Dicarbonylrhodium(I) complexes of pyridine alcohol ligands and their catalytic carbonylation reaction (original) (raw)
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Dicarbonylrhodium(I) complexes of functionalized pyridine ligands and their catalytic activities
Journal of Molecular Catalysis A: Chemical, 2007
Reactions of dimeric complex [Rh(CO) 2 Cl] 2 (1) with pyridine ester ligands methyl picolinate (a), methyl nicotinate (b), methyl isonicotinate (c), ethyl picolinate (d), ethyl nicotinate (e) and ethyl isonicotinate (f) in the 1:2 molar ratio afford the complexes of the type [Rh(CO) 2 ClL] (1a-f). The complexes 1a-f exhibit two equally intense ν(CO) bands in the range 1990-2091 cm −1 indicating cis-disposition of the two terminal carbonyl groups. The complexes 1a and 1d undergo partial decarbonylation reaction in solution to give the corresponding chelated monocarbonyl complexes [Rh(CO)Cl(methyl picolinate)] (1a) and [Rh(CO)Cl(ethyl picolinate)] (1d), respectively. The complexes 1a-f undergo oxidative addition reaction with different types of electrophiles like CH 3 I, C 2 H 5 I, C 6 H 5 CH 2 Cl and I 2 to yield [Rh(CO)(COCH 3)ClIL] (2a-f), [Rh(CO)(COC 2 H 5)ClIL] (3a-f), [Rh(CO)(COCH 2 C 6 H 5)Cl 2 L] (4a-f) and [Rh(CO)ClI 2 L] (5a-f) complexes, respectively. The complexes have been characterized by elemental analysis, IR and 1 H NMR spectroscopy. The time taken by the different complexes 1a-f for the completion of oxidative addition reactions of CH 3 I are different and the complex 1f took the shortest time while the complex 1b required the longest time. The catalytic activity of the complexes [Rh(CO) 2 ClL] (1) in carbonylation of methanol is higher (TON = 844-1251) than the well known [Rh(CO) 2 I 2 ] − species (TON = 653).
Inorganica Chimica Acta, 2011
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Journal of Molecular Catalysis A: Chemical, 2009
The products resulting from the progressive addition of pyridine (py) to a solution of [Rh 2 (µ-Cl) 2 (CO) 4 ] 1 have been found to depend both upon the solvent and the atmosphere (CO or N 2 ). In CH 2 Cl 2 under N 2 , cis-[Rh(CO) 2 Cl(py)] 2, [Rh(CO) 2 Cl(py) 2 ] 3 and [Rh 2 (µ-CO) 3 Cl 2 (py) 4 ] 4 were obtained successively; under CO, 4 was converted into 3 and under N 2 disproportionation of 4 slowly occurred to give 3 and trans-[Rh(CO)Cl(py) 2 ] 5 which reacted with CO to give 3. In more polar solvents (thf or MeOH), 1 reacted under N 2 to give the lightly solvent-stabilised complex [Rh(CO) 2 Cl(solv)] 6 (solv = thf a or MeOH b) and, in the presence of AgClO 4 , cis-[Rh(CO) 2 (solv) 2 ] ϩ 7 (solv = thf a or MeOH b); additionally, when solv = MeOH there was spectroscopic evidence for the formation of [Rh 2 (µ-CO) x (MeOH) y ] 2ϩ 8 (x = 2, y = 4 or x = 3, y = 6) which reacted with CO to give [Rh(CO) 2 (MeOH) 2 ] ϩ . Complex 7 reacted with py to give successively cis-[Rh(CO) 2 (py) 2 ] ϩ 9 and [Rh(CO)(py) 3 ] ϩ 10; under CO 10 was converted into 9. The stereochemistry of all the above complexes has been established through a combination of IR and multinuclear ( 13 C, 15 N, 103 Rh) NMR measurements and X-ray crystallography for 2 and 4. Analogous reactions have been carried out using trans-
Dicarbonylrhodium(I) complexes of aminophenols and their catalytic carbonylation reaction
Applied Organometallic Chemistry, 2007
The complexes [Rh(CO) 2 ClL](1), where L = 2-aminophenol (a), 3-aminophenol (b) and 4-aminophenol (c), have been synthesized and characterized. The ligands are coordinated to the metal centre through an N-donor site. The complexes 1 undergo oxidative addition (OA) reactions with various alkyl halides (RX) like CH 3 I, C 2 H 5 I and C 6 H 5 CH 2 Cl to produce Rh(III) complexes of the type [Rh(CO)(COR)XClL], where R =-CH 3 (2),-C 2 H 5 (3), X = I; R = C 6 H 5 CH 2-and X = Cl (4). The OA reaction with CH 3 I follows a two-stage kinetics and shows the order of reactivity as 1b > 1c > 1a. The minimum energy structure and Fukui function values of the complexes 1a-1c were calculated theoretically using a DND basis set with the help of Dmol 3 program to substantiate the observed local reactivity trend. The catalytic activity of the complexes 1 in carbonylation of methanol, in general, is higher (TON 1189-1456) than the species [Rh(CO) 2 I 2 ] − (TON 1159).
Dalton Transactions, 2013
The synthesis, structure determination and oxidative stability of novel Rh-NHC complexes which feature pyridine-derived ligands have been described. All complexes described herein were synthesized from common dinuclear precursors of general structure [Rh(NHC)(L)Cl] 2 , where L is a monodentate olefin. We demonstrate that the use of these precursors is critical for the formation of all complexes since related cyclooctadiene containing precursors ([Rh(NHC)(COD)Cl]) were completely unreactive under identical conditions. We further demonstrate that complexes with the general formula [Rh(NHC)(olefin)(Py)Cl] or ([Rh(NHC)(BiPy/Phen)Cl]) are extremely sensitive to oxygen, reacting initially to give an adduct with dioxygen, and then decomposing further. The series of compounds and their oxidation products gave a remarkable range of colours which may be useful in the preparation of colourometric oxygen sensors. † Electronic supplementary information (ESI) available. CCDC 886710-886713 and 886734. For ESI and crystallographic data in CIF or other electronic format see CH 3 ). Calc m/z for C 34 H 45 N 3 Rh (M − Cl): 598.26, found: 597.86. Preparation of [Rh(IPr)(Bpy)Cl] (5) Procedure (a) from [Rh(IPr)(C 2 H 4 )Cl] 2 . A solution of 2,2′bipyridine (BiPy) (7.08 mg, 0.045 mmol) in 2 mL of THF was added dropwise to a stirring solution of [Rh(IPr)(C 2 H 4 )Cl] 2 (1) (25.0 mg, 0.023 mmol) in 3 mL of THF. The reaction mixture immediately turned a deep dark green-blue colour. The
Organometallics, 2007
RhCl(COD)] 2 (COD ) 1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh 2 -(o-C 6 H 4 CHO)) (Rh/P ) 1:1) in the presence of pyridine to give an acyl hydrido species, [RhHCl(PPh 2 -(o-C 6 H 4 CO))(py) 2 ] (1). In chlorinated solvents exchange of hydride by chloride gives [RhCl 2 (PPh 2 (o-C 6 H 4 CO))(py) 2 ] (2). The reactions of 1 with PPh 3 and of 2 with biacetyl dihydrazone (bdh) gives the pyridine substitution products [RhHCl(PPh 2 (o-C 6 H 4 CO))(PPh 3 )(py)] (4) and [RhCl 2 (PPh 2 (o-C 6 H 4 CO))-(bdh)] (3), respectively. By using a 1:2 ratio of Rh to PPh 2 (o-C 6 H 4 CHO) [RhHCl(PPh 2 (o-C 6 H 4 CO))(κ 1 -PPh 2 (o-C 6 H 4 CHO))(py)] (5) with trans phosphorus atoms is formed. The aldehyde group may undergo two different reactions. In benzene 5 affords the acyl hydroxyalkyl species [RhCl(PPh 2 (o-C 6 H 4 CO))-(PPh 2 (o-C 6 H 4 CHOH))(py)] (6) with cis phosphorus atoms, via a pyridine dissociation path. 6 undergoes dehydrogenation, with H 2 evolution, to afford the diacyl derivative [RhCl(PPh 2 (o-C 6 H 4 CO)) 2 (py)] (8), which shows fluxional behavior in solution, with the values ∆H q ) 8.8 ( 0.4 kcal mol -1 and ∆S q ) -16.7 ( 1 eu. Opening of the acylphosphine chelate appears to be responsible for the fluxionality. In methanol 5 undergoes displacement of chloride by the aldehyde to afford the cationic acyl hydrido aldehyde [RhH(PPh 2 (o-C 6 H 4 CO))(κ 2 -PPh 2 (o-C 6 H 4 CHO))(py)] + (10), which can be isolated if precipitated immediately with an appropriate counterion. Longer reaction periods of 5 in methanol solution lead to a mixture of the diacyl 8 and the cationic acyl hydrido alcohol [RhH(PPh 2 (o-C 6 H 4 CO))(κ 2 -PPh 2 (o-C 6 H 4 -CH 2 OH))(py)] + (11). The spectroscopic characterization of some intermediates in this reaction evidence a bimolecular ionic mechanism as being responsible for the hydrogenation of the aldehyde with the hydroxyalkyl 6 being the source of both proton and hydride. Complex 11 can also be obtained by the reaction of 5 with NaBH 4 in methanol solution.
The Unexpected Role of CO in C À H Oxidative Addition by a Cationic Rhodium(I) Complex
The activation of strong carbon-hydrogen bonds by transition metals is one of the fundamental fields of current organometallic chemistry. This process occurs by one of several possible pathways that are generally dependant on the electron density at the metal center. [1] For electron-rich, low-valent transition metals the typical pathway for C À H cleavage is oxidative addition, which leads to the corresponding alkyl or aryl hydride complexes and is accompanied by a formal twoelectron oxidation of the metal. Transition metals that lack the electron density necessary for oxidative addition, such as early transition metals or high-valent late transition metals, can activate C À H bonds by alternative routes, namely s-bond metathesis, radical activation, 1,2-addition, and electrophilic substitution. [1] It is widely accepted that both s-bond metathesis and oxidative addition processes take place via scomplexes or agostic intermediates. [2] As far as the oxidative addition of CÀH bonds is concerned, the requirement for high electron density means that strong p-acceptor ligands, such as carbon monoxide, are normally expected to inhibit oxidative addition processes by drawing electron density away from the metal center. Herein, however, we describe an electron-poor cationic Rh I system in which addition of a CO ligand can actually promote oxidative addition of a strong C À H bond. This unique reaction pathway is supported by both experimental and theoretical evidence.