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Ambident PCN Heterocycles: N‐ and P‐Phosphanylation of Lithium 1,3‐Benzazaphospholides
Author(s) -
Aluri Bhaskar R.,
Burck Sebastian,
Gudat Dietrich,
Niemeyer Mark,
Holloczki Oldamur,
Nyulaszi Laszlo,
Jones Peter G.,
Heinicke Joachim
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200901753
Subject(s) - steric effects , chemistry , conformational isomerism , adduct , nuclear magnetic resonance spectroscopy , crystallography , spectroscopy , lithium (medication) , stereochemistry , ring (chemistry) , crystal structure , infrared spectroscopy , medicinal chemistry , molecule , organic chemistry , medicine , physics , quantum mechanics , endocrinology
Synthetic and structural aspects of the phosphanylation of 1,3‐benzazaphospholides 1 Li , ambident benzofused azaphosphacyclopentadienides, are presented. The unusual properties of phospholyl‐1,3,2‐diazaphospholes inspired us to study the coupling of 1 Li with chlorodiazaphospholene 2 , which led to the N‐substituted product 3 . Reaction of 1 Li with chlorodiphenyl‐ and chlorodicyclohexylphosphane likewise gave N ‐phosphanylbenzazaphospholes 4 and 5 , whereas with the more bulky di‐ tert ‐butyl‐ and di‐1‐adamantylchlorophosphanes, the diphosphanes 6 and 7 are obtained; in the case of 7 they are isolated as a dimeric LiCl(THF) adduct. Structural information was provided by single‐crystal X‐ray diffraction and solution NMR spectroscopy experiments. 2D exchange spectroscopy confirmed the existence of two rotamers of the aminophosphane 5 at room temperature; variable‐temperature NMR spectroscopy studies of 6 revealed two dynamic processes, low‐temperature inversion at ring phosphorus (Δ H ≠ =22 kJ mol −1 , Δ S ≠ =2 J K −1 mol −1 ) and very low‐temperature rotation of the t Bu 2 P group. Quantum chemical studies give evidence that 2‐unsubstituted benzazaphospholides prefer N‐phosphanylation, even with bulky chlorophosphanes, and that substituents at the 2‐position of the heterocycle are crucial for the occurrence of P–N rotamers and for switching to alternative P‐substitution, beyond a threshold steric bulk, by both P‐ and 2‐position substituents.