Zsolt Csók

Carbonylation (hydroformylation and hydrocarbalkoxylation) reactions in the presence of transition metal: p-tert-butyl-calix[4]arene-based phosphine and phosphinite systems

Abstract In this study, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-diphenylphosphinoxy-ethoxy)calix[4]arene (5) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-diphenylphosphinoethoxy)-calix[4]arene (6), as well as their platinum and palladium complexes (PtCl2)2(5), (PdCl2)2(5) were synthesised and characterised. In addition to these transition metal-containing complexes the catalytic systems formed in situ, from catalytic precursors PtCl2(PhCN)2, [Rh(nbd)Cl]2 and PdCl2(PhCN)2 and the corresponding calixarene ligand, were tested as catalysts in hydroformylation and hydrocarbalkoxylation, respectively. High chemoselectivity was obtained in hydroformylation in the presence of rhodium-containing catalysts both with the above calixarene-based phosphine and phosphinite ligands. The regioselectivity towards branched aldehyde shows a strong temperature dependence in case of phosphinite derivative. Although the platinum-containing systems show much lower catalytic activity, the regioselectivities are undoubtedly higher than those obtained with PtCl2(diphosphine)–SnCl2 systems.

Permittivity-dependent entropy driven complexation ability of cone and paco tetranitro-calix[4]arene toward para-substituted phenols.

Considering the importance of the polarizability of the rings of calixarenes in the entropy-driven interaction processes, we examined the effect of entropy compensation on the complex formation of cone and partial cone (paco) conformers of tetranitro-calix [4]arene, possessing O-ethyl substituents at the lower rim. Both calixarene conformers were fully characterized including X-ray crystallography. Various para-substituted phenols were used as guest molecules. Photoluminescence (PL) measurements and quantum-chemical (QC) investigations were used. A permittivity dependence of the molecular interactions was obtained in different alcohols as solvents. It was found that the cone conformer of the title calixarene derivative forms stable complexes with all phenols of the p-substituted series. The free enthalpy changes show very high complex stability of cone calixarene with p-nitro and p-chloro-substituted phenols. In the cases of parent phenol, p-cresol and p- tBu-phenol, the stability is significantly lower; however, it slightly increases with the increasing electron density on the aromatic ring of guest molecules. Similarly, the entropy changes are significantly different for these two separated groups: the entropy changes obtained in the former cases are nearly the same, while large differences in the formation entropy were obtained in the latter cases. Both the experimental and theoretical investigations revealed that no considerable interaction exists between phenols and the paco conformer of the title calixarene. It is probably due to the locking of the calixarene cavity by the bent O-ethyl chain.

Synthesis of steroid-ferrocene conjugates of steroidal 17-carboxamides via a palladium-catalyzed aminocarbonylation - Copper-catalyzed azide-alkyne cycloaddition reaction sequence

Steroids with the 17-iodo-16-ene functionality were converted to ferrocene labeled steroidal 17-carboxamides via a two step reaction sequence. The first step involved the palladium-catalyzed aminocarbonylation of the alkenyl iodides with prop-2-yn-1-amine as the nucleophile in the presence of the Pd(OAc)(2)/PPh(3) catalyst system. In the second step, the product N-(prop-2-ynyl)-carboxamides underwent a facile azide-alkyne cycloaddition with ferrocenyl azides in the presence of CuSO(4)/sodium ascorbate to produce the steroid-ferrocene conjugates. The new compounds were obtained in good yield and were characterized by (1)H and (13)C NMR, IR, MS and elemental analysis.

Role of the Conformational Freedom of the Skeleton in the Complex Formation Ability of Resorcinarene Derivatives toward a Neutral Phenol Guest

The interaction of phenol guest molecules with 2-methylresorcinarene and its methylene-bridged cavitand derivative has been investigated in methanol. The host molecules were selected according to the flexibility of their cavities by varying the conformational freedom of the molecular skeleton prior to molecular association. The results show stronger host-phenol interactions when the host molecule possesses a rigid molecular skeleton (i.e., cavitand) compared to that of the flexible resorcinarene with phenol. Although the enthalpy change associated with the molecular interactions was found to be the same in both cases, higher negative entropy change was obtained when the resorcinarene interacted with the phenol molecules at room temperature. As a result, stronger host-guest complexes are formed at room temperature when the host molecules, possessing a rigid molecular skeleton, participated in the complex formation. Furthermore, since the higher entropy change results in higher temperature-dependence of the interactions, the stability of the complexes formed with the flexible resorcinarene is smaller at higher temperature. These results highlight that the decreasing flexibility of the host molecular skeleton itself can determine the entropy change during the complexation process; therefore, the temperature dependence of the complex stabilities highly depends on the flexibility of the hosts molecular skeleton. This information might contribute to the development of selective and sensitive sensor molecules toward phenol derivatives.

Synthesis of ferrocene-labeled steroids via copper-catalyzed azide-alkyne cycloaddition. Reactivity difference between 2β-, 6β- and 16β-azido-androstanes

Copper-catalyzed cycloaddition of steroidal azides and ferrocenyl-alkynes were found to be an efficient methodology for the synthesis of ferrocene-labeled steroids. At the same time, a great difference between the reactivity of 2β- or 16β-azido-androstanes and a sterically hindered 6β-azido steroid toward both ferrocenyl-alkynes and simple alkynes, such as phenylacetylene, 1-octyne, propargyl acetate and methyl propiolate, was observed.

Facile, high-yielding synthesis of deepened cavitands: A synthetic and theoretical study

A wide variety of 2-methyl-resorcinol-based deepened cavitands were synthesised from readily available reagents in a four-step procedure with overall yields of up to 62%. A systematic variation of the rim was carried out by building up a flexible upper aromatic wall on the rigid cavitand platform through CH2, CH2O and CH2OCH2 spacers. These aromatic walls were further extended by a Suzuki cross-coupling reaction. Full characterisation of the synthesised cavitands was carried out. The solid-state structure of tetrakis(phenoxymethyl)cavitand was determined by X-ray crystallography. Gas-phase theoretical calculations for this molecule predict the presence of weak T-shaped interactions between the upper phenyl rings. The host–guest complex formation ability of two deepened cavitand hosts towards 4-chloro-benzotrifluoride was proved by photoluminescence method.

Synthesis and NMR investigation of Pt(CN)2(diphosphine) and [Pt(CN)(triphosphine)]Cl complexes

Abstract Pt(CN) 2 (Ph 2 P(CH 2 ) n PPh 2 ) ( n =2,3,4) and Pt(CN) 2 (P 1 P 2 ) (P 1 P 2 =1-diphenylphosphino-2,1′-[(1-diphenylphosphino)-1,3-propanediyl]-ferrocene, 1-diphenylphosphino-2,1′-[(1-dicyclohexylphosphino)-1,3-propanediyl]-ferrocene) were synthesised by reacting potassium cyanide and the corresponding PtCl 2 (diphosphine) complexes. PtCl(CN)(diphosphine) complexes were identified as minor products when KCN/PtCl 2 (diphosphine) molar ratio was kept below 2. The use of KCN in excess resulted in the formation of K 2 Pt(CN) 4 . [Pt(CN)({Ph 2 P(CH 2 ) 2 } 2 PPh)] + complex cation and Pt(CN) 2 )({Ph 2 P(CH 2 ) 2 } 2 PPh) five-coordinate covalent complex of fluxional behaviour were obtained at KCN/Pt ratio of 1 and 2, respectively. The platinum–cyano complexes were characterised by NMR spectroscopy. The direct PtCN bond was proved by 1 J ( 195 Pt, 31 P), 2 J ( 31 P, 13 C) coupling constants by using sodium cyanide- 13 C for ligand exchange reactions.

Synthetic and NMR Studies on Calix[n]Arene (n = 4,6,8) Triflates, Mesylates, and Tosylates

Abstract The synthesis and full characterization of eight new calix[n]arene sulfonate esters including their conformational analysis were carried out. While p-tBucalix[6]arene and p-tBu-calix[8]arene esters are conformationally labile in the temperature interval of 25–100°C, p-tBu-calix[4]arene mono-and diesters were isolated as stable conformers at ambient temperature. Two 1,3-functionalised compounds of these derivatives, p-tert-butylcalix[4]arene ditriflate (5) and dimesylate (6) were shown unexpectedly high conformational stability up to 100°C by dynamic NMR measurements. The NMR measurements confirm the pinched-cone conformation for both derivatives. For the dealkylated calix[4]arene derivatives the partial cone conformer of the triesters have been obtained as major products in all cases.

Synthesis of novel 13α-18-nor-16-carboxamido steroids via a palladium-catalyzed aminocarbonylation reaction.

13α-18-nor-16-Carboxamido steroids were synthesized via a palladium-catalyzed aminocarbonylation reaction of the corresponding iodoalkenes. The starting material was an unnatural 13α-16-keto steroid, obtained by a Wagner-Meerwein rearrangement of a 16α,17α-epoxide in the presence of [BMIM][BF4]. The 13α-16-keto steroid was converted to a mixture of 16-iodo-16-ene and 16-iodo-15-ene derivatives in two steps by Bartons methodology. Aminocarbonylation of the steroidal alkenyl iodides was carried out using different primary and secondary amines as nucleophiles. The products, 16-carboxamido-16-ene and 16-carboxamido-15-ene derivatives, were obtained in good yields and were characterized by (1)H and (13)C NMR, IR and MS. The reduction of the above two unsaturated carboxamides resulted in the same product, 17α-methyl-16α-carboxamido-androstane.

Dichlorobis(cumylcyclopentadienyl)titanium(IV)

The title compound, [Ti(C(14)H(15))(2)Cl(2)], belongs to a class of complexes that are potentially active as pre-catalysts in the stereospecific polymerization of olefins. In the crystal structure, molecules lie on C(2) axes with pseudo-tetrahedral coordination around the Ti atoms. Conformational features of the compound are discussed, in conjunction with calculations that demonstrate the existence of other energetically favorable conformations in addition to that found in the reported crystal structure.