Variable Pathways for Oxygen Atom Insertion into Metal-Carbon Bonds: The Case of Cp*W(O)₂(CH₂SiMe₃) Page: 430
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Journal of the American Chemical Society
Scheme 7. Calculated Free Energy for the Reaction of
Cp'WO( 2-O),(CHI2SiMe) (2) with HtaW O
+32
3+17 6
0R0
+22
+4
+ H(diiox})
U W-6H
O H
. -- 2 dox
2 1O
G .AG(H2O)
R - CH2SiMeB3OR
3
-75 s 9
- 6
OH
O R"The cation (H (diox) (diox - 1,4-dioxane)) was used to model the
proton, Nunmberis are free enegies (kcal nol ') for 1.4-dioxane (top,
bold) and water (bottom, italics) and are relative to complex 2.S
261 W
0 3.10
2.10c
1 168.9 1.87 t
C ae
Figure 9. DFT calculated organometallic IBaeyer-Vil]iger (ONIBV)
transition state for oxy-insertion of hy'droperoxide into W-C bond of
(:p* 'W(),(CHzSile3) ( i ). Bond lengths are given in A and bond
angles in degrees.
being broken is shorter (2..11 vs 2.61 A) for the periodate IS,
implying an earlier I'S tor the )MB\.' oxy-insertion with
periodate in relation to the h]cyidroperoxide conlgeert . l'he
tremendous kinetic and thermodynamic free energy. preference
for the O1M1B\' pathway itn relation to the pathways that lead to
reduced W"1 intermediates (nucleophilic substitution and
reductive elimination, Scheme 5) is interesting in connection
with the highly endeigosic single electron transfer reaction
modeled above, and supports the notion of the important role
of metal d orbital occupation in soxy-insertion, and further that430
movement away from d motifs will disfavor the (OMB3V
pathway. thus, while tunctionalization of alkyl-] ligands through
processes that formally reduce the metal center can be facile for
late transition metal complexes, similar reactions with middle
transition metals may have inherently and prohibitively high
activation barriers.
Reaction of Cp*W(0)( 2-O2)(CHSiMe3) (2) with
Bronsted Acid. t'he formation of alcohol is also observed
when complex 2 is treated with HC1 in ,.l dioxane. The
reaction is complete in .10 h at room temperature and produces
(.p*W(C)),C' and MI'.SCIH,l-1H in 90.t yield by 1'il N MR
spectroscopy (eq 1). The acid promoted reaction of 2 is slower3 e HCI, 23"C, 40 +
o dinne +ROH
O0 R -
2 R= CHSiMeS(4)
than the hydroxide promoted conversion. Ior example,
complex 2 with 3 eqiL' of NaoH quantitative]y forms
I'A ,C( OH in less than I[ h at room temperature.
liable I shows the conditions and results for the reactions of
complex 2 with various proton sources. Without a proton
Table 1. Reaction Conditions and Yields for Reaction of
(p''W(O)( 2-)2(CH2SitMez) (2) with Bronsted Acidno. solvent
1 belzonce
2 dioxanc"
3 dioxanc
4 dioxanc
5 dioxancwatcr
6 dioxane/watcr
7 dioxane
8 dioxane/water
9 diuoxaneacid
none
3 cquiv o IICl ,
(dioxanc)
3 cq I ICL (dioxanc)
3 cquiv oi" fItCt I351:)
05 equiv of It 112504 (98%)
5 cquiv ot 112504 98a)
none
IIOTf 99% )7" yield"
( c) , (b) ( )80
23
23
}0
23
-524
40
32
2I
too
too
12
24
1290
7060
80
>90
dccomp,
70
decomp,'"Yields of TISCH,I)H are based on integration of 'H NMRI spectra
versus an internal standard. ' 1.4-dioxane.
souLrce, when 2 is heated in benzene at 80 C" for 2. hi, no
alcohol is observed, and the starting material decomposes to
tform i complex 1 (entry 1). Heating increases the rate of
conversion but decreases the vield (entries. 3 and 1). The use of
strong acid in 1,.I dioxane results in decomposition of the
starting material with no alcohol production (entries - and 9).
Adding 1-"B4N 1 does not accelerate the reaction, which is
consistent with the acceleration by HC] resulting from the
addition of protons rather than chloride. Also, weaker acids,
such as ]ltidiniLmn, do not facilitate this reaction at room
temperature.
WVe have considered two roles for the acid in the conversion
of 2 and 111 to (WCp* \ )(0).I and lI HS(11l- (Scheme 6i)':
(1) the proton serves as a catalyst by} protonating the' p-petroxo
ligand, which would increase oxygen electrophilicity and
facilitate oxv-insertion. A similar mechanism was proposed for
the acid catalyzed rearrangement of an 1 peroxo la alklI] to
form oxo alkoxide derivatives. (2) i he proton is not a
catalyst, but rather, the acid serves to generate free alcohol from
(p* W(, O C Sikey).
1o investigate rate dependence of the reaction of 2 and 1(,
we attempted to use excess IICI to achieve pseudo rst-order
dx.doi.org10.1021/ja309755g I Am. Chem. Soc. 2013, 135, 424 435
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Mei, Jiajun; Carsch, Kurtis M.; Freitag, Cody R.; Gunnoe, T. Brent & Cundari, Thomas R., 1964-. Variable Pathways for Oxygen Atom Insertion into Metal-Carbon Bonds: The Case of Cp*W(O)₂(CH₂SiMe₃), article, December 24, 2012; [Washington, D.C.]. (https://digital.library.unt.edu/ark:/67531/metadc179685/m1/7/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.