Synthesis and reactivity of fluorinated ferracarborane anions

Abstract

The ferracarborane [N(PPh₃)₂][6,6,6,10,10,10-(CO)₆-closo-6,10,1-Fe₂CB₇H₈] (2) reacts in CH₂Cl₂ with 3 molar equivalents of Ag[PF₆] to yield the trifluoro-substituted species [N(PPh₃)₂][7,8,9-F₃-6,6,6,10,10,10-(CO)₆-closo-6,10,1-Fe₂CB₇H₅] (3). Compound 3 undergoes structural rearrangement in toluene at reflux temperatures, forming [N(PPh₃)₂][8,9,10-F₃-6,6,6,7,7,7-(CO)₆-closo-6,7,1-Fe₂CB₇H₅] (4). Alternatively, reaction of either 2 or 3 with a 10-fold excess of Ag[PF₆] in CH₂Cl₂ forms two species: namely, [N(PPh₃)₂][2,7,9,10-F₄-6,6,6,8,8,8-(CO)₆-closo-6,8,1-Fe₂CB₇H₄] (5), in which one further B–F substitution has occurred and the {Fe₂CB₇} cluster core has rearranged, plus a mono-iron co-product, [N(PPh₃)₂][3,8,9-F₃-7,7,7-(CO)₃-closo-7,1-FeCB₇H₅] (6) that is formed by polyhedral contraction. Treatment of 3 with [NO][BF₄] in CH₂Cl₂ results in CO substitution at the 4-connected iron vertex [Fe(10)], producing the zwitterionic complex [7,8,9-F₃-6,6,6,10,10-(CO)₅-10-NO-closo-6,10,1-Fe₂CB₇H₅] (7). Addition of Me₃NO to a mixture of 3 and PEt₃ in CH₂Cl₂ also results in CO substitution, forming the isomeric species [N(PPh₃)₂][7,8,9-F₃-6,6,m,10,10-(CO)₅-n-PEt₃-closo-6,10,1-Fe₂CB₇H₅] [m = 6, n = 10 (8a); m = 10, n = 6 (8b)] in a 5 : 1 ratio. Treatment of 8a with [NO][BF₄] and then CNBu^t in CH₂Cl₂ allows further, successive CO substitution at Fe(10) to yield first a neutral, zwitterionic complex [7,8,9-F₃-6,6,6,10-(CO)₄-10-NO-10-PEt₃-closo-6,10,1-Fe₂CB₇H₅] (9) and then [7,8,9-F₃-6,6,6-(CO)₃-10-CNBu^t-10-NO-10-PEt₃-closo-6,10,1-Fe₂CB₇H₅] (10). The molecular structures of compounds 3, 4, 5, 6, and 10 have been established by X-ray diffraction.