Ruthenium complexes carbamates

The oxidative carbonylation of amines has been performed using palladium complex catalysts. Rhodium and ruthenium complexes have also been sho vn to have catalytic activity in the preparation of carbamates and ureas [93, 94]. An example is sho vn in Eq. 11.47. The usual carbonylation of amines to give formamides vas discussed in Section 11.2.3. 

Since CO2 and R2NH give carbamic acid and its salts, this reaction is an extension of the addition of carboxylic acids [151] to terminal acetylenes to give enol ester catalyzed by ruthenium complexes (Eqs. 11.84 and 11.85). 

Dixneuf suggested that this reaction proceeds via the nucleophilic attack of a carbamate anion to the ruthenium vinylidene intermediate generated by the reaction of ruthenium complexes with terminal acetylene. The details of this reaction are discussed in Chapter 8. 

In the presence of ruthenium complexes, primary amines react with carbon dioxide at 120-140 °C to give Af,A -disubstituted symmetrical ureas Ruthenium complexes also catalyze the reaction of secondary amines with alkynes and carbon dioxide to give vinyl carbamates". ... 

Also, Os3(H)2(CO)9(PMe2Ph) reacts with p-tolyl isocyanate to give a bridged carbamate complex . When Os3(H)2(CO)io is used, formamide complexes and other products resulting from fragmentation reactions are obtained. For example, p-tolyl isocyanate reacts with the osmium hydride complex and ruthenium complexes to form formamido, ureylene... 

Backvall and coworkers have also developed a practical method for the chemo-enz3unatic DKR of primary amines using dibenzyl carbonate as acyl donor, combining the use of CAL-B and the ruthenium complex mentioned above in toluene at 90 °C for the production of enantioenriched (R)-carbamates (60-95% )deld, 90-99% ee Table 9.6) [243]. The main advantage of this method is that the benzyloxycarbonyl group (Cbz) can be easily removed by hydrogenolytic cleavage without any loss of the carbamate optical purity (compoimd in entry 1 of Table 9.6) [244]. 

Ru3(CO)i2 [23] and more efficiently mononuclear ruthenium complexes [24] catalyze the a f -Markovnikov addition of ammonium carbamates generated in situ from secondary amines and carbon dioxide to terminal alkynes, and selectively produce vinyl carbamates with the (Z)-product as major stereoisomer (Scheme 6) [24-26]. 

The ruthenium carbene catalysts 1 developed by Grubbs are distinguished by an exceptional tolerance towards polar functional groups [3]. Although generalizations are difficult and further experimental data are necessary in order to obtain a fully comprehensive picture, some trends may be deduced from the literature reports. Thus, many examples indicate that ethers, silyl ethers, acetals, esters, amides, carbamates, sulfonamides, silanes and various heterocyclic entities do not disturb. Moreover, ketones and even aldehyde functions are compatible, in contrast to reactions catalyzed by the molybdenum alkylidene complex 24 which is known to react with these groups under certain conditions [26]. Even unprotected alcohols and free carboxylic acids seem to be tolerated by 1. It should also be emphasized that the sensitivity of 1 toward the substitution pattern of alkenes outlined above usually leaves pre-existing di-, tri- and tetrasubstituted double bonds in the substrates unaffected. A nice example that illustrates many of these features is the clean dimerization of FK-506 45 to compound 46 reported by Schreiber et al. (Scheme 12) [27]. 

Oxidative amination of carbamates, sulfamates, and sulfonamides has broad utility for the preparation of value-added heterocyclic structures. Both dimeric rhodium complexes and ruthenium porphyrins are effective catalysts for saturated C-H bond functionalization, affording products in high yields and with excellent chemo-, regio-, and diastereocontrol. Initial efforts to develop these methods into practical asymmetric processes give promise that such achievements will someday be realized. Alkene aziridina-tion using sulfamates and sulfonamides has witnessed dramatic improvement with the advent of protocols that obviate use of capricious iminoiodinanes. Complexes of rhodium, ruthenium, and copper all enjoy application in this context and will continue to evolve as both achiral and chiral catalysts for aziridine synthesis. The invention of new methods for the selective and efficient intermolecular amination of saturated C-H bonds still stands, however, as one of the great challenges. 

Hydrolysis of the ester forms adipic acid, used to manufacture nylon—6. Carbonylations of nitroaromatics are used to synthesize an array of products including amines, carbamates, isocyanates, ureas and azo compounds. These reactions are catalyzed by iron, ruthenium, rhodium and palladium complexes. For example, carhonylation of nitrobenzene in the presence of methanol produces a carbamate ... 

Surprisingly, RuX2PR3(r 6-arene) complexes did not promote the addition of ammonium N,N-dialkyl carbamates to alkenylacetylenes. However, this reaction was catalyzed by tr-allyl ruthenium derivatives such as [Ph(CH2) PPh2]Ru(r 3-CH2=C(Me)CH2)2 (n = 1-4), and yielded 0-l-(l,3-dienyl)carbamates (4—62% yield)... 

Ammonium carbamates are readily and reversibly produced on reaction of secondary amines with carbon dioxide. In the presence of a ruthenium catalyst precursors such as Ru3(CO)12 [3], (arene)RuCl2(PR3) [4] or Ru(methallyl)2(dppe) [5] (dppe=bis(diphenylphosphino)ethane) complexes, the three-component combination of a secondary amine, a terminal alkyne, and carbon dioxide selectively provides vinylcarbamates resulting from addition of carbamate to the terminal carbon of the triple bond (Scheme 2). 

Arene ruthenium(II) complexes have been shown to catalyze the re-gioselective addition of ammonium carbamate to terminal alkynes, such as phenylacetylene and 1-hexyne, to produce vinylcarbamates. 

The carbonylation of nitro arenes can lead to amines, isocyanates, carbamates, azo compounds, or ureas.80 Iron, ruthenium, rhodium, or palladium complexes have been used as catalysts. The carbonylation to give isocyanates, for example, involves the steps... 

---