Synthesis of Mixed-Metal (Ru−Rh) Bimetallacarboranes via<i>exo</i>-<i>nido</i>- and<i>closo</i>-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<i>closo</i>-Ruthenacarborane Precursors

Abstract

The reaction of exo - nido -5,6,10-[Cl(PPh 3 ) 2 Ru]-5,6,10-(μ-H) 3 -10-H-7,8-C 2 B 9 H 8 ) ( 1 ) with [(η 4 -diene)RhCl] 2 in EtOH or with [(CO) 2 RhCl] 2 in MeOH in the presence of KOH produced novel mixed-metal bimetallacarboranes (η 4 -diene)Rh(μ-H)Ru(PPh 3 ) 2 (η 5 -C 2 B 9 H 11 ) ( 4, diene = COD; 5, diene = NBD) or (CO)(PPh 3 )Rh(μ-H)Ru(PPh 3 ) 2 (η 5 -C 2 B 9 H 11 ) ( 10 ) along with a small amount of the mononuclear complexes closo -(CO) 2 (PPh 3 )Ru(η 5 -C 2 B 9 H 11 ) and closo -(CO)(PPh 3 ) 2 Ru(η 5 -C 2 B 9 H 11 ), 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-(PPh 3 ) 2 -3-H-3,1,2-RuC 2 B 9 H 11 ] -, which is proposed to be the key intermediate in the reaction of 1 with [(η 4 -diene)RhCl] 2 . The reaction of (PPh 3 ) 3 RuHCl with [7,8-C 2 B 9 H 12 ][Me 3 NH] under reflux in THF in the presence of Et 4 NCl yielded [ closo -3,3-(PPh 3 ) 2 -3-Cl-3,1,2-RuC 2 B 9 H 11 ][Et 4 N] ( 7 ), which after reduction by LiAlH 4 in THF afforded [ closo -3,3-(PPh 3 ) 2 -3-H-3,1,2-RuC 2 B 9 H 11 ][Et 4 N] ( 8 ) in poor yield. Alternatively, treatment of (PPh 3 ) 3 RuHCl with Tl 2 [7,8-C 2 B 9 H 11 ] in THF at ambient temperature led to 8 in 84% yield. The anionic complex 8 and the known neutral closo -3,3-(PPh 3 ) 2 -3-Cl-3-H-3,1,2-RuC 2 B 9 H 11 ( 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 [ 1 H, 13 C{ 1 H}, 31 P{ 1 H}, and 11 B] for the new mononuclear and binuclear ruthenacarborane complexes are discussed in detail.