From ruthenium olefin metathesis catalyst to (η5-3- phenylindenyl)hydrido complex via alcoholysis

Article abstract of DOI:10.1039/c3cc49481k

The synthesis and characterisation of [Ru(H)(η⁵-3- phenylindenyl)(ⁱBu-Phoban)₂] 4 is reported ( ⁱBu-Phoban = 9-isobutyl-9-phosphabicyclo-[3.3.1]-nonane). 4 is obtained via alcoholysis of metathesis pre-catalyst M₁₁, in a process that was previously thought to be limited to analogous complex [RuCl ₂(PPh₃)₂(3-phenylindenylidene)] (M ₁₀). The Royal Society of Chemistry.

Full text of DOI:10.1039/c3cc49481k

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From ruthenium olefin metathesis catalyst
5
to (g -3-phenylindenyl)hydrido complex
Cite this:DOI: 10.1039/c3cc49481k
via alcoholysis†
Received 13th December 2013,
Accepted 10th January 2014
a
a
a
b
cd
Simone Manzini, David J. Nelson, Tomas Lebl, Albert Poater, Luigi Cavallo,
a
a
Alexandra M. Z. Slawin and Steven P. Nolan*
DOI: 10.1039/c3cc49481k
www.rsc.org/chemcomm
5
1
The synthesis and characterisation of [Ru(H)(g -3-phenylindenyl)- novel rearrangement process in which the Z -3-phenyl-
i
i
(
Bu-Phoban)
2
] 4 is reported ( Bu-Phoban = 9-isobutyl-9-phosphabicyclo- indenylidene rearranges to yield a ‘piano-stool’-type complex
3.3.1]-nonane). 4 is obtained via alcoholysis of metathesis pre-catalyst [RuCl(Z -3-phenylindenylidene)(PPh ) ] 3 (Scheme 1(a)). Further
5
9
[
3
2
M
11, in a process that was previously thought to be limited to analogous studies have established the utility of this complex in a range of
10–14
complex [RuCl
2
(PPh
3
)
2
(3-phenylindenylidene)] (M10).
transformations.
Seeking to understand if such behaviour is general for
Metathesis is now a staple technique in synthetic chemistry, with a indenylidene-bearing metathesis complexes, we exposed meta-
1
15
range of pre-catalysts available. The detailed understanding of pre- thesis complexes [RuCl
catalyst decomposition pathways is an important way in which to and [RuCl ( Bu-Phoban) (3-phenylindenylidene)] (M )
contribute to the development of the next generation of complexes. bears industrially-important phoban-type ligands) to similar
In many applications, particularly in total synthesis, pre-catalysts conditions (excess NEt3 in refluxing EtOH) (Scheme 1(b) and
2
(PCy
3 2 1
) (3-phenylindenylidene)] (M )
i
16,17
(which
2
2
11
18
2
1
are exposed to a plethora of functional groups, such as alcohols, (c)). While complex M yielded 1, in a manner analogous to the
amines and carboxylic acids. Understanding how complexes behave decomposition of G1, complex M11 yielded a different result,
in such situations is therefore very valuable, and can improve providing what appeared to be a mixture of complexes. A single
our understanding of various aspects of organometallic chemistry. crystal was obtained from a pentane solution during the work-up
The groups of Fogg and Mol have investigated the mechanistic of this reaction; X-ray analysis of these crystals revealed one of the
5
aspects regarding the decomposition of benzylidene metathesis products to be novel complex [Ru(H)(Z -3-phenylindenylidene)-
i
pre-catalysts [RuCl (PCy )(L) (Q CHPh)] (L = PCy , G1 or SIMes, G2) (Bu-Phoban) ] 4 (Fig. 1). The indenylidene ligand had rearranged from
2
3
3
2
1
5
in alcohol solutions to yield hydridocarbonyl complexes Z to Z , with the two phosphines now present in a cis-arrangement
RuCl(H)(CO)(PCy )(L)] (L = PCy , 1 or SIMes, 2) (SIMes = around a ruthenium centre that exhibits ‘piano-stool’ geometry.
,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene), first
[
3
3
1
3–5
reported by Grubbs.
Hydridocarbonyl ruthenium complexes
have shown activity in several reactions, particularly isomerisation,
hydrogenation and various dehydrogenative couplings, potentially
6,7
allowing access to tandem and one-pot methodologies.
While exploring the stability of metathesis pre-catalyst pre-
8
cursor M , which is itself metathesis-inactive, we discovered a
1
0
a
b
c
EaStCHEM School of Chemistry, University of St Andrews, North Haugh,
St Andrews, Fife KY16 9ST, UK. E-mail: snolan@st-andrews.ac.uk
Catalan Institute for Water Research (ICRA), Scientific and Technological Park of
2
the University of Girona, H O Building, Emili Grahit 101, E-17003 Girona, Spain
Department of Chemistry and Biology, University of Salerno,
Via Ponte don Melillo, Fisciano I-84084, Italy
d
KAUST Catalyst Center, Physical Sciences and Engineering Division, King Abdullah
University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
Electronic supplementary information (ESI) available. CCDC 976892 (4). For ESI
†
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3cc49481k
Scheme 1
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Fig. 1 X-ray crystal structure of complex 4; most hydrogen atoms are
omitted for clarity.
The Ru–P distances are shorter here (2.2587(7) and 2.2906(7) Å)
than in 3 (2.296(1) and 2.343(1) Å). 4 bears a hydride instead of the
chloride present in 3, despite their analogous synthetic routes.
i
An optimised reaction procedure, where PrOH was used in
place of EtOH, allowed the isolation of a clean sample of a red
powder in 76% yield; elemental analysis was consistent with 4.
However, NMR analysis suggested that this was in fact a mixture
1
of species; the H NMR spectrum indicated two hydride signals
(
in C
6
D
6
: d
H
= À15.95 ppm, t, J = 32.2 Hz and d = À17.25 ppm,
H
31 1
t, J = 32.2 Hz), while six signals were evident on the P{ H}
NMR spectrum. More detailed NMR experiments were carried
out to ascertain whether the product was truly a mix of species.
3
1
1
31
2
D
P-EXSY and [ H, P]-HMBC experiments (Fig. 2) recorded
at 265 K suggested that the multiple signals were simply a result
of different rotamers being present in solution, due to hindered
restriction around a bond. Unfortunately, it was not possible to
identify the structure of each rotamer by NMR methods. There-
fore, density functional theory (DFT) calculations (at the M06L/
TZVP//BP86/SVP level of theory) were used to identify the three
lowest energy rotamers. Three low-lying minima were identified,
in which the phoban ligand adopts different conformations
1
Fig. 2 NMR spectroscopic analyses of 4 at 265 K in toluene-d
8
31
: (a) [ H,
31
P]-HMBC spectrum optimised for JHP = 30 Hz; and (b) 2D P-EXSY
spectrum showing interconversion between conformers.
(Fig. 3); one places the two isobutyl groups on the opposite side
of the complex from the hydride, one where one isobutyl group
is close to the hydride, and one where both isobutyl groups are
on the same side as the hydride ligand. These have relative
À1
energies of 0, 2.6 and 5.5 kcal mol (respectively), with barriers
À1
to interconversion of 15.7 kcal mol , which is consistent with
the observation of all three rotamers at room temperature. Such
rotational isomerism is known to occur in ruthenium complexes
1
9
bearing phoban-type ligands.
Notably, this complex bears a hydride ligand rather than a
chloride ligand. The bulky ligands present in 4 may serve to
favour the smaller hydride ligand over the chloride. Indeed,
when 3 was re-exposed to the reaction conditions for a prolonged
5
time, hydride species [Ru(H)(Z -3-phenyl-indenyl)(PPh
3 2
) ] 5 was
obtained. 5 has previously been prepared from the reaction of 3
1
1
with excess NaOMe. This suggests that 4 may be formed by
onward reaction of the corresponding chloride, which could not
be isolated.
Fig. 3 DFT-derived conformers for complex 4, and their relative energies
À1
(
in kcal mol ) at the M06L/TZVP//BP86/SVP level of theory, in DCM
The isolation and characterisation of 4 is very interesting for solvent (PCM model).
a number of reasons. Firstly, it is the first example of this
rearrangement process to occur for a metathesis-active complex a pre-catalyst itself. Secondly, the ligand sphere around this
(M11); M10 is a precursor to metathesis pre-catalysts rather than complex is quite different, bearing two rather bulky and
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electron rich trialkylphosphine ligands, rather than two
triarylphosphines.
3 M. B. Dinger and J. C. Mol, Eur. J. Inorg. Chem., 2003, 2827–2833.
4
N. J. Beach, J. A. M. Lummiss, J. M. Bates and D. E. Fogg, Organo-
metallics, 2012, 31, 2349–2356.
In conclusion, we have isolated novel complex 4 from the
alcoholysis of metathesis pre-catalyst M . This species has been
5
N. J. Beach, K. D. Camm and D. E. Fogg, Organometallics, 2010, 29,
5450–5455.
11
1
31
1
6 T. J. Donohoe, T. J. C. O’Riordan and C. P. Rosa, Angew. Chem., Int.
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characterised by methods including detailed H and P{ H} NMR
studies, X-ray crystal diffraction, and DFT. These results show that this
decomposition pathway is not limited to the triphenylphosphine-
containing complex M10, and suggests that a range of such complexes
might be isolated. Detailed further studies are currently underway, in
order to elucidate the factors influencing the preferred decomposition
pathway in ruthenium-alkylidene metathesis pre-catalysts.
7
8
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J. R. Clark, J. R. Griffiths and S. T. Diver, J. Am. Chem. Soc., 2013, 135,
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and S. P. Nolan, Angew. Chem., Int. Ed., 2012, 51, 1042–1045.
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1
1
1
1
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0 S. Manzini, C. A. Urbina-Blanco and S. P. Nolan, Organometallics,
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2
Research leading to these results has received funding from the
European Community’s Seventh Framework Programme (FP7/
2 J. A. Fernand ´e z-Salas, S. Manzini and S. P. Nolan, Chem. Commun.,
2007–2013) under grant agreement no. CP-FP 211468-2 EUMET.
2013, 49, 5829–5831.
SPN thanks the ERC for Advanced Investigator Award ‘FUNCAT’.
SPN is a Royal Society Wolfson Research Merit Award holder. LC
thanks BSC (QCM-2010-2-0020), and the HPC team of Enea for
using the ENEA-GRID and the HPC facilities CRESCO in Portici
3 S. Manzini, D. J. Nelson and S. P. Nolan, ChemCatChem, 2013, 5,
2848–2851.
4 S. Manzini, A. Poater, D. J. Nelson, L. Cavallo and S. P. Nolan, Chem.
Sci., 2014, 5, 180–188.
5 F. Boeda, H. Clavier and S. P. Nolan, Chem. Commun., 2008,
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Chem., 2007, 73, 259–263.
7 G. S. Forman, A. E. McConnell, M. J. Hanton, A. M. Z. Slawin,
R. P. Tooze, W. J. van Rensburg, W. H. Meyer, C. Dwyer, M. M. Kirk
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(
Italy) for access to remarkable computational resources. AP thanks
the Spanish MICINN for a Ram o´ n y Cajal contract (RYC-2009-
4170) and Generalitat de Catalunya for a BE-DGR fellowship. We
0
thank Umicore for gifts of materials and ligands.
1
1
Notes and references
1
2
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2
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Chem. Commun.