Abstract: Square planar tetracoordinated Rh(Ⅰ) complex is a typical organometallic complex. In catalytic reactions its four-coordinated structure is the precursor of an active compound. The study on its structure is very important for investigating the catalytic procedure. In this paper, the intramolecular substitution reaction of a novel kind of square planar cis-dicarbonyl rhodium cationic complexes containing different N-coordinated tridentate ligands were studied. \%N,N\%-Bis(2-pyridylethyl)-aniline(DPBA), 1,2,3-tri(2-pyridyl) propane(TPP), tri(2-methylenepyridine) methane(TPM) were resolved in methanol respectively, into which an appropriate amount of [Rh(CO)₂Cl]₂ methanol solution was added under stirring at 0 ℃ and atmosphere of CO to get yellowish carbonyl rhodium complexes respectively. The changes of carbonyl rhodium complexes structures were analyzed by IR and XPS. It is shown that the uncoordinated electron donating nitrogen of the ligand, when heated, may replace the terminal carbonyl to form a new type of tridentate complexes, the weak N—Rh bond can replace the strong Rh—CO σ-π bond. The intramolecular substitution reaction is reversible. The formal cis-dicarbonyl bidentate N-coordinated complex recovers if the newly formed complex is put under the atmosphere of CO. So the rhodium complexes will not decompose for the drop of the terminal carbonyls and their stability is enhanced. There is no such reversible intramolecular substitution reaction in non square-planar cis-dicarbonyl rhodium complexes.

Key words: Intramolecular substitution, Rhodium complexes, Square planar