Half sandwich complexes of chalcogenated pyridine based bi-(N, S/Se) and terdentate (N, S/Se, N) ligands with (η6-benzene)ruthenium(ii): synthesis, structure and catalysis of transfer hydrogenation of ketones and oxidation of alcohols (original) (raw)
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European Journal of Inorganic Chemistry, 2018
A series of cationic [Ru(L)(PPh3)2Cl] + (1-3) and neutral [Ru(L)(PPh3)Cl2] (4-6) Ru(II) complexes have been synthesized by reacting [RuCl2(PPh3)2] with 4'-(aryl)-2,2':6',2''-terpyridyl based ligands (L1-L3) by varying the aryl groups (tolyl, phenyl and 4fluorophenyl). The synthesized Ru(II) complexes have been unambiguously characterized by various spectroscopic tools such as FTIR and multinuclear NMR as well as HRMS analyses. The neutral complexes (4-6) have also been structurally characterized by single crystal X-ray diffraction studies. Photophysical and electrochemical studies of the Ru(II) complexes have been carried out to understand the substituent effect of the 4′-aryl group of the ligands L1-L3. These Ru(II) complexes show good catalytic activity in transfer hydrogenation (TH) of ketones with a wide substrates scope in refluxing isopropanol. Optimization study reveals that the neutral Ru(II) complexes act as better catalysts over cationic Ru(II) complexes for TH reactions. Finally, [Ru(L1)(PPh3)2H] + (7) having [Ru(II)-H] functionality has been successfully synthesized, isolated and proposed as the catalytically active species. The controlled experiment by [Ru(II)-H] complex in the absence of base has been carried out to establish the mechanism of catalytic TH of ketones.
Inorganic Chemistry Communications, 2010
2,6-Bis((phenylseleno)methyl)pyridine] (L) a (Se, N, Se) pincer ligand synthesized by reacting PhSe − (in situ generated) with 2,6-bis(chloromethyl)pyridine reacts with [{(η 6 -C 6 H 6 )RuCl(μ-Cl)} 2 ] (2:1 molar ratio) by preferential substitution of ring resulting in the first Ru-(Se, N, Se) pincer ligand complex, mer-[Ru(CH 3 CN) 2 Cl(L)] [PF 6 ](1).H 2 O. Similar reaction in 4:1 molar ratio results in mer-[Ru(L) 2 ][ClO 4 ] 2 . The 1 H, 13 C{ 1 H} and 77 Se{ 1 H} NMR spectra of L, 1 and 2 were found characteristic. The single crystal structures of 1 and 2 were studied by X-ray crystallography. The geometry of Ru in both the complexes is distorted octahedral. The Ru-Se distances are in the ranges 2.4412(16)-2.4522(16) and 2.4583(14)-2.4707(15) Å´respectively for 1 and 2. The structural solutions from the crystal data in case of 2, due to inferior quality of its crystals, are suitable for supporting bonding mode of L with Ru(II) only. The 1 shows high catalytic activity for oxidation of primary and secondary alcohols (TON up to 9.7 × 10 4 ).
Applied Organometallic Chemistry, 2012
Ru(II) complexes of the general formula [RuCl 2 ('NNN _ _ ')(L)] (1: 'N = N b , L = MeOH; 2: 'N = N b , L = CH 3 CN; 3: 'N = N d , L = CH 3 CN; 4: 'N = N p , L = CH 3 CN), [Ru(p-cymene)(NN _ a-b)Cl]Cl (5a: N N a = 2,2´-bipyridine; 5b: N N b = 4,4 0-dimethyl-2,2 0-bipyridine), [Ru('NNN _ _ ') (NN _ a-b)Cl]Cl (6a: 'N = N b , NN _ a = 2,2 0-bipyridine; 6b: 'N = N b , NN _ b = 4,4 0-dimethyl-2,2 0-bipyridine; 7a: 'N = N d , NN _ a = 2,2 0-bipyridine; 7b: 'N = N d , NN _ b = 4,4 0-dimethyl-2,2 0-bipyridine; 8a: 'N = N p , NN _ a = 2,2 0-bipyridine; 8b: 'N = N p , NN _ b = 4,4 0-dimethyl-2,2 0-bipyridine) and [Ru(' NNN _ _ ')(NN _ a)Cl]BF 4 (9a: 'N = N b ; NN _ a = 2,2 0-bipyridine) were synthesized from the corresponding [RuCl 2 (p-cymene)] 2 dimer, 'NNN _ _ ' and NN _ a-b ligands. The compounds were characterized by elemental analysis, IR and NMR. Complex 9a was studied by X-ray diffraction, confirming its cationic-mononuclear [RuCl(b NNN _ _ b)(NN _ a)] + nature. The synthesized Ru(II) complexes (1-8) were employed as catalysts for the transfer hydrogenation of ketones to secondary alcohols in the presence of KOH using 2-propanol as a hydrogen source at 82 C. The rates of the transfer hydrogenation reactions strongly depended on the type of NNN
Organometallics, 2011
Pyridine-based tridentate triamine compounds ( 0 N kNkN 0 ) are very attractive ligands for coordination chemistry, and their transition-metal (TM) complexes have been successfully applied in homogeneous catalysis. 1À28 Although examples of the related Ru complexes are scarce, such complexes recently gained attention due to their use in catalysis and in other chemical applications. 29À48 For example, d N k N k N d -containing neutral Ru(II) complexes of the general formula [RuCl 2 ( d N k N k N d )L] (L = monodentate ligands such as CH 3 CN, PPh 3 , and CO) are effective catalysts for the transfer hydrogenation (TH) of ketones. 29,32 During the preparation of this paper, a report on unsymmetrical and asymmetrical [RuCl( 0 N k N k N 00 )(PPh 3 ) 2 ]Cl complexes which showed excellent TH activity has appeared. On the other hand, Ru(II) complexes bearing chelating amine ligands such as N-sulfonated 1,2-diamines have been successfully used in the TH of acetophenone by Noyori and others. 50À63 However, in spite of these developments, there is still demand for stable and easily handled complexes prepared from cheap starting materials which make them preferred catalyst precursors. In comparison with the extensive chemistry of sulfonated 1,2diamines, little research has been performed on pyridylsulfonamide compounds of the type C 5 H 4 NCH 2 NHSO 2 Ar, which are versatile bidentate ligands due to their ease of synthesis and variability of Ar groups. 64À68 Neutral sulfonamide ligands are expected to be poor ligands. Thus, the pyridyl-2-alkylsulfonamides generally coordinate to the metal center through the pyridyl nitrogen atom and the deprotonated nitrogen of the sulfonamide group. 69 However, Soltani et al. have recently shown that cationic Ir complexes containing neutral sulfonamide ligands are active catalysts for the TH of acetophenone derivatives in water. 70 More recently, Baratte and co-workers have shown that Ru(II) complexes containing nonsulfonated (2-aminomethyl)pyridine ligands display excellent catalytic activity in the TH of ketones. With the aim of contributing to the understanding of how geometric and electronic factors imposed by a combination of mixed tri-and bidentate ligands influence the catalyst performance, herein a series of novel Ru(II) complexes (1À10) were characterized and employed as catalysts for the TH of ketones.
Organometallics, 2001
DMSO)] (6b) in good yield. The crystal structures of 1a and 5b have been determined by X-ray diffraction. Compound 2a, containing two labile DMSO ligands, has been used as a precursor to synthesize the derivatives [RuCl 2 (κ 2 -P,N-2-Ph 2 PC 6 H 4 CHdN t Bu)L] [L ) PPh 3 (1a); PPh 2 Me (3a); PMe 2 Ph (4a)]. Complexes 1a, 2a, 5b, and 6b are active in catalytic transfer hydrogenation of aryl-alkyl and dialkyl ketones in propan-2-ol. The five-coordinate complexes 1a, 5b, and 6b show higher catalytic activity than the octahedral complex 2a. Complexes 1a and 5b are more efficient catalysts than the precursor complex [RuCl 2 (PPh 3 ) 3 ]. For the best catalyst, 1a, yields up to 91% were obtained and turnover frequencies may be as high as 41 400 h -1 .
Canadian Journal of Chemistry, 2018
A new (NNN) tridentate ligand was prepared, and its ability to coordinate ruthenium(II) was evaluated. The presence of different functional groups on the ligand allows bi- or tri-coordinated complexes to be obtained depending on complexation conditions. The catalytic activity of both bidentate and tridentate complexes was studied in asymmetric transfer hydrogenation of different aryl ketones, showing a comparable behavior of the two complexes in terms of efficiency and stereoselectivity.
Organometallics, 2021
The complex [Cp*RuCl(COD)] reacts with LH 2 Cl 2 (L = bis(3-methylimidazol-2-ylidene)) and LiBu n in tetrahydrofuran at 65°C furnishing the bis-carbene derivative [Cp*RuCl(L)] (2). This compound reacts with NaBPh 4 in MeOH under dinitrogen to yield the labile dinitrogen-bridged complex [{Cp*Ru(L)} 2 (μ-N 2)][BPh 4 ] 2 (4). The dinitrogen ligand in 4 is readily replaced by a series of donor molecules leading to the corresponding cationic complexes [Cp*Ru(X)(L)][BPh 4 ] (X = MeCN 3, H 2 6, C 2 H 4 8a, CH 2 CHCOOMe 8b, CHPh 9). Attempts to recrystallize 4 from MeNO 2 /EtOH solutions led to the isolation of the nitrosyl derivative [Cp*Ru(NO)(L)][BPh 4 ] 2 (5), which was structurally characterized. The allenylidene complex [Cp*RuCC CPh 2 (L)][BPh 4 ] (10) was also obtained, and it was prepared by reaction of 2 with HCCC(OH)Ph 2 and NaBPh 4 in MeOH at 60°C. Complexes 3, 4, and 6 are efficient catalyst precursors for the transfer hydrogenation of a broad range of ketones. The dihydrogen complex 6 has proven particularly effective, reaching TOF values up to 455 h −1 at catalyst loadings of 0.1% mol, with a high functional group tolerance on the reduction of a broad scope of aryl and aliphatic ketones to yield the corresponding alcohols.
Polyhedron, 2012
The ruthenium(II) complexes [RuH(CO)(6-OH-py-2-COO)(PPh 3) 2 ] (1) and [Ru(3-OH-py-2-COO) 2 (PPh 3) 2 ] (2) have been prepared in the reactions of [RuHCl(CO)(PPh 3) 3 ] and [RuCl 2 (PPh 3) 3 ] with 6-hydroxy-and 3-hydroxypyridine-2-carboxylic acids. The complexes have been characterized by IR, UV-Vis, NMR spectroscopy and X-ray crystallography. Based on the crystal structures, computational investigations were carried out in order to determine the electronic structures of the complexes. The electronic spectra were calculated with the use of time-dependent DFT methods, and correlated with the molecular orbitals of the complexes. The emission properties of the complexes have been examined and quantum efficiencies equal to 0.084 for the hydride carbonyl complex (1) and 0.046 for complex (2) have been determined. The catalytic activity in the reaction of the double bond migration in 4-allyloxybutan-1-ol for both the complexes was tested. Under properly selected reaction conditions, complex (1) selectively catalyzes double bond migration leading to 1-propenyloxyalcohol.
Organometallics, 2006
Terdentate ruthenium(II) complexes of general formula RuX(CNN)(dppb) (X) chloride, hydride, alkoxide; dppb) Ph 2 P(CH 2) 4 PPh 2), where CNN is a deprotonated 2-aminomethyl-6-arylpyridine ligand, have been prepared. The orthometalated derivative RuCl(b)(dppb) (1) has been obtained by reaction of RuCl 2 (PPh 3)(dppb) with N,N-dimethyl-2-aminomethyl-6-(4-methylphenyl)pyridine (Hb) in 2-propanol and in the presence of triethylamine by elimination of PPh 3 and HCl. Similarly, RuCl(a)(dppb) (2) and the chiral analogue RuCl(c)(dppb) (3), containing primary amine ligands, have been isolated starting from 2-aminomethyl-6-(4-methylphenyl)pyridine (Ha) and (R)-2,2-dimethyl-1-(6-phenylpyridin-2-yl)propylamine (Hc), respectively. The synthesis of the functionalized pyridines Ha-Hc is here described, whereas the crystal structure of 3 has been determined through an X-ray diffraction experiment. Treatment of 1-3 with sodium or potassium isopropoxide gives the corresponding hydrides RuH(b)(dppb) (4), RuH(a)(dppb) (5), and RuH(c)(dppb) (6) from the ruthenium isopropoxide complexes, via a-H elimination process. Studies in solution show that the isopropoxides bearing a NH donor group are in equilibrium with the corresponding hydrides (5 and 6). Reaction of 5 with benzophenone leads to the alkoxide Ru(OCHPh 2)(a)(dppb) (7), which has been proven to interact with benzhydrol in C 6 D 6 , leading to the adduct 7‚(HOCHPh 2), the alkoxide ligand, and the alcohol being in rapid exchange. Complexes 2 and 3 display a remarkable high catalytic activity for the transfer hydrogenation of ketones to alcohol in 2-propanol using a very small amount of catalyst. With the chiral complex 3 (0.005 mol %) methyl-aryl ketones can be quickly reduced (TOF ranging from 5.4 × 10 5 to 1.4 × 10 6 h-1) with an enatiomeric excess up to 88%.