Polyhedron Vol. 3, No. 3, pp. 325-329, 1984 Printed in Great Britain. 0277-5387/84 S3.00 + .OO Per@mon Prcs Ltd. zyxwvutsr 2,2,3,4,4-PENTAMETHYLPHOSPHETANIC ACID, C,H,,PO,H: SALTS, COMPLEXES AND A HYDROGEN BONDED AMINE ADDUCT JOHN EMSLEY,* AMANDA P. DUNNING, ROBERT J. PARKER and JOHN K. WILLIAMS Department of Chemistry, King’s College, Strand, London WC2R 2LS, England SHIRLEY BROWN, STELLA EARNSHAW and DAVID S. MOORE7 Department of Chemistry, Imperial College of Science and Technology, South Kensington, London SW7 2AY, England (Received 1 July 1983; accepted 25 July 1983) Abstract-The conjugate base of the title acid, i.e. CIIH,,P02-, has been investigated as its simple salts, as a ligand in transition metal complexes of cobalt and ruthenium, and as a secondary amonium salt in which hydrogen bonding between anion and cation occurs. zyxwvutsrqpo 1 - Chloro - 2,2,3,4,4 - pentamethylphosphetan l- oxide, C,H,,POCl, can be easily synthesized from 2,4,4-trimethylpent-2-ene and PCl, in the presence of Al,Cl,. iJ This chloride is slowly hydrolysed in air. The products of hydrolysis may be the acid, a phosphetanic acid, GH,6P02H, or the anhydride, C,H,6P(0)OP(O)C,H,,, depending on conditions.3 The latter is rapidly formed4 and is remarkably stable to further hydrolysis.3 Little has been written about C,H,,P02H be- yond reporting a few basic physical properties and spectra.5 It is a fairly strong acid, pK, 2.85.’ Its structure is assumed to be (I), based on that of other phosphetans.6 CHs CHa c \ ,y) ‘/ ‘p4 Side view : 4 j/o H’ ‘\C/ \ P / \CHOH \ OH CH3 3 (1) Whereas for the chloride there are two non- interconverting isomers, cti and trans, defined for the ring H and PO groups with respect to the plane *Author to whom correspondence should he ad- dressed. tPresent address: Priory House, Dover College, 6 Waterloo Crescent, Dover, Kent zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA CT16 lLA, England. of the ring, there can be only one form of the acid. The conjugate base, CsH16P02-, has a plane of symmetry bisecting the phosphetan ring. Because of the similarity of R2P02H and R2P02- to RCO,H and RC02-, it was thought likely that this phosphinic acid might also display some of the properties of a typical carboxylic acid in its ability (i) to act as a ligand, and (ii) to involve itself in hydrogen bonding including possibly very strong hydrogen bonding.7 These hopes have been real- ized and in this communication we present evi- dence of C,H,,P02- acting as a ligand towards certain transition metals and of C,H,,PO,H form- ing an adduct with secondary amines in which a cyclic hydrogen bonding system is suspected. EXPERIMENTAL Instruments. IR spectra as KBr discs were run on PE457 and PE580 machines. Nuclear magnetic spectra were taken on JEOL PMX60 SI, Bruker HFX90 and Bruker WM250 spectrometers. 3’P NMR spectra at 36.4 MHz are referenced to exter- nal H,PO,. UV spectra were taken on a UNICAM SP800 spectrometer Preparation of 2,2,3,4,4_pentamethylphosphetanic acid, &H16P02H GH,,POCl, made by the reported methods,‘*2 is hygroscopic. On exposure it the atmosphere for ca. 325