Search

The efficiency of various gold compounds containing bis(phosphino)ferrocene ligands for catalyzing ring-closing reactions was examined. Six commercially available bis(phosphino)ferrocene ligands: 1,1′-bis(ditert-butylphosphino)ferrocene (dtbpf), 1,1′-bis(diphenylphosphino)ferrocene (dppf), 1,1′-bis(dicylohexylphosphino)ferrocene (dcpf), 1,1′-bis(diiso-propylphosphino)ferrocene (dippf), 1-diphenylphosphino-1′-di-tert-butylphosphinoferrocene (dppdtbpf) and 1,1′-bis(5-methyl-2-furanylphosphino)ferrocene (dfurpf) were employed in this study. In addition to the previously reported [Au2Cl2(μ-PP)] (PP = dtbpf, dppf, dcpf, dippf or dppdtbpf) compounds, [Au2Cl2(μ-dfurpf)] was synthesized and characterized by NMR spectroscopy, cyclic voltammetry and X-ray crystallography. All of these gold compounds react with Na[BArF24] (BArF24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) to remove a chloride and yield the cationic monochlorides, [Au2(μ-Cl)(μ-PP)]+. The effectiveness of the [Au2Cl2(μ-PP)] and [Au2(μ-Cl)(μ-PP)][BArF24], either pre-formed or generated in situ, compounds for the catalytic intramolecular alkyne hydroalkoxylation of (Z)-3-methylpent-2-en-4-yn-1-ol was examined in CDCl3 and toluene-d8. The ring-closing of N-(prop-2-yn-1-yl)benzamide was also examined and was efficiently carried out in toluene-d8 using [Au2(μ-Cl)(μ-PP)][BArF24] (PP = dtbpf, dppf, dcpf, dippf, dppdtbpf or dfurpf). In addition, [Au2Cl2(μ-dppe)] and [Au2(μ-Cl)(μ-dppe)][BArF24] were examined as catalysts for these ring-closing reactions in order to determine if the ferrocene backbone of the bis(phosphino)ferrocene ligands was important for catalysis.

1,1′-bis(phosphino)ferrocene ligands are commonly employed in a variety of catalytic systems. These ligands are of particular interest as the steric and electronic properties of the phosphorus donor atoms can be altered by changing the substituents of the phosphines. In addition, the ferrocene backbone of the ligands provides unique electronic and conformational flexibility to these ligands. Previous investigations in this lab have examined catalytic ring closing reactions using a series of gold compounds with bis(phosphino)ferrocene ligands, [Au2Cl2(μ-PP)]. These gold compounds were shown to react with sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate, Na[BArF24], to generate a cationic species with the general formula [Au2(μ-Cl)(μ-PP)][BArF24] that are much more efficient catalysts than the [Au2Cl2(μ-PP)] compounds. In this study, a series of [Au2Cl2(μ-PP)] (μ-PP = 1,1′-bis(diphenylphosphino)ferrocene (dppf), 1,1′-bis(diiso-propylphosphino)ferrocene (dippf), 1,1′-bis(dicyclohexylphosphino)ferrocene (dcpf), 1,1′-bis(ditert-butylphosphino)ferrocene (dtbpf), 1-diphenylphosphino-1′-ditert-butylphosphinoferrocene (dppdtbpf) or 1,1ʹ-bis(5-methyl-2-furanylphosphino)ferrocene (dfurpf)) compounds were examined as catalysts for the intramolecular ring-closing hydroamination of 3-(vinyloxy)propan-1-amine and the intermolecular hydroamination of phenylacetylene with a variety of phenylamine reagents. The catalytic activity of the corresponding [Au2(μ-Cl)(μ-PP)][BArF24] compounds that were generated in situ was also explored. Two new [Au2Cl2(μ-PP)] compounds with chiral bis(phosphino)ferrocene ligands (PP = 1,1′-bis(2R,5R-dimethylphospholanyl)ferrocene (R-dMeplf) or 1,1′-bis(2S,5S-dimethylphospholanyl)ferrocene (S-dMeplf)) were prepared, characterized spectroscopically and electrochemically, and evaluated as catalysts in the ring-closing hydroamination reaction. In addition, the X-ray structures of [Au2Cl2(μ-PP)] (PP = dppdtbpf, R-dMeplf and S-dMeplf) were determined.

Two new 1,1′-disubstituted cobaltocenium compounds, [(C5H4CHEt2)2Co][PF6] and [(C5H4SiMe3)2Co][PF6], were synthesized and the X-ray crystal structures were determined. The electrochemistry of seven 1,1′-disubstituted cobaltocenium compounds and the analogous ferrocene compounds was studied in methylene chloride using cyclic voltammetry. The affect of the various substituents on the redox potentials of these compounds was examined and trends in the electrochemical data were explored.

The oxidative electrochemistry of group VI and group VII metal carbonyl compounds containing 1,1′-bis(phosphino)ferrocene ligands with the general formula [M(CO)4(P∩P)] (M = Cr, Mo, or W, P∩P = 1,1′-bis(diisopropylphosphino)ferrocene (dippf) or 1,1′-bis(dicyclohexylphosphino)ferrocene (dcpf)) and [M(CO)3Br(P∩P)] (M = Mn, P∩P = 1,1′-bis(diphenylphosphino)ferrocene (dppf) or dippf; M = Re, P∩P = dppf, dippf or dcpf) was investigated. Two reversible waves were observed in the electrochemistry of the Cr compounds, while the other compounds exhibited one wave with varying reversibility. The compounds were examined using spectroelectrochemistry, which was particularly useful in assigning the two waves in the Cr species. In addition, the X-ray structures of [Cr(CO)4(dippf)], [Cr(CO)4(dcpf)] and [Mn(CO)3Br(dippf)] were determined. The %Vbur values for dippf, dcpf and other bidentate phosphines have been calculated for these pseudo-octahedral Cr and Mn compounds and these structural studies have been supplemented by DFT optimized geometries for the Cr complexes.

The electrochemistry of 1,1′-bis(diphenylphosphino)cobaltocenium hexafluorophosphate ([dppc][PF6]), 1,1′-bis(dicyclohexylphosphino)cobaltocenium hexafluorophosphate ([dcpc][PF6]), 1,1′-bis(di-iso-propylphosphino)cobaltocenium hexafluorophosphate ([dippc][PF6]), and 1-(di-tert-butylphosphino)cobaltocenium hexafluorophosphate ([1-dtbpc][PF6]) was examined in methylene chloride with tetrabutylammonium hexafluorophosphate as the supporting electrolyte. A reversible reductive wave followed by an irreversible wave at more negative potentials was observed. Ten new phosphinothioyl ([dppcS2][PF6], [dcpcS2][PF6], [dippcS2][PF6], [1-dtbpcS][PF6], and 1,1′-bis(dicyclohexylphosphinothioyl)ferrocene) and phosphinoselenoyl derivatives ([dppcSe2][PF6], [dcpcSe2][PF6], [dippcSe2][PF6], [1-dtbpcSe][PF6], and 1,1′-bis(dicyclohexylphosphinoselenoyl)ferrocene) were prepared and characterized, and the structures of eight of these compounds were determined. The electrochemistry of these phosphinochalcogenyl cobaltocenium compounds, as well as the previously prepared [dppcO2][PF6], displayed two reversible reductive waves at potentials less negative than that of the free phosphines. A correlation was found to exist between the Hammett substituent constant σp and the reduction potentials of these compounds. In addition, the phosphinoselenoyl [dppcSe2][PF6], [dcpcSe2][PF6], and [dippcSe2][PF6] displayed an electrochemically irreversible oxidative wave, potentially indicating an intramolecular Se–Se bonded trication. The electrochemistry of three new and five previously reported transition metal complexes of the general formula [MnCl2(P∩P)][PF6] (M = Pd or Pt, n = 1, P∩P = dppc, dcpc or dippc; M = Au, n = 2, P∩P = dppc or dcpc)) was also examined displaying at least two reductive waves at potentials less negative than that of the free phosphines. Comparison of the electrochemical data with that previously obtained for analogous ferrocenes indicates that a correlation exists between the reduction potentials of the cobaltocenium phosphines and the potentials at which oxidation of the ferrocene phosphines occurs. In addition, the structure of [Au2Cl2(dppc)][PF6] was determined.

The oxidative electrochemistry of P(CH 2 Fc) 3 and three of its derivatives was examined. The electrochemistry of these compounds is sensitive to the functionality added to the phosphorus lone pair and the supporting electrolyte used.

New synthetic routes to 1-methyl-1-silaindane (1b) and 1-methyl-1-germaindane (1b) were developed and the desired products were obtained in good isolated yield. Compounds 1a and 1b were fully characterized by mass spectroscopy, 1H and 13C{1H} NMR, and infrared spectroscopy.

The oxidative electrochemistry of 11 chiral bis-phosphinoferrocene ligands, all within the Josiphos class of ligands, was examined in methylene chloride. The oxidation of these ligands displays multiple waves of varying chemical reversibility. Palladium(II) and platinum(II) complexes with the general formula [MCl2(P–P)] (M = Pd or Pt; P–P = Josiphos) were prepared, characterized by NMR and cyclic voltammetry. The electrochemistry simplifies greatly upon coordination of the Josiphos ligands. The X-ray structures of a palladium(II) and platinum(II) complex of the same Josiphos ligand are reported.

The electrochemistry of 1,1′-bis(dicyclohexylylphosphino)ferrocene (dcpf) was examined in methylene chloride with tetrabutylammonium hexafluorophosphate or tetrabutylammonium tetrakis(pentafluorophenyl)borate as the supporting electrolyte. The oxidation of dcpf is complicated by a follow-up reaction. Seven new complexes containing dcpf and one new compound containing 1,1′-bis(di-tert-butylphosphino)ferrocene (dtbpf) were prepared and characterized. The new complexes were analyzed by cyclic voltammetry and the oxidation of these complexes occurred at a more positive potential than the free ligand. In addition, the X-ray structure of [PdCl2(dcpf)] was determined and compared to other palladium complexes containing bisphosphinometallocene ligands. Five different palladium complexes containing bisphosphinometallocene ligands were examined as catalyst precursors in Buchwald–Hartwig catalysis.

The oxidative electrochemistry of 1,1′-bis(diphenylphosphino)osmocene (dppo) and 1,1′-bis(diphenylarsino)ferrocene (dpaf) was studied in dichloromethane with tetrabutylammonium hexafluorophosphate as the supporting electrolyte. The [MCl2(P∩P)] (M = Pd or Pt; P∩P = dppo or 1,1′-bis(diphenylphosphinoindenyl)iron) complexes were prepared, studied electrochemically and the X-ray structures of dppo and [PdCl2(dppo)] were determined.

A new chemical oxidant [N(4-C6H4Br)3][B(C6F5)4], was prepared and used to synthesize [Fe(C5H5)2][B(C6F5)4]. The crystal structure of [Fe(C5H5)2][B(C6F5)4] was determined.

The electrochemistry of 1,1′-bis(diphenylphosphino)ferrocene (dppf) derivatives of Ru3(CO)12 was investigated. Two known compounds [Ru3(CO)8(μ-dppf)2 (1) and Ru3(CO)10dppf (2)] and a new compound [Ru3(CO)11(μ-dppf)Ru3(CO)11 (3)] were prepared. Compound 3 was characterized spectroscopically and an X-ray crystal structure was obtained. The reductive electrochemistry of 1 and 2 showed an irreversible reduction and a follow-up oxidation, similar to Ru3(CO)12. The electrochemistry of compound 3 showed two irreversible waves and a follow-up oxidation. A trend in the reduction potential vs. the number of coordinated phosphorus atoms was noted. The oxidative electrochemistry of 1–3 showed a dppf-based chemically reversible wave, and an irreversible wave similar to that of Ru3(CO)12. Trends were also noted between the oxidation potential and the number of coordinated phosphorus atoms.

The oxidative electrochemistry of 1,1′-bis(diphenylphosphino)ferrocene (dppf) and 1,1′-bis(diphenylphosphino)ruthenocene (dppr) was investigated at a variety of temperatures and concentrations. In addition, the oxidative electrochemistry of [NiCl2(dppf)] and [MCl2(dppr)] (M=Ni, Pd or Pt) compounds was studied. During the preparation of the dppr compounds, crystals of [NiCl2(dppr)] and [(PdCl2(dppr)]·CH2Cl2 were obtained and the structures were determined. With the previously determined structures of [MCl2(dppf)] (M=Ni, Pd or Pt) and [PtCl2(dppr)], a thorough examination of the binding of dppf and dppr to Group 10 metals was performed.

The oxidation potentials for a series of diruthenium compounds have been measured. The heat of protonation (−ΔHMHM) and oxidation potentials (E1/2) for a series of Ru2Cp′2(CO)4 (Cp′=Cp2, Cp*2, C5H4CH2C5H4, (C5H4CH2)2, (C9H7)2, C10H8, (HBpz3)2) compounds and Ru2Cp2(CO)3(PMe3) were used to estimate the homolytic RuHRu bond dissociation enthalpy (BDEs) using a thermochemical cycle. Poor correlation between −ΔHMHM and E1/2 was observed, as anticipated, due to the effects of the bridging carbonyls on the heats of protonation. There is a correlation between the oxidation potentials and the average νCO bands for the protonated dimers as both are a measurement of the donor ability of the ligands. The calculated BDE values were also compared with values obtained for mononuclear ruthenium compounds.

The preparation of 1-ferrocenyl-2-propanol (5) from lithioferrocene and propylene oxide is described. The reaction of lithium diisopropylamide with 2-ferrocenylethanol (3) or 1-ferrocenyl-2-propanol (5), followed by the addition to hexachlorocyclotriphosphazane (1) provides N3P3Cl6−n (OCHRCH2C5H4FeCp)n [R=H, n=1 (3) or 2 (4); R=CH3, n=1 (6)]. The corresponding reactions with ferrocenylmethanol lead to degradation products via a phosphazene–phosphazene rearrangement. The substitution pattern observed for N3P3C14(OCH2CH2C5H4FeCp)2 (4) suggests that the reaction follows a predominantly cis-non-geminal pathway. The substituted phosphazene derivatives were characterized by standard means including 31P-NMR, mass spectrometry, elemental analysis and cyclic voltammetry. An X-ray crystal structure of N3P3C15(OCH2CH2C5H4FeCp) (3) was obtained.