Scheme 1. Relay catalysis of Ru-HAP for conversion of secondary amine to formamide.

Fig. 1. Kinetic analysis of methylamine (a) and dimethylamine (c) direct formylation. Arrhenius plot of methylamine (b) and dimethylamine (d) formylation.

Fig. 2. (a) Kinetic analysis of methylformamide transformylation with dimethylamine. (b) Arrhenius plot of transformylation reaction between dimethylamine and MF.

Scheme 2. Proposed pathway for relay-route to synthesize DMF with methylamine as a promoter.

Fig. 3. (a) FT-IR spectra of CO adsorption on Ru-HAP catalyst for 30 min at room temperature and desorption under Ar flow. (b) IR of liquid n-butylamine adsorption at room temperature and then desorption under Ar flow. (c) In situ IR spectra of consecutive adsorption of CO followed by n-butylamine. (d) The in situ IR spectra magnified in a range of 1900-2150 cm?1, which is associated with the adsorption of CO on Ru species.

Scheme 3. Proposed reaction mechanism of relay-route over Ru-HAP catalyst.

Fig. 4. The time-on-steam profile at 150 °C. Reaction conditions of relay-route (green dots): methylamine (1.0 mmol), dimethylamine (1.0 mmol), CO (0.9 MPa), Ru-HAP (0.05 g), methanol (2 mL). Reaction conditions of direct-route (orange dots): dimethylamine (1.0 mmol), CO (0.9 MPa), Ru-HAP (0.05 g), methanol (2 mL).

Fig. 5. (a) Effect of CO pressure on the yield of DMF and MF, as well as the nDMF/nMF mole ratio in relay route. Reaction conditions: dimethylamine (1.0 mmol), methylamine (1.0 mmol), CO, Ru-HAP (0.05 g), methanol (2 mL), 150 °C, 6 h. (b) Effect of the proportion of dimethylamine in the two amines on the RateDMF/RateMF ratio in relay route. Reaction conditions: the total mole number of dimethylamine and methylamine (2.0 mmol), CO (0.9 MPa), Ru-HAP (0.05 g), methanol (2 mL), 150 °C, 6 h.

Fig. 6. Reaction mixture transformylation with additional dimethylamine. (The dots represent the concentration of dimethylamine: 0.050 mol·gcat?1 (red dot), 0.030 mol·gcat?1 (purple dot), 0.015 mol·gcat?1 (green dot), 0.0010 mol·gcat?1 (yellow dot)). The reaction mixture was obtained via the relay route at 150 °C for 6 h at the standard conditions. Components of reaction mixture: CMF = 0.128 mmol·mL?1, CDMF = 0.204 mmol·mL?1. Reaction conditions: dimethylamine, Ru-HAP (0.05 g), methanol (2 mL), 150 °C, 6 h.

Fig. 7. The time-on-steam profile for relay-route. Reaction conditions: dimethylamine (1 mmol), methylamine (1 mmol), Ru-HAP (0.05 g), CO (0.9 MPa), methanol (2 mL), 150 °C.

Fig. 8. sE-factor, cE-factor, and E-factor analysis of the synthesis of DMF. Details of the calculation are shown in the Supporting Information.