Maria A. Massucci

Oxidative carbonylation of aniline catalyzed by Pd(II)-2,2'-bipyridyl complex intercalated in α-zirconium-phosphate

Abstract Palladium(II) and palladium(II)-copper(II) complexes (with N-donor ligands intercalated between the layers of α-zirconium phosphate) have been employed in the oxidative carbonylation of aniline. The catalytic activity of the materials has been studied together with the properties of α-zirconium phosphate as a supporting agent. Their very low activity observed in an initial induction period slowly increases to more marked levels in mild working conditions (80 °C, atmospheric pressure); in more drastic conditions diphenylurea and methyl carbamate are produced in a non-selective way due to a concomitant oxidation of aniline. By pre-heating the materials at 130 °C under CO or CO/O2, an increase of the catalytic activity is obtained, and the treated systems are able to catalyze selectively the carbonylation of aniline in mild conditions. By submitting the pretreated systems to a series of catalytic cycles and by re-employing the same catalyst in each cycle, a decrease in activity is observed until complete deactivation of the catalyst, when Pd is almost completely eliminated by the solid. On the basis of the analysis of the pretreated sample before and after deactivation, this behaviour is ascribed to migration of the Pd from the inner layers to the surface of the solid matrix and to its subsequent solubilization in the reaction medium.

Coordination of Co2+, Ni2+ and Cu2+ to 2,9 - dimethyl - 1,10 phenanthroline intercalated in α-zirconium phosphate: Evidence for dimers

2,9-Dimethyl-1,10-phenanthroline (dmp) intercalates into α-Zr(HPO4)2. (2EtOH) to form α-Zr(HPO4)2 (dmp)0.50. 2.5H2O at maximum uptake, at 25°C. This lamellar composite has an interlayer distance of 14.60(5) A, which changes little - to 13.58(5) A - when the pseudo-zeolitic water is lost. An almost vertical orientation of the dmp between the phosphate layers is proposed, as was found previously for the unsubstituted phenanthroline analogue. When the material is exchanged with Co2+, Ni2+, and Cu2+, under conditions such that [M] : [L] = 1:1 there is partial elution of the dmp, giving rise to materials of formulation α-ZrH1.3M(OH2)0.35(dmp)0.35(PO4)2·nH2O, with no change in interlayer distance. Spectroscopic evidence for the formation of dimers to the intercalated dmp is described.

Pillar chemistry. Part 5. Intercalation of 2,2′-bipyridine, 1,10-phenanthroline, and 2,9-dimethyl-1,10-phenanthroline into γ-zirconium phosphate and formation of interlayer copper(II) complexes

2,2′-Bipyridine (bipy), 1,10-phenanthroline (phen), and 2,9-dimethyl-1,10-phenanthroline (dmphen) can be intercalated into γ-Zr(HPO4)2·2H2O as such (i.e. without first pre-swelling the matrix) to give materials having the final formulation γ-Zr(HPO4)2Lx·n H2O (x= 0.48–0.50). With dmphen, if the γ-Zr(HPO4)2·2H2O is first pre-swelled using ethanol, a further, pure layered phase of composition γ-Zr(HPO4)2(dmphen)0.28·2H2O is obtained; bipy and phen do not give this latter phase. Indirect evidence, X-ray diffraction and i.r. spectroscopy, indicates that the orientations of the amines in the interlayer are different from those in the α-Zr(HPO4)2·H2O analogues, probably due to the presence of specific hydrogen bonding by the interlayer water molecules. All four materials exchange CuII. As expected, given its lower interlayer ligand density compared with the other materials, γ-Zr(HPO4)2(dmphen)0.28·2H2O takes up CuII most readily. Further, within the series γ-Zr(HPO4)2Lx·n H2O the order of uptake, phen > dmphen > bipy, is not that expected from ligand steric requirements alone and the uptake is in all cases slower than that in the α-Zr(HPO4)2·H2O analogues, both results indicating the importance of ligand–matrix interactions. The final pure layered materials obtained have [Cu2+]: [] ratios of 1:1 [γ-(dmphen)0.28] and 1:2 [γ-dmphen)0.48 and γ-(bipy)0.48]; γ-(phen)0.50 gave [Cu2+] : []= 0.8:1. Spectroscopic evidence shows that CuII co-ordinates to the amine ligand only in the bipy and phen cases, whereas both dmphen-containing materials exchange Cu2+ into cavities widened by the dmphen but without co-ordination to the intercalated ligand.

XPS studies on the host-guest interaction of 2,2′-Bipyridyl, 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline intercalated inα-zirconium phosphate

The host-guest interactions of 2,2′-bipyridyl, 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline intercalated between the layers of crystallineα-zirconium monohydrogen phosphate have been studied by X-ray photoelectron spectroscopy. Evidence that, on average, only one of the two nitrogen atoms of each aromatic diamine is protonated by the ≡P-OH groups of the host is given. The acid-base interaction is strongly reduced on dehydration of the materials. The role of the cointercalated water is discussed, together with the probable disposition of the guests within the interlayer region.

XPS characterization ofγ-zirconium phosphate and of some of its intercalation compounds. A comparison with the α-zirconium phosphate analogues

An X-ray photoelectron spectroscopic investigation ofγ-Zr (HP04)2·2 H2O and its intercalation compounds with 1,10-phenanthroline, Co2+-phenanthroline and Cu2+-phenanthroline is described. The analysis of theNls spectra of the compound containing only phenanthroline clearly shows that, on average, more than one nitrogen atom of the diamine interacts with the acid groups of the host, giving protonated species. XPS also provides evidence of the coordination of Co2+ and Cu2+ ions after their diffusion in the phenanthroline-γ-zirconium phosphate intercalation compound. They form mixed N-and O-coordinated species with the diamine and the oxygens of the interlayer region, but the presence of the characteristic peaks of uncoordinated phenanthroline, even at low intensity, shows that the diamine molecules anchored to the host are still present.A comparison is made with the analogous derivatives of α-Zr (HPO4)2·H2O and the differences between the two series of compounds are discussed.

Pillaring of layers in α-zirconium phosphate by 1,10-phenanthroline and bis(1,10-phenanthroline)copper(II): formation of complex pillars in situ

The complex [Cu(phen)2]2+(phen = 1,10-phenanthroline) can be diffused between the layers of α-zirconium phosphate only if the layers are first pre-swelled by preparing the diethanol intercalate, α-Zr(HPO4)2(EtOH)2. At maximum uptake a material of formula α-ZrH1.6[Cu(phen)2]0.20(PO4)2·3H2O is obtained and no further complex can be intercalated. X-Ray and spectroscopic evidence show that the [Cu(phen)2]2+ remains intact after intercalation, and probably has a tetragonal-octahedral geometry. A ‘complex pillared’ layer structure is still present after the zeolitic water has been removed. However, the geometry adopted by the [Cu(phen)2]2+ is now square-based pyramidal, and it is bonded asymmetrically between the phosphate layers. Further ions (Cu2+, Pd2+, or Ag+) can be exchanged into the pillared cavities, to form solid solutions. 1,10-Phenanthroline itself diffuses into α-Zr(HPO4)2(EtOH)2 to form the ‘intercalated ligand’ phase α-Zr(HPO4)2(phen)0.50·2H2O at maximum uptake. This is a pure, well ordered Stage I phase with an interlayer distance of 13.58 A, and it is suggested that the phen is ordered throughout the layers in a ‘slanted’ fashion. This phase exchanges Co2+, Ni2+, and Cu2+(in the order Cu2+ Co2+ > Ni2+) much more slowly than does the 2,2′-bipyridyl analogue, due to the steric hindrance caused by the bulkier ligand backbone and higher pillar density. Only in the case of Cu2+ does subsequent co-ordination to the phen proceed to complete formation of α-ZrH [Cu(phen)]0.50(PO4)2·3H2O. In the cobalt and nickel analogues there is competition between phen-co-ordinated and cavity-co-ordinated metal ion. Spectroscopic evidence (u.v.–visible, e.s.r.) is presented which shows that these complex pillars formed in situ have very distorted geometries, caused by the steric constraints imposed by the interlayer region.

Intercalation of heterocyclic compounds in α-zirconium phosphate: imidazole, benzimidazole, histamine and histidine

The intercalation of imidazole and some organic species containing the imidazole ring, between the layers of crystalline zirconium phosphate has been investigated. Fourteen new, well-ordered intercalation compounds are obtained with the batch procedure at r.t. and/or 60°C. A mechanism of formation of the various compounds is proposed on the basis of the interaction between the guest molecules (with their dimensions and geometries) and the free PO3OH groups available between the layers of the host. The new phases have been characterized by TG and X-ray methods.

Pillar chemistry. Part 4. Palladium(II)–2,2′-bipyridyl, –1,10-phenanthroline, and –2,9-dimethyl-1,10-phenanthroline complex pillars in α-zirconium phosphate

Palladium(II) can be exchanged into the layered composites α-Zr(HPO4)2(bipy)0.25·1.5H2O (bipy = 2,2′-bipyridyl), α-Zr(HPO4)2(phen)0.50·2H2O (phen = 1,10-phenanthroline), and α-Zr(HPO4)2(dmphen)0.50·2.5H2O (dmphen = 2,9-dimethyl-1,10-phenanthroline) to give new palladium(II) amine complex–pillared materials. In all three cases, both 1 :2 and 1 :1 PdII:amine complexes are formed between the layers. Pillared materials with an interlayer distance as high as 17.3 A can be obtained. Thus, using such in situ preparation methods, it is possible to prepare pillared materials with pore dimensions approaching those found in zeolite Y. Electronic spectral evidence for the presence of different geometries for the pillars is described (square planar for bipy and phen, but five-co-ordinate for both 1 :2 and 1 :1 dmphen pillared materials). All the materials exchange further metal ions, Co2+, Ni2+, and Cu2+, to high loading levels, a demonstration that they are indeed pillared. Evidence is presented which shows that uptake of Cu2+ occurs at different rates for the 1 :1 and 1 :2 complex–pillared materials, i.e. the cavities have different sizes and therefore different accessibilities. In addition, spectroscopic probing (visible–near u.v. and e.s.r.) of these cavity-exchanged ions clearly demonstrates that the new cavities formed have geometries different from those present in the parent α-Zr(HPO4)2·H2O.

Crystalline zirconium(IV) hydrogenarsenate hydrogenphosphate monohydrate: synthesis, ion-exchange properties, and thermal behaviour

A new crystalline layered inorganic ion-exchanger with formula Zr(HAsO4)(HPO4)·H2O has been prepared by refluxing the amorphous product. Its ion-exchange properties towards sodium ions and its thermal behaviour, together with that of the pure sodium phases obtained, are reported and discussed. The exchanger is very stable to hydrolysis and has a high exchange capacity. Its general behaviour is intermediate between that of Zr(HPO4)2·H2O and Zr(HAsO4)2·H2O.

Diffusion of large amine ligands into layered α-Zr(HPO4)2·H2O. Access to a solid-state co-ordination chemistry

2,2′-Bipyridyl and 1,10-phenanthroline can be diffused between the layers of pre-swelled α-Zr(HPO4)2·2H2O to give the materials α-Zr(HPO4)2[bipy]0.25·1.5H2O and α-Zr(HPO4)2[phen]0.5·2H2O; metal ions co-ordinate preferentially ot the stage I dispersed ligand with in situ formation of complex pillars.