Transcyclometalation: a novel route to (chiral) bis-ortho-chelated bisphosphinoaryl ruthenium(II) complexes

Article abstract of DOI:10.1021/om000340t

The Ru^II complexes [RuCl(R-PCP)(PPh₃)] (R-PCP = [C₆H₃{CH(Me)PPh₂}₂-2,6[^-(7a), [C₆H₃{CH(Et)PPh₂}₂-2,6[^- (7b), or [C₆H₂{CH₂PPh₂}₂-2,6- SiMe₃-[^MIN (9)) were synthesized using distinct synthetic routes. One of these routes consists of the reaction of the parent arene compound R-PCHP (i.e., C₆H₄{CH(Me)PPh₂}₂-1,3 (6a), C₆H₄{CH(Et)PPh₂}₂-1,3 (6b), or C₆H₃(CH₂PPh₂)₂-2,6-SiMe₃-4 (8)) with [RuCl₂(PPh₃)₃] in 1,2-dichloroethane. Following this procedure, complexes 7a and 7b were obtained. However, desilylation of 8 was observed with concomitant formation of complex [RuCl(C₆H₃{CH₂PPh₂}₂-2,6) (PPh₃)] (4). A second synthetic approach has been developed and applied in the high-yield synthesis of complexes 7a, 7b, and 9. This method, a transcyclometalation (TCM) reaction, involves the interconversion of one cyclometalated ligand metal complex, M(C,E), into another complex M(C,E′) with the concomitant consumption and formation of the corresponding arenes HC,E′ and HC,E, respectively. Using this method, previously observed problems such as nontolerance to the presence of a SiMe₃ group, contamination of the final product by uncoordinated PPh₃, or the formation of paramagnetic impurities were overcome. Investigations in solution of the formation of these square-pyramidal Ru complexes using two-dimensional NMR techniques (¹H-¹H COSY and ³¹P-¹H COSY) have shown that both synthetic routes were stereoselective, yielding only three of the four expected stereoisomers of complexes 7a and 7b.

Full text of DOI:10.1021/om000340t

4468
Organometallics 2000, 19, 4468-4476
Tr a n scyclom eta la tion : A Novel Rou te to (Ch ir a l)
Bis-Or th o-Ch ela ted Bisp h osp h in oa r yl Ru th en iu m (II)
Com p lexes
Paulo Dani, Martin Albrecht, Gerard P. M. van Klink, and Gerard van Koten*
Department of Metal-Mediated Synthesis, Debye Institute, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Received April 21, 2000
The RuII complexes [RuCl(R-PCP)(PPh3)] (R-PCP ) [C6H3{CH(Me)PPh2}2-2,6]- (7a ),
[C6H3{CH(Et)PPh2}2-2,6]- (7b), or [C6H2{CH2PPh2}2-2,6-SiMe3-4]- (9)) were synthesized
using distinct synthetic routes. One of these routes consists of the reaction of the parent
arene compound R-PCHP (i.e., C6H4{CH(Me)PPh2}2-1,3 (6a ), C6H4{CH(Et)PPh2}2-1,3 (6b),
or C6H3(CH2PPh2)2-2,6-SiMe3-4 (8)) with [RuCl2(PPh3)3] in 1,2-dichloroethane. Following this
procedure, complexes 7a and 7b were obtained. However, desilylation of 8 was observed
with concomitant formation of complex [RuCl(C6H3{CH2PPh2}2-2,6)(PPh3)] (4). A second
synthetic approach has been developed and applied in the high-yield synthesis of complexes
7a , 7b, and 9. This method, a transcyclometalation (TCM) reaction, involves the intercon-
version of one cyclometalated ligand metal complex, M(C,E), into another complex M(C,E′)
with the concomitant consumption and formation of the corresponding arenes HC,E′ and
HC,E, respectively. Using this method, previously observed problems such as nontolerance
to the presence of a SiMe3 group, contamination of the final product by uncoordinated PPh3,
or the formation of paramagnetic impurities were overcome. Investigations in solution of
the formation of these square-pyramidal Ru complexes using two-dimensional NMR
techniques (1H-1H COSY and 31P-1H COSY) have shown that both synthetic routes were
stereoselective, yielding only three of the four expected stereoisomers of complexes 7a and
7b.
In tr od u ction
During the last 10 years, the synthesis and reactivity
of organometallic species containing monoanionic
R-NCN,1 R-PCP,2-4 and R-SCS5 terdentate (pincer)
ligands (N ) NR2, P ) PR2, S ) SR, C ) aryl carbanion,
and R ) aryl or alkyl group; see Figure 1) have been
the subject of increasing research. Complexes of such
ligands have been used either as templates for the study
of fundamental chemical processes (e.g., the mechanism
of oxidative addition,6 C-C,1b,3,7 C-O,8 and C-Si9 bond
Figu r e 1. R-NCHN, R-PCHP, and R-SCHS type ligands
and their corresponding anions.
* To whom correspondence should be addressed. E-mail:
g.vankoten@chem.uu.nl. Fax: +(31) 30 2523615.
cleavage/bond formation) or in the field of catalysis (e.g.,
ketone reduction by hydrogen transfer,10 alkane dehy-
(1) (a) van Koten, G.; J astrzebski, J . T. B. H.; Noltes, J . G. J .
Organomet. Chem. 1978, 148, 233. (b) van Koten, G.; Timmer, K.;
Noltes, J . G.; Spek, A. L. J . Chem. Soc., Chem. Commun. 1978, 250.
(c) Canty, A. J .; van Koten, G. Acc. Chem. Res. 1995, 28, 406. (d)
Rietveld, M. H.; Grove, D. M.; van Koten, G. New J . Chem. 1997, 21,
751.
(6) (a) Gossage, R. A.; Ryabov, A. D.; Spek, A. L.; Stufkens, D. J .;
van Beek, J . A. M.; van Eldik, R.; van Koten, G. J . Am. Chem. Soc.
1999, 121, 2488. (b) van Beek, J . A. M.; van Koten, G.; Smeets, W. J .
J .; Spek, A. L. J . Am. Chem. Soc. 1986, 108, 5010.
(7) (a) Grove, D. M.; van Koten, G.; Louwen, J . N.; Noltes, J . G.;
Spek, A. L.; Ubbels, H. J . C. J . Am. Chem. Soc. 1982, 104, 6609. (b)
Albrecht, M.; Gossage, R. A.; Spek, A. L.; van Koten, G. J . Am. Chem.
Soc. 1999, 121, 11898.
(2) (a) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1976,
1020. (b) Creaser, C. S.; Kaska, W. C. Inorg. Chim. Acta 1978, 30, L325.
(c) Rimml, H.; Venanzi, L. M. J . Organomet. Chem. 1983, 259, C6. (d)
Cross, R. J .; Kennedy, A. R.; Muir, K. W. J . Organomet. Chem. 1995,
487, 227.
(3) Rybtchinski, B.; Milstein, D. Angew. Chem. Int. Ed. 1999, 38,
870, and references therein.
(8) van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; W. Shimon, L.
J .; Milstein, D. J . Am. Chem. Soc. 1998, 120, 6531, and references
therein.
(4) Karlen, T.; Dani, P.; Steenwinkel, P.; Grove, D.; van Koten, G.
Organometallics 1996, 15, 5687.
(5) (a) Dupont, J .; Beydoun, N.; Pfeffer, M. J . Chem. Soc., Dalton
Trans. 1989, 1715. (b) Huck, W. T. S.; van Veggel, F. C. J . M.;
Kropman, B. L.; Blank, D. H. A.; Keim, E. G.; Smithers, M. M. A.;
Reinhoudt, D. N. J . Am. Chem. Soc. 1995, 117, 8293. (c) Loeb, S. J .;
Shimizu, G. K. H.; Wisner, J . A. Organometallics 1998, 17, 2324. (d)
Dijkstra, H. P.; Steenwinkel, P.; Grove, D. M.; Lutz, M.; Spek, A. L.;
van Koten, G. Angew. Chem. Int. Ed. 1999, 38, 2186.
(9) (a) Valk, J .-M.; Boersma, J .; van Koten, G. J . Organomet. Chem.
1994, 483, 213. (b) Valk, J .-M.; Maassarani, F.; van der Sluis, P.; Spek,
A. L.; Boersma, J .; van Koten, G. Organometallics 1994, 13, 2320. (c)
Steenwinkel, P.; Gossage, R. A.; Maunula, T.; Grove, D. M.; Veldman,
N.; Spek, A. L.; van Koten, G. Chem. Eur. J . 1998, 4, 763.
(10) Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali, S.; van Koten, G.
Angew. Chem. Int. Ed. 2000, 39, 743.
10.1021/om000340t CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/28/2000

Transcyclometalation
Organometallics, Vol. 19, No. 22, 2000 4469
Sch em e 1. Syn th esis of [Ru (R-NCN)Ln ]
the ruthenation of functionalized carbosilane dendrim-
ers (i.e., R ) SiMe3, SiMe2Rdendritic), since the released
HCl was found to cleave the aryl C-Si bond even in
the presence of base. To increase the tolerance of various
R groups during the cyclometalation, we here report a
new synthetic procedure,21 a transcyclometalation (TCM)
reaction. The TCM reaction involves the selective
exchange of one bis-ortho-chelated ligand by another bis-
ortho-chelated ligand and has hitherto not been recog-
nized as such in the organometallic chemistry of tri-
dentate monoanionic ligands.22 An example is the 1:1
reaction of the meta-bisphosphinoarene ligand with a
bisaminoaryl ruthenium(II) compound, affording the
corresponding bisphosphinoarylruthenium(II) compound
and the meta-bisaminoarene ligand.22b This TCM reac-
tion sequence enables the direct synthesis of [RuX(H-
PCP)L] complexes under mild conditions (no HCl re-
lease) and is illustrated here for the preparation of the
(chiral) complexes 7 containing the monoanionic chiral
ligand [C6H3{CH(R′)PPh2}2-2,6]- (7a , R′ ) Me; 7b, R′)
Et).
Com p lexes
drogenation,11 Heck chemistry,12 Kharasch addition,13
and aldol condensation processes14,15a).
Recently, we reported on the synthesis of a variety of
[RuCl(H-NCN)Ln] (N ) NMe2) complexes (e.g., 2 and
3-R in Scheme 1) involving primarily a transmetalation
reaction of dimeric organolithium species [Li(C6H2{CH2-
NMe2}2-2,6-R-4)]2 (1-R), with common RuII starting
materials such as ([RuCl2(PPh3)n] (n ) 3 or 4) or [RuCl2-
(nbd)]n, nbd ) 1,5-norbornadiene).16,17
Despite the importance Ru compounds have as me-
diators and catalysts of organic transformations,18 only
a few examples of “pincer” Ru complexes containing PCP
ligands are known. Moreover, the existing, well-defined,
16-electron [RuIIX(R-PCP)L] complexes (in which
R-PCP ) [C6H2(CH2PPh2)2-2,6-R-4]- and L ) PPh3;
e.g., R ) H (4)4,19 and R ) Ph (5)4) have been synthe-
sized using [RuCl2(PPh3)3] as starting material.20 The
synthesis of these compounds comprises a direct cyclo-
metalation reaction of the meta-bisphosphinoarene ligand
R-PCHP with [RuCl2(PPh3)n] (n ) 3 or 4) followed by
net loss of one HCl. We have studied the scope of this
process and encountered some drawbacks concerning
Resu lts a n d Discu ssion
Liga n d Syn th esis. Ligands 6a ,b were synthesized
on the basis of protocols developed by Zhang et al. (see
Experimental Section for more details).15 It should be
noted that these chiral ligands were produced both via
a nonstereoselective synthetic route giving a racemic
mixture (i.e., a mixture of (S,S);(R,R)-enantiomers and
the meso-diastereomer) and a stereoselective route
(giving (S,S)-6). Residual minor impurities in the chiral
ligand precursors due to racemization were removed by
recrystallization from EtOAc, which left the meso-isomer
in solution.
Syn th esis of th e Ru th en iu m Com p lexes via Di-
r ect Cyclom eta la tion . The commonly applied route4
for the synthesis of [Ru(PCP)]-type complexes comprises
the reaction of a 1:1 molar mixture of the meta-
bisphosphinoarene ligand with [RuCl2(PPh3)3] in a
chlorinated solvent (e.g., 1,2-dichloroethane) at reflux
temperature.23 Therefore, the synthesis of the chiral
(11) (a) J ensen, C. M. Chem. Commun. 1999, 2443. (b) Gupta, M.;
Kaska, W. C.; J ensen, C. M. Chem. Commun. 1997, 461. (c) Gupta,
M.; Hagen, C.; Kaska, W. C.; Cramer, R. E.; J ensen, C. M. J . Am. Chem.
Soc. 1997, 119, 840.
(12) (a) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J . Am.
Chem. Soc. 1997, 119, 11687. (b) Bergbreiter, D. E.; Osburn, P. L.;
Liu, Y.-S. J . Am. Chem. Soc. 1999, 121, 9531. (c) Stark, M. A.; Richards,
C. J . Tetrahedron Lett. 1997, 38, 5881.
(13) Gossage, R. A.; van de Kuil, L. A.; van Koten, G. Acc. Chem.
Res. 1998, 31, 423.
(14) Gorla, F.; Togni, A.; Venanzi, L. M. Organometallics 1994, 13,
1607.
(21) Part of this work was communicated: Dani, P.; Karlen, T.;
Gossage, R. A.; Smeets, W. J . J .; Spek, A. L.; van Koten, G. J . Am.
Chem. Soc. 1997, 119, 11317.
(22) (a) The replacement of η2-C,N-cyclometalated amino ligands in
palladium and platinum complexes was recently reviewed: Ryabov,
A. D. In Perspectives in Coordination Chemistry; Williams, A. F.,
Floriani, C., Merbach, A. E., Eds.; VCH: Weinheim, 1992; p 271. (b)
In analogy with transamination and transesterification, a transcyclo-
metalation (TCM) process involves the interconversion of one cyclo-
metalated ligand complex into another. For example, a N,C-chelated
(15) (a) Longmire, J . M.; Zhang, X.; Shang, M. Organometallics 1998,
17, 4374. (b) Longmire, J . M.; Zhang, X. Tetrahedron Lett. 1997, 38,
1725.
(16) Sutter, J .-P.; J ames, S. L.; Steenwinkel, P.; Grove, D. M.;
Veldman, N.; Spek, A. L.; van Koten, G. Organometallics 1996, 15,
941.
(17) Steenwinkel, P.; J ames, S. L.; Grove, D. M.; Veldman, N.; Spek,
A. L.; van Koten, G. Chem. Eur. J . 1996, 2, 1440.
(18) For a recent review see: Naota, T.; Takaya, H.; Murahashi,
S.-I. Chem. Rev. 1998, 98, 2599.
(19) (a) J ia, G.; Lee, H. M.; Williams, I. D. J . Organomet. Chem.
1997, 534, 173. (b) J ia, G.; Lee, H. M.; Xia, H. P.; Williams, I. D.
Organometallics 1996, 15, 5453.
platinum(II) complex is converted into a P,C-chelated platinum
complex. The driving force in this reaction is the difference in
heteroatom-platinum bond strength, which is highest for the P-Pt
bond. Albrecht, M.; Dani, P.; Lutz, M.; Spek, A. L.; van Koten, G. J .
Am. Chem. Soc., in press. For early examples of TCM reactions,
although not formulated as such: (c) Maassarani, F.; Pfeffer, M.; Spek,
A. L.; Schreurs, A. M. M.; van Koten, G. J . Am. Chem. Soc. 1986, 108,
4222. (d) Dupont, J .; Beydoun, N.; Pfeffer, M. J . Chem. Soc., Dalton
Trans. 1989, 1715. (e) Djukic, J .-P.; Maisse, A.; Pfeffer, M. J . Orga-
nomet. Chem. 1998, 567, 65. (f) Pregosin, P. S.; Wombacher, F.;
Albinati, A.; Lianza, F. J . Organomet. Chem. 1991, 418, 249. (g)
Ryabov, A. D.; van Eldik, R. Angew. Chem. 1994, 106, 798, Angew.
Chem., Int. Ed. Engl. 1994, 33, 783.
(20) Recently, the first examples were published of ruthenium
complexes containing an η3-P,C,P′-bonded PCP ligand whose phos-
phorus substituents are not phenyl groups: (a) Reinhart, B.; Gusev,
D. G. New J . Chem. 1999, 1. (P ) PtBu2). (b) van der Boom, M. E.;
Kraatz, H.-B.; Hassner, L.; Ben-David, Y.; Milstein, D. Organometallics
1999, 18, 3873. (P ) PiPr2).
(23) The change of reaction solvent from CH2Cl2 (ref 3) to 1,2-
dichloroethane resulted in a reduced reaction time and an increased
yield. For instance, [RuCl2(PPh3)3] and C6H4(CH2PPh2)2-1,3 needed to
be refluxed for 3 days in CH2Cl2 in order to give the respective complex
5 in 58% yield. In 1,2-dichloroethane, this period was reduced to 2 h
with an isolated yield of 90%.

4470 Organometallics, Vol. 19, No. 22, 2000
Dani et al.
Sch em e 2. Dir ect Cyclom eta la tion of P CHP
Affor d in g 16-Electr on Ru th en iu m (II)-P CP
Com p lexes
Sch em e 3. Tr a n scyclom eta la tion (TCM) Rea ction
a s a Novel Meth od to P r ep a r e Ru (P CP ) Com p lexes
(a n d NCHN) fr om Ru (NCN) a n d P CHP
complexes 7a and 7b was first attempted using this
methodology (see Scheme 2).
Reflux of an equimolar solution of 6a and [RuCl2-
(PPh3)3] in 1,2-dichloroethane for 15 h afforded a green
solution, from which, after workup, 7a was obtained in
50% yield as a mixture of two diastereomers. Replace-
ment of the methyl groups at benzylic positions for
ethyl, i.e., the reaction of ligand 6b with [RuCl2(PPh3)3]
under the same conditions, had a pronounced effect on
the rate of formation of the cycloruthenated product.
The related green mixture of stereoisomers was ob-
tained after 48 h of heating at reflux temperature.
Unfortunately, 7b could not be obtained free from
uncoordinated PPh3 due to similar solubility properties
of these compounds in common organic solvents.
As complexes 7a and 7b were obtained as a mixture
of stereoisomers, the NMR spectra were somewhat
complicated but could be completely assigned (vide
infra). However, it should be noted that besides the
resonances related to the presence of 7a and 7b, the
31P NMR spectra of a solution of the crude reaction
mixtures in CD2Cl2 also showed two singlets: one at
ca. -4.5 ppm, related to free PPh3, and one at ca. 28
ppm, from an unknown compound. Indeed, addition of
benzene or toluene to this solution caused selective
precipitation of a red solid and concomitant disappear-
ance of the resonance at 28 ppm. The 1H NMR spectrum
of this red material in CD2Cl2 at room temperature
consisted of very broad resonances which remained
unaffected by temperature variation in the range -100
to +25 °C, suggesting that the peak broadness is not
caused by fluxional processes but more likely by the
presence of paramagnetic Ru species (e.g., a RuIII
complex). The long reaction time and the use of a
chlorinated solvent may be responsible for this oxidation
(although a subsequent reaction with the liberated HCl
cannot be ruled out). Accordingly, reflux of pure 7a or
7b in 1,2-dichloroethane led to slow formation of a
similar red material (31P NMR). Elemental analysis was
not conclusive, but indicated the presence of phosphorus
and chloride, the latter in a higher percentage as
compared with 7a or 7b, respectively.
the mixture of stereoisomers of 7b (31P NMR). Conse-
quently, the red solid is most likely comprised of
ruthenium and PCP ligand in a similar ratio as in 7b.
Syn th esis of [Ru Cl(R-P CP )(P P h 3)] Com p lexes
via Tr a n scyclom eta la tion (TCM). We observed that
the NCN anion in [RuCl(C6H3{CH2NMe2}2-2,6)(PPh3)]
(3) can be substituted quantitatively by the PCP anion
in a 1:1 molar reaction of 3 with the meta-bisphosphi-
noarene C6H4(CH2PPh2)2-1,3 (11).21 Therefore, this
reaction was also applied to PCHP-type ligands 6a and
6b (Scheme 3). Reaction of the ligands 6a or 6b with 3
in a 1:1 molar ratio in refluxing benzene afforded the
corresponding complexes 7a and 7b, respectively, in
nearly quantitative yield (as established by NMR) with
NCHN as the only other product. Isolation of the
complexes was achieved by precipitation with cold
hexane from a reaction solution in CH2Cl2 in 70 and
40% yield, respectively.
Str u ctu r a l Asp ects of 7a a n d 7b in Solu tion . Due
to the square-pyramidal geometry around ruthenium in
the complexes described here, up to four stereoisomers
of 7a (or 7b) are expected upon reaction of racemic 6a
(or 6b) with 3: the (S,S)-7;(R,R)-7 enantiomeric pair
(rac-7) and the two unique diastereomers (S,R)-R′endo
(meso-7endo) and (R,S)-R′exo (meso-7exo). Chart 1 shows
their stereochemistry and the expected 31P NMR pat-
terns. In the meso-7endo stereoisomer, both R′ groups,
i.e., the benzylic substituents methyl or ethyl, and the
apical PPh3 are on the same side of the Ru-Cipso-Cl-
P2 plane (Chart 1), whereas in the meso-7exo isomer, the
R′ groups and the PPh3 ligand are on opposite sides of
this plane. For the interpretation of the NMR spectra,
it is important to note that meso-7endo and meso-7exo are
diastereomers, i.e., have different NMR spectroscopic
properties. Note that by exchange of the PPh3 ligand
between apical positions via Ru-P bond dissociation/
association, these two diastereomers are interconverted.
In the case of the pair of enantiomers, one of the R′
groups is exo to the apical ligand while the other R′
group is orientated in an endo fashion. These isomers
have the same spectroscopic properties, i.e., give rise
to identical NMR resonance patterns. In conclusion,
when all four isomers (meso-7endo, meso-7exo, and rac-7)
are present in solution, in principle three different NMR
patterns are expected. Spectroscopic analysis pointed
out that 7a and 7b have similar structural features in
solution as was already established for [RuCl(C6H3{CH2-
NMe2}2-2,6)(PPh3)] (3)16 and [RuCl(C6H3{CH2PPh2}2-
2,6)(PPh3)] (4),4,19a,24 i.e., a distorted square-pyramidal
Reductive treatment of the red solid, isolated from the
reaction of 6b with [RuCl2(PPh3)3], with an excess of
zinc and PPh3 in refluxing THF (eq 1) afforded again

Transcyclometalation
Organometallics, Vol. 19, No. 22, 2000 4471
Ch a r t 1. New m a n P r ojection s of th e [Ru Cl(P CP )(P P h 3)] Com p lexes of th e Liga n d s 6a ,ba
aView of the benzylic substituents (a) along the P(PPh3)-Ru axis (PPh3snot shownsis in the front) and (b) along the C(4)-
Cipso-Ru-Cl axis (PPh2 and chloride ligands in the front not shown).
Ta ble 1. Selected 1H a n d 31P {1H} NMR Da ta of Com p ou n d s 7a a n d 7ba ,b
δ 1H (multiplicity)
δ
31P (multiplicity, 2J (PP) in Hz)
compound
ArC-H
PCP
PPh3
rac-7a
2.00-2.07 (m)
4.29-4.36 (m)
2.80-3.00 (m)
1.50-1.70 (m)
4.05-4.15 (m)
2.41-2.50 (m)
43.71 (dd, 20.7, 261.2)
58.37 (dd, 46.8, 261.7)
54.54 (d, 32.4)
38.04 (dd, 19.8, 254.4)
55.06 (dd, 48.0, 254.4)
55.03 (d, 32.4)
80.10 (dd, 20.7, 46.8)
meso-7a
rac-7bc
79.50 (t, 32.9)
79.81 (dd, 19.8, 48.0)
meso-7bc
77.73 (t, 32.4)
Spectra recorded at 25 °C in benzene-d6. 1H chemical shifts (ppm) referenced to residual solvent signal. 31P chemical shifts (ppm)
a
referenced to external 85% H3PO4. bd, doublet; dd, double doublet; m, multiplet; t, triplet. Spectra recorded at 25 °C in CD2Cl2.
c
geometry with the apical position occupied by the bulky
PPh3 ligand (see Scheme 2).
(see Chart 1). It is important to note that this finding
was not dependent on the synthetic route followed. The
independence of these two patterns was unequivocally
confirmed by a 31P-31P correlation NMR spectrum (31P-
31P COSY). The PCP and PPh3 phosphorus resonances
of the diastereomer appear as a doublet at 55.03 and a
triplet at 77.73 ppm, respectively (2J (PP) ) 32.4 Hz,
Table 1). Like in the case of the achiral compounds, the
observed spin system, coupling constants, and chemical
shifts are consistent with a square-pyramidal structure
containing one apical PPh3 ligand in a cis-arrangement
to two magnetically equivalent phosphorus atoms of the
cyclometalated PCP ligand.4,19,21
In earlier studies, we found that a “flip” of the fused
puckered five-membered chelate rings in [RuCl(R-
NCN)(PPh3)], 3-R, and [RuCl(R-PCP)(PPh3)], 4 and
5, is frozen on the NMR time scale (i.e., these com-
pounds have mirror plane puckering) and all Ru-P
bonds are persistent.16,21 Thus, one can assume that the
same is the case for the isomers of 7; that is, each PPh2
substituent has one equatorial and one axially orien-
tated Ph group (Chart 1). Finally, Chart 1 also shows
the view of representative isomers along the apical
P-Ru axis. These projections show that whereas in the
unique diastereomers meso-7endo and meso-7exo both
halves of the PCP ligand are enantiotopic, in the
enantiomeric pair these halves are diastereotopic. As a
result, the 31P{1H} NMR spectrum related to each meso-
All three phosphorus atoms of rac-7b have distinct
chemical shifts and appear in the 31P{1H} NMR spec-
trum as doublets of doublets centered at 38.04, 55.06
(PCP phosphorus nuclei), and 79.81 ppm (PPh3) (Figure
2). A characteristic trans-2J (PP) of 254.4 Hz is observed
for the trans-PCP phosphorus atoms, while the PPh3
coupling constants with the PCP-phosphorus are much
smaller and differ in magnitude (cis-2J (PP) ) 19.8 and
48.0 Hz).
In the 31P-1H COSY NMR spectrum of 7b (Figure
2), the cross-peaks mark the positions of either P-Ph
ortho-protons or benzylic protons related to the different
stereoisomers. Therefore, the phosphorus nuclei from
the unique diastereomer of meso-7b show four cross-
peaks in total: one related to the PPh3 at 6.90 ppm
(thus, all PPh3 ortho-protons are equivalent, implying
free rotation about the Ru-PPh3 bond on the NMR time
scale) and three associated with the PCP phosphorus
7
endo and meso-7exo diastereomer should be an AX2 spin
system (i.e., a doublet and a triplet) similar to the one
observed in the 31P NMR spectrum of the [RuCl(PCP)-
(PPh3)] compounds 4 and 9. However, in the 31P{1H}
NMR spectrum of the enantiomeric pair, an AMX spin
system is expected. In view of the similarity of the
spectroscopic data concerning these compounds, the
focus will be centered on the spectroscopic features of
7b.
The 31P{1H} NMR spectrum of 7b shows one AMX
spin system and only one AX2 spin system, suggesting
the formation of only one of the unique diastereomers
(24) Dani, P.; van Klink, G. P. M.; van Koten, G. Eur. J . Inorg. Chem
2000, 1465.

4472 Organometallics, Vol. 19, No. 22, 2000
Dani et al.
1
F igu r e 2. 121 MHz H-31P COSY of 7b (rac/ meso mixture) in CD2Cl2. Resonances labeled with (*) are from the free
bisaminoarene ligand and with (#) from residual nondeuterated solvent.
atoms at 6.90, 7.70, and 2.45 ppm. This pattern of cross-
peaks (already observed in similar analysis involving
Ru complexes of nonchiral PCP ligands)25 is a strong,
independent piece of evidence that the Ru-Cipso-Cl-
P2 plane is not a molecular symmetry plane, but the
orthogonal plane involving the Cl-Cipso-P(PPh3) atoms
is. Therefore, the ortho-protons of each diastereotopic
F igu r e 3. Newman projection of the obtained meso-7exo
phenyl group of the PPh2 fragments are also diaste-
diastereomer. View along the C(4)-Cipso-Ru-Cl axis. The
reotopic and appear with a distinct chemical shift
chloride ligand (not shown) is in front (forward direction).
yielding the two cross-peaks at 6.90 and at 7.70 ppm.
The only cross-peak at the nonaromatic region of the
These spectroscopic features are observed in the NMR
spectrum of the diastereomer and can be used to arrive
at an assignment of its configuration. Thus, the chemi-
diastereomer meso-7b (at 2.45 ppm in the 1H spectrum)
reveals only one type of benzylic proton, which is either
endo or exo orientated with respect to the apical
phosphine ligand. This result together with the presence
in the 13C NMR spectrum of only one type of benzylic
and methyl carbon for meso-7b is in accordance with
the earlier conclusion that only one unique meso dia-
stereomer is formed selectively.
cal shift of the benzylic proton at 2.45 ppm is consider-
ably upfield for a methine proton, and in the 1H-1H
COSY NMR spectrum, a cross-peak is present involving
this proton and the aryl protons H-3,5. Therefore, meso-
7bexo and not meso-7bendo is present, and a more refined
idea about the structure of this compound (in solution)
is depicted in Figure 3. It is important to note that the
presence of meso-7endo for both 7a and 7b has never been
detected by 31P NMR spectroscopy in the material
obtained from both synthetic routes. The relative amount
of meso-7bexo present after reaction, when compared
with the amount of the rac-7b enantiomeric pair,
implies that meso-7bendo, if ever formed, is being con-
verted into meso-7bexo and not, for instance, lost by
decomposition processes.
As pointed out earlier, a common structural feature
of [RuCl(R-PCP)(PPh3)] complexes is the axial/equato-
rial positioning of the PPh2 phenyl groups.25a Probably
for purely steric reasons, one phenyl ring on each PPh2
group occupies the vacant coordination site opposite the
PPh3 ligand. A consequence of this is a distinct pucker-
ing of the two fused five-membered rings which orien-
tates one of the benzylic substituents (in the case of 7
most likely the smaller one, i.e., H) near the apical
ligand; see Chart 1. This causes two interesting effects
The low molecular symmetry of the rac-7b is clearly
indicated by the spectrum depicted in Figure 2. All
phenyl rings of the PPh2 groups are distinct, and for
this reason four cross-peaks are present in the aromatic
region related to the PCP phosphorus nuclei (two for
1
in the H NMR spectra of these compounds that can be
used as structural probes:25a (i) an upfield shift of the
axial benzylic proton (most likely caused by shielding
effects from the PPh3 ligand), and (ii) the appearance
of a cross-peak in the 1H-1H COSY NMR spectrum
involving this axial benzylic proton and the xylylene
protons H-3,5 in the PCP ligand.26
(26) The detection of the indirect coupling between benzylic and
H-3,5 protons can be explained by analogy with allylic systems: the
smaller the torsional angle between the benzyl C-H bond and the axis
of the arene π-orbitals, the larger the four-bond coupling constant.
See: (a) Friebolin, H., Basic One- and Two-Dimensional NMR Spec-
troscopy, 2nd ed.; VCH: Weinheim, 1993; p 83. (b) Gu¨nther, H. NMR
Spectroscopy-An Introduction; J ohn Wiley & Sons: New York, 1980;
p 46.
(25) (a) Dani, P.; Richter, B.; van Klink, G. P. M.; van Koten, G.
Eur. J . Inorg. Chem., in press. (b) del R´ıo, I.; Gossage, R. A.; Lutz, M.;
Spek, A. L.; van Koten, G. J . Organomet. Chem. 1999, 583, 69.

Transcyclometalation
Organometallics, Vol. 19, No. 22, 2000 4473
Sch em e 4. P ossible In ter m ed ia tes Obta in ed
d u r in g th e F or m a tion of [Ru Cl(R-P CP )(P P h 3)]
Com p lexes via Dir ect Meta la tion
each phosphorus resonance). The two cross-peaks in the
nonaromatic region of the H spectrum are consistent
1
with the postulated structure and identify the reso-
nances of the inequivalent benzylic protons related to
each of the -CH(Et)PPh2 substituents. Importantly, one
of the benzylic protons (at 1.50-1.70 ppm) shows a
behavior similar to that observed with the benzylic
protons of meso-7bexo. Thus, the signal of the benzylic
proton at 1.62 ppm is considerably upfield for a methine
proton and shows also a cross-peak with H-3,5 in the
1H-1H COSY NMR spectrum. Therefore, this proton
should be in an axial situation, pointing toward the
apical position. Consequently, the other benzylic proton
is expected to be equatorial. Indeed, it has a regular
chemical shift (4.05-4.15 ppm) and does not show a
1
cross-peak with H-3,5 in the H-1H COSY NMR spec-
trum. These assignments were unequivocally deter-
mined by spectroscopic analyses of the ruthenium
complexes obtained by a TCM reaction of 3 with (S,S)-
6b (vide infra). All signals in the NMR spectra assigned
to the meso-complex were absent. Similarly, when (S,S)-
6a was used as ligand precursor in a TCM reaction, the
chiral complex (S,S)-7a was obtained in high yield. The
31P NMR spectrum showed the expected AMX spin
system only (Table 1), and two distinct signals for the
benzylic protons were observed in the 1H NMR spec-
trum. The methyl group appears as a multiplet around
1 ppm.
occur are probably accomplished by phosphine decoor-
dination, either of a PCHP or PPh3. In the case of an
η2-P,P′fη1-P rearrangement of the PCHP ligand, open
chain structures are formed (e.g., A′′ and A′′′, Scheme
4).25
F or m a tion of 7 via TCM. The reaction between 6b
and 3 (see Scheme 3) in benzene-d6 was followed by 31
P
NMR spectroscopy. No reaction was observed at room
temperature. The first signals of the final products
became visible only after 30 min at 60 °C. Besides the
resonances related to the starting materials and final
products, and a broad signal at -5 ppm indicating the
presence of free PPh3, no other species were observed.
Preliminary kinetic measurements at 60 °C showed this
reaction to be first-order in PCHP and in 3 but zero-
order in product formation. These results indicate that
the products are not directly formed from the reactants,
but through undetected intermediate species. Moreover,
the (pseudo) zero-order rate law deduced for product
formation indicates complicated reaction kinetics and
is not conclusive whether the final transformations
occur inter- or intramolecularly.28 It is difficult to
speculate on the structures of potential intermediate(s)
with the limited data available.
F or m a tion of 7 via Dir ect Cyclom eta la tion . Al-
though the result of both processes depicted in Scheme
2 and Scheme 3 is formally the substitution of an
aromatic proton by the cationic metal fragment [RuCl-
(PPh3)], the reaction profiles differ significantly. 31P
NMR analysis after 1 h of the reaction mixture obtained
by reacting 6a via direct cyclometalation showed the
presence of two distinct groups of AX2 and AMX spin
systems. One group was sharp and clearly results from
the formation of some of the rac-7a and meso-7a exo
stereoisomers. The other was broader and located at
much higher field (the AM part of the spin system was
spread between -5 and 20 ppm, while the X part was
observed between 40 and 42 ppm). During the course
of the reaction the latter group of signals disappeared
with concomitant increase of the intensity of the reso-
nances related to the final products (including a broad
singlet related to the paramagnetic material mentioned
above). The spin systems observed at higher field
indicate that the intermediates formed have three
phosphorus atoms per Ru center, and the chemical
shifts strongly suggest that the R-PCHP ligand has not
undergone a cyclometalation. An η2-P,P′-coordinated
R-PCHP ligand (e.g., A′ in Scheme 4) is a likely
structure to explain these facts. Other potential inter-
mediates include bridging R-PCHP ligands forming
open chain structures. However, this hypothesis is
weakened by the fact that ruthenium(II) compounds
containing (achiral) R-PCHP ligands in a µ-η1-P, η1-
P′, or η1-P bonding mode (i.e., species such as A′′ and
A′′′, respectively, with R′ ) H) have been observed and
all have 31P chemical shifts at lower field than 40 ppm.25
To get more insight into the mechanism of the TCM
reaction, 3 was reacted with the deuterated ligand
C6H3(CH2PPh2)2-1,3-D-2 (11-D (PCDP) in nondeuter-
1
2
ated benzene (Scheme 5). H and H NMR analysis of
the resulting Ru complex 4 did not reveal incorporation
of deuterium at any specific position in its structure.
However, similar analysis of the resulting meta-bisami-
noarene ligand showed a deuterium presence mainly at
the former ipso-carbon (i.e., at C-2) and a lower percent-
age (total ca. 25%) at the nonmutual ortho-positions
(C-4,6). In this case, it was not possible to confirm
whether monodeuterated or polydeuterated species were
formed. Most importantly, when [RuCl(PCP)(PPh3)], 4,
and C6H3(CH2NMe2)2-1,3-D-2 (10-D (NCDN) were re-
fluxed overnight in benzene, deuterium loss or inter-
(27) See for instance: (a) Bennett, M. A.; J ohnson, R. N.; Tomkins,
I. B. J . Organomet. Chem. 1977, 128, 73. (b) Lesueur, W.; Solari, E.;
Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Inorg. Chem. 1997, 36, 3354.
(c) Baltensperger, U.; Guenter, J . R.; Ka¨gi, S.; Kahr, G.; Marty, W.
Organometallics 1983, 2, 571
Species containing an η2-P,P′-R-PCHP ligand have
been proposed as intermediates for the selective meta-
lation of the ipso-carbon of R-PCP systems.2c,4,8,21,27
Vacant sites that are necessary for C-H activation to
(28) For example, in TCM reactions of [PtCl(H-NCN)] with H-PCHP
we were able to isolate a complex containing a µ-η1-P, η1-P′ H-PCHP
ligand with
cyclometalation process. See ref 22b.
a (Pt-)Cl‚‚‚H(-C) bond that is responsible for the

4474 Organometallics, Vol. 19, No. 22, 2000
Dani et al.
Sch em e 6. Clea va ge of th e Si-C Bon d d u r in g
Ru th en a tion of 8 u n d er Dir ect Cyclom eta la tion
Con d ition s
Sch em e 5. Ma p p in g of th e Deu ter iu m Tr a n sfer in
th e Tr a n scyclom eta la tion Rea ction (See Sch em e 2)
2 equiv of t-BuLi at -78 °C followed by a quench of the
reaction mixture with Me3SiCl.
Reaction of 8 under the conditions of direct cyclo-
metalation led to the formation of known [RuCl-
(C6H3{CH2PPh2}2-2,6)(PPh3)] (4) in 90% yield instead
of the expected para-trimethylsilyl-substituted 9 (Scheme
6).4,19 This was established by the identical spectroscopic
characteristics of the isolated material and authentic 4
and also by the lack of any proton resonance upfield of
2 ppm, indicating the loss of a Me3Si- group. Metathesis
of the Me3Si-C bond with the HCl formed during the
ruthenation process is most likely the reason for the
observed Si-C bond cleavage. Addition of base, for
example, NEt3, to the reaction mixture could only
partially prevent the cleavage of the Si-C bond (60%
yield of 9 based on NMR). This result indicated that the
presence of a silane functionality in the PCHP ligand
is not compatible with the conditions applied in the
direct cyclometalation. Consequently, direct ruthenation
of PCHP-terminated carbosilane dendrimers via direct
cyclometalation is not a viable option, because this
would lead to cleavage of the PCHP ligand from the
dendritic periphery.
However, the mild conditions characteristic for the
TCM reaction were suitable for the formation of 9.
Addition of 3 to 8 resulted in the formation of ruthen-
ated PCP complex 9. The 1H NMR spectrum of 9
revealed a singlet at 0.33 ppm integrating for nine
protons, confirming the presence of a Me3Si- group. It
also showed two characteristic multiplets at 2.45 (2H)
and 3.50 ppm (2H) related to the diastereotopic benzylic
protons. The 31P NMR spectrum was typical for this
class of complexes and consisted of a doublet at 36.98
ppm (PCP phosphorus nuclei) and a triplet at 82.73 ppm
(PPh3, 2J (PP) ) 32 Hz). The chemical shift32 and
coupling constant33 are characteristic of an apical phos-
phine in a cis arrangement to two magnetically equiva-
lent phosphorus atoms of a cyclometalated PCP
ligand.4,19,21
molecular deuterium scrambling was not detected,
indicating that complex 4 alone is not able to promote
the processes described previously.
The preferential transfer of a deuterium atom from
PCDP to the metalated ipso-carbon of the bisaminoaryl
NCN ligand can be understood on the basis of an initial
overall oxidative addition of the C-D bond of the PCDP
ligand to the ruthenium center, forming Ru-D interme-
diates29 that reductively eliminate NCDN. However, the
amino groups of the NCN ligand may play an important
role in the process of deuterium transfer as well as in
the mechanism that leads to the deuterium reallocation
from C-2 to the C-4,6 carbons of the meta-bisaminoaryl
ligand.28 Therefore, Ru-D species are not necessarily
involved. However, no clear evidence for such ligand
assistance could be observed, and further investigations
are currently underway.
Ap p lica tion of Tr a n scyclom eta la tion Rea ction .
The synthesis of the ligand C6H3(CH2PPh2)2-3,5-Me3-
Si-1 (8) can be seen as a model route for the grafting of
a PCHP ligand to a carbosilane dendrimer. A similar
approach has already been followed for the attachment
of NCHN ligands30a,b to the periphery of polymers and
dendrimers, which in turn can be used for the synthesis
of multisite catalysts.30,31 Ligand 8 was obtained in high
yield (93%) by treating C6H3(CH2PPh2)2-3,5-Br-1 with
The meta-bisaminoarene compound also formed dur-
ing the reaction was isolated and characterized as
H-NCHN (10) using NMR and mass spectrometric
analysis. As chlorinated solvents are not used and HCl
(29) Formally, these species can be either formulated as RuII-H+,
with intramolecular base assistance of the N from H-NCN, or as
RuIV-H-. See refs 1c and 22b.
(30) (a) 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. (b) van Koten, G.; J astrzebski, J . T. B. H. J . Mol. Catal.
A: Chem. 1999, 146, 317. (c) Hovestad, N. J .; Hoare, J . L.; J astrzebski,
J . T. B. H.; Canty, A. J .; Smeets, W. J . J .; Spek, A. L.; van Koten, G.
Organometallics 1999, 16, 2970. (d) Kleij, A. W.; Kleijn, H.; J astrzebski,
J . T. B. H.; Smeets, W. J . J .; Spek, A. L.; van Koten, G. Organometallics
1999, 18, 268. (e) Kleij, A. W.; Kleijn, H.; J astrzebski, J . T. B. H.; Spek,
A. L.; van Koten, G. Organometallics 1999, 18, 277. (f) Kleij, A. W.;
J astrzebski, J . T. B. H.; van Koten, G. In Dendritic Polymers; Fre´chet,
J . M. J ., Tomalia, D. A., Eds.; J ohn Wiley & Sons: Sussex, England,
2000, submitted.
(31) (a) van de Kuil, L. A.; Grove, D. M.; Zwikker, J . W.; J enneskens,
L. W.; Drenth, W.; van Koten, G. Chem. Mater. 1994, 6, 1675. (b)
Pathmamanoharan, C.; Wijkens, P.; Grove, D. M.; Philipse, A. P.
Langmuir 1996, 12, 4372.
(32) Hoffman, P. R.; Caulton, K. G. J . Am. Chem. Soc. 1975, 97,
4221.
(33) (a) Cole-Hamilton, D. J .; Wilkinson, G. J . Chem. Soc., Dalton
Trans. 1977, 797. (b) Cole-Hamilton, D. J .; Wilkinson, G. Nouv. J .
Chim. 1977, 1, 141.

Transcyclometalation
Organometallics, Vol. 19, No. 22, 2000 4475
Diagnostic signals for meso-6b‚2BH3: 1H NMR (300 MHz,
is not formally generated during a reaction via the
transcyclometalation procedure, this reaction protocol
suppresses undesired side reactions (cf. formation of a
red compound or Si-C bond cleavage).
3
CDCl3): δ 0.63 (t, J (HH) ) 7.2 Hz, 6H, CH3), 1.72-1.92 (m,
4H, CH2), 3.47 (ddd, 3J (HH) ) 11.4 Hz, 3J (HH) ) 3.3 Hz,
2J (HP) ) 16.5 Hz, 2H, CH-P). 13C{1H} NMR (75 MHz,
2
1
CDCl3): δ 23.63 (d, J (CP) ) 4.9 Hz, CH2), 44.94 (d, J (CP) )
30.9 Hz, CH-P), 135.46 (s, aryl). 31P{1H} NMR (81 MHz,
CDCl3): δ 23.97 (s).
Con clu sion
A new synthetic approach has been developed in
which a meta-bisaminoaryl terdentate ligand NCN was
quantitatively replaced by a corresponding meta-bis-
phosphinoaryl ligand R-PCP leading to the formation
of [RuCl(R-PCP)(PPh3)] complexes. Using this trans-
cyclometalation (TCM) reaction, problems such as the
presence of free phosphine or HCl or the need for the
use of chlorinated solvents, which may give rise to
secondary products, were overcome. The scope of this
TCM reaction with other types of transition metal-
NCN complexes is currently under investigation.
The borane protecting group was quantitatively removed
with HBF4‚OEt2 following the procedure described in the
literature.15
1
3
(S,S)-6b. H NMR (300 MHz, CDCl3): δ 0.69 (t, J (HH) )
7.2 Hz, 6H, CH3), 1.60-1.85 (m, 4H, CH2), 3.15-3.35 (m, 2H,
CH-P), 6.80-7.20 (m, 14H, aromatic), 7.35-7.50 (m, 6H,
aromatic), 7.60-7.75 (m, 4H, aromatic). 13C{1H} NMR (75
MHz, CDCl3): δ 12.52 (d, 3J (CP) ) 11.2 Hz, CH3), 26.69 (d,
1
2J (CP) ) 21.2 Hz, CH2), 47.23 (d, J (CP) ) 11.8 Hz, CH-P),
126.71, 127.25, 127.66 (all m, aryl), 127.85, 128.01, 128.07,
128.18 (all s, aryl), 128.45 (m, aryl), 129.01 (s, aryl), 129.75
(m, aryl), 130.92 (m, aryl), 133.11 (d, J (CP) ) 18.1 Hz, aryl),
133.25 (d, J (CP) ) 20.3 Hz, aryl), 137.00-137.60 (m, aryl),
140.60-140.95 (m, aryl). 31P{1H} NMR (81 MHz, CDCl3): δ
-0.61 (s).
Exp er im en ta l Section
Gen er a l Com m en ts. All experiments were carried out
under a dry nitrogen atmosphere using standard Schlenk
techniques. Benzene, toluene, alkanes, and THF were dried
over sodium using benzophenone as indicator. Dichloromethane
was dried over CaH2. 1,2-Dichloroethane was degassed using
the freeze-pump-thaw technique. 1H, 13C, and 31P NMR were
recorded at 25 °C on a Bruker AC200 or on a Varian Unity
INOVA 300 NMR spectrometer. Chemical shifts are in ppm
relative to residual solvent signal (1H and 13C NMR spectra)
and a capillary containing 85% H3PO4 (31P NMR spectra).
[RuCl2(PPh3)3]34 and [RuCl(C6H3{CH2NMe2}2-2,6)(PPh3)]16 (3)
were prepared according to literature procedures. The ligand
(S,S)-6a was prepared according to a modified literature
procedure15 and analogous to the synthesis of 6b (see below).
The alcohol C6H4(CH(Et)OH)2-1,3 was obtained enantiopure
or as a rac/ meso mixture according to literature procedures.35
All other reagents were purchased commercially.
Syn th esis of (S,S)-C6H4(CH(Et)P P h 2)2-1,3 ((S,S)-6b). A
modified literature procedure was used.15 To a THF (60 mL)
solution of C6H4(CH(OH)Et)2-1,3 (3.76 g, 19.4 mmol) was added
a solution of n-BuLi (30 mL, 45 mmol; 1.5 M in hexane) at
room temperature. The resulting purple suspension was cooled
to -80 °C, and MeSO2Cl (3.5 mL, 45 mmol) was added
dropwise during 20 min. After 2 h stirring, a THF solution of
LiP(BH3)Ph2 (prepared from n-BuLi (28 mL, 42 mmol) and HP-
(BH3)Ph2 (8.40 g, 42 mmol) in THF (30 mL)) was added and
the mixture stirred at -80 °C for 2 h. After slow warming to
room temperature and prolonged stirring (12 h), water was
added (80 mL) and the layers were separated. The aqueous
phase was extracted with Et2O (2 × 60 mL). The combined
organic layers were washed with brine, dried (MgSO4), and
filtered, and all volatiles were removed in vacuo. The residual
mixture was further purified by column chromatography (SiO2,
hexane/CH2Cl2, 3:1), yielding a white solid (4.10 g, 41%).
Recrystallization from EtOAc yielded analytically pure (S,S)-
6b‚2BH3. Anal. Calcd (Found): C 77.45 (77.46), H 7.58 (7.66),
Diagnostic signals for meso-6b: 1H NMR (300 MHz, CDCl3):
3
δ 0.71 (t, J (HH) ) 7.2 Hz, 6H, CH3). 13C{1H} NMR (75 MHz,
3
2
CDCl3): δ 12.63 (d, J (CP) ) 11.8 Hz, CH3), 26.50 (d, J (CP)
) 21.8 Hz, CH2). 31P{1H} NMR (81 MHz, CDCl3): δ -0.48 (s).
Syn th esis of [Ru Cl(C6H3{CH(Me)P P h 2}2-2,6)(P P h 3)] (7a).
Dir ect Cyclom eta la tion . Complexes 7a were synthesized
using ligand 6a following the same procedure described in
route 1 for complex 7b (see below). After overnight heating at
reflux temperature, the solution was concentrated and layered
with pentane, causing a coprecipitation of a red and a green
material. These species were washed with pentane until
analysis by 31P NMR spectroscopy indicated that free PPh3 was
no longer present. A subsequent extraction with benzene
followed by filtration separated 7a from the red solid (the latter
is insoluble in benzene). Yield: 50%. MS (FAB+): m/z 900.3
(M•+, C52H4635ClP3102Ru), 865.4 ([M - Cl]+), 638.1 ([M -
PPh3]+), 603.1 ([M - PPh3 - Cl]+).
Tr a n scyclom eta la tion . The same procedure described in
route 2 for complex 7b (see below) was used here, and complex
7a was obtained in 68% yield after overnight heating at reflux
temperature.
Note: During the synthesis of ligand 6a , the meso isomer
was partially lost by crystallization (only 22% of the meso form
was present). Consequently, not all spectroscopic features of
the meso-7a could be observed, particularly some 13C reso-
nances.
1
3
(S,S)-7a . H NMR (300 MHz, C6D6): δ 0.84 (dd, J (HH) )
7.5 Hz, 3J (HP) ) 14.7 Hz, 3H, CH3), 0.96 (dd, 3J (HH) ) 6.6
3
Hz, J (HP) ) 12.0 Hz, 3H, CH3), 2.00-2.07 (m, 1H, CH-Me),
4.29-4.36 (m, 1H, CH-Me), 6.20-8.60 (aromatic protons). 13C-
{1H} NMR (50 MHz, CD2Cl2): δ 15.09 (d, J (CP) ) 15.1 Hz,
2
2
1
CH3), 17.15 (d, J (CP) ) 2.8 Hz, CH3), 39.61 (d, J (CP) ) 30.4
1
Hz, CH), 45.09 (d, J (CP) ) 29.0 Hz, CH), 121.94 (d, J (CP) )
16.6 Hz), 122.89 (s,), 123.55 (d, J (CP) ) 15.7 Hz), 126.40-
130.40 (m), 132.09 (s), 133.20-136.00 (m), 136.97 (d, 1J (CP)
P
11.10 (11.05). Mp: 166-169 °C. 1H NMR (300 MHz,
) 50.7 Hz, Cquat-PPh3), 155.20 (d, J (CP) ) 15.2 Hz, Cquat
-
3
CDCl3): δ 0.67 (t, J (HH) ) 6.9 Hz, 6H, CH3), 1.86-2.09 (m,
4H, CH2), 3.38 (ddd, 3J (HH) ) 11.7 Hz, 3J (HH) ) 3.3 Hz,
2J (HP) ) 16 Hz, 2H, CH-P), 6.92-7.08 (m, 4H, aromatic),
7.14-7.36 (m, 9H, aromatic), 7.46-7.56 (m, 7H, aromatic),
7.84-7.94 (m, 4H, aromatic). 13C{1H} NMR (75 MHz, CDCl3):
δ 12.93 (d, J (CP) ) 13.4 Hz, CH3), 23.86 (d, J (CP) ) 4.9 Hz,
CH2), 45.21 (d, 1J (CP) ) 30.9 Hz, CH-P), 127.6-133.1 (11
aromatic signals), 135.85 (s, aryl). 31P{1H} NMR (81 MHz,
CDCl3): δ 24.75 (s).
CH2-PPh2), 157.94 (d, J (CP) ) 18.3 Hz, Cquat-CH2-PPh2),
171.56 (d, 1J (CP) ) 15.2 Hz, Ru-Cipso). 31P{1H} NMR (121.5
MHz, C6D6): δ 43.71 (dd, 2J (PP) ) 20.7 Hz, 2J (PP) ) 261.2
Hz, 1P, PPh2), 58.37 (dd, 2J (PP) ) 46.8 Hz, 2J (PP) ) 261.7
2
2
Hz, 1P, PPh2), 80.10 (dd, J (PP) ) 20.7 Hz, J (PP) ) 46.8 Hz,
PPh3).
3
2
(m eso)-7a . 1H NMR (300 MHz, C6D6): δ 1.30-1.40 (m,
residual signal of the CH3), 2.80-3.00 (m, residual signal of
the CH-Me), 6.20-8.60 (aromatic protons). 31P{1H} NMR
(121.5 MHz, C6D6): δ 54.54 (d, J (PP) ) 32.4 Hz, 2P, PPh2),
79.50 (t, J (PP) ) 32.9 Hz, 1P, PPh3).
2
(34) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.
1970, 12, 237.
(35) Seebach, D.; Beck, A. K.; Schmidt, B.; Wang, Y. M. Tetrahedron
1994, 50, 4363.
2
Syn th esis of [Ru Cl(C6H3{CH(Et)P P h 2}2-2,6)(P P h 3)] (7b).
Dir ect Cyclom eta la tion . A mixture (1.0 g, 1.9 mmol) con-

4476 Organometallics, Vol. 19, No. 22, 2000
Dani et al.
taining the R,R;S,S and R,S/ S,R isomers of the bisphosphine
C6H4(CH(Et)PPh2)2-2,6 (6b ) was dissolved in 1,2-dichloro-
ethane and then added to a boiling slurry of [RuCl2(PPh3)3]
(1.8 g, 1.9 mmol) in the same solvent. After 48 h of heating at
reflux, a green solution was formed containing free PPh3, an
unidentified compound, and a 1:1 mixture of the diastereomers
of 7b. Attempts to obtain pure 7b by precipitation from the
1,2-dichloroethane using hexane were not successful due to
the similar solubility of 7b and free PPh3.
The combined organic layers were washed once with degassed
water (10 mL) and then dried over MgSO4. Filtration of
insoluble material and removal of the ether under reduced
pressure resulted in a colorless waxlike material. Yield: 1.02
g (93%). Anal. Calcd (Found) for C 76.89 (76.66), H 6.64 (6.57),
P 11.33 (11.18). 1H NMR (300 MHz, CDCl3): δ 0.07 (s, 9H,
SiCH3), 3.38 (s, 4H, CH2), 6.77 (s, 2H, SiCCH), 7.02 (s, 1H,
CH ortho to both CH2PPh2 groups), 7.20-7.60 (m, 20H, PPh2
aromatic protons). 13C NMR (50 MHz, CDCl3): δ -1.12, (s,
1
2
CH3), 36.01 (d, J (CP) ) 16.20 Hz, CH2), 128.41 (d, J (CP) )
6.5 Hz, o-PPh2), 128.73 (s, p-PPh2), 131.00 (t, 3J (CP) ) 6.6 Hz,
CH ortho to both CH2PPh2 groups), 132.13 (m, C-CH2P), 133.10
(d, 3J (CP) ) 18.4 Hz, m-PPh2), 136.41 (dd, 3J (CP) ) 5.7 Hz,
5J (CP) ) 1.7 Hz, SiCCH), 138.40 (d, 1J (CP) ) 15.7 Hz,
P-Cquat), 139.92 (s, Si-C). 31P{1H} NMR (81 MHz, CDCl3): δ
-9.11 (s).
Tr a n scyclom eta la tion . A mixture (40 mg, 76 µmol) con-
taining the R,R;S,S and R,S/ S,R isomers of the bisphosphine
C6H4(CH(Et)PPh2)2-2,6 (6b) was dissolved in benzene (2 mL)
and transferred to a Schlenk flask containing [RuCl(C6H3{CH2-
NMe2-2,6})(PPh3)] (45 mg, 76 µmol) in 2 mL of benzene at room
temperature. After 48 h of heating at reflux, the reaction
mixture was concentrated in vacuo until only a small residual
amount of liquid remained. Hexane was added, causing the
formation of a green precipitate. Using a cannula containing
a small glass filter, the mother liquor was removed. To the
remaining green solid some drops of CH2Cl2 and cold hexane
were added. This procedure was repeated until no more free
Syn th esis of [Ru Cl(C6H2{CH2P P h 2}2-2,6-Me3Si-4)(P P h 3)]
(9). A solution of 8 (0.43 g, 0.78 mmol) in THF (10 mL) was
added to a boiling THF (20 mL) solution of 3 (0.49 g, 0.79
mmol) and heated to reflux for 8 h. The final product was
contaminated with a small amount (<5%) of 10. Yield: 0.51 g
(70%). Mp: 135-145 °C (decomp). 1H NMR (300 MHz, CD2-
Cl2): δ 0.33 (s, 9H, Si-CH3), 2.45 (m, 2H, CH2), 3.50 (m, 2H,
CH2), 6.50-8.00 (m, 37H, aromatic protons). 13C NMR (75
1
bisaminoarene ligand could be detected by H NMR spectros-
copy. Yield: 0.0280 g (30 µmol, 39%). Anal. Calcd (Found) for
C 69.37 (69.94), H 5.15 (5.20), P 10.32 (10.26). Transcyclo-
metalation of 3 with (S,S)-6b resulted in the formation of (S,S)-
7b . With help of the spectroscopic analyses of (S,S)-7b the
signals resulting from meso-7b in the mixture obtained by the
direct cyclometalation were unequivocally assigned.
1
MHz, CD2Cl2): δ 1.00 (s, Si-CH3), 40.49 (t, J (CP) ) 15 Hz,
CH2), 128.77 (d, J (CP) ) 10 Hz), 129.59 (t, J (CP) ) 19.1 Hz),
129.92 (t, J (CP) ) 4.2 Hz), 130.27 (t, J (CP) ) 4.3 Hz), 130.5-
131.0 (m), 131.65 (s), 133.5-134.0 (m), 134.1-135.0 (m), 135.99
(d, J (CP) ) 10.4 Hz), 136.2-138.5 (m), 152.31 (t, J (CP) ) 9.3
Hz), 176.74 (d, J (CP) ) 17.2 Hz, Ru-Cipso). 31P{1H} NMR (81
1
3
(S,S)-7b. H NMR (300 MHz, CD2Cl2): δ 0.73 (t, J (HH) )
7.4 Hz, 3H, CH3), 0.80-1.0 (m, 2H, CH2), 1.00 (t, 3J (HH) )
6.0 Hz, 3H, CH3), 1.50-1.70 (m, 3H CH-Et, CH2), 4.05-4.15
(m, 1H, CH-Et), 6.21 (vt, vtJ ) 8.4 Hz, 2H, o-PPh2), 6.53 (m,
2H, m-PPh2), 6.62 (d, J (HH) ) 6.9 Hz, 1H), 6.78-7.00 (m, 6H,
o-PPh3), 7.20-7.80 (m, 9H, m,p-PPh3), 8.25-8.32 (m, 2H,
2
MHz, CD2Cl2): δ 36.98 (d, J (PP) ) 31.8 Hz, 2P, PCP), 82.73
2
(t, J (PP) ) 31.8 Hz, 1P, PPh3).
Syn th esis of C6H3(CH2P P h 2)2-1,3-D-2 (11-D). To a solu-
tion of C6H3(CH2Br)2-1,3-D-236 in xylene was added 2 equiv of
Et(O)PPh2. After 2 h of reflux, the volatiles were removed, and
the remaining residue was extracted with hexane, resulting
in the formation of the corresponding phosphine oxide as a
white solid. The reduction was performed by adding HSiCl3
dropwise to a hot solution of the phosphine oxide in benzene.
The volatiles were removed in vacuo, and the oily residue was
treated with hexane to induce crystallization. The resulting
white waxlike precipitate was filtered off and dried under
vacuum. Yield: 70% (based on C6H3(CH2Br)2-1,3-D-2).
3
o-PPh2). 13C{1H} NMR (75 MHz, CD2Cl2): δ 13.45 (d, J (CP)
) 12.2 Hz, CH3), 15.87 (d, 3J (CP) ) 8.5 Hz, CH3), 22.54 (d,
2
2J (CP) ) 7.4 Hz, CH2), 23.62 (d, J (CP) ) 7.4 Hz, CH2), 47.66
(d, 1J (CP) ) 21.1 Hz, CH), 52.15 (d, 1J (CP) ) 28.1 Hz, CH),
121.80 (t, J (CP) ) 8.5, CH), 122.21 (s, CH), 122.30 (s, CH),
122.54 (d, J (CP) ) 15.9 Hz, CH), 123.57 (d, J (CP) ) 17.1 Hz,
CH), 127.16 (d, 3J (CP) ) 9.7 Hz, m-PPh3), 127.18 (d, 3J (CP) )
10.4 Hz, m-PPh3), 128.27-134.50 (m), 134.75 (d, 2J (CP) ) 10.9
Hz, o-PPh3), 137.30 (dt, 1J (CP) ) 47.6 Hz, 3J (CP) ) 2.4 Hz,
Cquat PPh3), 154.99 (d, J (CP) ) 14.6 Hz, Cquat), 155.37-155.61
(m, Cquat), 173.21 (d, 1J (CP) ) 20.2 Hz, Ru-Cipso). 31P{1H} NMR
(121.5 MHz, CD2Cl2): δ 38.04 (dd, 2J (PP) ) 19.8 Hz, 2J (PP) )
254.4 Hz, 1P, PPh2), 55.06 (dd, 2J (PP) ) 48.0 Hz, 2J (PP) )
254.4 Hz, 1P, PPh2), 79.81 (dd, 2J (PP) ) 19.8 Hz, 2J (PP) )
48.0 Hz, 1P, PPh3).
Even though the synthesis of C6H4(CH2PPh2)2-1,3 (11) was
reported some time ago, the available NMR data are incom-
plete. With the help of one- and two-dimensional NMR
techniques, all protons and carbons were located both for
C6H4(CH2PPh2)2-1,3 (11) and for its analogue 11-D. Due to the
obvious similarity between these two compounds, we will
describe only the NMR data of the former. 1H NMR (300 MHz,
CDCl3): δ 3.41 (s, 4H, CH2), 6.89 (m, 2H, CH-4,6), 7.09 (bs,
1H, CH-2), 7.06 (t, 3J (HH) ) 8.3 Hz, 1H, CH-5), 7.38 (m,
m-PPh2), 7.44 (m, p-PPh2), 7.48 (m, o-PPh2). 13C{1H} NMR (75
1
3
(m eso)-7b. H NMR (300 MHz, CD2Cl2): δ 1.06 (t, J (HH)
) 7.4 Hz, 6H, CH3), 1.50-1.70 (m, 2H, CH2), 1.75-1.90 (m,
2H, CH2), 2.41-2.50 (m, 2H, CH-Et), 6.78-7.80 (aromatic).
13C{1H} NMR (75 MHz, CD2Cl2): δ 16.10 (vt, vtJ (CP) ) 4.0
Hz, CH3), 25.56 (vt, vtJ (CP) ) 3.0 Hz, CH2), 47.47 (vt, vtJ (CP)
) 13.4 Hz, CH), 121.80 (t, J (CP) ) 8.5, CH), 122.21 (s, CH),
122.30 (s, CH), 122.54 (d, J (CP) ) 15.9 Hz, CH), 123.57 (d,
J (CP) ) 17.1 Hz, CH), 127.16 (d, 3J (CP) )9.7 Hz, m-PPh3),
127.48 (d, 3J (CP) ) 9.7 Hz, m-PPh2), 128.27-134.50 (m),
1
MHz, CDCl3): δ 35.89 (d, J (CP) ) 16.2 Hz, CH2), 126.99 (m,
CH-4,6), 128.12 (s, CH-5), 128.34 (d, 3J (CP) ) 7.1 Hz, m-PPh2),
3
128.65 (s, p-PPh2), 130.46 (t, J (CP) ) 7.1 Hz, CH-2), 132.90
(d, 2J (CP) ) 18.2 Hz, o-PPh2), 137.33 (dd, 2J (CP) ) 8.1 Hz,
4J (CP) ) 2.1 Hz, C-1,3), 138.33 (d, 1J (CP) ) 15.3 Hz, P-Cquat).
31P{1H} NMR (121 MHz, CDCl3): δ -9.52 (s).
2
1
134.67 (d, J (CP) ) 9.7 Hz, o-PPh3), 136.20 (dt, J (CP) ) 50.0
Hz, 3J (CP) ) 2.4 Hz, Cquat PPh3), 155.37-155.61 (m, Cquat),
Ack n ow led gm en t. This work was financially sup-
ported by the Conselho Nacional de Desenvolvimento
Cient´ıfico e Tecnolo´gico (CNPq), Brazil, and the Council
for Chemical Sciences of the Netherlands Organization
for Scientific Research (CW-NWO). Dr. R. A. Gossage
(Department of Chemistry, Acadia University, Wolfville,
Nova Scotia, Canada) is kindly thanked for discussions
and corrections of the manuscript.
1
171.94 (d, J (CP) ) 17.7 Hz, Ru-Cipso). 31P{1H} NMR (121.5
2
MHz, CD2Cl2): δ 55.03 (d, J (PP) )32.4 Hz, 2P, PPh2), 77.73
(t, J (PP) ) 32.4 Hz, 1P, PPh3).
2
Syn th esis of C6H3(CH2P P h 2)2-3,5-Me3Si-1 (8). To a solu-
tion of 1-C6H3(CH2PPh2)2-3,5-Br-1 (1.11 g, 2 mmol) in diethyl
ether (30 mL) at -78 °C was slowly added 2.1 equiv of t-BuLi.
After stirring for 30 min, an excess of trimethylsilyl chloride
was added (2 mL, 15.8 mmol). After 5 h, the resulting mixture
was allowed to warm to room temperature. All volatiles were
removed in vacuo. The oily residue was treated with degassed
water (10 mL) and extracted with diethyl ether (3 × 10 mL).
OM000340T
(36) Cruse, R. W.; Kaderli, S.; Meyer, C. J .; Zuberbu¨hler, A. D.;
Karlin, K. D. J . Am. Chem. Soc. 1988, 110, 5020.