Spectrochimica Acta. Vol. 46A. No. 8, pp. 1163-1167. 1990 0584~8539/90 $3.00+0.00 Printed in Gtiat Britain Pergamon Ptess plc Charge-transfer complexes with trivalent phosphorus compounds WILLIAMI. AWAD, NADIA G. KANDILE, WASN N. WASSEFand FATMA A. TOHAMY Chemistry Department, University College for Women, Ain Shams University, Heliopolis, Cairo, Egypt (Receiued 7 August 1989; in final form 11 December 1989; accepted 12 January 1990) Abstract-Charge-transfer complexes between triphenylphosphine and triethylphosphite as donors, and maleic, itaconic and citraconic anhydrides as acceptors are studied. INTRODUCTION As FAR as we are aware, trivalent phosphorus has not been used as a donor in charge-transfer (CT) complexes except in a very few cases [l-3]. However, maleic anhydride was used as a CT acceptor on several occasions, especially with aromatic hydocarbons [4-71. SCH~NBERG and ISMAIL[8] reported a colour reaction between maleic anhydride (and allied compounds) and triphenylphosphite. The colour was attributed to a betaine structure (I) and later on, the structure of the product was assigned as the phosphorus ylid [9, lo] (II). + PPhs I 6 I I/ I \ 0 ““\\C / PhaP=C- I CH,-- I 0- The coloured compound formed immediately after mixing of the components is not the betaine (I) nor the ylid (II) (A,, 289 nm, E,,, 37 x lo*), but can only be a CT complex between triphenylphosphine (TPP) as a donor and maleic anhydride as an acceptor. The complex formation (red) is a prior step to the final formation of the ylid. This complex has been followed up using both i.r. and the U.V. spectra. The i.r. spectra (Fig. 1) show a red shift (-70 cm-‘) in the vcco region in all cases where a complex is formed [ 111. In this study, maleic, itaconic and citraconic anhydrides are used as acceptors, and TPP as donor. Both maleic and itaconic anhydrides give intermediate colour complexes. However, citraconic anydride (in a pure form) failed to give any colour which is in contrast to previous findings [8]. This is also confirmed by the absence of any red-shift in the carbonyl stretching frequency (Fig. 1). The U.V. spectra have been used to verify the equilibrium constant (K) as well as the ratio of donor to the acceptor using the modified BENSI-HILDEBRAND equation [12] (see Experimental and Figs 2 and 3). It is well known that a 1:l adduct is a very common complex. Rarely [13] are there cases of ADZ. In the case of TPP, the maximum absorption in Fig. 2 shows a clear maximum at 0.4. This indicates that the ratio of A:D is 2:l. This can be easily explained when we imagine that the free lone pair of electrons on the trivalent phosphorus (D) approaches an M(A) )6:8-B zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 116-Z