Group 8 and 10 hyponitrite and dinitrosyl complexes

Article abstract of DOI:10.1016/j.poly.2007.05.009

cis-Hyponitrite complexes L_nM(N₂O₂) (M = Ni, Pt; L_n = PPh₃, PPh₂Me, dppe, and dppf) of divalent group 10 metals have been previously shown to be readily prepared by treating the corresponding L_nMCl₂ derivatives with sodium-(Z)-1-{4-(2,6-di-tert-butyl-4-methoxycyclohexadienonyl)}diazen-1-ium-1,2-diolate. These complexes adopt a diamagnetic square planar geometry with oxygen bound chelating planar cis-hyponitrite ligands. They are readily prepared at room temperature but thermally decompose above 90 °C with release of nitrous oxide. Electrophiles such as iodine, methyltriflate, and hydrochloric acid also react rapidly with the cis-hyponitrite complexes to give nitrous oxide. The structure of one of these previously prepared complexes, (PPh₃)₂Pt(N₂O₂), has been redetermined at -100 °C as a dichloromethane solvate with improved precision. The related tetrahedral group 8 dinitrosyl complexes, (PPh₃)₂M(NO)₂ (M = Ru, Os; L_n = PPh₃, dppe, and dppf) have been reexamined and new derivatives with chelating phosphines have been prepared by ligand substitution on the corresponding (PPh₃)₂M(NO)₂. The structures of Ru(dppf)(NO)₂ and Os(dppe)(NO)₂ have been determined. These two analogous families of cis-hyponitrite and dinitrosyl complexes illustrate the balance of metal dⁿ electron count and nitrosyl redox state with one having linear nitrosyls bound to low valent metal centers, and the former having coupled N₂ O₂^{2 -} ligands bound to a higher oxidation state metal center.

Full text of DOI:10.1016/j.poly.2007.05.009

Polyhedron 26 (2007) 4737–4745
www.elsevier.com/locate/poly
Group 8 and 10 hyponitrite and dinitrosyl complexes
a
b,
a
b
Navamoney Arulsamy , D. Scott Bohle *, Jerome A. Imonigie , Raecca C. Moore
a
Department of Chemistry, University of Wyoming, Department 3838, 1000 E. University Avenue, Laramie, WY 82071-3838, United States
b
Department of Chemistry, McGill University, 801 Sherbrooke Street, W., Montreal, PQ, Canada H3A 2K6
Available online 17 May 2007
Abstract
cis-Hyponitrite complexes LnM(N2O2) (M = Ni, Pt; Ln = PPh3, PPh2Me, dppe, and dppf) of divalent group 10 metals have been pre-
viously shown to be readily prepared by treating the corresponding LnMCl2 derivatives with sodium-(Z)-1-{4-(2,6-di-tert-butyl-4-meth-
oxycyclohexadienonyl)}diazen-1-ium-1,2-diolate. These complexes adopt a diamagnetic square planar geometry with oxygen bound
chelating planar cis-hyponitrite ligands. They are readily prepared at room temperature but thermally decompose above 90 ꢀC with
release of nitrous oxide. Electrophiles such as iodine, methyltriflate, and hydrochloric acid also react rapidly with the cis-hyponitrite com-
plexes to give nitrous oxide. The structure of one of these previously prepared complexes, (PPh3)2Pt(N2O2), has been redetermined at
ꢀ100 ꢀC as a dichloromethane solvate with improved precision. The related tetrahedral group 8 dinitrosyl complexes, (PPh3)2M(NO)2
(M = Ru, Os; Ln = PPh3, dppe, and dppf) have been reexamined and new derivatives with chelating phosphines have been prepared by
ligand substitution on the corresponding (PPh3)2M(NO)2. The structures of Ru(dppf)(NO)2 and Os(dppe)(NO)2 have been determined.
These two analogous families of cis-hyponitrite and dinitrosyl complexes illustrate the balance of metal dn electron count and nitrosyl
redox state with one having linear nitrosyls bound to low valent metal centers, and the former having coupled N2O22ꢀ ligands bound to a
higher oxidation state metal center.
ꢁ 2007 Elsevier Ltd. All rights reserved.
Keywords: Hyponitrite; Nitrosyl; Reductive coupling; Nitrous oxide
1. Introduction
for this trend. Nevertheless, NO’s amphoteric ability to
bind as either a bent or linear ligand [6], as well as its ability
to promote associative substitution reactions [7] compli-
cates its coordination chemistry
Perhaps one of the most striking differences between the
organometallic chemistries of carbonyl and nitrosyl com-
plexes is the remarkable prevalence of binary or homoleptic
metallocarbonyls [1] and the absence of the related metal-
lonitrosyls [2]. Thus although many homoleptic carbonyls
with the general formula My(CO)x are known, only one
nitrosyl analog, Cr(NO)4, can be considered to be well
characterized [3]. The evidence for the other proposed
homoleptic nitrosyls such as Fe(NO)4 and Co(NO)3 is con-
siderably less persuasive [4,5] and has recently been criti-
cally reappraised [2]. Given the well recognized isolobal
relationship between the carbonyl and nitrosonium ligands,
a priori there seems to be little theoretical basis to account
NO þ NOꢀ ½NOꢁ2
ð1Þ
ð2Þ
1
3NO ! NO2 þ N2O
Certainly, an important factor which can explain the pau-
city of homoleptic metallonitrosyls is synthetic; many
metallocarbonyls are prepared under reductive conditions
with high pressures of carbon monoxide [8], conditions
which are not suited to handling NO. Two important fea-
tures of nitric oxide chemistry are likely to limit the utility
of these direct approaches: (1) nitric oxide undergoes a
kinetically important dimerization to give [NO]2, 1 Eqs. (1);
and (2) nitric oxide, and its dimer, readily disproportionate,
Eq. (2). Moreover, NO and [NO]2 can engage in redox
chemistry either with low valent metals or with itself in
*
Corresponding author. Tel.: +1 514 398 7409; fax: +1 514 398 3797.
E-mail address: Scott.Bohle@Mcgill.ca (D.S. Bohle).
0277-5387/$ - see front matter ꢁ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.05.009

4738
N. Arulsamy et al. / Polyhedron 26 (2007) 4737–4745
the form of metal catalyzed disproportionation. And of
course any disproportionation, metal catalyzed or not,
leads to the formation of the very strongly oxidizing nitro-
gen dioxide. It is significant that the original syntheses of
Cr(NO)4 involves a photolytic substitution under a stream
of nitric oxide at atmospheric pressure [3,9,10], conditions
which favor the binding monomeric nitric oxide and not ni-
tric oxide disproportionation or the reaction of the com-
plex with the nitric oxide dimer.
In addition to these fundamental synthetic limitations
there is an additional reactivity pattern possible for polyni-
trosyl complexes which is not observed for polycarbonyls:
metal mediated nitric oxide coupling to give N–N bonded
derivatives either as hyponitrite [11–14], or nitrous oxide
[15] or in some cases ultimately to give dinitrogen [16].
Unfortunately, the evidence for the direct coupling of
two nitrosyls in the coordination sphere of a metal is lim-
ited and a clear unambiguous example of the reaction in
Eq. (3) would help us understand the nature of this trans-
formation. The ambiguity present here is mechanistic: Are
either of the nitrosyls coordinated to the metal before N–N
bond formation, Eq. (3), or do these N–N coupled prod-
ucts result from the reaction of the dimer 1 with the metal,
Eq. (4)?
instability and in particular their tendency to lose nitrous
oxide [24].
Ph3P
Ph3P
O
O
N
N
Pt
ð5Þ
Pt(PPh3)4 + 2NO
Ph2P
PPh2
Ph2P R2P PPh2
H
2NO
(OC)2Ru
Ru(CO)2
(OC)2Ru
Ru(CO)2
N
O
H
R2P
N
O
ð6Þ
O
N
O
(ON)2Co
Co(NO)2
excess(NO)
O
N
Co(CO)3NO
O
N
Co(NO)2
O
(ON)2Co
O
N
ð7Þ
ð8Þ
+4
(H3N)5Co
LnM(ηn- ON=NO)
LnM(NO)2
ð3Þ
O
excess(NO)
O
[Co(II)(NH3)6]+2
L
L
N
N
N
M
ð4Þ
LnM + [NO]2
O
N
O
1
(H3N)5Co
Examples of metal mediated nitric oxide reductive cou-
pling which give isolable hyponitrite complexes are rare
and correspond to the nitrosylation of several electron
rich late transition metal complexes, Eqs. (5)–(8) [12–
14]. In the ruthenium and platinum examples the corre-
sponding dinitrosyl complexes were not isolated, and have
not been reported. The reaction of Pt(PPh3)4 with nitric
oxide proceeds in a straightforward manner involving
the reductive dimerization of nitric oxide to yield a cis-
hyponitrite ligated Pt(II) complex (Eq. (5)) [12]. A more
complicated reaction between Co(CO)3(NO) and excess
nitric oxide also proceeds via reductive dimerization of ni-
tric oxide, Eq. (7). In this case the formation of the puta-
tive [Co(NO)3] intermediate is also proposed [13]. Finally,
the example shown of the reductive coupling of two
Co(II) nitrosyl complexes in Eq. (8), {CoNO}8 in the Fel-
tham–Enemark scheme [17], is a well studied [18–20]
example known since Werner’s pioneering chemistry
[21]. In the absence of added reductants nitric oxide cou-
pling can occur with metal oxidation [16] or by nitric
oxide disproportionation, Eq. (2). Thus, the reductive ni-
tric oxide coupling which occurs in Eqs. (5)–(8) are likely
to be quite common and most likely related to the general
metal catalyzed disproportionation of NO by transition
metals [15,22] and more recently by lanthanides [23].
The current scarcity of hyponitrite complexes as products
of reductive nitrosylation reactions is in part due to their
The facile loss of nitrous oxide from the cis-hyponitrite
complex is one of its key reactivity patterns; it is also
important for the uncoordinated ligand. We have attrib-
uted this to the instability of the monoalkyl or monoprot-
onated cis-hyponitrite. To demonstrate this point the
contrast with trans-hyponitrite and its conjugate acid and
esters is illustrative. Thus although a series of monoalky-
lated and protonated trans-hyponitrites are now recog-
nized, these correspond to the kinetically activated form
which releases nitrous oxide. Unlike trans-hyponitrite for
which stable dialkylated and diprotonated derivatives can
be isolated and characterized, neither is known for the cis
isomer. We attribute this tendency to the instability of
the monoprotonated and monoalkylated cis-hyponitrite:
addition of the second electrophile can not compete with
loss of nitrous oxide. This hypothesis accounts for the
instability of cis-hyponitrite complexes: any coordination
sphere lability which leads to a monohapto cis hyponitrite
could rapidly lose nitrous oxide. A second consequence of
this hypothesis is that the preparation of cis-hyponitrite
complexes will most likely require prior coordination of
the oxygens in the precursor or oxidative addition of the ni-
tric oxide dimer, rather than by direct coordination of the
preformed dianion. In this paper, we report: (1) the prepa-
ration and characteristics of cis-hyponitrite complexes; (2)

N. Arulsamy et al. / Polyhedron 26 (2007) 4737–4745
4739
the redetermination of the structure of one of these,
Pt(PPh3)2(N2O2), with a significantly improved precision;
(3) the syntheses and characterization of new dinitrosyl
complexes of ruthenium and osmium with chelating phos-
phines; and (4) the structures of two of these derivatives,
Ru(dppf)(NO)2 and Os(dppe)(NO)2.
2. Results and discussion
Two streams of experimental data are contrasted in this
paper: the stable group 10 M(II) hyponitrite complexes, 2,
for which the corresponding dinitrosyls are not known, and
the stable group 8 dinitrosyls, 3, for which stable mononu-
clear hyponitrite complexes have not been described
NO
NO
O
O
R3P
R3P
N
N
R3P
R3P
M
M
Fig. 1. ORTEP representation of the inner coordination sphere of 2a.
˚
Probability elliposoids shown at 45% and key metric parameters (A, ꢀ):
O(1)–N(1) = 1.370(8); N(1)–N(2) = 1.230(9); N(2)–O(2) = 1.363(8); O(1)–
2
Pt(1) = 2.013(4); O(2)–Pt(1) = 2.023(5); Pt(1)–P(1) = 2.2417(17); Pt(1)–
3
˚
P(2) = 2.2671(18) A; Pt(1)–O(1)–N(1) = 112.1(4); O(1)–N(1)–N(2) =
M = Pt, Ni
M = Ru, Os
118.9(7); N(1)–N(2)–O(2) = 118.5(7); N(2)–O(2)–Pt(1) = 112.3(5); O(1)–
Pt(1)–O(2) = 78.2(2); O(1)–Pt(1)–P(1) = 93.23(15); O(1)–Pt(1)–P(2) =
168.56(15); O(2)–Pt(1)–P(1) = 171.40(15); O(2)–Pt(1)–P(2) = 90.79.15(15);
P(1)–Pt(1)–P(2) = 97.80(7)ꢀ.
2.1. Coordinated hyponitrite
lar to the dianion in its sodium salt [25], but the latter struc-
ture is based on the Rietveld refinement of its powder data
and the key anion bond lengths and angles have high esd’s,
cf. O(1)–N(1)=1.40(3); N(1)–N(2) = 1.20(3); N(2)–O(2) =
1.41(3) A and N(2)–N(1)–O(1) = 120.8(4)ꢀ, N(1)–N(2)–
O(2) = 117.6(4)ꢀ which limits their interpretation.
It remains remarkable how few cis-hyponitrite com-
plexes there are and how poorly developed the chemistry
of this ostensibly simple dianion remains: in part this
reflects the extreme reactivity of its simple salts [24], of
which the disodium salt was only thoroughly characterized
in 1996 [25,26]. In contrast, there are many more reports
related to trans-hyponitrite, it is easier to prepare and it
has greater stability [27,28]. The first and until recently
unique example of the mononuclear cis-hyponitrite com-
plexes 2a with L = PPh3 and M = Pt was first prepared by
treating Pt(PPh3)4 with NO [11,12]. In 2002, we described
a new way to prepare these derivatives by treating MCl2L2,
M = Ni, Pt, with the diazeniumdiolate 4, Eq. (9). In addi-
tion to the generality of the possible substrates for the gen-
eration of 2 their yields and purity are higher with this
synthesis. Detailed spectroscopic and characteristic data
are listed in Section 4, 2a–e, and the structure for 2a has
been redetermined since the original had large esd’s for
the metric parameters for the hyponitrite ligand, and the
modeled solution had a very high R factor, R > 10% [12].
Although these crystallographic problems limited the
detailed interpretation of the structure of 2a it did confirm
its composition. These limitations are due to the original
data being acquired at room temperature, where there is
considerable decomposition. Our redetermination corre-
sponds to the ꢀ100 ꢀC structure. A side on view of the inner
coordination environment of 2a is shown in Fig. 1, and key
metric parameters are included in the caption. The geome-
try adopted by the cis-hyponitrite in 2a is similar to that
in Ni(dppf)(N2O2) [24] and the metric parameters are simi-
˚
O
Me3C
CMe3
MeO
N
N
O-
4
O
L
L
O
O
N
N
M
LnMCl2
O
Me3C
CMe3
2a-e
O
a
c
b
d
e
M
Ln
Pt
PPh3
Pt
Pt
Ni
Ni
PMePh2 dppf
diphos dppf
ð9Þ
In prior work [24], we have termed the reaction in Eq. (9)
an umpolung of the C–N bond: on a formal level the bond
cleaves heterolytically to give [N2O2]2ꢀ rather than to gen-
erate two NO radicals as do many diazeniumdiolates [29].
The quinone by-product has been quantified and corre-
sponds well to the yield of 2. Typically, two equivalents
of 4 are used for every metal complex, but when the stoichi-
ometry is 1:1 the yield of 2a is only slightly less than if two
equivalents are used. In understanding this transformation
the origin of the 4-oxygen of the quinone is crucial, but
uncertain. On the one hand the diazeniumdiolate 4 seems

4740
N. Arulsamy et al. / Polyhedron 26 (2007) 4737–4745
to require the methyloxy substituent as its alkyl substituted
relatives do not react as rapidly with acids to release ni-
trous oxide as readily as 4. This observation suggests that
coordination of 4 might lead to its facile demethylation
and that the oxygen is thus retained in the quinone. On
the other hand, when the reaction in Eq. (9) is performed
for Pt(PPh3)2Cl2 with anhydrous solvents the yield drops
from 72% to 11%. Thus a hydrolytic mechanism is impli-
cated in Eq. (9). Curiously none of our numerous attempts
to adapt this preparation to the related palladium com-
plexes has returned isolable crystalline products or prod-
of triphenylphosphine oxide formed was integrated against
a triphenylphosphine sulfide standard, and the integrated
ratio was identical to the calculated mole ratio.
The oxidative addition reactions of Pt(PPh3)2(N2O2)
with methyl iodide, methyl triflate, iodine, and hydrochlo-
ric acid have been examined to determine if it is possible to
isolate a Pt(IV) complex with a hyponitrite ligand. With
iodine as a solution in methylene chloride there is a rapid
reaction which ensues at ꢀ78 ꢀC and goes to completion
as the reaction is warmed over an hour to give a bright yel-
low precipitate of trans-Pt(PPh3)2I2. This same product
forms only slowly and in low yield when 2a is treated with
iodomethane under these conditions. In the later case even
after 48 h most of the 2a has not reacted and is recovered
from the reaction. In the latter case a peak for trans-
Pt(PPh3)2(CH3)I is not seen in the 31P NMR spectrum
ucts with the key IR bands at circa 1260, 790 cmꢀ1
.
Regardless of the mechanistic details of these syntheses,
the facile formation of new cis-hyponitrite complexes,
and the first examples of their nickel complexes, allows
for the systematic examination of their chemistry [24].
[31]. With methyltriflate
a
white precipitate of
*
L
L
L
L
O
O
[Pt(PPh3)2(l-OH)]2[OSO2CF3]2 forms in 71% yield in the
course of the warming the reaction mixture from ꢀ78 ꢀC
to room temperature.
L
L
N
N
-N2O
M+
O-
M
+ M
O
* proposed
intermediate
2
5
2.2. Dinitrosyls
ð10Þ
Although the dinitrosyls of group 8 metals were some
of the first prepared, cf. Roussin’s red and black salts of
iron [32], the isolation of a ruthenium dinitrosyl complex,
[RuCl(NO)2(PPh3)2]BF4, with both a bent and linear
nitrosyl ligands remains an excellent example of the
amphoteric nature of the nitrosyl ligand [6,33]. Perhaps
equally remarkable is the reduced neutral analog,
Ru(NO)2(PPh3)2 which has two linear nitrosyls and
remains one of the few isolable tetrahedral low valent
ruthenium derivatives [34]. In spite of their early and fac-
ile preparation, Eq. (11), which has since been optimized
[35], the chemistry of these derivatives remains surpris-
ingly limited to reports of its oxygenation [34], oxidative
addition [36–39], catalytic CO/NO metathesis [40–42],
and electrochemistry [43].
These group 10 square planar divalent hyponitrite com-
plexes are sensitive to heat, light, acids, and oxidation. Their
thermal decomposition has been monitored by differential
scanning calorimetry and they typically decompose exo-
thermally at T > 85 ꢀC. To date the only well characterized
products of these reactions are the oxide of the phosphine,
nitrous oxide, and in the case of the platinum complexes,
the colloidal metal. Phosphine oxide is also produced when
the decomposition is done with strict exclusion of oxygen.
This suggests that decomposition follows the stoichiometry
in Eq. (10) where colloidal platinum metal results from the
reductive formation of the phosphine oxide, after loss of ni-
trous oxide. The observed kinetics of nitrous oxide release
and complex decomposition are both first order with the
same rate constant, within experimental error [24]. The
trapping of the oxo intermediate with carbon disulfide
and carbon dioxide support its intermediacy [24], and we
note that a stable terminal platinum oxide in a Pt(IV) com-
plex has recently been reported [30]. What remains absent in
all of the decomposition products of 2 are complexes with
nitrosyl ligands as demonstrated by the absence of nitrosyl
peaks in their IR spectra. There is no evidence that nitric
oxide coupling is reversible in this system, nor is there evi-
dence for stable nitrous oxide complexes in the products.
Based on the yield of Pt(PPh3)2I2 and the observed for-
mation of triphenylphosphine oxide, the stoichiometric
equation was proposed to involve two moles of 2a and
one mole of iodine:
2NaNO2, Δ DMF, > 16 h
MCl2(CO)2(PPh3)2
M(NO)2(PPh3)2
- 2CO2, -2NaCl
3a,b
ð11Þ
L
L
L
NO
Δ, toluene, 24 h
-2PPh3
M(NO)2(PPh3)2
+
M
L
NO
3a,b
3c,d
a
b
c
d
M
L
Ru
Os
Ru
Os
PPh3
PPh3 dppf dppe
ð12Þ
Although nitric oxide exchange is reported to be fast for
3a [44], attempts to prepare pyridine, 2,20-bipyridine, and
1,10-phenanthroline complexes by ligand exchange with
the triphenylphosphine failed to generate new nitrogen
2PtðPPh3Þ2ðO2N2Þ þ l2 ! PtðPPh3Þ2l2 þ 2N2O þ 2OPPh3
þ Ptð0Þ
When the reaction between 2a and iodine was monitored
by 31P NMR with the proposed stoichiometry, the amount

N. Arulsamy et al. / Polyhedron 26 (2007) 4737–4745
4741
base analogs of 3a [35]. The inability of nitrogen based
donors, even chelating donors, to substitute for triphenyl-
phosphine is not surprising given that many low oxidation
state osmium complexes are known for phosphines but few
for ammines. We hypothesized that a chelating phosphine
could substitute for the two triphenylphosphine in 3a,b
and demonstrated this with the facile preparation of the
bisdiphenylphosphinoferrocene complex of ruthenium 3c,
and the diphenylphosphinoethane complex of osmium 3d,
Eq. (12). Both of these substitution reactions have to be
carried out in the strict exclusion of oxygen, but the prod-
ucts form in high yield and are readily isolated by recrystal-
lization of the reaction mixtures. All of the dinitrosyl
complexes 3 are a red-brown color which is due to a long
tailing UV band which has considerable extinction in the
visible. In the process of characterizing the UV–Vis activity
of 3c,d a slow oxygen independent photochemical decom-
position process was discovered. Nevertheless, 3d in partic-
ular is very reactive towards oxygen in solution or as a
solid and rapidly decomposes within 20 min of exposure
to oxygen. This is in contrast to the behavior of 3a,d which
decompose much more slowly and are readily purified by
recrystallization in the open. As was found for 3b the prod-
uct of the reaction of oxygen and 3d is a mononitrosyl with
a coordinated nitrate [34]. There is no precedence in this
system for nitrosyl coupling to give a stable or intermediary
hyponitrite ligand analogous to 2.
Fig. 3. ORTEP representation of 3d at 30% probability level and
hydrogens omitted. Key metric parameters: Os(1)–P(1) = 2.3143(15),
Os(1)–P(2) = 2.3210(14), Os(1)–N(1) = 1.782(5), Os(1)–N(2) = 1.783(4)
A; N(1)–Os(1)–N(2) = 138.7(2), P(1)–Os(1)–P(2) = 84.30(5), P(1)–Os(1)–
N(1) 98.80(16), P(1)–Os(1)–N(2) 109.98(19), P(2)–Os(1)–N(1) =
˚
107.42(17), and P(2)–Os(1)–N(2) = 104.42(17)ꢀ.
in the captions. As with M(NO)2(PPh3)2 which have been
characterized for M = Os [45] and Ru [46,47] both struc-
tures have a distorted tetrahedral geometry at the metal
with the angle separating the two nitrosyl ligands being
substantially larger, ca 139ꢀ as compared to the angle
between the two phosphorus atoms which are 101.8ꢀ and
84.3ꢀ in 3c and 3d, respectively. Although the angle
between the nitrosyl ligands is very similar to those found
for the bistriphenylphosphine complexes, 139.2ꢀ and
139.1ꢀ, the chelating phosphines in 3c and 3d in these struc-
ture reduces the angle between the phosphorus atoms from
103.9ꢀ and 103.5ꢀ for 3a,b, respectively to 84.3ꢀ in 3d. This
change in structure is also reflected in the nitrosyl stretch-
ing bands for 3c,d, which are separated by slightly greater
energies than in 3a,b. It is difficult to attribute the increased
reactivity of 3d with dioxygen to any one particular struc-
tural change found by crystallography. In general alkyl
phosphines are better donor ligands than their correspond-
ing aryl phosphine analogs. Therefore the increased sensi-
tivity of 3d to dioxygen may be simply due to increased
electron density on the metal from the better donor
phosphine.
To understand the structure and reactivity of 3c,d both
complexes have been characterized by single crystal X-ray
diffraction. ORTEP representations for both are depicted
in Figs. 2 and 3, with representative bond lengths listed
3. Conclusions
While the amphoteric coordination character of nitric
oxide, with its concomitant ability to bind in bent and lin-
ear geometries, is well known, another potential manifesta-
tion of its redox balance with transition metals is its ability
to couple to give a hyponitrite complex such as the five
examples described in this paper. But does the coordinative
Fig. 2. ORTEP representation of 3c at 30% probability level and hydrogens
omitted. Key metric parameters: Ru(1)–P(1) = 2.3478(14), Ru(1)–P(2) =
˚
2.3667(13), Ru(1)–N(1) = 1.762(5), Ru(1)–N(2) = 1.781(4) A; N(1)–
Ru(1)–N(2) = 132.1(2), P(1)–Ru(1)–P(2) = 101.80(5), P(1)–Ru(1)–N(1)
97.2(2), P(1)–Ru(1)–N(2) 108.98(16), P(2)–Ru(1)–N(1) = 111.50(18), and
P(2)–Ru(1)–N(2) = 101.729(16)ꢀ.

4742
N. Arulsamy et al. / Polyhedron 26 (2007) 4737–4745
reductive coupling of nitric oxide represent a real reactivity
pattern or mechanism? Among the ways to answer this
question would be with examples of the formation of a
nitrosyl complex from hyponitrite, or alternatively, the for-
mation of hyponitrite complex from a dinitrosyl complex.
At this time there are no unambiguous examples of either
reaction: the predominant reaction of hyponitrite com-
plexes is elimination of nitrous oxide, and polynitrosyl
complexes are not necessarily precursors to hyponitrites.
An important origin for this mechanistic uncertainty is
nitric oxide’s ability to dimerize and thus, as with many
of nitric oxides reactions, one of the key questions remains
does nitric oxide react as the monomer or dimer? More-
over, is the absence of stable homoleptic polynitrosyls in
part due to their tendency to undergo reductive coupling
as the first step in an oxidative decomposition pathway?
Until we have clear evidence for the presence of these metal
bound intermediates in these reactions, this hypothesis
remains suggestive.
ether, and hexanes gives 0.158 g, 72.4% of 2a. DSC: Tonset =
86.9 ꢀC, Tmax = 103.8 ꢀC, DH = 68.1 cal/g (53.1 kcal/
mole). IR (KBr, cmꢀ1): 1263 m, 1001 sh, 900.7 m, 793.7
m, 502.4 s.
UV–Vis (CH2Cl2, kmax, nm (e, Mꢀ1 cmꢀ1)): 238 (28674).
1H NMR (CD2Cl2, 400 MHz) d 7.20 (t, 12H), 7.32–7.40
(m, 18H); 13C NMR (CD2Cl2, 400 MHz) d 134, 131, 129,
128. 31P NMR (CD2Cl2, 400 MHz) d 11.0 (1JPtP
=
3564 Hz). The literature method [11] for the preparation
of 2a involves treating Pt(PPh3)4 with NO in benzene fol-
lowed by recrystallization. In addition to 2a a variety of
other products appear to be formed and in our hands the
synthesis above gives a higher yield of pure cis-hyponitrite
complex.
4.2.2. Pt(PPh2Me)2(N2O2) (2b)
Pt(PPh2Me)2Cl2 (0.3775 g, 0.566 mmol), and 4, 0.441 g,
1.34 mmol of are treated as for 2a, to give 0.254 g, 68.4%
2b as yellow crystals. Anal. Calc. for PtP2C26H26N2O2: C,
47.64; H, 4.00; N, 4.27. Found: C, 47.54; H, 4.10; N,
4. Experimental
3.89%.
DSC:
Tonset = 87.6 ꢀC,
Tmax = 99.0 ꢀC,
DH = 63.9 cal/g (41.9 kcal/mole). IR (KBr, cmꢀ1): 1286.4
4.1. General
w, 980.7 w, 851.5 w, 785.9 m, 608.5 m. UV–Vis (CH2Cl2,
k
1
max, nm (e, Mꢀ1 cmꢀ1)): 238, 268sh (27856, 10585) H
The reagents and solvents used were reagent grade and
used as supplied. Nitric oxide gas was obtained from Scott
Specialty Gases and was purified by passing through a col-
umn packed with sodium hydroxide pellets. The nitrosyla-
tion apparatus and instrumental methods for these
experiments are as described in prior publications [48,49].
Reagents were purchased from Aldrich and used as provided
or purified as described in prior reports. Specific precursors
were prepared by the literature methods including
PtCl2(PR3)2 [50,51], Ni(dppe)Cl2 [52], Pt(dppf)Cl2 [53],
Ni(dppf)Cl2 [52], Ru(NO)2(PPh3)2 [54,34], and Os(NO)2-
(PPh3)2 [34], Ni(N2O2)(dppf) [24], sodium-(Z)-1-{4-(2,6-di-
tert-butyl-4-methoxycyclohexadienonyl)}diazen-1-ium-1,2-
diolate [49], 4, and sodium-(Z)-1-{4-(2,6-di-tert-butyl-4-
methylcyclohexadienonyl)}diazen-1-ium-1,2-diolate (6) [49].
NMR (CD2Cl2, 400 MHz) d 1.86 (d, 4H), 7.30 (t, 8H),
7.38–7.48 (m, 12H); 13C NMR (CD2Cl2, 100 MHz) d 133,
132, 129, 128, 15.2. 31P NMR (CD2Cl2, 161.9 MHz) d
ꢀ11.6.
4.2.3. Pt(dppf)(N2O2) (2c)
Pt(dppf)Cl2 (0.103 g, 0.13 mmol), and 0.087 g,
0.27 mmol of 4 are treated as for 2a to give 0.69 g,79%
2b as yellow crystals. Anal. Calc. for PtFeP2C34H38N2O2:
C, 49.83; H, 4.67, N, 3.42. Found: C, 50.15; H, 3.87; N,
3.55%.
DSC:
Tonset = 85.1 ꢀC,
Tmax = 99.0 ꢀC,
DH = ꢀ52.5 cal/g, 43.1 kcal/mol. IR (KBr, cmꢀ1): 1330.5
m, 974 m, 890 s, 780.1 s, 611 s. UV–Vis (CH2Cl2, kmax
,
nm (e, Mꢀ1 cmꢀ1)): 238, 268sh (27856, 10585) H NMR
(CD2Cl2, 400 MHz) d 7.71 (m, 4H), 7.50 (m 8H), 7.40
(m, 8H), 4.41 (m, 4H), 4.24(d, J = 1.8 Hz, 4 H); 13C
NMR (CD2Cl2, 100 MHz) d 145.7, 134.8, 131.8, 128.8,
77.4 (d, J = 21 Hz), 76.4 (t, J = 2H), 74.2. 31P NMR
(CD2Cl2, 161.9 MHz) d 4.7 (1JPtP = 3625.5 Hz).
1
4.2. Preparation of complexes
4.2.1. Pt(PPh3)2(N2O2) (2a)
Pt(PPh3)2Cl2 (0.221 g, 0.280 mmol) is dissolved in 20 mL
of acetonitrile/methylene chloride (1:1) and sodium-(Z)-1-
{4-(2,6-di-tert-butyl-4-methoxycyclohexadienonyl)}diazen-
1-ium-1,2-diolate (0.196 g, 0.616 mmol), 4, dissolved in
25 mL of methanol, is added with constant stirring. The
solution immediately turns yellow, and the mixture is
allowed to stir for 5 min before all solvents are removed
in vacuo. The resulting brownish solid material is taken
up in 30 mL methylene chloride and allowed to stand for
10 min and filtered to remove any insoluble materials. Eth-
anol, 30 mL is then added, and solution volume concen-
trated to roughly half its volume and crystallization
induced. Further concentration to 5 mL followed by filtra-
tion and successive washes with 5 mL each of ethanol,
4.2.4. Ni(dppe)(N2O2) (2d)
Ni(dppe)Cl2 (0.2581 g, 0.489 mmol) was dissolved in
acetonitrile (120 mL) and a solution of sodium-(Z)-1-{4-
(2,6-di-tert-butyl-4-methoxycyclohexadienonyl)}diazen-1-
ium-1,2-diolate (0.3127 g, 0.982 mmol) in 50 mL of
methanol was added under nitrogen with constant stirring.
The solution immediately turns from reddish to yellow or
orange color and stirred for about 15–20 min. The solvent
was removed in vacuo. The crude yellow solid material was
dissolved in methylene chloride and allowed to stand for
10 min, and the solution filtered to remove any insoluble
material. The solvent was removed in vacuo. The crude
product was successively washed with ether until the ether

N. Arulsamy et al. / Polyhedron 26 (2007) 4737–4745
4743
washing is colorless. (Yield: 0.216 g, 77%), Anal. Calc. for
NiP2C26H24N2O2: C, 60.39; H, 4.68; N, 5.42. Found: C,
59.59; H, 4.73; N, 4.92%. DSC: Tonset = 97.3 ꢀC,
Tmax = 104.1 ꢀC, DH = 136.9 cal/g (70.8 kcal/mole). IR
(KBr, cmꢀ1): New hyponitrite bands are obscured by dppe
bands. UV–Vis (CH2Cl2, kmax, nm (e, Mꢀ1 cmꢀ1)): 236,
268, 408 (29513, 19539, 1012). 1H NMR (CD2Cl2,
400 MHz) d 2.43 (d, 4H), 7.45–7.52 (m, 12H), 7.87–7.91
(m, 8H); 13C NMR (CD2Cl2, 100 MHz) d 133, 132, 130,
129, 25.9, 31P NMR (CD2Cl2, 161.9 MHz) d 46.4.
was added; gas was observed and a light beige precipitate
formed. The solid was collected and washed with hexanes.
Yield: 25 mg (40%). The identity of cis-Pt(PPh3)2Cl2 was
confirmed by the absence of the IR bands characteristic
of 2a, as well as a comparison with the literature 31P
NMR spectrum of cis-Pt(PPh3)2Cl2 as prepared by Goel
[55].
Compounds 2a–c (0.05 g) were each suspended in etha-
nol and treated with dilute HCl solution. There was imme-
diate effervescence with gas evolution. The solid residue
was collected and characterized by NMR, IR and com-
pared with respective authentic dichloride samples. In
order to analyze the evolved gas upon addition of dilute
HCl solution, about 0.02 g of compound (2a) was placed
in an IR gas chamber and HCl gas was bubbled into the
gas chamber. The analysis of the evolved gas by FT-IR
confirms the presence of N2O.
Reaction of iodine with Pt(PPh3)2(N2O2) to give trans-
Pt(PPh3)2I2: 2a (0.1 g, 0.13 mmol) and triethylamine
(0.05 mL) were dissolved in methylene chloride (10 mL),
and degassed by freeze–thaw cycles. The amine is a preven-
tative measure to ensure that the solution remains basic.
The solution was cooled to ꢀ78 ꢀC and iodine (0.07 g,
0.26 mmol) was added. The reaction was allowed to warm
to room temperature over the span of 1 h. A bright yellow
precipitate formed and was collected by filtration. Yield:
0.056 g (45%) which is spectroscopically identical by IR,
and 31P NMR to literature results for Pt(PPh3)2I2 [56] this
same product is the only isolable compound from the reac-
tion of methyliodide or hydroiodic acid with 2a. In the case
of methyl iodide there is no evidence for a transitory prod-
uct corresponding[31] to trans-Pt(PPh3)2(CH3)I as its peak
at 28.1 ppm (1JPt–P = 3460 Hz) was not seen by 31P NMR
of the monitored reaction mixtures which are dominated
by peaks corresponding to the starting material and diio-
dide product.
4.2.5. Ru(dppf)(NO)2 (3c)
Ru(NO)2(PPh3)2, 3a, 81 mg, 0.012 mmol, and 1.2 equiv.
of dppf, 74 mg, 0.014 mmol, were heated at reflux for 14 h
in 20 mL toluene under an atmosphere of nitrogen. After
cooling the mixture was brought out of the inert atmo-
sphere box and the solvent removed in vacuo to give a
crude red-orange product which was dissolved in 10 mL
dichloromethane and recrystallized by the addition of
20 mL ethanol and concentration on a rotory evaporator
to give 132 mg, of 3c in 85% yield. Crystals suitable for
X-ray diffraction were grown from dichloromethane/etha-
nol. Anal. Calc. for C34H28FeN2O2P2Ru: C, 56.29; H,
5.28; N, 3.86. Found: C, 56.52; H, 3.87; N, 3.54%. IR
(cmꢀ1), KBr pellet: m(NO):1673.2s, 1629.8s, other charac-
teristic bands: 3350 br, 1304.8w, 1264.3w,1164.9m,
836.1w, 819.7m. UV–Vis (CH2Cl2), kmax
M
,
nm (e,
ꢀ1 cmꢀ1): 422 (1330) 1H NMR (CDCl3, 400 MHz) d
4.31 (t, J = 1.7, 4H), 4.24 (dd, J = 1.7, 1.9, 4H), 7.35–
7.37 (m, 12H), 7.53–7.58 (m, 8H); 13C NMR (CDCl3,
100 MHz) d 71.8(s), 75.1 (t, J = 4.9), 84.17 (d, J = 51.4),
128.4 (t, J = 5.8), 130.1 (s), 133.6 (t, J = 6.7), 136.4 (dd,
J = 46.3, 4.5) 31P NMR (CDCl3, 161.9 MHz) d 47.5.
4.2.6. Os(dppe)(NO)2 (3d)
Os(NO)2(PPh3)2, (3b) 65 mg, 0.0084. mmol, and
2.5 equiv. of bisdiphenylphosphinoethane, dppe, 83 mg,
0.0021 mmol, were heated at reflux for 30 h in 15 mL tolu-
ene under an atmosphere of nitrogen. After cooling the
mixture was stripped of solvent and the residue crystallized
twice in the inert atmosphere box from dichloromethane
and ethanol to give 45 mg of 3d as oxygen sensitive red-
brown crystals in 82% yield. Crystals suitable for X-ray dif-
fraction were grown from dichloromethane/ethanol. Anal.
Calc. for C26H24N2O2P2Os: C, 47.99; H, 3.72; N, 4.31.
Found: C, 48.28; H, 3.97; N, 4.33%. IR (cmꢀ1), KBr pellet:
m(NO): 1656.8s, 1604.7s. UV–Vis (CH2Cl2), kmax 288 nm.
1H NMR (CD2Cl2, 400 MHz) d 2.51 (d, 4H), 7.48–7.56
(m, 12H), 7.93–7.99 (m, 8H); 13C NMR (CD2Cl2,
100 MHz) d 134, 132, 130, 127, 28.1, 31P NMR (CD2Cl2,
161.9 MHz) d 31.4.
4.4. The stoichiometry of the reaction between
Pt(PPh3)2(N2O2) with iodine
The platinum complex 2a (0.025 g, 0.032 mmol) was dis-
solved in CD2Cl2 (0.5 mL) in an NMR tube. Iodine
(0.004 g, 0.016 mmol) was added and the mixture was son-
icated for 3 h. Once all of the cis-hyponitrite had reacted,
as confirmed by 31P NMR, a solution of triphenylphos-
phine sulfide (0.018 g, 0.061 mmol) in CD2Cl2 (0.3 mL)
was added to the NMR tube and the 31P NMR was mea-
sured, with a delay time of 1 s. The integration between tri-
phenylphosphine sulfide and triphenylphosphine oxide was
measured and compared to the expected value. Expected
ratio (P(S)Ph3:P(O)Ph3) 1.9:1. Measured ratio (P(S)Ph3:
P(O)Ph3) 2.1:1.
4.3. Reaction of hyponitrite complexes (2) with electrophiles
Reaction of Pt(PPh3)2(N2O2) with CF3SO3CH3: 2a
(0.1 g, 0.13 mmol) was dissolved in methylene chloride
(5 mL), and degassed through freeze–thaw methods. The
solution was cooled to ꢀ78 ꢀC and CF3SO3CH3
(0.02 mL, 0.2 mmol) was added. The reaction was allowed
Reaction of HCl with Pt(PPh3)(N2O2) to give cis-
Pt(PPh3)2Cl2: 2a (0.05 g, 0.07 mmol) was dissolved in
CH2Cl2 (2 mL). HCl (0.15 mmol) in CH3OH (0.17 mL)

4744
N. Arulsamy et al. / Polyhedron 26 (2007) 4737–4745
to warm to room temperature in the absence of light over
12 h. The white precipitate which formed was collected fil-
tration. Yield: 0.065 g (71%). The precipitate is insoluble in
organic solvents, alcohols, water, acetonitrile, and DMSO.
On the basis of IR the compound is determined to be
[Pt(PPh3)2(l-OH)]2[OSO2CF3]2. IR (KBr, cmꢀ1): 3548 m
(mOH), 1273vs (mSO), 1032vs (mSO). An authentic sample of
the product was also synthesized for comparison by treat-
ing, Pt(PPh3)Cl2 (0.05 g, 0.06 mmol), in 20 mL chloroform/
acetone (1:1) to which water (1 mL) and AgOSO2CF3
(0.02 g, 0.06 mmol) were then added. After 1 h the silver
chloride precipitate was removed by filtration through dia-
tomaceous earth and diethyl ether (10 mL) was added to
the filtrate. On standing for 12 h, a white precipitate of
[Pt(PPh3)2(l-OH)]2[OSO2CF3]2 was collected whose IR
spectrum contained the same mOH band at 3550 cmꢀ1. This
band is also present in [Pt(PPh3)2(l-OH)]2[BF4]2, prepared
by Phillips and coworkers [57].
program. Three standard reflections measured after every
97 reflections exhibited no significant loss of intensity.
The data were corrected for Lorentz-polarization effects
and absorption. The structure was solved by direct meth-
ods and refined by least-squares techniques on F2 using
SHELXTL.
The cis hyponitrite complex 2 is a redetermination of a
structure originally reported [12] as a benzene solvate from
crystals obtained from benzene/dichloromethane which
refined to R = 10.8%. In this original structure the unit cell
ꢀ
corresponds to the triclinic space group P1, with
˚
a = 12.199(6), b = 10.747(6), c = 15.730(8) A, a = 108.75
(4), b = 95.57(4), and c = 69.98(4)ꢀ with Z = 2, and V =
3
˚
1834.6 A . In our redetermination crystals were obtained
from dichloromethane/ethanol and crystallize in mono-
clinic space group P21n, with a = 13.037(2), b = 15.685(3),
˚
c = 17.023(3) A, a = c = 90, and b = 98.020(10)ꢀ with
3
˚
Z = 4, and V = 3446.9(10) A . The monoclinic form has a
dichloromethane solvate that is well defined and refined
anisotropically in the last least squares cycles to give a final
R1 of 3.44%, and Sgof of 1.027, and a relatively flat electron
density map with the largest difference peak being close to
the metal center.
The dinitrosyl complexes 3c and 3d were crystallized
from dichloromethane/ethanol as large deep orange
blocks. The diffraction data collection, solution, and refine-
ment all followed the outline above for 2a with key data
5. X-ray crystallographic data
X-ray diffraction data for 2 Æ CH2Cl2, 3c, and 3d were
collected on a Bruker P4 diffractometer equipped with a
molybdenum tube and a graphite monochromator, Table
1 contains diffraction data for 2 Æ CH2Cl2, 3c, and 3d.
Unit-cell dimensions were determined from several accu-
rately centered reflections in high 2h angles using XSCANS
Table 1
Crystallographic and structure refinement data for compounds 2, 3c and 3d
Compound
2
3c
3d
Molecular formula
Formula weight
Temperature (K)
Crystal system
Space group
C
864.58
293(2)
monoclinic
P21/n
37H32Cl2N2O2P2Pt
C34H30FeN2O3P2Ru
733.46
293(2)
C26H24N2O2OsP2
648.61
293(2)
monoclinic
P21/n
13.617(3)
triclinic
ꢀ
P1
˚
a (A)
13.037(2)
15.685(3)
9.363(3)
11.892(2)
˚
b (A)
11.964(2)
˚
c (A)
17.023(3)
14.870(3)
15.932(3)
a (ꢀ)
b (ꢀ)
c (ꢀ)
V (A )
Z
90
78.29(1)
86.38(2)
88.50(2)
1617.9(6)
90
105.22(2)
90
2504.5(8)
98.020(10)
90
3446.9(10)
4
1.666
4.355
3
˚
2
4
qcalc (Mg/m3)
1.506
1.050
744
1.720
5.245
1264
l (mmꢀ1
F(000)
)
1704
Crystal size (mm)
2h Range (ꢀ)
Index ranges
0.26 · 0.20 · 0.14
3.54–49.88
ꢀ1 6 h 6 14, ꢀ1 6 k 6 16,
ꢀ18 6 l 6 20
5853
0.70 · 0.24 · 0.20
4.02–50.00
ꢀ1 6 h 6 11, ꢀ13 6 k 6 13,
ꢀ17 6 l 6 17
7074
0.28 · 0.22 · 0.20
3.50–50.02
ꢀ16 6 h 6 1, ꢀ1 6 k 6 14,
ꢀ18 6 l 6 18
5458
Reflections collected
Independent reflections [Rint
Absorption correction type
]
4477 [0.0310]
psi-scan
5663 [0.0229]
psi-scan
4362 [0.0250]
psi-scan
Maximum and minimum transmissions
Refinement method
Data/restraints/parameter
Goodness-of-fit on F2
R [I > 2rI]
0.1617 and 0.1108
least-squares on F2
4477/0/415
1.027
R1 = 0.0344, wR2 = 0.0815
R1 = 0.0422, wR2 = 0.0867
2.857 and ꢀ 0.955
0.3908 and 0.3376
least-squares on F2
5663/0/388
1.093
R1 = 0.0494, wR2 = 0.1397
R1 = 0.0607, wR2 = 0.1490
1.995 and ꢀ0.512
0.1478 and 0.1180
least-squares on F2
4362/0/298
1.006
R1 = 0.0296, wR2 = 0.0607
R1= 0.0494, wR2 = 0.0670
0.607 and ꢀ0.772
R (all data)
3
˚
Largest difference in peak and hole (e A )

N. Arulsamy et al. / Polyhedron 26 (2007) 4737–4745
[17] R.D. Feltham, J. Enemark, Coord. Chem. Rev. 13 (1974) 339.
4745
collected in Table 1. During the final stages of the refine-
ment of 3c an extra intense solvate peak was located in
electron difference maps and was modeled as a water sol-
vate whose presence was confirmed by measurement of
the IR spectrum of other crystals from the same batch
which have a band at 3350 cmꢀ1 attributable to the water
solvate.
[18] H. Okamura, E. Miki, K. Mizumachi, T. Ishimori, Bull. Chem. Soc.
Jpn. 49 (1976) 666.
[19] M.E. Chacon Villalba, A. Navaza, J.A. Guida, E.L. Varetti, P.J.
Aymonino, Inorg. Chim. Acta 359 (2006) 707.
[20] B. Jezowska-Trzebiatowska, J. Hanuza, M. Ostern, J. Ziolkowski,
Inorg. Chim. Acta 6 (1972) 141.
[21] A. Werner, P. Karrer, Helv. Chim. Acta 1 (1918) 54.
[22] P.C. Ford, I.M. Lorkovic, Chem. Rev. 102 (2002) 993.
[23] G.H. Maunder, M.R. Russo, A. Sella, Polyhedron 23 (2004) 2709.
[24] N. Arulsamy, D.S. Bohle, J.A. Imonigie, S. Levine, Angew. Chem. 41
(2002) 2371.
6. Supplementary material
[25] C. Feldmann, M. Jansen, Angew. Chem. 35 (1996) 1728.
[26] C. Feldmann, M.Z. Jansen, Anorg. Allg. Chem. 623 (1997) 1803.
[27] M.N. Hughes, Quart. Rev., Chem. Soc. 22 (1968) 1.
[28] N. Arulsamy, D.S. Bohle, J.A. Imonigie, E.S. Sagan, Inorg. Chem. 38
(1999) 2716.
[29] J.A. Hrabie, L.K. Keefer, Chem. Rev. 102 (2002) 1135.
[30] T.M. Anderson, W.A. Neiwert, M.L. Kirk, P.M.B. Piccoli, A.J.
Schultz, T.F. Koetzle, D.G. Musaev, K. Morokuma, R. Cao, C.L.
Hill, Science 306 (2004) 2074.
CCDC 633311, 633312 and 635099 contain the supple-
mentary crystallographic data for 2 Æ 2CH2Cl2, 3c and 3d.
These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk.
[31] V.V. Grushin, I.S. Akhrem, M.E. Vol’pin, J. Organomet. Chem. 371
(1989) 403.
[32] E.J. Wharton, J.A. McCleverty, Inorg. Nucl. Chem. Lett. 6 (1970)
549.
Acknowledgements
We gratefully acknowledge NSERC for support in the
form of a Discovery Grant and the Air Force Office of Sci-
entific Research, Grants F49620-96-1-0417 and 98-1-0461,
for their financial support of this research.
[33] C.G. Pierpont, D.G. Van Derveer, W. Durland, R. Eisenberg, J. Am.
Chem. Soc. 92 (1970) 4760.
[34] K.R. Grundy, K.R. Laing, W.R. Roper, J. Chem. Soc., Chem.
Commun. (1970) 1500.
[35] B.C. Paul, S.C. Sarker, R.K. Poddar, J. Coord. Chem. 28 (1993) 245.
[36] E.B. Boyar, A. Dobson, S.D. Robinson, B.L. Haymore, J.C.
Huffman, J. Chem. Soc., Dalton Trans. (1985) 621.
[37] B. Haymore, J.C. Huffman, A. Dobson, S.D. Robinson, Inorg. Chim.
Acta 65 (1982) L231.
References
[1] F. Calderazzo, R. Ercoli, G. Natta, in: I. Wender, P. Pino (Eds.),
Organic Synthesis via Metal Carbonyls, vol. 1, Wiley Interscience,
New York, NY, 1968, pp. 1–272.
[38] J.A. McCleverty, C.W. Ninnes, I. Wolochowicz, J. Chem. Soc.,
Chem. Commun. (1976) 1061.
[39] A. Dobson, S.D. Robinson, J. Organometal. Chem. 99 (1975) C63.
[40] J. Reed, R. Eisenberg, Science 184 (1974) 568.
[41] S. Bhaduri, B.F.G. Johnson, C.J. Savory, J.A. Segal, R.H. Walter, J.
Chem. Soc., Chem. Commun. (1974) 809.
[2] T.W. Hayton, W.S. McNeil, B.O. Patrick, P. Legzdins, J. Am. Chem.
Soc. 125 (2003) 12935.
[3] M. Herberhold, A. Razavi, Angew. Chem., Int. Ed. Engl. 11 (1972)
1092.
[42] S. Bhaduri, B.F.G. Johnson, Trans. Met. Chem. 3 (1978) 156.
[43] G. Piazza, G. Innorta, Inorg. Chim. Acta 70 (1983) 111.
[44] A. Khair, Dhaka University Studies, Part B, Science 31 (1983) 35.
[45] B. Haymore, J.A. Ibers, Inorg. Chem. 14 (1975) 2610.
[46] A.P. Gaughan Jr., B.J. Corden, R. Eisenberg, J.A. Ibers, Inorg.
Chem. 13 (1974) 786.
[4] W.P. Griffith, J. Lewis, G. Wilkinson, J. Chem. Soc. (1958) 3993.
[5] I.H. Suberwal, A.B. Burg, J. Chem. Soc., Chem. Commun. (1970)
1001.
[6] C.P. Brock, J.P. Collman, G. Dolcetti, P.H. Farnham, J.A. Ibers, J.E.
Lester, C.A. Reed, Inorg. Chem. 12 (1973) 1304.
[7] F. Basolo, Chem. Brit. 5 (1969) 505.
[47] S. Bhaduri, G.M. Sheldrick, Acta Crystallogr., Sect. B 31 (1975) 897.
[48] N. Arulsamy, D.S. Bohle, J.A. Imonigie, E.S. Sagan, J. Am. Chem.
Soc. 122 (2000) 5539.
[49] D.S. Bohle, J.A. Imonigie, J. Org. Chem. 65 (2000) 5685.
[50] J. Chatt, R.G. Wilkins, J. Chem. Soc. (1956) 525.
[51] J. Chatt, R.G. Wilkins, J. Chem. Soc. (1952) 273.
[52] A.W. Rudie, D.W. Lichtenberg, M.L. Katcher, A. Davison, Inorg.
Chem. 17 (1978) 2859.
[53] G.M. Whitesides, J.F. Gaasch, E.R. Stedronsky, J. Am. Chem. Soc.
94 (1972) 5258.
[54] J.J. Levison, S.D. Robinson, Chem. Ind. (1969) 1514.
[55] R.G. Goel, Inorg. Nucl. Chem. Lett. 15 (1979) 437.
[56] S.H. Mastin, Inorg. Chem. 13 (1974) 1003.
[8] E.W. Abel, Quart. Rev. 17 (1963) 133.
[9] B.I. Swanson, S.K. Satija, J. Chem. Soc., Chem. Commun. (1973) 40.
[10] S.K. Satija, B.I. Swanson, Inorg. Synth. 16 (1976) 1.
[11] S. Cenini, R. Ugo, G. La Monica, S.D. Robinson, Inorg. Chim. Acta
6 (1972) 182.
[12] S. Bhaduri, B.F.G. Johnson, A. Pickard, P.R. Raithby, G.M.
Sheldrick, C.I. Zuccaro, J. Chem. Soc., Chem. Commun. (1977) 354.
[13] R. Bau, I.H. Sabherwal, A.B. Burg, J. Am. Chem. Soc. 93 (1971)
4926.
[14] H.-C. Boettcher, M. Graf, K. Mereiter, K. Kirchner, Organometallics
23 (2004) 1269.
[15] J.H. MacNeil, P.A. Berseth, E.L. Bruner, T.L. Perkins, Y. Wadia, G.
Westwood, W.C. Trogler, J. Am. Chem. Soc. 119 (1997) 1668.
[16] K. McNeill, R.G. Bergman, J. Am. Chem. Soc. 121 (1999) 8260.
[57] D.A. Phillips, M. Kubota, J. Thomas, Inorg. Chem. 15 (1976) 118.