Radical scission of symmetrical 1,4-dicarbonyl compounds: C-C bond cleavage with titanium(IV) enolate formation and related reactions

Article abstract of DOI:10.1021/om0107284

Reaction of Ti(NRAr¹)₃ (1, R = C(CH₃)₃, Ar¹ = 3,5-C₆H₃Me₂) with 0.5 equiv of symmetrical 1,4-diketones (ArCOCH₂)₂ (Ar = p-Tol or p-MeOC₆

Full text of DOI:10.1021/om0107284

Organometallics 2002, 21, 1329-1340
1329
Articles
Ra d ica l Scission of Sym m etr ica l 1,4-Dica r bon yl
Com p ou n d s: C-C Bon d Clea va ge w ith Tita n iu m (IV)
En ola te F or m a tion a n d Rela ted Rea ction s
Theodor Agapie, Paula L. Diaconescu, Daniel J . Mindiola, and
Christopher C. Cummins*
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,
Cambridge, Massachusetts 02139-4307
Received August 9, 2001
Reaction of Ti(NRAr1)3 (1, R ) C(CH3)3, Ar1 ) 3,5-C6H3Me2) with 0.5 equiv of symmetrical
1,4-diketones (ArCOCH2)2 (Ar ) p-Tol or p-MeOC6H4) in hydrocarbon solvents at e25 °C
resulted in carbon-carbon bond cleavage with clean formation of titanium-bound enolates,
1-OC(CH2)Ar. Treatment of Ti(NRAr1)3 with esters or amides of succinic acid, under the
same mild conditions, smoothly produced titanium(IV) compounds containing the corre-
sponding amide or ester enolate moiety. The amide enolate condenses with benzaldehyde
in an aldolic fashion. Differences in the observed reactivity of amido-enolate vs ketone-derived
enolate toward aldol condensation were interpreted with the help of computational methods.
Upon reaction with Ti(NRAr1)3, para-substituted acetophenones yielded equal amounts of
enolate and alkoxide products. Under similar experimental conditions, acetophenone itself
produced quantitatively a species whose proposed structure incorporates characteristics
reminiscent of a Gomberg dimer. This intermediate decomposes cleanly to the expected
enolate and alkoxide mixture upon heating. Ti(NRAr1)3 reductively complexes substrates
such as N-methyl phthalimide. Treatment of Ti(NRAr1)3 with 0.5 equiv of o-bromophenyl
allyl ether resulted in bromine atom abstraction followed by cyclization of the intermediate
aryl radical to generate a titanium-bound 3-methylenedihydrobenzofuran product.
In tr od u ction
nature of the ketyl radical intermediate came from the
research of Wolczanski et al., where a sterically encum-
bered Ti(III) tris-silox (silox ) [OSi-t-Bu]3) complex was
used to generate long-lived ketyl radicals.9,10 These
results highlight another major theme in the area of
inorganic reagent design for applications in synthetic
organic chemistry, namely, the use of steric control to
tune or to alter completely the reactivity of organome-
tallic compounds toward organic substrates. More re-
cently, ketyl radicals generated by lanthanide centers
have constituted the subject of intensive research.11,12
In this work we report on the reactions of Ti(NRAr1)3
(1, R ) C(CH3)3, Ar1 ) 3,5-C6H3Me2) with organic
substrates containing carbonyl and/or halogen function-
alities. Compound 1 contains a reducing and oxophilic
d1 metal center supported by sterically demanding
amide ligands. Previous reports regarding its reactivity
toward inorganic electrophiles show that 1 is a potent
1e reductant, making it suitable for studies with organic
substrates.13,14 Furthermore, 1 is easily accessible via
The development of inorganic and organometallic
compounds having applications in organic synthesis is
an active area of chemical research.1 Reductive coupling
of ketones and aldehydes to produce vicinal diols or
olefins is a useful method for carbon-carbon bond
formation.2-7 A variety of inorganic reagents based on
low-oxidation-state transition metals or lanthanides
has been utilized for such transformations. Heteroge-
neous and homogeneous reagents based on low-valent
Ti, V, Ce, Nb, or Sm have been used for pinacolic or
McMurry couplings.5-7 The typical postulated mecha-
nism for these reactions involves reduction of the
carbonyl group to form an intermediate ketyl radical,
which then undergoes coupling.8 Insights into the
(1) Spessard, G. O.; Miessler, G. L. Organometallic Chemistry;
Prentice Hall: Upper Saddle River, NJ , 1997.
(2) Molander, G. A.; Harris, C. R. Chem. Rev. 1996, 1, 307.
(3) Robertson, G. M. In Comprehensive Organic Synthesis; Trost,
B. M., Fleming, I., Eds.; Pergamon Press: New York, 1991.
(4) Furstner, A.; Bogdanovic, B. Angew. Chem., Int. Ed. Engl. 1996,
35, 2442.
(9) Covert, K. J .; Wolczanski, P. T.; Hill, S. A.; Krusic, P. J . Inorg.
Chem. 1992, 31, 66.
(5) Molander, G. A. Chem. Rev. 1992, 92, 29.
(6) Kahn, B. E.; Rieke, R. D. Chem. Rev. 1988, 88, 733.
(7) McMurry, J . E. Chem. Rev. 1989, 89, 1513.
(8) March, J . Advanced Organic Chemistry: Reactions, Mechanisms,
and Structure; Wiley-Interscience: New York, 1992.
(10) Covert, K. J .; Wolczanski, P. T. Inorg. Chem. 1989, 28, 4565.
(11) Hou, Z.; Wakatsuki, Y. In Lanthanides: Chemistry and Use in
Organic Synthesis; Kobayashi, S., Ed.; Springer-Verlag: Berlin, 1999.
(12) Hou, Z.; Fujita, A.; Zhang, Y.; Miyano, T.; Yamazaki, H.;
Watasuki, Y. J . Am. Chem. Soc. 1998, 120, 754.
10.1021/om0107284 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 03/03/2002

1330 Organometallics, Vol. 21, No. 7, 2002
Agapie et al.
salt elimination upon reaction of TiCl3(THF)3 with 3
equiv of Li(NRAr)(Et2O) in the presence of TMEDA.13
Resu lts a n d Discu ssion
Scission of pa r a -Su bstitu ted 1,2-Diben zoyleth -
a n e Der iva tives. Hoffmann et al. studied the SmI2-
mediated coupling of 1,4-diketones.15 Samarium diiodide
was found to promote classical pinacolic coupling of 1,4-
diketones forming polycyclic compounds. Subsequent
studies showed that treatment of certain carbonyl
compounds with SmI2 in the presence of HMPA (hex-
amethylphosphoramide) generates unexpected reaction
products.16-18 Ghosh et al. reported that addition of
HMPA to the reaction mixture can promote scission of
a carbon-carbon bond instead of ring formation for
several types of polycyclic compounds containing the 1,4-
diketone motif.16 Since the types of compounds employed
in these two studies involve quite different ring systems,
it is difficult to interpret the observed differences in
reactivity. A possible explanation is that intramolecular
coupling of the intermediate ketyl radicals in the
systems studied by Ghosh would engender a large
energetic barrier due to ring strain.16 An alternative
interpretation bears on the fact that HMPA can coor-
dinate to the metal centers and would sterically hinder
combination of metal-coordinated ketyl radicals.17 Re-
cently, Williams et al. observed carbon-carbon bond
fragmentation, in low yields, for unstrained 1,4-dike-
tones when treated with SmI2/HMPA.17,18 The studies
mentioned above16-18 indicate that the use of certain
bulky coordinating additives (HMPA) can induce carbon-
carbon bond cleavage in the reduction of 1,4-diketones
with SmI2 and disfavor classical pinacol coupling. The
role played by HMPA in these reactions is not very clear.
A likely consequence of HMPA coordination is an
increase of the steric bulk around the metal center.
Complex 1 sets the stage for an alternative scenario,
namely, the use of a well-defined, sterically hindered
metal center to control the reaction pathway rather than
relying on uncertain steric attributes embedded in the
reaction conditions. Acyclic 1,4-diketones were used in
the studies described below (eq 1). A green toluene
solution of 1 turns orange rapidly upon addition to a
colorless suspension of the 1,4-diketone, indicating
oxidation of titanium(III) to titanium(IV). The NMR
spectrum of the reaction mixture reveals the presence
of a single product exhibiting two singlets in the olefinic
region corresponding to the methylene protons. Pinacol
coupling products are not observed. Even though the
conversion to the enolates is quantitative (1H NMR), the
isolated yields of orange crystalline products range from
55 to 70% due to the high lipophilicity of these com-
pounds.
(III). Kinetic characterization of the system was at-
tempted using UV-vis spectroscopy. Absorbance mea-
surements were made at 792 and 645 nm, where the
titanium(III) complex has molar absorption λmax (ꢀ )
223 (cm M)-1 and 169 (cm M)-1, respectively) and the
enolate product has negligible absorption. Kinetic runs
were performed after quick manual mixing of the
reagents in a UV cell under inert atmosphere. Forma-
tion of a transient species was indicated by the time
profile of the spectra, different from that expected for a
simple decay of 1. The UV spectra of the sample
obtained by mixing solutions of Ti(NRAr1)3 and 1,2-di-
p-methylbenzoylethane display a broad transient ab-
sorption around 670 nm. This absorption is consistent
with the presence of a transient ketyl radical. Previously
reported ketyl radicals supported by tris-silox titanium
display absorption at 646 nm (for OCPh2) and 692 nm
(OCTol2).9
Enolate 1-OC(CH2)Ar2 was characterized structurally
by single-crystal X-ray diffraction (Figure 1). The Ti-
(NRAr1)3 group displays pseudo-C3 symmetry with the
tert-butyl groups forming a pocket around the enolate
ligand. From reported structural studies, organometallic
titanium enolates involving compounds containing the
titanocene motif display longer Ti-O distances (1.861-
(3)-1.903(2) Å) and smaller Ti-O-C angles (138.9(2)-
147.3(2)°) compared to the values for 1-OC(CH2)Ar2
(1.826(2) Å and 151.2(2)°).19,20 These structural differ-
ences suggest stronger donation from the oxygen p
orbitals into the metal d orbitals in the case of 1-OC-
(CH2)Ar2. The carbon-carbon distance is similar to
those reported previously.
Rea ction s of Com p lex 1 w ith pa r a -Su bstitu ted
Acetop h en on es. In the examples of the preceding
section, complex 1 severs the linkage between two ArC-
(O)CH2 groups. To expand the scope of this reaction,
studies of Ti(NRAr1)3 reactivity toward acetophenones
were performed. As anticipated, treatment of acetophe-
nones with 1 induced disproportionation with formation
of equal amounts of enolate and alkoxide Ti complexes
(Scheme 1), according to 1H NMR data. Pinacol conden-
sation products were not observed. The data suggest
that the proposed intermediate ketyl radical prefers to
decompose via disproportionation, a typical radical
annihilation fate.9
In the reaction presented here, a carbon-carbon
single bond is cleaved reductively by 2 equiv of titanium-
(13) Peters, J . C.; J ohnson, A. R.; Odom, A. L.; Wanandi, P. W.;
Davis, W. M.; Cummins, C. C. J . Am. Chem. Soc. 1996, 118, 10175.
(14) Wanandi, P. W.; Davis, W. M.; Cummins, C. C.; Russell, M. A.;
Wilcox, D. E. J . Am. Chem. Soc. 1995, 117, 2110.
(15) Hoffmann, H. M. R.; Mu¨nnich, I.; Nowitzki, O.; Stucke, H.;
Williams, D. J . Tetrahedron 1996, 52, 11783.
(16) Haque, A.; Ghosh, S. Chem. Commun. 1997, 21, 2039.
(17) Williams, D. B. G.; Blann, K.; Holzapfel, C. W. J . Org. Chem.
2000, 65, 2824.
(18) Williams, D. B. G.; Blann, K.; Holzapfel, C. W. J . Chem. Soc.,
Perkin Trans. 1 2001, 3, 219.

Radical Scission of 1,4-Dicarbonyl Compounds
Organometallics, Vol. 21, No. 7, 2002 1331
Sch em e 1
Sch em e 2
F igu r e 1. Structural drawing of 1-OC(CH2)Ar2 with
thermal ellipsoids at the 35% probability level. Selected
bond distances (Å) and angles (deg): Ti-N(1) 1.943(3),
Ti-N(2) 1.920(3), Ti-N(3) 1.904(3), Ti-O 1.826(2), O-C(2)
1.352(4), C(1)-C(2) 1.311(5), O-Ti-N(1) 109.36(11),
C(2)-O-Ti 151.2(2), O-C(2)-C(1) 122.3(3).
Rea ction s of Com p lex 1 w ith r-Ha lo-a cetop h e-
n on e. The goal of the experiments described in this
section was to explore the possibility of activating
linkages between ArCOCH2 and halogens (Cl and Br,
eq 2). Addition of 2 equiv of 1 to a solution of R-halo-
carbon bond cleavage, carbon-halogen bond cleavage,
or disproportionation through hydrogen atom transfer.
Attempts to observe the ketyl radical by EPR at low
temperatures were unsuccessful due to its fast conver-
sion to diamagnetic products. Stabilization of a ketyl
radical was achieved by inhibiting the possible radical
decomposition pathways. Taking advantage of the ab-
sence of â-linkages susceptible to radical fragmentation,
reaction of 1 with benzophenone allowed generation of
a stable ketyl-titanium complex 1-OCPh2 (Scheme 2).
Treatment of a toluene solution of 1 with benzophenone
at room temperature was accompanied by a color change
from forest green to dark brown-green. Storage at -35
°C caused a reversible color change from dark brown-
green to bright orange. This observation supports the
idea of an equilibrium between the ketyl complex
1-OCPh2 and the diamagnetic dinuclear complex (1-
OCPh2)2, reminiscent of the behavior of the trityl radi-
cal or of the ketyl radicals bound to metal centers
supported by bulky ligands.9,21,22 By analogy with the
trityl radical case, pinacolic coupling is obviated by
steric constraints. Steric hindrance in the asymmetric
dinuclear complex along with the presence of radical
species is invoked to account for the broadness and the
number of ligand peaks displayed in the 1H NMR
acetophenone affords clean formation of the titanium-
(IV) enolate (1-OC(CH2)Ph) and the halide (1-Cl and
1-Br). The experiments presented in the last two sec-
tions indicate facile activation of the bond positioned â
to a carbonyl group and smooth enolate formation as
the preferred reaction pathway.
(19) Veya, P.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Organome-
tallics 1993, 12, 4892.
(20) Curtis, M. D.; Thanedar, S.; Butler, W. M. Organometallics
1984, 3, 1855.
(21) Gomberg, M. J . Am. Chem. Soc. 1900, 22, 757.
(22) Neumann, W. P.; Uzick, W.; Zarkadis, A. K. J . Am. Chem. Soc.
1986, 98, 3762.
Rea ction of Ti(NRAr 1)3 w ith Ben zop h en on e. The
reactions presented so far bear on the proposed forma-
tion of intermediate ketyl radicals that undergo radical
decomposition by one of the available pathways: carbon-

1332 Organometallics, Vol. 21, No. 7, 2002
Agapie et al.
Sch em e 3
MePh)2 in 73% yield. Clean decomposition upon heating
to the expected enolate (1-OC(CH2)Ph and alkoxide (1-
OCHMePh) substantiates the idea that (1-OCMePh)2
is a resting state for a transient ketyl radical. Further-
more, slow reaction with n-Bu3SnH generates the
alkoxide 1-OCHMePh as the major product. Notably,
no significant conversion of (1-OCMePh)2 to the corre-
sponding enolate and alkoxide is observed, even after
several weeks, if stored at -35 °C.
Formation of a Gomberg dimer-type species for the
acetophenone ketyl radical raises two issues. First, the
intermediate ketyl radicals couple to form a new carbon-
carbon bond, but the coupling does not proceed in a
pinacolic manner, even though a methyl rather than a
phenyl abuts the ketone functionality. Massive steric
bulk generated by the amido ligands in close proximity
to the ketyl radical center may justify the observed
behavior by compensating for the smaller size of the
methyl substituent. Second, the intermediate ketyl
radical does not decompose through the available path-
way of â-hydrogen transfer. Bimolecular disproportion-
ation through H atom transfer may likewise be disfa-
vored for steric reasons. The ketyl radical clearly has
more access to the para position of the phenyl ring than
to the hydrogens on the methyl group. This kind of steric
control has been used for synthetic organic applications
in the SmI2/HMPA system.24,25 In such cases, benzal-
dehydes and acetophenones undergo activation of the
para position when treated with SmI2/HMPA to gener-
ate the phenyl-carbonyl coupling product, rather than
the pinacolic coupling product.24,25
spectrum of (1-OCPh2)2 at various temperatures. This
species displays peaks around 5-6 ppm, peaks that
increase in intensity at lower temperatures. This be-
havior indicates the presence of structures analogous
to the dimer of the trityl radical (i.e., the Gomberg
dimer).9,23 EPR analysis of the system indicated the
presence of a carbon-centered radical at room temper-
ature (g ≈ 1.9925 and sharp lines). Furthermore, a
toluene solution of species (1-OCPh2)2 shows an absorp-
tion at 641 nm, in good agreement with previous
spectroscopic reports for titanium-bound benzophenone
ketyl radical.9
Chemical means were employed also to test the
availability of the ketyl radical in a solution of the
titanium-ketyl complex (Scheme 2). Complex (1-OCPh2)2
was stirred in toluene in the presence of n-Bu3SnH to
generate cleanly a diamagnetic compound displaying
sharp peaks for a single NRAr ligand environment. The
1H NMR spectrum thereby obtained is assignable to
1-OCHPh2, the product of H atom abstraction from the
tin hydride.
Reaction of Ti(NRAr 1)3 with Acetoph en on e. Treat-
ment of acetophenone with a pentane solution of 1 at
low temperatures induces, upon mixing, a color change
from forest green to intense orange (Scheme 3). 1H NMR
spectroscopic analysis of the reaction mixture reveals,
surprisingly, the absence of enolate and alkoxide peaks,
compounds that formed cleanly in the case of para-
substituted acetophenones. Instead, features quite simi-
lar to those observed in the 1H NMR spectrum of
1-OCPh2 were in evidence. In particular, the peaks
between 4 and 5 ppm were indicative of the 2,5-
cyclohexadiene moiety as described by the structural
drawing of (1-OCMePh)2 in Scheme 3. Recrystallization
from diethyl ether/pentane affords isolation of (1-OC-
Rea ction of Ti(NRAr 1)3 w ith 1,2-Diben zoyleth -
a n e. Following a similar reactivity pattern, 1,2-diben-
zoylethane, (PhCOCH2)2, reacts with 1 to generate a
new compound ((1-OC(CH2)Ph)4, Scheme 4), displaying
broad peaks in its 1H NMR spectrum. The expected
enolate is a minor product when the reaction is run at
low temperatures. Compound (1-OC(CH2)Ph)4 can be
precipitated selectively from an acetonitrile/diethyl
1
ether mixture. The H NMR spectrum of (1-OC(CH2)-
Ph)4 does not supply useful information regarding the
molecular structure of this species, and crystals suitable
for X-ray crystallography were not obtained. By analogy
with the chemical reactivity of (1-OCMePh)2, the struc-
ture of (1-OC(CH2)Ph)4 is proposed to be based on the
Gomberg dimer-type motif. Oligomeric variants of (1-
OC(CH2)Ph)4 containing the same head-to-tail coupling
motif also are feasible. When heated in solution at 75
°C for 4 h, (1-OC(CH2)Ph)4 converts cleanly to expected
enolate 1-OC(CH2)Ph. Hence, (1-OC(CH2)Ph)4 behaves
as a resting state for the diketyl radical. The fact that
(1-OC(CH2)Ph)4 can be observed spectroscopically and
isolated suggests that the carbon-carbon cleavage
reaction is facile if two titanium centers activate in
concert the ketone groups (Scheme 4). If only one
titanium(III) activates the carbon-carbon bond in a fast
reaction, the intermediate monoketyl radical should
split to form 1-OC(CH2)Ph and the [PhCOCH2] radical,
which would trap in turn another equivalent of 1 with
no formation of byproduct (1-OC(CH2)Ph)4. However, if
the monoketyl radical does not promote fast carbon-
(24) Shiue, J .-S.; Liu, C.-C.; Fang, J .-M. Tetrahedron Lett. 1993, 34,
335.
(23) Lankamp, H.; Nauta, W. T.; MacLean, C. Tetrahedron Lett.
1968, 2, 249.
(25) Shiue, J .-S.; Lin, M.-H.; Fang, J .-M. J . Org. Chem. 1997, 62,
4643.

Radical Scission of 1,4-Dicarbonyl Compounds
Organometallics, Vol. 21, No. 7, 2002 1333
Sch em e 4
Sch em e 5
carbon bond splitting, it would prefer to rest in struc-
tures similar to (1-OCMePh)2 based on the arguments
discussed in the preceding section. When the second
ketone group of the substrate is reduced, carbon-carbon
bond cleavage is not facile if the initial ketyl radical is
coupled in the para position of a phenyl ring. Hence,
the second ketyl radical will also rest in structures
similar to (1-OCMePh)2. Species with diketyl radical
character are accessed upon heating and convert ir-
reversibly to the enolate.
Rea ction of Ti(NRAr 1)3 w ith 3,5-Di-ter t-bu tyl-
ben za ld eh yd e. To investigate the extent to which the
steric bulk of Ti(NRAr1)3 prohibits pinacol coupling, the
reaction of 1 with an aldehyde was pursued (eq 3, Ar4
) 3,5-C6H3(t-Bu)2). Aromatic aldehydes provide access
when Ti(NRAr1)3 is used as a reagent seems to indicate
that a subtle interplay of steric factors governs the
outcome of the reactions presented thus far. It is
important to note that the benzaldehyde employed in
this experiment cannot couple in the para position due
to the voluminous tert-butyl groups in close proximity.
Under similar reaction conditions, benzaldehyde gives
a mixture of products presumably due to head-to-tail
coupling besides pinacolic coupling.
Ca r bon -ca r bon Bon d Clea va ge in Ester s a n d
Am id es of Su ccin ic Acid . The previous sections have
focused on reactions of 1 with substrates containing a
carbonyl functionality. Extending the scope of these
reactions by using carboxylic acid derivatives is very
appealing (Scheme 5). Esters and amides of succinic acid
have been treated with 1 under conditions similar to
those employed for 1,4-diketones. The reaction is slower,
but conversion to the ester and amide enolates is nearly
to sterically more open ketyl radicals that do not contain
â-linkages vulnerable to activation. On the basis of the
color change of the toluene solution from green to yellow,
1
the reaction is complete in a few seconds. The H NMR
spectrum of the reaction mixture shows clean conversion
to a single product. However, the relatively broad peaks
do not rule out the possibility of hydrogen abstraction
from the solvent with formation of a benzyloxy ligand
2
1
coordinated to 1. In an additional experiment, no H
quantitative in 2-3 h, based on H NMR spectroscopy.
incorporation was observed when the reaction was
performed in C6D6. This result substantiates the forma-
tion of the pinacol coupling product, (1-OCHAr4)2 (eq
3). The fact that pinacol coupling is not totally forbidden
Longer reaction times may be attributed to decreased
oxidizing character of esters and amides as compared
with ketones. Besides representing a novel type of
carbon-carbon bond activation, the reactions presented

1334 Organometallics, Vol. 21, No. 7, 2002
Agapie et al.
F igu r e 3. HOMOs of 2-OCHCH2 (left) and 2-OC(NH2)-
CH2 (right).
respect to the effect on aldol condensation reactivity.
Treatment of 1-OC(CH2)NPhMe with excess PhCHO in
toluene at room temperature affords complete conver-
sion to the aldol condensation product 1-OCHPh-
(CH2CONPhMe) within 12 h (Scheme 5). A strong band
in the IR spectrum of 1-OCHPh(CH2CONPhMe) at 1659
cm-1 is diagnostic of an uncoordinated amide group. It
is interesting to note that the sterically encumbered
titanium center can be transferred from the enolate
oxygen to the benzaldehyde oxygen, as required for aldol
condensation.
F igu r e 2. Structural drawing of 1-OC(CH2)NPhMe with
thermal ellipsoids at the 35% probability level. Selected
bond distances (Å) and angles (deg): Ti-N(1) 1.931(3),
Ti-N(2) 1.936(3), Ti-O 1.847(3), O-C(2) 1.340(4),
C(41)-C(411) 1.309(5), N(4)-C(41) 1.417(5), O-Ti-N(1)
110.59(12), C(41)-O-Ti 159.0(2), O-C(41)-C(411) 123.4-
(4), C(411)-C(41)-N(4) 122.1(4), O-C(41)-N(4) 114.5(3).
Th eor etica l In vestiga tion of Tita n iu m En ola tes.
After successful aldol condensation of benzaldehyde
with amide enolate 1-OC(CH2)NPhMe, extension of the
same procedure to the ketone-derived enolate 1-OC-
(CH2)Ar2 was attempted. However, under identical
conditions, enolate 1-OC(CH2)Ar2 showed no reactivity
toward benzaldehyde. The decreased nucleophilicity of
the ketone-derived enolate compared to the amide
enolate may be invoked to account for the difference.
To detail the electronic differences between the ketone-
derived and the amide titanium enolates, a density
functional theory computational study was performed
on the model compounds 2-OCHCH2 (2 ) Ti(NH2)3) and
2-OC(NH2)CH2.29-32 Local C3v symmetry was imposed
for fragment 2. Calculated structural parameters for the
model compounds were in good agreement with the
experimental ones (see Supporting Information for
details). Hirshfeld charge analysis shows a significantly
higher electron density on the methylene carbon in
the case of the amide enolate (-0.178) as compared with
the unsubstituted enolate (-0.124), this being in agree-
ment with the predictions of valence bond theory.33
Furthermore, an analysis of the frontier molecular
orbitals shows that the HOMO of 2-OC(NH2)CH2 enjoys
a large contribution from the carbon-carbon π bond,
while the HOMO of 2-OCHCH2 is only a ligand-based
orbital comprised of amido nitrogen lone pairs (Figure
3). Also, the orbitals containing π electron density on
the carbon atoms are higher in energy for 2-OC(NH2)-
CH2. Although the X-ray study of 1-OC(CH2)NPhMe
indicated that in solid state there is no significant
interaction between the nitrogen lone pair and the
carbon-carbon π bond, the computational study pro-
here have provided a novel synthetic pathway for
accessing the ester 1-OC(CH2)OAr4 and amide 1-OC-
(CH2)NPhMe enolates. While alternative routes involve
strongly basic and polar reaction conditions, the syn-
theses presented here are performed under neutral
conditions in nonpolar media.
Considering the paucity of structural data available
for transition-metal amide enolates, an X-ray crystal-
lographic study of 1-OC(CH2)NPhMe was performed
(Figure 2). Comparison to the previously reported
transition-metal amide enolate structure containing the
zirconocene motif (Cp2ZrCl[OC(CH2)NPh2]) revealed
substantial similarity in the structural parameters; the
N-C, C-O, and C-C distances are very similar in the
two compounds.26 Important features in the structure
of 1-OC(CH2)NPhMe are the dihedral angles C(411)-
C(41)-N(4)-C(48) and C(411)-C(41)-N(4)-C(42) (56°
and 112°, respectively), which suggest that in the solid
state there is no significant 4e repulsive interaction
between the nitrogen lone pair and the carbon-carbon
π bond.
Ald ol Con d en sa tion of th e Am id e En ola te 1-OC-
(CH2)NP h Me w ith Ben za ld eh yd e. Amide enolates
enjoy widespread use in synthetic organic chemistry
particularly with regard to carbon-carbon bond forma-
tion.27,28 The presence of increased steric bulk close to
the amide enolate functionality is of interest also with
(29) Baerends, E. J .; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41.
(30) Versluis, L.; Ziegler, T. J . Chem. Phys. 1988, 88, 322.
(31) te Velde, G.; Baerends, E. J . J . Comput. Phys. 1992, 99, 84.
(32) Fonseca Guerra, C.; Snijders, J . G.; te Velde, G.; Baerends, E.
J . Theor. Chem. Acc. 1998, 99, 391.
(33) Pauling, L. The Nature of the Chemical Bond and the Structure
of Molecules and Crystals; an Introduction to Modern Structural
Chemistry; Cornell University Press: Ithaca, NY, 1960.
(26) Cozzi, P. G.; Veya, P.; Floriani, C.; Rotzinger, F. P.; Chiesi-
Villa, A.; Rizzoli, C. Organometallics 1995, 14, 4092.
(27) Heathcock, C. H. Comprehensive Organic Synthesis; Heathcock,
C. H., Ed.; Pergamon: Oxford, U.K., 1991.
(28) Kim, M. B.; Williams, S. F.; Masamune, S. In Comprehensive
Organic Synthesis; Heathcock, C. H., Ed.; Pergamon: Oxford, U.K.,
1991.

Radical Scission of 1,4-Dicarbonyl Compounds
Organometallics, Vol. 21, No. 7, 2002 1335
Sch em e 6
Sch em e 7
vides an elegant explanation for the observed solution-
phase reactivity.
Rea ction s of Ti(NRAr 1)3 w ith Su bstr a tes Con -
ta in in g Con ju ga ted π System s. The reactions de-
scribed in the foregoing sections document the ability
of 1 to sever σ bonds positioned â to a carbonyl group.
An extension to these reactions would be to use sub-
strates incorporating a π bond â to a carbonyl group.
The experiments depicted in Scheme 6 portray 2 equiv
of Ti(NRAr1)3 acting in concert to effect 2e reduction.
In the case of N-methylphthalimide (O2Phth), reduction
with 1 disrupts the aromaticity of the six-membered
ring, cleanly affording 12-O2Phth. The iso-indole motif
displayed by 12-O2Phth previously has been accessible
only in low yields, under a special electrolytic proce-
dure.34 Interesting to note is that treatment of 1 with
di-tert-butylazodicarboxylate (Dt-BuAD) led to reorga-
nization of the π framework rather than tert-butyl
radical loss.13
in both reagents (r ) k[Ti(NRAr1)3][PhZ]) for activation
of iodobenzene (k ) (6.6 ( 0.5) × 10-1 (s M)-1) and
bromobenzene (k ) (9.3 ( 0.1) × 10-3 (s M)-1). Chlorine
atom abstraction from chlorobenzene displays first-order
kinetics with respect to 1. The order in PhCl could not
be determined accurately due to the small variations
in the employed concentrations of PhCl. Very high
concentrations of PhCl were used (almost neat) in order
to promote the reaction on a reasonable time scale. The
pseudo-first-order rate constant (kobs) was found to be
(1.8 ( 0.3) × 10-4 s-1. No significant decay of 1 in neat
fluorobenzene solution was observed by UV-vis spec-
troscopy over 10 h. 1-F was prepared independently
for spectroscopic characterization by XeF2 fluorination
of 1.
Ha logen Abstr a ction fr om Ha loben zen es. In the
previous sections, 1 has been used for facile 1e reduction
of carbonyl groups, causing the cleavage or formation
of other bonds via radical pathways. A relatively unre-
active functionality prone to activation by Ti(NRAr1)3
is the aryl-Z bond (eq 4). Treatment of 1 with stoichio-
Rea ction of Ti(NRAr 1)3 w ith o-Br om op h en yl Al-
lyl Eth er . Halogen atom abstraction by 1 from ha-
lobenzenes is thought to occur with generation of a
transient phenyl radical. For substantiation of this
hypothesis, the reaction of 1 with o-bromophenyl allyl
ether was investigated (Scheme 7). This substrate offers
the opportunity for a transient aryl radical to undergo
cyclization.35 Examination of the reaction mixture by
1H NMR revealed two NRAr1 ligand environments, one
corresponding to 1-Br and the other assigned to 1-
CH2DHBF (DHBF ) dihydrobenzofuranyl). The inequiv-
alence of the methylene protons vicinal to the oxygen
atom (two peaks at 4.15 and 4.29 ppm) is indicative of
formation of a ring-closure product. Although attempts
to separate 1-CH2DHBF from the bromotitanium byprod-
uct were not successful, exhaustive hydrolysis of 1-CH2-
DHBF was found to generate 3-methyldihydrobenzofu-
metric amounts of iodo- or bromobenzene generates
cleanly the titanium(IV) halide complexes within less
than an hour at room temperature. Activation of chlo-
robenzene is considerably slower. Conversion of 1 to 1-Cl
is complete after stirring overnight in neat chloroben-
zene. A kinetic study of the halogen abstraction reac-
tions was performed using UV-vis spectroscopy. Decay
of 1 was monitored at 792 nm. Large concentrations of
halobenzenes were employed in order to provide pseudo-
first-order conditions for kinetic analysis. The reaction
was found to obey a second-order kinetic law, first order
(35) Curran, D. P.; Totleben, M. J . J . Am. Chem. Soc. 1992, 114,
6050.
(34) Hartmann, K.-H.; Troll, T. Tetrahedron 1995, 51, 4655.

1336 Organometallics, Vol. 21, No. 7, 2002
Agapie et al.
ran,36 consistent with the structural assignment for
1-CH2DHBF displayed in Scheme 7.
128.38 (t) ppm (C6D6); 7.27 ppm, and 77.23 (t) ppm (CDCl3),
1
for H and 13C data. CHN analyses were performed by H. Kolbe
Mikroanalytisches Laboratorium (Mu¨lheim, Germany).
Syn th esis of 1-OC(CH2)Ar : Gen er a l P r oced u r e. A cold
toluene solution of Ti(NRAr1)3 (1, 2 equiv) was added to a
thawing suspension of 1,4-diketone (1 equiv) in toluene. Upon
addition to the colorless suspension, the forest green solution
of 1 gradually turns orange. After 30 min of stirring, volatile
materials are removed in vacuo, providing an orange oily
residue containing pure product as assigned by 1H NMR
spectroscopy. No diketone starting material is present on the
basis of NMR data. Recrystallization from pentane or diethyl
ether resulted in the isolation of the orange crystalline enolate
product in 55-70% yield.
Con clu sion s
In this paper the chemical reactivity of Ti(NRAr1)3
with a series of organic substrates, especially carbonyl
compounds, has been elucidated. Complex 1 has been
shown to activate a variety of σ and π bonds situated â
to carbonyl groups. The presence of steric bulk in
proximity to the generated ketyl radical has been shown
dramatically to influence the outcome of the reactions.
Disproportionation, pinacol coupling, carbon-carbon
bond cleavage, and activation of the para position of
phenyl-substituted ketyl radicals were all observed
depending on the nature of the substrate. The synthetic
strategies developed in this context afforded clean
preparation of ester and amide enolates in neutral
nonpolar media via symmetrical scission of succinic acid
derivatives. The amide enolate synthesized through this
novel C-C bond cleavage pathway was shown to
undergo aldol condensation with benzaldehyde. Ti-
(NRAr1)3 was found to abstract atomic halogen from
halobenzenes. In the case of o-bromophenyl allyl ether,
the intermediate aryl radical undergoes ring closure
with formation of the dihydrobenzofuran moiety. Acti-
vation of a bond â to a ligating functional group
continues to be a dominant feature of the chemistry of
three-coordinate 1, a reactive and potent hydrocarbon-
soluble 1e reductant.
1-OC(CH2)Ar 2. 1H NMR (300 MHz, CDCl3): δ 1.12 (s, 27H,
C(CH3)3), 2.27 (s, 18H, ArCH3), 2.41 (s, 3H, enolate aryl-CH3),
4.70 and 4.77 (singlets, 2H, CH2), 6.24 (br s, 6H, aryl o-H),
6.74 (s, 3H, aryl p-H), 7.15 and 7.51 (doublets, 4H, enolate
aryl o- and m-H). 13C NMR (75 MHz, CDCl3): δ 21.6 (enolate
p-CH3), 21.8 (m-CH3), 30.8 (C(CH3)3), 61.8 (C(CH3)3), 94.4 (d
CH2), 115.5 (aryl), 125.9 (aryl), 126.5 (aryl), 127.7 (aryl), 128.4
(aryl), 137.4 (aryl), 151.8 (aryl), 166.2 (OCdC). Anal. Calcd
for TiN3OC45H63: C, 76.14; H, 8.93; N, 5.92. Found: C, 76.03;
H, 9.10; N, 5.99.
1
1-OC(CH2)Ar 3. H NMR (300 MHz, C6D6): δ 1.32 (s, 27H,
C(CH3)3), 2.25 (s, 18H, ArCH3), 3.32 (s, 3H OCH3), 4.94 and
5.00 (singlets, 2H, CH2), 6.48 (br s, 6H, aryl o-H), 6.72 (s, 3H,
aryl p-H), 6.86 and 7.71 (doublets, 4H, enolate aryl o- and
m-H). 13C NMR (75 MHz, C6D6): 22.2 (m-CH3), 31.4 (C(CH3)3),
55.2 (OCH3), 62.4 (C(CH3)3), 94.8 (dCH2), 113.9 (aryl), 126.9
(aryl), 128.6 (aryl), 132.5 (aryl), 136.9 (aryl), 152.7 (aryl), 160.4
(aryl), 167.1 (OCdC). Anal. Calcd for TiN3O2C45H63: C, 74.46;
H, 8.75; N, 5.78. Found: C, 74.44; H, 8.80; N, 5,71.
Rea ction of Ti(NRAr 1)3 w ith 1,2-Diben zoyleth a n e. A
cold toluene solution (10 mL) of 1 (550 mg, 0.95 mmol, 2 equiv)
was added to a thawing suspension of (PhCOCH2)2 (113.5 mg,
0.47 mmol, 1 equiv) in toluene (5 mL). Evacuation of volatile
material was started immediately after addition. The reaction
mixture turns dark brown-red, then intense orange. The 1H
NMR spectrum of the oily solid obtained upon removal of
volatile material displays sharp peaks corresponding to the
titanium enolate as well as broad peaks attributed to (1-OC-
(CH2)Ph)4. The oily solid was dissolved in the minimum
amount of diethyl ether, and acetonitrile was added to cause
precipitation of an orange solid collected on a sintered glass
frit. The isolated orange powder (236 mg) contains (1-OC(CH2)-
Ph)4 along with 20% enolate 1-OC(CH2)Ph. 1H NMR (300 MHz,
C6D6, tentative assignments): 1.09-1.43 (br m, C(CH3)3),
2.06-2.45 (br m, ArCH3), 5.4-8.30 (br m, olefin and aryl CH).
Syn th esis of 1-OC(CH2)P h . A cold toluene solution (5 mL)
of 1 (110 mg, 0.19 mmol, 2 equiv) was added to a thawing
suspension of (PhCOCH2)2 (22.7 mg, 0.095 mmol, 1 equiv) in
toluene (2 mL) and stirred for 1 h to reach room temperature
and then heated at 75 °C with stirring for four additional
hours. The reaction mixture was allowed to cool to room
temperature, followed by removal of volatile material in vacuo.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Unless stated otherwise, all
operations were performed in a Vacuum Atmospheres drybox
under an atmosphere of purified nitrogen or using Schlenk
techniques under an argon atmosphere. Anhydrous diethyl
ether was purchased from Mallinckrodt; pentane, n-hexane,
and tetrahydrofuran (THF) were purchased from EM Science.
Diethyl ether, toluene, benzene, pentane, and n-hexane were
dried and deoxygenated by the method of Grubbs.37 THF was
distilled under nitrogen from purple sodium benzophenone
ketyl. Distilled solvents were transferred under vacuum into
vacuum-tight glass vessels before being pumped into a Vacuum
Atmospheres drybox. Hexamethyldisiloxane was degassed and
dried over 4 Å sieves. C6D6 and CDCl3 were purchased from
Cambridge Isotopes and were degassed and dried over 4 Å
sieves. The 4 Å sieves, alumina, and Celite were dried in vacuo
overnight at a temperature just above 200 °C. Ti(NRAr1)3,13
1,4-diketones,38 o-bromophenyl allyl ether,39 esters, and amides
of succinic acid40 were synthesized according to literature pro-
cedures. Other chemicals were used as received. Solution infra-
red spectra were recorded on a Perkin-Elmer 1600 Series FTIR
using KBr plates. UV-vis spectra were recorded on a Hewlett-
Packard 8453 diode array spectrophotometer. Room-temper-
ature X-band EPR spectra were recorded on a Bruker EMX
spectrometer. 1H and 13C NMR spectra were recorded on Var-
ian XL-300, Mercury 300, or Varian INOVA-501 spectrometers
at room temperature, unless indicated otherwise. Chemical
shifts are reported with respect to internal solvent: 7.15 and
1
The oily residue contained pure Ti enolate as assigned by H
NMR spectroscopy. Recrystallization from pentane resulted in
the isolation, in two crops, of the orange crystalline enolate
1
product in 65% yield (86 mg, 0.12 mmol). H NMR (300 MHz,
C6D6): δ 1.30 (s, 27H, C(CH3)3), 2.25 (s, 18H, ArCH3), 4.94 and
4.99 (singlets, 2H, CH2), 6.46 (br s, 6H, aryl o-H), 6.71 (s, 3H,
aryl p-H), 7.15 (1H, phenyl p-H), 7.21 (t, 2H, phenyl m-H) and
7.73 (d, 2H, phenyl o-H). 13C NMR (75 MHz, CDCl3): 21.7 (m-
CH3), 30.7 (C(CH3)3), 61.8 (C(CH3)3), 94.9 (dCH2), 115.5 (aryl),
125.9 (aryl), 126.6 (aryl), 127.8 (aryl), 136.2 (aryl), 139.0 (aryl),
151.8 (aryl), 166.1 (OCdC). Anal. Calcd for TiN3OC44H61: C,
75.95; H, 8.83; N, 6.04. Found: C, 75.86; H, 8.90; N, 5.96.
Rea ction of Ti(NRAr 1)3 w ith Ar COCH3: Gen er a l P r o-
ced u r e. A diethyl ether solution of 1 (1 equiv) was added to a
suspension of ArCOCH3 (1 equiv) in diethyl ether, at room
(36) Boisvert, G.; Giasson, R. Tetrahedron Lett. 1992, 33, 6587.
(37) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518.
(38) Moriarty, R.; Prakash, O.; Duncan, M. P. J . Chem Soc., Perkin
Trans. 1987, 3, 559.
(39) Hoque, A.; Shine H. J .; Venkatachalam, T. K. Collect. Czech.
Chem. Commun. 1993, 58, 82.
(40) Weygand, C.; Hilgetag, G. Preparative Organic Chemistry;
Wiley-Interscience: New York, 1972.

Radical Scission of 1,4-Dicarbonyl Compounds
Organometallics, Vol. 21, No. 7, 2002 1337
temperature. Upon mixing of the reagents, the color of the
reaction mixture turned dark green-brown, then orange. After
5 min of stirring, volatile material was removed in vacuo. The
1H NMR spectra of the crude reaction mixture indicated
formation of two products in equal amounts, one of the
products being the enolate, the other being the corresponding
alkoxide.
31.4 (C(CH3)3), 61.4 (C(CH3)3), 91.1 (Ph2CH), 126.7 (aryl), 127.7
(aryl), 128.7 (aryl), 128.9 (aryl), 136.8 (aryl), 146.2 (aryl), 153.1
(aryl). Anal. Calcd for TiN3OC49H65: C, 77.38; H, 8.55; N, 5.52.
Found: C, 77.75; H, 8.85; N, 5.02.
Rea ction of Ti(NRAr 1)3 w ith Acetop h en on e. A cold
pentane solution (5 mL) of 1 (140 mg, 0.24 mmol, 1 equiv) was
added to a thawing solution of acetophenone (29 mg, 0.24
mmol, 1 equiv) in pentane (3 mL). Upon addition, the color of
the mixture changed to intense orange. Volatile material was
removed in vacuo while the solution was cold. Crystallization
from pentane at -35 °C afforded 125 mg of orange solid (1-
OCMePh)2 (0.09 mmol, 73% yield). Stored at -35 °C, com-
pound (1-OCMePh)2 does not decompose significantly to
enolate 1-OC(CH2)Ph and alkoxide 1-OCHMePh even over
several weeks. 1H NMR (300 MHz, C6D6, tentative assign-
ments): δ 1.24 (s), 1.36 (s), and 1-1.5 (br) assigned to C(CH3)3,
1.86, 2.02, 2.06, and 2.12 (broad singlets) assigned to OCCH3,
2.25 (s), 2.31 (s), and 2.39 (br s) assigned to ArCH3, 4.57 and
4.79 (br s) assigned to the olefinic protons, 6.23 (br app d),
6.55, 6.63, 6.74, 6.77, 6.80 (br app s), 6.88-7.10 (br m), 7.28-
7.35 (br m), 7.50, 7.73 (br s) assigned to aryl CH. 13C NMR
(125.8 MHz, CDCl3): after 6 h of data collection a considerable
quantity of 1-OC(CH2)Ph and 1-OCHMePh was formed based
1-OCHMeAr 3. 1H NMR (500 MHz, C6D6): δ ) 1.28 (s, 27H,
C(CH3)3), 1.71 (br s, 3H, CHCH3), 2.25 (s, 18H, ArCH3), 3.35
(s, 3H, OCH3), 5.71 (br s, 1H, CH3CH), 6.30 (br s, 6H, aryl
o-H), 6.71 (s, 3H, aryl p-H), 6.92 and 7.45 (app doublets, 4H,
alkoxide aryl o- and m-H). 13C (125.8 MHz, C6D6): δ 22.2 (m-
CH3), 27.7 (OCHCH3), 31.7 (C(CH3)3), 55.1 (OCH3), 60.9
(C(CH3)3), 85.1 (OCH), 114.3 (aryl), 126.5 (aryl), 129.0 (aryl),
129.1 (aryl), 136.7 (aryl), 139.0 (aryl), 153.5 (aryl), 160.0 (aryl).
1
1-OCHMeAr 2. H NMR (500 MHz, CDCl3): δ 1.15 (s, 27H,
C(CH3)3), 1.63 (br s, 3H, CHCH3), 2.29 (s, 18H, ArCH3), 2.43
(s, 3H, alkoxide aryl-CH3), 5.62 (br s, 1H, CH3CH), 6.14 (br s,
6H, aryl o-H), 6.77 (s, 3H, aryl p-H), 7.22 (d) and 7.39 (br s,
4H, alkoxide aryl o- and m-H). 13C (125.8 MHz, CDCl3): δ 21.7
(m-CH3), 27.3 (OCHCH3), 31.0 (C(CH3)3), 60.3 (C(CH3)3), 84.6
(OCH), 126.0 (aryl), 127.0 (aryl), 128.5 (aryl), 128.9 (aryl),
136.0 (aryl), 138.8 (aryl), 143.4 (aryl), 152.7 (aryl).
Rea ction of Ti(NRAr 1)3 w ith r-Ha lo-a cetop h en on es. A
diethyl ether solution (5 mL) of 1 was added to a suspension
of R-Br or R-Cl acetophenone in diethyl ether (2 mL) at room
temperature. Upon mixing the reagents, the color of the
reaction mixture turned dark brown, then orange. After 15
min of stirring, volatile material was removed in vacuo. The
1H NMR spectra of the reaction mixture showed formation of
the titanium tris-anilide halide (1-Cl and 1-Br) and enolate
(1-OC(CH2)Ph).
1
on H NMR analysis. The corresponding peaks in the 13C NMR
spectrum were shifted 0.4 ppm downfield. Peaks assigned to
(1-OCMePh)2 (tentative assignments): δ 14.8 (alkyl CH3), 19.8
(alkyl CH3), 22.3 (m-CH3), 23.0 (m-CH3), 31.3 (C(CH3)3), 31.5
(C(CH3)3), 61.2 (C(CH3)3), 61.8 (C(CH3)3), 62.3 (C(CH3)3), 93.3
(OCPh2R), 117.5 (aryl), 118.0 (aryl), 116.0 (aryl), 124.0-129.7
(aryl), 136.7 (aryl), 151.9 (aryl).
Th er m a l Decom p osition of (1-OCMeP h )2. Thawing tolu-
ene solutions of 1 (65.4 mg, 0.11 mmol, 1 equiv) and acetophe-
none (13.6 mg, 0.11 mmol, 1 equiv) were mixed and volatile
material was removed before the mixture reached room tem-
perature. The intense orange residue was dissolved in toluene
(5 mL) and heated at 80 °C with stirring. Within 30 min the
color of the solution turned yellow-orange. Volatile material
Rea ction of Ti(NRAr 1)3 w ith Ben zop h en on e. At room
temperature, a pentane solution (5 mL) of 1 (104 mg, 0.18
mmol, 1 equiv) was added to a suspension of benzophenone
(33 mg, 0.18 mmol, 1 equiv) in pentane (3 mL). The color
turned brown-green upon mixing. The reaction mixture was
stirred for 1 h at room temperature. During that time copious
precipitation of a yellow solid was observed. Volatile material
was removed under reduced pressure to leave a yellow residue,
which was partially soluble in pentane. Addition of pentane
generated a brown-green solution, the color of which turned
reversibly orange upon cooling to -35 °C. Compound (1-
OCPh2)2 precipitated as a yellow powder (101.2 mg, 0.067
1
was removed in vacuo after a total of 2 h of stirring. H NMR
spectroscopic analysis of the yellow-orange residue revealed
the presence of 1-OC(CH2)Ph and 1-OCHMePh in a 1:1 ratio.
Syn th esis of 1-OCHMeP h . Thawing pentane solutions of
1 (90 mg, 0.16 mmol, 1 equiv) and acetophenone (18.7 mg, 0.16
mmol, 1 equiv) were mixed and solvent was removed in vacuo
before the mixture reached 25 °C. The intense orange residue
was dissolved in 2 mL of n-Bu3SnH and allowed to stir at room
temperature for 36 h. The color of the reaction mixture
gradually turned yellow from intense orange. Excess tin
hydride was removed by distillation under reduced pressure.
The 1H NMR spectrum of the resulting oily residue showed
(n-Bu3Sn)2, the alkoxide product 1-OCHMePh, and trace
amounts of enolate 1-OC(CH2)Ph. The residue was dissolved
in pentane and cooled to -35 °C. The yellow precipitate was
collected on a sintered glass frit and washed with a small
amount of hexamethyldisiloxane. Alkoxide 1-OCHMePh ob-
tained in this manner (67 mg, 0.10 mmol, 62%) was contami-
nated with a small amount of enolate, from which it could not
be separated by recrystallization. Not performing the reaction
in neat n-Bu3SnH or heating it for fast completeness formed
considerable amounts of enolate. 1H NMR (500 MHz, C6D6):
δ 1.29 (s, 27H, C(CH3)3), 1.63 (br s, 3H, CHCH3), 2.25 (s, 18H,
ArCH3), 5.66 (br s, 1H, CH3CH), 6.32 (br s, 6H, aryl o-H), 6.74
(s, 3H, aryl p-H), 7.14 (t, 1H, alkoxide phenyl p-H), 7.27 (t,
2H, alkoxide phenyl m-H), 7.48 (app d, alkoxide phenyl o-H).
13C NMR (125.8 MHz, C6D6): δ 21.0 (m-CH3), 27.5 (OCHCH3),
31.6 (C(CH3)3), 60.9 (C(CH3)3), 85.5 (OCH), 126.5 (aryl), 127.6
(aryl), 127.9 (aryl), 128.8 (aryl), 129.1 (aryl), 136.7 (aryl), 146.8
(aryl), 153.3 (aryl). 13C NMR (125.8 MHz, CDCl3): δ 21.7 (m-
CH3), 27.2 (OCHCH3), 31.0 (C(CH3)3), 60.3 (C(CH3)3), 84.7
(OCH), 125.6 (aryl), 127.1 (aryl), 127.3 (aryl), 128.3 (aryl),
128.5 (aryl), 136.0 (aryl), 146.5 (aryl), 152.6 (aryl).
1
mmol, 74% yield). H NMR (500 MHz, C6D6, 25 °C, tentative
assignments): δ 0.47 (v br), 1.18 (s), and 1.59 (v br) assigned
to C(CH3)3, 2.28 (s) and 2.40 (br s) assigned to ArCH3, 5.0 (br
s) and 5.92 (br s) assigned to the olefinic protons, 6.76 (s),
6.99-7.03 (m), 7.24 (t), 7.31 (br s), 7.49 (d), 8.02, 8.24, 8.40
(br singlets) assigned to aryl CH. At lower temperatures, in
toluene-d8, the broad peaks become sharper and split. UV-
vis (toluene, RT): λmax 541, 641 nm. Anal. Calcd for TiN3-
OC49H64: C, 77.48; H, 8.43; N, 5.53. Found: C, 76.91; H, 8.37;
N, 5.11.
Syn th esis of 1-OCHP h 2. A pentane solution (10 mL) of 1
(254 mg, 0.44 mmol, 1 equiv) was added to a diethyl ether
suspension (5 mL) of benzophenone (80 mg, 0.44 mmol, 1
equiv). The reaction mixture was stirred for 30 min. After
evacuating volatile material, the orange residue was dissolved
in toluene (5 mL), and n-Bu3SnH (200 mg, 0.69 mmol, 1.5
equiv) was added to the solution. The reaction mixture was
placed in a 25 mL Schlenk tube and stirred at 65 °C for 5 h.
The color of the mixture gradually changed from dark green-
brown to dark red and then to bright orange. Volatile material
was removed in vacuo. Upon crystallization from pentane at
-35 °C, 136 mg of yellow crystalline 1-OCHPh2 were obtained
in two crops (0.18 mmol, 41% yield). 1H NMR (500 MHz,
C6D6): δ 1.22 (s, 27H, C(CH3)3), 2.26 (s, 18H, ArCH3), 6.52 (br
s, 6H, aryl o-H), 6.63 (br s, 1H, OCH), 6.71 (s, 3H, aryl p-H),
7.07 (t, 1H, phenyl p-H), 7.22 (t, 2H, phenyl m-H), 7.57 (br s,
2H, phenyl o-H). 13C NMR (125.8 MHz, C6D6): δ 22.1 (m-CH3),

1338 Organometallics, Vol. 21, No. 7, 2002
Agapie et al.
Rea ction of Ti(NRAr 1)3 w ith 3,5-Di-ter t-bu tylben za l-
d eh yd e. At room temperature, a pentane solution (5 mL) of
1 (127 mg, 0.22 mmol, 1 equiv) was added to a pentane solution
(3 mL) of 3,5-di-tert-butylbenzaldehyde (48 mg, 0.22 mmol, 1
equiv). Upon addition, the color turned briefly dark brown-
green, then yellow. After 30 min, solvent was removed in vacuo
and the yellow residue was crystallized from a diethyl ether/
THF mixture at -35 °C. The yellow crystalline precipitate was
collected on a sintered glass frit and washed with pentane. In
this manner, 142 mg (0.18 mmol, 81% yield) of yellow (1-
o-H), 7.31 (t, 2H, phenyl m-H). 13C NMR (75 MHz, CDCl3): δ
21.8 (m-CH3), 30.4 (C(CH3)3), 38.8 (NCH3), 61.8 (C(CH3)3), 88.9
(dCH2), 116.1 (aryl), 118.7 (aryl), 125.9 (aryl), 127.6 (aryl),
128.9 (aryl), 136.0 (aryl), 148.3 (aryl), 152.3 (aryl), 163.7 (OCd
). Anal. Calcd for TiN4OC45H64: C, 74.56; H, 8.90; N, 7.73.
Found: C, 74.20; H, 9.07; N, 7.68. IR (C6D6, cm-1): ν 2974 (s
br), 2867 (br m), 1597 (m), 1586 (m), 1500 (m), 1289 (w), 1247
(s), 1177 (m), 1150 (w), 1118 (m), 1021 (m), 940 (m), 695 (m).
Rea ction of 1-OC(CH2)NP h Me w ith Ben za ld eh yd e.
Excess benzaldehyde (0.08 mL, 0.78 mmol, 2.4 equiv) was
added via syringe to a toluene solution (5 mL) of 1-OC(CH2)-
NPhMe (235 mg, 0.32 mmol, 1 equiv). The reaction mixture
was stirred at 25 °C for 12 h. 1H NMR interrogation of the
reaction mixture showed complete consumption of the amido-
enolate and clean formation of a single product. Volatile
material was removed in vacuo. The yellow residue was
recrystallized from diethyl ether at -35 °C, collected on a
sintered glass frit, and washed with cold pentane. This
procedure provided 152 mg (0.18 mmol, 57%) of 1-OCHPh-
1
OCHAr4)2 were obtained in two crops. H NMR examination
after performing the reaction in C6D6 showed clean formation
2
of the same product, while the H NMR spectrum showed no
evidence of 2H incorporation. It would be reasonable to propose
the formation of a single product vs a mixture of diastereomers.
The 1H NMR spectrum is not of much help in making this kind
of decision because the broadness of the peaks can be due to
a mixture of diatereomers as well as to hindered rotation of
the substituents. The spectroscopic data do not give conclusive
information regarding the stereochemistry of this pinacolic
coupling reaction. 1H NMR (300 MHz, CDCl3): δ 0.96 (br s,
27H, NC(CH3)3), 1.45 (br s, 18H, ArC(CH3)3), 2.18 (br s, 18H,
ArCH3), 5.8 (v br s, 6H, aryl o-H), 6.68 (s, 3H, N-aryl p-H),
6.91, 7.49 (br singlets, 1H each, OCH and alkoxide aryl
p-H), 7.64 (v br s, 2H, alkoxide aryl o-H). 13C NMR (75
MHz, CDCl3): δ 21.9 (m-CH3), 31.4 (C(CH3)3), 32.2 (C(CH3)3),
35.4 (aryl-C(CH3)3), 60.4 (NC(CH3)3), 124.4 (aryl), 125.8 (aryl),
127.8 (aryl), 135.6 (aryl), 153.9 (aryl). Anal. Calcd for
Ti2N6O2C102H152: C, 77.09; H, 9.57; N, 5.29. Found: C, 76.98;
H, 9.65; N, 4.99.
1
(CH2CONPhMe) in three crops. H NMR (500 MHz, C6D6): δ
1.20 (s, 27H, C(CH3)3), 2.25 (s, 18H, ArCH3), 2.85 (br, s, 2H,
CHCH2), 2.93 (s, 3H, NCH3), 6.41 (br s, 9H, PhCHO, aryl o-H
and phenyl o-H), 6.70 (s, 3H, aryl p-H), 6.93-6.98 (m, 3H,
phenyl p-H and phenyl m-H), 7.14 (t, 1H, phenyl p-H), 7.25
(t, 2H, phenyl m-H), 7.59 (br s, 2H, phenyl o-H). 1H NMR (500
MHz, C6D6, 60 °C): δ 1.18 (s, 27H, C(CH3)3), 2.24 (s, 18H,
ArCH3), 2.85 (br, app d, 2H, CHCH2), 2.93 (s, 3H, NCH3), 6.31
(br, app dd, 1H, PhCHO), 6.38 (br s, 6H, aryl o-H), 6.51 (d,
2H, phenyl o-H), 6.69 (s, 3H, aryl p-H), 6.96 (t, 1H, phenyl
p-H), 7.00 (t, 2H, phenyl m-H), 7.14 (t, 1H, phenyl p-H), 7.24
(t, 2H, phenyl m-H), 7.56 (d, 2H, phenyl o-H). 13C NMR (125.8
MHz, CDCl3): δ 21.7 (m-CH3), 30.8 (C(CH3)3), 37.2 (CH2), 44.6
(NCH3), 60.4 (C(CH3)3), 85.8 (OCPh), 125.7 (aryl), 127.6 (aryl),
127.8 (aryl), 128.0 (aryl), 128.2 (aryl), 128.3 (aryl), 129.8 (aryl),
136.0 (aryl), 144.0 (aryl), 144.1 (aryl), 152.5 (aryl), 169.9 (Od
CN(MePh)). Anal. Calcd for TiN4O2C52H70: C, 75.16; H, 8.49;
N, 6.74. Found: C, 74.63; H, 8.50; N, 6.86. IR (C6D6, cm-1): ν
3030 (br w), 2959 (br m), 2922 (br m), 2865 (w), 1659 (s, amide
CdO stretch), 1596 (s), 1585 (s), 1495 (s), 1417 (w), 1376 (m),
1288 (m), 1185 (w), 1128 (s), 1092 (s), 1069 (s), 1028 (m), 968
(m), 701 (s).
Rea ction of Ti(NRAr 1)3 w ith Di(3,5-bis[t-Bu ]p h en yl)-
su ccin a te. A cold pentane solution (10 mL) of 1 (273 mg, 0.47
mmol, 2 equiv) was added to a thawing suspension of the
succinic acid ester (117 mg, 0.23 mmol, 1 equiv) in pentane (5
mL). The reaction mixture was allowed to stir for 2 h. The
color gradually changed from forest green to orange-brown.
Removal of volatile material in vacuo provided an oily residue,
which was inspected by 1H NMR spectroscopy. As determined
by 1H NMR spectroscopy, the major component in the mixture
is the ester enolate, but some tert-butyl-3,5-dimethylaniline
was found also to be present. Recrystallization from pentane
resulted in the isolation of the orange crystalline ester-enolate
product 1-OC(CH2)OAr4 (210 mg, 0.25 mmol) in 54% yield. 1H
NMR (300 MHz, CDCl3): δ 1.17 (s, 27H, NC(CH3)3), 1.37 (s,
18H, aryl C(CH3)3), 2.24 (s, 18H, ArCH3), 3.46 and 3.76
(doublets, 2H, CH2), 5.87 (br s, 6H, aryl o-H), 6.74 (s, 3H, aryl
p-H), 7.08 (d, 2H, enolate aryl o-H), 7.08 (t, 1H, enolate aryl
p-H). 13C NMR (75 MHz, CDCl3): δ 21.8 (m-CH3), 30.6 (NC-
(CH3)3), 31.8 (aryl-C(CH3)3), 35.2 (aryl-C(CH3)3), 61.9 (NC(CH3)3),
68.9 (dCH2), 114.3 (aryl), 117.7 (aryl), 125.9 (aryl), 127.5 (aryl),
136.1 (aryl), 152.2 (aryl), 152.3 (aryl), 155.4 (aryl), 166.6 (OCd
). Anal. Calcd for TiN3O2C52H77: C, 75.79; H, 9.42; N, 5.10.
Found: C, 75.73; H, 9.41; N, 5.10.
Rea ction of 1-OC(CH2)Ar 2 w ith Ben za ld eh yd e. A di-
ethyl ether solution (5 mL) of 1 (50 mg, 0.088 mmol, 2 equiv)
was added to a suspension of 1,4-diketone (11.6 mg, 0.044
mmol, 1 equiv) in diethyl ether (3 mL). The reaction mixture
was stirred at room temperature for 30 min, and then volatile
material was removed in vacuo. The oily residue was dissolved
in toluene (5 mL), and benzaldehyde (22.2 mg, 0.21 mmol, 4.8
equiv) was added to the reaction mixture. After 12 h of stirring,
1
the H NMR spectrum of the reaction mixture displayed only
the peaks for 1-OC(CH2)Ar2 and benzaldehyde.
Rea ction of Ti(NRAr 1)3 w ith N-Meth ylp h th a lim id e. A
pentane solution (5 mL) of 1 (115 mg, 0.2 mmol, 2 equiv) was
added to a suspension of N-methyl phthalimide (16 mg, 0.1
mmol, 1 equiv) in pentane (3 mL), at 25 °C. The color of the
reaction mixture turned dark blue upon mixing. After 30 min
of stirring, solvent was removed in vacuo. The 1H NMR
spectrum of the residue revealed formation of a single product.
The oily residue was dissolved in diethyl ether. Upon addition
of acetonitrile, a dark blue solid precipitated and was collected
Syn th esis of 1-OC(CH2)NP h Me. A pentane solution (10
mL) of 1 (585 mg, 1.01 mmol, 2 equiv) was added to a
suspension of succinic acid amide (150 mg, 0.51 mmol, 1 equiv)
in pentane (5 mL). The reaction mixture was allowed to stir
for 3 h at 25 °C. The color changed gradually from forest green
1
to yellow-brown. Analysis of the reaction mixture by H NMR
spectroscopy showed the presence of a single product. Abun-
dant precipitation of a yellow solid was observed. The reaction
mixture was stored at -35 °C for several hours and then
filtered through a sintered glass frit. The collected yellow
powder consisted of analytically pure amide enolate. The
filtrate was concentrated and cooled at -35 °C to provide
another crop of amide enolate. The solid amide enolate 1-OC-
(CH2)NPhMe obtained using this procedure amounted to 608
mg (0.84 mmol, 84%). 1H NMR (300 MHz, C6D6): δ 1.25 (s,
27H, C(CH3)3), 2.22 (s, 18H, ArCH3), 3.13 (s, 3H, NCH3) 4.46
and 4.60 (singlets, 2H, CH2), 6.11 (v br s, 6H, aryl o-H), 6.73
(s, 3H, aryl p-H), 6.89 (t, 1H, phenyl p-H), 7.19 (d, 2H, phenyl
on
a sintered glass frit and washed with cold pentane.
Compound 12-O2Phth obtained in this fashion amounted to 97
mg (0.074 mmol, 74% yield). 1H NMR (300 MHz, CDCl3): δ
1.13 (s, 27H, C(CH3)3), 2.23 (s, 18H, ArCH3), 3.26 (s, 3H, NCH3),
6.50 (s, 6H, aryl o-H), 6.56 (br s, 2H phthalimide aryl H), 6.72
(s, 3H, aryl p-H), 7.56 (br s, 2H phthalimide aryl H). 13C NMR
(75 MHz, CDCl3): δ 21.7 (m-CH3), 30.8 (C(CH3)3), 61.6
(C(CH3)3), 76.8 (NCH3), 105.2 (aryl), 117.4 (aryl), 119.4 (aryl),
125.9 (aryl), 127.6 (aryl), 136.4 (aryl), 140.8 (aryl), 151.0 (aryl).
Anal. Calcd for Ti2N7O2C81H115: C, 74.04; H, 8.76; N, 7.47.
Found: C, 73.88; H, 8.79; N, 7.28.

Radical Scission of 1,4-Dicarbonyl Compounds
Organometallics, Vol. 21, No. 7, 2002 1339
Rea ction of Ti(NRAr 1)3 w ith Di-ter t-Bu tyl Azod ica r -
boxyla te. Cold pentane solutions of 1 (171 mg, 0.30 mmol, 2
equiv) and di-tert-butyl azodicarboxylate (34 mg, 0.15 mmol,
1 equiv) were mixed and allowed to stir for 1 h. The color of
the reaction mixture turned orange. Solvent was removed in
vacuo, leaving an oily orange residue. Crystallization from
pentane at -35 °C afforded 135 mg of orange crystals of
12-Dt-BuAD (0.1 mmol, 66% yield). 1H NMR (300 MHz,
C6D6): δ 1.20 (s, 27H, NC(CH3)3), 1.69 (s, 18H, OC(CH3)3), 2.21
(s, 18H, ArCH3), 5.94 (br s, 6H, aryl o-H), 6.73 (s, 3H, aryl
p-H). 13C NMR (125.8 MHz, CDCl3): δ 22.0 (m-CH3), 29.7
(C(CH3)3), 31.0 (C(CH3)3), 61.6 (NC(CH3)3), 80.1 (OC(CH3)3),
125.6 (aryl), 127.2 (aryl), 135.7 (aryl), 152.7 (aryl). Anal. Calcd
for Ti2N8C82O4H126: C, 71.17; H, 9.18; N, 8.09. Found: C, 70.75;
H, 9.23; N, 8.15.
Ta ble 1. Cr ysta llogr a p h ic Da ta for a n d
1-OC(CH2)NP h Me a n d 1-OC(CH2)Ar 2
1-OC(CH2)NPhMe
1-OC(CH2)Ar2
formula
C45H64N4OTi
724.90
P1h
C45H63N3OTi
709.88
P21/c
fw
space group
a, Å
b, Å
c, Å
11.0950(12)
12.5053(12)
16.003(2)
88.924(2)
85.898(2)
71.085(2)
2095.1(4)
2
15.3749(5)
13.4837(2)
20.2826(6)
90
101.51
90
R, deg
â, deg
γ, deg
V, Å3
4120.2(2)
4
Z
cryst description
orange plate
1.149
0.241
784
1.087
orange plate
1.144
0.243
1536
1.193
D
calcd, g‚cm-3
Rea ction of Ti(NRAr 1)3 w ith P h Br . A pentane/bro-
mobenzene (26 mg, 0.16 mmol, 1.1 equiv) mixture (3 mL) was
added to a pentane solution (5 mL) of 1 (82 mg, 0.14 mmol, 1
equiv). The color of the solution turned intense orange in 1 h,
and an orange powder precipitated out. Solvent was removed
in vacuo. Crystallization from diethyl ether at -35 °C afforded
µ, mm-1
F(000)
GOFa on F2
R1 (Fo)b for I > 2σI
wR2 (Fo2)c for I > 2σI
0.0671
0.1305
0.0659
0.1470
GOF ) [∑[w(Fo - Fc2)2]/(n - p)]1/2
.
.
R1 ) ∑||Fo| - |Fc||/∑|Fo|.
a
2
b
1
c wR2 ) [∑[w(Fo - Fc2)2]/[∑w(Fc2)2]]1/2
2
58 mg (0.087 mmol, 62% yield) of orange 1-Br. H NMR (300
MHz, C6D6): δ 1.38 (s, 27H, C(CH3)3), 2.22 (s, 18H, ArCH3),
1
6.61 (br s, 6H, aryl o-H), 6.73 (s, 3H, aryl p-H). H NMR (300
spectroscopy. Subsequent recrystallizations did not provide the
cyclization product 1-CH2DHBF free of 1-Br. 1H NMR (500
MHz, C6D6): δ 1.24 (s, 27H, C(CH3)3), 2.25 (s, 18H, ArCH3),
4.15, 4.29 (app triplets, 2H, OCH2), 6.71 (s, 3H, N-aryl p-H),
6.78-6.81 (m, 3H, aryl CH), 6.90-6.93 (m, 1H, aryl CH), 6.97
(s, 6H, N-aryl o-H). 13C NMR (125.8 MHz, C6D6): δ 21.9 (m-
CH3), 31.2 (C(CH3)3), 45.5 (aliphatic CH), 62.2 (C(CH3)3), 80.3
(CH2), 82.9 (CH2), 110.0 (aryl), 120.6 (aryl), 123.9 (aryl), 127.6
(aryl), 130.7 (aryl), 137.5 (aryl), 137.7 (aryl), 147.6 (aryl), 160.2
(aryl). The filtrate obtained in the previous experiment was
dissolved in 10 mL of THF in a 25 mL round-bottom flask
capped with a septum and taken outside the box. Water (0.6
mL) was added via syringe. Immediate formation of a gray
precipitate was observed. Upon overnight stirring the solution
was colorless and an abundant gray precipitate was present.
Exposure to air caused the gray precipitate to turn white.
Volatile material was removed in vacuo, and the white residue
was extracted with diethyl ether. Removal of solvent afforded
a yellow oil. 1H NMR and 13C NMR analysis of this oil showed
the presence of tert-butyl-3,5-dimethylaniline and 3-meth-
yldihydrobenzofuran.36
MHz, CDCl3): δ 1.19 (s, 27H, C(CH3)3), 2.29 (s, 18H, ArCH3),
6.46 (br s, 6H, aryl o-H), 6.83 (s, 3H, aryl p-H). 13C NMR (75
MHz, CDCl3): δ 21.7 (m-CH3), 30.8 (C(CH3)3), 63.6 (C(CH3)3),
127.4 (aryl), 128.2 (aryl), 136.5 (aryl), 148.5 (aryl). Anal. Calcd
for TiN3BrC36H54: C, 66.46; H, 7.44; N, 6.46. Found: C, 66.35;
H, 7.42; N, 6.39.
Rea ction of Ti(NRAr 1)3 w ith P h Cl. Ti(NRAr1)3 (32.6 mg,
0.056 mmol, 1 equiv) was dissolved in neat PhCl (1.36 g, 12
mmol, 212 equiv). Upon overnight stirring, the color of the
reaction mixture turned intense orange-red. The NMR spec-
trum of the reaction mixture revealed clean formation of 1-Cl.41
Rea ction of Ti(NRAr 1)3 w ith P h I. Iodobenzene (0.020 mL,
0.18 mmol, 1 equiv) was added via syringe to a pentane
solution of Ti(NRAr1)3 (103.3 mg, 0.18 mmol, 1 equiv). The
color of the solution turned bright orange in less than 5 min,
and precipitation of an orange solid was observed. The 1H
NMR spectrum of the reaction mixture indicated clean forma-
tion of 1-I.13
Syn th esis of 1-F . A benzene solution (5 mL) of 1 (100 mg,
0.173 mmol, 1 equiv) was added to a benzene suspension (3
mL) of XeF2 (14.7 mg, 0.087, 0.5 equiv). After 1 h of stirring,
the reaction mixture turned dark red. Solvent was removed
in vacuo. 1H NMR analysis of the residue showed clean
formation of Ti(F)(NRAr)3. The residue was crystallized from
a THF/diethyl ether mixture at -35 °C, affording 82.3 mg
Kin etic Mea su r em en ts: Gen er a l P r oced u r e. Stock
solutions of 1, halobenzenes, and diketones in toluene were
used immediately after preparation or were stored at -35 °C.
The reagents were mixed in the UV cell immediately prior to
data collection. Compound 1 displays absorptions at 792 nm
(ꢀ ) 223 (cm M)-1) and 637 nm (ꢀ ) 169 (cm M)-1). The decay
of 1 was monitored at 792 nm.
1
(0.138 mmol, 80%) of bright orange crystals of 1-F. H NMR
(300 MHz, C6D6): δ 1.38 (s, 27H, C(CH3)3), 2.17 (s, 18H,
ArCH3), 5.98 (br s, 6H, aryl o-H), 6.73 (s, 3H, aryl p-H). 1H
NMR (300 MHz, CDCl3): δ 1.18 (s, 27H, C(CH3)3), 2.18 (s,
18H, ArCH3), 5.72 (br s, 6H, aryl o-H), 6.76 (s, 3H, aryl p-H).
13C NMR (75 MHz, CDCl3): δ 21.7 (m-CH3), 30.2 (C(CH3)3),
60.6 (C(CH3)3), 127.2 (aryl), 127.5 (aryl), 136.4 (aryl), 151.5
(aryl). 19F NMR (282 MHz, C6D6): δ -71.6. Anal. Calcd for
TiN3FC36H54: C, 72.46; H, 8.11; N, 7.04. Found: C, 71.86; H,
8.48; N, 6.95.
R ea ct ion of Ti(NR Ar 1)3 w it h o-Br om op h en yl Allyl
Eth er . A cold pentane solution (10 mL) of o-bromophenyl allyl
ether (302 mg, 1.4 mmol, 1 equiv) was added to a thawing
pentane solution (10 mL) of 1 (1.64 g, 2.8 mmol, 2 equiv). The
color gradually turned orange-red, and orange 1-Br precipi-
tated out. The reaction mixture was stirred for 3 h, then
concentrated and allowed to cool at -35 °C. Compound 1-Br
was collected partially on a sintered glass frit. The filtrate was
concentrated to dryness in vacuo and analyzed by NMR
Kin etics of Ha logen Abstr a ction fr om Ha loben zen e.
Concentrations in the range of 10-3-10-2 M were used for 1.
Concentrations in the range 0.1-0.5 M were used for iodo-
and bromobenzene. Measurements for rate constant determi-
nation were performed for various concentrations of 1 and
halobenzene for at least 4 kinetic runs through 3 half-lives.
kobs corresponding to the pseudo-first-order decay of 1 was
determined using an Origin curve-fitting to the equation A )
A∞ + A0[exp(-kobst)]. Variation of the original concentration
of the halobenzene allowed determination of the order in PhZ
(Z ) Br or I). By dividing kobs by the concentration of PhZ,
second-order rate constants were determined ((9.3 ( 0.1) ×
10-3 (s M)-1 for PhBr and (6.6 ( 0.5) × 10-1 (s M)-1 for PhI;
95% confidence interval). Large concentrations, in the range
6.5-8 M, were used for PhCl in order to ensure significant
decay of 1 in a time period over which 1 does not independently
decompose. The small variations in the concentration of PhCl
did not allow an accurate determination of the order in PhCl.
In this case, the pseudo-first-order rate constant (kobs) was
found to be (1.8 ( 0.3) × 10-4 s-1. No significant decay of 1
(41) J ohnson, A. R.; Wanandi, P. W.; Cummins, C. C.; Davis, W. M.
Organometallics 1994, 13, 2907.

1340 Organometallics, Vol. 21, No. 7, 2002
Agapie et al.
was observed by UV-vis spectroscopy for a solution in neat
fluorobenzene over an interval of 10 h.
approximation. The local density approximation functional
used was that of Vosko, Wilk, and Nusair, while the function-
als for the generalized gradient approximations took the form
of Becke (exchange) and Perdew (correlation).29-32
Kin etics of 1,4-Dica r bon yl Scission : Gen er a l P r oce-
d u r e. Concentrations in the range 10-3-10-2 M were used for
1 and for 1,4-diketones. The measurements were performed
after fast mixing. A new absorption, which decayed over time,
was observed around 650-670 nm.
Ack n ow led gm en t. For support of this work, the
authors are grateful to the National Science Foundation
(CHE-9988806), the Packard Foundation (Fellowship to
C.C.C., 1995-2000), and the National Science Board
(Alan T. Waterman award to C.C.C., 1998). T.A. thanks
MIT’s UROP (Undergraduate Research Opportunities
Program) for funding. The authors are grateful to Prof.
Karsten Meyer for EPR measurements.
X-r a y Cr ysta l Da ta : Gen er a l P r oced u r e. Crystals grown
from concentrated diethyl ether solutions at -35 °C were
removed quickly from a scintillation vial to a microscope slide
coated with Paratone N oil (an Exxon product). Samples were
selected and mounted on a glass fiber in wax and Paratone N
oil. Data collection was carried out at a temperature of 188 K
on a three-circle goniometer Siemens Platform with a CCD
detector using Mo KR radiation (λ ) 0.71073 Å). The data were
processed and refined by using the program SAINT supplied
by Siemens Industrial Automation, Inc. The structures were
solved by direct methods (SHELXTL v5.03, Sheldrick, G. M.,
and Siemens Industrial Automation, Inc., 1995) in conjunction
with standard difference Fourier techniques. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were
placed in calculated (dCH ) 0.96 Å) positions. Some details
regarding refined data and cell parameters are available in
Table 1. Selected bond distances and angles are supplied in
the captions of Figures 1 and 2.
Su p p or tin g In for m a tion Ava ila ble: Tables with bond
lengths, bond angles, atomic coordinates, and anisotropic
displacement parameters for the structures of 1-OC(CH2)Ar2
and 1-OC(CH2)NPhMe; solution EPR spectrum of 1-OCPh2;
1H NMR spectra of (1-OCMePh)2 and its disproportionation
products; decay of 1 monitored by UV-vis spectroscopy; IR
spectra of succinate diamide, 1-OC(CH2)NPhMe, and 1-OCHPh-
(CH2CONPhMe); details of the DFT calculations; pictorial
representations of the frontier molecular orbitals of 2-OCHCH2
and 2-OC(NH2)CH2 as obtained from the DFT calculations.
This information is available free of charge via the Internet
at http://pubs.acs.org.
DF T Ca lcu la tion s. Calculations were carried out with the
ADF2000.01 package, employing scalar relativistic corrections
for the non-hydrogen atoms in the context of the frozen core
OM0107284