Sergio Cenini

Organotin and organothallium ditiophosphinates and dithiocarbamates

Compounds with general formula R2Tl(SSPR′2), R2Sn(SSPR′2)2, R3Sn(SSPR′2), X2Sn(SSPR′2)2, R2Tl(SSCNR″2 were prepared (R = methyl, ethyl, phenyl; X = chlorine, bromine; R′ = ethyl, phenyl; R

Catalytic reductive carbonylation of organic nitro compounds

= methyl, ethyl, phenyl). The dithiocarbamato derivatives appear to be chelated and monomeric in solution with a four-coordinate thallium(III). Tl(SSCNEt2)3 was found to be six-coordinate in solution. The dithiophosphinates were found to be associated in solution and possible explanation for this are discussed Owing to the presence of association, the assignment of cis or trans structure to X2Sn(SSPR′2)2 or R2Sn(SSPR′2)2 compounds is difficult.

Carbonylation of nitrobenzene to phenyl isocyanate and methyl carbamate catalyzed by palladium and rhodium activated by chelating nitrogen donor ligands

Preface. List of Abbreviations. 1. Introduction. 2. Synthesis of Isocyanates. 3. Synthesis of Carbamates and Ureas. 4. Synthesis of Other Non-Cyclic Compounds. 5. Synthesis of Heterocycles. 6. Mechanistic Studies. Index.

Catalytic amination of unsaturated hydrocarbons : reactions of p-nitrophenylazide with alkenes catalysed by metallo-porphyrins

Abstract During our studies on the reductive carbonylation of nitrobenzene, we have found that palladium metal supported on alumina is an effective catalyst for the formation of phenyl isocyanate, PhNCO, when activated by ortho-phenanthroline or its derivatives, and by 2,4,6-trimethylbenzoic acid (TMBA) (T = 180 °C, P(CO) = 40 atm, in dry benzene). In similar conditions (T = 200 °C, P(CO) = 100 atm in toluene) rhodium metal showed very poor activity. However, when methanol was also present in the reaction medium, N-phenyl methyl carbamate was obtained in good yields and selectivities. The presence of TMBA was not required in the latter case. In both cases, at the end of the reaction, the catalytic solution showed the presence of metal complexes, suggesting the formation in situ of homogeneous catalytic systems. In fact, preformed Pd(O2CC6H2-2,4,6-Me3)2 and Rh4(CO)12 gave even better results when used as catalysts in the same experimental conditions.

Mechanistic studies of palladium-catalysed carbonylation reactions of nitro compounds to isocyanates, carbamates and ureas

Abstract Porphyrin derivatives of transition metals such as Ru(TPP)CO, Ru(OEP)CO and Co(OEP)(TPP=dianion of 5, 10, 15, 20-tetraphenylporphyrin, OEP=dianion of 2, 3, 7, 8, 12, 13, 17, 18-octaetylporphyrin) catalyse the reaction of p-nitrophenylazide with cyclohexene to give the corresponding allylamine in good yields. With other olefins such as cyclooctene, 1-octene, styrene and substituted styrenes the main product becomes the corresponding aziridine. The reaction of p-nitrophenylazide with Ru(TPP)CO has been investigated and the mechanism of the catalytic reactions is discussed.

Low oxidation states ruthenium chemistry VI. Stoichiometric and catalytic oxidation by molecular oxygen of primary amines bound to dichlorobis(triphenylphosphine)ruthenium(II)

Abstract Many different palladium-based catalytic systems have been reported for the carbonylation reactions of organic nitro compounds to isocyanates, carbamates and ureas. Almost all of these can be roughly divided into three groups: (i) those containing a second (or even a third) metal (usually a Lewis acid or a metal oxo compound or both), (ii) those in which phenanthroline or similar chelating nitrogen ligands are used and (iii) those in which monodentate phosphines are employed as ligands. The systems in which chelating phosphines are used as ligands lie in between the last two groups. The reaction mechanisms for the catalytic systems in each group appear to be related. Most of the information available does not derive from strictly mechanistic studies, but rather from synthetic studies and it is here critically analysed and compared with the information obtained from other related fields.

Synthesis of heterocycles via palladium-catalyzed carbonylation of ortho-substituted organic nitro compounds in relatively mild conditions

Abstract Under a strict nitrogen atmosphere Ru(PPh3)3Cl2 reacts with primary amines to give the complexes, Ru(PPh3)2(RNH2)2Cl2 [R = H (I), CH3(CH2)4 (II), C6H5CH2 (III), p-CH3OC6H4 (IV)]. Chelating ligands such as 5-methyl-1,2-phenylenediamine, ethylenediamine, benzoylhydroxylamine and benzoylhydrazine give the complexes Ru(PPH3)2(chel)Cl2, (V) - (VIII). Compounds (I) - (V) react with molecular oxygen at room temperature to give different products depending on the nature of R, while compounds (VI) - (VIII) are stable with respect to oxidation by O2. Compound (III) acts as a catalyst in the oxidation of benzylamine to benzonitrile with molecular oxygen at 80 °C. The reaction of (III) with molecular oxygen has been followed by ESR spectroscopy, and the intermediate formation of paramagnetic ruthenium-(III) species has been detected.

Mechanistic Study of the Palladium–Phenanthroline Catalyzed Carbonylation of Nitroarenes and Amines: Palladium–Carbonyl Intermediates and Bifunctional Effects

Abstract Carbonylation of o-nitroaniline in the presence of aldehydes catalyzed by the Pd (TMB)2/TMPhen/TMBH catalytic system (TMBH = 2,4,6-trimethyl benzoic acid; TMPhen = 3,4,7,8-tetramethyl-1,10-phenanthroline) at 140–180°C and 20–40 atm of carbon monoxide, gives the corresponding benzimidazoles, with a selectivity ranging from 10 to 80%, strongly depending on the aldehyde used. The main by-product was shown to be the 2(1H) benzimidazolone, derived by direct carbonylation of o-nitroaniline. The same catalytic system has been used in the carbonylation of o-nitrostyrenes at 120–180°C and 20–60 atm of carbon monoxide, obtaining the corresponding indoles with a selectivity generally ranging from 70 to 100%. Interestingly, in the latter case the presence of TMBH was not necessary in order to obtain good conversions and selectivities. On the contrary, the presence of excess TMBH is indispensable when nitrobenzene is catalytically converted to phenyl isocyanate. Moreover, in the catalytic synthesis of indoles no carbonylated products are formed. These observations suggest a catalytic cycle different from what has been proposed in the synthesis of phenyl isocyanate from nitrobenzene, catalyzed by palladium.

Rearrangement of N-aryl-2-vinylaziridines to benzoazepines and dihydropyrroles: a synthetic and theoretical study.

Palladium-phenanthroline complexes catalyze both the nitroarene carbonylation reaction and the amine oxidative carbonylation reaction to give, depending on the conditions, carbamates and ureas. There is evidence that the key step in both processes is the amine carbonylation. Here, we show that when the reaction is run in methanol key intermediate compounds have the general formula [Pd(RPhen)(COOMe)(2)] (1) (RPhen = 1,10-phenanthroline or one of its substituted derivatives). The kinetics of the reaction of 1 with toluidine in the presence of a carboxylic or phosphorus acid is first-order with respect to complex, acid, and toluidine. A CO atmosphere is also required for the reaction to proceed. Acid dimerization was shown not to be influential under the concentration conditions examined, but reaction between the acid and toluidine is not negligible and a correction has to be applied. Diphenylphosphinic acid is more effective than any carboxylic acid in promoting this reaction, as also observed under catalytic conditions. A series of equilibria and an irreversible acid-assisted proton transfer explain the observed data. Formation of an adduct between complexes of the kind 1 and CO was spectroscopically observed when RPhen = 2,9-Me(2)Phen. Several analogous complexes were also spectroscopically characterized and the X-ray structure of [Pd(2,9-Me(2)Phen)Cl(2)(CO)] was solved. This shows an asymmetric coordination of the nitrogen ligand. Kinetic measurements were also conducted under catalytic conditions. An Eyring plot shows that the effect of the acidic promoter is to decrease the DeltaS(double dagger) value, whereas no positive effect is observed on DeltaH(double dagger). A temperature-dependent correction for the reaction between the acid and aniline and phenanthroline present under the reaction conditions has to be applied. Comparison of the results obtained under stoichiometric and catalytic conditions strongly supports the view that 1 is involved even in the latter and that the acid is acting as a bifunctional promoter.

The intermetallic bond in some carbonyl compounds with a heterogeneous metal-metal bond

Herein we report the one-pot synthesis of several N-heterocyclic compounds by rearrangement reactions of N-aryl-2-vinylaziridines. The optimization of the synthetic methodology employed allowed us to obtain differently substituted 2,5-dihydro-1H-benzo[b]azepines in good yields and purities. The relationship between the nature of the starting N-aryl-2-vinylaziridine and the obtained N-heterocycle was also investigated. Finally, to rationalize all the experimental results reported in this paper a theoretical study was performed that casts light on the reaction mechanism.