Polymerization of 1-Phosphaisoprene: Synthesis and Characterization of a Chemically Functional Phosphorus Version of Natural Rubber

From phosphanylphosphaalkenes to coordination copper and silver polymers containing P-P bonds

This study was focused on the activation of the CP bond via reactions of Ph2CP-PtBu2 (1) with 1,6-hexanediol and selected dithiols (1,4-butanedithiol, 1,4-benzenedithiol and 1,4-benzenedimethanethiol). These reactions proceed according to a 1,2-addition mechanism, providing new compounds with formulas {(Ph)2(H)C-P-PtBu2}{μ2-(O-(CH2)6-O)}{tBu2P-P-C(H)(Ph)2} (2), {(Ph)2(H)C-P-PtBu2}{μ2-(S-(CH2)4-S)}{tBu2P-P-C(H)(Ph)2} (3a), {(Ph)2(H)C-P-PtBu2}{μ2-(S-C6H4-S)}{tBu2P-P-C(H)(Ph)2} (3b), and {(Ph)2(H)C-P-PtBu2}{μ2-(S-CH2-C6H4-CH2-S)}{tBu2P-P-C(H)(Ph)2} (3c). Next, the reactions of 3a and 3c with metal chlorides led to the growth of desired coordination polymers of copper(I) and silver(I). All the obtained compounds remained stable under atmospheric conditions.

Probing Radical Addition to 1-Phosphabutadienes by Employing Muonium as a "Light Isotope" of Hydrogen

Understanding free radical addition to multiple bonds is important to elucidating the mechanistic details of addition polymerization reactions, albeit the fleeting radical intermediates are very difficult to detect by conventional methodologies. Muon spin spectroscopy (μSR) is a highly sensitive method that can detect radical species at 106 spins (cf. EPR: 1012 spins, NMR: 1018 spins). Herein, we employ μSR to detect the radical-addition products from three 1-phosphabutadiene monomers, P-analogues of isoprene. We show that muonium (Mu), a "light" H-atom surrogate, adds predominantly at the C4 position of the P1 =C2 -C3 =C4 moiety to give unprecedented 1-phosphaallyl radicals as the major products. Our structural assignments are supported by assignment of muon, phosphorus and proton hyperfine coupling constants using DFT-calculations. A minor radical product is also detected that is tentatively assigned to an PC3 -heterocyclic free radical. On the basis of DFT-predictions, we speculate that its formation may involve initial addition of Mu+ at the C3 position followed by electron capture. These studies provide rare insights into the prospective radical (or cationic) polymerization of 1-phosphabutadienes, which have previously been polymerized using anionic initiation.

2H-Phosphindole-Enabled Dearomatization and [4+2] Cycloaddition of (Hetero)Arenes

The heavier main group multiple bonds offer an effective tool for small molecule activation. Transient 2H-phosphinidole working as a reactive phosphadiene system undergoes phospha-Diels-Alder reaction with a wide range of non-activated aromatic carbocycles and heterocycles, including naphthalene, anthracene, phenanthrene, furan, thiophene, pyrrole, pyridine, and benzo-fused heterocycles, affording concise access to a range of polycyclic fused rings feature with phosphorus at the bridgehead. These results demonstrate that non-activated (hetero)arenes are capable of acting as 2π systems in [4+2] cycloaddition with highly reactive 2H-phosphindole complex.

Chemical- and light-induced isomerization of the P=C bond of a 1-phosphabutadiene

Treatment of Mes*P=C(Si(CH3)3)Br with CH2=CHMgBr in the presence of Pd(0) affords 1-phosphabutadiene Mes*P=C(Si(CH3)3)–CH=CH2 (1) selectively as the Z isomer. Remarkably, treatment of Z-1 with n-BuLi (0.1 equiv.) resulted in quantitative formation of E-1. The exact role of the n-BuLi is unknown; however, it appears to be required to promote the isomerization in the absence of light. The isomerization of Z-1 to E-1 was also mediated by sunlight with the reaction mixture consisting of a ca. 1:9 ratio of Z-1 to E-1. DFT calculations were consistent with the thermodynamic favorability of the isomerization of Z-1 to E-1.

Diels-Alder reactions of 1-phosphabutadienes: a highly selective route to P[double bond, length as m-dash]C-substituted phosphacyclohexenes

Kinetically stabilized 1-phosphahaloprenes (2-halo-1-phosphabutadienes) as well as 1-phosphaisoprene undergo a hitherto unknown phospha-Diels-Alder dimerization of the P[double bond, length as m-dash]C-C[double bond, length as m-dash]C units upon heating. The [4+2] cyclodimerization is highly stereo- and regio-selective. The phosphaalkene-substituted phosphacyclohexene product is an unprecedented P(sp²),P(sp³) ligand that is of interest in polymer/materials science and catalysis.

Core and double bond functionalisation of cyclopentadithiophene-phosphaalkenes

Opto-electronic tuning by functionalisation of phosphorus heterofulvenoid cores. Oxidation, metal coordination at phosphorus, and substitution with donor and acceptor units at the carbon framework.

Organoiron- and Fluoride-Catalyzed Phosphinidene Transfer to Styrenic Olefins in a Stereoselective Synthesis of Unprotected Phosphiranes

Catalytic phosphiranation has been achieved, allowing preparation of trans-1-R-2-phenylphosphiranes (R = t-Bu: 1-t-Bu; i-Pr: 1-i-Pr) from the corresponding dibenzo-7-(R)-7-phospha-norbornadiene (RPA, A = C₁₄H₁₀, anthracene) and styrene in 73% and 57% isolated yields, respectively. The cocatalyst system requires tetramethylammonium fluoride (TMAF) and [Fp(THF)][BF₄] (Fp = Fe(η⁵-C₅H₅)(CO)₂). In the case of the t-Bu derivative, the reaction mechanism was probed using stoichiometric reaction studies, a Hammett analysis, and a deuterium labeling experiment. Together, these suggest the intermediacy of iron-phosphido FpP(F)(t-Bu) (2), generated independently from the stoichiometric reaction of [Fp(t-BuPA)][BF₄] with TMAF. Two other plausible reaction intermediates, [Fp(t-BuPA)][BF₄] and [Fp(1-t-Bu)][BF₄], were prepared independently and structurally characterized.

Thorium(IV) and Uranium(IV) Phosphaazaallenes

The synthesis of tetravalent thorium and uranium complexes with the phosphaazaallene moiety, [N(tBu)C=P(C6H5)]2−, is described. The reaction of the bis(phosphido) complexes, (C5Me5)2An[P(C6H5)(SiMe3)]2, An = Th, U, with two equivalents of tBuNC produces (C5Me5)2An(CNtBu)[η2-(N,C)-N(tBu)C=P(C6H5)] with concomitant formation of P(SiMe3)2(C6H5) via silyl migration. These complexes are characterized by NMR and IR spectroscopy, as well as structurally determined using X-ray crystallography.

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 P^V-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.

Reactivity studies of an imine-functionalised phosphaalkene; unusual electrostatic and supramolecular stabilisation of a σ2λ3-phosphorus motif via hydrogen bonding

Protonation with strong acids at an imine over addition to a phosphaalkene; resulting adducts display hydrogen bonding.