Selective Three-Component Coupling for CO₂ Chemical Fixation to Boron Guanidinato Compounds

A selective three-component coupling was employed to fix carbon dioxide to boron guanidinato compounds. The one-pot reaction of carbon dioxide, carbodiimides, and borylamines (ArNH)­BC₈H₁₄ afforded the corresponding 1,2-adducts {R­(H)­N}­C­{N­(Ar)}­(NR)­(CO₂)­BC₈H₁₄. Alternatively, the reaction with <i>p</i>-MeOC₆H₄NC or 2,6-Me₂C₆H₃NC gave the corresponding isocyanide 1,1-adducts {<i>i</i>-PrHN}­C­{N­(p-Me-C₆H₄)}­(N<i>i</i>-Pr)­{CNAr}­BC₈H₁₄. The molecular structures of products (2,6-<i>i</i>-Pr₂C₆H₃NH)­BC₈H₁₄ <b>7</b>, {<i>i</i>-Pr­(H)­N}­C­{N­(p-MeC₆H₄)}­(N<i>i</i>-Pr)­(CO₂)­BC₈H₁₄ <b>9</b>, {Cy­(H)­N}­C­{N­(<i>p</i>-MeC₆H₄)}­(Cy)­(CO₂)­BC₈H₁₄ <b>13</b>, and {<i>i</i>-PrHN}­C­{N­(<i>p</i>-MeC₆H₄)}­(N<i>i</i>-Pr)­{CNR″}­BC₈H₁₄ (R″ = <i>p</i>-MeOC₆H₄, 2,6-Me₂C₆H₃) <b>14</b> and <b>15</b> were established by X-ray diffraction. Density functional theory calculations at the M05-2X level of theory revealed that CO₂ fixation and formation of the corresponding adduct is exothermic and proceeds via a nonchelate boron guanidinato intermediate

Selective Three-Component Coupling for CO₂ Chemical Fixation to Boron Guanidinato Compounds

A selective three-component coupling was employed to fix carbon dioxide to boron guanidinato compounds. The one-pot reaction of carbon dioxide, carbodiimides, and borylamines (ArNH)­BC₈H₁₄ afforded the corresponding 1,2-adducts {R­(H)­N}­C­{N­(Ar)}­(NR)­(CO₂)­BC₈H₁₄. Alternatively, the reaction with <i>p</i>-MeOC₆H₄NC or 2,6-Me₂C₆H₃NC gave the corresponding isocyanide 1,1-adducts {<i>i</i>-PrHN}­C­{N­(p-Me-C₆H₄)}­(N<i>i</i>-Pr)­{CNAr}­BC₈H₁₄. The molecular structures of products (2,6-<i>i</i>-Pr₂C₆H₃NH)­BC₈H₁₄ <b>7</b>, {<i>i</i>-Pr­(H)­N}­C­{N­(p-MeC₆H₄)}­(N<i>i</i>-Pr)­(CO₂)­BC₈H₁₄ <b>9</b>, {Cy­(H)­N}­C­{N­(<i>p</i>-MeC₆H₄)}­(Cy)­(CO₂)­BC₈H₁₄ <b>13</b>, and {<i>i</i>-PrHN}­C­{N­(<i>p</i>-MeC₆H₄)}­(N<i>i</i>-Pr)­{CNR″}­BC₈H₁₄ (R″ = <i>p</i>-MeOC₆H₄, 2,6-Me₂C₆H₃) <b>14</b> and <b>15</b> were established by X-ray diffraction. Density functional theory calculations at the M05-2X level of theory revealed that CO₂ fixation and formation of the corresponding adduct is exothermic and proceeds via a nonchelate boron guanidinato intermediate

Migratory Insertion Reactions in Asymmetrical Guanidinate-Supported Zirconium Complexes

The new diguanidinate-supported dibenzylzirconium complexes [Zr­{κ²<i>N</i>,<i>N</i>′-(N-<i>i</i>-Pr)­(NAr)­CNH­(<i>i</i>-Pr)}₂(CH₂Ph)₂] (Ar = 4-<i>t</i>-BuC₆H₄ (<b>1</b>), 4-BrC₆H₄ (<b>2</b>)) and [Zr­{κ²<i>N</i>,<i>N</i>′-(NEt)­(N-<i>t</i>-Bu)­CNMe₂}₂(CH₂Ph)₂] (<b>3</b>) have been prepared. Complexes <b>1</b> and <b>2</b> were synthesized by protonolysis of [Zr­(CH₂Ph)₄] with the guanidine derivatives and complex <b>3</b> by treating [Zr­{κ²<i>N</i>,<i>N</i>′-(NEt)­(N-<i>t</i>-Bu)­CNMe₂}₂Cl₂] (<b>4</b>) with MgCl­(CH₂Ph). The treatment of <b>1</b>–<b>3</b> with 2,6-dimethylphenyl isocyanide (XyNC) results in migratory insertion and formation of the terminal imido species [Zr­{κ²<i>N</i>,<i>N</i>′-(N-<i>i</i>-Pr)­(N­(Ar))­CNH­(<i>i</i>-Pr)}₂{N­(2,6-Me₂C₆H₃)}] (Ar = 4-<i>t</i>-BuC₆H₄ (<b>7</b>), 4-BrC₆H₄ (<b>8</b>)) with <b>1</b> and <b>2</b>, respectively, whereas the analogous reaction with <b>3</b> leads to the enediamido complex [Zr­{κ²<i>N</i>,<i>N</i>′-(NEt)­(N-<i>t</i>Bu)­CNMe₂)}₂{N­(2,6-Me₂C₆H₃)­(CH₂Ph)­CC­(CH₂Ph)­N­(2,6-Me₂C₆H₃)}] (<b>9</b>). All the intermediate iminoacyl complexes have been characterized, and the molecular structures of <b>2</b>, <b>4</b>, and <b>9</b> have been determined by single-crystal X-ray diffraction

New Alkylimido Niobium Complexes Supported by Guanidinate Ligands: Synthesis, Characterization, and Migratory Insertion Reactions

A series of guanidine proligands, 2-(4-(<i>tert</i>-butyl)­phenyl)-1,3-diisopropylguanidine (<b>1</b>), 2-(4-bromophenyl)-1,3-diisopropylguanidine (<b>2</b>), 2-(4-methoxyphenyl)-1,3-diisopropylguanidine (<b>3</b>), and 2,2′-(1,4-phenylene)­bis­(2′,3-diisopropylguanidine) (<b>4</b>), has been reacted with [NbBz₃(N^tBu)] (<b>5</b>) through a protonolysis reaction to obtain new monoguanidinate-supported dibenzyl niobium complexes, {NbBz₂(N^tBu)­[(4-^tBuC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>6</b>), {NbBz₂(N^tBu)­[(4-BrC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>7</b>), {NbBz₂(N^tBu)­[(4-MeOC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>8</b>), and the dinuclear complex {[NbBz₂(N^tBu)]₂[(C₆H₄)­(NC­(NⁱPr)­(NHⁱPr))₂]} (<b>9</b>). Complexes <b>6</b>, <b>8</b>, and <b>9</b> were structurally characterized. These neutral complexes contain a η²-benzyl ligand coordinated to the metal center. Insertion migratory reactions with isocyanides resulted in the formation of bis-κ²-iminoacyl species, {Nb­(N^tBu)­(^tBuNCCH₂Ph)₂[(4-^tBuC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>10</b>), {NbBz₂(N^tBu) (^tBuNCCH₂Ph)₂[(4-BrC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>11</b>), {Nb­(N^tBu)­(^tBuNCCH₂Ph)₂[(4-MeOC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>12</b>), and the dinuclear complex {[Nb­(N^tBu)­(^tBuNCCH₂Ph)₂]₂[(C₆H₄)­(NC­(NⁱPr)­(NHⁱPr))₂]} (<b>13</b>), when ^tBuNC was used. The analogous reaction using XyNC (Xy = 2,6-Me₂C₆H₃) led to the formation of vinylamido species, {Nb­(N^tBu)­[N­(2,6-Me₂C₆H₃)­CHCHPh]­[BzCN­(2,6-Me₂C₆H₃)]­[(4-^tBuC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>14</b>), {Nb­(N^tBu)­[N­(2,6-Me₂C₆H₃)­CHCHPh]­[BzCN­(2,6-Me₂C₆H₃)]­[(4-BrC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>15</b>), {Nb­(N^tBu)­[N­(2,6-Me₂C₆H₃)­CHCHPh]­[BzCN­(2,6-Me₂C₆H₃)]­[(4-MeOC₆H₄)­NC­(NⁱPr)­(NHⁱPr)]} (<b>16</b>), and {[Nb­(N^tBu)­[N­(2,6-Me₂C₆H₃)­CHCHPh]­[BzCN­(2,6-Me₂C₆H₃)]]₂[(C₆H₄)­[NC­(NⁱPr)­(NHⁱPr)]₂]} (<b>17</b>), through a proposed 1,2-hydrogen shift mechanism from an iminoacyl intermediate similar to those obtained from the insertion of ^tBuNC. Complex <b>17</b> was structurally characterized

Reactivity of the Dimer [{RuCl(μ-Cl)(η³:η³‑C₁₀H₁₆)}₂] (C₁₀H₁₆ = 2,7-Dimethylocta-2,6-diene-1,8-diyl) toward Guanidines: Access to Ruthenium(IV) and Ruthenium(II) Guanidinate Complexes

The novel bis­(allyl)­ruthenium­(IV) guanidinate complexes [RuCl­{κ²(<i>N,N</i>′)-C­(NR)­(NⁱPr)-NHⁱPr}­(η³:η³-C₁₀H₁₆)] (C₁₀H₁₆ = 2,7-dimethylocta-2,6-diene-1,8-diyl; R = Ph (<b>3a</b>), 4-C₆H₄F (<b>3b</b>), 4-C₆H₄Cl (<b>3c</b>), 4-C₆H₄Me (<b>3d</b>), 3-C₆H₄Me (<b>3e</b>) 4-C₆H₄^tBu (<b>3f</b>)) have been synthesized by treatment of the dimeric precursor [{RuCl­(μ-Cl)­(η³:η³-C₁₀H₁₆)}₂] (<b>1</b>) with 4 equiv of the corresponding guanidine (ⁱPrHN)₂CNR (<b>2a</b>–<b>f</b>). The easily separable guanidinium chloride salts [(ⁱPrHN)₂C­(NHR)]­[Cl] (<b>4a</b>–<b>f</b>) are also formed in these reactions. Attempts to generate analogous Ru­(IV) guanidinate complexes from (ⁱPrHN)₂CNR (R = 2-C₆H₄Me (<b>2g</b>), 2,4,6-C₆H₂Me₃ (<b>2h</b>), 2,6-C₆H₃ⁱPr₂ (<b>2i</b>)) failed, due probably to the steric hindrance associated with the aryl group in these guanidines. On the other hand, the reaction of the dimer [{RuCl­(μ-Cl)­(η³:η³-C₁₀H₁₆)}₂] (<b>1</b>) with (ⁱPrHN)₂CN-4-C₆H₄CN (<b>2j</b>) led to the selective formation of the mononuclear derivative [RuCl₂(η³:η³-C₁₀H₁₆)­{NC-4-C₆H₄-NC­(NHⁱPr₂)₂}] (<b>5</b>), in which the guanidine coordinates to ruthenium through the pendant nitrile unit. This result contrasts with that obtained by employing the related Ru­(II) dimer [{RuCl­(μ-Cl)­(η⁶-<i>p</i>-cymene)}₂] (<b>6</b>), whose reaction with <b>2j</b> afforded the expected guanidinate complex [RuCl­{κ²(<i>N,N</i>′)-C­(N-4-C₆H₄CN)­(NⁱPr)-NHⁱPr}­(η⁶-<i>p</i>-cymene)] (<b>7</b>). Treatment of <b>7</b> with dimer <b>1</b> yielded the dinuclear Ru­(II)/Ru­(IV) derivative <b>8</b>, via cleavage of the chloride bridges of <b>1</b> by the CN group of <b>7</b>. Reductive elimination of the 2,7-dimethylocta-2,6-diene-1,8-diyl chain in [RuCl­{κ²(<i>N,N</i>′)-C­(NR)­(NⁱPr)-NHⁱPr}­(η³:η³-C₁₀H₁₆)] (<b>3a</b>–<b>f</b>) readily took place in the presence of an excess of 2,6-dimethylphenyl isocyanide, thus allowing the high-yield preparation of the octahedral ruthenium­(II) compounds <i>mer</i>-[RuCl­{κ²(<i>N,N</i>′)-C­(NR)­(NⁱPr)-NHⁱPr}­(CN-2,6-C₆H₃Me₂)₃] (<b>9a</b>–<b>f</b>). The structures of [RuCl­{κ²(<i>N,N</i>′)-C­(N-4-C₆H₄Me)­(NⁱPr)-NHⁱPr}­(η³:η³-C₁₀H₁₆)] (<b>3d</b>), [RuCl­{κ²(<i>N,N</i>′)-C­(N-4-C₆H₄CN)­(NⁱPr)-NHⁱPr}­(η⁶-<i>p</i>-cymene)] (<b>7</b>), and <i>mer</i>-[RuCl­{κ²(<i>N,N</i>′)-C­(N-4-C₆H₄^tBu)­(NⁱPr)-NHⁱPr}­(CN-2,6-C₆H₃Me₂)₃] (<b>9f</b>), as well as those of the guanidinium chloride salts <b>4a</b>–<b>c</b>, were unequivocally confirmed by X-ray diffraction methods. In addition, the catalytic behavior of the guanidinate complexes <b>3a</b>–<b>f</b> and <b>9a</b>–<b>f</b> in the redox isomerization of allylic alcohols was also explored

Ruthenium(II) Arene Complexes with Asymmetrical Guanidinate Ligands: Synthesis, Characterization, and Application in the Base-Free Catalytic Isomerization of Allylic Alcohols

The ruthenium­(II) arene dimer [{RuCl­(μ-Cl)­(η⁶-<i>p</i>-cymene)}₂] readily reacted with 4 equiv of guanidines (ⁱPrHN)₂CNR (R = ⁱPr (<b>1a</b>), 4-C₆H₄^tBu (<b>1b</b>), 4-C₆H₄Br (<b>1c</b>), 2,4,6-C₆H₂Me₃ (<b>1d</b>), 2,6-C₆H₃ⁱPr₂ (<b>1e</b>)) in toluene at room temperature to generate the mononuclear complexes [RuCl­{κ²<i>N</i>,<i>N</i>′-C­(NR)­(NⁱPr)­NHⁱPr}­(η⁶-<i>p</i>-cymene)] (<b>2a</b>–<b>e</b>) and the easily separable guanidinium chloride salts [(ⁱPrHN)₂C­(NHR)]­[Cl] (<b>3a</b>–<b>e</b>). Compounds <b>2a</b>–<b>e</b> and <b>3a</b>–<b>e</b> were fully characterized by elemental analysis and IR and NMR spectroscopy. The structures of [RuCl­{κ²<i>N</i>,<i>N</i>′-C­(NⁱPr)₂NHⁱPr}­(η⁶-<i>p</i>-cymene)] (<b>2a</b>) and [RuCl­{κ²<i>N</i>,<i>N</i>′-C­(N-4-C₆H₄^tBu)­(NⁱPr)­NHⁱPr}­(η⁶-<i>p</i>-cymene)] (<b>2b</b>) were also determined by X-ray diffraction analysis. Regardless of the steric requirements of the aromatic substituents, a nonsymmetric coordination of the guanidinate anions in <b>2b</b>–<b>e</b> was observed, in complete accord with theoretical calculations (DFT) on the corresponding [RuCl­{κ²<i>N</i>,<i>N</i>′-C­(NR)­(NⁱPr)-NHⁱPr}­(η⁶-<i>p</i>-cymene)] and [RuCl­{κ²<i>N</i>,<i>N</i>′-C­(NⁱPr)₂NHR}­(η⁶-<i>p</i>-cymene)] models. Remarkably, complexes <b>2a</b>–<b>e</b> were active catalysts for the redox isomerization of allylic alcohols in the absence of base, which represents the first catalytic application known for ruthenium guanidinate species

Guanidine Substitutions in Naphthyl Systems to Allow a Controlled Excited-State Intermolecular Proton Transfer: Tuning Photophysical Properties in Aqueous Solution

The excited-state intermolecular proton transfer process (ESPT) in aqueous solution is achieved and controlled by the incorporation of guanidine groups in a fluorescent structure. The bisguanidine under investigation exhibits a dual fluorescence emission with a very high Stokes shifts in water, ≈86 (7890) and 210 (14 500) nm (cm^–1), and an excited-stated deprotonation coupled to an intramolecular charge transfer (ICT) process contributes to this emission. The study demonstrates that the emission properties of the different protonation states are strongly dependent on the solvent environment, which also allows luminescence of the molecule to be tuned. The results of this work show the potential utility of guanidine substitution for the stabilization of ESPT–ICT processes in water and allow the subsequent logical design of new stimulus-responsive fluorophores

Catalytically Generated Ferrocene-Containing Guanidines as Efficient Precursors for New Redox-Active Heterometallic Platinum(II) Complexes with Anticancer Activity

The potential of structurally new ferrocene-functionalized guanidines as redox-active precursors for the synthesis of heterometallic platinum­(II)–guanidine complexes with anticancer activity was studied. To this end, an atom-economical catalytic approach was followed by using ZnEt₂ to catalyze the addition of aminoferrocene and 4-ferrocenylaniline to <i>N</i>,<i>N</i>′-diisopropylcarbodiimide. Furthermore, reaction of a platinum­(II) source with the newly obtained guanidines Fc–NC­(NHⁱPr)₂ (<b>3</b>) and Fc­(1,4-C₆H₄)–NC­(NHⁱPr)₂ (<b>4</b>) provided access to the heterometallic complexes [PtCl₂{Fc–NC­(NHⁱPr)₂}­(DMSO)] (<b>5</b>), [PtCl₂{Fc­(1,4-C₆H₄)–NC­(NHⁱPr)₂}­(DMSO)] (<b>6</b>), and [PtCl₂{Fc­(1,4-C₆H₄)–NC­(NHⁱPr)₂}₂] (<b>7</b>). Electrochemical studies evidence the remarkable electronic effect played by the direct attachment of the guanidine group to the ferrocene moiety in <b>3</b>, making its one-electron oxidation extremely easy. Guanidine-based Fe–Pt complexes <b>5</b> and <b>6</b> are active against all human cancer cell lines tested, with GI₅₀ values in the range 1.4–2.6 μM, and are more cytotoxic than cisplatin in the resistant T-47D and WiDr cell lines