Sequence-defined oligo(-arylene) foldamers derived from the benzannulation of (arylene ethynylene)s.

A Cu-catalyzed benzannulation reaction transforms (arylene ethynylene) oligomers into -arylenes. This approach circumvents iterative Suzuki cross-coupling reactions previously used to assemble hindered -arylene backbones. These derivatives form helical folded structures in the solid-state and in solution, as demonstrated by X-ray crystallography and solution-state NMR analysis.

Oxidatively Triggered Carbon-Carbon Bond Formation in Ene-amide Complexes.

Ene-amides have been explored as ligands and substrates for oxidative coupling. Treatment of CrCl2, Cl2Fe(PMe3)2, and Cl2Copy4 with 2 equiv of {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}Li afforded pseudosquare planar {η(3)-C,C,N-(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Cr (1-Cr, 78%), trigonal {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Fe(PMe3) (2-Fe, 80%), and tetrahedral {(2,6-(i)Pr2C6H3)(1-(c)Hexenyl)N}2Co(py)2 (3-Co, 91%) in very good yields. The addition of CrCl3 to 1-Cr, and FeCl3 to 2-Fe, afforded oxidatively triggered C-C bond formation as rac-2,2'-di(2,6-(i)Pr2C6H3N═)2dicyclohexane (EA2) was produced in modest yields.

Regioselective Synthesis of Polyheterohalogenated Naphthalenes via the Benzannulation of Haloalkynes.

Independent control of halide substitution at six of the seven naphthalene positions of 2-arylnaphthalenes is achieved through the regioselective benzannulation of chloro-, bromo-, and iodoalkynes. The modularity of this approach is demonstrated through the preparation of 44 polyheterohalogenated naphthalene products, most of which are difficult to access through known naphthalene syntheses. The outstanding regioselectivity of the reaction is both predictable and proven unambiguously by single-crystal X-ray diffraction for many examples.

Nitrene Insertion into C-C and C-H Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron.

The impact of redox non-innocence (RNI) on chemical reactivity is a forefront theme in coordination chemistry. A diamide diimine ligand, [{-CH=N(1,2-C6H4)NH(2,6-iPr2C6H3)}2](n) (n = 0 to -4), (dadi)(n), chelates Cr and Fe to give [(dadi)M] ([1Cr(thf)] and [1Fe]). Calculations show [1Cr(thf)] (and [1Cr]) to have a d(4) Cr configuration antiferromagnetically coupled to (dadi)(2-)*, and [1Fe] to be S = 2.

Electrochemical lithiation-induced polymorphism of anthraquinone derivatives observed by operando X-ray diffraction.

The use of organic molecules represents a very attractive and promising alternative for electrical energy storage applications. Quinones, in general, and anthraquinones, in particular, are especially attractive due to their ability to reversibly exchange multiple electrons per formula unit. When used as the active electrode material in a real lithium-ion battery (LIB), crystalline anthraquinone powders reversibly change crystal packing as a function of state-of-charge (redox state), with well-defined voltage plateaus appearing concomitantly with new phases.

Fe(iv) alkylidenes protonation of Fe(ii) vinyl chelates and a comparative Mössbauer spectroscopic study.

Treatment of -MeFe(PMe) with di-1,2-(-2-(pyridin-2-yl)vinyl)benzene ((bdvp)H), a tetradentate ligand precursor, afforded (bdvp)Fe(PMe) (-PMe) and 2 equiv. CH, C-H bond activation. Similar treatments with tridentate ligand precursors PhCH[double bond, length as m-dash]NCH(-CH[double bond, length as m-dash]CHPh) ((pipp)H) and PhCH[double bond, length as m-dash]N(2-CCMe-Ph) ((pipa)H) under dinitrogen provided -(pipp)Fe(PMe)N () and -(pipvd)Fe(PMe)N (), respectively; the latter one C-H bond activation, and a subsequent insertion of the alkyne into the remaining Fe-Me bond.

Titanium(IV) catalysts with ancillary imino-spiroketonato ligands: synthesis, structure and olefin polymerization.

New titanium(IV) complexes having two bidentate β-iminoethyl-spiro[4,5]decan-6-onato ligands with various N-aryl substituents have been synthesized. X-ray crystal structure analysis reveals that these titanium complexes all exhibit a C2-symmetric conformation with a distorted octahedral geometry, although the specific orientation of the ligands around the titanium center varies with the identity of the N-aryl moiety. Upon activation with methylaluminoxane (MAO), these complexes catalyze the polymerization of ethylene and propylene.

Iron and chromium complexes containing tridentate chelates based on nacnac and imino- and methyl-pyridine components: triggering C-X bond formation.

Nacnac-based tridentate ligands containing a pyridyl-methyl and a 2,6-dialkyl-phenylamine (i.e., (2,6-R2-C6H3N═C(Me)CH═C(Me)NH(CH2py); R = Et, {Et(nn)PM}H; R = (i)Pr, {(i)Pr(nn)PM}H) were synthesized by condensation routes.

Secondary alkene insertion and precision chain-walking: a new route to semicrystalline "polyethylene" from α-olefins by combining two rare catalytic events.

While traditional polymerization of linear α-olefins (LAOs) typically provides amorphous, low T(g) polymers, chain-straightening polymerization represents a route to semicrystalline materials. A series of α-diimine nickel catalysts were tested for the polymerization of various LAOs. Although known systems yielded amorphous or low-melting polymers, the "sandwich" α-diimines 3-6 yielded semicrystalline "polyethylene" comprised primarily of unbranched repeat units via a combination of uncommon regioselective 2,1-insertion and precision chain-walking events.

Iron complexes derived from {nacnac-(CH2py)2}- and {nacnac-(CH2py)(CHpy)}n ligands: stabilization of iron(II) via redox noninnocence.

Nacnac-based tetradentate chelates, {nacnac-(CH2py)2}(-) ({nn(PM)2}(-)) and {nacnac-(CH2py)(CHpy)}(n) ({nn(PM)(PI)}(n)) have been investigated in iron complexes. Treatment of Fe{N(TMS)2}2(THF) with {nn(PM)2}H afforded {nn(PM)2}FeN(TMS)2 [1-N(TMS)2], which led to {nn(PM)2}FeCl (1-Cl) from HCl and to {nn(PM)2}FeN3 (1-N3) upon salt metathesis. Dehydroamination of 1-N(TMS)2 was induced by L (L = PMe3, CO) to afford {nn(PM)(PI)}Fe(PMe3)2 [2-(PMe3)2] and {nn(PM)(PI)}FeCO (3-CO).

Enantioselective polymerization of epoxides using biaryl-linked bimetallic cobalt catalysts: a mechanistic study.

The enantioselective polymerization of propylene oxide (PO) using biaryl-linked bimetallic salen Co catalysts was investigated experimentally and theoretically. Five key aspects of this catalytic system were examined: (1) the structural features of the catalyst, (2) the regio- and stereoselectivity of the chain-growth step, (3) the probable oxidation and electronic state of Co during the polymerization, (4) the role of the cocatalyst, and (5) the mechanism of monomer enchainment. Several important insights were revealed.

C-C bond formation and related reactions at the CNC backbone in (smif)FeX (smif = 1,3-di-(2-pyridyl)-2-azaallyl): dimerizations, 3 + 2 cyclization, and nucleophilic attack; transfer hydrogenations and alkyne trimerization (X = N(TMS)2, dpma = (di-(2-pyridyl-methyl)-amide)).

Molecular orbital analysis depicts the CNC(nb) backbone of the smif (1,3-di-(2-pyridyl)-2-azaallyl) ligand as having singlet diradical and/or ionic character where electrophilic or nucleophilic attack is plausible. Reversible dimerization of (smif)Fe{N(SiMe3)2} (1) to [{(Me3Si)2N}Fe]2(μ-κ(3),κ(3)-N,py2-smif,smif) (2) may be construed as diradical coupling. A proton transfer within the backbone-methylated, and o-pyridine-methylated smif of putative ((b)Me2(o)Me2smif)FeN(SiMe3)2 (8) provides a route to [{(Me3Si)2N}Fe]2(μ-κ(4),κ(4)-N,py2,C-((b)Me,(b)CH2,(o)Me2(smif)H))2 (9).

Selective extraction of N2 from air by diarylimine iron complexes.

Treatment of cis-(Me3P)4FeMe2 with ortho-substituted diarylimines afforded 2 equiv of MeH, PMe3, and {mer-κC,N,C'-(Ar-2-yl)CH2N═CH(Ar'-2-yl)}Fe(PMe3)3 (Ar = 3,4,6-(F)3-C6H, Ar' = 3,5-(CF3)2-C6H2, 1a; Ar = 3,4,6-(F)3-C6H, Ar' = 3,4,5-(F)3-C6H, 1b; Ar = 4,5,6-(F)3-C6H, Ar' = 3,5-(CF3)2-C6H2, 1c; Ar = C6H4, Ar' = 3-(OMe)-C6H3, 1d; Ar = 4,5,6-(F)3-C6H, Ar' = 3,6-Me2-C6H3, 1e; Ar = C6H4, Ar' = 3,6-Me2-C6H2, 1f). Exposure of 1a-f to O2 caused rapid degradation, but substitution of the unique PMe3 with N2 occurred when 1a-f were exposed to air or N2 (1 atm), yielding {mer-κC,N,C'-(Ar-2-yl)CH2N═CH(Ar'-2-yl)}Fe(PMe3)2L (L = N2, 2a-f); CO, CNMe, and N2CPh2 derivatives (L = CO, 3a-d,f; L = CNMe, 8b; L = N2CPh2, 9b) were prepared. Dihydrogen or NH3 binding to {mer-κC,N,C'-(3,4,6-(F)3-C6H-2-yl)CH2N═CH-(3,4,5-(F)3-C6H-2-yl)}Fe(PMe3)2 (1b', S = 1 (calc)) to provide 5b (L = H2) or 6b (L = NH3) was found comparable to that of N2, while PMe3 (1b) and pyridine (L = py, 7b) adducts were unfavorable.

Phosphonium-functionalized polyethylene: a new class of base-stable alkaline anion exchange membranes.

A tetrakis(dialkylamino)phosphonium cation was evaluated as a functional group for alkaline anion exchange membranes (AAEMs). The base stability of [P(N(Me)Cy)(4)](+) was directly compared to that of [BnNMe(3)](+) in 1 M NaOD/CD(3)OD. The high base stability of [P(N(Me)Cy)(4)](+) relative to [BnNMe(3)](+) inspired the preparation of AAEM materials composed of phosphonium units attached to polyethylene.

Synthetic approaches to (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) reveal redox non-innocence and C-C bond-formation.

Attempted syntheses of (smif)(2)Ti (smif =1,3-di-(2-pyridyl)-2-azaallyl) based on metatheses of TiCl(n)L(m) (n = 2-4) with M(smif) (M = Li, Na), in the presence of a reducing agent (Na/Hg) when necessary, failed, but several apparent Ti(II) species were identified by X-ray crystallography and multidimensional NMR spectroscopy: (smif){Li(smif-smif)}Ti (1, X-ray), [(smif)Ti](2)(μ-κ(3),κ(3)-N,N(py)(2)-smif,smif) (2), (smif)Ti(κ(3)-N,N(py)(2)-smif,(smif)H) (3), and (smif)Ti(dpma) (4, dpma = di-2-pyridylmethyl-amide). NMR spectroscopy and K-edge XAS showed that each compound possesses ligands that are redox noninnnocent, such that d(1) Ti(III) centers AF-couple to ligand radicals: (smif){Li(smif-smif)(2-)}Ti(III) (1), [(smif(2-))Ti(III)](2)(μ-κ(3),κ(3)-N,N(py)(2)-smif,smif) (2), [(smif(2-))Ti(III)](κ(3)-N,N(py)(2)-smif,(smif)H) (3), and (smif(2-))Ti(III)(dpma) (4). The instability of (smif)(2)Ti relative to its C-C coupled dimer, 2, is rationalized via the complementary nature of the amide and smif radical dianion ligands, which are also common to 3 and 4.

Synthesis and characterization of (smif)2M(n) (n = 0, M = V, Cr, Mn, Fe, Co, Ni, Ru; n = +1, M = Cr, Mn, Co, Rh, Ir; smif =1,3-di-(2-pyridyl)-2-azaallyl).

A series of Werner complexes featuring the tridentate ligand smif, that is, 1,3-di-(2-pyridyl)-2-azaallyl, have been prepared. Syntheses of (smif)(2)M (1-M; M = Cr, Fe) were accomplished via treatment of M(NSiMe(3))(2)(THF)(n) (M = Cr, n = 2; Fe, n = 1) with 2 equiv of (smif)H (1,3-di-(2-pyridyl)-2-azapropene); ortho-methylated ((o)Mesmif)(2)Fe (2-Fe) and ((o)Me(2)smif)(2)Fe (3-Fe) were similarly prepared. Metatheses of MX(2) variants with 2 equiv of Li(smif) or Na(smif) generated 1-M (M = Cr, Mn, Fe, Co, Ni, Zn, Ru).

Carbon-carbon bond formation from azaallyl and imine couplings about metal-metal bonds.

Typical C-C bond-forming processes feature oxidative addition, insertion, and reductive elimination reactions. An alternative strategy toward C-C bond formation involves the generation of transient radicals that can couple at or around one or more metal centers. Generation of transient azaallyl ligands that reductively couple at CH positions possessing radical character is described.

Enantioselective epoxide polymerization using a bimetallic cobalt catalyst.

A highly active enantiopure bimetallic cobalt complex was explored for the enantioselective polymerization of a variety of monosubstituted epoxides. The polymerizations were optimized for high rates and stereoselectivity, with s-factors (k(fast)/k(slow)) for most epoxides exceeding 50 and some exceeding 300, well above the threshold for preparative utility of enantiopure epoxides and isotactic polyethers. Values for mm triads of the resulting polymers are typically greater than 95%, with some even surpassing 98%.

Pnictogen-hydride activation by (silox)3Ta (silox = (t)Bu3SiO); attempts to circumvent the constraints of orbital symmetry in N2 activation.

Activation of N(2) by (silox)(3)Ta (1, silox = (t)Bu(3)SiO) to afford (silox)(3)Ta═N-N═Ta(silox)(3) (1(2)-N(2)) does not occur despite ΔG°(cald) = -55.6 kcal/mol because of constraints of orbital symmetry, prompting efforts at an independent synthesis that included a study of REH(2) activation (E = N, P, As). Oxidative addition of REH(2) to 1 afforded (silox)(3)HTaEHR (2-NHR, R = H, Me, (n)Bu, C(6)H(4)-p-X (X = H, Me, NMe(2)); 2-PHR, R = H, Ph; 2-AsHR, R = H, Ph), which underwent 1,2-H(2)-elimination to form (silox)(3)Ta═NR (1═NR; R = H, Me, (n)Bu, C(6)H(4)-p-X (X = H (X-ray), Me, NMe(2), CF(3))), (silox)(3)Ta═PR (1═PR; R = H, Ph), and (silox)(3)Ta═AsR (1═AsR; R = H, Ph).

Isospecific polymerization of racemic epoxides: a catalyst system for the synthesis of highly isotactic polyethers.

A highly active bimetallic cobalt catalyst system is reported for the polymerization of racemic terminal epoxides to yield isotactic polyethers.

[(silox)(3)M](2)(mu:eta(1),eta(1)-P(2)) (M = Nb, Ta) and [(silox)(3)Nb](2){mu:eta(2),eta(2)-((c)P(3)-(c)P(3))} from (silox)(3)M (M = NbPMe(3), Ta) and P(4) (silox = (t)Bu(3)SiO).

Complexes containing the mu:eta(1),eta(1)-P(2) binding mode of diphosphorus have been prepared, along with a P(6)-containing byproduct.

On the mechanism of isospecific epoxide polymerization by salen cobalt(III) complexes: evidence for solid-state catalysis.

Mechanistic studies have revealed that the isospecific polymerization of epoxides by a discrete salen cobalt(III) catalyst occurs at the surface of the undissolved, crystalline complex.

Beta-amidoaldehydes via oxazoline hydroformylation.

4-Substituted oxazolines, which are readily synthesized from naturally occurring alpha-amino acids, are converted efficiently and stereospecifically to beta-amidoaldehydes in the presence of synthesis gas and catalytic dicobalt octacarbonyl.

Aryl-containing chelates and amine debenzylation to afford 1,3-di-2-pyridyl-2-azaallyl (smif): structures of {kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}FeBr and (smif)CrN(TMS)(2).

Aryl-bromide ligand precursors have been prepared with the potential to afford tetradentate chelates (2-pyridylmethyl)(3-x)N(CH(2)-2-Aryl)(x) (x = 1, 2) containing metal-aryl linkages that promise to impart stronger fields about first row transition metals. Oxidative addition to Ni(COD)(2) afforded two diamagnetic Ni(II) complexes, {kappa-C,N,N(py)-(2-pyridylmethyl)N(CH(2)(4-(t)Bu-phenyl-2-yl))(CH(2)(4-(t)Bu-phenyl-2-Br))}NiBr (1-Ni) and {(kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}NiBr (2-Ni) in 96% and 67% yield, respectively. Extending these synthetic efforts to iron provided {kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}FeBr (2-Fe, X-ray) in 91% yield via reduction of an adduct, {kappa-N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-Br))}FeBr(2) (3-Fe).

A ring-opening metathesis polymerization route to alkaline anion exchange membranes: development of hydroxide-conducting thin films from an ammonium-functionalized monomer.

We report the development of a facile ring-opening olefin metathesis route to alkaline anion exchange membranes via the copolymerization of a tetraalkylammonium-functionalized norbornene with dicyclopentadiene. The thin films generated are mechanically strong and exhibit high hydroxide conductivities and exceptional methanol tolerance.