Homo- and heterodehydrocoupling of phosphines mediated by alkali metal catalysts

Catalytic chemistry that involves the activation and transformation of main group substrates is relatively undeveloped and current examples are generally mediated by expensive transition metal species. Herein, we describe the use of inexpensive and readily available tBuOK as a catalyst for P–P and P–E (E = O, S, or N) bond formation. Catalytic quantities of tBuOK in the presence of imine, azobenzene hydrogen acceptors, or a stoichiometric amount of tBuOK with hydrazobenzene, allow efficient homodehydrocoupling of phosphines under mild conditions (e.g. 25 °C and < 5 min). Further studies demonstrate that the hydrogen acceptors play an intimate mechanistic role. We also show that our tBuOK catalysed methodology is general for the heterodehydrocoupling of phosphines with alcohols, thiols and amines to generate a range of potentially useful products containing P–O, P–S, or P–N bonds

Homo- and heterodehydrocoupling of phosphines mediated by alkali metal catalysts

Catalytic chemistry that involves the activation and transformation of main group substrates is relatively undeveloped and current examples are generally mediated by expensive transition metal species. Herein, we describe the use of inexpensive and readily available tBuOK as a catalyst for P–P and P–E (E = O, S, or N) bond formation. Catalytic quantities of tBuOK in the presence of imine, azobenzene hydrogen acceptors, or a stoichiometric amount of tBuOK with hydrazobenzene, allow efficient homodehydrocoupling of phosphines under mild conditions (e.g. 25 °C and < 5 min). Further studies demonstrate that the hydrogen acceptors play an intimate mechanistic role. We also show that our tBuOK catalysed methodology is general for the heterodehydrocoupling of phosphines with alcohols, thiols and amines to generate a range of potentially useful products containing P–O, P–S, or P–N bonds

Metal-free dehydropolymerisation of phosphine-boranes using cyclic (alkyl)(amino)carbenes as hydrogen acceptors

Polymers featuring p-block elements other than carbon are of interest for a range of applications, but access to highly-substituted examples remains challenging. Here the authors demonstrate that cyclic (alkyl)(amino)carbenes can mediate the dehydropolymerisation of phosphine-boranes, leading to the construction of P-disubstituted polyphosphinoboranes

Quantitative Multicolor Super-Resolution Microscopy Reveals Tetherin HIV-1 Interaction

Virus assembly and interaction with host-cell proteins occur at length scales below the diffraction limit of visible light. Novel super-resolution microscopy techniques achieve nanometer resolution of fluorescently labeled molecules. The cellular restriction factor tetherin (also known as CD317, BST-2 or HM1.24) inhibits the release of human immunodeficiency virus 1 (HIV-1) through direct incorporation into viral membranes and is counteracted by the HIV-1 protein Vpu. For super-resolution analysis of HIV-1 and tetherin interactions, we established fluorescence labeling of HIV-1 proteins and tetherin that preserved HIV-1 particle formation and Vpu-dependent restriction, respectively. Multicolor super-resolution microscopy revealed important structural features of individual HIV-1 virions, virus assembly sites and their interaction with tetherin at the plasma membrane. Tetherin localization to micro-domains was dependent on both tetherin membrane anchors. Tetherin clusters containing on average 4 to 7 tetherin dimers were visualized at HIV-1 assembly sites. Combined biochemical and super-resolution analysis revealed that extended tetherin dimers incorporate both N-termini into assembling virus particles and restrict HIV-1 release. Neither tetherin domains nor HIV-1 assembly sites showed enrichment of the raft marker GM1. Together, our super-resolution microscopy analysis of HIV-1 interactions with tetherin provides new insights into the mechanism of tetherin-mediated HIV-1 restriction and paves the way for future studies of virus-host interactions

Tuning the Reactivity of an Actor Ligand for Tandem CO₂ and C–H Activations: From Spectator Metals to Metal-Free

The 4,5-diazafluorenide ligand (L^–) serves as an actor ligand in the formal insertion of CO₂ into a C–H bond remote from the metal center. With the Ru­(II) complex of L^– as the starting point, Rh­(III), Rh­(I), and Cu­(I) were used as spectator metal centers to tune the reactivity of the actor ligand toward CO₂. In the case of Rh­(III)-diazafluorenide a room temperature reversible activation of CO₂ was observed, similar to the isoelectronic Ru­(II) analogue. In the case of Rh­(I)- and Cu­(I)-diazafluorenide CO₂ is trapped by the formation of dinuclear carboxylate complexes and diazafluorene (LH). The spectator metal center could even be replaced entirely with an organic group allowing for the first metal-free reversible tandem CO₂ and C–H activation

Tuning the Reactivity of an Actor Ligand for Tandem CO₂ and C–H Activations: From Spectator Metals to Metal-Free

The 4,5-diazafluorenide ligand (L^–) serves as an actor ligand in the formal insertion of CO₂ into a C–H bond remote from the metal center. With the Ru­(II) complex of L^– as the starting point, Rh­(III), Rh­(I), and Cu­(I) were used as spectator metal centers to tune the reactivity of the actor ligand toward CO₂. In the case of Rh­(III)-diazafluorenide a room temperature reversible activation of CO₂ was observed, similar to the isoelectronic Ru­(II) analogue. In the case of Rh­(I)- and Cu­(I)-diazafluorenide CO₂ is trapped by the formation of dinuclear carboxylate complexes and diazafluorene (LH). The spectator metal center could even be replaced entirely with an organic group allowing for the first metal-free reversible tandem CO₂ and C–H activation

Ring-opening polymerization of cyclic phosphonates : access to inorganic polymers with a PV–O main chain

We describe a new class of inorganic polymeric materials featuring a main chain consisting of PV–O bonds and aryl side groups, which was obtained with >70 repeat units by ring-opening polymerization of cyclic phosphonates. This monomer–polymer system was found to be dynamic in solution enabling selective depolymerization under dilute conditions, which can be tuned by varying the substituents. The polymers show high thermal stability to weight loss and can be easily fabricated into self-standing thin films. Structural characterizations of the cyclic 6- and 12-membered ring precursors are also described

Titanium‐Catalyzed Polymerization of a Lewis Base‐Stabilized Phosphinoborane

The reaction of the Lewis base-stabilized phosphinoborane monomer tBuHPBH2NMe3 (2 a) with catalytic amounts of bis(η5:η1-adamantylidenepentafulvene)titanium (1) provides a convenient new route to the polyphosphinoborane [tBuPH-BH2]n (3 a). This method offers access to high molar mass materials under mild conditions and with short reaction times (20 °C, 1 h in toluene). It represents an unprecedented example of a transition metal-mediated polymerization of a Lewis base-stabilized Group 13/15 compound. Preliminary studies of the substrate scope and a potential mechanism are reported

RuCp* Complexes of Ambidentate 4,5-Diazafluorene Derivatives: From Linkage Isomers to Coordination-Driven Self-Assembly

The coordination chemistry of the {RuCp*}⁺ fragment was studied toward several 4,5-diazafluorene derivatives. The ambidentate nature of these 4,5-diazafluorene derivatives with multiple coordination sites allowed for the syntheses of different linkage isomers and self-assembled macrocycles. Both a tetramer (<b>2</b>) and a monomer (<b>3</b>) of [RuCp*<b>L</b>] (where <b>L</b>^<b>–</b> = 4,5-diazafluorenide) were prepared with the <b>L</b>^<b>–</b> ligand. The dimeric head-to-tail macrocycles [Cp*Ru­(L_pH)]₂Cl₂ (<b>4</b>) and [Cp*RuL_p]₂ (<b>5</b>) were obtained with the ditopic <b>L</b>_<b>p</b><b>H</b> and <b>L</b>_<b>p</b>^<b>–</b> ligands (where <b>L</b>_<b>p</b><b>H</b> = 9-(2-(diphenylphosphino)­ethyl)-4,5-diazafluorene and <b>L</b>_<b>p</b>^<b>–</b> = 9-(2-(diphenylphosphino)­ethyl)-4,5-diazafluorenide). The bulky arene-substituted <b>L</b>_<b>Mes</b><b>H</b> ligand (where <b>L</b>_<b>Mes</b><b>H</b> = 3,6-dimesityl-4,5-diazafluorene) was prepared, and its coordination to {RuCp*}⁺ gave [Cp*Ru­(<b>L</b>_<b>Mes</b><b>H</b>)]Cl (<b>13</b>). The selective syntheses of different linkage isomers of [RuCp*­(<b>L</b>_<b>Mes</b>)] (<b>14</b> and <b>15</b>) (where <b>L</b>_<b>Mes</b>^<b>–</b> = 3,6-dimesityl-4,5-diazafluorenide) were also demonstrated

Non-Metal-Catalyzed Heterodehydrocoupling of Phosphines and Hydrosilanes: Mechanistic Studies of B(C₆F₅)₃‑Mediated Formation of P–Si Bonds

Non-metal-catalyzed heterodehydrocoupling of primary and secondary phosphines (R¹R²PH, R² = H or R¹) with hydrosilanes (R³R⁴R⁵SiH, R⁴, R⁵ = H or R³) to produce synthetically useful silylphosphines (R¹R²P–SiR³R⁴R⁵) has been achieved using B­(C₆F₅)₃ as the catalyst (10 mol %, 100 °C). Kinetic studies demonstrated that the reaction is first-order in hydrosilane and B­(C₆F₅)₃ but zero-order in phosphine. Control experiments, DFT calculations, and DOSY NMR studies suggest that a R¹R²HP·B­(C₆F₅)₃ adduct is initially formed and undergoes partial dissociation to form an “encounter complex”. The latter mediates frustrated Lewis pair type Si–H bond activation of the silane substrates. We also found that B­(C₆F₅)₃ catalyzes the homodehydrocoupling of primary phosphines to form cyclic phosphine rings and the first example of a non-metal-catalyzed hydrosilylation of P–P bonds to produce silylphosphines (R¹R²P–SiR³R⁴R⁵). Moreover, the introduction of PhCN to the reactions involving secondary phosphines with hydrosilanes allowed the heterodehydrocoupling reaction to proceed efficiently under much milder conditions (1.0 mol % B­(C₆F₅)₃ at 25 °C). Mechanistic studies, as well as DFT calculations, revealed that PhCN plays a key mechanistic role in facilitating the dehydrocoupling reactions rather than simply functioning as H₂-acceptor