Synthesis and reactivity of (DPPE){(C6H5)(C6H4)PCH 2CH2P(C6H5M)2}RuCl

Article abstract of DOI:10.1021/om970631a

The compound trans-(DPPE)₂RuCl₂ (1) undergoes reaction in neat trimethylaluminum to afford two products: trans-(DPPE)₂RuCH₃Cl (2) and (DPPE)-{(C₆H₅)(C₆H₄)PCH ₂

Full text of DOI:10.1021/om970631a

Organometallics 1997, 16, 5613-5615
5613
Syn th esis a n d Rea ctivity of
(DP P E){(C6H5)(C6H4)P CH2CH2P (C6H5)2}Ru Cl
Kayo Umezawa-Vizzini and T. Randall Lee*
Department of Chemistry, University of Houston, Houston, Texas 77204-5641
Received J uly 24, 1997X
Summary: The compound trans-(DPPE)2RuCl2 (1) un-
dergoes reaction in neat trimethylaluminum to afford
two products: trans-(DPPE)2RuCH3Cl (2) and (DPPE)-
{(C6H5)(C6H4)PCH2CH2P(C6H5)2}RuCl (3). Mechanistic
studies suggest that the ortho-metalation reaction pro-
ceeds via the cationic intermediate [(DPPE)2RuCH3]+ (5).
The X-ray crystal structures of complex 3 and the cation
of [(DPPE){(C6H5)(C6H4)PCH2CH2P(C6H5)2}Ru]+[PF6]-
(6) are reported.
Transition-metal compounds in combination with
Lewis acids are known to polymerize1 or oligomerize2
olefins. Late-transition-metal compounds are of current
interest in the development of new types of Ziegler-
Natta catalysts because they are less oxophilic than
earlier transition metals, which should lead to an
enhanced tolerance of polar functional groups.3,4 Cat-
ionic nickel- and palladium-based metal alkyls were
recently found to polymerize olefins to high-molecular-
weight and highly crystalline polymers.3 Although
ruthenium-based catalysts have been shown to be
effective in the metathesis polymerization of cyclic
olefins (where they are tolerant of functional groups and
aqueous environments),4 there are few examples of
olefin polymerization/oligomerization via a coordinative
insertion mechanism in Ru-based systems.5
F igu r e 1. ORTEP drawing (40% probability level) of
(DPPE){(C6H5)(C6H4)PCH2CH2P(C6H5)2}RuCl (3). Param-
eters: Ru-P(1) ) 2.260(1), Ru-P(2) ) 2.331(1), Ru-P(3)
) 2.371(1), Ru-P(4) ) 2.383(1), Ru-C(4) ) 2.12(4), Ru-
Cl ) 2.488(1) Å; P(1)-Ru-C(4) ) 67.7(2), P(2)-Ru-C(4)
) 84.6(1), P(3)-Ru-C(4) ) 89.3(1), P(4)-Ru-C(4) ) 164.6-
(2), Cl-Ru-C(4) ) 92.6(2)°.
Our research focuses on the development of ruthe-
nium alkyls for olefin polymerization. One of our early
targets has been cis-(DPPE)2RuCH3Cl, whose synthesis
is reported in the literature.6 Following the reported
procedure, we heated trans-(DPPE)2RuCl2 in neat AlMe3
at 80 °C for 5 min, which generated an oily red residue.
After washing with ethanol, analysis of the resulting
yellow solid surprisingly revealed a mixture of two
compounds: the monoalkylated trans-(DPPE)2RuCH3-
PCH2CH2P(C6H5)2RuCl (3)8 in about a 1:9 ratio, respec-
tively, rather than the reported cis-(DPPE)2RuCH3Cl.6
When the reaction was conducted at 90 °C, compound
3 was the sole product; conversely, when the tempera-
ture was held at 40 °C, compound 2 was the major
product (g95%). Also, 3 can be generated directly from
2 by heating the precursor to 90 °C in neat AlMe3.
The structure of 3 was determined by single-crystal
X-ray diffraction, which revealed a distorted octahedron
with the ortho-metalated ruthenium-carbon bond cis
to the chloride (Figure 1). The Ru-C(sp2) distance is
2.12 Å, which is consistent with those observed in ortho-
Cl (2)7 and the ortho-metalated (DPPE)(C6H5)(C6H4)-
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) Schmidt, G. F.; Brookhart, M. J . Am. Chem. Soc. 1985, 107, 1443.
Klabunde, U.; Ittel, S. D. J . Mol. Catal. 1987, 41, 123.
(2) J ones, J . R.; Symes, T. J . J . Chem. Soc. C 1971, 1124. Kawakami,
K.; Mizoroki, T.; Ozaki, A. Bull. Chem. Soc. J pn. 1978, 51, 21.
(3) Killian, C. M.; Tempel, D. J .; J ohnson, L. K.; Brookhart, M. J .
Am. Chem. Soc. 1996, 118, 11664. J ohnson, L. K.; Mecking, S.;
Brookhart, M. J . Am. Chem. Soc. 1996, 118, 267. J ohnson, L. K.;
Killian, C. M.; Brookhart, M. J . Am. Chem. Soc. 1995, 117, 6414.
(4) Hillmyer, M. A.; Lepetit, C.; McGrath, D. V.; Novak, B. M.;
Grubbs, R. H. Macromolecules 1992, 25, 3345.
metalated complexes such as Ru(C6H4PPh2)(PPh3)(η5-
C5H5) and related compounds.9,10 The bond angles in
(8) Prepared separately by heating 0.50 g of 1 (5.2 × 10-4 mol) in
neat AlMe3 (1.5 mL) for 5 min at 90 °C. The red oily product was
washed with hexane and stirred with EtOH. The resulting yellow
precipitates were extracted with benzene, and recrystallized from CH2-
Cl2/Et2O. Yield: 68% of yellow crystals. Crystal data: C52H47ClP4Ru,
Mr ) 932.32; orthorhombic; Pna21; a ) 16.366(3) Å, b ) 20.657(5) Å,
c ) 12.773(3) Å; V ) 4318 Å3; Z ) 4; D ) 1.43 g/cm3. 1H NMR (CD2Cl2;
300 MHz; 293 K): δ 5.0-4.6 (m, 8 H, Ph2PCH2CH2PPh2), 7.7-9.8 (m,
39 H, Ph2PCH2CH2PPh2. 13C NMR (CD2Cl2; 75.5 MHz; 293 K): δ 29.0
(m), 29.1 (m), 22.3 (m), 24.1 (m), 122.3-134.0 (m). 31P{1H} NMR (CD2-
Cl2; 121 MHz; 293 K): ABCD pattern, δ 12.7 (m), 32.2 (m), 41.2 (dd),
(5) J ames, B. R.; Markham, L. D. J . Catalysis 1972, 27, 442. Konita,
S.; Yamamoto, A.; Ikeda, S. Bull. Chem. Soc. J pn. 1975, 48, 101.
(6) Chatt, J .; Hayter, R. G. J . Chem. Soc. 1963, 6017. Ginsberg, A.
P.; Lindsell, W. E. Inorg. Chem. 1973, 12, 1983.
(7) Prepared separately by heating 0.50 g of 1 (5.2 × 10-4 mol) in
neat AlMe3 (1.5 mL) for 5 min at 40 °C. Yield: 34% of pale yellow
crystals (recrystallized from CH2Cl2/Et2O). 1H NMR (CD2Cl2; 300 MHz;
293 K): δ -1.9 (quint, 3 H, Ru-CH3, J PH ) 5.4 Hz), 2.5 (m, 8 H,
Ph2PCH2CH2PPh2), 6.5-8.0 (m, 40 H, Ph2PCH2CH2PPh2). 31P{1H}
43.6 (dd), 48.7 (dd), 51.5 (dd). Mp: 314 °C dec. Anal. Calcd for C52H47
ClP4Ru: C, 66.92; H, 5.04. Found: C, 66.61; H, 5.10.
-
NMR (CD2Cl2; 121 MHz; 293 K): δ 57.0 (s). Anal. Calcd for C53H51
Cl2P4Ru: C, 67.16; H, 5.39. Found: C, 66.89; H, 5.17.
-
(9) Bruce, M. I.; Cifuentes, M. P.; Humphrey, G.; Poczman, E.; Snow,
M. R.; Tiekink, E. R. T. J . Organomet. Chem. 1988, 338, 237.
S0276-7333(97)00631-6 CCC: $14.00 © 1997 American Chemical Society

5614 Organometallics, Vol. 16, No. 26, 1997
Communications
Sch em e 1
F igu r e 2. ORTEP drawing (40% probability level) of
[(DPPE){(C6H5)(C6H4)PCH2CH2P(C6H5)2}Ru]+ (cation of 6).
Parameters: Ru-P(1) ) 2.340(1), Ru-P(2) ) 2.349(1), Ru-
P(3) ) 2.319(1), Ru-P(4) ) 2.332(1), Ru-C(4) ) 2.12(5)
Å; P(1)-Ru-C(4) ) 68.3(1)°, P(2)-Ru-C(4) ) 100.2(1)°,
P(3)-Ru-C(4) ) 88.2(1)°, P(4)-Ru-C(4) ) 98.0(1)°.
carbon in an apical position (Figure 2). The Ru-C(sp2)
distance is 2.05 Å, which is shorter than the analogous
bond in 3.
the four-membered metallacycle are typical of those
reported in the literature;11 compound 3, for example,
has a P-Ru-C angle of 67.7°.
The structural relationship between the phenyl groups
and the chloride atoms in 1 and 3 prohibits direct
thermal elimination of HCl from 1 as the mechanism
for generating 3. Similarly, direct thermal elimination
of CH4 from 2 is untenable (see Scheme 1). The
generation of 3 might proceed via dissociation of one of
the DPPE phosphines in 1 followed by the oxidative
addition of an aryl C-H bond with consequent reductive
elimination of CH4 and reattachment of the phosphine.
Heating compound 1 in refluxing benzene or toluene in
the absence of AlMe3, however, fails to generate 3
(Scheme 1). Consequently, phosphine dissociation, if it
were to occur, would appear to require the assistance
of AlMe3. Since, however, the enthalpy of formation of
arylphosphine-AlX3 adducts is only weakly favorable,18
and the abstraction of chlorine from metal complexes
by alkylaluminum compounds is well-documented,19 the
role of AlMe3 is probably to abstract a chlorine (rather
than a phosphine) from 1. These factors suggest a
mechanism alternative to phosphine dissociation for the
generation of 3.
In experiments at room temperature, exposure of 3
in C6D6 to HCl generated cis- and trans-(DPPE)2RuCl2.12
Exposure of 3 in CD2Cl2 to H2 generated trans-(DPPE)2-
RuHCl.13 Complex 3 did not, however, appear to react
in CD2Cl2 with 1 atm of either CO or CH2dCH2.
Examples of the ortho-metalation of aryl phosphine
ligands during the alkylation of ruthenium are well-
known.10,11,14 The exact mechanism of the ortho-meta-
lation reaction, however, has not been firmly estab-
lished. We undertook several studies in an effort to
probe the mechanistic details of our system (Scheme 1).
The three cationic compounds [(DPPE)2RuCl]+[PF6]-
(4),15 [(DPPE)2RuCH3]+[PF6]- (5),16 and [(DPPE){(C6-
H5)(C6H4)PCH2CH2P(C6H5)2}Ru]+[PF6]- (6)17 were clean-
ly obtained by the reaction of 1-3, respectively, with
AgPF6 in CH2Cl2. Analysis by single-crystal X-ray
diffraction shows that the cation of 6 exists as a
distorted square pyramid with the orthometalated
(10) Advasio, V.; Diversi, P.; Ingrosso, G.; Lucherini A.; Marchetti,
F.; Nardelli, M. J . Chem. Soc., Dalton Trans. 1992, 3385. Diversi, P.;
Ingrosso, G.; Lucherini, A.; Marchetti F.; Adovasio, V.; Nardelli, M. J .
Chem. Soc. Dalton Trans. 1990, 1779.
(11) Cole-Hamilton, D. J .; Wilkinson, G. J . Chem. Soc., Dalton
Trans. 1977, 797. Chappell, S. D.; Engelhardt, L. M.; White, A. H. J .
Organomet. Chem. 1993, 462, 295. Fryzuk, M. D.; Montgomery, C. D.;
Rettig, S. J . Organometallics 1991, 10, 467.
There remain at least four plausible mechanisms by
which 3 might be produced during the attempted
synthesis of cis-(DPPE)2RuCH3Cl from 1. The first
involves isomerization of 1 to cis-(DPPE)2RuCl2 followed
(17) Prepared by reacting 0.100 g of 3 (1.07 × 10-4 mol) with 0.028
g of AgPF6 (1.1 × 10-4 mol) in 20 mL of CH2Cl2 at room temperature
for 30 min. The solvent was removed under vacuum, and the residue
was washed with hexane and then recrystallized from CH2Cl2/Et2O.
Yield: 90% of red crystals. Crystal data: C52H47F6P5Ru, Mr ) 1041.5;
monoclinic; P21/c; a ) 13.379(3) Å, b ) 26.742(6) Å, c ) 14.685(3) Å; V
) 5003 Å3; Z ) 4; D ) 1.50 g/cm3. 1H NMR (CD2Cl2; 300 MHz; 293 K):
δ 2.5-3.2 (m, 8 H, Ph2PCH2CH2PPh2), 5.8-7.7 (m, 39 H, Ph2PCH2-
CH2PPh2). 13C NMR (CD2Cl2; 75.5 MHz; 293 K): δ 22.5 (dd), 24.3 (dd),
28.5 (m), 122.5-134.4. 31P{1H} NMR (CD2Cl2; 121 MHz; 293 K): ABCD
pattern, δ 5.7 (dd), 7.7 (dd), 51.2 (dd), 53.2 (dd), 63.5 (dd), 65.4 (dd),
66.1 (dd), 68.1 (dd). A satisfactory analysis could not be obtained. Anal.
Calcd for C52H47F6P5Ru: C, 59.97, H, 4.51. Found: C, 59.23; H, 4.46.
(18) Levason, W.: McAuliffe, C. A. Coord. Chem. Rev. 1976, 19, 173.
(19) Eisch, J . J .; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J .
J . Am. Chem. Soc. 1985, 107, 7219. Tebbe, F. N.; Parshall, S. W.;
Reddy, G. S. J . Am. Chem. Soc. 1978, 100, 3611.
(12) Mason, R.; Meek, D. W.; Scollary, G. R. Inorg. Chim. Acta 1976,
16, L11.
(13) J ames, B. R.; Wang, D. K. W. Inorg. Chim. Acta 1976, 19, L17.
(14) Diversi, P.; Ingrosso, G.; Lucherini, A.; Marchetti, F.; Adovasio,
V.; Nardelli, M. J . Chem. Soc., Dalton Trans. 1991, 203.
(15) Chin, A.; Lough, A. J .; Morris, R. H.; Schweitzer, C. T.;
D’Agostino, C. Inorg. Chem. 1994, 33, 6278.
(16) Prepared by reacting 0.050 g of 2 (5.3 × 10-5 mol) with 0.013
g of AgPF6 (5.3 × 10-5 mol) in 15 mL of CH2Cl2 at room temperature
for 1 min. 1H NMR (CD2Cl2; 300 MHz; 293 K): δ -0.9 (quint, 3 H,
Ru-CH3, J PH ) 6 Hz), 2.4-2.7 (m, 8 H, Ph2PCH2CH2PPh2), 6.8-7.4
(m, 40 H, Ph2PCH2CH2PPh2). 31P{1H} NMR (CD2Cl2; 121 MHz; 293
K): δ 56.4 (s). These data strongly support
a square-pyramidal
structure for 5. Theoretical studies also support this geometry: Rachidi,
I. E.; Eisenstein, O.; J ean, Y. New J . Chem. 1990, 14, 671. Reihl, J .
F.; Eisenstein, O.; Pellissier, M. Organometallics 1992, 11, 729.

Communications
Organometallics, Vol. 16, No. 26, 1997 5615
by concerted thermal elimination of HCl. The second
involves alkylation of 1 to generate cis-(DPPE)2RuCH3-
Cl, which then undergoes concerted thermal elimination
of CH4. The third involves loss of Cl- from 1 to generate
the cation of 4, which then undergoes concerted thermal
elimination of HCl to generate 6 followed by readdition
of Cl-. The fourth involves alkylation of 1 and loss of
Cl- to generate the cationic intermediate 5; this inter-
mediate then undergoes concerted thermal elimination
of CH4 followed by readdition of Cl-.
reaction of trans-(DPPE)2RuCl2 with AlMe3 is consistent
with the formation of a cationic intermediate; the
cations of 4-6 are red.
The reaction of 6 with dodecyltrimethylammonium
chloride can be used to rationalize the observation that
treatment of the red oily product with ethanol gives the
yellow compound 3. The AlMe3Cl present in the mix-
ture reacts with ethanol to give Al(OEt)3 and Cl-. The
free Cl- reacts with 6 to give 3. This process probably
involves rearrangement of a phosphine in 6 followed by
the addition of Cl- cis to the ortho-metalated bond.
Simple addition of Cl- to the vacant trans site in 6 is
likely hindered by the presence of bulky chelating
ligands in the equatorial position of the square-
pyramidal structure; the two phenyl groups appear to
block the vacant trans site.22
Although we have no evidence for the presence of
either cis-(DPPE)2RuCl2 or cis-(DPPE)2RuCH3Cl under
the reaction conditions, we explored the likelihood of
generating 3 from these intermediates by examining the
reactivity of two closely related complexes where the
chloride and methyl ligands are constrained to be cis;
these complexes employ the tetradentate phosphine
ligand tris(2-(diphenylphosphino)ethyl)phosphine (PP3):
In conclusion, exposure of trans-(DPPE)2RuCl2 to
AlMe3 forms trans-2 and ortho-metalated 3. We propose
that the mechanism of the ortho metalation proceeds
via the unsaturated cationic intermediate 5. The direct
observation and apparent ortho metalation of 5 pro-
vides, to our knowledge, the first experimental evidence
for the existence of this type of intermediate in the
ortho-metalation chemistry of ruthenium.23
20
(PP3)RuCl2 and (PP3)RuCH3Cl.21 Stirring these com-
plexes at room temperature in CH2Cl2 for 2 days nor
refluxing in toluene for 24 h nor heating the solids to
100 °C for 2 days produced any trace of the analog to 3.
Although the arylphosphine ligands used here are
different from those in Scheme 1, these results are
nevertheless consistent with the notion that neither cis-
(DPPE)2RuCl2 nor cis-(DPPE)2RuCH3Cl is the direct
precursor to 3.
In other experiments (Scheme 1), compounds 1 and
2 failed to give 3 upon refluxing in benzene or toluene
for several hours or in CH2Cl2 for 3 days. Compound 4
failed to give either 3 or 6 upon refluxing in benzene,
toluene, or CH2Cl2 for 1 day. The latter observations
strongly suggest that the pathway to 3 does not proceed
through 4. Square-pyramidal 5 gradually underwent
ortho metalation at room temperature in CD2Cl2 to give
6. Compound 6 converted to 3 upon exposure to
dodecyltrimethylammonium chloride at room temper-
ature in CD2Cl2. Taken as a whole, these results are
consistent only with the fourth mechanism. Further-
more, the observation of a red oily product upon the
Ack n ow led gm en t. The National Science Founda-
tion (CAREER Award to T.R.L.; Grant No. CHE-
9625003), the Camille and Henry Dreyfus Foundation
(New Faculty Award to T.R.L.; Grant No. NF-93-040),
the University of Houston Limited Grant-In-Aid pro-
gram, and the University of Houston Environmental
Institute provided generous support for this research.
We thank Dr. J ames Korp for technical assistance with
X-ray crystallographic analyses, and we thank our
colleagues Tom Albright, David Hoffman, and J une-Ho
J ung for helpful comments.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
lengths, bond angles, atomic coordinates, and thermal param-
eters and figures giving unit cell views for 3 and 6 and a space-
filling structure for 6 (25 pages). Ordering information is given
on any current masthead page.
(20) Bianchini, C.; Perez, P. J .; Peruzzini, M.; Zanobini, F.; Vacca,
A. Inorg. Chem. 1991, 30, 279.
(21) Prepared by reacting 1.1 equiv of MeLi with 0.30 g of (PP3)-
RuCl2 (3.6 × 10-4 mol) for 2 h at room temperature in benzene. The
solvent was removed under vacuum, and the residue was washed with
hexane and then recrystallized from CH2Cl2/Et2O. Yield: 34% of pale
yellow crystals. 1H NMR (C6D6; 300 MHz; 293 K): δ -0.3 (m, 3 H,
Ru-CH3), 1.4-1.9 (m, 6, H, P(CH2CH2PPh2)3), 2.5-2.7 (m, 6 H,
P(CH2CH2PPh2)3), 6.5-8.4 (m, 30 H, P(CH2CH2PPh2)3). 13C NMR
(C6D6; 75.5 MHz; 293 K): δ 3.3 (m), 4.1 (m), 26.0-30.3 (m), 127.8-
142.0 (m). 31P{1H} NMR (C6D6; 121 MHz; 293 K): δ 40.7 (t), 46.9 (t),
154.3 (t). A satisfactory analysis could not be obtained. Anal. Calcd
for C43H45ClP4Ru: C, 62.80; H, 5.48. Found: C, 61.86; H, 5.50.
OM970631A
(22) The space-filling structure generated from the crystallographic
data shows that the two phenyl groups on the phosphine block the
empty site trans to the ortho-metalated carbon-Ru bond. A view of
the space-filling structure is included with the Supporting Information.
(23) Although a coordinatively unsaturated cation was proposed as
an intermediate in a related ortho-metalation reaction,14 no experi-
mental evidence was provided to support its existence.