Controlled protonolysis of (N f -N f )Pt(CH 3 ) 2 (1; N f -N f ) ArNdCMesCMedNAr, Ar ) 3,5-(CF 3 ) 2 C 6 H 3 ) with HBF 4 ‚Et 2 O in dichloromethane in the presence of small quantities of water gives the BF 4salt of the aqua complex (N f -N f )Pt(CH 3 )(H 2 O) + (6). When dissolved in trifluoroethanol (TFE), 6(BF 4 -) effects the activation of methane and benzene C-H bonds under very mild conditions. Thus, 6 reacted with benzene in TFE-d 3 at ambient temperature to quantitatively yield (N f -N f )Pt(C 6 H 5 )(H 2 O) + and methane after 2-3 h. The use of C 6 D 6 led to multiple incorporation of deuterium into the methane produced and suggests the involvement of methane σ-complex and benzene σ-or π-complex intermediates. When the solution of 6(BF 4 -) was exposed to 13 CH 4 , an exchange reaction produced ca. 50% of (N f -N f )Pt( 13 CH 3 )(H 2 O) + and CH 4 after ca. 48 h at 45 °C. The reaction was inhibited by added water, suggesting that water is reversibly lost from 6 before C-H activation takes place. The use of CD 4 resulted in multiple deuterium incorporation into the methane produced, again implying a Pt-methane σ-complex intermediate. Low-temperature protonation of 1 in dichloromethane-d 2 generated observable Pt(IV) hydride species (N f -N f )Pt(CH 3 ) 2 (H)(L) + . These decomposed via methane elimination, raising the possibility that the observed C-H activation proceeds by an oxidative addition pathway. The reaction between 6 and CH 4 was investigated by DFT calculations using a model system with the HNdCHsCHdNH ligand. The C-H activation was investigated for oxidative addition and σ-bond metathesis pathways starting from the four-coordinate methane complex (N-N)Pt(CH 3 )(CH 4 ) + . The oxidative addition pathway, thermodynamically uphill by 23 kJ/mol (ZPE-corrected data), was favored by 12 kJ/mol relative to the σ-bond metathesis. When a H 2 O ligand was added to the five-coordinate oxidative addition product, the overall oxidative addition reaction was thermodynamically downhill by 33 kJ/mol (partially ZPEcorrected) starting from an H 2 O adduct of (N-N)Pt(CH 3 )(CH 4 ) + with H 2 O electrostatically bonded at the diimine moiety. In this case, the oxidative addition pathway was favored by 20 kJ/mol. The calculations indicated that reductive elimination of methane from the six-coordinate (N-N)Pt(CH 3 ) 2 (H)(H 2 O) + with the hydride and H 2 O ligands trans disposed occurred in concert with dissociation of the aqua ligand.