Rhenium complexes in homogeneous hydrogen evolution (original) (raw)
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Homogeneous hydrogenations and related reductive reactions catalyzed by rhenium complexes
2013
Chapter 1 General Introduction Homogeneous Hydrogenations and Related Reductive Reactions Catalyzed by Rhenium Complexes hydrogen molecule can coordinate to a metal centre in a side-on fashion (ɳ 2) primarily via donation of its two σ electrons to a vacant d orbital of the metal to form a stable dihydrogen complex. The first structurally characterized dihydrogen metal complex W(CO) 3 (Pi-Pr 3) 2 (H 2) was discovered in 1983 by Kubas and co-workers. 2 The stabilization of ɳ 2-H 2 complexes arises from the back donation of electrons from a filled metal d orbital of metal to the σ* anti bonding orbital of H 2. The back donation is analogous to that of Dewar-Chatt-Duncanson model for olefin coordination (Figure. 1.1). 3 Homogeneous Hydrogenations and Related Reductive Reactions Catalyzed by Rhenium Complexes 1.4. Hydrogenation of Various Functional Groups 1.4.1. Hydrogenation of Alkenes The first documented example of homogeneous hydrogenation by metal compounds was reported by Calvin in 1938, reporting that quinoline solutions of copper acetate, at 100 °C, were found to be active catalysts for the hydrogenation of quinines 7. The most significant advances in homogeneous hydrogenation catalysis have been the discovery of rhodium phosphine complex [RhH(CO)(PPh 3) 3 ] by Bath and Vaska in 1963. 8 Later in few years, the catalytic activity of this complex for hydrogenation, isomerisation and hydroformylation reactions were reported by Wilkinson and co-workers. 9 The most important rhodium catalyst, the [RhCl(PPh 3) 3 ] complex, was reported during the period 1965-1966 independently by Wilkinson, Bennett and Vaska. 10 Wilkinson and co-workers extensively studied the remarkable catalytic properties of this complex, which is usually known as Wilkinson's catalyst. This turned out to be the first practical hydrogenation system working usually at room temperature and atmospheric pressure of hydrogen. During this time [IrCl(CO)(PPh 3) 2 ] was discovered by Vaska, called Vaska's complex, 11 which was susceptible for oxidative addition-reductive elimination with dihydrogen to form [IrH 2 Cl(CO)(PPh 3) 2 ] whose activity was very weak. Also, the iridium analogue of Wilkinson catalyst, [IrCl(PPh 3) 3 ] was also weakly active. 10b The almost inactivity of these complexes towards hydrogenation were due to inability to form vacant sites by dissociation of PPh 3 ligand from [IrH 2 (PPh 3) 3 ]. For the two decades, rhodium chemistry dominated in the field of hydrogenation, due to the remarkable investigations of Wilkinson, Kagan, Osborn, and Knowles. 12 Ruthenium was slowly developing during these period starting with studies by Halpern 6,13 and Wilkinson. 6,14 In 1965, Wilkinson and co-workers found that the reaction of RuCl 2 (PPh 3) 3 with hydrogen and a base gave the hydride complex RuHCl(PPh 3) 3 , a very active catalyst for hydrogenation. 13 This monohydride complex is formed by the abstraction of proton from the Homogeneous Hydrogenations and Related Reductive Reactions Catalyzed by Rhenium Complexes
Organometallics, 1995
Reaction of Re(C0)3(PPh3)&1 with MeC(CH2PPh2)3 (triphos) gives (triphos)Re(CO)zCl(l) which is converted to the hydride (triphos)Re(CO)aH (2) by treatment with LiAlh. An X-ray diffraction analysis of 2 shows that the rhenium atom is octahedrally coordinated by triphos, which occupies a triangular face of the coordination polyhedron, by two carbonyl groups and by a terminal hydride ligand. Treatment of 2 with Me30BF4 results in the evolution of methane and formation of the unsaturated complex [(triphos)Re(C0)2lBF4 (4) which is stabilized by a n agostic interaction between the rhenium center and a phenyl C-H bond of triphos. The q2-H2 complex [(triphos)Re(CO)2(Hz)IBF4 (3) is obtained either by protonation of 2 or by addition of H2 to the agostic complex 4. The presence of a n intact dihydrogen ligand in 3 is unambiguosly shown by 'H NMR spectroscopy [TI,,, = 8.6 ms (CD2C12, 300 MHz,-58 "C); JHD of 30.8 Hz for the monodeuteriated isotopomer [(triphos)Re(C0)2(HD)]-BF4 (3-ddI. Vinylidene derivatives of the formula [(triphos)Re(CO)~({C=C(H)R}lBP~ (R = Ph, 8; C02Et, 9; CsH13, 10) are obtained by reaction of either the q2-H2 complex 3 or the agostic complex 4 with terminal alkynes in the presence of N a B P b. The preference for the coordination of neutral groups a t rhenium in the [(triphos)Re(CO)zl+ fragment follows the order N2 C-H(agostic, < H2 < H C W R < CH3CN < CO. All the reactions described have been carried out in tetrahydrofuran or dichloromethane. formation of linear carbon chains C, (n = 1-5) between
Nanomaterials and Energy, 2013
Rhenium and rhodium complexes with bipyridyl ligands have been proven to be efficient homogeneous catalysts in the field of carbon dioxide and proton reduction. In this work, the authors provide several examples of these compounds with modified ligand structures and discuss their electro- and photo-catalytic capabilities toward carbon dioxide reduction and NAD+ cofactor regeneration. The electrocatalysis is studied by cyclic voltammetry and controlled potential electrolysis for determining the over potentials, Faradaic efficiencies and reaction rate constants. In addition, the photophysics of these compounds is discussed based on UV-visible absorption, photoluminescence and infrared absorption spectroscopy. Results on comparing two different rhenium catalysts for homogeneous photocatalytic carbon dioxide reduction using a sacrificial electron donor are reported.
Inorganic Chemistry, 1980
4 5 0 5 0 0 550 6 0 0 6 5 0 m) Registry No. I, 392-74-5; 11, 28563-38-4; 111, 71141-39-4; IV, 73746-85-7; Ru(bpy)2(4,4'-bpyMe)?+, 73746-86-8; ( d t~)~, 97-77-8. 40898-92-8; R~(bpy),~', 15158-62-0; Ru(bpy)j+, 56977-24-3; RU-(bpy)z(CN)z-, 73746-84-6; Ru(~,~'-[(CH~)~CHOOC]~~P~)~+, (29) Ishitani, A.; Kuwana, K.; Tsubomura, M.; Nagakura, S. Bull. Chem.
Polyhedron, 1990
The rhenium(V) complex [Re0(02C6H,&J-has been synthesized by reaction of [ReOCl,(PPh,),] with excess catechol in methanol in the presence of triethylamine under N2. If the reaction is carried out in air the rhenium(VI1) complexes [Re02(0,C,H,R,)2]-(R = H, Bu') can be isolated with a range of cations. Cyclic voltages coupled with convolution analysis showed that the rhenium(VI1) complexes undergo a reversible diffusion-controlled one-electron reduction. The X-ray crystal structure of the rhenium(VII) derivative with R = H revealed a distorted octahedral geometry with cis-0x0 groups. Catechol complexes are well known for most of the transition elements, including iron, molybdenum, osmium, manganese and chromium and a comprehensive review has appeared.' The recent research effort in this area has in part been due to the established wide occurrence of catechol-based metal ion siderophores in biological systems. However, cat-echo1 complexes are also of intrinsic interest from the standpoint-of their redox chemistry. Catecholate? ligands are suspect in Jorgensen's classification and redox reactions may occur either at the metal centre or within the catecholate ligand. We are currently interested in the chemistry of rhenium due to its close analogy with technetium which is used extensively as a radionuclide imaging agent. Recently some six-coordinate cathecholate complexes of rhenium of the type [Re(02C,H4),J2-were *Authors to whom ux-respondence. should be addressed. f We have adopted previously suggested nomenclature in using the term catecholato-complexes as X-ray crystal structural and spectroscopic data are consistent with the dianionic bonding mode.
Bioconjugate Chemistry, 2005
Development of new radiopharmaceuticals based on rhenium-188 depends on finding appropriate ligands able to give complexes with high in vivo stability. Rhenium(III) mixed-ligand complexes with tetradentate/monodentate (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;4 + 1&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;) coordination of the general formula [Re(NS(3))(PRR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)] (NS(3) = tris(2-mercaptoethyl)amine and derivatives thereof, PRR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; = phosphorus(III) ligands) appear to be among the promising tools to achieve this goal. According to this approach, we synthesized and characterized a series of rhenium model complexes. In vitro stabilities of the corresponding rhenium-188 complexes were determined by incubating 2-3 MBq or alternatively 37 MBq of the complexes in phosphate buffer, human plasma, and rat plasma, respectively, at 22 degrees C or 37 degrees C, followed by checking the amount of (188)ReO(4)(-) formed after 1 h, 24, and 48 h by thin-layer chromatography. The rate of perrhenate formation varied over a wide range, depending primarily on the nature of the phosphorus(III) ligand. Physicochemical parameters of the corresponding nonradioactive rhenium complexes were analyzed in detail to find out the factors influencing their different stability and furthermore to design new substitution-inert &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;4 + 1&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; complexes. Tolman&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s cone angle of phosphorus(III) ligands and the lipophilic character of the inner coordination sphere were found to be crucial factors to build up stable rhenium &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;4 + 1&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; complexes. Additional information useful to describe electronic and steric properties of these compounds were selected from electronic spectra (wavelength of the Re--&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;S charge-transfer band), cyclovoltammetric measurements (E degrees of the Re(III)/Re(IV) couple), and NMR investigations ((31)P chemical shift of coordinated P(III) ligands).
Inorganic Chemistry, 1992
The rhenium(V) oxo oxalate complex (HBpz')ReO(CzO4) (HBpz3 = hydridotris( 1-pyrazoly1)borato) has been synthesized in three steps from potassium perrhenate. It has been characterized spectroscopically and its molecular structure determined by X-ray crystallography. When irradiated with UV light, the oxo oxalate complex undergoes an internal redox reaction, predominantly losing carbon dioxide and generating a reactive rhenium complex. The characterization of the transient photoproduct as the rhenium(II1) oxo complex (HBpz3)Re(O) is inferred from its reactions with trapping reagents: for example, photolysis in the presence of phenanthrenequinone gives a rhenium-(V) oxo catecholate complex in good yield. (HBpz')Re(O) also reacts with 02, yielding the rhenium(VI1) complex (HBpz3)Re03, formally the result of four-electron oxidation. Labeling studies show that only one oxygen atom in the product comes from 02, with the second deriving from an oxalate ligand. That unimolecular four-electron reduction of oxygen does not occur readily in this system, despite its great exothermicity, may be due to a general symmetry-imposed barrier to cleavageof O2 at a single metal center. Crystal data for HB~Z~)R~O(C~~~).O.~C~ a = 8.082 (2) A, b = 9.125 (3) A, c = 13.219 (3) A, a = 84.03 (2)O, / 3 = 74.26 (2)O, y = 72.47 (2)O, triclinic, Pi, z = 2.