Isonitrile group

The first transition metal isonitrilate complex reported was the tetrahedral Co-1 complex [Co(C=NPh )4] where Ph = 2,6-Me2C6H3,96 characterized by a crystal structure analysis. Oxidation yields the zerovalent dimer Co2(C=NPh )8, which features two bridging isonitrile groups. 

Although use of radio and stable isotope labels involving the trio of covalently-bonded nitrogenous functions in 3 and in 78, provided evidence that isocyano is the precursor of the isothiocyano and formamido groups [30, 81], it remains to be shown that a biosynthetic equivalent of the in vitro chemically-proven fusion process between isocyano and free sulfur (e.g., cf. Introduction) exists in the cells of sponges. In marine biota, various ionic forms of sulfur in a number of oxidation states, as well as organo-polysulfides are known. However, any association with the isonitrile group and a sulfated species has yet to be established. 

The abundant physical evidence on the molecular structure of isonitriles— namely, infrared and Raman spectra (19), nuclear magnetic resonance (28), electron diffraction studies (9), and dipole moment measurements (3d)—indicates that the isonitrile group is best represented by the polar form, B. When coordinated to a metal, the isonitrile ligand acts as a donor, C, but also as an acceptor of electrons, D (5). 

Cyanopentakis(benzyl isonitrile)iron(II) bromide, which represents a new class of iron isonitrile complexes, was investigated in some detail. This complex is diamagnetic and dissociates in nitrobenzene into two univalent-univalent ions as indicated by cryoscopic and conductivity measurements. It exhibits two peaks in the triple bond region of the infrared spectrum one at 2200 cm.—1 assigned to the isonitrile groups and another at 2092 cm.-1 assigned to the cyano group. The structure proof of cyanopentakis (benzyl isonitrile) iron (II) bromide is ... 

It was considered of interest to see how the reactions of benzyl isonitrile, a model ligand, are modified by its coordination to iron and to determine whether other ligands in the octahedral complex influence the reactivity of the benzyl isonitrile group. 

Electrophilic Reactions. The isonitrile group is best represented by the polar... 

A similar anchimeric rate-accelerating effect was observed for I and III (Table II). The infrared spectrum of I indicates that the isonitrile band is shifted by 34 cm.-1 to higher frequencies and that of III by 77 cm.-1. Hence in both complexes the isonitrile group is more ionic than in benzyl isonitrile and the same arguments should apply as to complex II. 

For compounds containing bridging isonitrile groups a further source of isomerism and stereochemical nonrigid behavior is the orientations of the alkyl or aryl groups, which can give rise to syn (32) and anti (33) isomers (65). 

Cyclopenta-fused pyridines 48 have been synthesized through a cascade initiated by intermolecular addition of C radicals to the C = N triple bond in vinylisonitriles. The reaction in Scheme 2.8 shows addition of the nucleophilic alkynyl radical 49 to the carbon end of the isonitrile group in 46 to give vinyl radical 50, which undergoes a... 

Physical properties indicate that the dipolar contribution (1) is the major one and this structure actually accounts for the nucleophilic behavior of the terminal carbon of isonitriles. However, in terms of radical chemistry, the more interesting form is the divalent one (2). This clearly shows that the isonitrile group does not behave toward radical species like a vicinal radical acceptor/radical donor synthon, that is, like an usual unsaturated bond. It instead reacts like a geminal acceptor/donor synthon [2], where an incoming radical attacks the same carbon atom that will be the new radical center in the resulting imidoyl intermediate 3 (Scheme 1). Actually, isonitriles can serve as very efficient radical traps and this chapter reviews the structural, mechanistic, and synthetic studies carried out in this field, with outstanding results, in the last three decades. 

Takahashi previously reported some structurally related gold systems, 12a and 12b [21]. Complexes 12a showed Sa phases at elevated temperatures (170-270 °C), while the metal-free ligand showed nematic and Sa phases, depending on the chain length. Addition of an alkoxy chain in the ortho position, relatively to the isonitrile group, 12b, depressed considerably the transition temperatures (90-190 °C), and a nematic phase was observed in addition to the Sa phase. Here, complexation induced mesomorphism since the ligand itself was not liquid crystal. 

There are examples when photochemically generated radicals undergo an oxidative dimerization similar to some examples shown in Section 2.02.1.5. In the case of hapalindole E (223), irradiation leads to the dimer (224), presumably by a mechanism which involves photoinduced interaction between the indole ring and the isonitrile group to give an indolyl radical (Equation (68)) <89J0C719>. 

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