Ambiphilic defined

The philicity of singlet carbenes is an important concept to classify carbenes that was systematically studied by Moss. [9-11] The relative reactivity (selectivity) of a series of singlet carbenes in cyclopropanation reactions with electron rich and electron poor carbenes was used to quantify the carbene philicity. An empirical carbene philicity scale with a parameter niQ- (where X and Y are the substituents at the carbene center) was defined (Figure 1). Electrophilic carbenes show Wqxy values below 1, nucleophilic carbenes above 2, and ambiphiles are between. [10] Ambiphilic carbenes act as an electrophile towards electron-rich alkenes and as a nucleophile towards electron-poor alkenes. The niQ- Y values obey an empirical linear free energy relationship with the Taft substituent parameters and Oj. This allows to estimate the niQ- Y values of unknown carbenes. 

PhOCCl) and phenoxyfluoroearbene (PhOCF). [37] PhOCCl has w xy = 1.49 as ealeulated from Eq. 4, [36] nearly identieal to that of CF2, w xy = 1.48 (experimental) or 1.47 (calculated). [8] Despite the well expressed electrophilicity of CF2, [9] PhOCCl behaves as an ambiphile cf, Table 3. [38] Thus, W(2xy (calcd) = 1.49 already marks an empirical boundary for ambiphilic carbenes, at least as viewed through the lens defined by the aUcenes in Tables 2 and 3. PhOCF has w xy (calcd) = 1.74, considerably higher than that of PhOCCl, and 0.15 higher than that of the first ambiphile, MeOCCl (Table 2). The data of Table 3 indicate that PhOCF also behaves as an ambiphile. 

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