Robyn S. Hay-Motherwell

Functionalisation of saturated hydrocarbons. Part 1. Some reactions of a ferrous chloride–chloramine-T complex with hydrocarbons

The reactions of several hydrocarbon substrates with a ferrous chloride–chloramine-T complex, generated in situ, have been studied. Tosylamination of adamantane and chlorination of mesitylene proceed in good yield while naphthalene gives N,N′-bis(toluene-p-sulphonyl)-1,4-naphthoquinone di-imine. A variety of olefinic substrates undergo both cis- and trans-addition to the double bond as well as allylic functionalisation.

Chiral 2,6-lutidinyl-biscarbene complexes of palladium

Chiral complexes of palladium, 1, with the new tridentate ‘pincer’ ligand 2,6-lutidinyl-biscarbene (C⁁N⁁C), have been prepared; in the solid state they exhibit helical C2 symmetrical structures which are persistent in solution at least up to 80 °C; the chiral nature of 1 has been established by NMR methods using Pirkle’s acid as a chiral discriminating agent; racemic mixtures of 1 are highly active catalysts in Heck coupling reactions.

The reaction of thionitrites with barton esters: a convenient free radical chain reaction for decarboxylative nitrosation

Tertiary thionitrite esters react with primary and secondary O-acyl derivatives of N-hydroxy-2-thiopyridone to give trans nitroso dimers as the principal products of a free radical chain reaction

Model experiments pertaining to the mechanism of action of vitamin B12-dependent α-methyleneglutarate mutase

Photolysis of di-t-butyl 1-bromomethylcyclopropane-1,2-dicarboxylate (1a) in cyclopropane containing triethylsilane and di-t-butyl peroxide gave the 4-methylenepent-2-yl-1,5-dioic acid radical (3c), which was also produced from treatment of (1a), its cis-isomer (2b), di-t-butyl-2-bromo-4-methyleneglutarate (3a), or di-t-butyl 2-bromo-methyl-3-methylenesuccinate (4b), with triphenyltin hydride; these experiments support a mechanism via protein-bound free radicals for the B12-dependent enzyme α-methyleneglutarate mutase.

Functionalization of saturated hydrocarbons. Part 4. The Gif system for selective oxidation using molecular oxygen

Various systems for the selective oxidation of saturated hydrocarbons have been developed. These are based on the idea of an iron catalyst which is reduced by electron transfer and oxidized by molecular oxygen simultaneously in the presence of a source of protons. Four modifications of this system (the Gif system) have been devised of which the best (Gif IV) consists of an iron catalyst with metallic zinc as the reductant, acetic acid as the proton source and pyridine as the solvent. At room temperature, using oxygen or air saturated hydrocarbons are oxidized selectively to ketones in isolated yields superior to those reported for comparable model systems.

REACTIONS OF IRIDIUM AND RUTHENIUM COMPLEXES WITH ORGANIC AZIDES

Interaction of N 3 R with Ir(mes) 3 (mes = mesityl, C 6 H 2 Me 3 -2,4,6) gave products dependent on the nature of the azide. When R = mes, the tetrazenido amide complex 1 is obtained in which dehydrogenative coupling of the mesityl groups via the o-methyls has occurred; thermolysis of 1 in toluene resulted in cleavage of the tetrazene ring and formation of amide complex 2. When R = Ph, the aryl tetrazenido amide complex 3 is formed. Photolysis of a mixture of N 3 (mes) and [RuCl 2 (PPh 3 ) 3 ] followed by phosphine exchange gave the tetrazene complex [Ru II Cl 2 {N 4 (mes) 2 }(PMe 3 ) 2 ] 4. Thermal reaction of [RuCl 2 H 2 (PPr i 3 ) 2 ] with N 3 (mes) gave the triazenophosphorane complex [RuCl 3 (PPr i 3 ){N 3 (mes) PPr i 3 }] 5. The ruthenium allyl amide [Ru(PMe 3 ) 3 {NHC 6 H 3 Pr i (η 3 -CH 2 CCH 2 )}] 6 bearing a new hybrid ligand was obtained by interaction of trans-[RuCl 2 (PMe 3 ) 4 ] with Li[NH(C 6 H 3 Pr i 2 -2,6)] in di-n-butyl ether. Plausible reaction mechanisms accounting for the formation of the new compounds are proposed. Finally, the crystal structures of the complexes 1–6 have been determined. Complexes 1 and 2 have pseudo-square planar geometries involving the olefin formed by the coupled methyl groups of two mesityls and three (1) or two (2) amide nitrogens and a chlorine atom (2). Compound 3 has a trigonal bipyramidal metal centre with the axial Ir–N amide bonds longer than the equatorial ones; 4 has an octahedral structure with a bidentate tetragonal ligand and trans phosphines whilst 5 is distorted octahedral with a N,N-chelating phosphazide ligand. Complex 6 is also octahedral with the allyl groups occupying cis sites and the three Ru–P bonds in a facial arrangement.

Reduction of nitric oxide by tetramesityliridium(IV) and cobaltocene. Reactions of hyponitrite complexes and of the ether [Co(η5-C5H5)(η4-C5H5)](µ-O-exo) with nitroalkanes, acids and amines

The interactions of either Ir(mes)4(mes = C6H2Me3-2,4,6) or Co(cp)2(cp =η5-C5H5) with NO in light petroleum gave unstable solids the IR spectra of which allow them to be formulated as hyponitrite complexes, e.g.[Co(cp)2]2(N2O2)1; their reaction with MeNO2 is described. The compound Co(cp)2 with either NO or Ag2N2O2 in toluene gave N2O and the very reactive ether [Co(cp)(η4-C5H5)]2(µ-O-exo)2. This reacts with nitroalkanes where the product depends on the nature of the nitroalkane. Nitromethane produced both Co(cp)2+ CH2NO2–·H2O 3 and [Co(cp)(η4-C5H5)]2[(µ-CH(NO2)-exo]4, while Me2CH(NO2) gave Co(cp)[η4-C5H5(CMe2NO2)-exo] and EtNO2 corresponding species to 3 and 4(i.e.6 and 7). Reactions of 2 with alcohols or phenylacetylene gave mononuclear species of the same type as 4; treatment with NH2Ph or NHPh2 also gave similar exo complexes 8 and 9 respectively. All these exo species reacted with CHCl3 to give the exo-CCl3 compound by facile C–C bond cleavage. Mechanisms for the various reactions are discussed. The structures of compounds 2–4, 8 and 9 have been confirmed by X-ray crystallography: 2 and 4 contain Co(cp)(η4-C5H5) moieties bridged by oxygen or CH(NO2) groups while 8 and 9 are monomers with exo-NHPh or -NPh2 groups. In all cases but one (2) there are near-eclipsed C5CoC5 geometries; for one of the cobalts in 2 there is a twist of ca. 16° from the eclipsed configuration. Compound 3 has Co(cp)2+ and CH2NO2– ions the latter being involved in strong hydrogen bonding with the H2O molecule also present in the lattice. In both 8 and 9 there is structural evidence for π interaction between p lone pairs on the planar nitrogen atom and the π system of a phenyl ring.

Homoleptic mesityls of iridium(III,IV,V) and ruthenium(IV,V)

The interaction of IrCl3(tht)3, tht = tetrahydrothiophene, and mesityl (2,4,6-trimethylphenyl, mes)-magnesium bromide in diethyl ether gives Ir(mes)3 as a very air-sensitive crystalline solid. Interaction of partially dehydrated IrCl3 with mesityllithium in Et2O gives the air-stable, paramagnetic Ir(mes)4. Interaction of RuCl3(tht)3 with Mg(mes)2(thf)2(thf = tetrahydrofuran) gives Ru(mes)4. The tetramesityls can be oxidised by AgO3SCF3 or NOPF6 to give, respectively [IrV(mes)4]O3SCF3 and [RuV(mes)4]PF6, the former being diamagnetic and the latter paramagnetic. Cyclic voltammetric and some chemical studies have been made and nuclear magnetic and electron paramagnetic resonance spectra recorded. The NMR spectra of the diamagnetic compounds show that there is synchronous rotation of mesityl groups about the M–C bond. The X-ray crystal structures of Ir(mes)3, [Ir(mes)4]O3SCF3 and Ru(mes)4 have been determined; the tris(mesityl) is similar to that of Rh(mes)3 described earlier while the tetramesityl compounds are tetrahedral or slightly distorted tetrahedral.

Synthesis and X-ray crystal structure of trimesitylrhodium(III)

The first neutral homoleptic aryl of rhodium(III), Rh(2,4,6-Me3C6H2)3, has been made by interaction of RhCl3(C4H8S)3 and mesitylmagnesium bromide; the X-ray crystal structure suggests that there is ‘agostic’ interaction between Rh and an ortho-CH3 group in a distorted fac-octahedral geometry, but solution spectroscopic data show no evidence for agostic hydrogen bonding; 1H NMR spectra over a temperature range indicate synchronized rotation of the mesityl group about the Rh–C bond for which ΔG‡ is ca. 63 kJ mol–1.

Homoleptic methyl compounds of rhodium and iridium(III). X-Ray crystal structures of tetramethylethylenediamine lithium hexamethyl-rhodate(III) and -iridate(III)

The interaction of tetrahydrothiophen (tht) complexes, MCl3(tht)3, M = Rh, Ir, with methyl-lithium in Et2O followed by addition of tetramethylethylenediamine (tmed) gives [Li(tmed)]3[M(Me)6] as thermally and air sensitive crystals; the isostructural compounds have a slightly distorted octahedral MMe6 core with three pairs of cis-methyl groups bridged by Li(tmed) units via Li ⋯ H3C interactions; the symmetry of the MMe6 core is lowered from Oh to D3 by interaction of the MMe6 core with the Li(tmed) units.