Nucleophilic attack on cluster-bound acetylide ligands derived from the iron ketenylidene, [Fe3(CO)9(CCO)]2?

Reaction of the iron ketenylidene (PPN)2[Fe3(CO)9CCO] [PPN =bis (triphenylphosphine)nitrogen(+1)] with trifluoroacetic anhydride forms a highly electrophilic acetylide cluster (PPN)[Fe3(CO)9CCOC(O)CF3] (lc), analogous to the known compounds (PPN)[Fe3(CO)9CCOR] [R=Et, (Ia); Ac, (Ib)] prepared from the reaction of ethyl triflate and acetyl chloride on the ketenylidene. Reaction of phosphines and (Ib, c) yield phosphonium acetylides [Fe3(CO)9CCPR3] [(II),R=Ph], with loss of (PPN)[CH3CO2] or (PPN)[CF3CO2]. Additionally, (Ic) and triphenylarsine react to give an analogous arsonium acetylide [Fe3(CO)9CCAsPh3] (III). No reaction occurs when an excess of arsine is added to (Ib). The reaction of (Ib, c) with anionic nucleophiles is reported, including reaction of Na[CpFe(CO)2] and (Ib) to afford an unusual metallated acetylide cluster (PPN) [Fe3(CO)9CCFe(CO)2Cp] (IV). Clusters (II), (III), and (IV) are spectroscopically characterized and a single crystal x-ray structure determination of (IV) is reported. (PPN)[Fe3(CO)9CCFe(CO)2Cp] (IV) crystallizes in the monoclinic space group P21/n;a=17.793(2) A;b=16.108(3) A;c=18.157(3) A;β=107.62(1)0;V=4959(3) A3;Z=4. Refinement of 469 variables on 5981 observed [I>3σ(I)] reflections converged toR=3.5% andRw=4.7%.