Journal of the American Chemical Society p. 13614 - 13621 (2011)
Update date:2022-09-26
Topics:
Ley, David
Gerbig, Dennis
Wagner, J. Philipp
Reisenauer, Hans P.
Schreiner, Peter R.
Cyclopropylhydroxycarbene was generated by high-vacuum flash pyrolysis of cyclopropylglyoxylic acid at 960 °C. The pyrolysis products were matrix-isolated in solid Ar at 11 K and characterized by means of IR spectroscopy. Upon photolysis, the carbene undergoes ring expansion, thereby paralleling the reactivity of other known cyclopropylcarbenes. The ring expansion product, cyclobut-1-en-1-ol, was characterized for the first time. Matrix-isolated cyclopropylhydroxycarbene undergoes [1,2]H-tunneling through a barrier of approximately 30 kcal·mol-1, yielding cyclopropylcarboxaldehyde. The cyclopropyl moiety acts as a π-donor and increases the half-life by almost a factor of 10 compared to parent hydroxymethylene, resulting in a temperature-independent half-life of τ = 17.8 h at both 11 and 20 K. Hence, cyclopropylhydroxycarbene is the first hydroxycarbene that differs from other members of its family by a significantly prolonged half-life. As expected, the O-deuterated analogue does not show tunneling. Our findings are rationalized by accurate CCSD(T)/cc-pVnZ (n = D, T)//M06-2X/6-311++G(d,p) computations. The half-life of cyclopropylhydroxycarbene was verified by tunneling computations employing the Wentzel-Kramers-Brillouin formalism. By comparison with other experimentally known hydroxycarbenes, we determine the electronic donor capabilities of the carbenes' substituents to be a dominant factor governing their half-lives.
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