Iron-Mediated Coupling of Carbon Dioxide and Ethylene: Macrocyclic Metallalactones Enable Access to Various Carboxylates.

Treatment of (iPrPDI)Fe(N2)2 (iPrPDI, 2,6-(2,6-iPr2C6H3N═CMe)2C5H3N) with CO2 and ethylene resulted in the formation of a homologous series of saturated and unsaturated iron carboxylate products, (iPrPDI)Fe(O2CR), the distribution of which depends on the ratio of the reagents. The solid-state and electronic structures of a saturated product, (iPrPDI)Fe(O2CC2H5), were elucidated. Product distributions, deuterium labeling studies, and stoichiometric experiments support initial formation of a five-membered metallalactone intermediate, which undergoes subsequent ethylene insertions to generate macrocyclic metallalactones. Competitive ß-hydride elimination, CO2 insertion, or reaction with H2 determines the fate of the metallalactone, the latter accounting for formation of iron complexes with saturated carboxylates. Similar reactivity was observed upon addition of propiolactone and ethylene to (iPrPDI)Fe(N2)2, supporting C-O oxidative addition and C-C bond formation through metallacycle intermediates.

A nitrogen-rich ligand as a scaffold for slow magnetic relaxation in dysprosium-based 0D and 1D architectures.

A recently designed nitrogen-rich ligand is successfully applied as a scaffold for lanthanide ions to show that the intricate chemistry of energetic materials can be combined with other fields of research, including that of molecular magnetism. Herein, we report the synthesis of two different types of molecular architectures using a single ligand template, in which the discrete monomer exhibits single-molecule magnet-like behaviour along with two well-isolated modes of magnetic relaxation.

Iron(II) Complexes of a Hemilabile SNS Amido Ligand: Synthesis, Characterization, and Reactivity.

We report an easily prepared bis(thioether) amine ligand, SMeNHSMe, along with the synthesis, characterization, and reactivity of the paramagnetic iron(II) bis(amido) complex, [Fe(κ3-SMeNSMe)2] (1). Binding of the two different thioethers to Fe generates both five- and six-membered rings with Fe-S bonds in the five-membered rings (av 2.54 Å) being significantly shorter than those in the six-membered rings (av 2.71 Å), suggesting hemilability of the latter thioethers. Consistent with this hypothesis, magnetic circular dichroism (MCD) and computational (TD-DFT) studies indicate that 1 in solution contains a five-coordinate component [Fe(κ3-SMeNSMe)(κ2-SMeNSMe)] (2). This ligand hemilability was demonstrated further by reactivity studies of 1 with 2,2'-bipyridine, 1,2-bis(dimethylphosphino)ethane, and 2,6-dimethylphenyl isonitrile to afford iron(II) complexes [L2Fe(κ2-SMeNSMe)2] (3-5). Addition of a Brønsted acid, HNTf2, to 1 produces the paramagnetic, iron(II) amine-amido cation, [Fe(κ3-SMeNSMe)(κ3-SMeNHSMe)](NTf2) (6; Tf = SO2CF3). Cation 6 readily undergoes amine ligand substitution by triphos, affording the 16e- complex [Fe(κ2-SMeNSMe)(κ3-triphos)](NTf2) (7; triphos = bis(2-diphenylphosphinoethyl)phenylphosphine). These complexes are characterized by elemental analysis; 1H NMR, Mössbauer, IR, and UV-vis spectroscopy; and single-crystal X-ray diffraction. Preliminary results of amine-borane dehydrogenation catalysis show complex 7 to be a selective and particularly robust precatalyst.

Radical Behavior of CO2 versus its Deoxygenation Promoted by Vanadium Aryloxide Complexes: How the Geometry of Intermediate CO2 -Adducts Determines the Reactivity.

The reactivity of carbon dioxide with vanadium(III) aryloxo complexes has been investigated. The formation of either carbon monoxide or incorporation into the ligand system with the ultimate formation of organic ester was observed depending on the overall electron donor ability of the ligand field. DFT calculations were carried out to investigate the proposed mechanism for carbon dioxide coordination and reduction.

Electro- and Photocatalytic Generation of H2 Using a Distinctive CoII "PN3 P" Pincer Supported Complex with Water or Saturated Saline as a Hydrogen Source.

Efficient electrocatalytic production of H2 from mixed water/acetonitrile solutions was achieved using three new CoII complexes supported by the neutral pincer ligand bis(diphenylphosphino)-2,6-di(methylamino)pyridine ("PN3 P"). At -1.9 V vs. Fc/Fc+ , these catalysts showed 96 % Faradaic efficiency with added water or saturated aqueous saline at rates of up to 316 L(mol cat)-1 (cm2 )-1 h-1 using a glassy carbon working electrode. The complex [Co(κ3 -2,6-{Ph2 PNMe}2 (NC5 H3 )Br2 ] (1) was also able to photocatalytically reduce water to hydrogen in the presence of a Ru(bpy)32+ photosensitizer and a reductant.

Strong ferromagnetic exchange coupling in a {Ni} cluster mediated through an air-stable tetrazine-based radical anion.

A planar tetradentate 3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine (BpymTz) templating chelate affords the formation of an unprecedented BpymTz˙- radical anion bridged {Ni} complex. Detailed magnetic measurements performed on the isolated air stable [Ni(BpymTz˙-)Cl6(DMF)8]Cl·0.5(H2O) compound reveal strong ferromagnetic NiII-BpymTz˙- interactions with a coupling constant of J = 98.84 cm-1.

Stepwise crystallographic visualization of dynamic guest binding in a nanoporous framework.

Binding sites are at the heart of all host-guest systems, whether biological or chemical. When considering binding sites that form covalent bonds with the guest, we generally envision a single, highly specific binding motif. Through single-crystal X-ray crystallography, the dynamic binding of a guest that displays a variety of covalent binding motifs in a single site of adsorption is directly observed for the first time. The stepwise crystallographic visualization of the incorporation of I2 within a porous MOF is presented, wherein the preferred binding motifs throughout the uptake process are identified. The guest I2 molecules initially bind with terminal iodide atoms of the framework to form [I4]2- units. However, as the adsorption progresses, the I2 molecules are observed to form less energetically favorable I3- groups with the same framework iodide atoms, thereby allowing for more guest molecules to be chemisorbed. At near saturation, even more binding motifs are observed in the same pores, including both physisorbed and chemisorbed guest molecules. Herein, we present the successful identification of a unique set of host-guest interactions which will drive the improvement of high capacity iodine capture materials.

Electrocatalytic generation of H2 from neutral water in acetonitrile using manganese polypyridyl complexes with ligand assistance.

A Mn(i) tris(2-pyridylmethyl)amine complex fac-[Mn(κ3-tpa) (CO)3]+OTf- carries out electrocatalytic hydrogen evolution from neutral water in acetonitrile. Bulk electrocatalytic studies showed that the catalyst functions with a moderate Faradaic efficiency and turn over frequency. DFT computations support the role of the tpa ligand as a shuttle to transfer of protons to the metal center.

Confinement effects of a crystalline sponge on ferrocene and ferrocene carboxaldehyde.

The pivotal role of ππ interactions in the inclusion behaviour of a series of organometallic sandwich compounds is studied through single-crystal X-ray diffraction. The confinement effects of a crystalline sponge host are investigated where, notably, we observe an enhanced rotation of the ligand ring once encapsulated by the nanoporous framework, as evidenced by SSNMR experiments.

Cycloheptatrienyl trianion: an elusive bridge in the search of exchange coupled dinuclear organolanthanide single-molecule magnets.

The preparation of η-cyclopentadienyl (η5-C5R5), η-arene (η6-C6R6), and η-cyclooctatetraenyl (η8-C8R8) bridging motifs are common in organometallic chemistry; however, the synthetic preparation of η-cycloheptatrienyl (η7-C7R7) bridging motifs has remained a synthetic challenge in 4f chemistry. To this end, we have developed a synthetic route towards a series of rare dinuclear organolanthanide inverse sandwich complexes containing the elusive η7-C7H7 bridge. Herein, we present the structures and magnetic properties of the lanthanide inverse sandwich complexes [KLn2(C7H7)(N(SiMe3)2)4] (Ln = GdIII (1), DyIII (2), ErIII (3)) and [K(THF)2Er2(C7H7)(N(SiMe3)2)4] (4). These compounds are the first single-molecule magnets (SMMs) to feature this type of bridging motif. Furthermore, η7-C7H7 was found to efficiently promote ferromagnetic exchange interactions between metal ions. Variable temperature dc magnetic susceptibility measurements and subsequent simulations give significant exchange constants of J = +1.384, +1.798, and +3.149 cm-1 and dipolar constants of J = -0.603, -0.601, and -0.475 cm-1 for compounds 2-4, respectively. Frequency dependent ac susceptibility measurements under an applied static field resulted in the observation of dual relaxation processes, and brought forth a greater understanding of the intermolecularly driven process at high frequency. In particular, this type of analysis of compound 3 under 800 Oe elicited an energy barrier of Ueff = 58 K. Ab initio calculations were performed in order to understand the nature of magnetic coupling and the origin of slow relaxation of magnetisation. Through these studies, the effect of the amido ancillary ligands on the magnetic axiality of the lanthanide ions was found to be competitive with the crystal field of the η7-C7H7 π-electron cloud. Our findings suggest that the tunability of the dipolar and exchange components of the magnetic interactions lie within the dihedral angle imposed by the amido ligands, thus offering potential for the development of new exchange coupled lanthanide systems.

Generation of Hydrofluoronickelacycles from Trifluoroethylene and Ni(0): Ligand Effects on Regio-/Stereoselectivity and Reactivity.

Treatment of Ni(0) complexes 1a-e with sub-atmospheric pressures of trifluoroethylene (TrFE) affords hydrofluoronickelacyclopentanes L2Ni(C4F6H2) 2a-e (L = PPh3, P(O-o-tol)3, PPh2Me, PPhMe2, PMe3). Fluorine NMR analysis of 2a-e demonstrates predominant formation of three (of the possible six) isomers upon oxidative cycloaddition of TrFE: the cis and trans head-tail isomers and the trans head-head isomer, where the CHF group is defined as the TrFE "head". The respective ratios of L2Ni(C4F6H2) isomers are influenced by the nature of L, with smaller phosphines favoring the thermodynamically preferred (from DFT calculations) trans head-head isomer (cf. 50% with PMe3) and the largest affording small amounts of the tail-tail isomers. Lewis and Brønsted acids induce a surprising double C-F bond activation in 2c-d, affording small functionalized hydrofluoroalkenes. Interestingly, varying the acid employed dictates the organic product obtained from the head-tail isomers: BF3·OEt2 is selective for 1,1,2,3-tetrafluorocyclobutene, whereas Me3SiOTf and N,N-dimethylanilinium bromide yield (Z,E)-1,1,3,4-tetrafluorobutadiene as the major fluorinated product. Reaction intermediates were isolated, and possible pathways are discussed.

Oxidative Addition of Disulfides, Alkyl Sulfides, and Diphosphides to an Aluminum(I) Center.

The aluminum(I) compound NacNacAl (1) reacts with diphenyl disulfide and diethyl sulfide to form the respective four-coordinate bis(phenyl sulfide) complex NacNacAl(SPh)2 (2) and alkyl thiolate aluminum complex NacNacAlEt(SEt) (3). As well, reaction of 1 with tetraphenyl diphosphine furnishes the bis(diphenyl phosphido) complex NacNacAl(PPh2)2 (4). Production of 3 and 4 are the first examples of C(sp(3))-S and R2P-PR2 activation by a main-group element complex. All three complexes were characterized by multinuclear NMR spectroscopy and X-ray crystal structure analysis. Furthermore, a variable-temperature NMR spectroscopic study was undertaken on 4 to study its dynamic behavior in solution.

Structural and electronic trends for five coordinate 1(st) row transition metal complexes: Mn(ii) to Zn(ii) captured in a bis(iminopyridine) framework.

The preparation and characterization of a series of divalent 3d transition metal complexes supported by a tridentate planar bis(iminopyridine) ligand are reported. The complexes {2,6-[PhC[double bond, length as m-dash]N(tBu2C6H3)]2C5H3N}MBr2 (M = Mn, Fe, Co, Ni, Cu, Zn), 1-6, were characterized by single crystal X-ray structural studies revealing complexes with pentacoordinate distorted square pyramidal coordination environments. This assembly of complexes provided a unique array for examining the relationship between experimental structure and computed electronic structure. While experimental structural features basically correlated with the Irving-Williams series, some clear deviations were rationalized through the computational analysis. A balance of bis(imino)pyridine/metal with bonding/antibonding π interactions was used to explain the divergent directions of Fe(ii)-N and Co(ii)-N bond lengths. Similarly, orbital details were used to justify the opposing change in Cu-Brap and Cu-Brbas bond lengths. Furthermore, computational analysis provided a unique method to document a surprising low bond order for the M-N bonds of bis(imino)pyridine ligand in this series.

Unique molecular geometries of reduced 4- and 5-coordinate zinc complexes stabilised by diiminopyridine ligand.

Stepwise reduction of the diiminopyridine (dimpyr) complex, dimpyrZnCl2, by KC8 leads to molecular zinc compounds dimpyrZnCl (2) and dimpyrZnCl(DMAP) (3, DMAP = 4-dimethylaminopyridine), which were characterized by X-ray diffraction and EPR spectroscopy. Compound 2 shows an unusual nearly square planar geometry of the zinc atom equally ligated by two imine groups. X-ray crystallographic and EPR data suggest significant delocalization of the zinc 4p electron onto the non-innocent dimpyr ligand. The chloride in 2 can also be substituted by a methyl group upon addition of methyl lithium to generate compound 4, dimpyrZnMe. The novel alkylzinc compound displayed approximate square planar geometry around the zinc centre and significant delocalization of electron density onto the dimpyr ligand, as revealed by X-ray crystallographic studies and EPR spectroscopy, akin to 2. Further reduction of 3 leads to compound 5, dimpyrZn(DMAP)2. X-ray diffraction study of 5 revealed an unprecedented see-saw geometry around the four-coordinate zinc center with significant electron density transfer to the dimpyr ligand, supported by DFT calculations.

Electrocatalytic reduction of CO2 using Mn complexes with unconventional coordination environments.

New complexes, Mn{κ(3)-[2,6-{Ph2PNMe}2(NC5H3)]}(CO)3(+)Br(-) (1(+)Br(-)) and MnBr{κ(2)-(Ph2P)NMe(NC5H4)}(CO)3 (2), are reported and present new ligand environments for CO2 electrocatalytic reduction to CO. Compound 1(+) presents a unique metal geometry for CO production (96%) in the absence of added water while 2 required addition of water and generated both CO and H2 products.

Selective Activation of Fluoroalkenes with N-Heterocyclic Carbenes: Synthesis of N-Heterocyclic Fluoroalkenes and Polyfluoroalkenyl Imidazolium Salts.

Selective reactions between nucleophilic N,N'-diaryl-heterocyclic carbenes (NHCs) and electrophilic fluorinated alkenes afford NHC fluoroalkenes in high yields. These stable compounds undergo efficient and selective fluoride abstraction with Lewis acids to give polyfluoroalkenyl imidazolium salts. These salts react at Cß with pyrrolidine to give ammonium fluoride-substituted salts, which give rise to conjugated imidazolium-enamine salts through loss of HF. Alternatively, reaction with 4-(dimethylamino)-pyridine provides a Cα-pyridinium-substituted NHC fluoroalkene. These compounds were studied using multinuclear NMR spectroscopy, mass spectrometry, and X-ray crystallography. Insight into their electronic structure and reactivity was gained through the use of DFT calculations.

Halide Influence on Molecular and Supramolecular Arrangements of Iron Complexes with a 3,5-Bis(2-Pyridyl)-1,2,4,6-Thiatriazine Ligand.

A series of iron centered complexes, namely, [Fe(Py2TTA)Cl2] (1), [Fe(Py2TTA)Br2] (2), and [Fe(µ-F)(Py2TTAO)F]∞ (3), were isolated via complexation of 3,5-bis(2-pyridyl)-1,2,4,6-thiatriazine (Py2TTAH) with various ferric halides (e.g., FeF3, FeCl3, and FeBr3). Comparison of the optical and electrochemical spectroscopy, structural analysis, and magnetic studies reveal numerous similarities between the chlorido (1) and bromido (2) derivatives, which crystallize as discrete five-coordinate iron centered complexes with coordination geometries that are intermediate between trigonal bipyramidal and square base pyramid. Conversely, the fluorido derivative (3) results in a completely different structure due to oxidation of the ligand and the formation of a one-dimensional coordination polymer held together through a bridging fluoride ion. Consequently, the spectroscopic and magnetic behavior of 3 differs significantly compared with 1 and 2. Complexes 1 and 2 exhibit paramagnetic properties typical for a mononuclear S = 5/2 system with weak intermolecular antiferromagnetic interactions at low temperatures, whereas complex 3 demonstrates significant exchange couplings within the chain and weak antiferromagnetic interchain interactions, which stabilize a canted antiferromagnetic state below 4.2 K.

Capturing Re(i) in an neutral N,N,N pincer Scaffold and resulting enhanced absorption of visible light.

The organometallic and coordination chemistry of rhenium(i) has been largely restricted to bidentate α-diimine ligation and facial tricarbonyl coordination geometries. The thermal transformation of bidentate bis(imino)pyridine and bidentate terpyridine complexes at 200-240 °C under nitrogen led to a family of Re(i) pincer complexes [κ(3)-2,6-{ArN[double bond, length as m-dash]CMe}2(NC5H3)]Re(CO)2X (Ar[double bond, length as m-dash]C6H5, Me2C6H3, (i)Pr2C6H3; X = Cl, Br) and (κ(3)-terpy)Re(CO)2X (X = Cl, Br). The synthesis, single crystal X-ray structural and spectroscopic characterization of these eight species documents their Re coordination geometries and demonstrates the accessibility of such compounds. The basic photophysical features of these compounds show significant elaboration in both number and intensity of the d-π* transitions observed in the UV-vis spectra relative to the bidentate starting materials and these spectra were analyzed using time-dependent DFT computations.

Intercalation of Coordinatively Unsaturated Fe(III) Ion within Interpenetrated Metal-Organic Framework MOF-5.

Coordinatively unsaturated Fe(III) metal sites were successfully incorporated into the iconic MOF-5 framework. This new structure, Fe(III) -iMOF-5, is the first example of an interpenetrated MOF linked through intercalated metal ions. Structural characterization was performed with single-crystal and powder XRD, followed by extensive analysis by spectroscopic methods and solid-state NMR, which reveals the paramagnetic ion through its interaction with the framework. EPR and Mössbauer spectroscopy confirmed that the intercalated ions were indeed Fe(III) , whereas DFT calculations were employed to ascertain the unique pentacoordinate architecture around the Fe(III) ion. Interestingly, this is also the first crystallographic evidence of pentacoordinate Zn(II) within the MOF-5 SBU. This new MOF structure displays the potential for metal-site addition as a framework connector, thus creating further opportunity for the innovative development of new MOF materials.

Mononuclear, Dinuclear, and Trinuclear Iron Complexes Featuring a New Monoanionic SNS Thiolate Ligand.

The new tridentate ligand, S(Me)N(H)S = 2-(2-methylthiophenyl)benzothiazolidine, prepared in a single step from commercial precursors in excellent yield, undergoes ring-opening on treatment with Fe(OTf)2 in the presence of base affording a trinuclear iron complex, [Fe3(µ2-S(Me)NS(-))4](OTf)2 (1) which is fully characterized by structural and spectroscopic methods. X-ray structural data reveal that 1 contains four S(Me)NS(-) ligands meridionally bound to two pseudooctahedral iron centers each bridged by two thiolates to a distorted tetrahedral central iron. The combined spectroscopic (UV-vis, Mössbauer, NMR), magnetic (solution and solid state), and computational (DFT) studies indicate that 1 includes a central, high-spin Fe(II) (S = 2) with two low-spin (S = 0) peripheral Fe(II) centers. Complex 1 reacts with excess PMePh2, CNxylyl (2,6-dimethylphenyl isocyanide), and P(OMe)3 in CH3CN to form diamagnetic, thiolate-bridged, dinuclear Fe(II) complexes {[Fe(µ-S(Me)NS(-))L2]2}(OTf)2 (2-4). These complexes are characterized by elemental analysis; (1)H NMR, IR, UV-vis, and Mössbauer spectroscopy; and single crystal X-ray diffraction. Interestingly, addition of excess P(OMe)3 to complex 1 in CH2Cl2 produces primarily the diamagnetic, mononuclear Fe(II) complex, {Fe(S(Me)NS(-))[P(OMe)3]3}(OTf) (5).