Novel aryltitanium(IV) complexes containing η3-NCN- pseudofacial- and η3-NCN-meridional-bonded [C6H 3(CH2NME2)2-2,6]-(abbreviated as NCN) ligands.

Article abstract of DOI:10.1021/om970374+

Titanium(IV) derivatives of the chelating monoanionic aryldiamine ligand [C₆H₃(CH₂-NMe₂) ₂-2,6]^- (abbreviated as NCN) are prepared by treating [TiCl₃(OR)] (R = i-Pr, C₆H₄-OMe-4) with [Li(NCN)]₂. [TiCl₂(NCN)(O-i-Pr)] is smoothly methylated by methyllithium in toluene to give [TiClMe(NCN)(O-i-Pr)] and [TiMe₂(NCN)(O-i-Pr)]. Enhancement of the Lewis acidity of the titanium center has been studied by substituting chloro ligands for triflato ligands to give [TiCl(NCN)(O-i-Pr)(OTf)] and [Ti(NCN)(O-i-Pr)(OTf)₂]. X-ray studies of the dichloride and triflate complexes feature η³-pseudofacial and η³-meridional bonding modes for the NCN ligand, respectively. These different NCN bonding modes are explained in terms of the trans influence of the alkoxy and triflato ligands. A rare example of an organo titanium(IV) complex with a seven-coordinate titanium center is observed in the bis(triflate) complex as a result of bidentate O,O′-bonding mode of the triflato anion to one titanium center that is unprecedented in early transition metal chemistry. The triflato ligands exhibit a strong covalent bonding to titanium both in the solid state and in solution; the latter is demonstrated by the observation that cationic species are not formed upon addition of Lewis bases like THF, acetonitrile, and 1,2-bis(dimethylamino)ethane.

Full text of DOI:10.1021/om970374+

4174
Organometallics 1997, 16, 4174-4184
Novel Ar yltita n iu m (IV) Com p lexes Con ta in in g
η3-NCN-P seu d ofa cia l- a n d η3-NCN-Mer id ion a l-Bon d ed
[C6H3(CH2NMe2)2-2,6]- (Abbr evia ted a s NCN) Liga n d s.
Th e Cr ysta l Str u ctu r es of [TiCl2(η3-fa c-NCN)(O-i-P r )],
[TiCl(η3-m er -NCN)(O-i-P r )(OTf)] Con ta in in g a n
η1-O-Bon d ed Tr ifla te An ion , a n d th e Seven -Coor d in a ted
[Ti(η3-m er -NCN)(O-i-P r )(OTf)2] Con ta in in g η1-O- a n d
η2-O,O′-Bon d ed Tr ifla te An ion s
J ohannes G. Donkervoort,† J ohann T. B. H. J astrzebski,† Berth-J an Deelman,†,‡
Huub Kooijman,§ Nora Veldman,§ Anthony L. Spek,§,| and Gerard van Koten*,†
Department of Metal-Mediated Synthesis, Debye Institute, and Department of Crystal and
Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Received May 5, 1997X
Titanium(IV) derivatives of the chelating monoanionic aryldiamine ligand [C6H3(CH2-
NMe2)2-2,6]- (abbreviated as NCN) are prepared by treating [TiCl3(OR)] (R ) i-Pr, C6H4-
OMe-4) with [Li(NCN)]2. [TiCl2(NCN)(O-i-Pr)] is smoothly methylated by methyllithium in
toluene to give [TiClMe(NCN)(O-i-Pr)] and [TiMe2(NCN)(O-i-Pr)]. Enhancement of the Lewis
acidity of the titanium center has been studied by substituting chloro ligands for triflato
ligands to give [TiCl(NCN)(O-i-Pr)(OTf)] and [Ti(NCN)(O-i-Pr)(OTf)2]. X-ray studies of the
dichloride and triflate complexes feature η3-pseudofacial and η3-meridional bonding modes
for the NCN ligand, respectively. These different NCN bonding modes are explained in
terms of the trans influence of the alkoxy and triflato ligands. A rare example of an organo
titanium(IV) complex with a seven-coordinate titanium center is observed in the bis(triflate)
complex as a result of bidentate O,O′-bonding mode of the triflato anion to one titanium
center that is unprecedented in early transition metal chemistry. The triflato ligands exhibit
a strong covalent bonding to titanium both in the solid state and in solution; the latter is
demonstrated by the observation that cationic species are not formed upon addition of Lewis
bases like THF, acetonitrile, and 1,2-bis(dimethylamino)ethane.
In tr od u ction
amidinates,7 â-diketiminates,8 carboranes,9 and amido-
diphosphines.10
Group 4 based bent metallocene complexes are im-
portant catalyst precursors for a variety of oligomer-
ization and polymerization processes, of which homo-
geneous Ziegler-Natta type R-olefin polymerization is
probably the most important.1 To achieve better control
over the properties of the resulting polymer, new
catalyst systems have been developed through ligand
modifications of the ancillary cyclopentadienyl ligand(s).2
There is also an increased interest in the development
of new ancillary ligands which can be used as alterna-
tives for the cyclopentadienyl (abbreviated as Cp) ligand
systems. Among the systems that have been developed
are alkoxides,3 aryloxides,4 amides,5 porphyrins,6 benz-
Both the Cp and non-Cp ligand systems affect the
coordinative unsaturation and the Lewis acidity of the
metal center. An enhanced Lewis acidic metal center
is expected to increase the polymerization activity for
R-olefins.11 The linked amido-cyclopentadienyl ligands
introduced by Bercaw and Shapiro2a-e are an example
of a modified ligand system that provided complexes
with enhanced Lewis acidity as compared to metal-
(2) (a) Okuda, J .; Schattenmann, F. J .; Wocadlo, S.; Massa, W.
Organometallics 1995, 14, 789. (b) Woo, T. K.; Fan, L.; Ziegler, T.
Organometallics 1994, 13, 2252. (c) Herrmann, W. A.; Morawietz, M.
J . A. J . Organomet. Chem. 1994, 482, 169. (d) Shapiro, P. J .; Cotter,
W. D.; Schaefer, W. P.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 1994, 116, 4632. (e) Stevens, J . C.; Timmers, F. J .; Rosen, G. W.;
Knight, G. W.; Lai, S. Y. (Dow Chemical Co.). European Patent
Application EP 0 416 815 A2, 1991. (f) Canich, J . A. (Exxon Chemical
Co.). U.S. Patent 5,026,798, 1991. (g) Hajela, S.; Bercaw, J . E.
Organometallics 1994, 13, 1147. (h) Flores, J . C.; Chien, J . C. W.;
Rausch, M. D. Organometallics 1994, 13, 4140. (i) Hughes, A. K.;
Meetsma, A.; Teuben, J . H. Organometallics 1993, 12, 1936. (j)
Conticello, V. P.; Brard, L.; Giardello, M. A.; Tsuji, Y.; Sabat, M.; Stern,
C. L.; Marks, T. J . J . Am. Chem. Soc. 1992, 114, 7606.
(3) (a) van Doorn, J . A.; van der Heijden, H. Organometallics 1994,
13, 4271. (b) Hitchcock, P. B.; Lappert, M. F.; MacKinnon, I. A. J .
Chem. Soc., Chem. Commun. 1993, 1015. (c) Balaich, G. J .; Rothwell,
I. P. Organometallics 1992, 11, 1771. (d) Covert, K. J .; Neithamer, D.
R.; Zonnevylle, M. C.; LaPointe, R. E.; Schaller, C. P.; Wolczanski, P.
T. Inorg. Chem. 1991, 30, 2494. (e) Lubben, T. V.; Wolczanski, P. T.
van Duyne, G. D. Organometallics 1984, 3, 977.
* To whom correspondence should be addressed.
† Debye Institute.
‡ Affiliate of Elf Atochem Vlissingen BV at the Department of Metal-
Mediated Synthesis.
§ Bijvoet Center for Biomolecular Research.
| Address correspondence pertaining to crystallographic studies to
this author.
X Abstract published in Advance ACS Abstracts, August 15, 1997.
(1) (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b)
Barsan, F.; Baird, M. C. J . Chem. Soc., Chem. Commun. 1995, 1065.
(c) J eremic, D.; Wang, Q.; Quyoum, R.; Baird, M. C. J . Organomet.
Chem. 1995, 497, 143. (d) Quyoum, R.; Wang, Q.; Tudoret, M.-J .;
Baird, M. C. J . Am. Chem. Soc. 1994, 116, 6435. (e) Bochmann, M.;
Lancaster, S. J . Makromol. Chem., Rapid Commun. 1993, 14, 807.
S0276-7333(97)00374-9 CCC: $14.00 © 1997 American Chemical Society

Novel Aryltitanium(IV) Complexes
Organometallics, Vol. 16, No. 19, 1997 4175
F igu r e 1. Examples of monoanionic arylamine ligands.
locenes. In fact, the first examples of homogeneous
single-component living R-olefin polymerization cata-
lysts are represented by the corresponding scandium
complexes [(η5:η1-C5Me4SiMe2NCMe3)ScR].2d Further-
more, the stereoselectivity of propylene insertion was
shown to increase when cationic ethylene-bridged bis-
(indenyl)zirconium systems are used.12
Research in our group is focused on the use of ligand
systems that combine a hard anionic (cf. Cp) aryl carbon
atom with additional coordinating nitrogen donor atoms
(Figure 1). It has been shown that the monoanionic
aryldiamine ligand [C6H3(CH2NMe2)2-2,6]- (abbreviated
as NCN, Figure 1, II with R1 ) Me, R2 ) R3 ) H) can
coordinate to a variety of metal centers with different
bonding modes (Figure 2).13 The additional NMe2 units
can interact with the metal center thereby leading to
F igu r e 2. Previously reported bonding modes for NCN.
control of the coordinative unsaturation of the metal
center. This is in contrast to Cp ligands, which can only
change their coordination mode by ring slippage (η5, η3,
and η1). The unique properties of the NCN ligand led
to new organometallic complexes with interesting cata-
lytic activities different from those of the analogous Cp
complexes.13a,b For example, the tantalum(V) complex
[TaCl(dCCMe3)(NCN)(O-t-Bu)] showed a reactivity with
simple alkenes that varies from nonselective (probably
reductive rearrangement) reactions to very clean alkene
metathesis reactions.14
In this paper we present our initial results on the use
of the NCN ligand in titanium(IV) organometallic
chemistry. The synthesis and characterization of a
range of (NCN)titanium(IV) complexes is described
together with the molecular structures of [TiCl2(NCN)-
(O-i-Pr)], [TiCl(NCN)(O-i-Pr)(OTf)], and [Ti(NCN)(O-i-
Pr)(OTf)2].
(4) (a) van der Linden, A.; Schaverien, C. J .; Meijboom, N.; Ganter,
C.; Orpen, A. G. J . Am. Chem. Soc. 1995, 117, 3008. (b) Healy, M. D.;
Power, M. B.; Barron, A. R. Coord. Chem. Rev. 1994, 130, 63. (c)
Aaltonen, P.; Seppa¨la¨, J .; Matilainen, L.; Leskela¨, M. Macromolecules
1994, 27, 3136. (d) Caulton, K. G.; Hubert-Pfalzgraf, L. G. Chem. Rev.
1990, 90, 969. (e) Schenke, D.; Thiele, K. H. J . Organomet. Chem.
1990, 382, 109. (f) Hill, J . E.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1990, 9, 2211. (g) Floriani, C.; Corazza, F.; Lesueur,
W.; Chiesi-Villa, A.; Guestina, C. Angew. Chem., Int. Ed. Engl. 1989,
28, 66. (h) Duff, A. W.; Kamarudin, R. A.; Lappert, M. F.; Norton, R.
J . J . Chem. Soc., Dalton Trans. 1986, 489.
(5) (a) Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg,
H. Organometallics 1996, 15, 2672. (b) Warren, T. H.; Schrock, R. R.;
Davis, W. M. Organometallics 1996, 15, 562. (c) Clark, H. C. S.; Cloke,
F. G. N.; Hitchcock, P. B.; Love, J . B. J . Organomet. Chem. 1996, 506,
343. (d) Guerin, F.; McConville, D. H.; Vittal, J . J . Organometallics
1995, 14, 3154. (e) Cummins, C. C.; Schrock, R. R.; Davies, W. M.
Organometallics 1992, 11, 1452. (f) Cummins, C. C.; Schaller, C. P.;
van Duyne, G. D.; Wolczanski, P. T.; Chan, A. W. E.; Hofmann, R. H.
J . Am. Chem. Soc. 1991, 113, 2985. (g) tom Dieck, H.; Rieger, H. J .;
Fendesak, G. Inorg. Chim. Acta 1990, 177, 191.
Resu lts a n d Discu ssion
Our initial attempts to prepare (NCN)titanium(IV)
complexes involved the reactions of TiCl4 or TiCl4(THF)2
with [Li(NCN)]2 in 2:1 molar ratios in toluene at -78
°C. Immediately a color change to dark green was
observed with the concomitant formation of a precipitate
(LiCl). After complete addition, the color of the reaction
mixture had turned to black/brown. Unfortunately,
from these reaction mixtures no (NCN)titanium com-
plexes could be isolated in significant yield. We there-
(6) (a) Arnold, J .; Hoffman, C. G.; Dawson, D. Y.; Hollander, F. J .
Organometallics 1993, 12, 3645. (b) Schaverien, C. J .; Orpen, A. G.
Inorg. Chem. 1991, 30, 4968 and references cited therein.
(7) (a) Duchateau, R.; van Wee, C. T.; Meetsma, A.; van Duijnen, P.
Th.; Teuben, J . H. Organometallics 1996, 15, 2279. (b) Wedler, M.;
Kno¨sel, F.; Edelmann, F. T.; Behrens, U. Chem. Ber. 1992, 125, 1313.
(c) Roesky, H. W.; Meller, B.; Noltemeyer, M.; Schmidt, H.-G.; Scholz,
U.; Sheldrick, G. M. Chem. Ber. 1988, 121, 1403. (d) Dehnicke, K.;
Ergezinger, C.; Hartmann, E.; Zinn, A.; Ho¨sler, K. J . Organomet. Chem.
1988, 352, C1.
(8) (a) Deelman, B.-J .; Hitchcock, P. B.; Lappert, M. F.; Lee, H.-K.;
Leung, W.-P. J . Organomet. Chem. 1996, 513, 281. (b) Hitchcock, P.
B.; Lappert, M. F.; Liu, D.-S. J . Chem. Soc., Chem. Commun. 1994,
1699. (c) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. J . Chem. Soc.,
Chem. Commun. 1994, 2637. (d) Hitchcock, P. B.; Holmes, S. A.;
Lappert, M. F.; Tian, S. J . Chem. Soc., Chem. Commun. 1994, 2691.
(e) Lappert, M. F.; Liu, D.-S. Netherlands Patent PCT/NL95/00202,
1995.
(9) For an overview, see: Saxena, A. K.; Hosmane, N. S. Chem. Rev.
1993, 93, 1081.
(10) (a) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J . Organometallics
1992, 11, 2967. (b) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J .
Organometallics 1991, 10, 2026. (c) Fryzuk, M. D.; Haddad, T. S. J .
Am. Chem. Soc. 1988, 110, 8263.
(11) (a) Labinger, J . A.; Bercaw, J . E. Organometallics 1988, 7, 926.
(b) Bruno, J . W.; Stecher, H. A.; Morss, L. R.; Sonnenberger, D. C.;
Marks, T. J . Am. Chem. Soc. 1986, 108, 7275.
(12) Lee, I.-M.; Gauthier, W. J .; Ball, J . M.; Iyengar, B.; Collins, S.
Organometallics 1992, 11, 2115.
(13) (a) Rietveld, M. H. P.; Grove, D. M.; van Koten, G. New J . Chem.
1997, 21, 751. (b) van Koten, G. Pure Appl. Chem. 1989, 61, 1681.
η3-Meridional coordination: (c) Sutter, J . P.; J ames, S. L.; Steenwinkel,
P.; Karlen, T.; Grove, D. M.; Veldman, N.; Smeets, W. J . J .; Spek, A.
L.; van Koten, G. Organometallics 1996, 15, 941. (d) Contreras, L.;
Cowley, A. H.; Gabba¨ı, F. P.; J ones, R. A.; Carrano, C. J .; Bond, M. R.
J . Organomet. Chem. 1995, 489, C1. (e) Hogerheide, M. P.; Grove, D.
M.; Boersma, J .; J astrzebski, J . T. B. H.; Kooijman, H.; Spek, A. L.;
van Koten, G. Chem. Eur. J . 1995, 1, 343. (f) Alsters, P. L.; Baesjou,
P. J .; J anssen, M. D.; Kooijman, H.; Sicherer-Roetman, A.; Spek, A.
L.; van Koten, G. Organometallics 1992, 11, 4124. (g) Abbenhuis, H.
C. L.; Feiken, N.; Haarman, H. F.; Grove, D. M.; Horn, E.; Kooijman,
H.; Spek, A. L.; van Koten, G. Angew. Chem., Int. Ed. Engl. 1991, 30,
996. (h) Schumann, H.; Wassermann, W.; Dietrich, A. J . Organomet.
Chem. 1989, 365, 11. η3-Pseudofacial coordination: (i) Sutter, J . P.;
J ames, S. L.; Steenwinkel, P.; Karlen, T.; Grove, D. M.; Veldman, N.;
Smeets, W. J . J .; Spek, A. L.; van Koten, G. Organometallics 1996,
15, 941. (j) Carre´, F.; Chuit, C.; Corriu, R. J . P.; Mehdi, A.; Reye`, C.
Organometallics 1995, 14, 2754. (k) Yamamoto, Y.; Chen, X.; Kojima,
S.; Ohdoi, K.; Kitano, M.; Doi, Y.; Akiba, K. J . Am. Chem. Soc. 1995,
117, 3922. (l) Hogerheide, M. P.; Grove, D. M.; Boersma, J.; Jastrzebski,
J . T. B. H.; Kooijman, H.; Spek, A. L.; van Koten, G. Chem. Eur. J .
1995, 1, 343. (m) Abbenhuis, H. C. L.; Feiken, N.; Grove, D. M.;
J astrzebski, J . T. B. H.; Kooijman, H.; van der Sluis, P.; Smeets, W. J .
J .; Spek, A. L.; van Koten, G. J . Am. Chem. Soc. 1992, 114, 9773.
(14) Abbenhuis, H. C. L.; Rietveld, M. H. P.; Haarman H. F.;
Hogerheide, M. P.; Spek, A. L.; van Koten, G. Organometallics 1994,
13, 3259.

4176 Organometallics, Vol. 16, No. 19, 1997
Donkervoort et al.
Sch em e 1. Syn th esis of [TiCl2(NCN)(OR)]
[R ) i-P r (1a ), C6H4OMe-4 (1b)],
quantitative isolation of the mono- and dimethyl-
(NCN)titanium(IV) complexes 4 and 5, respectively.
Alternatively, 5 is also accessible by reacting a solution
of 3 in benzene with 2 equiv of MeLi at 5 °C. The
dichloride complex 1a was also reacted with 1 or 2 equiv
of n-BuLi under conditions similar to those used for the
preparation of 4 and 5. Upon addition a color change
of the reaction mixture to dark brown/black was ob-
served, but we were unable to isolate pure material from
these reactions.
[TiCl(NCN)(O-i-P r )(OTf)], 2, a n d
[Ti(NCN)(O-i-P r )(OTf)2], 3 (N ) NMe2)
The (NCN)titanium(IV) complexes 1-5 are air and
moisture sensitive materials with discrete melting
points of which the bis(triflate) complex 3 and the
dimethyl complex 5 melt with decomposition. In the
solid state, complexes 1-4 can be stored for months in
an inert atmosphere. This is in contrast with the
stability of the dimethyl complex 5, which is stable for
longer periods only below 0 °C. At room temperature 5
slowly decomposes to protonated NCN and unidentified
products which hampered the microanalysis of this
complex.
The complexes 1-3 are soluble in aromatic solvents
and ethers but are sparingly soluble in saturated
hydrocarbons, while the methyl complexes 4 and 5
readily dissolve in both polar and nonpolar solvents.
Solutions of 1 in toluene can be refluxed for several
hours without decomposition, whereas toluene solutions
of the triflate and methyl complexes 2-5 decompose to
give protonated NCN and products that have not been
identified.
Sch em e 2. Syn th esis of [TiClMe(NCN)(O-i-P r )], 4,
a n d [TiMe2(NCN)(O-i-P r )], 5 (N ) NMe2)
Molecular weight determinations (cryoscopy in ben-
zene) of 1a , 2, 4, and 5 showed these complexes to exist
as monomeric species in this solvent. A concentration
dependent molecular weight varying from 1.0 (c ) 6 m)
to 1.6 (c ) 55 m) was observed for the bis(triflate)
complex 3, which points to a monomer-dimer equilib-
rium. Molecular weight determination of 1b failed due
to its low solubility in benzene.
The 1H and 13C{1H} NMR data of the (NCN)titanium-
(IV) complexes (Table 1) confirmed their proposed
composition. The NCN resonances are observed at
chemical shift positions which are commonly encoun-
tered in (NCN)metal complexes.13 The Ti-Me reso-
nances in 4 (δ 0.95) and 5 (δ 0.68) have chemical shifts
similar to those observed for [Cp2TiMeR]15 (δ ) 0.61-
1.00) and [TiMe(O-i-Pr)3]15b (δ ) 0.98).
At low temperature (220 K), the dichloride (1), methyl
chloride (4), and dimethyl (5) complexes display four
N-Me resonances in both the 1H and 13C{1H} NMR
spectra. This indicates that at this temperature these
complexes have C1 molecular symmetry. In addition,
it indicates that both the NMe2 units are coordinated
to the titanium center as bidentate C,N-coordination of
NCN would result in three N-Me resonances in a 1:1:2
ratio and monodentate C-coordination of NCN in only
one N-Me resonance. Assuming a regular octahedral
coordination for these complexes, a number of geom-
etries can be considered which have either η3-(pseudo)-
facially or η3-meridionally coordinated NCN ligands
(Figure 3). It should be noted that in solutions of η3-
meridionally bonded (NCN)metal complexes, low energy
barriers are found for the ring-flippage of the two five-
membered chelate rings.13
fore turned to other titanium(IV) salts, i.e., trichloroti-
tanium(IV) alkoxide reagents.
The reaction of [Li(NCN)]2 with 2 equiv of [TiCl3(OR)]
(R ) i-Pr, C6H4OMe-4) in toluene at -78 °C gave the
new (diaminoaryl)titanium(IV) complexes [TiCl2(NCN)-
(OR)] (1a , b) [R ) i-Pr (1a ), C6H4OMe-4 (1b)] (Scheme
1). Due to the low solubility of the phenoxide complex
1b in common polar or nonpolar solvents further studies
on (NCN)titanium(IV) complexes were focused on the
(isopropoxy)titanium(IV) complex 1a .
As a potential route to enhance the Lewis acidity of
the metal center, we explored the preparation of (NCN)-
titanium(IV) triflate complexes. The reaction of 1a with
either 1 equiv of CuOTf or 2 equiv of AgOTf in benzene
at room temperature resulted in the formation of the
mono- and bis(triflate) complexes 2 and 3, respectively
(Scheme 1). The preparation of 3 can also be ac-
complished by reacting 2 with 1 equiv of AgOTf under
the same conditions.
To explore the preparation of (NCN)titanium(IV) alkyl
species the corresponding mono- and dimethyl com-
plexes have been prepared (Scheme 2). The reaction of
a solution of 1a in toluene with 1 or 2 equiv of MeLi
(solution in Et2O) at -78 °C resulted in the almost
(15) (a) Du¨rr, S.; Ho¨hlein, U.; Shobert, R. Organometallics 1992,
11, 2950. (b) Rausch, M. D.; Gordon, H. B. J . Organomet. Chem. 1974,
74, 85.

Novel Aryltitanium(IV) Complexes
Organometallics, Vol. 16, No. 19, 1997 4177
Ta ble 1. Releva n t 1H a n d 13C{1H} NMR Da ta of th e Dich lor o, Tr ifla to, a n d Meth yl(NCN)tita n iu m (IV)
Com p lexes 1-5a
13C{1H} NMR data
1H NMR data
complex
T (K)
CH2N
68.4
68.8, 67.4
69.0
d
71.5
71.5
d
64.3, 62.8
68.1
68.3, 67.4
NMe2
CH2N
4.7, 2.6
NMe2
[TiCl2(NCN)(O-i-Pr)], 1a
297b
220c
297b
220c
297b
297b
297b
220c
297b
220c
50.3, 46.6
50.6, 50.1, 47.0, 46.1
50.6, 45.4
2.8, 2.1
4.7, 4.5, 2.38, 2.39
4.5, 2.7
3.0, 2.6, 2.2, 1.6
2.8, 2.25
3.0, 2.55, 2.2, 1.8
2.61, 2.37
[TiCl2(NCN)(OC6H4OMe-4)] 1b
d
4.8, 4.35, 2.5e
3.79, 3.44
3.8, 3.3
[TiCl(NCN)(O-i-Pr)(OTf)], 2
[Ti(NCN)(O-i-Pr)(OTf)2], 3
[TiClMe(NCN)(O-i-Pr)], 4
52.1, 50.7
52.0, 49.6
2.6, 2.3
2.3
d
3.6e
44.7, 44.6, 41.6, 40.7
46.8
49.0, 46.4, 45.8, 45.7
4.8, 4.4, 2.5e
3.6
2.75, 2.38, 2.20, 1.68
2.25
2.50, 2.25, 2.15, 2.12
[TiMe2(NCN)(O-i-Pr)], 5
4.45, 4.35, 2.62e
a
b
d
Chemical shifts in δ are indirectly referenced to SiMe4 using solvent signals. In benzene-d6. c In toluene-d8. Not measured. e Two
overlapping doublets each of 1H intensity, assigned by selective 1H irradiation.
pected to have time-averaged Cs symmetry as a result
of rapid ring-flippage of the two five-membered chelate
rings.
F lu xion a l Beh a vior of th e (NCN)tita n iu m (IV)
1
Com p lexes in Solu tion . The H and 13C{1H} NMR
spectra of 1-5 show temperature dependent character-
istics, involving the N-Me, methylene, and aromatic
protons of the NCN ligand, the isopropoxy protons, and
the Ti-Me protons in 5, consistent with these species
being fluxional in solution. Experiments at variable
concentrations (for 3, concentrations lower than 10 m
were used to prevent dimer formation) showed these
fluxionalities to be concentration independent, indicat-
ing that intramolecular processes are operative. The
energy barriers (∆Gq) of the fluxional processes in 1-5
(calculated from the Eyring equation and the coales-
cence temperature Tc)16a are presented in Table 2a. The
∆Hq and ∆Sq of the fluxional processes in 1a and 3
(determined from an Eyring plot)16b are presented in
Table 2b.
In both the dichloride complexes (1), a low-energy and
a high-energy fluxional process are observed. In con-
F igu r e 3. Possible molecular geometries in regular octa-
hedral complexes containing an η3-N,C,N-bonded NCN
ligand.
trast, in the methyl chloride (4) and dimethyl (5)
complexes, which contain an η3-pseudofacially bonded
NCN ligand, only one fluxional process is observed. The
high-energy process in 1 and the fluxional processes in
4 and 5 are associated with the coalescence of the
N-Me, methylene, and, for 5, Ti-Me signals. One
possible explanation that would lead to this coalescence
pattern is a simple process involving the association and
dissociation of the Ti-N dative bond, thereby allowing
low-energy pyramidal inversion to take place at the
nitrogen atom. This conclusion is consistent with a
calculated positive ∆Sq value for the process in 1a (Table
2b) and the observation in the NMR spectra of N-Me
resonances for the NCN ligand which are, at the fast
exchange limit, at a position comparable to that for
protonated NCN. In addition, this type of process has
been proposed in many other (NCN)metal complexes.13
The lower energy process observed in the dichloride
complexes 1a ,b is associated with (Figure 4) the coa-
lescence of four N-Me signals to two signals and two
AX patterns of the methylene protons to one AX pattern.
Simultaneously, the coalescence of the alkoxy methyl
For 1 and 5 only geometries I, III, IV, and V need to
be considered. Structures III, IV, and V can be excluded
on the basis of symmetry (Cs, C2v, and Cs, respectively),
leaving only one possible structure, i.e., I, in which the
NCN ligand is facially coordinated and the alkoxy ligand
is positioned trans to one of the NMe2 units. Similar
arguments apply to 4, leading to structures I, II, and
III as possible geometries, all with facially coordinated
NCN ligands. For 1a the structural assignment pre-
sented above was confirmed by an X-ray diffraction
study (vide infra).
The triflate complexes 2 and 3 display only two NMe
resonances in their NMR spectra, indicative of a higher
symmetry of these complexes compared to 1, 4, and 5.
Considering that the triflato ligand can occupy either
one or two coordination sites at the metal center (vide
infra) and the fact that fluxional behavior cannot be
excluded a priori, a structural assignment is more
difficult. However, X-ray diffraction data revealed that
mononuclear 2 and 3 have (distorted) octahedral struc-
tures (when the η2-O,O′-bonded triflato ligand in 3 is
considered as one of the vertices) with meridionally
coordinated NCN ligands (vide infra), i.e., structure V
for both 2 and 3. This is in full agreement with the
NMR data since in solution these structures are ex-
(16) Eyring equation: ∆Gq ) -RTc ln[2πh(∆ν)/kTcx3] with ∆Gq
)
free energy of activation (J ), Tc ) coalescence temperature (K), and
∆ν ) chemical shift difference (Hz); the other symbols have their usual
meanings. (b) Eyring plot: ln(k/T) ) C + ∆S/R + (-∆H/R)(1/T), with
k ) rate constant (s-1), T ) temperature (K), C ) 23.758, ∆S ) entropy
value (J mol-1 K-1), R ) 8.314 J mol-1 K-1, ∆H ) enthalpy value (J
mol-1).

4178 Organometallics, Vol. 16, No. 19, 1997
Donkervoort et al.
Ta ble 2
(a) Calculateda Energy Barriers ((2 kJ mol-1) for the Observed Fluxional Processes in the
Dichloro, Triflato, and Methyl (NCN)titanium(IV) Complexes 1-5
∆Gq (Tc) (kJ mol-11 (K))
complex
NMe2
CH2
OCHMe2
Ti-Me
[TiCl2(NCN)(O-i-Pr)], 1a
56 (278)
64 (324)
52 (269)
60 (300)
66 (310)
69 (330)
52 (262)
43 (220)
56 (262)
63 (335)
52 (266)
59 (318)
64 (318)
69 (342)
51 (275)
45 (238)
56 (265)
b
b
b
b
b
b
b
b
b
b
b
b
[TiCl2(NCN)(OC6H4OMe-4)], 1b
[TiCl(NCN)(O-i-Pr)(OTf)], 2
[Ti(NCN)(O-i-Pr)(OTf)2], 3
[TiClMe(NCN)(O-i-Pr)], 4
[TiMe2(NCN)(O-i-Pr)], 5
52 (267)
43 (215)
43 (230)
(b) Calculatedc Activation Parameters for the Observed Fluxional Processes in the
Dichloride and Bis(triflate) Complexes 1a and 5
complex
coalescing groups
aromatic protons
∆Hq (kJ mol-1
)
∆Sq (J mol-1 K-1
)
[TiCl2(NCN)(O-i-Pr)], 1a
41 ( 4
36 ( 4
74 ( 2
86 ( 4
-52 ( 10
-74 ( 10
28 ( 5
d
CH2
CH2
e
[Ti(NCN)(O-i-Pr)(OTf)2], 3
NMe2
63 ( 10
a
b
d
Reference 16a. Not Observed. c Reference 16b. Low-temperature coalescence. e High-temperature coalescence.
operative. A similar conclusion was also made about
the fluxional processes in adducts of methyltitanium
trichloride with bidentate ligands as, for example,
dimethoxyethane or 1,2-bis(dimethylamino)ethane.17
The isomerization process in 1a probably involves either
(i) a change in the NCN coordination mode from
η3-pseudofacial to η3-meridional or (ii) site-exchange
processes of the alkoxy and chloro ligands. Site-
exchange processes which have been proposed in hexa-
coordinate species are (i) the trigonal or Bailar twist,18
(ii) the rhombic or Ray-Dutt twist,19 and (iii) the edge
inversion process.20
No evidence could be obtained that provided unequivo-
cal evidence about which process is operative. A tenta-
tive assumption is that the operative process involves
the change in the NCN coordination mode from η3-
pseudofacial to η3-meridional. An argument in favor of
this is that stable η3-pseudofacially bonded (NCN)-
titanium(IV) complexes have been prepared, i.e., the
triflate complexes 2 and 3 (vide infra).
In the triflate complexes 2 and 3 (with an η3-
meridionally bonded NCN ligand) only one fluxional
process is observed, associated with the coalescence of
the N-Me and methylene signals. For this process a
positive ∆Sq was determined (Table 2b) in agreement
with a dissociative process. A likely explanation that
would lead to the observed coalescence phenomena is a
simple process involving Ti-N dissociation/association.
This process is also observed in 1, 4, and 5 (vide supra)
and many other (NCN)metal complexes.13
F igu r e 4. 1H NMR spectra of 1a showing the coalescence
behaviour of 1a in solution.
protons in 1a and the aromatic protons H(3) and H(5)
is observed.
Using a NOESY NMR experiment (at 205 K) of a
sample of 1a we could assign the N-Me resonances of
each of the two NMe2 units of 1a . From this assignment
it was evident that the observed coalescence pattern is
obtained by rendering a N-Me group of one NMe2 unit
homotopic with a N-Me group of the other NMe2 unit.
Therefore, a process involving complete M-N dissocia-
tion can be excluded as this process would result in the
coalescence of N-Me resonances of the same NMe2 unit
through pyramidal inversion at the nitrogen atom. The
strongly negative ∆Sq value calculated for this process
(Table 2b) is in agreement with such a nondissociative
process. However, a process involving partial elongation
of the Ti-N dative bond, possibly leading to tbp-like
intermediates, cannot be excluded.
The NMR data provided unambiguous information
about the coordination mode of NCN in 1 and 5, but
not for 2, 3, and 4, nor about the coordination mode of
the triflato ligands in 2 and 3. We therefore subjected
single crystals of 1a , 2, and 3 to X-ray diffraction
studies. Attempts to crystallize the methyl derivatives
4 and 5 failed because of their high solubility in common
polar and nonpolar solvents while crystallization of the
(17) Clark, J . H.; McAlees, A. J . Inorg. Chem. 1972, 11, 342.
(18) Bailar, J . C., J r. J . Inorg. Nucl. Chem. 1958, 8, 165.
(19) Ray, P. C.; Dutt, N. K. J . Indian Chem. Soc. 1943, 20, 81.
(20) (a) Dixon, D. A.; Arduengo, A. J ., III. J . Chem. Phys. 1987, 91,
3195. (b) Dixon, D. A.; Arduengo, A. J ., III; Fukunaga, T. J . Am. Chem.
Soc. 1986, 108, 2461.
From these observations we conclude that a nondis-
sociative, intramolecular isomerization process must be

Novel Aryltitanium(IV) Complexes
Organometallics, Vol. 16, No. 19, 1997 4179
F igu r e 5. ORTEP drawing of complex 1a at the 30%
probability level. The hydrogen atoms are omitted for
clarity.
F igu r e 7. ORTEP drawing of complex 3 at the 30%
probability level. The hydrogen atoms are omitted for
clarity.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) F ou n d in [TiCl2(NCN)(O-i-P r )], 1a ,
[TiCl(NCN)(O-i-P r )(OTf)], 2, a n d
[Ti(NCN)(O-i-P r )(OTf)2], 3
1a
2
3
Ti-C(1)
2.090(3)
2.420(3)
2.379(2)
2.3439(10)
2.3006(12)
1.765(2)
2.086(5)
2.235(5)
2.252(5)
2.365(2)
2.098(5)
2.338(4)
2.301(4)
Ti-N(1)
Ti-N(2)
Ti-Cl(1)
Ti-Cl(2)
Ti-O(1)
1.731(3)
2.096(3)
1.730(3)
2.093(3)
2.324(3)
2.243(3)
147.26(15)
172.4(3)
150.7(2)
93.91(16)
97.04(18)
61.70(12)
106.40(19)
Ti-O(2)
Ti-O(5)
Ti-O(6)
N(1)-Ti-N(2)
Ti-O(1)-C(13)
Ti-O(2)-S(1)
Ti-O(5)-S(2)
Ti-O(6)-S(2)
O(5)-Ti-O(6)
O(5)-S(2)-O(6)
113.23(10)
149.22(18)
147.86(18)
157.2(4)
147.2(2)
F igu r e 6. ORTEP drawing of complex 2 at the 30%
probability level. The hydrogen atoms are omitted for
clarity.
compared to an η3-meridionally bonded NCN ligand.
Consequently, the smaller chloro ligand (Cl(2)), as
compared to the alkoxy ligand, is placed in between the
two NMe2 moieties. In addition, this coordination places
the alkoxy ligand (almost) trans to one of the NMe2
moieties. Interestingly, the arrangement of the terden-
tate NCN and monodentate alkoxy and chloro ligands
around the metal center renders the titanium atom in
1a a stereogenic center. Both enantiomers are found
in the unit cell of which the TPR-6-C22 is shown in
Figure 5.
The monotriflate complex [TiCl(NCN)(O-i-Pr)(OTf)],
2, is likewise a mononuclear species but with an
η3-meridionally bonded NCN ligand, in accord with the
NMR data (vide supra), and a distorted octahedral
geometry (Figure 6). Typical for an η3-meridionally
phenoxide complex 1b was hampered by its low solubil-
ity in these solvents.
Molecu la r Str u ctu r es of [TiCl2(η3-fa c-NCN)(O-i-
P r )], 1a , [TiCl(η3-m er -NCN)(O-i-P r )(OTf)], 2, a n d
[Ti(η3-mer -NCN)(O-i-P r )(OTf)2], 3, in th e Solid State.
The molecular structures of 1a , 2, and 3 are shown in
the Figures 5, 6, and 7, respectively, while selected bond
distances and angles can be found in Table 3. The
coordination sphere of the titanium center in the dichlo-
ride complex 1a (Figure 5) can best be described as
antiprismatic, which is a common geometry for d0 metal
complexes.21
The N(1)-Ti-N(2) angle (113.23(10)°) points to an η3-
pseudofacial coordination of the NCN ligand in accord
with the NMR data (Table 1) (vide supra). This
coordination mode for the NCN ligand has recently been
observed in several main group and transition metal
complexes.13a,i-m The η3-pseudofacial coordination places
the NMe2 moieties in closer proximity of each other as
(22) For the trigonal prismatic system, the configuration index is
derived from the CIP rank numbers of the ligating atoms opposite the
triangular face containing the greater number of ligating atoms of
highest CIP rank. The chirality symbol is assigned by viewing the
trigonal prism from above the prefered triangular face and noting the
direction of progression of the priority sequence for the less-preferred
triangular face. Leigh, G. J ., Ed. Nomenclature of Inorganic Chemistry.
Recommendations 1990; International Union of Pure and Applied
Chemistry; Blackwell Scientific Publications: Oxford, 1990.
(21) Morse, P. M.; Girolami, G. S. J . Am. Chem. Soc. 1989, 111, 4114.

4180 Organometallics, Vol. 16, No. 19, 1997
Donkervoort et al.
bonded NCN ligand13a,c-h the N(1), N(2), Ti, and Cipso
atoms are almost in one plane (maximum deviation from
least-squares plane 0.009(1) Å). The two nitrogen atoms
are in apical positions with a N(1)-Ti-N(2) bond angle
amounting to 147.86(18)°. The angular deviation from
perfect trans coordination is a result of the small N-Ti-
C(1) bite angles in the two five-membered chelate rings,
fused over the Ti-Cipso bond (74.21(18) and 73.66(18)°),
and is a general phenomenon observed in η3-meridion-
ally bonded (NCN)metal complexes.13a,c-h The triflato
anion is placed trans to the alkoxy ligand with an O(2)-
Ti-O(1) bond angle of 170.91(15)°, leaving the chloro
complexes (more than 10σ). An obvious difference
between 1a , 2, and 3 is the Ti-O-C bond angles, which
vary from 149.22(18) to 157.2(4) and 172.4(3)°, respec-
tively. As has been proposed,27 the M-O bond distance
and, in particular, the M-O-C bond angle in group 4
metal alkoxide complexes give an indication of the
degree of M-O dπ-pπ multiple bond character in the
alkoxy-metal bond. The M-O-C bond angle is influ-
enced by the hybridization of the oxygen atom, i.e.,
M-O-C bond angles of 109, 120, and 180° are expected
for sp3-, and sp2-, and sp-hybridized oxygen atoms,
respectively. The sp- and sp2-hybridized oxygen atoms
can π-donate four and two additional p-electrons, re-
spectively, into empty d orbitals of the metal center.
It is obvious that the M-O-C bond angles in 1a , 2,
and 3 point to a hybridization of the oxygen atom
between sp2 and sp. However, the increase of the
M-O-C bond angle in the series 1a , 2, and 3 indicates
that the consecutive replacement of a chloro ligand for
a triflato ligand increases the s character in the hybrid-
ization of the oxygen atom of the alkoxy ligand, i.e., the
dπ-pπ interaction between the titanium and oxygen
atoms increases in this series. This increase of the
M-O-C bond angle and thereby the M-O dπ-pπ
interaction reflects the enhanced Lewis acidity of the
titanium center as a result of the replacement of chloro
ligands for less electron donating triflato ligands. Fi-
nally, the almost linear M-O-C bond angle found in
the bis(triflate) complex 3 renders this complex formally
a 18-electron species, which is in line with the enhanced
stability of 3 toward air compared to the stability of
other (NCN)titanium(IV) complexes.
The substitution of the chloro ligands by triflato
ligands in going from 1a to 3 also causes a change in
coordination mode of NCN from η3-pseudofacial (1a ) to
η3-meridional (2 and 3). The electronic factors which
affect the molecular geometry of 1a , 2, and 3 are
illustrated by the position of the alkoxy ligand and the
variation of the Ti-N bond distance. A strong M-O-
(alkoxy) interaction is obtained by a position of the
alkoxy ligand trans to the ligated atom with the weakest
electron-donating capacity. This leads in the dichloride
complex 1a to the alkoxy ligand being observed trans
to one of the ligated nitrogen atoms and, as a result of
this orientation, to an η3-pseudofacially coordinated
NCN ligand.
ligand to be placed trans to Cipso
. The Ti-C bond
distance in 2 is not affected by the substitution of one
of the chloro ligands for a triflato ligand (cf. 2.086(5) Å
in 2 with 2.090(3) Å in 1a ).
The mononuclear, bis(triflate) complex [Ti(NCN)(O-
i-Pr)(OTf)2], 3, contains an η3-meridionally bonded NCN,
η1-O-bonded alkoxy and triflato ligands, and, surpris-
ingly, an η2-O,O′-bonded triflato ligand (Figure 7). The
geometry of 3 can best be described as pentagonal
bipyramidal with the η3-meridionally bonded NCN and
the η2-O,O′-bonded triflato ligands forming the equato-
rial plane (maximum deviation from the least-squares
plane is 0.227(3) Å) while the alkoxy and the η1-O-
bonded triflato ligands occupy apical positions (O(1)-
Ti-O(2) ) 172.89(14)°). The η1-O-bonded alkoxy ligand
shows a remarkable almost linear Ti-O(1)-C(13) bond
angle of 172.4(3)°. The Ti-C bond distance in 3 is again
unaffected by the substitution of the chloro ligand for
the triflato ligand, i.e., a distance of 2.098(5) Å is found,
which is comparable to this distance found in 1b and 2
(vide supra).
To the best of our knowledge 3 is the first structurally
characterized titanium(IV) complex containing an η2-
O,O′-bonded triflato ligand. In addition, the bidentate
bonding mode of the triflato ligand renders the metal
center as a rare example of an organo titanium(IV)
complex containing a seven-coordinate titanium(IV)
center. Only a few other organo titanium complexes
with seven-coordinate metal centers have been re-
ported.23 In addition, several inorganic titanium com-
plexes with seven-coordinate titanium centers are known
as, for example, the dimeric titanium tartrate complex
[Ti2(DIPT)3{ON(CH2Ph)2}2] (DIPT) ) (R,R)-diisopropyl-
tartrate), prepared and characterized by Sharpless et
al.24
In the triflate complexes 2 and 3 the alkoxy ligand is
positioned trans to an electron-withdrawing triflato
ligand, allowing for a stronger M-O(alkoxy) interaction
as compared with 1a (cf. M-O-C bond angles of 149.22-
(18)° in 1a and 157.2(4)° and 172.4(3)° in 2 and 3,
respectively). A trans alkoxy-triflato orientation can
only be accommodated by the titanium center when
NCN is η3-meridionally coordinated. In addition, an η3-
meridional bonding mode generally allows shorter M-N
bond distances, i.e., 2.24 Å (mean) and 2.32 Å (mean)
in 2 and 3, respectively, vs 2.40 Å (mean) in 1a , which
is in line with an enhanced Lewis acidic titanium(IV)
center in 2 and 3. In contrast to these substantial
changes in the Ti-N bond distances, the Ti-Cipso
distance seems unaffected (Table 3). Similar observa-
The Ti-O(alkoxy) bond distances in 1a (1.765(2) Å),
2 (1.731(3) Å), and 3 (1.730(3) Å) are comparable to
these distances found in related complexes (e.g., 1.750-
(2) Å in [{CpTiCl2}2(OCMe2CMe2O)]25 and 1.77(2) Å in
[{CpTiCl2}2O]26). However, it is worthwhile noting that
the Ti-O(alkoxy) bond distance in 2 and 3 is signifi-
cantly shorter than this distance in 1a and other related
(23) (a) Andras, M. T.; Duraj, S. A. Inorg. Chem. 1993, 32, 2874.
(b) Gomez-Sal, P.; Royo, B.; Royo, P.; Serrano, R.; Saez, I.; Martinez-
Carreras, S. J . Chem. Soc., Dalton Trans. 1991, 1575. (c) Scherer, O.
J .; Swarowsky, H.; Wolmershauser, G.; Kaim, W.; Koflman, S. Angew.
Chem., Int. Ed. Engl. 1987, 26, 1153. (d) Zank, G. A.; J ones, C. A.;
Rauchfuss, T. B.; Rheingold, A. L. Inorg. Chem. 1986, 25, 1886. (e)
Klein, H.-P.; Thewalt, U. J . Organomet. Chem. 1982, 232, 41. (f)
Steffen, W. L.; Chun, H. K.; Fay, R. C. Inorg. Chem. 1987, 17, 3498.
(24) Pedersen, S. F.; Dewan, J . C.; Eckman, R. R.; Sharpless, K. B.
J . Am. Chem. Soc. 1987, 109, 1279.
(25) Huffman, J . C.; Moloy, K. G.; Marsella, J . A.; Caulton, K. G. J .
Am. Chem. Soc. 1980, 102, 3009.
(26) Thewalt, V.; Schomburg, D. J . Organomet. Chem. 1977, 127,
169.
(27) (a) Coffindaffer, I. W.; Rothwell, I. P.; Huffmann, J . C. Inorg.
Chem. 1983, 22, 2906. (b) Reger, D. L.; Tarquini, M. E.; Lebioda, L.
Organometallics 1983, 2, 1763. (c) Lubben, T. V.; Wolczanski, P. T.;
van Duyne, G. D. Organometallics 1984, 3, 977. (d) Nadashi, T. T.;
Stephan, D. W. Can. J . Chem. 1991, 69, 167.

Novel Aryltitanium(IV) Complexes
Organometallics, Vol. 16, No. 19, 1997 4181
tions have been made earlier in other NCN-containing
compounds.13a
Besides electronic factors, also steric factors affect the
molecular geometry of these complexes. To accom-
modate the triflato ligand, a sterically more demanding
ligand as compared with a chloro ligand, a more obtuse
N-Ti-N bond angle is observed in 2 and 3 (Table 3),
resulting in an η3-meridionally coordinated NCN ligand.
The substitution of the second chloro ligand for a triflato
ligand places the NMe2 moieties of 3 in close proximity
to the oxygen atoms of the η2-O,O′-coordinated triflato
ligand. This is obvious from the short N-methyl C-H‚‚‚O
contacts (H‚‚‚O ) 2.31 Å (mean), C‚‚‚O ) 2.80 Å (mean))
and the C-H‚‚‚O bond angle of 109° (mean) found in 3.
The latter interactions could explain the slightly longer
Ti-N distances in 3 (2.32 Å (mean)) as compared to
these distances in 2 (2.24 Å (mean)).
Interestingly, the structural features of the η1-
coordinated triflato ligand in 2 and 3 strongly resemble
those of the bonding arrangement in the free anion.28
The S-O(3) and S-O(4) bond distances (1.43 Å mean)
are similar to the corresponding three sulfur-oxygen
bond distances in the free anion (1.43 Å mean). The
longer S-O(2) bond distance of 1.47 Å of the η1-bonded
oxygen atom falls in the range 1.44-1.50 Å observed
for this bond distance in other structurally related
complexes with η1-O-triflato bonding modes.29 The
elongated S-O(2) bond distance compared to the bond
distances found for S-O(3) and S-O(4) points to a
reduction in the S-O(2) bond order and hence in an
increase in the Ti-O(triflato) bond order. This increase
in bond order together with a Ti-O(triflato) bond
distance which is significantly shorter than the sum of
the van der Waals radii30 points to a covalently bonded
triflato ligand to the titanium center. Although the Ti-
O(triflato) bond distance (2.093(3) Å) is slightly longer
than that found in [(1,3-C5H3(SiMe3)2)Ti(CF3COCHCO-
CF3)2OTf] (2.018(5) Å)31 and [Cp2Ti(OTf)2] (2.003(7) Å),32
and therefore does not seem to support this conclusion,
a rather covalent Ti-O(triflato) bond would explain the
observation that our attempts to replace the triflato
ligands in 2 and 3 by other Lewis bases were not
successful (vide infra).
F igu r e 8. Proposed dimeric structure bis(triflato)(NCN)-
titanium(IV) complex 3.
bimetallic η2-O,O′-bridging bonding mode of triflato
ligands has been encountered for example in [{Cu4-
(OH)4(OTf)2(N(C5H5N)3)4}2+ 33 and [Me2Sn(OTf)2].34 All
]
other bond distances and angles found in the η2-O,O′-
bonded triflato ligand are comparable to those found in
the η1-O-bonded triflato ligand.
Rea ctivity of NCN-Tita n iu m Com p lexes. It was
shown by Thewalt et al. that the dissolved triflate
complexes [Cp2Ti(OTf)2] and [(C5Me5)2Ti(OTf)2] readily
form cationic species upon addition of Lewis bases like
THF, acetonitrile, DMF, or bipy.32 In contrast to these
observations, the (NCN)titanium(IV) triflate complexes
2 and 3 showed (1H NMR) no interaction with any of
these Lewis bases. Also mixtures of the dichloride
complex 1a and the bis(triflate) complex 3 in a 1:1 molar
ratio in polar or nonpolar solvents did not compropor-
tionate to the monotriflate complex 2. This leads us to
conclude that the (triflato)(NCN)titanium(IV) complexes
2 and 3 do not form cationic species in solution.
Apparently, the triflato ligands in 2 and 3 are strongly
bonded to titanium, which is in line with a high Lewis
acidity of the metal center.
Preliminary studies have been performed to investi-
gate the reactivity of the new (NCN)titanium(IV) com-
plexes as catalysts or catalyst precursors in well-known
titanium-mediated or -catalyzed organic reactions. As
the (NCN)titanium(IV) complexes were shown to be
Lewis acids with a stable and defined geometry, they
might be interesting precursors for Lewis acid catalyzed
organic reactions. The dichloride complex 1a , the bis-
(triflate) complex 3, and the methyl complex 4 were
shown to be catalytically active in the 1,2-addition
reaction of Et2Zn to benzaldehyde in toluene at room
temperature. After 3 h, 3 showed full conversion of
benzaldehyde into 1-phenyl-1-propanol while 1a and 4
gave full conversion after 5 h.35 This is in line with the
enhanced Lewis acidity of 3 as compared with 1a and
4. The nontransferability of the NCN ligand and the
presence of organometallic species during the catalytic
reaction became evident when the reaction mixture was
quenched with D2O. After acidic workup of the aqueous
phase, all NCN was recovered as its monodeuterio
derivative.
Similar arguments apply for the η2-O,O′-bonded tri-
flato anion in 3, which likewise cannot be substituted
by other nucleophiles (vide infra), indicating that this
η2-O,O′-bonded triflato ligand is covalently bonded to
the titanium(IV) center as well. The results of the
molecular weight determinations of 2 and 3 also cor-
roborate this conclusion. Whereas 2 is mononuclear, 3
seems to exist in benzene as a monomer at low concen-
tration while a monomer-dimer equilibrium exists at
higher concentrations. Dimer formation most likely
involves η2-bridging triflato ligands, thereby creating
two seven-coordinate titanium centers (Figure 8). This
No activity was observed for these neutral (NCN)-
titanium(IV) complexes in the Ziegler-Natta polymer-
ization of R-olefins.36
(28) (a) Cragel, J ., J r.; Pett, V. B.; Glick, M. D.; DeSimone, R. E.
Inorg. Chem. 1978, 17, 2885. (b) DeSimone, R. E.; Glick, M. D. Ibid.
1978, 17, 3574. (c) Peng, S.-M.; Ibers, J . A.; Millar, M.; Holm, R. H. J .
Am. Chem. Soc. 1976, 98, 8037. (d) For a review on coordinated
triflate, see: Lawrance, G. A. Chem. Rev. 1986, 86, 17.
(29) Frauenhoff, G. R.; Wilson, S. R.; Shapley, J . R. Inorg. Chem.
1991, 30, 78 and references cited.
(33) Dedert, P. L.; Sorrell, T.; Marks, T. J .; Ibers, J . A. Inorg. Chem.
1982, 21, 3509.
(34) Allen, F. A.; Lerbscher, J .; Trotter, J . J . Chem. Soc. A 1971
2507.
(35) The observed rates and selectivities are generally observed for
titanium(IV)-catalyzed 1,2-addition and Diels-Alder reactions. Reetz,
M. T. In Organotitanium Reagents in Organic Synthesis; Springer-
Verlag: Berlin, 1986.
(30) Bondi, A. J . Phys. Chem. 1964, 68, 441 (or covalent radius +
0.8 Å when not given).
(31) Winter, C. H.; Zhou, X.-X.; Heeg, M. J . Organometallics 1991,
10, 3799.
(32) Honold, B.; Thewalt, U. J . Am. Chem. Soc. 1986, 316, 291 and
references cited therein.
(36) Piloting experiments indicate that analogous (NCN)titanium-
(III) complexes, derived from 1a by a reduction with magnesium
amalgam, are active as catalyst precursors in the polymerization of
ethene and propene.

4182 Organometallics, Vol. 16, No. 19, 1997
Donkervoort et al.
ature for another 30 min. The crude product was isolated by
centrifugation of the reaction mixture and decantation of the
toluene fraction. The remaining solid was extracted with C6H6
(4 × 75 mL), after which the solvent from the combined organic
fractions was evaporated in vacuo. The obtained yellow/green
powder was washed with pentanes (3 × 25 mL) and dried in
vacuo to give 1a as a pale yellow powder (13.57 g, 74%).
Yellow needles, suitable for X-ray analysis, were obtained by
cooling a saturated solution of 1a in toluene to -20 °C for 3
days. Mp: 115 °C. Anal. Calcd for C15H26Cl2N2OTi: C, 48.80;
H, 7.10; N, 7.59. Found: C, 48.88; H, 7.04; N, 7.49. 1H NMR
(C6D6): 6.88 (t, J ) 7.40 Hz, 1H, ArH), 6.61 (d, J ) 7.40 Hz,
2H, ArH), 5.88 (sp, 3J ) 6.22 Hz, 1H, OCH), 1.22 (d, 3J ) 4.96
Hz, 6H, OCH(CH3)2). 13C{1H} NMR (C6D6): 206.5 ({Ar}CTi),
128.9-122.6 ({Ar}C), 86.6 (OCH), 25.3 (OCH(CH3)2). In
addition, see Table 1.
Con clu sion s
The results presented in this paper show that with
the terdentate-bonded NCN ligand new (NCN)titanium-
(IV) complexes containing chloro, methyl, or triflato
ligands are easily accessible in high yields. The versa-
tile bonding properties of the NCN ligand were il-
lustrated by the isolation of (NCN)titanium(IV) com-
plexes containing either an η3-meridionally or η3-
pseudofacially bonded NCN ligand.
The η3-meridional bonding mode of NCN led to the
isolation of novel (NCN)titanium(IV) triflate complexes
in which not only an η1-O-bonded triflato ligand was
observed but also an η2-O,O′-bonded triflato ligand,
unprecedented in early transition metal complexes. The
latter complex is, to the best of our knowledge, the first
structurally characterized seven-coordinate aryltita-
nium(IV) complex. The preparation of the (NCN)-
titanium(IV) bis(triflate) shows that the use of NCN can
lead to new complexes which exhibit interesting novel
structural features due to the complementary behavior
of the coordination chemistry of NCN compared to Cp.
Both (NCN)titanium(IV) triflate complexes were shown
to have enhanced Lewis acidic metal centers resulting
in remarkably strong covalently bonded triflato ligands.
As a result of this strong binding, no cationic species
were formed upon addition of Lewis bases.
Test experiments showed the (NCN)titanium(IV)
complexes to be catalytically active in the 1,2-addition
reaction of Et2Zn to benzaldehyde. As the NCN ligand
is acting as a nontransferable ligand and was shown to
be chemically inert during catalysis, new enantioselec-
tive catalysts are accessible with the use of chiral NCN
analogues.
3
3
P r ep a r a t ion of [TiCl2{C6H 3(CH 2NMe2)2-2,6}(OC6H 4-
OMe-4)], 1b. Following the same procedure as for 1a using
TiCl4 (21.19 mmol), Ti(OC6H4(OMe-4))4 (7.06 mmol), and [Li-
(NCN)]2 (14.13 mmol) resulted in 10.27 g (84%) of 1b as a dark
red powder. Mp: 117-118 °C. Anal. Calcd for C19H26Cl2N2O2-
Ti: C, 52.68; H, 6.05; N, 6.47. Found: C, 52.53; H, 6.08; N,
3
6.50. 1H NMR (C6D6): 7.05 (d, J ) 6.78 Hz, 2H, ArH), 6.90
(t, 3J ) 7.09 Hz, 1H, ArH), 6.60 (m, 4H, OC6H4OCH3), 3.24 (s,
3H, OCH3). 13C{1H} NMR (C6D6): 155.7 ({Ar}CO), 146.2
({Ar}C), 129.6-127.6 ({Ar}C), 122.5, 120.6, and 114.3 ({Ar}-
C), 55.1 (OCH3). In addition, see Table 1. The ({Ar}CTi)
carbon atom was not observed due to the low solubility of 1b
in benzene.
P r epar ation of [TiCl{C6H3(CH2NMe2)2-2,6}(OCHMe2)(O3-
SCF 3)], 2. To a vigorously stirred solution of 1a (1.65 mmol)
in C6H6 (25 mL) was added CuOTf (1.65 mmol), after which
stirring was continued for 45 min. After centrifugation of the
reaction mixture and decantation of the organic layer, the
remaining solid was extracted with C6H6 (3 × 25 mL). The
solvent from the combined organic fractions was evaporated
The (NCN)titanium(IV) dichloride complex 1a was
also shown to be a starting complex for the preparation
of related (NCN)titanium(III) complexes.36 Further
investigations are underway to identify these species
and investigate their scope and activity in Ziegler-
Natta R-olefin polymerization reactions. Results of
these investigations will be the subject of forthcoming
publications.
in vacuo to give 2 as an orange powder (0.75 g, 94%).
A
saturated solution of 2 in toluene was cooled to -30 °C for 3
days to give orange needles of 2 suitable for X-ray analysis.
Mp: 100-101 °C. The bis(triflate) 3 was always present in
variable amounts in samples of 2, hampering NMR and
elemental analysis. The latter was corrected for the presence
of 14% of 3. Anal. Calcd for C16H26ClF3N2O4STi: C, 38.98;
H, 5.28; N, 5.64. Found: C, 38.88; H, 5.40; N, 5.63. 1H NMR
3
3
(C6D6): 6.87 (t, J ) 7.40 Hz, 1H, ArH), 6.59 (d, J ) 7.20 Hz,
2H, ArH), 4.77 (sp, 1H, OCH), 1.13 (d, 3J ) 7.18 Hz, 6H, OCH-
(CH3)2). 13C{1H} NMR (C6D6): 205.7 ({Ar}CTi), 145.2 ({Ar}-
C), 125.7 and 122.1 ({Ar}CH), 84.7 (OCH), 24.9 (OCH(CH3)2).
In addition, see Table 1.
Exp er im en ta l Section
Gen er a l Com m en ts. All experiments were performed in
a dry nitrogen atmosphere using standard Schlenk techniques.
Solvents were stored over sodium benzophenone ketyl and
distilled prior to use. Elemental analyses were carried out by
H. Kolbe Mikroanalytisches Laboratorium, Mu¨lheim a. d.
P r ep a r a tion of [Ti{C6H3(CH2NMe2)2-2,6}(OCHMe2)(O3-
SCF 3)2], 3. To a solution of 1a (2.52 mmol) in C6H6 (25 mL)
was added AgOTf (5.04 mmol) with vigorous stirring. After
30 min of stirring at ambient temperature the crude product
was isolated by centrifugation of the reaction mixture followed
by decantation of the organic layer. The remaining silver salts
were extracted with C6H6 (2 × 25 mL), after which the solvent
of the combined organic fractions was evaporated in vacuo to
give 3 as an orange solid (1.35 g, 90%). Crystals suitable for
X-ray analysis were obtained by cooling a saturated solution
of 3 in toluene to -30 °C. Mp: 127-128 °C dec. Anal. Calcd
for C17H26F6N2O7S2Ti: C, 34.24; H, 4.39; N, 4.70. Found: C,
34.33; H, 4.31; N, 4.78. 1H NMR (C6D6): 6.88 (t, 3J ) 7.55,
1H, ArH), 6.60 (d, 3J ) 7.5 Hz, 2H, ArH), 4.5 (sp, 3J ) 6.0 Hz,
1H, OCH), 1.0 (d, 3J ) 5.97 Hz, 6H, OCH(CH3)2). 13C{1H}
NMR (C6D6): 207.49 ({Ar}CTi), 145.11 ({Ar}C), 122.04 and
129.31 ({Ar}CH), 87.67 (OCH), 24.67 (OCH(CH3)2). In addi-
tion, see Table 1.
1
Ruhr, Germany; H (200 or 300 MHz) and 13C{1H} (50 or 75
MHz) NMR spectra were recorded on Bruker AC200 or AC300
spectrometers at ambient temperature unless stated other-
wise. The following abbreviations have been used: s, singlet;
d, doublet; t, triplet; m, multiplet; sp, septet; br, broad signal.
37
[Li{C6H3(CH2NMe2)2-2,6}]2 was prepared according to a
literature procedure. All other reagents were commercially
obtained and used as such.
P r ep a r a tion of [TiCl2{C6H3(CH2NMe2)2-2,6}(OCHMe2)],
1a . To a stirred solution of TiCl4 (37.50 mmol) in toluene (250
mL) was added Ti(O-i-Pr)4 (12.50 mmol). The resulting yellow
solution was stirred for 15 min at room temperature, after
which it was cooled to -78 °C. At this temperature a solution
of [Li(NCN)]2 (25.0 mmol) in toluene (250 mL) was added
dropwise in 1 h. The yellow/green mixture was allowed to
warm to room temperature in 1 h and stirred at this temper-
P r ep a r a tion of 3 Sta r tin g fr om 2. To a vigorously stirred
solution of 2 (2.0 mmol) in C6H6 (25 mL) was added AgOTf
(2.0 mmol) at room temperature. The reaction mixture was
(37) J astrzebski, J . T. B. H.; van Koten, G.; Konijn, M.; Stam, C. H.
J . Am. Chem. Soc. 1982, 104, 5490.

Novel Aryltitanium(IV) Complexes
Organometallics, Vol. 16, No. 19, 1997 4183
Ta ble 4. Cr ysta llogr a p h ic Da ta for 1a , 2, a n d 3
1a
2
3
Crystal Data
formula
molecular weight
cryst syst
space group
a, Å
C15H26Cl2N2OTi
369.17
C16H26ClF3N2O4STi
482.79
orthorhombic
Pbca (No. 61)
15.5282(9)
C17H26F6N2O7S2Ti
596.40
monoclinic
P21/c (No. 14)
14.614(2)
9.618(2)
17.483(2)
98.458(9)
2430.6(7)
1.630
monoclinic
P21/c (No. 14)
10.0107(18)
10.3607(11)
17.8448(13)
94.424(12)
1845.3(4)
1.329
b, Å
c, Å
16.4782(14)
16.9143(13)
â, deg
V, Å3
4328.0(6)
1.482
8
D
Z
calc, g cm-3
4
4
F(000)
776
65.9 (Cu KR)
1.48 × 0.23 × 0.20
2000
6.6 (Mo KR)
0.50 × 0.25 × 0.20
1224
6.1 (Mo KR)
1.88 × 0.25 × 0.03
µ, cm-1
cryst size, mm
Data Collection
T, K
295
150
150
θ
min, θmax, deg
2.5, 75.0
1.2, 25.0
1.4, 27.4
SET4 θmin, θmax deg
wavelength, Å
filter/monochromator
scan type
18.27, 23.42 (15 rflns)
1.541 84 [Cu KR]
Ni filter
11.64, 13.85 (25 rflns)
0.710 73 [Mo KR]
graphite mon
ω/2θ
0.71 + 0.35 tan θ
3.00, 4.00
10.37, 13.82 (25 rflns)
0.710 73 (Mo KR)
graphite mon
ω/2θ
0.55 + 0.35 tan θ
1.88, 4.00
ω/2θ
∆ω, deg
0.50 + 0.14 tan θ
horizontal vertical apertures, mm
X-ray exposure time, h
linear instability, %
ref rflns
3.00, 6.00
49
1
22
2
19
18
2h20, 2h2h0, 1h32h
-12:9, -12:0, -22:22
6546
205, 4h2h4, 042
-19:19, 0:20, 0:21
7455
2h17, 4h2h4, 5h22h
-18:13, 0:12, -22:22
7825
data set
total data
total unique data
obsd data
DIFABS corr range
3804 (Rint ) 0.098)
2487 [I > 2.5σ(I)]
0.660, 2.031
3807 (Rint ) 0.059)
3807 [I > -3σ(I)]
5517 (Rint ) 0.080)
5517 [I > -3σ(I)]
Refinement
no. of refined params
210
259
319
final Ra
0.0417 [2487I > 2.5σ(I)]
0.0458
0.0626 [2170I > 2σ(I)]
0.0715 [2937I > 2σ(I)]
b
final Rw
e
final wR2
0.1582
0.1674
goodness of Fit
0.93
0.99
0.95
w-1 d
σ2(F) + 0.000265F2
0.014, 0.077
σ2(F2) + (0.0730P)2
0.000, 0.001
σ2(F2) + (0.0699P)2
0.000, 0.000
(∆/σ)av, (∆/σ)max
min and max
residual density, e Å-3
-0.34, 0.29
-0.32, 0.44
-0.56, 0.52
a
b
2
d
R ) ∑||Fo - |Fc||/∑|Fo|. Rw ) [∑[w(||Fo| - |Fc||)2]/∑[w(Fo2)]]1/2
.
c wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
P ) (Max(Fo2,0) + 2Fc2)/3.
stirred for 1 h at room temperature, after which the same
workup procedure was used as for the preparation of 3 starting
from 1a .
({Ar}C), 127.5, 122.9, and 123.1 ({Ar}CH), 77.6 (OCH), 56.0
and 48.4 (Ti(CH3)), 26.9 (OCH(CH3)2). In addition, see Table
1.
P r ep a r a tion of [TiClMe{C6H3(CH2NMe2)2-2,6}(OCH-
Me2)], 4. A solution of 1a (4.60 mmol) in toluene (50 mL) was
cooled to -78 °C, after which MeLi (2.9 mL of a 1.6 M solution
in Et2O; 4.60 mmol) was added. The reaction mixture was
allowed to warm to room temperature in 1 h. The solvent of
the reaction mixture was removed in vacuo. Extraction of the
obtained brown solid with hexanes (3 × 25 mL), followed by
removal of the solvent in vacuo from the combined organic
fractions, gave 1.58 g of 4 (98%) as a yellow solid. Mp: 104-
106 °C. Anal. Calcd for C16H29ClN2OTi: C, 55.10; H, 8.38;
N, 8.03. Found: C, 54.95; H, 8.30; N, 8.06. 1H NMR (C6D6):
6.95 (t, 3J ) 7.68 Hz, 1H, ArH), 6.71 (d, 3J ) 7.34 Hz, 2H,
ArH), 5.65 (sp, 3J ) 6.20 Hz, 1H, OCH), 1.35 (d, 3J ) 6.16 Hz,
6H, OCH(CH3)2), 0.95 (s, 3H, Ti(CH3)). 13C{1H} NMR (C7D8,
220 K): 196.7 ({Ar}CTi), 141.7 ({Ar}C), 139.6, 118.0, and 117.3
({Ar}OCH), 77.4 (CH), 49.6 (Ti(CH3)), 21.33 and 21.27 (OCH-
(CH3)2). In addition, see Table 1.
Th e 1,2-Ad d ition Rea ction of Et2Zn to Ben za ld eh yd e
Ca ta lyzed by 1a . To a solution of 1a (5 mol %) and
benzaldehyde (2.74 mmol) in toluene (25 mL) was added Et2-
Zn (2.74 mmol), and the mixture was stirred at room temper-
ature for 5 h for complete conversion (as indicated by GC-
MS analysis of a sample of the reaction mixture). The reaction
mixture was hydrolyzed with 50 mL of a 4 M HCl solution.
The organic layer was separated, the water layer was extracted
with Et2O (3 × 25 mL), and the combined organic fractions
were dried on MgSO4 and concentrated in vacuo. The crude
product was purified by flash distillation and identified by
comparing the NMR, GC, and MS data with those of authentic
samples. Yield: 0.40 g (93%). 1-P h en yl-1-p r op a n ol: GC-
MS (relative intensity) m/z 136 (M+, 8); 118 (M+ - H2O, 8);
107 (M+ - C2H5, 100). 1H NMR (CDCl3): 7.4 (m, 5H, ArH),
4.6 (t, 1H, ArCH), 2.7 (br s, 1H, OH), 1.8 (dq, 2H, CH2), 0.95
(t, 3H, CH3). 13C{1H} NMR (CDCl3): 144.8 ({Ar}C), 128.5,
127.6, and 126.3 ({Ar}CH), 76.0 (ArCH), 32.2 (CH2), 10.0 (CH3).
P r epar ation of [TiMe2{C6H3(CH2NMe2)2-2,6}(OCHMe2)],
5. Following the same procedure as for 4 using 1a (4.09 mmol)
and MeLi (5.1 mL of a 1.6 M solution in Et2O; 8.18 mmol) gave
5 (3.60 mmol, 88%) as a yellow, green powder. Mp: 110-112
Th e 1,2-Ad d ition Rea ction of Et2Zn to Ben za ld eh yd e
Ca ta lyzed by 3. A similar procedure as for the 1a -catalyzed
1,2-addition reaction was used, but starting with benzaldehyde
(2.01 mmol), 5 mol % of 3, and Et2Zn (2.01 mmol) in toluene
(25 mL), the reaction mixture was stirred for 3 h for complete
conversion (as indicated by GC-MS analysis of a sample of
the reaction mixture). The workup procedure is identical to
3
°C dec. 1H NMR (C6D6): 7.0 (t, J ) 6.62 Hz, 1H, ArH), 6.8
(d, 3J ) 7.3 Hz, 2H, ArH), 5.3 (sp, 3J ) 6.15 Hz, 1H, OCH),
3
1.42 (d, J ) 6.14 Hz, 6H, OCH(CH3)2), 0.68 (s, 6H, Ti(CH3)).
13C{1H} NMR (C7D8, 215 K): 197.3 ({Ar}CTi), 147.7 and 144.4

4184 Organometallics, Vol. 16, No. 19, 1997
Donkervoort et al.
that for the 1a -catalyzed 1,2-addition reaction, with identical
NMR, GC, and MS data for the product 1-phenyl-1-propanol.
Yield: 0.30 g (92%).
techniques (SHELXL-9344); no observance criteria were applied
during refinement of F2.
Hydrogen atoms were included in the refinement on calcu-
lated positions riding on their carrier atoms. The methyl
hydrogen atoms were refined as a rigid group, allowing for
rotation around the N-C or C-C bonds. All non-hydrogen
atoms were refined with anisotropic thermal parameters. The
hydrogen atoms of 1a were refined with two overall isotropic
displacement parameters. The hydrogen atoms of the other
compounds were included in the refinement with a fixed
isotropic displacement parameter related to the value of the
equivalent isotropic displacement parameter of their carrier
atoms.
Th e 1,2-Ad d ition Rea ction of Et2Zn to Ben za ld eh yd e
Ca ta lyzed by 4. A similar procedure as for the 1a -catalyzed
1,2-addition reaction was used, but starting with benzaldehyde
(4.0 mmol), 5 mol % of 4, and Et2Zn (4.0 mmol) in toluene (25
mL), the reaction mixture was stirred for 5 h for complete
conversion (as indicated by GC-MS analysis of a sample of
the reaction mixture). The workup procedure is identical to
that for the 1a -catalyzed 1,2-addition reaction, with identical
NMR, GC, and MS data for the product 1-phenyl-1-propanol.
Yield: 0.62 g (88%).
For compound 1a the neutral atom scattering factors were
taken from Cromer and Mann,45 anomalous dispersion cor-
rections from Cromer and Liberman.46 For the other com-
pounds neutral atom scattering factors and anomalous dis-
persion corrections were taken from the International Tables
for Crystallography.47 Geometrical calculations and illustra-
tions were performed with PLATON.48 All calculations were
performed on a DECstation 5000.
Cr ysta l Str u ctu r e Deter m in a tion of 1a , 2, a n d 3.
Crystals suitable for X-ray structure determination were either
sealed in a Lindemann-glass capillary and transferred to an
Enraf-Nonius CAD4-F sealed tube diffractometer (1a ) or glued
to the top of a glass fiber and transferred into the cold nitrogen
stream on an Enraf-Nonius CAD4-T diffractometer on a
rotating anode (2 and 3). The crystal of 1a consisted of two
individuals rotated by 4.5° with respect to each other. Ac-
curate unit-cell parameters and an orientation matrix were
determined by least-squares refinement of the setting angles
of a set of well-centered reflections (SET438). The unit-cell
parameters were checked for the presence of higher lattice
symmetry.39 Crystal data and details on data collection are
given in Table 4.
Data were corrected for Lp effects and for the linear decay
of three periodically measured reference reflections during
X-ray exposure time. For compound 1a the standard devia-
tions of the intensities as obtained by counting statistics were
increased according to an analysis of the excess variance of
the reference reflections: σ2(I) ) σ2cs(I) + (0.021I)2.40 An
empirical absorption correction (DIFABS41) was applied for
compound 1a .
Ack n ow led gm en t. This work was supported in part
(J .G.D., N.V., A.L.S.) by the Netherlands Foundation
of Chemical Research (SON) with financial aid from the
Netherlands Organization for Scientific Research (NWO).
Su p p or tin g In for m a tion Ava ila ble: Further details of
the structure determinations, including atomic coordinates,
bond lengths and angles, and thermal parameters for 1a , 2,
and 3 (18 pages). Ordering information is given on any current
masthead page.
OM970374+
(42) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garc´ıa-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF program system. Technical report of the Crystallography
Laboratory; University of Nijmegen: Nijmegen, The Netherlands,
1992.
(43) Sheldrick, G. M. SHELX76 Program for crystal structure
determination; University of Cambridge: Cambridge, England, 1976.
(44) Sheldrick, G. M. SHELXL-93 Program for crystal structure
refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(45) Cromer, D. T.; Mann, J . B. Acta Crystallogr. 1969, A24, 321.
(46) Cromer, D. T.; Liberman, D. J . Chem. Phys. 1970, 53, 1891.
(47) Wilson, A. J . C., Ed. International Tables for Crystallography;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C.
All structures were solved by automated Patterson methods
and subsequent difference Fourier techniques (DIRDIF-9242).
Refinement on F was carried out by full-matrix least-squares
techniques (SHELX7643) for compound 1a . The other com-
pounds were refined on F2 using full-matrix least-squares
(38) de Boer, J . L.; Duisenberg, A. J . M. Acta Crystallogr. 1984, A40,
C410.
(39) Spek, A. L. J . Appl. Crystallogr. 1988, 21, 578.
(40) McCandlish, L. E.; Stout, G. H.; Andrews, L. C. Acta Crystallogr.
1975, A31, 245.
(41) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(48) Spek, A. L. Acta Crystallogr. 1990, A46, C34.