Synthesis and reactivity of [(DMSC)Ti(η2-OCAr2)L2] complexes (DMSC = dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion, Ar = Aryl group, and L2 = delocalized diimine)

Article abstract of DOI:10.1021/om020487f

Reactions of titanapinacolate complexes [(DMSC)Ti(OCAr₂CAr₂O)] (1, Ar = Ph; 2, Ar = p-MeC₆H₄; DMSC = 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion) with 1 equiv of a delocalized diimine furnished titanium η²-ketone complexes [(DMSC)Ti(η²-OCAr₂)L₂] 3-6 (L₂ = bpy, dmbpy, or phen). The ketone is weakly bound in 3-6, and it is readily dissociated. The compounds dissolve in aromatic hydrocarbon solvents to give intense green solutions and undergo a photochemically assisted transformation into 1-aza-5-oxa-titanacyclopentene derivatives 8-11, in which C-H activation of the heterocyclic diimine ligand and hydride migration to a Ti-bound ketone to form an alkoxide group has occurred. The reaction of 3-6 with one or more equivalents of appropriate ketone gave 8-11 in high yield. The compounds were characterized by NMR (¹H and ¹³C) and microanalysis data, as well as by X-ray crystallography for [(DMSC)Ti{k³-OC(p-MeC₆H₄)₂ C₁₀H₇N₂}{OCH(p-MeC₆ H₄)₂}] (9). The ease of transformation of [(DMSC)Ti{η²-OC(p-MeC₆H₄)₂} L₂] complexes (4, L₂ = bpy; 5, L₂ = dmbpy; 6, L₂ = phen) into 9-11 tracks the facility of metal to diimine ligand charge transfer (MLCT) transition and increased in the order 5 < 4 ? 6. This transformation is suggested to occur by a mechanism that involves reversible coordination of ketone to titanium and a rate-limiting step that is dependent on ketone concentration.

Full text of DOI:10.1021/om020487f

136
Organometallics 2003, 22, 136-144
Syn th esis a n d Rea ctivity of [(DMSC)Ti(η2-OCAr 2)L2]
Com p lexes (DMSC ) Dim eth ylsilyl-Br id ged
p-ter t-Bu tylca lix[4]a r en e Dia n ion , Ar ) Ar yl Gr ou p , a n d
L2 ) Deloca lized Diim in e)
J esudoss V. Kingston, Vallipuram Sarveswaran,† Sean Parkin, and
Folami T. Ladipo*
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055
Received J une 20, 2002
Reactions of titanapinacolate complexes [(DMSC)Ti(OCAr2CAr2O)] (1, Ar ) Ph; 2, Ar )
p-MeC6H4; DMSC ) 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]arene dianion)
with 1 equiv of a delocalized diimine furnished titanium η2-ketone complexes [(DMSC)Ti-
(η2-OCAr2)L2)] 3-6 (L2 ) bpy, dmbpy, or phen). The ketone is weakly bound in 3-6, and it
is readily dissociated. The compounds dissolve in aromatic hydrocarbon solvents to give
intense green solutions and undergo a photochemically assisted transformation into 1-aza-
5-oxa-titanacyclopentene derivatives 8-11, in which C-H activation of the heterocyclic
diimine ligand and hydride migration to a Ti-bound ketone to form an alkoxide group has
occurred. The reaction of 3-6 with one or more equivalents of appropriate ketone gave 8-11
in high yield. The compounds were characterized by NMR (1H and13C) and microanalysis
data, as well as by X-ray crystallography for [(DMSC)Ti{κ3-OC(p-MeC6H4)2C10H7N2}{OCH-
(p-MeC6H4)2}] (9). The ease of transformation of [(DMSC)Ti{η2-OC(p-MeC6H4)2}L2] complexes
(4, L2 ) bpy; 5, L2 ) dmbpy; 6, L2 ) phen) into 9-11 tracks the facility of metal to diimine
ligand charge transfer (MLCT) transition and increased in the order 5 < 4 , 6. This
transformation is suggested to occur by a mechanism that involves reversible coordination
of ketone to titanium and a rate-limiting step that is dependent on ketone concentration.
In tr od u ction
[4]arene dianion)3 (Chart 1). Structural characterization
of 1 by X-ray crystallography revealed that the unit cell
contained two independent molecules and that the
OCPh2CPh2O fragment of each molecule possessed an
unusually long C-C bond [1.628(6) and 1.652(5) Å]. This
led us to wonder whether titanapinacolates 1 and 2
would serve as useful synthons to (DMSC)Ti(OCAr2)
species. Thus, we decided to explore the synthesis of
[(DMSC)Ti(OCAr2)L2] complexes in which L2 is a delo-
calized diimine, such as 2,2′-bipyridine (bpy), 4,4′-
dimethyl-2,2′-dipyridyl (dmbpy), or 1,10-phenanthroline
(phen). Delocalized diimine ligands were chosen because
they have been shown to support electron-rich low-
valent titanium centers.4
Transition metal-mediated reductive coupling reac-
tions of unsaturated organic substrates, such as imines,
alkynes, aldehydes, and ketones, are important to the
fields of organic synthesis and organometallic chemis-
try.1,2 In pinacol and McMurry reactions, metallapina-
colate complexes have been implicated as intermedi-
ates.2 We have recently reported the synthesis of well-
characterized titanapinacolate complexes, [(DMSC)Ti-
(OCAr2CAr2O)] (1, Ar ) Ph; 2, Ar ) p-MeC6H4; DMSC
) 1,2-alternate dimethylsilyl-bridged p-tert-butylcalix-
* To whom correspondence should be addressed. E-mail: fladip0@
uky.edu.
† Current address: Department of Chemistry and Biochemistry,
University of Notre Dame, Notre Dame, IN 46556.
Many aldehyde and ketone complexes of the transi-
tion metals are known, and metal-promoted reactivity
of carbonyl compounds has been investigated.5-8 Alde-
hyde and ketone complexes of the group 4 metals are
usually bimolecular with bridging carbonyl functions.8
(1) See for example: (a) Ozerov, O. V.; Patrick, B. O.; Ladipo, F. T.
J . Am. Chem. Soc. 2000, 122, 6423. (b) Armbruster, J .; Grabowski, S.;
Ruch, T.; Prinzbach, H. Angew. Chem., Int. Ed. Engl. 1998, 37, 2242.
(c) Balu, N.; Banerji, A. J . Org. Chem. 1998, 63, 3468. (d) Ojima, I.;
Tzamarioudaki, M.; Zhaoyang, L.; Donovan, R. J . Chem. Rev. 1996,
96, 635. (e) Hill, J . E.; Balaich, G.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1993, 12, 2911. (f) Kahn, B. E.; Rieke, R. D. Chem.
Rev. 1988, 88, 733. (g) Pons, J .-M.; Santelli, M. Tetrahedron 1988, 44,
4295. (h) Schore, N. E. Chem. Rev. 1988, 88, 1081. (i) Negishi, E. In
Comprehensive Organic Synthesis; Trost, B. M., Ed.; Permagon:
Oxford, 1991; Vol. 5, pp 1163-1184. (j) Roskamp, E. J .; Pedersen, S.
F. J . Am. Chem. Soc. 1978, 109, 6551.
(2) See for example: (a) Villiers, C.; Ephritikhine, M. Chem. Eur.
J . 2001, 7, 3043. (b) Eisch, J . J .; Gitua, J . N.; Otieno, P. O.; Shi, X. J .
Organomet. Chem. 2001, 624, 229. (c) Ephritikhine, M. J . Chem. Soc.,
Chem. Commun. 1998, 2549. (d) Wirth, T. Angew. Chem., Int. Ed. Engl.
1996, 35, 61. (e) Furstner, A.; Bogdanovic, B. Angew. Chem., Int. Ed.
Engl. 1996, 35, 2443. (f) McMurry, J . E. Chem. Rev. 1989, 89, 1513.
(g) Dushin, R. G. In Comprehensive Organometallic Chemistry II;
Hegedus, L. S., Ed.; Pergamon: Oxford, 1996; Vol. 12, p 1071.
(3) (a) Ozerov, O. V.; Parkin, S.; Brock, C. P.; Ladipo, F. T.
Organometallics 2000, 19, 4187. (b) Kingston, J . V.; Ozerov, O. V.;
Parkin, S.; Brock, C. P.; Ladipo, F. T. J . Am. Chem. Soc. 2002, in press.
(4) (a) Durfee, L. D.; Fanwick, P. E.; Rothwell, I. P.; Folting, K.;
Huffman, J . C. J . Am. Chem. Soc. 1987, 109, 4720. (b) Corbin, D. R.;
Willis, E. N.; Duesler, E. N.; Stucky, G. D. J . Am. Chem. Soc. 1980,
102, 5971. (c) McPherson, A. M.; Fieselmann, B. F.; Lichtenberger, D.
L.; McPherson, G. L.; Stucky, G. D. J . Am. Chem. Soc. 1979, 101, 3425.
(5) See for example the following and references therein: (a)
Helberg, L. E.; Gunnoe, T. B.; Brooks, B. C.; Sabat, M.; Harman, W.
D. Organometallics 1999, 18, 573. (b) Shambayati, S.; Schreiber, S. L.
In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I.,
Schreiber, S. L., Eds.; Pergamon: New York, 1991; Vol. 1, Chapter
1.10.
10.1021/om020487f CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/07/2002

[(DMSC)Ti(η2-OCAr2)L2] Complexes
Organometallics, Vol. 22, No. 1, 2003 137
benzophenone ketyl. All solvents were stored in the glovebox
over 4A molecular sieves that were dried in a vacuum oven at
150 °C for at least 48 h prior to use. Ph213CO, 1,10-phenan-
throline, 4,4′-dimethylbenzophenone, and 2,2′-bipyridine were
purchased from Aldrich and sublimed prior to use. [(DMSC)-
Ti(OCPh2CPh2O)] (1) and [(DMSC)Ti{OC(p-MeC6H4)2C(p-
MeC6H4)2O] (2) were prepared as previously reported.3 1H and
13C NMR spectra were recorded on a Varian Gemini-200
spectrometer or a Varian VXR-400 spectrometer at ca. 22 °C.
1H and 13C chemical shifts were referenced to residual solvent
peaks. Infrared spectra were recorded on a Nicolet Magna 560
spectrometer. Electronic spectra were recorded on a Hewlett-
Packard 8453 series UV-visible spectroscopy system. GC-
MS analyses were performed on a Hewlett-Packard 5890 series
II gas chromatograph with a Hewlett-Packard 5972 series
mass selective detector at an ionizing potential of 70 eV.
Elemental analyses were performed by Complete Analysis
Laboratories, Inc., Parsippany, NJ .
Ch a r t 1
Few well-characterized mononuclear group 4 metal-
ketone complexes bearing alkyl or aryl substituents,
such as η2-ketone complexes [Ti(OC6H3Ph2-2,6)2(η2-Ph2-
CO)(PMe3)]7d,e and [Hf(TC-3,5)(η2-OC(CH2Ph)2)]7f (TC-
3,5 ) tropocorand ligand), have been reported. Since the
coordination of an organic functional group to a transi-
tion metal complex is undoubtedly central to achieving
selectivity in transition metal-mediated reductive coup-
lings of unsaturated organic substrates, increased knowl-
edge of the structure and reactivity of organic carbonyl
complexes of titanium would greatly facilitate the
development of a greater control over titanium-mediated
reductive coupling reactions. In this paper, we describe
the synthesis, aspects of the structure, and reaction
chemistry of titanium η2-ketone complexes [(DMSC)Ti-
(η2-OCAr2)L2] supported by dimethylsilyl-bridged calix-
[4]arene ligation.
[(DMSC)Ti(η2-OCP h 2)(bp y)] (3). 2,2′-Bipyridine (30.0 mg,
0.192 mmol) was added into a 25 mL suspension of [(DMSC)-
Ti(OCPh2CPh2O)] (1) (0.219 g, 0.197 mmol) in pentane. The
reaction mixture was stirred for 30 min at room temperature,
during which time orange solids started to precipitate. The
resulting suspension was filtered, and the orange precipitate
was washed with pentane (10 mL) and dried under vacuum.
1
Yield: 0.213 g, 99%. H NMR (C6D6): δ 8.64 (d, J ) 5.0 Hz,
2H, arom CH), 7.73 (d, J ) 1.6 Hz, 2H, arom CH), 7.69 (d, J
) 1.4 Hz, 2H, arom CH), 7.62 (d, J ) 2.2 Hz, 2H, arom CH),
7.47 (d, J ) 2.6 Hz, 2H, arom CH), 7.12-6.64 (m, 14H, arom
CH), 6.07 (m, 2H, arom CH), 4.76 (d, J ) 15.6 Hz, 1H, calix-
CH2), 4.60 (d, J ) 16.0 Hz, 2H, calix-CH2), 4.33 (d, J ) 16.4
Hz, 2H, calix-CH2), 3.73 (d, J ) 15 Hz, 1H, calix-CH2), 3.19
(d, J ) 14.2 Hz, 1H, calix-CH2), 2.89 (d, J ) 13.6 Hz, 1H, calix-
CH2), 1.50 (s, 18H, t-Bu), 1.29 (s, 18, t-Bu), 0.35 (s, 3H, exo-
SiCH3), -1.15 (s, 3H, endo-SiCH3). 13C NMR could not be
recorded as the compound transforms to other species in
solution. 13C NMR (C6D6) for [(DMSC)Ti(η2-O13CPh2)(bpy)]
(3b): δ 117.9 (13CPh2). Anal. Calcd for C68H76O5N2SiTi: C,
75.81; H, 7.11. Found: C, 76.13; H, 7.32.
Exp er im en ta l Section
Gen er a l Deta ils. All experiments were performed under
dry nitrogen atmosphere using standard Schlenk techniques
or in a Vacuum Atmospheres, Inc. glovebox. Solvents were
dried and distilled by standard methods before use. Pentane
was distilled twice from sodium benzophenone ketyl with
addition of 1 mL/L of tetraethylene glycol dimethyl ether as a
solubilizing agent. Benzene-d6 was distilled from sodium
[(DMSC)Ti{η2-OC(p-MeC6H4)2}(bp y)] (4). 2,2′-Bipyridine
(53.2 mg, 0.34 mmol) was added into a 10 mL suspension of
[(DMSC)Ti{OC(p-MeC6H4)2C(p-MeC6H4)2O] (2) (0.399 g, 0.341
mmol) in pentane. The reaction mixture was stirred for 15 min,
during which time green solids started to precipitate. The
green solid was filtered and washed with pentane (4 × 5 mL)
and dried under vacuum. Yield: 0.279 g, 73%. 1H NMR
(C6D6): δ 8.68 (d, J ) 4.8 Hz, 2H, arom CH), 7.64 (d, J ) 2.2
Hz, 2H, arom CH), 7.46 (d, J ) 2.6 Hz, 2H, arom CH), 7.25 (d,
J ) 2.2 Hz, 2H, arom CH), 7.00 (d, J ) 2.6 Hz, 2H, arom CH),
6.81 (m, 6H, arom CH), 6.61 (m, 6H, arom CH), 6.07 (m, 2H,
arom CH), 4.76 (d, J ) 14.6 Hz, 1H, calix-CH2), 4.65 (d, J )
16.2 Hz, 2H, calix-CH2), 4.34 (d, J ) 16 Hz, 2H, calix-CH2),
3.74 (d, J ) 15 Hz, 1H, calix-CH2), 3.19 (d, J ) 14 Hz, 1H,
calix-CH2), 2.89 (d, J ) 13.8 Hz, 1H, calix-CH2), 2.21 (s, 6H,
Tol-CH3), 1.52 (s, 18H, t-Bu), 1.29 (s, 18, t-Bu), 0.34 (s, 3H,
exo-SiCH3), -1.15 (s, 3H, endo-SiCH3). 13C NMR could not be
recorded as the compound transforms to other species in
solution. Anal. Calcd for C71H80N2O5SiTi: C, 76.32; H, 7.22;
N, 2.51. Found: C, 76.38; H, 7.42; N, 2.41.
(6) For examples of η1-ketone complexes, see: (a) Foxman, B. M.;
Klemarczyk, P. T.; Liptrot, R. E.; Rosenblum, M. J . Organomet. Chem.
1980, 187, 253. (b) Boudjouk, P.; Woell, J . B.; Radonovich, L. J .; Eyring,
M. W. Organometallics 1982, 1, 582. (c) Gambarotta, S.; Pasquali, M.;
Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1981, 20, 1173.
(d) Crabtree, R. H.; Hlatky, G. G.; Parnell, C. P.; Segmuller, B. E.;
Uriarte, R. J . Inorg. Chem. 1984, 23, 354. (e) Dalton, D. M.; Gladysz,
J . A. J . Chem. Soc., Dalton Trans. 1991, 2741. (f) Sunkel, K.; Urban,
G.; Beck, W. J . Organomet. Chem. 1985, 290, 231. (g) Cicero, R. L.;
Protasiewicz, J . D. Organometallics 1995, 14, 4792. (h) Bachand, B.;
Wuest, J . D. Organometallics 1991, 10, 2015. (i) Fachinetti, G.; Del
Nero, S.; Floriani, C. J . Chem. Soc., Dalton Trans. 1976, 1046.
(7) For examples of η2-ketones with alkyl or aryl substituents, see:
(a) Williams, D. S.; Schofield, M. H.; Anhaus, J . T.; Schrock, R. R. J .
Am. Chem. Soc. 1990, 112, 6728. (b) Barry, J . T.; Chacon, S. T.;
Chisholm, M. H.; Huffmann, J . C.; Streib, W. E. J . Am. Chem. Soc.
1995, 117, 1974. (c) Harman, W. D.; Fairlie, D. P.; Taube, H. J . Am.
Chem. Soc. 1986, 108, 8223. (d) Hill, J . E.; Fanwick, P. E.; Rothwell,
I. P. Organometallics 1992, 11, 1771. (e) Thorn, M. G.; Hill, J . E.;
Warantuke, S. A.; J ohnson, E. S.; Fanwick, P. E.; Rothwell, I. P. J .
Am. Chem. Soc. 1997, 119, 8630. (f) Steinhuebel, D. P.; Lippard, S. J .
J . Am. Chem. Soc. 1999, 121, 11762. (g) Scott, M. J .; Lippard, S. J . J .
Am. Chem. Soc. 1997, 119, 3411. (h) Harman, W. D.; Sekine, M.; Taube,
H. J . Am. Chem. Soc. 1988, 110, 2439. (i) Okuda, J .; Herberich, G. E.
Organometallics 1987, 6, 2331.
A sample of 4 was decomposed with H2O in CH2Cl2. The
suspension was allowed to stand for a few minutes, the solids
were filtered off, and the filtrate was analyzed by GC-MS.
The only products observed were 2,2′-bipyridine (m/z 156, M+)
and OC(p-MeC6H4)2 (m/z 210, M+).
(8) (a) Erker, G. Acc. Chem. Res. 1984, 17, 103. (b) Kropp, K.; Skibbe,
V.; Erker, G.; Kruger, C. J . Am. Chem. Soc. 1983, 105, 3353. (c) Erker,
G.; Hoffmann, U.; Zwetler, R.; Betz, P.; Kruger, C. Angew. Chem., Int.
Ed. Engl. 1989, 28, 630. (d) Erker, G.; Czisch, P.; Schlund, R.;
Angermund, K.; Kruger, C. Angew. Chem., Int. Ed. Engl. 1986, 25,
364. (e) Stella, S.; Floriani, C. J . Chem. Soc., Chem. Commun. 1986,
1053. (f) Erker, G.; Dorf, U.; Czisch, P.; Petersen, J . L. Organometallics
1986, 5, 668. (g) Fachinetti, G.; Biran, C.; Floriani, C.; Villa, A. C.;
Guastini, C. Inorg. Chem. 1978, 17, 2995.
[(DMSC)Ti{η2-OC(p-MeC6H4)2}(dm bpy)] (5). 4,4′-Dimeth-
yl-2,2′-dipyridyl (62.8 mg, 0.341 mmol) was added into a 10
mL suspension of [(DMSC)Ti{OC(p-MeC6H4)2C(p-MeC6H4)2O]
(2) (0.399 g, 0.341 mmol) in pentane. The reaction mixture was
stirred for 15 min, during which time green solids started to
precipitate. The green solid was filtered and washed with
pentane (4 × 5 mL) and dried under vacuum. Yield: 0.350 g,

138 Organometallics, Vol. 22, No. 1, 2003
Kingston et al.
1
89%. H NMR (C6D6): δ 8.59 (d, J ) 5.63 Hz, 2H, arom CH),
32.2 {C(CH3)3}, 3.5 (exo-SiCH3), -0.81 (endo-SiCH3). Anal.
Calcd for C68H76O5N2SiTi: C, 75.81; H, 7.11. Found: C, 76.03;
H, 7.37.
7.67 (d, J ) 2.4 Hz, 2H, arom CH), 7.48 (d, J ) 2.8 Hz, 2H,
arom CH), 7.27 (d, J ) 2.4 Hz, 2H, arom CH), 7.06 (d, J ) 2.4
Hz, 2H, arom CH), 6.88 (s, 2H, arom CH), 6.75 (AB quartet,
8H, arom CH), 5.93 (d, J ) 5.6 Hz, 4H, arom CH), 4.78 (d, J
) 14.8 Hz, 1H, calix-CH2), 4.68 (d, J ) 16.4 Hz, 2H, calix-
CH2), 4.37 (d, J ) 16.4 Hz, 2H, calix-CH2), 3.75 (d, J ) 15.2
Hz, 1H, calix-CH2), 3.26 (d, J ) 14 Hz, 1H, calix-CH2), 3.01
(d, J ) 13.6 Hz, 1H, calix-CH2), 2.21 (s, 6H, Tol-CH3), 1.65 (s,
6H, dmbpy-Me), 1.54 (s, 18H, t-Bu), 1.31 (s, 18, t-Bu), 0.35 (s,
3H, exo-SiCH3), -1.12 (s, 3H, endo-SiCH3). 13C NMR (C6D6):
δ 161.0, 151.1, 149.7, 148.6, 147.9, 143.6, 141.5, 140.8, 131.9,
131.0, 130.8, 129.9, 129.4, 128.2, 127.2, 127.0, 126.9, 125.6,
125.2, 123.5, 120.8, 118.2 (CPh2), 41.2 (calix-CH2), 39.2 (calix-
CH2), 38.4 (calix-CH2), 34.7 (C(CH3)3), 34.4 (C(CH3)3), 32.4
(C(CH3)3), 32.3 (C(CH3)3), 21.3 (Tol-CH3), 20.9 (dmbpy-Me), 3.6
(exo-SiCH3), -1.7 (endo-SiCH3). Anal. Calcd for C73H84N2O5-
SiTi: C, 76.55; H, 7.39; N, 2.45. Found: C, 76.19; H, 7.47; N,
2.40.
[(D M S C )T i {K3 -O C (p -M e C 6 H 4 )2 C 1 0 H 7 N 2 }{O C H (p -
MeC6H4)2}] (9). Into a toluene (10 mL) solution of [(DMSC)-
Ti{η2-OC(p-MeC6H4)2}(bpy)] (4) (0.138 g, 0.123 mmol) was
added 4,4′-dimethylbenzophenone (62.0 mg, 0.294 mmol). The
resulting greenish brown solution was stirred for 12 h at room
temperature, during which time an orange solution resulted.
The orange solution was stripped to dryness under vacuum.
The gummy orange residue was washed with cold pentane (2
× 5 mL) and dried under vacuum to afford an orange powder.
Yield: 0.136 g, 83%. Single crystals were grown from a 60:40
toluene/pentane mixture at room temperature. 1H NMR
(C6D6): δ 8.09 (d, J ) 8 Hz, 2H, arom CH), 7.56 (d, 7.8 Hz,
2H, arom CH), 7.33-7.17 (m, 6H, arom CH), 7.07-6.72 (m,
14H, arom CH), 6.60-6.45 (m, 2H, arom CH), 6.36-6.15 (m,
4H, arom CH), 6.30 (d, J ) 14 Hz, 1H, calix-CH2), 5.90 (s, 1H,
OCH(p-MeC6H4)2, 4.84 (d, J ) 16 Hz, 1H, calix-CH2), 4.70 (d,
J ) 15 Hz, 1H, calix-CH2), 4.28 (d, J ) 15.8 Hz, 1H, calix-
CH2), 3.46 (d, J ) 15.8 Hz, 1H, calix-CH2), 3.24 (d, J ) 15.4
Hz, 1H, calix-CH2), 3.12 (d, J ) 16.4 Hz, 1H, calix-CH2), 2.71
(d, J ) 13.8 Hz, 1H, calix-CH2), 2.14 (s, 3H, p-MeC6H4), 2.08
(s, 3H, p-MeC6H4), 1.99 (s, 3H, p-MeC6H4), 1.90 (s, 3H,
p-MeC6H4), 1.38 (s, 9H, t-Bu), 1.32 (s, 9H, t-Bu), 1.30 (s, 9H,
t-Bu), 1.17 (s, 9H, t-Bu), 0.18 (s, 3H, exo-SiCH3), -1.02 (s, 3H,
endo-SiCH3). 13C NMR (C6D6): δ 171.6, 162.2, 161.9, 151.9,
151.2, 150.6, 149.3, 148.0, 144.1, 143.7, 143.1, 142.4, 141.9,
140.9, 137.9, 137.7, 137.6, 136.6, 136.5, 136.2, 135.9, 135.0,
134.5, 132.8, 131.0, 130.4, 129.1, 128.8, 128.6, 128.4, 128.2,
127.6, 1227.4, 127.1, 126.9, 126.6, 126.5, 125.3, 125.2, 124.5,
123.9, 123.8, 118.9, 116.9, 98.5 {OC(p-MeC6H4)2C10H7N2}, 84.8
{OCH(p-MeC6H4)2}, 41.7 (calix-CH2), 38.7 (calix-CH2), 36.8
(calix-CH2), 35.1 (calix-CH2), 33.8 {C(CH3)3}, 33.6 {C(CH3)3},
31.8 {C(CH3)3}, 31.7 {C(CH3)3}, 31.6 {C(CH3)3}, 31.5 {C(CH3)3},
20.9 (p-MeC6H4), 20.8 (p-MeC6H4), 20.7 (p-MeC6H4), 20.6 (p-
MeC6H4), 2.9 (exo-SiCH3), -1.46 (endo-SiCH3). Anal. Calcd for
Into a C6D6 solution of 5 in a NMR tube was added an excess
of distilled isopropyl alcohol under N2. The green color of the
solution turned purple, then red, and finally pale yellow. A
1H NMR spectrum of the pale yellow solution confirmed the
presence of (DMSC)H2, OC(p-MeC6H4)2, and 4,4′-dimethyl-2,2′-
bipyridine. The solution was hydrolyzed with D2O and ex-
tracted with CH2Cl2. GC-MS analysis of the CH2Cl2 extract
also revealed only 4,4′-dimethyl-2,2′-bipyridine (m/z 184, M+)
and OC(p-MeC6H4)2 (m/z 210, M+).
[(DMSC)Ti{η2-OC(p-MeC6H4)2}(p h en )] (6). 1,10-Phenan-
throline (74.3 mg, 0.412 mmol) was added into a 10 mL
suspension of [(DMSC)Ti{OC(p-MeC6H4)2C(p-MeC6H4)2O] (2)
(0.493 g, 0.421 mmol) in pentane. The reaction mixture was
stirred for 15 min, during which time green solids started to
precipitate. The precipitate was filtered and washed with
pentane (4 × 5 mL) and dried under vacuum to give 0.403 g
of a green powder. 1H NMR showed the presence of a 50:50
1
mixture of 6 and 11. H NMR (unobstructed resonances of 6)
C
86H94N2O6SiTi: C, 77.81; H, 7.13; N, 2.11. Found: C, 77.54;
(C6D6): δ 4.79 (d, J ) 11.6 Hz, 1H, calix-CH2), 4.75 (d, J )
13.2 Hz, 2H, calix-CH2), 4.41 (d, J ) 16.4 Hz, 2H, calix-CH2),
3.75 (d, J ) 14.8 Hz, 1H, calix-CH2), 3.21 (d, J ) 13.6, 1H,
calix-CH2), 2.14 (s, 6H, p-MeC6H4), 1.52 (s, 18H, t-Bu), 1.29
(s, 18H, t-Bu), 0.36 (s, 3H, exo-SiMe), -1.12 (s, 3H, endo-SiMe).
H, 6.98; N, 1.99.
Compound 9 was hydrolyzed by exposure to water in air,
and the residue was extracted with CH2Cl2. EI-GC-MS
analysis of the CH2Cl2 extract revealed both (p-MeC6H4)2-
CHOH (m/z 212 M+) and HOC(p-MeC6H4)2C10H7N2 (m/z 366
M+) were present.
[(DMSC)Ti{K3-OCP h 2C10H7N2}(OCHP h 2)] (8). Into a tolu-
ene (10 mL) solution of [(DMSC)Ti(η2-OCPh2)(bpy)] (3) (0.180
g, 0.166 mmol) was added benzophenone (32.0 mg, 0.176
mmol). The orange solution slowly turned to dark green within
30 min. The reaction mixture was stirred for 12 h at room
temperature, during which time an orange solution resulted.
This orange solution was stripped to dryness under vacuum.
The gummy orange residue was washed with pentane (4 × 5
mL) and dried under vacuum to afford an orange powder.
[(DMSC)Ti{K3-OC(p -Me C6H 4)2C10H 5Me 2N2}{OCH (p -
MeC6H4)2}] (10). Into a toluene (10 mL) solution of [(DMSC)-
Ti{η2-OC(p-MeC6H4)2}(dmbpy)] (5) (0.187 g, 0.163 mmol) was
added 4,4′-dimethylbenzophenone (39.7 mg, 0.189 mmol). The
resulting greenish brown solution was stirred for 24 h at room
temperature, during which time an orange solution resulted.
This orange solution was stripped to dryness under vacuum.
The gummy orange residue was washed with cold pentane (4
× 5 mL) and dried under vacuum to afford an orange powder.
Yield: 0.193 g, 88%. 1H NMR (C6D6): δ 8.15 (d, J ) 8 Hz, 2H,
arom CH), 7.56 (d, 8 Hz, 2H, arom CH), 7.35-7.22 (m, 6H,
arom CH), 7.07-6.74 (m, 14H, arom CH), 6.63 (d, J ) 2.4 Hz,
1H, arom CH), 6.47 (s, 1H, arom CH), 6.40-6.30 (m, 4H, arom
CH), 6.33 (d, J ) 14 Hz, 1H, calix-CH2), 5.89 (s, 1H, OCH(p-
MeC6H4)2, 4.83 (d, J ) 15.6 Hz, 1H, calix-CH2), 4.71 (d, J )
15.6 Hz, 1H, calix-CH2), 4.29 (d, J ) 16 Hz, 1H, calix-CH2),
3.50 (pseudo-triplet, J ) 16 Hz & 15.6 Hz, 2H, calix-CH2), 3.24
(d, J ) 16 Hz, 1H, calix-CH2), 2.74 (d, J ) 15.8 Hz, 1H, calix-
CH2), 2.11 (s, 3H, p-MeC6H4), 2.09 (s, 3H, p-MeC6H4), 2.08 (s,
3H, p-MeC6H4), 1.99 (s, 3H, p-MeC6H4), 1.87 (s, 3H, dmbpy-
Me), 1.65 (s, 3H, dmbpy-Me), 1.39 (s, 9H, t-Bu), 1.31 (s, 9H,
t-Bu), 1.26 (s, 9H, t-Bu), 1.18 (s, 9H, t-Bu), 0.19 (s, 3H, exo-
SiCH3), -0.99 (s, 3H, endo-SiCH3). 13C NMR (C6D6): δ 172.0,
162.9, 162.6, 152.9, 152.1, 151.3, 150.8, 149.9, 148.5, 147.4,
144.9, 144.4, 144.1, 143.4, 143.1, 141.4, 138.6, 138.3, 137.3,
137.1, 136.9, 135.2, 133.5, 132.4, 131.1, 129.9, 129.3, 129.2,
129.1, 128.8, 128.6, 128.0, 127.7, 127.5, 127.4, 127.1, 126.4,
1
Yield: 0.180 g, 85%. H NMR (C6D6): δ 8.11 (d, J ) 7.2 Hz,
2H, arom CH), 7.57 (d, 7.2 Hz, 2H, arom CH), 7.32-7.17 (m,
7H, arom CH), 7.06-6.82 (m, 16H, arom CH), 6.59 (m, 2H,
arom CH), 6.46-6.22 (m, 4H, arom CH), 6.38 (d, J ) 15.2 Hz,
1H, calix-CH2), 6.11 (d, J ) 7.2 Hz, 2H, arom CH), 5.89 (s,
1H, OCHPh2, 4.81 (d, J ) 16 Hz, 1H, calix-CH2), 4.68 (d, J )
15.6 Hz, 1H, calix-CH2), 4.26 (d, J ) 16.4 Hz, 1H, calix-CH2),
3.45 (d, J ) 16 Hz, 1H, calix-CH2), 3.20 (d, J ) 16 Hz, 1H,
calix-CH2), 3.12 (d, J ) 16.4 Hz, 1H, calix-CH2), 2.73 (d, J )
13.6 Hz, 1H, calix-CH2), 1.38 (s, 9H, t-Bu), 1.30 (s, 9H, t-Bu),
1.28 (s, 9H, t-Bu), 1.14 (s, 9H, t-Bu), 0.16 (s, 3H, exo-SiCH3),
-1.03 (s, 3H, endo-SiCH3). 13C NMR (C6D6): δ 172.0, 162.9,
162.7, 152.6, 151.8, 151.2, 149.9, 148.6, 147.4, 147.1, 146.2,
144.9, 143.7, 143.1, 141.9, 138.8, 138.7, 138.6, 136.6, 133.5,
131.6, 131.1, 129.7, 129.5, 129.3, 128.6, 128.1, 127.6, 127.5,
127.2, 126.7, 126.3, 126.0, 125.2, 124.6, 124.5, 119.7, 117.8,
99.3 (OCPh2C10H7N2), 85.6 (OCHPh2), 42.3 (calix-CH2), 39.4
(calix-CH2), 37.5 (calix-CH2), 35.6 (calix-CH2), 34.4 {C(CH3)3},
34.3 {C(CH3)3}, 32.4 {C(CH3)3}, 32.3 {C(CH3)3, 32.3 {C(CH3)3},

[(DMSC)Ti(η2-OCAr2)L2] Complexes
Ta ble 1. Cr ysta llogr a p h ic Da ta for
Organometallics, Vol. 22, No. 1, 2003 139
or phen) produced titanium η2-ketone complexes [(DM-
SC)Ti(η2-OCAr2)L2] (3-6, eq 1). All of the compounds
9‚(C7H8)0.5(C5H12
)
formula
fw
T, K
cryst syst
space group
Z
C94.5H110N2O6SiTi
1445.88
150.0(2)
monoclinic
Cc
8
a, Å
b, Å
c, Å
34.0940(14)
22.0310(10)
24.5200(10)
90
116.130(13)
90
R, deg
â, deg
γ, deg
V, Å3
16535.2(12)
1.165
d
calc, g/cm3
R indices [I>2σ(I)]: R1, wR2
0.0965, 0.2057
125.5, 124.7, 124.1, 120.9, 118.8, 99.1 {OC(p-MeC6H4)2C10H5-
Me2N2}, 85.3 {OCH(p-MeC6H4)2}, 42.3 (calix-CH2), 39.6 (calix-
CH2), 37.6 (calix-CH2), 35.8 (calix-CH2), 34.5 {C(CH3)3}, 34.3
{C(CH3)3}, 32.5 {C(CH3)3}, 32.3 {C(CH3)3}, 32.2 {C(CH3)3}, 22.1
(dmbpy-CH3), 21.5 (p-MeC6H4), 21.4 (p-MeC6H4), 21.3 (p-
MeC6H4), 3.5 (exo-SiCH3), -0.82 (endo-SiCH3). Anal. Calcd for
were isolated in high yield with the exception of
[(DMSC)Ti{OC(p-MeC6H4)2}phen] (6), which was iso-
lated along with [(DMSC)Ti{κ3-OC(p-MeC6H4)2C12H7N2}-
{OCH(p-MeC6H4)2}] (11)9 (Scheme 2) as a 50:50 mix-
ture. The reaction occurs essentially in the time of
mixing, and 3-6 precipitate from solution as air- and
moisture-sensitive orange (3) or green (4-6) solids. The
compounds are best stored in the solid state at low
temperature (below -15 °C) and protected from light.
For example, [(DMSC)Ti{η2-OC(p-MeC6H4)2}bpy] (4)
slowly decomposed with release of (p-MeC6H4)2CO when
it was stored as a solid under nitrogen atmosphere (in
a glovebox) at ambient temperature and unprotected
from light. All of the compounds dissolve well in
aromatic solvents but are only sparingly soluble in
aliphatic solvents. They yield intense green solutions
upon dissolution in benzene-d6 or methylene chloride-
d2.10
C
88H98N2O6SiTi: C, 77.96; H, 7.29; N, 2.07. Found: C, 77.75;
H, 7.38; N, 2.00.
[(DMSC)Ti{K3-OC(p -Me C6H 4)2C12H 7N2}{OCH (p -Me -
C6H4)2}] (11). Into a toluene (10 mL) solution of the 50:50
mixture of [(DMSC)Ti{η2-OC(p-MeC6H4)2}(phen)] (6) and [(DM-
SC)Ti{κ3-OC(p-MeC6H4)2C12H7N2}{OCH(p-MeC6H4)2}] (11)
(0.322 g) was added 59.2 mg (0.281 mmol) of 4,4′-dimethyl-
benzophenone. The resulting greenish brown solution was
stirred for 24 h at room temperature, during which time an
orange solution resulted. The orange solution was stripped to
dryness under vacuum. The gummy orange residue was
washed with cold pentane (4 × 5 mL) and dried under vacuum
to afford 0.298 g of orange powder. Yield: 73% based on 6
1
(0.161 g, 0.141 mmol). H NMR (C6D6): δ 8.20 (d, J ) 8.4 Hz,
2H, arom CH), 7.49 (br d, J ) 6.8 Hz, arom CH), 7.42-7.19
(m, 9H, arom CH), 7.10-6.74 (m, 12H, arom CH), 6.60-6.51
(m, 1H, arom CH), 6.56 (d, J ) 15.2 Hz, 1H, calix-CH2), 6.19
(d, J ) 2 Hz, 1H, arom CH), 5.90 (s, 1H, OCH(p-MeC6H4)2,
5.85 (AB quartet, 4H, arom CH), 4.91 (d, J ) 16 Hz, 1H, calix-
CH2), 4.72 (d, J ) 15.6 Hz, 1H, calix-CH2), 4.33 (d, J ) 16 Hz,
1H, calix-CH2), 3.51 (d, J ) 15.6 Hz, 1H, calix-CH2), 2.72 (m,
3H, calix-CH2), 2.10 (s, 3H, p-MeC6H4), 2.09 (s, 3H, p-MeC6H4),
1.99 (s, 3H, p-MeC6H4), 1.66 (s, 3H, p-MeC6H4), 1.39 (s, 9H,
t-Bu), 1.29 (s, 9H, t-Bu), 1.28 (s, 9H, t-Bu), 1.18 (s, 9H, t-Bu),
0.16 (s, 3H, exo-SiCH3), -1.04 (s, 3H, endo-SiCH3). 13C NMR
(C6D6): δ 171.7, 162.9, 162.5, 152.8, 151.7, 149.6, 149.3, 144.5,
143.9, 143.5, 143.4, 143.0, 142.0, 141.1, 138.6, 137.3, 136.9,
135.6, 135.0, 134.5, 131.2, 129.9, 129.6, 129.2, 128.9, 127.8,
127.5, 126.9, 125.9, 125.7, 124.8, 124.4, 123.9, 123.6, 99.9
{OC(p-MeC6H4)2C12H7N2}, 85.7 {OCH(p-MeC6H4)2}, 42.5 (calix-
CH2), 39.4 (calix-CH2), 37.3 (calix-CH2), 35.6 (calix-CH2), 34.5
{C(CH3)3}, 34.3 {C(CH3)3}, 32.5 {C(CH3)3}, 32.3 {C(CH3)3}, 32.2
{C(CH3)3}, 21.9 (p-MeC6H4), 21.6 (p-MeC6H4), 21.2 (p-MeC6H4),
21.0 (p-MeC6H4), 3.51 (exo-SiCH3), -0.93 (endo-SiCH3). Anal.
Calcd for C88H98N2O6SiTi: C, 77.96; H, 7.29; N, 2.07. Found:
C, 77.19; H, 6.88; N, 2.04.
The formulation and structure of 3-6 were character-
ized by spectroscopic methods (1H and 13C NMR, IR),
as well as by microanalysis for 3-5. The 1H NMR
spectra of 3-6 displayed sharp resonances that are
consistent with Cs-symmetry in solution and existence
1
of the DMSC ligand in 1,2-alternate conformation. H
NMR resonances for the endo-Me (located inside the
calixarene cavity) of the bridging SiMe2 group are
invariably strongly shielded compared to corresponding
signals for the exo-SiMe (located outside the calixarene
cavity).11 For 3-6, the endo-SiMe resonance is observed
in the δ -1.12 to -1.16 ppm range, while the exo-SiMe
resonance is found in the δ 0.34-0.36 ppm range (see
1
Experimental Section). Their H NMR spectra show two
singlets (integrating in 1:1 ratio) for the But groups and
four doublets and an AB system for the bridging
methylene protons of the calixarene ligand. The AB
(9) An attempt to exclusively produce [(DMSC)Ti{η2-OC(p-MeC6H4)2}-
phen] (6) by conducting the reaction of [(DMSC)Ti{OC(p-MeC6H4)2C-
(p-MeC6H4)2O}] (2) with 1,10-phenanthroline (1 equiv) in pentane at
low temperatures (-78 to 0 °C) was unsuccessful. No reaction was
observed at -78 °C, and a mixture of products resulted as the reaction
mixture was warmed.
Cr ysta llogr a p h ic Stu d y. The crystal data for 9‚(C7H8)0.5
-
(C5H12) are collected in Table 1. Further details of the crystal-
lographic study are given in the Supporting Information.
(10) [(DMSC)Ti(η2-OCPh2)bpy] (3) initially forms an orange suspen-
sion in benzene or toluene but dissolves gradually to give a green
solution. Although a green color is usually observed within 5 min, it
can take a few hours to completely dissolve all of 3, during which time
the formation of [(DMSC)Ti{κ3-OCPh2C10H7N2}(OCHPh2)] (8) occurs.
(11) See for example: (a) Ozerov, O. V.; Patrick, B. O.; Ladipo, F.
T. J . Am. Chem. Soc. 2000, 122, 6423. (b) Ozerov, O. V.; Ladipo, F. T.;
Patrick, B. O. J . Am. Chem. Soc. 1999, 121, 7941. (c) Fan, M.; Zhang,
H.; Lattman, M. Organometallics 1996, 15, 5216.
Resu lts a n d Discu ssion
Syn th esis of [(DMSC)Ti(η2-OCAr 2)L2] Com plexes.
The reaction in pentane of titanapinacolate complexes
[(DMSC)Ti(OCAr2CAr2O)](1, Ar )Ph;2, Ar )p-MeC6H4)
with 1 equiv of a delocalized diimine (L2 ) bpy, dmbpy,

140 Organometallics, Vol. 22, No. 1, 2003
Kingston et al.
Sch em e 1
Sch em e 2
have been described for aldehyde and ketone complexes
of transition metals: η1-bound through oxygen (σ-com-
plex)6 and η2-bound through both oxygen and carbon (π-
complex).7,8 Consistent with η2-coordination of the
ketone,13C NMR revealed a singlet resonance at δ 117.9
and 118.2 ppm for the Ar2C carbon of 3b and 5,
respectively. A singlet resonance at δ 91.4 ppm was
reported for the Ph2C carbon of the related complex [Ti-
(OC6H3Ph2-2,6)2(η2-Ph2CO)(PMe3)],7e perhaps reflective
of a greater degree of oxatitanacyclopropane character
for the latter complex. Solid-state (Nujol mull) and
solution-phase (CH2Cl2) measurements of the FTIR
spectra for 3 showed no carbonyl stretch above 1060
cm-1. Substitution of Ph213CO for Ph2CO resulted in
only a small lowering of the IR bands at 1054 and 996
cm-1 for [(DMSC)Ti(η2-OCPh2)bpy] (3) to 1043 and 976
cm-1 for [(DMSC)Ti(η2-O13CPh2)bpy] (3b).13 The band
at 1054 cm-1 has been assigned as the C-O stretch
(νC-O) on the basis of the IR data for Ph2CHOH14 as well
as related η2-ketone and aldehyde complexes (νC-O
range ) 1000-1200 cm-1).7,8 Both the 13C NMR and IR
data indicate significant π-back-bonding into the π*
orbital of the ketone, consistent with a π-ligating mode
for the ketone. These data parallel the trend reported
for previously characterized η2-aldehyde and ketone
species.7,8
system integrates as four protons and represents the
methylene groups not included in the mirror plane. A
singlet resonance in the range of δ 2.14-2.20 ppm
(integrating as six protons) is observed for the p-tolyl
methyls of 4-6, consistent with a mirror plane that
contains the C-O unit of the ketone but bisects the
p-tolyl substituents.
All of the compounds (3-6) are transformed into other
species in solution. The transformations occur on a
comparable or faster time-scale than that of the 13C
NMR experiment (vide infra), preventing acquisition of
solution 13C NMR data for every one of the compounds.
For the same reason, all attempts to obtain single
crystals of 3-6 suitable for an X-ray diffraction study
have so far been unsuccessful. Solution 13C NMR data
could only be obtained for [(DMSC)Ti(η2-O13CPh2)bpy]
(3b ), generated in-situ from reaction of [(DMSC)Ti-
(O13CPh213CPh2O)]with 2,2′-bipyridine,12 and for [(DMSC)-
Ti{OC(p-MeC6H4)2}dmbpy] (5). Two coordination modes
The intense green color of solutions of 3-6 presum-
ably results from metal to ligand charge-transfer (MLCT)
transitions.4,15,16 For 3-6, electron transfer from tita-
(12) A C6D6 solution of [(DMSC)Ti{1,2,4-(Me3Si)3C6H3}]11a (18.0 mg,
17.2 mmol) and Ph213CO (6.1 mg, 33.3 mmol) was heated at 65° C for
1 h. Next, 2.65 mg (16.9 mmol) of 2,2′-bipyridine was introduced into
the solution. The reaction was monitored at 25 °C by 1H and C NMR.
(13) A similar decrease in νCO from 1200 cm-1 for [Ta(η5-C5Me5)(η2-
OCMe2)Me2] to 1180 cm-1 for [Ta(η5-C5Me5)(η2-O13CMe2)Me2] was
noted by Schrock. See: Wood, C. D.; Schrock, R. R. J . Am. Chem. Soc.
1979, 101, 5421.
(14) For IR data of Ph2CHOH, see: Sommer, A.; Stamm, H.;
Woderer, A. Chem. Ber. 1988, 121, 387.
(15) See for example: (a) Loukova, G. V.; Strelets, V. V. Collect.
Czech. Chem. Commun. 2001, 66, 185. (b) Vleck, A., J r. Coord. Chem.
Rev. 1998, 177, 219. (c) Flamini, A.; Giuliani, A. M. Inorg. Chim. Acta
1986, 112, L7. (d) Fischer, E. O.; Aumann, R. J . Organomet. Chem.
1967, 9, P15. (e) Calderazzo, F.; Salzmann, J . J .; Mosimann, P. Inorg.
Chim. Acta 1967, 1, 65.
(16) (a) Covert, K. J .; Wolczanski, P. T. Inorg. Chem. 1989, 28, 4567.
(b) Covert, K. J .; Wolczanski, P. T.; Hill, S. A.; Krusic, P. J . Inorg.
Chem. 1992, 31, 66.

[(DMSC)Ti(η2-OCAr2)L2] Complexes
Organometallics, Vol. 22, No. 1, 2003 141
nium to either the diimine (Ti f L2) or the ketone (Tif
Ar2CO) is possible since both ligands are π-acids. In this
regard, thermally accessible singlet-triplet systems
have been described for Cp2TiL2 systems (L2 ) 2,2′-
bipyridyl or 1,10-phenanthroline derivatives) in which
one unpaired electron occupies a molecular orbital that
is localized on the Cp2Ti unit, while the other unpaired
electron resides in the lowest energy π* orbital of the
L2 ligand.4b,c Second, Wolczanski and colleagues have
The substitution of the ketone in 3-6 is facile.20 For
example, when the reaction of [(DMSC)Ti{η2-OC(p-
MeC6H4)2}bpy] (4) with 2,2′-bipyridine (1 equiv) in
benzene-d6 was monitored by 1H NMR spectroscopy,
release of (p-MeC6H4)2CO and formation of [(DMSC)-
Ti(bpy)2] (7)21 occurred immediately after mixing. To-
gether with (p-MeC6H4)2CO, a ∼2:2:1 ratio of 4, 7, and
9 was present in solution after 2 h (Scheme 1). This
result indicates that substitution of the ketone moiety
of 4 by 2,2′-bipyridine proceeds more efficiently than
reaction of 4 with (p-MeC6H4)2CO to produce 9. Release
of (p-MeC6H4)2CO also occurred during hydrolysis of 4
with distilled water in air and protonolysis of [(DMSC)-
Ti{η2-OC(p-MeC6H4)2}dmbpy] (5) with isopropyl alcohol
under nitrogen atmosphere. Both 1H NMR character-
ization of the reaction mixtures and GC-MS analysis
of CH2Cl2 extracts revealed that (p-MeC6H4)2CHOH was
not produced in either reaction. In contrast, Ph2CHOH
was the product of the hydrolysis of [Ti(OC6H3Ph2-2,6)2-
(η2-Ph2CO)(PMe3)],7e probably reflecting the latter com-
pound’s lower coordination number and increased oxa-
titanacyclopropane character.
characterized Ti(IV)-ketyl complexes, including [(But -
3
•
•
SiO)3Ti(OCPh2 )] and [(But SiO)3Ti{ OC(p-MeC6H4)2 }],
3
formed by electron transfer from Ti(III) to the ketone
upon reaction with [(But SiO)3Ti].16 Preliminary data
3
from room- and low-temperature (110 K) ESR studies
of [(DMSC)Ti{η2-OC(p-MeC6H4)2}dmbpy] (5) in the solid
state and in toluene indicate the presence of two radical
species.17 Although a precise determination of the
nature of the radical species must await further ESR
studies, among possible radical species that may be
envisioned are Ti(III) and Ti(IV) radical species [(DMSC)-
•
Ti{OC(p-MeC6H4)2 }dmbpy] and [(DMSC)Ti{OC(p-MeC6-
•
H4)2 }(dmbpy•)], respectively.18
The reaction between 4 and (p-MeC6H4)2CO was
examined in an effort to obtain 9 in high yield. In
benzene-d6, reaction of 1 equiv of (p-MeC6H4)2CO with
4 occurred cleanly to form 9 (Scheme 1). The reaction
was ∼66% complete after 2 h (by 1H NMR), and
complete conversion to 9 was observed after allowing
the solution to stand overnight. The rate with which
3-6 react with ketone to give 1-aza-5-oxa-titanacyclo-
pentene derivatives 8-11 (Scheme 2) depended on the
concentration of the ketone. Thus, the reaction of 4 with
8 equiv of (p-MeC6H4)2CO proceeded to ∼82% comple-
tion in 0.5 h, and quantitative formation of 9 was
observed in less than 2 h. This result suggests involve-
ment of a second ketone molecule in the rate-limiting
step. Interestingly, when the reaction in benzene-d6 of
Reactivity of [(DMSC)Ti(η2-OCAr 2)L2] Com plexes.
As mentioned before, 3-6 undergo further transforma-
tion in solution. For instance, upon dissolving a pure
sample of [(DMSC)Ti{η2-OC(p-MeC6H4)2}bpy] (4) in
benzene-d6 and allowing the dark green solution to
stand under N2, the solution slowly changed color to
orange. 1H NMR revealed that the orange solution
contained three DMSC-based products after 42 h. The
11c
two main products were identified as (DMSC)H2
(major product) and [(DMSC)Ti{κ3-OC(p-MeC6H4)2C10-
H7N2}{OCH(p-MeC6H4)2}] (9), in which C-H activation
of the bipyridyl ligand and hydride migration to a Ti-
bound ketone to form an alkoxide group had occurred
(Scheme 1). The transformation of 4 to 9 is photochemi-
cally assisted and progresses much more slowly when
the solution is protected from light.19 We reasoned that
a ketone molecule released by decomposition of 4 was
probably incorporated to produce 9 since (DMSC)H2 is
a characteristic decomposition product in this system.
1
4 with Ph213CO (1 equiv) was monitored by H NMR in
an attempt to discern which ketone molecule is trans-
formed into the alkoxide group, [(DMSC)Ti{κ3-OC(p-
MeC6H4)2C10H7N2}(O13CHPh2)] and [(DMSC)Ti(κ3-
O13CPh2C10H7N2){OCH(p-MeC6H4)2}] were observed in
∼1:1 ratio after 15 min.22,23 This result is consistent with
either (i) fast exchange of complexed and free ketone
molecules or (ii) coordination of the second ketone
(Ph213CO) and little preference for which metal-bound
ketone molecule {Ph213CO or OC(p-MeC6H4)2} is trans-
formed into the alkoxide group. No incorporation of
deuterium (from benzene-d6) into the alkoxide group
(17) Kingston, J . V.; Karapetyan, A.; Miller, A. F.; Ladipo, F. T.
Unpublished results.
(18) Reduction potentials for the ketone and diimine ligands are
listed in the table below. The data suggest that one electron transfer
to ketone is thermodynamically favored over one electron transfer to
diimine. However, further reduction of the resulting ketyl radical and
electron transfer to diimine have comparable thermodynamic feasibil-
ity.
1
was observed by either H or 13C NMR, indicating that
compound
E°/V vs SCE Ep2/Va vs SCE
the OCHAr2 moiety results exclusively from transfer of
hydrogen from the nitrogen heterocycle to a complexed
ketone molecule.
-2.13b
-2.20b
-1.99b
bpy
dmbpy
phen
-1.78c
-1.87c
-2.27c
-2.37c
Ph2CO
(20) More facile substitution of η2-ketone complexes bearing alkyl
or aryl moieties in comparison to η2-aldehydes has been attributed to
both steric crowding and the higher energy of the π* orbital for ketones
relative to the π* orbital for aldehydes.5a,7b,h,1
(p-MeC6H4)2CO
a
2
Ep ) peak potential for further reduction of the radical anion.
Krishnan, C. V.; Creutz, C.; Schwarz, H. A.; Sutin, N. J . Am. Chem.
b
(21) Ozerov, O. V.; Brock, C. P.; Carr, S.; Parkin, S.; Ladipo, F. T.
Organometallics 2000, 19, 5016.
Soc. 1983, 105, 5617. c Grimshaw, J .; Hamilton, R. J . Electroanal.
Chem. 1980, 106, 339.
(22) Both a singlet resonance at δ 5.90 ppm and a doublet resonance
centered at δ 5.90 ppm (in 1:1 ratio) were observed in the 1H spectrum
after 15 min. See the Experimental Section for 1H and 13C NMR
chemical shift values for 8-11.
(19) The transformation of [(DMSC)Ti{η2-OC(p-MeC6H4)2}bpy] (4)
into [(DMSC)Ti{κ3-OC(p-MeC6H4)2C10H7N2}{OCH(p-MeC6H4)2}] (9)
was slowed considerably when a d6-benzene solution of 4 (in a NMR
tube) was protected from light and allowed to stand at ambient
temperature under N2 atmosphere. After 5 days, 1H NMR revealed 4
and 9 in ∼1: 2 ratio, along with minor amounts of unidentified DMSC-
containing products.
(23) For typical 1H and 13C NMR chemical shift values for the Ti-
OCHAr2 group, see for example: Agapie, T.; Diaconescu, P. L.;
Mindiola, D. J .; Cummins, C. C. Organometallics 2002, 21, 1329, and
ref 16b.

142 Organometallics, Vol. 22, No. 1, 2003
Kingston et al.
The rate of the transformation of 3-6 into 8-11 also
depended on the nature of the diimine ligand (L2).
Qualitatively, the rate of reaction between [(DMSC)Ti-
{OC(p-MeC6H4)2}L2] (4-6) and (p-MeC6H4)2CO (1 equiv)
in benzene-d6 increases in the order L2 ) dmbpy < bpy
, phen. The reaction between [(DMSC)Ti{OC(p-MeC6-
H4)2}phen] (6) and (p-MeC6H4)2CO (1 equiv) to give 11
is essentially complete in the time of mixing. In an effort
to eliminate transformation of 3-6, via C-H activation
of the heterocyclic nitrogen ligand, and obtain η2-ketone
complexes with improved stability, we examined reac-
tions of [(DMSC)Ti{OC(p-MeC6H4)2C(p-MeC6H4)2O] (2)
with PMe3, 6,6′-dimethyl-2,2′-dipyridyl, and 2,2′-bithio-
phene. In none of these cases did we observe a reaction;
only decomposition of 2 was observed when a benzene-
d6 solution of 2 and 6,6′-dimethyl-2,2′-dipyridyl was
heated at 70 °C for 12 h. Presumably, 2 did not react
with 6,6′-dimethyl-2,2′-dipyridyl or PMe3 for steric
reasons. On the other hand, 2,2′-bithiophene is a much
poorer donor than the delocalized diimine compounds
utilized in this study.
F igu r e 1. Molecular structure of [(DMSC)Ti{κ3-OC(p-
MeC6H4)2C10H7N2}{OCH(p-MeC6H4)2}] (9) (50% probability
ellipsoids).
Ch a r a cter iza tion of 1-Aza -5-oxa -tita n a cyclop en -
ten e Der iva tives 8-11. Compounds 8-11 were iso-
lated in very good yield from reaction of 3-6 with the
appropriate ketone in toluene (Scheme 2). Both mi-
croanalysis and solution NMR (1H and 13C) data for
Ta ble 2. Selected Aver a ge Bon d Dista n ces (Å) a n d
An gles (d eg) for 9
1
8-11 are consistent with the proposed formulation. H
Ti-O1
1.863(8)
1.928(8)
1.888(8)
1.820(8)
2.256(10)
2.178(10)
77.3(3)
71.0(4)
73.8(4)
94.9(4)
98.4(4)
O6-Ti-O2
O1-Ti-O2
O5-Ti-O2
O6-Ti-N2
O1-Ti-N2
O2-Ti-N2
O6-Ti-N1
O5-Ti-N1
C25-O1-Ti
C26-O2-Ti
C55-O5-Ti
C70-O6-Ti
159.5(4)
91.2(4)
99.5(4)
85.9(4)
173.5(4)
86.0(3)
and 13C NMR data for 8-11 are consistent with C1-
Ti-O2
Ti-O5
symmetry in solution and existence of the DMSC ligand
Ti-O6
1
in 1,2-alternate conformation. In their H NMR spectra
Ti-N1
in benzene-d6, the endo-Me resonance is observed at ∼δ
-1.00 ppm, while the exo-SiMe resonance can be found
at ∼δ 0.17 ppm (see Experimental Section). Four equally
intense singlets are observed for the But groups, and
eight equally intense doublets are seen for the bridging
methylene protons of the calixarene ligand. For 9-11,
four singlet resonances in the range δ 1.65-2.14 ppm
(each integrating as three protons) are observed for the
four inequivalent p-tolyl methyl groups. The alkoxide
group hydrogen (Ti-OCHAr2) is observed as a singlet
at ∼δ 5.9 ppm for 8-11. The 13C NMR resonance for
the alkoxide-carbon (Ti-O-CHAr2) of 8-11 is observed
in the δ 84-86 ppm range.23 That this signal belonged
to a Ti-O-CHAr2 fragment was established by both
proton-coupled 13C NMR and DEPT experiments. For
Ti-N2
O2-Ti-N1
N2-Ti-N1
O5-Ti-N2
O6-Ti-O1
O6-Ti-O5
O1-Ti-O5
82.3(3)
144.8(4)
151.3(8)
145.4(7)
128.0(7)
154.9(7)
101.1(3)
the molecules is shown in Figure 1, and selected
metrical parameters are given in Table 2.29 The com-
pound adopts a distorted octahedral structure with a
meridional tridentate bipyridyl-alkoxide, cis-calixarene,
and alkoxide ligand environment. The distortion from
idealized octahedral geometry arises from acute bite
angles of the tridentate bipyridyl-alkoxide ligand [ca.
71° for N(2A)-Ti(2A)-N(1A) and ca. 74° for O(5A)-Ti-
(2A)-N(1A)], as well as steric constraints imposed by
example, a doublet centered at δ 85.6 ppm with J C-H
)
139 Hz was observed in the proton-coupled 13C NMR
spectrum of 8. The resonance for the Ti-O-C carbon
of the 1-aza-5-oxa-titanacyclopentene ring shows in the
range of δ 98-100 ppm.24 Four resonances were ob-
served in the 13C NMR spectra of 9-11 between δ 20.6
and 20.9 ppm for inequivalent p-tolyl methyl carbons.
X-ray analysis of single crystals of 9 confirmed the
structure assigned by spectroscopy. In space group Cc,27
the asymmetric unit contains two independent mol-
ecules of 9, one toluene, and two pentanes to give the
empirical formula 9‚(C7H8)0.5(C5H12). Bond lengths and
angles for the two molecules are very similar.28 One of
(27) Space group Cc was chosen in preference to C2/c for a number
of reasons. No satisfactory structure solution could be obtained in C2/
c. The two molecules per asymmetric unit in the Cc model could,
however, be almost superimposed by rotation about an axis that was
almost, but not exactly, parallel with the crystallographic b axis.
Moreover, the superposition was far from perfect, resulting in many
geometric clashes. The program PLATON was similarly unsuccessful
in reducing the Cc model to a satisfactory model in C2/c. The solvent,
which was partially disordered in the Cc model, would have been
hopelessly disordered in C2/c. Furthermore, the data collection had to
be performed at 150 K owing to a destructive phase transition on
cooling to below 150 K. It is quite possible that the symmetry of the
structure is indeed C2/c at room temperature, but owing to the unstable
nature of both the crystals and the molecule itself and the general
weakness of the diffraction pattern, data collection at room tempera-
ture was not feasible.
(28) Weak diffraction data were obtained due to the mediocre quality
of the crystal utilized in the X-ray diffraction study. However, light
atom positions in standard X-ray structure determinations are limited
to about 0.02 Å, even for perfect data. See for example: (a) Coppens,
P.; Sabine, T. M.; Delaplane, G.; Ibers, J . A. Acta Crystallogr. 1969,
B25, 2451. (b) Allen, F. H. Acta Crystallogr. 1986, B42, 515.
(29) In light of the similarity of the two molecules in the asymmetric
unit, bond lengths and angles are given as the average over both
molecules.
(24) Similar chemical shift values have been reported for related
compounds. 13C NMR (CD2Cl2): δ 93-97 ppm for [{κ2-OCAr2C5H4N}2-
Ti(NMe2)2] (Ar ) various aryl groups)25 and 13C NMR (CDCl3): δ 107
ppm for [CpTi{κ2-OCR2C5H4N}Cl2] (R ) Pri or Ph)26
(25) Kim, I.; Nishihara, Y.; J ordan, R. F.; Rogers, R. D.; Rheingold,
A. L.; Yap, G. P. A. Organometallics 1997, 16, 3314.
(26) Doherty, S.; Errington, R. J .; J arvis, A. P.; Collins, S.; Clegg,
W.; Elsegood, M. R. J . Organometallics 1998, 17, 3408.

[(DMSC)Ti(η2-OCAr2)L2] Complexes
Organometallics, Vol. 22, No. 1, 2003 143
Sch em e 3
the bidentate DMSC ligand. All of the Ti-O bond
distances {average ) 1.886(8) Å}30 are shorter than the
Ti-O σ-bond distance predicted on the basis of covalent
radii (ca. 1.99-2.05 Å),25 perhaps reflective of partial
Ti-O π-bonding. The Ti-O bond distance of the Ti-
OCH(p-MeC6H4)2 unit (average for the two molecules
1.820(8) Å) is especially short and may reflect a greater
degree of partial Ti-O π-bonding. Orange (or orange-
red) solids 8-11 are moisture-sensitive but moderately
air-stable. The rate of their decomposition in air is
noticeably slower than that of four-coordinate (DMSC)-
Ti-based complexes with Ti-C bonds but similar to that
of six-coordinate [(DMSC)Ti(η2-RCtCH)L2] (R ) But or
SiMe3; L2 ) bpy or dmbpy) complexes,21 probably
reflecting steric saturation of the coordination sphere.
Thus, 8 is stable in air as a solid for several days, and
even solutions of 8 are stable in air for hours. All of the
compounds are insoluble in pentane but quite soluble
in aromatic solvents. The compounds are thermally
stable in C6D6 and do not undergo any observable
decomposition at 22 °C for several days.
Mech a n istic Con sid er a tion s. We have recently
demonstrated that the mechanism of the reaction of
[(DMSC)Ti(OCAr2CAr2O)](1, Ar )Ph;2, Ar )p-MeC6H4)
with alkynes involves reversible dissociation of the
titanapinacolate complexes into (DMSC)Ti(η2-OCAr2)
species and Ar2CO, followed by rate-limiting reaction
of the (DMSC)Ti(η2-OCAr2) species with alkyne.3b It is
therefore reasonable to conclude that [(DMSC)Ti(η2-
OCAr2)L2] complexes (3-6) are produced via trapping
of (DMSC)Ti(η2-OCAr2) species with appropriate di-
imine (eq 2). We found that titanium-η2-ketones 3-6
the π-π* state energy gap is lowest for 1,10-phenan-
throline and the energy of metal to diimine charge
transfer (Ti f L2) transition is lowest for [(DMSC)Ti-
{η2-OC(p-MeC6H4)2}phen] (6).34 In this regard, it is
noteworthy that the rate of transformation of [(DMSC)-
Ti{η2-OC(p-MeC6H4)2}L2] complexes (4, L2 ) bpy; 5, L2
) dmbpy; 6 L2 ) phen) into 1-aza-5-oxa-titanacyclopen-
tene derivatives 9-11 followed the order 5 < 4 , 6,
which parallels the decrease in π-π* state energy gap
for the diimines.
Con clu sion s
The titanium-η2-ketone complexes [(DMSC)Ti(η2-
OCAr2)L2)] 3-6 (L2 ) 2,2′-bipyridine, 4,4′-dimethyl-2,2′-
dipyridyl, or 1,10-phenanthroline) were obtained in good
yield from reaction of [(DMSC)Ti(OCAr2CAr2O)] (1, Ar
undergo a photochemically assisted transformation to
yield 1-aza-5-oxa-titanacyclopentene derivatives 8-11.
In addition, the rate of formation of 8-11 increased with
an increase in ketone concentration. This result strongly
supports a mechanism that involves reversible coordi-
nation of ketone to titanium and a rate-limiting step
that is dependent on ketone concentration. A plausible
pathway for formation of 8-11 involves the interme-
diacy of 1-aza-5-oxa-titanacyclopentane species A31
(Scheme 3). Subsequent hydride migration to a metal-
bound ketone affords the alkoxide moiety and restores
aromaticity to the nitrogen heterocycle. The photode-
pendence of the reaction leads us to believe that metal
to diimine charge transfer and the resulting radical
species play important roles in the transformation. A
lowering of the energy of the π-π* state results with
increased conjugation in delocalized systems.33 Thus,
(31) 1-Aza-5-oxa-titanacyclopentane species A may be formed from
[(DMSC)Ti(η2-OCAr2)L2] via nucleophilic aromatic substitution of a
pyridyl ring at the 2-position32 and ketone complexation. Alternatively,
A may result from Ti(III) and Ti(IV) radical species such as [(DMSC)-
Ti(OCAr2•)L2] and [(DMSC)Ti(OCAr2•)(L2•)].
(32) A nucleophilic aromatic substitution step is involved in the
generally accepted mechanism for the Chichibabin reaction, through
which heterocyclic nitrogen compounds can be aminated with alkali
metal amides. See for example: (a) Smith, M. B.; March, J . March’s
Advanced Organic Chemistry; J ohn Wiley & Sons: New York, 2001; p
873. (b) Vobruggen, H. Adv. Heterocycl. Chem. 1990, 49, 117.
(33) See for example: (a) Wu, F.; Thummel, R. P. Inorg. Chim. Acta
2002, 327, 26. (b) Kaizu, Y.; Yazaki, T.; Torii, Y.; Kobayashi, H. Bull.
Chem. Soc. J pn. 1970, 43, 2068.
(34) In the electronic spectra of [(DMSC)Ti{η2-OC(p-MeC6H4)2}-
dmbpy] (5) and [(DMSC)Ti{η2-OC(p-MeC6H4)2}phen] (6) in methylene
chloride, strong bands are observed below 400 nm. In the visible region,
the absorbance maximum for 5 and 6 are observed at 427 and 467
nm, respectively. The bathochromic shift of the absorbance maximum
of 6 reflects the lower energy of the π* state of the 1,10-phenanthroline
ligand.
(30) Average Ti-O bond distances of ∼1.910(4) Å were reported for
the related octahedral Ti(IV) complexes, [{κ2-OCAr2C5H4N}2Ti(NMe2)2]
(CAr2 ) 9-fluorenyl and Ar ) 4-NEt2-C6H4).25

144 Organometallics, Vol. 22, No. 1, 2003
Kingston et al.
) Ph; 2, Ar ) p-MeC6H4) with the appropriate delocal-
ized diimine compound in pentane. The η2-ketone
moiety of 3-6 is readily dissociated. Hence slow decom-
position of 3-6 by release of a ketone was observed, and
the decomposition was found to be photochemically
assisted. Titanium η2-ketone complexes 3-6 undergo
facile reaction with a second ketone molecule to produce
1-aza-5-oxa-titanacyclopentene derivatives 8-11, via
C-H activation of the nitrogen heterocycle and hydride
migration to a Ti-bound ketone molecule. The transfor-
mation is suggested to proceed by a mechanism involv-
ing a photochemically assisted electron transfer from
titanium to diimine ligand. We are continuing our
investigations of synthesis and reactivity of titanium η2-
ketone complexes with emphasis on isolating more
stable complexes, as well as elucidating details of the
mechanism for the transformation of 3-6 into 8-11.
We are also investigating applications of 3-6 and
related complexes to prepare substituted diimine com-
pounds.
Ack n ow led gm en t. Thanks are expressed to the
U.S. National Science Foundation (grant number CHE-
9984776) for financial support of this work. NMR
instruments utilized in this research were funded in
part by the CRIF program of the U.S. National Science
Foundation (grant number CHE-9974810). The authors
also thank Professor J ack Selegue (University of Ken-
tucky) and the reviewers for helpful suggestions.
Su p p or tin g In for m a tion Ava ila ble: A summary of crys-
tallographic parameters, atomic coordinates and equivalent
isotropic displacement parameters, bond lengths and angles,
anisotropic displacement parameters, and hydrogen coordi-
nates and isotropic displacement parameters for 9. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM020487F