Matthew S. Ward

Synthesis and characterization of meso-[Ru(NO)Cl(dioxocyclam)] and the 1H NMR comparison with [MII(dioxocyclam)] complexes (MII=NiII and PdII) (dioxocyclam=1,4,8,11-tetraazacyclotetradecane-5,7-dione)

Abstract trans -[Ru(NO)X(dioxocyclam)], X=Cl − and OH − , dioxocyclam=(1,4,8,11-tetraazacyclotetradecane-5,7-dione) have been prepared and characterized by NMR, IR and ESI-MS techniques. The trans -[Ru(NO)Cl(dioxocyclam)] shows the nitrosyl stretch at 1846 versus 1875 cm −1 in the cyclam analogue, indicative of strong π-donation from the deprotonated dioxocyclam ligand to the Ru II center and, in turn, to the NO + group. Upon coordination, the dioxocyclam ligand no longer undergoes facile H/D exchange of the NH and C-6 protons. The methylene protons exist in symmetric patterns indicative of the meso isomer with both C-12 and C-14 methylene carbons projecting below the RuN 4 plane toward the side of the axial Cl − for the major product. A lesser amount of the rac isomer, wherein the C-12 and C-14 methylene carbons reside on opposite sides of the RuN 4 coordination plane, is detected. mmff 94 calculations determined that the meso form is more stable than rac by 3.33 kcal mol −1 . The Ru II –N(amide) bonds were calculated as having normal lengths (2.07 A), but the calculated Ru II –N(amine) bonds are elongated to 2.35 and 2.36 A. (It is known that molecular mechanics can overestimate bond lengths for second and third row metal centers by 0.10–0.15 A). Even after correcting for the over-calculated bond distance factor, it is seen that the amine–ruthenium distances are longer, and hence the bonds are weaker, than for ‘normal’ Ru II –amines. The presence of the axial Cl − is established by the ESI-MS ion fragments at m / z =394 for {d 2 -[Ru(NO)Cl(dioxocyclam)]H} + . Ions for {[Ru(NO)(H 2 O)(dioxocyclam)]} + ( m / z =377) and {[Ru(NO)(dioxocyclam)]} + ( m / z =359), the latter from loss of HCl or H 2 O from the 394 and 377 ions, are detected. 1 H and 13 C NMR data for meso -[Ru(NO)Cl(dioxocyclam)] are compared to the meso -[Pd II (dioxocyclam)] complex, and to the Ni II derivative that was synthesized at lower temperature than in previous literature reports. The meso -[Ni II (dioxocylam)] complex was identified previously. In the present work, it is shown that below 50°C the product for the Ni II system is rac -[Ni II (dioxocyclam)]. The assignments for the {Ru(NO)} 3+ , Ni II and Pd II dioxocyclam complexes as having the dominant isomeric forms as meso for {Ru(NO)} 3+ and Pd II , and rac for Ni II are supported by the H–H COSY spectrum for {RuNO)} 3+ , H–H and C–H COSY spectra for Ni II and the H–H COSY spectrum for Pd II derivatives.

[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 REVERSIBLE NO COMPLEX OF FEII(EDAMPDA) AND THE NIII(EDAMPDA) ANALOGUE (EDAMPDA2- = N, N'-BIS(PYRIDYLMETHYL) ETHYLENEDIAMINE-N, N'-DIACETATE)

Abstract NiII, CuII, ZnII and FeII complexes of edampda2− (N,N′-bis(pyridylmethyl)ethylenediamine-N,N′-diacetate) were prepared by the spontaneous chelation of a labile salt of each ion with the H2edampda in aqueous solution (with the FeII complex under N2). edampda2− is designed to have an intermediate ligand field stronger than edta4−, but less than tpen (N,N,N′,N′-tetrakis(pyridylmethyl)ethylenediamine). [FeII(edampda)] is a high-spin (S=2) complex at 25°C as shown by its ligand 1H NMR resonances appearing at low field (ortho pyridyl ring protons at 118 ppm, pyridylmethyl CH2 protons at 57 ppm, coordinated glycinato protons at 44 ppm) as broadened features. The differential pulse voltammogram of [FeII(edampda)] in solution is consistent with seven-coordinate species [FeII(edampda)(H2O)] (E1/2=0.44 V) and [FeII(edampda)Cl]− (E1/2=0.37 V) which are analogous to the known [FeII(edta)(H2O)]2− complex. As anticipated from ligand field factors the (II/III) reduction couple is intermediate in the series [FeII(edta)(H2O)]2−; 0.14 V

Comparison of Energy-Minimized Structures of [PdII(N-methyliminodiacetate)] Complexes of X1-His-X3-His-His Peptides as an Analysis of Steric and Specific Interactions with Synthetic Binding Tags for IMAC Separations

[PdII(mida)(peptide)] complexes for the series of peptides of sequence X1‐His‐X3‐His‐His were studied by molecular mechanics methods using Spartan, MMFF94, and SYBYL programs with X1 = X3 = glycine (G), phenylalanine (F), tyrosine (Y), tryptophan (W), and with X1 = glycine (G) and X3 = proline (P). For comparison purposes, data were also obtained for the Ser‐Pro‐His‐His‐Gly (SPHHG) and the (His)5 peptides. The latter two peptides and GHPHH are tags in current use for IMAC separations. These provide calibration points as to the binding affinities that have been determined for the entire series. The energies of the complexes, as an average trend found from the composite behavior of the three methods, were found to be SPHHG (205* kcal/mol) (most stable; * are values obtained by MMFF94 methods) < HH#HH#H# (222*; where # implies the site of attachment to match the other X1‐His‐X3‐His‐His peptides) < YHYHH (249*) < GHGHH (265*) < WHWHH (284*) ≈ GHPHH (286*) < FHFHH (311*) (least stable), implying that FHFHH might be a useful chromatographic tag for IMAC protein separations that would elute more readily than GHPHH from IMAC sites that are of square‐planar structure, such as CuII(ida‐supported) IMAC columns. Specific H‐bonded interactions are observed between the tyrosine X1 and pendant carboxylates and between X3 and the N‐terminal amine of [Pd(mida)(YHYHH)]. Face‐to‐π‐face ring stacking occurs between phenylalanine X1 and X3 units in [Pd(mida)(FHFHH)], whereas edge C‐H to π H‐bonding or π stacking occurs between the X1 and X3 tryptophans of [Pd(mida)(WHWHH)]. Two energy minima were found with tryptophan. The more stable form has the aromatic rings more parallel, similar to the stacked form of phenylalanine, rather than the edge C‐H to π H‐bonding, and virtually the same overall energy as for [Pd(mida)(GHPHH)]. The “perpendicular” structure was found as an initial local energy minimum, but additional MMFF94 calculations found the π ‐stacked arrangement at energy ca. 39 kcal/mol lower than that of the nearly “perpendicular” arrangement of the tryptophan rings, a composite effect of relaxation of the peptide, together with differences in stabilities imparted by the differing geometries. The use of the terms “π‐stacked ” and “perpendicular” forms represent the limiting cases available to the tryptophan side chain groups. A twist of about 15° to 20° in dihedral angle is all that is necessary to change between structures that are nearly described as one form or the other.

Formation of a mixed-valence Ru(IV)–Fe(II) binuclear complex via the reaction of [RuIII(edta)(H2O)]− and [FeIII(CN)6]3− in aqueous solution

The combination of [RuIII(edta)(H2O)]− (edta4−=ethylenediamine-N,N,N′N′-tetraacetate) and [FeIII(CN)6]3− in aqueous solution results in the rapid formation of [RuIII(edta)(NC)FeIII(CN)5]4− (1), which has been isolated and characterized by physical methods. An aqueous solution of complex 1 shows two characteristic absorption maxima in the visible spectral region located at 420 and 620 nm. Examination of the same solution after 72 h shows that a spectral change has occurred, forming a species with a new band maximum at 870 nm. Spectral (IR, UV–Vis, 1H and 13C NMR spectra showing a paramagnetic complex, and time-dependent magnetic susceptibility data) provide evidence for the formation of a mixed-valence [RuIV(edta)(NC)FeII(CN)5]4− complex 2 by the process, which causes the appearance of the 870 nm band. The results are compared with the known reactions between [RuIII(NH3)5(H2O)]3+ and [Fe(CN)6]3−, which have been reported by Taube and co-workers (V.G. Poupopoulu, Z.W. Li, H. Taube, Inorg. Chim. Acta 225 (1994) 173) to sequentially form {[RuIII(NH3)5(H2O)]3+, [FeIII(CN)6]3−} ion-pairs, converting to a (RuIIICN− bridged-FeIII) binuclear complex (an analogue of 1, and upon intramolecular electron transfer, the (RuIVCN− bridged-FeII) binuclear complex (an analogue of 2). The events reported for the conversion of 1 into 2 ensue without appreciable accumulation of ion pairs as both [RuIII(edta)(H2O)]− and [FeIII(CN)6]3− are anionic. Magnetic susceptibility data imply that both 1 and 2 are paramagnetic S=1 ions. The d electron manifold filling is dxy2dxz2dyz1 in 1 and dxy2dxz1dyz1 in 2, whereas a filling of dxy2dxz2dyz0 seems to account for the prior observations with the [RuIV(NH3)5(NC)FeII(CN)5] system studied by Taube and co-workers.

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.

ZINC(II) AND COPPER(II) COMPLEXES OF EDAMPDA2- : OCTAHEDRAL, TRIGONAL BIPYRAMIDAL AND IN BETWEEN EDAMPDA2- = N, N'-BIS-(PYRIDYLMETHYL)ETHYLENEDIAMINE- N, N'-DIACETATE

ZnII and CuII complexes of the ligand edampda2− [N,N′-bis(pyridylmethyl)-ethylenediamine-N,N′-diacetate] have been studied in solution by 1H n.m.r. and e.p.r. spectroscopies, respectively. [ZnII(edampda)] exists in solution in a major octahedral isomer (ca. 83%) in which the two carboxylate donors and two pyridylmethyl donors remain stereochemically rigid up to 333K at pD=6.0. The major octahedral complex has equivalent glycinato and pyridyl donors as shown by equivalent AB quartets for each type of chelate. By contrast, the [ZnII(edta)]2− analogue complex is known to have processes which rapidly equilibrate the coordinated carboxylates leading to coalesced, broad singlets instead of AB quartets down to 273K (freezing point of the sample). The minor [ZnII(edampda)] species has one pendant pyridylmethyl arm. The complex does not increase in abundance up to 333K via dissociation of the major species, suggesting that it possesses a different five-coordinate geometry (approximate trigonal bipyramid). The [CuII(edampda)] complex exhibits an e.p.r. spectrum that is intermediate between rhombic or tetragonal CuII complexes (near D4h) and the “reversed-e.p.r.” type of trigonal bipyramidal CuII complexes (ca. D3h). The single g value of 2.079 for g∥≅g⊥>2.03 identifies the [CuII(edampda)] complex as distorted toward trigonal bipyramidal whereas its [CuII(edtaH2)(H2O)] analogue is known to be distorted toward square pyramidal. A binuclear CuI complex of edampda2− is formed only as a transient, and it rapidly disproportionates into [CuII(edampda)] and Cu metal. A mononuclear [CuI(edampda)]− complex persists for up to 8 h, but is oxidized within 3 min by O2 to the CuII complex. [CuII(edampda)] oxidizes to CuIII with a highly irreversible wave on glassy-carbon at +1.09V compared to the [NiII/III(edampda)] wave at +1.32V.