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Lithium−halogen exchange of (Z)-1,2-diphenyl-3-(2-iodoethenyl)cyclopropene (1) and subsequent addition to (η4-1,5-cod)PtCl2 yields the platinabenzene (η5-C5H3Ph2)[PtC5H3Ph2] (7), in which the metallacyclic ring and C5H3Ph2 (Cp′) unit are both derived from the cyclopropene skeleton. Starting instead with (η5-C5Me5)Pt(CO)I, treatment with three nucleophilic (Z)-3-(2-lithiovinyl)cyclopropenes provides platinabenzenes (η5-C5Me5)[PtC5H3PhR] (R = Ph (8), t-Bu (9), Me (10)) in low to modest yield. All platinabenzenes have been fully characterized by NMR spectroscopy and X-ray crystallography. Intermediate σ-vinyl complexes (η5-C5Me5)Pt(σ-C5H3PhR) (R = Ph (14), t-Bu (15)) are also isolated from the reaction mixtures and convert cleanly to the corresponding platinabenzenes in near quantitative yield. Reactivity studies of (η5-C5Me5)[PtC5H3Ph2] with a variety of reagents/conditions are also reported.

Two cis-dioxomolybdenum(VI) complexes [MoO2L] (L: L 1, 2 and L: L 2, 3) in a phenol-based sterically encumbered N2O2 ligand environment have been synthesized, and their crystallographic characterizations are reported. The orange crystals of 2 are monoclinic, space group P21/a with unit cell dimensions as a=16.2407(17) A, b=7.2857(8) A, c=18.400(2) A, β=98.002(9)°, Z=4, and d cal=1.486 g cm−3. The light orange crystals of 3, however, are orthorhombic, space group, Pbcn, with unit cell dimensions a=8.3110(12) A, b=12.637(3) A, c=34.673(5) A, Z=4, and d cal=1.187 g cm−3. The structures were refined by a full-matrix least-squares procedure on F 2 to a final R=0.046 (0.055 for 3) using 4944 (3677) all independent data. In both the cases, the Mo atom exists in a distorted octahedral geometry defined by a N2O4 donor set, which features a cis-Mo(–O)2 and a trans-Mo(OPh)2 arrangement. Compound 2 undergoes a quasireversible one-electron reduction at −1.3 V vs Ag/AgCl reference due to MoVIO2/MoVO2 electron transfer and thus providing a rare example of steric solution to the comproportionation–dimerization problem encountered frequently in the development of valid biomimetic models for the active sites of oxomolybdenum enzymes.

Methods for the synthesis of cyclic monomers that have both metal–metal bonds and carbon–carbon double bonds are reported. Ring opening metathesis polymerization (ROMP) of these monomers would yield polymers that are photochemically degradable. The first method investigated involved substitution of Cp2Fe2(CO)4 by the bidentate phosphine ligand DPPEN (Ph2P $${-}$$ CH=CH–PPh2). Cp2Fe2(CO)2( $$\upmu$$ -DPPEN) was synthesized and the X-ray crystal structure is reported but the molecule could not be polymerized by a ROMP method using Grubbs’s catalyst. The inability of this monomer to polymerize (or copolymerize with cyclooctatetraene) was attributed to the bulky phenyl rings being in close proximity to the C=C in the DPPEN ligand, which prevents coordination of the monomer to the catalyst. To decrease the steric interactions, the DPPBN ligand was synthesized (DPPBN=Ph $$_{2}{-}$$ CH $$_{2}{-}$$ CH=CH $${-}$$ CH $$_{2}{-}$$ PPh2). However, the reaction of DPPBN with Cp2Fe2(CO)4 yielded the product Cp2Fe2(CO)2( $$\upmu$$ -1,2,4-triphos), where the 1,2,4-triphos ligand is a tridentate ligand formed by the formal additional of Ph2PH to DPPBN (1,2,4-triphos=Ph $$_{2}{-}$$ CH $$_{2}{-}$$ CH(PPh2) $${-}$$ CH $$_{2}{-}$$ CH $$_{2}{-}$$ PPh2). An X-ray structure of the Cp2Fe2(CO)2( $$\upmu$$ -1,2,4-triphos) complex revealed that the 1,2,4-triphos ligand chelates exclusively through the two phosphorus atoms that are bridged by two carbon atoms. It is suggested that this structural feature may simply reflect the increased stability of the 6-membered ring over the 7- and 8-membered rings. The reactions of the Cp2Mo2(CO)6 and Cp2Mo2(CO)4 dimers with DPPBN were investigated next. Reactions of Cp2Mo2(CO)6 and Cp2Mo2(CO)4 with the DPPEN and DPPBN ligands resulted in the disproportionation of the dimers. The X-ray crystal structure of [CpMo(CO)2(DPPEN)][CpMo(CO)3] was determined and is reported. The CpMo(CO)(DPPEN)Cl complex was formed when these same reactions were carried out in the presence of CH2Cl2. The X-ray crystal structure of this molecule is also reported.

Urea and thiourea functionalities, presenting opportunities for the formation of diverse hydrogen-bonded networks, represent powerful crystal engineering building blocks. Herein we report the synthesis and structural analysis of a series of meta-substituted aromatic bis(thiourea) derivatives in which the steric bulk of the aromatic group and of the thiourea side chains is systematically varied. Two limiting structural types are observedcyclic dimers and extended three-dimensional network structures, with considerable variability within each of these classes. Incomplete cyclic dimers observed in some cases appear to represent structures transitional between these two limiting classes. Thiourea conformations, hydrogen-bonding parameters, and solid-state packing issues, each playing a role in the determination of preferred solid-state structure, are discussed in detail.

The synthesis and characterization of seven platina-annulenes and their dehydrobenzoannulene (DBA) analogues are reported. Assembly of these macrocycles is accomplished via Sn transmetalation or am...

Novel liquid crystals based on fluorinated carbon chains and terminated with SF5 groups are presented for the first time. Attachment of an SF5 group separated from a benzylidine group by a fluorinated spacer leads to monotropic nematic and smectic phases, while an enantiotropic nematic phase is observed in mixtures. The phase sequence of these new compounds is comparable to hydrocarbon analogues of nO.m (n-alkoxy-m-alkylbenzylidine) series. Despite a long alkoxy chain, the nematic → smectic A transition is closer to second order, with ≈ 0.995 values that are even higher than for the nCB (n-alkylcyanobiphenyls) series. Single crystal and quantum computational studies suggest that electrostatic interactions play a major role in governing the value of MTCP. Molecular packing in the crystal structure exhibits monoclinic P21/a symmetry. A flexible synthetic strategy that allows the synthesis of another homologous series with a bend in the molecular structure is also presented. The bent core structure of 10O.2 ...

Our prediction that phase II of dipotassium hydrogen chromatoarsenate, K(2)[HCr(2)AsO(10)], is ferroelectric, based on the analysis of the atomic coordinates by Averbuch-Pouchot, DurifGuitel [Acta Cryst. (1978), B34, 3725-3727], led to an independent redetermination of the structure using two separate crystals. The resulting improved accuracy allows the inference that the H atom is located in the hydrogen bonds of length 2.555 (5) angstroms which form between the terminal O atoms of shared AsO(3)OH tetrahedra in adjacent HCr(2)AsO(10)(2-) ions. The largest atomic displacement of 0.586 angstroms between phase II and the predicted paraelectric phase I is by these two O atoms. The H atoms form helices of radius approximately 0.60 A about the 3(1) or 3(2) axes. Normal probability analysis reveals systematic error in seven or more of the earlier atomic coordinates.

A new route to substituted 2-phenyl-2H-indazoles through the cyclization of (2-ethynylphenyl)phenyldiazenes is presented. A coarctate reaction pathway forms the isoindazole carbene under neutral conditions, at moderate temperatures, and without the requirement of a carbene stabilizer. A wide variety of previously unknown diazene precursors was synthesized and cyclized. Trapping of the carbene with a silyl alcohol followed by deprotection affords the 3-hydroxymethyl-2-phenyl-2H-indazoles in good overall yield. The free carbene could also be trapped as a [2 + 1] cycloadduct with 2,3-dimethyl-2-butene.

The trans-palladium bis(σ-acetylide) complex (Et3P)2Pd(C30H12) (2) was synthesized from hexane 4 in 77% yield via a simple three-step process. The X-ray crystal structure of 2 shows a strained and warped annulenic core upon insertion of the organometallic fragment. UV–vis data of the molecule suggest limited electronic delocalization throughout the metallacycle.

This study explored the effect of radical size, chain length, and mass on the cage recombination efficiency of photochemically generated radical cage pairs. Radical cage pairs containing long-chain radicals of the type [(CpCH2CH2N(CH3)C(O)(CH2)nCH3)(CO)3Mo•, •Mo(CO)3(CpCH2CH2(CH3)NC(O)(CH2)nCH3)] were generated in hexanes/squalane solution by photolysis (λ = 546 nm) of the Mo−Mo bonds in (CpCH2CH2N(CH3)C(O)(CH2)nCH3)2Mo2(CO)6 (n = 3, 8, 18). The cage recombination efficiencies (denoted as FcP, where FcP = kcP/(kcP + kdP), kdP is the diffusion rate constant, and kcP is the radical recombination rate constant) for the radical cage pairs were obtained by extracting them from quantum yield measurements for the photoreactions with CCl4 (a metal-radical trap) as a function of solvent system viscosity. The results show that FcP increases as the length of the chain on a radical center increases. This finding likely provides at least one of the reasons why the quantum yields for photolytic polymer degradation (and...

Seven new iridabenzenes were prepared by the addition of (Z)-1,2-diphenyl-3-(2-lithioethenyl)-1-cyclopropene to the Vaska-type complexes [IrCl(CO)(PR3)2], containing differing phosphine ligands. The iridabenzenes could be isolated from the reaction mixture either by direct means or after heating of the crude solution. In the case of the reactions using PMe3 and PEt3, a σ-vinyl/η2-cyclopropene Ir(I) complex, best described as an iridabenzvalene, could be isolated and fully characterized. The metallabenzvalene intermediate could be cleanly converted to the corresponding iridabenzene by heating in solution. The PEt3-substituted iridabenzene and iridabenzvalene were characterized by X-ray crystallography. Plausible mechanisms for the formation of both iridacycles from the lithiated vinylcyclopropene as well as the isomerization of the benzvalene into the benzene are postulated.

The reaction of [Bi2W22O74(OH)2]12− with Cu2+ in hot aqueous solution in the presence of Na+ affords the polyoxometalate salt Na12[Cu3Bi2W18O66]⋅32H2O. Single-crystal X-ray analysis [monoclinic, space-group C2/m, a = 33.082(6) A, b = 19.615(5) A, c = 14.885(2) A, β = 90.632(12)°, Z = 4; R(F) = 0.065 for 6029 data with I>σ (I), wR(F2) = 0.135 for all 8793 independent reflections] shows that the anion [{Cu(H2O)}3{BiW9O33}2]12−, on a crystal mirror-plane, has noncrystallographic symmetry close to D3h. Two B-α-[BiIIIW9O33]9− units are linked by an equatorial belt of three Cu(H2O)2+ units. Three Na(H2O)2+ units are also attached in the equatorial plane. The bond geometry is square-pyramidal about each Cu atom and trigonal–prismatic about each Na.

The σ-2-(cycloprop-2-enyl)vinylplatinum(II) complex (PEt3)2Pt(Me)(CHCH-cyclo-C3HPh2) (5) was prepared and characterized by NMR spectroscopy and X-ray crystallography. Treatment of 5 with Bronsted acids results in selective splitting of the Pt−methyl bond to give chloro derivative (PEt3)2Pt(Cl)(CHCH-cyclo-C3HPh2) (6), or the rearranged η3-diphenylcyclopentadienyl cation 7+, depending on the acid employed. Formation of cation 7+ could also be accomplished by treatment of 6 with TlPF6. Monitoring the protonolysis reactions by NMR spectroscopy at −60 °C, however, showed no evidence for platinabenzene or platinabenzvalene intermediates.

A new route to isoindazoles and cinnolines through the cyclization of (2-alkynylphenyl)triazenes under neutral conditions is presented. The products that result from heating the starting triazenes depend on both the type of alkyne ortho to the triazene functionality and the temperature used. Butadiyne moieties ortho to dialkyltriazenes yield bis-isoindazole dimers when heated to 150 degrees C in MeI. A requirement for cyclization in MeI is that the (2-alkynylphenyl)triazene must contain a suitably electron-withdrawing substituent on the phenyl ring to deactivate the triazene toward methylation-induced decomposition to an iodoarene. Ethynyl moieties ortho to dialkyltriazenes yield both isoindazole dimers as well as 3-formylisoindazoles when subjected to the same conditions. Replacing MeI with 1,2-dichlorobenzene as solvent allows for the general cyclization of (2-ethynylphenyl)dialkyltriazenes. Heating to 170 degrees C results in a mixture of isoindazole and cinnoline products, whereas the cinnolines are produced exclusively in high yield at 200 degrees C. Alternatively, the isoindazoles can be obtained in good to excellent yield by stirring a 1,2-dichloroethane solution of the starting triazene with CuCl overnight at 50 degrees C.

The rational synthesis of an arsenic(V) oxopolymetalate cluster from an arsenic(III) oxopolymetalate cluster has been accomplished by a redox reaction. The sandwich Mn-complex of As V W 9 O 34 9− (Na 9 K[Mn II 4 (H 2 O) 2 (As V W 9 O 34 ) 2 ]·35H 2 O ( 1 ) was prepared from a tetrameric complex [As 4 W 40 O 140 ] 28− containing As III W 9 O 33 9− units using both Mn VII and Mn II salts as reagents. Structures of 1 and Na 27 K[As 4 W 40 O 140 ]·56H 2 O ( 2 ), are reported.

The compound bis(η5-cyclopentadienyl)hydridomolybdenum(IV) triflate, which was synthesized from Cp2MoH2 and methyl triflate, is water soluble and undergoes hydride deuteride exchange in D2O. The molybdocene monohydride reduces ketones and aldehydes in water under mild aqueous conditions (pH 7 and 40 °C), which underscores the utility of this metallocene hydride for further organic transformations. Mechanistic features for the ketone → alcohol reduction suggest that either the reduction process is promoted by acid protonation of the carbonyl oxygen or it follows the reverse pathway of the aqueous C−H activation of primary alcohols by Cp2MoCl2(aq) reported earlier by Balzarek and Tyler.

Dehydrobenzoannulene derivatives containing isolated alkene linkages were synthesized by combining an in-situ Pd/Cu-mediated cross-coupling with an intramolecular cyclization strategy. 1H NMR studies of these macrocycles and comparison with related systems verify that highly alkynylated dehydrobenzoannulenes possess weak induced ring currents, indicative of aromatic (4n+2 π-systems) and anti-aromatic (4n π-systems) behavior, in spite of their large size and extensive benzannulation.

Enhanced global delocalization throughout the "stepped" π-electron systems of the [2.2]paracyclophane/dehydrobenzoannulene (PC/DBA) hybrids 1 and 2 is strongly suggested by a comparison of their electronic absorption spectra with those of model compounds with complete and interrupted classical aromatic delocalization. A distinct bathochromic shift (for 1) and greater absorption intensity at higher wavelengths (for 1 and 2) is observed versus the corresponding model hydrocarbons.

The water-soluble iron–carbonyl complex Fe(CO) 3 (TPPTS) 2 ( 2 ) (TPPTS=triphenylphosphine trisulfonate, sodium salt) was prepared and its molecular structure was determined by X-ray crystallography to be distorted bipyramidal. The oxidation chemistry of 2 to the 17-electron organometallic radical 2 + was studied. Thus, complex 2 was oxidized chemically with Ce(IV) in H 2 O, resulting in rapid disproportionation of the intermediate 2 + to 2 and Fe(II) aq , with concomitant loss of both the CO and the TPPTS ligands. The oxidative disproportionation of 2 with AgNO 3 proceeded through formation of a linear [{(TPPTS) 2 (CO) 3 Fe} 2 Ag] + intermediate. Electrochemically, complex 2 was oxidized irreversibly at E p =466 mV (vs. Ag ∣ AgCl, 100 mV s −1 ) in H 2 O.

This paper outlines the development of a protocol that allows in situ generation of unstable alkynes under Pd-catalyzed cross-coupling conditions. Cu-mediated intramolecular cyclization of the resultant α,ω-polyynes provides dehydrobenzoannulenes as singular species, in very good overall yields, and in a variety of topologies that are inaccessible by traditional routes or previously available in low yield only. In addition, we will discuss the solid-state structure and reactivity of these macrocycles, as well as the ability of the planar dehydrobenzoannulenes to support weak induced ring currents.

Aqueous salt metathesis reactions of manganese(II) salts and various chromate, molybdate, and tungstate salts afford a series of manganese group 6 metal oxides. The chromate reactions form a previously unknown phase, KMn2(CrO4)2(OH)(H2O) (1), whereas the tungstate reactions afford a simpler, hydrated phase, MnWO4·H2O (4). In these reactions, the countercation appears to influence the crystal form and size of the products. The molybdate reactions display countercation-dependent phase selectivity. Sodium and ammonium molybdates afford hydrated manganese molybdenum oxide, MnMoO4·H2O (3), whereas potassium molybdate affords the new molydenum analogue of the chromate phase, KMn2(MoO4)2(OH)(H2O) (2). Counteranion effects are more subtle, with crystal form and size representing the primary differences between the products from reactions using sulfate, acetate, or chloride salts of manganese(II). Each phase undergoes thermal dehydration, affording α-MnMoO4 from 3 and MnWO4 (hubnerite) from 4.

From the crude mixtures of isomeric 4-nitrophenylthieno[2,3-b]pyridines (3) previously reported [1] were isolated three analytically pure samples, viz. the 2-isomer (yellow needles, mp 258°, 3a), the 6-isomer (red prisms, mp 182°, 3e), and a ternary mixture of the 2-, 3-, and 4-isomers (orange needles, mp 213°, 3a:3b:3c = 1.3:1.0:0.5). The 258° compound was identified as either 3a or 3b by its 1H nmr spectrum and definitively as the former by its x-ray crystallographic analysis. The isomeric identities of the 182° and 213° samples were established from their 1H nmr spectra only. No 5-isomer (3d) was identified. Semi-quantitatively, relative isomeric yields fit the pattern 2- (64%)>>6- (14%)≥3- (12%)>4- (6%)≥5-(≤4%). Crystallographic data for 3a are presented.

Pyridinium gambogate, (C5H6N)+(C38H43O8)−, crystallizes in space group P2 12121 with cell parameters a = 9.536(3) A, b = 18.502(4) A, c = 22.223(4) A, Z = 4. The X-ray structural analysis [R(F) = 0.098 for 1714 data with I ≥ σ(I); wR(F 2) = 0.157 for all 3874 independent data] confirms the structure assigned to gambogic acid on the basis of NMR analysis and of the X-ray structure of isomorellin p-bromobenzenesulfonate. A hydrogen bond links the pyridinium nitrogen atom to a carboxylate oxygen atom. The gambogate ion has two distinct faces that differ in polarity. The hydrophobic face is dominated by the alkenyl chains attached to C(2) and C(17) and a segment of the polycyclic ring system. The hydrophilic face includes the carboxylate ion and several oxygen atoms.

We describe below the syntheses of five macrocycles possessing two enediyne warheads, along with the structural and thermal analyses of these bis(enediyne) compounds. The solid-state packing of compound 6 suggests the possibility for the molecule to undergo a topochemical diacetylene polymerization.

Photochemical reductive dimerization of 3,3'-dimethoxybenzophenone (1b) gave the symmetrical benzopinacol 1,1,2,2-tetrakis(3-methoxyphenyl)ethane-1,2-diol (2b), which was rearranged to the benzopinacolone 1,2,2,2-tetrakis(3-methoxyphenyl)ethanone (3b) by means of I2 in boiling glacial HOAc. The structure of 3b was indicated by 1H NMR and determined definitively by X-ray crystallography. The crystals are monoclinic, space group P21/c, a = 12.250(2), b = 9.6997(12), c = 20.866(2) Å, β = 95.319(11)°, Z = 4, R = 0.053 for 4523 independent reflections. The structure establishes that the migrating 3-methoxyphenyl group retains bonding through its number 1' carbon atom to the parent C2-unit during the rearrangement process.Key words: X-ray structure, pinacol-pinacolone rearrangement, chemical bonding.

The mechanism of the catalytic H/D exchange in alcohol substrates promoted by molybdocenes in D2O was shown to occur by C−H bond activation. Primary alcohols selectively exchanged α-hydrogens in aqueous solutions containing the catalyst precursor [Cp‘2Mo(μ-OH)2MoCp‘2](OTs)2, while some additional β-hydrogen exchange was observed in secondary alcohols. Tertiary alcohols did not undergo H/D exchange. Formation of chelate complexes such as the independently synthesized and crystallographically characterized glycolate complex [Cp‘2MoOCH2CH2OH](OTs) inhibited the H/D exchange in multidentate alcohols. The exchange reaction was shown to proceed by formation of ketone hydride molybdocene intermediate [Cp‘2Mo(OCR1R2)H]+, which can reversibly dissociate the ketone ligand. The molybdocene hydride complex resulting from ketone dissociation was identified by independent synthesis and crystallographic characterization of the hydride complex Cp‘2MoH(OTf). The H/D exchange reaction proceeds stepwise, with the active cat...

Ammonium nitrate coordinates to 18-crown-6 through a near-ideal ‘tripod’ arrangement of hydrogen bonds to alternate crown ether oxygen atoms. Ion pairing interactions are apparent, with the strength of this ion pairing interaction appearing to be reduced by hydration, representing a potentially significant role of water in cation–molecule complexes. The bis(benzo-15-crown-5) complex of ammonium nitrate is of sandwich type structure, with the ammonium ion complexed between two roughly parallel crown ether rings through an unusual but efficient set of linear, bifurcated, and off-axis hydrogen bonding interactions.

X-ray crystallographic studies of thieno[2,3-b:4,5-b′]dipyridine (1) and its monohydroperchlorate salt (1a) show that 1 is protonated at N1 in ring A and not at N6 in ring C. In each compound individual rings are planar, but there is a small dihedral angle-of-twist between the A and C rings. On going from 1 to 1a the largest changes in bond angles and bond lengths occur in ring A. 1H and l3C nmr spectra of 1 plus the 13C nmr spectrum of 1a are reported.

Molybdocenes form monomeric and dimeric complexes upon dissolution in water. The solution structures of the molybdocenes at neutral pH are inferred as the monomeric [(CpR)2Mo(OH2)(OH)]+ and the dim...

Three tin compounds, Cs8Sn44, Cs8Ga8Sn38, and Cs8Zn4Sn42, representative of the type-I clathrate hydrate crystal structure are structurally characterized by temperature-dependent neutron powder diffraction, 87 K Sn-119 Mossbauer spectroscopy, and room-temperature single-crystal X-ray diffraction. These compounds form in cubic space group Pm (3) over bar n with alkalimetal atoms residing in the polyhedral cavities formed by the tetrahedrally bonded network of Sn atoms. Of particular interest are the atomic displacement parameters (ADPs) exhibited by the alkali-metal atom inside the polyhedral "cages" formed by the framework Sn atoms. The "guest" Cs atoms inside the larger tetrakaidecahedra show a relatively large room-temperature ADP for Cs8Ga8Sn38 and Cs8Zn4Sn42; however, in the defect Cs8Sn44 compound this is not the case. This is due to two Sn vacancies in Cs8Sn44 which affect the local symmetry and Sn-Sn bonding. Temperature-dependent ADPs for the defect Cs8Sn44 compound are compared to those for Cs8Zn8Sn42. These data help elucidate the cause of the different lattice thermal conductivities of these two compounds.

Single crystal X-ray structures of two polymorphs of 1-(1,6-dithiahexyl)anthracene-9,10-dione are reported. These structures reveal a conformational difference in the orientation of the hydrocarbon chain between the two polymorphs. This small change in the molecular conformation dramatically influences the packing of the anthraquinone ring systems; in one case the anthraquinone rings exist as discrete pairs, and in the other they exist in infinite lamellar stacks. Differences in the packing results in different thermal behavior and spectroscopic properties of the two polymorphs. The yellow, triclinic structure is lower melting, whereas the orange, monoclinic structure is higher melting. Uses of this compound as a model for de novo computation of crystal structures and tuning of crystal packing through side chain variation are discussed.

Several 1,2-diphenyl-3-alkynylcyclopropenes were prepared by the reaction of acetylenic nucleophiles with diphenylcyclopropenylium perchlorate. The cyclopropenes were converted into alkynylcyclopropenylium salts via hydride abstraction with triphenylmethyl cation. Attempts to prepare a dication from either ethyne-bridged or butadiyne-bridged biscyclopropenes produced only the corresponding monocations. A dication was prepared when an ethylene spacer was inserted between the acetylene groups of the butadiyne-bridged biscyclopropene. Single-crystal X-ray structures of three of the cyclopropenylium ions were obtained. pK(R+) titrations were carried out on two of the salts, which showed that acetylene substituents provide about the same degree of stability to the cyclopropenylium core as a phenyl group. Nucleophilic addition to the alkynylcyclopropenylium ions under kinetic conditions gave a statistical mixture of products; however, under thermodynamic reaction conditions, nucleophilic addition followed by ring opening produced only one of three possible products. Calculations at the ab initio level were carried out to determine the charge distribution of the cations.

Metal- halogen exchange of vinylcyclopropene 4 followed by addition of [(Me3P)2Ir(CO)Cl] produced iridabenzvalene 5. The metallabenzene valence isomer was characterized by NMR and IR spectroscopy and by X-ray crystallography. Isomerization of complex 5 to iridabenzene derivatives 6 and 13 was accomplished by thermolysis and by Ag+ ions, respectively. The former transformation was a clean and quantitative process that displayed first-order kinetics.

In methanol, the complexation reaction of palladium(II) with pentadentate N4S ligand having flexible pyrazolyl arms, appears to proceed through two parallel paths, one of which is thermodynamically controlled, generating product 1, while the other is kinetically driven to obtain product 2 in comparable yields. Structural anomeric effect plays a crucial role in the formation of 2.

Site specifically functionalized dehydrobenzo[18]annulenes (DBAs) with previously inaccessible topologies (C2v and Cs symmetry) were prepared by utilizing an in situ protiodesilylation/alkynylation reaction. By application of a stepwise synthetic route, donor and/or acceptor functional groups were introduced to the annulenic core in a designed manner. The electronic absorption spectra of the DBAs revealed moderate to dramatic changes in the electronic structure of the [18]annulene core when subtle changes were made in substitution patterns and/or functional groups. Macrocycles containing C2v symmetry exhibited progressive and predictable bathochromic shifts ranging from 20 to 80 nm along with increasing intramolecular excited state change transfer (CT) behavior. Asymmetric (Cs) molecules presented more interesting absorption behavior, such as accentuation of bands in the visible region. X-ray crystal structures of [18]DBAs 20, 22, 23, and 25 showed normal bond lengths and bond angles within the planar ann...

X-ray analysis of a crystalline product obtained by treatment of 5-ethylthieno[2,3-b]pyridine with excess acidified hypochlorite establishes its stereochemistry as trans-2,3-dichloro-5-ethyl-2,3-dihydrothieno-[2,3-b]pyridine syn-1-oxide (5), wherein the pyridine ring is planar and the dihydrothiophene ring is non-planar with a C2-S-C7a angle of 86.6°. The trans geometry is corroborated by a proton-proton coupling constant J2,3 of 6.8 Hz. Comparison of 1H and 13C nmr data for 5 with analogous crystalline 2,3-dichloro-1-oxide addenda isolated in the isosteric benzo[b]thiophene and thieno[2,3-b]pyridine parent systems indicates that some proposed stereochemical assignments are questionable.

This study explored the origins of the observation that the overall quantum yields for polymer photodegradation depend on the polymer chain length. The (CH3(CH2)nC(O)NHCH2CH2Cp)2Mo2(CO)6 (n = 3, 8, 13, 18) complexes (1−1−4−4) were synthesized and used as model complexes for the study. As is common for metal−metal bonded complexes of this type, irradiation of these molecules cleaved the metal−metal bonds and formed free radicals via the intermediate formation of a radical cage pair. Studies on previous model complexes showed that the quantum yields for degradation decreased as the chain length of the complex increased. The decrease in quantum efficiency was partially attributed to an increase in the radical cage effect as the chain length increased. Surprisingly, however, the overall quantum yields and cage effects for complexes 1−1−4−4 did not vary significantly with chain length. The similarity in the quantum yields and in the cage effects for these molecules is attributed to an internal trapping reactio...

Pentadentate N4S ligands based on methyl 2-aminocyclopent-1-ene-1-dithiocarboxylate with flexible pyrazolyl arms (Me2pzCH2)2NC2H3RNHC5H6CSSCH3 (R = H, Hmmecd and R = CH3, Hmmpcd) undergo a nickel(II)-induced alcoholysis reaction through the activation of a saturated C−N bond linkage. The products obtained are square-planar complexes 1−4 containing a modified ligand structure possessing an N3S donor set and a pendant arm that holds the alkoxy group provided by the solvent. [Ni(N3S)-CH2OMe]ClO4 1 crystallizes in the triclinic space group P1 with a = 10.4886(5) A, b = 10.706(1) A, c = 11.487(1) A, α = 108.784(4)°, β = 108.887(6)°, γ = 95.139(6)°, V = 1128.0(4) A3, and Z = 2; while [Ni(N3S)‘-CH2 OPrn]ClO4 4 has the monoclinic space group P21/n with a = 8.875(2) A, b = 18.629(2) A, c = 15.399(2) A, β = 91.37(2)°, V = 2545(1) A3, and Z = 4 per unit cell. Complexes 1−4 with acyclic ligand environments have interesting electrochemical behavior in acetonitrile, involving a reversible Ni(II)/Ni(I) reduction, E1/2 ...

In the presence of some hydroxylated compounds as substrates, complexations of nickel(II) with the pentadentate N4S ligand methyl 2-{2-bis[(3,5-dimethylpyrazol-1-ylmethyl)amino]propylamino}cyclopent-1-ene-1-carbodithioate (Hmmpcd) having a pair of flexible pyrazolyl arms proceeded through unusual reaction paths involving C–N bond cleavage process. For example, the product 1 obtained in methanol as substrate is a square planar compound with a modified ligand structure that includes a methoxy group provided by the solvent. With an acidic substrate viz. phenol the product is also a square planar compound 2 with one of the pendant arms of Hmmpcd being replaced by a hydrogen atom. On the other hand, in the presence of a basic substrate viz. ethanolamine the ligand undergoes more extensive breakdown to generate a binuclear complex 3 with a bridging pyrazolyl group. These complexes 1–3 were characterised by X-ray crystallography and 1H NMR spectroscopy. Compound 1 displayed a reversible one-electron NiII → NiI reduction at E½ ≈ –1.0 V vs. Ag–AgCl reference as established by cyclic voltammetry and combined coulometry/EPR experiments. Such reversibility of electron transfer is unusual for a square-planar nickel(II) compound in an acyclic ligand environment. Stabilisation of the reduced nickel(I) species by methoxy group co-ordination provides a probable explanation for this reversible electron transfer.

Products formed from dehydrative cyclization of cyclopentanone, cyclohexanone, and cycloheptanone with anthranilamide (2) under neutral or acidic conditions are established as the spiro compounds 2,2-polymethylene-1,2,3,4-tetrahydroquinazolin-4-ones 6 by means of (a) the presence of a 13C nmr signal at 66–79 ppm for atom C-2 and (b) X-ray crystallography on the tetramethylene compound 6a. Analogously, products from reactions of these cycloalkanones with 3-amino-2-carbamoylthiophene are now shown by 13C nmr spectra to have structures isosteric to 6, i.e. 5,5-polymethylene-4,5,6,7-tetrahydrothieno[2,3-e]pyrimidin-7-ones 5, rather than the chelate ring structures previously proposed. Additionally, conflicting literature reports on product 3 from reaction of acetone with 2 are partially clarified. Correlation of 13C chemical shifts in systems 3, 5, and 6 is presented.

In 2-hydroxy-2-phenylpropanamidinium chloride, C9H13N2O+.Cl−, the anion plays a central role in the hydrogen bond network, chelating to one amidinium group and forming inter­molecular links to neighbouring NH2 and OH− groups. The central feature in (S)-2-hydroxy-2-phenylbutanamidinium (R)-2-hydroxy-2-phenylethanoate, C10H15N2O+.C8H7O3−, is a ring linking the cation and anion through two hydrogen bonds. The structure is extended by intra- and intermolecular hydrogen bonds.

A new crystalline strontium-copper ethylene glycol complex has been isolated and structurally characterized by single-crystal X-ray diffraction. The solution-phase complex has also been investigated as a possible molecular precursor for use in sol-gel synthesis of SrCuO2. [Sr(C2H6O2)5][Cu(C2H4O2)2]·C2H6O2 has been isolated by crystallization from an ethylene glycol/methylethylketone solution of the strontium-copper salt. Crystallographic data are as follows: orthorhombic, space group Pna21, a = 18.494(3), b = 9.3076(8), c = 16.615(3)A, V = 2860(2) A 3 , Z = 4, R = 0.044 . In this molecule, copper is coordinated by two bidentate ethylene glycolate ligands in roughly a square planar geometry. Strontium is coordinated by three bidentate ethylene glycol molecules and two monodentate ethylene glycol molecules; the eight-fold coordination resembles a highly-distorted square antiprism. An additional ethylene glycol of crystallization is present which does not directly coordinate the strontium ion. Copper and strontium ion complexes are held together by hydrogen bonding. The solution-phase bimetallic complex is hydrolytically unstable, giving rise to a ‘muddy’ brown precipitate upon exposure to water. The apparent decomposition is in direct contrast with hydrolysis of similar barium-copper complexes which gives rise to stable blue gels. This decomposition made the strontium-copper diol complex unsuitable for use in alkoxide sol-gel synthesis of strontium-copper oxides.

Two new water-soluble chelating alkyl phosphines are described. The compounds are prepared by radical addition of allylic substrates to 1,2-bis(phosphino)ethane in methanol. Complexes with the stoichiometry of 1.5:1 diphosphine:rhodium(I) are effective in the hydrogenation of the olefins 1-hexene and crotonaldehyde. Catalyst solutions prepared with the ligand DSPrPE were found to be 3 times more active than those prepared with TPPTS (triphenylphosphine trisulfonate) under identical conditions. Several rhodium complexes of the two ligands are described, and the crystal structure of Rh{1,2-bis[(dihydroxypropyl)phosphino]ethane}2Cl was determined.

The orthorhombic crystal structures of [NEt3H]5[XCoIIW11O39]·3H2O for X = P and As have been determined with data collected at room temperature, and for X = P at –100 °C, using Mo-Kα radiation. For the latter the space group is Pna21, a= 21.670(11), b= 14.805(4), c= 20.393(5)A and Z= 4. The structure consists of chains of α-Keggin-type molecules joined by W–O–links aligned in the a-axis direction. The Co/W occupancy at the link is disordered, with 61% Co on one side and 39% on the other. Further probable disorder, by lamellar merohedral twinning on (001) and by misorientation of the triethylammonium ions, has obscured the ethyl groups and the water molecules. In polarized light the crystals are deep wine-red normal to the chains (in the b direction), but nearly colourless in the a and c directions. The structure of the arsenate is similar to that of the phosphate.

The syntheses of the water-soluble, chelating phosphines 1,2-bis(bis(hydroxybutyl)phosphino)ethane (1, n = 3; DHBuPE) and 1,2-bis(bis(hydroxypentyl)phosphino)ethane (1, n = 4; DHPePE) are reported. These ligands (and, in general, other 1,2-bis(bis(hydroxyalkyl)phosphino)ethane ligands) can be used to impart water solubility to metal complexes. As examples of this, the [Ni(DHPrPE)(2)Cl]Cl (2), [Rh(DHPrPE)(2)][Cl] (3), and [Ru(DHBuPE)(2)Cl(2)][Cl] (4) complexes were synthesized; they are indeed soluble in water (0.5 M). Crystals of DHPrPE (1, n = 2) are monoclinic, space group P2(1)/c, with a = 9.5935(8) Å, b = 9.353(2) Å, c = 10.655(2) Å, alpha = 90 degrees, beta = 100.03(1) degrees, gamma = 90, V = 941.5(5) Å(3), R = 0.051, and Z = 2. Crystals of [Ni(DHPrPE)(2)Cl]Cl (2) are monoclinic, space group I2, with a = 15.951(3) Å, b = 11.454(2) Å, c = 20.843(3) Å, alpha = 90 degrees, beta = 91.24(2) degrees, gamma = 90 degrees, V = 3807(2) Å(3), R = 0.062, and Z = 4. Crystals of [Rh(DHPrPE)(2)][Cl] (3) are triclinic, space group Ponemacr;, with a = 13.900(2) Å, b = 15.378(2) Å, c = 18.058(2) Å, alpha = 87.71(1) degrees, beta = 75.03(1) degrees, gamma = 85.24(1), V = 3715(2) Å(3), R = 0.044, and Z = 4. Crystals of [Ru(DHBuPE)(2)Cl(2)][Cl] (4) are monoclinic, space group C2/c, with a = 14.310(2) Å, b = 21.630(2) Å, c = 15.459(3) Å, alpha = 90 degrees, beta = 99.83(1) degrees, gamma = 90, V = 4715(1) Å(3), R = 0.056, and Z = 4.

Treatment of Cp*Pt(CO)I (8) with two nucleophilic (Z)-3-(2-lithiovinyl)cyclopropenes provides a rational synthesis of platinabenzenes 6 and 7. The intermediate σ-vinyl complexes 9 and 10 are also isolated from the reaction mixtures and convert cleanly to the corresponding platinabenzenes in near-quantitative yield.