Bent carbyne

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... 

Crystal-structure determinations performed on chromium carbonyl carbynes indicate an average Cr C bond length of 1.70 A, ca. 0.2 A shorter than the average Cr C(carbonyl) distance. An exception is seen in X(CO)4Cr=C-NR2, in which the Cr-C bond is somewhat longer and the C N bond somewhat shorter than expected. These findings are consistent with the presence of some double bond character. The Cr C-R bond angle is customarily very close to linear, but structures bent up to 12° are known. Chromium carbonyl carbynes are frequently employed as starting materials for the synthesis of carbenes inaccessible... 

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