Table 6. Effect of additives on the rate of CO₂ insertion into 6 in THF.

Entry	Additive	k 1 at 273 K a	Rate increase b	Activation parameters c
1	None	64 ± 6	—	ΔH‡ = 7.2 (4)
				ΔS‡ = –24 (2)
				ΔG‡298 K = 14.3 (5)
2	(nBu)4NPF6	4.0 (4) × 103	3	ΔH‡ = 6.7 (3)
				ΔS‡ = –17 (1)
				ΔG‡298 K = 11.7 (3)
3	LiOTf d	1.5 (2) × 104	9	ΔH‡ = 2.7 (3)
				ΔS‡ = –29 (1)
				ΔG‡298 K = 11.4 (4)
4	NaOTf	2.4 (2) × 104	15	ΔH‡ = 4.3 (3)
				ΔS‡ = –22 (1)
				ΔG‡298 K = 10.9 (3)
5	NaNTf2 e	3.0 (3) × 104	19	—
6	KNTf2	4.0 (4) × 104	25	—
7	LiPF6	4.9 (5) × 104	30	ΔH‡ = 1.8 (4)
				ΔS‡ = –30 (2)
				ΔG‡298 K = 10.7 (5)
8	LiNTf2	7.3 (7) × 104	46	—
9	LiBPh4·3DME f	1.2 (1) × 105	72	—
10	NaBPh4	1.3 (1) × 105	82	—
11	KB(C6F5)4	1.4 (1) × 105	88	—
12	NaBArF4	1.6 (2) × 105	100	ΔH‡ = 6.7 (3)
				ΔS‡ = –10 (1)
				ΔG‡298 K = 9.7 (3)

^aEntry 1 follows the second order rate law k₁[6][CO₂], where k₁ is in M^–1 s^–1; entries 2–12 are assumed to follow the third order rate law k₁[6][CO₂][LA], where k₁ is in M^–2 s^–1.

^bThe rate increase is based on the calculated rate of product formation (M s^–1) in the presence of 20 equivalents of LA (relative to [6]). This allows for the comparison of rates independent of overall reaction order. Due to the poor solubility of the LA, entries 9–12 were run with only 10 equivalents of LA and extrapolated to 20 equivalents. See ESI for further information.

^cΔH^‡ and ΔG^‡ in kcal mol^–1 and ΔS^‡ in cal mol^–1 K^–1.

^dOTF = trifluoromethanesulfonate.

^eNTf₂ = bis(trifluoromethane)sulfonamide.

^fLiBPh₄·3DME = lithium tetraphenylborate tris(1,2-dimethoxyethane).