Complex TpRu Research Articles

Direct Chlorination of Trispyrazolyl Borate Ligands in Tp-Ruthenium Complexes

Trispyrazolyl borate (Tp) ligands are highly modifiable to vary their steric and electronic properties, and the ability to selectively modify them after metal complexation would allow for rapid catalyst diversification. To this end, stable ruthenium complexes TpRu(cod)Cl (cod = 1,5-cyclooctadiene) and TpRu(nbd)Cl (nbd = norbornadiene) were selectively chlorinated at the 4-positions of the Tp pyrazole rings in high yields to afford TpClRu(cod)Cl and TpClRu(nbd)Cl. The chlorinated complexes could then undergo diene ligand exchange to afford phosphine complexes TpClRu(phosphine)Cl and TpClRu(phosphine)Cl2. Complexes were characterized via NMR spectroscopy, X-ray crystallography, UV–vis spectroscopy, and cyclic voltammetry.

Studies of the decomposition of the ethylene hydrophenylation catalyst TpRu(CO)(NCMe)Ph

TpRu(CO)(NCMe)Ph is a catalyst for the conversion of benzene and ethylene to ethylbenzene. Previously, the formation of ethylbenzene has been shown to occur through a pathway that involves ethylene coordination to Ru, insertion of ethylene into the Ru–phenyl bond and Ru–mediated benzene C–H activation. The effect of ethylene pressure and catalyst concentration (between 0.2 and 0.01 mol % based on benzene) on the decomposition of TpRu(CO)(NCMe)Ph was examined. Studies have shown that there are two competing catalyst deactivation pathways. At higher concentrations of TpRu(CO)(NCMe)Ph, the dominant deactivation pathway is likely initiated by a binuclear reaction of two Ru complexes that leads to formation of unidentified paramagnetic species. Kinetic studies reveal that this pathway for catalyst decomposition occurs with a second-order rate of 0.007 (1) M−1 s−1. At lower Ru concentrations, ethylene C–H activation to form the allyl complex TpRu(CO)(η3-C4H7) is the predominant deactivation pathway. The effect of ethylene pressure on catalyst decomposition was also examined. At higher ethylene pressure nearly quantitative formation of TpRu(CO)(η3-C4H7) was observed.

Synthesis and reactivity of di- and tri-metallic complexes containing the TpRu(PPh3) fragment

Treatment of the TpRu complex Tp(PPh3)2RuCl (Tp = HB(pz)3, pz = pyrazolyl) (1) with ethynylferrocene in MeOH gave the trimetallic alkenyl ketone complex Tp(PPh3)Ru{C(Fc) = CHC(O)CH2(Fc)} (Fc=(η5-C5H4)Fe(η5-C5H5)) (2). Intriguingly, a similar reaction was performed in the presence of NaOMe afforded the dimetallic acetylide complex Tp(PPh3)2Ru–CC-Fc (3). A number of new cationic vinylidene complexes [Tp(PPh3)2Ru{ = CC(Fc)CH2R}]+ [4a, R = CN; 4b, R = HCCH2; 4c, R = CHC(CH3)2; 4d, R = Ph] have been prepared by electrophilic addition of organic halides to complex 3. The substitution reaction of 4a with pyrazole is followed by an intramolecular nucleophilic addition of the nitrogen atom at the α-carbon atom and removal of HI to afford the metallacyclic complex, Tp(PPh3)Ru(C3H3NN)CC(Fc) CH2CN (5a). All of the complexes are identified by spectroscopic methods as well as elementary analysis. The structure of 2 has been determined by X-ray diffraction analysis. Pathways for the synthesis of these compounds are proposed.

Unprecedented formation of ruthenium 2-mercaptobenzothiazole complex

The CS2 insertion of ruthenium chloride complex Tp(Ph2CNH)(PPh3)Ru–Cl (1) in the presence of CH3OH resulted in the O-methyldithiocarbonate complex Tp(PPh3)Ru (κ2-S2COCH3) (3). Attractively, the analogous reaction with CS2 in the presence of PhN3 in toluene at reflux led to unprecedented formation of the ruthenium 2-mercaptobenzothiazole complex Tp(PPh3)Ru(κ2-S,N–NCS2C6H4) (4), possibly via the C–H activation of an imido intermediate. Theoretical calculations support the proposed mechanism.

Catalytic Hydroarylation of Ethylene Using TpRu(L)(NCMe)Ph (L = 2,6,7-Trioxa-1-phosphabicyclo[2,2,1]heptane): Comparison to TpRu(L′)(NCMe)Ph Systems (L′ = CO, PMe3, P(pyr)3, or P(OCH2)3CEt)

The Ru(II) complex TpRu[P(OCH2)2(OCCH3)](NCMe)Ph (4; Tp = hydridotris(pyrazolyl)borate) has been synthesized and isolated. At 90 °C, TpRu[P(OCH2)2OCCH3](NCMe)Ph in C6D6 produces TpRu[P(OCH2)2(OCCH3)](NCMe)Ph-d5 and C6H5D. TpRu[P(OCH2)2(OCCH3)](NCMe)Ph catalyzes the hydrophenylation of ethylene at 90 °C to produce ethylbenzene with 90 turnovers (TOs) after 50 h. Catalyst deactivation occurs by the formation of the η3-allyl complex TpRu[P(OCH2)2(OCCH3)](η3-C3H4Me). Kinetic studies of stoichiometric C6D6 activation by TpRu(L)(NCMe)Ph (L = CO, P(OCH2)3CEt, PMe3 P(OCH2)2(OCCH3)) to give TpRu(L)(NCMe)Ph-d5 and C6H5D reveal that the reactions occur with the following relative rates: PMe3 (kobs = [1.36(4)] × 10–5 s–1) > P(OCH2)3CEt (kobs = 1.20(2) × 10–5 s–1) > P(OCH2)2(OCCH3)(kobs = 7.2(5) × 10–6 s–1) > CO (kobs = [4.62(3)] × 10–6 s–1). These rates correlate linearly with Ru(III/II) potentials of the four TpRu(L)(NCMe)Ph complexes. DFT calculations have been used to model catalytic olefin hydroarylation by TpRu[P(OCH2)2(OCCH3)](NCMe)Ph (4) and to rationalize the observed differences in the various TpRu(L)(NCMe)Ph catalysts.

ChemInform Abstract: Hydro(trispyrazolyl)borato‐Ruthenium(II) Diphosphinoamino Complex‐Catalyzed Addition of β‐Diketones to 1‐Alkynes and anti‐Markovnikov Addition of Secondary Amines to Aromatic 1‐Alkynes.

The hydro(trispyrazolyl)borato-ruthenium(II) diphosphinoamino complex TpRu[4-CF 3 C 6 H 4 N(PPh 2 ) 2 ](OTf) (I) [Tp=hydro(trispyrazolyl)borate] catalyzes the Markovnikov addition of β-diketones to unactivated 1-alkynes in good to excellent yields. The reaction proceeds under solvent-free and additive-free conditions and the catalyst loading can be reduced down to 0.4 mol%. Complex I (1 mol%) also catalyzes the addition of secondary amines to aromatic terminal alkynes, unusual anti-Markovnikov products are exclusively formed.

Hydro(trispyrazolyl)borato‐Ruthenium(II) Diphosphinoamino Complex‐Catalyzed Addition of β‐Diketones to 1‐Alkynes and Anti‐Markovnikov Addition of Secondary Amines to Aromatic 1‐Alkynes

AbstractThe hydro(trispyrazolyl)borato‐ruthenium(II) diphosphinoamino complex TpRu[4‐CF3C6H4N(PPh2)2](OTf) (I) [Tp=hydro(trispyrazolyl)borate] catalyzes the Markovnikov addition of β‐diketones to unactivated 1‐alkynes in good to excellent yields. The reaction proceeds under solvent‐free and additive‐free conditions and the catalyst loading can be reduced down to 0.4 mol%. Complex I (1 mol%) also catalyzes the addition of secondary amines to aromatic terminal alkynes, unusual anti‐Markovnikov products are exclusively formed.

Nonclassical Ruthenium Silyl Dihydride Complexes TpRu(PPh3)(η3‐HSiR3H) [Tp = Hydridotris(pyrazolyl)borate]: Catalytic Hydrolytic Oxidation of Organosilanes to Silanols with TpRu(PPh3)(η3‐HSiR3H)

AbstractAn X‐ray crystallographic study showed that it is more appropriate to describe the complexes TpRu(PPh3)“H2SiR3” as TpRu(PPh3)(η3‐HSiR3H), a static structure containing H···Si···H bonding rather than a highly fluxional pair ofσ‐silane hydride species TpRu(PPh3)(Ha)(η2‐HbSiR3) [rlhar2] TpRu(PPh3)(Hb)(η2‐HaSiR3). One of the complexes was used for the catalytic hydrolytic oxidation of organosilanes to silanols. A mechanism, which does not involve the usual oxidative addition of silane to the metal center to form the silyl hydride species, is proposed, which is supported by theoretical calculations.

Synthesis and characterization of O-methyldithiocarbonate and triphenylphosphoniodithiocarboxylate complexes containing a tris(pyrazolyl)borato (Tp) ligand

The O-methyldithiocarbonate and triphenylphosphoniodithiocarboxylate complexes having a Tp ligand (Tp = BH(pyrazol-1-yl)3) were prepared. The CS2 insertion of ruthenium chloride complex Tp(PPh3)2Ru–Cl (1) in the presence of CH3OH resulted in the O-methyldithiocarbonate complex Tp(PPh3)Ru(κ2-S2COCH3) (3) and triphenylphosphoniodithiocarboxylate complex [Tp(PPh3)Ru(κ2-S2CPPh3)]Cl (4) with the zwitterion -S2CPPh3+ as a chelating ligand depending on the reaction conditions. Attractively, this outcome contrasts sharply with similar reaction of carbon disulfide with Cp(PPh3)2Ru–Cl, no reaction is observed, even under drastic, vigorous conditions. The structures of 3 and 4 have been determined by X-ray diffraction analysis.

Aromatization of a Dihydro-3-ruthenaindolizine Complex

The complex RuHCl(η2-H2)(PiPr3)2 (1) reacts with KTp (Tp = hydridotris(pyrazolyl)borate) to give the hydride−dihydrogen derivative RuHTp(η2-H2)(PiPr3) (2), which has been characterized by X-ray diffraction analysis (dH−H = 1.00(3) Å). Treatment of a toluene solution of 2 with 2-vinylpyridine leads to the 1,2-dihydro-3-ruthenaindolizine derivative Ru(CH2CH2−C5H4N)Tp(PiPr3) (3). Complex 3 aromatizes in toluene at 80 °C to afford the 3-ruthenaindolizine complex Ru(CHCH−C5H4N)Tp(PiPr3) (4) by loss of a hydrogen molecule in the absence of any hydrogen acceptor. The aromatic character of 4 is supported by X-ray diffraction analysis, NMR spectroscopy, and DFT calculations.

Mechanism of Catalytic Hydration of Nitriles with Hydrotris(pyrazolyl)borato (Tp) Ruthenium Complexes

The aquo-amido complexes TpRu(PPh3)(H2O)(NHC(O)R) (R = Me, Ph), which can be prepared by refluxing a THF solution of TpRu(PPh3)(RCN)H containing excess water or more conveniently by reacting TpRu(PPh3)(RCN)Cl with NaOH in THF in the presence of water, are found to be active for catalytic hydration of nitriles to amides. The catalysis proceeds via a mechanism that is distinctly different from the common ones involving intramolecular nucleophilic attack of a hydroxo (or aquo) ligand or external attack of a hydroxide ion (or water) at the carbon atom of the η1-coordinated nitrile to form the metal amide intermediate and subsequent protonation of amido ligand by an adjacent aquo ligand or solvent water. The new mechanism involves the intermediacy of a relatively stable complex containing a chelating N-imidoylimidato ligand; ring-opening nucleophilic attack of this ligand by water is the product-generating step. Formation of the N-imidoylimidato complex from TpRu(PPh3)(H2O)(NHC(O)R) involves several steps. The initial one is displacement of the H2O ligand by a nitrile molecule to yield the nitrile-amido species TpRu(PPh3)(RCN)(NHC(O)R). This is followed by an unusual linkage isomerization of the N-bonded amido ligand to an O-bonded imido, which then undergoes nucleophilic attack at the carbon atom of the nitrile ligand in the complex; facile 1,3-proton shift between the nitrogen atoms on the resulting ring completes the reaction. The N-imidoylimidato complexes TpRu(PPh3)(κ2-N,O-NH═CMeN═CMeO), TpRu(PPh3)(κ2-N,O-NH═CPhN═CPhO), and TpRu(PPh3)(κ2-N,O-NH═CMeN═CPhO) were independently prepared, and the molecular structure of TpRu(PPh3)(κ2-N,O-NH═CPhN═CPhO) was determined by X-ray crystallography. To study the feasibility of the proposed mechanism for nitrile hydration with the aquo-amido complexes, theoretical calculations were performed at the Becke3LYP level of DFT theory to examine the whole catalytic cycle. It is learned that there is a substantially high barrier for the hydrolysis of the highly stable N-imidoylimidato complex, a step involving the ring-opening nucleophilic attack of this ligand by water, and this is probably the reason for the requirement of a relatively high reaction temperature.

Aromatic C−H Activation and Catalytic Hydrophenylation of Ethylene by TpRu{P(OCH2)3CEt}(NCMe)Ph

The complexes TpRu{P(OCH2)3CEt}(L)R {L = PPh3 or NCMe; R = Cl, OTf (OTf = trifluoromethanesulfonate), or Ph; Tp = hydridotris(pyrazolyl)borate} and TpRu{P(OCH2)3CEt}(η3-C3H4Me) were synthesized and isolated. TpRu{P(OCH2)3CEt}(NCMe)Ph was found to initiate C−H activation of benzene and to catalyze the hydrophenylation of ethylene to produce ethylbenzene. Ethylene C−H activation to ultimately produce TpRu{P(OCH2)3CEt}(η3-C3H4Me) kinetically competes with the catalytic hydrophenylation of ethylene. Computational studies were undertaken on reactions in the proposed catalytic ethylene hydrophenylation cycle as well as key side reactions.

Catalytic H/D Exchange between Organic Compounds and D2O with TpRu(PPh3)(CH3CN)H (Tp = hydro(trispyrazolyl)borate). Reaction of TpRu(PPh3)(CH3CN)H with Water to Form Acetamido Complex TpRu(PPh3)(H2O)(NHC(O)CH3)

Deuteration of organic molecules using D2O as the deuterium source is affected with catalytic systems based on the ruthenium solvento hydride complex TpRu(PPh3)(CH3CN)H. The deuteration reactions c...

Reactivity of TpRu(L)(NCMe)R (L = CO, PMe 3; R = Me, Ph) systems with isonitriles: Experimental and computational studies toward the intra- and intermolecular hydroarylation of isonitriles

The Ru(II) phenyl complex TpRu(PMe 3)(NCMe)Ph {Tp = hydridotris(pyrazolyl)borate} reacts with isonitriles to form complexes of the type TpRu(PMe 3)(C NR)Ph (R = t Bu, CH 2Ph, CH 2CH 2Ph). Neither thermal nor photolytic reactions of these systems with excess isonitrile and benzene resulted in the production of corresponding imines. DFT studies that probed the energetics of the desired catalytic transformations revealed that (Tab)Ru(PH 3)(C NCH 2CH 2Ph)Ph {Tab = tris(azo)borate} is the most stable species in a proposed catalytic cycle. Exclusive of calculated transition states, the highest points on the calculated free energy surface are 34 kcal/mol, for (Tab)Ru(PH 3)( o,η 2- C, C-CNCH 2CH 2Ph)Ph {relative to the starting material (Tab)Ru(PH 3)(C NCH 2CH 2Ph)Ph}, and 27 kcal/mol for the C–H activation product (Tab)Ru(PH 3)( o-C 6H 4CH 2CH 2NC) and benzene. The substantial increases in free energy result primarily from the loss of the stable ruthenium–η 1-isonitrile interaction.

Octahedral [TpRu(PMe3)2OR]n+ Complexes (Tp = hydridotris(pyrazolyl)borate; R = H or Ph; n = 0 or 1): Reactions at Ru(II) and Ru(III) Oxidation States with Substrates that Possess Carbon−Hydrogen Bonds

The Ru(II) complexes TpRu(PMe3)2OR (R = H or Ph) react with excess phenylacetylene at elevated temperatures to produce the phenylacetylide complex TpRu(PMe3)2(C⋮CPh). Kinetic studies indicate that the reaction of TpRu(PMe3)2OH and phenylacetylene likely proceeds through a pathway that involves TpRu(PMe3)2OTf as a catalyst. The reaction of TpRu(PMe3)2OH with 1,4-cyclohexadiene at elevated temperature forms benzene and TpRu(PMe3)2H, while TpRu(PMe3)2OPh does not react with 1,4-cyclohexadiene even after 20 days at 85 °C. The paramagnetic Ru(III) complex [TpRu(PMe3)2OH][OTf] is formed upon single-electron oxidation of TpRu(PMe3)2OH with AgOTf. Reactivity studies suggest that [TpRu(PMe3)2OH][OTf] initiates reactions, including hydrogen atom abstraction, with C−H bonds that have bond dissociation energy < 80 kcal/mol. Experimentally, the O−H bond strength of the Ru(II) cation [TpRu(PMe3)2(OH2)][OTf] is estimated to be between 82 and 85 kcal/mol, while computational studies yield a BDE of 84 kcal/mol, which are in reasonable agreement with the observed reactivity of [TpRu(PMe3)2OH]+.

Evidence for the Net Addition of Arene C−H Bonds across a Ru(II)−Hydroxide Bond

TpRu(PMe3)2(OH) (1) reacts with C6D6 to initiate H/D exchange between the hydroxide ligand and the deuterated benzene. In addition, complex 1 catalyzes H/D exchange between H2O and C6D6. Mechanistic and computational studies suggest that a likely reaction pathway for the H/D exchange involves loss of PMe3 to produce {TpRu(PMe3)(OH)}, followed by the net addition of a benzene C-H(D) bond across the Ru-OH bond to form the putative complex TpRu(PMe3)(OH2)(Ph).

Reaction of the RuTp(PR 3)Cl fragment with alkynols: Formation of carbene, vinylidene, allenylidene, and carbyne complexes

The reaction of RuTp(COD)Cl ( 1) with PR 3 (PR 3 = PPh 2 i Pr, P i Pr 3, PPh 3) and propargylic alcohols HC CCPh 2OH, HC CCFc 2OH (Fc = ferrocenyl), and HC CC(Ph)MeOH has been studied.In the case of PR 3 = PPh 2 i Pr, P i Pr 3 and HC CCPh 2OH, the 3-hydroxyvinylidene complexes RuTp(PPh 2 i Pr)( C CHC(Ph) 2OH)Cl ( 2a) and RuTp(P i Pr 3)( C CHC(Ph 2)OH)Cl ( 2b) were isolated.With PR 3 = PPh 2 i Pr and HC CCFc 2OH as well as with PR 3 = PPh 3 and HC CCPh 2OH dehydration takes place affording the allenylidene complexes RuTp(PPh 2 i Pr)( C C CFc 2)Cl ( 3b) and RuTp(PPh 3)( C C CPh 2)Cl ( 3c).Similarly, with PPh 2 i Pr and HC CC(Ph)MeOH rapid elimination of water results in the formation of the vinylvinylidene complex RuTp(PPh 2 i Pr)( C CHC(Ph) CH 2)Cl ( 4).In contrast to the reactions of the RuTp(PR 3)Cl fragment with propargylic alcohols, with HC C(CH 2) n OH ( n = 2, 3, 4, 5) six-, and seven-membered cyclic oxycarbene complexes RuTp(PR 3)( C 4H 6O)Cl ( 5), RuTp(PR 3)( C 5H 8O)Cl ( 6), and RuTp(PR 3)( C 6H 10O)Cl ( 7) are obtained. On the other hand, with 1-ethynylcyclohexanol the vinylvinylidene complex RuTp(PPh 2 i Pr)( C CHC 6H 9)Cl ( 8) is formed. The reaction of the allenylidene complexes 3a– c with acid has been investigated. Addition of CF 3COOH to a solution of 3a– c resulted in the reversible formation of the novel RuTp vinylcarbyne complexes [RuTp(PPh 2 i Pr)( C–CH CPh 2)Cl] + ( 9a), [RuTp(PPh 2 i Pr)( C–CH CFc 2)Cl] + ( 9b), and [RuTp(PPh 3)( C–CH CPh 2)Cl] + ( 9c). The structures of 3a, 3b, and 5b have been determined by X-ray crystallography.

Conversions of Ruthenium(III) Alkyl Complexes to Ruthenium(II) through Ru−Calkyl Bond Homolysis

Single-electron oxidation of the Ru(II) complexes TpRu(L)(L‘)(R) (L = CO, L‘ = NCMe, and R = CH3 or CH2CH2Ph; L = L‘ = PMe3 and R = CH3) with AgOTf leads to alkyl elimination reactions that produce TpRu(L)(L‘)(OTf) and organic products that likely result from Ru−Calkyl bond homolysis. Density functional calculations on TpRu(CO)(NCMe)(Me) and its Ru(III) cation indicate that the Ru−CH3 homolytic bond dissociation enthalpy is substantially reduced (48.6 to 23.2 kcal/mol) upon oxidation.

Regioselective nucleophilic addition of triphenylphosphine to the nitrosylruthenium alkynyl complexes having a hydrotris(pyrazol-1-yl)borate: formation of phosphonio-alkenyl, alkynyl, and allenyl species

A nitrosylruthenium alkynyl complex of TpRuCl(C[triple bond]CPh)(NO)(1a) was reacted with PPh3 in the presence of HBF4.Et2O at room temperature to give a beta-phosphonio-alkenyl complex (E)-[TpRuCl{CH=C(PPh3)Ph}(NO)]BF4(2.BF4). On the other hand, for gamma-hydroxyalkynyl complexes TpRuCl{C[triple bond]CC(R)2OH}(NO)(R = Me (1b), Ph (1c), H (1d)), similar treatments with PPh3 were found to give gamma-phosphonio-alkynyl [TpRuCl{C[triple bond]CC(Me)2PPh3}(NO)]BF4(3.BF4),alpha-phosphonio-allenyl [TpRuCl{C(PPh3)=C=CPh2}(NO)]BF4(4.BF4), and a novel product of gamma-hydroxy-beta-phosphonio-alkenyl (E)-[TpRuCl{CH=C(PPh3)CH2OH}(NO)]BF4(5.BF4), respectively. Dominant factors for the selectivity in affording 3-5 were associated with the steric congestion and electronic properties at the gamma-carbons, along with those around the metal fragment. From the bis(alkynyl) complex TpRu(C[triple bond]CPh)2(NO)6, a bis(beta-phosphonio-alkenyl)(E,E)-[TpRu{CH=C(PPh3)Ph}2(NO)](BF4)2{7.(BF4)2} was produced at room temperature. However, similar reactions at 0 degrees C gave an alkynyl beta-phosphonio-alkenyl complex (E)-[TpRu(C[triple bondCPh){CH=C(PPh3)Ph}(NO)]BF4(8.BF4) as a sole product, of which additional hydration in the presence of HBF4.Et2O afforded a [small beta]-phosphonio-alkenyl ketonyl (E)-[TpRu{CH2C(O)Ph}{CH=C(PPh3)Ph}(NO)]BF(.9BF4). Five complexes, 2-5 and 7 were crystallographically characterized.

Reactions of TpRu(CO)(NCMe)(Me) (Tp = Hydridotris(pyrazolyl)borate) with Heteroaromatic Substrates: Stoichiometric and Catalytic C−H Activation

The Ru(II) complex TpRu(CO)(NCMe)(Me) (Tp = hydridotris(pyrazolyl)borate) initiates carbon−hydrogen bond activation at the 2-position of furan and thiophene to produce methane and TpRu(CO)(NCMe)(aryl) (aryl = 2-furyl or 2-thienyl). Solid-state structures have been determined for TpRu(CO)(NCMe)(2-thienyl) and [TpRu(CO)(μ-C,S-thienyl)]2. The complex TpRu(CO)(NCMe)(2-furyl) serves as a catalyst for the formation of 2-ethylfuran from ethylene and furan. DFT calculations of the C−H activation of furan by {(Tab)Ru(CO)(Me)} (Tab = tris(azo)borate) indicate that the C−H activation sequence does not proceed through a Ru(IV) oxidative addition intermediate.