Isocyanates metal complexes

Iron, tris(hexafluoroacetylacetone)-structure, 65 Iron, tris(oxalato)-chemical actinometer, 409 Iron, tris(l,10-phenanthroline)-absorptiometry, 549 racemization, 466 solid state, 467 structure, 64 Iron(O) complexes magnetic properties, 274 Iron(II) complexes magnetic behavior, 273 spectra, 253 Iron(III) complexes equilibrium constant solvent effect, 516 liquid-liquid extraction, 539 magnetic behavior, 272 spectra, 253 Iron(IV) complexes magnetic behavior, 272 Isocyanates metal complexes hydrolysis, 429 Isokinetic effect ligand exchange solid state, 469 Isomerism, 179-208 configurational, 180, 188 constitutional, 180,182 coordination, 183 detection, 180 history, 24... 

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. 

Ketenes and isocyanates also undergo facile [6 + 2]-photocycloaddition with metal complexed cyclic polyenes. Irradiation of 232 in the presence of diphenylketene gave 256 in good yield (Scheme 58)120. This should be contrasted with the normal behavior of ketenes toward alkenes, which typically involves [2 + 2]-cycloaddition. Isocyanates such as 257 work as well. The adducts are produced in high yields and have considerable potential in synthesis. 

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... 

Several groups have screened a variety of transition metal complexes for activity in the double silylation system, but only compounds of nickel, palladium, and platinum appear to be viable catalysts. The key factor appears to be the involvement of a M(0) species, although certain M(II) complexes can also be used, presumably with in situ reduction to M(0). Generalizations regarding the activity of the different transition metal complexes are difficult, as many variables exist in each system. However, the most active complexes seem to combine palladium metal centers with dba, small basic phosphine, or isocyanate ligands. 

The preparation of metal nitrides with N3 reagents typically employs d° metal complexes as starting materials. However, the reactions of r-butyl isocyanate with metal-oxo complexes of OsVI and RuVI represent rare examples of the use N3- reagents with d2-metals. It has been postulated that reaction of the isocyanate with metal-oxo 3 affords a four-membered ring intermediate 4, followed by the extrusion of carbon dioxide to yield r-butyl metal imide 5 (Scheme 1). Elimination of isobutylene from this complex then produces the metal nitride and the isobutylene. 

All types of electrophiles have been used with 2-lithio-l,3-dithiane derivatives, including alkyl halides, sulfonates, sulfates, allylic alcohols, arene-metal complexes, epoxides, aziridines, carbonyl compounds, imines, Michael-acceptors, carbon dioxide, acyl chlorides, esters and lactones, amides, nitriles, isocyanates, disulfides and chlorotrialkylsilanes or stannanes. The final deprotection of the dithioacetal moiety can be carried out by means of different types of reagents in order to regenerate the carbonyl group by heavy metal coordination, alkylation and oxidation184 or it can be reduced to a methylene group with Raney-nickel, sodium or LiAIII4. 

The molecular imprinting method can be used to synthesize enantioselective solid materials for asymmetric organic synthesis. The first attempt to use a metal complex with an attached chiral ligand as a template was attempted by Lemaire [52]. The Rh complex, ((15,25)-V,V -dimethyl-l,2-diphenylethane diamine)-[Rh(CgHj2)Cl]2 coordinated with optically pure l-(5)-phenylethoxide or phenylethoxide (Rh 1-phenylethanolate) (template) was polymerized in the presence of isocyanate, and the polyurea-supported Rh complex is reacted with isopropanol to extract the template from the polymer backbone. They reported the influence of molecular imprinting on catalytic performance (conversion and enantiomeric excess) for the asymmetric transfer hydrogenation (Table 22.2). The imprinted polymer exhibited higher enantioselectivity compared to a nonimprinted... 

The complexes 222-226 exhibited a high catalytic activity on the cyclotrimeriza-tion of aromatic isocyanates to produce triaryl isocyanurates (Scheme 83). They are the first reported Cp-free rare-earth metal complexes showing high activity and selectivity on the cyclotrimerization of aryl isocyanates. For comparison, the starting trisamide complex [Yb N(SiMe3)2 3( T-Cl)Li(THF)3] was studied for the catalysis and showed a catalytic activity comparable with those of the new complexes 222-226. All the complexes showed no catalytic activity on the cyclotrimerization of 4-nitrophenylisocyanate and exhibited a relatively low catalytic activity on the cyclotrimerization of aliphatic isocyanates [167]. 

Tricoordinated metal complexes should be involved in order to observe a high selectivity [951], The transition-state assembly is envisioned as having an ammonium enolate coordinated to the transition metal through the isocyanate residue 6.132 (Figure 6.104). 

Saunders and Frisch (2) cite certain catalysts used to Induce an isocyanate-urethane (allophanate) reaction. They are zinc octoate, cobalt napthanate and cobalt octoate and are claimed to yield 95% allophanate. An experiment was designed observing the catalytic effect of these metal complexes under varied concentrations and over time. Ferric acetylacetonate, a catalyst known to Influence an isocyanate-carboxyl reaction, was included 1n the study. The catalysts were added individually and 1n combinations of two into a polyurethane-polyisocyanate system. Concentrations varied from 1.50% to 8.00% by weight. 

Entelis assumes the formation of an activated alcohol-isocyanate binary complex during the catalysis of the methanol-phenyl isocyanate reaction by dibutyltin dilaurate (DBTDL) (3, 5) Activated alcohol-isocyanate-catalyst ternary complexes have also been proposed by others. However, significant differences can be noted in the structures of either the postulated one (2, 4, 6, 7) or two (8) coordination positions of the isocyanate to the metal. To explain the synergistic effects observed when tertiary amine and organometallic compounds are combined, several authors suggest the formation of an activated quaternary complex I, II or III (2, 6, 9, 10, 11, 27). 

From the above interactions schemes, Fig. 3 is proposed as a model for the structure of the activated alcohol-isocyanate-metal ternary complex M and Mx metals are considered separately. 

Adhesives which are meant to cure at temperatures of 120 or 171°C require curatives which are latent at room temperature, but react quickly at the cure temperatures. Dicyanodiamide [461-58-5], (TH INI is one such latent curative for epoxy resins. It is insoluble in the epoxy at room temperature but rapidly solubilizes at elevated temperatures. Other latent curatives for 171°C are complexes of imidazoles with transition metals, complexes of Lewis acids (eg, boron trifluoride and amines), and diaminodiphenylsulfone, which is also used as a curing agent in high performance composites. For materials which cure at lower temperatures (120°C), these curing agents can be made more soluble by alkylation of dicyanodiamide. Other materials providing latency at room temperature but rapid cure at 120°C are the blocked isocyanates, such as the reaction products of toluene diisocyanate and amines. At 120°C the blocked isocyanate decomposes to regenerate the isocyanate and liberate an amine which can initiate polymerization of the epoxy resin. Materials such as Monuron can also be used to accelerate the cure of dicyanodiamide so that it takes place at 120°C. 

Living polymerization of lactones has been successfully performed by the catalysis of rare earth metal complexes producing Mw/Mn values of 1.07-1.08 [5]. Polymerizations of acrylonitrile and alkyl isocyanates have been successfully realized using La[CH(SiMe3)2]2(C5Me5) as initiator, and those of various oxiranes have been made using Ln(acac)3/AlR3/H20 system [6]. 

Very reactive electrophiles such as tetracyanoethylene and isocyanates undergo metal-assisted cycloaddition reactions, the key step of which is thought to involve nucleophilic attack on a metal-complexed olefin to result in the formation of an >/ -alkylmetal complex. 

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