Isocyanides electrophilic additions

The parent TMM complex (190 R = H) undergoes photochemical ligand substitution with trifluorophosphine or trimethylamine Al-oxide assisted substitution with tertiary phosphines or t-butyl isocyanide (Scheme 5A) Trimethylamine A-oxide assisted substitution using isoprene as the incoming ligand results in C-C bond formation to afford the bis-TT-allyl complex (197). An intramolecular version of this reaction is also known.The parent complex (190 R = H) reacts with electrophiles. Addition of HCl or Br2 gives the methallyl complexes (192) and (198), respectively. Tetrafluoroethylene adds across the Fe bond to afford (199) under photochemical conditions. Complex (190) undergoes Friedel-Crafts-type acylation with... 

Recently, Addie and Taylor extended the synthetic utility of TosMIC by developing conditions to effect desulfonylation of a 5-substituted 4-tosyloxazole 405 (Scheme 1.109, p. 90). Their plan was to generate the dianion of 5-methyl-4-tosyloxazole 402 followed by quenching with an electrophile to produce a 5-substituted-4-tosyloxazole 404. Desulfonylation of 404 would provide a novel entry to 5-substituted oxazoles 405, thereby avoiding the use of toxic methyl isocyanide. In addition, desulfonylation of the 5-substituted 4-tosyloxazoles 406 normally obtained from reaction of TosMIC with an ester, acid chloride, or acid anhydride would further broaden the scope and use of this reaction. 

Electrophilic addition to anionic molybdenum isocyanide derivatives [Na][Tp Mo(CNR)(CO)2] is dominated by direct attack at nitrogen to form alkylidyne products however, alkylation at the metal followed by isonitrile insertion can lead to j -iminoacyl complexes in some cases. The aminocarbyne products Tp Mo(=CNRMe)(CO)2 are formed in high yield for methyl and phenyl isocyanide reagents. However, the formation of the corresponding tcrt-butylamino-alkylidyne complex is accompanied by formation of f/ -acyl and / -iminoacyl complexes (Scheme 22). ... 

Several types of reactivity for metal-bound nitriles and isocyanides should be recognized [1, 7, 8]. For instance, the nucleophilic addition to metal-bound nitriles allows the generation of imine complexes [1], electrophiUc addition produces metal-bound azavinylidenes [1], and the DCA results in coordinated heterocycUc imines (Route I, Scheme 13.1) [5, 6, 10]. With respect to the metal-ligated isocyanides, the addition of nucleophiles furnishes complexes with acycUc aminocarbenes [7, 9, 11], electrophilic addition gives aminocarbynes [8, 12], while the DCA brings about the formation of A-heterocyclic carbene derivatives (Route II, Scheme 13.1) [6, 10]. 

Isocyanides are converted, on addition of f-BuLi at the electrophilic carbon atom, to lithioimines—another class of anionic, nitrogen-containing functions which turn out to have good orf/zo-directing ability. The electrophile reacts at both lithium-bearing centres of 129 (Scheme 56). 

Another electrophile that can interact with the isocyanide-derived amide is an aldehyde. However, an additional carbonyl function cannot be introduced as such into one of the components without interfering with the Ugi process. Thus it is better used in masked form as an acetal (Fig. 9). Starting from amine 49 a series of oxopiperazines 51 has been prepared, also on solid phase [66],... 

Since their first isolation (Lieke, 1859 [23]), exceptional reactivity has been observed for isocyanides. For example, their easy formation of radicals and their ability to react both as a nucleophile and as an electrophile at the same atom (a-addition) is unrivaled by other functional groups. Although they are overall in the minority, IMCRs are considered to be more versatile and diverse than other MCRs. 

Other (less acidic) ot-substituted isocyano acetates (1, R = H, Me, /Bu, /Pr) [159]. Silver(l) salts (AgOAc) were found to accelerate the reaction, probably by coordination of the terminal NC carbon atom to Ag which increases the a-acidity and NC electrophilicity (Fig. 22). Remarkably, unlike most other reactions reported with a-acidic isonitriles, no additional base or acid is required for the three-component coupling to 2//-2-imidazolines 65. Most likely, the intermediate imine is basic enough to deprotonate the isocyanide. 

Platinum complexes (continued) with aryls, thallium adducts, 3, 399 with bis(alkynyl), NLO properties, 12, 125 with bisalkynyl copper complexes, 2, 182-186 with bis(3,5-dichloro-2,4,6-trifluorophenyl), 8, 483 and C-F bond activation, 1, 743 in C-H bond alkenylations, 10, 225 in C-H bond electrophilic activation studies, 1, 707 with chromium, 5, 312 with copper, 2, 168 cyclometallated, for OLEDs, 12, 145 in diyne carbometallations, 10, 351-352 in ene-yne metathesis, 11, 273 in enyne skeletal reorganization, 11, 289 heteronuclear Pt isocyanides, 8, 431 inside metallodendrimers, 12, 400 kinetic studies, 1, 531 on metallodendrimer surfaces, 12, 391 mononuclear Pt(II) isocyanides, 8, 428 mononuclear Pt(0) isocyanides, 8, 424 overview, 8, 405-444 d -cP oxidative addition, PHIP, 1, 436 polynuclear Pt isocyanides, 8, 431 polynuclear Pt(0) isocyanides, 8, 425 Pt(I) isocyanides, 8, 425 Pt(IV) isocyanides, 8, 430... 

The electron-rich ruthenium center can render the bound X ligand nucleophilic as has been demonstrated by the reactions of (rj5-C5H5)-(PPh3)2Ru—C=N (30) with a variety of electrophiles. Baird and Davies have shown, for example, that addition of alkyl halides to 30 gives the corresponding isocyanides in moderate yield [Eq. (32)] (29). Other... 

Addition of an electrophile (see Electrophile) to metal-bound cyanides will often form an isocyanide ligand (see Electrophile), -CsN-R. For example, the compound [Fe P(OMe)3 (NO)2(j7 -C3H4R)], which is a source of the allyl cation ( -C3H4R)+, reacts with trans-[Mn(CN)(CO)(dppm)2] to alkylate the cyanide, giving an allyl isocyanide ligand (equation 8). The tungsten alkyne... 

Alkylidenes have been prepared by reduction of alkyli-dynes, by C H oxidative addition from alkyls, and by treatment of unsaturated metal clusters with diazoalkanes. In most instances, the alkylidene adopts a /r2-h coordination mode. However, alkylidenes with heteroatom substituents may also be found in terminal coordination modes. The latter are typically prepared by the Fischer-type carbene route (see Fischer-type Carbene Complexes) (sequential addition of nucleophilic and electrophilic alkylating agents to carbonyl or isocyanide ligands), by condensation of metal fragments with mono- or dimetallic carbene complexes, or by C-H activation of alkylamines. These heteroatom substituted carbenes may also bind in a p3-ri mode, as in (12). 

Isocyanides, when bound to weak tt-donor metal centers, can also undergo addition of protic nucleophiles (HNu) to form aminocarbene M=C(Nu)NHR species. Hence, a parallelism of behavior is observed for nitriles and isocyanides. In both ligands, either the electrophilic or the nucleophilic addition occurs at the unsaturated atom at the jS-position that exhibits a higher reactivity than the metal coordinated terminal atom. 

Addition of electrophiles to electron-rich isocyanide complexes is a proven synthetic method for the synthesis of aminocarbyne complexes (5,6). Reaction of the trimethylsilyl isocyanide rhenium complex 34 with HBF4 was reported by Pombeiro and co-workers (68). It leads to loss of the trimethylsilyl group and formation of the parent aminocarbyne ligand CNHj [Eq. (28)]. The CNHj ligand is easily interconverted to the CNH... 

Aqueous inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid and, preferentially, sulfuric acid, as well as some Lewis acids, e.g. boron trifluoride etherate and titanium tetrachloride, catalyze the a-addition of the isocyanides, yielding the a-hydroxycarboxamides (24) in 12-88% The catalysis of this reaction by acids is due to an enhancement of the electrophilic reactivity of the carbonyl compound (4). 

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