Table 1.
Rate Constants for Different Lewis Acids Ranked by Acceptor Number
| k2 (M−1 s−1) | ||
|---|---|---|
| Lewis acid (A.N.)a | DTBP | xanthene |
| MnV(O)(TBP8Cz) | ||
| none | 2.9 ± 0.1 | (1.8 ± 0.2) × 10−3 |
| TFA (40) | – | (9 ± 1) × 10−4 |
| Zn2+ (68) | 17 ± 1 | (8.1 ± 0.4) × 10−3 |
| HBArF (102) | – | (1.9 ± 0.2) × 10−2 |
| B(C6F5)3 (82) | 107 ± 8 | (5.5 ± 0.3) × 10−2 |
| MnV(O)(tpfc) | ||
| none | 45 ± 0.3 | – |
| TFA | 32.6 ± 0.5 | – |
| Zn2+ | 943 ± 26 | – |
| Sc3+ | 27.3 ± 0.7 | – |
| Yb3+ | 42 ± 2 | – |
| Ca2+ | 1386 ± 5 | – |
| B(C6F5)3 | 271 ± 6 | – |
a
A.N. = acceptor number, which is proportional to the Lewis acid strength (see ref 21).