Variable Pathways for Oxygen Atom Insertion into Metal-Carbon Bonds: The Case of Cp*W(O)₂(CH₂SiMe₃) Page: 425
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Journal of the American Chemical Society
reaction of a iM-R moiety with an oxy en atom delivery'
reagent (' YO). One pathway involves a migration of the ligand
LR to a metal oxo intermediate. The second pathway
incorporates direct os -insertion from M(OY)R t..,) without
the formation of a metal-oxo intermediate. 'To be generally
useful for selective oxidations at high conversion, ideally, the
C- () bond tormiing step should proceed without the formation
of radical intermediates and can be facilitated by catalysts
incl] uding organocatalhsts, as recently reported with avinium
s,'and by metal oxo complexes as reported by (oldberg and
l'he 1.2-addition of C ---1-I bonds across 1- Ni IR and NI
OR bonds is known. in 2003, our groups stLudied and reported
intramolecular C - 1-1 activation by a PCP .-- Iu" 1 amido complex
and commented on the potential utility of this transformation
in catalytic transformations.2 Then, in 2005, we reported
intermolecular benzene C'-Ii activation by Rull hydroxide and
anilide complexes. R'l. 'Ielated chemistry includes an Ir"1'
complex and KRu" complexes by Periana, Goddard, and co
Workers,ti6,2? a Rh1 complex reported by leinekey, Goldberg,
and co-workersi . and a Rh' complex reported by Bgercaw,
Labinger, and co-workers."
While insertions of oxygen atoms into NI C bonds are
knosn , examples that occur by non-radical routes are rare. In a
1988 publication that focused on oxygen atom insertion into
la' hydrocarb-I bonds, blercaw and co workers stated, "lihe
details of the actual oxygen-transfer step in control led metal
mediated oxidations are still poorly understood...examples of
clean carbon -ox'ygen bond formation for well characterized
compounds are rarer still.'26 Despite a few recent exam-
ples, IO927-i we believe that this statement remains accurate.
Some early transition-metal complexes, such as group IV
complexes, initiate oxygen atom insertion into NI R bonds;
however, these reactions commonly proceed by radical
pathways. br iown and Mayer reported oxy linsertionl into
,\Al- Ar (Ai- an) bonds with Re'" via the migration of the Ar
group to an oxo ligand.-'' Similar mechanisms that involve
the formation of metal --oxo have also been proposed for the
ox ygen atom insertion of I'd complexes, but mechanistic studies
have not been disclosed. 1 illhouse and co workers have
reported net oxygen insertion into a series of Ni-R bonds and
a If Phll bond upon reaction with N,. . Espenson and co-
workers reported that methyltrioxorhenium ( IC') reacts with
oxidants to release methanol. Later, Periana, Goddard, and
co-workers investigated the mechanism of this reaction. A
pathway that involves migration of the methyl ligand to the
oxygen of the coordinated oxidant was proposed, and an
analogy between this reaction and the Baeyer \'illiger reaction
(conversion of ketones to esters) was made. ',','8
mechanisms and strateies to facilitate these transformations.
To our knowledge, detailed studies of reactions that give clean
oxyS.gen atom insertion into metal -hydrocarbx.I bonds are
limited to the studies of Re'" conplexes.t '9,31, , Herein, we
present studies of oxygen atom insertion into the W"
(It,Sikle. bond of Cp W(0_),(I I,SiMe.) (1) and (p*V-
(0)(m' 0O,)(CH,SiMe) (2). Complexes 1 and 2 have been
previously prepared and studied by Legzdins and co-worke's."
* RESULTS AND DISCUSSION
Reaction of Cp*W(O)',(CHSSiMe) (11 with Nal0,. The
reaction of Cp*W(),((C-ISi.le.) (1) with 11,0, has been
reported to yield e he i2-peroxo complex (:p*W0\.V )(0 ) -
O,)(Cll,SiNle :) (2);." however, the reaction of I with I1
equiv of Nal()4 in 1:1 '' " D, or 1 1:1 1.1 dioxane 1s) ,()
(viV) does not produce complex 2. Rather, 1'\ISC(:' ,0 I
I'\S - SilMe, trimethylsilyl) is formed without observation of
2 as an intermediate. lhe reaction is complete within two hours
at room temperature and produces l'\SC11,0H11 in almost
100% yield by 11 NMR spectroscopy (e 1t )i. 'o determine the
O 1 eq NalO4, 23C, 2hn ROH
0 1:1 THF:HZO (v:v) 10i
1 R = CH2 iMe3
pathway for the conversion of I and Nal)4 to IMSCH-I,C1H,
we rst considered the possibility that the -'-pe'oxo complex
Cp* \(C.)(q' (,)(('1 h},iMe. " (2) is formed as anm intermedi
ate, followed by oxv-insertion into the \V- C bond and
subsequent protonolvsis to give free I'\.SC:1-i,H1. Complex
2 was reacted with Nal)4 under the same conditions as the
alcohol release from I and Nalt o, and no alcohol was observed
b: 7H NNIMR spectroscopy after 2 1 hours. I' lur'thermore, 2 does
not react with Nal) or 1)20, to produce I'NMSCi,OH under
the same conditions. Thus, the evidence suggests that the
formation of T'M1C1,011 from I and NalO, does not likely
proceed via complex 2.
'ilhe reaction of 1 and Nal) (5 equiv) in 1:1 '1THF1-,d./[D,O
(vs v re ) iwas monitored at 1.3 ;C by ]H NIR spectroscopy.
During the conversion, the disappearance of 1, the emergence
of an interllmediate, and the appearance of 'MSC_'I,0H Cwere
observed. The formation of iNMSCI-1,01H occurs with t'. 10
main in approximately 1O0', yield. On the basis of iH N\Ilk
spectroscopy, the intermediate is proposed to be the tungsten
alkoxide complex C:p*W'(0)),(OC)CiiSiMe.,) (3): however, we
were not able to isolate 3. lThe 'H N\.IlR resonances of the
intermediate 3 are assigned as 1.1 ((' l,, s), 2.0.1 (( f, s),
-0. (SiMe, s) ppm. Ao.'), (),( OEt), exhibits a resonance due
to the O(11Ale at -1.6 ppm,45 and the similar complex
(bpy)Mo(0),(OEt)_ (bpy - 2,2 -bipyridine) exhibits a
methylene resonance at 3.86 ppm. In contrast, the Cl1,
groups of 1 and 2 resonate at 0..13 and 3.10 ppm, respectively.
In addition to Nal()4, complex 1 reacts with iodosobenzene
(Phi )) in I1,1-dioxane at room temperature to produce 3 in
20'.. yield in 20 min by ]H NiR spectroscopy (el 2)
however, at prolonged reaction times, an intractable mixture of
products is formed.
eq PhI, 23c, 20o #
O O dioane O O +Phi
R = CHSLMe3 -20%
Figure I depicts the cosce'ntration verss time plot for all
species observed in the conversion of 1 andi NaL(), to
I'NMS11,C~iH, based on the integration of the methylene
resonances of 1, the TI'N ESCI ,C)I H product, andi complex 3. 'The
sLum of concentrations of these three species (black X's, l'iguie
1) remains constant over the course of the reaction.
Scheme 2 depicts a proposed organometallic Baeyer-\ illiger
(C1\"1\') pathway for the formation of 'IN[SCH11,C)H from the
reaction of 1 with Nal)4. Periodate coordinates to complex 1,
followed by concerted migration of the alkyl ligand to the
dx.doi.org/10.1021/ja309755g IJ 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/m1/2/: accessed January 19, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.