Variable Pathways for Oxygen Atom Insertion into Metal-Carbon Bonds: The Case of Cp*W(O)₂(CH₂SiMe₃) Page: 428
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Journal of the American Chemical Society
mIncl] uLlsion of continuum solvent e ects (C'PCBM, water solvent)
increases the exergonlicity of this reaction to 20 kcal] mol-].
The calculations indicate that the increased driving force resuLlts
from more favorable solvation of the smaller iodate ion in
relation to periodate. h']us, the calculations predict that water
should enhance the thermodynamics of oxygen atom transfer
frilom 104-, but the extent to which this would enhance the ox.
insertion kinetics is uncertain without calculation of the
corresponding hydrated O\1BV transition state.
Explicit sol ationl e ects on periodate-mediated OMB\I V
reactions were modeled. Hy1-Ildrogel bonding a water molecule
to each oxo of the iodate leaving group in the O\t I'S resLilts
in a reduction of the calculated energy barrier from 28
kcal iol-1 (Scheme 3) to 21 kcal ol-] figuree 6), which is
C C -
1 C89 86,0
1j4 i 183,
\ 1 983 '.9 2' "
Figure 6. DFT-caculated TS with water for the oxy-insertion step of
the overall reaction Cp' W(0(),((CH2SiMe). (1) + 104 (p* W-
() '()CH SiN"Ie ) (3) + 10 . Bond lengths are given in A and bond
angles in degrees.
closer to the experimental value of 18 kcal mcol- (see above).
Bond lengths within the active site of the (OMB T' I'S figuree .1)
are little chaingedi LLIL hydrogen bonding with three water
molecules. What is more noticeable is the shortening of the 0-
H-O hydrogen bonds by 0.05 A from 2.00 A ( 104(?01), )1
to 1.95 A in the oxyw insertion IS. In conjunction with the
implicit solvation results above, these data lend credence to the
proposal that preferential solvation of the iodate leaving giroupi
enhances oxy-insertion of periodate into the \V C' bond of 1
both kinetically and therimodynamically, e ectively making the
iodate a better leaving group and the periodate a more potent
Reaction of Cp*W(O)( '-O)(CH2SiMe3) with NaOH.
Complex 2 reacts with Na)H to produce 'MSCH,0-H in 1:1
TH1I .L ,(i,0 or I,.I dioxane-i'/D.) (v/v). lThe reaction
produces 'MSC(H1,01 - in quantitative yield ('1- NMR) after
3 h at room temperature (eq 3).
a0-2 n .
l-' at 10.7
The slope of the plot in l[igure gives k -
Ss-, which corresponds to G - 19.1(I)
aoo ao a.c 100 0.160 0.2o
Figure 7. Plot of k bs VSOH for the reaction of (p .V( i.-
( _i(HCHiSiNle1). (21 with NaoH showing a rst-order dependence on
OH i (CR- 0.99).
''he irate of the reaction between 2 and NaOH was
monitored by 11 NMIR spectroscopy at 1.3, 10.7, 22. and
31.7 C. An Eyring plot (using ,k values that were corrected for
I O-, IFigure 8) was used to calculate H - 3.k(. 1)
kcal mol and - - 20(1) cal mol- K-.
0.0031 0.0033 0.0035 0.0037
Figure 8. Plot of In (k,. vs 1/7for the reaction of(p* W(O)liq-
Oi(C(HISiNIe}1 (21 with NaOH (5 equi) (R - 0.99).
'T'hree possible pathways for the reaction of complex 2 with
NaOH are shown in Scheme 1. in pathway A. the hydroxide
undergoes direct nucleophilic addition to the I'MS(C1H, ligand.
1or this pathway, the oxygen atom in the alcohol would
Scheme 4. Possible Pathways for Alcohol Release from the
Reaction of CpW(())( 2-(O)2(CH2SiMe3) (2) with NaGH
in 1:1 TlF-dI) 2() (viv)
I1 e NaOH, 23"C, 3h ROH
O 1:1 THF:H2O (v:v) 100%
2 R = CH2$SMe3
Under pseudo rst -order conditions, the reaction of 2 with
NalOH in 1:1 TH- l , v D,O ) (vv) as monitored at 10.7 C b-
i]- NMll. spectroscopv. Kinetic plots reveal a rst order decay
of 2, aind a plot of k0,o as a function of ( -I- shows that the
reaction of 2 with NaC)H has a rst-order dependence on
+ ~O' Elimination
O Of O O- o
O HO R O O O
2 + RO'H
- O-atom - -
nserlion H' transfer
o 7 0 W0 o o- o
HO' R HO ' O0,R
Pathways R = CH2SiMe ROH
dx.doi.org'10.1021/ja309755g J. 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.]. (digital.library.unt.edu/ark:/67531/metadc179685/m1/5/: accessed December 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.