Synthesis and Characterization of Heterobimetallic Tantalum–Rhodium and Tantalum–Iridium Complexes Connected by a Tantalacyclopentadiene Fragment

We report the synthesis of heterobimetallic Ta–Rh and Ta–Ir complexes bridged by a 2,5‐di‐ tert ‐butyltantalacyclopentadiene fragment. A mononuclear 2,5‐di‐ tert ‐butyltantalacyclopentadiene complex 2 was prepared by the reaction of ( η 2 ‐Me 3 SiC≡ CS iMe 3 )TaCl 3 (dme) ( 1 ) with excess amounts of 3,3‐dimethylbut‐1‐yne in the presence of AlCl 3 . The tantalacyclopentadiene moiety of complex 2 served as a η 4 ‐diene unit for coordinating the Rh and Ir centers; treatment of 2 with [M( μ ‐Cl)(cod)] 2 (M = Rh and Ir; cod = cycloocta‐1,5‐diene) in toluene gave TaRh( μ ‐C 4 H 2 t Bu 2 )Cl 4 (cod) ( 3 ) and [TaIr( μ ‐C 4 H 2 t Bu 2 )Cl 4 ] 2 ( 5 ), respectively. The X‐Ray diffraction study of 3 revealed a dative bond from an electron‐rich Rh toward an electron‐deficient Ta. Upon dissolving 3 in THF , [(thf)TaRh( μ ‐C 4 H 2 t Bu 2 )Cl 3 ] 2 ( μ ‐Cl) 2 ( 4 ) was isolated together with free cycloocta‐1,5‐diene. When complex 5 was treated with 1,2‐bis‐(diphenylphosphino)ethane (dppe), a monomeric Ta–Ir complex, TaIr( μ ‐C 4 H 2 t Bu 2 )Cl 4 (dppe) ( 6 ), was isolated. Ta–Rh and Ta–Ir heterobimetallic complexes 3 and 6 were reduced by a two‐electron process upon reaction with 2,3,5,6‐tetramethyl‐1,4‐bis(trimethylsilyl)‐1,4‐dihydropyrazine ( 7a : Si ‐Me 4 ‐ DHP ) or 2,5‐dimethyl‐1,4‐bis(trimethylsilyl)‐1,4‐dihydropyrazine ( 7b : Si ‐Me 2 ‐ DHP ) to afford the corresponding complexes TaM( μ ‐C 4 H 2 t Bu 2 )Cl 2 (L) ( 8 : M = Rh, L = cod; 9 : M = Ir, L = dppe), where the metallacycle moiety was assigned to have a tantalacyclopentadiene fragment with a large contribution of a tantalacyclopentatriene canonical form.