Reaction of ?NO thiolate and thiol complexes: Elimination of PhSNO from W(phen)(CO)2(SPh)2, CO from W(phen)(CO)2((-S)2Arene), and HNO from W(phen)(CO)3(RSH)

Article abstract of DOI:10.1021/ic990830h

Reaction of ?NO with W(phen)(CO)₂(SPh)₂ (phen = 1,10-phenanthroline) results in clean conversion to W(phen)-(CO)₂(NO)(SPh). Reduction of the W(II) bisthiolates to the W(0) nitrosyl thiolate occurs with simultaneous reducti

Full text of DOI:10.1021/ic990830h

6212
Inorg. Chem. 1999, 38, 6212-6217
Reaction of •NO Thiolate and Thiol Complexes: Elimination of PhSNO from
W(phen)(CO)2(SPh)2, CO from W(phen)(CO)2((-S)2Arene), and HNO from
W(phen)(CO)3(RSH)
Kenneth B. Capps,† Andreas Bauer,† Khalil A. Abboud,*,‡ and Carl D. Hoff*,†
Department of Chemistry, University of Miami, Coral Gables, Florida 33124, and Department of
Chemistry, University of Florida, Gainesville, Florida 32611
ReceiVed July 14, 1999
Reaction of •NO with W(phen)(CO)2(SPh)2 (phen ) 1,10-phenanthroline) results in clean conversion to W(phen)-
(CO)2(NO)(SPh). Reduction of the W(II) bisthiolates to the W(0) nitrosyl thiolate occurs with simultaneous reductive
elimination of PhS-NO, which is unstable but could be detected spectroscopically. Reaction of W(phen)(CO)2-
(1,2-S2-Arene), however, does not result in reductive elimination of either free or bound nitrosothiol. Carbon
monoxide is displaced, forming W(phen)(NO)2(1,2-S2-Arene) (1,2-S2-Arene ) 1,2-benzene dithiolate or toluene-
3,4-dithiolate). Complexes of butanethiol and thiophenol W(phen)(CO)3(RSH) react with excess •NO to form
nitrosyl thiolate complexes W(phen)(CO)2(NO)(SR). These reactions also produce N2O and HNO2, which are
attributed to decomposition of initially formed HNO. These observations indicate that •NO may be capable of
direct attack on complexed thiols. Crystal structures of W(phen)(CO)2(NO)(SPh) and W(phen)(NO)2(toluene-
3,4-dithiolate) are reported.
Introduction
Nitric oxide1-4 is one of the most powerful π-acid ligands
(1)
known. Theoretical calculation5 of the enthalpy of dissociation
(2)
of NO+ from M(CO)5(NO)+ yielded the following M-NO+
bond strengths: Cr ) 105.4, Mo ) 103.2, and W ) 108.6 kcal/
on a stronger bond. Reaction of thiols with the chromium radical
mol, exceptionally high values for a metal-ligand bond.6
was shown to follow net third-order reactivity12 according to
Recently we reported solution calorimetric measurements that
the mechanism shown in eq 3 below. The nearly zero enthalpy
yielded an estimated value for the dissociation of •NO from
Cr(NO)(CO)2C5Me5 of ∼70 kcal/mol.7 In contrast to its “strong”
•Cr + RSH h RSH‚‚‚•Cr + •Cr f CrH + CrSH (3)
character as a ligand, nitric oxide can be characterized as a
“weak” radical. Two quantitative measures of the “strength” of
a radical are its enthalpies of dimerization and of combination
with a hydrogen atom. The enthalpies of these reactions (kcal/
mole) are summarized in terms of increasing radical strength,
of activation of this reaction shows kinetic resemblance to the
well studied reaction of •NO and O2 (eq 4).13
•NO + O2 h ONO2• + •NO f ONOONO f 2•NO2 (4)
9
•NO8 < •Cr(CO)3C5Me5 < •SPh10 < •SMe.11
The weak nature of stable radicals such as •NO and •Cr-
(CO)3C5Me5 can be a source of net third-order reactivity, in
which two moles of the radical are needed in concerted attack
The rate of oxidative addition of butanethiol to the chromium
radical was found to be catalyzed by the complex W(phen)-
(CO)3(BuSH) according to the mechanism shown in eq 5. It
has been established that nitric oxide does not directly attack
the sulfur-hydrogen bond of free thiols.14,15 This work was
begun to see if the sulfur-hydrogen bond in the complex
W(phen)(CO)3(BuSH) would be attacked by •NO.
† University of Miami.
‡ University of Florida.
(1) Richter-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford University
Press: New York, 1992.
(2) (a) Feldman, P. L.; Griffith, O. W.; Stuehr, D. J. Chem. Eng. News
1993, 71, 26. (b) Culotta, E.; Koshland, D. E. Science 1992, 258,
1862-1865.
(9) (a) Kiss, G.; Zhang, K.; Mukerjee, S. L.; Hoff, C. D. J. Am. Chem.
Soc. 1990, 112, 5657. (b) Watkins, W. C.; Jaeger, T.; Kidd, C. E.;
Fortier, S.; Baird, M. C.; Kiss, G.; Roper, G. C.; Hoff, C. D. J. Am.
Chem. Soc. 1992, 114, 907. (c) Kiss, G. Ph.D. Dissertation, University
of Miami, 1993.
(10) Bordwell, F. G.; Zhang, X. M.; Satish, A. V.; Cheng, J. P. J. Am.
Chem. Soc. 1994, 116, 6605.
(11) CRC Handbook of Chemistry and Physics, 75th ed.; Lide, D. R., Ed.;
CRC Press: Boca Raton, FL, 1994. (Bond stengths for HSMe and
dimer.)
(12) Ju, T. D.; Lang, R. F.; Hoff, C. D. J. Am. Chem. Soc. 1996, 118,
5328.
(3) Lancaster, J. Nitric Oxide, Principles and Actions; Academic Press
Limited: London, 1996.
(4) (a) Legzdins, P.; Veltheer, J. E. Acc. Chem. Res. 1993, 26, 41. (b)
Cotton, F. A.; Wilkinson, G., Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry; Wiley-Interscience: New York, 1999.
(5) Ehlers, A. W.; Dapprich, S.; Vyboishchikov, S. F.; Grenking, G.;
Organometallics 1996, 15, 105.
(6) Hoff, C. D. Prog. Inorg. Chem. 1992, 40, 503.
(7) Capps, K. B.; Bauer, A.; Sukcharoenphon, K.; Hoff, C. D. Inorg. Chem.
1999, 38, 6206-6211.
(8) See ref 4b and Chase, M. W.; Davies, C. A.; Downey, J. R.; Frurip,
D. J.; McDonald, R. A.; Syverud, A. N. J. Chem. Phys. Ref. Data
1985, 14, supplement 1.
(13) For an excellent historical discussion of the third-order reactions of
NO, see: Laider, K. J. Chemical Kinetics, 3rd ed.; Harper & Row:
New York, 1987.
10.1021/ic990830h CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/10/1999

Elimination Reactions of •NO
Inorganic Chemistry, Vol. 38, No. 26, 1999 6213
structure of W(phen)(CO)2(SPh)(NO) is reported below. Strictly
analogous procedures yielded the following complexes characterized
by infrared spectroscopy: Mo(phen)(NO)(CO)2(SPh), νCO 2012, 1928
cm-1, νNO 1633 cm-1 in toluene; Mo(phen)(NO)(CO)2(SToluene), νCO
2014, 1929 cm-1, νNO 1635 cm-1 in CH2Cl2; W(phen)(NO)(CO)2(SBu),
νCO 1996, 1913 cm-1, νNO 1622 cm-1 in CH2Cl2.
(5)
Reaction of Nitric Oxide and W(phen)(CO)3(RSH) [R ) Bu, Ph].
A solution of W(phen)(CO)3(EtCN) (200 mg, 0.398 mmol) in 25 mL
of CH2Cl2 with 0.10 mL of BuSH (about 2 equiv of BuSH) was allowed
to stir in the reactor, producing W(phen)(CO)3(BuSH) with FT-IR peaks
at 1900 and 1783 cm-1. Using a Hamilton gastight syringe, 50 cm3 of
nitric oxide at 6 psi was added, with rapid formation of W(phen)(NO)-
(CO)2(SBu) with FT-IR peaks at 1996, 1913, and 1622 cm-1. The
presence of HNO was inferred by FT-IR on the basis of detection of
its decomposition products N2O (2220 cm-1) and HNO2 (3443 cm-1).
Reaction of W(phen)(CO)3(PhSH) proceeded in an analogous way and
yielded W(phen)(NO)(CO)2(SPh) characterized by observation of IR
bands: νCO 2002 and 1911; νNO 1608 cm-1 in CH2Cl2, in agreement
with those determined above.
Reaction of Nitric Oxide and W(phen)(CO)2(toluene-3,4-dithi-
olate). W(phen)(CO)2(tdt) (106 mg, 0.217 mmol) was dissolved in 15
mL of toluene under argon. An initial IR spectrum was taken, with
peaks at 1929 and 1853 cm-1. The atmosphere was then switched to
nitric oxide (6 psi), with the solution turning from dark purple to dark
green. W(phen)(CO)2(tdt) was rapidly converted to W(phen)(NO)2(tdt),
as seen by FT-IR, with peaks νNO at 1721 and 1630 cm-1 in toluene.
Crystal Growth of W(phen)(CO)2(SPh)(NO) and W(phen)(NO)2-
(tdt). Concentrated solutions of the complexes were prepared in the
glovebox by dissolving ∼250 mg of the solid in ∼7 mL of freshly
distilled CH2Cl2. The solution was filtered through a syringe filter into
a 50 mL Schlenk tube and layered with heptane. The solution was left
undisturbed for about a week, at which time crystals were collected
and used for X-ray diffraction analysis.
Experimental Section
General Procedures. All manipulations were carried out with
rigorous exclusion of oxygen using standard inert atmosphere tech-
niques. The complexes W(phen)(CO)3(RSH),16 W(phen)(CO)2(SR)2,17
and W(phen)(CO)2(tdt)18 [tdt ) toluene-3,4-dithiolate] were prepared
by literature methods. Toluene was distilled from sodium-benzophe-
none ketyl under argon atmosphere into flame-dried glassware. Me-
thylene chloride was distilled from P2O5 under argon. Nitric oxide (98%,
Matheson Gas) was passed through KOH pellets and a cold trap (dry
ice/acetone, -78 °C) to remove higher nitrogen oxides. FT-IR
measurements were made on a Perkin-Elmer Spectrum 2000 FT-IR
equipped with an i-series microscope. The crystal structures of W(phen)-
(NO) (CO)2(SPh) and W(phen)(NO)2(tdt) were determined at the
University of Florida. Data were collected at 173 K on a Siemens
SMART PLATFORM equipped with a CCD area detector and a
graphite monochromator. The structures were solved by the Direct
Methods in SHELXTL5 and refined using full-matrix least squares.
Reaction of Nitric Oxide and M(phen)(CO)2(SR)2 [M ) Mo, W;
R ) tolyl, Ph]. W(phen)(CO)2(SPh)2 (36 mg, 0.056 mmol) is dissolved
in 10 mL of CH2Cl2 in a Schlenk tube under argon. After running an
initial spectrum (1944 and 1847 cm-1), the atmosphere is changed to
nitric oxide (6 psi), with rapid formation of W(phen)(NO) (CO)2(SPh)
as seen by FT-IR with PhSNO at 1560 cm-1. Concentration of the
solution to about 2-3 mL followed by addition of heptane afforded
the red crystalline complex in 80% yield. W(phen)(CO)2(SPh)(NO) with
IR bands: νCO 2002 and 1911; νNO 1608 cm-1 in CH2Cl2. The NMR
spectrum of W(phen) (NO)(CO)2(SPh) was recorded in CDCl3 and
showed peaks assigned to the phenanthroline ligand (8H), 9.44(d), 8.47-
(d), 7.86(s), 7.85(dd), and S-C6H5 (5H), 6.37(br), 6.12(br). The crystal
Results
Reaction of Nitric Oxide with W(phen)(CO)2(SPh)2 and
W(phen)(CO)2(toluene-3,4-dithiolate). Reaction of •NO and
W(phen)(CO)2(SPh)2 proceeds as shown in eq 6. The metal
(6)
complex is formulated based on FT-IR, NMR, and (see later
section) X-ray structural analysis. The phenyl thiyl radical that
is eliminated from the complex forms PhS-NO, which is known
to undergo spontaneous decomposition according to eq 7. The
(14) Measurement of the W-H bond strength in W(PCy3)2(CO)3(H)(SPh),
which is obtained by oxidative addition of thiophenol to W(PCy3)2-
(CO)3, is very low. This has been attributed to stabilization of the
radical W(PCy3)2(CO)3(•SPh) due to electronic effects: Lang, R. F.;
Ju, T. D.; Kiss, G.; Hoff, C. D.; Bryan, J. C.; Kubas, G. J. Inorg.
Chim. Acta 1997, 259, 317.
(15) Goldstein, S.; Czapski, G. J. Am. Chem. Soc. 1996, 118, 3419.
(16) (a) Ju, T. D. Ph.D. Dissertation, University of Miami, 1996. (b) It is
possible that there is a rapid equilibrium between thiol complex and
thiolate hydride for both W(phen)(CO)3(BuSH) and W(phen)(CO)3-
(SPh)(H) and so while the equilibrium position is shifted for the two
thiols, it cannot be known at this time which form-complexed thiol,
or thiolate hydride complex is more rapidly attacked. Additional work
on this system is in progress.
2PhS-NO f PhS-SPh + 2•NO
(7)
presence of PhS-NO was confirmed on the basis of growth
and decay of νPhSNO at 1560 cm-1, in keeping with literature
reports.19 Similar reactivity was observed for the S-tolyl complex
and for analogous complexes of molybdenum.
Reaction of W(phen)(CO)2(tdt) with nitric oxide under
conditions similar to those for reaction of W(phen)(CO)2(SPh)2
(17) Lang, R. F.; Ju, T. D.; Kiss, G.; Hoff, C. D.; Bryan, J. C.; Kubas, G.
J. Inorg. Chem. 1994, 33, 3899.
(18) Lang, R.; Doctoral Dissertation, University of Miami, 1995.
(19) (a) Oae, S.; Kim, Y. H.; Fukushima, D.; Shinhama, K. J. Chem. Soc.,
Perkin Trans. 1 1978, 913. (b) Oae, S.; Shinhama, K.; Fujimori, K.;
Kim, Y. H. Bull. Chem. Soc. Jpn. 1980, 53, 775.

6214 Inorganic Chemistry, Vol. 38, No. 26, 1999
Capps et al.
Table 1. Crystal Data and Structure Refinement for
W(phen)(CO)2(SPh)(NO) and W(phen)(NO)2(toluene-3,4-dithiolate)
W(phen)(CO)2(SPh)(NO)
empirical formula
fw
C20H13N3O3SW
559.24
temp
wavelength
cryst syst
space group
173(2) K
0.71073 Å
orthorhombic
Pbca
unit cell dimensions
a ) 14.2099(7) Å
b ) 13.8261(7) Å
c ) 18.9295(9) Å
vol
R ) 90°
â ) 90°
γ ) 90°
3719.0(3) Å3
Z
8
density (calcd)
abs coeff
1.998 Mg/m3
6.351 mm-1
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.056
R1 ) 0.0164, wR2 ) 0.0358 [3617]
R1 ) 0.0227, wR2 ) 0.0381
W(phen)(NO)2(toluene-3,4-dithiolate)
empirical formula
fw
temp
wavelength
cryst syst
C23H22N4O3S2W
650.42
173(2) K
0.71073 Å
monoclinic
P2(1)/c
Figure 1. Molecular structure of W(phen)(CO)2(SPh)(NO) (ORTEP,
50% probability ellipsoids). W-NO ) 1.825(2) Å and W-N-O )
176.6(2)°.
as shown in eq 6 occurred with elimination of CO rather than
a thionitrite (eq 8). No sign of intermediate formation of a bound
space group
unit cell dimensions
a ) 9.5899(4) Å
b ) 16.7921(8) Å
c ) 15.5309(7) Å
vol
R ) 90°
â ) 100.359(1)°
γ ) 90°
2460.2(1) Å3
Z
4
density (calcd)
abs coeff
1.756 Mg/m3
4.897 mm-1
1.041
R1 ) 0.0358, wR2 ) 0.0755 [4292]
R1 ) 0.0577, wR2 ) 0.0845
goodness-of-fit on F2
final R indicesa [I > 2σ(I)]
R indices (all data)
a R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. wR2 ) [∑[w(Fo - Fc )2]/
2
2
∑[w(Fo )2]]1/2. S ) [∑[w(Fo - Fc2)2]/(n - p)]1/2; w ) 1/[s2(Fo ) +
2
2
2
(0.0370p)2 + 0.31p], p ) [max(Fo ,0) + 2Fc2]/3.
2
Table 2. Bond Lengths (Å) for W(phen)(CO)2(SPh)(NO)
(8)
W-N3
1.825(2)
1.982(3)
2.004(3)
2.213(2)
2.215(2)
2.5347(7)
1.769(3)
1.142(3)
1.152(3)
1.199(3)
1.336(3)
1.362(3)
1.328(3)
1.368(3)
1.393(3)
1.403(4)
C11-C12
C12-C13
C13-C14
C14-C15
C30-C31
C31-C32
C32-C33
C33-C34
C33-C40
C34-C35
C35-C36
C36-C37
C36-C41
C37-C38
C38-C39
C40-C41
1.378(4)
1.369(5)
1.378(4)
1.389(4)
1.399(4)
1.366(4)
1.407(4)
1.407(3)
1.432(4)
1.430(3)
1.403(3)
1.404(4)
1.436(4)
1.360(4)
1.404(4)
1.347(4)
W-C2
W-C1
W-N2
W-N1
thionitrite or other metal complex was detected in the infrared
spectrum except for the starting dicarbonyl and the product
dinitrosyl complex.
Crystal Structures of W(phen)(CO)2(NO)(SPh) and W-
(phen)(NO)2(toluene-3,4-dithiolate).
W-S1
S1-C10
O1-C1
O2-C2
O3-N3
N1-C30
N1-C34
N2-C39
N2-C35
C10-C15
C10-C11
The crystal structure of W(phen)(CO)2(NO)(SPh) has been
obtained and is shown in Figure 1. Crystal and experimental
data are summarized in Tables 1-3. The key features of this
nearly octahedral complex are that the W-N-O angle is
essentially linear at 176.6(2)°, with a W-NO bond length of
1.825(2) Å. The W-SPh distances are different in the starting
complex17 versus the final product. The average W-SPh
distance in W(phen)(CO)2(SPh)2 is 2.361(2) Å versus 2.5347-
(7) Å in W(phen)(CO)2(NO)(SPh). Because of the strong
π-acidity of NO,1,4 lengthening of the bond trans to nitric oxide
(SPh in this case) is expected. In six-coordinate mononitrosyl
complexes1, the trans M-L bonds appear to be “long and weak”
when the νNO values of the complexes are less than about 1800
cm-1. W(phen)(CO)2(NO)(SPh) is a mononitrosyl complex with
M(NO),6 and according to Enemark-Feltham20 notation, the
MNO link will be essentially linear.
Crystals of W(phen)(NO)2(toluene-3,4-dithiolate) were grown,
and the structure was solved as shown in Figure 2. The structure
of the starting material, W(phen)(CO)2(toluene-3,4-dithiolate),
is trigonal prismatic16,21 compared to the product, which is nearly
octahedral as shown in Figure 2. Crystal and experimental data
are summarized in Tables 4-5. The complex is cis in regards
(21) Lang, R. G.; Ju., T. D.; Bryan, J. C., Kubas, G. J.; Hoff, C. D.
Manuscript in preparation. There is a delicate balance of forces that
exist between octahedral and trigonal geometry in these complexes.
See also: (a) Templeton, J. L.; Ward, B. C. J. Am. Chem. Soc. 1980,
102, 6568. (b) Visscher, M. O.; Caulton, K. G. J. Am. Chem. Soc.
1972, 94, 5923. (c) Kubacek, P.; Hoffmann, R. J. Am. Chem. Soc.
1981, 103, 4320.
(20) Enemark, J. H.; Feltham, R. D. Coord. Chem. ReV. 1974, 13, 339.

Elimination Reactions of •NO
Inorganic Chemistry, Vol. 38, No. 26, 1999 6215
Table 4. Bond Lengths (Å) for
W(phen)(NO)2(toluene-3,4-dithiolate)
W-N4
1.815(5)
1.835(5)
2.185(4)
2.246(4)
2.423(1)
2.461(1)
1.755(7)
1.771(6)
1.338(7)
1.373(7)
1.339(7)
1.355(7)
1.180(6)
1.197(6)
1.197(6)
1.403(8)
1.381(10)
1.386(12)
1.409(10)
C13-C16
C14-C15
C20-C21
C21-C22
C22-C23
C23-C31
C23-C24
C24-C25
C25-C26
C26-C30
C26-C27
C27-C28
C28-C29
C30-C31
O1-C1
1.472(11)
1.405(8)
1.382(9)
1.360(10)
1.416(9)
1.411(8)
1.427(9)
1.339(10)
1.431(9)
1.403(7)
1.407(9)
1.361(10)
1.380(8)
1.419(8)
1.464(14)
1.479(12)
1.407(17)
1.549(18)
1.418(16)
W-N3
W-N2
W-N1
W-S1
W-S2
S1-C10
S2-C15
N1-C20
N1-C31
N2-C29
N2-C30
N3-O3
N4-O4
C10-C15
C10-C11
C11-C12
C12-C13
C13-C14
O1-C4
Figure 2. Molecular structure of W(phen)(NO)2(toluene-3,4-dithiolate)
(ORTEP, 50% probability ellipsoids). Selected bond distances (Å) and
angles (°): W-N3O3 ) 1.835(5) Å, W-N3-O3 ) 175.7(5)°;
W-N4O4 ) 1.815(5) Å, W-N4-O4 ) 175.5(4)°; N3-W-N4 )
88.8(2)°.
C1-C2
C2-C3
C3-C4
Table 5. Bond Angles (deg) for
W(phen)(NO)2(toluene-3,4-dithiolate)
Table 3. Bond Angles (deg) for W(phen)(CO)2(SPh)(NO)
N4-W-N3
N4-W-N2
N3-W-N2
N4-W-N1
N3-W-N1
N2-W-N1
N4-W-S1
88.8(2)
95.34(19)
99.3(2)
168.75(18)
89.2(2)
C12-C13-C16
C14-C13-C16
C15-C14-C13
C10-C15-C14
C10-C15-S2
C14-C15-S2
N1-C20-C21
C22-C21-C20
C21-C22-C23
C31-C23-C22
C31-C23-C24
C22-C23-C24
C25-C24-C23
C24-C25-C26
C30-C26-C27
C30-C26-C25
C27-C26-C25
C28-C27-C26
C27-C28-C29
N2-C29-C28
N2-C30-C26
N2-C30-C31
C26-C30-C31
N1-C31-C23
N1-C31-C30
C23-C31-C30
C1-O1-C4
120.1(8)
120.0(9)
120.5(7)
119.2(6)
122.3(5)
118.4(6)
122.6(6)
120.5(6)
119.3(6)
117.2(6)
118.4(6)
124.4(6)
121.3(6)
121.6(6)
116.6(6)
118.6(6)
124.8(6)
119.8(6)
120.2(6)
122.0(6)
122.9(5)
117.2(5)
119.8(5)
122.3(5)
117.4(5)
120.3(5)
104.7(10)
107.2(12)
104.7(11)
99.2(11)
107.8(10)
N3-W-C2
89.22(10)
89.47(11)
89.41(12)
96.21(8)
169.40(10)
99.71(10)
97.28(8)
96.23(10)
171.24(9)
74.09(7)
172.98(7)
88.55(8)
83.86(9)
87.08(5)
89.58(5)
107.66(8)
117.7(2)
126.21(16)
116.07(15)
117.8(2)
120.9(3)
122.8(2)
119.6(2)
119.6(2)
117.2(2)
118.9(2)
123.9(2)
N1-C34-C33
N1-C34-C35
C33-C34-C35
N2-C35-C36
N2-C35-C34
C39-N2-W
123.1(2)
116.9(2)
119.9(2)
122.8(2)
117.0(2)
126.15(17)
115.87(15)
176.6(2)
179.8(4)
176.5(2)
117.8(2)
121.3(2)
120.9(2)
120.8(3)
120.5(3)
120.1(3)
120.0(3)
120.2(2)
117.3(2)
118.4(2)
124.3(2)
119.8(2)
119.5(2)
122.7(2)
120.8(2)
121.8(2)
N3-W-C1
C2-W-C1
N3-W-N2
C2-W-N2
74.10(16)
101.58(15)
93.42(16)
159.03(12)
89.59(11)
93.90(16)
177.08(16)
81.70(12)
88.47(13)
84.84(5)
105.6(2)
104.3(2)
118.0(5)
127.7(4)
114.2(3)
118.4(5)
124.5(4)
117.1(3)
175.7(5)
175.5(4)
119.1(6)
122.7(5)
118.2(6)
121.9(7)
119.3(7)
119.8(7)
C1-W-N2
N3-W-N1
C2-W-N1
C35-N2-W
N3-W-S1
O3-N3-W
N2-W-S1
C1-W-N1
O1-C1-W
N1-W-S1
N2-W-N1
N3-W-S1
O2-C2-W
N4-W-S2
C15-C10-C11
C15-C10-S1
C11-C10-S1
C12-C11-C10
C13-C12-C11
C12-C13-C14
C13-C14-C15
C36-C35-C34
C35-C36-C37
C35-C36-C41
C37-C36-C41
C38-C37-C36
C37-C38-C39
N2-C39-C38
C41-C40-C33
C40-C41-C36
N3-W-S2
C2-W-S1
N2-W-S2
C1-W-S1
N1-W-S2
N2-W-S1
S1-W-S2
N1-W-S1
C10-S1-W
C15-S2-W
C20-N1-C31
C20-N1-W
C31-N1-W
C29-N2-C30
C29-N2-W
C30-N2-W
O3-N3-W
O4-N4-W
C15-C10-C11
C15-C10-S1
C11-C10-S1
C12-C11-C10
C11-C12-C13
C12-C13-C14
C10-S1-W
C30-N1-C34
C30-N1-W
C34-N1-W
C39-N2-C35
C14-C15-C10
N1-C30-C31
C32-C31-C30
C31-C32-C33
C34-C33-C32
C34-C33-C40
C32-C33-C40
C2-C1-O1
C1-C2-C3
to the two NO ligands. Given the strong π-acid nature of the
NO ligand, the majority of dinitrosyl complexes possess cis
geometry. Both NO ligands are essentially linear, as predicted
by Enemark-Feltham20 notation. The W-N3-O3 angle is
175.7(5)° with a W-NO length of 1.835(5) Å, and the W-N4-
O4 angle is 175.5(4)° with a W-NO length of 1.815(5) Å. The
N-W-N angle of 88.8(2)° ιs in accord with related group VI
structures of the form cis-M(NO)2(chelate)2.21 All other bond
distances and angles are within the expected range.
C4-C3-C2
C3-C4-O1
results in eq 10. The metal-containing products showed spec-
W(phen)(CO)3(RSH) + 2NO f
M(phen)(CO)2(SR)(NO) + “HNO” + CO (10)
Reaction of Nitric Oxide and Thiols Coordinated to Metal.
The complex W(phen)(CO)3(EtCN) has been shown to bind
thiols as shown in eq 9. In the case of PhSH, oxidative addition
troscopic parameters identical to those of W(phen)(CO)2(SR)-
(NO) complexes prepared from bisthiolates as described above.
The complex HNO is unstable and known to decompose
rapidly.22 In the presence of •NO, formation of N2O and HNO2
would be expected (eq 11). Formation of N2O and HNO2 are
W(phen)(CO)3(EtCN) + RSH f
W(phen)(CO)3(RSH) + EtCN (9)
(22) (a) Gallup, G. A. Inorg. Chem. 1975, 14, 563. (b) Walch, S. P.;
Rohlfing, C. M. J. Chem Phys. 1989, 91, 2939. (c) Guadagnini, R.;
Schatz, G. C.; Walch, S. P. J. Chem. Phys. 1995, 102, 774. (d)
Guadagnini, R.; Schatz, G. C.; Walch, S. P. J. Chem. Phys. 1995,
102, 784.
occurs, but for BuSH a thiol complex is formed.16a Generation
of the thiol adduct (BuSH) or the thiolate hydride16b complex
(PhSH) in methylene chloride followed by exposure to •NO

6216 Inorganic Chemistry, Vol. 38, No. 26, 1999
HNO + 2•NO f N2O + HNO2
Capps et al.
reaction. This may simply be the result of trapping an ejected
thiyl radical.24
(11)
Reaction 8 was investigated in hopes of trapping a bound
nitrosothiol. The complex W(phen)(benzene-3,4-dithiolate)(CO)2
has been prepared and structurally characterized.16,21 Reaction
in a fashion similar to that shown in eq 6 would be expected to
produce the complex W(phen)(NO)(CO)2(-S-Arene-S-NO).
No evidence for formation of such a complex, even as an
intermediate has been found. As shown in reaction 8, as well
as the crystal structure in Figure 2, it is CO and not a thiyl
radical or its nitrosylated derivative that are ejected from the
metal (eq 16).15 Disruption of the chelate system may provide
assigned on the basis of FT-IR data that were in agreement with
authentic samples prepared and studied under the same condi-
tions.
Discussion
The main goal of this work was to determine if •NO would
be able to attack the sulfur-hydrogen bond in the complex
W(phen)(CO)3(BuSH), as was shown to occur for the transition-
metal-based radical •Cr(CO)3C5Me5 as shown in eq 5. To be
able to characterize the metal-containing products, the reaction
of •NO with W(phen)(CO)2(SR)2 complexes was investigated
first. As shown in eq 6, the W(II) bisthiolate undergoes reductive
elimination of PhSNO and formation of the W(0) nitrosyl thiyl
complex, the crystal structure of which is shown in Figure 1.
The net driving force for elimination of RSNO is no doubt
formation of the strong W-NO bond in the complex. It has
been shown that CO rapidly adds to the 16 e- complex and
that the equilibrium17,18 shown in eq 12 is rapidly established.
resistance to reductive elimination of nitrosothiol in this system.
The structures in Figures 1 and 2 warrant additional comment.
Few complexes of the form M(NO)(SPh) have been isolated,
with even fewer being characterized by X-ray analysis. Richter-
Addo23 has synthesized (OEP)Os(NO)(SPh) by trans addition
of RSNO to (OEP)Os(CO), and Bohle25 has synthesized a
related complex, (TTP)Ru(NO)(S-p-tolyl), by a thiol exchange
reaction of the precursor methoxide, (TTP)Ru(NO)(OMe);
however, the crystal structure of neither has been reported. For
group VI metals, most M(NO)(SR) complexes are of the form
of the five-coordinate neutral M(NO)(SR)3(NH3) or anionic
[M(NO)(SR)4]- and M(NO)(SR)3Cl]- complexes (M ) Mo,
W; R ) alkyl, aryl).26
W(phen)(CO)2(SPh)2 + CO h W(phen)(CO)3(SPh)2
(12)
It is reasonable to predict that, because the M-NO bond appears
to be stronger than the M-CO bond,5,7 •NO would also rapidly
bind as shown in eq 13.12 A mechanistic study of whether the
The most interesting result of this work is the observation
that stable products (N2O and HNO2), which can be attributed
to decomposition of HNO, are formed when either W(phen)-
(CO)3(SPh)(H) or W(phen)(CO)3(HSBu) are exposed to •NO.
We have recently completed detailed mechanistic study of
reaction of H-Cr(CO)3C5Me5 and •NO proposed to proceed
by the mechanism shown in eq 17.16 The decomposition
proposed second step of reaction 13 is dissociative (loss of CO
or •SPh) or associative (attack by a second mole of •NO) is
planned.
In apparent contrast to our observed reductive elimination
of RSNO, Richter-Addo23 has recently reported oxidative
addition of thionitrosyls. Trans addition of RSNO compounds
to the metal center in ruthenium and osmium porphyrins of the
form (por)M(CO) [por ) octaethylporphyrinato dianion (OEP),
tetratolyporphyrinato dianion (TTP)] gives (por)M(NO)(SR) as
shown in eq 14. For the organochromium complexes shown in
products (N2O and HNO2) were again taken as sign of initial
formation of HNO. The enthalpy of activation for reaction 17
(∼12 kcal/mol7) is in keeping with thermochemical estimates
for the uphill H atom transfer in the first step. Because according
to eq 17 NO• is capable of slow abstraction of an H atom from
H-Cr and in eq 5 •Cr is capable of rapid abstraction of an H
atom from the W(phen)(CO)3(BuSH), it is proposed that reaction
10 may proceed in as shown in Scheme 1. The principle
difference between reaction 5 and Scheme 1 is the irreversible
oxidative addition of RSNO to form the metal nitrosyl complex
(Scheme 1) versus ligand displacement of bound BuS-Cr-
(CO)3C5Me5 by free BuSH in eq 5.
(por)M(CO) + RSNO f (por)M(SR)(NO) + CO (14)
eq 15, however, reductive elimination of RSNO has been shown7
RS-Cr(CO)3C5Me5 + 2•NO f
RSNO + Cr(NO)(CO)2C5Me5 (15)
to occur for R ) H, Me, Ph. It is clear that oxidative addition/
reductive elimination of RSNO depends critically on the
complex and conditions. It should be pointed out that the
reactions in which reductive elimination of RSNO was observed
(eqs 6 and 15) a metal-nitrosyl bond is formed during the
(24) Although it seems reasonable that RSNO should be eliminated from
the metal center, the strength of nitric oxide as a ligand may allow
direct elimination and subsequent trapping of a thiyl radical. See ref
7 for further discussion.
(25) Bohle, D. S.; Goodson, P. A.; Smith, B. D. Polyhedron 1996, 15,
3147.
(23) (a) Yi, G. B.; Chen, L.; Khan, M. A.; Richter-Addo, G. B. Inorg.
Chem. 1997, 36, 3876. (b) Yi, G. B.; Khan, M. A.; Richter-Addo, G.
B. Chem. Commun. 1996, 2045. (c) Chen, L.; Khan, M. A.; Richter-
Addo, G. B. Inorg. Chem. 1998, 37, 533. (d) Yi, G. B.; Khan, M. A.;
Powell, D. R.; Richter-Addo, G. B. Inorg. Chem. 1998, 37, 208.
(26) Bishop, P. T.; Dilworth, M. J. R.; Hutchinson, J.; Zubieta, J. J. Chem.
Soc., Dalton Trans. 1986, 967.

Elimination Reactions of •NO
Inorganic Chemistry, Vol. 38, No. 26, 1999 6217
Scheme 1
coordination or oxidative addition of a thiol to decrease the
effective sulfur-hydrogen bond strength than about any per-
ceived similarity of two such different radicals. The authors view
Scheme 1 as the most reasonable explanation of the observed
reactions reported here. Detailed additional work will be required
before the rates and mechanisms of so complicated a reaction
as shown in eq 10 can be established. Such work is in progress.27
Acknowledgment. Support of this work by the National
Science Foundation and the Petroleum Research Fund admin-
istered by the American Chemical Society is gratefully ac-
knowledged. K.A.A. wishes to acknowledge the National
Science Foundation and the University of Florida for funding
of the purchase of the X-ray equipment. A.B. thanks the
Deutsche Forschungsgemeinschaft (DFG) for the granted post-
doctoral fellowship.
Conclusion
Supporting Information Available: Two X-ray crystallographic
files in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
This work began to investigate if the “weak” main group
radical •NO would react in a way analogous to what was found
for the “weak” transiton metal radical •Cr(CO)3C5Me5. For the
complexes W(phen)(CO)3(HSBu) and W(phen)(CO)3(SPh)(H),16
transfer of hydrogen to •NO gave products consistent with
decomposition of HNO. This says more about the ability of
IC990830H
(27) Sukcharoenphon, K.; Capps, K. B.; Hoff, C. D. Work in progress.