A comparative study of the structures and reactivity of cyclometallated platinum compounds of N-benzylidenebenzylamines and cycloplatination of a primary amine

The reaction of cis-[PtCl(2)(dmso)2] with ligands 4-ClC(6)H(4)CHNCH(2)C(6)H(5) (1a) and 4-ClC(6)H(4)CHNCH(2)(4-ClC(6)H(4)) (1b) in the presence of sodium acetate and using either methanol or toluene as solvent produced the corresponding five-membered endo-metallacycles [PtCl{(4-ClC(6)H(3))CHNCH(2)C(6)H(5)}{SOMe(2)}] (2a) and [PtCl{(4-ClC(6)H(3))CHNCH(2)(4'-ClC(6)H(4))}{SOMe(2)}] (2b). An analogous reaction for ligands 2,6-Cl(2)C(6)H(3)CHNCH(2)C(6)H(5) (1c) and 2,6-Cl(2)C(6)H(3)CHNCH(2)(4-ClC(6)H(4)) (1d) produced five-membered exo-metallacycles [PtCl{(2,6-Cl(2)C(6)H(3))CHNCH(2)C(6)H(4)}{SOMe(2)}] (2c) and [PtCl{(2,6-Cl(2)C(6)H(3))CHNCH(2)(4'-ClC(6)H(3))}{SOMe(2)}] (2d) when the reaction was carried out in methanol and seven-membered endo-platinacycles [PtCl{(MeC(6)H(3))ClC(6)H(3)CHNCH(2)C(6)H(4)}{SOMe(2)}] (3c) and [PtCl{(MeC(6)H(3))ClC(6)H(3)CHNCH(2)(4'-ClC(6)H(3))}{SOMe(2)}] (3d) when toluene was used as a solvent. The reaction of 2,4,6-(CH(3))(3)C(6)H(2)CHNCH(2)(4-ClC(6)H(4)) (1e) produced in both solvents an exo-platinacycle [PtCl{(2,4,6-(CH(3))(3)C(6)H(2))CHNCH(2)(4'-ClC(6)H(3))}{SO(CH(3))(2)}] (2e). Cyclometallation of 4-chlorobenzylamine was also achieved to produce compound [PtCl{(4-ClC(6)H(3))CH(2)NH(2)}{SOMe(2)}] (2g). The reactions of endo- and exo-metallacycles with phosphines evidenced the higher lability of the Pt-N bond in exo-metallacycles while a comparative analysis of the crystal structures points out a certain degree of aromaticity in the endo-metallacycle.     

N,N-Dialkyl-2-iodoanilines: a versatile source for the synthesis of Pd(ii) complexes. Synthesis of novel OCP- and CCN-pincer palladium complexes

The reactivity of a series of N,N-dimethyl-2-iodoanilines bearing different chelating "arms" at the 3-position with Pd(2)(dba)(3) has been explored. 3-[(Diphenylphosphino)methyl]-2-iodo-N,N-dimethylaniline reacted with Pd(2)(dba)(3) and PPh(3) under aerobic conditions to give the OCP-pincer complex , which was formed by sequential C(sp(3))-H activation/oxidation at the alpha-position of the aniline N atom. On the other hand, under similar reaction conditions, 3-[2-(dimethylamino)ethyl]-2-iodo-N,N-dimethylaniline afforded the CCN-pincer complex , after a second C-H activation process at the formyl group of the initially formed OCN-pincer complex. In contrast, 2-iodo-3-(1H-1,2,4-triazol-1-ylmethyl)-N,N-dimethylaniline and 2-iodo-3-(pyrazol-1-ylmethyl)-N,N-dimethylaniline reacted with Pd(2)(dba)(3) and PPh(3), respectively, to give the 6-membered azapalladacycles and , in which the aniline nitrogen is merely a spectator substituent. Finally, treatment of iodide complex with Tl(TfO) afforded the CN-bidentate cationic complex. Solid-state structures of palladium complexes, and CH(2)Cl(2).3CH(3)OH.5H(2)O were determined by X-ray analysis.     

Enantioselective organocatalytic asymmetric allylic alkylation. Bis(phenylsulfonyl)methane addition to MBH carbonates

The highly enantioselective asymmetric allylic alkylation of Morita-Baylis-Hillman carbonates with bis(phenylsulfonyl)methane is presented. The reaction is simply catalyzed by cinchona alkaloid derivatives affording the final alkylated products in good yields and enantioselectivities.     

Biaryl formation in the synthesis of endo and exo-platinacycles

The reactions of cis-[Pt(2)(4-MeC(6)H(4))(4)(μ-SEt(2))(2)] with bifunctional ligands ArCH=NCH(2)(2-XC(6)H(4)) containing a C-X bond at the ortho positions of the benzyl ring (Ar = 4-ClC(6)H(4), X = Br (1d); Ar = 2,4,6-(CH(3))(3)C(6)H(2), X = Br (1e); Ar = 2,4,6-(CH(3))(3)C(6)H(2), X = Cl (1f); Ar = 2-CH(3)C(6)H(4), X = Br (1h); Ar = 2,6-F(2)C(6)H(3), X = Br (1i)) in refluxing toluene were studied. Several types of platinum(II) cyclometallated compounds containing a biaryl linkage were obtained: i) endo-five-membered with a Pt-C(sp(2)) bond (2d, 2h), ii) endo-six-membered with a Pt-C(sp(3)) bond (2e, 2f), and iii) exo-five membered with a Pt-C(sp(2)) bond (2i). The formed biaryl linkage involves the metallated ring for 2i and the non-metallated ring for the endo-metallacycles. The reaction of compounds 2 with PPh(3) produced the corresponding phosphine derivatives, some of which (3d, 3e, 3h and 3i) were characterised crystallographically. In addition, compound [PtBr{2-CH(3)C(6)H(3)C(6)H(4)CH=NCH(2)(2-C(6)H(4)Br)}SEt(2)] (2c) containing a seven-membered endo-metallacycle was also obtained and characterised crystallographically.     

P-Stereogenic monophosphines in Pd-catalysed enantioselective hydrovinylation of styrene

Two groups of P-stereogenic monodentate phosphines containing pendant groups bearing functionalities capable of having secondary interactions, PArPhR (Ar = 2-[(2′,6′-dimethoxy)-1,1′-biphenylyl] and R = OMe (6) or Me (8)) and PMeR(CH₂R′) (13, R = t-Bu or 14 R = Fc and R′ = SiMe₃ (a), SiMe₂Ph (b) or CH₂(2-naphthyl) (c)) have been prepared in enantiomerically pure form by the Jugé and Evans methodologies and characterised, including the crystal structure for the borane adduct of 12b. Reaction of the phosphines with the Pd dimer [Pd(η³-2-Me-allyl)(μ-Cl)]₂ produced neutral allylic complexes C [PdCl(η³-2-Me-C₃H₄)P1], which have been characterised in solution and shown to be a mixture of isomers with different absolute configuration at the Pd atom. After abstraction of the chloride ligand by AgBF₄, the solutions of cationic complexes have been used as catalyst precursors in the hydrovinylation of styrene under mild conditions. Very good activities (up to 1015 h^?1), moderate to good selectivities to 3-phenyl-1-butene and low to moderate enantioselectivities (<45% ee) have been found. Deep differences in the activity and enantioselectivity have been found depending on the structure of the ligand. In spite of that the results did not permit to confirm the improvement of the selectivities of the reaction by stabilization of the catalyst through secondary coordination with the potentially hemilabile ligands.     

Supramolecular assemblies of Al3+ complexes with vitamin D3 (cholecalciferol) and phenothiazine. Encapsulation and complexation studies in β-cyclodextrin

Ternary assemblies of β-cyclodextrin with cholecalciferol (or vitamin D₃) or phenothiazine and Al³⁺ ions were studied. The stability constants of aluminium binary complexes with cholecalciferol or phenothiazine and of ternary assemblies (β-cyclodextrin, cholecalciferol or phenothiazine and Al³⁺) were determined using potentiometric titrations at 25 °C (I = 0.100 M). The ¹³C NMR spectra of the supramolecular structures in the solid state showed that ternary supramolecular structures associating β-cyclodextrin, cholecalciferol or phenothiazine and aluminium(III) ions were obtained. Finally, X-ray powder diffraction patterns showed that the ternary assemblies with phenothiazine are channel type inclusion complexes.     

Stereoselective Aminoxylation of Biradical Titanium Enolates with TEMPO

A highly efficient and straightforward aminoxylation of titanium(IV) enolates from (S)‐N‐acyl‐4‐benzyl‐5,5‐dimethyl‐1,3‐oxazolidin‐2‐ones with TEMPO has been developed. A wide array of functional groups on the acyl moiety, including alkyl and aryl substituents, olefins, esters, or α‐cyclopropyl, as well as α‐trifluoromethyl groups, are well tolerated. This transformation can therefore produce the α‐aminoxylated adducts in excellent yields with high diastereomeric ratios (d.r.). In turn, parallel additions to the α,β‐unsaturated N‐acyl counterparts give the corresponding γ‐adducts with complete regioselectivity in moderate to good yields. Removal of the piperidinyl moiety or the chiral auxiliary converts the resultant adducts into enantiomerically pure α‐hydroxy carboxyl derivatives, alcohols, or esters in high yields under mild conditions. Finally, a new mechanistic model based on the biradical character of the titanium(IV) enolates has been proposed.     

Elucidating the 2D Magnetic Topology of the ‘Metal–Radical’ TTTA⋅Cu(hfac)2 System

The TTTA ? Cu(hfac)₂ polymer ( 1 ; in which TTTA=1,3,5‐trithia‐2,4,6‐triazapentalenyl, and hfac=(1,1,1,5,5,5)‐hexafluoroacetylacetonate) is one of the most prominent examples of the rational use of the ‘metal–radical’ synthetic approach to achieve ferromagnetic interactions. Experimentally, the magnetic topology of 1 could not be fully deciphered. Herein, the first‐principles bottom‐up procedure was applied to elucidate the nature and strength of the magnetic J_AB exchange interactions present in 1 . The computed J_AB values give rise to a 2D magnetic topology of ferromagnetic dimers (+11.9 cm^?1) coupled through weaker antiferromagnetic interactions (?3.0 and ?3.2 cm^?1) in two different spatial directions. The hitherto unknown origin of the antiferromagnetic interdimer interactions is thus unveiled. By using the 2D magnetic topology, the agreement between calculated and experimental χT(T) data is extraordinary. In the metal–radical TTTA ? Cu(hfac)₂ compound, the computational model transcends the local dimer cluster model owing to strong interactions between metal centers and organic radicals, thereby creating a de facto biradical. In addition, it is shown that the magnetic topology cannot be inferred from the polymeric [TTTA ??? Cu(hfac)₂]_n crystal motif, that is, from its chemical coordination pattern. Instead, one should think in terms of magnetic building blocks, namely, the de facto biradicals.     

A Theoretically‐Guided Optimization of a New Family of Modular P,S‐Ligands for Iridium‐Catalyzed Hydrogenation of Minimally Functionalized Olefins

A library of modular iridium complexes derived from thioether‐phosphite/phosphinite ligands has been evaluated in the asymmetric iridium‐catalyzed hydrogenation of minimally functionalized olefins. The modular ligand design has been shown to be crucial in finding highly selective catalysts for each substrate. A DFT study of the transition state responsible for the enantiocontrol in the Ir‐catalyzed hydrogenation is also described and used for further optimization of the crucial stereodefining moieties. Excellent enantioselectivities (enantiomeric excess (ee) values up to 99 %) have been obtained for a range of substrates, including E‐ and Z‐trisubstituted and disubstituted olefins, α,β‐unsaturated enones, tri‐ and disubstituted alkenylboronic esters, and olefins with trifluoromethyl substituents.     

Indene-based scaffolds. Design and synthesis of novel serotonin 5-HT6 receptor ligands

A series of novel indene derivatives designed by a scaffold selection gave access to several examples of (Z)-arylmethylideneindenes and indenylsulfonamides that acted as serotonin 5-HT(6) receptor ligands. Different synthetic multistep routes could be applied to these target compounds, each with their own complexity and limitations. A reasonable route involved the (3-indenyl)acetic acids as the key intermediates, and two alternatives were also examined. The first protocol used was a two-step sequence employing a modified Horner-Wadsworth-Emmons reaction, but better results were obtained with a procedure based on the condensation of indanones with the lithium salt of ethyl acetate, followed immediately by dehydration with acid and hydrolysis/isomerization under basic catalysis. (3-Indenyl)acetic acids were transformed to the corresponding acetamides, which were effectively reduced to indenylsulfonamides using an optimized procedure with AlH(3)-NMe(2)Et. The binding at the 5-HT(6) receptor was with moderate affinity (K(i) = 216.5 nM) for the (Z)-benzylideneindenylsulfonamide and enhanced affinity for the simple indenylsulfonamide counterpart (K(i) = 50.6 nM). Selected indenylsulfonamides were then tested, showing K(i) values as low as 20.2 nM.