Vinylidene nitrogen

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

Although the stoichiometric production of 9 and 10 was initially disappointing, it is consistent with the formation of a vinylidene ligand from 1-hexyne (see C, Scheme 3), and attack of a pendant heterocyclic nitrogen on C-l of the vinylidene. In this process, the heterocyclic nitrogen approaches C-l. Thus, we decided to slow the rate of heterocycle approach by adding a bulky substituent next to the nitrogen. 

This section deals with alkylidene complexes L M=CR2 and vinylidene complexes LnM=(C)n,=CR2 in which the metal-bound carbon atom bears only hydrogen, alkyl, or aryl groups, but neither heteroatoms (halogen, nitrogen, oxygen, or sulfur) nor electron-withdrawing groups. Dimetallacyclopropanes and ketene complexes will not be discussed. 

Optimized reaction conditions call for the use of Wilkinson s catalyst in conjunction with the organocatalyst 2-amino-3-picoline (60) and a Br0nsted add. Jun and coworkers have demonstrated the effectiveness of this catalyst mixture for a number of reactions induding hydroacylation and C—H bond fundionalization [25]. Whereas, in most cases, the Lewis basic pyridyl nitrogen of the cocatalyst ads to dired the insertion of rhodium into a bond of interest, in this case the opposite is true - the pyridyl nitrogen direds the attack of cocatalyst onto an organorhodium spedes (Scheme 9.11). Hydroamination of the vinylidene complex 61 by 3-amino-2-picoline gives the chelated amino-carbene complex 62, which is in equilibrium with a-bound hydrido-rhodium tautomers 63 and 64. 

For many polymerizations, MEHQ need not be removed instead, polymerization initiators are added. Vinylidene chloride from which the inhibitor has been removed should be refrigerated in the dark at -10°C, under a nitrogen atmosphere, and in a nickel-lined or baked phenolic-lined storage tank, If not used within one day, it should be reinhibited. 

Hydrocarbons, or Hydrogen sulfide, or Nitrogen oxide, or Sulfur dichloride, or Vinylidene chloride Braker, 1980, 578... 

As an illustration, Fig. 18.6 shows the permeability of nitrogen (at room temperature) for a great variety of polymers (elastomers, semi-crystalline polymers and glassy polymers). It can be seen that the values of P vary by a factor of nearly one million if silicone rubber on the one hand is compared with poly(vinylidene chloride) on the other ... 

The Step 1 product (0.12 mmol) dissolved in 1.2 ml of 1,1,2,-trichloro-1,2,2-trifluoroethane and 20 ml of distilled water were introduced into a 50 ml steel reactor equipped with a magnetic stirrer. The reactor contents were cooled with liquid nitrogen and evacuated to 1 x 10 mbar to remove trace amounts of oxygen. The reactor was next charged with 22 atm of vinylidene fluoride and the reactor temperature, raised to 57°C. Once the autoclave pressure decreased to 15 atm, additional vinylidene fluoride was added to maintain the reaction pressure at 20 atm. The polymerization was stopped after 48 hours, and the product was isolated in 90% yield. 

Cyano-derivatives can be readily obtained by a ruthenium-catalyzed addition of various hydrazines to terminal alkynes [89] in which the cyano carbon atom arises from the terminal alkyne carbon atom. The tris(pyrazolyl)borate (Tp) complex RuCl(Tp)(PPh3)2 (1 mol%) was found to be the most active catalyst, and N,N-dimethylhydrazine (5 equiv.) the best nitrogen source. The proposed mechanism involves the nucleophilic attack of the nitrogen nucleophile on the a-carbon of a vinylidene intermediate (Scheme 8.27). Proton migration in the resulting a-hydrazi-nocarbene, followed by deamination, would give the nitrile derivative and regenerate the catalytic species. 

Whereas the catalytic hydrosilylation of alkynes was one of the first methods of controlled reduction and functionalization of alkynes, the ruthenium-catalyzed hydroamination of alkynes has emerged only recently, but represents a potential for the selective access to amines and nitrogen-containing heterocydes. It is also noteworthy that, in parallel, the ruthenium activation of inert C-H bonds allowing alkyne insertion and C-C bond formation also represents innovative aspects that warrant future development. Among catalytic additions to alkynes for the production of useful products, the next decade will clearly witness an increasing role for ruthenium-vinylidenes in activation processes, and also for the development of ruthenium-catalyzed hydroamination and C-H bond activation. 

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