Ronald L. Halterman
University of Oklahoma
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Ronald L. Halterman.
Tetrahedron | 1997
Ronald L. Halterman; Shyi-Tai Jan; Heather L. Nimmons; David J. Standlee; Masood A. Khan
The condensation of the resolved C2-symmetric benzaldehyde, 1,2,3,4,5,6,7,8-octahydro-1:4,5:8-dimethanoanthracene-9-carboxyaldehyde, with pyrrole produced the first chiral tetraarylporphyrin 1 exhibiting D4-symmetry. The resolved benzaldehyde was synthesized in seven steps from p-benzoquinone and cyclopentadiene and included a resolution via diastereomeric ketals. A manganese chloride complex of porphyrin 1 was used as a catalyst for the asymmetric epoxidation of aromatic substituted alkenes in the presence of excess sodium hypochlorite in up to 7,200 turnovers and up to 76% e.e and >90% yield.
Langmuir | 2010
Anuradha Singh; Daminda H. Dahanayaka; Abhijit Biswas; Lloyd A. Bumm; Ronald L. Halterman
The cleavage of decanethioacetate (C10SAc) has been studied by (1)H nuclear magnetic resonance (NMR) spectroscopy and scanning tunneling microscopy (STM) imaging of in situ prepared decanethiolate self-assembled monolayers (SAMs) on Au(111). Solutions of C10SAc (46 mM) and previously reported cleavage reagents (typically 58 mM) in CD(3)OD were monitored at 20 degrees C by NMR spectroscopy. Cleavage by ammonium hydroxide, propylamine, or hydrochloric acid was not complete within 48 h; cleavage by potassium carbonate was complete within 24 h and that by potassium hydroxide or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) within 2 h. Similar cleavage rates were observed for phenylthioacetate. The degree of molecular ordering determined by STM imaging increased with increasing extent of in situ cleavage by these same reagents (2.5 mM C10SAc and 2.5 mM reagent in ethanol for 1 h, then 16 h immersion of Au/mica). Less effective cleavage reagents did not cleave the C10SAc sufficiently to decanethiol (C10SH) and gave mostly disordered SAMs. In contrast, KOH or DBU completely cleaved the C10SAc to C10SH and led to well-ordered SAMs composed of (square root(3) x square root(3))R30 degrees domains that are indistinguishable from SAMs grown from C10SH. Monolayer formation from thioacetates in the absence of cleavage agents is likely due to thiol or disulfide impurity in the thioacetates. Eliminating disulfide by using Bu(3)P as a sacrificial reductant also helped to produce good molecular order in the SAM. The methods presented here allow routine growth of molecularly ordered alkanethiolate SAMs from thioacetates using reagents of ordinary purity under ambient, benchtop conditions.
Tetrahedron Letters | 1992
Steven L. Colletti; Ronald L. Halterman
Abstract The asymmetric catalytic epoxidation of various unfunctionalized alkyl and aryl alkenes has been accomplished using the new C 2 -symmetrical 1,1′-binaphthyl-2,2′-dimethylene-bridged ansa -Bis(1-indenyl)titanium dichloride complex. Enantiomeric excesses of 22% and activities up to 61 turnovers were observed using the (R)(−)-BpDM-(1-ind) 2 TiCl 2 catalyst.
Tetrahedron Letters | 1999
Ronald L. Halterman; Chengian Zhu
Abstract An efficient new synthesis of 2- and 3-substituted indenes has been developed based on the nickel-catalyzed chromium(II)-promoted addition of aryl bromides to a tethered ketone carbonyl. Several tethered bromoaryl ketones were prepared through enolate alkylation of acyclic or cyclic ketones with 2-bromobenzyl bromide. Nozaki-Takai-Hiyama-Kishi closure of the resulting bromoaryl ketones followed by acid promoted dehydration gave substituted indenes in overall yields for the three-step sequence ranging from 29 to 58%.
Tetrahedron Letters | 1996
Ronald L. Halterman; Xiaodan Mei
Abstract A series of new enantiomerically pure D 2 - symmetric 5,10,15,20-tetraarylporphyrins has been synthesized by condensation of C 2 -symmetric substiuted benzaldehydes with achiral aryldipyrromethanes in 22–40% yield. The mild conditions used enable selective incorporation of the chiral arenes at the 5,15-positions and the achiral arenes at the 10,20-positions. Due to the incorporation of the C 2 -symmetric chiral arenes, no atropisomers are possible in these D 2 -symmetric ligands. Manganse complexes of these ligands are catalysts for the enantioselective epoxidation of cis-β-methylstyrene.
Journal of Organometallic Chemistry | 1995
Ronald L. Halterman; Timothy M. Ramsey; Nathan A. Pailes; Masood A. Khan
Abstract We have demonstrated a very efficient (5 steps, 28% yield from 1-octen-7-yne and 1,2-diiodobenzene) and novel synthesis of 1,2-bis(9-bicyclo[4.3.0]-non-1,6-dinyl)benzen. We utilized for the firstime in a bis(cyclopentadiene) synthesis the double Pauson-Khand cyclization and Shapiro-elimination methods. The double Pauson-Khand cyclization is also successful in the preparation of ethylene-bridged bis(cyclopentadienes). A novel iodine-promoted elimination of allyl methyl ethers was also applied in the preparation of bis(cyclopentadienes). The solid state structure of 1,2-bis(9-bicyclo[4.3.0]-non-1,6-dienyl)benzenedichlorotitanium ( dl - 4a ) was obtained and it shows a very obtuse angle between the cyclopentadienyl substituents. The crstallographic data for dl - 4a are as follows: C 24 H 24 Cl 2 Ti, monoclinic, C2/c. a = 15.805(2) A , b = 11.027(2) A , c = 13.323(3) A , β = 121.40(3)°, volume 1981.9 A 3 , Z = 4, R = 4.41, R w = 6.92%, goodness of fit 2.96.
Tetrahedron | 1995
Ronald L. Halterman; Alexander Tretyakov
Abstract Nazarov cationic π-cyclizations were employed in the synthesis of three substituted camphor-derived cyclopentadienyl ligands bearing a 3-methyl, 3-t-butyl or 3-phenyl substituent on the (1R,7S)-1,10,10-trimethyltricyclo[5,2,1,02,6]deca-2,5-diene framework. These ligands were converted to diastereomeric mixtures of bis(cyclopentadienyl)zirconium and -titanium dichlorides. In each case, a C2-symmetrical isomer was the major isomer in the crude reaction product mixture and in all but one case a pure C2-symmetrical diastereomer could be obtained by recrstallization.
Tetrahedron Letters | 2003
Ronald L. Halterman; Lisa D. Crow
Abstract A three-step procedure for the synthesis of chiral annulated indenes is described in which nopinone, verbenone and menthone are converted to their enolate form, alkylated with 2-bromomethylbromobenzene, ring-closed with CrCl 2 /cat. NiCl 2 and dehydrated with catalytic acid.
Tetrahedron | 1997
Ronald L. Halterman; Shyi-Tai Jan; Aladamash H. Abdulwali; David J. Standlee
Abstract Two new sterically-modified and two electronically-modified D4-symmetrical tetraarylporphyrin ligands have been prepared and the catalytic activity of their manganese complexes in epoxidations of aryl-substituted alkenes studied. Moderate reactivity changes were observed in catalytic epoxdiations with these electronically varied tetraaarylporphyrin complexes, the methoxy derivative giving slightly improved selectivity (83% e.e. with cis-β-methylstyrene).
European Journal of Inorganic Chemistry | 2002
Oleg Stenzel; Sebastian Dechert; Frank Girgsdies; Jochanan Blum; Dmitri Gelman; Ronald L. Halterman
Optically active rhodium complexes containing the chiral, menthyl-substituted indenyl ligands (−)-2-menthyl-4,7-dimethylindene and (−)-2-menthylindene are described. Metathesis reactions of the chiral lithium salts of these indenyl systems with the appropriate starting materials yielded the complexes (−)-(2-menthyl-4,7-dimethylindenyl)Rh(CO)2 (2), (−)-(2-menthyl-4,7-dimethylindenyl)Rh(dppe) (3), (+)-(2-men- thylindenyl)Rh(dppe) (5), (−)-(2-menthylindenyl)Rh(PMe3)2 (6), and (−)-(2-menthylindenyl)Rh(nbd) (8). All compounds obtained were diastereomerically pure. The structures of 2, 3, and 6 were determined by single crystal X-ray diffractome- try. Complexes 3 as well as (−)-bis(η2-ethylene)(η5-2-menthyl-4,7-dimethylindenyl)rhodium(I) (9), (−)-(cycloocta-1,5-diene)(η5-1-menthyl-4,7-dimethylindenyl)rhodium(I) (10), (−)-(cycloocta-1,5-diene)(η5-2-menthyl-4,7-dimethylindenyl)rhodium(I) (11), and (−)-(cycloocta-1,5-diene)(η5-2-menthylindenyl)rhodium(I) (12) were found to be active as double bond hydrogenation catalysts. Two of them proved to induce asymmetry up to 18% ee. These complexes also promote the hydroformylation of olefins yielding both linear and branched aldehydes in varying ratios but hardly transfer chirality.