Remote coordination approach for electronic tuning of a rhodium(I)-N-heterocyclic carbene (NHC)-complex

Article abstract of DOI:10.1016/j.ica.2019.01.002

A simple Lewis acid coordination at the remote binding site installed within a modular N-heterocyclic carbene (NHC) ligated rhodium(I) complex could induce desired electronic influence and thereby enhance the activity of the complex in a model styrene hyd

Full text of DOI:10.1016/j.ica.2019.01.002

Accepted Manuscript
Research paper
Remote Coordination Approach for Electronic Tuning of a Rhodium(I)-N-Het-
erocyclic Carbene (NHC)–Complex
Ranjeesh Thenarukandiyil, Babulal Maji, Joyanta Choudhury
PII:
S0020-1693(18)31363-X
https://doi.org/10.1016/j.ica.2019.01.002
ICA 18725
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
30 August 2018
1 January 2019
2 January 2019
Please cite this article as: R. Thenarukandiyil, B. Maji, J. Choudhury, Remote Coordination Approach for Electronic
Tuning of a Rhodium(I)-N-Heterocyclic Carbene (NHC)–Complex, Inorganica Chimica Acta (2019), doi: https://
doi.org/10.1016/j.ica.2019.01.002
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Remote Coordination Approach for Electronic Tuning of a Rhodium(I)-N-
Heterocyclic Carbene (NHC)–Complex
*
Ranjeesh Thenarukandiyil, Babulal Maji and Joyanta Choudhury
Organometallics & Smart Materials Laboratory, Department of Chemistry, Indian Institute of Science
Education and Research Bhopal, Bhopal 462 066 (India)
Corresponding author: Joyanta Choudhury (joyanta@iiserb.ac.in). Address: Organometallics & Smart
Materials Laboratory, Department of Chemistry, Indian Institute of Science Education and Research
Bhopal, Bhopal 462 066 (India)
th
Dedication: This work is dedicated to Professor Rabindranath Mukherjee on the occasion of his 65
birthday.
Abstract
A simple Lewis acid coordination at the remote binding site installed within a modular N-heterocyclic
carbene (NHC) ligated rhodium(I) complex could induce desired electronic influence and thereby
enhance the activity of the complex in a model styrene hydroboration reaction.
Graphical Abstract
Keywords
N-Heterocyclic carbene (NHC) / Remote coordination / Rhodium / Lewis acid / Hydroboration
Highlights


A monodentate NHC-rhodium(I) complex was designed with remote free pyridine ligand
Lewis acid coordination at the free pyridine site modulates electronic property of the rhodium
center

Remote coordination thus alters catalytic activity of the complex

1. Introduction
Regulating property and function of a molecule with external stimuli (light, pH, electric potential,
chemical species etc.) represents an alternative and attractive strategy [1], in parallel to the traditional
methods of covalent backbone modification, requiring extensive synthesis, to bring about the desired
changes. The key to such stimuli-controlled regulatory effect is to design a dynamically reversible
molecular platform with a stimuli-responsive functionality which can tune the requisite stereoelectronic
property of the system with utmost precision and delicacy leading to switchable modification. However,
this is a conceptual challenge to the synthetic chemists in contrast to the existence of many such
biological systems. Nevertheless, chemists succeeded in designing such reversible systems primarily via
capitalizing the redox property of a metal or ligand, and introducing pH, light or chemo-sensitive
functional group into the ligand backbone [1]. In the field of catalysis, this promising strategy led to the
inception of a rapidly-developing research area of “artificial switchable catalysis” [1]. In the past,
organometallic chemists applied redox-active and chemo-active phosphine- and nitrogen-based ligands to
design remote-controlled catalysis [1]. Very recently, influenced by an all-round tremendous success of
N-heterocyclic carbene (NHC) ligands, the idea of introducing stimuli-sensitive functional groups onto
NHCs to achieve switchable catalysis has received much attention. The major successes so far are in the
domain of light-, redox-, and pH-responsive systems as developed by many leading research groups
including our group [2, 3]. In parallel, we have programmed our efforts to apply a “remote coordination
approach” as a platform to regulate electronic property and catalytic activity of metal–NHC complexes
[
4]. We have demonstrated how a reversible coordination (by acid or metal center) at a remote pyridine
site of a metal-bound NHC ligand could fine-tune the electronic property of the active center which is
considered as prerequisite for switchable catalysis. Notably, in supramolecular chemistry, “weak-link
approach” utilises coordination-induced structural changes and resulting allosteric effect to tune catalysis
[
5]. Several other catalytic and stoichiometric reactions, such as polymerization [6], hydrogenation [7],
reductive elimination [8] etc. were also found to be triggered by the strategy of remote Lewis acid
binding. Herein, we demonstrate the tuning of electronic property of a rhodium(I)–NHC complex
consisting of a free-pyridine site via remote-coordination approach, followed by its effect in catalytic
alkene-hydroboration reaction (Fig. 1).
Fig. 1. Lewis acid coordination at a remote site as a stimulus for tuning property and activity at an active
catalytic metal center of a metal-NHC complex

2. Experimental
2.1. General methods and materials
1
13
1
H and C{ H} NMR spectra were recorded on Bruker AVANCE III 400 MHz NMR spectrometer at
room temperature unless mentioned otherwise. Chemical shifts (δ) are expressed in ppm using the
1
residual proton resonance of the solvent as an internal standard (CHCl : δ = 7.26 ppm for H spectra, 77.2
3
1
3
1
1
1
ppm for C{ H} spectra). All coupling constants (J) are expressed in hertz (Hz) and only given for H- H
couplings unless mentioned otherwise. The following abbreviations were used to indicate multiplicity: s
(
singlet), d (doublet), m (multiplet). ESI mass spectrometry was performed on a Bruker microTOF QII
spectrometer. Electrochemical experiments were done using CHI 620E Electrochemical Analyzer.
Deuterated solvents and RhCl .xH O were purchased from Aldrich. [RhCl(COD)] [9], compound 1 [4a],
3
2
2
complex 2 [4a], [IrCp*Cl ] [10], and [RhCp*Cl ] [11] were synthesized according to reported
2
2
2 2
procedures.
.2. Synthesis of Complex 3
A mixture of 2 (60 mg, 0.2 mmol) and [RhCl(COD)] (49 mg, 0.1 mmol) in degassed CH Cl (10 mL)
2
2
2
2
was stirred under N for 24 h. The reaction mixture was then filtered through a Celite plug and the solvent
2
was removed under vacuum, resulting in the desired product as a solid compound. The compound was
purified by precipitation from CH Cl -hexane. Pale yellow solid thus obtained was dried in vacuo. Yield:
2
2
1
8
2
0 mg (98%). H NMR (400 MHz, CDCl ): δ (ppm) = 8.81 (d, J = 6.1 Hz, 2H, CH ), 8.36 (d, J = 6.1 Hz,
3 pyr
H, CH ), 7.21 (d, J = 1.9 Hz, 1H, CH ), 7.04 (d, J = 1.9 Hz, 1H, CH ), 5.18 (m, 1H, CHCOD), 5.04
pyr
imz
imz
(
m, 1H, CHCOD), 4.26 (s, 3H, CH3imz), 3.23 (m, 1H, CHCOD), 2.52 (m, 1H, CHCOD), 2.45-2.17 (mbroad, 3H,
1
3
1
CH2COD), 1.90-1.55 (mbroad, 5H, CH2COD). C{ H} NMR (100 MHz, CDCl ): δ (ppm) = 185.7 (d, J
=
Rh-C
3
5
1.0 Hz, NCN), 151, 146.9, 123.9, 120.2, 118.6, 99.2 (d, JRh-C = 7 Hz, CHCOD), 98.7 (d, JRh-C = 7 Hz,
+
CHCOD), 68.9-68.7 (2 doublets, CHCOD), 39.0, 33.4, 32.0, 29.2, 28.6. HRMS (ESI, positive ion): M =
+
370.0803 (calculated 370.0790 for [C H N Rh] . Anal. Calcd for C H ClRhN (%): C, 50.32; H, 5.22;
17 21 3 17 21 3
N, 10.36. Found: C, 49.81; H, 5.17; N, 9.48).
2.3. Single crystal X-ray diffraction analysis of 3
Crystals of complex 3 suitable for single-crystal X-ray diffraction were obtained by diffusing hexane into
the CH Cl solution of complex 3 at ambient temperature. Single-crystal X-ray diffraction data were
2
2
collected using a Bruker SMART APEX II CCD diffractometer with graphite monochromated Mo Kα (λ
0.71073 Å) radiation at low temperature. Structure was solved with direct methods using SHELXS-97
=
2
and refined with full-matrix least-squares on F using SHELXL-97 [12]. Full crystallographic data of 3
CCDC 995437) can be obtained free of charge from The Cambridge Crystallographic data Center via
www.ccdc.cam.ac.uk/data_request/cif.
(
2
.4. Remote coordination of Lewis acid B(C F ) to Complex 3:
6 5 3
With tris pentafluorophenylborane (B(C F ) ): Complex
3
(3 mg, 7.4 µmol) and tris
6
5 3
pentafluorophenylborane (3.6 mg, 7.4 µmol) was added to an NMR tube and dissolved in CDCl (0.5
3
1
mL). The mixture was shaken well and the coordination was monitored by H NMR spectroscopy.

2.5. Electrochemical studies
The electrochemical measurements were carried out by a CHI Instrument (CHI 620E Electrochemical
Analyzer) at ambient temperature using a three electrode configuration (working electrode: Pt disk (1 mm
diameter); counter electrode: a Pt wire; reference electrode: saturated calomel electrode, SCE). All the
samples were prepared in dry acetonitrile (MeCN) and deoxygenated for 5 minutes with nitrogen gas
before starting the actual experiments. 1.0 mM solution of complex 3 and 0.02 mM solution of B(C F )
6
5 3
were used for the study. A 0.1 M solution of [NBu ]PF in dry DCE was used as the supporting
4
6
+
electrolyte. Ferrocene (E , Fc/Fc = 0.436 volts vs SCE) was used as external calibration standard for all
1/2
the measurements.
2.6. Catalytic studies
In a 5 mL Schlenk tube complex 3 (0.005 mol) or a mixture of complex 3 (0.005 mmol) and B(C F )
6
5 3
(
(
0.005 mmol) was taken and DCE (2 mL) was added to it. After that styrene (0.5 mmol) and mesitylene
0.5 mmol; used as an internal NMR standard) were added to the flask. Next, pinacolborane (1.25 mmol)
was added quickly and the mixture was started to stir at 30 °C. After the desired time intervals, small
volumes of aliquots were withdrawn, dissolved in CDCl , and the yields of the various products were
3
1
determined by H NMR spectroscopy.
3. Results and discussion
I
The modular Rh –NHC complex, 3 was synthesized by employing the versatile silver transmetalation
route. Thus, a reaction of the Ag–NHC complex 2 with 0.5 equiv. of rhodium(I) dimer, [(1,5-
I
COD)RhCl] in dichloromethane at ambient temperature afforded the Rh –NHC complex 3 exclusively in
2
excellent yield (Scheme 1). It is noteworthy that the free pyridine appended within the ligand did not
coordinate to rhodium(I) center and hence could be utilized for further controlled coordination of suitable
I
Lewis acids to tune the electronic property of the central metal. A similar Rh -NHC complex was reported
previously for binding of Zinc(II)-complexes [13]. Our group previously explored this ligand in the
III
context of catalytic annulation reactions wherein a bimetallic Rh -NHC complex was synthesized
III
consisting of the remote pyridine coordination by a Cp*Rh -fragment [14].
Scheme 1. Synthesis of complex 3. Reaction conditions: (a) Ag O, CH Cl -CH OH, 27 °C, 4 h, dark. (b)
2
2
2
3
I
[
Rh Cl(COD)] , CH Cl , 27 °C, 24 h.
2 2 2
1
13
1
Full characterization of complex 3 was accomplished by H and C{ H} NMR spectroscopy, high
resolution electrospray ionization mass spectroscopy (HR ESI-MS) and single-crystal X-ray diffraction
1
analyses. The H NMR spectrum of 3 in CDCl exhibited two doublets at 8.81 and 8.36 ppm respectively
3

with a coupling constant value of 6.1 Hz which correspond to the two sets of pyridyl backbone protons.
Four non-equivalent olefinic COD resonances at 5.18, 5.04, 3.23 and 2.52 ppm suggested a restricted
rotation of the NHC motif around the Rh–Ccarbene bond in 3. Moreover, the strong trans influencing NHC
ligand resulted in more downfield shifts of the corresponding trans-olefinic protons (at 5.18 and 5.04
1
3
1
ppm) as compared to the cis ones (at 3.23 and 2.52 ppm) (Fig. 2). The characteristic C{ H} NMR signal
of the Rh–Ccarbene carbon appeared at a much downfield region of 185.7 ppm as a doublet (JRh-C = 51 Hz)
1
due to coupling with the Rh atom. As in the H NMR spectrum, the olefinic COD carbons trans to NHC
resonated at more downfield region (99.2 and 98.7 ppm) than those cis to it (68.9-68.7 ppm) (see
Supplementary Information). The characteristic NMR chemical shift values (e.g., Rh-Carbene carbon)
were found similar to the previously reported Rh(COD)(NHC) complexes [13,15,16,17] The positive ion
electrospray ionization (ESI) mass spectrum of 3 exhibited a major intense peak at m/z = 370.0803
+
+
assigned to [M−Cl] (calcd for [3−Cl] 370.0790) (see Supplementary Information). A single crystal X-
ray diffraction study of complex 3 unambiguously confirmed the structural arrangement within the
8
molecule (Fig. 3). The coordination geometry around the d , 16e⁻ rhodium(I) center is square-planar
arranged with the NHC-carbon, the bidentate COD, and the chloro ligands. The distance between metal
center and olefinic group of COD which is trans to NHC group is much longer than other olefinic part as
expected from stronger trans influence of NHC compared to the chloro ligand. The Rh(I)‒Ccarbene bond
distance of 2.011(3) Å is slightly shorter than that reported for analogous Rh(I) complexes [13,15,16,17].
1
Fig. 2. H NMR spectrum of complex 3 (400 MHz, CDCl , 300 K).
3

Fig. 3. Molecular structure of complex 3. Selected bond lengths (Å) and angels (deg): C1‒Rh1 =
.011(3), Cl1‒Rh1 = 2.4013(9), C10‒Rh1 = 2.113(4), C11‒Rh1 = 2.118(3), C14‒Rh1 = 2.174(4),
2
C15‒Rh1 = 2.191(4), N1‒C1‒N2 = 103.7(3), C1‒Rh1‒Cl1 = 87.93(10), N1‒C1‒Rh1 = 128.2(3),
N2‒C1‒Rh1 = 128.1(3). CCDC 1465253, contains the supplementary crystallographic data for 3. These
data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Next we sought to investigate the remote coordination of Lewis acid B(C F ) , at the free pyridine site of
6
5 3
3
leading to the proposed formation of the adduct 3.LA (LA = Lewis acid, B(C F ) ) and its influence on
6 5 3
1
the electronic property of 3 (Scheme 2). The H NMR spectroscopic monitoring of such remote
coordination effect showed a good degree of downfield shifts of the pyridyl protons as well as the
imidazole backbone protons of the NHC–pyridyl scaffold in complex 3 upon gradual addition of
incremental amounts of B(C F ) in CDCl at ambient temperature (Fig. 4). This fact suggested a
6
5 3
3
plausible coordination of B(C F ) to the open pyridine ligand and thereby inducing a substantial
6
5 3
electron-deficiency into the system. Presumably, addition of one equivalent of Lewis acid completed
the formation of the proposed 3·LA adduct (Scheme 2) and after that no more change was observed
(
Figure 4).
Scheme 2. Coordination of Lewis acid B(C F ) to the free pyridine site of 3.
6
5 3

1
Fig. 4. H NMR (500 MHz, CDCl , 300 K) monitoring for controlled addition of B(C F ) to complex 3:
3
6 5 3
(
a) free complex, (b) 0.25 equiv., (c) 0.50 equiv., (d) 1.0 equiv., (e) 1.25 equiv., and (f) 1.50 equiv. of
B(C F ) .
6
5 3
After this NMR spectroscopic experiment, influence of such effect toward electronic perturbation directly
at the metal center (Rh) of complex 3 was evaluated further by electrochemical method which is an
I
II
extremely sensitive probe. The half-wave potential (E ) values of the Rh /Rh redox couple for free
1
/2
complex 3 [16,17], and the B(C F ) -coordinated 3, derived from differential pulse voltammetry (DPV)
6
5 3
are shown in Fig. 5 (obtained via gradual addition of a 0.02 mM solution of B(C F ) to a 1.0 mM
6
5 3
solution of complex 3). It was clearly evident from the study that coordination at the remote pyridine site
generated an electron-poor, less-donating NHC ligand compared to the free system. This trend was
I
II
ascertained from the higher Rh /Rh redox potential values in B(C F ) -coordinated 3 (E = 0.752 V vs
6
5 3
1/2
SCE in acetonitrile) by 40 mV compared to the free complex 3 (E1/2 = 0.712 V vs SCE in acetonitrile).

Complex 3 only
Complex 3+0.25 equiv. LA
Complex 3+0.50 equiv. LA
Complex 3+1.0 equiv. LA
Complex 3+ 1.25 equiv. LA
Complex 3+1.50 equiv. LA
3.0
2.0
1.0
0.0
0.0
0.4
0.8
1.2
1.6
Potential (V)
Fig. 5. DPV plots of complex 3 and its coordination study with B(C F ) (1 mM of complex 3 and 0.02
6
5 3
mM of B(C F ) in dry MeCN with 0.1 M [NBu ][PF ] as the supporting electrolyte; Ferrocene (E ,
6
5 3
4
6
1/2
+
Fc/Fc = 0.427 V vs. SCE) was used as external calibration standard). The additional peak at the higher
positive potential 1.2 V (vs SCE) for complex 3 might be due to the Cl-dissociated solvated complex [18].
Attempts were made to isolate the proposed 3·B(C F ) adduct (Scheme 2) and characterize the same.
6
5 3
1
19
After a few attempts, it was isolated and characterized by H and F NMR spectroscopy and also by CHN
1
19
analysis (see Supplemenatry Information). The changes in the H and F NMR chemical shift values for
the adduct from the free complex 3 and free B(C F ) respectively, suggested the formation of the
6
5 3
1
proposed adduct. Moreover, as expected, in the H NMR spectrum, the corresponding chemical shifts of
the characteristic protons matched well with the same as observed during the in-situ solution studies
described above.
Finally, a control complex 4 has been synthesized in which the 4-pyridyl substituent of the NHC ligand
was replaced with a phenyl group, and some control NMR and DPV experiments were performed. As
1
expected, during the H NMR spectroscopic monitoring, addition of the Lewis acid B(C F ) to the
6
5 3
solution of the control complex 4 effectively did not show shifts of the characteristic protons of the
phenyl ring and the imidazole ring, except some broadening effect as observed for the phenyl protons at
8.15 ppm (see Supplementary Information). Similarly, in the DPV experiment, the shift of redox potential
for the control complex 4 upon addition of Lewis acid B(C F ) (LA) was found to be negligible (see
6
5 3
Supplementary Information). These experiments suggested that for complex 3, the pyridine coordination
was relevant for the observed electronic effect upon Lewis acid addition.
After confirming the proposed remote-coordination-induced tuning of electronic property at the metal
center in complex 3 as demonstrated above, a model catalytic reaction was conducted to examine the
feasibility of translating such modulation into practical application. Rh(I)-catalyzed hydroboration of
styrene with pinacolborane (HBPin) was selected for this model study. As is evident from Fig. 6, the
catalytic activity was substantially increased with 3•B(C F ) catalyst system as compared to 3. However
6
5 3
the selectivity was not influenced much. The enhancement of activity might be due to an accelerated

reductive elimination step (proposed to be rate-determining in this type of olefin-hydroboration
catalysis)[19,20] with the electron-deficient catalytic metal center in 3•B(C F ) . A detailed investigation
6
5 3
toward the mechanistic aspect of such an accelerating effect will be the subject of future study.
1
Fig. 6. Catalytic hydroboration results. Yields were calculated by H NMR spectroscopy using an internal
standard. No conversion of styrene was observed in the absence of catalyst (with only B(C F ) ), or in the
6
5 3
absence of catalyst+B(C F ) .
6
5 3
4. Conclusion
In conclusion, this study demonstrated a simple strategy of remote coordination of chemical entity to tune
the electronic property of a metal complex, thus avoiding any pre- or post-synthetic structural
modification within the ligand backbone. It was observed that such coordination resulted in electron-
deficiency at the central metal center, as probed by NMR spectroscopy and electrochemical analysis.
Finally, it was also found that activity of the metal center toward a model catalytic styrene hydroboration
reaction could be influenced via such strategy. An in-depth understanding of the actual mechanistic
details as well as expanding this useful approach toward other application are the next goal of our
laboratory.
Acknowledgements

J.C. sincerely thanks DST-SERB (grant no. EMR/2016/003002) and IISER Bhopal for generous financial
support. R.T. and B.M. thank UGC, Govt. of India for fellowship. We sincerely thank the anonymous
reviewers for several constructive comments and suggestions.
Appendix
Supplementary content
Supplementary information containing spectral traces are available.
References
[
1]
Semwal, S. Synlett 2018, 29, 141−147; (c) Blanco, V.; Leigh, D. A.; Marcos, V. Chem. Soc. Rev.
015, 44, 5341−5370; (d) Neilson, B. M.; Bielawski, C. W. ACS Catal. 2013, 3, 1874−1885; (e)
For reviews, see: (a) Choudhury, J. Tetrahedron Lett. 2018, 59, 487−495; (b) Choudhury, J.;
2
Teator, A. J.; Lastovickova, D. N.; Bielawski, C. W. Chem. Rev. 2016, 116, 1969−1992; (f)
Romanazzi, G.; Degennaro, L.; Mastrorilli, P.; Luisi, R. ACS Catal. 2017, 7, 4100−4114; (g) Teator,
A. J.; Bielawski, C. W. J. Polym. Sci. Part A: Polym. Chem. 2017, 55, 2949–2960; (h) Yu, Z.; Hecht,
S. Chem. Commun. 2016, 52, 6639−6653; (i) Guillaume, S. M.; Kirillov, E.; Sarazin, Y.; Carpentier,
J-F. Chem. Eur. J. 2015, 21, 7988−8003; (j) Wang, F.; Liu, X.; Willner, I. Angew. Chem. Int. Ed.
2
015, 54, 1098−1129; (k) Schmittel, M. Chem. Commun. 2015, 51, 14956−14968; (l) Lifschitz, A.
M.; Rosen, M. S.; McGuirk, C. M.; Mirkin, C. A. J. Am. Chem. Soc. 2015, 137, 7252−7261; (m)
Göstl, R.; Senf, A.; Hecht, S. Chem. Soc. Rev. 2014, 43, 1982−1996; (n) Leibfarth, F. A.; Mattson,
K. M.; Fors, B. P.; Collins, H. A.; Hawker, C. J. Angew. Chem. Int. Ed. 2013, 52, 199−210; (o) Stoll,
R. S.; Hecht, S. Angew. Chem. Int. Ed. 2010, 49, 5054−5075; (p) Lüning, U. Angew. Chem. Int. Ed.
2
012, 51, 8163–8165.
[
2] (a) Benhamou, L.; César, V.; Gornitzka, H.; Lugan, N.; Lavigne, G. Chem. Commun. 2009
,
4
720–4722; (b) Benhamou, L.; Vujkovic, N.; César, V.; Gornitzka, H.; Lugan, N.; Lavigne, G.
Organometallics 2010, 29, 2616–2630; (c) Biju, A. T.; Hirano, K.; Fröhlich, R.; Glorius, F. Chem.
Asian J. 2009, 4, 1786–1789; (d) Neilson, B. M.; Lynch, V. M.; Bielawski, C. W. Angew. Chem. Int.
Ed. 2011, 50, 10322–10326; (e) Rosen, E. L.; Varnado Jr., C. D.; Tennyson, A. G.; Khramov, D. M.;
Kamplain, J. W.; Sung, D. H.; Cresswell, P. T.; Lynch, V. M.; Bielawski, C. W. Organometallics
2
009, 28, 6695–6706; (f) Khramov, D. M. ; Rosen, E. L.; Lynch, V. M.; Bielawski, C. W. Angew.
Chem. Int. Ed. 2008, 47, 2267–2270; (g) Vujkovic, N.; César, V.; Lugan, N.; Lavigne, G. Chem.
Eur. J. 2011, 17, 13151–13155.
[
3] (a) Neilson, B. M.; Bielawski, C. W. J. Am. Chem. Soc. 2012, 134, 12693–12699; (b) Neilson, B.
M.; Bielawski, C. W. Organometallics 2013, 32, 3121–3128; (c) Neilson, B. M.; Bielawski, C. W.
Chem. Commun. 2013, 49, 5453–5455; (d) Neilson, B. M.; Bielawski, C. W. ACS Catal. 2013, 3,
1
874–1885; (e) Süβner M.; Plenio, H. Angew. Chem. Int. Ed. 2005, 44, 6885–6888; (f) Tennyson, A.
G.; Lynch V. M.; Bielawski, C. W. J. Am. Chem. Soc. 2010, 132, 9420–9429; (g) Balof, S. L.; Yu,
B.; Lowe, A. B.; Ling, Y.; Zhang, Y.; Schanz, H-J. Eur. J. Inorg. Chem. 2009, 1717–1722.
[
9
4] (a) Mondal, M.; Ranjeesh, T. K.; Gupta, S. K.; Choudhury, J. Dalton Trans. 2014, 43, 9356-
362; (b) Gupta, S. K.; Choudhury, J. Chem. Commun. 2016, 52, 3384-3387; (c) Mondal, M.; Joji,
J.; Choudhury, J. Chem. Commun. 2017, 53, 3185-3188.

[
[
5] Gianneschi, N. C.; Masar, M. S.; Mirkin, C. A. Acc. Chem. Res. 2005, 38, 825−837.
6] (a) Lee, B. Y.; Bazan, G. C.; Vela, J.; Komon, Z. J. A.; Bu, X. J. Am. Chem. Soc. 2001, 123,
352 5353; (b) Kim, Y. H.; Kim, T. H.; Lee, B. Y.; Woodmansee, D.; Bu, X.; Bazan, G. C.
Organometallics 2002, 21, 3082 3084; (c) Azoulay, J. D.; Koretz, Z. A.; Wu, G.; Bazan, G. C.
Angew. Chem., Int. Ed. 2010, 49, 7890 7894; (d) Escobar, M. A.; Trofymchuk, O. S.; Rodriguez, B.
E.; Lopez-Lira, C.; Tapia, R.; Daniliuc, C.; Berke, H.; Nachtigall, F. M.; Santos, L. S.; Rojas, R. S.
ACS Catal. 2015, 5, 7338 7342; (e) Trofymchuk, O. S.; Gutsulyak, D. V.; Quintero, C.; Parvez, M.;
Daniliuc, C. G.; Piers, W. E.; Rojas, R. S. Organometallics 2013, 32, 7323 7333.
5
−
−
−
−
−
[
7] (a) Jiang, Y.; Hess, J.; Fox, T.; Berke, H. J. Am. Chem. Soc. 2010, 132, 18233
Y.; Huang, W.; Schmalle, H. W.; Blacque, O.; Fox, T.; Berke, H. Organometallics 2013, 32,
043 7052; (c) Jiang, Y.; Schirmer, B.; Blacque, O.; Fox, T.; Grimme, S.; Berke, H. J. Am. Chem.
Soc. 2013, 135, 4088 4102.
−18247; (b) Jiang,
7
−
−
[
8] (a) Liberman-Martin, A. L.; Bergman, R. G.; Tilley, T. D. J. Am. Chem. Soc. 2013, 135,
612 9615; (b) Liberman-Martin, A. L.; Levine, D. S.; Liu, W.; Bergman, R. G.; Tilley, T. D.
Organometallics 2016, 35, 1064 1069.
9
−
−
[
[
9] Giordano, G.; Crabtree, R.H. Inorg. Synth. 1979, 19, 218–220.
10] Ball, R. G.; Graham, W. A. G.; Heinekey, D. M.; Hoyano, J. K.; McMaster, A. D.; Mattson, B.
M.; Michel, S. T. Inorg. Chem. 1990, 29, 2023–2025.
[
[
[
11] Du, Y.; Hyster, T. K.; Rovis, T. Chem. Commun. 2011, 47, 12074–12076.
12] Sheldrick, G. M. Acta Crystallogr. Sect. A 2008, 64, 112–122.
13] Rubio, M.; Jellema, E.; Siegler, M. A.; Spek, A. L.; Reek, J. N. H.; de Bruin, B. Dalton Trans.
2
009, 8970–8976.
[
[
[
[
[
14] Thenarukandiyil, R.; Choudhury, J. Organometallics 2015, 34, 1890−1897.
15] Yu, X-Y.; Patrick, B. O.; James, B. R. Organometallics 2006, 25, 2359-2363.
16] Mejuto, C.; Guisado-Barrios, G.; Peris, E. Organometallics 2014, 33, 3205−3211.
17] Peng, H. M.; Webster, R.D.; Li, X. Organometallics 2008, 27, 4484–4493.
18] Brewster, T. P.; Blakemore, J. D.; Schley, N. D.; Incarvito, C. D.; Hazari, N.; Brudvig, G. W.;
Crabtree, R. H. Organometallics 2011, 30, 965–973.
[
[
19] Evans, D. A.; Fu, G. C.; Anderson, B. A. J. Am. Chem. Soc. 1992, 114, 6679-6685.
20] Musaev, D. G.; Mebel, A. M.; Morokuma, K. J. Am. Chem. Soc. 1994, 116, 10693-10702.