103751-59-3Relevant academic research and scientific papers
Organocobalt complexes with exceptionally poor electron-donating alkyl groups. Extension and quantitation of the relationship between structure and NMR spectra in B12 models
Zangrando, Ennio,Bresciani-Pahor, Nevenka,Randaccio, Lucio,Charland, Jean-Pierre,Marzilli, Luigi G.
, p. 1938 - 1944 (1986)
The crystal and molecular structures of the complex trans-bis(dimethylglyoximato)(chlorocyanomethyl)(pyridine)cobalt(III), (py)Co(DH)2CH(CN)Cl (I), are reported. I crystallizes in space group P21/n of the monoclinic system with a = 15.688 (4) ?, b = 12.714 (2) ?, c = 9.513 (3) ?, β = 93.12 (4)°, V = 1894.6 ?3, Z = 4, Dmeasd = 1.53 g cm-3, and Dcalcd = 1.55 g cm-3; R = 0.040 for 3007 independent reflections. The Co-N bond length in I of 2.017 (2) ? is the shortest such bond found thus far for a (py)Co(DH)2R compound. The Co-C bond length of 2.015 (3) ? is the shortest bond to Co from an α-C-disubstituted alkyl group found thus far in a B12 model. Other compounds, LCo(DH)2R with R = cyano-substituted alkyl groups and L = py, 4-CNpy, PhNH2, and P(OMe)3, were also prepared. The crystal and molecular structures of (Py)Co(DH)2CH2CH2CN (II) were determined. II crystallizes in space group P212121 of the orthorhombic system with a = 9.546 (3) ?, b = 12.615 (3) ?, c = 16.082 (3) ?, V = 1936.8 ?3, Z = 4, Dmeasd = 1.45 g cm-3, and Dcalcd = 1.45 g cm-3; R = 0.042 for 1606 independent reflections. The rate constants, k1, for dissociation of 4-CNpy from (4-CNpy)Co(DH)2R with R = CH(CN)Cl, CH(CN)CH2CN, CH(Me)CN, and CH2CH2CN were determined. Trends in 1H, 13C, and 31P NMR spectra were examined for several series of LCo(DH)2R complexes and compared with the large body of rate, structural, and spectroscopic data available for related LCo(DH)2R compounds. On the basis of the 13C NMR data for the γ-C in pyCo(DH)2R compounds, we derived a scale of substituent constants, Δ(Yi), for all substituents Yi on the α-C of R. Good correlations were found between Σi=13Δ(Yi) and Co-N bond length, log k1, 13C NMR shifts, and 31P NMR shifts. It was concluded that the influence of Yi on the properties evaluated is mainly electronic (electronic trans influence). The steric effect of Yi affects primarily the Co-C bond length (steric cis effect). The series of Δ(Yi) values in the order of increasing electron donation was NO2, CN, CF3, I ≈ CO2Me, Br, Cl ≈ CH2CN, C(Me)(CO2Et)2, H, Si(CH3)3, Ph, Me, Et and larger hydrocarbon groups, OMe.
