Synthesis, reactivity studies, structural aspects, and solution behavior of half sandwich ruthenium(II) N,N′,N″- triarylguanidinate complexes

Article abstract of DOI:10.1021/ic201343w

[(η⁶-C₁₀H₁₄)RuCl(μ-Cl)]₂ (η⁶-C₁₀H₁₄ = η⁶-p-cymene) was subjected to a bridge-splitting reaction with N,N′,N″- triarylguanidines, (ArNH)₂C=NAr, in toluene at

Full text of DOI:10.1021/ic201343w

Article
pubs.acs.org/IC
Synthesis, Reactivity Studies, Structural Aspects, and Solution
Behavior of Half Sandwich Ruthenium(II) N,N′,N″-Triarylguanidinate
Complexes
Taruna Singh,† Ram Kishan,† Munirathinam Nethaji,‡ and Natesan Thirupathi*,†
†Department of Chemistry, University of Delhi, Delhi 110 007, India
‡Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
S
* Supporting Information
ABSTRACT: [(η6-C10H14)RuCl(μ-Cl)]2 (η6-C10H14 = η6-p-cym-
ene) was subjected to a bridge-splitting reaction with N,N′,N″-
triarylguanidines, (ArNH)2CNAr, in toluene at ambient temper-
ature to afford [(η6-C10H14)RuCl{κ2(N,N′)((ArN)2C−N(H)Ar)}]
(Ar = C6H4Me−4 (1), C6H4(OMe)−2 (2), C6H4Me−2 (3), and
C6H3Me2−2,4 (4)) in high yield with a view aimed at understanding
the influence of substituent(s) on the aryl rings of the guanidine
upon the solid-state structure, solution behavior, and reactivity pattern of the products. Complexes 1−3 upon reaction with NaN3
in ethanol at ambient temperature afforded [(η6-C10H14)RuN3{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar = C6H4Me−4 (5),
C6H4(OMe)−2 (6), and C6H4Me−2 (7)) in high yield. [3 + 2] cycloaddition reaction of 5−7 with RO(O)C−CC−C(O)OR
(R = Et (DEAD) and Me (DMAD)) (diethylacetylenedicarboxylate, DEAD; dimethylacetylenedicarboxylate, DMAD) in CH2Cl2
at ambient temperature afforded [(η6-C10H14)Ru{N3C2(C(O)OR)2}{κ2(N,N′)((ArN)2C−N(H)Ar)}]·xH2O (x = 1, R = Et, Ar =
C6H4Me−4 (8·H2O); x = 0, R = Me, Ar = C6H4(OMe)−2 (9), and C6H4Me−2 (10)) in moderate yield. The molecular
structures of 1−6, 8·H2O, and 10 were determined by single crystal X-ray diffraction data. The ruthenium atom in the
aforementioned complexes revealed pseudo octahedral “three legged piano stool” geometry. The guanidinate ligand in 2, 3, and 6
revealed syn-syn conformation and that in 4, and 10 revealed syn-anti conformation, and the conformational difference was
rationalized on the basis of subtle differences in the stereochemistry of the coordinated nitrogen atoms caused by the aryl moiety
in 3 and 4 or steric overload caused by the substituents around the ruthenium atom in 10. The bonding pattern of the CN3 unit
of the guanidinate ligand in the new complexes was explained by invoking n−π conjugation involving the interaction of the
NHAr/NcoordAr lone pair with CNπ* orbital of the imine unit. Complexes 1, 2, 5, 6, 8·H2O, and 9 were shown to exist as a
single isomer in solution as revealed by NMR data, and this was ascribed to a fast C−N(H)Ar bond rotation caused by a less
bulky aryl moiety in these complexes. In contrast, 3 and 10 were shown to exist as a mixture of three and five isomers in about
1
1
1:1:1 and 1·0:1·2:2·7:3·5:6·9 ratios, respectively in solution as revealed by a VT H NMR, H−1H COSY in conjunction with
DEPT−90 13C NMR data measured at 233 K in the case of 3. The multiple number of isomers in solution was ascribed to the
restricted C−N(H)(o-tolyl) bond rotation caused by the bulky o-tolyl substituent in 3 or the aforementioned restricted C−
NH(o-tolyl) bond rotation as well as the restricted ruthenium-arene(centroid) bond rotation caused by the substituents around
the ruthenium atom in 10.
guanidines may be finely controlled by introducing distinct
substituents on the nitrogen atoms.
INTRODUCTION
■
Half sandwich ruthenium(II) amido complexes play a vital role
as enantioselective catalysts in numerous organic trans-
formations,1 as anticancer agents,2 as protein and lipid kinase
inhibitors,3 and as a potential organometallic molecular
motors.4 Further, this class of complexes are shown to be a
useful promoter for peptide synthesis,5 as scaffolds to study the
intriguing structural, reactivity pattern and bonding aspects.6−16
N,N′,N″-Trisubstituted guanidines, (RNH)2CNR (R = alkyl,
aryl and acetyl) is one of the interesting classes of N-donor
ligands because of their ability to form guanidinate(1−) (A)
and guanidinate(2−) (B) anions upon treatment with a strong
base (Chart 1). Further, the donor characteristics, steric
environment around the nitrogen atoms of this type of
The coordination chemistry aspects of (RNH)2CNR (R =
Ph (LH2Ph), iPr (LH2iPr), and Cy (LH2Cy)) have been explored
recently and these ligands have been shown to exhibit a rich
and diverse coordination modes toward metal ions depending
upon the substituent on the nitrogen atoms.17−19 Several
structurally characterized ruthenium(II) guanidinate(1−) com-
Ph
plexes of LH2 and one ruthenium(II) guanidinate(2−)
complex of (AcNH)2CNAc (Ac = C(O)Me; LH2Ac) are
known wherein the guanidinate ligand is shown to exhibit
Received: June 22, 2011
Published: December 8, 2011
© 2011 American Chemical Society
157
dx.doi.org/10.1021/ic201343w | Inorg. Chem. 2012, 51, 157−169

Inorganic Chemistry
Article
Caution! Metal azido complexes are potentially explosive, only a small
amount of material should be prepared with care.
Chart 1. Structures of Guanidinate(1−) and
Guanidinate(2−) Anions
Synthesis, Analytical and Spectroscopic Data of 1−10. [(η6-
C10H14)RuCl{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar = C6H4Me−4; 1). [(η6-
C10H14)RuCl(μ-Cl)]2 (100 mg, 0.163 mmol) was dispersed in toluene
(10 mL) in a 25 mL round-bottom flask and set to stir. To the
4‑tolyl
suspension, LH2
(215 mg, 0.653 mmol) was added in a portion
that immediately resulted in the formation of [LH34‑tolyl]+Cl− as
colorless solid. The reaction mixture was stirred for 2 h at ambient
temperature and filtered. The filtrate was concentrated under vacuum
to about 2 mL, and the concentrate was stored at ambient temperature
for several hours to afford 1 as orange crystals. Yield: 90% (175 mg,
0.292 mmol). Mp: 132 °C (decomp). IR (KBr, cm−1) νmax: 3372 (m,
NH), 1543 (vs, CN). 1H NMR (400 MHz, CDCl3, ppm): δH = 1.22
(d, JH,H = 6.8 Hz, 6H, CH(CH3)2), 2.09 (s, 3H, CH3), 2.21 (s, 2 × 3H,
CH3), 2.22 (s, 3H, CH3), 2.68−2.75 (m, 1H, CHMe2), 5.08, 5.32
(each d, JH,H = 6.0 Hz, 4H, C6H4), 5.88 (s, 1H, NH), 6.64, 6.70 (each
d, JH,H = 8.2 Hz, 4H, ArH), 6.91 (d, JH,H = 8.3 Hz, 4H, ArH), 7.05 (d,
JH,H = 8.2 Hz, 4H, ArH). 13C {1H} NMR (100 MHz, CDCl3, ppm): δC
= 19.1 (CH3), 20.6, 20.9 (CH3), 22.5 (CH(CH3)2), 31.3 (CHMe2),
78.7, 80.8, 97.8, 98.4 (p-cymene ArC), 119.9, 123.3, 128.9, 129.2,
129.8, 131.5, 131.7, 135.5, 144.3, 154.0 (ArC and CN). Note: Only
two carbon resonances were observed for CH3 carbon of the
guanidinate ligand rather than the expected three peaks and 10
carbon resonances were observed for ArC and CN carbons of the
guanidinate ligand rather than the expected 13 peaks, presumably
chelating bidentate, and bridging bidentate coordination
modes.20,21 The molecular structures of half-sandwich
ruthenium(II) guanidinate(1−) complexes, [(η6-C10H14)RuCl-
{κ2(N,N′)((RN)2C−N(H)R)}] (R = Ph (I),22 and iPr (II)23)
have also been determined but the results pertinent to II
remain unpublished.
In 2010, we have published synthesis and conformational
features of sym N,N′,N″-triarylguanidines, (ArNH)2CNAr
(Ar = C6H4Me−4 (LH24‑tolyl), C6H4Me−2 (LH22‑tolyl),
C6H4(OMe)−2 (LH22‑anisyl), C6H3Me2−3,5 (LH23,5‑xylyl),
C6H3Me2−2,4 (LH22,4‑xylyl), and C6H3Me2−2,6 (LH22,6‑xylyl)),24
and subsequently we have reported the synthesis, reactivity
because of overlapping peaks. TOF−MS+, m/z [ion, intensity (%)]:
4‑tolyl
601.097 [(M + 2H)+, 60], 599.088 [M+, 28], 328.316 [(LH2
−
H)+, 100]. Anal. Calcd. for C32H36N3ClRu (Mw: 599.17): C, 64.15; H,
6.06; N, 7.01. Found: C, 64.14; H, 6.06; N, 7.01.
2‑anisyl
studies, structural aspects, and solution dynamics of LH2
derived six-membered [C,N] palladacycles.25 Herein, we report
the synthesis and characterization of three types of half-
sandwich ruthenium(II) guanidinate complexes, namely [(η6-
C10H14)RuX{κ2(N,N′)((ArN)2C−N(H)Ar)}] (X = Cl; Ar =
C6H4Me−4 (1), C6H4(OMe)−2 (2), C6H4Me−2 (3),
C6H3Me2−2,4 (4) and X = N3; Ar = C6H4Me−4 (5),
C6H4(OMe)−2 (6), and C6H4Me−2 (7)), and the triazole
derivatives, [(η6 -C1 0 H1 4 )Ru{N3 C2 (C(O)OR)2 }-
{κ2(N,N′)((ArN)2C−N(H)Ar)}]·xH2O (x = 1, R = Et, Ar =
C6H4Me−4 (8·H2O); x = 0, R = Me, Ar = C6H4(OMe)−2 (9),
and C6H4Me−2 (10)). Complex 3 revealed a unique fluxional
behavior in that it exists as a mixture of three rotamers in
solution at temperatures ≤253 K and equilibrate via a restricted
C−N(H)(o-tolyl) bond rotation caused by the bulky o-tolyl
substituent of the guanidinate ligand.
[(η6-C10H14)RuCl{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar = C6H4(OMe)−2;
2). Complex 2 was prepared from [(η6-C10H14)RuCl(μ-Cl)]2 (100
mg, 0.163 mmol) and LH22‑anisyl (258 mg, 0.684 mmol) in toluene (10
mL) following the procedure previously described for 1. The filtrate
from the reaction mixture was concentrated under vacuum to about 2
mL and stored at ambient temperature for several hours to afford 2 as
orange crystals. Yield: 95% (200 mg, 0.309 mmol). Mp: 116 °C
(decomp). IR (KBr, cm−1) νmax: 3419 (br, NH), 3330 (m, NH), 2929
(m, C−H···Cl), 1534 (vs, CN). 1H NMR (400 MHz, CD2Cl2,
ppm): δH = 1.19 (d, JH,H = 6.8 Hz, 6H, CH(CH3)2), 2.19 (s, 3H,
CH3), 2.57−2.64 (m, 1H, CHMe2,), 3.76 (s, 3H, OCH3), 3.80 (s, 2 ×
3H, OCH3), 5.07, 5.24 (each d, JH,H = 6.0 Hz, 4H, C6H4), 6.25 (dt,
JH,H = 7.6; 1.2 Hz, 1H, ArH), 6.52 (dt, JH,H = 8.3; 1.6 Hz, 1H, ArH),
6.59 (dt, JH,H = 7.6; 1.5 Hz, 2H, ArH), 6.68 (dd, JH,H = 7.8; 1.8 Hz, 2H,
ArH), 6.83 (dt, JH,H = 7.4; 1.6 Hz, 2H, ArH), 6.88 (dt, JH,H = 7.5; 1.9
Hz, 2H, ArH), 7.30 (s, 1H, NH), 7.39 (dd, JH,H = 7.6; 2.0 Hz, 2H,
ArH). 13C{1H} NMR (75.5 MHz, CDCl3, ppm): δC = 18.7 (CH3),
22.1 (CH(CH3)2), 30.9 (CHMe2), 55.1, 55.3, 55.7 (OCH3), 79.6, 79.8,
96.1, 99.1 (p-cymene ArC), 108.7, 110.5, 111.0, 119.6, 120.5, 120.6,
121.0, 122.7, 124.0 (br), 125.1, 126.4 (br), 127.0, 136.8, 147.2, 151.3,
152.0, 153.8 (ArC and CN). Note: Only 17 carbon resonances were
observed for ArC and CN carbons of the guanidinate ligand rather
than the expected 19 peaks, presumably because of overlapping peaks.
Three rotamers were observed in about 1.0:0.05:0.04 ratios in CD3CN
EXPERIMENTAL SECTION
■
4‑tolyl
General Procedures. N,N′,N″-Triarylguanidines (LH2
,
LH22‑tolyl, LH22‑anisyl, LH22,4‑xylyl, and LH22,6‑xylyl)),24 and [(η6-C10H14)-
26
RuCl(μ-Cl)]2 were prepared following the literature procedures.
RuCl3·xH2O, RO(O)C−CC−C(O)OR (R = Me (DMAD), and Et
(DEAD)), NaN3, and deuterated solvents were purchased from Sigma-
Aldrich and used as received. The IR spectral data were obtained using
KBr pellets on Shimadzu IR435 spectrometer in the frequency range
400−4000 cm−1. TOF−MS spectra were recorded on a Micromass
LCT KC 455 instrument using electrospray positive ion mode. 1H and
13C NMR spectra were recorded on an Avance Bruker−300 NMR
spectrometer operating at 300 and 75.5 MHz, respectively and JEOL
ECX 400 NMR spectrometer operating at 400 and 100 MHz,
respectively. The chemical shifts are reported in parts per million
(ppm) relative to tetramethylsilane or residual solvent signal. A
1
as estimated from the integrals of p-cymene CH protons. H NMR
(400 MHz, CD3CN, ppm): δH = 1.16 (d, JH,H = 6.9 Hz, CH(CH3)2,
rotamers 1, 2 or 3), 1.30 (d, JH,H = 6.4 Hz, CH(CH3)2, rotamer 2 or
3), 2.10−2.33 (br, CH3, rotamers 1, 2 and 3), 2.48−2.55 (m, CHMe2,
rotamers 1, 2 or 3), 2.89−2.93 (m, CHMe2, rotamer 2 or 3), 3.77,
3.79, 3.83, 3.88 (s, OCH3, rotamers 1, 2 and 3), 5.10, 5.24 (each d, JH,H
= 5.3 Hz, C6H4, rotamer 1), 5.28, 5.43, 5.54 (each br, C6H4, rotamers 2
and 3), 6.19 (apparent t, JH,H = 7.1 Hz, ArH), 6.53 (m, ArH), 6.64 (d,
JH,H = 7.8 Hz, ArH), 6.73 (d, JH,H = 6.9 Hz, ArH), 6.84−6.92 (m,
ArH), 7.06−7.09 (m, ArH), 7.28 (d, JH,H = 7.3 Hz, ArH), 7.37 (d, JH,H
= 6.4 Hz, ArH), 7.49 (ArH), 8.61(br, NH). 13C{1H} NMR (100 MHz,
CD3CN, ppm): δC = 19.0 (CH3), 22.4 (CH(CH3)2), 31.9 (CHMe2),
56.0, 56.1, 56.4 (OCH3), 80.6, 80.8, 97.0, 99.9 (p-cymene ArC), 110.3,
111.8, 112.4, 119.8, 120.1, 121.5, 121.6, 123.8, 125.3, 125.8, 127.2,
127.8, 128.4, 137.6, 148.3, 151.3, 153.0, 153.1, 154.4 (ArC and CN).
The NMR peak assignments reported in CD3CN were independently
1
variable temperature (VT) H NMR spectra of 2, 3, and 10, and
DEPT−90 13C NMR spectrum of 3 were recorded on Bruker AV−
400 NMR spectrometer operating at 400, and 100 MHz, respec-
tively. Melting points of 1−3 were recorded on Buchi melting
point apparatus (Model: M−560), and the reported values are
uncorrected. The TGA/DTA thermogram of 8·H2O was measured
on PerkinElmer Diamond instrument under nitrogen atmosphere at
2 °C/min heating rate.
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Inorganic Chemistry
Article
confirmed by two-dimensional HETCOR NMR data (Figures S1−S3
in the Supporting Information). TOF−MS+, m/z [ion, intensity (%)]:
648.5574 [(M + H)+, 8]. Anal. Calcd. for C32H36N3ClO3Ru (Mw:
647.17): C, 59.39; H, 5.60; N, 6.49. Found: C, 59.62; H, 5.75; N, 6.75.
[(η6-C10H14)RuCl{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar = C6H4Me−2; 3).
Complex 3 was prepared from [(η6-C10H14)RuCl(μ-Cl)]2 (100 mg,
0.163 mmol) and LH22‑tolyl (225 mg, 0.683 mmol) in toluene (10 mL)
following the procedure previously described for 1. The filtrate from
the reaction mixture was concentrated under vacuum to about 2 mL
and stored at ambient temperature for several hours to afford 3 as
orange crystals. Yield: 92% (180 mg, 0.300 mmol). Mp: 120
°C(decomp). IR (KBr, cm−1) νmax: 3435 (br, NH), 2924 (vs, C−
because of overlapping peaks. Anal. Calcd for C32H36N6Ru·H2O (Mw:
623.76): C, 61.62; H, 6.14; N, 13.47. Found: C, 62.03; H, 6.00; N,
13.80.
[(η6-C10H14)RuN3{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar = C6H4(OMe)−2;
6). Complex 6 was prepared from 2 (100 mg, 0.154 mmol) and NaN3
(20.0 mg, 0.308 mmol) in ethanol (10 mL) following the procedure
previously described for 5. The sample was crystallized from diethyl
ether at −10 °C over a period of 24 h. Yield: 82% (83 mg, 0.127
mmol). IR (KBr, cm−1) νmax: 3336 (w, NH), 2026 (s, N3), 1531 (s,
1
CN). H NMR (300 MHz, CDCl3, ppm): δH = 1.20 (d, JH,H = 6.9
Hz, 6H, CH(CH3)2), 2.14 (s, 3H, CH3), 2.55−2.59 (m, 1H, CHMe2),
3.75 (s, 3H, OCH3), 3.85 (s, 2 × 3 H, OCH3), 4.94, 5.08 (each d, JH,H
= 4.5 Hz, 4H, C6H4), 6.33 (br m, 1H, ArH), 6.54 (br, 2H, ArH), 6.69,
6.72 (each s, 2H, ArH), 6.78−6.90 (m, 5H, ArH), 7.28 (s, 2H, ArH),
1
H···Cl), 2853 (s, C−H···Cl), 1591 (s, CN). H NMR (300 MHz,
CDCl3, ppm): δH = 1.17 (br, CH(CH3)2), 1.95, 2.00, 2.12, 2.22, 2.37
(br, CH3), 2.58 (br, CH3/CH), 5.05, 5.32 (each br, C6H4), 6.69−7.23
(br m), 7.49 (br, ArH and NH). Complex 3 revealed broad featureless
13C NMR signals presumably because of its fluxional behavior and thus
7.39 (s, 1H, NH). 13C{1H} NMR (100 MHz, CDCl3, ppm): δC
=
18.22 (CH3), 22.50 (CH(CH3)2), 30.91 (CHMe2), 55.34, 55.47
(OCH3), 79.71, 80.12, 95.78, 100.22 (p-cymene ArC), 108.94, 110.77,
120.06, 120.59, 120.64, 120.92, 121.30, 123.23, 124.96, 127.14, 127.23,
137.09, 147.42, 147.45, 152.17, 154.88, 154.91 (ArC and CN).
Note: Only two carbon resonances were observed for OCH3 carbon
rather than the expected 3 peaks and 17 carbon resonances were
observed for ArC and CN carbons of the guanidinate ligand rather
than the expected 19 peaks, presumably because of overlapping peaks.
Anal. Calcd for C32H36N6O3Ru (Mw: 653.74): C, 58.79; H, 5.55; N,
12.86. Found: C, 58.94; H, 5.64; N, 12.56.
precluded the unambiguous assignment of 13C NMR data. TOF−MS+,
2‑tolyl
m/z [ion, intensity (%)]: 599.5474 [M+, 5], 327.4343 [(LH2
−
2H)+, 97]. Anal. Calcd for C32H36N3ClRu (Mw: 599.17): C, 64.15; H,
6.06; N, 7.01. Found: C, 64.33; H, 6.14; N, 6.78.
[(η6-C10H14)RuCl{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar = C6H3Me2−2,4;
4). [(η6-C10H14)RuCl(μ-Cl)]2 (100 mg, 0.163 mmol) was dispersed
in toluene (10 mL) in a 25 mL round-bottom flask. To the suspension,
2,4‑xylyl
LH2
(255 mg, 0.686 mmol) was added in a portion that
immediately resulted in the formation of [LH32,4‑xylyl]+Cl− as colorless
solid. The reaction mixture was stirred for 2 h at room temperature
and filtered. The volatiles from the filtrate were removed under
vacuum to afford a gummy solid. The gummy solid was extracted with
diisopropyl ether, and the extract was left at ambient temperature for
24 h to afford 4 as orange crystals. Yield: 79% (165 mg, 0.257 mmol).
IR (KBr, cm−1) νmax: 3386 (w, NH), 2962 (s, C−H···Cl), 2921 (s, C−
[(η6-C10H14)RuN3{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar = C6H4Me−2;
7). Complex 7 was prepared from 3 (100 mg, 0.167 mmol) and
NaN3 (22.0 mg, 0.338 mmol) in ethanol (10 mL) following the
procedure previously described for 5. Complex 7 was crystallized from
diethyl ether at −10 °C over a period of several hours. Yield: 94% (94
mg, 0.155 mmol). IR (KBr, cm−1) νmax: 3295 (br w, NH), 2028 (vs,
N3), 1541 (s, CN). The 1H NMR spectrum of 7 revealed the
presence of two isomers as inferred from CH3 signals of the iPr
moiety, but their relative ratio was difficult to estimate because of
1
H···Cl), 1543 (m, CN). The H NMR spectrum of 4 revealed the
presence of three isomers in about 1.0:1.1:3.8 ratios as estimated from
1
the integrals of CH(CH3)2 protons. H NMR (300 MHz, CDCl3,
1
overlapping peaks. H NMR (300 MHz, CDCl3, ppm): δH = 1.10−
ppm): δH = 1.09 (d, JH,H = 6.3 Hz, CH(CH3)2, major isomer), 1.14 (d,
JH,H = 6.9 Hz, CH(CH3)2, minor isomer 1), 1.21 (d, JH,H = 6.9 Hz,
CH(CH3)2, minor isomer 2), 1.86, 1.92, 1.95 (each s, CH3), 2.11 (br,
CH3), 2.29 (br, CH3), 2.55−2.65 (m, CHMe2, major and minor
1.20 (br, CH(CH3)2, major isomer), 1.24 (d, JH,H = 8.4 Hz,
CH(CH3)2, minor isomer), 1.87 (CH3), 2.03 (br, CH3), 2.09
(CH3), 2.40 (CH3), 2.45 (br, CH3), 2.62−2.66 (m, CHMe2), 3.47−
3.49 (m, CHMe2), 4.91, 5.08, 5.25, 5.27, 5.32, 5.34 (each br, C6H4),
6.60−7.15 (br m, ArH and NH). Anal. Calcd for C32H36N6Ru (Mw:
605.74): C, 63.45; H, 5.99; N, 13.87. Found: C, 63.71; H, 6.04; N,
13.52.
isomers), 4.91−5.10 (br, C6H4), 5.20−5.28 (br, C6H4), 5.41 (d, JH,H
=
6.0 Hz, C6H4), 6.40−7.10 (br), 7.30 (br, ArH and NH). TOF−MS+,
m/z [ion, intensity (%)]: 641.6260 [M+, 37]. Anal. Calcd for
C35H42N3ClRu (Mw: 641.26): C, 65.56; H, 6.60; N, 6.55. Found: C,
65.09; H, 6.44; N, 6.67. Multiple attempts to obtain a better carbon
value were unsuccessful.
[(η6-C10H14)Ru{N3C2(C(O)OEt)2}{κ2(N,N′)((ArN)2C−N(H)Ar)}]·H2O
(Ar = C6H4Me−4; 8·H2O). Complex 5 (100 mg, 0.165 mmol) was
dissolved in CH2Cl2 (5 mL) in a 25 mL round-bottom flask. To the
aforementioned solution, a CH2Cl2 (5 mL) solution of DEAD (56 mg,
0.330 mmol) was slowly added, stirred at room temperature for 24 h,
and concentrated under vacuum to about 2 mL. The concentrate was
layered with n-hexane (5 mL) and stored at ambient temperature for
24 h to afford 8·H2O as yellow crystals. Yield: 60% (78 mg, 0.098
mmol). IR (KBr, cm−1) νmax: 3326 (m, NH), 1725, 1710 (each s, C
The reaction of [(η6-C10H14)RuCl(μ-Cl)]2 (100 mg, 0.163 mmol)
with LH22,6‑xylyl (255 mg, 0.686 mmol) in toluene (10 mL) at ambient
temperature did not afford any product as verified by TLC.
[(η6-C10H14)RuN3{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar = C6H4Me−4;
5). To a solution of 1 (100 mg, 0.167 mmol) in ethanol (10 mL)
was added NaN3 (22.0 mg, 0.338 mmol), and the resulting
homogeneous solution was stirred at ambient temperature for 6 h.
The reaction mixture was concentrated under vacuum to afford a
residue. The product was extracted from the residue with diethyl ether
(20 mL) and filtered. The filtrate was concentrated under vacuum to
about 5 mL and stored at −10 °C for 24 h to afford 5 as red crystals.
Yield: 82% (83 mg, 0.137 mmol). IR (KBr, cm−1) νmax: 3398 (w, NH),
1
O), 1540 (s, CN), 1439 (s, NN), 1290 (m, C−O). H NMR
(400 MHz, CDCl3, ppm): δH = 1.16 (d, JH,H = 7.0 Hz, 6H,
CH(CH3)2), 1.29 (t, JH,H = 7.2 Hz, 6H, CH2CH3), 2.01 (s, 3H, CH3),
2.08 (s, 3H, CH3), 2.19 (s, 2 × 3H, CH3), 2.67−2.72 (m, 1H,
CHMe2), 4.28 (q, JH,H = 7.2 Hz, 4H, CH2CH3), 5.27, 5.45 (each d,
JH,H = 5.9 Hz, 4H, C6H4), 5.85 (s, 1H, NH), 6.62 (d, JH,H = 8.4 Hz,
2H, ArH), 6.68 (d, JH,H = 8.4 Hz, 2H, ArH), 6.85 (d, JH,H = 8.4 Hz, 4H,
ArH), 6.89 (d, JH,H = 8.4 Hz, 4H, ArH). 13C{1H} NMR (100 MHz,
CDCl3, ppm): δC = 14.3 (CH2CH3), 18.7 (CH3), 20.7, 20.9 (CH3),
22.7 (CH(CH3)2), 31.2 (CHMe2), 60.6 (CH2CH3), 81.1, 83.0, 98.8,
101.2 (p-cymene ArC), 120.0, 123.5, 128.8, 129.2, 131.6, 131.7, 135.6,
139.8, 144.4, 155.3 (ArC and CN), 163.0 (OC(O)). Only 5 carbon
signals were observed for CH3 carbon rather than the expected 6
peaks, and 10 carbon resonances were observed for ArC and CN
carbons of the guanidinate and the triazolate ligands rather than the
expected 14 peaks, presumably because of overlapping peaks. Anal.
Calcd for C40H46N6O4Ru·H2O (Mw: 793.93): C, 60.51; H, 6.09; N,
10.58. Found: C, 60.23; H, 5.76; N, 10.83.
1
2030 (vs, N3), 1543 (s, CN). H NMR (400 MHz, CDCl3, ppm):
δH = 1.22 (d, JH,H = 6.8 Hz, 6H, CH(CH3)2), 2.09 (s, 3H, CH3), 2.21
(s, 2 × 3H, CH3), 2.22 (s, 3H, CH3), 2.68−2.75 (m, 1H, CHMe2),
5.08, 5.33 (each d, JH,H = 6.0 Hz, 4H, C6H4), 5.88 (s, 1H, NH), 6.64
(d, JH,H = 8.7 Hz, 2H, ArH), 6.70 (d, JH,H = 8.2 Hz, 2H, ArH), 6.90 (d,
JH,H = 8.3 Hz, 4H, ArH), 7.05 (d, JH,H = 8.2 Hz, 4H, ArH). 13C{1H}
NMR (100 MHz, CDCl3, ppm): δC = 19.2 (CH3), 20.7, 21.0 (CH3),
22.6 (CH(CH3)2), 31.5 (CH(CH3)2), 78.8, 80.9, 97.9, 98.5 (p-cymene
ArC), 120.0, 123.4, 129.0, 129.3, 130.0, 131.6, 131.9, 135.6, 144.3,
154.1 (ArC and CN). Note: Only 2 carbon resonances were
observed for CH3 carbon rather than the expected 3 peaks, and 10
carbon resonances were observed for ArC and CN carbons of the
guanidinate ligand rather than the expected 13 peaks, presumably
159
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Table 1. Crystallographic Data for 1−4
1
2
3
4
formula
Fw
C32H36N3ClRu
599.16
298(2)
0.71073
monoclinic
P21/n
C32H36N3ClO3Ru
647.16
100(2)
0.71073
monoclinic
P21
C32H36N3ClRu
599.16
100(2)
0.71073
monoclinic
P21
C35H42N3ClRu
641.24
100(2)
0.71073
monoclinic
C2/c
T/K
λ/Å
cryst syst
space group
a/Å
15.844(5)
9.534(5)
19.696(5)
90
18.565(2)
8.3952(11)
19.908(2)
90
10.355(5)
8.834(5)
15.100(5)
90
14.4275(13)
14.3557(13)
30.288(3)
90
b/Å
c/Å
α/deg
β/deg
γ/deg
V/Å3
Z
103.756(5)
90
109.837(5)
90
94.342(5)
90
90.809(7)
90
2889.9(19)
4
2918.8(6)
4
1377.3(11)
2
6272.6(10)
8
D
calcd/g cm−3
1.377
1.473
1.445
1.358
F(000)
μ/mm−1
1240
1336
620
2672
0.660
0.667
0.692
0.613
θ range/deg
reflns measured
reflns used
parameters
R1
3.0−26.4
5890
1.09−28.32
14327
1.35−27.92
6275
1.34−28.45
7812
4649
13184
5551
5892
340
734
340
371
0.0403
0.1079
1.051
0.0327
0.0704
1.180
0.0378
0.1032
1.203
0.0532
0.1345
1.124
wR2
goodness of fit on F2
Table 2. Crystallographic Data for 5, 6, 8·H2O, and 10
5
6
8·H2O
10
formula
Fw
C32H36N6Ru
605.74
298(2)
0.71073
orthorhombic
P212121
8.3950(2)
13.1183(3)
26.1858(8)
90
C32H36N6O3Ru
653.74
298(2)
0.71073
orthorhombic
P212121
9.1199(2)
17.6750(6)
18.9166(5)
90
C80H92N12O9Ru2
1567.80
298(2)
0.71073
monoclinic
C2/c
C38H42N6O4Ru
747.85
T/K
298(2)
λ/Å
0.71073
cryst syst
space group
a/Å
triclinic
PI
̅
32.390(5)
13.2154(9)
25.888(4)
90
10.277(5)
11.060(5)
16.638(5)
70.932(5)
77.569(5)
82.911(5)
1742.6(13)
2
b/Å
c/Å
α/deg
β/deg
γ/deg
V/Å3
Z
90
90
136.05(3)
90
90
90
2883.79(13)
4
3049.24(15)
4
7691(5)
4
D
calcd/g cm−3
1.395
1.424
1.354
1.425
F(000)
μ/mm−1
1256
1352
3264
776
0.575
0.557
0.457
0.499
θ range/deg
reflns measured
reflns used
parameters
R1
2.98−26.37
5665
3.10−26.37
5684
3.08−26.37
7849
1.32−23.35
4832
4787
4697
6582
4010
358
385
473
453
0.0357
0.0803
0.974
0.0331
0.0532
0.865
0.0394
0.0918
1.031
0.0503
0.1391
1.142
wR2
goodness of fit on F2
[(η6-C10H14)Ru{N3C2(C(O)OMe)2}{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar =
C6H4(OMe)−2; 9). Complex 9 was prepared from 6 (150 mg, 0.229
mmol) and DMAD (65 mg, 0.457 mmol) in CH2Cl2 (10 mL)
following the procedure previously described for 8·H2O. Complex 9
was purified by crystallization from CH2Cl2/n-hexane mixture at
ambient temperature over a period of 24 h. Yield: 73% (133 mg, 0.167
mmol). IR (KBr, cm−1) νmax: 3322 (w, NH), 1737, 1726 (each s, C
O), 1542 (s, CN), 1439 (s, NN), 1237 (s, C−O). 1H NMR (300
MHz, CDCl3, ppm): δH = 1.11 (d, JH,H = 6.9 Hz, 6H, CH(CH3)2),
2.01 (s, 3H, CH3), 2.53−2.58 (m, 1H, CHMe2), 3.75 (s, 3H, OCH3),
3.77 (s, 2 × 3H, OCH3), 3.82 (s, 2 × 3H, OCH3), 5.28 (apparent q,
JH,H = 5.6 Hz, 4H, C6H4), 6.28 (br m, 1H, ArH), 6.52 (s, 2H, ArH),
6.61 (d, JH,H = 7.8 Hz, 2H, ArH), 6.74 (t, JH,H = 7.4 Hz, 2H, ArH), 6.83
(t, JH,H = 7.5 Hz, 2H, ArH), 7.01 (d, JH,H = 7.5 Hz, 2H, ArH), 7.22 (d,
J
H,H = 8.1 Hz, 1H, ArH), 7.36 (s, 1H, NH). 13C{1H} NMR (100 MHz,
CDCl3, ppm): δC = 18.2 (CH3), 22.2 (CH(CH3)2), 30.8 (CHMe2),
51.7 (C(O)OCH3), 55.1, 55.2 (OCH3), 81.4, 82.4, 96.6, 102.4 (p-
160
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cymene ArC), 108.4, 110.4, 119.7, 120.8, 121.1, 121.7, 122.8, 125.0,
127.0 (ArC), 136.9 (C(C(O)OMe)), 139.4, 147.2, 152.0, 155.1 (ArC
and CN), 163.2 (OC(O)). Note: Only 2 carbon resonances were
observed for OCH3 rather than the expected 3 peaks, and 13 carbon
resonances were observed for ArC and CN carbons of the
guanidinate ligand rather than the expected 19 peaks, presumably
because of overlapping peaks. Anal. Calcd for C38H42N6O7Ru (Mw:
795.86): C, 57.35; H, 5.32; N, 10.56. Found: C, 57.12; H, 5.02; N,
10.32.
Scheme 1
[(η6-C10H14)Ru{N3C2(C(O)OMe)2}{κ2(N,N′)((ArN)2C−N(H)Ar)}] (Ar =
C6H4Me−2; 10). Complex 10 was prepared from 7 (200 mg, 0.330
mmol) and DMAD (94 mg, 0.661 mmol) in CH2Cl2 (10 mL)
following the procedure previously described for 8·H2O. Complex 10
was purified by crystallization from CH2Cl2/n-hexane mixture at
ambient temperature over a period of 24 h. Yield: 72% (178 mg, 0.238
mmol). IR (KBr, cm−1) νmax: 3379 (w, NH), 1726 (s, CO), 1541
(CN), 1461 (s, NN), 1223 (s, C−O). The 1H NMR spectrum of
10 revealed the presence of two isomers, but their relative ratios were
difficult to estimate because of overlapping peaks (see later). 1H NMR
(300 MHz, CDCl3, ppm): δH = 1.02 (d, JH,H = 6.3 Hz, CH(CH3)2,
major isomer), 1.12 (br, CH(CH3)2, minor isomer), 1.80 (br, CH3),
2.01 (CH3), 2.06 (CH3), 2.42 (br, CH3), 3.86 (s, OCH3)), 5.25, 5.50
(each br, C6H4), 6.67−7.01 (br, ArH), 7.42, 7.81 (ArH and NH). Anal.
Calcd for C38H42N6O4Ru (Mw: 747.86): C, 61.03; H, 5.66; N, 11.24.
Found: C, 60.94; H, 5.24; N, 11.18.
Scheme 2
Single Crystal X-ray Structure Determination. Intensity data
of suitably sized crystals of 1, 5, 6, and 8·H2O were collected on an
Oxford Xcalibur S diffractometer (4-circle κ goniometer, Sapphire-3
CCD detector, ω scans, graphite monochromator, and a single
wavelength Enhance X-ray source with MoKα radiation).27 Pre-
experiment, data collection, data reduction and absorption corrections
were performed with the CrysAlisPro software suite.28 Intensity data
of suitably sized crystals of 2−4 and 10 were collected on a Bruker
AXS SMART-APEX diffractometer with a CCD area detector, graphite
monochromator.29 The frames were collected by ω, ϕ, and 2θ rotation
at 10 s per frame with SMART. The measured intensities were
reduced to F2 and corrected for absorption with SADABS.30 The
structures were solved by direct methods using SIR 92,31 which
revealed the atomic positions, and refined using the SHELX-97
program package32 and SHELXL9733 (within the WinGX program
package).34 Non-hydrogen atoms were refined anisotropically. C−H
hydrogen atoms were placed in geometrically calculated positions by
using a riding model. The molecular structures were created with the
Diamond program.35 The X-ray crystallographic parameters, details
of data collection and structure refinement are presented in Tables 1
and 2.
bound triazolate metal complexes, respectively.36−46 Hence,
complex 5 was treated with diethylacetylenedicarboxylate
(DEAD) in CH2Cl2 at ambient temperature for 24 h to afford
8·H2O in 60% yield. Similarly, 6 and 7 upon reaction with
dimethylacetylenedicarboxylate (DMAD) in CH2Cl2 at am-
bient temperature afforded 9 and 10 in 73 and 72% yield,
respectively (Scheme 3). Complexes 5−7 were also treated
Scheme 3
RESULTS AND DISCUSSION
■
Synthesis. Complexes 1−4 were prepared in high yield
from the bridge-splitting reaction involving [(η6-C10H14)RuCl-
(μ-Cl)]2 and the respective N,N′,N″-triarylguanidine in toluene
in 1:4 mol ratio at ambient temperature for 2 h following the
procedure published for I.22 One mole of guanidine was
incorporated as a monoanion per ruthenium atom in 1−4, and
two moles of guanidine are lost as a guanidinium salt (C) in the
transformation shown in Scheme 1. The reaction of [(η6-
2,6‑xylyl
C10H14)RuCl(μ-Cl)]2 with a sterically more hindered LH2
in 1:4 mol ratio in toluene at ambient temperature for 2 h did
not afford any new complex.
Complexes 1−3 upon reaction with an excess of NaN3 in
ethanol at ambient temperature for 6 h afforded the
corresponding azido complexes 5−7 in high yield (Scheme
2). Half sandwich ruthenium(II) azido complexes are
interesting scaffolds from the point of view of their structures
and reactivity pattern, especially [3 + 2] cycloaddition reaction
of this class of complexes with nitrile, isonitrile, and alkynes to
afford nitrogen bound, carbon bound tetrazolate and nitrogen
with electron rich methylphenyl propiolate and diphenyl
acetylene separately in CH2Cl2 at ambient temperature for
24 h, but no new products were isolated from these reactions.
161
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Figure 1. Molecular structures of 1−4 at the 50% probability level. Two molecules crystallized in an asymmetric unit in the case of 2, but only
molecule 1 is shown for clarity. Only the hydrogen atom of the amino moiety is shown for clarity.
Molecular Structures. The molecular structures of 1−4
with atom labeling schemes are shown in Figure 1. Selected
bond parameters are listed in Table 3. The ruthenium atom in
1−4 is surrounded by the η6-bonded p-cymene ring, a chelating
N,N′,N″-triarylguanidinate ligand, and the chloride and thus
attains a pseudo octahedral “three legged piano stool”
geometry; the p-cymene ring constitutes a seat, the chloride
and two nitrogen atoms of the guanidinate ligand constitute
three legs. The structural features of 1−4 are listed in Table S1
in the Supporting Information.
In principle, four resonance forms, D−G, can be drawn for
the ruthenium bonded guanidinate ligand as illustrated in
Chart 2. An equal contribution of resonance forms D and E
would result in the π−delocalized form F and a symmetric
coordination of the nitrogen atoms of the guanidinate ligand.
The magnitude of ΔCN (= d(C−N) − d(CN)) and ΔCN′ (=
d(C−N(H)) − d(CN))25,47 gives an insight regarding the
relative contribution of a particular resonance form to the
overall structure and bonding of amidinate and guanidinate
complexes. The ΔCN values range from 0 Å in a π−delocalized
form F up to 0.10 Å in the π−localized forms D and E retaining
the C−N single bond and the CN double bond character.
The zwitterionic form G would be feasible when τ(N−C−
N(H)−C) torsion angle is close to 0 or 180° and when the
N(H)R nitrogen is sp2 hybridized and planar. Further, the
dihedral angle between the NCN plane of the chelate ring and
that of the NHC(R) unit should be close to zero.20c,48
In general, the ΔCN value is smaller than the ΔCN′ value for
1−4 (ΔCN; ΔCN′: 0.013(6); 0.059(6) (1), 0.009(6); 0.056(6)
(2; molecule 1), 0.001(9); 0.042(8) (3), and 0.007(6);
0.056(6) (4)) indicating a better alignment of the NcoordAr
lonepair than the NHAr lonepair with CNπ* orbital of the
imine unit. The CN3 carbon of the guanidinate ligand is planar.
The nitrogen atoms in 1−3 are planar (∑N ≈ 360°) or nearly
planar (∑N ≈ 354−358°). However, one of coordinated
nitrogen atoms in 4 significantly deviates from planarity (∑N:
348.6°), and the remaining nitrogen atoms are planar or nearly
planar (∑N: 356.8°). A slightly pyramidal geometry (∑N:
355.5°) of one of the coordinated nitrogen atoms and a
comparable Ru−N distances (2.098(2) and 2.105(2) Å) in 1 or
a planar geometry of the coordinated nitrogen atoms and an
unequal Ru−N distances (2.107(3), and 2.086(3) Å) in 2
(molecule 1) or a slightly pyramidal geometry (∑N: 353.8°) of
one of the coordinated nitrogen atoms and unequal Ru−N
distances (2.125(4) and 2.093(4) Å) in 3 support unequal
contributions of forms E and F. A nonplanar geometry of the
coordinated nitrogen atoms and unequal Ru−N distances
(2.105(3) and 2.149(3) Å) in 4 indicate unequal contributions
of forms D and E. The N−C−N(H)−C torsion angles in 4
(−42.9(5) and 140.0(4)°) deviate from 0 or 180° to a greater
extent than those found in 3 (23.4(10) and −153.8(5)°).
162
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Table 3. Selected Bond Distances (Å) and Angles (deg) for 1−4
1
2 (molecule 1)
3
4
Ru1−C(centroid)
Ru1−N1
Ru1−N3
Ru1−Cl1
N1−C1
N2−C1
N3−C1
N1−C2
N2−C9/N2−C10
N3−C16/N3−C18
Ru1−N1−C2
C2−N1−C1
Ru1−N1−C1
C9−N2−C1/C10−N2−C1
C1−N2−H2
C9−N2−H2/C10−N2−H2
Ru1−N3−C16/Ru1−N3−C18
C16−N3−C1/C18−N3−C1
Ru1−N3−C1
N1−C1−N2
N2−C1−N3
N3−C1−N1
Cl1−Ru1−N3
Cl1−Ru1−N1
N1−Ru1−N3
1.6648(8)
2.098(2)
2.105(2)
2.410(1)
1.319(4)
1.378(4)
1.332(4)
1.402(4)
1.422(4)
1.409(4)
135.1(2)
130.2(3)
94.6(2)
1.6526(4)
2.107(3)
2.086(3)
2.411(1)
1.333(4)
1.380(4)
1.324(4)
1.401(4)
1.420(4)
1.400(4)
137.1(2)
128.8(3)
94.0(2)
1.652(1)
2.125(4)
2.093(4)
2.412(2)
1.331(7)
1.372(6)
1.330(6)
1.423(7)
1.421(7)
1.404(6)
135.7(3)
125.5(4)
92.6(3)
1.6620(3)
2.105(3)
2.149(3)
2.397(9)
1.320(5)
1.376(4)
1.327(4)
1.406(5)
1.436(4)
1.422(5)
134.6(2)
127.9(3)
94.3(2)
124.3(2)
117.9(3)
117.8(2)
135.4(2)
126.3(3)
93.8(2)
124.5(3)
117.7(3)
117.7(3)
136.5(2)
127.9(3)
95.2(2)
126.7(4)
116.6(4)
116.6(4)
134.0(3)
131.9(4)
94.1(3)
122.4(3)
118.7(3)
118.9(3)
134.4(2)
122.1(3)
92.1(2)
126.6(3)
124.8(3)
108.6(3)
87.51(8)
85.63(8)
61.57(9)
122.0(3)
129.4(3)
108.5(3)
85.6(1)
123.7(5)
126.8(5)
109.4(4)
85.6(1)
125.7(3)
123.3(3)
111.0(3)
86.08(8)
85.40(9)
61.7(1)
87.6(1)
87.8(1)
61.9(1)
62.0(2)
a
Chart 2. Limiting Resonance Forms of 1−4
a
[Ru]: (η6-p-cymene)RuCl.
Further, the dihedral angle between the HNC(Ar) plane and
the chelate NCN plane is greater in 4 (41.4(3)°) than in 3
(25.0(5)°), possibly because of a greater pyramidal geometry of
one of the coordinated nitrogen atoms in the former, and this
in turn arises because of the greater donor strength of xylyl
substituent in 4 than tolyl substituent in 3. The RuNCN chelate
ring in 3 is more puckered than that in 4. This feature is
counterintuitive as one of the coordinated nitrogen atoms is
more pyramidal in the latter, but this appears to arise from the
difference in the conformation of the guanidinate ligand in
these complexes (see later).
Figure 2. Four possible conformations of 2, 3, and 4. The substituent
symbol on the aryl rings of the guanidinate ligand is omitted for clarity.
[Ru]: (η6-p-cymene)RuCl.
and 4 does not appear to originate from the conformational
difference between two guanidines from which these complexes
were obtained. A hypothetical syn-syn isomer of 4 is possibly a
kinetically controlled isomer of the bridge splitting reaction
shown in Scheme 1 and rearranges to a thermodynamically
controlled syn-anti isomer via an intermediate H shown in
Figure 3 because of a greater steric strain present in the former
isomer induced by a greater pyramidal geometry of one of the
coordinated nitrogen atoms. The rearrangement shown in
Figure 3 bears some resemblance to the rearrangement that
follows insertion of N,N′-diisopropylcarbodiimide into Ln−N
bond.50
The molecular structures of 5 and 6 are illustrated in
Figure 4. Selected bond parameters are listed in Table 4. The
coordination environment and bond parameters around the
ruthenium atom in 5 and 6 are nearly identical to those found
in 1 and 2, respectively, except that the chloride in the latter
The o-substituent of the aryl ring of the coordinated nitrogen
atoms can lie parallel (i.e, syn) or anti parallel (i.e, anti) to the
corresponding substituent of the aryl ring of the non-
coordinated nitrogen atom of the guanidinate ligand in 2−4.
Thus, syn-syn, syn-anti, anti-syn, and anti-anti conformations are
possible for 2−4, as illustrated in Figure 2.49 Accordingly, the
guanidinate ligand in 2 (molecule 1) and 3 adopts syn-syn
conformation while that in 4 adopts syn-anti conformation with
some distortion in the crystal lattice.
2‑tolyl
2,4‑xylyl
Guanidines LH2
and LH2
were shown to possess
2‑anisyl
anti-anti αβα conformation whereas LH2
was shown to
possess syn-anti αββ conformation in the crystal lattice.24 Thus,
the difference in conformation of the guanidinate ligand in 3
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the other (∑N: 347.7 and 359.1°) because of the presence of
more strongly donating p-tolyl substituent, but both coordi-
nated nitrogen atoms in 10 are nearly planar (∑N: 356.9 and
354.6°). The noncoordinated nitrogen atoms in 8·H2O and 10
are planar. The Ru(1)−N(1) distance, 2.089(2) Å in 8·H2O, is
slightly smaller than the Ru(1)−N(3) distance, 2.140(2) Å, but
the bond distance difference is smaller in 10 (2.088(5) versus
2.104(4) Å). Thus, forms D and F appear to contribute
unequally to the bonding of the guanidinate ligand in 8·H2O
whereas forms D, E, and F contribute to different extent to the
bonding of the same ligand in 10.
The guanidinate ligand in 10 possesses syn-anti conformation
in contrast to syn-syn conformation observed for the same
ligand in 3 and presumably in 7. The greater steric
encumbrance around the ruthenium atom in a hypothetical
syn-syn isomer of 10 as compared with that found in 3 or 7
probably facilitates the guanidine centered rearrangement such
as that shown in Figure 3 and during such rearrangement the
guanidinate ligand rearranges to a sterically less encumbered
syn-anti conformation.
Figure 3. Guanidine centered rearrangement of 4 illustrating amine-
imine tautomerization, ring-opening, C−N bond rotation, and ring
closing events. [Ru]: (η6-p-cymene)RuCl.
complexes is substituted by the azide in the former. The degree
of n−π conjugation within the RuNCN chelate ring (ΔCN
;
Δ
CN′: 0.021(6); 0.048(6) (5), and 0.011(4); 0.040(5) (6)) is
greater. The perusal of ΔCN values, angle sums around the
nitrogen atoms (∑N1: 353.0°, ∑N2, N3: 360.0° (5); ∑N1:
359.8°, ∑N2: 360.0° and ∑N3: 358.1° (6)) and Ru−N
distances (Ru1−N1/Ru1−N3: 2.103(2)/2.125(3) Å (5);
2.080(2)/2.108(2) Å (6)) indicate a major contribution of
form D to the bonding of 5 whereas forms E and F contribute
unequally to the bonding of 6. The guanidinate ligand in 6 is
shown to reveal syn-syn conformation. The azido ligand in 5
and 6 adopts an end-on terminal coordination mode, and the
bond parameters associated with this ligand are comparable
with those reported for [[(η6-C10H14)RuN3{κ2(N,N′)(5-(4-
nitrophenyl)dipyrromethene)}] (III).51
Spectroscopic Properties. The IR spectrum of 1 and 3−
10 revealed one band in 3295−3435 cm−1 region attributed to
the ν(NH) stretch. However, the IR spectrum of 2 revealed
two bands at 3419 and 3330 cm−1 attributed to the ν(NH)
stretch of two distinct molecules in the crystal lattice.
Complexes 5−7 also revealed a new band at 2030, 2026, and
2028 cm−1, respectively attributed to the ν(N3) stretch, and
values of these bands favorably matched with that reported for
the related half-sandwich ruthenium(II) azido complexes.36−44
Complexes 8·H2O and 9 revealed two bands (1710 and 1725
cm−1 (8·H2O); 1726 and 1737 cm−1 (9)), but complex 10
revealed one band at 1726 cm−1 attributed to the ν(CO)
stretch of the ester group. The presence of one water molecule
in the crystal lattice of 8 was confirmed by microanalytical data.
Further, the TGA thermogram of 8·H2O revealed 2.53% weight
loss (theoretical weight loss: 2.27%) in the temperature range
45−139.26 °C indicating the loss of one water molecule. The
water loss was also confirmed by a DTA experiment that
revealed a sharp endotherm at 139.26 °C (Figure S4 in the
Supporting Information).
The molecular structures of 8·H2O and 10 are illustrated in
Figure 5. Selected bond parameters are listed in Table 5. The
ruthenium atom in 8·H2O and 10 is surrounded by the η6-
bonded p-cymene ring, two nitrogen atoms of N,N′,N″-
triarylguanidinate ligand and the central nitrogen atom of the
triazolate ring (i.e., N2 bonded isomer) and thus revealed a
pseudo octahedral “three legged piano stool” geometry. The
Δ
CN: 0.004(4) Å value is smaller than ΔCN′: 0.038(4) Å value
for the guanidinate ligand in 8·H2O. However, ΔCN and ΔCN
′
values in 10 are comparable within the experimental
uncertainties (ΔCN: 0.001(10) Å; ΔCN′: 0.021(10) Å), possibly
because of an improved n−π conjugation involving the NHAr
lone pair with the CNπ* orbital of the imine unit. The
greater n−π conjugation in 10 than in 8·H2O is due to greater
π−acceptor character of the ruthenium atom caused by the less
strongly donating and more sterically encumbered o-tolyl
moiety of the guanidinate ligand in the former. One of the
coordinated nitrogen atoms in 8·H2O is more pyramidal than
Complex 3 was subjected to a VT 1H NMR study to
1
understand its fluxional behavior. The H NMR stack plot for
alkyl protons as a function of temperature is illustrated in
Figure 4. Molecular structures of 5 and 6 at the 50% probability level. Only the hydrogen atom of the amino moiety is shown for clarity.
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Table 4. Selected Bond Distances (Å) and Angles (deg) for 5 and 6
5
6
5
6
Ru1−C(centroid)
Ru1−N1
Ru1−N3
Ru1−N4
N1−C1
1.6767(2)
2.103(2)
2.125(3)
2.121(3)
1.342(4)
1.369(4)
1.6635(3)
2.080(2)
2.108(2)
2.116(3)
1.329(3)
1.369(4)
N3−C1
N1−C2
N2−C9
N3−C16
N4−N5
N5−N6
1.321(4)
1.398(4)
1.412(4)
1.400(4)
1.197(4)
1.149(4)
1.340(3)
1.401(4)
1.402(4)
1.383(4)
1.184(4)
1.151(4)
N2−C1
Ru1−N1−C2
C2−N1−C1
Ru1−N1−C1
C9−N2−C1
C1−N2−H2
C9−N2−H2
Ru1−N3−C16
Ru1−N3−C1
129.7(2)
128.2(3)
95.1(2)
132.8(2)
131.3(3)
95.7(2)
C16−N3−C1
N1−C1−N2
N2−C1−N3
N3−C1−N1
N1−Ru1−N3
N3−Ru1−N4
N4−Ru1−N1
N4−N5−N6
129.6(3)
126.2(3)
125.2(3)
108.6(3)
61.5(1)
130.7(3)
128.6(3)
123.7(3)
107.6(3)
61.9(9)
126.1(3)
117.0(3)
116.9(3)
135.6(2)
94.8(2)
125.0(3)
117.5(3)
117.5(3)
133.3(2)
94.1(2)
87.0(1)
89.0(1)
86.8(1)
86.2(1)
177.8(4)
175.5(4)
upon lowering the temperature and merges with the latter at
283 K. Upon further cooling to 253 K, three distinct signals
appeared at δH = 1.06 (br), 1.16 (d, JH,H = 6.8 Hz), and 1.30
(br) ppm. The inner and outer broad peaks became a doublet
(JH,H = 6.4 and 6.8 Hz) upon further lowering the temperature.
1
At temperatures ≤233 K, the H NMR spectra revealed three
well-defined doublets at δH = 1.04, 1.21, and 1.34 ppm (JH,H
=
6.8 Hz) in about 1:1:1 ratios indicating the presence of three
1
isomers in solution. The perusal of a VT H NMR pattern of
the p-cymene ring protons further confirmed the presence of
three isomers at temperatures ≤253 K (Figure S5 in the
Supporting Information).
Two-dimensional 1H−1H COSY NMR data was acquired for
3 at 233 K to gain an insight concerning the orientation of the
p-cymene ring with respect to the Ru−N and Ru−Cl bond
axes. The three pairs of off-diagonal peaks observed between
CH(CH3)2 protons and guanidinate o-CH3 protons of the
coordinated nitrogen atoms clearly indicated the proximity of
these two units in solution (Figure S6, inset a in the Supporting
Information). Of the three doublets observed for CH(CH3)2
protons, the inner and outer doublets are assigned to two
symmetric isomers, and the central doublet is assigned to a less
1
symmetric isomer based on the H−1H COSY NMR pattern
illustrated in Figure S6, inset a, in the Supporting Information
as well as from the growth pattern of these peaks illustrated in
1
Figure 6. The H−1H COSY NMR pattern of the p-cymene
ring protons also revealed the presence of two symmetric
isomers and one less symmetric isomer (Figure S6, inset b, in
the Supporting Information). The DEPT-90 13C NMR
spectrum of 3 measured at 233 K revealed six signals at δC =
77.8, 78.0, 78.2, 78.4, 80.5, and 82.0 ppm attributed to the CH
carbon of the p-cymene ring, and this spectral pattern further
confirmed the presence of three isomers in solution (Figure S7
in the Supporting Information).
The p-cymene ring in [(η6-p-cymene)RuX(NN)] (NN:
monoanionic bidentate N-donor ligand; X = Cl or N) can
orient in six different eclipsed conformations around the
ruthenium atom such as I−N (Figure S8 in the Supporting
Information). In addition, several staggered conformations are
also possible. The preference of a particular conformer of [(η6-
p-cymene)RuCl(NN)]+X− was shown to depend largely upon
the steric bulk of the substituents on the nitrogen atom.52−57
Further, various conformers of [(η6-p-cymene)Ru-
(ethylenediamine)Cl]+ were shown to differ in energy by ≤2
Figure 5. Molecular structures of 8·H2O and 10 at the 50% probability
level. The lattice water molecule is omitted for clarity in the case of
8·H2O. The O1 atom in 10 is disordered over three sites, but only one
site is shown for clarity. Only the hydrogen atom of the amino moiety
is shown for clarity.
Figure 6. At 313 K, an intense doublet was observed at δH =
1.18 ppm (JH,H = 6.8 Hz) accompanied by a minor doublet at
δH = 1.24 ppm (JH,H = 7.2 Hz) in about 6.5:1 ratio assignable to
CH(CH3)2 protons, and the former doublet gradually broadens
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Table 5. Selected Bond Distances (Å) and Angles (deg) for 8·H2O and 10
8·H2O
10
8·H2O
10
Ru1−C(centroid)
Ru(1)−N(1)
Ru(1)−N(3)
Ru(1)−N(5)
N(1)−C(1)
N(2)−C(1)
N(3)−C(1)
N(4)−N(5)
N(5)−N(6)
N(2)−C(1)−N(3)
N(3)−C(1)−N(1)
N(1)−C(1)−N(2)
C(1)−N(1)−Ru(1)
1.6753(5)
2.089(2)
2.140(2)
2.106(2)
1.330(3)
1.368(3)
1.334(3)
1.320(3)
1.341(3)
127.5(2)
108.5(2)
124.0(2)
95.2(2)
1.6746(6)
2.088(5)
2.104(4)
2.102(4)
1.330(7)
1.351(7)
1.331(7)
1.340(6)
1.328(6)
123.4(5)
108.6(4)
128.0(5)
94.7(3)
C(1)−N(1)−C(2)
C(2)−N(1)−Ru(1)
C(1)−N(2)−H(2)
C(1)−N(2)−C(9)
C(9)−N(2)−H(2)
C(1)−N(3)−Ru(1)
C(16)−N(3)−Ru(1)
C(16)−N(3)−C(1)
N(4)−C(23)−C(27)/N(6)−C(23)−C(26)
N(5)−N(6)−C(27)/N(5)−N(4)−C(26)
N(4)−N(5)−N(6)
N(5)−N(4)−C(23)/N(5)−N(6)−C(23)
N(4)−C(23)−C(27)/N(4)−C(26)−C(23)
128.0(2)
135.9(2)
116.3(2)
127.5(2)
116.2(3)
92.8(2)
128.4(5)
133.8(4)
116.3(5)
127.5(5)
116.2(5)
94.0(3)
129.6(2)
125.3(2)
107.8(2)
105.1(2)
112.7(2)
106.1(2)
107.8(2)
133.8(4)
126.8(4)
108.2(5)
105.4(4)
112.7(4)
105.9(4)
107.7(5)
observed for the p-cymene ring protons. Hence, the chiral at
ruthenium option is ruled out for 1−4.
[ML2{κ2(N,N′)((iPrN)2C−NR2}2] [M = Ti; L = Cl, R = Me
(IV);62 M = Hf; L = NEt2; R = Et (V)63] and a homoleptic
[Ga{κ2(N,N′)((iPrN)2C−NR2}3] (R = Me; VI48a) were shown
to undergo N−CHMe2 bond rotation or C−NR2 bond rotation
along the guanidinate C2 axis but the latter process appears to
be feasible in 3 for steric reason. Complex 3 in conformation I
can have three different ligand conformations, namely, syn-syn
illustrated in Figure 2, syn-syn a, and syn-syn b illustrated in
Chart 3. The syn-syn ↔ syn-syn a or syn-syn a ↔ syn-syn b
a
Chart 3. Plausible Structures of Two Rotamers of 3
a
[Ru]: (η6-p-cymene)RuCl.
interconversion requires 60° C−N(H)(o-tolyl) bond rotation
in a region away from the o-Me protons of the o-tolyl moiety
of the coordinated nitrogen atoms to minimize the unfavor-
able steric repulsion. A complete 180° C−N(H)(o-tolyl) bond
rotation would convert syn-syn conformer to anti-anti con-
former, but this process appears to be unfavorable because of
the repulsive interaction between the bulky o-tolyl moiety of
the coordinated nitrogen atoms with that of the non-
coordinated nitrogen atom. In solution, the three conformers
or more precisely the three rotamers of 3 are in rapid
equilibrium at ambient temperature because of the fast C−
N(H)Ar bond rotation, but upon lowering the temperature,
C−N(H)Ar bond rotation is slowed down because of the
presence of a bulky o-tolyl substituent of the guanidinate ligand
and occurs at a rate comparable with the NMR time scale.
That the three isomers of 3 in solution arise from the C−
N(H)Ar bond rotation rather than from the guanidine centered
rearrangement illustrated in Figure 3 gains further support from
the following points. (i) The C−N(H)Ar distance, 1.372(6) Å
in 3 indicates a single bond character and the N(H)Ar nitrogen
is planar. (ii) The energy requirement for ligand dissociation of
1
Figure 6. VT H NMR spectrum (400 MHz, CD2Cl2) of 3 for the
alkyl protons. The • symbol indicates adventitious proton signal of
H2O.
kcal/mol.58 Thus, complex 3 appears to exist as conformer I
i
wherein the Pr moiety of the p-cymene ring resides exactly
between o-Me substituent of two NcoordAr moieties, and the
guanidinate ligand appears to exist in syn-syn conformation as
found in the solid state.
Half-sandwich ruthenium(II) complexes of the type [(η6-
C10H14)RuCl(EE′)]n+ (EE′: monoanionic bidentate oxygen, and
nitrogen donor ligand or neutral bidentate oxygen and nitrogen
donor ligand; n = 0 or 1)2a,11,53a,55,59−61 were shown to reveal a
pair of doublets for CH(CH3)2 protons and two pairs of
doublets for the p-cymene ring protons, and this spectral
pattern was ascribed to the presence of two diastereomers that
stems from chirality of the ruthenium atom. The ruthenium
atom in 1 and 2 appears to be achiral as only one doublet was
observed for CH(CH3)2 protons and only a pair of doublet was
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a coordinatively saturated low-spin d6 complex of a second or
third row transition metals is rather high (ΔG*⟩ 25 kcal/
mol).64 (iii) Guanidine centered rearrangement converts a
more symmetric syn-syn conformer to a less symmetric syn-anti
conformer, but the observed solution conformation is I wherein
the guanidinate ligand is shown to adopt syn-syn conformation
(see above).
probably formed via the N1 bonded kinetic products of [3 + 2]
cycloaddition reaction.
The 1H NMR spectrum of 10 revealed broad peaks for alkyl/
1
aryl protons, and hence the sample was subjected to a VT H
NMR study (Figure S11 in the Supporting Information). At
233 K, five closely spaced doublets were observed at δH = 0.99,
1.06, 1.10, 1.13, and 1.24 ppm in about 1.0:1·2:2·7:3·5:6·9
ratios assignable to the CH(CH3)2 protons (Figure S12 in the
Supporting Information). The five species could possibly be
assigned to any three conformers from I−L shown in Figure S8
in the Supporting Information with one of them exhibiting a
restricted C−N(H)Ar bond rotation as previously discussed for
3. Although the guanidinate ligand in 4 and 10 revealed syn-anti
conformation in the solid-state, these complexes differ in the
number of solution species, possibly because of the bulkier
triazolate ring in the latter complex that permits both the
restricted ruthenium-arene(centroid) and C−N(H)Ar bond
rotations (Figure S13 in the Supporting Information). The
driving force for the fluxional behavior of 3 and 10 is the steric
overload caused by either the guanidinate ligand conformation
or the substituents around the ruthenium atom or both as
has been shown for [PtMe{κ2(N,N′)(dmphen)}{P(2-MeO-
C6H4)3}]SbF6·H2O [dmphen: 2,9-dimethyl-1,10-phenanthro-
line].68 Thus, it is clear that the number of rotamers in solution
depends upon ligand conformation which in turn depends
upon the bulkiness of the aryl moiety of the guanidinate ligand.
Further, a caveat has appeared sometime ago detailing the
presence of two diastereomers for a chiral complex that stems
from ligand conformation rather than from epimeric chiral
metal center.69
Complex 2 was also subjected to a VT 1H NMR study under
the condition identical to that mentioned previously for 3
(Figure S9 in the Supporting Information). However, no
noticeable change was observed in the 1H NMR pattern of both
alkyl and aryl protons throughout the temperature range
studied. The presence of less bulky o-anisyl substituent in 2
than the o-tolyl substituent in 3 permits a fast C−N(H)Ar bond
rotation in the former, and the rate of this process appears to be
greater than the NMR time scale even at low temperatures
studied. Moreover, the void space encircled by o-OMe
substituent in 2 is greater than that encircled by the o-Me
substituent in 3 (Figure S10 in the Supporting Information).
1
The H NMR spectrum of 2 revealed the presence of three
rotamers in about 1.0:0.05:0.04 ratios in CD3CN as estimated
from the integrals of CH protons of the p-cymene ring.
Perhaps, the NHAr proton in 2 is involved in intermolecular
N−H···N hydrogen bonding with CD3CN, and this would
make the NHAr nitrogen more pyramidal resulting in the
restricted C−NH(Ar) bond rotation even at ambient temper-
ature. The influence of CD3CN upon the number of rotamers
of fluorinated hydrazone is reported in the literature.65
The 1H NMR spectrum of 4 in CDCl3 revealed the presence
of three isomers in about 1.0:1.1:3.8 ratios as estimated from
the integrals of CH(CH3)2 protons, and these three isomers are
assigned to syn-syn, syn-syn a, and syn-syn b isomers as discussed
previously for 3. Probably, complexes such as 3 and 4 possess
only three rotatable Ncoord−C−N(H)−C(Ar) torsion angles
largely because of the steric constraint imposed by the o-Me
substituent of the guanidinate ligand. The barrier for the C−N
bond rotation was shown to be sufficient enough for the
isolation of rotamers of amides with bulky o-substituted aryl
groups.66
CONCLUSIONS
■
Half sandwich ruthenium guanidinate complexes of the types
[(η6-C10H14)RuX(NN)] and [(η6-C10H14)Ru{N3C2(C(O)-
OR)2}(NN)] (X = Cl and N3; NN = chelating N,N′,N″-
triarylguanidinate ligand; R = Me or Et) were isolated in
moderate to high yield, and eight of them were structurally
characterized. The syn-syn isomer of 3 was invoked as a kinetic
product while the syn-anti isomer of 4 was invoked as a
thermodynamic product of the bridge splitting reaction. The
syn-anti isomer of 10 and 8·H2O with N2 bonded triazolate ring
was suggested as a thermodynamic isomer of [3 + 2]
cycloaddition reaction. The ruthenium(II) N,N′,N″-tri(o-sub-
stituted aryl)guanidinate complexes revealed ligand centered
stereochemistry both in the solid-state and in solution. The
substitution pattern, donor property, and steric bulk of the aryl
moiety of the guanidinate ligand dictate the degree of n−π
conjugation between the NHAr/NcoordAr lone pair and the C
Nπ* orbital of the imine unit. In solution, 3 and 4 exist as a
mixture of three rotamers at temperatures ≤253 K and ambient
temperature, respectively, whereas 1 and 2 exist as a single
isomer. Thus, the barrier height for the C−N(H) bond rotation
appears to decrease in the following order: 4 > 3 ≫ 1, and 2.
The donor property of the aryl ring of the guanidinate ligand
dictates the nature of the conformer in the solid-state whereas
the steric property appears to dictate the number of conformers
in solution. To some extent, the donor property of the solvent
also influences the number of rotamers in solution. The greater
number of rotamers in the case of 10 as compared with 4 not
only arises because of steric factor associated with o-tolyl
moiety of the guanidinate ligand but also appears to arise from
the steric encumbrance caused by the substituents around the
ruthenium atom in the former.
1
The H and 13C NMR data of 5, 6, 8·H2O, and 9 in CDCl3
revealed the presence of only one isomer because of the
presence of less bulky p-tolyl substituent in 5 and 8·H2O and o-
anisyl substituent in 6 and 9 that permit a simultaneous and fast
C−N(H)Ar and ruthenium−arene(centroid) bond rotations,
and the rate of these processes appears to be greater than the
NMR time scale. In principle, [3 + 2] cycloaddition reaction of
metal azido complexes with alkynes can give either N1 (or
terminal nitrogen) or N2 (or central nitrogen) bonded metal
triazolate isomers or only N2 bonded metal triazolate isomer. It
has been suggested that the N1 bonded triazolate isomer is a
kinetically controlled product while the N2 bonded triazolate
isomer is a thermodynamically controlled product.67 The
transient formation of both the N(1) and N(2) bonded isomers
and their subsequent conversion to N(2) bonded isomer of
ruthenium(II) triazolate complex was detected by 31P NMR
spectroscopy.37,44 The molecular structures of two N(1)
bonded ruthenium(II) triazolate complexes have been reported
in the literature.42 The 1H NMR data of 8·H2O and 9 revealed
only one type of signal for C(O)OCH2CH3 and C(O)OCH3
protons, respectively, and thus suggested the presence of N2
bonded isomer in solution as well. The N2 bonded isomer of
8·H2O, 9, and 10 could be the thermodynamic products,
167
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C. F.; Schwarz, S.; Mestres, M. G.; Lop
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630, 91−96.
́
ez, S. T.; Strahle, J. Z. Anorg.
̈
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic data in CIF format, H, 13C{1H}, 2D
HETCOR NMR of 2 in CD3CN, Table S1, TGA-DTA
thermogram of 8·H2O, a VT 1H NMR stack plots of 2, 10 and
that of 3 for the p-cymene ring protons, a two-dimensional
1H−1H COSY, DEPT-90 13C NMR spectra of 3, space-filling
views of 2, 3, and 10. This material is available free of charge via
the Internet at http://pubs.acs.org.
1
(11) Marchetti, F.; Pettinari, C.; Pettinari, R.; Cerquetella, A.;
Cingolani, A.; Chan, E. J.; Kozawa, K.; Skelton, B. W.; White, A. H.;
Wanke, R.; Kuznetsov, M. L.; Martins, L. M. D. R. S.; Pombeiro, A. J.
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Pelizzi, C.; Rizzotti, U.; Rogolino, D. Organometallics 2005, 24, 5836−
5844.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: tnat@chemistry.du.ac.in, thirupathi_n@yahoo.com.
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J. L. Organometallics 2011, 30, 1616−1626. (b) Bhambri, S.; Bishop,
A.; Kaltsoyannis, N.; Tocher, D. A. J. Chem. Soc., Dalton Trans. 1998,
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ACKNOWLEDGMENTS
■
The Department of Science and Technology, New Delhi, is
gratefully acknowledged for the research grant (SR/S1/IC−22/
2004 and SR/S1/IC−04/2010). The authors thank the NMR
Research Centre, Indian Institute of Science, Bangalore 560
1
012, for VT H NMR measurements and University Science
Instrumentation Center, University of Delhi, Delhi 110 007, for
NMR, microanalytical, and single crystal X-ray diffraction data
for some complexes. Prof. U. P. Singh, Department of
Chemistry, Indian Institute of Technology Roorkee, Roorkee
247 667, is gratefully acknowledged for X-ray diffraction data of
2−4, and 10.
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