Phosphinines diaza

Derivatives of monoaza- and diaza-phosphinines 194—198 have been synthesized by Frison and Le Floch (Scheme 75).235 Calculations performed on such... 

Diels-Alder reaction at higher temperature (around 110-120 °C) to give azaphos-phabarrelenes 38 which finally decompose to yield the expected 2,3,5,6-tetrafunc-tional phosphinines 39. Importantly, the difference of reactivity between diaza and mono aza-phosphinine derivatives allows the successive use of two different alkynes. The general principle of this synthetic approach is presented in Scheme 10. It is important to mention that all these cycloaddition/cycloreversion sequences can be performed in the same flask and there is no need to isolate the 2-zaphosphinine formed after the first Diels-Alder reaction. 

Additional experiments were also carried out with complex 133 which results from the substitution of the COD ligand in 73 by a 1,4-diaza-l,3-diene (DAD) [48], The catalytic activity of 133 in the cyclodimerization of 1,3-butadiene was compared to that of its carbon counterpart the [Fe(r/6-toluene)(DAD)] complex. In this case, the toluene complex proved to be 10 times more efficient and yielded better TON than the phosphinine-based complex for the formation of COD (1,5-cyclooctadiene) and VCH (vinylcyclohexene). This lack of activity was ascribed to the stronger affinity of phosphinine ligands towards Fe(0) thus limiting the generation of the 12 VE [Fe(DAD)] complex which is the genuine catalytic active species (Scheme 27). 

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