus couplings) each f intensity approximately 12% relative to the central multiplet. The two sets of llites are not symmetrically disposed about the central multiplet, their tion being 180 Hz above the frequency of the main multiplet. The *07P spectrum at 20.84 MHz (Fig. 1) is of similar appearance (with different ph uplings) with lg5Pt satellites ( 16% of the central multiplet) unsymmetrically dissed about the central multiplet by 180 Hz to the lower frequency side of the spectrum. Spectra recorded at higher field (lg5Pt at 42.70 MHz, 207Pb at 41.74 MHz) show the asymmetry is decreased to 85 Hz. That the asymmetry is attributable to second-order coupling effects in the satellite spectrum rather than a large isotope effect is endorsed by several experimental observations. The above variation of the asymmetry with frequency is quite the opposite of that expected for an isotope effect, The central multiplets of both spectra have sharp, well-defined lines. In the platinum-195 spectrum this central multiplet corresponds to lg5Pt bonded to lead nuclei with spin 0 (*O’Pb 24%, “‘Pb 52%). gnitude of the asymmetry of the satellites suggests that for a genuine isoto ct the peaks of the central multiplet should be significantly broadened, if split into two multiplets, corresponding to lg5Pt bonded to each of those two nuclei.