Trinuclear Derivatives Research Articles

Chemistry of (η6-C6Me6)Ru(Cl)2(P(OMe)3) with AgOTf in different solvents, the high affinity for traces of water and structural characterization of mono-, di- and trinuclear derivatives

An extensive study of the reactions of (η6-C6Me6)Ru(Cl)2(P(OMe)3) (1) with AgOTf in three different deuterated and non-deuterated solvents: chloroform, acetone and nitromethane is described. A series of compounds with the moiety (η6-C6Me6)Ru(P(OMe)3) is isolated and characterized, along with their crystalline structures. A simple associative step assisted by coordination of the silver cation to two molecules of 1 through the Cl-Ru-Cl bonds affords [{(η6-C6Me6)Ru(Cl)2(P(OMe)3)}2(μ-Ag)](OTf) (2), loss of AgCl from 2 gives 1 and (η6-C6Me6)RuCl(OTf)(P(OMe)3) (3), meanwhile 3 dimerizes to [(η6-C6Me6)Ru(μ-Cl)(P(OMe)3)]2(OTf)2 (4) which in presence of P(OMe)3 gives [(η6-C6Me6)RuCl(P(OMe)3)2](OTf) (11OTf). A comparative study of the influence of the counterions OTf− and BF4− was carried out with the analogue [(η6-C6Me6)RuCl(P(OMe)3)2](BF4) (11BF4), as well as the corresponding demethylation of the coordinated trimethylphosphite ligands by the classical Michaelis-Arbuzov reactions. The resulting “quasi-chelate” (η6-C6Me6)RuCl(P(O)(OMe)2)(P(OH)(OMe)2) (17) where a bridging proton in the phosphinito-phosphinous acid ligands is replaced by BF2 affords (η6-C6Me6)RuCl({P(OMe)2(O)}2BF2) (18) which contains the chelating structure [Me2POBF2OPMe2]. The chemistry in solution at room temperature of 1 with AgOTf shows non-selective reactions, as can be determined by multinuclear NMR spectroscopy (1H, 13C{1H}, 31P, 19F). The mixture of products shows a great preference to coordinate water, even when it is in traces, as observed for the formation of [(η6-C6Me6)RuCl(H2O)(P(OMe)3)](OTf) (5), [(η6-C6Me6)Ru(H2O)(OTf)(P(OMe)3)]OTf (6) and [(η6-C6Me6)Ru(H2O)2(P(OMe)3)](OTf)2 (7), being the latter 7 the “sink” product. Also, in presence of anhydrous AgOTf compound 1 can be transformed into the highly hygroscopic (η6-C6Me6)Ru(OTf)2(P(OMe)3) (8) which readily replaces triflate ligands by trace water. Structural characterization by single crystal X-ray diffraction of trinuclear compound 2, dinuclear 4 and mononuclear 7, 11X (X = OTf, BF4), 18 and nitrile derivatives [(η6-C6Me6)Ru(NCR)2(P(OMe)3)](OTf)2 (R = Et, 9; Me,10) is discussed.

Tin complexes derived from nitrogen-based 1,3,5-heterocyclohexanes bearing 2-hydroxypropan-1-yl, 2-diphenylphosphitepropan-1-yl and 2-diphenylphosphinepropan-1-yl as pendant N-substituents

A series of Sn(IV)PhCl3, Sn(IV)Ph2Cl2, Sn(IV)Ph3Cl or Sn(II)Cl2 complexes of nitrogen based 1,3,5-hetero-cyclohexanes: 5-methyl-[1,3,5]-dithiazinane (1), (R)-2-hydroxy-prop-1-yl-[1,3,5]-dithiazinane (2), (R)-2-diphenylphosphinite-prop-1-yl-[1,3,5]-dithiazinane (3), 3,5-bis((R)-2-diphenylphosphinopropyl)-1,3,5-thiadiazinane (4) 1,3,5-tris((R)-2-diphenylphosphinoprop-1-yl)-1,3,5-triazinane (5) were synthesised and their structure analysed in solution by 119Sn, 31P, 13C and 1H and variable temperature NMR experiments. Gas phase DFT calculations were performed to obtain the preferred conformation of complexes and the configuration of tin atoms. Ligands 1-5 have in common that the heterocycle is in conformational equilibrium with the N-substituents in axial position, with exception of compound 5 that has one N-R in equatorial position. Ligands 1 and 3 afforded monodentate adducts, whereas 2, 4 and 5 produced bidentate complexes. Compound 4 gave binuclear bidentate complexes and 5 trinuclear derivatives. In the studied compounds, the phosphorus atoms are strongly coordinated to tin atoms, whereas the intracyclic nitrogen atoms gave weak coordination bonds. The pnicogen bonds N→P found in ligands 3-5 were preserved in the coordination products. By coordination, hypervalent tetra- [Sn(II)]; penta- and hexacoordinate [Sn(IV)] tin atoms were obtained. It was found that Sn(II)Cl2 is a suitable Lewis acid with low steric hindrance that gives strong bonds with these amine phosphines.

Yldiide Ligands as Building Blocks for Polynuclear Coinage Metal Complexes: Metal Squares, Triangles and Chains.

Yldiides have unique electronic properties and donor abilities, but as ligands in transition metal complexes they are scarcely represented in the literature. Here, the controlled synthesis of a series of polynuclear gold yldiide complexes derived from triphenyl(cyanomethyl)phosphonium bromide, [Ph3 PCH2 CN]Br, under mild conditions is described. Anionic dinuclear NBu4 [(AuX)2 {C(CN)PPh3 }] (X=Cl, C6 F5 ) or trinuclear derivatives NBu4 [Au3 X2 {C(CN)PPh3 }] bearing terminal chloride or pentafluorophenyl groups and bridging yldiide ligands have been prepared. These compounds evolve in solution giving rise to the formation of an unprecedented tetrameric gold cluster, [Au4 {C(CN)PPh3 }4 ], by the loss of the gold complex NBu4 [AuX2 ]. This gold cluster can also be prepared in high yield by a transmetalation reaction from the analogous tetrameric silver cluster, and two geometric isomers have been characterised, their formation dependent on the synthetic route. The triphenylphosphonium cyanomethyldiide ligand has also been used to build different dinuclear and trinuclear cationic complexes bearing phosphine or diphosphine ancillary ligands and bridging yldiide moieties. Further coordination through the cyano group of the yldiide ligand gives heterometallic trinuclear or pentanuclear derivatives. Structural characterisation of many of these compounds reveals the presence of complex molecular systems stabilised by gold⋅⋅⋅gold interactions and bridging yldiide ligands.

The reactions of [(μ-H)M3(CO)9(CCSiMe3)] (M=Fe, Ru) with thiols: Cleavage of M-M and formation of M-S bonds in isomeric structures

The reactions of the acetylide trinuclear derivatives [(μ-H)M3(CO)9(CCSiMe3)] (M=Fe, Ru) with the thiols C6H5SH and C6F5SH were carried out. Both reactions lead to the formation of products where cleavage of M-M bonds have occurred. In the case of the iron complex, two products are obtained in the reactions with both thiols: a trinuclear complex of formula [Fe3(CO)9(CCSiMe3)(SR)] (R=C6H5 and C6F5) and a dinuclear compound [Fe2(CO)6(CCSiMe3)(SR) (R=C6H5 and C6F5) which is found as anti and syn isomers in the case of C6H5 and only as the anti isomer in the fluorinated thiol. The reaction with the ruthenium complex under the same conditions gives only decomposition products, but when the reaction with pentafluorothiophenol is carried out in the presence of trimethylamine oxide, total cleavage of M-M bonds takes place to form a mononuclear complex [Ru(CO)3(SC6F5)3]. Spectroscopic and structural characterization of the iron complexes is given. Two isomeric crystal structures were obtained for the trinuclear fluorinated complex.

Group 11 Metal Complexes with Unsymmetrical Bifunctional Ferrocene Ligands

The reactions of two unsymmetrical P^N (L1) and P^P (L2) ferrocene (Fc) ligands towards group 11 metal complexes were studied. Ligand L1 shows different behavior with the three metals. Gold forms mononuclear derivatives with the metal center coordinated to the phosphorus atom, whereas the reactions with silver(I) or copper(I) complexes afford mononuclear or dinuclear compounds in which both donor atoms, phosphorus and nitrogen, are involved in the coordination to the metal center. The reactions of the diphosphine ligand [Fc(CH2PPh2)(PPh2)] (L2) with gold(I), gold(III), silver(I), or copper(I) complexes afford mono‐, di‐, or trinuclear derivatives. Some homo‐ and heterodinuclear compounds were obtained through the reactions of the mononuclear gold(III) complex [Au(C6F5)3{Fc(CH2PPh2)(PPh2)}] (6), in which one of the phosphorus atoms is free, with gold(I), gold(III), and silver(I) deriiivatives. Some of these derivatives were characterized by X‐ray diffraction analysis.

Structure‐Property Relationships in Tricyanoferrate(III) Building Blocks and Trinuclear Cyanide‐Bridged Complexes

The preparation, structures, and magnetic properties of two tricyanoferrates, [NEt4]2[(Tp*Me)FeII(CN)3]·MeCN (1) and [NEt4][(Tp*Me)FeIII(CN)3]·H2O (2), and three trinuclear derivatives, {[(Tp*Me)FeIII(CN)3]2[NiII(L)2]}·n(solvent) (L = bpy, 3; tren, 4; DETA, 5) are described. Magnetic measurements show that 2 is an S = 1/2 complex [g = 2.65(1)], while 3–5 display ST = 2 spin ground states, owing to cyanide‐mediated ferromagnetic exchange between FeIIILS (S = 1/2) and NiII (S = 1) ions. The χT vs. T data for 3–5 were modelled using an isotropic Heisenberg model and give J/kB and gavg values of +11.1(1) K and 2.48(1) for 3, 9.1(1) K and 2.6(1) for 4, and +11.2(1) K and 2.41(5) for 5 (with zJ′ = –0.28 K). High‐field/frequency EPR data indicates significant g‐anisotropy in 2 (gz = 3.6, gy = 2.2, gx = 2.0) and [NEt4][(Tp*)FeIII(CN)3]·H2O (6) (gz = 3.5, gy = 2.0, gx = 1.3), while 5 shows D = –2.09 cm–1, E = 0.08 cm–1, and B40 = –2.3 × 10–3 cm–1 with gz = 2.4 and gx = gy = 1.95. Despite significant magnetic anisotropy in 3–5, frequency‐dependent behavior is only seen for 5 above 1.8 K, suggesting that rapid quantum tunnelling of the magnetization is operative.

Amidinatogermylene derivatives of ruthenium carbonyl: new insights into the reactivity of [Ru3(CO)12] with two-electron-donor reagents of high basicity.

The reactivity of ruthenium carbonyl with amidinatogermylenes of the type Ge(R2bzam)(t)Bu (R2bzam = N,N'-disubstituted benzamidinate) was studied for R = (t)Bu (1tBu) and (i)Pr (1iPr). The mono-, bi-, and/or trinuclear derivatives [Ru(1R)(CO)4], [Ru(1R)2(CO)3], [Ru2(1iPr)(CO)7], [Ru3(1tBu)(CO)11], [Ru3(1tBu)2(CO)10], and [Ru3(1R)3(CO)9] (R = (t)Bu, (i)Pr) were isolated in yields that depend upon the reactant ratio and the reaction temperature. The experimental data are consistent with the proposal that, at room temperature, the trinuclear complexes [Ru3(CO)12], [Ru3(1R)(CO)11], and [Ru3(1R)2(CO)10] form an adduct with the germylene 1R that may evolve through two different reaction pathways, (a) releasing a CO ligand (thus leading to the corresponding trinuclear CO-substituted product) and/or (b) cleaving the cluster framework (thus leading to mononuclear germylene-containing products). At 90 °C, additional processes are also possible, such as the reactions of 1R with [Ru(1R)(CO)4] or [Ru3(1R)3(CO)9], which both give [Ru(1R)2(CO)3], or the reactions of [Ru(1tBu)(CO)4] and [Ru(1iPr)(CO)4] with [Ru3(CO)12], which give [Ru3(1tBu)(CO)11] and [Ru2(1iPr)(CO)7], respectively. This wide reaction panorama helps rationalize previously reported outcomes of reactions of [Ru3(CO)12] with other reagents of high basicity, such as trialkylphosphines or N-heterocyclic carbenes, including results for which no satisfactory explanation has been hitherto provided.

Gold(I) and related heterometallic derivatives of dimolybdenum complexes with asymmetric phosphinidene bridges.

The phosphinidene-bridged complexes [Mo2Cp2(μ-κ(1):κ(1),η(6)-PR*)(CO)2] (1), [Mo2Cp2(μ-κ(1):κ(1),η(4)-PR*)(CO)3] (2), [Mo2Cp(μ-κ(1):κ(1),η(5)-PC5H4)(η(6)-HR*)(CO)2] (3), and [Mo2Cp2(μ-κ(1):κ(1)-PH)(η(6)-HR*)(CO)2] (4) were examined as precursors of heterometallic gold(I) and related derivatives (Cp = η(5)-C5H5, R* = 2,4,6-C6H2(t)Bu3). These complexes reacted with [AuCl(THT)] to give the corresponding derivatives [AuMo2ClCp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2], [AuMo2ClCp2(μ-κ(1):κ(1):κ(1),η(4)-PR*)(CO)3] (Au-Mo = 2.8493(6) Å), [AuMo2ClCp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)], and [AuMo2ClCp2(μ3-PH)(CO)2(η(6)-HR*)] formally resulting from the addition of an acceptor AuCl moiety to the short Mo-P bond of the parent substrates almost perpendicular to the corresponding Mo2P plane. The chloride ligand was easily displaced upon reaction of the PC5H4-bridged gold complex with K[MoCp(CO)3] to give the tetranuclear derivative [AuMo3Cp2(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)5(η(6)-HR*)] (Au-Mo = 2.711(2) and 2.807(2) Å). Compound 1 also reacted with HgI2 to give a hexanuclear complex [HgMo2Cp2(μ-I)I(μ-κ(1):κ(1),η(6)-PR*)(CO)2]2 containing dative Mo→Hg bonds (2.820(1) and 2.827(1) Å), whereas complex 3 gave the μ3-PR bridged complex [HgMo2CpI2(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)]. Complexes 1 to 4 also reacted easily with [AuL(THT)]PF6 (L = THT, P(p-tol)3, PMe3, P(i)Pr3) to give the corresponding cationic trinuclear derivatives [AuMo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2L](PF6) (Au-Mo = 2.8080(3) Å for L = P(p-tol)3), [AuMo2Cp2(μ-κ(1):κ(1):κ(1),η(4)-PR*)(CO)3L](PF6), and [AuMo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*){P(p-tol)3}](PF6). The blue, analogous PH-bridged complexes were more conveniently isolated as tetra-arylborate salts [AuMo2Cp2(μ3-PH)(CO)2(η(6)-HR*)L](BAr'4) (Au-Mo = 2.8038(6) Å for L = P(i)Pr3; Ar'= 3,5-C6H3(CF3)2]. Compounds 1, 3, and 4 reacted readily with the cation [Au(THT)2](+) (as PF6(-) or BAr'4(-) salts) in a 2:1 ratio to give respectively the corresponding pentanuclear derivatives [Au{Mo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2}2](PF6), [Au{Mo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)}2](PF6) (Au-Mo = 2.7975(7) and 2.8006(7) Å), and [Au{Mo2Cp2(μ3-PH)(CO)2(η(6)-HR*)}2](BAr'4) (Au-Mo = 2.8233(8) and 2.8691(7) Å). Related silver complexes were obtained from the reaction of 3 and 4 with [AgCl(PPh3)]4 after spontaneous symmetrization, while reaction of 1 with [Cu(NCMe)4]PF6 in a 2:1 ratio yielded the analogous copper complex [Cu{Mo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2}2](PF6). All the above cationic gold complexes having (μ-κ(1):κ(1):κ(1),η(6)-PR*) ligands (but not the copper complex) rearranged into [Au{Mo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)}2](PF6) in refluxing 1,2-dichloroethane solution.

From a di- and trinuclear phosphanido fragment to tetra- and hexanuclear platinum(II) complexes

The di- and trinuclear derivatives [(RF)2Pt(μ-PPh2)2Pt(CH3CN)2], 1, [(RF)2Pt(μ-PPh2)2Pt(μ-PPh2)2Pt(CH3CN)2], 2, (RF=C6F5) behave as synthons of di- and trinuclear fragments. Addition of azide and oxalate ions to 1 and 2, even in an excess, provides a way to isolate the tetranuclear and hexanuclear platinum complexes [NBu4]2[{(RF)2Pt{(μ-PPh2)2Pt}n(μ-1,1-N3)}2] (n=1, 3; 2, 5), [NBu4]2[{(RF)2Pt(μ-PPh2)2Pt}2(μ-C2O4-κ2O,O′: κ2O″,O‴)}], 4, and [NBu4]2[{(RF)2Pt(μ-PPh2)2Pt(μ-PPh2)2Pt}2(μ-C2O4-κ2O,O′: κ2O″,O‴)}], 6. The structures of 3–6, determined by single crystal X-ray diffraction, show a linear arrangement of the platinum centres maintained through “Pt(μ-PPh2)2Pt” and “Pt(μ-1,1-N3)2Pt” or “Pt(μ-C2O4-κ2O,O′:κ2O″,O‴)Pt” bridging fragments. Finally, addition of KCN to 2 affords the trinuclear [NBu4]2[(RF)2Pt(μ-PPh2)2Pt(μ-PPh2)2Pt(CN)2], 7, in which two cyanido groups are bonded to the platinum centre in a terminal way.

Reactivity of a Bis(N-heterocyclic carbene) with Ruthenium Carbonyl. Synthesis of Mono- and Trinuclear Derivatives and Ligand Modification via C–H Bond Activation

The bis(N-heterocyclic carbene) 1,1′-dimethyl-3,3′-(o-xylylene)diimidazol-2,2′-diylidene (MeImCH2C6H4CH2ImMe) reacted with [Ru3(CO)12] at room temperature, in a 3/1 molar ratio, to give the mononuclear derivative [Ru(κ2C2-MeImCH2C6H4CH2ImMe)(CO)3] (1), which contains a chelating bis(NHC) ligand. However, the use of a 1/1 ratio of the reactants led to the trinuclear cluster [Ru3(μ-κ2C2-MeImCH2C6H4CH2ImMe)(CO)10] (2), which contains an edge-bridging bis(NHC) ligand and which, upon heating in refluxing THF, underwent a double C(sp3)–H bond activation process to give the dihydride derivative [Ru3(μ-H)2(μ3-κ3C3-MeImCC6H4CH2ImMe)(CO)8] (3).

Copper(II) compounds with NNO tridentate Schiff base ligands: Effect of subtle variations in ligands on complex formation, structures and magnetic properties

The formation and the magnetic properties of the copper(II) compounds [Cu(L1)(py)](ClO4) (1a) and [Cu(L2)(py)](ClO4) (2a), bearing the NNO tridentate Schiff base ligand L1−=(E)-2-((3-aminoethylimino)methyl)phenolate or L2−=(E)-2-((3-aminopropylimino)methyl)phenolate (obtained by monocondensation of salicylaldehyde, salH, and ethylenediamine, en, or 1,3-propylenediamine, tn, respectively) and pyridine (py) are presented. These complexes are converted into new mono-, di- and trinuclear derivatives, whose nature depends on the length of the diamine used and hence on the size of the corresponding metallacycle. Pyridine can be substituted by a molecule of N,N-dimethylformamide (DMF) in compound 2a, leading to the mononuclear [Cu(L2)(dmf)](ClO4) (2b), while 1a undergoes only decomposition under similar conditions. Pyrazine does not act as bridging ligand between two copper centres by substitution of py, but its reaction with 2a yields either the dinuclear compound [Cu2(L2)2(ClO4)2] (2c), with exclusion of pyridine, or the trinuclear [Cu3(L2)3(μ3-OH)](ClO4)2 (2d), where pyrazine acts as base generating OH−, and it does not appear in the product. Reaction of 1a with pyrazine yields only the trinuclear [Cu3(L1)3(μ3-OH)](ClO4)2 (1d). Also with 2,2′-bipyridine (2,2′-bpy) dinuclear complexes are not formed, but bpy acts as bidentate ligand to copper yielding the pentacoordinated mononuclear compounds [Cu(L1)(2,2′-bpy)](ClO4) (1e) and [Cu(L2)(2,2′-bpy)](ClO4) (2e). The crystal structures of compounds 2b, 2c and 1e have been solved and are reported. The magnetic susceptibilities χM(T) of 1a and 2a have been studied, showing the absence of any measurable Cu–Cu interaction for 1a (en, five-membered ring), while a weak but interesting intermolecular Cu–Cu ferromagnetic coupling (J=+0.96(3)cm−1) through the short dimeric Cu···O contacts is detected for 2a (tn, six-membered ring). The X-band EPR spectrum of 2a in a frozen methanol solution at 70K shows the hyperfine coupling of mononuclear copper with the three coordinated 14N atoms, yielding seven narrow lines.

Behavior of Neutral Phosphido Derivatives of Platinum and Palladium toward Silver Centers

The reaction of the neutral binuclear complexes [(R(F))(2)Pt(μ-PPh(2))(2)M(phen)] (phen = 1,10-phenanthroline, R(F) = C(6)F(5); M = Pt, 1; M = Pd, 2) with AgClO(4) or [Ag(OClO(3))(PPh(3))] affords the trinuclear complexes [AgPt(2)(μ-PPh(2))(2)(R(F))(2)(phen)(OClO(3))] (7a) or [AgPtM(μ-PPh(2))(2)(R(F))(2)(phen)(PPh(3))][ClO(4)] (M = Pt, 8; M = Pd, 9), which display an "open-book" type structure and two (7a) or one (8, 9) Pt-Ag bonds. The neutral diphosphine complexes [(R(F))(2)Pt(μ-PPh(2))(2)M(P-P)] (P-P = 1,2-bis(diphenylphosphino)methane, dppm, M = Pt, 3; M = Pd, 4; P-P = 1,2-bis(diphenylphosphino)ethane, dppe, M = Pt, 5; M = Pd, 6) react with AgClO(4) or [Ag(OClO(3))(PPh(3))], and the nature of the resulting complexes is dependent on both M and the diphosphine. The dppm Pt-Pt complex 3 reacts with [Ag(OClO(3))(PPh(3))], affording a silver adduct 10 in which the Ag atom interacts with the Pt atoms, while the dppm Pt-Pd complex 4 reacts with [Ag(OClO(3))(PPh(3))], forming a 1:1 mixture of [AgPdPt(μ-PPh(2))(2)(R(F))(2)(OClO(3))(dppm)] (11), in which the silver atom is connected to the Pt-Pd moiety through Pd-(μ-PPh(2))-Ag and Ag-P(k(1)-dppm) interactions, and [AgPdPt(μ-PPh(2))(2)(R(F))(2)(OClO(3))(PPh(3))(2)][ClO(4)] (12). The reaction of complex 4 with AgClO(4) gives the trinuclear derivative 11 as the only product. Complex 11 shows a dynamic process in solution in which the silver atom interacts alternatively with both Pd-μPPh(2) bonds. When P-P is dppe, both complexes 5 and 6 react with AgClO(4) or [Ag(OClO(3))(PPh(3))], forming the saturated complexes [(PPh(2)C(6)F(5))(R(F))Pt(μ-PPh(2))(μ-OH)M(dppe)][ClO(4)] (M = Pt, 13; Pd, 14), which are the result of an oxidation followed by a PPh(2)/C(6)F(5) reductive coupling. Finally, the oxidation of trinuclear derivatives [(R(F))(2)Pt(II)(μ-PPh(2))(2)Pt(II)(μ-PPh(2))(2)Pt(II)L(2)] (L(2) = phen, 15; L = PPh(3), 16) by AgClO(4) results in the formation of the unsaturated 46 VEC complexes [(R(F))(2)Pt(III)(μ-PPh(2))(2)Pt(III)(μ-PPh(2))(2)Pt(II)L(2)][ClO(4)](2) (17 and 18, respectively) which display Pt(III)-Pt(III) bonds.

Metal–Metal Bonding in Bis(alkylthio)hexacarbonyldicobalt Complexes: Open Structures vs. Butterfly and Tetrahedrane Structures

AbstractDensity functional calculations on the Co2(CO)6(SR)2 compounds (R = CH3, CF3) predict both open and butterfly structure types of similar energies. The open Co2(CO)6(μ‐SR)2 structures have non‐planar central Co2S2 units with two bridging RS groups and ca. 3.4 Å Co···Co distances indicating a lack of direct metal–metal bonding. The butterfly Co2(CO)5(μ‐SR)(μ‐CO)(SR) structures have direct Co–Co bonds of lengths ca. 2.5 Å forming the “body” of the butterfly, one terminal RS group, one bridging RS group, and one bridging CO group. The lowest energy Co2(CO)6(SCH3)2 structure is an open isomer. However, this open isomer lies only 0.4 kcal/mol below the corresponding butterfly isomer. For the corresponding fluorinated derivative Co2(CO)6(SCF3)2 a butterfly structure with a direct Co–Co bond and a bridging CO group lies at a slightly lower energy than the lowest energy open structures. The relative energy difference between open and butterfly Co2(CO)6(SCF3)2 structures is more than five times higher than for the Co2(CO)6(SCH3)2 structures. The electronegativity of the RS group in the Co2(CO)6(SR)2 structures has little effect on the geometric parameters but exerts a significant influence on the atomic charge distribution. The butterfly structures with a direct metal–metal bond are predicted to be nearly isoenergetic to open structures without a Co–Co bond. Unsuccessful attempts to optimize a previously proposed Co2(CO)6(μ‐η2:η2‐S2R2) structure with a central Co2S2 tetrahedrane unit with one Co–Co bond, one S–S bond, and four Co–S bonds are consistent with the previous reformulation of the originally claimed Co2S2 tetrahedranes Co2(CO)6[μ‐η2:η2‐S2(C6X5)2] (X = F, Cl) as the trinuclear derivatives Co3(μ3‐S)(C6F5)(CO)8.

ChemInform Abstract: Chemistry of Palladium and Platinum with Selenium and Tellurium Ligands

Reactions of NaER (E = Se, Te; R = Ph, substituted Ph or 2-pyridyl) with a number of mono- and bi-nuclear palladium and platinum complexes have been investigated. Complexes of the type [M(Sepy)2], [M(ER)2(PR3)2], [M2Cl2(μ-ER)2(PR3)2] and [M2Cl2(μ-Cl)(μ-ER)(PR3)2] (M = Pd, Pt) were isolated. They were characterized by elemental analysis, NMR (1H, 13C, 31P, 77Se, 125Te, 195Pt) data and in a few cases by X-ray diffraction studies. The [M(Sepy)2(PPh3)2] dissociates into PPh3 and [M(Sepy)(η2-Sepy)(PPh3)] in solution. 2-Selenopyridine in its complexes acts in a monodentate (bonding through selenium) as well as in chelating (Se⌢N) or bridging fashion. The mononuclear complexes [M(ER)2(PR3)2] are useful precursors for stepwise synthesis of cationic bi- and tri-nuclear derivatives.

Reductive Dimerization of Triruthenium Clusters Containing Cationic Aromatic N‐Heterocyclic Ligands

The cationic cluster complexes [Ru(3)(mu-H)(mu-kappa(2)N,C-L(1) Me)(CO)(10)](+) (1(+); HL(1) Me=N-methylpyrazinium), [Ru(3)(mu-H)(mu-kappa(2)N,C-L(2) Me)(CO)(10)](+) (2(+); HL(2) Me=N-methylquinoxalinium), and [Ru(3)(mu-H)(mu-kappa(2)-N,C-L(3) Me)(CO)(10)](+) (3(+); HL(3) Me=N-methyl-1,5-naphthyridinium), which contain cationic N-heterocyclic ligands, undergo one-electron reduction processes to become short lived, ligand-centered, trinuclear, radical species (1-3) that end in the formation of an intermolecular C--C bond between the ligands of two such radicals, thus leading to neutral hexanuclear derivatives. These dimerization processes are selective, in the sense that they only occur through the exo face of the bridging ligands of trinuclear enantiomers of the same configuration, as they only afford hexanuclear dimers with rac structures (C(2) symmetry). The following are the dimeric products that have been isolated by using cobaltocene as reducing agent: [Ru(6)(mu-H)(2){mu(6)-kappa(4)N(2),C(2)-(L(1) Me)(2)}(CO)(18)] (5; from 1(+)), [Ru(6)(mu-H)(2){mu(6)-kappa(4)N(2),C(2)-(L(2) Me)(2)}(CO)(18)] (6; from 2(+)), and [Ru(6)(mu-H)(2){mu(4)-kappa(8)N(2),C(6)-(L(3) Me)(2)}(CO)(18)] (7; from 3(+)). The structures of the final hexanuclear products depend on the N-heterocyclic ligand attached to the starting materials. Thus, although both trinuclear subunits of 5 and 6 are face-capped by their bridging ligands, the coordination mode of the ligand of 5 is different from that of the ligand of 6. The trinuclear subunits of 7 are edge-bridged by its bridging ligand. In the presence of moisture, the reduction of 3(+) with cobaltocene also affords a trinuclear derivative, [Ru(3)(mu-H)(mu-kappa(2)N,C-L(3') Me)(CO)(10)] (8), whose bridging ligand (L(3') Me) results from the formal substitution of an oxygen atom for the hydrogen atom (as a proton) that in 3(+) is attached to the C(6) carbon atom of its heterocyclic ligand. The results have been rationalized with the help of electrochemical measurements and DFT calculations, which have also shed light on the nature of the odd-electron species, 1-3, and on the regioselectivity of their dimerization processes. It seems that the sort of coupling reactions described herein requires cationic complexes with ligand-based LUMOs.

Abstract 2494: A non-covalent binding platinum drug, TriplatinNC, induces a G1 phase cell cycle arrest and p53-independent mechanisms of apoptosis

Abstract TriplatinNC, is a novel trinuclear derivative of the Phase II clinical drug, BBR3464. The binding to DNA is through non-covalent (hydrogen bonding and electrostatic) interactions. The absence of substation-labile leaving groups results in insensitivity to glutathione concentration in vitro while the high (8+) charge results in enhanced cellular accumulation compared to BBR3464 and especially cisplatin. The antitumor activity of TriplatinNC was examined in vivo showing higher activity against 2008 ovarian carcinoma cells than c-DDP at the doses administered. Studies using HCT116 colon carcinoma cells have shown that TriplatinNC is cytotoxic in the presence and absence of p53. Cell cycle studies show that TriplatinNC differs from BBR3464 in inducing a G1 arrest rather than a G2 arrest in HCT116 cells. A p53-independent activation of caspase 8 and caspase 9 leading to the cleavage of caspase 3 and its downstream substrate, PARP-1, may indicate that TriplatinNC induces both intrinsic and extrinsic pathways of cell death. Our study illustrates fundamental differences in the mechanisms of action between non-covalent binding drugs like TriplatinNC and related covalent binding drugs such as c-DDP, oxaliplatin, and BBR3464. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2494.

Preparation of a Building Block for a Pyrazole Expanded Porphyrin and Isolation of a Tripyrrolyl Ketone Decomposition Product

Dipyrrolylpyrazole 3, obtained from l,3-di-(1H-pyrrol-2-yl)propane-1,3-dione (2), was prepared as a building block for pyrazole-based binuclear expanded porphyrins. An unusual transformation of 2, in solution or on chromatography, afforded l,3,3-tri-(1H-pyrrol-2-yl)prop-2-en-1-one (4) in good yield. HRMS indicated the presence of an unstable pyrazole-based expanded porphyrin 1 and its trinuclear Mg derivative 5 on condensation of 3 with benzaldehyde.

From two-electron via four-electron to six-electron donor carbonyl groups in trinuclear derivatives of the oxophilic metal niobium

Trinuclear cyclopentadienylniobium carbonyls are of interest since Cp3Nb3(CO)7 (Cp=eta5-C5H5) is a stable molecule having a unique face-bridging carbonyl group formally donating six electrons to the Nb3 triangle through one Nb-C sigma-bond and two orthogonal pi-bonds. In this connection, the molecules Cp3Nb3(CO)n (n=9, 8, 7, 6) have been examined by density functional theory. The saturated derivative Cp3Nb3(CO)9 is predicted to have a structure with all terminal carbonyl groups and a singly bonded Nb3 triangle with 3.361 A edges. The singly bonded Nb3 triangle is retained in the lowest energy structure for Cp3Nb3(CO)8, which has a four-electron donor edge-bridging carbonyl group in addition to seven terminal carbonyl groups. An alternative structure for Cp3Nb3(CO)8 at approximately 8 kcal mol(-1) above this global minimum has an unusual four-electron donor carbonyl group bridging all three niobium atoms. The two lowest energy structures found for Cp3Nb3(CO)7 are a pair of stereoisomers within approximately 1 kcal mol(-1) of energy, having a six-electron donor carbonyl group bridging all three niobium atoms, in addition to six terminal carbonyl groups. The structure and nu(CO) frequencies of one of these stereoisomers, including the unusually low nu(CO) frequency of approximately 1330 cm(-1) for the six electron donor carbonyl group, are in close agreement with experiment. In contrast to Cp3Nb3(CO)8 and Cp3Nb3(CO)7, the lowest energy structure for the even more unsaturated Cp3Nb3(CO)6 has only two-electron donor carbonyl groups, three of which are edge-bridging and three of which are terminal. However, in this Cp3Nb3(CO)6 structure, two of the Nb[double bond, length as m-dash]Nb distances in the Nb3 triangle are shortened to approximately 2.8 A, suggesting a formal bond order of at least two.

Reactions of Conjugated Dienes with a Triruthenium Hydrido Carbonyl Cluster: Synthesis and Reactivity of Trinuclear Derivatives Having an Edge-Bridging Allyl Ligand

The reactions of the hydrido triruthenium complex [Ru3(μ-H)(μ3-κ2-HNNMe2)(CO)9] (1; H2NNMe2 = 1,1-dimethylhydrazine) with conjugated dienes give trinuclear derivatives that contain edge-bridging al...

Reactions of [Fe 3Cp 2(CO) 3(μ-CO)(μ 3-CO)(μ 3-CF 3C 2CF 3)] with diphosphines: X-ray structure of a complex in which two tri-iron clusters are linked only by Ph 2PCH 2CH 2PPh 2

Reactions of the trinuclear iron cluster [Fe 3Cp 2(CO) 3(μ-CO)(μ 3-CO)(μ 3-CF 3C 2CF 3)] ( 1) with the bis(phosphino) ligands dppm and dppe give different results: dppe yields mainly the hexanuclear compound ( 2) in which two tri-iron cluster units are linked by the diphosphine, although a trinuclear derivative ( 3) with a chelating dppe ligand is also obtained as a minor product, whereas dppm displaces carbonyl to give complexes containing exclusively a single tri-iron unit, though the phosphine may be either dangling ( 4) or chelating ( 5). The complexes 2– 5 have been characterised by elemental analyses and from their IR and NMR spectra, supplemented in the case of 2 by a single crystal X-ray diffraction analysis.