Results and Discussion
IR and NMR Studies
Reactions of M(CO)6; M=Mo or W with isatin in the presence of PPh3 resulted in the formation of [M(CO)3(isatH)(PPh3)] complexes. The IR spectra of the complexes exhibited characteristic bands of the isatin and PPh3 ligands with the corresponding shifts, Table 2. In addition, the IR spectra of the complexes showed that the νCO of isatin ligand exerted 20–45 cm−1 shift to lower frequency
suggesting that the coordination of isatin occurred in the range of ketoform in both complexes. On the other hand, the IR spectra of the two complexes exhibited three bands in the metal terminal carbonyl region [7] with shifts toward the low-frequency region, Table 2. Also, the IR spectra exhibited two medium bands at 1099, 1102 cm−1 characteristic ν(P–CPh) bands indicates the presence of coordinated PPh3 in the complexes, similar to the literature trend [8] and suggesting similarity of the structure of the two complexes. It is generally difficult to determine the stretching frequency υ(M-P) that contains PPh3 because it has many stretching frequencies in the lower-frequency region [9]. However, the IR spectra of the two complexes showed interesting differences. The νCO of the three terminal carbonyls in the tungsten complex exhibit more shift to lower frequencies than that of the molybdenum complex. This can be contributed to the difference in the metal and arrangements of the ligands in the two complexes. From the positions of the three CO groups and their intensities, it can be concluded that the complex [Mo(CO)3(isatH)(PPh3)] could be presented in the meridional (mer)-isomer in the solid state and tungsten complex in the facial (fac)-isomer as shown in Scheme 1.