Reaction of [(η 5 -C 5 H 4 Me) 4 Fe 4 (HCCH)-(HCCBr)](PF 6 ) ([2](PF 6 )) with AgPF 6 in acetonitrile gave [(η 5 -C 5 H 4 Me) 4 Fe 4 (HCCH)(HCCNCMe)](PF 6 ) 2 ([3]-(PF 6 ) 2 ). The X-ray diffraction study revealed that the cationic [CCH] subunit is stabilized through coordination of the acetonitrile molecule to the cationic carbon atom. As a synthon for a donor-free [(η 5 -C 5 H 4 Me) 4 Fe 4 (HCCH)(HCC)] 2+ , [(η 5 -C 5 H 4 Me) 4 Fe 4 (HCCH)(HCCL)](PF 6 ) 2 ([6](PF 6 ) 2 , L = pyrazine) was synthesized by the reaction of [2](PF 6 ) with AgPF 6 in the presence of pyrazine. Treatment of [6](PF 6 ) 2 with tertiary amines in acetonitrile led to deprotonation of acetonitrile to form [(η 5 -C 5 H 4 Me) 4 Fe 4 (HCCH)-(HCCCH 2 CN)](PF 6 ) ([11](PF 6 )). Treatment of [6](PF 6 ) 2 with maleimide in the presence of tertiary amine in acetonitrile allowed the functionalization of the coordinated acetonitrile through the nucleophilic attack of maleimide at the nitrile carbon atom.

The reactivity of [(η5-C5H4Me)4Fe4(HCCH)(HCC-NC4H4N)](PF6)2 (1) toward isocyanides and hydrosilanes was examined. The reaction of 1 with tert-butyl isocyanide led to C(sp3)-N(sp) bond cleavage to give [(η5-C5H4Me)4Fe4(HCCH)(HCC-CN)](PF6) (2), 1-tert-butylpyrazinium salt, and isobutene. In the reactions with cyclohexyl and benzyl isocyanides, isocyanide adducts [(η5-C5H4Me)4Fe4(HCCH)(HCC-CNR)](PF6)2 (R = Cy (5), CH2Ph (6)) were obtained and further transformed to 2 (70 °C, 10 h for 5; RT, 120 h for 6). The reactions of 1 with aryl isocyanides such as 2,6-dimethylphenyl and 2,4,6-tri-tert-butylphenyl isocyanides yielded thermally stable [(η5-C5H4Me)4Fe4(HCCH)(HCC-CNAr)](PF6)2 (Ar = 2,6-Me2C6H3 (8), 2,4,6-tBu3C6H2 (9)). The Si–H bonds of R3SiH (R = Et, Ph), Ph2SiH2, and PhSiH3 were activated to give [(η5-C5H4Me)4Fe4(HCCH)2](PF6) together with the corresponding fluorosilanes. Coordination of the substrates with a cationic [CCH] subunit promoted the cleavage of the carbon–nitrogen and silicon–hydrogen bonds to give the products.

Reaction of [(η5-C5H4Me)4Fe4(HCCH)(HCC–NC4H4N)](PF6)2 (1) with tert-butyl isocyanide led to C(sp3)–N(sp) bond activation to give [(η5-C5H4Me)4Fe4(HCCH)(HCC–CN)](PF6) (2). The resulting tert-butyl cation was trapped as the adduct with pyrazine. Reactions of 1 with 2,6-dimethylphenyl isocyanide and cyclohexyl isocyanide led to the coordination of the isocyanides to the cationic [CCH] subunit. Thermolysis of [(η5-C5H4Me)4Fe4(HCCH)(HCC–CNCy)](PF6)2 (6) yielded 2.

Review: [27 refs.