Dirhodium Carboxylates Research Articles

Supercritical and Liquid Solvent Effects on the Enantioselectivity of Asymmetric Cyclopropanation with Tetrakis[1-[(4-tert-butylphenyl)- sulfonyl]-(2S)-pyrrolidinecarboxylate]dirhodium(II)

The enantioselectivity of the cyclopropanation of styrene and methyl phenyldiazoacetate in the presence of a dirhodium carboxylate catalyst was found to be dependent on both the dielectric constant and the coordinating ability of the solvent. The enantiomeric excess is pressure dependent in supercritical fluoroform, changing from as low as 40% ee at pressures above 100 bar to nearly 80% ee at pressures near the critical point. The pressure dependence is caused by the changing dielectric constant of the fluoroform. Reactions in some coordinating liquid solvents had greater enantioselectivities than expected on the basis of dielectric constant alone. The crystal structure of the catalyst was obtained along with spectroscopic data in order to elucidate the causes of the solvent-dependent enantioselectivity.

Enantioselective intermolecular 1,3-dipolar cycloaddition via ester-derived carbonyl ylide formation catalyzed by chiral dirhodium(II) carboxylates

Enantioselective 1,3-dipolar cycloaddition of the ester-carbonyl ylides derived from methyl 2-(diazoacetyl)benzoate and 3-(diazoacetyl)-2-naphthoate with dipolarophiles has been effected with the aid of dirhodium(II) tetrakis[ N-phthaloyl-( S)- tert-leucinate], affording cycloadducts in up to 93% ee.

A rigid dirhodium(II) carboxylate as an efficient catalyst for the asymmetric cyclopropanation of olefins

The dirhodium(II) complex 7 of (1 S,3 R,4 R)-2-( p- tert-butylphenylsulphonyl)-2-aza-bicyclo[2.2.1]heptane-3-carboxylic acid ( 3) (or its enantiomer) was synthesised in four steps from cyclopentadiene, ( R)- or ( S)-phenylethylamine and methyl glyoxylate. Complex 7 was evaluated as a catalyst in the asymmetric cyclopropanation of alkenes with vinyl- and phenyl-diazoesters, resulting in enantioselectivity of up to 92%.

Studies of dirhodium(II) tetra(trifluoroacetate). 5. Remarkable examples of the ambidentate character of dimethyl sulfoxide.

The ambidentate character of dimethyl sulfoxide, already known for dirhodium carboxylates, has been remarkably manifested in new ways. Three novel complexes of dirhodium(II) tetra(trifluoroacetate) with the DMSO ligand, namely, [Rh2(O2CCF3)4]m(DMSO)n with m:n = 7:8 (1), 1:1 (2), and 3:2 (3), have been obtained by deposition from the vapor phase, and their crystal structures have been determined by X-ray crystallography. The crystallographic parameters are as follows: for 1, monoclinic space group P2(1)/c with a = 28.261(2) A, b = 16.059(4) A, c = 17.636(2) A, beta = 92.40(4) degrees, and Z = 2; for 2, triclinic space group P1 with a = 8.915(2) A, b = 10.592(2) A, c = 11.916(2) A, alpha = 84.85(1) degrees, beta = 88.86(1) degrees, and gamma = 65.187(8) degrees, and Z = 2; and for 3, triclinic space group P1 with a = 8.876(2) A, b = 9.017(2) A, c = 19.841(3) A, alpha = 101.91(2) degrees, beta = 97.144(8) degrees, gamma = 100.206(9) degrees, and Z = 1. In the oligomeric molecule of 1, six DMSO ligands bridge seven dirhodium tetra(trifluoroacetate) units in a bidentate fashion via S and O atoms, and two additional DMSO molecules terminate the chain. In the structure of the monoadduct Rh2(O2CCF3)4(DMSO) (2), the dirhodium blocks are bridged through the O atoms of DMSO ligands, forming a one-dimensional polymeric chain. Compound 3 also has an infinite chain structure with the molecules of dimethyl sulfoxide acting in a bidentate mu-DMSO-S,O mode. Every second DMSO molecule is missing in 3, so that two of every three Rh2(O2CCF3)4 units are associated through the O atoms of carboxylate groups to give the overall composition [Rh2(O2CCF3)4]3(DMSO)2.

Studies of Dirhodium(II) Tetrakis(trifluoroacetate). 6. The First Structural Characterization of Axial Alkyne Complexes, Rh2(O2CCF3)4(Ph2C2)n(n= 1, 2): Diphenylacetylene as a Bifunctional Ligand

The solid-state reactions of Rh2(O2CCF3)4 with diphenylacetylene (Ph2C2) have produced the first two dirhodium(II,II) carboxylate complexes with coordinated alkynes having overall compositions of 1...

Dirhodium(II) carboxylate complexes as building blocks. Synthesis and structures of square boxes with tilted walls †

The crystal structures of four new molecular boxes with substituted benzene-1,4-dicarboxylate side walls are described, showing how substituents larger than hydroxyl cause the walls to tilt in the solid state.

Studies of Dirhodium Tetra(trifluoroacetate). 3. Solid State Isomers of the Compound Rh(2)(O(2)CCF(3))(4)(THF) Prepared by Sublimation.

The monoadduct of dirhodium tetra(trifluoroacetate) with THF has been obtained by deposition from the vapor phase. The compound Rh(2)(O(2)CCF(3))(4)(THF) crystallizes in two isomeric forms, 1 and 2, whose structures have been determined by X-ray crystallography. The crystallographic parameters are as follows: for 1, triclinic space group P&onemacr; with a = 9.557(2) Å, b = 10.126(2) Å, c = 11.840(4) Å, alpha = 95.97(2) degrees, beta = 90.40(2) degrees, gamma = 115.58(1) degrees, and Z = 2; for 2, triclinic space group P&onemacr; with a = 8.6347(3) Å, b = 9.678(1) Å, c = 13.773(4) Å, alpha = 73.182(5) degrees, beta = 74.622(5) degrees, gamma = 89.76(1) degrees, and Z = 2. Compound 1 is unique as the only extended structure where dirhodium carboxylate molecules are bridged by a single exogenous atom. The oxygen atom of the THF ligand coordinates to the axial positions of two Rh(2) units so that a one-dimensional zigzag chain is formed. The bridging is slightly asymmetric with Rh-O(THF) distances of 2.363(6) and 2.407(6) Å, and the Rh-O(THF)-Rh angle is 111.8(3) degrees. The crystal structure of 2 is not polymeric. Pairs of Rh(2)(O(2)CCF(3))(4)(THF) units are associated through O atoms of carboxylate groups to produce a dimer of dimers. The lengths of the terminal Rh-O(THF) and axial bridging Rh.O(Ac) interactions are 2.214(7) and 2.406(6) Å, respectively.

ChemInform Abstract: Enantiocontrol in Tandem Carbonyl Ylide Formation and Intermolecular 1,3‐Dipolar Cycloaddition of α‐Diazo Ketones Mediated by Chiral Dirhodium(II) Carboxylate Catalyst.

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Studies of Tetrakis(trifluoroacetate) Dirhodium. 2. A Pi Complex of Hexamethylbenzene with Tetrakis(trifluoroacetate) Dirhodium(II,II)

The solid-state reaction of Rh2(O2CCF3)4 with C6Me6 yields a one-dimensional copolymer [Rh2(O2CCF3)4·C6Me6]∞ (1), which constitutes the first example of a dirhodium(II,II) carboxylate complex with arene. Compound 1 has been characterized by elemental analysis and IR and mass spectroscopy, and its structure has been determined by X-ray diffraction. In the crystal structure of 1 the alternating arrangement of Rh2(O2CCF3)4 and C6Me6 units forms infinite chains extended along the [100] direction. The coordination of hexamethylbenzene to the dirhodium unit is unsymmetrical, with two opposite edges of the arene ring approaching the axial sites of the dimers. This off-centered complexation causes no distortion of the aromatic system. The closest Rh−Carene contacts (2.770(6) and 2.787(6) A) are the longest for any axial interactions to dirhodium carboxylates known to date. At the same time, the Rh−Rh distance (2.422(1) A) is not as short as might have been expected in the case of total absence of axial donation.

Enantiocontrol in Tandem Carbonyl Ylide Formation and Intermolecular 1,3-Dipolar Cycloaddition of α-Diazo Ketones Mediated by Chiral Dirhodium(II) Carboxylate Catalyst

Enantiocontrol in Tandem Carbonyl Ylide Formation and Intermolecular 1,3-Dipolar Cycloaddition of α-Diazo Ketones Mediated by Chiral Dirhodium(II) Carboxylate Catalyst

ChemInform Abstract: Parallel Synthesis Techniques in the Identification of New Chiral Dirhodium(II) Carboxylates for Asymmetric Carbenoid Insertion Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Highly Enantioselective Construction of the Key Azetidin‐2‐ones for the Synthesis of Carbapenem Antibiotics via Intramolecular C—H Insertion Reactions of α‐Methoxycarbonyl‐α‐diazoacetamides Catalyzed by Chiral Dirhodium(II) Carboxylates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Parallel synthesis techniques in the identification of new chiral dirhodium(II) carboxylates for asymmetric carbenoid insertion reactions

New chiral dirhodium(II) carboxylate catalysts for asymmetric carbenoid SiH insertion reactions have been identified using solution phase parallel synthesis techniques.

Highly enantioselective construction of the key azetidin-2-ones for the synthesis of carbapenem antibiotics via intramolecular C–H insertion reactions of α-methoxycarbonyl-α-diazoacetamides catalysed by chiral dirhodium() carboxylates

A highly enantioselective construction of 3-oxa-1-azabicyclo[4.2.0]octanes (up to 96% ee) has been achieved by intramolecular C–H insertion of α-methoxycarbonyl-α-diazoacetamides catalysed by dirhodium(II) complexes incorporating N-phthaloyl-(S)-amino acids as chiral bridging ligands, which provides a new, catalytic asymmetric route to key intermediates for carbapenem antibiotics.

Characterization of supported and unsupported transition metal compounds by liquid secondary ion mass spectrometry

The positive ion liquid secondary ion mass spectra (LSIMS) of metal acetylacetonates (acacs) contain cluster ions that involve multiple metal centers. Several metal acacs form adduct ions with m-nitrobenzyl ( m-NBA) alcohol used as the LSIMS support matrix. In these adduct ions, deprotonated m-NBA molecules act as bridges between metal centers. The LSIMS of a series of dirhodium carboxylates show that the electron-withdrawing strength of the carboxylate group controls whether the base peak in the mass spectrum is the molecular ion or an adduct ion formed between the molecule and a matrix molecule of sulfolane. However, no cluster ions are formed for these dirhodium compounds. Similarly, highly charged cationic compounds do not form cluster ions, nor do they form adduct ions with the LSIMS solvent. Instead, the counter ion is retained to maintain a single positive charge in the ion. LSIMS spectra of neutral and charged metallocene compounds are compared. Contrary to the assertions that these compounds cluster extensively in the gas phase, the LSIMS provide no evidence for this process. To support studies of surfaces prepared for catalytic studies, silica- and clay-supported transition metal acacs were characterized by LSIMS. Release of the supported transition metal compounds from the surface occurs during ion exchange.

ChemInform Abstract: Site‐ and Enantiocontrol in Intramolecular C‐H Insertion Reactions of . alpha.‐Diazo Carbonyl Compounds Catalyzed by Dirhodium(II) Carboxylates

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Site- and Enantiocontrol in Intramolecular C-H Insertion Reactions of .ALPHA.-Diazo Carbonyl Compounds Catalyzed by Dirhodium(II) Carboxylates.

The full potential of rhodium (II) -catalyzed intramolecular C-H insertion reactions of α-diazo carbonyl compounds as a powerful tool for the construction of both carbocycles and heterocycles has been developed by variation of the bridging ligands of the dirhodium (II) catalysts : (1) Dirhodium (II) tetrakis (triphenylacetate) featured by the steric bulk of the bridging ligands on the rhodium has been demonstrated to exhibit an exceptionally high order of selectivity for C-H insertion into methylene over methine on a cycloalkane ring as well as for aromatic substitution over aliphatic C-H insertion. (2) Dirhodium (II) complexes incorporating N-phthaloyl- (S) -amino acids as bridging ligands have proven to be the chiral catalysts of choice for allowing high levels of differentiation of enantiotopic methylene C-H bonds and enantiotopic benzene rings, affording optically active cyclopentanone, 2-azetidinone, and 2-indanone derivatives in up to 80%, 96%, and 98% ee, respectively.

Diastereoselective Rh-Mediated Construction of 2,3,5-Trisubstituted Tetrahydrofurans.

Dirhodium(II) carboxylate catalyzed cyclization of a series of gamma-alkoxy-alpha-diazo esters 1 has been shown to proceed with substantial diastereoselectivity, producing the 2,3,5-trisubstituted tetrahydrofurans 2 and 3. The diastereoselectivity of the cyclization improved as the electron-withdrawing ability of the substituent R increased. A mechanistic hypothesis is presented.

ChemInform Abstract: Enantioselective Intramolecular C‐H Insertion Reactions of N‐Alkyl‐N‐ tert‐butyl‐α‐methoxycarbonyl‐α‐diazoacetamides Catalyzed by Dirhodium(II) Carboxylates: Catalytic, Asymmetric Construction of 2‐ Azetidinones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Asymmetric Creation of Quaternary Carbon Centers by Enantiotopically Selective Aromatic C‐H Insertion Catalyzed by Chiral Dirhodium(II) Carboxylates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.