N-heterocyclic carbene tethered amido complexes of palladium and platinum

With a view to applications in bifunctional catalysis, a modular cross-coupling strategy has been used to prepare amine bis(imidazolium) salts (3a and 3b) and an amine mono(imidazolium) salt (6) as precursors to chelating amido-NHC ligands. Treating the pro-ligands 3 with 3 equivalents of the bulky base KHMDS and Pd(OAc)(2) or PtCl(2)(COD) gave the four amido bis(N-heterocyclic carbene) pincer complexes [CNC-R]M-I [M = Pd (7) or Pt (8); R = i-Pr (a) or n-Bu (b)], including the first examples of platinum complexes of a CNC ligand. The reaction of 7a with AgOTf in pyridine gave the cationic complex {[CNC-i-Pr]Pd-py}OTf (9a). Heating a mixture of amine mono(imidazolium) salt 6 with PdCl(2) or K(2)PtCl(4), K(2)CO(3) and KI in pyridine at 100 °C gave the complexes [C,NH]MI(2)py [M = Pd (10) or Pt (11)], in which the amine arm of the NHC ligand is not deprotonated and does not coordinate to the metal. For a solution of 10 in 1,4-dioxane, deprotonation of the amine occurred in a biphasic reaction with aqueous KOH at 40 °C, giving the dimeric amido complex {[C,N]Pd(μ-OH)}(2) (12). The more inert Pt analogue 11 was unreactive under the same conditions. Solid-state structures of the complexes 7a, 7b, 9a, 10, 11 and 12 have been determined by single crystal X-ray diffraction.     

On/off regulation of catalysis by allosteric control of metal complex nuclearity

The nature of the allosteric metal ion M (Pd2+ or Pt2+) in complexes ML of a polytopic ligand controls uptake of additional Cu2+ ions; while [Cu2Pd(L-4H)]2+ is a highly active catalyst for phosphodiester cleavage, [CuPt(L-4H)] is inactive.     

Pd, Pt, and Ru complexes of a pincer bis(amino)amide ligand

An improved synthesis of pincer ligand bis[(2-dimethylamino)phenyl]amine ((Me)N(2)NH) was reported. Reaction of the Li complex of (Me)N(2)N with suitable Pd, Pt, and Ru precursors gave the corresponding metal complexes. The structures of the Pd, Pt, and Ru complexes were determined. The Ru complex showed activity in catalytic transfer hydrogenation of aryl and alkyl ketones.     

Synthesis, characterisation and speciation studies of heterobimetallic pyridinehydroxamate-bridged Pt(II)/M(II) complexes (M = Cu, Ni, Zn). Crystal structure of a novel heterobimetallic 3-pyridinehydroxamate-bridged Pt(II)/Cu(II) wave-like coordination polymer

The reaction of cis-[Pt(NH3)2(3-pyhaH)2]2+ (3-pyhaH = 3-pyridinehydroxamic acid) and cis-[Pt(NH3)2(4-pyhaH)2]2+ (4-pyhaH = 4-pyridinehydroxamic acid) with Cu(II), Ni(II) or Zn(II) in aqueous solution affords novel heterobimetallic pyridinehydroxamate-bridged complexes, {cis-[Pt(NH3)2(mu-3-pyha)M(mu-3-pyha)].SO4.xH2O}n and {cis-[Pt(NH3)2(mu-4-pyha)M(mu-4-pyha)].SO4.xH2O}n respectively. The crystal and molecular structure of one of these, {cis-[Pt(NH3)2(mu-3-pyha)Cu(mu-3-pyha)]SO4.8H2O}n 3a, has been determined and was found to be a novel heterobimetallic wave-like coordination polymer, the structure of which contains interlinked pyridinehydroxamate-bridged repeating units of Pt(II) and Cu(II) ions in slightly distorted square-planar N4 and O4 coordination environments respectively and extensive hydrogen-bonding through the Pt ammines and the deprotonated hydroxamate O and via the O of the SO4(2-) counterions and the H(N) of the hydroxamate moiety. Spectrophotometric and speciation studies on the other heterobimetallic systems confirm that very similar species are being formed in solution and based on elemental analysis and spectroscopic results analogous complexes are formed in the solid-state. In this paper, we report the first examples of coordination polymers incorporating both Pt(II)/Cu(II), Pt(II)/Ni(II) and Pt(II)/Zn(II) and containing pyridinehydroxamic acids as bridging scaffolds.     

Syntheses and ligand interconversions of copper(II) derivatives of the metalloligand [Pt2(mu-S)2(PPh3)4

The reactivity of the metalloligand [Pt2(micro-S)2(PPh3)4] towards a variety of copper(II)-ligand systems has been studied. Reaction of [Pt2(mu-S)2(PPh3)4] with copper(II) halide complexes [CuCl2L](L = 2,2'-bipyridine and 1,10-phenanthroline) gave trinuclear dicationic products [Pt2(mu-S)2(PPh3)4CuL]2+, and the 8-hydroxyquinolinate (hq) complex [Cu(hq)2] gave [Pt2(mu-S)2(PPh3)4Cu(hq)]+, isolated as their BPh4- or PF6- salts. Related cationic complexes with other ancillary amine ligands (1,2-diaminoethane, 1,2-diaminopropane, 1,2-diaminocyclohexane) were obtained by reactions of [Pt2(mu-S)2(PPh3)4] with CuCl2 and the amine. In contrast, reaction of [Pt2(mu-S)2(PPh3)4] with CuCl2 and NH3 in methanol gave the intensely blue methoxy-bridged dicopper complex [{Pt(2)(mu-S)2(PPh3)4Cu(OMe)}2]2+, isolated as its hexafluorophosphate salt. Copper beta-diketonate complexes reacted with [Pt2(mu-S)2(PPh3)4] giving [Pt2(mu-S)2(PPh3)4Cu(beta-diketonate)]+PF6- complexes, with the CH3COCHCOCH3(acac) and CF3COCHCO(2-thienyl)(tta) derivatives characterised by X-ray structure determinations. The local Cu(II) environment ranges from distorted square-planar to an intermediate form of square-planar and tetrahedral. The beta-diketonate derivatives show varying stability towards methanolysis, giving [{Pt2(mu-S)2(PPh3)4Cu(OMe)}2]2+.     

Heterobimetallic dioxygen activation: synthesis and reactivity of mixed Cu-Pd and Cu-Pt bis(mu-oxo) complexes

Heterobimetallic CuPd and CuPt bis(mu-oxo) complexes have been prepared by the reaction of (PPh3)2MO2 (M=Pd, Pt) with LCu(I) precursors (L=beta-diketiminate and di- and triamine ligands) and characterized by low-temperature UV-vis, resonance Raman, and 1H and 31P[1H] NMR spectroscopy in conjunction with DFT calculations. The complexes decompose upon warming to yield OPPh3, and in one case this was shown to occur by an intramolecular process through crossover experiments using double-labeling (oxo and phosphine). The reactivity of one of the complexes, LMe2Cu(mu-O)2Pt(PPh3)2 (LMe2 = beta-diketiminate), with a variety of reagents including CO2, 2,4-di-tert-butylphenol, 2,4-di-tert-butylphenolate, [NH4][PF6], and dihydroanthracene, was compared to that of homometallic Pt2 and Cu2 counterparts. Unlike typical [Cu2(mu-O)2]2+ cores which have electrophilic oxo groups, the oxo groups in the [Cu(mu-O)2Pt]+ core behave as bases and nucleophiles, similar to previously described Pt2 compounds. In addition, however, the [Cu(mu-O)2Pt]+ core is capable of oxidatively coupling 2,4-di-tert-butylphenol and 2,4-di-tert-butylphenolate. Theoretical evaluation of the electron affinities, basicities, and H-atom transfer kinetics and thermodynamics of the Cu2 and CuM (M=Pd, Pt) cores showed that the latter are more basic and form stronger O-H bonds.     

Design and self-assembly of ditopic and tetratopic cavitand complexes

The self-assembly of open ditopic and tetratopic cavitand complexes has been investigated by using monofunctionalized cavitand ligands and suitable metal precursors. In the case of ditopic complexes, self-assembly protocols, leading exclusively to the formation of both thermodynamically stable cis-Pt square-planar complexes 8 and 9 and the kinetically inert fac-Re octahedral complex 14, have been elaborated. The use of cis-[Pt(CH3)CN)2Cl2] as metal precursor led to the formation of monotopic trans-10 and ditopic trans-11 cavitand complexes, while cis-[Pt(dmso)2Cl2] afforded both cis-13 and trans-11 isomers. The self-assembly of tetratopic cavitand complexes has been achieved by using mononuclear [Pd(CH3CN)4(BF4)2] and dinuclear [M2(tppb)(OTf)4] (19: M = Pt; 20: M = Pd) metal precursors. Only the tetratopic dinuclear complexes 21 and 22 were stable. The ligand configuration with two phosphorus and two cavitand ligands at the metal centers is the most appropriate to build tetratopic cavitand complexes with sufficient kinetic stability.     

Deposition of oriented zeolite A films: in situ and secondary growth

Zeolite A suspensions with a monomodal, narrow particle size distribution have been prepared. The suspended particles in a TMAOH water solution at pH 9 are negatively charged with a zeta potential of −43 mV. Modification of the external surface of the zeolite particles by a silylation reaction produces particles that, when they are suspended in water, are positively charged and have a zeta potential of +40 mV.The suspensions of the negatively or positively charged particles can be used for the preparation of adsorbed layers of particles on oppositely charged substrates by electrostatic attraction. This deposition process leads to a high coverage of the substrate with well-adhered particles. The cubic morphology of the zeolite particles results in preferential orientation after deposition. The particles are oriented with their {h 0 0} planes (cube faces) parallel and perpendicular to the substrate (out-of-plane orientation). The particles are randomly oriented with respect to the direction perpendicular to the substrate (in-plane orientation). Although, under optimized conditions, the coverage is high and only one adsorption cycle is necessary, the particles are not closely packed.Alternately, the zeolite particle suspensions can be used to deposit close-packed arrays of particles by convective particle transport during dip coating on substrates bearing the same charge as the zeolite particles. Using monodispersed zeolite A suspensions and slow speed dip coating close-packed hexagonal colloidal crystals were prepared. The type of colloidal crystal deposits formed range from continuous sublayers, monolayers, or multilayers to isolated discoidal clusters consisting of few zeolite particles. Factors affecting the deposited layer(s) structure are particle concentration of the suspension and withdrawal speed. In addition to close packing, the layers prepared by dip coating exhibit preferred orientation with the particle faces lying parallel and perpendicular to the substrate surface. Moreover, this second route of precursor film formation by colloidal crystallization leads to domains of well-aligned zeolite particles in three dimensions, i.e. with their faces parallel to each other. The oriented domains span the length of several particles; however, low angle boundaries and other defects during colloidal crystallization prevent the formation of macroscopically three-dimensionally ordered zeolite particles.The precursor layers were subjected to secondary growth in order to prepare continuous intergrown films. Secondary growth proceeds initially by local epitaxy on the deposited particles. Later in the process, deposition proceeds by incorporation of particles from solution along with re-nucleation on the growing film. The intergrown films have predominately [h 0 0] out-of-plane orientation; however, after extended secondary growth treatment a population of [h h h] grains appears on the surface of the regrown films.     

Synthesis,characterization, cytotoxicity,and molecular docking studies of ampyrone-based transition metal complexes

Transition Metal Chemistry - A novel series of mononuclear transition metal complexes, [Cu(L)Cl] 1, [Zn(L)Cl] 2, [Pd(L)Cl] 3, [Cd(L)I] 4, [Pt(L)Cl] 5, and [Hg(L)Cl] 6, was constructed from a...     

Synthesis and coordination chemistry of an alkyne functionalised bis(pyrazolyl)methane ligand

The alkyne functionalised bidentate N-donor ligand (2-propargyloxyphenyl)bis(pyrazolyl)methane was prepared in high yield from the reaction of (2-hydroxyphenyl)bis(pyrazolyl)methane with propargyl bromide in the presence of base. A series of transition-metal complexes including [MCl2] (M=Cu, Co, Ni, Zn, Pt), [M2](NO3)2 (M=Cu, Co, Ni, Zn), [Ag]NO3 and [Pd(dppe)](OTf)2 were prepared and characterised by spectroscopic techniques. In addition, ligand as well as the Co(II) and Zn(II) complexes [CoCl2]2, [ZnCl2] were structurally characterized by single-crystal X-ray diffraction. The organometallic gold(I) and platinum(II) acetylide complexes [Pz2CH(C6H(4)-2-OCH2C[triple bond, length as m-dash]CAuPPh3)] and trans-[{Pz2CHC6H(4)-2-OCH2C[triple bond, length as m-dash]C}2Pt(PPh3)2] were prepared from and [AuCl(PPh3)] and trans-[PtCl2(PPh3)2], respectively. Treatment of these complexes with [Pd(OTf)2(dppe)] or [Cu(MeCN)4]PF6 results in formation of the cationic, mixed-metal complexes, which were isolated (Pt/Pd, Au/Pt) or detected by electrospray mass spectrometry (Au/Cu, Pt/Cu).     

Homo- and heteropolynuclear platinum complexes stabilized by dimethylpyrazolato and alkynyl bridging ligands: synthesis, structures, and luminescence

This work describes the synthesis of cis-[Pt(C[triple bond]CPh)2(Hdmpz)2] (1) and its use as a precursor for the preparation of homo- and heteropolynuclear complexes. Double deprotonation of compound 1 with readily available M(I) (M = Cu, Ag, Au) or M(II) (M = Pd, Pt) species affords the discrete hexanuclear clusters [{PtM2(mu-C[triple bond]CPh)2(mu-dmpz)(2)}(2)] [M = Cu (2), Ag (3), Au (4)], in which both "Pt(C[triple bond]CPh)2(dmpz)(2)" fragments are connected by four d(10) metal centers, and are stabilized by alkynyl and dimethylpyrazolate bridging ligands, or the trinuclear complexes [Pt(mu-C[triple bond]CPh)2(mu-dmpz)(2){M(C/\P)}2] (M = Pd (5), Pt (6); C/\P = CH(2)-C(6)H(4)-P(o-tolyl)2-kappaC,P), respectively. The X-ray structures of complexes 1-4 and 6 are reported. The X-ray structure of the platinum-copper derivative 2 shows that all copper centers exhibit similar local geometry being linearly coordinated to a nitrogen atom and eta(2) to one alkynyl fragment. However in the related platinum-silver (3) and platinum-gold (4) derivatives the silver and gold atoms present three different coordination environments. The complexes have been studied by absorption and emission spectroscopy. The hexanuclear complexes exhibit bright luminescence in the solid state and in fluid solution (except 4 in the solid state at 298 K). Dual long-lived emission is observed, being clearly resolved in low-temperature rigid media. The low-energy emission is ascribed to MLM'CT Pt(d)/pi(C[triple bond]CPh)-->Pt(p(z))/M'(sp)/pi*(C[triple bond]CPh) modified by metal-metal interactions whereas the high-energy emission is tentatively attributed to an emissive state derived from dimethylpyrazolate-to-metal (d(10)) LM'CT transitions pi(dmpz)-->M'(d(10)).     

Synthesis, catalytic activity, and photophysical properties of 5,6-membered Pd and Pt SCS'-pincer complexes based on thiophosphorylated 3-amino(hydroxy)benzoic acid thioanilides

Novel unsymmetrical SCS'-pincer ligands, 1-[PhNHC(S)]-3-[Ph(2)P(S)NH]-C(6)H(4) (3) and 1-[PhNHC(S)]-3-[Ph(2)P(S)O]C(6)H(4) (7), bearing a thiocarbamoyl moiety in combination with thiophosphorylamino- and thiophosphoryloxy-donating groups, respectively, were obtained via thiophosphorylation of 3-amino- and 3-hydroxy-benzoic acid (thio)anilides 1 and 6. Direct cyclometallation of the central benzene ring in the ligands 3 and 7 in reaction with (PhCN)(2)MCl(2) (M = Pd, Pt) as a metal precursor afforded κ(3)-SCS'-hybrid pincer complexes 8, 9 with 5- and 6-membered fused metallacycles in good to high yields (67-95%). The complexes 8 and 9 were characterized by multinuclear NMR ((31)P, (1)H, (13)C) and IR spectroscopy as well as single-crystal X-ray crystallography. Palladium complexes 8a and 9a were shown to be active catalysts for the Suzuki-Miyaura cross-coupling reaction. In the solid state the ligands 3 and 7 as well as their Pt(II) and Pd(II) complexes 8 and 9 are luminescent at 300 K. The emission of the complexes has the different origin depending on the metal nature.     

Metal-metal interactions in heterobimetallic d8-d10 complexes. Structures and spectroscopic investigation of [M'M' '(mu-dcpm)2(CN)2]+ (M' = Pt,Pd; M' ' = Cu,Ag, Au) and related complexes by UV-vis absorption and resonance Raman spectroscopy and ab initio calculations

X-ray structural and spectroscopic properties of a series of heterodinuclear d(8)-d(10) metal complexes [M'M' '(mu-dcpm)(2)(CN)(2)](+) containing d(8) Pt(II), Pd(II), or Ni(II) and d(10) Au(I), Ag(I), or Cu(I) ions with a dcpm bridging ligand have been studied (dcpm = bis(dicyclohexylphosphino)methane; M' = Pt, M' ' = Au 4, Ag 5, Cu, 6; M' ' = Au, M' = Pd 7, Ni 8). X-ray crystal analyses showed that the metal...metal distances in these heteronuclear metal complexes are shorter than the sum of van der Waals radii of the M' and M' ' atoms. The UV-vis absorption spectra of 4-6 display red-shifted intense absorption bands from the absorption spectra of the mononuclear trans-[Pt(phosphine)(2)(CN)(2)] and [M' '(phosphine)(2)](+) counterparts, attributable to metal-metal interactions. The resonance Raman spectra confirmed assignments of (1)[nd(sigma)-->(n + 1)p(sigma)] electronic transitions to the absorption bands at 317 and 331 nm in 4 and 6, respectively. The results of theoretical calculations at the MP2 level reveal an attractive interaction energy curve for the skewed [trans-Pt(PH(3))(2)(CN)(2)-Au(PH(3))(2)(+)] dimer. The interaction energy of Pt(II)-Au(I) was calculated to be ca. 0.45 ev.     

Palladium(II) and platinum(II) organometallic complexes with 4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine. Antitumor activity of the platinum compounds

Palladium and platinum complexes with HmtpO (where HmtpO=4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine, an analogue of the natural occurring nucleobase hypoxanthine) of the types [M(dmba)(PPh3)(HmtpO)]ClO4[dmba=N,C-chelating 2-(dimethylaminomethyl)phenyl; M=Pd or Pt], [Pd(N-N)(C6F5)(HmtpO)]ClO4[N-N=2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), or N, N, N', N'-tetramethylethylenediamine (tmeda)] and cis-[M(C6F5)2(HmtpO)2] (M=Pd or Pt) (head-to-head atropisomer in the solid state) have been obtained. Pd(II) and Pt(II) complexes with the anion of HmtpO of the types [Pd(tmeda)(C6F5)(mtpO)], [Pd(dmba)(micro-mtpO)] 2, and [NBu4]2[M(C6F5)2(micro-mtpO)]2(M=Pd or Pt) have been prepared starting from the corresponding hydroxometal complexes. Complexes containing simultaneously both the neutral HmtpO ligand and the anionic mtpO of the type [NBu4][M(C6F5)2(HmtpO)(mtpO)] (M=Pd or Pt) have been also obtained. In these mtpO-HmtpO metal complexes, for the first time, prototropic exchange is observed between the two heterocyclic ligands. The crystal structures of [Pd(dmba)(PPh 3)(HmtpO)]+, cis-[Pt(C6F5)2(HmtpO)2].acetone, [Pd(C6F5)(tmeda)(mtpO)].2H2O, [Pd(dmba)(micro-mtpO)]2, [NBu4]2[Pd(C6F5)2(micro-mtpO)]2.CH2Cl2.toluene, [NBu4]2[Pt(C6F5)2(micro-mtpO)](2).0.5(toluene), and [NBu4][Pt(C6F5)2(mtpO)(HmtpO)] have been established by X-ray diffraction. Values of IC50 were calculated for the new platinum complexes cis-[Pt(C6F5)2(HmtpO)2] and [Pt(dmba)(PPh3)(HmtpO)]ClO4 against a panel of human tumor cell lines representative of ovarian (A2780 and A2780 cisR), lung (NCI-H460), and breast cancers (T47D). At 48 h incubation time, both complexes were about 8-fold more active than cisplatin in T47D and show very low resistance factors against an A2780 cell line, which has acquired resistance to cisplatin. The DNA adduct formation of cis-[Pt(C6F5)2(HmtpO)2] and [Pt(dmba)(PPh3)(HmtpO)]ClO4 was followed by circular dichroism and electrophoretic mobility. Atomic force microscopy images of the modifications caused by these platinum complexes on plasmid DNA pB R322 were also obtained.     

Effects of the intramolecular NH...S hydrogen bond in mononuclear platinum(II) and palladium(II) complexes with 2,2'-bipyridine and benzenethiol derivatives

A series of complexes, [M(bpy)(SAr)2] (M = platinum(II) or palladium(II), bpy = 2,2'-bipyridine, SAr = 2- or 4-(acylamino)benzenethiolate, or 2-(alkylcarbamoyl)benzenethiolate), were synthesized and characterized on the basis of 1H NMR, IR, and electrochemical properties. The structures of [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) and [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3) were determined by X-ray analysis. The complexes have intramolecular NH...S hydrogen bonds between the amide NH group and the sulfur atom. A weak NH...S hydrogen bond in these complexes and [Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4) is detected from the 1H NMR spectra and the IR spectra in chloroform and in the solid state. [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) exhibits a remarkably high-energy-shifted lowest-energy band in UV-visible spectra and has a positively shifted oxidation potential. The blue-shift of 42 nm and the positive shift of +0.24 V, as compared to those of [Pt(bpy)(SC6H5)2), are due to the effect of the NH...S hydrogen bond.     

Ring-opening reactions induced by gold(I) of five- and four-coordinate palladium(II) and platinum(II) complexes containing tripodal or linear polyphosphines

The tripodal ligands NP(3)(tris[2-(diphenylphosphino)ethyl]amine) and PP(3)(tris[2-(diphenylphosphino)ethyl]phosphine), form five-coordinate [Pd(NP(3))X]X [X = Cl (1), Br (2)], [M(PP(3))X]X [M = Pd: X = Cl (4), Br (5), I (6); M = Pt, X = Cl (7), Br (8), I (9)] and four-coordinate[Pd(NP(3))I]I (3) complexes containing three fused rings around the metal. The interaction between Au(tdg)X (tdg = thiodiglycol; X = Cl, Br) or AuI and the respective ionic halo complexes 1-9 in a 1:1 stoichiometric ratio occurs via a ring-opening reaction with formation of the heterobimetallic systems PdAu(NP(3))X(3)[X = Cl (11), Br (12), I (13)], [MAu(PP(3))X(2)]X [M = Pd: X = Cl (14), Br (15), I (16); M = Pt: X = Cl (17), Br (18), I (19)]. The cations of complexes 17 and 18 were shown, by X-ray diffraction, to contain a distorted square-planar Pt(II) arrangement (Pt(P(2)P)X) where PP(3) is acting as tridentate chelating ligand and an almost linear PAuX moiety bearing the dangling phosphorus formed in the ring-opening process. PPh(3) coordinates to Au(I) and not to M(II) when added in excess to 14 and 17. Complexes 14-17 and [Pt(P(4))](BPh(4))(2) (10) (P4=linear tetraphosphine) also react with A(I), via chelate ring-openings to give MAu(2)(PP(3))X(4) [M = Pd: X = Cl (20), Br (21), I (22); M = Pt: X = Cl (23)] and [Pt(2)Au(2)(mu-Cl)(2)(mu-P(4))(2)](BPh(4))(4) (24), respectively.     

Metal "capture" by a heterotrimetalloligand, heterometallic d(10)-d(10) interactions, and unexpected iron-to-platinum silyl ligand migration: a combined experimental and theoretical study

The heterotrinuclear chain complex Hg[Fe{Si(OMe)(3)}(CO)(3)(dppm-P)](2) (dppm = Ph(2)PCH(2)PPh(2)) 1 which has a transoid arrangement of the phosphine donors was used as a versatile chelating metallodiphosphine ligand owing to the easy rotation of its metal core about the Fe-Hg sigma-bonds. Its reaction with the labile Pt(0) olefin complex [Pt(C(7)H(10))(3)] yielded [HgPt{Si(OMe)(3)}Fe(2)(CO)(6){Si(OMe)(3)}(mu-dppm)(2)] 5 which resulted, after coordination of the dangling phosphine donors to Pt, from an unprecedented intramolecular rearrangement involving a very rare example of silyl ligand migration between two different metal centers, and the first one in metal cluster chemistry. The major structural differences observed between the heterometallic complexes obtained from 1 and d(10) Cu(I), Pd(0), or Pt(0) precursors have been established by X-ray diffraction. The bonding situation in the silyl migrated Pt complex 5 was analyzed and compared to those in the isoelectronic, but structurally distinct complexes obtained from Cu(I) and Pd(0) precursors, [Hg{Fe[Si(OMe)(3)](CO)(3)(mu-dppm)}(2)Cu](+) (2) and [Hg{Fe[Si(OMe)(3)](CO)(3)(mu-dppm)}(2)Pd] (4), respectively, by means of extended Hückel interaction diagrams. DFT calculations then allowed the energy minima associated with the three structures to be compared for 2, 4, and 5. All three minima are in close competition for the Pd complex 4, but silyl migration is favored by approximately 10 kcal mol(-)(1) for 5, mainly due to the more electronegative character of Pt with respect to Pd.     

Comparative density functional theory study of the binding of ligands to Cu+ and Cu2+: Influence of the coordination and oxidation state

BP86, B3LYP and MP2 methods, generally used to study large systems containing transition metals, were compared for their ability to accuratly evaluate bond dissociation energies of copper complexes. Various [Cu-L]+ and [Cu-L]2+ complexes in which L are small ligands and the higher coordinated complexes, [Cu(NH3)(4)]+ and [Cu(NH3)4]2+ were studied. For monoligated complexes, the BDEs calculated by the three methods differed by 2 to 60 kcal/mol, the larger differences being obtained for [Cu-L]2+ complexes. The BDEs calculated using the B3LYP functional were in general close to the experimental values whereas the BDEs calculated using the BP86 functional were too high and the BDEs calculated using the MP2 were too low. If we rank the whole ligands according to their increased bond strength, the resulting orders obtained with the three methods are different for the [Cu-L]+ complexes, the B3LYP giving the same order as the experimental one. This result indicates that the BDEs of [Cu-L]+ complexes are better modeled using the B3LYP than using the BP86 and MP2 methods. For [Cu-L]2+, B3LYP also gave the most reliable results whereas BP86 gave too large BDEs and MP2 gave too small BDEs. However, symmetries of ground states can be different using DFT and post-Hartree-Fock methods. For [Cu-N2O]2+ the use of the B1LYP provides a better symmetry of the complex than the B3LYP, as has been recently shown in the literature for [Cu-H2O]2+. MP2 led to an incorrect bent structure for [Cu-N2]2+ in contrast to a linear structure obtained with the other methods, including CCSD(T). However, due to the lack of experimental data for [Cu-L]2+ complexes and to contrasted results for the methods, it is not possible to conclude definitely. For the high coordinated complexes [Cu(NH3)4]+ and [Cu(NH3)4]2+, the PBE calculation method was used in addition to the BP86, B3LYP and MP2. The BDE values were very close to each other when there is no change of the oxidation state during the reaction. On the basis of these calculations, the choice of the method was less crucial for high coordinated complexes [Cu(NH3)4]+ and [Cu(NH3)4]2+ so long as the oxidation state remained the same during the reaction. In contrast, when [Cu(NH3)4]2+ is reduced in [Cu(NH3)3]+ and NH3, the BDE calculated using the four methods were markedly different.     

Isomeric equilibria in aqueous solution involving aromatic ring stacking in the sexternary complexes formed by the quaternary cis-(NH3)2Pt(2'-deoxyguanosine-N7)(dGMP-N7) complex and the binary Cu(2,2'-bipyridine)2+ or Cu(1,10-phenanthroline)2+ complexes (dGMP2- = 2'-deoxyguanosine 5'-monophosphate)

To the best of our knowledge, for the first time the stabilities of sexternary complexes are determined by potentiometric pH titrations in aqueous solution at 25 degrees C and I = 0.1 M (NaNO3). The sexternary complexes form by binding of the binary Cu(Arm)2+ complexes, where Arm = 2,2'-bipyridine (Bpy) or 1,10-phenanthroline (Phen), to the -PO3(2-) group present in the quaternary cis-(NH3)2Pt(dGuo)(dGMP) complex. It is shown by stability constant comparisons and spectrophotometric measurements (observation of charge-transfer bands for the Phen system) that the [cis-(NH3)2Pt(dGuo)(dGMP).Cu(Arm)]2+ complexes can fold in such a way that aromatic ring stacking between the aromatic rings of Bpy or Phen and a guanine residue (most probably the one of dGMP2-) becomes possible. The formation degree of the stacks reaches approximately 25 and 50% for the [cis-(NH3)2Pt-(dGuo)(dGMP).Cu(Bpy)]2+ and [cis-(NH3)2Pt(dGuo)(dGMP).Cu(Phen)]2+ species, respectively. By comparisons with Cu(Arm)(dGMP) complexes, it is shown that the cis-(NH3)2Pt2+ unit coordinated to N7 of the guanine residues in the sexternary complexes inhibits stacking but does not prevent it. This result is of general importance because it demonstrates that in aqueous solution purine residues of nucleotides or nucleic acids that carry a metal ion at N7 can still undergo stacking interactions with other suitable aromatic ring systems.     

Two stereoisomers of an S-bridged RhIII2PtII2 tetranuclear complex [{Pt(NH3)2}2{Rh(aet)3}2]4+ that lead to a discrete and a 1D RhIII2PtII2AgI structures by reacting with AgI (aet = 2-aminoethanethiolate)

An S-bridged RhIII2PtII2 tetranuclear complex having two nonbridging thiolato groups, [{Pt(NH3)2}2{Rh(aet)3}2]4+ ([1]4+), in which two fac(S)-[Rh(aet)3] units are linked by two trans-[Pt(NH3)2]2+ moieties, was synthesized by the 1:1 reaction of fac(S)-[Rh(aet)3] (aet = 2-aminoethanethiolate) with trans-[PtCl2(NH3)2] in water. Complex [1]4+ gave both the meso (DeltaLambda) and racemic (DeltaDelta/LambdaLambda) forms, which were separated by fractional crystallization. Of two possible geometries, syn and anti, which arise from the arrangement of two nonbridging thiolato groups, the meso and racemic forms of [1]4+ selectively afforded the anti and syn geometries, respectively. The DeltaLambda-anti and DeltaDelta/LambdaLambda-syn isomers of [1]4+ reacted with Ag+ using two nonbridging thiolato groups to produce a {RhIII2PtII2AgI}n) polymeric complex, {[Ag{Pt(NH3)2}2{Rh(aet)3}2]5+}n) ([2]5+), and a RhIII2PtII2AgI pentanuclear complex, [Ag{Pt2(mu-H2O)(NH3)2}{Rh(aet)3}2]5+ ([3]5+), respectively, which contain octahedral RhIII, square-planar PtII, and linear AgI centers. In [2]5+, each DeltaLambda-anti-[{Pt(NH3)2}2{Rh(aet)3}2]4+ tetranuclear unit is bound to two AgI atoms to form a one-dimensional zigzag chain, indicating the retention of the parental S-bridged structure in DeltaLambda-anti-[1]4+. In [3]5+, two Delta- or Lambda-fac(S)-[Rh(aet)3] units are linked by a [Pt2(mu-H2O)(NH3)2]4+ dinuclear moiety, together with an AgI atom, indicating that two NH3 molecules in [1]4+ have been replaced by a water molecule that bridges two PtII centers, while the parental DeltaDelta/LambdaLambda-syn configuration is retained. The complexes obtained were characterized on the basis of electronic absorption, CD, and NMR spectra, along with single-crystal X-ray analyses.