Tetranuclear Mo2Rh2 Complexes Obtained from Reactions between Triple Cubane-Type Oxide Cluster [(Cp*Rh)4Mo4O16] (Cp* = η5-C5(CH3)5) and Methanethiol: [{Cp*Rh(μ-SCH3)3MoO2}2(μ-O)] and [{Cp*Rh(μ-SCH3)3MoO}2(μ-X)(μ-Y)] (X, Y = O and X = O, Y = S). Synthesis, X-Ray Structures, and Dynamic Behavior in Nonaqueous Media

Abstract

Abstract A new series of linear-type Mo2Rh2 tetranuclear complexes, [{Cp*RhIII(μ-SCH3)3MoVIO2}2(μ-O)] (1), [{Cp*RhIII(μ-SCH3)3MoVO}2(μ-O)2] (2), and [{Cp*RhIII(μ-SCH3)3MoVO}2(μ-O)(μ-S)] (3), has been prepared from reactions of the triple cubane-type oxide cluster [(Cp*Rh)4Mo4O16]·2H2O with CH3SH. These tetranuclear complexes have been characterized by elemental analysis, infrared, electronic, and 1H, 13C, and 17O NMR spectroscopies as well as X-ray analysis. Complex 1 crystallizes in the monoclinic space group P21/n (No. 14) with a = 15.348(3), b = 14.059(3), c = 17.879(3) Å, β = 107.11(2)°, V = 3690(1) Å3, and Z = 4. Complex 2 crystallizes in the monoclinic space group C2/c (No. 15) with a = 25.334(4), b = 21.271(2), c = 17.831(3) Å, β = 129.70(5)°, V = 7393(2) Å3, and Z = 8. Complex 3 crystallizes in the orthorhombic space group Pcab (No. 61) with a = 16.902(3), b = 26.631(3), c = 16.855(2) Å, V = 7587(3) Å3, and Z = 8. Complex 1 involves a nearly linear “O2MoVI(μ-O)MoVIO2” framework, to which two Cp*RhIII units are linked by μ-SCH3 ligands. Complexes 2 and 3 have an analogous tetranuclear MoV2RhIII2 structure in which the MoV and RhIII atoms are bridged by three μ-SCH3 ligands. Complex 2 contains a doubly-bridged “OMoV(μ-O)2MoVO” framework with an Mo–Mo distance of 2.564(1) Å, while 3 contains a “OMoV(μ-O)(μ-S)MoVO” framework with an Mo–Mo distance of 2.666(1) Å. Complexes 2 and 3 retain the tetranuclear structure but are fluxional in solution. The fluxional behaviors are due to intramolecular rotations of the “Cp*Rh(μ-SCH3)” moieties on the trigonal planes of the octahedral Mo centers. Line-shape analyses of variable-temperature 1H NMR spectra measured in C6D5Cl yield activation parameters of ΔH‡ = +80.2 kJ mol−1, ΔS‡ = +22.1 J K−1 mol−1, and ΔG‡298 K = +73.6 kJ mol−1 for the rotation in 2 and ΔH‡ = +76.8 kJ mol−1, ΔS‡ = +21.1 J K−1 mol−1, and ΔG‡298 K = +70.5 kJ mol−1 for that in 3.