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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.

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.

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 [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...

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.

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...

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 reactivities of several ruthenium complexes with closely related ligands Cp, Cp*, PCP (2,6-(PPh 2 CH 2 ) 2 C 6 H 3 ) and Tp (hydrotris(pyrazolyl)borate) towards terminal acetylenes are compared. While reactions of terminal acetylenes with ruthenium complexes such as CpRuCl(PR 3 ) 2 , Cp*RuCl(PR 3 ) 2 and TpRuCl(PR 3 ) 2 usually give vinylidene, allenylidene, hydroxyvinylidene or vinylvinylidene complexes, unusual coupling products are produced in the reactions of terminal acetylenes with analogous Ru(PCP) complexes. The structures of group 8 metal hydride complexes of the formula LRuH 3 (L′) (L=Cp, Cp*, Tp; L′=PPh 3 ) and [LMH 2 (L′) 2 ] + (L=Cp, Cp*, Tp; L′=tertiary phosphine) have also been compared in terms of the relative stability of dihydrogen vs. dihydride forms and cis vs. trans -dihydride isomers. Although both Cp and Tp are isoelectronic and both facially coordinate to metal centers, they have different abilities to stabilize the dihydrogen ligand. The difference is reflected in the fact that CpRuH 3 (PPh 3 ) and [CpRuH 2 (PPh 3 ) 2 ] + are classic metal hydride complexes but TpRuH(H 2 )(PPh 3 ) and [TpRu(H 2 )(PPh 3 ) 2 ] + are dihydrogen complexes. Complexes of the formula [C 5 R 5 )MH 2 (PP)] + (M=Fe, Ru, Os; PP=chelating diphosphine) can adopt either the pure dihydrogen form, or a mixture of dihydrogen and trans -dihydride forms, or pure trans -dihydride form, or a mixture of cis - and trans -dihydride forms, depending on metals, C 5 R 5 and the chelating ring sizes of diphosphines.

Addition of 1 equiv of HBF4 to (η5-C5H4(CH2)nNMe2)RuH(dppm) (n = 2, 3) gave [(η5-C5H4(CH2)nNMe2H+)RuH(dppm)]BF4, in which the amine function was protonated. Relaxation time T1 measurements indicated the existence of an intramolecular N−H···H−Ru hydrogen-bonding interaction in these complexes. A spin saturation transfer study and H/D exchange experiment with [(η5-C5H4(CH2)3NMe2H+)RuH(dppm)]BF4 revealed fast exchange, probably via a dihydrogen complex intermediate, between the hydride ligand and N−H. An attempt to grow single crystals of [(η5-C5H4(CH2)3NMe2H+)RuH(dppm)]BPh4 for X-ray study resulted in isolation of crystals of the complex, [(η5:η1-C5H4(CH2)3NMe2)Ru(dppm)]BPh4, with the chelating (3-(dimethylamino)propyl)cyclopentadienyl ligand. Exposure of [(η5:η1-C5H4(CH2)3NMe2)Ru(dppm)]BF4 to 60 atm of H2 at 60 °C gave [(η5-C5H4(CH2)3NMe2H+)RuH(dppm)]BF4 within 30 min. Reacting [(η5:η1-C5H4(CH2)3NMe2)Ru(dppm)]BAr‘4 (Ar‘ = 3,5-(CF3)2C6H3) with Ph2SiH2 yielded [(η5-C5H4(CH2)3NMe2H+)RuH(dppm)]BAr‘4; it is pro...

Protonation of [RCnRuH(L)(L‘)]+ (RCn = 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane; L,L‘ = (PPh3)2, dppe, and CO,PPh3) produced the corresponding dicationic dihydrogen complexes [RCnRu(H2)(L)(L‘)]2+. Protonation of TpRuH(dppe) (Tp = hydrotris(pyrazolyl)borato) yielded the new monocationic dihydrogen complex [TpRu(H2)(dppe)]+. The acidity of the dihydrogen complexes [RCnRu(H2)(L)(L‘)]2+ and monocationic dihydrogen complexes [TpRu(H2)(L)(L‘)]+ (L,L‘ = dppe, (PPh3)2, CH3CN,PPh3, and CO,PPh3) has been studied. It was found that the dicationic complexes are more acidic than their monocationic Tp and Cp counterparts. [MeCnRu(H2)(CO)(PPh3)]2+ was found to be more acidic than [HCnRu(H2)(CO)(PPh3)]2+, probably due to the stronger H−H interaction in the latter complex. It is also noted that triazacyclononane and hydrotris(pyrazolyl)borato dihydrogen complexes with pseudo aqueous pKa values well above that of H3O+ can be deprotonated by H2O to form the corresponding monohydride complexes in o...

Treatment of TpRuCl(PPh3)(CH3CN) (Tp = hydrotris(pyrazolyl)borate) with NaBH4 in ethanol did not yield the expected hydride complex TpRuH(PPh3)(CH3CN) (2) but rather the methyl carbonyl complex TpRu(CH3)(CO)(PPh3) (1b). Formation of 1b was due to decarbonylation of ethanol by 2 generated in situ by NaBH4 reduction of TpRuCl(PPh3)(CH3CN). Analogous reactions in the presence of other primary alcohols RCH2OH (R = H, C2H5, n-C3H7, C6H5, C6H4CH3-4, and C6H4Cl-4) led to the corresponding σ-organyl complexes TpRuR(CO)(PPh3). A common feature of the reactions is that the R groups of alcohols RCH2OH become the σ-organyl groups in the final metal complexes. A mechanism involving metal−η2-aldehyde and −η2-dihydrogen intermediates is proposed for the decarbonylation reaction. This is supported by the observation of the η2-dihydrogen complex TpRuH(H2)(PPh3) (3) during the decarbonylation reaction. 3 was synthesized independently by heating a THF solution of 2 under 40 atm of H2 at 60 °C for 48 h or by heating 2 in CH3...

A series of new hydrotris(1-pyrazolyl)borate complexes of ruthenium were synthesized. Reaction of RuCl(HB(pz)3)(PPh3)2 with NaBH4 in ethanol produced the yellow monohydride complex RuH(HB(pz)3)(PPh3)2. Protonation of the monohydride complex RuH(HB(pz)3)(PPh3)2 with HBF4·Et2O in dichloromethane gave the molecular dihydrogen complex [Ru(HB(pz)3)(PPh3)2(H2)]BF4. Reactions of the dihydrogen complex [Ru(HB(pz)3)(PPh3)2(H2)]BF4 with L (L = CH3CN, H2O, N2) produced the adducts [Ru(HB(pz)3)(PPh3)2(L)]BF4. The dihydrogen complex [Ru(HB(pz)3)(PPh3)2(H2)]BF4 could be regenerated by reactions of [Ru(HB(pz)3)(PPh3)2(L)]BF4 (L = CH3CN, H2O) with pressurized H2. Deprotonation of the molecular dihydrogen complex [Ru(HB(pz)3)(PPh3)2(H2)]BF4 occurred with NEt3 or H2O under hydrogen pressure. Treatment of RuCl(HB(pz)3)(PPh3)2 with LiBF4 in acetonitrile produced the bis-solvento complex [Ru(HB(pz)3)(PPh3)(CH3CN)2]BF4. Heating a THF/CH3CN (9/1) solution of RuCl(HB(pz)3)(PPh3)2 at 60 °C led to the formation of RuCl(HB(pz)3)(PP...

Protonation of CpFeH(P-P) (P-P = dppe, dppp) with HBF4 produced the molecular dihydrogen complexes [CpFe(H2)(P-P)]BF4. Protonation of CpOsH(P-P) (P-P = dppm, dppe, dppp) with HBF4 at −78 °C gave a mixture of cis-[CpOsH2(P-P)]BF4 and trans-[CpOsH2(P-P)]BF4. Depending on the size of the chelating rings, the thermodynamically stable structures of the protonated products at room temperature may be exclusively trans-[CpOsH2(P-P)]BF4 or a mixture of cis-[CpOsH2(P-P)]BF4 and trans-[CpOsH2(P-P)]BF4. At room temperature in dichloromethane solutions, [CpOsH2(dppm)]BF4 exists as a mixture of cis and trans isomers in a ratio of 10:1, [CpOsH2(dppe)]BF4 exists as a mixture of cis and trans isomers in a ratio of 1:70, and [CpOsH2(dppp)]BF4 adopts only trans geometry.

The 6,6′-dichloro-2,2′-bipyridine complex of ruthenium,cis-[Ru(6,6′-Cl2bpy)2(H2O)2] (CF3SO3)21 in ethanol and in the presence of triethylamine, is a very effective catalyst for the hydrogenation of carbon dioxide to formic acid. The formic acid thus produced formed a salt or an adduct with the amine; yields up to 5000 moles per mole of ruthenium can be achieved. In the absence of triethyl amine, the product is ethyl formate and the turnover number is much lower.

A Ru(II)—dichlorobipyridine complex (Ia) efficiently catalyzes the redox isomerization of terminal and internal allylic alcohols to give the corresponding ketones, e.g. (III), (V) or (VII), in high to excellent conversion.

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.

An efficient palladium-catalyzed cyanation of aryl chlorides is established. In the presence of a highly effective Pd/CM-phos catalyst, cyanation of aryl chlorides proceeds at 70 °C in general, which is the mildest reaction temperature achieved so far for this process. Common functional groups such as keto, aldehyde, ester, nitrile and −NH2, and heterocyclic coupling partners including N−H indoles are well tolerated. Moreover, a sterically hindered nonactivated ortho,ortho-disubstituted electrophile is shown to be a feasible coupling partner in cyanation.

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 efficient palladium-catalyzed cyanation of aryl chlorides is established. In the presence of a highly effective Pd/CM-phos catalyst, cyanation of aryl chlorides proceeds at 70 °C in general, which is the mildest reaction temperature achieved so far for this process. Common functional groups such as keto, aldehyde, ester, nitrile and -NH(2), and heterocyclic coupling partners including N-H indoles are well tolerated. Moreover, a sterically hindered nonactivated ortho,ortho-disubstituted electrophile is shown to be a feasible coupling partner in cyanation.

The water soluble ruthenium complex cis -[Ru(6,6′-Cl 2 bpy) 2 (OH 2 ) 2 ] (CF 3 SO 3 ) 2 , (6,6′-Cl 2 bpy = 6,6′-dichloro-2,2′-bipyridine) 1 was found to be an effective catalyst for the hydrogenation of organic carbonyl compounds and olefins in biphasic aqueous/organic systems. The catalyst could be reused after simple decantation. Complex 1 was capable of catalysing the H/D exchange reaction between H 2 and D 2 O. Incorporation of deuterium into the hydrogenation product of acetophenone was observed in catalysis performed in a D 2 O/cyclohexane biphasic medium. A mechanism for the hydrogenation reaction in biphasic media is proposed. It is suggested that an η 2 -dihydrogen complex of ruthenium has been formed during the catalysis and that its deprotonation to generate the metal hydride is the crucial step.

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%.

Treatment of OsH3Cl(PPh3)3 in benzene with excess CH3C⋮CPh produced cis-CH3CHCHPh and the novel complex OsCl(C(CH3)CHPh)(CH2CCHPh)(PPh3)2, which contains a β-agostic vinyl ligand and a phenylallene ligand. The structure of the latter unusual complex has been confirmed by a single-crystal X-ray diffraction study.

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.

Reaction of Cp*RuH(COD) with HBF4·OEt2 at −76 °C produced [Cp*Ru(H2)(COD)]BF4, which transformed to [Cp*Ru(η6-1,3,5-COT)]BF4 on warming to room temperature. Reaction of Cp*RuH(NBD) with HBF4·OEt2 produced a mixture of nortricyclene and the novel bimetallic complex [(Cp*Ru)2(μ-H)(μ-C5H5−CHCH2)]BF4.

The off-the-shelf reagent PPN+Cl- and PPN-manganese carbonylates [PPN]+[Mn(CO)4L]- (L = CO, PPh3) are good catalysts for the coupling reactions of CO2 with neat epoxides without the use of organic solvents to afford cyclic carbonates. PPN salts with weak nucleophilic anions such as PPN+BF4- and PPN+OTf- are, however, inactive for the coupling reactions.

Dihydrogen(olefin) complexes have been proposed as active species in catalytic hydrogenation reactions. We have studied the hydrogen-transfer reactions of dihydrogen(olefin) complexes, especially those containing the norbornadiene (NBD) ligand, in order to address the following questions: (i) how the alignment of a H2 ligand relative to an olefin ligand may affect their reactivity; (ii) in general, what is the detailed pathway for intramolecular hydrogen transfer from an H2 ligand to an olefin ligand; and (iii) how will the hydrogen transfer reactions proceed in the presence of both an H2 and a hydride ligand. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)