Amelio Vázquez de Miguel

Cyclopentadienyl dithiocarbamate and dithiophosphate molybdenum and tungsten complexes

Reactions of [MCp*Cl4 ]( MMo, W; Cp*h 5 -C5Me5) with salts of the N,N-diethyldithiocarbamate [Et2dtc] and O,O%-diethyldithiophosphate [Et2dtp] anions yield the paramagnetic metal(V) complexes [MCp*Cl3(Et2dtc)] (M Mo, W) and [MCp*Cl3(Et2dtp)] (MMo, W), respectively. Hydrolytic oxidation of both dithiocarbamate‐molybdenum complexes with aqueous hydrogen peroxide leads to h 2 -coordinated peroxo compounds [MoCp*Cl(O‐O)O], which were also obtained from [MoCp*Cl4]. The related complexes [MCp%Cl(O‐O)O] (M Mo, Cp%h 5 -C5H5 ;M W, Cp%h 5 -C5Me5) were isolated in a similar way. Reduction of a THF solution of [MoCp*Cl4] with one equivalent of 10% Na:Hg followed by the addition of one equivalent of ammonium dithiophosphate gives [MoCp*Cl2(Et2dtp)] which was also obtained via the reaction of [MoCp*Cl3(Et2dtp)] with MeMgCl, whereas reduction with three equivalents of Na:Hg in the presence of CN t Bu leads to the molybdenum(II) complex [MoCp*(Et2dtp)(CN t Bu)2] in high yield. All these compounds were characterized by elemental analysis, IR, 1 H- and 13 C-NMR spectroscopy, magnetic susceptibility measurements and the molecular structures of [Mo(h 5 -C5H5)Cl(O‐ O)O] and [Mo(h 5 ‐C5Me5)Cl3{h 2 -S2P(OEt)2}] were determined by X-ray diffraction studies.

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.

μ-Methylene rhodium complexes with SH ligand: Synthesis and structures of [Rh2Cp★2(μ-CH2)2(μ-SH)]BPh4 and trans-[Rh 2Cp★2(μ-CH2)2(SH)2] (Cp ★ = η5-C5Me5)

Abstract The μ-methylene rhodium complex with a hydrosulphide ligand, [Rh 2 ,Cp★ 2 (μ-CH 2 ) 2 ,(μ-SH)IBPh 4 ( 2b ), has been isolated from the reaction of trans -[Rh 2 Cp★ 2 (μ-CH 2 ) 2 Cl 2 ] ( 1 ) with H 2 S in CH 3 OH and readily converted to trans -[Rh 2 Cp★ 2 (μ-CH 2 ) 2 (SH) 2 ] ( 3 ) in the presence of NEt 3 and H 2 S; 2b and 3 have been characterized crystallographically.

SYNTHESIS OF CHLORO AND METHYL IMIDO CYCLOPENTADIENYL MOLYBDENUM AND TUNGSTEN COMPLEXES. X-RAY MOLECULAR STRUCTURES OF WCP*CL3(NTBU), MOCP*CLME2(NTBU) AND WCP*CLME2(NTBU)

The authors acknowledge DGICYT (Project PB92-0178-C) and CAM (I + D 0033/94) for financial support.

Reactions of dimethyl(dimethylsulphoxide)pentamethylcyclopentadienyl-rhodium and -irridum with acids

Abstract The complexes [C 5 Me 5 MMe 2 (Me 2 SO)] (Ia, M = Rh; Ib, M = Ir) react with p -toluenesulphonic acid in acetonitrile to give [C 5 Me 5 MMe(Me 2 SO)(MeCN)] + , (II), and with trifluoroacetic acid to give first [C 5 Me 5 MMe(Me 2 SO)(O 2 CCF 3 )] and then [C 5 Me 5 M(Me 2 SO)(O 2 CCF 3 ) 2 ]. Complexes II react with halide (X − ) to give the halomethyl complexes [C 5 Me 5 MMe(X)(Me 2 SO)]. The IR, far-IR, 1 H and 13 C NMR spectra are all in agreement with structures proposed.

Synthesis and properties of tetramethyl(η5-pentamethylcyclopentadienyl)iridium(V), dimethyl-di-µ-methylene-bis[(η5-pentamethylcyclopentadienyl)iridium(IV)], and related complexes from reactions of di-µ-chloro-dichlorobis[(η5-pentamethylcyclopentadienyl)iridium(III)] with hexamethyldialuminium

The intermediate [{(C5Me5)IrMe3}2AlMe](2b) from reaction of [{(C5Me5)Ir}2Cl4] and Al2Me6 in pentane, reacted with ligands (L = PPh3 or C2H4) to give [(C5Me5)IrMe2L], and with a hydrogen-acceptor (acetone) to give the dimethyl-di-µ-methylene complex [{(C5Me5)IrMe}2(µ-CH2)2]. The most unusual reaction of (2b) was the oxygenation to give a 40% yield of the iridium(V) complex [(C5Me5)IrMe4]. Other complexes which were formed in these reactions in lower yields include the chloro(methyl)-di-µ-methylene complex [{(C5Me5)Ir}2Me(Cl)(µ-CH2)2] and the trinuclear di-µ3-methylidyne complex [{(C5Me5)Ir}3(µ3-CH)2]. The complexes have been characterised spectroscopically and by comparison with their rhodium analogues. Mechanisms for the reactions are proposed.

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.

Arene substitution by iridium complexes under mild conditions

[(C5Me5Ir)2Cl4] reacts with Al2Me6 in saturated hydrocarbons to give [C5Me5IrMe4) or cis- and trans-[C5Me5Ir)2Me2(α-CH2)2], depending on workup conditions. In benzene or toluene solution the main product is [(C5Me5Ir)2Me(Aryl)(α-CH2)2] (aryl = Ph or m- plus p-tolyl, ratio 2/1); if CO is introduced into the benzene solution the products are [C5Me5Ir(CO)R1R2] (R1 = Me, R2 = Ph; R1 = R2 = Me or Ph).

Alkyl and alkylidene imido cyclopentadienyl tungsten complexes

This paper reports the alkylation of the cyclopentadienyl imido tungsten complexes [WCp%(N t Bu)Cl3] (Cp%h 5 -C5H5, h 5 -C5Me5) with b-hydrogen containing alkyl groups to render halo alkyl and trialkyl complexes [WCp%(N t Bu)Cl3 nRn ]( REt, n-Pr). Thermal decomposition of the trialkyl compounds gives the alkylidene derivatives [WCp%(N t Bu)(CHR)(CH2R)] (RMe, Et) by a-hydrogen elimination. All of the compounds were characterized by NMR spectroscopy and the molecular structure of [W(h 5 -C5Me5)(N t Bu)Et3] was determined by X-ray diffraction methods.