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The deoxygenation of tosylated arenes catalyzed by a palladium complex is described. This method represents one of the first general examples of reductive C–O bond cleavage of aryl tosylates via palladium catalysis. By simply employing isopropanol as a mild reducing agent, a variety of tosylated arenes can be smoothly reduced. Labelling experiments revealed that the H source is isopropanol.

This study describes the efficacy of P,N-type benzimidazolyl phosphine ligands, which can be easily synthesized from commercially available and inexpensive starting materials. The application of this ligand array in palladium-catalyzed Suzuki–Miyaura coupling reaction of aryl chlorides with potassium aryltrifluoroborates is described. The air stable benzimidazolyl phosphines in combination with a palladium metal precursor provides highly effective catalysts for the Suzuki–Miyaura coupling of unactivated aryl chlorides and can achieve a catalyst loading of only 0.05 mol %.

This study describes an efficient class of hemilabile benzimidazolyl–phosphane ligands that can be easily accessed from commercially available and inexpensive starting materials. The application of this ligand array in the palladium-catalyzed Suzuki–Miyaura coupling reaction of aryl chlorides with arylboronic acids is described. The palladium catalyst generated from this hemilabile phosphane is highly effective in the Suzuki–Miyaura coupling of unactivated aryl chlorides, and catalyst loadings as low as 1 ppm can be achieved.

This study describes the efficacy of benzimidazolyl phosphine ligands, which are easily synthesized from inexpensive and commercially available o-phenylenediamine, 2-bormobenzoic acid, and chlorophosphines, in the Buchwald-Hartwig amination of aryl chlorides. Primary and secondary aromatic/aliphatic amines are effective substrates in this catalytic system. Functional groups such as keto and esters are also compatible. The catalyst loading can be reduced to 0.1 mol% Pd.

A dicationic dichloro-bipyridine-ruthenium complex shows very high catalytic activity in redox isomerization of allylic alcohols but a relatively low one in transfer hydrogenation of ketones; surprisingly, the analogous dimethyl-bipyridine-ruthenium complex shows reverse catalytic activities in the two reactions.

The first general examples of palladium-catalyzed direct and selective oxidative C3-acetoxylation of indoles are presented. The mild reaction conditions (70 °C and with weak base, KOAc) in this indole C-H-acetoxylation are notable.

An X-ray crystallographic study showed that it is more appropriate to describe the complexes TpRu(PPh 3 )"H 2 SiR 3 " as TpRu(PPh 3 )(η 3 -HSiR 3 H), a static structure containing H···Si···H bonding rather than a highly fluxional pair of σ-silane hydride species TpRu(PPh 3 )(H a )(η 2 -HbSiR 3 ) ⇆ TpRu(PPh 3 )(H b )(η 2 -H a SiR 3 ). 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.

The first general examples of palladium-catalyzed Suzuki-type cross-coupling of aryl and heteroaryl mesylates with potassium aryl and heteroaryltrifluoroborates are presented. In addition to biaryl couplings, the cross-coupling reactions of aryl mesylates with alkyl and vinyltrifluoroborate salts have also been successfully accomplished.

Aminocyclopentadienyl ruthenium complexes, [(eta(5)-C(5)H(4)NMe(2))Ru(PPh(3))(2)(CH(3)CN)](+)BF(4)(-) and [(eta(5)-C(5)H(4)NEt(2))Ru(PPh(3))(2)(CH(3)CN)](+)BF(4)(-), are moderately active catalysts for alpha-alkylation of arylacetonitriles with primary alcohols; on the other hand, the analogous unsubstituted cyclopentadienyl ruthenium complex [(eta(5)-C(5)H(5))Ru(PPh(3))(2)(CH(3)CN)](+)BF(4)(-) shows very low catalytic activity. On the basis of experimental results and theoretical calculations, rationalization for the much higher catalytic activity of the aminocyclopentadienyl complexes over that of the unsubstituted Cp complex is provided. In the catalytic systems with the former, it is possible to regenerate the active solvento complexes via protonation of the metal hydride intermediates and subsequent ligand substitution; this process is, however, very nonfacile in the catalytic system with the latter.

In this paper, we described the process involved in the structure determination of TpRu ( PPh 3){κ2-N, O- NH = C ( Ph ) N = C ( Ph ) O } and demonstrated the tremendous help of computational chemistry in the molecular structure elucidation.

Aryl mesylates are found to be applicable as electrophiles in organosilicon-mediated coupling reactions. The catalyst system comprising 2 mol % of Pd(OAc)(2) and CM-phos supporting ligand is highly effective in catalyzing Hiyama cross-coupling of various aryl and heteroaryl mesylates. Interesting acid additive effects show that the presence of 0.25-0.50 equiv of acetic acid efficiently suppresses the mesylate decomposition and generally promotes the coupling product yields.

Cyclopentadienyl (Cp), hydrotris(pyrazolyl)borato (Tp), and bipyridine ruthenium complexes were found to be active catalysts for the β-alkylation of secondary alcohols with primary alcohols. Mechanistic aspects of the Cp and Tp complexes-catalyzed reactions were investigated; the crucial hydrido complexes were identified. Carbonyl complexes resulting from aldehyde decarbonylation were formed in some cases, and surprisingly, they were also found to be active for the catalytic processes.

A family of indolyl phosphine ligands was applied to Suzuki-Miyaura cross-coupling of aryl tosylates. Catalyst loading can be reduced to 0.2 mol % for coupling of nonactivated aryl tosylate. A challenging example for room temperature coupling is realized. The scope of this highly active Pd/L2 system can be extended to other boron nucleophiles, including trifluoroborate salts and boronate esters. The ligand structural comparisons toward the reactivity in tosylate couplings are also described.

This study describes a new class of indolylphosphine ligands, which can be easily accessed by a simple one-pot assembly from commercially available indoles, acid chlorides, and chlorophosphines. A combination of these three starting materials provides a high diversification of the ligand structure. The application of this ligand array in palladium-catalyzed Suzuki-Miyaura coupling reaction of aryl chlorides with arylboronic acids is described. A catalyst loading down to 0.01 mol % of Pd can be achieved.

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...

The perchlorate salt of the dicationic bipy-ruthenium complex cis-[Ru(6,6'-Cl2bipy)2(H2O)2]2+ effectively catalyzes addition of beta-diketones to secondary alcohols and styrenes to yield the alpha-alkylated beta-diketones. In a catalytic addition reaction of acetylacetone to 1-phenylethanol, the kappa2-acetylacetonate complex [Ru(6,6'-Cl2bipy)2(kappa2-acac)]ClO4 was isolated after the catalysis; this complex is readily synthesized by reacting cis-[Ru(6,6'-Cl2bipy)2(H2O)2](ClO4)2 with acetylacetone. [Ru(6,6'-Cl2bipy)2(kappa2-acac)]ClO4 is unreactive toward 1-phenylethanol in the presence of HClO4; it also fails to catalyze the addition of acetylacetone to 1-phenylethanol. On the basis of these observations, it is proposed and confirmed by independent experiments that the catalytic addition of beta-diketones to the secondary alcohols is in fact catalyzed by the Brønsted acid HClO4, which is generated by the reaction of cis-[Ru(6,6'-Cl2bipy)2(H2O)2](ClO4)2 with the beta-diketone.

The transfer of the hydrogen atoms from the η 2 -H 2 ligand to the cis -disposed olefin ligand in a ruthenium olefin–dihydrogen complex is discussed. It is realized that H 2 O and NEt 3 exhibit promoting effects in the catalytic hydrogenation of olefins with a couple of hydro(trispyrazolyl)borate (Tp)-supported ruthenium complexes. A reaction mechanism that accounts for the promoting effect has been proposed. A Tp-supported ruthenium solvento hydride complex TpRu(PPh 3 )(CH 3 CN)H was found to react with H 2 and R 3 SiH to form the fluxional dihydrogen–hydride, and η 2 -silane–hydride complexes, respectively. Although no stable and isolable σ-complex was formed with CH 4 , the solvento hydride complex was found to be active in catalyzing H/D reactions of CH 4 with some deuterated common organic solvents. In the catalytic CO 2 hydrogenation reactions in THF/H 2 O or alcohol, the complex TpRu(PPh 3 )(CH 3 CN)H generates the metal-ligand bifunctional catalyst TpRu(PPh 3 )(ROH)H (R = H or alkyl) which transfers the hydride and a proton from ROH to the CO 2 molecule in a concerted manner, without coordination of the latter to the metal center. Aminocyclopentadienyl ruthenium complexes, which exhibit intramolecular Ru–H⋯H–N dihydrogen-bonding interactions were synthesized and characterized. These complexes provide good models for the study of heterolytic cleavage of η 2 -H 2 ligand and its reverse-protonation of metal hydride to form dihydrogen complex. An indenyl ruthenium hydride complex was synthesized and found to be good catalyst for nitrile hydration reactions to give amides; these reactions nicely demonstrate the principle of utilizing dihydrogen bond to promote catalytic reactions.

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...

The heterobimetallic complexes [(η 5 -C 5 H 5 )Ru(CO)(μ-dppm)Mn(CO) 4 ] and [(η 5 -C 5 Me 5 )Ru(μ-dppm)(μ-CO) 2 Mn(CO) 3 ] (dppm= bisdiphenylphosphinomethane) have been prepared by reacting the hydridic complexes [(η 5 -C 5 H 5 )Ru(dppm)H] and [(η 5 -C 5 Me 5 )Ru(dppm)H], respectively, with the protonic [HMn(CO) 5 ] complex. The bimetallic complexes can also be synthesized through metathetical reactions between [(η 5 -C 5 R 5 )Ru-(dppm)Cl] (R=H or Me) and Li + [Mn(CO) 5 ] - . Although the complexes fail to catalyze the hydrogenation of CO 2 to formic acid, they catalyze the coupling reactions of epoxides with carbon dioxide to yield cyclic carbonates. Two possible reaction pathways for the coupling reactions have been proposed. Both routes begin with heterolytic cleavage of the Ru-Mn bond and coordination of an epoxide molecule to the Lewis acidic ruthenium center. In Route I, the Lewis basic manganese center activates the CO 2 by forming the metallocarboxylate anion which then ring-opens the epoxide; subsequent ring-closure gives the cyclic carbonate. In Route II, the nucleophilic manganese center ring-opens the ruthenium-attached epoxide to afford an alkoxide intermediate; CO 2 insertion into the Ru-O bond followed by ring-closure yields the product. Density functional calculations at the B3LYP level of theory were carried out to understand the structural and energetic aspects of the two possible reaction pathways. The results of the calculations indicate that Route II is favored over Route I.

The η2-dihydrogen complex [TpRu(L2)(H2)]+ (L2 = dppm, dppp, or (PPh3)2) prepared in situ by protonation of the hydride precursor reacts with O2 to yield the paramagnetic RuIII-superoxo complex [TpRuIII(L2)(O2)]+, in which antiferromagnetic coupling between the RuIII ion (d5, S = 1/2) and the coordinated superoxide radical (S = 1/2) does not seem to be present. In THF, the superoxo moiety of the complex readily abstracts a hydrogen atom from the solvent to generate the hydroperoxo (−OOH-) group, which then changes into the hydroxo ligand by transferring an oxygen atom to a phosphine ligand. Density functional theory calculation at the B3LYP level on the model complex [TpRu(PH3)2(O2)]+ shows that the RuIII-superoxo(O2-) structure with a triplet state is more stable than the RuIV-peroxo(O22-) structure with a singlet state by 5.2 kcal/mol. On the other hand, the analogous Cp model complex [CpRu(PH3)2(O2)]+ prefers the RuIV-peroxo(O22-) structure over the RuIII-superoxo(O2-) structure by 2.9 kcal/mol.

Catalytic hydrogenation of CO2 to formic acid with the (solvento)metal hydride complex, TpRu(PPh3)(CH3CN)H [Tp = hydrotris(pyrazolyl)borate], in various alcohols was studied. High-pressure NMR monitoring of the catalytic reaction in non-acidic methanol shows that the observable intermediate is a formate complex resulting from CO2 insertion into the Ru−H bond and is stabilized by the hydrogen-bonding interaction between the formato ligand and a methanol molecule. However, in the case of the acidic alcohol, CF3CH2OH, the observable intermediates are [TpRu(PPh3)(CH3CN)2]+CF3CH2O− and the alkyl carbonate complex, TpRu(PPh3)(η2-O2COCH2CF3), which are formed by the reaction of CO2 with the alkoxide species, TpRu(PPh3)(CH3CN)(OCH2CF3), generated by a very facile reaction between TpRu(PPh3)(CH3CN)H and CF3CH2OH. We propose that the productive catalytic cycles of the reactions conducted in a variety of alcohols are similar to the one we formulated for the catalytic hydrogenation of CO2 in hydrous THF. The formic acid is produced by the transfer of a hydride and a proton from the transient alcohol hydride intermediate, TpRu(PPh3)(ROH)H, to an approaching CO2 molecule. The activity of TpRu(PPh3)(CH3CN)H is higher in CF3CH2OH than in methanol and other non-acidic alcohols and it is probably due to the enhanced electrophilicity of the carbon atom of CO2, which results from the strong interaction between the proton of the highly acidic alcohol in TpRu(PPh3)(CF3CH2OH)H and an oxygen atom of CO2. The electrophilic carbon atom of CO2 could in turn abstract the hydride from Ru−H in a more facile manner. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The indenylruthenium hydride complex (eta(5)-C(9)H(7))Ru(dppm)H was found to be active in catalyzing the hydration of nitriles to amides. The chloro analogue (eta(5)-C(9)H(7))Ru(dppm)Cl was, however, found to be inactive. Density functional theory calculations at the B3LYP level provide explanations for the effectiveness of the hydride complex and the ineffectiveness of the chloro complex in the catalysis. It is learned that the presence of a Ru-H.H-OH dihydrogen-bonding interaction in the transition state lowers the reaction barrier in the case of (eta(5)-C(9)H(7))Ru(dppm)H, but in the chloro system, the corresponding transition state does not contain this type of interaction and the reaction barrier is much higher. A similar dihydrogen-bond-promoting effect is believed to be responsible for the catalytic activity of the hydrotris(pyrazolyl)borato (Tp) ruthenium complex TpRu(PPh(3))(CH(3)CN)H in CH(3)CN hydration. The chloro analogue TpRu(PPh(3))(CH(3)CN)Cl shows no catalytic activity.

Theoretical calculations on the metathesis process, [Tp(PH3)MR(eta 2-H[bond]CH3)] --> [Tp(PH3)M(CH3)(eta 2-H[bond]R)] (M=Fe, Ru, and Os; R=H and CH3), have been systematically carried out to study their detailed reaction mechanisms. Other than the one-step mechanism via a four-center transition state and the two-step mechanism through an oxidative addition/reductive elimination pathway, a new one-step mechanism, with a transition state formed under oxidative addition, has been found. Based on the intrinsic reaction coordinate calculations, we found that the trajectories of the transferring hydrogen atom in the metathesis processes studied are similar to each other regardless of the nature of reaction mechanisms.

The ruthenium complex TpRu(PPh3)(CH3CN)H (Tp = hydrotris(pyrazolyl)borate) catalyzes H/D exchange between CH4 and some deuterated organic solventsbenzene-d6, tetrahydrofuran-d8, diethyl ether-d10, ...

The heterobimetallic complexes [(η5-C5R5)Ru(CO)(μ-dppm)M(CO)2(η5-C5H5)] (M = Mo, W; R = H, CH3) (1–4) are prepared by metathetical reactions between (η5-C5R5)Ru(dppm)Cl and Na+[(η5-C5H5)M(CO)3]−. IR spectroscopic and X-ray structural studies show that each of these complexes contains a semi-bridging carbonyl ligand. The low activity of these complexes in catalytic CO2 hydrogenation to formic acid might be attributed to their non-facile reactions with H2 to yield the active dihydride species. The metal–metal bonds can be protonated to form the cationic complexes, which contain strong Ru–H–M bridges. The bridging hydrogen atom is weakly acidic since it can be removed by a strong base, and it protonates BPh4− to give BPh3 and benzene. It also reacts with the hydridic hydrogen of Et3SiH to yield H2. The bridging hydrogen, however, cannot be removed by hydride scavengers such as Ph3C+OTf− and Me3Si+OTf−. The sluggishness of the catalytic formic acid decomposition by 1–4 is attributable to the stability of the protonated bimetallic intermediate [(η5-C5R5)Ru(CO)(μ-dppm)(μ-H)M(CO)2(η5-C5H5)]+HCOO− formed during the catalysis.

Treatment of [RuCl(PPh3)(PCP)] (PCP = 2,6-(Ph2PCH2)2C6H3) with norbornadiene (NBD) in the presence of CuCl produces [RuCl(NBD)(PCP)]. Reaction of [RuCl(NBD)(PCP)] with TlOTf gives [Ru(OTf)(NBD)(PCP)], which reacts with NaBH4 to produce [RuH(NBD)(PCP)]. Protonation of [RuH(NBD)(PCP)] with acetic acid in the presence of PPh3 gives norbornene and [Ru(OAc)(PPh3)(PCP)]. Protonation of [RuH(NBD)(PCP)] with HOTf gives norbornane and [Ru(OTf)(NBD)(PCP)]. Protonation of [RuH(NBD)(PCP)] with HOTf in the presence of MeCN gives norbornene, [Ru(MeCN)(NBD)(PCP)]OTf, and [Ru(MeCN)3(PCP)]OTf. In the protonation reactions, the NBD is likely hydrogenated through the dihydrogen intermediate [Ru(H2)(NBD)(PCP)]+. A computational study shows that hydrogen transfer from the dihydrogen to the NBD ligand of [Ru(H2)(NBD)(PCP)]+ proceeds through a stepwise mechanism.

Treatment of [OsClH3(PPh3)3] with (E)-Ph2P(CH2)2CH=CH(CH2)2PPh2 produced [OsClH(PPh3){Ph2P(CH2)2CH=CH(CH2)2PPh2}], which reacted with HOTf to give the dihydrogen(olefin) complex [OsCl(H2)(PPh3){Ph2P(CH2)2CH=CH(CH2)2PPh2}]OTf. Treatment of the latter complex with H2 did not result in hydrogenation of the olefin double bond, but gave the (hydrido)dihydrogen complex [OsH(H2)(PPh3){Ph2P(CH2)2CH=CH(CH2)2PPh2}]OTf. A density functional theory study suggested that hydrogenation of the double bond in [OsCl(H2)(PPh3){Ph2P(CH2)2CH=CH(CH2)2PPh2}]OTf was thermodynamically feasible but kinetically unfavorable. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Reaction of cis -1,4-dichlorobut-2-ene with dicyclohexylphosphine in the presence of KI in acetone produces [ cis -Cy 2 PHCH 2 CHCHCH 2 PHCy 2 ]I 2 , which is converted to cis -Cy 2 PCH 2 CHCHCH 2 PCy 2 on treatment with NaOH. Reactions of cis -Cy 2 PCH 2 CHCHCH 2 PCy 2 with MHCl(CO)(PPh 3 ) 3 (M=Ru, Os) yield MHCl(CO)(PPh 3 )(Cy 2 PCH 2 CHCHCH 2 PCy 2 ). The ruthenium complex RuCl(CO)(PPh 3 )(Cy 2 PCH 2 CH(CH 2 ) 2 PCy 2 ) is obtained by refluxing RuHCl(CO)(PPh 3 )(Cy 2 PCH 2 CHCHCH 2 PCy 2 ) in methanol–CH 2 Cl 2 . Reaction of RuCl(CO)(PPh 3 )(Cy 2 PCH 2 CH(CH 2 ) 2 PCy 2 ) with H 2 in the presence of NaBPh 4 produces RuHCl(CO)(PPh 3 )(Cy 2 P(CH 2 ) 4 PCy 2 ). Reaction of OsCl(PPh 3 )(2,6-(Ph 2 PCH 2 ) 2 C 6 H 3 ) with H 2 produces OsCl(H⋯H)(PPh 3 )(2,6-(Ph 2 PCH 2 ) 2 C 6 H 3 ) which contains an elongated dihydrogen ligand.

Replacement of the dppm ligand in (η5-C5H4(CH2)2NMe2H+)Ru(dppm)H with two less donating triphenyl phosphite ligands reduces the strength of the intramolecular Ru−H···H−N dihydrogen bond to such an extent that it is hardly evidenced by NMR measurements. Unlike its dihydrogen-bonded dppm analogue, the triphenyl phosphite complex (η5-C5H4(CH2)2NMe2H+)Ru(P(OPh)3)2H shows no catalytic activity for reduction of carbon dioxide to formic acid.

Protonation of [RuH(Cl)(PPh3)2(NBD)] (NBD = norbornadiene) in benzene with a limiting amount of HOTf gives [RuH(OTf)(PPh3)2(NBD)], norbornene, and [RuCl2(PPh3)2]2. In dichloromethane, [RuH(Cl)(PPh3...

A strong promoting effect of water in the catalytic hydrogenation of CO2 to formic acid with the solvento metal hydride species TpRu(PPh3)(CH3CN)H is observed. High-pressure NMR monitoring of the c...

Treatment of OsCl2(PPh3)(PNP) (PNP = 2,6-(Ph2PCH2)2C5H3N) with LiC⋮CPh produced OsCl(PPh3)(2-Ph2PCH(CPhCH)-6-Ph2PCH2C5H3N). The structure of the latter, unusual complex has been confirmed by an X-ray diffraction study. Reaction of OsCl(PPh3)(2-Ph2PCH(CPhCH)-6-Ph2PCH2C5H3N) with H2 and K2CO3 in the presence of NaBF4 in methanol produced OsH(PPh3)(2-Ph2PCH(CPhCH)-6-Ph2PCH2C5H3N). Protonation of OsH(PPh3)(2-Ph2PCH(CPhCH)-6-Ph2PCH2C5H3N) with HBF4 gave [Os(H2)(PPh3)(2-Ph2PCH(CPhCH)-6-Ph2PCH2C5H3N)]BF4, which reacted with H2 to give [OsH(H2)(PPh3)(2-Ph2PCH(CPhCH2)-6-Ph2PCH2C5H3N)]BF4.

Treatment of RuHCl(NBD)(PPh3)2 (NBD = norbornadiene) with AgOTf produced RuH(OTf)(NBD)(PPh3)2. Reaction of RuH(OTf)(NBD)(PPh3)2 with H2 in benzene gave norbornene and [(η6-C6H6)RuH(PPh3)2]OTf. The same reaction in CD2Cl2 in the presence of added PPh3 produced norbornane and [RuH(PPh3)4]OTf. Reaction of OsH3Cl(PPh3)3 with norbornadiene produced OsHCl(NBD)(PPh3)2, which was converted to OsH(OTf)(NBD)(PPh3)2 on treatment with AgOTf. Reaction of OsH(OTf)(NBD)(PPh3)2 with H2 in benzene gave norbornane and [(η6-C6H6)OsH(PPh3)2]OTf. In dichloromethane, OsH(OTf)(NBD)(PPh3)2 reacted with H2 in the presence of added PPh3 to produce norbornane and [OsH3(PPh3)4]OTf. Supported by computational studies, it is assumed that the dihydrogen complexes [MH(H2)(NBD)(PPh3)2]+ (M = Ru, Os) were involved in the hydrogenation reactions. Two reaction pathways for the conversion of [RuH(H2)(NBD)(PH3)2]+ to [RuH(NBE)(PH3)2]+ (NBE = norbornene) have been studied by density functional theory calculations. The results show that the fir...

Treatment of OsCl2(PPh3)3 with HC⋮CCMe3produced a mixture of OsCl3(⋮CCH2CMe3)(PPh3)2 and OsCl(CCHCMe3)(C(C⋮CCMe3)CHCMe3)(PPh3)2. The structures of the new complexes have been confirmed by X-ray diffraction studies.

Protonation of indenyl complexes (η5-C9H7)Ru(dppm)H and (η5-C9H7)Ru(PPh3)2H with CF3SO3H or HBF4·Et2O at −60 °C gives the η2-dihydrogen complex [(η5-C9H7)Ru(dppm)(H2)]+ and the dihydride [(η5-C9H7)Ru(PPh3)2H2]+, respectively. Upon warming to room temperature, proton shift from the η2-H2 ligand of the former to the indenyl ligand and subsequent migration of the metal fragment from the five-membered ring to the six-membered ring of the indene ligand results in the formation of the η6-indene complex [(η6-C9H8)Ru(dppm)H]+. The PPh3 analogue [(η6-C9H8)Ru(PPh3)2H]+ is formed in a similar fashion, but in this case, the proton shift is from Ru−H to the indenyl ligand. Low-temperature acidification of (η5-C9H7)Ru(dppe)H and (η5-C9H7)Ru(dppp)H yield mixtures of η2-dihydrogen complex and dihydride in both cases. Similar to the dppm and PPh3 analogues, η6-indene complexes [(η6-C9H8)Ru(dppe)H]+ and [(η6-C9H8)Ru(dppp)H]+ are generated upon warming solutions of the η2-dihydrogen complex/dihydride mixtures to room temper...

in CD2Cl2 yielded, in a straightforward manner, the dicationic η2-dihydrogen complex [tpmRu(PPh3)2(H2)](BF4)2, which, as expected, is more acidic than its monocationic Tp [Tp = hydrotris(pyrazolyl)borate] analog [TpRu(PPh3)2(H2)]BF4 (pKa: 2.8 vs. 7.6). The complex [tpmRu(PPh3)2(H2)](BF4)2 is unstable towards H2 loss at ambient temperature. However, acidification of [tpmRu(PPh3)2H]BF4 with excess aqueous HBF4 or aqueous triflic acid in [D8]THF gave very interesting results. Variable-temperature 1H- and 31P-NMR studies revealed that the aqueous acid did not fully protonate the metal hydride to form the dihydrogen complex, but a hydrogen-bonded species was obtained. The feature of this species is that the strength of its Ru–H···H–(H2O)m interaction decreases with temperature; this phenomenon is unusual because other complexes containing dihydrogen bonds show enhanced M–H···H–X interaction as the temperature is lowered. Decrease of the dihydrogen-bond strength with temperature in the present case can be attributed to the decline of acidity that results from the formation of larger H+(H2O)n (n > m) clusters at lower temperatures; steric hindrance of these large clusters also contribute to the weakening of the dihydrogen bonding interactions. At higher temperatures, facile H/H exchange occurs in Ru–H···H–(H2O)m via the intermediacy of a “hydrogen-bonded dihydrogen complex” Ru–(H2)···(H2O)m. To investigate the effect of the H+(H2O)m cluster size on the strength of the dihydrogen bonding in [tpmRu(PPh3)2H]+, molecular orbital calculations at the B3LYP level have been performed on model systems, [tpmRu(PH3)2H]+ + H+(H2O) and [tpmRu(PH3)2H]+ + H+(H2O)2. The results provide further support to the notion that the formation of larger H+(H2O)n clusters weakens the Ru–H····H(H2O)n dihydrogen bonding interaction.

The electrocatalytic carboxylation of 4-(trifluoromethyl)benzyl chloride, 4-methoxybenzyl chloride and diphenylmethyl chloride in N,N-dimethylformamide (DMF) by [Co(dobpy)] (dobpy=6,6′-bis(2-hydroxyphenyl)-2,2′-bipyridine dianion) has been investigated. Electrocarboxylation of the arylmethyl chlorides in CO2-saturated DMF solution in the presence of the cobalt catalyst resulted in the formation of a mixture of the corresponding arylacetic acid and substituted toluene. The ratio of carboxylic acid to hydrocarbon in the product mixture was dependent on the nature of the arylmethyl chlorides and the electrolysis potential. Voltammetric studies indicated that the electrogenerated [CoI(dobpy)]− underwent oxidative addition with RCl to give [CoIII(dobpy)R]. The unstable one-electron-reduced complex [CoII(dobpy)R]− underwent homolytic CoC bond cleavage to generate R, which in turn could undergo further reduction to give the carbanion R− either at the electrode or in the solution. On the one hand, R− was trapped by CO2 to produce carboxylic acid; on the other hand, the protonation of R− and hydrogen-atom abstraction by R would lead to the production of RH. [Co(dobpy)] is a more selective catalyst in the production of carboxylic acid than [Co(TPP)] (TPP=5,10,15,20-meso-tetraphenylporphine dianion) and a more robust catalyst than [Co(salen)] (salen=N,N′-bis(salicylidene)ethane-1,2-diamine dianion).

The structures of Group 8 metal complexes [LMH2(L′)(L′′)]+ (L=cyclopentadienyls, hydrotris(pyrazolyl)borate (Tp)) and [LMH2(L′)(L′′)]2+ (L=1,4,7-triazacyclononane derivatives (RCn), 1,3-(Ph2PCH2)2C5H3N (PMP)) are compared. While complexes [(C5R5)MH2(L′)(L′′)]+ (M=Fe, Ru, Os) at room temperature can exist in either the dihydride form, or the dihydrogen form, or a mixture of both, the analogous Tp, RCn, and PMP complexes are all in the dihydrogen form. Equilibrium studies have shown that the relative acidities of these hydride complexes are strongly affected by the auxiliary ligands, metals, and possibly also the H–H interaction. [TpM(H2)(PR3)2]+ (M=Ru, Os) were found to be slightly more acidic than the analogous [CpMH2(PR3)2]+ complexes, and the dicationic RCn dihydrogen complexes [RCnM(H2)(L′)(L′′)]2+ are much more acidic than the corresponding Cp and Tp analogs. Significant acidity enhancement upon substitution of PPh3 for CO is observed for related dihydrogen complexes such as [RuCl(H2)(L)(PMP)]+, [TpRu(H2)(L)(PPh3)]+, and [HCnRu(H2)(L)(PPh3)]2+ (L=CO, PPh3). At the end of the article, several reactions which may involve heterolytic cleavage of the dihydrogen ligand and proton transfer from coordinated dihydrogen to olefin ligands are described.

Reactions of TpRuH(CH3CN)(PPh3) with free silanes HSiR3 (R3 = Et3, (EtO)3, Ph3, HEt2, HPh2, and H2Ph) in THF yield the complexes TpRu(PPh3)(H)(η2-HSiR3), the formulation of which is inferred from NMR spectroscopic data. The chemical equivalence of the two hydrogen atoms of TpRu(PPh3)(H)(η2-HSiR3) down to −100 °C is attributed to rapid fluxionality between the two, i.e., TpRu(PPh3)(Ha)(η2-HbSiR3) ⇋ TpRu(PPh3)(Hb)(η2-HaSiR3). Molecular orbital calculations at the B3LYP level have been performed to investigate the stereochemistry and the interconversion processes of various structural isomers for TpRu(PPh3)(H)(η2-HSiR3). The results further support the existence of a η2-silane formulation for these complexes. Two stable structures, with a nonclassical η2-silane ligand, have been found. These two structural isomers are found to be in equilibrium with a low reaction barrier (7.5 kcal/mol). The interconversion between the enantiomeric pair of the most stable structure has almost no reaction barrier (0.5 kcal/mo...

A rhodium complex of the phosphinite ligand spirOP was found to be an effective catalyst for the asymmetric catalytic hydrogenation of α-substituted enamides with ee values ranging from 85.1% to 97.4%.

The new molecular dihydrogen complex [TpOs(H2)(PPh3)2]BF4 was prepared by protonation of TpOsH(PPh3)2 with HBF4. The pseudo-aqueous pKa values of [CpOsH2(PR3)2)]BF4 ((PR3)2 = (PPh3)2, dppm, dppe, dppp) and [TpOs(H2)(PPh3)2]BF4 have been determined in dichloromethane. [TpOs(H2)(PPh3)2]BF4 was found to be more acidic than trans-[CpOsH2(PPh3)2]BF4. While [TpOs(H2)(PPh3)2]BF4 is less acidic than [TpRu(H2)(PPh3)2]BF4 by 1.3 pKa units, trans-[CpOsH2(PPh3)2]BF4 is less acidic than trans-[CpRuH2(PPh3)2]BF4 by 5.1 pKa units.

The effect of four weak Bronsted acids, 2,2,2-trifluoroethanol, phenol, methanol and water on the electrocatalytic reduction of CO 2 by [Re(bpy)(CO) 3 (py)] 2+ (bpy=2,2′-bipyridine, py=pyridine) in acetonitrile was investigated. The addition of weak Bronsted acids enhances the rate of the catalytic process and improves the lifetime of the rhenium catalyst. Under the experimental conditions employed in this study, CO was produced as the only product with faradaic efficiency close to 100%. Kinetic analysis indicated that the reaction order in acid is 2. The Bronsted acids probably stabilise the rhenium–carbon dioxide intermediate through protonation and facilitate the cleavage of one of the C–O bonds to yield CO. The efficiency of the acid increases with its acidity. Thus, trifluoroethanol and phenol are more effective in enhancing the rate of catalysis than methanol and water. Even though the acid strength of water and methanol are very similar, water is much less effective in enhancing the rate of CO 2 reduction. This can be attributed to the relatively strong ligating property of water, which would compete with CO 2 for the binding site on rhenium.