Bunsho Kure

Facile Insertion of Carbon Dioxide into Cu2(μ-H) Dinuclear Units Supported by Tetraphosphine Ligands

Reactions of meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm) with Cu(I) species in the presence of NaBH4 afforded di- and tetranuclear copper hydride complexes, [Cu2(μ-H)(μ-dpmppm)2]X (1) and [Cu4(μ-H)2(μ4-H)(μ-dpmppm)2]X (2) (X=BF4, PF6). Complex 1 undergoes facile insertion of CO2 (1 atm) at room temperature, leading to a formate-bridged dicopper complex [Cu2(μ-HCOO)(dpmppm)2]X (3). The experimental and DFT theoretical studies clearly demonstrate that CO2 insertion into the Cu2(μ-H) unit occurred with the flexible dicopper platform. Complex 2 also undergoes CO2 insertion to give a formate-bridged complex, [Cu4(μ-HCOO)3(dpmppm)2]X, during which the square Cu4 framework opened up to a linear tetranuclear chain.

Self‐Alignment of Low‐Valent Octanuclear Palladium Atoms

A linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm) was used to synthesize linear octapalladium-extended metal atom chains as discrete molecules of [Pd8(μ-dpmppm)4](BF4)4 (1) and [Pd8(μ-dpmppm)4L2](BF4)4 (L=2,6-xylyl isocyanide (XylNC; 2), acetonitrile (3), and N,N-dimethylformamide (dmf; 4)), which are stable in the solution states and show interesting temperature-dependent photochemical properties in the near IR region. Variable temperature NMR studies demonstrated that at higher temperature T≈140 °C the Pd8 chains were dissociated into Pd4 fragments, which were thermodynamically self-aligned to restore the Pd8 chains at lower temperature T<60 °C. The coldspray ionization mass spectra suggested a possibility for further aggregation of the linear tetrapalladium units.

Wheel-Shaped Icosanuclear Homo- and Heterometallic Complexes of NiII, CoII, and CuII Ions Supported by Unsymmetrical Aminoalcohol Ligands

Reactions of M(OAc)2·4H2O (M = Ni, Co) with 3-[benzyl(2-hydroxyethyl)amino]-1-propanol (H2L) in the presence of pyridine or triethylamine afforded novel homometallic icosanuclear wheel-shaped complexes [M20L4(HL)4(OAc)28] (M = Ni (1), Co (2)), which consist of a central M(II)12 single-stranded, nearly planar loop with four peripheral [M2(HL)(OAc)2] fragments attached in an S4 symmetrical fashion. The complexes can alternatively be recognized as saddle-shaped wheel structures, in which four tetranuclear units of [M4L(HL)(OAc)7](2-) are connected by four M(2+) ions (M5). The tetranuclear unit itself can be derived from an ideal C2 symmetrical [M4(HL)2(μ-η(2)-OAc)4(μ-η(1),η(1)-OAc)2(η(1),η(1)-OAc)](-) structure through deprotonation of the HL(-) ligand, and is composed of two plane-shared M3O4 incomplete cubanes in which the M2 and M3 atoms are involved in the central fused plane and the M1 and M4 atoms are disposed at the apex sites. Mixed-metal icosanuclear complexes [NixM20-xL4(HL)4(OAc)28] (3, M = Co, x = 9.5) and [Ni12M8L4(HL)4(OAc)28] (4, M = Cu) were also synthesized by using equimolar amounts of Ni(II) and M(II) ions, and were shown to have similar structures to 1 and 2. X-ray crystallographic and fluorescent analyses revealed that complex 3 contains nonstoichiometric amounts of Ni(2+) and Co(2+) ions in the ratio of 9.5:10.5 and that these are disordered at every metal site. In striking contrast, complex 4 has a stoichiometric formula of Ni12Cu8, which was confirmed by the Jahn-Teller elongation of Cu(2+) ions, and consequently, the M2 and M5 positions are occupied exclusively by the Cu(2+) ions. The temperature-dependent direct current (dc) magnetic susceptibility data showed the presence of ferromagnetic exchange interactions in the Ni homometallic (1) and NiCu bimetallic (4) complexes, while the Co homometallic (2) and NiCo bimetallic (3) complexes exhibited antiferromagnetic interactions due to spin-orbit coupling effects of the octahedral Co(II) ions. The present results demonstrate that the unsymmetrical aminoalcohol ligand H2L is quite effective in organizing the homo- and heterometallic icosanuclear wheel-shaped metal arrangements.

Reversible dioxygen binding on asymmetric dinuclear rhodium centres

Electron-deficient dinuclear rhodium complexes [Rh2Cl2(μ-dpmppp)(RNC)] (1), with the linear tetraphosphine ligand dpmppp, showed reversible binding of molecular oxygen to form asymmetric dirhodium η(2)-peroxo complexes [Rh2Cl2(O2)(μ-dpmppp)(RNC)] (2) stabilized by a Rh→Rh dative bond.

A Fluxional Cu8H6 Cluster Supported by Bis(diphenylphosphino)methane and its Facile Reaction with CO2

A copper hydride cluster [Cu8 (μ-H)6 (μ-dppm)5 ](PF6 )2 (dppm=bis(diphenylphosphino)methane) was prepared from reaction of [CuH(PPh3 )]6 with dppm in the presence of [Cu(CH3 CN)4 ]PF6 and exhibited fluxional behaviors in solution where the hydrides and the phosphines are scrambling around the trans-bicapped octahedral Cu8 framework. The Cu8 H6 complex showed facile reactivity with CO2 (1 atm, RT) to afford a tricopper complex, [Cu3 (μ-H)(μ-O2 CH)(μ-dppm)3 ]PF6 , which could be developed to unprecedented hydrosilylation of CO2 catalyzed by multinuclear CuH species under mild conditions.

Chiral Self‐Recognition between Stereogenic Tetrapalladium Units Affording Pd8 Chains Supported by Homochiral Tetraphosphines

By using a chiral tetraphosphine, rac-bis[(diphenylphosphinomethyl)phenylphosphino]methane (rac-dpmppm), linear octapalladium chains were synthesized as discrete molecules of [Pd8 (μ-rac-dpmppm)4 L2 ](BF4 )4 (L=CH3 CN, dmf, XylNC), [Pd8 (μ-rac-dpmppm)4 ](BF4 )4 , and [Pd8 (μ-rac-dpmppm)4 (Cl)2 ](BF4 )2 , which are stable in the solution states and characterized by spectroscopic and crystallographic methods to reveal the octapalladium chains supported by homochiral four tetraphosphines. Variable-temperature NMR studies for a 1:1 mixture of [Pd8 (μ-rac-dpmppm)4 (dmf)2 ](BF4 )4 and [Pd8 (μ-meso-dpmppm)4 (dmf)2 ]-(BF4 )4 in [D7 ]DMF revealed that the Pd8 chains were dissociated at higher temperature (T≈140 °C) into the Pd4 units of {Pd4 (μ-rac-dpmppm)2 }2+ and {Pd4 (μ-meso-dpmppm)2 }2+ , and they were thermodynamically self-aligned to restore the Pd8 chains at lower temperature (T<60 °C), through perfect chiral self-recognition between the stereogenic tetrapalladium units.

Gold and Silver Chains Supported by Linear Hexaphosphine Ligands

A new linear hexaphosphine, rac-cis,cis,trans-bis{[(diphenylphosphinomethyl)phenylphosphinomethyl]phenylphosphino}methane (P6), was synthesized and isolated as a pure isomer, confirmed by transforming to the corresponding phosphine sulfide. The methylene-bridged linear hexaphosphine readily organized flexible gold(I) and silver(I) hexanuclear chains, [M6(μ-P6)2]X6 (X6 = (OTf)6, M = Au (1), Ag (2); X6 = Cl2(PF6)4, M = Au (3)). The hexaphosphine also supported a tetrasilver(I) complex [Ag4(μ-P6)2](OTf)4 (4), which was readily transformed by treatment with AgOTf into 3, revealing a drastic alternation of the two P6 arrangement. The hexagold(I) chains exhibited a considerably red-shifted absorption (∼410 nm) and emission (540-580 nm) to (1) [5dσ*→6pσ] and from (3) [5dσ*→6pσ] excited states of the metal centers, respectively. The new linear hexaphosphine could be a useful tool to construct linear metal clusters as subnano building blocks.

Extraction of Electrons from H2with a NiIRuICatalyst

The mechanism of extraction of electrons from H2 catalyzed by hydrogenases has proven challenging to elucidate. Catalytic extraction of electrons from H2 has been achieved by use of a low-valent Ni...