(ETA-6-ARENE(CO)2CR) AS ORGANOMETAL 16-ELECTRON COMPLEX FRAGMENTS - SYNTHESIS AND PROPERTIES OF STIBINIDE COMPLEXES [(ETA-6-ARENE(CO)2CR)2SBX]

Transition metal complexes with doubly bridging antimony(I) halide ligands, [{eta6-arene(CO)2Cr}2 SbX] (1-4) have been synthesized by photochemically induced reductive dehalogenation of SbX3 (X = Cl, Br, 1). The electronic and steric features of the complexes 1-4 were modified by varying the coordinated arene (arene = C6H6, mesitylene, hexamethylbenzene, C6H5CF3). 1-4 are more sensitive than analogous complexes with isoelectronic complex fragments {eta5-CpR(CO)2Mn}, their instability increasing with increasing number of + I-substituents at the arene. Two X-ray crystal structure investigations confirmed the expected trigonal planar coordination of Sb(I)). The complexes [{arene(CO)2Cr}2SbX] proved to be less acidic at the Sb centre than other complexes of the type [{L(n)M}2SbX] (L(n)M = (CO)5Cr, CpR(CO)2Mn) revealing a high pi-backbonding capacity of the complex fragments {arene(CO)2Cr}.