Randy F. Johnston

Synthesis and characterization of substituted cyclopentadienide ligands that may form chelates or metal dimers

Abstract Nine different substituted cyclopentadienyl ligands, which have substituents that may either chelate or bridge to second metal center, have been prepared from nucleophilic substitution reactions of esters or alkyl halides with NaCp. The sodium or thallium salts of these ligands were isolated as solids and characterized by 1 H NMR. The alkyl halide and NaCp reaction proved to yield the purer salts of the ligands because of the milder reaction conditions. These salts were reacted futher with Mn(CO) 5 Br to form the corresponding manganese tricarbonyl derivatives (i.e. (C 5 H 4 R)Mn(CO) 3 ; where R = C(O)CH 2 OCH 3 , C(O)CH 2 SCH 3 , C(O)CH 2 CH 2 SCH 3 , CH 2 CO 2 CH 3 , CH 2 CO 2 CH 2 CH 3 , CH 2 CH 2 CO 2 CH 3 , CH 2 CH 2 CO 2 CH 2 CH 3 , CH 2 CH 2 O 2 CCH 3 , and CH 2 CH 2 OCH 3 ) and Na(C 5 H 4 C(O)CH 2 OCH 3 ) was reacted with Co 2 (CO) 8 to form (C 5 H 4 C(O)CH 2 OCH 3 )Co(CO) 2 . The manganese and cobalt compounds were characterized by elemental analysis, IR, 1 H, and 13 C NMR spectra.

Investigation of the electrochemical properties of substituted titanocene dichlorides

The electrochemical properties of (η5-C5Me5)2TiCl2, (η5-C5H4Me)2TiCl2, (η5-C5H4Cl)2TiCl2, (η5-C5H4CO2Me)2TiCl2, and (η5-C5H5)2TiCl2 were examined in THF. two reduction processes. The first reduction processes of (η5-C5H4Me)2TiCl2, (η5-C5H4Cl)2TiCl2 and (η5-C5H5)2TiCl2 are characterized as one-electron reversible reductions. The other two compounds have one-electron reduction followed by the loss of a chloride in a slow chemical reaction (ie EC mechanism). Steric bulk of the pentamethyl derivative and the possibility of chelation in the carbomethoxy derivative enhance the loss of a chloride ion. AnE1/2 range of 550mV was obtained for the five titanocenes andE1/2 decreased to more negative values in the order:C5H4CO2Mes>C5H4C1 s>C5H5 s>C5Me5.

Substituent effects on the frontier molecular orbitais of aryl isonitriles

Abstract An investigation of the frontier molecular orbitais ofo- and p-RC6H4NC (R=H, CH3, NO2, F, Cl, CF3, OCH3) was carried out so that a thorough understanding of the intricacies of σ donation and π acceptance could be developed and used to modify subtly the electron density on metal centers. The results of this study-Indicate that the substituent position (ortho vs. para ) does alter the electron density in the ligand appreciably and that substitution of the phenyl ring with the groups indicated has a smaller effect on the σ-donating ability than it does on the π-accepting ability of the isonitrile ligand. The π-accepting abilities of the isonitrile ligands increase in the order o-, p-CH3OC6H4NC, o-, p-CH3C6H4NC, o-, p-C6H5NC, o-, p-FC6H4NC, o-, p-CF3C6NC, o-, p-ClC6H4NC, o-, p-NO2C6H4NC while the σ-donating ability decreases in this order. The energies of the σ-donor and π-acceptor orbitais are shown to correlate well with observed E 1 2 values of Cr(RC6H4NC)6 and Mn(RC6H4NC)6+1 complexes. This demonstrates how the theoretical results can be useful in understanding the observed physical properties of isonitrile-metal complexes.

Preparation, characterization, and reactivity studies of chelated substituted cyclopentadienylmanganesedicarbonyl complexes

Abstract Chelates of the parent compounds ( η 5 -C 5 H 4 C(O)CH 2 OCH 3 )Mn(CO) 3 ( 1 ). ( η 5 -C 5 H 4 C(O)CH 2 SCH 3 )Mn(CO) 3 ( 2 ), ( η 5 -C 5 H 4 C(O)CH 2 CH 2 SCH 3 )Mn(CO) 3 ( 3 ), ( η 5 -C 5 H 4 CH 2 COOCH 3 )Mn(CO) 3 ( 4 ), and ( η 5 -C 5 H 4 C(O)CH 2 COOCH 3 )Mn(CO) 3 ( 5 ) were prepared by photolysis. Only the chelates ( η 1 : η 5 -C 5 H 4 C(O)CH 2 SCH 3 )Mn(CO) 2 ( 2chelate ) and ( η 1 : η 5 -C 5 H 4 C(O)CH 2 CH 2 SCH 3 )Mn(CO) 2 ( 3chelate ) were stable enough to be isolated. The X-ray structure of 2chelate was determined and demonstrated ring strain in the chelate ring. Derivatives of the chelates were obtained by thermal substitution of the chelated group. Substitution of the chelated groups in ( η 1 : η 5 -C 5 H 4 C(O)CH 2 OCH 3 )Mn(CO) 2 ( 1chelate ), ( η 1 : η 5 -C 5 H 4 CH 2 COOCH 3 )Mn(CO) 2 ( 4chelate ), and ( η 1 : η 5 -C 5 H 4 CH 2 CH 2 COOCH 3 )Mn(CO) 2 ( 5chelate ) occurred within a few minutes, whereas 2chelate and 3chelate required refluxing for several hours to convert them to the substituted products. The substituted products have the general formula ( η 5 -C 5 H 4 R)Mn(CO) 2 L (where R is the substituent of either 1–5 and L is either a phosphine, phosphite, or tetrahydrothiophene). The weaker MnO bond was suggested for the differences in the reactivities of the chelated complexes.

An investigation of electron transfer properties of (Cp)Mn(CO)3 and substituted Cp derivatives

Abstract The results of an electrochemical investigation of the reduction of (η 5 -C 5 H 5 )Mn(CO) 3 , (η 5 -C 5 H 4 COOCH 3 )Mn(CO) 3 , (η5-C 5 H 4 CH 3 )Mn(CO) 3 and (η 5 -C 5 H 4 Cl)Mn(CO) 3 are reported. Each compound was characterized with at least a single one-electron EC process. However, for (η 5 C 5 H 4 COOCH 3 )Mn(CO) 3 and (η 5 -C 5 H 4 CI)Mn(CO) 3 additional reduction processes were also observed. The first reduction potential of these compounds exhibits a potential range of 340 mV and a correlation with the Hammett parameter (σ p ). Voltammetric and IR analysis of the reduced solutions indicate that several species are formed upon reduction. A possible reaction scheme is suggested, although isolation of the proposed products and intermediates for identification has not been possible.

EFFECTS OF MULTIPLE SUBSTITUENTS ON THE PHYSICAL PROPERTIES OF PENTACARBONYLARYLISOCYANIDECHROMIUM COMPOUNDS

Abstract Eight arylisocyanides containing one or more electron-withdrawing substituents were synthesized. The σ-donating and π-accepting abilities of these isocyanides were evaluated by examining the spectroscopic and electrochemical properties of the pentacarbonyl(isocyanide)chromium derivatives. Linear relationships between the Hammett parameters of the para-substituted isocyanides, 13C NMR chemical shifts, and ν(CN) with the E 1/2 were found. Ortho substitutions of the isocyanide stabilized the HOMO of the Cr(CO)5L more than para substitutions. Furthermore, each successively added substituent caused a similar shift in the observed oxidation potential relative to its position on the isocyanide.

Accumulation of Hg(II) by adsorbed polyuridylic acid: differentiation of coordinated Hg(II) and covalently mercurated species

Abstract The voltammetric behavior of polyuridylic acid+mercuric acetate solutions at hanging mercury drop electrodes has been studied in neutral aqueous solution. Adsorbed polyuridylic acid (poly(U)) efficiently accumulates mercury, resulting in a peak voltammogram at ca. −0.6 V vs. SCE for the reduction of Hg(II) coordinated to the poly(U) film. The size of this wave was markedly dependent on the accumulation time. The magnitude of the charge associated with the peak voltammogram indicated formation of multilayer poly(U)–Hg(II) electroactive films. This voltammetric current could be distinguished from the reduction of covalent carbon–mercury bonds in mercurated poly(U), poly(U–Hg), prepared by treating the former with mercury(II)acetate at elevated temperature. Analysis of the surface voltammetry of poly(U–Hg) gave an estimate of the extent of mercuration.

The mechanism of substitution of cymantrene derivatives by phosphines and phosphites

Abstract The kinetics of the thermal substitution of (η5-C5H4C(O)CH3)Mn(CO)2SC4H8, (η1:η5-C5H4C(O)CH2SCH3)Mn(CO)2 and (η1:η5-C5H4C(O)CH2CH2SCH3)Mn(CO)2 by phosphines and phosphites have been measured in toluene and xylene. A proposed dissociative mechanism involving cleavage of the manganese–sulfur bonds as the rate-determining step is supported by the activation parameters obtained.

Structure of (chloranilato)bis(tri-n-butylphosphine)palladium(II)

Abstract(Chloranilato)bis(tri-n-butylphosphine)palladium(II), [Pd(C6Cl2O4){P(C4H9)3}2] (chloranilic acid=2,5-dichloro-3,6-dihydroxy-p-benzoquinone): FW=718.02,P21/c,a=21.729(6),b=17.293(5),c=21.010(9) Å,β=112.62(3)°,V=7287.42 Å3,Z=8,Dc=1.309mg m−3, Mo, λ=0.710730 Å,μ=0.76 mm−1,F(000)=3008, finalR=0.087, 2594 observed reflections. Palladium is ligated by a distorted square planar P2O2 coordination sphere in the title compound. The two molecules per asymmetric unit differ in the arrangement of phosphine n-butyl chains, yielding two unique metal centers.