Comparisons of photoinduced oxidative addition of B-H, B-B, and Si-H bonds at rhodium(η5-cyclopentadienyl)phosphine centers

Article abstract of DOI:10.1021/om060500m

Ultraviolet irradiation of [Rh(η⁵-C₅H ₅(PMe₃)(C₂H₄] (1a), [Rh(η₅-C₅H₅)(PPh₃)(C ₂H₄)] (1b), and [Rh(η⁵-C₅H ₄CF₃)(PMe₃)(C₂H₄)] (1c) (collectively abbreviated as [Rh(Cp′)(PR₃)(C₂H ₄)]) in the presence of HBpin (pinacolate = pin = l,2-O ₂C₂Me₄) results in elimination of C ₂H₄ and B-H oxidative addition, leading to the formation of boryl hydride complexes [Rh(Cp′)(Bpin)(H)(PR₃)]. Complete conversion is achieved in liquid HBpin or by photolysis in hexane at -10 °C. Similarly, photolysis of la-c in the presence of B₂pin₂ in hexane at -10 °C leads to B-B oxidative addition products, [Rh(Cp′)(Bpin)₂(PR₃)]. Irradiation at room temperature leads to formation of [Rh(Cp′)(PRs)₂] in addition to the desired products. The rhodium boryl products were characterized by multinuclear NMR spectroscopy and, in the case of [Rh(η⁵-C ₅H₅)(Bpin)(H)(PPh₃)], by X-ray crystallography. The structure reveals a Rh-B distance of 2.0196(15) A. The H...B separation of 2.09(2) Atogether with the bond angles at the metal suggest some residual H...B interaction. Photolysis of 1a-c in the presence of tertiary and secondary silanes (HSiEt₃, HSiⁱPr ₃, HSi(OMe)₃, HSiMe₂Et, HSiMeEt₂, and H₂SiEt₂) results in rhodium silyl hydride complexes [Rh(Cp′)(SiR′₂R″)(H)(PR₃)]. The structure of [Rh(η⁵-C₅H₅)(Si ⁱPr₃)(H)(PMe₃)] was determined by single-crystal X-ray diffraction, yielding a Rh-Si bond length of 2.3617(3) A and a Rh-H bond length of 1.508(17) A. The H...Si distance of 2.278(17) A and the very unequal H-Rh-P and H-Rh-Si angles suggest some residual H...Si interaction. Competition reactions were performed with Ib dissolved in hexane in the presence of HBpin and B₂pin₂ simultaneously. ³¹P NMR measurements, made after brief irradiation, showed a slight preference for B-B oxidative addition over B-H oxidative addition. Similar experiments with three-way competition among HBpin, HSiMe ₂Et, and HC₆F₅, analyzed by ¹H NMR spectroscopy, showed negligible selectivity among H-B, H-C, and H-Si oxidative addition. Molecular structures were also determined by single-crystal X-ray diffraction for 1b, 1c, [Rh(η⁵-C₅H₅) (PPh₃)₂], and [Rh(η₅-C₅H ₅)Cl₂(PPh₃)].

Full text of DOI:10.1021/om060500m

Organometallics 2006, 25, 5093-5104
5093
Comparisons of Photoinduced Oxidative Addition of B-H, B-B,
and Si-H Bonds at Rhodium(η5-cyclopentadienyl)phosphine
Centers
Marius V. Caˆmpian,† Jeremy L. Harris,† Naser Jasim,† Robin N. Perutz,*,†
Todd B. Marder,‡ and Adrian C. Whitwood†
Department of Chemistry, UniVersity of York, York, U.K., YO10 5DD, and Department of Chemistry,
UniVersity of Durham, Durham, U.K., DH1 3LE
ReceiVed June 6, 2006
Ultraviolet irradiation of [Rh(η5-C5H5)(PMe3)(C2H4)] (1a), [Rh(η5-C5H5)(PPh3)(C2H4)] (1b), and [Rh-
(η5-C5H4CF3)(PMe3)(C2H4)] (1c) (collectively abbreviated as [Rh(Cp′)(PR3)(C2H4)]) in the presence of
HBpin (pinacolate ) pin ) 1,2-O2C2Me4) results in elimination of C2H4 and B-H oxidative addition,
leading to the formation of boryl hydride complexes [Rh(Cp′)(Bpin)(H)(PR3)]. Complete conversion is
achieved in liquid HBpin or by photolysis in hexane at -10 °C. Similarly, photolysis of 1a-c in the
presence of B2pin2 in hexane at -10 °C leads to B-B oxidative addition products, [Rh(Cp′)(Bpin)2-
(PR3)]. Irradiation at room temperature leads to formation of [Rh(Cp′)(PR3)2] in addition to the desired
products. The rhodium boryl products were characterized by multinuclear NMR spectroscopy and, in the
case of [Rh(η5-C5H5)(Bpin)(H)(PPh3)], by X-ray crystallography. The structure reveals a Rh-B distance
of 2.0196(15) Å. The H‚‚‚B separation of 2.09(2) Å together with the bond angles at the metal suggest
some residual H‚‚‚B interaction. Photolysis of 1a-c in the presence of tertiary and secondary silanes
(HSiEt3, HSiiPr3, HSi(OMe)3, HSiMe2Et, HSiMeEt2, and H2SiEt2) results in rhodium silyl hydride
complexes [Rh(Cp′)(SiR′2R′′)(H)(PR3)]. The structure of [Rh(η5-C5H5)(SiiPr3)(H)(PMe3)] was determined
by single-crystal X-ray diffraction, yielding a Rh-Si bond length of 2.3617(3) Å and a Rh-H bond
length of 1.508(17) Å. The H‚‚‚Si distance of 2.278(17) Å and the very unequal H-Rh-P and H-Rh-
Si angles suggest some residual H‚‚‚Si interaction. Competition reactions were performed with 1b dissolved
in hexane in the presence of HBpin and B2pin2 simultaneously. 31P NMR measurements, made after
brief irradiation, showed a slight preference for B-B oxidative addition over B-H oxidative addition.
1
Similar experiments with three-way competition among HBpin, HSiMe2Et, and HC6F5, analyzed by H
NMR spectroscopy, showed negligible selectivity among H-B, H-C, and H-Si oxidative addition.
Molecular structures were also determined by single-crystal X-ray diffraction for 1b, 1c, [Rh(η5-C5H5)-
(PPh3)2], and [Rh(η5-C5H5)Cl2(PPh3)].
) 4,4′-di-tert-butyl-2,2′-bipyridine), proceeding via the reac-
tion intermediate [Ir(Bpin)3(dtbpy)].6,11 The borylation of het-
eroaromatics and polycyclic aromatics with this catalyst has
proved very effective.6,12 The reactions of late transition met-
al complexes with boranes, HB(OR)2 [(OR)2 is usually pina-
colate ) pin ) 1,2-O2C2Me4 or catecholate ) cat ) 1,2-
O2C6H4] can involve either B-H oxidative addition to yield
boryl hydride complexes5,13 or formation of σ-B-H com-
Introduction
In the last few years, major advances have been made in
transition-metal-catalyzed borylation of C-H bonds in arenes,
alkanes, and heterocyclic compounds.1-10 These reactions
can be considered as a combination of C-H bond activation
with either B-H or B-B activation. One of the most effective
catalysts is recognized to be [Ir(cod)(OMe)]2 + dtbpy (dtbpy
* Corresponding author. E-mail: mp1@york.ac.uk.
† University of York.
(7) (a) Iverson, C. N.; Smith, M. R., III. J. Am. Chem. Soc. 1999, 121,
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2831. (c) Cho, J. Y.; Iverson, C. N.; Smith, M. R., III. J. Am. Chem. Soc.
2000, 122, 12868. (d) Chotana, G. A.; Rak, M. A.; Smith, M. R., III. J.
Am. Chem. Soc. 2005, 127, 10539.
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Soc. 2004, 126, 15334.
(9) Dick, A. R.; Sanford, M. S. Tetrahedron 2006, 62, 2439.
(10) Kurotobi, K.; Miyauchi, M.; Takakura, K.; Murafuji, T.; Sugihara,
Y. Eur. J. Org. Chem. 2003, 3663.
‡ University of Durham.
(1) (a) Waltz, K. M.; Hartwig, J. F. Science 1997, 277, 211. (b) Chen,
H.; Schlecht, S.; Semple, T. C.; Hartwig, J. F. Science 2000, 287, 1995. (c)
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I. A. I.; Coventry, D. N.; Albesa-Jove´, D.; Batsanov, A. S.; Howard, J. A.
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Ishida, K.; Takagi, J.; Miyaura, N. Chem. Lett. 2001, 1082. (c) Takagi, J.;
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10.1021/om060500m CCC: $33.50 © 2006 American Chemical Society
Publication on Web 09/15/2006

5094 Organometallics, Vol. 25, No. 21, 2006
Caˆmpian et al.
plexes.14,15 B-H oxidative addition is also implicated in catalytic
hydroboration and dehydrogenative borylation of alkenes.2,16,17
Equivalent principles apply to borylation with diboranes (RO)2BB-
(OR)2 where B-B oxidative addition dominates.5,18 The forma-
tion and properties of metal boryl complexes, key intermediates
in all of these reactions have been reviewed.19 Borylation
reactions have also been studied in detail by theoretical
methods.20
Photochemical B-H oxidative addition was first mentioned
by Hartwig as a very low yield process for [W(η5-C5H5)2H2].21
In 2004, we reported photoinduced B-H oxidative addition of
HBpin at [Ru(depe)2H2] and [Rh(triphos)H3].22 We used laser
flash photolysis to measure the second-order rate constants for
oxidative addition of boranes and found that the rate constants
for reaction of {Ru(depe)2} and the related intermediates
followed the order k(H2) > k(HBpin) > k(Et3SiH). Photochemi-
cal B-B oxidative addition occurs cleanly on irradiation of
[W(η5-C5H5)2H2] with B2(cat-3,5-tBu)2, yielding [W(η5-C5H5)2-
(Bcat-3,5-tBu2)2]; notably, B-B activation occurs in preference
to C-H activation of the benzene solvent or the C-H bonds
of the substrate.21 Similarly, irradiation of [Re(η5-C5Me5)(CO)3]
with B2pin2 yields cis and trans isomers of [Re(η5-C5Me5)-
(Bpin)2(CO)2].1c
Hartwig et al. have shown that the photochemical reaction
of HBpin in cyclohexane with [Rh(η5-C5Me5)(η4-C6Me6)] yields
boryl hydride complex [Rh(η5-C5Me5)(H)2(Bpin)2], which reacts
in neat HBpin to form [Rh(η5-C5Me5)(H)(Bpin)3] and release
H2; both complexes are formally in the Rh(V) oxidation state.
Structural and computational investigations suggest that these
complexes each involve one partial B‚‚‚H bond.23 These two
complexes and [Rh(η5-C5Me5)(η4-C6Me6)] are active catalysts
for the borylation of hydrocarbons.8,23 Thermal reaction of [Rh-
(η5-C5Me5)(H)2(Bpin)2] with P(p-tol)3 yields the Rh(III) complex
[Rh(η5-C5Me5)(H)(Bpin){P(p-tol)3}], while reaction of [Rh(η5-
C5Me5)(H)(Bpin)3] with PEt3 yields [Rh(η5-C5Me5)(Bpin)2-
(PEt3)]. Thermal or photochemical reaction of [Rh(η5-C5Me5)-
(H)2(SiEt3)2] with HBpin yields [Rh(η5-C5Me5)(H)2(SiEt3)(Bpin)],
another complex with partial B‚‚‚H bonding. This species reacts
with P(p-tol)3 to give a mixture of boryl hydride and silyl
hydride complexes of [Rh(η5-C5Me5){P(p-tol)3}].24 The very
closely related complex [Ir(η5-C5Me5)(H)(Bpin)(PMe3)] was
synthesized by Iverson and Smith by displacement of cyclo-
hexane from the cyclohexyl hydride complex with HBpin and
was the first complex demonstrated to be a catalyst precursor
for the borylation of benzene.7
Photoinduced Si-H bond oxidative addition is long estab-
lished,25 and we have used it as a benchmark in laser studies of
the reaction of coordinatively unsaturated complexes derived
by photolysis of metal dihydride complexes.26 We have also
studied the oxidative addition of trialkylsilanes at rhodium by
photolysis of [Rh(η5-C5H5)(C2H4)2] and its derivatives.27 Related
reactions have been reported at C5Me5 complexes28 and at
dinuclear rhodium complexes with linked cyclopentadienyl
groups.29 Silyl hydride species are key intermediates in catalytic
hydrosilation,30 a process that is practiced on an industrial
scale.31
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leads to the formation of an unsaturated 16e- species capable
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Photoinduced OxidatiVe Addition at Rh Centers
Table 1. Selected NMR Spectroscopic Data in C6D6 [δ (J/Hz)] for Precursors and Products of Photoreaction with Boranes
1a 1b 1c
Organometallics, Vol. 25, No. 21, 2006 5095
1H Cp
5.09 s, 5H
5.06 s, 5H
5.18 br m, 2H
4.99 br m, 2H
0.71 dd, JPH 9.6
JRhH 1.1, 9H
2.80 br m, 2H,
1.49 br m, 2H
1H PR3
1H C2H4
0.77 dd, JPH 9.2,
RhH 1.1, 9H
6.75-7.65 m, 15H
J
2.74 m, 2H
1.46 m, 2H
4.4 d, JRhP 200
2.83 m, 2H
1.31 m, 2H
59.5 d, JRhP 210
31P{1H}
6.9 dq, JRhP 198, JPF
-54.4 m
2
19F
2a
2b
2c
1H hydride
1H Cp
-14.04 dd, JPH 33.7, JRhH 35.1
-13.04 dd, JPH 29.6, JRhH 32.8
-14.58 dd, JPH 34.6, JRhH 36.8
5.19 br s, 5.31 br s, 5.52 br s, 5.75 br s
13.7 d, JRhP 169
5.36 s
5.33 s
31P{1H}
11B
12.4 d, JRhP 170
45.4
62.5 d, JRhP 180
44.8
43.9
3a
3b
3c
1H Cp
5.29 s
-2.2 d, JRhP 217
5.10 s
58.3 d, JRhP 223
4.64 br s, 5.01 br s, 5.30 br s, 5.52 vs
-0.8 d, JRhP 215
31P{1H}
4a
4b
4c
1H Cp
31P{1H}
11B
5.46 s
14.8 d, JRhP177
45.1
5.41 s
55.5 d, JRhP 182
43.7
5.43 br s, 5.76 br s
19.0 d, JRhP 176
43.8
of activating aromatic C-H bonds and Si-H bonds. The
photochemistry of [Rh(η5-C5H5)(PMe3)(C2H4)] (1a) was inten-
sively studied by Perutz et al. in C-H bond activation reactions
of arenes34 and partially fluorinated aromatic hydrocarbons.35
The activation of a C-H bond of benzene was shown by laser
flash photolysis to occur via an η2-C6H6 intermediate. Further
investigations revealed stable η2-arene complexes, equilibria
between aryl hydride and η2-arene complexes, and C-F bond
activation reactions.36,37 Complementary studies of η5-C5Me5
analogues, usually formed by thermal reaction of [Rh(η5-C5-
Me5)(PMe3)(C6H5)(H)] or by photochemical reaction of [Rh-
(η5-C5Me5)(PMe3)(H)2], have been studied extensively by Jones
et al.35,36,38,39
The effect of an electron-withdrawing CF3 group on the
properties of metallocenes and methylated metallocenes was
investigated by Gassman et al.44,45 Notably, the redox potential
of [Fe(η5-C5H4CF3)(η5-C5H5)] is shifted by 0.64 V with respect
to ferrocene. The C5H4CF3 group also has a marked effect on
the kinetics of substitution reactions of cyclopentadienyl
rhodium dicarbonyls,46 but little effect on charge-transfer
complexes with sulfur dioxide.47
In this paper, we describe the photochemical reactivity of
complexes 1a, 1b, and [Rh(η5-C5H4CF3)(PMe3)(C2H4)] (1c) in
the presence of B-H-, B-B-, and Si-H-containing reagents.
We show that 1a-c undergo B-H oxidative addition with
HBpin, B-B oxidative addition with B2pin2, and Si-H oxida-
tive addition with a variety of silanes. All of the products were
characterized by NMR spectroscopy, and a few representative
examples were chosen for more detailed spectroscopy and
crystallography. We also report the relative yields of oxidative
addition of B-H, B-B, Si-H, and C-H bonds investigated
by competition reactions, the first such comparison.
The complex [Rh(η5-C5H5)(PPh3)(C2H4)] (1b) was first
reported by Oliver and Graham;40 it was also observed as a
photolytic27 or thermal41 reaction product of [Rh(η5-C5H5)-
(C2H4)2] in the presence of PPh3. The photochemistry of 1b
resembles that of 1a, but has not been investigated as exten-
sively. Partially fluorinated benzenes form C-H bond activation
products that are stable at room temperature. Irradiation of 1b
in neat tertiary alkyl silanes R3SiH (R ) Et, iPr) generates single
products assigned to the Si-H activation complexes; [Rh(η5-
C5H5)(PPh3)(SiiPr3)(H)] has been characterized crystallographi-
cally.42 The related complexes [Rh(η5:η1-C5H4SiMe2CH2PPh2)-
(C2H4)] and [Rh(η5:η1-C5H4SiMe2CH2PPh2)(H)2] have been
studied by Jones et al.43
Results
Starting Materials. Complexes 1a and 1b were synthesized
by standard procedures, but 1c has not been reported previously.
The sample of 1c was synthesized by a procedure similar to
that for 1b, but using Tl(η5-C5H4CF3) instead of Li(C5H5).44
NMR data for 1a, 1b, and 1c are summarized in Table 1.
Crystals of 1b, suitable for X-ray diffraction, were obtained
from hexane at -18 °C; the molecular structure of 1b is shown
(34) (a) Belt, S. T.; Duckett, S. B.; Helliwell, M.; Perutz, R. N. J. Chem.
Soc., Chem. Commun. 1989, 928. (b) Belt, S. T.; Dong, L.; Duckett, S. B.;
Jones, W. D.; Partridge, M. G.; Perutz, R. N. J. Chem. Soc., Chem. Commun.
1991, 266.
(35) Selmeczy, A. D.; Jones, W. D.; Partridge, M. G.; Perutz, R. N.
Organometallics 1994, 13, 522.
(36) (a) Belt, S. T.; Helliwell, M.; Jones, W. D.; Partridge, M. G.; Perutz,
R. N. J. Am. Chem. Soc. 1993, 115, 1429. (b) Chin, R. M.; Dong, L.;
Duckett, S. B.; Partridge, M. G.; Jones, W. D.; Perutz, R. N. J. Am. Chem.
Soc. 1993, 115, 7685.
(37) Ballhorn, M.; Partridge, M. G.; Perutz, R. N.; Whittlesey, M. K. J.
Chem. Soc., Chem. Commun. 1996, 961.
(38) Jones, W. D. Inorg. Chem. 2005, 44, 4475.
(43) Lefort, L.; Crane, T. W.; Farwell, M. D.; Baruch, D. M.; Kaeuper,
J. A.; Lachicotte, R. J.; Jones, W. D. Organometallics 1998, 17, 3889.
(44) Gassman, P. G.; Winter, C. H. J. Am. Chem. Soc. 1986, 108, 4228.
(45) Gassman, P. G.; Mickelson, J. W.; Sowa, J. R. J. Am. Chem. Soc.
1992, 114, 6942.
(46) Cheong, M.; Basolo, F. Organometallics 1988, 7, 2041.
(47) Hall, C.; Harris, J. L.; Killey, A.; Maddox, T. P.; Palmer, S.; Perutz,
R. N.; Rooney, A. D.; Goff, S. E. J.; Kazarian, S. G.; Poliakoff, M. J.
Chem. Soc., Dalton Trans. 1994, 3515.
(39) Jones, W. D. Acc. Chem. Res. 2003, 36, 140.
(40) Oliver, A. J.; Graham, W. A. G. Inorg. Chem. 1971, 10, 1165.
(41) Belt, S. T.; Duckett, S. B.; Haddleton, D. M.; Perutz, R. N.
Organometallics 1989, 8, 748.
(42) Heaton, S. N.; Partridge, M. G.; Perutz, R. N.; Parsons, S. J.;
Zimmermann, F. J. Chem. Soc., Dalton Trans. 1998, 2515.

5096 Organometallics, Vol. 25, No. 21, 2006
Caˆmpian et al.
Figure 1. Molecular structure of 1c (thermal ellipsoids shown at
50% probability, hydrogen atoms omitted).
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1c
Rh-P(1)
2.2149(5)
2.106(3)
2.106(2)
1.407(5)
1.473(3)
C(6)-Rh(1)-C(7)
C(7)-Rh(1)-P(1)
C(8)-Rh(1)-P(1)
39.02(14)
94.84(8)
91.46(8)
Figure 2. Molecular structure (50% thermal ellipsoids) of 2b, with
hydrogen atoms omitted except for H1A.
Rh(1)-C(7)
Rh(1)-C(8)
C(7)-C(8)
C(1)-C(6)
C(6)-F
P(1)-Rh(1)-C(1) 162.38(6)
carbon shows an upfield shift on borylation. The chirality of
the rhodium center could be expected to lead to four inequivalent
1.313(3)-1.353(3)
Rh(1)-C(Cp) 2.232(2)-2.295(2)
1
methyl resonances in the 13C and in the H NMR spectra. The
presence of only two Bpin methyl resonances in the 13C
in Figure S1 (Supporting Information). The ethene hydrogen
atoms were located and refined. The structure is similar to those
of [Rh(η5-C5Me5)(PPh3)(C2H4)]48 and [Rh(η5-C5H5)(PPh3)-
(CO)].49
Crystals of 1c suitable for X-ray crystallography were
obtained by very slow sublimation under vacuum. The Rh-C
bond lengths of the coordinated ethene ligand (Table 2, Figure
1) are equal (2.106 Å) and insignificantly different from those
of 1b; changes in other bond lengths are also minimal. As for
1b, we can define an approximate mirror plane passing through
the rhodium and phosphorus atoms and the center of the ethene
CdC bond.
spectrum is consistent with rapid rotation about the Rh-B bond;
1
the corresponding H resonances are not resolved.
Traces of the bis(phosphine) byproduct 3a were also observed
by NMR spectroscopy in reactions of the fragment {Rh(η5-
C5H5)(PMe3)} in the presence of partially fluorinated arenes.50
Complex 3a exhibits a doublet in the 31P{1H} NMR spectrum
at δ -2.2 with a JRhP value of 217 Hz characteristic of a half-
sandwich Rh(I) complex.51
The photolysis of 1b at room temperature in the presence of
HBpin follows the same path as that for 1a. The product, [Rh-
(η5-C5H5)(H)(Bpin)(PPh3)] (2b), shows spectra similar to 2a,
but the coupling constants, JPH ) 29.6 and JRhH ) 32.8 Hz, of
the products are smaller than for the PMe3 analogue, while JRhP
is characteristically larger. Similar changes are observed in the
spectra of other complexes on replacing PMe3 by PPh3 (see
below). Both the 1H and the 13C NMR spectra show two closely
spaced resonances for the Bpin methyl groups. The full widths
at half-height of the hydride peaks for 2b are essentially identical
to those for analogues in which the boryl group is replaced by
a silyl or a fluoroaryl group (see Competition Reactions below).
It follows that any residual BH spin-spin coupling is negligible.
Initial reactions carried out on a small scale yielded mixtures
of 2b and 3b. A larger scale reaction, with careful control of
the photolysis time, yielded 2b only, with complete conversion
to product; chromatographic purification yielded an analytically
pure sample.
It was already known that 3b is formed photochemically from
[Rh(η5-C5H5)(C2H4)2] in the presence of 2 equiv of PPh341 and
also thermally from reaction of [Rh(η5-C5H5)(PPh3)(C2H4)] with
PPh3.27 To establish the source of 3b, we investigated the
thermal reaction of each of 1b and 2b with triphenylphosphine
by heating to 75 °C overnight. [Rh(η5-C5H5)(PPh3)2] (3b) was
formed both from the Rh(I) and from the Rh(III) species.
We succeeded in avoiding the formation of complexes 3a
and 3b and in obtaining only the boryl complexes, by lowering
the photolysis temperature to -10 °C and/or by using HBpin
as a solvent as well as a substrate. This strategy also resulted
in the desired product [Rh(η5-C5H4CF3)(Bpin)(H)(PMe3)] (2c)
on photolysis of [Rh(η5-C5H4CF3)(PMe3)(C2H4)] (1c). Relevant
Reactions with HBpin. Photochemical reaction of a solution
of 1a and HBpin in hexane, contained in a Pyrex NMR tube (λ
> 290 nm), at room temperature, leads to formation of the
hydride boryl complex [Rh(η5-C5H5)(H)(Bpin)(PMe3)] (2a) and
the bis(phosphine) complex [Rh(η5-C5H5)(PMe3)2] (3a). When
the photolysis temperature is reduced to about -10 °C, 2a is
still formed, but there is a drastic decrease in formation of
byproduct 3a. Irradiation of 1a in neat HBpin at -10 °C leads
to formation of the desired product 2a only; after 15 h,
conversion is complete (Scheme 1). Complex 2a can be purified
by sublimation at 35 °C, yielding a white solid. The boryl
complex 2a exhibits a doublet in the 31P{1H} NMR spectrum
at δ 12.4 with a coupling constant JRhP ) 170 Hz characteristic
of a half-sandwich Rh(III) complex. In this complex, and its
analogues, the 31P resonance is shifted downfield of the
precursor, here 1a. With partial 1H decoupling, the 31P resonance
becomes a doublet of doublets, consistent with the presence of
a single hydride in the molecule. In keeping with a Rh(III)
complex, the 1H NMR spectrum reveals a hydride resonance at
δ -14.04 as a doublet of doublets (JPH ) 33.7, JRhH ) 35.1
Hz). The Bpin methyl groups are all coincident at δ 1.16 in the
1H NMR spectrum. The 11B NMR spectrum of the boryl product
2a reveals a broad resonance at δ 45.4 in the region charac-
teristic of metal-boryl complexes19 and to low field of HBpin
(δ 27.2). Broad-band proton decoupling did not affect the 11B
resonance of 2a or of the other boryl complexes reported here.
In the 13C{1H} spectrum, the Bpin resonances of 2a are found
at 81.2 (s, BO2C2(CH3)4), 25.4 (s, BO2C2(CH3)4), and 25.3 (s,
BO2C2(CH3)4) compared to free HBpin, which resonates at δ
83.1 and 24.9. As has been observed previously,22 the quaternary
(50) Cronin, L.; Higgitt, C. L.; Perutz, R. N. Organometallics 2000, 19,
672.
(48) Porzio, W.; Zocchi, M. J. Am. Chem. Soc. 1978, 100, 2048.
(49) Choi, M.-G.; Brown, T. L. Inorg. Chem. 1993, 32, 5603.
(51) Jones, R. A.; Mayor Real, F.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1981, 126.

Photoinduced OxidatiVe Addition at Rh Centers
Organometallics, Vol. 25, No. 21, 2006 5097
Scheme 1. Photochemical Reactions of 1a-1c
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2b
analogue of 2b. NMR spectroscopic data include a hydride
resonance at δ -13.08 (JRhH ) JPH ) 33.8 Hz) and a JRhP value
of 179 Hz, as well as an 11B resonance at δ 42.3.23 They reported
no NMR spectroscopic evidence for B‚‚‚H interaction. The
molecular structure of [Rh(η5-C5Me5)(H)(Bpin){P(p-tol)3}] was
also determined by X-ray diffraction data at 183 K, which gave
Rh-B ) 2.029(4) Å, Rh-H ) 1.42(3) Å, B-Rh-H ) 78.5-
(12)°, and a resulting H‚‚‚B separation of 2.23(3) Å.
Rh(1)-P(1) 2.2157(4)
Rh(1)-B(1) 2.0196(15)
B(1)-Rh(1)-P(1)
88.82(4)
O(1)-B(1)-Rh(1) 125.87(10)
O(2)-B(1)-Rh(1) 123.44(10)
B(1)-O(1)
B(1)-O(2)
1.3835(18)
1.3909(18)
O(1)-B(1)-O(2)
110.67(12)
Rh(1)-C(Cp) 2.2233(14)-2.3198(14) H(1A)-Rh(1)-B(1) 71.0(8)
C(6)-O(1)
C(7)-O(2)
1.4533(16)
1.4601(16)
Rh(1)-H(1A) 1.50(2)
H(1A)-Rh(1)-P(1) 88.5(8)
B(1)‚‚‚H(1A) 2.09(2)
We would anticipate that the degree of formal oxidative
addition of the B-H bond will be enhanced by electron-rich
metal centers. Comparison of the structures of 2b and [Rh(η5-
C5Me5)(H)(Bpin){P(p-tol)3}] show changes in the expected
direction with a decrease in r(Rh-H), an increase in H‚‚‚B,
and a less acute B-Rh-H angle. The differences are on the
order of 3σ in r(Rh-H), but 7σ in the B-Rh-H angle. DFT
calculations18 on the model complex [Rh(η5-C5H5)(H)(BOCH2-
CH2O)(PH3)], where the C5Me5 was replaced by C5H5, Bpin
by BOCH2CH2O, and P(p-tol)3 by PH3, gave Rh-B ) 2.033
Å, Rh-H ) 1.56 Å, B-Rh-H ) 71.7°, and a resulting B‚‚‚H
separation of 2.14 Å. These values are indeed closer to the
measurements on 2b as expected by the reduction in electron-
donating ability of the ligands. Importantly, there must be a
continuum of structures available representing various degrees
of oxidative addition, and the differences in structure between
2b and [Rh(η5-C5Me5)(H)(Bpin){P(p-tol)3}], especially in the
B-Rh-H angle, show this clearly. In 2b, the B‚‚‚H interaction
is demonstrably stronger than in [Rh(η5-C5Me5)(H)(Bpin){P(p-
tol)3}], although neither can be described as a σ-borane complex,
and the lack of BH coupling in solution is significant.53
A hexane solution containing a mixture of 2b and 3b, formed
by photoreaction of 1b with HBpin at room temperature, was
left at -18 °C, yielding orange crystals, which were also
investigated by X-ray diffraction. The crystal structure reveals
NMR spectroscopic data for the products are summarized in
Table 1 and illustrated in the Supporting Information (Figures
S8-S10).
Orange crystals of 2b, from the large-scale preparation, were
grown from hexane at room temperature. The crystal structure
(Figure 2, Table 3) confirmed the identity of the product and
showed a Rh-B distance of 2.0196(15) Å. The puckering of
the boronate ring was indicated by the torsional angle B(1)-
O(1)-C(6)-C(7) of -19.69(14)°. The B(1)-Rh(1)-P(1) angle
is 88.82(4)°, close to the expected value for a pseudo-octahedral
complex. The hydride was located in the difference map and
was refined at a Rh(1)-H(1A) distance of 1.50(2) Å with an
acute B(1)-Rh(1)-H(1A) angle of 71.0(8)°, leading to an
H‚‚‚B separation of 2.09(2) Å. The P(1)-Rh(1)-H(1A) angle
is considerably larger at 88.5(8)°. Since the B(1)-Rh(1)-P(1)
angle is so close to 90°, we see no steric reason for the acute
B-Rh-H angle. These parameters are very similar to those
determined by X-ray diffraction at 120 K for [Rh(Cl)(H)(Bpin)-
(PiPr3)2], for which Rh-H ) 1.47(2) Å, B-Rh-H ) 70.0(8)°,
and H‚‚‚B ) 2.02(2) Å.52 However, Rh-H distances determined
by accurate X-ray diffraction measurements are systematically
underestimated by ca. 0.1 Å, although the direction of the bond
can be obtained with reasonable accuracy.52 In [Rh(Cl)(H)-
(Bpin)(PiPr3)2], neutron diffraction data obtained at 20 K gave
Rh-H ) 1.571(5) Å and B-Rh-H ) 67.8(2)°, resulting in an
H‚‚‚B separation of 2.013(5) Å.52 DFT studies on [Rh(Cl)(H)-
(Bpin)(PiPr3)2] showed evidence for a weak residual H‚‚‚B
interaction, although the structure is much closer to that of a
formal hydrido-boryl complex than that of a σ-borane complex
(e.g., r(B-H) ) 1.35 Å in ref 14). Thus, given the strong
similarity of the structural data for 2b and [Rh(Cl)(H)(Bpin)-
(PiPr3)2], a similar description seems appropriate.
(53) Comparisons may be drawn to M(η5-C5R5)(H)2(Bcat′) (M ) Nb,
Ta; R ) H, Me; cat′ ) O2C6H4 or O2C6H3-3-tBu). The Ta complexes are
best described as boryl hydride complexes, while the dominant form of the
niobium complexes is the dihydridoborate. However, isotopic perturbation
1
of the H resonance shows that the niobium complexes are in equilibrium
with another species, either the boryl hydride complexes or Nb(H)(η2-HBcat)
(Hartwig, J. F.; De Gala, S. R. J. Am. Chem. Soc. 1994, 116, 3661. Lantero,
D. R.; Ward, D. L.; Smith, M. R., III. J. Am. Chem. Soc. 1997, 119, 9699).
A related situation exists for Rh and Ir compounds, where the former prefer
a square-planar RhI hydridoborate structure, while the latter prefer an
octahedral IrIII(H)2(BR2) structure (Baker, R. T.; Ovenall, D. W.; Calabrese,
J. C.; Westcott, S. A.; Taylor, N. J.; Williams, I. D.; Marder, T. B. J. Am.
Chem. Soc. 1990, 112, 9399. Baker, R. T.; Ovenall, D. W.; Harlow, R. L.;
Westcott, S. A.; Taylor, N. J.; Marder T. B. Organometallics 1990, 9, 3028.
Westcott, S. A.; Marder, T. B.; Baker, R. T.; Calabrese, J. C.; Harlow, R.
L.; Lam, K. C.; Lin, Z. Polyhedron 2004, 23, 2665).
Hartwig et al. reacted [Rh(η5-C5Me5)(H)2(Bpin)2] with P(p-
tol)3 to form [Rh(η5-C5Me5)(H)(Bpin){P(p-tol)3}], a close
(52) Lam, W. H.; Shimada, S.; Batsanov, A. S.; Lin, Z.; Marder, T. B.;
Cowan, J. A.; Howard, J. A. K.; Mason, S. A.; McIntyre, G. J. Organo-
metallics 2003, 22, 4557.

5098 Organometallics, Vol. 25, No. 21, 2006
Caˆmpian et al.
Table 4. NMR Spectroscopic Data [solvent C6D6, δ (J/Hz)] for Products of Photoreaction of 1a-1c with Silanesa
5a SiMe2Et
6a SiMeEt2
7a Si(OMe)3
8a SiEt2H
-14.6 dd,
JPH 33.5,
RhH 32.1
9a SiEt3
-14.55 t,
JPH 32.3,
RhH 31.5
10a SiiPr3
-14.6 dd,
JPH 33.2,
RhH 29.8
1H hydride
-14.5 dd,
PH 33.1,
RhH 32.1
-14.58 dd,
JPH 33.1,
RhH 32.4
-14.06 t,
JPH 31.5,
RhH 32.3
J
J
J
J
J
J
J
1H Cp
5.10 s
5.5 d, JRhP 171
5.11 s
5.3 d, JRhP 171
5.22 s
9.6 d, JRhP 160
5.10 s
8.2 d, JRhP 165
5.14 s
5.2 d, JRhP 171
5.12 s
0.87 d, JRhP 174
31P{1H}
5b
6b
7b
8b
9b42
10b42
1H hydride
-13.38 dd,
-13.40 app t,
JPH 29.3,
-12.99 dd,
JPH 28.3,
-13.57 dd,
JPH 29.9,
-13.49 app t,
JPH 29.1,
-13.60 dd,
JPH 29.9,
J
J
PH 29.3,
RhH 30.2
J
RhH 29.3
J
RhH 29.1
J
RhH 29.5
J
RhH 29.1
J
RhH 28.2
5.10 t, JRhH
PH 0.5
1H Cp
5.07 s
5.08 s
5.21 s
5.13 s
5.10 s
)
J
31P{1H}
62.5 d, JRhP 184
5c
62.0 d, JRhP 185
59.2 d, JRhP 175
62.8 d, JRhP 178
59.6, JRhP 188
56.8, JRhP 185
6c
7c
8c
9c
10c
1H hydride
-15.24 ddq,
-15.20 ddq,
JPH 33.3,
-14.52 ddq,
JPH 31.1,
-15.14 ddq,
JPH 33.3,
-15.14 ddq,
JPH 35.7,
-14.91 ddq,
JPH 33.2,
J
J
PH 33.3,
RhH 33.1 JFH 2.8
J
RhH 32.8 JFH 2.8
J
RhH 33.1, JFH
2
J
RhH 32.8 JFH 2.9
J
RhH 32.8 JFH 2.9
J
J
RhH 30.7,
FH 2.9
1H Cp
4.72 s, 5.18 s,
5.30 s, 5.39 s
6.8 d, JRhP 171
4.73 s, 5.20 s,
5.29 s, 5.41 s
8.7 d, JRhP 171
4.93 s, 5.27 s,
5.42 s, 5.57 s
9.6 d, JRhP 160
4.74 s, 5.06 s,
5.38 s, 5.43 s
9.1 d, JRhP 165
4.76 s, 5.21 s,
5.28 s, 5.44 s
4.7 d, JRhP 171
4.86 s, 5.21 s,
5.37 s, 5.40 s
0.3 d, JRhP 174
31P{1H}
1
a Values of JRhH were determined by recording H{31P} spectra; app ) apparent.
The above procedure was also used for the photochemical
reactions of complex 1b and 1c to give the B-B activation
products [Rh(η5-C5H5)(Bpin)2(PPh3)] (4b) and [Rh(η5-C5H4-
CF3)(Bpin)2(PMe3)] (4c), respectively, with complete conver-
sion. Selected NMR data for the boryl complexes are summa-
rized in Table 1 and illustrated in the Supporting Information
(Figures S11-S13); full data may be found in the Experimental
Section. Hartwig et al. have reacted [Rh(η5-C5Me5)(H)(Bpin)3]
with PEt3 at 70 °C in cyclohexane, yielding the analogue [Rh-
(η5-C5Me5)(Bpin)2(PEt3)], which exhibits an 11B resonance at
δ 42.3 and a doublet in the 31P NMR spectrum with a JRhP value
of 169 Hz.23
Figure 3. Molecular structure of 10a (50% thermal ellipsoids,
hydrogen atoms omitted except H1A).
The limiting factor in the synthesis of 4b is the solubility of
the precursor 1b in inert solvents. We attempted to irradiate 1b
with B2pin2 in a variety of alternative solvents without success.
Photolysis in chlorinated solvents yielded [Rh(η5-C5H5)Cl2-
(PPh3)] (11b), which was crystallized from toluene. Details of
the molecular structure are given in the Supporting Information.
Reactions with Tertiary and Secondary Silanes. Complex
1a was irradiated in neat trialkyl or trialkoxy silanes HSiR3 (R
) Et, iPr, OMe) or mixed trialkyl silanes HSiMe2Et, HSiMeEt2,
and H2SiEt2, at room temperature, on an NMR scale (Table 4).
The most thoroughly characterized reaction was that of 1a with
iPr3SiH. The reaction generated [Rh(η5-C5H5)(SiiPr3)(H)(PMe3)]
(10a) in greater than 90% yield (by NMR spectroscopy) together
with traces of [Rh(η5-C5H5)(SiiPr3)2(H)2] (δ -14.5 d, JRhH 30
Hz)27 and another {Rh(η5-C5H5)(PMe3)} product that could not
be identified. Complex 10a exhibits a characteristic doublet of
doublets in the 1H NMR spectrum (δ -14.6, JRhH 29.8 and JPH
33.2 Hz) and a doublet in the 31P NMR spectrum (δ 0.87, JRhP
174 Hz). The {1H-29Si} correlation linked the isopropyl
resonances to a 29Si resonance at δ 52.1 with passive doublet
couplings to rhodium and phosphorus of 14 and 33 Hz,
respectively. We could not establish a correlation to the hydride
resonance, implying that JSiH for the hydride is very small, with
a value less than 2 Hz. In contrast, [Rh(η5-C5H5)(SiiPr3)2(H)2]
exhibited a correlation from hydride to 29Si at δ 52.1 with JRhSi
) 15 Hz.
that 2b and 3b had cocrystallized (Figure S4 and S5, Tables
S1). The bond lengths and angles measured for 2b in this
structure are similar to those in the crystal structure described
above, but are less well determined. The most notable feature
of the structure of 3b is a π-π interaction between a phenyl
ring of one phosphine and a phenyl ring of the other phosphine,
with a centroid-to-centroid distance of 3.6069(17) Å and an
angle between planes of 4.2°.
Reaction with B2(pin)2. The complex 1a was irradiated in
the presence of a 2-fold excess of B2pin2 in hexane solution.
At room temperature, the product of B-B bond activation, [Rh-
(η5-C5H5)(Bpin)2(PMe3)] (4a), was formed along with the bis-
(phosphine) complex 3a, but this byproduct could be avoided
by carrying out the photolysis at -10 °C. The reaction was taken
to complete conversion to 4a; elution of a hexane solution of
the mixture through a silica column separated the boryl complex
4a from boron-containing impurities. Final purification of 4a
was achieved by sublimation. The product 4a exhibits a doublet
at δ 14.7 with a JRhP value of 177 Hz in the 31P{1H} NMR
spectrum, downfield of 1a (contrast to 2a). Further evidence
1
for the identity of the complex came from the H and 13C
resonances of the Bpin groups, the 11B NMR resonance at δ
45.1 to low field of that of B2pin2 at δ 34.4 (Figure S11,
Supporting Information), and the parent ion in the mass
spectrum. We also observed the characteristic upfield shift in
the 13C resonance of the quaternary carbons of the Bpin ligands.
Crystals were grown from hexane as very thin plates, but the
quality of the resulting diffraction data was low. Nevertheless,
the data were consistent with the formulation.
Crystals of 10a were grown from hexane, and the structure
was determined (Figure 3, Table 5). The Rh-Si bond length is
2.3617(3) Å, and the Si-Rh-P angle is 99.224(11). The hydride
was located, leading to a Rh-H bond length of 1.508(17) Å

Photoinduced OxidatiVe Addition at Rh Centers
Organometallics, Vol. 25, No. 21, 2006 5099
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
10a
bonds, we conducted photochemical experiments in the presence
of two or three of the substrates HBpin, HSiEt3, HSiMe2Et,
HC6F5, and B2pin2 simultaneously. The results are summarized
in Table 6.
Rh(1)-P(1) 2.2251(3)
Rh(1)-Si(1) 2.3617(3)
Si(1)-Rh(1)-P(1) 99.224(11)
H(1A)-Rh(1)-P(1) 84.7(6)
Rh(1)-C(Cp) 2.2556(11)-2.3057(11) H(1A)-Rh(1)-Si(1) 68.0(6)
Rh(1)-H(1A) 1.508(17)
Complex 1b was irradiated in hexane in the presence of
HBpin (10 equiv) and B2pin2 (10 equiv), and product formation
was followed in situ by 31P{1H} NMR spectroscopy (Figure
4a). Integration (quantitative 31P NMR and 31P{1H} gave
identical results) shows a ratio of boryl hydride 2b to bis-boryl
4b complex of 1:3.2 after 30 min of photolysis, increasing to
1:4 after 90 min of photolysis, indicating a significant preference
for B-B over B-H oxidative addition.
Formation of [Rh(η5-C5H5)(C6F5)(H)(PPh3)] (12b) on irradia-
tion of 1b with HC6F5 was reported previously.42 Irradiation of
1b in C6D12, in the presence of HBpin and HC6F5, was followed
by 1H NMR spectroscopy in the hydride region. There is a very
slight selectivity for B-H over C-H oxidative addition. A three-
way competition reaction among HBpin, HC6F5, and HSiMe2-
Et is illustrated in Figure 4b and again shows only a slight
selectivity. The choice of silane was governed by the need to
avoid overlap of the hydride resonances. Finally, competition
between HBpin and HSiEt3 showed only a slight selectivity after
short irradiation, although there was preference for Si-H
oxidative addition on longer irradiation. Figure 4b also illustrates
the absence of broadening of the hydride resonance of the boryl
hydride complex 2b compared to the aryl hydride and silyl
hydride analogues, 12b and 5b.
Si‚‚‚H(1A)
2.278(18)
and a Si‚‚‚H distance of 2.278(17) Å. The H-Rh-P and
H-Rh-Si angles are 84.7(6)° and 68.0(6)°, respectively. It is
striking that these two angles are so different and that the very
acute angle is associated with silicon despite the greater steric
demand of the SiiPr3 group compared to the PMe3 group. For
comparison, Maitlis et al. determined the structure of [Rh(η5-
C5Me5)(SiEt3)2(H)2] by X-ray and neutron diffraction at 20 K.
The neutron determination gave an average Rh-H bond length
of 1.581(3) Å and an average Si‚‚‚H distance of 2.27(6) Å.54
Sabo-Etienne et al. have published several structures with both
σ-disilane and hydride ligands and have highlighted the role of
secondary Si‚‚‚H interactions (SISHA interactions). Their
importance has been demonstrated by structure determinations,
NMR dynamics, and DFT calculations. These SISHA Si‚‚‚H
distances are typically close to 2.2 Å.55 In conclusion, the
structure of 10a suggests the presence of some residual Si‚‚‚H
interaction, although there is negligible SiH coupling in the
solution NMR spectrum.
Photochemical reaction of 1a in the presence of the other
silanes leads to formation of [Rh(η5-C5H5)(SiR2R′)(H)(PMe3)]
5a-9a assigned on the basis of NMR spectra as the major
products (Table 4). Traces of the rhodium(V) hydride [Rh(η5-
C5H5)(SiR2R′)2(H)2] are also formed. In addition, other minor
products are observed in the 31P{1H} NMR spectrum that have
no associated hydride resonances. These complexes have not
been identified conclusively and hamper full characterization.
In the case of HSi(OMe)3, the reaction is as clean as for HSii-
Pr3. The value of JRhP is 160 Hz for [Rh(η5-C5H5){Si(OMe)3}-
(H)(PMe3)], compared to 171-174 Hz for the trialkylsilyl
derivatives.
The results of the competition reactions could reflect kinetic
or thermodynamic selectivity. Since it would be possible, in
principle, for the Rh(III) products to equilibrate, we carried out
control experiments as follows: (a) 4b + excess HSiEt3; (b)
5b + excess HBpin; (c) 5b + B2pin2; (d) 2b + HSiEt3. The
1
solutions were made up in C6D6 and followed by H and 31P
NMR spectroscopy; they were left to stand at room temperature
for at least 2 h, except for the first solution, which was heated
to 75 °C. In no case, was any reaction observed. We can
therefore exclude thermal equilibration of the final products.
Photochemical equilibration of the final products was also
excluded since the reactions were taken to relatively small
conversion and the product distribution varied only slightly with
photolysis time. Moreover, such Rh(III) species absorb very little
light in the region λ > 290 nm.
It is more difficult to exclude equilibration between the Rh-
(I) reaction intermediates that may be involved in most of these
reactions (Scheme 2). The intermediacy of η2-arene complexes
is already established in arene C-H bond activation.34 Consid-
ering that η2-silane and η2-borane complexes are well
known,15,55,56 species of the type [Rh(η5-C5H5)(η2-HE)(PPh3)]
(HE ) HBpin, HSiR3) are likely to act as intermediates in the
reactions with HBpin and with silanes. The rate constant for
conversion of [Rh(η5-C5H5)(η2-C6H6)(PMe3)] to [Rh(η5-C5H5)-
(Ph)(H)(PMe3)] at 263 K may be estimated to be ca. 50 s-1
from published data.34 If we assume that the lifetime of species
such as [Rh(η5-C5H5)(η2-HSiEt3)(PPh3)] and [Rh(η5-C5H5)(η2-
C6HF5)(PPh3)] is of the same order, equilibration would become
competitive if the rate constant for cross-reactions such as HBpin
+ [Rh(η5-C5H5)(η2-HSiEt3)(PPh3)] were greater than about 500
dm3 mol-1 s-1. We conclude that the observed selectivity in
the competition reactions represents either kinetic selection of
[Rh(η5-C5H5)(PPh3)(S)] (S ) hexane solvent) for substrates or
The irradiation of 1b with HSiEt3 and HSiiPr3 leading to [Rh-
(η5-C5H5)(SiR3)(H)(PPh3)] (R ) Et, 9b; R ) iPr, 10b) has been
reported previously, and the structure of 10b has been deter-
mined.42 The current experiments were conducted on an NMR
scale in neat silane HSiMe2Et, HSiMeEt2, H2SiEt2, and HSi-
(OMe)3 at -10 °C. In contrast to 1a, photochemical reactions
of triphenylphosphine complex 1b lead to formation of single
products, [Rh(η5-C5H5)(SiR3)(H)(PPh3)], with NMR spectra
similar to the PMe3 analogues (Table 4).
Irradiation at -10 °C of complex 1c in the presence of neat
silanes results in rhodium hydride silyl complexes as the major
products. For instance, the reaction of 1c in HSiMeEt2 leads to
1
formation of a single product, assigned on the basis of H and
31P NMR spectra as [Rh(η5-C5H4CF3)(SiMeEt2)(H)(PMe3)] (6c).
The hydride region of the 1H NMR spectrum reveals a ddq pat-
tern at δ -15.2 (JPH 33.3, JRhH 32.8, JFH 2.8 Hz). The 31P{1H}
spectrum shows a doublet at δ 8.5 (JRhP 171 Hz), and a doublet
is also observed in the 19F NMR spectrum (δ -53.6. J 2.7 Hz).
NMR spectra are summarized in Table 4 and illustrated in
the Supporting Information (Figures S14-S27).
Competition Reactions. To investigate the selectivity of
reaction of the complex 1b for the activation of E-H and B-B
(54) Fernandez, M.-J.; Bailey, P. M.; Bentz, P. O.; Ricci, J. S.; Koetzle,
T. F.; Maitlis, P. M. J. Am. Chem. Soc. 1984, 106, 5458.
(55) (a) Lachaize, S.; Sabo-Etienne, S. Eur. J. Inorg. Chem. 2006, 2115.
(b) Atheaux, I.; Delpech F.; Donnadieu, B.; Sabo-Etienne, S.; Chaudret, B.
Hussein, K.; Barthelat, J. C.; Braun, T.; Duckett, S. B.; Perutz, R. N.
Organometallics 2002, 21, 5347.
(56) (a) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175.
(b) Lin, Z. Chem. Soc. ReV. 2002, 31, 239. (c) Nikonov, G. I. AdV.
Organomet. Chem. 2005, 53, 217.

5100 Organometallics, Vol. 25, No. 21, 2006
Caˆmpian et al.
Table 6. Results of Competition Reactions
substrates
HBpin/B2pin2
HBpin/HC6F5
HBpin/HC6F5/HSiMe2Et
HBpin/HSiEt3
HBpin/HSiEt3
conc rel to 1b/eq
NMR method
10:10
10:10
1H
10:10:10
1H
10:10
1H
15:5
1H
31P{1H}
irradiation
time/min
integrationsa
2b:4b:1b
integrationsa
2b:12b
integrationsa
2b:12b:5b
integrationsa
integrationsa
2b:9b
2b:9b
30
60
90
1:3.2:7.7
1:3.8:2.6
1:4.0:2.4
1:0.91
1:0.89
1:0.94
1:0.97
1:0.94:1.06
1:0.99:1.07
1:1.01:0.95
1:1.07
1:2.5
120
1:0.64
a The error bars on relative integration are estimated as (10%.
Scheme 2. Basis for Selectivity in an Illustrative
Competition Reaction
4). A recent DFT study of a broad range of complexes trans-
[Pt(T)(Cl)(PMe3)2] established the following order of trans
influence based on the variation in the Pt-Cl bond length: T
) SiMe3 > Bpin > Bcat ≈ SiH3> H > C6H5.58 Crystallographic
data for [Pt(Ph2CH2CH2PPh2)X2] show the following mean
Pt-P distances: X ) Bcat 2.318(2) > X ) SiiPr2H 2.304(3)
> X ) C6F5 2.276(3) Å.59 Thus the Rh-P coupling constants
reflect the σ-donor strengths of the X ligands (also related to
their trans influence),58 with larger values of JRhP reflecting
increased electron density at the metal center.
Figure 4. Competition reactions of 1b after 30 min of photolysis:
(a) 31P NMR spectrum in hexane with HBpin and B2pin2; (b)
hydride region of 1H NMR spectrum in C6D12 with C6F5H, HBpin,
and HSiMe2Et.
equilibration between Rh(I) intermediates (Scheme 2). It is worth
mentioning that no such Rh(I) intermediate is anticipated in the
case of B2pin2.
Comparisons of NMR Data. Comparison of the 31P NMR
spectra of the Rh(I) complexes 1a, 1b, and 1c shows that JRhP
is 10 Hz higher for the PPh3 complex than for the PMe3
complexes, but the CF3 group changes JRhP by only 2 Hz when
compared to 1a. The changes in 3a-3c are similar (Table 1).
The NMR data for Rh(III) complexes [Rh(η5-C5H5)(X)(H)-
(PPh3)] show that the values of JPH for the PPh3 complexes are
consistently about 4 Hz lower than those of the PMe3 complexes.
In contrast, the values of JRhP are consistently 10-15 Hz higher
for the PPh3 complexes than for the PMe3 complexes. Further-
more, the values of JRhP follow the order X (J/Hz) ) SiR3 (188-
184) > B(OR)2 (180) > Si(OMe)3 (175) > H ∼ C6H5 (166) >
C6F5 (155).57
Conclusions
Photochemical reactions of half-sandwich rhodium complexes
[Rh(Cp′)(PR3)(C2H4)] (R ) Me, Ph; Cp′ ) (η5-C5H5), η5-C5H4-
CF3) at room temperature in the presence of mono- and diboron
(57) The dihydride complex [Rh(η5-C5H5)(H)2(PPh3)] gives a 31P signal
1
at δ 64.5 (d, JRhP ) 167 Hz) and H resonances at δ 5.23 (s, 5H, C5H5),
-13.27 (dd, 2H, JPH ) 35.1, JRhH ) 26.7 Hz). Campian, M. V.; Perutz, R.
N. Unpublished data.
(58) Zhu, J.; Lin, Z.; Marder T. B. Inorg. Chem. 2005, 44, 9384.
(59) (a) Lesley, G.; Nguyen, P.; Taylor, N. J.; Marder, T. B.; Scott, A.
J.; Clegg, W.; Norman, N. C. Organometallics 1996, 15, 5137. (b) Pham,
E. K.; West R. Organometallics 1990, 9, 1517. (c) Deacon, G. B.; Elliott,
P. W.; Erven, A. P.; Meyer, G. Z. Anorg. Allg. Chem. 2005, 631, 843.
To our surprise, the CF3 substituent on the Cp ring had a
negligible effect on the values of JPH and JRhP (Tables 1 and

Photoinduced OxidatiVe Addition at Rh Centers
Organometallics, Vol. 25, No. 21, 2006 5101
Young’s PTFE stopcocks. Deuterated solvents were dried by stirring
over potassium and were distilled under high vacuum into small
ampules with potassium mirrors.
Photochemical reactions, at room temperature, were performed
in glass NMR tubes fitted with PTFE taps, using a 125 W medium-
pressure mercury vapor lamp with a water filter (10 cm). UV-vis
irradiations, at lower temperatures, were performed using a 300 W
Oriel 66011 xenon lamp with a thermostatically controlled cooling
system based on gaseous nitrogen boil-off obtained from a JEOL
NMR spectrometer.
reagents, HBpin and B2pin2, lead to formation of the boryl
complexes along with byproducts. Lowering the photolysis
temperature to -10 °C permitted the selective formation, in
good yield, of the oxidative addition products of B-H and B-B
bonds. Alternatively, pure boryl hydride complexes were formed
by photolysis in liquid HBpin. To prevent the formation of C-H
bond activation products, it is essential to avoid the presence
of aromatic C-H bonds in the solvent or in the boronate esters.
Thus, use of benzene as a solvent and/or HBcat as the borane
resulted in mixtures of products. This observation appears to
contrast with that for [W(η5-C5H5)2H2], which reacts photo-
chemically with diboron dicatecholates even in benzene solution,
although the selectivity of {W(η5-C5H5)2} may have been
dictated by the tert-butyl substituents on the catechol groups.21
Photolysis of [Rh(η5-C5H5)(PPh3)(C2H4)] in the presence of
silanes leads to clean conversion to silyl hydride complexes.
However, the photoreactions of [Rh(η5-C5H5)(PMe3)(C2H4)] and
[Rh(η5-C5H4CF3)(PMe3)(C2H4)] generate the silyl hydride com-
plexes cleanly only in certain cases, such as with HSiiPr3. Crystal
and molecular structures of the complexes [Rh(η5-C5H5)(PPh3)-
(C2H4)] (1b), [Rh(η5-C5H4CF3)(PMe3)(C2H4)] (1c), [Rh(η5-
C5H5)(Bpin)(H)(PPh3)] (2b), [Rh(η5-C5H5)(SiiPr3)(H)(PMe3)]
(10a), and [Rh(η5-C5H5)(PPh3)2] (3b) were determined by
single-crystal X-ray diffraction.
All NMR spectra were recorded on Bruker AMX500 spectrom-
1
eters in glass tubes fitted with Young’s PTFE stopcocks. All H
and 13C chemical shifts are reported in ppm (δ) relative to
tetramethylsilane and are referenced using the chemical shifts of
residual protio solvent resonances (benzene, δ 7.16). The 31P{1H}
and 11B NMR spectra were referenced to external H3PO4 and BF3‚
Et2O, respectively. In general, 1H decoupling did not affect the 11
spectra reported in this paper.
B
Mass spectra were recorded on a VG-Autospec spectrometer and
are quoted for 11B.
Syntheses and NMR Experiments. [Rh(η5-C5H5)(PR3)(C2H4)]
(R ) Me, Ph) complexes were synthesized by literature procedures,
but replacing TlCp by LiCp.33,40 Tl(η5-C5H4CF3) was synthesized
by the literature method, via reaction of nickelocene with CF3I
followed by thallium ethoxide.44
Comparisons of NMR coupling constants show that the values
of the phosphorus-hydride coupling, JPH, for the PPh3 com-
plexes are consistently lower than those of the PMe3 complexes,
while JRhP is consistently higher. The values of JRhP are also
sensitive to the substituent X in Rh(III) complexes [Rh(η5-
C5H5)(X)(H)(PPh3)] and increase with the σ-donor strength of
X. Surprisingly, the CF3 group appears to exert no significant
effect on the reactivity toward oxidative addition or on the NMR
parameters of the products.
Competition reactions reveal that the photogenerated frag-
ment, {Rh(η5-C5H5)(PPh3)}, is remarkably unselective. There
is a slight preference for B-B over B-H oxidative addition,
but no significant difference among B-H, Si-H, and C-H
bond activation processes. The lack of selectivity originates
either in very similar rate constants for reaction of [Rh(η5-C5H5)-
(PPh3)(alkane)] with the substrates or in fast equilibration
between Rh(I) intermediates of the type [Rh(η5-C5H5)(PPh3)-
(η2-HE)] (Scheme 2).
In conclusion, photoinduced B-H and B-B oxidative
addition reactions are as straightforward as Si-H oxidative
addition. It is striking that B-H and B-B oxidative additions
are efficient at {Rh(η5-C5H5)(PPh3)}, whereas C-H oxidative
addition yields stable products only for those arenes such as
HC6F5 with exceptionally strong rhodium-carbon bonds in the
product. The effectiveness of such reactions is often determined
by the thermodynamic stability of the products60 and points
again to the strong σ-donor properties of the Bpin ligand.20e,58
[Rh(η5-C5H4CF3)(C2H4)(PMe3)], 1c. Complex 1c was prepared
by reaction of Tl(η5-C5H4CF3) (1 g, 3 mmol) with [RhCl(C2H4)-
(PMe3)]2 (0.51 g, 1.3 mmol) in THF at 0 °C. The mixture was
stirred for 3 h at 0 °C and was then allowed to warm to room
temperature. The supernatant was decanted, and the solid residue
was washed with hexane. The combined liquors were pumped to
dryness, yielding a dark brown solid. The latter was extracted with
hexane, forming a dark yellow solution, which was eluted through
a 5 cm Celite column with hexane. The solution was pumped to
dryness, and the resulting yellow solid was sublimed without heating
onto a liquid-nitrogen-cooled finger (10-4 mbar). The product was
washed off the finger with hexane and pumped down slowly,
yielding yellow crystals. Yield: 0.72 g, 49%. The sample for
analysis was recrystallized from hexane. Crystals for X-ray dif-
fraction were grown by very slow sublimation in an ampule sealed
under vacuum and left at room temperature in the dark. Anal. Calcd
for C11H17F3PRh: C, 38.84; H, 4.69. Found: C, 38.88; H, 5.04.
1
NMR (C6D6 300 K), H: δ 5.18 (m, 2H, C5H4), 4.99 (m, 2H,
C5H4), 2.8 (m, 2H, C2H4), 1.49 (m, 2H, C2H4), 0.71 (dd, JPH
)
9.6, JRhH ) 1.1 Hz, 9H, Me); 31P{1H}: δ 6.9 (dq JRhP ) 198, JFP
) 2 Hz). 19F: -54.4 (m); 13C{1H} NMR (75.4 MHz, toluene-d8
300 K): δ 86.76 (m C5H4), 84.76 (s C5H4), 26.89 (dd JPC ) 16,
JRhC ) 3 Hz, C2H4), 18.80 (d JPC ) 29.5 Hz, Me); 13C{1H} NMR
(THF-d8 300 K): 125.3 (q, JCF ) 267 Hz, CF3), 93.6, q, JCF ) 38
Hz, CCF3), 86.4 (s br, C5H4), 84.3 (s, C5H4), 25.8 (dd, JPC ) 17,
JRhC ) 3 Hz, C2H4), 18.2 (d, JPC ) 29 Hz, Me). MS (EI, m/z) 340
(26%, M+), 312 (100%, M+ - C2H4), 293 (11%, M+ - C2H4 -
F), 236 (13%, Rh(C5H4CF3)+) 178 (69%, Rh(PMe3)+). HRMS
m/z: exp 340.00753, calcd for C11H17F3PRH 340.00750, difference
0.03 mDa.
Experimental Section
[Rh(η5-C5H5)(Bpin)(H)(PMe3)], 2a. An 8 mm diameter NMR
tube, fitted with a Young’s tap, was charged with 1a (55 mg) and
HBpin (1.5 mL) and irradiated at -10 °C with the Oriel Xe arc
(17 h), resulting in 100% conversion to 2a. The excess HBpin was
recovered by vacuum transfer on the high-vacuum line, leaving a
brown oil. The oil was transferred to the glovebox, redissolved in
toluene, and passed through a neutral alumina column (3 cm long,
1 cm diam) eluting with further toluene in order to remove boron-
containing impurities. The eluent was pumped to dryness and
redissolved in hexane to give a brown solid. In a smaller-scale
reaction, an NMR tube was charged with a solution of complex 1a
(1-2 mg, 4-7 µmol) in neat HBpin (1 mL) and irradiated at ca.
General Procedures. All operations were performed under a
nitrogen or argon atmosphere, either on a high-vacuum line (10-4
mbar) using modified Schlenk techniques, on standard Schlenk
(10-2 mbar) lines, or in a glovebox. Solvents for general use (THF,
benzene, toluene) were of AR grade, dried by distillation over
classical reagents, and stored under Ar in ampules fitted with
(60) (a) Jones, W. D.; Hessell, E. T. J. Am. Chem. Soc. 1993, 115, 554.
(b) Wick, D. D.; Jones, W. D. Organometallics 1999, 18, 495. (c) Clot, E.;
Besora, M.; Maseras, F.; Me´gret, C.; Eisenstein, O.; Oelckers, B.; Perutz,
R. N. Chem. Commun. 2003, 490. (d) Clot, E.; Oelckers, B.; Klahn, A. H.;
Eisenstein, O.; Perutz, R. N. Dalton Trans. 2003, 4065.

5102 Organometallics, Vol. 25, No. 21, 2006
Caˆmpian et al.
-5 °C for 15 h. All volatiles were removed under vacuum to give
a dark orange solid. Further purification by sublimation onto a
liquid-nitrogen-cooled finger at 35 °C at 10-4 mbar yielded a white
[Rh(η5-C5H5)(Bpin)(H)(PPh3)], 2b. A 15 mm diameter NMR
tube, fitted with a Young’s tap, was charged with 1b (40 mg) and
HBpin (5.5 mL) and irradiated with a medium-pressure Hg arc (6
h), resulting in 100% conversion to 2b. The excess HBpin was
recovered by vacuum transfer on a high-vacuum line, leaving a
brown oil. The oil was transferred to a glovebox, redissolved in
toluene, and passed through a neutral alumina column (3 cm long,
1 cm diam) eluting with further toluene in order to remove boron-
containing impurities. The eluent was pumped to dryness and
redissolved in hexane. Slow evaporation of the solution in the
glovebox gave brown crystals of 2b. In a smaller-scale reaction, a
5 mm diameter NMR was charged with 1b (3 mg) and HBpin (ca.
1 mL) and irradiated similarly for 6 h. The HBpin was removed
under vacuum and the residue was dissolved in hexane and cooled
to -18 °C, yielding cocrystals of 2b‚3b. NMR (C6D6, 300 K), 1H:
δ 7.68-6.68 (m, 15H, C6H5), 5.33 (s, 5H, C5H5), 0.95 (s, 6H
BO2C6H12), 0.88 (s, 6H BO2C6H12), -13.04 (dd, 1H, JPH ) 29.6,
JRhH ) 32.8 Hz, RhH); 31P{1H}: δ 62.5 (d, JRhP ) 180 Hz); 13C-
{1H}: δ 134.4 (d, JPC ) 11.9 Hz, o-Ph), 132.5 (d, JPC ) 9.6 Hz,
m-Ph), 131.6 (d, JPC ) 2.8 Hz, p-Ph), 89.2 (t, JPC ) JRhC ) 2.5
Hz, C5H5), 82.9 (s, BO2C2(CH3)4), 24.59 (s, BO2C2(CH3)4), 24.58
(s, BO2C2(CH3)4); 11B{1H}: δ 44.8. MS (EI, m/z: 558 (3%, M+),
430 (100%, M+ - HBpin), 286 (26%), 183 (20%), 168 (7%).
HRMS (FAB m/z): exp 581.1271 (M + Na+), calcd for C29H33-
BO2NaPRh 581.1264, difference 0.7 mDa. Anal. Calcd for C29H33-
BO2NaPRh: C, 62.39; H, 5.96. Found: C, 62.38; H, 5.97.
[Rh(η5-C5H5)(Bpin)2(PPh3)], 4b. A 15 mm diameter NMR tube
fitted with a Young’s tap was charged with 1b (15 mg) in hexane
and B2pin2 (26 mg) and irradiated at -20 °C with the medium-
pressure Hg arc (14 h), resulting in 100% conversion (by NMR
spectroscopy) to 4b. The solution was pumped to dryness, leaving
an orange-brown solid. The solid was transferred to the glovebox,
redissolved in toluene, and passed through a neutral alumina column
(3 cm long, 1 cm diam) eluting with further toluene in order to
remove boron-containing impurities. The eluent was pumped to
dryness, and the excess B2pin2 was removed by sublimation to give
an orange-brown solid. A smaller-scale reaction at room temperature
gave a mixture of two products that were eluted through an alumina
column with toluene to give 4b. NMR (C6D6, 300 K), 1H: δ 7.68-
6.68 (m, 15H, Ph), 5.41 (s, 5H, C5H5), 1.07 (s, 6H BO2C6H12),
1.04 (s, 6H BO2C6H12); 31P{1H}: δ 55.5 (d, JRhP ) 182 Hz); 13C-
{1H}: δ 134.8 (d, JPC ) 11.7 Hz, o-Ph), 129.1 (d, JPC ) 2.3 Hz,
p-Ph), 127.3 (d, JPC ) 10.2 Hz, m-Ph), 91.9 (t, JPC ) JRhC ) 2.2
Hz, C5H5), 81.35 (s, BO2C2(CH3)4), 25.21 (s, BO2C2(CH3)4), 25.14
(s, BO2C2(CH3)4); 11B{1H}: δ 43.7. MS, (ESI, m/z): 707 (100%,
M + Na+), 579 (5%, M + Na+ - Bpin), 501 (25%).
1
solid, which darkened on standing. NMR (C6D6, 300 K), H: δ
5.36 (s, 5 H, C5H5), 1.29 (d, 9 H JPH ) 10.7 Hz, P(CH3)3), 1.16 (s,
12H BO2C6H12), -14.04 (dd, 1H, JPH ) 33.7 Hz, JRhH ) 35.1 Hz,
RhH); 31P{1H}: δ 12.4 (d, JRhP ) 170.4 Hz); 13C{1H}: δ 87.5 (t,
C5H5, JPC ) JRhC ) 2 Hz), 81.2 (s, BO2C2(CH3)4), 25.4 (s, BO2C2-
(CH3)4), 25.3 (s, BO2C2(CH3)4), 24.2 (dd, JPC ) 32, JRhC ) 1 Hz,
P(CH3)3); 11B{1H}: δ 45.4. MS m/z: 372 (4%), 369 (1%), 272
(2%), 244 (100%, [Rh(C5H5)(PMe3)]+). HRMS m/z: exp 372.09090,
calcd for C14H27BO2PRh 372.08968, difference 1.2 mDa
[Rh(η5-C5H5)(Bpin)2(PMe3)], 4a. An 8 mm diameter NMR tube,
fitted with a Young’s tap, was charged with 1a (55 mg) in hexane
and a ca. 2-fold excess of B2pin2 and irradiated at -10 °C with the
Oriel Xe arc (37 h), resulting in 100% conversion to 4a. The
solution was pumped to dryness, leaving an orange-brown solid.
The solid was transferred to the glovebox, redissolved in toluene,
and eluted through a neutral alumina column (3 cm long, 1 cm
diam) with toluene in order to remove boron-containing impurities;
the eluent was pumped to dryness. Fractional sublimation (sample
at 40 °C) onto a liquid-nitrogen-cooled finger initially removed
excess B2pin2. On heating for longer periods, the product 4a also
sublimed; multiple sublimations yielded off-white 4a. NMR (C6D6,
300 K), 1H: δ 5.46 (s, 5 H, C5H5), 1.41 (dd, 9 H JPH ) 10.6 JRh-H
) 1.3 Hz, P(CH3)3), 1.19 (s, 24 H, BO2C6H12); 31P{1H}: δ 14.8
(d, JRhP ) 177 Hz); 13C{1H}: δ 89.7 (t, C5H5, JPC ) JRhC ) 2.29
Hz), 81.09 (s, BO2C2(CH3)4), 25.4 (s, BO2C2(CH3)4), 25.3 (s,
BO2C2(CH3)4), 23.6 (dd, JPC ) 32.0, JRhC ) 1.5 Hz, P(CH3)3);
11B: δ 45.1. MS, (EI, m/z: 498 (2%, M+), 414 (3.8%, M+ - C2-
Me4), 371 (25%, M+ - Bpin), 244 (100%, M+ - B2pin2).
[Rh(η5-C5H5)(SiMe2Et)(H)(PMe3)], 5a. An NMR tube was
charged with 1a (1-2 mg, 4-7 µmol) and neat Me2EtSiH (1 mL)
and irradiated at room temperature for 10 h. All volatiles were
removed under vacuum, giving a brown oil. NMR (C6D6, 300 K),
1H: δ 5.10 (s, 5H, C5H5), 1.22 (t, 3 H, JHH 7.9 Hz, CH3), 1.02 (d,
9 H, JPH ) 9.5 Hz, P(CH3)3), 0.86 (m, 2 H, CH2), 0.51(s, 3 H,
CH3), 0.48 (s, 3 H, SiCH3), -14.5 (dd, 1 H, JRhH ) 32.1 Hz, JPH
) 33.1 Hz, RhH); 31P{1H}: δ 5.5 (d, JRhP ) 171 Hz).
[Rh(η5-C5H5)(SiMeEt2)(H)(PMe3)], 6a. The same procedure
1
was followed as for 5a. NMR (C6D6, 300 K), H: δ 5.11 (s, 5 H,
C5H5), 1.20 (t, 6 H, JHH ) 7.7 Hz, CH3), 1.01 (d, 9 H, JPH ) 10.8
Hz, P(CH3)3), 0.88 (m, 4 H, CH2), 0.43 (s, 3 H SiCH3), -14.58
(dd, 1 H, JRhH ) 32.4, JPH ) 33.1 Hz, RhH); 31P{1H}: δ 5.3 (d,
JRhP ) 171 Hz).
[Rh(η5-C5H5){Si(OMe)3}(H)(PMe3)], 7a. The same procedure
[Rh(η5-C5H5)(SiMe2Et)(H)(PPh3)], 5b. An NMR tube was
charged with 1b (1-2 mg, 2-4 µmol) and neat Me2EtSiH (1 mL)
and irradiated at ca. -10 °C for 15 h. All volatiles were removed
under vacuum to give a dark brown oil. NMR (C6D6, 300 K), 1H:
1
was followed as for 5a. NMR (C6D6, 300 K), H: 5.22 (s, 5 H,
C5H5), 3.61 (s, 9H, CH3), 1.18 (dd, 9H, JPH ) 10.5, JRhH ) 1 Hz,
P(CH3)3), -14.06 (dd, 1 H, JPH ) 31.5, JRhH ) 32.3 Hz, RhH);
31P{1H}: δ 9.6 (d, JRhP ) 160 Hz).
δ 7.68-6.68 (m, 15H, Ph), 5.07 (s, 5H, C5H5), 1.16 (t, 3H, JHH
)
[Rh(η5-C5H5)(SiEt2H)(H)(PMe3)], 8a. The same procedure was
followed as for 5a. NMR (C6D6, 300 K), 1H: δ 5.10 (s, 5 H, C5H5),
3.94 (d, 1H, JHP ) 16 Hz, SiH), 1.31 (m, 6 H, CH3), 1.07 (d, 9 H
JPH ) 9.5 Hz, P(CH3)3), 0.96 (m, 4 H, CH2), -14.6 (dd, 1 H, JPH
) 33.5, JRhH ) 32.1 Hz, RhH); 31P{1H}, δ 8.2 (d, JRhP ) 165 Hz).
7.7 Hz CH3), 0.75 (m, 2H, CH2), 0.3 (s, 3H, CH3), 0.1 (s, 3H,
CH3), -13.38 (dd, 1H, JPH ) 29.3, JRhH ) 30.2 Hz, RhH); 31P-
{1H}: δ 62.5 (d, JRhP ) 184 Hz).
[Rh(η5-C5H5)(SiMeEt2)(H)(PPh3)], 6b. The same procedure was
1
[Rh(η5-C5H5)(SiEt3)(H)(PMe3)], 9a. The same procedure was
followed as for 5a. NMR (C6D6, 300 K), 1H: δ 5.14 (s, 5 H, C5H5),
1.27 (t, 9H, JHH ) 7.8 Hz, CH3), 0.99 (d, 9H, JPH ) 10.1 Hz,
followed as for 5b. NMR (C6D6, 300 K), H: δ 7.68-6.68 (m,
15H, Ph), 5.08 (s, 5H, C5H5), 1.13 (m, 6H, CH3), 0.89 (m, 2H,
CH2), 0.78 (2H, CH2), 0.07 (m, 3H, CH3), -13.4 (apparent t, 1H,
JPH ∼ JRhH ) 29.3 Hz, RhH); 31P{1H}: δ 62 (d, JRhP ) 185 Hz).
P(CH3)3), 0.86 (m, 6H, CH2), -14.55 (dd, 1H, JPH ) 32.3, JRhH
)
[Rh(η5-C5H5){Si(OMe)3}(H)(PPh3)], 7b. The same procedure
31.5 Hz, RhH) 31P{1H}: δ 5.2 (d, JRhP ) 171 Hz).
1
[Rh(η5-C5H5)(SiiPr3)(H)(PMe3)], 10a. The same procedure
was followed as for 5a. Slow evaporation of a hexane solution in
was followed as for 5b. NMR (C6D6, 300 K), H: δ 7.69-7.03
(m, 15H, Ph), 5.21 (s, 5H, C5H5), 3.4 (s, 9H, CH3), -12.99 (dd, 1
H, JPH ) 28.3, JRhH ) 29.1 Hz, RhH); 31P{1H}: δ 59.2 (d, JRhP
175 Hz).
)
1
the glovebox gave yellow crystals. NMR (C6D6, 300 K), H: δ
5.12 (s, 5 H, C5H5), 1.23 (dd, 18H, JHH ) 13.7 Hz, CH3), 1.13 (m,
3H, CH), 0.95 (d, 9H, JPH ) 9.6 Hz, P(CH3)3), -14.6 (dd, 1H, JPH
) 33.2, JRhH ) 29.8 Hz, RhH); 31P{1H}: δ 0.87 (d, JRhP ) 174
Hz).
[Rh(η5-C5H5)(SiEt2H)(H)(PPh3)], 8b. The same procedure was
1
followed as for 5b. NMR (C6D6, 300 K), H: δ 7.68-6.68 (m,
15H, Ph), 5.13 (s, 5H, C5H5), 3.82 (d, 1H, JHP ) 15 Hz, SiH), 1.31

Photoinduced OxidatiVe Addition at Rh Centers
Organometallics, Vol. 25, No. 21, 2006 5103
Table 7. Summary of Crystallographic Data for 1b, 1c, 2b, 2b‚3b, 10a, and 11b‚C6H5CH3
1b
1c
2b
2b‚3b
10a
11b‚C6H5CH3
formula
fw
temp (K)
cryst syst
space group
a (Å)
C25H24PRh
458.32
115(2)
monoclinic
P21/n
19.6790(18)
9.6720(9)
21.451(2)
90
95.435(2)
90
C11H17F3PRh
340.13
115(2)
orthorhombic
Pbca
10.7234(6)
14.3049(8)
16.7704(10)
90
90
90
2572.5(3)
8
C29H33BO2PRh
558.24
110(2)
triclinic
P1h
10.7735(7)
10.9101(7)
11.7832(7)
77.068(1)
77.854(1)
77.895(1)
1300.29(14)
2
C70H68BO2P3Rh2
1250.78
115(2)
triclinic
P1h
12.0010(7)
14.0158(8)
18.2082(11)
72.634(1)
85.868(1)
89.726(1)
2915.0(3)
2
C17H36PRhSi
402.43
110(2)
triclinic
P1h
8.6515(4)
10.4606(5)
12.1019(6)
74.981(1)
71.512(1)
72.050(1)
972.20(8)
2
C30H28Cl2PRh
593.30
110(2)
monoclinic
P21/c
13.5551(15)
10.2404(11)
19.151(2)
90
100.272(2)
90
2615.8(5)
4
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
4064.6(7)
8
density (calcd)
1.498
1.756
1.426
1.425
1.375
1.507
(Mg/m3)
F(000)
1872
1360
576
1288
424
1208
no. of reflns
collected
no. of ind reflns
no. of ind reflns
[I > 2σ(I)]
no. of data/
restraints/
params
22 114
27 291
14 651
23 235
11 103
19 928
7168
4455
3743
3413
7284
6836
16 255
11762
5479
5285
4621
3766
7168/0/487
3743/0/160
7284/0/315
16 255/0/711
5479/0/194
4621/0/308
H atoms
riding + diff
0.930
riding + diff
1.033
riding + diff
1.060
riding + diff
0.996
riding + diff
1.049
riding
1.019
goodness-of-fit
on F2
final R indices
[I > 2σ (I)]
R indices (all data)
R1 ) 0.0349,
wR2 ) 0.0695
R1 ) 0.0786,
wR2 ) 0.0822
0.807 and -0.757
R1 ) 0.0251,
wR2 ) 0.0645
R1 ) 0.0284,
wR2 ) 0.0662
1.117 and -0.360
R1 ) 0.0223,
wR2 ) 0.0574
R1 ) 0.0243,
wR2 ) 0.0583
0.830 and -0.567
R1 ) 0.0400,
wR2 ) 0.0838
R1 ) 0.0687,
wR2 ) 0.0960
1.111 and -0.543
R1 ) 0.0158,
wR2 ) 0.0407
R1 ) 0.0166,
wR2 ) 0.0409
0.549 and -0.240
R1 ) 0.0364,
wR2 ) 0.0833
R1 ) 0.0503,
wR2 ) 0.0887
1.165 and -0.945
max. diff peak
and hole (e/Å3)
CCDC no.
616691
616692
616693
616694
616695
616696
(t, 3H, JHH ) 7.7 Hz CH3), 1.03-1.10 (m, 7H, CH3 + 2CH2),
-13.57 (dd, 1 H, JPH ) 29.9, JRhH ) 29.5 Hz, RhH); 31P{1H}: δ
62.8 (d, JRhP ) 178 Hz).
1.39 (d, 9 H JPH ) 12.7 Hz, P(CH3)3), 1.14 (s, 24 H (BO2C6H12)2);
31P{1H}: δ 19 (d, JRhP ) 176 Hz); 11B{1H}: δ 43.8; 19F: δ -53.5
(s).
[Rh(η5-C5H4CF3)(SiMe2Et)(H)(PMe3)], 5c. An NMR tube was
charged with 1c (0.01 g, 23 µmol) and neat Me2EtSiH (1 mL) and
irradiated at at ca. -10 °C for 4 h. All volatiles were removed to
give an orange-brown oil. NMR (C6D6, 300 K), 1H: δ 5.39 (s, 1H,
C5H4), 5.30 (s, 1H, C5H4), 5.18 (s, 1H, C5H4), 4.72 (s, 1H, C5H4),
[Rh(η5-C5H5)Cl2(PPh3)], 11b. An NMR tube was charged with
1b (10 mg) in 1,2-dichloroethane and a 2-fold excess of B2pin2
and irradiated at room temperature with the medium-pressure Hg
arc (5 h), resulting in 100% conversion to 11b. All volatiles were
removed to give an orange solid. The solid was transferred to the
glovebox, redissolved in toluene, and eluted through a neutral
alumina column with additional toluene in order to remove boron-
containing impurities, followed by sublimation of B2pin2. Slow
evaporation of the toluene solution in the glovebox gave orange
1.13 (t, 3H, JHH ) 7.7 Hz, CH3), 0.97 (dd, 9H JPH ) 12.7, JRhH
)
1.4 Hz, P(CH3)3), 0.77 (m, 2H, CH2), 0.44 (s, 3H, CH3), 0.39 (s,
3H, CH3), -15.24 (ddq, 1H, JPH ) 33.5, JRhH ) 33.1, JFH ) 2.8
Hz, RhH); 31P{1H}: δ 6.8 (d, JRhP ) 171 Hz); 19F: δ -53.71 (s).
[Rh(η5-C5H4CF3)(SiMeEt2)(H)(PMe3)], 6c. The same procedure
1
crystals of 11b. NMR (C6D6, 300 K), H: δ 7.87-6.99 (m, 15H,
Ph), 5.4 (s, 5H, C5H5); 31P{1H}: δ 32.8 (d, JRhP ) 136 Hz).
[Rh(η5-C5H4CF3)(Bpin)(H)(PMe3)], 2c. An NMR tube was
charged with 1c (1-2 mg, 2-4 µmol) and neat HBpin (∼1 mL)
and irradiated at ca. -10 °C for 15 h. All volatiles were removed
under vacuum to give a dark orange solid. NMR (C6D6, 300 K),
1H: δ 5.75 (s, 1H, C5H4), 5.52 (s, 1H, C5H4), 5.31 (s, 1H, C5H4),
5.19 (s, 1H, C5H4), 1.23 (s, 6H, BO2C2(CH3)4), 1.25 (s, 6H, BO2C2-
(CH3)4), 0.95 (d, 9H, JPH ) 9.7 Hz, P(CH3)3), -14.58 (dd, 1H, JPH
) 34.6, JRhH ) 36.8 Hz, RhH); 31P{1H}: δ 13.7 (d, JRhP ) 169
Hz); 13C{1H}: δ 125.5 (q JCF ) 267, CF3), 95.3 (qd, JCF ) 38,
JCRh ) 3 Hz, C-CF3), 90.0 (apparent sextet, J ) 3 Hz C5H4), 89.6
was followed as for 5c. NMR (C6D6, 300 K), H: δ 5.41 (s, 1H,
1
C5H4), 5.29 (s, 1H, C5H4), 5.20 (s, 1H, C5H4), 4.73 (s, 1H, C5H4),
1.12 (t, 6H, JHH ) 7.8 Hz, CH3), 0.96 (d, 9H JPH ) 12.7 Hz,
P(CH3)3), 0.79 (m, 4H, CH2), 0.35 (s, 3H, CH3), -15.2 (ddq, 1H,
JPH ) 33.3, JRhH ) 32.8, JFH ) 2.8 Hz, RhH); 31P{1H}: δ 8.7 (d,
JRhP ) 171 Hz); 19F: δ -53.6 (d, JFRh ) 3 Hz).
[Rh(η5-C5H4CF3){(SiOMe)3}(H)(PMe3)], 7c. The same proce-
1
dure was followed as for 5c. NMR (C6D6, 300 K), H: δ 5.57 (s,
1H, C5H4), 5.42 (s, 1H, C5H4), 5.27(s, 1H, C5H4), 4.93 (s, 1H, C5H4),
3.52 (s, 9H, CH3), 1.15 (d, JPH ) 10.7, 9H, P(CH3)3), -14.52 (ddq,
1H, JPH ) 31.1, JRhH ) 33.2, JFH ) 2 Hz, RhH); 31P{1H}: δ 9.6
(d, JRhP ) 160 Hz); 19F: δ -53.72 (s).
(m, C5H4), 89.3 (s, C5H4), 85.6 (overlapping dq, JCRh ) 5, JCF
)
3 Hz, C5H4), 81.6 (s, BO2C2(CH3)4), 25.2 (s, BO2C2(CH3)4), 24.8
(s, BO2C2(CH3)4), 22.9 (dd, JPC ) 34, JRhC ) 2 Hz, P(CH3)3,);
11B{1H}: δ 43.9; 19F: δ -54.0 (s). MS, (EI, m/z): 440 (13%, M+),
355 (1%, M+ - C6H13), 312 (100%, M+ - HBpin). HRMS: exp
440.077062, calcd 440.077680, difference 0.618 mDa.
[Rh(η5-C5H4CF3)(SiEt2H)(H)(PMe3)], 8c. The same procedure
1
was followed as for 5c. NMR (C6D6, 300 K), H: δ 5.43 (s, 1H,
C5H4), 5.38 (s, 1H, C5H4), 5.06 (s, 1H, C5H4), 4.74 (s, 1H, C5H4),
3.99 (d, 1H, JHP ) 16 Hz, SiH), 1.22 (t, 6H, JHH ) 7.7 Hz, CH3),
1.02 (d, 9H, JPH ) 10.4 Hz, P(CH3)3), 0.94 (m, 4H, CH2), -15.14
(ddq, 1H, JPH ) 33.3, JRhH ) 32.8, JFH ) 2.9 Hz, RhH); 31P{1H}:
δ 9.1 (d, JRhP ) 165 Hz); 19F: δ -53.93 (s).
[Rh(η5-C5H4CF3)(Bpin)2(PMe3)], 4c. An NMR tube was charged
with a hexane solution of 1c (0.01 g, 22.7 µmol) and a ca. 4-fold-
excess of B2pin2 (0.02 g, 78.74 µmol) and irradiated at ca. -10 °C
for 15 h. All volatiles were removed under vacuum to give a dark
brown solid. NMR (C6D6, 300 K), 1H: δ 5.76, 5.43 (s, 4 H, C5H4),
[Rh(η5-C5H4CF3)(SiEt3)(H)(PMe3)], 9c. The same procedure
1
was followed as for 5c. NMR (C6D6, 300 K), H: δ 5.44 (s, 1H,
C5H4), 5.28 (s, 1H, C5H4), 5.21 (s, 1H, C5H4), 4.76 (s, 1H, C5H4),

5104 Organometallics, Vol. 25, No. 21, 2006
Caˆmpian et al.
1.21 (t, 6H, JHH ) 7.7 Hz, CH3), 0.96 (dd, 9H, JPH ) 9.7, JRhH
)
SHELXL-97 (Sheldrick, 1997).61 All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms bound to carbon were
placed using a “riding model” and included in the refinement at
calculated positions with the exception of the C2H4 hydrogen atoms
in 1b and 1c. These hydrogen atoms and the hydrides were located
on difference maps after all non-hydrogen atoms had been located
and were refined isotropically.
The structure of 1b was refined in P21/n and showed two
independent molecules in the asymmetric unit, which differed only
by the orientation of one phenyl ring. An attempt to refine in a
P21/c cell with a reduced by a factor of 2 to 9.8395 Å and Z reduced
by a factor of 2 resulted in a structure with unsatisfactory anisotropic
displacement parameters.
1.0 Hz, P(CH3)3), 0.77 (m, 4H, CH2), -15.14 (ddq, 1H, JPH ) 35.7,
JRhH ) 32.8, JFH ) 2.9 Hz, RhH); 31P{1H}: δ 4.7 (d, JRhP ) 171
Hz); 19F: δ -53.4 (d, JFRh ) 3 Hz).
[Rh(η5-C5H4CF3)(SiiPr3)(H)(PMe3)], 10c. The same procedure
1
was followed as for 5c. NMR (C6D6, 300 K), H: δ 5.40 (s, 1H,
C5H4), 5.37 (s, 1H, C5H4), 5.21 (s, 1H, C5H4), 4.86 (s, 1H, C5H4),
1.1-1.21 (m, 21H, CH3 + CH), 0.97 (dd, 9H, JPH ) 9.8, JRhH
1.0 Hz, P(CH3)3), -14.91 (ddq, 1H, JPH ) 33.2, JRhH ) 30.7, JFH
) 2.9 Hz, RhH); 31P{1H}: δ 0.3 (d, JRhP ) 174 Hz); 19F: δ -53.0
(d, JFRh ) 3 Hz).
)
Competition Reactions. An NMR tube was charged with 1b (5
mg, 0.011 mmol), HBpin (10 eq, 15.8 µL), and Et3SiH (10 equiv,
17.4 µL), all dissolved in hexane (-1 mL), and irradiated at -10
°C for a specified period. Several similar reactions were carried
out with different combinations of reagents in competition (Table
6). In some cases, the reactions were followed by 31P{1H} NMR
spectroscopy with no lock. Otherwise, all volatiles were removed
Acknowledgment. We acknowledge the support of EPSRC
and the European Union (Marie Curie Host Fellowship scheme),
assistance from Prof. S. B. Duckett, and useful discussions with
Dr. Sylviane Sabo-Etienne and Mr. Richard Lindup.
Supporting Information Available: Crystal and molecular
structure of 1b; intermolecular interactions for 2b; crystal and
molecular structure of 2b‚3b, including intramolecular π-π
interaction for 2b and intermolecular interactions in 2b‚3b; crystal
and molecular structure of 11b‚C6H5CH3; intermolecular interac-
tions for 11b‚C6H5CH3; 1H, 31P, and (where appropriate) 11B NMR
spectra of 2a-2c, 4a-4c, 5a-5c, 6a-6c, 7a-7c, 8a-8c, 9a, 9c.
This material is available free of charge via the Internet at
http://pubs.acs.org.
1
under vacuum, C6D6 was added, and the H NMR spectrum was
1
recorded. The reactions followed by H NMR were carried out in
C6D12 and those by 31P NMR spectroscopy, in hexane.
X-ray Crystallography. Crystallographic data are listed in Table
7. Diffraction data were collected on a Bruker Smart Apex
diffractometer with Mo KR radiation (λ ) 0.710 73 Å) using a
SMART CCD camera. Diffractometer control, data collection, and
initial unit cell determination were performed using “SMART”
(v5.625 Bruker-AXS). Frame integration and unit-cell refinement
was carried out with “SAINT+” (v6.22, Bruker AXS). Absorption
corrections were applied using SADABS (v2.03, Sheldrick).
Structures were solved by direct methods using SHELXS-97
(Sheldrick, 1997) and refined by full-matrix least squares using
OM060500M
(61) Sheldrick, G. M. SHELXS-97, Program for Structure Solution;
University of Go¨ttingen: Go¨ttingen, Germany, 1997. Sheldrick, G. M.
SHELXL-97, Program for the Refinement of Crystal Structures; University
of Go¨ttingen: Go¨ttingen, Germany, 1997.