Carbodiimides types

In the household-refrigerator industry, however, the one-shot process employing crude TDI (which has a lower percent NCO and contains oligomeric compounds, such as isocyanurate- and carbodiimide-types of oligomers) is still widely employed because of its low cost. 

An intramolecular Diels-Alder cyclization produces excellent yields of 2-aminoquinoline-3-carboxylate esters (57). Equally fine yields of the requited carbodiimides have been reported, making this an attractive route to an unusual substitution type. 

One inherent weakness of Vulkollan-type materials is their susceptibility to hydrolysis. Life in a humid environment may, however, be doubled by the incorporation of 2 pphr (parts per hundred resin) of a carbodiimide. 

Diazametallacycles of the type Cp2Zr[Bu NC( = NR )NR ] have been prepared according to Scheme 92 from terminal zirconium imides and carbodiimides. A second series of analogous compounds was synthesized starting... 

Closely related mixed amido/imido/guanidinato tantalum complexes of the type Ta(NR R )[(R R2N)C(NR )2]( = NR ) (R R = Me, Et R = Cy, Pr R = Pr", BuO were synthesized by the insertion of carbodiimides into to tantalum-amide bonds in imidotantalum triamide precursors, and the effects of ligand substitution on thermal properties were studied by TGA/DTA measurements. In addition, selected compounds were pyrolyzed at 600 °C and the decomposition products were studied by GC-MS and NMR spectroscopy. ... 

Oxalamidinate anions represent the most simple type of bis(amidinate) ligands in which two amidinate units are directly connected via a central C-C bond. Oxalamidinate complexes of d-transition metals have recently received increasing attention for their efficient catalytic activity in olefin polymerization reactions. Almost all the oxalamidinate ligands have been synthesized by deprotonation of the corresponding oxalic amidines [pathway (a) in Scheme 190]. More recently, it was found that carbodiimides, RN = C=NR, can be reductively coupled with metallic lithium into the oxalamidinate dianions [(RN)2C-C(NR)2] [route (c)J which are clearly useful for the preparation of dinuclear oxalamidinate complexes. The lithium complex obtained this way from N,N -di(p-tolyl)carbodiimide was crystallized from pyridine/pentane and... 

Majetich and Hicks <96SL649> have reported on the epoxidation of isolated olefins (e.g., 61) using a combination of 30% aqueous hydrogen peroxide, a carbodiimide (e.g., DCC), and a mildly acidic or basic catalyst. This method works best in hydroxylic solvents and not at all in polar aprotic media. Type and ratios of reagents are substrate dependent, and steric demand about the alkene generally results in decreased yields. 

Out of three phases reported for Ca3N2 [12], to date only the cubic (a) nitride phase is confirmed, crystallizing in the anti-bixbyite type structure. In addition, the carbodiimide nitride Ca4(CN2)N2 [13] may hold for another unconfirmed calcium nitride phase, and Can(CN2)2N6 stands for the ill-defined CauNg [14]. Here we note again that carbon impurities may produce significant difficulties in reactions. 

Note that carbon monoxide inserts into the Zr-H bond of 1 (2 equiv.) to afford an T -formaldehydo-type complex [(Cp2ZrCl)]2(g-CH20) [200-202]. Iminoacyl zir-conocene complexes are formed after addition of 1 to isonitriles [203]. Carbon dioxide [183, 202] is reduced to formaldehyde with 1 (2 equiv.). C02-like molecules such as isocyanates RNCO [204], isothiocyanates RNCS [205], and carbodiimides RNCNR [204] are readily converted to the corresponding bidentate form-amido ligands. 

In aqueous solutions, the easiest method for forming this type of bond is to use the water-soluble carbodiimide EDC (Chapter 3, Section 1.1). For proteins and other water-soluble macromolecules, EDC reacts with their available carboxylate groups to form an intermediate, highly reactive, o-acylisourea. This active ester species may further react with nucleophiles such as a hydrazide to yield a stable imide product (Figure 1.109). 

Carbodiimides are used to mediate the formation of amide or phosphoramidate linkages between a carboxylate and an amine or a phosphate and an amine, respectively (Hoare and Koshland, 1966 Chu et al., 1986 Ghosh et al., 1990). Regardless of the type of carbodiimide, the reaction proceeds by the formation of an intermediate o-acylisourea that is highly reactive and short-lived in aqueous environments. The attack of an amine nucleophile on the carbonyl group of this ester results in the loss an isourea derivative and formation of an amide bond (see Reactions 11 and 12). The major competing reaction in water is hydrolysis. 

Another possible approach to the synthesis of this type of dinucleotide utilizes transesterification by means of carbodiimide derivatives.93 ... 

Amidines and cyclic amidines are also converted into 1,2,4-thiadiazoles by reaction with isothiocyanates, imino-sulfenyl chlorides, di- and trichloromethyl sulfenyl chlorides, and carbon disulfide in the presence of sulfur. Ureas, thioureas, guanidines, carbodiimides, and cyanimides react with chlorocarbonylsulfenyl chloride to produce 1,2,4-thiadiazol-5-one derivatives in another example of a type B synthesis <1996CHEC-II(4)307>. 

Thiadiazoles are also obtained when the thermolysis is carried out in the presence of isocyanates and carbodiimides <1996CHEC-II(4)307>. There have been no new reports of this type of rearrangement since the publication of CHEC-II(1996). 

In contrast to 4-alkyl-5-sulfonylimino-A -l,2,3,4-thiatriazolines (58) (Section 4.19.5.1.2), 4-alkyl-5-alkylimino-A -l,2,3,4-thiatriazolines (50) react with immediate nitrogen evolution when added to electron-rich alkenes or to heterocumulenes such as enamines, carbodiimides, isocyanates, isothiocyanates, or styrene. Reaction kinetics for certain of this type of system show that they undergo bimolecular processes as described below. 

The palladium-phosphine-catalyzed cycloaddition reactions of vinyloxetanes 530 with aryl isocyanates or diaryl-carbodiimides led to 4-vinyl-l,3-oxazin-2-ones 531 or l,3-oxazin-2-imines 532, respectively (Scheme 101). In the absence of phosphine ligands (PPhs, bis(diphenylphosphino)ethane (DPPE), l,3-bis(diphenylphosphino)propane (dppp), no conversion of heterocumulenes was observed. Starting from fused-bicyclic vinyloxetanes, both types of cycloadditions proceeded in a highly stereoselective fashion, affording only the r-isomers of alicycle-condensed 1,3-oxazine derivatives <1999JOC4152>. 

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