Synthesis, Structure, and DFT Calculation of (Phosphino-o-carboranyl)silyl Group 10 Metal Complexes: Formation of Stable trans-Bis(P,Si-chelate)metal Complexes

Article abstract of DOI:10.1021/om034112l

Addition of the silane (HSiMe₂)C₂B₁₀H ₁₀(PR₂) (R = Me (2a), OEt (2b)) to (PPh₃) ₂Pt(CH₂-CH₂) (3) affords the trans-bis(chelates) Pt(Cab^P,Si)₂ (4a,b; Cab ^P,Si = η²-[(SiMe₂)(PR₂)C ₂B₁₀H₁₀P,Si]) in high yield; the same product was also formed from Pt(cod)₂ (9), as confirmed by NMR spectroscopy (¹H, ³¹P). Using Pd₂(dba)₃ (6), the analogue trans-bis(chelate) Pd(Cab^p,st)₂ (7a) was obtained as a mixture of trans and cis isomers in which the former predominates, as established by NMR spectroscopy (¹H, ³¹P). Thus, a series of kinetically stabilized transbis(chelate) metal complexes, trans-(Cab^P,Si)₂M. (M = Pt (4a,b), Pd (7a)), bearing bulky o-carboranylphosphine tethers, were synthesized from the reaction of phosphinosilanes (2) with d¹⁰ metal complexes. In the presence of dimethyl acetylenedicarboxylate (DMAD), the trans isomer 4a,b thermally rearranges to the thermodynamically favored cis isomer cis(Cab ^P,Si)₂Pt (5a,b). In addition, the oxidative addition of the Si-H bond to the sterically bulky diphenylphosphino silane (HSiMe ₂)C₂B₁₀H₁₀(PPh₂) (2c) by 3 can be controlled to produce the mono(chelate) species (Cab ^P,Si)Pt(H)(PPh₃) (10a). The related mono(chelate) product (Cab^P,Si)Pt(H)(Cab^P) (10b; Cab^P = (PPh ₂)C₂B₁₀H₁₁) results from the oxidative addition of 2c by 3, in which one PPhs ligand is displaced by Cab ^P. The structures of compounds 4a, 5a,c, 8c, and 10a,b were determined using single-crystal X-ray crystallography.

Full text of DOI:10.1021/om034112l

Organometallics 2004, 23, 203-214
203
Syn th esis, Str u ctu r e, a n d DF T Ca lcu la tion of
(P h osp h in o-o-ca r bor a n yl)silyl Gr ou p 10 Meta l
Com p lexes: F or m a tion of Sta ble
tr a n s-Bis(P ,Si-ch ela te)m eta l Com p lexes
Young-J oo Lee,† J ong-Dae Lee,† Sung-J oon Kim,† Samrok Keum,† J aejung Ko,*,†
Il-Hwan Suh,† Minserk Cheong,‡ and Sang Ook Kang*,†,§
Department of Chemistry, Korea University, 208 Seochang, Chochiwon,
Chung-nam 339-700, Korea, and Department of Chemistry and Research Institute for Basic
Sciences, Kyung Hee University, Seoul 130-701, Korea
Received August 14, 2003
Addition of the silane (HSiMe2)C2B10H10(PR2) (R ) Me (2a ), OEt (2b)) to (PPh3)2Pt(CH2-
CH2) (3) affords the trans-bis(chelates) Pt(CabP,Si)2 (4a ,b; CabP,Si ) η2-[(SiMe2)(PR2)C2B10H10-
P,Si]) in high yield; the same product was also formed from Pt(cod)2 (9), as confirmed by
NMR spectroscopy (1H, 31P). Using Pd2(dba)3 (6), the analogue trans-bis(chelate) Pd(CabP,Si
)
2
(7a ) was obtained as a mixture of trans and cis isomers in which the former predominates,
as established by NMR spectroscopy (1H, 31P). Thus, a series of kinetically stabilized trans-
bis(chelate) metal complexes, trans-(CabP,Si)2M (M ) Pt (4a ,b), Pd (7a )), bearing bulky
o-carboranylphosphine tethers, were synthesized from the reaction of phosphinosilanes (2)
with d10 metal complexes. In the presence of dimethyl acetylenedicarboxylate (DMAD), the
trans isomer 4a ,b thermally rearranges to the thermodynamically favored cis isomer cis-
(CabP,Si)2Pt (5a ,b). In addition, the oxidative addition of the Si-H bond to the sterically
bulky diphenylphosphino silane (HSiMe2)C2B10H10(PPh2) (2c) by 3 can be controlled to
produce the mono(chelate) species (CabP,Si)Pt(H)(PPh3) (10a ). The related mono(chelate)
product (CabP,Si)Pt(H)(CabP) (10b; CabP ) (PPh2)C2B10H11) results from the oxidative addition
of 2c by 3, in which one PPh3 ligand is displaced by CabP. The structures of compounds 4a ,
5a ,c, 8c, and 10a ,b were determined using single-crystal X-ray crystallography.
In tr od u ction
tioned context, comparatively few trans-bis(chelates)3c
have received scrutiny, principally because of their
inaccessibility. Recent reports of unusually stable cyclic
bis(o-carboranylsilyl)metal complexes4 appear to imply
that the properties of these complexes, such as their
chelation, rigid conformation, and o-carboranyl ligand
backbones might be ideal for the kinetic stabilization
of metal silyl intermediates in the double-silylation
process.5 Therefore, to increase the kinetic stability of
this type of ligand framework, we have synthesized
(phosphinoalkyl)silane precursors with a two-carbon
skeleton connecting the silicon and phosphorus atoms
that is part of a bulky o-carboranyl unit. These new
(phosphino-o-carboranyl)silanes were used in this study
to isolate a series of trans-bis(chelate)metal complexes,
which are formed by “chelate-assisted” oxidative addi-
(Phosphinoalkyl)silanes are used as chelate ligands
in a wide range of oxidative addition reaction processes
with transition metals1 and have been studied in
considerable detail, principally to obtain a better un-
derstanding of industrially important metal-catalyzed
reactions such as hydrosilylation.2 Such molecules
undergo oxidative addition at low-valent transition-
metal centers in which Si-M bond formation is ac-
companied by chelation with phosphine donors, afford-
ing ((phosphinoalkyl)silyl)metal complexes. Although
many examples of bis(chelate) metal complexes with a
cis arrangement of the (phosphinoalkyl)silyl ligands in
a typical square-planar M(II) (M ) Pd, Pt) environment
have been synthesized3 and evaluated in the aforemen-
† Korea University.
‡ Kyung Hee University.
(3) (a) Gossage, R. A.; McLennan, G. D.; Stobart, S. R. Inorg. Chem.
1996, 35, 1729. (b) Grundy, S. L.; Holmes-Smith, R. D.; Stobart, S. R.;
Williams, M. A. Inorg. Chem. 1991, 30, 3333. (c) Schubert, U.; Muller,
C. J . Organomet. Chem. 1989, 373, 165. (d) Holmes-Smith, R. D.;
Stobart, S. R.; Cameron, T. S.; J ochem, K. J . Chem. Soc., Chem.
Commun. 1981, 937.
(4) (a) Kang, Y.; Ko, J .; Kang, S. O. Organometallics 2000, 19, 1216.
(b) Kang, Y.; Ko, J .; Kang, S. O. Organometallics 1999, 18, 1818. (c)
Kang, Y.; Lee, J .; Kong, Y. K.; Ko, J .; Kang, S. O. Chem. Commun.
1998, 2343.
(5) (a) Uchimaru, Y.; Lautenschlager, H. J .; Wynd, A. J .; Tanaka,
M.; Goto, M. Organometallics 1992, 11, 2639. (b) Tanaka, M.; Uchi-
maru, Y.; Lautenschlager, H. J . Organometallics 1991, 10, 16. (c)
Eaborn, C.; Metham, T. N.; Pidcock, A. J . Organomet. Chem. 1973,
63, 107.
§ Tel: +82-41-860-1334. Fax: +82-41-867-5396. E-mail: sangok@
korea.ac.kr.
(1) (a) Okazaki, M.; Ohshitanai, S.; Iwata, M.; Tobita, H.; Ogino,
H. Coord. Chem. Rev. 2002, 226, 167. (b) Brost, R. D.; Bruce, G. C.;
J oslin, F. L.; Stobart, S. R. Organometallics 1997, 16, 5669. (c) J oslin,
F. L.; Stobart, S. R. Inorg. Chem. 1993, 32, 2221. (d) Ang, H. G.; Chang,
B.; Kwik, W. L. J . Chem. Soc., Dalton Trans. 1992, 2161. (e) J oslin, F.
L.; Stobart, S. R. J . Chem. Soc., Chem. Commun. 1989, 504. (f) Holmes-
Smith, R. D.; Stobart, S. R.; Vefghi, R.; Zaworotko, M. J .; J ochem, K.;
Cameron, T. S. J . Chem. Soc., Dalton Trans. 1987, 969. (g) Auburn,
M. J .; Stobart, S. R. Inorg. Chem. 1985, 24, 318. (h) Auburn, M. J .;
Holmes-Smith, R. D.; Stobart, S. R. J . Am. Chem. Soc. 1984, 106, 1314.
(2) (a) Speier, J . L. Adv. Organomet. Chem. 1979, 407. (b) Chalk,
A. J .; Harrod, J . F. J . Am. Chem. Soc. 1965, 87, 16.
10.1021/om034112l CCC: $27.50 © 2004 American Chemical Society
Publication on Web 12/12/2003

204 Organometallics, Vol. 23, No. 2, 2004
Lee et al.
Sch em e 1. Selective F or m a tion of
tr a n s-Bis(P ,Si-ch ela te)m eta l Com p lexes 4a ,b
a n d 7a
Sch em e 3. P r ep a r a tion of Tr a n s P la tin u m Meta l
Ch ela tes 4a ,ba
a
Conditions: (i) (PPh3)2Pt(C2H4) (3), toluene, 25 °C.
Syn th esis of [η2-(P h osp h in o-o-ca r bor a n yl)silyl]-
m eta l Com p lexes (Ca bP ,Si)2M (Ca bP ,Si ) η2-(P R2)-
(SiMe2)C2B10H10-P ,Si; M ) P t (4, 5), P d (7, 8)). Metal
chelates with η2-[(PR2)(SiMe2)C2B10H10-P,Si] were syn-
thesized using the reaction of coordinatively unsatur-
ated metal complexes with the (phosphinoalkyl)silanes
2 via coordination of the phosphine moiety and the
oxidative addition of the Si-H bond. When 2 equiv of
the (phosphinoalkyl)silanes 2a ,b was treated with 1
equiv of (PPh3)2Pt(C2H4) (3) in toluene at 25 °C, an
immediate color change from pale yellow to deep yellow
occurred (Scheme 3).
Sch em e 2. Syn th esis of
(P h osp h in o-o-ca r bor a n yl)sila n e 2a
Standard workup and crystallization from toluene-
pentane gave (CabP,Si)2Pt (4a ,b) in 73-76% yield as a
yellow, crystalline solid which was stable in air and
stable during brief heating to 100-110 °C. The unusual
thermal stability of 4a ,b may be related to the advanta-
geous properties of the o-carboranyl unit, including both
its electronic and steric effects. Compounds 4a ,b were
soluble in toluene, THF, and chloroform and were
characterized using 1H, 13C, and 31P NMR and elemental
analysis. A trans arrangement of the (phosphinoalkyl)-
silyl ligands in a typical square-planar Pt(II) environ-
a
Conditions: (i) (a) BunLi, THF, -78 °C; (b) R2PCl (R )
Me (a ), OEt (b), Ph (c)), THF, -78 °C; (ii) (a) BunLi, THF,
-78 °C; (b) Me2SiHCl, THF, -78 °C.
tion at palladium or platinum, as shown in Scheme 1.
The early results of this study have previously been
communicated.6
1
Resu lts a n d Discu ssion s
ment is proposed here on the basis of the J Pt-P values,
which are in the range 2702-4049 Hz for 4a ,b.7 In
P r ep a r a tion of (P h osp h in o-o-ca r bor a n yl)sila n es
(2). The (phosphino-o-carboranyl)silanes (2) were syn-
thesized according to Scheme 2. A synthetic route to 2
is provided by the action of 1-lithio-o-carborane on
chlorodialkylphosphine. This route affords 1-(dialky-
lphosphino)-o-carborane (1) in good yield as a colorless
solid; then lithiation of 1 at low temperature followed
by reaction with dimethylchlorosilane produces 2
(Scheme 2). A wide variety of (phosphino-o-carboranyl)-
silanes (2) with a Si-H bond were synthesized in this
way as ligand precursors.
Each product (2a -c) was recovered as a colorless,
rather waxy solid in ca. 82-92% yield; survival of the
silyl (i.e. Si-H) functionality was obvious from the
strong IR absorptions of these products near 2162-2170
cm-1 and from the observation of 1H NMR signals at δ
4.32 (2a ), 4.31 (2b), and 4.50 (2c) (δ(Si-H)) as multip-
lets that were integrated correctly vs alkyl or aryl
protons. Further characterization was provided by the
13C NMR (alkyl or aryl carbons) and 31P NMR chemical
shifts (Table 1).
1
particular, the H NMR chemical shift of δ 1.87 for 4a
as distorted triplets (2J H-P ) 3 Hz) resembles the values
reported for the typical virtual coupling in trans-
Pt(PMe2R)2X2 (R ) Me, Ph) complexes.8 This conclusion
was substantiated for complex 4a by using a single-
crystal X-ray study. This molecule has a square-planar
coordination around the Pt center with two mutually
trans SiMe2- units, as shown in Figure 1. The Pt-Si
bond is elongated (2.408(1) Å) by the large influence of
the SiMe2 ligand in the trans position. The reaction in
Scheme 2 proceeds with high stereoselectivity, resulting
preferentially in the formation of the trans isomer. This
is unusual, as the chelate-assisted oxidative addition
of (phosphinoalkyl)silanes with d10 metal complexes
usually occurs with cis stereochemistry3b,d due to the
(7) (a) Kalt, D.; Schubert, U. Inorg. Chim. Acta 2000, 306, 211. (b)
Kim, Y.-J .; Park, J .-I.; Lee, S.-C.; Osakada, K.; Tanabe, M.; Choi, J .-
C.; Koizumi, T.-A.; Yamamoto, T. Organometallics 1999, 18, 1349.
(8) (a) Yamashita, H.; Tanaka, M.; Goto, M. Organometallics 1997,
16, 4696. (b) Rieger, A. L.; Carpenter, G. B.; Rieger, P. H. Organome-
tallics 1993, 12, 842. (c) Brown, M. P.; Puddephatt, R. J .; Upton, C. E.
J . Chem. Soc., Dalton Trans. 1974, 2457. (d) Duddel, D. A.; Evans, J .
G..; Goggin, P. L.; Goodfellow, R. J .; Rest, A. J .; Smith, J . G. J . Chem.
Soc. A 1969, 2134.
(6) Lee, Y.-J .; Bae, J .-Y.; Kim, S.-J .; Ko, J .; Choi, M.-G.; Kang, S. O.
Organometallics 2000, 19, 5546.

Stable trans-Bis(P,Si-chelate)metal Complexes
Ta ble 1. NMR Sp ectr oscop ic Da ta (δ) for Com p ou n d s 2, 4, 5, 8, 10, a n d 12a
1H 13C
Organometallics, Vol. 23, No. 2, 2004 205
compd
31P
2
1
2a
0.37 (d. 6H, SiMe2, J Si-H ) 4 Hz)
-2.25 (d, SiMe2, J Si-C ) 8 Hz)
-11.56 (PMe2)
2
1
1.26 (d. 6H, PMe2, J P-H ) 5 Hz)
15.37 (d, PMe2, J P-C ) 17 Hz)
4.32 (m, 1H, SiH)
2
1
2b
0.37 (dd, 6H, SiMe2, J Si-H ) 4 Hz,
-2.20 (d, SiMe2, J Si-C ) 7 Hz)
-91.97 (P(OCH2Me)2)
17.46 (PPh2)
3J H-H ) 1 Hz)
3
3
1.31 (t, 6H, POCH2Me, J H-H ) 7 Hz)
16.96 (d, PMe2, J P-C ) 9 Hz)
64.64 (d, POCH2, J P-C ) 31 Hz)
2
3.98 (q, 4H, POCH2Me)
4.31 (m, 1H, SiH)
2
1
2c
4a
4b
0.42 (d, 6H, SiMe2, J Si-H ) 6 Hz)
-2.13 (d, SiMe2, J Si-C ) 10 Hz)
4.50 (m, 1H, SiH)
128.70, 129.12, 131.00, 131.41, 132.92, 133.17,
7.45, 7.46, 7.74, 7.78, 7.82, (m, 10H, PPh)
0.33 (d, 12H, SiMe2, J Pt-H ) 13 Hz)
1.87 (dt, 12H, PMe2, J Pt-H ) 35 Hz, J P-H
134.93, 135.07, 135.45, 135.59, 135.82 (PPh)
6.43 (d, SiMe2, J Pt-C ) 44 Hz)
18.09 (d, PMe2, J Pt-C ) 39 Hz)
3
2
1
48.60 (d, PMe2, J Pt-P
2702 Hz)
)
3
3
2
)
3 Hz)
3
0.40 (d, 12H, SiMe2, J Pt-H ) 13 Hz)
6.53 (SiMe2)
164.80 (d, P(OCH2Me)2,
1J Pt-P ) 4049 Hz)
3
1.38 (t, 12H, P(OCH2Me)2, J H-H ) 7 Hz)
4.19 (m, 8H, P(OCH2Me)2)
0.41 (dd, 12H, SiMe2, J Pt-H ) 27 Hz,
16.29 (P(OCH2Me)2)
66.73 (P(OCH2Me)2)
3
1
5a
5b
5c
1.99 (d, SiMe2, 2J Pt-C ) 229 Hz)
55.05 (d, PMe2, J Pt-P
1626 Hz)
)
2J Si-H ) 2 Hz)
1.72 (dd, 12H, PMe2,3J Pt-H ) 17 Hz,
19.00 (PMe2)
1.96 (SiMe2)
2J P-H ) 7 Hz)
0.41 (dd, 12H, SiMe2, 3J Pt-H ) 27 Hz,
2J Si-H ) 2 Hz)
1.36 (t, 12H, P(OCH2Me)2, J H-H ) 7 Hz),
4.11 (m, 8H, P(OCH2Me)2)
-71.50 (d, P(OCH2Me)2,
3
25.82 (P(OCH2Me)2)
47.85 (P(OCH2Me)2)
6.56 (d, SiMe2, J Pt-C ) 111 Hz)
1J Pt-P ) 2492 Hz)
3
2
1
0.56 (dd, 12H, SiMe2, J Pt-H ) 28 Hz,
70.99 (d, PPh2, J Pt-P
)
2J Si-H ) 2 Hz)
7.12, 7.38 (m, 20H, PPh2)
128.03, 128.17, 128.52, 131.79, 134.86 (PPh2)
5.72 (SiMe2)
1814 Hz)
41.68 (PMe2)
2
8a
8b
0.41 (d, 12H, SiMe2, J Si-H ) 2 Hz)
2
1.60 (d, 12H, PMe2, J P-H ) 5 Hz)
21.62 (PMe2)
5.40 (SiMe2)
0.35 (s, 12H, SiMe2)
171.26 (P(OCH2Me)2)
62.37 (PPh2)
3
1.38 (t, 12H, P(OCH2Me)2, J H-H ) 7 Hz)
4.10 (m, 8H, P(OCH2Me)2)
0.52 (s, 12H, SiMe2)
16.42 (P(OCH2Me)2),
66.58 (P(OCH2Me)2)
6.32 (SiMe2)
8c
7.13, 7.35 (m, 20H, PPh2)
128.13, 128.20, 128.27, 131.56, 134.51,
134.62, 134.72 (PPh2)
7.31 (dd, SiMe2, J Pt-C ) 107 Hz, J Si-C ) 6 Hz)
1
2
1
1
10a
-0.75 (ddd, 1H, PtH, J Pt-H ) 1119 Hz,
34.65 (d, PPh3, J Pt-P
1747 Hz)
)
)
2
2J P-H(trans) ) 164 Hz, J P-H(cis) ) 22 Hz)
3
0.62 (d, 6H, SiMe2, J Pt-H ) 32 Hz)
127.71, 128.16, 129.89, 131.38, 133.96,
80.99 (d, PPh2, 1J Pt-P
2660 Hz)
7.11, 7.14, 7.32, 7.78 (m, 25H, PPh)
135.76 (m, PPh)
1
2
1
10b
-1.33 (ddd, 1H, PtH, J Pt-H ) 1122 Hz,
7.07 (dd, SiMe2, J Pt-C ) 106 Hz, J Si-C ) 7 Hz)
127.91, 131.60, 134.97, 135.17, 135.24,
135.43 (m, PPh)
64.32 (d, (Cab)PPh2,
2
2J P-H(trans) ) 156 Hz, J P-H(cis) ) 20 Hz)
1J Pt-P ) 1756 Hz)
3
1
0.65 (d, 6H, SiMe2, J Pt-H ) 32 Hz,
77.27 (d, PPh3, J Pt-P
)
2J Si-H ) 2 Hz)
4.78 (s, 1H, CHCab
)
2744 Hz)
7.04, 7.36, 7.60 (m, 20H, PPh)
0.60 (s, 12H, SiMe2)
1.27 (d, 12H, PMe2, J P-H ) 5 Hz)
12a
12b
2.87 (SiMe2)
15.54 (PMe2)
5.40 (SiMe2)
16.42 (P(OCH2Me)2)
66.58 (P(OCH2Me)2)
2.13 (SiMe2)
-17.60 (PMe2)
2
0.65 (s, 12H, SiMe2)
-88.45 (P(OCH2Me)2)
3
1.41 (t, 12H, P(OCH2Me)2, J H-H ) 7 Hz)
4.10 (m, 8H, P(OCH2Me)2)
0.72 (s, 12H, SiMe2)
12c
11.50 (PPh2)
7.40, 7.42, 7.47, 7.49, 7.69, 7.72, 7.75,
7.79 (20H, PPh2)
128.77, 129.21, 130.59, 131.11, 133.71,
133.88, 134.68, 135.01, 135.50 (PPh2)
a
CDCl3 was used as the solvent, and the chemical shifts are reported relative to the residual H of the solvent.
strong trans influence of the silyl group. The increased
stability of the trans products 4a ,b is most likely a
consequence of the formation of the two bis(chelate)
rings imposed by the bulky o-carborane backbones.
Initial attempts to isomerize the trans isomers were
unsuccessful. The dissolution of trans-4a ,b in toluene
and heating of the solutions for 1 day at 110 °C resulted
in no changes in trans-4a ,b. However, in the presence
of dimethyl acetylenedicarboxylate (DMAD) at 110 °C,
the trans isomers 4a ,b cleanly rearranged to the
thermodynamically favored cis isomers, cis-(CabP,Si)2-
Pt (5a ,b), within 1 h (Scheme 4).
tronic influences on the course of the reaction. The
isomerization of toluene solutions of trans-4a ,b (0.20
mmol) and DMAD (1.0 mmol) at 110 °C for 1 h afforded
high yields of cis-5a ,b (92-96%) as colorless solids.
The 1H and 31P{1H} NMR spectra of cis-5a ,b in CDCl3
contain signals of their isomers generated in the solu-
tion. The spectra were assigned to cis-(CabP,Si)2Pt (5a ,b)
1
on the basis of a J Pt-P value (1626-2492 Hz) smaller
than that exhibited by trans-4a ,b (1J Pt-P ) 2702-4049
Hz) and because of their similarity to those values
previously reported for cis-Pt(SiR3)2(PR′3)2 type com-
plexes.9 The solution NMR spectral data of the cis-5a ,b
complexes are unambiguous and consistent with the cis
geometry found in the crystal structure of cis-5a . Figure
2 depicts the molecular structure of 5a , which has a
Interestingly, only the trans isomers 4a ,b with acti-
vated acetylene such as DMAD can promote the isomer-
ization to the cis form, indicating that there are elec-

206 Organometallics, Vol. 23, No. 2, 2004
Lee et al.
F igu r e 1. Molecular structure of trans-4a with thermal
ellipsoids drawn at the 30% level.
F igu r e 2. Molecular structure of cis-5a with thermal
ellipsoids drawn at the 30% level.
Sch em e 4. Tr a n s to Cis Isom er iza tion of
Bis(ch ela te)p la tin u m Meta l Com p lexesa
the reaction of Ph2PCH2CH2SiHR1R2 (R1, R2 ) H, Me,
Ph) with Pt(cod)2.11 It is well established that the
hydrosilylation of low-valent metal complexes by the
functional silane PPh2CH2CH2SiMe2H provides access
to a family of new bis(chelate) derivatives of the silyl
PPh2CH2CH2SiMe2-, in which the silicon-transition-
metal bond is supported by phosphine coordination to
the metal.
The isomerization of cis-(PhMe2P)2Pt(SiMe2Ph)2 into
trans-(PhMe2P)2Pt(SiMe2Ph)2 catalyzed by di- and oli-
gosilanes has been recently reported.7a In particular,
similar trans-cis isomerization has been observed in
the work of Kim et al.7b on trans-Pt(SiHPh2)2(PMe3)2,
which is readily converted upon dissolution in THF or
CD2Cl2 into the thermodynamically more stable cis
isomer. In contrast, trans-4a ,b are more robust and do
not undergo trans-cis isomerization as readily in solu-
tion. The increased stability of the trans products 4a ,b
is most likely a consequence of the formation of the two
bis-chelate rings imposed by the bulky o-carborane
backbones. In addition, we have used density functional
calculations to study both trans-4a and cis-5a bis-
(chelate) platinum complexes and found that the trans-
4a structure is preferred over that of cis-5a by 1.66 kcal/
mol (Figure 3).
a
Conditions: (i) DMAD, toluene, 110 °C.
distorted-square-planar coordination around the metal
center with two dimethylsilyl units in the cis positions.
The Pt-P and Pt-Si distances of the terminal ligands
and the chelated (phosphino-o-carboranyl)silyl ligand do
not differ significantly, and the Pt-Si distances are
comparable to those found in other Pt(II) silyl com-
plexes.10
Similar cyclic bis[((diphenylphosphino)ethyl)dior-
ganosilyl]platinum complexes have been prepared using
Other group 10 metal complexes, such as Pd2(dba)3
(6) and Pt(cod)2 (9), were tested for the chelate-assisted
oxidative addition of 2, as shown in Schemes 5 and 6
and in Table 2. The reaction of 6 with 2a results in the
bis(chelates) trans-(CabP,Si)2Pd (7a ) and cis-(CabP,Si)2-
Pd (8a ), in 34% yield with a trans:cis ratio of 2:1. On
the other hand, the reaction of 6 with 2b,c is cis-
selective, producing 60-65% yields of cis-(CabP,Si)2Pd
(8b,c). These results indicate that the stereoselectivity
of the reaction is dependent on the electronic and steric
characteristics of the ligands around the metal center.
(9) (a) Yamashita, H.; Tanaka, M.; Goto, M. Organometallics 1992,
11, 3227. (b) Holmes-Smith, R. D.; Stobart, S. R.; Cameron, T. S.;
J ochem, K. J . Chem. Soc., Chem. Commun. 1981, 937. (c) Chatt, J .;
Eaborn, C.; Ibekwe, S. D.; Kapoor, P. N. J . Chem. Soc. A 1970, 1343.
(10) Recent articles on silylplatinum complexes: (a) Ozawa, F.;
Hikida, T. Organometallics 1996, 15, 4501. (b) Goikhman, R.; Aizen-
berg, M.; Shimon, L. J . W.; Milstein, D. J . Am. Chem. Soc. 1996, 118,
10894. (c) Levy, C. J .; Vittal, J . J .; Puddephatt, R. J . Organometallics
1996, 15, 2108. (d) Levy, C. J .; Puddephatt, R. J .; Vittal, J . J .
Organometallics 1994, 13, 1559. (e) Ozawa, F.; Hikida, T.; Hayashi,
T. J . Am. Chem. Soc. 1994, 116, 2844. (f) Yamashita, H.; Tanaka, M.;
Goto, M. Organometallics 1993, 12, 988. (g) Sakaki, S.; Ieki, M. J . Am.
Chem. Soc. 1993, 115, 2373. (h) Braunstein, P.; Knorr, M.; Hirle, B.;
Reinhard, G.; Schubert, U. Angew. Chem., Int. Ed. Engl. 1992, 31,
1583. (i) Tanaka, M.; Uchimaru, Y.; Lautenschlager, H.-J . J . Orga-
nomet. Chem. 1992, 428, 1. (j) Yamashita, H.; Tanaka, M.; Goto, M.
Organometallics 1992, 11, 3227. (k) Heyn, R. H.; Tilley, T. D. J . Am.
Chem. Soc. 1992, 114, 1917. (l) Grundy, S. L.; Holmes-Smith, R. D.;
Stobart, S. R.; Williams, M. A. Inorg. Chem. 1991, 30, 3333. (m) Pham,
E. K.; West, R. Organometallics 1990, 9, 1517.
(11) (a) Grundy, S. L.; Holmes-Smith, R. D.; Stobart, S. R.; Williams,
M. A. Inorg. Chem. 1991, 30, 3333. (b) Holmes-Smith, R. D.; Stobart,
S. R.; Cameron, T. S.; J ochem, K. J . Chem. Soc., Chem. Commun. 1981,
937.

Stable trans-Bis(P,Si-chelate)metal Complexes
Organometallics, Vol. 23, No. 2, 2004 207
F igu r e 3. Energy profiles of trans-4a and cis-5a .
Sch em e 5. Rea ction of P d 2(d ba )3 (6) w ith
Sch em e 6. Rea ction of P t(cod )2 (9) w ith
(P h osp h in o-o-ca r bor a n yl)sila n e (2)a
(P h osp h in o-o-ca r bor a n yl)sila n e (2)a
a
Conditions: (i) 2 2, toluene, 25 °C.
structures. In addition, we established the structure of
cis-8c unambiguously using single-crystal X-ray analy-
sis, as shown in Figure 4. The crystallographic data and
processing parameters are given in Table 3; selected
bond distances and angles are given in Tables 4 and 5,
respectively. Complex cis-8c has a slightly distorted
square-planar geometry with a cis arrangement of the
two silicon atoms. The equatorial plane is defined by
the Pd(1), P(1), P(2), Si(1), and Si(2) atoms and is
relatively planar with an average atomic displacement
of 0.0426 Å. The two five-membered metallacycles
(Pd(1), C(1), C(2), Si(1), P(1); Pd(1), C(17), C(18), Si(2),
P(2)) are twisted with respect to each other at a dihedral
angle of 8.8(1)°. These metallacycles are also twisted
with respect to the equatorial plane, with dihedral
a
Conditions: (i) 2 2a , toluene, 25 °C; (ii) 2 2b,c, toluene,
25 °C.
The 1H, 13C, and 31P NMR spectral data for the
resulting palladium species trans-7 and cis-8 are sum-
marized in Table 1. All the complexes exhibit NMR
spectra that are in agreement with their proposed

208 Organometallics, Vol. 23, No. 2, 2004
Lee et al.
Ta ble 2. Ch ela te-Assisted Oxid a tive Ad d ition
Rea ction of 2
(CabSi,P)2M
sub-
strate
yield
entry
MLn
trans
cis
(%)b
1
2
3
4
5
6
7
8
2a
2b
2a
2b
2c
2a
2b
2c
(PPh3)2Pt(C2H4) (3)
(PPh3)2Pt(C2H4) (3)
Pd2(dba)3 (6)
Pd2(dba)3 (6)
Pd2(dba)3 (6)
Pt(cod)2 (9)
4a
4b
none
none
1 8a c
8b
73
76
34
65
60
59
51
43
2 7a c
none
none
2 4a c
1 4bc
1 4cc
8c
1 5a c
1 5bc
6 5cc
Pt(cod)2 (9)
Pt(cod)2 (9)
a
b
Conditions: 0.60 mmol of 2, benzene, 25 °C, Ar atm. Yields
determined after recrystallization or chromatography. c Stereoi-
someric ratios were determined by NMR.
F igu r e 5. Molecular structure of cis-5c with thermal
ellipsoids drawn at the 30% level.
intermediates in the Pd-catalyzed bis-silylation of
alkynes.16 This suggested that an investigation of the
reactivity of cis-(CabP,Si)2Pd (8b,c) with alkynes might
be useful. However, these cis isomers are inactive
toward bis-silylation, indicating that the bulky o-car-
borane backbone confers some additional strength to the
Pd-Si bond.
In contrast, the route using Pt(cod)2 (9) does not
exhibit sufficient stereoselectivity. The use of 2a gives
4a and 5a with a trans:cis ratio of 2:1, whereas 2b yields
4b and 5b with a trans:cis ratio of 1:1. On the other
hand, when 9 is reacted with 2c, the major product
formed is the cis isomer 5c, as well as a minor amount
of the trans isomer 4c. A cis arrangement of the chelated
1
ligands in complex 5c is indicated by J Pt-P ) 1814 Hz,
which is close to that reported for cis-[Pt(PPh2CH2CH2-
SiMe2)2] (1608 Hz), which has mutually cis phosphines.3b
This conclusion was corroborated by the results of an
X-ray crystal structure determination (Figure 5). The
four bulky groups bonded to the platinum atom are
accommodated in the square plane by distortion of the
bond angles centered at Pt. The Pt-P and Pt-Si
distances of the terminal ligands and the chelated
(phosphino-o-carboranyl)silyl ligand do not differ sig-
nificantly, and the Pt-Si distances are comparable to
those in other Pt(II) silyl complexes.10
Although a wide range of kinetically stabilized trans
isomers can be obtained under mild conditions, the
stereochemistry of the reaction nevertheless appears to
be dependent on which silane and metal complex are
employed. For example, changing the alkyl substituent
on the phosphorus center of the silane to one that is
more electron donating and less sterically demanding,
as is the case in 2a , exclusively leads to the trans
isomer. Increased stereoselectivity is also found for
metal complexes such as 3 and 6; whether the trans or
F igu r e 4. Molecular structure of cis-8c with thermal
ellipsoids drawn at the 30% level.
angles of 17.1(1) and 8.4(1)°, respectively. The Pd-Si
bond distance (2.358(2)-2.361(2) Å) of cis-8c is in
agreement with the values observed for Pd(SiMe2CH2-
CH2PPh2)2 (2.367(1) Å)12 and (dcpe)Pd(SiHMe2)2 (2.3561
Å)13 and for analogous complexes (2.34-2.41 Å).14 The
1H, 13C, and 31P NMR spectra of cis-8c are consistent
with the structure determined by X-ray crystallography.
1
An H NMR signal ascribable to the Pd-SiMe2 moiety
was observed at 0.52 ppm. The 31P NMR signal had
clearly shifted, moving from a value of 17.46 ppm for
2c to 62.37 ppm for cis-8c.
Bis(silyl)palladium complexes have already been re-
ported by Ito et al.15 and have been implicated as key
(12) Murakami, M.; Yoshida, T.; Ito, Y. Organometallics 1994, 13,
2900.
(13) Pan, Y.; Mague, J . T.; Fink, M. J . Organometallics 1992, 11,
3495.
(14) (a) Suginome, M.; Oike, H.; Park, S.; Ito, Y. Bull. Chem. Soc.
J pn. 1996, 69, 289. (b) Michalczyk, M. J .; Tilley, T. D. J . Am. Chem.
Soc. 1992, 114, 1917. (c) Holmes-Smith, R. D.; Stobart, S. R.; Cameron,
T. S.; J ochem, K. J . Chem. Soc., Chem. Commun. 1981, 937.
(15) (a) Murakami, M.; Yoshida, T.; Kawanami, S.; Ito, Y. J . Am.
Chem. Soc. 1995, 117, 6408. (b) Murakami, M.; Yoshida, T.; Ito, Y.
Organometallics 1994, 13, 2900.
(16) (a) Murakami, M.; Suginome, M.; Fujimoto, K.; Ito, Y. Angew.
Chem., Int. Ed. Engl. 1993, 32, 1473. (b) Obora, Y.; Tsuji, Y.;
Kawamura, T. Organometallics 1993, 12, 2853 and references therein.

Stable trans-Bis(P,Si-chelate)metal Complexes
Organometallics, Vol. 23, No. 2, 2004 209
Ta ble 3. X-r a y Cr ysta llogr a p h ic Da ta a n d P r ocessin g P a r a m eter s for Com p ou n d s 4a , 5a ,c, 8c, a n d 10a ,c
4a
5a
5c
8c
10a
10b
formula
B
10C19H52Si2-
P2Pt
B
20C12H44Si2-
P2Pt
B
20C32H52Si2-
P2Pt
B
20C32H52Si2-
P2Pd
B
10C34H42Si-
P2Pt
B
20C30H48Si-
P2Pt
fw
810.03
triclinic
P1h
717.88
monoclinic
P21/n
966.15
monoclinic
P21/c
877.46
monoclinic
P21/c
843.90
monoclinic
P21/c
910.00
triclinic
P1h
cryst class
space group
Z
1
4
4
4
4
2
cell constants
a, Å
b, Å
8.6548(3)
11.0158(8)
11.0685(7)
104.516(5)
106.106(4)
98.033(4)
956.3(1)
9.5000(9)
22.673(1)
14.6629(6)
11.8496(8)
15.686(2)
23.404(1)
11.880 (1)
15.645 (1)
23.405 (2)
13.0608(6)
18.296(1)
16.3890(7)
11.9428(6)
12.8016(6)
13.681(2)
96.647(8)
95.711(8)
92.512(4)
2064.0(4)
3.531
c, Å
R, deg
â, deg
90.564(5)
93.792(5)
93.557(7)
103.262(4)
γ, deg
V, Å3
3141.8(4)
4.652
4340.7(6)
3.389
4341.9(6)
0.583
3811.9(3)
3.821
µ, mm-1
cryst size, mm
3.830
0.3 × 0.45 × 0.45
0.2 × 0.2 × 0.3 0.35 × 0.5 × 0.5 0.4 × 0.4 × 0.5 0.3 × 0.3 × 0.3
0.2 × 0.3 × 0.3
d
calcd, g/cm3
1.413
1.518
1408
1.478
1920
1.342
1792
1.470
1672
1.464
F(000)
400
900
radiation
θ range, deg
h, k, l collected
Mo KR (λ ) 0.7107)
1.96-25.97
1.66-25.97
1.56-25.98
0-14, 0-19,
-28 to +28
8974
1.57-25.97
0-14, 0-19,
-28 to +28
8886
1.60-25.97
1.51-25.97
0-10, +13 to -13, 0-11, 0-27,
-16 to +16, 0-22, 0-14, 0-15,
+13 to -13,
4060
3758
3709
-18 to +18
6558
6142
5079
0-20
7793
-16 to +16
8535
no. of rflns measd
no. of unique rflns
no. of rflns used in
refinement (I > 2σ(I))
no. of params
R1a
8510
6676
8459
5760
7481
4919
8086
7320
199
362
558
558
471
534
0.0288
0.0732
1.078
0.0342
0.1539
1.236
0.0298
0.0699
1.076
0.0614
0.2080
1.057
0.0389
0.1143
0.710
0.0311
0.1317
1.116
wR2a
GOF
R1 ) ∑Fo - Fc (based on reflections with Fo2 > 2σF2). wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]1/2; w ) 1/[σ2(Fo2) + (0.095P)2]; P ) [max(Fo
,
a
2
0) + 2Fc2]/3 (also with Fo > 2σF2).
2
Ta ble 4. Selected In ter a tom ic Dista n ces (Å) for Com p ou n d s 4a , 5a ,c, 8c, a n d 10a ,c
Compound 4a
Pt(1)-P(1)
P(1)-C(4)
Si(1)-C(2)
2.251(1) Pt(1)-Si(1)
1.824(5) P(1)-C(1)
1.950(4) C(1)-C(2)
2.408(1) Pt(1)-P(1)#1 2.251(1) Pt(1)-Si(1)#1 2.408(1) P(1)-C(3)
1.813(5)
1.888(5)
1.869(4) P(1)-C(4)
1.824(5) Si(1)-C(5)
1.878(5) Si(1)-C(6)
1.676(6) C(10)-C(11)
1.23(2)
C(11)-C(12)
1.34(2)
C(12)-C(13) 1.17(3)
C(10)-C(12)#2 1.42(2)
C(12)-C(10)#2 1.42(2)
Compound 5a
Pt(1)-P(1)
P(1)-C(4)
Si(1)-C(5)
Si(2)-C(8)
2.3122(2)
1.818(9)
1.874(8)
1.947(7)
Pt(1)-P(2)
P(1)-C(1)
Si(1)-C(6)
C(1)-C(2)
2.3085(2)
1.884(8)
1.886(9)
1.667(1)
Pt(1)-Si(1)
P(2)-C(9)
Si(1)-C(2)
2.3492(2)
1.785(8)
1.928(7)
Pt(1)-Si(2)
P(2)-C(10)
Si(2)-C(11)
2.3532(2)
1.817(9)
1.859(9)
P(1)-C(3)
P(2)-C(7)
Si(2)-C(12)
1.811(9)
1.851(8)
1.866(9)
Compound 5c
Pt(1)-P(1)
P(1)-C(2)
P(1)-C(5)
P(2)-C(27)
2.338(1)
1.887(4)
1.812(4)
1.829(4)
Pt(1)-Si(1)
Si(2)-C(17)
P(1)-C(11)
2.362(1)
1.950(5)
1.825(4)
Pt(1)-P(2)
P(2)-C(18)
Si(2)-C(19)
2.337(1)
1.882(4)
1.879(5)
Pt(1)-Si(2)
Si(1)-C(3)
Si(2)-C(20)
2.361(1)
1.871(5)
1.882(5)
Si(1)-C(1)
Si(1)-C(4)
P(2)-C(21)
1.953(5)
1.889(5)
1.823(4)
Compound 8c
Pd(1)-P(1)
P(1)-C(2)
P(1)-C(5)
P(2)-C(27)
2.363(2)
1.890(7)
1.814(7)
1.832(8)
Pd(1)-Si(1)
Si(2)-C(17)
P(1)-C(11)
2.361(2)
1.951(8)
1.821(7)
Pd(1)-P(2)
P(2)-C(18)
Si(2)-C(19)
2.357(2)
1.881(7)
1.889(8)
Pd(1)-Si(2)
Si(1)-C(3)
Si(2)-C(20)
2.358(2)
1.875(9)
1.874(8)
Si(1)-C(1)
Si(1)-C(4)
P(2)-C(21)
1.959(7)
1.887(8)
1.822(7)
Compound 10a
Pt(1)-P(1)
P(1)-C(1)
Si(1)-C(15)
2.271(2)
1.907(6)
1.875(2)
Pt(1)-Si(1)
P(2)-C(17)
Si(1)-C(2)
2.307(2)
1.823(6)
1.942(7)
Pt(1)-P(2)
P(2)-C(23)
2.353(2)
1.830(6)
P(1)-C(3)
P(2)-C(29)
1.808(6)
1.837(6)
P(1)-C(9)
Si(1)-C(16)
1.832(6)
1.861(2)
Compound 10b
Pt(1)-P(1)
P(1)-C(1)
Si(1)-C(15)
2.2804(1)
1.864(6)
1.877(1)
Pt(1)-Si(1)
P(2)-C(19)
Si(1)-C(2)
2.3228(2)
1.826(6)
1.941(7)
Pt(1)-P(2)
P(2)-C(25)
2.3642(1)
1.837(7)
P(1)-C(3)
P(2)-C(17)
1.822(6)
1.896(6)
P(1)-C(9)
Si(1)-C(16)
1.824(6)
1.877(9)
the cis isomer is produced depends on the steric bulk of
the phosphine substituent.
cis-[(hydridosilyl)PtII] complex18 (CabP,Si)Pt(H)(PPh3)
(10a ). In contrast, such a hydridosilyl mono(chelate) was
Of the silanes we studied, 2c failed to produce an
appreciable amount of trans-bis(chelates). Interestingly,
3 reacted with 2c by displacement of the ethylene ligand
and the oxidative addition of the Si-H bond17 to
generate the chelating (phosphinoalkyl)silane stabilized
(17) (a) Schubert, U. In Progress in Organosilicon Chemistry;
Marciniec, B., Chojnowski, J ., Eds.; Gordon and Breach: Lausanne,
Switzerland, 1995; pp 287-307. (b) Sakaki, S.; Ieki, M. J . Am. Chem.
Soc. 1993, 115, 2373. (c) Schubert, U. Adv. Organomet. Chem. 1990,
30, 151.

210 Organometallics, Vol. 23, No. 2, 2004
Ta ble 5. Selected In ter a tom ic An gles (d eg) for Com p ou n d s 4a , 5a ,c, 8c, a n d 10a ,c
Lee et al.
Compound 4a
P(1)-Pt(1)-P(1)#1
C(4)-P(1)-C(1)
P(1)-Pt(1)-Si(1)#1
C(1)-P(1)-Pt(1)
180.0
104.2(2)
P(1)#1-Pt(1)-Si(1)
C(4)-P(1)-Pt(1)
92.12(4) P(1)#1-Pt(1)-Si(1)#1
87.88(4) C(3)-P(1)-C(4)
103.9(3)
87.88(4)
118.5(2)
113.9(2)
C(6)-Si(1)-Pt(1)
C(3)-P(1)-C(1)
C(2)-Si(1)-Pt(1)
117.6(2)
101.2(2)
106.54(1)
P(1)-Pt(1)-Si(1)
C(3)-P(1)-Pt(1)
92.12(4) Si(1)-Pt(1)-Si(1)#1 180.0
113.3(1)
C(5)-Si(1)-Pt(1)
118.9(2)
Compound 5a
P(2)-Pt(1)-P(1)
P(1)-Pt(1)-Si(2)
C(4)-P(1)-C(1)
C(9)-P(2)-C(10)
C(10)-P(2)-Pt(1)
C(2)-Si(1)-Pt(1)
97.36(7)
174.57(7)
104.1(4)
102.3(5)
115.8(3)
106.9(2)
P(2)-Pt(1)-Si(1)
Si(1)-Pt(1)-Si(2)
C(3)-P(1)-Pt(1)
C(9)-P(2)-C(7)
C(7)-P(2)-Pt(1)
C(11)-Si(2)-Pt(1)
175.11(7)
87.61(7)
118.7(4)
101.7(4)
111.5(2)
119.3(3)
P(1)-Pt(1)-Si(1)
C(3)-P(1)-C(4)
C(4)-P(1)-Pt(1)
C(10)-P(2)-C(7)
C(5)-Si(1)-Pt(1)
C(12)-Si(2)-Pt(1)
87.03(7)
104.0(5)
114.9(4)
105.3(4)
122.2(3)
115.8(3)
P(2)-Pt(1)-Si(2)
C(3)-P(1)-C(1)
C(1)-P(1)-Pt(1)
C(9)-P(2)-Pt(1)
C(6)-Si(1)-Pt(1)
C(8)-Si(2)-Pt(1)
87.97(7)
101.0(4)
112.3(2)
118.5(3)
113.2(3)
108.1(2)
Compound 5c
P(1)-Pt(1)-Si(1)
C(2)-P(1)-Pt(1)
C(18)-C(17)-Si(2)
C(5)-P(1)-C(11)
87.51(4)
110.1(1)
116.2(3)
104.7(2)
Si(2)-Pt(1)-Si(1)
C(1)-C(2)-P(1)
C(17)-Si(2)-Pt(1)
C(21)-P(2)-C(27)
86.69(4)
112.1(3)
107.6(1)
111.5(2)
P(2)-Pt(1)-Si(2)
C(2)-C(1)-Si(1)
C(17)-C(18)-P(2)
87.76(4)
116.1(3)
112.4(3)
P(2)-Pt(1)-P(1)
C(1)-Si(1)-Pt(1)
C(18)-P(2)-Pt(1)
98.00(4)
105.9(1)
112.1(1)
Compound 8c
P(1)-Pd(1)-Si(1)
Pd(1)-P(1)-C(2)
Si(2)-C(17)-C(18)
C(5)-P(1)-C(11)
88.08(7)
109.9(2)
117.2(4)
104.2(3)
Si(1)-Pd(1)-Si(2)
P(1)-C(2)-C(1)
Pd(1)-Si(2)-C(17)
C(21)-P(2)-C(27)
84.71(7)
111.5(4)
107.0(2)
110.8(3)
Si(2)-Pd(1)-P(2)
C(2)-C(1)-Si(1)
C(17)-C(18)-P(2)
88.01(7)
117.6(4)
112.1(4)
P(1)-Pd(1)-P(2)
C(1)-Si(1)-Pd(1)
C(18)-P(2)-Pd(1)
99.11(6)
105.1(2)
111.8(2)
Compound 10a
P(1)-Pt(1)-Si(1)
C(3)-P(1)-C(1)
C(1)-P(1)-Pt(1)
C(29)-P(2)-Pt(1)
90.91(7)
101.7(3)
110.7(2)
116.0(2)
P(1)-Pt(1)-P(2)
C(9)-P(1)-C(1)
C(17)-P(2)-C(23)
C(16)-Si(1)-Pt(1)
105.18(5)
105.3(3)
105.4(3)
114.8(4)
Si(1)-Pt(1)-P(2)
C(3)-P(1)-Pt(1)
C(17)-P(2)-Pt(1)
C(15)-Si(1)-Pt(1)
163.81(7)
114.4(2)
111.7(2)
116.3(4)
C(3)-P(1)-C(9)
C(9)-P(1)-Pt(1)
C(23)-P(2)-Pt(1)
C(2)-Si(1)-Pt(1)
105.6(3)
117.6(2)
117.2(2)
107.7(2)
Compound 10b
P(1)-Pt(1)-Si(1)
C(3)-P(1)-C(1)
C(1)-P(1)-Pt(1)
C(19)-P(2)-Pt(1)
C(2)-Si(1)-Pt(1)
91.16(6)
104.7(3)
110.43(2)
116.0(2)
106.82(2)
P(1)-Pt(1)-P(2)
C(9)-P(1)-C(1)
C(19)-P(2)-C(25)
C(25)-P(2)-Pt(1)
99.34(5)
101.6(2)
107.8(3)
107.4(2)
Si(1)-Pt(1)-P(2)
C(3)-P(1)-Pt(1)
C(16)-Si(1)-Pt(1)
C(17)-P(2)-Pt(1)
163.46(7)
112.30(2)
110.7(4)
C(3)-P(1)-C(9)
C(9)-P(1)-Pt(1)
C(25)-P(2)-C(17)
C(15)-Si(1)-Pt(1)
110.2(3)
116.46(2)
104.3(3)
121.2(4)
117.56(2)
Sch em e 7. P r ep a r a tion of cis-[(h yd r id osilyl)P tII]
not observed for the oxidative addition of analogous
(phosphinoalkyl)silanes.3 Thus, as can be seen in Scheme
7, an increase in the steric bulk of the phosphine
substituent appears to retard the second oxidative
addition, as manifested in the higher yields obtained
for 10a . Given this steric constraint, we next turned to
determining whether high yields of the mono(chelate)
could be obtained if 2c was reacted with 9 in the
presence of the bulky ancillary o-carboranylphosphine
ligand (Cab)PPh2. Indeed, 2c was found to cleanly react
with 9 and (Cab)PPh2 to provide the sterically encum-
bered cis-[(hydridosilyl)PtII] complex (CabP,Si)Pt(H)-
[(Cab)PPh2] (10b), which is stable well above 100 °C.
The structures of 10a ,b agree with the conclusions from
the solution NMR data that the atoms are arranged in
a square-pyramidal framework. The hydride ligand was
not located by X-ray diffraction; however, its presence
was confirmed by the appearance of its 1H NMR
resonance at around δ -1 (1J PtH ≈ 1119 Hz).
Com p lexes 10a ,ba
Figure 6 shows the structure of 10a as determined
by X-ray crystallography. The coordination geometry
around the Pt center of the complexes can be rational-
ized as a distorted square plane containing two PPh2R
(R ) Ph, o-carborane) ligands at mutually cis positions
and a dimethylsilyl unit and a hydrido ligand coordi-
nated to the Pt(II) center. The Pt-Si bond distances
(2.307(2) Å) are in the range previously reported for
a
Conditions: (i) (PPh3)2Pt(C2H4) (3), toluene, 25 °C; (ii)
Pt(cod)2 (9), (Cab)PPh2, toluene, 25 °C.
(18) (a) Mullica, D. F.; Sappenfield, E. L.; Hampden-Smith, M. J .
Polyhedron 1991, 10, 867. (b) Clark, H. C.; Hampden-Smith, M. J .
Coord. Chem. Rev. 1987, 79, 229. (c) Clark, H. C.; Hampden-Smith,
M. J . J . Am. Chem. Soc. 1986, 108, 3829. (d) Azizian, H.; Dixon, K. R.;
Eaborn, C.; Pidcock, A.; Shuaib, N. M.; Vinaixa, J . J . Chem. Soc., Chem.
Commun. 1982, 1020.
silylplatinum complexes (2.34-2.40 Å).10 The Pt(1)-P(2)
bond (2.353(2) Å) is longer than the Pt(1)-P(1) bond
(2.271(2) Å), indicating that the trans influence of the
dimethylsilyl ligand is more significant than that of the

Stable trans-Bis(P,Si-chelate)metal Complexes
Organometallics, Vol. 23, No. 2, 2004 211
deviation of -1.004(2) Å), probably as a result of the
maximal space requirement for the bulky o-carboranyl
phosphine ligand. It has been established that the
greater trans influence of the dimethylsilyl group
compared with that of the hydride means that the Pt-
(1)-P(2) bond is longer than the Pt(1)-P(1) bond.19 The
measured Pt(1)-Si(1) distance is comparable to other
previously published values.10
1
The H NMR spectrum of 10a contains a signal due
to the hydride ligand at δ -0.75 as a doublet of doublets
flanked with satellites caused by the 195Pt metal center
(1J Pt-H ) 1119 Hz). The large difference between the
2
two J P-H values (164 and 22 Hz) indicates that the
phosphine ligands occupy mutually cis positions. The
31P{1H} NMR spectrum contains signals at δ 80.99 and
1
34.65 with J Pt-P values of 2660 and 1747 Hz, respec-
tively. The latter is assigned to the phosphine ligand
at the trans position of the dimethylsilyl ligands on the
basis of a comparison of the 1J values with those of
already reported silylplatinum complexes.10 This as-
signment is consistent with the relative magnitude of
the trans influence of SiMe3 and H ligands observed in
the crystallographic results. Complex 10b gives rise to
similar NMR spectra. Although several cis-Pt(H)(SiAr3)-
(PPh3)2 type complexes have already been prepared from
the reaction of HSiAr3 with Pt(PPh3)4 and with 3,19,20
there have been no reports of similar P,Si-chelate
complexes. The preferential cis configuration of 10a ,b
can be attributed to the fact that the trans influence of
both the dimethylsilyl and hydride ligands is much
greater than that of PPh3, rendering the trans structure
unstable.
F igu r e 6. Molecular structure of 10a with thermal el-
lipsoids drawn at the 30% level.
P r ep a r a tion of th e Lin ea r Bis(p h osp h in o)d isi-
lan e 1,2-Bis(1-P R2-o-car bor an yl)-1,1,2,2-tetr am eth yl-
1,2-d isila n e (R ) Me (12a ), OEt (12b), P h (12c)). The
bis(phosphino)disilanes (12) were readily prepared from
the dilithium salt of the bis(o-carboranyl)disilanes (11)
with 2 equiv of PR2Cl (R ) Me (a ), OEt (b), Ph (c)). The
dilithium salt of bis(o-carboranyl)disilane generated by
the reaction of n-BuLi with bis(o-carboranyl)disilane
(11) was reacted with dialkylchlorophosphine to give the
bis(phosphino)disilanes (12) in 62-70% yield (Scheme
8). The colorless products 12 were crystalline solids that
were relatively stable in air and during brief heating
to 110-120 °C. The compounds 12 were readily soluble
in hexane, toluene, and THF. The 1H, 13C, and 29Si NMR
spectra and the elemental analysis of 12 were found to
be consistent with the proposed structures. The 29Si
NMR chemical shift of -7.2 to -9.0 ppm was shifted
downfield from -3.29 ppm for 12a -c.
F igu r e 7. Molecular structure of 10b with thermal
ellipsoids drawn at the 30% level.
hydride. An analogous PPh3-coordinated complex, cis-
[Pt(H)(SiPh3)(PPh3)2], also has dissimilar Pt-P bonds
(2.332(2) and 2.298(3) Å), which arises because the trans
influence of the SiPh3 ligand is greater than that of the
hydride.19 Serious deviation of the bond angles around
the metal center from the ideal 90 or 180° can be
attributed to the more severe steric repulsion between
the silyl and phosphine ligands than exists between the
hydride and other ligands.
A similar distorted-square-planar arrangement about
the platinum atom is found in (CabP,Si)Pt(H)[(PPh2)-
C2B10H11] (10b) (Figure 7). The platinum atom is bonded
to a hydrogen atom, two phosphorus atoms, and a silicon
atom. The atoms of the first platinum coordination
sphere display major deviations from planarity (mean
R ea ct ion of 12 w it h t h e P a lla d iu m Com p lex
P d 2(d b a )3 (6). Treatment of the disilanes 12 with
Pd2(dba)3 (6) in toluene at room temperature for 30 min
resulted in the oxidative addition of the Si-Si bond21
to the palladium center to form the cis-bis(chelate)
palladium complexes 8 (Scheme 9).
The composition and stereochemistry of 8 were elu-
1
cidated from their 31P, H, and 13C NMR spectra and
(20) Azizian, H.; Dixon, K. R.; Eaborn, C.; Pidcock, A.; Shuaib, N.
M.; Vinaixa, J . J . Chem. Soc., Chem. Commun. 1982, 1020.
(21) (a) Ozawa, F.; Sugawara, M.; Hayashi, T. Organometallics 1994,
13, 3237. (b) Murakami, M.; Yoshida, T.; Ito, Y. Organometallics 1994,
13, 2900. (c) Pan, Y.; Mague, J . T.; Fink, M. J . Organometallics 1992,
11, 3495. (d) Michalczyk, M. J .; Recatto, C. A.; Calabrese, J . C.; Fink,
M. J . J . Am. Chem. Soc. 1992, 114, 7955. (e) Heyn, R. H.; Tilley, T. D.
J . Am. Chem. Soc. 1992, 114, 1917 and references therein.
(19) Latif, L. A.; Eaborn, C.; Pidcock, A. P.; Weng, N. S. J .
Organomet. Chem. 1994, 474, 217.

212 Organometallics, Vol. 23, No. 2, 2004
Lee et al.
Sch em e 8. Syn th esis of
Bis(p h osp h in o-o-ca r bor a n yl)d isila n e 12a
palladium center by replacement of the dba ligands. The
reaction is not restricted to the PR2 (R ) Me (2a ), OEt
(2b)) derivatives; the bulkier bis((diphenylphosphino)-
o-carboranyl)disilane (2c) also results in the correspond-
ing cis-bis(chelate) 8c after oxidative addition of the
Si-Si bond, but only after extended reaction times.
Con clu sion s
The use of an o-carboranyl unit as the auxiliary ligand
backbone was found to result in an increase in the
difference in kinetic stability between the cis and trans
isomers, which enabled the isolation and full charac-
terization of 4a ,b and 7a , all having trans structures.
Thus, the steric bulkiness of the backbone connecting
Si to P in these CabP,Si systems engenders steric
constraints on the metal center that increase the kinetic
stability of the metal chelates. Therefore, our examina-
tion of the chelate-assisted oxidative addition reactions
of the phosphinosilanes has enabled us to reach the
following conclusions. Our success in demonstrating the
formation of kinetically stabilized trans-bis(chelates)
relies on the following two factors: (1) the bulkiness of
the alkyl groups in the phosphinosilanes and (2) the
rapid bis-chelation of the phosphinosilanes with a rigid
o-carborane backbone. We intend to use these principles
as we continue our research into the stereoselectivity
of the chelate-assisted oxidative addition reactions of
the d10 metal complexes.
a
Conditions: (i) 2 BunLi, THF, -78 °C; (ii) 2 PR2Cl, THF,
-78 °C.
Sch em e 9. Rea ction of P d 2(d ba )3 (6) w ith
Bis(p h osp h in o-o-ca r bor a n yl)d isila n e 2a
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under a dry, oxygen-free nitrogen or argon atmosphere using
standard Schlenk techniques or in a Vacuum Atmospheres
HE-493 drybox. Diethyl ether, toluene, hexane, and pentane
were distilled under nitrogen from sodium/benzophenone.
Dichloromethane was dried with CaH2. Benzene-d6 was dis-
tilled under nitrogen from sodium and stored in a Schlenk
storage flask until needed. CDCl3 was predried under CaH2
and vacuum-transferred. n-BuLi (1.6 M in hexanes) and
Pd2(dba)3 (6) were used as received from Aldrich. (PPh3)2Pt-
(CH2CH2) (3)22 and Pt(cod)2 (9)23 were obtained by literature
methods. All 1H (300.1 MHz, measured in CDCl3), 13C (75.4
MHz, measured in CDCl3), 31P (121.4 MHz, measured in
CDCl3), and 29Si NMR spectra (59.60 MHz, measured in
CDCl3) were recorded on a Varian Mercury-300BB spectrom-
eter unless otherwise stated. 1H and 13C NMR chemical shifts
are reported relative to Me4Si and were determined by
reference to the residual 1H or 13C solvent peaks. The IR
spectra were recorded on a Biorad FTS-165 spectrophotometer.
Elemental analyses were performed with a Carlo Erba Instru-
ments CHNS-O EA1108 analyzer.
P r ep a r a tion of (P h osp h in o-o-ca r bor a n yl)sila n es 2. A
representative procedure is as follows: to a solution of 0.721
g (5.0 mmol) of o-carborane in 20 mL of THF, precooled to -78
°C, was added 3.2 mL of n-butyllithium (1.6 M in hexanes).
The reaction mixture was warmed to room temperature and
stirred for 2 h, whereupon it was transferred, via cannula, to
a suspension of 5.5 mmol (1.1 equiv) of chlorodimethylphos-
phine in 20 mL of Et2O that was cooled to -78 °C. The
resultant yellow mixture was warmed to room temperature
and stirred for 2 h. The volatiles were then removed under
reduced pressure; the crude mixture was taken up in a
minimal amount of Et2O and the solution filtered through a 1
a
Conditions: (i) Pd2(dba)3 (6), toluene, 25 °C.
microanalysis data. Indeed, the NMR spectra of the
palladium complexes are in complete agreement with
an authentic sample of 8 (vide infra).
Although we did not investigate the mechanism in
detail, we believe that the phosphine tethers force the
Si-Si linkage into the proximity of the metal center by
precoordination and this accelerates the oxidative ad-
dition. The Si-Si bond then oxidatively adds to the
(22) Hartley, F. R. Organomet. Chem. Rev., Sect. A 1970, 6, 119.
(23) Spencer, J . L.; Ittel, S. D.; Cushing, M. A., J r. Inorg. Synth.
1979, 19, 213.

Stable trans-Bis(P,Si-chelate)metal Complexes
Organometallics, Vol. 23, No. 2, 2004 213
× 5 cm pad of silica gel on a glass frit. Removal of the volatiles
provided the final crude product, which was further crystal-
lized from toluene at -5 °C to provide pure o-carboranyl
phosphine 1a as a colorless solid.
Si2Pt: C, 23.84; H, 6.5. Found: C, 23.91; H, 6.69. Mp: 208-
210 °C dec. IR (KBr pellet, cm-1): 2955 w, 2928 w (νCH), 2577
s (νBH).
Gen er a l P r oced u r e for cis-5c a n d 8. Toluene (20 mL)
was added to a mixture of suitable metal reagent (0.30 mmol)
and 2 (0.60 mmol, 2 equiv). The mixture was stirred for 12 h,
and then the volatile compounds were removed under reduced
pressure. Extraction of the residue with toluene (2 × 15 mL),
followed by concentration and chromatography on silica with
1:1 hexane/benzene as eluent gave bis(chelates) as yellow
solids.
cis-5c. Anal. Calcd for B20C32H52P2Si2Pt: C, 39.78; H, 5.42.
Found: C, 39.85; H, 5.52. Mp: 245-248 °C dec. IR (KBr pellet,
cm-1): 3060 w, 2957 w, 2900 w (νCH), 2575 s (νBH).
cis-8a . Anal. Calcd for B20C12H44P2Si2Pd: C, 22.91; H, 7.05.
Found: C, 22.97; H, 7.10. Mp: 225-228 °C dec. IR (KBr pellet,
cm-1): 2959 w, 2917 w (νCH), 2606 s, 2561 s (νBH).
cis-8b. Anal. Calcd for B20C16H52O2P2Si2Pd: C, 26.79; H,
7.31. Found: C, 26.85; H, 7.42. Mp: 206-208 °C dec. IR (KBr
pellet, cm-1): 2992 w (νCH), 2603 s, 2567 s (νBH).
cis-8c. Anal. Calcd for B20C32H52P2Si2Pd: C, 43.80; H, 5.97.
Found: C, 43.85; H, 6.02. Mp: 225-227 °C dec. IR (KBr pellet,
cm-1): 3063 w, 2961 w (νCH), 2604 s, 2563 s (νBH).
THF (40 mL) and 4.0 mmol of 1a were added to the reaction
flask. The solution was cooled to -78 °C, n-butyllithium (2.6
mL, 4.16 mmol, 1.6 M in hexanes) was added. The solution
was warmed to room temperature, whereupon a thick suspen-
sion of white precipitate formed. After the reaction mixture
had been stirred for 1 h at room temperature, it was again
cooled to -78 °C and chlorodimethylsilane (1.1 equiv) was
added as a neat liquid. The solution was warmed to -5 °C
very slowly (for over 1 h) and stirred at -5 °C for a total of 3
h. The volatiles were then removed under reduced pressure;
the crude mixture was taken up in a minimal amount of Et2O
and filtered through a 1 × 5 cm pad of silica gel on a glass
frit. Removal of the volatiles provided the final crude product,
which was further crystallized from toluene at -5 °C to provide
pure ((dimethylphosphino)-o-carboranyl)silane (2a ) as a color-
less waxy solid. Yield: 92% (0.966 g, 3.7 mmol). Anal. Calcd
for B10C6H23PSi: C, 27.25; H, 8.77. Found: C, 27.17; H, 8.74.
IR (KBr pellet, cm-1): 2966 w, 2909 w (νCH), 2611 s, 2570 w
(νBH), 2162 w (νSiH).
10a . A solution containing 3 (0.30 mmol) and 2c (1 equiv)
in toluene was stirred for 2 h; conversion into 10a , as
monitored by 1H NMR spectroscopy, was quantitative. Re-
moval of the volatile material under reduced pressure gave a
light yellow oil, to which toluene (5 mL) was added. Cooling
the mixture to -5 °C resulted in precipitation of 10a as
colorless microcrystals. Yield: 89% (0.225 g, 0.27 mmol). Anal.
Calcd for B10C34H42P2SiPt: C, 48.39; H, 5.02. Found: C, 48.44;
H, 5.10. Mp: 198 °C dec. IR (KBr pellet, cm-1): 3051 w, 2957
w (νCH), 2581 s (νBH), 2029 s (νPtH).
10b. To a 20 mL solution containing 9 (0.3 mmol) in toluene
were added sequentially 1 equiv of 1c and 1 equiv of 2c, to
generate 10b in quantitative yield. The solution was filtered,
the volatiles were removed, and the resulting solid was
crystallized from toluene to give colorless microcrystals.
Yield: 82% (0.224 g, 0.25 mmol). Anal. Calcd for B20C30H48O2P2-
SiPt: C, 39.6; H, 5.32. Found: C, 40.01; H, 5.48. Mp: 225 °C
dec. IR (KBr pellet, cm-1): 3055 w, 3033 w, 2962 w (νCH), 2603
s, 2579 s, 2544 s (νBH), 2034 w, 1992 m (νPtH).
2b. A procedure analogous to the preparation of 2a was
used, but starting from chlorodiethoxyphosphine (0.861 g, 5.5
mmol) in benzene. Thus, 2b was crystallized from toluene at
-5 °C. Yield: 89% (1.148 g, 3.6 mmol). Anal. Calcd for
B
10C8H27O2PSi: C, 29.61; H, 8.39. Found: C, 29.51; H, 8.36.
IR (KBr pellet, cm-1): 2979 w, 2930 w (νCH), 2576 s (νBH), 2165
w (νSiH).
2c. A procedure analogous to the preparation of 2a was
used, but starting from chlorodiphenylphosphine (1.214 g, 5.5
mmol) in benzene. Thus, 2c was crystallized from toluene at
-5 °C. Yield: 82% (1.209 g, 3.3 mmol). Anal. Calcd for
B
10C16H27PSi: C, 49.45; H, 7.01. Found: C, 49.26; H, 7.03. IR
(KBr pellet, cm-1): 3058 m (νCH), 2570 s (νBH), 2170 m (νSiH).
Syn th esis of [η2-(p h osp h in o-o-ca r bor a n yl)silyl]m eta l
Com p lexes (Ca bP ,Si)2M. A representative procedure is as
follows: toluene (15 mL) was added to a mixture of (PPh3)2-
Pt(C2H4) (3; 0.224 g, 0.30 mmol) and 2a (0.157 g, 0.60 mmol).
The mixture was stirred for 3 h, and then the volatile
compound was removed under reduced pressure. Extraction
of the residue with toluene (20 mL), followed by concentration
of the extract to approximately half its volume and cooling to
-5 °C, resulted in crystallization of pure trans-4a . Yield: 73%
(0.157 g, 0.22 mmol). Anal. Calcd for B20C12H44P2PtSi2: C,
20.08; H, 6.18. Found: C, 20.12; H, 6.22. Mp: 235-237 °C dec.
IR (KBr pellet, cm-1): 2960 m, 2903 w (νCH), 2627 s, 2598 s,
2571 s (νBH).
P r ep a r a tion of th e Lin ea r Bis(p h osp h in o)d isila n e 1,2-
Bis(1-P R 2-o-ca r b or a n yl)-1,1,2,2-t e t r a m e t h yl-1,2-d isi-
la n e (R ) Me (12a ), OEt (12b), P h (12c)). A representative
procedure is as follows: to a solution of 0.806 g (2.0 mmol) of
bis(o-carboranyl)disilane 11 in 20 mL of THF, precooled to -78
°C, was added 2.5 mL of n-butyllithium (1.6 M in hexanes).
The reaction mixture was warmed to room temperature and
stirred for 2 h, whereupon it was transferred, via cannula, to
a suspension of 4.4 mmol (2.2 equiv) of chlorodimethylphos-
phine in 20 mL of Et2O that was cooled to -78 °C. The
resultant yellow mixture was warmed to room temperature
and stirred for 2 h. The volatiles were then removed under
reduced pressure; the crude mixture was taken up in a
minimal amount of Et2O and filtered through a 1 × 5 cm pad
of silica gel on a glass frit. Removal of the volatiles provided
the final crude product, which was further crystallized from
toluene at -5 °C to provide pure bis((dimethylphosphino)-o-
carboranyl)disilane (12a ) as a colorless solid. Yield: 70% (0.734
g, 1.4 mmol). Anal. Calcd for B20C12H44PSi: C, 27.35; H, 8.42.
tr a n s-4b. A procedure analogous to the preparation of 4a
was used, but starting from 2b (0.193 g, 0.60 mmol) in toluene.
Thus, 4b was crystallized from toluene at -5 °C. Yield: 76%
(0.184 g, 0.23 mmol). Anal. Calcd for B20C16H52O2P2Si2Pt: C,
23.84; H, 6.5. Found: C, 23.90; H, 6.72. Mp: 200-203 °C dec.
IR (KBr pellet, cm-1): 2985 w, 2896 w (νCH), 2611 s, 2566 s
(νBH).
cis-5a . DMAD (0.12 mL, 1.0 mmol) was added to a solution
of trans-4a (0.144 g, 0.20 mmol) in toluene (20 mL), and the
mixture was heated for 1 h at 110 °C; conversion into cis-5a ,
as monitored by 1H NMR spectroscopy, was quantitative. The
solvent was removed in vacuo and the resulting solid crystal-
lized from toluene at -5 °C to give 0.138 g (0.19 mmol) of
yellow microcrystals (96% yield). Anal. Calcd for B20C12H44P2-
PtSi2: C, 20.08; H, 6.18. Found: C, 20.15; H, 6.25. Mp: 239-
241 °C dec. IR (KBr pellet, cm-1): 2956 w, 2924 w, 2852 w
(νCH), 2607 s, 2568 s (νBH).
Found: C, 27.27; H, 8.39. Mp: 225-227 °C. 29Si NMR:
δ
-9.03. IR (KBr pellet, cm-1): 2982 m, 2910 m (νCH), 2611 s,
2586 s, 2569 s (νBH).
12b. A procedure analogous to the preparation of 12a was
used, but starting from chlorodiethoxyphosphine (0.689 g, 4.4
mmol) in benzene. Thus, 12b was crystallized from toluene at
-5 °C. Yield: 62% (0.743 g, 1.2 mmol). Anal. Calcd for
cis-5b. A procedure analogous to the preparation of cis-5a
was used, but starting from trans-4b (0.161 g, 0.20 mmol) in
toluene. Thus, cis-5b was crystallized from toluene at -5 °C.
Yield: 92% (0.148 g, 0.184 mmol). Anal. Calcd for B20C16H52O2P2-
B
20C16H52O2PSi: C, 31.25; H, 8.53. Found: C, 31.35; H, 8.50.
Mp: 230-233 °C. 29Si NMR: δ -8.95. IR (KBr pellet, cm-1):
2975 m, 2940 m (νCH), 2601 s, 2577 s, 2568 s (νBH).

214 Organometallics, Vol. 23, No. 2, 2004
Lee et al.
12c. A procedure analogous to the preparation of 12a was
used, but starting from chlorodiphenylphosphine (0.971 g, 4.4
mmol) in benzene. Thus, 12c was crystallized from toluene at
-5 °C. Yield: 68% (1.046 g, 1.4 mmol). Anal. Calcd for
configurations of the molecular systems were described by
double-ú STO basis sets with polarization functions for the H,
B, and C atoms, while triple-ú Slater type basis sets were
employed for the Si, P, and Pt atoms.31,32 The 1s electrons of
B and C, the 1s-2p electrons of Si and P, and the 1s-4d
electrons of Pt were treated as frozen cores. A set of auxiliary33
s, p, d, f, and g STO functions, centered on all nuclei, was used
in order to fit the molecular density and the Coulomb and
exchange potentials in each SCF cycle. Energy differences were
calculated by augmenting the local exchange-correlation po-
tential by Vosko et al.34 with Becke’s35 nonlocal exchange
corrections and Perdew’s36 nonlocal correlation corrections
(BP86). Geometries were optimized including nonlocal correc-
tions at this level of theory. First-order Pauli scalar relativistic
corrections37,38 were added variationally to the total energy for
all systems. In view of the fact that all systems investigated
in this work show a large HOMO-LUMO gap, a spin-
restricted formalism was used for all calculations. No sym-
metry constraints were used.
B
20C32H52PSi: C, 49.58; H, 6.77. Found: C, 49.41; H, 6.75.
Mp: 247-248 °C. 29Si NMR: δ -7.19. IR (KBr pellet, cm-1):
3051 w, 2955 w (νCH), 2611 w, 2575 s (νBH).
Rea ction of 12 w ith th e P a lla d iu m Com p lex P d 2(d ba )3
(6). Representative procedure: Toluene (15 mL) was added
to a mixture of Pd2(dba)3 (6; 0.092 g, 0.1 mmol) and 12a (0.115
g, 0.22 mmol). The mixture was stirred for 3 h, and then the
volatile compounds were removed under reduced pressure.
Extraction of the residue with toluene (20 mL), followed by
concentration of the extract to approximately half its volume
and cooling to -5 °C, resulted in crystallization of pure cis-
8a . Yield: 84% (0.107 g, 0.17 mmol).
cis-8b. A procedure analogous to the preparation of cis-8a
was used, but starting from 12b (0.122 g, 0.22 mmol) in
toluene. Thus, cis-8b was crystallized from toluene at -5 °C.
Yield: 81% (0.115 g, 0.16 mmol).
cis-8c. A procedure analogous to the preparation of cis-8a
was used, but starting from 12c (0.170 g, 0.22 mmol) in
toluene. Thus, cis-8c was crystallized from toluene at -5 °C.
Yield: 86% (0.150 g, 0.17 mmol).
Ack n ow led gm en t. We are grateful to the Korea
Research Foundation (Grant No. KRF-2002-015-CP0200)
for their financial support.
Cr ysta l Str u ctu r e Deter m in a tion . Crystals of 4a , 5a ,c,
8c, and 10a ,b were obtained from toluene, sealed in glass
capillaries under argon, and mounted on the diffractometer.
Data were collected and corrected for Lorentz and polarization
effects. Each structure was solved by the application of direct
methods using the SHELXS-96 program24a and least-squares
refinement using SHELXL-97.24b After anisotropic refinement
of all non-H atoms, several H atom positions could be located
in difference Fourier maps. These were refined isotropically,
while the remaining H atoms were calculated in idealized
positions and included in the refinement with fixed atomic
contributions. Further detailed information is given in Table
3.
Com p u ta tion a l Deta ils. Stationary points on the potential
energy surface were calculated using the Amsterdam Density
Functional (ADF) program, developed by Baerends et al.25,26
and vectorized by Ravenek.27 The numerical integration
scheme applied for the calculations was developed by te Velde
et al.28,29 The geometry optimization procedure was based on
the method due to Versluis and Ziegler.30 The electronic
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data (excluding structure factors) for the structures 4a , 5a ,c,
8c, and 10a ,b reported in this paper and listings giving
optimized geometries of the crucial structures (4a and 5a )
reported (Cartesian coordinates, in Å); crystallographic data
are also available in electronic form as CIF files. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM034112L
(28) te Velde, G.; Baerends, E. J . J . Comput. Chem. 1992, 99, 84.
(29) Boerrigter, P. M.; te Velde, G.; Baerends, E. J . Int. J . Quantum
Chem. 1988, 33, 87.
(30) Versluis, L.; Ziegler, T. J . Chem. Phys. 1988, 88, 322.
(31) Snijders, J . G.; Baerends, E. J .; Vernoijs, P. At. Nucl. Data
Tables 1982, 26, 483.
(32) Vernoijis, P.; Snijders, J . G.; Baerends, E. J . Slater Type Basis
Functions for the Whole Periodic System; Internal Report (in Dutch);
Department of Theoretical Chemistry, Free University: Amsterdam,
The Netherlands, 1981.
(33) Krijn, J .; Baerends, E. J . Fit Functions in the HFS Method;
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(27) Ravenek, W. In Algorithms and Applications on Vector and
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