ISSN:
0009-2940
Keywords:
Ylides, dichloro- and dibromophosphanyl-
;
Enamines, dichlorophosphanyl-
;
Phosphonium ions, chlorophosphaalkenyl-
;
Stereoelectronic (anomeric) effect and anionic hyperconjugation
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Ylidyl-dihalophosphanes Provide Structural Snapshots on Their Way to DissociationThe reaction of phosphonium ylides with phosphorus trihalides has been studied for the synthesis of ylidyl-dihalophos-phanes (= dihalophosphanyl ylides) Ph3P=CR—PX2 3, X = Cl, and 9, X = Br. Compounds 3, R = aryl, are readily prepared from the phosphonium bromides [Ph3P—CH2R]Br, compounds 3, R = alkyl, SiMe3 or PCl2, and 9 are obtained from silylylides Ph3P=CR—SiMe3, compound 3, R = PPh3+ results from the addition of PCl3 to the hexaphenylcarbodiphosphorane. A (β-morpholinovinyl)dichlorophosphane 12 has also been prepared. Ylides 3 are oxidized by sulfur and selenium and are converted to ylidyl-chlorophosphenium (= chloro-phosphaalkenyl-phosphonium) salts [Ph3P—CR=PCl]AlCl4 10. In the 31P-NMR spectra of 3 and 9 the geminal coupling 2JPP indicates the phosphorus lone pair to be synperiplanar to the phosphonio group. In one case the P(III)—C rotation barrier has been estimated from VT-31P-NMR spectra. By X-ray crystallography the structures of 3, R = Me, 2,6-Cl2C6H4, 4-NO2C6H5, PCl2, of 9, R = Me (two molecules), SiMe3, of an ylidyl-selenophosphonyl dichloride (11b), and of 12 have been analyzed. They provide representatives for the full range of rotation from the symmetric conformer with two equal P—X bonds to the conformer with one P—X bond perpendicular to the PCP plane and with this bond being extremely elongated. Thus, they map out the pathway to P—X bond breaking. On this way the initial charge transfer from the ylidic carbon to the antibonding P—X orbital ends up in a π donation and P—X dissociation.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19951280410
