Synthesis and reactivity of titanium and zirconium complexes supported by a multidentate monoanionic [N2 P2] ligand

Article abstract of DOI:10.1021/om8011932

The coordination chemistry of titanium and zirconium complexes supported by the monoanionic multidentate ligand [N₂P₂] (where [N ₂P₂]) t BuN^-SiMe₂N(CH ₂CH₂Pⁱ

Full text of DOI:10.1021/om8011932

3338
Organometallics 2009, 28, 3338–3349
Synthesis and Reactivity of Titanium and Zirconium Complexes
Supported by a Multidentate Monoanionic [N2P2] Ligand
Wayne A. Chomitz, Andrew D. Sutton, Jamin L. Krinsky, and John Arnold*
Department of Chemistry, UniVersity of California, Berkeley, California 94720-1460
ReceiVed December 17, 2008
The coordination chemistry of titanium and zirconium complexes supported by the monoanionic
multidentate ligand [N2P2] (where [N2P2] ) tBuN-SiMe2N(CH2CH2PiPr2)2) is presented. The zirconium(IV)
halide complex [N2P2]ZrCl3 (1) serves as a precursor to the alkyl species [N2P2]Zr(CH2SiMe3)3 (2) and
[N2P2]ZrMe3 (3). The coordination behavior of the [N2P2] ligand in compound 3 is determined using
NMR and X-ray diffraction data, and protonation of 3 results in the formation of the cationic species
{[N2P2]ZrMe2}{B(C6H5)4} (4). The reduction of 1 in the presence of various traps leads to the isolation
of ([N2P2]ZrCl)2(µ-η2:η2-N2) (5), ([N2P2]ZrCl)2(µ-Cl)2 (6), and [N2P2]ZrAr* (9). The titanium(III) halide
complex [N2P2]TiCl2 (10) also serves as a precursor to alkyl and reduced species [N2P2]TiMe2 (11) and
([N2P2]TiCl)2(µ-N2) (12). Alkylation of 12 results in the formation of ([N2P2]TiCH2SiMe3)2(µ-N2) (13),
and the degree of reduction of the N2 moiety in 12 and 13 is examined using X-ray crystallography and
Raman spectroscopy. A series of titanium(IV) imido complexes [N2P2]TiCl(NtBu) (14), [N2P2]TiMe(NtBu)
(15), and {[N2P2]Ti(NtBu)}{MeB(C6F5)3)} (16) are synthesized, and the coordination behavior of the
[N2P2] ligand is presented.
are involved.9-11 We therefore undertook the synthesis of a
range of early-metal alkyl and reduced-metal complexes to
Introduction
The seminal work of Fryzuk et al.1-3 and the work of
Mindiola et al.4,5 and Ozerov et al.6,7 demonstrated that “mixed-
donor” ligands (containing N and P donors) can stabilize early-
metal alkyl, alkylidene, and alkylidyne complexes as well as
low-oxidation-state early-metal species. We recently reported
the synthesis of the new multidentate monoanionic ligand [N2P2]
and demonstrated the versatility of its coordination geometry
through the synthesis and structural characterization of a series
of first-row transition-metal halide complexes. We extended this
work to include main-group coordination compounds where an
additional coordination mode (κ2-NP) was observed.8 These
initial results are promising for the application of this ligand to
support a variety of metal-based reactivities because of the
ability of this ligand to adapt to the steric and electronic
preferences of the metal center.
establish the stability of the [N2P2] ligand framework under
related conditions. The utility of the metal alkyl compounds as
precursors to alkylidene complexes was examined, as was the
synthesis and substitution chemistry of a series of titanium imido
complexes. A portion of this work has been communicated.12-14
Experimental Section
All reactions were performed using standard Schlenk-line
techniques or in an MBraun drybox (<1 ppm O2/H2O) unless noted
otherwise. All glassware, cannulae, and Celite were stored in an
oven at >425 K. Pentane, toluene, diethyl ether, and tetrahydrofuran
(THF) were purified by passage through a column of activated
alumina and degassed with nitrogen prior to use.15 Hexamethyld-
isiloxane was distilled from sodium and degassed with nitrogen
prior to use. Deuterated solvents (C6D6, Tol-d8) were vacuum
transferred from sodium/benzophenone. NMR spectra were recorded
at ambient temperature on Bruker AV-300, AVQ-400, AVB-400,
and DRX-500 spectrometers. 1H and 13C{1H} NMR chemical shifts
are given relative to residual solvent peaks, and coupling constants
(J) are given in hertz (Hz). 31P{1H} NMR chemical shifts are
referenced to an external standard of P(OMe)3 set to 1.67 ppm. IR
This paper focuses on early-transition-metal derivatives of
the [N2P2] ligand, with the aim of exploring the scope of
reactivity supported by this ligand set. Intramolecular C-H bond
activation has been reported with other TDMA ligand systems
examined by our group and others when reactive metal centers
* To whom correspondence should be addressed.
(1) Fryzuk, M. D.; Giesbrecht, G.; Rettig, S. J. Organometallics 1996,
15, 3329–3336.
(2) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J.; Macgillivray, L. R.
J. Am. Chem. Soc. 1993, 115, 5336–5337.
(3) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. J. Am. Chem. Soc. 1990,
112, 8185–8186.
(4) Bailey, B. C.; Fan, H. J.; Huffman, J. C.; Baik, M. H.; Mindiola,
D. J. J. Am. Chem. Soc. 2007, 129, 8781–8793.
(9) Bambirra, S.; Boot, S. J.; van Leusen, D.; Meetsma, A.; Hessen, B.
Organometallics 2004, 23, 1891–1898.
(10) Chomitz, W. A.; Minasian, S. G.; Sutton, A. D.; Arnold, J. Inorg.
Chem. 2007, 46, 7199–7209.
(11) Marinescu, S. C.; Agapie, T.; Day, M. W.; Bercaw, J. E.
Organometallics 2007, 26, 1178–1190.
(12) As we reported with main-group derivatives of the [N2P2] ligand,
fluxional behavior with “hard” metals is common. Accordingly, we have
found that assessing the solution structures of these compounds by 1H NMR
spectroscopy is complicated. In contrast, 31P NMR spectroscopy is a useful
diagnostic tool, and a good deal of structural information on the reported
compounds is based on these data.
(13) Chomitz, W. A.; Arnold, J. Chem. Commun. 2007, 4797–4799.
(14) Chomitz, W. A.; Arnod, J. Chem.sEur. J. 2009, 15, 2020–2030.
(15) Alaimo, P. J.; Peters, D. W.; Arnold, J.; Bergman, R. G. J. Chem.
Educ. 2001, 78, 64–64.
(5) Kilgore, U. J.; Yang, X. F.; Tomaszewski, J.; Huffman, J. C.;
Mindiola, D. J. Inorg. Chem. 2006, 45, 10712–10721.
(6) Gerber, L. C. H.; Watson, L. A.; Parkin, S.; Weng, W.; Foxman,
B. M.; Ozerov, O. V. Organometallics 2007, 26, 4866–4868.
(7) Weng, W.; Yang, L.; Foxman, B. M.; Ozerov, O. V. Organometallics
2004, 23, 4700–4705.
(8) Minasian, S. G.; Arnold, J. Dalton Trans. 2009, 1714–1720.
10.1021/om8011932 CCC: $40.75
2009 American Chemical Society
Publication on Web 05/11/2009

Titanium and Zirconium Complexes
Organometallics, Vol. 28, No. 12, 2009 3339
Table 1. Physical Properties of 1-6, 8, 9, and 11-16
coordination mode
of [N2P2]
compound no.
compound name
color
mp (°C)
yield (%)
1
2
3
4
5
6
8
9
11
12
13
14
15
16
[N2P2]ZrCl3
[N2P2]Zr(CH2SiMe3)3
[N2P2]ZrMe3
{[N2P2]ZrMe2}{B(C6H5)4}
([N2P2]ZrCl)2(µ-η2:η2-N2)
([N2P2]ZrCl)2(µ-Cl)2
[N2P2]ZrII(Cl)CtN(2,6-Mes2)C6H3
[N2P2]ZrAr*
colorless
colorless
colorless
yellow
purple
137-138
82
quant.
46
82
17
20
quant.
18
58
57
κ3-N2P
64-65
κ3-N2P
κ4-N2P2
κ3-N2P
κ3-N2P
κ3-N2P
κ3-N2P
κ3-N2P
κ3-N2P
κ3-N2P
κ3-N2P
κ3-N2P
κ4-N2P2
175-176
82-83 (dec)
green
forest green
orange
blue
74-75
[N2P2]TiMe2
114-115
124-126
135-136
107-108
73-75
([N2P2]TiCl)2(µ-N2)
([N2P2]TiCH2SiMe3)2(µ-N2)
[N2P2]TiCl(NtBu)
purple
orange
orange
yellow
orange
34
76
62
quant.
[N2P2]TiMe(NtBu)
{[N2P2]Ti(NtBu)}{MeB(C6F5)3}
samples were prepared as Nujol mulls and taken between KBr disks.
Magnetic susceptibility (µeff) values were determined using the
solution Evans method at ambient temperature (22 °C).16 Melting
points were determined using sealed capillaries prepared under
nitrogen and are uncorrected. Li[N2P2],17 ZrCl4(THF)2,18
[PhNMe2H][B(C6H5)4],19 TiCl3(THF)3,20 [N2P2]TiCl2 (10),17 2,6-
Mes2C6H3NH2,21 and Cl2(py)3Ti(NtBu)22 were prepared following
the literature procedures, and unless otherwise noted, all reagents
were acquired from commercial sources. Elemental analyses and
mass spectral data were determined at the College of Chemistry,
University of California, Berkeley. X-ray structural determinations
were performed at CHEXRAY, University of California, Berkeley.
A full list of compounds and their physical properties is provided
in Table 1.
extracted with pentane. Following the removal of solvent under
1
vacuum, analytically pure 2 (as determined by H and 31P NMR
spectroscopy) was isolated as a colorless oil in quantitative yield.
1H NMR (500 MHz, Tol-d8): δ 0.22 (s, 27 H, -CH2Si(CH3)3);
0.48 (s, 6 H, Si(CH3)2); 0.92 (s, 6 H, -CH2Si(CH3)3); 1.02 (m, 24
t
H, PCH(CH3)2); 1.42 (s, 9 H, Bu); 1.58 (m, 4 H, PCH(CH3)2);
1.72 (m, 4 H, -CH2CH2-); 3.31 (m, 4 H, -CH2CH2-). 13C{1H}
NMR (125 MHz, Tol-d8): δ 3.16 (s); 18.84 (d); 19.87 (d); 20.01
(d); 23.30 (d); 34.67 (s); 50.17 (d); 54.28 (s); 65.08 (s). 31P{1H}
NMR (500 MHz, Tol-d8): δ 8.11 (s).
[N2P2]ZrMe3 (3). Methyllithium (1.6 M in Et2O, 3.2 mL, 4.8
mmol) was added via syringe to a suspension of 1 (1.0 g, 1.6 mmol)
in 20 mL of Et2O at -40 °C. The reaction mixture was allowed to
warm to room temperature and stirred for 2 h. The volatiles were
removed under vacuum, and the crude product was extracted with
pentane. Colorless crystals of 3 were collected in 46% yield (0.42
g) following cooling of a pentane solution at -40 °C overnight.
1H NMR (400 MHz, C6D6): δ 0.48 (s, 6 H, Si(CH3)2); 0.90 (s, 9
H, -CH3); 1.08 (m, 24 H, PCH(CH3)2); 1.25 (m, 2 H, PCH(CH3)2);
[N2P2]ZrCl3 (1). A solution of Li[N2P2] (1.5 g, 3.4 mmol) in 20
mL of toluene was added dropwise to a suspension of ZrCl4(THF)2
(1.3 g, 3.4 mmol) in 20 mL of toluene, and the reaction mixture
was stirred overnight. The solution was filtered, and the solvent
was removed under vacuum. The crude product was washed with
pentane and dried under vacuum to afford analytically pure 1 as a
t
1.50 (s, 9 H, Bu); 1.68 (m, 6 H, -CH2CH2-, PCH(CH3)2); 2.99
1
(m, 2 H, -CH2CH2-); 3.16 (m, 2 H, -CH2CH2-). 13C{1H} NMR
(125 MHz, C6D6): δ 5.02 (s); 19.74 (d); 20.21 (d); 20.72 (d); 24.20
(d); 34.79 (s); 45.32 (d); 46.28 (d); 54.69 (s). 31P{1H} NMR (400
MHz, C6D6): δ 2.75 (s). IR (cm-1): 1357 (m); 1297 (w); 1248 (s);
1194 (s); 1123 (m); 1065 (m); 1036 (s); 1017 (s); 965 (w); 939
(m); 923 (w); 894 (s); 883 (m); 821 (m); 802 (m); 744 (m); 720
(m); 688 (w); 674 (w); 627 (w); 614 (w); 539 (m); 502 (m); 463
(w). Anal. Calcd for C25H60N2P2SiZr: C, 52.66; H, 10.63; N, 4.91.
Found: C, 53.02; H, 10.77; N, 5.21. Mp: 64-65 °C.
colorless solid (1.8 g, 82% yield). H NMR (500 MHz, C6D6): δ
0.46 (s, 3 H, Si(CH3)2); 0.52 (s, 3 H, Si(CH3)2); 1.03 (m, 20 H,
t
PCH(CH3)2); 1.37 (m, 4 H, PCH(CH3)2); 1.48 (s, 9 H, Bu); 1.53
(m, 4 H, PCH(CH3)2); 1.65 (m, 2 H, -CH2CH2-); 2.34 (m, 2 H,
-CH2CH2-); 2.87 (m, 1 H, -CH2CH2-); 3.21 (m, 1 H, -CH2-
CH2-); 3.52 (m, 1 H, -CH2CH2-); 3.77 (m, 1 H, -CH2CH2-).
13C{1H} NMR (125 MHz, C6D6): δ 1.85 (s); 5.25 (s); 19.12 (d);
19.23 (d); 19.54 (d); 20.01 (d); 20.26 (d); 20.38 (d); 20.57 (d);
20.70 (d); 21.16 (d); 21.53 (d); 23.65 (d); 23.96 (d); 27.01 (d);
27.40 (d); 34.60 (s); 44.94 (d); 51.72 (s); 51.97 (s); 56.17 (s).
31P{1H} NMR (500 MHz, C6D6): δ 2.59 (s, 1 P); 16.38 (s, 1 P). IR
(cm-1): 1308 (w); 1259 (s); 1226 (m); 1181 (s); 1095 (w); 1061
(m); 1036 (w); 1011 (w); 984 (s); 954 (m); 919 (m); 883 (m); 845
(s); 798 (m); 755 (s); 644 (m); 584 (m); 547 (m); 503 (m); 471
(m); 446 (m). Anal. Calcd for H51C22Cl3N2P2SiZr: C, 41.85; H,
8.16; N, 4.44. Found: C, 42.21; H, 8.22; N, 4.28. Mp: 137-138
°C.
Generation of {[N2P2]ZrMe2}{B(C6H5)4} (4). A solution of
[PhNMe2H][B(C6H5)4] (0.16 g, 0.35 mmol) in 5 mL of THF was
added to a solution of 3 (0.20 g, 0.35 mmol) in 10 mL of THF at
-40 °C. The reaction mixture was allowed to warm to room
temperature and stirred for 1 h. The solvent was removed under
vacuum, and the product was washed with pentane (3 × 10 mL).
The remaining solid was dried under vacuum and isolated as a
yellow solid in 80% yield (0.24 g). 1H NMR (400 MHz, C6D6): δ
0.13 (s, 6 H, Si(CH3)2); 0.26 (s, 6 H, -CH3); 0.91 (m, 28 H,
Generation of [N2P2]Zr(CH2SiMe3)3 (2). A solution of
LiCH2SiMe3 (0.14 g, 1.4 mmol) was added to a solution of 1 (0.30
g, 0.48 mmol) in 5 mL of toluene at -40 °C. The reaction mixture
was allowed to warm to room temperature and stirred for 3 h. The
volatile material was removed under vacuum, and the product was
t
PCH(CH3)2 and PCH(CH3)2); 1.17 (s, 9 H, Bu); 1.43 (m, 2 H,
-CH2CH2-); 1.62 (m, 2 H, -CH2CH2-); 1.76 (m, 2 H,
-CH2CH2-); 2.51 (m, 2 H, -CH2CH2-); 7.34 (m, 8 H, Ar-H);
7.68 (d, JHH ) 6.8 Hz, 4 H, Ar-H); 7.95 (d, JHH ) 6 Hz, 8 H,
Ar-H). 31P{1H} NMR (400 MHz, C6D6): δ 15.61 (s).
([N2P2]ZrCl)2(µ-η2:η2-N2) (5). A suspension of KC8 (0.14 g,
1.0 mmol) in 10 mL of THF was added to a thick-walled reaction
flask containing a solution of 1 (0.30 g, 0.48 mmol) in 5 mL of
THF at -70 °C. The reaction mixture was stirred at -70 °C under
nitrogen for 3 h, and the vessel was sealed. The reaction mixture
was allowed to warm to room temperature and stirred overnight.
The solution was transferred to a new reaction flask, and the solvent
was removed under vacuum. The crude product was extracted with
(16) Piguet, C. J. Chem. Educ. 1997, 74, 815–816.
(17) Chomitz, W. A.; Mickenberg, S. F.; Arnold, J. Inorg. Chem. 2008,
47, 373–380.
(18) Manzer, L. E. Inorg. Synth. 1982, 21, 135–140.
(19) Crane, F. E. Anal. Chem. 1956, 28, 1794–1797.
(20) Jones, N. A.; Liddle, S. T.; Wilson, C.; Arnold, P. L. Organome-
tallics 2007, 26, 755–757.
(21) Gavenonis, J.; Tilley, T. D. Organometallics 2002, 21, 5549–5563.
(22) Carmalt, C. J.; Newport, A. C.; Parkin, I. P.; White, A. J. P.;
Williams, D. J. J. Chem. Soc., Dalton Trans. 2002, 4055–4059.

3340 Organometallics, Vol. 28, No. 12, 2009
Chomitz et al.
pentane, and the solution was cooled at -40 °C overnight. Purple
crystals of 5 were isolated in 17% yield (0.045 g). A 3:2 mixture
of isomers was determined by 31P{1H} NMR. 1H NMR (400 MHz,
C6D6): δ 0.36 (s, 9 H, Si(CH3)2); 0.85 (s, 3 H, Si(CH3)2); 0.92 (s,
3 H, Si(CH3)2); 1.12 (m, 45 H, PCH(CH3)2); 1.28 (m, 12 H,
PCH(CH3)2 and -CH2CH2-); 1.51 (m, 15 H, PCH(CH3)2);
1.61-1.71 (m, 8 H, PCH(CH3)2 and -CH2CH2-); 1.74 (s, 13.5
H, Bu); 1.75 (s, 9 H, Bu); 2.11 (m, 4 H, -CH2CH2-); 2.26 (m,
1 H, -CH2CH2-); 2.71 (m, 2 H, -CH2CH2-); 3.11 (m, 1 H,
-CH2CH2-); 3.75 (m, 1 H, -CH2CH2-); 4.05 (m, 1 H,
-CH2CH2-). 31P{1H} NMR (400 MHz, C6D6): δ 17.08 (s, 2 P);
14.46 (s, 3 P); 1.54 (s, 2 P); 0.07 (s, 3 P). IR (cm-1): 1297 (w);
1247 (m); 1197 (m); 1046 (s); 969 (w); 930 (w); 880 (m); 848 (s);
818 (m); 762 (s); 704 (s); 676 (w); 611 (w); 530 (m); 493 (w).
Anal. Calcd for C44H102Cl2N6P4Si2Zr2: C, 45.99; H, 8.97; N, 7.32.
Found: C, 46.35; H, 9.25; N, 6.97. Mp: 175-176 °C.
2.27 (s, 6 H, Ar-CH3); 2.35 (s, 6 H, Ar-CH3). 31P{1H} NMR
(400 MHz, C6D6): δ -2.96 (s, 1 P); 22.40 (s, 1 P). IR (cm-1):
1872 (C-N).
[N2P2]ZrAr* (9). A suspension of KC8 (0.14 g, 1.0 mmol) in
10 mL of Et2O was added to a suspension of 1 (0.30 g, 0.48 mmol)
and 7 (0.16 g, 0.48 mmol) in 10 mL of Et2O at -40 °C. The
colorless solution turned dark green, and the reaction mixture was
allowed to warm to room temperature and stirred overnight. The
resulting yellow/green solution was filtered, concentrated, and stored
at -40 °C overnight. Orange crystals of 9 were collected in 18%
yield (0.075 g). The -CH2CH2- hydrogens were not visible in
t
t
1
the H NMR spectrum at room temperature and are not reported.
1H NMR (500 MHz, C6D6): δ 0.32 (s, 3 H, Si(CH3)2); 0.39 (s, 3
t
H, Si(CH3)2); 0.97 (br s, 24 H, PCH(CH3)2); 1.16 (s, 9 H, Bu);
2.02 (s, 3 H, Ar-CH3); 2.19 (s, 3 H, Ar-CH3); 2.33 (s, 3 H,
Ar-CH3); 2.56 (s, 3 H, Ar-CH3); 2.63 (s, 3 H, Ar-CH3); 4.90 (s,
1 H, Ar-H); 5.00 (s, 1 H, Ar-H); 6.59 (s, 1 H, Ar-H); 6.89
(s, 1 H, Ar-H); 6.99 (m, 1 H, Ar-H); 7.02 (m, 1 H, Ar-H); 8.29
(d, 1 H, JHH ) 8 Hz, Ar-H). 13C{1H} NMR (125 MHz, C6D6): δ
6.37 (d); 19.14 (s); 20.02 (s); 21.12 (d); 23.93 (s); 29.59 (d); 35.17
(s); 54.44 (s); 66.94 (s); 74.16 (s); 83.73 (s); 89.68 (s); 90.67 (s);
91.89 (s); 115.01 (s); 118.29 (s); 120.02 (s); 121.82 (s); 135.80
(s); 136.56 (s); 136.64 (s); 137.40 (s); 137.97 (s). 31P{1H} NMR
(400 MHz, C6D6): δ 2.70 (br s); 3.58 (br s). IR (cm-1): 3471 (w);
1311 (m); 1249 (s); 1227 (m); 1191 (m); 1090 (m); 1051 (w); 1018
(m); 926 (m); 880 (m); 844 (s); 793 (m); 767 (m); 739 (s); 690
(w); 496 (w). Anal. Calcd for C47H77N3P2SiZr: C, 65.23; H, 8.99;
N, 4.86. Found: C, 64.84; H, 9.37; N, 5.17. Mp: 74-75 °C.
[N2P2]TiMe2 (11). Methylmagnesium bromide (3.0 M in Et2O,
0.36 mL, 1.1 mmol) was added via syringe to a suspension of 10
(0.30 g, 0.54 mmol) in 10 mL of Et2O at -40 °C. The resulting
deep-blue solution was stirred for 3 h at room temperature. Solvent
was removed under vacuum, and the crude product was extracted
with Et2O. Following concentration and cooling at -40 °C, bright-
([N2P2]ZrCl)2(µ-Cl)2 (6). A suspension of KC8 (0.12 g, 0.87
mmol) in 10 mL of Et2O was added to a suspension of 1 (0.30 g,
0.79 mmol) in 10 mL of Et2O at -40 °C. The reaction mixture
was allowed to warm to room temperature. Over the course of 1 h,
the reaction mixture turned green. The solution was filtered and
concentrated. Green crystals of 6 were collected in 20% (0.047 g)
yield following cooling at -40 °C overnight. A 4:1 mixture of
1
isomers was determined by 31P{1H} NMR. H NMR integrations
are reported relative to an assignment of 1.00 H for the peak at
5.17 ppm. 1H NMR (500 MHz, C6D6): δ 0.43 (s, 3.2 H); 0.88 (m,
4.16 H); 0.97 (s, 3.16 H); 1.06 (s, 14.40 H); 1.21 (m, 20.99 H);
1.41 (m, 3.34 H); 1.47 (s, 0.64 H); 1.63 (m, 1.35 H); 1.76 (m, 5.51
H); 1.93 (m, 2.13 H); 2.21 (m, 1.05 H); 2.36 (m, 1.34 H); 2.46 (m,
0.83 H); 2.93 (m, 1.03 H); 3.75 (m, 1.06 H); 4.02 (m, 1.00 H);
5.17 (m, 1.00 H). 31P{1H} NMR (500 MHz, C6D6): δ 0.09 (s, 1 P);
0.88 (s, 4 P); 14.19 (s, 1 P); 15.93 (s, 4 P). IR (cm-1): 1336 (m);
1253 (s); 1191 (m); 1100 (m); 1015 (s); 921 (w); 885 (w); 849 (s);
809 (m); 767 (m); 721 (s); 610 (m). Anal. Calcd for C44H102
-
Cl4N4P4Si2Zr2: C, 44.34; H, 8.64; N, 4.70. Found: C, 44.55; H,
8.83; N, 4.91. Mp: 82-83 °C (dec).
1
blue crystals of 11 were isolated in 58% yield (0.27 g). H NMR
(400 MHz, C6D6): δ -4.11 (br s); -0.42 (br s); 1.07 (br s); 1.17
(br s); 3.25 (s); 3.74 (br s). IR (cm-1): 1354 (s); 1290 (w); 1247
(s); 1204 (s); 1099 (m); 1050 (s); 1020 (s); 941 (w); 880 (m); 850
(s); 825 (m); 801 (m); 770 (s); 697 (m); 662 (m); 640 (w); 611
(m); 543 (m); 483 (m). Anal. Calcd for C24H57N2P2SiTi: C, 56.32;
H, 11.25; N, 5.48. Found: C, 54.83; H, 11.05; N, 5.34. Mp:
114-115 °C. µeff: 1.7 µB.
2,6-Mes2C6H3NtC (7). A modified literature procedure was
used.23 A solution of 2,6-Mes2C6H3NH2 (5.0 g, 15 mmol) in 30
mL of methylene chloride was added to a mixture of 50% aqueous
sodium hydroxide (40 mL), chloroform (6 mL), and benzyltriethy-
lammonium chloride (0.30 g, 1.3 mmol), and the resulting solution
was refluxed for 2 h. The reaction mixture was allowed to cool to
room temperature before the organic layer was separated and
washed with (1) water and (2) a saturated sodium chloride solution
before being dried over K2CO3. The solvent was removed under
vacuum, yielding a white solid. Washing with pentane removed
excess aniline. The remaining solid was crystallized from methylene
chloride at -40 °C to afford colorless crystals of 7 (2.9 g, 57%
yield). 1H NMR (300 MHz, CDCl3): δ 2.05 (s, 12 H, o-Me); 2.26
(s, 6 H, p-Me); 6.99 (s, 4 H, Mes-H); 7.24 (d, 2 H, o-H); 7.53 (t,
1 H, p-H). 13C{1H} NMR: 20.40 (s, o-Me); 21.45 (s, p-Me); 128.71
(s); 129.57 (s); 129.73 (s); 134.44 (s); 135.87 (s); 138.03 (s); 139.68
(s); 167.11 (s, NtC). IR (cm-1): 2119 (s, νCtN), 1612 (m), 1272
(m), 1032 (m), 852 (m), 806 (m), 759 (m), 737 (m), 608 (w). Anal.
Calcd for C25H25N: C, 88.50; H, 7.36; N, 4.12. Found: C, 88.20;
H, 7.56; N, 4.08.
([N2P2]TiCl)2(µ-N2) (12). A suspension of KC8 (0.26 g, 1.9
mmol) in 15 mL of Et2O was added to a solution of 10 (0.95 g, 1.7
mmol) in 15 mL of Et2O at -40 °C. The reaction mixture was
warmed to room temperature and stirred overnight. The solution
was filtered, and the remaining solid was washed with Et2O (20
mL). Concentration of the solution followed by cooling at -40 °C
overnight resulted in the formation of purple crystals of 12 (0.52
g, 57% yield). 1H NMR (500 MHz, C6D6): δ 0.23 (s, 3 H, Si(CH3)2);
0.68 (s, 3 H, Si(CH3)2); 1.05 (m, 20 H, PCH(CH3)2); 1.16 (s, 9 H,
tBu); 1.40 (m, 4 H, PCH(CH3)2); 1.55 (m, 4 H, PCH(CH3)2); 2.24
(m, 1 H, -CH2CH2-); 2.47 (m, 1 H, -CH2CH2-); 2.57 (m, 1 H,
-CH2CH2-); 2.74 (m, 1 H, -CH2CH2-); 3.03 (m, 1 H, -CH2-
CH2-); 3.21 (m, 1 H, -CH2CH2-); 3.48 (m, 1 H, -CH2CH2-);
3.69 (m, 1 H, -CH2CH2-). 13C{1H} NMR (125 MHz, C6D6): δ
1.76 (s); 3.49 (s); 5.38 (s); 18.31 (s); 19.28 (m); 20.53 (s); 20.70
(d); 20.86 (s); 21.29 (d); 23.43 (d); 23.60 (s); 23.75 (s); 23.84 (d);
24.01 (d); 34.07 (s); 36.17 (s); 37.69 (s); 38.02 (s); 49.44 (s); 56.79
(s). 31P{1H} NMR (500 MHz, C6D6): δ 0.92 (s, 1 P); 32.56 (s, 1
P). IR (cm-1): 1301 (m); 1251 (s); 1200 (m); 1154 (m); 1109 (m);
1054 (s); 1021 (s); 964 (m); 933 (m); 892 (m); 847 (s); 820 (m);
771 (m); 614 (w); 546 (w); 506 (w). Raman (cm-1): 1300 (νN-N).
Anal. Calcd for C44H102Cl2N6P4Ti2: C, 49.75; H, 9.69; N, 7.91.
Found: C, 49.87; H, 9.90; N, 7.94. Mp: 124-126 °C.
Generation of [N2P2]ZrIICl[CtN(2,6-Mes2)C6H3] (8). A 1:1
mixture of 6 and 7 was added to an NMR tube and dissolved in
C6D6 at room temperature. The solution immediately turned dark
1
forest green, indicating the presence of 8. The H and 31P NMR
spectra display resonance peaks suggestive of a 1:1 mixture of 1
and 8. Because of a high degree of overlap in the 1H NMR
spectrum, only some signals could be assigned. 1H NMR (400 MHz,
t
C6D6): δ 0.02 (s, 9 H, Bu); 0.25 (s, 3 H, Si(CH3)2); 0.58 (s, 3 H,
Si(CH3)2); 1.00 (m, 24 H, PCH(CH3)2); 2.20 (s, 6 H, Ar-CH3);
([N2P2]TiCH2SiMe3)2(µ-N2) (13). A solution of LiCH2SiMe3
(0.071 g, 0.75 mmol) in 10 mL of pentane was added to a
(23) Weber, W. P.; Ugi, I. K.; Gokel, G. W. Angew. Chem., Int. Ed.
Engl. 1972, 11, 530.

Titanium and Zirconium Complexes
Organometallics, Vol. 28, No. 12, 2009 3341
suspension of 12 (0.40 g, 0.38 mmol) in 10 mL at -40 °C. The
reaction mixture was allowed to warm to room temperature and
stirred overnight. The solution was filtered and concentrated until
a crystalline material began to precipitate. Cooling at -40 °C
overnight led to the isolation of orange bladelike crystals of 13 in
1096 (w); 1061 (s); 1018 (m); 940 (m); 889 (m); 848 (s); 821 (m);
798 (m); 770 (m); 746 (m); 694 (w); 624 (w); 539 (w); 512 (m);
438 (w).
Generation of {[N2P2]Ti(NtBu)}{MeB(C6F5)3} (16). Et2O (10
mL) was added to a flask containing crude 15 (0.27 g, 0.48 mmol)
and B(C6F5)3 (0.24 g, 0.48 mmol). The reaction mixture quickly
changed color from yellow to orange. The solution was stirred for
1 h before the solvent was removed under vacuum, leaving a thick
orange oil. The resonance peaks for both species present in the
31P{1H} NMR spectrum of 15 have vanished and have been replaced
1
34% yield (0.15 g). H NMR (500 MHz, C6D6): δ -0.62 (d, JSiH
) 10 Hz, 1 H, CH2Si(CH3)3); 0.39 (s, 3 H, Si(CH3)2); 0.48 (s, 9 H,
CH2Si(CH3)3); 0.77 (s, 3 H, Si(CH3)2); 0.98-1.25 (m, 24 H,
PCH(CH3)2); 1.59 (m, 4 H, PCH(CH3)2); 1.71 (m, 4 H, -CH2-
t
CH2-); 1.78 (s, 9 H, Bu); 2.30 (m, 1 H, -CH2CH2-); 2.44 (d,
1
by one major resonance peak at 23.90 ppm. H NMR (400 MHz,
JSiH ) 10 Hz, 1 H, CH2Si(CH3)3); 2.61 (m, 1 H, -CH2CH2-);
3.06 (m, 1 H, -CH2CH2-); 3.41 (m, 1 H, -CH2CH2-). 13C{1H}
NMR (125 MHz, C6D6): δ 5.98 (s); 6.36 (s); 13.81 (d); 17.49 (d);
18.90 (d0; 19.19 (d); 19.41 (d); 19.66 (d); 20.45 (d); 20.86 (d);
21.16 (m); 21.72 (m); 22.97 (d); 23.91 (d); 37.89 (s); 45.14 (d);
45.67 (s); 45.92 (s); 50.26 (s); 56.33 (s). 31P{1H} NMR (500 MHz,
C6D6): δ 22.45 (s, 1 P); 0.73 (s, 1 P). IR (cm-1): 1664 (w); 1589
(w); 1254 (s); 1227 (m); 1177 (m); 1109 (m); 1053 (m); 1020 (s);
985 (m); 927 (m); 882 (m); 857 (m); 796 (s); 477 (m). Raman
(cm-1): 1270 (νN-N). Anal. Calcd for C52H124N6P4Si4Ti2: C, 53.57;
H, 10.74; N, 7.21. Found: C, 51.46; H, 10.75; N, 7.11. Mp:
135-136 °C.
C6D6): δ 0.08 (s, 6 H, Si(CH3)2); 0.71 (s, 3 H, H3CB(C6F5)3); 0.85
(m, 24 H, PCH(CH3)2); 1.06 (m, 4 H, PCH(CH3)2); 1.19 (s, 9 H,
tBu); 1.29 (s, 9 H, tBu); 1.68 (m, 4 H, -CH2CH2-); 2.31 (m, 2 H,
-CH2CH2-); 2.95 (m, 2 H, -CH2CH2-). 31P{1H} NMR (400
MHz, C6D6): 23.90 (s, 1 P). 19F NMR (400 MHz, C6D6): -130.83
(d, JFF ) 20 Hz, 2 F, o-F); -163.44 (t, JFF ) 24 Hz, 1 F, p-F);
-165.92 (m, 2 F, m-F).
Crystallographic Analysis. Single crystals of 3, 5, 6, 9-11,
13, and 14 were coated in Paratone-N oil, mounted on a Kaptan
loop, transferred to a Siemens SMART diffractometer or a Bruker
APEX CCD area detector,24 centered in the beam, and cooled by
a nitrogen flow low-temperature apparatus that had been previously
calibrated by a thermocouple placed at the same position as the
crystal. Preliminary orientation matrices and cell constants were
determined by the collection of 60 30-s frames, followed by spot
integration and least-squares refinement. An arbitrary hemisphere
of data was collected, and the raw data were integrated using
SAINT.25 Cell dimensions reported were calculated from all
reflections with I > 10σ. The data were corrected for Lorentz and
polarization effects, but no correction for crystal decay was applied.
Data were analyzed for agreement and possible absorption using
XPREP.26 An empirical absorption correction based on a compari-
son of redundant and equivalent reflections was applied using
SADABS.27 The structures were solved using SHELXS28 and refined
on all data by full-matrix least squares with SHELXL-97.29 ORTEP
diagrams were created using ORTEP-3. A summary of the X-ray
diffraction data is presented in Table 2.
[N2P2]TiCl(NtBu) (14). A solution of Li[N2P2] (0.30 g, 0.68
mmol) in 5 mL of Et2O was added to a suspension of
Cl2(py)3Ti(NtBu) (0.30 g, 0.68 mmol) in 5 mL of Et2O at -40 °C.
The reaction mixture was allowed to warm and stirred for 5 h.
Solvent was removed under vacuum, and the crude product was
extracted with pentane. Following concentration and cooling at -40
1
°C, orange crystals of 14 were isolated in 76% yield (0.30 g). H
NMR (400 MHz, C6D6): δ 0.24 (s, 3 H, Si(CH3)2); 0.77 (m, 3 H,
PCH(CH3)2); 0.82 (s, 3 H, Si(CH3)2); 1.06 (m, 16 H, PCH(CH3)2);
t
1.31 (m, 5 H, PCH(CH3)2); 1.38 (s, 9 H, Bu); 1.49 (m, 2 H,
t
PCH(CH3)2); 1.62 (m, 3 H, -CH2CH2-); 1.67 (s, 9 H, Bu); 1.78
(m, 2 H, PCH(CH3)2); 2.32 (m, 2 H, -CH2CH2-); 3.02 (m, 1 H,
-CH2CH2-); 3.32 (m, 1 H, -CH2CH2-); 4.10 (m, 1 H,
-CH2CH2-). 13C{1H} NMR (125 MHz, C6D6): δ 4.50 (s); 4.91(s);
15.44 (d); 16.19 (d); 18.57 (m); 19.19 (m); 21.90 (d); 23.27 (m);
32.82 (s); 35.60 (s); 46.47 (d); 50.69 (s); 51.02 (s); 53.70 (s); 69.01
(s); 96.96 (s); 99.94 (s). 31P{1H} NMR (400 MHz, C6D6): δ 3.61
(s, 1 P); 27.53 (s, 1 P). IR (cm-1): 1245 (s); 1204 (m); 1123 (w);
1056 (s); 1019 (m); 941 (w); 886 (m); 849 (s); 821 (m); 801 (w);
772 (m); 749 (m). Anal. Calcd for C26H60ClN3P2SiTi: C, 53.08; H,
10.30; N, 7.14. Found: C, 53.28; H, 10.55; N, 7.22. Mp: 107-
108 °C.
Results and Discussion
The reaction of Li[N2P2] and ZrCl4(THF)2 in toluene at -40
°C resulted in the formation of 1, which was isolated as a
colorless solid in 82% yield following filtration, removal of the
solvent under vacuum, and washing with pentane. The 1H NMR
spectrum displays resonances suggestive of a low-symmetry
molecule in solution with two SiMe2 and six -CH2CH2-
resonance peaks. This is further supported by the 31P{1H} NMR
spectrum, which contains two resonances at 2.59 and 16.38 ppm,
indicating that only one phosphine donor is coordinated (16.38
ppm) and the ligand is bound κ3-N2P. We propose that the
structure of 1 is similar to that of the related titanium(III)
complex [N2P2]TiCl2, with the addition of a chloride atom in
Generation of [N2P2]TiMe(NtBu) (15). Methylmagnesium
bromide (3.0 M in Et2O, 0.60 mL, 1.7 mmol) was added via syringe
to a solution of 14 (1.0 g, 1.7 mmol) in 15 mL of Et2O at -40 °C.
The reaction mixture was allowed to warm to room temperature
and stirred for 3 h. Solvent was removed under vacuum, and the
crude product was extracted with pentane. Following the removal
of solvent under vacuum, a pale-yellow oil was obtained. Two
species appear to be present, as evidenced by 31P{1H} NMR in a
9:2 ratio, and the vast majority of the peaks are coincident. The
1
material was used without further purification (see 16 below). H
NMR (500 MHz, C6D6): δ 0.31 (s, 3 H, Si(CH3)2); 0.73 (s, 3 H,
Si(CH3)2); 0.86 (2 s, 3 H, Ti-CH3); 1.03 (m, 24 H, PCH(CH3)2);
1.23 (m, 2 H, PCH(CH3)2); 1.36 (m, 2 H, PCH(CH3)2); 1.59 (s, 9
(24) SMART: Area-Detector Software Package; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1995-1999.
(25) SAINT: SAX Area-Detector Integration Program, version 7.06;
Siemens Industrial Automation, Inc.: Madison, WI, 2005.
(26) XPREP (V6.12): Part of the SHELXTL Crystal Structure Determi-
nation Package; Bruker AXS Inc.: Madison, WI, 1995.
(27) Sheldrick, G. SADABS (V2.10): Siemens Area Detector ABSorption
correction program; Bruker Analytical X-ray Systems Inc.: Madison, WI,
2005.
t
t
H, Bu); 1.64 (s, 9 H, Bu); 1.92 (m, 2 H, -CH2CH2-); 2.45 (m,
2 H, -CH2CH2-); 3.00 (m, 2 H, -CH2CH2-); 3.23 (m, 1 H,
-CH2CH2-); 3.89 (m, 1 H, -CH2CH2-). 13C{1H} NMR (125
MHz, C6D6): δ 5.59 (s); 5.75 (s); 16.72 (d); 17.08 (d); 19.17 (d);
19.38 (d); 19.80 (d); 20.13 (d); 20.48 (d); 20.61 (d); 22.50 (d);
22.75 (d); 23.78 (d); 24.13 (d); 34.08 (s); 35.84 (s); 36.92 (s); 46.14
(d); 49.60 (d); 49.86 (s); 53.50 (s); 67.52 (s). 31P{1H} NMR (500
MHz, C6D6): δ 2.18 (s, 2 P); 3.48 (s, 9 H); 19.24 (s, 2 P); 24.98 (s,
9 P). IR (cm-1): 1406 (w); 1353 (m); 1246 (s); 1204 (s); 1122 (w);
(28) XS: Program for the Refinement of X-ray Crystal Structures, Part
of the SHELXTL Crystal Structure Determination Package; Bruker Analyti-
cal X-ray Systems Inc.: Madison, WI, 1995-1999.
(29) XL: Program for the Refinement of X-ray Crystal Structures, Part
of the SHELXT Crystal Structure Determination Package; Bruker Analytical
Systems Inc.: Madison, WI: 1995-1999.

3342 Organometallics, Vol. 28, No. 12, 2009
Chomitz et al.
Table 2. Crystal Data and Structure Refinement for 3, 5, 6, 9, 11, 13, and 14
3
5
6
9
11
13
14
compound name [N2P2]ZrMe3
([N2P2]ZrCl)2(µ-η2:η2-N2) ([N2P2]ZrCl)2(µ-Cl)2 [N2P2]ZrAr*
[N2P2]TiMe2
([N2P2]TiCH2SiMe3)2 (µ-N2) [N2P2]TiCl(NtBu)
empirical formula C25H60N2P2SiZr C44H102Cl2N6P4Si2Zr2
C44H102Cl4N4P4Si2Zr2 C47H77N3P2SiZr C24H57N2P2SiTi C59.5H142N6P4Si4Ti2
C26H60ClN3P2SiTi
588.15
160(2)
orthorhombic
Pca21
18.935(3)
17.017(2)
21.658(3)
90
fw
570.00
574.36
151(2)
triclinic
1191.63
155(2)
monoclinic
P21/n
865.39
151(2)
monoclinic
P21/n
511.65
133(2)
orthorhombic
Pbcn
1274.84
148(2)
monoclinic
P21/c
temperature (K) 155(2)
cryst syst
space group
a (Å)
triclinic
j
j
P1
P1
8.0482(17)
9.626(2)
23.012(5)
94.477(3)
96.876(3)
111.824(3)
1628.5(6)
2
11.956(2)
12.070(3)
12.438(2)
111.752(4)
110.138(3)
100.111(3)
1467.6(5)
2
11.0595(12)
25.137(3)
13.1081(14)
90
18.455(7)
18.696(7)
16.811(6)
90
32.287(4)
8.8785(11)
21.700(3)
90
19.224(4)
18.899(4)
23.297(5)
90
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
91.4150(10)
90
115.02(5)
90
90
90
109.599(2)
90
90
90
3642.9(7)
4
5255.9(3)
4
6220.7(13)
8
7974(3)
4
6979.0(17)
8
λ (Å)
0.710 73
0.487
0.710 73
0.630
0.710 73
0.580
0.710 73
0.328
0.710 73
0.430
0.710 73
0.380
0.710 73
0.466
µ (cm-1
)
no. of rflns
R(int)
Robs (%)
Rwobs (%)
4833
0.0336
3.17
8.08
3736
0.1337
6.51
13.36
5636
0.0319
3.60
5725
0.0720
5.35
4756
0.0313
3.95
3235
0.0856
5.83
7887
0.0588
4.33
10.08
13.65
10.25
11.87
9.43
Scheme 1. Synthesis of [N2P2]ZrR3 Complexes
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 3
the open coordination site in the zirconium case.17 The solid-
state structure is unknown at this time.
Zr1-N1
Zr1-C24
Zr1-N2
2.111(2)
2.277(3)
2.660(2)
Zr1-C23
Zr1-C25
Zr1-P1
2.297(3)
2.278(3)
2.8909(9)
Given the success that “mixed-donor” ligands have had at
supporting species containing metal-ligand multiple bonds,
alkyl derivatives of 1 were pursued as potential precursors to
alkylidene and alkylidyne complexes. The reaction of 1 with 3
equiv of LiCH2SiMe3 led cleanly to the highly soluble trialkyl
N1-Zr1-C24
C24-Zr1-C25
C24-Zr1-C23
N1-Zr1-N2
C25-Zr1-N2
N1-Zr1-P1
C25-Zr1-P1
N2-Zr1-P1
94.26(10)
90.56(13)
81.67(11)
65.00(7)
147.50(10)
108.79(6)
79.51(9)
N1-Zr1-C25
N1-Zr1-C23
C25-Zr1-C23
C24-Zr1-N2
C23-Zr1-N2
C24-Zr1-P1
C23-Zr1-P1
116.25(11)
136.61(10)
107.00(12)
121.94(11)
80.64(8)
1
compound 2 in quantitative yield (Scheme 1a). The H NMR
spectrum displays resonances suggestive of a C2-symmetric
molecule in solution with equivalent -CH2SiMe3 moieties,
likely because of fast exchange on the NMR time scale. The
31P{1H} NMR spectrum displays one resonance at 8.11 ppm,
and the relatively high-field nature of this resonance suggests
that both phosphine donors are uncoordinated or are exchanging
quickly through a fluxional process. A variable-temperature
NMR experiment was undertaken to determine the nature of
the fluxional process; however, even at -70 °C, only moderate
line broadening is observed, indicating that the exchange process
is still too fast to be resolved on the NMR time scale at this
temperature.
The reaction of 1 with 3 equiv of methyllithium (1.6 M in
Et2O) led to the isolation of 3 following crystallization from
pentane as colorless crystals in 46% yield (Scheme 1b). The
1H and 31P{1H} NMR spectra of 3 are similar to those observed
for 2 with equivalent alkyl groups and only one 31P NMR
resonance peak (2.75 ppm). Again, a fluxional process that
cannot be resolved by low-temperature NMR spectroscopy is
operative. An ORTEP diagram of 3 is shown in Figure 1 with
selected bond lengths and angles provided in Table 3. In the
solid state, the [N2P2] ligand is coordinated κ3-N2P, and the
zirconium center is six-coordinate. This differs from the solution
NMR data, where both phosphines are equivalent and appear
to be unbound. The Zr-CH3 bond distances of 2.278(3),
2.277(3), and 2.297(3) Å are similar to values observed in
(PNP)ZrMe3 [2.255(7), 2.285(7), and 2.253(7) Å]7 and tBu2(2-
C6H4Ph)PNZrMe3 [2.233(6), 2.239(5), and 2.247(6) Å].30 The
anionic Zr-N [2.111(2) Å] and Zr-P [2.8909(9) Å] distances
are also comparable to the values observed in the related
156.94(9)
81.45(8)
70.31(5)
compound (PNP)ZrMe3 [Zr-N ) 2.223(4) Å; Zr-P )
2.7549(17) and 2.7984(18) Å].7
Metal-ligand multiple bonds are of significant interest given
their role in many catalytic cycles,31 and although numerous
stable complexes possessing metal-ligand multiple bonds exist,
they are primarily located in the middle of the transition-metal
series and in the second and third rows.32 C-H bond activation
and group-transfer reactions have been observed with early and
late transition metals,4,33-41 and the development of oxo, imido,
and carbene/alkylidene functionalities with these metals is of
Figure 1. Thermal ellipsoid (50%) plot of 3. Hydrogen atoms and
isopropylmethyl and tert-butylmethyl groups have been omitted for
clarity.
(30) Ghesner, I.; Fenwick, A.; Stephan, D. W. Organometallics 2006,
25, 4985–4995.

Titanium and Zirconium Complexes
Organometallics, Vol. 28, No. 12, 2009 3343
N2 functionalization has been achieved with H2, silanes, and
alkynes.43-45
The reduction of 1 with 2 equiv of KC8 in THF under an
atmosphere of N2 resulted in a color change of colorless to
purple. Following crystallization from pentane, 5 was isolated
1
as purple crystals in 17% yield. The H and 31P{1H} NMR
spectra of 5 display resonances suggesting the presence of two
isomers (3:2 ratio) in solution, but attempts to further character-
ize these species in solution have been hampered by the
Figure 2. (PNP) and [N2P2] ligand sets.
1
complexity of the data because of overlap of the H NMR
resonance peaks. In the solid state, we have evidence for only
one isomer upon crystallization, as judged by X-ray diffraction.
interest. To gain access to these reactive metal-ligand frag-
ments, proper electronic and steric conditions must be met
through a prudent choice of ligand. Attempts to generate an
alkylidene complex from 3 or 4 either by thermolysis or
photolysis were unsuccessful and resulted in gradual decom-
position. This contrasts with the recent results of Ozerov et al.,
who found that the formation of the tribenzyl complex
(PNP)Zr(CH2Ph)3 was quickly followed by the elimination of
toluene and the formation of the alkylidene species
(PNP)Zr(dCHPh)(CH2Ph).7 One possible reason for the dif-
ference in reactivity is the flexible nature of the [N2P2] ligand,
which has been shown to change coordination modes to
accommodate the geometric and electronic preferences of the
metal center. In contrast, the pincer ligand (PNP) used by Ozerov
et al. (Figure 2) has a strong chelate effect due to the phenyl
linker bridges that enforce rigid coordination of the ligand.
To determine the coordination mode of the N2 moiety in 5,
an X-ray diffraction study was undertaken. The ORTEP diagram
is shown in Figure 3 with selected bond lengths and angles
provided in Table 4. The solid-state structure of 5 reveals a
six-coordinate zirconium complex with the [N2P2] ligand bound
κ3-N2P and a side-on-bound bridging N2 moiety. Although the
Zr1-N3 and Zr1-N3′ distances are on the short end of typical
at 2.084(5) and 1.975(5) Å, the N-N bond distance is extremely
long at 1.576(9) Å13,43 and is longer than the single N-N bond
in hydrazine (1.45 Å). The distance is comparable, however, to
the N-N bond lengths observed in the related compounds
{[N(SiMe2CH2PiPr2)2]Zr}2(µ-η2:η2-N2)3 [1.548(7) Å], {PhP-
(CH2SiMe2NPh)2Zr(THF)}2(µ-η2:η2-N2)46 [1.503(3) Å], and
{[PhP(CH2SiMe2NSiMe2CH2)2PPh]Zr}(µ-η2:η2-N2)44 [1.43(1)
Å]. The low yield of 5 has hindered further reactivity studies.
Full κ4-coordination of the [N2P2] ligand in a derivative of 3
was achieved by lowering of the coordination number at the
zirconium center via protonation of a methyl group. The reaction
of 3 and [PhNMe2H][B(C6H5)4] led cleanly to the cationic
species 4 in quantitative yield on the basis of NMR spectroscopy
In an attempt to increase the yield of 5, the reduction of 1
under different reaction conditions was explored. When a less
polar solvent such as pentane, Et2O, or toluene was used, the
reaction mixture turned green prior to turning dark purple
(suggestive of the presence of 5). We were interested in the
nature of the green intermediate, which led to the examination
of the reaction of 1 with 1 equiv of KC8 in Et2O. The addition
of a suspension of KC8 to a suspension of 1 in Et2O at -40 °C
resulted in a green solution. Removal of the solvent under
vacuum, extraction with pentane, and cooling at -40 °C led to
the isolation of bright-green crystals of 6 in 20% yield.
1
(Scheme 2). The H and 31P{1H} NMR spectra indicate a C2-
symmetric molecule in solution. The 31P{1H} NMR resonance
peak shifts downfield from 2.75 to 15.64 ppm. The downfield
shift of the 31P NMR resonance suggests coordination of both
phosphine donors and a change in the coordination mode of
the [N2P2] ligand to κ4-N2P2.
Although the 1H and 31P{1H} NMR spectra of 6 indicate the
presence of a new diamagnetic compound, the assignment of
resonances from the 1H NMR spectrum of 6 is complicated by
the presence of two non-interchanging isomers (mirror and
inversion symmetry), similar to the results obtained for 5. More
informative is the 31P{1H} NMR spectrum, which displays two
sets (4:1 ratio) of two 31P NMR resonance peaks at 0.09 and
14.19 ppm and at 0.88 and 15.93 ppm and is suggestive of κ3-
N2P coordination of the [N2P2] ligand. These chemical shifts
are similar to those previously observed from spectra of 1 and
5, which possessed κ3-N2P-bound [N2P2] ligands. An ORTEP
diagram of 6 is shown in Figure 4 with selected bond lengths
and angles provided in Table 5. Compound 6 is a chloride-
bridged zirconium(III) dimer with a Zr-Zr distance of 3.2190(5)
Å, which falls in the expected range of 3.20-3.48 Å for a typical
Zr-Zr single bond.47 Each zirconium atom lies in a distorted
octahedral geometry with the [N2P2] ligand-bound κ3-N2P, and
Reduction Chemistry of 1. Encouraged by the stability of
the zirconium alkyl compounds, low-valent zirconium species
were targeted. Though only a limited number of side-on-bound
N2 complexes of zirconium have been isolated,42 a number of
these compounds have shown remarkable reactivity in which
(31) Chauvin. Y.; Grubbs, R. H.; Schrock, R. R.“for the development
of the metathesis method in organic synthesis”.
(32) Nugent, W. A.; Mayer, J. M. Metal-ligand multiple bonds; John
Wiley & Sons Inc.: New York, 1988.
(33) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc.
1988, 110, 8729–8731.
(34) Bart, S. C.; Lobkovsky, E.; Bill, E.; Chirik, P. J. J. Am. Chem.
Soc. 2006, 128, 5302–5303.
(35) Dewith, J.; Horton, A. D. Angew. Chem., Int. Ed. Engl. 1993, 32,
903–905.
(36) Jenkins, D. M.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2002,
124, 11238–11239.
(37) Kogut, E.; Wiencko, H. L.; Zhang, L. B.; Cordeau, D. E.; Warren,
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1543.

3344 Organometallics, Vol. 28, No. 12, 2009
Scheme 2. Synthesis of the Cationic Zirconium Bisalkyl 4
Chomitz et al.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 5
[2.830(2) and 2.839(2) Å], possibly because of greater steric
congestion at the metal center.
Zr1-N3
Zr1-N1
Zr1-P1
N3′-N3
2.084(5)
2.179(4)
2.7976(15)
1.576(9)
Zr1-N3′
Zr1-N2
Zr1-Cl1
1.975(5)
2.456(4)
2.4757(16)
The diamagnetism of 6 indicates either a Zr-Zr two-electron
bond or antiferromagnetic coupling between the metal centers.50
To clarify this point, B3LYP51/LACVP*52-56 hybrid density
functional theory optimizations57 were performed on a closed-
shell singlet model of 6 (Zrd,model) and its hypothetical d0,
yttrium(III) analogue (Yd,model). The constraint of inversion
symmetry was imposed during the initial optimization of each
structure and then removed for a final, nonconstrained optimiza-
tion. The gas-phase structure of Zrd,model is shown in Figure 5
(top). The overall geometry is reproduced fairly well, although
the Zr-Zr bond distance of 3.13 Å is somewhat too short. By
contrast, the analogous Y-Y distance of 4.17 Å in Yd,model
(Figure 5, bottom) clearly shows that a significant metal-metal
bonding contribution must be present for the geometric param-
eters of 6 to be realized.
N3′-Zr1-N3
N3-Zr1-N1
N3-Zr1-N2
N3′-Zr1-Cl1
N1-Zr1-Cl1
N3′-Zr1-P1
N1-Zr1-P1
Cl1-Zr1-P1
45.6(2)
N3′-Zr1-N1
N3′-Zr1-N2
N1-Zr1-N2
N3-Zr1-Cl1
N2-Zr1-Cl1
N3-Zr1-P1
N2-Zr1-P1
104.06(18)
98.53(19)
68.30(15)
104.74(15)
152.83(11)
91.29(13)
73.27(10)
142.87(18)
92.54(17)
108.56(16)
105.93(12)
136.42(14)
111.53(12)
85.34(5)
Table 5. Selected Bond Lengths (Å) and Angles (deg) for 6
Zr1-N1
Zr1-N2
Zr1-Cl1
2.145(2)
2.478(2)
2.4928(7)
Zr1-Zr1
Zr1-Cl2
Zr1-P1
3.2190(5)
2.5401(7)
2.7366(8)
The frontier orbitals (HOMO and LUMO, bottom and top,
respectively) of Zrd,model are depicted in Figure 6. As expected,
the HOMO consists of two d-type zirconium orbitals forming
an s bond, with almost no orbital contribution from neighboring
atoms. The calculated LUMO is localized, and bonding, and
thus the electron density resulting from a one- or two-electron
reduction, might be centered in a stabilizing d-d p bond;
however, accessible decomposition pathways appear to render
such a complex nonisolable.
N1-Zr1-N2
N1-Zr1-Cl2
Cl1-Zr1-Cl2
N1-Zr1-Cl2
N2-Zr1-P1
Cl2-Zr1-P1
68.99(8)
111.44(6)
90.13(2)
97.36(6)
78.55(6)
165.18(2)
N1-Zr1-Cl1
N2-Zr1-Cl2
N1-Zr1-P1
N2-Zr1-Cl2
Cl1-Zr1-P1
148.90(6)
169.06(6)
84.79(6)
88.50(6)
80.87(2)
a center of inversion relates the two “[N2P2]ZrCl2” fragments.
The bridging Zr-Cl bond distance of 2.5401(7) Å is typical48,49
as is the terminal Zr-Cl bond [2.4928(7) Å].48,49 The Zr1-N1,
Zr1-N2, and Zr1-P1 distances are also similar to those
observed in 5. A related compound reported by Schrock et al.,
[ZrCl3(PBu3)2]2, has structural parameters comparable with a
Zr-Zr bond distance of 3.182(1) Å, terminal Zr-Cl distances
of 2.433(2) and 2.429(2) Å, and bridging Zr-Cl distances of
2.546(1) and 2.542(2) Å.50 The Zr-P bond distance of 2.7366(8)
Å in 6 is shorter than the ones observed in [ZrCl3(PBu3)2]2
As with 5, we have been unable to isolate 6 in yields greater
than 20%. We attribute this problem to the instability of the
“[N2P2]ZrIIICl2” fragment, which, unless it can dimerize to form
6, decomposes. Substitution of KC8 with stronger reductants,
such as sodium naphthalide, results in over-reduction to give
5, and the use of milder reducing reagents (Na/Hg and Mg)
leads to slower reactions that result in decomposition (see
below). Compound 6 is stable in the solid state: samples stored
in the glovebox at room temperature showed no decomposition
1
after 1 month. In solution, monitoring of the H and 31P{1H}
NMR spectra of a sample of 6 in C6D6 showed that dispropor-
tionation to 1 and an unknown, NMR-silent product occurs over
12 h.
The reactivity of 6 with neutral ligands was probed in attempts
to determine the propensity for homolytic or heterolytic Zr-Zr
(48) Cotton, F. A.; Diebold, M. P.; Kibala, P. A. Inorg. Chem. 1988,
27, 799–804.
(49) Hoffman, D. M.; Lee, S. Inorg. Chem. 1992, 31, 2676–2677.
(50) Wengrovius, J. H.; Schrock, R. R.; Day, C. S. Inorg. Chem. 1981,
20, 1844–1849.
(51) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J.
Phys. Chem. 1994, 98, 11623–11627.
(52) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon,
M. S.; DeFrees, D. J.; Pople, J. A. J. Phys. Chem. 1982, 77, 3654–3665.
(53) Hay, P. J.; Wadt, W. R. J. Phys. Chem. 1985, 82, 299–310.
(54) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Phys. Chem. 1971, 54,
724–728.
(55) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Phys. Chem. 1972, 56,
2257–2261.
(56) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213–
222.
(57) Jaguar, version 6.5;Schrodinger, LLC: New York, 2005.
(58) Maestro, version 7.5; Schrondinger, LLC: New York, 2005.
Figure 3. Thermal ellipsoid (50%) plot of 5. Hydrogen atoms and
isopropylmethyl and tert-butylmethyl groups have been omitted for
clarity.

Titanium and Zirconium Complexes
Organometallics, Vol. 28, No. 12, 2009 3345
Figure 4. Thermal ellipsoid (50%) plot of 6. Hydrogen atoms and
isopropylmethyl and tert-butylmethyl groups have been omitted for
clarity.
Figure 6. HOMO (bottom) and LUMO (top) diagrams for Zrd,model
.
Only the zirconium centers, chlorides, and ligand backbones are
shown. Legend: C, black; Cl, green; N, blue; P, purple; Si, yellow;
Zr, slate.
Figure 5. Diagrams58 of optimized Zrd,model (top) and Yd,model
(bottom) at the B3LYP/LACVP* level of theory. Hydrogen atoms
Figure 7. Thermal ellipsoid (50%) plot of 9. Hydrogen atoms and
isopropylmethyl and tert-butylmethyl groups have been omitted for
clarity.
have been removed for clarity. Zrd,model bond lengths (Å): Zr-Clterm
,
2.54; Zr-Clbridge, 2.59, 2.66; Zr-Namide, 2.12; Zr-Namine, 2.59;
Zr-P, 2.72; Zr-Zr, 3.13. Yd,model bond lengths (Å): Y-Clterm, 2.60;
Y-Clbridge, 2.73, 2.76; Y-Namide, 2.21; Y-Namine, 2.70; Y-P, 2.90;
Y-Y, 4.17. Legend: C, black; Cl, green; N, blue; P, purple; Si,
yellow; Y, red; Zr, slate.
22.40 ppm, indicative of κ3-N2P coordination of the [N2P2]
ligand. The IR spectrum revealed a C-N absorption at 1872
cm-1 (free isocyanide νCN ) 2119 cm-1), suggesting significant
back-bonding into the C-N π* orbitals. Isolation of 8 was
complicated by the presence of 1 and its decomposition within
hours of its generation in solution at room temperature.
bond cleavage. The reaction of 6 with carbon monoxide, 2,6-
dimethylphenyl isocyanide, diphenylacetylene, and trimeth-
ylphosphine resulted in either no reaction or the re-formation
of 1 and other intractable, paramagnetic products. Alkylation
of 6 with LiCH2SiMe3 led cleanly to the formation of 2 as well
as uncharacterized, NMR-silent products. To obtain 2, com-
pound 6 could disproportionate to 1 (which is then alkylated)
and “[N2P2]ZrIICl”, which decomposes.
The isolation of 8 was attempted through an alternative
synthetic route. The addition of 2 equiv of KC8 to a colorless
solution of 1 and 7 resulted in an immediate color change of
the solution to dark forest green. The reaction mixture was
allowed to warm to room temperature before the solvent was
removed under vacuum. Extraction with pentane gave a dark-
green solution, which, following concentration and cooling at
-40 °C overnight, yielded bright-orange crystals of 9 in 18%
yield. An ORTEP diagram of 9 is shown in Figure 7, with
selected bond lengths and angles provided in Table 6. The [N2P2]
ligand is coordinated κ3-N2P, and the new aryl ligand, Ar*,
appears to be coordinated in a distorted η7 fashion. Five of the
Zr-C bonds are shorter than the other two, with an average
distance of 2.377(33) Å. The remaining two Zr-C bonds are
significantly longer (>3σ), with bond distances of 2.576(4) and
The addition of the terphenylisocyanide59 7 to a solution of
6 resulted in an immediate color change from bright lime green
1
to dark forest green. The H and 31P{1H} NMR spectra of the
resulting reaction mixture revealed a 1:1 mixture of 1 and what
we postulate to be the zirconium(II) species 8 (Scheme 3).
Compound 8 displays two 31P NMR resonances at -2.96 and
(59) For recent work with terphenylisocyanides, see: Fox, B. J.; Sun,
Q. Y.; DiPasquale, A. G.; Fox, A. R.; Rheingold, A. L.; Figueroa, J. S.
Inorg. Chem. 2008, 47, 9010–9020.

3346 Organometallics, Vol. 28, No. 12, 2009
Scheme 3. Formation of a Transient Zirconium(II) Isocyanide Complex
Chomitz et al.
Table 6. Selected Bond Lengths (Å) and Angles (deg) for 9
unusual reaction have been hampered by the low yields and
complexity of the products formed.
Zr1-N1
Zr1-C27
Zr1-C26
Zr1-C23
Zr1-N2
2.151(3)
2.358(4)
2.406(4)
2.576(4)
2.652(3)
Zr1-C25
Zr1-C28
Zr1-C24
Zr1-C29
Zr1-P1
2.334(4)
2.373(4)
2.412(4)
2.612(4)
2.7943(11)
As described previously,17 10 is monomeric and paramagnetic
in contrast to the zirconium(III) analogue 6, which is dimeric
and diamagnetic. We were therefore curious to explore potential
reactivity differences between the two congeners. In contrast
to the synthesis of 2 and 3, attempts to synthesize organometallic
titanium(III) species with alkyllithium reagents failed to yield
isolable products. Nonetheless, milder reagents proved to be
more effective: the reaction of 10 with 2 equiv of methylmag-
nesium bromide in Et2O at -40 °C resulted in a color change
from purple to bright blue. Following removal of the solvent
under vacuum, extraction with Et2O, and cooling at -40 °C,
bright-blue crystals of 11 were isolated in 58% yield (Scheme
5). The results of an X-ray diffraction study are shown in Figure
8, with selected bond lengths and angles provided in Table 7.
As with compound 10, the [N2P2] ligand is bound κ3-N2P. The
Ti-CH3 bond distances were found to be 2.168(2) and 2.139(2)
Å. These values are similar to those reported for other
titanium(III) methyl complexes such as [TiMe(η5-C5Me4-
(SiMe3)2] [2.213(2) Å],62 [PhC(NSiMe3)2]2TiMe [2.120(5) Å],63
and {HC[C(Me)NAr]2}TiMe2 (Ar ) mesityl) [2.131(3) and
2.123(3) Å].64 The solution magnetic susceptibility is 1.7 µB,
N1-Zr1-C25
C25-Zr1-C27
C25-Zr1-C28
N1-Zr1-C26
C27-Zr1-C26
N1-Zr1-C24
C27-Zr1-C24
C26-Zr1-C24
C25-Zr1-C23
C28-Zr1-C23
C24-Zr1-C23
C25-Zr1-C29
C28-Zr1-C29
C24-Zr1-C29
N1-Zr1-N2
C27-Zr1-N2
C26-Zr1-N2
C23-Zr1-N2
N1-Zr1-P1
C27-Zr1-P1
C26-Zr1-P1
C23-Zr1-P1
N2-Zr1-P1
115.93(13)
64.81(14)
86.04(14)
101.31(13)
34.49(14)
143.21(13)
83.50(13)
64.87(13)
61.03(13)
62.25(13)
32.72(12)
80.14(13)
33.43(12)
62.24(12)
65.16(11)
153.20(13)
120.53(12)
111.69(11)
93.61(9)
N1-Zr1-C27
N1-Zr1-C28
C27-Zr1-C28
C25-Zr1-C26
C28-Zr1-C26
C25-Zr1-C24
C28-Zr1-C24
N1-Zr1-C23
C27-Zr1-C23
C26-Zr1-C23
N1-Zr1-C29
C27-Zr1-C29
C26-Zr1-C29
C23-Zr1-C29
C25-Zr1-N2
C28-Zr1-N2
C24-Zr1-N2
C29-Zr1-N2
C25-Zr1-P1
C28-Zr1-P1
C24-Zr1-P1
C29-Zr1-P1
104.15(13)
121.22(13)
34.92(14)
34.62(13)
65.90(14)
35.07(13)
85.63(13)
175.79(13)
77.44(13)
77.73(12)
152.27(13)
60.59(13)
78.97(13)
31.80(12)
96.70(12)
171.04(12)
91.71(11)
138.61(11)
140.97(10)
100.44(10)
106.51(9)
84.62(8)
134.54(11)
163.56(10)
87.88(8)
1
in agreement with an S ) /2 spin state.
The reduction chemistry of 10 was explored to see how it
compared to that of 1. The reduction of 10 with KC8 in Et2O
under an atmosphere of N2 resulted in a color change of purple
to brown (Scheme 5). Following crystallization from the same
solvent, 12 was isolated as fluffy purple crystals in 57% yield.
Raman spectroscopy is consistent with a high degree of
reduction of the N-N bond, with νN-N at 1300 cm-1. The
reaction of 12 with 2 equiv of LiCH2SiMe3 in pentane, followed
by filtration and crystallization from pentane, yielded orange-
brown crystals of the diamagnetic compound 13 in 34% yield.
An ORTEP diagram is shown in Figure 9 with selected bond
lengths and angles provided in Table 8. The solid-state structure
of 13 reveals a five-coordinate titanium in a square-based
pyramidal geometry with an end-on bridging N2 moiety. The
[N2P2] ligand is bound κ3-N2P to the metal center, and because
of steric constraints, the second phosphine is unable to
coordinate to the titanium center. To the best of our knowledge,
this is the first report of alkylation at the metal center of a
dinitrogen complex.65 The short Ti-µ-N2 bond distances
[1.783(4) and 1.782(3) Å] and the elongated N-N bond length
[1.286(4) Å] are similar to those of related non-cyclopentadi-
enyl-supported diamagnetic titanium dinitrogen compounds such
as {[PhC(NSiMe3)2]2Ti}2(µ-N2)63 [1.771(5) and 1.759(5) Å
72.09(7)
2.612(4) Å. Although this suggests η5 coordination, the C-C
distances of the new seven-membered ring do not deviate
significantly from one another [ave 1.423(14) Å, min 1.412(5)
Å, and max 1.452(5) Å], thus suggesting a closed π system
and η7 coordination. While no N-H bond was located in the
difference Fourier map, the IR spectrum reveals a moderate
N-H stretch at 3471 cm-1. Though the aforementioned reaction
does produce a small quantity of 8, as seen by NMR spectros-
copy of the crude reaction mixture, the primary product observed
is 9 along with some other uncharacterized side-products.
We believe the reason the reduction of 1 in the presence of
7 yields 9 primarily instead of 8 is due to a precoordination
event, which lowers the reduction potential of the zirconium
center, making the reduction of the proposed intermediate
[N2P2]ZrCl3CN(2,6-Mes2)C6H3 to [N2P2]ZrICN(2,6-Mes2)C6H3
more facile than that of 1 to “[N2P2]ZrI”. Although no
intermediates have been observed along the reaction coordinate
of 1 to 9, the mechanism likely involves (i) the reduction of
[N2P2]ZrCl3CN(2,6-Mes2)C6H3 to [N2P2]ZrCN(2,6-Mes2)C6H3
as the first step. This is followed by (ii) the metal-assisted
insertion of the isocyanide carbon into the C-C bond of the
mesityl group of the terphenyl ligand. Finally, (iii) reduction
of the resulting aromatic system by the zirconium(I) center
(returning Zr to a 4+ oxidation state) and protonation of the
anionic nitrogen atom (by solvent or adventitious water) gives
9 (Scheme 4). A conceptually related insertion reaction by a
ruthenium carbene complex was recently reported.60 In addition,
reactions involving photolytically induced isocyanide insertion
into an adjacent aromatic ring have been known for many
years.61 Our efforts to shed light on the mechanism of this
(60) Galan, B. R.; Gembicky, M.; Dominiak, P. M.; Keister, J. B.; Diver,
S. T. J. Am. Chem. Soc. 2005, 127, 15702–15703.
(61) Boyer, J. H.; Jong, J. D. J. Am. Chem. Soc. 1969, 91, 5929–5930.
(62) Pinkas, J.; Lukesova, L.; Gyepes, R.; Cisarova, I.; Lonnecke, P.;
Kubista, J.; Horacek, M.; Mach, K. Organometallics 2007, 26, 3100–3110.
(63) Hagadorn, J. R.; Arnold, J. J. Am. Chem. Soc. 1996, 118, 893–
894.
(64) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485–1494.

Titanium and Zirconium Complexes
Organometallics, Vol. 28, No. 12, 2009 3347
Scheme 4. Proposed Reaction Pathway to the Formation of 9
Scheme 5. Substitution Chemistry of 10
{[PhP(CH2SiMe2NSiMe2CH2)2PPh]Ti}(µ-N2)46 [1.783(4) Å
(Ti-µ-N2) and 1.255(7) Å (N-N)]. The νN-N value at 1270
cm-1 indicates a high degree of activation of the N2 moiety
and agrees well with the value observed in the spectrum of 12
as well as the previously reported literature value of 1284 cm-1
for [(Me3Si)2NTiCl(TMEDA)]2(µ-N2)].67
The Ti-µ-N2 bond distances in 13 [1.783(4) and 1.782(3)
Å] are closer in length to Ti-N double bonds (1.709 Å) than
Ti-N single bonds (1.932 Å),47 suggesting that the Ti-N bond
may have some double-bond character. This observation
prompted the synthesis of monomeric [N2P2]-supported titanium
imido species to determine how the coordination mode of the
ligand would change when going from a dimer to a monomer
and how the [N2P2] ligand would affect the Ti-Nimido bond.
Titanium imido complexes are also of interest because they have
proven to be competent hydroamination catalysts68 and have
shown interesting reactivity with small molecules such as
CO2.69-71 We were therefore interested in exploring imido
complexes in our [N2P2] systems. The reaction of Li[N2P2] and
Cl2(py)3Ti(NtBu) in toluene at -40 °C resulted in the formation
Table 7. Selected Bond Lengths (Å) and Angles (deg) for 11
Ti1-N1
Ti1-C23
Ti1-P1
2.0024(16)
2.168(2)
2.6215(6)
Ti1-C24
Ti1-N2
2.139(2)
2.4441(16)
N1-Ti1-C24
C24-Ti1-C23
C24-Ti1-N2
N1-Ti1-P1
109.70(8)
100.71(9)
98.56(7)
125.20(5)
85.75(6)
N1-Ti1-C23
N1-Ti1-N2
C23-Ti1-N2
C24-Ti1-P1
N2-Ti1-P1
113.92(8)
71.00(6)
156.68(7)
116.15(6)
73.98(4)
C23-Ti1-P1
(Ti-µ-N2)and1.275(6)Å(N-N)],{[(Me3Si)2N]TiCl(C6H5N)2}2(µ-
N2)66 [1.759(3) Å (Ti-µ-N2) and 1.263(7) Å (N-N)], and
Figure 8. Thermal ellipsoid (50%) plot of 11. Hydrogen atoms
and isopropylmethyl and tert-butylmethyl groups have been omitted
for clarity.
Figure 9. Thermal ellipsoid (50%) plot of 13. Hydrogen atoms
and isopropylmethyl and tert-butylmethyl groups have been omitted
for clarity.

3348 Organometallics, Vol. 28, No. 12, 2009
Chomitz et al.
Scheme 6. Formation of Cationic 16
Table 8. Selected Bond Lengths (Å) and Angles (deg) for 13
of 14, which was isolated as bright-orange crystals in 76% yield
following crystallization from pentane at -40 °C. The solid-
state structure of 14 was determined by X-ray crystallography.
An ORTEP diagram is shown in Figure 10, with selected bond
lengths and angles provided in Table 9. The ligand is bound
κ3-N2P, and the imido group occupies the axial position of the
square-based pyramid surrounding the titanium atom. Two
nonsymmetry-related molecules are present in the asymmetric
unit. The two Ti-Nimido bond distances are identical [1.698(4)
Ti1-N5
Ti1-C23
Ti1-P1
Ti2-N3
Ti2-N4
N5-N6
1.783(4)
2.166(4)
2.5875(14)
2.018(3)
2.520(3)
1.286(4)
Ti1-N1
Ti1-N2
Ti2-N6
Ti2-C49
Ti2-P3
2.012(3)
2.497(3)
1.782(3)
2.161(4)
2.6227(15)
N5-Ti1-N1
N1-T1-C23
N1-Ti1-N2
N5-Ti1-P1
C23-Ti1-P1
N6-Ti2-N3
N3-Ti2-C49
N3-Ti2-N4
N6-Ti2-P3
C49-Ti2-P3
110.14(14)
118.12(15)
70.50(12)
89.01(11)
107.89(12)
107.44(14)
116.36(15)
69.77(12)
90.51(11)
104.68(13)
N5-Ti1-C23
N5-Ti1-N2
C23-Ti1-N2
N1-Ti1-P1
N2-Ti1-P1
N6-Ti2-C49
N6-Ti2-N4
C49-Ti2-N4
N3-Ti2-P3
N4-Ti2-P3
102.08(15)
158.80(13)
95.59(13)
123.55(10)
74.36(8)
107.13(16)
155.69(14)
95.04(15)
126.46(11)
73.98(9)
t
and 1.700(4) Å] as are the Ti-N-CBu angles [166.3(3)° and
166.9(4)°], which moderately deviate from 180°. The Ti-Nimido
bond distance is close to the mean value of 1.708 Å of all
structurally characterized titanium(IV) imidos recorded (>70
compounds) in the Cambridge Structural Database. The coor-
dination number does appear to have a slight affect on Ti-Nimido
t
bond lengths. The six-coordinate complex Ti(O2 BuNN′)-
(NtBu)(py) has a Ti-Nimido bond of 1.719(2) Å,72 whereas the
five-coordinate compounds [Ti(NtBu){PhC(NSiMe3)2}(CH2Si-
Me3)(py)] [1.690(2) Å]73 and [Ti(η8-C8H8)(NtBu)] [1.699(6)
Å]74 have shorter Ti-Nimido bond distances and are closer to
the values observed in 14. The remaining structural features
are similar to those of related complexes.
Table 9. Selected Bond Lengths (Å) and Angles (deg) for 14
Ti1-N3
Ti1-N2
Ti1-P1
1.701(4)
2.332(3)
2.6067(14)
Ti1-N1
Ti1-Cl1
2.011(4)
2.3646(13)
N3-Ti1-N1
N1-Ti1-N2
N1-Ti1-Cl1
N3-Ti1-P1
N2-Ti1-P1
118.22(16)
73.19(13)
105.25(11)
106.63(13)
76.04(9)
N3-Ti1-N2
N3-Ti1-Cl1
N2-Ti1-Cl1
N1-Ti1-P1
Cl1-Ti1-P1
99.81(14)
103.47(12)
153.89(10)
128.73(10)
86.03(5)
As demonstrated in the case of compound 4, the coordina-
tion mode of the [N2P2] ligand can be altered to accommodate
a change at the metal center (see above). With this in mind,
the synthesis of a cationic titanium imido species was
examined. The reaction of 14 with 1 equiv of methylmag-
nesium bromide (3.0 M in Et2O) in Et2O resulted in a slight
color change from orange to yellow. Following removal of
the solvent under vacuum, extraction with pentane, and
evaporation of the volatile material, 15 was isolated as a
yellow oil. Because of the high solubility of 15, a solid
material could not be obtained; however, further reaction of
15 with 1 equiv of B(C6F5)3 in Et2O resulted in the formation
of the cationic species 16 (Scheme 6). The 31P{1H} NMR
spectrum of 16 displays one major resonance at 23.90 ppm,
in the region associated with coordinated phosphine. Ad-
ditional evidence for phosphine coordination and ion-pair
formation was obtained by 19F NMR spectroscopy using
Horton’s criteria: the separation between the m- and p-fluorine
resonance peaks is 2.47 ppm, indicating complete abstraction
of a methyl ligand.75
Conclusions
The [N2P2] ligand has proven to be stable and capable of
supporting early-metal alkyl, imido, and reduced early-metal
species. A range of coordination modes and geometries were
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Figure 10. Thermal ellipsoid (50%) plot of 14. Hydrogen atoms
and isopropylmethyl and tert-butylmethyl groups of the [N2P2]
ligand have been omitted for clarity.

Titanium and Zirconium Complexes
Organometallics, Vol. 28, No. 12, 2009 3349
observed, including fac and mer coordination. With electro-
positive metals, the [N2P2] ligand appears to prefer a κ3-N2P
binding mode; however, upon abstraction of an alkyl group,
the ligand binds κ4-N2P2, as was seen in the cases of 4 and
16. The reduction of 1 led to isolation of a zirconium(III)
dimer and a formal zirconium(IV) side-on-bound bridging
dinitrogen complex. Compound 6 could be observed to cleave
heterolytically to 1 and a transient zirconium(II) center if
the appropriate trapping reagent was used. The reduction of
1 in the presence of a terphenylisocyanide resulted in the
isolation of an unusual insertion product involving the
cleavage of an aromatic C-C bond. The substitution and
reduction chemistry of related Ti [N2P2] complexes was also
explored, and many differences between the two congeners
were seen. The reduction of 10 resulted in the isolation of
an end-on bridging dinitrogen compound, which was stable
to substitution reactions with strongly alkylating reagents.
In addition, a series of titanium imido complexes were
synthesized, and no decomposition of the [N2P2] ligand was
observed. The reactivity of 14-16 with small molecules will
be the focus of future work.
Acknowledgment. We are grateful to the National Science
Foundation for financial support for this work and Dr. Fred
Hollander and Dr. Antonio DiPasquale for crystallographic
assistance.
Supporting Information Available: Crystallographic informa-
tion files (CIFs). This material is available free of charge via the
Internet at http://pubs.acs.org.
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OM8011932