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Summary

121

readily convert at room temperature over several weeks to the thermodynamic even more

stable base adduct 104 (Figure 47). This isomerisation can be also achieved by heating a

solution of 103 to 60 °C for 4 hours.

Figure 47. Neutral borylene base adducts 102−104.

Treating 53 with an excess of these Lewis bases does not result in further reactions. However,

when adding CO to 103 the borylene-carbonyl coupling product 105 is formed (Figure 48).

Figure 48. Synthesis of 105.

When two equivalents of the N-heterocyclic carbene ItBu are used, the reaction with 53 yields

[(



-C

)(OC)

Mn(ItBu)] and the NHC-stabilised borane 106 (Scheme 91). The mechanism

for the formation of 106 remains uncertain. However, it is relatively safe to assume that the

first step of this reaction consists of the generation of an intermediate, unstable analogue of

105. Induced by a C−H bond activation of one of the carbene’s tert-butyl groups, dissociation

of the metal−boron bond ensures and results in the formation of 106.

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Schwank ITBU User Manual Page 143