Reaction of Tp^menthylMgCH₂CH₃ with Bu^tCOMe

Addition of one equivalent of Bu^tCOMe to 2.1 gave an off white solid that was identified as 2.4 by 1H NMR (equation 2.5).

Two singlets at d 4.31 and 3.86 ppm were assigned to two vinylidene protons, characteristic of an enolate derivative. IR data confirms the formation of an enolate. As well as nB-H at 2455 cm-1 (Tp^menthylMgCH₂CH₃ gives nB-H at 2467cm-1), nC=C is observed at 1606 cm-1. 13C NMR also gave olefinic resonances at d 78.5 and 174.7 ppm. The data were similar to those obtained by Parkin et al[43] for TpBu^tMg{h1-OC(=CH₂)Bu^t} . The data show that the enolate 2.4 is formed.

Reaction of Tp^menthylMgCH₂CH₃ with CyC(O)Me

The reaction of Tp^menthylMgCH₂CH₃ (2.1) with 1 equivalent of CyC(O)Me afforded a white solid that was analysed by 1H NMR and IR (equation 2.6).

The 1H NMR showed a singlet at d 3.97 and 4.22 ppm, again indicative of enolate formation. The cyclohexyl protons were obscured by the ^menthylpyrazolyl protons and hence they could not be assigned. However, IR spectroscopy confirmed the formation of an enolate with nC=C at 1611 cm-1 and nB-H at 2458 cm-1. The limited solubility of the compound prevented a 13C NMR spectrum from being recorded.

Reaction of Tp^menthylMgCH₂CH₃ with Acetone

The reaction of Tp^menthylMgCH₂CH₃ (2.1) with one equivalent of acetone afforded a white solid in 81% yield (equation 2.7).

The product was only slightly soluble in C6D6, hence the 1H NMR was very weak and broad, but resonances at d 3.95 and 4.12 ppm support enolate formation as do IR absorptions nC=C at 1616 cm-1 and nB-H at 2457 cm-1.

Magnesium enolates can be isolated for sterically demanding ketones such as Bu^tC(O)Et [52] or (2,4,6-Me₃C₆H₂)C(O)CH₃ [53] and our observation of the formation of an enolate with Bu^tCOMe and CyC(O)Me is not surprising, but the formation of an enolate with acetone demonstrates that the reactivity of the Mg-R bond is not typical of Grignard reagents and appears to be unique to tris(pyrazolyl)hydroborato magnesium alkyls.