P. C. Bharara

31P and 1H NMR studies of the transesterification polymerization of polyphosphonate oligomers

Abstract Polymeric phosphonate esters are an interesting class of organophosphorus polymers because both the polymer backbone and phosphorus substituents can be modified. These polymers have been prepared by ring-opening polymerizations of cyclic phosphites, stoichiometric polycondensations of dimethyl phosphonate with diols in conjunction with diazomethane treatment and by transesterification of polyphosphonate oligomers. Our initial attempts to prepare high molecular weight polymeric phosphonate esters by the transesterification methods were unsuccessful. Results indicate that the reactions of dimethyl phosphonate with diols to form polyphosphonate oligomers with only methyl phosphonate end groups are plagued by a serious side reaction that forms phosphonic acid end groups. These end groups do not participate in the transesterification reaction and limit the molecular weights of the polymers that can be obtained. The phosphonic acid end groups can be converted into reactive methyl phosphonate end groups by treatment with diazomethane, however diazomethane is explosive and the polymerization is slow. An alternative route for the production of high molecular weight polymers is the transesterification of the 1,12-bis(methyl phosphonato)dodecane, formed by the reaction of excess dimethyl phosphonate and 1,12-dodecanediol, with a Na 2 CO 3 promoter. This allows polymers with molecular weights of up to 4.5×10 4 to be prepared, and no phosphonic acid end groups are observed in these polymers. Thermal analyses of the poly(1,12-dodecamethylene phosphonate) have shown that this polymer has reasonable thermal stability (onset of thermal decomposition at 273 °C). This polymer also undergoes a cold crystallization process at 15 °C similar to that which has been observed in some polyesters, polyamides and elastomers.

N-Methylaminoalkoxides of Zirconium

Abstract N-Methylaminoalkoxides of zirconium of the type, Zr(OPri)4-n(O.CHR′.CH2.NR″R′)n, where R′ = R′ = H, R′ = Me; R′ = H, R′ = R′ = Me; R′ = R′ = R′ = Me; and n = 1–4, have been synthesized by the reactions of zirconium isopropoxide with aminoalcohols. These are characterized by elemental analyses and IR spectra. Insertion reactions of zirconium aminoalkoxides have been studied for the first time and have been shown to yield interesting derivatives with Zr-N bonds.

Titanocene and zirconocene dichloride derivatives with hydroxylic reagents

Abstract The reaction of Cp 2 TiCl 2 (Cp = C 5 H 5 ) with ethanol in the presence of Et 3 N in acetonitrile yields the derivatives CpTiCl(OEt) 2 or CpTiCl 2 (OEt). Similar reactions of Cp 2 MCl 2 (M = Ti or Zr) with glycols (GH 2 = 1,2-propanediol, 2,3-butanediol, pinacol or hexylene glycol) or fluoro-β-diketones (KeH = hexafluoroacetylacetone(hfa), benzoyltrifluoroacetone (bta) or 2-thenoyltrifluoroacetone (tta)) gave CpMCl(G) or CpMCl(Ke) 2 .

Alcoholate complexes of chromium(III) chloride

SummaryA number of alcoholate complexes of chromium chloride with the general formula, CrCl3 · xROII (R = Me, Et, i-Pr, n-Bu and n-Ilexyl; x = 3 and 4) have been synthesized by the reactions of CrCl3 · 3 TIIF with an excess of the appropriate alcohols under reflux. Physicochemical studies such as i.r., visible reflectance, electron spin resonance spectra and thermogravimetric measurements, in addition to elemental analyses, throw light on the structure of these complexes.

Fluoro-β-Diketone Derivatives of Titanium

Abstract Fluoro-β-diketone derivatives of titanium of the general formula (OR)4 −nTi [OC(CF3) = CHCOR′]n (R = Et and Pr1; R′ = CF3. Ph and C4H3S and n = 1 or 2), have been synthesized by the reaction of titanium alkoxides with fluoro-β-diketones. A few interchange reactions with tertiary butyl or amyl alcohols have also been studied.

Preparation of dichloro(2,4,6-tribromophenoxy)(1,2-diphenoxy)phosphorane and its nonoxidative chlorination reactions with alkyl and aryl phosphonates

Abstract The reaction of tetrachloro(2,4,6-tribromophenoxy)phosphorane, (TBPO)PCl 4 , with o -catechol yields dichloro(2,4,6-tribromophenoxy)(1,2-diphenoxy)phosphorane, (TBPO)(DP)PCl 2 . Quantitative 31 P[ 1 H] NMR spectroscopic studies demonstrate that this compound quantitatively converts secondary phosphonates into chlorophosphites. The chlorophosphites have been characterized by their reactions with tetracarbonylnorbornadienemolybdenum(0), Mo(CO) 4 (NBD), to form cis -Mo(CO) 4 (P(OR) 2 Cl) 2 . These reactions are also quantitative. The (TBPO)(DP)PCl 2 has major advantages over other nonoxidative chlorinating agents. The compound can be prepared in quantitative yield from stoichiometric amounts of the starting materials, the synthesis of the (TBPO)(DP)PCl 2 and the subsequent nonoxidative chlorination reaction can be carried out in one pot, and the byproduct of the reaction does not contain active chlorides.

31P{1H} NMR Studies of the Preparation of Dichlorotris(2,4,6-tribromophenoxy)phosphorane, Trichlorobis(2,4,6-tribromophenoxy)phosphorane and Tetrachloro(2,4,6-tribromophenoxy)phosphorane, and their Nonoxidative Chlorination Reactions with Dimethyl Phosphonate

Dichlorotris(2,4,6-tribromophenoxy)phosphorane can serve as a nonoxidative chlorinating agent for the conversion of secondary phosphites into chlorophosphites. However, the route reported for the synthesis of this material only gives a 22% yield, and the product contains significant impurities. To better understand the reasons for this poor yield, detailed 31P{1H} NMR studies of the reactions of phosphorus pentachloride with one, two and three equivalents of 2,4,6-tribromophenol have been carried out. These studies demonstrate that mixtures of the phosphoranes in which one, two and three of the chlorides are substituted by 2,4,6-tribromophenoxy groups are obtained even when a 3: 1 ratio of the phenol to PCl5 is used. Studies of the reactions of these mixtures with dimethyl phosphonate indicate that all three phosphoranes are equally capable of transforming dimethyl phosphonate into dimethyl chlorophosphonite in quantitative yield. The more highly substituted phosphoranes are very sensitive to water and di...

Poly(alkylene Phosphates): Synthetic Strategies

Poly(alkylene phosphate)s are an interesting class of polymers because both the polymer chain and the polymer substituents can be readily varied. Several synthetic methods are available for the preparation of these polymers. The most versatile involve poly(alkylene phosphonate) s as intermediates. Two of the most promising methods for the preparation of poly(alkylene phosphonate)s are the ring opening polymerizations of cyclic phosphonates and the condensation polymerizations of dimethyl phosphite and dialcohols. The ring opening polymerizations of the cyclic phosphonates catalyzed by triisobutylaluminum are very sentitive to the nature of the alkylene group. With R = −(CH2)3−, the polymerization gives a monomer: polymer mole ratio of 1:1. The polymer can be readily separated from the monomer using fractional precipitation, and the polymer only very slowly reeuilibrates to form monomer. In contrast, with R = −(CH2)2− the polymerization occurs without catalyst to give a monomer: polymer mole ratio of 1:9. The polymer is of very low molecular weight and cannot be separated from the monomer by fractional crystallization due to rapid reequilibration. With R = −(CH2CH(CH2OMe))−, no polymerization occurs in the absence of a catalyst, and the polymerization gives a monomer: polymer mole ratio of 1:1. Attempts to purify the polymer by fractional crystallization gave poor yields of the polymer. Reaction of the −(CH2)2− or −(CH2CH(CH2OMe))− monomer-polymer mixtures with chlorine and then with either imidazole and methanol or with excess diethylamine gives poly(alkylene phosphate)s that are readily separated from the monomeric impurities by fractional precipitation. The condensation polymerizations of dimethyl phosphite with triethylene glycol and 1,12-dodecanediol have been carried out and followed by 1H, 13C and 31P NMR spectroscopy. These studies indicate that, under the reaction conditions used in these polymerizations, the polymers form at a much lower temperatures than are reported in the literature, and that the first step in the polymerization appears to be displacement of one of the methoxy groups from the phosphite by one mole of the diol. Attempts to generate higher molecular weight polymers by heating the reaction mixture to 180 – 200 °C for long periods of time caused decomposition of the polymers.