INFIQC   05475
INSTITUTO DE INVESTIGACIONES EN FISICO- QUIMICA DE CORDOBA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
indirect determination of carbene carbons by hmbc-nmr experiments
Autor/es:
ANABEL LANTERNA; ALEJANDRO M. GRANADOS
Lugar:
Alta Gracia
Reunión:
Congreso; Magnetic Resonance in a Cordubensis Perspective; 2011
Resumen:
Fischer Carbene Complexes (FCC) are compounds of the general structure 1 (figure 1). M is a transition metal, L are ligands while X and Y represent a variety of groups including alkyl, aryl, vinyl, alkynyl, amino, alkoxy, alkylthio, halo, and others; typically X or Y is a pi-donor such as alkoxy, amino, or alkylthio which provides stabilization of the electron deficient carbon. Figure 1 FCC have, over the last 30 years, become a major focus of many synthetic groups and the chemistry of these complexes has developed into an important branch of organometallic chemistry . We use these compounds to obtain molecules with new functional groups like 2 and 3 (figure 2), that remain the carbene carbon (pink circle). This carbon can be compare with carbonylic carbon of an ester group (compound 1) or an amide group (compound 2), but it can be lost after isolation. Figure 2 In order to choose the isolation method, we use 1H-13C HMBC-NMR experiments to determine the presence of carbene carbon in the reaction crude, and after purification. 2D HMBC (Heteronuclear Multiple Bond Correlation) experiment correlates chemical shifts of two types of nuclei separated from each other with two or more chemical bonds. 1H-13C HMBC is frequently used for assigning of quaternary and carbonyl carbons. The choice of 1H-13C HMBC instead of other 2D NMR techniques depends on the fact that it furnishes a relatively high number of well-defined signals related to the correlations chemical shifts of protons with carbons separated with two or three bonds. Moreover, this technique detects quaternary carbons in a few minutes that cannot be detected for other sequences. This sensitivity appears to be sufficient to the aim of this study because signals are acquired on the proton channel, preventing partially the low sensitivities typical of 13C spectroscopy . REFERENCES: The 1D and 2D NMR spectra were recorded on Bruker Avance 400 MHz spectrometer in CDCl3. The acquisition parameters of 1H-13C HMBC spectra were as follows: number of scans, 4; dummy scans, 4; number of data points, 2K in F2 (1H) and 256 in F1 (13C); spectral width, 4000.000 Hz in F2 (1H) and 40256.176 Hz in F1 (13C). Total acquisition time was 22 min and 8 s.