Pablo J. Sanz Miguel

Single layers of a multifunctional laminar Cu(I,II) coordination polymer

A multifunctional bidimensional mixed-valence copper coordination polymer [Cu2Br(IN)2]n (IN = isonicotinato) has been characterized in crystal phase and isolated on graphite surface as single sheets.

Effective Fixation of CO2 by Iridium-Catalyzed Hydrosilylation†

Financial support from MINECO/FEDER (CTQ2010-15221, CSD2009-00050 CONSOLIDER-INGENIO 2010, CTQ2011-27593, “Ramon y Cajal” (P.J.S.M.) and “Juan de la Cierva” (M.I.) programs), and DGA/FSE (group E7), is acknowledged.

An Alternative Mechanistic Paradigm for the β-Z Hydrosilylation of Terminal Alkynes: The Role of Acetone as a Silane Shuttle

The β-Z selectivity in the hydrosilylation of terminal alkynes has been hitherto explained by introduction of isomerisation steps in classical mechanisms. DFT calculations and experimental observations on the system [M(I)2{κ-C,C,O,O-(bis-NHC)}]BF4 (M=Ir (3a), Rh (3b); bis-NHC=methylenebis(N-2-methoxyethyl)imidazole-2-ylidene) support a new mechanism, alternative to classical postulations, based on an outer-sphere model. Heterolytic splitting of the silane molecule by the metal centre and acetone (solvent) affords a metal hydride and the oxocarbenium ion [R3Si-O(CH3)2](+), which reacts with the corresponding alkyne in solution to give the silylation product [R3Si-CH=C-R](+). Thus, acetone acts as a silane shuttle by transferring the silyl moiety from the silane to the alkyne. Finally, nucleophilic attack of the hydrido ligand over [R3Si-CH=C-R](+) affords selectively the β-(Z)-vinylsilane. The β-Z selectivity is explained on the grounds of the steric interaction between the silyl moiety and the ligand system resulting from the geometry of the approach that leads to β-(E)-vinylsilanes.

Electrical conductivity in platinum-dimer columns.

Three new compounds of formula [Pt2(SSCR)4] (R = CH3, (CH2)4CH3, cyclohexyl) have been prepared and characterized by X-ray diffraction. Their crystal structures consist of one-dimensional linear chains formed by stacking of the dimetallic complexes in which the alkyl group on the dithioacetate modulates the intermetallic distances between dimetallic entities. Direct current electrical conductivity studies show that crystals of the three compounds behave as semiconductors and their conductivity values are directly connected to the intermolecular metal-to-metal distances. These experimental results are supported by density functional theory calculations.

Electrostatics Plus O–π Interactions Rather Than “Directed” Hydrogen Bonding Keep SO42− in a Triangular Pt3Pd3–Tris(2,2′‐bipyrazine) Host

Sulfate binding to host molecules in the solvent water represents a major challenge due to its strongly negative hydration energy of DGh 1100 kJ mol . The predominant strategy for capturing SO4 2 by synthetic hosts is therefore to take advantage of “directed” hydrogen bonds. After all, nature does the same in the sulfate-binding protein. The moderate basicity of SO4 2 (pKa of HSO4 is ca. 2) is of advantage in this respect and the propensity of SO4 2 to engage in multiple hydrogen-bonding interactions with its neighbors (e.g. up to 12 hydrogen bonds) have led to numerous approaches to construct sulfate receptors on this basis. Interest in sulfate-selective complexation comes, among others, from the need to remove the corrosion-inducing SO4 2 from nuclear waste. The use of sulfate as a templating agent in supramolecular chemistry relies on very similar principles as does the generation of receptors. A positive charge on the synthetic receptor, as achieved by protonation of receptor atoms, or metal coordination, can markedly improve SO4 2 binding. In fact, remarkably high association constants between 10 and 10 in water have been reported by us for flat, triangular, and square metal complexes containing three and four trans-{(NH3)2Pt } entities. Here we report on a rare case of sulfate encapsulation in the hydrophobic cavity of a triangular, vase-shaped host cation in water. The host is built up of three cis-{(NH3)2Pt } and three {(en)Pd} units (en=ethylenediamine) as well as three bridging 2,2’-bipyrazine (bpz) ligands. The host cis[{(NH3)2Pt(N4,N4’-bpz-N1,N1’)Pd(en)}3] 12+ (1) is an analogue of the complex containing {(en)Pt} instead of cis{(NH3)2Pt }, [{(en)Pt(N4,N4’-bpz-N1,N1’)Pd(en)}3] 12+ (2), which we have previously reported on. 11] A unique feature of the solid-state structure of [2]ACHTUNGTRENNUNG(NO3)4ACHTUNGTRENNUNG(PF6)8 was the capture of two different anions in the hydrophobic cavity of the vase, with the NO3 covering the floor of vase, and a PF6 anion sitting on top of it. Solution studies in D2O with the pure nitrate salt [2]ACHTUNGTRENNUNG[NO3]12 and alkali salts with different anions revealed moderately strong binding of SO4 2 (Kass = 256 57 m ), in contrast to weaker binding of the tetrahedral anions ClO4 and BF4 . Attempts to crystallize 2 as its SO4 2 salt and to understand the special behavior of sulfate binding to 2 had failed. With 1, obtained upon reaction of cis-[(NH3)2Pt ACHTUNGTRENNUNG(H2O)2]SO4 with bpz and [(en)PdACHTUNGTRENNUNG(H2O)2]SO4, and analyzing as [1] ACHTUNGTRENNUNG(SO4)6 · 24.5 H2O crystallization was now successful. The X-ray crystal structure of this compound reveals that one of the six SO4 2 ions is encapsulated in the vase, together with a water molecule (Figure 1). The sulfate anion in 2 is disordered over two positions, occupying two of the interior corners of the triangular vase. On both corners, an oxygen atom (O41/O51) from each disordered moiety is anchored to the electron-deficient region localized between the two upright pyrazine rings, thus stabilizing both sulfate positions. This feature was not previously observed with sulfate ions, but is more common with perchlorate. Anion–p interactions involving sulfate are scarce. The third corner of the vase is occupied by a water molecule (O1w) which, again, displays lone pair–p interactions. The lone electron pairs of O1w point towards the centroids of the rings in an evident tetrahedral disposition (O–centroids distance: 2.96 , 3.01 , angle: 108.58), as O41 and O51 do in the case of the sulfate anion. There is hydrogen bonding between the protons of the water molecule and the trapped disordered SO4 2 (O1w···O44/O53, ca 2.53 ), yet no hydrogen bonding between the cationic vase and the encapsulated guests. Distances between the oxygen atoms of SO4 2 and the closest H3 atoms (not C3!), are between 2.5 and 3.0 , yet the C-H3-O ACHTUNGTRENNUNG(SO3) angles are unfavorable for hydrogen bond formation. Within the crystal, pairs of centrosymmetrically arranged cations 1 are oriented in such a way as to produce a Ptcapped block consisting of twelve metal ions, six bpz ligands, [a] A. Galstyan, Dr. P. J. Sanz Miguel, Prof. Dr. B. Lippert Fakult t Chemie, Technische Universit t Dortmund 44221 Dortmund (Germany) Fax: (+49) 231-755-3797 E-mail : pablo.sanz@tu-dortmund.de bernhard.lippert@tu-dortmund.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000500.

Rationalizing the structural variability of the exocyclic amino groups in nucleobases and their metal complexes: cytosine and adenine.

The exocyclic amino groups of cytosine and adenine nucleobases are normally almost flat, with the N atoms essentially sp(2) hybridized and the lone pair largely delocalized into the heterocyclic rings. However, a change to marked pyramidality of the amino group (N then sp(3) hybridized, lone pair essentially localized at N) occurs during i) involvement of an amino proton in strong hydrogen bonding donor conditions or ii) with monofunctional metal coordination following removal of one of the two protons.

Exploring the metal coordination properties of the pyrimidine part of purine nucleobases: isomerization reactions in heteronuclear Pt(II)/Pd(II) of 9-methyladenine.

The synthesis and characterization of three heteronuclear Pt(2)Pd(2) (4, 5) and PtPd(2) (6) complexes of the model nucleobase 9-methyladenine (9-MeA) is reported. The compounds were prepared by reacting [Pt(NH(3))(3)(9-MeA-N7)](ClO(4))(2) (1) with [Pd(en)(H(2)O)(2)](ClO(4))(2) at different ratios r between Pt and Pd, with the goal to probe Pd(II) binding to any of the three available nitrogen atoms, N1, N3, N6 or combinations thereof. Pd(II) coordination occurs at N1 and at the deprotonated N6 positions, yet not at N3. 4 and 5 are isomers of [{(en)Pd}(2){N1,N6-9-MeA(-)-N7)Pt(NH(3))(3)}(2)](ClO(4))(6)·nH(2)O, with a head-head orientation of the two bridging 9-MeA(-) ligands in 4 and a head-tail orientation in 5. 6 is [{(en)Pd}(2)(OH)(N1,N6-9MeA(-)-N7)Pt(NH(3))(3)](ClO(4))(4)·4H(2)O, hence a condensation product between [Pt(NH(3))(3)(9-MeA-N7)](2+) and a μ-OH bridged dinuclear (en)Pd-OH-Pd(en) unit, which connects the N1 and N6 positions of 9-MeA(-) in an intramolecular fashion. 4 and 5, which slowly interconvert in aqueous solution, display distinct structural differences such as significantly different intramolecular Pd···Pd contacts (3.124 0(16) Å in 4; 2.986 6(14) Å in 5), among others. Binding of (en)Pd(II) to the exocyclic N6 atom in 4 and 5 is accompanied by a large movement of Pd(II) out of the 9-MeA(-) plane and a trend to a further shortening of the C6-N6 bond as compared to free 9-MeA. The packing patterns of 4 and 5 reveal substantial anion-π interactions.

PdII-Catalyzed Condensation of a Mononuclear Pt–Nucleobase Complex to Its Head–Tail Dimer: Characterization of a Key Intermediate and an End Product

Interest in reactions catalyzed by metal species is mainly driven by the quest for more efficient synthetic routes to bulk and fine chemicals. The understanding of the role of metal ions in biochemical transformations is yet another source of interest in homogeneous catalysis. Here we report a simple reaction from the field of coordination chemistry, namely the condensation of a model nucleobase complex of Cisplatin, cis-[Pt ACHTUNGTRENNUNG(NH3)2ACHTUNGTRENNUNG(1-MeC-N3)ACHTUNGTRENNUNG(H2O)]2+ (1) to the head–tail dimer cis-[{Pt(1-MeC -N3,N4) ACHTUNGTRENNUNG(NH3)2}2]2+ (2) (with 1-MeC=neutral 1-methylcytosine; 1-MeC =1methylcytosine anion, deprotonated at N4), and demonstrate that it can be catalyzed by [Pd(en) ACHTUNGTRENNUNG(H2O)2]2+ (Scheme 1). To the best of our knowledge, this is a rare case

Design of molecular wires based on one-dimensional coordination polymers

The authors report the results of ab initio calculations for the structural and electronic properties of one-dimensional coordination polymers with the general formula [M(6-MP)2]n (where 6-MP=6-mercaptopurinate, and M=MnII, FeII, CoII, NiII, and CuII). A common stable structure, consistent with the experimental data for [Cd(6-MP)2]n, is found for all metal cations studied, with the exception of MnII. Polymers containing FeII, NiII, and CoII are found to be ferromagnetic semiconductors, while [Cu(6-MP)2]n shows a Peierls-unstable paramagnetic metallic phase that undergoes a transition to a ferromagnetic semiconductor one under small stretching.

Synthesis of Poly(silyl ether)s by Rhodium(I)–NHC Catalyzed Hydrosilylation: Homogeneous versus Heterogeneous Catalysis

The preparation of 1‐(3‐triisopropoxysilylpropyl)‐3‐(2‐methoxyethyl)‐imidazolium bromide or chloride salts and their reaction with [Rh(COD)(μ‐OMe)]2 (COD=1,5‐cyclooctadiene) to afford the corresponding [Rh(COD)(NHC)X] (X=Br, Cl; NHC=1‐(3‐triisopropoxysilylpropyl)‐3‐(2‐methoxyethyl)‐2‐ilydene‐imidazol) species is described. These new compounds were used as catalyst precursors for acetophenone hydrosilylation. The higher activity of the rhodium‐chlorido complex evidences a clear halide effect in the activation of the catalyst. Immobilization of the catalytic precursor [Rh(COD)(NHC)Cl] on mobile crystalline material 41 (MCM‐41) allows for the preparation of the corresponding heterogeneous catalyst. Reduction of acetophenone to PhMeCH‐O‐SiMe(OSiMe3)2 by hydrosilylation with 1,1,1,3,5,5,5‐heptamethyltrisiloxane is effectively catalyzed by both the homogeneous and the heterogeneous catalysts, in which the homogeneous system is the more active. Interestingly, the heterogeneous catalyst is reusable. Both homo‐ and heterogeneous catalysts are also effective for the copolymerization of terephthalaldehyde and 1,1,3,3,5,5‐hexamethyltrisiloxane, which affords the corresponding poly(silyl ether). The catalyst yields the heterogeneous system polymers with higher molecular weights (Mw=94 000 g mol−1) and a narrow molecular weight distribution (PDI=1.5–1.7).