Heavy Metals Make a Chain: A Catenated Bismuth Compound.

Catenation is common for the light main-group elements whereas it is rare for the heavy elements. Herein, we report the first example of a neutral molecule containing a Bi4 chain. It is prepared in a one-step reaction between bismuth trichloride and bis(diisopropylphosphino)amine in methanol suspension. The same reaction carried out in dichloromethane gives quite different products. All products have been characterized spectroscopically and using single-crystal X-ray analysis.

Hydrogenolysis of Dinuclear PCNR Ligated PdII µ-Hydroxides and Their Mononuclear PdII Hydroxide Analogues.

The hydrogenolysis of mono- and dinuclear PdII hydroxides was investigated both experimentally and computationally. It was found that the dinuclear µ-hydroxide complexes {[(PCNR )Pd]2 (µ-OH)}(OTf) (PCNH =1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole; PCNMe =1-[3-[(di-tert-butylphosphino)methyl]phenyl]-5-methyl-1H-pyrazole) react with H2 to form the analogous dinuclear hydride species {[(PCNR )Pd]2 (µ-H)}(OTf). The dinuclear µ-hydride complexes were fully characterized, and are rare examples of structurally characterized unsupported singly bridged µ-H PdII dimers. The {[(PCNMe )Pd]2 (µ-OH)}(OTf) hydrogenolysis mechanism was investigated through experiments and computations. The hydrogenolysis of the mononuclear complex (PCNH )Pd-OH resulted in a mixed ligand dinuclear species [(PCNH )Pd](µ-H)[(PCC)Pd] (PCC=a dianionic version of PCNH bound through phosphorus P, aryl C, and pyrazole C atoms) generated from initial ligand "rollover" C-H activation. Further exposure to H2 yields the bisphosphine Pd0 complex Pd[(H)PCNH ]2 . When the ligand was protected at the pyrazole 5-position in the (PCNMe )Pd-OH complex, no hydride formed under the same conditions; the reaction proceeded directly to the bisphosphine Pd0 complex Pd[(H)PCNMe ]2 . Reaction mechanisms for the hydrogenolysis of the monomeric and dimeric hydroxides are proposed.

Synthesis and characterization of thallium-salen derivatives for use as underground fluid flow tracers.

A pair of thallium salen derivatives was synthesized and characterized for potential use as monitors (or taggants) or as models for Group 13 complexes for subterranean fluid flows. These precursors were isolated from the reaction of thallium ethoxide with N,N'-bis(3,5-di-tert-butylsalicylidene)-ethylenediamine (H2-salo-But), or N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamine (H2-saloPh-But). The products were identified by single crystal X-ray diffraction as: [((µ-O)2,κ1-(N)(N')salo-But)Tl2] (1) and {[((µ-O)2saloPh-But)Tl2][((µ-O)2,κ1-(N)(N')saloPh-But)Tl2]} (2). Both structures are similar, wherein each O atom of the salo moiety bridges the two Tl atoms, leading to a TlTl interaction, which is further stabilized by an intramolecular π-bond with neighboring phenyl rings. For 1, an additional TlN interaction was solved for each metal center; whereas, for 2, one of the two molecules in the matrix has a weak TlN interaction but no bonding noted in the other molecule. Both Density Functional Theory (DFT) calculations and variable temperature solution 205Tl NMR studies of 1 and 2 further confirmed the TlTl interaction. The UV-vis absorbance spectra of these compounds had an absorbance peak at 392 nm for 1 and a broad absorbance peak centered at 469 nm for 2, which were found to be in good agreement with the DFT calculated spectra that were dominated by the singlet state. Fluorescence emission and excitation studies reveal absorptions at 360 and 380 nm for 1 and 2, respectively, which are attributed to the TlTl metal centers. To demonstrate practicality, fluorescence spectra of 1 and 2 were obtained using a handheld 405 nm cw laser pointer and portable spectrometer where compound 1 was found to glow 15 times brighter than compound 2. Only compound 1 was found to survive the simulated deep-well conditions explored, which was attributed to the TlN interaction noted for 1 but not for 2.

Synthesis and Characterization of Structurally Diverse Alkaline-Earth Salen Compounds for Subterranean Fluid Flow Tracking.

A family of magnesium and calcium salen-derivatives was synthesized and characterized for use as subterranean fluid flow monitors. For the Mg complexes, di- n-butyl magnesium ([Mg(Bu n)2]) was reacted with N, N'-ethylene bis(salicylideneimine) (H2-salen), N, N'-bis(salicylidene)-1,2-phenylenediamine (H2-saloPh), N, N'-bis(3,5-di- t-butylsalicylidene)-ethylenediamine (H2-salo-Bu t), or N, N'-bis(3,5-di- t-butylsalicylidene)-1,2-phenylenediamine (H2-saloPh-Bu t), and the products were identified by single-crystal X-ray diffraction as [(κ3-(O,N,N'),µ-(O')saloPh)(µ-(O),(κ2-(N,N'),µ-(O')saloPh)2(µ-(O),κ3-(N,N',O')saloPh')Mg4]·2tol (1·2tol; saloPh' = an alkyl-modified saloPh derivative generated in situ), [(κ4-(O,N,N',O')saloPh)Mg(py)2]·py (2·py), [(κ4-(O,N,N',O')salo-Bu t)Mg(py)2] (3), [(κ4-(O,N,N',O')saloPh-Bu t)Mg(py)2]·tol (4·tol), and [(κ3-(O,N,N'),µ-(O')saloPh-Bu t)Mg]2 (5), where tol = toluene; py = pyridine. For the Ca species, a calcium amide was independently reacted with H2-salo-Bu t and H2-saloPh-Bu t to generate the crystallographcially characterized compounds: [(κ4-(O,N,N',O')salo-Bu t)Ca(py)3] (6), [(κ4-(O,N,N',O')saloPh-Bu t)Ca(py)3]·py (7·py). The bulk powders of these compounds were further characterized by a number of analytical tools, where 2-7 were found to be distinguishable by Fourier transform infrared and resonance Raman spectroscopies. Structural properties obtained from quantum calculations of gas-phase analogues are in good agreement with the single-crystal results. The potential utility of these compounds as taggants for monitoring subterranean fluid flows was demonstrated through a series of experiments to evaluate their stability to high temperature and pressure, interaction with mineral surfaces, and elution behavior from a loaded proppant pack.

P- and N-Coordination of the Ambidentate Ligand HN[P(i-Pr)2]2 with Group 13 Trihalides.

Five different coordination motifs were observed upon reaction of the simple group 13 Lewis acids MCl3 (M = In, Ga, Al, B) or BF3·Et2O with the ambidentate bis(diisopropylphosphino)amine ligand HN[P(i-Pr)2]2. In a 1:1 reaction mixture, the softer Lewis acids InCl3, GaCl3 and BCl3 coordinate to one of the two P atoms of the ligand. In contrast, AlCl3 and BF3 prefer coordination to the harder N atom. In all cases, the acidic N-H proton is shifted to P upon complexation with a metal. By altering the reaction stoichiometry, 2:1 metal-ligand complexes could be isolated for three of the combinations. BCl3 gives a bis-adduct via the two P atoms. GaCl3 produces a salt consisting of a [GaCl4]- anion and a P,P-chelated [LGaCl2]+ cation. Most unexpectedly, the reaction with InCl3 in methanol resulted in solvent deprotonation by the ligand to give two symmetric [(i-Pr2PH)2N]+ cations in which all the basic P sites are coordinated to H rather than the group 13 Lewis acid. These cations are balanced by the unique complex dianion [(MeO)6In4Cl8·2MeOH]2-. All complexes were characterized with a combination of multinuclear NMR spectroscopy and single-crystal X-ray diffraction.

Crystal structure of catena-poly[di-ammonium [di-µ-oxalato-cuprate(II)]].

The structure of the title compound, {(NH4)2[Cu(C2O4)2]} n , at 100 K has monoclinic (P21/c) symmetry with the CuII atom on an inversion center. The compound has a polymeric structure due to long Cu⋯O inter-actions which create [Cu(C2O4)2] chains along the a axis. The structure also displays inter-molecular N-H⋯O hydrogen bonding, which links these chains into a three-dimensional network.

Facilitated carbon dioxide reduction using a Zn(II) complex.

Two new Zn(II) complexes have been prepared and evaluated for their capacity to activate and reduce CO2. The electrochemical properties of dichlorobis[diphenyl-(2-pyridyl)phosphine-κ(1)-N]zinc(II) [corrected]. and dichloro[diphenyl-(2-pyridyl)phosphine-κ(1)-N]zinc(II) 2 are compared using cyclic voltammetry. Electrochemical results indicate that 2 leads to a facilitated CO2 reduction to evolve CO at a glassy carbon electrode.

Rapid, Reversible, Solid-Gas and Solution-Phase Insertion of CO2 into In-P Bonds.

The P,P-chelated heteroleptic complex bis[bis(diisopropylphosphino)amido]indium chloride [(i-Pr2P)2N]2InCl was prepared in high yield by treating InCl3 with 2 equiv of (i-Pr2P)2NLi in Et2O/tetrahydrofuran solution. Samples of [(i-Pr2P)2N]2InCl in a pentane slurry, a CH2Cl2 solution, or in the solid state were exposed to CO2, resulting in the insertion of CO2 into two of the four M-P bonds to produce [O2CP(i-Pr2)NP(i-Pr2)]2InCl in each case. Compounds were characterized by multinuclear NMR and IR spectroscopy, as well as single-crystal X-ray diffraction. ReactIR solution studies show that the reaction is complete in less than 1 min at room temperature in solution and in less than 2 h in the solid-gas reaction. The CO2 complex is stable up to at least 60 °C under vacuum, but the starting material is regenerated with concomitant loss of carbon dioxide upon heating above 75 °C. The compound [(i-Pr2P)2N]2InCl also reacts with CS2 to give a complicated mixture of products, one of which was identified as the CS2 cleavage product [S═P(i-Pr2)NP(i-Pr2)]2InCl]2(µ-Cl)[µ-(i-Pr2P)2N)].

Unexpected formal insertion of CO2 into the C-Si bonds of a zinc compound.

Reaction of [κ2-PR2C(SiMe3)Py]2Zn (R = Ph, 2a; iPr, 2b) with CO2 affords the products of formal insertion at the C­Si bond, [κ2-PR2CC(O)O(SiMe3)Py]2Zn (R = Ph, 3a; iPr, 3b). Insertion product 3b was structurally characterized. The reaction appears to be a stepwise insertion and rearrangement of CO2 based on kinetic data.

Structurally simple complexes of CO2.

The ability to bind CO2 through the formation of low-energy, easily-broken, bonds could prove invaluable in a variety of chemical contexts. For example, weak bonds to CO2 would greatly decrease the cost of the energy-intensive sorbent-regeneration step common to most carbon capture technologies. Furthermore, exploration of this field could lead to the discovery of novel CO2 chemistry. Reduction of complexed carbon dioxide might generate chemical feedstocks for the preparation of value-added products, particularly transportation fuels or fuel precursors. Implementation on a large scale could help to drastically reduce CO2 concentrations in the atmosphere. However, literature examples of weakly bonded complexes of CO2 are relatively few and true coordination complexes to a 'naked' CO2 fragment are nearly unheard of. In this review article, a variety of complexes of CO2 featuring diverse binding modes and reactivity will be examined. Topics covered include: (A) inclusion complexes of CO2 in porous materials. (B) Zwitterionic carbamates produced from the reaction of CO2 with polyamines. (C) Carbamate salts produced from reaction of CO2 with two equivalents of an amine. (D) Insertion products of CO2 into acid-base adducts (e.g., metal complexes). (E) Lewis acid-base activated CO2, such as frustrated Lewis pair complexes. (F) Simple base-CO2 adducts, wherein the base-CO2 bond is the only interaction formed. Complexes in the last category are of particular interest, and include imidazol-2-carboxylates (N-heterocyclic carbene adducts of CO2) as well as a few other examples that lie outside NHC chemistry.

Metal complexes (M = Zn, Sn, and Pb) of 2-phosphinobenzenethiolates: insights into ligand folding and hemilability.

The divalent metal complexes M(II){(SC6H4-2-PR2)-κ(2)S,P}2 (3-7, and 9-11) (M = Zn, Sn, or Pb; R = (i)Pr, (t)Bu, or Ph), the Sn(IV) complexes Sn{(SC6H4-2-PR2)-κ(2)-S,P}Ph2Cl (12 and 13) (R = (i)Pr and (t)Bu), and the ionic Sn(IV) complexes [Sn{(SC6H4-2-PR2)-κ(2)-S,P}Ph2][BPh4] (14 and 15) (R = (i)Pr and (t)Bu) have been prepared and characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction when suitable crystals were afforded. The Sn(II) and Pb(II) complexes with R = Ph, (i)Pr, or (t)Bu (5, 6, 9, and 10) demonstrated ligand "folding" hinging on the P,S vector-a behavior driven by the repulsions of the metal/phosphorus and metal/sulfur lone pairs and increased M-S sigma bonding strength. This phenomenon was examined by density functional theory (DFT) calculations for the compounds in both folded and unfolded states. The Sn(IV) compound 13 (R = (t)Bu) crystallized with the phosphine in an axial position of the pseudotrigonal bipyramidal complex and also exhibited hemilability in the Sn-P dative bond, while compound 12 (R = (i)Pr), interestingly, crystallized with phosphine in an equatorial position and did not show hemilability. Finally, the crystal structure of 15 (R = (t)Bu) revealed the presence of an uncommon, 4-coordinate, stable Sn(IV) cation.

NH/PH isomerization and a Lewis pair for carbon dioxide capture.

Bis(di-i-propylphosphino)amine 1 reacts with B(C6F5)3 to form an adduct with concomitant N/P H-isomerization. This species reacts smoothly with carbon dioxide. An attempt to prepare an anionic derivative resulted in the formation of a novel heterocycle derived from the PNP ligand and B(C6F5)3.

Addition of aluminum and gallium species to aromatic and alkyl-substituted 1,4-diaza-1,3-butadiene ligands.

In this report, we investigate the interactions of Me(x)MCl(3-x) (x = 0-3, M = Al, Ga) with various aromatic and alkyl-substituted 1,4-diaza-1,3-butadiene (R)DAB ligands (or α-diimine ligands) to give a variety of structures in solution and in the solid state. In combination with other previously reported structures, certain general trends of reactivity of these species can be deduced, although there are still some unexplained modes of reactivity. The methylated Al species react with aromatic-substituted (R)DAB ligands to provide final products that result from C═N insertion into the Al-CH(3) group followed by rearrangement reactions. The addition of methyl groups onto the backbone of the (R)DAB ligand is insufficient to stop the insertion and rearrangement processes from occurring. In the case of MeAlCl(2) with the bulky (DiPP)DAB ligand, the reaction could be followed spectroscopically from the monoadduct through the inserted/rearranged final product. Methylated Ga species, however, are much less predictable in their behavior with aromatic-substituted (R)DAB ligands. Depending on the exact species and ratios used, coordinated adducts can be formed and identified, or inserted/rearranged products similar to the aluminum reactions can be obtained. Quite interestingly, cation/anion pairs can also be formed in which GaCl(3) or MeGaCl(2) act as a chloride acceptors. This behavior was unique and substantially different from the analogous Al reactions which formed either a dicoordinated adduct or an inserted/rearranged complex. When the stronger-donating alkyl-substituted (R)DAB ligands were used with Me(2)GaCl, only cation/anion pairs were obtained. Surprisingly, when the same reactions were performed using Me(2)AlCl as a reagent, irreproducible results were obtained.

Formation of phosphino-substituted isocyanate by reaction of CO2 with group 2 complexes based on the (Me3Si)(i-Pr2P)NH ligand.

The group 2 complexes [(Me(3)Si)(i-Pr(2)P)N](2)M(THF)(x) (M = Mg, x = 1; M = Ca/Sr, x = 2) as well as an unusual dimagnesium complex {[(Me(3)Si)(i-Pr(2)P)N](3)Mg}Mg(n-C(4)H(9)) have been prepared and characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction. Each complex was shown to react with CO(2) under extremely mild conditions (15 min, 1 atm, room temperature) to give the isocyanate (i-Pr)(2)P-N═C═O. The independent syntheses of (i-Pr)(2)P-N═C═O and the carbodiimide dimer [(i-Pr)(2)PNCNP(i-Pr)(2)](2) are also reported.

Formation of a reversible, intramolecular main-group metal-CO2 adduct.

The P,P-chelated stannylene [(i-Pr(2)P)(2)N](2)Sn takes up 2 equiv of carbon dioxide (CO(2)) to form an unusual product in which CO(2) binds to the Sn and P atoms, thus forming a six-membered ring complex. Gentle heating of the solid product releases CO(2), indicating that CO(2) is bound as an adduct to the main-group complex. The groups bound to the CO(2) fragment are not particularly sterically crowded or highly acidic, thus indicating that "frustrated" Lewis acid-base pairs are not required in the binding of CO(2) to main-group elements.

Hydrogenolysis of palladium(II) hydroxide, phenoxide, and alkoxide complexes.

A series of pincer ((tBu)PCP)Pd(II)-OR complexes ((tBu)PCP = 2,6-bis(CH(2)P(t)Bu(2))C(6)H(3), R = H, CH(3), C(6)H(5), CH(2)C(CH(3))(3), CH(2)CH(2)F, CH(2)CHF(2), CH(2)CF(3)) were synthesized to explore the generality of hydrogenolysis reactions of palladium-oxygen bonds. Hydrogenolysis of the Pd hydroxide complex to generate the Pd hydride complex and water was shown to be inhibited by formation of a water-bridged, hydrogen-bonded Pd(II) hydroxide dimer. The Pd alkoxide and aryloxide complexes exhibited more diverse reactivity. Depending on the characteristics of the -OR ligand (steric bulk, electron-donating ability, and/or the presence of ß-hydrogen atoms), hydrogenolysis was complicated by hydrolysis by adventitious water, a lack of reactivity with hydrogen, or a competing dissociative ß-hydride abstraction reaction pathway. Full selectivity for hydrogenolysis was observed with the partially fluorinated Pd(II) 2-fluoroethoxide complex. The wide range of Pd-OR substrates examined helps to clarify the variety of reaction pathways available to late-transition-metal alkoxides as well as the conditions necessary to tune the reactivity to hydrogenolysis, hydrolysis, or dissociative ß-hydride abstraction.

Unsymmetrical (R)PNP(R') pincer ligands and their group 10 complexes.

Two new unsymmetrical (R)PNP(R')-type pincer ligands based on a bis(tolyl)amine framework have been synthesized and characterized by a variety of techniques, including X-ray crystallography. These ligands have been coordinated to Ni, Pd, and Pt precursors to provide a number of well-characterized group 10 halides. Conversion of these metal halides to metal hydrides was accomplished using borohydride reagents, or by direct interaction of the ligand with the zerovalent metal precursor. The insertion of oxygen into these hydrides in an attempt to prepare metal hydroperoxides has been examined; however, we were unable to obtain stable and isolable hydroperoxide species.

A unique three-dimensional coordination cluster based on a silver carbene complex.

In an attempt to perform a simple anion-exchange reaction on a pincer-carbene-ligated nickel complex using AgNO(3), we instead obtained an unexpected three-dimensional (3D) Ag(7) cluster containing a [Ag(6)] core in a twisted-bowtie geometry. The reverse-transmetalation reaction by which the carbene is transferred from nickel to silver is virtually unprecedented. The CNC pincer-carbene ligands exhibit unusual bridging modes of ligand bonding for all three donor atoms. Another unique feature is that the final structure exhibits a 3D structure brought about by the connection of two-dimensional layers of the [Ag(6)] core via a seventh Ag ion.

Reactivity of bis(2,2,5,5-tetramethyl-2,5-disila-1-azacyclopent-1-yl)tin with CO(2), OCS, and CS(2) and comparison to that of bis[bis(trimethylsilyl)amido]tin.

The heterocumulenes carbon dioxide (CO(2)), carbonyl sulfide (OCS), and carbon disulfide (CS(2)) were treated with bis(2,2,5,5-tetramethyl-2,5-disila-1-azacyclopent-1-yl)tin {[(CH(2))Me(2)Si](2)N}(2)Sn, an analogue of the well-studied bis[bis(trimethylsilyl)amido]tin species [(Me(3)Si)(2)N](2)Sn, to yield an unexpectedly diverse product slate. Reaction of {[(CH(2))Me(2)Si](2)N}(2)Sn with CO(2) resulted in the formation of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane, along with Sn(4)(µ(4)-O){µ(2)-O(2)CN[SiMe(2)(CH(2))(2)]}(4)(µ(2)-N═C═O)(2) as the primary organometallic Sn-containing product. The reaction of {[(CH(2))Me(2)Si](2)N}(2)Sn with CS(2) led to formal reduction of CS(2) to [CS(2)](2-), yielding [{[(CH(2))Me(2)Si](2)N}(2)Sn](2)CS(2){[(CH(2))Me(2)Si](2)N}(2)Sn, in which the [CS(2)](2-) is coordinated through C and S to two tin centers. The product [{[(CH(2))Me(2)Si](2)N}(2)Sn](2)CS(2){[(CH(2))Me(2)Si](2)N}(2)Sn also contains a novel 4-membered Sn-Sn-C-S ring, and exhibits a further bonding interaction through sulfur to a third Sn atom. Reaction of OCS with {[(CH(2))Me(2)Si](2)N}(2)Sn resulted in an insoluble polymeric material. In a comparison reaction, [(Me(3)Si)(2)N](2)Sn was treated with OCS to yield Sn(4)(µ(4)-O)(µ(2)-OSiMe(3))(5)(η(1)-N═C═S). A combination of NMR and IR spectroscopy, mass spectrometry, and single crystal X-ray diffraction were used to characterize the products of each reaction. The oxygen atoms in the final products come from the facile cleavage of either CO(2) or OCS, depending on the reacting carbon dichalogenide.