LIGAND SUBSTITUTION REACTIONS IN TETRAKIS(BENZYLISOCYANIDE)-BIS(TRI-p-TOLYARSINE OXIDE)COBALT(III) TETRAFLUOROBORATE: AN EXAMPLE OF A LABILE SIX-COORDINATE COBALT(III) COMPLEX

• Published in: Synthesis and reactivity in inorganic and metal-organic chemistry Vol. 31; no. 9; pp. 1545 - 1552
• Main Authors: Becker, Clifford A. L., Motladiile, Saidy
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 31.10.2001
• ISSN: 0094-5714; 1532-2440
• DOI: 10.1081/SIM-100107701

The six-coordinate, two-electron paramagnetic (intermediate-spin) cobalt(III) complex, trans-[Co(CNCH 2 Ph) 4 {OAs(C 6 H 4 -Me-p) 3 } 2 ](BF 4 ) 3 , is shown to undergo labile ligand-substitution reactions with trialkylphosphine ligands. The white, diamagnetic Co(III) complexes, trans-[Co(CNCH 2 Ph) 4 - (PR 3 ) 2 ] (BF 4 ) 3 , PR 3 = P(C 3 H 7 -n) 3 , P(C 4 H 9 -n) 3 , are prepared in moderate yields (40-50%) by apparently instantaneous reaction at room temperature. The relatively low yields are attributed to the solution instability of the starting material. Analogous reaction with the P(C 8 H 17 -n) 3 ligand failed to yield a crystalline product. The observation of labile ligand-substitution reactions for intermediate-spin six-coordinate Co(III), a type of cation hitherto not previously investigated, is compatible with the accepted ranking of the inert/labile character of the metal cations and is readily explained in terms of a dissociative reaction mechanism involving a probable five-coordinate square-pyramidal activated complex.