Hydrogen migrations in rhodium silyl complexes: Silylene intermediates vs oxidative addition/reductive elimination

Article abstract of DOI:10.1021/om980158g

Reaction of (PMe₃)₄RhMe with H₂SiPh₂ results in elimination of CH₄ and generation of the rhodium silyl complex (Me₃P)₄RhSiHPh₂ (1; 62% isolated yield). Compound 1, which appears to adopt a trigonal bipyramidal geometry with the silyl group in an axial position, is in equilibrium with the 16-electron complex (Me₃P)₃RhSiHPh₂ (2). Reaction of (Me₃P)₃-RhCl with (THF)₂LiSiHMes₂ (Mes = 2,4,6-trimethylphenyl) in toluene resulted in formation of the metalated species fac-(Me₃P)₃Rh(H)Si(H)(Mes)C₆H ₂Me₂CH₂ (3), which was characterized by X-ray crystallography. Compound 3 was also prepared by the reaction of (Me₃P)₄-RhMe with H₂SiMes₂. The reaction of (Me₃P)₄RhMe with 1 equiv of D₂SiMes₂ in toluene resulted in distribution of deuterium between the Rh-H, SiH, RhCH₂, and o-Me positions of 3. Since the rate of this equilibration is not reduced in the presence of excess PMe₃, we propose that successive Si-H and C-H reductive-elimination/oxidative-addition cycles are responsible for the deuterium-scrambling process.

Full text of DOI:10.1021/om980158g

2912
Organometallics 1998, 17, 2912-2916
Hyd r ogen Migr a tion s in Rh od iu m Silyl Com p lexes:
Silylen e In ter m ed ia tes vs Oxid a tive Ad d ition /Red u ctive
Elim in a tion †
Gregory P. Mitchell and T. Don Tilley*
Department of Chemistry, University of California, Berkeley, Berkeley, California 94720-1460
Received March 4, 1998
Reaction of (PMe3)4RhMe with H2SiPh2 results in elimination of CH4 and generation of
the rhodium silyl complex (Me3P)4RhSiHPh2 (1; 62% isolated yield). Compound 1, which
appears to adopt a trigonal bipyramidal geometry with the silyl group in an axial position,
is in equilibrium with the 16-electron complex (Me3P)3RhSiHPh2 (2). Reaction of (Me3P)3-
RhCl with (THF)2LiSiHMes2 (Mes ) 2,4,6-trimethylphenyl) in toluene resulted in formation
of the metalated species fac-(Me3P)3Rh(H)Si(H)(Mes)C6H2Me2CH2 (3), which was character-
ized by X-ray crystallography. Compound 3 was also prepared by the reaction of (Me3P)4-
RhMe with H2SiMes2. The reaction of (Me3P)4RhMe with 1 equiv of D2SiMes2 in toluene
resulted in distribution of deuterium between the Rh-H, SiH, RhCH2, and o-Me positions
of 3. Since the rate of this equilibration is not reduced in the presence of excess PMe3, we
propose that successive Si-H and C-H reductive-elimination/oxidative-addition cycles are
responsible for the deuterium-scrambling process.
In tr od u ction
reactivity studies have been reported.4 However, direct
observation of an intramolecular migration leading to
a silylene complex has not been reported, although
numerous reports suggest this possibility on the basis
of indirect evidence.5,6 A detailed understanding of how
silylene complexes might arise via migratory rearrange-
ments is key to developing this area further, since
catalytic processes based on transition-metal silylene
intermediates would undoubtedly involve such migra-
tions.2
A primary focus of studies on transition-metal silicon
compounds has long been development of chemistry for
metal-bound silylene ligands.1,2 Possible applications
in catalysis have largely driven this interest,2 and
significant progress toward defining the properties and
reactivities of silylene complexes (LnMdSiR2) has been
made in recent years.3,4 Several routes to metal com-
plexes of divalent silicon are now established, and initial
† Dedicated to Professor Warren Roper, on the occasion of his 60th
birthday.
We have been interested in observing 1,2- and 1,3-
migrations which might generate unsaturated silicon
centers in transition-metal silicon compounds. Our
approach has involved the use of coordinatively unsat-
urated, electron-rich metal complexes that may initiate
1,2-migrations of a group from silicon to the metal
center. In related rhodium and iridium complexes, this
strategy has resulted in observation of several complex
rearrangements, which probably involve silylene inter-
mediates.6 Although intermediates of this type are
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S0276-7333(98)00158-7 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 06/05/1998

Hydrogen Migrations in Rhodium Silyl Complexes
Organometallics, Vol. 17, No. 13, 1998 2913
often invoked to explain observed rearrangements or
conversions in transition-metal-silicon systems, defini-
tive proof for their existence remains lacking, and
alternative mechanisms (most notably, based on oxida-
tive-addition/reductive-elimination sequences) are often
more likely. In this contribution, we describe rear-
rangements in a rhodium silyl complex which are in fact
most likely due to processes of the latter type.
via the reaction of (PMe3)3,4RhMe with HSiPh3.10 To
our knowledge, the five-coordinate complex (PMe3)4-
RhSiPh3 was not observed in the latter system, possibly
due to steric crowding about rhodium. In an analogous
iridium system, the hydride (PMe3)4IrH was reported
to react with Ph2SiH2 to give the Ir(III) silyl hydride
fac-(PMe3)3IrH2(SiHPh2).11
Compound 1 is somewhat thermally sensitive, decom-
posing to several unidentified hydride complexes upon
heating to 70 °C (1 h, benzene-d6). The presence of
greatly complicated Si-H and aryl regions in the 1H
NMR spectrum suggests that metalations of the phenyl
rings may represent major decomposition pathways.12
Attempts to induce hydride migration from silicon to
rhodium by removal of a phosphine ligand with B(C6F5)3
resulted in formation of a red-black solution and several
Resu lts a n d Discu ssion
Addition of 1 equiv of H2SiPh2 to (Me3P)4RhMe in
pentane resulted in gas evolution and formation of an
orange solution from which an orange powder was
1
isolated in 62% yield. The H NMR spectrum of this
compound (benzene-d6) indicates the absence of a meth-
yl ligand, and a new singlet at δ 5.50 is attributed to
an Si-H functionality (the latter resonance appears as
a complex multiplet at e-60 °C). The resonance for
the PMe3 ligands appears as a doublet at δ 1.09 (2J HP
) 3.6 Hz), and the integrated intensities in the spectrum
suggest formulation of the compound as (Me3P)4-
RhSiHPh2 (1; eq 1).
1
unidentified products (by H NMR spectroscopy).
In an attempt to observe clean hydrogen-migration
chemistry, we examined a related rhodium silyl complex
with sterically demanding mesityl groups. Reaction of
(Me3P)3RhCl with (THF)2LiSiHMes2 (Mes ) 2,4,6-
trimethylphenyl) in toluene resulted in formation of a
light yellow solution, from which colorless crystals of a
new product (3) were isolated after workup. The
presence of both Rh-H (δ -9.90) and Si-H (δ 5.76)
resonances in the 1H NMR spectrum of 3, and five
separate methyl signals, suggested the structure shown
in eq 2. Note that a similar intramolecular C-H
Variable-temperature 31P NMR studies suggest flux-
ional behavior attributed to two or more independent
processes. A broad signal in the 31P NMR spectrum at
δ -26.1 is observed at room temperature, and cooling
to -60 °C (toluene-d8) revealed two resonances at -8.43
and -26.21, in an approximate ratio of 1:3. Both
resonances are still somewhat broad at this tempera-
ture, with the upfield peak appearing as an unresolved
multiplet and the other peak as a doublet. This pattern
was observed previously for (PMe3)4RhMe7 and is
consistent with a trigonal-bipyramidal structure with
the silyl group in an axial position. Continued cooling
of the solution of 1 gives rise to further broadening of
the signals, and at -100 °C, three separate resonances
are present as a sharp signal at δ -63.2 (assigned to
free PMe3) and broad resonances at -9.2 and -34.5 ppm
(2:1 ratio; Rh-P and P-P couplings are obscured),
which are assigned to exchanging phosphine ligands of
square-planar 2.
activation of a mesityl-substituted silyl group in an
iridium(III) system was recently reported by Tobita and
Ogino.13
The structure of 3 was confirmed by X-ray diffraction
(Figure 1). The Rh-Si distance of 2.365(7) Å is slightly
longer than that reported for mer-RhCl(H)(SiHPh2)-
(PMe3)3 (2.313(4) Å),14 and hydrogen atoms on rhodium
and silicon were located and refined to provide Rh-H
and Si-H distances of 1.541(3) and 1.456(3) Å, respec-
tively. The small Si-Rh-C(1) angle of 80.16(7)° is
indicative of some strain in the five-membered ring.
Note that the substitution pattern about Rh is analo-
gous to that in fac-(Me3P)3Ir(CH3)(H)(SiPh3), formed via
oxidative addition of HSiPh3 to (PMe3)3IrMe.15 Al-
though 3 possesses two stereo centers, only one diaste-
reomer of the product was observed. Compound 3 is
considerably more stable than 1 and decomposes over
Although Rh(I) silyl complexes are in general some-
what rare,6,8-10 a few compounds of the type (PMe3)3-
RhSiR3 have been reported. Milstein prepared (PMe3)3-
RhSiMe2Ph, which displays C-F activation chemistry,9
and our group has reported the thermally unstable
complex (PMe3)3RhSiMe2SiMe(SiMe3)2.6 The square-
planar complex (PMe3)3RhSiPh3 has also been prepared
(11) Zarate, E. A.; Kennedy, V. O.; McCune, J . A.; Simons, R. S.;
Tessier, C. A. Organometallics 1995, 14, 1802.
(12) Aizenberg, M.; Milstein, D. Angew. Chem., Int. Ed. Engl. 1994,
33, 317.
(13) Okazaki, M.; Tobita, H.; Ogino, H. Chem. Lett. 1996, 477.
(14) Osakada, K.; Sarai, S.; Koizumi, T.; Yamamoto, T. Organome-
tallics 1997, 16, 3973.
(7) Price, R. T.; Andersen, R. A.; Muetterties, E. L. J . Organomet.
Chem. 1989, 376, 407.
(8) (a) J oslin, F. L.; Stobart, S. R. J . Chem. Soc., Chem. Commun.
1989, 504. (b) Hofmann, P.; Meier, C.; Hiller, W.; Heckel, M.; Riede,
J .; Schmidt, M. U. J . Organomet. Chem. 1995, 490, 51.
(9) Aizenberg, M.; Milstein, D. Science 1994, 265, 359.
(10) Thorn, D. L.; Harlow, R. L. Inorg. Chem. 1990, 29, 2017.
(15) Aizenberg, M.; Milstein, D. J . Am. Chem. Soc. 1995, 117, 6456.

2914 Organometallics, Vol. 17, No. 13, 1998
Mitchell and Tilley
the rates of rearrangement was observed (t1/2 ≈ 6 h),
implying that phosphine dissociation is not required for
hydrogen scrambling. We therefore propose that Si-H
and C-H reductive-elimination/oxidative-addition cycles
lead to the observed hydrogen migration reactions.
Note that C-H bond reductive elimination, coupled with
bond rotations in the resulting -CH2[3,5-Me2(2-SiHMes)-
C6H2] ligand, would distribute deuterium to the o-Me
positions of the mesityl groups. Caulton has recently
proposed that exchange of Si-H and Ru-H sites in the
16-electron complex RuH(SiHPh2)(CO)(PtBu2Me)2 takes
place via a similar mechanism, albeit at a much faster
rate (ca. 1 s-1).16 Attempts to observe the square-
planar intermediates shown in Scheme 1, by monitoring
the reaction by 31P NMR spectroscopy at -80 °C, were
not successful. Although the relative rates of Si-H vs
C-H reductive elimination are difficult to measure with
certainty, similar rates are implied by the 2H NMR
signals, all of which appear throughout the equilibration
in a ratio commensurate with a statistical distribution
of deuterium.
F igu r e 1. Molecular structure of 3.
2 days at 80 °C (benzene-d6) to a variety of uncharac-
terized products.
As expected, 3 may also be prepared via the reaction
of (Me3P)4RhCl with (THF)2LiSiHMes2 and by the
reaction of (Me3P)4RhMe and H2SiMes2. The former
reaction may involve the intermediate (Me3P)4-
RhSiHMes2, which is analogous to 1. However, no
intermediates were observed by monitoring the latter
reaction at 0 °C in toluene-d8 by 31P NMR spectroscopy,
suggesting that loss of PMe3 and metalation are ex-
tremely rapid at this temperature. Unfortunately, at
significantly lower temperatures, the reaction is too slow
to be monitored conveniently by NMR spectroscopy. A
large excess (ca. 30 equiv) of PMe3 does not generate
(Me3P)4RhSiHMes2, as determined by 1H and 31P NMR
spectroscopy.
Con clu sion
In this work, we have identified relatively simple
migration reactions in a rhodium silyl complex. On the
basis of the mechanistic information available, it ap-
pears that these reactions occur via oxidative-addition/
reductive-elimination steps. An alternative mechanism,
based on 1,2-migration of hydrogen from silicon to
rhodium, seems much less likely, on the basis of the
absence of a phosphine dependence on the rate of
hydrogen scrambling in 3. This conclusion is also
supported by the known chemical properties reported
for transition-metal silyl complexes.1 Thus, whereas
reductive-elimination/oxidative-addition cycles are facile
and commonly observed, direct observation of a 1,2-
migration reaction that produces a silylene ligand has
not yet been reported. Our efforts to observe such
migrations are continuing.
To investigate the mechanism of the process in eq 2,
we examined the reaction of (Me3P)4RhMe with 1 equiv
of D2SiMes2 in toluene. After 30 min at room temper-
ature, exclusive formation of fac-(Me3P)3Rh(H)Si(D)-
(Mes)C6H2Me2CH2 was observed (by 1H and 2H{1H}
Exp er im en ta l Section
NMR spectroscopy). Over 1 day, however, scrambling
1
of hydrogen into the Si-H position is observed (by H
All manipulations were performed under an inert atmo-
sphere using standard Schlenk techniques. Dry, oxygen-free
solvents were employed throughout. Diethyl ether, pentane,
and THF were distilled from sodium/benzophenone and stored
under nitrogen. Benzene-d6 and toluene-d8 were distilled from
Na/K alloy. The compounds (Me3P)4RhMe,7 (Me3P)3RhCl,17
NMR spectroscopy), and 2H{1H} NMR spectroscopy
demonstrated that deuterium had washed into the
Rh-H (δ -12.35), RhCH2 (δ 3.40), and o-Me (δ 2.84,
2.45, 2.23) positions of 3. On the basis of integrated
intensities for the deuterium resonances, it appears that
this deuterium scrambling gives a statistical distribu-
tion of deuterium over the Rh-H, Si-H, RhCH2, and
o-Me sites.
(THF)2LiSiHMes2,18 and H2SiMes2 were prepared according
19
to known procedures. The silane D2SiMes2 was prepared by
20
the reduction of Cl2SiMes2 with LiAlD4 in diethyl ether.
Diphenylsilane was purchased from Aldrich and used as
received. Elemental analyses were performed by the mi-
croanalytical laboratory at the University of California, Ber-
keley. IR samples were prepared as KBr pellets, and all
Several mechanisms for hydrogen exchange are pos-
sible, some of which are illustrated in Scheme 1.
Dissociation of PMe3 would create a 16-electron inter-
mediate, which could undergo a 1,2-hydrogen shift to
produce a silylene (or carbene) intermediate. Alterna-
tively, hydrogen scrambling may occur via oxidative-
addition/reductive-elimination cycles involving Si-H
and C-H bond activations. Since these two general
mechanisms may be distinguished by the phosphine
concentration dependence on the rate of scrambling, we
simultaneously monitored two scrambling reactions (by
2H{1H} NMR spectroscopy), one of which occurred in
the presence of ca. 40 equiv of PMe3. No difference in
absorptions are reported in units of cm-1 2H{1H} spectra were
.
(16) Gusev, D. G.; Nadasdi, T. T.; Caulton, K. G. Inorg. Chem. 1996,
35, 6772.
(17) J ones, R. A.; Real, F. R.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B.; Malik, K. M. A. J . Chem. Soc., Dalton Trans. 1980,
511.
(18) Roddick, D. M.; Heyn, R. H.; Tilley, T. D. Organometallics 1989,
8, 324.
(19) Braddock-Wilking, J .; Schieser, M.; Brammer, L.; Huhmann,
J .; Shaltout, R. J . Organomet. Chem. 1995, 499, 89.
(20) Fink, M. J .; Michalczyk, M. J .; Haller, K. J .; West, R.; Michl,
J . Organometallics 1984, 3, 793.

Hydrogen Migrations in Rhodium Silyl Complexes
Organometallics, Vol. 17, No. 13, 1998 2915
Sch em e 1
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 3
Ta ble 2. Cr ysta l a n d Da ta Collection P a r a m eter s
for 3
(a) Bond Distances
(a) Crystal Parameters
Rh-Si
2.3651(1)
2.302(1)
2.328(1)
2.354(2)
2.172(3)
C(1)-C(2)
C(2)-C(9)
Si-C(9)
1.514(4)
1.402(4)
1.886(3)
1.514(3)
1.456(3)
formula
fw
RhSiP3C27H40
598.60
Rh-P(1)
Rh-P(2)
Rh-P(3)
Rh-C(1)
cryst color, habit
cryst size, mm
cryst syst
space group
a, Å
colorless block
0.20 × 0.20 × 0.30
monoclinic
P21/ n (No. 14)
9.1148(1)
17.8498(1)
19.4996(3)
100.055(1)
3123.80(5)
4
Rh-H(1)
Si-H(2)
(b) Bond Angles
P(1)-Rh-Si
P(2)-Rh-Si
P(3)-Rh-Si
P(1)-Rh-P(2)
P(2)-Rh-P(3)
P(2)-Rh-C(1)
P(1)-Rh-Si
169.00(8)
96.77(3)
160.62(3)
97.84(3)
99.26(3)
88.92(8)
90.38(3)
C(2)-C(9)-Si
Rh-Si-C(9)
P(1)-Rh-P(3)
Si-Rh-C(1)
Rh-C(1)-C(2)
P(3)-Rh-C(1)
C(1)-C(2)-C(9)
113.3(2)
103.49(8)
98.13(3)
80.16(7)
117.9(2)
89.29(7)
119.4(2)
b, Å
c, Å
â, deg
V, Å3
Z
D(calc), g cm-3
µ(Mo KR), cm-1
temp, K
1.272
7.50
151
obtained with samples dissolved in toluene, and all other
spectra were recorded on samples in benzene-d6 solution.
(Me3P )4Rh SiHP h 2 (1). To a solution of (PMe3)4RhMe
(0.200 g, 0.474 mmol) in 10 mL of pentane was added a
pentane solution (5 mL) of H2SiPh2 (0.090 g, 0.488 mmol) over
a period of ca. 1 min. The reaction mixture immediately
changed from bright yellow to orange, with accompanying
evolution of gas. After the mixture was stirred for 15 min,
the solvent was removed under reduced pressure to leave an
orange residue, which was crystallized from 5 mL of pentane
at -78 °C to give 0.173 g (62%) of the product as an orange
powder. Anal. Calcd for RhSiP4C24H47: C, 48.82; H, 8.02.
Found: C, 48.50; H, 8.23. Mp: 100-102 °C dec. 1H NMR
(b) Data Collection
diffractometer
radiation
scan type
Siemens SMART
Mo KR (λ ) 0.710 69 Å)
ω (0.30° per frame)
20
12 976
4872 (Rint ) 0.027)
3905 (I > 3.00σ(I))
scan rate, s per frame
total no. of rflns collected
no of unique rflns
no. of observns
(c) Refinement
rflns/param ratio
R(F), %
R(wF), %
9.02
2.3
3.0
goodness of fit indicator
max peak in final diff map, e Å-3
min peak in final diff map, e Å-3
1.27
0.29
-0.28
2
(benzene-d6, 400 MHz, 25 °C): δ 1.09 (d, J HP ) 4.8 Hz, 36 H,
PMe3), 5.50 (s, 1 H, Si-H), 7.21 (t, 1 H, Ph), 7.31 (t, 2 H, Ph),
8.03 (d, 2 H, Ph). 1H NMR (toluene-d8, 400 MHz, -60 °C): δ
0.89 (s, axial PMe3), 1.16 (s, equatorial PMe3), 5.56 (m, SiH),
7.29 (t, Ar H), 7.41 (t, Ar H), 8.10 (d, Ar H). 13C{1H} NMR
(benzene-d6, 100.6 MHz): δ 23.5 (br s, PMe3), 126.5 (s, Ph),
127.0 (s, Ph), 137.7 (s, Ph), 149.7 (s, Ph). 31P{1H} NMR
(benzene-d6, 121.5 MHz, 25 °C): δ -26.1 (br s). 31P{1H} NMR
mL). Concentration of the combined extracts to ca. 10 mL and
cooling to -78 °C gave 0.361 g (75%) of pure 3. Anal. Calcd
for RhSiP3C27H40: C, 55.10; H, 6.85. Found: C, 54.94; H, 7.01.
Mp: 145-150 °C dec. 1H NMR (benzene-d6, 400 MHz): δ
-9.90 (dq, 1J HRh ) 160, 2J HP ) 10 Hz, 1 H, RhH), 0.87 (d, 2J HP
2
) 6.4 Hz, 9 H, PMe3), 1.00 (d, J HP ) 5.6 Hz, 9 H, PMe3), 1.03
2
(d, J HP ) 6.8 Hz, 9 H, PMe3), 2.21 (s, 3 H, Me), 2.32 (s, 3 H,
1
(toluene-d8, 121.5 MHz, -60 °C): δ -26.21 (br d, J PRh ) 158
Me), 2.45 (s, 3 H, Me), 2.67 (s, 3 H, Me), 3.03 (s, 3 H, Me), 3.45
(br s, 2 H, CH2), 5.76 (m, 1 H, Si-H), 6.75 (s, 1 H, Ar H), 6.82
(s, 1 H, Ar H), 7.01 (s, 1 H, Ar H), 7.23 (s, 1 H, Ar H). 13C{1H}
NMR (benzene-d6, 100.6 MHz): δ 18.3 (m, PMe3), 21.2 (s, Me),
21.5 (s, Me), 22.2 (s, Me), 23.7 (m, PMe3), 23.9 (m, PMe3), 25.64
(s, Me), 25.7 (s, Me), 34.9 (m, CH2), 125.9 (s, Ph), 126.2 (s, Ph),
128.2 (s, Ph), 128.6 (s, Ph), 128.8 (s, Ph), 130.0 (s, Ph), 136.1
(s, Ph), 136.6 (s, Ph), 141.9 (s, Ph), 142.1 (s, Ph), 142.4 (s, Ph),
141.9 (s, Ph), 146.8 (s, Ph). 31P{1H} NMR (toluene-d8, 121.5
Hz, equatorial PMe3), -8.43 (m, axial PMe3). 31P{1H} NMR
(toluene-d8, 121.5 MHz, -100 °C): δ -63.2 (s, free PMe3),
-34.5 (br s), -9.2 (br s). IR (KBr): 2909 s, 2856 s, 2005 s,
1324 m, 1292 s, 1256 s, 1151 s, 1124 m, 1092 m, 934 s, 764 m,
678 w, 621 w.
fa c-(Me3P )3Rh (H)SiH(Mes)C6H2Me2CH2 (3). A toluene
solution (15 mL) of (THF)2LiSiHMes2 (0.342 g, 0.818 mmol)
was added to a solution of (Me3P)3RhCl (0.300 g, 0.818 mmol)
in 15 mL of toluene. Stirring the resulting mixture for 5 h
resulted in formation of a light yellow solution and an off-white
precipitate. The solvent was removed under reduced pressure,
the resulting residue was then extracted into Et2O (2 × 10
1
2
MHz): δ -21.07 (dt, J PRh ) 82.6 Hz, J PP ) 25.9 Hz), -18.18
1
1
(dt, J PRh ) 93.9 Hz), -12.41 (dt, J PRh ) 89.1 Hz). IR (KBr):
2962 s, 2902 s, 2059 m, 1967 m, 1552 w, 1432 m, 1417 m, 1299
m, 1282 m, 943 s, 846 s, 782 s, 598 w, 551 w.

2916 Organometallics, Vol. 17, No. 13, 1998
Mitchell and Tilley
X-r a y Cr ysta l Str u ctu r e Deter m in a tion for 3. A color-
less trapezoidal crystal was mounted on a glass fiber using
Paratone N hydrocarbon oil. X-ray data were collected using
a Siemens SMART diffractometer with a CCD area detector.
The preliminary orientation matrix and unit cell parameters
were determined by collecting 60 10-second frames, followed
by spot integration and least-squares refinement. A hemi-
sphere of data was collected at a temperature of -112 ( 1 °C
using ω scans of 0.30° and a collection time of 20 s per frame.
Frame data were integrated using SAINT and corrected for
Lorentz and polarization effects. An absorption correction was
applied using XPREP (µR ) 0.08, Tmax ) 0.90, Tmin ) 0.82).
The 12 976 reflections which were integrated were averaged
were included at calculated positions but not refined. The
number of variable parameters was 433, giving a data/
parameter ratio of 9.02. The maximum and minimum peaks
on the final difference Fourier map corresponded to 0.29 and
-0.28 e/Å3: R ) 0.023, Rw ) 0.030, GOF ) 1.27. Selected bond
distances and angles are given in Table 1, and crystal and data
collection parameters are given in Table 2.
Ack n ow led gm en t is made to the National Science
Foundation for their generous support of this work.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal,
data collection, and refinement parameters, bond distances
and angles, and anisotropic displacement parameters (7
pages). Ordering information is given on any current mast-
head page.
in point group 2/m to yield 4872 unique reflections (Rint
)
0.027). No decay correction was necessary. The space group
was determined to be P21/n (No. 14). The structure was solved
using direct methods (SIR92) and refined by full-matrix least-
squares methods using teXsan software. The non-hydrogen
atoms were refined anisotropically, while the hydrogen atoms
OM980158G