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Ylidyl‐dihalogenphosphane – Strukturbilder einer sich anbahnenden Dissoziation
Author(s) -
Schmidpeter Alfred,
Nöth Heinrich,
Jochem Georg,
Schrödel HansPeter,
Karaghiosoff Konstantin
Publication year - 1995
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19951280410
Subject(s) - chemistry , phosphonium , geminal , conformational isomerism , lone pair , aryl , medicinal chemistry , carbanion , alkyl , crystallography , molecule , ylide , nmr spectra database , stereochemistry , iodide , nuclear magnetic resonance spectroscopy , spectral line , inorganic chemistry , polymer chemistry , organic chemistry , physics , astronomy
Ylidyl‐dihalophosphanes Provide Structural Snapshots on Their Way to Dissociation The reaction of phosphonium ylides with phosphorus trihalides has been studied for the synthesis of ylidyl‐dihalophos‐phanes (= dihalophosphanyl ylides) Ph 3 PCRPX 2 3 , X = Cl, and 9 , X = Br. Compounds 3 , R = aryl, are readily prepared from the phosphonium bromides [Ph 3 PCH 2 R]Br, compounds 3 , R = alkyl, SiMe 3 or PCl 2 , and 9 are obtained from silylylides Ph 3 PCRSiMe 3 , compound 3 , R = PPh 3 + results from the addition of PCl 3 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 [Ph 3 PCRPCl]AlCl 4 10 . In the 31 P‐NMR spectra of 3 and 9 the geminal coupling 2 J PP 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‐ 31 P‐NMR spectra. By X‐ray crystallography the structures of 3 , R = Me, 2,6‐Cl 2 C 6 H 4 , 4‐NO 2 C 6 H 5 , PCl 2 , of 9 , R = Me (two molecules), SiMe 3 , 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 PX bonds to the conformer with one PX bond perpendicular to the PCP plane and with this bond being extremely elongated. Thus, they map out the pathway to PX bond breaking. On this way the initial charge transfer from the ylidic carbon to the antibonding PX orbital ends up in a π donation and PX dissociation.