Seichi Okeya

Synthesis, cyclic voltammetry and 31P {H} NMR spectra of [M3E2L3]2+ clusters; M=Ni, Pd or Pt; E=S, Se or Te; L=bis(diphenylphosphino)methane, 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, or 1,4-bis(diphenylphosphino)butane

Abstract Cluster [M 3 E 2 (bis(diphenylphosphino)methane) 3 ] 2+ ([M 3 E 2 (dppm) 3 ] 2+ ; M=Pd or Pt, E=S; M=PtE=Se), [M 3 E 2 (1,3- bis(diphenylphosphino)propane) 3 ] 2+ ([M 3 E 2 (dppp) 3 ] 2+ ; M=Ni, Pd or Pt, E=S or Se; M=Pd or Pt, E=Te) and [M 3 E 2 (1,4- bis(diphenylphosphino)butane) 3 ] 2+ ([M 3 E 2 (dppgb) 3 ] 2+ ; M=Pd, M=Ni, Pd or E=Se; M=Pd or Pt, E=Te) were prepared, and their cyclic voltammaograms and 31 P {H} NMR spectra were measured. The cyclic voltammograms of the clusters depend on the chelate ring size and their chemical reversibilit varies in the order dppe>dppp>dppb=dppm. Three [M 3 Te 2 (dppe) 3 ] 2+ (M=Ni, Pd or clusters synthesized previously give quasi-reversible cyclic voltammograms at 298 K and their standard heterogeneous charge-transfer rates, k s , were estimated. The increase in the 31 P chemical shift for the ligands is in the order dppe>dppb>dppp>dppm, for clusters which have the same metal and chalcogenido ions; the order of the chemical shift for the metals follows the trend Ni>Pd>Pt, for clusters containing the same chalcogenido ion and the same phosphine. Computer simulation of the 31 P {H} NMR spectra for the [Pt 3 Se 2 L 3 ] 2+ L=dppm, dppe, dppp or doppb) clusters was carried out to estimate the NMR parameters. The magnitude of 2 J (Pt−Pt) depends on the chelate ring size and follows the order dppm > dppe > dppp > dppb.

Chloride-bridged methylpalladium(II) dimers. Preparation, carbonylation and bridge-splitting reactions with tertiary phosphines

Abstract [Pd 2 (μ-Cl) 2 Cl 2 L 2 ] (L = PEt 3 , PBu 3 or PMe 2 Ph) reacts with AlMe 3 in ether, THF or a mixture of these solvents depending on L to give [Pd 2 (μ-Cl) 2 Me 2 L 2 ] in high yield, which has been characterized by IR and NMR spectroscopy as well as elemental analysis. Treatment of [Pd 2 (μ-Cl) 2 Me 2 L 2 ] with CO yields [Pd 2 (μ-Cl) 2 (COMe) 2 L 2 ], while its reaction with L leads to trans -[PdClMeL 2 ]. The preparative method and the characteristic data of these complexes are discussed in comparison with the earlier work on the analogous aryl and aralkyl complexes.

Synthesis and crystal structures of cis- and trans-dimethyl-di-µ-methylene-bis(pentamethylcyclopentadienyl)dirhodium(IV)

Reaction of [{Rh(C5Me5)Cl}2(µ-Cl)2](1) with Li4Me4 or Al2Me6 gives, after air-oxidation, cis- or trans-[{Rh(C5Me5)Me}2(µ-CH2)2][(2a)(28%) and (2b)(15%) respectively] which are formally of RhIV. The structures were elucidated spectroscopically and were confirmed by a single-crystal X-ray determination of the cis isomer (2a). This showed a dinuclear complex with each rhodium bound to one methyl and one η5-C5Me5, and with two bridging methylenes about a rhodium–rhodium bond [2.620(1)A]. The two hydrogens on each methylene bridge are inequivalent as can be seen from the 1 H n.m.r. spectrum. Nuclear Overhauser effect experiments, interpreted in the light of the X-ray structure, showed that it was only the equatorial hydrogen which was coupled to the rhodiums. The cis isomer (2a) was converted into trans-(2b) on reaction with Lewis acids (e.g. Al2Me6); (2b) also reacted with AI2Et6 to give trans-[{Rh(C5Me5)Et}2(µ-CH2)2] suggesting a common pathway for substitution and isomerisation. When the yellow solution obtained by reaction of (1) and AI2Me6 in hydrocarbons was reacted with acetone at –78 °C the cis isomer (2a) was obtained in good yield; if the reaction was carried out at higher temperature the trans isomer (2b) was isolated in 89% yield. The results of experiments when perdeuterio-(1) was reacted with AI2Me6 and the reactions quenched (a) with air and (b) with acetone are discussed.

Decomposition reactions of dimethyl-di-µ-methylene-bis(η-pentamethylcyclopentadienyl)dirhodium and their relation to the mechanism of the Fischer-Tropsch reactions; the formation of propylene from three C1 ligands

Thermal decomposition of [{C5(CH3)5Rh}2(µ-CH2)2(CH3)2](1) at temperatures from 275 to 375 °C yielded methane, propylene, ethylene, and some ethane. Using (1) selectively labelled with 13C in the Rh–methylene and/or the Rh–methyl ligands showed that (a) the gases are formed in intramolecular decompositions not involving the C5(CH3)5 rings, (b) the methane arises from both the rhodium–methyls and the rhodium–methylenes, and (c) the C2 and C3 gases arise predominantly from the coupling of a Rh–methyl and one or two Rh–methylenes; direct coupling of two methylenes or of two methyls is not a favourable process here. Very similar gas mixtures are formed (but at 20–50 °C) on reaction of complex (1) with excess IrCl62–(or other one-electron oxidisers and electrophiles). Carbon-13 and deuterium labelling studies show that these reactions are again intramolecular and do not involve the C5(CH3)5 rings, or the coupling of two methyl or two methylene ligands. Methane arises mainly by combination of a Rh–CH3 and a methylene hydrogen, probably after a two-electron oxidation, leaving a transient species (A) formulated as [{C5(CH3)5Rh}2(µ-CH2)(µ-CH)(CH3)]2+. The C2 products must be formed from (A) by the coupling of the Rh–CH3 with the methylene, to give an Rh–ethyl intermediate which β-eliminates to give ethylene (or acquires a hydrogen to give ethane). The labelling shows propylene to arise from the coupling of one methyl and two methylenes. It can be formed via migration of the methyl onto the µ-methyne in (A), giving a µ-methylene-µ-ethylidene species which couples to give propylene directly. Implicit in the route is the need for two metal centres to allow three C1 fragments to couple together to form propylene. Labelling studies rule out appreciable ethylene formation from a Rh–ethylidene. Direct coupling of the methylenes does occur in the thermal decompositions of [{C5(CH3)5Rh}2(µ-CH2)2X2](X = halide, SCN, or N3), to give ethylene; the main product is again methane. The data are contrasted with results from the decomposition of the iridium analogue of (1) and of [C5(CH3)5Ir(CH3)4]. The relationships of the mechanisms proposed to current models for the mechanism of the Fischer-Tropsch reaction on metal surfaces are discussed.

Synthesis and structure of pentanuclear clusters bridged by tellurido ions

Abstract Pentanuclear clusters [M{Pd2(μ2-Te)2(dppe)2}2]2+ (MPt or Hg; dppe = 1,2-bis(diphenylphosphino)ethane) and [M{Pt2(μ3-Te)2-(dppe)2}2]2+ (MPd or Pt) have been synthesized and characterized by 31P{1H} NMR spectroscopy. A single crystal X-ray crystallographic analysis of [Pt{Pd2(μ3-Te)2(dppe)2}2] [BPh4]2 reveals that the central Pt(II) is linked by four tellurido ions of the two dinuclear [Pd2(μ2-Te)2(dppe)2] units in the square planar coordination.

Synthesis and characterisation of disubstituted di-µ-methylene-bis(η-pentamethylcyclopentadienyl)dirhodium(IV) complexes; X-ray structure of [{(C5Me5)Rh}2(µ-CH2)2(CO)2]2+

Reaction of either cis- or trans-[{(C5Me5)Rh}2(µ-CH2)2Me2] with HCl in pentane gave the trans-dichloro-complex [{(C5Me5)Rh}2(µ-CH2)2X2](4a; X = Cl), from which a variety of other complexes (4; X = Br, I, SCN, N3, CN, or NCO) were made by metathesis. Reaction of (4a; X = Cl) with neutral ligands (L) in the presence of non-co-ordinating anions gave first the monocations, [{(C5Me5)Rh}2(µ-CH2)2(L)Cl]+, and then the dications, [{(C5Me5)Rh}2(µ-CH2)2L2]2+(5; L = MeCN, CO, or H2O). The X-ray crystal structure of (5b; L = CO) shows the trans configuration predicted on the basis of the 1H n.m.r. spectra. Reaction of (5b) with methanol and base gave the bis(methoxycarbonyl) complex [{(C5Me5)Rh}2(µ-CH2)2(CO2Me)2]. cis Complexes [{(C5Me5)Rh}2(µ-CH2)2X]n+(X = O2CMe or O2CCF3, n= 1; X = pyridazine or Ph2PCH2PPh2, n= 2) were isolated and identified by their 1H n.m.r. spectra which showed the diastereotopic methylene protons as two resonances, only one of which was coupled to the rhodiums. The nitrate complex [{(C5Me5)Rh}2(µ-CH2)2(NO3)2] was found to exist as two isomers, one trans and the other cis with one bridging and one ionic nitrate, as shown by the n.m.r. spectra.

A new type of linkage isomerism: bis(acetylacetonato-O)bis(piperidine)platinum(II) and (acetylacetonato-O,O′)bis(piperidine)platinum(II) acetylacetonate

Der Pt-Chelatkomplex (I) reagiert mit Piperidin bei 70°C zum aus Benzol filtrierten Komplex (II).

Pentanuclear cluster of palladium(II) bridged by telluride ions: synthesis and crystal structure of [Pd5(µ3-Te)4(Ph2PCH2CH2PPh2)4]2+

A pentanuclear palladium(II) cluster [Pd5(µ3-Te)4(dppe)4]2+[dppe = 1,2-bis(diphenylphosphino)ethane] has been synthesized and characterized by an X-ray diffraction study; the cluster comprises two dinuclear [Pd2Te2(dppe)2] units the PdP2Te2 co-ordination planes of which fold along the common Te ⋯ Te axis with the four telluride ions of the two dinuclear units additionally co-ordinated to a central palladium(II).

The syntheses, 31P{1H} NMR spectra and cyclic voltammetry of trinuclear [Pd2M(μ3-Se)2(dppe)3]2+ {M=Ni or Pt; dppe=1,2-bis(diphenylphoshino)ethane} and pentanuclear [M′{Pd2(μ3-Se)2(dppe)2}2]2+ (M′=Ni, Pd or Pt) clusters with selenido bridges

Trinuclear [Pd2M(μ3-Se)2(dppe)3]2+ (M=Ni or Pt) and pentanuclear [M′{Pd2(μ3-Se)2(dppe)2}2]2+ (M′=Ni, Pd or Pt) clusters have been prepared using a metalloligand [Pd2(μ-Se)2(dppe)2] and characterized by 31P{1H} NMR spectroscopy and cyclic voltammetry. [Pd2Ni(μ3-Se)2(dppe)3]2+ gives two chemically reversible couples, [Pd2Pt(μ3-Se)2(dppe)3]2+ exhibits one chemically reversible couple and pentanuclear clusters show three couples in each cyclic voltammogram of the reduction process at 255 K. The redox behavior of the clusters is discussed.

Monoalkyl-di-µ-methylene-bis[(η-pentamethylcyclopentadienyl)-rhodium(IV)] complexes and the intramolecular migration of alkyl groups between two metal atoms

Reaction of the trans dimethyl complex [{(C5Me5)Rh}2(µ-CH2)2Me2](1) with one equivalent of acid in the presence of acetonitrile gave the methyl–acetonitrile complex [{(C5Me5)Rh}2(µ-CH2)2(Me)(MeCN)]PF6(2a); the acetonitrile could be replaced by other ligands to give [{(C5Me5)Rh}2-(µ-CH2)2(Me)(L)]PF6[L = ButCN (2b), PhCN (2c), pyridine (2d), 2-methylpyridine (2e), or CO (2f)]. Reaction of (2a) with halide gave [{(C5Me5)Rh}2(µ-CH2)2(Me)X][X = Cl (3) or I (4)]. The other monoalkyl complexes [{(C5Me5)Rh}2(µ-CH2)2(R)(MeCN)]PF6[R = Et (9), Prn(10), or Bun(11)] were obtained analogously from reaction of the appropriate dialkyl complexes [{(C5Me5)Rh}2(µ-CH2)2R2] which were in turn synthesised from the trans dichloro-complex [{(C5Me5)Rh}2(µ-CH2)2Cl2]. The n.m.r. spectra of (2a) showed the presence of cis and trans isomers (ratio ca. 1 : 2) at –80 °C and of dynamic behaviour at higher temperatures. The dynamic behaviour arises from loss of the MeCN, movement of the methyl into a bridging position in a transition state, followed by readdition of the MeCN. Overall this corresponds to an intramolecular migration of the methyl from one rhodium to the other. The other complexes (2) behave similarly but (2d) and (2f) show the ‘frozen-out’ spectra even at +22 °C. Under identical conditions the complexes (9)–(11) exhibited similar behaviour to (2a), but the rates of alkyl migration were ca. 10 times faster. Complex (2a) also disproportionated to give (1) on reaction with base; this involves an intermolecular methyl migration. The other alkyl complexes did not undergo this reaction. The halide complexes (3) and (4) were rigid and of cis configuration in benzene but showed more complex behaviour in dichloromethane.