Suggestion of a "Twist" Mechanism in the Oligomerisation of a Dimeric Phospha(III)zane: Insights into the Selection of Adamantoid and Macrocyclic Alternatives

• Published in: Chemistry : a European journal Vol. 8; no. 24; pp. 5723 - 5731
• Main Authors: Bashall, Alan, Doyle, Emma L., García, Felipe, Lawson, Gavin T., Linton, David J., Moncrieff, David, McPartlin, Mary, Woods, Anthony D., Wright, Dominic S.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 16.12.2002; WILEY‐VCH Verlag; Wiley
• Subjects: Chemistry; Chemistry, Multidisciplinary; density functional calculations; nitrogen; phosphorus; Physical Sciences; rearrangement; Science & Technology; density functional calculations; CORRELATED MOLECULAR CALCULATIONS; nitrogen; REACTIVITY; rearrangement; GAUSSIAN-BASIS SETS; phosphorus
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20021216)8:24<5723::AID-CHEM5723>3.0.CO;2-D

The reaction of the dimeric phospha(III)zane [ClP(μ‐Npy)]2 (1) (py=2‐pyridyl) with pyNHLi (2:1 equivalents, respectively) in THF/Et3N leads to rapid formation of the bicyclic nona‐phospha(III)zane [{ClP(Npy)2}2{P2(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)2P}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 PCl3 with 6‐Me‐pyNHLi. The syntheses and X‐ray structures of 1, 2 and 4 are reported, together with 31P 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. The reaction of the dimeric phospha(III)zane [ClP(μ‐Npy)]2 (1) (py=2‐pyridyl) with pyNHLi in THF/Et3N leads to rapid formation of the bicyclic nona‐phospha(III)zane [{ClP(Npy)2}2{P2(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)2P}2(μ‐Npy)] (3), a process that provides a fundamental mechanistic relationship for the majority of previously reported imidophosphospha(III)zanes.