Thermal and photochemical reactions of azidoruthenium(III) complexes of macrocyclic tertiary amines and the structure of the (phosphoraniminato) ruthenium(III) complex trans-[Ru(14-TMC)(N3)(NPPh3)] +

Article abstract of DOI:10.1002/ejic.201100771

The bis(azido)ruthenium(III) complexes, trans-[Ru(L)(N₃) ₂]⁺ [L = 14-TMC (1) and 16-TMC (4)] have been prepared. These complexes undergo facile thermal or photo-decomposition in RCN (R = Me, Bu, Ph, 4-MePh, 2-MeOPh) soluti

Full text of DOI:10.1002/ejic.201100771

FULL PAPER
DOI: 10.1002/ejic.201100771
Thermal and Photochemical Reactions of Azidoruthenium(III) Complexes of
Macrocyclic Tertiary Amines and the Structure of the
(Phosphoraniminato)ruthenium(III) Complex trans-[Ru(14-TMC)(N3)-
(NPPh3)]+
Chi-Ming Ho,[a] Hiu-Chi Leung,[a] Shuixing Wu,[a] Kam-Hung Low,[a] Zhenyang Lin,[b] and
Chi-Ming Che*[a]
Keywords: Ruthenium / N ligands / Macrocyclic ligands / Azides / Nitrides
The bis(azido)ruthenium(III) complexes, trans-[Ru(L)(N3)2]+
[L = 14-TMC (1) and 16-TMC (4)] have been prepared. These
complexes undergo facile thermal or photo-decomposition in
RCN (R = Me, Bu, Ph, 4-MePh, 2-MeOPh) solutions to pro-
duce the corresponding azidoruthenium(II) complexes trans-
[Ru(L)(N3)(RCN)]+ [L = 14-TMC, R = Me (2a), Bu (2b), Ph (2c),
4-MePh (2d), 2-MeOPh (2e); L = 16-TMC, R = Me (5a), =
Ph (5b)] and cis-[Ru(Tet-Me6)(N3)(MeCN)]+ (6). Complex 1
reacted with PPh3, by a nitrogen atom transfer reaction, to
give trans-[Ru(14-TMC)(N3)(NPPh3)]+ (3) in 80% yield. The
crystal structures of 2e(PF6), 3(PF6) and 5b(ClO4) have been
determined by X-ray diffraction analysis. Complex 3 is the
first structurally characterized (phosphoraniminato)rutheni-
um(III) complex with Ru–N distances of 1.991(7)–2.014(6) Å
and a nearly linear Ru–N–P moiety [ЄRu–N–P = 168.2(5)–
171.5(6)°]. Density functional theory (DFT) calculations on 3
and the proposed [RuV(14-TMC)(N)(N3)]+ intermediate have
been performed.
Introduction
planar [(PNP)RuIVN] complex that was formed by the
decomposition of [(PNP)RuIIN3] [PNP = (tBu2PCH2-
SiMe2)2N].[13a]
The transformation of metal azides to metal nitrides in-
volving a two-electron oxidation of the metal center and a
release of N2 is a useful strategy for the preparation of reac-
tive metal-nitrido complexes.[1–2] Notable recent examples
include the photolysis at low temperature of azido-FeIII and
FeIV complexes of macrocyclic amine ligands to generate
the respective nitrido-FeV and FeVI complexes,[3–6] and the
structural characterization of tetrahedral nitrido-FeV com-
plexes.[7] However, there are only a handful of examples of
azidoruthenium complexes; cis-[RuIII(en)2(N3)2]+ and cis-
[RuIII(trien)(N3)2]+ (en = ethylene diamine; trien = triethyl-
enetetramine) were reported in 1970 by Basolo and Pear-
son, and reactive ruthenium nitrene or imido intermediates
were proposed in the thermal or photolytic decomposition
reactions of azidoruthenium complexes.[8] Since then,
azidoruthenium complexes bearing bipyridine,[9] thiolate,
thioether,[10] and tetradentate anionic N2O2 ligands,[11] and
azido diruthenium complexes[12] have been studied. Caulton
et al. have reported the crystal structure of the square
Over the past decades, we have been studying the synthe-
sis and reactivities of oxygen- and nitrogen-multiple bonded
ruthenium and osmium complexes that are supported by
tertiary amine ligands.[14] Macrocyclic tertiary amine li-
gands are optically transparent in the UV/Vis spectral re-
gion, and are electrochemically inert upon coordination to
metal ions. In this work, we report the synthesis of a series
of azido-RuII and RuIII complexes supported by tertiary
amine ligands, and their thermal and photolytic decomposi-
tion reactions (Figure 1). A proposed mechanism for these
[a] Department of Chemistry and Open Laboratory of Chemical
Biology of the Institute of Molecular Technology for Drug
Discovery and Synthesis, The University of Hong Kong,
Pokfulam Road, Hong Kong, China
Fax: +852-2857-1586
E-mail: cmche@hku.hk
[b] Department of Chemistry, The Hong Kong University of
Science and Technology,
Clear Water Bay, Kowloon, Hong Kong, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100771.
Figure 1. Azidoruthenium(II) and (III) complexes that have been
prepared in this work.
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C.-M. Ho, H.-C. Leung, S. Wu, K.-H. Low, Z. Lin, C.-M. Che
FULL PAPER
reactions that involves a nitridoruthenium(V) intermediate isotope pattern. Cluster peaks located at m/z = 400, 414
is discussed.
and 428 are assigned to [Ru(14-TMC)(N3)]+, [Ru(14-
TMC)(N)(N3)]+ and [Ru(14-TMC)(N2)(N3)]+, respectively.
The presence of [Ru(14-TMC)(N3)]+ and [Ru(14-
TMC)(N)(N3)]+ is probably due to in-source fragmentation.
The detection of [Ru(14-TMC)(N3)(N2)]+ is attributed to
the reaction of [Ru(14-TMC)(N)(N3)]+ with 1 (see kinetics
Results and Discussion
Synthesis and Characterization
Complex 1 was prepared by the reaction of trans-[Ru(14- section).
TMC)Cl2]Cl (14-TMC 1,4,8,11-tetramethy1-1,4,8,11- Collision induced dissociation (CID) of metal azide com-
=
tetraazacyclotetradecane) with 10 equiv. of NaN3 in a plexes is known to generate metal nitride species with the
MeOH/H2O mixture at 0 °C, and upon addition of NaPF6 expulsion of N2 in the gas phase.[19–20] In this work, the
–
to the mixture 1 was isolated as a PF6 salt in 90% yield. collisional activation of 1 lead to mass differences (Δm) of
Complex 1(PF6) is a bright red solid that is light sensitive –28 and –42, associated with the major fragmentation path-
both in solution and in the solid state. It is stable for weeks way, in the CID spectra recorded over the whole range of
when kept in the dark at –20 °C, as revealed by UV/Vis collision energies. To further confirm the mass differences
spectrophotometry.
of 28 and 42, we performed CID of the mass selected ion
Treatment of trans-[Ru(16-TMC)Cl2]Cl (16-TMC
1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane)
with zinc amalgam, NaN3, followed by air oxidation, af-
=
of 15N labeled 1 at m/z 444, which is mainly attributed to
[
102Ru(14-TMC)(15N14N14N)2]+. The fragmentation of
102Ru(14-TMC)(15N14N14N)2]+ induced 14N14N and
[
forded a red species tentatively assigned as trans-[Ru(16- 14N15N losses (Δm = –28 and –29), the peaks for which
TMC)(N3)2]+ (4). However, attempts to isolate 4 in a pure were equal in intensity, as well as the expulsion of neutral
form were not successful, and this species was found to have 15N14N14N (Δm = –43). These results reveal that the azido
a short lifetime (half-life ca. 300 s) at room temperature. group of the complex could be eliminated via an oxidative
The direct reaction between trans-[Ru(16-TMC)Cl2]+ with pathway [Equation (1)] and a reductive pathway [Equa-
excess NaN3 to produce 4 was not successful, presumably tion (2)].
due to the low reactivity of the chloride ligand towards sub-
k
[RuIII(14-TMC)(N3)2]+ Ǟ [RuV(14-TMC)(N)(N3)]+ + N2
(1)
(2)
stitution reactions. Attempts to prepare cis-[Ru(Tet-Me6)-
(N3)2]+ (Tet-Me6 = 1,1,4,7,10,10-Hexamethyltriethylene-
tetramine) resulted in the formation of a solid that exploded
upon mechanical impact, and this product was not isolated.
The UV/Vis spectrum of 1 shows two absorption bands
at 583 and 408 nm, bands that can be assigned to
N3– ǞRuIII ligand to metal charge transfer (LMCT) transi-
tions. It is also pertinent to compare these absorption λmax
values with the LMCT transition energy of trans-[Ru(14-
TMC)Br2]+ in MeCN (λmax = 471 nm) and trans-[Ru(14-
TMC)(NCS)2]+ in MeCN (λmax = 594 nm), which reveal
[RuIII(14-TMC)(N3)2]+ Ǟ [RuII(14-TMC)(N3)]+ + N3
As depicted in Figure 2, loss of N2 is readily observed at
a collision energy nominally set to ECM = 0 eV, indicating
that the activation energy of this pathway is the lowest of
the two. By increasing ECM, the relative abundance of [1]-
N2 gradually increased. In contrast, the loss of the azido
ligand is less sensitive to the experimental conditions we
investigated. We propose that the ionic fragment [1]-N2
formed in the reaction could correspond to the trans-
–
that N3 has an optical electronegativity comparable to
NCS–.[13] For 1, The RuIII/II redox process is reversible on
the cyclic voltammetric timescale with E1/2 = –0.59 V vs.
Cp2Fe+/0 and with an E1/2 value comparable to that of the
trans-[Ru(14-TMC)Cl2]+/0 couple (E1/2
= –0.62 V vs.
Cp2Fe+/0).[15] Complex 1 exhibits one νas(N3) band in its
spectrum with a stretching frequency of 2047 cm–1, which
is similar to νas(N3) frequencies for other metal complexes
containing terminal azide ligand such as trans-
[Cr(14aneN4)(N3)2]PF6 (2085, 2069 cm–1, 14aneN4
=
1,4,8,11-tetraazacyclotetradecane),[16] trans-[Mn(14aneN4)-
(N3)2]ClO4 (2069, 2047 cm–1)[17] and trans-[Fe(14aneN4)-
(N3)2]PF6, (2044 cm–1).[18] This assignment is further sup-
ported by the expected shift of this peak to 2035 cm–1 in
the spectrum of trans-[Ru(14-TMC)(15N14N14N)2]+ (15N la-
beled 1).
The ESI-MS spectrum of 1 in MeCN shows a cluster
peak that can be attributed to the molecular cation of 1 at
m/z 442, this value is equivalent to that calculated for 1 with
a formula of C14H32N10Ru and with the most abundant
Figure 2. Collision induced fragmentation of mass selected [1]+ as
a function of collision energy (center of mass frame). [1]-N2 and
[1]-N3 are [RuV(14-TMC)(N)(N3)]+ and [RuII(14-TMC)(N3)]+,
102Ru isotope, furthermore the spectrum has the expected respectively.
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Azidoruthenium Complexes of Macrocyclic Tertiary Amines
[RuV(14-TMC)(N)(N3)]+ cation. Although isolation of changes with an isosbestic point at 291 nm were observed.
trans-[RuV(14-TMC)(N)(N3)]+ has not been realized so far, The intense charge-transfer bands at 409 and 538 nm grad-
the mass spectroscopic data suggests considerable thermal ually decreased in intensity with the concomitant formation
stability of trans-[RuV(14-TMC)(N)(N3)]+ in the gas phase of a new band at 246 nm. The decomposition of 1 followed
(see DFT calculation section). A similar finding has been first order kinetics [Equation (2)]. The pseudo first order
reported for the CID of [Fe(cyclam-acetato)(N3)]+ (cyclam- rate constant (kobs) was independent of the initial concen-
acetato = 1,4,8,11-tetraazacyclotetradecane-1-acetato).[20]
tration of 1, which was in the range of 0.05–1.0 mm [Table 1
and Equation (4)].
Thermally Induced Decomposition of [Ru(L)(N3)2]+ in RCN
–d[Ru(14-TMC)(N3)2]+/dt = kobs[Ru(14-TMC)(N3)2]+
(4)
Decomposition of [Ru(L)(N3)2]+ (L = 14-TMC, 16-
TMC, Tet-Me6) in RCN at room temperature gave the
[Ru(L)(N3)(RCN)]+ complexes in good to excellent yields.
In MeCN, complex 1 gradually decomposed with the evol-
ution of gas, and converted to 2a after 24 h. GC–MS analy-
sis confirmed that the evolved gas was N2, 1.5Ϯ0.1 mol of
which was produced per mol of 1. The reaction is depicted
by [Equation (3)].
Table 1. Rate constants for the decomposition of 1.
Entry
Temperature [K]
[1] [mM]
kobs [s–1]
1
2
3
4
5
6
7
8
9
10
287
292
0.10
0.05
0.1
0.25
0.50
1.0
0.1
0.1
0.1
0.1
2.62ϫ10–5
7.06ϫ10–5
7.12ϫ10–5
6.48ϫ10–5
6.44ϫ10–5
6.24ϫ10–5
2.30ϫ10–4
6.12ϫ10–4
1.34ϫ10–3
2.48ϫ10–3
2[Ru(14-TMC)(N3)2]+ + 2RCN Ǟ
301
307
312
319
2[Ru(14-TMC)(RCN)(N3)]+ + 3N2 (3)
With trans-[Ru(14-TMC)(15N14N14N)2]+, the N2 released
was found to be a mixture of 14N14N, 14N15N and 15N15N
in the ratio of 5.5:6:1, indicating that both N atoms come
We propose that the rate determining step in the decom-
position of 1 is the cleavage of the N–N bond of the azide
ligand with the subsequent formation of [RuV(14-TMC)-
(N)(N3)]+ and N2 [Equation (1)]. [RuV(14-TMC)(N)(N3)]+
reacts with another molecule of 1 to give two molecules of
[Ru(14-TMC)(N3)(N2)]+, the latter further decomposes to
give 2a [Equation (5) and Equation (6)]. Thus, the rate of
decomposition of 1 is directly related to the rate of forma-
tion of 2a [Equation (7)].
–
from the coordinated N3 ligand. This ratio is consistent
with the pathway involving reaction of [RuV(14-
TMC)(N)(N3)] with 1 (calculated 14N14N: 14N15N: 15N15N
= 5: 6: 1). A slightly higher value of 14N2 found in experi-
mental data is attributed to a leak of the gas syringe. A
pathway that involves the homolytic cleavage of a Ru–N3
bond with the generation of an azide radical that sub-
sequently reacts with another azide radical to produce N2
is not favored. This is because the presence of a 70 fold
excess of acrylamide, a well known trapping agent for the
azide radical,[9] did not cause any decrease in the pro-
duction of N2 in the thermal decomposition reaction.
The rate of decomposition of 1(PF6) in MeCN was ex-
amined by UV/Vis spectrophotometry (Figure 3). Spectral
[Ru(14-TMC)(N)(N3)]+ + [Ru(14-TMC)(N3)2]+
2[Ru(14-TMC)(N2)(N3)]+ (5)
Ǟ
[Ru(14-TMC)(N2)(N3)]+ + MeCN Ǟ
[Ru(14-TMC)(MeCN)(N3)]+ + N2 (6)
kobs = 2k
(7)
We determined the effect of temperature over the 287–
319 K range on the thermal decomposition of 1 in MeCN.
A good linear correlation was obtained for the Eyring plot
of ln(k/T) vs. 1/T. The activation parameters ΔH϶ and ΔS϶
are 25.9Ϯ1.2 kcalmol–1 and 9.4Ϯ4.0 calmol–1 K–1, respec-
tively. The positive value for ΔS϶ indicates a gain in en-
tropy, which is consistent with the dissociation of N2 from
the azide ligand [Equation (1)]. It is pertinent to compare
the activation parameters for 1 with those for the decompo-
sition of other metal azide complexes e.g. [Cp*2Mo(N3)2]
(Cp* = C5Me5 anion): ΔH϶ = 26.6Ϯ0.2 kcalmol–1 and
ΔS϶ = 3.5Ϯ0.7 calmol–1 K–1;[21] cis-[RuIII(en)(N3)2]PF6:
ΔH϶ = 23.8 kcalmol–1, ΔS϶ = –2 calmol–1 K–1;[8] cis-
[RuIII(trien)(N3)2]PF6: ΔH϶ = 22.9 kcalmol–1, ΔS϶
=
–2 calmol–1 K–1.[8] The [Cp*2Mo(N3)2] system also has a
positive ΔS϶ value. The reason for the discrepancy in the
ΔS϶ value determined by Basolo and ours is not clear, but
Figure 3. Time resolved UV/Vis spectral changes observed for
1(PF6) (0.1 mm) in MeCN at 301 K. Insert is the absorbance trace
monitored at 538 nm.
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we note that the two azide ligands in cis-[RuIII(en)(N3)2]+ Structure of 5b(ClO4)
and cis-[RuIII(trien)(N3)2]+ are in
whereas in 1 they are in a trans-configuration.
a
cis-configuration
In 5b, the methyl groups of the macrocyclic 16-TMC li-
gand adopt a “2-up and 2-down” or R,R,S,S geometry, and
the average Ru–N(amine) bond length is 2.251 Å. The
lengths of the Ru–N(azide) and Ru–N(PhCN) bonds are
2.084(5) and 1.958(4) Å, respectively (Figure 5).
Structure of 2e(PF6)
In the structure of 2e the four methyl groups of the
macrocyclic 14-TMC ligand adopt a “3-up and 1-down” or
R,S,R,R geometry; three methyl groups are in a syn orienta-
tion with the 2-MeOPhCN ligand. The average Ru–N-
(amine) distance is 2.143 Å. The Ru–N(2-MeOPhCN) dis-
tance in 2e [1.955(3) Å] is significantly shorter than the Ru–
N(MeCN) distance in trans-[Ru(14-TMC)(O)(MeCN)]2+
[2.149(6) Å] revealing that RuIV=O has a larger trans effect
than RuII–N3.[22] The length of the Ru–N(azide) bond in 2a
[2.107(10) Å][23] is comparable to that within 2e [2.115(3) Å]
(Figure 4).
Thermal Decomposition of 1 in the Presence of PPh3
It is well documented that phosphane compounds react
with electrophilic metal nitride complexes.[1,24] In this work,
a RuIII phosphoraniminato complex was obtained in 80%
yield when PPh3 was added to 1. The direct reaction of 1
with PPh3 to produce 3 is unlikely since there is no signifi-
cant change in the rate of decomposition of 1 in the pres-
ence of PPh3. Thus, our results indicate that complex 3 was
produced by a nitrogen atom transfer reaction between elec-
trophilic trans-[RuV(14-TMC)(N)(N3)]+ and PPh3. The IR
spectrum of 3 exhibits a peak at 1167 cm–1 that is assignable
to ν(P=N). A similar ν(P=N) value has been reported for
[Ru(NPPh3)L(py)Cl] [L = 2,6-bis(hydroxy-2,2-diphenyl-
ethyl)pyridine], ν(P=N) = 1160 cm–1.[23] This ν(P=N) as-
signment is also supported by the expected shift of this
peak to 1152 cm–1 in the spectrum of 15N labeled complex
3.
Crystal Structure of 3(PF6)
A perspective view of the structure of 3(PF6) and selected
bond lengths and bond angles for this complex are shown
in Figure 6. There are two crystallographically independent
units per unit cell. In both units the methyl groups of the
Figure 4. Molecular structure of the 2e cation (ellipsoids are drawn
at the 30% probability level. Hydrogen atoms have been omitted
for clarity). Selected bond lengths [Å]: Ru1–N(1) 2.136(3), Ru(1)–
N(2) 2.139(3), Ru(1)–N(3) 2.160(3), Ru(1)–N(4) 2.136(3), Ru(1)–
N(5) 1.955(3), Ru(1)–N(6) 2.115(3).
Figure 6. Molecular structure of one of two crystallographically
independent 3 cations (ellipsoids are drawn at the 30% probability
level. Hydrogen atoms have been omitted for clarity). Selected bond
lengths [Å] and angles [°] (values for the second independent mole-
cule are given in square parentheses): Ru(1)–N(5) 2.069(9)
Figure 5. Molecular structure of the 5b cation (ellipsoids are drawn
at the 30% probability level. Hydrogen atoms have been omitted
for clarity). Selected bond lengths [Å] for 5b: Ru(1)–N(1) 2.239(4),
Ru(1)–N(2) 2.257(4), Ru(1)–N(3) 2.266(4), Ru(1)–N(4) 2.241(4), [2.078(8)], Ru(1)–N(8) 2.014(6) [1.991(7)], P(1)–N(8) 1.542(7)
Ru(1)–N(5) 2.084(5), Ru(1)–N(8) 1.958 (4). [1.551(7)], ЄRu(1)–N(8)–P(1) 168.2(5) [171.5(6)].
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Azidoruthenium Complexes of Macrocyclic Tertiary Amines
macrocyclic 14-TMC ligand adopt a “3-up and 1-down” or 40.2 and 90.6 kcal/mol greater, respectively, than that of the
R,S,R,R geometry; one methyl group is facing the NPPh3 doublet state.
group. The Ru–N(phosphoraniminato) distances are
In trans-[RuV(14-TMC)(N)(N3)]+, the computed RuVϵN
1.991(7)–2.014(6) Å, and the Ru–N–P bond angles are distance of 1.723 Å is comparable to the RuVϵN distances
171.5(6) and 168.2(5)° (see DFT calculations section). Both of 1.74/1.78 Å found in nitridoruthenium(V) complexes of a
the linear M–N–P and short M–NPPh3 distances (1.65– meso-octamethylporphyrinogen tetraanion,[26] but is longer
1.86 Å) are generally found in metal phosphoraniminato than the RuVIϵN distances reported in the literature that
complexes and are indicative of the multiple bond character range from 1.59 to 1.66 Å.[1,27–29] On the basis of the DFT
of the M–N bonds.[24]
calculations (Figure 7), the highest singly occupied molecu-
lar orbital (SOMO) is best considered to be one of the Ru–
N π* antibonding orbitals. Occupancy of these π* orbitals
reduces the Ru–N bond order, thus accounting for the
“elongated” Ru-nitrido distance in trans-[RuV(14-
TMC)(N)(N3)]+.
Photo-Induced Decomposition of 1
The decomposition of 1 in MeCN can be activated by
light irradiation. When a MeCN solution of 1 was irradi-
ated with a 300 W Xenon lamp with a low pass filter at
400 nm in an Ar atmosphere at 273 K the solution under-
went a rapid color change from red to yellow that was ob-
served within 5 min. The light activated decomposition of
1 gave 2a as the major product, which was accompanied by
a small amount of trans-[Ru(14-TMC)(MeCN)2]2+ (m/z =
220) that was detected in the resultant solution by ESI-MS
analysis. Quantitative determination of the light induced
decomposition of 1 showed that 1.5Ϯ0.1 mol of N2 was
produced per mol of ruthenium complex. No decrease in
the production of N2 was observed for the photo-induced
decomposition of 1 in the presence of a 70 fold excess of
acrylamide.[9]
Figure 7. Left: Optimized structure of trans-[RuV(14-
TMC)(N)(N3)]+ calculated with BP/TZ2P, hydrogen atoms have
been omitted. Right: Kohn–Sham (KS) Molecular orbital diagram
for trans-[RuV(14-TMC)(N)(N3)]+.
Density Functional Theory (DFT) Calculations
DFT calculations are a useful tool for understanding and
rationalizing the electronic structure of metal complexes. In
this work, ESI-MS studies revealed that 1 underwent expul-
sion of N2 to afford trans-[RuV(14-TMC)(N)(N3)]+ upon
collisional activation. Attempts to isolate and characterize
trans-[RuV(14-TMC)(N)(N3)]+ were not successful. In order
to obtain more information about the electronic structure
of trans-[RuV(14-TMC)(N)(N3)]+, DFT (BP/TZ2P) calcula-
tions were performed. In addition, the crystal structure of
3 determined by us reveals a long Ru–NPPh3 distance and
that the Ru–N–P moiety is nearly linear, findings that are
not commonly encountered in the literature.[23] We per-
formed DFT (BP/TZ2P) calculations on 3 to rationalize its
structure. The calculations are described as follows.
Complex trans-[Ru(14-TMC)(NPPh3)(N3)]+ (3)
In this work, DFT (BP/TZ2P) calculations on 3 and the
simplified model complex trans-[Ru(14-TMC)(NPH3)-
(N3)]+ (Model 1), in which the phenyl groups are replaced
by H atoms, were performed (Figure 8). The doublet state
of 3 is most favorable as the quartet and sextet states are
31.3 and 67.0 kcal/mol higher in energy than the doublet
state, respectively. The quality of the optimized structure
Complex trans-[RuV(14-TMC)(N)(N3)]+
Among the seven optimized conformers of trans-
[RuV(14-TMC)(N)(N3)]+ in the doublet state (see Support-
ing Information, Figure S1), the energy of the conformer
with “two-up, two-down” or R,R,S,S geometry, which dis-
plays compromise between steric hindrance and the tension
of ethylene and 1,3-propenyl groups, was found to be the
lowest. A R,R,S,S geometry for 14-TMC was found for the
trans-[RuIV(14-TMC)(O)(NCO)]+ cation.[25] The quartet
and sextet states of this conformer were also calculated and
Figure 8. Optimized structures of complex 3 (left) and a simplified
model of 3 (Model 1, right). These structures were calculated with
were found to be unfavorable since their energy values are BP/TZ2P. Hydrogen atoms have been omitted.
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Table 2. The NBO descriptors for the bonds involving the (phosphoraniminato)-N atom within 3; the hybrid contributions of the nitrogen
atom (hN), percentage polarization toward the nitrogen atoms (cN2) and the occupancy number (occ.) are given.
α Spin
hN
β Spin
hN
2
2
Character
cN [%]
Occ.
cN [%]
Occ.
BDP–N
BDRu–N
LPN
σP–N
s36.7p63.0
68.1
0.987
–
0.810
0.885
0.878
s38.3p61.4
67.8
70.7
–
–
–
0.988
0.918
0.813
0.878
πRu–N
σdonorǞRu
2pN
–
–
–
–
–
p99.8
s33.3p66.7
s10.2p89.6
s19.5p80.3
s31.6p68.4
s29.7p70.1
–
2pNЈ
was checked by comparing it with the crystal structure of 3
determined by X-ray diffraction analysis. The calculated
Ru–N(phosphoraniminato) distance and Ru–N–P angle are
2.069 Å and 162.3°, which are in agreement with the experi-
mental values (Ru–N 1.991–2.014 Å and ЄRu–N–P 168.2–
171.6°).
Conclusions
In this work, we have synthesized azidoruthenium(II)
and (III) complexes that are supported by chelating macro-
cyclic tertiary amine ligands, and have studied their thermal
and photo-decomposition. On the basis of ESI-MS results,
kinetic measurements, and a trapping experiment we pro-
pose that an electrophilic ruthenium(V) nitride species is
generated in these processes, as depicted in Scheme 1.
The frontier Kohn–Sham (KS) molecular orbitals (Fig-
ure 9) show that there are three singly occupied MOs that
feature antibonding interactions between the Ru and (phos-
phoraniminato)-N atoms. Occupancy of these orbitals
would reduce the Ru–N(phosphoraniminato) bond order
causing elongation of the Ru–N(phosphoraniminato) bond.
In addition, natural bond orbital (NBO) analysis (Table 2)
showed that all σ bonds (σP–N in both spin states, and
σdonorǞRu in both spin states) involving the (phosphorani-
minato)-N atom have a contribution from sp2 orbitals of
the (phosphoraniminato)-N atom. These findings suggest
the the (phosphoraniminato)-N atom prefers to adopt an
sp2-hybridized state. Indeed, this observation is further sup-
ported by the fact that in Model 1, in which the structure
is subject to less steric hindrance than the other computa-
tionally determined structures, the Ru–N(phosphoranimin-
ato) distance is shortened from 2.069 to 2.017 Å, and the
angle ЄRu–N–P is reduced from 162.3 to 157.1°. Thus, the
long length of the Ru–N(phosphoraniminato) bond in 3
may be due to a combination of both electronic and steric
effects.
Scheme 1.
Experimental Section
General: All reagents and solvents were of analytical grade unless
otherwise stated. RuCl3·xH2O (Strem), Na15N14N14N (98 atom-%,
Cambridge Isotope), triphenylphosphane (Aldrich), butyronitrile
(Aldrich), benzonitrile (Aldrich), 2-methylbenzonitrile (Aldrich), 2-
methoxybenzonitrile (Aldrich) were obtained from commercial
sources and were used as received. MeCN was purified and dried
before use. Water was purified with a nanoPure system (Barnstead,
USA).
Caution! Metal azides are potentially explosive and should be han-
dled only in small quantities (Ͻ 100 mg) and with appropriate pre-
cautions.
Infrared spectra were recorded with KBr discs or Nujol mulls on
a Nicolet 20 SXC FTIR spectrophotometer. UV/Vis spectra were
recorded on a HP 8453 diode array spectrophotometer. GC–MS
measurements were carried out on an Agilent 6890N gas chromato-
graph interfaced with an Agilent 5973 mass selective spectrometer.
Electro-spray ionization (ESI) mass spectrometry was performed
on a hybrid Q-ToF mass spectrometer (Q-STAR XL, Applied Bio-
systems, collision gas: Ar). NMR spectra were obtained with a
Bruker Advance 400 pulsed Fourier transform instrument. Elemen-
Figure 9. Diagram of the frontier KS molecular orbitals of 3.
156
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 151–159

Azidoruthenium Complexes of Macrocyclic Tertiary Amines
tal analyses were performed by the Institute of Chemistry of the
Chinese Academy of Sciences or MEDAC Ltd, UK.
Complex 4(PF6): A mixture of trans-[Ru(16-TMC)Cl2]Cl (100 mg,
0.203 mmol) and zinc amalgam (0.5 g, 1.88 mmol) in methanol
(15 mL) was refluxed for 1 h in an Ar atmosphere. A solution of
NaN3 (132 mg, 2.03 mmol) in H2O (1 mL) was added, and the re-
action mixture was stirred at 80 °C for about 1 h. The solution was
cooled to room temperature and filtered. Addition of a saturated
aqueous solution of NaPF6 (1 mL) to the reaction mixture gave a
bright red solid. The solid was collected by filtration and washed
with water. The solid is stable at –20 °C for a few days; yield ca.
50%. IR (KBr): νas(N3) 2035.
trans-[Ru(14-TMC)(N3)2]PF6 [(1)PF6]: NaN3 (70 mg) in H2O
(1 mL) was added to a methanolic solution (9 mL) of trans-
[Ru(TMC)Cl2]Cl (50 mg, 0.108 mmol) at 0 °C. After 5 min of vig-
orously stirring, the color of the solution changed from yellow to
bright red. Addition of a saturated aqueous solution of NaPF6
(1 mL) gave a bright red solid, 1(PF6). The solid was collected by
filtration and washed with water and methanol. The solid is stable
at –20 °C for weeks; yield 90%. IR (KBr): νas(N3) 2047. UV/Vis
λmax/nm (ε/dm3 mol–1 cm–1) (MeCN): 235 (16000), 408 (1900), 488
(sh, 2200), 538 (8100). C14H32F6N10PRu (586.51): calcd. C 22.43,
H 4.84, N 20.56; found C 22.90, H 4.73, N 20.28. ESI-MS: m/z =
442 [M]+. 15N Labeled form of 1: trans-[Ru(14-TMC)-
(15N14N14N)2]PF6. IR (KBr): νas(N3) 2035.
Complex 5a(PF6): Yellow solid; yield 90%. IR (KBr): νas(N3) 2066,
ν(CϵN) 2241. UV/Vis λmax/nm (ε/dm3 mol–1 cm–1) (CH2Cl2): 245
(6800), 431 (250). C18H39F6N8P2Ru (644.57): calcd. C 35.23, H
6.41, N 18.26; found C 36.39, H 6.53, N 17.95. ESI-MS: m/z = 469
[M]+ and 428 [M – MeCN]+.
Complex 5b(ClO4): Yellow solid. Crystals suitable for X-ray crystal-
lography were grown by slow diffusion of Et2O into a PhCN solu-
tion of 5b(ClO4); yield 72%. IR (KBr): νas(N3) 2065, ν(CϵN) 2187.
UV/Vis λmax/nm (ε/dm3 mol–1 cm–1) (CH2Cl2): 232 (12000), 259
(10000), 344 (5400), 386 (5200). C23H41N8Ru·ClO4: calcd. C 43.84,
H 6.56, N 17.78; found C 43.53, H 6.65, N 17.62. ESI-MS: m/z =
531 [M]+ and 428 [M – PhCN]+.
trans-[Ru(L)(N3)RCN]PF6, L = 14-TMC, R = Me (2a), Bu (2b), Ph
(2c), 4-MePh (2d), 2-MeOPh (2e); L = 16-TMC, R = Me (5a), Ph
(5b): [Ru(L)(N3)2]PF6 (100 mg) was dissolved in RCN (15 mL) with
gentle stirring. After 24 h, the bright red solution gradually
changed to yellow and gas bubbles evolved at room temperature.
The solution was concentrated under vacuum and a yellow solid
was obtained by slow diffusion of Et2O into the RCN solution.
Complex 6(PF6): cis-[Ru(Tet-Me6)Cl2]PF6 (100 mg, 0.183 mmol)
was mixed with silver toluene-p-sulfonate (0.112 g, 0.402 mmol) in
water (15 mL). The suspension was stirred and heated to 100 °C
for 1 h, or until no further silver chloride precipitated, to leave a
clear orange supernatant solution. After AgCl was removed, the
filtrate was cooled in an ice bath. A deep red solution was obtained
when NaN3 (0.35 g, 17 mmol) was added to the solution. Addition
of an aqueous solution of NH4PF6 (saturated, 2 mL) gave a red
precipitate, proposed to be cis-[Ru(Tet-Me6)(N3)2]PF6. Without
further purification, the red precipitate was redissolved in MeCN,
and the solution stirred overnight. The solid that formed was col-
lected after vacuum evaporation of the solvent. Yellow crystals were
obtained by recrystallization of the crude product from MeCN/
Et2O; yield 37%. IR (KBr): νas(N3) 2045, ν(CϵN) 2249. UV/Vis
λmax/nm (ε/dm3 mol–1 cm–1) (CH2Cl2): 231(10380), 408 (sh, 380).
C14H33F6N8PRu (559.50): calcd. C 30.05, H 5.94, N 20.03; found
C 29.95, H 5.77, N 19.83. ESI-MS: m/z = 415 [M]+ and 374 [M –
MeCN]+.
Complex 2a(PF6): Yellow solid; yield 99%. IR (KBr): νas(N3) 2068,
ν(CϵN) 2239. UV/Vis λmax/nm (ε/dm3 mol–1 cm–1) (CH2Cl2): 252
(15500), 379 (520). C16H35F6N8PRu·0.5MeCN (2a·PF6·0.5MeCN):
calcd. C 31.69, H 6.07, N 19.64; found C 31.47, H 6.02, N 19.35.
ESI-MS: m/z = 441 [M]+ and 400 [M – MeCN]+. 15N Labeled form:
trans-[Ru(14-TMC)(15N14N14N)(MeCN)]PF6. IR (KBr): νas(N3)
2054, ν(CϵN) 2241. ESI-MS: m/z = 441 [M]+ and 400 [M –
MeCN]+.
Complex 2b(PF6): Orange-yellow solid; yield 80%. IR (KBr):
νas(N3) 2064, ν(CϵN) 2218. UV/Vis λmax/nm (ε/dm3 mol–1 cm–1)
(CH2Cl2): 259 (18000), 379 (770). C14H32F6N7PRu (544.49): calcd.
C 36.36, H 6.58, N 18.16; found C 36.28, H 6.55, N 17.90. ESI-
MS: m/z = 483 [M]+ and 400 [M – BuCN]+.
Complex 2c(PF6): Orange solid; yield 78%. IR (KBr): νas(N3) 2062,
ν(CϵN) 2187. UV/Vis λmax/nm (ε/dm3 mol–1 cm–1) (CH2Cl2): 229
(17000), 271 (15000), 366 (sh, 8200), 400 (11000). C20H37F6N7PRu
(621.59): calcd. C 38.95, H 5.76, N 17.30; found C 39.14, H 5.68,
N 17.04. ESI-MS: m/z = 503 [M]+ and 400 [M – PhCN]+.
Single Crystal Structure Determinations: X-ray diffraction data for
5b(ClO4) were collected on a Bruker X8 Proteum diffractometer
with Cu-Kα radiation (1.54178 Å), and the X-ray diffraction data
for 2e(PF6) and 3(PF6) were collected on a Bruker Smart CCD
1000 with graphite monochromated Mo-Kα radiation (0.71073 Å).
The images were interpreted and the peak intensities were inte-
grated with the PROTEUM2 suite or DENZO program. The struc-
tures were solved by direct method employing the SHELXS-97 pro-
gram.[30] The structure refinements were performed on F2 by a full-
matrix least-squares technique. The positions of the H atoms were
calculated based on riding modes, and the H atoms were refined
with their thermal parameters equal to 1.2 times those of the asso-
ciated C atoms, and they participated in the calculation of final R
indices. In the final stages of the least-square refinements all non-
hydrogen atoms were refined anisotropically (Table 3).
Complex 2d(PF6): Orange solid; yield 76%. IR (KBr): νas(N3) 2073,
ν(CϵN) 2172. UV/Vis λmax/nm (ε/dm3 mol–1 cm–1) (CH2Cl2): 232
(16000), 266 (17000), 358 (sh, 6900), 395 (9800). C21H39F6N7PRu
(635.62): calcd. C 39.94, H 5.94, N 16.94; found C 40.02, H 5.84,
N 16.65. ESI-MS: m/z = 517 [M]+ and 400 [M – 4-MePhCN]+.
Complex 2e(PF6): Orange solid; yield 81%. IR (KBr): νas(N3) 2073,
ν(CϵN) 2172. UV/Vis λmax/nm (ε/dm3 mol–1 cm–1) (CH2Cl2): 234
(11000), 271 (12000), 401 (7400). C21H39F6N7OPRu (651.62):
calcd. C 5.80, H 5.80, N 16.54; found C 39.12, H 4.34, N 16.97.
ESI-MS: m/z = 533 [M]+ and 400 [M – 2-MeOPhCN]+.
Complex 3(PF6): 1(PF6) (50 mg, 0.085 mmol) was dissolved in
MeCN (15 mL). PPh3 (559 mg, 2.13 mmol) was added to the solu-
tion while it was stirred. After 24 h, the solution developed a yellow
color. After removal of the solvent by rotary evaporation, the yel-
low solid that had formed was washed with Et2O, and was recrys-
tallized by slow diffusion of Et2O into a MeCN solution of the
product (56 mg); yield 80%. IR (KBr): νas(N3) 2073, ν(N=P) 1167.
UV/Vis λmax/nm (ε/dm3 mol–1 cm–1) (MeCN): 245 (22000), 380
(900), 530 (610). C36H53F6N10P2Ru·2MeCN: calcd. C 47.89, H
5.92, N 15.51; found C 47.10, H 5.90, N 15.35. ESI-MS: m/z = 676
[M]+ and 648 [M – 28]+.
CCDC-833472 [for 2e(PF6)], -833473 [for 3(PF6)], -833474 [for
5b(ClO4)] contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Kinetic Measurements: Experiments were performed on a Hewlett–
Packard 8453 diode array spectrophotometer. The decay of 1 was
Eur. J. Inorg. Chem. 2012, 151–159
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
157

C.-M. Ho, H.-C. Leung, S. Wu, K.-H. Low, Z. Lin, C.-M. Che
FULL PAPER
Table 3. Crystallographic data for 2e(PF6), 3(PF6) and 5b(ClO4).
2e(PF6)
3(PF6)·MeCN
5b(ClO4)
Formula
C22H36N8ORuF6P
yellow, block
674.63
C34H50N9P2F6Ru
yellow, bar
861.84
C23H41N8RuClO4
orange, plate
630.15
Color, habit
Mr [gmol–1]
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
100
301
100
0.71073
orthorhombic
P212121
13.486(2)
13.909(3)
14.582(3)
90
0.71073
orthorhombic
Pna21
19.725(4)
9.683(2)
40.215(8)
90
1.54178
monoclinic
P21/c
16.5262(11)
13.0711(6)
13.3390(7)
90
β [°]
90
90
2735.3(9)
4
1.638
90
90
7681(3)
8
1.491
109.949(2)
90
2708.5(3)
4
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3]
1.545
F(000)
1380
2.5 to 28.0
17319
6490
6490/352/21
1.01
0.0391
0.0927
0.73 and –0.42
3560
2.0 to 27.5
46889
15763
15763/945/927
1.01
0.0803
0.2068
2.57 and –1.40
1312
2.8 to 65.7
19499
4573
4573/338/0
1.14
0.059
0.155
1.94 to –0.84
Theta range for data collection [°]
Reflections collected
Independent reflections
Data/parameters/restraints
GoF
[a]
R1 [IϾ2σ(I)]
[b]
wR2 [IϾ2σ(I)]
Residual peak/hole (eÅ–3)
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = [Σw(|Fo| – |Fc|)2/Σw|Fo|2]1/2
.
monitored at 538 nm. The reaction followed first order kinetics and
the first order rate constant, kobs, was obtained by nonlinear least-
squares fits of the At vs. t data with the equation At = Aϱ + (A0 –
Aϱ)exp(–kt), where A0 and Aϱ are the initial and final absorbance
values, respectively.
Acknowledgments
The work was supported by the Hong Kong Research Grants
Council (CRF/HKU1/08) and the Area of Excellence (AoE/P 10/
01) established under the University Grants Committee of the
Hong Kong SAR. The authors thank Dr. Yuhe Kan for his assist-
ance on the preliminary DFT calculations.
ESI-MS Measurements: ESI-MS experiments were performed with
a hybrid Q-ToF mass spectrometer (Q-STAR XL, Applied Biosys-
tems). For the experiments, micromolar solutions of 1 in MeCN
were freshly prepared and were introduced to the ESI source
through a capillary fitted with a syringe pump (ca. 5 μL min–1).
Nitrogen was the nebulizing gas. For CID at low collision energies,
the ions of interest were mass selected in Q1, interact with argon
(collision gas) in the quadrupole under nearly single collision con-
ditions, which are typically 2ϫ 10–4 mbar, and with adjustable col-
lision energy (Elab = 0–15 eV). The collision energy in the center-
of-mass frame (Ecm) was determined by Ecm = Elab [mc/(mc + mi)],
where Elab = kinetic energy of the ion that is provided by the elec-
tric fields in the mass spectrometer, mc = mass of the collision gas
atom, and mi = mass of the ion.
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Received: July 25, 2011
Published Online: November 24, 2011
Eur. J. Inorg. Chem. 2012, 151–159
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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