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1,2,3‐Triphosphetenes, First Examples of a New Class of Phosphorus Heterocycles
Author(s) -
Pucknat Heike,
Grobe Joseph,
Le Van Duc,
Broschk Burkhardt,
Hegemann Marianne,
Krebs Bernt,
Läge Mechtild
Publication year - 1996
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.19960020213
Subject(s) - ylide , lone pair , chemistry , crystallography , aromaticity , bond length , phosphorus , nitrogen atom , alkyl , stereochemistry , molecule , crystal structure , organic chemistry
Hitherto unknown 1,2,3‐triphosphetenes RCPPCF 3 PCF 3 ( 3a–d ) are formed as main products in reactions of phosphaalkynes RCP [R = i Pr 2 N ( 1a ), t Bu ( 1b ), Me 2 EtC ( 1c ), 1‐methylcyclohexyl ( 1d )] with the cyclotetraphosphane (PCF 3 ) 4 ( 2 ). According to NMR results the CF 3 groups in 3a–d have a trans disposition; an X‐ray diffraction study of 3a confirms this structure. The PP bond lengths in 3a are equal [2.201 (2) and 2.204 (2) Å] and correspond to single bonds. A considerable shortening is observed for the sp 2 ‐C–N bond (1.336 Å) which, together with the elongation of the PC bond (1.746 Å), indicates effective π donation of the lone pair on nitrogen. Surprisingly, 3a can be prepared in quantitative yields by reaction of the PP ylide Me 3 PPCF 3 ( 6 ) with 1 a (molar ratio: 2:1). In contrast, the corresponding reactions of 6 with the alkyl‐substituted phosphaalkynes 1b–d lead to the novel phosphorus ylides Me 3 PC(R)PPCF 3 PCF 3 PCF 3 [R = t Bu ( 10a ), Me 2 EtC ( 10b ), 1‐methylcyclohexyl ( 10c )] in good yields. In their molecular groundstate structures, determined by X‐ray diffraction, the lone pair on the phosphano P atom prefers the syn position with respect to the ylidic PC bond. An unusual lengthening of the sp 2 ‐C–C bond [1.553 (4) ( 10a ), 1.543 (6) ( 10b ), 1.551 (4) Å ( 10c )] to values typical for sp 3 ‐C/sp 3 ‐C distances is observed.