Multinuclear Copper(I) Guanidinate Complexes

A series of multinuclear Copper­(I) guanidinate complexes have been synthesized in a succession of reactions between CuCl and the lithium guanidinate systems Li­{<b>L</b>} (<b>L</b> = Me₂NC­(^<i>i</i>PrN)₂ (<b>1a</b>), Me₂NC­(CyN)₂ (<b>1b</b>), Me₂NC­(^<i>t</i>BuN)₂ (<b>1c</b>), and Me₂NC­(DipN)₂ (<b>2d</b>) (^<i>i</i>Pr = iso-propyl, Cy = cyclohexyl, ^<i>t</i>Bu = <i>tert</i>-butyl, and Dip = 2,6-<i>di</i>sopropylphenyl) made in situ, and structurally characterized. The <i>di</i>-copper guanidinates systems with the general formula [Cu₂{<b>L</b>}₂] (<b>L</b> = {Me₂NC­(^<i>i</i>PrN)₂} (<b>2a</b>), {Me₂NC­(CyN)₂} (<b>2b</b>), and {Me₂NC­(DipN)₂} (<b>2d</b>) differed significantly from related amidinate complexes because of a large torsion of the dimer ring, which in turn is a result of transannular repulsion between adjacent guanidinate substituents. Attempts to synthesis the <i>tert</i>-butyl derivative [Cu₂{Me₂NC­(^<i>t</i>BuN)₂}₂] result in the separate formation and isolation of the <i>tri</i>-copper complexes [Cu₃{Me₂NC­(^<i>t</i>BuN)₂}₂(μ-NMe₂)] (<b>3c</b>) and [Cu₃{Me₂NC­(^<i>t</i>BuN)₂}₂(μ-Cl)] (<b>4c</b>), both of which have been unambiguously characterized by single crystal X-ray diffraction. Closer inspection of the solution state behavior of the lithium salt <b>1c</b> reveals a previously unobserved equilibrium between <b>1c</b> and its starting materials, LiNMe₂ and <i>N,N</i>′-di-<i>tert</i>-butyl-carbodiimide, for which activation enthalpy and entropy values of Δ<i>H</i>^⧧ = 48.2 ± 18 kJ mol^–1 and Δ<i>S</i>^⧧ = 70.6 ± 6 J/K mol have been calculated using 1D-EXSY NMR spectroscopy to establish temperature dependent rates of exchange between the species in solution. The molecular structures of the lithium complexes <b>1c</b> and <b>1d</b> have also been determined and shown to form tetrameric and dimeric complexes respectively held together by Li–N and agostic Li···H–C interactions. The thermal chemistry of the copper complexes have also been assessed by thermogravimetric analysis

Multinuclear Copper(I) Guanidinate Complexes

A series of multinuclear Copper­(I) guanidinate complexes have been synthesized in a succession of reactions between CuCl and the lithium guanidinate systems Li­{<b>L</b>} (<b>L</b> = Me₂NC­(^<i>i</i>PrN)₂ (<b>1a</b>), Me₂NC­(CyN)₂ (<b>1b</b>), Me₂NC­(^<i>t</i>BuN)₂ (<b>1c</b>), and Me₂NC­(DipN)₂ (<b>2d</b>) (^<i>i</i>Pr = iso-propyl, Cy = cyclohexyl, ^<i>t</i>Bu = <i>tert</i>-butyl, and Dip = 2,6-<i>di</i>sopropylphenyl) made in situ, and structurally characterized. The <i>di</i>-copper guanidinates systems with the general formula [Cu₂{<b>L</b>}₂] (<b>L</b> = {Me₂NC­(^<i>i</i>PrN)₂} (<b>2a</b>), {Me₂NC­(CyN)₂} (<b>2b</b>), and {Me₂NC­(DipN)₂} (<b>2d</b>) differed significantly from related amidinate complexes because of a large torsion of the dimer ring, which in turn is a result of transannular repulsion between adjacent guanidinate substituents. Attempts to synthesis the <i>tert</i>-butyl derivative [Cu₂{Me₂NC­(^<i>t</i>BuN)₂}₂] result in the separate formation and isolation of the <i>tri</i>-copper complexes [Cu₃{Me₂NC­(^<i>t</i>BuN)₂}₂(μ-NMe₂)] (<b>3c</b>) and [Cu₃{Me₂NC­(^<i>t</i>BuN)₂}₂(μ-Cl)] (<b>4c</b>), both of which have been unambiguously characterized by single crystal X-ray diffraction. Closer inspection of the solution state behavior of the lithium salt <b>1c</b> reveals a previously unobserved equilibrium between <b>1c</b> and its starting materials, LiNMe₂ and <i>N,N</i>′-di-<i>tert</i>-butyl-carbodiimide, for which activation enthalpy and entropy values of Δ<i>H</i>^⧧ = 48.2 ± 18 kJ mol^–1 and Δ<i>S</i>^⧧ = 70.6 ± 6 J/K mol have been calculated using 1D-EXSY NMR spectroscopy to establish temperature dependent rates of exchange between the species in solution. The molecular structures of the lithium complexes <b>1c</b> and <b>1d</b> have also been determined and shown to form tetrameric and dimeric complexes respectively held together by Li–N and agostic Li···H–C interactions. The thermal chemistry of the copper complexes have also been assessed by thermogravimetric analysis

Long-Range Intramolecular Electronic Communication in Bis(ferrocenylethynyl) Complexes Incorporating Conjugated Heterocyclic Spacers: Synthesis, Crystallography, and Electrochemistry

A new series of bis­(ferrocenylethynyl) complexes, <b>3</b>–<b>7</b>, and a mono­(ferrocenylethynyl) complex, <b>8</b>, have been synthesized incorporating conjugated heterocyclic spacer groups, with the ethynyl group facilitating an effective long-range intramolecular interaction. The complexes were characterized by NMR, IR, and UV–vis spectroscopy as well as X-ray crystallography. The redox properties of these complexes were investigated using cyclic voltammetry and spectroelectrochemistry. Although there is a large separation of ∼14 Å between the two redox centers, Δ<i>E</i>_1/2 values in this series of complexes ranged from 50 to 110 mV. The appearance of intervalance charge-transfer bands in the UV–vis–near-IR region for the monocationic complexes further confirmed effective intramolecular electronic communication. Computational studies are presented that show the degree of delocalization across the Fc–CC–CC–Fc (Fc = C₅H₅FeC₅H₄) highest occupied molecular orbital