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]^-

Abstract

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 CBBFeBB 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 sigma 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-(mu-H)-9,9,9-(CO)3-arachno-9,6-FeCB8H11] (6), in which the B-Fe sigma bond of the precursor has been converted to a B-H right harpoon-up Fe linkage. In contrast, 3 with {M(PPh3)}+ gives the trimetallic species [1,3,4,9-{MFe(CO)4(PPh3)}-1,3-(mu-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 Me(3)NO 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 In the latter, the formerly exo-polyhedral {Fe(CO)4} fragment has been replaced by a PEt3 ligand, with a second PEt3 substituting one CO group at the remaining cluster iron vertex.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.

Paramagnetic 10-Vertex Ferramonocarboranes

“…Under these conditions, E o ′ for the one-electron oxidation of [Fe(η-C 5 Me 5 ) 2 ] and [Fe(η-C 5 H 5 ) 2 ], added to the test solutions as internal calibrants, was −0.08 and 0.47 V respectively. Compound 1 was synthesized according to the literature method; all other materials were used as received.…”

“…Except for a single 11-vertex manganacarborane, these compounds are diamagnetic in nature, an imbalance that extends across the metallacarborane literature . To date, our reports of closo ferramonocarboranes have been of diamagnetic, Fe(II) species, achieved after oxidative insertion of either one or two zerovalent {Fe(CO) 3 } fragments into a closo carborane cage, recent examples of which include [N(PPh 3 ) 2 ][6,6,6,10,10,10-(CO) 6 - closo -6,10,1-Fe 2 CB 7 H 8 ] and [N(PPh 3 ) 2 ][6,6,6-(CO) 3 - closo -6,1-FeCB 8 H 9 ] ( 1 ; Chart ) . Surprisingly, both compounds proved unreactive toward carbonyl substitution by conventional chemical methods; the former, however, was induced to do so by fluorination of the carborane cage …”

Metal Complexes of Monocarbon Carboranes: A Neglected Area?

“…A range of both closed-cage and open-cluster types having between nine and twelve vertexes has been prepared (see Figure 3), typically by direct reaction of a monocarborane precursor with [Fe 3 (CO) 12 ]. [17] As they are relatively easily prepared and in good yield, their derivative chemistry has also been comparatively well-explored.…”

Synthesis and reactivity of fluorinated ferracarborane anions

“…At convergence, these occupancies were in the approximate ratio 35 : 7 : 25 : 33 [B(2) : B(3) : B(4) : B(5)]. In addition, for 6 the anion was disordered about a pseudomirror plane containing C(1), Fe(1), B(9), and F (9). The two parts were assigned complementary occupancies that converged in the approximate ratio 62 : 38.…”