Reactions of di- and trimethylplatinum(IV) complexes with N-(phosphonomethyl)glycine (glyphosate) and iminobis(methylenephosphonic acid). Crystal structures of three dimethylplatinum(IV) complexes with N-(phosphonomethyl)glycine coordinated facially

Abstract

Reaction of “cis- [Pt(CH)(OD)]” with N-(phosphonomethyl)glycine (glyphosate, Himpa) in DO at pD 11 gave a mixture of two isomers of [Pt(CH)(OD)(impa-N,O)] (N and either carboxylate O (O) or phosphonate O (O) trans to methyl). When the pH of a similar solution in HO was decreased to 3.4, and the solution was allowed to stand, crystals of [Pt(CH)(Himpa-.N,O,O,)(HO)]•HO deposited. The crystal structure was determined by X-ray diffraction: space group Pbca; a = 7.937(6), b = 10.484(2), c = 26.795(6) A; Z = 8; R = 0.030, for 1418 reflections. The isomer was that with N and O trans to the methyl groups. When an alkaline solution (pD 10.5) was allowed to stand, the isomer of [Pt(CH)(OD)(impa-N,O,O)] with N and O trans to methyl formed fac-[PtBr(CH)(HO)] with glyphosate gave isomers of [PtBr(CH)(Himpa-N,O,O)]. At high pH, where coordinate phosphonate was deprotonated, the preferred isomer had N and O trans to methyl, while at low pH, where coordinated phosphonate was protonated, the preferred isomer had N and O trans to methyl. The crystal structure of the silver salt of the latter isomer, Ag[PtBr(CH)(Himpa)], was determined by X-ray diffraction: space group Pna2; a = 8.4009(9), b = 12.790(2), c = 10.467(2) A; Z = 4; R = 0.022, 928 reflections. The silver ion was bound by bridging bromide and by three O atoms to give an approximately tetrahedral environment about the metal and a two-dimensional network structure. UV irradiation of a DO solution containing the isomers of [PtBr(CH)(impa)] with N trans to methyl gave the thermodynamically most stable isomer, with N trans to bromide and O, O trans to methyl. Acidification and addition of silver ion gave crystals of Ag[PtBr(CH) (Himpa)] [PtBr(CH)(impa)]•1.5HO, whose structure was determined by X-ray diffraction: space group P2/c; a = 13.78(2),b= 14.523(4) A, c= 14.38(2) A; β = 118.33(5)°; Z= 4; R = 0.044. The two different anionic complex units form the basis of an extended ribbon structure, linked together through three independent silver ions by triply-bridging bromide ions and oxygen atoms from both carboxylate and phosphonate groups. Iminobis- (methylenephosphonic acid) (Hidmp) with fac-[Pt(CH)(DO)] in DO at pD 5.5 gave a complex with the ligand coordinated tridentate, but broadening of peaks from ligand protons was interpreted in terms of a rapid process in which metal-oxygen bonds were ruptured. [PtBr(CH)(DO)] with Didmp, on long standing at pD 4, gave [PtBr(CH)(Didmp-N,O,O)]. “cis- [Pt(CH)(OD)]” with (methylimino)bis(methylenephosphonate) (midmp) in DO at pD 12.5 gave [Pt(CH)(OD)(midmp-N,O)], but when the solution was acidified, the ligand dissociated. The relative instability of complexes with iminobis(methylenephosphonate) ligands coordinated tridentate may be due to steric interactions between phosphonate oxygen atoms and other ligands bound to the metal.