Substitution and reaction chemistry of cobalt complexes supported by [N2P2] ligands

Article abstract of DOI:10.1021/ic802337t

The coordination chemistry of mono- and divalent cobalt complexes supported by the monoanionic multidentate ligands, [N₂P₂] (where [N₂P₂] ) ^tBuN^(-)SiMe ₂N(CH₂CH₂PⁱPr₂)2) and [N₂P₂ ^tolyl] (where [N₂P₂ ^tolyl] ) MeC₆H₄N^(-)SiMe ₂(CH₂CH₂PⁱPr₂) ₂), is presented. The Co(II) halide complex [N₂P ₂]CoI (2) serves as a precursor to the alkyl, hydride, and amide species [N₂P₂]CoMe (3), [N₂P ₂]CoCH₂SiMe₃ (4), [N₂P ₂]CoH (5), [N₂P₂]CoNHPh (10), and [N ₂P₂]CoNHC₆H₄Me (11). Reduction of 2 results in the formation of a stable, monomeric Co(I) species, [N ₂P₂]Co (6). Compound 6 can be trapped with CO to form either [N₂P₂]Co(CO) (7) or [^tBuN(CdO)SiMe ₂N(CH₂CH₂PⁱPr₂) ₂]Co(CO)₂ (8) depending on the number of equivalents of CO introduced. Compound 6 also serves as a precursor to transient Co(III) imido species. The Co(II) halide complex [N₂P₂ ^tolyl]Col (16) is synthesized through an analogues reaction to that of 2. Reduction of 16 results in the formation of [N₂P₂ ^tolyl]Co (17), and differences in the coordination and reaction chemistry of 6 and 17 are described.

Full text of DOI:10.1021/ic802337t

Inorg. Chem. 2009, 48, 3274-3286
Substitution and Reaction Chemistry of Cobalt Complexes Supported by
[N2P2] Ligands
Wayne A. Chomitz and John Arnold*
Department of Chemistry, UniVersity of California, Berkeley, California 94720-1460
Received December 6, 2008
The coordination chemistry of mono- and divalent cobalt complexes supported by the monoanionic multidentate ligands,
[N2P2] (where [N2P2] ) BuN(-)SiMe2N(CH2CH2PiPr2)2) and [N2P2tolyl] (where [N2P2tolyl] ) MeC6H4N(-)SiMe2(CH2CH2PiPr2)2),
t
is presented. The Co(II) halide complex [N2P2]CoI (2) serves as a precursor to the alkyl, hydride, and amide species
[N2P2]CoMe (3), [N2P2]CoCH2SiMe3 (4), [N2P2]CoH (5), [N2P2]CoNHPh (10), and [N2P2]CoNHC6H4Me (11). Reduction of
2 results in the formation of a stable, monomeric Co(I) species, [N2P2]Co (6). Compound 6 can be trapped with CO to
form either [N2P2]Co(CO) (7) or [tBuN(CdO)SiMe2N(CH2CH2PiPr2)2]Co(CO)2 (8) depending on the number of equivalents
of CO introduced. Compound 6 also serves as a precursor to transient Co(III) imido species. The Co(II) halide complex
[N2P2tolyl]CoI (16) is synthesized through an analogues reaction to that of 2. Reduction of 16 results in the formation of
[N2P2tolyl]Co (17), and differences in the coordination and reaction chemistry of 6 and 17 are described.
Introduction
dinitrogen moieties on a range of transition metals, as well
as showing that the [N2P2] ligand was capable of stabilizing
low-valent first-row metal complexes.
Numerous advances in reaction chemistry have resulted
from the development of ligand scaffolds capable of engen-
dering new and unusual reactivity at metal centers. These
include the isolation of middle-to-late transition metal
complexes containing metal-ligand multiple bonds such as
terminal metal-oxos,1-4 metal-imidos,5-18 and metal-
nitrides.19-21 Metal-imido complexes are of particular interest
given their role in hydroamination22 and C-H bond activa-
tion,23-25 in addition to acting as isoelectronic analogues to
oxo functionalities.
The synthesis of late first-row transition metal imides
frequently involves the addition of alkyl- or arylazide to a
low-valent metal complex followed by reduction of azide,
releasing N2. Over the past few years, our group has
examined the utility of tetradenate monoanionic ligands
(TDMA) for stabilizing reactive complexes that exhibit
interesting and unusual chemistry.26-30 Recently we reported
the synthesis and reduction chemistry of a number of first-
row transition metal complexes supported by the monoan-
Given the promising nature of our initial results, we wished
to extend this work with the aim of synthesizing compounds
exhibiting reactive metal-ligand multiple bonds, whose
subsequent reactivity with small molecules could be probed.
To establish a well-behaved system on which to expand,
Co(III) imidos were initially targeted because they are
typically low-spin, allowing for characterization by NMR
spectroscopy.6,8,9,11 Though group transfer reactions by first-
row metal imido complexes have been observed,5,10-12,14
the results with Co have been limited. Interestingly, however,
spin-crossover behavior leading to intramolecular C-H
activation has been observed.16,17
Here we report on our results on the synthesis and
characterization of a range of organometallic and reduced
metal species that establish the versatility of the [N2P2] ligand
set for stabilizing a range of potentially useful starting
materials. Work toward supporting transient Co(III) imido
species which undergo H-atom abstraction and nitrene group
transfer reactions is also described. Some of these results
have been communicated in preliminary form.27
ionic multidentate [N2P2] ligand, where [N2P2]
)
[tBuN(-)SiMe2N(CH2CH2PiPr2)2]. This work demonstrated
how hemilabile ligands such as [N2P2] could be used to
stabilize unusual metal-ligand bonds such as bridging
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
* To whom correspondence should be addressed. E-mail: arnold@
berkeley.edu.
3274 Inorganic Chemistry, Vol. 48, No. 7, 2009
10.1021/ic802337t CCC: $40.75  2009 American Chemical Society
Published on Web 03/04/2009

Substitution and Reaction Chemistry of Cobalt Complexes
Table 1. Physical Properties of 2-12 and 16-18
compound number
compound name
color
green
M.P. (°C)
173-174
yield (%) µeff (µB) coordination mode
2
3
4
5
6
7
8
9
10
11
12
16
17
18
[N2P2]CoI
83
53
57
69
84
54
80
53
72
73
1-15
80
72
43
4.0
1.8
4.2
2.0
3.0
3.0
κ3-NP2
κ4-N2P2
κ3-N2P
κ4-N2P2
κ4-N2P2
κ3-NP2
[N2P2]CoMe
[N2P2]CoCH2SiMe3
[N2P2]CoH
green
(dec) 140
lime-green 74-76
olive-green 135-136
[N2P2]Co
[N2P2]Co(CO)
blue
126-128
151-152
(dec) 115-117
199-200
green
yellow
green
red-orange 99-101
red 105-107
[tBuN(CdO)SiMe2N(CH2CH2PiPr2)2]Co(CO)2
[N2P2]CoBr
4.1
3.8
4.1
4.1
4.2
3.0
2.8
κ3-NP2
κ3-N2P
κ3-N2P
[N2P2]CoNHC6H5
[N2P2]CoNHC6H5CH3
[PhN)PiPr2(CH2)2NPh] [tBuNHSiMe2N(CH2)2PiPr2]Co lime-green 132-135
[N2P2tolyl]CoI
[N2P2tolyl]Co
brown
green
red
208-209
85-87
162-163
κ3-NP2
κ4-N2P2
[N2P2tolyl]Co(CO)
oven at >425 K. Pentane, toluene, diethyl ether, and tetrahydrofuran
were purified by passage through a column of activated alumina
and degassed with nitrogen prior to use.31 Deuterated solvent was
vacuum transferred from sodium/benzophenone (benzene). NMR
spectra were recorded at ambient temperature on Bruker AV-300,
AVQ-400, AVB-400, and DRX-500 spectrometers. 1H and 13C{1H}
chemical shifts are given relative to residual solvent peaks, and
coupling constants (J) are given in hertz. 31P{1H} chemical shifts
are referenced to an external standard of P(OMe)3 set to 1.67 ppm.
Infrared 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).32
Melting points were determined using sealed capillaries prepared
under nitrogen and are uncorrected. Li[N2P2],28 [N2P2]CoCl (1),28
phenylazide,33 and p-tolylazide33 were prepared using 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. The X-ray structural determination was
performed at CHEXRAY, University of California, Berkeley. A
full list of compounds and their physical properties is provided in
Table 1.
[N2P2]CoI (2). A solution of Li[N2P2] (4.00 g, 9.08 mmol) in
50 mL of toluene was added to a suspension of CoI2 (2.83 g, 9.07
mmol) in 50 mL of toluene at -70 °C. The reaction mixture was
warmed to room temperature and was stirred overnight. The
resulting dark green solution was filtered, and the remaining solid
was washed with 30 mL of toluene. The combined filtrates were
concentrated and stored at -40 °C overnight, resulting in the
1
formation of dark green crystals in 83% yield (4.66 g). H NMR
(C6D6): δ 0.25 (s); 1.09 (s); 1.18 (s); 2.12 (s); 3.09 (s); 3.25 (s);
4.13 (s); 4.78 (br s); 8.74 (br s); 23.27 (br s). IR (cm-1): 1410 (w);
1350 (w); 1306 (w); 1245 (s); 1198 (s); 1105 (m); 969 (w); 926
(m); 884 (w); 845 (s); 797 (m); 760 (m); 738 (s); 696 (w); 655 (s);
602 (w); 532 (w); 478 (m). Anal. Calcd for C22H51CoIN2P2Si: C:
42.64; H: 8.31; N: 4.52. Observed. C: 42.86; H: 8.37; N, 4.85. mp
) 173-174 °C. µeff ) 4.0 µB.
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[N2P2]CoMe (3). Methyl lithium (1.6 M in Et2O, 0.45 mL, 0.71
mmol) was added to a suspension of 2 (0.40 g, 0.64 mmol) in 10
mL of Et2O at -70 °C. The reaction mixture was warmed to room
temperature and was stirred overnight. Following the removal of
solvent under vacuum, the crude product was extracted with
pentane. Following concentration and cooling at -40 °C, dark green
1
crystals were isolated in 53% yield (0.17 g). H NMR (300 MHz,
C6D6): δ -30.58 (br s); -1.52 (br s); -0.65 (br s); 1.17 (m); 2.28
(br s); 5.69 (br s); 10.56 (br s); 12.05 (br s); 17.86 (br s); 31.17 (br
s); 35.19 (br s); 41.89 (br s). IR (cm-1): 1344 (m); 1239 (m); 1215
(m); 1200 (s); 1087 (m); 1039 (m); 1018 (w); 909 (w); 882 (m);
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Inorganic Chemistry, Vol. 48, No. 7, 2009 3275

Chomitz and Arnold
848 (s); 788 (m); 753 (m); 729 (m); 678 (w); 651 (m); 530 (w);
484 (w). Anal. Calcd C23H54CoN2P2Si. C: 54.48; H: 10.76; N: 5.53.
s); 28.46 (br s); 36.48 (br s); 47.30 (br s); 88.47 (br s); 111.37
(br s). IR (cm-1): 1881 (s); 1345 (m); 1305 (w); 1238 (m); 1195
(m); 1115 (w); 1095 (w); 1051 (m); 1017 (w); 969 (w); 926 (w);
908 (w); 882 (w); 840 (s); 793 (m); 753 (m); 731 (m); 678 (w);
652 (m); 605 (m); 530 (w); 464 (w). Anal. Calcd C23H51CoN2OP2Si.
C: 53.05; H: 9.89; N: 5.38. Observed. C: 52.74; H: 9.83; N: 5.13.
mp ) 151-152 °C. µeff ) 3.0 µB.
Observed. C: 54.73; H: 11.09; N: 5.48. mp (dec) ) 140 °C. µeff
1.8 µB.
)
[N2P2]CoCH2SiMe3 (4). A solution of LiCH2SiMe3 (0.046 g,
0.48 mmol) in 5 mL of THF was added to a solution of 2 (0.30 g,
0.48 mmol) in 5 mL of THF at -40 °C. The reaction mixture was
allowed to warm to room temperature and was stirred overnight.
The solvent was removed under vacuum, and the crude product
was extracted with pentane. Following concentration and cooling
[tBuN(CdO)SiMe2N(CH2CH2PiPr2)2]Co(CO)2 (8). Method
A. A solution of phenylazide (0.036 g, 0.30 mmol) in 5 mL of
pentane was added to a cooled (-116 °C) solution of 6 (0.15 g,
0.30 mmol) in 5 mL of pentane, and a green precipitate formed
instantly. The flask was filled with an atmosphere of CO and sealed
using a Teflon stopcock. The reaction mixture was allowed to warm
to room temperature, during which time the green color faded to
yellow. The volatile materials were vacuum transferred for analysis
by GCMS. The remaining solid was extracted with toluene, and
the resulting solution was stored at -40 °C overnight. Yellow
crystals of 8 were collected in 78% yield (0.13 g).
1
at -40 °C, green crystals were isolated in 57% yield (0.16 g). H
NMR (300 MHz, C6D6): δ -53.97 (br s); -44.93 (br s); -34.37
(br s); -30.85 (br s); -7.68 (br s); -6.61 (br s); -5.55 (br s);
0.01 (s); 0.036 (s); 1.08 (m); 3.93 (br s); 4.97 (br s); 13.72 (br s);
18.59 (br s); 28.68 (br s); 33.49 (br s); 39.49 (br s); 41.54 (br s);
96.18 (br s); 103.93 (br s). IR (cm-1): 1348 (m); 1292 (w); 1233
(s); 1174 (m); 1076 (s); 1056 (s); 1037 (m); 923 (w); 882 (s); 845
(s); 817 (s); 791 (m); 769 (m); 738 (m); 719 (m); 687 (w); 667
(m); 642 (w); 608 (m); 537 (w); 521 (m); 490 (w); 459 (w). Anal.
Calcd C26H62CoN2P2Si2. C: 53.84; H: 10.80; N: 4.83. Observed.
C: 53.79; H: 11.12; N: 4.81. mp ) 74-76 °C. µeff ) 4.2 µB.
[N2P2]CoH (5). N-butyl lithium (1.6 M in hexanes, 0.30 mL,
0.48 mmol) was added to a solution of 2 (0.30 g, 0.48 mmol) in 5
mL of THF at -40 °C. The cold bath was removed, and the reaction
mixture was allowed to warm to room temperature and was stirred
for 3 h. Following the removal of solvent under vacuum, the crude
product was extracted with pentane. The resulting solution was
concentrated and cooled at -40 °C overnight, resulting in the
Method B. An atmosphere of CO was introduced to a flask
containing a solution of 6 (0.20 g, 0.41 mmol) in 10 mL of pentane
at -70 °C. The flask was sealed off, and the reaction mixture was
allowed to warm to room temperature and was stirred for 1 h. As
the reaction warmed, a yellow precipitate formed. Following the
removal of solvent under vacuum, the crude product was extracted
with toluene. The yellow solution was concentrated and cooled
overnight at -40 °C, resulting in the formation of large yellow
crystals in 80% yield (0.19 g).1H NMR (C6D6): δ 0.28 (s, 3 H,
SiMe2); 0.53 (s, 3 H, SiMe2); 0.86-1.25 (m, 26 H, PCH(CH3)2,
1
t
isolation of olive green crystals in 69% yield (0.16 g). H NMR
PCH(CH3)2); 1.55 (s, 9 H, Bu); 1.67-1.74 (m, 4 H, -CH2CH2-,
(300 MHz, C6D6): δ -30.52 (br s); -1.78 (br s); -0.58 (br s);
1.11 (m); 2.05 (s); 5.69 (s); 12.05 (br s); 17.91 (br s); 31.18 (br s);
35.27 (br s); 41.95 (br s); 120.13 (br s). IR (cm-1): 1800 (s); 1343
(m); 1226 (s); 1207 (s); 1171 (w); 1095 (m); 1034 (m); 984 (w);
930 (w); 882 (m); 848 (s); 810 (w); 788 (m); 754 (m); 726 (m);
674 (w); 653 (w); 608 (w); 532 (w); 484 (w); 459 (w). Anal. Calcd
C22H52CoN2P2Si. C: 53.52; H: 10.64; N: 5.68. Observed. C: 53.57;
H: 10.80; N: 5.78. mp ) 135-136 °C. µeff ) 2.0 µB.
[N2P2]Co (6). A suspension of KC8 (0.460 g, 3.39 mmol) in 15
mL of THF was added to a solution of 2 (2.00 g, 3.23 mmol) in 15
mL of THF at -40 °C. A color change of green to blue was
observed as the reaction mixture warmed to room temperature.
Following stirring for 3 h, the volatile materials were removed under
vacuum, and the product was extracted with Et2O (40 mL). The
resulting blue solution was passed through a bed of Celite before
being concentrated. Cooling at -40 °C overnight resulted in the
formation of large dark blue needles in 84% yield (1.34 g). 1H NMR
(C6D6): δ -30.61 (br s); -0.72 (br s); 0.35 (s); 2.10 (s); 5.75 (s);
10.62 (br s); 12.12 (br s); 18.01 (br s); 31.38 (br s); 35.33 (br s);
42.02 (br s). IR (cm-1): 1345 (s); 1321 (w); 1225 (s); 1170 (m);
1093 (s); 1036 (s); 986 (w); 968 (w); 923 (w); 884 (s); 845 (s);
818 (m); 787 (m); 753 (s); 733 (s); 664 (m); 594 (s); 536 (w); 511
(w); 475 (w); 455 (w). Anal. Calcd for C22H51CoN2P2Si. C: 53.71;
H: 10.47; N: 5.70. Observed. C: 53.96; H: 10.37; N: 5.80. mp )
126-128 °C. µeff ) 3.0 µB.
PCH(CH3)2); 1.96 (m, 1 H, -CH2CH2-); 2.30-2.48 (m, 3 H,
-CH2CH2-); 2.68-2.76 (m, 2 H, -CH2CH2-).13C NMR (C6D6): δ
3.33; 18.00; 18.38; 18.53; 18.77; 19.44; 20.05; 20.65; 22.54; 22.79;
24.09; 24.54; 25.55; 53.70; 56.71; 59.19; 197.98. 31P NMR (C6D6):
δ 5.80 (s, 1 P); 77.26 (s, 1 P). IR (cm-1): 1952 (s); 1893 (s); 1583
(s); 1359 (m); 1289 (w); 1251 (m); 1197 (m); 1095 (s); 1069 (s);
1033 (m); 990 (m); 924 (w); 884 (w); 840 (w); 824 (w); 804 (w);
778 (w); 726 (w). mp (dec) ) 115-117 °C. Anal. Calcd for
C25H51CoN2O3P2Si. C: 52.06; H, 8.93; N, 4.86. Observed. C: 51.85;
H, 9.01; N: 4.75.
[N2P2]CoBr (9). Bromine (32 µL, 0.61 mmol) was added via
syringe to a solution of 6 (0.30 g, 0.61 mmol) in 10 mL of Et2O at
-40 °C. A green precipitate formed as the reaction mixture warmed
to room temperature, and the reaction mixture was stirred for 1 h
before the solvent was removed under vacuum. The crude product
was extracted with toluene, and following concentration and cooling
at -40 °C green crystals of 9 were isolated in 53% yield (0.20 g).
1H NMR (300 MHz, C6D6): δ -1.83 (br s); 1.41 (m); 5.55 (br s);
12.85 (br s); 14.24 (br s); 17.47 (br s); 23.65 (br s). IR (cm-1):
1410 (w); 1348 (m); 1307 (w); 1242 (s); 1200 (s); 1106 (m); 1055
(s); 1018 (m); 970 (w); 928 (w); 885 (w); 846 (s); 796 (m); 757
(m); 737 (m); 690 (w); 655 (m); 602 (w); 531 (w); 478 (w). Anal.
Calcd C: 46.14; H: 8.99; N: 4.89. Observed. C: 46.03; H: 9.06; N:
4.77. mp ) 199-200 °C. µeff ) 4.1 µB.
Reaction of 6 with MeI. Methyl iodide (0.087 g, 0.61 mmol)
was added to a solution of 6 (0.30 g, 0.61 mmol) in 10 mL of Et2O
at -40 °C. The solution changed color from blue to green and
material precipitated. The reaction mixture was allowed to stir for
30 min. Solvent was removed under vacuum, and the crude product
was extracted with toluene. Following concentration and cooling
at -40°, 2 was isolated in 58% yield (0.24 g).
[N2P2]Co(CO) (7). Three freeze pump thaw cycles were done
on a solution of 6 (0.20 g, 0.41 mmol) in 5 mL of pentane before
the addition of 1 equiv of CO. The bright blue solution turned dark
green over the course of 1 h, and the reaction mixture was allowed
to stir for 2 h. Following concentration and cooling at -40 °C,
1
dark green needles of 7 were isolated in 54% yield (0.13 g). H
NMR (300 MHz, C6D6): δ -30.91 (br s); -9.28 (br s); -2.10 (br
s); -0.74 (br s); 0.23 (s); 1.08 (s); 1.81 (s); 2.08 (s); 3.24 (s); 5.67
(br s); 7.80 (br s); 10.40 (br s); 12.09 (br s); 17.99 (br s); 23.08 (br
Reaction of 6 with I2. A solution of I2 (0.053 g, 0.21 mmol) in
5 mL of Et2O was added to a solution of 6 (0.20 g, 0.41 mmol) in
5 mL of Et2O at -40 °C. The reaction mixture was allowed to
3276 Inorganic Chemistry, Vol. 48, No. 7, 2009

Substitution and Reaction Chemistry of Cobalt Complexes
warm to room temperature and was stirred for 1 h over which time
the solution changed color from blue to green. Solvent was removed
under vacuum, and the crude product was extracted with toluene.
Following concentration and cooling at -40 °C, 2 was isolated in
61% yield (0.16 g).
Reaction of 4 with H2. An atmosphere of H2 was introduced to
a bomb containing a solution of 4 (0.30 g, 0.52 mmol) in 10 mL
of THF at room temperature. The reaction mixture was stirred for
2 d. The contents were transferred to a Schlenk tube, and the solvent
was removed under vacuum. The crude product was extracted with
pentane, and following concentration and cooling 5 was isolated
in 73% yield (0.19 g).
[N2P2]CoNHC6H5 (10). Method A. A solution of LiNHC6H5
(0.048 g, 0.48 mmol) in 5 mL of THF was added to a flask
containing a solution of 2 (0.30 g, 0.48 mmol) in 5 mL of THF at
-40 °C. The solution color changed from green to red instantly,
and the reaction mixture was allowed to warm to room temperature
and was stirred overnight. The volatile materials were removed
under vacuum, and the crude product was extracted with pentane.
The filtrate was concentrated, then stored at -40 °C overnight,
resulting in the formation of red-orange blade-like crystals in 72%
yield (0.20 g).
Method B. A solution of phenylazide (0.061 g, 0.51 mmol) in
5 mL of pentane was added to a solution of 6 (0.25 g, 0.51 mmol)
in 5 mL of pentane at -40 °C, resulting in a color change of blue
to dark red concomitant with bubbling. The reaction mixture was
allowed to warm to room temperature and was stirred for 2 h. The
solution was filtered and concentrated until crystals began to
precipitate. The solution was stored at -40 °C overnight, resulting
in the formation of red-orange crystals (170 mg, 57%). Repeating
the above in THF yielded 102 mg (34%), in toluene 70 mg (23%).
1H NMR (C6D6): δ -87.12 (s); -3.20 (br s); -0.82 (s); 0.25 (s);
1.09 (s); 1.18 (s); 1.49 (s); 1.66 (s); 3.25 (s); 4.14 (s); 30.04 (br s);
39.39 (br s). IR (cm-1): 1585 (s); 1486 (m); 1352 (w); 1295 (s);
1243 (m); 1218 (m); 1169 (w); 1073 (m); 1054 (w); 1023 (w); 986
(w); 900 (m); 848 (s); 816 (w); 796 (w); 767 (m); 745 (s); 688
(m); 661 (w); 568 (w); 506 (w). Anal. Calcd for C28H57CoN3P2Si.
C: 57.5; H: 9.84; N: 7.19. Observed. C: 57.28; H: 10.06; N: 7.13.
mp ) 99-101 °C. µeff ) 3.8 µB.
N: 7.03. Observed. C: 57.91; H: 9.86; N: 6.72. mp ) 105-107
°C. µeff ) 4.1 µB.
[PhN)PiPr2(CH2)2NPh][tBuNHSiMe2N(CH2)2PiPr2]Co (12).
The compound was isolated by fractional crystallization from the
reaction mixture of 10. Solvent ) pentane (<1%); THF (0.025 g,
1
7.3%); toluene (0.050 g, 15%). H NMR (C6D6): δ -59.05 (s);
-28.92 (s); -25.95 (s); -16.04 (s); -15.49 (s); -6.76 (d); -5.29
(s); -0.76 (s); 0.88 (s); 1.40 (s); 10.23 (s); 15.06 (s); 19.33 (s);
41.91 (s); 49.38 (s); 54.74 (s). IR (cm-1): 3386 (w); 1586 (s); 1301
(m); 1279 (m); 1241 (s); 1179 (m); 1069 (s); 1033 (m); 1005 (s);
984 (m); 922 (w); 903 (s); 837 (m); 815 (m); 778 (m); 741 (m);
700 (m); 663 (w); 621 (w); 601 (w); 526 (w); 494 (w); 466 (w).
Anal. Calcd for C34H62CoN4P2Si. C: 60.41; H: 9.26; N: 8.29.
Observed. C: 60.34; H: 8.94; N: 8.57. mp ) 132-135 °C. µeff
4.1 µB.
)
ClSiMe2N(CH2CH2PiPr2)2 (13). A 20 mL pentane solution of
Li[PNP] (5.05 g, 16.2 mmol) was added to a solution of Me2SiCl2
(2.49 g, 19.3 mmol) in 30 mL of pentane at -40 °C The reaction
mixture was warmed to room temperature and was stirred overnight.
The solution was filtered, and the remaining white solid was washed
with pentane (20 mL). The volatile material was removed under
vacuum, leaving 13 in quantitative yield as determined by 1H NMR
spectroscopy. Compound 13 was used without further purification.
1H NMR (300 MHz, C6D6): δ 0.44 (s, 6 H, SiMe2); 1.03 (m, 24 H,
PCH(CH3)2); 1.62 (m, 8 H, PCH(CH3)2 and -CH2CH2-); 3.18 (m,
4 H, -CH2CH2-). 31P NMR (400 MHz, C6D6): δ 1.10 (s).
H[N2P2tolyl] (14). A solution of 13 (6.45 g, 16.2 mmol) in 20
mL of pentane was added dropwise to
a suspension of
LiNHC6H4CH3 (1.83 g, 16.2 mmol) in 30 mL of pentane at -40
°C. The reaction mixture was allowed to warm to room temperature
and was stirred overnight. The solution was filtered, and the
remaining solid was washed with pentane (30 mL). Solvent was
removed under vacuum leaving 14 as an orange oil in 90% yield
(6.83 g). 1H NMR (300 MHz, C6D6): δ 0.26 (s, 6 H, SiMe2); 1.10
(m, 24 H, PCH(CH3)2); 1.56 (m, 8 H, PCH(CH3)2 and -CH2CH2-)-
; 2.17 (s, 3 H, Ar-CH3); 3.22 (m, 4 H, -CH2CH2-); 6.68 (d, 2 H,
JHH ) 8 Hz, Ar-H); 6.97 (d, 2 H, JHH ) 8 Hz, Ar-H). 31P NMR
(400 MHz, C6D6): δ -1.66 (s).
Li[N2P2tolyl] (15). N-butyl lithium (1.6 M in hexanes, 10 mL, 16
mmol) was syringed to a solution of 14 (7.5 g, 16 mmol) in 40 mL
of pentane at -70 °C. The reaction mixture was warmed to room
temperature and was stirred for 3 h. The reaction flask was cooled
at -40 °C, resulting in the formation and isolation of colorless
[N2P2]CoNHC6H5CH3 (11). Method A. The addition of a
solution of LiNHC6H5CH3 (0.073 g, 0.48 mmol) in 5 mL of THF
to a solution of 2 (0.30 g, 0.48 mmol) in 5 mL of THF at -40 °C
was accompanied by a color change of dark green to dark red. The
reaction mixture was allowed to warm to room temperature and
was stirred overnight. Following the removal of the volatile
materials under vacuum, the crude product was extracted with
pentane, concentrated, and cooled at -40 °C overnight, resulting
in the formation of dark red blade-like crystals (0.21 g, 0.35 mmol)
in 73% yield.
1
crystals in 71% yield (5.4 g). H NMR (300 MHz, C6D6): δ 0.58
(s, 6 H, SiMe2); 0.97 (m, 24 H, PCH(CH3)2); 1.41 (m, 4 H,
PCH(CH3)2); 1.59 (m, 4 H, -CH2CH2-); 2.29 (s, 3 H, Ar-CH3); 3.03
(m, 4 H, -CH2CH2-); 6.93 (d, 2 H, JHH ) 8.4 Hz, Ar-H); 7.05 (d,
2 H, JHH ) 8.4 Hz, Ar-H); 31P NMR (400 MHz, C6D6): δ -3.35
(br s). IR (cm-1): 1603 (m); 1377 (m); 1286 (s); 1247 (m); 1172
(w); 1088 (m); 1056 (m); 992 (w); 951 (s); 899 (m); 822 (s); 765
(m); 718 (w); 699 (w); 667 (w); 650 (w); 605 (w); 510 (m). Anal.
Calcd C25H49LiN2P2Si. C: 63.25; H: 10.42; N: 5.90. Observed. C:
63.08; H: 10.45; N: 5.68. mp ) 133-134 °C.
Method B. A 5 mL solution of p-tolylazide (0.068 g, 0.51 mmol)
in pentane was added to a solution of 6 (0.25 g, 0.51 mmol) in 5
mL of pentane at -40 °C. The solution changed from blue to dark
red instantly upon addition of azide. The reaction mixture was
allowed to warm to room temperature and was stirred for 2 h. The
solution was filtered and concentrated until crystals began to
precipitate. The solution was stored at -40 °C overnight, resulting
[N2P2tolyl]CoI (16). A solution of 15 (2.0 g, 4.2 mmol) was added
dropwise to a suspension of CoI2 (1.3 g, 4.2 mmol) in 20 mL of
toluene, and the reaction mixture was stirred overnight. Solvent
was removed under vacuum, and the crude product was dissolved
in THF and filtered through a bed of Celite. An equal volume of
pentane was added, and the resulting solution was cooled at -40
°C overnight. Brown crystals were isolated in 80% yield (2.2 g).
1H NMR (500 MHz, C6D6): δ -53.11 (br s); 0.96 (m); 8.99 (s);
10.72 (s); 12.40 (s); 22.24 (s); 39.16 (s); 52.96 (br s); 55.21 (s);
66.75 (br s); 67.97 (br s); 92.70 (br s). IR (cm-1): 1604 (s); 1500
1
in the formation of dark red crystals in 32% yield (0.095 g). H
NMR (C6D6): δ -113.03 (br s); -3.09 (s); 0.25 (s); 1.10 (s); 1.67
(s); 3.24 (s); 29.61 (br s); 42.19 (s); 102.05 (s). IR (cm-1): 1605
(s); 1501 (s); 1347 (m); 1289 (s); 1246 (s); 1223 (s); 1173 (m);
1071 (s); 1052 (m); 1036 (m); 933 (w); 899 (m); 846 (s); 809 (s);
771 (s); 758 (m); 741 (s); 691 (w); 666 (w); 608 (w); 579 (w); 546
(m); 505 (m). Anal. Calcd for C29H59CoN3P2Si. C: 58.23; H: 9.96;
Inorganic Chemistry, Vol. 48, No. 7, 2009 3277

Chomitz and Arnold
Table 2. Crystal Data and Structure Refinement for 2-8, 10, 12, 16, and 17
compound number
2
3
4
5
6
7
compound
name
[N2P2]CoI
[N2P2]CoMe
[N2P2]CoCH2SiMe3
[N2P2]CoH
[N2P2]Co
[N2P2]Co(CO)
empirical formula
fw
temperature (K)
crystal system
space group
a (Å)
C22H51CoIN2P2Si
619.51
168(2)
monoclinic
P21/c
9.356(2)
34.812(8)
9.299(2)
90
105.015(4)
90
2925.4(11)
4
C23H54CoN2P2Si C26H62CoN2P2Si2
C22H52CoN2P2Si C22H51CoN2P2Si C23H51CoN2OP2Si
507.64
114(2)
monoclinic
P21/c
579.83
158(2)
triclinic
493.62
168(2)
orthorhombic
Pna21
15.0594(19)
10.9722(14)
16.739(2)
90
492.61
244(2)
orthorhombic
Pnma
14.742(4)
11.265(3)
17.148(5)
90
520.62
168(2)
orthorhombic
P212121
11.409(4)
15.440(5)
16.068(6)
90
j
P1
16.546(6)
11.679(4)
14.610(5)
90
91.834(5)
90
8.6829(5)
9.8323(6)
21.6331(12)
98.3500(10)
99.4850(10)
103.8940(10)
1735.09(17)
2
b (Å)
c (Å)
R (deg)
ꢀ (deg)
90
90
90
γ (deg)
90
90
90
V (Å3)
2821.8(18)
4
2765.8(6)
4
2847.6(13)
4
2830.5(17)
4
Z
λ (Å)
0.71073
1.804
5914
0.0457
3.96
8.81
0.71073
0.776
2772
0.1043
5.67
12.28
0.71073
0.672
5916
0.0258
4.03
0.71073
0.79
3695
0.0257
2.84
7.23
0.71073
0.768
2931
0.0423
5.28
14.29
0.71073
0.778
3509
0.0989
6.32
14.59
µ (cm-1
)
no. of refl
R(int)
Robs (%)
Rwobs (%)
12.22
compound number
8
10
12
16
17
compound
name
empirical formula
fw
temperature (K)
crystal system
space group
a (Å)
[tBuN(CdO)SiMe2N-
[N2P2]CoNHC6H5 [PhN)PiPr2(CH2)2NPh]-
[tBuNHSiMe2N(CH2)2PiPr2]Co
C28H57CoN3P2Si C34H62CoN4P2Si C25H49CoIN2P2Si C25H49CoN2P2Si
[N2P2tolyl]CoI
[N2P2tolyl]Co
(CH2CH2PiPr2)2]Co(CO)2
C25H51CoN2O3P2Si
576.64
160(2)
monoclinic
P21
8.3023(11)
12.2795(17)
15.354(2)
90
93.718(2)
90
1562.1(4)
2
584.73
151(2)
monoclinic
P21/n
675.84
167(2)
monoclinic
P21/n
653.52
151(2)
monoclinic
P21/c
526.62
124(2)
monoclinic
P21/c
13.154(5)
15.801(6)
16.304(6)
90
11.044(3)
14.324(4)
23.454(6)
90
12.2546(14)
13.8526(16)
17.881(2)
90
13.176(2)
14.784(3)
14.826(3)
90
b (Å)
c (Å)
R (deg)
ꢀ (deg)
102.657(5)
90
93.105(4)
90
101.541(2)
90
91.062(2)
90
γ (deg)
V (Å3)
3307(2)
4
3704.7(16)
4
2974.0(6)
4
2887.5(9)
4
Z
λ (Å)
0.71073
0.716
5638
0.0336
4.17
71073
0.672
4423
0.0745
5.31
0.71073
0.61
7547
0.0455
4.36
0.71073
1.779
3642
0.0774
4.24
0.71073
0.762
4328
0.0247
4.46
µ (cm-1
)
no. of refl
R(int)
Robs (%)
(s); 1303 (w); 1256 (s); 1242 (m); 1181 (w); 1167 (w); 1106 (s);
1062 (m); 1044 (m); 997 (w); 970 (w); 920 (s); 883 (w); 842 (s);
819 (m); 795 (m); 770 (s); 684 (m); 661 (m); 620 (w); 597 (w);
548 (w); 514 (m); 481 (w). Anal. Calcd C25H49CoIN2P2Si. C: 45.94;
H: 7.57; N: 4.29. Observed. C: 45.97; H: 7.61; N: 4.24. mp )
208-209 °C. µeff ) 4.2 µB.
for 2 h. Solvent was removed under vacuum, and the crude product
was extracted with toluene. Following concentration and cooling
at -40 °C, dark red blocks of 18 were isolated in 43% yield (0.090
1
g). H NMR (300 MHz, C6D6): δ -1.83 (br s); 0.27 (s); 1.07 (s);
1.32 (s); 1.58 (s); 1.82 (s); 2.16 (s); 6.07 (br s); 12.31 (br s); 15.53
(br s); 20.04 (br s); 27.49 (br s); 42.49 (br s); 65.22 (br s). IR (cm-1):
1898 (s); 1605 (m); 1497 (s); 1314 (m); 1268 (s); 1246 (m); 1179
(w); 1111 (w); 1093 (w); 1045 (w); 928 (m); 885 (w); 839 (m);
817 (m); 801 (m); 757 (m); 672 (w); 600 (w); 516 (w); 458 (w).
Anal. Calcd C26H49CoN2OP2Si. C: 56.29; H: 8.92; N: 5.05.
[N2P2tolyl]Co (17). A suspension of KC8 (0.42 g, 3.1 mmol) in
10 mL of DME was added to a brown solution of 16 (2.0 g, 3.0
mmol) in 15 mL of DME at -40 °C. A color change from brown
to green was observed as the reaction mixture warmed to room
temperature. Following stirring for 3 h, the solvent was removed
under vacuum, and the crude product was extracted with pentane.
The green solution was concentrated and cooled at -40 °C
overnight, resulting in the isolation of green crystals in 72% yield
Observed. C: 56.34; H: 9.24; N: 4.87. mp ) 162-163 °C. µeff
2.8 µB.
)
Crystallographic Analysis. Single crystals of 2-8, 10, 12, 16,
and 17 were coated in Paratone-N oil, mounted on a Kaptan loop,
transferred to a Siemens SMART diffractometer or a Bruker APEX
CCD area detector,34 centered in the beam, and cooled by a nitrogen
flow low-temperature apparatus that has been previously calibrated
by a thermocouple placed at the same position as the crystal.
Preliminary orientation matrices and cell constants were determined
by 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.35 Cell
dimensions reported were calculated from all reflections with I >
1
(1.2 g). H NMR (500 MHz, C6D6): δ -66.52 (br s); -30.26 (br
s); -0.33 (s); 0.88 (s); 3.49 (s); 8.25 (br s); 12.38 (br s); 15.59 (br
s); 26.15 (s); 32.38 (br s); 39.84 (br s); 41.64 (br s); 65.57 (s);
106.75 (br s). IR (cm-1): 1602 (m); 1377 (m); 1317 (s); 1244 (m);
1172 (w); 1088 (w); 1039 (m); 959 (m); 908 (w); 883 (w); 831
(m); 813 (m); 762 (w); 739 (w); 666 (m); 634 (w); 605 (m); 553
(w); 516 (w); 460 (w). Anal. Calcd C25H49CoN2P2Si. C: 57.00; H:
9.40; N: 5.32. Observed. C: 56.91; H: 9.48; N: 5.31. mp ) 85-87
°C. µeff ) 3.0 µB.
[N2P2tolyl]Co(CO) (18). Three freeze pump thaw cycles were
done on a solution of 17 (0.20 g, 0.38 mmol) in 5 mL of Et2O
before 1 equiv of CO was added. The green solution turned slightly
yellow and material precipitated. The reaction mixture was stirred
(34) SMART Area-Detector Software Package; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1995-1999.
(35) SAINT SAX Area-Detector Integration Program, V7.06; Siemens
Industrial Automation, Inc.: Madison, WI, 2005.
3278 Inorganic Chemistry, Vol. 48, No. 7, 2009

Substitution and Reaction Chemistry of Cobalt Complexes
Figure 2. Thermal ellipsoid (50%) plot of 3. Hydrogen atoms, iso-propyl
methyl, and tert-butyl methyl groups have been omitted for clarity.
Figure 1. Thermal ellipsoid (50%) plot of 2. Hydrogen atoms, iso-propyl
methyl, and tert-butyl methyl groups have been omitted for clarity.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for [N2P2]CoI
(2)
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.36 An empirical
absorption correction based on comparison of redundant and
equivalent reflections was applied using SADABS.37 The structures
were solved using SHELXS38 and refined on all data by full-matrix
least-squares with SHELXL-97.39 Thermal parameters for all non-
hydrogen atoms were refined anisotropically. Oak Ridge Thermal
Ellipsoid Plot (ORTEP) diagrams were created using ORTEP-3.
A summary of the X-ray diffraction data is presented in Table 2.
Co(1)-I(1)
2.7229(7)
1.957(3)
119.01(10)
107.43(4)
96.55(3)
Co(1)-P(1)
2.3947(12)
2.3993(13)
112.20(10)
114.58(9)
105.30(4)
Co(1)-N(1)
Co(1)-P(2)
N(1)-Co(1)-P(1)
P(1)-Co(1)-P(2)
P(1)-Co(1)-I(1)
N(1)-Co(1)-P(2)
N(1)-Co(1)-I(1)
P(2)-Co(1)-I(1)
Scheme 1. Synthesis of [N2P2]CoR Complexes
Results and Discussion
As an entry into Co(II) organometallic and reduced metal
species, the synthesis of metal-halide starting materials
[N2P2]CoX (X ) Cl, I) was explored. The synthesis of
[N2P2]CoCl (1) has been described previously,28 and
[N2P2]CoI (2) was synthesized through an analogous reaction
to that of 1 but with toluene as the reaction solvent. Dark
green blocks of 2 were isolated in 83% yield following
crystallization from toluene at -40 °C. The solution magnetic
susceptibilities of 1 and 2 (4.1 µB and 4.0 µB, respectively)
Table 4. Selected Bond Lengths (Å) and Angles (deg) for [N2P2]CoMe
(3)
Co(1)-N(1)
Co(1)-N(2)
Co(1)-P(1)
1.985(4)
2.134(4)
2.2647(16)
Co(1)-C(23)
Co(1)-P(2)
1.995(5)
2.2636(15)
N(1)-Co(1)-C(23) 98.96(18)
N(1)-Co(1)-N(2)
78.48(14)
124.15(13)
85.97(11)
C(23)-Co(1)-N(2) 177.23(19) N(1)-Co(1)-P(2)
C(23)-Co(1)-P(2)
N(1)-Co(1)-P(1)
N(2)-Co(1)-P(1)
94.67(16)
N(2)-Co(1)-P(2)
124.03(13) C(23)-Co(1)-P(1) 95.72(16)
86.65(11) P(2)-Co(1)-P(1) 107.87(6)
3
agree with an S ) /2 spin-state (high-spin). The solid-state
the stability of the [N2P2] ligand under these circumstances,
the synthesis of various organometallic complexes was
attempted.
structures of 1 and 2 display similar structural features with
both Co(II) centers lying in distorted tetrahedral geometries
(Figure 1). Relevant bond lengths and angles are provided
in Table 3. The significantly higher isolated yield of 2
compared to that of 1 distinguished it as the starting material
of choice.
Substitution Chemistry of 2. Supporting ligands used for
the stabilization of reactive metal fragments are often
susceptible to undesirable, non-innocent behavior. In the case
of organometallic complexes, for example, the polarity of
M-C bonds renders them especially reactive and for TDMA
systems, decomposition of the supporting ligand via intramo-
lecular C-H bond activation has been observed. To probe
Reaction of 2 with MeLi (1.6 M in Et2O) in Et2O resulted
in the isolation of [N2P2]CoMe (3) as dark green crystals in
53% yield following crystallization from pentane at -40 °C
(Scheme 1a). Crystals suitable for an X-ray diffraction study
were grown from an Et2O solution at -40 °C, and an ORTEP
diagram is shown in Figure 2 with selected bond lengths
and angles provided in Table 4. The geometry of 3 has altered
from distorted tetrahedral in 2 to trigonal bipyramidal by a
change in the binding mode of the [N2P2] ligand from κ3-
NP2 to κ4-N2P2. A change in the spin-state is also observed
with the solution magnetic susceptibility of 3 indicating the
presence of a low-spin species (µeff ) 1.8 µB). The
Co(1)-C(23) bond distance of 1.994(5) Å is slightly shorter
than the values observed in the related Co(II) compounds
[Ph2PC6H4N(H)]CoMe(PMe3)2 (2.019(3) Å, C.N. ) 5),40
[PhTttBu]CoMe (2.052(3) Å, C.N. ) 4),41 PhB(tBuIm)3CoMe
(2.042(2) Å, C.N. ) 4),42 and [Tpt-Bu,Me]CoMe (2.115(14)
(36) XPREP, Part of the SHELXTL Crystal Structure Determination
Package, v6.12; Bruker AXS Inc.: Madison, WI, 1995.
(37) Sheldrick, G. SADABS, Siemens Area Detector ABSorption correction
program, v2.10; Siemens Industrial Automation, Inc.: Madison, WI,
2005.
(38) XS Program for the Refinement of X-ray Crystal Structures, Part of
the SHELXTL Crystal Structure Determination Package; Bruker
Analytical X-ray Systems, Inc.: Madison, WI, 1995-1999.
(39) XL Program for the Refinement of X-ray Crystal Structures, Part of
the SHELXT Crystal Structure Determination Package; Bruker
Analytical X-ray Systems, Inc.: Madison, WI, 1995-1999.
(40) Klein, H. F.; Beck, R.; Florke, U.; Haupt, H. J. Eur. J. Inorg. Chem.
2003, 240–248.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3279

Chomitz and Arnold
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
[N2P2]CoCH2SiMe3 (4)
Co(1)-N(1)
1.9261(18)
2.2499(17)
122.93(9)
111.41(8)
119.27(7)
Co(1)-C(23)
2.033(2)
2.4089(6)
76.56(7)
117.71(6)
84.63(5)
Co(1)-N(2)
Co(1)-P(1)
N(1)-Co(1)-C(23)
C(23)-Co(1)-N(2)
C(23)-Co(1)-P(1)
N(1)-Co(1)-N(2)
N(1)-Co(1)-P(1)
N(2)-Co(1)-P(1)
Table 6. Selected Bond Lengths (Å) and Angles (deg) for [N2P2]CoH
(5)
Co(1)-N(1)
1.9301(18) Co(1)-N(2)
2.1974(9)
1.39(3)
2.1069(17)
2.2052(9)
Co(1)-P(2)
Co(1)-P(1)
Co(1)-H(52)
N(1)-Co(1)-N(2)
N(2)-Co(1)-N(2)
N(2)-Co(1)-N(1)
80.38(7)
88.78(8)
88.73(8)
N(1)-Co(1)-P(2)
N(1)-Co(1)-P(1)
N(2)-Co(1)-P(1)
127.66(10)
116.51(10)
114.22(3)
N(1)-Co(1)-N(52) 99.4(11)
N(2)-Co(1)-P(52) 179.0(18)
N(2)-Co(1)-N(52) 90.6(17)
N(1)-Co(1)-P(52) 92.3(17)
Å, C.N. ) 4).43 The remaining bond distances are also very
similar to those observed in [Ph2PC6H4N(H)]CoMe(PMe3)2
(C.N. ) 5).40
Figure 3. Thermal ellipsoid (50%) plot of 4. Hydrogen atoms, iso-propyl
methyl, and tert-butyl methyl groups have been omitted for clarity.
Reaction of 2 with LiCH2SiMe3 resulted in the formation
of [N2P2]CoCH2SiMe3 (4), which was isolated in 57% yield
as large lime-green plates following crystallization from
pentane at -40 °C (Scheme 1b). The solution magnetic
susceptibility of 4 is 4.2 µB, indicating a potential difference
in the geometry around the Co(II) center compared to that
found in 3. To determine if this were the case, the solid-
state structure of 4 was determined via X-ray diffraction (see
Figure 3; selected bond lengths and angles are provided in
Table 5). In contrast to 1-3, the [N2P2] ligand is bound κ3-
N2P in compound 4. One phosphine arm in 4 remains
uncoordinated likely because of steric congestion at the Co
center. The geometry around the Co atom is tetrahedral, and
the Co(1)-C(23) bond distance of 2.033(2) Å is very close
to the values seen in the two previously reported examples
(P-P)CoCl(CH2SiMe3) (2.013(2) Å) and (P-P)Co(CH2Si-
Me3)2 (2.039(7) and 2.043(7) Å), where (P-P) is a phos-
phorus-bridged ferrocenophane ligand.44
Late metal hydrides are well-known and have been shown
to play key roles in a wide range of stoichiometric and
catalytic transformations.45-49 The reactivity of 3 and 4 with
H2 was explored to determine if either was a useful starting
material for a metal-hydride. A flask containing a solution
of 3 in THF was heated at 65 °C for 72 h under an
atmosphere of H2, but no reaction was observed. In contrast,
exposure of compound 4 to H2 at 1 atm over 48 h at room
Figure 4. Thermal ellipsoid (50%) plot of 5. Hydrogen atoms, and iso-
propyl methyl groups have been omitted for clarity.
temperature resulted in the clean formation of [N2P2]CoH
(5), which was isolated as dark olive needles in 73% yield.
The IR spectrum of 5 features a sharp absorption at 1800
cm-1, indicative of a metal-hydride moiety. The solution
1
magnetic susceptibility of 5 is 2.0 µB (S ) /2), similar to
that in 3. An X-ray diffraction study confirmed the geometry
around the Co atom as trigonal bipyramidal. An ORTEP
diagram is shown in Figure 4 with selected bond lengths
and angles provided in Table 6. As in compound 3, the ligand
in 5 is bound κ4-N2P2 with similar metal-ligand geometrical
parameters. The hydride was located in the Fourier map and
refined to give a Co-H bond distance of 1.39(3) Å, in
agreement with other crystallographically characterized
Co-H compounds.50 A number of factors such as coordina-
tion number and spin-state may discourage the reactivity of
H2 with 3 compared to that of 4 and H2. Complex 5 was
also synthesized by reaction of 2 with alkylating reagents
containing ꢀ-hydrogens such as ethyl magnesium chloride
and n-BuLi (Scheme 2). One likely mechanism for this
transformation involves ꢀ-hydride elimination by a transient
Coalkyl species, which results in the release of alkene and
the formation of 5. We note that in an effort to probe the
reverse of this process, no reaction was observed between 5
and 1 atm ethylene in a sealed NMR tube at room
temperature.
(41) Schebler, P. J.; Mandimutsira, B. S.; Riordan, C. G.; Liable-Sands,
L. M.; Incarvito, C. D.; Rheingold, A. L. J. Am. Chem. Soc. 2001,
123, 331–332.
(42) Cowley, R. E.; Bontchev, R. P.; Duesler, E. N.; Smith, J. M. Inorg.
Chem. 2006, 45, 9771–9779.
(43) Jewson, J. D.; Liable-Sands, L. M.; Yap, G. P. A.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1999, 18, 300–305.
(44) Imamura, Y.; Mizuta, T.; Miyoshi, K.; Yorimitsu, H.; Oshima, K.
Chem. Lett. 2006, 35, 260–261.
(45) Sadique, A. R.; Gregory, E. A.; Brennessel, W. W.; Holland, P. L.
J. Am. Chem. Soc. 2007, 129, 8112–8121.
(46) Yu, Y.; Sadique, A. R.; Smith, J. M.; Dugan, T. R.; Cowley, R. E.;
Brennessel, W. W.; Flaschenriem, C. J.; Bill, E.; Cundari, T. R.;
Holland, P. L. J. Am. Chem. Soc. 2008, 130, 6624–6638.
(47) Bart, S. C.; Bowman, A. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem.
Soc. 2007, 129, 7212.
(48) Bart, S. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2004,
126, 13794–13807.
Reduction Chemistry of 2. Chemical reduction of com-
pound 2 was explored to determine whether a low-valent
(49) Krische, M. J.; Yongkui, S. Acc. Chem. Res. 2007, 40, 1237–1237.
(50) Allen, F. H. Acta Crystallogr. 2002, B58, 380–388.
3280 Inorganic Chemistry, Vol. 48, No. 7, 2009

Substitution and Reaction Chemistry of Cobalt Complexes
Scheme 2. Synthesis of 5
Table 7. Selected Bond Lengths (Å) and Angles (deg) for [N2P2]Co (6)
Co species could be isolated. Reduction of 2 with KC8 in
THF resulted in a color change of dark green to deep blue
and allowed for the isolation of [N2P2]Co (6) in 84% yield
as large blue needles following crystallization from Et2O at
-40 °C. The results of an X-ray diffraction study of 6 are
shown in Figure 5, with selected bond lengths and distances
provided in Table 7. An open axial coordination site was
created upon reduction and alteration of the coordination
mode of the [N2P2] ligand from κ3-NP2 in 2 to κ4-N2P2 in 6.
The geometry around the Co center is trigonal pyramidal,10
and the solution magnetic susceptibility of 6 (3.0 µB), in
accord with an S ) 1 ground state.
Co(1)-N(1)
1.917(4)
2.207(4)
126.46(4)
105.17(6)
88.91(8)
Co(1)-P(1)
2.2124(11)
2.2124(11)
126.46(4)
79.76(18)
88.92(8)
Co(1)-N(2)
Co(1)-P(2)
N(1)-Co(1)-P(1)
P(1)-Co(1)-P(2)
P(2)-Co(1)-P(2)
N(1)-Co(1)-P(2)
N(1)-Co(1)-N(2)
N(1)-Co(1)-N(2)
Table 8. Selected Bond Lengths (Å) and Angles (deg) for
[N2P2]Co(CO) (7)
Co(1)-C(23)
1.800(7)
2.294(2)
1.151(8)
113.0(3)
112.50(19)
123.20(18)
Co(1)-N(1)
Co(1)-P(1)
1.966(5)
2.302(2)
Co(1)-P(2)
O(1)-C(23)
C(23)-Co(1)-N(1)
N(1)-Co(1)-P(2)
N(1)-Co(1)-P(1)
C(23)-Co(1)-P(2)
C(23)-Co(1)-P(1)
P(2)-Co(1)-P(1)
103.0(2)
97.7(2)
104.82(7)
The reactivity of 6 with a number of small molecules
including N2, MeI, I2, Br2, H2, CO, ethylene, N3 Bu, H3SiPh,
t
and N3Ar (Ar ) C6H5, C6H4CH3) was surveyed. Unlike
related Co compounds,6,51 compound 6 does not coordinate
N2 in solution or the solid-state as demonstrated by IR
spectroscopy and X-ray diffraction studies. Exposure of a
pentane solution of 6 to 1 equiv of CO resulted in a solution
color change of blue to green upon warming to room
temperature. Following concentration and cooling of the
solution at -40 °C, dark green needles of [N2P2]Co(CO)
(7) were isolated in 54% yield. A single, strong absorption
in the IR spectrum at 1881 cm-1 supports the formation of
a monocarbonyl and is in agreement with similar four
coordinate Co(I) carbonyl complexes.52,53 However, the νCO
is significantly lower than the value observed in TpNpCo(CO)
(1950 cm-1)54 and CpCo(CO) (1993-1999 cm-1)55,56 Fur-
ther confirmation of the connectivity of 7 was achieved by
an X-ray diffraction study (see Figure 6 and Table 8).
Coordination by the basal nitrogen is no longer observed in
7, with the binding mode of the [N2P2] ligand returning again
to κ3-NP2, as was observed in the solid-state structures of 1
and 2. The solution magnetic susceptibility of 7 (3.0 µB) is
in agreement with a high-spin Co(I) center.
Figure 5. Thermal ellipsoid (50%) plot of 6. Hydrogen atoms, iso-propyl
methyl, and tert-butyl methyl groups have been omitted for clarity.
A quite different carbonyl derivative was obtained when
6 was exposed to an excess of CO. Addition of an atmosphere
of CO to a solution of 6 in pentane at -70 °C resulted in a
color change of blue to yellow with concomitant formation
of a precipitate. Following the removal of solvent under
vacuum, extraction with toluene, concentration, and cooling
Figure 6. Thermal ellipsoid (50%) plot of 7. Hydrogen atoms, iso-propyl
methyl, and tert-butyl methyl groups have been omitted for clarity.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3281

Chomitz and Arnold
Scheme 3. Oxidation Reactions with 6
Figure 7. Thermal ellipsoid (50%) plot of 8. Hydrogen atoms, iso-propyl
methyl, and tert-butyl methyl groups have been omitted for clarity.
Table 9. Selected Bond Lengths (Å) and Angles (deg) for
[tBuN(CdO)SiMe2N((CH2)2PiPr2)2]Co(CO)2 (8)
Co(1)-C(23)
Co(1)-C(25)
Co(1)-P(1)
1.983(4)
1.740(4)
2.2379(10)
Co(1)-C(24)
Co(1)-N(2)
1.765(4)
2.114(3)
oxidant such as Br2 was also examined, and again the
reaction of 6 with 1 equiv of Br2 resulted in the exclusive
isolation of [N2P2]CoBr (9) in 53% yield. Similar to 1 and
2, the solution magnetic susceptibility of 9 is 4.1 µB,
indicative of a high-spin metal center. The reaction of 6 with
H2 and ethylene was also examined; however, no reaction
between these substrates and the Co(I) center was observed.
C(25)-Co(1)-C(24) 117.5(2)
C(25)-Co(1)-C(23) 86.45(16)
C(25)-Co(1)-N(2)
C(24)-Co(1)-C(23) 88.13(15)
119.16(15)
88.88(13)
95.34(11)
85.57(8)
C(24)-Co(1)-N(2)
C(25)-Co(1)-P(1)
C(23)-Co(1)-P(1)
122.92(17) C(23)-Co(1)-N(2)
95.78(13) C(24)-Co(1)-P(1)
174.42(11) N(2)-Co(1)-P(1)
at -40 °C, yellow crystals of the diamagnetic complex
[tBuN(CdO)SiMe2N((CH2)2PiPr2)2]Co(CO)2 (8) were iso-
lated in 80% yield. In contrast to the IR spectrum of 7,
complex 8 shows three C-O bands at 1952, 1893, and 1583
cm-1. An X-ray diffraction study (Figure 7; Table 9)
confirmed the connectivity of 8. The low frequency stretch
at 1583 cm-1 is assigned to the CO molecule that has inserted
itself into the Co-amide bond.57-59 The Co atom adopts a
trigonal bipyramidal geometry with one “dangling” phos-
phine because of electronic saturation (18 e-) at the metal
center. Compound 8 demonstrates the stronger affinity of
the Co(I) center to CO over the neutral phosphine, as
expected.
The reactivity of 6 with various oxidants was also
explored. Reaction of 6 with 1 equiv of MeI in THF resulted
in a solution color change of blue to dark green. Following
the removal of solvent under vacuum, extraction with
toluene, concentration, and cooling at -40 °C, dark green
blocks of 2 were isolated in 53% yield. Similar results were
obtained from the reaction of 6 with 1 equiv of I2 (Scheme
3). In contrast to related work by Caulton et al., the formation
of a Zwitterionic product by addition of a second equivalent
of I2 was not observed.60 Reaction of 6 with a stronger
Generation and Reactivity of Transient Co(III) Imido
Species. Initial attempts to synthesize a Co(III) imido species
t
by the addition of N3 Bu to 6 only resulted in the isolation
of starting material. In contrast, reaction of phenylazide with
6 in pentane takes place rapidly at -116 °C (Et2O/N2(l)) to
form a green precipitate (A). When allowed to warm to room
temperature, species A quickly disappeared and a dark red
solution was formed. When phenylazide was added to a
solution of 6 at or above -70 °C, a similar dark red solution
formed immediately. Following filtration, concentration, and
cooling, red-orange crystals of [N2P2]CoNHPh (10) were
collected in 57% yield. Analogous results were observed with
p-tolylazide, and [N2P2]CoNHC6H4CH3 (11) was isolated in
32% yield as red blocks following crystallization from
pentane at -40 °C.
An ORTEP diagram showing the molecular structure of
10 is given in Figure 8, with selected bond lengths and angles
provided in Table 10. As was observed in the case of 4, the
[N2P2] ligand is bound κ3-N2P with one “dangling” phosphine
because of steric congestion around the metal center. The
geometry about the Co is best described as distorted
tetrahedral with angles of 77.03(16)° {N(1)-Co(1)-N(2)},
118.23(13)°{N(1)-Co(1)-P(1)},131.49(17)°{N(1)-Co(1)-N(3)},
and 109.78(16)° {N(2)-Co(1)-N(3)}. The Co(1)-N(3)
bond distance (1.906(4) Å) is in accord with a Co-N aryl
single bond (1.940 Å).50 While the N-H hydrogen was
located in the Fourier map, a fixed position was used for the
structural refinement. The solution magnetic susceptibility
(51) Egan, J. W.; Haggerty, B. S.; Rheingold, A. L.; Sendlinger, S. C.;
Theopold, K. H. J. Am. Chem. Soc. 1990, 112, 2445–2446.
(52) Ingleson, M. J.; Pink, M.; Caulton, K. G. J. Am. Chem. Soc. 2006,
128, 4248–4249.
(53) Fout, A. R.; Basuli, F.; Fan, H.; Tomaszewski, J.; Huffman, J. C.;
Baik, M.; Mindiola, D. J. Angew. Chem., Int. Ed. 2006, 45, 3291–
3295.
(54) Detrich, J. L.; Konecny, R.; Vetter, W. M.; Doren, D.; Rheingold,
A. L.; Theopold, K. H. J. Am. Chem. Soc. 1996, 118, 1703–1712.
(55) Bengali, A. A.; Bergman, R. G.; Moore, C. B. J. Am. Chem. Soc.
1995, 117, 3879.
(56) Dougherty, T. P.; Heilweil, E. J. J. Chem. Phys. 1994, 100, 4006.
(57) Rahim, M.; Bushweller, C. H.; Ahmed, K. J. Organometallics 1994,
13, 4952–4958.
3
of 10 is 3.8 µB, in agreement with an S ) /2 ground state.
Complexes 10 and 11 were also independently synthesized
through the reaction of 2 with LiNHPh and LiNHC6H4CH3,
respectively. The yields from the metathesis reactions (72%
and 73%, respectively) were much improved compared to
(58) Joslin, F. L.; Johnson, M. P.; Mague, J. T.; Roundhill, D. M.
Organometallics 1991, 10, 2781–2794.
(59) Fagan, P. J.; Manriquez, J. M.; Vollmer, S. H.; Day, C. S.; Day, V. W.;
Marks, T. J. J. Am. Chem. Soc. 1981, 103, 2206–2220.
(60) Ingleson, M. J.; Pink, M.; Fan, H.; Caulton, K. G. J. Am. Chem. Soc.
2008, 130, 4262–4276.
3282 Inorganic Chemistry, Vol. 48, No. 7, 2009

Substitution and Reaction Chemistry of Cobalt Complexes
transformations need to occur on the [N2P2] ligand, including
oxidation of one of the phosphines by a nitrene group,10,65
and C-N bond cleavage. The solution magnetic susceptibil-
ity of 12 is 4.1 µB, in agreement with a high-spin Co(II)
center. The yield of 12 was found to be solvent dependent
with the highest isolated yield of 12 (15%) obtained using
toluene or benzene. A summary of the yields of 10 and 12
in different solvents is provided in Table 12. Analysis of
the crude reaction mixture revealed the presence of starting
material 6 along with 10 and 12, in addition to a small
quantity of another, unidentified product. The paramagnetic
nature of this latter material, its low yield, and poor
crystallinity has made identification elusive.
Our data suggest that two competing reactions are opera-
tive in the formation of 10 and 12. The solvent-dependent
yields and the deuterium labeling experiment suggest that
the formation of 10 involves an imido assisted hydrogen atom
abstraction from solvent by the tert-butyl group of the ligand
(Scheme 5). Examining how the number of equivalents of
azide used effects the reaction further supports hydrogen
atom abstraction as the route of reduction. Adding 0.5 equiv
of phenylazide to 6 led to crude reaction mixtures of 6 and
10, with no 12 observed. Increasing the amount of azide
added to 2 equiv led to reaction mixtures that would not
yield crystalline products. Though the yields of 10 and 12
do not follow an obvious trend, they are likely the result of
a combination of the solvent polarity and the BDE of
available C-H bonds in solution. Under certain conditions
(toluene and sufficient amounts of N3Ph), intramolecular
nitrene group transfer is more competitive with hydrogen
abstraction, which leads to a higher isolated yield of 12.
When the reaction of 6 and phenylazide is performed in the
presence of 1,2-diphenylhydrazine in toluene only 10 is
isolated; compound 12 is not observed, further supporting
the premise that 12 forms in the absence of sufficient
hydrogen-atom donors.
To test whether intermolecular nitrene group transfer
reactions could be achieved with intermediate A, it was
exposed to an atmosphere of CO at -116 °C.5,11,12,14,16,17
Upon addition of CO, the flask was sealed, and the cold bath
was removed. As the flask warmed, the green suspension
changed color to yellow. The volatile materials were vacuum-
transferred and analyzed by GCMS. Apart from solvent,
phenyl-isocyanate was the only other organic product
observed, albeit in low yield (30%). Extraction of the
remaining yellow solid led to the isolation of 8 in 78% yield.
Related attempts to engender nitrene group transfer to other
substrates such as alkenes, alkynes, isocyanides, and isocy-
anates were unsuccessful.
Figure 8. Thermal ellipsoid (50%) plot of 10. Hydrogen atoms, iso-propyl
methyl, and tert-butyl methyl groups have been omitted for clarity.
Table 10. Selected Bond Lengths (Å) and Angles (deg) for
[N2P2]CoNHPh (10)
Co(1)-N(1)
1.908(4)
1.906(4)
131.49(17)
77.03(16)
118.24(13)
Co(1)-N(2)
2.241(4)
Co(1)-N(3)
Co(1)-P(1)
2.3826(17)
109.77(16)
110.18(13)
86.61(11)
N(3)-Co(1)-N(1)
N(1)-Co(1)-N(2)
N(1)-Co(1)-P(1)
N(3)-Co(1)-N(2)
N(3)-Co(1)-P(1)
N(2)-Co(1)-P(1)
those from the reactions of 6 with azide due, we assume, to
the absence of side-reactions (see below).
Hydrogen atom abstraction by a transient metal imido
species has been reported.8,61-63 A common test for identify-
ing such reactivity is to carry the reaction out in the presence
of 1,2-diphenylhydrazine, which is converted to azoben-
zene.61,64 Accordingly, when the reactions of 6 with an
arylazides (phenylazide, p-tolylazide) were performed in the
presence of 0.5 equiv of 1,2-diphenylhydrazine, quantitative
conversion of 1,2-diphenylhydrazine to azobenzene was
observed by 1H NMR spectroscopy. Compound 6 and
phenylazide were also combined in C6D6, and the resulting
complex was analyzed for deuterium incorporation (Scheme
4). The IR spectrum revealed no N-D band in the expected
region (based on reduced mass calculations)sonly the N-H
absorption at 3320 cm-1 was observed. The high resolution
EIMS, however, revealed incorporation of deuterium into
the tert-butyl group of the [N2P2] ligand as seen by the
change in the molecular ionization peak from 57.1 m/z (C4H9)
to 58.1 m/z (C4H8D) when deuterated solvent was used.
Similar results have been observed with a related transient
Co oxo species supported by the Tp′ (Tp′ ) hydridotris(3-
tert-butyl-5-methylpyrazolylborate) ligand.51
In addition to red-orange crystals of 10, bright green
crystals of a second product were isolated following the
reaction of 6 with phenylazide. The identity of this material
was determined with the aid of an X-ray diffraction study
(see Figure 9; Table 11). In forming this product [PhN)PiPr2-
(CH2)2NPh]-[tBuNHSiMe2N(CH2)2PiPr2]Co (12), at least two
Direct confirmation of complex A as a Co(III) imido was
hampered by its instability above -70 °C. Our experimental
results do, nonetheless, infer the presence of a transient
[N2P2]CodNAr species. The observed H-atom abstraction
to obtain 10 and the nitrene group transfer observed in
forming 12 lends support to this notion.
(61) Lucas, R. L.; Powell, D. R.; Borovik, A. S. J. Am. Chem. Soc. 2005,
127, 11596–11597.
(62) Eckert, N. A.; Vaddadi, S.; Stoian, S.; Lachicotte, R. J.; Cundari, T. R.;
Holland, P. L. Angew. Chem., Int. Ed. 2006, 45, 6868–6871.
(63) Thyagarajan, S.; Shay, D. T.; Incarvito, C. D.; Rheingold, A. L.;
Theopold, K. H. J. Am. Chem. Soc. 2003, 125, 4440–4441.
(64) Harman, W. H.; Chang, C. J. J. Am. Chem. Soc. 2007, 129, 15128.
(65) Ingleson, M. J.; Pink, M.; Fan, H.; Caulton, K. J. Am. Chem. Soc.
2008, 130, 4262–4276.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3283

Chomitz and Arnold
Scheme 4. Formation and Reactivity of a Transient Co(III) Imido
Ligand Modification. With the aim of tuning the reactivity
of “[N2P2]CodNAr” to encourage additional group transfer
reactions, a modification to the [N2P2] ligand was examined
in which a p-tolyl group replaced the tert-butyl functionality.
The p-tolyl group was chosen so as to discourage hydrogen
atom abstraction from the ligand, thus promoting cleaner
nitrene group transfer reactions. The resulting ligand,
[N2P2tolyl], was synthesized in a straightforward manner as
follows.
Reaction of Li[PNP] with a slight excess of Cl2SiMe2 in
pentane resulted in the isolation of ClSiMe2N(CH2CH2PiPr2)2
(13) in quantitative yield. Interaction of 13 with LiNH-
C6H4CH3 in pentane gave H[N2P2tolyl] (14) in 90% yield
following filtration and the removal of solvent under vacuum.
Deprotonation of 14 with n-BuLi resulted in the formation
of Li[N2P2tolyl] (15), which was isolated in 71% yield as a
colorless crystalline solid following crystallization from
pentane at -40 °C.
Cobalt derivatives with this new [N2P2] variant proceeded
straightforwardly. Reaction of 15 with CoI2 in toluene led
to the isolation of [N2P2tolyl]CoI (16) as dark brown needles
in 80% yield, following crystallization from THF layered
with pentane at room temperature. The solution magnetic
susceptibility of 16 (4.2 µB) indicates the same spin-state as
in the tert-butyl analogue 2, and an X-ray diffraction study
of 16 revealed a four-coordinate Co center in a distorted
tetrahedral geometry similar to that observed in 2. An
ORTEP diagram is shown in Figure 10 with selected bond
lengths and angles provided in Table 13. The bond distances
observed in 2 and 16 are statistically indistinguishable with
the exception of a shorter Co(1)-I(1) bond distance in 16
(2.6916(7) vs 2.7229(7) Å).
Figure 9. Thermal ellipsoid (50%) plot of 12. Hydrogen atoms, iso-propyl
methyl, and tert-butyl methyl groups have been omitted for clarity.
Table 11. Selected Bond Lengths (Å) and Angles (deg) for
[PhN)PiPr2(CH2)2NPh][tBuNHSiMe2N(CH2)2PiPr2]Co (12)
Co(1)-N(2)
1.950(2)
2.0694(19)
1.619(2)
Co(1)-N(4)
Co(1)-P(1)
1.9779(19)
2.4248(8)
Co(1)-N(3)
P(2)-N(3)
N(2)-Co(1)-N(4)
N(4)-Co(1)-N(3)
N(4)-Co(1)-P(1)
121.02(9)
103.59(8)
114.26(6)
N(2)-Co(1)-N(3)
N(2)-Co(1)-P(1)
N(3)-Co(1)-P(1)
119.95(8)
86.90(6)
110.47(6)
Table 12. Solvent Dependent Yields of 10a and 12a
solventb
Yield of 10 (%)
Yield of 12 (%)
pentane
toluene
benzene
THF
57
23
20
34
<1
15
15
7.3
Reduction of 16 with KC8 in DME resulted in a color
change of brown to green. Following the removal of solvent
under vacuum, extraction with pentane, and cooling at -40
°C, green crystals of [N2P2tolyl]Co (17) were isolated in 84%
a Isolated yield. b Approximate BDE (kcal/mol) for pentane (98), toluene
(110 and 85), benzene (110), and THF (95).
3284 Inorganic Chemistry, Vol. 48, No. 7, 2009

Substitution and Reaction Chemistry of Cobalt Complexes
Scheme 5. Ligand Assisted H-Atom Abstraction
Table 13. Selected Bond Lengths (Å) and Angles (deg) for
[N2P2tolyl]CoI (16)
yield. The solid-state structure of 17 was determined by
X-ray crystallography, and an ORTEP diagram is shown in
Figure 11 with selected bond lengths and angles provided
in Table 14. As in 6, the Co center in 17 lies in a four
coordinate trigonal pyramidal geometry with the ligand
bound κ4-N2P2, and an open axial coordination site is present.
The metal-ligand bond distances in 17 are similar to those
observed in 6, and the solution magnetic susceptibility of
17 is 3.0 µB (S ) 1). As was seen with 16, compound 6 and
17 possess almost identical geometric parameters.
Exposure of a frozen pentane solution of 17 to 1 equiv of
CO resulted in a color change of green to brown and,
following the removal of solvent under vacuum, extraction
with toluene, concentration, and cooling at-40 °C, brown
crystals of the monocarbonyl species [N2P2tolyl]Co(CO) (18)
were isolated in 43% yield. One C-O band is present in the
IR spectrum (1899 cm-1); the solution magnetic susceptibility
is 2.8 µB (S ) 1), similar to compound 7. The C-O
stretching frequencies of the related Co(I) monocarbonyls 7
(1881 cm-1) and 18 (1899 cm-1) indicate that the Co center
in 7 is slightly more electron rich and that the [N2P2] ligand
Co(1)-N(1)
1.958(4)
Co(1)-P(1)
2.3860(14)
2.6916(7)
110.10(12)
118.65(11)
103.23(4)
Co(1)-P(2)
2.3913(14)
107.98(12)
121.00(5)
95.83(4)
Co(1)-I(1)
N(1)-Co(1)-P(1)
P(1)-Co(1)-P(2)
P(1)-Co(1)-I(1)
N(1)-Co(1)-P(2)
N(1)-Co(1)-I(1)
P(2)-Co(1)-I(1)
Table 14. Selected Bond Lengths (Å) and Angles (deg) for
[N2P2tolyl]Co (17)
Co(1)-N(1)
1.939(3)
2.216(2)
131.90(7)
89.14(6)
117.35(3)
Co(1)-P(2)
2.2077(9)
2.2327(8)
78.94(9)
108.87(7)
88.78(6)
Co(1)-N(2)
Co(1)-P(1)
N(1)-Co(1)-P(2)
P(2)-Co(1)-N(2)
P(2)-Co(1)-P(1)
N(1)-Co(1)-N(2)
N(1)-Co(1)-P(1)
N(2)-Co(1)-P(1)
Table 15. Electrochemical Data for 2 and 16
compound
reductiona,b,c
oxidationa,b,c
2
16
-1.54V
-1.47V
-0.35 V, 0.08 V
0.04 V, 0.42 V
a Reported relative to Fc/Fc+. b 0.3 M [nBu4N][PF6] in CH2Cl2. c 50
mV/s scan rate, non-reversible.
is a slightly better donor than [N2P2tolyl]. To further probe
the electronic differences between complexes supported by
[N2P2] and [N2P2tolyl], electrochemical data on the parent
metal-halide complexes 2 and 16 were collected. Cyclic
voltammograms of these two complexes are similar with both
possessing one reductive and two oxidative events in the
solvent window (Table 15). The electrochemical data also
suggests that the [N2P2] ligand in 2 is slightly more electron
releasing on the basis of a higher reduction potential and
lower oxidation potential as compared to 16.
Imido Trapping Reactions. As with 6, a precipitate
formed at low temperature (-116 °C) in pentane upon the
addition of azide to 17, and when allowed to warm to room
temperature, a color change of green to red-brown was
observed. The identity of the resulting complex has yet to
be determined because of difficulties in isolating clean
material; however, we suspect based on our observations of
the reactivity of 6 that a new Co(II) amide might be formed,
similar to 10 and 11. In an effort to detect nitrene functional-
ity, the reactivity of the low temperature species
“[N2P2tolyl]CodNAr” (Ar ) C6H4CH3) (B), was probed with
a number of unsaturated substrates.
Figure 10. Thermal ellipsoid (50%) plot of 16. Hydrogen atoms and iso-
propyl methyl groups have been omitted for clarity.
As was seen with A, addition of an excess of CO to a
suspension of B resulted in the formation of p-tolylisocyanate
in 58% yield, as observed by GCMS analysis of the reaction
mixture. Also present was a trace quantity of 1,3-di-p-
tolylcarbodiimide (4% yield). Similarly, the addition of
p-tolylisocyanide or p-tolyl isocyanate to B resulted in the
formation of 1,3-di-p-tolylcarbodiimide in 7% and 8% yield,
Figure 11. Thermal ellipsoid (50%) plot of 17. Hydrogen atoms and iso-
propyl methyl groups have been omitted for clarity.
Inorganic Chemistry, Vol. 48, No. 7, 2009 3285

Chomitz and Arnold
respectively. The carbodiimides likely form through nitrene
group transfer reactions; however, these reactions appear to
be slow compared to the thermal decomposition of B based
on the low yields of the organic products. Given our inability
to isolate any of the metal containing products from these
reactions, we cannot definitively say that nitrene group
transfer by a transient Co(III) imido is taking place.
Nonetheless, given the similarities in the structure and
reactivity of 2 and 16 and 6 and 17, it is reasonable to infer
that A and B would exhibit similar chemistries.
valent Co(I) compound supported solely by the [N2P2] ligand
possessing an open axial coordination site was also isolated,
and its reactivity with a number of small molecules was
probed. Changes in reactivity in select Co complexes was
probed following the replacement of the tert-butyl group on
the anionic nitrogen of [N2P2] with a p-tolyl group. Though
only minor changes were observed in the structural features
of the resulting complexes, increased nitrene group transfer
reactions were achieved.
Acknowledgment. We are grateful to the National Science
Foundation for financial support for parts of this work and
Dr. Fred Hollander and Dr. Antonio DiPasquale for crystal-
lographic assistance.
Conclusions
A range of Co complexes supported by [N2P2] ligands have
been explored. Complexes 3-5 demonstrate the robustness
of the [N2P2] ligand toward reactive Co-C and Co-H
functional groups. A common feature of this ligand set is
again evidenced in its Co chemistry, namely the coordination
mode of the [N2P2] framework can change to accommodate
steric and electronic demands of the metal center. A low-
Supporting Information Available: Crystallographic informa-
tion files (CIFs). This material is available free of charge via the
Internet at http://pubs.acs.org.
IC802337T
3286 Inorganic Chemistry, Vol. 48, No. 7, 2009