Metal-isonitrile complexes

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. 

The imino complexes are prepared by (i) insertion into complexes containing a metal-carbon bond, (ii) oxidative addition of RX to zero-valent isonitrile complexes and subsequent insertion of the coordinated isonitrile, (iii) nucleophilic reaction of R with halogeno-metal isonitrile complexes and (iv) reaction of anionic isonitrile complexes with alkyl halides. 

Some metal carbonyl or metal isonitrile complexes react with isocyanates via [2+2] cycloaddition sequences to cause exchange reactions. In the first step, the carbonyl complex reacts with the isocyanate to give an isonitrile complex 63 and carbon dioxide. The generated isonitrile complex reacts subsequently with a second molecule of the isocyanate to give a carbodiimide 64 with generation of the original complex". ... 

It is assumed that compound (37) is produced by an analogous mechanism to that postulated for the synthesis of Fischer carbenes from metal-carbonyl or metal-isonitrile complexes according to Scheme 2.20. 

Malatesta, L., and Bonati, F., Isonitrile Complexes of Metals. Wiley, New York (1969). 

Despite a common perception that organometallic chemistry essentially belongs in the province of catalysis rather than in vivo applications because of high reactivity of metal carbon bonds, certain organometallic species have very high kinetic stability. Indeed, this point is highlighted by the present wide application of the isonitrile complex Tc(ses-tamibi), [Tc(2-methoxyisobutylisonitrile)6]+, in myocardial imaging. Rhenium tricarbonyl and cyclopentadienyl complexes offer further ex-... 

Multicomponent condensations have also been described in these an isonitrile, a carbonyl compound and a suitable transition metal complex are combined in one step to afford heterocycloalkylidene complexes. Examples of the use of isolated or intermediate isonitrile complexes for the preparation of aminocarbene complexes are given in Table 2.4. 

Figure 1. Summary of metals that form isonitrile complexes...

The problem of to what extent and how the reactivity of the isonitrile ligand is altered by coordination to a metal has an important bearing on the function of transition metals as homogeneous catalysts. It is also of interest from the standpoint of energy transfer in vivo, to determine whether or not there is any correlation between the reactivities of isonitrile complexes and their conductivities. In this paper we summarize some recent work on the syntheses and reactions of iron isonitrile complexes. 

Gold(I) isonitrile complexes were first reported (131) in 1956, when it was found that they were generally less stable than the isonitrile complexes of other transition metals. This was attributed to the low tendency of gold to form bonds with double bond character. A number of isonitrile complexes have been made, however, and they have been used extensively in the preparation of carbene and imino complexes of gold(I). 

Metalocycles are also formed by the reaction of acetylenes with metal carbonyls or with isonitrile complexes (3, 73, 99-102). Their formation may involve monohaptoacetylene intermediates. 

Isocyanides (RNC) are better a donors and poorer xr acceptors than CO, as indicated by the observation that typical homoleptic isonitrile complexes of many metals are in higher oxidation states than the typical carbonyl complexes of the same metal. Some metal isocyanide complexes are given in Table 7-4. It should be pointed out that there are no carbonyl analogues of those compounds in the higher oxidation... 

The isolation of cyclopentanecarboxylates from 1,3-diiodopropane and an acrylate in the presence of metallic copper and an alkyl isonitrile has been reported by Saegusa and coworkers (equation 39). The reaction is proposed to involve formation of a transient 3-iodopropylcopper-isonitrile complex (47) from the diiodopropane, which then adds to the unsaturated ester in a Michael fashion (equation 40). The nonconcertedness of this reaction results in stereoselective cycloaddition. For example, Iratfa diethyl ma-leate and fumarate produce the same cyclopentane adduct in identical yields (equation 41). The generality of this cycloaddition has not been explored. 

Nitriles are resistant to hydrometallation by transition metal hydride complexes. The complex Cp2ZrHCl reacts with nitriles A rhenium complex bridged by adinuc-lear hydride undergoes insertion with several isonitriles and with acetonitrile. The product in the case of the isonitrile results from a 1,1-inertion (see 11.2.8) ... 

In 1988 Lalor reported the synthesis and spectroscopic characterization of some new poly(benzo-triazolyl)borate salts (Scheme 8).180 The regiospecifity of the synthesis of I I B( Btz)4 differs from that of pyrazole/BH4 reaction in that B—N bond formation takes place in a manner that maximizes steric crowding at boron (i.e., at the triazole N(l) atoms). In 1989 Shiu describes some new metal carbonyls of HB(Btz)3.181 The synthesis and spectroscopic characterization of some first-row transition metal complexes was reported by Cecchi,182 whereas Hill described some new Rh183 and Ru184 carbonyl and isonitrile complexes. The formation of isonitrile derivatives was proposed to proceed through an associative mechanism involving an intermediate complex... 

Metal carbamoyl complexes can readily be converted into isonitrile complexes with phosgene (in the presence of NEtj), a procedure which can be utilized to prepare complexes of isonitriles which do not exist in the free state [635] ... 

The second case involves attack of R-Y-H on the electron-deficient carbon of the isonitrile ligand, followed by proton transfer. It is adjustable with regard to nucleophile since amines (Y = N), unhindered alcohols (Y = O), and thiols (Y = S) add to the isonitrile carbon to form the corresponding diamino, aminoalkoxy, and aminothio carbenes. Isonitrile complexes of several different metals undergo this reaction, although Pd and Pt complexes have been the most thoroughly investigated.25... 

Under N, 1.48 g (5 mmol) of 1,3-diiodopropane in 4 tnL of toluene are added dropwise with stirring over 30 min to a preheated mixture of 1.27 g (20 mmol) of metallic copper. 4.40 g (40 mmol) of cyclohexyl isoevanide. 1.72 g (10 mmol) of diethyl fumarate and 6 mL of toluene at 110 CC. The reaction mixture is heated for 12 h at 110 C and is then treated with Et,<) to remove the copper iodidc/isonitrile complex. The extract is concentrated and distilled in vacuo yield 0.82g (90%) by preparative GC. 

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