Ten-Vertex Iron−Monocarbollide Complexes:  Synthesis and Reactivity of the Anion [4,9-{Fe(CO)4}-9,9,9-(CO)3-arachno-9,6-FeCB8H11]

• Published in: Inorganic chemistry 2006-03, Vol.45 (6), p.2669-2677
• Main Authors: Franken, Andreas, McGrath, Thomas D, Stone, F. Gordon A
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic051946i

The reagent [arachno-4-CB8H14] reacts with [Fe3(CO)12] in tetrahydrofuran (THF) at reflux temperatures, followed by addition of [N(PPh3)2]Cl, to afford [N(PPh3)2][4,9-{Fe(CO)4}-9,9,9-(CO)3-arachno-9,6-FeCB8H11] (3). In the anion of 3, one iron atom is part of the open face of a 10-vertex {arachno-9,6-FeCB8} cage, to which the second iron atom is attached via an Fe−Fe bond and an additional exo-polyhedral Fe−B σ bond. Upon heating 3 in refluxing toluene, the closed 10-vertex species [N(PPh3)2][2,2,2-(CO)3-closo-2,1-FeCB8H9] (4) is obtained, whereas the isomeric compound [N(PPh3)2][6,6,6-(CO)3-closo-6,1-FeCB8H9] (5) is isolated upon heating [closo-4-CB8H9]- and [Fe3(CO)12] in refluxing THF with subsequent addition of [N(PPh3)2]Cl. Protonation of 3 using CF3SO3H in CH2Cl2 gives the charge-compensated compound [4,9-{Fe(CO)4}-4-(μ-H)-9,9,9-(CO)3-arachno-9,6-FeCB8H11] (6), in which the B−Fe σ bond of the precursor has been converted to a B−H ⇀ Fe linkage. In contrast, 3 with {M(PPh3)}+ gives the trimetallic species [1,3,4,9-{MFe(CO)4(PPh3)}-1,3-(μ-H)2-9,9,9-(CO)3-arachno-9,6-FeCB8H9] (M = Cu (7), Ag (8)) in which the three metal centers form a V-shaped M−Fe−Fe unit. Compound 6 reacts with PEt3 in the presence of Me3NO to yield [4,9-(PEt3)2-9,9-(CO)2-nido-9,6-FeCB8H10] (9). In the latter, the formerly exo-polyhedral {Fe(CO)4} fragment has been replaced by a PEt3 ligand, with a second PEt3 substituting one CO group at the remaining cluster iron vertex. The novel structural features of compounds 3−9 have been confirmed by single-crystal X-ray diffraction studies.