Photolytic, radical-mediated hydrophosphination: a convenient post-polymerisation modification route to P-di(organosubstituted) polyphosphinoboranes [RR'PBH2] n

UV induced hydrophosphination of dimethyl 2-vinylcyclopropane-1,1-dicarboxylate towards phosphine chalcogenides

Dimethyl 2-vinylcyclopropane-1,1-dicarboxylate underwent a hydrophosphination reaction with either a primary or secondary phosphine under photolytic conditions. Notably, a free radical initiator was not required. The resulting tertiary phosphines were derivatized using S₈ to afford moisture and air stable yellow or colorless oils in a 27%-73% isolated yield. A series of control reactions were performed, and we propose that this UV induced hydrophosphination reaction proceeds through a radical mechanism.

Three- and Five-Membered Anionic Chains of Pnictogenylboranes

An unprecedented family of three- and five-membered substituted anionic derivatives of parent pnictogenylboranes is herein reported. Reacting various combinations of the pnictogenylboranes H₂ E'-BH₂ -NMe₃ (E'=P, As) with pnictogen-based nucleophiles MER1R2 (E=P, As; R1=H, R2=^t Bu; R1=R2=Ph; M=Na, K) allows for the isolation of the unsymmetrical products [Na(18-crown-6)][H₂ E'-BH₂ -EH^t Bu] (3: E=E'=P; 4: E=E'=As; 5: E=As, E'=P) and [M(C)][H₂ E'-BH₂ -EPh₂ ] (7: E=E'=P, M=Na, C=18-crown-6; 8: E=E'=As; M=K, C=[2.2.2]cryptand; 9: E=P, E'=As, M=Na, C=[2.2.2]cryptand; 10: E=As, E'=P, M=K, C=[2.2.2]cryptand). [Na(18-crown-6)][H₂ As-BH₂ -^t BuPH-BH₃ ] (6) is only accessible by a different pathway, using ^t BuPH₂ , BH₃  ⋅ SMe₂ and NaNH₂ as starting materials. Additionally, the synthesis of symmetrical diphenyl-substituted compounds [M(18-crown-6)][Ph₂ E-BH₂ -EPh₂ ] (11: E=P, M=Na; 12: E=As, M=K) is reported which can be regarded as isostructural inorganic, negatively charged analogs of dppm (1,1-bis(diphenylphosphino)methane) and dpam (1,1-bis(diphenylarsino)methane). Furthermore, an elongation of the pnictogen boron backbone in compounds 3, 7 and 9' (similar compound to 9, stabilized however by 18-crown-6), is attainable by reacting them with the pnictogenylboranes H₂ E'-BH₂ -NMe₃ leading to corresponding five-membered chain-like compounds [Na(18-crown-6)][H₂ E-BH₂ -R1R2P-BH₂ -E'H₂ ] (E=E'=P, R1=H, R2=^t Bu (13); E=E'=P, R1=R2=Ph (14); E=E'=As, R1=R2=Ph (15); E=P, E'=As, R1=R2=Ph (16)). Finally, the thermodynamics of the reaction pathways were evaluated by quantum chemical computations.

Polyphosphinoborane Block Copolymer Synthesis Using Catalytic Reversible Chain-Transfer Dehydropolymerization

An amphiphilic block copolymer of polyphosphinoborane has been prepared by a mechanism-led strategy of the sequential catalytic dehydropolymerization of precursor monomers, H₃ B ⋅ PRH₂ (R=Ph, n-hexyl), using the simple pre-catalyst [Rh(Ph₂ PCH₂ CH₂ PPh₂ )₂ ]Cl. Speciation, mechanism and polymer chain growth studies support a step-growth process where reversible chain transfer occurs, i.e. H₃ B ⋅ PRH₂ /oligomer/polymer can all coordinate with, and be activated by, the catalyst. Block copolymer [H₂ BPPhH]₁₁₀ -b-[H₂ BP(n-hexyl)H]₁₁ can be synthesized and self-assembles in solution to form either rod-like micelles or vesicles depending on solvent polarity.

Transition-Metal-Free Dehydropolymerization of Phosphine-Boranes at Ambient Temperature

Stoichiometric reaction of phosphine-borane adducts RR'PH⋅BH₃ (R=Ph, R'=H, Ph, Et, and R=R'=^t Bu) with the strong acid HNTf₂ (Tf=SO₂ CF₃ ) leads to H₂ elimination and the formation of the triflimido derivatives, RR'PH⋅BH₂ (NTf₂ ). Subsequent deprotonation by using bases, such as diisopropylethylamine or the carbene IPr (IPr=N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), led to the formation of P-mono- or -disubstituted polyphosphinoboranes [RR'P-BH₂ ]_n . Evidence for the intermediacy of transient phosphinoborane monomers, RR'PBH₂ , was provided by trapping reactions.

Photochemical Alkene Hydrophosphination with Bis(trichlorosilyl)phosphine

Bis(trichlorosilyl)phosphine (HP(SiCl₃)₂, 1) was prepared from [TBA][P(SiCl₃)₂] ([TBA]2, TBA = tetra-n-butylammonium) and triflic acid in 36% yield. Phosphine 1 is an efficient reagent for hydrophosphination of unactivated terminal olefins under UV irradiation (15-60 min) and gives rise to bis(trichlorosilyl)alkylphosphines (RP(SiCl₃)₂, R = (CH₂)₅CH₃, 88%; (CH₂)₇CH₃, 98%; (CH₂)₂C(CH₃)₃, 76%; CH₂Cy, 93%; (CH₂)₂Cy, 95%; CH₂CH(CH₃)(CH₂)₂CH₃, 82%; (CH₂)₃O(CH₂)₃CH₃, 95%; (CH₂)₃Cl, 83%; (CH₂)₂SiMe₃, 92%; (CH₂)₅C(H)CH₂, 44%) in excellent yields. The products require no further purification beyond filtration and removal of volatile material under reduced pressure. The P-Si bonds of prototypical products RP(SiCl₃)₂ (R = -(CH₂)₅CH₃, -(CH₂)₇CH₃) are readily functionalized to give further phosphorus-containing products: H₃C(CH₂)₇PCl₂ (56%), [H₃C(CH₂)₅P(CH₂Ph)₃]Br (84%), H₃C(CH₂)₇PH₂ (61%), H₃C(CH₂)₅P(O)(H)(OH) (81%), and H₃C(CH₂)₅P(O)(OH)₂ (55%). Experimental mechanistic investigations, accompanied by quantum chemical calculations, point toward a radical-chain mechanism. Phosphine 1 enables the fast, high-yielding, and atom-efficient preparation of compounds that contain phosphorus-carbon bonds in procedures that bypass white phosphorus (P₄), a toxic and high-energy intermediate of the phosphorus industry.

Macrocyclic Photoinitiator Based on Prism[5]arene Matching LEDs Light with Low Migration

In this work, a naphthalene-based macrocycle prism[5]arene (NP₅ OCH₃ ) is developed as a novel kind of photoinitiator. When NP₅ OCH₃ is irradiated under light, the bond between methylene and naphthalene can be quickly broken owning to the existence of ring tension. The macrocycle is cleaved to linear oligomer biradicals, which can effectively initiate the free radical photopolymerization of acrylate monomers. Compared with conventional photoinitiators, NP₅ OCH₃ has strong light absorption in the wavelength range of 365-405 nm, so it can well match the environment-friendly light-emitting diodes (LEDs) light source to realize highly efficient initiation. In addition, there is no small molecule fragment generated during NP₅ OCH₃ fracture, and the resulted linear oligomer biradicals can be immobilized in the polymer after initiating polymerization, so NP₅ OCH₃ photoinitiators show much lower migration rate and cytotoxicity. Cleavable macrocycle prismarene may provide a new idea for the design of safe and efficient photoinitiators matching long wavelength light.

Interaction of dicoordinate phosphorus with boranes: chemistry of 3a,6a-diaza-1,4-diphosphapentalene as masked phosphinidene

Treatment of 3a,6a-diaza-1,4-diphosphapentalene (DDP) with an excess of PhBCl2 yields the corresponding bis(borane) adduct DDP(PhBCl2)2 (14), demonstrating the availability of two lone pairs on the phosphorus center. The reaction between DDP and B(C6F5)3 yields (1 : 1) phosphino-borane complex 16. The free lone electron pair on the pyramidal P atom in 16 participates in the intramolecular non-covalent interactions P(1)F(1) and P(1)F(6) giving additional 3.9 and 2.8 kcal mol-1, respectively, for stabilization of the complex. This through-space interaction appears in the 31P NMR spectrum as large spin-spin coupling constants of 271 and 219 Hz. The addition of water to 16 (1 : 1) leads to the formation of the insertion product 17 having -H2P-O-B(C6F5)3 moiety. The reaction of DDP with BH3·SMe2 proceeds in several stages, which include the insertion of the masked phosphinidene into the B-H and P-H bonds of the intermediate compounds followed by the dehydrocoupling step and formation of diphosphine 18. The last compound exists in solution as a set of stereoisomers.

Stability and Electronic Structure of Donor-Acceptor Stabilized Group 13/15 Oligomers

Electronic structures and thermodynamic characteristics of chain inorganic group 13-15 oligomers [H₂MEH₂]_n (M = B, Al, Ga, E = P, As; n = 4-15) are presented. Donor-acceptor interaction with both Lewis acids and Lewis bases effectively stabilizes chain isomers with respect to spontaneous cyclization and significantly changes their electronic structure.

Hydrostibination of Alkynes: A Radical Mechanism*

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring open-shell neutral intermediates. Density-functional theory (DFT) calculations are consistent with this model, predicting an activation barrier that is in agreement with the experimental value (Eyring analysis) and a rate limiting step that is congruent with the experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring Sb^II and Sb^III intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a synthetic methodology.

Synthesis and Post-Polymerization Functionalization of Halogen-Substituted Polyphosphinoboranes to Access Alkyne-Functionalized Derivatives

Catalytic dehydropolymerization of halogen-functionalized phosphine-boranes (4-X-C₆ H₄ )PH₂ ⋅BH₃ (1a: X = Br, 1b: X = I) with [CpFe(CO)₂ (OTf)] at 100 °C provides convenient access to halogen-functionalized polyphosphinoboranes [(4-X-C₆ H₄ )PH-BH₂ ]_n (2a: X = Br, 2b: X = I). These polymers are useful precursors for post-polymerization functionalization, which is demonstrated by Sonogashira coupling under mild conditions to yield the alkynyl-functionalized polyphosphinoborane [(4-PhCC-C₆ H₄ )PH-BH₂ ]_n (3).