A.F. Schreiner

Preparation and characterization of tetra(4-pyridyl)porphyrinatomanganese(III) cation supported covalently on poly(siloxane)

Abstract Tetra(4-pyridyl)porphyrinatomanganese(III), [Mn III (TPyP)] + , has been covalently bonded to the surface of a chlorinated crosslinked poly(siloxane) which contains the immobilized chloropropyl group, -CH 2 CH 2 CH 2 Cl. The metalloporphyrin complex was found to react with the immobilized ligand via a quaternization reaction of the 4-pyridine N -atom. The porphyrin binding involves a chemical process rather than physical adsorption. There is evidence that two porphyrins species coexist, both bonded to the surface, one being [Mn III (TPyP)] + and the other (H 2 TPyP), both in the quaternary salt forms, when the quaternization reaction is carried out at higher temperature (150 °C). At moderate reaction temperatures (70–80 °C) the quaternization reaction resulted in only one species, supported [Mn III (TPyP)] + , as evident from electronic spectra of the solid. Also, visible absorption spectra taken of the solution remaining after the quaternization reaction showed no demetallated porphyrm. Solid state electronic absorption, dispersive IR and FT-IR spectra have been used for confirmation.

Chemistry and optical properties of 4d and 5d transition metal compounds. II. synthesis and optical spectra of acetatopentammineruthenium(III) and pseudohalogenpentammineruthenium(III) compounds

Abstract A number of acidopentammineruthenium(III) compounds having C4v micro-symmetry about RuIII were prepared and characterized. Solution optical spectra below 50 kK were recorded, and charged-transfer, dd, and internal transitions were observed. Tetragonal spin-orbit components of the charge-transfer π(NCSe−) →(Ru(xz,yz) transitions are only weakly antibonding, on the basis of band widths, relative to the ground state Γ7t(2Et0. dd transitions are assigned to 2T1g, 2T2gb, and Eg. The latter are not split sufficiently to permit observation of ther C4v components. The observed spectrochemical series of L in [Ru(NH3)5L]Q is NH3>NCO−>OAc−>SCN−>SeCn− on the basis of the energy of the first dd band.

The catalytic activity of poly(siloxane)-supported metalloporphyrins in olefin oxidation reactions: the effect of the support on the catalytic activity and selectivity

Abstract Supported tetra(-4-pyridyl)porphyrinato-manganese(III) [MnIII(TPyP)]+ and -tin(IV) [SnIV(TPyP)]2+ have been prepared. The solid support was iodonated poly(siloxane) surface prepared by condensation reactions of (EtO)4Si with (MeO)3Si(CH2)3I. The supported metalloporphyrins were employed as catalysts for the oxidation reactions of 1-octene and of cyclohexene. NaBH4 was used to reduce [MnIII(TPyP)]+ and [SnIV(TPyP)]2+ back to their catalytically active MnII and SnII forms, respectively. Contrary to their homogeneous counterparts, both of the supported metalloporphyrins catalysed the cyclohexene oxidation reaction to yield only 2-cyclohexen-1-one with no other products over a reaction time of 10 h. In addition to cyclohexene oxidation, the supported [MnIII(TPyP)]+ catalysed 1-octene oxidation as well, whereas the supported [SnIV(TPyP)]2+ was inactive for the oxidation of 1-octene.

Investigation of the catalytic activity of poly (siloxane)-supported tetra (4-pyridyl) porphyrinatomanganese (III) in olefin oxidation reactions

Abstract Supported tetra(4-pyridyl)porphyrinatomanganese(III), [MnIII (TPyP)]+, has been used as a chemically regenerated catalyst for the oxidation of cyclohexene to cyclohex-2-en-1-one. NaBH4 was used to reduce [MnIII(TPyP)]+ back to its catalytically active MnIII form. The reaction was selective to produce the cyclohexenone, and the catalyst showed high activity, with turnovers up to 14 × 103. The effects of solvent, temperature, recovery, and reactant concentrations on the rate of the reaction have also been studied. The rate of the reaction was first order with respect to the catalyst. At higher olefin or oxygen concentrations the reaction was slower. A slower reaction was observed also in the absence of NaBH4. The reaction was faster in nonpolar solvents than in polar ones. These results are also discussed.

The crystal and molecular structure of diiodotetrakis(pyridine)nickel(II) [Nipy4I2]

Abstract The crystal structure of diiodotetrakis(pyridine)nickel (II), [Nipy 4 I 2 ] has been determined accurately by three-dimensional, single-crystal X-ray analysis. The orthorhombic cell of space group Pbcn has a = 9.678(4) A, b = 16.077(6) A, and c = 14.004(4) A, with four molecules per unit cell (density = 1.88 g/cm 3 experimental, and 1.92 g/cm 3 calculated). The structural refinement was terminated at R = 0.042. The molecule was found to have the geometric trans configuration, and this supports electronic spectroscopic conclusions. The nickel atom is surrounded by the four nitrogen atoms of pyridine molecules so that the group (NiN 4 ) defines a plane. The four nitrogen atoms deviate but slightly from defininig a square. The INiI moiety is nearly linear so that any one NiI) vector deviates only slightly (∼2) from being perpendicular to the (NiN 4 ) plane. The average NiN distance in [Nipy 4 I 2 ] is the largest (2.127(7) A) such bond length yet observed for high-spin Ni II -pyridine complexes. Regarding the pyridine ring, the average CC bond distances of coordinated pyridine are found to be shorter than those of the free pyridine molecule. It is also interesting that the two planes of each pair of trans pyridine molecules are found to be staggered (∼90°) whereas both eclipsed and staggered configurations were previously reported for other, but somewhat related molecules. Each of the four pyridine molecules has a pitch angle of ca. 45° with respect to the near-C 4 axis along NiI. The pyridine molecules also define a four-blade propeller, since this “C 4 ” axis brings one pyridine molecule nearly into coincidence with the others. The structural relationships of [Nipy 4 I 2 ] are also compared with those of other metal-pyridine complexes.

Preparation and characterization of poly(siloxane)-supported metalloporphyrins: the effect of the support on the electronic absorption spectra

Preparation and characterization of several supported metalloporphyrins are known, and have been evaluated as electrocatalysts for redoxreactions [l-6]. The support used was either the electrode itself or a polymer coating modification of the electrode surface. Modified organic polymer surfaces have also been reported as supports for metalloporphyrins [7, 81. In our search for new supported catalysts for olefin oxidation reactions, we have employed halogenated poly(siloxane) surfaces [9a] Sil-(CH&X, as supports for the metalloporphyrin catalyst, [Mn”‘(TPyP)]. Quatemization reactions have been used to bind the [Mn’n(TPyP)] species to the surface [9b]. We now report our studies of the effect of support on the electronic absorption spectra of several supported metalloporphyrins [M(TPyP)].

A new silica-supported platinum-amine catalyst for the reaction of silanes with alcohols

Abstract A supported platinum catalyst has been prepared and evaluated for the reactions of HSiR3 (R = Et, OEt) and Me3SiOSi(H)(Me)OSiMe3 with alcohols ROH (R = Me, Et, n-Pr, i-Pr, t-Bu). The supporting surface was prepared by a condensation reaction of (EtO)4Si with the ligand (RO)3SiCH2CH2CH2NH2 in the presence of water. The catalyst partially retains its activity on recovery after three different reaction times. Moreover, the catalytic activity is highly reproducible within the same batch, and among different prepared batches. Variation of the types of silanes and of the alcohols affects the rate of the reaction. The reaction is first order with respect to the catalyst and the silane. A first-order reaction with respect to alcohol is observed at low concentrations, whereas at higher concentrations the rate is independent of the alcohol concentration. There is no evidence of a reaction between the supported amine ligand and the silane. The effects of temperature, solvent polarity and added ligands are also reported.

Mass spectrometry data for tris(dimethyldithiocarbamato)chromium(III) and -indium(III), Cr(dmtc)3 and In(dmtc)3

Abstract Mass spectrometry data were collected and compared for the interesting tris-dithiocarbamato chelates named in the above title, with the Cr III complex containing the potential π-acceptor t 2g 3 subshell and the In III complex with its complete shell t 2g 6 e g 4 . One part of the comparison shows that the parent ion CrL 3 + appears in large abundance, but that InL 3 + is virtually absent. However, the chelate-deficient species ML 2 + and ML + were observed for both Cr and In. A brief comparison was also made with similar data for Cr (acac) 3 of previous work.

The pfeiffer CD activity of dd electronic excitations of (CoIIIS6) and (CrIIIS6) chromophores and of [Co(acac)3]

Six molecular complexes of the tris chelate type containing the (CoIIIS6) and (CrIIIS6) chromophores (dithiocarbamate, dithiophosphate, and dithioxanthate ligands) were found to have Pfeiffer CD activity (PCD). Three combinations of environment compounds and solvents were found to induce such optical activity in dd excitations. However, the PCD effect could only be observed under conditions of using very large. concentration ratios of optically active environmental compound to the complex racemate. The PCD bands of magnetically allowed parents, 4T2g(Cr) and 1T1g(Co), are found to be most intense. Furthermore. it is established that the trigonal components 4E(Cr) and 1E(Co) have much greater intensity than 4A1(Cr) and 1A2(Co), respectively. It is also found that the empirical model which has previously been used with success to relate absolute configurations of ionic complexes to the chirality of the environment compound leads to ambiguous conclusions when the attempt is made to study (neutral) molecular complexes in this manner.

Magnetic CD spectra of chlorophylls, chlorophyllides, and zinc(II) and copper(II) pheophytins and pheophorbides

Abstract Magnetic circular dichroism (MCD) spectra of the ten metal-containing title molecules were measured at room temperature, and spectra of copper-pheophorbide-a were measured at 23 °K, 47 °K, and 63 °K Electronic excited states are assigned, systematic structural features are discussed, and it is found that MCD distinguishes with ease between forms a and b of these molecules. A preliminary MCD study in which the temperature of Cu(ll)-pheophorbide-a is varied between 23 °K and 63 °K indicates that the Cu(II) “d-orbital” which presumably contains the one lone electron is not significantly interactant with the π orbitals involved in the electronic excitations.