Oxidative Addition Of Methyl Iodide Research Articles

Formation and cleavage of platinacycles containing a fluorinated imine. Crystal structure of [PtMe(3,4,5-C 6HF 3CHNCH 2C 6H 5)PPh 3

The reaction of [Pt 2Me 4(μ-SMe 2) 2] with the ligand 3,4,5-C 6H 2F 3CHNCH 2C 6H 5 ( L) yielded the cyclometallated platinum(II) compound [PtMe(3,4,5-C 6HF 3CHNCH 2C 6H 5)SMe 2] ( 1), in which the imine acts as a [C,N]-bidentate ligand. Compounds [PtMe(3,4,5-C 6HF 3CHNCH 2C 6H 5)DMSO] ( 2) (DMSO=dimethyl sulfoxide) and [PtMe(3,4,5-C 6HF 3CHNCH 2C 6H 5)PPh 3] ( 3) were obtained from a displacement reaction of SMe 2 for DMSO or PPh 3, respectively. Oxidative addition of methyl iodide to compounds 1– 3 produced, respectively, [PtMe 2I(3,4,5-C 6HF 3CHNCH 2C 6H 5)SMe 2] ( 4a/ 4b) as two isomers, [{PtMe 2I(3,4,5-C 6HF 3CHNCH 2C 6H 5)} 2] ( 5) and [PtMe 2I(3,4,5-C 6HF 3CHNCH 2C 6H 5)PPh 3] ( 6). Platinum(II) metallacycles can be cleaved upon reaction with an excess of PPh 3 or with the diphosphine dppe to yield, respectively, compounds [PtMe(3,4,5-C 6HF 3CHNCH 2C 6H 5)(PPh 3) 2] ( 7) and [PtMe(3,4,5-C 6HF 3CHNCH 2C 6H 5)dppe] ( 8) in which the imine acts as a monodentate [C] ligand. Analogous compounds could not be obtained for platinum(IV) since in this case neither PPh 3 nor dppe can cleave the metallacycle. The reaction of 4a/ 4b with dppe produced [{PtMe 2I(3,4,5-C 6HF 3CHNCH 2C 6H 5)} 2dppe] ( 11), a binuclear compound in which the diphosphine bridges two platinum(IV) moieties with the imine acting as a [C,N]-bidentate ligand. All compounds were characterised by analytical and spectroscopic techniques and compound 3 was also characterised crystallographically.

Stereoselective oxidative addition of methyl iodide to chiral cyclometallated platinum(II) compounds derived from ( R)-(+)-1-(1-naphthylethylamine). Crystal structure of [PtMe{3-( R)-(C 10H 7)CHMeNCHC 4H 2S}PPh 3

The reaction of 3-( R)-(C 10H 7)CHMeNCHC 4H 3S ( 2a) with [Pt 2Me 4(μ-SMe 2) 2] in acetone gave the new chiral cyclometallated platinum(II) compound [PtMe{3-( R)-(C 10H 7)CHMeNCHC 4H 2S}SMe 2] ( 3a). Addition of PPh 3 produced compound [PtMe{3-( R)-(C 10H 7)CHMeNCHC 4H 2S}PPh 3] ( 4a) which was characterized by X-ray diffraction methods. While oxidative addition of methyl iodide to 3a gave two pairs of diastereomers, the analogous reaction for 4a produced only one diastereomer of the platinum(IV) compound [PtMe 2I{3-( R)-(C 10H 7)CHMeNCHC 4H 2S}PPh 3] ( 7a). Subsequent isomerization of the resulting platinum(IV) compound gave a new pair of diastereomers in relative amounts 90 and 10%. Analogous proportions of final diastereomers were obtained for the oxidative addition of methyl iodide to the new chiral compounds [PtMe{3-( R)-(C 10H 7)CHMeNCHAr}PPh 3] (Ar=C 6H 4 ( 4b), 2-FC 6H 3 ( 4c), 2-CF 3C 6H 3 ( 4d)). The reaction of [Pt 2Me 4(μ-SMe 2) 2] with imines ( R)-(C 10H 7)CHMeNCH(2-BrC 6H 4) ( 2e) and ( R)-(C 10H 7)CHMeNCH(2,6-Cl 2C 6H 3) ( 2f) produced intramolecular oxidative addition to yield platinum(IV) compounds with some degree of stereoselectivity.

Methyl iodide reactions on the surface of mechanically pre-activated platinum(II) salt in the heterogeneous system: K 2PtCl 4 powder–MeI vapor

Mechanically pre-activated K 2PtCl 4 salt consumes methyl iodide producing methyl chloride at room temperature. The reaction mechanism includes the following steps sequence: oxidative addition of methyl iodide to platinum(II) complexes with intermediate formation of methyl platinum(IV) complexes and further decomposition of the latter in the course of innersphere reductive elimination yielding methyl chloride. The first step of the reaction proceeds owing to the assistance of active centers regenerated in the course of each event of MeI into MeCl transformation taking part in the chain halogen substitution process. It could be assumed that the role of active centers is played by coordinatively unsaturated platinum(II) complexes located on the surface. These species bearing a positive efficient charge can render electrophilic assistance for the nucleophilic substitution. The chain termination can be caused by recombination of coordinatively unsaturated platinum(II) complexes and interstitial chloride ions forming an inactive K 2PtCl 4 complex.

The oxidative addition and migratory 1,1-insertion in the Monsanto and Cativa processes. A density functional study of the catalytic carbonylation of methanol

Density functional theory with hybrid B3LYP exchange and correlation functional has been used to investigate the first two catalytic reactions, the oxidative addition and migratory 1,1-insertion of the Monsanto and Cativa processes. One of the main interests has been to study if the previously unidentified trans forms of the active catalytic species [Rh(CO) 2I 2] − ( 1) or [Ir(CO) 2I 2] − ( 2) have any significance in these processes. The oxidative addition has been studied using both cis and trans forms of 1 and 2. We have also studied the oxidative addition of methyl iodide to [Rh(CO) 2I 3] 2− ( 3). In addition, different isomers of dicarbonyls [CH 3Rh(CO) 2I 3] − ( 4) and [CH 3Ir(CO) 2I 3] − ( 5) and tricarbonyl [CH 3Ir(CO) 3I 2] ( 8) has been used in the 1,1-insertion study to see if these could provide new, alternative reaction pathways. The calculated free energies of activation for the oxidative addition of methyl iodide to cis- 1 and cis- 2 are 20.8 and 16.9 kcal/mol, respectively. The corresponding free energy barriers for trans- 1 and trans- 2 are 15.0 and 13.2 kcal/mol, respectively. The oxidative addition is the rate-determining step in the Monsanto process and the reaction with trans- 1 is predicted to accelerate that step. The presence of 3 could enhance the addition even more; the free energy of activation is only 5.6 kcal/mol. For the 1,1-insertions we have found similar activation energies in fac, cis- and mer, trans-structures. In the rhodium system, the free energies of activation are in the order of 20 kcal/mol and in the iridium system 30 kcal/mol. Interestingly, the insertions in mer, cis-dicarbonyls have considerably lower activation energies, half of those calculated for the insertions in mer, trans- and fac, cis-structures. The iodide dissociation from fac, cis- 5 could provide the path to mer, cis- 5 and so significantly enhance the rate of the insertion in the iridium system. The rate of the insertion should also increase if experimentally proposed tricarbonyl 8 is used instead of 5. According to our calculations of different isomers of 8, this seem to be true although the insertion barrier in mer, cis- 5 is calculated to be even lower. Our results are consistent with the experiments and other computational results. These results show that the geometrical arrangement of the ligands has a very large effect on the catalytic activity of the complexes and this suggests possible improvements to these industrially important processes.

Coordinatively saturated cyclometallated Pt(IV) azobenzene complexes: synthesis and mesomorphic behaviour

The mesomorphic 4,4-bis[4-n-octyloxybenzoyloxy]azobenzene dinuclear chloro-bridged cycloplatinated complex [(Azo)Pt(mu;-Cl)]2 (smectic C between 263 and 342 C) has been reacted with different chelating ligands, giving rise to a family of square-planar ortho-platinated derivatives, [(Azo)Pt(L)] (L = tropolonate, 8-hydroxyquinolinate and 1,1,1,5,5,5-hexafluoro2,4-pentanedionate). Thermotropic mesomorphism is preserved for these mononuclear complexes which exhibit at least a nematic mesophase and transition temperatures lower by over 100° C than that of the corresponding dimeric precursor. Oxidative addition to the Pt(II) [(Azo)Pt(L)] species of electrophilic substrates such as I2 or CH3I eventually led to the corresponding octahedral [(Azo)Pt(L)(I)(X)] products. The introduction of two further ligands leads to Pt(IV) derivatives showing smectic and nematic mesophases for all L ligands. For the hexacoordinated [(Azo)Pt(L)(I)(CH3)] complexes it has been verified that the oxidative addition of methyl iodide is a thermally reversible process, indicating that these species have potential applications as switchable systems.

Oxidative addition of alkyl halides to chiral cyclometallated platinum(II) complexes with thienyl imines. X-ray crystal structure of [PtMe{3-(( S)-PhCHMeNCH)C 4H 2S}SMe 2

The reaction of [Pt 2Me 4(μ-SMe 2) 2] with ligand 3-(( S)-PhCHMeNCH)C 4H 3S ( 1) produced the chiral cyclometallated compound [PtMe{3-(( S)-PhCHMeNCH)C 4H 2S}SMe 2] ( 2) which was characterized structurally. The reactions of 2 with phosphines gave compounds [PtMe{3-(( S)-PhCHMeNCH)C 4H 2S}L] (L=PPh 3 ( 3), P(2-MeC 6H 4) 3 ( 4), Ph 2PCH 2CH 2PPh 2 ( 5)). The oxidative addition of methyl iodide to compounds 2 and 3 gave two diastereoisomers each of compounds [PtMe 2I{3-(( S)-PhCHMeNCH)C 4H 2S}L] (L=SMe 2 ( 6a/ 6a′), PPh 3 ( 7a/ 7a′)) in a ratio 2.1:1 and 2.4:1, respectively. Subsequent isomerization gave, in each case, a new pair of diastereoisomers. Compounds 4 and 5 failed to react with methyl iodide, while platinum(II) compounds [PtX{3-(( S)-PhCHMeNCH)C 4H 2S}PPh 3] (X=I ( 8), Br ( 9)) were obtained in the reactions of 3 with ethyl iodide or benzylbromide.

Solvent effects on the rate of oxidative addition of methyl iodide to di(4-thiocresol)(2,2′-bipyridyl) platinum(II)

The reaction of methyl iodide with di(4-thiocresol)(2,2′-bipyridyl) platinum(II) to give iodo (methyl) di(4-thiocresol)(2,2′-bipyridyl) platinum(IV) follows the rate law, rate= K 2[Pt-(4-thiocresol) 2 (2,2′-bipyridyl)] [MeI]. The values of K 2 increase with increasing polarity of the solvent, suggesting a polar transition state for the reaction.

Cyclometallated platinum complexes with thienyl imines. X-ray crystal structure of [PtMe{3-(PhCH 2NCH)C 4H 2S}PPh 3

The reaction of [Pt 2Me 4(μ-SMe 2) 2] with ligands 3-(Me 2NCH 2CH 2NCH)C 4H 3S ( 2a) and 3-(PhCH 2NCH)C 4H 3S ( 2b) produced cyclometallation at the α-position of the thiophene ring to give the platinum(II) complexes [PtMe{3-(Me 2NCH 2CH 2NCH)C 4H 2S}] ( 4a) and [PtMe{3-(PhCH 2NCH)C 4H 2S}SMe 2] ( 4b), containing [C,N,N′] or [C,N] ligands, respectively. The reaction of these compounds with triphenylphosphine produced [PtMe{3-(Me 2NCH 2CH 2NCH)C 4H 2S}PPh 3] ( 5a) and [PtMe{3-(PhCH 2NCH)C 4H 2S}PPh 3] ( 5b). Compound 5b was structurally characterized. Attempts to achieve the cyclometallation of the ligands 2-(Me 2NCH 2CH 2NCH)C 4H 3S ( 2c) and 2-(PhCH 2NCH)C 4H 3S ( 2d) were unsuccessful and only compounds [PtMe 2{2-(Me 2NCH 2CH 2NCH)C 4H 3S}] ( 3c) and [PtMe 2{2-(PhCH 2NCH)C 4H 3S}SMe 2] ( 3d), in which the imine behaves as a [N,N′] or [N]-donor ligand, respectively, could be obtained. The electrochemical properties of the compounds based on cyclic voltammetry or square-wave voltammetry were studied at various temperatures. Reversible one-electron reductions, assigned to ligand-centered processes, were observed at room temperature for 5b and at lower temperatures for 4a, 4b and 5a. The reversibility varies with the ligand trans to the thienyl moiety. The one-electron oxidations always occurred in an irreversible manner and were assigned to oxidation at the platinum center. Oxidative addition of methyl iodide to 4a yielded [PtMe 2I{3-(Me 2NCH 2CH 2NCH)C 4H 2S}] ( 6a), while the reactions of methyl iodide with 4b and 5b each gave mixtures of isomers, arising from oxidative addition with trans stereochemistry followed by isomerization of the resulting platinum(IV) compounds. The reaction of methyl iodide with compound 5a yielded a complex mixture of compounds.

Complexes of platinum(II), platinum(IV), rhodium(III) and iridium(III) containing orthometallated triphenylphosphine

Treatment of [PtCl2(SEt2)2] or [RhCl3(SEt2)3] with 2-LiC6H4PPh2 gives four-membered ring chelate arylplatinum(II) or arylrhodium(III) complexes [Pt{C6H4(PPh2)-2}2] and [Rh{C6H4(PPh2)-2}3], respectively, whereas the corresponding reaction of [IrCl3(SEt2)3] gives IrCl{C6H4(PPh2)-2}2(PPh3)] arising from cleavage of an Ir–C6H4(PPh2) bond. The chemistry of [Pt{C6H4(PPh2)-2}2] is dominated by the lability of the Pt–P bonds, which are displaced sequentially by ligands at room temperature to give complexes containing monodentate C6H4(PPh2), i.e. [Pt{C6H4(PPh2)-2}{η1-C6H4(PPh2)-2}(L)] [L = PPh3, P(OPh)3, P(OMe)3 or ButNC] and [Pt{η1-C6H4(PPh2)-2}2(R2PCH2CH2PR2)] (R = Ph, Me or Cy). In the cases of Me2PCH2CH2PMe2 and Cy2PCH2CH2PCy2, binuclear intermediates can be detected in which these ligands bridge two platinum atoms. Oxidative addition of methyl iodide or iodine to [Pt{C6H4(PPh2)-2}2] gives initially platinum(IV) complexes [PtI(R){C6H4(PPh2)-2}2] (R = Me or I) in which the added groups are mutually trans; in the final, stable products the added groups and the phosphorus atoms are, separately, mutually cis. Oxidative addition of bromine to [Pt{C6H4(PPh2)-2}2] gives initially trans-[PtBr2{C6H4(PPh2)-2}2] but subsequent oxidation and hydrolysis at the phosphorus atoms gives chelate tertiary phosphine oxide complexes of platinum(IV). The molecular structures of [Rh{C6H4(PPh2)-2}3] and cis-[PtI(Me){C6H4(PPh2)-2}2] have been determined by X-ray crystallography.

Cyclometallated platinum compounds with chiral imines. Crystal structure of [PtMe(2-FC6H3CHN-(S)-CHMePh)(PPh3)

The reactions of [Pt2Me4(μ-SMe2)2] (1) with ligands ArCHN-(S)-CHMePh (Ar2-BrC6H4 (2a), 2,6-Cl2C6H3 (2b), C6F5 (2c), 2-FC6H4 (2d), 2-CF3C6H4 (2e)), give either cyclometallated compounds [PtMe2X(RCHN-(S)-CHMePh)(SMe2)] (3), by intramolecular activation of C–X (X=Br, Cl or F) bonds, or compounds [PtMe(RCHN-(S)-CHMePh)(SMe2)] (5), by orthometallation, followed by methane elimination. The reactions of these compounds with PPh3 result in the formation of [PtMe2X(RCHN-(S)-CHMePh)(PPh3)] (4), or [PtMe(RCHN-(S)-CHMePh)(PPh3)] (6), respectively. Oxidative addition of methyl iodide to compounds 6 produces the corresponding complexes 4. The NMR spectra of compounds 3 and 4 indicate that these are formed as two diastereomers. The X-ray structure of [PtMe(2-FC6H3CHN-(S)-CHMePh)(PPh3)] (6d) is reported.

Oxidative addition of methyl iodide and iodine to new binuclear rhodium(I) and iridium(I) compounds containing diaminoanthraquinonate-bridging ligands. Crystal structure of [Rh 2(μ-1,4-DA)(CO) 2(PPh 3) 2] (1,4-H 2DA = 1,4-diaminoanthraquinone)

The binuclear rhodium and irridum complexes containing the 1,4-diaminoanthraquinonate ligand (1,4-DA) [M 2(μ-1,4-DA)L 2] (L = COD, M = Rh ( 1), Ir ( 2); L = (CO) 2, M = Rh ( 3), Ir ( 4) L = (CO)(PPh 3), M = Rh ( 5), Ir, ( 6)) have been prepared and oxidative addition of the electrophiles MeI and I 2 has been investigated. The molecular structure of an isomer of compound 5 has been determined by X-ray diffraction methods. Complex 5a crystallised in the triclinic space group P-1, with a = 9.711(5), b = 13.701(7), c = 17.990(9) A ̊ . a = 68.53(2), β = 76.98(3), γ = 79.72(3)°, and Z = 2. The molecule is binuclear with the metals bridged by an approximately planar tetradentate dianionic 1,4-DA ligand. Both rhodium centres exhibit slightly distorted square-planar coordinations with both phosphine groups rans disposed to the aminic nitrogen atoms. Addition of MeI to the rhodium complex 5 leads to the diacyl-dirhodium(III) derivative [Rh 2(μ-1,4-DA)(COMe) 2] 2(PPh 1) 2] ( 7). However, addition MeI to the isoelectronic iridium compound 6 yields the dimethyldiiridium(III) compound [Ir 2(μ-1,4-DA)] 2(Me) 2(CO) 2(PPh 3) 2] ( 8). Reaction of iodine with compounds 5 and 6, in a molar ratio M/I 2 = 1/1, yields the symmetrical complexes [M 2(μ-1,4-DA)I 4(CO) 2(PPh 4) 2] (M = Rh ( 9, Ir( 10)).

Stoichiometric and Catalytic Conversion of Alkynes to Conjugated (Z,Z)-Dienes and Cyclopentadienes via Palladacyclopentadienes and 1,3-Dienylpalladium(II) Halide and Triorganopalladium(IV) Halide Compounds Containing Chelating Nitrogen Ligands

Palladacyclo-2,4-pentadiene compounds containing a chelating bidentate nitrogen ligand Pd{(C(E)C(E)-C(E)C(E)}(NN) 1a−f (E = CO2Me, NN = Ph-bip, Ar-bian, bpy, dcm-bpy, bpym) and 2a,b (E = CF3, NN = Ph-bip, (p-tol)-bian) have been prepared from Pd(dba)2, the appropriate bidentate N-ligand, and electron-deficient acetylenes dimethyl 2-butynedioate or hexafluorobutyne. X-ray crystal structures were obtained for compounds 1a (NN = Ph-bip) and 1d (NN = 2,2‘-bpy). In solution, an equilibrium between the monomer and a dimer exists for compounds 1d and 1e (NN = bipyrimidine); in the solid state, 1d is a monomer. The dimeric form of 1d is of the same type as the zerovalent palladium compound [(μ-3,3‘-dicarbomethoxy-2,2‘-bipyridine)Pd(tcne)]2 in which the two bipyridine derivatives bridge between the two palladium centers, as determined from the X-ray crystal structure of this compound (7). The palladacycles 1 undergo oxidative addition of methyl iodide, benzyl bromide, or iodobenzene. Subsequent reductive eliminati...

Synthesis of [Ir 2( μ-Pz) 2(CH 3)(CO) 2(PiPr 3) 2] +. A key intermediate in S N2 oxidative addition of halocarbons to dinuclear complexes

The unusual compound of formula [Ir 2( μ-Pz) 2(CH 3)(CO) 2(PiPr 3) 2](ClO 4) ( 3) has been prepared. This complex is the proposed intermediate species for the S N2 oxidative addition of methyl iodide to the dinuclear compound [Ir( μ-Pz)(CO)(PiPr 3)] 2 ( 1). The spectroscopic and X-ray diffraction data obtained for 3, together with EHMO calculations and reactivity studies, indicate that the compound can be described as an Ir(III)–Ir(I) species containing a weak metal–metal bond. The implications of these electronic features in the regioselectivity of halocarbons oxidative additions to dinuclear complexes are discussed.

Cyclometallated platinum compounds with N-benzylidenebenzylamines bearing trifluoromethyl groups. Crystal structure of [PtMe}3-(CF 3) C 6H 3CHNCH 2Ph{(PPh 3)

The reaction of [Pt 2Me 4(μ-SMe 2) 2] ( 1) with the imine 3-(CF 3)C 6H 4CHNCH 2Ph ( 2a) yields the cyclometallated compound [PtMe}3-(CF 3)C 6H 3CHNCH 2Ph{(SMe 2)] ( 3a) by selective metallation at the less hindered of the two ortho positions of the aryl ring followed by loss of methane. A similar reaction for imine 2-(CF 3)C 6H 4CHNCH 2Ph ( 2c) yields the cyclomettallated compound [PtMe}2-CF 3)C 6H 3CHNCH 2Ph{ (SMe 2)] ( 3c). The reactions of these compounds with triphenylphosphine in (1:1) ratio produce compounds [PtMe}3-(CF 3)C 6H 3CHNCH 2Ph{(PPh 3)] ( 4a) and [PtMe}2-(CF 3)C 6H 3CHNCH 2Ph{ (PPh 3)]( 4c). The X-ray structure of 4a is reported. An excess of triphenylphosphine produces metallacycle cleavage and [PtMe}3-(CF 3)C 6H 3CHNCH 2Ph{(PPh 3) 2] ( 5a) is formed with the imine acting as a [C −] unidentate ligand. Oxidative addition of methyl iodide to compounds 4a and 4c gives cyclometallated platinum(IV) complexes. Imines 3,5-(CF 3) 2C 6H 3CHNCH 2Ph ( 2b) and 2-F-6-(CF 3)C 6H 3CHNCH 2Ph ( 2d) fail to react with [Pt 2Me 4(μ-SMe 2) 2] ( 1).

Kinetic study on the carbonylation of methyl acetate to acetic anhydride catalyzed by partially quaternized poly(4-vinylpyridine) bound rhodium complexes

The carbonylation of methyl acetate to acetic anhydride catalyzed by a partially quaternized poly(4-vinylpyridine) bound rhodium complex with methyl iodide as the promotor has been investigated. The reaction was verified to be first order with respect to both rhodium and methyl iodide in the presence of lithium acetate and provided that the partial pressure of carbon monoxide was above 1.5 MPa. The oxidative addition of methyl iodide to the active rhodium species and the subsequent reaction of acetyl iodide with methyl acetate to produce acetic anhydride were discovered to be the two rate-determining steps, of which the latter depended on the concentration of lithium acetate. A possible reaction mechanism was suggested. The activation parameters were determined and revealed that a higher catalytic activity of the partially quaternized poly(4-vinylpyridine) bound rhodium complex for the carbonylation of methyl acetate to acetic anhydride was essentially due to the reduction of activation energy. © 1997 John Wiley & Sons, Ltd.

Carbonylation of methanol catalyzed by polymer-protected rhodium colloid

Poly( N-vinyl-2-pyrrolidone)(PVP) protected rhodium colloid (Rh-PVP) was used as a catalyst for methanol carbonylation under elevated temperature (140°C) and high pressure (5.4 MPa). The activity of Rh-PVP colloid catalyst increased while recycled for 6 times totally lasting 56.5 h. During the reaction, the catalyst was still in a colloidal state verified by TEM observation. XPS and IR studies of the catalyst demonstrated that colloidal rhodium metal particles partially changed to [Rh(CO) 2I 2] − under the reaction conditions. The rhodium ions in the reaction mixture amounted to 29% of the total charged rhodium after 13 h carbonylation. An additional XPS investigation of the catalyst was carried out; the results showed that oxidative addition of methyl iodide to rhodium colloid caused the transformation of rhodium species from Rh 0 to Rh 1+.

Theoretical and Experimental Evidence for SN2 Transition States in Oxidative Addition of Methyl Iodide to cis-[M(CO)2I2]- (M = Rh, Ir)

Theoretical and Experimental Evidence for S_N2 Transition States in Oxidative Addition of Methyl Iodide to <i>cis</i>-[M(CO)₂I₂]^- (M = Rh, Ir)

Methanol carbonylation revisited: thirty years on

Monsanto initiated development of its rhodium- and iodide-catalysed process for the carbonylation of methanol to acetic acid in 1966. Ownership of the technology was acquired in 1986 by BP Chemicals who have further extended it. The work of the Sheffield group, in developing a deeper understanding of the mechanism of the process, is reviewed. The rate-determining step in the rhodium–iodide catalysed reaction is the oxidative addition of methyl iodide to [Rh(CO)2I2]–1a: the product from this reaction, the reactive intermediate [MeRh(CO)2I3]–2a has been detected and fully characterised spectroscopically. The rates of the reversible reactions linking 1a, 2a and the acetyl complex [(MeCO)Rh(CO)I3]–3a, as well as activation parameters for several of the processes involved, have been measured. The efficiency of methanol carbonylation arises primarily from rapid conversion of 2a into 3a, leading to a low standing concentration of 2a, and minimising side reactions such as methane formation. By contrast, in the iridium-catalysed carbonylation, for which similar cycles can be written, the reaction of [MeIr(CO)2I3]–2b with CO to give [(MeCO)Ir(CO)2I3]–4b is rate determining. Model studies show that while kRh/kIr is ca. 1 : 150 for the oxidative addition, it is ca. 105–106 : 1 for migratory CO insertion. The migratory insertion for iridium can be substantially accelerated by adding either methanol or a Lewis acid (SnI2); both appear to facilitate substitution of an iodide ligand by CO, resulting in easier methyl migration. The carbonylation of higher alcohols (ROH) has also been successfully modelled; the corresponding alkyl iodides (RI) react much more slowly than MeI with [M(CO)2I2]–, but again give the acyls [(RCO)M(CO)I3]– for M = Rh and the alkyls [RM(CO)2I3]– for M = Ir. The greater stability of [MeIr(CO)2I3]– compared with [MeRh(CO)2I3]– accounts for the very different characters of the reactions catalysed by the two metals. It is suggested that the broad features of the Rh/Ir reactivities can be rationalised since the M–C bond to a 5d metal is generally stronger than that to the corresponding 4d metal; thus if metal–ligand bond making plays a key role in a step, then the 5d metal is more likely to react faster (e.g. in the oxidative addition), but if a metal–ligand bond-weakening or -breaking step plays a key role in a process (e.g. in the migration), it is likely that the 4d metal will be faster.

Cyclometallated platinum(II) and platinum(IV) compounds of N-benzylidene-2-chlorobenzylamine. Crystal structure of [PtMe(PPh 3)(C 6H 4CHNCH 2C 6H 4C1-2)

The cyclometallated compound [PtMe(SMe 2)(C 6H 4CHNCH 2C 6H 4C1-2)] ( 1) undergoes a displacement reaction with PPh 3 to yield a cyclometallated platinum(II) compound [PtMe(PPh 3)(C 6H 4CHNCH 2C 6H 4C1-2)] ( 2), which has been characterized crystallographically. Complex 2 crystallizes in the monoclinic space group C2/ c, with a = 38.402(4) Å, b = 7.993(3) Å, c = 18.563(3) Å, β = 101.34(3)° and Z = 8. The reaction of 1 with 1,2-bis (diphenylphosphino)ethane (dppe) yields [PtMe(dppe)(C 6H 4CHNCH 2C 6H 4C1-2)]( 3) containing an unidentate C donor imine ligand and a chelating diphosphine. Oxidative addition of methyl iodide to 1 yields a cyclometallated platinum(IV) compound [PtMe 2I(SMe 2)(C 6H 4CHNCH 2C 6H 4C1-2)] ( 4), which undergoes a displacement reaction of SMe 2 by PPh 3 to yield [PtMe 2I(PPh 3)(C 6H 4CHNCH 2C 6H 4C1-2)] ( 5). Compound 5 can also be obtained by oxidative addition of methyl iodide to 2. The stereochemistry of compounds 4 and 5 is discussed.

Reinvestigation of the oxidative addition of methyl iodide, hydrogen, and oxygen to Ir(CO)(Cl)L2. Quantitative analysis of ligand effects (QALE)

Reinvestigation of the oxidative addition of methyl iodide, hydrogen, and oxygen to Ir(CO)(Cl)L2. Quantitative analysis of ligand effects (QALE)