Reaction of the Cyclic Thionylphosphazene NSOCl[NPCl2]2 with Halide Abstraction Agents: An Ambient Temperature Ring-Opening Polymerization (ROP) Route to Poly(thionylphosphazenes)

Polymers and the p-block elements

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.

Polymeric materials based on main group elements: the recent development of ambient temperature and controlled routes to polyphosphazenes

This Perspective discusses the development of new routes to polyphosphazenes, [R(2)P[double bond, length as m-dash]N](n), that occur at ambient temperature and, in some cases, allow molecular weight control and access to narrow molecular weight distributions and block copolymers. For example, the room temperature silyl-carborane initiated ring-opening polymerisation of (NPCl(2))(3) is described together with chain growth condensation polymerisations of phosphoranimines Cl(3)P[double bond, length as m-dash]NSiMe(3) and BrMePhP[double bond, length as m-dash]NSiMe(3). Recent works on donor-stabilised cationic phosphoranimines are also discussed.

Phosphorus Copies of PPV: π-Conjugated Polymers and Molecules Composed of Alternating Phenylene and Phosphaalkene Moieties

A new class of pi-conjugated macromolecule, poly(p-phenylenephosphaalkene) (PPP), is reported. PPPs are phosphorus analogues of the important electronic material poly(p-phenylenevinylene) (PPV) where P=C rather than C=C bonds space phenylene moieties. Specifically, PPPs [-C(6)R(4)-P=C(OSiMe(3))-C(6)R'(4)-C(OSiMe(3))=P-](n)() (1: R = H, R' = Me; 11: R = Me, R' = H) were synthesized by utilizing the Becker reaction of a bifunctional silylphosphine, 1,4-C(6)R(4)[P(SiMe(3))(2)](2), and diacid chloride 1,4-C(6)R'(4)[COCl](2). Several model compounds for PPP are reported. Namely, mono(phosphaalkene)s R-P=C(OSiMe(3))-R' (4: R = Ph, R' = Mes; 7: R = Mes, R' = Ph), C-centered bis(phosphaalkene)s R-P=C(OSiMe(3))-C(6)R'(4)-C(OSiMe(3))=P-R (5: R = Ph, R' = Me; 8: R = Mes, R' = H), and P-centered bis(phosphaalkene)s R-C(OSiMe(3))=P-C(6)R'(4)-P=C(OSiMe(3))-R (6: R = Mes, R' = H; 10: R = Ph, R' = Me). Remarkably, selective Z-isomer formation (i.e., trans arylene moieties) is observed for PPPs when bulky P-substituents are employed while E/Z-mixtures are otherwise obtained. X-ray crystal structures of Z-7, Z,Z-8, and Z,Z-10 suggest moderate pi-conjugation. The twist angles between the P=C plane and unsubstituted arenes are 16 degrees -26 degrees , while those between the P=C plane and methyl-substituted arenes are 59 degrees -67 degrees . The colored PPPs and their model compounds were studied by UV/vis spectroscopy, and the results are consistent with extended pi-conjugation. Specifically, weakly emissive polymer E/Z-1 (lambda(max) = 338 nm) shows a red shift in its absorbance from model E/Z-4 (lambda(max) = 310 nm), while a much larger red shift is observed for Z-11 (lambda(max) = 394 nm) over Z-7 (lambda(max) = 324 nm).

Anionic ring-opening polymerization of a strained phosphirene: A route to polyvinylenephosphines

A strained 1-phenyl-2,3-dimethylphosphirene undergoes anionic ring-opening polymerization upon initiation with n-butyl lithium at ambient temperature to yield polyvinylenephosphine, an unsaturated organophosphorus polymer.

Synthesis and properties of Ph2S(=N-(Ph2)S[triple bond]N)2

A new type of lambda6-sulfanenitrile with an SN triple bond at both ends, Ph2S(=N-(Ph2)S[triple bond]N)2 (5), was prepared in excellent yield from the one-pot synthesis of diphenylsulfimide (Ph2SNH) with fluoro(diphenyl)-lambda6-sulfanenitrile (Ph2FSN) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene. Its molecular structure was determined by X-ray crystallographic analysis. Compound 5 reacted further with methyl triflate and trifluoromethanesulfonic anhydride to afford the corresponding bis-N-methylated and -N-sulfonated compounds.

Reversible Skeletal Transmetalations of Inorganic Rings: Isolation of Aluminatophosphazenes, a Zwitterionic Phosphazene, and a Donor-Stabilized Alumazine−Phosphazene Hybrid Cation

Synthesis of the cyclic aluminatophosphazene ring N(PCl2NMe)2AlMeCl (5) has been achieved via a skeletal transmetalation reaction between AlMe3 and the boratophosphazene N(PCl2NMe)2BCl2 (1). Reaction of 5 with various halogenated Lewis acids such as GaCl3 yielded the fully chlorinated aluminum heterocycle N(PCl2NMe)2AlCl2 (8) through a methyl-halogen exchange process. In contrast, treatment of 5 with excess AlMe3 resulted in complete methylation at aluminum to give N(PCl2NMe)2AlMe2 (6). Compound 5 was reacted with various Ag+ salts with weakly coordinating anions, including Ag[OSO2CF3], which afforded the triflate-substituted heterocycle N(PCl2NMe)2AlMe(OSO2CF3) (9). The reaction of 5 with Ag[BF4] surprisingly produced the previously known fluorinated boratophosphazene N(PCl2NMe)2BF2 (10). The transformation of 1 to 5 and then to 10 represents a rare, formally reversible, skeletal transmetalation process involving boron and aluminum. Treatment of 5 with Ag[PF6] led to the insertion of phosphorus in place of aluminum to form the novel zwitterionic fluorinated phosphorus(V) heterocycle N(PCl2NMe)2PF4 (11). The ethyl-substituted aluminatophosphazene N(PCl2NMe)2AlMeEt (14) reacted cleanly with a 1:1 mixture of [Ph3C][B(C6F5)4] and THF to give the novel donor-stabilized alumazine-phosphazene hybrid cation, [7.THF]+, as the [B(C6F5)4]- salt [N(PCl2NMe)2AlMe.THF][B(C6F5)4] (15).

Gallium Halide Induced Heterocycle Expansion of Dihalodiphosphadiaryldiazanes [(XPNR)2] to the Corresponding Triphosphatriazanes [(XPNR)3]

Reactions of the cyclic diphosphadiazanes (XPNR)(2) (X = Cl, Br; R = 2,6-dimethylphenyl = Dmp, 2,6-diisopropylphenyl = Dipp) with GaX(3) followed by 4-(dimethylamino)pyridine (DMAP) give the corresponding trimers (XPNR)(3). An unusual cyclophosphazanium tetrachlorogallate salt [(DippN)(3)P(3)Cl(2)][GaCl(4)] has been isolated from the reaction of (ClPNDipp)(2) with GaCl(3) and represents an intermediate in the disproportionation process. Dissociation of the gallate ion on reaction of [(DippN)(3)P(3)Cl(2)][GaCl(4)] with DMAP releases a halide ion, which associates with the dicoordinate phosphenium center to give (ClPNDipp)(3). The observations indicate that the presence of medium-sized substituents at nitrogen (R) thermodynamically destabilize the dimer with respect to the trimer, without offering sufficient stabilization of the monomer, as observed for MesNPX (Mes* = 2,4,6-tri-tert-butylphenyl) (Mes* > Dipp > Dmp). Nevertheless, lability of the N-P bond in these derivatives of (XPNR)(2) allows for transformations between dimer and trimer that may include transient existence of the corresponding monomer. Manipulation of substituent steric strain to modify the relative stability of phosphazane oligomers provides a new methodology for diversification of phosphazane chemistry.

Synthesis of linear and cyclic carbophosphazenes via an oxidative chlorination strategy

The use of a mild, oxidative chlorination route for the synthesis of linear and cyclic carbophosphazenes is described. For example, chlorination of the linear PNCN chain Ph(2)P-N=C(Ph)-N(SiMe(3))(2) (1) with C(2)Cl(6) led to the clean formation of the previously known 8- and 6-membered rings [Ph(2)PNC(Ph)N](2) (2) and [Ph(2)PNC(Ph)NP(Ph)(2)N] (3), respectively. In a similar fashion, the N-alkyl-substituted PNCN derivatives, Ph(2)P-N=C(Ph)-N((t)Bu)SiMe(3) (4) and Ph(2)P-N=C(Ph)-N(i)Pr(2) (7) were readily converted by C(2)Cl(6) into the halogenated derivatives ClPh(2)P=N-C(Ph)=N(t)Bu (5) and [ClPh(2)P=N=C(Ph)-N(i)Pr(2)]Cl (8), respectively. Protonation of 5 was accomplished using HCl and gave the carbophosphazenium salt [ClPh(2)P=N-C(Ph)=N((t)Bu)H]Cl (6). In addition, the isolation of a rare 8-membered P(2)N(4)C(2) heterocycle [(Cl(3)P=N)ClPNC(Ph)NP(Cl)(2)NC(Ph)N] (9) from the reaction of PCl(5) and Li[PhC(NSiMe(3))(2)] is reported. Treatment of 9 with one equivalent of GaCl(3) led to the discovery of an unusual Lewis acid-induced ring contraction reaction whereby the (PNCN)(2) ring in 9 is converted into the novel 6-membered P(2)N(3)C heterocyclic adduct [(Cl(3)P=N)ClPNP(Cl)(2)NC(Ph)N].GaCl(3) (10) with concomitant release of PhCN. Structural characterization of compounds 1, 5, 6, and 8-10 by single-crystal X-ray diffraction is also provided.

Syntheses and reactions of the fluorinated cyclic thionylphosphazene NSO(Ar)[NPF(2)]2(Ar = 4-t-BuC(6)H(4)-) with difunctional reagents

The S-aryl substituted thionylphosphazene (Cl(2)PN)(2)[4-t-BuC(6)H(4)(O)SN] (1) was prepared by Friedel-Craft's reaction of NSOCl(NPCl(2))(2) with tert-butylbenzene. When it reacted with excess KSO(2)F at 110 degrees C, the P-Cl bonds of 1 were fluorinated, yielding the tetrafluorothionylphosphazene, (F(2)PN)(2)[4-t-BuC(6)H(4)(O)SN] (2). An equimolar reaction of 2 with dilithiated 1,3-propanediol in THF at -78 degrees C resulted in the formation of the ansa-substituted compound CH(2)(CH(2)O)(2)[FPN](2)[4-t-BuC(6)H(4)(O)SN] (3). The crystal structures of 2 and 3 were determined. In 3 the ansa ring is trans on the PNS heterocycle with respect to the aryl group. Reaction of 2 with the disiloxane (CF(2)CH(2)OSiMe(3))(2), in the presence of catalytic amounts of CsF in THF at 90 degrees C, resulted in the formation of the dispiro compound [(CF(2)CH(2)O)(2)PN](2)[4-t-BuC(6)H(4)(O)SN] (4). Compounds 1-4 were characterized by IR, NMR ((1)H, (13)C, (19)F, (31)P), mass spectral, and elemental analyses.

Synthesis and reactivity of perhalogenated acyclic and metallacyclic tantalum(V) phosphoraniminato complexes: discovery of an unexpected ligand coupling reaction to form the novel phosphazenium salt

The reaction of TaCl5 with a single equivalent of Cl3P=NSiMe3 resulted in the isolation of the perhalogenated (phosphoraniminato) tantalum(V) complex TaCl4(N=PCl3) (1). Reaction of 1 with an excess of THF and subsequent cooling produced crystals of TaCl4(N=PCl3)(THF) (1.THF), which possesses a distorted octahedral Ta center with a THF molecule coordinated trans to the phosphoraniminato ligand. The reaction of 1 with the aminophosphoranimine, (Me3Si)2NPCl2=NSiMe3, resulted in a [3 + 1] cyclocondensation reaction to form the metallacyclic complex, TaCl3(N=PCl3)[N(SiMe3)PCl2N(SiMe3)] (2), which contains a TaNPN four-membered ring and a phosphoraniminato ligand (N=PCl3). The analogous [3 + 1] cyclocondensation reaction between (Me3Si)2NPCl2=NSiMe3 and TaCl5 led to the isolation of TaCl4[N(SiMe3)PCl2N(SiMe3)] (3). An attempt to cleave the NPN ligand from the Ta center in 2 via protonolysis with HCl led to an unusual phosphoraniminato ligand coupling reaction to yield the novel phosphazenium salt [N(PCl2NH2)2][TaCl6] (4). All new compounds (1.THF and complexes 1-4) were characterized by single-crystal X-ray diffraction.