Complexes [PhBP3Ph]RuH(eta(3)-H2SiRR') (R,R' = Me,Ph, 1a; RR' = Ph-2, 1b) react with XylNC (Xyl = 2,6-dimethylphenyl) to form Fischer carbene complexes [PhBP3Ph]Ru(H) = [C(H)(N(Xyl)(eta(2)-H-SiRR'))] (2a,b) that feature a gamma-agostic Si-H bond. The ruthenium isocyanide complexes [PhBP3Ph]Ru(H)-(CNXyl)(eta(2)-HSiHRR') (6a,b) are not intermediates as they do not convert to 2a,b. Experimental and theoretical investigations indicate that XylNC is activated by initial coordination to the silicon center in 1a,b, followed by 1,1-insertion into an Si-H bond of the coordinated silane and then rearrangement to 2a,b.