Some Aspects of the Reactivity of Metal Ion–Sulfur Bonds

Kuehn, Christian; Isied, Stephan S.

doi:10.1002/9780470166284.ch3

Cited by 64 publications

(12 citation statements)

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“…Some papers in the past summarized what is known to date about the electronic and structural properties of the species. [1][2][3] The behaviour of the disulfide group as a donor in transition metal complexes has not been subjected to such detailed study as a number of other donor groups. This arises in part, because the disulfide group often gives metal ion derivatives that are extremely insoluble, bridged, or even polymeric.…”

Section: Introductionmentioning

confidence: 99%

Transition Metal Bis(2-Bromophenyl)disulfide Complexes

Anacona

Gómez

2008

J. Chil. Chem. Soc.

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Section: Introductionmentioning

confidence: 99%

Transition Metal Bis(2-Bromophenyl)disulfide Complexes

Anacona

Gómez

2008

J. Chil. Chem. Soc.

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“…Disulfides are poor ligands, and are usually tethered to a chelating ligand in order to assist their coordination via η 1 -(end-on), η 2 -(side-on), or a μ-fashion (Chart ). Bridging disulfide complexes (tethered or not) comprise >60% of disulfide structures deposited in the Cambridge Crystallographic Database; the next most common coordination mode is tethered end-on, while side-on and nontethered end-on modes are rare.…”

Section: Resultsmentioning

confidence: 99%

Thiol, Disulfide, and Trisulfide Complexes of Ru Porphyrins: Potential Models for Iron–Sulfur Bonds in Heme Proteins

2012

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Thirty-two Ru(porp)L(2) complexes have been synthesized, where porp = the dianion of meso-tetramesitylporphyrin (TMP) or meso-tetrakis(4-methylphenyl)porphyrin (H(2)T-pMe-PP), and L = a thiol, a sulfide, a disulfide, or a trisulfide. Species studied were with RSH [R = Me, Et, (n)Pr, (i)Pr, (t)Bu, Bn (benzyl), and Ph], RSR (R = Me, Bn), RSSR (R = Me, Et, (n)Pr, Bn) and MeSS(t)Bu, and RSSSR (R = Me, Bn). All the species except two, which were the isolated Ru(T-pMe-PP)((t)BuSH)(2) and Ru(TMP)(MeSSMe)(2), were characterized in situ. The disulfide complex was characterized by X-ray analysis. (1)H NMR data for the coordinated thiols are the first reported within metalloporphyrin systems, and are especially informative because of the upfield shifts of the axial sulfur-containing ligands due to the porphyrin π-ring current effect, which is also present in the di- and trisulfide species. The disulfide in the solid state structure of Ru(TMP)(MeSSMe)(2) is η(1)(end-on) coordinated, the first example of such bonding in a nontethered, acyclic dialkyl disulfide; (1)H-(1)H EXSY NMR data in solution show that the species undergoes 1,2-S-metallotropic shifts. Stepwise formation of the bis(disulfide) complex from Ru(TMP)(MeCN)(2) in solution occurs with a cooperativity effect, resembling behavior of Fe(II)-porphyrin systems where crystal field effects dominate, but ligand trans-effects are more likely in the Ru system. The η(1)(end-on) coordination mode is also favored for the trisulfide ligand. Discussed also are the remarkable linear correlations that exist between the ring-current shielding shifts for the axial ligand C(1) protons of Ru(porp)(RS(x)R)(2) and x (the number of S atoms). The Introduction briefly reviews literature on Ru- and Fe porphyrins (including heme proteins) with sulfur-containing ligands or substrates, and relationships between our findings and this literature are discussed throughout the paper.

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“…During early optimization studies of the TMAL process with hydrocinnamaldehyde ( 1a ) and ketene acetals 2 , 7 , and 8 , we discovered that the formation of β-lactones, as opposed to typical aldol adducts, was highly dependent on the ketene acetal and Lewis acid employed in terms of both product distribution and diastereoselectivity (Table ). Use of phenoxy ketene acetal 7a ( E / Z , 7:1) with BF 3 ·OEt 2 , TiCl 4 , and MgCl 2 delivered primarily aldol adduct 10a (entries 1, 2) or led to no reaction (entry 3) . Application of MgBr 2 ·OEt 2 at reduced temperature (−40 °C) to avoid known reactions of β-lactones with this Lewis acid (e.g., dyotropic rearrangements), delivered β-lactone 3a in 23% yield and excellent diastereoselectivity (>19:1) favoring the trans -β-lactone, but accompanied by significant quantities of aldol adducts 9a / 10a (entry 4).…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Investigations of the ZnCl₂-Mediated Tandem Mukaiyama Aldol Lactonization: Evidence for Asynchronous, Concerted Transition States and Discovery of 2-Oxopyridyl Ketene Acetal Variants

et al. 2012

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The ZnCl(2)-mediated tandem Mukaiyama aldol lactonization (TMAL) reaction of aldehydes and thiopyridyl ketene acetals provides a versatile, highly diastereoselective approach to trans-1,2-disubstituted β-lactones. Mechanistic and theoretical studies described herein demonstrate that both the efficiency of this process and the high diastereoselectivity are highly dependent upon the type of ketene acetal employed but independent of ketene acetal geometry. Significantly, we propose a novel and distinct mechanistic pathway for the ZnCl(2)-mediated TMAL process versus other Mukaiyama aldol reactions based on our experimental evidence to date and further supported by calculations (B3LYP/BSI). Contrary to the commonly invoked mechanistic extremes of [2+2] cycloaddition and aldol lactonization mechanisms, investigations of the TMAL process suggest a concerted but asynchronous transition state between aldehydes and thiopyridyl ketene acetals. These calculations support a boat-like transition state that differs from commonly invoked Mukaiyama "open" or Zimmerman-Traxler "chair-like" transition-state models. Furthermore, experimental studies support the beneficial effect of pre-coordination between ZnCl(2) and thiopyridyl ketene acetals prior to aldehyde addition for optimal reaction rates. Our previously proposed, silylated β-lactone intermediate that led to successful TMAL-based cascade sequences is also supported by the described calculations and ancillary experiments. These findings suggested that a similar TMAL process leading to β-lactones would be possible with an oxopyridyl ketene acetal, and this was confirmed experimentally, leading to a novel TMAL process that proceeds with efficiency comparable to that of the thiopyridyl system.

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Some Aspects of the Reactivity of Metal Ion–Sulfur Bonds

Cited by 64 publications

References 258 publications

Transition Metal Bis(2-Bromophenyl)disulfide Complexes

Transition Metal Bis(2-Bromophenyl)disulfide Complexes

Thiol, Disulfide, and Trisulfide Complexes of Ru Porphyrins: Potential Models for Iron–Sulfur Bonds in Heme Proteins

Mechanistic Investigations of the ZnCl₂-Mediated Tandem Mukaiyama Aldol Lactonization: Evidence for Asynchronous, Concerted Transition States and Discovery of 2-Oxopyridyl Ketene Acetal Variants

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Some Aspects of the Reactivity of Metal Ion–Sulfur Bonds

Cited by 64 publications

References 258 publications

Transition Metal Bis(2-Bromophenyl)disulfide Complexes

Transition Metal Bis(2-Bromophenyl)disulfide Complexes

Thiol, Disulfide, and Trisulfide Complexes of Ru Porphyrins: Potential Models for Iron–Sulfur Bonds in Heme Proteins

Mechanistic Investigations of the ZnCl2-Mediated Tandem Mukaiyama Aldol Lactonization: Evidence for Asynchronous, Concerted Transition States and Discovery of 2-Oxopyridyl Ketene Acetal Variants

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Mechanistic Investigations of the ZnCl₂-Mediated Tandem Mukaiyama Aldol Lactonization: Evidence for Asynchronous, Concerted Transition States and Discovery of 2-Oxopyridyl Ketene Acetal Variants