Toluene Ligand Research Articles

Tricarbonyl rhenium complexes of bis(pyrazol-1-yl)methane and bis(3,5-dimethylpyrazol-1-yl)methane – Synthesis, spectroscopic characterization, X-ray structure and DFT calculations

Two novel tricarbonyl rhenium complexes based on the bidentate heterocyclic N–N ligands [bis(pyrazol-1-yl)methane(bpzm) and bis(3,5-dimethylpyrazol-1-yl)methane(bdmpzm)] have been synthesized by heating at reflux [Re(CO) 5Cl] with the appropriate N–N ligand in toluene. The compounds have been characterized by IR and UV–Vis spectroscopy and X-ray analysis. Density functional theory (DFT) and time-dependent (TD) DFT calculations have been carried out for the [Re(CO) 3(bdmpzm)Cl] complex.

Ru(xantsil)(CO)(η6-toluene)]: Synthon for a Highly Unsaturated Ruthenium(II) Complex through Facile Dissociation of the Toluene Ligand [xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)

The reactions of [Ru(xantsil)(CO)(η6-C6H5CH3)] [1a, xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl))] with some electron-donating molecules were reported. When 1a was dissolved in benzene, benzene replaced the η6-toluene ligand easily at room temperature to give [Ru(xantsil)(CO)(η6-C6H6)] (1b). The η6-toluene ligand was also substituted by sterically less demanding two-electron donors smoothly at room temperature to afford [Ru(xantsil)(CO)L3] (L = CH3CN (2), tBuNC (3), and PMe3 (4)). The X-ray diffraction studies revealed that they take a typical octahedral geometry, in which the xantsil ligand is coordinated to the Ru(II) center in κ2(Si,Si) fashion. Reactions of 1a with sterically demanding phosphines gave [Ru(xantsil)(CO)(PR3)] (R = iPr (5) and Cy (6)). According to the X-ray diffraction study, complex 6 takes a square-pyramidal geometry, in which the xantsil ligand is bound to the Ru(II) center in κ3(Si,Si,O) fashion and one of the silyl groups occupies the apical position. The coordinativ...

Di-μ-chlorido-bis[chlorido(η6-toluene)ruthenium(II)

In the centrosymmetric dinuclear title complex, [Ru2Cl4(η6-C6H5CH3)2], accessible from RuCl3·nH2O and 1-methylcyclohexa-1,4-diene, the toluene ligand is planar with a ruthenium–centroid distance of 1.646 Å.

Sensitized Near-IR Luminescence of Ln(III) Complexes with Benzothiazole Derivatives

Lanthanide complexes with benzothiazole derivatives (Btz-R, R = OCH(3) and OH) and terpyridine (tpy) ligands were synthesized, and their photophysical properties were precisely investigated. The free Btz-OCH(3) ligand in toluene, excited with UV light, produced the normal emission bands around 410 nm, whereas Btz-OH produced a strong excited-state intramolecular proton transfer (ESIPT) band at 510 nm. The Ln(III) complexes (Ln = Nd, Er, and Yb) exhibited sensitized near-IR luminescence when the Btz-R ligands were excited. The sensitized luminescence quantum yields (Phi(Ln)) of the lanthanide complexes were markedly enhanced by ESIPT: for [Nd(Btz-R)(tpy)] in toluene solution, Phi(Ln) = 0.04% for Btz-OCH(3) and 0.39% for Btz-OH. The sensitized luminescence of the Er(III) complexes (Phi(Ln) = 0.002% for Btz-OCH(3) and 0.009% for Btz-OH) was less efficient than that of the Nd(III) complexes. This difference is due to the smaller energy gap between the emitting and ground levels of the Er(III) ion. The rate constants for the energy transfer from Btz-R to Ln(III) were about approximately 10(9) s(-1), as evaluated by the Förster resonance energy transfer mechanism.

Thallium(I) Sandwich, Multidecker, and Ether Complexes Stabilized by Weakly-Coordinating Anions: A Spectroscopic, Structural, and Theoretical Investigation

The reaction of thallium ethoxide with [H(OEt2)2][H2N{B(C6F5)3}2] in diethyl ether afforded [Tl(OEt2)3][H2N{B(C6F5)3}2] (2a), [Tl(OEt2)4][H2N{B(C6F5)3}2] (2b), or [Tl(OEt2)2][H2N{B(C6F5)3}2].CH2Cl2 (2c), depending on the reaction conditions. The dication in the hydrolysis product [Tl4(mu3-OH)2][H2N{B(C6F5)3}2]2.4CH2Cl2 consists of two bridging and two terminal Tl+ ions bound to triply bridging hydroxides. Heating Et2O complexes in toluene afforded [Tl(eta6-toluene)n][H2N{B(C6F5)3}2] (4, n = 2, 3), while C6Me6 addition gave the first thallium-C6Me6 adduct, [Tl(eta6-C6Me6)2][H2N{B(C6F5)3}2].1.5CH2Cl2 (5a), a bent sandwich complex with very short Tl...centroid distances. These arene complexes show no close contacts between cations and anions. Displacement of toluene ligands by ferrocene gave [Tl2(FeCp2)3][H2N{B(C6F5)3}2]2.5CH2Cl2 (6) which contains the multidecker cations [Tl(FeCp2)]+ and [Tl(FeCp2)2]+ in a 1:1 ratio. By contrast, decamethylferrocene leads to electron transfer; the isolable thallium-ferrocene complexes may therefore be viewed as precursor complexes for this redox step. With 18-crown-6 the complexes [Tl(18-crown-6)2][H2N{B(C6F5)3}2] (11a) and [Tl(18-crown-6)][H2N{B(C6F5)3}2].2CH2Cl2 (11b) were isolated. The structure of the latter shows an eight-coordinate thallium ion, where the coordination to the six oxygen donors in equatorial positions is completed by axial contacts to two F atoms of the counter anions. The bonding between thallium(I) and arenes was explored by density-functional theory (DFT) calculations. The optimized geometry of [Tl(tol)3]+ converged to a structure very similar to that obtained experimentally. Calculations on [Tl(C6Me6)2]+ (5b) to establish whether a linear or bent geometry is the most stable revealed a very flat potential-energy surface for distortions of the Ctr(3)-Tl-Ctr(4) angle. Overall, there is very little energetic preference for one particular geometry over another above about 140 degrees , in good agreement with the crystallographic geometry. The calculated Tl-arene interaction energies increase from 73.7 kJ mol-1 for toluene to 121.7 kJ mol-1 for C6Me6.

Photophysical properties and computational investigations of tricarbonylrhenium(I)[2-(4-methylpyridin-2-yl)benzo[ d]-X-azole]L and tricarbonylrhenium(I)[2-(benzo[ d]-X-azol-2-yl)-4-methylquinoline]L derivatives (X = N–CH 3, O, or S; L = Cl −, pyridine)

We report a combined experimental and computational study of new rhenium tricarbonyl complexes based on the bidentate heterocyclic N–N ligands 2-(4-methylpyridin-2-yl)benzo[ d]-X-azole (X = N–CH 3, O, or S) and 2-(benzo[ d]-X-azol-2-yl)-4-methylquinoline (X = N–CH 3, O, or S). Two sets of complexes are reported. Chloro complexes, described by the general formula Re(CO) 3[2-(4-methylpyridin-2-yl)benzo[ d]-X-azole]Cl (X = N–CH 3, 1; X = O, 2; X = S, 3) and Re(CO) 3[2-(benzo[ d]-X-azol-2-yl)-4-methylquinoline]Cl (X = N–CH 3, 4; X = O, 5; X = S, 6) were synthesized heating at reflux Re(CO) 5Cl with the appropriate N–N ligand in toluene. The corresponding pyridine set {Re(CO) 3[2-(4-methylpyridin-2-yl)benzo-X-azole]py}PF 6 (X = N–CH 3, 7; X = O, 8; X = S, 9) and {Re(CO) 3[2-(benzo[ d]-X-azol-2-yl)-4-methylquinoline]py}PF 6 (X = N–CH 3, 10; X = O, 11; X = S, 12) was synthesized by halide abstraction with silver nitrate of 1– 6 followed by heating in pyridine and isolated as their hexafluorophosphate salts. All complexes have been fully characterized by IR, NMR, electrochemical techniques and luminescence. The crystal structures of 1 and 7 were obtained by X-ray diffraction. DFT and time-dependent (TD) DFT calculations were carried out for investigating the effect of the organic ligand on the optical properties and electronic structure of the reported complexes.

Copper Catalyzed ATRP of Methyl Methacrylate Using Aliphatic α‐Bromo Ketone Initiator

AbstractThe atom transfer radical polymerization (ATRP) of MMA was examined using 3‐bromo‐3‐methyl‐butanone‐2 (MBB) as an initiator in the presence of CuBr as catalyst and 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine (BPIEP) as a tridentate N‐donor ligand. The effect of various other N‐donor ligands including a bisoxazoline ligand, namely, 2,6‐bis(4,4‐dimethyl‐2‐oxazolin‐2‐yl) pyridine (dmPYBOX) was studied in ATRP and reverse ATRP of MMA. The ATRP of MMA in toluene at 90 °C using MBB as initiator was relatively slow in the case of bidentate and faster in the case of tridentate N‐donor ligands. The apparent rate constant, kapp, with MBB as initiator and BPIEP as ligand in toluene (50%, v/v) at 90 °C was found to be 7.15 × 10−5 s−1. In addition, reverse ATRP of MMA in diphenylether at 70 °C using BPIEP/CuBr2 as catalyst system was very effective in reducing the reaction time from several hours to 24 h for polymerization of MMA.

Enantioselective Michael Addition of Dialkylzinc to α,β-Unsaturated Imines

Cu(I)-catalyzed conjugated addition of dialkylzinc to α,β-unsaturated (2-pyridyl)sulfonyl ketimine afforded the corresponding enamine product in good yield. Good ee was obtained in the case of dimethylzinc addition using 10 mol% CuTC and 10mol% Feringa’s monodentate phosphoramidite ligand in toluene at -20 ºC.

Electronic structure and electrophilic reactivity of discrete copper diphenylcarbenes

The β-diketiminato Cu(I) arene adduct {[Me 3NN]Cu} 2(μ-toluene) ( 3) is prepared in 62% isolated yield by addition of the neutral β-diketimine H[Me 3NN] to copper t-butoxide in toluene. An X-ray structure of 3 shows that the bridging toluene ligand exhibits η 2-bonding to each Cu center via four contiguous C atoms. Reaction of the dicopper 3 with 1 equiv. N 2CPh 2 provides {[Me 3NN]Cu} 2(μ-CPh 2) ( 4) as purple crystals in 70% isolated yield. Dicopper carbene 4 possesses a Cu–Cu distance of 2.485(1) Å in the solid state and dissociates a [Me 3NN]Cu fragment in arene solvents to provide low concentrations of [Me 3NN]Cu CPh 2 ( 2) and [Me 3NN]Cu(arene). DFT calculations performed on terminal carbene 2 and dicopper carbene 4 illustrate relationships between these two bonding modes and suggest electrophilic reactivity at the carbene carbon atom bound to Cu. Dicopper carbene 4 undergoes efficient carbene transfer to HC CPh and PPh 3 resulting in the formation of 1,3,3-triphenylcyclopropene and Ph 3P CPh 2 while reaction with the isocyanide CNAr (Ar = 2,6-Me 2C 6H 3) results in loss of the carbene as Ph 2C CPh 2. In each case, the [Me 3NN]Cu fragment is trapped by the incoming nucleophile as the three-coordinate [Me 3NN]Cu(L). Reaction of 4 with O 2 rapidly generates benzophenone and {[Me 3NN]Cu} 2(μ-OH) 2.

Syntheses of some new group 4 non‐Cp complexes bearing schiff‐base, thiophene diamide ligands respectively and their catalytic activities for α‐olefin polymerization

AbstractTotally sixteen new titanium and zirconium non‐Cp complexes supported by Schiff‐base, or thiophene diamide ligands have been synthesized. The complexes are obtained by the reaction of M(OPT‐i)4 (M=Ti, Zr) with the corresponding Schiff‐base ligand in 1: 1 molar ratio in good yield. The thiophene diamide titanium complex has been prepared from trimethylsilyl amine [N,S,N] ligand and TiCl4 in toluene at 120 °C. All complexes are well characterized by 1H NMR, IR, MS and elemental analysis. When activated by excess methylaluminoxane (MAO), complexes show moderate catalytic activity for ethylene polymerization, and complex 1f (R1=CH3, R2=Br) exhibits the highest activity for ethylene and styrene polymerization. When the complexes were preactivated by triethylaluminum (TEA), both polymerization activities and syndiotacticity of the polymers were greatly improved.

Encapsulation of Fe(III) and Cu(II) complexes in NaY zeolite.

The use of nonporphyrin complexes encapsulated in zeolites as catalysts for oxidation reactions has been improved in the past decades by the discovery of increasing numbers of nonheme monoxygenases. The zeolite lattice can change the oxidative chemistry of the metallocomplexes, resulting in a catalytic effect different from those observed in homogeneous reactions. We report the encapsulation of iron and copper metallocomplexes with the ligand (2-hydroxybenzyl)(2-methylpyridyl)amine, Hbpa, and iron complexes with the ligand N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-methylpyridyl) ethylenediamine, H(2)bbpen. The zeolite-encapsulated metallocomplexes were prepared by diffusion of the ligands through the pores of the zeolites, already exchanged with the respective metal. The syntheses were performed in methanol and toluene solutions. Elemental analysis of solids with the Hbpa ligand have indicated better complexation for synthesis in toluene, where 74% of the iron atoms were coordinated by the ligand, against 37% for the synthesis in methanol. For the immobilization with the H(2)bbpen ligand in toluene it was observed that 46% of the iron atoms are coordinated, showing that the diffusion of the small ligand Hbpa through the zeolite cage was facilitated. The EPR spectra of the solids show signals at g = 2.0, which was attributed to an Fe-Fe interaction from the noncoordinated atoms, and g = 4.3 attributed to iron (III) in a rhombic geometry.

Preparation of dinuclear, constrained geometry zirconium complexes with polymethylene bridges and an investigation of their polymerization behavior

We have prepared the polymethylene-bridged, dinuclear, half-sandwich constrained geometry catalysts (CGC) [Zr(η5:η1-C9H5SiMe2NCMe2NCMe3)]2 [(CH2)n] [n=6 (9),n=12 (10)] by treating 2 equivalents of ZrCl4 with the corresponding tetralithium salts of the ligands in toluene.1H and13C NMR spectra of the synthesized complexes provide firm evidence for the anticipated dinuclear structure. In1H NMR spectra, two singlets representing the methyl group protons bonded at the Si atom of the CGC are present at 0.88 and 0.64 ppm, which are considerably downfield positions relative to the shifts of 0.02 and 0.05 ppm of the corresponding ligands. To investigate the catalytic behavior of the prepared dinuclear catalysts, we conducted copolymerizations of ethylene and styrene in the presence of MMAO. The prime observation is that the two dinuclear CGCs9 and10 are not efficient for copolymerization, which definitely distinguishes them from the corresponding titanium-based dinuclear CGC. These species are active catalysts, however, for ethylene homopolymerization; the activity of catalyst10, which contains a 12-methylene bridge, is larger than that of9 (6-methylene bridge), which indicates that the presence of the longer bridge between the two active sites contributes more effectively to facilitate the polymerization activity of the dinuclear CGC. The activities increase as the polymerization temperature increases from 40 to 70 °C. On the other hand, the molecular weights of the polyethylenes are reduced when the polymerization temperature is increased. We observe that dinuclear metallocenes having different-length bridges give different polymerization results, which reconfirms the significant role that the nature of the bridging ligand has in controlling the polymerization properties of dinuclear catalysts.

Characterization of Cu(II) Bipyridine Complexes in Halogen Atom Transfer Reactions by Electron Spin Resonance

Electron spin resonance was used to investigate structural features of CuII complexes with dNbpy (4,4‘-di(5-nonyl)-2,2‘-bipyridine) and dnNbpy (4,4‘-di-n-nonyl-2,2‘-bipyridine) ligands in methyl isobutyrate (MIB) and toluene. With 1 or 2 equiv of either dNbpy or dnNbpy ligands, CuIIBr2 forms predominantly the neutral complexes CuII(dNbpy)Br2 and CuII(dnNbpy)Br2, respectively. Bromine atom transfer between [CuI(dnNbpy)2]+[CuIBr2]- and ethyl 2-bromoisobutyrate (EBriB) in MIB does not yield CuII(dnNbpy)Br2. Instead, it leads to the complex [CuII(dnNbpy)2Br]+[CuIBr2]-. The latter species is also formed in an equilibration reaction of CuII(dnNbpy)Br2 with [CuI(dnNbpy)2]+[CuIBr2]- (K ≥ 100 M-1/2, 23 °C, MIB).

Unusual Enhancement of Ethylene Polymerization Activity of Benzyl Zirconium Complexes by Benzylation of the Imino Moiety of 2-(N-Aryliminomethyl)pyrrolyl Ligand

Abstract Reaction of Zr(CH2Ph)4 (1) with one equiv. of 2-(N-aryliminomethyl)pyrrolyl ligands (2a–e) in toluene afforded two types of products, depending upon the bulkiness of the aryl moiety. The reactions of 1 with two equiv. of the most sterically bulky 2e afforded complex 5e, whose pseudo octahedral geometry around the zirconium atom and totally dissymmetric cis-dibenzyl structure were elucidated. The high catalytic activity for ethylene polymerization was obtained by using complexes 3a and 3b.

Synthetic, Spectroscopic and Structural Studies of the Rhenium(I) Dicarbonyl Complexes of Phosphite, Phosphonite, and Phosphinite Ligands: cis, mer‐[ReBr(CO)2{PPh3‐n(OR)n}3] (R = Me, Et; n = 1—3)

AbstractThe reaction of [ReBr(CO)5] with phosphite and phosphonite ligands in toluene yielded cis, mer‐[ReBr(CO)2L3] (2: L = P(OMe)3 2a: P(OEt)3 2b: PPh(OMe)2 2c: PPh(OEt)2 2d). Compounds 2c and 2d were also obtained, as were the phosphinite complexes 2e [L = PPh2(OMe)] and 2f [L = PPh2(OEt)], by reaction of the corresponding phosphorus ligand with trans, mer‐[ReBr(CO)3L2]. Compounds 2 were all characterized by elemental analysis, mass spectrometry and NMR spectroscopy, and the structures of 2b, 2c and 2d were determined by X‐ray diffractometry. Compounds 2a‐d are stable in chloroform and dichloromethane, but 2e and 2f are transformed into the corresponding trans, mer‐[ReBr(CO)3L2] complexes by a reaction for which a partial mechanism is put forward.

Crown ether complexes of titanium(iv) chloride and bromide and the structures of the hydrolysis products [Ti2Cl6(µ-O)(18-crown-6)2] and [Ti4Cl8(µ-O)4(15-crown-5)4

The titanium(IV) complexes of 12-crown-4, 15-crown-5 and 18-crown-6 and of 1,4-dithia-7,10,13-trioxacyclopentadecane (L′) of type [TiX4(η2-L)] (X = Cl or Br, L = 15-crown-5 or 18-crown-6; X = Br, L = 12-crown-4) and [TiCl4(L′)] have been prepared from TiX4 and the ligands in anhydrous toluene, and characterised by analysis, IR, UV-visible and 1H NMR spectroscopy. Complexes with TiI4 do not form under similar conditions. The [TiCl4(L′)] complex contains the thia-oxa-crown coordinated via sulfur to the titanium. The complexes are extremely readily hydrolysed and examples of the first two stages of the hydrolysis have been characterised by X-ray crystallography. These are the dimer [(18-crown-6)Cl3Ti(μ-O)TiCl3(18-crown-6)] which contains a single non-linear oxo-bridge linking two six-coordinate titanium centres also coordinated η2 to 18-crown-6 and to three (mer) chlorines. The second product is the tetrameric [{TiOCl2(15-crown-5)}4] in which there is an eight-membered ring composed of alternating Ti and O, each titanium also coordinated η2 to 15-crown-5 and two terminal (cis) chlorines.

Room‐Temperature Ammonia Formation from Dinitrogen on a Reduced Mesoporous Titanium Oxide Surface with Metallic Properties.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Influence of Substituents on Cation−π Interactions. 2. Absolute Binding Energies of Alkali Metal Cation−Fluorobenzene Complexes Determined by Threshold Collision-Induced Dissociation and Theoretical Studies

Threshold collision-induced dissociation of M + (C 6 H 5 CH 3 ) x with Xe is studied using guided ion beam mass spectrometry. M + include the following alkali metal ions: Li + , Na + , K + , Rb + , and Cs + . Both mono- and bis-complexes are examined (i.e., x = 1 and 2). In all cases, the primary and lowest energy dissociation channel observed is endothermic loss of an intact toluene ligand. Sequential dissociation of a second toluene ligand is observed at elevated energies in the bis-complexes. Minor production of ligand exchange products, M + Xe and M + (C 6 H 5 CH 3 )Xe, is also observed. The cross section thresholds for the primary dissociation channel are interpreted to yield 0 and 298 K bond dissociation energies for (C 6 H 5 CH 3 ) x - 1 M + -C 6 H 5 CH 3 , x = 1-2, after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energies of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level of theory are used to determine the structures of these complexes and provide molecular constants necessary for the thermodynamic analysis of the experimental data. Theoretical binding energies are determined from single point calculations at the MP2(full)/6-311+G(2d,2p) and B3LYP/6-311+G(2d,2p) levels using the B3LYP/ 6-31G* geometries. Zero-point energy and basis set superposition error corrections are also included. The agreement between theory and experiment is reasonably good when full electron correlation is included (for Li + , Na + , and K + ) but is less satisfactory when effective core potentials are used (for Rb + and Cs + ). In all cases, the experimentally determined bond dissociation energies are greater than the theoretically determined values. In most cases, better agreement is found for the MP2 values than the B3LYP values. The trends in M + (C 6 H 5 CH 3 ) x binding energies are explained in terms of varying magnitudes of electrostatic interactions and ligand-ligand repulsion in the complexes. Comparisons are also made to previous experimental bond dissociation energies of M + (C 6 H 6 ) x to examine the influence of the methyl substituent on the binding, and the factors that control the strength of cation-π interactions.

Room-temperature ammonia formation from dinitrogen on a reduced mesoporous titanium oxide surface with metallic properties.

Mesoporous titanium oxide was treated with bis(toluene) titanium under nitrogen at room temperature in toluene, leading to a new blue black material possessing conductivity values of up to 10(-)(2) Omega(-)(1) cm(-)(1). XRD and nitrogen adsorption showed that the mesostructure was fully retained. Elemental analysis indicated that the material absorbed Ti from the organometallic, without any incorporation of the toluene ligand. There was also an increase of nitrogen from below the detection limit to 1.16%. XPS studies showed that the Ti framework was reduced by the organometallic and that the material had reduced nitride on the surface. There was also an emission at the Fermi level, suggesting metallic behavior. This was confirmed by variable-temperature conductivity studies, which showed a gradual decrease of resistivity with temperature. SQUID magnetometer studies revealed spin glass behavior with a degree of temperature independent paramagnetism, consistent with metallic properties. Solid-state (15)N NMR studies on materials synthesized in the presence of labeled dinitrogen showed that the source of the nitride was the reaction atmosphere. IR and (15)N NMR demonstrated that this nitrogen species was surface ammonia, suggesting that the initially formed nitride species had reacted with moisture imbedded in the walls of the mesostructure. The direct conversion of dinitrogen to ammonia is a very rare process and this work represents the first example of this process mediated by a molecular sieve.

Influence of Substituents on Cation−π Interactions. 1. Absolute Binding Energies of Alkali Metal Cation−Toluene Complexes Determined by Threshold Collision-Induced Dissociation and Theoretical Studies

Threshold collision-induced dissociation of M + (C 6 H 5 CH 3 ) x with Xe is studied using guided ion beam mass spectrometry. M + include the following alkali metal ions: Li + , Na + , K + , Rb + , and Cs + . Both mono- and bis-complexes are examined (i.e., x = 1 and 2). In all cases, the primary and lowest energy dissociation channel observed is endothermic loss of an intact toluene ligand. Sequential dissociation of a second toluene ligand is observed at elevated energies in the bis-complexes. Minor production of ligand exchange products, M + Xe and M + (C 6 H 5 CH 3 )Xe, is also observed. The cross section thresholds for the primary dissociation channel are interpreted to yield 0 and 298 K bond dissociation energies for (C 6 H 5 CH 3 ) x - 1 M + -C 6 H 5 CH 3 , x = 1-2, after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energies of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level of theory are used to determine the structures of these complexes and provide molecular constants necessary for the thermodynamic analysis of the experimental data. Theoretical binding energies are determined from single point calculations at the MP2(full)/6-311+G(2d,2p) and B3LYP/6-311+G(2d,2p) levels using the B3LYP/ 6-31G* geometries. Zero-point energy and basis set superposition error corrections are also included. The agreement between theory and experiment is reasonably good when full electron correlation is included (for Li + , Na + , and K + ) but is less satisfactory when effective core potentials are used (for Rb + and Cs + ). In all cases, the experimentally determined bond dissociation energies are greater than the theoretically determined values. In most cases, better agreement is found for the MP2 values than the B3LYP values. The trends in M + (C 6 H 5 CH 3 ) x binding energies are explained in terms of varying magnitudes of electrostatic interactions and ligand-ligand repulsion in the complexes. Comparisons are also made to previous experimental bond dissociation energies of M + (C 6 H 6 ) x to examine the influence of the methyl substituent on the binding, and the factors that control the strength of cation-π interactions.