720 Inorg. Chem. 1986, zyxwvu 25, zyxwvut 120-125 Articles Contribution from the Department of Chemistry, University of Queensland, Brisbane 4067, Australia Multinuclear NMR Study of Reactions of Methylphosphonic Acid, CH3P03H2, and (Aminoalky1)phosphonic Acids, NH2(CH2)nP03H2 zyxw (n zyxwv = 1-3), with the cis -Diamminediaquaplatinum( 11) Cation and cis -Diamminedihydroxoplatinum( 11) Trevor G. Appleton, John R. Hall,* and Ian J. McMahon Received September 17, 1985 3iP, “N, and, in some cases, 195Pt NMR spectroscopy has been used to study the reactions of c ~ ~ - P ~ ( N H ~ ) ~ ( H , O ) , ~ + and C~~-P~(NH,)~(OH), (using ‘SN-substituted ammine) with CH3P03H2 (mpH2) and NH2(CH2),P03H2 zyxwv (n = 1, ampH,; n = 2, aepH2; n = 3, appH,). Each initially gives at pH 1.5 and 4 a complex in which the ligand is bound only through oxygen. At pH 4 subsequent reaction occurs to give a complex in which Pt atoms are bridged by phosphonate and hydroxo groups. With amp, further reaction occurs at pH 1.5 and 4 to give the chelate complex Pt(NH3),(ampH-N,0)+. At pH 4 an intermediate, Pt- zy (NH3)2(po,o,-amp-N)Pt(NH3)2(H20)2+, is detected. In alkaline solution amp2-gives ultimately ~is-Pt(NH,),(amp-Y~~-, while aep2-gives cis-Pt(NH,),(aep-N,O), and app2-does not react. These differences are rationalized in terms of decreasing nucleo- philicity of the ammine group of NH2(CH2),P032- as n increases. Introduction (Aminoalky1)phosphonic acids, NH2(CH2),P03H2,1 are formal analogues of amino acids, NH2(CHz),COOH. The most obvious difference is that the phosphonic acid group is diprotic. (2- Aminoethy1)phosphonic acid, &ciliatine, occurs naturally in several lower life-forms.2 The coordination chemistry of amino acids has been extensively investigated, and the behavior of the (am- inoalky1)phosphonates as ligands might be expected to show comparable diversity and richness. While it is clear from stability constant measurements involving labile metal ions that the (am- inoalky1)phosphonatescan act as ligands over a wide pH range,’s little is known of the structures of the complexes formed. Probably because they are usually much more soluble than complexes of amino acid analogues, very few solid complexes of (amino- alky1)phosphonates have been prepared, and no crystal structures have yet been reported. It is therefore appropriate to study the coordination behavior of these complexes in solution, for which purpose 31P NMR is a technique with obvious potential. When 15N-substituted ammine is used, ISN and 195Pt NMR can also greatly assist in characterizing complexes formed in solution in reactions of ammineplatinum(1I) We have recently used NMR to study the reactions of cis-Pt- (NH3)2(H20)22+ (I) and cis-Pt(NH,),(OH), (11) with glycine (glyH).”s12 Most notable was the formation in acid solution of a complex 111 in which glycine acts as an 0-bound unidentate ( 1) Although the (aminoalky1)phosphonic acids usually exist as zwitterions, +NH3(CH2),,P03H-, unless this is being emphasized they will be written in the unionized form NH2(CH2)nP03H2. (2) (a) Horiguchi, M.; Kandatsu, M. Nature (London) 1959, 184,901. (b) Kittredge, J. S.; Roberts, E.; Simonsen, D. G. Biochemistry 1962, I, 624. (3) Mohan, M. S.; Abbott, E. J. J. Coord. Chem. 1978, 8, 175. (4) Wozniak, M.; Nowogrocki, G. Talanta 1978, 25, 633. (5) Wozniak, M.; Nowogrocki, G. Talanta 1979, 26, 1135. (6) Ismail, I. M.; Sadler, P. J. In “Platinum, Gold, and other Metal Che- motherapeutic Agents”; Lippard, S. J., Ed.; American Chemical Society: Washington, DC, 1983; ACS Symp. Ser. No. 209, p 171. (7) Alei, M.; Vergamini, P. J.; Wageman, W. E. J. Am. Chem. SOC. 1979, 101, 5415. (8) Kerrison, S. J. S.; Sadler, P. J. J. Chem. Soc., Chem. Commun. 1981, 61. (9) Boreham, C. J.; Broomhead, J. A,; Fairlie, D. P. Aust. J. Chem. 1981, 34, 659. (IO) Nee, M.; Roberts, J. D. Biochemistry 1982, 21, 4920. (1 I) Appleton, T. G.; Hall, J. R. J. Chem. Soc., Chem. Commun. 1983, 911. (12) Appleton, T. G.; Hall, J. R.; Ralph, S. F. Inorg. Chem. 1985, 24, 673. 0020- 166918611325-0720$01 SO10 DC H3 N / “OH2 In ligand, with rearrangement to the chelate complex IV being very - + E slow. Also relevant to the present study is a recent investigation by NMR of the interaction between I and phosphate ion.I3 Under acid conditions (pH S l S ) , V forms, in which phosphate is uni- 0 /I R m P OH 1 IX CH2N% 2 XTX ICH212NY 2 Xxm IC%$NY 2 dentate. At pH 3-5, a number of additional species form of which VI predominates, and these solutions eventually turn blue. For an N M R investigation of the reaction of the ligands with the platinum complexes, it is important to be able to identify peaks due to the free ligand and to know the protonation state of the ligand under the reaction conditions. We have recently reported14 31P, I3C, and ‘H NMR spectra as a function of pH for each of the ligands dealt with here: methylphosphonic acid, CH3P03H2 !a cti3 1 (13) Appleton, T. G.; Berry, R. D.; Davis, C. A,; Hall, J. R.; Kimlin, H. A. Inorg. Chem. 1984, 23, 3514. (14) Appleton, T. G.; Hall, J. R.; Harris, A. D.; Kimlin, H. A,; McMahon, I. J. Aust. J. Chem. 1984, 37, 833. 0 1986 American Chemical Society