Synthesis of large palladium clusters. The preparation of Pd38(CO)28(PR3)12 (R = Et,Bun) and Pd34(CO)24(PEt3)12

Several methods for the synthesis of the Pd₃₈(CO)₂₈L₁₂ cluster (L = PEt₃) by treatment of Pd₁₀(CO)₁₂L₆ with CF₃COOH-Me₃NO, CF₃COOH-H₂O₂, Pd(OAc)₂-Me₃NO, and Pd₂(dba)₃ mixtures (dba is dibenzylideneacetone) were proposed. The tri-n-butylphosphine analog, Pd₃₈(CO)₂₈(PBu₃)₁₂, was synthesized by the reaction of Pd₁₀(CO)₁₄(PBu₃)₄ with Me₃NO. The reaction of Pd₄(CO)₅L₄ with Pd₂(dba)₃ yields clusters with an icosahedral packing of the metal atoms, Pd₃₄(CO)₂₄L₁₂ and Pd₁₆(CO)₁₃L₉.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 167–170, January, 1995.     

Distribution of ligands in polynuclear palladium complexes: DFT study of isomerism of Pd4(L)4(RCO2)4 (L = CO,CH2, NO) complexes

Structural isomerism of the Pd₄(L)₄(RCO₂)₄ (L = CO, CH₂, NO; R = CC1₃, CF₃, CH₃) complexes was studied in the framework of the density functional theory (DFT). Among the Pd₄(CO)₄(RCO₂)₄ and Pd₄(CH₂)4(RCO₂)₄ complexes the most stable were the isomers with alternate coordination of pairs of carbonyl and carboxylate ligands on the sides of a planar rectangular metal core. The isomers with the pairwise coordination of NO/RCO₂ on one side of the metal core are the most stable between the Pd₄(NO)₄(RCO₂)₄ complexes. The features of mutual coordination of ligands in polynuclear complexes of palladium are clarified using the obtained results.

     

Reactions of palldium(II) compounds with carbon monoxide in alcohol/amine systems : a new route to palladium(O) carbonyl and carboalkoxy-palladium(II) complexes

Palladium(O) carbonyl complexes, Pd(CO)(PPh₃)₃ Pd₃(CO)₃(PPh₃)₃ and Pd₃(CO)₃(PPh₃)₄, can conveniently be prepared by the reaction of (PPh₃)₂PdCl₂ with carbon monoxide at room temperature in methanol/amine systems involving primary and secondary amines such as diethylamine and cyclohexylamine. These carbonyl complexes are interconvertible under suitable conditions. On the other hand, use of tertiary amine such as triethylamine and tri-n-butylamine in place of the above amines give selectively a carbomethoxy complex (PPh₃)₂PdCl(COOCH₃).     

Synthesis and structure of the new heteronuclear palladium-mercury cluster

Interaction of the tetra-nuclear phosphinecarbonyl complex of zero-valent palladium, Pd₄(CO)₅(PEt₃)₄ (I), with a four-fold excess of 8-(α-bromomercuryethyl)quinoline gives a new neutral heteronuclear cluster Pd₄Hg₂Br₂(CO)₄(PEt₃)₄ (IV). The structure of (IV) was determined by an X-ray analysis. The molecule of (IV) contains a “butterfly” Pd₄(μ₂-CO)₄(PEt₃)₄ moiety, whose triangular “wings” are capped by Hg atoms bonded also to bromo-ligands. The metal Hg₂Pd₄ polyhedron consists of two heteroatomic Pd₃Hg tetrahedra with a common PdPd edge. The IR- and ³¹P-NMR spectra of (IV) were also studied.     

Synthesis and Stereochemical/Electrochemical Analyses of Cuboctahedral-Based Pd23(CO) x (PR3)10 Clusters (x=20 with R3=Bu n 3, Me2Ph; x=20, 21, 22 with R3=Et3): Geometrically Analogous Pd23(PEt3)10 Fragments with Variable Carbonyl Ligations and Resulting Implications

This research was an outgrowth of previous reactions with [Pd₁₃Ni₁₃(CO)₃₄]^4? which produced a tetragonal crystal form of Pd₂₃(CO)₂₀(PEt₃)₁₀ (1) that has the same cuboctahedral-based Pd₂₃ framework with an identical number of PEt₃ ligands but two fewer CO ligands than the monoclinic crystal form of Pd₂₃(CO)₂₂(PEt₃)₁₀ (3) originally reported from reactions with Pd₁₀(CO)₁₂(PEt₃)₆. A subsequent investigation presented herein to establish whether the carbonyl capacity is influenced by the nature of the phosphine ligands has led to syntheses of Pd₂₃(CO) _x (PR₃)₁₀ [R₃=Et₃ (1), Bu ⁿ ₃ (4), and Me₂Ph (5)] with 20 CO ligands (x=20) from corresponding Pd₁₀(CO)₁₂(PR₃)₆ precursors either by deligation with Pd(OAc)₂, CF₃CO₂H, Ni(1,5-COD)₂, [NMe₄]₂[Ni₆(CO)₁₂], or HCO₂H or by spontaneous enlargement; yields varied from 15 to 79%. Although attempts to obtain the original Pd₂₃(CO)₂₂(PEt₃)₁₀ (3) were unsuccessful, a highly significant outcome was the isolation (one time) of another monoclinic crystal form possessing the triethylphosphine Pd₂₃(CO) _x (PEt₃)₁₀ cluster with 21 COs (2). Both the compositions and atomic arrangements for each of five Pd₂₃ clusters [1a (solvated); 1b (unsolvated); 2, 4, and 5] were unambiguously established from low-temperature single-crystal CCD X-ray crystallographic determinations in accordance with their nearly identical IR carbonyl frequencies. Solution ³¹P{¹H} NMR spectra of 1 and 4 at room temperature displayed three distinct signals with expected integral ratios of 2/4/4 that are consistent with the solid-state structures of Pd₂₃(CO)₂₀(PR₃)₁₀ [R₃=Et₃ (1), Bu ⁿ ₃ (4)] remaining intact in solution. The metal-core geometries of all of these Pd₂₃(CO) _x (PR₃)₁₀ clusters, including the thermodynamically stable ones with 20 CO ligands and the kinetic products with additional CO ligands (x=21, 22), are essentially the same. The common Pd₂₃ core may be best described as possessing a centered hexacapped cuboctahedral Pd₁₉ kernel (alternatively denoted as a centered ν₂ Pd₁₉ octahedron) with four edge-connected exopolyhedral wingtip Pd(exo) atoms that reduce the pseudo metal-core symmetry from O_h to D_2h. The 10 PR₃ ligands are linked to the six tetracapped Pd(cap) and four edge-capped wingtip Pd(exo) atoms; the latter four Pd(exo) atoms are each composed of four trigonal-planar Pd(μ₂-CO)₂(PR₃) units. These crystallographic results provide compelling geometrical evidence for a heretofore unknown stereochemical example involving variable carbonyl ligation (x=20, 21, 22) of a close-packed nanosized Pd _n (CO) _x (PR₃) _y cluster (in this case with identical PEt₃ ligands) without significant changes being induced in either the overall metal-core architecture or steric dispositions of the same number of PR₃ ligands. These experimental findings have particular relevance to the long-standing Muetterties cluster/surface science analogy in showing that the different number (as well as different modes) of carbonyl ligations observed in these large metal carbonyl clusters are directly related to pressure-induced dissociative/nondissociative migratory coverages in CO chemisorptions on metal surfaces. The observed expanded capacity of CO coordination on the same Pd₂₃ polyhedron without notable changes in geometry is no doubt a consequence of its virtually nanosized metal-core architecture; distances between outermost centrosymmetrically related pairs of Pd(cap) and Pd(exo) atoms in the Pd₂₃ framework are 0.8 and 0.9 nm, respectively. An electrochemical (CV) study revealed that 1 undergoes one quasi-reversible two-electron reduction to 1 ^2? (E_1/2=?0.91 V) and two consecutive quasi-reversible one-electron oxidations to 1/1 ⁺ at E_1/2=0.08 V and 1 ⁺/1 ²⁺ at E_1/2=0.32 V (THF; Ag/AgCl as reference electrode). A stereochemical/electronic analysis with the isostructural Au₂Pd₂₁(CO)₂₀(PEt₃)₁₀ analogue (9) and resulting implications are given.     

Palladium(II), Copper(II), Iron(III), and Vanadium(V) Complexes with Heteropolyanion PW9O9–34: 31P, 183W, 51V NMR and IR Spectroscopy Studies

The formation of Pd(II)-containing and mixed Pd(II),Cu(II), Pd(II),Fe(III), and Pd(II),V(V) complexes with heteropolyanion PW₉O^9– ₃₄was studied using ³¹P, ¹⁸³W, ⁵¹V NMR, visible UV and IR spectroscopy, and the differentiating dissolution methods. In an aqueous solution and at optimal pH (3.7), the monometallic complexes [Pd₃(PW₉O₃₄)₂]^12–and [Pd₃(PW₉O₃₄)₂Pd _n O _x H _y ] ^q–(n _av= 3), the bimetallic complexes [Pd₂Cu(PW₉O₃₄)₂]^12–, [Pd₂Fe(PW₉O₃₄)₂]^11–, and [PdFe₂(PW₉O₃₄)₂]^10–, and a mixture of the [Pd₃(PW₉O₃₄)₂Pd _n O _x H _y ] ^q–(n _av 10) + [(VO)₃(PW₉O₃₄)₂]^9–complexes are formed. The title complexes were isolated from solution as Cs⁺solid salts belonging to the same [M₃(PW₉O₃₄)₂] structural type.     

Reversible Mechanical Interlocking of D‐Shaped Molecular Karabiners bearing Coordination‐Bond Loaded Gates: Route to Self‐Assembled [2]Catenanes

Complexation of 1,4‐phenylenebis(methylene) diisonicotinate, L1 , with cis‐protected Pd^II components, [Pd( L′ )(NO₃)₂], in an equimolar ratio yielded binuclear complexes, 1 a – d of [Pd₂( L′ )₂( L1 )₂](NO₃)₄ formulation where L′ stands for ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′‐bipyridine (bpy), and phenanthroline (phen). The combination of 4,4′‐bipyridine, L2 , with the cis‐protected Pd^II units is known to yield molecular squares, 2 a – d . However, 2 b – d coexist with the corresponding molecular triangles, 3 b – d . Combination of an equivalent each of the ligands L1 and L2 with two equivalents of cis‐protected Pd^II components in DMSO resulted in the D ‐shaped heteroligated complexes [Pd₂( L′ )₂( L1 )( L2 )](NO₃)₄, 4 a – d . Two units of the D ‐shaped complexes interlock, in a concentration dependent fashion, to form the corresponding [2]catenanes [Pd₂( L′ )₂( L1 )( L2 )]₂(NO₃)₈, 5 a – d under aqueous conditions. Crystal structures of the macrocycle [Pd₂(tmeda)₂( L1 )( L2 )](PF₆)₄, 4 b′′ , and the catenane [Pd₂(bpy)₂( L1 )( L2 )]₂(NO₃)₈, 5 c , provide unequivocal support for the proposed molecular architectures.     

Dynamic Open Coordination Cage from Nonsymmetrical Imidazole–Pyridine Ditopic Ligands for Turn‐On/Off Anion Binding

This work demonstrates a new nonconventional ligand design, imidazole/pyridine‐based nonsymmetrical ditopic ligands ( 1 and 1 ^S ), to construct a dynamic open coordination cage from nonsymmetrical building blocks. Upon complex formation with Pd²⁺ at a 1:4 molar ratio, 1 and 1 ^S initially form mononuclear PdL₄ complexes (Pd²⁺( 1 )₄ and Pd²⁺( 1 ^S )₄) without formation of a cage. The PdL₄ complexes undergo a stoichiometrically controlled structural transition to Pd₂L₄ open cages ((Pd²⁺)₂( 1 )₄ and (Pd²⁺)₂( 1 ^S )₄) capable of anion binding, leading to turn‐on anion binding. The structural transitions between the Pd₂L₄ open cage and the PdL₄ complex are reversible. Thus, stoichiometric addition (2 equiv) of free 1 ^S to the (Pd²⁺)₂( 1 ^S )₄ open cage holding a guest anion ((Pd²⁺)₂( 1 ^S )₄?G^?) enables the structural transition to the Pd²⁺( 1 ^S )₄ complex, which does not have a cage and thus causes the release of the guest anion (Pd²⁺( 1 ^S )₄+G^?).     

Metallation of the methyl group ino-nitrosotoluene: synthesis and the molecular structure of the binuclear complex [o-(NO)(CH2)C6H4)]2Pd2(μ-OOCCF3)2

The reaction of the tetranuclear cluster Pd₄(CO)₄(OOCCF₃)₄ witho-nitrosotoluene afforded the Pd¹¹-containing complex [o-(NO)(CH₂)C₆H₄]₂Pd₂(μ-OOCCF₃)₂. The elimination of CO₂ and the formation of organic products of transformation of tolylnitrene species (azotoluene, ditolylamine, and tolylisocyanate) were observed in the course of the reaction. The title complex was characterized by IR and¹H NMR spectroscopy. Its structure was established by X-ray diffraction analysis. It was suggested that the reaction proceeds through intermediate formation of nitrene complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 147–150, January, 2000.     

The Pyrolysis of Isonitrile Substituted Derivatives of Triosmium Dodecacarbonyl

The pyrolysis of the isonitrile substituted complexes Os₃(CO)_12?x(CNR)x (R = Bu^t, x = 1,2) in refluxing octane has been studied. From these pyrolysis reactions and from the reaction of Os₃(CO)₁₂ with Bu^tNC in refluxing octane the series of hexanuclear complexes Os₆(CO)_18?x(CNBu^t)_x (x = 1?5) has been isolated. The pyrolysis of Os₃(CO)₁₁(CNBuⁿ) also leads to the formation of higher nuclearity clusters and evidence is presented that one product of the reaction is Os₆(CO)₁₇(CNBuⁿ)₂. Possible structures for these isonitrile substituted hexanuclear complexes are discussed in the light of the known structures of Os₆(CO)₁₆(CNBu^t)₂ and Os₆(CO)₁₈(CNC₆H₄Me)₂.     

Palladium and platinum organochalcogenolates and their transformation into metal chalcogenides

Platinum group metal chalcogenides find extensive applications in catalysis and in the electronic industry. To develop an efficient low temperature clean preparation of these materials, molecular routes have been explored. Thus the chemistry of mononuclear organochalcogenolates of the type [M(ER’)₂(PR₃)₂], binuclear benzylselenolates, [M₂Cl₂(μ-SeBz)₂(PR₃)₂], allylpalladium complexes [Pd₂(μ-ER)₂(η³-C₄H₇)₂] and palladium/platinum sulphido/selenido-bridged complexes, [M₂(μ-E)₂L₄] (M = Pd or Pt; E = S, Se or Te; L = tertiary phosphine ligand) has been investigated. All the complexes have been characterized by elemental analysis, NMR (¹H,³¹P,⁷⁷Se,¹⁹⁵Pt) spectroscopy and in some cases by X-ray diffraction. The thermal behaviour of these complexes has been studied by TGA. The pyrolysis of allylpalladium complexes in refluxing xylene yields Pd₄E as established by analysis and XRD patterns.     

Palladium nitrosyl carboxylate clusters: Synthesis and reactivity. X-ray structures of Pd4(μ-CO)2(μ-NO)(μ-RCO2)5 (R = Pr, Bu)

New palladium nitrosyl carboxylate complexes Pd₈(CO)_4−m(NO)_m(NO₂)₄(RCO₂)₈ (m = 2, 4) were obtained by the treatment of palladium carbonyl carboxylates clusters cyclo-Pd_n(μ-CO)_n(μ-RCO₂)_n (n = 6) (1) with gaseous nitrogen monoxide. These complexes are the products of CO substitution in early described Pd₈(CO)₄(NO₂)₄(RCO₂)₈ clusters. By adding an excess of corresponding acid to reaction mixture Pd₄(CO)₂(NO)(RCO₂)₅ complexes were obtained, their structures were determined by X-ray diffraction analysis. These clusters are intermediate products of transformation of 6-nuclear initial clusters into various 8-nuclear complexes. This fact demonstrates that carboxylate ligands can be used as stabilizers for intermediate unstable polynuclear palladium compounds.     

Formyl complexes of transition metal carbonyl clusters : II. Spectroscopic study by 2H NMR of the synthesis of [Ir4(CO)12-x(CHO)x]x−, [OS3(CO)11(CHO)]− and [Ru3(CO)11(CHO)]− (x = 1,2)

The reactions of LiHB(C₂H₅)₃ and LiDB(C₂H₅)₃ with Re₂(CO)₁₀, Ir₄(CO)₁₂, Os₃(CO)₁₂, Ru₃(CO)₁₂ and Rh₄(CO)₁₂ have been studied by ¹H, ²H and ¹³C NMR techniques. Results suggest the formation of formaldehyde and methanol in these systems, as well as the existence of previously unreported formyl complexes. A ²H isotope effect is noted in the apparent increase in stability of cluster formyl complexes.     

Pincer‐Type Heck Catalysts and Mechanisms Based on PdIV Intermediates: A Computational Study

Pincer‐type palladium complexes are among the most active Heck catalysts. Due to their exceptionally high thermal stability and the fact that they contain Pd^II centers, controversial Pd^II/Pd^IV cycles have been often proposed as potential catalytic mechanisms. However, pincer‐type Pd^IV intermediates have never been experimentally observed, and computational studies to support the proposed Pd^II/Pd^IV mechanisms with pincer‐type catalysts have never been carried out. In this computational study the feasibility of potential catalytic cycles involving Pd^IV intermediates was explored. Density functional calculations were performed on experimentally applied aminophosphine‐, phosphine‐, and phosphite‐based pincer‐type Heck catalysts with styrene and phenyl bromide as substrates and (E)‐stilbene as coupling product. The potential‐energy surfaces were calculated in dimethylformamide (DMF) as solvent and demonstrate that Pd^II/Pd^IV mechanisms are thermally accessible and thus a true alternative to formation of palladium nanoparticles. Initial reaction steps of the lowest energy path of the catalytic cycle of the Heck reaction include dissociation of the chloride ligands from the neutral pincer complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Cl)] [X=NH, R=piperidinyl ( 1 a ); X=O, R=piperidinyl ( 1 b ); X=O, R=iPr ( 1 c ); X=CH₂, R=iPr ( 1 d )] to yield cationic, three‐coordinate, T‐shaped 14e^? palladium intermediates of type [{2,6‐C₆H₃(XPR₂)₂}Pd]⁺ ( 2 ). An alternative reaction path to generate complexes of type 2 (relevant for electron‐poor pincer complexes) includes initial coordination of styrene to 1 to yield styrene adducts [{2,6‐C₆H₃(XPR₂)₂}Pd(Cl)(CH₂?CHPh)] ( 4 ) and consecutive dissociation of the chloride ligand to yield cationic square‐planar styrene complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(CH₂?CHPh)]⁺ ( 6 ) and styrene. Cationic styrene adducts of type 6 were additionally found to be the resting states of the catalytic reaction. However, oxidative addition of phenyl bromide to 2 result in pentacoordinate Pd^IV complexes of type [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(C₆H₅)]⁺ ( 11 ), which subsequently coordinate styrene (in trans position relative to the phenyl unit of the pincer cores) to yield hexacoordinate phenyl styrene complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(C₆H₅)(CH₂?CHPh)]⁺ ( 12 ). Migration of the phenyl ligand to the olefinic bond gives cationic, pentacoordinate phenylethenyl complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(CHPhCH₂Ph)]⁺ ( 13 ). Subsequent β‐hydride elimination induces direct HBr liberation to yield cationic, square‐planar (E)‐stilbene complexes with general formula [{2,6‐C₆H₃(XPR₂)₂}Pd(CHPh?CHPh)]⁺ ( 14 ). Subsequent liberation of (E)‐stilbene closes the catalytic cycle.     

Synthesis of palladium-tin carbonylphosphine clusters and X-ray study of the Pd3Sn2(acac)4(CO)2(PPh3)3 cluster

It has been shown for the first time that the reaction of bi-valent tin acetyl-acetonate with palladium carbonylphosphine clusters, Pd₄(CO)₅(PPh₃)₄ (I), Pd₄(CO)₅(PEt₃)₄ (II) and Pd₃(CO)₃(PPh₃)₄ (III), results in the formation of heterometal pentanuclear clusters of general formula Pd₃Sn₂(acac)₄(CO)₂(PR₃)₃; R  Ph (IV), Et (V). X-ray analysis of Pd₃Sn₂(acac)₄(CO)₂(PPh₃)₃ at 20°C (λ(Mo), 4396 reflections, space group P2₁/n, Z = 4, R = 0.037) shows that IV in the form of the crystalline hydrate, Pd₃Sn₂(acac)₄(CO)₂(PPh₃)₃ · χH₂O (χ ∼ 1), contains a distorted “propeller”-shaped Pd₃Sn₂ metal frame with PdSn distances of 2.679–2.721(1) Å; two short PdPd bonds, 2.708 and 2.720(1) Å, bridged by μ₂-CO ligands, and an elongated central Pd(1)Pd(2) bond of 2.798 Å. Sn atoms have distorted octahedral coordination, the dihedral angles formed by Pd₃ moieties and two Pd₂Sn triangles are 127.6 and 106.5°; and the angle between Pd₂Sn moieties is 126.0°.     

Synthesis and structure of polynuclear carbonylphosphine clusters of palladium

Reductive condensation of Pd(OAc)₂ in dioxane in the presence of CO and PR₃ (R = Et, Buⁿ) with addition of CF₃COOH leads to the formation of decanuclear Pd₁₀(μ₃-CO)₄(μ₂-CO)₈(PBuⁿ₃)₆ (I) and Pd₁₀(CO)₁₄(PBuⁿ₃) (II) at Pd(OAc)₂:PR₃ molar ratios of 1:4–1:10 and 1:1.5–1:2.5, respectively. The use of CH₃COOH instead of CF₃COOH results in tetranuclear clusters Pd₄(CO)₅(PR₃)₄ (III) and Pd₄(μ₂-CO)₆(PBuⁿ₃) (IV). I ? III and III → IV transformations occur in organic media. The structures of I (space group P2₁/n, Z = λMo, 12125 independent reflections, R = 0.047) and IV (Pz:3, Z = λMo, 3254 reflections, R = 0.098) were established by X-Ray diffractions analysis. Cluster I is a 10-vertex Pd₁₀ polyhedron, an octahedron with four unsymmetrically centered non-adjacent faces. The average PdPd distances in the octahedron are 2.825 Å, in the eight short Pd_oct.Pd_cap. bonds with the “equatorial” Pd atoms of the inner octahedron, bridged by the μ₂-CO ligands, are 2.709 Å, and in the four elongated (without bridging CO groups) bonds with the apical Pd atoms of the octahedron are 3.300–3.422 Å. The PBuⁿ₃ ligands are coordinated to the apical Pd atoms and the capping atoms (PdP 2.291–2.324 Å). Cluster IV is tetrahedral, with the CO ligands symmetrically bridged; PdPd 2.778–2.817; PdP 2.232–2.291; PdC 2.06 Å (average).     

Reactivity of Pd3(dppm)3(CO)n+ and Pd3(dppm)3(CO)(RCCR)n+ (n?=?0, +1, +2) Towards F?. Evidence of Reactive Intermediates and X-Ray Structure of [Pd3(dppm)3(MeO2CC≡CCO2Me)(F)]PF6

Abstract  

The reactivity of the trinuclear palladium cluster [Pd₃(dppm)₃(CO)] ⁿ⁺ (dppm = bis(diphenylphosphinomethane); n = 2, 1) towards F⁻ was investigated by electrochemical and spectroscopic methods. The reaction depends on the charge of the cluster. The chemical reduction of the cluster dication is observed in the presence of F⁻ generating the paramagnetic monocationic cluster. Spin-trapping experiments with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) provided evidence for the radical F^• as an intermediate. In a similar manner to the dication, the monocationic cluster [Pd₃(dppm)₃(CO)]⁺ is also reduced, but in a slower process, by the F⁻ ion to produce [Pd₃(dppm)₃(CO)]⁰. Additionally, the alkyne cluster adducts [Pd₃(dppm)₃(CO)(RCCR)] ⁿ⁺ (n = 2, 1; R = CO₂Me) are also reactive towards F⁻. Particularly, the dication adduct leads to a metastable fluoride adduct [Pd₃(dppm)₃(CO)(RCCR)(F)]⁺. The electroreductive behavior of this adduct involves electron-transfer steps and F⁻ exchange equilibriums, for which digital simulation enables the extraction of the thermodynamic parameters (standard potentials and equilibrium constants). Concurrently, the monocation adduct [Pd₃(dppm)₃(CO)(RCCR)]⁺ with F⁻, leads to a disproponation generating 0.5 equiv. of [Pd₃(dppm)₃(CO)(RCCR)(F)]⁺ and 0.5 equiv. of [Pd₃(dppm)₃(CO)(RCCR)]⁰. The former slowly evolves to [Pd₃(dppm)₃(RCCR)(F)]⁺, which was described by X-ray diffraction method.     

The activation and transformations of acenaphthylene by osmium carbonyl cluster complexes

The reaction of Os₃(CO)₁₀(NCMe)₂ (1) with an excess of acenaphthylene at room temperature provided the complex Os₃(CO)₁₀(μ-H)(μ-η²-C₁₂H₇) (2). Compound 2 contains a σ-π coordinated acenaphthyl ligand bridging an edge of the cluster. Compound 2 was converted to the complex Os₃(CO)₉(μ-H)₂(μ₃-η²-C₁₂H₆) (3) when heated to reflux in a cyclohexane solution. Compound 3 contains a triply bridging acenaphthyne ligand. Compound 3 reacts with acenaphthylene again at 160 °C to yield four new cluster complexes: Os₄(CO)₁₂(μ₄-η²:η²-C₁₂H₆) (4); Os₂(CO)₆(μ-η⁴-C₂₄H₁₂) (5); Os₃(CO)₉(μ-H)(μ₃-η⁴-C₂₄H₁₃) (6); and Os₂(CO)₅(μ-η⁴-C₂₄H₁₂)(η²-C₁₂H₈) (7). All compounds were characterized crystallographically. Compound 4 is a butterfly cluster of four osmium atoms bridged by a single acenaphthyne ligand. Compounds 5 and 7 are dinuclear osmium clusters containing metallacycles formed by the coupling of two equivalents of acenaphthyne. Compound 6 is a triosmium cluster formed by the coupling of an acenaphthyne ligand to an acenapthyl group that is coordinated to the cluster through a combination of σ and π-bonding.     

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-Ph₂PCH₂P(Ph)CH₂P(Ph)CH₂PPh₂ (meso-dpmppm) ligands, [Pd₈(meso-dpmppm)₄(L)₂](BF₄)₄ (L=none ( 1 ), solvents: CH₃CN ( 2 a ), dmf ( 2 b ), dmso ( 2 c ), RN≡C: R=Xyl ( 3 a ), Mes ( 3 b ), Dip ( 3 c ), ^tBu ( 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, ¹H and ³¹P 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-Ph₂PCH₂P(H)CH₂P(H)CH₂PH₂)₄(CH₃CN)₂]⁴⁺ ( [Pd₈Ph₈]⁴⁺ ) and [Pd₈(meso-H₂PCH₂P(H)CH₂P(H)CH₂PH₂)₄(CH₃CN)₂]⁴⁺ ( [Pd₈H₈]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=CH₃CN), 3 , and 13 (R=Xyl, Mes, ^tBu, 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 CH₂Cl₂ deposited insoluble coordination polymers, {[Pd₈(meso-dpmppm)₄(BI)](BF₄)₄}_n ( 5 ), and interestingly, they were soluble in acetonitrile, ³¹P{¹H} and ¹H 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.