Synthesis of 2,6-Dimesitylphenyl-C,C-Dibromophosphaalkene

Abstract

A facile one-pot transformation of Dmp-I to Dmp-P=CBr 2 (Dmp = 2,6-dimesitylphenyl), a valuable precursor for other unsaturated phosphorus compounds, is described. VT-1 H-NMR experiments reveal a hindered rotation of the m-terphenyl structure with a rotational barrier of approx. 14 kcal/mol. Bromination of Dmp-I gives selective substitution of all aromatic protons of the mesityl substituents.

Precursors for the Development of π‐Conjugated Low‐Coordinate Phosphorus Compounds

“…NMR investigations – Signal broadening in the 1 H and 13 C NMR spectra of DmpP=CBr 2 ‐type compounds is a frequently encountered feature, [9] and a similar spectroscopic behavior was also observed for C,C‐ dibromophosphaalkenes 11‐TIPS and 12 . Such a spectroscopic behavior stems from the restricted rotational freedom, as the mesityl rings of the Dmp group clash sterically with the −P=CBr 2 moiety.…”

“…On the cathodic scans, irreversible reductions can be observed at a peak potential of À 1.87, À 2.07 and À 2.13 V for 12, 11-TIPS, and DmpP=CBr 2 , respectively. The CV of 5 (not shown) does not show a reduction within the solvent window, indicating that the redox features observed for 12, 11-TIPS, and DmpP=CBr 2 involve the phosphaalkene Cyclic voltammograms of DmpP=CBr 2 (purple), [9] and C,C-dibromophosphaalkenes 11-TIPS (green) and 12 (red) (1 mM solutions of compounds in DCM, 0.1 M NBu 4 PF 6 , ν = 100 mVs À 1 , vs. Fc + /0 ).…”

“…Previous work has shown that the direct bromination of the phenyl unit of the Dmp group is not possible and tetrabromination of the mesityl groups occurs instead, leaving the central phenyl ring unaffected [9] . A better strategy would then be to start the reaction sequence with a compound that already contains a bromide at its para position.…”

“…UV/Vis investigations – UV/Vis absorption spectra of the synthesized C,C ‐dibromophosphaalkenes 11‐TIPS and 12 , bis(Dmp)butadiyne 5 , and previously reported monomeric phosphaalkenes DmpP=CBr 2 [9] were recorded to investigate the effect of dimerization on the optical properties (Figure 6). As expected, the spectrum of dimeric 12 with the most extended π‐system exhibits the most red‐shifted absorptions of all the compounds.…”

“…Figure 7. Cyclic voltammograms of DmpP=CBr 2 (purple),[9] and C,C-dibromophosphaalkenes 11-TIPS (green) and 12 (red) (1 mM solutions of compounds in DCM, 0.1 M NBu 4 PF 6 , ν = 100 mVs À 1 , vs. Fc + /0 ).…”