Inorganic Chemistry:Investigation of Tetrahedral Mixed-Metal Carbonyl Clusters by Two-Dimensional 59Co COSY and DQFCOSY NMR Experiments

Inorg. Chem., 45 (8), 3378 -3383, 2006. 10.1021/ic051544a S0020-1669(05)01544-2 Web

Investigation of Tetrahedral Mixed-Metal Carbonyl Clusters by Two-Dimensional 59Co COSY and DQFCOSY NMR Experiments
Pierre Kempgens, Karim Elbayed, Jésus Raya, Pierre Granger, Jacky Rosé, and Pierre Braunstein*
Laboratoire de RMN de la Matière Condensée (UMR 7177 CNRS), Université Louis Pasteur, Institut de Chimie, BP 296, F-67008 Strasbourg Cedex, France, and Laboratoire de Chimie de Coordination (UMR 7177 CNRS), Université Louis Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Cedex, France

Abstract: Two-dimensional (2D) 59Co correlation spectroscopy (COSY)/double-quantum-filtered (DQF)COSY experiments are reported for three tetrahedral mixed-metal clusters HFeCo3(CO)11L with L = PPh3, P(OMe)3, and PCy3 (Cy = cyclohexyl) in which the L-substituted Co center is chemically different from the other two. The 2D 59Co COSY and DQFCOSY NMR spectra of these clusters in solution prove the existence of a scalar coupling constant between the 59Co nuclei. To determine this value for each cluster, 2D 59Co COSY and DQFCOSY NMR spectra have been simulated by numerical density-matrix calculations. The predicted spectra mimic well the features of the experimental spectra if a scalar coupling is introduced between the Co nuclei. It was initially observed that the scalar coupling constants between the Co nuclei obtained from the 2D COSY and DQFCOSY NMR spectra differed significantly. In contrast to the 2D COSY spectra, the diagonal and cross peaks are of comparable intensity in the 2D DQFCOSY spectra, which leads to a considerable increase in the accuracy of the determination of the scalar coupling constant.