Isocyanide ligands aminocarbyne complexes

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... 

The ligating isocyanide is activated toward electrophilic attack and aminocarbyne-type species are formed by reactions with acids or alkylating agents. The nucleophilicity of the isocyanide ligand in those electron-rich complexes is in contrast to its usual electrophilic character " reported for this ligand when it binds a metal ion in its normal or higher oxidation states. 

This type of activation of an isocyanide ligand and, therefore, the corresponding route for aminocarbyne species (eq.11) were previously discovered for trans-[M(CNR)2(dppe)y] (M=Mo or W) [21], but the derived aminocarbyne complexes commonly present a much lower stability than ( ) (see section 3.2). 

Moreover, in accordance with the expected decrease of the TT-electron acceptance of the isocyanide ligand which did not undergo protonation, at trans-[Mo(CNHMe) (CNMe) (dppe) ], a strengthening of the corresponding unsaturated C-N bond has occurred (the Ti-overlap population has increased) [33], also as indicated by IR data [a shift of v(CN) to a higher value, i.e., from ca. 1860 in the parent diisocyanide complex to ca. 2160 cm in that aminocarbyne product]. 

ABSTRACT. The redox properties of a variety of isocyanide, rutrile arvj alkyne-derived vinylidene and phenylatlene complexes, commonly with an electron-rich Re(l) or Fe(ll)-phosphinic centre, as well as of the derived protonated species (with aminocarbyne, methyteneamido, carbyne, i vinyl or hydride ligands), as studied by < dic voltammetry and controlled potential electrolysis in aprotic media, are discussed in terms of ligand and metal site effects on the redox potential, and the values of the electrochemical parameter which measures the ligand net etectron-donor/acceptor character are also presented for these ligands. Expressions are indicated which allow to predict the oxidation potential for the octahedral-type 18-electron complexes or 3) or [MsU-1-... 

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