The all-trans isomer of Ru(IMe 4 ) 2 (PPh 3 ) 2 H 2 (ttt-4; IMe 4 = 1,3,4,5-tetramethylimidazol-2-ylidene) reacts with C 6 F 6 at 70 °C to afford the hydride fluoride complex Ru(IMe 4 ) 2 (PPh 3 ) 2 HF (ttt-6). At room temperature, ttt-6 reacts with Et 3 SiH to give a mixture of products, one of which is assigned as the silyl trihydride complex Ru(IMe 4 ) 2 (PPh 3 )-(SiEt 3 )H 3 (8) by comparison to the isolated and structurally characterized analogue Ru(IMe 4 ) 2 (PPh 3 )(SiPh 3 )H 3 (9). As ttt-4 was re-formed cleanly upon heating ttt-6 with Et 3 SiH, it was tested in the catalytic hydrodefluorination (HDF) of C 6 F 6 (10 mol %, 90 °C), along with 9, Ru(IMe 4 ) 2 (P-P)HF (P-P = Ph 2 P(CH 2 ) 2 PPh 2 (dppe, cct-13), Ph 2 P(CH 2 ) 3 PPh 2 (dppp, cct-14), Ph 2 PCH 2 PPh 2 (dppm, cct-15)), Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 HF (cct-7; IEt 2 Me 2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)), and Ru(IEt 2 Me 2 ) 2 (dppe) 2 HF (cct-16) for comparison. Both cct-13 and cct-14 brought about near-quantitative conversion to C 6 FH 5 in 24 h, in comparison to ca. 50% conversion with ttt-4 in 144 h.