Syntheses, characterization, and electrochemistry of compounds containing 1-diphenylphosphino-1′-(di-tert-butylphosphino)ferrocene (dppdtbpf)

Cleavage of [Pd2(PP)2(μ-Cl)2][BArF24]2 (PP = Bis(phosphino)ferrocene, BArF24 = Tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) with Monodentate Phosphines

The addition of Na[BArF24] (BArF24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) to [Pd(PP)Cl2] (PP = 1,1'-bis(phosphino)ferrocene ligands) compounds results in the loss of a chloride ligand and the formation of the dimeric species [Pd2(PP)2(μ-Cl)2][BArF24]2. In most cases, the addition of a monodentate phosphine, PR3, to these dimeric species leads to cleaving of the dimer and formation of [Pd(PP)(PR3)Cl][BArF24]. While these reactions are readily observed via a significant color change, the 31P{1H} NMR spectra offer more significant support, as the singlet for the dimer is replaced with three doublets of doublets. The reaction seems to take place for a wide range of PR3 ligands, although there do appear to be steric limitations to the reaction. The compounds were thoroughly characterized by NMR, and X-ray crystal structures of several of the compounds were obtained. In addition, the ferrocenyl backbone of the 1,1'-bis(phosphino)ferrocene ligands provides an opportunity to examine the oxidative electrochemistry of these compounds. In general, the potential at which oxidations of these compounds occurs shows a dependence on the phosphine substituents.

Transition-metal complexes of group 12 with 1,1'-bis(phosphanyl)ferrocene ligands

The syntheses of four new cadmium and zinc complexes with 1,1'-bis(phosphanyl)ferrocene ligands and their phosphine chalcogenide derivatives are reported. The complexes were characterized by elemental analyses and IR, ¹H NMR, ³¹P NMR and electronic absorption spectroscopy. The crystal structures of dichlorido[1-diphenylphosphinoyl-1'-(di-tert-butylphosphanyl)ferrocene-κ²O,P]cadmium(II), [CdCl₂{(C₁₇H₁₄OP)(C₁₃H₂₂P)Fe}] or CdCl₂(κ²P,O-dppOdtbpf) (1), bis[μ-(tert-butyl)(1'-diphenylphosphinoylferrocen-1-yl)phosphinato-κ³O,O':O'']bis[chloridozinc(II)], [Zn₂{(C₉H₁₃O₂P)(C₁₇H₁₄OP)Fe}₂Cl₂] or [ZnOCl{κ²O,O'-Ph₂POFcPO₂(t-Bu)}]₂ (2), 1,1'-bis(di-tert-butylthiophosphinoyl)ferrocene, [Fe(C₁₃H₂₂PS)₂] or dtbpfS₂ (3), and [1,1'-bis(dicyclohexylphosphanyl)ferrocene-κ²P,P'][chlorido/cyanido(0.25/1.75)]zinc(II), [Zn(CN)_1.75Cl_0.25{(C₁₇H₂₆P)₂Fe}] or Zn(CN)₂(κ²-dcpf) (4), were determined crystallographically. Compound 1 has tetrahedral geometry in which the Cd^II centre is coordinated by one dppOdtbpf ligand in a κ²-manner and by two Cl atoms, while compound 2 displays a centrosymmetric dimeric unit in which two oxide atoms bridge the two Zn atoms to generate an eight-membered ring. Compound 3 revealed a sandwich structure with both phosphane groups sulfurized. In compound 4, the Zn^II atom adopts a tetrahedral geometry by coordinating to the 1,1'-bis(dicyclohexylphosphanyl)ferrocene ligand in a κ²-manner and to two cyanide ligands.

C2-Symmetric P-Stereogenic Ferrocene Ligands with Heavier Chalcogenophosphinous Acid Ester Donor Sites

tert-Butyl-substituted diphospha[2]ferrocenophane was used as a stereochemically confined diphosphane to investigate the addition of various dichalcoganes (R2Ch2; Ch = S, Se, Te and R = Me, Ph). Bischalcogenophosphinous acid esters bearing four soft donor sides were obtained as a mixture of rac and meso diastereomers and characterized by means of multinuclear NMR and X-ray analysis. The coordination chemistry of multidentate ligand 3b was explored toward d¹⁰ coinage metal centers (Cu(I), Ag(I), and Au(I)), yielding various bimetallic complexes.

Bulky 1,1'-bisphosphanoferrocenes and their coordination behaviour towards Cu(i)

Two bulky mesityl substituted dppf-analogues Fe(C₅H₄PMes₂)₂ (Mes = 2,4,6-Me₃C₆H₂, 1) and Fe(C₅H₄PMes₂)(C₅H₄PPh₂) (Mes = 2,4,6-Me₃C₆H₂, Ph = C₆H₅, 3) have been prepared and their properties as donor ligands have been explored using heteronuclear NMR spectroscopy and in particular via¹J_P-Se coupling, cyclic voltammetry and DFT calculations. Based on the results obtained, a series of mono- and dinuclear Cu(i) complexes have been prepared with these new diphosphane ligands using Br^-, I^-, and BF₄^- as counter anions. For the very bulky ligand 1 rare and unprecedented double bridging complexation modes have been observed containing two non-planar Cu₂Br₂ units, while for the other dinuclear complexes planar Cu₂Br₂ units have been found. The Cu(i) complexes of 1 and 3 were then used as catalysts for CO₂-fixation reaction with terminal alkynes, and complexes with ligand 3 were found to be more efficient than those with 1. DFT calculations performed on compounds 1, 3 and their Cu(i) complexes were able to verify the trend of these catalytic reactions.

Oligophosphine-thiocyanate Copper(I) and Silver(I) Complexes and Their Borane Derivatives Showing Delayed Fluorescence

The series of chelating phosphine ligands, which contain bidentate P² (bis[(2-diphenylphosphino)phenyl] ether, DPEphos; 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Xantphos; 1,2-bis(diphenylphosphino)benzene, dppb), tridentate P³ (bis(2-diphenylphosphinophenyl)phenylphosphine), and tetradentate P⁴ (tris(2-diphenylphosphino)phenylphosphine) ligands, was used for the preparation of the corresponding dinuclear [M(μ₂-SCN)P²]₂ (M = Cu, 1, 3, 5; M = Ag, 2, 4, 6) and mononuclear [CuNCS(P³/P⁴)] (7, 9) and [AgSCN(P³/P⁴)] (8, 10) complexes. The reactions of P⁴ with silver salts in a 1:2 molar ratio produce tetranuclear clusters [Ag₂(μ₃-SCN)(t-SCN)(P⁴)]₂ (11) and [Ag₂(μ₃-SCN)(P⁴)]₂²⁺ (12). Complexes 7–11 bearing terminally coordinated SCN ligands were efficiently converted into derivatives 13–17 with the weakly coordinating ^–SCN:B(C₆F₅)₃ isothiocyanatoborate ligand. Compounds 1 and 5–17 exhibit thermally activated delayed fluorescence (TADF) behavior in the solid state. The excited states of thiocyanate species are dominated by the ligand to ligand SCN → π(phosphine) charge transfer transitions mixed with a variable contribution of MLCT. The boronation of SCN groups changes the nature of both the S₁ and T₁ states to (L + M)LCT d,p(M, P) → π(phosphine). The localization of the excited states on the aromatic systems of the phosphine ligands determines a wide range of luminescence energies achieved for the title complexes (λ_em varies from 448 nm for 1 to 630 nm for 10c). The emission of compounds 10 and 15, based on the P⁴ ligand, strongly depends on the solid-state packing (λ_em = 505 and 625 nm for two crystalline forms of 15), which affects structural reorganizations accompanying the formation of electronically excited states.

Copper(I) and silver(I) thiocyanate complexes containing di-, tri-, and tetraphosphine ligands show efficient TADF in the solid state, dominated by the ligand to ligand SCN → π(phosphine) charge transfer, which is changed to d,p(M, P) → π(phosphine) transitions for the isothiocyanatoborate derivatives. The wide variation of the emission color from blue (448 nm) to red-orange (630 nm) is attributed to the nature of the P-donor ligands and the packing effects, influencing structural distortions in the excited state.

Aliphatic Radical Relay Heck Reaction at Unactivated C(sp3 )-H Sites of Alcohols

The Mizoroki-Heck reaction is one of the most efficient methods for alkenylation of aryl, vinyl, and alkyl halides. Given its innate nature, this protocol requires the employment of compounds possessing a halogen atom at the site of functionalization. However, the accessibility of organic molecules possessing a halogen atom at a particular site in aliphatic systems is extremely limited. Thus, a protocol that allows a Heck reaction to occur at a specific nonfunctionalized C(sp3 )-H site is desirable. Reported here is a radical relay Heck reaction which allows selective remote alkenylation of aliphatic alcohols at unactivated β-, γ-, and δ-C(sp3 )-H sites. The use of an easily installed/removed Si-based auxiliary enables selective I-atom/radical translocation events at remote C-H sites followed by the Heck reaction. Notably, the reaction proceeds smoothly under mild visible-light-mediated conditions at room temperature, producing highly modifiable and valuable alkenol products from readily available alcohols feedstocks.

Softening the Donor-Set: From [Cu(P^P)(N^N)][PF6] to [Cu(P^P)(N^S)][PF6]

We report the synthesis and characterization of [Cu(P^P)(N^S)][PF6] complexes with P^P = bis(2-(diphenylphosphino)phenyl) ether (POP) or 4,5-bis(diphenylphosphino)-9,9- dimethylxanthene (xantphos) and N^S = 2-(iso-propylthio)pyridine (iPrSpy) or 2-(tert-butylthio)pyridine (tBuSpy). The single crystal structures of [Cu(POP)(iPrSPy)][PF6] and [Cu(POP)(tBuSPy)][PF6] have been determined and confirm a distorted tetrahedral copper(I) centre and chelating P^P and N^S ligands in each complex. Variable temperature (VT) 1H and 31P{1H} NMR spectroscopy reveals dynamic behavior with motion of the POP backbone in [Cu(POP)(iPrSPy)][PF6] and [Cu(POP)(tBuSPy)][PF6] frozen out at 238 K. VT NMR spectroscopic data including EXSY peaks in the ROESY spectrum of [Cu(xantphos)(tBuSPy)][PF6] at 198 K reveal that two conformers exist in an approximate ratio of 5:1. Replacing bpy by the N^S ligands shifts the Cu+/Cu2+ oxidation to a higher potential. The copper(I) compounds are weak emitters in the solid state with PLQY values of <2%. These values are similar to those for [Cu(POP)(bpy)][PF6] and [Cu(xantphos)(bpy)][PF6] in the solid state.

[Cu(POP)(N^S)][PF6] and [Cu(xantphos)(N^S)][PF6] compounds with 2-(thiophen-2-yl)pyridines

A series of [Cu(POP)(N^S)][PF₆] and [Cu(xantphos)(N^S)][PF₆] compounds (POP = bis(2-(diphenylphosphino)phenyl)ether, xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) in which the N^S ligand is a 2-(thiophen-2-yl)pyridine (1), 2-(thiophen-2-yl)-6-methylpyridine (2), 2-(5-methylthiophen-2-yl)pyridine (3) or 2-(5-methylthiophen-2-yl)-6-methylpyridine (4) have been prepared and characterized in solution and the solid state. Single crystal structures of [Cu(POP)(1)][PF₆], [Cu(xantphos)(1)][PF₆], [Cu(xantphos)(2)][PF₆], [Cu(POP)(3)][PF₆]·CH₂Cl₂, and [Cu(xantphos)(4)][PF₆] confirm chelating N^S and P^P ligands, and distorted tetrahedral copper(i) centres. There is close cation⋯anion association, particularly in [Cu(xantphos)(1)][PF₆]. Although the compounds are stable over days in CH₂Cl₂ solution, they are susceptible to the effects of competing ligands such as chloride ion and MeCN. Analysis of the NMR spectroscopic data of a solution of [Cu(POP)(3)][PF₆] with added Cl⁻, gives a K_d value of 0.14 ± 0.03 mM, indicative of ion-pairing. [Cu(POP)(N^S)][PF₆] and [Cu(xantphos)(N^S)][PF₆] exhibit quasi-reversible or irreversible Cu⁺/Cu²⁺ oxidations. They are blue emitters in solution, and the presence of the 5-methyl group in the thiophene ring in 3 and 4 leads to a red-shift in the emission. The highest photoluminescence quantum yields are for [Cu(POP)(2)][PF₆] (30.8%) and [Cu(POP)(4)][PF₆] (33.2%), both of which have a 6-methyl-substituted pyridine ring in the N^S ligand. Excited-state lifetimes are <5 ns. On going from solution to powder samples, red-shifts of 133 to 163 nm are observed leading to yellow emitters. The brightest emitter, [Cu(xantphos)(1)][PF₆], was tested in a LEC device but showed poor electroluminescence and poor charge transporting characteristics.

[Cu(P^P)(N^S)][PF₆] with N^S = 2-(thiophen-2-yl)pyridines show close cation⋯anion association in the solid-state; complex cation association with Cl⁻ occurs in solution. The compounds are blue-emitters in solution with a red-shift of the emission on going to the solid.

Heterobimetallic complexes with highly flexible 1,1′-bis(phospholanoalkyl)ferrocene ligands

Flexible 1,1′-bis(phospholanoalkyl)ferrocenes react selectively with platinum(ii), gold(i) and rhodium(i) to give macrocyclic chelate complexes.

1,1′-Bis(di-tert-butylphosphino)ferrocene copper(i) complex catalyzed C–H activation and carboxylation of terminal alkynes

Reaction of CuX (X = Br, I) and 1,1′-bis(di-tert-butylphosphino) ferrocene (dtbpf) in 1 : 1, 2 : 1 and 6 : 1 molar ratio in DCM–MeOH (50 : 50 V/V) afforded copper(i) complexes. These complexes were shown to be efficient catalysts in comparison with CuI for the conversion of terminal alkynes into propiolic acids with CO₂ at room temperature.