Rocco Paciello

Phosphabenzenes as Monodentate π-Acceptor Ligands for Rhodium-Catalyzed Hydroformylation

A new class of phosphinine/rhodium catalysts for the hydroformylation of terminal and internal alkenes is presented in this study. A series of phosphabenzenes 1-14 has been prepared by condensation of phosphane or tris(trimethylsilyl)phosphane with the corresponding pyrylium salt. Trans-[(phosphabenzene)2RhCl(CO)] complexes 21-25 have been prepared and studied spectroscopically and by X-ray crystal-structure analysis. The hydroformylation of oct-1-ene has been used to identify optimal catalyst preformation and reaction conditions. Hydroformylation studies with 15 monophosphabenzenes have been performed. The catalytic performance is dominated by steric influences, with the phosphabenzene 8/rhodium system being the most active catalyst. Turnover frequencies of up to 45370 h(-1) for the hydroformylation of oct-1-ene have been determined. In further studies, hydroformylation activity toward more highly substituted alkenes was investigated and compared with the standard industrial triphenylphosphane/rhodium catalyst. The reactivity differences between the phosphabenzene and the triphenylphosphane catalyst increase on going to the more highly substituted alkenes. Even tetrasubstituted alkenes reacted with the phosphabenzene catalyst, whereas the triphenylphosphane system failed to give any product. In situ pressure NMR experiments have been performed to identify the resting state of the catalyst. A monophosphabenzene complex [(phosphinine 8)Ir(CO)3H] could be detected as the predominant catalyst resting state.

Chelated Bisphosphites with a Calix[4]arene Backbone: New Ligands for Rhodium-Catalyzed Low-Pressure Hydroformylation with Controlled Regioselectivity

Extremely high regioselectivities were achieved in the rhodium-catalyzed low-pressure hydroformylation of 1-octene to n-nonanal with chelate bisphosphites that contain a p-tert-butylcalix[4]arene backbone (shown in the picture). It was possible to tailor the structures and ultimately the catalytic properties of these complexes using molecular modeling calculations.

Übergangsmetall-carbin-komplexe: XCI. Synthese isonitril-substituierter, neutraler und kationaischer diethylaminocarbin-komplexe des wolframs in niedriger und mittlerer oxidationszahl

Abstract The pyridine ligands incis-I(CO)2(py)2ue5fcCNEt2 (I) can be readily replaced by CH3NC or t-C4H9NC to yield the stable, neutral carbyne complxescis-I(CO)2(RNC)2Wue5fcCNEt2 (R = CH3 (II), t-C4H9 (III0). Upon oxidative decarbonylation with iodine, II and III are quantitatively transformed to the reactive to the reactive seven-coordinated carbonyl-containing carbyne complexes (I)3(CO)(RNC)2Wue5fcCNEt2 (R = CH3(IV), t-C4H9 (V)) with tungsten in a higher oxidation state. Compounds IV and V react with an excess of RNC (R = CH3, t-C4H9) upon elimination of the CO ligand and displacement of one iodine ligand from the coordination sphere to form the seven-coordinated cationic carbyne complexes [(I)2(RNC)4Wue5fcCNEt2]+I− R = CH3 (VI), t-C4H9 (VII). The composition and structure of the new compounds were determined by elemental analyses and by IR, 1H NMR, and 13C NMR spectroscopy.

Structure-activity relationship for chelating phosphite ligands used in rhodium-catalyzed hydroformylations

Abstract A simplified kinetic model was developed for the rhodium-catalyzed low-pressure hydroformylation using chelating phosphite ligands. This allowed the determination of the relative rate constants for linear and branched aldehyde formation starting with terminal olefins using data from complex product mixtures. Structural data were obtained using X-ray crystallography and served as the basis for molecular modeling of rhodium complexes with such chelating ligands. The interaction of linear and branched alkyl groups with the ligand environment in such complexes was quantified using molecular modeling. The energy differences obtained with molecular modeling were plotted against the energy differences obtained from kinetic experiments and a linear correlation was found. This type of approach, i.e., development of a structure–activity relationship, can be used to quickly and efficiently investigate such catalytic systems.

Chelatbisphosphite mit Calix[4]arenrückgrat: neue Liganden für die rhodiumkatalysierte Niederdruckhydroformylierung mit steuerbarer Regioselektivität

Erstaunlich hohe Regioselektivitaten werden bei der rhodiumkatalysierten Niederdruckhydroformylierung von 1-Octen zu n-Nonanal mit Chelatbisphosphiten erzielt, die ein p-tert-Butylcalix[4]aren-Ruckgrat aufweisen (siehe Bild). Mit Hilfe von Molecular-Modeling-Rechnungen konnten die Strukturen und damit die katalytischen Eigenschaften der Komplexe masgeschneidert werden.

Synthesis of Industrially Relevant Carbamates towards Isocyanates using Carbon Dioxide and Organotin(IV) Alkoxides.

A straightforward phosgene-free synthesis of aromatic isocyanates and diisocyanates is disclosed. Theoretical investigations suggested that the insertion of carbon dioxide (CO2 ) by dialkyltin(IV) dialkoxides could be used to convert aromatic amines into aromatic mono- and dicarbamates. Here we show, that methyl phenylcarbamate (MPC) from aniline using organotin(IV) dimethoxide and CO2 can be formed in high yield of up to 92u2009%, experimentally corroborating the predictions of density functional theory (DFT) calculations. MPC was then separated from the tin oxide residues and converted into phenyl isocyanate. Furthermore, organotin(IV) alkoxides could be regenerated from the tin oxide residues and reused, paving the way for a continuous industrial process. Extension of the scope to the synthesis of diurethanes from toluene 2,4-diamine and 4,4-methylenedianiline could potentially allow the efficient production of industrially relevant diisocyanates.

Organorheniumhalogenide: Synthesen, Strukturen und Reaktivität gegenüber Alkinen

The organorhenium(V) complexes (η5-C5Me5)ReX4 (2a, X = Cl; 2b, X = Br; Me = CH3) undergo stepwise dehalogenation upon treatment with various reducing agents, e.g. with HgCl2-activated aluminium powder, forming the isolable ReIV and ReIII dimers [η5-C5Me5)ReCl3]2 (3a) and [η5-C5Me5)ReX2]2 (4a, X = Cl;4b, X = Br), respectively. The weak metal-metal single bond of 3a (307.4(0) pm; X-ray diffraction study) is disrupted upon reaction with alkynes yielding the ReIII derivatives (η5-C5Me5)ReCl2(η2-R1CCR2) (9a-e; R1, R2: alkyl, aryl) and novel rhenium(V)- allylidenyl complexes of type (η5-C5Me5)ReCl2[η1:η3-R1CC(Cl)CHR3] (10a-d; R1: alkyl. aryl; R3: H, alkyl). Reduction of 2a (Al/HgCl2) in the presence of alkynes gives a complex reaction mixture of 9a-c, 10a - c and bis(π-alkyne) complexes [(η5-C5Me5)ReCl(η2-R1CCR2)2] + [AlCl4]-(11a-c) (X-ray diffraction study of the related derivative [(η5-C5Me5)ReBr(η2-MeCCMe)2] + [SbF6]-).