Reactions of Tp-Os nitrido complexes with the nucleophiles hydroxide and thiosulfate

Article abstract of DOI:10.1016/j.ica.2005.11.033

The reaction between TpOs(N)Cl₂ (1) [Tp = hydrotris(1-pyrazolyl)borate] and aqueous (ⁿBu₄N)(OH) in THF-d₈ forms the nitrosyl complex TpOs(NO)Cl₂ (5) among other products, suggesting an initial hydroxi

Full text of DOI:10.1016/j.ica.2005.11.033

Inorganica Chimica Acta 359 (2006) 2842–2849
www.elsevier.com/locate/ica
Reactions of Tp–Os nitrido complexes with the nucleophiles
hydroxide and thiosulfate
1
Adam Wu, Ahmad Dehestani, Erik Saganic, Thomas J. Crevier, Werner Kaminsky ,
1
*
Dawn E. Cohen , James M. Mayer
Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195-1700, USA
Received 14 October 2005; accepted 20 November 2005
Available online 5 January 2006
Dedicated to Professor Brian R. James on the occasion of his 70th birthday and in recognition of his many contributions to inorganic chemistry.
Abstract
The reaction between TpOs(N)Cl2 (1) [Tp = hydrotris(1-pyrazolyl)borate] and aqueous (nBu4N)(OH) in THF-d8 forms the nitrosyl
complex TpOs(NO)Cl2 (5) among other products, suggesting an initial hydroxide attack at the nitrido ligand. In contrast, the reaction
of the acetate complex TpOs(N)(OAc)2 (2) with NaOH in Me2CO/H2O yields the osmium bis-hydroxide complex TpOs(N)(OH)2 (3),
which has been structurally characterized by single-crystal X-ray diffraction. Acetate for hydroxide exchange could occur by ligand sub-
stitution or by nucleophilic attack at the carbonyl carbon of the acetate ligands (saponification). Reacting 2 with Na18OH in H218O/
CD3CN yields predominantly doubly 18O-labeled TpOs(N)(18OH)2 (3-18O2) and unlabeled acetate, by ESI/MS and 13C{1H} NMR. This
indicates that hydroxide reacts by substitution rather than by attack at the ligand. The reaction of 2 with the softer nucleophile thiosul-
fate occurs at the nitrido ligand, giving the thionitrosyl complex TpOs(NS)(OAc)2 (4). Reacting 4 with NaOH in (CD3)2CO/D2O also
generates the bis-hydroxide complex 3.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Osmium; Tp; Hydroxide; Nitrido; Acetate; Thionitrosyl; Nitrosyl
1. Introduction
ido ligand to produce imido complexes Os(NMe)R4
(R = Me, CH2SiMe3, CH2CMe3, or CH2Ph) [1]. Recently,
protonation of (g5-C5H5)Os(N)(CH2SiMe3)2 by HBF4 or
CF3SO3H has been found to occur at the nitrido ligand
rather than at an alkyl group [2]. In contrast, the nitrido
ligand in TpOs(N)Cl2 (1) [Tp = hydrotris(1-pyraz-
olyl)borate] is electrophilic. For example, PPh3 reacts rap-
idly with the nitride to form the phosphinidine complex
TpOs(NPPh3)Cl2 [3], and PhMgCl and BPh3 effect Phꢀ
addition to the nitrido, yielding TpOs(NHPh)Cl2 after
hydrolytic workup [4]. An unusual bicyclic Os-amido com-
plex TpOs(NC6H8)Cl2, is prepared from 1 and 1,3-cyclo-
hexadiene [5]. In these latter cases, there is a two-electron
reduction of the metal center, OsVI ! OsIV, as is common
when a nucleophile adds to a ligand. A formal four-
electron reduction to OsII occurs when a chalcogen atom
Metal complexes typically involve electron-rich ligands
binding to Lewis-acidic metal centers. Therefore, the addi-
tion of nucleophiles usually proceeds by attack at the metal
center, while electrophiles typically add to ligands. In some
complexes, however, these roles can be reversed. The nitr-
ido ligand is interesting in this regard because it can react
with both nucleophiles and electrophiles. Shapley and co-
workers have reported that anionic OsVI-nitrido complexes
with electron-donating alkyl ligands react with electrophilic
methylating agents (Me3O)(BF4) or CF3SO3Me at the nitr-
*
Corresponding author. Tel.: +1 206 543 2083; fax: +1 206 685 8665.
E-mail address: mayer@chem.washington.edu (J.M. Mayer).
UW Chemistry crystallographic facility.
1
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.11.033

A. Wu et al. / Inorganica Chimica Acta 359 (2006) 2842–2849
2843
protons. The addition of a drop of D2O results in an upfield
shift of this peak, which indicates rapid exchange between
TpOs(N)(OH)2 and water and confirms their assignment.
The IR spectrum of 3 in KBr shows m(O–H) at 3420 cmꢀ1
and m(Os„N) at 1080 cmꢀ1, typical of TpOs(N)X2 com-
plexes [7]. The labeled compound TpOs(15N)(OH)2 (3-15N)
exhibits m(Os„15N) at 1044 cmꢀ1, very close to the value
of 1046 cmꢀ1 calculated from a simple diatomic harmonic
oscillator model [8]. The ESI/MS spectrum of 3 shows the
most abundant peaks at 454 [M+H]+, 476 [M+Na]+, and
492 m/z [M+K]+; 3-15N shows similar isotopic clusters
one m/z unit greater. Electrochemical reduction of 3þ=i0n
Scheme 1.
is transferred to the nitrido ligand in 1, from Me3NO or
elemental sulfur or selenium, to give the chalconitrosyl
complexes TpOs(NE)Cl2 (E = O, S, or Se) [6].
Most of the reactions of 1 that we have examined occur
at the nitrido ligand, while the chloride ligands remain
inert. With the addition of AgOAc, however, the chloride
ligands are replaced by acetate to form TpOs(N)(OAc)2
(2) (Scheme 1) [7]. Under acidic conditions, the acetate
ligands in 2 are labilized by protonation, allowing prepara-
tion of a series of TpOs(N)X2 complexes using acidic HX
reagents (X = Br, NO3, O2CCF3, O2CCCl3, O2CCBr3, or
X2 = oxalate) [7]. Reported here are reactions of 2 and
related compounds with the non-acidic nucleophilic
reagents hydroxide and thiosulfate, leading to the syntheses
of TpOs(N)(OH)2 (3) and TpOs(NS)(OAc)2 (4). The reac-
tivity of 1, 2, and 3 with hydroxide, at the metal or at a
ligand, is also described.
MeCN is irreversible at ꢀ1.53 V (Ep,c) versus FeCp2
,
analogous to other TpOs(N)X2 complexes [7].
High valent metal–hydroxide complexes are not so
common because they often readily condense to l-oxo deriv-
atives. Other OsVI examples include trans-[OsO2(OH)4]2ꢀ
[9,10], trans-[Os(N)(OH)(CN)4]2ꢀ [11], and trans–cis-
OsO2(OH)2(phen), which can be converted to the bis-l-
oxo complex [OsO2(phen)(l-O)]2 in boiling water (phen =
1,10-phenanthroline) [12,13]. Related OsVI and RuVI bis-l-
hydroxo dimeric complexes [M(N)(CH2SiMe3)2(l-OH)]2
(M = Ru or Os) [14], ½OsO2Lðl-OHÞꢁ22ꢀ, and [Os(N)L(l-
OH)]2 have also been described (H2L = 1,2-bis(p-toluene-
sulfonylamido)benzene) [15]. The OsVIII complexes
[OsO4(OH)]ꢀ and cis-[OsO4(OH)2]2ꢀ are hydroxide adducts
of OsO4 [9]. A ReV analog of 3, TpMe2ReO(OH)2, has been
prepared by reduction of TpMe2ReO3 by PPh3 in H2O/
THF[TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate][16].
2. Results and discussion
2.1. Synthesis and spectroscopic characterization of
TpOs(N)(OH)2 (3)
2.2. X-ray structure of TpOs(N)(OH)2 (3)
Stirring TpOs(N)(OAc)2 (2) and 4 equiv. of NaOH in
Me2CO/H2O at room temperature for 30 min yielded the
orange bis-hydroxide complex TpOs(N)(OH)2 (3) in 60%
yield, isolated via silica gel chromatography (Scheme 2).
The 1H NMR spectrum of 3 displays a diamagnetic
2:2:2:1:1:1 integration pattern of six pyrazole resonances,
and six pyrazole peaks are seen in the 13C{1H} NMR spec-
trum as well. Thus, 3 has Cs symmetry similar to 1, 2, and
other TpOs(N)X2 compounds [7]. A resonance at d 5.09
observed for 3 in dry CD2Cl2 is assigned to the hydroxide
Crystals of 3 were grown from CH2Cl2/hexanes solu-
tions, and the structure was solved by direct methods.
There are two independent molecules in the unit cell, one
of which is disordered about the quasi-threefold axis of
the TpOs unit. The discussion that follows uses the metrical
parameters (Table 1) of the non-disordered molecule,
which is drawn in Fig. 1 (see Section 4.7 for selected crys-
tallographic data). The ORTEP of 3 shows a distorted
octahedral molecule with all of the ligands bent away from
Table 1
Selected bond lengths and angles for TpOs(N)(OH)2 (3)a
˚
Bond length (A)
Bond angle (ꢁ)
Os(1)–N(1)
Os(1)–N(3)
Os(1)–N(5)
Os(1)–N(7)
Os(1)–O(1)
Os(1)–O(2)
B(1)–N(2)
B(1)–N(4)
B(1)–N(6)
N(1)–N(2)
N(3)–N(4)
N(5)–N(6)
a
2.084(10)
2.099(10)
2.328(9)
1.651(10)
1.941(8)
N(1)–Os(1)–N(3)
N(3)–Os(1)–N(5)
N(1)–Os(1)–N(7)
N(3)–Os(1)–N(7)
N(5)–Os(1)–N(7)
O(1)–Os(1)–N(7)
O(2)–Os(1)–N(7)
O(1)–Os(1)–O(2)
O(1)–Os(1)–N(3)
O(2)–Os(1)–N(1)
O(2)–Os(1)–N(3)
O(2)–Os(1)–N(5)
89.2(4)
78.5(4)
93.2(4)
90.7(4)
166.9(4)
106.0(4)
102.6(4)
87.7(3)
163.3(4)
164.1(3)
88.3(4)
84.6(3)
1.956(7)
1.527(18)
1.544(18)
1.544(17)
1.384(13)
1.374(14)
1.356(12)
Scheme 2.
Metrical data for the non-disordered molecule in the structure.

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A. Wu et al. / Inorganica Chimica Acta 359 (2006) 2842–2849
Scheme 3.
patterns centered at 456/458 [3-16O18O+H/3-18O2+H]+,
480 [3-18O2+Na]+, and 496 m/z [3-18O2+K]+ (Fig. 2a).
The patterns for the Na+ and K+ clusters are roughly four
m/z units greater than those of unlabeled 3 (Fig. 2b). Anal-
ysis of these clusters indicates an average isotopic composi-
tion of 84% 3-18O2, 16% 3-18O16O, and <3% 3-16O2 (each
10%) (calculated isotopic patterns for 3-18O2 are shown
in the insets of Fig. 2a). The protonated cluster at 456/458
m/z shows a higher abundance of the mono-labeled species
[3-18O16O+H]+ (456 m/z), because protonation occurs at a
hydroxide ligand and facilitates 16O exchange between
[3-18O2+H]+ and trace H216O in the electrospray solvent.
In a control experiment, unlabeled 3 was reacted with
Na18OH in H218O/CH3CN. The ESI/MS spectrum of the
reaction solution showed predominately peaks for
unlabeled 3, with some 18O exchange observed for the
Fig. 1. ORTEP of the non-disordered molecule in the structure of
TpOs(N)(OH)2 (3). Hydrogen atoms are omitted for clarity, except for the
hydroxides.
the nitrido N(7), typical of complexes with a single nitrido or
˚
oxo group [17]. The Os„N distance of 1.651(10) A is within
˚
the 1.602(20)–1.70(2) A range of such bond lengths in
TpOs(N)X2 complexes (X = O2CCF3, NO3, Cl, Me, Ph)
˚
[4a,7]. The Os–OH distances of 3 at 1.956(7) and 1.941(8) A
are shorter than those of trans–cis-OsO2(OH)2(phen)
2ꢀ
˚
(1.982(4) and 1.984(5) A) [12], trans-[Os(N)(OH)(CN)4]
2ꢀ
˚
˚
(2.123(5) A) [11], trans-[OsO2(OH)4] (2.03 A) [9,10], and
cis-[OsO4(OH)2]2ꢀ (2.10 and 2.17 A) [9], and those of
˚
bridging hydroxide complexes [15].
2.3. 18O-Labeled study: ligand substitution of
TpOs(N)(OAc)2 (2) and Na18OH
The formation of 3 from 2 and NaOH is a formal sub-
stitution of hydroxide for acetate. This contrasts with reac-
tions of other nucleophiles such as alkoxides, which do not
substitute for acetate. We therefore considered two possible
mechanisms for this reaction: saponification via an initial
hydroxide attack at the carbonyl carbon of the acetate
ligands, or direct substitution of hydroxide for acetate.
The mechanisms can be distinguished by reacting 2 with
Na18OH. Ligand substitution would involve cleavage of
the Os–O bonds to form TpOs(N)(18OH)2 (3-18O2) and
unlabeled acetate, while saponification would retain the
Os–O bonds and yield unlabeled 3 and singly 18O-labeled
18OOCMeꢀ (Scheme 3). A saponification mechanism has
previously been indicated for hydroxide reactions with
[Co(NH3)5(O2CCX3)]2+ (X = H, Cl, or F) [18].
The reaction of 2 with Na18OH was conducted in
CD3CN instead of acetone, in order to eliminate the possi-
ble exchange of 18O label with the solvent. Addition of
95%-enriched Na18OH to 2 in H218O/CD3CN produced iso-
topically enriched 3. The ESI/MS spectrum showed isotopic
Fig. 2. Partial ESI/MS spectra of (a) labeled TpOs(N)(*OH)2 (mostly
3-18O2) from TpOs(N)(OAc)2 (2) + Na18OH and (b) TpOs(N)(OH)2 (3)
from 2 + NaOH, with calculated isotopic patterns shown in the insets.

A. Wu et al. / Inorganica Chimica Acta 359 (2006) 2842–2849
2845
protonated cluster [3+H]+ (454 m/z). This shows that 3 does
not exchange with basic H218O/CH3CN but that some
exchange occurs under the acidic conditions of the electro-
spray experiment.
dominantly unlabeled acetate (<20% 18O16OCMeꢀ,
Fig. 3b) is formed in the reaction of 2 with Na18OH. These
experiments must be done by spiking with authentic sam-
ples because the absolute chemical shift of the carboxylate
carbon varies from sample to sample (d 180.2 0.2),
apparently due to changes in effective pH.
The isotopic enrichment of the acetate product was
probed by 13C{1H} NMR, using the known upfield shift
of the carboxylate carbons on substitution of 16O for 18O
[19]. For aqueous acetic acid, this shift is reported to be
25 ppb at pH 2.0 and 27 ppb at pH 8.0 [20]. 18O-Enriched
sodium acetate was prepared from H218O hydrolysis of
triethylorthoacetate (MeC(OEt)3) [21], and the 13C{1H}
NMR spectrum (Fig. 3a) showed two carboxylate 13C res-
onances, for singly and doubly 18O-labeled acetate (ꢂ40%
18O2, ꢂ50% 18O16O, and <10% 16O2, based on integration
and Lorentzian line fitting [22]). The 13C{1H} NMR spec-
trum of the 2 + Na18OH reaction mixture in H218O/
CD3CN showed a single peak in the carboxylate region
(Fig. 3b). Spiking this solution with unlabeled NaOAc gave
only a single carboxylate carbon resonance (Fig. 3c). Spik-
ing with the Na18O2CMe/Na18O16OCMe prepared from
triethylorthoacetate showed three carboxylate 13C peaks
(Fig. 3d, Dd @ 27 ppb), assigned to unlabeled, singly, and
doubly 18O-labeled acetate. Thus, we conclude that pre-
In a control experiment, a reaction of 2 + Na16OH in
H216O/CD3CN
was
spiked
with
Na18O2CMe/
Na18O16OCMe. The 13C{1H} NMR spectrum showed
three carboxylate 13C resonances, for all three isotopomers.
Thus, under the reaction and spectroscopic conditions (ca.
12 h), exchange of the acetate oxygen atoms with the
H216O solvent is too slow to significantly deplete the 18O
label from the acetate. If exchange with the excess water
had been fast, only 16O2CMeꢀ would have been observed.
In sum, the ESI/MS and NMR data both indicate that
18OHꢀ substitution for acetate occurs predominately with
Os–O bond cleavage, yielding 3-18O2 and unlabeled ace-
tate. The data rule out a saponification pathway, which
would have yielded unlabeled 3 and 18OOCMeꢀ. The
observation that hydroxide and not alkoxides substitute
for acetate may be due to the small size of hydroxide.
2.4. Synthesis and spectroscopic characterization of
TpOs(NS)(OAc)2 (4)
Refluxing 2 and 10 equiv. of sodium thiosulfate
(Na2S2O3 Æ 5H2O) in MeCN for 2 h yielded the blue OsII-
thionitrosyl complex TpOs(NS)(OAc)2 (4) in 41% yield,
isolated via silica gel chromatography (Scheme 2). As with
1
3, the H and 13C{1H} NMR spectra of 4 indicate Cs sym-
metry. The EI/MS spectrum shows an isotopic cluster at
569 m/z (M+ for 4), which appears at 570 m/z for
TpOs(15NS)(OAc)2 (4-15N). The IR spectrum of 4 shows
a band at 1278 cmꢀ1, which appears at 1257 cmꢀ1 in
4-15N, consistent with a thionitrosyl ligand. This vibration
likely has some of the character of a diatomic N–S stretch
[m(N„S)] and some of the asymmetric stretch of a tri-
atomic Os–N–S unit (see [23]). This is why a simple dia-
tomic oscillator approximation overestimates the isotopic
shift: calculated m(15N„S) = 1248 cmꢀ1. The cyclic vol-
tammogram of 4 in MeCN shows reversible oxidation
and reduction waves centered at 0.96 and ꢀ1.32 V versus
FeCp2þ=0, respectively. These are ꢂ0.2 V more negative
than those of the chloride analog, TpOs(NS)Cl2 (E1/2
=
1.20, ꢀ1.15 V) [6], indicating stronger electron donation
of acetate versus chloride ligands.
The thionitrosyl complex 4 is likely formed by direct sul-
fur atom transfer from thiosulfate to 2. This is a formal four-
electron reduction of the osmium, two-electron reduction of
the central sulfur in thiosulfate, and a six-electron oxidation
of the nitrido nitrogen atom. The use of thiosulfate as a sul-
fur atom donor to a nitrido ligand has previously been
described in the formation of mer-L3Tc(NS)Cl2 (L = py,
4-Me-py, or 3,5-Me2-py) from (Bu4N)[Tc(N)Cl4], Na2S2O3,
and L [24]. We find that thiosulfate can also be used to con-
vert 1 to TpOs(NS)Cl2, which has previously been prepared
Fig. 3. Partial 13C{1H} NMR spectra of the carboxylate carbon
resonances of free acetate prepared from (a) H218O + MeC(OEt)3, (b)
TpOs(N)(OAc)2 (2) + Na18OH in H218O/CD3CN, (c) 2 + Na18OH in
H218O/CD3CN then + Na16O2CMe, and (d) 2 + Na18OH in H218O/
CD3CN then + Na18O2CMe/Na18O16OCMe. All peaks appear at
d
180.2 0.2, varying by a few tenths of ppm from sample to sample
presumably depending on the pH.

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A. Wu et al. / Inorganica Chimica Acta 359 (2006) 2842–2849
ꢀ
from 1 and propylene sulfide [6], S8 [6], CS2 þ N3 [25], or
Mo(N)(S2CNEt2)3 [26]. Closely related thionitrosyl Os com-
plexes [(tpm)Os(NS)Cl2]+ (tpm = tris(1-pyrazolyl)methane)
[25] and trans-[(tpy)Os(NS)Cl2]+ (tpy = 2,20:60,200-terpyri-
dine) [27] have also been reported. Dilworth et al. first syn-
thesized thionitrosyl metal complexes Mo(NS)(S2CNR2)3
(R = Me, Et, or R2 = (CH2)5), from Mo(N)(S2CNR2)3
and propylene sulfide or S8 [28].
Crystals of 4 were grown from Me2CO/Et2O solutions,
and the structure was examined by direct methods. The
structure is disordered about a mirror plane containing
C(1), C(2), Os(1), and C(13), with all of the other atoms
being 50/50 disordered about this plane. The ORTEP dia-
gram in Fig. 4 shows one set of atoms; a drawing showing
all of the duplicated atoms is given in the Supporting infor-
mation. Due to the extensive disorder, a large number of
restraints were required to achieve a reasonable refinement.
Thus, the bond lengths and angles are not well defined, and
only evidence of connectivity is obtained (see Section 4.7
for selected crystallographic data).
Scheme 4.
identified by ESI/MS (976 m/z) and IR (m(N„N) =
2011 cmꢀ1) as the l-N2 OsII–OsIII dimer [TpCl2Os–(l-
N2)–OsCl2Tp]ꢀ, previously reported by Meyer et al. [31].
The reaction of hydroxide to 1 likely proceeds by an ini-
tial hydroxide attack at the nitrido ligand, parallel to the
addition of other nucleophiles such as phosphines and car-
banions [3,4]. This would give an anionic OsIV(NOH)ꢀ
intermediate, which must undergo subsequent loss of two
electrons and a proton to form the nitrosyl product 5
(Scheme 4). The reducing equivalents are in part consumed
in the formation of [TpCl2Os–(l-N2)–OsCl2Tp]ꢀ, which
can also be formed by reduction of 1 with an one-electron
reductant cobaltocene [31]. We were not able to determine
the fate of the proton (there does not appear to be any gas
evolution in the reaction). While no OsNOH complexes
have been reported, OsCl2(NHOH)(NO)(PPh3)2 is formed
on protonation of Os(NO)2(PPh3)2 with 2 equiv. of HCl
[32].
2.5. Reactions of hydroxide with TpOs(N)Cl2 (1),
TpOs(N)(OH)2 (3), and TpOs(NS)(OAc)2 (4)
The reaction between 1 and 1.2 equiv. of aqueous
(nBu4N)(OH) in THF-d8 immediately produces a number
of products, including the known nitrosyl complex
Complex 3 does not react with 4 equiv. of NaOH in
CD3CN/D2O over half an hour at room temperature. After
16 h, 1H NMR indicated 19% decomposition of 3 and 11%
of free Tpꢀ, which was confirmed by spiking with KTp.
The addition of hydroxide to 3 is much slower than the
analogous reaction of 1. This is most likely because reduc-
tion of 3 is less favorable, as indicated by the irreversible
1
TpOs(NO)Cl2 (5) in 24% yield by H NMR integration.
Complex 5 was identified by 1H NMR and IR spectra
(e.g., m(N„O) = 1832 cmꢀ1). It was previously prepared
from 1 by oxygen transfer from Me3NO [6], similar to
the synthesis of [(tpy)Os(NO)Cl2]+ [29]. The reaction of 1
with NO also generates 5, in a multi-step reaction [30].
Column chromatography separates a number of the species
of this reaction. One of the paramagnetic products was
electrochemical reduction potentials: Ep,c = ꢀ1.53 V for
þ=0
3, ꢀ1.34 V for 1 [7] (both versus FeCp2
in MeCN).
The more facile reduction of 1 favors hydroxide attack at
the nitrido ligand to form the reduced OsIV(NOH)ꢀ inter-
mediate. Similarly, hydroxide does not rapidly react with
the nitride in 2, due to an even more negative Ep,c
(ꢀ1.83 V [7]). In contrast, hydroxide reacts rapidly with 2
at the osmium, likely because acetate is a better leaving
group than the chloride ligands in 1.
The thionitrosyl complex 4 also reacts with hydroxide.
Reacting 4 with 4 equiv. of NaOH in (CD3)2CO/D2O gave
a 26% yield of TpOs(N)(OH)2 (3) in 30 min (by 1H NMR).
This conversion involves both desulfurization of the thioni-
trosyl to a nitrido ligand and substitution of the acetate
ligands of 4. The other osmium products were apparently
paramagnetic, as 3 was the only Tp complex observed by
1H NMR. ESI/MS confirmed 3 as a product, and showed
a small amount of the nitrido-bis(acetate) complex 2 as well
as other isotopic clusters for as yet unidentified osmium
species. The fate of the sulfur is not evident. A possible
pathway for this reaction would involve initial addition
of hydroxide to the NS ligand in 4, resulting in desulfuriza-
tion and formation of 2, which is then converted to 3.
Desulfurization of thionitrosyl metal complexes with phos-
phines as reductants has been accomplished in a number of
Fig. 4. ORTEP of one of the disordered positions of TpOs(NS)(OAc)2 (4),
with hydrogen atoms omitted for clarity.

A. Wu et al. / Inorganica Chimica Acta 359 (2006) 2842–2849
2847
cases, including Mo(NS)(S2CNR2)3 + PnBu3 ! Mo(N)(S2-
CNR2)3 (R = Me, Et, or R2 = (CH2)5) [28]. Treatment of
TpOs(NS)Cl2 with PPh3 yields TpOs(NPPh3)Cl2 via the
formation of SPPh3 and 1, which is rapidly trapped by a
second equivalent of PPh3 [6]. [(tpm)Os(NS)Cl2]+ reacts
with PPh3 analogously [25]. The reaction of [(tpm)O-
sII(NS)Cl2]+ with Me3NO gives [(tpm)OsIII(NSO)Cl2] by
oxygen atom transfer to the sulfur [25]. Hydroxide is also
known to add to the nitrogen of nitrosyl ligands in ruthe-
nium complexes [33].
bridge Isotope Laboratories. CD2Cl2 was dried over
CaH2 and vacuum transferred, and CD3CN over CaH2
then P2O5. (nBu4N)(OH) (40% wt. in H2O), NaH, NaOH,
and NaOAc (Aldrich) were used without purification.
KTp [34], TpOs(N)Cl2 (1) [4], TpOs(N)(OAc)2 (2) [7],
and TpOs(15N)(OAc)2 (2-15N) [7] were prepared according
to the literature procedures.
18O-Enriched sodium acetate was prepared from H218O
hydrolysis of triethylorthoacetate (MeC(OEt)3) following
the literature procedure [21]. 1H NMR: 1.78 (s, CH3).
13C{1H} NMR: 24.55 (CH3); 180.042 (C18O2), 180.065
(C18O16O). Integration of the 13C{1H} NMR spectrum
indicated an isotopic composition of ꢂ40% 18O2, ꢂ50%
18O16O, and <10% 16O2. The NMR spectra were obtained
in 350 lL CD3CN + 100 lL H216O containing ꢂ1 mg
NaH, in order to be comparable to spectra obtained as part
of the 18O-labeling study described in Section 4.3.
3. Conclusions
Hydroxide reacts with each of TpOs(N)(OAc)2 (2) and
TpOs(NS)(OAc)2 (4) to form TpOs(N)(OH)2 (3). An 18O-
labeling study indicates that the mechanism for the forma-
tion of 3 from 2 + hydroxide is direct substitution rather
than saponification of the acetate ligands. In contrast,
hydroxide does not substitute for the chloride ligands in
TpOs(N)Cl2 (1), but instead reacts rapidly with the nitride
to form the nitrosyl complex TpOs(NO)Cl2 (5) among
other products. That hydroxide attacks the nitride ligand
rapidly in 1 but not in 2 or 3 is likely due to the facility
of reduction of the osmium centers in the three com-
pounds, as indicated by the irreversible reduction poten-
4.1. Synthesis of TpOs(N)(OH)2 (3)
A solution of 2 (240 mg, 0.45 mmol) and NaOH (71 mg,
1.78 mmol) in Me2CO/H2O (20 mL/2 mL) was stirred for
30 min. The solvent was removed in vacuo, and the residue
was chromatographed on silica gel with EtOAc/MeOH
(90:10) and dried in vacuo at room temperature to yield
121 mg (0.27 mmol, 60%) of orange powder. 1H NMR
(CD2Cl2): 6.00 (t), 7.32 (d), 7.45 (d) (1H each, pz); 6.49
(t), 7.91 (d), 8.17 (d) (2H each, pz0); 5.09 (br s, 2H, OH).
13C{1H} NMR (CD2Cl2): 105.69, 134.19, 141.51 (pz);
108.48, 138.54, 145.92 (pz0). ESI/MS: 454 [M+H]+, 476
[M+Na]+, 492 [M+K]+. UV–Vis: 409 (210). IR: 1080
m(Os„N), 3420 m(O–H). CV: Ep,c = ꢀ1.53 V (OsVI/V).
Anal. Calc. for C9H12N7O2BOs: C, 23.95; H, 2.68;
N, 21.73. Found: C, 23.65; H, 2.57; N, 21.62%. TpOs-
(15N)(OH)2 (3-15N) was synthesized analogously from
2-15N. ESI/MS: 455 [M+H]+, 477 [M+Na]+, 493
[M+K]+. IR: 1044 m(Os„15N).
tials: Ep,c = ꢀ1.34 (1), ꢀ1.83 (2), and ꢀ1.53 V (3) (versus
þ=0
FeCp2
in MeCN).
4. Experimental
All reactions were conducted under air, unless stated
1
otherwise. H and 13C{1H} NMR spectra were recorded
on Bruker spectrometers (300 and 500 MHz) at ambient
temperatures and referenced to a residual solvent peak: d
(multiplicity, number of protons, assignment). All pyrazole
3
resonances display JHH = 2 Hz. Electrospray ionization
mass spectra (ESI/MS) were obtained on a Bruker
Esquire-LC ion trap mass spectrometer, and reported as
m/z for the most isotopically abundant peak in an Os iso-
topic pattern. Samples were infused as a MeCN solution
and acquired in positive or negative ionization mode. Elec-
tron impact mass spectra (EI/MS) were obtained on a Kra-
tos Profile HV-3 direct probe instrument. UV–Vis spectra
were acquired with a Hewlett–Packard 8453 diode array
spectrophotometer in anhydrous CH2Cl2, and reported as
4.2. Synthesis of TpOs(NS)(OAc)2 (4)
A
suspension of
2
(100 mg, 0.19 mmol) and
Na2S2O3 Æ 5H2O (464 mg, 1.87 mmol) in MeCN (30 mL)
was refluxed for 2 h. The mixture was cooled to room tem-
perature and filtered. The filtrate was evaporated to dry-
ness, and the residue was chromatographed on silica gel
with CH2Cl2/MeOH (90:10). The blue fraction was
stripped to dryness, re-precipitated with CH2Cl2/hexanes,
filtered off, and dried in vacuo at 78 ꢁC to yield 44 mg
(0.08 mmol, 41%) of light blue powder. 1H NMR
(CD2Cl2): 6.27 (t), 7.65 (d), 7.78 (d) (1H each, pz); 6.42
(t), 7.77 (d), 8.01 (d) (2H each, pz0); 2.16 (s, 6H, CH3).
13C{1H} NMR (CD2Cl2): 106.77, 136.50, 143.02 (pz);
108.30, 137.82, 145.79 (pz0); 23.55 (CH3); 177.18 (CO2).
EI/MS: 569 [M]+, 510 [MꢀOAc]+, 464 [MꢀOAcꢀNS]+.
UV–Vis: 413 (260), 642 (190). IR: 1278 m(N„S). CV:
E1/2 = 0.96 (OsIII/II), ꢀ1.32 V (OsII/I). Anal. Calc. for
C13H16N7O4BSOs: C, 27.52; H, 2.84; N, 17.28. Found:
k
max/nm (e/Mꢀ1 cmꢀ1). IR spectra were obtained as KBr
pellets using Perkin–Elmer 1720 and Bruker Vector 33
FT-IR spectrometers, and are reported in cmꢀ1 at 4 cmꢀ1
resolution. Cyclic voltammetry (CV) measurements in
0.1 M (nBu4N)(PF6)/MeCN were performed using a Pt disc
working electrode, a Pt wire auxiliary electrode, and an Ag
wire/AgNO3 reference electrode with FeCp2 as an interþn=a0l
standard, and potentials are reported versus FeCp2
.
Elemental analyses were performed by Atlantic Microlab.
All reagent grade solvents were purchased from Fisher
Scientific or EMD Chemicals. Deuterated solvents and
H218O (95% 18O-enrichment) were obtained from Cam-

2848
A. Wu et al. / Inorganica Chimica Acta 359 (2006) 2842–2849
C, 27.71; H, 2.81; N, 17.01%. TpOs(15NS)(OAc)2 (4-15N)
was synthesized analogously from 2-15N. EI/MS: 570
4.6. Reaction of TpOs(NS)(OAc)2 (4) with NaOH
15
[M]+, 511 [MꢀOAc]+, 464 [MꢀOAcꢀ NS]+. IR: 1257
An NMR tube was charged with a solution of 4 (2 mg,
3.5 lmol) in (CD3)2CO/D2O (350/100 lL) and a capillary
containing (Me3Si)2O in CD3CN as a standard. After tak-
ing an 1H NMR, 14 lL of 1 M NaOH/H2O (14 lmol) was
m(15N„S).
4.3. 18O-Labeled study: reaction of TpOs(N)(OAc)2 (2)
and Na18OH
1
added, and the tube was allowed to stand for 30 min. H
NMR showed the formation of 3 in 26% yield, based on
integration relative to the standard. The tube was spiked
with authentic 3 to confirm the identity of the product.
1H NMR: 5.97 (t), 7.33 (d), 7.55 (d) (1H each, pz); 6.53
(t), 8.07 (d), 8.23 (d) (2H each, pz0). ESI/MS: 454
[M+H]+, 476 [M+Na]+, 492 [M+K]+.
NaH (1 mg, 0.04 mmol) and dry CD3CN (350 lL) were
charged into a J-Young NMR tube, and H218O (100 lL)
was added to generate a solution of Na18OH in H218O/
CD3CN. Complex 2 (5.6 mg, 0.01 mmol) was then added,
and the tube was shaken until a solution was formed, to
generate TpOs(N)(*OH)2 (mostly 3-18O2) and 16O2CMeꢀ.
13C{1H} NMR: 180.209 (C16O2). The tube was then spiked
with Na16O2CMe (3 mg), and 13C{1H} NMR was obtained:
180.281 (C16O2). The above experiment was duplicated
except spiking with Na18O2CMe/Na18O16OCMe (3 mg).
13C{1H} NMR: 180.044 (C18O2), 180.068 (C18O16O),
180.097 (C16O2). ESI/MS of 3-18O2: 458 [M+H]+, 480
[M+Na]+, 496 [M+K]+. In a control experiment, NaH
(1 mg), CD3CN (350 lL), H216O (100 lL), and 2 (5.6 mg)
were added into a J-Young NMR tube to generate unla-
beled 3 and 16O2CMeꢀ, and the tube was spiked with
Na18O2CMe/Na18O16OCMe (3 mg). 13C{1H} NMR:
180.186 (C18O2), 180.214 (C18O16O), 180.234 (C16O2).
4.7. X-ray structural determination of TpOs(N)(OH)2 (3)
and TpOs(NS)(OAc)2 (4)
Crystals of 3 were obtained from slow evaporation of
CH2Cl2/hexanes solutions and were mounted onto a glass
capillary with oil. The data were collected on a Nonius
Kappa CCD diffractometer. Selected crystallographic data
for 3: C9H12BN7O2Os, formula weight = 451.27,
0.14 · 0.14 · 0.10 mm, monoclinic, space group P21/c
˚
˚
(No. 14), a = 13.3050(9) A, b = 14.6520(13) A, c =
3
˚
˚
15.0850(8) A, b = 115.984(4)ꢁ, V = 2643.5(4) A , qcalc
=
2.268 Mg mꢀ3
,
Z = 8, 2hmax = 4.14–24.71ꢁ, Mo Ka
˚
radiation (k = 0.71070 A), F(000) = 1696, T = 130(2) K,
total/independent reflections = 21816/4287 (Rint = 6.18%),
observed data = 7165 (I > 2 r(I)), restraints/parame-
ters = 3/377, absorption correction: semi-empirical (hkl-
SCALEPACK), maximum (minimum) transmission:
0.4450 (0.1037), R1 (wR2) = 5.21 (10.4)% for I > 2r(I), R1
(wR2) = 9.27 (11.5)% for all data, GOF = 0.958, largest dif-
4.4. Reaction of TpOs(N)Cl2 (1) with (nBu4N)(OH)
In an NMR tube, (nBu4N)(OH) (40% wt. in H2O,
3.2 lL, 4.9 lmol) was added to a solution of 1 (2 mg,
4.1 lmol) in THF-d8 (400 lL), containing a small amount
of C6H6 as an internal standard. The tube was shaken,
and a 1H NMR spectrum showed TpOs(NO)Cl2 (5) in
24% yield, based on integration relative to the standard.
ference in peak (hole) = 1.307 (ꢀ1.581) e Aꢀ3. Solution by
˚
direct methods (SIR-92) produced a complete heavy-atom
phasing model consistent with the proposed structure.
The heavy atoms were refined anisotropically by full-matrix
least-squares, and the hydrogen atoms were placed using a
riding model. However, one of the two chemically identical
molecules was found to be disordered about the TpOs
pseudo-threefold axis. O3b, O4b, and N14b of the minor
form, 19.07(3)% of the molecules were refined isotropically
with fixed thermal parameters (0.05).
1
The product was confirmed by comparing its H NMR
spectrum with that of 5 prepared by the literature method
[6]. 1H NMR: 6.27 (t), 7.78 (d), 7.96 (d) (1H each, pz); 6.49
(t), 7.94 (d), 8.00 (d) (2H each, pz0). IR: 1832 m(N„O).
Another product [TpCl2Os–(l-N2)–OsCl2Tp]ꢀ [31] was
identified by ESI/MS and IR; the observed ESI/MS isoto-
pic pattern matched the calculated one. ESI/MS: 976 [M]ꢀ.
IR: 2011 m(N„N).
Crystals of 4 were grown from slow evaporation of
Me2CO/Et2O solutions. Selected crystallographic data
for 4: C13H16BN7O4SOs, formula weight = 567.44,
0.17 · 0.17 · 0.08 mm, orthorhombic, space group Pbcm
4.5. Reaction of TpOs(N)(OH)2 (3) with NaOH
An NMR tube was charged with a solution of 3 (2 mg,
4.4 lmol) in CD3CN/D2O (350/100 lL) and a capillary
containing (Me3Si)2O in CD3CN as a standard. After tak-
ing an 1H NMR, 18 lL of 1 M NaOH/D2O (18 lmol) was
added. No change by NMR was detected after 30 min. 81%
of 3 remained after 16 h, at which time 11% of free Tpꢀ was
observed, based on integration relative to the standard.
The identity of Tpꢀ was confirmed by spiking with authen-
tic KTp. 1H NMR of 3: 6.02 (t), 7.29 (d), 7.55 (d) (1H each,
pz); 6.52 (t), 8.03 (d), 8.19 (d) (2H each, pz0); free Tpꢀ: 6.13
(t), 7.31 (d), 7.46 (d) (1H each, pz).
˚
˚
(No. 57), a = 9.2380(6) A, b = 15.1010(10) A, c =
3
˚
˚
13.3830(10) A, a = b = c = 90ꢁ, V = 1867.0(2) A , qcalc
=
2.019 Mg mꢀ3, Z = 4, 2hmax = 2.20–28.31ꢁ, Mo Ka radia-
tion (k = 0.71073 A), F(000) = 1088.0, T = 130(2) K,
˚
total/independent reflections = 29644/2393 (Rint = 7.44%),
observed data = 4254 (I > 2r(I)), restraints/parameters =
64/228, absorption correction: semi-empirical from equiva-
lents, maximum (minimum) transmission: 0.58 (0.32), R1
(wR2) = 5.19 (11.9)% for I > 2 r(I), R1 (wR2) = 12.7
(15.1)% for all data, GOF = 1.011, largest difference in

A. Wu et al. / Inorganica Chimica Acta 359 (2006) 2842–2849
2849
peak (hole) = 0.880 (ꢀ1.557) e Aꢀ3. The structure of 4 was
˚
[8] R.M. Silverstein, F.X. Webster, in: Spectrometric Identification of
Organic Compounds, sixth ed., Wiley, New York, 1998, p. 71.
[9] W.P. Griffith, in: G. Wilkinson (Ed.), Comprehensive Coordination
Chemistry, vol. 4, Pergamon Press, Oxford, 1987, p. 519.
[10] (a) L.O. Atovmyan, V.G. Andrianov, M.A. Porai-Koshits, J. Struct.
Chem. 3 (1962) 660 (Engl. Transl.);
(b) M.A. Porai-Koshits, L.O. Atovmyan, V.G. Andrianov, J. Struct.
Chem. 2 (1961) 686 (Engl. Transl.).
[11] H.J. van der Westhuizen, S.S. Basson, J.G. Leipoldt, W. Purcell,
Transition Met. Chem. 19 (1994) 582.
solved by direct methods (SIR-97), and the heavy and
hydrogen atoms were refined similar to those of 3. The
structure is disordered, and one set of the molecule is
reflected into the other by application of a crystallographic
mirror plane through C(1), C(2), Os(1), and C(13).
Additional crystallographic information is given in the
Supporting information.
[12] A.M.R. Galas, M.B. Hursthouse, E.J. Behrman, W.R. Midden, G.
Green, W.P. Griffith, Transition Met. Chem. 6 (1981) 194.
[13] C.-H. Chang, W.R. Midden, J.S. Deetz, E.J. Behrman, Inorg. Chem.
18 (1979) 1364.
[14] (a) P.A. Shapley, J.J. Schwab, S.R. Wilson, J. Coord. Chem. 32
(1994) 213;
(b) P.A. Shapley, W.A. Reinerth, Organometallics 15 (1996) 5090.
[15] W.-H. Leung, E.K.-F. Chow, S.-M. Peng, Polyhedron 12 (1993)
1635.
[16] K.P. Gable, E.C. Brown, J. Am. Chem. Soc. 125 (2003) 11018.
[17] W.A. Nugent, J.M. Mayer, in: Metal–Ligand Multiple Bonds, Wiley,
New York, 1988, p. 157.
Acknowledgements
´
We are grateful to Dr. Martin Sadılek and Mr. Loren
Kruse for assistance with mass spectrometry, and Dr. Eric
Watson and Dr. Ian Rhile for helpful discussions. We
thank the US National Science Foundation for financial
support to J.M.M. (CHE0204697), and for funds toward
the purchase of the Esquire-LC mass spectrometer
(CHE9807748).
[18] F. Basolo, R.G. Pearson, in: Mechanisms of Inorganic Reactions: A
Study of Metal Complexes in Solution, second ed., Wiley, New York,
1967, p. 229.
Appendix A. Supporting information
[19] P.E. Hansen, in: G.A. Webb (Ed.), Annual Reports on NMR
Spectroscopy, vol. 15, Academic Press, London, 1983, p. 105.
[20] J.M. Risley, R.L. Van Etten, J. Am. Chem. Soc. 103 (1981)
4389.
[21] C.R. Hutchinson, C.T. Mabuni, J. Labelled Compd. Radiopharm. 13
(1977) 571.
[22] NUTS – NMR Utility Transform Software for Windows, 1D version;
Acorn NMR Inc., 2003.
[23] (a) A.M. English, K.R. Plowman, I.S. Butler, Inorg. Chem. 20 (1981)
2553;
(b) A.M. English, K.R. Plowman, I.S. Butler, Inorg. Chem. 21 (1982)
338.
[24] J. Lu, M.J. Clarke, Inorg. Chem. 29 (1990) 4123.
[25] E.-S. El-Samanody, K.D. Demadis, L.A. Gallagher, T.J. Meyer, P.S.
White, Inorg. Chem. 38 (1999) 3329.
CCDC 243292 and 286567 contain the crystallographic
data for 3 and 4. The data can be obtained free of charge
via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Center, 12, Union
Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033;
or deposit@ccdc.cam.ac.uk). Supplementary data associ-
ated with this article, including additional discussion of
the structure of 4, with ORTEP and the unit cell diagrams
showing all the disordered atoms can be found in the online
version, at doi:10.1016/j.ica.2005.11.033.
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