Metal-Templated Hydrogen Bond Donors as “Organocatalysts” for Carbon–Carbon Bond Forming Reactions: Syntheses, Structures, and Reactivities of 2‑Guanidinobenzimidazole Cyclopentadienyl Ruthenium Complexes

The reaction of 2-guanidinobenzimidazole (GBI) and (η⁵-C₅H₅)­Ru­(PPh₃)₂(Cl) in refluxing toluene gives the chelate [(η⁵-C₅H₅)­Ru­(PPh₃)­(GBI)]⁺Cl^– (<b>1</b>⁺Cl^–; 96%). Subsequent anion metatheses yield the BF₄^–, PF₆^–, and BAr_f^– (B­(3,5-C₆H₃(CF₃)₂)₄^–) salts (77–85%). Reactions with CO give the carbonyl complexes [(η⁵-C₅H₅)­Ru­(CO)­(GBI)]⁺X^– (<b>2</b>⁺X^–; X^– = Cl^–, BF₄^–, PF₆^–, BAr_f^–; 87–92%). The last three salts can also be obtained by anion metatheses of <b>2</b>⁺Cl^– (77–87%), as can one with the chiral enantiopure anion P­(<i>o</i>-C₆Cl₄O₂)₃^– ((Δ)-TRISPHAT^–; 81%). The reaction of [(η⁵-C₅H₅)­Ru­(CO)­(NCCH₃)₂]⁺PF₆^– and GBI also gives <b>2</b>⁺PF₆^– (81%). The pentamethylcyclopentadienyl analogues [(η⁵-C₅Me₅)­Ru­(CO)­(GBI)]⁺X^– (<b>3</b>⁺X^–; X^– = Cl^–, BF₄^–, PF₆^–, BAr_f^–; 61–84%) are prepared from (η⁵-C₅Me₅)­Ru­(PPh₃)₂(Cl), GBI, and CO followed (for the last three) by anion metatheses. An indenyl complex [(η⁵-C₉H₇)­Ru­(PPh₃)­(GBI)]⁺Cl^– (96%) is prepared from (η⁵-C₉H₇)­Ru­(PPh₃)₂(Cl) and GBI. All complexes are characterized by NMR (¹H, ¹³C, ³¹P, ¹⁹F, ¹¹B), with 2D spectra aiding assignments. Crystal structures of <b>1</b>⁺PF₆^–·CH₂Cl₂ and <b>1</b>⁺BAr_f^–·CH₂Cl₂ are determined; the anion is hydrogen bonded to the cation in the former. Complexes <b>1</b>–<b>3</b>⁺X^– are evaluated as catalysts (10 mol %, RT) for condensations of indoles and <i>trans</i>-β-nitrostyrene. The chloride salts are ineffective (0–5% yields, 48–60 h), but the BAr_f^– salts exhibit excellent reactivities (97–46% yields, 1–48 h), with the BF₄^– and PF₆^– salts intermediate. Evidence for hydrogen bonding of the nitro group to the GBI ligand is presented. GBI shows no catalytic activity; a BAr_f^– salt of methylated GBI is active, but much less so than <b>2</b>–<b>3</b>⁺BAr_f^–

Octahedral Gyroscope-like Molecules Consisting of Rhenium Rotators within Cage-like Dibridgehead Diphosphine Stators: Syntheses, Substitution Reactions, Structures, and Dynamic Properties

Reactions of Re­(CO)₅(X) (X = Cl, Br) or [Re₂(CO)₄(NO)₂(μ-Cl)₂(Cl)₂] and the phosphines P­((CH₂)_<i>m</i>CHCH₂)₃ (<i>m</i> = 6, <b>a</b>; 7, <b>b</b>; 8, <b>c</b>) give <i>mer,trans</i>-Re­(CO)₃(X)­(P­((CH₂)_<i>m</i>CHCH₂)₃)₂ (53–95%) or <i>cis,trans</i>-Re­(CO) (NO) (Cl)₂(P­((CH₂)₆CHCH₂)₃)₂ (57%), respectively. Additions of Grubbs’ catalyst (5–10 mol %, 0.0010–0.0012 M) and subsequent hydrogenations (PtO₂, ≤5 bar) yield the gyroscope-like complexes <i>mer,trans</i>-Re­(CO)₃(X)­(P­((CH₂)_<i>n</i>)₃P) (<i>n</i> = 2<i>m</i> + 2; X = Cl, <b>7a</b>,<b>c</b>; Br, <b>8a</b>,<b>c</b>; 18–61%) or <i>cis,trans</i>-Re­(CO)(NO)(Cl)₂(P­((CH₂)₁₄)₃P) (14%), respectively, and/or the isomers <i>mer,trans</i>-Re­(CO)₃(X)­(P­(CH₂)_<i>n</i>−1CH₂)­((CH₂)_<i>n</i>)­(P­(CH₂)_<i>n</i>−1CH₂) (X = Cl, <b>7′a</b>–<b>c</b>; Br, <b>8′b</b>; 6–27%). The latter are derived from a combination of interligand and intraligand metatheses. Reactions of <b>7a</b> or <b>8a</b> with NaI, Ph₂Zn, or MeLi give <i>mer,trans</i>-Re­(CO)₃(X)­(P­((CH₂)₁₄)₃P) (X = I, <b>11a</b>; Ph, <b>12a</b>; Me, <b>13a</b>; 34–87%). The ¹³C NMR spectra of <b>7a</b>–<b>c</b>, <b>8a</b>–<b>c</b>, <b>11a</b>, and <b>13a</b> show rotation of the Re­(CO)₃(X) moieties to be fast on the NMR time scale at room temperature (and at −90 °C for <b>8a</b>). In contrast, the phenyl group in <b>12a</b> acts as a brake, and two sets of ¹³C NMR signals (2:1) are observed for the methylene chains. The crystal structures of <b>7a</b>, <b>8a</b>, <b>12a</b>, and <b>13a</b> are analyzed with respect to Re­(CO)₃(X) rotation in solution and the solid state

Synthesis and Properties of Arylvinylidene-Bridged Triphenylamines

A series of arylvinylidene-bridged triphenylamines were efficiently synthesized through the thionation/Barton–Kellogg olefination sequence from their corresponding carbonyl precursors. The electrochemical investigations identified these highly distorted scaffolds as fairly strong electron donors capable of several reversible oxidation steps with the first oxidation occurring at a potential comparable to that of ferrocene for the <i>n</i>-hexyl-substituted diphenylvinylidene-bridged compound

Coordination of Terpyridine to Li⁺ in Two Different Ionic Liquids

On the basis of ⁷Li NMR experiments, the complex-formation reaction between Li⁺ and the tridentate N-donor ligand terpyridine was studied in the ionic liquids [emim]­[NTf₂] and [emim]­[ClO₄] as solvents. For both ionic liquids, the NMR data implicate the formation of [Li(terpy)₂]⁺. Density functional theory calculations show that partial coordination of terpyridine involving the coordination of a solvent anion can be excluded. In contrast to the studies in solution, X-ray diffraction measurements led to completely different results. In the case of [emim]­[NTf₂], the polymeric lithium species [Li­(terpy)­(NTf₂)]<i>_n</i> was found to control the stacking of this complex, whereas crystals grown from [emim]­[ClO₄] exhibit the discrete dimeric species [Li­(terpy)­(ClO₄)]₂. However, both structures indicate that each lithium ion is formally coordinated by one terpy molecule and one solvent anion in the solid state, suggesting that charge neutralization and π stacking mainly control the crystallization process

Gyroscope-Like Platinum and Palladium Complexes with Trans-Spanning Bis(pyridine) Ligands

Pyridines with one or two substituents terminating in vinyl groups are prepared. Intramolecular ring-closing metatheses of <i>trans</i>-MCl₂ adducts and hydrogenations supply the title compounds. Williamson ether syntheses using the alcohols HO­(CH₂)_<i>n</i>CHCH₂ (<i>n</i> = 1 (<b>a</b>), 2 (<b>b</b>), 3 (<b>c</b>), 4 (<b>d</b>), 5 (<b>e</b>), 6 (<b>f</b>), 8 (<b>h</b>), 9 (<b>i</b>)) and appropriate halides give the pyridines 2-NC₅H₄(CH₂O­(CH₂)_<i>n</i>CHCH₂) (<b>1a</b>,<b>b</b>), 3-NC₅H₄(CH₂O­(CH₂)_<i>n</i>CHCH₂) (<b>2a</b>–<b>e</b>,<b>h</b>,<b>i</b>), and 2,6-NC₅H₃(CH₂O­(CH₂)_<i>n</i>CHCH₂)₂ (<b>4a</b>–<b>d</b>) in 92–45% yields. Reactions of 3,5-NC₅H₃(COCl)₂ and HO­(CH₂)_<i>n</i>CHCH₂ afford the diesters 3,5-NC₅H₃(COO­(CH₂)_<i>n</i>CHCH₂)₂ (<b>5a</b>–<b>f</b>,<b>h</b>, 90–41%). The reaction of 3,5-NC₅H₃(4-C₆H₄OH)₂, Br­(CH₂)₅CHCH₂, and Cs₂CO₃ yields 3,5-NC₅H₃(4-C₆H₄O­(CH₂)₅CHCH₂)₂ (<b>8</b>; 32%). Reactions of PtCl₂ with <b>1a</b>,<b>b</b>, <b>2a</b>–<b>e</b>,<b>h</b>,<b>i</b>, <b>4a</b>,<b>b</b> (but not <b>4c</b>,<b>d</b>), <b>5a</b>,<b>c</b>–<b>f</b>,<b>h</b>, and <b>8</b> afford the corresponding bis­(pyridine) complexes <i>trans</i>-<b>10a</b>,<b>b</b> (40–12%), <i>trans</i>-<b>12a</b>–<b>e</b>,<b>h</b>,<b>i</b> (84–46%), <i>trans</i>-<b>17a</b>,<b>b</b> (88–22%), <i>trans</i>-<b>19a</b>,<b>c</b>–<b>f</b>,<b>h</b> (94–63%), and <i>trans</i>-<b>22</b> (96%). Selected adducts are treated with Grubbs’ catalyst and then H₂ (Pd/C) to give <i>trans</i>-PtCl₂[2,2′-(NC₅H₄(CH₂O­(CH₂)_2<i>n</i>+2OCH₂)­H₄C₅N)] (<i>trans</i>-<b>11a</b>,<b>b</b>; 79–63%), <i>trans</i>-PtCl₂[3,3′-(NC₅H₄(CH₂O­(CH₂)_2<i>n</i>+2OCH₂)­H₄C₅N)] (<i>trans</i>-<b>13</b>,<b>d</b>,<b>h</b>,<b>i</b>; 93–80%), <i>trans</i>-PtCl₂[2,6,2′,6′-(NC₅H₃(CH₂O­(CH₂)_2<i>n</i>+2OCH₂)₂H₃C₅N)] (<i>trans</i>-<b>18a</b>,<b>b</b>; 22–10%), <i>trans</i>-PtCl₂[3,5,3′,5′-(NC₅H₃(COO­(CH₂)_2<i>n</i>+2OCO)₂H₃C₅N)] (<i>trans-</i><b>20d</b>–<b>f</b>,<b>h</b>; 45–14%), and <i>trans</i>-PtCl₂[3,5,3′,5′-(NC₅H₃(4-C₆H₄O­(CH₂)₁₂O-4-C₆H₄)₂H₃C₅N)] (40%). A previously reported ring-closing metathesis of <i>trans</i>-PdCl₂[2,6-NC₅H₃(CH₂CH₂CHCH₂)₂]₂ is confirmed, and the new hydrogenation product <i>trans</i>-PdCl₂[2,6,2′,6′-(NC₅H₃((CH₂)₆)₂H₃C₅N)] (<i>trans-</i><b>16</b>; 62%) is isolated. Additions of CH₃MgBr to <b>12b</b>,<b>h</b> and <b>13d</b>,<b>h</b> afford the corresponding PtClCH₃ species (94–41%), but analogous reactions fail with 2-substituted pyridine adducts. The reaction of <i>trans</i>-<b>19c</b> with PhCCH and CuI/<i>i</i>-Pr₂NH gives the corresponding PtCl­(CCPh) adduct (18%). The crystal structures of <i>trans</i>-<b>17a</b>, <i>trans</i>-<b>11b</b>, <i>trans</i>-<b>13d</b>, <i>trans</i>-<b>13h</b>·CH₂Cl₂, <i>trans</i>-<b>16</b>, <i>trans</i>-<b>18a</b>,<b>b</b>, and <i>trans</i>-<b>20e</b>·2CHCl₃ are determined. Steric effects in the preceding data, especially involving 2-substituents and the MCl₂ or MCl­(X) rotators, are analyzed in detail

Coordination of Terpyridine to Li⁺ in Two Different Ionic Liquids

On the basis of ⁷Li NMR experiments, the complex-formation reaction between Li⁺ and the tridentate N-donor ligand terpyridine was studied in the ionic liquids [emim]­[NTf₂] and [emim]­[ClO₄] as solvents. For both ionic liquids, the NMR data implicate the formation of [Li(terpy)₂]⁺. Density functional theory calculations show that partial coordination of terpyridine involving the coordination of a solvent anion can be excluded. In contrast to the studies in solution, X-ray diffraction measurements led to completely different results. In the case of [emim]­[NTf₂], the polymeric lithium species [Li­(terpy)­(NTf₂)]<i>_n</i> was found to control the stacking of this complex, whereas crystals grown from [emim]­[ClO₄] exhibit the discrete dimeric species [Li­(terpy)­(ClO₄)]₂. However, both structures indicate that each lithium ion is formally coordinated by one terpy molecule and one solvent anion in the solid state, suggesting that charge neutralization and π stacking mainly control the crystallization process

Partially Shielded Fe(CO)₃ Rotors: Syntheses, Structures, and Dynamic Properties of Complexes with Doubly <i>trans</i> Spanning Diphosphines, <i>trans</i>-Fe(CO)₃(PhP((CH₂)_<i>n</i>)₂PPh)

Reactions of Fe­(CO)₃(η⁴-benzylideneacetone) and PhP­((CH₂)_<i>m</i>CHCH₂)₂ (<i>m</i> = <b>a</b>, 4; <b>b</b>, 5; <b>c</b>, 6) give <i>trans</i>-Fe­(CO)₃(PhP­((CH₂)_<i>m</i>CHCH₂)₂)₂ (<b>2a</b>–<b>c</b>, 28–70%), which are treated with Grubbs’ catalyst (15 mol %; refluxing CH₂Cl₂). NMR analyses of the crude <i>inter</i>ligand metathesis products <i>trans</i>-Fe­(CO)₃(PhP­((CH₂)_<i>m</i>CHCH­(CH₂)_<i>m</i>)₂PPh) (<b>3a</b>–<b>c</b>, 30–31%) suggest <i>Z</i>/<i>E</i> CC mixtures and/or byproducts from <i>intra</i>ligand metathesis or oligomers. Subsequent hydrogenations (5 bar/cat. Rh­(Cl)­(PPh₃)₃ or PtO₂) afford <i>trans</i>-Fe­(CO)₃(PhP­((CH₂)_<i>n</i>)₂PPh) (<b>4a</b>–<b>c</b>, 69–77%; <i>n</i> = 2<i>m</i> + 2, <i>synperiplanar</i> phenyl groups), which density functional theory calculations show to be more stable than isomers derived from other metathesis modes. Crystallizations give (<i>E</i>,<i>E</i>)-<b>3a</b> and <b>4b</b>, the X-ray structures of which are determined and analyzed. Variable-temperature ¹³C­{¹H} NMR experiments show that rotation of the Fe­(CO)₃ moiety in <b>4b</b> is rapid on the NMR time scale (RT to 0 °C; Δ<i>G</i>^⧧_273 K ≤ 12.8 kcal/mol), but that in <b>4a</b> is not (RT to 105 °C; Δ<i>G</i>^⧧_378 K ≥ 17.9 kcal/mol). These data indicate rotational barriers lower than those in analogues in which three methylene chains connect the phosphorus atoms, <i>trans</i>-Fe­(CO)₃(P­((CH₂)_<i>n</i>)₃P)

Polyyne Rotaxanes: Stabilization by Encapsulation

Active metal template Glaser coupling has been used to synthesize a series of rotaxanes consisting of a polyyne, with up to 24 contiguous <i>sp-</i>hybridized carbon atoms, threaded through a variety of macrocycles. Cadiot–Chodkiewicz cross-coupling affords higher yields of rotaxanes than homocoupling. This methodology has been used to prepare [3]­rotaxanes with two polyyne chains locked through the same macrocycle. The crystal structure of one of these [3]­rotaxanes shows that there is extremely close contact between the central carbon atoms of the threaded hexayne chains (C···C distance 3.29 Å vs 3.4 Å for the sum of van der Waals radii) and that the bond-length-alternation is perturbed in the vicinity of this contact. However, despite the close interaction between the hexayne chains, the [3]­rotaxane is remarkably stable under ambient conditions, probably because the two polyynes adopt a crossed geometry. In the solid state, the angle between the two polyyne chains is 74°, and this crossed geometry appears to be dictated by the bulk of the “supertrityl” end groups. Several rotaxanes have been synthesized to explore gem-dibromoethene moieties as “masked” polyynes. However, the reductive Fritsch–Buttenberg–Wiechell rearrangement to form the desired polyyne rotaxanes has not yet been achieved. X-ray crystallographic analysis on six [2]­rotaxanes and two [3]­rotaxanes provides insight into the noncovalent interactions in these systems. Differential scanning calorimetry (DSC) reveals that the longer polyyne rotaxanes (C16, C18, and C24) decompose at higher temperatures than the corresponding unthreaded polyyne axles. The stability enhancement increases as the polyyne becomes longer, reaching 60 °C in the C24 rotaxane

Gyroscope-Like Complexes Based on Dibridgehead Diphosphine Cages That Are Accessed by Three-Fold Intramolecular Ring Closing Metatheses and Encase Fe(CO)₃, Fe(CO)₂(NO)⁺, and Fe(CO)₃(H)⁺ Rotators

Reactions of <i>trans</i>-Fe­(CO)₃(P­((CH₂)_<i>m</i>CHCH₂)₃)₂ (<i>m</i> = <b>a</b>/4; <b>b</b>/5, <b>c</b>/6, <b>e</b>/8) and Grubbs’ catalyst (12–24 mol %, CH₂Cl₂, reflux) give the cage-like trienes <i>trans</i>-Fe­(CO)₃(P­((CH₂)_<i>m</i>CHCH­(CH₂)_<i>m</i>)₃P) (<b>3a</b>–<b>c</b>,<b>e</b>, 60–81%). Hydrogenations (ClRh­(PPh₃)₃, 60–80 °C) yield the title compounds <i>trans</i>-Fe­(CO)₃(P­((CH₂)_<i>n</i>)₃P) (<b>4a</b>–<b>c</b>,<b>e</b>, 74–86%; <i>n</i> = 2<i>m</i> + 2), which have idealized <i>D</i>_3<i>h</i> symmetry. A crystal structure of <b>4c</b> suggests enough van der Waals clearance for the Fe­(CO)₃ moiety to rotate within the three P­(CH₂)₁₄P linkages; structures of <i>E</i>,<i>E</i>,<i>E</i>-<b>3a</b> show rotation to be blocked by the shorter P­(CH₂)₄CHCH­(CH₂)₄P linkages. Additions of NO⁺BF₄^– give the isoelectronic and isosteric cations [Fe­(CO)₂(NO)­(P­((CH₂)_<i>n</i>)₃P)]⁺BF₄^– (<b>5a</b>–<b>c</b>⁺BF₄^–; 81–98%). Additions of [H­(OEt₂)₂]⁺BAr_f^– (BAr_f = B­(3,5-C₆H₃(CF₃)₂)₄) afford the metal hydride complexes <i>mer</i>,<i>trans</i>-[Fe­(CO)₃(H)­(P­((CH₂)_<i>n</i>)₃P)]⁺BAr_f^– (<b>6a</b>–<b>c</b>,<b>e</b>⁺BAr_f^–; 98–99%). The behavior of the rotators in the preceding complexes is probed by VT NMR. At ambient temperature in solution, <b>5a</b>,<b>b</b>⁺BF₄^– and <b>6a</b>⁺BAr_f^– show two sets of P­(CH₂)_<i>n</i>/2 ¹³C NMR signals (2:1), whereas <b>5c</b>⁺BF₄^– and <b>6b</b>,<b>c</b>⁺BAr_f^– show only one. At higher temperatures, the signals of <b>5b</b>⁺BF₄^– coalesce; at lower temperatures, those of <b>5c</b>⁺BF₄^– and <b>6b</b>⁺BAr_f^– decoalesce. These data give Δ<i>H</i>^⧧/Δ<i>S</i>^⧧ values (kcal/mol and eu) of 8.3/–28.4 and 9.5/–6.5 for Fe­(CO)₂(NO)⁺ rotation (<b>5b</b>,<b>c</b>⁺) and 6.1/–23.5 for Fe­(CO)₃(H)⁺ rotation (<b>6b</b>⁺). ¹³C CP/MAS NMR spectra show that the Fe­(CO)₃ moiety in polycrystalline <b>4c</b> (but not <b>4a</b>) undergoes rapid rotation between −60 and 95 °C. Approaches to minimizing these barriers and developing molecular gyroscopes are discussed

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