Simonetta Antonaroli

PREPARATION AND REACTIONS OF PALLADIUM(0)-OLEFIN COMPLEXES WITH IMINOPHOSPHINE LIGANDS

Abstract The complexes [Pd(η2-ol){o-(Ph2P)–C6H4–CHNR}] [ol, dimethyl fumarate (dmf), 1,4-naphtoquinone (nq), fumaronitrile (fn); R=C6H4OMe-4, CMe3, Me, bornyl] can be prepared in good yields from the reaction of the allyl derivatives [Pd(η3-C3H5) {o-(Ph2P)–C6H4–CHNR}]BF4 with an excess of NHEt2 in the presence of the activated olefin ol. The complex [Pd(η2-ma){o-(Ph2P)–C6H4-CHNC6H4OMe-4}] (ma, maleic anhydride) is more conveniently obtained via olefin substitution from [Pd(η2-dmf){o-(Ph2P)–C6H4–CHNC6H4OMe-4}]. The α-diimine ligand of [Pd(η2-fn)(py-2-CHNC6H4OMe-4)] is quantitatively displaced by the appropriate iminophosphine to give [Pd(η2-fn){o-(Ph2P)–C6H4–CHNC6H4OMe-4}]. The new zerovalent complexes with P–N ligands are characterized by multinuclear NMR spectroscopy. In solution, olefin rotation or olefin exchange are generally slow. The compound [Pd(η2-fn){o-(Ph2P)–C6H4–CHNC6H4OMe-4}] reacts with a second molecule of iminophosphine yielding [Pd(η2-fn){o-(Ph2P)–C6H4–CHNC6H4OMe-4}2] in which the iminophosphines act essentially as P-monodentate ligands. [Pd(η2-dmf) {o-(Ph2P)–C6H4–CHNC6H4OMe-4}] undergoes fast oxidative addition of allyl chloride to [Pd(η3-C3H5){o-(Ph2P)–C6H4–CHNC6H4OMe-4}]+.

Iminophosphine - palladium(0) complexes as catalysts for the Stille reaction

The cross-coupling of iodobenzene with tributylphenylethynylstannane or tributylvinylstannane is efficiently catalysed by iminophosphine–palladium(0)–olefin complexes of the type [Pd(η2-dmf)(P-N)] (dmf, dimethylfumarate; P-N, 1-(PPh2)-C6H4-2-CNR (R=alkyl, aryl)). The catalytic activity depends on the R substituent of the imino group: the highest reaction rates are obtained using aryl-substituted iminophosphines. Equivalent catalytic systems can be obtained using a palladium source such as Pd(OAc)2 or Pd(dba)2 (dibenzylideneacetone, dba) in combination with the iminophosphine ligands. In the coupling of iodobenzene with tributylphenylethynylstannane, the highest reaction rates are obtained using an iminophosphine/palladium molar ratio of 2:1, while in the vinylstannane–iodobenzene coupling the best P-N/Pd ratio is 1:1.

Characterization of biofilm-forming cyanobacteria for biomass and lipid production

This work reports on one of the first attempts to use biofilm‐forming cyanobacteria for biomass and lipid production.

Iminophosphine-palladium(0) complexes as catalysts in the alkoxycarbonylation of terminal alkynes

Abstract In the presence of methanesulfonic acid, the palladium(0)-olefin complexes: [Pd(η 2 -ol)(P N)] [ol=dimethyl fumarate or fumaronitrile, P N=1-(Ph 2 P)C 6 H 4 -2-CH NR (R=CMe 3 or C 6 H 4 OMe-4)] catalyse the alkoxycarbonylation of terminal alkynes. Moderately good rates are obtained when the catalysts are promoted with two equivalents of the free P N ligand and a large excess of acid at 120°C. The catalytic data suggest that derivatives of the type [Pd(alkyne)(P N) n ] ( n =2–3) are the active catalytic species.

Structural studies on iminophosphine ligands and their palladium complexes

The crystal and molecular structures of the iminophosphine o-(Ph2P)C6H4CH=NC6H4OMe-4 (1) and its palladium complexes [Pd(η3-C3H5){o-(Ph2P)C6H4CH=NC6H4OMe-p}]BF4 (2) and [Pd(η2-fn){o-(Ph2P)C6H4CH=NC6H4OMe-4}] [fn = fumaronitrile, (3)] have been determined by X-ray analysis. In the free ligand (1), the planar imino group of E configuration is oriented, relative to the PPh2 unit, so that the CH=N hydrogen atom points towards phosphorus, with the nitrogen atom on the opposite side. In (2) and (3) the iminophosphine behaves as a P,N-chelate ligand, this coordination mode being achieved by the imino group rotation of 169.3 ° and 145.3 °, respectively, around its bond with the ortho disubstituted phenyl ring. Complex (2) shows a structural disorder with two different orientations of the allyl ligand. The trigonal planar coordination around the central metal in complex (3) involves the P- and N-donor atoms of (1) and the η2-bound olefin, with a marked lengthening of the olefinic carbon-carbon bond. In both the complexes, the chelate six-membered ring of the iminophosphine with palladium is not coplanar with the N-Pd-P coordination plane, the imino carbon atom and the ortho disubstituted phenyl group lying on the same side out of the N-Pd-P plane, whereas the N-substituent and one of the PPh2 groups are on the opposite side. The 1H-n.m.r. spectra at low temperatures of (2) and (3), and of [Pd(η2-tmetc){o-(Ph2P)C6H4CH=NCMe3}] [tmetc = tetramethyl ethylenetetracarboxylate, (4)] are interpreted on the basis of a non-rigid conformation of the chelate iminophosphine, which undergoes a fast dynamic process whereby the N- and P-substituents move above and below the coordination plane.

Kinetics and mechanism of regioselective amination of the 1-phenylallyl group in cationic palladium(II) complexes bearing bidentate ligands

Abstract The complexes [Pd(η3-1-PhC3H4)(L–L′)]+ [L–L′=2-(PPh2)C6H4-1-CHNR (R=Me (1a), i-Pr (1b), t-Bu (1c), (R)-bornyl (1d), C6H4OMe-4 (1e), C6H3Me2-2,6 (1f), C6H3(i-Pr)2-2,6 (1g)), 6-MeC5H3N-2-CHNC6H4OMe-4 (2a), C5H4N-2-CHN-t-Bu (2b) and C5H4N-2-CH2S-t-Bu (3a)] are generally present in solution as two geometrical isomers, the relative abundance of which depends essentially on the steric requirements of the L–L′ ligand. In the presence of fumaronitrile the cationic complexes undergo a regioselective amination by secondary amines HY at the CH2 allyl terminus, yielding [Pd(η2-fn)(L–L′)] and the allylamines (E)-PhCHCHCH2Y. Under pseudo-first-order conditions the amination rates (kobs) are found to depend on the k2[HY] term for 2a and 3a, and on the sum k2[HY]+k3[HY]2 for the other complexes. The second-order term k2 is related to direct nucleophilic attack on the CH2 allyl terminus of the substrate whereas the third-order term k3 is ascribed to parallel attack by a further HY molecule on the intermediate [Pd(1-PhC3H4)(L–L′)(HY)]+. The k2 values depend on the steric and electronic properties of both the amine HY and the ligand L–L′. For complexes 1a–1g, the relatively higher k2 values and their increase with increasing steric crowding at the nitrogen-bonded carbon of substituent R are interpreted in terms of a greater reactivity of the isomer with the CH2 allyl terminus trans to phosphorus and cis to the NR group. The high amination rate of 2a, as compared with that of 2b, is related to substantial steric interaction of the CH2 allyl terminus with the 6-Me pyridine group in close proximity in the predominant isomer.

[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki-Miyaura reaction

The complex [PdCl2(P–N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)quinoline ligand (P–N) is a highly efficient catalyst for the coupling of phenylboronic acid with aryl bromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 � C in toluene with K 2CO3 as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h

Palladium complexes with a tridentate PNO ligand. Synthesis of η1-allyl complexes and cross-coupling reactions promoted by boron compounds.

The iminophosphine 2-(2-Ph(2)P)C(6)H(4)N=CHC(6)H(4)OH (P-N-OH) reacts with [Pd(mu-Cl)(eta(3)-C(3)H(5))](2) yielding [PdCl(P-N-O)] and propene. In the presence of NEt(3), the reaction of P-N-OH with [Pd(mu-Cl)(eta(3)-1-R(1),3-R(2)C(3)H(3))](2) (R(1) = R(2) = H, Ph; R(1) = H, R(2) = Ph) affords the eta(1)-allyl derivatives [Pd(eta(1)-1-R(1),3-R(2)C(3)H(3))](P-N-O)] (R(1) = R(2) = H: 1; R(1) = H, R(2) = Ph: 2; R(1) = R(2) = Ph: 3). In solution, the complexes 1 and 3 undergo a slow dynamic process which interconverts the bonding site of the allyl ligand. The X-ray structural analysis of 1 indicates a square-planar coordination geometry around the palladium centre with a P,N,O,-tridentate ligand and a sigma bonded allyl group. The complexes [PdR(P-N-O)] (R = C(6)H(4)Me-4, C[triple bond]CPh) react slowly with p-bromoanisole in the presence of p-tolylboronic acid to give [PdBr(P-N-O)] and the coupling product RC(6)H(4)OMe-4. The latter reactions also proceed at a low rate under catalytic conditions. The coupling of allyl bromide with p-tolylboronic acid is catalyzed by [PdCl(P-N-O)]/K(2)CO(3) to give 4-allyltoluene.

Mechanism of nucleophilic attack by diethylamine on cationic palladium(II) allyl complexes containing α-diimine ligands

The reactions of the cationic complexes [Pd(η3-allyl)(N–N′)]ClO4(allyl = 4-methoxycyclohexenyl, allyl or 2-methylallyl; N–N′= 1, 2-bis(imino)ethanes or pyridine-2-carbaldimines) with diethylamine, in the presence of an activated olefin, in chloroform at 25 °C have been studied. They involve a fast equilibrium displacement of the co-ordinated α-diimine to yield [Pd(η3-allyl)(NHEt2)2]+, accompanied by slow nucleophilic attack at the allyl ligand of the [Pd(η3-allyl)(N–N′)]+ substrate producing [Pd(η2-olefin)(N–N′)](olefin = dimethyl fumarate or fumaronitrile) and allyldiethylamine. As shown by the stereochemical course of the reaction with [Pd(1–3-η3-C6H8OMe)(C5H4N-2-CHNC6H4OMe4)]ClO4, the nucleophilic attack takes place on the allyl face opposite the metal. The equilibrium constants for α-diimine displacement have been determined. They are strongly affected by the structure of the N–N′ ligand and decrease in the order RNCH–CHNR RNC(Me)–C(Me)NR ≈ C5H4N-2-CHNR > C5H4N-2-CHNCMe3(R = C6H4OMe-4). Kinetic studies showed that the pseudo-first-order rate constants (kobs) for the slow amination path display both a first- and second-order dependence on the NHEt2 concentration of type kobs=k2[NHEt2]+k2′[NHEt2]2. The k2 term is related to direct bimolecular attack of NHEt2 on the terminal allyl carbon, whereas the k2′ term is ascribed to a parallel nucleophilic attack by a hydrogen-bonded diethylamine dimer arising from amine self-association.

Phosphorus removal coupled to bioenergy production by three cyanobacterial isolates in a biofilm dynamic growth system

ABSTRACT In the present study a closed incubator, designed for biofilm growth on artificial substrata, was used to grow three isolates of biofilm-forming heterocytous cyanobacteria using an artificial wastewater secondary effluent as the culture medium. We evaluated biofilm efficiency in removing phosphorus, by simulating biofilm-based tertiary wastewater treatment and coupled this process with biodiesel production from the developed biomass. The three strains were able to grow in the synthetic medium and remove phosphorus in percentages, between 6 and 43%, which varied between strains and also among each strain according to the biofilm growth phase. Calothrix sp. biofilm turned out to be a good candidate for tertiary treatment, showing phosphorus reducing capacity (during the exponential biofilm growth) at the regulatory level for the treated effluent water being discharged into natural water systems. Besides phosphorus removal, the three cyanobacterial biofilms produced high quality lipids, whose profile showed promising chemical stability and combustion behavior. Further integration of the proposed processes could include the integration of oil extracted from these cyanobacterial biofilms with microalgal oil known for high monounsaturated fatty acids content, in order to enhance biodiesel cold flow characteristics.