Azadipyrromethene Complexes of d⁸ Metal Centers: Rhodium(I), Iridium(I), Palladium(II), and Platinum(II)

Azadipyrromethenes are blue pigments that chelate main-group and d-block Lewis acids. Reported here are azadipyrromethene complexes of d⁸ metal centers. The new compounds are prepared in salt metathesis reactions with chlorinated organometallic precursors. Sixteen new complexes are reported. The principal absorption features are an intense peak near 600 nm and transitions in the ultraviolet; all are characteristic of the azadipyrromethene chromophore. All compounds are dark solids that yield blue or blue-violet solutions. Ten complexes are crystallographically characterized. The structures uniformly show backbone strain, with a <i>meso</i>-nitrogen atom that dilates from pure sp²-hybridization. Structural comparisons are made to related dipyrromethene and tetra-azaporphyrin complexes. The electron-donating capacity of azadipyrromethene ligands is evaluated from CO stretching frequencies of three rhodium­(I) carbonyl complexes and from density-functional theory calculations. Frontier orbitals are confined to the azadipyrromethene ligand. HOMO–LUMO energy gaps are almost unperturbed from those of the free, anionic azadipyrromethene

Azadipyrromethene Complexes of d⁸ Metal Centers: Rhodium(I), Iridium(I), Palladium(II), and Platinum(II)

Azadipyrromethenes are blue pigments that chelate main-group and d-block Lewis acids. Reported here are azadipyrromethene complexes of d⁸ metal centers. The new compounds are prepared in salt metathesis reactions with chlorinated organometallic precursors. Sixteen new complexes are reported. The principal absorption features are an intense peak near 600 nm and transitions in the ultraviolet; all are characteristic of the azadipyrromethene chromophore. All compounds are dark solids that yield blue or blue-violet solutions. Ten complexes are crystallographically characterized. The structures uniformly show backbone strain, with a <i>meso</i>-nitrogen atom that dilates from pure sp²-hybridization. Structural comparisons are made to related dipyrromethene and tetra-azaporphyrin complexes. The electron-donating capacity of azadipyrromethene ligands is evaluated from CO stretching frequencies of three rhodium­(I) carbonyl complexes and from density-functional theory calculations. Frontier orbitals are confined to the azadipyrromethene ligand. HOMO–LUMO energy gaps are almost unperturbed from those of the free, anionic azadipyrromethene

Gold(I) Complexes of Brominated Azadipyrromethene Ligands

Azadipyrromethenes are luminescent, red-light absorbing dyes that readily bind BF₂⁺ and metals. Their framework allows for structural modification at the phenyl arms and the two pyrrolic carbon positions. Here we report five new gold­(I) complexes with azadipyrromethene ligands brominated at the pyrrolic carbons and/or the four phenyl substituents. New complexes are characterized by multinuclear NMR spectroscopy, X-ray crystallography, optical absorption and emission spectroscopy, and elemental analysis. The new compounds have a perturbed two-coordinate geometry in the crystalline state, with gold­(I) binding one dimethylphenylphosphine ancillary ligand and one pyrrole nitrogen of the azadipyrromethene. The second azadipyrromethene pyrrole nitrogen perturbs the linear coordination. These complexes maintain the absorption features of the free ligands. Excitation in the near-ultraviolet generates emission in the near-UV and visible regions. Density-functional theory calculations indicate that the photoproperties of the new compounds arise almost entirely from the conjugated ligands and not from the (phosphine)­gold­(I) fragments

Gold(I) Complexes of Brominated Azadipyrromethene Ligands

Azadipyrromethenes are luminescent, red-light absorbing dyes that readily bind BF₂⁺ and metals. Their framework allows for structural modification at the phenyl arms and the two pyrrolic carbon positions. Here we report five new gold­(I) complexes with azadipyrromethene ligands brominated at the pyrrolic carbons and/or the four phenyl substituents. New complexes are characterized by multinuclear NMR spectroscopy, X-ray crystallography, optical absorption and emission spectroscopy, and elemental analysis. The new compounds have a perturbed two-coordinate geometry in the crystalline state, with gold­(I) binding one dimethylphenylphosphine ancillary ligand and one pyrrole nitrogen of the azadipyrromethene. The second azadipyrromethene pyrrole nitrogen perturbs the linear coordination. These complexes maintain the absorption features of the free ligands. Excitation in the near-ultraviolet generates emission in the near-UV and visible regions. Density-functional theory calculations indicate that the photoproperties of the new compounds arise almost entirely from the conjugated ligands and not from the (phosphine)­gold­(I) fragments

Azido, Triazolyl, and Alkynyl Complexes of Gold(I): Syntheses, Structures, and Ligand Effects

Gold­(I) triazolyl complexes are prepared in [3 + 2] cycloaddition reactions of (tertiary phosphine)­gold­(I) azides with terminal alkynes. Seven such triazolyl complexes, not previously prepared, are described. Reducible functional groups are accommodated. In addition, two new (<i>N</i>-heterocyclic carbene)­gold­(I) azides and two new gold­(I) alkynyls are described. Eight complexes are crystallographically authenticated; aurophilic interactions appear in one structure only. The packing diagrams of gold­(I) triazolyls all show intermolecular hydrogen bonding between N-1 of one molecule and N-3 of a neighbor. This hydrogen bonding permeates the crystal lattice. Density-functional theory calculations of (triphenylphosphine)­gold­(I) triazolyls and the corresponding alkynyls indicate that the triazolyl is a stronger <i>trans</i>-influencer than is the alkynyl, but the alkynyl is more electron-releasing. These results suggest that <i>trans-</i>influences in two-coordinate gold­(I) complexes can be more than a simple matter of ligand donicity

Azido, Triazolyl, and Alkynyl Complexes of Gold(I): Syntheses, Structures, and Ligand Effects

Gold­(I) triazolyl complexes are prepared in [3 + 2] cycloaddition reactions of (tertiary phosphine)­gold­(I) azides with terminal alkynes. Seven such triazolyl complexes, not previously prepared, are described. Reducible functional groups are accommodated. In addition, two new (<i>N</i>-heterocyclic carbene)­gold­(I) azides and two new gold­(I) alkynyls are described. Eight complexes are crystallographically authenticated; aurophilic interactions appear in one structure only. The packing diagrams of gold­(I) triazolyls all show intermolecular hydrogen bonding between N-1 of one molecule and N-3 of a neighbor. This hydrogen bonding permeates the crystal lattice. Density-functional theory calculations of (triphenylphosphine)­gold­(I) triazolyls and the corresponding alkynyls indicate that the triazolyl is a stronger <i>trans</i>-influencer than is the alkynyl, but the alkynyl is more electron-releasing. These results suggest that <i>trans-</i>influences in two-coordinate gold­(I) complexes can be more than a simple matter of ligand donicity

Subpicosecond Intersystem Crossing in Mono- and Di(organophosphine)gold(I) Naphthalene Derivatives in Solution

Femtosecond-to-microsecond broadband transient absorption experiments are reported for Cy₃PAu­(2-naphthyl) (<b>1</b>), (Cy₃PAu)₂(2,6-naphthalenediyl) (<b>2</b>), and (Cy₃PAu)₂(2,7-naphthalenediyl) (<b>3</b>), where Cy = cyclohexyl. Global and target analyses of the data, based on a sequential kinetic model, reveal four spectral components. These components are assigned to (1) excited state absorption (ESA) of the ligand-centered S₁ state; (2) ESA of a receiver ligand-to-metal or metal-to-ligand charge transfer triplet state (τ₁ ≤ 300 fs); (3) ESA of the vibrationally excited, ligand-centered T₁ state (τ₃ = 7–10 ps); and (4) ESA of the relaxed T₁ state. Intersystem crossing (ISC) occurs in hundreds of femtoseconds, while internal conversion (IC) in the triplet manifold is slow (τ₂ ≈ 2 ps). The relaxed T₁ state shows biphasic decay kinetics in <b>2</b> and <b>3</b> with lifetimes of hundreds of picoseconds and hundreds of nanoseconds in air-saturated conditions, while only monophasic decay is observed in <b>1</b> under identical conditions. The primary decay pathway of the T₁ state is assigned to quenching by O₂, while the secondary channel is tentatively assigned to self-quenching or triplet–triplet annihilation. The ISC rate in <b>1</b> is not modulated significantly by the incorporation of a second heavy-atom group effecter. Instead, the position at which the second Au­(I)–phosphine group is attached plays a noticeable role in the ISC rate, showing a 3-fold decrease in that of <b>2</b> compared to that of <b>3</b>. The results challenge the conventional view that the rate of IC is larger than that of ISC, lending further support to the emerging kinetic model proposed for other transition-metal complexes. Gold­(I) now joins the exclusive group of transition metals known to form organometallic complexes exhibiting excited-state nonequilibrium dynamics

Arylgold(I) Complexes from Base-Assisted Transmetalation: Structures, NMR Properties, and Density-Functional Theory Calculations

The synthesis of gold­(I) complexes of the type LAuR (L = PCy₃, IPr; R = aryl; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) starting from LAuX (X = Br, OAc) and boronic acids in the presence of Cs₂CO₃ has been investigated. The reactions proceed smoothly in good to excellent yields over the course of 24–48 h in isopropyl alcohol at 50–55 °C. The aryl groups include a variety of functionalities and steric bulk, and in two cases, are heterocyclic. All of the products have been characterized by multinuclear NMR spectroscopy and elemental analysis and most by X-ray crystallography. This work affirms that, almost without exception, base-assisted auration is a useful and reliable way to form gold–carbon bonds

Arylgold(I) Complexes from Base-Assisted Transmetalation: Structures, NMR Properties, and Density-Functional Theory Calculations

The synthesis of gold­(I) complexes of the type LAuR (L = PCy₃, IPr; R = aryl; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) starting from LAuX (X = Br, OAc) and boronic acids in the presence of Cs₂CO₃ has been investigated. The reactions proceed smoothly in good to excellent yields over the course of 24–48 h in isopropyl alcohol at 50–55 °C. The aryl groups include a variety of functionalities and steric bulk, and in two cases, are heterocyclic. All of the products have been characterized by multinuclear NMR spectroscopy and elemental analysis and most by X-ray crystallography. This work affirms that, almost without exception, base-assisted auration is a useful and reliable way to form gold–carbon bonds

Excited-State Dynamics of (Organophosphine)gold(I) Pyrenyl Isomers

Ultrafast dynamics of isomeric (tricyclohexylphosphine)gold(I) pyrenyl complexes have been measured in chloroform and cyclohexane at room temperature. Internal conversion from an upper excited singlet (S_<i>n</i>) to the S₁ state occurs in less than 200 fs after 340 nm excitation. Internal conversion in the singlet manifold is followed by 11−100 ps intersystem crossing to a receiver triplet state depending on the site of pyrene metalation. The receiver triplet state (T_<i>n</i>) then decays to the T₁ state on an ultrafast time scale, which decays back to the S₀ state on a microseconds time scale in N₂-saturated conditions. Time-dependent density functional theory calculations on model complexes predict an accidental degeneracy of the S₁ and T₂ states of the 1-pyrenyl. No such degeneracy occurs for the 2-pyrenyl isomer. A small S₁−T₂ energy gap promotes the 10-fold increase in the intersystem crossing rate in the 1-pyrenyl complex