COMPARATIVE-STUDY OF THE STRUCTURES AND REACTIVITY OF THE PI-CYCLOPENTADIENYL-BONDED AND METAL-BONDED SUCCINIMIDYL ESTER COMPLEXES (METAL=MO, FE) - X-RAY MOLECULAR-STRUCTURES OF [(ETA(5)-C5H4COONS)MO(CO)(3)ME] AND [(ETA(5)-C5H5)MO(CO)(3)(ETA(1)-CH2COONS)] (-NS=N-SUCCINIMIDYL)

The activated ester compounds [(eta(5)-C5H4COONS)Mo(CO)(3)Me] (5) and [(eta(5)-C5H4COONS)-Fe(CO)(2)Me] (6) were obtained by treatment of the novel organometallic carboxylic acid complexes [(eta(5)-C5H4COOH)Mo(CO)(3)Me] (2) and [(eta(5)-C5H4COOH)Fe(CO)(2)Me] (4) with N-hydroxysuccinimide in THF in the presence of DCC (dicyclohexylcarbodiimide) or with DSC (disuccinimidyl carbonate) in CH3CN in the presence of pyridine. These activated ester complexes were identified spectroscopically, and in addition, the X-ray molecular structure of 5 was determined. Compound 5 crystallizes in the triclinic space group P $$($) over bar 1: a = 8.684(4) Angstrom, b = 12.764(8) Angstrom, c = 16.522(10) Angstrom, alpha = 65.13(4)degrees, beta = 72.52(4)degrees, gamma = 71.34(4)degrees, V = 1544.6 Angstrom(3), Z = 4. Similarly, the metal-activated ester complex [(eta(5)-C5H5)Mo(CO)(3)(eta(1)-CH2COONS)] (7) was obtained by treatment of the dimer [Cp(2)Mo(2)(CO)(6)] with Na/Hg followed by addition of 2 equiv of ClCH2COONS in THF; in this compound the ester unit is bonded directly to the metal center rather than to the pi-bonded cyclopentadienyl. Complex 7 was characterized by spectroscopic methods, and its molecular structure was ascertained by X-ray crystallography which showed that it belongs to the well-known carbon-bound molybdenum 2-oxaalkyl (eta(1)-enolate) category. Complex [(eta(5)-C5H5)Mo(CO)(3)(eta(1)-CH2COONS)] (7) crystallizes in the monoclinic space group C2/c: a 19.484(2) Angstrom, b = 11.393(2) Angstrom, c = 13.694(2) Angstrom, beta = 98.91(2)degrees, V = 3000 Angstrom(3), Z = 8. The reactivity of pi-bonded activated ester complexes 5 and 6 with ISiMe(3) gave respectively the iodo derivatives [(eta(5)-C5H4COONS)Mo(CO)(3)I] (9) and [(eta(5)-C5H4COONS)Fe(CO)(2)I] (10) as deep red microcrystalline solids. The reactivity of the pi-bonded activated ester complexes 5 and 6 and that of the metal-bonded activated ester 7 with amino esters are presented and discussed.