SYNTHESIS AND CHARACTERIZATION OF TETRARUTHENABORANE CLUSTERS - MOLECULAR-STRUCTURE OF [HRU4(CO)12AU2(PPH3)2B]

The tetraruthenaborane cluster HRu4(CO)12BH2 (1) has been synthesized and characterized spectroscopically. Deprotonation to [HRu4(CO)12BH]- (2) occurs via the loss of an Ru–H–B bridging proton. Compounds 1 and 2 are structural analogues of the ferraboranes HFe4(CO)12BH2 and [HFe4(CO)12BH]-, although, compared to [HFe4(CO)12BH]-, 2 exhibits a higher activation barrier for endo-hydrogen exchange, in line with the increased M–H–M and M–H–B bond energies in going from M = Fe to Ru. The reaction of 2 with PPh3AuCl leads to HRu4(CO)12Au(PPh3)BH (3) and HRu4(CO)12Au2(PPh3)2B (4), and as one progresses across the series of clusters 1–4, the boron atom is converted from a borane to a borido environment. The tetraruthenium butterfly framework present in compounds 1–4 has been confirmed by a single-crystal X-ray crystallographic characterization of 4: triclinic, PĪ, a = 13.212 (3) Å, b = 13.366 (3) Å, c = 15.261 (4) Å, α = 96.92 (2)°, β = 94.40 (2)°, γ = 103.91 (2)°, V = 2581.2 (10) Å3, Z = 2, RF = 3.94%. The structure of 4 is similar to that found for HFe4(CO)12Au2(PEt3)2B but differs significantly from that of Fe4(CO)12Au2(PPh3)2BH. Subtle differences between the carbonyl orientations in 4 and HFe4-(CO)12Au2(PEt3)2B, and between the exact geometries of the M4Au2B cores (M = Fe, Ru) in the two compounds, support our earlier postulates regarding the sterically controlled pathway for isomer interconversion between Fe4(CO)12Au2(PR3)2BH and HFe4(CO)12Au2(PR3)2B (R = alkyl, aryl), a pathway that involves hydrogen atom migration triggered by a rearrangement of the gold(I) phosphine groups and reorientation of one {Fe(CO)3} fragment. © 1990, American Chemical Society. All rights reserved.