Stephan Pitter

Phosphinoalkyl nitriles as hemilabile ligands: New aspects in the homogeneous catalytic coupling of CO2 and 1,3-butadiene

Abstract ‘In situ’ catalysts prepared from (η5-C5H5)Pd(η3-C3H5) 9 and phosphinoalkyl nitriles 10a–e of the general formula (iC3H7)2P(CH2)nCN have been used to catalyse the co-oligomerisation of 1,3-butadiene and carbon dioxide. The δ-lactone 2-ethylidene-6-heptene-5-olid 1 is formed, yielding up to 74%. Different solvent systems have been used of which pyridine provides the best result. The catalysis may also be performed without additional solvent. A minimum of five CH2 units (n = 5) within the ligand is necessary to produce 1 with a selectivity higher than 29% in a solvent-free reaction. Therefore, phosphinoalkyl nitriles of the type described here are acting as hemilabile ligands in the catalytic cycle.

Synthesis of Hemilabile P,N Ligands: ω-2-Pyridyl-n-alkylphosphines

Summary. A series of P,N ligands of the general formula (2-py)-(CH2)n-PR2 (2-py: 2-pyridyl; R: i-Pr (n=1, 4–7), Ph (n=5–7)) 4a–g and 6a has been synthesized. Starting from 2-picoline (1), 2-(ω-chloroalkyl)pyridines 3a–d are prepared. The reactions of 3a–d with (i-Pr)2PLi and Ph2PLi, respectively, result in the title compounds 4a–g in up to 89% yield. Reaction of Cl-(CH2)3-P(i-Pr)2 with 2-picolyllithium (2) is an alternative route to 4a. Additionally, P,P,N ligands 7a and 9 are synthesized by similar methods. All new compounds were fully characterized. The formation of cyclic pyridinium derivatives 5a and 5b from intramolecular SN reactions of 3a and 3b is discussed in detail.Zusammenfassung. Ausgehend von 2-Picolin (1) werden die homologen P,N-Liganden (2-py)-(CH2)n-PR2 (2-py: 2-Pyridyl; R: i-Pr (n=1, 4–7), Ph (n=5–7) 4a–g und 6a dargestellt. Über die entsprechenden 2-(ω-Chloralkyl)pyridine 3a–d erhält man durch nachfolgende Umsetzung mit (i-Pr)2PLi bzw. Ph2PLi die Titelverbindungen 4a–g in bis zu 89% Ausbeute. Alternativ erhält man Verbindung 4a durch Umsetzung von Cl-(CH2)3-P(i-Pr)2 mit 2-Picolyllithium (2). Ähnliche Synthesemethoden eröffnen einen einfachen Zugang zu den P,P,N-Liganden 7a und 9. Alle neuen Verbindungen wurden vollständig charakterisiert. Die Bildung der zyklischen Pyridiniumderivate 5a und 5b durch intramolekulare SN-Reaktionen von 3a bzw. 3b wird im Detail diskutiert.

Die heterogen katalysierte Co-oligomerisation von 1,3-Butadien und CO2 mit immobilisierten Palladiumkomplexen

Abstract Immobilized catalysts prepared from [Pd(η 5 -C 5 H 5 )(η 3 -C 3 H 5 )] ( 5 ) and polymer bound phosphines 4a–c are used to catalyse C,C coupling reactions of carbon dioxide and any organic co-substrate for the first time in a heterogeneous way. These phosphines, synthesised from chloromethylated polystyrene, are characterised by their elemental analysis data and NMR spectra. The immobilized catalyst from polymer 4a and 5 catalyses the formation of the δ-lactone 2-ethylidene-6-heptene-5-olid ( 1 ). With low reaction rates, up to 72% selectivity to 1 is observed, These catalysts can be used in multiple reactions. In an analogous procedure using polymer 4b , the synthesis of C 17 carboxylic esters is successful.

Control of homogeneously catalyzed reactions by phase equilibriaThis work was presented at the Green Solvents for Catalysis Meeting held in Bruchsal, Germany, 13–16th October 2000.

Carbon dioxide was used not only as a reaction medium but also as a renewable C1 feedstock for the palladium catalyzed coupling reaction of butadiene and carbon dioxide. By utilization of nitrile modified phosphine ligands, in the liquid phase complete butadiene conversion and selectivity for the formation of (3E)-3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (1) up to 47% were achieved. Phase equilibrium considerations were used for process development in order to realize single-phase conditions for the reaction. In contrast to a CO2 enriched phase composition, variation of the density only enables moderate conversion rates also with single-phase conditions and without further catalyst modification.

Rhodium-Catalyzed Amination of Aromatic Olefins

Summary. The oxidative amination of styrene with secondary amines in the presence of cationic rhodium catalysts yields regiospecifically the corresponding anti-Markovnikov enamines. Styrene as the hydrogen acceptor gave concomitantly ethylbenzene. In the presence of 1,5-cyclooctadiene (cod) preferential reduction to cyclooctene takes place. The addition of cod reduces the rate of the reaction, but also the amount of ethylbenzene produced. Here, for the first time the ratio of enamine: ethylbenzene is > 1, which is favourable in case of more expensive styrene derivatives. A screening of various ligands for oxidative amination reveals that hemilabile 2-(ω-phosphino-n-alkyl)-pyridines are superior ligands for this reaction compared to simple alkyl and aryl phosphines.

Evaluation of Supercritical Carbon Dioxide as a Tuneable Reaction Medium for Homogeneous Catalysis

The present contribution highlights the relationship between scCO 2properties, its solubilization power, and its use as a reaction medium for homogeneous catalysis.Current research activities under the lighthouse project “Smart Solvents, Smart Ligands”are presented, the focus being on criteria of conducting catalyzed processes in future applications.

Phosphinoalkylnitrile: Synthese und Koordinationsverhalten an Palladiumzentren / Phosphinoalkylnitnles: Synthesis and Coordination Behaviour at Palladium Centres

Phosphinoalkylnitriles R2P-(CH2)n-CN {R = isopropyl (ipr), phenyl (ph), cyclohexyl (chex), n = 3, 6, 10} have been prepared starting from the corresponding secondary phosphines in an easy three step synthesis. All new compounds were characterized by their 1H -, 13C and 31P NMR data. Some of these new P, N ligands were used to prepare complexes [{R2P- (CH2)n-CN}2PdCl2] which were also identified by their NMR data. In addition the crystal structures of three derivatives, [{ipr2P-(CH2)3-CN}2PdCl2] 7a, [{ph2P-(CH2)3-CN}2PdCl2) 7b and [{ph2P-(CH2)6-CN}2PdCl2] 8b were determined by X-ray analysis. The coordination mode of the phosphinoalkylnitriles in these complexes was found to be P-bonded resulting in a trans configuration. Palladium catalysts with 5a as ligand show high activies in the co-oligomerization of butadiene and carbon dioxide. The δ-lactone 11a is formed under very mild conditions.