ca01 only detailed ToC 1..24

2.6.6 Complexes with Triply Bonded Heteroelement Ligands 123
2.6.5.3 Method 3:
By Addition of Alkenes to Carbene Complexes
This method is specific for metallacyclobutane complexes. For stability reasons this method
has been mostly applied to the preparation of high oxidation state tungstacyclobutane
derivatives. Given the equilibrium shown in Scheme 32, the use of excess alkene may result
in further exchange processes. The preparation of 82 in Scheme 35 is a two-step process
involving the elimination of 3,3-dimethylbut-1-ene. [29]
Scheme 35 Metallacyclobutanes by Alkene Addition to Carbene Complexes [29]
Pr i
Pri N
W
ButHC OCMe(CF OCMe(CF3) 2
3) 2
(excess)
TMS
pentane, rt, 2 h
ca. quant
Pr i
Pr i
N
OCMe(CF3) 2
W TMS
TMS
OCMe(CF3) 2
82
1,2-Bis(trimethylsilyl)propane-1,3-diyl(2,6-diisopropylphenylimido)bis(1,1,1,3,3,3-hexafluoro-2-methylpropan-2-olato)tungsten(VI)
(82); Typical Procedure: [29]
Trimethyl(vinyl)silane (124 ìL) was added to a soln of [W(=CHt-Bu)(=NC 6H 3-2,6-iPr 2){OC-
Me(CF 3) 2} 2] (212 mg) in pentane (15 mL). The solvent was removed in vacuo after 2 h to
give a light yellow product that was recrystallized from pentane to give light yellow crystals.
The yield of the crude product was essentially quantitative.
2.6.6 Product Subclass 6:
Complexes with Triply Bonded Heteroelement Ligands
The only known examples are nitride complexes, whereas terminal phosphide and arsenide
complexes are known only without metal-carbon bonds. The lone pair on the nitride
ligand retains sufficient Lewis basicity for coordination. Consequently, electronically
unsaturated derivatives yield polymeric or oligomeric structures where nitrido groups
bridge two metal centers symmetrically or asymmetrically. [140,141] Mononuclear complexes
with terminal nitrido ligands are only found when the Lewis acidity of the metal
center is suppressed by ð-donation from other ligands, e.g. amido ligands as in bis(diisopropylamido)[(dimethylphenylsilyl)methyl]nitridochromium(VI).
[142] In addition, oligonuclear
structures where the nitrogen atom forms bonds of lower order with more metal atoms
may be preferred to a triply bonded mononuclear structure.
Almost all organometallic nitride complexes have been obtained by adding the organic
group(s) to inorganic substrates that already contain the M”N function. An example
is the synthesis of compound 57 shown in Scheme 23. [103] A large number of methods for
assembling a metal-nitrogen triple bond in inorganic compounds are outlined in a review.
[143] Some of these methods are also of potential applicability to organometallic substrates
and are, therefore, briefly mentioned here (Scheme 36).
The exchange of three halides with a nitride can be accomplished by use of the
[Hg 2N] + ion, tris(trimethylsilyl)amine, or ammonia, with elimination of mercury(II) salts,
trimethylsilyl halide, or hydrogen halide, respectively. In the latter case, excess ammonia
is needed to neutralize the acid. The ammonolysis of trialkyl or alkyl–carbene complexes
has been used successfully to prepare organometallic nitride complexes of group 4 and 5
metals (see Sections 2.8–2.11) and could potentially be used for group 6 metals as well.
Ammonolysis of a carbyne complex would appear to have the same potential.
Nitride complexes are also obtained by exchange of a halide with groups capable of
readily eliminating a stable byproduct while leaving a nitrogen atom bonded to the met-
for references see p 135