Nuclear magnetic resonance studies of stereochemical rearrangements in pentagonal-bipyramidal (.eta.5-cyclopentadienyl)tris(N,N-dimethyldithiocarbamato)titanium(IV), -zirconium(IV), and -hafnium(IV)
“…Broadening of the N-alkyl resonances due to hindered rotation about the C−N bond is well documented in DTC complexes, Scheme . − Rate constants for the exchange of N-alkyl groups were determined by total line shape analysis (TLSA) as described in the Experimental Section, and activation parameters obtained from the least-squares straight lines of the log( k / T ) vs 1/ T and log k vs 1/ T (Supporting Information, S2) and given in Table . The Δ H ⧧ values obtained fall within the range (10−19 kcal) previously reported for rotation about the C−N bond in DTC derivatives. − The range of Δ S ⧧ values is much broader (from −13 to +17 cal), and thus, Δ G ⧧ varies accordingly. − To our knowledge, this is the first time that these parameters have been obtained for oxygenated DTC ligands, and more generally, the first example of such exchange processes being affected by insertion into a ligand-to-metal bond. 3 …”
Section: Resultsmentioning
confidence: 99%
“…14 Broadening of the N-alkyl resonances due to hindered rotation about the C-N bond is well documented in DTC complexes, Scheme 3. [25][26][27][28] Rate constants for the exchange of N-alkyl groups were determined by total line shape analysis (TLSA) as described in the Experimental Section, and activation parameters obtained from the least-squares straight lines of the log(k/T) vs 1/T and log k vs 1/T (Supporting Information, S2) and given in Table 1. The ∆H q values obtained fall within the range (10-19 kcal) previously reported for rotation about the C-N bond in DTC derivatives.…”
Section: Resultsmentioning
confidence: 99%
“…The ∆H q values obtained fall within the range (10-19 kcal) previously reported for rotation about the C-N bond in DTC derivatives. [25][26][27][28] The range of ∆S q values is much broader (from -13 to +17 cal), and thus, ∆G q varies accordingly. [25][26][27][28] To our knowledge, this is the first time that these parameters have been obtained for oxygenated DTC ligands, and more generally, the first example of such exchange processes being affected by insertion into a ligand-to-metal bond.…”
S-oxygenation of dithiocarbamate (DTC) complexes has been implicated in their function as industrial anti-oxidants, as well as in their use as pesticides and most recently in their cumulative toxicity, but little is known of the species generated. Several S-oxygenated derivatives of N,N-disubstituted DTCs have been synthesized, characterized by a variety of methods, and their structure and reactivity examined. Low-temperature reaction of bis(N,N-diethyldithiocarbamato)zinc(II), Zn(deDTC)2 1, with oxygenating reagents (hydrogen peroxide, m-chloroperbenzoic acid, urea hydrogen peroxide) yields mono-oxygenated DTC complexes (N,N-peroxydiethyldithiocarbamato)(N,N-diethyldithiocarbamato)zin(II), Zn(O-deDTC)(deDTC), 2 and bis(N,N-peroxydiethyldithiocarbamato)zinc(II), Zn(O-deDTC)2, 3. The tetraoxygenated derivative bis(N,N-diethylthiocarbamoylsulfinato)zinc(II), Zn(O(2)-deDTC)2, 4, was cleanly obtained by initial reaction of the DTC salts with stoichiometric oxidant prior to complexation with Zn(II). X-ray crystallographic analysis of 2, 3, and 4 show that the peroxydithiocarbamate ligands are S,O-bound. Similar derivatives were obtained from the homoleptic dimethyl and pyrollidine DTC Zn complexes. These oxygenated species display unique 1H and 13C NMR variable-temperature spectra, as the symmetry of DTC ligand is broken upon oxygenation; total line shape analysis (TLSA) was used to compare the energetic parameters for rotation about the C-N bond in several derivatives. Compounds 2, 3, and 4 were deoxygenated by alkyl phosphine, regenerating the parent dithiocarbamate 1. The peroxydithiocarbamate complexes were susceptible to base-catalyzed hydrolytic decomposition, giving ligand-based products indicative of S-oxidation and S-extrusion.
“…Broadening of the N-alkyl resonances due to hindered rotation about the C−N bond is well documented in DTC complexes, Scheme . − Rate constants for the exchange of N-alkyl groups were determined by total line shape analysis (TLSA) as described in the Experimental Section, and activation parameters obtained from the least-squares straight lines of the log( k / T ) vs 1/ T and log k vs 1/ T (Supporting Information, S2) and given in Table . The Δ H ⧧ values obtained fall within the range (10−19 kcal) previously reported for rotation about the C−N bond in DTC derivatives. − The range of Δ S ⧧ values is much broader (from −13 to +17 cal), and thus, Δ G ⧧ varies accordingly. − To our knowledge, this is the first time that these parameters have been obtained for oxygenated DTC ligands, and more generally, the first example of such exchange processes being affected by insertion into a ligand-to-metal bond. 3 …”
Section: Resultsmentioning
confidence: 99%
“…14 Broadening of the N-alkyl resonances due to hindered rotation about the C-N bond is well documented in DTC complexes, Scheme 3. [25][26][27][28] Rate constants for the exchange of N-alkyl groups were determined by total line shape analysis (TLSA) as described in the Experimental Section, and activation parameters obtained from the least-squares straight lines of the log(k/T) vs 1/T and log k vs 1/T (Supporting Information, S2) and given in Table 1. The ∆H q values obtained fall within the range (10-19 kcal) previously reported for rotation about the C-N bond in DTC derivatives.…”
Section: Resultsmentioning
confidence: 99%
“…The ∆H q values obtained fall within the range (10-19 kcal) previously reported for rotation about the C-N bond in DTC derivatives. [25][26][27][28] The range of ∆S q values is much broader (from -13 to +17 cal), and thus, ∆G q varies accordingly. [25][26][27][28] To our knowledge, this is the first time that these parameters have been obtained for oxygenated DTC ligands, and more generally, the first example of such exchange processes being affected by insertion into a ligand-to-metal bond.…”
S-oxygenation of dithiocarbamate (DTC) complexes has been implicated in their function as industrial anti-oxidants, as well as in their use as pesticides and most recently in their cumulative toxicity, but little is known of the species generated. Several S-oxygenated derivatives of N,N-disubstituted DTCs have been synthesized, characterized by a variety of methods, and their structure and reactivity examined. Low-temperature reaction of bis(N,N-diethyldithiocarbamato)zinc(II), Zn(deDTC)2 1, with oxygenating reagents (hydrogen peroxide, m-chloroperbenzoic acid, urea hydrogen peroxide) yields mono-oxygenated DTC complexes (N,N-peroxydiethyldithiocarbamato)(N,N-diethyldithiocarbamato)zin(II), Zn(O-deDTC)(deDTC), 2 and bis(N,N-peroxydiethyldithiocarbamato)zinc(II), Zn(O-deDTC)2, 3. The tetraoxygenated derivative bis(N,N-diethylthiocarbamoylsulfinato)zinc(II), Zn(O(2)-deDTC)2, 4, was cleanly obtained by initial reaction of the DTC salts with stoichiometric oxidant prior to complexation with Zn(II). X-ray crystallographic analysis of 2, 3, and 4 show that the peroxydithiocarbamate ligands are S,O-bound. Similar derivatives were obtained from the homoleptic dimethyl and pyrollidine DTC Zn complexes. These oxygenated species display unique 1H and 13C NMR variable-temperature spectra, as the symmetry of DTC ligand is broken upon oxygenation; total line shape analysis (TLSA) was used to compare the energetic parameters for rotation about the C-N bond in several derivatives. Compounds 2, 3, and 4 were deoxygenated by alkyl phosphine, regenerating the parent dithiocarbamate 1. The peroxydithiocarbamate complexes were susceptible to base-catalyzed hydrolytic decomposition, giving ligand-based products indicative of S-oxidation and S-extrusion.
“…For pentacoordinate species, specific examples include P(V) halides (Figure b)this being called Berry pseudorotation. , While these examples involve coordination at a nonmetallic central atom, the geometry-changing processes are equally applicable to the far more numerous metallic elements. Additionally, metals generally have a potential for larger coordination numbers, hence development of the model gravitated toward a much wider application within the field of inorganic chemistry. − ,− …”
Section: Introductionmentioning
confidence: 99%
“…Presented as a general approach for arbitrary n -coordination and geometries, the model was successfully applied to pentacoordinate phosphorus species ,,− including chelating ligands. , The early work also examined the unusual case of pentacoordinate carbon species . Further development of the model led to its generalization to describe dynamical behavior in tricoordinate p-block species; tetracoordinate s-block, , p-block, − and d-block ,− species; pentacoordinate d-block ,− and further work on p-block − species; hexacoordinate d-block ,− and p-block , species; heptacoordinate general , and d-block − species; octacoordinate ,,,− species; and nonacoordinate species. Interest in the model also stimulated the synthesis of numerous chemical systems designed to probe new or unresolved questions regarding polytopal rearrangement mechanisms. ,,,,− …”
The term “polytopal rearrangement” describes
any
shape changing process operating on a coordination “polyhedron”the
solid figure defined by the positions of the ligand atoms directly
attached to the central atom of a coordination entity. Developed in
the latter third of the last century, the polytopal rearrangement
model of stereoisomerization is a general mathematical approach for
analyzing and accommodating the complexity of such processes for any
coordination number. The motivation for the model was principally
to deal with the complexity, such as Berry pseudorotation in pentavalent
phosphorus species, arising from rearrangements in inorganic coordination
complexes of higher coordination numbers. The model is also applicable
to lower coordination centers, for example, thermal “inversion”
at nitrogen in NH3 and amines. We present the history of
the model focusing on its essential features, and review some of the
more subtle aspects addressed in recent literature. We then introduce
a more detailed and rigorous modern approach for describing such processes
using an assembly of existing concepts, with the addition of formally
described terminology and representations. In our outlook, we contend
that the rigorous and exhaustive application of the principles of
the polytopal rearrangement model, when combined with torsional isomerism,
will provide a basis for a mathematically complete, general, and systematic
classification for all stereoisomerism and stereoisomerization. This
is essential for comprehensively mapping chemical structure and reaction
spaces.
Temperaturabhängige 1H‐NMR‐spektroskopische Untersuchungen bestätigen in den pentagonal‐bipyramidalen Titelkomplexen (I) drei kinetische Prozesse: Austausch von Dithiocarbamat‐Methylgruppen zwischen den äquatorialen Liganden, sowie zwischen den äquatorialen und den einzelnen Liganden sowie Austausch der äquatorialen und einzelnen Liganden.
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