PHYSICOCHEMICAL STUDIES OF THE REACTIONS OF SOME METAL CARBONYLS WITH CERTAIN NITROGEN AND OXYGEN DONOR LIGANDS

Abstract

The hexacarbonyls of group (VI) transition metals are extremely useful intermediates in the preparation of either organometallic or coordination compounds of chromium, molybdenum and tungsten. Numerous compounds can be obtained by the nucleophilic substitution of one or more CO groups with other Lewis base ligands. Ligands containing both nitrogen and oxygen donor atoms are very diverse. The three ligands 4-(2- thiazolylazo)resorcinol (TAR), 2-pyrazinecarboxamide (PCA) and I ,5-diphenylcarbazone (DPC) were chosen in this study. Reactions ofM(C0)6 , M = Cr or Mo, with each ligand were tried either in air or under reduced pressures.

Heating either Cr(C0)6 or Mo(C0)6 with TAR under reduced pressure gave the bis 4-(2-thiazolylazo)resorcinolato derivatives M(TAR)2 . The spectroscopic studies of these two complexes showed that the ligand acted as a tridentate species. The 1 H NMR study of the molybdenum derivative also explored that the proton of the resorcinol OH group bonded ortho to the azo group was missing in the complex. This observation suggested the oxidative-addition mechanism of formation of the complex. 2-pyrazinecarboxamide reacted with Cr(C0)6 in benzene either in air or under vacuum to give the tris derivative Cr(PCA)J. On the other hand, Mo(C0)6 reacted with PCA to give the mono derivative Mo(C0)4(PCA). TheIR spectrum of the molybdenum complex illustrated a pattern of four bands of symmetries 2a 1+b 1+b2 due to four metal carbonyl groups. Spectroscopic