Phosphine-borane polymer

The preparation of phosphine-borane polymer (Figure 9.15) was reported. It was claimed to be a lire retardant but no lire test results were given98... 

Manners, I. and H. Dorn, 2002. Linear phosphine-borane polymers and methods of preparation therefore. U.S. Patent 6,372,873. 

ROM has been used to prepare phosphine-containing polymer supports (Scheme 20). Norbornyl-substituted monomer 22 was prepared in two steps from d-bromo-iodobenzene. This was then polymerized with diene 23. It was initially envisioned that it would be necessary to convert the phosphine to the borane adduct in order not to poison the metathesis catalyst. Although protection was needed when using the Grubb s type 1 complex as a catalyst, when employing the more active second-generation complex 24, the free phosphine monomer could be used. This has been attributed to the lower affinity of the active form of the catalyst toward coordination of phosphines due to the presence of the electron-rich heterocyclic carbene ligand. 

The addition of reagents containing X-H bonds in which X is more electronegative than H typically lead to addition across the M-C bond in the direction opposite to the addition of silane or borane to the early metal catalysts. Polymerization of etiiylene with lanthanide catalysts in the presence of phosphines generates phosphine-terminated polymers (Scheme 22.12) - by a mechanism in which the alkyl chain is protonated, and a metal-phosphido complex is generated. This phosphido complex then inserts olefin to start the growth of a phosphine-functionalized polyolefin. Marks subsequently showed that a similar process can be conducted witii amines. In this case, the bulky dicyclohexylamine was needed to sufficiently retard the rate of protonation to allow chain growth. The steric bulk also makes the olefin insertion more favorable thermodynamically. 

Polyphosphinoboranes containing phosphorus and boron linked to each other in polymeric chains have remained elusive for a long time. Recently, catalytic dehydrogenation of the phosphine-borane adducts has been found to be effective to prepare the linear polymer. Thus, thermal treatment of PhPH2.BH3 in the presence of catalytic amounts of [(l,5-COD)Rh( j,-Cl)] affords the linear polymer poly(phenylphosphinoborane), [PhHPBH2]n (see Eq. 1.13) [28-30]. High polymers with of about 33,000 have been isolated by this procedure. 

Polyphosphinoboranes, [RPH-BH2]n, are a recent class of polymers that contain a P-B repeat unit in the polymer backbone [25, 26]. These polymers are prepared by a rhodium-catalyzed dehydropolymerization procedure. The monomers that have been used for these polymers are the phosphine-borane adducts, RPH2.BH3. Dehydropolymerization of these adducts occurs by the use of rhodium complexes such as [ Rh(p-Cl)(l,5-cod) 2] or even by simple rhodium salts such as RhCU or RhCl3.xH20. The polymerization is carried out in neat conditions (no solvent) (see Eq.5.13). 

The molecular weights of these polymers have been determined by various methods. For example, the molecular weights (M ) of [PhPHBH2]n and [iBuPHBH2]n as determined by static light scattering methods are 20,000 and 13,100, respectively. The phosphorus chemical shifts of the phosphine-borane adducts and the linear polymers are nearly similar. Thus, while the P-NMR signal of PhPHz.BHj is at -47 ppm, the linear polymer resonates at -48.9 ppm. 

Adducts of secondary phosphines have also been studied in the context of MO VCD precursors,29 as well as the dehydrocoupling of borane and phosphines to form B-P bond-based polymers.158 Low to medium molecular weight poly(phenylphosphino-boranes) were isolated in the B(C6F5)3 catalyzed dehydrocoupling of PhPH2 BH3. 

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