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Suggestion of a “Twist” Mechanism in the Oligomerisation of a Dimeric Phospha( III )zane: Insights into the Selection of Adamantoid and Macrocyclic Alternatives
Author(s) -
Bashall Alan,
Doyle Emma L.,
García Felipe,
Lawson Gavin T.,
Linton David J.,
Moncrieff David,
McPartlin Mary,
Woods Anthony D.,
Wright Dominic S.
Publication year - 2002
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 - 10.1002/1521-3765(20021216)8:24<5723::aid-chem5723>3.0.co;2-d
Subject(s) - stereochemistry , steric effects , chemistry , ring (chemistry) , ring strain , pyridine , bicyclic molecule , crystallography , medicinal chemistry , organic chemistry
The reaction of the dimeric phospha( III )zane [ClP( μ ‐Npy)] 2 ( 1 ) (py=2‐pyridyl) with pyNHLi (2:1 equivalents, respectively) in THF/Et 3 N leads to rapid formation of the bicyclic nona‐phospha( III )zane [{ClP(Npy) 2 } 2 {P 2 (Npy)}] ( 2 ). This novel rearrangement can be rationalised by a mechanism involving “twisting (or swivelling)” of the central P( μ ‐Npy)P fragment of the presumed intermediate [{ClP( μ ‐Npy) 2 P} 2 ( μ ‐Npy)] ( 3 ), a process that provides a fundamental mechanistic relationship between the majority of previously reported imidophosphospha( III )zanes. This process is fundamentally reliant on relief from ring strain on going from the four‐membered ring units of 3 to the six‐membered units of 2 . The rearrangement observed for 1 is suppressed on steric grounds by Mesubstitution of the pyridine ring at the 6‐position, the dimeric phosphazane [ClP( μ ‐N‐6‐Me‐py)] 2 ( 4 ) (6‐Me‐py=6‐methyl‐2‐pyridyl) being formed almost exclusively in the 1:1 reaction of PCl 3 with 6‐Me‐pyNHLi. The syntheses and X‐ray structures of 1, 2 and 4 are reported, together with 31 P NMR spectroscopic and DFT calculational studies of the conversion of models of 1 into 2 . The combined studies pinpoint relief from ring strain as the key factor dictating the rearrangement.