Isonitrile complexes formation

In vivo the metal may assume two functions by virtue of complex formation It may modify the reactivity of the coordinated ligand and it may influence the energy transfer between molecules. Hence, it was of interest to compare the reactivities and electron displacements in benzyl isonitrile iron (II) complexes in solution to their conductivities in the solid state. 

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. 

Although carbonyl and cyclopentadienyl complexes are well known for Tc(I) and Tc(III), none appear to have been reported for Tc(II). This may be ascribed to the tendency to follow the 18-electron rule, which, due to the odd number of electrons, would require dimer formation for compliance. Similarly, no Tc(II) cyano or isonitrile complexes appear to have been isolated. 

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. 

Treatment of alkylating agents with metal cyanides should in principle be the method of choice for preparing isocyanides (equation 25). But as the cyanide ion again represents an ambident nucleophile, the well-known problems already discussed will arise (Section 1.8.2.1.i). It remains to be stated that simple alkylation of alkali metal cyanides with halogen compounds or dialkyl sulfates is not useful for the preparation of isonitriles. The formation of nitriles always prevails and isocyanides are at best obtained in yields of up to 25%. " The prospects are much tetter in the alkylation of heavy metal cyanides, if the reaction is done under conditions which initially give rise to isocyanide-transition metal complexes (equation 26). These will then be transformed into isonitriles by treatment with KCN. Under optimized conditions this technique yielded 55% of ethyl isocyanide. ... 

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... 

Reaction of bis(disilanyl)dithiane 32 with the corresponding palladium(O)-isonitrile complex affords a four-membered cyclic bis(silyl)palladium(II) complex 34 quantitatively together with the formation of a disilane (Eq. 15) [30]. The formal intramolecular metathesis of the two Si-Si bonds of 32 may proceed through initial formation of tetrakis(silyl)Pd(IV) complex, corresponding to the platinum complex 33. The double oxidative addition of the two Si-Si bonds may be followed by reductive elimination of the disilane with accompanying formation of four-membered bis(silyl)palladium complex 34, due to difficulty in reductive elimination leading to formation of a three-membered cyclic disilane. 

These displacements are so facile that Ni(l,5-COD)2 has been described as naked nickeF. In some cases the reactions are carried out in two stages with intermediate formation of, for example, an isonitrile complex ... 

The isocyanide-substituted complexes can be correspondingly obtained following thermal decarbonylation of the bromotetracarbonyl species with tert-butyl isonitrile to produce the cationic aminocarbyne complex [Cr(=CN Pr2)(CO)(CN Bu)4]. Subsequent treatment with Na[Cp] or K[Tp ] in tetrahydrofuran at 50 °C results in formation of LCr(=CN Pr2)(CO)(CN Bu) (L = Cp or Tp in 61 and 58% yield, respectively). In both reactions the minor product [Cr(=CN Pr2)(CN Bu)5] is formed by a competitive carbonyl-substitution reaction of the tetra(isonitrile) complex with liberated CN Bu. ... 

Hydrolysis of this metallacycle with aqueous HPF6 led to the formation of the cationic isonitrile complex [TpFe(CNTr)(CO)2]PF6 in 60% yield which is only obtained if the reaction is carried out under an atmosphere of carbon monoxide. 

Addition of PrNH2 to solutions of the isonitrile complexes ReBr(CO)4(CNPh) results in formation of the caibene complexes ReBr(CO)4 =C(NHPh)(NHPr). The Pr> derivative undergoes carbonyl substitution in its reaction with PPha to form ReBr(CO)3(PPh3) =C(NHPh)(NHPr ). t29 Addition of bis(imidazolium)iodide to NMe4[Re2(CO)6(OMe)3], formed in the carbonylation of NH4[Re04] in MeOH (100-110 bar), results in the hu-caibene complex SS. t o... 

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