Rhodium Coordination Research Articles

Unlocking catalytic potential: a rhodium(II)-based coordination polymer for efficient carbene transfer reactions with donor/acceptor diazoalkanes.

Herein, we report the use of a molecular-defined rhodium(II) coordination polymer (Rh-CP) as a heterogeneous, recyclable catalyst in carbene transfer reactions. We showcase the application of this heterogeneous catalyst in a range of carbene transfer reactions and conclude with the functionalization of natural products and drug molecules.

Structure and bonding in rhodium coordination compounds: a 103Rh solid-state NMR and relativistic DFT study.

This study demonstrates the application of 103Rh solid-state NMR (SSNMR) spectroscopy to inorganic and organometallic coordination compounds, in combination with relativistic density functional theory (DFT) calculations of 103Rh chemical shift tensors and their analysis with natural bond orbital (NBO) and natural localized molecular orbital (NLMO) protocols, to develop correlations between 103Rh chemical shift tensors, molecular structure, and Rh-ligand bonding. 103Rh is one of the least receptive NMR nuclides, and consequently, there are very few reports in the literature. We introduce robust 103Rh SSNMR protocols for stationary samples, which use the broadband adiabatic inversion-cross polarization (BRAIN-CP) pulse sequence and wideband uniform-rate smooth-truncation (WURST) pulses for excitation, refocusing, and polarization transfer, and demonstrate the acquisition of 103Rh SSNMR spectra of unprecedented signal-to-noise and uniformity. The 103Rh chemical shift tensors determined from these spectra are complemented by NBO/NLMO analyses of contributions of individual orbitals to the 103Rh magnetic shielding tensors to understand their relationship to structure and bonding. Finally, we discuss the potential for these experimental and theoretical protocols for investigating a wide range of materials containing the platinum group elements.

Planar Chiral Rhodium Complex Based on the Tetrahydrofluorenyl Core for Enantioselective Catalysis.

A simple four-step route to a chiral tetrahydrofluorenyl rhodium catalyst from naturally occurring (-)-α-pinene was developed. Our approach does not use multistep and time-consuming procedures such as chiral HPLC or diastereomeric resolution. The key to success lies in the face-selective coordination of rhodium to the sterically hindered tetrahydrofluorenyl ligand, giving only one diastereomeric complex. This catalyst proved to be highly efficient for asymmetric C-H annulation of aryl hydroxamates with alkenes (yield up to 95%, 91% ee) at low loading (up to 0.4 mol % based on Rh).

1,4-Phenylene incorporated decaphyrin tetrarhodium(I) complex: Synthesis, structures, and chiroptical properties

1,4-Phenylene-incorporated decaphyrin(1.0.1.0.0.1.0.1.0.0) 1 has been previously synthesized and optically resolved in the free-base form; however, it undergoes racemization at elevated temperature. In this study, we fixed the figure-of-eight conformation by means of rhodium(I) coordination. The resulting tetranuclear Rh(I) complex 1-Rh[Formula: see text], which is scarcely reported to date, exhibited considerable conformational stability. Accordingly, it could be readily resolved by high-performance liquid chromatography (HPLC) on a chiral stationary phase, and no racemization was observed even at 110[Formula: see text]C. Importantly, the tetranuclear porphyrinoid complex bearing a unique edge-to-edge alignment of the two 1,4-phenylene spacers revealed a relatively large molar circular dichroism (CD) with an absorption dissymmetry factor ([Formula: see text] of 0.018. While a two-fold larger [Formula: see text] of up to 0.036 was seen for the structural congener 1, wherein the 1,4-phenylene spacers adopt a face-to-face orientation. Thus, it serves to be an attractive basis to explore the structural effect on the chiroptical properties of the expanded porphyrinoid.

Two Rhodium(III) Ions Confined in a [18]Porphyrin Frame: 5,10,15,20-Tetraaryl-21,23-Dirhodaporphyrin.

Tetraaryl‐21,23‐dirhodaporphyrin and a series of related monorhodaporphyrins have been obtained by tellurium‐to‐rhodium exchange in a reaction of tetraaryl‐21,23‐ditelluraporphyrin with [RhCl(CO)2]2. These organometallic metallaporphyrins contain rhodium(III) centers embedded in rhodacyclopentadiene rings, incorporated within the porphyrin frames. The skeletons of 21,23‐dirhodaporphyrin and 21‐rhoda‐23‐telluraporphyrin are strongly deformed in‐plane from the rectangular shape typical for porphyrins, due to rhodium(III) coordination preferences, the large size of the two core atoms, and the porphyrin skeleton constrains. These two metallaporphyrins exhibit fluxional behavior, as studied by 1H NMR and DFT, involving the in‐plane motion and the switch of the rhodium center(s) between two nitrogen donors. A side product detected in the reaction mixture, 21‐oxa‐23‐rhodaporphyrin, results from tellurium‐to‐oxygen exchange, occurring in parallel to the tellurium‐to‐rhodium exchange. The reaction paths and mechanisms have been analyzed. The title 21,23‐dirhodaporphyrin contains a bridged bimetallic unit, Rh2Cl2, in the center of the macrocycle, with two rhodium(III) ions lying approximately in the plane of the porphyrinoid skeleton. The geometry of the implanted Rh2Cl2 unit is affected by macrocyclic constrains.

Rhodium-Catalyzed Regioselective Double Annulation of Enaminones with Propargyl Alcohols: Rapid Access to Arylnapthalene Lignan Derivatives.

We present here a rhodium-catalyzed oxidative three-point double annulation of enaminones with propargylic alcohols via a C-H and a C-N bond activation to access arylnaphthalene-based lignan derivatives. The key step in the reaction is the regioselective insertion of propargylic alcohol into the rhoda-cycle, a result of hydroxyl rhodium coordination. Necessary control experiments and KIE studies were conducted to determine the mechanism.

Shape-Programmable Architectured Hydrogels Sensitive to Ultrasound.

On-demand motion of highly swollen polymer systems can be triggered by changes in pH, ion concentrations, or by heat. Here, shape-programmable, architectured hydrogels are introduced, which respond to ultrasonic-cavitation-based mechanical forces (CMF) by directed macroscopic movements. The concept is the implementation and sequential coupling of multiple functions (swellability in water, sensitivity to ultrasound, shape programmability, and shape-memory) in a semi-interpenetrating polymer network (s-IPN). The semi-IPN-based hydrogels are designed to function through rhodium coordination (Rh-s-IPNH). These coordination bonds act as temporary crosslinks. The porous hydrogels with coordination bonds (degree of swelling from 300 ± 10 to 680 ± 60) exhibit tensile strength σmax up to 250 ± 60 kPa. Shape fixity ratios up to 90% and shape recovery ratios up to 94% are reached. Potential applications are switches or mechanosensors.

Synthesis and rhodium complexes of macrocyclic PNP and PONOP pincer ligands

The synthesis of macrocyclic variants of commonly employed phosphine-based pincer ligands derived from lutidine (PNP-14) and 2,6-dihydroxypyridine (PONOP-14) is described, where the P-donors are trans-substituted with a tetradecamethylene linker. This was accomplished using an eight-step procedure involving borane protection, ring-closing olefin metathesis, chromatographic separation from the cis-substituted diastereomers, and borane deprotection. The rhodium coordination chemistry of these ligands has been explored, aided by the facile synthesis of 2,2'-biphenyl (biph) adducts [Rh(PNP-14)(biph)][BArF4] and [Rh(PONOP-14)(biph)][BArF4] (ArF = 3,5-(CF3)2C6H3). Subsequent hydrogenolysis enabled generation of dihydrogen, ethylene and carbonyl derivatives; notably the ν(CO) bands of the carbonyl complexes provide a means to compare the donor properties of the new pincer ligands with established acyclic congeners.

Mechanisms of Rh-Catalyzed Oxyaminofluorination and Oxyaminotrifluoromethylthiolation of Diazocarbonyl Compounds with Electrophilic Reagents.

Density functional theory calculations were performed to study the detailed reaction mechanisms of rhodium-catalyzed oxyaminofluorination and oxyaminotrifluoromethylthiolation of diazocarbonyl compounds with electrophilic N-F and N-SCF3-based reagents. The calculations show that the operating mechanisms for the two reactions are identical. The catalytic cycle starts with N2 dissociation to provide a rhodium-carbene intermediate, followed by nucleophilic attack of tetrahydrofuran on the carbene and a rhodium coordination change generating a rhodium-enolate intermediate. Subsequent electrophilic attack introduces the fluorine or the SCF3 moiety, and it is followed by nucleophilic attack of the remaining amino group to yield the final product.

Synthesis of Heterobimetallic Complexes by Coordination of Rhodium(III) and Iridium(III) Poly-N,O-NHC Complexes to Silver(I), Copper(II), and Zinc(II)

The reaction of [RhCl2(Cp*)]2 with 2-trimethylsiloxyphenyl isocyanide (1) led to the mononuclear diisocyanide complex [RhCl(Cp*)(1)2]. Cleavage of the Si–O bonds of the coordinated isocyanide ligands with a catalytic amount of KF and H2O gave the neutral rhodium(III) complex [RhCl(Cp*)(NH,O-NHC)(N,O-NHC)] ([2]) bearing a C2-metalated N,O-benzoxazolinato ligand and an NH,O-benzoxazolin-2-ylidene ligand. In the presence of AgBF4 the same reaction sequence with [MCl2(Cp*)]2 (M = Rh, Ir) and 1 led to the removal of all halogeno ligands and formation of the complexes [M(Cp*)(NH,O-NHC)(N,O-NHC)2] (M = Rh, [3]; M = Ir, [4]) bearing one C-metalated NH,O-NHC benzoxazolin-2-ylidene and two C-metalated N,O-benzoxazolinato ligands. Deprotonation of the remaining N–H function in complexes [3] and [4] generated complexes with three amido donor functions which act as tripodal metalloligands for the coordination to additional transition metals such as AgI, CuII, and ZnII, thus allowing the preparation of the polynuclear ...

Pyridine Functionalized N-Heterocyclic Silane Complexes of Iridium and Rhodium–An Unexpected Change in Coordination

A new pyridine functionalized N-heterocyclic silane with ambident reactivity as a ligand has been synthesized and characterized by NMR spectroscopy (1H, 13C{1H}, 29Si), mass spectrometry, elemental analysis, and X-ray crystallography. This ligand reacts with iridium and rhodium cod precursors (cod = 1,5-cyclooctadiene) to yield two new complexes that possess divergent, and unexpected, binding properties. In particular, no oxidative addition occurs at the intraligand Si-H unit. With the iridium(I) center, the ligand acts as a tertiary amino-pyridine chelator, whereas coordination of rhodium(I) to the ligand occurs with arene π-complexation on an opposite side. The latter interaction yields an unprecedented, electronically induced, coordination change at the silicon center over a long spatial distance. The new iridium and rhodium compounds are of high interest as they provide two potentially different reactions sites in one complex and as these sorts of complexes are known to activate small molecules like d...

Kinetics and Thermodynamics of Non-Canonical DNA

Many native nucleic acid hairpins contain various non-canonical structures, including mismatches, bubbles and loops. The thermodynamic landscape of these hairpins containing these motifs are not well understood. We combine optical tweezers with an energy based model to reconstruct the energy landscape for DNA hairpin unfolding. Overall hairpin stability, and the unfolding kinetics show the destabilizing effects of non-canonical elements in DNA hairpin structure. Finally, the stabilizing effect of the rhodium coordination complex [Rh(bpy)2(chrysi)]3+ is probed. Rhodium chrysi preferentially binds to defects and mismatches in hairpin stems, enhancing duplex stability. Rhodium chrysi binding thus allows interrupted hairpins to resemble fully formed ones.

Silicon‐Tin‐Ordering in RE3Rh9Si2Sn3 (RE = Y, Sm, Gd – Lu)

AbstractThe quaternary intermetallic compounds RE3Rh9Si2Sn3 (RE = Y, Sm, Gd – Lu) were obtained from the elements by arc‐melting and investigated by powder X‐ray diffraction. Needle‐shaped single crystals of Ho3Rh9Si2Sn3 and Lu3Rh9Si2Sn3 were grown in bismuth fluxes and their structures were refined from single‐crystal X‐ray diffractometer data: P$\bar{6}$2m, a = 968.3(2), c = 345.6(1) pm, wR2 = 0.0278, 426 F2 values, 22 variables for Ho3Rh9Si2Sn3, and a = 962.4(2), c = 343.1(2) pm, wR2 = 0.0260, 501 F2 values, 23 variables for Lu3Rh9Si2Sn3. The phases RE3Rh9Si2Sn3 adopt a new simple structure type with complete silicon‐tin ordering. The silicon atoms have trigonal prismatic rhodium coordination (239 pm Si–Rh in Ho3Rh9Si2Sn3) and the tin atoms are located in slightly distorted square prisms of rhodium (268–274 pm Sn–Rh in Ho3Rh9Si2Sn3). Magnetic investigations were performed for RE3Rh9Si2Sn3 (RE = Y, Gd – Yb). Except of Y3Rh9Si2Sn3, all investigated compounds exhibit Curie‐Weiss paramagnetism, but ferromagnetic ordering could only be observed for samples containing Gd – Er as rare earth metal. 119Sn Mössbauer spectroscopic measurements were carried out on Gd3Rh9Si2Sn3. A single resonance at an isomer shift of 1.52(1) mm·s–1 clearly underlines that tin is not part of the polyanionic network and therefore not of a stannide character. Representative 29Si solid state NMR spectroscopy investigations were carried out on the diamagnetic yttrium compound Y3Rh9Si2Sn3. The spectrum indicates the existence of only one distinct Si site consistant with the refined single crystal data.

Very Low Pressure Rh-Catalyzed Hydroformylation of Styrene with (S,S,S-Bisdiazaphos): Regioselectivity Inversion and Mechanistic Insights

Rates and selectivities of styrene hydroformylation as catalyzed by the rhodium coordination complex of (S,S,S)-bis-diazaphos (BDP) under extremely low pressures of syngas (CO/H2) are reported. At pressures <10 psia, the catalyst system is selective for the linear regioisomer, 3-phenyl-1-propanal, whereas at high pressure, it is highly selective for branched (R)-2-phenylpropanal. Lowered pressures severely degrade the enantioselectivity of the branched product. Qualitative kinetic data reveal large changes in the form of the apparent rate law, suggesting significant changes in catalyst speciation prior to selectivity-determining transformations. Most strikingly, under low-pressure conditions, the qualitative kinetic data imply that the catalyst accumulates as either 4-coordinate (bisphosphine)Rh(CO)(alkyl) (4) or 5-coordinate (bisphosphine)Rh(CO)(alkyl)(styrene) (5) complexes, neither of which have been previously observed as hydroformylation resting states under catalytic conditions. Although styrene is ...

Cobalt, Rhodium, Iridium, and Ruthenium Carbonyl Complexes with Stanna-closo-dodecaborate:103Rh NMR,119Sn Mössbauer Spectroscopy, and Solid-State119Sn NMR

Depending on the stoichiometry stanna-closo-dodecaborate [SnB11H11]2– reacts with the dimeric carbonyl complex [Rh(CO)2Cl]2 to give a dinuclear rhodium coordination compound with bridging tin ligands, [Et3MeN]6[Rh2(CO)4(SnB11H11)4] (1), or a pentagonal-bipyramidal complex, [Et4N]5[Rh(CO)2(SnB11H11)3] (2), with the carbonyl ligands in axial position. The analogous iridium and cobalt complexes [Et4N]5[Ir(CO)2(SnB11H11)3] (3) and [Me4N]5[Co(CO)2(SnB11H11)3] (4) exhibit a pentacoordinated structure with the tin ligands in axial positions. The dimeric ruthenium chlorocarbonyl complex [Ru(CO)3Cl2]2 reacts with four equivalents of the tin nucleophile to give the octahedrally coordinated ruthenium complex [Et3MeN]4[Ru-cis-(CO)2-cis-Cl2-trans-(SnB11H11)2] (5). The synthesized coordination compounds were characterized by X-ray crystal structure analysis, by 103Rh, 119Sn, and 11B NMR spectroscopy in solution, and in the case of the rhodium complexes 1 and 2 by 119Sn solid-state NMR and 119Sn Mössbauer spectroscopy.

Chemical conversions of rhodium selenochloride Rh2Se9Cl6

Rhodium selenochloride Rh2Se9Cl6 (1) reacts with aqueous solutions of KCN and CsCl and 4-cyanopyridine (4-CNPy) to give complexes KCs2Rh(CN)6 (2) and RhCl3(4-CNPy)3 (3). According to X-ray diffraction data, 2 and 3 have mononuclear structures in which the rhodium atoms are in the oxidation state III and six-coordinate environment. Reactions 1 with CN-containing ligands lead to complete displacement of selenium-containing ligands from the rhodium coordination sphere.

Chlorido(η4-cycloocta-1,5-diene)(N,N′-diethylthiourea-κS)rhodium(I)

In the title rhodium(I) complex, [RhCl(C8H12)(C5H12N2S)], N,N′-diethyl­thio­urea acts as a monodenate S-donor ligand. The rhodium(I) coordination sphere is completed by the Cl atom and the COD [= 1,5-cyclo­octa­diene] ligand inter­acting through the π-electrons of the double bonds. If the midpoints of these two bonds are taken into account, the Rh atom exhibits a distorted square-planar coordination. The syn conformation of the N,N′-diethyl­thio­urea ligand with respect to the Cl atom is stabilized by an intra­molecular N—H⋯Cl hydrogen bond. A weak inter­molecular N—H⋯Cl inter­action links mol­ecules along the a axis.

Photocatalytic Hydrogen Production from Water Using Heterogeneous Two-dimensional Rhodium Coordination Polymer [Rh2(p-BDC)2]n

Abstract Heterogeneous dinuclear rhodium(II) coordination polymer, [Rh2(p-BDC)2]n (p-BDC = 1,4-benzenedicarboxylate), which formed self-assembly infinite two-dimentional slit sheets structure was performed as hydrogen production catalyst for photochemical reduction of water under visible light irradiation in the presence of a multicomponent system containing Ru(bpy)32+, MV2+, and EDTA–2Na.

Synthesis, characterization, and catalytic application of a new chiral P,N-indene ligand derived from (R)-BINOL

Abstract Lithiation of 2-dimethylaminoindene followed by quenching with [( R )-(1,1′-binaphthalene-2,2′-diyl)]chlorophosphite and treatment with triethylamine afforded the crystallographically characterized enantiopure P,N-indene 3 in 71% isolated yield. In the course of rhodium coordination chemistry studies involving 3 , the formation of the isolable complex [(κ 2 - P , N - 3 )(κ 1 - P ,N- 3 )RhCl] ( 7 ) (81%) was observed, thereby confirming the propensity of this new ligand to form L n Rh( 3 ) 2 complexes. Such coordination chemistry behavior may contribute in part to the generally poor catalytic performance exhibited by mixtures of 3 and rhodium precursor complexes in the asymmetric hydrogenation and hydrosilylation studies described herein.

Diastereoselective Synthesis of New Rhodium-Based Amphiphilic Polyol-Cp Systems

The cyclopentadienide nucleophilic ring opening on the cyclopentene oxide affords diastereoselectively an efficient entry to a new polyalcoholic (1,2,4)-C5H2[CH(CH2)3CHOH]3 propeller-like, hybrid ligand CpOOO. The diastereoselective rhodium complexation gives rise almost quantitatively to a new class of racemic CpOOORh(L,L) (L,L = nbd, cod, C2H4, CO) complexes. Thermal treatment gives predominantly the air-stable CpOOORh(nbd) rac-4a (73.5%), having SP planar chirality, as determined by X-ray diffraction studies. It has also been possible to isolate its stable atropisomer rac-4c (20.5%), while the minor kinetic isomer rac-4b, showing opposite planar chirality (∼10%), has been identified by NOESY NMR experiments. The high solubility in water and benzene, evidencing the amphiphilic character, has been measured by the n-octanol/water partition coefficient. The intermolecular H-binding, due to the hydroxy groups, plays a crucial role in selecting the rhodium coordination in the reaction mixture, whereas in the...