Coordinatively unsaturated W(IV)-bis(pyridine) complexes, a reactive source of W(IV)

Article abstract of DOI:10.1021/ic010195r

Addition of 2 equiv of a σ-donor ligand (L = pyridine, 4-picoline, or quinoline) to complexes of the type [W(NPh)(η⁴-arene)(o-(Me₃SiN)₂C ₆H₄)] (arene = CH₃CH₂C₆H₅ (3), CH₃CH₂CH₂C₆H₅ (4)) gave the W(IV)L₂ compounds, [W(NPh)(o-(Me₃SiN)₂C₆H₄)(C ₅H₅N)₂] (5), [W(NPh)(o-(Me₃SiN)₂C₆H₄)(p-C ₆H₇N)₂] (6), and [W(NPh)(o-(Me₃SiN)₂C₆H₄)(C ₉H₇N)₂] (7). Synthesis of compounds 5 and 6 by Na° reduction of [W(NPh)(o-(Me₃SiN)₂C₆H₄)Cl ₂] in the presence of 3 equiv of L (L = 5, pyridine or 6, 4-picoline) is also presented. Compounds 5, 6, and 7 display hindered rotation of the donor ligands about the W-N bonds, resulting from a steric interaction with the Me₃Si groups of the diamide ligand. The coordinative unsaturation of 5 and 6 has also been explored. Compounds 5 and 6 readily react with either CO and PMe₃ to generated the six coordinate complexes [W(NPh)(o-(Me₃SiN)₂C₆H₄)(C ₅H₅N)₂(CO)] (8a), [W(NPh)(o-(Me₃SiN)₂C₆H₄)(C ₆H₇N)₂(CO)] (8b), [W(NPh)(o-(Me₃SiN)₂C₆H₄)(C ₆H₅N)(PMe₃)₂] (10a), and [W(NPh)(o-(Me₃SiN)₂C₆H₄)(C ₆H₇N)(PMe₃)₂] (10b), respectively.

Full text of DOI:10.1021/ic010195r

Inorg. Chem. 2001, 40, 5077-5082
5077
Coordinatively Unsaturated W(IV)-Bis(pyridine) Complexes, a Reactive Source of W(IV)
R. C. Mills, S. Y. S. Wang, K. A. Abboud, and J. M. Boncella*
Department of Chemistry and Center for Catalysis, University of Florida,
Gainesville, Florida 32611-7200
ReceiVed February 15, 2001
Addition of 2 equiv of a σ-donor ligand (L ) pyridine, 4-picoline, or quinoline) to complexes of the type [W(NPh)-
(η4-arene)(o-(Me3SiN)2C6H4)] (arene ) CH3CH2C6H5 (3), CH3CH2CH2C6H5 (4)) gave the W(IV)L2 compounds,
[W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)2] (5), [W(NPh)(o-(Me3SiN)2C6H4)(p-C6H7N)2] (6), and [W(NPh)(o-(Me3-
SiN)2C6H4)(C9H7N)2] (7). Synthesis of compounds 5 and 6 by Na° reduction of [W(NPh)(o-(Me3SiN)2C6H4)Cl2]
in the presence of 3 equiv of L (L ) 5, pyridine or 6, 4-picoline) is also presented. Compounds 5, 6, and 7
display hindered rotation of the donor ligands about the W-N bonds, resulting from a steric interaction with the
Me3Si groups of the diamide ligand. The coordinative unsaturation of 5 and 6 has also been explored. Compounds
5 and 6 readily react with either CO and PMe3 to generated the six coordinate complexes [W(NPh)(o-(Me3-
SiN)2C6H4)(C5H5N)2(CO)] (8a), [W(NPh)(o-(Me3SiN)2C6H4)(C6H7N)2(CO)] (8b), [W(NPh)(o-(Me3SiN)2C6H4)-
(C5H5N)(PMe3)2] (10a), and [W(NPh)(o-(Me3SiN)2C6H4)(C6H7N)(PMe3)2] (10b), respectively.
Introduction
examining the chemistry of the chelate stabilized W(IV)-arene
complexes 3 and 4. To our disappointment, the reactivity of
compounds 3 and 4 has been limited, presumably due to a robust
metal-arene interaction. However, as has been observed and
well studied for other arene compounds,7-10 compounds 3 and
4 are susceptible to arene displacement by σ-donor ligands. In
continuation of our earlier work with W(IV)-arene compounds,4
we report the synthesis of a series of coordinatively unsaturated
W(IV)L2 compounds through arene displacement and initial
reactivity studies that suggest these compounds are a more
reactive source of W(IV) than the arene complexes.
In the course of our recent studies of the reactivity of
â-hydrogen containing W(VI)-dialkyl complexes of the type
W(NPh)(o-(Me3SiN)2C6H4)R2 (where R ) CH2CH3, CH2CMe3)1,2
with H2,3 we have established that d2 tungsten-arene complexes
with the general formula W(NPh)(η4-arene)(o-(Me3SiN)2C6H4)
(arene ) CH3CH2C6H5 (3), CH3CH2CH2C6H5 (4)) can be
synthesized by hydrogenolysis of the â-hydrogen containing
dialkyl complexes W(NPh)(o-(Me3SiN)2C6H4)(CH2CH2C6H5)2
(1) and W(NPh)(o-(Me3SiN)2C6H4) (CH2CH2CH2C6H5)2 (2), eq
1.4
Experimental Section
General Methods. All experimental procedures were conducted
under an inert atmosphere, either in a N2-filled drybox or by using
standard Schlenk techniques under an argon atmosphere. Anhydrous
tetrahydrofuran, pentane, and toluene were purchased from Sigma-
Aldrich, passed over a column of activated alumina, stored over 4 Å
molecular sieves, and degassed prior to use. Pyridine, 4-picoline, and
quinoline were degassed and stored over 4 Å molecular sieves prior to
use. PMe3 was purchased from Sigma-Aldrich and used without further
purification, and CO was passed over a column of activated 4 Å sieves
prior to use. W(NPh)[o-(Me3SiN)2C6H4]CH2CH2Ph)21 (1) and W(NPh)-
[o-(Me3SiN)2C6H4](CH2CH2CH2Ph)2 (2)4 were prepared according to
previously reported literature procedures. All other reagents were
obtained from Aldrich Chemicals and used as received unless otherwise
noted.
Since its beginnings in the mid 50’s, the chemistry of
transition metal π-arene complexes has been investigated in
considerable detail.5 Reports have demonstrated that a coordi-
nated arene can behave as a spectator ligand, labile ligand, or
substrate ligand.6 For these reasons, we became interested in
1H, 13C, and 31P NMR spectra were obtained on Varian Gemini 300,
VXR 300, or Mercury 300 instruments in C6D6 solutions, referenced
to residual solvent peaks, and reported relative to TMS. We have been
unable to obtain satisfactory elemental analyses of compounds 5, 6, 7,
8(a,b), 9(a,b), and 10(a,b). The carbon and nitrogen data are typically
* To whom correspondence should be addressed.
(1) Wang, S. Y. S.; Abboud, K. A.; Boncella, J. M. J. Am. Chem. Soc.
1997, 119, 11990-11991.
(2) Boncella, J. M.; Wang, S. Y. S.; Vanderlende, D. D.; Huff, R. L.;
Abboud, K. A.; Vaughn, W. M. J. Organomet. Chem. 1997, 530, 59-
70.
(3) Boncella, J. M.; Wang, S. Y. S.; Vanderlende, D. D. J. Organomet.
Chem. 1999, 591, 8-13.
(7) Lancaster, S. J.; Robinson, O. B.; Bochmann, M.; Coles, S. J.;
Hursthouse, M. B. Organometallics 1995, 14, 2456-2462.
(8) Lockwood, M. A.; Fanwick, P. E.; Rothwell, I. P. Polyhedron 1995,
14, 3363-3366.
(4) Mills, R. C.; Abboud, K. A.; Boncella, J. M. Organometallics 2000,
19, 2953-2955.
(5) Marr, G.; Rockett, B. W. The Chemistry of the Metal-Carbon Bond;
John Wiley & Sons: New York, 1982.
(9) Musso, F.; Solari, E.; Floriani, C.; Schenk, K. Organometallics 1997,
16, 4889-4895.
(6) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University
Science Books: 1987.
(10) Parker, K. G.; Noll, B.; Pierpont, C. G.; Dubois, M. R. Inorg. Chem.
1996, 35, 3228-3234.
10.1021/ic010195r CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/24/2001

5078 Inorganic Chemistry, Vol. 40, No. 20, 2001
Mills et al.
1-1.5% below the calculated values even for multiply recrystallized
samples, while the hydrogen data are within the acceptable range. We
suspect that the formation of W carbide and nitride during the
combustion process is responsible for these results. Proton NMR spectra
are included as Supporting Information.
and cooled to -78 °C. Two equivalents of PhMgCl (1.12 mL, 3.36
mmol) was then added by syringe. The reaction was allowed to warm
to room temperature and stir for 2 h, during which time the solution
became brown in color and a precipitate formed. The solvent was then
removed under reduced pressure, and the remaining brown-orange
solid was dried in vacuo. The solid was then extracted with pentane
and filtered until the filtrate was clear. The solution was concentrated
to 10 mL and cooled to -78 °C for 3 h. The resulting orange solid
was isolated by filtration and dried in vacuo to yield 0.77 g (68%) of
W(NPh)(o-(Me3SiN)2C6H4)Ph2 as a orange crystalline solid. 1H NMR
(25 °C, C6D6): δ 0.12 (s, 18H, SiMe3), 6.80-7.66 (m, 19H, aromatic).
13C NMR (25 °C, C6D6): δ 0.72 (SiMe3), aromatic: 123.14, 124.93,
125.69, 125.80, 128.18, 129.09, 131.67, 136.71, 156.25, 196.30. Anal.
Calcd for C32H41N3Si2W: C, 54.31; H, 5.84; N, 5.94. Found: C, 53.98;
H, 5.61; N, 5.69.
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)2 (5). Pyridine
(0.13 mL, 1.57 mmol) was added dropwise to a room-temperature
toluene solution of 4 (0.51 g, 0.79 mmol). Upon addition of pyridine,
the solution became dark purple in color. The mixture was stirred for
1 h at which time the solvent was stripped off, and the resulting solid
was dried in vacuo for 1 h. Subsequent washing with several portions
of cold pentane (0 °C), followed by drying the remaining solid in vacuo,
1
yielded 0.39 g (73%) of 5 as a dark purple solid. H NMR (25 °C,
C6D6): δ 0.45 (s, 18H, SiMe3), 4.97 (t, 2H, p-C5H5N), 5.71 (d, 2H,
o-C5H5N), 6.28 (t, 4H, m-C5H5N), 6.90 (m, 1H, p-WtNC6H5), 7.03
(m, 2H, o-pdaC6H4), 7.10-7.12 (m, 4H, o,m-WtNC6H5), 7.41 (m, 2H,
m-pdaC6H4), 7.82 (d, 2H, o-C5H5N). 13C NMR (25 °C, C6D6): δ 5.58
(SiMe3), 118.64 (o-pdaC6H4), 118.66 (m-pdaC6H4), 121.62 (m-C5H5N),
122.17 (m-C5H5N), 124.23 (p-WtNC6H5), 124.65 (o-WtNC6H5),
127.75 (m-WtNC6H5), 129.40 (p-C5H5N), 137.91 (o-C5H5N), 142.14
(o-C5H5N), 152.08 (pda C6H4), 158.76 (WtNC6H5).
Synthesis of 5 From W(NPh)(o-(Me3SiN)2C6H4)Cl2. To a disper-
sion of Na° (0.17 g, 7.24 mmol) in THF was added a THF solution of
W(NPh)(o-(Me3SiN)2C6H4)Cl2 (2.16 g, 3.62 mmol) and pyridine (0.88
mL, 10.09 mmol) at room temperature. The mixture was stirred for 30
min, during which time the solution changed from bright to dark purple
in color. The solvent was removed under reduced pressure, and the
resulting solid was extracted with toluene. Subsequent evaporation of
the toluene and drying in vacuo gave 2.25 g (91%) of 5.
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)2(CO) (8a). An
ampule fitted with a Teflon valve was charged with W(NPh)(o-(Me3-
SiN)2C6H4)(C5H5N)2 (5) (0.20 g, 0.29 mmol) and toluene (40 mL). The
mixture was frozen in liquid N2, and the flask was evacuated. Upon
warming to room temperature, the flask was charged with CO (20 psi).
The solution immediately turned brown in color. After stirring at room
temperature for 30 min, the reaction solvent was removed, and the
resulting solid was extracted with pentane. The filtrate was dried in
vacuo for 3 h to give 0.13 g (65%) of 8a as a dark-brown crystalline
1
solid. H NMR (C6D6, 25 °C): δ 0.35 (s, 9H, SiMe3), 0.37 (s, 9H,
SiMe3), 6.26 (t, 4H, m-C5H5N), 6.46 (t, 2H, p-C5H5N), 6.65 (m, 2H,
o-pdaC6H4), 6.86-7.10 (m, 5H, aromatic), 7.29 (d, 2H, o-WtNC6H5),
8.77 (d, 4H, o-C5H5N). 13C NMR (C6D6, 25 °C): δ 3.79 (SiMe3), 4.20
(SiMe3), aromatic; 115.62, 118.60, 119.16, 121.01, 124.02, 124.31,
125.03, 129.63, 137.08, 149.73, 150.64, 154.03, 158.57, 281.05 (Ct
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(p-C6H7N)2 (6). 4-Picoline
(0.07 mL, 0.77 mmol) was added dropwise to a room-temperature
toluene solution of 4 (0.25 g, 0.39 mmol). Upon addition of 4-picoline,
the solution became dark-purple in color. The mixture was stirred for
1 h at which time the solvent was stripped off, and the resulting solid
was dried in vacuo for 1 h. Subsequent washing with several portions
of cold pentane (0 °C), followed by drying the remaining solid in vacuo,
O). IR νCO ) 1889 cm-1
.
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(C6H7N)2(CO) (8b). Fol-
lowing the procedure used for the synthesis of 8a, W(NPh)(o-(Me3-
SiN)2C6H4)(p-C6H7N)2 (6) (0.75 g, 1.05 mmol) was exposed to a
positive pressure (20 psi) of CtO. Compound 8b (0.58 g, 76%) was
1
isolated as a dark-brown crystalline solid. H NMR (C6D6, 25 °C): δ
1
yielded 0.20 g (73%) of 6 as a dark purple solid. H NMR (C6D6, 25
0.41 (s, 9H, SiMe3), 0.45 (s, 9H, SiMe3), 1.47 (s, 6H, C6H7N), 6.17 (d,
4H, C6H7N), 6.65 (m, 2H, o-pdaC6H4), 6.88 (t, 1H, p-WtNC6H5),
6.94-7.13 (m, 6H, aromatic), 7.34 (d, 2H, o-WtNC6H5), 8.77 (d, 4H,
C6H7N). 13C NMR (C6D6, 25 °C): δ 3.89 (SiMe3), 4.29 (SiMe3), 20.44
(C6H7N) aromatic; 115.53, 118.62, 119.16, 121.00, 124.07, 124.91,
125.20, 129.60, 138.22, 149.25, 150.87, 153.64, 158.84, 283.91 (Ct
°C): δ 0.50 (s, 18H, SiMe3), 2.37 (s, 3H, C6H7N), 5.78 (d, 2H,
o-C6H7N), 6.28 (t, 4H, m-C6H7N), 6.93 (m, 1H, p-WtNC6H5), 7.07
(m, 2H, o-pdaC6H4), 7.10-7.14 (m, 4H, o,m-WtNC6H5), 7.48 (m, 2H,
m-pdaC6H4), 7.88 (d, 2H, o-C6H7N). 13C NMR (C6D6, 25 °C): δ 5.79
(SiMe3), 17.75 (p-CH3(C6H7N)), 118.51 (o-pdaC6H4), 118.64 (m-
pdaC6H4), 123.84 (m-C6H7N), 124.52 (m-C6H7N), 126.52 (p-Wt
NC6H5), 128.02 (o-WtNC6H5), 128.89 (m-WtNC6H5), 129.66 (p-
C6H7N), 141.13 (o-C6H7N), 142.26 (o-C6H7N), 152.88 (pdaC6H4),
159.29 (WtNC6H5).
Synthesis of 6 From W(NPh)(o-(Me3SiN)2C6H4)Cl2. To a disper-
sion of Na° (0.16 g, 7.24 mmol) in THF was added a THF solution of
W(NPh)(o-(Me3SiN)2C6H4)Cl2 (2.14 g, 3.62 mmol) and 4-picoline (0.88
mL, 10.09 mmol) at room temperature. The mixture was stirred for 30
min, during which time the solution changed from bright to dark purple
in color. The solvent was removed under reduced pressure, and the
resulting solid extracted with toluene. Subsequent evaporation of the
toluene and drying in vacuo gave 2.41 g (93%) of 6.
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(C9H7N)2 (7). Quinoline
(0.09 mL, 0.77 mmol) was added dropwise to a room-temperature
toluene solution of 4 (0.25 g, 0.39 mmol). Upon addition of quinoline,
the solution became turquoise in color. The mixture was stirred for 1
h at which time the solvent was stripped off, and the resulting solid
was dried in vacuo for 1 h. Subsequent washing with several portions
of cold pentane (0 °C), followed by drying the remaining solid in vacuo,
yielded 0.19 g (63%) of 7 as a black solid. 1H NMR (25 °C, C6D6): δ
0.38 (s, 18H, SiMe3), 5.00 (d, 2H, C9H7N), 5.55 (d, 2H, C9H7N), 6.38
(m, 2H, C9H7N), 6.49 (m, 2H, C9H7N), 6.76 (m, 4H, C9H7N), 6.97 (m,
1H, p-WtNC6H5), 7.05 (m, 2H, o-pdaC6H4), 7.25 (m, 2H, m-Wt
NC6H5), 7.39 (m, 2H, m-pdaC6H4), 7.51 (d, 2H, o-WtNC6H5), 8.91
(d, 2H, C9H7N). 13C NMR (25 °C, C6D6): δ 5.49 (SiMe3), aromatic;
116.08, 118.64, 118.85, 125.05, 125.17, 125.33, 125.95, 126.40, 129.66,
129.81, 131.29, 135.48, 142.90, 150.20.
O). IR νCO ) 1878 cm-1
.
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)(PMe3)(CO) (9a).
W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)2(CO) (8a) (0.30 g, 0.42 mmol) was
dissolved in pentane at room temperature, and to the resulting solution
was added PMe3 (0.04 mL, 0.42 mmol). The solution was allowed to
stir at room temperature for 30 min. The reaction solvent was removed,
and the resulting solid was extracted with pentane. The filtrate was
1
dried in vacuo to give 9a (0.22 g, 74%) as a dark-brown solid. H
NMR (C6D6, 25 °C): δ 0.21 (s, 9H, SiMe3), 0.30 (s, 9H, SiMe3), 0.97
(d, 9H, PMe3, 2JP-H ) 9.0 Hz), 6.38 (t, 2H, m-C5H5N), 6.80-7.12 (m,
8H, aromatic), 7.24 (d, 2H, o-WtNC6H5), 8.70 (d, 2H, o-C5H5N). 13
C
NMR (C6D6, 25 °C): δ 3.15 (SiMe3), 3.70 (SiMe3), 16.65 (PMe3, 1JP-C
) 28.4 Hz), aromatic; 114.98, 118.44, 118.52, 121.26, 122.99, 123.23,
123.82, 129.08, 137.20, 148.75, 150.90, 151.70, 158.21, 271.50 (Ct
O). 31P NMR (C6D6, 25 °C): δ -10.76 (PMe3, 1JW-P ) 188.8 Hz). IR
νCO ) 1905 cm-1
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(C6H7N)(PMe3)(CO) (9b).
Following the procedure used for the synthesis of 9a, W(NPh)(o-(Me3-
SiN)2C6H4)(p-C6H7N)2(CO) (8a) (0.25 g, 0.34 mmol) was reacted with
PMe3 (0.04 mL, 0.34 mmol) at room temperature. Compound 9b (0.21
g, 87%) was isolated as a dark-brown crystalline solid. 1H NMR (C6D6,
25 °C): δ 0.25 (s, 9H, SiMe3), 0.34 (s, 9H, SiMe3), 0.99 (d, 9H, PMe3,
2JP-H ) 9.3 Hz), 1.53 (s, 3H, C6H7N), 6.29 (d, 2H, C6H7N), 6.74-
7.05 (m, 7H, aromatic), 7.26 (d, 2H, o-WtNC6H5), 8.63 (d, 2H,
C6H7N). 13C NMR (C6D6, 25 °C): δ 3.69 (SiMe3), 4.25 (SiMe3), 17.00
1
(PMe3, JP-C ) 27.9 Hz), 20.66 (C6H7N), aromatic; 115.42, 118.91,
119.00, 121.74, 123.52, 123.64, 124.96, 125.42, 129.56, 149.39, 151.50,
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)Ph2. W(NPh)(o-(Me3-
SiN)2C6H4)Cl2 (1.0 g, 1.68 mmol) was dissolved in 50 mL of Et2O
151.86, 158.79, 273.20 (CtO). 31P NMR (C6D6, 25 °C): δ -10.71
1
(PMe3, JW-P ) 188.0 Hz). IR νCO ) 1903 cm-1
.

W(IV)-Bis(pyridine) Complexes
Inorganic Chemistry, Vol. 40, No. 20, 2001 5079
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)(PMe3)2 (10a).
W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)2 (5) (0.20 g, 0.29 mmol) was placed
in a Schlenk tube and dissolved in toluene (40 mL). To this solution
was added 2 equiv of PMe3 (0.06 mL, 0.59 mmol) at room temperature.
An immediate color change from purple to dark brown was observed.
The mixture was stirred at room temperature for 30 min, at which time
the reaction solvent was removed, and the resulting brown solid was
extracted with pentane. The filtrate was dried in vacuo for 3 h.
Compound 10a (0.15 g, 67%) was isolated as a dark-brown crystalline
Table 1. Selected Bond Distances (Å) and Angles (Deg) for 6
W-N1
W-N3
W-N2
W-N5
W-N4
1.753(3)
2.060(2)
2.062(3)
2.083(3)
2.109(3)
N3-W-N2
N5-W-N4
N2-W-N5
N3-W-N4
C1-N1-W
78.34(10)
80.33(10)
87.91(10)
88.80(10)
169.7(3)
Table 2. Selected Bond Distances (Å) and Angles (Deg) for 8a
W-N1
1.787(3)
2.139(3)
2.112(3)
2.203(3)
2.215(3)
1.985(4)
1.165(5)
92.67(14)
92.18(14)
173.39(12)
N1-W-C29
C29-W-N3
C29-W-N2
N1-W-N2
N2-W-N3
C29-W-N4
C29-W-N5
N3-W-N4
N3-W-N5
N2-W-N5
N2-W-N5
84.62(16)
86.83(15)
164.10(4)
110.34(14)
78.08(12)
96.07(14)
88.85(15)
89.23(12)
86.63(12)
88.77(12)
85.34(13)
1
solid. H NMR (C6D6, 25 °C): δ 0.13 (s, 9H, SiMe3), 0.19 (s, 9H,
W-N2 cis imido
W-N3 trans imido
W-N4
SiMe3), 1.10 (d, 9H, PMe3, 2JP-H ) 7.8 Hz), 1.43 (d, 9H, PMe3, 2JP-H
) 6.3 Hz), 6.40 (t, 1H, C5H5N), 6.51 (t, 1H, C5H5N), 6.70-7.10 (m,
8H, aromatic), 7.32 (d, 2H, o-WtNC6H5), 8.52 (d, 1H, C5H5N), 8.79
(d, 1H, C5H5N). 13C NMR (C6D6, 25 °C): δ 4.16 (SiMe3), 6.22 (SiMe3),
W-N5
W-C29
1
1
C29-O1
22.39 (PMe3, JP-C ) 24.5 Hz), 26.26 (PMe3, JP-C ) 22.4 Hz),
aromatic; 113.96, 118.66, 118.85, 120.95, 121.40, 121.56, 122.02,
125.07, 129.36, 136.40, 149.16, 152.23, 153.59, 155.62, 160.24. 31P
N1-W-N5
N1-W-N5
N4-W-N5
1
2
NMR (C6D6, 25 °C): δ -40.31 (PMe3, JW-P ) 157.9 Hz, JP-P
10.0 Hz), -24.09 (PMe3, JW-P ) 190.0 Hz, JP-P ) 10.0 Hz).
)
1
2
Synthesis of W(NPh)(o-(Me3SiN)2C6H4)(C6H7N)(PMe3)2 (10b).
Following the procedure used for the synthesis of 10a, W(NPh)(o-
(Me3SiN)2C6H4)(p-C6H7N)2 (6) (0.20 g, 0.28 mmol) was reacted with
PMe3 (0.06 mL, 0.56 mmol). Compound 10b (0.19 g, 86%) was isolated
benzene) (3) and W(NPh)[o-(Me3SiN)2C6H4) ](η4-propylben-
zene) (4) rapidly react with 2 equiv of pyridine, 4-picoline, or
quinoline at room temperature, giving W(NPh)(o-(Me3SiN)2-
C6H4)(C5H5N)2 (5) and W(NPh)(o-(Me3SiN)2C6H4)(p-C6H7N)2
(6) as dark purple solids and W(NPh)(o-(Me3SiN)2C6H4)-
(C9H7N)2 (7)as a black solid in good yield (60-75%), eq 2.
1
as a dark-brown crystalline solid. H NMR (C6D6, 25 °C): δ 0.17 (s,
9H, SiMe3), 0.24 (s, 9H, SiMe3), 1.11 (d, 9H, PMe3, 2JP-H ) 8.1 Hz),
1.46 (d, 9H, PMe3, 2JP-H ) 6.3 Hz), 1.83 (s, 3H, C6H7N), 6.24 (d, 1H,
C6H7N), 6.69 (d, 1H, C6H7N), 6.76 (t, 1H, p-WtNC6H5), 6.85-7.10
(m, 8H, aromatic), 8.51 (d, 1H, C6H7N), 8.72 (d, 1H, C6H7N). 13C NMR
(C6D6, 25 °C): δ 4.20 (SiMe3), 6.28 (SiMe3), 20.14 (C6H7N), 22.72
1
1
(PMe3, JP-C ) 24.2 Hz), 26.25 (PMe3, JP-C ) 22.4 Hz), aromatic;
113.90, 118.64, 118.87, 120.98, 121.43, 121.50, 122.04, 124.91, 125.11,
129.37, 148.48, 152.14, 153.49, 155.79, 160.43. 31P NMR (C6D6, 25
1
2
°C): δ -39.93 (PMe3, JW-P ) 159.0 Hz, JP-P ) 10.0 Hz), -24.09
1
2
(PMe3, JW-P ) 192.5 Hz, JP-P ) 10.0 Hz).
X-ray Experimental for Compounds 6 and 8a. Crystals of 6
suitable for diffraction studies were obtained from an unstirred pentane
reaction mixture at room temperature. Crystals of 8a were obtained
from a concentrated Et2O solution that was stored at -40 °C for 1
week. Data were collected at 173 K on a Siemens SMART PLAT-
FORM equipped with A CCD area detector and a graphite monochro-
mator utilizing Mo KR radiation (λ ) 0.71073 Å). Cell parameters
were refined using up to 8192 reflections. A hemisphere of data (1381
frames) was collected using the ω-scan method (0.3° frame width).
The first 50 frames were remeasured at the end of data collection to
monitor instrument and crystal stability (maximum correction on I was
< 1%). Absorption corrections by integration were applied based on
measured indexed crystal faces.
Additional purification of the crude products is possible through
subsequent washings with cold pentane (0 °C) followed by
1
drying the resulting solid in vacuo. The room temperature H
and 13C NMR spectra of 5, 6, and 7 are consistent with
monomeric L2 adducts where the donor ligands are coordinated
in an η1(N) fashion. In particular, upon coordination the
resonances for the donor ligand protons are shifted upfield with
respect to the free ligand.12 Interestingly, the ortho ring protons
of the nitrogen donor ligands display significantly different
chemical shifts (5.69 and 7.80 ppm, for 5), Figure 1, suggesting
that there is hindered rotation of the rings about the W-N bonds
with respect to the time scale of the NMR experiment. In
addition, it is important to note that at 300 MHz the meta protons
appear as overlapping triplets (6.28 ppm), however, at 500 MHz
two triplets are observed. The corresponding carbon atoms are
resolved at 300 MHz and resonate at 121.62 and 122.17 ppm,
respectively.
The structures were solved by the direct methods in SHELXTL511
and refined using full-matrix least squares. The non-H atoms were
treated anisotropically, whereas the hydrogen atoms were calculated
in ideal positions and were riding on their respective carbon atoms.
For compound 6, the N1 imido and the N5 methylpyridyl ligands are
slightly disordered in their planes but could not be resolved. This is
evidenced by the larger than normal and elongated thermal ellipsoids
of their atoms. A total of 351 parameters were refined in the final cycle
of refinement using 6092 reflections with I > 2σ(I) to yield R1 and
wR2 of 2.48% and 5.63%, respectively. Refinement was done using
F2. For compound 8a, the asymmetric unit consists of one complex
and a half diethyl ether disordered over a center of inversion (1/2 ether
in the asymmetric unit). The ether was refined in two parts and their
occupancy was fixed at 50% due to symmetry. A total of 369 parameters
were refined in the final cycle of refinement using 6907 reflections
with I > 2σ(I) to yield R1 and wR2 of 3.07% and 7.48%, respectively.
Refinement was done using F2. Details of data collection, solution,
and refinement are given in Table 3.
The structure of the L2 adducts was confirmed by an X-ray
diffraction analysis of a single crystal of 6, grown from an
unstirred reaction mixture in pentane at room temperature,
Figure 2. Selected bond lengths and angles are presented in
Table 1. The coordination geometry about the W atom in 6 is
best described as distorted square pyramidal, with the W atom
displaced 0.69 Å out of the N2-N3-N4-N5 plane. The W-N1
bond length of 1.753(3) Å is consistent with typical W-N imido
bond lengths,2,4,13 and the W-N(pic) distances of 2.083(3) and
Results and Discussion
Arene Displacement Reactions. Pentane solutions of the
W(IV)-arene complexes W(NPh)[o-(Me3SiN)2C6H4) ](η4-ethyl-
(12) Kriley, C. E.; Fanwick, P. E.; Rothwell, I. P. J. Am. Chem. Soc. 1994,
116, 5225-5232.
(13) Blosch, L. L.; Gamble, A. S.; Abboud, K.; Boncella, J. M. Organo-
metallics 1992, 11, 2342-2344.
(11) Sheldrick, G. M. SHELLXT [Nicolet XRD]. Madison, WI, 1986.

5080 Inorganic Chemistry, Vol. 40, No. 20, 2001
Mills et al.
Table 3. Crystal Data and Structure Refinement Details for 6 and 8a
6
8a
empirical formula
FW
temp.
C30 H41 N5 Si2 W
711.71
173(2) K
C31 H42 N5 O Si2 W
748.73
173(2) K
wavelength
Cryst syst
space group
unit cell dimensions
0.71073 Å
monoclinic
P2(1)/c
a ) 13.6142(7) Å R ) 90°
b ) 12.7895(6) Å â ) 101.720(1)°
c ) 19.0541(1) Å γ ) 90°
3248.4(3) Å3
0.71073 Å
triclinic
P-1
a ) 10.0740(7) Å R ) 69.341(1)°
b ) 12.0912(9) Å â ) 78.022(1)°
c ) 15.336(1) Å γ ) 76.008(1)°
1680.6(2) Å3
volume
Z
4
2
density (calculated)
absorption coefficient
F(000)
cryst size
θ range for data collection
index ranges
1.455 Mg/m3
1.480 Mg/m3
3.656 mm-1
3.540 mm-1
1432
754
0.30 × 0.18 × 0.06 mm3
0.39 × 0.32 × 0.02 mm3
1.93-27.50°
1.83-27.50°
-17 e h e 16, -16 e k e 14,
-24 e l e 23
-13 e h e 12, -15 e k e 8,
-19 e l e 18
reflns collected
22571
11730
independent reflections
Completeness to θ ) 27.49°
absorption correction
max. and min. transmission
Refinement method
7453 [R(int) ) 0.0352]
7565 [R(int) ) 00399]
99.9%
98.1%
integration
integration
0.8168 and 0.4250
full-matrix least-squares on F2
7453/0/351
0.9287 and 0.3380
Full-matrix least-squares on F2
7565/0/369
data/restraints/parameters
GOF on F2
1.034
1.061
Final R indices [I > 2σ(I)]
R indices (all data)
largest diff. peak and hole
R1 ) 0.0248, wR2 ) 0.0563
R1 ) 0.0366, wR2 ) 0.0626
1.375 and -0.720 e.Å-3
R1 ) 0.0307, wR2 ) 0.0748
R1 ) 0.0359, wR2 ) 0.0801
1.330 and -1.534 e.Å-3
1
Figure 1. Room temperature H NMR spectra of [W(NPh)[o-(Me3-
SiN)2C6H4](C5H5N)2] (5) with pyridine ring proton assignments.
Figure 2. Molecular structure of [W(NPh)(o-(Me3SiN)2C6H4)(p-
C6H7N)2] (6), showing 50% thermal ellipsoids and the atom labeling
scheme.
2.109(3) Å are shorter than what is typically found (2.30 Å)
for W-N(py) bond lengths.12,14-16
Bonding Explanation for Hindered Rotation in 5, 6, and
7. The structural data for 6 combined with a basic understanding
of the bonding in these complexes provides an explanation for
the unexpected slow rotation of the pyridine rings at room
center.1 Maximum π donation occurs when the N p orbitals are
rotated into the xy plane of the metal center. To approach this
conformation, the ligand folds along the N-N vector, giving
the observed structures. Recently, DFT calculations performed
by Galindo17 have confirmed these qualitative arguments.
In contrast to the W(VI) complexes, compound 6 has an
almost planar diamide ligand (fold angle ) 5.3°). The structural
difference arises because in 6 the dxy orbital contains a pair of
electrons. To avoid a filled-filled interaction between the dxy
orbital and nitrogen pπ orbitals, the nitrogen pπ orbitals rotate
out of the xy plane, away from the dxy orbital. Upon rotation,
the diamide ligand is flattened. This conformation moves the
SiMe3 groups into the xy plane (The plane of the pyridine rings).
This creates a steric interaction between the SiMe3 groups and
the Py ligands that is the source of the observed hindered rotation
of the pyridine rings about the W-N bonds.
1
temperature that is observed in the H NMR spectra of 5, 6,
and 7. The conformation of the diamido ligand in 6 is
significantly different from that observed in the W(VI) com-
pounds we have previously studied.2 In the W(VI) complexes,
an angle of ca. 50° is formed by the plane defined by the W
and two amide N atoms and the plane defined by the two amide
N atoms and the phenylene ring. We suggested that the folding
of the TMS2pda ligand in the do complexes arises because of π
donation from the amide N atoms to the LUMO (dxy) on the W
(14) Chisholm, M. H.; Cook, C. M.; Folting, K.; Streib, W. E. Inorg. Chim.
Acta 1992, 200, 63-77.
(15) Arnaudet, L.; Bougon, R.; Buu, B.; Lance, M.; Nierlich, M.; Thuery,
P.; Vigner, J. J. Fluor. Chem. 1995, 71, 123-129.
(16) Wesemann, L.; Waldmann, L.; Ruschewitz, U.; Ganter, B.; Wagner,
T. J. Chem. Soc., Dalton Trans. 1997, 6, 1063-1068.
(17) Galindo, A.; Ienco, A.; Mealli, C. New J. Chem. 2000, 24, 73-75.

W(IV)-Bis(pyridine) Complexes
Inorganic Chemistry, Vol. 40, No. 20, 2001 5081
We have synthesized the complex W(NPh)[o-(Me3SiN)2C6H4]-
Ph2 as a W(VI) model of compounds 5-7, and we observe free
rotation of the phenyl rings about the W-C bonds. Because
this compound has a d0 electronic configuration, we would
expect that the o-(Me3SiN)2C6H4 ligand is folded along the N-N
vector as it is in all other M(VI) (M ) Mo, W) complexes of
this type. This folding of the ligand moves the SiMe3 groups
out of the xy plane of the molecule, thus relieving the steric
congestion in the complex that would cause hindered rotation
about the W-C bonds.
Na° Reduction of W(NPh)[o-(Me3SiN)2C6H4]Cl2 with
Pyridine or Picoline. Although our initial discovery of the
W(IV)L2 compounds through arene displacement from either 3
or 4 allowed us to characterize compounds 5, 6, and 7. To study
their chemistry more easily, a more efficient synthetic pathway
was necessary. In light of this, we have discovered that
compounds 5 and 6 can be generated from W(NPh)(o-(Me3-
SiN)2C6H4)Cl2 in one step. Na° reduction of a THF solution of
the W(VI)-dichloride, in the presence of pyridine or 4-picoline,
produces 5 and 6 with improved purity and yield (> 90%), eq
3.
Figure 3. Molecular structure of [W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)2-
(CO)] (8a), showing 50% thermal ellipsoids and the atom labeling
scheme.
center. As a result, there is a slight lengthening of the W-N1-
(imido) bond distance (1.787(3) Å) of 8a in comparison to that
observed for complex 6 (1.753(3) Å), where position trans to
the imido is unoccupied. The largest distortions from a purely
octahedral geometry are the N1-W-N2 (110.34(14)°) and N2-
W-N3 (78.08(12)°) bond angles, which can be attributed to
the restricted bite of the chelate ring.
The value of the CO stretching frequencies, νCO ) 1890 cm-1
(8a) and 1878 cm-1 (8b), are unusually low for what might be
expected for high oxidation state (W(IV), d2) complexes. It is
likely that the ability of the W to backbond to the CO ligand is
significantly enhanced relative to what might be expected
because the amide N that is trans to the CO ligand is a π donor
ligand, which enhances the backbonding thereby relieving an
unfavorable Npπ-Wdπ filled-filled interaction.
Isolation of pure 5 and 6 is accomplished by removal of the
THF in vacuo followed by toluene extraction to separate the
desired products from NaCl, the major byproduct of the reaction.
Subsequent removal of toluene from the filtrate solution
followed by drying the resulting solid in vacuo for 3 h yields 5
and 6 as dark purple, crystalline solids.
Addition of a Sixth Ligand to W(IV)L2. We have found
that the W(IV)L2 compounds are coordinatively unsaturated and
readily accommodate additional ligands. For example, reaction
of W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)2 (5) or W(NPh)(o-(Me3-
SiN)2C6H4)(p-C6H7N)2 (6) with CO (20 psi) results in the rapid
formation of the six coordinate complexes W(NPh)(o-(Me3-
SiN)2C6H4)(C5H5N)2(CO) (8a) and W(NPh)(o-(Me3SiN)2C6H4)-
(C6H7N)2(CO) (8b), eq 4.
The room temperature 1H NMR spectra of 8a and 8b display
two peaks (0.34 and 0.37 ppm (8a), 0.41 and 0.45 ppm (8b))
that are assigned to inequivalent Si(CH3)3 groups. The inequiva-
lence of the Si(CH3)3 groups is consistent with the structural
result which places the NSiMe3 groups cis and trans to the imido
1
group.3 In contrast to the H NMR spectra of the W(IV)L2
compounds 5, 6, and 7, there is only one set of pyridine ring
protons for 8a and 8b due to unhindered rotation and the
equivalency of the rings in the octahedral geometry. The 13C
NMR spectra of 8a and 8b display resonances at 281 and 284
ppm, respectively, corresponding to the CO ligands.
Ligand Substitution Reactivity. Examination of the chem-
istry of the six-coordinate compounds 8a and 8b led to the
observation that one of the N donor ligands is labile and can
be displaced. This was demonstrated by the reaction of W(NPh)-
(o-(Me3SiN)2C6H4)(C5H5N)2(CO) (8a) and W(NPh)(o-(Me3-
SiN)2C6H4)(C6H7N)2(CO) (8b) with PMe3 to give the substi-
tution products W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)(CO)(PMe3)
(9a) and W(NPh)(o-(Me3SiN)2C6H4)(C6H7N)(CO)(PMe3) (9b),
eq 5.
An X-ray diffraction study was performed on a single crystal
of 8a, which was grown from a concentrated Et2O solution at
-40 °C. The molecular structure is shown in Figure 3 and
selected bond distances and angles are presented in Table 2.
Complex 8a adopts a pseudo-octahedral geometry about the W
atom, with the pyridine groups occupying mutually trans
positions. Consequently, the phenyl-imido is cis and trans to
the NSiMe3 groups, and CO occupies the remaining equatorial
position. As a consequence of this geometrical arrangement of
ligands (imido trans to amide), there is competition between
the π-donation of the imido and amide ligands to the metal
As was found for 8a and 8b, the 1H NMR spectra of compounds
9a and 9b are consistent with rapidly rotating N donor ligands.

5082 Inorganic Chemistry, Vol. 40, No. 20, 2001
Mills et al.
Due to the coordinative saturation of 8a and 8b, we believe
that the reaction proceeds through a dissociative pathway in
which a five coordinate W(NPh)(o-(Me3SiN)2C6H4)(CO)L
intermediate is trapped by the incoming PMe3 ligand.
In agreement with the proposed lability of one of the N donor
ligands in the six coordinate complexes 8a and 8b, reaction of
W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)2 (5) or W(NPh)(o-(Me3-
SiN)2C6H4)(C6H7N)2 (6) with 2 equiv of PMe3 results in the
rapid formation of W(NPh)(o-(Me3SiN)2C6H4)(C5H5N)(PMe3)2
(10a) and W(NPh)(o-(Me3SiN)2C6H4)(C6H7N)(PMe3)2 (10b),
respectively, with loss of 1 equiv of pyridine, eq 6.
Hz) for 10a and (2JP-P ) 10.0 Hz) for 10b that have 183W
1
satellites (1JW-P ) 190 and 158 Hz (10a), JW-P ) 193 and
159 Hz (10b)). The small 2JP-P values are consistent with a cis
orientation (axial and equatorial) of the PMe3 groups,18 leaving
the pyridine group as the remaining ligand of the octahedral
complex. A cis-orientation of the PMe3 groups also accounts
1
1
for the difference in the JW-P values. The larger JW-P value
corresponds to the PMe3 group which is trans to pyridine, and
the smaller value for the PMe3 trans to amide, as would be
expected with the amide group having a greater trans influence
than pyridine.
Summary and Conclusions
The Na° reduction of W(NPh)[o-(Me3SiN)2C6H4]Cl2 in the
presence of donor ligands such as pyridine or 4-picoline provides
a simple and efficient means for producing the coordinatively
unsaturated W(IV)L2 compounds 8a and 8b. The reactions of
compounds 5 and 6 with additional ligands, presented in this
paper, serve to demonstrate the reactive nature of these
compounds. In addition to the increased reactivity with respect
to the W(IV)-arene complexes, the W(IV)L2 compounds are,
to our knowledge, very rare examples of bispyridine complexes
with hindered rotation about the M-N(py) bonds. Based on
our initial observations of the lability of the N donor ligands
upon formation of six-coordinate complexes, we believe that
these compounds will display very rich chemistry and are
currently exploring this possibility.
Displacement of pyridine or 4-picoline by a second PMe3 group
to generate compounds 10a and 10b is preferred; this is
demonstrated by the reaction of compound 5 or 6 with 1 equiv
of PMe3, which produces a 1:1 mixture of the bisphosphine
complexes 10a or 10b and W(IV)L2, as determined by NMR
spectroscopy.
1
Similar to compounds 8a and 8b, the room temperature H
Acknowledgment. J.M.B. thanks the National Science
Foundation (CHE 9523279 and CHE 0094404) for funding of
this work, and K.A.A. thanks the NSF and the University of
Florida for funding X-ray equipment purchases.
NMR spectra of 10a and 10b display two peaks (0.14 and 0.20
ppm (10a), 0.17 and 0.24 ppm (10b)) assigned to the inequiva-
lent Si(CH3)3 groups, again due to a cis and trans orientation
with respect to the imido group.3 Unlike the previously described
six-coordinate complexes, the N donor ligand of 10a and 10b
display hindered rotation. The PMe3 protons appear as doublets
at 1.09 ppm (2JP-H ) 7.3 Hz) and 1.43 ppm (2JP-H ) 6.3 Hz)
for 10a and 1.12 ppm (2JP-H ) 8.1 Hz) and 1.46 (2JP-H ) 6.3
Hz) for 10b, which is consistent with inequivalent PMe3 groups.
The 31P NMR spectra of 10a and 10b confirm this inequiva-
lence, as the PMe3 groups appear as two doublets (2JP-P ) 9.5
Supporting Information Available: X-ray crystallographic files
for 6 and 8a, in CIF format, and 1H NMR spectra of compounds 5-10b.
This material is available free of charge via the Internet at http://
pubs.acs.org.
IC010195R
(18) Pregosin, P. S. Stereochemistry of Metal Complexes in Phosphorus-
31 NMR Spectroscopy; VCH: Florida, 1987.