Insertion of ethyne into the Ru-B bond of a coordinatively unsaturated ruthenium boryl complex. X-ray crystal structure of Ru(CH=CH[BOC6H4O])Cl(CO)(PPh3)2

Article abstract of DOI:10.1021/om970618q

Ethyne inserts readily into the Ru-B bond of the five-coordinate boryl complex Ru(BO₂C₆H4)Cl(CO)(PPh₃)₂ (1) to form the borylalkenyl complex Ru(CH=CH[BOC₆H₄O])Cl-(CO)(PPh₃)₂ (2). Complex 2 has been characterized by IR and multinuclear NMR spectroscopy and by an X-ray crystal structure determination. In the solid state, the Ru atom in 2 is six coordinate through weak attachment of a catechol oxygen to ruthenium. Two further products, Ru(CH=CHB[OCH₂CH₂O])Cl(CO)(PPh₃)₂ (3) and Ru(CH=CHB[OEt][OEt])Cl(CO)-(PPh₃)₂ (4), which result from transesterification of 2 with HOCH₂CH₂OH and 3 with CH₃-CH₂OH, respectively, are also described. The relevance of the observed ethyne insertion for metal-catalyzed hydroboration is discussed.

Full text of DOI:10.1021/om970618q

Organometallics 1997, 16, 5499-5505
5499
In ser tion of Eth yn e in to th e Ru -B Bon d of a
Coor d in a tively Un sa tu r a ted Ru th en iu m Bor yl Com p lex.
X-r a y Cr ysta l Str u ctu r e of
Ru (CHdCH[BOC6H4O])Cl(CO)(P P h 3)2
George R. Clark, Geoffrey J . Irvine, Warren R. Roper,* and L. J ames Wright*
Department of Chemistry, The University of Auckland, Private Bag 92019,
Auckland, New Zealand
Received J uly 21, 1997X
Ethyne inserts readily into the Ru-B bond of the five-coordinate boryl complex Ru-
(BO2C6H4)Cl(CO)(PPh3)2 (1) to form the borylalkenyl complex Ru(CHdCH[BOC6H4O])Cl-
(CO)(PPh3)2 (2). Complex 2 has been characterized by IR and multinuclear NMR spectros-
copy and by an X-ray crystal structure determination. In the solid state, the Ru atom in 2
is six coordinate through weak attachment of a catechol oxygen to ruthenium. Two further
products, Ru(CHdCHB[OCH2CH2O])Cl(CO)(PPh3)2 (3) and Ru(CHdCHB[OEt][OEt])Cl(CO)-
(PPh3)2 (4), which result from transesterification of 2 with HOCH2CH2OH and 3 with CH3-
CH2OH, respectively, are also described. The relevance of the observed ethyne insertion
for metal-catalyzed hydroboration is discussed.
In tr od u ction
mechanism is very similar to the more thoroughly
studied rhodium-catalyzed hydrometalation reactions,
namely, hydroformylation, hydrogenation, and hydrosi-
lylation.4 The mechanism involves initial oxidative
addition of the B-H bond to Rh(I), followed by alkene
coordination and subsequent insertion into the Rh-H
bond to afford a mixed alkyl, boryl complex. Reductive
deborylation via B-C elimination then liberates the
hydroborated product and regenerates the catalyst.
Support for this mechanism has been afforded by stoi-
chiometric reaction chemistry. RhHCl(BO2C6H4)(PPh3)2,5
which is readily generated by treatment of RhCl(PPh3)3
with catecholborane, reacts stoichiometrically with al-
kenes, resulting in hydroboration and regeneration of
RhCl(PPh3)2.1 Computational studies have also sup-
ported this mechanism.6h However, the formation of
vinylboranes and vinylboronate esters during some
metal-promoted B-H additions to alkenes has pointed
to the possibility of an alternative mechanistic pathway
in which insertion of the alkene into the metal-boron
bond occurs in preference to insertion into the metal-
hydride bond.6a-g In a competing side reaction, â-H
elimination from the resulting intermediate borylalkyl
complex then affords the vinylborane byproduct. Sup-
port for this proposed mechanism was recently obtained
Migratory insertion reactions play an essential role
in the mechanisms of many late transition metal-
catalyzed processes, and for metal-catalyzed hydrobo-
ration, the possibility of alkene or alkyne insertion into
a M-B bond as a key step must be considered.
In 1985, Ma¨nnig and No¨th1 reported that, in the
presence of RhCl(PPh3)3, catecholborane hydroborated
a number of alkenes under very mild conditions with a
high degree of chemoselectivity. A variety of transition
metal complexes are now known to effectively catalyze
the hydroboration of alkenes and alkynes, and many
examples are derivatives of the platinum group metals.2
The most commonly employed catalysts are those of
rhodium. In addition to offering rate enhancements, the
catalyzed reactions afford substantially modified chemo-,
regio-, and stereoselectivities when compared to the
uncatalyzed reaction.3a-n
A widely accepted mechanistic pathway for the hy-
droboration of alkenes catalyzed by platinum group
metals is that first proposed by Ma¨nnig and No¨th. This
X Abstract published in Advance ACS Abstracts, November 15, 1997.
(1) Ma¨nnig, D.; No¨th, H. Angew. Chem., Int. Ed. Engl. 1985, 24,
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1988, 110, 6917. (b) Hayashi, T.; Ito, Y.; Matsumoto, Y. J . Am. Chem.
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Evans, D. A.; Fu, G. C.; Hoveyda, A. H. J . Am. Chem. Soc. 1992, 114,
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1993, 12, 589. (l) Pereira, S.; Srebnik, M. Organometallics 1995, 14,
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Chem. 1995, 498, 109. (n) Iverson, C. M.; Smith, M. R., III. J . Am.
Chem. Soc. 1995, 117, 4403.
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tallics 1983, 2, 1693. (b) Lynch, A. T.; Sneddon, L. G. J . Am. Chem.
Soc. 1989, 111, 6201. (c) Brown, J . M.; Lloyd-J ones, G. C. J . Chem.
Soc., Chem. Commun. 1992, 710. (d) Baker, R. T.; Calabrese, J . C.;
Marder, T. B.; Nguyen, P.; Westcott, S. A. J . Am. Chem. Soc. 1993,
115, 4367. (e) Baker, R. T.; Marder, T. B.; Westcott, S. A. Organome-
tallics 1993, 12, 975. (f) Baker, R. T.; Blom, H. P.; Calabrese, J . C.;
Marder, T. B.; Nguyen, P.; Taylor, N. J .; Westcott, S. A. In Current
Topics in the Chemistry of Boron; Kabalka, G. W., Ed.; Royal Society
of Chemistry: Cambridge, U.K., 1994; pp 68-71. (g) Mebel, A. M.;
Morokuma, K.; Musaev, D. G. J . Am. Chem. Soc. 1994, 116, 10693.
(h) Dorigo, A. E.; Schleyer, P. v. R. Angew. Chem., Int. Ed. Engl. 1995,
34, 115.
S0276-7333(97)00618-3 CCC: $14.00 © 1997 American Chemical Society

5500 Organometallics, Vol. 16, No. 25, 1997
Clark et al.
Sch em e 1
from a study which compared alkene insertion into the
iridium-hydrogen or iridium-boron bonds of suitable
model compounds.7 It was found that insertion into the
Ir-B bond was thermodynamically slightly more favor-
able than insertion into the Ir-H bond. However, in
this particular case, the close similarity in ∆H terms
for each insertion process suggested that there could be
competition between the two insertion pathways and
that kinetic factors would determine selectivity between
them. Additional support for the feasibility of alkene
insertion into metal-boron bonds during metal-cata-
lyzed hydroboration comes from two recent studies of
alkene or alkyne insertion into M-B bonds in which the
presence of borylalkyl or borylalkenyl intermediates
were clearly indicated.6d,8
Recently it was suggested that it may be necessary
to consider yet another mechanistic variation in some
cases. Hartwig and co-workers found that treatment
of CpRu(Me)(PPh3)2 with catecholborane in arene sol-
vent at room temperature produced CpRu(H)(PPh3)2
and methylcatecholborane quantitatively. On careful
study of this reaction, strong evidence was obtained that
the B-C bond formation step did not proceed via a
sequence of oxidative and reductive steps but rather via
a σ-bond metathesis pathway.9
Few mechanistic investigations have appeared that
address catalytic alkyne hydroboration, but more at-
tention has been directed toward metal-catalyzed dibo-
rylation of alkynes.10a-d It seems likely that alkyne
insertion into a metal-boron bond is a key step in both
of these processes. Although considerable evidence for
the intermediacy of borylalkyl and borylalkenyl moieties
in alkene and alkyne insertion, respectively, has been
obtained, as yet no stable examples of such species
resulting from the corresponding stoichiometric reac-
tions have been isolated.6d,8 The work reported here
describes the synthesis and characterization of the first
example of a stable metalated vinyl boronate ester
derived from the formal insertion of ethyne into the
Ru-B bond of Ru(BO2C6H4)Cl(CO)(PPh3)2.11 The re-
activity of this compound, and the implications for
transition metal-catalyzed hydroboration, are also dis-
cussed.
has formally inserted into the Ru-B bond (see Scheme
1). Since coordinatively unsaturated d6 complexes are
usually strongly colored, the very pale color of this
product suggested that in the solid state the ruthenium
center was coordinatively saturated. One way this could
be achieved would be by having an oxygen atom of the
catecholboryl group interact with the metal center.
The infrared spectrum of 2 displayed a very sharp ν-
(CO) band at 1915 cm-1 which was ∼25 cm-1 lower than
ν(CO) in the starting material 1 but in a position similar
to that reported for the alkenyl complex of ruthenium,
RuCl(PhCdCHPh)(CO)(PPh3)2.12 Other significant bands
were observed at 1339, 1283, 1246, and 1227 cm-1
.
Complete IR data for this and other reported compounds
are given in Table 1. A band that could be assigned to
ν(CdC) was not readily discernible. However, the
presence of the alkenyl moiety was confirmed by NMR
spectroscopy (see Tables 2 and 3). Resonances for each
of the alkenyl carbon atoms were clearly visible in the
13C NMR spectrum. The triplet centered at 207.3 ppm
(J CP ) 10.7 Hz) was assigned to the metalated alkenyl
carbon (CR), and a broad singlet at 122.2 ppm was
assigned to the remote carbon atom (Câ). The broadness
of this latter signal is consistent with there being a
direct connectivity to the quadrupolar boron nucleus.
1
The alkenyl proton resonances were observed in the H
NMR spectrum as two sets of doublets of triplets, one
set centered at 5.79 ppm and the other at 9.69 ppm. In
each case, this pattern arises from coupling to the two
mutually trans phosphorus nuclei as well as coupling
to the other alkenyl proton. The magnitude of the
vicinal H, H coupling constant for the alkenyl protons
(3J HH ) 11.7 Hz) is very close to the normally encoun-
tered limits for both (Z)- and (E)-alkenyl complexes,13
and so unambiguous assignment of structure on this
basis is not possible. However, the results of an X-ray
structure determination (see below) clearly show a Z
geometry about the double bond in the solid state.
Assignment of the resonances due to the two alkenyl
protons was achieved by examination of the 13C-1H
cross-peaks in the 2D (H,C)-COSY spectrum. This
showed that the proton that appeared at 9.69 ppm is
bonded to the metalated carbon (CR) whereas the proton
that appears at 5.79 ppm is attached to (Câ). Both
proton resonances show coupling to the two mutually
Resu lts a n d Discu ssion
In ser tion of Eth yn e in to th e Ru -B Bon d of Ru -
(BO2C6H4)Cl(CO)(P P h 3)2 (1). When a benzene solu-
tion of 1 was treated with ethyne under low pressure
(1 atm), at a temperature of ∼65 °C, the initially pale
yellow solution turned golden yellow over the course of
20 min. The nearly colorless product, which was
isolated in good yield from solution, was formulated as
Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2 (2), where ethyne
(7) Rablen, P. R.; Hartwig, J . F. J . Am. Chem. Soc. 1994, 116, 4121.
(8) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J . Am. Chem.
Soc. 1993, 115, 11018.
(9) Bhandari, S.; Hartwig, J . F.; Rablen, P. R. J . Am. Chem. Soc.
1994, 116, 1839.
(10) (a) Ishiyama, T.; Matsuda, N.; Murata, M.; Ozawa, F.; Suzuki,
A.; Miyaura, N. Organometallics 1996, 15, 713. (b) Sakaki,S.; Kikuno,
T. Inorg. Chem. 1997, 36, 226. (c) Lesley, G.; Nguyen, P.; Taylor, N.
J .; Marder, T. B.; Scott, A. J .; Clegg, W.; Norman, N. C. Organome-
tallics 1996, 15, 5137. (d) Iverson, C. N.; Smith, M. R., III Organome-
tallics 1996, 15, 5155.
3
4
trans phosphorus nuclei with J HRP ) 1.3 Hz and J HâP
(12) Ros, J .; Santos, A.; Torres, M. R.; Vegas, A. J . Organomet. Chem.
1986, 309, 169.
(11) Irvine, G. J .; Roper, W. R.; Wright, L. J . Organometallics 1997,
16, 2291.
(13) Maddock, S. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J .
Organometallics 1996, 15, 1793.

Coordinatively Unsaturated Ru Boryl Complex
Ta ble 1. In fr a r ed Da ta (cm -1
Organometallics, Vol. 16, No. 25, 1997 5501
for Ru th en iu m Com p lexes
a
)
complex
ν(CtO)
other bandsb
1915 vs
1412 w, 1339 m, 1283 m, 1246 m, 1227, 1192 w, 869 w, 814 w
Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2 (2)
Ru(CHdCH[BOCH2CH2O])Cl(CO)(PPh3)2 (3)
Ru(CHdCHB[OEt][OEt])Cl(CO)(PPh3)2 (4)
1907 vs
1914 vs
1492, 1403 m, 1363 m sh, 1247, 1190 m, 1014 m, 945 w, 848 w
1490 sh, 1408 w, 1320 m, 1297 m sh, 1266, 1207 m,
1160 w, 1028 m, 885 m, 724 m
a
b
All intensities strong unless denoted otherwise. Bands associated with vinyl-boronate ligand.
Ta ble 2. 1H NMR Da ta for Ru th en iu m Com p lexes
complex
1H, δ (ppm)a
Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2 (2)
3
4
recorded at 298 Kb
5.79 dt, J HH ) 11.7, J HP ) 1.8, 1H, CHdCH[BO2C6H4]; 6.56 s br, 2H,
CHdCH[BO2C6H4]; 7.10-7.22 m, 7.61-7.73 m, 32H, PPh3,
3
3
CHdCH[BO2C6H4]; 9.69 dt, J HH ) 11.7, J HP ) 1.3, 1H, CHdCH[BO2C6H4]
3
4
recorded at 230 K
5.79 dt, J HH ) 11.7, J HP ) 1.8, 1H, CHdCH[BO2C6H4]; 6.40 ddd,
J HH ) 8.1, 6.7, 2.1, 1H, CHdCH[BO2C6H4]; 6.65 m, 2H, CHdCH[BO2C6H4];
7.10-7.22 m, 7.61-7.73 m, 20H, PPh3; 7.30 m, 1H, CHdCH[BO2C6H4];
3
3
7.61-7.73 m, 10H, PPh3; 9.71 dt, J HH ) 11.7, J HP ) 1.3, 1H, CHdCH[BO2C6H4]
3
3
1.98 t, J HH ) 7.7, 2H, BOCH2CH2O; 3.25 t, J HH ) 7.7, 2H, BOCH2CH2O; 5.40 dt,
Ru(CHdCH[BOCH2CH2O])Cl(CO)(PPh3)2 (3)
Ru(CHdCHB[OEt][OEt])Cl(CO)(PPh3)2 (4)
3J HH ) 11.1, J HP ) 1.7, 1H, CHdCH[BOCH2CH2O]; 7.32-7.40 m, 7.62-7.76 m,
4
3
30H, PPh3; 9.31 d br, J HH ) 11.0, 1H, CHdCH[BOCH2CH2O]
3
3
0.19 t, J HH ) 7.0, 3H, B[OCH2CH3] (O-metalated); 1.21 t, J HH ) 7.0, 3H,
3
B[OCH2CH3]; 2.85 qt, J HH ) 7.0, 2H, B[OCH2CH3] (O-metalated); 3.90 qt,
3J HH ) 7.0, 2H, B[OCH2CH3]; 5.49 dt, J HH ) 11.1, J HP ) 1.8, 1H,
3
4
3
CHdCHB[OEt]2; 7.30-7.40 m, 7.61-7.77 m, 30H, PPh3; 8.89 dt, J HH
)
3
11.0, J HP ) 2.1, 1H, CHdCHB[OEt]2
a
b
Coupling constants in hertz. Two O2C6H4 resonances obscured beneath PPh3.
Ta ble 3. 13C NMR Da ta for Ru th en iu m Com p lexes
complex
13C, δ (ppm)a
Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2 (2)
2,4
1,3
recorded at 298 K
122.2 s br, CHdCH[BO2C6H4]; 128.4 t′,
J
J
) 9.6, PPh3
CP
CP
2
ortho; 130.1 s, PPh3 para; 132.4 t′, q,
) 44.4, PPh3 ipso;
3,5
134.3 t′,
J
) 11.4, PPh3 meta; 207.3 t, J CP ) 10.7,
CP
2
CHdCH[BO2C6H4]; 207.7 t, q, J CP ) 17.0, CO
111.3 s, BO2C6H4; 113.0 s br, CHdCH[BO2C6H4]; 115.7 s,
BO2C6H4; 121.4 s, BO2C6H4
recorded at 250 Kb
Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2 (2)
2,4
recorded at 250 Kb
121.9 s, BO2C6H4; 128.0 t′,
J
) 10.1, PPh3 ortho; 129.5 s,
CP
1,3
PPh3 para; 131.8 t′, q,
J
) 44.3, PPh3 ipso; 133.7 t′,
CP
3,5
J
) 11.1, PPh3 meta; 145.1 s, q, BO2C6H4; 146.9 s, q,
CP
2
BO2C6H4; 207.1 t, J CP ) 10.8, CHdCH[BO2C6H4]
61.8 s, BOCH2CH2O; 65.6 s, BOCH2CH2O; 113.3 s br,
Ru(CHdCH[BOCH2CH2O])Cl(CO)(PPh3)2 (3)
Ru(CHdCHB[OEt][OEt])Cl(CO)(PPh3)2 (4)
2,4
CHdCH[BOCH2CH2O]; 128.1 t′,
129.7 s, PPh3 para; 133.0 t′, q,
J
) 9.1, PPh3 ortho;
CP
1,3
J
) 43.3, PPh3 ipso;
CP
2
3,5
134.3 t′,
J
) 11.1, PPh3 meta; 203.9 t, J CP ) 10.6,
CP
2
CHdCH[BOCH2CH2O]; 207.2 t, q, J CP ) 17.1, CO
14.1 s, B[OCH2CH3] (O-metalated); 17.5 s, B[OCH2CH3];
60.5 s, B[OCH2CH3] (O-metalated); 61.8 s, B[OCH2CH3];
117.3 s br, CHdCHB[OEt]2; 128.1 t′,
2,4
J
) 8.0, PPh3 ortho;
CP
1,3
129.6 s, PPh3 para; 133.3 t′, q,
J
) 42.3, PPh3 ipso; 134.5 t′,
CP
2
3,5J CP ) 10.1, PPh3 meta; 202.7 t, J CP ) 11.6, CHdCHB[OEt]2;
2
206.6 t, q, J CP ) 18.6, CO
a
b
Coupling constants in hertz. CO not observed.
) 1.8 Hz. Larger J HP values for Hâ than HR have been
observed before.13 The 11B NMR spectrum (referenced
to BF3‚Et2O, δ ) 0 ppm) showed a broad signal centered
at 14.2 ppm which is appropriate for the presence of
non-metal-substituted tricoordinate boron and this can
be compared with the chemical shift of 45.6 ppm
observed for the parent compound, Ru(BO2C6H4)Cl(CO)-
(PPh3)2. This chemical shift for 2, however, is at least
10 ppm upfield of typical alkenylboronate esters.
only a very broad resonance centered at 6.56 ppm was
seen in the H NMR spectrum. However, as the tem-
1
perature was lowered to 230 K, this broad signal split
into two sets of multiplets (see Table 2). Furthermore,
an additional multiplet appeared at 7.30 ppm between
the resonances of the phenyl protons of the triphen-
ylphosphine ligands. These three resonances account
for all four catechol protons as measured by peak
integrals.
1
Surprisingly, the characteristic H NMR resonances
normally associated with a catecholate substituent were
not observed at 298 K. Instead, at this temperature
Likewise, the 13C NMR spectrum at 298 K showed
no signals for the catechol substituent. However, at the
lower temperature of 250 K, four methine and two qua-

5502 Organometallics, Vol. 16, No. 25, 1997
Clark et al.
plexes that contain mutually trans triphenylphosphine
ligands.14 The P(1)-Ru-P(2) angle is 179.32(7)°, show-
ing essentially linear geometry for the two phosphine
ligands. The carbonyl carbon atom is bonded to ruthe-
nium at a distance of 1.801(8) Å, and this is close to the
average distance found for other terminal carbonyls
coordinated to ruthenium(II). The Ru-Cl distance
(2.476(2) Å) is slightly longer than the mean bond
distance found for terminal Ru(II)-Cl bonds and this
probably reflects the trans labilising influence of the
alkenyl group.14 The alkenyl carbon, C(2), is bonded to
the ruthenium at a distance of 2.055(8) Å, which is very
similar to the corresponding distances observed in the
σ-bonded alkenyl complexes, Ru(η2-O2CMe)(HCCPh)-
(CO)(PPh3)2 (2.030(15) Å) and RuCl(PhCdCHPh)(CO)-
(PPh3)2 (2.03(1) Å).12,15 The Z geometry at the double
bond allows a close approach of the boronate ester to
the metal affording a dative bonding interaction be-
tween a catecholate oxygen atom and ruthenium. The
Ru-O bond length is 2.275(6) Å, and this is shorter than
those found in the η2-acyl complexes RuI(η2-C[O]Me)-
(CO)(PPh3)2 (2.47(2) Å) or RuI(η2-C[O]-p-tolyl)(CO)-
(PPh3)2 (2.36(1) Å)16 but similar to that found in
RuCl(MeO[O]CCdC{C[O]OMe}CHdCHCMe3)(CO)-
(PPh3)2 (2.291(9) Å), which was derived from the inser-
tion of dimethylacetylenedicarboxylate into the alkenyl
complex RuCl(CHdCHCMe3)(CO)(PPh3)2.17 In com-
parison to typical ruthenium-oxygen single bond dis-
tances,14 however, this bond length is very long, indi-
cating only a modest bonding interaction between
oxygen and ruthenium.
F igu r e 1. Molecular structure of Ru(CHdCH[BOC6H4O])-
Cl(CO)(PPh3)2 (2) showing atoms as 50% probability el-
lipsoids. Each phenyl ring is numbered from Cn1 (attached
to P) to Cn6 as indicated.
ternary resonances were observed for this fragment.
This indicates that at this temperature the six ring car-
bon atoms are magnetically inequivalent and that the
symmetry of the free catecholate group has been low-
ered.
These variable-temperature 1H and 13C NMR data are
consistent with the catecholboryl group coordinating to
ruthenium through one oxygen atom but also undergo-
ing a dynamic process in which the oxygen dissociates
from ruthenium, the catecholate group rotates about the
B-Câ bond, and the other oxygen atom then coordinates
to ruthenium. This process is rapid at 298 K on both
The catecholboryl fragment and the ethenyl unit to
which it is bonded are coplanar. The C(2)-C(3) bond
length of 1.266(12) Å is appropriate for a double bond.
Both hydrogen atoms were located in the Fourier
difference map and are shown in Figure 1. Other bonds
within the catecholboryl unit are normal.
A recent ab initio theoretical study of the RhCl-
(PH3)2-catalyzed hydroboration of alkenes6g revealed
that the most favorable pathway involves oxidative
addition of the borane to the Rh center followed by
insertion of ethene into the Rh-B bond. The calcu-
lated structure of the resulting intermediate complex,
1
the H and 13C NMR time scales, but at 230 K where it
is slow, each of the unique ring atoms of the coordinated
catecholate group can be observed.
In order to confirm the bidentate coordination mode
of the vinyl boronate ester moiety, and to verify unam-
biguously that insertion of ethyne into the Ru-B bond
had occurred, a single-crystal X-ray diffraction study of
2 was undertaken.
Rh(CH2CH2B[OH][OH])HCl(PH3)2, is very similar to
that found for Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2. In
X-r a y Cr yst a l St r u ct u r e of R u (CH dCH -
[BOC6H4O])Cl(CO)(P P h 3)2 (2). The molecular struc-
the calculated structure, one of the oxygen atoms bonded
to boron interacts weakly with the rhodium center and
the Rh-O bond distance is 2.26 Å (cf. 2.275(6) Å for 2).
Complex 2 therefore serves as a useful model for one of
the key intermediates in some metal-catalyzed alkene
and alkyne hydroboration reactions. Furthermore, the
observation that ethyne formally inserts into the Ru-B
bond of 1 to give the borylalkenyl complex 2 indicates
that it is entirely feasible that this process could also
occur as a key step in metal-catalyzed hydroboration
reactions of alkynes and, by inference, alkenes.
ture of Ru(CHdCH[BOC6H4O])(CO)(PPh3)2 is depicted
in Figure 1. The molecular geometry about ruthenium
is approximately octahedral. The ruthenium atom is
bonded to two mutually trans triphenylphosphine ligands,
a carbonyl, a chloride, and a bidentate vinyl catechol-
boronate ester group. The geometry about the double
bond of this latter group is Z and coordination to
ruthenium is through an alkenyl carbon atom and one
of the oxygen atoms of the catechol group. Accordingly,
this makes the complex coordinatively saturated. The
major distortion from ideal octahedral geometry is
associated with the bonding requirements of the vinyl
catecholboronate ester ligand with the angle C(2)-Ru-
O(2) being 77.01(29)°.
We have no information regarding details of the
mechanism by which ethyne inserts into the Ru-B bond
(14) From a search of the Cambridge Crystallographic Database.
(15) Loumrhari, H.; Perales, A.; Ros, J .; Torres, M. R. J . Organomet.
Chem. 1990, 385, 379.
(16) Roper, W. R.; Taylor, G. E.; Waters, J . M.; Wright, L. J . J .
Organomet. Chem. 1979, 182, C46.
(17) Ros, J .; Santos, A.; Torres, M. R.; Vegas, A. J . Organomet. Chem.
1987, 326, 413.
The Ru-P distances of 2.390(2) and 2.388(2) Å are
typical of those observed for other ruthenium(II) com-

Coordinatively Unsaturated Ru Boryl Complex
Organometallics, Vol. 16, No. 25, 1997 5503
of 1 to give 2. However, if ethyne initially adds trans
to the boryl ligand in 1, then it would be necessary that
an isomerization brings the boryl and ethyne ligands
mutually cis before formal insertion could occur.
above) and may be because the oxygen atoms of the
aliphatic diol group are much better donors toward
ruthenium than the oxygens of the catechol group. The
enhanced basicity of the oxygen atoms in 3 may also be
responsible for the increased stability of the dioxaboro-
lidine group toward transesterification. It was found
that 3 could be recrystallized from dichloromethane/
ethanol without exchange of the diol occurring.
Su bstitu tion a t th e Bor on Cen ter of Ru (CHdCH-
[BOC6H4O])Cl(CO)(P P h 3)2. In compound 1 where the
catecholboryl group is directly bonded to ruthenium, the
boron center shows no reactivity toward alcohols. In
contrast, the compound 2 readily undergoes substitution
chemistry centered at boron. This reaction chemistry
is typically associated with organoboronate esters,
where transesterification with other alcohols may be
accomplished with relative ease. However, on treat-
ment of 2 with simple alcohols like methanol or ethanol,
only complex mixtures of products were produced which
could not be easily separated. Therefore, reaction with
the diol 1,2-dihydroxyethane (ethylene glycol) was
investigated. This reagent is often used in organic
synthesis for the preparation of boronic esters via
esterification of boronic acids, and it is known to form
very stable cyclic derivatives.18
Attempts to carbonylate Ru(CHdCH[BOC6H4O])Cl-
(CO)(PPh3)2 led only to mixtures of products that could
not be separated or identified. On the other hand,
treatment of a dichloromethane solution of Ru(CHdCH-
[BOCH2CH2O])Cl(CO)(PPh3)2 with CO followed by ad-
dition of ethanol afforded a colorless, microcrystalline
product in moderate yield. Rather than the antici-
pated dicarbonyl derivative, “Ru(CHdCH[BOCH2CH2O])-
Cl(CO)2(PPh3)2,” this complex was determined to be
Ru(CHdCHB[OEt][OEt])Cl(CO)(PPh3)2 (4), the bis-
(ethoxy) boronate ester analogue of the parent diol
complex 3 (see Scheme 1).
Treatment of Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2
The one carbonyl ligand in 4 gives rise to one sharp
ν(CO) band in the IR spectrum at 1914 cm-1 and other
significant bands occur at 1320, 1266, 1207, 1028, 885,
with ethylene glycol in a dichloromethane/ethanol so-
lution resulted in formation of a colorless product,
1
and 724 cm-1. Doublet of triplet resonances in the H
Ru(CHdCH[BOCH2CH2O])Cl(CO)(PPh3)2 (3) (see Scheme
NMR spectrum at both 5.49 and 8.89 ppm were assigned
to the two protons of the ethenyl group, and a broad
singlet at 117.3 ppm and a sharp triplet at 202.7 ppm
in the 13C NMR spectrum were assigned to the two
carbon atoms of this same group. In place of the two
triplet resonances observed in the 1H NMR spectrum
for the two methylene groups in 3, two triplet (0.19 and
1.21 ppm) and two quartet (2.85 and 3.90 ppm) reso-
nances were found for 4. These were assigned to the
two ethoxy groups attached to boron. The inequivalence
of these two groups arises because the oxygen atom of
one of the ethoxy groups is coordinated to ruthenium.
As for 3, rotation about the C-B bond in 4 must also
be slow on the NMR timescale.
Compound 4 can also be formed by treatment of a
dichloromethane solution of 3 with acetonitrile and
ethanol, although this procedure gives a lower yield of
4. In the absence of CO or acetonitrile, 3 can be
recovered unchanged from dichloromethane/ethanol
solutions. It is possible that the role of the CO or
acetonitrile in promoting alkoxide group exchange at
boron is to displace the coordinated oxygen from the
metal center and thereby facilitate attack at the boron
center. Alternatively, these Lewis bases may displace
the chloride from the metal, and the resulting cationic
species may then display a much higher susceptibility
to nucleophilic attack by ethanol. In either case, the
initial Lewis base coordination would then have to be
reversed after the ethanolysis and this could possibly
occur during the product isolation step.
1). The infrared spectrum of this product displayed a
sharp ν(CO) band at 1907 cm-1 as well as other
significant bands at 1492, 1403, 1247, 1190, and 1014
1
cm-1. The H NMR spectrum confirmed that transes-
terification had taken place. The broad resonance
associated with the catechol moiety at 6.56 ppm was
replaced by two new triplet resonances at 1.98 and 3.25
ppm each of which integrated for two protons. These
resonances were assigned to the two sets of methylene
protons of the dioxaborolidine moiety. The appearance
of two signals and the nearly colorless nature of the
complex is again consistent with a bonding interaction
between ruthenium and an oxygen of the dioxaboroli-
dine ligand. The ethenyl proton resonances were ob-
served at 5.40 and 9.31 ppm. Both signals were
observed as doublets (3J HH ) 11 Hz) of triplets, although
the smaller coupling to phosphorus for the lower field
signal was not well resolved. The assignments of these
resonances were made by comparison with the assign-
ments made for the corresponding signals in 2 (see
Table 2).
The 13C NMR spectra corroborated the above formu-
lation for 3 and the presence of the two methylene
carbon resonances was observed at 61.8 and 65.6 ppm.
The assignment of the methylene signals was confirmed
by a DEPT 135 experiment. A broad singlet at 113.3
ppm was assigned to the ethenyl carbon attached to
boron, and a triplet resonance centered at 203.9 ppm
was assigned to the ethenyl carbon bound directly to
2
the metal with J CP ) 10.6 Hz.
Rea ction of Com p ou n d 2 w ith HBO2C6H4. Since
opening the chelate ring in 2 produces a five-coordinate
organoruthenium compound of the type RuRCl(CO)-
(PPh3)2 (in this case R ) CHdCHBO2C6H4), it was to
be expected that reaction with HBO2C6H4 would result
in formation of the “parent” boryl complex 1.11 This
expectation was confirmed, and when 2 was treated
with HBO2C6H4 in benzene under reflux for 30 min, 1
The observation of sharp, well-resolved signals for the
two methylene groups in both the 1H and 13C NMR
spectra at 298 K shows that any rotation about the C-B
bond in 3 is very slow on the corresponding NMR time
scales. This is in contrast to the situation for 2 (see
(18) Bhat, N. G.; Brown, H. C.; Somayaji, V. Organometallics 1983,
2, 1311.

5504 Organometallics, Vol. 16, No. 25, 1997
Clark et al.
Ta ble 4. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for Ru (CHdCH[BOC6H4O])Cl(CO)(P P h 3)2‚
2.5C6H6 (2)
was produced in nearly quantitative yield. This obser-
vation could be relevant for the development of com-
pounds like 1 as hydroboration catalysts.
In vestiga tion s of Oth er Closely Rela ted In ser -
tion Rea ction s. The generality of the ethyne insertion
reaction involved in the formation of 2 was tested by
examining reactions with other related metal-boryl
complexes. No pure products could be isolated from
treatment of either Ru(B[NH]2C6H4)Cl(CO)(PPh3)211 or
empirical formula
formula weight
temperature
wavelength
C45H36BCLO3P2Ru‚2.5C6H6
1029.28
193(2) K
0.710 69 Å
cryst syst
P21/c
space group
monoclinic
11
unit cell dimens
a ) 13.381(5) Å, b ) 13.601(2) Å,
c ) 27.907(6) Å; R ) 90.00°,
â ) 102.36(2)°, γ ) 90.00°
4961(2) Å3
Ru(B[NH]SC6H4)Cl(CO)(PPh3)2 with ethyne. In con-
trast, the osmium-boryl complex Os(BO2C6H4)Cl(CO)-
11
(PPh3)2 did give an isolable product with this alkyne
volume
but with loss of the boryl group. The product proved to
have an η3-allylic moiety which was derived from the
cyclotrimerization of acetylene. This product will be the
subject of a separate paper.
Z
4
density (calcd)
absorption coeff
range of absorptn corrns
F(000)
1.378 mg m-3
0.491 mm-1
0.777-1.000
2116
The possibility of inserting other unsaturated sub-
strates into the Ru-B bond of 1 was also investigated.
The terminal alkynes, 1-propyne and 1-butyne, both
gave insertion products, and the full characterization
of these compounds is currently being studied. In
contrast, no tractable boryl-containing products were
isolated when 1 was treated with phenylacetylene,
diphenylacetylene, 2-butyne, dimethylacetylenedicar-
boxylate, propargyl alcohol, ethene, cyclohexene, carbon
dioxide, and sulfur dioxide.
crystal size
0.31 × 0.19 × 0.09 mm,
off-white needles
1.49-25.97 °
θ range for data collection
index ranges
-16<)h<)0, -16<)k<)0,
-33<)l<)34
no. of reflctns collected
no. of independent reflctns
refinement method
10 116
9665 [R(int) ) 0.0372]
full-matrix least-squares on F2
9650/0/712
data/restraints/parameters
goodness of fit on F2
1.023
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole
R1 ) 0.0672, wR2 ) 0.1715
R1 ) 0.1611, wR2 ) 0.2295
1.893 and -0.954 e Å-3
Su m m a r y a n d Con clu sion s
However, ethanol displaces the ethanediol group in 3
in the presence of CO or acetonitrile and the bis(ethoxy)-
The complex Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2
boronate ester complex Ru(CHdCHB[OEt][OEt])Cl-
(CO)(PPh3)2 (4) is formed. Displacement of the coordi-
nated oxygen atom from ruthenium in 3 by CO or
acetonitrile or the formation of a cationic complex
through chloride displacement may be responsible for
the increased reactivity of the boron center in this case.
(2) is the first example of a structurally characterized
product resulting from the stoichiometric, formal inser-
tion of an unsaturated molecule into a metal-boron
bond. This complex has been fully characterized by IR
and multinuclear NMR spectroscopies as well as by
single-crystal X-ray diffraction analysis. The geometry
about the double bond of the vinylboronate ligand is Z
with an oxygen of the catecholboryl group interacting
weakly with the metal. Variable-temperature NMR
spectroscopy shows that the catecholboryl group under-
goes a dynamic process in solution which can be
explained in terms of rotation about the Câ-B bond. The
observation that ethyne formally inserts into the Ru-B
bond of 1 to give the alkenyl complex 2 indicates it is
feasible that such a process could also occur in some
metal-catalyzed hydroboration reactions of alkynes and,
by inference, alkenes.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. The general experimental and
spectroscopic techniques employed in this work were the same
as those described previously.11,13
Ru (CHdCH[BOC6H4O])Cl(CO)(P P h 3)2 (2). Ru(BO2C6H4)-
11
Cl(CO)(PPh3)2 (1.200 g, 1.485 mmol) was added to benzene
(40 mL) in a Fisher-Porter bottle and placed under a pressure
of C2H2 (1 atm) (CAUTION, potential explosion hazard). The
solution was then heated to ∼65 °C for 20 min or until such
time as any suspended starting material had dissolved. The
resulting clear golden yellow solution was reduced in volume
in vacuo to ∼8 mL. Slow addition of n-hexane effected the
crystallization of an off-white microcrystalline solid. Following
filtration, the solid was then washed with several small
portions of n-hexane. The product at this point was sufficiently
pure for conversion to the other derivatives described below;
however, for microanalysis it was recrystallized from benzene/
n-hexane (1.194 g, 96 %). Anal. Calcd for C45H36BClO3P2Ru:
C, 64.80; H, 4.35; Cl, 4.25. Found C, 64.84; H, 4.24; Cl, 3.96.
A crystal suitable for X-ray study (see below) was grown from
The complex Ru(CHdCH[BOCH2CH2O])Cl(CO)(PPh3)2
(3) was prepared via a facile transesterification reaction
of Ru(CHdCH[BOC6H4O])Cl(CO)(PPh3)2 (2) with eth-
ylene glycol. In contrast, no catecholate substitution
reactions were observed under similar conditions for 1
where the boron atom is directly bonded to ruthenium.
Although the boron center is more sterically protected
in 1 than in 2, the major factor responsible for this
reduced reactivity is most probably the reduced elec-
trophilicity of the boron that results from the direct
interaction with ruthenium.
benzene and proved to be the benzene solvate, Ru(CHdCH-
[BOC6H4O])Cl(CO)(PPh3)2‚2.5C6H6.
The increased basicity of the ethanediol group oxygen
atoms in 3, compared to the catecholate oxygens in 2,
reduces the susceptibility of the boron center toward
nucleophilic attack in 3. Therefore, unlike 2, 3 can be
recrystallised unchanged in the presence of ethanol.
Ru (CHdCH[BOCH2CH2O])Cl(CO)(P P h 3)2 (3). Ru(CHd
CH[BOC6H4O])Cl(CO)(PPh3)2 (0.325 g, 0.390 mmol) was added
to a mixture of ethanol (20 mL) and ethylene glycol (1 mL).
The resulting suspension was then stirred rapidly while

Coordinatively Unsaturated Ru Boryl Complex
Organometallics, Vol. 16, No. 25, 1997 5505
Ta ble 5. Selected In ter a tom ic Dista n ces (Å) for
Ta ble 6. Selected Bon d An gles (d eg) for
Ru (CHdCH[BOC6H4O])Cl(CO)(P P h 3)2 (2)
Ru (CHdCH[BOC6H4O])Cl(CO)(P P h 3)2 (2)
bond
distance
bond
distance
bond
angle
bond
angle
Ru-P(1)
Ru-P(2)
Ru-Cl
Ru-O(2)
Ru-C(1)
Ru-C(2)
C(2)-C(3)
C(3)-B
B-O(2)
B-O(3)
2.390(2)
2.388(2)
2.476(2)
2.275(6)
1.801(8)
2.055(8)
1.266(12)
1.535(12)
1.413(11)
1.384(11)
C(1)-O(1)
O(2)-C(4)
O(3)-C(9)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(4)-C(9)
1.147(9)
1.406(9)
P(1)-Ru-P(2)
P(1)-Ru-Cl
P(1)-Ru-C(1)
P(1)-Ru-C(2)
P(1)-Ru-O(2)
P(2)-Ru-Cl
P(2)-Ru-C(1)
P(2)-Ru-C(2)
P(2)-Ru-O(2)
Cl-Ru-C(1)
Cl-Ru-C(2)
Cl-Ru-O(2)
C(1)-Ru-C(2)
179.32(7)
92.75(7)
89.02(25)
89.09(21)
89.49(14)
87.92(7)
90.73(25)
90.30(21)
91.66(14)
102.30(24)
163.64(26)
86.75(15)
93.98(35)
C(1)-Ru-O(2)
C(2)-Ru-O(2)
Ru-C(1)-O(1)
Ru-C(2)-C(3)
Ru-O(2)-B
Ru-O(2)-C(4)
C(2)-C(3)-B
C(3)-B-O(2)
C(3)-B-O(3)
O(2)-B-O(3)
B-O(2)-C(4)
B-O(3)-C(9)
170.88(27)
77.01(29)
1.376(10)
1.373(12)
1.379(13)
1.380(15)
1.376(14)
1.394(12)
1.393(12)
177.71(65)
122.07(65)
109.37(49)
144.94(49)
115.95(78)
115.49(77)
133.51(81)
110.96(73)
105.39(64)
105.36(68)
dichloromethane was added to effect dissolution (∼35 mL). The
resulting yellow-brown mixture was stirred at room temper-
ature for 5-10 min. Slow evaporation of solvent under
reduced pressure gave a gray microcrystalline precipitate.
Recrystallization from dichloromethane/ethanol afforded nearly
Table 4. Selected interatomic distances (Å) are listed in Table
5, and selected bond angles (deg) are listed in Table 6.
The structure was solved by Patterson and electron density
syntheses. Refinement on F2 employed SHELXL-93,20 mini-
colorless microcrystals of Ru(CHdCH[BOCH2CH2O])Cl(CO)-
2
2 2
mizing the function ∑w||Fo| - |Fc| | . Atomic scattering factors
were for neutral atoms.21 After initial isotropic refinement,
anisotropic thermal parameters were refined for all non-
hydrogen atoms. The X-ray analysis showed the presence of
2.5 benzene molecules of solvation, and these were included
in all subsequent calculations. Thirteen hydrogen atoms were
placed in calculated positions and refined using the riding
model; a further 29 hydrogens (including the two ethenyl
hdrogens) were located in a difference map and refined as
individual atoms with isotropic temperature factors. The two
hydrogen atoms on the ethenyl group refined to C-H distances
of 0.837 and 0.838 Å. There was disorder apparent in the
benzene rings and atoms C(82) and C(83) were each split into
two half-atoms to better model that ring.
(PPh3)2 (0.145 g, 47 %). The 1H NMR spectrum of this sam-
ple indicated 0.5 equiv of water solvate. Anal. Calcd for
C
4.91.
41H36BClO3P2Ru‚H2O: C, 61.94; H, 4.69. Found C, 62.11; H,
Ru (CHdCHB[OEt][OEt])Cl(CO)(P P h 3)2 (4). Ru(CHdCH-
[BOCH2CH2O])Cl(CO)(PPh3)2 (0.050 g, 0.064 mmol) was dis-
solved in dichloromethane (10 mL) and the solution added to
a Fisher-Porter bottle. This was then rapidly pressurized with
carbon monoxide (4 atm) at room temperature while being
stirring vigorously. After 5 min the pressure was released and
ethanol was added. Slow reduction of the solvent volume on
a rotary evaporator resulted in crystallization of the nearly
colorless product. Recrystallization from dichloromethane/
Weights used in the least-squares refinement were w )
1/[(σ2(Fo)2 + (aP)2 + bP)], where P ) [(Fo)2 + 2(Fc)2]/3, and the
final values of a and b are 0.122 and 8.08 respectively.
ethanol gave colorless crystals of Ru(CHdCHB[OEt][OEt])-
1
Cl(CO)(PPh3)2 (0.022 g, 42 %). The H NMR spectrum of this
sample indicated 1.5 equiv of water solvate. Anal. Calcd for
C
43H42BClO3P2Ru‚F(3,2) H2O: C, 61.26; H,5.38. Found C,
Ack n ow led gm en t. We thank The University of
Auckland Research Committee for partial support of
this work through grants-in-aid.
61.09; H, 5.19.
X-r a y Diffr a ction Stu d y of Com p ou n d 2. A crystal
suitable for intensity data collection was mounted on a glass
fiber and positioned on a Nonius CAD-4 diffractometer. Unit
cell dimensions were derived from least-squares fits to the
observed setting angles of 25 reflections distributed throughout
reciprocal space, using monochromated Mo KR radiation at
193(2) K. Intensity data collection employed the 2θ/ω tech-
nique with a total peak/background count time of 2:1. Reflec-
tions were counted for 60 s or until σ(I)/I was 0.02. Crystal
alignment and decomposition were monitored throughout data
collection by measuring three standard reflections every 100
measurements; no statistically significant variation was ob-
served. The data were corrected for Lorentz and polarization
effects. Absorption corrections were applied using ψ scans19
and equivalent reflections averaged. Details of crystal data
and intensity data collection parameters are summarized in
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, bond lengths and angles, anisotropic thermal
parameters, and hydrogen atom positions for 2 (9 pages). See
any current masthead page for ordering and Internet access
instructions.
OM970618Q
(19) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(20) Sheldrick, G. M. SHELXL93. Program for the Refinement of
Crystal Structures. Univ. of Go¨ttingen, Germany, 1993.
(21) Atomic Scattering Factors are from International Tables for
X-ray Crystallography, Kynoch Press: Birmingham, England 1992;
Vol. C.