Influences of Ligand Environment on the Spectroscopic Properties and Disproportionation Reactivity of Copper-Nitrosyl Complexes
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- 作者：Jamie L. Schneider ; Susan M. Carrier ; Christy E. Ruggiero ; Victor G. Young ; Jr. ; and William B. Tolman
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：November 11, 1998
- 年：1998
- 卷：120
- 期：44
- 页码：11408 - 11418
- 全文大小：149K
- 年卷期：v.120,no.44(November 11, 1998)
- ISSN：1520-5126
文摘
In studies of the chemistry of new copper-nitrosyl complexes supported by tris(3-(trifluoromethyl)-5-methylpyrazol-1-yl)hydroborate (TpCF3,CH3) and tris(3-mesitylpyrazol-1-yl)hydroborate (TpMs,H), significanteffects of the scorpionate ligand substituents on the properties of the {CuNO}11 unit were found that haveimplications for environmental influences on similar species in biological and catalytic systems. Thecopper(I) complexes TpMs,HCu(THF) and TpCF3,CH3Cu(CH3CN) were structurally characterized by X-raycrystallography, and their respective CO and NO adducts were studied by FTIR, EPR, NMR, and/or UV-visspectroscopies in solution. Both nitrosyl complexes disproportionate in the presence of excess NO to N2Oand TpR,R'Cu(NO2); an X-ray structure of the latter product supported by TpCF3,CH3 was determined. Unlikepreviously studied paramagnetic [CuNO]11 compounds that exhibit EPR signals with g < 2.0 and large ANOvalues at temperatures below ~40 K (Ruggiero, C. E.; Carrier, S. M.; Antholine, W. E.; Whittaker, J. W.;Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 1993, 115, 11285-11298), TpMs,HCu(NO) is EPR silent at4.2 K and exhibits an NMR spectrum (238 K, toluene-d8) with sharp signals. Peak assignments for the NMRspectrum were deduced from integrated intensities, temperature-dependent isotropic shifts, and the nuclearrelaxation rates. The unique NMR spectral behavior for the TpMs,H complex, which only differs from thoseof analogues with simple phenyl substituents by virtue of the shape of the substrate binding pocket enforcedby the mesityl methyl groups, suggests that caution should be exercised in characterizing such adducts inproteins and heterogeneous systems; subtle environmental effects may determine the applicability of EPRversus NMR methods. The electron-withdrawing effects of the trifluoromethyl substituents in TpCF3,CH3Cu(NO) perturb 
(NO) and the Cu(I) 
NO MLCT energy in the respective FTIR and UV-vis spectra andinduce a significant slowing of its disproportionation rate. These results, in conjunction with those obtainedfrom kinetic and spectroscopic studies on the TpMs,H system, support a mechanism for the disproportionationinvolving generation of the CuNO adduct from NO and the Cu(I) precursor in a preequilibrium step, followedby electrophilic attack of a second NO molecule on the adduct that is rate-controlling.
(NO) and the Cu(I) NO MLCT energy in the respective FTIR and UV-vis spectra andinduce a significant slowing of its disproportionation rate. These results, in conjunction with those obtainedfrom kinetic and spectroscopic studies on the TpMs,H system, support a mechanism for the disproportionationinvolving generation of the CuNO adduct from NO and the Cu(I) precursor in a preequilibrium step, followedby electrophilic attack of a second NO molecule on the adduct that is rate-controlling.