Novel Types of Pyrazolyl Amidine Complexes: Mechanistic Aspects of Their Syntheses and Exchange Reactions with Acetonitrile

The bis(pyrazolato) pyrazole complex [(η 5 -C 5 Me 5 )Ir(pz) 2 (Hpz)] ( 1 ) reacts with AgBF 4 and nitriles N⋮CR to give the tetranuclear Ir 2 Ag 2 pyrazolyl amidine complexes [{(η 5 -C 5 Me 5 )Ir(μ-pz)(μ-N C(R)pz)Ag} 2 ][BF 4 ] 2 [R = Me ( 2 ), Ph ( 3 ), Bz ( 4 )]. In acetonitrile solution, complexes 3 and 4 are converted into 2 by exchange of the nitrile moiety. Protonation of complexes 2 and 4 affords the mononuclear pyrazolyl amidines [(η 5 -C 5 Me 5 )Ir(Hpz)[HN C(R)pz][BF 4 ] 2 [R = Me ( 5 ), Bz ( 6 )], respectively, which in turn, in basic media, react with AgBF 4 to yield 2 and 4 . The molecular structure of 3 has also been elucidated. The tetranuclear cation contains an inversion center which relates the two bimetallic halves of the molecule. The iridium atoms display half-sandwich pseudooctahedral environments while the coordination around the silver is almost linear, the distortion from linearity most probably arising from an intermetallic Ag···Ag interaction (Ag···Ag separation 2.965(1) Å).