Mechanistic control of product selectivity. Reactions between cis-/trans-[Os(VI)(tpy)(Cl)2(N)]+ and triphenylphosphine sulfide

Article abstract of DOI:10.1021/ic991425t

Reactions between the Os(VI)-nitrido complexes cis- and trans-[Os(VI)(tpy)(Cl)₂(N)]⁺ (tpy is 2,2':6',2_-terpyridine) and triphenylphosphine sulfide, SPPh₃, give the corresponding Os(IV)-phosphoraniminato, [Os(IV)(tpy)(Cl)₂-(NPPh₃)]⁺, and Os(II)-thionitrosyl, [Os(II)(tpy)(Cl)₂(NS)]⁺, complexes as products. The Os-N bond length and Os-N-P angle in cis-[Os(IV) (tpy)(Cl)₂(NPPh₃)](PF₆) are 2.077(6) A and 138.4(4)°. The rate law for formation of cis- and trans-[Os(IV)(tpy)(Cl)₂(NPPh₃)]⁺ is first order in both [Os(VI)(tpy)(Cl)₂(N)]⁺ and SPPh₃ with k(trans)(25 °C, CH₃CN) = 24.6 ± 0.6 M^-1 s^-1 and k(cis)(25 °C, CH₃CN) = 0.84 ± 0.09 M^-1 s^-1. As found earlier for [Os(II)-(tpm)(Cl)₂(NS)]⁺, both cis- and trans-[Os(II)(tpy)(Cl)₂(NS)]⁺ react with PPh₃ to give [Os(IV)(tpy)(Cl)₂(NPPh₃)]⁺ and SPPh₃. For both complexes, the reaction is first order in each reagent with k(trans)(25 °C, CH₃CN) = (6.79 ± 0.08) x 10² M^-1 s^-1 and k(cis)(25 °C, CH₃CN) = (2.30 ± 0.07) x 10² M^-1 s^-1. The fact that both reactions occur rules out mechanisms involving S atom transfer. These results can be explained by invoking a common intermediate, [Os(IV)(tpy)(Cl)₂(NSPPh₃)]⁺, which undergoes further reaction with PPh₃ to give [Os(IV)(tpy)(Cl)₂(NPPh₃)]⁺ and SPPh₃ or with [Os(VI)(tpy)(Cl)₂(N)]⁺ to give [Os(IV)(tpy)(Cl)₂(NPPh₃)]⁺ and [Os(II)(tpy)(Cl)₂(NS)]⁺.

Full text of DOI:10.1021/ic991425t

Inorg. Chem. 2000, 39, 2825-2830
2825
Mechanistic Control of Product Selectivity. Reactions between cis-/trans-[OsVI(tpy)(Cl)2(N)]+
and Triphenylphosphine Sulfide
My Hang V. Huynh, Peter S. White, and Thomas J. Meyer*,†
Venable and Kenan Laboratories, Department of Chemistry, The University of North Carolina
at Chapel Hill, Chapel Hill, North Carolina 27599-3290
ReceiVed December 14, 1999
Reactions between the Os(VI)-nitrido complexes cis- and trans-[OsVI(tpy)(Cl)2(N)]+ (tpy is 2,2′:6′,2′′-terpyridine)
and triphenylphosphine sulfide, SPPh3, give the corresponding Os(IV)-phosphoraniminato, [OsIV(tpy)(Cl)2-
(NPPh3)]+, and Os(II)-thionitrosyl, [OsII(tpy)(Cl)2(NS)]+, complexes as products. The Os-N bond length and
Os-N-P angle in cis-[OsIV(tpy)(Cl)2(NPPh3)](PF6) are 2.077(6) Å and 138.4(4)°. The rate law for formation of
cis- and trans-[OsIV(tpy)(Cl)2(NPPh3)]+ is first order in both [OsVI(tpy)(Cl)2(N)]+ and SPPh3 with ktrans(25 °C,
CH3CN) ) 24.6 ( 0.6 M-1 s-1 and kcis(25 °C, CH3CN) ) 0.84 ( 0.09 M-1 s-1. As found earlier for [OsII-
(tpm)(Cl)2(NS)]+, both cis- and trans-[OsII(tpy)(Cl)2(NS)]+ react with PPh3 to give [OsIV(tpy)(Cl)2(NPPh3)]+
and SPPh3. For both complexes, the reaction is first order in each reagent with ktrans(25 °C, CH3CN) ) (6.79 (
0.08) × 102 M-1 s-1 and kcis(25 °C, CH3CN) ) (2.30 ( 0.07) × 102 M-1 s-1. The fact that both reactions occur
rules out mechanisms involving S atom transfer. These results can be explained by invoking a common intermediate,
[OsIV(tpy)(Cl)2(NSPPh3)]+, which undergoes further reaction with PPh3 to give [OsIV(tpy)(Cl)2(NPPh3)]+ and
SPPh3 or with [OsVI(tpy)(Cl)2(N)]+ to give [OsIV(tpy)(Cl)2(NPPh3)]+ and [OsII(tpy)(Cl)2(NS)]+.
[OsII(tpm)(Cl)2(NS)]+ + PPh3 f
Introduction
[OsIV(tpm)(Cl)2(NSPPh3)]+ (3a)
In an earlier paper, we described a reaction between
[OsII(tpm)(Cl)2(NS)]+ (tpm ) tris(pyrazol-1-yl)methane) and
PPh3 which gives as products [OsIV(tpm)(Cl)2(NPPh3)]+
and SPPh3, eq 1.1 The reaction is first order in both
followed by rapid reaction with PPh3
[OsIV(tpm)(Cl)2(NSPPh3)]+ + PPh3 f
[OsIV(tpm)(Cl)2(NPPh3)]+ + SPPh3 (3b)
[OsII(tpm)(Cl)2(NS)]+ + 2PPh3 f
[OsIV(tpm)(Cl)2(NPPh3)]+ + SPPh3 (1)
We have subsequently discovered that both cis- and trans-
[OsVI(tpy)(Cl)2(N)]+ (tpy is 2,2′:6′,2′′-terpyridine) undergo
reactions with SPPh3 to give the corresponding cis and trans
isomers of [OsII(tpy)(Cl)2(NS)]+ and [OsIV(tpy)(Cl)2(NPPh3)]+,
eq 4. Both of the thionitrosyl complexes also undergo reactions
[OsII(tpm)(Cl)2(NS)]+ and PPh3 with k(25 °C, CH3CN) ) 40
( 1 M-1 s-1. One mechanism that was proposed was S atom
transfer
2[OsVI(tpy)(Cl)2(N)]+ + SPPh3 f
[OsII(tpm)(Cl)2(NS)]+ PPh3 f
[OsII(tpy)(Cl)2(NS)]+ + [OsIV(tpy)(Cl)2(NPPh3)]+ (4)
[OsVI(tpm)(Cl)2(N)]+ + SPPh3 (2a)
with PPh3 to give SPPh3 as in eq 1. We show here that the fact
that both reactions occur rules out mechanisms involving simple
S atom transfer. The results can be explained by invoking a
common intermediate that undergoes subsequent reactions with
either [OsVI(tpy)(Cl)2(N)]+ or PPh3.
The following abbreviations are used in this study: trans-
[OsVItN]+, trans-[OsVI(tpy)(Cl)2(N)]+, trans-[OsII-NS]+, trans-
[OsII(tpy)(Cl)2(NS)]+ , trans-[OsIV-NPPh3]+, trans-[OsIV(tpy)-
(Cl)2(NPPh3)]+, cis-[OsVItN]+, cis-[OsVI(tpy)(Cl)2(N)]+,
cis-[OsII-NS]+, cis-[OsII(tpy)(Cl)2(NS)]+, cis-[OsIV-NPPh3]+,
cis-[OsIV(tpy)(Cl)2(NPPh3)]+, tpy, 2,2′:6′,2′′-terpyridine; triphenyl-
phosphine sulfide, SPPh3; TBAH, tetra-n-butylammonium
hexafluorophosphate.
followed by reaction between the released nitrido complex and
PPh3 which is known to be rapid2
[OsVI(tpm)(Cl)2(N)]+ + PPh3 f
[OsIV(tpm)(Cl)2(NPPh3)]+ (2b)
A second mechanism proposed formation of an intermediate
† Current address: Associate Laboratory Director for Strategic and
Supporting Research, Los Alamos National Laboratory, MS A127, Los
Alamos, NM 87545. E-mail: tjmeyer@lanl.gov. Phone: 1-505-667-8597.
Fax: 1-505-667-5450.
(1) El-Samanody, E.-S.; Demadis, K. D.; Gallagher, L. A.; Meyer, T. J.;
White, P. S. Inorg. Chem. 1999, 38, 3329.
Experimental Section
(2) (a) Bakir, M.; Dovletoglou, A.; White, P. S.; Meyer, T. J. Inorg. Chem.
1991, 30, 2835. (b) Demadis, K. D.; Bakir, M.; Klesczewski, B. G.;
William, D. S.; Meyer, T. J.; White, P. S. Inorg. Chim. Acta 1998,
270, 511.
Materials. House-distilled water was purified with a Barnstead
E-Pure deionization system. High-purity acetonitrile was used as
received from Burdick & Jackson. Osmium tetraoxide (>99%) was
10.1021/ic991425t CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/09/2000

2826 Inorganic Chemistry, Vol. 39, No. 13, 2000
Huynh et al.
Table 1. Summary of Crystal Data, Intensity Collection Details,
purchased from Alfa-AESAR. SPPh3 was purchased from Aldrich and
used without further purification. TBAH was recrystallized three times
from boiling ethanol and dried under vacuum at 120 °C for 2 days.
Common laboratory chemicals employed in the preparation of com-
pounds were of reagent grade and were used without further purification.
Instrumentation and Measurements. FTIR, 1H NMR, UV-visible,
and near-IR spectroscopy, elemental analyses, cyclic voltammetry, and
kinetic studies with UV-visible monitoring were performed similarly
to those of ref 1. All kinetic studies were performed in CH3CN at 25.0
( 0.1 °C with pseudo-first-order excesses of SPPh3 and PPh3. The
concentrations of solutions containing [OsVItN]+ were 8.16 × 10-6
M for trans-[OsVItN]+ and 4.90 × 10-5 M for cis-[OsVItN]+. The
concentrations of SPPh3 were varied from 6.70 × 10-5 to 6.70 × 10-4
M for trans-[OsVItN]+ and from 5.72 × 10-4 to 5.72 × 10-3 M for
cis-[OsVItN]+. The concentrations of solutions containing [OsII-NS]+
were 1.05 × 10-5 M for trans-[OsII-NS]+ and 1.35 × 10-5 M for
cis-[OsII-NS]+. The concentrations of PPh3 were varied from 1.16 ×
10-4 to 1.16 × 10-3 M for trans-[OsII-NS]+ and from 1.62 × 10-4 to
1.62 × 10-3 M for cis-[OsII-NS]+. All rate constants cited in this work
are reported as the averages of at least three independent experiments.
Synthesis and Characterization. The following complexes and
compounds were prepared by literature procedures: trans-[OsVI(tpy)-
(Cl)2(N)](PF6),3 trans-[OsII(tpy)(Cl)2(NS)](PF6),4 trans-[OsIV(tpy)(Cl)2-
(NPPh3)](PF6),2 and cis-[OsVI(tpy)(Cl)2(N)](PF6).3
cis-[OsII(tpy)(Cl)2(NS)](PF6) and cis-[OsIV(tpy)(Cl)2(NPPh3)](PF6).
In a two-necked, round-bottom flask, cis-[OsVI(tpy)(Cl)2(N)]+ (300 mg,
0.459 mmol) was stirred in 150 mL of CH3CN under an argon
atmosphere for 15 min. A 1.1 equiv amount of SPPh3 (150 mg, 0.509
mmol) in 20 mL of CH3CN was bubbled with argon for 5 min and
added to the cis-[OsVI(tpy)(Cl)2(N)]+ solution through a pressure-
equalizing dropping funnel. The reaction mixture was continuously
stirred under argon for 3 h, after which it was filtered through a fine
frit. The brown filtrate was reduced to a small volume by rotary
evaporation, and the concentrate was chilled in an ice bath for 1 h to
precipitate a solid that was identified as cis-[OsII(tpy)(Cl)2(NS)](PF6).
Upon addition of Et2O to the concentrated filtrate, a second solid,
cis-[OsIV(tpy)(Cl)2(NPPh3)](PF6), was obtained and recrystallized from
CH3CN/Et2O.
and Structure Refinement Parameters for
cis-[OsIV(tpy)(Cl)2(NPPh3)](PF6)
empirical formula
mol wt
a (Å)
b (Å)
c (Å)
OsC33H26N4Cl2P2F6
915.63
9.2444(4)
17.6325(8)
20.1026(9)
91.310(1)
3275.9(3)
4
â (Å)
V (Å3)
Z
crystal system
space group
crystal size (mm)
monoclinic
P21/c
0.40 × 0.05 × 0.05
d
calcd (g/cm3)
1.857
diffractometer
radiation; λ (Å)
collcn temp (°C)
abs coeff, µ (cm-1
F(000)
Siemens CCD Smart
Mo KR; 0.710 73
-100
5.75
1783.63
50.0
14 004
5771
4222
0.037
434
0.059
0.045
0.000
-1.750
1.980
0.0549
)
2θmax (deg)
no. of tot. reflns
no. of unique reflns
no. of refined reflns
merging R value
no. of params
R (%)a
Rw (%)b
goodness of fitc
deepest hole (e/Å3)
highest peak (e/Å3)
σ
2
a R ) ∑|Fo - Fc|/∑|Fo|. b Rw ) [∑w(Fo - Fc)2/∑wFo ]1/2
.
c GoF )
[∑w(Fo - Fc)2/(no. of reflns - no. of params)]1/2
.
V (NS+ f NS•), E1/2 ) -0.28 V (NS• f NS-), and E1/2 ) 0.97 V
(Os(III/II)) vs SSCE in 0.1 M TBAH, 1:1 (v/v) DMF/CH3CN.
X-ray Structural Determination. Single crystals of cis-[OsIV(tpy)-
(Cl)2(NPPh3)](PF6) were obtained by slow diffusion of Et2O into a CH3-
CN solution. Crystal data, intensity collection details, and structure
refinement parameters are listed in Table 1. The structure was solved
by direct methods. The remaining non-hydrogen atoms were located
in subsequent difference Fourier maps. Empirical absorption corrections
were applied with SADABS. The ORTEP plotting program was used
to computer-generate the structure shown in Figure 1.5 Hydrogen atoms
were included in calculated positions with thermal parameters derived
from the atoms to which they were bonded. All computations were
performed by using the NRCVAX suite of programs.6 Atomic scattering
factors were taken from a standard source7 and corrected for anomalous
dispersion. The final positional parameters along with their standard
deviations as estimates from the inverse matrix, hydrogen atom
parameters, thermal parameters, and bond distances and angles for cis-
[OsIV(tpy)(Cl)2(NPPh3)](PF6) are available as Supporting Information.
Selected bond distances and angles for the cation are listed in Tables
2 and 3, respectively.
cis-[OsII(tpy)(Cl)2(NS)](PF6): yield 0.126 g (40.0%). Anal. Calcd
for OsC15H11N4Cl2SPF6: C, 26.29; H, 1.62; N, 8.17. Found: C, 26.40;
H, 1.73; N, 8.25.
cis-[OsIV(tpy)(Cl)2(NPPh3)](PF6): yield 0.192 g (45.7%). Anal. Calcd
for OsC33H26N4Cl2P2F6: C, 43.29; H, 2.86; N, 6.12. Found: C, 43.18;
H, 2.73; N, 6.23. Infrared data (cm-1; KBr disks): ν(14NdP) 1112 (vs);
ν(tpy) 1474 (vs), 1449 (vs), 1384 (vs). UV-vis data [CH3CN; λmax
,
nm (ꢀ, M-1 cm-1)]: 724 (310); 484 (2.18 × 103); 464 (2.40 × 103);
406 (2.75 × 103); 364 (9.77 × 103); 318 (2.05 × 104); 276 (3.00 ×
104); 236 (4.59 × 104); 216 (4.83 × 104). Cyclic voltammetry data:
E1/2 ) 1.06 V (Os(IV/III)) and E1/2 ) -0.16 V (Os(III/II)) vs SSCE in
0.1 M TBAH/CH3CN.
cis-[OsII(tpy)(Cl)2(NS)](SCN). A 100 mg (46 µmol) quantity of cis-
[OsVI(tpy)(Cl)2(N)]+ was dissolved in 15 mL of acetone and 60 mL of
CS2. A solution of (PPN)N3 (PPN+ ) bis(triphenylphosphoranylidene)-
ammonium cation) (27 mg, 46 mmol) in 15 mL of acetone was added
dropwise to the mixture under stirring. The brown reaction mixture
was stirred at room temperature for 2 h, during which a brown solid
formed. This solid was filtered off, washed with acetone and Et2O,
and recrystallized from CH3CN/Et2O: yield 78.6 mg (85.8%). Anal.
Calcd for OsC16H11N5Cl2S2‚1.5H2O: C, 30.72; H, 2.26; N, 11.02.
Found: C, 31.05; H, 2.22; N, 10.55. UV-vis data [CH3CN; λmax, nm
(ꢀ, M-1 cm-1)]: 603 (400); 410 (1.20 × 103); 362 (8.45 × 103); 346
(9.63 × 103); 274 (2.69 × 104); 238 (3.54 × 104); 216 (3.60 × 104).
Infrared data (cm-1; KBr disk): ν(tpy) 1473 (vs), 1450 (vs), 1397 (vs);
ν(NtS) 1287; ν(SCN) 2045. Cyclic voltammetry data: E1/2 ) -0.09
Results
Synthesis and Mechanism of Formation. In the preparations
of cis-[OsII(tpy)(Cl)2(NS)]+ and cis-[OsIV(tpy)(Cl)2(NPPh3)]+,
stoichiometric addition of triphenylphosphine sulfide in CH3-
CN (1.53 × 10-2 M) to cis-[OsVI(tpy)(Cl)2(N)]+ in CH3CN (2.55
× 10-3 M) resulted in a color change from brown to darker
brown within 20 min. After 3 h of stirring, the brown solution
(5) Johnson, C. K. ORTEP: A Fortran Thermal Ellipsoid Plot Program;
Technical Report ORNL-5138; Oak Ridge National Laboratory: Oak
Ridge, TN, 1976.
(6) Gabe, E. J.; Le Page, Y.; Charland, J.-P.; Lee, F. L.; White, P. S. J.
Appl. Crystallogr. 1989, 22, 384.
(7) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, U.K., 1974; Vol. IV.
(3) (a) Ware, D. C.; Taube, H. Inorg. Chem. 1991, 30, 4598. (b) Pipes,
D. W.; Bakir, M.; Vitols, S. E.; Hodgson, D. J.; Meyer, T. J. J. Am.
Chem. Soc. 1990, 112, 5507.
(4) (a) Demadis, K. D.; El-Samanody, E.-S.; Meyer, T. J.; White, P. S.
Inorg. Chem. 1998, 37, 838. (b) Demadis, K. D.; Meyer, T. J.; White,
P. S. Inorg. Chem. 1998, 37, 3610.

Mechanistic Control of Product Selectivity
Inorganic Chemistry, Vol. 39, No. 13, 2000 2827
average of three independent experiments. On the basis of the
experimental slopes and the above rate law, ktrans(25 °C, CH3-
CN) ) 24.6 ( 0.6 M-1 s-1 and kcis(25 °C, CH3CN) ) 0.84 (
0.09 M-1 s-1
.
A rapid reaction occurs upon mixing excess PPh3 and
[OsII(tpy)(Cl)2(NS)]+ in CH3CN. The products of the reaction
were determined to be [OsIV(tpy)(Cl)2(NPPh3)]+ by UV-visible
measurements at 470, 412, and 354 nm and SPPh3 by IR with
characteristic bands at 1434 (vs), 1306, 1103 (vs), 714, and 517
cm-1 matched to those of an authentic sample (Aldrich).1 On
the basis of the results of a kinetics study with UV-visible
monitoring, the rate law was first order in each reagent:
-d[OsII-NS+]
) k[OsII-NS+][PPh3] ) kobs[OsII-NS+]
dt
Figure 1. ORTEP diagram (30% ellipsoids) and labeling scheme for
with kobs ) k[PPh3]. From the slope of a plot of kobs vs [PPh3],
the cation cis-[OsVI(tpy)(Cl)2(NPPh3)]+ in the PF6 salt.
-
k
trans(25 °C, CH3CN) ) (6.79 ( 0.08) × 102 M-1 s-1 and kcis(25
°C, CH3CN) ) (2.30 ( 0.07) × 102 M-1 s-1
.
1H NMR Spectroscopy. The 1H NMR spectrum of cis-
[OsIV(tpy)(Cl)2(NPPh3)]+ shows that the complex is diamag-
netic, with resonances for the aromatic protons from the tpy
and PPh3 ligands appearing from 7.35 to 10.54 ppm. Earlier 1H
NMR measurements on trans-[OsIV(tpy)(Cl)2(NPPh3)]+ revealed
that it is paramagnetic.2b As expected, trans- and cis-[OsII(tpy)-
(Cl)2(NS)]+ are diamagnetic. For trans-[OsII(tpy)(Cl)2(NS)]+,
aromatic protons for the tpy ligand appear at 7.91-7.95 ppm
(triplet of 5- and 5′′-protons), 8.16-8.22 ppm (triplet of 4- and
4′′-protons), 8.47-8.52 ppm (triplet of 4′-protons), 8.53-8.59
ppm (doublet of 3-, 3′-, 5′-, and 3′′-protons), and 8.72-8.75
ppm (doublet of 6- and 6′′-protons). The protons of the tpy
ligand in cis-[OsII(tpy)(Cl)2(NS)]+ appeared in a similar pat-
tern: 8.06-8.10 ppm (triplet of 5- and 5′′-protons), 8.51-8.57
ppm (triplet of 4- and 4′′-protons), 8.73-8.78 ppm (triplet of
4′-protons), 8.97-9.00 ppm (doublet of 3-, 3′-, 5′-, and
3′′-protons), and 9.29-9.30 ppm (doublet of 6- and 6′′-protons).
UV-Visible Spectroscopy. The UV spectrum of cis-
[OsIV(tpy)(Cl)2(NPPh3)]+ is dominated by intense π f π*(tpy)
bands at 318, 276, 236, and 216 nm and a band for the phenyl-
containing phosphoraniminato ligand at 280 nm. A series of
relatively intense charge-transfer bands appear in the visible
region at 724, 484, 464, 406, and 364 nm, and two weak
interconfigurational (IC) dπ f dπ bands appear in the near-IR
region at 1765 and 1913 nm.
Figure 2. Plots of kobs versus [SPPh3] for the formations of cis-
[OsIV(tpy)(Cl)2(NPPh3)](PF6) (O) and trans-[OsIV(tpy)(Cl)2(NPPh3)]-
(PF6) (9) in CH3CN at 25.0 ( 0.1 °C.
was reduced to a small volume and then chilled in an ice-
-
water bath for 1 h. The PF6 salt of cis-[OsII(tpy)(Cl)2(NS)]+
that precipitated was filtered off, washed with a small amount
of cold CH3CN, and air-dried. The filtrate was further concen-
-
trated and added dropwise to Et2O to precipitate the PF6 salt
of cis-[OsIV(tpy)(Cl)2(NPPh3)]+, which was recrystallized from
CH3CN/Et2O.
Reaction between cis-[OsVI(tpy)(Cl)2(N)]+ and SPPh3 pro-
vides a useful synthetic route to cis-[OsII(tpy)(Cl)2(NS)]+ and
cis-[OsIV(tpy)(Cl)2(NPPh3)]+, which were previously unknown.
The structure of cis-[OsIV(tpy)(Cl)2(NPPh3)]+ is shown in Figure
1. This is also a convenient synthetic procedure for trans-
[OsII(tpy)(Cl)2(NS)]+ compared to the earlier reaction involving
Ligand-to-metal charge-transfer bands (LMCT) arising from
Cl- f OsIV charge transfer in trans-[OsIV(PEt3)2(Cl)4] have been
assigned at 465 and 380 nm. E1/2(OsIV/III) ) 0.33 V (vs SSCE
in CH2Cl2) for this complex2b,8 compared to -0.10 V for cis-
[OsIV(tpy)(Cl)2(NPPh3)]+, consistent with the assignment of the
bands at 406 and 364 nm for the latter to ligand-to-metal charge-
-
N3 and CS2.4b SPPh3 may be a useful reagent for the
-
transfer (LMCT) transitions from Cl- or NPPh3 to Os(IV).
preparation of other metal-thionitrosyl complexes from metal-
nitrido complexes.
The visible absorption bands at 724, 484, and 464 nm can
be assigned to metal-to-ligand charge-transfer (MLCT) dπ f
π*(tpy) bands.2b The MLCT assignments are reasonable on
energetic grounds. For example, for trans-[OsII(tpy)(Cl)2(4-
Kinetics. The kinetics and stoichiometry of the reactions
between cis- and trans-[OsVI(tpy)(Cl)2(N)]+ and SPPh3 were
studied in CH3CN at 25.0 ( 0.1 °C by following characteristic
changes in the absorption spectra of [OsVI(tpy)(Cl)2(N)]+ under
pseudo-first-order conditions in SPPh3. As shown by the plots
of kobs vs [SPPh3] in Figure 2, the kinetics are first order in
SPPh3, consistent with the rate law
(CH3)3Cpy)],4b max occurs at 500 nm with E1/2(OsIII/II) ) 0.02
λ
V (vs SSCE in CH3CN) compared to λmax at 484 nm and
E
E
1/2(OsIV/III) ) -0.10 V for cis-[OsIV(tpy)(Cl)2(NPPh3)]+. The
1/2 value for the Os(IV/III) couple shows that the dπ-π*(tpy)
energy gap is comparable to that for the Os(II) complex since
π*1(tpy) is the common acceptor level in both complexes.4b
Molar absorptivities are lower than those for typical Os(II)
MLCT absorption bands, consistent with less dπ(Os(IV) f
π*(tpy)) overlap as expected for the higher oxidation state.
-d[OsVItN+]
) k[OsVItN+][SPPh3] ) kobs[OsVItN+]
dt
with kobs ) k[SPPh3]. Each rate constant in Figure 2 is the

2828 Inorganic Chemistry, Vol. 39, No. 13, 2000
Huynh et al.
Table 2. Selected Bond Lengths (Å) for cis-[OsIV(tpy)(Cl)2(NPPh3)](PF6)
Os(1)-Cl(1)
Os(1)-Cl(2)
Os(1)-N(1)
Os(1)-N(11)
Os(1)-N(21)
Os(1)-N(31)
P(1)-N(1)
P(1)-C(41)
P(1)-C(51)
P(1)-C(61)
N(11)-C(12)
C(43)-C(44)
C(51)-C(52)
C(53)-C(54)
C(61)-C(62)
C(63)-C(64)
2.3780(17)
2.3714(20)
2.071(6)
2.077(6)
1.943(6)
2.064(7)
1.619(7)
1.788(8)
1.784(8)
1.7792(7)
1.315(11)
1.375(14)
1.397(11)
1.384(14)
1.384(12)
1.392(12)
N(11)-C(16)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(15)-C(16)
C(16)-C(22)
N(21)-C(22)
N(21)-C(26)
C(22)-C(23)
C(23)-C(24)
C(24)-C(25)
C(44)-C(45)
C(51)-C(56)
C(54)-C(55)
C(61)-C(66)
C(64)-C(65)
1.403(10)
1.383(13)
1.370(15)
1.382(16)
1.380(13)
1.464(13)
1.390(10)
1.329(11)
1.402(11)
1.369(18)
1.378(18)
1.383(12)
1.403(11)
1.382(13)
1.411(11)
1.383(13)
C(25)-C(26)
C(26)-C(32)
N(31)-C(32)
N(31)-C(36)
C(32)-C(33)
C(33)-C(34)
C(34)-C(35)
C(35)-C(36)
C(41)-C(42)
C(41)-C(46)
C(42)-C(43)
C(45)-C(46)
C(52)-C(53)
C(55)-C(56)
C(62)-C(63)
C(65)-C(66)
1.370(12)
1.506(13)
1.384(11)
1.341(11)
1.383(13)
1.367(18)
1.400(18)
1.385(14)
1.402(11)
1.406(11)
1.385(12)
1.384(12)
1.374(13)
1.385(13)
1.392(11)
1.381(11)
Table 3. Selected Bond Angles (deg) for cis-[OsIV(tpy)(Cl)2(NPPh3)](PF6)
Cl(1)-Os(1)-N(11)
Cl(1)-Os(1)-N(1)
Cl(1)-Os(1)-N(21)
Cl(1)-Os(1)-N(31)
Cl(2)-Os(1)-N(1)
Cl(2)-Os(1)-N(11)
Cl(2)-Os(1)-N(21)
Cl(2)-Os(1)-N(31)
N(1)-Os(1)-N(11)
N(1)-Os(1)-N(21)
N(l)-Os(1)-N(31)
N(11)-Os(1)-N(21)
N(11)-Os(1)-N(31)
Os(1)-N(31)-C(32)
N(1)-P(1)-C(51)
C(44)-C(45)-C(46)
C(41)-C(46)-C(45)
C(26)-C(32)-C(33)
N(31)-C(32)-C(33)
P(1)-C(51)-C(56)
C(52)-C(53)-C(54)
C(51)-C(56)-C(55)
C(62)-C(61)-C(66)
C(63)-C(64)-C(65)
100.25(18)
88.36(17)
177.26(21)
99.34(19)
174.58(18)
88.31(18)
86.57(20)
90.99(20)
97.10(25)
93.92(25)
83.8(3)
Cl(1)-Os(1)-Cl(2)
Os(1)-N(31)-C(36)
P(1)-C(51)-C(56)
N(21)-C(26)-C(25)
C(23)-C(24)-C(25)
N(21)-C(26)-C(32)
C(22)-C(23)-C(24)
C(24)-C(25)-C(26)
C(32)-N(31)-C(36)
N(21)-C(22)-C(23)
N(21)-Os(1)-N(31)
Os(1)-N(1)-P(1)
91.02(7)
129.2(6)
125.2(6)
122.5(9)
121.1(8)
111.4(7)
119.7(9)
118.0(9)
117.4(7)
118.0(8)
79.4(3)
138.4(4)
129.5(5)
112.1(5)
115.1(3)
119.3(7)
114.3(17)
118.2(9)
120.0(9)
118.0(8)
119.6(8)
121.5(6)
120.4(7)
120.3(7)
C(16)-C(22)-N(21)
C(22)-N(21)-C(26)
C(13)-C (14)-C(15)
N(11)-C(16)-C(15)
N(11)-C(16)-C(22)
C(14)-C(15)-C(16)
Os(1)-N(21)-C(22)
Os(1)-N(21)-C(26)
C(51)-P(1)-C(61)
C(41)-P(1)-C(61)
C(33)-C(34)-C(35)
C(41)-P(1)-C(51)
P(1)-C(41)-C(42)
P(1)-C(41)-C(46)
C(41)-C(42)-C(43)
C(42)-C(43)-C(44)
C(43)-C(44)-C(45)
N(31)-C(36)-C(35)
C(25)-C(26)-C(32)
C(51)-C(52)-C(53)
C(54)-C(55)-C(56)
P(1)-C(61)-C(66)
C(62)-C(63)-C(64)
C(61)-C(66)-C(65)
113.5(6)
120.5(7)
119.2(9)
119.4(8)
115.1(7)
120.7(8)
117.9(5)
121.4(5)
110.5(4)
106.2(4)
119.3(9)
104.0(4)
120.1(6)
120.6(6)
120.2(8)
119.7(8)
121.1(9)
123.5(9)
126.0(9)
121.1(8)
120.4(8)
119.1(6)
119.6(8)
119.9(8)
81.0(3)
160.4(3)
113.3(5)
109.0(4)
120.0(8)
119.7(8)
124.1(8)
121.5(9)
125.2(6)
120.4(8)
120.5(8)
119.4(7)
120.3(7)
Os(1)-N(11)-C(12)
Os(1)-N(11)-C(16)
N(1)-P(1)-C(41)
C(42)-C(41)-C(46)
C(26)-C(32)-N(31)
C(34)-C(35)-C(36)
C(32)-C(33)-C(34)
C(52)-C(51)-C(56)
C(53)-C(54)-C(55)
P(1)-C(61)-C(62)
C(61)-C(62)-C(63)
C(64)-C(65)-C(66)
2
2
0
Given the ground-state configuration dπ1 dπ2 dπ3 , the IC bands
at 1765 and 1913 nm can be assigned to the transitions
dπ12dπ22dπ30 f dπ11dπ22dπ31 and dπ12dπ22dπ30 f dπ12dπ21dπ31,
respectively.2b
In the spectrum of cis-[OsIV(tpy)(Cl)2(NS)](SCN), an intense
band for ν(NtS) appears at 1287 cm-1, which is in the normal
range of 1150-1400 cm-1 found for related complexes.10 An
intense band appears at 2045 cm-1 for ν(SCN), and intense
bands at 1473, 1450, and 1397 have their origin in the tpy ligand.
Redox Properties. In cyclic voltammograms of cis-[OsIV(tpy)-
(Cl)2(NPPh3)]+ in 0.1 M TBAH/CH3CN, waves appear at E1/2
) 1.06 and -0.16 V (vs SSCE), arising from Os(V/IV) and
Os(IV/III) couples. There is no evidence for an Os(III/II) wave
to the solvent limit. For comparison, E1/2(OsV/IV) ) 0.92 V and
The UV spectral region for cis-[OsII(tpy)(Cl)2(NS)]+ is
dominated by intense π-π*(tpy) bands at 274, 238, and 216
nm. Bands of relatively low intensity appear at 603, 410, 362,
and 346 nm. Defining the OsII-NS bond to lie along the
molecular z axis, we can assign the bands at 603 and 410 nm
to the Os(II) f NS MLCT transitions dxy f π1*(NS) and dxy
f π2*(NS), respectively.1,9 For the trans isomer, π f π*(tpy)
bands appear at 280, 244, and 218 nm and dxy f π*(NS) bands
at 658 and 434 nm. These data were summarized in the
Experimental Section.
E
1/2(OsIV/III) ) -0.27 V for the trans isomer.2b
In 0.1 M TBAH, 1:1 (v/v) DMF/CH3CN, reduction of trans-
[OsII(tpy)(Cl)2(NS)]+ occurs at E1/2 ) 0.0 and -0.21 V. In the
same solvent, reduction of the cis isomer gives chemically quasi-
reversible couples at E1/2 ) -0.09V and -0.28 V. These
reduction waves appear to be associated with thionitrosyl ligand-
based reductions. Analogous waves have been reported for
trans-[OsII(tpy)(Cl)2(NO)]+ and [OsII(tpm)(Cl)2(NS)]+.1,11 On
the reverse, oxidative, scan, there is evidence for a reversible
oxidation of the trans isomer at 0.91 V and a quasi-reversible
oxidation of the cis isomer at 0.97 V.
Infrared Spectroscopy. Both symmetrical and unsymmetrical
vibrations of the Os-NdP unit in cis-[OsIV(tpy)(Cl)2(NPPh3)]-
(PF6) are observed in KBr, with ν(NdP) appearing at 1112
cm-1. The range for other Os-phosphoraniminato complexes
-
is 1100-1120 cm-1.2 An intense PF6 band appears at 841
cm-1, and intense bands for tpy appear at 1474 (vs), 1449 (vs),
and 1384 (vs) cm-1
.
(10) (a) Roesky, H. W.; Pandey, K. K. AdV. Inorg. Chem. Radiochem. 1983,
26, 337 and references therein. (b) Pandey, K. K. Prog. Inorg. Chem.
1992, 40, 445 and references therein.
(11) (a) Murphy, W. R., Jr.; Takeuchi, K. J.; Meyer, T. J. J. Am. Chem.
Soc. 1982, 104, 517. (b) Ooyama, D.; Nagao, H.; Ito, K.; Nagao, N.;
Howell, F. S.; Mukaida, M. Bull. Chem. Soc. Jpn. 1997, 70, 2141.
(8) Cipriano, R. A.; Levason, W.; Mould, R. A. S.; Pletcher, D.; Webester,
M. J. Chem. Soc., Dalton Trans. 1990, 339.
(9) With the OsII-NS bond axis defined as the z axis, dπ f π*(NS)
mixing is dominated by the dxz and dyz orbitals. The dxy orbital is
orthogonal to these interactions.1

Mechanistic Control of Product Selectivity
Inorganic Chemistry, Vol. 39, No. 13, 2000 2829
Scheme 1
Structure and Bonding. An ORTEP diagram of the cation
cis-[OsIV(tpy)(Cl)2(NPPh3)]+ with a labeling scheme is presented
in Figure 1. The crystal contains discrete cis-[OsIV(tpy)(Cl)2-
(NPPh3)]+ cations and PF6- anions. The Cl- ligands remain in
the cis configuration of the parent nitrido complex. There is
evidence in the structure of cis-[OsVI(tpy)(Cl)2(N)]+ for a trans
effect due to the nitrido ligand with the bond length of Os-Cl
trans to the nitrido ligand being 2.518(1) Å and the bond length
of Os-Cl trans to tpy being 2.357(1) Å.12 There is no evidence
for a trans effect in cis-[OsIV(tpy)(Cl)2(NPPh3)]+. The Os-Cl
bond lengths are 2.378(2) and 2.371(2) Å, nearly the same as
the length of Os-Cl trans to tpy in the parent nitrido complex,
2.357(1) Å. The PdN bond length of 1.619(7) Å lies within
the normal range of 1.503-1.656 Å.2b,14 The Cl-Os-N(tpy)
and Cl-Os-N(PPh3) angles are near 180° at 177.26(21) and
174.58(18)°. The Os-N-P angle of 138.4(4)° is in the lower
range of M-N-P angles, 125.3-180°.15
There is no evidence for a trans influence due to NPPh3- or
for Os-N multiple bonding. The Os-N(PPh3) bond length is
2.071(6) Å, which is in the upper range of M-NPR3 bond
lengths (1.65-2.33 Å) and is indicative of a bond order of 1.2b,13
This and the Os-N(PPh3) bond length in the cis isomer (2.071
Å) are comparable to the Os-N bond lengths of the noncentral
pyridyl rings (2.064-2.081 Å) of the tpy ligand. These bond
lengths are relatively isomer independent and consistent with a
single bond. The acute Os-N-P angle of 138.4(4)° is also
consistent with the absence of significant Os-N(PPh3) multiple
bonding.2b This is true even though there are well-established
examples of M-N multiple bonding,14b including a Ti-N bond
length of 1.734(3) Å and a Ti-N-P angle of 160.0(2)° in
[TiIV(Cl)3(NPEt3)(THF)2] consistent with double bonding16 and
a V-N bond length of 1.653(3) Å and a V-N-P angle of
171.8(2)° in [VV(NPMePh2)(Cl)4(NCCH3)] consistent with triple
bonding.17
Discussion
In an earlier study, [OsII(tpm)(Cl)2(NS)]+ was shown to react
with PPh3 to give [OsIV(tpm)(Cl)2(NPPh3)]+ and SPPh3 by a
rate law first order in both reagents.1 In this study, we report
the analogous reactions of cis- and trans-[OsII(tpy)(Cl)2(NS)]+
with PPh3 to give [OsIV(tpy)(Cl)2(NPPh3)]+ and SPPh3, eq 5,
[OsII(tpy)(Cl)2(NS)]+ + 2PPh3 f
[OsIV(tpy)(Cl)2(NPPh3)]+ + SPPh3 (5)
as well as reactions of cis- and trans-[OsVI(tpy)(Cl)2(N)]+ with
SPPh3 to give [OsIV(tpy)(Cl)2(NPPh3)]+ and [OsII(tpy)(Cl)2-
(NS)]+, eq 4.
At first glance, these two reactions seem incompatible. In eq
5, a reaction occurs between [OsII(tpy)(Cl)2(NS)]+ and PPh3
that results in net S atom transfer to PPh3. In eq 4, a reaction
occurs between [OsVI(tpy)(Cl)2(N)]+ and SPPh3 that results in
net S atom transfer in the opposite sense to give [OsII(tpy)-
(Cl)2(NS)]+ and [OsIV(tpy)(Cl)2(NPPh3)]+. The reaction in eq
4 is energetically favored because of the formation of the
coproduct, [OsIV(tpy)(Cl)2(NPPh3)]+.
The fact that both of these reactions occur shows that neither
occurs by a simple S atom transfer mechanism. The results can
be explained by invoking a common intermediate, [OsIV(tpy)-
(Cl)2(NSPPh3)]+. A proposed mechanism is shown in Scheme
1.
If the reaction between [OsII(tpy)(Cl)2(NS)]+ and PPh3
occurred by a S atom transfer mechanism (reaction 4) and path
1 in Scheme 1, the initial products would be [OsVI(tpy)-
(Cl)2(N)]+ and SPPh3. Once formed, they would undergo the
reaction in path 2 of Scheme 1 to give [OsIV(tpy)(Cl)2(NPPh3)]+
and [OsII(tpy)(Cl)2(NS)]+. The actual products are [OsIV(tpy)-
(Cl)2(NPPh3)]+ and SPPh3.
Similarly, if the reaction between [OsVI(tpy)(Cl)2(N)]+ and
SPPh3 occurred by S atom transfer (reaction 2) and path 3 in
Scheme 1, the initial products would be [OsII(tpy)(Cl)2(NS)]+
and PPh3 and the final products would be [OsIV(tpy)(Cl)2-
(NPPh3)]+ and SPPh3 via path 4 in Scheme 1. The actual
products are [OsIV(tpy)(Cl)2(NPPh3)]+ and [OsII(tpy)(Cl)2(NS)]+.
(12) Huynh, M. H. V.; White, P. S.; Meyer, T. J. Unpublished results, 1998.
(13) (a) Dehnicke, K.; Stra¨hle, J. Polyhedron 1989, 707. (b) Ru¨benstahl,
T.; Well, F.; Harms, K.; Dehnicke, K.; Fenske, D.; Baum, G. Z. Anorg.
Allg. Chem. 1994, 620, 1741.
(14) (a) Anfang, S.; Harms, K.; Dehnicke, K. Unpublished results, 1998.
(b) Dehnicke, K.; Krieger, M.; Massa, W. Coord. Chem. ReV. 1999,
182, 19.
(15) (a) Nussha¨r, D.; Weller, F.; Dehnicke, K. Z. Anorg. Allg. Chem. 1993,
619, 1121. (b) Ru¨benstahl, T.; Wolff von Gudenberg, D.; Weller, F.;
Dehnicke, K.; Goesmann, H. Z. Naturforsch. 1994, 49B, 15.
(16) Stahl, M. M.; Faza, N.; Massa, W.; Dehnicke, K. Z. Anorg. Allg. Chem.
1998, 624, 209.
(17) Schomber, B. M.; Ziller, J. W.; Doherty, N. M. Inorg. Chem. 1991,
30, 4488.

2830 Inorganic Chemistry, Vol. 39, No. 13, 2000
Huynh et al.
Both results can be explained by invoking a common
intermediate, I, which forms via paths 5 and 6 in Scheme 1.
Under the condition of the reaction between [OsII(tpy)(Cl)2-
(NS)]+ and PPh3, once I forms via path 5 in Scheme 1, it does
not build up as an intermediate. Its subsequent reaction with
PPh3 via path 7 in Scheme 1 is more rapid than its formation.
This is shown by the rate law which is first order in [OsII(tpy)-
(Cl)2(NS)]+ and first order in PPh3. [OsVI(tpy)(Cl)2(N)]+ is not
present in the solution, and only PPh3 is available to capture I.
Similarly, in the formation of I via path 6 in Scheme 1, I
does not build up as an intermediate. Its subsequent reaction
with [OsVI(tpy)(Cl)2(N)]+ via path 8 in Scheme 1 is more rapid
than its formation as shown by the rate law. PPh3 is not present,
and only [OsVI(tpy)(Cl)2(N)]+ is available to capture I.
It is not possible to conduct a convenient competition
experiment, for example, by observing the product distribution
in a reaction between [OsVI(tpy)(Cl)2(N)]+ and SPPh3 with
added PPh3 because the reaction between [OsVI(tpy)(Cl)2(N)]+
and PPh3 is too rapid with k(25 °C, CH3CN) ) (1.36 ( 0.08)
× 104 M-1 s-1 for trans-[OsVI(tpy)(Cl)2(N)]+.2b
electrophilic displacement of the thionitrosyl complex by the
nitrido complex, eq 7. There is presumably an initial electronic
interaction between the P atom and vacant dπ*OsN orbitals,
largely localized on the metal:
(7)
Electron pair donation from the P atom to the π*NS orbital is
important in the reactions between cis- and trans-[OsII(tpy)-
(Cl)2(NS)]+ and PPh3, eq 8.
(8)
Intermediate I can be viewed as an Os(IV) complex contain-
ing a N-bound monoanionic ligand which is either SNPPh3- or
NSPPh3-. There is precedent for the S-N-P core in the
structure of Ph3PdN-SN3S2.18 Assuming the same for I, in a
formal sense, the reaction between [OsVI(tpy)(Cl)2(N)]+ and
SPPh3 involves net N- transfer from the nitrido complex to
SPPh3:19
This can be inferred from the fact that the rate constant for trans-
[OsII(tpy)(Cl)2(NS)]+ (ktrans(25 °C, CH3CN) ) (6.79 ( 0.08)
× 102 M-1 s-1) is ∼3 times larger than that for cis-[OsII(tpy)-
(Cl)2(NS)]+. This reactivity parallels the two-electron potentials
for reduction of the NS+ ligand, -0.11 and -0.19 V for trans-
[OsII(tpy)(Cl)2(NS)]+/- and cis-[OsII(tpy)(Cl)2(NS)]+/- (0.1 M
TBAH in 1:1 (v/v) DMF/CH3CN, vs SSCE).21
The kinetics data for the reactions between cis- and trans-
[OsVI(tpy)(Cl)2(N)]+ with SPPh3 are also revealing. Reaction
with trans-[OsVI(tpy)(Cl)2(N)]+ is ∼30 times faster than that
with cis-[OsVI(tpy)(Cl)2(N)]+ even though the order of the
irreversible one-electron reduction potentials is the opposite with
Epc ) -0.28 V for cis-[OsVI(tpy)(Cl)2(N)]+/0 and Epc ) -0.41
V for trans-[OsVI(tpy)(Cl)2(N)]+/0 (0.1 M TBAH/CH3CN, vs
SSCE).19 This observed reactivity is inconsistent with initial
one-electron transfer and more consistent with the importance
of initial electron donation from the nitrido complex to SPPh3.
An important part of this reaction may be initial electron
donation from a filled dπ-pN orbital, largely localized on the
nitrido ligand,20 to a π*PS orbital on SPPh3.
The reaction between I and PPh3 may involve initial electron
donation from PPh3 to a largely S-based π*NS orbital on
-
N(S)PPh3 followed by displacement of SPPh3, eq 6.
Acknowledgments are made to the National Science Foun-
dation (Grant CHE-9503738) for support of this research.
Supporting Information Available: Listings of the X-ray experi-
mental details, atomic coordinates, thermal parameters, and bond
distances and angles for cis-[OsIV(tpy)(Cl)2(NPPh3)](PF6). This material
is available free of charge via the Internet at http://pubs.acs.org.
(6)
IC991425T
The reaction between I and [OsVI(tpy)(Cl)2(N)]+ involves
(20) Williams, D. S.; Coia, G. M.; Meyer, T. J. Inorg. Chem. 1995, 34,
586.
(18) Holt, E. M.; Holt, S. L. Chem. Commun. 1970, 1704.
(19) Huynh, M. H. V.; El-Samanody, E.-S.; Demadis, K. D.; White, P. S.;
Meyer, T. J. Inorg. Chem., in press.
(21) The E1/2 values are the averages of E1/2 values for the sequential one-
electron reductions of [OsII(tpy)(Cl)2(NS)]+.