Self-Alignment of Low-Valent Octanuclear Palladium Atoms

Unsymmetric Ir2 and RhIr Dinuclear Complexes Supported by a Linear Tetraphosphine meso-dpmppp, Showing High Reactivity for O2, H2, and HCl

Unsymmetric dinuclear Ir(I) complexes, [Ir2Cl2(L)(meso-dpmppp)] (L = XylNC (1aIr2), tBuNC (1bIr2), CO (1cIr2)), were synthesized using meso-Ph2PCH2P(Ph)(CH2)3P(Ph)CH2PPh2 (meso-dpmppp), which supports cis-P,P (M1) and trans-P,P (M2) metal sites, and exhibited high reactivity for O2, H2, and HCl. The IrRh heterodinuclear complexes, [M1M2Cl2(L)(meso-dpmppp)] (1xM1M2) (M1M2 = IrRh, RhIr; L = XylNC, CO (x = a, c)), were also synthesized and used together with the Rh2 complexes (1a,cRh2) to elucidate the role of each metal site. For the reactions of O2, 1aIr2 and 1aRhIr showed higher reactivity than those of 1aIrRh and 1aRh2, giving η2-peroxide complexes [{M1Cl2}{M2(η2-O2)(XylNC)}(meso-dpmppp)] (2aIr2, 2aRhIr), from which O2 would not dissociate. All the CO complexes 1cM1M2 (M1, M2 = Ir or Rh) showed no reactivity for O2. In the reactions with H2, 1aIr2 reacted with H2 to give the dihydride complex, [{IrCl2}{Ir(H)2L}(meso-dpmppp)] (11aIr2) and the tetrahydride complex, [{Ir(H)Cl2}(μ-H){Ir(H)2L}(meso-dpmppp)] (12aIr2), while 1aRhIr gave the dihydride complex, and 1aIrRh and 1aRh2 gave no hydride complexes. Reactions of 1a,cM1M2 with HCl afforded the dihydride complexes, [{IrCl3}(μ-H){Ir(H)Cl(XylNC)}(meso-dpmppp)] (14aIr2), [{Ir(H)Cl2}(μ-H){M2Cl2(L)}(meso-dpmppp)] (M2 = Ir, L = CO (15cIr2); M2 = Rh, L = XylNC (15aIrRh), CO (15cIrRh)), and [{Rh(H)Cl2}(μ-Cl){Ir(H)Cl(XylNC)}(meso-dpmppp)] (18aRhIr), the structures varying depending on M1 and M2 as well as L.

Pd8(PDip)6: Cubic, Unsaturated, Zerovalent

Atomically precise nanoclusters hold promise for supramolecular assembly and (opto)electronic- as well as magnetic materials. Herein, this work reports that treating palladium(0) precursors with a triphosphirane affords strongly colored Pd8(PDip)6 that is fully characterized by mass spectrometry, heteronuclear and Cross-Polarization Magic-Angle Spinning (CP-MAS) NMR-, infrared (IR), UV-vis, and X-ray photoelectron (XP) spectroscopies, single-crystal X-Ray diffraction (sc-XRD), mass spectrometry, and cyclovoltammetry (CV). This coordinatively unsaturated 104-electron Pd(0) cluster features a cubic Pd8-core, µ4-capping phosphinidene ligands, and is air-stable. Quantum chemical calculations provide insight to the cluster's electronic structure and suggest 5s/4d orbital mixing as well as minor Pd─P covalency. Trapping experiments reveal that cluster growth proceeds via insertion of Pd(0) into the triphosphirane. The unsaturated cluster senses ethylene and binds isocyanides, which triggers the rearrangement to a tetrahedral structure with a reduced frontier orbital energy gap. These experiments demonstrate facile cluster manipulation and highlight non-destructive cluster rearrangement as is required for supramolecular assembly.

Recent advances in atomic cluster synthesis: a perspective from chemical elements

Despite its potential significance, "cluster chemistry" remains a somewhat marginalized topic within the chemistry field. However, atomic clusters with their unusual and unique structures and properties represent a novel material group situated between molecules and nanoparticles or solid matter, judging from both scientific standpoints and historical backgrounds. Surveying an entire material group, including all substances that can be regarded as a cluster, is essential for establishing cluster chemistry as a more prominent chemistry field. This review aims to provide a comprehensive understanding by categorizing, summarizing, and reviewing clusters, focusing on their constituent elements in the periodic table. However, because numerous disparate synthetic processes have been individually developed to date, their straightforward and uniform classification is a challenging task. As such, comprehensively reviewing this field from a chemical composition viewpoint presents significant obstacles. It should be therefore noted that despite adopting a synthetic method-based classification in this review, the discussions presented herein could entail inaccuracies. Nevertheless, this unorthodox viewpoint unfolds a new scientific perspective which accentuates the common ground between different development processes by emphasizing the lack of a definitive border between their synthetic methods and material groups, thus opening new avenues for cementing cluster chemistry as an attractive chemistry field.

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.

Aiming for dynamic behaviours of molecular metal chains

The dynamical functions of molecular metal chains, that could be derived from unique physical and chemical properties coupled with self-assembly of metal chain components, have largely been unexplored, and this review paper focuses on the dynamic behaviours of Pd chains supported by linear tetraphosphines, meso- and rac-Ph₂PCH₂P(Ph)CH₂P(Ph)CH₂PPh₂ recently reported, and the current development on fine-tuning of metal chains by introducing heterometal atoms, i.e. heterometallic molecular metal chains, that are considered as promising dynamical components in the next generation.

Electrochemical hydrogen formation catalysed by a Pd8 string

The linear Pd₈ complex supported by tetraphosphines reacted with HBF₄ to give an unprecedented linear tetrapalladium complex with a terminal hydride, which promoted electrocatalytic hydrogen formation from HBF₄ in acetonitrile. The 1D coordination polymer of Pd₈ chain confined within Nafion film was applied to the electrocatalytic H₂ formation.

Octapalladium Strings Trap C60 and C70 Fullerenes Affording Metal-Chain-Wired Bucky Balls

Reactions of Pd₈ strings supported by meso-Ph₂ PCH₂ P(Ph)CH₂ P(Ph)CH₂ PPh₂ (meso-dpmppm) ligands, [Pd₈ (meso-dpmppm)₄ (L)₂ ]⁴⁺ (L=CH₃ CN (1), XylNC (2)) with C₆₀ resulted in the exclusive formation of unprecedented metal-chain-wired C₆₀ bucky balls, [{Pd₄ (meso-dpmppm)₂ (L)}₂ (C₆₀ )]⁴⁺ (L=CH₃ CN (11), XylNC (12)), in which a C₆₀ fullerene is trapped in the central Pd-Pd junction, as unambiguously established by spectroscopic, X-ray crystallographic, and theoretical techniques. The similar reaction of Pd₈ strings supported by rac-dpmppm, [Pd₈ (rac-dpmppm)₄ (CH₃ CN)₂ ]⁴⁺ (3) also afforded a racemic mixture of [{Pd₄ ((R*,R*)-dpmppm)₂ (CH₃ CN)}₂ (C₆₀ )]⁴⁺ (13) without scrambling the Pd₄ fragments with (R,R)- and (S,S)-dpmppm ligands. Consequently, those of enantiopure chiral Pd₈ strings, [Pd₈ ((R*,R*)-dpmppm)₄ (CH₃ CN)₂ ]⁴⁺ , certainly afforded chiral bucky balls of [{Pd₄ ((R*,R*)-dpmppm)₂ (CH₃ CN)}₂ (C₆₀ )]⁴⁺ (13_RR and 13_SS ), that exhibit mirror-image circular dichroism spectra. The reactions of 1 and 2 were also applied for trapping a C₇₀ fullerene to give 2 : 1 adducts of [{Pd₄ (meso-dpmppm)₂ (L)}₂ (C₇₀ )]⁴⁺ (L=CH₃ CN (21), XylNC (22)). These results provide useful information for creating a platform to develop dimensionally and chirality controlled metal-carbon nanocomposite materials.

Fine Tunable, Redox Active Octapalladium Chains Supported by Linear Tetraphosphines, Leading to Dynamically 1D Self-Assembled Coordination Polymers

A series of the octapalladium chains supported by meso-Ph₂ PCH₂ P(Ph)CH₂ P(Ph)CH₂ PPh₂ (meso-dpmppm) ligands, [Pd₈ (meso-dpmppm)₄ (L)₂ ](BF₄ )₄ (L=none (1), solvents: CH₃ CN (2 a), dmf (2 b), dmso (2 c), RN≡C: R=Xyl (3 a), Mes (3 b), Dip (3 c), ^t Bu (3 d), Cy (3 e), CH₃ (CH₂ )₇ (3 f), CH₃ (CH₂ )₁₁ (3 g), CH₃ (CH₂ )₁₇ (3 h)) and [Pd₈ (meso-dpmppm)₄ (X)₂ ](BF₄ )₂ (X=Cl (4 a), N₃ (4 b), CN (4 c), SCN (4 d)), were synthesized by using 2 a as a stable good precursor, and characterized by spectroscopic (IR, ¹ H and ³¹ P NMR, UV-vis-NIR, ESI-MS) measurements and X-ray crystallographic analyses (for 1, 2 a, b, 3 a, b, e, f, 4 a-d). On the basis of DFT calculations on the X-ray determined structure of 2 b ([2b-Pd₈ ]⁴⁺ ) and the optimized models [Pd₈ (meso-Ph₂ PCH₂ P(H)CH₂ P(H)CH₂ PH₂ )₄ (CH₃ CN)₂ ]⁴⁺ ([Pd₈ Ph₈ ]⁴⁺ ) and [Pd₈ (meso-H₂ PCH₂ P(H)CH₂ P(H)CH₂ PH₂ )₄ (CH₃ CN)₂ ]⁴⁺ ([Pd₈ H₈ ]⁴⁺ ), with and without empirically calculating dispersion force stabilization energy (B3LYP-D3, B3LYP), the formation energy between the two Pd₄ fragments is assumed to involve mainly noncovalent interactions (ca. -70 kcal/mol) with four sets of interligand C-H/π interactions and Pd⋅⋅⋅Pd metallophilic one, while electron shared covalent interactions are almost canceled out within the Pd₈ chain. All the compounds isolated are stable in solution and exhibit characteristic absorption at ∼900 nm, which is assignable to a spin allowed HOMO to LUMO transition, and shows temperature dependent intensity change with variable absorption coefficients presumably due to coupling with some thermal vibrations. The structures and electronic states of the Pd₈ chains are found finely tunable by varying the terminal capping ligands. In particular, theoretical calculations elucidated that the HOMO-LUMO energy gap is systematically related to the central Pd-Pd distance (2.7319(6)-2.7575(6) Å) by two ways with neutral ligands L (1, 2, 3) and with anionic ligands X (4), which are reflected on the NIR absorption energy of 867-954 nm. The isocyanide terminated Pd₈ complexes (3) further reacted with excess of RNC (6 eq) to afford the Pd₄ complexes, [Pd₄ (meso-dpmppm)₂ (RNC)₂ ](BF₄ )₂ (13), and the cyclic voltammograms of 2 a (L=CH₃ CN), 3, and 13 (R=Xyl, Mes, ^t Bu, Cy) demonstrated wide range redox behaviors from 2{Pd₄ }⁴⁺ to 2{Pd₄ }⁰ through 2{Pd₄ }²⁺ ↔{Pd₈ }⁴⁺ , {Pd₈ }³⁺ , and {Pd₈ }²⁺ strings. The oxidized complexes, [Pd₄ (meso-dpmppm)₂ (RNC)₃ ](BF₄ )₄ (16), were characterized by X-ray analyses, and the two-electron reduced chain of [Pd₈ (meso-dpmppm)₄ ](BF₄ )₂ (7) was analyzed by spectroscopic and electrochemical techniques and DFT calculations. Reactions of 2 a with 1 equiv. of aromatic linear bisisocyanide (BI) in CH₂ Cl₂ deposited insoluble coordination polymers, {[Pd₈ (meso-dpmppm)₄ (BI)](BF₄ )₄ }_n (5), and interestingly, they were soluble in acetonitrile, ³¹ P{¹ H} and ¹ H DOSY NMR spectra as well as SAXS curves suggesting that the coordination polymers may exist in acetonitrile as dynamically 1D self-assembled coordination polymers comprising ca. 50 units of the Pd₈ rod averaged within the timescale.

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.

Modulation of Band Gaps toward Varying Conductivities in Heterometallic One-Dimensional Chains by Ligand Alteration and Third Metal Insertion

A heterometallic one-dimensional (1-D) chain consisting of multiple kinds of metals, Rh, Pt, and Pd, with direct metal-metal bonds was successfully obtained by mixing a Rh dinuclear complex and Pt-Pd-Pt trinuclear complex. The Pt-Pd-Pt trinuclear complex can be reversibly one-electron-oxidized or -reduced, where the electron paramagnetic resonance spectrum of the one-electron-oxidized one shows an axially symmetric signal with hyperfine splitting by two Pt and Pd, indicating that an unpaired electron is delocalized to the d _{z ²} orbital of Pt-Pd-Pt. Utilized with the highest occupied molecular orbital and lowest unoccupied molecular orbital interaction at the d _{z ²} orbital, simple mixing of the Pt-Pd-Pt trinuclear complex and Rh dinuclear complex in adequate solvents afforded heterometallic 1-D chains, which are aligned as -Rh-Rh-Pt-Pd-Pt-. Several physical measurements revealed that the metal oxidation state is +2. Diffuse reflectance spectra and theoretical calculations show that heterometallic 1-D chains have σ-type conduction and valence bands where π*(Rh₂) are lying between them, whose gaps become narrower than the prototype chains aligned as -Rh-Rh-Pt-Pt-Pt-Pt-. The narrower band gaps are induced by destabilization of the σ-type valence bands and accompanied by insertion of Pd ions because the d-orbital energy level of Pd is closer in value to Rh compared with Pt. Flash-photolysis time-resolved microwave conductivity measurements exhibited an increase in the product of charge carrier mobility and its generation efficiency (8.1 × 10^-5 to 4.6 × 10^-4 cm² V^-1 s^-1) with narrowing the band gaps, suggesting that the better conductivity is attributed to shorter metal-metal distances in 1-D chains. These results imply the possibilities of controlling band gap with ligand modification and third metal insertion in heterometallic 1-D chains to show various conductivities.

Theoretical Study on the Difference in Electron Conductivity of a One-Dimensional Penta-Nickel(II) Complex between Anti-Ferromagnetic and Ferromagnetic States-Possibility of Molecular Switch with Open-Shell Molecules

The electron conductivity of an extended metal atom chain (EMAC) that consisted of penta-nickel(II) ions bridged by oligo-α-pyridylamino ligands was examined by density functional theory (DFT) and elastic scattering Green’s functions (ESGF) calculations. The calculated results revealed that an intramolecular ferromagnetic (FM) coupling state showed a higher conductivity in comparison with an anti-ferromagnetic (AFM) coupling state. The present results suggest the potential of the complex as a molecular switch as well as a molecular wire.

Photo-induced translocation of a Pdn moiety (n = 2, 7) on a conjugated polyene ligand

The Pd₂-translocation on a tetraene ligand is switchable between the thermodynamic equilibrium state and the photo-stationary state. The Pd₇-translocation on a carotene ligand proceeds smoothly under photo-irradiation.

Pre-programmed self-assembly of polynuclear clusters

This perspective reviews our recent efforts towards the self-assembly of polynuclear clusters with ditopic and tritopic multidentate ligands HL1 (2-phenyl-4,5-bis{6-(3,5-dimethylpyrazol-1-yl)pyrid-2-yl}-1H-imidazole) and H2L2 (2,6-bis-[5-(2-pyridinyl)-1H-pyrazole-3-yl]pyridine), both of which are planar and rigid molecules. HL1 was found to be an excellent support for tetranuclear [Fe4] complexes, [FeII4(L1)4](BF4)4 ([FeII4]) and [FeIII2FeII2(L1)4](BF4)6 ([FeIII2FeII2]). The homovalent system was found to exhibit multistep spin crossover (SCO), while the mixed-valence [FeIII2FeII2] complex shows wavelength-dependent tuneable light-induced excited spin state trapping (LIESST). For H2L2, a variety of polynuclear complexes were obtained through complexation with different transition metal ions, allowing the isolation of rings, grids, and helix structures. The rigidity of the ligand, difference in its coordination sites, and affinity for different metal ions dictates its coordination behaviour. In this paper, we summarise these ligand pre-programmed self-assembled clusters and their diverse physical properties.

Planar PtPd3 Complexes Stabilized by Three Bridging Silylene Ligands

A heterobimetallic PtPd₃ complex supported by three bridging diphenylsilylene ligands, [Pt{Pd(dmpe)}₃ (μ₃ -SiPh₂ )₃ ] (1, dmpe=1,2-bis(dimethylphosphino)ethane), has been synthesized from mononuclear Pd and Pt complexes. The hexagonal core composed of Pt, Pd, and Si atoms is slightly larger than that of the tetrapalladium complex, [Pd{Pd(dmpe)}₃ (μ₃ -SiPh₂ )₃ ] (2). Reaction of PhSiH₃ with complex 1 in the presence and absence of Ph₂ SiH₂ results in the formation of a tetranuclear complex with silyl and hydride ligands at the Pt center, [PtH(SiPh₂ H){Pd(dmpe)}₃ (μ₃ -SiHPh)₃ ] (3), and an octanuclear complex, [{Pt{Pd(dmpe)}₃ (μ₃ -SiHPh)₃ }₂ (κ² -dmpe)] (5), respectively. Both M-Si (M=Pt, Pd) bond lengths and the ²⁹ Si NMR chemical shifts of 1 and 2 are located between those of mononuclear late transition-metal complexes with a silylene ligand and complexes with donor-stabilized silylene ligands. CuI and AgI adducts of 1 and 2, formulated as [M(μ-M'I){Pd(dmpe)}₃ (μ₃ -SiPh₂ )₃ ] (M=Pt, Pd; M'=Cu, Ag), undergo elimination of CuI (AgI) and regenerate the tetrametallic complexes upon heating or addition of a chelating diphosphine. Elimination of AgI from 2-AgI occurs more rapidly than elimination of CuI from 2-CuI, as determined from the results of kinetics experiments.

Electron-rich linear triplatinum complexes stabilized by a spinning tetraphosphine, tris(diphenylphosphinomethyl)phosphine

Linear triplatinum complexes with 48e(-), [Pt3(μ-tdpmp)2(RNC)2](PF6)2 (R = 2,6-xylyl (3), (t)Bu (4)), were synthesized by using a branched tetraphosphine, tris(diphenylphosphinomethyl)phosphine (tdpmp), and characterized by crystallographic and spectroscopic analyses to show their novel dynamic behaviour in the solution state, in which the linear Pt3 unit was stabilized by two spinning tetraphosphine ligands.

Oxidative addition of an aromatic ortho C-H bond of tetraphosphine to asymmetric diiridium(i) centres

Reactions of a tetraphosphine, meso-bis{[(diphenylphosphinomethyl)phenyl]phosphino}propane (dpmppp), with [IrCl(cod)]2 and CO (1 atm) or isocyanide (RNC) in the presence of NH4PF6 at 80-100 °C in dichloromethane/acetonitrile/acetone and/or methanol mixed solvents afforded asymmetric diiridium(ii) complexes, [Ir2(H)(Cl)(μ-(dpmppp-H)-κP(4)C)(CO)3]PF6 (1) and [Ir2(H)(μ-(dpmppp-H)-κP(4)C)(RNC)4)]-(PF6)2 (R = 2,6-xylyl (2), 2,4,6-mesityl (3); dpmppp-H = {PPh(o-C6H4)CH2P(Ph)(CH2)3P(Ph)CH2PPh2}(-)). A similar reaction with (t)BuNC resulted in the formation of a mononuclear Ir(III) complex of [Ir(H)(dpmppp-κP(3))((t)BuNC)2](PF6)2 (4). Complexes 1-3 were characterized by ESI mass spectrometry, (1)H and (31)P NMR spectroscopy and X-ray diffraction analyses. They were found to consist of cis/trans-P,P asymmetric Ir(II)-Ir(II) bonded dinuclear structures derived from oxidative addition of an ortho C-H bond of dpmppp (Ir-Ir = 2.8044(2) Å (1), 2.8569(2) Å (2), and 2.8524(5) Å (3)), resulting in a [IrPCCIr] intermetallic cyclometal-bridge and a terminal hydride. DFT calculations indicated the presence of Ir-Ir, Ir-H, and Ir-Cortho covalent bonds. Initial stages of the reactions with CO and XylNC at room temperature were investigated by (31)P{(1)H} NMR spectroscopy and found to contain a symmetrical Ir(I) dinuclear unit with dpmppp that was readily transformed into 1 and 2 upon heating. The Ir intermediate with XylNC, [Ir2(XylNC)4(μ-dpmppp)](PF6)2 (6), was isolated and characterized by X-ray crystallography and DFT calculations as an electron-deficient 32e(-) Ir species involving a Ir(I)→Ir(I) dative bond (2.7989(5) Å). The reaction pathways from 6 to 2 were investigated by DFT calculations. The present study suggested that a novel oxidative addition of an ortho C-H bond proceeded on the cis/trans-P,P asymmetric diiridium(i) scaffold supported by the tetraphosphine, dpmppp, which was assumed to be facilitated by dimetal cooperation with switching Ir→Ir dative interactions.

Construction of copper chains with new fluorescent guanidino-functionalized naphthyridine ligands

A high charge and a low coordination number are the characteristics of fluorescent Cu₄ chain complexes with 2,7-bisguanidino-naphthyridine ligands.

Stepwise Expansion of Pd Chains from Binuclear Palladium(I) Complexes Supported by Tetraphosphine Ligands

Reaction of [Pd2(XylNC)6]X2 (X = PF6, BF4) with a linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), afforded binuclear Pd(I) complexes, [Pd2(μ-dpmppm)2]X2 ([2]X2), through an asymmetric dipalladium complex, [Pd2(μ-dpmppm)(XylNC)3](2+) ([1](2+)). Complex [2](2+) readily reacted with [Pd(0)(dba)2] (2 equiv) and an excess of isocyanide, RNC (R = 2,6-xylyl (Xyl), tert-butyl ((t)Bu)), to generate an equilibrium mixture of [Pd4(μ-dpmppm)2(RNC)2](2+) ([3'](2+)) + RNC ⇄ [Pd4(μ-dpmppm)2(RNC)3](2+) ([3](2+)), from which [Pd4(μ-dpmppm)2(XylNC)3](2+) ([3a](2+)) and [Pd4(μ-dpmppm)2((t)BuNC)2](2+) ([3b'](2+)) were isolated. Variable-temperature UV-vis and (31)P{(1)H} and (1)H NMR spectroscopic studies on the equilibrium mixtures demonstrated that the tetrapalladium complexes are quite fluxional in the solution state: the symmetric Pd4 complex [3b'](2+) predominantly existed at higher temperatures (>0 °C), and the equilibrium shifted to the asymmetric Pd4 complex [3b](2+) at a low temperature (∼-30 °C). The binding constants were determined by UV-vis titration at 20 °C and revealed that XylNC is of higher affinity to the Pd4 core than (t)BuNC. In addition, both isocyanides exhibited higher affinity to the electron deficient [Pd4(μ-dpmppmF2)2(RNC)2](2+) ([3F'](2+)) than to [Pd4(μ-dpmppm)2(RNC)2](2+) ([3'](2+)) (dpmppmF2 = meso-bis[{di(3,5-difluorophenyl)phosphinomethyl}phenylphosphino]methane). When [2]X2 was treated with [Pd(0)(dba)2] (2 equiv) in the absence of RNC in acetonitrile, linearly ordered octapalladium chains, [Pd8(μ-dpmppm)4(CH3CN)2]X4 ([4]X4: X = PF6, BF4), were generated through a coupling of two {Pd4(μ-dpmppm)2}(2+) fragments. Complex [2](2+) was also proven to be a good precursor for Pd2M2 mixed-metal complexes, yielding [Pd2Cl(Cp*MCl) (Cp*MCl2)(μ-dpmppm)2](2+) (M = Rh ([5](2+)), Ir ([6](2+)), and [Au2Pd2Cl2(dpmppm-H)2](2+) ([7](2+)) by treatment with [Cp*MCl2]2 and [AuCl(PPh3)], respectively. Complex [7](2+) contains an unprecedented PC(sp(3))P pincer ligand with a PCPCPCP backbone, dpmppm-H of deprotonated dpmppm. The present results demonstrated that the binuclear Pd(I) complex [2](2+) was a quite useful starting material to extend the palladium chains and to construct Pd-involved heteromultinuclear systems.

Multinuclear metal-binding ability of a carotene

Carotenes are naturally abundant unsaturated hydrocarbon pigments, and their fascinating physical and chemical properties have been studied intensively not only for better understanding of the roles in biological processes but also for the use in artificial chemical systems. However, their metal-binding ability has been virtually unexplored. Here we report that β-carotene has the ability to assemble and align ten metal atoms to afford decanuclear homo- and heterometal chain complexes. The metallo–carotenoid framework shows reversible metalation–demetalation reactivity with multiple metals, which allows us to control the size of metal chains as well as the heterobimetallic composition and arrangement of the carotene-supported metal chains.

Carotenes are naturally abundant, widely studied unsaturated hydrocarbon pigments but their metal-binding ability has been virtually unexplored. Here, the authors demonstrate that they can be used to reversibly assemble and align homo- and hetero-metallic decanuclear chain complexes.