SUBSTITUENT HETEROATOM EFFECTS ON THE CHEMISTRY OF TRIIRON ALKYNE CLUSTERS DERIVED FROM [FE3(CO)9CCER]- - E = O VERSUS E = S

The sulfonic acetylides [PPN][Fe3(CO)9CCOSO2R] (R = p-C6H4Me, CF3) [PPN = bis(triphenylphosphine)nitrogen(1+) cation], prepared from the action of sulfonic anhydrides on the iron ketenylidene [PPN]2[Fe3(CO)9(CCO)], react with thiolate salts to afford the thiolate-substituted acetylide compounds [PPN][Fe3(CO)9CCSR] (Ia-d) (R = a, Me; b, Et; c, n-Pr; d, i-Pr). The formation of alkyne ligands from Ia,b was accomplished by addition of PMe3 to give 48-electron phosphonium alkyne compounds, II or by protonation to yield 46-electron complexes of terminal alkynes, III. The alkynes undergo further isomerization; the phosphonium alkyne loses thiolate, forming a neutral phosphonium acetylide, and the terminal alkynes rearrange, yielding vinylidene ligands. Both of these reactions are completely different from those of the ethoxide analogues previously prepared from [PPN] [Fe3(CO)9CCOEt]. The divergent behaviors and reactivity between the oxygen and sulfur heteroatom systems are attributed to diminished pi donation from sulfur which prevents the rapid alkyne cleavage observed for the 46-electron alkyne Fe3(CO)9HC=COEt. Additionally, the weaker C-SR bond is thought to be responsible for the thiolate displacement from the 48-electron compound [Fe3(CO)9Me3PC=-CSMe].