Mechanistic interpretation of orders in catalyst greater than one

On the Use of Triarylsilanols as Catalysts for Direct Amidation of Carboxylic Acids

“…Accordingly, a “same excess” experiment using catalyst 6h for the model system (cf., Figure a) and time-adjusted analysis showed that the reaction profiles did not overlay (Figure a), in line with our expectations regarding the previously observed loss of catalyst integrity as determined by NMR spectroscopy (cf., Figures and ) and by the observation of disiloxane formation when using secondary amines. However, a second same excess experiment with added product amide 3a gave plots that nearly overlaid (Figure b), showing instead that for this acid–amine combination, amide product inhibition is the dominant factor at play rather than catalyst decomposition, and these findings are also consistent with the determined catalyst order . A further reaction with water added instead (Figure c) shows that it also contributes to the inhibition (although we expect it is lost as it is generated in refluxing toluene).…”

“…Purification by column chromatography (hexane) gave tri-ptolylsilane (5c) (542 mg, 1.8 mmol, 40%) as a white solid; mp 81.6− 83.0 °C. ATR−FTIR 2114 cm −1 ; 1 H NMR (400 MHz, CDCl 3 ): δ 7.51 (d,J = 7.7 Hz,6H),7.23 (d,J = 7.7 Hz, 6H), 5.47 (s, 1 J Si−H = 197.6 Hz, 1H), 2.40 (s, 9H); 13 C{ 1 H} NMR (101 MHz, CDCl 3 ): δ 139. 8, 135.9, 130.3, 129.0, 21.7; 29 Si{ 1 H} NMR (80 MHz, CDCl 3 ): δ −18.6.…”

“…Tris(4-(t-butyl)phenyl)silanol (6d) was prepared according to general procedure B3 using silane 5d to give tris(4-(t-butyl)phenyl)silanol (6d) (444 mg, 1.0 mmol, 100%) as a white solid; mp 226−227 °C. ATR−FTIR 3662 cm −1 ; 1 H NMR (400 MHz, CDCl 3 ): δ 7.60 (d,J = 8.3 Hz,6H),7.41 (d,J = 8.3 Hz,6H), 2.39 (s, 1H), 1.33 (s, 27H); 13 C{ 1 H} NMR (101 MHz, CDCl 3 ): δ 153. 1, 135.0, 132.2, 125.0, 34.9, 31.4; 29 Si{ 1 H} NMR (80 MHz, CDCl 3 ): δ −12.4; HRMS (APCI − ) m/z: [M − H] − calcd for C 30 H 39 OSi, 443.2765;found, 443.2753.…”

“…Purification by silica plug, followed by eluting with hexane, to remove non-polar components, and then with Et 2 O gave tris(4-(trifluoromethyl)phenyl)silanol (6j) (595 mg, 1.24 mmol, 85%) as a white solid; mp 101.8−102.9 °C. ATR−FTIR 3194 cm −1 ; 1 H NMR (400 MHz, CDCl 3 ): δ 7.74 (d,J = 7.8 Hz,6H),7.68 (d,J = 7.8 Hz, 6H), 3.19 (s. 1H); 13 C{ 1 H} NMR (101 MHz, CDCl 3 ): δ 138. 3,135.3,132.8 (q,J = 32.3 Hz), 125.0 (q, J = 3.8 Hz), 124.0 (q, J = 272.5 Hz); 19 Tris (3,4,5-trifluorophenyl)silanol (6k).…”

Catalyst or Catalyst System? Nonlinear Behaviour and the Limits of Mechanistic Understanding in Proline-Based Asymmetric Catalysis.

“…4), which is consistent with catalytically active monomers; [23] catalytically active dimers would have an order between 1 and 2. [26] Thus, we are facing here a catalytic scheme identical to the case of the DAIB ligand described by Noyori, that is, an active monomeric species in equilibrium with inactive dimers (Fig. 2c).…”