Isocyanides lability

The [Co(DH)2L] complexes react with oxygen 137) to give j -peroxo complexes LCo(DH)2-02-Co(DH)2L, isolated using several ligands (not isocyanides however). These adducts are labile, and oxygen is easily lost. On standing these complexes can undergo oxidation, however, to /x-superoxo... 

The palladium-isocyanide complex is effective for silastannation of ethoxyethyne, a labile alkyne, to produce (Z)-1-ethoxy-l-silyl-2-stannylethene with high regioselectivity (Equation (106)).253 The regioselectivity observed has also been studied by computation.263... 

Tokitoh et al. have synthesized a sterically hindered disilene TbtMesSiSiMesTbt 210 that is kinetically stable but thermally labile, thus providing the corresponding silylene TbtMesSi 211, whose reaction with isocyanides bearing bulky substituents has resulted in the formation of the first stable silylene isocyanide complexes TbtMesSiCNR (212, R = Tbt 213, R = Mes ) (Scheme 30).327... 

Convertible isocyanide reagent 66 allows a mild and chemoselective in situ post-Ugi activation of the isonitrile bom amide with simultaneous deprotection of the nucleophilic amine, that is, liberation and activation of two Ugi-reactive groups, if desired also under subsequent lactam formation [33]. Another recently introduced convertible isocyanide, l-isocyano-2-(2,2-dimethoxyethyl)-benzene 73, was shown effective by Rhoden et al. In the course of this short sequence, a hydrolytically labile W-acylindole 78 is formed, which is displaced intramolecularly by the amine portion of the former Boc-protected amino acid 75 (Scheme 13). 

Ligand displacement from labile precursors has led to the homoleptic clusters Ni4(CNR)7, Ni4(CNR)6 and Ni8(CNBu )12 (27,22), Pt3(CNR)6 (23), and Pt7(CNXylyl),2 (20), which represent rare examples of polynuclear homoleptic metal(O)-isocyanide clusters. 

To date, only nickel, palladium, and platinum have formed homoleptic metal(O) isocyanide clusters. This may be due to two factors, either the greater tendency to nucleation in the group or simply the ready access to the highly labile metal(O) precursors M(COD)2 [M = Ni (137), Pt (138)]. 

This catalytic labilization of carbonyl groups has been extended to the replacement of carbonyls in metal carbonyl clusters. Metal cluster complexes are at present the subject of extensive studies, partly because of their possible relevance as models for chemisorbed metal surfaces and because of their catalytic activity. The majority of these clusters contain carbonyl ligands, and these have been prepared from the vast number of metal carbonyl precursors generally available by a variety of synthetic methods usually without recourse to designed or rational procedures. In metal isocyanide chemistry, however, suitable precursors are lacking, and as a consequence, there are few routes to homoleptic metal-isocyanide clusters, and few isocyanide clusters are known (see Section IV,A). 

Other interesting carbonyl substitutions have been reported. The lability of ammonia in [V(CO)5NH3] has been utilized as a route to the isocyanide carbonyl anions [V(CO)5CNR] (R = Me, Bu, C6HM, Ph), one of the few anionic complexes containing isocyanide ligands known (178). Mixing... 

Uson and collaborators described an A-frame PdPt complex [C6F5Pd (p-C=N-p-tolyl)(p,-dppa)2PtC6F5] (75),85 and more recently, [XPd(p,-dppm)2 (p-C=N-R)Pt(CN-R)]+ (76-78) and [ClPd(p,-dppm)2(p,-C=N-R)PtCl] (79-81) were reported by Knorr and collaborators86-88 (Fig. 32). In the bis(isonitrile) heterobimetallics 76—78, a site selectivity in the second CNR ligand coordination (Pd vs. Pt) was noticed. The additional isocyanide is systematically coordinated on the Pt site.86,88 This distinct selectivity between Pd and Pt was explained by the greater lability of the Cl- ion on the Pt center as well as a better stabilization of the positive charge on the electron-rich Pt1 center.88 The question arises as to why the addition of ligand isocyanide sometimes produces the A-frame compound whereas under similar conditions, a d9-d9 isocyanide... 

The lability of the N2 ligand towards alkyl and aryl isocyanides has been demonstrated by equation (2) which occurs readily with both alkyl and aryl isocyanides.40 The resulting complexes are electron rich , the alkyl isocyanide derivatives ReCl(CNR)(dppe) (R = Me or Bul) undergoing electrophilic attack upon treatment with HBF4 to form the carbyne complexes trcms-[ReCl(CNHR)(dppe)2]BF4.41 Other noteworthy features of the series of complexes ReCl(CNR)(dppe)2 and ReCl(CNAr)(dppe)2, are the low value of v(CN), the presence of a bent M—CNR coordination mode, and their ease of oxidation (as measured by cyclic voltammetry) to the corresponding rhenium(II) monocations.40... 

Finally, although not a reaction of isocyanide complexes as such, except as labile intermediates, it can be noted that metal hydrido or alkyl compounds can undergo insertion reactions to give acylimidoyl complexes, which can react further ... 

A suspension of polymeric cupric dimethoxide in pyridine reacts with CO2 to yield the cupric methyl carbonate. The CO2 moiety is, however, very labile the insertion could be reversed by heating the reaction mixture at 80" under a stream of nitrogen [SO]. Another reversible carbon dioxide carrier was found in copper(I) rerr-butoxide, which was stabilized by rerr-butyl isocyanide. The rerr-butyl carbonato complex was formed during the reaction with CO2 [811. Carbon dioxide also reacts with ROCu(PPh3)2 0 produce (ROCOj)Cu(PPhj>3, Hydrolysis or thermolysis of these alkylcarbonato complexes gives the binuctear carbonato copper (I) complex (PPhj>2 CuCK Oj Cu(PPhj)2, which can be further convened into the bicarbonate complex f(HC)C02)Cu(PPh3)3] by reaction with CO2 in moist solvents [82],... 

The quite labile acyl isocyanides on the other hand may be obtained from acyl iodides with AgCN in CH2CI2 similarly imidoyl bromides give rise to imidoyl isocyanides (Scheme 25). Both types of compounds decompose quite easily under comparatively mild conditions. Acyloxy isocyanides are well known too. ... 

Generation of 1-stannaallene 35 was suggested as an intermediate in the synthesis of the first stable distannirane 36, by Escudie et al. (Scheme 2.9.12). Because of the probable lability of the Sn—C double bond, 35 could behave as a stannylene-vinylidene carbene complex, as observed in the related 1-stannaketenimine 31, which behaves as a stannylene-isocyanide complex. Therefore, the generation of the final product of this reaction, 36, should be most likely interpreted in terms of the [2+ l]-cycloaddition of 35 with the stannylene 37, which should be generated in an equilibrium amount. 

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