Iridaoxacyclohexadiene-Bridged Mixed-Valence Iridium Cyclooctadiene Complex: Oxidative Addition and Hydrogen-Transfer to Coordinated Cyclooctadiene

The systematic exploration of the synthesis of heteropentadienyl metal complexes leads us to study the metathesis reaction of [(η⁴-COD)­Ir­(μ₂-Cl)]₂ with lithium 2,4-dimethyl­oxopentadienide, which affords the dinuclear Ir⁰–Ir^II compound (η⁴-COD)­Ir­[η^1:1-μ₂-η⁴-CHC­(Me)­CHC­(Me)­O)]­Ir­(η⁴-COD) (<b>1</b>) with a metal–metal bond. The COD ligands are coordinated η⁴ to each Ir center, whereas the oxopentadienyl ligand is bridging both Ir atoms, allowing the formation of a novel iridapyran complex with Ir^II and bonding η⁴ with Ir⁰. The addition of CO, PMe₃, and PMe₂Ph to the coordinatively unsaturated complex <b>1</b> has led, under mild conditions, to the corresponding dinuclear coordinatively saturated compounds (η⁴-COD)­Ir­[η^1:1-μ₂-η³-CHC­(Me)­CHC­(Me)­O)]­Ir­(η⁴-COD)­(μ₂-CO) (<b>2</b>) and (η⁴-COD)­Ir­[η^1:1-μ₂-η⁴-CHC­(Me)­CHC­(Me)­O)]­Ir­(η⁴-COD)­(PR₃) (R = Me, <b>3</b>; PR₃ = PMe₂Ph, <b>4</b>). Compound <b>3</b> showed a reversible reaction by dissociation of PMe₃, recovering compound <b>1</b>. The reaction of <b>1</b> with H₂ and PMe₃, PMe₂Ph, and P­(<i>n</i>-Bu)₃ allows the isolation of cyclooctenyl derivatives (η⁴-COD)­Ir­[η^1:1-μ₂-η³-CHC­(Me)­CHC­(Me)­O)]­Ir­(μ₂-H)­(η¹:η²-C₈H₁₃)­(PR₃) (R = Me, <b>5</b>; R₃ = Me₂Ph, <b>6</b>; R = <i>n</i>-Bu, <b>7</b>), where the hydrogen promotes the formation of a metal-hydride, as well as hydrogen-transfer to one of the coordinated cyclooctadiene ligands. In the presence of molecular hydrogen, <b>4</b> leads also to the formation of <b>6</b> in better yield. The iridaoxacycle bridging ligand stabilizes these dinuclear iridium complexes, which easily undergo intermolecular insertion into activated C–H bonds. When the more sterically demanding phosphine P­(<i>i</i>-Pr)₃ is added in the presence of H₂, a different reaction takes place, with the displacement of one COD ligand and the formation of (η⁴-COD)­Ir­(μ₂-H)­[η^1:1-μ₂-η³-CHC­(Me)­CHC­(Me)­O)]­Ir­(H)­(P<i>i</i>-Pr₃)₂ (<b>8</b>). The novel complexes <b>1</b>–<b>8</b> have been fully characterized, where <b>1</b> shows dynamic behavior in one of the COD ligands in solution and gives evidence of two different isomers present in the crystalline structure. Molecular structures of <b>1</b>–<b>3</b> and <b>5</b>–<b>8</b> have been determined by single-crystal X-ray diffraction studies

Iridaoxacyclohexadiene-Bridged Mixed-Valence Iridium Cyclooctadiene Complex: Oxidative Addition and Hydrogen-Transfer to Coordinated Cyclooctadiene

The systematic exploration of the synthesis of heteropentadienyl metal complexes leads us to study the metathesis reaction of [(η⁴-COD)­Ir­(μ₂-Cl)]₂ with lithium 2,4-dimethyl­oxopentadienide, which affords the dinuclear Ir⁰–Ir^II compound (η⁴-COD)­Ir­[η^1:1-μ₂-η⁴-CHC­(Me)­CHC­(Me)­O)]­Ir­(η⁴-COD) (<b>1</b>) with a metal–metal bond. The COD ligands are coordinated η⁴ to each Ir center, whereas the oxopentadienyl ligand is bridging both Ir atoms, allowing the formation of a novel iridapyran complex with Ir^II and bonding η⁴ with Ir⁰. The addition of CO, PMe₃, and PMe₂Ph to the coordinatively unsaturated complex <b>1</b> has led, under mild conditions, to the corresponding dinuclear coordinatively saturated compounds (η⁴-COD)­Ir­[η^1:1-μ₂-η³-CHC­(Me)­CHC­(Me)­O)]­Ir­(η⁴-COD)­(μ₂-CO) (<b>2</b>) and (η⁴-COD)­Ir­[η^1:1-μ₂-η⁴-CHC­(Me)­CHC­(Me)­O)]­Ir­(η⁴-COD)­(PR₃) (R = Me, <b>3</b>; PR₃ = PMe₂Ph, <b>4</b>). Compound <b>3</b> showed a reversible reaction by dissociation of PMe₃, recovering compound <b>1</b>. The reaction of <b>1</b> with H₂ and PMe₃, PMe₂Ph, and P­(<i>n</i>-Bu)₃ allows the isolation of cyclooctenyl derivatives (η⁴-COD)­Ir­[η^1:1-μ₂-η³-CHC­(Me)­CHC­(Me)­O)]­Ir­(μ₂-H)­(η¹:η²-C₈H₁₃)­(PR₃) (R = Me, <b>5</b>; R₃ = Me₂Ph, <b>6</b>; R = <i>n</i>-Bu, <b>7</b>), where the hydrogen promotes the formation of a metal-hydride, as well as hydrogen-transfer to one of the coordinated cyclooctadiene ligands. In the presence of molecular hydrogen, <b>4</b> leads also to the formation of <b>6</b> in better yield. The iridaoxacycle bridging ligand stabilizes these dinuclear iridium complexes, which easily undergo intermolecular insertion into activated C–H bonds. When the more sterically demanding phosphine P­(<i>i</i>-Pr)₃ is added in the presence of H₂, a different reaction takes place, with the displacement of one COD ligand and the formation of (η⁴-COD)­Ir­(μ₂-H)­[η^1:1-μ₂-η³-CHC­(Me)­CHC­(Me)­O)]­Ir­(H)­(P<i>i</i>-Pr₃)₂ (<b>8</b>). The novel complexes <b>1</b>–<b>8</b> have been fully characterized, where <b>1</b> shows dynamic behavior in one of the COD ligands in solution and gives evidence of two different isomers present in the crystalline structure. Molecular structures of <b>1</b>–<b>3</b> and <b>5</b>–<b>8</b> have been determined by single-crystal X-ray diffraction studies

Phosphine-Substituted (η⁵‑Pentadienyl) Manganese Carbonyl Complexes: Geometric Structures, Electronic Structures, and Energetic Properties of the Associative Substitution Mechanism, Including Isolation of the Slipped η³‑Pentadienyl Associative Intermediate

The molecule (η⁵-Me₂Pdl)­Mn­(CO)₃ (η⁵-Me₂Pdl = 2,4-dimethyl-η⁵-pentadienyl) has been prepared by a new method and used as a starting material to prepare the molecules (η⁵-Me₂Pdl)­Mn­(CO)_<i>n</i>(PMe₃)_3–<i>n</i> (<i>n</i> = 2, 1) by phosphine substitution for carbonyls. The first carbonyl substitution is achieved thermally in refluxing cyclohexane, and the second carbonyl substitution requires photolysis. At room temperature in benzene the associative intermediate (η³-Me₂Pdl)­Mn­(CO)₃(PMe₃) that precedes the initial loss of carbonyl is observed. Single-crystal structures are reported for all complexes, including the associative intermediate of the first substitution in which the pentadienyl ligand has slipped to the η³ bonding mode. These molecules offer an opportunity to examine fundamental principles of the interactions between metals and pentadienyl ligands in comparison to the well-developed chemistry of metal cyclopentadienyl (Cp) complexes as a function of electron richness at the metal center. Photoelectron spectra of these molecules show that the Me₂Pdl ligand has π ionizations at energy lower than that for the analogous Cp ligand and donates more strongly to the metal than the Cp ligand, making the metal more electron rich. Phosphine substitutions for carbonyls further increase the electron richness at the metal center. Density functional calculations provide further insight into the electronic structures and bonding of the molecules, revealing the energetics and role of the pentadienyl slip from η⁵ to η³ bonding in the early stages of the associative substitution mechanism. Computational comparison with dissociative ligand substitution mechanisms reveals the roles of dispersion interaction energies and the entropic free energies in the ligand substitution reactions. An alternative scheme for evaluating the computational translational and rotational entropy of a dissociative mechanism in solution is offered

Phosphine-Substituted (η⁵‑Pentadienyl) Manganese Carbonyl Complexes: Geometric Structures, Electronic Structures, and Energetic Properties of the Associative Substitution Mechanism, Including Isolation of the Slipped η³‑Pentadienyl Associative Intermediate

The molecule (η⁵-Me₂Pdl)­Mn­(CO)₃ (η⁵-Me₂Pdl = 2,4-dimethyl-η⁵-pentadienyl) has been prepared by a new method and used as a starting material to prepare the molecules (η⁵-Me₂Pdl)­Mn­(CO)_<i>n</i>(PMe₃)_3–<i>n</i> (<i>n</i> = 2, 1) by phosphine substitution for carbonyls. The first carbonyl substitution is achieved thermally in refluxing cyclohexane, and the second carbonyl substitution requires photolysis. At room temperature in benzene the associative intermediate (η³-Me₂Pdl)­Mn­(CO)₃(PMe₃) that precedes the initial loss of carbonyl is observed. Single-crystal structures are reported for all complexes, including the associative intermediate of the first substitution in which the pentadienyl ligand has slipped to the η³ bonding mode. These molecules offer an opportunity to examine fundamental principles of the interactions between metals and pentadienyl ligands in comparison to the well-developed chemistry of metal cyclopentadienyl (Cp) complexes as a function of electron richness at the metal center. Photoelectron spectra of these molecules show that the Me₂Pdl ligand has π ionizations at energy lower than that for the analogous Cp ligand and donates more strongly to the metal than the Cp ligand, making the metal more electron rich. Phosphine substitutions for carbonyls further increase the electron richness at the metal center. Density functional calculations provide further insight into the electronic structures and bonding of the molecules, revealing the energetics and role of the pentadienyl slip from η⁵ to η³ bonding in the early stages of the associative substitution mechanism. Computational comparison with dissociative ligand substitution mechanisms reveals the roles of dispersion interaction energies and the entropic free energies in the ligand substitution reactions. An alternative scheme for evaluating the computational translational and rotational entropy of a dissociative mechanism in solution is offered

Phosphine-Substituted (η⁵‑Pentadienyl) Manganese Carbonyl Complexes: Geometric Structures, Electronic Structures, and Energetic Properties of the Associative Substitution Mechanism, Including Isolation of the Slipped η³‑Pentadienyl Associative Intermediate

The molecule (η⁵-Me₂Pdl)­Mn­(CO)₃ (η⁵-Me₂Pdl = 2,4-dimethyl-η⁵-pentadienyl) has been prepared by a new method and used as a starting material to prepare the molecules (η⁵-Me₂Pdl)­Mn­(CO)_<i>n</i>(PMe₃)_3–<i>n</i> (<i>n</i> = 2, 1) by phosphine substitution for carbonyls. The first carbonyl substitution is achieved thermally in refluxing cyclohexane, and the second carbonyl substitution requires photolysis. At room temperature in benzene the associative intermediate (η³-Me₂Pdl)­Mn­(CO)₃(PMe₃) that precedes the initial loss of carbonyl is observed. Single-crystal structures are reported for all complexes, including the associative intermediate of the first substitution in which the pentadienyl ligand has slipped to the η³ bonding mode. These molecules offer an opportunity to examine fundamental principles of the interactions between metals and pentadienyl ligands in comparison to the well-developed chemistry of metal cyclopentadienyl (Cp) complexes as a function of electron richness at the metal center. Photoelectron spectra of these molecules show that the Me₂Pdl ligand has π ionizations at energy lower than that for the analogous Cp ligand and donates more strongly to the metal than the Cp ligand, making the metal more electron rich. Phosphine substitutions for carbonyls further increase the electron richness at the metal center. Density functional calculations provide further insight into the electronic structures and bonding of the molecules, revealing the energetics and role of the pentadienyl slip from η⁵ to η³ bonding in the early stages of the associative substitution mechanism. Computational comparison with dissociative ligand substitution mechanisms reveals the roles of dispersion interaction energies and the entropic free energies in the ligand substitution reactions. An alternative scheme for evaluating the computational translational and rotational entropy of a dissociative mechanism in solution is offered

Chemistry of Iridium(I) Cyclooctadiene Compounds with Thiapentadienyl, Sulfinylpentadienyl, and Butadienesulfonyl Ligands

The metathesis reaction of [(η⁴-COD)­Ir­(μ-Cl)]₂ (<b>4</b>) with two equivalents of the sodium thiapentadienide (<b>1Na</b>) or potassium sulfinylpentadienide salt (<b>2K</b>) led to the formation of the corresponding dimers [(η⁴-COD)­Ir­(μ₂-1-2,5-η-CH₂CHCHCHS)]₂ (<b>5</b>) and [(η⁴-COD)­Ir­(μ₂-1-2,5-η-CH₂CHCHCHSO)]₂ (<b>9</b>). The single-crystal analysis of <b>5</b> and <b>9</b> reveals the presence of the thiapentadienyl or sulfinylpentadienyl ligands bridging through the sulfur atoms and the terminal double bonds to both iridium centers. Treatment of <b>5</b> with two equivalents of PMe₃ produces [(η⁴-COD)­Ir­(1-2,5-η-CH₂CHCHCHS)­PMe₃] (<b>6</b>), while compound Ir­(1-2,5-η-CH₂CHCHCHS)­(CO)­(PPh₃)₂ (<b>8</b>) is obtained from reaction of Ir­(CO)­(Cl)­(PPh₃)₂ (<b>7</b>) with potassium thiapentadienide (<b>1K</b>). The ¹H and ¹³C NMR support the preferred U conformation and the same η^2,1-bonding mode of the thiapentadienyl ligand in each case. The reaction of <b>4</b> with butadienesulfinate salts M­[CH₂CHCHCHSO₂] (<b>3M</b>) (M = Li, K) affords the ion-pair complexes [(η⁴-COD)­IrCl­(1-2,5-η-CH₂CHCHCHS­(O₂^–M⁺)] (M = Li, <b>10</b>; M = K, <b>11</b>). Compound (η⁴-COD)­Ir­(μ-Cl)­(1-2-η-S,O-μ-OSOCHCHCHCH₂)­Ir­(η⁴-COD) (<b>12</b>) can be isolated if the reaction of <b>4</b> with <b>3K</b> is carried out at low temperature and after a short period of time in solution. The crystal structure of <b>12</b> shows a dinuclear compound where the butadienesulfonyl is bridging through the S and one of the O atoms to the iridium center. In solution, <b>12</b> dissociates in the presence of coordinating solvents, such as DMSO-<i>d</i>₆ or THF-<i>d</i>₈, while the dinuclear asymmetric structure of <b>12</b> remains in CDCl₃. The series of pentacoordinated Ir­(I) complexes of general formula [(η⁴-COD)­Ir­(1-2,5-η-CH₂CHCHCHSO₂)­L] (L = PMe₃, <b>14</b>; PMe₂Ph, <b>15</b>; PMePh₂, <b>16</b>; PPh₃, <b>17</b>; DMSO, <b>18</b>; and CO, <b>19</b>) can be obtained, under mild conditions, from <b>11</b> and the corresponding ligand L, which shows different σ or π donor–acceptor properties. The disubstituted phosphine derivative [(η⁴-COD)­Ir­(5-η-CH₂CHCHCHSO₂)­(PMe₃)₂] (<b>20</b>) can be prepared directly from <b>14</b> and an excess of PMe₃. A comparative study of these derivatives was carried out through the analysis of the IR, mass spectrometry, and ¹H, ¹³C, and ³¹P NMR spectroscopy, as well as through the crystalline structures of <b>12</b>, <b>14</b>, <b>15</b>, and <b>17</b>–<b>20</b>, and allowed establishing trends among them. The presence of the butadienesulfonyl ligand in complexes <b>14</b>–<b>19</b> induces a total asymmetry that is reflected through the ¹H and ¹³C NMR. The preferred coordination mode (1-2,5-η-) in the butadienesulfonyl ligand for complexes <b>14</b>–<b>19</b> was confirmed. A better synthetic procedure for <b>14</b> is described if [(η⁴-COD)­IrClPMe₃] (<b>21</b>) reacts with <b>3K</b>. In contrast, no synthetic advantage was found in the formation of <b>17</b> or <b>20</b> when [(η⁴-COD)­IrClPPh₃] (<b>22</b>) or [(η⁴-COD)­IrCl­(PMe₃)₂] (<b>23</b>) is used as a precursor. Monitoring reactions through ¹H and ³¹P NMR of <b>11</b>, <b>12</b>, and <b>14</b> in the presence of PMe₃ and <b>23</b> with <b>3K</b> afforded mixtures of compounds, from which an equilibrium in the reaction mixture is proposed

Half-Sandwich Ruthenium-Phosphine Complexes with Pentadienyl and Oxo- and Azapentadienyl Ligands

Treatment of RuCl₂(PPh₃)₃ and RuHCl­(PPh₃)₃ with the tin compound CH₂C­(Me)­CHC­(Me)­CH₂SnMe₃ gives the corresponding acyclic pentadienyl half-sandwich (η⁵-CH₂C­(Me)­CHC­(Me)­CH₂)­RuX­(PPh₃)₂ [X = Cl, (<b>2</b>); H, (<b>3</b>)]. The steric congestion in <b>2</b> is most effectively relieved by formation of the cyclometalated complex (η⁵-CH₂C­(Me)­CHC­(Me)­CH₂)­Ru(C₆H₄PPh₂)­(PPh₃) (<b>4</b>). Addition of 1 equiv of PHPh₂ to (η⁵-CH₂CHCHCHCH₂)­RuCl­(PPh₃)₂ (<b>1</b>) affords the chiral complex (η⁵-CH₂CHCHCHCH₂)­RuCl­(PPh₃)­(PHPh₂) (<b>5</b>), while compound (η⁵-CH₂C­(Me)­CHC­(Me)­CH₂)­RuCl­(PPh₃)­(PHPh₂)] (<b>6</b>) is directly obtained from the reaction of RuCl₂(PPh₃)₃ with CH₂C­(Me)­CHC­(Me)­CH₂Sn­(Me)₃ and PHPh₂. Treatment of RuCl₂(PPh₃)₃ with the corresponding Me₃SnCH₂CHCHCHNR (R = Cy, <i>t-</i>Bu) affords (1-3,5-η-CH₂CHCHCHNCy)­RuCl­(PPh₃)₂ (<b>7</b>) and [1-3,5-η-CH₂CHCHCHN­(<i>t</i>-Bu)]RuCl­(PPh₃)₂ (<b>8</b>). The hydrolysis of <b>7</b>, on a silica gel chromatography column, allows the isolation of RuCl­(η⁵-CH₂CHCHCHO)­(PPh₃)₂ (<b>9</b>). The azapentadienyl complex <b>7</b> reacts with 1 equiv of PHPh₂ to afford [1-3,5-η-CH₂CHCHCHN­(Cy)]­RuCl­(PPh₃)­(PHPh₂) (<b>10</b>), while the corresponding product [1-3,5-η-CH₂CHCHCHN­(<i>t</i>-Bu)]­RuCl­(PPh₃)­(PHPh₂) (<b>11</b>) from <b>8</b> is only observed through ¹H and ³¹P NMR spectroscopy as a mixture of isomers. Two equivalents of PHPh₂ gives spectroscopic evidence of [η³-CH₂CHCHCHN­(<i>t</i>-Bu)]­RuCl­(PHPh₂)₃. A mixture of products [η⁵-CH₂C­(Me)­CHC­(Me)­O]­RuCl­(PPh₃)₂ (<b>12</b>) and [η⁵-CH₂C­(Me)­CHC­(Me)­O]­RuH­(PPh₃)₂ (<b>13</b>) is obtained from reaction of RuCl₂(PPh₃)₃ with Li­[CH₂C­(Me)­CHC­(Me)­O]. In contrast, the oxopentadienyl compound <b>13</b> is cleanly formed from RuHCl­(PPh₃)₃ and Li­[CH₂C­(Me)­CHC­(Me)­O]. An attempt to separate compounds <b>12</b> and <b>13</b> by crystallization gives an orthometalated product [η⁵-CH₂C­(Me)­CHC­(Me)­O]­Ru­(C₆H₄PPh₂)­(PPh₃) (<b>14</b>), which is the oxopentadienyl analogue to <b>4</b>. The bulky [1-3,5-η-CH₂C­(<i>t</i>-Bu)­CHC­(<i>t</i>-Bu)­O]­RuH­(PPh₃)₂ (<b>15</b>) analogue to <b>13</b> has also been prepared from RuHCl­(PPh₃)₃ and Li­[CH₂C­(<i>t</i>-Bu)­CHC­(<i>t</i>-Bu)­O]. Compounds <b>3</b>, <b>5</b>, <b>6</b>, <b>7</b>, and <b>12</b>–<b>15</b> have been structurally characterized. The preferred heteropentadienyl orientations and the relative positions of the H, Cl, PPh₃, and PHPh₂ ligands have been established in the piano-stool structures for all compounds, and it can be definitively surmised that the chemistry involved in the heteropentadienyl half-sandwich compounds studied is dominated by steric effects