Cassandra T. Eagle

Chiral rhodium(II) carboxamides. A new class of catalysts for enantioselective cyclopropanation reactions

Abstract Chiral Rh2L4 (L = 4-substituted-oxazolidinones and methyl 2-pyrrolidone-5-carboxylate) having two nitrogen-rhodium bonds in the cis geometry at each rhodium face are effective catalysts for enantioselective intermolecular cyclopropanation reactions.

Transition metal complexes with macrocyclic oxathiaethers

Abstract Complexation studies with Ni(II), Co(III), Co(II), Cd(II), and Cu(II) for the two mixed oxathia crown ligands 1-oxa-4,7-dithiacyclononane (9S2O) and 1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane (18S4O2) are reported. These ten complexes have been characterized by a variety of means including electronic spectroscopy, cyclic voltammetry, and nuclear magnetic resonance spectroscopy. Furthermore, the complexes [Ni(18S4O2](BF4)2, [Cu(9S2O)2](BF4)2 and [Ni(9S2O)2](ClO4)2, have been characterized by single crystal X-ray diffraction. For the complex [Ni(18S4O2](BF4)2 the diastereoisomer obtained is the one which contains the two oxygen atoms trans to each other and a meridional positioning of the diethylene SOS moiety. Selectivity for this particular stereoisomer is also supported by NMR data for the Cd(II) and Co(III) complexes, and this selectivity arises from the conformational preferences of the individual CO and CS bonds in the macrocycle. Both the nickelsulfur and nickeloxygen bonds in the complex are highly compressed due to the rigid macrocyclic structure and are among the shortest of these types of bonds found in any crown Ni(II) complex. The copper(II) complex, [Cu(9S2O)2](BF4)2, shows an interesting Jahn–Teller distortion from an octahedral geometry resulting in coordinate bonds which are all remarkably similar in length (CuS(4) 2.3293(6); CuS(7) 2.3336(6); and CuO(1) 2.355(2) A). The oxygen atoms are found in a trans position around the copper(II) center, and the axial CuO bonds are elongated due to the Jahn–Teller distortion. In all of these complexes, the two oxathiaether ligands function as much weaker field ligands than do their crown thioether analogs. Also, cyclic voltammetric experiments reveal that the oxathia crowns do not have the ability to stabilize less common metal oxidation states, a common property of many crown thioether ligands.

Structural and electronic properties of (2,2-trans)-dirhodium(II) tetrakis(N-phenylacetamidate)

Abstract We have synthesized and characterized the first known 2,2-trans isomer of the N-substituted dirhodium(II) tetrakisacetamidate, Rh2(RNAc)4, class of compounds. The bis benzonitrile adduct exhibits a unique orthogonal arrangement of the axial aromatic rings in the solid state. Structural and electronic features suggest the presence of π-backbonding.

Bis(diphenylphosphino)methane complexes of rhodium(III) halides as synthons for dinuclear rhodium(III) complexes

Several rhodium(II1) complexes have been synthesized by the reaction of dirhodium tetraacetate, Rh,(O,CCH,),, with bis(dipheny1phosphino)methane (dppm), in the presence of trimethylsilyl halides. Octahedral complexes of formula RhC13(dppm)(CH3CN) (1) and Rh13(dppm)(CH3CN) (2) have been isolated as minor products in the reaction between Rh,(OC for 2: space group Cc, a = 11.897(2), b= 17.110(3), c= 15.246(l) A, p= 106.04(g)“, V=2983(1) A3, Z=4; for 3: space group p2,2,21, a = 15.914(4), b = 19.819(6), c= 12.207(3) A, I’=3850(2) A3, 2=4.

cis-Enhanced cyclopropanation catalysts: reaction chemistry of three isomers of Rh2[N(C6H5)COCH3]4

Abstract The catalytic activities of three structural isomers of Rh 2 [N(C 6 H 5 )COCH 3 ] 4 in cyclopropanation reactions were surveyed. These studies showed cis cyclopropanation selectivity with bulky alkenes for 2,2- cis - and 2,2- trans -Rh 2 [N(C 6 H 5 )COCH 3 ] 4 .

Design, synthesis, and structure of novel cesium receptors

The podand, bis(2-methoxyphenoxy)m-xylene (1), was designed and synthesized as a potential host for the cesium ion. Its structure was determined by single crystal X-ray diffraction. It crystallizes in P21/c with cell dimensions: a = 8.5723(7) Å, b = 8.3931(14) Å, c = 25.2879(26) Å, β = 96.224(9)○, and V = 1808.7(4) Å3. A crown derivative, tribenzo-21-crown-6 (2), was also prepared and structurally characterized. It also crystallizes in P21/c with cell dimensions: a = 15.5825(13) Å, b = 15.8648(16) Å, c = 8.8266(7) Å, β = 95.247(6)○, and V = 2172.9(3) Å3. The structures exhibit hydrogen bonding, and are evaluated in terms of complementarity and preorganization for cesium binding.

Dicarbonyl(η5-cyclopentadienyl)(pyrrolyl-N)iron(II)

The crystal structure of the title compound, [Fe(C 5 H 5 )-(C 4 H 4 N)(CO) 2 ], shows a discrete molecular structure with a distorted tetrahedral geometry about the Fe atom. The bond angles between the ligands in the tripod and the Fe-Cp centroid vector range from 121.9 to 123.7 (3)°, and the angles between the tripod ligands range from 90.5 (4) to 96.0 (4)°. The mean Fe-C carbonyl and Fe-C Cp distances are 1.776(4) and 2.098(16)A, respectively [Fe-Cp centroid 1.722(4)A], and the Fe-N pyrrole distance is 1.962(3)A. The Cp and pyrrole rings are both planar (maximum deviations of 0.007 and 0.006 A, respectively). The rotational orientation of the Cp ring with respect to the tripod ligands is approximately eclipsed with respect to the Fe-N pyrrole bond [N(1)-Fe(1)-Cp centroid -C(8) -3.1°]. The dihedral angle between the pyrrole ring and the N(1)-Fe(1)-Cp centroid plane is 73.7°.

Electrochemical synthesis and spectroscopic characterization of a mercury–platinum–hydride complex

Abstract Controlled potential bulk reductive electrolysis of trans -[PtI 2 (PEt 3 ) 2 ] in 5:2 C 6 H 5 CN:C 6 H 6 (saturated with NaClO 4 ) at a Hg pool electrode at −1.5 V (vs. Ag/AgCl) and at approximately 0°C, yielded two compounds detectable by 31 P{ 1 H} NMR spectroscopy. One compound was the starting material, trans -[PtI 2 (PEt 3 ) 2 ], while the other displayed a complex spectrum. Analysis of the 1 H, 31 P{ 1 H} and 195 Pt{ 1 H} NMR spectra suggested that the compound contained an unaccounted for spin one-half nucleus. Scanning electron microscopy–energy dispersive spectroscopy and inductively coupled plasma atomic emission spectroscopy indicated that the compound contained mercury and the spectra could be satisfactorily interpreted in terms of a mercury–platinum–hydride structure.

Kinetic and electrochemical study of nitrile adducts of tetrachloro-bis (1,2-bis(diphenylphosphine)methane)dirhenium(II)

SummaryThe addition of two nitrile ligands to the complex Re2Cl4-(dppm)2 (dppm= 1,2-bis(diphenylphosphine)methane)in CH2Cl2 solution has been investigated electrochemically. Upon addition of one equivalent of nitrile NCR (R = aromatic or aliphatic group) to the CH2Cl2/0.1mtetra-N-butylammonium hexafluorophosphate (TBAH) solution, Re2Cl4(dppm)2(NCR) is formed immediately, without dissociation of chloride; electrochemical investigation indicates this nitrile addition is reversible upon oxidation of the dirhenium complex. On addition of two or more equivalents of nitrile, a slow ligand substitution takes place with addition of a second nitrile and concomitant loss of a chloride ion to form [Re2Cl3-(dppm)2(NCR)2]+. The rate of addition of nitrile to Re2Cl4(dppm)2(NCR) appears to depend on the electrondonating or electron-withdrawing abilities of the ligand. The change from monoadduct to diadduct was followed with differential pulse voltammetry for various concentrations of added nitrile. The addition was found to be first order in nitrile.

Electrochemistry of Platinum Phosphine Complexes: C-H and C-X Activation by Highly Reactive Intermediates

The electrochemical reduction of cis-[PtX2L2](X = halide, L = tertiary phosphine) complexes in CH3CN/C6H6/TBAP (Hg electrode) generates [PtL2] equivalents. The reactivity of these complexes is determined by the nature of the monodentate phosphine ligands, e.g. when L = PPh3 the complex does not react with benzonitrile but when L = PEt3 the complex reacts with PhCN via oxidative addition of the rather inert C-CN bond. When the monodentate ligands are replaced by a bidentate ligand, electrochemical reduction leads to the generation of nonlinear [Pt(bidentate)] complexes. The reactivity is altered by the presence of the bidentate ligand, e.g. when L2 = (c-Hx)2P(CH2)3P(c-Hx)2, generation of [Pt(bidentate)] in CH3CN/C6H6/TBAP results in C-H oxidative addition of benzene to produce a phenylplatinum(II) hydride complex. This contrasts with the electrochemical generation of [Pt(PEt3)2] in the same medium where a subsequent acid/base reaction with the N(η-Bu)4 + cation leads to the formation of trans- [PtH(Cl)(PEt3)2] with production of tri(η-butyl)amine. Electrochemical reduction of trans- [PtH(Cl)(PEt3)2] in CH3CN/C6H6/TBAP (Hg electrode) results in H transfer to CH3CN and then further reactions due to the cyanomethyl anion that is produced. Electrochemical oxidation of trans-[PtH(Cl)(PEt3)2] at a platinum mesh electrode does not lead to transformation of Pt(II) into Pt(IV) but rather induces the formal oxidation of H- to H+. Reduction of the platinum(II) aryl complex [PtPh2L2] (L2 = Ph2PCH2CH2PPh2) in CH3CN/TBAP (Hg electrode) leads to cleavage of the Pt-C bonds and formation of benzene (but not biphenyl) through scavenging of the organic fragments. Cleavage of Pt-C bonds can similarly be induced by oxidation in certain cases and this process is the main focus of the current report. Thus, although oxidative electrolysis of cis-[PtPh2(PEt3)2] in CH3CN produces the expected [PtPh2(CH3CN)2(PEt3)2]2+ without Pt-C bond cleavage, oxidation of the benzylplatinum(II) complexes trans-[PtBz(Cl)(PEt3)2] and cis- [PtBz2(PEt3)2] generates benzyl alcohol and benzaldehyde via oxidation of the cleaved organic fragments. These results demonstrate not only that C-H and C-X bond cleavage, accompanied by Pt-H, Pt-X, and Pt-C bond formation, can be induced by electrochemical strategies but also that Pt-H and Pt-C cleavage processes, accompanied by the formation of useful organic products, can be achieved with the use of electrochemical methods.