Replacement of a cyclometalated terdentate diamino ligand by a phosphorus analogue. Isolation and crystallographic characterization of an intermediate in aryl C-H bond activation in models of dendrimer-bound organometallic catalysts

Full text of DOI:10.1021/ja9710060

J. Am. Chem. Soc. 1997, 119, 11317-11318
Replacement of a Cyclometalated Terdentate
11317
Diamino Ligand by a Phosphorus Analogue.
Isolation and Crystallographic Characterization of
an Intermediate in Aryl C-H Bond Activation in
Models of Dendrimer-Bound Organometallic
Catalysts
Figure 1.
defined carbosilane dendritic supports (“dendrimer catalysts”).7
We report herein some aspects of the chemistry of d6 Ru(II)
PCP′ complexes which are employed as models for TM
compounds which are tethered to carbosilane dendrimers.7c This
work has in turn led to the isolation and characterization (NMR,
IR, X-ray Crystallography) of a rare intermediate in aryl C-H
bond activation of a PCP′-H ligand. It is also shown that aryl-
Si bond cleavage reactions can predominate the chemistry of
carbosilane dendrimers incorporating ligand fragments such as
[PCP′]- (2).
Paulo Dani,† Thomas Karlen,† Robert A. Gossage,†
Wilberth J. J. Smeets,‡ Anthony L. Spek,‡ and
Gerard van Koten*,†
Debye Institute, Department of Metal-Mediated Synthesis
and BijVoet Centre for Biomolecular Research
Laboratory of Crystal Chemistry, Utrecht UniVersity
Padualaan 8, 3584 CH Utrecht, The Netherlands
t
Treatment of 3,5-(Ph2PCH2)2C6H3Br with 2 equiv of BuLi
ReceiVed March 31, 1997
at -78 °C produces the lithium compound [3,5-(Ph2PCH2)2C6H3-
Li]n (3). Quenching of 3 with TMS-Cl (TMS ) trimethylsilyl)
yields the TMS substituted ligand 2c in 93% isolated yield.8
This synthesis can be envisioned as a model for the grafting of
a PCP′-H ligand to a carbosilane dendrimer which is terminated
by reactive -SiR2Cl groups.7c,9 Our desire was then to chelate
the dendrimer bound PCP′ ligand to a Ru metal center.
Ruthenium(II) complexes of this class are known hydrogenation
and hydrogen transfer catalysts and can participate in alkyne
and aryl coupling reactions.3 To our surprise, however, treat-
ment of 2c with the Ru(II) precursor RuCl2(PPh3)310 led to the
isolation in 98% yield of the known para-H complex 4a
(Scheme 1; i.e., incorporating the PCP′ fragment 2b).3a,b The
high yield of 4a indicates that aryl-Si bond cleavage (i.e.,
protondesilylation) is readily facilitated by the reaction condi-
tions.11 The desilylation of ligand 2c could not be prevented
with the addition of NEt3. Thus, the direct attachment of a Ru
moiety on to a PCP′ terminated carbosilane dendrimer cannot
be accomplished in this manner because the subsequent ruptur-
ing of the aryl-Si bond will release the resulting complex from
the dendrimer framework.
The chemistry of the potentially monoanionic, terdentate
diaminoaryl ligand [NCN′]- (1) and its phosphorus analogue
bisphosphinoaryl [PCP′]- (2, Figure 1) have been extensively
studied in this laboratory and others1-3 due to their strong
propensity to form stable transition metal (TM) and main-group
organometallic complexes, often in unusual geometries and/or
oxidation states.4 A number of these TM compounds are
effective catalysts for the synthesis of commodity and fine
chemicals, and they have also been used as molecular probes
in a number of fundamental chemical processes, notably C-H
bond activation.2-6 We have been interested in using func-
tionalized aryl ligands as templates for the incorporation of
catalytically active TM fragments onto polymeric or well-
† Debye Institute.
‡ Bijvoet Centre for Biomolecular Research.
(1) (a) Mayer, H. A.; Kaska, W. C. Chem. ReV. 1994, 94, 1239-1272.
(b) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Zanobini, F. Coord.
Chem. ReV. 1992, 120, 193-208. (c) Cotton, F. A.; Hong, B. Prog. Inorg.
Chem. 1992, 40, 179-290.
(2) (a) van der Kuil, L. A.; Luitges, H.; Grove, D. M.; Zwikker, J. W.;
van der Linden, J. G. M.; Roelofsen, A. M.; Jenneskens, L. W.; Drenth,
W.; van Koten, G. Organometallics 1994, 3, 468-477. (b) Steenwinkel,
P.; James, S. L.; Grove, D. M.; Veldman, N.; Spek, A. L.; van Koten, G.
Chem. Eur. J. 1996, 2, 1440-1445. (c) Davies, P. J.; Veldman, N.; Grove,
D. M.; Spek, A. L.; Lutz, B. T. G.; van Koten, G. Angew. Chem., Int. Ed.
Engl. 1996, 35, 1959-1961.
Fortunately, it was discovered that the reaction of the
analogous complex RuCl[2,6-(Me2NCH2)2C6H3](PPh3) (5)3a,c
reacts with ligand precursor 2c to give the desired complex 6
in 70% overall yield (Scheme 1).12 This reaction, which is
unprecedented in the organometallic chemistry of tridentate
monoanionic ligands, represents a useful synthetic protocol for
(3) (a) Karlen, T.; Dani, P.; Grove, D. M.; Steenwinkel, P.; van Koten,
G. Organometallics 1996, 15, 5687-5694. (b) Jia, G.; Lee, H. M.; Xia,
H. P.; Williams, I. D. Organometallics 1996, 15, 5453-5455. (c) Sutter,
J.-P.; James, S. L.; Steenwinkel, P.; Karlen, T.; Grove, D. M.; Veldman,
N.; Smeets, W. J. J.; Spek, A. L.; van Koten, G. Organometallics 1996,
15, 941-948. (d) Liou, S.-Y.; Gozin, M.; Milstein, D. J. Chem. Soc., Chem.
Commun. 1995, 1965-1966, J. Am. Chem. Soc. 1995, 117, 9774-9775.
(e) Gozin, M.; Weismann, A.; Ben-David, Y.; Milstein, D. Nature 1993,
364, 699-701. (f) Gozin, M.; Aizenberg, M.; Liou, S.-Y.; Weismann, A.;
Ben-David, Y.; Milstein, D. Nature 1994, 370, 42-44. (g) Kaska, W. C.;
Nemeh, S.; Shirazi, A.; Potuznik, S. Organometallics 1988, 7, 13-15. (h)
Creaser, C. S.; Kaska, W. C. Inorg. Chim. Acta 1978, 30, L325-L326. (i)
Gorla, F.; Togni, A.; Venanzi, L. M.; Albinati, A.; Lianza, F. Organome-
tallics 1994, 13, 1607-1616. (j) Rimml, H.; Venanzi, L. M. Phosphorus
Sulfur 1987, 30, 297-300, and references therein. (k) Vigalok, A.; Ben-
David, Y.; Milstein, D. Organometallics 1996, 15, 1839-1844. (l) Fryzuk,
M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics 1991, 10, 467-
473. (m) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976,
1020-1024. (n) Perera, S. D.; Shaw, B. L. J. Chem. Soc., Dalton Trans.
1995, 3861-3866. (o) Cross, R. J.; Kennedy, A. R.; Manojlovic-Muir, L.;
Muir, K. W. J. Organomet. Chem. 1995, 493, 243-249. (p) Nemeh, S.;
Jensen, C.; Binamira-Soriaga, E.; Kaska, W. C. Organometallics 1983, 2,
1442-1447. (q) Gupta, M.; Hagen, C.; Kaska, W. C.; Cramer, R. E.;
Jensen, C. M. J. Am. Chem. Soc. 1997, 119, 840-841. (r) Gupta, M.;
Hagen, C.; Kaska, W. C.; Flesher, R.; Jensen, C. M. Chem. Commun. 1996,
2083-2084.
(7) Polymeric: (a) van der Kuil, L. A.; Grove, D. M.; Zwikker, J. W.;
Jenneskens, L. W.; Drenth, W.; van Koten, G. Chem. Mater. 1994, 6, 1675-
1683. (b) Pathmamanoharan, C.; Wijkens, P.; Grove, D. M.; Philipse, A.
P. Langmuir 1996, 12, 4372-4377. Dendrimeric: (c) Knapen, J. W. J.;
van der Made, A. W.; de Wilde, J. C.; van Leeuwen, P. W. N. M.; Wijkens,
P.; Grove, D. M.; van Koten, G. Nature 1994, 372, 659-663. Also see:
(d) Bhyrappa, P.; Young, J. K.; Moore, J. S.; Suslick, K. S. J. Mol. Catal.
Part A: Chemical 1996, 113, 109-116.
(8) Synthesis of 2c: Prepared from a reaction of 3,5-(Ph2PCH2)2C6H3-
Br (1.11 g, 2.0 mmol) in Et2O (30 mL) with tBuLi (2.1 equiv, 0.6 M pentane
solution) at -78 °C, stirred (30 min) and then quenched with TMS-Cl (2.0
mL, 16 mmol). Yield: 1.02 g (93%), colorless oil. For full details see the
Supporting Information.
(9) (a) Alonso, B.; Cuadrado, I.; Mora´n, M.; Losada, J. J. Chem. Soc.,
Chem. Commun. 1994, 2575-2576. (b) Alonso, B.; Mora´n, M.; Casado,
C. M.; Lobete, F.; Losada, J.; Cuadrado, I. Chem. Mater. 1995, 7, 1440-
1442. (c) Lobete, F.; Cuadrado, I.; Casado, C. M.; Alonso, B.; Mora´n, M.;
Lasada, J. J. Organomet. Chem. 1996, 509, 109-113.
(10) (a) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Syn.
1970, 13, 237-244. (b) Hoffman, P. R.; Caulton, K. G. J. Am. Chem.
Soc. 1975, 97, 4221-4228. (c) La Placa, S. J.; Ibers, J. A. Inorg. Chem.
1965, 4, 778-783.
(11) (a) von Fritz, G.; Kummer, D. Z. Anorg. Allg. Chem. 1961, 308,
105-121. (b) Eaborn, C. Organometallic Compounds of the Group IV
Elements; Vol. 1, MacDiarmid, A. G., Ed.; Marcel Dekker, Inc.: New York,
1968; Chapter 2, pp 105-536.
(4) (a) van Koten, G. Pure Appl. Chem. 1989, 61, 1681-1694. (b)
Rietveld, M. H. P.; Grove, D. M.; van Koten, G. New J. Chem. 1997, 21,
751-771.
(5) (a) Grove, D. M.; Verschuuren, A. H. M.; van Koten, G. J. Mol.
Catal. 1988, 45, 169-174. (b) Grove, D. M.; Verschuuren, A. H. M.; van
Koten, G.; van Beek, J. A. M. J. Organomet. Chem. 1989, 372, C1-C6.
(6) (a) Canty, A. J.; van Koten, G. Acc. Chem. Res. 1995, 28, 406-413.
(b) Ryabov, A. D. Chem. ReV. 1990, 90, 403-424. (c) Green, M. L. H.;
O’Hare, D. Pure Appl. Chem. 1985, 57, 1897-1910.
(12) Synthesis of 6: A solution of 2c (0.43 g, 0.78 mmol) in THF (10
mL) was added to a boiling THF (20 mL) solution of 5 (0.46 g, 0.79 mmol),
and then refluxed for 8 h. The final product was contaminated with a small
amount (<5%) of 1a. Yield: 0.51 g (70%). For full details see the
Supporting Information.
S0002-7863(97)01006-8 CCC: $14.00 © 1997 American Chemical Society

11318 J. Am. Chem. Soc., Vol. 119, No. 46, 1997
Communications to the Editor
Scheme 1
Figure 2. Perspective view (ORTEP, 50% probability) of cation 7,
showing aryl C-H‚‚‚Ru interaction. Other protons and phenyl groups
have been omitted for clarity. Bond distances (Å) and angles (deg):
Ru1-P11 2.3732(9), Ru1-P21 2.4432(9), Ru1-P12 2.3716(9), Ru1-
P22 2.3575(9), Ru1-C12 2.115(3), Ru1-H 1.76(4), Ru1‚‚‚C11
2.395(4), C11-H 1.15(4), P11-Ru1-P21 152.74(3), P12-Ru1-P22
153.64(3), P11-Ru1-P12 91.62(3), P11-Ru1-P22 95.89(3),
C11-Ru1-C12 171.47(11), Ru1-H-C11 109(3).
of a cationic [PCP′Ru]+ fragment (i.e., either an agostic type
C-H‚‚‚M interaction or a 3c-2e bond are limiting interaction
models).3n,16 The local symmetry around the metal center is
best described as a highly distorted octahedral environment. The
inequivalence of all four P donor atoms is clearly visible in the
structure, and the 31P{1H} NMR data strongly suggest that this
geometry is retained in solution. This complex also confirms
our recent proposal that chelation of the neutral PCP′-H ligand
occurs Via initial trans coordination of both P atoms and that
this precedes electrophilic attack of the metal center on the C-H
the incorporation of catalytically active Ru(II) metal centers into
carbosilane dendrimers.
The cyclometalation reaction 2c to 6 must involve an aryl
C-H oxidative-addition/reductive-elimination (i.e., aryl C-H
bond activation) process. Attempts to monitor the conversion
of 5 to 6 Via NMR spectroscopy revealed the intermediacy of
a PCP′-H-bridged Ru dimer.13 In an attempt to gain further
insight into this type of reaction, the examination of the addition
of a second equiv of 2a with the related triflate complex 4b
was undertaken. We chose to use the diphosphine 2a because
its inherit NMR active P atoms would allow for facile
spectroscopic investigation. We also felt the use of the known
triflate analogue of 4a (complex 4b) was prudent as the presence
of the triflate anion (kinetically, a good leaving group; although
strongly bound to complex 4b, cf. complex 4a3a,b) may enhance
the exchange of ligands from the metal coordination sphere.
Treatment of 4b with 2a in CH2Cl2 solution led to the isolation
of a yellow diamagnetic complex 7 (Scheme 1).14 The 1H NMR
spectrum of 7 revealed a number of aryl resonances between δ
5.9 and 7.8 ppm in addition to a broad multiplet pattern at δ
3.4 ppm that is assigned to the benzylic CH2 protons of the
PCP′ fragments. The 31P{1H} NMR spectrum of 7 shows the
presence of four magnetically distinct P atoms at low temper-
ature.14 As a conclusive structural assignment of 7 could not
be made from the available spectroscopic data, crystals of this
compound that were suitable for X-ray structure determination
were grown from a solution in CH2Cl2/ether/toluene.15 The
ORTEP diagram of 7 is shown in Figure 2 along with selected
bond lengths and angles. The location of the hydrogen on C11
of the “incoming” trans-spanning PCP′-H ligand was clearly
refined on the final difference map (see Supporting Informa-
tion)15 and reveals that this H is pushed out of the plane of the
arene ring forming an apparent interaction with the Ru center
1
bond.3a Our attempts to observe the appropriate H and 13C
nuclei of the C-H‚‚‚Ru interaction have thus far been thwarted
by the large number of aromatic resonances and low abundance
of the signals of interest. An IR study of 7 did reveal, however,
a medium intensity band at 2864 cm-1, which is tentatively
assigned to the agostic C-H stretching vibration.16 Deuteration
1
and H, 31P heteronuclear decoupling NMR experiments are
currently underway to unequivocally assign the agostic C-H
fragment.
In conclusion, this report has shown that the incorporation
of reactive Ru(II) PCP′ complexes into carbosilane dendrimers
can be accomplished by a facile ligand displacement of the
NCN′-H ligand (1a) from compound 5. Attempts to directly
add the Ru metal center Via the traditional precursor RuCl2-
(PPh3)3 leads to aryl-Si bond cleavage and hence would result
in degradation of the dendrimer molecule. The direct observa-
tion of an intermediate in the C-H bond activation of a neutral
PCP′-H ligand has been shown for the first time in these
systems and has confirmed that most likely P donor chelation
precedes C-H bond activation with a d6 Ru(II) metal center.
We are currently pursuing an extended investigation of this novel
C-H bond activation chemistry in addition to the attachment
of complexes similar to 6 to dendrimeric macromolecules.
Acknowledgment. We thank the Conselho Nacional de Desen-
volvimento Cient´ıfico e Tecnolo´gico (CNPq, Brazil), the Swiss National
Science Foundation, CIBA-GEIGY-Jubila¨ums-Stiftung, the Netherlands
Foundation of Chemical Research (SON), and the Netherlands Orga-
nization for Scientific Research (NWO) for financial support.
(13) Full details of this bridged mechanism will be reported separately.
It should be noted that the initial displacement of PPh3 by an incoming
PCP′ ligand at room temperature is very rapid for complexes such as 5 and
6.
Supporting Information Available: Tables of crystal data, thermal
parameters, bond distances, bond angles, and atomic coordinates for 7
and the 31P{1H} NMR spectra of 7 (210 and 298 K) and the detailed
syntheses and NMR data for 2c and 6 (24 pages). See any current
masthead page for ordering and Internet access instructions.
(14) Synthesis of 7: Ligand 2a (0.47 g, 1.0 mmol) was added to complex
4b (1.0 g, 1.0 mmol) in CH2Cl2 (15 mL). The mixture was stirred at room
temperature (0.5 h), and then Et2O was added to precipitate 7 as an orange
solid, which was subsequently washed with Et2O and dried in Vacuo.
Yield: 0.97 g (81%). 1H NMR (200 MHz, CD2Cl2, 298 K): δ 3.10-3.70
(br, 4H, CH2), 6.30-7.81 (m, 47 H, ArH). 31P{1H} NMR: The complicated
second order spectrum is contained in the Supporting Information. The
presence of large trans pseudo-coupling constants and smaller cis coupling
constants strongly suggest that the solid-state structure of 7 is retained in
solution. Examination of complex 7 Via 2D 31P-31P NMR (large couplings
are fully resolved) spectroscopy also supports this conclusion. Full details
of the NMR characterization of 7 will be reported in a forthcoming full
paper. Anal. Calcd (Found) for C65H55O3F3P4SRu‚0.75CH2Cl2: C 62.61
(62.93), H 4.48 (4.56).
JA9710060
(15) Crystal data for 7: [C64H55P4Ru][CF3O3S]‚CH2Cl2‚C4H10O, Mr )
1357.23, triclinic, space group P1, a ) 12.7745(11), b ) 15.8943(11), c )
17.0745(11) Å, R ) 110.669(5), â ) 96.973(6), γ ) 101.871(6)°, V )
3102.2(4) Å3, Dx ) 1.453 g cm-3, Z ) 2, T ) 150 K, MoKR, R1 ) 0.0461
for 10 014 reflections with I > 2σ(I). The hydrido H was located from a
difference map and its position refined.
(16) (a) Brookhart, M.; Green, M. L. H.; Wong, L.-L. Prog. Inorg. Chem.
1988, 36, 1-124. (b) Crabtree, R.; Hamilton, D. G. AdV. Organomet. Chem.
1988, 28, 299-338.