Mixed-metal assemblies involving ferrocene−naphthyridine hybrids

Covalent attachment of one and two NP moieties to a ferrocenyl unit provides organometallic ligands 1,8-naphthyrid-2-yl-ferrocene (FcNP) and 1,1′-bis(1,8-naphthyrid-2-yl)ferrocene (FcNP<SUB>2</SUB>). Coordination of FcNP to transition metal ions Fe<SUP>II</SUP>, Cu<SUP>II</SUP>, Zn<SUP>II</SUP>, and Cd<SUP>II</SUP> provides [FeCl<SUB>2</SUB>(κN<SUB>8</SUB>-FcNP)<SUB>2</SUB>] (1), [Cu(κN<SUB>8</SUB>-FcNP)<SUB>2</SUB>(NO<SUB>3</SUB>)<SUB>2</SUB>] (2), [Zn(κN<SUB>8</SUB>-FcNP)<SUB>4</SUB>][OTf]<SUB>2</SUB> (3), and [Cd(κN<SUB>8</SUB>-FcNP)<SUB>2</SUB>(κ<SUP>2</SUP>N<SUB>1</SUB>,N<SUB>8</SUB>-FcNP)<SUB>2</SUB>][BF<SUB>4</SUB>]<SUB>2</SUB> (4), respectively. Dirhodium(II) compound [Rh<SUB>2</SUB>(μ-FcNP)<SUB>2</SUB>(μ-O<SUB>2</SUB>CCH<SUB>3</SUB>)<SUB>2</SUB>(H<SUB>2</SUB>O)][OTf]<SUB>2</SUB> (5) is isolated when acetonitrile-solvated [Rh<SUB>2</SUB>(μ-O<SUB>2</SUB>CCH<SUP></SUP>)<SUB>2</SUB>]<SUP>2+</SUP> is employed as a precursor. Diverse bonding modes of the NP unit, including monodentate, bidentate chelating, or binuclear bridging, are revealed in these FcNP clusters. Metallamacrocycles [M<SUB>2</SUB>(FcNP<SUB>2</SUB>)<SUB>3</SUB>][X]<SUB>2</SUB> (M = Cu, X = ClO<SUB>4</SUB> (6); M = Ag, X = OTf (7)), [PdCl<SUB>2</SUB>(FcNP<SUB>2</SUB>)] (8), and [ZnCl<SUB>2</SUB>(FcNP<SUB>2</SUB>)]<SUB>4</SUB> (10) are obtained by the reaction of CuClO<SUB>4</SUB>, AgOTf, Pd(C<SUB>6</SUB>H<SUB>5</SUB>CN)<SUB>2</SUB>Cl<SUB>2</SUB>, and ZnCl<SUB>2</SUB> with FcNP<SUB>2</SUB> in 1:1 ratios. Treatment of CuI and FcNP<SUB>2</SUB> in a 2:1 ratio provides [Cu<SUB>2</SUB>(FcNP<SUB>2</SUB>)][ClO<SUB>4</SUB>]<SUB>2</SUB> (9). Molecular structures of compounds 1−10 have been determined by X-ray diffraction studies. Interconversion between 1:1 dimer 6 and 2:1 dimer 9 occurs by the addition of a requisite amount of Cu<SUP>I</SUP> or FcNP<SUB>2</SUB>. ESI-MS experiments reveal that the predominant species is the 1:1 complex {Cu(FcNP<SUB>2</SUB>)}<SUP>1+</SUP> in solution for both 6 and 9. Synthesis, structures, mass spectroscopy, and electrochemistry of the transition metal compounds of FcNP and FcNP<SUB>2</SUB> are discussed

Effects of axial coordination on the Ru−Ru single bond in diruthenium paddlewheel complexes

The 1,8-naphthyridine-based (NP-based) ligands with furyl, thiazolyl, pyridyl, and pyrrolyl attachments at the 2-position have been synthesized. Reactions of 3-MeNP (3-methyl-1,8-naphthyridine), fuNP (2-(2-furyl)-1,8-naphthyridine), tzNP (2-(2-thiazolyl)-1,8-naphthyridine), pyNP (2-(2-pyridyl)-1,8-naphthyridine), and prNP- (2-(2-pyrrolyl)-1,8-naphthyridine) with [Ru2(CO)4(CH3CN)6]2+ lead to [Ru2(3-MeNP)2(CO)4(OTf)2] (1), [Ru2(fuNP)2(CO)4]2[BF4]2 (2), [Ru2(tzNP)2(CO)4][ClO4]2 (3), [Ru2(pyNP)2(CO)4][OTf]2 (4), and [Ru2(prNP)2(CO)4] (5). The molecular structures of complexes 1−5 have been established by X-ray crystallographic studies. The modulation of the Ru−Ru single-bond distances with axial donors triflates, furyls, thiazolyls, pyridyls, and pyrrolyls has been examined. A small and gradual increase in the Ru−Ru distance is measured with various donors of increasing strengths. The shortest Ru−Ru distance of 2.6071(9) Å is observed for the axially coordinated triflates in complex 1, and the longest Ru−Ru distance of 2.6969(10) Å is measured for axial pyrrolyls in complex 5. The Ru−Ru distances in complexes 3 (2.6734(7) Å) and 4 (2.6792(9) Å), having thiazolyls and pyridyls at axial sites respectively, are similar. The Ru−Ru distance for axial furyls in complex 2 (2.6261(9) Å) is significantly shorter than the corresponding distances in 3, 4, and 5. DFT calculations provide insight into the interaction of the Ru−Ru σ orbital with axial donors. The Ru−Ru σ orbital is elevated to a higher energy because of the interaction with axial lone pairs. The degree of destabilization depends on the nature of axial ligands:  the stronger the ligand, higher the elevation of Ru−Ru σ orbital. The lengthening of Ru−Ru distances with respect to the axial donors in compounds 1−5 follows along the direction pyrrolyl > pyridyl ≈ thiazolyl > furyl > triflate, and the trend correlates well with the computed destabilization of the Ru−Ru σ orbitals

Ferrocene-appended anionic N-heterocyclic carbene and its complex with silver(I): Synthesis, structure and catalytic evaluation

1072-1077A binuclear Ag(I) complex (1) bridged by two anionic N-heterocyclic carbene (NHC) ligands <span style="mso-ansi-language: DE;mso-bidi-font-weight:bold" lang="DE">ferrocenoyl(1-mesityl-imidazol-2-ylidine-3-yl)amide is synthesized. X-ray structure reveals a [Ag<span style="mso-fareast-font-family: " ms="" mincho";mso-ansi-language:de;mso-fareast-language:ja"="" lang="DE">···Ag] core spanned by two ligands, each bridging two metals through carbene carbon and amido nitrogen. The neutral complex (<b style="mso-bidi-font-weight: normal">1) is highly soluble in a variety of organic solvents and is thermally stable. Complex (1) efficiently catalyses aniline-mediated synthesis of substituted quinolines from 2-aminobenzaldehyde and terminal alkynes. </span

Novel heterobimetallic metallamacrocycles based on the 1,1‘-bis(1,8-naphthyrid-2-yl)ferrocene (FcNP2) ligand: structural characterization of the complexes [{M(FcNP<SUB>2</SUB>)}<SUB>2</SUB>]<SUP>2+</SUP>(M = Cu<SUP>I</SUP>, Ag<SUP>I</SUP>) and {MCl<SUB>2</SUB>(FcNP<SUB>2</SUB>)}<SUB>4</SUB>(M = Zn<SUP>II</SUP>, Co<SUP>II</SUP>)

Self-assembly reactions of 1,1'-bis(1,8-naphthyrid-2-yl)ferrocene (FcNP2) with CuI/AgI afford dimeric [{CuI/AgI(FcNP2)}2]2+ and with ZnCl2/CoCl2 yield tetrameric metallamacrocycles {ZnII/CoIICl2(FcNP2)}4

Is copper(I) hard or soft? A density functional study of mixed ligand complexes

Fully optimized structures of three- and four-coordinated Ni (0), Cu(I) and Zn(II) complexes with varied combination of hard $(H_2O \hspace{2mm} or H_3N)$ and soft $(H_2S, H_3P)$ ligands were computed using density functional theory (DFT). Frequency calculations were carried out to ascertain that the structures were true minima. In the case of Cu(I) and Zn(II), the heat of formation (HOF) values are smaller with larger number of soft ligands. The increase in the HOF on replacing a soft ligand with a hard ligand is less for Cu(I) than for Zn(II). The corresponding HOF is negative for Ni(0) which is not stable with a complement of four hard ligands. The calculated chemical hardness parameters based on vertical ionization potentials clearly indicate the preference of four hard ligands for Zn(II) and four soft ligands for Ni(0). Significantly, the maximum chemical hardness was computed for Cu(I) complex $[Cu(PH_3)_3(NH_3)]^+$, a combination of three soft and one hard ligand. The conclusions derived from absolute hardness data computed for the complexes closely parallel the experimentally observed stability of Cu(I) with an optimum number of hard and soft ligands in its coordination sphere in solution

Naphthyridine–imidazole hybrid ligands for the construction of multinuclear architecture

Reaction of 2-imidazolyl-5,7-dimethyl-1,8-naphthyridine (L<SUP>1</SUP>) with [Rh(COD)Cl]<SUB>2</SUB> (COD = 1,5-cyclooctadiene) affords the dinuclear complex [Rh(COD)Cl]<SUB>2</SUB>(μ-L<SUP>1</SUP>) (1). Elimination of chloride from the metal coordination sphere leads to a self-assembled tetranuclear macrocycle [Rh(COD)L<SUP>1</SUP>]<SUB>4</SUB>[ClO<SUB>4</SUB>]<SUB>4</SUB> (2). A subtle alteration in the ligand framework results in the polymeric chain compound {Rh(COD)(L<SUP>2</SUP>)}<SUB>n</SUB>(PF<SUB>6</SUB>)<SUB>n</SUB> (3) (L<SUP>2</SUP> = 2-imidazolyl-3-phenyl-1,8-naphthyridine). In all these complexes, the imidazole nitrogen and one of the naphthyridine nitrogen (away from the imidazole substituent) bind the metal. The ‘parallel’ and ‘perpendicular’ dispositions of nitrogens are observed in these compounds contributing to different Rh···Rh separations. The L<SUP>1</SUP> ligand adopts planar configuration, whereas the naphthyridine–imidazole rings deviate from planarity in L<SUP>2</SUP> yielding a polymeric structure. The extent of deviation is less in the polymeric structure {Mo<SUB>2</SUB>(OAc)<SUB>4</SUB>(L<SUP>2</SUP>)}<SUB>n</SUB> (4) in which the ligand exhibits weak axial interactions to the metal

Reactions of acids with naphthyridine-functionalized ferrocenes: protonation and metal extrusion

Reaction of 1,8-naphthyrid-2-yl-ferrocene (FcNP) with a variety of acids affords protonated salts at first, whereas longer reaction time leads to partial demetalation of FcNP resulting in a series of Fe complexes. The corresponding salts [FcNP·H][X] (X = BF<SUB>4</SUB> or CF<SUB>3</SUB>SO<SUB>3</SUB> (1)) are isolated for HBF<SUB>4</SUB> and CF<SUB>3</SUB>SO<SUB>3</SUB>H. Reaction of FcNP with equimolar amount of CF<SUB>3</SUB>CO<SUB>2</SUB>H for 12 h affords a neutral complex [Fe(FcNP)<SUB>2</SUB>(O<SUB>2</SUB>CCF<SUB>3</SUB>)<SUB>2</SUB>(OH<SUB>2</SUB>)<SUB>2</SUB>] (2). Use of excess acid gave a trinuclear FeII complex [Fe<SUB>3</SUB>(H<SUB>2</SUB>O)<SUB>2</SUB>(O<SUB>2</SUB>CCF<SUB>3</SUB>)<SUB>8</SUB>(FcNP·H)<SUB>2</SUB>] (3). Three linear iron atoms are held together by four bridging trifluoroacetates and two aqua ligands in a symmetric fashion. Reaction with ethereal solution of HCl afforded [(FcNP·H)<SUB>3</SUB>(Cl)][FeCl<SUB>4</SUB>]<SUB>2</SUB> (4) irrespective of the amount of the acid used. Even the picric acid (HPic) led to metal extrusion giving rise to [Fe<SUB>2</SUB>(Cl)<SUB>2</SUB>(FcNP)<SUB>2</SUB>(Pic)<SUB>2</SUB>] (5) when crystallized from dichloromethane. Metal extrusion was also observed for CF<SUB>3</SUB>SO<SUB>3</SUB>H, but an analytically pure compound could not be isolated. The demetalation reaction proceeds with an initial proton attack to the distal nitrogen of the NP unit. Subsequently, coordination of the conjugate base to the electrophilic Fe facilitates the release of Cp rings from metal. The conjugate base plays an important role in the demetalation process and favors the isolation of the Fe complex as well. The 1,1′-bis(1,8-naphthyrid-2-yl)ferrocene (FcNP<SUB>2</SUB>) does not undergo demetalation under identical conditions. Two NP units share one positive charge causing the Fe-Cp bonds weakened to an extent that is not sufficient for demetalation. X-ray structure of the monoprotonated FcNP<SUB>2</SUB> reveals a discrete dimer [(FcNP<SUB>2</SUB>·H)]<SUB>2</SUB>[OTf]<SUB>2</SUB> (6) supported by two N–H···N hydrogen bonds. Crystal packing and dispersive forces associated with intra- and intermolecular &#960;–&#960; stacking interactions (NP···NP and Cp···NP) allow the formation of the dimer in the solid-state. The protonation and demetalation reactions of FcNP and FcNP<SUB>2</SUB> with a variety of acids are reported

Reactions of Acids with Naphthyridine-Functionalized Ferrocenes: Protonation and Metal Extrusion

Reaction of 1,8-naphthyrid-2-yl-ferrocene (FcNP) with a variety of acids affords protonated salts at first, whereas longer reaction time leads to partial demetalation of FcNP resulting in a series of Fe complexes. The corresponding salts [FcNP·H]­[X] (X = BF₄ or CF₃SO₃ (<b>1</b>)) are isolated for HBF₄ and CF₃SO₃H. Reaction of FcNP with equimolar amount of CF₃CO₂H for 12 h affords a neutral complex [Fe­(FcNP)₂(O₂CCF₃)₂(OH₂)₂] (<b>2</b>). Use of excess acid gave a trinuclear Fe^II complex [Fe₃(H₂O)₂(O₂CCF₃)₈(FcNP·H)₂] (<b>3</b>). Three linear iron atoms are held together by four bridging trifluoroacetates and two aqua ligands in a symmetric fashion. Reaction with ethereal solution of HCl afforded [(FcNP·H)₃(Cl)]­[FeCl₄]₂ (<b>4</b>) irrespective of the amount of the acid used. Even the picric acid (HPic) led to metal extrusion giving rise to [Fe₂(Cl)₂(FcNP)₂(Pic)₂] (<b>5</b>) when crystallized from dichloromethane. Metal extrusion was also observed for CF₃SO₃H, but an analytically pure compound could not be isolated. The demetalation reaction proceeds with an initial proton attack to the distal nitrogen of the NP unit. Subsequently, coordination of the conjugate base to the electrophilic Fe facilitates the release of Cp rings from metal. The conjugate base plays an important role in the demetalation process and favors the isolation of the Fe complex as well. The 1,1′-bis­(1,8-naphthyrid-2-yl)­ferrocene (FcNP₂) does not undergo demetalation under identical conditions. Two NP units share one positive charge causing the Fe-Cp bonds weakened to an extent that is not sufficient for demetalation. X-ray structure of the monoprotonated FcNP₂ reveals a discrete dimer [(FcNP₂·H)]₂[OTf]₂ (<b>6</b>) supported by two N–H<b>···</b>N hydrogen bonds. Crystal packing and dispersive forces associated with intra- and intermolecular π–π stacking interactions (NP···NP and Cp···NP) allow the formation of the dimer in the solid-state. The protonation and demetalation reactions of FcNP and FcNP₂ with a variety of acids are reported