Investigation of the C−H Activation Potential of [Hydrotris(1H‐pyrazolato‐κN1)borato(1−)]iridium (IrTpx) Fragments Featuring Aromatic Substituents x at the 3‐Position of the Pyrazole Rings,The Choice of the Precursor

A series of pyrazole‐substituted hydrotris(1H‐pyrazolato‐κN¹)borato(1?)]iridium complexes of the general composition Ir(Tp^x)(olefin)₂] (Tp^x=Tp^Ph and Tp^Th) and their capability to activate C?H bonds is presented. As a test reaction, the double C?H activation of cyclic‐ether substrates leading to the corresponding Fischer carbene complexes was chosen. Under the reaction conditions employed, the parent compound Ir(Tp^Ph)(ethene)₂] was not isolable; instead, (OC‐6‐25)‐Ir(Tp^PhκC^Ph,κ³N,N′,N″)(ethyl)(η²‐ethene)] ( 1 ) was formed diastereoselectively. Upon further heating, 1 could be converted exclusively to (OC‐6‐24)‐Ir(Tp^Phκ²C^Ph,C^Ph,κ³N,N′,N″)(η²‐ethene)] ( 2 ). Complex 1 , but not 2 , reacted with THF to give (OC‐6‐35)‐Ir(Tp^Phκ³N,N′,N″)H(dihydrofuran‐2(3H)‐ylidene)] ( 3 ), a cyclic Fischer carbene formed by double C?H activation of THF. Accordingly, complexes of the general formula Ir(Tp^x)(butadiene)] (see 4 – 6 ; butadiene=buta‐1,3‐diene, 2‐methylbuta‐1,3‐diene (isoprene), 2,3‐dimethylbuta‐1,3‐diene) reacted with THF to yield 3 or the related derivative 9 . The reaction rate was strongly dependent on the steric demand of the butadiene ligand and the nature of the substituent at the 3‐position of the pyrazole rings.