OCTANUCLEAR HETEROMETALLIC CLUSTERS WITH RHOMBIC DODECAHEDRAL CORES - THE SYNTHESIS, STRUCTURAL CHARACTERIZATION, AND PROPERTIES OF THE (FE6S6(P-RPHO)6[M(CO)3]2)N- CLUSTERS (M=MO,N=3,R=ME,OME,NME2-M=W,N=3,R=ME-M=MO,N=4,R=ME,OME,COME) - PRECURSORS FOR SYNTHETIC ANALOGS FOR THE FE/MO/S SITE IN NITROGENASE

The synthesis and characterization of new members of the [Fe6S6(p-RPhO)6]3 prismane series (R = OMe, N(Me)2, COMe) and of the {Fe6S6(p-RPhO)6[M(CO)3]2}n− adducts (M = Mo, n = 3, R = Me, OMe, NMe2; M = W, n = 3, R = Me; M = Mo, n = 4, R = Me, OMe, COMe) are described. The crystal and molecular structures of (Et4N)3{Fe6S6(p-OMePhO)3} (I), (Et4N)3{Fe6S6(p-OMePhO)6[Mo(CO)3]2} (II), (Et4N)3{Fe6S6(p-MePhO)6[W(CO)3]2((III), and (Et4N)4}Fe6S6(p-COMePhO)6-[Mo(CO)3]2} (IV) are described in detail. I crystallizes in the monoclinic space group P21/n with cell dimensions a = 14.699 (6) Ǻ, b = 12.008 (3) Ǻ, c = 44.026 (18) Ǻ, β = 91.77 (3)°, and Z = 4. II crystallizes in the triclinic space group {formula-omited} with cell dimensions a = 12.581 (3) Ǻ, b = 13.0511 (2) Ǻ, c = 14.8404 (4) Ǻ, a = 93.93 (2)°, β = 89.96 (3)°, γ = 116.087 (2)°, and Z = 1. III crystallizes in the triclinic space group {formula-omited} with cell dimensions a = 12.352 (2) Ǻ, b = 13.402 (4) Ǻ, c = 14.375 (4) Ǻ, α = 95.35 (2)°, β = 93.81 (2)°, γ = 63.27 (2)°, and Z = 1. IV crystallizes in the triclinic space group P\ with cell dimensions a= 12.238 (4) k,b= 13.030 (5) Ǻ, c = 18.564 (9) Ǻ, α = 92.80 (3)°, β = 106.73 (4)°, γ = 114.88 (3)°, and Z = 1. Intensity data for I–IV were collected on a four-circle computer-controlled diffractometer with use of the θ–2θ scan technique for II–IV and the ω scan technique for I. The structures were solved by conventional or direct-method techniques on 3410, 3253, 4336, and 3338 reflections for I–IV, respectively (for I> 3σ(I)). The structures were refined by full-matrix least-squares techniques (464 parameters for I, 468 parameters for II, 425 parameters for III, and 496 parameters for IV, to final R values of 0.071 (I), 0.047 (II), 0.054 (111), and 0.054 (IV). Complex I contains the (Fe6S6)3+ core, complexes II and III contain the (Mo2Fe6S6)3+ and (W2Fe6S6)3+ cores, respectively, and complex IV contains the (Mo2Fe6S6)2+ core. Coordination of the M(CO)3 units to the (Fe6S6)n+ central cages of II–IVresults in an elongation of the latter along the idealized 6-fold axes. As a result of this elongation, the Fe-S bonds parallel to the {formula-omited}-fold axes in II–IV are in the range from 2.338 (6) to 2.348 (4) Ǻ and are significantly longer than the corresponding bonds in I at 2.309 (7) Ǻ. The Mo-S distance in II at 2.614 (5) Ǻ is slightly shorter than that in IV at 2.646 (8) Ǻ, but similar to the W-S distance in III at 2.590 (3) Ǻ. The Fe-M distances in II–IV are 2.99 (2), 2.96 (2), and 3.00 (2) Ǻ. The electronic, cyclic voltammetric, and Mössbauer properties of the {Fe6S6(p-RPhO)6}n− prismanes and the (Fe6S6(p-RPhO)6[M(CO)3]2)n− adducts are affected by the type of para substituents and are discussed in detail. In the trianionic Mo(CO)3 adducts, strongly electron-releasing para substituents on the terminal p-RPhO ligands, such as −NMe2, facilitate the dissociation of one of the Mo(CO)3 fragments and generation of the {Fe6S6(p-RPhO)6[Mo(CO)3]}3− heptametallic clusters. © 1990, American Chemical Society. All rights reserved.