Nitrene

In chemistry, a nitrene or imene (R−:Ṅ·) is the nitrogen analogue of a carbene. The nitrogen atom is uncharged and univalent,^[1] so it has only 6 electrons in its valence level—two covalent bonded and four non-bonded electrons. It is therefore considered an electrophile due to the unsatisfied octet. A nitrene is a reactive intermediate and is involved in many chemical reactions.^[2][3] The simplest nitrene, HN, is called imidogen, and that term is sometimes used as a synonym for the nitrene class.^[4]

Electron configuration

In the simplest case, the linear N–H molecule (imidogen) has its nitrogen atom

• From
  diazo compounds
  .
• From isocyanates, with expulsion of carbon monoxide. This method is analogous to the formation of carbenes from ketenes.

Reactions

Nitrene reactions include:

• Nitrene C–H insertion. A nitrene can easily insert into a carbon to hydrogen
  retention of configuration. In one study^[6] a nitrene, formed by oxidation of a carbamate with potassium persulfate, gives an insertion reaction into the palladium to nitrogen bond of the reaction product of palladium(II) acetate with 2-phenylpyridine to methyl N-(2-pyridylphenyl)carbamate in a cascade reaction
  :

A nitrene intermediate is suspected in this C–H insertion involving an oxime, acetic anhydride leading to an isoindole:^[7]

• Nitrene cycloaddition. With
  catalyst such as copper, palladium, or gold:^{[8][9][10][11][12]}

In most cases, however, [N-(p-nitrophenylsulfonyl)imino]phenyliodinane (PhI=NNs) is prepared separately as follows:

Nitrene transfer takes place next:

In this particular reaction both the

trans form (not depicted) result in the same trans-aziridine product, suggesting a two-step reaction mechanism. The energy difference between triplet and singlet nitrenes can be very small in some cases, allowing interconversion at room temperature. Triplet nitrenes are thermodynamically more stable but react stepwise allowing free rotation and thus producing a mixture of stereochemistry.^[13]