Insertion isocyanates

Chromatography cyclophosphazenes, 21 46, 59 technetium, 11 48-49 Chromites, as spinel structures, 2 30 Chromium, see Tetranuclear d-block metal complexes, chromium acetylene complexes of, 4 104 alkoxides, 26 276-283 bimetallics, 26 328 dimeric cyclopentdienyl, 26 282-283 divalent complexes, 26 282 nitrosyls, 26 280-281 trivalent complexes, 26 276-280 adamantoxides, 26 320 di(/ >rt-butyl)methoxides, 26 321-325 electronic spectra, 26 277-279 isocyanate insertion, 26 280 substitution reactions, 26 278-279 [9]aneS, complexes, 35 11 atom... 

Isocyanates insert into RO and RN bonds. Cyclic ethers, such as oxiranes, are known to undergo reactions with isocyanates to form 2-oxazolidinones in high yield (38—40). 

Other isocyanates inserted into the Zr-N bond as well as the Zr-C bond, resulting after workup in urea products 33 as well as the expected amides 32 [21]. The product ratio (Table 5) was independent of solvent and governed largely by the size of R. For R=i-Pr both products were formed but the major product was the amide. For small R (R=Et, Me, Bn) the major product was the urea. 

The reaction can be run in reverse at high [THF], with bis-(trimethylsilyl) carbodiimide replaced by THF. The rate is independent of [THF], consistent with rate-limiting extrusion of carbodiimide, i.e., with the operation of a similar dissociative mechanism in reverse. Similarly, addition of trimethylphos-phine to 35 results in extrusion of the carbodiimide to form the phosphine-stabilized zirconaaziridine [49]. In contrast, the isocyanate insertions are effectively irreversible. 

Isocyanate insertions presumably go through the same 16-electron intermediate, which explains why the Zr-N/Zr-C ratio from those reactions is inde-... 

Organocopper compounds react slowly with nitriles or not at all 124, 233). Only a low yield of benzanilide was obtained from the reaction between phenylcopper and phenyl isocyanate 124). Isocyanate insertion reactions with vinylcopper compounds in HMPT in the presence of P(0C2H5)3 afford acrylamides 225a). 

Just to illustrate the real synthetic interest of these heterocyclobutadienes, it appeared that trimethylsilyl isocyanate inserts into the P-N bond of 28 leading to 38, which after hydrolysis afforded 39 in 50 % yield. Interestingly, 39 exists as a hydrogen-bonded dimer in the solid state and has a structure very similar to that of cytosine, the C(NH2) being replaced by a P(N/Pr2)2 group it could be considered as a labelled cytosine (Scheme 15). 

Most of the combination processes outlined earlier [11.5.1, reactions (c)-(j)] are observed for isocyanate insertions . 

Scheme 2 Isocyanate insertion into a metal-element bond to generate amidate (left) or ureate (right) complexes...

Furthermore, the complexes formed are also susceptible to further isocyanate insertions leading to product mixtures. [27]... 

Phenyl isocyanate inserts the Si-P bond of bis-silylphosphines to give the adduct which eliminates siloxane to yield the dimer with a four-membered C2P2 ring (equation 23). 

Both alkyl- and aryl isocyanates insert readily into As-N bonds In contrast, As(NMc2)3 reacts with fluorosulfonyl isocyanate to give a rearrangement product 322. ... 

Alkyl isocyanates insert into tungsten and iron hydride complexes to give the insertion products resulting from insertion into the metal-hydrogen bond. For example, reaction of CpW(CO)3H with methyl isocyanate affords the carbamate complex . Likewise, CpFe(CO)2H reacts with t-butyl isocyanate to give the carbamate complex 329 . 

Scheme 36 Catalytic framation of amides by isocyanate insertion into C-H bonds...

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

Insertion Reactions. Isocyanates also may undergo iasertion reactions with C—H bonds. Acidic compounds, such as 1,3-dicarbonyl compounds (6), react readily at room temperature to form carboxyamides. At higher temperatures carboxyamides frequentiy undergo secondary reactions leading to cyclized products (33,34). 

It is worth noting that the 2-pyridone 42 (99MI1) and thione 43 (88H(27)733), which could react in either of the two ways as shown, with an isocyanate or isothiocyanate and with a nitrile respectively, actually give a one-carbon insertion. There is a case of formation of 2,3 and 3,4 bonds in the preparation of 8-hydroxy-triazolopyridine 44 (83MI1). 

Urethane gels and ultrasoft elastomers are a more recent development.18 They are made primarily by reacting high-molecular-weight polyether polyols with a stoichiometric deficiency of isocyanate. The low NCO-to-OH ratio allows for a wide latitude in hardness adjustment. These low-hardness elastomers are used for seating applications (such as gel bicycle seats), shoe inserts, and soft padding for orthopedic devices. 

Reactions of the cyclopentadienyl-amidinate-supported imidotitanium complexes with CO2 proceed via initial cycloaddition reactions, but depending on the imido Af-substituent go on to yield products of either isocyanate extrusion or unprecedented double CO2 insertion (Scheme 89). ... 

A (pentamethylcyclopentadienyl)iridium chelating guanidinate complex has been conveniently prepared by treatment of [Cp IrCl2]2 with N,N, N"-th-p-tolylguanidine and base in THF at room temperature followed by recrystallization of the green product from toluene and pentane (Scheme 154). Insertion reactions of the product with heterocumulenes (diaryl carbodiimides, aryl isocyanates) have been investigated. It was found that the complex serves as highly active catalyst for the metathesis of diaryl carbodiimides with each other and for the more difficult metathesis of diaryl carbodiimides with aryl isocyanates (cf. Section V.C). ... 

Most 1,3-diazepine syntheses employ the insertion of a single carbon fragment between the two nitrogen atoms. This is further exemplified by the use of tosyl isocyanate and methyl isothiocyanate in the preparation of the bicyclic imidazo[4,5-e][l,3]diazepines 46 and the imidazo[4,5-rf][l,3]diazepines 47 respectively <96JHC855, 96JCS(P1)2257>. 

The reactivities of hydrido(phenoxo) complexes of trons-[MH(OPh)L2] (6 M = Ni 7 M = Pt) (L = phosphine) were examined (Eqs. 6.29, 6.30 Scheme 6-16), and a high nucleophiUdty for the metal-bound phenoxide was suggested [9, 10]. Reaction with methyl iodide produced anisole and trans-[MH(I)L2] for both Ni and Pt complexes. Phenyl isocyanate also provided the insertion products into the metal-phenoxo... 

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. 

N-benzylaniline with phosgene, and then with sodium azide to produce carbonyl azide 52. On heating, nitrogen is evolved and a separable mixture of nitrene insertion product 53 and the desired ketoindazole 54 results. The latter reaction appears to be a Curtius-type rearrangement to produce an N-isocyanate (54a), which then cyclizes. Alkylation of the enol of 54... 

With isocyanates R"N=C=0 as unsymmetrical heterocumulenes the reactivity to yield bis(insertion)products is markedly higher and there are many more possibilities (2) for isomerism. In fact, we find now that the product selection is more varied than reported in a previous article [3], and that e. g. the use of 1 R,R = Me, and phenyl- or isopropylisocyanate results in mixtures of isomers, even at low temperatures. Sterically more discriminating derivatives of 1 with R = Me, R = rm-Bu and R = wo-Pr, R = H yield one major stable isomer with PhN=C=0 which could be identified as the (cis O, N ) form by NMR spectroscopy. 

Related alkoxides, such as (272), and the amide (277) display a similar activity to the acetate,964 suggesting that both alkoxide and carbonate intermediates are formed during the reaction, ll NMR spectroscopy has been used to demonstrate that (334) reacts reversibly with CHO to generate an alkoxide intermediate which subsequently inserts C02. The amide complex initiates the copolymerization by first inserting C02 into the Zn—N bond and subsequent elimination of trimethylsilyl isocyanate.965... 

A3-Pyrroline formation with carbonyl insertion also occurs during the reaction of /V-sulfinylarylamines with diphenylcyclopropenone in the presence of nickel carbonyl (Scheme 36).64 Phenyl isocyanate does not give a pyrroline product under these reaction conditions, hence the SO-CO exchange probably occurs within an intermediate metallocycle. The reaction... 

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