Reactions of titanium imido complexes with α-diimines: Complexation versus Ti=N/C=N bond metathesis

Article abstract of DOI:10.1039/a806393a

The reactions of the titanium imido complexes [Ti(NR)Cl₂(py)₃] (R = Bu^t 1, C₆H₃Me₂-2,6 2 or C₆H₃Prⁱ₂-2,6 3) with α-diimines (1,4-diaza-1,3-butadienes) of the type ArNC(R′)C(R′)NAr (Ar = phenyl or substituted phenyl, R′ = H or methyl) are reported. The reaction products and metal complex stability are critically dependent on the nature of both the imido N- and diimine N- and backbone C-substituents. Reaction of 3 with PhNC(Me)C(Me)NPh gave the crystallographically characterised adduct [Ti(NC₆H₃Prⁱ₂-2,6)Cl ₂{η²-PhNC(Me)C(Me)NPh}(py)] 4 which posseses mutually trans Cl ligands and has one diimine nitrogen atom cis and one trans to the arylimido group. The compound 4 is the first crystallographically characterised titanium complex to have a formally neutral (i.e. non-reduced) α-diimine ligand and decomposes fairly quickly in solution at room temperature. ¹H NMR evidence only is presented for the formation of the tert-butyl- and 2,6-dimethylphenyl-imido homologues of 4, namely [Ti(NR)Cl₂{η²-ArNC(Me)C(Me)NAr}(py)] (R = Bu^t or C₆H₃Me₂-2,6; Ar = Ph or tolyl, Tol): these compounds are considerably less stable in solution, rapidly decomposing to a number of products including the corresponding amines RNH₂ and [Ti(NR)Cl₂(py)_n] (H = 2 or 3). Reaction of 1 with α-diimines of the type ArNC(H)C(H)NAr (Ar = Tol or 2,6-C₆H₃Me₂), i.e. without methyl substituents in the backbone, do not give detectable adducts analogous to 4. In these cases titanium imide/organic imine metathesis occurs to form [Ti(NAr)Cl₂(py)_n] (n = 2 or 3) and Bu^tNC(H)C(H)NAr and/or Bu^tNC(H)C(H)NBu^t.

Full text of DOI:10.1039/a806393a

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Reactions of titanium imido complexes with á-diimines:
complexation versus Ti᎐N/C᎐N bond metathesis
᎐
᎐
Jacqueline M. McInnes, Alexander J. Blake and Philip Mountford*†
School of Chemistry, University of Nottingham, Nottingham, UK NG7 2RD
Received 13th August 1998, Accepted 14th September 1998
The reactions of the titanium imido complexes [Ti(NR)Cl2(py)3] (R = But 1, C6H3Me2-2,6 2 or C6H3Pri2-2,6 3) with
α-diimines (1,4-diaza-1,3-butadienes) of the type ArNC(RЈ)C(RЈ)NAr (Ar = phenyl or substituted phenyl, RЈ = H
or methyl) are reported. The reaction products and metal complex stability are critically dependent on the nature
of both the imido N- and diimine N- and backbone C-substituents. Reaction of 3 with PhNC(Me)C(Me)NPh gave
the crystallographically characterised adduct [Ti(NC6H3Pri2-2,6)Cl2{η2-PhNC(Me)C(Me)NPh}(py)] 4 which
posseses mutually trans Cl ligands and has one diimine nitrogen atom cis and one trans to the arylimido group.
The compound 4 is the first crystallographically characterised titanium complex to have a formally neutral (i.e.
non-reduced) α-diimine ligand and decomposes fairly quickly in solution at room temperature. 1H NMR evidence
only is presented for the formation of the tert-butyl- and 2,6-dimethylphenyl-imido homologues of 4, namely
[Ti(NR)Cl2{η2-ArNC(Me)C(Me)NAr}(py)] (R = But or C6H3Me2-2,6; Ar = Ph or tolyl, Tol): these compounds
are considerably less stable in solution, rapidly decomposing to a number of products including the corresponding
amines RNH2 and [Ti(NR)Cl2(py)n] (n = 2 or 3). Reaction of 1 with α-diimines of the type ArNC(H)C(H)NAr
(Ar = Tol or 2,6-C6H3Me2), i.e. without methyl substituents in the backbone, do not give detectable adducts
analogous to 4. In these cases titanium imide/organic imine metathesis occurs to form [Ti(NAr)Cl2(py)n] (n = 2
or 3) and ButNC(H)C(H)NAr and/or ButNC(H)C(H)NBut.
R'
Introduction
R
N
N
R
N
R
R
N
The α-diimines (also commonly known as 1,4-diaza-1,3-
butadienes) of the type RNC(RЈ)C(RЈ)NR (I and II where typi-
cally R = alkyl, phenyl or substituted phenyl, RЈ = H, phenyl or
methyl) represent a class of ligand that has received sustained
and extensive attention synthetically, theoretically and spectro-
scopically for a range of main group-, transition-, lanthanide-
and actinide-metal complexes.1–11 α-Diimines are typically
prepared by condensation reactions of amines or anilines,
RNH2, with glyoxal or the correpsonding α-diketone RЈC(O)-
C(O)RЈ,12 and adopt the s-trans conformation I in preference to
the s-cis alternative II in the absence of bulky R- and/or RЈ-
substituents.1,2 α-Diimines may coordinate as neutral bidentate
ligands (as in III), but most commonly act as formally mono- or
di-anionic (IV) moieties owing to their ability to accept electron
density into the π3 lowest unoccupied molecular orbital,4,8
which results in a shortening of the diimine C–C and lengthen-
ing of the C–N bonds in comparison to those of the free
ligand.1,2
R'
R'
R'
s-trans
s-cis
I
II
R
N
R
N
R'
R'
R'
MLn
MLn
R'
N
R
N
R
neutral ligand
2- ligand
III
IV
But
Ar
N
Ar
But
H
N
N
N
py
Cl
py
Ti
Cl
py
Cl
py
+
+
(1)
Ti
Cl
Ph
H
Ph
As part of an ongoing study of early transition metal imido
chemistry13–19 we recently reported the stoichiometric imide/
imine metathesis reactions of [Ti(NBut)Cl2(py)3] 120 with
monoimines of the type PhC(NAr)H [Ar = C6H3Me2-2,6 or
tolyl, Tol, eqn. (1)].21
py
py
1
Experimental
Such imide/imine metathesis reactions are very uncommon
transformations in transition metal chemistry,22–24 even though
the corresponding carbene(alkylidene)/alkene metathesis reac-
tion is very well established and widely applied.25 In the context
of these previous studies we were therefore interested to study
the reactions of α-diimines with the previously described
titanium imido complexes [Ti(NR)Cl2(py)3] (R = But 1, C6H3-
Me2-2,6 2 and C6H3Pri2-2,6 3).‡,20
General methods and instrumentation
Manipulations were carried out under an atmosphere of
dinitrogen or argon using either standard Schlenk-line or
dry-box techniques. Solvents were pre-dried over molecular
sieves and refluxed over potassium (hexane), sodium (tolu-
ene), sodium–potassium alloy (pentane) or calcium hydride
‡ Although for ease of representation all titanium–imido linkages are
† Present address: Inorganic Chemistry Laboratory, South Parks Road,
Oxford, UK OX1 3QR. E-mail: philip.mountford@chemistry.oxford.
ac.uk
drawn “Ti᎐NR”, the formal Ti–N bond order in the complexes
᎐
[Ti(NR)Cl2{η2-RNC(RЈ)C(RЈ)NR}(py)] is generally best thought of as
three (pseudo-σ2π4 triple bond) rather than as two.35
J. Chem. Soc., Dalton Trans., 1998, 3623–3628
3623

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1
(dichloromethane) under an atmosphere of dinitrogen and col-
lected by distillation. C6D6 was dried over molten potassium
and CDCl3 and CD2Cl2 were dried over calcium hydride at
room temperature (r.t.). All NMR solvents were distilled under
reduced pressure and stored under N2 in Young’s ampoules in a
dry-box. NMR samples were prepared in a dry-box in Teflon
valve (Young’s) 5 mm tubes.
tions, and the H NMR spectra were recorded immediately.
Solutions of 5, 6 and 7 showed extensive decomposition after
less than ca. 4 hours, 1 hour and 10 minutes at r.t., respectively.
1H NMR (CDCl3, 300.1 MHz, 298 K) data for 5: δ 8.89 (m, 2 H,
ortho-NC5H5), 7.66 (m, 1 H, para-NC5H5), 7.39–6.97 (over-
lapping m, 12 H, ortho- and meta-C6H4Me, meta-NC5H5), 6.71
(strongly second order d, 2 H, meta-C6H3Pri2), 6.62 (strongly
second order t, 1 H, para-C6H3Pri2), 4.40 (septet, 2 H, J = 6.8,
CHMe2), 2.35 (s, 3 H, NC(Me)C(Me)N), 2.30, 2.24 (2 × s, 2 × 3
H, para-C6H4Me), 2.14 (s, 3 H, NC(Me)C(Me)N), 0.97 (d, 12
H, J = 6.8, CHMe2); for 6: δ 8.85 (m, 2 H, ortho-NC5H5), 7.52
(m, 1 H, para-NC5H5), 7.23–6.95 (overlapping m, 14 H, C6H5
and meta-NC5H5), 6.47 (d, 2 H, J = 7.3, meta-C6H3Me2), 6.31
(t, 1 H, J = 7.3, para-C6H3Me2), 2.34 (s, 3 H, NC(Me)C(Me)N),
2.29 (s, 6 H, C6H3Me2), 2.34 (s, 3 H, NC(Me)C(Me)N); for 7:
δ 9.08 (m, 2 H, ortho-NC5H5), 7.64 (m, 1 H, para-NC5H5), 7.40–
7.20 (overlapping m, 4 H, C6H4Me), 7.02 (m, 2 H, meta-
NC5H5), 6.80–6.70 (overlapping m, 4 H, C6H4Me), 2.38 (s, 3 H,
NC(Me)C(Me)N), 2.18, 2.11 (2 × s, 2 × 3 H, 2 × C6H4Me), 2.07
(s, 3 H, NC(Me)C(Me)N), 0.35 (s, 9 H, But).
1H and 13C NMR spectra were recorded on a Bruker DPX
300 spectrometer at ambient temperature unless stated other-
wise. The spectra were referenced internally to residual
protio-solvent (1H) or solvent (13C) resonances and are reported
relative to tetramethylsilane (δ = 0 ppm). Chemical shifts are
quoted in δ (ppm) and coupling constants in Hz. Assignments
were supported by DEPT-135 and DEPT-90, homo- and
hetero-nuclear and one- and two-dimensional experiments as
appropriate. Elemental analysis was carried out by the analysis
laboratory of this department.
Literature preparations
The titanium imido complexes [Ti(NR)Cl2(py)3] (R = But,
C6H3Me2-2,6, C6H3Pri2-2,6) were prepared according to liter-
ature methods.20 α-Diimines RNC(RЈ)C(RЈ)NR were prepared
by condensation reactions12 of the corresponding α-dicarbonyl
compounds (RЈ = H or Me) and amines (R = But, Ph, Tol,
C6H3Me2-2,6 or C6H3Pri2-2,6) according to literature pro-
cedures and purified either by distillation or recrystallisation
from appropriate solvents.26–29
Preparative scale reaction of [Ti(NBut)Cl2(py)3] 1 with ArNC-
(H)C(H)NAr (Ar ؍ C6H3Me2-2,6). A solution of [Ti(NBut)-
Cl2(py)3] (0.60 g, 1.40 mmol) and ArNC(H)C(H)NAr (0.40 g,
1.5 mmol, ca. 1.1 equivalents) in toluene (20 ml) was heated at
100 ЊC for 7 days. The volatiles were removed under reduced
pressure to give spectroscopically pure [Ti(NC6H3Me2-
2,6)Cl2(py)2] 2Ј as a green powder after washing with pentane
and drying in vacuo. Yield of 2Ј ca. 100%. The compound 2Ј
was characterised by comparison with an authentic sample.20
Syntheses
[Ti(NC6H3Pri2-2,6)Cl2{ç2-PhNC(Me)C(Me)NPh}(py)] 4. To
a solution of [Ti(NC6H3Pri2-2,6)Cl2(py)3] (0.31 g, 0.58 mmol) in
CH2Cl2 (5 ml) was added a solution of PhNC(Me)C(Me)NPh
(0.16 g, 0.68 mmol) in CH2Cl2 (5 ml). The solution immediately
turned deep green. After 10 minutes hexane (20 ml) was added
to afford a green powder which was washed with hexane (2 × 5
ml) and dried in vacuo. Yield: 0.30 g (75%, for [Ti(NC6H3-
Pri2-2,6)Cl2{η2-PhNC(Me)C(Me)NPh}(py)]ؒ0.8CH2Cl2). The
product contained ca. 0.8 equivalent of residual CH2Cl2 (by 1H
NMR and elemental analysis). Diffraction quality crystals
of 4ؒCH2Cl2 were grown at Ϫ25 ЊC by layering a saturated
dichloromethane solution with hexane. 1H NMR (CD2Cl2,
300.1 MHz, 298 K): δ 8.79 (d, 2 H, J = 5.0, ortho-NC5H5), 7.57
(tt, 1 H, J = 7.6, J = 1.6, para-NC5H5), 7.37 (d, 2 H, J = 8.4,
ortho-C6H5), 7.24 (t, 2 H, J = 8.4, meta-C6H5), 7.13–7.00 (m,
2 H, meta-NC5H5; 2 H meta-C6H5; 2 H, ortho-C6H5; 2 × 1 H,
2 × para-C6H5), 6.55 (d, 2 H, J = 7.3, meta-C6H3Pri2), 6.45 (t,
1 H, J = 7.3, para-C6H3Pri), 4.36 (septet, 2 H, J = 6.8, CHMe2),
2.28 (s, 3 H, NC(Me)C(Me)N), 2.15 (s, 3 H, NC(Me)C(Me)N),
0.87 (d, 12 H, J = 6.8, CHMe2). 13C-{1H} NMR (CD2Cl2, 62.5
MHz, 258 K): δ 165.7 (C(Me)NPh), 154.7 (ipso-C6H3Pri2),
151.0, 146.3 (2 × ipso-C6H5), 151.0 (ortho-NC5H5), 146.8 (ortho-
C6H3Pri2), 138.2, (para-NC5H5), 128.8 (meta-C6H5), 128.7
(meta-C6H5), 120.6, 121.1 (2 × ortho-C6H5), 126.0 (para-C6H5),
123.5 (meta-NC5H5), 121.4 (ortho-C6H5), 121.3 (meta-C6H3-
Pri2), 121.2, (para-C6H3Pri2), 26.7 (CHMe2), 24.3 (CHMe2),
20.2 (NC(Me)C(Me)N), 19.7 (NC(Me)C(Me)N) [Found (calc.
for C33H38Cl2N4Tiؒ0.8CH2Cl2): C, 59.5 (59.9); H, 5.7 (5.9); N,
8.0 (8.3)%].
NMR tube scale reactions of [Ti(NBut)Cl2(py)3] 1 with
ArNC(H)C(H)NAr (Ar ؍ C6H3Me2-2,6). (i) A mixture of
[Ti(NBut)Cl2(py)3] (12 mg, 0.028 mmol) and ArNC(H)C(H)-
NAr (8 mg, 0.03 mmol, ca. 1.1 equivalents) in CDCl3 (1 ml)
was heated for 6 days at 60 ЊC. The resultant 1H NMR spectra
showed the formation of [Ti(NC6H3Me2-2,6)Cl2(py)2] 2Ј,
ArNC(H)C(H)NBut G, and ButNC(H)C(H)NBut F in the ratio
1:0.21:0.40, along with 0.63 equivalent of unchanged
ArNC(H)C(H)NAr E. The diimine F and [Ti(NC6H3Me2-
2,6)Cl2(py)2] 2Ј were characterised by comparison with authen-
1
tic samples.20,27 The mixed diimine G was characterised by H
NMR spectroscopy in situ. 1H NMR (CDCl3, 300.1 MHz, 298
K) data for G: δ 7.1–6.9 [m, 3 H, C6H3Me2 (partially obscured)],
2.15 (s, 6 H, C6H3Me2), 1.34 (s, 9 H, But). NC(H)C(H)N reson-
ances obscured.
(ii) When the above reaction was carried out with a ca. 2:1
ratio of [Ti(NBut)Cl2(py)3] to ArNC(H)C(H)NAr only the
diimine ButNC(H)C(H)NBut F and [Ti(NC6H3Me2-2,6)Cl2-
(py)2] 2Ј were observed.
NMR tube scale reaction of [Ti(NBut)Cl2(py)3] 1 with Tol-
NC(H)C(H)NTol E. A mixture of [Ti(NBut)Cl2(py)3] (34 mg,
0.08 mmol) and TolNC(H)C(H)NTol (9 mg, 0.04 mmol, ca. 0.5
equivalent) in CDCl3 (1 ml) was allowed to stand at r.t. for 24
1
hours. H NMR examinaton of the reaction mixture showed
quantitative conversion to [Ti(NTol)Cl2(py)3] and ButNC(H)-
C(H)NBut F which were characterised by comparison with
authentic samples.20,27
NMR tube scale syntheses of [Ti(NC6H3Pri2-2,6)Cl2{ç2-Tol-
NC(Me)C(Me)NTol}(py)] 5, [Ti(NC6H3Me2-2,6)Cl2{ç2-PhNC-
Crystal structure determination of [Ti(NC6H3Pri2-2,6)Cl2{ç2-
PhNC(Me)C(Me)NPh}(py)]ؒCH2Cl2 (4ؒCH2Cl2)
(Me)C(Me)NPh}(py)]
6
and [Ti(NBut)Cl2{ç2-TolNC(Me)-
C(Me)NTol}(py)] 7. Because of their instability (especially for 6
and 7) these compounds were prepared and characterised only
by 1H NMR according to the following general procedure.
CDCl3 solutions of [Ti(NR)Cl2(py)3] (R = C6H3Pri2-2,6,
C6H3Me2-2,6 or But, ca. 0.07 mmol in 0.5 ml) and either
PhNC(Me)C(Me)NPh A or TolNC(Me)C(Me)NTol B (ca. 0.07
mmol in 0.5 ml) were mixed in the dry-box to give green solu-
Crystal data collection and processing parameters are given in
Table 1. An orange-brown block was mounted in a film of
RS3000 perfluoropolyether oil (Hoechst) on a glass fibre
and transferred to a Stoë Stadi-4 four-circle diffractometer
equipped with an Oxford Cryosystems low-temperature
device.30 Data were collected at 150 K using ω–θ scans with
Mo-Kα radiation (λ = 0.71073 Å) and an absorption correction
3624
J. Chem. Soc., Dalton Trans., 1998, 3623–3628

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R
N
Ti
R
N
R'
R'
Me
Cl
N
py
py
Cl
Cl
py
N
N
+
Ti
Me
Cl
R'
Me
N
py
R' = H A or Me B
R = But 1,
Me
R'
C6H3Me2-2,6 2
or C6H3Pri2-2,6 3
R = C6H3Pri2-2,6, R' = H 4 or Me 5
R = C6H3Me2-2,6, R' = H 6
R = But, R' = Me 7
But
N
R'
Me
R'
N
N
py
Ti
Cl
py
+
R'
Cl
No reaction
Me
R'
R' = Me C or Pri D
py
1
Scheme 1 Reactions of titanium imido complexes with α-diimine ligands containing methyl groups in their backbone.
Table 1 X-Ray data collection and processing parameters for [Ti-
(NC6H3Pri2-2,6)Cl2{η2-PhNC(Me)C(Me)NPh}(py)]ؒCH2Cl2 4ؒCH2Cl2
H atom substituents result in imide/imine metathesis with no
detectable new complex being formed [eqn. (2) and (3)].
Formula
M
System, space group
a/Å
C33H38Cl2N4TiؒCH2Cl2
But
N
694.43
Triclinc, P1
¯
11.093(3)
b/Å
c/Å
α/Њ
β/Њ
12.533(5)
12.687(5)
82.49(3)
85.22(2)
py
Cl
Cl
Ti
Me
Me
py
N
γ/Њ
85.28(3)
1738.1(8)
2
0.58
py
U/Å3
Ti
py
Cl
Cl
Z
1
µ/mmϪ1
py
Reflections collected
Total independent, Rint
6159
5722, 0.040
0.080, 0.089 for 4220 data with I > 2σ(I)
2'
+
Final R,a Rw
b
Me
Me
¹
a R = Σ||Fo| Ϫ |Fc||/Σ|Fo|. b Rw = {Σw(|Fo| Ϫ Fc|)2/ΣwFo }².
2
N
+
(2)
N
Me
was applied to the data. Equivalent reflections were merged and
the structures were solved by direct methods (SIR9231). Sub-
sequent Fourier-difference syntheses revealed the positions
of all other non-hydrogen atoms. Residual electron density
was modelled as a full-occupancy dichloromethane molecule
solvent (in a general position). All non-H atoms were refined
anisotropically and hydrogen atoms were placed geometrically:
these were refined in a riding model with fixed isotropic displace-
ment parameters. A Chebychev weighting scheme32 was applied
towards the end of the refinements. Examination of the refined
secondary extinction parameter33 and an agreement analysis
suggested that no extinction correction was required. Crystal-
lographic calculations were performed using SIR9231 and
CRYSTALS-PC.34
Me
But
N
But
N
E
F
+
Me
N
But
N
Me
G
CCDC number 186/1162.
See http://www.rsc.org/suppdata/dt/1998/3623/ for crystallo-
graphic files in .cif format.
As shown in Scheme 1, reaction of PhNC(Me)C(Me)NPh A
or TolNC(Me)C(Me)NTol with [Ti(NR)Cl2(py)3] gives
immediate formation of the new complexes [Ti(NR)Cl2{η2-
B
Results and discussion
ArNC(Me)C(Me)NAr}(py)] (R = C6H3Pri2-2,6, Ar = Ph
4
The reactions of [Ti(NR)Cl2(py)3] (R = But 1, C6H3Me2-2,6 2
and C6H3Pri2-2,6 3) with α-diimines divide into two types.
α-Diimines with methyl substituents in the backbone give rise
to coordination complexes (Scheme 1), while those with only
or Tol 5; R = C6H3Me2-2,6, Ar = Ph 6; R = But, Ar = Tol 7).
Compound 4 was fully characterised by 1H and 13C NMR
spectroscopy, elemental analysis and X-ray crystallography (see
below). Although stable in the solid state and in solution at
J. Chem. Soc., Dalton Trans., 1998, 3623–3628
3625

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Table 2 Selected bond distances (Å) and angles (Њ) for [Ti(NC6H3Pri2-
2,6)Cl2{η2-PhNC(Me)C(Me)NPh}(py)] 4
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–N(3)
Ti(1)–N(4)
Ti(1)–Cl(1)
Ti(1)–Cl(2)
1.729(4)
2.200(5)
2.317(4)
2.222(5)
2.399(2)
2.391(2)
N(2)–C(13)
N(2)–C(17)
N(3)–C(14)
N(3)–C(23)
C(13)–C(14)
C(13)–C(15)
C(14)–C(16)
1.290(7)
1.457(8)
1.268(7)
1.434(8)
1.509(8)
1.487(8)
1.513(7)
N(1)–Ti(1)–N(2)
N(1)–Ti(1)–N(3)
N(2)–Ti(1)–N(3)
N(1)–Ti(1)–N(4)
N(2)–Ti(1)–N(4)
N(3)–Ti(1)–N(4)
N(1)–Ti(1)–Cl(1)
N(2)–Ti(1)–Cl(1)
N(3)–Ti(1)–Cl(1)
N(4)–Ti(1)–Cl(1)
N(1)–Ti(1)–Cl(2)
N(2)–Ti(1)–Cl(2)
N(3)–Ti(1)–Cl(2)
N(4)–Ti(1)–Cl(2)
98.3(2)
169.1(2)
70.8(2)
97.0(2)
164.6(2)
93.8(2)
100.6(2)
88.2(1)
80.5(1)
88.3(1)
100.7(2)
88.4(1)
78.7(1)
89.4(1)
Cl(1)–Ti(1)–Cl(2)
Ti(1)–N(1)–C(1)
Ti(1)–N(2)–C(13)
Ti(1)–N(2)–C(17)
C(13)–N(2)–C(17)
Ti(1)–N(3)–C(14)
Ti(1)–N(3)–C(23)
C(14)–N(3)–C(23)
N(2)–C(13)–C(14)
N(2)–C(13)–C(15)
C(14)–C(13)–C(15)
N(3)–C(14)–C(13)
N(3)–C(14)–C(16)
C(13)–C(14)–C(16)
158.94(6)
179.0(4)
120.6(4)
120.4(3)
118.9(5)
116.7(4)
122.9(3)
120.3(5)
114.9(5)
125.9(6)
119.2(5)
116.2(5)
125.0(5)
118.8(5)
Fig. 1 Displacement ellipsoid (35%) plot of [Ti(NC6H3Pri2-2,6)Cl2-
{η2-PhNC(Me)C(Me)NPh}(py)] 4. Hydrogen atoms and dichloro-
methane molecule of crystallisation are omitted.
But
N
Me
complex.13,35 The trans (with respect to the imido group) bond
from titanium to nitrogen of the α-diimine [Ti(1)–N(3) =
2.317(4) Å] is significantly longer than that to the cis nitrogen
[Ti(1)–N(2) = 2.200(5) Å], consistent with the well-known trans
influence of the imido group.20,36,37 The [Ti(1)N(2)C(13)C(14)-
N(3) ring is effectively planar (maximum deviation from the
best fit plane is 0.054 Å] and the PhNC(Me)C(Me)NPh ligand
adopts an s-cis conformation as required for bidentate coordin-
ation. The internal C=N [N(2)–C(13) = 1.290(7), N(3)–
C(14) = 1.268(7) Å] and C–C [C(13)–C(14) = 1.509(8) Å] dis-
tances are indicative of double and single bonds respectively,
py
Cl
Cl
2
Ti
py
N
py
py
Cl
Cl
Ti
1
2
py
+
py
+
Me
(3)
N
N
being comparable to those of free α-diimines [average C᎐N =
᎐
Me
1.28(2) and C–C = 1.52(4) Å for four crystallographically-
characterised examples].38 These data therefore show that the
diimine is coordinated as a neutral σ-donor ligand as in III
above, as expected since the Ti() centre in the {Ti(NC6H3Pri2-
2,6)Cl2(py)} moiety has no d-electrons available for back-
donation to the diimine ligand.
But
N
N
But
H
F
Ϫ25 ЊC, room temperature solutions of pure 4 decompose sub-
stantially over ca. 4 hours (also in CDCl3, C6D6 or CD2Cl2 in
sealed NMR tubes) to complex mixtures containing
[Ti(NC6H3Pri2-2,6)Cl2(py)2] 3Ј and free aniline H2NC6H3Pri2-
2,6. The fate of the α-diimine ligand is unknown but the simul-
taneous appearance of a fairly viscous, oily material points
towards α-diimine oligomer and/or polymer formation. The
compounds 6 and 7 were substantially less stable in solution,
NMR tube scale reactions showing extensive decomposition of
the first-formed diimine complexes after ca. 1 hour and 10 min-
utes, respectively. Although these compounds and 5 were there-
[Ti(NC6H3Pri2-2,6)Cl2{η2-PhNC(Me)C(Me)NPh}(py)] 4 is
the first structurally characterised example of a titanium com-
plex with a neutral α-diimine ligand, and only the third for
Group 4.6,7 It is interesting to compare the Ti–N(diimine),
diimine C᎐N and backbone C–C distances for 1 with those of
᎐
nine previously described α-diimine complexes of titanium in
which the ligand may be assigned a formal negative charge
between Ϫ1 and Ϫ2.38 For these reduced diimine complexes
substantially shorter Ti–N(diimine) [average 1.96(8) Å] and
diimine C–C [average 1.39(2) Å] distances, and longer diimine
C᎐N [average 1.37(2) Å] distances are found, consistent with a
᎐
1
fore characterised by H NMR spectroscopy only, the close
significant contribution from resonance form IV above.
The solution 1H and 13C NMR (recorded at 258 K owing to
its limited solution stability) data for 4 are consistent with the
solid state structure. In particular the 13C resonances for the
similarity of these spectra (exhibiting, for example, two differ-
ent ArNC(Me)C(Me)NAr methyl group resonances) to those
for the fully-characterised 4 lends confidence to the structures
proposed in Scheme 1. Single crystals of [Ti(NC6H3Pri2-
2,6)Cl2{η2-PhNC(Me)C(Me)NPh}(py)]ؒCH2Cl2 were grown at
Ϫ25 ЊC by layering a saturated dichloromethane solution of 4
with hexane. A view of the molecular structure of 4 is shown in
Fig. 1 and selected bond lengths and angles are given in Table 2.
Molecules of 4 contain a six-coordinate Ti centre ligated by a
2,6-diisopropylphenylimido group with one pyridine and two
mutually trans Cl ligands cis to it. The coordination sphere is
completed by an η2-coordinated PhNC(Me)C(Me)NPh ligand
with one nitrogen cis and one trans to the imido group. The
titanium–imido nitrogen, –pyridine nitrogen and –chloride dis-
tances are unexceptional for this type of six-coordinate imido
PhN᎐C imino carbons appear at δ 165.7, very close to the cor-
᎐
responding signals for free diimines ArNC(Me)C(Me)NAr, and
not substantially upfield (i.e. more olefinic) as would be
expected for a reduced diimine as in IV.39 The 1H NMR data for
the less stable compounds 5, 6 and 7 are very similar to those of
1 and so also consistent with the structures illustrated in
Scheme 1.
As shown in Scheme 1, attempts to synthesise complexes
using the aryl ring-substituted α-diimines ArNC(Me)C(Me)-
NAr (Ar = C6H3Me2-2,6 C or C6H3Pri2-2,6 D) were unsuccess-
ful and led to no reaction. However, heating a toluene solution
of tert-butylimido complex [Ti(NBut)Cl2(py)3] 1 with ca. 1.1
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J. Chem. Soc., Dalton Trans., 1998, 3623–3628

View Article Online
equivalents of ArNC(H)C(H)CNAr (Ar = C6H3Me2-2,6 E, i.e.
with no methyl groups in the backbone) at 100 ЊC for 1 week
followed by subsequent workup afforded the previously
described20 arylimido bis(pyridine) complex [Ti(NC6H3Me2-
2,6)Cl2(py)2] 2Ј as the only metal-containing product [eqn. (2)].
When the reaction was monitored on an NMR tube scale
(ratio of 1:E again ca. 1.0:1.1) at 60 ЊC in CDCl3, resonances
for [Ti(NC6H3Me2-2,6)Cl2(py)2] 2Ј grew in over 6 days until all
of the starting complex 1 was converted to 2Ј. The NMR tube
experiment also revealed the organic side products of the reac-
tion to be ButNC(H)C(H)NBut F and ArNC(H)C(H)NBut
(Ar = C6H3Me2-2,6 G). The ratio of 2:G:F:unchanged starting
diimine E was ca. 1.0:0.21:0.40:0.63. No resonances for α-
diimine complexes of either the starting or product diimines
were observed at any time. When the NMR tube reaction of 1
and E was carried out on a ca. 2:1 scale (i.e. a 1:1 ratio of
Ti᎐NBut to C᎐NAr functional group) negligible quantities of
most likely that the process of complex formation in these cases
makes accessible facile diimine oligomerisation and/or polymer-
isation routes not otherwise available (under analogous condi-
tions in the absence of metal imide complex the α-diimines A
and B are stable in solution). Thus although there might be a
pathway for imide/imine metathesis reactions of A and B it
presumably cannot compete with the rapid α-diimine complex
formation and subsequent degradation.
Conclusions
We have described the first metal imide/α-diimine metathesis
reactions together with a rare example of a structurally-
characterised, neutral α-diimine metal complex (the first such
derivative for titanium). The transition metal and organic
products obtained are highly dependent on the nature of
the imido N-group and the α-diimine N- and backbone
C-substituents.
᎐
᎐
the mixed aryl-tert-butyl diimine G were formed, the major
observed products being imido complex 2Ј and diimine F.
In order to make a better comparison with the complex
formation reactions of the methyl-substituted diimines (Scheme
1) and the imide/imine metathesis reaction in eqn. (2) the
reaction of the di-p-tolyl-α-diimine H with 1 was followed by
1H NMR [eqn. (3)]. The reaction of 1 with H (ratio of 1:H ca.
2:1, i.e. a 1:1 ratio of Ti᎐NBut to C᎐NTol functional group)
Acknowledgements
This work was supported by grants from the EPSRC, Lever-
hulme Trust and Royal Society. We are grateful to Dr W.-S. Li
for help with X-ray data collection, Dr R. A. Fisher (Exxon
Chemical Company) for a gift of certain α-diimines, and Dr A.
G. Moody for a sample of ButNC(H)C(H)NBut and helpful
discussions. We also acknowledge the use of the EPSRC
Chemical Database Service at CLRC Daresbury Laboratory.
Philip Mountford is the Royal Society of Chemistry Sir Edward
Frankland Fellow for 1998–1999.
᎐
᎐
proceeds smoothly and cleanly at room temperature to give
quantitative formation of the previously described [Ti-
(NTol)Cl2(py)3]20 and ButNC(H)C(H)NBut F after 24 hours.
Examination of the reaction at intervals showed no evidence
for formation of
a
complex such as [Ti(NBut)Cl2{η2-
TolNC(H)C(H)NTol}(py)] that would be analogous to 4
(Scheme 1), although signals attributable to the expected
intermediate mixed α-diimine TolNC(H)C(H)NBut were
observed at intermediate stages of the reaction.
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᎐
J. Chem. Soc., Dalton Trans., 1998, 3623–3628
3627

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Paper 8/06393A
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J. Chem. Soc., Dalton Trans., 1998, 3623–3628