The chloride effect: Structural dependence of ruthenium silyl complexes on phosphorus and silicon substituents

Article abstract of DOI:10.1021/om034226x

The structures for a series of Cp(PR₃)₂RuSiX₃ {PR₃ = PMe₃, SiX₃ = SiCl₃, SiMeCl₂, SiPhCl₂; PR₃ = PMe₂Ph, SiX₃ = SiCl₃} complexes were determined and compared. The Ru-Si and Si-Cl distances in these complexes increased when Cl was replaced with Me or Ph groups and correlated with the observed spectroscopic properties of these complexes. The structural variations were explained by d(Ru)-σ*(Si-Cl) π-back-bonding interactions.

Full text of DOI:10.1021/om034226x

Organometallics 2004, 23, 1153-1156
1153
Notes
Th e Ch lor id e Effect: Str u ctu r a l Dep en d en ce of
Ru th en iu m Silyl Com p lexes on P h osp h or u s a n d Silicon
Su bstitu en ts
Samuel T. N. Freeman,† J effrey L. Petersen,‡ and Fredrick R. Lemke*,†
Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701, and
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506
Received October 9, 2003
Summary: The structures for a series of Cp(PR3)2RuSiX3
{PR3 ) PMe3, SiX3 ) SiCl3, SiMeCl2, SiPhCl2; PR3 )
PMe2Ph, SiX3 ) SiCl3} complexes were determined and
compared. The Ru-Si and Si-Cl distances in these
complexes increased when Cl was replaced with Me or
Ph groups and correlated with the observed spectroscopic
properties of these complexes. The structural variations
were explained by d(Ru)-σ*(Si-Cl) π-back-bonding
interactions.
In tr od u ction
Metal-silicon compounds have generated much inter-
est in the past decade1-4 owing to their intermediacy
in reactions such as hydrosilylation5,6 and dehydroge-
native silylation.7-9 Consequently, special attention has
been given to the influence of transition metal frag-
ments on the bonding and reactivity of silicon atoms.
Previously, we had reported the effect of different silicon
and phosphorus substituents on the spectroscopic prop-
erties for a series of ruthenium silyl compounds of the
type Cp(PR3)2RuSiX3.10,11 Our studies indicated that the
Ru-Si bond strengthened as the substituents on silicon
became more electron-withdrawing (as evidenced by an
2
increase in J SiP, Figure 1 top) but was unaffected by
changes in the phosphine ligand. Also, we observed that
the ruthenium silyl groups were differentiated into
three classes (a dichlorosilyl, a monochlorosilyl, and a
non-chlorosilyl class; Figure 1 bottom); these classes
† Ohio University.
‡ West Virginia University, crystal structure determinations.
(1) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rap-
poport, Z., Eds.; J ohn Wiley & Sons: New York, 1991; pp 245-307.
(2) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rap-
poport, Z., Eds.; J ohn Wiley & Sons: New York, 1991; pp 309-364.
(3) Sharma, H. K.; Pannell, K. H. Chem. Rev. 1995, 95, 1351-1374.
(4) Corey, J . Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99, 175-
292.
2
(5) Speier, J . L. Adv. Organomet. Chem. 1979, 17, 407-447.
F igu r e 1. Top: J SiP (Hz) vs Σ øi(SiX3) for ruthenium silyl
complexes of the type Cp(PR3)2RuSiX3 {PR3 ) PMe3 (O),
PMe2Ph (0), PMePh2 (])}. Bottom: 29Si NMR chemical
shift of the silyl groups vs Σ øi(SiX3) for ruthenium silyl
complexes of the type Cp(PR3)2RuSiX3 {PR3 ) PMe3 (O),
PMe2Ph (0), PMePh2 (])} showing the three silyl classes:
dichlorosilyl (solid line), monochlorosilyl (dashed line), and
non-chlorosilyl (dotted line).
(6) Ojima, I.; Li, Z.; Zhu, J . In The Chemistry of Organic Silicon
Compounds; Rappoport, Z., Apeloig, Y., Eds.; J ohn Wiley & Sons: New
York, 1998; Vol. 2, pp 1687-1792.
(7) Ezbiansky, K.; Djurovich, P. I.; LaForest, M.; Sinning, D. J .;
Zayes, R.; Berry, D. H. Organometallics 1998, 17, 1455-1457.
(8) Christ, M. L.; Sabo-Etienne, S.; Chaudret, B. Organometallics
1995, 14, 1082-1084.
(9) Delpech, F.; Mansas, J .; Leuser, H.; Sabo-Etienne, S.; Chaudret,
B. Organometallics 2000, 19, 5750-5757.
(10) Lemke, F. R.; Galat, K. J .; Youngs, W. J . Organometallics 1999,
18, 1419-1429.
were attributed to varying degrees of d(Ru)-σ*(Si-Cl)
π-back-bonding.
(11) Freeman, S. T. N.; Lofton, L. L.; Lemke, F. R. Organometallics
2002, 21, 4776-4784.
10.1021/om034226x CCC: $27.50 © 2004 American Chemical Society
Publication on Web 01/24/2004

1154 Organometallics, Vol. 23, No. 5, 2004
Notes
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for Cp (P R3)2Ru SiX3
2
1a
3
4
PR3
SiX3
Ru-Si
Ru-P(1)
Ru-P(2)
Ru-Cntb
Si-Cl(1)
Si-Cl(2)
Si-Zc
PMe2Ph
SiCl3
2.2811(11) 2.265(2) 2.294(2)
2.2912(10) 2.273(2) 2.276(2)
2.2797(10) 2.280(2) 2.261(2)
1.903
2.124(2)
2.119(2)
PMe3
SiCl3
PMe3
SiMeCl2
PMe3
SiPhCl2
2.31019(9)
2.2712(9)
2.2754(8)
1.910
2.1545(12)
2.1335(11)
1.904(3)
91.02(4)
93.72(3)
122.3
1.887
2.122(3) 2.145(3)
2.114(3) 2.153(3)
1.917
2.1130(14) 2.121(3) 1.905(7)
P(1)-Ru-Si
P(2)-Ru-Si
Cnt-Ru-Sib
P(1)-Ru-P(2)
91.09(4)
92.67(4)
120.0
92.60(7) 93.22(7)
93.00(7) 94.42(8)
121.2
95.80(7) 95.42(8)
123.2 123.6
119.1
97.64(4)
95.27(3)
123.1
F igu r e 2. Perspective view of the molecular structure of
Cp(PMe2Ph)2RuSiCl3 (2) with atom labels provided for all
unique non-hydrogen atoms.
Cnt-Ru-P (av)b 123.6
Ru-Si-Cl(1)
Ru-Si-Cl(2)
Ru-Si-Zc
Cl(1)-Si-Cl(2)
Cl(2)-Si-Zc
Cl(1)-Si-Zc
117.53(5) 116.8(1) 114.92(10) 112.87(4)
114.89(6) 115.0(1) 122.22(10) 121.84(4)
125.20(6) 125.6(1) 119.2(3)
98.93(6)
98.21(7)
97.30(6)
120.35(9)
99.0(1) 97.96(13) 97.39(5)
98.8(1) 99.0(3)
96.9(1) 99.1(3)
99.74(9)
100.29(9)
a
b
Data taken from ref 10. Cnt ) the centroid of the cyclopen-
tadienyl ring. c Z represents either chlorine or a carbon bonded to
silicon.
Our spectroscopic studies indicated that the ruthe-
nium silicon interaction was more dependent on the
substituents on silicon than on the substituents on phos-
phorus. A major question concerning these Cp(PR3)2-
RuSiX3 complexes still remained. How were the spec-
troscopically observed substituent effects manifested in
the structures of Cp(PR3)2RuSiX3? To address this
question, we have determined the structures of several
Cp(PR3)2RuSiX3 {SiX3 ) SiCl3, PR3 ) PMe3 (1),
PMe2Ph (2); PR3 ) PMe3, SiX3 ) SiMeCl2 (3), SiPhCl2
(4)} complexes. A comparison between the structural
and spectroscopic trends of 1-4 is reported herein. Prior
to this study, only the structure of Cp(PMe3)2RuSiCl3
(1) had been reported;10 selected interatomic distances
and angles for 1 are listed in Table 1.
F igu r e 3. Perspective view of the molecular structure of
Cp(PMe3)2RuSiMeCl2 (3) with atom labels provided for all
unique non-hydrogen atoms.
Str u ctu r es of Cp (P R3)2Ru SiX3. The crystal struc-
tures of 2-4 were determined by X-ray diffraction at
295 K, and selected interatomic distances and angles
are listed in Table 1. The molecular structures of 2-4
(Figures 2-4, respectively) adopted a three-legged
“piano-stool” geometry around ruthenium with “legs”
composed of one silyl group and two phosphine groups.13
The Ru-Si distances of 2.28-2.31 Å were consistent
with a single bond and fall on the low end of the range
(2.27-2.51 Å) observed for related d6 ruthenium silyl
complexes.1,2,10,14-16 The Si-Cl distances of 2.11-2.15
Å were considerably longer than the Si-Cl distance in
Resu lts a n d Discu ssion
Syn th esis of Ru th en iu m Silyl Com p lexes. The
complexes Cp(PMe2Ph)2RuSiCl3 (2)11 and Cp(PMe3)2-
RuSiMeCl2 (3)10,12 were prepared by published methods.
Cp(PMe3)2RuSiPhCl2 (4) was prepared by the direct
reaction of Cp(PMe3)2RuH with PhSiCl3 in CH2Cl2 (eq
1); the cationic dihydride [Cp(PMe3)2RuH2]Cl was a
byproduct of this reaction. Complex 4 was obtained in
good yields as a yellow solid and exhibited NMR
resonances (1H, 29Si, and 31P) characteristic of silyl
complexes containing the Cp(PR3)2Ru half-sandwich
moiety.10,11
(12) Lemke, F. R. J . Am. Chem. Soc. 1994, 116, 11183-11184.
(13) A preliminary structural analysis of Cp(PMePh2)2RuSiCl3
showed that this compound crystallizes in a C-centered monoclinic
crystal lattice with dimensions a ) 15.168(1) Å, b ) 12.121(1) Å, c )
17.369(1) Å, and â ) 106.358(1)°. The X-ray diffraction data indicated
either that the entire molecule was disordered about a crystallographic
2-fold axis or that the lattice dimensions were extended along one
direction. Efforts to refine the molecular structure in the centrosym-
metric space group C2/c with four pairs of half-molecules with each
pair symmetrically disposed about a different crystallographic 2-fold
axis were sufficient to verify the atom connectivity. A perspective view
of the molecular structure of Cp(PMePh2)2RuSiCl3 showed that the
Me substituent of each diphenylmethylphosphine ligand was directed
away from the cyclopentadienyl ligand. The overall structure was
consistent with that expected for a three-legged piano stool, with the
three legs consisting of two PMePh2 groups and one SiCl3 group.

Notes
Organometallics, Vol. 23, No. 5, 2004 1155
Figu r e 5. Interaction of the Cp(PMe3)2Ru fragment HOMO
and HOMO-1 with linear combinations of Si-X σ* orbitals.
Changing the phosphine from PMe3 to PMe2Ph had
structurally very little effect. The bond distances and
angles around ruthenium and silicon in 1 and 2 were
essentially the same; the only exception was a slight
lengthening of the Ru-Si distance from 2.27 Å in 1 to
2.28 Å in 2. This similarity in structural parameters
for 1 and 2 was consistent with the little to no phosphine
dependence observed in the spectroscopic properties of
these complexes (Figure 1).
F igu r e 4. Perspective view of the molecular structure of
Cp(PMe3)2RuSiPhCl2 (4) with atom labels provided for all
unique non-hydrogen atoms.
On the other hand, changes in the substituents on
silicon had more of an effect on the bond distances and
angles around ruthenium and silicon. A lengthening of
the Ru-Si distance was observed when an electrone-
gative Cl (Ru-Si 2.265 Å in 1) was replaced with less
electronegative Me (Ru-Si 2.294 Å in 3) and Ph
(Ru-Si 2.310 Å in 4) groups. This lengthening of the
free polychlorosilanes (2.02 Å)17 and other group 8
trichlorosilyl complexes (2.03-2.09 Å).18-25
Complexes 1-4 adopted a staggered conformation
about the Ru-Si bond with the cyclopentadienyl and a
chloride in an anti relationship (average cyclopentadi-
enyl centroid-Ru-Si-Cl dihedral angle ) 166.1 ( 9.1°).
The silyl groups had a distorted tetrahedral geometry
with an average Cl-Si-Z (Z ) Cl, C) angle of 98.6 (
0.6° and an average Ru-Si-Z angle of 118.9 ( 2.4°. The
Ru-Si-Cl angles (123.7 ( 1.4° average) anti to the Cp
group were significantly larger than the non-anti
Ru-Si-Z angles (116.5 ( 1.7° average). In related
three-legged piano-stool ruthenium silyl complexes, the
Ru-Si-Z angle for substituents anti to a Cp or benzene
group have also been observed to be larger (generally
g 10°) than the Ru-Si-Z angles of the other substit-
uents on silicon: Cp(PMe3)2RuSiCl2Cp* [Ru-Si-Cl-
(anti) 119.9° vs Ru-Si-Cl 109.2°],14 Cp*(PMe3)2-
RuSiPh2H [Ru-Si-H(anti) 112.9° vs Ru-Si-Ph 98.8°
(av)],26 Cp*(PMe3)2RuSiPh2OTf [Ru-Si-OTf(anti) 118.2°
vs Ru-Si-Ph 96.9° (av)],16 (C6H6)(PPh3)Ru(SiX3)2 (SiX3
) SiCl3, SiMeCl2, SiMe3) [Ru-Si-X(anti, X ) Cl, C)
125.2° (av) vs Ru-Si-X 113.4° (av)].27
2
Ru-Si distances correlated with a decrease in J SiP for
1, 3, and 4 (Figure 1, top). The Ru-Si distance in 4 was
longer than expected probably due to the larger steric
demand of SiPhCl2 compared to SiMeCl2.
The long Si-Cl distances in 1-4 (range 2.11-2.15 Å)
were attributable to d(Ru)-σ*(Si-X) π-back-bonding
between the Cp(PMe3)2Ru and SiX3 groups. Linear
combinations of the Si-X (X ) Cl, Ph, Me) σ* orbitals
of the silyl group gave rise to an a1 and e set, assuming
localized C3v symmetry at silicon. The HOMO and
HOMO-1 of the Cp(PMe3)2Ru moiety28-30 had the cor-
rect symmetry to interact with the doubly degenerate e
set of Si-X σ* orbitals,31,32 as shown in Figure 5. The
magnitude of the d(Ru)-σ*(Si-X) π-back-bonding in-
teraction depended on the silicon substituents and
followed the order Cl . Ph ≈ Me.25 A ramification of
this d(Ru)-σ*(Si-Cl) π-back-bonding interaction was
a substantial lengthening of the Si-Cl distances com-
pared to other group 8 trichlorosilyl complexes (range
2.04-2.09 Å).18-25
The Si-Cl distances also exhibited a significant
dependence with respect to the other substituents on
silicon. The average Si-Cl distance in 1 and 2 (2.119 (
0.004 Å) was shorter than the average Si-Cl distance
in 3 and 4 (2.147 ( 0.009 Å). This difference in Si-Cl
distances can be attributed to more electron density in
the σ*(Si-Cl) orbitals of 3 and 4 compared to the
amount of electron density in the σ*(Si-Cl) orbitals of
1 and 2. If the amount of electron density transferred
from ruthenium to silicon by the d(Ru)-σ*(Si-X) π-back-
bonding interaction was constant in 1-4, then the
(14) Lemke, F. R.; Simons, R. S.; Youngs, W. J . Organometallics
1996, 15, 216-221.
(15) Straus, D. A.; Tilley, T. D.; Rheingold, A. J .; Geib, S. J . J . Am.
Chem. Soc. 1987, 109, 5872-5873.
(16) Grumbine, S. K.; Straus, D. A.; Tilley, T. D. Polyhedron 1995,
14, 127-148.
(17) Kaftory, M.; Kapon, M.; Botoshansky, M. In The Chemistry of
Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; J ohn
Wiley & Sons: New York, 1998; Vol. 2, pp 181-265.
(18) Einstein, F. W. B.; J ones, T. Inorg. Chem. 1982, 21, 987-990.
(19) Schubert, U.; Kraft, G.; Walther, E. Z. Anorg. Allg. Chem. 1984,
519, 96-106.
(20) Asirvatham, V. S.; Yao, Z.; Klabunde, K. J . J . Am. Chem. Soc.
1994, 116, 5493-5494.
(21) Yao, Z.; Klabunde, K. J .; Asirvatham, A. S. Inorg. Chem. 1995,
34, 5289-5294.
(22) Connolly, J . W.; Cowley, A. H.; Nunn, C. M. Polyhedron 1990,
9, 1337-1340.
(23) Manojlovic-Muir, L.; Muir, K. W.; Ibers, J . A. Inorg. Chem. 1970,
9, 447-452.
(27) Burgio, J .; Yardy, N. M.; Petersen, J . L.; Lemke, F. R. Orga-
nometallics 2003, 22, 4928-4932.
(24) Vancea, L.; Benneett, M. J .; J ones, C. E.; Smith, R. A.; Graham,
W. A. G. Inorg. Chem. 1977, 16, 897-902.
(28) Kost´ıc, N. M.; Fenske, R. F. Organometallics 1982, 1, 974-982.
(29) Grumbine, S. K.; Tilley, T. D.; Arnold, F. P.; Rheingold, A. L.
J . Am. Chem. Soc. 1994, 116, 5495-5496.
(25) Hu¨bler, K.; Hunt, P. A.; Maddock, S. M.; Rickard, C. E. F.;
Roper, W. R.; Salter, D. M.; Schwerdtfeger, P.; Wright, L. J . Organo-
metallics 1997, 16, 5076-5083.
(30) Arnold, F. P., J r. Organometallics 1999, 18, 4800-4809.
(31) Orpen, A. G.; Connelly, N. G. J . Chem. Soc., Chem. Commun.
1985, 1310-1311.
(26) Straus, D. A.; Zhang, C.; Quimbita, G. E.; Grumbine, S. D.;
Heyn, R. H.; Tilley, T. D.; Rheingold, A. L.; Geib, S. J . J . Am. Chem.
Soc. 1990, 112, 2673-2681.
(32) Orpen, A. G.; Connelly, N. G. Organometallics 1990, 9, 1206-
1210.

1156 Organometallics, Vol. 23, No. 5, 2004
Notes
CaH2. CH2Cl2, CD2Cl2, and hexanes were degassed and
vacuum transferred prior to use.
Si-Cl distances will depend on the number of chlorines
on the silicon. Thus, 1 and 2, with three chlorines on
silicon, will have on average less electron density in
σ*(Si-Cl) orbitals and subsequently shorter Si-Cl
bonds than 3 and 4, with only two chlorines on silicon.
Crystals of 2 and 4 suitable for X-ray diffraction were grown
by liquid diffusion of hexanes into a CH2Cl2 solution of the
corresponding ruthenium silyl complex at -30 °C.
P r ep a r a tion of Cp (P Me3)2Ru SiP h Cl2 (4). Compound 4
was prepared by an adaptation of the literature method.10 In
a typical reaction, PhSiCl3 (0.75 equiv) was added via syringe
to a solution of Cp(PMe3)2RuH (100 mg, 0.313 mmol) in
CH2Cl2 (∼15 mL). The reaction mixture was allowed to stir at
ambient temperature for 1 h. The volume was reduced by one-
half in vacuo. Hexanes were added to the flask to initiate
precipitation of [Cp(PMe3)2RuH2]Cl. The suspension was fil-
tered, and the yellow filtrate was dried in vacuo to give 4 as
a yellow residue (66 mg, 85%). 1H NMR (250 MHz, CD2Cl2):
δ 7.74 (m, 2H, SiPh), 7.33 (m, 3H, SiPh) 4.66 (s, 5H, Cp), 1.49
(fd, N ) 8.7 Hz, 18H, PMe3). 29Si{1H} NMR (79.5 MHz,
CD2Cl2): δ 76.82 (t, J PSi ) 35.8 Hz). 31P{1H} NMR (101 MHz,
CD2Cl2): δ 10.20. Anal. Calcd for C17H28P2Cl2RuSi (4): C,
41.30; H, 5.71. Found: C, 41.48; H, 5.54.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations of the ruthe-
nium-containing compounds were conducted under an inert
atmosphere of argon. The compounds were stored in an
M-Braun glovebox, and reactions were carried out using high-
vacuum techniques.33 1H NMR (250 MHz), 13C{1H} NMR (62.9
MHz), and 31P{1H} NMR (101.3 MHz) spectra were obtained
using a Bruker 250 MHz spectrometer. 29Si DEPT NMR (79.5
MHz) spectra were obtained using a Varian VXR 400S
spectrometer. All NMR data were obtained in CD2Cl2. 1H NMR
data were referenced to the residual proton signal of the
solvent at 5.32 ppm. 31P NMR data were externally referenced
(0.00 ppm) to a sealed capillary containing H3PO4 (85%) in a
NMR tube containing CD2Cl2. 13C NMR data were referenced
to the carbon signal of the CD2Cl2 solvent at 53.8 ppm. 29Si
NMR data were externally referenced to a CD2Cl2 solution of
TMS at 0.00 ppm. Elemental analyses were performed by
Desert Analytics (Tucson, AZ).
Ack n ow led gm en t. F.R.L. would like to thank the
Research Challenge and Condensed Matter and Surface
Science programs at Ohio University, and Dow Corning
Corporation for financial support. J .L.P. acknowledges
the financial support provided by the Chemical Instru-
mentation Program of the National Science Foundation
(CHE-9120098) to acquire a Siemens P4 X-ray diffrac-
tometer.
Ma t er ia ls. Cp(PMe3)2RuH,34 Cp(PMe2Ph)2RuSiCl3 (2),11
Cp(PMePh2)2RuSiCl3,11 and Cp(PMe3)2RuSiMeCl2 (3)10 were
prepared according to the literature procedure. PhSiCl3 (Gelest)
was degassed and stored in the glovebox. Hexanes was dis-
tilled from K/benzophenone and stored over [Cp2TiCl]2ZnCl2.35
CH2Cl2 and CD2Cl2 (Cambridge Isotope Labs) were dried over
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, data collection and refinement parameters, interatomic
distances, and interatomic angles for 2, 3, and 4. Full crystal-
lographic data in CIF format for 2, 3, and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
(33) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley-Interscience: New York, 1986.
(34) Lemke, F. R.; Brammer, L. Organometallics 1995, 14, 3980-
3987.
(35) Sekutowski, D. G.; Stucky, G. D. Inorg. Chem. 1975, 14, 2192-
2199.
OM034226X