Carbonyl(cycloheptatrienyl)iodo(phosphorus donor)tungstens ([wI(C7H7)(CO)L]; L = P(OMe),, la; L = P[O(i-Pr)],, lb; L = PPh,, lc) were prepared from dicarbonyl(cycloheptatrieny1)iodotungsten ([wI(C,H,)(CO),]) via a carbonyl-substitution process. Similarly, bromocarbonyl(phosphorus donor)( 1,2,4,6-tetramethylcycloheptatrieny1)tungstens ([wBr(Me4C7H3),, 6b; L = PPh,, 6c) were obtained from the reaction of bromodicarbonyl( 1,2,4,6-tetramethylcycloheptatrienyl)tungsten ([wBr(Me4C7H3)(CO)2]; 4) with L. The reduction of la-, 4, and 6a,b with sodiumdihydridobis(2-methoxyethoxy)aluminium in toluene led to. Complexes 2a and 7b were characterized by X-ray structure analyses.Introduction. -In recent papers, we have reported about the activating influence of NO ligands on M-H bonds [14]. In order to further test the hypothesis that hydride complexes with odd-electron ligands and the odd electron in an antibonding orbital can achieve enhanced reactivity of the transition-metal-hydrogen bond, we focussed on the synthesis of (cycloheptatrieny1)hydridotungsten complexes. Among related systems with VIb transition metal centers, Green and coworkers reported the [MoH(C,H,)(dppe)] compound (dppe = ethane-1,2-diylbis[diphenylphosphanel) [ 51, which appeared quite stable at room temperature. Because of that observation, it seemed appropriate to attempt syntheses of heavy-element hydride derivatives preferably with phosphorusdonor substitution in which stable M-H bonds could be expected.
