The Influence of Stepwise P‑Oxidation on the Coordination and Redox Behavior of W–Bisphosalkyne Complex Ligands

The terminal phosphine groups at the tungsten bisphosphine alkyne complex [Tp*W­(CO)­(I)­(η²-<i>C,C</i>′-Ph₂PC₂PPh₂)] (<b>2</b>) {Tp* = hydridotris­(3,4,5-trimethylpyrazolyl)­borate} were selectively oxidized by common methods to form the alkyne complexes <b>2EE</b> (E = O, S) with either two phosphine oxide or two phosphine sulfide substituents. The respective mono-oxidized analogues <b>2E</b> (E = O, S) were obtained by subjecting the already oxidized intermediates [Tp*W­(CO)­(I)­(η²-<i>C,C</i>′-Ph₂P­(E)­C₂H)] <b>1E</b> (E = O, S) to a late-stage phosphine introduction at the complex template. These modulations of the peripheral alkyne moiety have a clear impact on the redox potential of the metal-based oxidation altering the W­(II/III) potential by +0.1 V on average per oxidized phosphine. In contrast to the comparable redox behavior of <b>2O</b> and <b>2S</b>, the coordination behavior of these complex ligands differs substantially. XRD studies show that complex <b>2</b> and the sulfide <b>2S</b> act either as a <i>P</i>,<i>P’</i>- or <i>P</i>,<i>S</i>-chelate ligand leading to the dinuclear complexes [(<b>2</b>)­PdCl₂], <b>3</b>, and [(<b>2S)</b>PdCl₂], <b>3S</b>. In contrast, the corresponding PdCl₂ complex of the monoxide <b>2O</b> is connected by the free phosphine group and the W-bonded iodide as a μ²-bridging ligand leaving the phosphine oxide pending. A similar binding mode was found for the trinuclear gold complex [(<b>2</b>)₂Au]­[PF₆] (<b>5</b>-PF₆). Furthermore, these findings explain the undesired outcome in the reaction of [Pd­(NCMe)₄]­[BF₄]₂ with two equivalents of <b>2</b>, which resulted in the iodide abstraction product [(<b>2</b>)­PdI₂] (<b>4</b>)

A New Class of Azadipnictiridines Generated by an Unusual Rearrangement Reaction

Dipnictadiazanediyls, [E­(μ-NR)]₂ (E = P, As), the pnictogen analogues of cyclobutandiyl, were found to react readily with alkynes forming [2.1.1]­bicyclic structures. These, in turn, rearrange in an unprecedented reaction to [3.1.o]­bicycles leading to the isolation of the first azadiarsiridine and the determination of its solid-state structure. All new species were comprehensively characterized, and the reaction pathways and bonding situations were computationally studied

Ultrafast Energy Transfer in Dinuclear Complexes with Bridging 1,10-Phenanthroline-5,6-Dithiolate

We report herein the preparation and characterization of dinuclear complexes with the bridging ligand 1,10-phenanthroline-5,6-dithiolate (<b>phendt^2–</b>) bearing Ru­(bpy)₂ or Ir­(ppy)₂ at the diimine moiety and Ni­(dppe), Ni­(dppf), CoCp, RhCp*, and Ru­(<i>p</i>-Me-ⁱPr-benzene) at the dithiolate unit. In comparison with the mononuclear precursors used in the synthesis, all dinuclear complexes were characterized by absorption and photoluminescence spectroscopy as well as cyclic voltammetry. Because of the beneficial spectral and electrochemical properties of the Ir/Co complex for a light-driven charge separation, this complex was investigated in detail by time-resolved luminescence {nanosecond (ns)-resolution} and transient absorption spectroscopy {femtosecond (fs)-resolution}. All measurements supported by DFT calculations show that the observed effective luminescence quenching by the dithiolate coordinated metal is caused by an ultrafast singlet–singlet Dexter energy transfer

Understanding the Excited State Behavior of Cyclometalated Bis(tridentate)ruthenium(II) Complexes: A Combined Experimental and Theoretical Study

The synthesis and characterization of the donor–acceptor substituted cyclometalated ruthenium­(II) polypyridine complex isomers [Ru­(dpb-NHCOMe)­(tpy-COOEt)]­(PF₆) <b>1</b>(PF₆) and [Ru­(dpb-COOEt)­(tpy-NHCOMe)]­(PF₆) <b>2</b>(PF₆) (dpbH = 1,3-dipyridin-2-ylbenzene, tpy = 2,2′;6,2″-terpyridine) with inverted functional group pattern are described. A combination of resonance Raman spectroscopic and computational techniques shows that all intense visible range absorption bands arise from mixed Ru → tpy/Ru → dpb metal-to-ligand charge transfer (MLCT) excitations. <b>2</b>(PF₆) is weakly phosphorescent at room temperature in fluid solution and strongly emissive at 77 K in solid butyronitrile matrix, which is typical for ruthenium­(II) polypyridine complexes. Density functional theory calculations revealed that the weak emission of <b>2</b>(PF₆) arises from a ³MLCT state that is efficiently thermally depopulated via metal-centered (³MC) excited states. The activation barrier for the deactivation process was estimated experimentally from variable-temperature emission spectroscopic measurements as 11 kJ mol^–1. In contrast, <b>1</b>(PF₆) is nonemissive at room temperature in fluid solution and at 77 K in solid butyronitrile matrix. Examination of the electronic excited states of <b>1</b>(PF₆) revealed a ligand-to-ligand charge-transfer (³LL′CT) as lowest-energy triplet state due to the very strong push–pull effect across the metal center. Because of the orthogonality of the participating ligands, emission from the ³LL′CT is symmetry-forbidden. Hence, in this type of complex a stronger push–pull effect does not increase the phosphorescence quantum yields but completely quenches the emission

Spontaneous Formation of an η⁴‑Ethylene Bis(carbene) Ligand by Alkyne Coupling at Rhenium(III)

The C/C coupling activity of the cationic Re­(III) species [(C₅H₅)­ReBr]⁺ with different heteroatom-substituted alkynes was investigated. By using the sulfide-substituted bis­(benzylsulfanyl)­acetylene an unprecedented rhenacyclopentatriene complex was obtained. An XRD structure determination of [(C₅H₅)­ReBr­(CSBn)₄]⁺ uncovered the coordination of the remote ethylene moiety at Re leading to an η⁴-coordination mode of the C₄(SBn)₄ ligand and a folded five-membered metallacycle. In contrast, reaction of the monoalkyne complex [(C₅H₅)­ReBr­(CSBn)₂]⁺ with diphenylacetylene as well as diiodoacetylene led to the mixed bis­(alkyne) complexes. The different behavior is attributed to kinetic reasons according to DFT calculations. XRD as well as IR studies with the cationic bis­(alkyne) complexes [(C₅H₅)­ReBr­(CSBn)₂(C₂Ph₂)]⁺ and [(C₅H₅)­ReBr­(CSBn)₂(C₂I₂)]⁺ revealed clear differences in the bond strengths of the coordinated alkynes at the same metal center. Further investigations on the coupling activity resulted in addition products with H₂O and a trimerization of two diphenylacetylene molecules and one bis­(benzylsulfanyl)­acetylene, both as byproducts and involved in a sulfide bond cleavage

Dinuclear Ru/Ni, Ir/Ni, and Ir/Pt Complexes with Bridging Phenanthroline-5,6-dithiolate: Synthesis, Structure, and Electrochemical and Photophysical Behavior

We report the synthesis and full characterization of dinuclear complexes with the bridging ligand phenanthroline-5,6-dithiolate (phendt^2–) featuring the [Ru­(bpy)₂]²⁺ or Ir­(ppy)₂]⁺ fragment at the diimine donor center and the [Ni­(dppe)]²⁺ or [Pt­(phen)]²⁺ complex moiety at the dithiolate group. The molecular structures of the mononuclear complexes [(C₅H₅)₂Ti­(<i>S</i>,<i>S</i>′-phendt)] and [(ppy)₂Ir­{<i>N</i>,<i>N</i>′-phendt-(C₂H₄CN)₂}]­(PF₆) as well as the dinuclear complex [(C₅H₅)­(PPh₃)­Ru­(phendt)­Ni­(dppe)]­(PF₆) determined by X-ray diffraction (XRD) studies are compared. Photophysical studies with mononuclear [(bpy)₂Ru­{phendt-(C₂H₄CN)₂}]²⁺ and [(ppy)₂Ir­{phendt-(C₂H₄CN)₂}]⁺ as well as dinuclear [(bpy)₂Ru­(phendt)­Ni­(dppe)]²⁺ and [(ppy)₂Ir­(phendt)­Ni­(dppe)]⁺ uncovered an effective luminescence quenching in the dinuclear complexes. Lifetime measurements at room temperature, steady-state measurements at low temperature, electrochemical investigations, and DFT calculations provide evidence for a very efficient energy transfer from the Ru/Ir to the Ni complex moiety with a rate constant <i>k</i> > 5 × 10⁹ s^–1. In comparison, the [Ru]­phendt­[Ni] complex displays a higher quenching efficiency with reduced excited state lifetime, whereas the [Ir]­phendt­[Ni] complex is characterized by an unaltered lifetime of the thermally equilibrated excited state