Investigation of the C-H activation potential of [hydrotris(1H-pyrazolato-kappa N-1)borato(1-)]iridium (IrTp(x)) fragments featuring aromatic substituents x at the 3-position of the pyrazole rings Part 1 - The choice of the precursor

A series of pyrazole-substituted [hydrotris(1H-pyrazolato-kappaN(1))borato( 1-)]iridium complexes of the general composition [Ir(Tp(1))(olefin)(2)] (Tp (x) drop Tp(Ph) and Tp(Th)) and their capability to activate C-H bonds is p resented. As a test reaction, the double C-H activation of cyclic-ether sub strates leading to the corresponding Fischer carbene complexes was chosen. Under the reaction conditions employed. the parent compound [Ir(Tp(Ph))(eth ene)(2)] was not isolable: instead, (OC-6-25)-[Ir(Tp(Ph)kappaC(Ph).kappa N- 3,N',N')(ethyl)(eta (2)-ethene)] (1) was formed diastereoselectively. Upon further heating, 1 could be converted exclusively to (OC-6-24)-[Ir(Tp(ph)ka ppa C-2(Ph),C-Ph,kappa N-3,N',N') (eta (2)-ethene)] (2). Complex 1. but not 2, reacted with THF to give (OC-6-35)-[Ir(Tp(Ph)kappa N-3,N',N " )H(dihydr ofuran-2(3H)-ylidene)] (3). a cyclic Fischer carbene formed by double C-H a ctivation of THF. Accordingly, complexes of the general formula [Ir(Tp(3))( butadiene)] (see 4-6: butadiene = buta-1,3-diene, 2-methylbuta-1,3-diene (i soprene). 2,3-dimethylbuta-1,3-diene) reacted with THF to yield 3 or the re lated 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-p osition of the pyrazole rings.