ca01 only detailed ToC 1..24

2.6.8 Complexes with Singly Bonded Heteroelement Ligands 131
1-[(Diphenylphosphino-kP)methyl]-N-{[(diphenylphosphino-kP)methyl]dimethylsilyl}-
1,1-dimethylsilanamido-k,N](phenylsulfido)methylchromium(III) (96): [170]
To a red-brown soln of [CrMe{N(SiMe 2CH 2PPh 2) 2}] (0.16 g, 0.27 mmol) in toluene (10 mL)
cooled to 08C was added a soln of PhSSPh (0.03 g, 0.14 mmol) in toluene (5 mL). Immediately,
the soln changed to a dark purple color. After the mixture was stirred for 1 h at 0 8C,
the soln was warmed to rt and the solvent was removed almost to dryness. The residue
was quickly dissolved in hexane (1 mL) and filtered through Celite, and the solvent was
removed in vacuo. Recrystallization from hexanes/toluene (1 mL: 3 drops) in a –408C
freezer yielded a thick oil, which upon agitation gave 96 as purple crystals; yield: 0.12 g
(66%).
2.6.8.2 Method 2:
By Transmetalation
Compounds that already contain a single bond between the metal and a heteroatom ligand
may exchange the latter upon treatment with a suitable salt of the desired new
ligand. The ubiquitous substrates are the halides, especially the chlorides which are easily
accessible by oxidative procedures (Section 2.6.8.1 above) or from inorganic halide precursors.
One example is the synthesis of 20 in Scheme 7. Like the alkylating agents discussed
previously (Sections 2.6.3.1 and 2.6.4.1), some salts are potential reducing agents,
especially alkyl and aryl sulfides, phosphides, and amides. The reaction of precursor 97
(Scheme 44) with a variety of lithium salts always affords the metathesis product in
good yield when X 1 = alkoxo or amido. [171,172] When X 1 = chloro, 5% of reduction is afforded
by the 4-tolylamide salt with the molybdenum system, while the diphenylphosphido reagent
yields exclusively reduction products for both molybdenum and tungsten. [173]
Scheme 44 Transmetalation [171–173]
M
Cl NO
X1 97
+ LiX 2
25−82%
M = Mo, W; X 1 = Cl, NHt-Bu, Ot-Bu; X 2 = NHt-Bu, Ot-Bu, PPh 2
M
X 2 NO
X 1
Bis(2,6-diisopropylphenolato)(2,6-diisopropylphenylimido)(2,2-dimethylpropylidene)tungsten;
Typical Procedure: [17]
The lithium salt of 2,6-diisopropylphenoxide (1.60 g, 6.19 mmol) was added to [W(=CHt-
Bu)Cl 2(=NC 6H 3-2,6-iPr 2)(DME)] (1.82 g, 3.09 mmol) in Et 2O (50 mL) at –40 8C. The soln was
warmed to 258C and stirred for 45 min. The mixture was filtered, and the filtrates were
concentrated to afford an orange solid. Recrystallization of this material from a minimum
of pentane afforded the product as a bright yellow solid in two crops; yield: 1.74 g (72%).
2.6.8.3 Method 3:
From ó-Alkyl Complexes
Protonolysis of the typically polar bond between a group 6 metal and a hydrocarbyl ligand
is usually considered to be an unwanted decomposition reaction. When metal-heteroatom
bonds are desired, however, selective alkane-elimination reactions can sometimes offer
significant advantages, such as ready availability and stability of the protonated
source of the desired ligand (such as carboxylic acids, alcohols, or amines) and the absence
of inorganic salts as byproducts (the resulting alkane is normally easily removed
for references see p 135