Reactions of imines with half-open titanocenes: Substituent effects and tandem couplings with nitriles and isonitriles

Article abstract of DOI:10.1021/om990463h

The syntheses and characterizations of half-open titanocenes containing bulky Cp ligands are described. Such species include Ti[1,3-C₅H₃(t-C₄H₉) ₂](Pdl)(PX₃) (Pdl = 2,4-C₇H₁₁, X = Me; Pdl = C₅H₇, X = Me or Et) and Ti[1,3-C₅H₃(SiMe₃)₂](2,4-C ₇H₁₁)(PMe₃) (C₇H₁₁ = dimethylpentadienyl). The structure of Ti[1,3-C₅H₃(t-C₄H₉) ₂](C₅H₇)PMe₃ was determined, and revealed markedly shorter Ti-C bonds for the open dienyl ligand as compared to the cyclic one. The first 2,4-C₇H₁₁ complex undergoes a coupling reaction with imines, generating a chiral center with the opposite stereochemistry, as demonstrated by a solid-state structural determination, as occurs in a similar coupling reaction with the Ti(C₅H₅)(2,4-C₇H₁₁) fragment. In addition, mixed coupling reactions can be achieved through the addition of nitriles or isonitriles to the C₆H₅C(H)=N(i-C₃H₇)-Ti(C ₅H₅)(2,4-C₇H₁₁) coupling product. These reactions result in the incorporation of either one equivalent of nitrile (p-CH₃C₆H₄CN) or four equivalents of isonitrile (P-CH₃C₆H₄NC). Structures of both of these species were determined, and a mechanism is proposed for the latter reaction.

Full text of DOI:10.1021/om990463h

4174
Organometallics 1999, 18, 4174-4182
Rea ction s of Im in es w ith Ha lf-Op en Tita n ocen es:
Su bstitu en t Effects a n d Ta n d em Cou p lin gs w ith Nitr iles
a n d Ison itr iles
Robert Tomaszewski,† Kin-Chung Lam,‡ Arnold L. Rheingold,*,‡ and
Richard D. Ernst*,†
The Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, and the
University of Delaware, Newark, Delaware 19716
Received J une 14, 1999
The syntheses and characterizations of half-open titanocenes containing bulky Cp ligands
are described. Such species include Ti[1,3-C5H3(t-C4H9)2](Pdl)(PX3) (Pdl ) 2,4-C7H11, X )
Me; Pdl ) C5H7, X ) Me or Et) and Ti[1,3-C5H3(SiMe3)2](2,4-C7H11)(PMe3) (C7H11
)
dimethylpentadienyl). The structure of Ti[1,3-C5H3(t-C4H9)2](C5H7)PMe3 was determined,
and revealed markedly shorter Ti-C bonds for the open dienyl ligand as compared to the
cyclic one. The first 2,4-C7H11 complex undergoes a coupling reaction with imines, generating
a chiral center with the opposite stereochemistry, as demonstrated by a solid-state structural
determination, as occurs in a similar coupling reaction with the Ti(C5H5)(2,4-C7H11) fragment.
In addition, mixed coupling reactions can be achieved through the addition of nitriles or
isonitriles to the C6H5C(H)dN(i-C3H7)-Ti(C5H5)(2,4-C7H11) coupling product. These reactions
result in the incorporation of either one equivalent of nitrile (p-CH3C6H4CN) or four
equivalents of isonitrile (p-CH3C6H4NC). Structures of both of these species were determined,
and a mechanism is proposed for the latter reaction.
In tr od u ction
half-open titanocenes and examined the effects that
bulky substituents have on the coupling processes. In
addition, new tandem coupling reactions of an imine
with a nitrile or isonitrile were investigated.
The coupling reactions of half-open titanocenes with
some ketones,1 isonitriles,1 and alkynes2 lead to multiple
incorporations of the unsaturated molecules, but inter-
mediate products have not to date been observable. This
is perhaps an indication that once the first coupling
occurs, the original dienyl fragment is converted to an
even more reactive coordinated diene. In contrast, for
reactions with imines, one equivalent is incorporated
quite rapidly,1 but the incorporation of a second equiva-
lent can also be achieved, in a reaction which is
significantly slower as a presumed result of greater
steric demands of the imines which have been em-
ployed.3 As a result, this has led to the possibility of
bringing about mixed coupling reactions, in which an
imine is first incorporated, followed by a second sub-
strate, such as a ketone or isonitrile. In these reactions,
a chiral center is generated selectively at the coupled
imine carbon atom, and there is a potential for generat-
ing further chiral centers through subsequent reac-
tions.4 Because it could be possible for highly modified
cyclopentadienyl ligands to alter the course of these
coupling reactions, we therefore prepared several new
Exp er im en ta l Section
All preparations, reactions, and manipulations of these
compounds were carried out under a prepurified nitrogen
atmosphere, using either Schlenk techniques or a glovebox.
Hydrocarbon, ethereal, and aromatic solvents were dried and
deoxygenated by distillation from sodium benzophenone ketyl
under a nitrogen atmosphere. Spectroscopic data were ob-
tained as previously described.5 The 13C NMR spectra were
not precisely integrated, but numbers of carbon atoms are
reported in accord with their assignments. Elemental analyses
were obtained from E & R Microanalytical Labs, Robertson
Microanalytical Labs, or Desert Analytics. Pentadienyl anions6
and Ti(C5H5)(2,4-C7H11)(PEt3)7 (C7H11 ) dimethylpentadienyl)
were prepared as previously described.
Ti(1,3-t-Bu 2C5H3)(C5H7)[P (CH3)3] 1. To a red solution of
Ti(1,3-t-Bu2C5H3)Cl3 (3.00 g, 9.05 mmol) in 50 mL tetrahydro-
furan (THF) under a nitrogen atmosphere was added activated
zinc dust (2.00 g, 30.6 mmol), which led to the formation of a
green-blue solution, and the mixture was then stirred over-
night. To the aquamarine solution was then added P(CH3)3
(0.940 mL, 9.08 mmol) and the mixture was stirred for 3 h.
The solution was then cooled to -78° and K(C5H7) (3.00 g, 28.2
* To whom correspondence should be addressed.
† University of Utah.
‡ University of Delaware.
(1) Waldman, T. E.; Wilson, A. M.; Rheingold, A. L.; Mele´ndez, E.;
Ernst, R. D. Organometallics 1992, 11, 3201.
(2) Wilson, A. M.; Waldman, T. E.; Rheingold, A. L.; Ernst, R. D. J .
Am. Chem. Soc. 1992, 114, 6252.
(3) Tomaszewski, R.; Arif, A. M.; Ernst, R. D. J . Chem. Soc., Dalton
Trans. 1999, 1883.
(5) Newbound, T. D.; Stahl, L.; Ziegler, M. L.; Ernst, R. D. Orga-
nometallics 1990, 9, 2962.
(6) (a) Yasuda, H.; Ohnuma, Y.; Yamauchi, M.; Tani, H.; Nakamura,
A. Bull. Chem. Soc. J pn. 1979, 52, 203. (b) Hartmann, J .; Schlosser,
M. Helv. Chim. Acta. 1976, 59, 453. (c) Wilson, D. R.; Stahl, L.; Ernst,
R. D. Organomet. Synth. 1986, 3, 136.
(4) Wilson, A. M.; West, F. G.; Arif, A. M.; Ernst, R. D. J . Am. Chem.
Soc. 1995, 117, 8490.
(7) Mele´ndez, E.; Arif, A. M.; Ziegler, M. L.; Ernst, R. D. Angew.
Chem., Intl. Ed. Engl. 1988, 27, 1099.
10.1021/om990463h CCC: $15.00 © 1999 American Chemical Society
Publication on Web 08/31/1999

Reactions with Half-Open Titanocenes
Organometallics, Vol. 18, No. 20, 1999 4175
mmol) in 50 mL of THF was added dropwise via a pressure
equalizing addition funnel. The green solution turned violet
immediately and was allowed to warm to room temperature,
during which time it turned red-brown. The solvent was then
removed in vacuo to give a brown-red solid. The solid was
extracted with three 100 mL portions of ether and filtered
through a Celite pad on a coarse frit. Concentration in vacuo
of the red-brown filtrate to approximately 100 mL and cooling
to -30° for 3 days gave 1.80 g (55%) of the product as air-
) 14 Hz, C-1,5), 33.6 (q of quintets, 6C, J ) 126, 5 Hz,
(CH3)3C), 32.6 (s, 2C, (CH3)3C), 31.9 (q of m, 2C, J ) 126 Hz,
CH3-Pdl), 20.1 (q, 3C, J ) 128 Hz, J C-P ) 12 Hz, P(CH3)3).
Ti{1,3-[(CH3)3Si]2C5H3}(2,4-C7H11)[P (CH3)3], 4. A solution
9
of Ti{1,3-[(CH3)3Si]2C5H3}Cl3 (1.80 g, 4.95 mmol) in 50 mL
THF under nitrogen was stirred with activated zinc dust (0.70
g, 11 mmol) for 24 h. To the blue-green solution, P(CH3)3 (0.560
mL, 5.41 mmol) was then added at 0°. After overnight stirring,
the mixture was cooled to -78° and K(2,4-C7H11) (2.00 g, 14.9
mmol) in 50 mL THF was added dropwise through a pressure
equalizing addition funnel. After identical treatment as in the
compound above, the red-brown filtrate was concentrated in
vacuo to ca. 50 mL, and was cooled to -30° for 3 days to gave
0.32 g (15%) of the product as air-sensitive orange crystals (mp
sensitive yellow crystals (mp 139-141°). Anal. Calcd. for
1
C
21H37PTi: C, 68.01; H, 10.49. Found: C, 68.46; H, 10.12. H
NMR (benzene-d6, ambient): δ 6.41 (t, 1H, J ) 10 Hz, H-3),
6.36 (m, 2H, Cp), 4.74 (q, 2H, J ) 10 Hz, H-2,4), 4.23 (t, 1H,
J ) 2.4 Hz, Cp), 1.83 (t, 2H, J ) 8 Hz, H-1,5exo), 0.96 (d, 9H,
J ) 5.4 Hz, P(CH3)3), 0.73 (s, 18H, (CH3)3C), -0.87 (q, 2H, J
) 8 Hz, H-1,5endo). 13C NMR (benzene-d6, ambient): δ 134.0
(s, 2C, Cp), 112.6 (d, 1C, J ) 158 Hz, C-3), 94.2 (dt, 1C, J )
167, 5 Hz, Cp), 93.5 (dt, 2C, J ) 158, 9 Hz, C-2,4), 89.8 (dt,
2C, J ) 166, 7 Hz, Cp), 52.6 (tt, 2C, J ) 148 Hz, J C-P ) 8 Hz,
C-1,5), 32.4 (s, 1C, (CH3)3C), 31.3 (q of quintets, 6C, J ) 125,
4 Hz, (CH3)3C), 19.9 (qd, 3C, J ) 127 Hz, J C-P ) 12 Hz,
P(CH3)3).
Ti(1,3-t-Bu 2C5H3)(C5H7)[P (CH2CH3)3] 2. To a red solution
of Ti(1,3-t-Bu2C5H3)Cl3 (3.00 g, 9.05 mmol) in 50 mL THF
under a nitrogen atmosphere was added activated zinc dust
(2.00 g, 30.6 mmol), leading to the formation of a green-blue
solution, which was then stirred overnight. To the aquamarine
solution was then added P(CH2CH3)3 (1.60 mL, 10.8 mmol) and
the mixture was stirred for 3 h. Then the solution was cooled
to -78° and K(C5H7) (3.00 g, 28.2 mmol) in 50 mL of THF was
added dropwise via a pressure equalizing addition funnel.
After identical treatment as above, the red-brown filtrate was
concentrated to ca. 100 mL, and was cooled to -30° for 3 days
to gave 1.48 g (40%) of the product as air-sensitive yellow-
brown crystals (mp 119-121°). 1H NMR (benzene-d6, ambi-
ent): δ 6.41 (d, 2H, J ) 2.5 Hz, Cp), 6.35 (t, 1H, J ) 9.8 Hz,
H-3), 4.81 (q, 2H, J ) 9.9 Hz, H-2,4), 4.11 (t, 1H, J ) 2.5 Hz,
Cp), 2.00 (dd, 2H, J ) 7, 11 Hz, H-1,5exo), 1.38 (m, 6H, P(CH2-
CH3)3), 0.74 (s, 18H, (CH3)3C), 0.71 (m, 9H, P(CH2CH3)3), -0.82
(dd, 2H, J ) 7, 11 Hz, H-1,5endo). 13C NMR (benzene-d6,
ambient): δ 134.0 (s, 2C, Cp), 111.3 (d, 1C, J ) 158 Hz, C-3),
94.9 (dt, 1C, J ) 164, 6 Hz, Cp), 93.6 (dd, 2C, J ) 156, 10 Hz,
C-2,4), 89.9 (dt, 2C, J ) 166, 7 Hz, Cp), 54.3 (td, 2C, J ) 149,
9 Hz, C-1,5), 32.4 (s, 2C, (CH3)3C), 31.3 (q of quintets, 6C, J )
125, 5 Hz, (CH3)3C), 19.1 (t, 3C, J ) 131 Hz, J C-P ) 7 Hz,
P(CH2CH3)3), 8.1 (q, 3C, J ) 126 Hz, P(CH2CH3)3).
1
160-162°). H NMR (benzene-d6, ambient): δ 7.81 (d, 1H, J
) 6.7 Hz, Cp), 6.01 (s, 1H, H-3), 4.09 (d, 2H, J ) 1.9 Hz, Cp),
1.98 (s, 6H, CH3-Pdl), 1.74 (d, 2H, J ) 5.3 Hz, H-1,5exo), 0.98
(d, 9H, J ) 4.9 Hz, P(CH3)3), 0.10 (s, 18H, (CH3)3Si), -0.75 (t,
2H, J ) 4.9 Hz, H-1,5endo). 13C NMR (benzene-d6, ambient): δ
122.2 (d, 1C, J ) 166 Hz, Cp), 113.3 (d, 1C, J ) 158 Hz, C-3),
111.4 (d, 2C, J ) 170 Hz, Cp), 111.3 (s, 2C, Cp), 102.5 (s, 2C,
C-2,4), 54.5 (t, 2C, J ) 147 Hz, C-1,5), 31.2 (q, 2C, J ) 119
Hz, CH3-Pdl), 21.0 (q, 3C, J ) 137 Hz, P(CH3)3), 1.5 (q, 6C, J
) 117 Hz, (CH3)3Si).
Ti(1,3-t-Bu 2C5H3)(NMeCHP h CH 2CMedCHCMedCH2),
6. To a solution of Ti(1,3-t-Bu2C5H3)(2,4-C7H11)[P(CH3)]3] (0.25
g, 0.63 mmol) in 30 mL THF at -78° under a nitrogen
atmosphere was added C6H5C(H)NCH3 (0.080 mL, 0.65 mmol).
On warming to room temperature a color change from orange
to dark red resulted and the mixture was stirred overnight.
The solvent was next removed in vacuo and the red sticky
residue was extracted with two 30 mL portions of pentane.
The extracts were filtered through a Celite pad on a coarse
frit. The red filtrate was concentrated in vacuo to ca. 10 mL
prior to cooling at -30° for 2 days. Removal of the supernatant
via syringe and drying in vacuo gave 0.12 g (42%) of the
product as an air-sensitive red microcrystalline powder (mp
92-94°). Anal. Calcd. for C28H41NTi: C, 76.51; H, 9.40; N, 3.20.
Found: C, 76.39; H, 9.33; N, 3.16. 1H NMR (benzene-d6,
ambient): δ 7.2-7.0 (m, 5H, Ph), 6.02 (t, 1H, J ) 3 Hz, Cp),
4.88 (t, 1H, J ) 3 Hz, Cp), 4.59 (dd, 1H, J ) 7, 11 Hz), 4.13 (t,
1H, J ) 3 Hz, Cp), 4.09 (s, 1H, H-3), 3.06 (obscd., 1H), 3.05 (s,
3H, NCH3), 2.51 (d, 1H, J ) 7 Hz), 2.26 and 2.23 (2m, 2H),
2.14 (s, 3H, CH3-Pdl), 1.94 (s, 3H, CH3-Pdl), 1.29 (s, 9H,
(CH3)3C), 1.21 (s, 9H, (CH3)3C). 13C NMR (benzene-d6, ambi-
ent): δ 145.5 (s, 1C, Ph), 142.6 (s, 1C, Cp), 142.5 (s, 1C, Cp),
126-129 (m, 5C, Ph), 122.3 (s, 1C, C-2 or 4), 116.6 (d, 1C, J )
152 Hz, C-3), 107.1 (dt, 1C, J ) 165, 7 Hz, Cp), 102.8 (dt, 1C,
J ) 169, 7 Hz, Cp), 100.6 (dt, 1C, J ) 168, 8 Hz, Cp), 92.8 (s,
1C, C-2 or 4), 75.4 (d, 1C, J ) 135 Hz, C(H)N), 60.6 (t, 1C, J
) 149 Hz, C-5), 48.4 (q, 1C, J ) 132 Hz, N(CH3)), 47.0 (t, 1C,
J ) 127 Hz, C-1), 33.8 (s, 1C, (CH3)3C), 33.5 (s, 1C, (CH3)3C),
32.8 (q of quintets, 1C, J ) 126, 7 Hz, CH3-Pdl), 32.0 (q of
quintets, 1C, J ) 126, 5 Hz, (CH3)3C), 31.7 (q of quintets, 1C,
J ) 126, 5 Hz, (CH3)3C), 29.4 (q of quintets, 1C, J ) 126, 7
Hz, CH3-Pdl).
Ti(C5H 5){N(i-P r )CH P h CH 2CMe CH CMe CH 2C[p -CH 3-
(C6H4)]N}, 8. To a stirred solution of Ti(C5H5)(2,4-C7H11)-
[C6H5C(H)NCH(CH3)2]3 (0.40 g, 1.1 mmol) in 50 mL ether
under nitrogen at -78° was added p-tolunitrile (0.20 mL, 1.7
mmol, 1.5 eq). A rapid color change from dark red to bright
red occurred upon the addition. After the mixture was warmed
with stirring to room temperature, the solvent was removed
in vacuo, yielding a red solid. The solid was in turn extracted
with three 50 mL portions of pentane. The extracts were
filtered through a Celite pad on a coarse frit. The bright red
filtrate was concentrated in vacuo to ca. 20 mL and placed
into a -30 °C freezer for 2 days. Removal of the supernatant
via syringe and drying in vacuo gave 0.40 g (76%) of the
Ti(1,3-t-Bu 2C5H3)(2,4-C7H11)[P (CH3)3], 3. To a red solution
8
of Ti(1,3-t-Bu2C5H3)Cl3 (3.00 g, 9.05 mmol) in 50 mL THF
under nitrogen was added activated zinc dust (2.00 g, 30.6
mmol), after which a green-blue color formed and the mixture
was stirred overnight. To the aquamarine solution was added
P(CH3)3 (0.940 mL, 9.08 mmol) and the resulting green
solution was stirred for 3 h. The solution was then cooled to
-78° and K(2,4-C7H11) (3.60 g, 26.8 mmol) in 50 mL of THF
was added dropwise via a pressure equalizing addition funnel.
After identical treatment as in the compound above, the red-
brown filtrate was concentrated in vacuo to ca. 50 mL, and
was cooled to -90° for over 3 weeks to gave 0.902 g (25%) of
the product as an air-sensitive yellow-brown, lumpy solid (mp
55-58°). Anal. Calcd. for C23H41PTi: C, 69.68; H, 10.42.
Found: C, 69.44; H, 10.31; N, 0.00. 1H NMR (toluene-d8,
ambient): δ 7.38 (t, 1H, J ) 2.7 Hz, Cp), 5.80 (s, 1H, H-3),
3.64 (d, 2H, J ) 2.6 Hz, Cp), 2.20 (s, 6H, CH3-Pdl), 1.67 (dd,
2H, J ) 4.6, 2.0 Hz, H-1,5exo), 1.00 (s, 18H, (CH3)3C), 0.93 (d,
9H, J ) 4.5 Hz, P(CH3)3), -0.48 (d, 2H, J ) 5.9 Hz, H-1,5endo).
13C NMR (toluene-d8, ambient): δ 126.6 (s, 2C, Cp), 111.4 (d,
1C, J ) 156 Hz, C-3), 104.7 (s, 2C, C-2,4), 102.3 (dt, 1C, J )
163, 7 Hz, Cp), 99.6 (dt, 2C, J ) 171, 5 Hz, Cp), 57.4 (t, 2H, J
(8) J ibril, I.; Abu-Orabi, S.; Klaib, S. A.; Imhof, W.; Huttner, G. J .
Organometal. Chem. 1992, 433, 253.
(9) Okuda, J .; Herdtweck, E. Inorg. Chem. 1991, 30, 1516.

4176 Organometallics, Vol. 18, No. 20, 1999
Tomaszewski et al.
Ta ble 1. Cr ysta l, Da ta , a n d Refin em en t P a r a m eter s for C21H37P Ti, C28H41NTi, C30H36N2Ti, a n d
C56H63N5O0.5Ti
formula
C21H37PTi
736.75
233
0.71073
monoclinic
P21/n
C28H41NTi
439.5
224
0.71073
triclinic
P1h
C30H36N2Ti
472.5
298
0.71073
monoclinic
C2/c
C56H63N5O0.5Ti
862.0
298
0.71073
triclinic
P1h
formula weight
temperature (K)
λ, Å
crystal system
space group
unit cell dimensions
a, Å
13.403(4)
19.143(8)
17.708(4)
90
108.39(2)
90
4312(2); 8
1.135
4.70
2.1-21.0°
-1 e h e 13
-1e k e 19
-17e l e 17
5781
10.420(4)
13.733(4)
18.843(7)
69.18(4)
81.24(4)
89.48(3)
2488(1); 4
1.173
12.303(2)
26.807(4)
15.535(3)
90
92.50(3)
90
5118(1); 8
1.226
3.54
2.0-25.0°
-14 e h e 14
0e k e 31
0e l e 18
5368
11.286(3)
12.832(2)
19.672(4)
79.05(1)
82.17(2)
67.66(2)
2581(1); 2
1.109
b, Å
c, Å
R
â
γ
volume (Å3); Z
density (calc)
abs coeff, cm-1
θ range
3.58
2.06
2.0-22.5°
-11 e h e 11
-13e k e 14
0e l e 20
6758
2.1-22.5°
-1e h e 12
-13e k e 13
-21e l e 17
7512
limiting indices
reflns collected
indpendent reflns; n: I > nσ(I)
4620; 2
0.047
0.106
6527; 2
0.077
0.094
0.64/-0.20
4467; 2
0.053
0.090
6328; 2
0.106
0.237
0.61/-0.70
R(F)
R(wF2)
max/min diff. Fourier peak (e/Å3)
0.50/-0.28
0.36/-0.38
product as an air-sensitive red solid (mp 138-140°). Anal.
1. Suitable crystals were selected and mounted in thin-walled,
nitrogen-flushed, glass capillaries. No absorption corrections
were required because ψ-scan data revealed less than a 10%
variation in azimuthal scans. Each structure was solved by
direct methods, subsequent difference Fourier syntheses, and
least-squares refinements. All hydrogen atoms were treated
as idealized contributions, and except for 12, all non-hydrogen
atoms were refined anisotropically.
Preliminary photographic data for 1 indicated a monoclinic
crystal system and the systematic absences in the diffraction
data were uniquely consistent with the reported space group.
The asymmetric unit consisted of two independent, but chemi-
cally equivalent molecules.
No evidence of symmetry higher than triclinic was observed
in either the photographic or diffraction data for 6. The
E-statistics suggested the centrosymmetric alternative (P1h)
which was confirmed by the chemically reasonable results of
refinement. There are two independent but chemically equiva-
lent molecules in the asymmetric unit. The phenyl rings were
fixed as rigid groups in order to keep a reasonable data/
parameter ratio.
The photographic data, unit-cell parameters, diffraction
symmetry, and systematic absences in the diffraction data of
8 were consistent with either of the monoclinic space groups
C2/c or Cc. The E-statistics suggested the centrosymmetric
space group which was verified by the chemically reasonable
results of refinement.
For complex 12, no evidence of symmetry higher than
triclinic was observed in either the photographic or diffraction
data. E-statistics suggested a centrosymmetric space group
and P1h was chosen. The space group choice was subsequently
verified by chemically reasonable and computationally stable
results of refinement. After 15 crystals of this sample were
screened, the best crystal was selected for data collection. The
crystal was a very weak diffractor (I/σ ) 3.5) with broad peak
widths. All attempts to grow better crystals of this compound
were unsuccessful. The carbon atoms in the phenyl and para-
tolyl groups groups were refined isotropically. All phenyl rings
and the cyclopentadienyl ring were refined as rigid planar
groups to conserve data. There is a partially occupied solvent
molecule of diethyl ether in the asymmetric unit and its
occupancy refined to 50%. The hydrogen atoms on the solvent
molecule were ignored. All software and sources of the scat-
tering factors are contained in the SHELXTL (5.3) program
library (G. Sheldrick, Siemens XRD, Madison, WI).
Calcd. for C30H36N2Ti: C, 76.25; H, 7.68; N, 5.93. Found: C,
76.08; H, 7.72; N, 5.86. 1H NMR (benzene-d6, ambient):
δ
7.39-6.98 (9H), 6.69 (s, 1H), 5.77 (s, 5H, Cp), 4.91 (d, 1H, J )
6.2 Hz), 4.69 (s, 1H), 4.49 (s, 1H), 4.07 (septet, 1H, J ) 6.5
Hz, CH(CH3)2), 3.15 (dd, 1H, J ) 6, 12 Hz, CHPh), 2.26 (d,
1H, J ) 12.4 Hz), 2.08 (s, 3H, CH3), 1.88 (s, 3H, CH3), 1.70 (s,
3H, CH3), 0.70 (d, 3H, J ) 6.4 Hz, CH(CH3)2), 0.66 (d, 3H, J )
6.7 Hz, CH(CH3)2). 13C NMR (benzene-d6, ambient): δ 155.8
(s, 1C, CdN), 151.8 (s, 1C, Ph), 138.5 (s, 1C, Ph), 134.0 (s, 1C,
Ph), 129-124.5 (9C, Ph), 120.2 (s, 1C, C-2 or 4), 111.2 (s, 1C,
C-2 or 4), 109.0 (d of quintets, 5C, J ) 171, 7 Hz, Cp), 93.8 (d,
1C, J ) 166, C-3), 81.5 (d, 1C, J ) 131 Hz, CHPh), 57.2 (d,
1C, J ) 135 Hz, CH(CH3)2), 46.6 (2t, 2C, J ) 127 Hz, C-1,5),
30.4 (q, 1C, J ) 128 Hz, CH3-Pdl), 28.8 (q, 1C, J ) 127 Hz,
CH3-Pdl), 24.6 (q, 1C, J ) 127 Hz, p-CH3Ph), 22.4 (q, 1C, J )
125 Hz, CH(CH3)2), 21.2 (q, 1C, J ) 125 Hz, CH(CH3)2).
Ti(C5H5)(2,4-C7H11)[C6H5C(H)NCH(CH3)2][4-CH3(C6H4)-
NC]4, 12. A 250 mL flask equipped with a magnetic stirring
bar and nitrogen inlet was charged with Ti(C5H5)(2,4-C7H11)-
[C6H5C(H)NCH(CH3)2]3 (0.50 g, 1.4 mmol) and 40 mL of THF.
The mixture was next cooled to -78° and p-tolylisocyanide
(0.91 mL, 7.0 mmol) was added via syringe. A rapid color
change from dark red to dark orange occurred. The reaction
mixture was allowed to warm to room temperature, after
which a reddish-orange mixture remained. The solvent was
removed in vacuo to yield an orange-brown solid. Extraction
of the solid with a 50:50 ether-pentane mixture and filtration
through a Celite pad gave a dark orange filtrate. Placement
of the flask into the -30° freezer gave a dark red-orange solid
which upon recrystallization gave 0.41 g (35%) of the title
compound as a dark red crystalline powder (mp 145-147°).
Anal. Calcd. for C54H57N5Ti: C, 78.71; H, 6.97; N, 8.49.
Found: C, 78.53; H, 6.98; N, 8.48. 1H NMR (benzene-d6,
ambient, some peaks obscured): δ 7.35-6.52 (21H, Ph), 6.18
(s, 5H, Cp), 5.06 (s, 1H), 3.92 (d, 1H, J ) 17.5 Hz), 3.12 (septet,
1H, J ) 6.5 Hz), 2.88 (dd, 1H, J ) 11, 14 Hz), 2.52 (dd, 1H, J
) 6, 15 Hz), 2.35 (d, 1H, J ) 17.5 Hz), 2.22 (s, 3H, CH3), 2.12
(s, 3H, CH3), 1.95 (s, 3H, CH3), 1.93 (s, 3H, CH3), 1.64 (s, 3H,
CH3), 1.43 (d, 3H, J ) 6.6 Hz, CH(CH3)2), 1.40 (s, 3H, CH3),
0.51 (d, 3H, J ) 6.1 Hz, CH(CH3)2). IR (Nujol mull): 1629 (m),
1601 (w), 1503 (vs), 1348 (m), 1261 (vs), 1099 (vs), 1021 (vs),
865 (w), 802 (vs), 701 (w).
Cr ysta llogr a p h ic Str u ctu r a l Deter m in a tion s. Crystal,
data collection, and refinement parameters are given in Table

Reactions with Half-Open Titanocenes
Organometallics, Vol. 18, No. 20, 1999 4177
Resu lts a n d Discu ssion
Although half-open titanocenes, M(C5H5)(Pdl)(L), have
been prepared with a variety of pentadienyl ligands
10
(e.g., Pdl ) C5H7,10 3-C6H9,11 2,4-C7H11
,
6,6-dmch,4
C8H11; L ) CO, PMe3, PEt3; C6H9 ) methylpentadienyl,
C7H11 ) dimethylpentadienyl, dmch ) dimethylcyclo-
hexadienyl, C8H11 ) cyclooctadienyl)12 and found to
have rich and diverse structural natures and chemical
reactivities, no efforts have yet been made to explore
the potentially significant benefits that might arise from
the use of bulkier analogues of the C5H5 ligand. It has
now been proven possible to make a variety of such
species by a procedure essentially identical to that
employed for the other half-open titanocenes (eq 1).
Ti(1,3-R2C5H3)Cl2(THF)2 + PR3′ + 2KPdl f
Ti(1,3-R2C5H3)(Pdl)(PR3′) (1)
F igu r e 1. Perspective View of Ti[C5H3(t-C4H9)2](C5H7)-
(PMe3), 1.
where Pdl ) C5H7, R ) CMe3, R′ ) Me (1) or Et (2); Pdl
) 2,4-C7H11, R ) CMe3 (3) or SiMe3 (4), R′ ) Me.
Confirmation of this assignment has been obtained for
1 (Figure 1 and Table 2). In this case, two independent
molecules are found in the unit cell, but there are no
significant differences between them.
Their PMe3 ligands have one methyl group rotated
around the Ti-P bond by ca. 19.4° away from the center
of the open edge of the C5H7 ligands, intermediate
between the generally observed extremes of 0° and 30°
(“90°”). The bulky t-C4H9 groups are oriented away from
the PMe3 ligand and the open dienyl edge. As in other
half-open titanocenes, the M-C(Pdl) bond distances are
significantly shorter than those for the aromatic π
ligand. The Ti-C bond distances for the open ligands
thus average14 2.242(2) vs 2.391(1) Å for the cyclic
ligands, leading to a remarkable difference of 0.15 Å!
These values can be compared to those for Ti(C5H5)(2,4-
C7H11)(PEt3) (5), 2.240(3) and 2.346(4) Å, respectively.
It appears that the bulky t-C4H9 substituents have
selectively weakened the bonding for the cyclic ligand,
and although it could be possible that higher thermal
libration for the C5H5 ligand simply led to a systematic
shortening of the apparent Ti-C(C5H5) bond lengths in
5, the Ti-Cp centroid distance here (2.065 Å) is longer
than that in 5 (2.049 Å). The Ti-C bonds for the cyclic
ligands are not very regular. Those for C(8,9), at the
uncrowded end of the ring, are significantly shorter than
The resulting 16 electron complexes are air-sensitive
and diamagnetic, as are all previously reported half-
open titanocenes.4,10-12,13 Spectroscopic data for these
complexes are consistent with the general structures
previously established for half-open titanocenes, e.g., 5.
(10) Hyla-Kryspin, I.; Waldman, T. E.; Mele´ndez, E.; Trakarnpruk,
W.; Arif, A. M.; Ziegler, M. L.; Ernst, R. D.; Gleiter, R. Organometallics
1995, 14, 5030.
(11) Wilson, A. M. Ph.D. Thesis, University of Utah, Salt Lake City,
UT 1994.
(12) Tomaszewski, R.; Hyla-Kryspin, I.; Mayne, C. L.; Arif, A. M.;
Gleiter, R.; Ernst, R. D. J . Am. Chem. Soc. 1998, 120, 2959.
(13) Varga, V.; Pola´sˇek, M.; Hiller, J .; Thewalt, U.; Sedmera, P.;
Mach, K. Organometallics 1996, 15, 1268.
(14) The esd’s accompanying average values are derived from the
esds of the values being averaged, and therefore reflect the uncertainty
in the average value, but not the distribution of the individual values.

4178 Organometallics, Vol. 18, No. 20, 1999
Tomaszewski et al.
Sch em e 1
Figu r e 2. Perspective view of Ti(1,3-t-Bu2C5H3)(NMeCHPh-
CH2CMedCHCMedCH2), 6.
cally, a single crystal diffraction study was performed.
Two crystallographically independent molecules were
found in the unit cell, but any differences between them
were observed to be insignificant. The result (Figure 2
and Table 3) revealed that while the original open dienyl
fragment has again retained its U conformation, the
relative configuration at the imine’s coupled carbon
atom (C19) has been reversed as compared to that found
for the C5H5 complex, 7 (Scheme 1). In this case, the
phenyl ring is oriented toward the open edge of the
original dienyl fragment, rather than away from it.
Thus, the stereochemistry generated at the imine
carbon atom can be substantially controlled by the
choice of the cyclopentadienyl substituents.
In any case, the observed product may be considered
to be a 16 electron Ti(Cp)(diene)(amide) complex, given
that the bonds about the amide are nearly planar (vide
infra), reflecting its formal donation of three electrons.
The bonding in the “diene” unit, however, appears more
similar to an enediyl coordination mode because the Ti-
C(14,17) bonds appear shorter than Ti-C(15,16) bonds,
2.241(4) vs 2.286(4) Å, and the C-C (external) distances
appear longer than the C-C (internal) distances, 1.420-
(6) vs 1.400(9) Å. Actually, the Ti-C(14) and Ti-C(17)
bonds appear to differ somewhat, presumably as a result
of distortions brought about by the bridge between the
enediyl and amide ligands. Some evidence for this can
be seen by the 35.7° tilt of C(18) from the diene plane,
a much smaller value than would be expected.5,10,15,16
The amide f Ti interaction appears to involve a 3
electron donation, because the angles about the nitrogen
centers average 119.7°, and the average Ti-N distance
those for C(6,7,10), whereas for the C5H7 ligand all
bonds are fairly similar in length.
As in 5, the greater girth of the five metal-bonded
carbon atoms in the C5H7 ligand leads to a much closer
approach of the metal center to the C5H7 plane, com-
pared to its cyclic counterpart (average 1.562 vs 2.065
Å). The Ti-P vector is nearly parallel to the C5H7 plane
(∆ ) 0.8°), but is significantly tilted relative to the cyclic
ligand plane (14.4°). The quaternary carbon atoms of
the t-C4H9 substituents are tilted by an average of 10.1°
away from the metal center.
The reaction of 3 with C6H5CHdNCH3 led to incor-
poration and coupling of a single imine equivalent,
yielding 6 (Scheme 1). Unlike the product resulting from
the C5H5 complex,1 however, this product could be
isolated as a well-behaved crystalline solid. Spectro-
scopic data for both species clearly revealed that cou-
pling involving only one of the pentadienyl terminal CH2
groups had occurred, as indicated by a low J (13C-H)
value (here, 127 vs 149 Hz for the other end), reflecting
formal sp3 hybridization. Because neither the backbone
geometry nor the relative configuration for the imine’s
coupled carbon atom could be determined spectroscopi-
(15) (a) Wilson, D. R.; Ernst, R. D.; Kralik, M. S. Organometallics
1984, 3, 1442. (b) Arif, A. M.; Ernst, R. D.; Mele´ndez, E.; Rheingold,
A. L.; Waldman, T. E. Organometallics, 1995, 14, 1761. (c) Ernst, R.
D.; Ma, H.; Sergeson, G.; Zahn, T.; Ziegler, M. L. Organometallics 1987,
6, 848.
(16) The sine of the tilt angle is defined by the deviation of the
substituent from the diene plane divided by the distance from the
substituent to its attached carbon atom in the diene plane. For
comparison, the tilt determined from torsion angles (e.g., C15-C16-
C17-C18) would be 42.2°.

Reactions with Half-Open Titanocenes
Organometallics, Vol. 18, No. 20, 1999 4179
F igu r e 4. Perspective view of complex 12, “Ti(C5H5)(2,4-
C7H11)[C6H5C(H)NCH(CH3)2][p-CH3(C6H4)NC]4.”
F igu r e 3. Solid-state structure of Ti(C5H5){N(i-Pr)-
CHPhCH2CMeCHCMeCH2C[p-CH3(C6H4)]N}, 8.
Ta ble 2. P er tin en t Bon d in g P a r a m eter s for
Ti[C5H3(t-C4H9)2](C5H7)(P Me3)
Bond Distances
of 1.936(5) Å is similar to values observed for other
apparent 3 electron amide f Ti donations, but much
shorter than values observed for otherwise similar but
bridging amides.10 The Ti-C(Cp) bonds are longest for
the t-butyl substituted carbon atoms (2.421(4) Å), short-
est for the C(1,1′) atoms (2.362(6) Å), and intermediate
for the others (2.389(5) Å). The average C-C distance
is 1.409(4) Å. The t-C4H9 groups experience reasonable
(vide supra) tilts of ca. 8.6° out of the Cp plane, away
from the metal center.
Ti(1)-P(1)
Ti(1)-C(1)
Ti(1)-C(2)
Ti(1)-C(3)
Ti(1)-C(4)
Ti(1)-C(5)
Ti(1)-C(6)
Ti(1)-C(7)
Ti(1)-C(8)
Ti(1)-C(9)
Ti(1)-C(10)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
2.529(2)
2.233(4)
2.265(5)
2.262(5)
2.236(5)
2.227(5)
2.423(4)
2.436(4)
2.368(4)
2.337(4)
2.400(4)
1.424(7)
1.417(7)
1.403(7)
1.402(7)
Ti(2)-P(2)
Ti(2)-C(1′)
Ti(2)-C(2′)
Ti(2)-C(3′)
Ti(2)-C(4′)
Ti(2)-C(5′)
Ti(2)-C(6′)
Ti(2)-C(7′)
Ti(2)-C(8′)
Ti(2)-C(9′)
Ti(2)-C(10′)
C(1′)-C(2′)
C(2′)-C(3′)
C(3′)-C(4′)
C(4′)-C(5′)
2.525(2)
2.239(5)
2.235(5)
2.253(5)
2.247(5)
2.219(4)
2.404(4)
2.399(4)
2.346(4)
2.362(4)
2.438(4)
1.427(7)
1.411(7)
1.405(7)
1.416(6)
Because it was found to be possible to carry out
tandem couplings of one equivalent of an imine with a
second unsaturated coupling partner (imine, ketone, or
isonitrile),3 it was of interest to determine if this could
be extended to nitriles. Such a possibility could not be
taken for granted, because a reported mono(nitrile)
coupling product appears unreactive under normal
conditions to further couplings with either nitriles or
ketones.17 However, in situ generation of a mono(imine)
coupling product, followed by addition of an excess of
p-tolunitrile, was found to lead readily to the desired,
mixed coupling product (8, Scheme 1). Reactions were
observed as well with a variety of other nitriles, but
p-tolunitrile was found to provide a more nicely crystal-
line product. As with the other tandem coupling prod-
ucts, NMR spectroscopic data revealed that both open
dienyl termini had coupled, as well as the imine’s
originally unsaturated carbon atom, because J (13C-H)
values characteristic of sp3 hybridization were observed
(ca. 127, 131 Hz). A single-crystal diffraction study
(Figure 3 and Table 4) confirmed this and other expec-
tations. As a starting point the product may be consid-
ered to be a 16 electron Ti(C5H5)(π-allyl)(π-amide)(σ-
imide) species, the π-amide coordination being derived
from the original imine, and the σ-imide coordination
being derived from the nitrile. The geometry about the
amide donor site (N(1)) is nearly trigonal planar, and
along with the Ti-N(1) distance of 1.955(3) Å, seems to
implicate its participation as a 3 electron donor. The
longer Ti-N(2) distance of 2.046(3) Å would then be
consistent with 1 electron donation, and from the Ti-
N(2)-C(10) angle of 103.0(2)°, it is clear that the lone
Bond Angles
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(7)-C(6)-C(10)
C(6)-C(7)-C(8)
C(7)-C(8)-C(9)
C(8)-C(9)-C(10)
C(6)-C(10)-C(9)
125.0(5)
129.6(5)
126.7(5)
108.8(4)
107.6(4)
108.3(4)
108.6(4)
106.8(4)
C(1′)-C(2′)-C(3′)
C(2′)-C(3′)-C(4′)
C(3′)-C(4′)-C(5′)
C(7′)-C(6′)-C(10′)
C(6′)-C(7′)-C(8′)
C(7′)-C(8′)-C(9′)
C(8′)-C(9′)-C(10′)
C(6′)-C(10′)-C(9′)
126.8(5)
129.0(5)
126.2(5)
109.8(4)
106.6(4)
107.6(4)
109.1(4)
106.9(3)
pair of electrons on N(2) could not be interacting with
the metal center (either intra- or intermolecularly),
unlike a dimeric mono(nitrile) coupling product.3 How-
ever, the Ti-N(2) distance is still shorter than the Ti-
N(amide) bridging distances in the mono(acetonitrile)
coupling product, which ranged from 2.117(3) to 2.187-
(3) Å. In addition, the C(10)-N(2) distance of 1.364(5)
Å is notably longer than the bridging imide’s average
C-N distance of 1.266(3) Å in the dimer. Hence, there
could be an additional interaction with the C(10)dN(2)
bond. Although its orientation is not optimal for a σ
donor interaction of its π cloud to the metal center, some
degree of π donation could be occurring, analogous to 4
electron alkyne donation,18 and could then lead to an
18 electron count. In fact, the Ti-C(10) distance of
2.702(4) Å is significantly shorter than an expected van
der Waals separation, although what would normally
have been described as a nonbonded Ti-C(9) contact is
actually found to be remarkably short, at 2.615(4) Å.
The extent to which a (CdN) f Ti interaction (or even
(17) Tomaszewski, R.; Ernst, R. D. Unpublished results.
(18) Templeton, J . L. Adv. Organomet. Chem. 1989, 29, 1.

4180 Organometallics, Vol. 18, No. 20, 1999
Tomaszewski et al.
Ta ble 3. P er tin en t Bon d in g P a r a m eter s for
Ti(1,3-t-Bu 2C5H3)(NMeCHP h CH2CMed
CHCMedCH2) (6)
Ta ble 5. P er tin en t Bon d in g P a r a m eter s for
“Ti(C5H5)(2,4-C7H11)[C6H5CHdN(i-C3H7)]-
(p-CH3C6H4NC)4”
Bond Distances
Bond Distances
Ti-N(1)
1.949(8)
C(6)-C(7)
1.400(13)
1.52(2)
1.469(14)
1.60(2)
1.571(14)
1.541(14)
1.264(14)
1.50(2)
1.558(13)
1.59(2)
1.361(13)
1.491(11)
1.464(12)
1.450(13)
1.515(12)
Ti-N
1.932(5)
2.360(9)
2.423(8)
2.393(8)
2.387(9)
2.428(10)
2.213(8)
2.302(8)
2.282(9)
2.275(10)
1.430(12)
1.390(13)
1.446(10)
1.506(10)
1.535(11)
1.488(12)
1.472(10)
Ti′-N′
1.940(8)
2.363(7)
2.399(7)
2.386(10)
2.388(11)
2.434(9)
2.220(8)
2.289(8)
2.271(7)
2.265(7)
1.424(13)
1.409(12)
1.412(13)
1.562(15)
1.513(11)
1.489(10)
1.451(10)
Ti-N(2)
1.958(9)
C(6)-C(15)
C(15)-C(23)
C(23)-C(24)
C(23)-C(27)
C(24)-C(25)
C(25)-C(26)
C(26)-C(27)
C(27)-C(30)
C(30)-C(31)
N(4)-C(7)
Ti-C(1)
Ti′-C(1′)
Ti-N(5)
1.924(10)
2.370(12)
2.326(12)
2.337(13)
2.412(12)
2.400(11)
2.379(13)
2.458(12)
1.361(12)
1.404(12)
1.377(12)
1.459(11)
1.245(11)
1.422(12)
Ti-C(2)
Ti′-C(2′)
Ti-C(1)
Ti-C(3)
Ti′-C(3′)
Ti-C(2)
Ti-C(4)
Ti′-C(4′)
Ti-C(3)
Ti-C(5)
Ti′-C(5′)
Ti-C(4)
Ti-C(14)
Ti-C(15)
Ti-C(16)
Ti-C(17)
C(14)-C(15)
C(15)-C(16)
C(16)-C(17)
C(17)-C(18)
C(18)-C(19)
C(19)-N
Ti′-C(14′)
Ti′-C(15′)
Ti′-C(16′)
Ti′-C(17′)
C(14′)-C(15′)
C(15′)-C(16′)
C(16′)-C(17′)
C(17′)-C(18′)
C(18′)-C(19′)
C(19′)-N′
C(27′)-N′
Ti-C(5)
Ti-C(6)
Ti-C(7)
N(1)-C(6)
N(1)-C(13)
N(2)-C(7)
N(2)-C(53)
N(3)-C(15)
N(3)-C(21)
N(4)-C(23)
N(4)-C(46)
N(5)-C(31)
N(5)-C(38)
Bond Angles
C(27)-N
N(1)-Ti-N(2)
N(1)-Ti-N(5)
N(2)-Ti-N(5)
Ti-N(1)-C(6)
Ti-N(1)-C(13)
C(6)-N(1)-C(13)
Ti-N(2)-C(7)
Ti-N(2)-C(53)
C(7)-N(2)-C(53)
86.6(3)
105.7(3)
111.8(4)
90.1(7)
143.8(8)
124.1(9)
93.3(6)
N(2)-C(7)-N(4)
128.5(9)
135.1(11)
120.4(11)
104.4(9)
105.1(9)
110.0(8)
112.0(8)
N(3)-C(15)-C(6)
N(3)-C(15)-C(23)
C(6)-C(15)-C(23)
N(4)-C(23)-C(15)
N(4)-C(23)-C(24)
N(4)-C(23)-C(27)
Bond Angles
C(14)-C(15)-C(16) 124.8(7) C(14′)-C(15′)-C(16′) 124.5(9)
C(15)-C(16)-C(17) 130.0(7) C(15′)-C(16′)-C(17′) 130.5(9)
C(16)-C(17)-C(18) 121.1(7) C(16′)-C(17′)-C(18′) 119.2(8)
C(17)-C(18)-C(19) 111.9(7) C(17′)-C(18′)-C(19′) 110.7(7)
142.1(7)
120.8(9)
C(15)-C(23)-C(24) 112.7(9)
C(15)-C(23)-C(27) 114.8(10)
C(18)-C(19)-N
C(19)-N-C(27)
C(19)-N-Ti
C(27)-N-Ti
N-C(19)-C(26)
105.7(6) C(18′)-C(19′)-N′
109.3(6) C(19′)-N′-C(27′)
119.9(5) C(19′)-N′-Ti′
129.6(6) C(27′)-N′-Ti′
114.2(6) N′-C(19′)-C(26′)
107.5(7)
108.9(7)
119.1(5)
131.2(6)
113.3(6)
C(15)-N(3)-C(21) 131.1(11) C(24)-C(23)-C(27) 102.4(9)
C(7)-N(4)-C(23)
C(7)-N(4)-C(46)
108.2(8)
119.3(9)
C(23)-C(24)-C(25) 104.5(9)
C(24)-C(25)-C(26) 109.6(11)
C(25)-C(26)-C(27) 117.4(12)
C(23)-C(27)-C(26) 103.2(10)
C(23)-C(27)-C(30) 117.8(8)
C(26)-C(27)-C(30) 108.9(9)
C(23)-N(4)-C(46) 124.5(9)
Ti-N(5)-C(31)
Ti-N(5)-C(38)
113.9(6)
131.3(7)
Ta ble 4. P er tin en t Bon d in g P a r a m eter s for
Ti(C5H5){N(i-P r )CHP h CH2CMeCHCMeCH2C-
[p-CH3(C6H4)]N} (8)
C(31)-N(5)-C(38) 113.7(9)
N(1)-C(6)-C(7)
N(1)-C(6)-C(15)
C(7)-C(6)-C(15)
N(2)-C(7)-C(6)
N(4)-C(7)-C(6)
121.0(11) C(27)-C(30)-C(31) 128.9(9)
132.8(9)
N(5)-C(31)-C(30)
119.4(8)
115.0(10)
Bond Distances
105.7(10) N(5)-C(31)-C(37)
Ti(1)-C(4)
Ti(1)-C(6)
Ti(1)-C(7)
Ti(1)-C(10)
Ti(1)-C(11)
Ti(1)-C(12)
Ti(1)-C(13)
Ti(1)-C(14)
Ti(1)-C(15)
2.504(4)
2.352(4)
2.224(4)
2.702(4)
2.378(4)
2.352(5)
2.371(5)
2.448(4)
2.447(5)
Ti(1)-N(1)
Ti(1)-N(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(6)
C(6)-C(7)
C(7)-C(9)
C(9)-C(10)
C(10)-N(2)
1.955(3)
2.046(3)
1.545(5)
1.519(5)
1.378(5)
1.394(5)
1.496(5)
1.380(5)
1.364(5)
114.8(11) C(30)-C(31)-C(37) 108.6(9)
112.4(10)
one of the nitrogen atoms than does C(7). Some evidence
for a geometric contribution can be seen in the C(2)-
C(3)-C(4) and C(7)-C(9)-C(10) angles, which are
significantly larger than expected, whereas the C(9)-
C(10)-N(2) angle is significantly smaller than expected.
The Ti-Cp bonding is also somewhat asymmetric,
with longer bonds to C(14,15) than to C(11-13) (aver-
ages of 2.448(3) vs 2.367(3) Å). The presumed weakening
of the Ti-C(14,15) bonds can readily be accounted for
as a result of their being situated most nearly opposite
to N(1), leading to a competition for π bonding with the
metal center.
The course of the tandem imine-isonitrile coupling
process is particularly complex, because a total of four
equivalents of isocyanide was incorporated. As a result,
spectroscopic data provided little information regarding
the nature of product that was formed, and the nature
of the product could only be elucidated through an X-ray
diffraction study. The result may be seen in Figure 4,
while important bonding parameters are contained in
Table 5. A possible mechanism for the formation of the
product is presented in Scheme 2.
Bond Angles
N(1)-Ti(1)-N(2)
C(1)-N(1)-C(2)
N(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(6)
100.25(13)
115.0(3)
107.7(3)
114.9(3)
123.4(4)
C(4)-C(6)-C(7)
C(6)-C(7)-C(9)
C(7)-C(9)-C(10)
C(9)-C(10)-N(2)
130.0(4)
122.9(4)
118.6(4)
115.1(4)
C-CfTi agostic interactions12) may be taking place is
clearly arguable, but it appears reasonable that some
interaction will be present as long as an appropriate
acceptor orbital is available on the metal center.
Some degree of ambiguity also characterizes the Ti-
allyl interaction due to its asymmetry, i.e., respective
Ti-C(4,6,7) distances of 2.504(4), 2.352(4), and 2.224-
(4) Å. However, the respective C(4)-C(6) and C(6)-C(7)
bond lengths of 1.378(5) and 1.394(5) Å do not differ
noticeably, suggesting a significant degree of η3 interac-
tion. Perhaps a key indicator of the presence of an η1
interaction would be significantly differing C-C dis-
tances, and a Ti-C(σ-allyl) distance of ca. 2.15 Å, as
were observed in some related species formulated as η1-
allyl complexes.1 Conceivably, the asymmetry experi-
enced here could arise either from geometric constraints
imposed on coordination by the chelating nature of the
ligands, and/or from a trans weakening influence,19
because C(4) comes closer to being situated opposite to
As depicted in the scheme, the unsaturated carbon
atom of the first equivalent of isonitrile is coupled to
the ends of the diene ligand, leading to species 9. In fact,
related species were isolated from coupling reactions
utilizing the bulkier t-C4H9NC ligand.3 In the present
case, however, this species is susceptible to further
(19) The large N(1)-C(2)-C(28) angle of 117.3(3)° might also
indicate some steric problems.

Reactions with Half-Open Titanocenes
Organometallics, Vol. 18, No. 20, 1999 4181
Sch em e 2a
a
R ) p-CH3C6H4.
reaction, and a second isonitrile inserts in the Ti-C
bond formed from the first isonitrile. This results,
however, in another Ti-C bond, leading to another
insertion, giving an additional Ti-C bond (10). A final
insertion reaction produces 11. A formal reductive
elimination, forming a C-N bond, then yields the basic
skeleton of the final product. Coordination of a diaza-
diene unit (actually present in more of an enediamide
form, vide infra) then completes the reaction. Note that
the reductive elimination step creates a five-membered
ring (part of a spiro fused ring), which then accounts
for the need to have continually inserted additional
isonitriles. Through the depicted process one not only
constructs a relatively strain-free five-membered ring,
but also arrives at a product in which, except for the
C5H5 ligand, the titanium center may be regarded as
bonding only to electronegative nitrogen donor sites
(vide infra).
and amide ligands is straightforward, and will be
considered first. The Ti-N(5) distance of 1.924(10) Å,
along with the nearly trigonal disposition of bonds
around N(5) (358.9°), point to its role as a 3 electron (π)
donor. In fact, this distance is significantly shorter than
the Ti-N(1) value of 1.983(5) Å in 13, perhaps due to
the presence of a phenyl substituent on N(1). There is
an asymmetry in the Ti-N(5)-C(31,38) angles, how-
ever, that indicates that the bridge between the N(5)
and diazadiene coordination sites must be somewhat
strained. In fact, the C-C-C bond angles within the
C(23-C27-30-31)-N(5) chain are all significantly
greater than would be expected for their formal sp3
hybridizations, in accord with this conclusion. In addi-
ion, there is an angle of 18.3° between the C15-C23-
N4 and C15-C6-C7-N4 best planes, again appearing
to reflect an attempt to “stretch” N(5) out to a more
optimal position for bonding to the metal center. One
other distortion associated with N(5) appears to be an
asymmetry in the Ti-Cp bonding. The Ti-C(4,5) bonds
are significantly longer than the others, as an apparent
result of their being positioned more nearly opposite
N(5), and subsequent competition for π bonding to the
metal. Such behavior has also been observed for other
related complexes.3
The structure of the product, 12, is quite similar to
that found earlier in another isonitrile coupling product,
13, in which coordination to a Cp, amide, and diazadiene
ligand was also found.
As for 13, the diazadiene coordination is somewhat
complex. The sums of the angles about N(1 and 2) equal
358.0 and 356.2°, respectively, indicating a significant
approach to sp2 hybridization, and perhaps then π
donation from these two nitrogen centers, each of which
could be considered to be a 3 electron donor, as in 14.
The Ti-N(1,2) distances are short enough to provide
support for this formulation. Nonetheless, C(6) and C(7)
both make close approaches of ca. 2.4 Å to Ti (as in 13),
which also suggests the possibility of a σ donor interac-
tion from the C-C double bond (cf., enediyl complexes).
However, even if it were geometrically possible to
In the present case, the coordination involving the Cp

4182 Organometallics, Vol. 18, No. 20, 1999
Tomaszewski et al.
Cp ligand substituents can allow for the selective
isolation of either isomeric coupled species. Subse-
quently, additional functionalization of the dienyl frag-
ment can be effected with ketones, imines, nitriles, or
isonitriles. In these reactions, it has been observed that
substituents present in the partner coupling substrates
can also influence the course of the reactions. In the
cases in which bis(coupling) products are isolated, one
obtains organic fragments in which two heteroatoms are
separated by seven carbon atoms; related reactions for
diene complexes yield similar species, with heteroatoms
separated by six carbon atoms.20 Further efforts to
develop the chemistry of these complexes are underway.
achieve favorable interactions involving Ti, the olefin,
and two π-amide donor sites, this would lead to a 20
electron complex. In all likelihood, partial σ donation
from the olefin and π donation from the amide lone pairs
are all taking place in competition with each other (and
with the Cp ligand). The fact that Ti does not lie in the
diazadiene plane either in 12 or 13 provides some
support for this formulation. One notable difference
between 12 and 13, however, lies in the presence of a
short C7-N2 bond (1.377(12) Å) in the former, suggest-
ing some delocalization in the structure, resulting in
partial C7-N2 multiple bonding.
Ack n ow led gm en t. R.D.E. is grateful to the Uni-
versity of Utah and the National Science Foundation
for partial support of this work.
Su p p or tin g In for m a tion Ava ila ble: Positional coordi-
nates, anisotropic thermal parameters, additional bonding
parameters, and mass spectral data. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM990463H
The coupling reactions of metal pentadienyl com-
pounds with imines generate chiral centers, and it has
now been demonstrated that the appropriate choice of
(20) Yasuda, H.; Nakamura, A. Angew. Chem., Intl. Ed. Engl. 1987,
26, 723.