Richard A. Kortes

[RuII(hedta)]− complexes of 2,2′-dipyridylamine (dpaH) and a bifunctional tethered analog, N,N,N′,N′-tetrakis(2-pyridyl)adipamide (tpada)

Abstract [RuII(hedta)L]− complexes (hedta3−=N-hydroxyethylethylenediamine-N,N,N′-triacetate); L=dpaH (2,2′-dipyridylamine) and tpada (N,N,N′,N′-tetrakis(2-pyridyl)adipamide)) have been studied by 1H NMR and electrochemical methods in aqueous solution. The bidentate rings of dpaH and tpada are differentiated as shown by NMR upon coordination to RuII due to differences in the local environment. The dpa–R headgroup of each ligand binds ‘in-plane’ with the en backbone of hedta3− and with one pyridyl ring being nearer the amine of hedta3− having the pendant glycinato group (matching the known arrangement with bpy (2,2′-bipyridine)). RuII/III E1/2 values follow the order dpaH (0.32 V)

A comparison of the solution behavior of Pt(II) complexes of N,N′- and N,N-ethylenediaminediacetate (edda and uedda)

Abstract Pt(II) complexes of N , N ′-ethylenediaminediacetate (edda) and N , N -ethylenediaminediacetate (uedda) have been prepared from K 2 PtCl 4 by stepwise addition of the nitrogen backbone donors at pH ∼ 2.9 (50–60 °C, 60 h) and further coordination of the deprotonated carboxylate donors at pH ≥ 4 (65–75 °C, 24 h). Coordination of the glycinato donors was shown by 1 H and 13 C NMR and IR methods. The symmetrical edda ligands form 38.3% ( R , R )/( S , S )-[Pt(edda)] isomers and 61.7% meso ( R , S )/( S , R )-[Pt(edda)] isomers. All four forms of [Pt(edda)] undergo aquation of one in-plane glycinato donor in 72 h as detected by the appearance of a 13-line 1 H NMR pattern which may be deconvoluted into four AB glycinato sets. These results are indicative of pendant or ion-paired glycinato donor for [Pt(edda) (H 2 O)] which is placed either on the same side, or the opposite side, of the PtN 2 O 2 plane and coordinated glycinato donor. 195 Pt NMR shows that H 2 O is actually replaced by Cl − , i.e.[Pt(edda)Cl] − . The unsymmetrical [Pt II (uedda) X] (X = H 2 O, Cl − , OH − ) complex exhibits no major change over long time intervals (≥ 10 days, pD ∼ 6). The presence of a minor species at 15% abundance may be a similarly structured species as for [Pt(edda)(H 2 O)] with a pendant glycinato functionality. The major complex in solution is shown by the 1 H NMR with [NaCl] and [NaClO 4 ]-dependence studies to be [Pt(uedda)(H 2 O)] at low [Cl − ] and [Pt(uedda)Cl] − at 1.0 M Cl − . 195 Pt NMR confirms the formulation of X = H 2 O at low [Cl − ]. 1 H and 13 C NMR evidence supports one axially associated and one in-plane coordinated glycinato donor each for the major [Pt(uedda)(H 2 O)] complex. The 13 C NMR shows only one type of glycinato donor with a chemical shift of 189.3 ppm for the major species, and two types for the 15% species (185.6 and 170.5 ppm). The major species of [Pt(uedda)(H 2 O)] has only one type of carboxylate stretch in the IR spectra (1661 cm −1 ; shoulder feature at 1639 cm −1 ) which compares favorably with the fully-coordinated pair of glycinato donors of [Pt(edda)] (1640 cm −1 ). It is proposed that the structures of [Pt(uedda)(H 2 O] and [Pt(uedda)Cl] − are pseudo-square pyramids which illustrates the capacity of Pt(II) to adopt five-coordinate, 18-electron complexes when a suitable chelate ligand offers a fifth associable donor. These species are similar to the five-coordinate intermediates of ligand substitution reactions of typical square-planar Pt(II) complexes.

pH-dependent coordination of the glycinato donors of nitrilotriacetatoplatinate(II), [PtII(nta)]−

Abstract Two main species are formed when nitrilotriacetic acid (H3nta) displaces Cl− ligands from PtCl42−. The resultant [PtII(nta)Cl]2− and [Pt(ntaH, Cl]− complexes were examined by 1H and 13C NMR methods. The 1:1 complex is responsive to changes in pH, indicating a titratable glycinato arm in [PtII(nta)Cl]2− rather than a [PtII(nta)], polymer previously prepared by Smith and Sawyer. The major species (∼82% at pH 4.5) has two in-plane glycinato donors exhibiting an AB 1 NMR quartet (Ha = 4.40 ppm, Hb = 4.25 ppm, Jab = 16.3 Hz, area 2) and a singlet for the third glycinato donor (3.85 ppm, area 1). The latter is assigned as a weakly axially-associated glycinato donor which renders [PtII(nta)Cl]2− as a five-coordinate entity. The minor component (∼ 17%) is the dichloro derivative having two pendant glycinato arms (AB quartet: Ha = 3.91 ppm, Hb = 3.83 ppm, Jab = 16.7 Hz, area 2) and a lone in-plane glycinato donor (singlet, 4.03 ppm, area 1). At pH=3.0 the major species exhibits proton exchange-induced shifts of the glycinato singlet as well as near coalescence of the in-plane glycinato donors, indicative of an associative/dissociative equilibrium of the axial glycinato donor which alters the coordination number of the PtII center. This exchange is frozen out at pH 1.2 where the axial donor is fully removed by protonation as a pendant group in [Pt(ntaH)Cl]− (1H NMR singlet, 4.08 ppm, area 1, pendant glycinato; AB quartet, Hb = 4.36 ppm, Hb = 4.26 ppm, Jab = 16.4 Hz area 2, in-plane pair of glycinato donors). Further proton-induced dechelations of the in-plane glycinato donors occur over a 14 day period, forming a monodentate N-bound species thought to be [PtII(ntaH3)Cl3]− with one glycinato 1H NMR singlet (4.30 ppm). The existence of one chloride in [PtII(nta)Cl]2−, the major (82%) species, and two chlorides in the lesser (17%) species was confirmed by 195Pt NMR. The 195Pt NMR spectra indicate that the axial interaction in [PtII(nta)Cl]2− is very weak, with δPt shifts of −1309 ppm compared to −1317 ppm for mer-[Pt(mida)Cl]−, an authentic four-coordinate analogue.

A temperature-dependent dynamic rearrangement of cis-(R,S)-[Pd(egta)]2– (egta4–=glycine, N,N′-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]) in aqueous solution

The cis-(R,S)-[Pd(egta)]2– complex, egta4–=glycine, N,N′-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]), has been examined by 1H- and 13C-n.m.r. methods over the 18.0 to 95.0°C range in D2O. A dynamic process occurs above 65°C which makes the protons on the NCH2 functionalities of the egta tether become 1H-n.m.r. equivalent. The two states that interconvert coalesce at 81°C. Evidence from 13C-n.m.r. spectra obtained at 81°C show that the in-plane coordinated carboxylates are not lost, but rather a pendant carboxylate becomes attached with loss of the central imino donor. The resultant palladium(II)NO3 intermediate is able to reform cis-(R,S)-[Pd(egta)]2– or, presumably, give trans-(R,R)-[Pd(egta)]2–. The rate limiting step occurs with a rate constant of 178s–1 at 81°C and an activation energy of 20.5kJ/mol. However, competitive aquation of glycinato donors above 85°C prevents isolation of a stable trans-(R,R)-[Pd(egta)]2– isomer.

Attack of cadmium(II) and palladium(II) on cis-(R, S)-[Pd(egta)]2−: coordination rearrangements facilitated by pendant carboxylates

Cd(H2O)2+6–8 reacts with cis-(R, S)-[Pd(egta)]2− producing equimolar amounts of [Cd(egta)]2− and [Pd2(egta)Cl2]2−. The progress of the reaction and products have been followed by recording 1H- and 13C-n.m.r spectra as a function of time. The PdII released in forming [Cd(egta)]2− is thousands of times more reactive than CdII, and intercepts another [Pd(egta)]2− to form the 2:1 complex [Pd2(egta)Cl2]2−; the 2:1 complex is not attacked by CdII. The role of pendant carboxylates below the PdN2O2 plane of cis-(R, S)-[Pd(egta)]2− in supplying a site for ‘docking’ of an incoming CdII or PdII centre, and in leading the metal near the lone pair of rupturing Pd–N bond of [Pd(egta)]2−, or simply by increasing the residence time of CdII or PdII nearby to accelerate the number of collisions between the ruptured N-base and external metal ions, is described. Although mixed-metal [Cd(Pd)(egta)] intermediates are required for the reaction, no such species achieves a detectably large enough concentration to be seen by 1H-n.m.r. The observed spectra are the sum of the reactant, [Pd(egta)]2−, and products, [Cd(egta)]2− and [Pd2(egta)Cl2]2−, throughout the time-dependent change.

An investigation of mononuclear and binuclear palladium(II) complexes of egta (egta = glycine, N,N′-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]) by 1H-, 13C- and 15N-n.m.r. methods

Abstract1:1 and 2:1 palladium(II) complexes of egta4− (egta4− = glycine, N,N′-(1,2-ethanediylbis)(oxy-2,1-ethanediyl)bis[N-carboxymethyl]) were prepared by 1:1 and 2:1 addition of K2PdCl4 to K4egta, and examined by 1H-, 13C- and 15N-n.m.r. methods. The 1:1 complex, [Pd(egta)]2− in solution, utilizes a square-planar coordination comprised of two nitrogen and two glycinato carboxylate donors of egta4−, leaving two glycinato carboxylates pendant. The complex has a cis-(R,S) stereochemistry which places both pendant carboxylates below the PdN2O2 square plane and the tether backbone of egta4− in the “up, up” sense above the same plane. The cis-(R,S) assignment was assisted by computer simulations of the 13C-n.m.r. spectrum for four possible isomers. Only cis-(R,S) and trans-(R,R) calculated 13C-spectra were compatible with the observed 13C-n.m.r. pattern. The HH NOESY spectrum of [Pd(egta)]2− detects long range coupling of the backbone –OCH2CH2O– linkage with both coordinated and pendant glycinato CH2 moieties. The cis-(R,S) isomers tortional movements allow such contacts whereas a trans-(R,R) isomer does not. The 2:1 complex, [Pd2(egta)(H2O)2] in solution has an extended-chain structure with each palladium(II) center coordinated in the mer-iminodiacetate-like coordination with two bound glycinato-functionalities.