Mixed-Valence Tetrametallic Iridium Chains

Neutral [X-{Ir2 }-{Ir2 }-X] (X=Cl, Br, SCN, I) and dicationic [L-{Ir2 }-{Ir2 }-L]2+ (L=MeCN, Me2 CO) tetrametallic iridium chains made by connecting two dinuclear {Ir2 } units ({Ir2 }=[Ir2 (μ-OPy)2 (CO)4 ], OPy=2-pyridonate) by an iridium-iridium bond are described. The complexes exhibit fractional averaged oxidation states of +1.5 and electronic delocalization along the metallic chain. While the axial ligands do not significantly affect the metal-metal bond lengths, the metallic chain has a significant impact on the iridium-L/X bond distances. The complexes show free rotation around the unsupported iridium-iridium bond in solution, with a low-energy transition state for the chloride chain. The absorption spectra of these complexes show characteristic bands at 438-504 nm, which can be fine-tuned by varying the terminal capping ligands.

Unsymmetric Dinuclear RhI2 and RhIRhIII Complexes Supported by Tetraphosphine Ligands and Their Reactivity of Oxidative Protonation and Reductive Dechlorination

Two linear tetradentate phosphine ligands, meso-Ph₂PCH₂P(Ph)CH₂XCH₂P(Ph)CH₂PPh₂ (X = CH₂ (meso-dpmppp), NBn (meso-dpmppmNBn; Bn = benzyl)) were utilized to synthesize unsymmetrical dinuclear Rh^I complexes, [Rh₂Cl₂(meso-dpmppp)(L)] (L = XylNC (1a), CO (1b)) and [Rh₂Cl₂(meso-dpmppmNBn)(L)] (L = XylNC (1c), CO (1d)), where electron-deficient Rh^I → Rh^I centers with 30 valence electrons are supported by a tetraphosphine in an unusual cis-/trans-P,P coordination mode. The Rh^I dimers of 1a-d were treated with HCl under air to afford the Rh^I → Rh^III dimers with 32 e^-, [Rh₂Cl₄(meso-dpmppp)(L)] (L = XylNC (4a), CO (4b)) and [Rh₂Cl₄(meso-dpmppmNBn)(L)] (L = XylNC (4c), CO (4d)), via intermediate hydride complexes, [{RhCl₂(μ-H)RhCl(L)}(meso-dpmppp)] (L = XylNC (2a), CO (2b)) and [{RhCl₂(μ-H)RhCl(L)}(meso-dpmppmNBn)] (L = XylNC (2c), CO (2d)), and [{Rh(H)Cl₂(μ-Cl)Rh(L)}(meso-dpmppp)] (L = XylNC (3a), CO (3b)) and [{Rh(H)Cl₂(μ-Cl)Rh(L)}(meso-dpmppmNBn)] (L = XylNC (3c), CO (3d)). The hydride intermediates 2 and 3 were monitored under nitrogen by ¹H{³¹P} and ³¹P{¹H} NMR techniques to reveal two reaction pathways depending on the terminal auxiliary ligand L. Further, the reductive dechlorination converting Rh^IRh^III (4b,d) to Rh^I₂ (1b,d) was accomplished with a CO terminal ligand by reacting with various amines that acted as one-electron reducing agents through an inner-sphere electron transfer mechanism. DFT calculations were performed to elucidate the electronic structures of 1a-d and 4a-d and to estimate the structures of the hydride intermediate complexes 2 and 3.

Tetra- and hexanuclear string complexes of the coinage metals

Reaction of the PNNP ligand system N,N'-bis[(2-diphenylphosphino)phenyl]formamidinate (dpfam) featuring different coordination compartments with [AuCl(tht)], [CuMes]₅, [AgMes]₄, or [AuC₆F₅(tht)] (tht = tetrahydrothiophene) resulted in tetranuclear homo- and heterometallic coinage metal complexes, as well as a hexanuclear gold complex. All of them feature a metal string conformation. Photophysical investigation revealed a significant dependence of the photoluminescence properties on the metal composition. Below 100 K, the PL efficiency of three compounds approaches nearly 100%.

Transition Metal Chain Complexes Supported by Soft Donor Assembling Ligands

The chemistry of discrete molecular chains constituted by metals in low oxidation states, displaying metal-metal proximity and stabilized by suitable metal-bridging, assembling ligands comprising at least one soft donor atom is comprehensively reviewed; complexes with a single (hard or soft) bridging atom (e.g., μ-halide, μ-sulfide, or μ-PR₂ etc.) as well as "closed" metal arrays (that fall in the realm of cluster chemistry) are excluded. The focus is on transition metal-based systems, with few excursions to cases combining transition and post-transition elements. Most relevant supporting ligands have neutral C, P, O, or S donor (mainly, N-heterocyclic carbene, phosphine, ether, thioether) or anionic donor (mainly phenyl, ylide, silyl, phosphide, thiolate) groups. A supporting-ligand-based classification of the metal chains is introduced, using as the classifying parameter the number of "bites" (i.e., ligand bridges) subtending each intermetallic separation. The ligands are further grouped according to the number of donor atoms interacting with the metal chain (called denticity in the following) and the column of the Periodic Table to which the set of donor atoms belongs (in ascending order). A complementary metal-based compilation of the complexes discussed is also provided in a concise tabular form.

Gold(I) Complexes Containing Phosphanyl- and Arsanylborane Ligands

The structural and photophysical properties of a series of new Au^I compounds have been studied. The reactions of AuCl(tht) with the phosphanyl- and arsanylboranes RR^' EBH₂ NMe₃ (E=P, As; R=H, Ph; R'=H, Ph, tBu) afford the complexes [AuCl(RR^' EBH₂ NMe₃ )]. In the solid state, [AuCl(H₂ PBH₂ NMe₃ )]₂ (2 a) is a dimer showing unsupported intermolecular aurophilic interactions with short Au⋅⋅⋅Au distances. In contrast, [AuCl(H₂ AsBH₂ NMe₃ )]_n (2 b) aggregates to form 1D chains. Organic substituents on the pnictogen atoms lead to discrete molecules in [AuCl(RR^' PBH₂ NMe₃ )] (2 c: R=H, R'=tBu; 2 d: R=R'=Ph). To increase the aurophilicity, the ionic homoleptic complexes [Au(RR^' EBH₂ NMe₃ )₂ ][AlCl₄ ] (3 a-d) have been synthesized, for which 3 a,b form chains in the solid state and exhibit luminescence. The emissions show a drastic redshift with temperature decrease, correlating with decreasing Au⋅⋅⋅Au distances. DFT calculations provide insight into the bonding situation of the products.