Complementary Synthetic Approaches toward 9-Phosphatriptycene and Structure-Reactivity Investigations of Its Association with Sterically Hindered Lewis Acids

Regulating iminophosphorane PN bond reactivity through geometric constraints with cage-shaped triarylphosphines

Structure-reactivity investigations and quantum-chemical parametrization of steric and electronic properties of geometrically constrained iminophosphoranes enabled the design of new frustrated Lewis pairs and revealed unusual properties at the phosphonium center embedded in the cage-shaped triptycene tricyclic scaffold.

Geometrically Deformed and Conformationally Rigid Phosphorus Trisamides Featuring an Unsymmetrical Backbone

Nonclassical P(III) centers have attracted much attention in recent years. Incorporating a P(III) center in a rigid bicyclic platform offers a particularly attractive way to invoke significant geometric distortion of the phosphorus atom that may in turn induce unusual reactivity. Although still relatively scarcely explored, phosphorus centers enforced in a non-C3 symmetry have gained significant traction lately. However, the current scaffolds are based on a relatively limited set of design principles and ligand platforms associated therewith. This work is focussed on the synthesis as well as versatile oxidation, addition and coordination chemistry of a geometrically distorted P(III) species featuring a synthetically modular, nonsymmetric trisamine platform derived from 2-(methylamino)-N-(2-(methylamino)phenyl)benzenesulfonamide.

Water-Soluble Pd-Imidate Complexes as Versatile Catalysts for the Modification of Unprotected Halonucleosides

Modification of unprotected nucleosides has been attracting continuous interest, since these building blocks themselves and their phosphate-upgraded corresponding nucleotides have shown a plethora of uses in fields like biochemistry or pharmacy. Pd-catalyzed cross-coupling reactions, conducted in water or its mixtures with polar organic solvents, have frequently been the researchers' choice for the functionalization of the purine/pyrimidine base of the unprotected nucleosides. In this scenario, the availability of hydrophilic ligands and its water-soluble palladium complexes has markedly set the pace of the advances. The approach of our group to the synthesis of such complexes, Pd-imidates specifically, has faced critical stages, namely the jump to synthesize water soluble complexes from our experience working in conventional solvents, the preparation of phosphine free complexes and the overall goal of getting catalytic systems able to work close to room temperature. The continuous feedback with Kapdi's group, experienced in the chemistry of nucleosides, has produced over the last decade the interesting results in both fields presented here.

9-Phosphatriptycene Derivatives: From Their Weak Basicity to Their Application in Frustrated Lewis Pair Chemistry

The accurate prediction of the basicity of tertiary phosphines in acetonitrile and water is reported by the linear correlation between computed ΔpK_a's obtained by density functional theory (DFT) and experimental values extracted from the literature. This method is applied to the prediction of pK_a values of 9-phosphatriptycene derivatives and showed that they are weaker Brønsted bases than their triphenylphosphine analogues. This lower reactivity is attributed to their high pyramidalization that increases their lone pair 3s character, stabilizing its energy level. Their potential application in frustrated Lewis pair chemistry is then considered by investigating the hydrogenation of 1,1-diphenylethylene by the tris(pentafluorophenyl)borane/1-chloro-9-phosphatriptycene frustrated Lewis pair.

Phosphorus or Nitrogen - The first Phosphatriptycene in Coordination Polymer Chemistry

Phosphasilatriptycene, a phenylene spacer and a pyridyl moiety represent the building blocks of TRIP-Py, the first heteroditopic ligand featuring a phoshatriptycene scaffold. The P and N donor sites located at...

Triptycene Derivatives: From Their Synthesis to Their Unique Properties

Since the first preparation of triptycene, great progress has been made with respect to its synthesis and the understanding of its properties. Interest in triptycene-based systems is intense; in recent years, advances in the synthetic methodology and properties of new triptycenes have been reported by researchers from various fields of science. Here, an account of these new developments is given and placed in reference to earlier pivotal works that underpin the field. First, we discuss new approaches to the synthesis of new triptycenes. Progress in the regioselective synthesis of sterically demanding systems is discussed. The application of triptycenes in catalysis is also presented. Next, progress in the understanding of the relations between triptycene structures and their properties is discussed. The unique properties of triptycenes in the liquid and solid states are elaborated. Unique interactions, which involve triptycene molecular scaffolds, are presented. Molecular interactions within a triptycene unit, as well as between triptycenes or triptycenes and other molecules, are also evaluated. In particular, the summary of the synthesis and useful features will be helpful to researchers who are using triptycenes as building blocks in the chemical and materials sciences.

Sterically hindered ortho-substituted phosphatriptycenes as configurationally stable P-chirogenic triarylphosphines

ortho-Substituted and unsymmetrical 9-phospha-triptycenes were synthesized via two synthetic approaches involving densely functionalized ortho-halogenated triarylmethane or phosphine precursors. ortho-Substituents imposed a considerable steric shielding due to the tricyclic cage-shaped structure with the aryl rings p-systems orthogonal to the phosphorus electron pair. A series of Au(i) and Rh(i) complexes were analysed in the solid state to determine Tolman electronic parameters, cone angles and buried volumes of these unprecedented functionalized phosphines. Quantum chemical calculations of electronic and steric descriptors revealed that these cage-shaped phosphines are electron-poor and that single methyl substituent is enough to provide the largest effect on steric shielding reported so far in triarylphosphines. An unsymmetrically substituted 9-phosphatriptycene was resolved by chiral HPLC, opening the avenue towards stable P-chirogenic triarylphosphines with unlimited configurational stability for new catalyst development in asymmetric transition-metal catalysis.

1,3,5-Triaza-7-phosphaadamantane (PTA) Derived Caged Phosphines for Palladium-Catalyzed Selective Functionalization of Nucleosides and Heteroarenes

Phosphines have, in combination with transition metals, played a pivotal role in the rapid development of efficient catalytic processes. Caged phosphines constitute a class of three-dimensional scaffolds providing unique control over steric and electronic properties. The versatility of the caged phosphine ligands has been demonstrated elegantly by the groups of Verkade, Gonzalvi as well as Stradiotto. Our research group has also been working extensively for the past several years in the development of 1,3,5-triaza-7-phosphaadamantane-based caged ligands and in this personal note we have summarized these applications pertaining to the modification of biologically useful nucleosides and heteroarenes.