[BH3·PPh2CH2C6H 4CH2PPh2·RuO-cymCI2]: A new bifunctional compound and prototype of a linked borane/metal cluster species

Full text of DOI:10.1021/ic990687s

5468
Inorg. Chem. 1999, 38, 5468-5470
[BH3‚PPh2CH2C6H4CH2PPh2‚Ru(p-cym)Cl2]: A
New Bifunctional Compound and Prototype of a
Linked Borane/Metal Cluster Species
Paul McQuade, Nigam P. Rath, and
Lawrence Barton*
Department of Chemistry, University of MissourisSt. Louis,
St. Louis, Missouri 63121
Figure 1. Diagrammatic representation of compounds 1-3.
ReceiVed June 15, 1999
Introduction
warming to room temperature and purification using radial
chromatography, allows separation of a brick-red solid powder,
[PPh2CH2C6H4CH2Ph2P‚Ru(p-cym)Cl2] (2), in 62% yield. The
species was identified by NMR spectroscopy and by elemental
analysis. Treatment of 1 with BH3‚thf under essentially the same
conditions followed by similar workup allowed the isolation of
the brick-red crystalline solid [BH3‚PPh2CH2C6H4CH2PPh2‚Ru(p-
cym)Cl2] (3) in 75% yield. In both cases the use of simple
chromatography was not adequate for the separation of the
products, but careful use of a chromatotron allowed purification.
NMR spectral data are given for compounds 2 and 3 in the
Experimental Section.
Bidentate phosphine ligands have been used extensively in
coordination and organometallic chemistry.1 They are best
known as chelating ligands and as such have seen many
applications in catalysis;2 however, they can also be found in
bridging situations. Thus they have been used to bridge simple
metal-containing moieties3 and metal clusters.4 There are also
many examples wherein the bidentate ligand is coordinated at
one end only so that the other end is “dangling”.5 Such chemistry
has been described in the literature recently, as have examples
of such ligands bridging various groups. In this report we
describe the use of the phosphine with a rigid backbone, R,R′-
bis(diphenylphosphino)-p-xylene (PPh2CH2C6H4CH2PPh2, 1),
in linking a main group moiety with a transition metal-
containing moiety.
Drawings of the structures of 1-3 are given in Figure 1 and
they are used to compare the NMR spectral data. In compound
1 the methylene protons of the p-xylene are observed as a singlet
at 3.37 ppm (4H). Two-dimensional [1H-31P]-COSY experi-
Results and Discussion
2
ments on compound 1 showed no evidence of JH-P coupling,
Treatment of the rigid backbone base PPh2CH2C6H4CH2PPh2
so the coupling constant here can be assumed to be ap-
(1) with [Ru(p-cym)Cl2]2 in CH2Cl2 at -78 °C, followed by
proximately zero. In compound 2 the methylene protons Ha exist
as a doublet at 3.86 ppm with JH-P ) 8.87 Hz, while the
2
(1) (a) King, R. B. Acc. Chem. Res. 1972, 5, 177. (b) Puddephatt, R. J.
Chem. Soc. ReV. 1983, 99. (c) Cotton, F. A.; Hong,; B. Prog. Inorg.
Chem. 1992, 40, 179. (d) Chaudret, B.; Delavaux, B.; Poilblanc. R.
Coord. Chem. ReV. 1988, 86, 191.
(2) (a) See for example: (a) Knowles, W. S. Acc. Chem. Res. 1983, 16,
106. (b) Casey, C. P.; Paulsen, E. L.; Beuttenmueller, E. W.; Proft,
B. R.; Matter, B. A.; Powell, D. R. J. Am. Chem. Soc. 1999, 121, 63.
(c) Gomes da Rosa, R.; Ribeiro de Campos, J. D.; Buffon, R. J. Mol.
Catal. A 1999, 137, 297.
(3) (a) Wegner, P. A.; Evans, L. F.; Haddock, J. Inorg. Chem. 1975, 14,
1975. (b) Keiter, R. L.; Fasig, K. M.; Cary, L. W. Inorg. Chem. 1975,
14, 201. (c) Keiter, R. L.; Benedik, J. E., Jr.; Cary, L. W. Inorg. Nucl.
Chem. Lett. 1977, 13, 455. (d) Sullivan, B. P.; Meyer, T. J. Inorg.
Chem. 1980, 19, 752 (e) Keiter, R. L.; Borger, R. D.; Madigan, M. J.;
Kaiser, S. L.; Rowley, D. L. Inorg. Chim. Acta, 1983, 76, L5. (f)
Faraone, F.; Bruno, G.; Schiavo, S. L.; Bombieri, G. J. Chem. Soc.,
Dalton Trans. 1984, 533. (g) Shaw, B. L. Proc. Indian Natl. Sci. Acad.,
A. 1986, 52, 744 and references therein. (h) Jacobsen, G. B.; Shaw,
B. L.; Thornton-Pett, M. J. Chem. Soc., Dalton Trans. 1987, 1509. (i)
Barney, A. A.; Fanwick, P. E.; Kubiak, C. P. Organometallics 1997,
16, 1793. (j) Benson, J. W.; Keiter, R. L.; Keiter, E. A.; Rheingold,
A. L.; Yap, G. P. A.; Mainz, V. V. Organometallics 1998, 17, 4275.
(k) Shimada, S. Rao, M. L.; Tanaka, M. Organometallics 1999, 18,
291.
methylene protons Hb are seen as a singlet at 3.18 ppm. Thus
there is coupling between P(1) and Ha, but approximately zero
coupling between P(2) and Hb. This is again confirmed in 2D
[1H-31P]-COSY experiments on compound 2. Another interest-
ing feature of this compound is that long-range coupling between
P(1) and P(2) with 7JP-P ) 4.10 Hz is observed. This coupling
is confirmed in 2D [31P-31P]-COSY experiments. Whether this
represents through bond coupling involving seven bonds is
unclear, and most likely there is delocalization through the
π-cloud of the benzene ring, which assists coupling. However,
there are examples of seven-bond coupling to 31P in the
literature,6a and we have observed other relatively long-range
31P-31P coupling in related systems.6b,c In compound 3 the
methylene protons Ha exist as a doublet at 3.86 ppm (2JH-P
)
8.85 Hz), while the methylene protons Hb are also observed as
a doublet at 3.36 ppm (2JH-P ) 11.94 Hz). Again, we were
able to confirm this pattern in 2D [1H-31P]-COSY experiments
on 3. As in the case with 2 there is long-range coupling observed
between P(1) and P(2) (7JP-P ) 5.58 Hz). The 31P resonance
for P(1) is a doublet at δ ) 29.84 ppm, while P(2) is observed
a broad singlet at 17.94 ppm, as expected for a P atom bonded
to boron.
(4) (a) Honrath, U.; Shu-Tang, L.; Vahrenkamp, H. Chem. Ber. 1985,
118, 132. (b) Adatia, T.; Salter, I. D. Polyhedron 1995, 15, 597. (c)
Imhof, D.; Burckhardt, U.; Dahmen, K.-H.; Joho, F.; Nesper, R. Inorg.
Chem. 1997, 36, 1813. (d) Housecroft, C. E.; Rheingold, A. L.; Waller,
A.; Yap, G. P. A. J. Organomet. Chem. 1998, 565, 105.
Presumably the differences observed in the 1H-31P coupling
for 2 and 3 can be attributed to the hybridization of the
phosphorus atom. When the phosphorus is trigonal pyramidal
(PR3), the hybridization of phosphorus is p3, with the s orbital
primarily located on the lone pair. However, when the phos-
(5) (a) Isaacs, E. E.; Graham, W. A. G. Inorg. Chem. 1975, 14, 2560. (b)
Pringle, P. G.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1982,
957. (c) Keiter, R. L.; Rheingold, A. L.; Hamerski, J. J.; Castle, C. K.
Organometallics 1983, 2, 1635-9 and refs therein. (d) Blagg, A.;
Cooper, G. R.; Pringle, P. G.; Robson, R.; Shaw, B. L. J. Chem. Soc.,
Chem. Commun. 1984, 933. (e) Elliot, D. J.; Levy, C. J.; Puddephatt,
R. J.; Holah, D. G.; Hughes, A. N.; Magnuson, V. R.; Moser, I. M.
Inorg. Chem. 1990, 29, 5014. (f) Keiter, R. L.; Benson, J. W.; Keiter,
E. A.; Lin, W.; Jia, Z.; Olson, D. M.; Brandt, D. E.; Wheeler, J. L.
Organometallics 1998, 17, 4291. (g) Benson, J. W.; Keiter, R. L.;
Keiter, E. A.; Rheingold, A. L.; Yap, G. P. A.; Mainz, V. V.
Organometallics 1998, 17, 4275 and references therein.
(6) (a) Gholivand, K.; Mahmoudkhani, A. H.; Khosravi, M. Phosphorus,
Sulfur Silicon Relat. Elem. 1995, 106 173. (b) Mac´ıas, R.; Rath, N.
P.; Barton, L. Chem. Commun. 1998, 1081. (c) McQuade, P.; Barton,
L. To be published.
10.1021/ic990687s CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/19/1999

Notes
Inorganic Chemistry, Vol. 38, No. 23, 1999 5469
Figure 3. Alternative view illustrating the syn-orientation of the P
atoms of 3.
Figure 2. Projection of the structure of [(p-cym)RuCl2PPh2CH2C6-
H4CH2Ph2P‚BH3], 3, with 50% thermal ellipsoids.
Cmethylene-P planes have a dihedral angle of 4.5°, indicating two
effectively coplanar linkages perpendicular to the connecting
C6H4 ring. The actual angles between the interconnecting C6H4
ring and the planes C(15)-C(18)-P(2) and C(12)-C(11)-P(1)
are 95.9° and 100.7°, respectively. This conformation appears
to be the least sterically hindered, and it is illustrated in the
alternative view, generated from the structural data, given in
Figure 3. Thus on P(1) the largest substituent, RuCl2(p-cym),
points away from the basketlike arrangement of the PCH2C6-
H4CH2P skeleton in a pseudo-exo orientation and the less
sterically demanding phenyl groups are in equivalent pseudo-
endo positions, twisted so as to reduce interaction. Similarly,
the groups on P(2) adopt the positions of minimum steric
interaction with the small BH3 moiety and one of the phenyl
groups in endo-type positions. Thus the BH3 group interacts
least with the C6H5 groups on P(2). On the other hand, the
mutual arrangement of the groups around P(2) reflects that the
C6H5 planes are able to twist to minimize interaction with each
other, whereas the steric influence of the BH3 group on the
proximal phenyl groups is more important. Thus the ipso-carbon
or methylene-P(2)-B(1) angles are in the range 111.6°-
114.4°, whereas the corresponding angles between the C atoms
on P(2) are less than the tetrahedral angle and fall in the range
103.2°-107.7°. The B(1)-P(2) distance is 1.923(9) Å and is
essentially the same as the value for PPh3‚BH3 (1.933 Å).8
Adding to the steric demands of the Ru moiety is the fact that
the metal is effectively octahedral, assuming that the p-cymene
ligand occupies three coordination positions with the two Cl
atoms and the P atom occupying the others. Thus the angles to
the Cl atoms and P are approximately 90°, their values ranging
from ca. 85°-88°, reflecting the steric bulk of the p-cymene
ligand. It is informative to compare the structural features around
the Ru atom to those for such species as [(p-cym)RuCl2P-
(CH2Ph)3], in which the angles between the P and Cl atoms are
somewhat smaller, reflecting less steric hindrance in 3.9
Table 1. Summary of Crystallographic Data for 3
formula
temp, K
cryst syst
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
C44H49BCl6P2Ru fw
964.35
217(2)
radiation (λ, Å) Mo KR (0.71073)
monoclinic
11.7101(2)
15.8196(2)
24.4240(4)
90
space group
P21/n
4520.75(12)
2
V, Å3
Z
Dcalcd
cryst size
abs coeff
refl measured
refl used
wR2a
1.417 Mg/m3
0.1 × 0.1 × 0.05 mm3
0.803 mm-1
8262 ((h, (j, (l)
8262 with I > 2σ(I)
0.1504
92.339(1)
90
no. variables 494
0.078
R
a wR2 ) [∑ω(Fo - Fc)2/∑ωFo ]1/2
.
2
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 3
P(2)-B(1)
P(2)-C(25)
P(1)-Ru(1)
P(1)-C(37)
1.923(9)
1.813(5)
2.3619(13)
1.820(5)
P(2)-C(18)
P(2)-C(19)
P(1)-C(11)
P(1)-C(31)
1.833(8)
1.808(5)
1.847(5)
1.828(5)
C(25)-P(2)-C(18) 106.4(2)
C(25)-P(2)-C(19) 107.7(2)
C(19)-P(2)-C(18) 103.2(2)
C(11)-P(1)-Ru(1) 113.39(17)
C(37)-P(1)-Ru(1) 110.82(16)
C(37)-P(1)-C(11) 107.0(2)
C(19)-P(2)-B(1)
C(25)-P(2)-B(1)
C(18)-P(2)-B(1)
112.8(3)
111.6(3)
114.4(3)
P(1)-Ru(1)-Cl(1)
P(1)-Ru(1)-Cl(2)
Cl(1)-Ru(1)-Cl(2)
P(1)-Ru(1)-cena
Cl(1)-Ru(1)-cen
85.18(4)
87.29(4)
87.79(4)
130.6
125.8
126.1
C(31)-P(1)-C(37) 103.7(2)
C(31)-P(1)-C(11) 103.2(3)
C(31)-P(1)-Ru(1) 117.68(17) Cl(2)-Ru(1)-cen
a cen is the centroid of the C6 ring in p-cymene.
phorus forms an adduct (i.e., becomes pseudotetrahedral) the
hybridization changes to essentially sp3. Thus, since coupling
information is communicated via the s electrons, the more s
character a bond has, the higher the coupling between the atoms.
This is demonstrated in 1, where both the P atoms may be
considered to be p3 hybridized, and as a result there is
approximately no coupling to the methylene protons. In 2, P(1)
becomes sp3 hybridized and shows coupling to protons Ha, while
P(2) remains p3 hybridized and shows no coupling to protons
Hb. In 3, both P(1) and P(2) are sp3 hybridized and show
coupling to Ha and Hb, respectively. Similar observations of
very low or effectively zero 1H-31P coupling have been made
previously and accounted for in terms of the hybridization of
the P atoms.7
The species 3 is novel and may be considered as prototypical
of a new type of linked borane/metal cluster system. The RuC5
system is a cluster of atoms and the BH3 group, or a phosphine-
borane group, may be incorporated into a larger borane cluster
system. Linked borane cluster to metal cluster systems are quite
rare, to our knowledge; the only ones which have appeared in
the literature are the Os3C-B5H8 and -C-C2B10 systems
reported by Shore et al. several years ago.10 There are, however,
several examples of clusters involving carboranes linked by a
variety of organic groups, which we are not addressing herein.11
Of related interest to the chemistry we describe is the use of
Bright red rectangular crystals of 3, containing 2 mol of
CH2Cl2 solvent, were grown from a toluene/CH2Cl2/Et2O
solution at -5 °C. A projection of the structure is given in Figure
2 and a summary of crystallographic data is given in Table 1.
Selected bond angles and distances are given in Table 2. The
(8) Huffman, J. C. Cryst. Struct. Commun. 1982, 11, 1435.
(9) Serron, S. A.; Nolan, S. P.; Abramov, Yu. A.; Brammer, L.; Petersen,
J. L. Organometallics 1998, 17, 104.
(10) Wermer, J. R.; Shore, S. G. Mol. Struct. Energetics 1988, 5, 13. (b)
Wermer, J. R.; Jan, D.-Y.; Getman, T. D.; Mohrer, E.; Shore, S. G.
Inorg. Chem. 1988, 27, 4274. (c) Shore, S. G. Pure. Appl. Chem. 1994,
66, 263.
two P atoms in 3 are essentially syn to each other and the CC H
-
6
4
(7) McFarlane, W. Proc. R. Soc. Ser. A, 1968, 306, 185. (b) Kennedy, J.
D.; McFarlane, W.; Rycroft, D. S. Inorg. Chem. 1973, 12, 2742.

5470 Inorganic Chemistry, Vol. 38, No. 23, 1999
Notes
NMR (CDCl3): p-cymene, δ 0.88 (d, J ) 6.95 Hz, 6H, CHMe2), 1.81
(s, 3H, Me), 2.47 (sept, J ) 6.95 Hz, 1H, CHMe2), 5.10 (d, J ) 5.80
Hz, 2H, MeC6H4CHMe2), 5.23 (d, J ) 5.80 Hz, 2H, MeC6H4CHMe2);
PPh2CH2C6H4CH2PPh2, δ 3.18 (s, 2H, PPh2CH2), 3.86 (d, 2JH-P ) 8.87
Hz, 2H, CH2PPh2‚Ru(p-cym)Cl2), 6.19 (d, J ) 7.24 Hz, 2H,
CH2C6H4CH2), 6.51 (d, J ) 7.24 Hz, 2H, CH2C6H4CH2), 7.15-7.77
the dppf (1,1′-bis(diphenylphosphino)ferrocene) ligand, which
has been shown to chelate metals coordinating to boron atoms
12
in B3H7 and, in studies pertinent to this one, link a series of
identical borane species ranging from BH3 to systems such as
SB9H11 and C2B10H12.13 Our formation of 3 relates to other work
in our laboratory involving the formation of linked cluster
systems,14,15 and we intend to report on these soon.
7
(m, 20H, Ph). 31P{1H} NMR (CDCl3): δ -9.57 (d, JP-P ) 4.10 Hz,
PPh2CH2), 29.78 (d, 7JP-P ) 4.10 Hz, CH2PPh2.Ru(p-cym)Cl2). Anal.
Calcd for C42H42P2Cl2Ru: C, 64.61; H, 5.43. Found: C, 64.07; H, 5.44.
Synthesis of [BH3‚PPh2CH2C6H4CH2PPh2‚Ru(p-cym)Cl2]. In a 50
mL two-necked round-bottom flask was placed 60 mg (0.077 mmol)
of PPh2CH2C6H4CH2PPh2‚Ru(p-cym)Cl2 together with a stir bar. The
flask was connected to the high vacuum line and evacuated. The vessel
was then cooled to -78 °C, 20 mL of CH2Cl2 was condensed in, and
the vessel was filled with dry N2 at that temperature. Then BH3‚thf
solution (0.3 mmol) was introduced via a syringe, under a positive N2
flow. The solution was stirred at this temperature for 15 min, warmed
slowly to room temperature, exposed to air, reduced to 1 mL in volume,
and applied to the radial chromatograph using CH2Cl2 as the mobile
phase. CH3CN was then slowly added to the eluent until a red band
was detected. The bright red solution obtained from this band was then
evacuated to dryness, giving 46 mg (75.3%) of a brick-red solid which
was characterized as [BH3‚PPh2CH2C6H4CH2PPh2‚Ru(p-cym)Cl2], 3.
Crystals suitable for X-ray diffraction were grown from a toluene/
CH2Cl2/Et2O solution at -5 °C. 1H NMR (CDCl3): p-cymene, δ 0.90
(d, J ) 7.20 Hz, 6H, CHMe2), 1.80 (s, 3H, Me), 2.47 (sept, J ) 7.20
Hz, 1H, CHMe2), 5.10 (d, J ) 5.06 Hz, 2H, MeC6H4CHMe2), 5.23 (d,
J ) 5.06 Hz, 2H, MeC6H4CHMe2); PPh2CH2C6H4CH2PPh2, δ 3.36 (d,
Experimental Section
General. Reactions were carried out under a dry nitrogen atmosphere
on a high vacuum line. Solvents used were reagent grade and dried
before use. PPh2Cl (Strem) and BH3‚thf solution (Aldrich) was used
as received, while R,R′dibromo-p-xylene (Eastman Organic) was
sublimed before use. The compounds PPh2CH2C6H4CH2PPh24c and [(p-
16
cym)RuCl2]2 were prepared according to published procedures.
Products were purified on a radial chromatograph using a 25 cm
diameter circular plate coated with 0.1 cm of silica gel (EM Science).
31P NMR spectra (referenced to 85% H3PO4), 11B spectra (referenced
1
to Et2O‚BF3), and H spectra (referenced to SiMe4) were carried out
on a Brucker ARX 500 spectrometer. Mass spectra were recorded by
the Washington University Mass Spectrometry Resource, an NIH
Research Resource (Grant No. P41RR0954), and elemental analyses
were carried out by Atlantic Microlabs Inc., Norcross, GA.
Synthesis of [PPh2CH2C6H4CH2PPh2‚Ru(p-cym)Cl2]. In a 50 mL
two-necked round-bottom flask was placed 500 mg (1.05 mmol) of
PPh2CH2C6H4CH2PPh2 together with a stir bar. A tipper tube charged
with 60 mg (0.100 mmol) of [(p-cym)RuCl2]2 was then attached. The
flask was then connected to the high vacuum line and evacuated, at
which point it was cooled to -78 °C and 20 mL of CH2Cl2 was
condensed in and the [(p-cym)RuCl2]2 added. The mixture was stirred
for 30 min, warmed slowly to room temperature, filled with dry
nitrogen, and then exposed to the air. The solution was then reduced
to 1 mL in volume and applied to the radial chromatograph using
CH2Cl2 as eluent. A colorless band was observed which was shown to
be unreacted phosphine, then CH3CN was slowly added to the eluent
until a red band was detected, which was later characterized as
[PPh2CH2C6H4CH2PPh2‚Ru(p-cym)Cl2]. The solvent was then removed,
leaving 97 mg (62.1%) of [PPh2CH2C6H4CH2PPh2‚Ru(p-cym)Cl2]. 1H
2
2JH-P ) 11.9 Hz, 2H, BH3PPh2CH2), 3.86 (d, JH-P ) 8.8 Hz, 2H,
CH2PPh2‚Ru(p-cym)Cl2), 6.17 (d, J ) 7.58 Hz, 2H, CH2C6H4CH2),
6.39 (d, J ) 7.58 Hz, 2H, CH2C6H4CH2), 7.14-7.80 (m, 20H, Ph);
2
BH3, δ 0.83 (d, JH-P )15.9, 3H, BH3). 31P{1H} NMR (CDCl3): δ
17.94 (br, BH3‚PPh2CH2), 29.84 (d, 7JP-P ) 5.58 Hz, CH2PPh2‚Ru(p-
cym)Cl2). 11B{1H} NMR (CDCl3): δ -38.81 (s, BH3). HRMS: FAB
12
7
(NBA-Li)
C
1H4531P237Cl211B1Ru1 Li, 801.1670 (calcd), 801.1705
42
(obsd), standard deviation 4.3 ppm.
Acknowledgment. We thank the National Science Founda-
tion (Grant #CHE 9727570) and UM-St. Louis Research
Incentive Awards for support of this work. We also acknowledge
the National Science Foundation, the Department of Energy and
the UMsSt. Louis Center for Molecular Electronics for funds
to purchase the NMR spectrometers and the X-ray Diffracto-
meter. Mass spectrometry was provided by the Washington
University Mass Spectrometry Resource, an NIH Research
Resource (Grant No. P41RR0954). We thank Dr. J. D. Kennedy
for useful discussions.
(11) For example see: (a) Jiang, W.; Knobler, C. B.; Hawthorne, M. F.
Inorg. Chem. 1996, 35, 3056 (b) Grimes, R. N. In AdVances in Boron
Chemistry; Siebert, W., Ed.; Royal Society of Chemistry: Cambridge,
U.K., 1997; p 321-332.
(12) (a) Housecroft, C. E.; Owen, S. M.; Raithby, P. R.; Shaykh, B. A. M.
Organometallics 1990, 9, 1617. (b) Haggerty, B. S.; Housecroft, C.
E.; Rheingold, A. L.; Shaykh, J. Chem. Soc., Dalton Trans. 1991,
2175.
(13) Donaghy, K. J.; Carroll, P. J.; Sneddon, L. G. Inorg. Chem. 1997, 36,
547.
(14) Mac´ıas, R.; Rath, N. P.; Barton, L. Organometallics 1999, 18, 3637.
(15) McQuade, P.; Hupp, K.; Bould, J.; Fang, H.; Rath, N. P.; Thomas, R.
Ll.; Barton, L. Inorg. Chem., in press.
Supporting Information Available: CIF file of crystallographic
data. This material is available free of charge via the Internet at
http://pubs.acs.org.
(16) Bennett, M. A.; Huang, T.-N.; Matteson T. W.; Smith, A. K. Inorg.
Synth. 1982, 21, 74.
IC990687S