Charles F.H. Tipper

Reactions and properties of some trimethyleneplatinum(IV) complexes : I. Thermal decomposition studies

Abstract The thermal decomposition of the complexes PtX2(C3H6), PtX2(C3H6)L2 and PtX2(C3H6)(LL) [where X = Cl, Br; L = pyridine, 4-methylpyridine; LL = 2,2′-bipyridyl, ethylenediamine] has been studied by differential scanning calorimetry and thermogravimetric analysis. The first estimated PtC bond strength for platinum—trimethylene complexes is reported.

1H,13 and 195Pt NMR studies of some platinumcyclopropane compounds

The 1H, 13C and 195Pt NMR spectral parameters of some platinum—cyclopropane complexes are reported. The NMR parameters, particularly the 13CH coupling constants, suggest the presence of a PtCH2CH2CH2 ring in these compounds. However, there is probably some interaction between platinum and the β-carbon atom acioss the 4-membered ring.

Reactions and properties of some trimethyleneplatinum(IV) complexes : II. Reactions with added ligands

Abstract The ligands L in the compounds PtX2(C3H6)L2 (X = Cl, Br) are found to be replaced in the order, tetrahydrofuran, pyridine, 4-methylpyridine, ethylenediamine, without displacement of the trimethylene moiety. A dimethylformamide derivative of trimethyleneplatinum(IV) was also prepared, but dimethyl sulphoxide and olefins (ethylene, cyclooctadiene) displace the C3H6 under some conditions. No reaction with triphenylphosphine, arsine and stibine in DMSO and DMF occurs if L2 = ethylenediamine or 2.2′-bipyridine, but when L = C5H5N or 4-CH3C5H4N, reductive elimination occurs with evolution of cyclopropane. The yield of gas depends, however, on the nature of L, X and the entering ligand, due to the parallel formation of coloured products, in which the platinum trimethylene ring is intact, under some conditions. The kinetics of the cyclopropane displacement have been studied and a mechanism involving ionic intermediates is proposed.

Reactions and properties of some trimethyleneplatinum(IV) complexes

Summary The photolysis of platinum-cyclopropane compounds, [X2PtCH2CH2CH2(L L)][where X = Cl, Br and L L = 2,2′-bipyridine, 1,10-phenanthroline] in solution at 25°C gives cyclopropane (plus a little propene) and [X2Pt(L L)]. The kinetics indicate that the C3H6moiety is ejected from the excited molecule in a single step.

The photodecomposition of platinacycloalkanes in solution.: I. 1,3-propanediylplatinum(IV) compounds

Abstract The gaseous products of the photolysis at 25°C of the platinacyclobutane compounds [X2 PtCH 2 CH 2 C H2(N-N)] where X = Cl, Br and N-N = 1,10-phenanthroline, 2,2′-bipyridine, (CH2NMe2)2, (C5H5N)2 in several solvents, in the absence and presence of various additives, have been determined. With solvents of relatively low dielectric constant (e.g. CH2Cl2), over 85 mol % of the hydrocarbon products was propene, the formation of which appears to involve a direct transfer of a hydrogen atom between neighbouring groups in the ring. With solvents of relatively high dielectric constant (MeCN, Me2SO) in the presence of species, e.g. I−, SbPh3, having a high trans effect, cyclopropane is the main volatile product. The effect of added halide ion and of the mixed solvents Me2SO/PhMe and Me2SO/PhSH indicates that ionisation of the platinacyclobutane and the formation of platinum substituted propyl ion-radicals precede the formation of cyclopropane (and the small amounts of ethylene produced). The photolysis of [X2 PtCH 2 CH 2 C H2(MeCN)2] in methyl cyanide solution in the presence of Et3RNX′ (X′ = Cl, R = H; X′ = Br, R = Et) gives appreciable amounts of ethylene in the products (up to 25 mol %). It is suggested that the halide ions add to the platinum to give negatively charged platinacyclobutane species, the photodecomposition of which may give C2H4.

The photolysis of methylplatinum(IV) compounds

Abstract The UV photolysis of three methylplatinum(IV) compounds has been studied with special emphasis on the products formed in the presence and absence of deuterium in the solvent. It is concluded that free radicals are formed and abstract hydrogen, or combine, in solvent cages or in the bulk of the solution.

Reactions and properties of some trimethyleneplatinum(IV) complexes: V. The kinetics and mechanism of formation from arylcyclopropanes

Abstract The kinetics of the reaction of arylcyclopropanes (4-XC 6 H 4 C 3 H 5 , X = H, Me, EtO) with either [Pt 2 Cl 2 (μ-Cl) 2 (C 2 H 4 ) 2 ] or [{ PtCl 2 (CH 2 CH 2 C H 2 )} in tetrahydrofuran to give in each case [{ PtCl 2 (CHArCH 2 C H 2 )} 4 ] and ethylene or cyclopropane, respectively, have been studied. The reactions are essentially first order in both arylcyclopropane and platinum complexes. The order of reactivity follows the series X = EtO > > Me > H, and [Pt 2 Cl 2 (μ-Cl) 2 (C 2 H 4 ) 2 ]> [{ PtCl 2 (CH 2 CH 2 C H 2 )}4] and the rate is accelerated in polar solvents. Mechanisms in which the arylcyclopropane first coordinates to platinum and then undergoes ring opening reactions are proposed.

The reaction of platinacyclobutanes with phosphines

Abstract The volatile products of the thermal and photochemical reactions of phosphines (Ph 2 PCH 2 PPh 2 , PPh 3 , PHPh 2 ) with the platinacyclobutane compounds [X 2 PtCH 2 CH 2 C H 2 (NN)] (where X  Cl, Br and NN  1,10-phenanthroline, 2,2′-bipyridine, (CH 2 NMe 2 ) 2 ) in several solvents have been determined. The hydrocarbons formed were ethylene, propene and cyclopropane with small amounts of methane, and also propane with PHPh 2 . Very high relative yields of C 2 H 4 (over 80%) were obtained under some conditions, notably with CH 3 CN and (CH 3 ) 2 SO as solvents. Chloromethane (or bromomethane) was also produced with DMSO as solvent. It is suggested that the formation of ethylene involves dissociation of a halide ion and is accompanied by the production of platinum ylids. Hydrogen transfer from PHPh 2 can lead to the formation of C 3 H 8 .

The photodecomposition of platinacycloalkanes in solution: II. 1,4-butanediylplatinum(II) and (IV) compounds☆

Abstract The products of the photolysis of a number of platinacyclopentanes in solution at 25°C under a variety of conditions have been determined. With [I 2 P tCH 2 CH 2 CH 2 C H 2 (L 2 )] (L = PMe 2 Ph, PPh 3 ) in CH 2 Cl 2 , CH 2 Br 2 and (CH 3 ) 2 SO the hydrocarbon products are exclusively ethylene and but-1-ene. Formation of the latter through a 1,3-hydrogen shift is preceded by phosphine ligand dissociation. The photolysis of [ICH 3 P tCH 2 CH 2 C H 2 (L 2 )] gave methane, ethylene, but-1-ene and n-pentane together with a little n-butane, the methane being formed from internal hydrogen abstraction by the CH 3 group in the excited reactant molecule. Photodecomposition of the platinum(II) compounds [P tCH 2 CH 2 CH 2 C H 2 (L 2 )] (L = (PMe 2 Ph) 2 , (PPh 3 ) 2 , Ph 2 PCH 2 CH 2 PPh 2 ) gave ethylene, but-1-ene, pent-1-ene (with the halogenated solvents) and with some systems appreciable yields of n-butane, the latter being the results of internal abstraction of two hydrogen atoms by the C 4 H 8 moiety. The formation of pentene is probably preceeded by the addition of CH 2 Cl 2 or CH 2 Br 2 to the excited reactant molecule. Addition of diphenylphosphine promotes the production of n-butane.

Reactions and properties of some trimethyleneplatinum(IV) complexes: VII. Kinetics and mechanism of displacement of cyclopropane by alkenes☆

The kinetics of the reaction of alkenes (e.g. cis-pent-2-ene, hex-1-ene, cyclopentene) with [PtX2(CH2CH2CH2)(THF)2] (X = Cl or Br, THF = tetrahydrofuran) or with [PtCl2(CHPhCH2CH2)(THF)2] in THF solution have been studied. The reactions occur with displacement of cyclopropane or phenylcyclopropane to give [PtCl2(olefin)(THF)], and follow essentially second order kinetics, first order in both platinum complex and olefin. The mechanism of reaction is discussed.