“…Preparation of α-hydroxyl-ω-(carboxylic acid) PCL's (HA-PCL's) was carried out by bulk polymerization at 150 °C using water as co-initiator (see Scheme ). “In situ” thermal conversion of ammonium heptamolybdate (NH 4 ) 6 [Mo 7 O 24 ] (Hep) to ammonium decamolybdate (the actual catalytic species (NH 4 ) 8 [Mo 10 O 34 ], (Dec)) takes place at this temperature. ,, It is important to note that under these reaction conditions (a) reaction times are reasonable (on the order of 2 h) and (b) monomer diffusion is promoted, as the reaction product (namely, poly(ε-caprolactone)) remains melted during polymerization. 1 …”
Asymmetric telechelic α-hydroxyl-ω-(carboxylic acid) poly(ε-caprolactone) (HA-PCL) and
α-hydroxyl-ω-(carboxylic acid) poly(δ-valerolactone) (HA-PVL) were synthesized by ring-opening polymerization of ε-caprolactone (CL) and δ-valerolactone (VL), respectively. HA-PCL oligomers were obtained
at 150 °C in 2 h using ammonium decamolybdate (NH4)8[Mo10O34] as catalyst and water as initiator. A
control of the number-average molecular weight (measured by NMR) can be achieved in the range between
212 and 2198 Da, based on the initial monomer/initiator ratio. Number-average molecular weight (M
n)
shows a linear dependence with CL/H2O ratio in this range. The nature of hydroxyl and carboxylic acid
end groups of HA-PCL and HA-PVL was studied by MALDI-TOF and 1H and 13C NMR. Changes in the
chemical shifts observed in the NMR spectra as a function of molecular weight were explained in terms
of hydrophobic interactions. Formation of macrocyclic species was studied by MALDI-TOF. It was found
that macrocyclic species are favored at longer reaction times. Insertion of alcohols and polycondensation
reactions occurring after complete monomer conversion were also studied. Alcohol insertion for this system
depends on the nature of alcohol. Polycondensation reactions vary with reaction times and affect the
polymer molecular weight in a nonlinear manner. Finally, the α-hydroxyl-ω-(sodium carboxylate) PCL
salt (HC-PCL) was prepared from HA-PCL and characterized by FT-IR and solution and solid-state NMR.
Important differences between CP-MAS and MAS spectra are observed and discussed in terms of
morphology and polarization transfer.
“…Preparation of α-hydroxyl-ω-(carboxylic acid) PCL's (HA-PCL's) was carried out by bulk polymerization at 150 °C using water as co-initiator (see Scheme ). “In situ” thermal conversion of ammonium heptamolybdate (NH 4 ) 6 [Mo 7 O 24 ] (Hep) to ammonium decamolybdate (the actual catalytic species (NH 4 ) 8 [Mo 10 O 34 ], (Dec)) takes place at this temperature. ,, It is important to note that under these reaction conditions (a) reaction times are reasonable (on the order of 2 h) and (b) monomer diffusion is promoted, as the reaction product (namely, poly(ε-caprolactone)) remains melted during polymerization. 1 …”
Asymmetric telechelic α-hydroxyl-ω-(carboxylic acid) poly(ε-caprolactone) (HA-PCL) and
α-hydroxyl-ω-(carboxylic acid) poly(δ-valerolactone) (HA-PVL) were synthesized by ring-opening polymerization of ε-caprolactone (CL) and δ-valerolactone (VL), respectively. HA-PCL oligomers were obtained
at 150 °C in 2 h using ammonium decamolybdate (NH4)8[Mo10O34] as catalyst and water as initiator. A
control of the number-average molecular weight (measured by NMR) can be achieved in the range between
212 and 2198 Da, based on the initial monomer/initiator ratio. Number-average molecular weight (M
n)
shows a linear dependence with CL/H2O ratio in this range. The nature of hydroxyl and carboxylic acid
end groups of HA-PCL and HA-PVL was studied by MALDI-TOF and 1H and 13C NMR. Changes in the
chemical shifts observed in the NMR spectra as a function of molecular weight were explained in terms
of hydrophobic interactions. Formation of macrocyclic species was studied by MALDI-TOF. It was found
that macrocyclic species are favored at longer reaction times. Insertion of alcohols and polycondensation
reactions occurring after complete monomer conversion were also studied. Alcohol insertion for this system
depends on the nature of alcohol. Polycondensation reactions vary with reaction times and affect the
polymer molecular weight in a nonlinear manner. Finally, the α-hydroxyl-ω-(sodium carboxylate) PCL
salt (HC-PCL) was prepared from HA-PCL and characterized by FT-IR and solution and solid-state NMR.
Important differences between CP-MAS and MAS spectra are observed and discussed in terms of
morphology and polarization transfer.
“…Two linkage isomers have been observed (Figure ). The stereochemical positions of the groups X are the same in [Mo 8 O 26 X 2 ] 4- (X = pyridine 77 imidazole, pyrazole 92 ), [Mo 8 O 26 X 2 ] 6- (X = NCS, HCO 2 ,), [Mo 8 O 26 (OH) 2 ] 6- ,101a [Mo 8 O 26 X 2 ] 2- (X = d - or l -lysH 2 ),101b [Mo 8 O 24 (OH) 2 (metO) 2 ] 4- , and [Mo 8 O 22 (OH) 4 X 2 ] 2- (X = N -propylsalicylideneiminate) 102 but are different from those found in [Mo 8 O 24 (OMe) 4 ] 4- 65a and [Mo 8 O 26 (MoO 4 ) 2 ] 8- 15 The different stereochemical positions of the ligands X in [Mo 8 O 26 X 2 ] (2 n +4)- (ref ).…”
Section: Polyoxometalates Incorporating Group
15
Element-centered Lig...mentioning
ContentsI. Introduction 77 II. Scope and Organization of the Review 78 III. Polyoxometalates Incorporating Halides 79 IV. Polyoxometalates Incorporating Group 16 Element-Centered Ligands 81 A. Peroxopolyoxometalates 81 B. Polyoxoalkoxometalates 82 1. Polyoxoalkoxometalates Involving Unidentate Alcohols 82 2. Polyoxoalkoxometalates Involving Chelating Triols 83 C. Heavier Group 16 Element-Centered Ligands 85 1. Thiopolyoxometalates 85 2. Organosulfur and Organoselenium Ligands 85 V. Polyoxometalates Incorporating Group 15 Element-Centered Ligands 86 A. Singly Bonded Nitrogen-Donating Ligands 86 1. Amine and Related Ligands 86 2. Amide Oximes [RC(NH 2 )NOH] and Oximes 87 B. Multiply Bonded Nitrogen Ligands 89 1. Nitrido Derivatives 89 2. Organoimido Derivatives 89 3. Hydrazido and Diazenido Derivatives of Polyoxometalates 90 4. Nitrosyl Derivatives 92 C. Organophosphorus, Organoarsenic, and Organoantimony Ligands 94 1. Organophosphonate and Organoarsonate Ligands 94 2. Organophosphinate and Organoarsinate Ligands 97 VI. Polyoxometalates Incorporating Group 14 Element-Centered Ligands 97 A. Oxocarbon Ligands 97 1. Carbonate 97 2. Carboxylates 97 3. Oxalate and Squarate 97 4. Carbonyl Derivatives 98 B. Silicon Derivatives 98 C. Germanium Derivatives 99 D. Tin and Lead Derivatives 99 VII. Organometallic Derivatives of Polyoxometalates 100 A. Cyclopentadienyl Derivatives of Polyoxometalates 100 B. Cyclopentadienyl Oxide Clusters of Groups 5 and 6 100 C. Organometallic Polyoxometalates 100 1. Polyoxometalate-incorporated Organometalic Complexes 101 2. Polyoxometalate-Supported Organometallic Complexes 101 3. Integrated Cubane-Type Clusters 105 4. Organometallic Cation Salts of Keggin-Type Anions 105 VIII. Concluding Remarks 106 IX. Acknowledgments 106 X. Abbreviations 106 XI. References 106
“…Thus, it is unfortunate that its molybdenum counterpart, [Mo 10 O 32 ] 4- , is unknown, which precludes a comparison between the photochemical properties of these two species. The only isolated decamolybdate that has been characterized to date, [Mo 10 O 34 ] 8- , is built up by connecting one Mo 8 O 28 unit at corners to two MoO 4 octahedra . We report here the synthesis and physicochemical characterization of some derivatives of the putative [Mo 10 O 32 ] 4- anion, namely [Mo 10 O 25 (OMe) 6 (NO)] - ( II ) and two isomers of [Mo 10 O 24 (OMe) 7 (NO)] 2- ( IVa , b ).…”
Reaction of either
(n-Bu4N)2[Mo5O13(OMe)4(NO){Na(MeOH)}]·xMeOH
or
(n-Bu4N)3[Mo6O18(NO)]
with
various reducing agents, including
N2H4·2HCl, in methanol or in a mixture
of methanol and acetonitrile, yields
reduced nitrosyl decamolybdates, among which
(n-Bu4N)[Mo10O25(OMe)6(NO)]
((n-Bu4N)II) and two forms of
(n-Bu4N)2[Mo10O24(OMe)7(NO)]
((n-Bu4N)2
IVa and
(n-Bu4N)2
IVb) have been
crystallographically characterized.
IVa,b
are diastereoisomers that differ in the location of methoxo groups.
The molecular structures of II and IV are
closely
related to that of
[W10O32]4-, the
so-called decatungstate Y, and consist of two halves of five
edge-sharing octahedra
connected through four quasi-linear Mo−O−Mo bridges. Besides
the four electrons essentially residing at the
Mo(II) center bearing the nitrosyl ligand, II and
IV further accommodate two and four delocalized “blue”
electrons,
respectively. II and IV thus contain
molybdenum atoms in three different oxidation states, Mo(II),
Mo(V), and
Mo(VI). On the basis of their optical spectra, they are best
described as class II mixed-valence complexes according
to the classification of Robin and Day. Their intimate electronic
structure has been further investigated by means
of extended Hückel calculations on the model compound
[Mo10O26(OH)6]. The
composition of the HOMO clearly
demonstrates that the “blue” electrons are circulating among the
eight equatorial molybdenum sites, the delocalization
being strongly favored by the quasi-linear M−O−Mo
bridges.
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