FEBRUARY
1960
TRIPHENYLARSONIUMFLUORENYLIDE
[CONTRIBUTION FROM
183
MELLON INSTITUTE]
The Chemistry of Ylids. IV. Triphenylarsoniumfluorenylide' A. WILLIAM JOHNSON Received September 9, 1959 Triphenylarsoniumfluorenylide ( IIIe), the first example of an isolable arsenic-containing ylid, has been prepared. Its chemical and physical properties have been examined.
(IIIc) and its 2,7-dinitro derivativeQbhave been described. Three nitrogen ylids, trimethylammoniumcyclopentadienylide (IIb),I0 l-pyridiniumcyclof pentadienylide (IIc) l1 and 1-pyridiniumfluorenylide X-Rt--,X=R (IIId) l 2 have been prepared and isolated. However, Ia Ib none of this latter group is comparable in stability X = heteroatom group to the phosphorus and sulfur ylids. R = hydrocarbon group The unique stability of phosphorus- and sulfurwas discovered in 1919 by Staudinger and Meyer!2 Containing ylids is attributed to d-orbital resonance. it is only recently that its full scope and potential This phenomenon depends on the ability of these have been realized. Wittig and eo-workers3 demon- hetero atoms to expand their octet to a decet by strated the synthetic usefulness of triphenylphos- accepting an electron pair from a carbon 2pphoniummethylide (I, X = (C6H5)3P1R = CHZ) orbital into a vacant sulfur or phosphorus 3dand its derivatives as olefin-forming reagents. orbital, thereby allowing the contribution of strucSince that time numerous examples of the prepa- ture I b as well as I a to the resonance hybrid. If ration and reactions of these ylids have been re- such is in fact the case, one may select other hetero atoms which should behave similarly and p~rted.~ Few isolable, crystalline ylids have been charac- expect to produce stable, isolable ylids from a terized. In the phosphorus series triphenylphos- properly constructed molecule. Accordingly, we phoniumbenzylide (I, X = (C6H5)3P1 R = c6- have undertaken to examine the ability of arsenicH5CH),5 triphenylphosphoniumbenzhydrylide (I, containing compounds to form stable ylids and to X = (ce&,)~P,R = ~(C~HE,)Z),~ triphenylphospho- compare their behavior to the phosphorus analog. There is but little evidence in the literature coniiiumcyclopentadienylide (IIa),' triphenylphosphoniumfluorenylide (IIIa),la and tributylphos- cerning the ability of arsenic to expand its octet. phoniumfluorenylide (1IIb)g are known. In the By examining the deuteroxide-catalyzed exchange sulfur series, only dimethylsulfoniumfluorenylide of deuterium in tetramethylphosphonium and trimethylsulfonium salts, Doering and HoffmannI3 concluded that the heats of activation were lowered from the expected values (calculated on the basis of coulombic interactions only) by 15.4 and 17.2 I I +Y +x kcal., respectively. This lowering was ascribed to IIIa. X = (CeH5)IP IIa. X = (CaHs)::l: d-orbital resonance in each case. In a less precise IIIh. X = (C4HS)rP Ilh. X = (CH3)3h but analogous manner they indicated that in proIIc. X = 1-pyridinium IIIc. X = (CHXLS TIM. S = 1-nvridinium ceeding down the group JT elements, the contriiiie: x = ( C 6 H S ) 3 A S bution of d-orbital resonance should remain nearly IIIf. X = ( C H ~ ) ~ A S constant, the rate of exchange decreasing in pro(1) For previous papers in this series see (a) 111, A. W. portion to and due solely to the increased bond Johnson, J . Org. Chem., 24, 282 (1959); ( b ) 11, A. W.John- distance. Chatt and c o - ~ o r k e r s 'claimed ~ that arAlthough the reaction of ylids of type I (X = (C6H6)3P)with carbonyl compounds
son and R. B. LaCount, Chem. and Ind., 52 (1959); (c) I, A. W. Johnson and R. B. LaCount, Chem. and Ind., 1440 ( 1958). ( 2 ) H. Staudinger snd J. ;\foyer, HeZv., 2, 610 (1919). (3) 0. Wittig and U. Schollkopf, Ber., 87, 1318 (1954) and succeeding papers. (4) For a recent review of this reuction see J. Ilevisallw, /31cll. Soc. chin$.,1020 (1958). (5) 6. Wittig and C . Grisslrr, .-1nn., 580, 44 (1955). (6) C. S. Marvel and C. Coffmsnn, J . Am. Chem. Soc., 5 1 3496 (1929). ( 7 ) F. Ramirex and S. I,evy, J . . l m . Cheni. Soc., 79, 67
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(1957). ( 8 ) .\. 11.. Johnson and It. I3. T,aCoiint, Tptrahedron, i n press.
(9) ( a ) c. I. Hughes and I
