The synthesis and reactions of bimetallic Zr(II)-Mo(0) complexes with bridging C5H4PPh2 ligands (henceforth abbreviated as Cp') are described. Reaction of Cp-2'ZrCl2 (1) with n-butyllithium in THF produces a metastable material tentatively formulated as Cp-2'Zr.2 LiCl.4 THF (2). Diphenyldisulfide instantaneously converts 2 into the Zr(IV) dithiolate Cp'Zr-2(SPh)(2) (3). When 2 is treated with [Mo(CO)(4)(norbornadiene)], an unstable intermediate is formed which can be trapped in good yield with tert-butylisocyanide to give [Cp-2'Zr(CNt-Bu)(2)Mo(CO)(4)] (4). Treatment of [Cp-2'Zr(Cl)(Me)Mo(CO)(3)L] (L=CO (5a), PMe3 (5b)) with cyclohexenyllithium in the presence of PMe3 gives the corresponding binuclear cyclohexyne complexes [Cp-2'Zr(PMe3)(C6H8)Mo(CO)(3)L] (6a, b). These complexes are fluxional on the NMR timescale due to a flip motion of the cyclohexyne ligand between two equivalent positions (Delta G(not equal) = (40+/-8) kJ/mol). Protonation in THF converts 6a into the cyclohexenyl zirconium complex [Cp-2'Zr(THF)(C6H9)Mo(CO)(4)]BPh4 (7). Alkenes such as styrene, 4-chlorostyrene or norbornadiene give the expected insertion products 8a-c which, due to their insufficient stability, could not be isolated. Stable insertion products were, however, obtained with ketones such as benzophenone (9a), 1,3-diphenylacetone (9b) and cyclohexanone (9c). (C) 1998 Elsevier Science S.A.