Effect of the Positioning of Metal Centers on a Cavitand in the Ruthenium-Catalyzed N-Alkylation of Amines

Two bis-ruthenium(II) complexes, namely N,N'-{5,17-diamino-4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arene}-bis-[dichloro-(p-cymene)-ruthenium(II)] (1) and N,N'-{5,11-diamino-4(24),6(10),12(16), 18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arene}-bis-[dichloro-(p-cymene)-ruthenium(II)] (2) were synthesized and tested as catalysts in the N-alkylation of primary amines with arylmethyl alcohol using the green "hydrogen borrowing" methodology. The catalytic results were compared with those obtained when the N-{5-amino-4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentyl-resorcin[4]arene}-[dichloro-(p-cymene)-ruthenium(II)] (3) complex was employed as catalyst. The rate of the N-alkylation of aniline with benzyl alcohol increased in the order 3 < 1 ≪ 2, which highlights the importance of the relative positioning of the two metal centers on the upper rim of the resorcin[4]arene. Theoretical investigations suggest that the grafting of the two "RuCl2(p-cymene)NH2" moieties on two distal aromatic rings of the cavitand allows a cooperative effect between a ruthenium atom and the coordinated amine of the second metal center.

Diametric calix[6]arene-based phosphine gold(I) cavitands

We report the synthesis and characterization, in low polarity solvents, of a novel class of diametric phosphine gold(I) cavitands characterized by a 1,2,3-alternate geometry. Preliminary catalytic studies were performed on a model cycloisomerization of 1,6-enynes as a function of the relative orientation of the bonded gold(I) nuclei with respect to the macrocyclic cavity.

Merging Molecular Recognition and Gold(I) Catalysis with Triphoscalix[6]arene Ligands

We report the synthesis and characterization of novel triphosphine calix[6]arene ligands. These supramolecular wheels, with recognition features governed by the hydrogen-bonding domain, were employed to synthesize multitasking trinuclear gold(I) complexes as a new platform for the synthesis of interwoven (pseudo)rotaxane species. In parallel, the multivalent, metal-bonded upper rim displayed catalytic features promoting highly selective gold-catalyzed cycloisomerization reactions of 1,6-enynes.