Stabilized carbonyl formation

Iron(II) alkyl anions fFe(Por)R (R = Me, t-Bu) do not insert CO directly, but do upon one-electron oxidation to Fe(Por)R to give the acyl species Fe(Por)C(0)R, which can in turn be reduced to the iron(II) acyl Fe(Por)C(0)R]. This process competes with homolysis of Fe(Por)R, and the resulting iron(II) porphyrin is stabilized by formation of the carbonyl complex Fe(Por)(CO). Benzyl and phenyl iron(III) complexes do not insert CO, with the former undergoing decomposition and the latter forming a six-coordinate adduct, [Fe(Por)(Ph)(CO) upon reduction to iron(ll). The failure of Fe(Por)Ph to insert CO was attributed to the stronger Fe—C bond in the aryl complexes. The electrochemistry of the iron(lll) acyl complexes Fe(Por)C(0)R was investigated as part of this study, and showed two reversible reductions (to Fe(ll) and Fe(l) acyl complexes, formally) and one irreversible oxidation process."" ... 

Reactions of acyclic derivatives with carbon electrophiles have also been examined.33,34 An illustrative reaction involving methylation of the unsubstituted complex [MnCr 4-butadiene)(CO)3], (19), is shown in Scheme 16. Again, the reaction is presumed to occur via a methylmanganese species (20) and after methyl migration the unsaturated metal center is stabilized by formation of a Mn—H—C bridge (isomers 21a and 21b). Deprotonation of equilibrating (21a and 21b) yields the [Mn(l-methylbutadiene)(CO>3]-complex (22), which has exclusively trans stereochemistry.34 This sequence represents alkylation of the terminal carbon of butadiene and complements the iron carbonyl chemistry, where terminal acylation has been achieved as described above. Unpublished results indicate that a second methylation of (22) occurs... 

Condensation reactions between carbonyl compounds and primary amines have played a central role in the synthesis of new macrocyclic ligands [28-34]. Usually, though not in all cases, such reactions are conducted in the presence of metal ions which can serve to direct the condensation preferentially to cyclic rather than oligomeric/polymeric products and to stabilize the macrocycle once formed. The relative atomic radius of the templating ion has a considerable effect on the size of the macrocycle formed. For instance, in what is now classic work, cations such as Mg(Il) (r = 0.72 A) were found to stabilize the formation of macrocycles such as 60 from 1 1 condensations [35], while larger cations such as Sr(II)... 

The addition of CaCO, to PP causes a slight reduction in carbonyl formation. The efficiency of some antioxidants, such as Irganox 1010, was found to be reduced by the presence of CaCO,. In another study, PP stability was increased by the addition of CaCO, especially in combination with small addition of TiO, (0.5%) or HALS. In polyurethanes, CaCO, acts as a heat sink. ... 

Bagri A, Grantab R, Medhekar NV, Shenoy VB (2010) Stability and formation mechanisms of carbonyl- and hydroxyl-decorated holes in graphene oxide. J Phys Chem C 114 12053-12061... 

TINUVIN 770 takes place at about 210 Mlxh (megaluxhours), and during this time no carbonyl formation can be detected (7-8). The concentration of the stabilizing transformation product of TINUVIN 770 (the N-oxyl radical) decreases slowly, even at very high dose it can be assumed that the N-oxyl radicals may be regenerated from the product formed in the course of the stabilization (9-10). 

In photooxidation, however, a different effect can be observed which can be demonstrated by plotting the induction period of carbonyl formation as a function of TINUVIN 770 content (Figure 6). The three curves refer to the different amounts of phenolic antioxidant in the polymer. As shown in the figure, the increase of the amine content does not cause a linear increase in the photostability. On the other hand, in the presence of higher IRGANOX concentration, the stability curve runs lower. This points to an antagonistic effect between the amine and the phenolic antioxidant in the course of the photooxidation. 

Figure 6. Induction period of carbonyl formation in photooxidation as a function of stabilizer content.

T. acidophilum LplA-oriented toward the carbonyl oxygen of lipoyl-AMP, suggesting that it might be important in charge stabilization upon formation of the tetrahedral intermediate during transfer. 

Metal ion cofactors have varied roles to enhance the catalytic efficiency of enzymes in hydrolytic reactions, including facilitate substrate binding (water and organic substrate), gathering/template effects, function as an electrostatic catalyst (carbonyl polarization and transition state stabilization), function as a Lewis acid to lower the pA a of metal-water and stabilize the formation of the leaving group. Although their properties make several... 

As for the reactions of vibrationally excited carbonyl oxides formed above, the formation of OH radicals by unimolecular decomposition and stabilized carbonyl oxides by collisional deactivation can be conceived. 

CO specpure from either Matheson or Praxair was used as a molecular probe in order to assess the Lewis acidic properties of coordinatively unsaturated (cus) cations either located in the dehydrated zeolite nanocavities as charge-balancing cations, or exposed at the dehydrated surface of oxidic materials. CO is capable of interacting with the cus cations leading to the formation of adducts of different stability according to the chemical nature of the cation. Weak electrostatic adducts are formed on alkaline metal cations, u-coordinated species of intermediate stability on non d/d metal cations, whereas high-stability carbonyl-like species originated by a a-coordination -l-7r-back donation of d electrons are formed on d block metal cations. 

The mechanism for formation of benzaldehyde diethyl acetal which proceeds m two stages is presented m Figure 17 9 The first stage (steps 1-3) involves formation of a hemiacetal m the second stage (steps 4-7) the hemiacetal is converted to the acetal Nucleophilic addition to the carbonyl group characterizes the first stage carbocation chemistry the second The key carbocation intermediate is stabilized by electron release from oxygen... 

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