Cationic Methyl Complexes Research Articles

Organometallics in Superacidic Media: Characterization of Remarkably Stable Platinum–Methyl Bonds in HF/SbF5 Solution

The protolytic stability of (dfepe)PtMe2 (dfepe = (C2F2)2PCH2CH2P(C2F5)2) and cis-(dfmp)2PtMe2 (dfmp = (C2F5)2PMe) and NMR characterization of their corresponding products in SbF5–HF superacid solvent mixtures are reported. Dissolution of (dfepe)Pt(Me)2 in 10 mol % of SbF5–HF at −60 °C resulted in the clean protonolysis of a single Pt–Me bond to form the cationic methyl complex (dfepe)Pt(Me)+; further conversion of (dfepe)Pt(Me)+ to (dfepe)Pt2+ occurred upon warming to −20 °C and followed pseudo-first-order kinetics (k = [1.4(2)] × 10–2 min–1). In contrast, dissolution of the nonchelating analogue cis-(dfmp)2PtMe2 in 10 mol % of SbF5–HF at 20 °C evolved methane and cleanly produced the stable monomethyl complex trans-(dfmp)2Pt(Me)+. trans-(dfmp)2Pt(Me)+ is the most protolytically stable organometallic known: 33% conversion to the cis dicationic product cis-(dfmp)2Pt2+ requires 2 weeks in 10 mol % of SbF5–HF at 20 °C, whereas >90% conversion was observed in 30 h in 50 mol % of SbF5–HF. Dissolution of cis-(...

Rhodium(III) cationic methyl complexes containing dimethylformamide ligand, cis-[Rh(β-diket)(PPh3)2(CH3)(DMF)][BPh4] (β-diket = acetylacetonate or benzoylacetonate), in comparison with their acetonitrile analogs

The rhodium(III) cationic methyl complexes, cis-[Rh(Acac)(PPh3)2(CH3)(DMF)][BPh4] (1) and cis-[Rh(BA)(PPh3)2(CH3)(DMF)][BPh4] (2) are formed upon reactions of cis-[Rh(β-diket)(PPh3)2(CH3)(MeCN)][BPh4] (β-diket = acetylacetonate, Acac, or benzoylacetonate, BA) with excess of dimethylformamide (DMF) in CH2Cl2 solution at ambient temperature. Complexes 1 and 2 were characterized by elemental analysis, 31P{1H} and 1H NMR spectra, and single crystal X-ray crystallography. The cations of 1 and 2 have slightly distorted octahedral geometry. The “equatorial” plane contains the β-diketonate and two PPh3 ligands; methyl and DMF ligands occupy the axial positions. Peculiar features of complexes 1 and 2 in solid state are: (i) unusually long Rh–O(DMF) bond and (ii) non-symmetrical orientation of the formyl C–H bond in relation to two oxygen atoms of the β-diketonate ligand. The signals from formyl protons in the 1H NMR spectra of 1 and 2 are shifted significantly upfield relatively to free DMF. The hydrogen bonding between formyl proton and one of the β-diketonate oxygen atoms is considered. In solutions, 1 and 2 show dynamic behavior at ambient temperature and keep their solid-state geometry at −70 °C.

Bis(diisopropylphosphinomethyl)amine Nickel(II) and Nickel(0) Complexes: Coordination Chemistry, Reactivity, and Catalytic Decarbonylative C–H Arylation of Benzoxazole

The facile one-step synthesis of five new bis(diisopropylphosphinomethyl)amine ligands RN(CH2DIP)2 (DIP = diisopropylphosphine, R = Me–, iPr–, PhCH2–, 2-ThCH2–, and 2-FuCH2−) based on the use of the air-stable phosphonium salt [DIP(CH2OH)2]Cl is presented. The phosphonium salt cleanly reacts with primary amines to afford amine-bridged bisphosphine ligands with variable backbone substitution in good yields. These DIP ligands are useful model systems for their chiral bisphospholane analogues. The coordination chemistry of neutral nickel(II) complexes [(RDIP)NiCl2], [(RDIP)Ni(CH3)2], [(iPrDIP)Ni(Cl)CH2Si(CH3)3], and [(RDIP)Ni(CH2Ph)2], as well as coordinatively unsaturated cationic nickel(II) complexes [(RDIP)Ni(THF)CH3]+BArF– and [(RDIP)NiCH2Ph]+BArF–, has been studied by spectroscopic and X-ray diffraction methods. The cationic methyl complexes reacted cleanly with 2-butyne and 1,1-dimethylallene, yielding allylic complexes [(RDIP)Ni(pmcb)]+BArF– and [(RDIP)Ni(tma)]+BArF–, respectively (pmcb: η3-1,2,3,4,4-...

Synthesis and characterization of acetamidine rhodium(III) cationic methyl complex, trans-[Rh(Acac)(PPh3)2(CH3){NH[dbnd]C(NH2)CH3}][BPh4], produced by ammination of acetonitrile ligand in trans-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4

The rhodium(III) cationic methyl acetamidine complex, trans-[Rh(Acac)(PPh3)2(CH3){NHC(NH2)CH3}][BPh4], (1) is formed upon the reaction of trans-[Rh(Acac)(PPh3)2(CH3)(CH3CN)][BPh4] with ammonia gas in CH2Cl2 solution at temperatures between −15 °C and −20 °C. Complex 1 was characterized by elemental analysis, 31P{1H} and 1H NMR spectra, and single crystal X-ray diffraction study. The cation of 1 has a slightly distorted octahedral structure. The equatorial plane contains the acetylacetonate, methyl, and acetamidine ligands; two PPh3 ligands occupy the axial positions . The acetamidine ligand adopts the Z-configuration stabilized by hydrogen bonding with the oxygen atom of the acetylacetonate ligand, HN–H⋯O (1.90 Å). Complex 1 reacts with ammonia gas at temperatures between 0 °C and 20 °C to form cationic monophosphine complex [Rh(Acac)(PPh3)(CH3){NHC(NH2)CH3}(NH3)][BPh4] (2). Complex 2 was characterized by 31P{1H} and 1H NMR spectra without isolation.

CH Activation versus Yttrium–Methyl Cation Formation from [Y(AlMe4)3] Induced by Cyclic Polynitrogen Bases: Solvent and Substituent‐Size Effects

The reaction of 1,3,5-triisopropyl-1,3,5-triazacyclohexane (TiPTAC) with [Y(AlMe(4))(3)] resulted in the formation of [(TiPTAC)Y(Me(3)AlCH(2)AlMe(3))(μ-MeAlMe(3))] by C-H activation and methane extrusion. In contrast, the presence of bulkier cyclohexyl groups on the nitrogen atoms in 1,3,5-tricyclohexyl-1,3,5-triazacyclohexane (TCyTAC) led to the formation of the cationic dimethyl complex [(TCyTAC)(2)YMe(2)][AlMe(4)]. The investigations reveal a dependency of the reaction mechanism on the steric bulk of the N-alkyl entity and the solvent employed. In toluene C-H activation was observed in reactions of [Y(AlMe(4))(3)] with 1,3,5-trimethyl-1,3,5-triazacyclohexane (TMTAC) and TiPTAC. In THF molecular dimethyl cations, such as [(TCyTAC)(2)YMe(2)][AlMe(4)], [(TMTAC)(2)YMe(2)][AlMe(4)] and [(TiPTAC)(2)YMe(2)][AlMe(4)], could be synthesised by addition of the triazacyclohexane at a later stage. The THF-solvated complex [YMe(2)(thf)(5)][AlMe(4)] could be isolated and represents an intermediate in these reactions. It shows that cationic methyl complexes of the rare-earth metals can be formed by donor-induced cleavage of the rare-earth-metal tetramethylaluminates. The compounds were characterised by single-crystal X-ray diffraction or multinuclear and variable-temperature NMR spectroscopy, as well as elemental analyses. Variable-temperature NMR spectroscopy illustrates the methyl group exchange processes between the cations and anions in solution.

Platinum complexes with diamino-substituted phosphorus ligands: Synthesis, characterization, and their reactivity with a Lewis acid

Abstract Reaction of dialkyl- or diaryl-platinum complexes PtR2(cod) (cod = η2, η2-1,5-cyclooctadiene, R = Me, p-tol) with diamino-substituted phosphorus ligands P(NMeCH2)2(R′) (R′ = OMe, NEt2) produced neutral complexes, cis-[Pt(R)2{P(NMeCH2)2(R′)}2]. On the other hand, reaction of dihalogeno platinum complex PtX2(cod) (X = Cl, I) with P(NMeCH2)2(OMe) yielded a cationic complex [PtX{P(NMeCH2)2(OMe)}3]X. A platinum complex having both methyl and halogeno ligands, PtMeX(cod), reacted with P(NMeCH2)2(OMe) to give a cationic methyl complex [PtMe{P(NMeCH2)2(OMe)}3]X, by contrast, it reacted with P(NMeCH2)2(NEt2) to yield a neutral methyl complex [PtMeX{P(NMeCH2)2(NEt2)}2]. Reaction of [PtMe{P(NMeCH2)2(OMe)}3]X with BF3·OEt2 and then NaBPh4 afforded [PtX{P(NMeCH2)2(OMe)}3]BPh4, showing preferential Me group abstraction on the Pt center rather than the OMe abstraction on the phosphorus atom, followed by the coordination of X to the Pt center. All new complexes were fully characterized using 1H, 13C{1H}, and 31P{1H} NMR measurements and elemental analyses. In addition, structures of several complexes were determined by single crystal X-ray diffraction studies.

Cationic rare-earth-metal methyl complexes: a new preparative access exemplified for Y and Pr

A new procedure for the generation of cationic methyl complexes of rare-earth metals has been developed for yttrium and praseodymium as two examples from the rare-earth series. The reactions of the rare-earth-metal tetramethylaluminates [Ln(AlMe(4))(3)] of yttrium and praseodymium with three differently sized crown ethers in thf, namely [12]crown-4, [15]crown-5 and [18]crown-6, respectively, led to the compounds [YMe([12]crown-4)(2)](2+)[AlMe(4)](-)(2) (1), [PrMe([12]crown-4)(2)](2+)[AlMe(4)](-)(2) (2), [YMe([15]crown-5)(thf)(2)](2+)[AlMe(4)](-)(2) (3), [Pr([15]crown-5)(2)](3+)[AlMe(4)](-)(3) (4), [YMe([18]crown-6)(thf)](2+)[AlMe(4)](-)(2) (5) and [PrMe([18]crown-6)(thf)(2)](2+) [AlMe(4)](-)(2) (6). With the exception of 4, all compounds contain molecular di-cations with a Ln-CH(3) unit bonded to one (3, 4, 6) or two (1, 2) crown-ether molecules. The compounds were characterised by determination of their crystal structures, by elemental analyses and in the case of the yttrium compounds by variable temperature NMR spectroscopy. The latter gives insights into molecular dynamic processes and methyl group exchange between cations and anions in solution.

Cationic Methyl Complexes of the Rare-Earth Metals: An Experimental and Computational Study on Synthesis, Structure, and Reactivity

Synthesis, structure, and reactivity of two families of rare-earth metal complexes containing discrete methyl cations [LnMe(2-x)(thf)n]((1+x)+) (x = 0, 1; thf = tetrahydrofuran) have been studied. As a synthetic equivalent for the elusive trimethyl complex [LnMe3], lithium methylates of the approximate composition [Li3LnMe6(thf)n] were prepared by treating rare-earth metal trichlorides [LnCl3(thf)n] with 6 equiv of methyllithium in diethyl ether. Heteronuclear complexes of the formula [Li3Ln2Me9L(n)] (Ln = Sc, Y, Tb; L = Et2O, thf) were isolated by crystallization from diethyl ether. Single crystal X-ray diffraction studies revealed a heterometallic aggregate of composition [Li3Ln2Me9(thf)n(Et2O)m] with a [LiLn2Me9](2-) core (Ln = Sc, Y, Tb). When tris(tetramethylaluminate) [Ln(AlMe4)3] (Ln = Y, Lu) was reacted with less than 1 equiv of [NR3H][BPh4], the dimethyl cations [LnMe2(thf)n][BPh4] were obtained. The coordination number as well as cis/trans isomer preference was studied by crystallographic and computational methods. Dicationic methyl complexes of the rare-earth metals of the formula [LnMe(thf)n][BAr4]2 (Ln = Sc, Y, La-Nd, Sm, Gd-Lu; Ar = Ph, C6H4F-4) were synthesized, by protonolysis of either the ate complex [Li3LnMe6(thf)n] (Ln = Sc, Y, Gd-Lu) or the tris(tetramethylaluminate) [Ln(AlMe4)3] (Ln = La-Nd, Sm, Dy, Gd) with ammonium borates [NR3H][BAr4] in thf. The number of coordinated thf ligands varied from n = 5 (Ln = Sc, Tm) to n = 6 (Ln = La, Y, Sm, Dy, Ho). The configuration of representative examples was determined by X-ray diffraction studies and confirmed by density-functional theory calculations. The highly polarized bonding between the methyl group and the rare-earth metal center results in the reactivity pattern dominated by the carbanionic character and the pronounced Lewis acidity: The dicationic methyl complex [YMe(thf)6](2+) inserted benzophenone as an electrophile to give the alkoxy complex [Y(OCMePh2)(thf)5](2+). Nucleophilic addition of the soft anion X(-) (X(-) = I(-), BH4(-)) led to the monocationic methyl complexes [YMe(X)(thf)5](+).

Cationic methyl complexes of rhodium(III): synthesis, structure, and some reactions

Cationic methyl complex of rhodium(III), trans-[Rh(Acac)(PPh 3) 2(CH 3)(CH 3CN)][BPh 4] ( 1) is prepared by interaction of trans-[Rh(Acac)(PPh 3) 2(CH 3)I] with AgBPh 4 in acetonitrile. Cationic methyl complexes of rhodium(III), cis-[Rh(Acac)(PPh 3) 2 (CH 3)(CH 3CN)][BPh 4] ( 2) and cis-[Rh(BA)(PPh 3) 2(CH 3)(CH 3CN)][BPh 4] ( 3) (Acac, BA are acetylacetonate and benzoylacetonate, respectively), are obtained by CH 3I oxidative addition to rhodium(I) complexes [Rh(Acac)(PPh 3) 2] and [Rh(BA)(PPh 3) 2] in acetonitrile in the presence of NaBPh 4. Complexes 2 and 3 react readily with NH 3 at room temperature to form cis-[Rh(Acac)(PPh 3) 2(CH 3)(NH 3)][BPh 4] ( 4) and cis-[Rh(BA)(PPh 3) 2(CH 3)(NH 3)][BPh 4] ( 5), respectively. Complexes 1– 5 were characterized by elemental analysis, 1H and 31P{ 1H} NMR spectra. Complexes 1, 2, 3 and 4 were characterized by X-ray diffraction analysis. Complexes 2 and 3 in solutions (CH 2Cl 2, CHCl 3) are presented as mixtures of cis-(PPh 3) 2 isomers involved into a fluxional process. Complex 2 on heating in acetonitrile is converted into trans-isomer 1. In parallel with that isomerization, reductive elimination of methyl group with formation of [CH 3PPh 3][BPh 4] takes place. Replacement of CH 3CN in complexes 1 and 2 by anion I − yields in both cases the neutral complex trans-[Rh(Acac)(PPh 3) 2(CH 3)I]. Strong trans influence of CH 3 ligand manifests itself in the elongation (in solid) and labilization (in solution) of rhodium–acetonitrile nitrogen bond.

Elusive Niobium Alkyl Cations Related to Ethylene Polymerization

Elusive cationic methyl complexes of niobium, [TpMe2NbMe(L)(MeC⋮CMe)][BArf4] (L = OEt2, PMe2Ph, PEt3), that model the active species in alkene polymerization by group 5 metals have been prepared. The X-ray crystal structure of the diethyl ether adduct has been obtained.

Neutral and Cationic Methyl Complexes of Platinum(II) with 6-Substituted 2,2′-Bipyridines: Synthesis, Characterisation and Reactivity with Carbon Monoxide − Molecular Structures of [PtCl(methyl)(6-ethyl-2,2′-bipyridine)] and of [Pt(methyl)(acetonitrile)(6-ethyl-2,2′-bipyridine)][BF4

The complex trans-[PtCl(Me)(SMe2)2] reacts with 6-R-substituted 2,2′-bipyridine, HLn (n = 1, R = H; n = 2, R = Me; n = 3, R = Et; n = 4, R = iPr; n = 5, R = CH2Ph; n = 7, R = Ph), to afford the neutral complexes [PtCl(Me)(HLn)]. Only one isomer is formed (R cis to Cl) with all the ligands, but one (R = Ph). When R = C(Me)2Ph (HL6), only an (N−N−C) cyclometallated species is formed. The stereoselectivity observed is interpreted in terms of the nature of the substituent R, and of the hydrogen bond formed between H−C(α) of the R substituent and the chloride ion bound to the platinum center. The molecular structure of [PtCl(Me)(HL3)] has been resolved by an X-ray analysis and shows that the above-mentioned hydrogen bond length is 2.28 Å. The reactivity of three representative complexes (R = H, Et, CH2Ph) with carbon monoxide has been studied. The reaction affords the ionic species [Pt(Me)(CO)(HLn)]+[PtCl2(Me)(CO)]− and the free ligand. There is evidence of the formation of an acyl species, which does not contain the bipyridine ligand, only when working at high pressures of CO. The above cations are also obtained by direct carbonylation of the solvent species, [Pt(Me)(MeCN)(HLn)][BF4], achieve by halide abstraction from the neutral complexes. The molecular structure of [Pt(Me)(MeCN)(HL3)][BF4] has been resolved by an X-ray analysis.

Key factors determining the course of methyl iodide oxidative addition to diamidonaphthalene-bridged diiridium(I) and dirhodium(I) complexes.

The course of methyl iodide oxidative addition to various nucleophilic complexes, [Ir2(mu-1,8-(NH)2naphth)(CO)2(PiPr3)2] (1), [IrRh(mu-1,8-(NH)2naphth)(CO)2(PiPr3)2] (2), and [Rh2(mu-1,8-(NH)2naphth)(CO)2(PR3)2] (R = iPr, 3; Ph, 4; p-tolyl, 5; Me, 6), has been investigated. The CH3I addition to complex 1 readily affords the diiridium(II) complex [Ir2(mu-1,8-(NH)2naphth)I(CH3)(CO)2(PiPr3)2] (7), which undergoes slow rearrangement to give a thermodynamically stable stereoisomer, 8. The reaction of the Ir-Rh complex 2 gives the ionic compound [IrRh(mu-1,8-(NH)2naphth)(CH3)(CO)2(PiPr3)2]I (10). The dirhodium compounds, 3-5, undergo one-center additions to yield acyl complexes of the formula (Rh2(mu-1,8-(NH)2naphth)I(COCH3)(CO)(PR3)2] (R = iPr, 12; Ph, 13; p-tolyl, 14). The structure of 12 has been determined by X-ray diffraction. Further reactions of these Rh(III)-Rh(I) acyl derivatives with CH3I are productive only for the p-tolylphosphine derivative, which affords the bis-acyl complex [Rh2(mu-1,8-(NH)2naphth)(CH3CO)2I2(P(p-tolyl)3)2] (15). The reaction of the PMe3 derivative, 6, allows the isolation of the bis-methyl complex [Rh2(mu-1,8-(NH)2naphth)(mu-I)(CH3)2(CO)2(PMe3)2]I (16a), which emanates from a double one-center addition. Upon reaction with methyl triflate, the starting materials, 1, 2, 3, and 6, give the isostructural cationic methyl complexes 9, 11, 17, and 18, respectively. The behavior of these cationic methyl compounds toward CH3I, CH3OSO2CF3, and tetrabutylamonium iodide is consistent with the role of these species as intermediates in the SN2 addition of CH3I. Compounds 18 and 17 react with an excess of methyl triflate to give [Rh2(mu-1,8-(NH)2naphth)(mu-OSO2CF3)(CH3)2(CO)2(PMe3)2][CF3SO3] (19) and [Rh2(mu-1,8-(NH)2naphth)(OSO2CF3)(COCH3)(CH3)(CO)(PiPr3)2][CF3SO3] (20), respectively. Upon treatment with acetonitrile, complexes 17 and 18 give the isostructural cationic acyl complexes [Rh2(mu-1,8-(NH)2naphth)(COCH3)(NCCH3)(CO)(PR3)2][CF3SO3] (R = iPr, 21; Me, 22). A kinetic study of the reaction leading to 21 shows that formation of these complexes involves a slow insertion step followed by the fast coordination of the acetonitrile. The variety of reactions found in this system can be rationalized in terms of three alternative reaction pathways, which are determined by the effectiveness of the interactions between the two metal centers of the dinuclear complex and by the steric constraints due to the phosphine ligands.

Mechanistic Studies of Pd(II)−α-Diimine-Catalyzed Olefin Polymerizations1

Mechanistic studies of olefin polymerizations catalyzed by aryl-substituted α-diimine−Pd(II) complexes are presented. Syntheses of several cationic catalyst precursors, [(N∧N)Pd(CH3)(OEt2)]BAr‘4 (N∧N = aryl-substituted α-diimine, Ar‘ = 3,5-(CF3)2C6H3), are described. X-ray structural analyses of [ArNC(H)C(H)NAr]Pd(CH3)(Cl) and [ArNC(Me)C(Me)NAr]Pd(CH3)2 (Ar = 2,6-(iPr)2C6H3) illustrate that o-aryl substituents crowd axial sites in these square planar complexes. Low-temperature NMR studies show that the alkyl olefin complexes, (N∧N)Pd(R)(olefin)+, are the catalyst resting states and that the barriers to migratory insertions lie in the range 17−19 kcal/mol. Following migratory insertion, the cationic palladium alkyl complexes (N∧N)Pd(alkyl)+ formed are β-agostic species which exhibit facile metal migration along the chain (“chain walking”) via β-hydride elimination/readdition reactions. Model studies using palladium−n-propyl and −isopropyl systems provide mechanistic details of this process, which is responsible for introducing branching in the polyethylenes made by these systems. Decomposition of the cationic methyl complexes (ArN∧NAr)Pd(CH3)(OEt2)+ (Ar = 2,6-(iPr)2C6H3, 2-tBuC6H4) occurs by C−H activation of β-C−H bonds of the ortho isopropyl and tert-butyl substituents and loss of methane. The rate of associative exchange of free ethylene with bound ethylene in (N∧N)Pd(CH3)(C2H4)+ is retarded by bulky substituents. The relationship of these exchange experiments to chain transfer is discussed.

Coordination properties of novel hemilabile acetamide-derived P,O phosphine ligands. Crystal structures of Ph2PNHC(O)Me and [PdMe{PPh2NHC(O)Me}{PPh2NHC(O)Me}][O3SCF3] †

Cationic methyl Pd(II) complexes are described in which the new heterofunctional phosphine ligands Ph2PNHC(O)Me 1 or Ph2PN(Me)C(O)Me 3 behave as rigid and/or hemilabile P,O chelates. The chelating ability of 3 is higher than that of 1 and both are compared to that of other P,O ligands, such as the keto- and amido-phosphines Ph2PCH2C(O)Ph and Ph2PCH2C(O)NPh2, respectively. The crystal structure of 1 reveals the presence in the solid-state of an intermolecular hydrogen-bonded network N–H⋯O and that of [PdMe{PPh2NHC(O)Me}{PPh2NHC(O)Me}][O3SCF3] 12b establishes the presence of both a chelating and a monodentate ligand 1 in the same complex. Carbonylation of the cationic methyl complexes 8a, 17, 18a and 20a afforded the corresponding acetyl complexes in which this ligand occupies a position cis to phosphorus, irrespective of that of the alkyl ligand in the precursor complex.

Synthesis and structure of Pd(II) complexes containing chelating (phosphinomethyl)oxazoline P,N-type ligands; copolymerisation of ethylene/CO †

The ligands (2-oxazoline-2-ylmethyl)diphenylphosphine (III or PCH2ox) and (2-oxazoline-2-ylmethyl-4,4-dimethyl)diphenylphosphine (IV or PCH2oxMe2) have been used as chelates towards Pd(II) methyl complexes. The complexes [PdMe(Cl)(PCH2ox)] 2a and [PdMe(Cl)(PCH2oxMe2)] 2b were obtained from [PdMe(Cl)(cod)] (cod = cycloocta-1,5-diene) in 83% and 94% yield, respectively, and compared to [PdCl2(PCH2oxMe2)] 1 which was characterised by X-ray diffraction. A series of cationic methyl complexes obtained by chloride abstraction in the presence of MeCN, SMe2, P(OPh)3 or no added donor except the counter ion were prepared in order to evaluate their catalytic performances in ethylene/CO copolymerisation.

The performance of density-functional/Hartree–Fock hybrid methods: Cationic transition-metal methyl complexes MCH+3 (M=Sc–Cu,La,Hf–Au)

Hybrid methods, including a mixture of Hartree–Fock exchange and density functional exchange-correlation treatment have been applied to the cationic methyl complexes MCH+3 of the first and third-row transition metals (M=Sc–Cu,La,Hf–Au). Bond dissociation energies and optimum geometries obtained with the ‘‘Becke-Half-and-Half-Lee–Yang–Parr’’ and ‘‘Becke-3-Lee–Yang–Parr’’ functionals and from calibration calculations employing quadratic configuration interaction with single and double excitations and with a perturbative estimate of triple excitations are reported. A comparison of the results for the 3d-block species to earlier high-level ab initio calculations and experimental data is carried out in order to assess the reliability of hybrid methods as a practical tool in organometallic chemistry. Furthermore, the bond dissociation energies of the cationic 5d-block transition-metal methyl complexes, many of which have not been investigated so far, are predicted.