Complexed PHBs

The yellow, four-coordinated high-spin (S = 2) chloride complex [PhB(CH2PPh2)3]FeCl 155 (as well as corresponding bromo and iodo derivatives) was obtained by the interaction of the T1 complex 153a (R = Ph) with FeCl2 <2003JA322>. 

In a similar way to the corresponding thallium salts 153, cobalt(n) complexes [PhB(CH2PPh2)3]CoI 156 <2001CC2152>, [PhBtCfTPTr lCoCl 157, and [PhB(CH2PiPr2)3]CoI 158 <2003IC5074> iron(n)... 

Reduction of low-spin Fe(m) imide 165 with hydrogen (1 atm, 20 °C) proceeds stepwise leading first to anilido complex 168 and then to 77-cyclohexadienyl complex 169 via hydrogenolysis of the Fe=NR linkage (Scheme 64). It should be mentioned that the similar low-spin cobalt complex [PhB(CH2PPh2)3]Co N-/>-Tol is stable to hydrogen pressure (1-3 atm) up to 70 °C <2004JA4538>. 

Treatment of the yellow chloride 159 with lithium diphenylamide gave rise to a thermally stable red iron amide complex [PhB(CH2PiPr2)3]FeNPh2, which was characterized structurally <2004JA6252>. 

Freeze-fracture electron microscopy studies of the membranes of E. coli and A. vinelandii by Reusch et al.24 provide evidence of structural changes that support the fluorescence data (Figure 10). Freeze-fracture micrographs of log-phase cells show a typical mosaic of particles and pits on both concave and convex surfaces of the plasma membranes. However, as complexed PHB was increasingly incorporated into the membranes, as determined by analysis of the purified membranes and evidenced by the intensity of the thermotropic transition at - 56 °C, the micrographs revealed the formation of small semi-regular plaques in the plasma membranes (arrows) that possess shallow particles. The plaques grew in size and frequency as the concentration of membrane PHB and intensity of the PHB/polyP transition increased. 

Recently, iron(V) nitride complex [PhB( Bulm)3Fe =N]BArF24 (PhB( Bulm)3 = phenyltris(3-tert-butylimidazol-2-ylidene)borato BArp24 = B(3,5-(CF3)2QH3)4 ) has been prepared [100]. This complex has a four-coordinate iron ion with a terminal nitride ligand. The characterization of the complex by Mossbauer and electron paramagnetic resonance spectroscopy demonstrated d iron(V) metal center in a low-spin (S= 1/2) electron configuration. The decomposition of the complex by water at low temperature formed ammonia and iron(ll) species. 

An improved synthesis of MeB(OH)2 was described via the reaction of B(OCHM 3 with MeLi and subsequent hydrolysis the compounds are useful intermediates for the preparation of technetium-99m dioxime complexes. PhB(OCH2CF3)2 was... 

The complexed PHB that has been found in eukaryotes [83, 84] is in too minute amounts to serve as reserve material. Its biological function has still not been totally explained. 

Complex 165 reacts with CO at room temperature to give />-tolyl isocyanate and the golden dicarbonyl compound 166. The latter can also be generated by reaction of 164 with excess of CO and converted back to imide 165 by the addition of 2 equiv of /> toly 1 azide (2003JA322). Reaction of cobalt(m) imide 167 analogous to 165, available from [PhB(CH2PPh2)3]CoI 156 by the same procedure as for 165, with CO proceeds similarly <2002JA11238>. 

Anionic complexes of boron (boronates, borinates, etc.) have been introduced as convenient reagents in cross-coupling reactions of broad scope, particularly interesting for the transfer of alkynyl and primary alkyl residues, which cannot be accomplished using the standard protocols of the Suzuki-Miyaura reaction. Readily available Ph4BNa can be used as a convenient reagent for phenylation in place of the much more expensive PhB(OH)2, and all four phenyl groups can be utilized when the reaction is carried out with a phosphine-free catalyst in aqueous solutions.244... 

A more substantial departure from the classical pyrazolylborate motif is the replacement of two pyrazolyl moities with / rZ-butylthiomethyl groups, a substitution which creates A,A,A-donor ligands. Thus, metallation of PhB(Pz)(CH2SBut)2 with dimethylzinc furnished the monomethylzinc complex 157 (Figure 72). 

Most of this section is devoted to derivatives containing CO and Cp-type ligands. An exception is a family of coordinatively unsaturated, silyl complexes LFeSiR2R involving the tripodal ligand [PhB(CH2PPr 3)3]-.170... 

The C4 aldol intermediate of the Weizmann process is also key in the aerobic fermentation of sugars to poly(3-hydroxybutyric acid) or PHB (-0[-CH(CH3)-CH2-COO - [70]. This natural and biodegradable polymer is produced inside microorganisms, e.g., Ralstonia eutropha. A complex processing is required to extract and purify the polymer granules from the microorganism. 

Here and are the equilibrium bond lengths and xh and hb are the parameters that describe the decreasing bond order. It is obvious that at or rxH = the Pxh and Phb transform to unity. Then, going to the hydrogen bound to bo X and B atoms in a hydrogen-bonded complex X-H- B, its total valence remains equal to unity ... 

Fig. 27 Highly active amino-alkoxy-bis(phenolate)yttrium complexes, which yield syndiotactic PHB in a very controlled manner...

A completely new type of ROP catalyst was recently reported by Rieger and coworkers. Chromium salphen complexes (Fig. 32) convert racemic (3-BL to slightly isotactic-enriched PHB (0.60 < Pm < 0. 70) with a molecular weight of up to 800,000 g/mol (PD up to 8.5). These catalysts combine high activity and high molecular weight products, featuring the desired stereocontrol at moderate reaction conditions [13]. 

NMR (CeDg, 125.7 MHz, 25°C) 139.8, 132.5, 128.8-129.1 (overlapping resonances), 124.6, 17.0 (br). B NMR (CgDg, 128.3 MHz, 25°C) -10.96 ppm. The compound is a versatile precursor to a wide range of transition metal complexes supported by the tris(phosphino)borate ligand. It is air- and water-stable for extended periods, and, unlike the lithium and ammonium salts of [PhB(CH2PPh2)3] , it is both soluble and stable in chloroform and dichloromethane for days, making these useful solvents available for subsequent trans-metallation chemistry. 

The final stage of this investigation was to study the reaction of the hydroxy dimer 7 with phenylboronic acid to test whether 7 is able to undergo efficient phenylation. The reaction with PhB(OH)2 was found to proceed smoothly and, when conducted in the presence of PPh3, gave the stable four-coordinate complex 4 which had already been characterised, Scheme 12.4. As 4 was already known to be effective as a pro-catalyst (see above), this process formally closed the circle to constitute a very convincing and conclusive collection of experiments. 

Headspace-GC-MS analysis is useful for the determination of volatile compounds in samples that are difficult to analyze by conventional chromatographic means, e.g., when the matrix is too complex or contains substances that seriously interfere with the analysis or even damage the column. Peak area for equilibrium headspace gas chromatography depends on, e.g., sample volume and the partition coefficient of the compound of interest between the gas phase and matrix. The need to include the partition coefficient and thus the sample matrix into the calibration procedure causes serious problems with certain sample types, for which no calibration sample can be prepared. These problems can, however, be handled with multiple headspace extraction (MHE) [118]. Headspace-GC-MS has been used for studying the volatile organic compounds in polymers [119]. The degradation products of starch/polyethylene blends [120] and PHB [121] have also been identified. 

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