Experimental and DFT Studies of cationic imido titanium alkyls: Agostic interactions and C-H bond and solvent activation reactions of isoiobal analogues of group 4 metallocenium cations

Article abstract of DOI:10.1021/om060096r

Synthesis, reactions, and DFT studies of macrocycle-supported imido titanium alkyl cations derived from Ti(N^tBu)(Me₃[9] aneN₃)R₂ (R = Me (1) or CH₂SiMe₃ (2)) are described (Me₃[9]aneN₃ = 1,4,7- trimethyltriazacyclononane). Reaction of 1 with 1 equiv of [Ph ₃C][BAr₄^F] or BAr₃^F (Ar^F = C₆F₅) in C₆D₅Br afforded the methyl cation [Ti(N^tBu)(Me₃[9]aneN ₃)Me]⁺ (6⁺), whereas with half an equivalent of [Ph₃C][BAr₄^F] the fluxional methyl-bridged homo-binuclear cation [Ti₂(N^tBu)₂(Me ₃[9]aneN₃)₂Me₂(μ-Me)] ⁺ (10⁺) was formed. Reaction of 1 with [Ph ₃C][BAr₄^F] in CD₂C1₂ formed the monochloride cation [Ti(N^tBu)(Me₃[9]aneN ₃)Cl]⁺ (8⁺), which was also prepared from Ti(N^tBu)(Me₃[9]aneN₃)Cl(Me) and [Ph ₃C][BAr₄^F]. Cation 8⁺ reacted with pyridine to give the adduct [Ti(N^tBu)(Me₃[9]aneN ₃)Cl(py)]⁺ (9⁺) and with Ti(N ^tBu)(Me₃[9]aneN₃)Me₂ to form the chloride-bridged cation [Ti₂(N^tBu)₂(Me ₃[9]aneN₃)_2- Me₂(μ-Cl)] ⁺ (11⁺). Reaction of 2 with [Ph₃C][BAr ₄^F] gave [Ti(N^tBu)(Me₃[9]aneN ₃)(CH₂SiMe₃)]⁺ (7⁺), which is stabilized by a β-Si-C agostic interaction characterized by a high-field-shifted ²⁹Si NMR resonance. Attempts to generate 7 ⁺ by reaction of 2 with [PhNMe₂H][BAr₄ ^F] in CH₂C1₂ led to Ti(N^tBu)(Me ₃[9]aneN₃)Cl₂ and [PhNMe₂(CH ₂Cl)][BAr₂^F] (12-BAr₄^F) via a series of solvent activation reactions, the details of which have been elucidated. Reaction of 6⁺ or 7⁺ with Ph₃PO afforded the adducts [Ti(N^tBu)(Me₃[9]aneN ₃)R(Ph₃PO)]⁺, whereas with pyridine a C-H bond activation reaction occurred to give Ti(N^tBu)(Me₃[9] aneN₃(NC₅H₄)]⁺ (17⁺) and the corresponding alkane RH. Density functional theory calculations of the isolobal d⁰ fragments [Ti(NR)(R′₃[9]aneN ₃)]²⁺ and [Cp₂Ti]²⁺ found that their frontier orbitals, although broadly similar, featured important differences in their shapes and energies. These account for the absence of any α-C-H agostic interaction in 6⁺, whereas [Cp₂TiMe]⁺ is stabilized by a weak interaction of this type as judged by DFT-computed geometries. The experimentally observed increase in Ti-Me group average ¹J_CH on forming either 6⁺ from 1 or [Cp ₂TiMe]⁺ from Cp₂TiMe₂ is reproduced by DFT and attributed to intrinsic global changes in carbon 2s orbital contribution to the Ti-C and C-H bonds upon cation formation. These changes were shown to mask the otherwise expected decrease in average ¹J _CH for the α-agostic methyl in [Cp₂TiMe] ⁺. The difference between the Ti-Me ¹J_CH values in 1 (111 Hz) and isolobal Cp₂TiMe₂ (124 Hz) was also attributed to differences in Ti center electrophilicity. The experimental high-field-shifted ²⁹Si NMR resonance in 7⁺ was well reproduced in the DFT-computed β-Si-C agostic structure, and upper and lower limits for the strength of the agostic interaction were estimated. An NBO analysis of the Ti-CH₂SiMe₃ bonding found several different contributions, including negative hyperconjugation (population of σ*(Si_β-C_γ)) and formal C _α-Si_β→Ti and Si_β-C _γ→Ti bond pair donation.

Full text of DOI:10.1021/om060096r

2806
Organometallics 2006, 25, 2806-2825
Experimental and DFT Studies of Cationic Imido Titanium Alkyls:
Agostic Interactions and C-H Bond and Solvent Activation
Reactions of Isolobal Analogues of Group 4 Metallocenium Cations
Paul D. Bolton,† Eric Clot,*,‡ Nico Adams,† Stuart R. Dubberley,† Andrew R. Cowley,† and
Philip Mountford*,†
Chemistry Research Laboratory, UniVersity of Oxford, Mansfield Road, Oxford OX1 3TA, U.K., and
LSDSMS (UMR CNRS 5636), Institut Charles Gerhardt, cc 14, UniVersite´ Montpellier 2,
34095 Montpellier Cedex 5, France
ReceiVed January 31, 2006
Synthesis, reactions, and DFT studies of macrocycle-supported imido titanium alkyl cations derived
from Ti(NtBu)(Me3[9]aneN3)R2 (R ) Me (1) or CH2SiMe3 (2)) are described (Me3[9]aneN3 ) 1,4,7-
trimethyltriazacyclononane). Reaction of 1 with 1 equiv of [Ph3C][BArF ] or BArF (ArF ) C6F5) in
4
3
C6D5Br afforded the methyl cation [Ti(NtBu)(Me3[9]aneN3)Me]+ (6+), whereas with half an equivalent
of [Ph3C][BArF ] the fluxional methyl-bridged homo-binuclear cation [Ti2(NtBu)2(Me3[9]aneN3)2Me2(µ-
4
Me)]+ (10+) was formed. Reaction of 1 with [Ph3C][BArF ] in CD2Cl2 formed the monochloride cation
4
[Ti(NtBu)(Me3[9]aneN3)Cl]+ (8+), which was also prepared from Ti(NtBu)(Me3[9]aneN3)Cl(Me) and
[Ph3C][BArF ]. Cation 8+ reacted with pyridine to give the adduct [Ti(NtBu)(Me3[9]aneN3)Cl(py)]+ (9+)
4
and with Ti(NtBu)(Me3[9]aneN3)Me2 to form the chloride-bridged cation [Ti2(NtBu)2(Me3[9]aneN3)2-
Me2(µ-Cl)]+ (11+). Reaction of 2 with [Ph3C][BArF ] gave [Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)]+
4
(7+), which is stabilized by a â-Si-C agostic interaction characterized by a high-field-shifted 29Si
NMR resonance. Attempts to generate 7+ by reaction of 2 with [PhNMe2H][BArF ] in CH2Cl2 led to
4
Ti(NtBu)(Me3[9]aneN3)Cl2 and [PhNMe2(CH2Cl)][BArF ] (12-BArF ) via a series of solvent activation
4
4
reactions, the details of which have been elucidated. Reaction of 6+ or 7+ with Ph3PO afforded the
adducts [Ti(NtBu)(Me3[9]aneN3)R(Ph3PO)]+, whereas with pyridine a C-H bond activation reaction
occurred to give [Ti(NtBu)(Me3[9]aneN3)(NC5H4)]+ (17+) and the corresponding alkane RH. Density
functional theory calculations of the isolobal d0 fragments [Ti(NR)(R′3[9]aneN3)]2+ and [Cp2Ti]2+ found
that their frontier orbitals, although broadly similar, featured important differences in their shapes and
energies. These account for the absence of any R-C-H agostic interaction in 6+, whereas [Cp2TiMe]+
is stabilized by a weak interaction of this type, as judged by DFT-computed geometries. The experimentally
1
observed increase in Ti-Me group average JCH on forming either 6+ from 1 or [Cp2TiMe]+ from
Cp2TiMe2 is reproduced by DFT and attributed to intrinsic global changes in carbon 2s orbital contribution
to the Ti-C and C-H bonds upon cation formation. These changes were shown to mask the otherwise
1
expected decrease in average JCH for the R-agostic methyl in [Cp2TiMe]+. The difference between the
1
Ti-Me JCH values in 1 (111 Hz) and isolobal Cp2TiMe2 (124 Hz) was also attributed to differences in
Ti center electrophilicity. The experimental high-field-shifted 29Si NMR resonance in 7+ was well
reproduced in the DFT-computed â-Si-C agostic structure, and upper and lower limits for the strength
of the agostic interaction were estimated. An NBO analysis of the Ti-CH2SiMe3 bonding found several
different contributions, including negative hyperconjugation (population of σ*(Siâ-Cγ)) and formal
CR-SiâfTi and Siâ-CγfTi bond pair donation.
of academic and industrial interest. Of particular relevance to
this contribution is the ability of certain transition metal imido
compounds (general type LnMdNR) to act as olefin polymer-
ization catalysts.11 The first catalysts of this type were bis-
(imido)chromium dichloride and dialkyl compounds Cr(NR)2X2
Introduction
Homogeneous group 4 metallocene,1-5 constrained geometry,6
and a wide variety of “post-metallocene”7-10 Ziegler-Natta type
olefin polymerization catalysts have been a continuing focus
t
i
(R ) Bu or 2,6-C6H3 Pr2; X ) Cl, Me, or CH2Ph),12,13 and
* To whom correspondence should be addressed. E-mail: eric.clot@
univ-montp2.fr; philip.mountford@chem.ox.ac.uk.
activities of up to 66 kg(PE) mol-1 h-1 bar-1 were reported.
† University of Oxford.
‡ LSDSMS.
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Ed. 1999, 38, 429.
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1493.
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N.; Matsui, S.; Mohri, J.; Furuyama, R.; Terao, H.; Bando, H.; H., T.; Fujita,
T. Chem. Rec. 2004, 4, 137.
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10.1021/om060096r CCC: $33.50 © 2006 American Chemical Society
Publication on Web 04/21/2006

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2807
Figure 1. Isolobal relationships between d0 fragments in transition metal imido chemistry.
NMR evidence for the monobenzyl cation [Cr(NtBu)2(η2-
CH2Ph)]+ (a proposed initiating species in olefin polymerization
by Cr(NtBu)2(CH2Ph)2) was advanced and a PMe3 adduct
identified also by NMR. A notable feature of group 6 bis(imido)
and group 5 cyclopentadienyl-imido catalysts of the type
M(NR)2X2 and CpM(NR)X2, respectively, is their isolobal
relationship14 with the group 4 metallocene-derived systems
Cp2MX2. This arises from the relationships summarized in
Figure 1 for [Cp2M]2+ (M ) group 4), [CpM(NR)]2+ (group
5), and [M(NR)2]2+ (group 6), as has been discussed and
documented elsewhere.15-18
Cl2 are also isolobal analogues of the group 4 metallocenes
Cp2MCl2 (Figure 1).
We have also shown that activation of the dialkyls
Ti(NtBu)(Me3[9]aneN3)R2 (R ) Me (1) or CH2SiMe3 (2)) with
[Ph3C][BArF ] (ArF ) C6F5) gives highly active catalysts for
4
ethylene polymerization, presumably through the formation of
the corresponding alkyl cations [Ti(NtBu)(Me3[9]aneN3)R]+.28
Surprisingly, although a great deal is known about metallo-
cenium and nonmetallocenium alkyl cations (widely accepted
as being the active species in Ziegler-Natta olefin polymeri-
zation),5,30 little has been reported about imido-supported alkyl
cations,28,31-34 or indeed cationic imido compounds in gen-
eral.25,35-40 In this contribution we describe the synthesis, prop-
erties, and Lewis base adducts of tert-butyl imido titanium
monoalkyl cations, along with detailed DFT studies of them
and comparisons with the bis(cyclopentadienyl) isolobal ana-
logue [Cp2TiMe]+. Part of this work has been communicated.41
As part of our broad program in titanium imido chemistry,19-21
we have targeted compounds of the type Ti(NR)(fac-L3)Cl2
(fac-L3 ) triazacyclohexane,22 triazacyclononane,23-25 tris-
(3,5-dimethylpyrazolyl)methane;26,27 (NR)(fac-L3) ) ansa-type
κ4 -coordinated macrocycle-imido ligand23) as potential polym-
erization catalysts. We recently reported a library of ca. 50
1,4,7-trimethyl triazacyclononane (Me3[9]aneN3)-supported im-
ido titanium catalysts Ti(NR)(Me3[9]aneN3)Cl2 in which the
imido N-R substitutent was varied.28 Some of these were the
most active imido-based Ziegler-Natta polymerization cata-
lysts reported to date, with ethylene polymerization productivi-
ties of up to 105 kg(PE) mol-1 h-1 bar-1. Furthermore, since
both a six-electron-donor imido dianion NR2- and a neutral
conical fac-L3 donor29 such as Me3[9]aneN3 are isolobal with
Results and Discussion
Reactions of Ti(NtBu)(Me3[9]aneN3)R2 (R ) Me (1)
or CH2SiMe3 (2)) with BArF or [Ph3C][BArF ]. The di-
3
4
alkyl compounds Ti(NtBu)(Me3[9]aneN3)R2 (R ) Me (1) or
CH2SiMe3 (2)) were prepared as described.28 The new monoalkyl-
monochloride Ti(NtBu)(Me3[9]aneN3)Cl(CH2SiMe3) (3) was
prepared from 2 and Ph3CCl42 (41% recrystallized yield) since
the reaction of Ti(NtBu)(Me3[9]aneN3)Cl2 (4)24 with 1 equiv
of LiCH2SiMe3 gave a mixture of 2 and 3, which could not be
separated by fractional crystallization. The reactions of 1 and 2
with BArF and [Ph3C][BArF ] (ArF ) C6F5) (commonly used
-
the C5H5 monoanion, the compounds Ti(NR)(Me3[9]aneN3)-
(12) Coles, M. P.; Dalby, C. I.; Gibson, V. C.; Clegg, W.; Elsegood, M.
R. J. J. Chem. Soc., Chem. Commun. 1995, 1709.
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3
4
reagents for alkyl anion abstraction43-45) are summarized in
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Chem. Commun. 2001, 705.
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C.; Sealey, A. J.; Selby, J. D.; Zuideveld, M.; Cowley, A. R.; Mountford,
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2808 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
Scheme 1. Reactions of Ti(NtBu)(Me3[9]aneN3)R2 (R ) Me or CH2SiMe3) and Ti(NtBu)(Me3[9]aneN3)Cl(Me) with BArF or
3
[Ph3C][BArF ]a
4
a Anions omitted for clarity.
Scheme 1. Complementary studies with the previously described
Ti(NtBu)(Me3[9]aneN3)Cl(Me) (5)46 are shown in Schemes 1
and 3.
[Ti(NtBu)(Me3[9]aneN3)Cl]+ (8+). Reaction of 1 with BArF
3
in C6D5Br also cleanly gave 6+ and the expected counteranion
side-product [MeBArF ]-. Surprisingly, reaction of 2 with BArF
3
3
in either C6D5Br or CD2Cl2 gave ill-defined mixtures. The NMR
spectra of 6+ were independent of the counteranion (i.e., either
[BArF ]- or [MeBArF ]-), and neither the 1H nor 19F NMR data
4
3
for the [MeBArF ]- anion in 6-MeBArF3 showed any evidence
3
for significant interaction with the cation.47 It is possible,
however, that one or both of the cations 6+ and 7+ are weakly
stabilized by halogenated solvent coordination.36,48-53
The formation of [Ti(NtBu)(Me3[9]aneN3)Me]+ (6+) from
1 and [Ph3C][BArF ] was accompanied by the expected
4
1
Reaction of 1 or 2 with [Ph3C][BArF ] in C6D5Br quantita-
Ph3CMe organic side-product. Unexpectedly, however, the H
4
and 29Si NMR and other data for the organic side-product
tively formed well-defined monoalkyl cations [Ti(NtBu)(Me3-
[9]aneN3)Me]+ (6+) and [Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)]+
(7+), respectively, on an NMR tube scale. The nature of the
organic side-product “Ph3CCH2SiMe3” formed in the synthesis
of 7+ is discussed below. Although reasonably stable in solution
at room temperature, these coordinatively unsaturated, formally
14 valence electron species could be isolated only as adducts
(see below). The 19F NMR spectra showed no evidence for
“Me3SiCH2CPh3” formed in the synthesis of 7+ from 2 and
[Ph3C][BArF ] were more complicated than expected for a single
4
(47) Horton, A. D.; de With, J.; van der Linden, A. J.; van de Weg, H.
Organometallics 1996, 15, 2672.
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125, 5622.
coordination of the [BArF ]- counteranion. Reaction of 2 with
4
[Ph3C][BArF ] in CD2Cl2 also afforded 7+. Remarkably, these
4
(51) Stoebenau, E. J.; Jordan, R. F. J. Am. Chem. Soc. 2003, 125, 3222.
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solutions remained unchanged for several days at room tem-
perature, whereas reaction of 1 with either BArF or [Ph3C]-
3
[BArF ] in CD2Cl2 instantaneously gave the monochloride cation
4
(46) Wilson, P. J. Ph.D. Thesis, Nottingham University, 1999.

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2809
Scheme 2. Likely Fluxional Processes for [Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)]+
Scheme 3. Reaction ofTi(NtBu)(Me3[9]aneN3)Cl(Me) with
[BArF ]. Neither a high-vacuum, short-path distillation nor
4
[Ph3C][BArF ] and Subsequent Trapping of the in
preparative scale HPLC experiment was able to separate the
components of the mixture, which was therefore analyzed by
GC-MS. This confirmed the presence of three species in the
mixture. In order of elution, the first fraction was identified as
4
Situ-Generated [Ti(NtBu)(Me3[9]aneN3)Cl]+ Cationa
1
Ph3CH in accordance with the H and 13C NMR spectra. The
second and third fractions both gave parent ion peaks at m/z
330, corresponding to “[Me3SiCH2CPh3]+”. Although the
fragmentation patterns of each isomer were somewhat different,
most of the fragments could not be identified.
The trigonal bipyramidal structure shown for 6+ in Scheme
1
1 is supported by DFT calculations presented below. The H
NMR spectrum of 6+ in C6D5Br revealed that this five-
coordinate cation is highly fluxional at room temperature. The
Ti-Me and tert-butyl groups appeared as sharp singlets, whereas
the macrocycle methyl groups appeared as a single broad
resonance (9 H) and the methylene protons as two broad
multiplets of relative intensity 6 H each. The presence of two
sets of methylene resonances (i.e., “up” and “down” with respect
to the metal) confirms that the ligand remains bound to the
cationic metal center, but that there is a rapid exchange of all
three N-donor sites on the NMR time scale. Cooling to 248 K
resulted in a broadening of the macrocycle resonances (the
Ti-Me and tert-butyl groups remaining as sharp singlets), but
a slow exchange limiting spectrum could not be obtained before
the freezing point of the solvent was reached.
a Anions omitted for clarity.
species. Thus (in addition to the resonances for 7+) the H
1
Since 6+ is a 14 valence electron monomethyl cation, this
suggests the possibility of R-C-H agostic interactions between
the Ti-Me hydrogens and the metal center.54-56 Interestingly,
however, the Ti-Me 1JCH coupling constant increases slightly
from 111 Hz in the dimethyl precursor 1 (also in C6D5Br) to
116 Hz in 6+. We note that the methyl titanocenium system
NMR spectrum of the reaction mixture featured two singlets at
-0.01 and -0.32 ppm (the expected region for SiMe3 reso-
nances) and two methylene resonances at 2.12 and 2.06 ppm.
The ratio of the SiMe3 to methylene resonance intensities for
each of the two presumed isomers of “Me3SiCH2CPh3” was
9:2. The 1H resonances for each isomer correlated (via a
1H-29Si HMQC (1H-observed) NMR spectrum) to two 29Si
resonances at 0.7 and -1.1 ppm. The ratio of the two isomers
of “Me3SiCH2CPh3” was ca. 2:1. In addition there was also
always a small amount of Ph3CH formed (ca. 15% by integration
compared to “Me3SiCH2CPh3”).
[Cp2TiMe][MeBArF ] has been reported to display an R-agostic
3
interaction on the basis of vibrational spectroscopic studies.56
1
For comparison with the data for 1 and 6+ we measured JCH
for the Ti-Me groups in Cp2TiMe2 (124 Hz) and [Cp2TiMe]-
[BArF ] (129 Hz) in C6D5Br. There is again a small increase in
4
In an attempt to better understand these products, the reaction
of LiCH2SiMe3 with Ph3CCl in benzene was carried out. This
yielded a yellow oil having NMR spectra comparable to those
of organic side-products from the reaction of 2 and [Ph3C]-
(54) Brookhart, M.; Green, M. L. H.; Wong, L.-L. Prog. Inorg. Chem.
1988, 36, 1.
(55) Clot, E.; Eisenstein, O. Struct. Bond. 2004, 113, 1.
(56) Scherer, W.; McGrady, G. S. Angew. Chem., Int. Ed. 2004, 43, 1782.

2810 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
1JCH on going from the neutral dimethyl species to the
corresponding monomethyl cation. Furthermore, both Cp2TiMe2
and [Cp2TiMe]+ possess 1JCH values that are 13 Hz greater than
in the macrocycle-imido analogues. Grubbs has shown previ-
ously that small changes in average Ti-Me group 1JCH values
can in principle be attributed to changes in the effective
electronegativity of a metal center.57 The electronic and mo-
lecular structures of macrocycle-imido and bis(cyclopentadienyl)
titanium methyl compounds are addressed by DFT later on.
The trimethylsilylmethyl cation 7+ is also fluxional on the
NMR time scale at room temperature, but in this case the
fluxional process(es) can be partially “frozen out”. Cooling a
CD2Cl2 sample to 213 K led to the observation of two
macrocycle NMe groups (relative ratio 6 H:3 H, attributed to
those lying cis and trans to the NtBu ligand, respectively). The
CH2SiMe3 ligand methylene and methyl groups still appeared
as broad singlets at 213 K. Notably, the 29Si chemical shift for
7+ in CD2Cl2 (-15.9 ppm) or C6D5Br (-17.5 ppm) is
significantly upfield from that of the neutral dialkyl 2 (-1.8
ppm in CD2Cl2 or -3.1 ppm in C6D5Br). A comparison can
also be made with the monoalkyl-monochloride Ti(NtBu)(Me3-
[9]aneN3)Cl(CH2SiMe3) (3), the 29Si shift of which appears at
-1.8 ppm in CD2Cl2. Horton has reported58 cationic zirconium
vinyl compounds (e.g., [Cp2Zr{C(dCMe2)SiMe3}]+) that pos-
sess agostic Si-Me‚‚‚Zr interactions (supported in one case by
X-ray crystallography) and have associated high-field-shifted
29Si resonances. Eisch has structurally characterized a similar
compound for a titanocenium system, but no 29Si NMR data
were presented.59
Si-Me‚‚‚M interactions are fairly widespread, especially in
neutral group 3 and lanthanide systems, notably for compounds
with CH(SiMe3)2 or N(SiMe3)2 ligands.55,56,60 With regard to
cationic group 4 silyl-alkyl systems we note that Eisch has
advanced spectroscopic evidence for the titanocene trimethyl-
silylmethyl cation [Cp2TiCH2SiMe3]+ as part of an ion pair with
[AlCl4]-.61 Marks has reported that SiMe3 group exchange can
be “frozen out” at low temperature for the bulky CH(SiMe3)2
ligand in the cation [(η-C5H3Me2)2Zr{CH(SiMe3)2}]+ and has
attributed this to either steric congestion or an agostic interac-
tion.62 Very recently, Bochmann, Macchioni, and co-workers
attributed the restricted SiMe3 group rotation in the cations
[{rac-Me2Si(1-Indenyl)2}MCH2SiMe3]+ (M ) Zr or Hf)63 to
an agostic interaction of one of the methyl groups with the metal
centers. For M ) Hf in this latter system the SiMe3 rotation
could be “frozen out”, whereas for M ) Zr the slow exchange
limit could not be reached.63 In none of these cases were 29Si
NMR data reported.
The broad spectrum suggesting Cs symmetry observed at 213
K implies that the â-Si-C agostic interaction is rather weak
and that the likely fluxional processes shown in Scheme 2
(enantiomer interconversion and/or SiMe3 methyl group ex-
change) have low activation energies. However, the fact that
7+ is fairly stable in CD2Cl2 (whereas the methyl cation 6+ is
not) suggests that the â-Si-C‚‚‚Ti interaction (possibly in
conjunction with increased steric protection) nevertheless
provides a significant stabilizing effect. DFT studies of 7+ and
models of the possible transition states/intermediates 7a+ and
7b+ are described below.
Further experiments confirmed the identity of 8+ as the
monochloride cation [Ti(NtBu)(Me3[9]aneN3)Cl]+. The NMR
tube scale reaction of Ti(NtBu)(Me3[9]aneN3)Cl(Me) (5) with
[Ph3C][BArF ] gave clean conversion to 8+ and Ph3CMe.
4
Samples of 8+ made in this way have 1H NMR spectra identical
to those generated above from 1 and [Ph3C][BArF ] in CD2Cl2.
4
Like [Ti(NtBu)(Me3[9]aneN3)Me]+ (6+), five-coordinate 8+ is
highly fluxional at room temperature, with the three macrocycle
methyl groups and the methylene resonances appearing as a
series of broad multiplets, while the tert-butyl group appears
as a sharp singlet. Unlike 6+, however, the low-temperature (213
K) spectrum showed the presence of several tert-butyl and
macrocycle environments. This suggests some degree of dimer-
ization or other aggregation (possibly via µ-Cl or/and µ-NtBu
bridges) at lower temperatures. We note that the neutral and
isolobal analogue “CpTi(NtBu)Cl” exists as an imido-bridged
dimer Cp2Ti2(µ-NtBu)2Cl2 in the solid state64 and that the
chloride-bridged cyclopentadienyl-phosphinimide dication
[Cp2Ti2(NPtBu3)2(µ-Cl)2]2+ has recently been structurally char-
acterized.65 Regardless of the presence of different species
present in solution, addition of pyridine to NMR samples of 8+
gave complete conversion to a single product, namely, the C1-
symmetric, nonfluxional cation [Ti(NtBu)(Me3[9]aneN3)Cl(py)]+
(9+), as indicated by sharp resonances for a nonsymmetric
Me3[9]aneN3 ligand, a terminal tert-butyl imido ligand, and a
coordinated pyridine. The compound 9-BArF4 was isolated on
the preparative scale as an orange crystalline solid in 81%
yield (Scheme 3), and its X-ray crystal structure has been
determined.
The molecular structure of [Ti(NtBu)(Me3[9]aneN3)Cl(py)]+
(9+) is shown in Figure 2, and selected distances and angles
are listed in Table 1. The structure is in agreement with the
NMR data, and the bond lengths and angles around titanium
and associated with the ligands themselves are within the
expected ranges.66,67 There are no unusually close contacts
between the cation and the [BArF ]- anion. The Ti-Cl and
4
Ti-N distances are all slightly shorter than the corresponding
ones in the neutral dichloride Ti(NtBu)(Me3[9]aneN3)Cl2 (4),24
as would be expected from the cationic nature of 9+.
The presence of an otherwise 14 valence electron center in
7+ would provide a driving force for the â-Si-C‚‚‚Ti+
interaction depicted in Scheme 1, and the upfield 29Si NMR
shift appears to be consistent with this. However, a static C1
symmetric structure of the type illustrated should lead to three
independent macrocycle ligand methyl group resonances of
equal intensity and also to three different Si-Me resonances.
Methyl- and Chloride-Bridged Homobimetallic Cations.
Reaction of dimethyl compound 1 with 0.5 equiv of [Ph3C]-
[BArF ] in C6D5Br gave the cationic, methyl-bridged dinuclear
4
species [Ti2(NtBu)2(Me3[9]aneN3)2Me2(µ-Me)]+ (10+, Scheme
1). Reaction with a further half equivalent of [Ph3C][BArF ]
4
gave 6+. Interestingly, 10+ can also be generated in CD2Cl2, in
which it is moderately stable (unlike 6+, which immediately
forms 8+). The cation 10+ is fluxional at room temperature,
(57) Finch, W. C.; Anslyn, E. V.; Grubbs, R. H. J. Am. Chem. Soc. 1988,
110, 2406.
(58) Horton, A. D.; Orpen, A. G. Organometallics 1991, 10, 3910.
(59) Eisch, J. J.; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J.; Lee,
F. L. J. Am. Chem. Soc. 1985, 107, 7219.
(60) Nikonov, G. I. J. Organomet. Chem. 2001, 635, 24.
(61) Eisch, J. J.; Caldwell, K. R.; Werner, S.; Kruger, C. Organometallics
1991, 10, 3417.
(62) Beswick, C. L.; Marks, T. J. J. Am. Chem. Soc. 2000, 122, 10358.
(63) Song, F.; Lancaster, S. J.; Cannon, R. D.; Schormann, M.;
Humphrey, S. M.; Zuccaccia, C.; Macchioni, A.; Bochmann, M. Organo-
metallics 2005, 24, 1315.
(64) Vroegop, C. T.; Teuben, J. H.; van Bolhuis, F.; van der Linden, J.
G. M. J. Chem. Soc., Chem. Commun. 1983, 550.
(65) Cabrera, L.; Hollink, E.; Stewart, J. C.; Wei, P.; Stephan, D. W.
Organometallics 2005, 24, 1091.
(66) Allen, F. H.; Kennard, O. Chem. Des. Autom. News 1993, 8, 1&31.
(67) The United Kingdom Chemical Database Service. Fletcher, D. A.;
McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput. Sci. 1996, 36, 746.

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2811
by a new set of signals. These are assigned to the µ-Cl-bridged
cation [Ti2(NtBu)2(Me3[9]aneN3)2Me2(µ-Cl)]+ (11+), which, like
10+, exists as mixture of diastereomers. This compound
probably forms by dissociation of 10+ into dimethyl 1 and
monomethyl cation 6+, which then immediately converts to
chloride 8+. Trapping of 8+ by 1 would then (after rearrangment
to put the better bridging ligand (i.e., Cl) in the bridging position)
lead to 11+. Conclusive evidence for 11+ was obtained by the
sequential treatment of 5 with [Ph3C][BArF ] (1 equiv, generat-
4
ing 8+) and 1 (Scheme 3). The organometallic product (11+)
of this reaction sequence was identical to that arising from the
slow solvent activation reaction of 10+ in CD2Cl2. Treatment
of dimeric 11+ in CD2Cl2 with [PPN]Cl quantitatively re-formed
5 (PPN+ ) [Ph3PNPPh3]+). Compound 11-BArF4 was isolated
as a yellow solid in 70% yield on the preparative scale according
to Scheme 3.
Reactions of Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2) with
[PhNMe2H][BArF ] in CD2Cl2 and CH2Cl2. N,N-Dialkyl-
4
substituted anilinium salts such as [PhNMe2H][BArF ] are also
4
well-established reagents for the generation of metal cations
Figure 2. Displacement ellipsoid plot (25% probability) of the
cation [Ti(NtBu)(Me3[9]aneN3)Cl(py)]+ (9+). H atoms omitted for
clarity.
from metal-alkyl precursors (via formal protonolysis of a M-C
bond).43 However, reaction of 2 with [PhNMe2H][BArF ] (1
4
equiv) in CD2Cl2 did not afford 7+, but instead gave ca. 50%
conversion to the dichloride Ti(NtBu)(Me3[9]aneN3)Cl2 (4),
together with 1 equiv of SiMe4 (eq 1). The expected side-product
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
[Ti(NtBu)(Me3[9]aneN3)Cl(py)]+ (9+)
Ti(1)-N(3)
Ti(1)-N(6)
Ti(1)-N(9)
Ti(1)-N(1)
2.275(4)
2.244(4)
2.392(3)
1.686(4)
Ti(1)-N(2)
Ti(1)-Cl(1)
N(1)-C(10)
2.277(3)
2.3819(13)
1.451(6)
Cl(1)-Ti(1)-N(3)
Cl(1)-Ti(1)-N(6)
N(3)-Ti(1)-N(6)
Cl(1)-Ti(1)-N(9)
N(3)-Ti(1)-N(9)
N(6)-Ti(1)-N(9)
Cl(1)-Ti(1)-N(1)
N(3)-Ti(1)-N(1)
160.5(1)
89.5(1)
N(6)-Ti(1)-N(1)
N(9)-Ti(1)-N(1)
Cl(1)-Ti(1)-N(2)
N(3)-Ti(1)-N(2)
N(6)-Ti(1)-N(2)
N(9)-Ti(1)-N(2)
N(1)-Ti(1)-N(2)
Ti(1)-N(1)-C(10)
99.45(15)
170.62(16)
91.0(1)
97.98(12)
168.80(13)
92.53(12)
91.42(14)
171.4(3)
78.36(12)
87.32(9)
75.07(12)
76.32(12)
101.11(14)
95.96(16)
but the exchange processes are significantly slowed at 233 K.
At this temperature there are twice as many resonances observed
for 10+ as would be expected for the single Ci-symmetric
structure shown in Scheme 1. The ratio of the two sets of
resonances is ca. 2.1:1.0, and in both cases there are resonances
for bridging (δ 0.26 and 0.30 ppm, intensity 3 H) and terminal
(-0.06 and 0.04 ppm, intensity 6 H) Ti-Me groups. We assign
the two species as diastereomers, which differ in the relative
orientations of the Ti(NtBu)(Me3[9]aneN3)Meterminal fragments
with either trans (as shown in Scheme 1) or cis arrange-
ments of the terminal Ti-Me ligands across the Ti(µ-Me)Ti
bridge. Similar features were reported recently for some meth-
yl-bridged cyclopentadienyl-ketimide68 and -phosphinimide65
homobimetallic cations, and isomeric forms of methyl-bridged
â-diketiminate-supported cations have also been described.69
of the reaction, namely, PhNMe2, was not present among the
reaction products, and instead the cation [PhNMe2(CD2Cl)]+
(12+-d2) was identified from the NMR spectrum and an
electrospray mass spectrum (positive ion mode) of the product
mixture. Reaction of 2 (eq 1) with 2 equiv of [PhNMe2H]-
[BArF ] on an NMR tube or preparative scale gave com-
4
plete conversion to 4 together with formation of 2 equiv of either
[PhNMe2(CD2Cl)][BArF ] (reaction in CD2Cl2) or [PhNMe2-
4
(CH2Cl)][BArF ] (12-BArF , reaction in CH2Cl2) and SiMe4.
The compound [Ti2(NtBu)2(Me3[9]aneN3)2Me2(µ-Me)][BArF ]
4
4
4
(10-BArF ) was successfully isolated in 64% yield on scale-up
4
(70) Bochmann, M.; Lancaster, S. J. Angew. Chem., Int. Ed. Engl. 1994,
33, 1634.
(71) Chen, Y.; Stern, C. L.; Yang, S.; Marks, T. J. J. Am. Chem. Soc.
1996, 118, 12451.
(72) Jia, L.; Yang, Z.; Stern, C. L.; Marks, T. J. Organometallics 1997,
16, 842.
(73) Coles, M. P.; Jordan, R. F. J. Am. Chem. Soc. 1997, 119, 8125.
(74) Bochmann, M.; Green, M. L. H.; Powell, A. K.; Sassmannshausen,
J.; Triller, M. U.; Wocadlo, S. J. Chem. Soc., Dalton Trans. 1999, 43.
(75) Lancaster, S. J.; Bochmann, M. J. Organomet. Chem. 2002, 654,
221.
in C6H5Cl.
Cation 10+ is formally an adduct between 6+ and dimethyl
1. A number of cationic compounds containing {M2Me2(µ-Me)}
units are now known.32,63,65,68-77 The relative stability of 10+
in CD2Cl2 shows that the coordination of 1 to 6+ stabilizes the
monomethyl cation (as mentioned, free 6+ decomposes im-
mediately in CD2Cl2). However, on standing in CD2Cl2,
resonances for 10+ slowly decrease in intensity and are replaced
(76) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc. 2002,
124, 2132.
(77) Mehrkhodavandi, P.; Schrock, R. R.; Pryor, L. L. Organometallics
2003, 22, 4569.
(68) Zhang, S.; Piers, W. E. Organometallics 2001, 20, 2088.
(69) Vollmerhaus, R.; Rahim, M.; Tomaszewski, R.; Xin, S.; Taylor, N.
J.; Collins, S. Organometallics 2000, 19, 2161.

2812 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
Figure 3. (a) Displacement ellipsoid plot (25% probability) of the cation-anion pair [PhNMe2(CH2Cl)][BArF ] (12-BArF ) with H atoms
4
4
omitted for clarity. (b) Intermolecular arrangements in the solid state. Atoms carrying the suffixes “A” and “B” are related to their counterparts
1
1
by the symmetry operators [x, /2-y, z-1/2] and [x, /2-y, z+1/2] respectively.
within error. Numerous structures containing the [BArF ]- anion
Table 2. Selected Distances (Å) and Angles (deg) for
4
[PhNMe2(CH2Cl)][BArF ] (12-BArF )a
have been reported.66,67 However, unlike Choukroun’s com-
4
4
pound, crystals of 12-BArF4 show clear evidence for supramo-
lecular C‚‚‚F interactions between the cations and anions as
illustrated in Figure 3b. Each 12+ cation interacts with two
N(1)-C(1)
1.498(4)
1.516(4)
107.1(3)
105.2(2)
111.5(3)
112.3(2)
N(1)-C(3)
N(1)-C(4)
C(1)-N(1)-C(3)
C(1)-N(1)-C(4)
C(3)-N(1)-C(4)
1.518(4)
1.514(4)
110.5(3)
112.3(2)
110.0(2)
N(1)-C(2)
C(1)-N(1)-C(2)
C(2)-N(1)-C(3)
C(2)-N(1)-C(4)
N(1)-C(3)-Cl(1)
neighboring [BArF ]- anions via a combination of offset face-
4
to-face (interplanar spacing 3.49 Å) and edge-to-face C‚‚‚F
interactions. The closest intermolecular C‚‚‚F distances are in
the range 2.965(3)-3.394(4) Å. Supramolecular interactions
between fluorinated and nonfluorinated rings are well estab-
Closest Intermolecular C‚‚‚F Distances for the
[NPhMe2(CH2Cl)]+ Cation
C(4)‚‚‚F(17)
C(6)‚‚‚F(5)
C(7)‚‚‚F(18)
3.386(3)
3.210(4)
3.394(4)
C(8)‚‚‚F(6A)
C(8)‚‚‚F(18)
C(9)‚‚‚F(6A)
3.386(4)
3.380(4)
2.965(3)
lished, and the contacts in 12-BArF are within previously
4
described ranges.79-82 In addition to Choukroun’s dichlo-
romethane-activation reaction of Cp2VMe2 with [PhNMe2H]-
[BPh4] in CH2Cl2,78 Jordan has reported that the zirconium
a Atoms carrying the suffixes “A” and “B” are related to their
counterparts by the symmetry operators [x, 1/2-y, z-1/2] and [x,
1/2-y, z+1/2], respectively. Interplanar spacing between the cation
phenyl ring [C(4),C(5),C(6),C(7),C(8),C(9)] and the anion ring
[C(28),C(29),C(30),C(31),C(32),C(33)] ) 3.49 Å.
t
alkyl cation [Zr(F6-acen)(CH2 Bu)(PhNEt2)]+ decomposes in
CH2Cl2 to form [PhNEt2(CH2Cl)]+ and the chloride-bridged
cation [Zr2(F6-acen)2(CH2 Bu)2(µ-Cl)]+ (F6-acen ) CF3C(O)-
t
CHC(O)CF3).83 Recently, Stephan has reported phosphine-
based CH2Cl2 solvent activation mediated by transient [CpTi-
The organic product 12-BArF was isolated and the X-ray
4
structure determined.
(NPtBu3)Me(CH2Cl2)]+ to form [(2-C6H4Me)3P(CH2Cl)][BArF ]
A view of the asymmetric unit of 12-BArF is shown in
4
4
Figure 3a, and selected distances and angles are listed in Table
2. The cation 12+ has previously been structurally charac-
terized by Choukroun as its [BPh4]- salt (formed by reaction
of Cp2VMe2 with [PhNMe2H][BPh4] in CH2Cl2).78 The distances
and angles for 12+ in our determination are identical to this
(79) Naae, D. G. Acta Crystallogr. 1979, B35, 2765.
(80) Coates, G. W.; Dunn, A. R.; Henling, L. M.; Ziller, J. W.;
Lobkovsky, E. B.; Grubbs, R. H. J. Am. Chem. Soc. 1998, 120, 3641.
(81) Vangala, V. R.; Nangia, A.; Lynch, V. M. Chem. Commun. 2002,
1304.
(82) Watt, S. W.; Dai, C.; Scott, A. J.; Burke, J. M.; Viney, C.; Clegg,
W.; Marder, T. B. Angew. Chem., Int. Ed. 2004, 43, 3061.
(83) Tjaden, E. B.; Swenson, D. C.; Jordan, R. F.; Petersen, J. L.
Organometallics 1995, 14, 371.
(78) Choukroun, R.; Douziech, B.; Pan, C.; Dahan, F.; Cassoux, P.
Organometallics 1995, 14, 4471.

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2813
Scheme 4. Mechanism for the Double-Solvent Activation Reaction of Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2) on Activation with
a
[PhNMe2H][BArF ] (2 equiv) in CH2Cl2
4
a Anions omitted for clarity.
and the chloride-bridged cations rac- and meso-[Cp2Ti2-
(NPtBu3)2Me2(µ-Cl)]+.65
leads to immediate CH2Cl2 activation, while no corresponding
solvent activation reaction occurs with pyridine (see Scheme 3
and below). Indeed, the adduct formed with 8+ (i.e., 9+) appears
to be indefinitely stable in CH2Cl2 or CD2Cl2. The different
behavior of the two amines may be explained in terms of
their relative nucleophilicities and Lewis basicities as pre-
viously discussed by Jordan for the different reactivities of
A likely reaction pathway leading to 4 and 12+ is given
in Scheme 4. The proposed sequence involves successive
Ti-CH2SiMe3 bond protonolysis and solvent activation steps
(via nucleophilic attack of the PhNMe2 coproduct on a
CH2Cl2 molecule activated by a highly electrophilic 7+ or 8+
cation). To account for the 50% conversion of 2 to 4 in the
[Zr(F6-acen)(CH2 Bu)]+ with the amines NEt3, NEt2Ph,
t
reaction with 1 equiv of [PhNMe2H][BArF ], it is necessary to
NMe2Ph, and NMePh2.83
4
postulate that the reaction of 3 to form 8+ is faster than that of
Reactions of Monoalkyl Cations [Ti(NtBu)(Me3[9]aneN3)R]+
(R ) Me (6+) or CH2SiMe3 (7+)) with Lewis Bases. Reactions
of the in situ-generated monoalkyl cations 6+ and 7+ with
Ph3PO and pyridine are summarized in Scheme 6. The reactions
with Ph3PO formed the simple adducts [Ti(NtBu)(Me3[9]-
aneN3)R(Ph3PO)]+ (R ) Me (14+) or CH2SiMe3 (15+)) in ca.
70-80% isolated yield. These fully characterized products gave
the expected C1-symmetric NMR spectra. The 29Si NMR shift
of -0.7 ppm (CD2Cl2) for 15+ is in the normal range,
confirming that the high-field-shifted value of -15.9 ppm in
7+ is not simply an inductive or similar effect of the overall
positive charge on this cation. Surprisingly, attempts to form
corresponding adducts with THF or PMe3 were unsuccessful,
giving ill-defined mixtures.
2 to form 7+.
Scheme 5 summarizes a series of NMR tube scale reactions
carried out to test the key steps proposed in Scheme 4 for the
double solvent activation reaction. Generation of 7+ in CD2Cl2
(using 2 and [Ph3C]+) followed by addition of PhNMe2 gave
conversion of ca. 50% of the aniline to [PhNMe2(CD2Cl)]+
(12+-d2) and a new organometallic product assigned as
[Ti2(NtBu)2(Me3[9]aneN3)2(CH2SiMe3)2(µ-Cl)]+ (13+). The cat-
ion 13+ is related to Jordan’s [Zr2(F6-acen)2(CH2 Bu)2(µ-Cl)]+
t
and is the direct analogue of the fully characterized µ-Cl-bridged
methyl titanium species 11+ (Scheme 3). Cation 13+ reacts only
very slowly with the remaining PhNMe2. Its formation presum-
ably involves nucleophilic attack by PhNMe2 on the CD2Cl2
solvent (promoted by 7+) to form the monoalkyl-monochloride
product Ti(NtBu)(Me3[9]aneN3)Cl(CH2SiMe3) (3) as proposed
in Scheme 4. However, it appears that when 3 is formed in the
presence of a large excess of unreacted and highly Lewis acidic
7+, it is trapped as the µ-Cl-bridged cation 13+. In agreement
with this hypothesis we found (Scheme 5) that addition of
preformed 3 to alkyl cation 7+ quantitatively formed 13+. The
cationic dimer itself can be cleaved by addition of [PPN]Cl to
form 3. Cation 7+ is therefore competent for CD2Cl2 solvent
activation with PhNMe2, validating the first part of the sequence
proposed in Scheme 4. We also found that reaction of 3 with
[PhNMe2H]+ in CD2Cl2 cleanly formed 4 (Scheme 5) in
accordance with the final part of the sequence proposed in
Scheme 4. Reaction of preformed choride cation 8+ with
PhNMe2 in CD2Cl2 also led to the formation of 12+-d2 and 4,
showing that both the alkyl cation 7+ and the chloride cation
8+ are capable of promoting the solvent activation reaction.
It is interesting to note that addition of PhNMe2 to
[Ti(NtBu)(Me3[9]aneN3)X]+ (X ) CH2SiMe3 (7+) or Cl (8+))
Reaction of cation 6+ with pyridine at low temperature gave
the anticipated adduct [Ti(NtBu)(Me3[9]aneN3)Me(py)]+ (16+)
in 52% isolated yield. Compound 16-BArF has been fully
4
characterized, and its NMR spectra are consistent with a C1-
symmetric cation. Although 16+ is reasonably stable in the solid
state, a new species was cleanly formed after 2 days in solu-
tion at room temperature. This was identified as the cation
[Ti(NtBu)(Me3[9]aneN3)(NC5H4)]+ (17+, Scheme 6), containing
an ortho-metalated pyridine ligand. The NMR tube scale reac-
tion of 7+ with pyridine showed immediate conversion to 17+
with no observation of the expected pyridine adduct [Ti(NtBu)-
(Me3[9]aneN3)(CH2SiMe3)(py)]+. Compound 17-BArF was
4
obtained on a preparative scale from the reaction of pyridine
with in situ-generated 7-BArF . Although it was not possible
4
to obtain an analytically pure sample, the spectroscopic data
were fully consistent with the structure proposed in Scheme 6.
1
The room-temperature H NMR spectrum of 17+ featured
broad resonances in the macrocycle region (3.20-2.50 ppm).
Cooling of the sample to 203 K failed to give a “frozen out”

2814 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
Scheme 5. Reactions Associated with the Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2/[PhNMe2H][BArF ] Solvent Activation Systema
4
a Anions omitted for clarity.
Scheme 6. Reactions of [Ti(NtBu)(Me3[9]aneN3)R]+ (R )
gives rise to two multiplets at 3.07 and 2.94 ppm, corresponding
to methylene protons “up” and “down” with respect to the metal
center, and a broad singlet at 2.60 ppm corresponding to the
N-methyl groups. This is reminiscent of the five-coordinate
methyl cation 6+. Four sharp multiplets at 8.50, 7.97, 7.75, and
7.35 ppm, each of integral 1 H, correspond to the NC5H4 lig-
and. These multiplets showed the expected couplings in a
1H-1H COSY spectrum and, along with the 13C resonances,
are in excellent agreement with those of the metalated pyridine
in [Cp2Zr(NC5H4)(L)]+ (L ) py or THF) reported by Jordan.84
On the basis of this literature precedent and the pronounced
Lewis acidity of the 14 valence electron cations [Ti(NtBu)(Me3-
[9]aneN3)X]+, we favor the 16 valence electron η2-bound isomer
as illustrated (Scheme 6). However, the highly fluxional nature
of this cation indicates that the interaction between the pyridyl
nitrogen and the metal center may be rather weak.
Me or CH2SiMe3) with Ph3PO and Pyridinea
The NMR tube scale reaction of 7+ with pyridine-d5 in
CH2Cl2 formed [Ti(NtBu)(Me3[9]aneN3)(NC5D4)]+ (17+-d4) as
the organometallic product. The 2H NMR spectrum of the
product mixture featured resonances for an ortho-metalated
2-NC5D4 ligand of 17+-d4, together with an additional resonance
at 0.0 ppm (integrating as 1 D with respect to the 2-NC5D4
ligand), which is attributed to the expected side-product
SiMe4-d1.
a Anions omitted for clarity.
spectrum, so spectra were recorded for convenience at 313 K
in the fast exchange limit. At this temperature the macrocycle
(84) Jordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organometallics 1990,
9, 1546.

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2815
Figure 5. Model dicationic model systems compared using DFT
with the chosen coordinate system.
titanocenium systems, but instead to compare the metallocene
and imido-macrocyclic systems using an identical methodology
(DFT (B3PW91)) and basis sets, and to use these results to aid
interpretation of the available experimental observables.
Comparison of the Isolobal Fragments [Cp2Ti]2+ and
[Ti(NMe)(H3[9]aneN3)]2+. The ligands fac-R3[9]aneN3 (R )
H or hydrocarbyl), η5-C5R5-, and RN2- formally donate six
electrons to a metal center through one σ and two π type
interactions. Therefore, as anticipated in Figure 1, the dicationic
macrocycle-imido fragment [Ti(NR)(R3[9]aneN3)]2+ should be
isolobal with [Cp2Ti]2+. However, the spatial details and
energies of the frontier orbitals of these two fragments may be
expected to differ in certain ways (for example, the all-carbon
donor C5R5 ligands also have δ acceptor properties, whereas
the N-coordinated R3[9]aneN3 and RN possess only donor
characteristics). We therefore start our discussion with a
comparison of the two model fragments [Ti(NMe)(H3[9]-
aneN3)]2+ (I) and [Cp2Ti]2+ (II), as illustrated in Figure 5.
In their seminal paper,88 Lauher and Hoffmann used EHT
calculations to describe the frontier orbitals of bis(cyclopenta-
dienyl) complexes Cp2MLn. For d0 metals it was shown that a
C2V bent geometry for the Cp2M fragment was preferred over
the analogous D5h structure with coplanar η-C5H5 rings. The
three lowest unoccupied molecular orbitals (MOs, illustrated
in Figure 6) are ideally suited to bind one or more ligands L in
the equatorial (yz) plane. For the purposes of comparison with
the frontier MOs of I (vide infra), DFT (B3PW91) calculations
were carried out on [Cp2Ti]2+ (II). These yielded results
analogous to those found with EHT, with a minimized C2V bent
structure (ring centroid-Ti-centroid angle ) 138.6°) being 85.1
kJ mol-1 more stable than the corresponding D5h one with
coplanar C5H5 rings, i.e., III. The shapes and energies of the
Figure 4. Model triazacyclononane-imido titanium dialkyl and
monoalkyl systems studied by DFT.
The ortho-metalation of pyridine in this way is reminiscent
of the reaction of the zirconocene methyl cation [Cp2ZrMe-
(THF)]+ with this ligand,84 but contrasts with reports that the
cationic titanocene [Cp2TiMe(py)][BPh4]85 and cyclopentadi-
enyl-phosphinimide species [CpTi(NPtBu3)Me(L)]+ (L ) py,
t
4-NC5H4Et, 4-NC5H4 Bu, 4-NC5H4NMe2)65 are stable in this
regard. We note also that the related neutral compound
Cp*Ti(NtBu)(CH2SiMe3)(py) does not undergo ortho-metala-
tion of the pyridine ligand, and neither does the 14 valence
electron benzamidinate species Ti(NtBu){PhC(NSiMe3)2}-
(CH2SiMe3)(py).86
DFT Studies. The remainder of this contribution focuses
mainly on the electronic and molecular structures and
NMR properties of the monoalkyl cations [Ti(NtBu)(Me3[9]-
aneN3)Me]+ (6+) and [Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)]+
(7+). We are also interested in comparisons with the isolobal
[Cp2TiMe]+ system, for which we have measured 1JCH values.
The model macrocycle-imido alkyl systems used are shown in
Figure 4. Systems with labels carrying the suffix “Q” correspond
exactly to the experimental species (Scheme 1) modeled in full,
whereas those with the labels “q” have the macrocycle and
imido N-substituents Me and tert-butyl replaced by H and Me,
respectively. The systems “q” allow us to probe the underlying
electronic factors, while the computationally more expensive
systems “Q” include the full steric and electronic influences of
the N-donor ligands. We begin with a comparison of the frontier
orbitals of [Cp2Ti]2+ and [Ti(NR)(R3[9]aneN3)]2+ and the basic
structural preferences of the monocationic model hydrido
complexes [Cp2TiH]+ and [Ti(NMe)(H3[9]aneN3)H]+. The
structure and bonding of metallocene compounds of the type
[Cp2MX]n+ (n ) 0, 1; X ) none, H, methyl) have been
extensively studied by a number of computational methods
including extended Hu¨ckel theory (EHT), restricted Hartree-
Fock (RHF), generalized valence bond (GVB), and density
functional theory (DFT), sometimes with contradictory
results.54-56,87-95 The purpose of our studies was not to
re-evaluate or reinvestigate previous computational work on
(87) Green, J. C. Chem. Soc. ReV. 1998, 27, 263.
(88) Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 1729.
(89) Kawamura-Kuribayasbi, H.; Koga, N.; Morokuma, K. J. Am. Chem.
Soc. 1992, 114, 8687.
(90) Ziegler, T.; Folga, E.; Berces, A. J. Am. Chem. Soc. 1993, 115,
636.
(91) Bierwagen, E. P.; Bercaw, J. E.; Goddard, W. A. J. Am. Chem.
Soc. 1994, 116, 1481.
(92) Woo, T. K.; Fan, L.; Ziegler, T. Organometallics 1994, 13, 2252.
(93) Fan, L.; Harrison, D.; Woo, T. K.; Ziegler, T. Organometallics 1995,
14, 2018.
(85) Bochmann, M.; Wilson, L. M.; Hursthouse, M. B.; Short, R. L.
Organometallics 1987, 6, 2556.
(86) Stewart, P. J.; Blake, A. J.; Mountford, P. Organometallics 1998,
17, 3271.
(94) Yoshida, T.; Koga, N.; Morokuma, K. Organometallics 1995, 14,
746.
(95) Green, J. C.; Jardine, C. N. J. Chem. Soc., Dalton Trans. 2001,
274.

2816 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
angle constrained to be 180°) was found to be less stable than
the ground-state structure I, but only by 19.7 kJ mol-1. The
fragment I, bearing π-donor ligands, is therefore easier to distort
from its ground-state geometry than the classical metallocene
II, as already observed by Ziegler on smaller model systems.96
It is likely that the inclusion of sterically demanding R-groups
in [Ti(NR)(R3[9]aneN3)]2+ would destabilize the Cs type struc-
ture I relative to a C3-symmetric alternative of the type IV.
The shapes of three lowest unoccupied molecular orbitals of
I (Figure 7) are, at first sight, generally analogous to those of
the isolobal metallocenium system II (as anticipated from the
isolobal analogy). The LUMO of I is predominantly a non-
Figure 6. C2V-symmetric Cp2M unit, the chosen coordinate system,
and the three lowest unoccupied molecular orbitals that lie in the
yz molecular plane.88
2
2
bonding 3dz -y orbital (see Figure 7 for the definition of the
coordinate system) formally originating from the t2g orbital set
of a σ-only bonded octahedron. The two other members of this
t2g set (3dxz and 3dxy) are pushed up in energy as a result of
strong π-donation from the imido ligand. The LUMO+1 in
Figure 7 (mainly 3dyz) is derived from the eg set of this former
octahedron and stabilized by the formal removal of the two cis
ligands. The orbitals of the cis-divacant octahedral fragment
ML4 have been described previously.97 DFT calculations were
also carried out on the fully N-substituted system [Ti(NtBu)-
(Me3[9]aneN3)]2+ (V). The shapes of the frontier orbitals of V
are the same as those of I, but the incorporation of the electron-
releasing N-alkyl groups clearly leads to a destabilization of
the three frontier orbitals by some 0.7-0.8 eV.
Although the three frontier MOs of [Ti(NMe)(H3[9]aneN3)]2+
(I) and [Cp2Ti]2+ (II) are broadly similar, there are some
important key differences. First, the MOs of II lie globally at
significantly lower energies than those of I or V, making the
latter two fragments much less electrophilic than II. A second
key difference concerns the shapes of the LUMOs and their
energies relative to the LUMO+1 and LUMO+2 levels. For II
the LUMO lies close in energy to the LUMO+1 (difference
ca. 0.1 eV) but some 1.2 eV below LUMO+2. In I and V there
is a more sizable gap between the LUMO and LUMO+1
(0.5-0.6 eV) but a somewhat smaller one between LUMO and
LUMO+2 (0.7-0.8 eV). Furthermore, the LUMO in I and V
is spatially rather well oriented to form a σ bond with a donor
ligand approaching along the molecular z axis, whereas that of
II is rather poor in this regard, as discussed previously.88 In
fact, a better σ overlap is achieved with LUMO+2, the highest
energy of the three frontier orbitals of a d0 Cp2M frag-
ment.88 As a consequence of the particular shapes and energies
of the frontier orbitals, Lauher and Hoffmann predicted (using
EHT) that the model σ donor hydride ligand in hypothetical
[Cp2TiH]+ (VI) would not lie on the molecular C2 rotation axis,
but would move off this axis by an angle (R) of ca. 65° and
hence achieve an optimum overlap/interaction with all three
frontier orbitals of the metallocene unit. Ab initio (GVB)
calculations have confirmed this result for VI.91 In general,
previous calculations for model group 4 metallocenium cations
[Cp2MX]+ (X ) H, Me)89,91,92,94 and cationic constrained
geometry analogues [(η5,η1-C5H4SiH2NH)M-Me]+ (M ) Ti,
Zr)93 have found either a clear bias toward analogous distorted
geometries or that the potential surface toward such a distorted
geometry is rather flat.
Figure 7. Three lowest unoccupied MOs for [Cp2Ti]2+ (II,
left) and [Ti(NMe)(H3[9]aneN3)]2+ (I, right), their corresponding
energies (eV), and the chosen coordinate system. Values for
[Ti(NtBu)(Me3[9]aneN3)]2+ (V) are given in parentheses.
three lowest unoccupied molecular orbitals of II (Figure 7) are
very similar to those obtained at the EHT level and consist
2
2
2
essentially of 3dy (1a1), 3dyz (1b2), and 3dx -z (2a1) orbital
character in the coordinate system chosen.
The optimized geometry of [Ti(NMe)(H3[9]aneN3)]2+ is the
Cs-symmetric structure I illustrated in Figure 5 and is best
described as an octahedron lacking two cis ligands in the yz
plane. However, it can also be compared to that of a “bent
metallocene” if the H3[9]aneN3 and NMe ligands are taken to
formally replace two Cp rings. In this sense it is interesting to
compare the N3 ligand centroid-Ti-Nimide angle of 142.7° in
I with the computed ring centroid-Ti-centroid angle of 138.6°
in minimized II. The C3-symmetric isomer of [Ti(NMe)(H3[9]-
aneN3)]2+ (illustrated as IV in Figure 5) is the isolobal analogue
of the D5h isomer of [Cp2Ti]2+ (III). The DFT-calculated
structure IV (minimized with the N3 ring centroid-Ti-Nimide
As a simple probe of the geometric preferences of a five-
coordinate system [Ti(NR)(R′3[9]aneN3)X]+ (reference points
for studies of the real systems [Ti(NtBu)(Me3[9]aneN3)Me]+
(6+) and [Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)]+ (7+)), we car-
(96) Margl, P.; Deng, L.; Ziegler, T. Top. Catal. 1999, 7, 187.
(97) Albright, T. A.; Burdett, J. K.; Whangbo, M.-H. Orbital Interactions
in Chemistry; Wiley-Interscience: New York, 1985.

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2817
Figure 9. DFT(B3PW91)-optimized geometry for [Cp2TiMe]+
(left) and [Ti(NMe)(H3[9]aneN3)Me]+ (6q, right).
agreement between experimental and calculated structures for
Cp2TiMe2 is also excellent (Table S1), lending further credit to
our computational approach.
Monomethyl Cations: Geometry and Electronic Struc-
tures. The experimental 29Si NMR data for [Ti(NtBu)-
(Me3[9]aneN3)(CH2SiMe3)]+ (7+) (vide supra) indicate strongly
that this otherwise 14 valence electron cation possesses a
â-Si-C‚‚‚Ti agostic interaction. The nature of this interaction
and other aspects associated with 7+ are addressed using DFT
later on. The methyl titanium cation [Ti(NtBu)(Me3[9]aneN3)-
Me]+ (6+) also has a formal 14 valence electron count, assuming
Figure 8. Variation of the relative energies of [Cp2TiH]+ (VI)
and [Ti(NMe)(H3[9]aneN3)H]+ (VII) as the angle R is varied from
-50° to +50°.
ried out a series of calculations on the model hydride cation
[Ti(NMe)(H3[9]aneN3)H]+ (VII), in which the angle R was
varied from -50° to +50° (see Figure 8). For the purposes of
comparison using the same methodology and basis functions,
analogous calculations were performed with DFT for [Cp2TiH]+
(VI). For VI a minimum was found for R ) 42°, which
compares favorably with the value of 65° found by EHT. The
geometry with R ) 42° lies 9.6 kJ mol-1 below that with R )
0° (which in fact corresponds to a transition state). In contrast,
the isolobal cation VII is most stable when R ) 0° (i.e., a
nondistorted trigonal bipyramid), while at R ) 42° it has an
energy some 18 kJ mol-1 above that for R ) 0°. The stability
of VII to distortion is attributed to the more favorable shape of
the LUMO for σ bonding in the z axis direction and the larger
energy between LUMO and the LUMO+1 (note again that the
frontier orbitals of I already lie ca. 2.5 eV above those of II).
Neutral Titanium Alkyl Compounds. The neutral macro-
cycle-imido dialkyl systems (see Figure 4) and Cp2TiMe2 were
computed as reference points for the changes induced by the
cationic nature of the monoalkyls and also to test the accuracy
of our computational strategy since the X-ray structures for both
1 and Cp2TiMe2 are available.28,98 Details of the optimized
geometries are given in Figures S1 (Cp2TiMe2, 1q, 1Q) and S2
(2q, 2Q) and Tables S1 (Cp2TiMe2, 1q, 1Q) and S2 (2q, 2Q)
of the Supporting Information. The agreement between the
experimental and the calculated structures is very good for the
simple model 1q, whereas 1Q presents some deviations for the
least strongly bound ligand, Me3[9]aneN3, which is pushed
further away from the metal center in 1Q than in the experi-
mental system 1. This may be due to the steric repulsions
between the bulky ligands (Me3[9]aneN3 and NtBu) in 1Q
not being compensated for by crystal-packing forces as in the
X-ray structure. However, the bonding situation for the imido
ligand is better reproduced in 1Q than in 1q, with an N-C
bond distance (1, 1.438(3) Å; 1q, 1.423 Å; 1Q, 1.438 Å) and
a Ti-N-C angle (1, 171.5(2)°; 1q, 175.8°; 1Q, 170.1°) in
excellent agreement with the experimental data. Moreover, the
that solvation by C6D5Br or interactions with [BArF ]- are not
4
significant. Hence nonclassical (in this case R-C-H agostic)
interaction(s) might be expected in this species also. However,
it is well-known that low valence electron counts for d0 titanium
compounds are, by themselves, no guarantee for occurrence of
an R-C-H‚‚‚Ti interaction (the classic examples being TiMeCl3
(nonagostic56) and TiMeCl3(dmpe) (R-agostic99)).
We have explored the structure of 6+ and its relationship to
the isolobal [Cp2TiMe]+ using DFT. As mentioned, the methyl
titanocenium system [Cp2TiMe][MeBArF ] has been reported
3
to display an R-agostic interaction on the basis of vibrational
spectroscopic studies.56 Computational studies of group 4
metallocenium89,91,92,94 and related93,95 methyl cations have been
reported before. While the extent of any R-agostic interaction
predicted, and distortion of the methyl group in general,
somewhat depends on the particular model system chosen and
the method of calculation employed, it is generally found that
the associated energies (either against or in favor) are rather
small and typically no more than ca. 10-12 kJ mol-1. The
results we present for Cp2TiMe+ are not inconsistent with these
previous studies.
The geometry of [Cp2TiMe]+ (Figure 9) is typical of a bent
metallocene with one ligand lying in the equatorial plane. Due
to the cationic nature of the complex, all bond distances to Ti
are shorter than in the neutral Cp2TiMe2 (Table S1). At the
DFT (B3PW91) level the geometry of the methyl group in
[Cp2TiMe]+ clearly indicates the presence of an R-agostic
interaction. One C-H bond lies in the equatorial plane and is
tilted toward Ti with a significantly reduced Ti-C-H angle
(83.9° vs 121.4° and 121.3° for the nonagostic C-H bonds).
Moreover, the agostic C-H bond is elongated with respect to
the two others (1.125 vs 1.089 and 1.080 Å). As in [Cp2TiH]+,
the Ti-CMe bond in [Cp2TiMe]+ no longer lies on the molecular
z axis (see above definition), but the departure from the
(99) Dawoodi, Z.; Green, M. L. H.; Mtetwa, V. S. B.; Prout, K.; Schultz,
A. J.; Williams, J. M.; Koetzle, T. F. J. Chem. Soc., Dalton Trans. 1986,
1629.
(98) Thewalt, U.; Wohrle, T. J. Organomet. Chem. 1994, 464, C17.

2818 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
symmetric structure as measured by the R angle is less
pronounced than in [Cp2TiH]+ ([Cp2TiMe]+, R ) 18°;
[Cp2TiH]+, R ) 42°).91
As noted above, globally the MOs of II lie at significantly
lower energies than those of I or V, making the two latter
complexes relatively much less electrophilic. It is therefore
expected that electron transfer from CH3 to the Ti center should
be larger in [Cp2TiMe]+ than in 6q and that the Ti-C bond
has larger covalent character in the former than in the latter.
We have computed the bond dissociation energy (BDE) for
homolytic cleavage of the Ti-C bond for [Cp2TiMe]+, 6q, and
In d0 methyl complexes, the driving force for any deformation
is the increase of the number of nd orbitals used to make bonds
to the methyl group.55,56,100 Upon tilting, some occupied orbitals
of CH3 may interact with the low-lying empty orbitals, es-
sentially of d character, of the metallic fragment. Such a mixing
is efficient only where an empty MO of appropriate symmetry
is close in energy to the occupied MO centered on CH3. This
tilting will be favored only when mixing among the empty
orbitals allows for the main bonding Ti-C interaction to be
preserved. In R-agostic [Cp2TiMe]+, the main bonding interac-
tion for a sp3 lone pair of CH3 is with the 1b2 orbital of
[Cp2Ti]2+ (II) and leads to the computed distorted geometry
(R * 0). The small energy difference between the 1a1 and 1b2
MOs of II allows efficient mixing between them to maintain
efficient overlap with the CH3 lone pair upon tilting. It also
leaves the 1b2 MO more available to accept electron density
from the σ(C-H) bond of CH3 in the equatorial plane, as
previously discussed by Eisenstein and Jean.100 This bonding
pattern is best illustrated by the participation of the CH3 sp3
lone pair and σ(C-H) bond in the LUMO and LUMO+1 of
Cp2TiMe+ (Figure S3 in the Supporting Information). It appears
that it is the requirement for both the sp3 lobe of CH3 and the
in-plane R-agostic C-H to interact with the relevant frontier
MOs of II that provides for a smaller deformation angle R in
[Cp2TiMe]+ (R ) 18°) than in [Cp2TiH]+ (R ) 42°), which
needs only consider the overlap of the isotropic H 1s orbital.
6Q, and the values amount to 153.1, 238.2, and 222.0 kJ mol-1
,
respectively. This is in line with the general observation that
transition metal-carbon bonds have a significant ionic com-
ponent that makes an important contribution to the strength of
the bond. A natural bonding orbital analysis (NBO) points to
the same conclusion with the natural charges on Ti and CH3 in
agreement with a larger ionic character of Ti-C in 6q (Ti, 1.428;
CH3, -0.426) than [Cp2TiMe]+ (Ti, 1.206; CH3, -0.192).
Finally, the weight of the hybrid on C in the σ(Ti-C) NBO is
larger in 6q (76.5%) than in [Cp2TiMe]+ (65.1%) and the
percentage 2s character in the hybrid on C is also larger in 6q
(25.6%) than [Cp2TiMe]+ (22.7%). This confirms the rather
different electronic demands of the Ti centers in the two isolobal
complexes with a larger ionic component in the Ti-C bond of
6q. Such a difference in effective electronegativity of the Ti-
containing fragment should be reflected in different NMR
parameters, as the latter are very sensitive to the actual properties
of the electron density (vide infra).
To estimate the strength of the agostic interactions in
[Cp2TiMe]+ and 6q, the complexes were optimized under the
geometry constraints that all valence Ti-C-H angles were fixed
at a value of 109.5° and the Ti-C bond distance was kept frozen
in the optimal geometry value in order not to introduce energy
contributions associated with varying the Ti-C bond distances.
For [Cp2TiMe]+, the constrained geometry complex was 4.9
kJ mol-1 less stable than the ground-state structure, whereas
for 6q the destabilization was only 1.4 kJ mol-1. These energies
do not reflect solely the strength of the agostic interaction, as
they also contain the energy required to distort the CH3 groups.
This explains why, even though the agostic interaction is
apparently stronger in [Cp2TiMe]+ (as judged by the more
distorted geometry, see Figure 9), the estimated values for the
strength of the agostic interaction are very close. This also
illustrates the difficulty in establishing an unbiased method of
evaluating the strength of any agostic interaction, for by its very
nature this interaction does not involve only donation from a
C-H bond to a transition metal center.55,56
The deformation of the methyl group in [Ti(NMe)(H3[9]-
aneN3)Me]+ (6q, Figure 9) is much less pronounced than in
[Cp2TiMe]+. Nonetheless, one C-H bond lies in the equatorial
plane and is tilted toward Ti with a smaller Ti-C-H angle
than the two other bonds (105.9° vs 115.7° and 113.8°).
However, there is no substantial lengthening of that bond (1.105
Å) with respect to the other values (1.100 and 1.094 Å). The
difference between 6q and [Cp2TiMe]+ can again be traced to
the differences in shape and energies of the frontier orbitals of
[Ti(NMe)(H3[9]aneN3)]2+ (I) and [Cp2Ti]2+ (II). Unlike the case
for [Cp2TiMe]+, the Ti-CMe bond in 6q is essentially the result
of the interaction of the HOMO of CH3- with the LUMO of I,
which, as described above, is well oriented for forming a σ bond
along the molecular z axis. This orbital is already at a relatively
high energy compared with those of II (Figure 7), and the
LUMO+1 is at an even higher energy and thus is not available
to provide significant extra stabilization of the CH3 group upon
tilting. Nevertheless, there are small participations of the CH3
sp3 lone pair and σ(C-H) bond in the LUMO and LUMO+1
of 6q (Figure S3) that could be traced to a very weak R-agostic
interaction in 6q.
Introduction of the real groups in model 6Q (model of the
experimental system 6+) further modifies the bonding situation.
As mentioned, the three lowest unoccupied orbitals of the
fragment [Ti(NtBu)(Me3[9]aneN3)]2+ (V) are even higher in
energy than those of I (Figure 7) as a result of the more electron-
releasing nature of the ligand set. Consequently, the interaction
of the C-H bond in the equatorial plane (already weak in 6q)
is not favorable, and no distortion of the Ti-Me group is
observed.
Monomethyl Cations: NMR Parameters. NMR spectros-
1
copy (including trends in JCH) has been used previously to
probe R-C-H‚‚‚M interactions.54,56 The experimental average
1JCH value of 116 Hz for the Ti-Me group in 6+, however,
shows an increase in magnitude from the value of 111 Hz for
the dimethyl precursor 1. The isolobal species [Cp2TiMe]+
(again assuming negligible C6D5Br or counterion interaction)
1
also shows an increase in Ti-Me average JCH (rising to 129
Hz) in comparison with the neutral, nonagostic precursor
Cp2TiMe2 (1JCH ) 124 Hz). Interestingly, in the same NMR
solvent, Cp2TiMe2 and [Cp2TiMe]+ both have average Ti-Me
1JCH values that are ca. 13 Hz higher than their isolobal
analogues 1 and 6+, respectively.
1
The computed JCH coupling constants within the Ti-Me
ligand for Cp2TiMe2, [Cp2TiMe]+, 1q, 1Q, 6q, and 6Q are listed
in Table 3. The calculated average 1JCH value for 1q is 5.3 Hz
lower than that for 6q, whereas the 1JCH value for Cp2TiMe2 is
2.4 Hz lower than that for [Cp2TiMe]+. Including the actual
substituents on the macrocycle and imido ligands (models 1Q
(100) Eisenstein, O.; Jean, Y. J. Am. Chem. Soc. 1985, 107, 1177.

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2819
1
Table 3. Calculated JCH Coupling Constants for the C-H
We thought it possible that the intrinsic redistribution of %2s
character between the Ti-C and C-H bonds on [Cp2TiMe]+
cation formation might mask the effects of an R-agostic
Bonds of the Methyl Ligand and 2s Character (%2s) of the
Hybrid on CH3 Used to Build the Corresponding Bond to H
or Tia
1
interaction on the average JCH when compared to the neutral
[Cp2TiMe]+
1JCH
%2s
85.5 22.7
dimethyl. As mentioned above, the model cation [Cp2TiMe]+
has also been optimized with all Ti-C-H angles fixed at a
value of 109.5°. The average 1JCH in this species was calculated
to be 121.3 Hz, ca. 4 Hz higher than that of the optimized
agostic cation (Table 3), showing that the formation of the
agostic interaction does give the expected reduction of average
1JCH, but not in comparison with the neutral precursor.
Trimethylsilylmethyl Cation 7+: Geometry and Electronic
Structures. The experimental results speak in favor of the
presence of a â-Si-C agostic interaction in [Ti(NtBu)-
(Me3[9]aneN3)CH2SiMe3]+ (7+), as indicated by the upfield shift
of the 29Si NMR resonance in comparison with the neutral
dialkyl Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2). However, the
system is highly fluxional and the proposed unsymmetric agostic
structure could not be “frozen out” by NMR (Scheme 2). The
optimized geometry for 2q is shown in Figure S3 in the
Supporting Information, and that of 7q is given in Figure 10.
Selected geometrical parameters are given in Table S2 in the
Supporting Information. The model dialkyl complex 2q does
not possess any agostic interaction. The angles subtended at
the Ti-CH2-Si methylene carbons are within the normal
ranges, and the Siâ-Cγ bond distances are all similar. In
contrast, there is a clear â-Si-C‚‚‚Ti agostic interaction in 7q
with a Ti‚‚‚Si contact of 2.534 Å. The TiCH2SiMe3 group is
strongly distorted, with a Ti-CH2-Si angle of 90.7° and one
very elongated Siâ-Cγ agostic bond (1.973 Å) for the methyl
group closest to Ti. One Cγ-H bond of this methyl group is
very slightly longer than the other two (1.109 vs 1.096 and 1.095
Å), possibly as a result of an interaction with the metal center.
Two different interpretations have been offered in the
literature to describe â-Si-C‚‚‚metal agostic interactions and,
in particular, the significant lengthening of one of the Siâ-Cγ
bonds. Some authors consider that the elongation originates from
a negative hyperconjugative donation of σ(metal-CR) into
σ*(Siâ-Cγ) as a result of the large ionic component of the
metal-C bond.55,56,60 Others consider that the main driving force
is donation from the σ(Siâ-Cγ) bond into an empty valence
orbital on the metal, following the classical description of agostic
interactions.104-106 We note that although Duce´re´ and Cavallo
have very recently used DFT to model Bochmann’s cation63
[{rac-Me2Si(1-Indenyl)2}ZrCH2SiMe3]+ and found a â-Si-C
stabilized geometry,107 no description of the bonding was
advanced.
1q
6q
Cp2TiMe2
1JCH
%2s
99.2 23.6 113.1 23.7
1JCH
%2s
1JCH
%2s
C-Heq 100.0 23.4
C-H
C-H
Ti-C
Jav
102.8 23.3 104.2 24.8 115.3 24.8 132.7 27.2
103.9 23.2 119.2 25.9 115.3 24.8 132.7 27.2
30.0
25.6
26.6
22.7
102.2
107.5
114.6
117.0
a C-Heq stands for the C-H bond lying in the equatorial plane, and the
average Jav value is given.
and 6Q) did not lead to any significant difference (1Q, average
1JCH ) 102.6 Hz; 6Q, average JCH ) 108 Hz). For such a
1
1
very sensitive parameter as JCH these results match very well
those obtained in the experimental systems. Indeed, an accuracy
of ca. 10% is considered to be excellent for calculations on
systems of this size,101 and therefore the DFT results can be
considered to be in nearly quantitative agreement with the
experimental data.
The agostic interaction in [Cp2TiMe]+ does not induce a
1
lowering of aVerage JCH (117.0 Hz, Table 3) compared to
Cp2TiMe2 (114.6 Hz), as might intuitively be expected. Al-
though the coupling constant for the agostic C-H bond lying
in the equatorial (yz) plane in the cationic complex is indeed
lower (85.5 Hz) than that for the neutral complex, because the
values for the two other C-H bonds are significantly larger
(132.7 Hz), an overall average value of 117.0 Hz results. We
will return to this point shortly.
The difference of 13 Hz in experimentally observed average
1JCH between Cp2TiMe2 and 1, and between [Cp2TiMe]+ and
6+, is comparable to that between 1JCH for CH4 and MeCN (125
and 136 Hz, respectively).102 For these simple organic com-
pounds the change in 1JCH has been attributed to the difference
in the amount of carbon 2s atomic orbital character in the C-H
bonds. Thus, CN, being more electronegative than H, is
associated with the increased value for 1JCH in MeCN because
(according to Bent’s rule103) there is less 2s orbital contribution
in bonds directed to more electronegative substituents. We also
1
note Grubbs’ report that JCH values for Ti-Me groups in
substituted metallocenes (CpR)2TiMeCl vary with the electron-
donating properties of CpR (CpR ) substituted cyclopentadienyl),
but only over a relatively narrow range (ca. 3 Hz).57
An NBO analysis was performed to evaluate the amount of
2s character (%2s) in the hybrid on C used to create the Ti-C
and C-H bonds in the neutral and cationic complexes shown
in Table 3. The %2s value in the hybrid on CH3 used to make
the bond to Ti is lower for Cp2TiMe2 relative to 1q, in agreement
with a higher effective electronegativity of Ti in fragment II
compared to I. Consequently, and in excellent agreement with
the experimental observations, the average JCH value for the
titanocene system is ca. 12 Hz larger than that for the
macrocycle-imido analogue. The same reasoning explains the
We performed an NBO analysis of 7q and 7Q, and in
particular examined the second-order perturbation interaction
energy terms between occupied and empty NBO (Table S3 in
the Supporting Information). The absolute values of these energy
terms should not be considered by themselves, but the relative
values are indicative of the importance of the various contribu-
tions. There is not a single strong contribution and many terms
are involved in the agostic interaction. The hyperconjugative
donation is the weakest, as bonding to d-block metals is less
ionic than bonding to 4f-block metals, where this interaction
was shown to be crucial.108 Classical donation from both
1
1
relative average JCH values for the cationic systems 6q and
[Cp2TiMe]+, for which there is an excellent correlation between
average 1JCH and %2s. The overall positive charge in Cp2TiMe+
and 6q increases the effective electronegativity of the LnTi
fragments for the cationic complexes and accounts, in each
1
(103) Bent, H. A. Chem. ReV. 1961, 61, 275.
instance, for the larger value obtained for JCH relative to the
(104) Koga, N.; Morokuma, K. J. Am. Chem. Soc. 1988, 110, 108.
(105) Clark, D. L.; Gordon, J. C.; Hay, P. J.; Martin, R. L.; Poli, R.
Organometallics 2002, 21, 5000.
neutral systems.
(101) Autschbach, J. Struct. Bond. 2004, 112, 1.
(102) Maciel, G. E.; McIver, J. W.; Ostlund, N. S.; Pople, J. A. J. Am.
Chem. Soc. 1970, 92, 1.
(106) Brady, D. E.; Clark, D. L.; Gordon, J. C.; Hay, P. J.; Keogh, D.
W.; Poli, R.; Scott, B. L.; Watkin, J. G. Inorg. Chem. 2003, 6682.
(107) Duce´re´, J.-M.; Cavallo, L. Organometallics 2006, 25, 1431.

2820 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
Figure 10. DFT(B3PW91)-optimized geometries and relative energies (kJ mol-1) for 7q-TS1 (left), 7q (center), and 7q-TS2 (right).
Figure 11. LUMO (left) and LUMO+1 (right) for [Ti(NMe)(H3[9]aneN3)(CH2SiMe3)]+ (7q). H atoms omitted for clarity.
Siâ-Cγ and Cγ-H is an important contributor, but even more
important is donation from CR-Siâ to an empty 3d orbital on
Ti. This 3d orbital is the LUMO of I (Figure 7), and canting
the Ti-CH2 bond away from the molecular z axis allows this
orbital to interact with the CR-Siâ bond. These two principal
contributions are highlighted by their antibonding component
clearly visible in LUMO and LUMO+1 of 7q (Figure 11). The
bonding situation for â-Si-C‚‚‚metal agostic complexes is thus
best described as a combination of several interactions whose
respective weights depend on the precise chemical structure of
the molecule under study.
to low temperatures. The transition state for isomerizing the
CH2SiMe3 chain (7q-TS2 in Figure 10) was found at only 24.9
kJ mol-1 above 7q, in agreement with an overall facile fluxional
process. The energy of 7q-TS2 could serve as an upper limit
for the strength of the agostic interaction, and therefore the latter
could be considered to lie between 14.8 and 24.9 kJ mol-1. A
transition state akin to 7q-TS2 for the real system 7+ would
render equivalent the two cis NMe groups on the Me3[9]aneN3
ligand. For the model of the real system (7Q) a transition-
state structure similar to 7q-TS1 could not be located and
only a transition state for the overall exchange (7Q-TS2) was
found. Despite the steric congestion imposed by the NtBu and
Me3[9]aneN3 ligands, the energy of this transition state is only
33.4 kJ mol-1 above 7Q, in excellent agreement with the
observation of equivalent cis Me groups for the Me3[9]aneN3
ligand of 7+, even at low temperature.
The transition states involved in the fluxional process
observed experimentally for 7+ were located for the smaller
model 7q and are shown in Figure 10. 7q-TS1 is the transition
state associated with the exchange of the methyl groups on
SiMe3 between the agostic and nonagostic positions. Its energy
relative to 7q is only 14.8 kJ mol-1, confirming the facile nature
of the exchange process at SiMe3 indicated by the solution NMR
studies on 7+. The energy of this transition state could serve as
an approximate estimate of the strength of the agostic interaction.
However, computing the strength of an agostic interaction is
not straightforward, as the definition of a suitable nonagostic
reference system is not trivial. For example, in the case of
7q-TS1, the Si-Me bond distances are not all equal, even
though none is significantly elongated (Table S2). Moreover,
the angle Ti-CH2-Si slightly increases in 7q-TS1 without
reaching a value similar to that in 2q. There is thus some
distortion within CH2SiMe3 speaking against an entirely agostic-
free situation. Nevertheless, we prefer to consider that breaking
the agostic interaction requires at least the exchange of the Me
groups, and therefore the energy of 7q-TS1 is a lower limit of
the strength of the agostic bond.
Trimethylsilylmethyl Cation 7+: NMR Parameters. Cal-
culations of the Si chemical shift for the neutral and cationic
complexes yielded results in excellent agreement with the
experimental data (δ -1.8 (CD2Cl2) or -3.1 (C6D5Br) ppm for
2; δ -15.9 (CD2Cl2) or -17.5 (C6D5Br) ppm for 7+). Thus the
calculated Si chemical shift in the neutral dialkyls is very close
to zero (-1.2 ppm for 2q; 0.0 ppm for 2Q), whereas it is
significantly shifted upfield in the cations (-17.6 ppm, 7q,
-20.0 ppm, 7Q). These results lend further support for the
presence of the â-Si-C agostic interaction in solution for the
real cation 7+. They also show that the 29Si chemical shift is a
very sensitive probe to characterize the presence of an agostic
interaction and may be used experimentally and computationally
to characterize nonclassical bonding situations in homologous
series of silicon-containing molecules.
Experimentally, the two cis (with respect to NtBu) NMe
groups on the Me3[9]aneN3 ligand of 7+ are equivalent down
Conclusions
We have presented a comprehensive experimental and DFT
study of imido titanium alkyl cations supported by Me3[9]aneN3.
The Lewis acidic nature of the readily prepared cations
(108) Perrin, L.; Maron, L.; Eisenstein, O.; Lappert, M. F. New J. Chem.
2003, 27, 121.

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2821
2
[Ti(NtBu)(Me3[9]aneN3)R]+ (6+ and 7+) is exemplified by the
formation of homobimetallic methyl- or chloride-bridged dimers,
the orthometalation of pyridine, and a double solvent activation
reaction when 7+ is generated using [PhNMe2H]+ in CH2Cl2.
The presence (or not) of R-C-H or â-Si-C agostic interactions
in [Ti(NtBu)(Me3[9]aneN3)R]+ has been established and inter-
preted by a combination of NMR and DFT techniques. A DFT
comparison of the isolobal species [Ti(NR)(R′3[9]aneN3)X]n+
and [Cp2TiX]n+ (in conjunction with NMR studies of Cp2TiMe2
and [Cp2TiMe]+) has highlighted and explained the key dif-
2.11 (1H, m, NCH2), 1.94 (1H, m, NCH2), 1.89 (1H, d, J 10.3
Hz, CHaHbSiMe3), 1.71 (1H, m, NCH2), 1.62-1.54 (2H, overlap-
ping m, NCH2), 1.50-1.39 (2H, overlapping m, NCH2), 1.41
2
(9H, s, NCMe3), 0.67 (9H, s, SiMe3), -0.33 (1H, d, J 10.3 Hz,
CHaHbSiMe3). 13C{1H} NMR (C6D6, 75.4 MHz, 293 K): 67.1
(NCMe3), 56.7 (CH2), 56.4 (CH2), 55.8 (CH2), 55.5 (CH2), 54.8
(CH2), 54.1 (CH2), 53.2 (NMe), 52.8 (NMe), 49.3 (NMe), 43.7
(CH2SiMe3), 32.4 (NCMe3), 4.7 (SiMe3). 29Si NMR (HMQC H-
1
observed, CD2Cl2, 299.9 MHz, 293 K): -1.8 (CH2SiMe3). IR (NaCl
plates, Nujol mull, cm-1): 1497 (w), 1349 (w), 1299 (w), 1242
(s), 1204 (w), 1155 (w), 1067 (m), 1011 (s), 885 (m), 851 (m),
818 (m), 781 (w), 745 (w), 681 (w), 665 (w). FIMS: m/z 414.2
(5%) [M + H]+, 325.2 (67%) [M - CH2SiMe3]+, 244.1 (100%)
[M - Me3[9]aneN3 + 3H]+, 171.2 (39%) [Me3[9]aneN3]+, 73.0
(10%) [tBuNH2]+. Anal. Found (calcd for C17H41ClN4SiTi): C 49.6
(49.4), H 10.0 (10.0), N 13.7 (13.6).
1
ferences between them. Use of JCH coupling constants to
identify R-C-H agostic interactions on the basis of differences
between observed values for neutral and cationic systems may
be inappropriate in cases where there are significant changes
in the carbon 2s orbital contributions to the M-C and C-H
bonds on cation formation.
NMR Tube Scale Synthesis of [Ti(NtBu)(Me3[9]aneN3)Me]-
[BArF ] (6-BArF ). Ti(NtBu)(Me3[9]aneN3)Me2 (1, 0.008 g, 0.025
4
4
mmol) and [Ph3C][BArF ] (0.023 g, 0.025 mmol) were dissolved
Experimental Section
4
in C6D5Br (0.75 mL). After 10 min a 1H NMR spectrum was
General Methods and Instrumentation. All manipulations were
carried out using standard Schlenk line or drybox techniques under
an atmosphere of argon or of dinitrogen. Protio- and deutero-
solvents were predried over activated 4 Å molecular sieves and
were refluxed over the appropriate drying agent, distilled, and stored
under dinitrogen in Teflon valve ampules. NMR samples were
prepared under dinitrogen in 5 mm Wilmad 507-PP tubes fitted
with J. Young Teflon valves. 1H, 13C{1H}, 19F, 31P{1H}, 29Si, and
2H NMR spectra were recorded on Varian Mercury-VX 300, Varian
Unity Plus 500, and Bruker AV500 spectrometers. 1H and 13C
assignments were confirmed when necessary with the use of DEPT-
recorded, which showed quantitative conversion to 6-BArF and
4
Ph3CMe. 1H NMR (C6D5Br, 499.9 MHz, 293 K): 2.32 (6H, br m,
CH2), 2.17 (9H, s, NMe), 2.11 (6H, br m, CH2), 0.89 (9H, s,
NCMe3), 0.65 (3H, s, JC-H 116 Hz, TiMe). 13C{1H} NMR
(C6D5Br, 75.4 MHz, 293 K): 148.8 (br d, JC-F 239 Hz, 2-C6F5),
1
1
1
1
138.6 (br d, JC-F 251 Hz, 4-C6F5), 136.7 (br d, JC-F 246 Hz,
3-C6F5), 69.9 (NCMe3), 55.0 (CH2), 50.5 (NMe), 40.3 (TiMe), 31.4
(NCMe3). 19F NMR (C6D5Br, 282.1 MHz, 293 K): -131.8 (d, J
3
3
10.6 Hz, 2-C6F5), -161.8 (t, J 21.2 Hz, 4-C6F5), -165.8 (app t,
3
app J 18.1 Hz, 3-C6F5).
NMR Tube Scale Synthesis of [Ti(NtBu)(Me3[9]aneN3)Me]-
1
135, DEPT-90, and two-dimensional H-1H and 13C-1H NMR
[MeBArF ] (6-MeBArF ). Ti(NtBu)(Me3[9]aneN3)Me2 (1, 0.007 g,
3
3
experiments. 1H and 13C spectra were referenced internally to
residual protio-solvent (1H) or solvent (13C) resonances and are
reported relative to tetramethylsilane (δ ) 0 ppm). 19F, 31P{1H},
and 29Si spectra were referenced externally to CFCl3, 85% H3PO4,
and tetramethylsilane, respectively. Chemical shifts are quoted in
δ (ppm) and coupling constants in Hertz. Infrared spectra were
prepared as Nujol mulls between NaCl plates and were recorded
on Perkin-Elmer 1600 and 1710 series FTIR spectrometers. Infrared
data are quoted in wavenumbers (cm-1). Mass spectra were recorded
by the mass spectrometry service of Oxford University’s Depart-
ment of Chemistry and elemental analyses by the analytical services
of the University of Oxford Inorganic Chemistry Laboratory or by
the Elemental Analysis Service at the London Metropolitan
University.
0.022 mmol) and BArF (0.011 g, 0.022 mmol) were dissolved in
3
C6D5Br (0.75 mL). After 10 min a 1H NMR spectrum was recorded,
which showed quantitative conversion to 6-MeBArF . H NMR
1
3
(C6D5Br, 499.9 MHz, 293 K): as above with additional peak at
1.03 (3H, br s, BMe). 19F NMR (C6D5Br, 282.5 MHz, 293 K):
-132.2 (d, J 18.3 Hz, 2-C6F5), -163.7 (t, J 16.0 Hz, 4-C6F5),
3
3
3
-166.4 (app t, app J 19.8 Hz, 3-C6F5).
NMR Tube Scale Synthesis of [Ti(NtBu)(Me3[9]aneN3)-
(CH2SiMe3)][BArF ]
(7-BArF ).
Ti(NtBu)(Me3[9]aneN3)-
4
4
(CH2SiMe3)2 (2, 0.010 g, 0.022 mmol) and [Ph3C][BArF ] (0.020
4
g, 0.022 mmol) were dissolved in CD2Cl2 (0.75 mL). After 10 min
an H NMR spectrum was recorded, which showed quantitative
conversion to 7-BArF4 and “Me3SiCH2BArF ”. 1H NMR (CD2Cl2,
1
3
500.0 MHz, 213 K): 3.63 (2H, m, NCH2), 3.06 (2H, m, NCH2),
2.95 (6H, s, NMe cis), 2.90-2.50 (8H, overlapping m, NCH2), 2.40
(3H, s, NMe trans), 2.02 (2H, s, CH2SiMe3), 1.11 (9H, s, NCMe3),
0.17 (9H, s, CH2SiMe3). 13C{1H} NMR (CD2Cl2, 125.7 MHz, 213
K): 147.6 (br d, 1JC-F 247 Hz, 2-C6F5), 137.8 (br d, 1JC-F 225 Hz,
4-C6F5), 135.9 (br d, 1JC-F 247 Hz, 3-C6F5), 69.8 (NCMe3), 55.9-
54.9 (series of overlapping singlets, NCH2 and CH2SiMe3), 51.5
(NMe cis), 48.7 (NMe trans), 30.7 (NCMe3), 1.3 (SiMe3). 19F NMR
Literature Preparations and Other Starting Materials. The
compounds Ti(NtBu)(Me3[9]aneN3)R2 (R ) Me (1) or CH2SiMe3
(2)),28 Ti(NtBu)(Me3[9]aneN3)Cl(Me) (5),46 Ti(NtBu)(Me3[9]-
aneN3)Cl2 (4),24 and Cp2TiMe2109 were prepared according to pub-
lished methods. The compounds [Ph3C][BArF ] and [HNMe2Ph]-
4
[BArF ] were provided by DSM Research. All other compounds
4
and reagents were purchased and used without further purification.
Ti(NtBu)(Me3[9]aneN3)Cl(CH2SiMe3) (3).
A solution of
3
(CD2Cl2, 282.1 MHz, 293 K): -133.5 (d, J 10.6 Hz, 2-C6F5),
Ph3CCl (0.120 g, 0.43 mmol) in benzene (15 mL) was added to a
stirred solution of Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2, 0.200
g, 0.43 mmol) in benzene (15 mL) at 5 °C in the absence of light
and heated to 60 °C for 16 h. The volatiles were removed under
reduced pressure, and most of the resulting yellow-brown solid was
dissolved in a mixture of hexane (20 mL) and benzene (2 mL).
The solution was filtered away from the remaining brown solid
and cooled to -30 °C for 5 days to give 3 as yellow crystals.
Yield: 0.072 g (41%). 1H NMR (C6D6, 499.9 MHz, 293 K): 2.79
(3H, s, NMe), 2.78-2.65 (3H, overlapping m, NCH2), 2.57 (3H,
s, NMe), 2.44-2.33 (2H, overlapping m, NCH2), 2.37 (3H, s, NMe),
3
3
-164.0 (t, J 20.4 Hz, 4-C6F5), -167.9 (app t, app J 18.1 Hz,
3-C6F5). 29Si NMR (HMQC 1H-observed, CD2Cl2, 299.9 MHz, 293
K): -15.9 (CH2SiMe3). 29Si NMR (HMQC 1H-observed, C5D5Br,
299.9 MHz, 293 K): -17.5 (CH2SiMe3).
Synthesis of “Me3SiCH2CPh3” from LiCH2SiMe3 and Ph3CCl.
Cold benzene (20 mL) was added to a mixture of Ph3CCl (0.50 g,
1.79 mmol) and LiCH2SiMe3 (0.17 g, 1.79 mmol) at 5 °C with
vigorous stirring. The orange suspension was allowed to warm to
room temperature and then stirred for 1 h, after which it was filtered
and the volatiles were removed under reduced pressure. The
resulting orange oily solid was extracted into CH2Cl2 (20 mL) and
filtered, and the volatiles were removed under reduced pressure to
give an orange-yellow oil, which was distilled under reduced
(109) Erskine, G. J.; Hartgerink, J.; Weinberg, E. L.; McCowan, J. D. J.
Organomet. Chem. 1979, 170, 51.

2822 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
pressure (4 × 10-2 mbar, 185-195 °C). Yield: 0.30 g. Apart from
a quantity (ca. 30% by 1H integration) of Ph3CH, the main
components of the oil are two isomers of “Me3SiCH2CPh3” in
the ratio ca. 45 (isomer “A”):ca. 25 (isomer “B”). 1H NMR
(CD2Cl2, 299.9 MHz, 293 K): 7.37-6.85 (overlapping m, Ph), 5.57
(s, Ph3CH), 2.12 (s, Me3SiCH2CPh3 of isomer A), 2.06 (s,
Me3SiCH2CPh3 of isomer B), -0.01 (s, Me3SiCH2CPh3 of iso-
mer B), -0.32 (s, Me3SiCH2CPh3 of isomer A). 13C{1H} NMR
(CD2Cl2, 75.4 MHz, 293 K): 149.6 (1-C6H5), 144.3 (1-C6H5), 129.7
(2 or 3-C6H5), 129.5 (2 or 3-C6H5), 129.3 (2 or 3-C6H5, Ph3CH),
128.7 (2 or 3-C6H5), 128.0 (2 or 3-C6H5), 127.9 (2 or 3-C6H5,
Ph3CH), 126.7 (4-C6H5), 126.1 (4-C6H5), 125.9 (4-C6H5,
Ph3CH), 57.2 (Ph3CH), 32.0 (Me3SiCH2CPh3 of isomer A), 26.6
(Me3SiCH2CPh3 of isomer B), 0.3 (Me3SiCH2CPh3 of isomer A),
-1.9 (Me3SiCH2CPh3 of isomer B). 29Si NMR (HMQC 1H-
observed, CD2Cl2, 299.9 MHz, 293 K): 0.7 (SiMe3 of isomer B),
-1.1 (SiMe3 of isomer A). GC-MS (EI): retention time 10.72 min,
m/z 244 (100%) [Ph3C]+, 165 (77%) (not assigned); retention time
11.99 min, m/z 330 (5%) [Me3SiCH2CPh3]+, 243 (100%) [Ph3C]+,
178 (15%) (not assigned), 165 (34%) (not assigned), 135 (28%)
(not assigned); retention time 12.42 min, m/z 330.1 (100%)
[Me3SiCH2CPh3]+, 256 (20%) (not assigned), 243 (18%)
[Ph3C]+, 178 (19%) (not assigned), 165 (35%) (not assigned), 73
(20%) [SiMe3]+. EI-HRMS: m/z found (calcd for C23H26Si,
[Me3SiCH2CPh3]+) 330.1802 (330.1804).
0.98 (9H, s, NCMe3). 13C{1H} NMR (CD2Cl2, 75.4 MHz, 293 K):
151.7 (2-NC5H5), 148.5 (br d, JC-F 241 Hz, 2-C6F5), 141.1 (4-
NC5H5), 138.6 (br d, 1JC-F 247 Hz, 4-C6F5), 136.7 (br d, 1JC-F 250
Hz, 3-C6F5), 125.7 (3-NC5H5), 72.2 (NCMe3), 58.1 (CH2), 57.5
(CH2), 56.3 (CH2), 55.9 (CH2), 55.5 (CH2), 55.0 (CH2), 54.4 (NMe),
54.2 (NMe), 48.9 (NMe), 30.7 (NCMe3). 19F NMR (CD2Cl2, 282.1
1
3
3
MHz, 293 K): -133.5 (d, J 10.6 Hz, 2-C6F5), -164.0 (t, J 20.4
3
Hz, 4-C6F5), -167.9 (app t, app J 18.1 Hz, 3-C6F5). IR (NaCl
plates, Nujol mull, cm-1): 1644 (s), 1608 (w), 1514 (s), 1494 (w),
1276 (m), 1238 (s), 1084 (s), 1046 (w), 1000 (m), 980 (s), 774
(m), 756 (s), 704 (w), 682 (m), 660 (m). ES+MS (MeCN): m/z
404.1 (12%) [M]+, 325.1 (100%) [M - C5H5N]+. Anal. Found
(calcd for C42H35BClF20N5Ti): C 46.7 (46.5), H 3.2 (3.3), N 6.5
(6.5), Cl 3.3 (3.3).
[Ti2(NtBu)2(Me3[9]aneN3)2Me2(µ-Me)][BArF ] (10-BArF ). To
4
4
a solution of Ti(NtBu)(Me3[9]aneN3)Me2 (1, 0.069 g, 0.217 mmol)
in C6H5Cl (1 mL) at -35 °C was added [Ph3C][BArF ] (0.100 g,
4
0.108 mmol), resulting in a yellow solution. Hexane (4 mL) was
added with stirring, resulting in a yellow oil. The mother liquor
was decanted and the yellow oil triturated and washed with pentane
(3 × 5 mL) to give 10-BArF4 as a yellow powder, which was dried
in vacuo. Yield: 0.090 g (64%). The cation is observed as a mixture
of two diastereomers, hereafter referred to as isomer A and isomer
B, in a 2.3:1 ratio. Data for isomer “A”: 1H NMR (CD2Cl2, 500.0
MHz, 233 K): 3.50-2.60 (series of mutually overlapping m, some
corresponding to isomer B, CH2), 2.91 (6H, s, NMe), 2.88 (6H, s,
NMe), 2.48 (6H, s, NMe), 1.12 (18H, s, NCMe3), 0.26 (3H, s, TiMe
bridging), -0.06 (6H, s, TiMe terminal). 13C{1H} NMR (CD2Cl2,
125.7 MHz, 233 K): 66.6 (NCMe3), 56.7-54.8 (series of singlets
overlapping with isomer B, CH2), 52.7 (NMe), 51.8 (NMe), 48.7
(NMe), 32.3 (NCMe3), 29.8 (TiMe terminal), 24.2 (TiMe bridging).
Data for isomer “B”: 1H NMR (CD2Cl2, 500.0 MHz, 233 K):
3.50-2.60 (series of mutually overlapping m, some corresponding
to isomer A, CH2), 2.90 (6H, s, NMe), 2.84 (6H, s, NMe), 2.59
(6H, s, NMe), 1.10 (18H, s, NCMe3), 0.30 (3H, s, TiMe bridging),
0.04 (6H, s, TiMe terminal). 13C{1H} NMR (CD2Cl2, 125.7 MHz,
233 K): 66.8 (NCMe3), 56.7-54.8 (series of singlets overlapping
with isomer A, CH2), 51.8 (NMe), 51.6 (NMe), 49.1 (NMe), 32.2
(NCMe3), 30.0 (TiMe terminal), 22.8 (TiMe bridging). Data for
[B(C6F5)4]- anion: 13C{1H} NMR (CD2Cl2, 500.0 MHz, 233 K):
NMR Tube Scale Synthesis of [Cp2TiMe][BArF ]. Cp2TiMe2
4
(0.0044 g, 0.021 mmol) and [Ph3C][BArF ] (0.0195 g, 0.021 mmol)
4
1
were dissolved in C6D5Br (0.75 mL). After 10 min a H NMR
spectrum was recorded, which showed quantitative conversion to
1
the title compound and Ph3CMe. H NMR (C6D5Br, 299.9 MHz,
1
293 K): 5.83 (10H, s, C5H5), 0.96 (3H, s, JC-H 129 Hz, Me).
1
13C{1H} NMR (C6D5Br, 75.4 MHz, 293 K): 148.8 (br d, JC-F
1
239 Hz, 2-C6F5), 138.6 (br d, JC-F 251 Hz, 4-C6F5), 136.7 (br d,
1JC-F 246 Hz, 3-C6F5), 119.1 (C5H5), 75.6 (Me). 19F NMR
3
(C6D5Br, 282.1 MHz, 293 K): -131.8 (d, J 10.6 Hz, 2-C6F5),
3
3
-161.8 (t, J 21.2 Hz, 4-C6F5), -165.8 (app t, app J 18.1 Hz,
3-C6F5).
NMR Tube Scale Synthesis of [Ti(NtBu)(Me3[9]aneN3)Cl]-
[BArF ] (8-BArF ) from Ti(NtBu)(Me3[9]aneN3)Cl(Me) (5) or
4
4
Ti(NtBu)(Me3[9]aneN3)Me2 (1) and [Ph3C][BArF ] in CD2Cl2.
4
1
1
Ti(NtBu)(Me3[9]aneN3)Cl(Me) (5, 0.005 g, 0.015 mmol) and [Ph3C]-
147.6 (br d, JC-F 247 Hz, 2-C6F5), 137.8 (br d, JC-F 225 Hz,
4-C6F5), 135.9 (br d, JC-F 247 Hz, 3-C6F5). 19F NMR (CD2Cl2,
1
[BArF ] (0.014 g, 0.015 mmol) were dissolved in CD2Cl2 (0.75 mL).
4
282.5 MHz, 293 K): -133.5 (d, 3J 10.6 Hz, 2-C6F5), -164.0 (t, 3J
20.4 Hz, 4-C6F5), -167.9 (app t, app 3J 18.1 Hz, 3-C6F5). IR (NaCl
plates, Nujol mull, cm-1): 1643 (m), 1513 (s), 1351 (w), 1298
(w), 1275 (m), 1239 (s), 1206 (w), 1084 (s), 1005 (s), 980 (s), 891
(w), 776 (m), 756 (m), 684 (m), 661 (m). Anal. Found (calcd for
C53H69BF20N8Ti2): C 48.8 (48.8), H 5.2 (5.3), N 8.5 (8.6).
After 10 min the 1H NMR showed quantitative conversion to
8-BArF and Ph3CMe. Alternatively, Ti(NtBu)(Me3[9]aneN3)Me2
4
(1, 0.007 g, 0.020 mmol) and [Ph3C][BArF ] (0.019 g, 0.020 mmol)
4
were dissolved in CD2Cl2 (0.75 mL) to give quantitative conversion
to 8-BArF and Ph3CMe. Subsequent addition of [PPN]Cl or
4
pyridine to samples of 8+ generated in this way showed quantitative
conversion to 4 or 9+, respectively. 1H NMR (CD2Cl2, 499.9 MHz,
293 K): 4.00-2.30 (21H, br overlapping peaks, Me3[9]aneN3), 1.08
[Ti2(NtBu)2(Me3[9]aneN3)2Me2(µ-Cl)][BArF ] (11-BArF ). To
4
4
a solution of Ti(NtBu)(Me3[9]aneN3)Cl(Me) (5, 0.037 g, 0.108
1
mmol) in CH2Cl2 (1 mL) was added [Ph3C][BArF ] (0.100 g, 0.108
(9H, s, NCMe3). A low-temperature H spectrum recorded at 213
4
mmol). After 2 min Ti(NtBu)(Me3[9]aneN3)Me2 (1, 0.035 g, 0.108
mmol) was added, resulting in a color change from orange to
yellow. Pentane (4 mL) was added with stirring, resulting in an
orange oil. The mother liquor was decanted and the yellow oil
washed with pentane (3 × 5 mL). When a reduced pressure was
K showed a mixture of different species.
[Ti(NtBu)(Me3[9]aneN3)Cl(py)][BArF ] (9-BArF ). Ti(NtBu)-
4
4
(Me3[9]aneN3)Cl(Me) (5, 0.11 g, 0.31 mmol) and [Ph3C][BArF ]
4
(0.29 g, 0.31 mmol) were dissolved in CH2Cl2 (10 mL) and stirred
for 10 min. Pyridine (27.9 µL, 0.35 mmol) was added and the
orange solution stirred for 16 h. The solution was concentrated to
5 mL, after which pentane was added with stirring, resulting in an
orange precipitate. The supernatant was filtered off and the orange
precipitate washed with pentane (3 × 5 mL) and dried in vacuo.
Yield: 0.28 g (81%). Diffraction quality single crystals were
applied to the oil, 11-BArF was obtained as a yellow powder.
4
Yield: 0.100 g (70%). Addition of [PPN]Cl (1 equiv) to a sample
of 11-BArF in CD2Cl2 re-formed 5. The cation 11+ is formed as
4
a mixture of two diastereomers, hereafter referred to as isomer “A”
and isomer “B”, in a 2.5:1 ratio. Data for isomer “A”: 1H NMR
(CD2Cl2, 499.9 MHz, 253 K): 3.50-2.55 (series of mutually
overlapping m, some corresponding to isomer B, CH2), 3.06 (6H,
s, NMe), 2.99 (6H, s, NMe), 2.52 (6H, s, NMe), 1.10 (18H, s,
NCMe3), 0.35 (6H, s, TiMe). 13C{1H} NMR (CD2Cl2, 125.7 MHz,
253 K): 67.7 (NCMe3), 57.0 (CH2), 56.0 (CH2), 55.5 (CH2), 55.3
(CH2), 55.2 (CH2), 54.7 (CH2), 53.2 (NMe), 52.0 (NMe), 48.7
1
obtained by slow diffusion of pentane into a CH2Cl2 solution. H
3
4
NMR (CD2Cl2, 299.9 MHz, 293 K): 9.20 (2H, dd, J 6.6 Hz, J
3
4
1.6 Hz, 2-NC5H5), 8.10 (1H, tt, J 7.8 Hz, J 1.5 Hz, 4-NC5H5),
7.68 (2H, app t, app 3J 7.0 Hz, 3-NC5H5), 3.92 (1H, m, CH2), 3.69
(1H, m, CH2), 3.40 (3H, s, NMe), 3.40-2.60 (9H, overlapping m,
CH2), 3.29 (3H, s, NMe), 2.33 (1H, m, CH2), 2.13 (3H, s, NMe),

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2823
1
1
(NMe), 33.9 (TiMe), 31.7 (NCMe3). Data for isomer “B”: H NMR
(CD2Cl2, 499.9 MHz, 253 K): 3.50-2.55 (series of mutually
overlapping m, some corresponding to isomer A, CH2), 3.04 (6H,
s, NMe), 3.00 (6H, s, NMe), 2.56 (6H, s, NMe), 1.09 (18H, s,
NCMe3), 0.45 (3H, s, TiMe). 13C{1H} NMR (CD2Cl2, 125.7 MHz,
253 K): 68.0 (NCMe3), 56.8 (CH2), 56.2 (CH2), 55.5 (CH2), 55.4
(CH2), 55.1 (CH2), 54.4 (CH2), 52.4 (NMe), 51.9 (NMe), 48.8
16 h the H NMR spectrum showed quantitative conversion to 4
and 12-d2-BArF .
4
NMR Tube Scale Synthesis of [Ti2(NtBu)2(Me3[9]aneN3)2-
(CH2SiMe3)2(µ-Cl)][BArF ] (13-BArF ). To a solution of 7-BArF
4
4
4
{generated in situ from Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2,
0.0050 g, 0.011 mmol) and [Ph3C][BArF ] (0.0099 g, 0.011 mmol)}
4
in CD2Cl2 (0.75 mL) was added Ti(NtBu)(Me3[9]aneN3)Cl-
(CH2SiMe3) (3, 0.0044 g, 0.011 mmol), resulting in a bright orange
solution. After 10 min an 1H NMR spectrum was recorded, which
(NMe), 34.2 (TiMe), 31.8 (NCMe3). Data for [BArF ]- anion:
4
1
13C{1H} NMR (CD2Cl2, 125.7 MHz, 253 K): 148.0 (br d, JC-F
1
showed quantitative conversion to 11-BArF . Addition of [PPN]-
239 Hz, 2-C6F5), 138.2 (br d, JC-F 243 Hz, 4-C6F5), 136.3 (br d,
4
1JC-F 243 Hz, 3-C6F5). 19F NMR (CD2Cl2, 282.1 MHz, 293 K):
Cl (1 equiv) to solutions of 13+ forms 3 quantitatively. The cation
3
3
13+ is a mixture of isomers. H NMR (CD2Cl2, 499.9 MHz, 203
-133.5 (d, J 10.6 Hz, 2-C6F5), -164.0 (t, J 20.4 Hz, 4-C6F5),
-167.9 (app t, app 3J 18.1 Hz, 3-C6F5). IR (NaCl plates,
Nujol mull, cm-1): 1643 (m), 1513 (s), 1352 (m), 1297 (w), 1275
(m), 1241 (s), 1207 (w), 1086 (s), 1005 (s), 979 (s), 892 (w),
775 (m), 756 (m), 684 (m), 662 (m). Anal. Found (calcd for
C52H66BClF20N8Ti2): C 47.2 (47.1), H 4.9 (5.0), N 8.4 (8.5).
1
K): 3.7-2.2 (48H, series of mutually overlapping m, NCH2), 3.09
(6H, s, NMe), 2.99 (12H, 2 × overlapping s, NMe), 2.95 (6H, s,
NMe), 2.52 (6H, s, NMe), 2.38 (6H, s, NMe), 1.14 (4H, app d,
app 2J 9.3 Hz, CHaHbSiMe3), 1.05 (36H, 2 × overlapping s,
2
2
NCMe3), 0.53 (2H, d, J 8.8 Hz, CHaHbSiMe3), 0.33 (2H, d, J
9.3 Hz, CHaHbSiMe3), -0.02 (18H, s, CH2SiMe3), -0.05 (18H, s,
CH2SiMe3). 13C{1H} NMR (CD2Cl2, 125.7 MHz, 203 K): 147.2
NMR Tube Scale Reaction of Ti(NtBu)(Me3[9]aneN3)-
(CH2SiMe3)2 (2) with [PhNMe2][BArF ] (1 equiv). Ti(NtBu)-
4
1
1
(Me3[9]aneN3)(CH2SiMe3)2 (2, 0.007 g, 0.015 mmol) and [PhNMe2H]-
(br d, JC-F 244 Hz, 2-C6F5), 137.5 (br d, JC-F 242 Hz, 4-C6F5),
135.5 (br d, 1JC-F 244 Hz, 3-C6F5), 68.3 (NCMe3), 68.2 (NCMe3),
55.7 (NMe), 53.2 (NMe), 51.9 (2 × NMe), 49.1 (NMe), 48.8
(NMe), 31.8 (NCMe3), 31.7 (NCMe3), 3.3 (SiMe3), 3.1 (SiMe3).
The CH2 resonances were too broad to be observed in a 13C
spectrum or DEPT-135. 19F NMR (CD2Cl2, 282.4 MHz, 293 K):
[BArF ] (0.012 g, 0.015 mmol) were dissolved in CD2Cl2 (0.75 mL).
4
The 1H NMR spectrum showed a 1:1 mixture of Ti(NtBu)(Me3[9]-
aneN3)Cl2 (4) and Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2) along
with resonances attributable to [PhNMe2(CD2Cl)][BArF ] (12-d2-
4
BArF ) and SiMe4. ES+MS (MeCN) for 12+-d2: m/z 172.1 (100%)
4
[M]+.
3
3
-133.5 (d, J 10.6 Hz, 2-C6F5), -164.0 (t, J 20.4 Hz, 4-C6F5),
-167.9 (app t, app J 18.1 Hz, 3-C6F5). 29Si NMR (HMQC H-
3
1
Reaction of Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2) with
[PhNMe2H][BArF ] (2 equiv). To a stirred solution of Ti(NtBu)-
observed, CD2Cl2, 299.9 MHz, 293 K): -1.8 (CH2SiMe3).
[Ti(NtBu)(Me3[9]aneN3)Me(Ph3PO)][MeBArF ] (14-MeBArF ).
4
(Me3[9]aneN3)(CH2SiMe3)2 (2, 0.20 g, 0.43 mmol) in CH2Cl2 (10
3
3
mL) at 0 °C was added [PhNMe2H][BArF ] (0.69 g, 0.86 mmol) in
To a solution of Ti(NtBu)(Me3[9]aneN3)Me2 (1, 0.050 g, 0.156
mmol) in C6H5Cl (2 mL) was added BArF3 (0.080 g, 0.156 mmol)
in C6H5Cl (2 mL). After 5 min a solution of Ph3PO (0.043 g, 0.156
mmol) in C6H5Cl (2 mL) was added, resulting in a color change
from orange to yellow. The volatiles were removed under reduced
4
CH2Cl2 (20 mL). The orange solution was allowed to warm to room
temperature and stirred for a further 16 h. The solution was
concentrated to approximately 10 mL, then hexane (10 mL) was
added with stirring to give an orange oil. The oil was redissolved
in CH2Cl2 (3 mL) and carefully layered with hexane. After 10 days
pressure to give 14-MeBArF as an orange oil containing 1 equiv
3
colorless diffraction-quality crystals of [PhNMe2(CH2Cl)][BArF ]
of C6H5Cl per titanium. Yield: 0.150 g (80%). 1H NMR (C6D5Br,
4
(12-BArF ) had formed, which were filtered off and dried in vacuo.
3
3
4
299.9 MHz, 293 K): 7.57 (6H, dd, JP-H 12.9 Hz, JH-H 6.9 Hz,
2-PPh3), 7.27 (3H, m, 4-PPh3), 7.21 (6H, m, 3-PPh3), 2.86 (2H, m,
CH2), 2.73 (2H, m, CH2 ring), 2.65 (3H, s, NMe), 2.35 (3H, s,
NMe), 2.23-1.70 (8H, overlapping m, CH2), 1.56 (3H, s, NMe),
1.04 (3H, br s, BMe), 0.93 (9H, s, NCMe3), 0.30 (3H, s, TiMe).
1
Yield: 0.137 g (37%). H NMR (CD2Cl2, 499.9 MHz, 293 K):
7.74-7.70 (3H, overlapping m, 2- and 4-C6H5), 7.58 (2H, m,
3-C6H5), 5.25 (2H, s, CH2Cl), 3.67 (6H, s, NMe2). 13C{1H} NMR
(CD2Cl2, 125.7 MHz, 293 K): 148.4 (br d, 1JC-F 244 Hz, 2-C6F5),
1
1
1
13C{1H} NMR (C6D5Br, 75.4 MHz, 293 K): 149.0 (br d, JC-F
138.7 (br d, JC-F 246 Hz, 4-C6F5), 136.6 (br d, JC-F 246 Hz,
3-C6F5), 132.8 (4-C6H5), 132.0 (2-C6H5), 120.0 (3-C6H5), 74.0
(CH2Cl), 54.0 (NMe2). 19F NMR (CD2Cl2, 282.4 MHz, 293 K):
1
243 Hz, 2-C6F5), 137.9 (br d, JC-F 243 Hz, 4-C6F5), 136.2 (br d,
2
1JC-F 243 Hz, 3-C6F5), 134.1 (4-C6H5), 133.1 (d, JC-P 11.4 Hz,
3
3
-133.5 (d, J 10.6 Hz, 2-C6F5), -164.0 (t, J 20.4 Hz, 4-C6F5),
-167.9 (app t, app 3J 18.1 Hz, 3-C6F5). ES+MS (MeCN): m/z 170.1
(100%) [M]+.
2-C6H5), 129.2 (d, obscured by solvent resonance, 3-C6H5), 67.7
(NCMe3), 56.7 (CH2), 56.3 (NMe), 55.1 (CH2), 54.8 (overlapping
NMe and CH2), 53.9 (NMe), 53.1 (CH2), 51.4 (CH2), 47.3 (CH2),
32.5 (NCMe3), 31.4 (TiMe). 19F NMR (C6D5Br, 282.1 MHz, 293
K): -132.1 (d, 3J 20.0 Hz, 2-C6F5), -164.2 (t, 3J 21.2 Hz, 4-C6F5),
NMR Tube Scale Reaction of [Ti(NtBu)(Me3[9]aneN3)-
(CH2SiMe3)][BArF ] (7-BArF ) with PhNMe2. To a solution
4
4
of 7-BArF {generated in situ from Ti(NtBu)(Me3[9]aneN3)-
3
-166.7 (app t, app J 20.0 Hz, 3-C6F5). 31P{1H} NMR (C6D5Br,
4
(CH2SiMe3)2 (2, 0.010 g, 0.022 mmol) and [Ph3C][BArF ] (0.020
121.4 MHz, 293 K): 44.9 (PPh3). IR (NaCl plates, thin film, cm-1):
3064 (m), 2965 (s), 2920 (s), 2865 (s), 2360 (w), 2342 (w), 1640
(s), 1591 (m), 1511 (s), 1454 (br s), 1383 (m), 1366 (m), 1354
(m), 1298 (m), 1268 (s), 1236 (s), 1206 (m), 1140 (br s), 1084 (br
s), 999 (br s), 935 (s), 893 (w), 841 (m), 803 (m), 782 (m), 746
(s), 727 (s), 696 (s), 660 (m), 643 (w). ES+MS (MeCN): m/z 583.3
(40%) [M]+, 172.2 (100%) [Me3[9]aneN3H]+. ES+-HRMS
(MeCN): m/z found (calcd for C32H48N4OPTi, [M]+) 583.3025
(538.3045). Anal. Found (calcd for C51H51BF15N4OPTi‚C6H5Cl):
C 55.2 (55.5), H 4.7 (4.7), N 4.2 (4.5).
4
g, 0.022 mmol)} in CD2Cl2 (0.75 mL) was added PhNMe2 (2.7
1
µL, 0.022 mmol). After 10 min the H NMR spectrum showed
quantitative conversion to 13 along with resonances for 12-d2-BArF
4
and unreacted PhNMe2.
NMR Tube Scale Reaction of Ti(NtBu)(Me3[9]aneN3)Cl-
(CH2SiMe3) (3) with [PhNMe2H][BArF ]. Ti(NtBu)(Me3[9]-
4
aneN3)Cl(CH2SiMe3) (3, 0.007 g, 0.017 mmol) and [PhNMe2H]-
[BArF ] (0.014 g, 0.017 mmol) were dissolved in CD2Cl2 (0.75 mL).
4
After 10 min an 1H NMR spectrum showed a mixture of products.
After 16 h the 1H NMR spectrum showed quantitative conversion
[Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)(Ph3PO)][BArF ] (13-BArF ).
4
4
to 4 and 12-d2-BArF .
To a solution of Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2, 0.050 g,
4
0.108 mmol) in CH2Cl2 (2 mL) was added [Ph3C][BArF ] (0.100
NMR Tube Scale Reaction of [Ti(NtBu)(Me3[9]aneN3)Cl]-
4
[BArF ] (8-BArF ) with PhNMe2. To a solution of 8-BArF
4
g, 0.108 mmol) in CH2Cl2 (2 mL). After 5 min Ph3PO (0.030 g,
0.108 mmol) was added, resulting in a color change from orange
to yellow. The solution was concentrated to approximately 1 mL,
after which hexane (2 mL) was added, resulting in a yellow oil.
4
4
{generated in situ from Ti(NtBu)(Me3[9]aneN3)Cl(Me) (5, 0.006
g, 0.017 mmol) and [Ph3C][BArF ] (0.016 g, 0.017 mmol)} in
4
CD2Cl2 (0.75 mL) was added PhNMe2 (2.2 µL, 0.017 mmol). After

2824 Organometallics, Vol. 25, No. 11, 2006
Bolton et al.
Table 4. X-ray Data Collection and Processing Parameters
for [Ti(NtBu)(Me3[9]aneN3)Cl(py)][BArF ] (9-BArF ) and
The mother liquor was decanted away and the oil washed with
hexane (3 × 2 mL). When a reduced pressure was applied to the
oil, a yellow powder was obtained, which contained 0.33 equiv of
hexane per titanium by 1H NMR. Yield: 0.101 g (69%). 1H NMR
(CD2Cl2, 499.9 MHz, 293 K): 7.83 (6H, m, 2-PPh3), 7.76 (3H, m,
4-PPh3), 7.62 (6H, m, 3-PPh3), 3.45 (1H, m, NCH2), 3.34 (1H, m,
NCH2), 3.15 (3H, s, NMe), 2.95-2.75 (2H, overlapping m, NCH2),
2.82 (3H, s, NMe), 2.63 (2H, overlapping m, NCH2), 2.53 (2H,
overlapping m, NCH2), 2.50-2.32 (4H, overlapping m, NCH2),
2.07 (3H, s, NMe), 1.12 (9H, s, NCMe3), 0.95 (1H, d, 2J 10.2 Hz,
CHaHbSiMe3), 0.10 (1H, d, 2J 10.2 Hz, CHaHbSiMe3), 0.04 (9H, s,
CH2SiMe3). 13C{1H} NMR (CD2Cl2, 125.7 MHz, 293 K): 148.5
4
4
[PhNMe2(CH2Cl)][BArF ] (12-BArF )
4
4
9-BArF
12-BArF
4
4
empirical formula
fw
temp/K
C42H35BClF20N5Ti
1083.90
150
C33H13BClF20N
849.70
150
wavelength/Å
space group
a/Å
b/Å
c/Å
0.71073
P21/c
13.1935(2)
21.1046(3)
15.6878(3)
90
90.9546(8)
90
4367.6(1)
4
0.71073
Pbca
13.8835(2)
18.8229(3)
24.5280(5)
90
90
90
6409.8(2)
8
1.761
R/deg
1
1
â/deg
(br d, JC-F 244 Hz, 2-C6F5), 138.6 (br d, JC-F 246 Hz, 4-C6F5),
136.8 (br d, 1JC-F 246 Hz, 3-C6F5), 134.5 (d, 4JC-P 2.7 Hz, 4-C6H5),
133.6 (d, 2JC-P 11.4 Hz, 2-C6H5), 129.7 (d, 3JC-P 6.1 Hz, 3-C6H5),
69.4 (NCMe3), 57.7 (CH2), 56.9 (CH2), 56.2 (CH2), 56.0 (CH2),
55.1 (CH2), 54.0 (CH2), 53.7 (NMe), 52.2 (NMe), 50.0 (CH2SiMe3),
48.9 (NMe), 33.1 (NCMe3), 4.1 (SiMe3). 19F NMR (CD2Cl2, 282.1
γ/deg
V/Å3
Z
d(calcd)/Mg‚m-3
abs coeff/mm-1
R indices
[I > 3σ(I)]a
1.648
0.383
R1 ) 0.0580
0.265
0.0372
3
3
MHz, 293 K): -133.5 (d, J 10.6 Hz, 2-C6F5), -164.0 (t, J 20.4
Hz, 4-C6F5), -167.9 (app t, app 3J 18.1 Hz, 3-C6F5). 31P{1H} NMR
(CD2Cl2, 121.5 MHz, 293 K): 43.4 (PPh3). 29Si NMR (HMQC
1H-observed, CD2Cl2, 299.9 MHz, 293 K): -0.7 (CH2SiMe3). IR
(NaCl plates, Nujol mull, cm-1): 1643 (m), 1592 (w), 1513 (s),
1412 (w), 1354 (w), 1299 (w), 1275 (m), 1231 (m), 1205 (w), 1141
(s), 1121 (s), 1086 (s), 1007 (m), 980 (s), 907 (m), 849 (m), 820
(m), 775 (m), 755 (m), 726 (s), 695 (m), 684 (m), 662 (m). Anal.
Found (calcd for C59H56BF20N4OPSiTi‚0.33C6H14): C 53.9 (53.7),
H 4.6 (4.5), N 4.1 (4.1).
Rw ) 0.0680
0.0396
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) x{∑w(|Fo| - |Fc|)2/∑(w|Fo| }.
3J 5.3 Hz, 4J 1.2 Hz, 6-NC5H4), 7.97 (1H, dt, 3J 7.6 Hz, 4J 1.2 Hz,
3-NC5H4), 7.75 (1H, td, 3J 7.6 Hz, 4J 1.2 Hz, 4-NC5H4), 7.35 (1H,
3
4
ddd, J 7.6 Hz, 5.3 Hz, J 1.2 Hz, 5-NC5H4), 3.07 (6H, m, CH2),
2.94 (6H, m, CH2), 2.60 (9H, br s, NMe), 0.79 (9H, s, NCMe3).
13C{1H} NMR (CD2Cl2, 75.4 MHz, 313 K): 212.4 (2-NC5H4),
151.9 (6-NC5H4), 148.5 (br d, 1JC-F 241 Hz, 2-C6F5), 145.2, 141.2
(3- and 4-NC5H4), 138.6 (br d, 1JC-F 247 Hz, 4-C6F5), 136.7 (br d,
1JC-F 250 Hz, 3-C6F5), 131.7 (5-NC5H4), 69.3 (NCMe3), 55.8 (CH2
ring), 50.8 (NMe), 31.8 (NCMe3). 19F NMR (CD2Cl2, 282.4 MHz,
293 K): -133.5 (d, 3J 10.6, 2-C6F5), -164.0 (t, 3J 20.4 Hz, 4-C6F5),
[Ti(NtBu)(Me3[9]aneN3)Me(py)][BArF ] (16-BArF ). To a stirred
4
4
solution of Ti(NtBu)(Me3[9]aneN3)Me2 (1, 0.050 g, 0.156 mmol)
and pyridine (14.0 µL, 0.172 mmol) in CH2Cl2 (2 mL) at -78 °C
was added [Ph3C][BArF ] (0.144 g, 0.156 mmol) in CH2Cl2 (2 mL).
4
3
-167.9 (app t, app J 18.1 Hz, 3-C6F5). IR (NaCl plates, Nujol
The resulting light yellow solution was concentrated to ap-
proximately 1 mL, after which hexane (5 mL) was added with
stirring, resulting in a bright yellow precipitate. The precipitate was
mull, cm-1): 1643 (s), 1605 (m), 1514 (s), 1275 (s), 1244 (m),
1155 (w), 1088 (s), 979 (s), 863 (m), 775 (s), 757 (s), 725 (w),
705 (m), 684 (s), 662 (s). A satisfactory elemental analysis could
not be obtained.
1
filtered off and dried in vacuo. Yield: 0.086 g (52%). H NMR
3
(CD2Cl2, 299.9 MHz, 213 K): 8.75 (2H, d, J 6.5 Hz, 2-NC5H5),
Crystal Structure Determinations of [Ti(NtBu)(Me3[9]aneN3)-
Cl(py)][BArF ] (9-BArF ) and [PhNMe2(CH2Cl)][BArF ] (12-
3
3
8.00 (1H, t, J 7.6 Hz, 4-NC5H5), 7.58 (2H, app t, app J 6.5 Hz,
3-NC5H5), 3.49 (2H, overlapping m, CH2), 3.09 (3H, s, NMe), 3.02
(3H, s, NMe), 3.15-2.62 (8H, overlapping m, CH2), 2.50 (1H, m,
CH2), 2.45 (3H, s, NMe), 2.34 (1H, m, CH2), 1.01 (9H, s, NCMe3),
0.46 (3H, s, TiMe). 13C{1H} NMR (CD2Cl2, 75.4 MHz, 213 K):
4
4
4
BArF ). Crystal data collection and processing parameters are given
4
in Table 4. Crystals were mounted on a glass fiber using per-
fluoropolyether oil and cooled rapidly to 150 K in a stream of cold
N2 using an Oxford Cryosystems CRYOSTREAM unit. Diffraction
data were measured using an Enraf-Nonius KappaCCD diffracto-
meter. Intensity data were processed using the DENZO-SMN
package.110 The structures were solved using the direct-methods
program SIR92,111 which located all non-hydrogen atoms. Subse-
quent full-matrix least-squares refinement was carried out using
the CRYSTALS program suite.112 Coordinates and anisotropic
thermal parameters of all non-hydrogen atoms were refined.
Disorder of the CH2CH2 linkages in the Me3[9]aneN3 ring of 9+
was satisfactorily modeled. Hydrogen atoms were positioned
geometrically. Full listings of atomic coordinates, bond lengths and
angles, and displacement parameters have been deposited at the
Cambridge Crystallographic Data Center. See Guidelines for
Authors, Issue No. 1.
1
150.4 (2-NC5H5), 147.5 (br d, JC-F 240 Hz, 2-C6F5), 139.9 (4-
NC5H5), 137.7 (br d, 1JC-F 242 Hz, 4-C6F5), 135.8 (br d, 1JC-F 245
Hz, 3-C6F5), 124.7 (3-NC5H5), 68.4 (NCMe3), 55.6 (CH2), 55.5
(2 x CH2), 55.4 (CH2), 54.4 (CH2), 54.3 (CH2), 52.9 (NMe),
52.3 (NMe), 49.1 (NMe), 34.9 (TiMe), 30.9 (NCMe3). 19F NMR
3
(CD2Cl2, 282.1 MHz, 213 K): -133.9 (d, J 10.6 Hz, 2-C6F5),
3
3
-163.1 (t, J 20.4 Hz, 4-C6F5), -167.1 (app t, app J 18.1 Hz,
3-C6F5). IR (NaCl plates, Nujol mull, cm-1): 1643 (m), 1607 (w),
1514 (s), 1354 (w), 1298 (w), 1277 (m), 1245 (m), 1209 (w), 1084
(s), 1002 (m), 979 (s), 775 (m), 757 (m), 707 (w), 683 (m), 661
(m). Anal. Found (calcd for C43H38BF20N5Ti): C 48.4 (48.6), H
3.8 (3.6), N 6.4 (6.6).
[Ti(NtBu)(Me3[9]aneN3)(NC5H4)][BArF ] (17-BArF ). To a
4
4
solution of Ti(NtBu)(Me3[9]aneN3)(CH2SiMe3)2 (2, 0.100 g, 0.215
Computational Details. All the calculations have been per-
formed with the Gaussian03 package113 at the B3PW91 level.114,115
The titanium atom was represented by the relativistic effective core
potential (RECP) from the Stuttgart group (12 valence electrons)
and its associated basis set,116 augmented by an f polarization
function (R ) 0.869).117 The silicon atom was represented by RECP
mmol) in CH2Cl2 (1 mL) was added [Ph3C][BArF ] (0.198 g, 0.215
4
mmol) in CH2Cl2 (1 mL). Pyridine (17.4 µL, 0.015 mmol) was
added, resulting in a color change from orange to yellow. Pentane
(5 mL) was added with stirring, resulting in a yellow oil. The
supernatant was decanted and the yellow oil washed with pentane
(3 × 2 mL). When a reduced pressure was applied to the oil, a
yellow powder was obtained. Yield: 0.148 g (66%). The corre-
(110) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode; Academic Press: New York, 1997.
(111) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(112) Betteridge, P. W.; Cooper, J. R.; Cooper, R. I.; Prout, K.; Watkin,
D. J. J. Appl. Crystallogr. 2003, 36, 1487.
sponding NMR tube scale reaction of 7-BArF in CH2Cl2 with
4
pyridine-d5 afforded [Ti(NtBu)(Me3[9]aneN3)(NC5D4)][BArF ]
4
(17-d4-BArF ) and SiMe4-d1, which showed the expected 2H NMR
4
resonances. 1H NMR (CD2Cl2, 299.9 MHz, 313 K): 8.50 (1H, dt,

Studies of Cationic Imido Titanium Alkyls
Organometallics, Vol. 25, No. 11, 2006 2825
from the Stuttgart group and the associated basis set,118 augmented
by a d polarization function.119 The remaining atoms (C, H, N)
were represented by a 6-31G(d,p) basis set.120 Full optimizations
of geometry without any constraint were performed, followed by
analytical computation of the Hessian matrix to confirm the nature
of the located extrema as minima or transition states on the potential
energy surface. The nature of the transition states was checked by
slightly perturbing the TS geometry along the TS vector in both
directions and optimizing the resulting geometries as local minima
to ensure the nature of the connected intermediates. NMR chemical
shifts and JCH coupling constants were computed using the GIAO
method121,122 at the B3PW91 level. For the NMR parameters, all
electron calculations were considered where the basis set for Ti
was the TZP basis set of Ahlrichs,123 and all the other atoms were
described with the IGLOO-II basis set.124 Natural bonding orbital
analysis125 was performed as implemented in Gaussian03.
(113) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A.
G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, ReVision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
Acknowledgment. We thank the EPSRC, DSM Research
BV, SABIC EuroPetrochemicals, Millennium Pharmaceuticals,
CNRS, and the British Council for support, and Professor G. I.
Nikonov and Dr. N. H. Rees for technical assistance and helpful
discussions.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of [Ti(NtBu)-
(Me3[9]aneN3)Cl(py)][BArF ] (9-BArF ) and [PhNMe2(CH2Cl)]-
4
4
[BArF ] (12-BArF ), and further details of the DFT calculations.
4
4
This material is available free of charge via the Internet at http://
pubs.acs.org.
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