Unusually Lewis basic Pro‐azaphosphatranes

Abstract

The title compounds of the type P(RNCH₂CH₂)₃N (1, R = H; 2, R = Me; 3, R = CHz₂Ph) display the unexpected basicity trend 1 < 2 < 3 with respect to protonation which forms the azaphosphatranes magnified image (4, R = H; 5, R = Me; 6, R = CH₂Ph). The unusual basicity order 1 < 2 < 3 is also supported by the trend in ¹J_PSe values obtained for SeP(RNCH₂CH₂)₃N (8, R = H; 9, R = CH₂Ph; 10, R = Me). Deprotonation of 4 is shown to produce a variety of deprotonated derivatives which were trapped by alkylation with MeI. A favored rationale for the unusual weakness of 4 as a protonic acid (pKa in DMSO, 29.6) is an unusual stability of the axial three‐center four‐electron bond signalled by the unusually high field ³¹P chemical shift of this cation (—42 ppm).