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The [NEt4]+ (1a), [NHMe3]+ (1b), and [N(PPh3)2]+ (1c) salts of the monoanion [Fe(CO)3(η 5-7-CB10H11)]- have been prepared via the reaction between [Fe3(CO)12] and [NHMe3][nido-7-CB10H13] in THF (tetrahydrofuran). The complexes [N(PPh3)2][Fe(CO)2(L)(η 5-7-CB10H11)] (L = PPh3 (2), CNBut (3)) were obtained by treating 1c in THF with PPh3 and CNBut, respectively, in the presence of Me3NO. The compound [N(PPh3)2][Mo(CO)4(η 5-7-CB10H11)] (4) has been synthesized from [Na]3[nido-7-CB10H11] and [Mo(CO)3(NCMe)3] in the presence of CO and with addition of HBF4·Et2O and [N(PPh3)2]Cl. An X-ray diffraction study established that in the anion of 4 the Mo atom is coordinated on one side by the four CO molecules and on the other by a nido-7-CB10H11 carborane in a η5 manner. In reactions with PPh3 and CNBut, the salt 4 gives the species [N(PPh3)2][Mo(CO)3(L)(η 5-7-CB10H11)] (L = PPh3 (5a), CNBut (6)). Salts of the anions [Fe(CO)3(η 5-7-CB10H11)]- and [Mo(CO)3(PPh3)(η 5-7-CB10H11)]- react with donor molecules (THF, OEt2, SMe2) in the presence of acids and other hydride abstracting reagents to give zwitterionic complexes:  [Fe(CO)3(η 5-9-L-7-CB10H10)] (L = O(CH2)4 (7), OEt2 (8), SMe2 (9)) and [Mo(CO)3(PPh3)(η 5-9-L-7-CB10H10)] (L = O(CH2)4 (10), OEt2 (11)), formed as single isomers. That the donor molecules L are bonded to a boron atom which lies in a β-site with respect to the carbon in the ring ligating the metal was established by X-ray diffraction studies on 7 and 10. In the latter the PPh3 molecule is transoid to the BO(CH2)4 group, presumably for steric reasons. Alkyne−molybdenum complexes [N(PPh3)2][Mo(CO)2(ButC⋮CH)(η 5-7-CB10H11)] (13) and [N(PPh3)2][Mo(CO)2(PhC⋮CR)(η 5-7-CB10H11)] (R = H (14), Ph (15)) have also been prepared.

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