Highly selective organometallic ruthenium catalysts for aldehyde olefination

Inorg. Chem. Front., 2015

Highly active phosphine free ruthenium-arene complex, [(η 6 -C 6 H 6 )RuCl 2 (C 6 H 5 NH 2 )], exhibit ex-6 cellent catalytic performance for one-pot conversion of aldehydes to primary amides at low tem-7 perature (60 °C), in water and without any inert gas protection. The reported catalyst performed 8 exceptionally well for a huge range of aldehydes, ranging from aromatic, heteroaromatic, aliphat-9 ic and conjugated systems, with high tolerance to other functional groups. The development of 10 such highly active catalysts using simple reagents will offer new opportunities for the develop-11 ment of improved phosphine-free catalytic systems for this and other related catalytic reactions.

Journal of the American Chemical Society, 2009

This work details the development of ruthenium(II) catalysts for the enantioselective alkylation of chiral racemic secondary phosphines. The reactions proceed through the intermediacy of nucleophilic phosphido species, which have low barriers to pyramidal inversion; this allows for a dynamic kinetic asymmetric alkylation. The initially discovered [((R)-iPr-PHOX) 2 Ru(H)][BPh 4 ] (6) catalyst was found to be effective in the reaction with benzylic chlorides; moreover, the alkylation displayed an unusual temperature dependence. However, the limited scope of alkylation of 6 motivated further studies which led to the development of two complementary chiral mixed ligand Ru(II) catalysts of type [L 1 L 2 Ru(H)] +. These catalysts were derived from a combination of one chiral and one achiral ligand, where a synergistic interaction of the two ligands creates an effective asymmetric environment around the ruthenium center. The (R)-MeO-BiPHEP/dmpe (dmpe) 1,2-bis(dimethylphosphino)ethane) catalyst (10) was found to be effective for the asymmetric alkylation of benzylic chlorides, while the (R)-DIFLUORPHOS/dmpe catalyst (11) was optimal for the nucleophilic substitution of less activated alkyl bromides; the scope of the respective catalysts was also explored.

A series of new mixed ligand penta-coordinated square pyramidal ruthenium(II) complexes containing benzaldehyde or its substituents and triphenylphosphine or triphenylarsine have been synthesized and characterized. In the electronic spectra, three well-defined peaks in the visible region were observed and assigned to d-d transitions in D 4h and low spin axially distortion from O h symmetry. The spectrochemical parameters of the complexes were calculated and placed the ligands in the middle of the spectrochemical series. The redox properties and stability of the complexes toward oxidation were related to the electron-withdrawing or releasing ability of the substituent in the phenyl ring of the benzaldehyde. The electron-withdrawing substituents stabilized Ru 2+ complexes, while electron-donating groups favored oxidation to Ru 3+. The mechanism and kinetics of the catalytic oxidation of benzyl alcohol by the complex [RuCl 2 (Pph 3)(C 6 H 5 CHO) 2 ] in the presence of N-methylmorpholine-N-oxide have also been studied.

Journal of Molecular Catalysis A: Chemical, 2011

The synthesis of a new tripodal phosphine ligand, N(CH 2 PEt 2 ) 3 , N-TriPhos Et is reported, and the use of tripodal ligands of this type, N(CH 2 PR 2 ) 3 (R = Ph, Et), in conjunction with ruthenium for the catalysed hydrogenation of dimethyl oxalate (DMO) is reported and contrasted with catalysis using the MeC(CH 2 PPh 2 ) 3 (TriPhos Ph ) ligand. A different order of reaction with respect to the DMO substrate is found, and the rate is slower. A study of the kinetics and mechanism of the hydrogenation of DMO with Ru(acac) 3 /TriPhos Ph is described, along with the effect of different additives to the system. The performance of Ru(acac) 3 /TriPhos Ph /Zn system with unactivated ester substrates is probed and found to proceed significantly slower. Finally, based upon experimental observations, a mechanism is proposed for ester hydrogenation using ruthenium catalysts with tripodal phosphine ligands.

Inorganic Chemistry, 1994

The water-soluble phosphine complex of ruthenium(II), cis-RuClz(PTA)4 (3), has been prepared by the reduction of RuC13 in ethanol in the presence of the air-stable phosphine 1,3,5-triaza-7-phosphaadamantane (2). Complex 3 is an effective catalyst for the regioselective conversion of unsaturated aldehydes to unsaturated alcohols using a biphasic aqueous/organic medium with sodium formate as the source of hydrogen, thus affording facile catalyst recovery and recycle. Both aromatic and aliphatic aldehydes were reduced to the corresponding alcohols. The formate ion was shown to directly be the hydrogen source by deuterium labeling experiments. The rate of hydrogenation of benzaldehyde was found to be first order in catalyst concentration, first order in substrate concentration (in the low-concentration regime), and independent of formate concentration at concentrations > 2.5 M. The reduction process was greatly retarded by the presence of excess phosphine ligand. The apparent activation energy determined was 23.9 kcal mol-'. A catalytic cycle was proposed which involves the rapid formation of a ruthenium hydride formate complex followed by phosphine dissociation and aldehyde addition in a slower step. Subsequent formation of a metal alkoxide intermediate and protonation completes the cycle. Recycling experiments demonstrated the catalyst to be quite robust. Complex 3 crystallized in the monoclinic system, space group P2'/n, with a = 11.399(7) A, b = 19.281(8) A, c = 15.068(7) A, / 3 = 110.85(4)', V = 3095(3)A3, and Dcald = 1.718 g cm-3 for Z = 4 from a water solution. Complex 4, RuC12(PTA)4*2HCl, crystallized in the orthorhombic space group Fdd2, with a = 23.403(5) A, b = 16.317(4) A, c = 19.588(5) A, Y = 7480(3)A3, and Dcald = 1.679 g cm-3 for Z = 8 from a dilute HCl solution of 3. In addition a small quantity of R U C I~(P T A)~*~H C~ (5) crystallized in the triclinic space group pi, with a = 7.496(2) A, b = 8.028(2) A, c = 11.593(4) A, a = 72.73(3)', 0 = 72.98(2)', 7 = 78.08(2)', v = 631.5(3) A3, and Dcald = 1.753 g ~m-~ for Z = 1.

Journal of Organometallic Chemistry, 2010

The synthesis and characterization of latent 18-electron ruthenium benzylidene complexes (PCy 3 )(( k N, O)-picolinate) 2 RuCHPh and (H 2 IMes)(( k N,O)-picolinate) 2 RuCHPh (6) are described. Both complexes appear as two isomers. The ratio between the isomers is dependent on L-type ligand. The complexes are inactive in ring-closing metathesis and ring-opening metathesis polymerization reactions even at elevated temperatures in the absence of stimuli. Upon addition of HCl, complexes 5 and 6 become highly active in olefin metathesis reactions. The advantage of the latent catalysts is demonstrated in the ringopening metathesis polymerization of dicyclopentadiene, where the latency of 6 assures adequate mixing of catalyst and monomer before initiation. Trapping experiments suggests that the acid converts the 18-electron complexes into their corresponding highly olefin metathesis active 14-electron benzylidenes.

Journal of Molecular Catalysis A: Chemical, 1997

NMR data for two Ru-TPPMS complexes previously described as unsaturated monomeric species have led to their reformulation as the chloro-bridged dimers [RuCl(TPPMS),(p-Cl)], (1) and [RuH(TPPMS)& p-Cl)], (2); three new water-soluble complexes OsH,(TPPMSl, (3), OsHCl(COXTPPMS), (41, and [OSCKTPPMS),(p-Cl)], (5) have been synthesized and characterized. Complexes 1-5, as well as mixtures of Ru and OS salts with TPPMS and TPPTS catalyze the hydrogenation of cinnamaldehyde under mild reaction conditions in aqueous biphasic systems; the activities and selectivities of these catalysts have been compared with those of homogeneous PPh, analogues. In general there is a clear advantage in using the aqueous biphasic mixtures over their analogous homogeneous solutions, since catalyst recovery and recycling are easy and because the regioselectivity towards the production of the (Y, P-unsaturated alcohol is considerably enhanced on going from the homogeneous PPh, to the biphasic TPPMS and TPPTS systems, particularly in the case of Ru.

Inorganica Chimica Acta, 2003

The novel diamine Á/bis(ether Á/phosphine)ruthenium(II) complexes Cl 2 Ru(h 1 -Ph 2 PCH 2 Ã/CH 2 OCH 3 ) 2 (diamine) 2 (3L 1 Á/3L 11 ) have been obtained by reaction of equimolar amounts of Cl 2 Ru(PS/O) 2 (2) with the respective diamines L 1 Á/L 11 in good yields. X-ray structural investigations of 3L 2 and 3L 8 show monoclinic unit cells with the space group P 2 1 /c . The octahedrally coordinated ruthenium atoms have each two trans-chlorides and cis -phosphines which is in agreement with NMR studies in solution. With the exception of 3L 4 all mentioned ruthenium complexes are highly catalytically active in the hydrogenation of the a,b-unsaturated ketone trans -4-phenyl-3-butene-2-one. In most cases the conversions and selectivities toward the formation of the unsaturated alcohol trans -4-phenyl-3-butene-2-ol were 100% with high turnover frequencies under mild conditions. #

Advanced Synthesis & Catalysis, 2002

Reaction of RuHCl(PPh 3 ) 3 4 with 3-chloro-3-methyl-1-butyne effects transformation into RuCl 2 (PPh 3 ) 2 ( CHCH CMe 2 ) 1c. Starting 4 is available commercially, or via quantitative reaction of RuCl 2 (PPh 3 ) 3 with one equivalent of alkali phenoxides or isopropoxides in refluxing benzene-2-propanol. Phosphane exchange between 1c and PCy 3 or 1,3-(CH 2 PCy 2 ) 2 C 6 H 4 is rapid at RT, affording RuCl 2 (PCy 3 ) 2 ( CHCH CMe 2 ) 1b or the novel alkylidene complex RuCl 2 [1,3-(CH 2 PCy 2 ) 2 C 6 H 4 ]( CHCH CMe 2 ) 7. Much slower exchange occurred on use of RuCl 2 (PCy 3 ) 2 ( CHPh) (1a) as precursor. Complex 1c is stable indefinitely (months) in the solid state at RT under N 2 , but dimerizes slowly in solution to give RuCl(PPh 3 ) 2 (m-Cl) 3 Ru(PPh 3 ) 2 ( CHCH CMe 2 ) 6a. 2,7-Dimethyl-octa-2,4,6-triene, the formal product of carbene coupling, is observed by 1 H NMR. Dimerization does not compete with phosphane exchange. A side-product arising from use of excess 3-chloro-3methyl-1-butyne in the synthesis of 1c was identified as Ru(IV) carbyne complex RuCl 3 (PPh 3 ) 2 ( CCH CMe 2 ) 5, the structure of which was confirmed by X-ray crystallography.

Journal of Organometallic Chemistry, 2005

(2) have been synthesized from reactions of [Ru(PPh 3 ) 3 Cl 2 ] with Na[BPh 4 ] and NaClO 4 AE H 2 O, respectively, in acetonitrile. The compound 1 has been structurally characterized. The geometry of this complex is that of a distorted octahedral, with cationic Ru(II) center bonded two triphenylphosphine ligands in the axial position and three acetonitrile and one chloride ligands present in the basal positions. The ruthenium compounds are catalytically active for the conversion of aldehydes and ketones to alcohols at 90°C using 2-propanol as the source of hydrogen in the presence of K 2 CO 3 .