Self-Assembly, Chiroptical Properties, and Host−Guest Chemistry of Chiral Pt−Pt and Pt−Pd Tetranuclear Macrocycles. Circular Dichroism Studies on Neutral Guest Inclusion Phenomena

Homo- and heterometallic chiral dynamic architectures from allyl-palladium(II) building blocks

New chiral tetranuclear square-like homo- and heterometallamacrocycles containing allyl-palladium and either {Pd(P-P)*} or {Pt(P-P)*} optically pure moieties (P-P* = (2S,3S)-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphanyl)butane ((S,S)-DIOP) and (2S,4S)-2,4-bis(diphenylphosphanyl)pentane ((S,S)-BDPP)) have been obtained by the self-assembly of [Pd(η³-2-Me-C₃H₄)(4-PPh₂py)₂]⁺ and [M(P-P)*(H₂O)₂]²⁺ building blocks in a 1 : 1 molar ratio. The supramolecular assemblies thus prepared [{Pd(η³-2-Me-C₃H₄)}₂(4-PPh₂py)₄{M(P-P)*}₂](CF₃SO₃)₆ (M = Pd, Pt) have been fully characterised by multinuclear NMR spectroscopy and MS spectrometry. The structures display remarkable differences on their dynamic behaviour in solution that depend on the lability and thermodynamic strength of M-py bonds. The structural characteristics of the new metallamacrocyles obtained have also been unambiguously established by XRD analysis. The architectures have been assayed as catalytic precursors in the asymmetric allylic alkylation reaction.

A square-shaped complex with an electron-acceptor ligand: unique cubic crystal symmetry and similarity to the inorganic mineral katoite

We successfully obtained a Pt square complex having an electron-accepting ligand, which shows a strong similarity to the high-pressure phase of the natural mineral katoite in the solid state.

1,1'-Binaphthyl-substituted diphosphene: synthesis, structures, and chiral optical properties

1,1'-Binaphthyl-substituted diphosphene 1 possessing a P[double bond, length as m-dash]P double bond and an axially chiral 1,1'-binaphthyl group was synthesized and fully characterized. Diphosphene 1 was prepared as an optically active form and thus is the first example of a chiral diphosphene. The CD spectra of 1 showed apparent circular dichroism in the longer wavelength region, caused by the P[double bond, length as m-dash]P moiety.

Self-assembly of ambidentate pyridyl-carboxylate ligands with octahedral ruthenium metal centers: self-selection for a single-linkage isomer and anticancer-potency studies

The synthesis of six new [2+2] metallarectangles through the coordination-driven self-assembly of octahedral Ru(II)-based acceptors with ambidentate pyridyl-carboxylate donors is described. These molecular rectangles are fully characterized by (1)H NMR spectroscopy, high-resolution electrospray mass spectrometry, and single-crystal X-ray diffraction. In each case, despite the possible formation of multiple isomers, based on the relative orientation of the pyridyl and carboxylate groups (head-to-head versus head-to-tail), evidence for the formation of a single preferred ensemble (head-to-tail) was found in the (1)H NMR spectra. Furthermore, the cytotoxicities of all of the rectangles were established against A549 (lung), AGS (gastric), HCT-15 (colon), and SK hep 1 (liver) human cancer cell lines. The cytotoxicities of rectangles that contained the 5,8-dihydroxy-1,4-naphthaquinonato bridging moiety between the Ru centers (9-11) were particularly high against AGS cancer cells, with IC50 values that were comparable to that of reference drug cisplatin.

Photophysical and computational investigations of bis(phosphine) organoplatinum(II) metallacycles

A series of endohedral and exohedral amine-functionalized ligands were synthesized and used in the construction of supramolecular D(2h) rhomboids and a D(6h) hexagon. These supramolecular polygons were obtained via self-assembly of 120° dipyridyl donors with 180° or 120° diplatinum precursors when combined in 1:1 ratios. Steady-state absorption and emission spectra were collected for each ligand and metallacycle. Density functional theory (DFT) and time-dependent DFT calculations were employed to probe the nature of the observed optical transitions for the rhomboids. The emissive properties of these bis(phosphine) organoplatinum metallacycles arise from ligand-centered transitions involving π-type molecular orbitals with modest contributions from metal-based atomic orbitals. The D(2h) rhomboid self-assembled from 2,6-bis(4-pyridylethynyl)aniline and a 60° organoplatinum(II) acceptor has a low-energy excited state in the visible region and emits above 500 nm, properties which greatly differ from those of the parent 2,6-bis(4-pyridylethynyl)aniline ligand.

The Chemistry of Transition Metal Ethyne-1,2-diyl Complexes

The chemistry and reactivity of ethyne-1,2-diyl compounds, LnM–CC–MLn, is reviewed. These complexes are simple analogues of organic alkynes, or dimetalloalkynes, and there appears to be no general route to the preparation of these complexes, except perhaps using acid/base methodology. Reactivity patterns, in general, mimic those of simple organic alkynes but have the added dimension of reactive M–C(sp) bonds that sometimes participate in the formation of multimetallic compounds with metal electrophiles.

From solvolysis to self-assembly

My sojourn from classical physical-organic chemistry and solvolysis to self-assembly and supramolecular chemistry, over the last forty years, is described. My contributions to unsaturated reactive intermediates, namely vinyl cations and unsaturated carbenes, along with my decade-long involvement with polyvalent iodine chemistry, especially alkynyliodonium salts, as well as my more recent research with metal-ligand, coordination driven, and directed self-assembly of finite supramolecular ensembles are discussed.

Organometallic molecular materials: self-assembly through hydrogen bonding of an organoplatinum network structure with zeolite-like topology

The complex [Pt(OH)(2)Me(2)(dpa)], dpa = di-2-pyridylamine, undergoes a remarkable form of self-assembly through hydrogen bonding in the solid state; there are cyclic tetramer units formed by head-to-head association between pairs of hydroxyl groups, and cyclic hexamer units formed by head-to-tail association between NH and OH groups; these building blocks then self-assemble to form a complex network structure containing large interconnected cavities, reminiscent of zeolites.

Synthesis and characterization of a trigonal bipyramidal supramolecular cage based upon rhodium and platinum metal centers

The reaction of 4-ethynyl-pyridine with tert-butyl lithium followed by its addition to (Me3tacn)RhCl3 affords the facial octahedral complex (Me3tacn)Rh(CCPy)3, condensation of which with the square planar complex cis-(DCPE)Pt(NO3)2 results in a self-assembled trigonal bipyramidal cage with Rh(III) and Pt(II) atoms occupying the vertices.

Synthesis of Chiral Self-Assembling Rhombs and Their Characterization in Solution, in the Gas Phase, and at the Liquid−Solid Interface

Chiral, enantiopure metallo-supramolecular rhombs self-assemble in solution through coordination of bis-pyridyl-substituted ligands with (en)M(NO3)2 (en = ethylenediamine, M = Pd(II), Pt(II)). Characterization by NMR and CD spectroscopy in solution and by ESI-FT-ICR mass spectrometry in the gas phase suggests that an equilibrium exists in water/methanol of a major 2:2 complex and a minor 3:3 complex of ligands and metal corners. In the gas phase, doubly charged 2:2 complexes fragment into two identical singly charged halves followed by metal-mediated C-H and C-C bond activation reactions within the ethylenediamine ligands. Electrochemical scanning tunneling microscopy (EC-STM) provides in situ imaging of the complexes even with submolecular resolution. Flat-lying rhombs are deposited under potential control from an aqueous electrolyte on a Cu(100) electrode surface precovered by a tetragonal pattern of chloride anions from the supporting electrolyte. Chirality induces the formation of only one domain orientation. Density functional calculations help to interpret the STM images.

Neutral Pyridyl-Functionalized C,N-ortho-Chelated Aminoaryl Platinum(II) Corner Building Blocks for Application in Coordination Reactions

Two homoleptic pyridyl-functionalized C,N-ortho-chelating aminoaryl platinum(II) complexes, cis-[Pt(eta(2)-C,N)] (3a,b), were prepared via an unconventional method involving the initial synthesis of a bromide-functionalized C,N-chelating aminoaryl platinum(II) precursor complex 8, to which subsequently pyridyl groups were attached via a Suzuki-Miyaura C-C coupling reaction. The electron-donating properties of the pyridyl nitrogen atoms of the resulting complexes (3a,b) were used in complexation reactions with monocationic NCN-pincer (NCN = [C6H3(CH2NMe2)(2-)2,6]-) platinum(II) (11a) and palladium(II) (12a) nitrate complexes [M(NCN)(NO3)], thereby obtaining four trimetallic coordination complexes 16-19. The difference in the pyridine-metal coordination behavior between platinum and palladium was studied by varying the ratios of the reagents and by variable-temperature NMR experiments. IR and Raman analyses of 11a and 12a were performed to determine the coordination behavior of the nitrate counteranion, and it was found that both NO3- and H2O coordinate to the metal centers. The crystal structure determinations of free pyridyl complex 3a, [Pt(NCN)(NO3)] (11a), and [Pt(NCN)(NO3)].(H2O) (11b), as well as the crystal structure of trisplatinum coordination complex 16, are reported.