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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

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+ (13RR and 13SS ), 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.

Binuclear Pd(II) and Pt(II) complexes supported by rac-dpmppm (bis[(diphenylphosphinomethyl)phenylphosphino]methane) in a triply-bridged Z-form, [M2Cl4(rac-dpmppm)] (M = Pd (3a), Pt (3b)), readily reacted with 2,6-xylyl isocyanide (XylNC) in the presence of NH4PF6 to afford [M2Cl2(rac-dpmppm)(XylNC)2](PF6)2 (M = Pd (4a), Pt (4b)), in which each metal center accommodates one isocyanide ligand at the trans position to the inner P atom of dpmppm. Similarly, treatment of 3a and 3b with axially chiral (R/S)-1,1'-binaphthyl-2,2'-bisisocyanide (rac-Binac) in the presence of NH4OTf gave cyclic tetranuclear complexes, [{M2Cl2(rac-dpmppm)(rac-Binac)}2](OTf)4 (M = Pd (5), Pt (8)), where two {M2Cl2(rac-dpmppm)}2+ fragments are connected by two rac-Binac ligands through chirality sorting of (R*,R*)-dpmppm and (R*)-Binac. Complex 5 could be transformed into the halide exchanged tetranuclear complexes, [{Pd2X2(rac-dpmppm)(rac-Binac)}2](OTf)4 (X = Br (6), I (7)), to show that the rectangular arrangement of four Pd(II) ions is elongated by repulsive interaction between halide ligands. By using (R)- and (S)-Binac, enantiopure Pd4 complexes, [{Pd2Cl2((R*,R*)-dpmppm)((R*)-Binac)}2](OTf)4 (5RR/R and 5SS/S), were successfully isolated as pure crystalline forms, from which enantiopure (R,R)- and (S,S)-dpmppm were obtained by treatment with NaCN aqueous solution. Namely, optical resolution of rac-dpmppm was established through the tetranuclear Pd complexes, which is the first example for methylene-bridged polyphosphines, R2P(CH2PR)nCH2PR2 (n > 0). Furthermore, chiral octapalladium chains, [Pd8((R*,R*)-dpmppm)4(N≡CCH3)2](BF4)4 (2RR and 2SS), were synthesized by reacting enantiopure P-chiral dpmppm with [Pd2(CH3CN)6](BF4)2 and [Pd2(dba)3]·C6H6 and were characterized by spectroscopic and X-ray crystallographic analyses, to determine the absolute configurational structures. The Pd8 chains are the longest enantiopure chiral single-metal-atom chains structurally characterized, thus far, and the electronic structures were examined on the basis of DFT calculations of 2RR.

The Pd8 string supported by linear tetraphosphine ligands reacted with H+ to afford a Pd4H complex with a terminal hydride, and was applied to the electrocatalytic H2 formation from H+ by making a chemically modified electrode with Nafion film.

Rationally designed topological arrangement of multinuclear transition metal centers is of fundamental importance to create diverse functions applicable to catalysts, electronic, photochemical, and...

Two linear tetradentate phosphine ligands

A P-stereogenic linear tetraphosphine tetraoxide, (R,R)- or (S,S)-dpmppm(=O)

The linear Pd

By using a linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), nona- and hexadecanuclear copper hydride clusters, [Cu9 H7 (μ-dpmppm)3 ]X2 (X=Cl (1 a), Br (1 b), I (1 c), PF6 (1 d)) and [Cu16 H14 (μ-dpmppm)4 ]X2 (X2 =I2 (2 c), (4/3) PF6 ⋅(2/3) OH (2 d)) were synthesized and characterized. They form copper-hydride cages of apex-truncated supertetrahedral {Cu9 H7 }2+ and square-face-capped cuboctahedral {Cu16 H14 }2+ structures. The hydride positions were estimated by DFT calculations to be facially dispersed around the copper frameworks. A kinetically controlled synthesis gave an unsymmetrical Cu8 H6 cluster, [Cu8 H6 (μ-dpmppm)3 ]2+ (3), which readily reacted with CO2 to afford linear Cu4 complexes with formate bridges, leading to an unprecedented hydrogenation of CO2 into formate catalyzed by {Cu4 (μ-dpmppm)2 } platform. The results demonstrate that new motifs of copper hydride clusters could be established by the tetraphosphine ligands, and the structures influence their reactivity.

Reaction of [IrCl(CO)(PPh3)2] with meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (meso-dpmppm) afforded a mononuclear IrI complex, [Ir(meso-dpmppm−κ3)(CO)2]Cl (1), which showed excellent reactivity towards HX, H2, HCOOH, and R3SiH to yield a series of IrIII hydride complexes, [IrH(meso-dpmppm−κ3)(CO)2]X2 (X = Cl (2), PF6 (2*)), [Ir(H)2(meso-dpmppm−κ3)(CO)]Cl (4), and [IrH(SiR3)(meso-dpmppm−κ3)(CO)]Cl (R3 = Me2Ph (5a), Ph2H (5b)). The hydride IrIII complexes with isocyanides, [IrH(meso-dpmppm−κ3)(RNC)2](PF6)2 (R = Xyl (2,6-xylyl) (3a), Mes (2,4,6-mesityl) (3b), Cy (cyclohexyl) (3c), tBu (tert-butyl) (3d)), were also prepared by reacting [IrCl(cod)]2 with meso-dpmppm and RNC in the presence of NH4PF6. Complexes 2–5 were characterized by 1H and 31P NMR and ESI−MS spectroscopies and X-ray diffraction analyses (3a, 4, 5a,b) to have distorted octahedral IrIII structures supported by a meso-dpmppm in meridional mode as an unsymmetrical PPP−κ3 pincer ligand, coordinating with two outer and one inner phosphorus atoms to form fused six- and four-membered chelate rings and bearing an uncoordinate inner phosphine unit. The terminal hydride occupied the axial open site surrounded by the equatorially oriented phenyl groups of meso-dpmppm and is trans to the carbonyl (2, 4) and isocyanide ligands (3) nested in the closed site with respect to the {Ir(meso-dpmppm−κ3)} pincer plane. The remaining equatorial site is coordinated by CO (2), RNC (3), hydride (4), and silyl (5) ligand. These structural features demonstrated that oxidative additions of H+, H2, and R3SiH occurred at the axial open site of 1. The uncoordinate inner phosphine of 1 is readily reacted with [Cp*IrCl2]2 to give [Ir(μ−meso-dpmppm−κ3)(η5−Cp*IrCl2)(CO)2]Cl (1∙Cp*IrCl2, Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl), which further transformed by oxidative addition of H2 and HCl to [Ir(H)2(μ−meso-dpmppm−κ3)(η5−Cp*IrCl2)(CO)]Cl (4∙Cp*IrCl2) and [IrH(μ−meso-dpmppm−κ3) (η5−Cp*IrCl2)(CO)2]Cl2 (2∙Cp*IrCl2), respectively, and however addition of bulky Me2PhSiH resulted in a disproportionation mixture of [IrH(Me2PhSi)(μ−meso-dpmppm−κ3)(η5-Cp*IrCl2)(CO)]Cl (5a∙Cp*IrCl2) as well as 4∙Cp*IrCl2, indicating an allosteric influence by attaching Cp*IrCl2 unit on the uncoordinate phosphine of the {Ir(meso-dpmppm−κ3)} unsymmetric pincer unit in 1.

A new linear tetraphosphine containing a PNP phosphazane bridge, rac-bis[(diphenylphosphinomethyl)phenylphosphino]phenylamine (rac-dpmppan), was synthesized and utilized to support a series of Pd/Pt mixed metal tetranuclear chains, [Pd4-n Ptn (μ-rac-dpmppan)2 (XylNC)2 ](PF6 )2 (XylNC=xylyl isocyanide; n=0: Pd4 (1), 1: PtPd3 (2), 2: PtPd2 Pt (3), 2: Pt2 Pd2 (4), 3: Pt2 PdPt (5)), in which the number and positions of additional Pt atoms were successfully controlled depending on the respective synthetic procedures using transformations from 1 to 3 through 2 and from 4 to 5 by redox-coupled exchange reactions. The 31 P{1 H} NMR and ESI mass spectra and X-ray diffraction analyses revealed almost identical tetranuclear structures, with slight contraction of metal-metal bonds according to incorporation of Pt atoms. The electronic absorption spectra of 1-5 exhibited characteristic bands at 635-510 nm with an energy propensity depending on the number and positions of Pt centres, which were assigned to HOMO (dσ*σσ*) to LUMO (dσ*σ*σ*) transition by theoretical calculations. The present results demonstrated that the electronic structures of Pd/Pt mixed-metal tetranuclear complexes are finely tuned as orbital-overlapping alloyed metal chains by atomically precise Pt incorporation in the Pd4 chain.

A linear tetraphosphine meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (meso-dpmppm), was utilized to prepare a PtI dinuclear complex, [Pt2(μ−meso-dpmppm−κ2,κ1)(XylNC)3](PF6)2 (2), which was derived from reaction of [PtII(meso-dpmppm−κ3)(XylNC)](PF6)2 (1) with 1/3 equiv. of [Pt3(XylNC)6]. Treatment of 2 with 1/3 equiv. of [Pt3(XylNC)6] gave an A-frame Pt3 complex, [Pt3(μ−meso-dpmppm−κ2,κ1)(XylNC)5](PF6)2 (3), demonstrating that a meso-dpmppm ligand effectively support the expansion of platinum nuclearity from Pt2+ through {Pt2}2+ to {Pt3}2+ cores in stepwise fashion. Reaction of 2 with 1 equiv. of meso-dpmppm afforded [Pt2(μ−meso-dpmppm−κ2,κ1)2](PF6)2 (4), which would not react with [Pt3(XylNC)6], and in contrast, treatment of 3 with excess of [Pt3(XylNC)6] gave birth to a decanuclear platinum complex, [Pt10(μ−meso-dpmppm−κ2,κ1,κ1)2(XylNC)18](PF6)6, (5), comprised of a linear Pt4 chain {Pt4(XylNC)8}2+ terminated by two Pt3 A-frame units of {Pt3(μ−meso-dpmppm−κ2,κ1,κ1)(XylNC)5}2+, which is an interesting nano-ordered Pt cluster constructed with small size multinuclear building blocks, and notably contains the longest metal–metal bonded Pt chain without any bridging ligands.

Multinuclear copper hydride complexes were synthesized by using a triphosphine, bis(diphenylphosphinomethyl)phenylphosphine (dpmp). The reaction of [Cu(MeCN)4]PF6 with dpmp in 2 : 1 ratio in the presence of Me4NBH4 or NaBH4 yielded a hexanuclear complex, [Cu6(μ3-H)5(μ-dpmp)3]PF6 (1), together with a minor product [Cu8(μ-H)2(μ4-H)4(μ-dpmp)4](PF6)2 (2) in a very low yield. Complex 1 was also prepared from [CuH(PPh3)]6, [Cu(MeCN)4]PF6, and dpmp in 87%, but the yield of 2 could not be improved presumably due to its instability in solution. A tetranuclear complex, [Cu4(μ-H)(μ3-H)2(μ-dpmp)3]PF6 (4), was obtained from the reaction of [Cu(MeCN)4]PF6 with dpmp in 4 : 3 ratio, or that of [Cu3(μ-dpmp)2(MeCN)4](PF6)3 (3) and dpmp, in the presence of Me4NBH4 for both cases. The structures of 1, 2, and 4 were determined by X-ray crystallography, and the positions of hydride ligands were elucidated by DFT optimization. Complex 1 consists of a distorted trigonal anti-prismatic Cu6 core bridged by three L-shaped dpmp ligands and five μ3-hydrides, and 2 is composed of three edge-shared tetrahedral Cu4 units supported by four L-shaped dpmp ligands and two μ2-hydrides in the two outer Cu4 units and four μ4-hydride ligands in the central Cu4 units. The structures of two outer Cu4 units in 2 resemble those of 4, where a Cu4 tetrahedron is supported by two L-shaped dpmp ligands and one dpmp-κ2P,P′ bridge, in addition to one μ2- and two μ3-hydrides. Natural bond orbital analyses suggest that the hydrides act as glue between the multinuclear copper centres through electron-deficient delocalized bonding interactions, which result in partial electron migration from hydrides to CuI centres.

Reaction of [PtCl2(cod)] with a tetraphosphine meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (meso-dpmppm), afforded mononuclear PtII complexes, [PtCl(meso-dpmppm−κ3)]X (X = Cl (1a), PF6 (1b)); the meso-dpmppm ligand coordinates to the PtII ion tightly with two outer and one inner phosphorus atoms to form fused six- and four-membered chelate rings which is regarded as an asymmetric PPP pincer ligand bearing an uncoordinate inner phosphine unit. Complex 1 readily reacted with RNC in the presence of NH4PF6 to afford [Pt(meso-dpmppm−κ3)(RNC)](PF6)2 (R = Xyl (2a), Cy (2b), tBu (2c)). When 2a and 2b were reacted with excess of benzylamine (BnNH2), N-acyclic carbene complexes, [Pt(meso-dpmppm−κ3){C(NHR)(NHBn)}](PF6)2 (R = Xyl (3a), Cy (3c)), were obtained, and a similar treatment of 2a with n-octylamine (C8H17NH2) afforded [Pt(meso-dpmppm−κ3)- {C(NHXyl)(NHC8H17)}](PF6)2 (3b). In contrast, complex 2c was transformed into a cyanide complex, [Pt(CN)(meso-dpmppm−κ3)]PF6 (4), through N C(tBu) bond cleavage when heated at 80 °C with BnNH2 or PhNH2. Complexes 1–4 were characterized by 1H and 31P NMR and ESI-MS spectroscopies and X-ray diffraction analyses. The uncoordinate inner phosphine of 1b is readily reacted with [Cp*MCl2]2 to give heterodimetallic complexes, [PtCl(η5-Cp*MCl2)(μ−meso-dpmppm−κ3,κ1)]PF6 (M = Ir (5a), Rh (5b); Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl). Complex 2a also reacted with [Cp*IrCl2]2 to yield [Pt(η5-Cp*IrCl2)(μ−meso-dpmppm−κ3,κ1)(XylNC)]PF6 (6a) together with 5a, and however, 6a would not react with BnNH2, just releasing XylNC to result in 5a. Attachment of the metal fragment of {Cp*IrCl2} to the uncoordinated phosphine caused a crucial conformational change of the six-membered chelate ring from a stable chair conformation to a twist-boat structure, which concomitantly reduced reactivity of the isocyanide ligand toward nucleophilic attack of the amine by steric hindrance of meso-dpmppm pincer ligand. These results could be recognized as on/off switching of the asymmetric {PtII(meso-dpmppm−κ3)} pincer complex.

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) A) 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.

Binuclear Pd(II) and Pt(II) complexes supported by

Three types of tetradentate phosphine ligands with different central methylene chains and configurations, meso- and rac-Ph2PCH2P(Ph)(CH2)nP(Ph)CH2PPh2 (n = 2, meso- and rac-dpmppe; n = 3, meso-dpmppp) were utilized to synthesize a new series of tri- and tetranuclear copper hydride complexes. Reactions of meso-dpmppe or meso-dpmppp with CuCl/NH4PF6 or [Cu(CH3CN)4]PF6 in the presence of NaBH4 afforded trinuclear copper hydride complexes, [Cu3(μ3-H)(meso-dpmppe)2](PF6)2 (1) and [Cu3(μ3-H)(meso-dpmppp)2](PF6)2 (2), while a similar reaction with rac-dpmppe resulted in the formation of a tetranuclear copper dihydride complex, [Cu4(μ3-H)2(rac-dpmppe)2](PF6)2 (5). Complexes 1 and 5 further reacted with RNC (R = tBu, Cy, Xyl) to give [Cu3(μ3-H)(meso-dpmppe)2(XylNC)](PF6)2 (3), [Cu4(μ3-H)2(meso-dpmppe)2(RNC)2](PF6)2 (R = tBu (4a), Cy (4b)) and [Cu4(μ3-H)2(rac-dpmppe)2(RNC)2](PF6)2 (R = tBu (6a), Cy (6b), Xyl (6c)), respectively. Complexes 1–6 were characterized by ESI-MS and 1H and 31P NMR spectroscopy and X-ray di...

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.

By treating [Pt6(µ-H)(H)2(µ-dpmp)4]BH4 [4, dpmp = bis(diphenylphosphinomethyl)phenylphosphine] with an excess amount of HBF4 in N,N-dimethylformamide (DMF), a triplatinum tetrahydride complex, [Pt3(µ-H)2(H)2(µ-dpmp)2](BF4)2 (5), was obtained in 51 % yield and was characterized by IR, UV/Vis, 1H NMR, and 31P{1H} NMR spectroscopy in addition to ESI mass spectrometry, X-ray crystallography, and DFT calculations. Complex 5 is composed of linear trinuclear platinum centers supported by two dpmp ligands, {Pt3(µ-dpmp)2}6+, which accommodate two terminal and two bridging hydrides in a HPtHPtHPtH zigzag structure. The hydride positions were determined by DFT optimization with B3LYP/GD3BJ functionals. Variable-temperature 1H{31P} NMR spectroscopy in [D7]DMF revealed that the bridging hydrides exhibit fluxional behavior and migrate along the Pt3 chain by switching the bridging site, whereas the terminal hydrides are not exchanged with the bridging ones. The present results suggest that the divalent linear triplatinum unit of {Pt3(µ-dpmp)2}2+ (Pt3II), which is a building block to construct [Pt6(µ-H)(H)2(µ-dpmp)4]+ (4, Pt3IIPt3II), formally acts as a four-electron source to result in [Pt3(µ-H)2(H)2(µ-dpmp)2]2+ (5, Pt3VI) through protonation.

By using a linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), nona- and hexadecanuclear copper hydride clusters, [Cu

Hexanuclear copper hydride complexes, [Cu

A new linear tetraphosphine containing a PNP phosphazane bridge, rac-bis[(diphenylphosphinomethyl)phenylphosphino]phenylamine (rac-dpmppan), was synthesized and utilized to support a series of Pd/Pt mixed metal tetranuclear chains, [Pd

A linear tetraphosphine, meso-Ph2PCH2P(Ph)CH2P(Ph)CH2PPh2 (meso-dpmppm), was found to support a series of bent tetranuclear rhodium(I) arrays of [Rh4(μ−Cl)Cl2(CO)4(meso-dpmppm)2]Cl (1), [Rh4(μ−Cl)2(meso-dpmppm)2]X2 (X = PF6 (2a), BF4 (2b), TfO (2c), BPh4 (2d)), and [Rh4(μ−Cl)(CH3CN)2(CO)4(meso-dpmppm)2](TfO)3 (3) which are regarded as tetranuclear extended Vaska-type RhI complexes. Two meso-dpmppm ligands with mutual syn-arrangement established a flexible bending chains of {Rh4(meso-dpmppm)2}4+ which accommodated a variety of ligand sets of {(μ−Cl)Cl2(CO)4}3‒, {(μ−Cl)2(CO)4}2‒, and {(μ−Cl)(CH3CN)2(CO)4}‒ with Rh–Rh–Rh angles of 142.18(1)–161.54(1)°. The tetranuclear rhodium(I) core of 2 was interestingly reactive toward H2 (1 atm) under mild conditions at room temperature to afford {Rh4H3}3+ hydride complexes with linear RhI∙∙∙RhII–RhII∙∙∙RhI array, [Rh4(μ−Cl)2(μ−H)3(μ−CO)(CO)2(meso-dpmppm)2]X (X = PF6 (4a), BF4 (4b), TfO (4c)), where the positions of three hydride ligands were estimated with 1H, 1H{31P}, and 31P{1H} NMR spectra, a single crystal X-ray diffraction analysis, and DFT calculations. The linearly ordered {Rh4H3}3+ species that store four electrons from dihydrogen molecules is the first example of linear Rh hydride chains and would be useful platform for exploring cooperative reactions promoted by constrained multimetallic centers.

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

A series of SNn mixed-donor ligands [n = 2: H2NC2H4SCH2-2-pyridyl (2-NSpy) (1a), H2NC2H4SCH2-4-pyridyl (4-NSpy) (1b), n = 3: 2-pyridylCH2NHC2H4SCH2-2-pyridyl (2-pyNSpy) (2), n = 4: (2-pyridylCH2)2NC2H4SCH2-2-pyridyl (2-py2NSpy) (3)] was utilized to support homo- and heterodinuclear complexes including Cp*MIII units (M = Rh, Ir; Cp* = pentamethylcyclopentadienyl). Reactions of [Cp*MCl2]2 with 2-pyNSpy (2), 2-py2NSpy (3), and 4-NSpy (1b) afforded homodinulear complexes, [(Cp*MCl)(2-pyNSpy)(Cp*MCl)](PF6)2 [M = Rh (5a), Ir (5b)], [(Cp*M)(2-py2NSpy)(Cp*MCl)](PF6)3 [M = Rh (6a), Ir (6b)], [(Cp*MCl)(4-NSpy)(Cp*MCl2)]Cl [M = Rh (8a), Ir (8b)]. Heterodinuclear complexes [(Cp*MCl)(4-NSpy)(Cp*M′Cl2)]Cl [M, M′ = Rh, Ir (8c), Ir, Rh (8d)] were prepared using mononuclear complexes [(Cp*MCl)(4-NSpy)]Cl [M = Rh (7a), Ir (7b)] reacted with [Cp*MCl2]2 (M = Ir, Rh), respectively. Complexes 5–8 were characterized by X-ray crystallography to determine the configurations around the M, M′, S, and N centers. The solid-state structures of 6 are retained in acetonitrile solution whereas four diastereomers are generated in the case of 5 due to low stereoselectivity around the coordinated amine nitrogen atom, in contrast to the sulfur atom. Heterodinuclear complexes 8c,d are unstable in solution at 55 °C, readily affording mixtures of 8a–d via intra- and intermolecular coordination-site-exchange reactions of Cp*M fragments between the SN moiety and the py site. In order to evaluate the selectivity of Cp*M fragments for the SN and py coordination sites, several competitive reactions of [Cp*MCl2]2 (M = Rh, Ir) with H2NC2H4SCH2C6H5 (NSph) (4) and/or 4-methylpyridine (4-Mepy) were carried out to demonstrate predominant formation of iridium complexes 9b and 10b among [(Cp*MCl)(NSph)]Cl [M = Rh (9a), Ir (9b)] and [(Cp*MCl)(4-Mepy)]Cl [M = Rh (10a), Ir (10b)]. These reactions indicated higher affinity of the Cp*Ir fragment to both the NS and py sites relative to the rhodium analogue.

The reaction of Cu(NO3)2·3H2O with an N2O2 tetradentate amino alcohol, N,N-dibenzyl-N′,N′-bis(2-hydroxyethyl)ethylenediamine (H2L), afforded the mononuclear copper complex [Cu(H2L)(NO3)](NO3) (1), which has been used to construct a series of di-, tri-, and tetranuclear homo- and heterometallic complexes. Complex 1 dimerized in the presence of NEt3 to form the Cu2 complex [Cu2(HL)2](NO3)2 (2) by the deprotonation of one of the two hydroxy groups in the H2L ligand. The reaction of 1 with Cu(OCOH)2 in the presence of NEt3 afforded the Cu3 complex [Cu3(HL)2(OCOH)2](NO3)2 (5). The metalloligand {Cu(HL)}+ derived from 1 reacted with M(OAc)2 (M = Cu, Co, Zn, Ni) in the absence of NEt3 to form the asymmetric CuM dinuclear complexes [CuM(HL)(OAc)(NO3)2] [M = Cu (3a), Co (3b), Zn (3c), Ni (3d)], whereas in the presence of NEt3 a unit of M(OAc) was captured by two metalloligands to give the bent CuMCu trinuclear complexes [Cu2M(HL)2(OAc)2(NO3)](NO3) [M = Cu (4a), Co (4b), Mn (4c)], which were further transformed into the linear CuMCu trinuclear complexes [Cu3(HL)2{(PhO)2PO2}2](NO3)2 (7a) and [Cu2M(HL)2{(PhO)2PO2}2(MeOH)2](NO3)2 [M = Co (7b), Mn (7c)] with the aid of diphenyl phosphate bridging ligands. When (PhO)PO2(OH) was used as an auxiliary bridging ligand in the reaction of 1 with M(OAc)2 and NEt3, the Cu2M2 tetranuclear complexes [Cu2M2(HL)2{(PhO)PO3}2(NO3)2] [M = Co (8a), Zn (8b)] were synthesized. These results demonstrate that the mononuclear copper synthon with the N2O2 tetradentate amino alcohol ligand {Cu(H2L)}2+ generates the quite useful metalloligand {Cu(HL)}+ by the deprotonation of a hydroxy group, and subsequent reactions lead to the construction of a series of homo- and heterometal complexes containing Cu2, CuM (M = Cu, Co, Zn, Ni), bent-CuMCu (M = Cu, Co, Mn), linear-CuMCu (M = Cu, Co, Mn), and Cu2M2 (M = Co, Mn) cores in a systematic and selective manner.

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.

Reaction of AgOTf with a tetraphosphine, rac-bis[(diphenylphosphinomethyl) phenylphosphino]methane (rac-dpmppm), afforded [Ag4(rac-dpmppm)2](TfO)4 (3) which consists of zigzag-arrayed tetranuclear silver(I) ions supported by syn-arrangement of two enantiomeric (RR/SS) dpmppm ligands. Complex 3 readily reacted with XylNC (Xyl = 2,6-dimethylphenyl) to give [Ag4(rac-dpmppm)2(XylNC)2](TfO)4 (4), where two terminal isocyanides attach to the outer Ag sites. Complex 3 has been shown a good precursor for Pt-Ag-Ag-Pt mixed metal array as incubation of 3 with trans-[Pt(C CPh)2(PPh3)2] yielded [Ag2Pt2(C CPh)4(rac-dpmppm)2](TfO)2 (5). Two trans-Pt(C CPh)2 units are incorporated into the terminal positions in a site-selective fashion and the Pt-Ag-Ag-Pt tetranuclear core also adopts a zigzag array supported by syn-arrangement of two rac-dpmppm ligands. The d8 and d10 closed-shell mixed metal centers of 5 exhibited an intense photoluminescence at 534 nm, mainly from an unsymmetric triplet state generated by charge transfer transitions from ligand (acetylide π) to metal centers (Ag2 and PtAg s/pσ), 3LMCT, and to ligands (acetylide π* and dpmppm), 3LLCT. The present results provide fundamental and useful information to construct multinuclear closed-shell metal alignments by utilizing polyphosphine ligands.

Reactions of [Cp*MCl2]2 with meso- or rac-dpmppm in the presence of NH4PF6 afforded mixtures of stereoisomers formulated as [(Cp*MCl)2(meso- or rac-dpmppm)](PF6)2, from which the major isomers, rac-M2-[(Cp*MCl)2(meso-dpmppm)](PF6)2 (M = Rh (1a), Ir (1b)) and rac-M2-[(Cp*MCl)2(rac-dpmppm)](PF6)2 (M = Rh (2a), Ir (2b)), were isolated and characterized by IR, UV–vis, ESI mass, and 1H and 31P{1H} NMR spectroscopy and X-ray crystallography, where dpmppm is bis{[(diphenylphosphinomethyl)phenyl]phosphino}methane and Cp* is η5-pentamethylcyclopentadienyl. The isomeric tetraphosphine incorporates two {Cp*MCl} fragments with four-membered chelation through a pair of outer and inner phosphine units, and fixes them ca. 6.9 A apart from each other. The configurations around the metal centers in 2 were determined to avoid repulsive interaction between the phenyl group on the inner P atom and the M-bound chloride anion, while those in 1 would be determined by minimizing not only the Ph/Cl repulsion but also repulsion between the two metal fragments. In the dichloromethane solutions, the major isomers 1 and 2 were not converted to any other minor isomers even at high temperature, but in dmf and dmso, only 1a was readily transformed into the minor isomer, meso-M2-[(Cp*RhCl)2(meso-dpmppm)](PF6)2. Cyclic voltammograms of 1a,b and 2a,b demonstrated two irreversible 2e− reduction waves corresponding to MIIIMIII → MIMIII → MIMI, in which the mixed-valence states with meso-dpmppm could be stabilized to a larger extent than with rac-dpmppm. Complex 1a heated in acetonitrile with AgOTf/NH4OTf afforded a Rh2Ag2 mixed-metal complex, [(Cp*Rh(CH3CN))2Ag2(OTf)2(meso-dpmppm)2](OTf)4 (5).

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.

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.

A copper hydride cluster [Cu

Reactions of [PdCl(Me)(cod)] with two NPPN mixed-donor tetradentate ligands, meso-2-pyridylCH2(Ph)P(CH2)2P(Ph)CH2-2-pyridyl (meso-picppe) and rac-2-pyridylCH2(Ph)P(CH2)4P(Ph)CH2-2-pyridyl (rac-picppb), afforded dinuclear palladium complexes [(PdCl(Me))2(meso-picppe)] (1) and [(PdCl(Me))2(rac-picppb)] (2), which were further converted with 2,6-xylyl isocyanide (XylNC) to [(PdCl(C( NXyl)Me))2(meso-picppe)] (3) and [(PdCl(C( NXyl)Me))2(rac-picppb)] (4) through insertion of XylNC into the Pd–Me bonds. Complexes 3 and 4 possess two imidoyl moieties which are of potential donors and readily capture d10 group 11 metal ions depending on their stereostructures of the NPPN ligands. Reactions of 3 with CuCl or AuCl(tht) afforded Pd2M2 mixed-metal tetranuclear complexes [(PdCl(C( NXyl)Me)(MCl))2(meso-picppe)] (M = Cu (5a), Au (5b)), where each imidoyl moiety captures a MCl fragment in a Ci symmetrical fashion. Similar reactions of 4 with [Cu(MeCN)4]BF4 or AgBF4 resulted in Pd2M trinuclear complexes [(PdCl(C( NXyl)Me)2M(rac-picppb)]BF4 (M = Cu (6a), Ag (6b)), in which two imino groups chelate a MI ion with a pseudo C2 symmetrical structure.

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.

The reactions of M(OAc)2·4H2O (M = Ni, Co) with three unsymmetrical amine-diol ligands RN(CH2CH2OH)(CH2CH2CH2OH) (H2Ln: n = 1, R = benzyl; n = 2, R = 4-methylbenzyl; n = 3, R = 2-naphthalenylmethyl) in the presence of NEt3 or pyridine in MeOH or BnOH gave the tetranuclear complexes [M4(HLn)2(OAc)6(MeOH)2] {M = Ni, n = 1 (1a), 2 (1b), 3 (1c); M = Co, n = 1 (4a), 2 (4b), 3 (4c)} and [M4(HLn)2(OAc)6(BnOH)2] {M = Ni, n = 1 (2a), 2 (2b), 3 (2c); M = Co, n = 1 (5a), 2 (5b), 3 (5c)}. When p-xylene-α,α′-diol was used instead of monoalcohols, the tetranuclear {M4O6} units were linked by p-xylene-α,α′-diol to form the 1D coordination polymers [M4(HLn)2(OAc)6(p-HOCH2C6H4CH2OH)]m {M = Ni, n = 1 (3a), 2 (3b); M = Co, n = 1 (6a), 2 (6b)}. The structures of 1–6 were determined by X-ray crystallography and consist of centrosymmetrical tetranuclear {M4O6} face-shared defective double-cubane cores supported by two monodeprotonated (HLn)– ligands. The mixed-metal tetranuclear complexes [Ni2.2Co1.8(HL1)2(OAc)6(MeOH)2] (7) and [Mn1.7Ni2.3(HL1)2(OAc)5(OMe)2] (8) were also synthesized by using equimolar amounts of Ni2+ and M2+ (M = Co, Mn) ions. X-ray crystallographic and fluorescent analyses revealed that 7 is isomorphous with 1a and 4a and contains nonstoichiometric amounts of disordered Ni2+ and Co2+ ions in an average ratio of 2.2:1.8 with different occupancies for the two crystallographically independent metal centers. In contrast, 8 consists of a C2-symmetrical face-shared defective double-cubane {MII3MnIIIO6} core with a Ni/Mn ratio of 2.3:1.7; the amounts of Ni2+ and Mn2+ ions vary depending on the metal sites, and one of the C2 axial positions is exclusively occupied by Mn3+ ions. Detailed magnetostructural analyses on the nickel (1a, 2a, 3a) and cobalt (4a) complexes with appropriate spin-Hamiltonian models showed that both ferro- and antiferromagnetic spin exchange interactions were involved within the tetranuclear units, and their extent depends on the combination of the metal ions and the ligand systems in a delicate fashion.

Mononuclear complexes with a P2S2 ligand, [M(meppp)] (M = Ni (1a), Pd (1b), Pt (1c); H2meppp = meso-1,3-bis[(mercaptoethyl)phenylphosphino]propane), were treated with [M′Cp*Cl2]2 or [M′Cp*(NO3)2] (Cp* = η5-pentamethylcyclopentadienyl) to afford a series of bisthiolate-bridged MIIM′III heterodinuclear complexes, [M(μ-meppp)M′Cp*X]X′ (M = Ni, Pd, Pt; M′ = Rh, Ir; X = Cl, NO3; X′ = Cl, PF6, NO3). The nitrate complexes [M(μ-meppp)-M′Cp*(NO3)]NO3 (M′ = Rh ([4a–c]NO3), Ir ([5a–c]NO3); M = Ni (a), Pd (b), Pt (c)) further reacted with sodium formate in water or methanol to be transformed into bisthiolate- and hydride-bridged complexes, [M(μ-meppp)(μ-H)M′Cp*]NO3 (M′ = Rh ([6a–c]NO3), Ir ([8a–c]NO3); M = Ni (a), Pd (b), Pt (c)). Complexes [6a]NO3 (M = Ni, M′ = Rh) and [8a]NO3 (M = Ni, M′ = Ir) were characterized by X-ray analyses to reveal that a hydride is stabilized in a semibridging mode on the heterometal centers. In the PdIIRhIII ([6b]NO3) and PtIIRhIII ([6c]NO3) complexes, the hydrides were extremely unstable...

Electron-deficient Pt2M2Pt2 hexanuclear clusters, [Pt4M2(μ-dpmp)4(XylNC)2](PF6)4 (M = Pt (7), Pd (8); dpmp = bis((diphenylphosphino)methyl)phenylphosphine), were synthesized by oxidation of hydride-bridged hexanuclear clusters [Pt4M2(μ-H)(μ-dpmp)4(XylNC)2](PF6)3 (M = Pt (2), Pd (3)) and were revealed to involve a linearly ordered Pt2M2Pt2 array joined by delocalized bonding interactions with 84 cluster valence electrons, which are discussed on the basis of DFT calculations. The central M–M distances of 7 and 8 are significantly reduced upon the apparent loss of a hydride unit from the M–H–M central part of 2 and 3, indicating that the bonding electrons in the adjacent M–Pt bonds migrate into the central M–M bond to result in a dynamic structural change during two-electron oxidation of the hexanuclear metal strings. A similar Pt6 complex terminated by two iodide anions, [Pt6I2(μ-dpmp)4](PF6)2 (9), was synthesized from [Pt6(μ-H)I2(μ-dpmp)4](PF6) (5) by treatment with [Cp2Fe][PF6]. Complexes 7 and 8 were rea...