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Andreas Bauer

Publications and source records attributed to Andreas Bauer.

42 records · Page 3Linked to original sources
PubMed1999

Kinetic and Thermodynamic Studies of Reaction of *Cr(CO)(3)C(5)Me(5), HCr(CO)(3)C(5)Me(5), and PhSCr(CO)(3)C(5)Me(5) with *NO. Reductive Elimination of Thermodynamically Unstable Molecules HNO and RSNO Driven by Formation of the Strong Cr-NO Bond.

Reaction of H-Cr(CO)(3)C(5)Me(5) with *NO at 1-2 atm pressure in toluene solution yields Cr(NO)(CO)(2)C(5)Me(5) as the sole metal-containing product in addition to N(2)O and HNO(2) as the principle nitrogen-containing products. N(2)O and HNO(2) are attributed to decomposition of the initial product HNO. Kinetic studies yield the rate law d[P]/dt = -k(2nd)( )(order)[HCr(CO)(3)C(5)Me(5)][*NO]; k(2nd)( )(order) = 0.14 M(-)(1) s(-)(1) at 10 degrees C, with DeltaH() = 11.7 +/- 1.5 kcal/mol and DeltaS() = -16.3 +/- 3.5 cal/(mol deg). The rate of reaction is not inhibited by CO. The kinetic isotope effect for reaction of D-Cr(CO)(3)C(5)Me(5) is k(H)/k(D) = 1.7. These observations are consistent with a first step involving direct H (D) atom transfer from the metal hydride to *NO, forming HNO. Also supporting this mechanism is the approximately 150-times slower reaction of H-Mo(CO)(3)C(5)Me(5) and failure to observe reaction for H-W(CO)(3)C(5)Me(5) in keeping with metal-hydrogen bond strengths Cr < Mo < W. Reaction of PhS-Cr(CO)(3)C(5)Me(5) with NO at 1-2 atm pressure in toluene solution also forms Cr(NO)(CO)(2)C(5)Me(5) as the sole metal-containing product. The initial product is the unstable nitrosothiol PhS-NO. Kinetic studies yield the rate law d[P]/dt = -k(1st)( )(order)[PhS-Cr(CO)(3)C(5)Me(5)]; k(1st)( )(order) = 3.1 +/- 0.3 x 10(-)(3) s(-)(1) at 10 degrees C, with DeltaH() = 21.6 +/- 1.2 kcal/mol, DeltaS() = + 3.9 +/- 1.5 cal/(mol deg). The rate of reaction is independent of both NO and CO pressure. The transition state in the first-order process is proposed to involve migration of bound thiolate to coordinated CO, forming Cr(CO)(2) (eta(2)-C(=O)SPh)C(5)Me(5). The enthalpy of reaction of *Cr(CO)(3)C(5)Me(5) and NO yielding Cr(NO)(CO)(2)C(5)Me(5) and CO has been measured by solution calorimetry: DeltaH degrees = -33.2 +/- 1.8 kcal/mol. The Cr-NO bond strength is estimated as approximately 70 kcal/mol and provides the net thermodynamic driving force for the proposed elimination of the unstable molecules HNO and PhSNO.

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PubMed1999

Reaction of *NO Thiolate and Thiol Complexes: Elimination of PhSNO from W(phen)(CO)(2)(SPh)(2), CO from W(phen)(CO)(2)((-S)(2)Arene), and HNO from W(phen)(CO)(3)(RSH).

Reaction of *NO with W(phen)(CO)(2)(SPh)(2) (phen = 1,10-phenanthroline) results in clean conversion to W(phen)(CO)(2)(NO)(SPh). Reduction of the W(II) bisthiolates to the W(0) nitrosyl thiolate occurs with simultaneous reductive elimination of PhS-NO, which is unstable but could be detected spectroscopically. Reaction of W(phen)(CO)(2)(1,2-S(2)-Arene), however, does not result in reductive elimination of either free or bound nitrosothiol. Carbon monoxide is displaced, forming W(phen)(NO)(2)(1,2-S(2)-Arene) (1,2-S(2)-Arene = 1,2-benzene dithiolate or toluene-3,4-dithiolate). Complexes of butanethiol and thiophenol W(phen)(CO)(3)(RSH) react with excess *NO to form nitrosyl thiolate complexes W(phen)(CO)(2)(NO)(SR). These reactions also produce N(2)O and HNO(2), which are attributed to decomposition of initially formed HNO. These observations indicate that *NO may be capable of direct attack on complexed thiols. Crystal structures of W(phen)(CO)(2)(NO)(SPh) and W(phen)(NO)(2)(toluene-3,4-dithiolate) are reported.

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PubMed1999

The Enthalpy of Insertion of Sulfur into the Metal-Hydrogen Bond. Synthetic, Structural, and Calorimetric Study of the Complexes HS-M(CO)(3)C(5)R(5) [M = Cr, Mo, W; R = H, Me].

Synthetic and calorimetric studies of the sulfhydryl complexes HS-M(CO)(3)C(5)R(5) (M = Cr, R = Me; M = Mo, W, R = H, Me) are reported. The Mo and W complexes can be obtained in high yield by reaction of the hydrido complexes H-M(CO)(3)C(5)R(5) with Ph(3)Sb=S, which readily undergoes single S atom transfer to the metal-hydrogen bond yielding the metal-sulfhydryl complex. Direct reaction between the metal hydrides and a limited amount of sulfur also yields the sulfhydryl complexes as the dominant organometallic product. At sulfur atom/metal hydride ratios higher than 1/1, additional products formulated as HS(n)()-M(CO)(3)C(5)R(5) are detected. The enthalpies of insertion of sulfur from Ph(3)Sb=S and S(8) into the metal-hydrogen bond have been determined by solution calorimetry. The HS-M(CO)(3)C(5)R(5) complexes (M = Mo, W) are readily desulfurized by PCy(3) for R = H, but not for R = Me. The M-SH bond strength estimates for the complexes HS-M(CO)(3)C(5)Me(5) increases in the order Cr (46) < Mo (55) < W (63) (kcal/mol). The HS-Mo(CO)(3)C(5)Me(5) group has a pK(a) value at least 4 pK(a) units less acidic than that of H-Mo(CO)(3)C(5)Me(5). The crystal structure of HS-W(CO)(3)C(5)Me(5) is reported.

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PubMed1997

Beryllium Chelation by Dicarboxylic Acids in Aqueous Solution.

Maleic and phthalic acids are found to react with Be(OH)(2), generated in situ from BeSO(4)(aq) and Ba(OH)(2)(aq), in aqueous solution at pH 3.0 or 4.4, respectively (25 degrees C), to give solutions containing the complexes (H(2)O)(2)Be[(OOCCH)(2)] (1) and (H(2)O)(2)Be[(OOC)(2)C(6)H(4)] (3). The products can be isolated in high yield and identified by microanalytical data. With 2 equiv of the dicarboxylic acids and the pH adjusted to 5.5 and 5.9, respectively, by addition of ammonia, the bis-chelate complexes [(NH(4))(+)](2){[Be[(OOCCH)(2)](2)}(2)(-) (2) and [(NH(4))(+)](2){Be[(OOC)(2)C(6)H(4)](2)}(2)(-) (4) are obtained, which can also be isolated. The compounds show distinct (9)Be, (1)H, and (13)C resonances in their NMR spectra in aqueous solutions. Layering of an aqueous solution of compound 4 with acetone at ambient temperature leads to the precipitation of single crystals suitable for an X-ray structure determination. This salt (5) was found to contain the bis-chelated dianion {Be[(OOC)(2)C(6)H(4)](2)}(2)(-) with the beryllium atom in the spiro center of two seven-membered rings and an overall geometry approaching closely C(2) symmetry. These anions are associated with two crystallographically independent but structurally similar counterions [MeC(O)CH(2)CMe(2)NH(3)](+), which are the product of a condensation reaction of the ammonium cation with the acetone solvent. In the crystal the ammonium hydrogen atoms of the cations form N-H.O hydrogen bonds with the oxo functions of the dianion.

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