Carbon-Carbon vs Carbon-Hydrogen Bond Activation by Ruthenium(II) and Platinum(II) in Solution

Article abstract of DOI:10.1021/om990282f

Reaction of RuCl₂(PPh₃)₃ with the bisphosphine {1,3,5-(CH₃)₃-2,6-(ⁱPr₂PCH ₂)₂C₆H} (1) under 30 psi H₂ results in quantitative C-C activation of an Ar-CH₃ bond to afford Ru(Cl)-(PPh₃){2,6-(ⁱPr₂PCH₂) ₂-3,5-(CH₃)₂C₆H} (2) and CH₄, whereas reaction of RuCl₂(PPh₃)₃ with 1 in the presence of NaO^tBu results in selective ArCH₂-H bond activation to afford the benzylic complex Ru(Cl)(PPh₃H{1-CH₂-2,6-(ⁱPr₂PCH ₂)₂-3,5-(CH₃)₂C₆H} (7). The identity of the 16-electron complex 2 was confirmed by reaction of the bisphosphine {2,6-(ⁱPr₂PCH₂)₂-3,5-(CH ₃)₂C₆H₂} (3), lacking the Ar-CH₃ group between the phosphine arms, with RuCl₂(PPh₃)₃. Metal insertion into an Ar-Et bond was observed as well. Follow-up of the reaction of RuHCl-(PPh₃)₃ with 1 by NMR and deuterium labeling studies reveal that the kinetic products of ArCH₂-H bond activation (7 and H₂) are irreversibly converted into the thermodynamically more stable products of Ar-C bond activation (2 and CH₄) via reversal of the C-H activation process. Reaction of (COD)PtCl₂ (COD = cycloocta-1,5-diene) with a stoichiometric amount of 1 at room temperature results in the exclusive formation of the benzylic Pt(II) complex Pt(Cl){1-CH₂-2,6-(ⁱPr₂PCH₂) ₂-3,5-(CH₃)₂C₆H} (8) and HCl. The iodide analogue of 8 has been characterized by X-ray analysis. Reaction of 8 with a 10-fold excess of HCl results in selective C-C bond activation to afford Pt(Cl){2,6-(ⁱPr₂PCH₂)₂-3,5-(CH ₃)₂C₆H} (10) and MeCl. The activation parameters for the overall process are ΔH? = 10.6 kcal/mol, ΔS? = -40.1 eu, and ΔG?₍₂₉₈₎ = 23.1 kcal/mol in a benzene/dioxane solution (5.5:1 v/v) and ΔH? = 2.1 kcal/mol, ΔS? = -65.4 eu, and ΔG?₍₂₉₈₎ = 21.6 kcal/mol in dioxane.

Full text of DOI:10.1021/om990282f

Organometallics 1999, 18, 3873-3884
3873
Ca r bon -Ca r bon vs Ca r bon -Hyd r ogen Bon d Activa tion
by Ru th en iu m (II) a n d P la tin u m (II) in Solu tion
Milko E. van der Boom, Heinz-Bernhard Kraatz, Lawrence Hassner,
Yehoshoa Ben-David, and David Milstein*
Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
Received April 21, 1999
Reaction of RuCl2(PPh3)3 with the bisphosphine {1,3,5-(CH3)3-2,6-(iPr2PCH2)2C6H} (1) under
30 psi H2 results in quantitative C-C activation of an Ar-CH3 bond to afford Ru(Cl)-
(PPh3){2,6-(iPr2PCH2)2-3,5-(CH3)2C6H} (2) and CH4, whereas reaction of RuCl2(PPh3)3 with
1 in the presence of NaOtBu results in selective ArCH2-H bond activation to afford the
benzylic complex Ru(Cl)(PPh3){1-CH2-2,6-(iPr2PCH2)2-3,5-(CH3)2C6H} (7). The identity of the
16-electron complex 2 was confirmed by reaction of the bisphosphine {2,6-(iPr2PCH2)2-3,5-
(CH3)2C6H2} (3), lacking the Ar-CH3 group between the phosphine arms, with RuCl2(PPh3)3.
Metal insertion into an Ar-Et bond was observed as well. Follow-up of the reaction of RuHCl-
(PPh3)3 with 1 by NMR and deuterium labeling studies reveal that the kinetic products of
ArCH2-H bond activation (7 and H2) are irreversibly converted into the thermodynamically
more stable products of Ar-C bond activation (2 and CH4) via reversal of the C-H activation
process. Reaction of (COD)PtCl2 (COD ) cycloocta-1,5-diene) with a stoichiometric amount
of 1 at room temperature results in the exclusive formation of the benzylic Pt(II) complex
Pt(Cl){1-CH2-2,6-(iPr2PCH2)2-3,5-(CH3)2C6H} (8) and HCl. The iodide analogue of 8 has been
characterized by X-ray analysis. Reaction of 8 with a 10-fold excess of HCl results in selective
CsC bond activation to afford Pt(Cl){2,6-(iPr2PCH2)2-3,5-(CH3)2C6H} (10) and MeCl. The
activation parameters for the overall process are ∆Hq ) 10.6 kcal/mol, ∆Sq ) - 40.1 eu, and
∆Gq
) 23.1 kcal/mol in a benzene/dioxane solution (5.5:1 v/v) and ∆Hq ) 2.1 kcal/mol,
(298)
∆Sq ) -65.4 eu, and ∆Gq
) 21.6 kcal/mol in dioxane.
(298)
In tr od u ction
on ArCH2-H vs Ar-CH3 bond activation with Ru(II) and
Pt(II) in solution using aryl PCP-type ligands (PCP )
[1,3,5-(CH3)3-2,6-(iPr2PCH2)2C6R], R ) H, OMe, C(O)-
OMe) and show that C-C bond activation in these
systems is thermodynamically more favorable than the
competing kinetically preferred C-H bond activation
process. We have also observed de-ethylation of an
aromatic system. A benzylic PCP-Pt(II) complex was
fully characterized by X-ray analysis. Part of this work
related to the Pt(II) chemistry has been communicated.6
Activation of an Ar-Si bond by Pd(II) and Pt(II) was
published recently.14-16 To unambiguously identify the
products of C-C bond activation, the PCP-type Ru(II)
and Pt(II) complexes were independently prepared.
Various aryl PCP-type complexes are known,2-12,17-36
Transition metal insertion into strong C-C single
bonds in solution is rare, and mechanistic information
about this process is scarce.1 We have reported on C-C
bond activation using phosphine-based substrates and
various d8 transition metals of group 9 and 10 in
stoichiometric and even catalytic amounts.2-13 Fluori-
nated substrates were used as well.11,12 We report here
* To whom correspondence should be addressed. Fax: +972-8-
9344142. E-mail: comilst@wiccmail.weizmann.ac.il.
(1) For reviews regarding C-C bond activation: (a) Rybtchinski,
B.; Milstein, D. Angew. Chem., Int. Ed. Engl. 1999, 38, 870. (b)
Murakami, M.; Ito, Y. In Topics in Organometallic Chemistry; Murai,
S., Ed.; Springer-Verlag: New York, 1999; Vol. 3, pp 97-129.
(2) Gozin, M.; Weisman, A.; Ben-David, Y.; Milstein, D. Nature 1993,
364, 699.
(3) Gozin, M.; Aizenberg, M.; Liou, S.-Y.; Weisman, A.; Ben-David,
Y.; Milstein, D. Nature 1994, 370, 42.
(4) Liou, S.-Y.; Gozin, M.; Milstein, D. J . Am. Chem. Soc. 1995, 117,
9774-9775.
(14) Valk, J .-M.; van Belzen, R.; Boersma, J .; Spek, A. L.; van Koten,
G. J . Chem. Soc., Dalton Trans. 1994, 2293.
(15) Steenwinkel, P.; J ames, S. L.; Grove, D. M.; Kooijman, H.; Spek,
A. L.; van Koten, G. Organometallics 1997, 16, 513.
(16) Steenwinkel, P.; Gossage, R. A.; van Koten, G. Chem. Eur. J .
1998, 4, 759.
(17) van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Vigalok, A.;
Milstein, D. Angew. Chem., Int. Ed. Engl. 1997, 36, 625.
(18) van der Boom, M. E.; Liou, S.-Y.; Shimon, L. J . W.; Ben-David,
Y.; Milstein, D. J . Am. Chem. Soc. 1998, 120, 6531.
(19) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1976,
1020.
(20) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J . Am.
Chem. Soc. 1997, 119, 11687.
(21) Nemeh, S.; J ensen, C.; Binamira-Soriaga, E.; Kaska, W. C.
Organometallics 1983, 2, 1442.
(22) Rimml, H.; Venanzi, L. M. J . Organomet. Chem. 1983, 259, C6.
(23) Kraatz, H.-B.; Milstein, D. J . Organomet. Chem. 1995, 488, 223.
(5) Liou, S. Y.; Gozin, M.; Milstein, D. Chem. Commun. 1995, 1965.
(6) van der Boom, M. E.; Kraatz, H. B.; Ben-David, Y.; Milstein, D.
Chem. Commun. 1996, 2167.
(7) Rybtchinski, B.; Vigalok, A.; Ben-David, Y.; Milstein, D. J . Am.
Chem. Soc. 1996, 118, 12406.
(8) Gandelman, M.; Vigalok, A.; Shimon, L. J . W.; Milstein, D.
Organometallics 1997, 16, 3981.
(9) Liou, S.-Y.; van der Boom, M. E.; Milstein, D. Chem. Commun.
1998, 1996, 2167.
(10) van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Gozin, M.;
Milstein, D. J . Am. Chem. Soc. 1998, 120, 13415.
(11) van der Boom, M. E.; Ben-David, Y.; Milstein, D. Chem.
Commun. 1998, 971.
(12) van der Boom, M. E.; Ben-David, Y.; Milstein, D. J . Am. Chem.
Soc., in press
(13) Rybtchinski, B.; Milstein, D. J . Am. Chem. Soc. 1999, 121, 4528.
10.1021/om990282f CCC: $18.00 © 1999 American Chemical Society
Publication on Web 08/17/1999

3874 Organometallics, Vol. 18, No. 19, 1999
van der Boom et al.
Sch em e 1
and the formation and reactivity of related Ru(II)
complexes is of current interest.16,37-44 For instance,
reactions of Ru(Cl)(PPh3){2,6-(Ph2PCH2)2C6H3} with
various terminal alkynes resulted in their insertion into
the Ru-C(aryl) bond.38,45 An agostic interaction of an
Ar-H bond of an aryl PCP ligand at a Ru(II) center was
recently reported.37
35 psi) at 100 °C in a Fischer Porter pressure vessel
resulted in quantitative formation of the air-sensitive,
thermally stable complex 2 (Scheme 1). No other
complexes were detected by 1H and 31P{1H} NMR
analysis of the green product solution. The gas phase
was collected by standard vacuum line techniques and
was analyzed by GC, showing formation of CH4 in a
nearly quantitative amount (>85%). Similar results
were obtained using the phenylphosphine analogue of
1 {1,3,5-(CH3)3-2,6-(Ph2PCH2)2C6H}. Only the methyl
group located between the two phosphine arms under-
goes C-C bond activation. The fact that the other two
Ar-CH3 groups remain unaffected suggests that the
C-C bond activation takes place in an intermediate in
which the two phosphines are coordinated to the metal
center, as observed for similar PCP substrates with Pt-
(II).27 Phosphorus chelation precedes Ar-H bond activa-
tion in a PCP system with Ru(II).37 Complex 2 was
unambiguously identified by various NMR techniques,
by MS, and by comparison to an authentic sample. It
was obtained independently by reaction of a THF
solution of RuCl2(PPh3)3 with 3, lacking one methyl
substituent at the aromatic ring, at 100 °C in a sealed
pressure vessel (Scheme 1). The mass spectrum of 2
contains the molecular ion (M+ 763), having a correct
isotope pattern, and a signal at m/z 728 corresponding
to the elimination of Cl. Analogous square-pyramidal
Ru(II) complexes having a meridional PCP-type ligand
and PPh3 occupying the apical position were re-
ported.38,40,45 The NMR data of 2 are fully consistent
with such a geometry,38,40,45-48 which is theoretically
favored over a trigonal bipyramidal structure for d6
metal complexes in the absence of steric effects.49,50 For
instance, the 13C{1H} NMR spectrum of 2 contains two
Resu lts a n d Discu ssion
Ar -CH3 a n d Ar -CH2CH3 Bon d Activa tion w ith
Ru (II) u n d er H2. Reaction of a THF solution of RuCl2-
(PPh3)3 with a stoichiometric amount of 1 under H2 (30-
(24) Kennedy, A. R.; Cross, R. J .; Muir, K. W. Inorg. Chim. Acta
1995, 2.
(25) Gorla, F.; Venanzi, L. M.; Albinata, A. Organometallics 1994,
13, 43.
(26) Bennett, M. A.; J in, H.; Willis, A. C. J . Organomet. Chem. 1993,
451, 249.
(27) van der Boom, M. E.; Gozin, M. E.; Ben-David, Y.; Shimon, L.
J . W.; Frolow, F.; Kraatz, H.-B.; Milstein, D. Inorg. Chem. 1996, 35,
7068.
(28) Weisman, A.; Gozin, M.; Kraatz, H.-B.; Milstein, D. Inorg.
Chem. 1996, 35, 1792.
(29) Rybtchinski, B.; Ben-David, Y.; Milstein, D. Organometallics
1997, 16, 3786.
(30) Kaska, W. C.; Nemeh, S.; Shirazi, S.; Potuznik, S. Organome-
tallics 1988, 7, 13.
(31) Albinati, A.; Lianza, F.; Pregosin, P. S.; Mu¨ller, B. Inorg. Chem.
1994, 33, 2522.
(32) Vigalok, A.; Shimon, L. W. J .; Milstein, D. J . Am. Chem. Soc.
1998, 120, 477.
(33) Vigalok, A.; Milstein, D. J . Am. Chem. Soc. 1997, 119, 7873.
(34) Steffey, B. D.; Miedaner, A.; Maciejewski-Farmer, M. L.;
Bernatis, P. R.; Herning, A. M.; Allured, V. S.; Carperos, V.; DuBois,
D. L. Organometallics 1994, 13, 4844.
(35) Huck, W. T. S.; Snellink-Ru¨el, B.; van Veggel, F. C. J . M.;
Reinhoudt, D. N.; Rimml, H.; Venanzi, L. J . Organomet. Chem. 1984,
260, C52.
(36) Gupta, M.; Hagen, C.; Kaska, W. C.; Cramer, R. E.; J ensen, C.
M. J . Am. Chem. Soc. 1997, 119, 840.
(37) Dani, P.; Karlen, T.; Gossage, R. A.; Smeets, W. J . J .; Spek, A.
L.; van Koten, G. J . Am. Chem. Soc. 1997, 119, 11317.
(38) J ia, G.; Lee, H. M.; Xia, H. P.; Williams, I. D. Organometallics
1996, 15, 5453.
(39) J ia, G.; Lee, H. M.; Williams, I. D. J . Organometallic. Chem.
1997, 534, 173.
(40) Sutter, J . P.; J ames, 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.
characteristic resonances at δ 172.74 (dt, cis-2J PC ) 18.3
(2+4)
and 4.7 Hz), and at δ 33.28 (vt,
J
) 24.4 Hz),
PC
which may be interpreted (using 13C-DEPT-135 NMR)
as the ipso carbon σ bound to the metal center in cis
position to the phosphine ligands and the magnetically
equivalent carbons of the ArCH2P moieties, receptively.
(41) Steenwinkel, P.; J ames, S. L.; Grove, D. M.; Veldman, N.; Spek,
A. L.; van Koten, G. Chem. Eur. J . 1996, 2, 1440.
(42) Pape, A.; Lutz, M.; Mu¨ller, G. Angew. Chem., Int. Ed. Engl.
1994, 33, 2281.
(43) Steenwinkel, P.; Kolmschot, S.; Gossage, R. A.; Dani, P.;
Veldman, N.; Spek, A. L.; van Koten, G. Eur. J . Inorg. Chem. 1998,
477.
(46) J ia, G.; Lee, I.; Meek, D. W.; Gallucci, J . C. Inorg. Chim. Acta
1990, 177, 81.
(47) Armit, P. W.; Boyd, A. S. F.; Stephenson, T. A. J . Chem. Soc.,
Dalton Trans. 1975, 1663.
(48) J ung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G. Inorg.
Chem. 1984, 23, 726.
(44) Karlen, T.; Dani, P.; Grove, D. M.; Steenwinkel, P.; van Koten,
G. Organometallics 1996, 15, 5687.
(45) Lee H. M.; Yao J . Z.; J ia G. C. Organometallics 1997, 16, 3927.
(49) Pearson, R. G. J . Am. Chem. Soc. 1969, 91, 4947.
(50) Hoffman, P. R.; Caulton, K. G. J . Am. Chem. Soc. 1975, 91,
4221.

Ar-CH3 vs ArCH2-H Bond Activation
Organometallics, Vol. 18, No. 19, 1999 3875
Sch em e 2
The 31P{1H} spectrum displays two signals at δ 76.47
(t, PPh3) and δ 45.83 (d, PCP) with cis-2J PP ) 31.5 Hz
in the expected 1:2 ratio. The large downfield shift of
the η1-bound PPh3 ligand (∆δ ∼77 ppm) is characteristic
for square-pyramidal Ru(II) complexes with apical
phosphine ligands.38,39,44,46-48 The 1H NMR shows a
typically ABq pattern at δ 2.32 with ∆AB ) 460 Hz and
2J HH ) 16.9 Hz coupled by two magnetically equivalent
phosphorus atoms of the PCP ligand ((2+4)J PH ) 9.9 Hz)
for the diastereotopic ArCH2P groups.
It is noteworthy that Bergman reported C-C bond
cleavage in hexafluoroacetone with (Me2PCH2CH2PMe2)2-
Ru(H)(OH) to afford (Me2PCH2CH2PMe2)2Ru(H)(OC(O)-
CF3) and CF3H and the stepwise degradation of a
neopentyl ligand to a trimethylene-methane ligand by
Ru(II) via a â-alkyl migration process.53-56 Chaudret et
al. demonstrated that reaction of the electrophilic
[Cp*Ru+] species with the A-rings of steroids resulted
in cleavage of various C-X bonds including C-C and
C-C bonds driven by an aromatization process.57,58
Electrochemically induced two-electron oxidative cleav-
age of a C-C single bond of cyclooctatetraene with [Cp2-
Ru2(µ-cyclo-C8H8)] is also known.59
De-ethylation was observed upon treatment of a THF
solution of the phosphine 1-Et-2,6-(iPr2PCH2)2C6H3 (4)
and RuCl2(PPh3)3 with H2 (30-35 psi) at 100 °C in a
Fischer Porter pressure vessel, resulting in formation
of complex 5 and C2H6 in a low yield (∼15% by 31P{1H}
NMR and GC; mainly starting material remained).
Although 5 was not isolated, it was readily identified
by comparison to an authentic sample, which was
prepared by reaction of a THF solution of RuCl2(PPh3)3
with 6 at 100 °C in a sealed pressure vessel (Scheme
1). Complexes 2 and 5 have almost identical spectro-
Ar CH2-H Bon d Activa tion w ith Ru (II). Reaction
of RuCl2(PPh3)3 with a stoichiometric amount of 1 and
tBuONa in THF at 80 °C (∼30 min in a sealed tube)
resulted in the formation of the benzylic Ru(II) complex
7 by a selective sp3 C-H bond activation process
(Scheme 2). Products resulting from metal insertion into
the stronger Ar-CH3 bond were not observed by 1H and
31P{1H} NMR (∆BDE ) Ar-CH3 - ArCH2-H ) 14 kcal/
mol).51 PPh3 is readily displaced by the bisphosphine
ligand 1, but its removal from the product solutions is
difficult. The reaction proceeds also in the absence of
base but rather sluggishly. Complex 7 was characterized
by various NMR techniques, MS, and elemental analy-
sis. The 31P{1H} NMR spectrum of 7 showed a doublet
resonance at δ 24.1 for the magnetically equivalent
phosphorus atoms of the meridional bisphosphine ligand
and a triplet resonance at δ 73.6 with cis-2J PP ) 29.6
Hz for the apical PPh3 ligand. The structure is fully
supported by 1H and 13C NMR spectroscopy. For in-
stance, the ArCH2Ru moiety appears in the 13C{1H}
1
scopic properties in the H, 31P{1H}, and 13C{1H} NMR.
Similar results were obtained using the Ph analogue of
4 (with phenyl groups replacing isopropyl substituents
on P), affording C2H6 and the known complex Ru(Cl)-
(PPh3){2,6-(Ph2PCH2)2C6H3} also in ∼15% yield.37-39
The latter and the related square-pyramidal complex
RuCl(PPh3)(2,6-(Me2NCH2)2C6H3) were recently fully
characterized by X-ray analysis.39,40 The low yield with
4 in comparison to the Ar-H and Ar-CH3 PCP systems
(1, 3, and 6) is most probably a result of a significantly
increased steric hindrance imposed by the ethyl group.
The Ar-CH3 bond is slightly stronger than the Ar-CH2-
CH3 bond (compare bond dissociation energy (BDE) of
Ph-CH3 ) 102 kcal/mol vs Ph-CH2CH3 ) 96.3 kcal/
mol).51,52 Although a consecutive sp3-sp3, sp2-sp3 Cs
C bond activation process forming 5 and 2 equiv of CH4
would have been thermodynamically more favorable (by
about 28 kcal/mol),5,52 CH4 was not observed by GC
analysis. Direct Ar-Et bond activation was also ob-
served upon reaction of Rh(I) with 4 and with its Ph or
2
NMR spectrum at δ 13.56 as a virtual quartet with J PC
≈ 5.5 Hz, respectively, and in the 13C-DEPT-135 NMR
a negative signal is observed indicative of an even
1
number of protons. In the H NMR spectrum of 7, the
2
ArCH2Ru group appears as a triplet at δ 3.28 with J PH
(51) McMillen, D. F.; Golden, D. M. A. Rev. Phys. Chem. 1982, 33,
493.
(52) Egger, K. W.; Cocks, A. T. Helv. Chim. Acta 1973, 56, 1516.
(53) McNeill, K.; Andersen, R. A.; Bergman, R. G. J . Am. Chem.
Soc. 1997, 119, 11244.
(54) Hartwig, J . F.; Andersen, R. A.; Bergman, R. G. J . Am. Chem.
Soc. 1989, 111, 2717.
(55) Kaplan, A. W.; Bergman, R. G. Organometallics 1997, 16, 1106.
(56) Kaplan, A. W.; Bergman, R. G. Organometallics 1998, 17, 5072.
(57) Chaudret, B. Bull. Soc. Chim. Fr. 1995, 132, 268.
(58) Urbanos, F.; Halcrow, M. A.; Fernandez-Baeza, J .; Dahan, F.;
Labroue, D.; Chaudret, B. J . Am. Chem. Soc. 1993, 115, 3484.
(59) Geiger, W. E.; Salzer, A.; Edwin, J .; von Philipsborn, W.;
Piantini, U.; Rheingold, A. L. J . Am. Chem. Soc. 1990, 112, 7113.
t
tBu analogues (containing Ph and Bu groups instead
of isopropyl substituents on P) in quantitative yield,9,10
indicating that sp2-sp3 C-C bond activation is kineti-
cally preferable to sp3-sp3 C-C bond activation in these
Ar-Et PCP systems, regardless of the higher bond
strength (∆BDE{Ph-CH2CH3 - PhCH2-CH3} ) ∼24.5
kcal/mol)33,34 and of the electron density and the bulk
at the d6 Ru(II) or d8 Rh(I) transition metal center.5,10

3876 Organometallics, Vol. 18, No. 19, 1999
van der Boom et al.
Sch em e 3
Sch em e 4
) 15.0 Hz, which collapses into a singlet resonance in
the 1H{31P} NMR spectrum. The ipso carbon of the
aromatic ring is probably close to the metal center,38
but no evidence for any bonding interaction nor distor-
tion of aromaticity is observed. For instance, the two
magnetically equivalent Ar-CH3 groups appear in the
1H NMR spectrum as a sharp singlet at δ 2.20, while
in the free ligand 1 and in the Ar-Ru complex 2 these
groups are observed at δ 2.38 and δ 2.21, respectively.
The mass spectrum of 7 shows the molecular ion (M+
777) having a correct isotope pattern. Complex 7 is
thermally stable under the applied reaction conditions
for at least 24 h, even in the presence of 1 equiv of HCl.
However, addition of excess HCl (3-10 equiv) afforded
mixtures of unknown products at 80 °C. No products
indicative of C-C bond activation were observed either
NMR. In the absence of H2, complex 7 is stable under
these reaction conditions (Scheme 3).
Deuterium incorporation into the Ar-CH2-Ru group
1
of 7 and C-C bond activation were observed by H and
31P{1H} NMR upon treatment of a C6D6 solution of 7
with 2 equiv of D2 at 60 °C (∼30% H/D exchange and
∼10% C-C bond activation after 2 h in a sealed tube),
indicating that the sp3 C-H bond activation is reversible
and fast in comparison with the competing C-C bond
activation process. In the case of Ir(I) and Rh(I) and the
tBu analogue of 1, C-C activation is kinetically (and
thermodynamically) more favorable than C-H activa-
tion, with ∆∆G#
) 0.342 kcal/mol for Ir(I) and
(CH-CC)
0.501 kcal/mol for Rh(I) in benzene at 293 K.7
While the Ar-CH3 bond is substantially stronger than
the ArCH2-H bond, this is apparently more than
compensated by the formed CH3-H and Ar-M bonds.
The chelate ring size may also play a role, although for
related Rh(I) complexes electronic factors play a domi-
nant role in controlling the relative stability of the
products of C-H and C-C bond activation.4
Ar CH2-H vs Ar -CH3 Bon d Activa tion Usin g
P ar a-Su bstitu ted Meth oxy an d Car bom eth oxy P CP
Su bstr a tes. To evaluate the role of the aromatic ring
in the C-H and C-C bond activation processes, we
prepared the new substrates 1-R (R ) OMe, C(O)OMe)
by bromomethylation of mesitylene derivatives,7,60 fol-
lowed by phosphination (Scheme 4).7
Reactions of RuHCl(PPh3)3 with 1 equiv of the ligands
1, 1-OMe and 1-C(O)OMe, respectively, in THF at 58
°C were monitored by 31P{1H} NMR at room tempera-
ture in a sealed NMR tube, showing the initial forma-
tion of the product of C-H bond activation (7, 7-R,
Figure 1). Formation of 7, 7-R is reversible (see below),
and they are gradually transformed into the C-C
1
by H or 31P{1H} NMR.
Ar CH2-H vs Ar -CH3 Bon d Activa tion w ith Ru -
(II). Reacting the hydrido complex RhHCl(PPh3)3 with
a stoichiometric amount of 1 in THF at 100 °C in a
sealed vessel resulted in quantitative formation of
complex 2 and CH4, as judged by NMR analysis of the
product solution and the GC analysis of the gas phase,
using authentic samples. Notably, no additional reagent
is necessary in this system in order to the drive the C-C
bond activation process. Monitoring the reaction at 60
°C in THF and at 110 °C in dioxane by 31P{1H} NMR
reveals the initial formation of the benzylic Ru(II)
complex 7, which converts in time irreversibly to 2 and
CH4 (by GC). This shows that the C-C bond activation
process generating an Ar-Ru(II) species 2 and CH4 is
thermodynamically more favorable than the competing
C-H bond activation process generating an ArCH2-Ru-
(II) complex 7 and presumably H2. Formation of H2 was
not detected directly. In support of this, reaction of 7
with 1 equiv of H2 in THF-d8 at 80 °C in a sealed tube
resulted in the formation of complex 2 and CH4 (∼90%
(60) van der Made, A. W.; van der Made, R. H. J . Org. Chem. 1993,
58, 1262.
1
conversion) after 24 h, as observed by H and 31P{1H}

Ar-CH3 vs ArCH2-H Bond Activation
Organometallics, Vol. 18, No. 19, 1999 3877
C-C ) 1:0.47). No intermediate compounds were ob-
served and the ratio between 1-OMe and 1-C(O)OMe
did not change during the experiment, indicating that
chelation of the PCP ligands occurs with the same rate
and is relatively slow.
Deuterium incorporation into the Ar-CH2-Ru group
of 7-R was observed by 1H{31P} and 31P{1H} NMR upon
treatment of a C6D6 solution of an equimolar amount
of 7-OMe and 7-C(O)OMe with 1 equiv of D2 at room
temperature. After 22 h, approximately 40% H/D ex-
change was observed for 7-C(O)OMe and only 10% for
1
7-OMe by H{31P} and 31P{1H} NMR, unambiguously
showing that the rate of the H/D exchange process is
significantly dependent on R: C(O)OMe > OMe regard-
less of the rate-determining step. The process was
readily reversed upon treatment of the reaction mixture
with H2 at room temperature. No C-C bond activation
took place and no intermediates were observed under
these conditions. As is well documented, cyclometalation
can be a highly reversible process.2,3,63-67 A rare case
of catalytic benzylic C-H bond activation involving a
Ru(II)/Ru(0) mechanism was reported.68,69
F igu r e 1. 31P{1H} NMR follow-up of the reaction of
1-OMe (10 mg, 0.024 mmol) with 1 equiv of RuHCl(PPh3)3
(25 mg, 0.025 mmol) in 1 mL of THF at 58 °C in a sealed
tube.
activation products (2, 2-R). Interestingly, the rate of
conversion of the products of C-H bond activation into
the products of C-C bond activation is dependent on
the substituent para to the cleaved C-C bond, following
the order C(O)OMe > H > OMe. For instance, after 10
h the ratios of the products of C-H and C-C bond
activation are distinctively different: C-H:C-C ) 1:1.4
for R ) C(O)OMe, 1:1 for R ) H, and 1:0.4 for R ) OMe.
Thus, it seems possible to influence the overall ArCH2-H
vs Ar-CH3 bond activation processes by altering the
electron density on the aromatic ring of the PCP ligand
1. Identification of the methoxy- and carboxy-substitut-
ed products of C-H and C-C bond activation was done
by independent preparation of authentic compounds. As
shown for ligand 1 (Schemes 1 and 2), treatment of
1-OMe and 1-C(O)OMe with RuCl2(PPh3)3 under H2
afforded the products of C-C bond activation (2-R and
CH4), whereas reaction of 1-R with RuCl2(PPh3)3 in the
Mechanistically, oxidative addition of H2 affording a
Ru(IV) intermediate such as A is possible (Scheme 5).
Six-coordinated dihydrido-Ru(IV) phosphine complexes
are known.70 No C-C bond activation was observed by
1H and 31P{1H} NMR spectroscopy during the H/D
exchange with 7-OMe and 7-C(O)OMe at room tem-
perature, clearly demonstrating that the reversible
ArCH2-H reductive elimination/oxidative addition pro-
cess (A T B) occurs prior to the slower C-C bond
activation step. The rate of H/D exchange between D2
and the benzylic protons (Ar-CH2-Ru) of a 1:1 mixture
of 7-OMe and 7-C(O)OMe follows the same trend as
observed for the conversion of the products of C-H bond
activation (7, 7-R, and H2) into the products of C-C
bond activation (2, 2-R, and CH4), indicating that the
observed substituent effect on the overall process pri-
marily originates from the reversible C-H bond activa-
tion step. The net substituent effect on the C-C bond
activation step, if any, seems insignificant. This might
point toward a concerted oxidative addition process C
with little, if any, participation of the aromatic π system.
Formation of an arenium species D in the rate-
determining step would have expected to show an
opposite substituent effect. van Koten et al. postulated
the formation of an arenium species in the activation
of an Ar-H bond in a PCP ligand by a Ru(II) dichloride
complex.40 The postulated methyl-hydrido-Ru(IV) spe-
cies E is expected to undergo rapid and irreversible
C-H reductive elimination, yielding complex 2 and CH4.
A three-center nonpolar transition state was recently
elucidated for the direct Ar-CH3 bond activation with
t
presence of BuONa yielded the products of C-H bond
activation (7-R). The benzylic (7-R) and aryl (2-R)
compounds exhibit almost identical spectroscopic prop-
1
erties in the H, 31P{1H}, and 13C{1H} NMR, except for
the presence of the methoxy or carboxy groups. The
electronic difference is quite pronounced in 13C NMR,
which is an excellent tool for analyzing electronic trends
in σ aryl-bound metal complexes.28,61,62 For instance, in
complex 2 the ipso carbon σ bound to the metal center
is observed at δ 172.74, while in 2-OMe this charac-
teristic carbon is observed at δ 165.03, shifted upfield
due to the higher electron density on the aromatic ring.
To ensure identical reaction conditions, we performed
a competition experiment by reacting 1 equiv of RuHCl-
(PPh3)3 with an equimolar amount of ligands 1-OMe
and 1-C(O)OMe at 65 °C in THF in one sealed tube
(Figure 2). Monitoring this reaction by 31P{1H] NMR at
room temperature unambiguously showed that in the
case of the electron-withdrawing carboxy substituent
1-C(O)OMe the product of C-C bond activation 2-C(O)-
OMe is dominant (after 10 h, ratio C-H:C-C ) 1:1.9),
whereas the C-H activation product prevails with the
electron-donating methoxy group (after 10 h, ratio C-H:
(63) van der Boom, M. E.; Ott, J .; Milstein, D. Organometallics 1998,
17, 4263.
(64) Beller, M.; Riermeier, T.-H.; Haber, S.; Kleiner, H.-J .; Herr-
mann, W. A. Chem. Ber. 1996, 129, 1259.
(65) Thorn, D. L. Organometallics 1998, 17, 348.
(66) Aizenberg, M.; Milstein, D. Organometallics 1996, 15, 3317.
(67) Steenwinkel, P. J ., S. L.; Gossage, R. A.; Grove, D. M.; van
Koten, G.; Kooijman, H.; Smeets, W. J . J .; Spek, A. L.; van Koten, G.
Organometallics 1998, 17, 4680.
(61) van de Kuil, L. A.; Luitjes, H.; Grove, D. M.; Zwikker, J . W.;
van der Linden, J . G. M.; Roelofsen, A. M.; J enneskens, L. W.; Drenth,
W.; van Koten, G. Organometallics 1994, 13, 468.
(62) Bromilow, J .; Brownlee, R. T. C.; Craick, D. J .; Sader, M.; Taft,
R. W. J . Org. Chem. 1980, 45, 2429.
(68) J ones, W. D.; Kosar, W. P. J . Am. Chem. Soc. 1986, 108, 5640.
(69) Hsu, G. C.; Kosar, W. P.; J ones, W. D. Organometallics 1994,
13, 385.
(70) Gru¨nwald, C.; Gevert, O.; Wolf, J .; Gonza´lez-Herreo, P.; Werner,
H. Organometallics 1996, 15, 5., 1960.

3878 Organometallics, Vol. 18, No. 19, 1999
van der Boom et al.
F igu r e 2. 31P{1H} NMR spectrum of a competition experiment with ligands 1-OMe, 1-C(O)OMe (5 mg, 0.012 mmol,
each), and RuHCl(PPh3)3 (25 mg, 0.025 mmol) in 1 mL of THF at 65 °C after ∼10 h. Only the PiPr2 groups are shown.
Sch em e 5
t
the Bu analogue of 1 and Rh(I) and Ir(I), which takes
place even at room temperature.7 However, other path-
ways cannot be rigorously excluded in this system.71
Regardless of the exact mechanism, selective sp2-sp3
Ar-C bond cleavage with Ru(II) takes place under mild
reaction conditions with significantly different electron
densities at the aryl moiety of the PCP ligands, and the
overall process (7 + H2 f 2 + CH4) is clearly promoted
by an electron-withdrawing carboxy substituent para
to the cleaved C-C bond of 7.
(COD ) cycloocta-1,5-diene) at room temperature re-
sults in C-H bond activation to form HCl and 8
quantitatively by 31P{1H} NMR (Scheme 2). A lower
yield (∼50%) of 8 is obtained with (MeCN)2PtCl2 and 1
in CH2Cl2.6 Activation of benzylic C-H bonds by Pt(II)
has been reported.8,63,72,73 Displacement of COD from
(COD)PtCl2 by the analogue of 1 in THF at room
temperature results in the quantitative formation of a
compound with two coordinated phosphines to one metal
center Pt(Cl2){1,3,5-(CH3)3-2,6-(Ph2PCH2)2C6H}.27 Such
a species is likely to be an intermediate in the reaction
of 1 as well. The benzylic Pt(II) complex 8 has been
Ar CH2-H vs Ar -CH3 Bon d Activa tion w ith P t-
(II). Treatment of a THF solution of 1 with (COD)PtCl2
1
identified by H, 31P, and 13C NMR spectroscopy, FD-
(71) We were not able to observe the formation of Ru(II)-H or Ru(O)
species by 1H and 31P{1H} NMR when the H/D exchange was per-
formed in the presence of ∼1 equiv of triethylamine. Therefore a σ-bond
metathesis mechanism involving release of HCl and formation of a
Ru(0) complex by ArCH2-H reductive elimination from a benzylic Ru-
(II)-H species seems less likely.
(72) Hackett, M.; Whitesides, G. M. J . Am. Chem. Soc. 1988, 110,
1449.
(73) van der Boom, M. E.; Liou, S.-Y.; Shimon, L. W. J .; Ben.-David,
Y.; Milstein, D. Organometallics 1996, 15, 2562.

Ar-CH3 vs ArCH2-H Bond Activation
Organometallics, Vol. 18, No. 19, 1999 3879
MS, and elemental analysis. The methylene group
(ArCH2Pt) of 8 appears in the 13C{1H} NMR spectrum
2
as a triplet at δ 1.12 (cis J PC ) 4.8 Hz) clearly flanked
by 195Pt satellites (1J PtC ) 432.0 Hz), and the 13C-DEPT-
135 NMR indicated an even number of protons. In the
1H NMR spectrum this alkyl group appears as a triplet
at δ 2.32 (3J PH ) 9.9 Hz) flanked by 195Pt satellites (2J PtH
) 92.0 Hz), which collapses into a singlet upon 31P
decoupling. The geometry renders the protons of the
i
ArCH2P groups (AB quartet) and the four Pr substit-
uents magnetically nonequivalent. Importantly, the two
Ar-CH3 groups and the para proton appear as singlets
at δ 2.18 and 6.51, respectively, clearly demonstrating
that there is no distortion of aromaticity due to an Ar‚
‚‚M interaction, as recently proposed for PCP-Ru(II)
complexes.38 The FD-MS of 8 shows the molecular ion
(M+ 610) having the expected isotopic pattern. The 31P-
{1H} NMR spectrum of 8 shows a sharp resonance at δ
69.05 flanked by 195Pt satellites (1J PtP ) 3539 Hz),
indicating that both phosphorus atoms are mutually
trans and magnetically equivalent. The low-field chemi-
cal shift reflects a deshielding effect of the phosphorus
atoms due to the formation of two six-membered che-
lated rings. The iodide analogue of 8 was obtained by
its reaction with MeI at 100 °C in toluene-d8.74 The
X-ray analysis of this complex 9 reveals that the ipso-
carbon is close to the metal center (Pt(1)‚‚‚C(1) ) 2.726
Å), but no additional evidence for any bonding interac-
tion is observed. The aromaticity is not distorted, as
indicated by the normal sp2-sp2 C-C distances (range
1.382(1)‚‚‚1.403(10) Å) and by the ring planarity. Least-
squares planar analysis through the aromatic ring
shows a mean deviation from planarity of 0.0314 Å. The
sp2-sp3 C-C bond (C(1)-C(10) ) 1.476(10) Å) is not
weakened by bonding of C(10) to the metal center, and
the C(1)-C(10)-Pt(1) angle (98.9(4)°) is indicative of an
approximate tetrahedral geometry around C(10).
F igu r e 3. ORTEP view of Pt(I){1-CH2-2,6-(iPr2PCH2)2-3,5-
(CH3)2C6H}, 9. Selected bond lengths (Å): Pt(1)-C(10) )
2.075(6); Pt(1)-P(3) ) 2.296(2); Pt(1)-P(2) ) 2.307(2); Pt-
(1)-I(1) ) 2.6864(6); C(1)-C(10) ) 1.476(10); C(3)-C(8)
) 1.519(11); C(5)-C(7) ) 1.509(10). Selected bond angles
(deg): C(1)-C(10)-Pt(1) ) 98.9(4); C(10)-Pt(1)-P(3) )
81.4(2); C(10)-Pt(1)-P(2) ) 83.9(2); P(3)-Pt(1)-P(2) )
153.08(7); C(10)-Pt(1)-I(1) ) 177.5(2); P(3)-Pt(1)-I(1) )
98.89(5); P(2)-Pt(1)-I(1) ) 96.75(5).
In contrast to the reactivity of the benzylic Ru(II)
complex 7 with H2 (Scheme 3), complex 8 was recovered
unchanged after treatment with H2 (30 psi) at temper-
atures up to 150 °C in various solvents. However, mild
heating of the thermally stable 8 in a dioxane solution
with a 10-fold excess of HCl results in the selective
formation of methyl chloride and the Ar-Pt complex 10
(Scheme 2), whereas treatment of the analogous Ru(II)
complex 7 with a slight excess of HCl resulted in
decomposition. The C-C bond activation proceeds even
at room temperature (∼20% conversion in 2 days by 31P-
{1H} NMR, starting material remained). Apparently,
the choice of the methylene scavenger and the transition
metal is crucial for reversing the kinetically preferred
C-H bond cleavage and enabling a thermodynamically
favorable C-C bond activation process.75 Metal-selective
bond activation has been demonstrated in C-H vs
F igu r e 4. 31P{1H} NMR follow-up of the reaction of 8 (24
mg, 0.041 mmol) in benzene (550 µL) with HCl (4 M
dioxane solution; 100 µL) to 10 and MeCl at 82 °C.
C-C,8 C-H vs C-Si,14-16 and alkyl vs aryl-O bond
activation.17,18 Characterization of complex 10 is unam-
1
biguous and is based on H, 13C{1H}, and 31P{1H} NMR
spectroscopy, elemental analysis, and FD-MS. In ad-
dition, complex 10 was prepared independently by
reaction of ligand 3, lacking the Ar-CH3 group between
the phosphine arms, with (COD)PtCl2 in toluene at 120
°C for 2 h (in a sealed vessel). The spectroscopic features
of 10 are similar to analogous d8 transition metal PCP
(74) Treatment of 8 with a 10-fold excess of 13CH3I in toluene-d8 at
100 °C in a sealed tube resulted in halide exchange to afford 13CH3Cl
and Pt(I){1-CH2-2, 6-(iPr2PCH2)2-3,5-(CH3)2C6H} (9). Formation of
13CH3Cl was observed by 1H and13C{1H} NMR of the product solution.
The reaction was monitored by 31P{1H} NMR at room temperature
t
complexes of group 10.18-20,23,26 The Bu analogue of 10
1
was first reported by Shaw et al.19 The H spectrum of
showing that the overall process (8 f 9) is first order in 8 with kobs
)
1.33 × 10-3 s-1 at 100 °C, corresponding to ∆Gq
) 20.5 kcal/mol.
(373K)
10 shows one sharp triplet resonance at δ 2.72 with J PH
) 4.2 Hz for the four protons of the two equivalent CH2P
groups. The signal collapses to a singlet flanked by
platinum satellites with J PtH ) 8.5 Hz upon phosphorus
decoupling in the 1H{31P} NMR. The 31P{1H} NMR
exhibits one sharp singlet resonance at δ 56.4 ac-
No intermediate species were observed.
(75) Reacting a THF solution of 7 with a 9-fold excess of HSi(OEt)3
at 80 °C overnight in a sealed tube resulted in the formation of 2 and
CH3Si(OEt)3 in a low yield (∼20%; no starting material 7 remained),
as judged by 31P{1H} NMR and GC-MS analysis of the product
solution. No C-C bond activation was observed upon treatment of 8
with HSi(OEt3).

3880 Organometallics, Vol. 18, No. 19, 1999
van der Boom et al.
Sch em e 6
companied by platinum satellites (1J PPt ) 2857 Hz),
kcal/mol and -65.4 eu, respectively, and ∆Gq(298) ) 21.6
kcal/mol. An inverse isotope effect of kD/kH ≈ 1.5 was
observed at 130 °C (by 31P{1H} NMR) when the reaction
of 8 and HCl was compared in dioxane/H2O vs dioxane/
D2O solutions (Figure 5). Both normal and inverse
isotope effects have been reported for C-H reductive
elimination from alkylhydrido-Pt(IV) species, and the
values differ widely. It is likely that C-C bond activa-
tion becomes more competitive with C-H bond cleavage
upon deuterium incorporation in the ArCH3 group.
Complex 10 was recovered unchanged when treated
with excess CH3Cl at elevated temperatures. This
indicates that the C-C bond activation process generat-
ing CH3Cl is thermodynamically more favorable than
the competing C-H bond activation process which
generates HCl, while the latter process is kinetically
preferred. Although the CH3-Cl bond is weaker than
the H-Cl bond (BDE 84 vs 103 kcal/mol, respectively)78
and the Ar-CH3 bond is stronger than the ArCH2-H
bond by about 14 kcal/mol,51 the C-C bond activation
process thermodynamics are compensated by the formed
strong Ar-Pt and H-CH2Cl bonds (BDE H-CH2Cl )
100.9 kcal/mol). Moreover, the Ar-M σ bond is expected
to be much stronger than the benzylic ArCH2-M
bonds.79,80 Thus, the kinetic products of C-H bond
activation of 1 by Pt(II) (8 + HCl) can be readily
converted into the thermodynamically more favored
ones (10 + MeCl) by an irreversible C-C bond activa-
tion process using a 10-fold excess of HCl. Reaction of
8 with H2 to afford 10 and CH4 would have been even
more favorable thermodynamically, suggesting that the
lack of reactivity of 8 with H2 is for kinetic reasons.
rendering both phosphorus atoms magnetically equiva-
1
lent. The J PtP coupling is typical for two trans phos-
phorus atoms coordinated to Pt(II). The FD-MS spec-
trum shows the molecular ion (M+ 596) and a logical
isotope pattern. Formation of methyl chloride was
confirmed by NMR and GC analysis of the product
solution and by comparison with an authentic sample.
31P{1H} NMR follow-up of the reaction of complex 8
with a 10-fold excess of HCl in a benzene/dioxane
solution (5.5:1 v/v) reveals the formation of a new species
(presumably F , Figure 4; Scheme 6), giving rise to a
small singlet at δ 35.23 ppm flanked by platinum
satellites (1J PtP ) 1919.3 Hz). Addition of the base
H2N(CH2)3OH to the reaction mixture resulted in disap-
pearance of F and an increase of 8. The relatively small
platinum-phosphorus coupling constant might suggest
a Pt(IV) complex,76 although further identification is
hampered by the low concentration and instability of
the intermediate. Formation of F was not observed in
dioxane or at temperatures above 100 °C. Regardless
of the exact nature of this adduct, the addition of HCl
to the Pt(II) complexes is not the rate-determining step.
HCl oxidative addition to Pt(II) complexes is known to
be reversible and relatively fast. Bercaw et al. observed
that trans-(PEt3)2Pt(II)(CH3)Cl reacts with HCl in CD2-
Cl2 at low temperatures to give (PEt3)2Pt(IV)(CH3)(H)-
Cl2 prior to C-H reductive elimination to afford CH4
and (PEt3)2Pt(II)Cl2.77 The process 8 f 10 slows down
t
upon addition of 2.5 equiv of Bu4NCl to the dioxane
solution, which has been shown to bring about depro-
tonation of alkylhydrido-Pt(IV) species.77 The activation
parameters for the conversion of 8 with a 10-fold excess
of HCl to 10 and MeCl in dioxane and in benzene/
dioxane (5.5:1 v/v) solutions were determined by 31P-
{1H} NMR. The overall process (8 f 10) is first order
in 8 with ∆Hq ) 10.6 kcal/mol, ∆Sq ) -40.1 eu, and
∆Gq(298) ) 23.1 kcal/mol in a benzene/dioxane (5.5:1 v/v)
solution. In dioxane the values of ∆Hq and ∆Sq are 2.1
Mechanistically, protonation of the kinetically favored
C-H activation product 8 with excess HCl probably
results in formation of F , which can form complex G by
reductive elimination. G is likely to be a common
intermediate for both the C-H and C-C bond activation
(78) CRC Handbook of Chemistry and Physics, 57 ed.; CRC Press:
Cleveland, OH.
(76) Allen, F. H.; Pidcock, A. J . Chem. Soc. A 1968, 2700.
(77) Stahl, S. S.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem. Soc.
1996, 118, 5961.
(79) Martinho-Simoes, J . A.; Beauchamp, J . L. Chem. Rev. 1990,
90, 629.
(80) J ones, W. D.; Feher, F. J . J . Am. Chem. Soc. 1984, 106, 1650.

Ar-CH3 vs ArCH2-H Bond Activation
Organometallics, Vol. 18, No. 19, 1999 3881
Sch em e 7
-H2O
F igu r e 5. 31P{1H} NMR follow-up of the reaction of 8 (24
mg, 0.041 mmol) with HCl (4 M dioxane solution; 100 µL)
in H2O (20 µL)/dioxane (550 µL) and D2O (20 µL)/dioxane
(550 µL), respectively.
type Pt(II) complex 11 (NCN ) 1,3-(Me2NCH2)2-C6H3),
similar to 10, reacts reversibly with MeI to yield a stable
arenium complex 12 analogous to I (Scheme 7). This
process was proven to proceed via an unobserved Pt-
(IV) intermediate K, akin to J . A theoretical study
predicted that a 1,2 methyl shift between the ipso
carbon of the aromatic group and the Pt center of 11 is
an allowed process.94 The reported C-C bond cleavage
of the arenium cation is driven by the generation of the
aromatic system and, interestingly, can be triggered
with H2O. It is noteworthy that no C-C bond activation
was observed upon reacting the Pd(II) analogue of
complex 8 with HCl.20 This observation is consistent
with the mechanism postulated here involving a Pt(II)/
Pt(IV) oxidative addition process. Reacting Pd(X){1-
CH2-2,6-(R2PCH2)2-3,5-(CH3)2-C6H3} (R ) Ph, Me; X )
Cl, CF3CO2) with HCl resulted in the formation of 16-
membered macrocycles.54,86
(Scheme 6). It is known that six-coordinated alkylhy-
drido-Pt(IV) complexes are relatively stable,81 whereas
analogous unsaturated Pt(IV) complexes undergo facile
C-H reductive elimination.82,83 Unsaturation seems
also to play an important role in C-C bond activa-
tion.1,7,13 The observation of F , which can be deproto-
nated, shows that the rate-determining step is not
protonation of the metal center, but probably involves
a later step such as the formation of a 14-electron
complex (G) or the C-C bond activation itself (G f J ).
Complex J can be formed directly from G by a concerted
oxidative addition process (H). Oxidative addition of
strained C-C bonds to Pt(II) is well-known,1,84-87
although here a nonstrained, strong C-C bond is
involved. Oxidative addition of cyclopropane to Zeise’s
dimer is limited to substrates bearing electron-donating
groups, suggesting that the C-C bond breaking process
proceeds by an electrophilic attack of the Pt(II) center.88
Alternatively, compound G might undergo an electro-
philic attack by the metal on the ipso carbon of the
aromatic ring, resulting in an arenium complex I, which
can undergo a reversible 1,2 methyl shift, affording the
Pt(IV) complex J , regenerating the aromatic π system.
Reductive elimination from J can give 10 and CH3Cl.
CH3X reductive elimination from Pt(IV) is known.89
The postulated mechanism involving an arenium
intermediate is well precedented by the work of van
Koten et al.,14,90-93 in which it was shown that a NCN-
Su m m a r y a n d Con clu sion s
In conclusion, this study demonstrates that it is
possible, using a model system, to achieve selective
activation of an unstrained C-C single bond with two
metals, Ru(II) and Pt(II), under mild reaction conditions
in solution with an overall retention of the metal
oxidation state. An aromatic PCP system having three
Ar-CH3 groups is selectively dealkylated by sp2-sp3
C-C bond activation. The C-C bond activation process
might be driven thermodynamically by reaction of the
kinetic products of C-H bond activation with another
substrate. Using a slight excess of HCl, it is possible to
drive the reaction with Pt(II) toward a thermodynami-
cally favorable C-C bond activation process. Remark-
ably, this process proceeds even at room temperature.
Methylene transfer from benzylic PCP-Rh(I) complexes
to nonpolar H-C, H-Si, and even Si-Si bonds was
reported.3 Formally, the transformation from 8 to 10
can be viewed as another entry into this fascinating
“methylene transfer” chemistry in which a methylene
group is selectively transferred to HCl by activation of
a strong C-C single bond. The balance between a C-H
and C-C bond activation process with Ru(II) is readily
(81) De Felice, V.; De Renzi, A.; Panunzi, A.; Tesauro, P. J .
Organomet. Chem. 1995, 488, C13.
(82) Stahl, S. S.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem. Soc.
1995, 117, 9371.
(83) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J . Organometallics
1995, 14, 4966, 10779.
(84) Crabtree, R. H. Chem. Rev. 1985, 85, 245.
(85) Tipper, C. F. H. J . Chem. Soc. 1955, 2045-2046.
(86) J ennings, P. W.; J ohnson, L. Chem. Rev. 1994, 94, 2241.
(87) Bischop, B. C., III. Chem. Rev. 1994, 94, 2241.
(88) Powell, K. G.; McQuillin, F. J . J . Chem. Soc., Dalton Trans.
1972, 2123.
(89) Goldberg, K. I.; Yan, J .-Y.; Winter, E. L. J . Am. Chem. Soc.
1994, 116, 1573.
(90) van Koten, G.; Timmer, J . G.; Noltes, J . G.; Noltes, J . G.; Spek,
A. L. J . Chem. Soc., Chem. Commun. 1978, 250.
(91) Grove, D. M.; van Koten, G.; Ubbles, H. J . C. Organometallics
1982, 1, 1366.
(93) Steenwinkel, P.; Kooijman, H.; Smeets, W. J . J .; Spek, A. L.;
Grove, D. M.; van Koten, G. Organometallics 1998, 17, 5411.
(94) Ortiz, J . V.; Havlas, Z.; Hoffmann, R. Helv. Chim. Acta 1984,
67, 1.
(92) Grove, D. M.; van Koten, G.; Louwen, J . N.; Nolles, J . G.; Spek,
A. L.; Ubbels, H. J . C. J . Am. Chem. Soc. 1982, 104, 6609.

3882 Organometallics, Vol. 18, No. 19, 1999
van der Boom et al.
yield 3.4 g, 35%). Mp ) 122-123 °C. 1H NMR (CDCl3) δ: 4.51
(s, 4H, CH2Br), 3.90 (s, 3H, CO2CH3), 2.43 (s, 3H, CH3), 2.29
(s, 6H, CH3). 13C{1H} NMR (CDCl3) δ: 170.44 (CdO), 138.29,
134.58, 134.19, 133.03 (all s, Ar), 28.97 (s, CO2CH3), 28.93 (s,
CH2Br2), 16.70 (s, ArCH3), 15.03 (s, ArCH3). IR (KBr): λ )
1732, 1218, 1208, 1178, 1041, 560.
tuned by addition of H2 or utilizing a metal precursor,
which generates H2 upon the kinetically favorable C-H
bond activation. Both C-H and C-C bond activation
were observed with RuHCl(PPh3)3, the C-H activation
product being ultimately converted into the C-C one,
whereas with RuCl2(PPh3)3 benzylic C-H bond activa-
tion is the only observed process. This indicates that
Ru(II) phosphine complexes may be selected for either
C-C or C-H bond activation.
(d ) P h osp h in a tion . An acetone solution (25 mL) of 2,6-
bis(bromomethyl)-4-carbomethoxymesitylene (3.8 g, 0.010 mol)
was treated with an acetone solution (25 mL) of iPr2PH (2.4 g,
0.020 mol) at room temperature, resulting in the formation of
white crystals. The phosphonium salt was decanted from the
mother liquid and decomposed with H2O (40 mL) followed by
an aqueous solution (40 mL) of NaOAc (11 g, 7.5 mol). The
product was obtained as an oil after extraction with ether (3.9
Exp er im en ta l Section
Gen er a l P r oced u r es. The procedures and spectroscopic
analyses are similar to those previously reported.10,18 Assign-
ments of 1H and 13C{1H} NMR signals were done with 1H-
{31P} and 13C-DEPT-135 NMR, respectively. All reactions were
carried out under an inert atmosphere. Solvents were dried,
distilled, and degassed before use. RuCl2(PPh3)3 and RuHCl-
(PPh3)3 were prepared by published procedures.3,95 Reaction
flasks were washed with deionized water, followed by acetone,
and then oven-dried prior to use. GC analyses were performed
on a Varian 3300 gas chromatograph equipped with a molec-
ular sieve column. Elemental analyses were carried out at the
Hebrew University, J erusalem. Field desorption (FD) mass
spectra were measured at the Institute of Mass Spectrometry,
the University of Amsterdam. The organometallic Ru(II)
products containing iPr substituents on the phosphorus atoms
are difficult to separate from the liberated PPh3 due to similar
solubility properties.
1
g, 85%). For 1-C(O)OMe: 31P{1H} NMR (C6D6) δ: 6.4 (s). H
NMR (C6D6) δ: 3.66 (s, 3H, CO2Me), 2.83 (s, 4H, CH2P), 2.72
(s, 3H, ArCH3), 2.50 (s, 6H, ArCH3), 1.76 (m, 4H, CH(CH3)2),
1.1 (dq, 24H, CH(CH3)2). 13C NMR (C6D6) δ: 171.63 (s, CO2-
Me), 136.29, 135.35, 129.66 (all s, Ar), 51.27 (s, CO2Me), 24.6
(d, 1J PC ) 16.9 Hz, CH2P), 23.60 (d, J PC ) 17.2 Hz, CH(CH3)2),
19.70 (t, J PC ≈ 14.0 Hz, CH(CH3)2), 18.97 (t, ArCH3), 18.51 (d,
ArCH3). IR (neat) λ: 1728 cm-1. Compound 1-OMe was
obtained in
a similar manner by phosphination of R,R′-
dibromo-2-methoxymesitylene.7 For 1-OMe: 31P{1H} NMR
(CDCl3) δ: 8.0 (s). 1H NMR (CDCl3) δ: 3.59 (s, 3H, OMe), 2.87
(d, 2J PH ) 2.2 Hz, 4H, CH2P), 2.43 (s, 3H, ArCH3), 2.31 (s, 6H,
ArCH3), 1.81 (m, 3J HH ) 7.0 Hz, 4H, CH(CH3)2), 1.10 (dd, 3J HH
3
3
) 7.1 Hz, J PH ) 12.2 Hz, 12H, CH(CH3)2), 0.98 (dd, J HH
)
3
7.0 Hz, J PH ) 12.0 Hz, 12H, CH(CH3)2). 13C NMR (CDCl3) δ:
155.15 (s, Ar), 135.29 (m, Ar), 130.50 (m, Ar), 129.59 (t, J PC
)
1
P r ep a r a tion of Liga n d s. The new ligands 1-R (R ) OMe,
C(O)OMe) were prepared by bromomethylation of mesitylene
derivatives followed by phosphination.
5.0 Hz, Ar), 59.91 (s, OMe), 24.4 (d, J PC ) 22.1 Hz, CH2P),
23.60 (d, J PC ) 12.7 Hz, CH(CH3)2), 19.56 (t, J PC ≈ 14.0 Hz,
CH(CH3)2), 18.20 (t, J PC ) 7.3 Hz, ArCH3), 13.66 (d, J PC ∼ 5.2
Hz, ArCH3). Anal. Calcd for C24H44O1P2: C, 70.21; H, 10.80.
Found: C, 69.99; H, 10.36
P r ep a r a tion of 1-C(O)OMe: (a ) F or m a tion of 2,4,6-
Tr im eth ylben zoic Acid . A solution of 2-bromomesitylene
(38.9 g, 30.4 mL, 0.195 mol) in 100 mL of dry ether was added
dropwise to Mg tunings (5.1 g, 0.21 mol) in dry ether (50 mL).
Initiation of the reaction required the addition of I2 and heating
with a fan blower. The reaction mixture was refluxed for 1 h
and stirred overnight at room temperature under argon. CO2
was passed through H2SO4 and bubbled into the Grignard
reaction for approximately 1 h. The reaction mixture was
acidified with HCl and ice, and the resulting solid was
extracted with CH2Cl2. The combined organic layers were dried
with Na2SO4, filtered, and then concentrated under vacuum.
The crude solid was suspended in pentane and filtered on a
sintered funnel (16.6 g, 51%). 1H NMR (CDCl3) δ: 9.0 (br,
CO2H), 6.88 (s, 2H, ArH), 2.41 (s, 3H, p-Me) 2.28 (s, 6H, o-Me).
(b) F or m a tion of Meth yl 2,4,6-Tr im eth ylben zoa te. A
solution of CH2N2 in ether (under KOH) was added to an ether
solution (150 mL) of 2,4,6-trimethylbenzoic acid (14.2 g, 0.0865
mol) until a yellow color persisted and TLC indicated full
conversion of the acid to a new less polar product. The reaction
mixture was concentrated under vacuum, and the residue was
distilled under high vacuum (0.2 mm.) The fraction distilling
at 83-85 °C contained the desired product (14.5 g, 94%). Anal.
Calcd for C11H14O2: C, 74.13; H 7.92. Found: C, 73.78; H, 8.13.
MS: m/z 179 (M+ + 1, calc m/z 178). IR (neat): λ ) 2953, 2924,
2560 (all m), 1732, 1268, 1087 (all s).
Hyd r ogen olysis of th e Ar -CH3 Bon d . A THF solution
(2 mL) of 1 (30 mg, 0.078 mmol) was added dropwise to a
stirred THF suspension (2 mL) of RuCl2(PPh3)3 (75 mg, 0.078
mmol). The reaction mixture was stirred under H2 (30-35 psi)
at 110 °C for 17 h in a 90 cm3 Fischer Porter pressure vessel.
Quantitative analysis of the gas phase by GC showed the
formation of CH4 (>85%). 31P{1H} NMR analysis of the green
reaction solution indicated the selective formation of complex
2 and PPh3, with no starting materials remaining. Removal
of the volatiles under vacuum resulted in the quantitative
formation of a green powder. It is possible to remove the
liberated PPh3 only partly by multiple washings of the solid
with cold (-30 °C) pentane. Ligands 1-OMe and 1-C(O)OMe
can be used as well, affording CH4 and 2-OMe and 2-C(O)-
OMe, respectively. For 2: 1H NMR (C6D6) δ: 7.6-6.9 (ArH),
2
(2+4)
PH
2.89 (dvt, left part of ABq, J HH ) 16.9 Hz,
J
) 9.9 Hz,
2H, CH2P), 2.61 (m, 2H, CH), 2.21 (s, 6H, ArCH3), 1.74 (dvt,
right part of ABq, 2J HH ) 16.8 Hz, (2+4)J PH is not resolved, 2H,
CH2P), 1.52 (m {d upon 31P decoupling}, J HH
Hz, J PH )
3
3
)
7.1
Hz, CH3), 1.35 (m, 2H, CH), 1.16 (m {d upon 31P decoupling},
3J HH ) 7.0 Hz, CH3), 1.06 (m {d upon 31P decoupling}, J HH
)
7.0 Hz
3
7.1 Hz, CH3), 0.78 (m {d upon 31P decoupling}, J HH
,
3
)
CH3). 13C{1H} NMR (C6D6) δ: 172.74 (dt, J PC
,
) 18.3, 4.7
2
PC
(2+4)
Hz, Cipso), 149-125 (CAr), 33.28 (vt,
J
) 24.4 Hz, CH2P),
PC
26.64 (vt, (1+3)J PC ) 18.3 Hz, CH), 26.28 (vt, (1+3)J PC ) 17.1 Hz,
(c) Br om om eth yla tion . A mixture of methyl 2,4,6-tri-
methyl benzoate (4.7 g, 0.026 mol), HBr (48%, 20 mL), glacial
acetic acid (4.0 mL), trioxane (4.8 g, 0.053 mol), and MeNEt3-
Br (0.3 g, 1.5 mmol) was heated for 24 h and poured over H2O/
ice. The product was extracted with CH2Cl2, and the combined
organic layers were washed twice with H2O until neutral, dried
with Na2SO4, filtered, and concentrated under vacuum. The
product, 2,6-Βis(bromomethyl)-4-carbomethoxymesitylene, was
purified by column chromatography (eluent hexane/ether, 9:1;
CH), 22.62 (s, ArCH3), 20.73 (s, CH3) 20.03 (CH3), 19.65 (vt,
(2+4)
(2+4)
J
) 4.5 Hz, CH3), 17.63 (vt,
J
) 4.4 Hz, CH3). 31P-
PC
PC
{1H} NMR (C6D6) δ: 76.47 (t, J PP ) 62.9 Hz, 1P), 45.83 (d,
2J PP ) 31.5 Hz, 2P). Anal. Calcd for C40H54Cl1P3Ru‚PPh3: C,
67.86; H, 6.77. Found: C, 67.28; H, 6.37. MS: m/z 763 (M+,
calc m/z 764), 728 (M+ - Cl, calc m/z 729); correct isotope
patterns. Similar results were obtained using the analogue of
1 with phenyl groups replacing isopropyl substituents on P,
affording Ru[2,6-(Ph2PCH2)2-3,5-(CH3)2C6H](PPh3)Cl and CH4.
1H NMR (C6D6): δ 8.1-6.7 (ArH), 3.57 (dvt, left part of ABq,
2
(95) Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. J . Chem. Soc.
(A) Inorg. Phys. Theor. 1968, 3143.
2
(2+4)
PH
left part of ABq, J HH ) 16.5 Hz,
J
is not resolved, 2H,

Ar-CH3 vs ArCH2-H Bond Activation
Organometallics, Vol. 18, No. 19, 1999 3883
2
CH2P), 2.30 (s, 6H, ArCH3), 2.12 (dvt, right part of ABq, right
Hz, ArCH2Ru). 31P{1H} NMR (C6D6) δ: 73.58 (t, J PP ) 59.4
2
(2+4)
2
part of ABq, J HH ) 16.5 Hz,
J
) 12.0 Hz, 2H, CH2P).
Hz, 1P), 24.1 (d, J PP ) 29.6 Hz, 2P).
PH
31P{1H} NMR (C6D6) δ: 80.81 (t, 2J PP ) 63.0 Hz, 1P), 39.84 (d,
Rea ction of Ru HCl(P P h 3)3 w ith 1. A dioxane solution (1
mL) of 1 (10 mg, 0.025 mmol) was added to RuHCl(PPh3)3 (23
mg, 0.025 mmol). The violet suspension was heated for 5 min
in a sealed tube at 110 °C. 31P{1H} analysis of the green
reaction solution showed the presence of complexes 2 and 7
in a 2.7:1 ratio. Continuous heating for another 10 min shows
2 and 7 in a 3.8:1 ratio. After 75 min only traces of 7 remained
(<5%). Analysis of the gas phase by GC showed the formation
of CH4. Monitoring the reaction at 60 °C by 31P{1H} NMR
reveals also the formation of 2 and 7. Heating a THF solution
(2 mL) of 1 (10 mg, 0.025 mmol) and RuHCl(PPh3)3 (23 mg,
0.025 mmol) for 17 h in a sealed vessel results in exclusive
formation of 2 and CH4 (85% by GC).
Ar -C Bon d Clea va ge w ith Ru (II); Rea ction of 7 w ith
H2. Reaction of a THF-d8 (1 mL) solution of 7 (37 mg, 0.048
mmol) with 1 equiv of H2 (1 mL, 0.045 mmol) at 80 °C in a
sealed tube resulted in the selective formation of complex 2
and CH4 (∼90% conversion after 24 h by 1H and 31P{1H} NMR).
Complex 7 is stable under those reaction conditions in the
absence of H2.
H/D Exch a n ge w ith 7 a n d 7-R. A C6D6 solution (1 mL)
of 7-OMe (19 mg, 0.024 mmol) and 7-CO(OMe) (20 mg, 0.023
mmol) was treated with D2 (1 mL, 0.045 mmol) at room
temperature in a sealed tube (total volume ) 2.5 mL). The
exchange progress was monitored by 1H and 31P{1H} NMR
showing ∼40% H/D exchange for R ) C(O)OMe and only ∼10%
H/D exchange for R ) OMe after 22 h. Flushing the tube with
N2 and treatment of the reaction mixture with H2 reversed
this labeling process. No other formation of Ru(0) or Ru(II)-H
was observed when the reaction was performed in the presence
of 1 equiv of triethylamine (8 µL, 0.058 mmol). Deuterium
incorporation into the ArCH2Ru group of 7 and C-C bond
activation were observed upon treatment of a C6D6 solution
(1 mL) of 7 (19 mg, 0.024 mmol) with excess of D2 (2 mL, 0.090
mmol) at 60 °C in a sealed tube (total volume ) 2.5 mL, ∼30%
H/D exchange after 2h).
F ollow -Up Exp er im en ts. (a) Three THF solutions (1 mL
each) of 1, 1-OMe, 1-C(O)OMe (10 mg, each), and RuHCl-
(PPh3)3 (25 mg, 0.025 mmol) were heated simultaneously in
sealed tubes in an oil bath at 58 °C and monitored by 31P{1H}
NMR at room temperature. In all three cases formation of the
products of C-H bond activation (7, 7-R) was observed first.
After 10 h the ratios of the products of C-H and C-C bond
activation are distinctively different: C-H:C-C ) 1:1.4 for R
) C(O)OMe, 1:1 for R ) H, and 1:0.4 for R ) OMe. The results
for 1-OMe are presented in Figure 1. Formation of CH4 was
observed by GC analysis of the gas phase. (b) A THF solution
(1 mL) of 1-OMe, 1-C(O)OMe (5 mg each), and RuHCl(PPh3)3
(25 mg, 0.025 mmol) was heated in a sealed tube in an oil bath
at 65 °C and monitored by 31P{1H} NMR at room temperature.
The ratio between the ligands remained constant during the
reaction. After 10 h, C-H:C-C ) 1:1.9 for R ) C(O)OMe and
C-H:C-C ) 1:0.47 for R ) C(O)OMe (Figure 2). No interme-
diate compounds were observed, and during the experiment
the ratio between 1-OMe and 1-C(O)OMe did not change.
Formation of CH4 was observed by GC analysis of the gas
phase.
2J PP ) 32.4 Hz, 2P). MS: m/z 899; correct isotope patterns.
F or m a tion of Com p lexes 2 a n d 5 by Ar -H Activa tion .
A THF solution (2 mL) of 3 or 6 (40 mg or 37 mg, 0.11 mmol)
was added dropwise to a stirred THF suspension (2 mL) of
RuCl2(PPh3)3 (105 mg, 0.11 mmol). The solution was stirred
for 10 h at 110 °C in a sealed pressure vessel. 31P{1H} analysis
of a green aliquot showed complex 2 or 5 and PPh3 as the only
products. Consequently, the reaction mixture was filtered
through a cotton pad, pumped to dryness, washed with cold
pentane (-30 °C, 3 × 5 mL), and dried in vacuo, affording a
green powder (68%). Complex 2 and the analogous complex 5,
having two methyl substituents in the 3 and 5 positions of the
aromatic ring, exhibit similar spectroscopic features. For 5:
Anal. Calcd for
C38H50Cl1P3Ru‚H2O: C, 60.51; H, 6.95.
Found: C, 60.67; H, 7.17. 1H NMR (C6D6) δ: 7.65 (m, 6H,
ortho-H of PPh3), 7.0-6.8 (m, 12H, Ar), 2.86 (dvt, left part of
2
(2+4)
PH
ABq, J HH ) 16.5 Hz,
J
) 10.2 Hz, 2H, CH2P), 2.57 (m,
2
(2+4)
2H, CH), 2.03 (dvt, right part of ABq, J HH ) 16.5 Hz,
) 7.4 Hz, 2H, CH2P), 1.50 (vq, 6H, J HH ) 7.2 Hz,
J
PH
3
(3+5)
J
)
PH
3
7.4 Hz, CH3), 1.34 (m, 2H, J HH ) 7.2 Hz, CH), 1.1 (m, 12H,
3J HH ≈ 6.9 Hz, CH3), 0.75 (dvt, 6H, J HH ) 7.1 Hz,
J
)
(3+5)
PH
5.4 Hz, CH3). 13C{1H} NMR (C6D6) δ: 174.1 (dt, 2J PC
, PC ) 18.2,
(2+4)
≈ 4 Hz, Cipso), 153-121 (CAr), 36.29 (vt,
J
) 23.6 Hz,
PC
(1+3)
(1+3)
CH2P), 26.15 (vt,
J
) 16.4 Hz, CH), 26.12 (vt,
J
)
PC
PC
16.4 Hz, CH), 20.84, 20.08, 19.57, 17.86 (all s, CH3). 31P{1H}
2
2
NMR (C6D6) δ: 79.11 (t, J PP ) 62.8 Hz, 1P), 43.91 (d, J PP
)
31.9 Hz, 2P).
Hyd r ogen olysis of th e Ar -CH2CH3 Bon d . A THF solu-
tion (2 mL) of 4 (29 mg, 0.079 mmol) was added dropwise to a
stirred THF suspension (2 mL) of RuCl2(PPh3)3 (75 mg, 0.078
mmol). The resulting solution was stirred for 5 days under H2
(30-35 psi) at 110 °C in a 90 mL Fischer Porter pressure
vessel. The resulting green solution was analyzed by 31P{1H}
NMR, showing the formation of 5 in ∼15% yield and unreacted
starting materials. Quantitative analysis of the gas phase by
GC showed the formation of 1 equiv of C2H6 (∼15% yield). No
CH4 formation was observed. Similar results were obtained
using the Ph analogue of 4, affording the known Ru[2,6-(Ph2-
PCH2)2C6H3](PPh3)Cl and C2H6 in a low yield (∼15% yield
based on 31P{1H} and GC).38,39 The Ar-Ru complexes were
identified by 31P{1H} NMR using authentic samples.
Ar CH2-H Bon d Activa tion w ith Ru Cl2(P P h 3)3 a n d
tBu ONa ; F or m a tion of 7. A THF solution (1 mL) of 1 (30
t
mg, 0.078 mmol) and BuONa (10 mg, 0.104 mmol) was added
to a THF suspension (1 mL) of RuCl2(PPh3)3 (75 mg, 0.078
mmol) and heated at 80 °C for 30 min in a sealed tube. 31P-
{1H} analysis of the reaction solution showed the selective
formation of complex 7. Subsequently, the volatiles were
evaporated and the residue was dissolved in benzene (5 mL),
filtered through a cotton pad, and dried in vacuo. It is possible
to remove the liberated PPh3 by multiple washings of the solid
with cold (-30 °C) pentane. Ligands 1-OMe and 1-C(O)OMe
can be used as well, affording 7-OMe and 7-C(O)OMe,
respectively. For 7: Anal. Calcd for C41H56Cl1P3Ru: C, 63.27;
H, 7.25. Found: C, 64.01; H, 7.83. MS: m/z 777 (M+, calc 778),
742 (M+ - Cl, calc m/z 743), correct isotope patterns. 1H NMR
Ar CH2-H Bon d Activa tion w ith (COD)P tCl2; F or m a -
tion of 8. To a stirred slurry of (COD)PtCl2 (105 mg, 0.281
mmol) in THF (10 mL), a solution of 1 (110 mg, 0.289 mmol)
in THF (10 mL) was added dropwise over a period of 5 min at
room temperature. The clear yellow solution was stirred for
12 h, then filtered through a cotton pad, and reduced in volume
to about 1 mL. Addition of cold pentane (10 mL, - 30 °C)
caused precipitation of the slightly yellow product, which was
washed twice with cold pentane (-30 °C, 2 × 10 mL) and then
dried in vacuo to give an off-white powder 8 in nearly
(C6D6) δ: 8.3-6.6 (ArH), 3.28 (t, {s upon 31P decoupling}, 3J PH
2
) 15.0 Hz, 2H, ArCH2Ru), 3.01 (dvt, left part of ABq, J HH
)
14.6 Hz, (2+4)J PH is not resolved, 2H, CH2P), 2.38 (m, 2H, CH),
2.20 (s, 6H, ArCH3), 1.72 (m, 2H, CH), 1.45 (m {d upon 31P
decoupling}, J HH ) 6.9 Hz, CH3), 1.40 (m {d upon 31P
3
decoupling}, J HH ) 7.0 Hz, CH3), 0.87 (m {d upon 31P
3
decoupling}, J HH ) 6.8 Hz, CH3), 0.66 (m {d upon 31P
3
decoupling}, J HH ) 6.8 Hz, CH3). 13C{1H} NMR (C6D6) δ:
3
(1+3)
140-126 (CAr), 33.03 (vt,
J
) 16.8 Hz, CH), 22.17 (vt,
) 18.8 Hz, CH2P), 20.10, 19.67, 19.41, 17.67 (s, CH3),
PC
(2+4)
J
quantitative yield (171 mg, 0.28 mmol). Anal. Calcd for C23H41
Cl1P2Pt‚0.5 THF: C, 46.47; H, 7.02. Found: C, 46.52; H, 6.81.
-
PC
(2+4)
2
16.83 (vt,
J
) 4.7 Hz, CH3), 13.56 (vq, J PC ) 5.3, 11.0
PC

3884 Organometallics, Vol. 18, No. 19, 1999
van der Boom et al.
Ta ble 1. Cr ysta l Da ta for 9
observed by GC analysis of the gas phase. Similar results were
obtained using THF or toluene at 150 °C.
formula
fw
C23H41P2PtI
701.49
Ar -C Bon d Act iva t ion w it h P t (II); F or m a t ion of
Com p lex 10. In a typical experiment complex 8 (24 mg, 0.041
mmol) was dissolved in C6D6 (0.55 mL) and loaded into a 5
mm screw-cap NMR tube (5 mm high-pressure NMR tubes
were used as well). A solution of HCl in dioxane (4 M; 100 µL,
0.40 mmol) was added. The tube was sealed and heated to 82
°C. The progress of the reaction was monitored by 31P{1H}
NMR at room temperature. After 35 min the reaction was
complete, as judged by 31P{1H} NMR spectroscopy. The reac-
tion solution was evaporated and the solid washed with cold
pentane (2 × 5 mL; -30 °C) and then dried in vacuo (20 mg;
80% yield). The formation of MeCl was unambiguous based
on GC experiments and NMR spectroscopy of the reaction
solution and by comparison to an authentic sample of MeCl
space group
crystal system
a, Å
P2(1)/c (no. 14)
monoclinic
9.042(2)
b, Å
c, Å
17.059(3)
16.703(3)
â, deg
104.450(3)
2494.9(8)
1.868
V, Å3
D
Z
calcd, g cm-3
4
µ(Mo KR), mm-1
crystal size, mm3
T, K
6.997
0.2 × 0.2 × 0.4
110
no. of reflns collected
no. of indep reflns
final R indices [I > 2σ(I)]
R indices (all data)
11633
5730[R(int))0.0533]
R1 ) 0.0448, R2 ) 0.0821
R1 ) 0.0614, R2 ) 0.0927
t
in BuOMe. The follow-up measurements were performed at
58, 82, 101, and 125 °C in C6D6/dioxane and at 90, 115, and
150 °C in dioxane. For each set of experiments, samples were
prepared from the same batch of 8. For 10; Anal. Calcd for
FD-MS: M+ 610 (correct isotope pattern). 1H (C6D6) δ: 6.51
2
(s, 1H, ArH), 2.91 (dt, left part of AB quartet, J HH ) 14.9 Hz,
C
22H39Cl1P2Pt: C, 44.33; H, 6.60. Found: C, 43.89; H, 6.37.
(2+4)
3
J
) 6.8 Hz, J PtH ) 54.6 Hz, 2H, CH2P), 2.27 (m, 2H,
FD-MS: M+ 596 (correct isotope pattern). 31P{1H} (161.9 MHz,
PH
2
CH), 2.53 (d, left part of AB quartet, J HH ) 14.9 Hz, 2H,
1
1
C6D6): δ 56.37 (s, J PtP ) 2857 Hz). H (C6D6): δ 6.75 (s, 1 H;
ArH), 2.72 (vt, J PH ) 4.2 Hz, J PtH ) 18.5 Hz, 4H, CH2P), 2.26
(m, 4H, CH), 2.19 (s, 6H; ArCH3), 1.39 (dd, J HH ) 7.2 Hz, J PH
) 16.4 Hz, 12H, CH3), 0.91 (dd, J HH ) 7.1 Hz, J PH ) 14.7 Hz,
12H, CH3). 13C{1H} (C6D6): δ 150.19 (s, Cipso), 145.42 (vt, J PC
3
2
CH2P), 2.32 (t, J PH ) 9.9 Hz, J PtP ) 92.0 Hz, 3H, ArCH2Pt),
2.18 (s, 6H, ArCH3), 1.89 (m, 2H, CH), 1.20 (m, 3J HH ) 8.0 Hz,
3J HH ) 7.6 Hz, J PH ) 14.9 Hz, J PH ) 15.5 Hz, 12H, CH3),
3
3
3
3
1.05 (m, J HH ) 7.2 Hz, J PH ) 15.0 Hz, 6H, CH3), 0.84 (dd,
3J HH ) 7.2 Hz, J PH ) 13.3 Hz, 6H, CH3). 31P{1H} (C6D6) δ:
3
2
) 9.5 Hz, J PtC ) 95.4 Hz, Cortho), 131.34 (vt, J PC ) 8.3 Hz,
69.05 (s, J PtP ) 3599 Hz). 13C{1H} (C6D6) δ: 145.34 (t, J PC
)
1
3
4
C
meta), 127.44 (s, J PtC ) 6.4 Hz, Cpara), 31.72 (vt, J PC) 5.3 Hz,
2
3
6.0 Hz, J PtC ) 41.0 Hz, Cipso), 132.51 (vt, J PC ) 2.9 Hz, J PtC
3J PtC ) 108.0 Hz, CH2P), 24.34 (vt, J PC ) 14.6 Hz, 2J PtC ) 54.7
4
) 9.3 Hz, Cortho), 128.00 (vt, J PC ) 1.5 Hz, J PtC ) 19.3 Hz,
2
Hz CH), 18.47 (s, J PtC ≈ 14 Hz, CH3), 17.76 (s, J PtC ) 26.1
C
meta), 124.93 (s, J PtC ) 9.6 Hz, Cpara), 26.77 (vt, J PC ) 9.9 Hz,
Hz, CH3).
CH), 24.44 (vt, J PC ) 12.6 Hz, CH), 21.17 (vt, J PC ) 13.0 Hz,
J PtC ) 22.0 Hz, CH2P), 19.43 (vt, J PC ) 1.9 Hz, 3J PtC ) 7.8 Hz,
CH3), 18.82 (vt, J PC ) 2.4 Hz, CH3), 18.35 (s, CH3), 17.41 (s,
Ar -C Bon d Activa tion w ith P t(II); Kin etic Isotop e
Effect. Complex 8 (24 mg, 0.041 mmol) was dissolved in
dioxane (0.55 mL) and loaded into a 5 mm screw-cap NMR
tube. A solution of HCl in dioxane (4 M; 100 µL, 0.040 mmol)
and H2O or D2O (20 µL, 1.1 mmol) was added. The tube was
sealed and heated to 130 °C. The progress of the reaction was
monitored by 31P{1H} NMR at room temperature. The results
are presented in Figure 5.
P r ep a r a tion of Com p lex 10. A toluene solution (10 mL)
of 3 (76 mg, 0.20 mmol) was added to a stirred toluene
suspension (10 mL) of (COD)PtCl2 (75 mg, 0.20 mmol). The
reaction mixture was heated for 2 h at 150 °C in a pressure
flask. All volatiles were removed in vacuo, and the product
was extracted with excess pentane (∼30 mL) and obtained as
a waxy solid in 80% yield (91 mg).
2
1
3J PtC ) 9.6 Hz, CH3), 1.12 (t, J PC ) 4.8 Hz, J PtC ) 432.0 Hz,
ArCH2Pt).
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of 9. Yellow
crystals suitable for X-ray diffraction studies were obtained
by slow evaporation of the benzene solvent. A prismatic crystal
(0.2 × 0.2 × 0.4 mm3) was mounted on a glass fiber and flash
frozen in a cold nitrogen stream (at 110 K) on a Rigaku AFC5R
four-circle diffractometer mounted on a rotating anode with
Mo KR radiation (λ ) 0.71073 Å) and a graphite monochro-
mator. Accurate unit-cell dimensions were obtained from a
least-squares fit to setting angles of 25 reflections in the range
1.73° e θ e 27.50°. The SHELXS-92 and SHELXL-93 program
packages installed on a Silicon Graphics workstation were
used for structure solution and refinement. The structure was
solved using direct methods (SHELXS-92) and refined by full-
matrix least-squares techniques based on F2 (SHELXL-93).
The final cycle of the least-squares refinement for 9 gave an
agreement factor R ) 0.0448 (based on F2) for all data with I
> 2σI and R ) 0.0614 for all data based on 5711 reflections.
Hydrogens were calculated from difference Fourier maps and
refined in a riding mode with individual temperature factors.
ORTEP views of the molecular structures and the adopted
numbering schemes are shown in Figure 3. Table 1 gives
details of the crystal structure determination.
Ack n ow led gm en t. This work was supported by the
US-Israel Binational Science Foundation, J erusalem,
Israel, and by the MINERVA Foundation, Munich,
Germany. We thank Dr. L. J . W. Shimon for performing
the X-ray structural analysis of complex 9. D.M. is the
holder of the Israel Matz Professorial Chair of Organic
Chemistry.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data and structure refinement, atomic coordinates,
bond lengths and angles, anisotropic displacement parameters,
and hydrogen atomic coordinates for 9. This material is
available free of charge via the Internet at http://pubs.acs.org.
Attem p ted Rea ction of 8 a n d H2. A yellowish C6D6
solution (2 mL) of 8 (25 mg) was loaded into a 90 mL Fischer
Porter pressure vessel, charged with H2 (30 psi), and heated
at 120 °C for 24 h. 1H and 31P{1H} NMR analysis showed only
the presence of unreacted 8. No methane formation was
OM990282F