The saturated trihydride IrH 3 {κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (1; xant(P i Pr 2 ) 2 = 9,9-dimethyl-4,5bis(diisopropylphosphino)xanthene) coordinates the Si-H bond of triethylsilane, 1,1,1,3,5,5,5-heptamethyltrisiloxane, and triphenylsilane to give the σ-complexes IrH 3 (η 2 -H-SiR 3 ){κ 2 -cis-P,P-[xant(P i Pr 2 ) 2 ]}, which evolve to the dihydride-silyl derivatives IrH 2 (SiR 3 ){κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (SiR 3 = SiEt 3 (2), SiMe(OSiMe 3 ) 2 (3), SiPh 3 (4)) by means of the oxidative addition of the coordinated bond and the subsequent reductive elimination of H 2 . Complexes 2-4 activate a C-H bond of symmetrically and asymmetrically substituted arenes to form silylated arenes and to regenerate 1. This sequence of reactions defines a cycle for the catalytic direct C-H silylation of arenes. Stoichiometric isotopic experiments and the kinetic analysis of the transformations demonstrate that the C-H bond rupture is the rate determining step of the catalysis. As consequence, the selectivity of the silylation of substituted arenes is generally governed by ligand-substrate steric interactions.