A survey of the state-of-the-art in the development of synthetic methods to incorporate p-block elements into polymers is given. The incorporation of main group elements (groups 13-16) into long chains provides access to materials with fascinating chemical and physical properties imparted by the presence of inorganic groups. Perhaps the greatest impedance to the widespread academic and commercial use of p-block element-containing macromolecules is the synthetic challenge associated with linking inorganic elements into long chains. In recent years, creative methodologies have been developed to incorporate heteroatoms into polymeric structures, with perhaps the greatest advances occurring with hybrid organic-inorganic polymers composed of boron, silicon, phosphorus and sulfur. With these developments, materials are currently being realized that possess exciting chemical, photophysical and thermal properties that are not possible for conventional organic polymers. This review focuses on highlighting the most significant recent advances whilst giving an appropriate background for the general reader. Of particular focus will be advances made over the last two decades, with emphasis on the novel synthetic methodologies employed.

The synthesis and study of main-group-element analogues of alkenes and alkynes containing genuine (p À p)p bonds involving p-block elements is a central theme of inorganic chemistry. [1,2] The prospect to "copy" the predictable and sophisticated reaction chemistry of C=C and CC bonds utilizing functional inorganic systems is particularly enticing. However, in many instances, the investigation of multiple bonds of heavy elements leads to fascinating, albeit unexpected, outcomes that reinforce the fundamental differences between the first and subsequent periods.Inspired by the intriguing analogy between P=C and C=C bonds in molecular chemistry, [3] we developed the addition polymerization of phosphaalkenes as a route to new functional phosphorus-containing polymers (Scheme 1). [4] Although the synthesis of phosphorus-containing macromolecules is of widespread interest because of their attractive properties and potential applications, [5] the study of the addition polymerization of P = C bonds remains in its infancy. Our studies showed that MesP=CPh 2 (1) and related monomers polymerize in the presence of radical or anionic initiators to afford poly(methylenephosphine) (Scheme 1). [6] The living anionic polymerization of 1 permits the formation of functional phosphine-containing block copolymers, [7,8] and the radical-initiated copolymerization of 1 with styrene affords random copolymers. [9] In order to explore the mechanism of radical addition to P = C bonds during polymerization, we investigated the reactions of monomer 1 with TEMPO-derived radical sources. Herein, we report the discovery of a fascinating isomerization polymerization of phosphaalkene 1 in the presence of radical alkoxyamine initiators. These striking results led to a revision of the proposed microstructure for poly(methylenephosphine) that was produced by a radical reaction.In an effort to understand the initiation step in the radical polymerization of 1, we investigated its reaction with TEMPO (1-2 equiv). 31 P NMR spectroscopic analysis of the reaction mixtures suggested the formation of multiple products, including radical species, which were detected by EPR spectroscopy. To date, none of these products have been successfully isolated or unambiguously identified. In contrast, employing the complex 1·AuCl [10,11] instead of 1 affords a single product with TEMPO. Specifically, treatment of a solution of 1·AuCl in toluene with TEMPO (1 equiv) resulted in 50 % conversion of 1·AuCl (d = 167.1) to a new species, as determined by 31 P NMR spectroscopy. Addition of more TEMPO (1 equiv, that is, 2 equiv total) resulted in complete conversion of 1·AuCl to two products in a ratio of approximately 1:3, which displayed 31 P signals at 135.6 ppm (d, J PH = 18 Hz) and 130.5 ppm (d, J PH = 18 Hz). The magnitudes of the 31 P-1 H coupling constants are not consistent with the expected product Mes(TEMPO)P(AuCl)-C-(TEMPO)Ph 2 .Colorless crystals were obtained by slow diffusion of hexanes into the reaction mixture at À30 8C. Analysis of the crystals by X-ray crys...

The synthesis of phosphaalkenes, ArP=C(R)Ph (1, a: Ar = Ph, R = Ph; b: Ar = o‐Tol, R = Ph; c: Ar = Mes, R = H), bearing sterically less hindered substituents is reported. Phosphaalkenes 1a–b were prepared by treating Ph2C=O with ArP(Li)SiMe3, whereas 1c was accessed from the AlCl3‐mediated reaction of ArP(SiMe3)2 and PhC(O)H. Both 1a and 1b dimerize to afford their respective 1,2‐diphosphetanes (2a and 2b). Compound 2a was characterized by X‐ray crystallography. Dissolution of pure 2a in THF resulted in a temperature dependent equilibrium with monomer 1a (ΔHo = –94.6 ± 14.6 kJ mol–1; ΔSo = –284 ± 48 J mol–1 K–1). Although monomer E/Z‐1c was identified in solution by its characteristic downfield 31P NMR chemical shift (δ = 247.1, 231.5), it was accompanied by the formation of what we believe are oligomers (δ = –25 to 10 ppm, br.). Attempts to trap phosphaalkenes 1a and 1b by treatment with W(CO)5(MeCN) afforded mixtures of complexes W(CO)5(1a–b) (4a–b) and W(CO)4(1a–b)2 (5a–b), the disubstituted species being subjected to X‐ray crystallographic characterization (5a).

The design of a synthetic route to a class of enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha-Peterson reaction) was used as the P=C bond-forming step. Attempted condensation of PhC(=O)Ox (Ox = CNOCH(iPr)CH(2)) and MesP(SiMe(3))Li gave the unusual heterocycle (MesP)(2)C(Ph)=CN-(S)-CH(iPr)CH(2)O (3). However, PhAk-Ox (S,E)-MesP=C(Ph)CMe(2)Ox (1 a) was successfully prepared by treating MesP(SiMe(3))Li with PhC(=O)CMe(2)Ox (52 %). To demonstrate the modularity and tunability of the phospha-Peterson synthesis several other phosphaalkene-oxazolines were prepared in an analogous manner to 1 a: TripP=C(Ph)CMe(2)Ox (1 b; Trip = 2,4,6-triisopropylphenyl), 2-iPrC(6)H(4)P=C(Ph)CMe(2)Ox (1 c), 2-tBuC(6)H(4)P=C(Ph)CMe(2)Ox (1 d), MesP=C(4-MeOC(6)H(4))CMe(2)Ox (1 e), MesP=C(Ph)C(CH(2))(4)Ox (1 f), and MesP=C(3,5-(CF(3))(2)C(6)H(3))C(CH(2))(4)Ox (1 g). To evaluate the PhAk-Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1 a and styrene were subjected to radical-initiated copolymerization conditions to afford [{MesPC(Ph)(CMe(2)Ox)}(x){CH(2)CHPh}(y)](n) (9 a: x = 0.13n, y = 0.87n; GPC: M(w) = 7400 g  mol(-1) , PDI = 1.15).

The synthesis and study of main-group-element analogues of alkenes and alkynes containing genuine (p À p)p bonds involving p-block elements is a central theme of inorganic chemistry. [1,2] The prospect to "copy" the predictable and sophisticated reaction chemistry of C=C and CC bonds utilizing functional inorganic systems is particularly enticing. However, in many instances, the investigation of multiple bonds of heavy elements leads to fascinating, albeit unexpected, outcomes that reinforce the fundamental differences between the first and subsequent periods.Inspired by the intriguing analogy between P=C and C=C bonds in molecular chemistry, [3] we developed the addition polymerization of phosphaalkenes as a route to new functional phosphorus-containing polymers (Scheme 1). [4] Although the synthesis of phosphorus-containing macromolecules is of widespread interest because of their attractive properties and potential applications, [5] the study of the addition polymerization of P = C bonds remains in its infancy. Our studies showed that MesP=CPh 2 (1) and related monomers polymerize in the presence of radical or anionic initiators to afford poly(methylenephosphine) (Scheme 1). [6] The living anionic polymerization of 1 permits the formation of functional phosphine-containing block copolymers, [7,8] and the radical-initiated copolymerization of 1 with styrene affords random copolymers. [9] In order to explore the mechanism of radical addition to P = C bonds during polymerization, we investigated the reactions of monomer 1 with TEMPO-derived radical sources. Herein, we report the discovery of a fascinating isomerization polymerization of phosphaalkene 1 in the presence of radical alkoxyamine initiators. These striking results led to a revision of the proposed microstructure for poly(methylenephosphine) that was produced by a radical reaction.In an effort to understand the initiation step in the radical polymerization of 1, we investigated its reaction with TEMPO (1-2 equiv). 31 P NMR spectroscopic analysis of the reaction mixtures suggested the formation of multiple products, including radical species, which were detected by EPR spectroscopy. To date, none of these products have been successfully isolated or unambiguously identified. In contrast, employing the complex 1·AuCl [10,11] instead of 1 affords a single product with TEMPO. Specifically, treatment of a solution of 1·AuCl in toluene with TEMPO (1 equiv) resulted in 50 % conversion of 1·AuCl (d = 167.1) to a new species, as determined by 31 P NMR spectroscopy. Addition of more TEMPO (1 equiv, that is, 2 equiv total) resulted in complete conversion of 1·AuCl to two products in a ratio of approximately 1:3, which displayed 31 P signals at 135.6 ppm (d, J PH = 18 Hz) and 130.5 ppm (d, J PH = 18 Hz). The magnitudes of the 31 P-1 H coupling constants are not consistent with the expected product Mes(TEMPO)P(AuCl)-C-(TEMPO)Ph 2 .Colorless crystals were obtained by slow diffusion of hexanes into the reaction mixture at À30 8C. Analysis of the crystals by X-ray crys...

The radical-initiated copolymerization of phosphaalkene-oxazoline, MesP[double bond, length as m-dash]C(Ph)CMe2Ox [1, Ox = CNOCH(iPr)CH2] with different loadings of styrene affords poly(methylenephosphine-co-styrene)s [2a (1 : S = 1 : 2): Mw = 7400 g mol(-1), PDI = 1.1; 2b (1 : S = 1 : 5): Mw = 18 000 g mol(-1), PDI = 1.2; 2c (1 : S = 1 : 10): Mw = 16 000 g mol(-1), PDI = 1.3]. Copolymers 2a-2c are demonstrated as viable macromolecular ligands for rhodium(i). By comparison with the crystallographically characterized model P,N-bidentate complex, [Mes(Me)P-CH(Ph)CMe2Ox·Rh(cod)]BF4, the polymer complexes [2·Rh(cod)]BF4 were prepared. The macromolecular metal complexes were characterized by GPC {for [2a·Rh(cod)]BF4: Mw = 14 000 g mol(-1), PDI = 1.2}, UV/Vis spectroscopy, (1)H, (13)C and (31)P NMR spectroscopy. Integration of the (31)P NMR spectra of mixtures of 2 and [Rh(cod)2]BF4 permitted the determination of the mol% of incorporation of monomer 1 in copolymer 2 (2a: 17%; 2b: 5%; 2c: 4%). These results compared favorably with those determined by elemental analysis (2a: 17%; 2b: 6%).

Keywords: Ligand design / Carbene ligands / Nitrogen heterocycles / Rhodium / IridiumThe synthesis and structures of Rh I and Ir I complexes bearing 4-phosphinoyl-and 4,5-bis(phosphinoyl)imidazol-2-ylidene ligands (NHC P ) is reported. Deprotonation of the corresponding imidazolium hydrogen sulfate salts by KOtBu in the presence of [M(cod)Cl] 2 afforded complexes of the formula [M(cod)Cl(NHC P )] [5a/5b: NHC P = 4-Ph 2 P(O)-IiPrMe, 5a: M = Rh, 5b: M = Ir and 7a/7b: NHC P = 4,5-{Ph 2 P(O)} 2 -InBuMe]. The Rh I complexes 5a and 7a were then converted into [Rh(CO) 2 Cl(NHC P )] 8a and 9a via reaction with carbon monoxide; the average CO stretching frequencies [8a: ν (CO) av = [a]

These studies provide the first evidence for styrene–phosphaalkene connectivities in a phosphaalkene copolymer. The synthesis and structural characterization of new phosphaalkene–oxazolines, ArPC­(Ph)­(3-C6H4Ox) [1a,b, Ar = Mes (1a), Mes* (1b), Ox = CNOCH­( i Pr)­CH2], are reported. The radical-initiated homo- and copolymerization of 1a with styrene affords P-functional poly­(methylene­phosphine) (4a: M n = 5300 g mol–1, PDI = 1.2) and poly­(methylene­phosphine-co-styrene) (5a: M n = 4000 g mol–1, PDI = 1.1). Multinuclear NMR spectroscopic analyses of 4a and 5a provided evidence for the predominance of an addition-isomerization mechanism for the radical polymerization of 1a. In addition, signals could be assigned to CHPh–P­(CHPhAr) (i.e., S–1a) and ArCH2–CH2 (i.e., 1a–S) linkages in copolymer 5a. With a monomer feed ratio of 1a:S (1:2, 33 mol % 1a) the inverse gated 13C­{1H} NMR spectrum suggested an incorporation of 19 mol % 1a in copolymer 5a. Polymers 4a and 5a were further functionalized to Au­(I)-containing macromolecules [4a·AuCl: M n = 13 000, PDI = 1.2; 5a·AuCl: M n = 7500, PDI = 1.1].