Indenyl complexes of Group 8 metals

nThe present review article is concerned with the state of the art of the chemistry of indenyl Group 8 metal complexes which has undergone significant progress during the last decade. It deals mainly with complexes of the types: (a) bis(indenyl) sandwich compounds [M(eta(5)-C9H7-xRx)(2)] (R = H, Me); (b) half-sandwich derivatives [M(eta(5)-C9H7-xRx)(CO)(2)](2) and [M(eta(5)-C9H7-xRx)XL2] (X = halides, H, alkyl, acetylide; L = two electron donor ligands); (c) cationic complexes [M(eta(5)-C9H7-xRx)L2L'](+) (L, L' = two electron donor ligands). A detailed account of the synthesis, structural and reactivity aspects is presented including kinetic studies and catalytic processes. A discussion of the structural features and coordination modes of the indenyl group with special attention to its distortion parameters is presented. The reactivity studies include redox (chemical and electrochemical) processes, insertion reactions, ring transformations as well as ligand exchange processes in half-sandwich derivatives [M(eta(5)-C9H7-xRx) XL2]. In particular, a detailed discussion of the ability of the moiety [M(eta(5)-C9H7-xRx)L-2] to stabilize unsaturated carbene groups such as vinylidene (C=CR2, allenylidene =C=C=CR2 and alpha,beta-unsaturated alkenyl carbene =C(H)C(R-1)-CRR' complexes is presented. The influence of the indenyl ring on the regio- and stereoselective nucleophilic additions to these carbene groups allows selective synthesis leading to either allenyl or functionalized alkynyl complexes. A large number of the latter have been synthesized some of them showing excellent non-linear optical properties. (C) 1999 Elsevier Science S.A. All rights reserved.