Synthesis of Mixed-Metal (Ru−Rh) Bimetallacarboranes via exo-nido- and closo-Ruthenacarboranes. Molecular Structures of (η⁴-C₈H₁₂)Rh(μ-H)Ru(PPh₃)₂(η⁵-C₂B₉H₁₁) and (CO)(PPh₃)Rh(μ-H)Ru(PPh₃)₂(η⁵-C₂B₉H₁₁) and Their Anionic closo-Ruthenacarborane Precursors

The reaction of exo-nido-5,6,10-[Cl(PPh₃)₂Ru]-5,6,10-(μ-H)₃-10-H-7,8-C₂B₉H₈) (1) with [(η⁴-diene)RhCl]₂ in EtOH or with [(CO)₂RhCl]₂ in MeOH in the presence of KOH produced novel mixed-metal bimetallacarboranes (η⁴-diene)Rh(μ-H)Ru(PPh₃)₂(η⁵-C₂B₉H₁₁) (4, diene = COD; 5, diene = NBD) or (CO)(PPh₃)Rh(μ-H)Ru(PPh₃)₂(η⁵-C₂B₉H₁₁) (10) along with a small amount of the mononuclear complexes closo-(CO)₂(PPh₃)Ru(η⁵-C₂B₉H₁₁) and closo-(CO)(PPh₃)₂Ru(η⁵-C₂B₉H₁₁), respectively. Complexes 4 and 10 were characterized by single-crystal X-ray diffraction studies which revealed the existence of two types of bridging bonds Ru−H−Rh and B−H···Rh in these species. The bridging hydrogen atoms are asymmetrically disposed within these linkages. Several separate experiments have been carried out for the synthesis of the anionic complex [closo-3,3-(PPh₃)₂-3-H-3,1,2-RuC₂B₉H₁₁]^-, which is proposed to be the key intermediate in the reaction of 1 with [(η⁴-diene)RhCl]₂. The reaction of (PPh₃)₃RuHCl with [7,8-C₂B₉H₁₂][Me₃NH] under reflux in THF in the presence of Et₄NCl yielded [closo-3,3-(PPh₃)₂-3-Cl-3,1,2-RuC₂B₉H₁₁][Et₄N] (7), which after reduction by LiAlH₄ in THF afforded [closo-3,3-(PPh₃)₂-3-H-3,1,2-RuC₂B₉H₁₁][Et₄N] (8) in poor yield. Alternatively, treatment of (PPh₃)₃RuHCl with Tl₂[7,8-C₂B₉H₁₁] in THF at ambient temperature led to 8 in 84% yield. The anionic complex 8 and the known neutral closo-3,3-(PPh₃)₂-3-Cl-3-H-3,1,2-RuC₂B₉H₁₁ (6) have been substituted for 1 in the synthesis of 4 under the same conditions. Structures of both anionic closo-ruthenacarboranes 7 and 8 have been confirmed by single-crystal X-ray diffraction studies. The NMR data [¹H, ¹³C{¹H}, ³¹P{¹H}, and ¹¹B] for the new mononuclear and binuclear ruthenacarborane complexes are discussed in detail.