Reductions of β-diketiminato-titanium (III) complexes

Article abstract of DOI:10.1021/om060076p

The reductions of (Nacnac)Ti(III) complexes (Nacnac = (HC(CMeNC ₆H₃(i-Pr)₂)₂) are examined. Treatment of (Nacnac)TiCl₂ with K/Na alloy in the presence of CH ₂(PPh₂)₂ afforded the dark red product [K(C(Me)CHC(Me)NAr)Ti(NAr)(μ-H)]₂ (2). This Ti(III)-imido-hydride complex is a product of Nacnac ligand cleavage. The Ti(III) species (Nacnac)CpTiCl (3) and (Nacnac)(C₅Me₄H)TiCl (4) were prepared and characterized. While compound 3 was readily alkylated with n-BuLi to give (Nacnac)CpTiBu (5), reduction of 3 with Na/K gave the dinitrogen complex ((Nacnac)CpTi)₂(μ-η²-N₂) (6). In contrast, treatment of 4 with t-BuLi or n-BuLi or Na/K amalgam afforded the ligand cleavage product (C₅Me₄H)[(ArNC-(Me)CHC(Me)]Ti(NAr) (7). Compounds 2-7 are crystallographically characterized. The effects of the nature of the ancillary ligands on the course of these reactions are considered.

Full text of DOI:10.1021/om060076p

Organometallics 2006, 25, 2649-2655
2649
Reductions of â-Diketiminato-Titanium(III) Complexes
Guangcai Bai, Pingrong Wei, and Douglas W. Stephan*
Department of Chemistry and Biochemistry, UniVersity of Windsor, Windsor, Ontario, Canada, N9B3P4
ReceiVed January 24, 2006
The reductions of (Nacnac)Ti(III) complexes (Nacnac ) (HC(CMeNC6H3(i-Pr)2)2) are examined.
Treatment of (Nacnac)TiCl2 with K/Na alloy in the presence of CH2(PPh2)2 afforded the dark red product
[K(C(Me)CHC(Me)NAr)Ti(NAr)(µ-H)]2 (2). This Ti(III)-imido-hydride complex is a product of Nacnac
ligand cleavage. The Ti(III) species (Nacnac)CpTiCl (3) and (Nacnac)(C5Me4H)TiCl (4) were prepared
and characterized. While compound 3 was readily alkylated with n-BuLi to give (Nacnac)CpTiBu (5),
reduction of 3 with Na/K gave the dinitrogen complex ((Nacnac)CpTi)2(µ-η2-N2) (6). In contrast, treatment
of 4 with t-BuLi or n-BuLi or Na/K amalgam afforded the ligand cleavage product (C5Me4H)[(ArNC-
(Me)CHC(Me)]Ti(NAr) (7). Compounds 2-7 are crystallographically characterized. The effects of the
nature of the ancillary ligands on the course of these reactions are considered.
the formation of low-coordinate â-diketiminato transition metal
Introduction
complexes.7,13-25,47-49 For example, Warren and co-workers
â-Diketiminate ligand (Nacnac) complexes have been the
subject of a considerable renaissance in recent years. For
example, these ligands have been used in main group1-8 and
lanthanide3,9-12 chemistry, as well as a variety of transition metal
chemistry.7,13-46 A number of recent studies have focused on
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* To whom correspondence should be addressed. E-mail: stephan@
uwindsor.ca.
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10.1021/om060076p CCC: $33.50 © 2006 American Chemical Society
Publication on Web 04/01/2006

2650 Organometallics, Vol. 25, No. 10, 2006
Bai et al.
Scheme 1. Nacnac Ligand Structure
(CMeNC6H3(i-Pr)2)2 and Ar ) CMeNC6H3(i-Pr)2. The compound
(Nacnac)TiCl2 (1) was prepared by known methods.40,54
Synthesis of [(η2-ArNC(Me)CHC(Me))(ArN)Ti(µ-H)]2K2, 2.
Compound 1 (1.072 g, 2.0 mmol), CH2(Ph2P)2 (0.768 g, 2.0 mmol),
and K/Na alloy (0.234 g K, 6.0 mmol; 0.066 g Na, 2.8 mmol) were
combined in toluene (15 mL) at 25 °C and stirred for one week.
After filtration and concentration to 5 mL in vacuo, dark red crystals
of 2 (0.12 g) were obtained upon standing of this solution at -35
°C. Further concentration to 3 mL and standing at -35 °C yielded
more crystals of 2. Total yield of crystalline product: 0.23 g (23%).
IR (Nujol) (cm-1): 1954 (br w), 1883 (br w), 1810 (br w), 1716
(w), 1698 (w), 1684 (w), 1653 (br w), 1575 (s), 1463 (s), 1432 (s),
1407 (s), 1378 (s), 1356 (m), 1323 (s), 1254 (s), 1210 (m), 1177
(m), 1136 (m), 1094 (s), 1041 (m), 1025 (m), 999 (m), 917 (s),
795 (m), 744 (s), 696 (s), 603 (m), 502 (m), 480 (m), 421 (m).
EPR(C7H8): g ) 1.918. Anal. Calcd for C58H84N4Ti2K2 (1011.3):
C 68.9, H 8.4. Found: C 68.5, H 7.5. (N analysis was performed
repeatedly on crystalline samples and was consistently low. This
is attributed to the formation of TiN.)
Synthesis of (Nacnac)CpTiCl, 3, and (Nacnac)(C5Me4H)TiCl,
4. These compounds were prepared in a similar fashion, and thus
one preparation is detailed. THF (25 mL) was added to the mixture
of 1 (2.144 g, 4.0 mmol) and CpLi (0.288 g, 4.0 mmol) at 25 °C.
Stirring was continued overnight, and the solvent was removed.
Toluene (20 mL) was added, and the suspension was stirred for
0.5 h. After filtration and subsequent concentration (to 10 mL) in
vacuo, the resulting deep brown solution was kept at -35 °C
overnight to isolate dark red crystals of 3 (1.25 g). After concentra-
tion of the filtrate to 3 mL, the solution was kept at -35 °C for 3
days. An additional crop of 3 (0.81 g) was formed. Yield: 2.06 g
(91%). IR (Nujol): 1923 (w), 1868 (w), 1837 (w), 1796 (w), 1772
(m), 1697 (m), 1650 (m), 1519 (s), 1460 (s), 1374 (s), 1310 (s),
1250 (s), 1168 (m), 1100 (m), 1014 (s), 927 (m), 849 (m), 800 (s),
764 (m), 728 (m), 699 (w), 669 (w), 640 (w), 522 (m), 446 (m)
cm-1. EPR: 1.973. Anal. Calcd for C34H46ClN2Ti (566.1): C 72.1,
H 8.2, N 5.0. Found: C 72.3, H 8.7, N 5.0. 4: Yield 2.9 g (78%).
IR (Nujol): 1924 (w), 1861 (w), 1796 (w), 1624 (w), 1532 (s),
1434 (s), 1382 (s), 1312 (s), 1274 (s), 1249 (s), 1173 (s), 1110 (s),
1097 (s), 1057 (m), 1020 (s), 969 (m), 922 (s), 846 (s), 794 (s),
761 (s), 727 (m), 698 (m), 638 (m), 613 (m), 563 (w), 522 (s), 492
(w), 459 (m), 441 (m) cm-1. EPR: 1.954. Anal. Calcd for C38H54-
ClN2Ti (622.20): C 73.4, H 8.8, N 4.5. Found: C 73.5, H 8.8, N
4.6.
have described three-coordinate â-diketiminato-nickel25 and
-cobalt30 complexes derived from Ni(I) and Co(I) precursors,
while Holland and co-workers41 have described the chemistry
of a three-coordinate â-diketiminato-iron hydride complex. Our
interests in related chemistry have focused on the synthesis and
chemistry of low-valent â-diketiminato complexes. In our first
report of efforts in this area, we recently described the complex
[(Nacnac)Ni)2(µ-η3-η3-C6H5Me)], which acts as a synthon for
a variety of â-diketiminato Ni(I) complexes,50 while a subse-
quent report described the reactivity of Ni(I) and Fe(I) species
with primary phosphines.51 Low-valent early metal complexes
have drawn limited attention to date, although Mindiola and
co-workers have described â-diketiminato Zr complexes.29 They
showed that reduction of such species led to â-diketiminato
ligand cleavage reactions and the formation of Zr-imido
complexes. The Mindiola group has also recently probed the
chemistry of â-diketiminato-Ti-alkylidenes.52,53 In this article,
we examine the reduction chemistry of (Nacnac)Ti(III) com-
plexes (Scheme 1) resulting in the formation of a Ti-dinitrogen
complex as well as products of â-diketiminato ligand cleavage
reactions. The nature of these products and the impact of
ancillary ligands on the reaction course are discussed.
Experimental Section
General Data. All preparations were done under an atmosphere
of dry, O2-free N2 employing both Schlenk line techniques and a
Vacuum Atmospheres inert atmosphere glovebox. Solvents were
purified employing a Grubbs-type solvent purification system
manufactured by Innovative Technology. Deuterated solvents were
purified using the appropriate techniques. All organic reagents were
1
purified by conventional methods. H and 13C{1H} NMR spectra
Synthesis of (Nacnac)CpTiBu, 5. n-BuLi (2.5 M in hexane;
0.4 mL, 1.0 mmol) was added to a solution of 3 (0.57 g, 1.0 mmol)
in toluene (10 mL) at 25 °C. Stirring was continued overnight, and
the solution was filtered and subsequently concentrated to 5 mL in
vacuo. The resulting deep brown solution was kept at -35 °C
overnight to isolate dark red crystals of 5 (0.45 g). After concentra-
tion of the filtrate to 3 mL, the solution was kept at -35 °C for 3
days. An additional crop of 5 (0.09 g) was formed. Yield: 0.54 g
(92%). IR (Nujol): 1923 (w), 1860 (w), 1797 (w), 1716 (w), 1682
(w), 1622 (w), 1603 (w), 1580 (w), 1529 (s), 1459 (s), 1436 (s),
1381 (s), 1311 (s), 1277 (m), 1253 (s), 1190 (w), 1168 (m), 1056
(m), 1040 (m), 1020 (s), 959 (m), 930 (s), 867 (w), 849 (m), 794
(s), 757 (m), 728 (m), 698 (m), 623 (m), 601 (w), 542 (w), 522
(m), 445 (m) cm-1. EPR: 1.967. Anal. Calcd for C38H55N2Ti
(587.76): C 77.7, H 9.4, N 4.8. Found: C 77.9, H 9.6, N 4.6.
Synthesis of ((Nacnac)CpTi)2(µ-η2-N2), 6. Toluene (15 mL) was
added to the mixture of 3 (0.580 g, 1.00 mmol) and K/Na alloy
(0.030 g K, 0.77 mmol; 0.011 g Na, 0.48 mmol) at 25 °C and was
stirred for one week. After filtration and subsequent concentration
(to 5 mL) in vacuo, the resulting deep red solution was kept at
-35 °C for one week to isolate dark red crystals of 6 (0.22 g).
After concentration of the filtrate to 3 mL, the solution was kept at
were recorded on Bruker Avance-300 and -500 spectrometers. All
NMR spectra were recorded in C6D6 at 25 °C. Trace amounts of
protonated solvents were used as references, and chemical shifts
are reported relative to SiMe4. EPR spectra were recorded on an
X-band Bruker ESP 300E spectrometer equipped with an electro-
magnet capable of providing a magnetic field from 50 G to 15 kG,
a gaussmeter, and a microwave counter. Typical measurement
conditions were microwave power 20 mW, microwave frequency
9.7 GHz, modulation amplitude 3.830 G, and 4K data points
covering a sweep range of 4000 G. IR spectra were recorded on a
Bruker FTIR spectrometer. Combustion analyses were done in-
house employing a Perkin-Elmer CHN analyzer. In this paper, the
abbreviation Nacnac refers to the â-diketiminate ligand (HC-
(47) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.; Lachicotte,
R. J. J. Am. Chem. Soc. 2002, 124, 14416-14424.
(48) Zhang, D.; Jin, G.-X.; Weng, L.-H.; Wang, F. Organometallics 2004,
23, 3270-3275.
(49) Kogut, E.; Wiencko Heather, L.; Zhang, L.; Cordeau Douglas, E.;
Warren Timothy, H. J. Am. Chem. Soc. 2005, 127, 11248-11249.
(50) Bai, G.; Wei, P.; Stephan, D. W. Organometallics 2005, 24, 5901-
5908.
(51) Bai, G.; Wei, P.; Das, A.; Stephan, D. W. Dalton Trans. 2006, 0000.
(52) Basuli, F.; Bailey, B. C.; Watson, L. A.; Tomaszewski, J.; Huffman,
J. C.; Mindiola, D. J. Organometallics 2005, 24, 1886-1906.
(53) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. Organo-
metallics 2005, 24, 3321-3334.
(54) Budzelaar, P. H. M.; Oort, A. B. v.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485.

Reductions of â-Diketiminato-Ti(III) Complexes
Organometallics, Vol. 25, No. 10, 2006 2651
Table 1. Crystallographic Data
2
3
4
5
6‚2C6H6‚THF
7
formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C58H86K2N4Ti2
1013.30
monoclinic
P21/n
11.920(4)
15.273(5)
15.817(5)
C34H46ClN2Ti
566.08
monoclinic
P21/n
10.2513(10)
25.950(3)
12.4811(12)
C38H54ClN2Ti
622.18
triclinic
P1h
10.6011(14)
12.4442(16)
14.6844(19)
105.829(2)
94.417(2)
106.856(2)
1757.8(4)
2
1.175
0.347
17 021
0.0378
6179
379
C38H55N2Ti
587.74
orthorhombic
Pnma
17.009(3)
20.219(3)
10.0920(15)
C78H106N6OTi2
1239.49
triclinic
P1h
12.4323(15)
14.2063(17)
21.938(3)
94.297(2)
103.003(2)
97.792(2)
3718.1(8)
2
1.107
0.260
36 087
0.0929
13 015
712
C38H54N2Ti
586.73
triclinic
P1h
10.2831(19)
11.695(2)
16.354(3)
74.933(2)
73.761(2)
70.496(2)
1749.4(6)
2
1.114
0.271
16 635
0.0675
6137
90.312(7)
105.8820(10)
2879.6(16)
2
3193.5(5)
4
3470.6(9)
4
Z
d(calc) (gcm-1
)
1.164
0.460
13 924
0.0794
4206
1.177
0.379
30 470
0.0480
5622
1.125
0.273
31 899
0.0507
3141
µ (mm-1
)
no. of data collected
R(int)
no. of data Fo2 >3σ(Fo )
2
no. of variables
306
343
205
370
R
Rw
GOF
0.0561
0.1399
1.016
0.0575
0.1408
1.045
0.0555
0.1465
1.025
0.0475
0.1223
1.061
0.0845
0.2137
0.971
0.0655
0.1467
1.025
-35 °C for 3 days. An additional crop of 6 (0.10 g) was formed.
Yield: 0.32 g (59%). IR (Nujol): 1935 (w), 1866 (w), 1799 (w),
1697 (w), 1620 (w), 1582 (m), 1526 (s), 1497 (s), 1462 (s), 1436
(s), 1422 (s), 1384 (s), 1367 (s), 1344 (s), 1312 (s), 1278 (m), 1256
(s), 1231 (m), 1187 (m), 1170 (s), 1105 (s), 1056 (m), 1041 (m),
1018 (sw), 964 (m), 930 (s), 898 (m), 852 (m), 796 (s), 759 (s),
728 (m), 717 (m), 837 (w) 626 (m), 603 (w), 542 (w), 527 (m),
3JHH ) 7 Hz, 1 H, CHMe2), 2.82 (sept, 3JHH ) 7 Hz, 1 H, CHMe2),
2.48, 2.47 (ds, 3 H, TiCMe), 2.11 (s, 3 H, Me4C5H), 2.09 (s, 3 H,
Me4C5H), 1.99 (s, 3 H, Me4C5H), 1.90 (s, 3 H, Me4C5H), 1.54 (s,
3 H, NCMe), 1.34 (d, 3JHH ) 7 Hz, 6 H, CHMe2), 1.27 (d, 3JHH
)
7 Hz, 3 H, CHMe2), 1.01 (d, 3JHH ) 7 Hz, 6 H, CHMe2), 0.94 (dd,
3
3JHH ) 7 and 7 Hz, 6 H, CHMe2), 0.80 (d, JHH ) 7 Hz, 3 H,
CHMe2). 13C NMR: 252.8 (TiCMe), 178.7 (NC), 155.9 (Ar), 145.0,
144.6, 143.5, 140.8, 127.4, 126.9, 125.9, 123.9, 122.8, 122.7, 121.5,
121.3, 121.0, 119.7 (Ar or CMe of Me4C5H), 111.3 (TiCMe), 31.2
(CH of Me4C5H), 28.2, 28.1, 27.8 (CHMe2), 25.7, 25.6, 24.9, 24.5,
24.3 (CHMe2), 24.3(NCMe), 24.0 (TiCMeCHCMe), 13.9, 13.7,
12.7, 12.5 (Me4C5H). Anal. Calcd for C38H54N2Ti (586.75): C 77.8,
H 9.3, N 4.8. Found: C 77.9, H 9.4, N 4.6.
1
510 (w), 455 (m) cm-1. H NMR: 7.21-6.99 (m, Ar), 5.96 (s, 5
H, Cp), 5.68 (s, 1 H, γ-CH), 3.74 (sept, 3JHH ) 7 Hz, 1 H, CHMe2),
3.30 (sept, 3JHH )7 Hz, 1 H, CHMe2), 2.90, 2.89 (d sept, 3JHH )7
3
Hz, 2 H, CHMe2), 1.85, 1.84 (ds, 6 H, CMe), 1.77 (d, JHH ) 7
Hz, 3 H, CHMe2), 1.38, 1.36, 1.35 (td, 3JHH ) 6 Hz, 9 H, CHMe2),
3
3
1.22, 1.21 (dd, JHH ) 6, 6 Hz, 9 H, CHMe2), 1.14 (d, JHH ) 7
Hz, 3 H, CHMe2). 13C NMR: 166.9, 166.4 (NC), 149.8, 147.7,
145.5, 143.8, 142.4, 141.4, 125.9, 125.0, 124.8, 124.8, 124.0, 112.6
(Ar), 105.2 (γ-C), 28.6, 28.5, 27.7, 27.1 (CHMe2), 27.0, 26.3, 26.3,
26.0, 25.8, 25,7, 25.6, 25.4 (CHMe2), 24.9, 24.6 (NCMe). Anal.
Calcd for C68H92N6Ti2 (1089.29): C 75.0, H 8.5, N 7.7. Found: C
75.2, H 8.9, N 6.9.
X-ray Data Collection and Reduction. Crystals were manipu-
lated and mounted in capillaries in a glovebox, thus maintaining a
dry, O2-free environment for each crystal. Diffraction experiments
were performed on a Siemens SMART System CCD diffractometer.
The data were collected in a hemisphere of data in 1448 frames
with 10 s exposure times (4.5° < 2θ < 45-50.0°). The observed
extinctions were consistent with the space groups in each case. The
intensities of reflections within these frames showed no statistically
significant change over the duration of the data collections. The
data were processed using the SAINT and XPREP processing
packages. An empirical absorption correction based on redundant
data was applied to each data set. Subsequent solution and
refinement were performed using the SHELXTL solution package.
Structure Solution and Refinement. Non-hydrogen atomic
scattering factors were taken from the literature tabulations.55 The
heavy atom positions were determined using direct methods
employing the SHELXTL direct methods routine. The remaining
non-hydrogen atoms were located from successive difference
Fourier map calculations. The refinements were carried out by using
full-matrix least squares techniques on F, minimizing the function
Synthesis of (C5Me4H)[(ArNC(Me)CHC(Me)]Ti(NAr), 7.
Method A: THF (25 mL) was added to the mixture of 1 (2.144 g,
4.0 mmol) and Me4HC5Li (0.513 g, 4.0 mmol) at 25 °C and stirred
for 8 h. t-BuMgBr (2.0 M in ether; 2 mL, 4.0 mmol) was added to
the above mixture. The resulting reddish-brown solution was stirred
overnight. After removal of THF, toluene (20 mL) was added, and
the suspension was stirred for 0.5 h. After filtration and subsequent
concentration (to ca. 5 mL) in vacuo, hexane (10 mL) was added.
The resulting deep red solution was kept at -35 °C overnight to
isolate dark red crystals of 7 (1.12 g). After removal of the solvents,
hexane (5 mL) was added, and the solution was kept at -35 °C
for 3 days. An additional crop of 7 (0.25 g) was formed. Yield:
1.37 g (58%). Method B: Toluene (30 mL) was added to a mixture
of 4 (0.622 g, 1.00 mmol) and K/Na alloy (0.030 g K, 0.77 mmol;
0.011 g Na, 0.48 mmol) at room temperature. The mixture was
stirred for one week at this temperature. After filtration and
subsequent concentration (to 5 mL) in vacuo, the resulting deep
red solution was kept at -35 °C for one week to isolate dark red
crystals of 7 (0.20 g). After concentration of the filtrate to 3 mL,
the solution was kept at -35 °C for 3 days. An additional crop of
7 (0.07 g) was formed. Yield: 0.27 g (46%). Method C: Treatment
of 4 with 1 equiv of n-BuLi led also to 7 in a yield similar to that
in method A. IR (Nujol): 1897 (w), 1792 (w), 1693 (w), 1582
(m), 1528 (m), 1460 (s), 1416 (s), 1377 (s), 1342 (s), 1280 (s),
1253 (s), 1179 (m), 1104 (m), 1027 (s), 959 (m), 920 (m), 880 (s),
2
2
w(Fo - Fc)2, where the weight w is defined as 4Fo /2σ(Fo ) and Fo
and Fc are the observed and calculated structure factor amplitudes.
In the final cycles of each refinement, all non-hydrogen atoms were
assigned anisotropic temperature factors in the absence of disorder
or insufficient data. In the latter cases atoms were treated isotro-
pically. In the case of compound 1 the methyl group of toluene
was modeled by a 50:50 two-site disorder. C-H atom positions
were calculated and allowed to ride on the carbon to which they
are bonded assuming a C-H bond length of 0.95 Å. H atom
temperature factors were fixed at 1.10 times the isotropic temper-
ature factor of the C atom to which they are bonded. The H atom
1
794 (s), 679 (m), 605 (m), 525 (m) cm-1. H NMR: 7.05-6.82
(m, 6 H, Ar), 6.44, 6.43, 6.43, 6.42 (s, 1 H, Me4C5H), 5.61 (s, 1 H,
CMeCHCMe), 3.90 (sept, 3JHH ) 7 Hz, 2 H, CHMe2), 3.70 (sept,
(55) Cromer, D. T.; Waber, J. T. Int. Tables X-ray Crystallogr. 1974, 4,
71-147.

2652 Organometallics, Vol. 25, No. 10, 2006
Bai et al.
contributions were calculated, but not refined. The locations of the
largest peaks in the final difference Fourier map calculation as well
as the magnitude of the residual electron densities in each case
were of no chemical significance. Additional details are provided
in the Supporting Information.
Results and Discussion
The reaction of 140,54 with K/Na alloy was performed in
toluene at 25 °C. The reaction mixture was stirred for 1 week
and then concentrated and cooled to -35 °C. Efforts to isolate
a product from this reduction led only to oils that could not be
characterized. Similarly addition of donor ligands including
PMe3 and pyridine afforded no isolable solids. However,
execution of the reduction in the presence of CH2(PPh2)2,
followed by concentration of the solution and standing at -35
°C, afforded dark red crystals of a new product, 2. A second
crop of 2 was obtained following isolation of the crystals and
further standing at -35 °C, to give an overall yield of 23%.
Crystals of 2 redissolved in toluene at 25 °C gave rise to an
EPR resonance at g ) 1.918, with a line width of about 20 G,
typical of Ti(III) compounds.56,57 IR data for 2 showed consider-
able changes in the fingerprint region in comparison to the IR
spectrum of the precursor complex 1,54 suggesting the presence
of ligand fragments. NMR data revealed only broad resonances
and thus were not informative. It is noteworthy that removal of
the solvent from the mother liquor gave a red oil, which was
confirmed to be 2 by EPR spectroscopy, suggesting that the
relatively low isolated yield of 2 is due to difficulties in
crystallizing this compound.
The structure of 2 was unambiguously determined by an
X-ray crystallographic study. Suitable crystals of 2 were
obtained by recrystallization from toluene, and the structural
solution revealed the formulation as [K(C(Me)CHC(Me)NAr)-
Ti(NAr)(µ-H)]2 (Figure 1). Despite the fact that the observation
of an EPR signal for 2 suggests a momeric formulation in
solution, this species is a centrosymmetric dimer in the solid
state. The two Ti centers are each coordinated to a terminal
imido and ene-imine fragments and bridged by two hydrides.
The two K cations are situated between the pairs of arene rings
on imide and ene-imine fragments (Figure 1).
The imido fragment in the asymmetric unit of 2 gives rise to
a Ti-N bond length of 1.770(4) Å and a Ti-N-C angle of
175.3(3)°. This Ti-N bond distance is slightly longer than the
corresponding Ti-N imido bond length of 1.729(4) Å in the
Ti(IV)-imido species (PhNC(Me)C(Me)NPh)TiCl2(NAr)(py),58
consistent with the respective oxidation states.58 The planar ene-
imine fragment gives rise to a Ti-N distance of 2.029(3) Å.
The Ti-C(3) bond distance is 2.189(4) Å, consistent with a
formal σ-bond. The Ti-C distances to the carbons R and â to
C(3) are 2.343(4) and 2.352(4) Å, respectively. These data
together with the N(1)-C(1) and C-C distances in the ene-
imine fragment of 1.400(5), 1.380(6), and 1.414(6) Å, respec-
tively, are consistent with a π-interaction between Ti and the
ene-imine unit analogous to that described for the Zr(IV) species
[(C(t-Bu)CHC(t-Bu)NAr)ZrCl(THF)(NAr)].29
Figure 1. POV-ray drawing of the dimeric structure of 2. Hydrogen
atoms except for the hydrides are omitted for clarity. Color
scheme: Ti: wheat, N: blue, K: yellow-green, C: black; H: light-
grey. Selected bond distances (Å) and angles (deg): Ti(1)-N(2)
1.770(4), Ti(1)-N(1) 2.029(3), Ti(1)-C(1) 2.343(4), Ti(1)-C(2)
2.352(4), Ti(1)-C(3) 2.189(4), Ti(1)-K(1) 3.5432(17), Ti(1)-H(1)
1.824(3), Ti(1)-H(1)′ 1.818(3), N(1)-C(1) 1.400(5), N(1)-C(6)
1.435(5), C(1)-C(2) 1.380(6), C(2)-C(3) 1.414(6), N(1)-K(1)
3.042(4), N(2)-K(1) 2.807(3), N(2)-Ti(1)-N(1) 125.48(14), Ti-
(1)-H(1)-Ti(1)′ 115.9(3)°, N(2)-Ti(1)-C(3) 116.17(19), N(1)-
Ti(1)-C(3) 86.79(15), N(2)-Ti(1)-C(1) 105.86(16), N(1)-Ti(1)-
C(1) 36.47(14), C(3)-Ti(1)-C(1) 66.65(16), N(2)-Ti(1)-C(2)
103.55(15), N(1)-Ti(1)-C(2)65.83(14), C(3)-Ti(1)-C(2) 36.05-
(16), C(1)-Ti(1)-C(2) 34.17(14), C(1)-N(1)-C(6) 117.0(3),
C(1)-N(1)-Ti(1) 84.1(2), C(6)-N(1)-Ti(1) 156.5(3), Ti(1)-
N(2)-C18) 175.3(3), C(2)-C(1)-N(1) 119.1(4).
in 2 compare with the Ti-H distances, Ti-H-Ti′ angles, and
Ti-Ti′ separations of 1.77(3) Å, 1.88(3) Å, 107(2)°, and 2.931-
59
(3) Å found in [(Me3SiNCH2CH2)2NSiMe3)Ti(µ-H)]2 and
1.90(3) Å, 113.9(14)°, and 3.2288(18) Å found in [(Indenyl)2-
(CH2CH2)Ti(µ-H)]2.60 In addition, the Ti-Ti′ separation in the
paramagnetic product 2 is much longer than that found in the
triply hydride-bridged diamagnetic compound [Li3(THF)2(Et2O)-
(Ti(t-BuC6H2O(C6H2CH2(t-Bu)MeO)2))2(µ-H)3] (2.6210(10) Å).61
The K+ ions are positioned between the arene rings of imido
and ene-imine fragments on the opposing Ti atoms (Figure 1).
This positioning gives rise to K-N distances of 2.807(3) and
3.042(4) Å, which compares with the K-N distances of 2.8484-
(12), 2.770(3), and 2.803(3) Å seen in KC(SiMe3)2(SiMe2-
NMe2)62 and [K[N(SiMe3)2)]2, respectively.63 The K is posi-
tioned nearly symmetrically with respect to the ipso and alpha
carbons with K-C distances of 2.884(3), 3.200(5), and 3.3311-
(5) Å, respectively. With respect to the imido-aryl group the K
approaches isopropyl carbons at distances of 2.938(4), 3.100-
(5), and 3.304(5) Å, respectively. The latter K-C approach also
results in a K-isopropyl hydrogen approach of 2.894(4) Å. These
K-C distances are in the range seen in the benzoid radical salt
[(18-crown-6)K(η6-C6H5Me)], where the K-C distances range
from 3.044(5) to 3.311 Å,64 or in LuCH(SiMe3)2(µ-Cl)K(η6-
The hydride atoms in 2 were located and refined. The Ti2-
(µ-H)2 core is planar with Ti-H distances of 1.824(3) and 1.818-
(3) Å and Ti-H-Ti′ angles of 115.9(3)°. This geometry results
in a Ti-Ti′ separation of 3.0872(16) Å. These metric parameters
(59) Love, J. B.; Clark, H. C. S.; Cloke, F. G. N.; Green, J. C.; Hitchcock,
P. B. J. Am. Chem. Soc. 1999, 121, 6843-6849.
(60) Xin, S.; Harrod, J. F.; Samuel, E. J. Am. Chem. Soc. 1994, 116,
11562-11563.
(61) Matsuo, T.; Kawaguchi, H. Organometallics 2003, 22, 5379.
(62) Al-Juaid, S. S.; Eaborn, C.; El-Hamruni, S.; Farook, A.; Hitchcock,
P. B.; Hopman, M.; Smith, J. D.; Clegg, W.; Izod, K.; O’Shaughnessy, P.
Dalton Trans. 1999, 3267-3273.
(63) Tesh, K. F.; Hanusa, T. P.; Huffman, J. C. Inorg. Chem. 1990, 29,
1584-1586.
(56) Dick, D. G.; Stephan, D. W. Organometallics 1991, 10, 2811-16.
(57) Sung, R. C. W.; Courtenay, S.; McGarvey, B. R.; Stephan, D. W.
Inorg. Chem. 2000, 39, 2542-2546.
(58) McInnes, J. M.; Blake, A. J.; Mountford, P. Dalton Trans. 1998,
3623-3628.

Reductions of â-Diketiminato-Ti(III) Complexes
Organometallics, Vol. 25, No. 10, 2006 2653
Scheme 2. Proposed Mechanism of Formation of 2
Figure 2. POV-ray drawing of 3. Hydrogen atoms are omitted
for clarity. Color scheme: Ti: wheat, Cl: green, N: blue, C: black.
Selected bond distances (Å) and angles (deg): Ti(1)-N(1) 2.086-
(2), Ti(1)-N(2) 2.088(3), Ti(1)-Cl(1) 2.2997(13), N(1)-Ti(1)-
N(2) 87.41(10), N(1)-Ti(1)-Cl(1) 101.03(8), N(2)-Ti(1)-Cl(1)
102.69(8), N(1)-Ti(1)-C(37) 108.4(2).
C6H5Me)2, where the K-centroid distances are reported to be
3.003 and 3.128 Å.65 The Ti-K separations are 3.5432(17) and
3.7482(19) Å, while the approach of K to the proximal bridging
hydride is 2.272 Å.
Figure 3. POV-ray drawing of 4. Hydrogen atoms are omitted
for clarity. Color scheme: Ti: wheat, Cl: green, N: blue, C: black.
Selected bond distances (Å) and angles (deg): Ti(1)-N(2) 2.119-
(3), Ti(1)-N(1) 2.125(2), Ti(1)-Cl(1) 2.3049(10), N(2)-Ti(1)-
N(1) 86.14(10), N(2)-Ti(1)-Cl(1) 99.94(8), N(1)-Ti(1)-Cl(1)
100.00(7).
Relatively few Ti-hydride compounds have been isolated and
fully characterized. The cyclopentadienyl complexes [Cp2Ti-
(µ-H)]2,66 [(IndenylCH2)2Ti(µ-H)]2,60 [CpTi(µ-H)(µ-fulvalene)]2,67
[(C5Me4Ph)2Ti(µ-H)2]2Mg, and (C5Me4Ph)[C5Me4(o-C6H4)]Ti(µ-
68
H)2Mg(THF)2 are known, while the known nonmetallocene
to be the reaction of K/Na with CH2(PPh2)2, although this could
not be unambiguously confirmed.
Ti-hydride complexes include [TiH((Me3SiNCH2CH2)2NSi-
Me3)]2,59 [Li3(THF)2(Et2O)(Ti(t-BuC6H2O(C6H2CH2(t-Bu)Me-
O)2))2(µ-H)3],61 and Ti(t-Bu2CHNC6H3(t-Bu)(µ-H)Mg(THF)2)2-
(µ-Cl).69 Thus, compound 2 represents a rare example of such
nonmetallocene Ti(III)-hydride species containing Ti-C bonds.
In an effort to further explore the relationship between
reduction and ligand cleavage, new Ti(III) species were
prepared. Compound 1 was reacted with CpLi or (C5Me4H)Li
to give deep red crystals of compounds formulated as (Nacnac)-
CpTiCl (3) and (Nacnac)(C5Me4H)TiCl (4) in 91 and 92% yield,
respectively. These compounds give rise to EPR signals with g
values of 1.975 and 1.955, respectively, typical of Ti(III) species.
Crystallographic studies of these compounds confirmed the
anticipated pseudo-tetrahedral geometries at Ti. In the case of
compound 3 (Figure 2) the Ti-N distances were found to be
2.086(2) and 2.088(3) Å, while the Ti-Cl distance was observed
to be 2.2997(13) Å. The corresponding distances in 4 (Figure
3) are 2.119(3), 2.125(2), and 2.3049(10) Å. The slightly longer
distances in 4 were consistent with the greater electron donation
from (C5Me4H) in comparison to the Cp ligand. The bite angles
for the Nacnac ligands in 3 and 4 were similar at 87.41(10)°
and 86.14(10)°, respectively.
Alkyllithium reagents are known in some cases to act as
reductants; however, reaction of 3 with n-BuLi proceeds in a
straightforward fashion to effect alkylation at Ti. Red crystals
of 5 are isolated in 92% yield. The EPR spectrum of 5 shows
a slight shift in the g value, suggesting a new Ti(III) derivative.
X-ray crystallographic studies of 5 confirmed the formulation
as (Nacnac)CpTiBu (Figure 4). Similar to 3, the geometry at
Ti is pseudotetrahedral with a Ti-N bond length of 2.0873-
(18) Å and Ti-Cbutyl distance of 2.142(4) Å. The Ti-N bond
lengths are longer in 5 than those seen in 3, consistent with
The reaction mechanism affording 2 is the subject of
speculation (Scheme 2). Related recent work by Mindiola and
co-workers29 described the reduction of the Zr(IV) species (HC-
(C(Me)Ar)2)ZrCl3, which results in ligand cleavage and forma-
tion of the Zr(IV) product [(C(t-Bu)CHC(t-Bu)NArZrCl(THF)-
(NAr)]. It is proposed that reduction of the Ti(III) compound
(HC(C(Me)NAr)2)TiCl2 proceeds in a similar fashion through
a transient Ti(II) species (HC(C(Me)NAr)2)TiCl, which effects
oxidative ligand cleavage to give an intermediate Ti(IV)
compound [(C(Me)CHC(Me)NAr)TiCl(NAr)] (Scheme 2). This
compound is again reduced by excess reductant and trapped by
KH to give 2. Similar ligand rupture has been reported for
related Ti(III)-alkylidene complexes employing the t-Bu-
substituted Nacnac ligand.52 The source of the hydride is thought
(64) Hitchcock, P. B.; Lappert, M. F.; Protchenko, A. V. J. Am. Chem.
Soc. 2001, 123, 189-190.
(65) Schaverien, C. J.; Mechelen, J. B. v. Organometallics 1991, 10,
1704-1709.
(66) Bercaw, J. E.; Brintzinger, H. H. J. Am. Chem. Soc. 1969, 91, 7301.
(67) Bercaw, J. E.; Brintzinger, H. H. J. Am. Chem. Soc. 1970, 92, 6182.
(68) Kupfer, V.; Thewalt, U.; Horacek, M.; Petrusova, L.; Mach, K.
Inorg. Chem. Commun. 1999, 2, 540-544.
(69) Mokuolu, Q. F.; Duckmanton, P. A.; Blake, A. J.; Wilson, C.; Love,
J. B. Organometallics 2003, 22, 4387.

2654 Organometallics, Vol. 25, No. 10, 2006
Bai et al.
Figure 5. POV-ray drawing of 6. Hydrogen atoms are omitted
for clarity. Color scheme: Ti: wheat, N: blue, C: black. Selected
bond distances (Å) and angles (deg): Ti(1)-N(5) 1.801(5), Ti-
(1)-N(2) 2.128(5), Ti(1)-N(1) 2.129(4), Ti(2)-N(6) 1.806(5), Ti-
(2)-N(4) 2.111(5), Ti(2)-N(3) 2.116(5), N(5)-N(6) 1.273(6),
N(5)-Ti(1)-N(2) 107.81(18), N(5)-Ti(1)-N(1) 100.89(18), N(2)-
Ti(1)-N(1) 89.90(18), N(6)-Ti(2)-N(4) 108.83(18), N(6)-Ti(2)-
N(3) 104.24(18), N(4)-Ti(2)-N(3) 90.48(18), N(6)-N(5)-Ti(1)
165.9(4), N(5)-N(6)-Ti(2) 162.6(4).
Figure 4. POV-ray drawing of 5. Hydrogen atoms are omitted
for clarity. Color scheme: Ti: wheat, N: blue, C: black. Selected
bond distances (Å) and angles (deg): Ti(1)-N(1) 2.0873(18), Ti-
(1)-C(4) 2.142(4), N(1)-Ti(1)-N(1)′ 88.74(10), N(1)-Ti(1)-C(4)
104.90(9).
Scheme 3. Reductions of 3 and 4
hydrazine (1.46 Å). The N-N distance in 6 is similar to those
seen in [((Me2NC(Ni-Pr)2)2Ti]2(N2) (1.28(1) Å),70 [(PhCNSi-
Me3)2)2Ti]2(N2) (1.275(6) Å),71 [((Me3Si)2N)TiCl(TMEDA)]2-
(N2) (1.289(9) Å),72 and [((Me3Si)2N)TiCl(py)]2(N2) (1.263(7)
Å)73 and significantly longer than those in titanocene derivatives
[Cp′2Ti]2(N2) (Cp′ ) Cp* 1.165 Å,74,75 Me4C5H 1.170(4) Å76).
While these similarities suggest a bonding description involving
delocalization over the TiN2Ti fragment in 6, it is also
noteworthy that this moiety is nonlinear, with Ti-N-N angles
of 165.9(4)° and 162.6(4)°, respectively, presenting a transoid
disposition. Significant reduction of the N2 fragment is also
consistent with the stability of 6, even on storage under N2 for
several months at 30 °C.
Attempts to effect reduction of 4 in reactions analogous to
those achieved with 3 were undertaken. Reactions of 4 with
t-BuLi or n-BuLi or Na/K amalgam all led to the formation
and isolation of the same new product 7 in yields ranging from
stronger sigma donation from the alkyl group in 5. This also
results in a corresponding increase in the Nacnac ligand bite
angle in 5 to 88.74(10)°. Notably this Ti(III)-alkyl compound
5 proved to be remarkably stable under thermal duress. On
standing in solution at 120 °C for 24 h, 5 showed no evidence
of degradation. Apparently, the Lewis acidity of the Ti(III)
center is insufficient to initiate â-hydride abstraction and
liberation of butene, at least under these conditions. A related
Ti(III) alkyl species, recently reported by Miniola and co-
workers, exhibits similar stablity.53
Compound 4 reacts with the stronger reductant Na/K amal-
gam to afford the isolation of the new dark red species 6 in
59% yield. 1H and 13C{1H} NMR characterization of 6 reveals
that it is a diamagnetic compound with resonances attributable
to intact Nacnac and Cp ligands. As these data were not
conclusive in the structural determination, X-ray crystallography
was used to determine that 6 is in fact formulated as ((Nacnac)-
CpTi)2(µ-η2-N2), 6 (Scheme 3). In this species, dinitrogen
bridges the two Ti centers, each of which is coordinated to Cp
and Nacnac ligands (Figure 5). The Ti-N bond lengths in 6
for the Nacnac ligands average 2.121(5) Å, slightly longer than
those in the precursor 3. The corresponding Nacnac ligand bite
angles were found to be 89.90(18)° and 90.48(18)°, again
slightly larger than that found in 3. The Ti-N distances for the
bridging dinitrogen moiety average 1.803(5) Å, while the N-N
distance is 1.273(6) Å. While this latter distance is consistent
with significant reduction of the N-N triple bond in free N2
(1.0975 Å), it is much shorter than the N-N single bond in
1
46 to 58%. H NMR data for 7 reveal signals at 6.42 ppm
attributable to the Me4C5H ligand. The resonances at 1.34, 1.27,
1.01, 0.94, and 0.80 ppm are attributable to isopropyl methyl
groups, suggesting that the Nacnac ligand symmetry has been
disrupted. An X-ray crystallographic study of 7 confirmed that
the Nacnac ligand had undergone C-N bond scission, affording
(C5Me4H)[(ArNC(Me)CHC(Me)]Ti(NAr) (Scheme 3, Figure 6).
In this species the Nacnac ligand has been cleaved to imido
and ene-imine fragments similar to those seen in 2. In contrast
to 2, however, 7 is monomeric, presumably a result of the
inclusion of the sterically demanding substituted cyclopentadi-
enyl ligand. The Ti-N bond lengths for these fragments were
found to be 2.202(3) and 1.730(3) Å, respectively. The Ti-N
(70) Mullins, S. M.; Duncan, A. P.; Bergman, R. G.; Arnold, J. Inorg.
Chem. 2001, 40, 6952.
(71) Hagadorn, J. R.; Arnold, J. J. Am. Chem. Soc. 1996, 118, 893.
(72) Duchateau, R.; Gambarotta, S.; Beydoun, N.; Bensimon, C. J. Am.
Chem. Soc. 1991, 113, 8986.
(73) Beydoun, N.; Duchateau, R.; Gambarotta, S. Chem. Commun. 1992,
244.
(74) Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J.
Am. Chem. Soc. 1972, 94, 1219.
(75) Sanner, R. D.; Duggan, M. D.; McKenzie, T. C.; Marsh, R. E.;
Bercaw, J. E. J. Am. Chem. Soc. 1976, 98, 8358.
(76) de Wolf, J. M.; Blaauw, R.; Meetsma, A.; Teuben, J. H.; Gyepes,
R.; Varga, V.; Mach, K.; Veldman, N.; Spek, A. Organometallics 1996,
15, 4977.

Reductions of â-Diketiminato-Ti(III) Complexes
Organometallics, Vol. 25, No. 10, 2006 2655
in N2 binding is reminencent of the recent Zr chemistry reported
by Chirik and co-workers, although in that case, use of
tetramethylcyclopentadienyl ligands allowed interception of N2
complexes.77-79 Presumably in the present Ti case, an analogous
N2 complex would be destabilized by the steric conflict
generated by the required proximity of substituted cyclopenta-
dienyl ligands on the Ti centers. In addition, the Ti center in
the transient species “(Me4C5H)Ti(Nacnac)” is more election
rich than in the Cp analogue, prompting internal redox chemistry
and reductive ligand cleavage with concurrent oxidation of the
metal center. A similar mechanism has been put forward by
Mindiola et al. for a closely related Zr system.29
Summary
Reductions of (Nacnac)Ti(III) complexes generating transient
“(Nacnac)Ti(II)” species result in the Nacnac ligand cleavage
products 2 and 7. This view is supported by the isolation of 6,
which is best described as the product of N2 interception of the
putative Ti(II) species. It is clear that both the electronic and
steric nature of ancillary ligands play a role in determining the
course of such reduction reactions. We are continuing to study
related chemistry of reduced Nacnac complexes.
Figure 6. POV-ray drawing of 7. Hydrogen atoms are omitted
for clarity. Color scheme: Ti: wheat, N: blue, C: black. Selected
bond distances (Å) and angles (deg): Ti(1)-N(1) 2.202(3), Ti-
(1)-N(2) 1.730(3), Ti(1)-C(11) 2.160(4), N(2)-Ti(1)-C(11)
106.95(14), N(2)-Ti(1)-N(1) 101.87(12), C(11)-Ti(1)-N(1)
78.88(14), C(27)-N(2)-Ti(1) 178.1(3).
bond length for the imido group is similar to that seen in the
Ti-imido species Ti(NAr)(NC5H5)(PhNCMeCMeNPh) by Mount-
ford and co-workers.58 This and the linear geometry at N are
consistent with the formal Ti-N double-bond character. The
geometry of the ene-imine fragment is similar to that observed
for the species [(C(t-Bu)CHC(t-Bu)NAr)ZrCl(THF)(NAr)]29
reported recently by Mindiola and co-workers.
Acknowledgment. Financial support from NSERC of Canada
is gratefully acknowledged.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
The mechanism of formation of 7 is the subject of speculation.
It is reasonable to suggest that reduction of the precursor 4
generates a putative Ti(II) species “(Me4C5H)Ti(Nacnac)”. This
view is supported to some extent by the isolation of 6, as 6
represents the interception of the putative Ti(II) species “CpTi-
(Nacnac)” by N2. In the parallel reactions of 4, the species
“(Me4C5H)Ti(Nacnac)” is not intercepted by N2. This variation
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