Tetrahedral carbonyl

For instance let us consider the case of the tetrahedral carbonyl cluster [Rh4(CO)i2], together with the theoretical analysis of its molecular orbitals, Figure 1. 

Figure 3. Ac-Leu Leu-Val-Phe-NH2 (solid), where denotes a tetrahedral carbonyl (-CH0H-NH-), matched onto isovaleryl-Val-Val-Sta-Ala-Sta,l, (dashed, pepstatin) as in the complex with R, chinensis aspartyl protease.

Now it is straightforward to show that, for tetrahedral carbonyl complexes M(CO)4 with 7 d symmetry,... 

Schmid, G. Tetrahedral carbonyl cobalt clusters, Angew. Chem., Int. Ed. Engl 1978, 17, 392 Angew. Chem. 1978, 90, 417. 

Tetrahedral carbonyls and nitrosyl-carbonyls. Lecture lOICCC... 

Elimination of thiamine. The product of the enamine reaction with lipoamide is itself a tetrahedral carbonyl addition product, which can eliminate thiamine pyrophosphate. This elimination, the exact reverse of step 1, generates the carbonyl compound acetyl dihydrolipoamide. 

Dialkyl acylphosphonates are sensitive to water in neutral and alkaline conditions and hydrolyse rapidly to the corresponding carboxylic acids and to dialkyl hydrogen-phosphonate (equation 47) This occurs following the rapid addition of water to the carbonyl group with the formation of stable hydrates. The involvement of stable carbonyl hydrates in the hydrolysis of dimethyl acetylphosphonate and aroylphosphonates was established by H NMR and UV spectroscopy, respectively. In the latter case, the rates of formation and decomposition of the tetrahedral carbonyl hydrates were also determined. 

Examples of 0x0 clusters obtained from metal alkoxides have been reported and the analogy between [W4Cl(0)(0Pr )9] and [W4(0)(OPr )io] and tetrahedral carbonyl clusters has been discussed. Trirhenium neopentoxide clusters give interesting reactions with ethylene and alkynes. ... 

The partially positive charge on the carbonyl carbon (Section 12.3) is the cause of the most common reaction theme of the carbonyl group, the addition of a nucleophile to form a tetrahedral carbonyl addition intermediate. In the following general reaction, the nucleophilic reagent is written as Nu to emphasize the presence of its unshared pair of electrons ... 

STEP 2 Reaction of an electrophile and a nucleophile to form a new covalent bond. Addition of the alkoxide ion to the carbonyl gives a tetrahedral carbonyl addition intermediate ... 

STEP 3 Add a proton. Proton transfer from water to the tetrahedral carbonyl addition intermediate gives the hemiacetal and regenerates the hydroxide ion catalyst ... 

The key step in the metal hydride reduction of an aldehyde or a ketone is the transfer of a hydride ion from the reducing agent to the carbonyl carbon to form a tetrahedral carbonyl addition intermediate. In the reduction of an aldehyde or a ketone to an alcohol, only the hydrogen atom attached to carbon comes from the hydride-reducing agent the hydrogen atom bonded to oxygen comes from the water added to hydrolyze the metal alkoxide salt. 

Nucleophiles react with aldehydes and ketones to form tetrahedral carbonyl addition intermediates. (12.4)... 

The addition of ammonia or a primary amine to the carbonyl group of an aldehyde or a ketone forms a tetrahedral carbonyl addition intermediate. Loss of water from this intermediate gives an imine (a Schiff base) ... 

Pattern 6 Collapse of the tetrahedral carhonyl addition intermediate to eject a leaving group and regenerate the carhonyl group. After addition of a nucleophile (Nu) to a carbonyl, one possible mechanism is for the tetrahedral carbonyl intermediate to collapse back to a C = 0 while ejecting a leaving group (Lv). We will see, in this and the chapters to come, that both Nu and Lv can take many forms. 

STEP 3 Take a proton away. Proton transfer from the oxonium ion to a second molecule of alcohol gives a tetrahedral carbonyl addition intermediate (TCAI) ... 

STEP 5 Collapse of the tetrahedral carbonyl addition intermediate to eject a leaving group and regenerate the carbonyl group. Loss of water from this oxonium ion gives the ester and regenerates the acid catalyst ... 

The most common reaction theme of acid halides, anhydrides, esters, and amides is the addition of a nucleophile to the carbonyl carbon to form a tetrahedral carbonyl addition intermediate. To this extent, the reactions of these functional groups are similar to nucleophilic addition to the carbonyl groups in aldehydes and ketones (Section 12.4). The tetrahedral carbonyl addition intermediate (TCAI) formed from an aldehyde or a ketone then adds H". The result of this reaction is nucleophilic addition to a carbonyl group of an aldehyde or a ketone ... 

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