The azophosphine-selenides were prepared by addition of an excess of grey selenium to a toluene solution of the azophosphine 1-R (Scheme 2). Full conversion to the azophosphine-selenide was confirmed by 31 P{ 1 H} NMR spectroscopy. A similar trend in the 31 P chemical shift to that of 1-R is observed for the azophosphine-selenides, increasing in ppm from 3-NMe2 to 3-CF3 (Table ). The value of the 1 JP-Se coupling constant increases from 3-NMe2 to 3-CF3, which demonstrates that the phosphorus centres in the azophosphine ligands 1-R become a poorer σ donor as R gets increasingly electronwithdrawing, as expected. Scheme 2. Synthesis of azophosphine-selenides 3-R. 735 Hz in CDCl3) are significantly lower than those of azophosphines 1-R, and the azophosphines are therefore much poorer donors. The influence of the electron-withdrawing azo group on the donor ability of 3-R can be seen by comparing 3-H (806 Hz) and 3-CF3 (810 Hz) with the selenides of the analogous PhP t Bu2 (708 Hz in CDCl3) and (p-(CF3)C6H4)P t Bu2 (720 Hz in CDCl3), respectively. 3-H and 3-CF3 are both approximately 100 Hz greater in 1 JP-Se value than their non-azo analogues. These data show that in general azophosphines are relatively weak phosphine donors, and that within this chemical space it is possible to fine-tune the donor properties by varying the R group.