A. B. Permin

The effect of the solvent upon the rates and mechanisms of organometallic reactions : V. PMR spectra and structure of molecular complexes of methyltin halides in solutions

The complexation of methyltin halides in electron-donating solvents such as acetone, dioxane, dimethoxyethane, pyridine, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoric triamide, and tetramethylethylenediamine has been studied by means of PMR spectroscopy. Equilibrium constants have been evaluated for Me3SnHal·D (D = donor) complexes. The concentration and temperature dependences of J(119SnC1H) in methyltin halides suggest some conclusions on the electron and spatial structures of complexes in solutions.Abstract The complexation of methyltin halides in electron-donating solvents such as acetone, dioxane, dimethoxyethane, pyridine, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoric triamide, and tetramethylethylenediamine has been studied by means of PMR spectroscopy. Equilibrium constants have been evaluated for Me3SnHal·D (D = donor) complexes. The concentration and temperature dependences of J(119SnC1H) in methyltin halides suggest some conclusions on the electron and spatial structures of complexes in solutions.

The mutual influence of ligands and the nature of chemical bonds in tin(IV) octahedral complexes

Abstract By considering the bond length Sn-Lig, determined by X-ray structure analysis in cis- and trans-complexes of general formula (CH3)nSnHal4 − n · 2 D, where n = 0–2, Hal = Cl or Br, D = hexamethylphosphoric triamide, dimethyl sulphoxide or dimethyl formamide, it was observed that in all complexes the tin atom is surrounded by ligands in a slightly deformed octahedral. The interactions of ligands in the considered complexes differ strongly from the interactions of ligands in octahedral and quadratic complexes of transition metals. All bond lengths are in good agreement with contributions from HVI, HVII hypervalent and covalent bonds in the formations of SnLig bonds and also with the participation of the 5d-orbital of tin.

A STUDY OF THE MECHANISM OF PLATINUM(II)/TIN(II) DICHLORIDE MEDIATED HYDROGENATION OF ALKYNES AND ALKENES EMPLOYING PARAHYDROGEN-INDUCED POLARIZATION

The mechanism of hydrogenation of alkynes catalyzed by the [(PR3)2PtHX]/SnX2 system (PR3 = PPh3, PMePh2; × = Cl, Br) has been studied by means of parahydrogen-induced polarization of 1H spectra (PHIP). Dihydride intermediates confirming the stepwise hydrogenation at room temperature were observed when the reaction was run in acetone. The obtained 1H-PHIP spectra, together with NMR data for related species, are consistent with the formulation of these intermediates as cis-[H2Pt(PR3)(SnX3)(σ-alkenyl)(acetone)], where the σ-alkenyl ligand originates from an insertion reaction of the alkyne (1-phenyl-1-propyne, 1-phenyl-1-butyne, diphenylacetylene, 3,3-dimethylbutyne). At elevated temperatures, the hydrogenation in acetone proceeds as a cis-synchronous transfer of the two hydrogen atoms of parahydrogen to the substrate molecule. A mechanism for this synchronous hydrogenation is suggested.

Alkyl derivatives of platinum and rhodium as intermediates in homogeneous reactions of olefin hydrogenation and isomerisation

Abstract Literature data and results obtained on the mechanisms of olefin hydrogenation and isomerisation using platinum and rhodium complexes, in particular, with PtSn and RhSn bonds were analysed. The role of alkyl derivatives of platinum and rhodium in these reactions is discussed.

On the interaction of trifluoromethyl derivatives of mercury with organic compounds of tin and platinum

Abstract It has been shown that CF 3 HgX molecules react easily with trimethyltrifluoromethyltin and cis -bis(triphenylphosphine)dimethylplatinum in inert solvents, to give typical alkyl exchange reaction products.

In situ NMR Detection of Dihydrides in the Systems [RhH(SnCl3)5]3–/Tertiary Phosphanes/Parahydrogen

The oxidative addition of dihydrogen to the [RhH(SnCl3)5]3–/PR3 system (PR3 = PPh3, PEtPh2, PEt3) leads to the formation of previously unknown dihydride complexes, the 1H-NMR spectra of which have been studied by means of the ParaHydrogen Induced Polarization (PHIP) method. The composition of the resulting complexes crucially depends on the type of the added phosphane. With PEt3 as the phosphane and acetonitrile as the solvent, a complex with a SnCl2L ligand (L = CD3CN) can be detected. All systems examined catalyze the hydrogenation of phenylacetylene. During these reactions, both the 1H-NMR resonances of the dihydride complexes and those of styrene, the hydrogenation product of phenylacetylene, can be detected simultaneously. In the case of SnBr3 ligands, hydrogen addition in the presence of phosphanes leads to similar dihydride complexes, which were also identified via 1H-NMR spectroscopy. Furthermore, a mixed complex of the structure [Rh(SnBr3)nBr6–n]3– has been isolated.

THE STUDY OF ALKENE ISOMERIZATION CATALYZED BY THE SYSTEM : RHODIUM DIMERIC COMPLEX-TERTIARY PHOSPHINE-TIN DICHLORIDE

Rhodium(I) dimeric complexes, [(Ph3P)4Rh2Cl2] and [(C2H4)4Rh2Cl2], form active catalysts for alkenes isomerization on interaction with tertiary phosphine and tin dichloride in CH2Cl2. Besides 2-methylbut-2-ene, which is the normal product of 1,2-double bond migration, 3-methylbut-1-ene gives the product of unusual 1,3-double bond migration, 2-methylbut-1-ene, which is formed at early stages of the reaction under kinetic control in over-equilibrium quantities. The proposed mechanism for 1,3-double bond migration includes the methyl C−H bond activation, followed by intramolecular transfer hydrogenation.

31P and1H NMR study of reaction between hydride complexes of platinum and divalent tin halides

Conclusions1.In acetone or ethyl acetate, cis-[PtH(SnX3)(PPh3)2] is formed at the first stage of the reaction between [PtHX(PPh3)2] and SnX2; in inert solvent the trans-isomer is the reaction product.2.With increase in temperature, redistribution of the phosphine ligands in cis-[PtH-(SnX3) (PPh3)2] takes place, and [PtH(PPh3)3]+, trans-[PtH(SnX3)2(PPh3)]−, and a platinum complex without phosphine are formed.

Reaction of the rhodium hydridotrichlorostannyl complex [Bu4N]3[HRh(SnCl3)5] with tributylphosphine

Conclusions1.The hydridotrichlorostannyl rhodium complex [HRh(SnCl3)5]3− reacts with tributylphosphine in organic solvents to give, depending on the P∶Rh ratio, mono- and diphosphine hydrido complexes of RhIII, together with the complex [RhISnCl3)3 (Bu3P)2]2−, the composition of the reaction mixture depending on the solvent.2.Two types of reaction occur in the system [HRh(SnCl3)5]3− + Bu3P, namely, rapid reversible deprotonation of the rhodium hydrido complexes, and the slower stepwise replacement of the SnCl3− ligands by Bu3P.3.The strongly solvating solvent THF facilitates the replacement of the SnCl3− ligands by Bu3P.4.The monovalent rhodium complex [RhI(SnCl3)3(Bu3P)2]2− reacts with molecular hydrogen at atmospheric pressure to give dihydrido diphosphine and triphosphine complexes.

Effect of structural factors and solvation character on rearrangements of 1(2)-bromo-2(1)-acetoxypropanes, accompanied by 1,2-migration of the bromine atom

ConclusionsThe 2(1)-bromopropyl tosylates are not isomerized via the 1,2-migration of bromine under the conditions of isomerizing the bromoacetoxypropanes. Three possible mechanisms of the indicated rearrangement are discussed: acylonium (a) and via the ionization of either the C-O bond (b) or the O-Br bond (c) in the initial reaction step. Mechanism b was rejected on the basis of the experimental data.