R-Group reversal of isomer stability for RuH(X)L2(CCHR) vs. Ru(X)L2(CCH2R): Access to four-coordinate ruthenium carbenes and carbynes

Article abstract of DOI:10.1039/b006971j

NaOPh converts equimolar RuHClL₂(=C=CHR) (L=PPr₃/ⁱ and PCy₃) first to RuH(OPh)L₂(=C=CHR), but then, only for R = H, these isomerize to the more stable carbynes Ru(OPh)L₂(C-CH₃); the rate of isomerization is slowed considerably by THF. RuH(OPh)L₂(=C=CHR) can also be synthesized by reaction of RuCl₂L₂[=CH(CH₂R)] with 2 NaOPh; again, only when R = H does the hydrido vinylidene isomerize to the carbyne. While phenoxide converts RuCl₂L₂(=CHPh) to Ru(OPh)L₂(CPh), via the observable intermediates RuCl_2-n(OPh)_nL₂(=CHPh), alkoxides OBuⁱ and OAdamantyl cause phosphine displacement to give the four-coordinate carbenes Ru(OR)₂L(=CHPh). DFT (B3PW91) calculations show these d⁶ species have a traditional cis-divacant octahedral structure with trans OR groups.

Full text of DOI:10.1039/b006971j

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R-Group reversal of isomer stability for RuH(X)L (CCHR) vs.
2
Ru(X)L (CCH R): access to four-coordinate ruthenium carbenes and
2
2
carbynes¤
Joseph N. Coalter, III,a John C. Bollinger,a Odile Eisenstein*b and Kenneth G. Caulton*a
L e t t e r
a Department of Chemistry and the Molecular Structure Center, Indiana University, Bloomington,
IN 47405-7102, USA. E-mail: caulton=indiana.edu
b L aboratoire de Structure et Dynamique des Systemes Moleculaires et Solides
(CNRS UMR 5636), Universite de Montpellier 2, 34095 Montpellier cedex 5, France.
E-mail: eisenst=lsd.univ-montp2.fr
Received (in New Haven, CT, USA) 23rd August 2000, Accepted 15th September 2000
First published as an Advance Article on the web 6th November 2000
NaOPh converts equimolar RuHClL (2C2CHR) (L = PPri
the range [14 to [17 ppm, shifted slightly from those of the
2
3
and PCy ) Ðrst to RuH(OPh)L (2C2CHR), but then, only for
parent chloride compound and displaying similar J values.
3
2
PH
R = H, these isomerize to the more stable carbynes
Ru(OPh)L (C–CH ); the rate of isomerization is slowed con-
Aromatic signals for the new phenoxide ligand are present,
and the characteristic vinylidene and 31P resonances are seen.
2
3
siderably by THF. RuH(OPh)L (2C2CHR) can also be synthe-
Remarkably, when R \ H (and L \ PPri or PCy ), the new
2
3
3
sized by reaction of RuCl L [2CH(CH R)] with 2 NaOPh;
complexes spontaneously isomerize within \1 h in arene sol-
vents to four-coordinate carbynes Ru(OPh)L (CÈCH ); no
2 2
2
again, only when R = H does the hydrido vinylidene isomerize
2
3
to the carbyne. While phenoxide converts RuCl L (2CHPh) to
such rearrangement for the R \ Ph complexes is seen at room
or higher temperatures or in the presence of added NEt [eqn.
2 2
Ru(OPh)L (CPh),
¿ia
the
observable
intermediates
2
3
RuCl (OPh) L (2CHPh), alkoxides OBut and OAdamantyl
(2)]. The parent chlorides (R \ H or Ph) also show no ten-
2—n
n 2
cause phosphine displacement to give the four-coordinate carb-
dency to isomerize to carbyne. For example, immediate NMR
observation of samples of RuHClL (CCH ) that were treated
enes Ru(OR) L(2CHPh). DFT (B3PW91) calculations show
2
2
2
these d6 species have a traditional cis-divacant octahedral struc-
with NaOPh in C D (L \ PPri ; a drop of THF-d was
6
6
3
8
ture with trans OR groups.
added for rapid NaOPh solubility) showed the major ([90%)
product was RuH(OPh)L (CCH ), but isomerization to
2
2
For more than a decade, Ðve-coordinate vinylidene complexes
carbyne quickly ensued. The isomerization does proceed in
of the type Ru(X)(Y)L (2C2CRR@) (L \ phosphine) have been
THF, but at a much slower rate (t B days).
2
1@2
proposed as intermediates in or used as catalyst precursors for
many useful organometallic transformations, though isomeric
four-coordinate carbynes Ru(X)L (CÈC(Y)RR@) remained
2
unknown.1 A recent study investigated the possibility that
such isomers, which were shown through DFT calculations to
be of similar (within ^3 kcal mol~1) energy, might exist in
rapid (t D 1 s) equilibrium through 1,3-H shifts (Y \ H);
(2)
1@2
this was proven to be false [see eqn. (1), which gives the acti-
vation energy for unimolecular hydrogen migration].2 We
now detail the synthesis and characterization of such unsatu-
rated four-coordinate carbynes, Ru(X)L (CÈCH R), and illus-
2 2
X and R in determining the
trate the inÑuence of
thermodynamic preference over a hydrido vinylidene. A corol-
lary study of X ligand replacement in RuCl (2CHPh)L
reveals unprecedented phosphine loss behavior, yielding a
2
2
The new carbynes are characterized by the lack of a high-
Ðeld 1H signal and no diastereotopic phosphine alkyl signals
by 1H or 13C NMR, suggesting a planar structure, and only
three aromatic 1H NMR signals are observed for the OPh
four-coordinate carbene Ru(2CHPh)(OR) L.
2
unit. The RuCCH protons appear in the characteristic region
3
(1)
of 0.0 to [0.5 ppm5 with resolved 4J values of 3 or 4 Hz;
PH
13C NMR shows the a and b carbons of the ethylidyne moiety
at 261 (J \ 21 Hz) and 28 ppm, respectively (L \ PCy ).
PC
3
The 31P NMR spectra shows singlets at 55 and 46 ppm for
L \ PPri and PCy , respectively.
Hydrido vinylidene complexes RuHClL (2C2CHR) (L \
2
PPri , PCy ; R \ H, Ph)3,4 react cleanly with NaOPh in
3
3
3
3
During the course of our investigation, we reasoned that
toluene or THF at room temperature to Ðrst form simple
vinylidenes RuH(OPh)L (2C2CHR) should be accessible by
halide-metathesis products RuH(OPh)L (2C2CHR). These
2
2
dehydrohalogenation of the carbenes RuCl L [2CH(CH R)]
species are characterized by 1H NMR hydride resonances in
2 2
2
since treatment of the former with HCl readily generates the
carbenes.4 Addition [eqn. (3)] of NaOPh to THF solutions of
RuCl L (2CHCH ) (2 : 1 mole ratio),6 with L \ PPri , gener-
¤ Electronic supplementary information (ESI) available: complete
experimental and computational details. See http://www.rsc.org/
suppdata/nj/b0/b006971j/
2 2
free
3
3
complex
ates
phenol
and
the
vinylidene
DOI: 10.1039/b006971j
New J. Chem., 2000, 24, 925È927
925
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2000

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RuH(OPh)L (CCH ) within 1 h at 25 ¡C, which persists, in
agreement with the above observations for isomerization in
characterized by NMR with the lack of a high-Ðeld 1H signal,
no diastereotopic 1H or 13C signals for the phosphine ligands,
2
2
T HF. However, when RuCl L (2CHCH ) was mixed with
and aromatic resonances consistent with C
symmetry.
2 2
3
2v
NaOPh (1 : 2 mole ratio) in C D , the isomeric carbyne
Again, 31P NMR shows only singlets at 55 and 44 ppm, and
6 6
Ru(OPh)L (CCH ) was formed after 12 h and only a trace
the RuCPh carbon (L \ PPri ) resonates at 248 ppm in 13C
2
3
3
amount of vinylidene was present. Consistent with the results
above with R \ Ph, treatment of the benzyl substituted
carbene, RuCl L [CH(CH Ph)], with NaOPh yields clean
conversion to vinylidene complex RuH(OPh)L (CCHPh) in
either solvent, but no subsequent isomerization to carbyne.
NMR (t, J \ 20 Hz), again shifted ca. 40 ppm upÐeld with a
PC
large PÈC coupling relative to other Ru carbynes.8 To verify
our proposed atom connectivity and planar geometry for
these novel complexes, we determined the structure of
2 2
2
2
Ru(OPh)(PPri ) (CPh) by X-ray crystallography (Fig. 1).9
3 2
The presence of liberated HOPh when preparing the hydrido
vinylidenes from carbenes [eqn. (3)] shows little e†ect on the
rate of isomerization (with R \ H).
(4)
(3)
Aliphatic alkoxides show remarkably di†erent behavior
[eqn. (4b)]. The carbenes RuCl L (2CHPh), with L \ PPri or
2 2
3
PCy , react (3 h, THF) with sodium alkoxides (NaOR;
The dramatic rate decrease in the isomerization of
RuH(OPh)L (CCH ) to Ru(OPh)L (CCH ) in THF solvent
suggests that its donor potential might act to hinder the H
3
R \ But or adamantyl) to form four-coordinate carbene com-
plexes, Ru(OR) L(2CHPh) with liberation of equimolar free
phosphine. Solution NMR studies on these molecules at 25 ¡C
show equivalent OR groups and diastereotopic CH H signals
for the RuÈOAd protons c to Ru.10
The structure of these molecules was established by DFT
(B3PW91) geometry optimization of Ru(OCH ) (CH )(PH )
2
2
2
3
2
exchange. When L \ PPri and R \ Ph, evidence for this is
3
seen in the preparation of RuH(F)L (2C2CHR) by treatment
a
b
2
of RuHClL (2C2CHR) with NMe F. During the halide
metathesis in C D , an intermediate is observed after 30 min;
its NMR spectroscopy is consistent with six-coordinate
2
4
6
6
3 2
2
3
as a model using e†ective core potential for Ru and P and a
double f quality basis set with added polarization functions
for all atoms but Ru (see Electronic supplementary informa-
tion for details) with GAUSSIAN 98.11 Various geometrical
starting points di†ering in the coordination at the metal (cis
or trans methoxy groups in particular) and orientation at the
carbene all converged to the same ““saw-horseÏÏ (i.e., cis-
divacant octahedron) geometry in which the two OMe ligands
are mutually transoid and CH and PH are mutually cis.
[RuH(F)ClL (2C2CHR)]NMe , an adduct of the two
2
4
reagents (A). Apparently this species is metastable because the
cation in the Ñuoride source lacks the electrophilicity (cf. Na`)
to rapidly remove Cl~. A trans disposition of the hydride and
Ñuoride are suggested in A by the large J of 80 Hz, and
coordinative saturation is implied by the 4 ppm downÐeld
FH
shift of the 1H resonance relative to the Ðve-coordinate vinyl-
idene. The triplet structure of the hydride signal establishes
the retention of two phosphines. The NMe 1H signal is
2
3
4
This is quite the same geometry as we have shown and
observed at 2.8 ppm, and all other expected 1H and 31P reso-
analyzed earlier for the other d6 species.12h16 RuH(CO)L `,
RuPh(CO)L `, Ir(H) L ` and monomeric RuHClL . The
nances are seen displaced from those of the starting chloride.
2
The 19F signal for this adduct appears at [252 ppm, strongly
2
2 2
2
shifted from that in the Ðnal product RuH(F)L (C2CHPh)
2
([155 ppm), which forms within 12 h in C D . The fact that
6
6
F~ binds strongly to the vacant site in RuHClL (2C2CHR)
2
suggests that the donation of THF in a solvating environment
could indeed hinder the vinylidene-to-carbyne transformation
if a Ñexible coordination sphere about Ru is required for isom-
erization.
Since the four-coordinate phenoxy ethylidynes were found
to be stable and accessible from dichloro carbenes, we pre-
sumed that the analogous benzylidynes might also be acces-
sible and resistant to isomerization due to their lack of b
protons. Treatment of the benzylidenes RuCl L (2CHPh)7
2 2
with 2 equiv. of NaOPh in THF [eqn. (4a)] leads within 3 h to
the formation of carbynes Ru(OPh)L (CPh), with L \ PPri
2
3
intermediates
or
PCy ,
in
good
yields;
the
Fig. 1 ORTEP drawing (30% probability ellipsoids)
of
3
RuCl(OPh)L (CHPh) and Ru(OPh) L (CHPh) are detected.
Ru(OPh)(CPh)(PPri ) , omitting hydrogens. Ru occupies a crystallo-
2
2 2
3 2
Free HOPh is observed by 1H NMR, but free L is absent.
graphic site of inversion symmetry, leading to disorder of O with the
Like their ethylidyne counterparts, these molecules are also
carbyne C. RuÈC/O \ 1.873(3) A; RuÈP \ 2.379(2) A.
926
New J. Chem., 2000, 24, 925È927

View Article Online
6
7
8
9
C. Grunwald, O. Gevert, J. Wolf, P. GonzalezÈHerrero and H.
Werner, Organometallics, 1996, 15, 1960.
p-acid carbene ligand is trans to an empty site (both
nCÈRuÈO \111¡) and the orientation of the OMe ligands
P. Schwab, R. H. Grubbs and J. W. Ziller, J. Am. Chem. Soc.,
1996, 118, 100.
are transoid (nOÈRuÈO \ 134¡), so that the Ru(carbene)(O)
2
substructure is nearly planar (sum of angles \ 356¡). The
W. Stuer, J. Wolf, H. Werner, P. Schwab and M. Schultz, Angew.
Chem., Int. Ed., 1998, 37, 3421.
phosphorus lies 2.19 A out of this plane with a PÈRuÈC angle
of 91¡. In sum, this structure is that of RuX L (CHR)
Crystal data for Ru(CPh)(CPh)(PPri ) : M \ 603.7, triclinic,
3 2
2 2
space group P1, a \ 8.884(3), b \ 11.352(4), c \ 16.041(6) A,
(X \ OR) with one L removed and with little modiÐcation of
a \ 93.353(8), b \ 92.003(8), c \ 97.681(11)¡, U \ 1598.9
AŽ 3,
the remaining ligands [eqn. (5)].
Z \ 2. 68114 measured and 19002 independent reÑections,
R(int) \ 0.097, R(F) \ 0.055, R (F2) \ 0.140. CCDC reference
w
number 440/220. See http://www.rsc.org/suppdata/nj/b0/
b006971j/ for crystallographic Ðles in .cif format.
(5)
10 M. S. Sanford, L. M. Henling, M. W. Day and R. H. Grubbs,
ACS National Meeting Book of Abstracts, American Chemical
Society, Washington, DC, 2000, INOR235, reports the synthesis
of examples of these four-coordinate ruthenium carbenes.
11 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr.,
R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D.
Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Cli†ord, J. Ochterski, G. A. Petersoon, P. Y. Ayala, Q.
Cui, K. Morokuma, D. K. Malick, A. D. Rabuck, K. Raghava-
chari, J. B. Foresman, J. Cioslowski, J. V. Ortiz, A. G. Baboul, B.
B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.
Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C.
Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P. M.
W. Gill, B. Johnson, W. Chen, M. W. Wong, J. L. Andres, C.
Gonzalez, M. Head-Gordon, E. S. Replogle and J. A. Pople,
GAUSSIAN 98, rev. A7, Gaussian, Inc., Pittsburgh, Pennsylva-
nia, 1998.
These results of isomer stability reversal and phenol or
phosphine loss show a subtle interplay of steric factors,
X-group BrÔnsted basicity vs. nucleophilicity, and probably
conjugative stabilization of Ru2C2CHR when R is phenyl.
These e†ects, when employed judiciously, permit access to
new classes of ruthenium reagents for further study.
This work was supported by the donors of the Petroleum
Research Fund, administered by the American Chemical
Society, the University of Montpellier 2, the CNRS and the
Indiana University computer center.
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