ca01 only detailed ToC 1..24

128 Science of Synthesis 2.6 Complexes of Cr, Mo, and W without CO Ligands
Scheme 40 Synthesis from a Complex Containing a
Triply Bonded Heteroelement Ligand [159]
Mo(CH2Bu t )3( N)
X = F, Cl, Br, I, OPh, OSiPh 3
HX, THF
40−85%
H
N
Bu t H2C Mo
X
89
CH2Bu t
CH 2Bu t
Tris(2,2-dimethylpropyl)imido(triphenylsilanolato)molybdenum(VI) (89, X = OSiPh 3);
Typical Procedure: [159]
[Mo(CH 2t-Bu) 3(”N)] (1.0 mmol) and triphenylsilanol (1.0 mmol) were placed in a Schlenk
tube under argon and dissolved in THF (30 mL). The mixture was stirred at 60 8C for 48 h.
Removal of the solvent under reduced pressure and extraction of the residue with hexane
(5 mL) afforded [Mo(CH 2t-Bu) 3(=NH)(OSiPh 3)] as a white powder. Recrystallization from
hexane at 08C gave white crystals; yield: 240 mg (40%); IR (Nujol) í~ max:(N-H) 3371 cm –1 .
2.6.7.4 Method 4:
By Oxidative Processes
The most useful oxidizing agents for the preparation of organometallic oxo compounds
have been nitrogen oxides such as trimethylamine oxide, nitrous oxide, and nitric oxide,
allowing the preparation of compounds that cannot be accessed by other methods, although
the oxidations are often accompanied by the formation of other products. [160] For
selected systems, oxidation of a low-valent precursor with the heteroelement itself in its
natural state (e.g., O 2,S 8) is sufficiently clean to be synthetically useful for the preparation
of oxo and sulfido complexes. This is especially true for ç 5 -cyclopentadienyl and ç 5 -pentamethylcyclopentadienyl
systems. The synthesis of 90 (Scheme 41), involving exhaustive
decarbonylation, represents a typical example. [161] Photochemical activation of the carbonyl
precursor is necessary in some cases. [162] Occasionally, elemental oxygen can be replaced
by hydrogen peroxide, as, for example, in the synthesis of 91, but this requires the
use of a strict stoichiometric ratio to avoid further conversion into peroxo analogues. [163]
Hydrogen sulfide also leads to oxidation, with expulsion of dihydrogen, in the synthesis
of compound 92. [164] The synthetic utility of the oxidation with a diazene to yield a bis(imido)
product has only been illustrated for inorganic target systems. [165]
Scheme 41 Oxidative Processes [161,163,164]
{MCp(CO) 2} 2
MCp(NO)R 1 2
R 1 = Me, CH 2TMS; M = Mo, W
Me 3P
H
Me 3P
PMe3 PMe2
Mo
PMe 3
air, CHCl3 or benzene, rt
M = Mo 69%
M = W 14%
30% aq H2O2, rt, 1 h
ca. 10−50%
H2S, pentane, −78 o C
− H 2
60%
(CpMO2)O 90
MCpO 2R 1
91
Me3P
S
Mo
PMe3 Me3P S
PMe3 92