Complexes of an anionic gallium(I) N-heterocyclic carbene analogue with group 14 element(II) fragments: synthetic, structural and theoretical studies

The reactions of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue, [K(tmeda)][:Ga{[N(Ar)C(H)]2}], Ar = C6H3Pri2-2,6, with the heavier group 14 alkene analogues, R2E=ER2, E = Ge or Sn, R = -CH(SiMe3)2, have been carried out. In 2:1 stoichiometries, these lead to the ionic [K(tmeda)][R2EGa{[N(Ar)C(H)]2}] complexes which exhibit long E-Ga bonds. The nature of these bonds has been probed by DFT calculations, and the complexes have been compared to neutral NHC adducts of group 14 dialkyls. The 4:1 reaction of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with R2Sn=SnR2 leads to the digallyl stannate complex, [K(tmeda)][RSn[Ga{[N(Ar)C(H)]2}]2], presumably via elimination of KR. In contrast, the reaction of the gallium heterocycle with PbR2 affords the digallane4, [Ga{[N(Ar)C(H)]2}]2, via an oxidative coupling reaction. For sake of comparison, the reactions of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with Ar'2E=EAr'2, E = Ge, Sn or Pb, Ar' = C6H2Pri3-2,4,6, were carried out and led to either no reaction (E = Ge), the formation of [K(tmeda)][Ar'2SnGa{[N(Ar)C(H)]2}] (E = Sn), or the gallium(III) heterocycle, [Ar'Ga{[N(Ar)C(H)]2}] (E = Pb). Salt elimination reactions between [K(tmeda)][:Ga{[N(Ar)C(H)]2}] and the guanidinato group 14 complexes [(Giso)ECl], E = Ge or Sn, Giso = [Pri2NC{N(Ar)}2]-, gave the neutral [(Giso)EGa{[N(Ar)C(H)]2}] complexes. All complexes have been characterized by NMR spectroscopy and X-ray crystallographic studies.     

Erstmaliger Einbau eines späten Übergangsmetalls in ein Silsesquioxan‐Gerüst: Synthese und strukturelle Charakterisierung von Cy7Si7O12Fe(tmeda)

Silsesquioxane Chemistry. VIII First Incorporation of a Late Transition Metal into a Silsesquioxane Cage: Synthesis and Structural Characterization of Cy₇Si₇O₁₂Fe(tmeda) Cy₇Si₇O₁₂Fe(tmeda) ( 3 , Cy = cyclohexyl, tmeda = N,N,N′,N′‐tetramethylethylenediamine) has been prepared by reacting in situ generated Cy₇Si₇O₉(OLi)₃ ( 2 ) with anhydrous FeCl₃ followed by treatment with tmeda. Pale yellow crystalline 3 represents the first example of a metallasilsesquioxane in which a late transition metal is incorporated into a silsesquioxane cage. The compound crystallizes as discrete monomers in which the coordination sphere around Fe is saturated by addition of a chelating tmeda ligand ( 3 : monoclinic space group Cc, Z = 4, lattice dimensions at –100 °C: a = 2469.0(2), b = 1529.9(2), c = 1010.4(2) pm, β = 116.68(1)°, R = 0.052).     

Structural and mechanistic investigations of the oxidation of dimethylplatinum(II) complexes by dioxygen

The oxidation of (tmeda)Pt(II)(CH(3))(2) (1, tmeda = N,N,N',N'-tetramethylethylenediamine) to (tmeda)Pt(IV)(OH)(OCH(3))(CH(3))(2) (3) by dioxygen in methanol proceeds via a two-step mechanism. The initial reaction between (tmeda)Pt(CH(3))(2) and dioxygen yields a hydroperoxoplatinum(IV) intermediate, (tmeda)Pt(OOH)(OCH(3))(CH(3))(2) (2), which reacts with a second equivalent of (tmeda)Pt(CH(3))(2) to afford the final product 3. Both 2 and 3 have been fully characterized, including X-ray crystallographic structure determinations. The effect of ligand variation on the oxidation of several dimethylplatinum(II) complexes by 2 as well as by dioxygen has been examined.     

Zur Reaktion der Alkin-Kupfer(I)-Komplexe [CuX(S-Alkin)] (X = Cl,Br, I; S-Alkin = 3,3,6,6-Tetramethyl-1-thia-4-cycloheptin) mit dem Chelat-Liganden N,N,N′,N′-Tetramethylethylendiamin (tmeda)

Organometallic Compounds of Copper. XVII. On the Reaction of the Alkyne-Copper(I) Complexes [CuX(S-Alkyne)] (X = Cl, Br, I; S-Alkyne = 3,3,6,6-Tetramethyl-1-thiacyclohept-4-yne) with the Chelate Ligand N,N,N′,N′-Tetramethylethylendiamine (tmeda) The alkyne copper(I) chloride complex [CuCl(S-Alkyne)]_n ( 2 a ) (S-Alkyne = 3,3,6,6–tetramethyl-1-thiacyclohept-4-yne) adds tetramethylethylene diamine (tmeda) to form the mononuclear compound [CuCl(S-Alkyne)(tmeda)] ( 4 ). The alkyne copper halide complexes [CuBr(S-Alkyne)]_n ( 2 b ) and [CuI(S-Alkyne)]_n ( 2 c ) react with tmeda to yield the complex salts [Cu(S-Alkyne)(tmeda)]⁺ [CuX₂(S-Alkyne)]^– (X = Br ( 5 a ), X = I ( 5 b )). X-ray diffraction studies on all new compounds 4 and 5 reveal distorted tetrahedral coordination of the copper atom in complex 4 and trigonal-planar coordinated copper atoms in the cations and anions of the ionic compounds 5 .     

Complexes of a gallium heterocycle with transition metal dicyclopentadienyl and cyclopentadienylcarbonyl fragments, and with a dialkylmanganese compound

The reactivity of several transition metal half sandwich complexes towards an anionic gallium(I) heterocyclic complex, [K(tmeda)][Ga{[N(Ar)C(H)]2}](Ar = C6H3Pri2-2,6), has been investigated. This has led to the anionic half sandwich complexes, [K(tmeda)][(C5H4R)M(CO)n[Ga{[N(Ar)C(H)]2}]](M = V, R = H, n= 3; M = Mn, R = Me, n= 2; M = Co, R = H, n= 1), which crystallographic studies show to form dimers (M = Mn and Co) or a polymer (M = V) through bridging potassium cations. The metal-gallium bond lengths in all complexes are very short which, combined with some spectroscopic evidence, is suggestive of M-Ga pi-bonding. Density functional theory studies of models of all complexes indicate that the level of back-bonding in these complexes is, however, minimal and of a similar order to that seen in analogous complexes incorporating neutral N-heterocyclic carbene ligands. Reactions of the metallocenes, [M(C5H4Me)2](M = V or Cr), with the digallane4, [Ga{[N(Ar)C(H)]2}]2, have afforded the neutral complexes, [M(C5H4Me)2[Ga{[N(Ar)C(H)]2}]], which are thought to be formed via an initial oxidative insertion of the transition metal centre into the Ga-Ga bond of the digallane. X-Ray crystallography shows the complexes to be monomeric. One (M = V) reacts with one equivalent of [K(tmeda)][Ga{[N(Ar)C(H)]2}] to give the crystallographically characterised, anionic bis(gallyl)-complex, [K(tmeda)][V(C5H4Me)2[Ga{[N(Ar)C(H)]2}]2]. For comparison, the reaction of [K(tmeda)][Ga{[N(Ar)C(H)]2}] with [Mn{CH(SiMe3)2}2] was carried out and gave the monomeric, anionic complex, [K(tmeda)][Mn{CH(SiMe3)2}2[Ga{[N(Ar)C(H)]2}]].     

Pd2Ag triangle supported by two micro3-amidopyridine ligands

[Pd(tmeda)(Hampy-N1)(H2O)]2+ (tmeda=N,N,N',N'-tetramethylethylenediamine; Hampy=2-aminopyridine) forms in the presence of Ag+ at pH 8-9 a triangular Pd2Ag complex containing two deprotonated ampy- ligands. It has been crystallized and structurally characterized with nitrate anions and a second co-crystallized AgNO3, [{Pd(ampy)(tmeda)}2Ag(micro-NO3)2Ag(NO3)2]. The two amidopyridine ligands are triply bridging, binding to Ag+ in a monodentate fashion viaN1, and to two PdII centres in a micro2-bridging fashion via the monodeprotonated N2 position. The resulting four-membered Pd(ampy)2Pd metallacycle is syn-planar with Pd[dot dot dot]Pd separations of 3.0878(13) A. The Pd...Ag distances are 3.0879(14) A in (isosceles triangle). In solution (D2O), the two ampy- ligand in are non-equivalent as concluded from a detailed 1H NMR spectroscopic study and confirmed by a 13C NMR spectrum. Removal of Ag+ from, as achieved by addition of Cl-, causes cluster degradation and linkage isomerization of PdII(tmeda) from the exocyclic N2 to the endocyclic N1 position.     

The rich chemistry of [Zn2Cp*2]: trapping three different types of zinc ligands in the PdZn7 complex [Pd(ZnCp*)4(ZnMe)2{Zn(tmeda)}

The synthesis, structural characterization, and bonding situation analysis of a novel, all-zinc, hepta-coordinated palladium complex [Pd(ZnCp*)(4)(ZnMe)(2){Zn(tmeda)}] (1) is reported. The reaction of the substitution labile d(10) metal starting complex [Pd(CH(3))(2)(tmeda)] (tmeda = N,N,N',N'-tetramethyl-ethane-1,2-diamine) with stoichiometric amounts of [Zn(2)Cp*(2)] (Cp* = pentamethylcyclopentadienyl) results in the formation of [Pd(ZnCp*)(4)(ZnMe)(2){Zn(tmeda)}] (1) in 35% yield. Compound 1 has been fully characterized by single-crystal X-ray diffraction, (1)H and (13)C NMR spectroscopy, IR spectroscopy, and liquid injection field desorption ionization mass spectrometry. It consists of an unusual [PdZn(7)] metal core and exhibits a terminal {Zn(tmeda)} unit. The bonding situation of 1 with respect to the properties of the three different types of Zn ligands Zn(R,L) (R = CH(3), Cp*; L = tmeda) bonded to the Pd center was studied by density functional theory quantum chemical calculations. The results of energy decomposition and atoms in molecules analysis clearly point out significant differences according to R vs L. While Zn(CH(3)) and ZnCp* can be viewed as 1e donor Zn(I) ligands, {Zn(tmeda)} is best described as a strong 2e Zn(0) donor ligand. Thus, the 18 valence electron complex 1 nicely fits to the family of metal-rich molecules of the general formula [M(ZnR)(a)(GaR)(b)] (a + 2b = n ≥ 8; M = Mo, Ru, Rh; Ni, Pd, Pt; R = Me, Et, Cp*).     

Oxidation reactions of an anionic gallium(I) N-heterocyclic carbene analogue with group 16 compounds

The reactivity of an anionic gallium(I) heterocycle, [K(tmeda)][:Ga([N(Ar)C(H)]2)], Ar = C6H3Pr(i)2-2,6, towards sources of elemental chalcogens and diorgano-dichalcogenides has been investigated and comparisons drawn with the reactivity of the valence isoelectronic N-heterocyclic carbene class of ligand. The reactions of the heterocycle with N2O or (Te)PEt3 yielded the dimeric, dianionic gallium(III) complexes, [K(L)]2[(mu-E)Ga([N(Ar)C(H)]2)]2, E = O, L = tmeda; E = Te, L = THF. Treatment of [K(tmeda)][:Ga([N(Ar)C(H)]2)] with the diphenyl dichalcogenides, PhEEPh, E = Se or Te, gave the one dimensional polymer, [K[(PhSe)2Ga([N(Ar)C(H)]2)]]infinity and the monomeric complex, [K(OEt2)3][(PhTe)2Ga([N(Ar)C(H)]2)], respectively. The X-ray crystal structures of the four complexes are reported.     

Synthesis, characterization, and reactivity of ruthenium diene/diamine complexes including catalytic hydrogenation of ketones

Thermal reactions between [RuCl2(diene)]n (diene = 2,5-norbornadiene, nbd; 1,5-cyclooctadiene, cod) with an excess of N,N,N',N'-tetramethylethylene diamine (tmeda) afforded derivatives [RuCl2(diene)(tmeda)] (diene = nbd, 1; cod, 2) as a mixture of cis and trans isomers. When thermolysis was performed under H2 mixtures of hydride species [RuCl(H)(diene)(tmeda)] (diene = nbd, 3; cod, 4) and the bis-tmeda adduct trans-[RuCl2(tmeda)2] (5) were obtained in different ratios depending upon the reaction conditions and reaction times. Heating polymeric Ru(II) precursors in toluene in the presence of a 5-fold excess of the bulkier N,N,N',N'-tetraethylethylene diamine (teeda) resulted in a rare diamine dealkylation process with formation of trans-[RuCl2(nbd)(Et2NCH2CH2NHEt)] (6) and trans-[RuCl2(cod)(EtHNCH2CH2NHEt)] (7) in high yields. The presence of N-H functionalities in the coordinated diamine ligands of 6 and 7 was unambiguously established by single-crystal X-ray diffraction studies. The dealkylation process of the teeda ligand seems to proceed intramolecularly as shown by solution NMR studies performed with the soluble Ru(II) precursors trans-[RuCl2(amine)2(diene)] (diene = nbd, amine = morpholine, 9; diene = cod, amine = Et2NH, 10). The above complexes [RuCl2(diene)(diamine)] have been tested as precatalysts in the hydrogenation of ketones both for transfer as well as direct hydrogenation, the latter route being the most effective.     

Synthesis and structures of the [benzamidinato]3- complexes Li3(tmeda)(L1)]2 and [Li(thf)4][Li5(L2)(OEt2)2] [L1 = N(SiMe3)C(Ph)N(SiMe3) and L2 = N(SiMe3)C(C6H4-4)NPh

Reduction at ambient temperature of each of the lithium benzamidinates [Li(L(1))(tmeda)] or [{Li(L(2))(OEt(2))(2)}(2)] with four equivalents of lithium metal in diethyl ether or thf furnished the brown crystalline [Li(3)(L(1))(tmeda)] (1) or [Li(thf)(4)][Li(5)(L(2))(2)(OEt(2))(2)] (2), respectively. Their structures show that in each the [N(R(1))C(R(3))NR(2)](3-) moiety has the three negative charges largely localised on each of N, N' and R = Aryl); a consequence is that the "aromatic" 2,3- and 5,6-CC bonds of R(3) approximate to being double bonds. Multinuclear NMR spectra in C(6)D(6) and C(7)D(8) show that 1 and 2 exhibit dynamic behaviour. [The following abbreviations are used: L(1) = N(SiMe(3))C(Ph)N(SiMe(3)); L(2) = N(SiMe(3))C(C(6)H(4)Me-4)N(Ph); tmeda = (Me(2)NCH(2)-)(2); thf = tetrahydrofuran.] This reduction is further supported by a DFT analysis.     

Zinc chalcogenolate complexes as precursors to ZnE and Mn/ZnE (E = S, Se) clusters

The ternary clusters (tmeda)(6)Zn(14-x)Mn(x)S(13)Cl(2) (1a-d) and (tmeda)(6)Zn(14-x)Mn(x)Se(13)Cl(2) (2a-d), (tmeda = N,N,N',N'-tetramethylethylenediamine; x ≈ 2-8) and the binary clusters (tmeda)(6)Zn(14)E(13)Cl(2) (E = S, 3; Se, 4;) have been isolated by reacting (tmeda)Zn(ESiMe(3))(2) with Mn(II) and Zn(II) salts. Single crystal X-ray analysis of the complexes confirms the presence of the six "(tmeda)ZnE(2)" units as capping ligands that stabilize the clusters, and distorted tetrahedral geometry around the metal centers. Mn(II) is incorporated into the ZnE framework by substitution of Zn(II) ions in the cluster. The polynuclear complexes (tmeda)(6)Zn(12.3)Mn(1.7)S(13)Cl(2)1a, (tmeda)(6)Zn(12.0)Mn(2.0)Se(13)Cl(2)2a, and (tmeda)(6)Zn(8.4)Mn(5.6)Se(13)Cl(2)2d represent the first examples of "Mn/ZnE" clusters with structural characterization and indications of the local chemical environment of the Mn(II) ions. The incorporation of higher amounts of Mn into 1d and 2d has been confirmed by elemental analysis. Density functional theory (DFT) calculations indicate that replacement of Zn with Mn is perfectly feasible and at least partly allows for the identification of some sites preferred by the Mn(II) metals. These calculations, combined with luminescence studies, suggest a distribution of the Mn(II) in the clusters. The room temperature emission spectra of clusters 1c-d display a significant red shift relative to the all zinc cluster 3, with a peak maximum centered at 730 nm. Clusters 2c-d display a peak maximum at 640 nm in their emission spectra.     

Cyclic trimer versus head-tail dimer in metal-nucleobase complexes: importance of relative orientation (syn, anti) of the metal entities and relevance as a metallaazacrown compound

The formation and crystal structure analysis of a cyclic trinuclear Pd complex with bridging 1-methylcytosinato model nucleobases is reported: [[(tmeda)Pd(1-MeC(-)-N3,N4)]3] (ClO4)3.5.5H2O (tmeda = N,N,N',N'-tetramethylethylenediamine; 1-MeC- = 1-methylcytosine deprotonated at exocyclic amino group) is obtained, among others, from the hydroxo-bridged dinuclear species [[(tmeda)Pd(OH)]2](ClO4)2, which likewise has been characterized by X-ray crystallography, and 1-MeC (1-MeC = neutral 1-methylcytosine) in aqueous solution. The usual head-tail dimer (HT1) appears not to be formed presumably because of the steric bulk of the tmeda ligand, which prevents a close approach of two tmeda ligands. There is also no evidence for formation of an alternative head-tail dimer structure (HT2) which, in principle, would not lead to any steric clash of ligands, but would require an orientation of the metal at N4 that is almost perpendicular to the nucleobase plane. In the Pd3 compound, the bridging metals are approximately in an anti arrangement, thereby leading to Pd...Pd separations within the Pd3 triangle close to 5.2 angstroms. This arrangement is reflected in the 1H NMR spectrum by a strongly deshielded H5 resonance of the nucleobase, occurring at 6.56 ppm (D2O). The overall structure of the Pd3 is that of a double cone, with ClO4- counterions approaching the cavities from either side. The trinuclear structure is also maintained in Me2SO-d6. In this solvent, Pd3 acts as a fluoride anion receptor, with F- binding to the N4H protons, as evident from large downfield shifts of these protons. The compound is compared with cyclic adeninato complexes of hexacoordinated metal ions, and a conceptional analogy with [12]metallacrown-3 species is outlined.     

Mononuclear Formamidinate Complexes of Lithium and Sodium

Treatment of N,N′‐bis(aryl)formamidines (FXylH = N,N′‐bis(2,6‐dimethylphenyl)formamidine, FEtH = N,N′‐bis(2,6‐diethylphenyl)formamidine, FisoH = N,N′‐bis(2,6‐diisopropylphenyl)formamidine) with nBuLi in the presence of tmeda (= N,N,N′,N′‐tetramethylethylenediamine) led to deprotonation of the amidine affording [Li(FXyl)(tmeda)] ( 1 ), [Li(FEt)(tmeda)] ( 2 ) and [Li(Fiso)(tmeda)] ( 3 ) respectively. Similar treatment of FXylH and FisoH with [Na{N(SiMe₃)₂}] in THF and pmdeta (= N,N,N′,N″,N″‐pentamethyldiethylenetriamine) yielded [Na(FXyl)(pmdeta)] ( 4 ) and [Na(Fiso)(pmdeta)] ( 5 ). All complexes were characterised by spectroscopy (NMR and IR) and X‐ray crystallography. Due to the bulkiness of the formamidinate ligands and the multidentate nature of the supporting neutral amine ligands (tmeda and pmdeta), all compounds were mononuclear with η²‐chelating formamidinate ligands in the solid state.     

Synthesis and structural characterization of silanethiolato complexes having tert-butyldimethylsilyl and trimethylsilyl groups

Treatment of cyclotrisilathiane (Me2SiS)3 with 3 equiv. of RLi (R = Me, But) in hexane-Et2O afforded the lithium silanethiolates LiSSiMe2R, and the tmeda adduct [(tmeda)LiSSiMe2But]2 1 (tmeda =N,N,N',N'-tetramethylethylenediamine) was isolated in the case of R = But. Reaction of Fe(CH3CN)2(CF3SO3)2, CoCl2, and [Cu(CH3CN)4](PF6) with 1 gave rise to the silanethiolato complexes M(SSiMe2But)2(tmeda)(M = Fe 2, Co 3), and [Cu(SSiMe2But)]4 4, respectively. Complexes (C5H5)2Ti(SSiMe2R)2(R = Me 5, But 6) and Ni(SSiMe2R)2(dppe)[R = Me 7, But 8; dppe = 1,2-bis(diphenylphosphino)ethane] were prepared from treatments of (C5H5)2TiCl2 and NiCl2(dppe) with the corresponding lithium silanethiolates. Complex 7 readily reacted with (C5H5)TiCl3 to produce the Ti-Ni heterobimetallic compound (C5H5)TiCl(mu-S)2Ni(dppe) 9, in which silicon-sulfur bond cleavage took place. Characterization of all compounds through spectroscopic techniques and elemental analyses are also described. X-Ray structural data for compounds 1 and 3-9 are reported.     

Phosphonate- and ester-substituted 2-cyanoethylene-1,1-dithiolate clusters of zinc: aerial CO2 fixation and unusual binding patterns

Treatment of [Zn(tmeda)Cl2] (tmeda = N, N, N', N'-tetramethylethylenediamine) with a phosphonate-substituted 2-cyanoethylene-1,1-dithiolato ligand in air yields a tetranuclear zinc-carbonate complex 1 having the formula of [Zn4(tmeda)3(mu3-CO3){S2CC(CN)P(O)(OEt)2}3] in which four zinc atoms form a trigonal pyramid with the apical zinc atom in a hitherto unknown S3O3 coordination sphere. It is the first example of aerial CO2 fixation to afford a metal-carbonato compound incorporating 1,1-ethenedithiolate ligands. In sharp contrast, reaction with an isobutyl ester-substituted 2-cyanoethylene-1,1-dithiolate forms a trimeric zinc complex [Zn(tmeda){S2CC(CN)(CO2(i)Bu)}]3, 2, which does not contain the metal-bound carbonate. Compound 2 is the first example of a trinuclear zinc complex composed of four-, five-, and six-coordinated Zn atoms. The unsymmetrical ligand orientation around three zinc centers in 2 suggests that the other structural isomer, which would have an idealized C3 axis, may exist. The reaction of the ethyl ester derivative of 2-cyanoethylene-1,1-dithiolate with [Zn(tmeda)Cl2] affords [{Zn(tmeda)Cl}2{S2CC(CN)(CO2Et)}], 3. The ester-functionalized 1,1-dithiolate ligands in compounds 2 and 3 display a bimetallic, triconnective coordination mode, which is rare for these types of ligands. Some probable intermediates generated from the formation of compound 1 have also been proposed.     

Au(CN)4]- as both an intramolecular and intermolecular bidentate ligand with [(tmeda)Cu(mu-OH)] dimers: from antiferro- to ferromagnetic coupling in polymorphs

Two polymorphic products, [[Cu(tmeda)(mu-OH)}2Au(CN)4][Au(CN)4] (1) and [Cu(tmeda)(mu-OH)Au(CN)4]2 (2), were synthesized from {Cu(tmeda)(mu-OH)}(2)X(2) (tmeda = N,N,N',N'-tetramethylethylenediamine, X = ClO4-, BF4-) and 2 equiv of K[Au(CN)4], and their X-ray structures were determined. Both compounds have [Cu(tmeda)(mu-OH)}2(2+) dimers with [Au(CN)4]- units bound in the axial positions. However, in 1, two trans N-donor cyanides of each [Au(CN)4]- unit bind to adjacent copper(II) dimers, forming a 1-D chain, whereas complex 2 is molecular, with two mono-coordinated [Au(CN)4]- units. The 1-D polymorph 1 is formed from aqueous solution, while the molecular polymorph 2 is obtained with X = BF4- in methanol. The polymorphs have slightly different Cu-O-Cu angles, a key magnetostructural parameter, such that the 1-D chain 1, with an angle of 96.6(2) degrees, shows ferromagnetic interactions with 2J = +57.5 cm(-1) and g = 2.097, whereas the molecular complex 2, with an angle of 98.92(17) degrees, shows antiferromagnetic interactions with 2J = -143.6 cm(-1) and g = 2.047. A similar Cu(II) complex, [[Cu(tmeda)(mu-OH)]2Au(CN)4][ClO4].MeOH (3), was synthesized in methanol when X = ClO4-, in which the [Au(CN)4]- unit bridges the two Cu(II) centers within the dimer in an intramolecular fashion via cis N-donor cyanides. The average Cu-O-Cu angle of 98.4(2) degrees in 3 generates antiferromagnetic interactions with 2J = -64.8 cm(-1) and g = 2.214. Complexes 1-3 represent the first examples of [Cu(tmeda)(mu-OH)]2(2+) dimers with Cu-O-Cu angles under 100 degrees, thereby extending the range of 2J coupling constants for this moiety from 149 to 566 cm(-1). The switch to ferromagnetic interactions in 1 as a result of the coordinating, bridging [Au(CN)4]- anion suggests that cationic, dinuclear moieties that are typically antiferromagnetically coupled may, with an appropriate coordinating counterion, become ferromagnetic units.     

An electron paramagnetic resonance study of Mn2(H2O)(OAc)4(tmeda)2 (tmeda = N,N,N',N'-tetramethylethylenediamine): a model for dinuclear manganese enzyme active sites

The complex Mn2(H2O)(OAc)4(tmeda)2 (tmeda = N,N,N',N'-tetramethylethylenediamine) is a model for the active site of hydrolase enzymes containing acetate-bridged dimanganese cores. The two high-spin Mn(II) ions are antiferromagnetically coupled, as determined by previous magnetic susceptibility studies (Yu, S.-B; Lippard, S. J.; Shweky, I; Bino, A. Inorg. Chem. 1992, 31, 3502-3504) to yield a spin "ladder" with total spin S = 0, 1, 2, ..., 5 in increasing energy. In this study, the complex was characterized by Q-band and X-band EPR spectroscopy in frozen solution. Analysis of the temperature dependence of these EPR spectra indicates that the primary spectral contribution is from the S = 2 manifold. The EPR spectra were simulated using a full spin Hamiltonian for this manifold of a coupled spin system, which provided the fit parameters J = -2.9 cm-1, g = 2.00, and D2 = -0.060 +/- 0.003 cm-1. An additional multiline EPR signal is observed which is proposed to arise from the total spin S = 5/2 ground state of a Mn(II) trimer of the type Mn3(OAc)6(tmeda)2.     

Different rotamer states of cytosine nucleobases in heteronuclear PtPd-, PtPd2, and Pt2Pd2Ag complexes derived from [Pt(2,2'-bpy)(1-MeC-N3)2]2+ (1-MeC = 1-methylcytosine): first examples of species with head-head oriented 1-MeC(-) ligands

[Pt(2,2'-bpy)(1-MeC-N3)(2)](NO(3))(2) (1) (2,2'-bpy = 2,2'-bipyridine; 1-MeC = 1-methylcytosine) exists in water in an equilibrium of head-tail and head-head rotamers, with the former exceeding the latter by a factor of ca. 20 at room temperature. Nevertheless, 1 reacts with (en)Pd(II) (en = ethylenediamine) to give preferentially the dinuclear complex [Pt(2,2'-bpy)(1-MeC(-)-N3,N4)(2)Pd(en)](NO(3))(2)·5H(2)O (2) with head-head arranged 1-methylctosinato (1-MeC(-)) ligands and Pd being coordinated to two exocyclic N4H(-) positions. Addition of AgNO(3) to a solution of 2 leads to formation of a pentanuclear chain compound [{Pt(2,2'-bpy)(1-MeC(-))(2)Pd(en)}(2)Ag](NO(3))(5)·14H(2)O (5) in which Ag(+) cross-links two cations of 2 via the four available O2 sites of the 1-MeC(-) ligands. 2 and 5 appear to be the first X-ray structurally characterized examples of di- and multinuclear complexes derived from a Pt(II) species with two cis-positioned cytosinato ligands adopting a head-head arrangement. (tmeda)Pd(II) (tmeda = N,N,N',N'-tetramethylethylenediamine) and (2,2'-bpy)Pd(II) behave differently toward 1 in that in their derivatives the head-tail orientation of the 1-MeC(-) nucleobases is retained. In [Pt(2,2'-bpy)(1-MeC(-))(2){Pd(2,2'-bpy)}(2)](NO(3))(4)·10H(2)O (4), both (2,2'-bpy)Pd(II) entities are pairwise bonded to N4H(-) and O2 sites of the two 1-MeC(-) rings, whereas in [Pt(2,2'-bpy)(1-MeC(-))(2){Pd(tmeda)}(2)(NO(3))](NO(3))(3)·5H(2)O (3) only one of the two (tmeda)Pd(II) units is chelated to N4H(-) and O2. The second (tmeda)Pd(II) is monofunctionally attached to a single N4H(-) site. On the basis of these established binding patterns, ways to the formation of mixed Pt/Pd complexes and possible intermediates are proposed. The methylene protons of the en ligand in 2 are special in that they display two multiplets separated by 0.64 ppm in the (1)H NMR spectrum.     

The beta-dialdiminato ligand [{N(C6H3Pri(2)-2,6)C(H)}2CPh]-: the conjugate acid and Li, Al, Ga and In derivatives

The synthesis of the following crystalline complexes is described: [Li(L)(thf)2] (), [Li(L)(tmeda)] (), [MCl2(L)] [M=Al (), Ga ()], [In(Cl)(L)(micro-Cl)2Li(OEt2)2] (), [In(Cl)(L){N(H)C6H3Pri(2)-2,6}] (), [In(L){N(H)C6H3Pri(2)-2,6}2] (), [{In(Cl)(L)(micro-OH)}2] (), [L(Cl)In-In(Cl)(L)] () (the thf-solvate, the solvate-free and the hexane-solvate), [{In(Cl)L}2(micro-S)] () and [InCl2(L)(tmeda)] () ([L]-=[{N(C6H3Pri(2)-2,6)C(H)}2CPh]-). From H(L) (), via Li(L) in Et2O, and thf, tmeda, AlCl3, GaCl3 or InCl3 there was obtained , , , or , respectively in excellent yield. Compound was the precursor for each of , and [{InCl3(tmeda)2{micro-(OSnMe2)2}}] () by treatment with one () or two () equivalents of K[N(H)(C6H3Pri(2)-2,6)], successively Li[N(SiMe3)(C6H3Pri(2)-2,6)] and moist air (), Na in thf (), tmeda (), or successively tmeda and Me3SnSnMe3 (). Crystals of (with an equivalent of In) and were obtained from InCl or thermolysis of [In(Cl)(L){N(SiMe3)(C6H3Pri(2)-2,6)}] () {prepared in situ from and Li[N(SiMe3)(C6H3Pri(2)-2,6)] in Et2O}, respectively. Compound was obtained from a thf solution of and sulfur. X-Ray data for crystalline , , , , , and are presented. The M(L) moiety in each (not the L-free ) has the monoanionic L ligated to the metal in the N,N'-chelating mode. The MN1C1C2C3N2 six-membered M(L) ring is pi-delocalised and has the half-chair (, and ) or boat (, and ) conformation.     

From a cycloheptatrienylzirconium allyl complex to a cycloheptatrienylzirconium imidazolin-2-iminato "pogo stick" complex with imido-type reactivity

The reaction of the cycloheptatrienylzirconium half-sandwich complex [(η(7)-C(7)H(7))ZrCl(tmeda)] (1) (tmeda = N,N,N',N'-tetramethylethylenediamine) with Li(Im(Dipp)N), generated from bis(2,6-diisopropylphenyl)imidazolin-2-imine (Im(Dipp)NH) with methyllithium, yields the imidazolin-2-iminato complex [(η(7)-C(7)H(7))Zr(Im(Dipp)N)(tmeda)] (2). The corresponding tmeda-free complex [(η(7)-C(7)H(7))Zr(Im(Dipp)N)] (5) can be synthesized via the 1,3-bis(trimethylsilyl)allyl complex [(η(7)-C(7)H(7))Zr{η(3)-C(3)H(3)(TMS)(2)}(THF)] (3; TMS = SiMe(3)), which undergoes an acid-base reaction with Im(Dipp)NH to form 5 and 1,3-bis(trimethylsilyl)propene. 5 exhibits an unusual one-legged piano stool ("pogo stick") geometry with a particularly short Zr-N bond of 1.997(2) ?. Addition of 2,6-dimethylphenyl or tert-butyl isocyanide affords the complexes [(η(7)-C(7)H(7))Zr(Im(Dipp)N)(CNR)] (R = o-Xy, 6; R = t-Bu, 7), while the reaction with 2,6-dimethylphenyl isocyanate results in a [2 + 2] cycloaddition to form the ureato(1-) complex [(η(7)-C(7)H(7))Zr{Im(Dipp)N(C═O)N-o-Xy}] (8). 5 can also act as an initiator for the ring-opening polymerization of ε-caprolactone. These reactivity patterns together with density functional theory calculations reveal a marked similarity of the bonding in imidazolin-2-iminato and conventional imido transition-metal complexes.