Switching of carbene spin states: effect of hydrogen bond donors

Figures & data

Figure 1 Proposed reactions of singlet and triplet carbenes with an alcohol.

Note: Methanol was the alcohol used in this figure.

Table 1 B3LYP calculated gas phase singlet–triplet energy separations (kcal/mol) for carbenes

Entry	Calculated, ΔΕSΤ at 6-311 ++G(d, p)		ΔΕST at Aug-cc-pVDZ without ZPE
	With ZPE	Without ZPE
H2C	11.73	12.15 (12.06)	11.13
Me2C	−0.75	−0.36 (−0.38)	−1.02
Et2C	−3.18	−2.45	−3.05
Ph2C	5.64	5.92	4.82

Notes: Values in parentheses were calculated at CCSD(T)/6-311++G(d, p) level without ZPE correction. Basis set used are 6-311++G(d, p) and Aug-cc-pVDZ.

Abbreviations: ΔE_ST, singlet–triplet energy separation; ZPE, zero-point energy.

Table 2 Gas-phase B3LYP/6-311++G(d, p) calculated singlet–triplet energy separations (in kcal/mol) and dipole moments (in debye) for carbene–solvent complexes^a,b

Entry	∆EST		∆(∆EST)	μ
	With ZPE	Without ZPE		S	T
H2C…H–OH	7.95	7.04 (7.74)	3.78	3.95	2.50
H2C…H–OCH3	7.74	7.10 (7.76)	3.99	3.70	2.06
Me2C…H–OH	−5.73	−6.03 (−4.15)	4.98	4.26	2.66
Me2C…H–OCH3	−5.82	−5.97	5.07	4.22	2.40
Et2C…H–OH	−3.75	−4.18	0.57	4.36	2.74
Et2C…H–OCH3	−3.91	−4.28	0.73	4.37	2.67
Ph2C…H–OH	−0.45	−0.62	6.09	4.47	2.72
Ph2C…H–OCH3	−0.18	−0.42	5.92	4.36	2.53

Notes: Values in parentheses refer to CCSD(T)/6-311++G(d, p) energies without ZPE correction. ^aΔ(ΔE_ST) = ΔE_ST (free carbene) – ΔE_ST (carbene…solvent complex); ^bsinglet states are more stable. The … signifies a weak interaction between atoms.

Abbreviations: ΔE_ST, singlet–triplet energy separation; ZPE, zero-point energy; μ, dipole moment; S, singlet; T, triplet.

Figure 2 B3LYP/6-311++G(d, p) optimized singlet state geometries of carbene–solvent complexes.

Figure 3 Spin cross-over for Ph₂C…H−OCH₃ complex calculated at the B3LYP/6-311++G(d, p) level without zero-point energy correction.

Note: The … signifies a weak interaction between atoms.
Abbreviation: E_el, electronic energy.

Figure 4 Molecular graph of the Me₂C…H−OCH₃ complex showing the topological parameters at the C…HO bond critical point. All values are in atomic units.

Note: The … signifies a weak interaction between atoms.
Abbreviations: ρ, electron density; ∇²ρ, laplacian of electron density; H(r), local energy density; ELF, electron localization function.

Table 3 Topological analysis of the C…H−O bond for the complexes

Entry		ρ (rho)	▽^2ρ	H(r)	ELF
H2C…H–OH		0.029	0.051	−0.003	0.181
H2C…H–OCH3		0.031	0.050	−0.004	0.194
Me2C…H–OH		0.033	0.049	−0.005	0.197
Et2C…H–OH		0.042	0.048	−0.006	0.215
Et2C…H–OCH3		0.046	0.052	−0.007	0.221
Me2C…H–OCH3		0.034	0.048	−0.006	0.254
Ph2C…H–OH		0.034	0.062	−0.003	0.232
Ph2C…H–OCH3		0.035	0.066	−0.004	0.241

Notes: All values are in atomic units. The … signifies a weak interaction between atoms.

Abbreviations: ELF, electron localization function; ρ, electron density; ∇²ρ, laplacian of electron density; H(r), local energy density.