Synthesis and Structures of Cuprous Triptycylthiolate Complexes

A synthesis of 1-(thioacetyl)­triptycene (<b>5</b>), a convenient protected form of 1-(thiolato)­triptycene [STrip]⁻, is described, a key transformation being the high yield conversion of <i>tert</i>-butyl 1-triptycenyl sulfide (<b>8</b>) to <b>5</b> by a protocol employing BBr₃/AcCl. Syntheses of the two-coordinate copper­(I) compounds [Bu₄N]­[Cu­(STrip)₂], [Bu₄N]<b>10</b>, and [(Cu­(IMes)­(STrip)] (<b>13</b>) proceed readily by chloride displacement from CuCl and [Cu­(IMes)­Cl], respectively. Reaction of <b>10</b> with Ph₃SiSH or Me₃SiI produces the heteroleptic species [Cu­(STrip)­(SSiPh₃)]⁻ (<b>11</b>) and [Cu­(STrip)­I]⁻ (<b>12)</b>, detected by mass spectrometry, in mixture with the homoleptic bis­(thiolate) anions. Structural identification by X-ray crystallography of the ligand precursor molecules 9-(thioacetyl)­anthracene (<b>4</b>, triclinic and orthorhombic polymorphs), <i>tert</i>-butyl 9-anthracenyl sulfide (<b>7</b>), <b>5</b>, and <i>tert</i>-butyl 1-triptycenyl sulfide (<b>8</b>) are presented. Crystallographic characterization of bis­(9-anthracenyl)­sulfide (<b>3</b>), which features a C–S–C angle of 104.0° and twist angle of 54.8° between anthracenyl planes, is also given. A crystal structure of [Bu₄N]­[(STrip)], [Bu₄N]<b>9</b>, provides an experimental measure of 144.6° for the ligand cone angle. The crystal structures of [Bu₄N]<b>10</b> and <b>13</b> are reported, the former of which reveals an unexpectedly small C–S···S–C torsion angle of ∼41° (average of two values), which confers a near “cis” disposition of the triptycenyl groups with respect the S–Cu–S axis. This conformation is governed by interligand π···π and CH···π interactions. A crystal structure of an adventitious product, [Bu₄N]­[(Cu-STrip)₆(μ₆-Br)]·[Bu₄N]­[PF₆], [Bu₄N]<b>14</b>·[Bu₄N]­[PF₆] is described, which reveals a cyclic hexameric structure previously unobserved in cuprous thiolate chemistry. The Cu₆S₆ ring displays a centrosymmetric cyclohexane chair type conformation with a Br^– ion residing at the inversion center and held in place by apparent soft–soft interactions with the Cu­(I) ions

Synthesis and Structures of Cuprous Triptycylthiolate Complexes

A synthesis of 1-(thioacetyl)­triptycene (<b>5</b>), a convenient protected form of 1-(thiolato)­triptycene [STrip]⁻, is described, a key transformation being the high yield conversion of <i>tert</i>-butyl 1-triptycenyl sulfide (<b>8</b>) to <b>5</b> by a protocol employing BBr₃/AcCl. Syntheses of the two-coordinate copper­(I) compounds [Bu₄N]­[Cu­(STrip)₂], [Bu₄N]<b>10</b>, and [(Cu­(IMes)­(STrip)] (<b>13</b>) proceed readily by chloride displacement from CuCl and [Cu­(IMes)­Cl], respectively. Reaction of <b>10</b> with Ph₃SiSH or Me₃SiI produces the heteroleptic species [Cu­(STrip)­(SSiPh₃)]⁻ (<b>11</b>) and [Cu­(STrip)­I]⁻ (<b>12)</b>, detected by mass spectrometry, in mixture with the homoleptic bis­(thiolate) anions. Structural identification by X-ray crystallography of the ligand precursor molecules 9-(thioacetyl)­anthracene (<b>4</b>, triclinic and orthorhombic polymorphs), <i>tert</i>-butyl 9-anthracenyl sulfide (<b>7</b>), <b>5</b>, and <i>tert</i>-butyl 1-triptycenyl sulfide (<b>8</b>) are presented. Crystallographic characterization of bis­(9-anthracenyl)­sulfide (<b>3</b>), which features a C–S–C angle of 104.0° and twist angle of 54.8° between anthracenyl planes, is also given. A crystal structure of [Bu₄N]­[(STrip)], [Bu₄N]<b>9</b>, provides an experimental measure of 144.6° for the ligand cone angle. The crystal structures of [Bu₄N]<b>10</b> and <b>13</b> are reported, the former of which reveals an unexpectedly small C–S···S–C torsion angle of ∼41° (average of two values), which confers a near “cis” disposition of the triptycenyl groups with respect the S–Cu–S axis. This conformation is governed by interligand π···π and CH···π interactions. A crystal structure of an adventitious product, [Bu₄N]­[(Cu-STrip)₆(μ₆-Br)]·[Bu₄N]­[PF₆], [Bu₄N]<b>14</b>·[Bu₄N]­[PF₆] is described, which reveals a cyclic hexameric structure previously unobserved in cuprous thiolate chemistry. The Cu₆S₆ ring displays a centrosymmetric cyclohexane chair type conformation with a Br^– ion residing at the inversion center and held in place by apparent soft–soft interactions with the Cu­(I) ions

Hairpin Furans and Giant Biaryls

The thermal reaction of two cyclopentadienones with 5,5′-binaphthoquinone or 6,6′-dimethoxy-5,5′-binaphthoquinone in refluxing nitrobenzene (210 °C) gives, in a single synthetic step that includes two Diels–Alder additions, two decarbonylations, and two dehydrogenations, giant biaryl bisquinones (compounds <b>13</b>, <b>14</b>, <b>15</b>, <b>18</b>, and <b>21</b>). However, when two cyclopentadienones react with 6,6′-dimethoxy-5,5′-binaphthoquinone in nitrobenzene at higher temperatures (250–260 °C), the resulting products are molecular ribbons composed of two twisted aromatic systems fused to a heteropentahelicene (<b>19</b>, <b>20</b>, and <b>22</b>). These molecules are representatives of a new class of chiral polycyclic aromatic compounds, the “hairpin furans”. Interestingly, reheating a dimethoxy-substituted giant biaryl (e.g., <b>21</b>) in nitrobenzene at 260 °C does not yield the corresponding hairpin furan (<b>22</b>), and mechanistic studies indicate that some intermediate or byproduct of the synthesis of the giant biaryls is a reagent or catalyst necessary for the conversion of the dimethoxybiaryl to the furan

Hairpin Furans and Giant Biaryls

The thermal reaction of two cyclopentadienones with 5,5′-binaphthoquinone or 6,6′-dimethoxy-5,5′-binaphthoquinone in refluxing nitrobenzene (210 °C) gives, in a single synthetic step that includes two Diels–Alder additions, two decarbonylations, and two dehydrogenations, giant biaryl bisquinones (compounds <b>13</b>, <b>14</b>, <b>15</b>, <b>18</b>, and <b>21</b>). However, when two cyclopentadienones react with 6,6′-dimethoxy-5,5′-binaphthoquinone in nitrobenzene at higher temperatures (250–260 °C), the resulting products are molecular ribbons composed of two twisted aromatic systems fused to a heteropentahelicene (<b>19</b>, <b>20</b>, and <b>22</b>). These molecules are representatives of a new class of chiral polycyclic aromatic compounds, the “hairpin furans”. Interestingly, reheating a dimethoxy-substituted giant biaryl (e.g., <b>21</b>) in nitrobenzene at 260 °C does not yield the corresponding hairpin furan (<b>22</b>), and mechanistic studies indicate that some intermediate or byproduct of the synthesis of the giant biaryls is a reagent or catalyst necessary for the conversion of the dimethoxybiaryl to the furan

Element Misidentification in X‑ray Crystallography: A Reassessment of the [MCl₂(diazadiene)] (M = Cr, Mo, W) Series

A series of reports describing the syntheses and structures of [MCl₂(diazadiene)] (M = Cr, Mo, W) complexes is reassessed in the context of known chemistry of low-valent Group VI metal complexes, crystallographic trends such as M–Cl bond lengths and unit cell volumes, and calculated metal–ligand bond lengths. Crystallographic data and computational results are inconsistent with any of these species being second or third row transition metal complexes. A review of the crystallographic information files accompanying the [MCl₂(diazadiene)] (M = Mo, W) published structures reveals that the metal atoms were inappropriately treated with partial site occupancy factors (0.775 for Mo; 0.4005 and 0.417 for W), the effect of which was to manifest lighter-element behavior and better refinement in accord with the metal atoms’ correct identity. A deliberate synthesis and characterization by X-ray diffraction of [ZnCl₂(^Mesdad^Me)] (^Mesdad^Me = 1,4-bis­(2,4,6-trimethylphenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene) are reported. Refinement of this structure with the same combination of second or third row metal and offsetting partial site occupancy is shown to provide final refinement statistics essentially the same as with the correct model employing M = Zn at site occupancy 1.00. Use of the published method for synthesis of [WCl₂(diazadiene)] with ^Mesdad^Me and [WBr₄(MeCN)₂] in lieu of [WCl₄(MeCN)₂] is shown to produce [ZnBr₂(^Mesdad^Me)], which has also been characterized by X-ray diffraction. It is concluded that the unusual putative 12-electron [MCl₂(diazadiene)] (M = Cr, Mo, W) complexes are in all cases the corresponding [ZnCl₂(diazadiene)] complexes, Zn having been commonly employed as reducing agent in their synthesis

Element Misidentification in X‑ray Crystallography: A Reassessment of the [MCl₂(diazadiene)] (M = Cr, Mo, W) Series

A series of reports describing the syntheses and structures of [MCl₂(diazadiene)] (M = Cr, Mo, W) complexes is reassessed in the context of known chemistry of low-valent Group VI metal complexes, crystallographic trends such as M–Cl bond lengths and unit cell volumes, and calculated metal–ligand bond lengths. Crystallographic data and computational results are inconsistent with any of these species being second or third row transition metal complexes. A review of the crystallographic information files accompanying the [MCl₂(diazadiene)] (M = Mo, W) published structures reveals that the metal atoms were inappropriately treated with partial site occupancy factors (0.775 for Mo; 0.4005 and 0.417 for W), the effect of which was to manifest lighter-element behavior and better refinement in accord with the metal atoms’ correct identity. A deliberate synthesis and characterization by X-ray diffraction of [ZnCl₂(^Mesdad^Me)] (^Mesdad^Me = 1,4-bis­(2,4,6-trimethylphenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene) are reported. Refinement of this structure with the same combination of second or third row metal and offsetting partial site occupancy is shown to provide final refinement statistics essentially the same as with the correct model employing M = Zn at site occupancy 1.00. Use of the published method for synthesis of [WCl₂(diazadiene)] with ^Mesdad^Me and [WBr₄(MeCN)₂] in lieu of [WCl₄(MeCN)₂] is shown to produce [ZnBr₂(^Mesdad^Me)], which has also been characterized by X-ray diffraction. It is concluded that the unusual putative 12-electron [MCl₂(diazadiene)] (M = Cr, Mo, W) complexes are in all cases the corresponding [ZnCl₂(diazadiene)] complexes, Zn having been commonly employed as reducing agent in their synthesis

Redox-Controlled Interconversion between Trigonal Prismatic and Octahedral Geometries in a Monodithiolene Tetracarbonyl Complex of Tungsten

The tetracarbonyl compounds [W­(mdt)­(CO)₄] (<b>1</b>) and [W­(Me₂pipdt)­(CO)₄] (<b>2</b>) both have dithiolene-type ligands (mdt^2– = 1,2-dimethyl-1,2-dithiolate; Me₂pipdt = 1,4-dimethylpiperazine-2,3-dithione) but different geometries, trigonal prismatic (TP) and octahedral, respectively. Structural data suggest an ene-1,2-dithiolate ligand description, hence a divalent tungsten ion, for <b>1</b> and a dithioketone ligand, hence W(0) oxidation state, for <b>2</b>. Density functional theory (DFT) calculations on <b>1</b> show the highest occupied molecular orbital (HOMO) to be a strong W–dithiolene π bonding interaction and the lowest unoccupied molecular orbital (LUMO) its antibonding counterpart. The TP geometry is preferred because symmetry allowed mixing of these orbitals via a configuration interaction (CI) stabilizes this geometry over an octahedron. The TP geometry for <b>2</b> is disfavored because W–dithiolene π overlap is attenuated because of a lowering of the sulfur content and a raising of the energy of this ligand π orbital by the conjugated piperazine nitrogen atoms in the Me₂pipdt ligand. A survey of the Cambridge Structural Database identifies other W­(CO)₄ compounds with pseudo <i>C</i>_4<i>v</i> disposition of CO ligands and suggests a d⁴ electron count to be a probable common denominator. Reduction of <b>1</b> induces a geometry change to octahedral because the singly occupied molecular orbital (SOMO) is at lower energy in this geometry. The cyclic voltammogram of <b>1</b> in CH₂Cl₂ reveals a reduction wave at −1.14 V (vs Fc⁺/Fc) with an unusual offset between the cathodic and the anodic peaks (Δ<i>E</i>_p) of 0.130 V, which is followed by a second, reversible reduction wave at −1.36 V with Δ<i>E</i>_p = 0.091 V. The larger Δ<i>E</i>_p observed for the first reduction is evidence of the trigonal prism-to-octahedron geometry change attending this process. Tungsten L₁-edge X-ray absorption (XAS) data indicate a higher metal oxidation state in <b>1</b> than <b>2</b>. Electron paramagnetic resonance data for [<b>1</b>]⁻ and [<b>2</b>]⁻ are <i>both</i> diagnostic of dithiolene ligand-based sulfur radical, indicating that one-electron reduction of <b>1</b> <i>involves two-electron reduction of tungsten and one-electron oxidation of dithiolene ligand</i>

Redox-Controlled Interconversion between Trigonal Prismatic and Octahedral Geometries in a Monodithiolene Tetracarbonyl Complex of Tungsten

The tetracarbonyl compounds [W­(mdt)­(CO)₄] (<b>1</b>) and [W­(Me₂pipdt)­(CO)₄] (<b>2</b>) both have dithiolene-type ligands (mdt^2– = 1,2-dimethyl-1,2-dithiolate; Me₂pipdt = 1,4-dimethylpiperazine-2,3-dithione) but different geometries, trigonal prismatic (TP) and octahedral, respectively. Structural data suggest an ene-1,2-dithiolate ligand description, hence a divalent tungsten ion, for <b>1</b> and a dithioketone ligand, hence W(0) oxidation state, for <b>2</b>. Density functional theory (DFT) calculations on <b>1</b> show the highest occupied molecular orbital (HOMO) to be a strong W–dithiolene π bonding interaction and the lowest unoccupied molecular orbital (LUMO) its antibonding counterpart. The TP geometry is preferred because symmetry allowed mixing of these orbitals via a configuration interaction (CI) stabilizes this geometry over an octahedron. The TP geometry for <b>2</b> is disfavored because W–dithiolene π overlap is attenuated because of a lowering of the sulfur content and a raising of the energy of this ligand π orbital by the conjugated piperazine nitrogen atoms in the Me₂pipdt ligand. A survey of the Cambridge Structural Database identifies other W­(CO)₄ compounds with pseudo <i>C</i>_4<i>v</i> disposition of CO ligands and suggests a d⁴ electron count to be a probable common denominator. Reduction of <b>1</b> induces a geometry change to octahedral because the singly occupied molecular orbital (SOMO) is at lower energy in this geometry. The cyclic voltammogram of <b>1</b> in CH₂Cl₂ reveals a reduction wave at −1.14 V (vs Fc⁺/Fc) with an unusual offset between the cathodic and the anodic peaks (Δ<i>E</i>_p) of 0.130 V, which is followed by a second, reversible reduction wave at −1.36 V with Δ<i>E</i>_p = 0.091 V. The larger Δ<i>E</i>_p observed for the first reduction is evidence of the trigonal prism-to-octahedron geometry change attending this process. Tungsten L₁-edge X-ray absorption (XAS) data indicate a higher metal oxidation state in <b>1</b> than <b>2</b>. Electron paramagnetic resonance data for [<b>1</b>]⁻ and [<b>2</b>]⁻ are <i>both</i> diagnostic of dithiolene ligand-based sulfur radical, indicating that one-electron reduction of <b>1</b> <i>involves two-electron reduction of tungsten and one-electron oxidation of dithiolene ligand</i>

Redox-Controlled Interconversion between Trigonal Prismatic and Octahedral Geometries in a Monodithiolene Tetracarbonyl Complex of Tungsten

The tetracarbonyl compounds [W­(mdt)­(CO)₄] (<b>1</b>) and [W­(Me₂pipdt)­(CO)₄] (<b>2</b>) both have dithiolene-type ligands (mdt^2– = 1,2-dimethyl-1,2-dithiolate; Me₂pipdt = 1,4-dimethylpiperazine-2,3-dithione) but different geometries, trigonal prismatic (TP) and octahedral, respectively. Structural data suggest an ene-1,2-dithiolate ligand description, hence a divalent tungsten ion, for <b>1</b> and a dithioketone ligand, hence W(0) oxidation state, for <b>2</b>. Density functional theory (DFT) calculations on <b>1</b> show the highest occupied molecular orbital (HOMO) to be a strong W–dithiolene π bonding interaction and the lowest unoccupied molecular orbital (LUMO) its antibonding counterpart. The TP geometry is preferred because symmetry allowed mixing of these orbitals via a configuration interaction (CI) stabilizes this geometry over an octahedron. The TP geometry for <b>2</b> is disfavored because W–dithiolene π overlap is attenuated because of a lowering of the sulfur content and a raising of the energy of this ligand π orbital by the conjugated piperazine nitrogen atoms in the Me₂pipdt ligand. A survey of the Cambridge Structural Database identifies other W­(CO)₄ compounds with pseudo <i>C</i>_4<i>v</i> disposition of CO ligands and suggests a d⁴ electron count to be a probable common denominator. Reduction of <b>1</b> induces a geometry change to octahedral because the singly occupied molecular orbital (SOMO) is at lower energy in this geometry. The cyclic voltammogram of <b>1</b> in CH₂Cl₂ reveals a reduction wave at −1.14 V (vs Fc⁺/Fc) with an unusual offset between the cathodic and the anodic peaks (Δ<i>E</i>_p) of 0.130 V, which is followed by a second, reversible reduction wave at −1.36 V with Δ<i>E</i>_p = 0.091 V. The larger Δ<i>E</i>_p observed for the first reduction is evidence of the trigonal prism-to-octahedron geometry change attending this process. Tungsten L₁-edge X-ray absorption (XAS) data indicate a higher metal oxidation state in <b>1</b> than <b>2</b>. Electron paramagnetic resonance data for [<b>1</b>]⁻ and [<b>2</b>]⁻ are <i>both</i> diagnostic of dithiolene ligand-based sulfur radical, indicating that one-electron reduction of <b>1</b> <i>involves two-electron reduction of tungsten and one-electron oxidation of dithiolene ligand</i>

Synthesis and Structures of [LCu(I)(SSi^<i>i</i>Pr₃)] (L = triphos, carbene) and Related Compounds

The mononuclear Cu­(I) complexes [LCu^I­(SSi^<i>i</i>Pr₃)] (L = 1,1,1-tris­(diphenylphosphinomethyl)­ethane (triphos), 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes)) have been prepared by ligand displacement from [LCu^ICl] with ^<i>i</i>Pr₃SiS^–. Both compounds are colorless, diamagnetic species and have been characterized structurally by X-ray crystallography. The compounds [(IMes)­Cu­(η¹κ^S-SC­(O)­CH₃)] and [(triphos)­Cu­(η¹κ^S-SC­(S)­OCH₃)] have been prepared in the context of synthesis aimed at [LCu­(η¹κ^S-SCOS)] and [LCu­(η¹κ^S-SCS₂)] complexes, which are intended as synthons toward an analogue of the Mo­(μ-OSCO)Cu intermediate proposed as occurring in the catalytic cycle of carbon monoxide dehydrogenase (CODH)