Chemistry of Solvated Cations in Acetonitrile

Siddique, Rana Muhammad (1988) Chemistry of Solvated Cations in Acetonitrile. PhD thesis, University of Glasgow.

Abstract

The solution chemistry of solvated cations, [Fe(NCMe)6]2+, [Cu(NCMe)4]+, [Cu(NCMe)6]2+, [T1(NCMe)6]3+ and [I(NCMe)2]+, in acetonitrile is described in this thesis. The ligands used in this study are the simple N,P and S-donor species such as NH3, NMe3, pyridine(py), PMe3, P(OMe)3, Me2S and tetramethylthiourea(tmtu). Macrocyclic N-donor ligands such as 1,4,8,11-tetraazacyclotetradecane ([14]-aneN4) and 1,4,8,12-tetraazacyclopentadecane([15]-aneN4), are also used in some cases. A 205 T1 n.m.r. study of the T1 I salts having diamagnetic complex fluoroanions, PF6- and WF7-, in MeCN solution indicates a high field shift of the 205T1 n.m.r. resonances with an increase in salt concentration. The increase in the concentration of the T1 I salts with paramagnetic anions, MoF6 and UF6, on the other hand, results in a low field shift. The concentration dependent behaviour observed for 205T1 n.m.r. resonances in the T1 I salts, in MeCN indicates that some degree of ion-pairing is present in these solutions. The effect of paramagnetic anions on the 205 T1 resonances in the T1 I salts is far greater but their effect on T1 III is very small. It is suggested that T1 3+ is more effectively solvated by MeCN as compared with T1+ hence direct ion-pairing is less important. The 205T1 shielding of T1 I and T1 III is decreased respectively in the presence of T1 III and T1 I. Coordinated acetonitrile in the cation [Fe(NCMe)6]2+, is replaced readily by NH3 and pyridine (L) at room temperature to form [FeL6]2+ . Only one Me3N ligand is coordinated to Fe II under normal conditions to form [Fe(NMe3)(NCMe)5]2+. The reaction of [Fe(NCMe)6]2+ with tmtu in MeCN presumably results in the formation of [Fe(tmtu)6]2+ whereas no reaction is observed when Me2S is reacted with [Fe(NCMe)6]2+ The cation, [Fe(NMe3)(NCMe)5]2+, reacts with P(OMe)3 in MeCN solution forming [Fe(P(OMe)3}5(NMe3)]2+ as the final product. The reaction involves a stepwise substitution of P(OMe)3 for coordinated MeCN and is followed by 31P-{1H} n.m.r. spectroscopy. The formation of the first low spin species, cis and trans-[Fe{P(OMe)3}2- (NMe3)(NCMe)3]2+ is followed by stopped-flow spectrophotometry and confirmed by 31P-{1H} n.m.r. spectroscopy. The species, [Fe{P(OMe)3}2(NMe3)(NCMe)3]2+, on further substitution forms fac-[Fe{P(OMe)3}3(NMe3)(NCMe)2]2+. The formation of the final product, [Fe{P(OMe)3}5(NMe3)]2+, from fac-[Fe{P(OMe)3}3(NMe3) (NCMe)2]2+ occurs via the route in which the cation, trans-[Fe{P(OMe)3}4(NMe3)-(NCMe)]2+ is dominant whereas in the [FeL6]2+ (L= NCMe or py) and P(OMe)3 systems, the route involving the cation, cis-[Fe{P(OMe)3)4L2]2+ is important. The cations, [FeL6]2+, L = NCMe, py or NH3, and [Fe(NMe3) (NCMe)5]2+ react with PMe3 in MeCN at room temperature forming low spin iron(II) cations with three ligated PMe3 molecules. The dominant cations are the fac-(Fe(PMe3)3L3]2+ or fac[Fe(PMe3)3(NMe3) (NCMe)2]2+. The complexes having four ligated PMe3 molecules, cis-[Fe(PMe3)4L2]2+ or cis-[Fe(PMe3)4(NMe3)(NCMe)]2+ are present only in trace quantities. The replacement of nitrogen donor ligands by PMe3 at iron(II) in MeCN is very fast as compared with P(OMe)3. The reactions are complete within the time of mixing the reactants. The reaction of [Cu(NCMe)4]+ with Me2S or Me3N in MeCN does not result in the coordination of the ligand whereas the cations, [CuL4]+ L = PMe3 or tmtu, are formed when [Cu(NCMe)4]+ is reacted with PMe3 or tmtu. T1 IUF6. reacts with Me3N or Me3P(L) in MeCN solution forming insoluble T1 I salts, [TIL2][UF6]. Dimethyl sulphide on the other hand does not react with T1 I in MeCN solution. The cations, [Cu(NCMe)6]2+ and [T1(NCMe)6]3+, react with Me2S, Me3N, Me3P and tmtu, in MeCN solution undergoing redox reactions. Solvated Cu2+ and solvated T13+ cations in these redox reactions are reduced to the +1 oxidation state whereas the ligands are oxidised to the corresponding monomeric radical cations. The radical cations, Me2S+ or Me3N+ formed in the redox reactions involving Me2S or Me3N, combine with free ligands forming the dimeric radical cations, [Me2S-SMe2]+ or [Me3N-NMe3]+. The dimeric radical cations then lose methyl radicals, Me, forming the cations [Me2S-SMe]+ or [Me3N-NMe2]+. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Organic chemistry
• Date of Award: 1988
• Depositing User: Enlighten Team
• Unique ID: glathesis:1988-77634
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77634