Synthesis and Reactivity of Three-Coordinate (dtbpe)Rh Silylamides: CO₂ Bond Cleavage by a Rhodium(I) Disilylamide

Rhodium­(I) silylamide complexes supported by the 1,2-bis­(di-<i>tert</i>-butylphosphino)­ethane (dtbpe) ligand have been prepared and their structures and reactivity studied. Although the complexes degrade over time to release the corresponding silylamines, they react cleanly with silver­(I) salts to transfer the amido group at ambient temperature. The bis­(trimethylsilyl)­amide complex (dtbpe)­Rh–N­(TMS)₂ reacts with CO₂ to form a carbamate complex that decomposes via loss of hexamethyldisiloxane to form a bis­(μ-isocyanate) dimer, suggesting that silylamides may be useful nitrene-group and nitrogen-atom sources through selective N–Si bond cleavage

Chalcogen Extrusion from Heteroallenes and Carbon Monoxide by a Three-Coordinate Rh(I) Disilylamide

We report the reactions of several heteroallenes (carbon disulfide, carbonyl sulfide, and phenyl isocyanate) and carbon monoxide with a three-coordinate, bis­(phosphine)-supported Rh­(I) disilylamide (<b>1</b>). Carbon disulfide reacts with <b>1</b> to afford a silyltrithiocarbonate complex similar to an intermediate previously invoked in the deoxygenation of CO₂ by <b>1</b>, and prolonged heating affords a structurally unusual μ-κ²(<i>S</i>,<i>S</i>′):κ²(<i>S</i>,<i>S</i>′)-trithiocarbonate dimer. Carbonyl sulfide reacts with <b>1</b> to afford a structurally unique Rh­(SCNCS) metallacycle derived from two insertions of OCS and N-to-O silyl-group migrations. Phenyl isocyanate reacts with <b>1</b> to afford a dimeric bis­(phenylcyanamido)-bridged complex resulting from multiple silyl-group migrations and nitrogen-for-oxygen metathesis, akin to reactivity previously observed with carbon dioxide. The ability of <b>1</b> to activate carbon–chalcogen multiple bonds via silyl-group migration is further supported by its reactivity with carbon monoxide, where a nitrogen-for-oxygen metathesis is also observed with expulsion of hexamethyldisiloxane. For all reported reactions, intermediates are observable under appropriate conditions, allowing the formulation of mechanisms where insertion of the unsaturated substrate is followed by one or more silyl-group migrations to afford the observed products. This rich variety of reactivity confirms the ability of metal silylamides to activate exceptionally strong carbon–element multiple bonds and suggests that silylamides may be useful intermediates in nitrogen-atom and nitrene-group-transfer schemes

Chalcogen Extrusion from Heteroallenes and Carbon Monoxide by a Three-Coordinate Rh(I) Disilylamide

We report the reactions of several heteroallenes (carbon disulfide, carbonyl sulfide, and phenyl isocyanate) and carbon monoxide with a three-coordinate, bis­(phosphine)-supported Rh­(I) disilylamide (<b>1</b>). Carbon disulfide reacts with <b>1</b> to afford a silyltrithiocarbonate complex similar to an intermediate previously invoked in the deoxygenation of CO₂ by <b>1</b>, and prolonged heating affords a structurally unusual μ-κ²(<i>S</i>,<i>S</i>′):κ²(<i>S</i>,<i>S</i>′)-trithiocarbonate dimer. Carbonyl sulfide reacts with <b>1</b> to afford a structurally unique Rh­(SCNCS) metallacycle derived from two insertions of OCS and N-to-O silyl-group migrations. Phenyl isocyanate reacts with <b>1</b> to afford a dimeric bis­(phenylcyanamido)-bridged complex resulting from multiple silyl-group migrations and nitrogen-for-oxygen metathesis, akin to reactivity previously observed with carbon dioxide. The ability of <b>1</b> to activate carbon–chalcogen multiple bonds via silyl-group migration is further supported by its reactivity with carbon monoxide, where a nitrogen-for-oxygen metathesis is also observed with expulsion of hexamethyldisiloxane. For all reported reactions, intermediates are observable under appropriate conditions, allowing the formulation of mechanisms where insertion of the unsaturated substrate is followed by one or more silyl-group migrations to afford the observed products. This rich variety of reactivity confirms the ability of metal silylamides to activate exceptionally strong carbon–element multiple bonds and suggests that silylamides may be useful intermediates in nitrogen-atom and nitrene-group-transfer schemes

Cu₄I₄ Clusters Supported by P^∧N-type Ligands: New Structures with Tunable Emission Colors

A series of Cu₄I₄ clusters (<b>1</b>–<b>5</b>) supported by two P^∧N-type ligands 2-[(di<b>R</b>phosphino)­methyl]­pyridine (<b>1</b>, R = phenyl; <b>2</b>, R = cyclohexyl; <b>3</b>, R = <i>tert</i>-butyl; <b>4</b>, R = <i>iso</i>-propyl; <b>5</b>, R = ethyl) have been synthesized. Single crystal X-ray analyses show that all five clusters adopt a rare “octahedral” geometry. The central core of the cluster consists of the copper atoms arranged in a parallelogram with μ⁴-iodides above and below the copper plane. The copper atoms on the two short edges of the parallelogram (Cu–Cu = 2.525(2)–2.630(1) Å) are bridged with μ²-iodides, whereas the long edges (Cu–Cu = 2.839(3)–3.035(2) Å) are bridged in an antiparallel fashion by the P^∧N ligands. This Cu₄I₄ geometry differs significantly from the “cubane” and “stairstep” geometries reported for other Cu₄I₄L₄ clusters. Luminescence spectra of clusters <b>3</b> and <b>4</b> display a single emission around 460 nm at room temperature that is assigned to emission from a triplet halide-to-ligand charge-transfer (³XLCT) excited state, whereas clusters <b>1</b>, <b>2</b>, and <b>5</b> also have a second band around 570 nm that is assigned to a Cu₄I₄ cluster-centered (³CC) excited state. The structural and photophysical properties of a dinuclear Cu₂I₂(P^∧N)₂ complex obtained during the sublimation of cluster <b>3</b> is also provided

Cu₄I₄ Clusters Supported by P^∧N-type Ligands: New Structures with Tunable Emission Colors

A series of Cu₄I₄ clusters (<b>1</b>–<b>5</b>) supported by two P^∧N-type ligands 2-[(di<b>R</b>phosphino)­methyl]­pyridine (<b>1</b>, R = phenyl; <b>2</b>, R = cyclohexyl; <b>3</b>, R = <i>tert</i>-butyl; <b>4</b>, R = <i>iso</i>-propyl; <b>5</b>, R = ethyl) have been synthesized. Single crystal X-ray analyses show that all five clusters adopt a rare “octahedral” geometry. The central core of the cluster consists of the copper atoms arranged in a parallelogram with μ⁴-iodides above and below the copper plane. The copper atoms on the two short edges of the parallelogram (Cu–Cu = 2.525(2)–2.630(1) Å) are bridged with μ²-iodides, whereas the long edges (Cu–Cu = 2.839(3)–3.035(2) Å) are bridged in an antiparallel fashion by the P^∧N ligands. This Cu₄I₄ geometry differs significantly from the “cubane” and “stairstep” geometries reported for other Cu₄I₄L₄ clusters. Luminescence spectra of clusters <b>3</b> and <b>4</b> display a single emission around 460 nm at room temperature that is assigned to emission from a triplet halide-to-ligand charge-transfer (³XLCT) excited state, whereas clusters <b>1</b>, <b>2</b>, and <b>5</b> also have a second band around 570 nm that is assigned to a Cu₄I₄ cluster-centered (³CC) excited state. The structural and photophysical properties of a dinuclear Cu₂I₂(P^∧N)₂ complex obtained during the sublimation of cluster <b>3</b> is also provided

Formation of Chlorosilyl Pincer-Type Rhodium Complexes by Multiple Si–H Activations of Bis(phosphine)/Dihydrosilyl Ligands

The synthesis and metalation of two bis­(phosphine)/dihydrosilyl ligands at rhodium­(I) sources is reported. Irrespective of the substitution at silicon (diaryl versus diamino), multiple Si–H activations and chloride migration afford tridentate bis­(phosphine)/chlorosilyl complexes of Rh­(I). For the diarylsilyl ligand, reaction with a cationic rhodium­(I) triflate precursor gives the analogous triflatosilyl complex. The [P₂Si]­H₂ proligands and their Rh complexes provide distinct opportunities for exploring metal/silicon cooperative reactivity

Formation of Chlorosilyl Pincer-Type Rhodium Complexes by Multiple Si–H Activations of Bis(phosphine)/Dihydrosilyl Ligands

The synthesis and metalation of two bis­(phosphine)/dihydrosilyl ligands at rhodium­(I) sources is reported. Irrespective of the substitution at silicon (diaryl versus diamino), multiple Si–H activations and chloride migration afford tridentate bis­(phosphine)/chlorosilyl complexes of Rh­(I). For the diarylsilyl ligand, reaction with a cationic rhodium­(I) triflate precursor gives the analogous triflatosilyl complex. The [P₂Si]­H₂ proligands and their Rh complexes provide distinct opportunities for exploring metal/silicon cooperative reactivity

Structural and Photophysical Studies of Phosphorescent Three-Coordinate Copper(I) Complexes Supported by an N‑Heterocyclic Carbene Ligand

A series of four neutral luminescent three-coordinate Cu­(I) complexes (IPr)­Cu­(N^∧N), where IPr is a monodentate N-heterocyclic carbene (NHC) ligand (IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) and N^∧N denotes monoanionic pyridyl-azolate ligands, have been synthesized and characterized. A monomeric, three-coordinate geometry, best described as distorted trigonal planar, has been established by single-crystal X-ray analyses for three of the derivatives. In contrast to the previously reported (IPr)­Cu­(N^∧N) complexes, the compounds described here display a perpendicular orientation between the chelating N^∧N ligands and the imidazolylidene ring of the carbene ligand. The geometrical preferences revealed by X-ray crystallography correlate well with the NMR data. The conformational behavior of the complexes, investigated by variable-temperature ¹H NMR spectroscopy, indicate free rotation about the C_NHC–Cu bond in solution. The complexes display broad, featureless luminescence at both room temperature and 77 K, with emission maxima that vary between 555 and 632 nm depending on sample conditions. Luminescence quantum efficiencies of the complexes in solution (Φ ≤ 17%) increase markedly in the solid state (Φ ≤ 62%). On the basis of time-dependent density functional theory (TD-DFT) calculations and the experimental data, luminescence is assigned to phosphorescence from a metal-to-ligand charge-transfer (MLCT) triplet state admixed with ligand-centered (LC) character

Structural and Photophysical Studies of Phosphorescent Three-Coordinate Copper(I) Complexes Supported by an N‑Heterocyclic Carbene Ligand

A series of four neutral luminescent three-coordinate Cu­(I) complexes (IPr)­Cu­(N^∧N), where IPr is a monodentate N-heterocyclic carbene (NHC) ligand (IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) and N^∧N denotes monoanionic pyridyl-azolate ligands, have been synthesized and characterized. A monomeric, three-coordinate geometry, best described as distorted trigonal planar, has been established by single-crystal X-ray analyses for three of the derivatives. In contrast to the previously reported (IPr)­Cu­(N^∧N) complexes, the compounds described here display a perpendicular orientation between the chelating N^∧N ligands and the imidazolylidene ring of the carbene ligand. The geometrical preferences revealed by X-ray crystallography correlate well with the NMR data. The conformational behavior of the complexes, investigated by variable-temperature ¹H NMR spectroscopy, indicate free rotation about the C_NHC–Cu bond in solution. The complexes display broad, featureless luminescence at both room temperature and 77 K, with emission maxima that vary between 555 and 632 nm depending on sample conditions. Luminescence quantum efficiencies of the complexes in solution (Φ ≤ 17%) increase markedly in the solid state (Φ ≤ 62%). On the basis of time-dependent density functional theory (TD-DFT) calculations and the experimental data, luminescence is assigned to phosphorescence from a metal-to-ligand charge-transfer (MLCT) triplet state admixed with ligand-centered (LC) character

Photophysical Properties of Cyclometalated Pt(II) Complexes: Counterintuitive Blue Shift in Emission with an Expanded Ligand π System

A detailed examination was performed on photophysical properties of phosphorescent cyclometalated (C^∧N)­Pt­(O^∧O) complexes (ppy)­Pt­(dpm) (<b>1</b>), (ppy)­Pt­(acac) (<b>1</b>′), and (bzq)­Pt­(dpm) (<b>2</b>) and newly synthesized (dbq)­Pt­(dpm) (<b>3</b>) (C^∧N = 2-phenylpyridine (ppy), benzo­[<i>h</i>]­quinoline (bzq), dibenzo­[<i>f</i>,<i>h</i>]­quinoline (dbq); O^∧O = dipivolylmethanoate (dpm), acetylacetonate (acac)). Compounds <b>1</b>, <b>1</b>′, <b>2</b>, and <b>3</b> were further characterized by single crystal X-ray diffraction. Structural changes brought about by cyclometalation were determined by comparison with X-ray data from model C^∧N ligand precursors. The compounds emit from metal-perturbed, ligand-centered triplet states (<i>E</i>_0–0 = 479 nm, <b>1</b>; <i>E</i>_0–0 = 495 nm, <b>2</b>; <i>E</i>_0–0 = 470 nm, <b>3</b>) with disparate radiative rate constants (<i>k</i>_r = 1.4 × 10⁵ s^–1, <b>1</b>; <i>k</i>_r = 0.10 × 10⁵ s^–1, <b>2</b>; <i>k</i>_r = 2.6 × 10⁵ s^–1, <b>3</b>). Zero-field splittings of the triplet states (Δ<i>E</i>_III–I = 11.5 cm^–1, <b>1</b>′; Δ<i>E</i>_III–I < 2 cm^–1, <b>2</b>; Δ<i>E</i>_III–I = 46.5 cm^–1, <b>3</b>) were determined using high resolution spectra recorded in Shpol’skii matrices. The fact that the <i>E</i>_0–0 energies do not correspond to the extent of π-conjugation in the aromatic C^∧N ligand is rationalized on the basis of structural distortions that occur upon cyclometalation using data from single crystal X-ray analyses of the complexes and ligand precursors along with the triplet state properties evaluated using theoretical calculations. The wide variation in the radiative rate constants and zero-field splittings is also explained on the basis of how changes in the electronic spin density in the C^∧N ligands in the triplet state alter the spin–orbit coupling in the complexes