Four members of a new family of powerful bispyridinylidene organic reducing agents have been prepared, which exploit iminophosphorano (-N=PR3; R = Ph, Cy) π-donor substituents. Electrochemical studies show exceptionally high oxidation potentials, ranging from 1.30 to 1.51 V versus SCE. These new reductants were shown to effectively convert 1-bromonaphthalene to naphthalene under mild reaction conditions. From the redox potentials, substituent constants (σp(+)) for the iminophosphorano groups Ph3P=N- (-1.82) and Cy3P=N- (-2.21) were determined, demonstrating their superior π-donating properties compared to traditional amino substituents.

Bispyridinylidenes (BPYs) have emerged as an important class of neutralo rganic electron donors, with redox potentials that vary widely with choice of substituent. Methods to predict the effect of substitution on the redox potential are therefore highly desirable. Here we show that the redox potential of BPYs featuring iminophosphoranos ubstituents (R 3 P = N-), which representt he most reducing class of BPYs, can be predicted basedo n the well-knownT olman electronic parameter(TEP) for the respective phosphine fragment (R 3 P). Moreover,b uilding on earlier work relatingr edox potentials to Hammett-type substituent constants, it is now possible to quantitatively predict s p + values for iminophosphoranos ubstituents from TEP values. Theser esultsp rovide ap ath for precisely tailoringr edoxp otentials of iminophosphorano-substituted BPYs, but also give quantitative descriptors for how these highly versatile iminophosphorano substituents can impactt he properties of any molecular scaffold. Scheme1.Reductions of iodoester 4 to products 5 or 6 in varying isolated yields depending on the strengthoft he OEDused (1, 2,o r3).

Four pyridines decorated with π-donating iminophosphorano substituents (R3PN-) in the 4-position were assessed as acylation catalysts. These catalysts display high sensitivity to the groups at phosphorus, with activities that are...