Structural and spectroscopic studies of 16-electron, unsaturated derivatives of low-valent, group 6 carbonyl complexes containing π-donor ligands

Article abstract of DOI:10.1021/ic9804216

Several eighteen- and sixteen-electron derivatives of tungsten(0), molybdenum(0), and chromium(0) carbonyl complexes, including [PPN]₂[Cr(CO)₃(O,S-C₆H₄)] (2c), [PPN]₂[W(CO)₃(NH,S-C₆H₄)] (5c), [PPN]₂[W(CO)₃(O,SC₆H₄)] (6c), [PPN]₂[W(CO)₄(S,S-C₆H₄)] (7b) have been synthesized from the reaction of photochemically generated M(CO)₅THF with a series of doubly deprotonated 1,2-disubstituted benzene rings with the appropriate oxygen, nitrogen, and sulfur donor atoms. These complexes have been characterized in the solid state by X-ray crystallography and in solution by IR and ¹³C NMR spectroscopies. The crystal of 2c (C₈₄H₇₁N₃O₅P₄Cr) is triclinic P1?, a = 13.869(3) ?, b = 23.128(5) ?, c= 12.056(2) ?, α = 104.84(3)°, β= 106.91(3)°, γ = 95.29(3)°, Z = 2; that of 5c (C₈₉H₇₇N₇O₃P₄SW) is monoclinic P2_1, a = 11.054(2) ?, b = 28.140(6) ?, c = 12.566(2) ?, β = 90.58(1)°, Z = 2; that of 6c (C₈₅H₇₀N₄O₄P₄SW) is triclinic P1?, 12.236(2) ?, b = 14.419(2) ?, c = 22.748(4) ?, α = 76.44(1)°, β= 75.98(2)°, β = 70.98(1)°, Z = 2; that of 7b (C₈₂H₆₄N₂O₄P₄S ₂W) is triclinic P1?, a = 12.650(1) ?, b = 14.810(1) ?, c = 21.053(2) ?, α = 77.182(7)°, β = 78.334(7)°, γ = 66.579(7), Z = 2; and that of 8 (C₁₀H₈O₄P₂W) is monoclinic P2₁/c, a = 11.582(1) ?, b = 10.791(1) ?, c = 10.449(1) ?, β = 100.867(7)°, Z = 2. The average v(CO) frequencies for each tricarbonyl species reported are compared to those related dianions previously reported in order to gauge the π-donor character of the different ligands. The ¹³C NMR spectrum for each tricarbonyl derivative consists of a single sharp peak for the three inequivalent carbonyls as a result of a low-energy, fast intramolecular exchange process. Both inter- and intramolecular CO-exchange processes have been probed via variable temperature ¹³C NMR. In the case of the 16-electron species the geometry of the metal dianion is that of a distorted trigonal bipyramid consisting of three carbonyl ligands and a five-membered chelate ring bound through the π-donor atoms at an equatorial and an axial position, with the stronger π-donor atom in the equatorial site. The equatorial site for the most effective π-donor is preferred over the axial position because the unoccupied d_xy orbital lies in the equatorial plane, and may be stabilized via a π-donor ligand in the equatorial position. The axial position exhibits a filled/filled repulsion as both orbitals available for π-bonding are filled.

Full text of DOI:10.1021/ic9804216

Inorg. Chem. 1999, 38, 4705-4714
4705
Structural and Spectroscopic Studies of 16-Electron, Unsaturated Derivatives of
Low-Valent, Group 6 Carbonyl Complexes Containing π-Donor Ligands
Donald J. Darensbourg,* Jennifer D. Draper, Brian J. Frost, and Joseph H. Reibenspies
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842
ReceiVed April 13, 1998
Several eighteen- and sixteen-electron derivatives of tungsten(0), molybdenum(0), and chromium(0) carbonyl
complexes, including [PPN]2[Cr(CO)3(O,S-C6H4)] (2c), [PPN]2[W(CO)3(NH,S-C6H4)] (5c), [PPN]2[W(CO)3(O,S-
C6H4)] (6c), [PPN]2[W(CO)4(S,S-C6H4)] (7b) have been synthesized from the reaction of photochemically generated
M(CO)5THF with a series of doubly deprotonated 1,2-disubstituted benzene rings with the appropriate oxygen,
nitrogen, and sulfur donor atoms. These complexes have been characterized in the solid state by X-ray
crystallography and in solution by IR and 13C NMR spectroscopies. The crystal of 2c (C84H71N3O5P4SCr) is
triclinic P1h, a )13.869(3) Å, b ) 23.128(5) Å, c ) 12.056(2) Å, R ) 104.84(3)°, â ) 106.91(3)°, γ ) 95.29(3)°,
Z ) 2; that of 5c (C89H77N7O3P4SW) is monoclinic P21, a ) 11.054(2) Å, b ) 28.140(6) Å, c ) 12.566(2) Å,
â ) 90.58(1)°, Z ) 2; that of 6c (C85H70N4O4P4SW) is triclinic P1h, 12.236(2) Å, b ) 14.419(2) Å, c ) 22.748(4)
Å, R ) 76.44(1)°, â ) 75.98(2)°, γ ) 70.98(1)°, Z ) 2; that of 7b (C82H64N2O4P4S2W) is triclinic P1h, a )
12.650(1) Å, b ) 14.810(1) Å, c ) 21.053(2) Å, R ) 77.182(7)°, â ) 78.334(7)°, γ ) 66.579(7), Z ) 2; and that
of 8 (C10H8O4P2W) is monoclinic P21/c, a ) 11.582(1) Å, b ) 10.791(1) Å, c ) 10.449(1) Å, â ) 100.867(7)°,
Z ) 2. The average ν(CO) frequencies for each tricarbonyl species reported are compared to those related dianions
previously reported in order to gauge the π-donor character of the different ligands. The 13C NMR spectrum for
each tricarbonyl derivative consists of a single sharp peak for the three inequivalent carbonyls as a result of a
low-energy, fast intramolecular exchange process. Both inter- and intramolecular CO-exchange processes have
been probed via variable temperature 13C NMR. In the case of the 16-electron species the geometry of the metal
dianion is that of a distorted trigonal bipyramid consisting of three carbonyl ligands and a five-membered chelate
ring bound through the π-donor atoms at an equatorial and an axial position, with the stronger π-donor atom in
the equatorial site. The equatorial site for the most effective π-donor is preferred over the axial position because
the unoccupied dxy orbital lies in the equatorial plane, and may be stabilized via a π-donor ligand in the equatorial
position. The axial position exhibits a filled/filled repulsion as both orbitals available for π-bonding are filled.
Introduction
Scheme 1
(A)
(B)
The dissociative mechanism that affords an intermediate of
reduced coordination number, is by far the most common
pathway for substitution reactions involving 18-electron metal
carbonyl derivatives. It has been well established that ancillary
ligands capable of π-donation can stabilize these coordinatively
unsaturated intermediates generated in ligand substitution reac-
tions.1,2 This stabilization due to π-donation may have two
outcomes: (i) the rate of exchange increases in proportion to
the degree of stabilization imparted by the π-donor (D) to result
in product B (Scheme 1)3 or (ii) the π-donation is sufficient to
stabilize the unsaturated intermediate, A; i.e., the intermediate
is stabilized to the extent that the formation of a M-X bond is
either thermodynamically unfavorable or only slightly favorable
such that A is isolable.4-8
Over the last several years, considerable efforts have been
directed into understanding the nature of π-donor ligands as
they relate to A and B above. That is, what are the properties
of π-donor ligands that cause B to be favored over A? Pursuant
to answering these questions the synthesis and structural
characterizations of several group 6 zerovalent unsaturated
carbonyl species consistent with A (Scheme 1) have been
published.7-11
In previous studies the exclusive use of ligands containing
oxygen and nitrogen donor atoms, both exceptional π-donors,
limited the ability to examine the equilibrium between A and
(1) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
John Wiley & Sons: New York, 1988.
(2) Basolo, F.; Pearson, R. G. Mechanisms of Inorganic Reactions, 2nd
ed.; Wiley and Sons: New York, 1967.
(3) Darensbourg, D. J.; Sanchez, K. M.; Reibenspies, J. H.; Rheingold,
A. L. J. Am. Chem. Soc. 1989, 111, 7094.
(4) Lunder, D. M.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G. J.
Am. Chem. Soc. 1991, 113, 1837.
(5) Ashby, M. T.; Enemark, J. H. J. Am. Chem. Soc. 1986, 108, 730.
(6) Hubbard, J. L.; McVicar, W. K. Inorg. Chem. 1992, 31, 910.
(7) Sellmann, D.; Wilke, M.; Knoch, F. Inorg. Chem. 1993, 32, 2534.
(8) Sellmann, D.; Ludwig, W.; Huttner, G.; Zsolnai, L. J. Organomet.
1985, 294, 199.
(9) Darensbourg, D. J.; Klausmeyer, K. K.; Mueller, B. C.; Reibenspies,
J. H. Angew. Chem., Int. Ed. Engl. 1992, 31, 1503.
(10) Darensbourg, D. J.; Klausmeyer, K. K.; Reibenspies, J. H. Inorg. Chem.
1996, 35, 1529.
(11) Darensbourg, D. J.; Klausmeyer, K. K.; Reibenspies, J. H. Inorg. Chem.
1996, 35, 1535.
10.1021/ic9804216 CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/23/1999

4706 Inorganic Chemistry, Vol. 38, No. 21, 1999
Darensbourg et al.
C6H4)2-,(O,S-C6H4)2-, or (S,S-C6H4)2-] was accomplished in yields in
excess of 80% by the reaction of 1 equiv of M(CO)5THF (prepared by
the photolysis of 0.300 g of Cr(CO)6, 0.400 g of Mo(CO)6, or 0.500 g
of W(CO)6 in THF) with 1 equiv (1.4 mmol) of the appropriate
deprotonated ligand at ambient temperature.
B by favoring the formation of the 16-electron product.
Specifically of interest now is eq 1, where M ) Cr(0), Mo(0),
or W(0), and X and Y are π-donor atoms appended to the phenyl
ring.
Synthesis of [PPN]2[M(CO)4(X)] Derivatives (1b-7b). The syn-
thesis of [PPN]2[M(CO)4(X)] was accomplished by the slow addition
of a second equivalent (1.4 mmol) of NaOMe and PPNCl, dissolved
in 5 mL in a 1:1 CH3CN/CH3OH, to the THF solution of the
pentacarbonyl derivative (1a-7a) to yield a dark red solution. The
M(CO)5THF intermediates were identified by their ν(CO) infrared
spectra: M ) Cr, 2073 (w), 1936 (s), 1894 (m); M ) W, 2073(w),
1929 (s), 1890 (m) cm-1. Longer photolysis times for W(CO)6 will
lead to production of cis-W(CO)4(THF)2, ν(CO): 2013 (w), 1876 (vs),
1830 (m) cm-1. The mixture was allowed to stir 60 min after which
the solvent was removed via vacuum overnight. The resulting dark red
powder was dissolved in CH3CN, filtered through Celite to remove
the insoluble NaCl and washed several times with 10 mL portions of
hexanes to remove any residual M(CO)6. Anal. Calcd for [PPN]2[Cr-
(CO)4(NH,S-C6H4)] (1b) (C82H65N3O4P4SCr): C, 72.19; H, 4.80; N,
3.08. Found C, 71.92; H, 4.75; N, 2.98. [PPN]2[Cr(CO)4(O,S-C6H4)]
(2b) (C82H64N2O5P4SCr): C, 72.13; H, 4.72; N, 2.05. Found: C, 71.30;
H, 4.54; N, 1.93. [PPN]2[Mo(CO)4(O,S-C6H4)] (4b) (C82H64N2O5P4-
SMo): C, 69.89; H, 4.58; N, 1.99. Found: C, 68.93; H, 4.35; N, 2.03.
[PPN]2[W(CO)4(O,S-C6H4)] (6b) (C82H64N2O5P4SW): C, 65.78; H,
4.31; N, 1.87. Found: C, 65.32; H, 4.24; N, 1.82. [PPN]2[W(CO)4-
(S,S-C6H4)] (7b) (C82H64N2O4P4S2W): C, 65.08; H, 4.26; N, 1.85.
Found: C, 64.04; H, 4.24; N, 1.89.
Synthesis of [PPN]2[M(CO)3(X)] Derivatives (1c-7c). The syn-
thesis of the unsaturated, 16-electron tricarbonyl derivative was
accomplished by bubbling Argon through a gently heated (40 °C) CH3-
CN solution of the tetracarbonyl derivative. Because of their extreme
air-sensitivity, and because of their propensity to exist as a mixture of
tetra- and tricarbonyl species, elemental analyses were in general not
obtained for complexes 1c-7c. However, infrared spectroscopy studies
in the υ(CO) region carried out on the crystals of 1c, 5c, and 6c offered
spectra that match that of the bulk sample. Furthermore, it was possible
to obtain satisfactory elemental analysis for 6c which crystallized with
two molecules of acetonitrile in the lattice. Anal. Calcd for [PPN]2-
[W(CO)3(O,S-C6H4)]‚2CH3CN (C85H70N4O4P4SW): C, 65.81; H, 4.55;
N, 3.61. Found: C, 65.02; H, 4.38; N, 3.54.
Synthesis of W(CO)4(PH2C6H4PH2), 8. The synthesis of W(CO)4-
(PH2C6H4PH2) was accomplished in 75% yield by the reaction of 0.10
g (0.704 mmol) of diphosphinobenzene (31P NMR (CD3CN) δ -124.6
ppm) with 1 equiv of W(CO)4(piperidine)2 [IR, ν(CO): THF, 2002.0
(w), 1860.2 (vs), 1824.6 (m)] at 40 °C in THF for 2 h. The solvent and
free piperidine were removed via vacuum to yield a light brown powder.
IR, ν(CO): CH3CN, 2033.8 (w), 1944.1 (w), 1924.8 (vs) (in CH3CN).
31P NMR (CD3CN) δ -62.4 ppm, 1JW-P ) 212.3 Hz. Anal. Calcd for
W(CO)4(PH2,PH2-C6H4) (8) (C10H8O4P2W): C, 27.42; H, 1.84; O,
14.60. Found: C, 27.26; H, 1.74; O, 14.19. Attempts to doubly
deprotonate 8 via NaH, NaOMe, n-butyllithium, or Et4NOH were
carried out by the slow, stepwise addition of 2 equiv of the appropriate
reagent to a dilute solution of 8 in CH3CN, resulting in the formation
of a bright yellow product which decomposed rapidly to a dark brown
solution.
X-ray Crystallography of [PPN]2[M(CO)3(X)] Derivatives (2c,
5c, and 6c) [M ) Cr, X ) (O,S-C6H4)2- (1c), M ) W, X ) (NH,S-
C6H4)2- (5c), M ) W, X ) (O,S-C6H4)2- (6c)]. Crystal data and details
of data collection are given in Table 1. A bright red block of 2c, a
medium red block of 5c, and a dark-red block of 6c were mounted on
glass fibers with epoxy cement at room temperature and cooled to 193
K in a liquid nitrogen cold stream. Preliminary examination and data
collection were performed on a Rigaku AFC5R X-ray diffractometer
(Cu KR, λ ) 1.541 78) for 2c and a Siemens P4 X-ray diffractometer
(Mo KR, λ ) 0.710 73 Å radiation) for 5c and 6c. Cell parameters
were calculated from the least-squares fitting of the setting angles for
24 reflections.
y
-COz M(CO)3(X,Y-C6H4)2- (1)
+CO
2-
M(CO)4(X,Y-C6H4)
A number of 1,2-disubstituted benzene rings with varying
O, N, S, and P donor atoms were selected to function as the
ancillary potentially π-donating ligands. The purpose served here
is 2-fold: (i) the π-donating ability of sulfur and phosphorus
are significantly weaker than that of nitrogen and oxygen,12,13
increasing the chances of observing the exchange dynamics
between the tetracarbonyl and tricarbonyl derivatives in eq 1
and (ii) the interactions of atoms with significantly diverse
π-donor qualities, i.e., nitrogen and sulfur, that generate an
unsaturated species are of interest.
Herein, the synthesis and characterization, both spectroscopic
and crystallographic, of several new group 6 low-valent tricar-
bonyl derivatives, are presented. In addition, spectroscopic data
relevant to the tetracarbonyl analogues of the unsaturated species
has been gathered. Infrared and variable temperature 13C NMR
studies that divulge the state of the equilibrium between the
saturated vs the unsaturated species in solution will be presented.
Finally, these findings will be compared and contrasted with
results published previously, as well as compared to computa-
tions performed on a series of these complexes. Overall
conclusions regarding the nature of π-donor ligands will be
discussed.
Experimental Section
Methods and Materials. All manipulations were performed on a
double-manifold Schlenk vacuum line under an atmosphere of argon
or in an argon-filled glovebox. Solvents were dried and deoxygenated
by distillation from the appropriate reagent under a nitrogen atmosphere.
Photolysis experiments were performed using a mercury arc 450W UV
immersion lamp purchased from Ace Glass Co. Infrared spectra were
recorded on a Mattson 6022 spectrometer with DTGS and MCT
detectors. Routine infrared spectra were collected using a 0.10-mm CaF2
cell. 13C NMR spectra were obtained on a Varian XL-200 spectrometer.
13CO was purchased from Cambridge Isotopes and used as received.
Cr(CO)6 and W(CO)6 were purchased from Strem Chemicals, Inc., and
used without further purification. Sodium methoxide, bis(triphenylphos-
phoranylidiene)ammonium chloride (PPNCl), Mo(CO)6, 2-aminothiophe-
nol (NH2,SH-C6H4), and 1,2-dithiobenzene (SH,SH-C6H4) were pur-
chased from Aldrich. 2-Hydroxythiophenol (OH,SH-C6H4) was purchased
from Lancaster Synthesis; 1,2-diphosphinobenzene (PH2,PH2-C6H4) was
purchased from Strem Chemicals. W(CO)4(piperidine)2 was prepared
by the literature method cited.14 Microanalyses were performed by
Canadian Microanalytical Service, Ltd., Delta, B.C.
Synthesis of [PPN][HX] [X ) (O,S-C6H4)2-, (NH,S-C6H4)2-, or
dtb (S,S-C6H4)2-] Salts. The synthesis of these salts was accomplished
in greater than 90% yield by the slow addition of 1 equiv (1.4 mmol)
each of NaOMe and PPNCl in 10 mL of a 1:1 solvent mix of CH3CN
and CH3OH to 20 mL of a clear [X ) (O,S-C6H4)2-] or yellow [X )
(NH,S-C6H4)2- or (S,S-C6H4)2-] solution of the appropriate ligand in
CH3CN. This mixture was stirred for 60 min at ambient temperature
and the solvent was removed by vacuum overnight, yielding an off-
white [X ) (O,S-C6H4)2-] or bright yellow [X ) (NH,S-C6H4)2- or
(S,S-C6H4)2-] powder.
Synthesis of [PPN][M(CO)5(HX)] Derivatives (1a-7a). The
synthesis of [PPN][M(CO)5HX] [M ) W, Mo, or Cr; X ) (NH,S-
(12) Poulton, J. T.; Folting, K.; Streib, W. E.; Caulton, K. G. Inorg. Chem.
1992, 31, 3191.
(13) Poulton, J. T.; Sigalas, M. P.; Folting, K.; Streib, W. E.; Eisenstein,
O.; Caulton, K. G. Inorg. Chem. 1994, 33, 1476.
Omega scans for several intense reflections indicated acceptable
crystal quality. Data were collected for 4.0° g 2θ g 50°. Three control
reflections, collected for every 97 reflections, showed no significant
(14) Darensbourg, D. J.; Kump, R. L. Inorg. Chem. 1978, 17, 2680.

16-Electron Unsaturated Derivatives of Group 6 Complexes
Inorganic Chemistry, Vol. 38, No. 21, 1999 4707
Table 1. Crystallographic Data for Complexes 2c, 5c, 6c, 7b, and 8
2c
5c
6c
7b
8
empirical formula
fw
C84H71N3O5P4SCr
1410.35
P1h
C89H77N7O3P4SW
1629.5
P21
3908.6(1)
2
C85H70N4O4P4SW
1549.5
P1h
C82H64N2O4 P4 S2W
1511.5
P1h
3500.0(5)
2
C10H8O4P2W
438.0
P21/c
1282.5(2)
2
1.134
space group
V, Å3
3517.5(1)
2
3628.0(1)
2
Z
d
calc, g/cm3
1.329
1.384
1.418
1.434
a, Å
b, Å
c, Å
13.869(3)
23.128(5)
12.056(2)
104.84(3)
106.91(3)
95.29(3)
193
0.340
0.710 73
8.15
11.054(2)
28.140(6)
12.566(2)
-
12.236(2)
14.419(2)
22.748(4)
76.44(1)
75.98(2)
70.98(1)
193
1.764
0.710 73
7.13
12.650(1)
14.810(1)
21.053(2)
77.182(7)
78.334(7)
66.579(7)
193
1.855
0.710 73
3.46
11.582(1)
10.791(1)
10.449(1)
-
R, deg
â, deg
90.58(1)
-
100.867(7)
-
γ, deg
T, K
193
3.283
0.710 73
3.62
8.54
193
9.254
0.710 73
4.27
10.64
µ(Mo KR), mm-1
wavelength, Å
RF,a %
R
wF,b %
18.78
13.57
8.19
a RF ) ∑|Fo - Fc|/∑Fo. RwF ) {[∑w(Fo - Fc2)2]/(∑wFo )}1/2
.
b
2
2
Scheme 2a
a For S,NH2-C6H4-, 1a ) Cr, 3a ) Mo, and 5a ) W; for S,SH-C6H4-, 7a ) W.
trends. Background measurements by stationary-crystal and stationary-
counter techniques were taken at the beginning and end of each scan
for half the total scan time. Lorentz and polarization corrections were
applied to 9174 reflections for 2c, 7017 for 5c, and 12743 for 6c. A
semiempirical absorption correction was applied to 2c and 6c. A total
of 9151 unique reflections for 2c, 7007 for 5c, and 12 730 for 6c, with
|I| g 2.0σ(I), were used in further calculations. All three structures
were solved by direct methods [SHELXS program package, Sheldrick
(1993)]. Full-matrix least-squares anisotropic refinement for all non-
hydrogen atoms yielded R ) 0.0815, Rw ) 0.1878, and S ) 1.003 for
2c, R ) 0.0854, Rw ) 0.0362, and S ) 1.051 for 5c, and R ) 0.0713,
Rw ) 0.1357, and S ) 1.017 for 6c. Hydrogen atoms were placed in
idealized positions with isotropic thermal parameters fixed at 0.08.
Neutral-atom scattering factors and anomalous scattering correction
terms were taken from International Tables for X-ray Crystallography.
X-ray Crystallography of [W(CO)4(PH2,PH2-C6H4)], 8. Crystal
data and details of data collection are given in Table 1. A beige block
of 8 was mounted on a glass fiber with epoxy cement at room
temperature and cooled in a liquid nitrogen cold stream. Preliminary
examination and data collection were performed on a Siemens P4 X-ray
diffractometer (Mo KR, λ ) 0.710 73). Data collection methods and
parameters are identical to that described for complexes 2c, 5c, and
6c. Lorentz and polarization corrections were applied to 2254 reflections
for 8. A total of 2254 unique reflections were used in further
calculations. Anisotropic refinement for all non-hydrogen atoms yielded
R ) 0.0427, Rw ) 0.1064, and S ) 1.026.
Computational Details. Theoretical calculations were carried out
on a series of [M(CO)4(X,Y-C6H4)]2-/[M(CO)3(X,Y-C6H4)]2- systems
where M ) W, Cr; X ) N, O, S; Y ) N, O, S. All calculations were
performed using Gaussian 9415 running on a SGI power challenge.
Geometry optimizations were performed starting from crystal structures
where possible and modifications of existing structures when no
structure was readily available. Geometry optimizations were performed
on all complexes at the Hartree-Fock (HF) level using the LANL2DZ
X-ray Crystallography of [PPN]2[W(CO)4(S,S-C6H4)], 7b. Crystal
data and details of data collection are given in Table 1. A red block of
7b was mounted on a glass fiber with epoxy cement at room temperature
and cooled in a liquid nitrogen cold stream. Preliminary examination
and data collection were performed on a Siemens P4 X-ray diffracto-
meter (Mo KR, λ ) 0.710 73). Data collection methods and parameters
are identical to that described for complexes 2c, 5c, and 6c. Lorentz
and polarization corrections were applied to 12 257 reflections for 7b.
A semiempirical absorption correction was applied to 7b. A total of
12 257 unique reflections were used in further calculations. Anisotropic
(15) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson,
B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G. A.;
Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.;
Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen,
W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.: Baker, J.;
Stewart, J. P.; Head-Gordon, M.; Gonzalez, C.; and Pople, J. A.
GAUSSIAN 94, Rev. D.4; Gaussian, Inc.: Pittsburgh, PA, 1995.
refinement for all non-hydrogen atoms yielded R ) 0.0346, Rw
0.0819, and S ) 1.070.
)

4708 Inorganic Chemistry, Vol. 38, No. 21, 1999
Darensbourg et al.
Table 2. Carbonyl Stretching Frequencies of [M(CO)5(HX)]- and [M(CO)4,3(X)]2- Derivatives
complexa
ν(CtO), cm-1
av ν(CtO), cm-1
Cr(CO)5(S,NH2-C6H4)-
Cr(CO)5(S,OH-C6H4)-
Mo(CO)5(S,NH2-C6H4)-
Mo(CO)5(S,OH-C6H4)-
W(CO)5(S,NH2-C6H4)-
W(CO)5(S,OH-C6H4)-
W(CO)5(S,SH-C6H4)-
Cr(CO)4(NH,S-C6H4)2-
Cr(CO)4(O,S-C6H4)2-
Mo(CO)4(NH,S-C6H4)2-
Mo(CO)4(O,S-C6H4)2-
W(CO)4(NH,S-C6H4)2-
W(CO)4(O,S-C6H4)2-
W(CO)4(S,S-C6H4)2-
Cr(CO)3(NH,S-C6H4)2-
Cr(CO)3(O,S-C6H4)2-
Mo(CO)3(NH,S-C6H4)2-
Mo(CO)3(O,S-C6H4)2-
W(CO)3(NH,S-C6H4)2-
W(CO)3(O,S-C6H4)2-
1a
2a
3a
4a
5a
6a
7a
1b
2b
3b
4b
5b
6b
7b
1c
2c
3c
4c
5c
6c
2044.4(w)
2045.4(w)
2053.1(w)
2057.0(w)
2052.1(w)
2056.0(w)
2061.3(w)
1989.5(w)
1991.4(w)
1984.6(w)
1980.8(w)
1992.3(w)
1971.1(w)
1976.9(w)
1857.3(m)
1871.8(m)
1866.0(m)
1875.7(m)
1853.5(m)
1865.1(m)
1916.2(s)
1857.3(m)b
1853.8(m)b
1854.4(m)b
1861.2(m)b
1853.5(m) b
1857.3(m)b
1860.6(m)b
1876.6(sh)
1815.9(sh)
1821.7(sh)
1814.9(sh)
1839(sh)
1808(sh)
1810.1(sh)
-
-
1939
1939
1943
1947
1939
1943
1947
1889
1856
1866
1853
1870
1844
1850
1792
1805
1802
1808
1789
1798
1916.2(s)
1921.0(s)
1922.9(s)
1911.3(s)
1915.2(s)
1919.8(s)
1877.6(vs)
1849.6(vs)
1862.2(vs)
1850.6(vs)
1857.5(vs)
1834.2(vs)
1845.8(s)
1726.2(s)c
1737.8(s)c
1739.7(s)c
1741.6(s)c
1724.3(s)c
1731.0(s)c
-
-
-
-
-
-
1811.1(m)c
1761.9(m)c
1797.6(m)c
1766.7(m)c
1792.7(m)c
1762.8(m)c
1765.7(m)c
-
-
-
-
-
-
-
-
-
-
-
W(CO)3(S,S-C6H4)2-
7c
1867.9(m)
1745.5(s)c
-
-
1807
a As the PPN salt. b Spectra determined in THF. c Spectra determined in CH3CN.
Table 3. Average ν(CO) Frequency in M(CO)3((X,Y-C6H4)2-
Derivatives
complex
av ν(CtO), cm-1
ref
Cr(CO)3(NH,S-C6H4)2-
Cr(CO)3(dtb-O,O-C6H4)2-
Cr(CO)3(O,S-C6H4)2-
1792
1801
1805
this worka
10a
this workb
Mo(CO)3(dtb-O,O-C6H4)2-
Mo(CO)3(NH,S-C6H4)2-
Mo(CO)3(O,S-C6H4)2-
1801
1802
1808
10a
this workb
this workb
W(CO)3(NH,NH-C6H4)2-
W(CO)3(NH,O-C6H4)2-
W(CO)3(NH,S-C6H4)2-
W(CO)3(dtb-O,O-C6H4)2-
W(CO)3(O,O-C6H4)2-
W(CO)3(O,S-C6H4)2-
W(CO)3(S,S-C6H4)2-
1773
1783
1789
1790
1795
1798
1807
11a
11a
this workb
10a
9a
this workb
this workb
a As the tetraethylammonium salt. b As the PPN salt.
basis set. Density functional calculations (B3LYP)16-18 were also
performed on a couple of complexes for comparitive purposes. The
two geometries were almost identical, therefore the less expensive HF
calculations were used for the remainder of the study. Single-shot energy
calculations were performed at the HF geometries using density
functional theory with the B3LYP functional.
Results
Synthesis, Spectral, and Structural Characterization.
[PPN]2[M(CO)3X] and [PPN]2[M(CO)4X]. Several eighteen-
and sixteen-electron derivatives of zerovalent group 6 metal
carbonyl complexes have been synthesized using a series of
1,2-disubstituted benzene rings with varying oxygen, nitrogen,
and sulfur donor atoms. The reactions occur in better than 78%
yield by the labile ligand displacement reaction between
M(CO)5THF, obtained via photolysis of Cr(CO)6, Mo(CO)6, or
W(CO)6 in tetrahydrofuran, with the singly deprotonated PPN
salts of 2-aminothiophenol (NH2,SH-C6H4), 2-hydroxythiophe-
nol (OH,SH-C6H4), or dithiobenzene (SH,SH-C6H4) (complexes
1-7). Scheme 2 uses 2-hydroxythiophenol to summarize the
approach employed in the synthesis of complexes 1-7. The
Figure 1. Variable temperature 13C NMR spectra for 5c + 13CO h
5b.
reaction proceeds, as evident by the time-dependent ν(CO)
infrared spectrum(see Table 2), by way of the displacement of
THF by the deprotonated sulfur atom (1a-7a). The addition
of another equivalent of base is followed shortly by the chelation
to the metal center with concomitant loss of CO to produce the
metal tetracarbonyl ligand complex exhibiting a four-band
pattern in the carbonyl region of the infrared spectrum consistent
with a cis-disubstituted tetracarbonylmetal center (1b-7b).
Depending on the metal and the ligand, this complex may
spontaneously dissociate CO to form the tricarbonyl complex
(16) Becke, A. D. Phys. ReV. A. 1988, 38, 3098.
(17) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(18) Lee, C.; Yang, W.; Parr, R. G. Phy. ReV. B 1988, 37, 785.

16-Electron Unsaturated Derivatives of Group 6 Complexes
Inorganic Chemistry, Vol. 38, No. 21, 1999 4709
Table 4. 13C NMR Data for the Carbonyl Ligands in [M(CO)4,3((X,Y-C6H4)]2- Anionsa,b
13C resonance, ppm
CO (equatorial)
complex
CO (axial)
Mo(CO)4(O,S-C6H4)2-
Mo(CO)4(NH,S-C6H4)2-
W(CO)4(NH,S-C6H4)2
3b
4b
5b
209.2
211.4
222.7
223.8
213.9
227.5
227.4
216.9
205.4
1JW-C ) 120 Hz
206.9
1JW-C ) 160 Hz
215.8
1JW-C ) 162 Hz
219.7
W(CO)4(O,S-C6H4)2
W(CO)4(S,S-C6H4)2
6b
7b
1JW-C ) 130 Hz
205.1
1JW-C ) 170 Hz
1JW-C ) 156 Hz
217.9
1JW-C ) 120 Hz
1JW-C ) 160 Hz
Cr(CO)3(NH,S-C6H4)2-
Cr(CO)3(O,S-C6H4)2-
Mo(CO)3(NH,S-C6H4)2-
Mo(CO)3(O,S-C6H4)2-
W(CO)3(NH,S-C6H4)2
1c
2c
3c
4c
5c
249.8
247.3
242.1
240.0
239.1
1JW-C ) 176 Hz
236.0
W(CO)3(O,S-C6H4)2
W(CO)3(S,S-C6H4)2
6c
7c
1JW-C ) 180 Hz
236.2
1JW-C ) 130 Hz
a Spectra determined in acetonitrile-d3. b PPN salt.
Figure 2. Thermal ellipsoid drawing of the anion of complex 2c with
atomic numbering scheme.
Figure 3. Thermal ellipsoid drawing of the anion of complex 5c with
atomic numbering scheme.
derivative of approximately C3V symmetry. CO ligands are good
probes of the electron-donating ability of the ancillary ligands
in metal carbonyl derivatives. It is of interest to compare the
average ν(CO) values of each tricarbonyl derivative reported
upon herein with each other and with other tricarbonyl species
of this nature.9-11 That is, in [M(CO)3X]2-, the average ν(CO)
values should shift to lower frequencies as X becomes a better
π-donor. The average ν(CO) frequencies for a number of low
valent group 6 tricarbonyl derivatives, including Cr(0), Mo(0)
and W(0) tricarbonyl derivatives of 3,5-di-tert-butylcatecholate-
(dtb-O,O-C6H4)2-, 2-amidophenoxide, and diamidobenzene,9-11
are provided in Table 3.
Scheme 3
(1c-7c); however, some metal and ligand combinations require
either gentle heating (40 °C) and/or an argon purge to facilitate
CO dissociation. The synthesis of the tungsten tetracarbonyl
derivative of 1,2-diphosphinobenzene (8) has been accomplished
in good yield via the labile ligand displacement reaction between
W(CO)4(piperidine)2 and neutral 1,2-diphosphinobenzene.
The infrared frequencies of the pentacarbonyl, tetracarbonyl,
and tricarbonyl derivatives of the metal ligand complex are
provided in Table 2. The pentacarbonyl derivatives, 1a-7a,
display a three-band pattern in the ν(CO) region of the infrared
consistent with a monosubstituted pentacarbonyl. Complexes
1b-7b exhibit a four-band pattern in the carbonyl region typical
of a cis-disubstituted tetracarbonyl. The tricarbonyl derivatives,
1c-7c, demonstrate a two-band pattern consisting of a medium
sharp peak and a large broad peak, consistent with a tricarbonyl
Table 4 lists the 13C NMR data for complexes 3b-7b and
1c-7c in the CO regions of the spectra. Chemical shift data
for the metal tetracarbonyl moieties reveal a slight electronic
difference between the CO ligand trans to oxygen versus the
CO ligand trans to nitrogen. The 13C NMR spectra of complexes
3b-6b display three signals for the carbonyl carbons in an
approximate 2:1:1 intensity ratio. The more intense resonance
for the two carbonyl ligands cis to both π-donors is observed
upfield from the two smaller signals assigned to the carbonyl
ligands trans to one π-donor. On the other hand, the 13C NMR
spectrum of the symmetrically substituted derivative, 7b, reveals

4710 Inorganic Chemistry, Vol. 38, No. 21, 1999
Darensbourg et al.
Table 6. Bond Lengths [Å] and Angles [deg] for the Dianion,
[W(CO)3(NH,S-C6H4)]2-, of 5ca
W(1)-C(3)
W(1)-C(1)
W(1)-C(2)
W(1)-N(1)
W(1)-S(1)
S(1)-C(9)
O(1)-C(1)
O(2)-C(2)
1.902(8)
1.913(9)
1.942(9)
2.106(7)
2.501(2)
1.732(9)
O(3)-C(3)
N(1)-C(4)
C(4)-C(5)
C(4)-C(9)
C(5)-C(6)
C(6)-C(7)
1.182(10)
1.364(11)
1.407(13)
1.415(12)
1.380(13)
1.400(14)
1.389(13)
1.411(12)
1.196(11) C(7)-C(8)
1.165(11) C(8)-C(9)
C(3)-W(1)-C(1)
C(3)-W(1)-C(2)
C(1)-W(1)-C(2)
85.4(4)
83.3(4)
88.2(4)
O(2)-C(2)-W(1) 176.0(9)
O(3)-C(3)-W(1) 174.9(7)
N(1)-C(4)-C(5) 123.3(8)
N(1)-C(4)-C(9) 117.4(8)
C(5)-C(4)-C(9) 119.3(8)
C(6)-C(5)-C(4) 120.9(9)
C(5)-C(6)-C(7) 121.0(9)
C(8)-C(7)-C(6) 118.3(8)
C(7)-C(8)-C(9) 122.4(9)
C(8)-C(9)-C(4) 118.2(8)
C(3)-W(1)-N(1) 126.1(3)
C(1)-W(1)-N(1) 148.5(4)
C(2)-W(1)-N(1)
C(3)-W(1)-S(1) 103.1(2)
C(1)-W(1)-S(1) 98.0(3)
C(2)-W(1)-S(1) 171.4(3)
N(1)-W(1)-S(1) 76.9(2)
C(9)-S(1)-W(1) 100.5(3)
C(4)-N(1)-W(1) 126.0(6)
O(1)-C(1)-W(1) 175.4(9)
94.8(3)
C(8)-C(9)-S(1)
C(4)-C(9)-S(1)
123.4(7)
118.3(6)
Figure 4. Thermal ellipsoid drawing of the anion of complex 6c with
atomic numbering scheme.
a Estimated standard deviations are given in parentheses.
Table 5. Bond Lengths [Å] and Angles [deg] for the Dianion,
[Cr(CO)3(O,S-C6H4)]2-, of 2ca
Table 7. Bond Lengths [Å] and Angles [deg] for the Dianion,
[W(CO)3(O,S-C6H4)]2-, of 6ca
Cr(1)-C(1)
Cr(1)-C(2)
Cr(1)-C(3)
Cr(1)-O(4)
Cr(1)-S(1)
S(1)-C(5)
O(1)-C(1)
O(2)-C(2)
1.793(10) O(3)-C(3)
1.814(9) O(4)-C(4)
1.758(10) C(4)-C(9)
1.207(10)
1.333(10)
1.390(12)
1.432(12)
1.371(12)
1.392(13)
1.416(12)
1.372(12)
W(1)-C(3)
W(1)-C(1)
W(1)-C(2)
W(1)-O(4)
W(1)-S(1)
S(1)-C(4)
O(2)-C(2)
O(1)-C(1)
1.887(12) O(3)-C(3)
1.910(13) O(4)-C(9)
1.923(11) C(4)-C(5)
1.217(13)
1.321(11)
1.392(13)
1.423(13)
1.382(14)
1.37(2)
1.986(6)
2.372(3)
1.749(9)
1.186(10) C(7)-C(8)
1.186(10) C(8)-C(9)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
2.085(6)
2.482(3)
C(4)-C(9)
C(5)-C(6)
1.727(10) C(6)-C(7)
1.204(12) C(7)-C(8)
1.188(12) C(8)-C(9)
1.357(14)
1.390(13)
O(1)-C(1)-Cr(1) 175.7(8)
O(2)-C(2)-Cr(1) 176.5(8)
O(3)-C(3)-Cr(1) 175.1(8)
O(4)-C(4)-C(9) 121.9(8)
O(4)-C(4)-C(5) 119.3(8)
C(9)-C(4)-C(5) 118.9(8)
C(6)-C(5)-C(4) 118.3(9)
C(6)-C(5)-S(1)
C(4)-C(5)-S(1)
C(5)-C(6)-C(7) 123.6(9)
C(6)-C(7)-C(8) 116.8(9)
C(9)-C(8)-C(7) 121.1(9)
C(8)-C(9)-C(4) 121.1(9)
C(3)-Cr(1)-C(1)
C(3)-Cr(1)-C(2)
C(1)-Cr(1)-C(2)
81.1(4)
85.6(4)
92.3(4)
C(3)-W(1)-C(1)
C(3)-W(1)-C(2)
C(1)-W(1)-C(2)
80.9(5)
91.4(4)
82.9(4)
C(6)-C(5)-C(4) 121.1(10)
C(7)-C(6)-C(5) 120.7(10)
C(3)-Cr(1)-O(4) 133.4(3)
C(1)-Cr(1)-O(4) 145.5(4)
C(8)-C(7)-C(6) 119.1(10)
C(7)-C(8)-C(9) 122.6(10)
O(4)-C(9)-C(8) 122.1(9)
O(4)-C(9)-C(4) 119.5(8)
C(8)-C(9)-C(4) 118.5(9)
O(1)-C(1)-W(1) 176.5(9)
O(3)-C(3)-W(1) 171.9(9)
C(5)-C(4)-C(9) 118.0(9)
C(2)-Cr(1)-O(4)
91.8(3)
C(3)-W(1)-O(4) 144.7(4)
C(3)-Cr(1)-S(1) 100.3(3)
C(1)-W(1)-O(4) 134.3(3)
124.9(7)
116.8(7)
C(1)-Cr(1)-S(1) 90.4(3)
C(2)-W(1)-O(4)
C(3)-W(1)-S(1)
91.7(3)
96.4(3)
C(2)-Cr(1)-S(1) 173.9(3)
O(4)-Cr(1)-S(1)
C(5)-S(1)-Cr(1)
82.9(2)
98.0(3)
C(1)-W(1)-S(1) 104.0(3)
C(2)-W(1)-S(1) 170.3(3)
C(4)-O(4)-Cr(1) 122.8(5)
O(4)-W(1)-S(1)
C(4)-S(1)-W(1)
78.6(2)
99.2(3)
C(5)-C(4)-S(1)
C(9)-C(4)-S(1)
123.9(8)
118.1(7)
C(9)-O(4)-W(1) 124.6(6)
a Estimated standard deviations are given in parentheses.
O(2)-C(2)-W(1) 176.9(9)
two CO 13C NMR signals in a 1:1 intensity ratio. The resonance
for the two carbonyl ligands cis to both sulfurs is upfield of the
signal due to the carbonyls trans to sulfur. Each resonance for
complexes 5b-7b reveals satellites due to coupling with the
183W nucleus. Appropriate coupling constants are listed in Table
4.
a Estimated standard deviations are given in parentheses.
Scheme 3 specifically for 5c + CO h 5b is greater than zero.
That is, the tetracarbonyl species are thermodynamically favored
over the tricarbonyl complexes plus carbon monoxide. Within
a metal series the equilibrium position is a function of the
π-donating ability of the appended ligands, e.g., the concentra-
tion ratio of W(CO)3(NH,S-C6H4)2-/W(CO)4(NH,S-C6H4)2-
(5b/5c) is greater than that of W(CO)3(O,S-C6H4)2-/W(CO)4-
(O,S-C6H4)2- (6c/6b) at the same [CO]. As anticipated, the
stronger π-donating amido ligand stabilizes the “16-electron”
species to a greater extent than the phenoxide ligand. In other
words at a given temperature equilibrium process 5c + CO h
5b lies further to the left than that of 6c + CO h 6b. In addition
it is clear that the three inequivalent carbonyl ligands in the
tricarbonyl dianions are fluxional at the lowest temperature
attained(-30 to -40 °C), as previously observed in other closely
related derivatives.9-11 This is indicative of a low-energy barrier
for intramolecular CO exchange, as is generally noted in five-
coordinate metal carbonyl derivatives.
The 13C NMR spectra of complexes 1c-7c in acetonitrile
(concentrated ∼0.05 M) in the presence of one atmosphere of
13CO (solubility ∼6 × 10-3 M) display resonances in the
carbonyl region due to both tri- and tetracarbonyl dianions.
Figure 1 depicts a representative assembly of temperature-
dependent 13C NMR spectra for the mixture of complexes
[PPN]2[W(CO)4(NH,S-C6H4)] (5b) and [PPN]2[W(CO)3(NH,S-
C6H4)] (5c). In all complexes studied the 13C signals are broad
near ambient temperature or above. This is the result of a rapid
intermolecular exchange process between the tri- and tetracar-
bonyl species as illustrated for complexes 5b and 5c in Scheme
3. The ratio of tricarbonyl to tetracarbonyl dianions was found
to decrease in going from chromium to tungsten, where under
this set of conditions the chromium form is mostly tricarbonyl
and the tungsten species is mostly tetracarbonyl. However, in
all cases the equilibrium constant for the process defined in
The structures of complexes 2c, 5c, and 6c have been
determined by crystallographic analysis; thermal ellipsoid

16-Electron Unsaturated Derivatives of Group 6 Complexes
Inorganic Chemistry, Vol. 38, No. 21, 1999 4711
Table 9. Bond Lengths [Å] and Angles [deg] for the Dianion,
[W(CO)4(S,S-C6H4)]2-, of 7ba
W(1)-C(3)
W(1)-C(4)
W(1)-C(2)
W(1)-C(1)
W(1)-S(2)
W(1)-S(1)
S(1)-C(10)
S(2)-C(5)
O(1)-C(1)
1.944(5)
1.947(5)
2.015(5)
2.045(5)
2.5451(11) C(5)-C(10)
2.5520(11) C(6)-C(7)
1.763(4)
1.755(4)
1.141(6)
O(2)-C(2)
O(3)-C(3)
O(4)-C(4)
C(5)-C(6)
1.159(5)
1.175(5)
1.174(5)
1.399(6)
1.410(6)
1.387(6)
1.381(7)
1.383(6)
1.401(6)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(3)-W(1)-C(4)
C(3)-W(1)-C(2)
C(4)-W(1)-C(2)
C(3)-W(1)-C(1)
C(4)-W(1)-C(1)
86.6(2)
89.9(2)
89.9(2)
93.2(2)
91.2(2)
C(3)-W(1)-S(1)
95.56(14)
C(4)-W(1)-S(1) 176.96(13)
C(2)-W(1)-S(1)
C(1)-W(1)-S(1)
S(2)-W(1)-S(1)
87.97(12)
90.81(14)
81.23(3)
C(2)-W(1)-C(1) 176.8(2)
C(10)-S(1)-W(1) 106.32(14)
C(5)-S(2)-W(1) 106.43(14)
O(1)-C(1)-W(1) 176.7(5)
O(3)-C(3)-W(1) 177.2(4)
O(4)-C(4)-W(1) 177.5(4)
C(5)-C(10)-S(1) 122.6(3)
C(9)-C(10)-C(5) 118.4(4)
C(9)-C(10)-S(1) 119.0(3)
C(3)-W(1)-S(2) 175.53(13)
C(4)-W(1)-S(2)
C(2)-W(1)-S(2)
C(1)-W(1)-S(2)
96.76(13)
93.06(12)
83.8(2)
O(2)-C(2)-W(1) 177.7(4)
C(6)-C(5)-C(10) 118.7(4)
C(6)-C(5)-S(2)
118.2(3)
Figure 5. Schematic drawings of complexes 2c, 5c, and 6c where the
dianions are represented ideally as having trigonal bipyramidal
geometry.
C(10)-C(5)-S(2) 123.1(3)
C(7)-C(6)-C(5) 121.5(4)
C(8)-C(9)-C(10) 122.3(4)
C(6)-C(7)-C(8)
C(9)-C(8)-C(7)
120.1(4)
119.0(4)
Table 8. Comparative Structural Parameters for Tungsten
a Estimated standard deviations are given in parentheses.
Tricarbonyl Dianions
dev. from
r1
(Å)
r2
θ
φ
planarity
(Å)
complex
(Å) (deg) (deg)
W(CO)3(NH,NH-C6H4)2-
W(CO)3(NH,O-C6H4)2-
2.125 2.156 82.2 166.4 0.003
2.078 2.143 83.3 170.7 0.005
W(CO)3(dtb-O,O-C6H4)2- a 2.059 2.154 85.6 166.7 0.026
W(CO)3(NH,S-C6H4)2-
W(CO)3(O,S-C6H4)2-
2.105 2.501 85.3 171.4 0.0184
2.085 2.482 80.9 170.3 0.0214
Mo(CO)3(dtb-O,O-C6H4)2- a 2.083 2.193 85.5 168.5 0.0773
Cr(CO)3(dtb-O,O-C6H4)2- a 1.924 2.048 80.0 146.8 0.0419
Cr(CO)3(O,S-C6H4)2-
1.986 2.372 81.1 173.9 0.0150
2-
a dtb-O,O-C6H4 ) 3,5-di-tert-butylcatecholate.
Figure 7. Thermal ellipsoid drawing of the anion of complex 8 with
atomic numbering scheme.
plane consists of two carbonyl ligands, the metal center and
one of the π-donating atoms of the chelating ligand. The axial
positions contain the remaining carbonyl ligand and π-donating
atom. In each case, the stronger π-donor is located in the
equatorial position. In the chromium derivative, the average Cr-
CO bond distance is 1.788(10) Å and the Cr-S bond distance
is 2.372(3) Å. The oxygen donor atom is located in the
equatorial plane; the Cr-O bond distance is 1.986(6) Å. The
bite angle of the chelate ring is 82.9(2)° in 2c.
Figure 6. Thermal ellipsoid drawing of the anion of complex 7b with
atomic numbering scheme.
The average W-CO bond length in 5c, W(CO)3(NH,S-
C6H4)2-, is 1.919(9) Å, somewhat longer than the average
W-CO bond distance of 1.907(12) Å found in W(CO)3(O,S-
C6H4)2- (6c). In W(CO)3(NH,S-C6H4)2- (5c), the nitrogen is
located in the equatorial plane. The W-N bond distance is
2.106(7) Å while the W-S bond length is 2.501(2) Å. In the
W(CO)3(O,S-C6H4)2- derivative (6c), the W-O bond distance
is 2.085(6) Å and the W-S bond length is 2.482(3) Å,
somewhat shorter than the W-S bond in the W(CO)3(NH,S-
Ph)2- derivative. The shortening of the axial ligand in 6c vs 5c
is due to the weaker π-donation of oxygen relative to nitrogen.
This results in a greater electron deficiency at the tungsten center
and hence an increase in π-donation from the sulfur and a
drawings of the dianions are provided in Figures 2-4 with
selected bond lengths and angles in Tables 5-7. The dianions
of complexes 2c, 5c, and 6c consist of a 2-hydroxythiophenolate
(2c, 6c) or a 2-amidothiophenolate (5c) residue that forms a
five-membered chelate ring to the M(CO)3 center through its
deprotonated thiol and hydroxyl (2c, 6c) or amino (5c) groups.
Two PPN cations are present to balance the charge. Noninter-
acting solvent molecules were found in the crystal lattices of
all three compounds, i.e., 2c (CH3CN and CH3OH), 5c (4CH3-
CN), 6c (2CH3CN). The geometry of the five-coordinate metal
center is that of a distorted trigonal bipyramid. The equatorial

4712 Inorganic Chemistry, Vol. 38, No. 21, 1999
Darensbourg et al.
Table 10. Bond Lengths [Å] and Angles [deg] for
W(CO)4(PH2,PH2-C6H4), 8a
Table 13. Ab Initio Calculations of W and Cr 16- and 18-Electron
Complexes (kJ/mol)
W(1)-C(2)
W(1)-C(1)
W(1)-C(3)
W(1)-C(4)
W(1)-P(1)
W(1)-P(2)
P(1)-C(5)
P(2)-C(6)
O(1)-C(1)
1.992(11) O(2)-C(2)
2.005(12) O(3)-C(3)
2.014(10) O(4)-C(4)
2.034(11) C(5)-C(10)
1.165(13)
1.149(13)
1.156(14)
1.41(2)
1.402(14)
1.392(14)
1.37(2)
complex
HF
B3LYP single-shotb
[W(CO)4(NH,NH-C6H4)]2-
[W(CO)3(NH,NH-C6H4)]2-
[W(CO)4(NH,O-C6H4)]2-
[W(CO)3(NH,O-C6H4)]2-
[W(CO)4(NH,S-C6H4)]2-
[W(CO)3(NH,S-C6H4)]2-
[W(CO)4(O,O-C6H4)]2-
[W(CO)3(O,O-C6H4)]2-
[W(CO)4(O,S-C6H4)]2-
[W(CO)3(O,S-C6H4)]2-
[W(CO)3(S,O-C6H4)]2-
[W(CO)4(S,S-C6H4)]2-
[W(CO)3(S,S-C6H4)]2-
0.000
21.724
0.000
38.899
0.000
49.704
0.000
60.898
0.000
0.000
82.109
0.000
97.153
0.000
103.865
0.000
119.646
0.000
2.465(3)
2.466(2)
C(5)-C(6)
C(6)-C(7)
1.818(10) C(7)-C(8)
1.840(10) C(8)-C(9)
1.153(14) C(9)-C(10)
1.36(2)
1.40(2)
C(2)-W(1)-C(1)
C(2)-W(1)-C(3)
C(1)-W(1)-C(3)
C(2)-W(1)-C(4)
C(1)-W(1)-C(4)
C(3)-W(1)-C(4) 173.9(4)
C(2)-W(1)-P(1) 170.7(3)
96.4(4)
87.7(4)
88.3(4)
86.2(4)
91.8(4)
C(6)-P(2)-W(1) 111.7(3)
O(1)-C(1)-W(1) 177.6(10)
O(2)-C(2)-W(1) 178.9(9)
O(3)-C(3)-W(1) 177.8(9)
O(4)-C(4)-W(1) 175.3(10)
C(10)-C(5)-C(6) 119.0(10)
C(10)-C(5)-P(1) 122.2(8)
68.546
78.968
0.000
122.968
127.262
0.000
85.871
132.445
[Cr(CO)4(O,O-C6H4)]2-
[Cr(CO)3(O,O-C6H4)]2-
[Cr(CO)4(O,S-C6H4)]2-
[Cr(CO)3(O,S-C6H4)]2-
0.000
45.671
0.000
-
-
-
-
C(1)-W(1)-P(1)
C(3)-W(1)-P(1)
C(4)-W(1)-P(1)
C(2)-W(1)-P(2)
92.9(3)
94.0(3)
92.1(3)
91.8(3)
C(6)-C(5)-P(1)
C(7)-C(6)-C(5)
C(7)-C(6)-P(2)
C(5)-C(6)-P(2)
C(8)-C(7)-C(6)
C(9)-C(8)-C(7)
118.7(8)
119.7(10)
122.4(8)
117.9(7)
121.0(11)
119.9(11)
54.045
a Energies relative to the 18-electron complex in each set. b Single-
shot energy calculations done at the HF geometry.
C(1)-W(1)-P(2) 171.8(3)
C(3)-W(1)-P(2)
C(4)-W(1)-P(2)
P(1)-W(1)-P(2)
91.1(3)
89.6(3)
79.03(8)
C(8)-C(9)-C(10) 121.6(11)
Table 14. Comparison of Selected Experimental (in Parentheses)
and Calculated Bond Lengths [Å] and Angles [deg] in 1,
[W(CO)3(O,S-C6H4)]2- (6c), and [W(CO)3(S,O-C6H4)]2- (6d)
C(5)-C(10)-C(9) 118.8(11)
C(5)-P(1)-W(1) 112.0(3)
a Estimated standard deviations are given in parentheses.
[W(CO)3(O,S-C6H4)]2- a [W(CO)3(S,O-C6H4)]2- b
W-S
2.664 (2.482(3))
2.110 (2.085(6))
1.942 (1.899[12])
1.945 (1.923(11))
75.5 (78.6(2))
2.622
2.160
1.937
1.949
Table 11. Comparison of Selected Experimental and Calculated
Bond Lengths [Å] and Angles [deg] in [W(CO)3(NH,S-C6H4)]2-, 5c
W-O
W-Ceq
W-Cax
O-W-S
HF
B3LYP
Experimental
2.501(2)
2.106(7)
1.942(9)
1.902(8), 1.913(9)
75.6
W-S
2.649
2.122
1.937
1.953
2.630
2.110
1.936
1.939
W-N
W-Cax
W-Ceq
Ceq-W-Ceq
Ceq-W-Cax
Xeq-W-Ceq
Xeq-W-Cax
Xax-W-Cax
Xax-W-Ceq
85.4 (80.9(5))
90.5 (87.2[4])
137.2 (139.5[4])
91.6 (91.7(3))
167.1 (170.3(3))
98.9 (100.2(3))
86.8
90.1
136.5
98.2
168.5
98.2
Ceq-W-Ceq
Ceq-W-Cax
N-W-S
Ceq-W-S
Cax-W-S
86.2
90.5
76.0
136.8
168.5
86.9
90.3
76.5
136.5
168.7
85.4(4)
83.3(8), 88.2(4)
76.9(2)
126.1(3), 148.5(4)
171.4(3)
a S in the axial position O in the equatorial position. b S in the
equatorial position O in the axial position.
Table 12. Comparison of Calculated Bond Lengths [Å] and Angles
[deg] in [W(CO)4(NH,S-C6H4)]2-, 5b
complexes published in studies prior to this one, including the
W, Mo, or Cr tricarbonyl derivatives of 3,5-di-tert-butylcat-
echolate, 2-amidophenoxide, and diamidobenzene.9-11
Bright red crystals of the tungsten tetracarbonyl derivative
of dithiobenzene, complex 7b, were obtained by the slow
diffusion of diethyl ether into a concentrated CH3CN solution
of the complex. Figure 6 shows a drawing of the dianion while
selected bond angles and lengths are listed in Table 9. The
structure of W(CO)4(S,S-C6H4)2- consists of a tungsten tetra-
carbonylmetal center chelated by doubly deprotonated dithiophe-
nolate; the charge is balanced by the presence of two PPN
cations. The geometry of the metal center is that of a distorted
octahedron; the average W-C bond length of the carbonyls trans
to sulfur is 1.946(5) Å, and the average bond length of the
carbonyls cis to the sulfurs is 1.930(5) Å. The W-S bond
lengths are 2.552(1) and 2.545(1) Å, significantly longer than
the W-S bond lengths observed in the W(CO)3(O,S-C6H4)2-
(2.482(3) Å) and W(CO)3(NH,S-C6H4)2- (2.501(2) Å) unsatur-
ated derivatives.
HF
B3LYP
W-S
2.698
2.215
1.949
1.971
2.055
2.677
2.183
1.951
1.976
2.029
W-N
W-Ctrans-S
W-Ctrans-N
W-Ccis-S,N
Ctrans-S-W-Ctrans-N
Ccis-W-Ccis
91.2
178.4
75.4
172.1
96.7
172.1
96.7
92.3
172.9
76.2
171.4
96.2
172.5
95.2
N-W-S
S-W-Ctrans-S
S-W-Ctrans-N
N-W-Ctrans-N
N-W-Ctrans-S
therefore a shorter W-S distance. Finally, the bite angle of the
chelate ring is similar in both the W(CO)3(O,S-C6H4)2- deriva-
tive (78.6(2)°) and in the W(CO)3(NH,S-C6H4)2- complex
(76.9(2)°). In each case, the sulfur donor atom is located in the
axial position, indicating that the O- and N-donor atoms,
respectively, are the better π-donors.
Figure 5 provides schematic drawings of 2c, 5c, and 6c where
their geometry is represented as trigonal bipyramidal. However,
the structural parameters indicated in Figure 5 and summarized
in Table 8 reveal that significant distortions from trigonal
bipyramidal are observed. Also included, for purposes of
comparison, are those parameters for the 16-electron, tricarbonyl
Yellow-brown X-ray-quality crystals were obtained for
complex 8, W(CO)4(PH2,PH2-C6H4), via sublimation at 40 °C.
The instability of the doubly deprotonated analogue of 8
prevented examination of the π-donor character of the phosphido
group. A thermal ellipsoid drawing of complex 8 is given in
Figure 7; bond lengths and angles are listed in Table 10. The
geometry of the metal center is that of a distorted octahedron.

16-Electron Unsaturated Derivatives of Group 6 Complexes
Inorganic Chemistry, Vol. 38, No. 21, 1999 4713
The structure consists of the diphosphinobenzene ligand bound
to a W(CO)4 center with a chelate bite angle of 79.03(8)°. The
W-CO bond distances for the carbonyls trans to phosphorus
are 2.01(1) and 2.03(1) Å; the average bond length of the two
axial CO’s, cis to phosphorus, is 2.02(1) Å.
Theoretical Calculations
Ab initio geometry optimizations and energy calculations
were performed on a series of related 16e and 18e complexes
reported herein. This study was undertaken in order to determine
the relative stability of the 16e vs 18e complexes. We have also
undertaken an investigation into the bonding between the
π-donor and the metal in these systems to determine why the
better π-donor occupies an equatorial site in the trigonal
bipyramidal geometry of the 16-electron tricarbonyl complexes.
Hartree-Fock geometry optimizations were performed on all
complexes, with optimizations using density functional theory
being performed on selected complexes for comparative pur-
poses. Both HF and DFT geometry optimizations gave virtually
identical results in good agreement with experimentally deter-
mined distances and angles, Tables 11 and 12. This is in accord
with our previous work which demonstrated that HF and DFT
geometry optimizations in tungsten carbonyl anions are very
similar.19 The computationally less expensive HF geometry
optimizations were used for the remainder of the computations
reported upon here.
The energy differences between the 16- and 18-electron
complexes were examined as a measure of the relative stability
of the two complexes. In all cases examined, the 18-electron
dianion was calculated to be the more stable species. The extent
to which the 18-electron complex was more stable was variable
depending on which π-donor groups were in the chelating
ligand, i.e., the relative stability between the 16- and 18-electron
complexes is readily tuned. This energy gap gets increasing large
as one goes from good π-donor atoms such as N and O to
weaker π-donors such as S, Table 13, the trend in the energy
difference between the sixteen- and eighteen-electron complexes
is as follows: NH,NH < NH,O < O,O < NH,S < O,S < S,S.
This is in conformity with the experimental observations(vide
supra) that heat and/or an argon flow are required to form the
sixteen electron tricarbonyl complexes in compounds that
contain weaker π-donor atoms.
The [W(CO)4(O,S-C6H4)]2-/[W(CO)3(O,S-C6H4)]2- system
was examined in detail in order to determine why the best
π-donor (O in this case) falls in the equatorial position in the
16-electron dianion. Specifically, geometry optimizations were
performed on [W(CO)4(O,S-C6H4)]2- (6b) and on the two
tricarbonyl isomers of the [W(CO)3(O,S-C6H4)]2- (6c) and
[W(CO)3(S,O-C6H4)]2- (6d). From the calculations it was
determined that the isomer in which the oxygen atom is in the
equatorial plane (6c) is about 10.4 kJ/mol more stable than the
isomer which contains the sulfur in the equatorial plane (6d).
This is in agreement with the crystal structure obtained for the
tricarbonyl complex, Figure 4, in which the oxygen is indeed
in the equatorial plane. Frequency calculations were performed
on these three complexes (6b, 6c, 6d). From these calculations
is was determined that complexes 6b and 6c are indeed minima
(no negative frequencies) and that complex 6d is in fact a
transition state (one negative frequency). Thermal and zero point
corrections on complexes 6b-d lowered the energy about 7-10
kJ/mol, and narrowed the gap between 6b and 6c from 68.5 to
Figure 8. Orbital diagram for the metal d orbitals for idealized trigonal
bipyramidal geometry.
61.0 kJ/mol. The gap between the two isomers 6c and 6d was
also narrowed from 10.4 to 7.7 kJ/mol. These corrections are
however not large enough to overcome the energy difference
between the sixteen and eighteen complexes, in which the
smallest energy gap is 21.7 kJ/mol.
The exchange of the axial oxygen and the equatorially
positioned sulfur had some effects on the calculated bond
distances in the two isomers 6c and 6d. The tungsten sulfur
bond length was shortened by about 0.04 Å in going from the
equatorial position to the axial position, and the tungsten oxygen
distance increases 0.05 Å in going from the axial to the
equatorial position. Table 14 contains selected bond distances
and angles for complexes 6c and 6d. This change indicates a
stronger ability for the equatorial site to bind a π-donor ligand.
A comparison of the computer generated orbitals in com-
plexes 6c and 6d revealed that the orbital structure is very
similar, as one might expect. However, there were some subtle
differences, most notably was the lower energy of the tungsten-
equatorial π-bonding orbitals in complex 6c versus 6d. This
can be explained based on a general molecular orbital diagram
starting from the idealized trigonal bipyramidal geometry shown
in Figure 8. The complexes examined here are distorted from
idealized trigonal bipyramidal geometry in the following ways.
The Ceq-W-Ceq angle has been reduced to approximately 85°,
and the two Ceq-W-Xeq angles are inequivalent at ap-
proximately 125° and 148°. These changes affect the molecular
2
2
orbital diagram by lowering the energy of the dx -y orbital with
2
respect to the dxy orbital. The dz orbital is also lowered due to
deviation from linearity of the Cax-W-Xax angle, however, this
orbital is still much higher in energy than the dxy orbital and is
therefore not of interest here. The result of these changes is
6
2
2
that in a d metal complex only the dzy, dyz, and dx -y are
occupied. The dxy orbital is available for π-donation from the
π-donor ligand in the equatorial plane. The stronger the π-donor
ligand the more stabilized the dxy orbital will be and the more
stable the complex. However, when a π-donor ligand is in the
axial position we obtain a situation which Caulton has described
as a filled/filled interaction.20
Conclusions
Herein the synthesis and characterization of a number of low-
valent, group six metal carbonyl complexes containing ancillary
ligands capable of π-donation has been described. As expected,
the stability of the coordinatively unsaturated, 16-electron
complex increases as the ancillary ligand becomes a better
(19) Darensbourg, D. J.; Frost, B. J.; Derecskei-Kovacs, A.; Reibenspies,
J. H. Inorg. Chem. 1999, 38, 4715.
(20) Caulton, K. G. New J. Chem. 1994, 18, 25.

4714 Inorganic Chemistry, Vol. 38, No. 21, 1999
Darensbourg et al.
π-donor. The tungsten tricarbonyl species of 2-amidothiophe-
nolate and 2-hydroxythiophenolate were observed to be rela-
tively stable. Both the 18-electron tetracarbonyl and the 16-
electron tricarbonyl derivatives were characterized not only by
ν(CO) IR and 13C NMR spectroscopies but also by X-ray
crystallography when possible. The structures of these coordi-
natively unsaturated metal complexes contain a metal tricarbonyl
center chelated by the doubly deprotonated ligand under
consideration in approximately trigonal bipyramidal geometry.
In each case the stronger π-donor atom of the two chelating
linkages was observed to prefer the equatorial rather than axial
position in trigonal bipyramidal geometry. It was concluded that
this phenomenon is due to the availability of an empty orbital
of appropriate symmetry in the equatorial plane.
in the axial position. We have also shown that the order of
π-donation computed follows that determined from experiment
and in is indeed: NH,NH < NH,O < O,O < NH,S < O,S <
S,S. This was determined computationally by comparing the
energy differences between the sixteen and eighteen electron
complex of each ligand and ordering them based on the smallest
energy gap equals the most stable sixteen electron complex and
hence contains the better π-donating ligand. Finally, frequency
calculations have shown that the complex with the better
π-donor in the axial plane is indeed a transition state and not a
local or global minimum.
Acknowledgment. The financial support of this research by
the National Science Foundation (Grant CHE96-15866) and the
Robert A. Welch Foundation is greatly appreciated.
Calculations on these systems have been shown to be in good
agreement with the experimentally determined data. It has been
demonstrated via ab initio calculations that the tricarbonyl
complexes in which the better π-donor is in the equatorial plane
are more stable than the same complex with the better π-donor
Supporting Information Available: X-ray crystallographic files,
in CIF format, for the structure determinations of (2c, 5c, 6c, 7b, and
8) are available free of charge via the Internet at http://pubs.acs.org.
IC9804216