Utilization of CS2 as a source of C1 synthetic units for the preparation of bis(alkylthio)methanes and alkyl dithioformates

Double insertion of CS2 into two Ru-H bonds of [(dppm)2Ru(H)2] (dppm = Ph2PCH2PPh2) affords the methanedithiolate complex [(dppm)2Ru(eta2-S2CH2)]. The methanedithiolate moiety has been functionalized using 2 equiv of RX resulting in bis(alkylthio)methane derivatives [(dppm)2Ru(RSCH2SR)][X]2. The bis(alkylthio)methane complex loses the bis(alkylthio)methane moiety under very mild conditions and in turn affords the [(dppm)2RuX2] complex from which the starting dihydride [(dppm)2Ru(H)2] has been regenerated via reaction with KOH/EtOH. On the other hand, insertion of CS2 into one Ru-H bond of [(dppe)2Ru(H)2] (dppe = Ph2PCH2CH2PPh2) followed by functionalization using RX results in alkyl dithioformate complex trans-[(dppe)2Ru(H)(SC(SR)H)][X]. In this case also, the alkyl dithioformate moiety gets eliminated under very mild conditions to afford the [(dppe)2Ru(H)(X)] derivative from which the starting dihydride has been regenerated via reaction with NaBH4. The reactions presented here constitute utilization of CS2 as a C1 synthetic source for the generation of useful organic compounds.     

Synthesis and biological evaluation of Rhizobium sin-1 lipid A derivatives

A highly convergent strategy for the synthesis of several derivatives of the lipid A of Rhizobium sin-1 has been developed. The approach employed the advanced intermediate 3-O-acetyl-6-O-(3-O-acetyl-4,6-O-benzylidene-2-deoxy-2-phthalimido-beta-d-glucopyrano-syl)-2-azido-4-O-benzyl-2-deoxy-1-thio-alpha-d-glucopyranoside (5), which is protected in such a way that the anomeric center, the C-2 and C-2' amino groups, and the C-3 and C-3' hydroxyls can be selectively functionalized. The synthetic strategy was used for the preparation of 2-deoxy-6-O-[2-deoxy-3-O-[(R)-3-hydroxy-hexadecanoyl]-2-[(R)-3-octacosanoyloxy-hexadecan]amido-beta-d-glucopyranosyl]-2-[(R)-3-hydroxy-hexadecan]amido-3-O-[(R)-3-hydroxy-hexadecanoyl]-alpha-d-glucopyranose (11) and 2-deoxy-6-O-[2-deoxy-3-O-[(R)-3-hydroxy-hexadecanoyl]-2-[(R)-3-octacosanoyloxy-hexadecan]amido-beta-d-glucopyranosyl]-2-[(R)-3-hydroxy-hexadecan]amido-3-O-[(R)-3-hydroxy-hexadecanoyl]-d-glucono-1,5-lactone (13), which contain an unusual octacosanoic acid moiety and differ in the oxidation state of the anomeric center. The results of biological studies indicate that 11 and 13 lack the proinflammatory effects of Escherichia coli lipopolysaccharides (LPS). Furthermore, 13 emulated the ability of heterogeneous R. sin-1 LPS to antagonize enteric LPS, providing evidence for the critical role of the gluconolactone moiety of R. sin-1 LPS in mediating this antagonistic effect. Compound 13 is the first example of a lipid A derivative that is devoid of phosphate but possesses antagonistic properties, making it an attractive lead compound for development of a drug to use in the treatment of Gram-negative septicemia.     

A concise approach to both enantiomers of phytoprostane B1 type II

The synthesis of enantiomeric phytoprostane B₁ type II methyl esters has been accomplished in approximately 30% overall yield via two basic transformations starting from 3-[(dimethoxyphosphoryl)methyl]cyclopentenone as a key reagent. They include ethylation of the ring C(2) carbon and a Horner olefination reaction using the phosphonate moiety at C(3). The novel components of the Horner reaction, the enantiomeric methyl 9-formyl-9-hydroxynanoates, were easily prepared from racemic methyl 9-hydroxy-10-undecenoate via asymmetric Sharpless epoxidation (kinetic resolution) followed by ozonolysis.     

Unprecedented [5.5.5.6]Dioxafenestrane Ring Construction in Fungal Insecticidal Sesquiterpene Biosynthesis

Fenestranes, a specific class of natural products, contain four fused rings that share a central quaternary carbon atom. The fungal natural product penifulvin A ( 1 ) is a potent insecticidal sesquiterpene that features the [5.5.5.6]dioxafenestrane ring. Although the chemical synthesis of 1 has been achieved recently, the enzymes catalysing the cyclization and oxidation of FPP to 1 remain unknown. In this work, we identified a concise pathway that uses only three enzymes to produce 1 . A new sesquiterpene cyclase (PeniA) generates the angular triquinane scaffold silphinene ( 6 ). A cytochrome P450 (PeniB) and a flavin‐dependent monooxygenase (PeniC) catalyse a series of oxidation reactions to transform 6 into 1 , including oxidation of the C15 methyl group to a carboxylate moiety, oxidative coupling of the C15 carboxylate and the C1‐C2 olefin to form a γ‐lactone, and Baeyer–Villiger oxidation to form a δ‐lactone. Our results demonstrate the highly concise and efficient ways in which fungal biosynthetic pathways can generate complex sesquiterpene scaffolds.     

Selective recognition of configurational substates of zinc cyclam by carboxylates: implications for the design and mechanism of action of anti-HIV agents

The interaction of metal cyclams with carboxylate groups is thought to play an important role in their binding to the CXCR4 chemokine receptor and in their anti-HIV activity. Here we report the synthesis of acetate, phthalate, perchlorate and chloride complexes of Zn(II) cyclam (1,4,8,11-tetraazacyclotetradecane). The X-ray crystal structures of [Zn(cyclam)(phthalate)](n)(CH(3)OH)(2n) and [Zn(cyclam)(H(2)O)(2)](OAc)(2) contain octahedral Zn(II) centres. Phthalate acts as a bridging ligand in the former complex, binding through monodentate carboxylate groups, and giving rise to infinite chains in the lattice together with extensive hydrogen bonding between carboxylate donor oxygen atoms and amine and methanol acceptor atoms. The uncoordinated acetate groups and the aqua ligand in the acetate complex are also involved in a rich network of hydrogen bonds and this may account for the unusually long Zn[bond]O distance (2.27 A). In both crystalline complexes, the macrocycle adopts the trans-III (S,S,R,R) configuration. 1D (1)H NMR spectra of all four complexes have been fully assigned by a combination of 2D [(1)H, (1)H] COSY and TOCSY, and [(1)H, (13)C] and [(1 )H, (15)N] HSQC NMR data. In aqueous solution, the stable trans-III configuration found in the solid-state equilibrates slowly (hours at 298 K) with trans-I (R,S,R,S) and cis-V (R,R,R,R) configurations. The trans-III configuration is predominant in aqueous solution for both the chloride and perchlorate complexes, but for the acetate and phthalate complexes, the cis-V configuration dominates. Carboxylate groups appear to stabilize the cis-V configuration in solution through Zn(II) coordination and hydrogen bonding. Titration of the chloride Zn(II)-cyclam complex with acetate confirmed that carboxylates strongly induce formation of the cis-V configuration. This implies that carboxylates can exert a strong influence over configurational selectivity. Cyclam NH hydrogen bonding is prevalent both in the solid state and in solution, and is relevant to the anti-HIV activity of Zn(II) and other metal cyclam complexes and to their ability to recognize the CXCR4 transmembrane co-receptor.     

Structural flexibility and role of vicinal 2-thienyl rings in 2,3-dicyano-5,6-di(2-thienyl)-1,4-pyrazine, [(CN)2Th2Pyz], its palladium(II) complex [(CN)2Th2Pyz(PdCl2)2], and the related pentametallic pyrazinoporphyrazines [(PdCl2)4Th8TPyzPzM] (M = Mg(II)(H2O), Zn(II))

The solid state and solution structure of 2,3-dicyano-5,6-di(2-thienyl)-1,4-pyrazine, [(CN)(2)Th(2)Pyz], and its Pd(II) derivative, [(CN)(2)Th(2)Pyz(PdCl(2))(2)]·H(2)O, formed by reaction of [(CN)(2)Th(2)Pyz] with [(C(6)H(5)CN)(2)PdCl(2)] were characterized by X-ray, UV-visible, (1)H and (13)C NMR, and extended X-ray absorption fine structure (EXAFS) spectral measurements. The X-ray crystal structure of [(CN)(2)Th(2)Pyz] shows the presence of one thienyl ring positioned orthogonal to the rest of the molecule, with the two vicinal thienyl rings lying orthogonal to each other in a rare arrangement. NMR studies of [(CN)(2)Th(2)Pyz] in the solid state and in solutions of dimethylformamide or dimethyl sulfoxide confirm a nonequivalence of the thienyl rings in the solid state and also in solution. EXAFS results indicate that two distinct Pd(II) coordination sites are formed at the di(2-thienyl)pyrazino moiety of [(CN)(2)Th(2)Pyz(PdCl(2))(2)]·H(2)O, with identical Pd-N(pyz) (2.03(3) ?) and Pd-Cl (2.36(3) ?) bond lengths but with different Pd-S1 (2.25(4) ?) and Pd-S2 (3.21(5) ?) bond distances in an overall asymmetric molecular framework. Density functional theory (DFT) and time-dependent DFT (TDDFT) theoretical studies also provide information about the structure and spectral behavior of the precursor and its metalated Pd(II) derivative. (1)H/(13)C NMR and UV-visible spectral measurements were also carried out on two heteropentametallic porphyrazine macrocycles which were prepared by a reaction of PdCl(2) with [Th(8)TPyzPzM] where Th(8)TPyzPz = tetrakis-2,3-[5,6-di-(2-thienyl)-pyrazino]porphyrazinato dianion and M = Mg(II)(H(2)O) or Zn(II). Spectroscopic data on the newly synthesized [(PdCl(2))(4)Th(8)TPyzPzM] compounds suggest that the binding of PdCl(2) involves coordination sites of the type S(2(th))PdCl(2) with the two thienyl rings of each di(2-thienyl)pyrazino fragment bound to Pd(II) in an equivalent manner ("th-th" coordination). This is similar to what was found for the corresponding octapyridinated analogues ("py-py" coordination).     

Utilization of CS2 as a source of C1 chemistry for the generation of methyldithioformate

Insertion of CS(2) into the Ru-H bond of cis-[(dppe)(2)Ru(H)(2)] takes place to afford the hydride dithioformate complex trans-[(dppe)(2)Ru(H)(SC(S)H)]. The hydride dithioformate complex reacts under very mild conditions with MeX (X = OTf, I) to give the hydride methyldithioformate derivative trans-[(dppe)(2)Ru(H)(SC(SMe)H)][X]. Three different pathways have been found to cleave off the ester moiety from the metal complex. A method to recover the ruthenium starting material upon elimination of the methyldithioformate is presented. This is a novel case of C(1) chemistry using carbon disulfide.     

Metal complexes with 2,3-bis(diphenylphosphino)-1,4-diazadiene ligands: synthesis,structures, and an intramolecular metal-mediated [4 + 2] cycloaddition employing a benzene ring as a dienophile

2,3-Bis(diphenylphosphino)-1,4-diazadienes RN=C(PPh2)-C(PPh2)=NR (1a, R = 4-tolyl; 1b, R = 4-tert-butylphenyl; 1c, R = mesityl) were used as novel ligands for transition metals. The metal complexes [(1c)Mo(CO)4] (2a), [(1c)[Mo(CO)4]2] (2b), [(1a)Cu(Cl)(PPh3)] (3), and [(1b)[(NiBr2(THF))]2] (4) were characterized by elemental analysis, MS, and 31P[1H], 1H, and 13C NMR spectra (except the paramagnetic complex 4). Additionally, the molecular structure of the complexes in the solid state was determined by single-crystal X-ray diffraction. In 2a and 2b the chelating ligand coordinates via the N,P donor set, whereas in 3 the chelating ligand coordinates via the two P atoms. 4 contains a square-planar (P,P)NiBr2 moiety on the one side of the bridging ligand 1b. On the opposite side the 1,2-dimine unit bonds to another Ni center having octahedral geometry. The bulkier ligand 1c reacts to form the mononuclear compound 5. X-ray diffraction analysis of single crystals shows that 5 contains a quinoxaline derivative with a cyclohexa-1,3-diene ring in the peripheral position. Furthermore, it contains a bis(diphenylphosphino)-ethylene unit coordinating the NiBr2. This arrangement is the result of an intramolecular [4 + 2] cycloaddition between the 1,2-diimine unit (as diheterodiene) and the benzene ring of the 4-tolyl-N substituent (as dieneophile). The same type of ring-closing reaction followed by a tautomerization reaction to form the mononuclear compound 6 occurred by dissolution of the binuclear complex 4 in methanol. This reaction can be used as a simple method for the synthesis of novel 1,2-bis(diarylphosphanyl)ethylenes containing a quinoxaline backbone.     

Scalar coupling across [C-H···F-C] interactions in (σ-aryl)-chelating post-metallocenes

The nature and importance of C-H···F-C interactions is a topical yet controversial issue, and the development of spectroscopic methods to probe such contacts is therefore warranted. A series of Group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N-R(1)] ligands bearing a fluorinated R(1) group (CF(3) or F) in the vicinity of the metal has been prepared. The X-ray crystal structure of the CF(3)-substituted Hf derivative features intramolecular C-H···F-C and Hf···F-C contacts. All complexes have been characterized by multinuclear NMR spectroscopy. The (1)H and (13)C NMR spectra of [M(O,C,N-CF(3))(CH(2)Ph)(2)] derivatives display coupling (assigned to (1h)J(HF) and (2h)J(CF) for Ti; (3)J(HF) and (2)J(CF) (through M···F) for Hf and Zr) between the benzyl CH(2) and CF(3) moieties. [(1)H,(19)F]-HMBC NMR experiments have been performed for the M-[O,C,N-R(1)] complexes and their [O,N,C] counterparts, revealing significant scalar coupling across the C-H···F-C interactions for Ti-[O,C,N] and [O,N,C] species.     

Synthesis of Novel Bis[(5‐cyanopyridin‐6‐yl)sulfanyl]butanes,Bis(2‐S‐alkylpyridines), and Bis(3‐aminothieno[2,3‐b]pyridines) Incorporating 2,6‐Dibromophenoxy Moiety

The synthetic precursors pyridine‐2(1H)‐thiones 2a , b and bis(pyridine‐2(1H)‐thione) derivative 4 , using aldehydes 1a , b incorporating 2,6‐dibromophenoxy moiety, were prepared and used to synthesize the novel target materials bis[(5‐cyanopyridin‐6‐yl)sulfanyl]butanes 5a , b , bis(2‐S‐alkylpyridines) 8a , b , and bis(3‐aminothieno[2,3‐b]pyridines) 13a–c through facile procedures. Characterization of the newly prepared compounds via elemental analyses and spectral data is established.     

Ring‐Opening Reactions of 3‐Aryl‐1‐benzylaziridine‐2‐carboxylates and Application to the Asymmetric Synthesis of an Amphetamine‐Type Compound

Nucleophilic ring‐opening reactions of 3‐aryl‐1‐benzylaziridine‐2‐carboxylates were examined by using O‐nucleophiles and aromatic C‐nucleophiles. The stereospecificity was found to depend on substrates and conditions used. Configuration inversion at C(3) was observed with O‐nucleophiles as a major reaction path in the ring‐opening reactions of aziridines carrying an electron‐poor aromatic moiety, whereas mixtures containing preferentially the syn‐diastereoisomer were generally obtained when electron‐rich aziridines were used (Tables 1–3). In the reactions of electron‐rich aziridines with C‐nucleophiles, S_N2 reactions yielding anti‐type products were observed (Table 4). Reductive ring‐opening reaction by catalytic hydrogenation of (+)‐trans‐(2S,3R)‐3‐(1,3‐benzodioxol‐5‐yl)aziridine‐2‐carboxylate (+)‐trans‐ 3c afforded the corresponding α‐amino acid derivative, which was smoothly transformed into (+)‐tert‐butyl [(1R)‐2‐(1,3‐benzodioxol‐5‐yl)‐1‐methylethyl]carbamate((+)‐ 14 ) with high retention of optical purity (Scheme 6).     

Lipophilicity coefficients of potential tumor imaging agents, positron-labeled O(6)-benzylguanine derivatives

Novel radiolabeled O(6)-benzylguanine (O(6)-BG) derivatives, 6-O-[(11)C]-[(methoxymethyl)benzyl]guanines ([(11)C]p-O(6)-MMBG, 1a; [(11)C]m-O(6)-MMBG, 1b; [(11)C]o-O(6)-MMBG, 1c), 2-amino-6-O-[(11)C]-[(methoxymethyl)benzyloxy]-9-methyl purines ([(11)C]p-O(6)-AMMP, 2a; [(11)C]m-O(6)-AMMP, 2b; [(11)C]o-O(6)-AMMP, 2c), 2-amino-6-O-[(11)C]-[(methoxymethyl)benzyloxy]-9-benzyl purines ([(11)C]p-O(6)-AMBP, 3a; [(11)C]m-O(6)-AMBP, 3b; [(11)C]o-O(6)-AMBP, 3c), 2-amino-6-O-benzyloxy-9-[(11)C]-[(methoxycarbonyl)methyl]purine ([(11)C]ABMMP, 4), and 2-amino-6-O-benzyloxy-9-[(11)C]-[(4'-methoxycarbonyl)benzyl]purine ([(11)C]ABMBP, 5), have been synthesized for evaluation as potential novel positron emission tomography tumor imaging agents. The ability of O(6)-BG analogs to penetrate the blood--brain barrier in brain tumor could be due, at least in part, to their lipophilicity. In this paper, we measured lipophilicity coefficients (log P) of compounds 1--5 by the C(18) HPLC method. These log P values were compared, and correlations between lipophilicity and biological activity of selected analogs were made. The results suggest the appropriate level of lipophilic character in this class of compounds as useful imaging agents appears to be in the range of 1.4--2.6.     

Synthesis and spectroscopic and X-ray structural characterization of R2Sn(IV)-oxydiacetate and -iminodiacetate complexes

Seven novel R2Sn(IV)-oxydiacetate (oda) and -iminodiacetate (ida) compounds of the form [R2Sn(oda)(H2O)]2 (R = Me, nBu, and Ph) (1-3), [(R2SnCl)2(oda)(H2O)2]n (R = Et, iBu, and tBu) (4-6), and [Me2Sn(ida)(MeOH)]2 (7) have been synthesized and characterized by IR, 1H, 13C, and 119Sn NMR (solution), solid-state 119Sn CPMAS NMR, and (119m)Sn M?ssbauer spectroscopy. The crystal structure of [Me2Sn(oda)(H2O)]2, 1, shows it to be dinuclear (centrosymmetric), with two seven-coordinated tin atoms, bridged by one arm of the carboxylate group from each oda. By contrast, the crystal structure of [(Et2SnCl)2(oda)(H2O)2]n, 4, comprises a zigzag polymeric assembly containing a pair of different alternating subunits, {Et2SnCl(H2O)} and {Et2SnCl(H2O)(oda)}, which are connected by way of bridging oda carboxylates, thus giving seven-coordinate tin centers in both components. Finally, the structure of [Me2Sn(ida)(MeOH)]2, 7, also centrosymmetric dinuclear, is comprised of a pair of mononuclear units with seven-coordinate tin. The 119Sn solid-state CPMAS NMR and (119m)Sn Mossbauer suggest the presence of seven-coordinate Sn metal atoms in some derivatives and the existence of two different tin sites in the [(R2SnCl)2(oda)(H2O)2]n compounds.     

C-linked disaccharide analogue of the Thomsen-Friedenreich (T)-epitope alpha-O-conjugated to L-serine

Condensation of a silylated beta-D-galactopyranosylaldehyde (3) with isolevoglucosenone (4) in the presence of Et(2)AlI provided bicyclic enone 5. Subsequent addition of BnNHOMe gave adduct 6, which was converted into 4-O-acetyl-1,6-anhydro-3-C-[(1 R)-1,3,4,5,7-penta-O-acetyl-2,6-anhydro-D-glycero-L-manno-heptitol-1-C-yl]-2-azido-2,3-dideoxy-beta-D-galacto-hexopyranose after liberation of the 2-amino group, its transformation into a 2-azido moiety, desilylation, and peracetylation. Ring-opening of the 1,6-anhydro galactopyranosyl unit and O-glycosidation with Fmoc-Ser-O-tBu afforded a 5:1 mixture of alpha- and beta-galactosides. Treatment with CH(3)COSH gave pure N-[(9H-fluoren-9-ylmethoxy)carbonyl]-{4,6-di-O-acetyl-3-C-[(1 R)-2,6-anhydro 1,3,4,5,7-penta-O-acetyl-D-glycero-L-manno-heptitol-1-C-yl]-2-[(N-acetyl)amino]-2,3-dideoxy-alpha-D-galactopyranosyl}-l-serine tert-butyl ester (2), a protected form of a C-disaccharide analogue of the Thomsen-Friedenreich (or T) epitope (beta-D-Galp-(1-->3)-alpha-D-GalNAcp) alpha-O-conjugated to L-serine.     

Ytterbocene charge-transfer molecular wire complexes

A systematic study of the novel charge-transfer [(f)14-(pi)0-(f)14 --> (f)13-(pi)2-(f)13] electronic state found in 2:1 metal-to-ligand adducts of the type [(Cp)2Yb](BL)[Yb(Cp)2] [BL = tetra(2-pyridyl)pyrazine (tppz) (1), 6',6' '-bis(2-pyridyl)-2,2':4',4':2',2'-quaterpyridine (qtp) (2), 1,4-di(terpyridyl)-benzene (dtb) (3), Cp = (C5Me5)] has been conducted with the aim of determining the effects of increased Yb-Yb separation on the magnetic and electronic properties of these materials. The neutral [(f)13-(pi)2-(f)13], cationic [(f)13-(pi)1-(f)13] and dicationic [(f)13-(pi)0-(f)13] states of these complexes were studied by cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, NMR, X-ray crystallography, and magnetic susceptibility measurements. The spectroscopic and magnetic data for the neutral bimetallic complexes is consistent with an [(f)13(pi)2(f)13] ground-state electronic configuration in which each ytterbocene fragment donates one electron to give a singlet dianionic bridging ligand with two paramagnetic Yb(III) centers. The voltammetric data demonstrate that the electronic interaction in the neutral molecular wires 1-3, as manifested in the separation between successive metal reduction waves, is large compared to analogous transition metal systems. Electronic spectra for the neutral and monocationic bimetallic species are dominated by pi-pi and pi-pi transitions, masking the f-f bands that are expected to best reflect the electronic metal-metal interactions. However, these metal-localized transitions are observed when the electrons are removed from the bridging ligand via chemical oxidation to yield the dicationic species, and they suggest very little electronic interaction between metal centers in the absence of pi electrons on the bridging ligands. Analysis of the magnetic data reveals that the qtp complex displays antiferromagnetic coupling of the type Yb(alpha)(alphabeta)Yb(beta) at approximately 13 K.     

A series of [3 + 2] cycloaddition products from the reaction of rhenium oxo complexes with diphenyl ketene

The reaction of rhenium (VII) trioxo complexes containing the ligand sets scorpionate, [HB(pz)3]ReO3 (6), [Ph-B(pz)3]ReO3 (7), and [[HC(pz)3]ReO3][ReO4] (8) and pyridine/pyridine-type ligands [(4,7-diphenyl-1,10-phen)(Br)ReO3] (12), [(4,4'-di-tert-butyl-2,2'-dipyridyl)(Cl)ReO3] (13), and [(py)2Re(Cl)O3] (4), with diphenyl ketene, has led to the isolation of six novel [3 + 2] cycloaddition products. These air-stable solids 9-11 and 15-17 are the result of [3 + 2] addition of the O=Re=O motif across the ketene C=C double bond. Five of the six [3 + 2] cycloaddition products have been structurally characterized by single-crystal X-ray diffraction and in all cases by 13C NMR and IR spectroscopies.     

Dipolar double-quantum filtered rotational-echo double resonance

The homonuclear dipolar coupling of a directly bonded (13)C-(13)C pair has been used to create a dipolar double-quantum filter (D-DQF) to remove the natural-abundance (13)C background in (13)C[(2)H] rotational-echo double-resonance (REDOR) experiments. The most efficient version of this experiment has the D-DQF excitation and reconversion preceding the REDOR evolution period. Calculated and observed (13)C[(2)H]D-DQF-REDOR dephasings were in agreement for a test sample of mixed recrystallized labeled alanines.     

An example of O2 binding in a cobalt(II) corrole system and high-valent cobalt-cyano and cobalt-alkynyl complexes

The novel cobalt corrolazine (Cz) complexes (TBP)(8)CzCoCN (1) and (TBP)(8)CzCo(CCSiPh(3)) (2) have been synthesized and examined in light of the recent intense interest regarding the role of corrole ligands in stabilizing high oxidation states. In the case of 2, the molecular structure has been determined by X-ray crystallography, revealing a short Co[bond]C distance of 1.831(4) A and an intermolecular pi-stacking interaction between Cz ring planes, and this structure has been analyzed in regards to the electronic configuration. By a combination of spectroscopic techniques it has been shown that 1 is best described as a cobalt(III)[bond]pi-cation-radical complex, whereas 2 is likely best represented as the resonance hybrid (Cz)Co(IV)(CCSiPh(3)) <--> (Cz+*)Co(III)(CCSiPh(3)). The reduced cobalt(II) complex, [(TBP)(8)CzCo(II)(py)](-), has been generated in situ and shown to bind dioxygen at low temperature to give [(TBP)(8)CzCo(III)(py)(O(2))](-). For the reduced complex [(TBP)(8)CzCo(II)(py)](-), the EPR spectrum in frozen solution is indicative of a low-spin cobalt(II) complex with a d(z)2 ground state. Exposure of [(TBP)(8)CzCo(II)(py)](-) to O(2) leads to the reversible formation of the cobalt(III)-superoxo complex [(TBP)(8)CzCo(III)(py)(O(2))](-), which has been characterized by EPR spectroscopy. VT-EPR measurements show that the dioxygen adduct is stable up to T approximately 240 K. This work is the first observation, to our knowledge, of O(2) binding to a cobalt(II) corrole.     

Solvent effects on the structural and formyl substrate reactivity properties of a nitrogen/sulfur-ligated zinc hydroxide complex

The solution structural and formyl substrate reactivity properties of a nitrogen/sulfur-ligated zinc hydroxide complex, [(bmnpaZn)2(mu-OH)2](ClO4)2 (1, bmnpa = N,N-bis-2-(methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine), in acetonitrile and methanol are reported. In CH3CN, 1 has a binuclear cation [(bmnpaZn)2(mu-OH)2]2+ that is stabilized by secondary hydrogen bonding and CH/pi interactions involving the bmnpa chelate ligand. In CH3OH, 1 undergoes reaction with solvent to yield a zinc methoxide species, as determined by 1H NMR and electrospray mass spectral analysis. Treatment of 1 with methyl formate in CH3CN results in stoichiometric hydrolysis of the formyl ester to produce [(bmnpa)Zn(O2CH)]ClO4 (2) and methanol. The formate complex was identified via independent synthesis and characterization (X-ray crystallography, 1H and 13C NMR, FTIR, LRFAB-MS, conductance, and elemental analysis). In the solid state, 2n has a formate-bridged coordination polymer-type structure. However, in CH3CN, 2 behaves as 1:1 electrolyte, indicating cleavage of the polymer structure into mononuclear [(bmnpa)Zn(O2CH)]ClO4 species. Treatment of 1 with a stoichiometric amount of formanilide in CH3CN for 48 h at 45 degrees C results in decomposition of the zinc hydroxide complex to yield the free bmnpa ligand and an inorganic solid, presumably a zinc hydroxide or oxide species. Treatment of 1 with a stoichiometric amount of ethyl formate in CD3OD results in rapid, quantitative transesterification of the formyl carboxylate ester. A control reaction indicates that this transesterification reaction does not occur on the same time scale in the absence of the catalyst. Treatment of 1 with an excess of ethyl formate in CD3OD results in catalytic formyl carboxylate ester transesterification, with approximately 1000 turnovers in 60 min at 22(1) degrees C. Treatment of a CD3OD solution of 1 (0.5 equiv) with formanilide (1 equiv) results in the formation of aniline, d3-methyl formate, and the zinc formate complex 2. While aniline is produced stoichiometrically, the yield of d3-methyl formate varied from 30 to 50%, and the yield of 2 varied from 50 to 70% in repetitive experiments. Formation of both d3-methyl formate and 2 indicates that both methanolysis and hydrolysis reactions take place.