Silica-Supported Triptycene-Type Phosphine. Synthesis, Characterization, and Application to Pd-Catalyzed Suzuki–Miyaura Cross-Coupling of Chloroarenes

Suzuki-Miyaura Cross-Coupling Reaction Using Palladium Catalysts Supported on Phosphine Periodic Mesoporous Organosilica

Phosphine periodic mesoporous organosilicas (R-P-PMO-TMS: R=Ph, tBu), which possess electron-donating alkyl substituents on the phosphorus atom, were synthesized using bifunctional compounds with alkoxysilyl- and phosphino groups, bis[3-(triethoxysilyl)propyl]phenylphosphine borane (1 a) and bis[3-(triethoxysilyl)propyl]-tert-butylphosphine borane (1 b). Immobilization of Pd(0) species was performed to give R-P-Pd-PMO-TMS: R=Ph (2 a), tBu (3 a), respectively. The Pd(0) immobilized 2 a and 3 a were applicable as catalysts for Suzuki-Miyaura cross-coupling reactions of aryl chlorides with phenylboronic acid. It was revealed that 3 a bearing more electron-donating tBu groups exhibited higher catalytic activity. Various functional groups including both electron withdrawing and donating substituents were compatible in the system. The recyclability of 3 a was examined to support its moderate utility for the recycle use.

Fusing Triphenylbismuth and PnPh3 (Pn = P-Bi): Synthesis, Isolation, and Characterization of 9-Bisma-10-Pnictatriptycenes

The first series of 9-bisma-10-pnictatriptycenes Bi(C6H4)3Pn (2-Pn, Pn = P-Bi; see graphic) has been synthesized in a two-step procedure via suitable tris(2-bromophenyl)pnictanes 1-Pn and characterized in solution as well as in the solid state. DFT calculations suggest preferential interactions between 2-Pn and soft Lewis acids via the lighter pnictogen donor atom. Experimental studies demonstrate that even the weakest Lewis base in the series of 2-Pn, namely the dibismatriptycene 2-Bi, interacts with Lewis acidic [BiMe2(SbF6)] in solution. Analytical techniques include (VT-)NMR spectroscopy, DOSY NMR spectroscopy, high-resolution mass spectrometry, single-crystal X-ray diffraction analyses, and DFT calculations.

Porous Supramolecular Assemblies for Efficient Suzuki Coupling of Aryl Chlorides

The development of catalytic systems that can activate aryl chlorides for palladium-catalyzed cross-coupling reactions is at the forefront of ongoing efforts to synthesize fine chemicals. In this study, a facile ligand-template approach is adopted to achieve active-site encapsulation by forming supramolecular assemblies; this bestowed the pristine inert counterparts with reactivity, which is further increased upon the construction of a porous framework. Experimental results indicated that the isolation of ligands by the surrounding template units is key to the formation of catalytically active monoligated palladium complexes. Additionally, the construction of porous frameworks using the resulting supramolecular assemblies prevented the decomposition of the Pd complexes into nanoparticles, which drastically increased the catalyst lifetime. These findings, along with the simplicity and generality of the synthesis scheme, suggest that the strategy can be leveraged to achieve unique reactivity and potentially enable fine-chemical synthesis.

A Rigid Linker for Site-Selective Coordination of Transition Metal Cations: Combining an Acetylacetone with a Caged Phosphine

The combination of a soft phosphorus and a hard oxygen donor in the new ligand HacacTRIP leads to excellent site selectivity for the coordination of two different metal cations of matching Pearson character. The deprotonation step required for coordinating the acetylacetone oxygen donor further increases the selectivity. In contrast to most phosphines, the use of the caged phosphatriptycene motif enables a rigid and directional orientation of the phosphorus binding site which is required to form stable coordination network structures. In addition to the synthesis of HacacTRIP, we present its selective coordination. The deprotonated acetylacetone was selectively bound to Cu^II and Fe^III. The solid state structure of the former displays a rare axial coordination of chloroform molecules. The phosphorus donor was selectively coordinated to the monovalent coinage metal cations Cu^I, Ag^I, and Au^I. The Cu^I and Ag^I complexes represent the first examples in which a phosphatriptycene is bound to these metal cations. Heterometallic coordination compounds were characterized with combinations of these two groups. They comprise an oligonuclear Cu^I/Cu^II mixed-valence compound in which iodide binds to both Cu^I and Cu^II cations and a complex in which acacTRIP^- bridges Cu^II and Au^I. In addition to these discrete aggregates, the ligand has been used to link Fe^III and Ag^I into a 2D coordination polymer with unprecedented trigonal planar coordination of three bulky phosphatriptycenes to a cation and resulting honeycomb topology. Its almost regular hexagons underline the desired rigidity of the ditopic acacTRIP^- ligand.

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...

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.

A comprehensive review of caged phosphines: synthesis, catalytic applications, and future perspectives

Caged phosphines are versatile ligands due to their rigid backbones, exhibiting a range of catalytic activities, as depicted through the given pictorial representation.

Air-stable Pd(0) catalyst bearing dual phosphine ligands: a detailed evaluation of air stability and catalytic property in cross-coupling reactions

We have synthesised an air-stable Pd(0) catalyst bearing donor and acceptor phosphine ligands (Complex 1). This study revealed the long-term air stability and catalytic property of Complex 1 as a catalyst for cross-coupling reactions, where it was stable in air for eight months. DFT calculations revealed that the acceptor ligands in Complex 1 decreased the HOMO energy level, which provided the observed air stability. Complex 1 successfully served as a catalyst for direct C-H arylation reactions and Suzuki-Miyaura cross-coupling reactions, and catalysed the reaction of a relatively inactive substrate, 2-chrolopyridine, which could not be achieved by conventional, air-stable Pd(0) catalysts. Isolating the intermediates of the coupling reactions revealed that each intermediate possessed the donor ligand (PCy3), which was determined to be responsible for imparting the high catalytic activity exhibited by Complex 1.

Hollow porous organic nanospheres for anchoring Pd(PPh3)4 through a co-hyper-crosslinking mediated self-assembly strategy

A facile synthesis of Pd(PPh₃)₄-functionalized hollow porous organic nanospheres with excellent catalytic activity is reported for the first time.

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

Two practical and high-yielding syntheses of 9-phosphatriptycene are reported. In both approaches, the key step is based on the cyclization of a (tris)lithio-triphenylmethane or a (tris)lithio-triphenylphosphine intermediate on a phosphorus or a carbon electrophile, respectively. The association of 9-phosphatriptycene with representative boron- and carbon-centered Lewis acids was investigated by IR, NMR, and UV-vis titration experiments and by computational methods, shedding light on its steric hindrance, σ-donating ability, and Brønsted and Lewis basicities.

Fusing triphenylphosphine with tetraphenylborate: introducing the 9-phosphatriptycene-10-phenylborate (PTB) anion

In a fusion of two ubiquitous organometallic reagents, triphenylphosphine (PPh3) and tetraphenylborate (BPh4-), the 9-phosphatriptycene-10-phenylborate (PTB) anion has been prepared for the first time. This borato species has been fully characterized by a suite of spectroscopic methods, and initial reactivity studies introduce it as a competent ligand for transition metals, including Co(ii) and Fe(ii).

Synthesis and Catalytic Applications of a Triptycene-Based Monophosphine Ligand for Palladium-Mediated Organic Transformations

1-Methoxy-8-(diphenylphosphino)triptycene (1), featuring high structural rigidity and steric bulkiness around the phosphine functionality, was synthesized as a new chiral monophosphine ligand for transition metal-catalyzed reactions. In the presence of 5-10 mol ppm (i.e., 0.0005-0.001 mol %) Pd(OAc)₂ and 1 (2 equiv for Pd), Suzuki-Miyaura cross-coupling reactions of aryl bromides and arylboronic acids proceeded effectively under mild atmospheric conditions to give the corresponding biaryl compounds in a high yield. The single-crystal X-ray analysis of a Pd(II) complex of 1 revealed its coordination structure, in which two homochiral molecules form a dimer, suggesting that triptycene could provide a chiral environment for asymmetric organic transformations. In fact, optically active 1 obtained by optical resolution showed good enantioselectivity in the palladium-catalyzed asymmetric hydrosilylation of styrene, which represents, for the first time, the asymmetric catalytic activity of triptycene-based monophosphine ligands.

Tridentate Lewis-acids based on triphenylsilane

Triphenylsilanes are versatile propeller-shaped building blocks and have been used for the syntheses of several novel poly-Lewis-acids. The first solid-state structure of a bisma-silatriptycene as well as investigations in host–guest chemistry of a triple alane with a threefold amine are reported.