Pentacarbonyl(4‐phenylpyridine)­tungsten(0) and pentacarbonyl(2‐phenylpyridine)chromium(0)

In penta­carbonyl(4‐phenyl­pyridine)­tungsten(0), [W­(C₁₁H₉N)(CO)₅], the mol­ecules have mm site symmetry and the pyridine ligand, with m symmetry, is completely planar. In penta­carbonyl(2‐phenyl­pyridine)­chromium(0), [Cr(C₁₁­H₉N)(CO)₅], the mol­ecules are in general positions and the phenyl and pyridine rings of the ligand are twisted by 67.7 (3)° with respect to one another by rotation about the C—C bond joining them. In both compounds, the axial M—C_carbonyl bond trans to the M—N_ligand bond is significantly shorter than the equatorial M—C_carbonyl bonds.     

<!?tlsb=‐0.06pt>Bromido(η5‐carboxycyclopentadienyl)dinitrosylchromium(0) and (η5‐benzoylcyclopentadienyl)bromidodinitrosylchromium(0)

In the structures of each of the title compounds, [CrBr(C₆H₅O₂)(NO)₂], (I), and [CrBr(C₁₂H₉O)(NO)₂], (II), one of the nitrosyl groups is located at a site away from the exocyclic carbonyl C atom of the cyclopentadienyl (Cp) ring, with twist angles of 174.5 (3) and 172.5 (1)°. The observed orientation is surprising, since the NO group is expected to be situated trans to an electron‐rich C atom in the ring. The organic carbonyl plane is turned away from the Cp ring plane by 5.6 (8) and 15.2 (3)°in (I) and (II), respectively. The exocyclic C—C bond in (I) is bent out of the Cp ring plane towards the Cr atom by 2.8 (3)°, but is coplanar with the Cp ring in (II); the angle is 0.1 (1)°.     

Pentacarbonyl(di‐2‐pyridyl­amine)tungsten(0)

In the title molecular complex, (I), the W atom is in an octahedral environment with four equatorial carbonyl ligands and a fifth in an axial position trans to the monodentate dipyridyl­amine ligand. The long dimension of this last bisects the angle between two of the equatorial carbonyl groups and while the non‐bonded pyridyl N atom is directed away from the W atom, the bridging amine group is directed towards it. Thus, in addition to the N atom to which it is attached, the amino H has two nearest neighbour C atoms of equatorial carbonyl groups but does not participate in hydrogen bonding in any real or usual sense. The W—C bond distance for the axial carbonyl group is notably less than those of the equatorial groups.     

Hydrogen‐bonding and π–π stacking interactions in aquachloridobis(1,10‐phenanthroline)cobalt(II) chloride dichloridobis(1,10‐phenanthroline)cobalt(II) hexahydrate

The title compound, [CoCl(C₁₂H₈N₂)₂(H₂O)]Cl·[CoCl₂(C₁₂H₈N₂)₂]·6H₂O, is the first example of a new 1:1 cocrystal of the octahedral [CoCl₂(phen)₂] and [CoCl(phen)₂(H₂O)]⁺·Cl⁻ complexes (phen is 1,10‐phenanthroline). The latter form heterochiral dimers held by strong π–π stacking interactions via their phenathroline ligands, which confirms that π stacking is an important and reliable synthon in supramolecular design. In addition, the crystal structure is networked by H₂O...H₂O, H₂O...Cl⁻ and H₂O...Cl hydrogen bonds, which interconnect the different units of the cobalt complexes.     

Redox‐Switchable 20π‐, 19π‐, and 18π‐Electron 5,10,15,20‐Tetraaryl‐5,15‐diazaporphyrinoid Nickel(II) Complexes

The first examples of air‐stable 20π‐electron 5,10,15,20‐tetraaryl‐5,15‐diaza‐5,15‐dihydroporphyrins, their 18π‐electron dications, and the 19π‐electron radical cation were prepared through metal‐templated annulation of nickel(II) bis(5‐arylamino‐3‐chloro‐8‐mesityldipyrrin) complexes followed by oxidation. The neutral 20π‐electron derivatives are antiaromatic and the cationic 18π‐electron derivatives are aromatic in terms of the magnetic criterion of aromaticity. The meso N atoms in these diazaporphyrinoids give rise to characteristic redox and optical properties for the compounds that are not typical of isoelectronic 5,10,15,20‐tetraarylporphyrins.     

Gold(III) π‐Allyl Complexes

Gold(III) π‐complexes have been authenticated recently with alkenes, alkynes, and arenes. The key importance of Pd^II π‐allyl complexes in organometallic chemistry (Tsuji–Trost reaction) prompted us to explore gold(III) π‐allyl complexes, which have remained elusive so far. The (P,C)Au^III(allyl) and (methallyl) complexes 3 and 3′ were readily prepared and isolated as thermally and air‐stable solids. Spectroscopic and crystallographic analyses combined with detailed DFT calculations support tight quasi‐symmetric η³‐coordination of the allyl moiety. The π‐allyl gold(III) complexes are activated towards nucleophilic additions, as substantiated with β‐diketo enolates.     

Enantioselective Palladium(0)‐Catalyzed Nazarov‐Type Cyclization

A Pd⁰‐catalyzed asymmetric Nazarov‐type cyclization is described. The optimized ligand for the reaction incorporates a weakly coordinating pyridine ring into a TADDOL‐derived phosphoramidite (TADDOL=α,α,α,α‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol). The reaction leads to the formation of cyclopentenones as single diastereoisomers that incorporate two contiguous asymmetric centers, one tertiary and one an all‐carbon‐atom quaternary stereocenter, in high yield and optical purity. It is noteworthy that the reaction does not require that substrates should be activated by aryl substituents.     

Intramolecular π–π stacking in diaquabis(2‐hydroxybenzoato‐κO)bis(1,10‐phenanthroline‐κ2N,N′)strontium(II)

In the title compound, [Sr(C₇H₅O₃)₂(C₁₂H₈N₂)₂(H₂O)₂], the Sr^II ion is located on a twofold rotation axis and assumes a distorted square‐antiprism SrN₄O₄ coordination geometry, formed by two phenanthroline (phen) ligands, two 2‐hydroxybenzoate anions and two water molecules. Within the mononuclear complex molecule, intramolecular π–π stacking is observed between nearly parallel coordinated phen ligands, while normal intermolecular π–π stacking occurs between parallel phen ligands of adjacent complex molecules. Classic O—H...O and weak C—H...O hydrogen bonding helps to stabilize the crystal structure.     

Bis(glycinato‐κ2N,O)dinitrosylmolybdenum(0) and bis(2‐aminoethanethiolato‐κ2N,S)dinitrosylmolybdenum(0) acetonitrile monosolvate

The title compounds, [Mo(C₂H₄NO₂)₂(NO)₂], (I), and [Mo(C₂H₆NS)₂(NO)₂]·CH₃CN, (II), contain distorted octahedral complexes in which the monoanionic N,S‐ and N,O‐bidentate ligands coordinate the molybdenum centres in different modes. The anionic O atoms of the glycinate ligands in (I) are coordinated trans to the nitrosyl ligands and the amine N atoms are located trans to each other, whereas in (II) the anionic S atoms are coordinated trans to each other and the amine N atoms are located trans to the nitrosyl ligands. Each compound has a single complete complex in the asymmetric unit on a general position. Six N—H...O contacts with N...O distances of less than 3.2 Å are observed in (I) between the amine groups and the nitrosyl and carboxylate O atoms. In the 1:1 solvate (II), the acetonitrile molecule forms short N—H...N contacts (N...N < 3.2 Å) between the solvent N atoms and one of the amine H atoms. In addition, three weak intermolecular N—H...S interactions (N...S > 3.3 Å) contribute to the stabilization of the structure of (II).     

π–π stacking motifs in dialkylbis{5‐[(E)‐2‐aryldiazen‐1‐yl]‐2‐hydroxybenzoato}tin(IV) complexes

The diorganotin(IV) complexes of 5‐[(E)‐2‐aryldiazen‐1‐yl]‐2‐hydroxybenzoic acid are of interest because of their structural diversity in the crystalline state and their interesting biological activity. The structures of dimethylbis{2‐hydroxy‐5‐[(E)‐2‐(4‐methylphenyl)diazen‐1‐yl]benzoato}tin(IV), [Sn(CH₃)₂(C₁₄H₁₁N₂O₃)₂], and di‐n‐butylbis{2‐hydroxy‐5‐[(E)‐2‐(4‐methylphenyl)diazen‐1‐yl]benzoato}tin(IV) benzene hemisolvate, [Sn(C₄H₉)₂(C₁₄H₁₁N₂O₃)₂]·0.5C₆H₆, exhibit the usual skew‐trapezoidal bipyramidal coordination geometry observed for related complexes of this class. Each structure has two independent molecules of the Sn^IV complex in the asymmetric unit. In the dimethyltin structure, intermolecular O—H…O hydrogen bonds and a very weak Sn…O interaction link the independent molecules into dimers. The planar carboxylate ligands lend themselves to π–π stacking interactions and the diversity of supramolecular structural motifs formed by these interactions has been examined in detail for these two structures and four closely related analogues. While there are some recurring basic motifs amongst the observed stacking arrangements, such as dimers and step‐like chains, variations through longitudinal slipping and inversion of the direction of the overlay add complexity. The π–π stacking motifs in the two title complexes are combinations of some of those observed in the other structures and are the most complex of the structures examined.     

(S)‐Tricarbonyl[(1,2,3,4‐η)‐(5R,6S)‐1‐chloro‐5,6‐dimethoxycyclohexa‐1,3‐diene]iron(0)

The title compound, [Fe(C₈H₁₁ClO₂)(CO)₃], has been synthesized, isolated and characterized by single‐crystal X‐ray diffraction. The mol­ecule crystallizes in the orthorhombic space group P2₁2₁2₁. The metal–ligand arrangement is typical of (1,3‐diene)­tri­carbonyl­iron complexes.     

Comb Poly(Oligo(2‐Ethyl‐2‐Oxazoline)Methacrylate)‐Peptide Conjugates Prepared by Aqueous Cu(0)‐Mediated Polymerization and Reductive Amination

The controlled synthesis of poly(oligo(2‐ethyl‐2‐oxazoline)methacrylate) (P(OEtOxMA)) polymers by Cu(0)‐mediated polymerization in water/methanol mixtures is reported. Utilizing an acetal protected aldehyde initiator for the polymerization, well‐defined polymers are synthesized (>99% conversion, Ð < 1.25) with subsequent postpolymerization deprotection resulting in α‐aldehyde end group containing comb polymers. These P(OEtOxMA) are subsequently site‐specifically conjugated, via reductive amination, to a dipeptide (NH₂‐Gly‐Tyr‐COOH) as a model peptide, prior to conjugation to the functional peptide oxytocin. The resulting oxytocin conjugates are evaluated in comparison to poly(oligo(ethylene glycol) methyl ether methacrylate) combs synthesized in the same manner for potential effects on thermal stability in comparison to the native peptide.

     

Pyridine–pyridine π–π stacking interactions in penta­carbonyl­[pyridine‐4(1H)‐thione]­tungsten(0)

In the title compound, [W(C₅H₅NS)(CO)₅], the pyridine‐4‐thiol ligand coordinates through the sulfur in the thione mode. The coordination sphere around the W atom is distorted from octahedral geometry by intermolecular hydrogen bonding and steric interactions between the pyridine ring and two CO ligands. An intermolecular pyridine–pyridine ring distance of 3.47 (1) Å indicates π–π stacking interactions between these ligand units.     

Palladium(0)‐Catalyzed Intermolecular Arylative Dearomatization of β‐Naphthols

The first Pd⁰‐catalyzed intermolecular arylative dearomatization of β‐naphthols with aryl halides is described. It was found that Q‐Phos could facilitate the palladium‐catalyzed cross‐coupling‐type dearomatization of β‐naphthols, while avoiding O‐arylation, to construct 2‐naphthalenones in excellent yields and with high chemoselectivity.     

Molecular complexes between π‐excedent heterocycles (indoles and carbazole) and π‐deficient polynitrobenzenes

Five charge‐transfer complexes 1–5 derived from indoles (including a carbazole) and halogenopolynitrobenzenes (ClDNB, FDNB, ClTNB) as well as their individual components have been studied in the solid state by ¹³C CPMAS NMR. The stacking effects on the ¹³C chemical shifts have been rationalized by means of M05‐2X functional and GIAO/B3LYP/6‐311 ++G(d,p) calculations. The results, although only semiquantitative, are very promising for studying such structures. Copyright © 2009 John Wiley & Sons, Ltd.     

(E)‐2‐(1,3‐Benzothiazol‐2‐yl)‐3‐(4‐fluorophenyl)acrylonitrile: a chain of π‐stacked hydrogen‐bonded rings

The title compound, C₁₆H₉FN₂S, crystallizes as a nonmerohedral twin with twin rotation about the reciprocal‐lattice vector [10]*. The molecules are nearly planar and the dihedral angle between the planes of the two aryl rings is only 4.4 (2)°. The molecules are linked by pairs of C—H...N hydrogen bonds to form cyclic centrosymmetric R₂²(18) dimers, which are linked into chains by an aromatic π–π stacking interaction. Comparisons are made with some related 3‐aryl‐2‐thienylacrylonitriles.     

Tricarbonyl(η5‐formylcyclopentadienyl)manganese(I) and tricarbonyl(η5‐formylcyclopentadienyl)rhenium(I) containing short π(CO)...π(CO) and π(CO)...π interactions

The structures of tricarbonyl(formylcyclopentadienyl)manganese(I), [Mn(C₆H₅O)(CO)₃], (I), and tricarbonyl(formylcyclopentadienyl)rhenium(I), [Re(C₆H₅O)(CO)₃], (II), were determined at 100 K. Compounds (I) and (II) both possess a carbonyl group in a trans position relative to the substituted C atom of the cyclopentadienyl ring, while the other two carbonyl groups are in almost eclipsed positions relative to their attached C atoms. Analysis of the intermolecular contacts reveals that the molecules in both compounds form stacks due to short attractive π(CO)...π(CO) and π(CO)...π interactions, along the crystallographic c axis for (I) and along the [201] direction for (II). Symmetry‐related stacks are bound to each other by weak intermolecular C—H...O hydrogen bonds, leading to the formation of the three‐dimensional network.     

(E)‐3‐{4‐[(7‐Chloroquinolin‐4‐yl)oxy]‐3‐methoxyphenyl}‐1‐(4‐methylphenyl)prop‐2‐en‐1‐one: a ladder‐like structure resulting solely from π–π stacking interactions

In the title compound, C₂₆H₂₀ClNO₃, the quinoline fragment is nearly orthogonal to the adjacent aryl ring, while the rest of the molecular skeleton is close to being planar. The crystal structure contains no hydrogen bonds of any sort, but there are two π–π stacking interactions present. One, involving the quinoline ring, links molecules related by inversion, while the other, involving the two nonfused aryl rings, links molecules related by translation, so together forming a ladder‐type arrangement