Tetraheptylammonium salts of various transition-metal-substituted heteropolyanions with alpha-Keggin ([XW(11)O(39)M](n)()(-)), alpha-Wells-Dawson ([P(2)W(17)O(61)M](m)(-)), and Weakley and Finke structures ([P(2)W(18)O(68)Co(4)](10)(-)) were investigated with respect to their reactivity with CO(2) in nonpolar solvents. It was found that copper(II)- and manganese(III)-substituted heteropolyanions do not react with CO(2). Germano- and silicotungstates with the alpha-Keggin structure do form complexes with CO(2) when substituted with Co(II), Ni(II), and Mn(II). In contrast, boro- and phosphotungstates substituted with Co(II), Ni(II), and Mn(II) are unreactive. The alpha(2) isomers of Wells-Dawson phosphotungstates show reactivity similar to that of alpha-Keggin silicotungstates-i.e., Co(II), Ni(II), and Mn(II) derivatives do react with CO(2). On the other hand, the alpha(1) isomer of the Co(II)-substituted Wells-Dawson anion does not react with CO(2), and neither does the Weakley and Finke cobaltotungstate. When reactions do occur, they are completely reversible. An excess of water decomposes the complexes. Traces of water are, however, necessary for the reactions to take place. The CO(2) adducts were characterized by UV/vis, IR, and (13)C NMR. The IR data could be explained as originating either from CO(2) complexes with a direct eta(1) metal-carbon bond or from bicarbonato complexes. IR spectra with isotopically enriched (13)CO(2) and C(18)O(2) support the presence of a eta(1) metal-carbon bond. The (13)C NMR spectra indicate the presence of two different kinds of paramagnetic CO(2) complexes after the reaction of alpha-[SiW(11)O(39)Co](6)(-) with CO(2) (chemical shifts 792 and 596 ppm at 26 degrees C). The variable-temperature experiments are consistent with the chemical exchange between these two species. UV/vis, IR, and NMR studies in the presence of controlled amounts of water or ethanol suggest the existence of H-bonding in the CO(2) complexes, similar to that reported in the past for complexes between heteropolyanions and dioxygen.
This communication reports the free radical
incorporation of a titanium(IV) complex containing
polymerizable aryloxide ligands into a rigid and porous
polystyrene/divinylbenzene-based matrix. This yields a
yellow-orange insoluble polymer that can be converted
into a dark red polymer with SiCl4; the latter polymer
is a good catalyst for the Diels−Alder reaction.
Highly cross-linked macroporous polymers are excellent supports for heterogenizing rhodium alkene hydrogenation and hydroboration catalysts. The permanent pore structure of the support enables high conversions and excellent yields with minimal workup (filtering). These heterogenized catalysts can be reused, and due to the permanent pore structure, they function in a broad range of solvents including polar protic. Control experiments reveal that catalysis occurs exclusively within the polymer matrix, and not due to leached catalyst.
A procedure for converting titanium diethylamidos to the corresponding dihalides (Cl, Br, I) and a
complementary method for converting titanium dichlorides into dibromides and diiodides are reported. These
methods were utilized to synthesize a family of homogeneous and polymer-supported Diels−Alder catalysts
with the general formula (ArO)2TiX2 (X = Cl, Br, I; Ar
= 2-tert-butyl-6-methylphenyl).
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