Amine Arm Research Articles

Nickel complexes incorporating an amido phosphine chelate with a pendant amine arm: Synthesis, structure, and catalytic Kumada coupling

A series of organonickel(II) complexes incorporating an amido phosphine ligand tethered with an amino pendant have been prepared and characterized. Deprotonation of N-(dimethylaminoethyl)-2-diphenylphosphinoaniline (H[PNN]) with one equivalent of n-BuLi in ethereal or hydrocarbon solutions at -35 °C generates cleanly dimeric {Li[PNN]}(2) as yellow crystals. The reaction of NiCl(2)(DME) with {Li[PNN]}(2) in THF at -35 °C affords green crystalline [PNN]NiCl. Treating [PNN]NiCl with NaX in acetone solutions gives [PNN]NiX (X = Br, I). Alkylation or arylation of [PNN]NiCl with appropriate Grignard reagents in THF at -35 °C produces red crystalline [PNN]NiR (R = Me, Et, i-Bu, n-hexyl, CH(2)Ph, Ph). The chloride complex [PNN]NiCl was found to be an active catalyst precursor for Kumada coupling reactions of PhX (X = I, Br, Cl) with aryl or alkyl Grignard reagents, including those containing β-hydrogen atoms. The X-ray structures of {Li[PNN]}(2) and [PNN]NiX (X = Cl, Br, Me, Et, n-hexyl) are reported.

Coordination chemistry of 1,4-bis[bis(2-pyridylmethyl)aminomethyl]benzene with copper(II)

The interaction of 1,4-bis[bis(2-pyridylmethyl)aminomethyl]benzene ( p-Xy DPA) with CuCl 2·2H 2O has resulted in the isolation of the dinuclear compound [Cu 2( p-Xy DPA)Cl 4]·H 2O ( 1). When the reaction was performed in presence of sodium perchlorate, sodium azide, sodium dicyanamide (Nadca) and disodium squarate (Na 2C 4O 4) the compounds [Cu 2( p-Xy DPA)(ClO 4) 2Cl 2] ( 2), [Cu 2( p-Xy DPA)(N 3) 4]·2H 2O ( 3), [Cu 2( p-Xy DPA)(dca) 4]·4H 2O ( 4), and [Cu 2( p-Xy DPA)Cl 2(H 2O) 2](C 4O 4)·5.4H 2O ( 5) were obtained, respectively. The complexes were characterized by IR and UV–vis. spectroscopy. The visible spectra of the complexes revealed the square pyramidal geometry around the central Cu 2+ ions. The molecular structures of the complexes 2, 3, 4 and 5 were determined by single crystal X-ray crystallography. This study revealed the dinuclear nature of the complexes and showed that the Cu(II) centers have distorted five-coordinate square pyramidal geometry with N 3-donor atoms of the dipicolyl amine arms and the remaining coordination positions are occupied by the chloro and perchlorato ligands in 2, the monodentate azido ligands in 3 or the monodentate terminal nitrile dca in 4 and by the chloro and aqua ligands in 5 with the squarate dianion as counter ion.

Synthesis of Amides from Esters and Amines with Liberation of H2 under Neutral Conditions

Efficient synthesis of amides directly from esters and amines is achieved under mild, neutral conditions with the liberation of molecular hydrogen. Both primary and secondary amines can be utilized. This unprecedented, general, environmentally benign reaction is homogeneously catalyzed under neutral conditions by a dearomatized ruthenium-pincer PNN complex and proceeds in toluene under an inert atmosphere with a high turnover number (up to 1000). PNP analogues do not catalyze this transformation, underlining the crucial importance of the amine arm of the pincer ligand. A mechanism is proposed involving metal-ligand cooperation via aromatization-dearomatization of the pyridine moiety and hemilability of the amine arm.

N-heterocyclic carbene tethered amido complexes of palladium and platinum

With a view to applications in bifunctional catalysis, a modular cross-coupling strategy has been used to prepare amine bis(imidazolium) salts (3a and 3b) and an amine mono(imidazolium) salt (6) as precursors to chelating amido-NHC ligands. Treating the pro-ligands 3 with 3 equivalents of the bulky base KHMDS and Pd(OAc)(2) or PtCl(2)(COD) gave the four amido bis(N-heterocyclic carbene) pincer complexes [CNC-R]M-I [M = Pd (7) or Pt (8); R = i-Pr (a) or n-Bu (b)], including the first examples of platinum complexes of a CNC ligand. The reaction of 7a with AgOTf in pyridine gave the cationic complex {[CNC-i-Pr]Pd-py}OTf (9a). Heating a mixture of amine mono(imidazolium) salt 6 with PdCl(2) or K(2)PtCl(4), K(2)CO(3) and KI in pyridine at 100 °C gave the complexes [C,NH]MI(2)py [M = Pd (10) or Pt (11)], in which the amine arm of the NHC ligand is not deprotonated and does not coordinate to the metal. For a solution of 10 in 1,4-dioxane, deprotonation of the amine occurred in a biphasic reaction with aqueous KOH at 40 °C, giving the dimeric amido complex {[C,N]Pd(μ-OH)}(2) (12). The more inert Pt analogue 11 was unreactive under the same conditions. Solid-state structures of the complexes 7a, 7b, 9a, 10, 11 and 12 have been determined by single crystal X-ray diffraction.

Amine influence in vanadium-based ethylene polymerisation pro-catalysts bearing bis(phenolate) ligands with ‘pendant’ arms

Two families of vanadium complexes bearing diphenolate ligands with different ‘pendant’ arms have been screened under various conditions for the polymerisation behaviour of ethylene. The presence of a bound amine arm was found to favour enhanced thermal stability.

Two-Way Street Transformation of Boronium and Borane Complexes Facilitated by Amino-Linked N-Heterocyclic Carbene

We have obtained boronium complexes upon reaction of an amino-NHC lithium bromide adduct with borane. Unexpectedly, the treatment of the boronium complexes with silver triflate led to the isolation of a bis-borane compound containing two chemically different boron centers. The bis-borane and boronium complexes can interconvert via a four-membered intermediate metallacycle consisting of a three-center, two-electron B−H−B bonding motif assisted by the pendant amine arm.

Anionic d8 Alkyl Hydrides – Selective Formation and Reactivity of Anionic cis‐PtII Methyl Hydride

AbstractThe pincer‐type complexes [(PCN)PtR] {R = H, 2; Me, 4; PCN = C6H4[CH2P(tBu)2](CH2)2N(CH3)2} react with MeLi or Et3BHNa, to give anionic cis‐Pt(Me)H complexes [(PCN*)Pt(H)(Me)]–Li+ (Me trans to P; PCN* denotes the PCN ligand in which the amine arm is not coordinated) and [(PCN*)Pt(Me)(H)]–Na+ (H trans to P). Only the isomer in which the incoming nucleophile is situated trans to the phosphane ligand is formed. These first d8 anionic alkyl hydride complexes were fully characterized spectroscopically. The hemilabile PCN ligand allows for reversible de‐coordination of the amine arm, thereby providing a desirable balance of stability vs. reactivity. Theoretical calculations on model systems indicate a concerted mechanism in which the nucleophilic attack and the amine dissociation occur concurrently. The (unobserved) methane reductive elimination from the stable anionic methyl hydride complex [(PCN*)Pt(Me)(H)]–Li+ (3) is thermodynamically and kinetically unfavorable, as indicated by DFT. This complex reacts with electrophiles, such as water and methyl iodide, to yield exclusively methane and the corresponding organometallic product (either 2 or 4). This reactivity was also further examined by DFT.

Solid-state and solution structures of hetero-aggregates formed between nBuLi and NCN pincer aryl lithium

The reaction of NCNLi pincers (NCN = [2,6-(R(2)NCH(2))(2)C(6)H(3)](-), R = Me (), Et ()) with various equivalents of nBuLi in non-polar solvent results in the generation of novel mixed alkyl-aryl organolithium hetero-aggregates. The identification (variable temperature (1)H, (13)C, (7)Li and 2D NMR spectroscopy and X-ray crystallography) of multiple, equilibrating mixed-aggregates that form in these reactions has been achieved. Fluxional processes in the parent [NCNLi](2) dimeric homo-aggregates were re-evaluated and Li-N bond rupture was found to be in operation, a prerequisite towards further aggregation chemistry. The crystallized aggregates, with the formula (2).[nBuLi](2) or (2).[nBuLi](2), shows one amine arm from each NCNLi fragment stabilizing a [nBuLi](2) dimer. The core of the aggregates exhibit a roughly cubic Li(4)C(4) configuration with each aryl carbanion eta(3) coordinated to Li(3) triangular faces. Dissolution of microcrystalline powders of (2).[nBuLi](2) or (2).[nBuLi](2) regenerates the observed equilibria. Based on the NMR data, the remaining mixed aggregates are proposed to have the formula .[nBuLi](3) and .[nBuLi](3), respectively; the solution structure is again based on a Li(4)C(4) cluster. The relative concentration of the constituents in these equilibria was found to vary depending on the steric size of the amine groups. In the case of , the predominant species is the (2).[nBuLi](2) aggregate while for , the dimer (2) is favoured.

Amine side arm effect on the ion selectivity of 12-crown-O 3N derivatives with an amine arm in aqueous and acetonitrile solutions

Molecular geometries of crown ether derivatives play an important role in capturing and transporting alkali metal ions such as Li + and Na +. As selectivity of the ions is observed in solution, it is necessary to know their molecular structures in solutions. Recently, we investigated stable conformations of 12-crown-O 3N and its alkali ion complexes in aqueous and acetonitrile solutions. In the present study, we applied a procedure similar to that in previous papers to investigate the side arm effect of 12-crown-O 3N with an amine arm for capturing Li + and Na + in the two solutions. It was confirmed that the stable structures of Li + and Na + complexes in solutions, especially the geometry of the amine side arm, are highly solvent-dependent. This conformational difference is the key to understanding the high Li + selectivity of 12-crown-O 3N derivatives with an amine side arm in acetonitrile.

C-Metalated Diazoalkane Complexes of Platinum Based on PCP- and PCN-Type Ligands

A series of the first C-metalated diazoalkane complexes of Pt, based on pincer-type PCN and PCP ligands (PCP = C6H3[CH2P(iPr)2]2; PCN = C6H3[CH2P(tBu)2](CH2)2N(CH3)2), with the general formula (PCX)Pt[C(N2)R] (2, X = N, R = Ph; 3, X = N, R = SiMe3; 5, X = P, R = Ph) were prepared via direct nucleophilic attack of RCN2-Li+ at the metal center. These remarkably stable complexes were characterized by 1H, 31P{1H}, and 13C NMR and IR spectroscopy. Complex 2 was also characterized by single-crystal X-ray crystallography. Reactions of the C-metalated diazoalkane Pt complexes with Cu(I) (reported to catalyze decomposition of diazoalkanes) were strongly influenced by the nature of the pincer ligand. Bimolecular coupling to generate diphenylacetylene and (PCP)Pt−OTf (6) was observed in the case of the rigid PCP-based complex 5, while the hemilabile PCN-based complex 2 was converted to an ylide-bridged dimeric structure, the formation of which was promoted by the decoordination of the ligand amine arm. In addition, ...

High-Spin Diimine Complexes of Iron(II) Reject Binding of Carbon Monoxide: Theoretical Analysis of Thermodynamic Factors Inhibiting or Favoring Spin-Crossover

A new series of Fe(II) complexes, FeCl2[N(R)=C(Me)C(Me)=N(R)], containing diimine ligands with hemilabile sidearms R (R = CH2(CH2)2NMe2, 1, CH2(CH2)2OMe, 2, CH2(CH2)2SMe), 3) were synthesized. The crystal structure of 1 showed 6-coordination where both amine arms were attached, whereas 2 was a 5-coordinate 16e species with one methoxy arm dangling free. Extensive attempts were made to bind CO to these species to synthesize precursors for dihydrogen complexes but were unsuccessful. Reaction of 1 with 1 or 2 equiv of AgOTf under CO atmosphere resulted in isolation of only a 6-coordinate bis(triflate)-containing product [Fe[N(R)=C(Me)C(Me)=N(R)](OTf)2] (R = CH2(CH2)2NMe2), 5. Reaction of 5-coordinate 2 with AgSbF6 under CO did not give a CO adduct but afforded instead a dicationic dinuclear complex [Fe[N(R)=C(Me)C(Me)=N(R)](mu-Cl)]2[SbF6]2 (R = CH2(CH2)2OMe), 4, containing a weakly bound SbF6. Thus coordination of hard-donor anions to iron was favored over CO binding. The unexpected rejection of binding of CO is rationalized by the iron being in a high-spin state in this system and energetically incapable of spin crossover to a low-spin state. Theoretical calculations on CO interaction with Fe(II) centers in spin states S = 0, 1, and 2 for both the 16e complexes and their CO adducts aid further understanding of this problem. They show that interaction of CO with a high-spin 5-coordinate Fe model diimine complex is essentially thermoneutral but is exergonic by about 48 kcal/mol to a comparable but low-spin diphosphine fragment. Spin crossover is thus disfavored thermodynamically rather than kinetically (e.g. a "spin block" effect); i.e., the ligand field strengths of the primarily N-donor groups are apparently insufficient to give a low-spin CO adduct.

Intramolecular C−H and N−H Transfer by Ruthenium(II) Amidophosphine Complexes

The formation of ruthenium amidophosphine complexes was accomplished by the addition of [P 2 N 2 ]Li 2 (Diox) (where P 2 N 2 is PhP(CH2SiMe2NSiMe2CH2)2PPh and Diox is 1,4-dioxane) to [RuCl 2 (cod)] x to generate [P 2 N 2 ]Ru(cod), or to RuCl 2 (PPh 3 ) 3 to generate [P 2 NNH]Ru(C 6 H 4 -PPh 2 ). In the former complex, the Ru(II) center is in an octahedral environment perched above the P 2 N 2 macrocycle having two formally anionic amido donors; in the latter complex, there is only one amido ligand with the other as an amine donor where the proton originates from the cyclometalated triphenylphosphine group. Reaction of the tridentate amidophosphine ligand precursor [NPN]Li 2 (THF) 2 (where NPN is PhP(CH 2 SiMe 2 NPh) 2 ) with [RuCl 2 -(cod)] x results in the formation of two diastereomeric complexes of the formula [NPNH]Ru(η 3 : η 2 -C 8 H 1 1 ), wherein the cyclooctadiene ligand has been deprotonated by the ancillary ligand to generate a cyclooctadienyl unit. These Ru(II) complexes are five-coordinate with a bidentate PN ligand and a dangling amine unit. The diastereomers are in equilibrium, as shown by variable-temperature NMR studies. The fluxional process that interconverts diastereomers involves proton transfer from the dangling amine arm to the amido unit, a process that equilibrates the two ends of the tridentate NPN ligand on the chemical time scale. Deprotonation of the amine arm by MN(SiMe 3 ) 2 generates a series of ruthenate complexes of the formula [M(THF)]([NPN]Ru(η 3 :η 2 -C 8 H 1 1 )), where M = Li or Na. Addition of Me 3 SiCl results in the formation of new diastereomers that contain silylated dangling arms, and these diastereomers do not interconvert.

Pincer “Hemilabile” Effect. PCN Platinum(II) Complexes with Different Amine “Arm Length”

The reactivity of the “long arm” PCN-type pincer ligand C6H4[CH2P(tBu)2](CH2)2N(CH3)2 (1), which forms complexes bearing a six-membered amine chelate and a five-membered phosphine chelate, was compared with that of the new “normal” PCN ligand C6H4[CH2P(tBu)2](CH2)N(CH2CH3)2 (2), which leads to formation of complexes bearing two five-membered chelates. The chloride complexes (PCN)PtCl (3, 4) and the unsaturated cationic complexes [(PCN)Pt]+X- (X = BF4, OTf) (5, 6, 7), based on both PCN ligands, were prepared and reacted with different reagents to give aqua, [(PCN-1)Pt(H2O)]+BF4- (10); hydroxo, (PCN-1)Pt(OH) (11); carbonyl [(PCN)Pt(CO)]+BF4- (8, 9); and hydride, (PCN-1)PtH (16) complexes. The structures of complexes 4, 6, 8, 10, 11, and 12 were determined by X-ray crystallography. When both carbonyl complexes were treated with hydrogen gas, the “long arm” PCN-1-based complex 8 led to formation of a trimeric cluster, [C6H6[CH2P(tBu)2](CH2)2N(CH3)2Pt(CO)]3 (12), while the “normal” PCN-based complex 9 remained unchanged under the same conditions. This observation clearly demonstrates the very significant effect of the amine arm length (five- vs six-membered chelate) on the hemilability of the ligand and the reactivity of the corresponding complexes.

Substituted N-picolylethylenediamines of the type (ArNHCH2CH2){(2-C5H4N)CH2}NR [R = Me, 4-CH2CH(C6H4)CH2, (2-C5H4N)CH2] and their transition metal(ii) halide complexes

Alkylation of (ArNHCH2CH2){(2-C5H4N)CH2}NH with RX [RX = MeI, 4-CH2=CH(C6H4)CH2Cl) and (2-C5H5N)CH2Cl] in the presence of base has allowed access to the sterically demanding multidentate nitrogen donor ligands, {(2,4,6-Me3C6H2)NHCH2CH2}{(2-C5H4N)CH2}NMe (L1), {(2,6-Me3C6H3)NHCH2CH2}{(2-C5H4N)CH2}NCH2(C6H4)-4-CH=CH2 (L2) and (ArNHCH2CH2){(2-C5H4N)CH2}2N (Ar = 2,4-Me2C6H3 L3a, 2,6-Me2C6H3 L3b) in moderate yield. L3 can also be prepared in higher yield by the reaction of (NH2CH2CH2){(2-C5H4N)CH2}2N with the corresponding aryl bromide in the presence of base and a palladium(0) catalyst. Treatment of L1 or L2 with MCl2 [MCl2 = CoCl2.6H2O or FeCl2(THF)1.5] in THF affords the high spin complexes [(L1)MCl2](M = Co 1a, Fe 1b) and [(L2)MCl2](M = Co 2a, Fe 2b) in good yield, respectively; the molecular structure of reveals a five-coordinate metal centre with bound in a facial fashion. The six-coordinate complexes, [(L3a)MCl2](M = Co 3a, Fe 3b, Mn 3c) are accessible on treatment of tripodal L3a with MCl2. In contrast, the reaction with the more sterically encumbered leads to the pseudo-five-coordinate species [(L3b)MCl2](M = Co 4a, Fe 4b) and, in the case of manganese, dimeric [(L3b)MnCl(mu-Cl)]2 (4c); in 4a and 4b the aryl-substituted amine arm forms a partial interaction with the metal centre while in 4c the arm is pendant. The single crystal X-ray structures of , 1a, 3b.MeCN, 3c.MeCN, 4b.MeCN and 4c are described as are the solution state properties of 3b and 4b.

Nucleophilic de-coordination and electrophilic regeneration of "hemilabile" pincer-type complexes: formation of anionic dialkyl, diaryl, and dihydride Pt(II) complexes bearing no stabilizing pi-acceptors.

Novel anionic dialkyl, diaryl, and dihydride platinum(II) complexes based on the new "long-arm" hemilabile PCN-type ligand C6H4[CH2P(tBu)2](CH2)2N(CH3)2 with the general formula Li+[Pt(PCN)(R)2]- (R=Me (4), Ph (6) and H (9)) were prepared by reaction of [Pt(PCN)(R)] complexes (obtained from the corresponding chlorides) with an equivalent of RLi, as a result of the opening of the chelate ring. Alkylating agents based on other metals produce less stable products. These anionic d8 complexes are thermally stable although they bear no stabilizing pi acceptors. They were characterized by 1H, 31P[1H], 13C, and 7Li NMR spectroscopy; complex 9 was also characterized by single crystal X-ray crystallography, showing that the Li+ ion is coordinated to the nitrogen atom of the open amine arm and to the hydride ligand (trans to the P atom) of a neighboring molecule (H--Li=2.15 A), resulting in a dimeric structure. Complexes 4 and 9 exhibit high nucleophilic reactivity, upon which the pincer complex is regenerated. Reaction of 4 with water, methyl iodide, and iodobenzene resulted in the neutral complex [Pt(PCN)(CH3)] (3) and methane, ethane, or toluene, respectively. Labeling studies indicate that the reaction proceeds by direct electrophilic attack on the metal center, rather than attack on the alkyl ligand. The anionic dihydride complex 9 reacted with water and methyl iodide to yield [Pt(PCN)(H)] (8) and H2 or methane, respectively.

C-C versus C-H activation and versus agostic C-C interaction controlled by electron density at the metal center.

Based on the PCN ligand 2, a remarkable degree of control over C-C versus C-H bond activation and versus formation of an agostic C-C complex was demonstrated by choice of cationic [Rh(CO)(n)(C(2)H(4))(2-n)] (n=0, 1, 2) precursors. Whereas reaction of 2 with [Rh(C(2)H(4))(2)(solv)(n)]BF(4) results in exclusive C-C bond activation to yield product 5, reaction with the dicarbonyl precursor [Rh(CO)(2)(solv)(n)]BF(4) leads to formation of the C-H activated complex 9. The latter process is promoted by intramolecular deprotonation of the C-H bond by the hemilabile amine arm of the PCN ligand. The mixed monocarbonyl monoethylene Rh species [Rh(CO)(C(2)H(4))]BF(4) reacts with the PCN ligand 2 to give an agostic complex 7. The C-C activated complex 5 is easily converted to the C-H activated one (9) by reaction with CO; the reaction proceeds by a unique sequence of 1,2-metal-to-carbon methyl shift, agostic interaction, and C-H activation processes. Similarly, the C-C agostic complex 7 is converted to the same C-H activated product 9 by treatment with CO.

η3-Coordination of Hexadentate N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (tpen) to a Mononuclear fac-ReVIIO3 Center. The Isolation of a New Class of Metal-containing Ligands

Abstract Reaction of ReVOCl3(PPh3)2 with an equimolar amount of tpen affords fac-[ReVIIO3(η3-tpenH)](ClO4)2 (1), in which the tpen ligand coordinates to the fac-ReVIIO3 center in a η3-mode, and the dangling bis(2-pyridylmethyl)amine arm in 1 is subsequently used to produce a heterobimetallic complex fac-, fac-[ReVIIO3(μ-η3:η3-tpen)ReI(CO)3](ClO4)2.

Revealing the diastereomeric nature of pincer terdentate nitrogen ligands 2,6-bis(arylaminomethyl)pyridine through coordination to palladium

Palladium complexes of formula [PdLCl]X (X = Cl 1, BF42) containing the pincer terdentate ligands L [L = 2,6-(ArNHCH2)2C5H3N (Ar = 4-MeC6H41a and 2a, 4-MeOC6H41b and 2b); L = 2,6-(4-MeC6H4NMeCH2)2C5H3N 1c and 2c] have been synthesised as cis–trans diastereomeric mixtures. The chiral nature of both amine arms of the pincer ligands accounts for the mixtures of isomers. All the complexes show dynamic behavior assigned to conversion between diastereomers. A ΔG‡273 of 68.9 kJ mol−1 for 2a and a ΔG‡273 of 65.8 kJ mol−1 for 2c were found through complete DNMR line-shape analysis of the –CH2– signals in the 1H spectra. The cis–trans conversion requires the inversion of the pyramidal nitrogen of one of the coordinated amine arms. Two putative pathways have been proposed for such inversion: a) dissociation of one of the amine nitrogen atoms followed by inversion of the nitrogen atom and reformation of the nitrogen–palladium bond and b) deprotonation of one of the N–H bond leading to an amido intermediate which can reprotonate on the other side. Experimental evidence is given for both mechanisms. The structural characterization of 1a is described.

Density Functional Study on the Hydrido Migration to CO2 and CS2 of the (η5-C5H4(CH2)3NH3+)MH(H2PCH2PH2) (M = Fe, Ru, and Os) Complexes Promoted by the Protonated Amine Arm. Which Path Does the Reaction Take, Abstraction or Insertion?

We have performed theoretical calculations for the hydrido migration to the CO2 and CS2 carbon of the Fe, Ru, and Os complexes which have an intramolecular N−H···H−M H-bond by the hybrid density functional method (B3LYP) using the model complexes (η5-C5H4(CH2)3NH3+)MH(H2PCH2PH2) (M = Fe, Ru, and Os). In the previous study (Matsubara, T. Organometallics 2001, 20, 19−24), we investigated the reaction mechanism for the Ru complex assuming the two considered pathways, i.e., (a) the abstraction of the hydrido ligand by an incoming CO2 without direct coordination of CO2 to the Ru atom, and (b) the insertion of CO2 to the Ru−H bond with the η2-CO precoordination of CO2 to the Ru atom, and found a quite interesting fact that the generally unlikely path a due to its energetical difficulty is more favorable than path b, which has been considered in most cases. This is because the protonated amine arm effectively functions to promote only the electrophilic attack of CO2 in path a and remarkably stabilizes the product to make the potential energy surface of the reaction quite smooth. In the present study, we have further examined the effects of the metal and solvent on the reactivity and the mechanism and also the hydrido migration to CS2, which is completely different from CO2 in the charge distribution, to search the other significant factors that determine the reactivity and the reaction path.

Promotion Effect of the Protonated Amine Arm of a Ruthenium Complex on Hydrido Migration to CO2: A Density Functional Study

The hydrido migration to the carbon of CO2 on the experimentally synthesized novel N−H···H−Ru H-bonded complex (η5-C5H4(CH2)3NMe2H+)RuH(dppm), 2, was examined by means of the hybrid density functional method (B3LYP), assuming the following two generally considered reaction paths: (a) the abstraction of the hydrido ligand by an incoming CO2 without direct coordination of CO2 to the Ru atom, and (b) the insertion of CO2 to the Ru−H bond with the η2-CO precoordination of CO2 to the Ru atom. Without the contribution of the protonated amine arm of the Ru complex, the reaction is uphill in path a, while 8.1 kcal/mol exothermic in path b, requiring the energy barrier of 6.8 kcal/mol. However, when the proton bonded to N of the amine arm has a H-bonding with an oxygen of CO2, the energetics in path a completely changes, and the potential energy surface becomes quite smooth, where only the small energy barrier of 2.6 kcal/mol is needed. On the other hand, in path b although the potential energy surface of the rea...