C-C bond activation of a cyclopropyl phosphine: isolation and reactivity of a tetrameric rhodacyclobutane

Article abstract of DOI:10.1021/om100105p

Reaction of the functionalized phosphine P^tBu₂CH ₂(C₃H₅) with [Rh(C₈H ₁₄)₂Cl]₂ (C₈H₁₄ = cis-cyclooctene) resulted in selective C-C bond activation of the cyclopropyl group and formation of a tetrameric rhodacyclobutane, [RhCl(-³-P ^tBu₂CH₂CH(CH₂)₂)] ₄, which was characterized in the solid state by X-ray crystallography. This complex acts as a latent source of the [Rh(- ³-P^tBu₂CH₂CH(CH₂) ₂)]⁺ fragment, forming a range of new complexes by salt metathesis with NaCp, [RhCp(-³-P^tBu₂CH ₂CH(CH₂)₂)], chloride abstraction in the presence of arenes, [Rh(-⁶-arene)(-³-P^tBu ₂CH₂CH(CH₂)₂)][BAr^F ₄] [arene = C₆H₅F, C₆H ₃Me₃; Ar^F = 3,5-C₆H ₃(CF₃)₂], or fragmentation by addition of phosphine ligands, trans-[RhCl(PR₃)(-³-P ^tBu₂CH₂CH(CH₂)₂)] (R = ⁱBu, Cy). In contrast, reaction with carbon monoxide results in the reductive elimination of the tethered cyclopropane, demonstrating reversible C-C bond activation, and formation of cis-[RhCl(CO)₂(P ^tBuCH₂(C₃H₅))]. These complexes were characterized in solution by NMR spectroscopy and in the solid state by X-ray diffraction. Chloride abstraction from [RhCl(PⁱBu₃)(- ³-P^tBu₂CH₂CH(CH₂) ₂)] resulted in the regioselective isomerization of the tethered cyclopropane to a terminal alkene, viz., the formally 14-electron complex [Rh(PⁱBu₃)(-³-P^tBu ₂CH₂CH₂CH - CH₂)][BAr ^F₄], notable for the presence of a strong agostic interaction with a phosphine ⁱBu substituent, apparent both from the solid-state structure and in solution by ¹H NMR spectroscopy. Addition of hydrogen to this complex resulted in hydrogenation of the alkene and formation of [Rh(H)₂(PⁱBu₃)(P ^tBu₂ⁿBu)][BAr^F₄]. These steps overall correspond to selective C-C bond functionalization (hydrogenation) of the tethered cyclopropane and are of direct significance to a related catalytic process [J. Am. Chem. Soc. 2003, 125, 886] and, more generally, to the rhodium-mediated transformation of alkanes.

Full text of DOI:10.1021/om100105p

2332 Organometallics 2010, 29, 2332–2342
DOI: 10.1021/om100105p
C-C Bond Activation of a Cyclopropyl Phosphine: Isolation and
Reactivity of a Tetrameric Rhodacyclobutane
Adrian B. Chaplin and Andrew S. Weller*
Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, OX1 3QR Oxford, U.K.
Received February 10, 2010
Reaction of the functionalized phosphine PtBu2CH2(C3H5) with [Rh(C8H14)2Cl]2 (C8H14 = cis-
cyclooctene) resulted in selective C-C bond activation of the cyclopropyl group and formation of a
tetrameric rhodacyclobutane, [RhCl(κ3-PtBu2CH2CH(CH2)2)]4, which was characterized in the solid
state by X-ray crystallography. This complex acts as a latent source of the [Rh(κ3-PtBu2CH2CH(CH2)2)]þ
fragment, forming a range of new complexes by salt metathesis with NaCp, [RhCp(κ3-PtBu2CH2CH-
(CH2)2)], chloride abstraction in the presence of arenes, [Rh(η6-arene)(κ3-PtBu2CH2CH(CH2)2)][BArF ]
4
[arene= C6H5F, C6H3Me3; ArF =3,5-C6H3(CF3)2], or fragmentation by addition of phosphine ligands,
trans-[RhCl(PR3)(κ3-PtBu2CH2CH(CH2)2)] (R = iBu, Cy). In contrast, reaction with carbon monoxide
results in the reductive elimination of the tethered cyclopropane, demonstrating reversible C-C bond
activation, and formation of cis-[RhCl(CO)2(PtBuCH2(C3H5))]. These complexes were characterized in
solution by NMR spectroscopy and in the solid state by X-ray diffraction. Chloride abstraction from
[RhCl(PiBu3)(κ3-PtBu2CH2CH(CH2)2)] resulted in the regioselective isomerization of the tethered
cyclopropane to a terminal alkene, viz., the formally 14-electron complex [Rh(PiBu3)(κ3-PtBu2-
CH2CH2CHdCH2)][BArF ], notable for the presence of a strong agostic interaction with a phosphine
4
iBu substituent, apparent both from the solid-state structure and in solution by 1H NMR spectroscopy.
Addition of hydrogen to this complex resulted in hydrogenation of the alkene and formation of
[Rh(H)2(PiBu3)(PtBu2 Bu)][BArF ]. These steps overall correspond to selective C-C bond functionali-
n
4
zation (hydrogenation) of the tethered cyclopropane and are of direct significance to a related catalytic
process [J. Am. Chem. Soc. 2003, 125, 886] and, more generally, to the rhodium-mediated transformation
of alkanes.
Introduction
hydrogenolysis,3,4 ring-opening,4,5 ring expansion,6 alkene
carboacylation,7 lactone formation,8 and C-C bond cou-
pling with alkenes and alkynes.9 A notable recent highlight is
the development of enantioselective ring expansion pro-
cesses based on successive rhodium-mediated C-C and
C-H bond activation.10
Key intermediates in the ring-opening of cyclopropanes
are metallacyclobutanes, compounds further notable for
their relevance to olefin metathesis.11 Metallacyclobutanes
The transition-metal-mediated cleavage and subsequent
fuctionalization of C-C single bonds is an area of significant
contemporary interest.1 The selective activation of these
traditionally unreactive bonds is a challenging aspect of
organometallic chemistry owing to, in general, unfavorable
kinetics and thermodynamics for oxidative addition and
competing C-H activation processes.1 In spite of these
limitations considerable progress has been made by use of
substrates containing intrinsically strained C-C bonds (e.g.,
cyclopropanes and cyclobutanes), with the relief of ring
strain and orbital directionality promoting oxidative addi-
tion, or by tight chelation control.1,2 Rhodium phosphine
catalysts feature prominently in these processes and have
been used for a wide range of transformations, including
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*Corresponding author. E-mail: andrew.weller@chem.ox.ac.uk.
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van der Eide, E. F.; Romero, P. E.; Piers, W. E. J. Am. Chem. Soc. 2008, 130,
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r
pubs.acs.org/Organometallics
Published on Web 04/23/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 10, 2010 2333
Chart 1
Scheme 1. Preparation of 1
while addition of Lewis bases results in irreversible reduc-
tive C-C bond elimination.18b,19 Similar σ-C-C bond-
ing intermediates have been observed in solution during
intramolecular C-C bond activation in rhodium and
platinum systems.20 The presence of σ-C-C bonding
interactions in cyclopropyl niobium complexes has also
been discussed.21
As part of our investigations into C-C bond activation by
rhodium phosphine compounds,18 we targeted the synthesis
of rhodium complexes containing the cyclopropyl phosphine
PtBu2CH2(C3H5)22 in an attempt to recreate the bonding
modes observed in D. The synthesis and characterization
of a tetrameric rhodacyclobutane, [RhCl(κ3-PtBu2CH2CH-
(CH2)2)]4 (1), resulting from C-C bond activation, is de-
scribed along with related mononuclear derivatives. We also
demonstrate the reversibility of this C-C bond cleavage, by
reaction with CO, and isomerization of the metallacylobu-
tane group to give a terminal alkene, which can be sub-
sequently hydrogenated within the coordination sphere of
the metal. Previous complexes containing PtBu2CH2(C3H5),
and activated derivatives, have been described by Ibers,
although limited to platinum,22 palladium,23 and iridium
examples.24
of transition metals are well established;12 platinacyclo-
butanes, in particular, constitute a well-known class since
the first preparation in 1955 by Tipper of the tetrameric
platinum(IV) metallacyclobutane [PtCl2(C3H6)]4 (A, Chart 1)
from reaction of cyclopropane with H2[PtCl6].13 Well-
characterized examples of rhodacyclobutanes, however,
are comparatively rare. This is surprising, given both the
isoelectronic relationship between Rh(III) and Pt(IV) and
their important role as intermediates in C-C bond activa-
tion. A pertinent rhodium example is the metallacyclobu-
tane B, prepared from reaction between the latent
[RhCp*(PMe3)] fragment and cyclopropane at low tem-
perature.14 A range of related rhodium cylcopentadienyl
complexes are also known.15 The [RhCp*(PMe3)] frag-
ment has, in addition, been shown to undergo insertion
into the C-C bonds of cyclobutane and biphenylene.14a,16
Other notable, well-characterized rhodacyclobutane ex-
amples include the hydridotris(pyrazolyl)borate complex
C,17 formed by rearrangement of a hydrido-cyclopropyl
precursor, and the cationic rhodium phosphine complexes
D.18 The latter are significant not only for the adoption of
metallacyclobutane rings, but for additional stabilizing
σ-C-C bonding interactions between the rhodium centers
and adjacent cyclopropane groups of the coordinated
BINOR-S ligands. These bonding interactions in D are
found to be in rapid equilibrium at room temperature,
demonstrating reversible C-C bond activation in solution,
Results and Discussion
Reaction of the dimeric rhodium precursor [Rh(C8H14)2Cl]2
(C8H14 = cis-cyclooctene) with PtBu2CH2(C3H5) in pentane-
heptane at 80 ꢀC resulted in the precipitation of a yellow
microcrystalline solid, characterized as the tetrameric rhodacy-
clobutane [RhCl(κ3-PtBu2CH2CH(CH2)2)]4 (1, Scheme 1), in
high yield (79%). Complex 1 could also be prepared at
room temperature in pentane, but required long reaction
times (ca. days) due to insolubility of the starting material.
Formation of this complex is notable for the selective C-C
bond activation of the tethered cyclopropane group,
with ring-opening occurring at the least substituted posi-
tion. Similar selective C-C bond activation of cyclopro-
panes has been demonstrated by Bergman by reaction of
1,1-dimethylcyclopropane with the [RhCp*(PMe3)] frag-
ment.14a
(12) (a) Jennings, P. W.; Johnson, L. J. Chem. Rev. 1994, 94, 2241. (b)
Chappell, S. D.; Cole-Hamilton, D. J. Polyhedron 1982, 1, 739. (c)
Puddephatt, R. J. Coord. Chem. Rev. 1980, 33, 149.
(13) (a) Binns, S. E.; Cragg, R. H.; Gillard, R. D.; Heaton, B. T.;
Pilbrow, M. F. J. Chem. Soc. A 1969, 1227. (b) Tipper, C. F. H. J. Chem.
Soc. 1955, 2045.
(14) (a) Periana, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1986, 108,
7346. (b) Periana, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1984, 106, 7272.
(15) (a) Tjaden, E. B.; Stryker, J. M. Organometallics 1992, 11, 16. (b)
Tjaden, E. B.; Stryker, J. M. J. Am. Chem. Soc. 1990, 112, 6420. (c)
Andreucci, L.; Diversi, P.; Ingrosso, G.; Lucherini, A.; Marchatti, F.;
Adovasio, V.; Nardelli, M. J. Chem. Soc., Dalton Trans. 1986, 477.
(16) Perthuisot, C.; Jones, W. D. J. Am. Chem. Soc. 1994, 116, 3647.
(17) Wick, D. D.; Northcutt, T. O.; Lachicotte, R. J.; Jones, W. D.
Organometallics 1998, 17, 4484.
(20) (a) Madison, B. L.; Thyme, S. B.; Keene, S.; Williams, B. S. J.
Am. Chem. Soc. 2007, 129, 9538. (b) Gandelman, M.; Vigalok, A.;
Konstantinovski, L.; MIlstein, D. J. Am. Chem. Soc. 2000, 122, 9848.
(21) (a) Boulho, C.; Keys, T.; Coppel, Y.; Vendier, L.; Etienne, M.;
Locati, A.; Bessac, F.; Maseras, F.; Pantazis, D. A.; McGrady, J. E.
Organometallics 2009, 28, 940. (b) Jaffart, J.; Cole, M. L.; Etienne, M.;
Reinhold, M.; McGrady, J. E.; Maseras, F. Dalton Trans. 2003, 4057.
(22) Youngs, W. J.; Ibers, J. A. Organometallics 1983, 2, 979.
(23) Youngs, W. J.; Mahood, J.; Simms, B. L.; Swepston, P. N.; Ibers,
J. A.; Maoyu, S.; Jinling, H.; Jiaxi, L. Organometallics 1983, 2, 917.
(24) (a) Youngs, W. J.; Simms, B. L.; Ibers, J. A. J. Organomet. Chem.
1984, 272, 295. (b) Youngs, W. J.; Ibers, J. A. J. Am. Chem. Soc. 1983, 105,
639.
(18) (a) Brayshaw, S. K.; Sceats, E. L.; Green, J. C.; Weller, A. S.
Proc. Natl. Acad. Sci. 2007, 104, 6921. (b) Brayshaw, S. K.; Green, J. C.;
€
Kociok-Kohn, G.; Sceats, E. L.; Weller, A. S. Angew. Chem., Int. Ed. 2006,
45, 452.
(19) (a) Chaplin, A. B.; Weller, A. S. Angew. Chem., Int. Ed. 2010, 49,
581. (b) Chaplin, A. B.; Poblador-Bahamonde, A. I.; Sparkes, H. A.; Howard,
J. A. K.; Macgregor, S. A.; Weller, A. S. Chem. Commun. 2009, 244.

2334 Organometallics, Vol. 29, No. 10, 2010
Chaplin and Weller
a
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for 1
parameter
(about Rh1)
Rh1
Rh2
Rh3
Rh4
Rh1-P1
2.2591(12) 2.2578(12) 2.2609(11) 2.2640(12)
2.4814(11) 2.4921(10) 2.4877(10) 2.5079(11)
2.6324(10) 2.613(5) 2.6327(10) 2.6243(11)
2.6132(11) 2.6205(11) 2.5917(11) 2.6271(10)
Rh1-Cl1
Rh1-Cl2
Rh1-Cl4
Rh1-C3
Rh1-C4
2.078(4)
2.078(5)
2.261(7)
2.084(5)
2.056(4)
2.219(7)
2.086(5)
2.076(4)
2.231(7)
2.079(5)
2.067(4)
2.230(7)
C3 C4
3 3 3
P1-Rh1-Cl1
169.16(4) 170.23(4) 169.23(4) 169.44(4)
P1-Rh1-Cg(C3,C4) 80.26(11) 80.24(13) 80.05(13) 80.24(11)
Cl1-Rh1-Cl2
Cl1-Rh1-Cl4
Cl2-Rh1-Cl4
C3-Rh1-C4
Rh1-P1-C1
P1-C1-C2
80.82(3)
86.70(3)
78.14(3)
65.91(8)
98.3(2)
80.51(3)
84.36(3)
78.53(3)
64.8(2)
98.3(2)
102.3(3)
94.6(4)
79.82(3)
85.05(3)
78.82(3)
64.8(2)
98.0(2)
102.5(3)
95.2(4)
80.53(4)
85.86(3)
77.50(3)
65.1(2)
97.9(2)
103.1(3)
94.1(4)
102.3(3)
95.4(3)
C3-C2-C4
a Parameters grouped by metal center.
[RhI(η5-C4H4BR)]4 (R = Me, Ph),29 [Rh(η5-Ph2C2B9H9)-
(OH)]4,30 and [RuCp*Cl]4.31
Figure 1. Solid-state structure of 1. Thermal ellipsoids are
drawn at 50%; phosphine ligands are colored individually,
and H atoms are omitted for clarity.
The structure of 1 observed in the solid state appears to be
retained in solution. The 31P{1H} NMR spectrum exhibits a
single resonance at 113.1 ppm, which shows coupling to
103Rh (1JRhP = 206 Hz), at significantly lower field than free
ligand (28.5 ppm), consistent with chelation of the phos-
phine.32 Two environments, C3 and C4 (see Scheme 1 for
NMR labeling), are observed for the coordinated carbon
centers by 13C{1H} NMR spectroscopy, consistent with the
S4 symmetry observed in the solid state. These resonances are
shifted downfield from the free ligand (10.7, 12.1 ppm vs
7.2 ppm), and both show large coupling to 103Rh of ca. 20 Hz,
confirming that they remain bound in solution. A downfield
shift of similar magnitude is observed for the coordinated
carbon resonances in D [R = iPr; 25.30 ppm (1JRhP = 22 Hz,
200 K) vs free ligand 16.9 ppm].18 For comparison, the
corresponding signals in B [-22.9 ppm (1JRhC = 19 Hz)]14
and C [-16.4 ppm (1JRhC = 16 Hz)]17 are significantly upfield
shifted from cyclopropane (-2.8 ppm), in accordance with
trends observed for other metallacyclobutanes.12 The pseudo-
S4 symmetry seen in the solid-state structure of 1 is not apparent
within resolution limits (500 MHz NMR spectrometer) for the
H1 and tBu group resonances, which are observed as a single set
of peaks by 1H and 13C{1H} NMR spectroscopy. An interesting
feature to note for 1 is the large magnitude of the 3JPH coupling
constant associated with H2 (66.5 Hz), presumably resulting
from the enforced anti-conformation of H2 with the phosphorus
center (av P-C1-C2-H2 dihedral =179.51ꢀ) on formation of
the chelate.32 Similar large coupling constants are observed for
the new compounds described below, and the magnitude of this
coupling correlates with the P-C1-C2-H2 dihedral angle, as
measured in the solid state (Table 2). Complex 1 readily reacts in
solution with a range of ligands (Cp-, C6H5F, C6H3Me3, PR3,
CO), resulting in new complexes 2-5. These reactions are
summarized in Scheme 2 and discussed in turn. Selected solution
and solid-state data are compiled in Table 2.
The solid-state structure of 1 is shown in Figure 1 and
establishesthepresence offourrhodium atoms, eachbearinga
chelating phosphine ligand bound through the phosphorus
center and metalation of the tethered cyclopropane group
(by C-C bond cleavage). The chelate bite angle of ca. 80ꢀ
[P-Rh-Cg(Rh-C,Rh-C), Cg = centroid] is comparable to
dppe (78ꢀ).25 The metallacyclobutane rings are evident from
˚
short Rh-C bonds [2.056(4)-2.086(5) A] and elongated
˚
Rh(C C) distances [2.219(7)-2.261(7) A] (Table 1). These
3 3 3
parameters are in line with those of B-D, in which the values
of Rh-C and Rh(C C) are in the ranges 2.03-2.11 and
3 3 3
14,17,18
˚
2.21-2.42 A, respectively.
The four rhodium phos-
phine fragments are linked by bridging chloride ligands, in a
similar manner to that suggested for Tipper’s tetrameric
platinacyclobutane A,26 resulting in a distorted (noncrystallo-
graphy imposed) S4 symmetrical framework. Long Rh
Rh
3 3 3
˚
distances (>3.6 A) rule out metal-metal bonding. The
Rh-Cl bonds trans to metallacyclobutane rings are signifi-
cantly lengthened in comparison to those trans to the coordi-
nated phosphine group, as expected on the basis of the relative
trans influences of these ligands [2.5917(11)-2.6327(10) vs
˚
2.4814(11)-2.5079(11) A]. Closely related compounds to 1
include [RhCl(η4-C11H8F6)]4,27 [RhF(η2-C2H4)(η2-C2F4)]4,28
(25) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.;
Dierkes, P. Chem. Rev. 2000, 100, 2741.
(26) The structure of A is supported by comparison to the platinium-
(IV) tetramer [PtMe3Cl]4, which has been characterised in the solid state
by X-ray diffraction (Rundle, R. E.; Sturdivant, J. H. J. Am. Chem. Soc.
1947, 69, 1561).
(27) The organic fragment in this complex results from the
Diels-Alder addition of hexafluorobut-2-yne to norbornadiene and
binds through coordination of an alkene and adoption of a metallocy-
clobutane ring (Evans, J. A.; Kemmitt, R. D. W.; Kimura, B. Y.; Russell,
D. R. J. Chem. Soc., Chem. Commun. 1972, 509).
(28) Burch, R. R.; Harlow, R. L.; Ittel, S. D. Organometallics 1987, 6,
982.
(29) Herberich, G. E.; Eckenrath, H. J.; Englert, U. Organometallics
Reaction of 1 with a slight excess of NaCp in CH2Cl2 at room
temperature resulted in the quantitative formation, by NMR
spectroscopy, of the mononuclear cyclopentadienyl rhodacylo-
butane [RhCp(κ3-PtBu2CH2CH(CH2)2)] (2, Scheme 2). Com-
plex 2 is an analogue of B and the closely related cyclopendienyl
1997, 16, 4292.
(30) Hodson, B. E.; Ellis, D.; McGrath, T. D.; Monaghan, J. J.;
Rosair, G. M.; Welch, A. J. Angew. Chem., Int. Ed. 2001, 40, 715.
(31) Fagan, P. J.; Mahoney, W. S.; Calabrese, J. C.; Williams, I. D.
Organometallics 1990, 9, 1843.
(32) Nelson, J. H. Nuclear Magnetic Resonance Spectroscopy; Pretence
Hall: Upper Saddle River, NJ, 2003.

Article
Organometallics, Vol. 29, No. 10, 2010 2335
Table 2. Selected Solution and Solid-State Data for 1-5a
0
ligand
Rh(C3 C ) /A
3 b
δ(H2)
3JPH/Hz
—
c/deg
δ(C3)
1JRhC/Hz
Δδ(H3, H3 )
δ(P)
1JRhP/Hz
˚
DH
3 3 3
1
2
2.219(7)-2.261(7)
2.249(10)
2.220(4)
2.76
3.77
3.10
3.38
3.38
3.27
66.5
55.6
66.7
64.4
56.5
58.7
179.51d
178.38
179.87
179.08
10.7, 12.1
-0.9
10.2
12.8
-2.3
-2.1
20, 20
21
18
19
19
0.22, 0.64
0.47
-
0.32
0.66
0.42
113.1
124.9
133.2
125.2
83.4
206
196
194
194
129
132
Cp
e
3a
3b
4a
4b
5
C6H5F
C6H3Me3
PiBu3
2.213(6)
f
f
-
-
PCy3
2.147(3)
1.483(5)
1.496(4)
178.39
19.91
37.09
19
83.8
e
CO
0.88
-
8.9
-
0.13
58.1
127
a NMR data recorded in C6D6 for 1, 2, 4, and 5; CD2Cl2 for 3. Refer to Schemes 1 and 2 for NMR labeling. For simplicity, data for H4/C4 are
combined with H3/C3 for 1. b Rh(C3 C4) for 1. c P-C1-C2-H2 dihedral angle measured in the solid state; H atoms in calculated positions. d Average
3 3 3
value. e Not resolved (<10 Hz, 0.03 ppm). f No solid-state data available.
Scheme 2. Reactivity of 1; Preparation of Complexes 2-5
Figure 2. Solid-state structure of 2. Thermal ellipsoids are
t
drawn at 50%; minor disordered components (Cp and Bu
groups) and H atoms are omitted for clarity. Selected bond
˚
complexes [RhCp(PiPr3)(CRHCR0HCH2)] E, prepared by
lengths (A) and angles (deg): Rh1-CCp, 2.240(13)-2.288(13);
nucleophilic addition to [CpRh(PiPr3)(η3-allyl)]þ.15a It is identi-
Rh1-P1, 2.250(2); Rh1-C8, 2.101(7); Rh1-C9, 2.147(6);
fied by a doublet resonance at 124.9 ppm by 31P{1H} NMR
C8 C9, 2.249(10); P1-Rh1-Cg(C8,C9), 80.6(2); C8-Rh1-
3 3 3
spectroscopy (1JRhP = 196 Hz) and a coordinated 5H cyclopen-
tadienyl resonace at 5.13 ppm by 1H NMR spectroscopy [cf. 5.17
ppm in E (R = Me, R0 = H)]. The 13C{1H} NMR spectrum
exhibits a significantly upfield metallacyclobutane C3 resonance
[-0.9 ppm (1JRhC = 21 Hz)], in contrast to 1, and a coordinated
cyclopentadienyl resonance at 86.2 ppm [cf. 90.8 ppm in E (R =
Me, R0 = H)]. The structure of 2 has been further verified by X-
ray crystallography, although the overall quality of the data is
poor (R1 = 0.08; see Experimental Section for further details).
Bonding parameters of the chelated phosphine ligand are not
remarkably different from those of 1 (Figure 2).
C9, 63.9(3); Rh1-P1-C6, 98.4(2); P1-C6-C7, 104.5(4);
C8-C7-C9, 94.0(5).
spectrum in this solvent shows coordinated arene resonances
at 111.0, 100.4, and 95.0 ppm. Similar 13C signals for the
phosphine ligand are observed for 3a compared to 1; in
particular, the metallacyclobutane C3 resonance is observed
at 10.2 ppm (cf. 10.7, 12.1 ppm). The solid-state structure
of 3a is depicted in Figure 3 and further substantiates the
η6-coordination of fluorobenzene ligand. The Rh-C bonds
of the coordinated fluorobenzene ligand are in the range
˚
Chloride abstraction from 1 using Na[BArF4] [ArF = 3,5-
C6H3(CF3)2] in C6H5F solution resulted in the formation of
the η6-arene rhodacyclobutane [Rh(C6H5F)(κ3-PtBu2CH2-
CH(CH2)2)][BArF4] (3a, Scheme 2), a cationic π-complex
analogue of 2. The formation of 3a is evidenced by the
presence of coordinated fluorobenzene signals at 6.23,
5.97, and 5.72 ppm (in a 2:2:1 ratio) in the 1H NMR spectrum
(cf. 6.82-7.17 ppm for free C6H5F). The formation of this
arene adduct is also accompanied by a 20 ppm 31P downfield
shift [130.8 ppm (1JRhP = 192 Hz)] from 1. No other species
were observed by NMR spectroscopy during this reac-
tion, and 3a was isolated in high yield following recrystal-
lization (76%). Addition of a stoichiometric amount of
[Ph3PNPPh3]Cl to a flourobenzene solution of isolated 3a
resulted in the immediate and quantitative re-formation of 1,
demonstrating reversible chloride abstraction from this spe-
cies. Fluorobenzene coordination is retained on redissolving
isolated crystalline material in CD2Cl2. The 13C{1H} NMR
2.278(3)-2.390(3) A, with the shorter distances trans to the
˚
phosphine group [2.278(3)-2.305(3) A], similar to those in
[Rh(C6H5F)(κ3-P(C5H9)2(C5H7))][BArF4], containing in-
33
˚
stead a phosphine-olefin ligand [2.244(2)-2.327(3) A].
The distances trans to the metallacyclobutane ring are long-
˚
er, in the range 2.370(3)-2.390(3) A, in line with the high
trans influence of this ligand. Bonding parameters of the
chelated phosphine ligand are, like those of 2, comparable
to 1. A η6-mesitylene rhodacylobutane complex, [Rh(C6H3-
Me3)(κ3-PtBu2CH2CH(CH2)2)][BArF ] (3b), was readily pre-
4
pared analogously to 3a, by reaction of 1 with Na[BArF ] in
4
CH2Cl2/mesitylene, and shows directly comparable solution
and solid-state data (see Experimental Section and Figure 3).
Reaction of 1 with triisobutyl- or tricyclohexyl-phosphine
resulted in the fragmentation of the tetrameric motif
and formation of 16-electron bis-phosphine complexes,
^
(33) Douglas, T. M.; Le Notre, J.; Brayshaw, S. K.; Frost, C. G.;
Weller, A. S. Chem. Commun. 2006, 3408.

2336 Organometallics, Vol. 29, No. 10, 2010
Chaplin and Weller
Figure 3. Solid-state structures of 3a and 3b. Thermal ellipsoids
are drawn at 50%; minor disordered components (C6H5F and
tBu groups in 3a), anions, solvent molecules, and H atoms are
˚
omitted for clarity. Selected bond lengths (A) and angles (deg),
3a: Rh1-CArene, 2.278(3)-2.390(3); Rh1-P1, 2.2883(7); Rh1-
C9, 2.104(3); Rh1-C10, 2.103(3); C9 C10, 2.220(4); P1-Rh1-
3 3 3
Cg(C9,C10), 79.49(7); C9-Rh1-C10, 63.69(12); Rh1-P1-C7,
98.07(10); P1-C7-C8, 103.8(2); C9-C8-C10, 94.1(2). 3b:
Rh1-CArene, 2.260(3)-2.449(3); Rh1-P1, 2.2968(9); Rh1-C12,
Figure 4. Solid-state structure of 4b. Thermal ellipsoids are
drawn at 50%; solvent molecule and H atoms are omitted for
˚
clarity. Selected bond lengths (A) and angles (deg): Rh1-P1,
2.100(3); Rh1-C13, 2.103(3); C12 C13, 2.213(6); P1-Rh1-
3 3 3
2.3477(6); Rh1-P2, 2.3504(6); Rh1-Cl1, 2.4401(6); Rh1-C3,
Cg(C12,C13), 79.59(10); C12-Rh1-C13, 63.6(2); Rh1-P1-C10,
98.03(13); P1-C10-C11, 103.8(2); C12-C11-C13, 93.6(3).
2.083(2); Rh1-C4, 2.081(2); C3 C4, 2.147(3); P1-Rh1-P2,
3 3 3
177.40(2); P1-Rh1-Cl1, 91.88(2); P2-Rh1-Cl1, 90.60(2); P1-
Rh1-Cg(C3,C4), 80.92(6); P2-Rh1-Cg(C3,C4), 96.78(6); Cl1-
Rh1-Cg(C3,C4), 168.02(6); C3-Rh1-C4, 62.07(10); Rh1-P1-
C1, 96.79(7); P1-C1-C2, 105.13(14); C3-C2-C4, 89.7(2);.
trans-[RhCl(PR3)(κ3-PtBu2CH2CH(CH2)2)] [4, Scheme2, R=
iBu (a), Cy (b)], in quantitative yield by NMR spectroscopy.
Formation of these complexes is apparent from 31P{1H} NMR
spectra, which show distinctive pairs of doublets of doublets
2
Scheme 3. Reaction of 1 with PtBu2CH2(C3H5)
with large JPP couplings of 396 and 382 Hz, respectively,
consistent with the trans coordination of the phosphine cen-
ters.32 Large upfield 31P shifts of ca. 30 ppm for the chelating
phosphine are observed for 4 in comparison to 1. Retention of
the metallocylobutane ring is confirmed by the presence of
high-field C3 resonances at ca. -2 ppm in the 13C{1H} NMR
spectrum with large coupling to 103Rh of ca. 19 Hz. Reaction
of 1 with excess (1.25 equiv/Rh) cyclopropyl phosphine,
PtBu2CH2(C3H5), also resulted in the formation of a bis-
phosphine complex, trans-[RhCl(κ3-PtBu2CH2CH(CH2)2)-
(PtBu2CH2(C3H5))] (4c); however, the reaction did not go to
completion, and instead an equilibrium was established be-
tween 1 and 4c [Keq = 10.5 (293 K), Scheme 3]. Presumably this
is a consequence of the larger steric bulk of this ligand in
comparison to triisobutyl- and tricyclohexyl-phosphine; for
example, the crystallographic cone angle34 of PCy3 in 4b is
152ꢀ, while that of PtBu2CH2(C3H5) in 5 is 160ꢀ (vide infra).
The structures of 4 have been confirmed by the determina-
tion of the solid-state structure of 4b by X-ray diffraction
(Figure 4). The rhodium center in this complex adopts a
distorted trigonal-bipyramidal geometry, with the phopshine
centers coordinated in a trans arrangement in the axial posi-
tions [P1-Rh1-P2 = 177.40(2)ꢀ], as expected on the basis of
corresponding reductions of the C3-Rh1-C4 and C3-
C2-C4 angles [62.07(10)ꢀ and 89.7(2)ꢀ vs 63.6(2)-65.91(8)ꢀ
and 93.6(3)-95.4(3)ꢀ, respectively]. The chelate bite angle is
slightly wider in comparison to 1 and 3 [80.92(6)ꢀ vs 79.49(7)-
80.26(11)ꢀ]; this also appears to be the trend compared to 2, but
the difference is not statistically significant [80.6(2)ꢀ].
The further reactivity of 4a was investigated. Reaction
with Na[BArF4] resulted in chloride abstraction and isome-
rization of the activated tethered cyclopropane group to
a terminal alkene, viz., the formally 14-electron [Rh(PiBu3)-
(κ3-PtBu2CH2CH2CHdCH2)][BArF4] (6, Scheme 4). This
complex is the only product observed by NMR spectroscopy
after 20 h and is isolated in high yield (73%).36 The formation
of 6 is shown by 1H NMR spectroscopy by the appearance of
2
the large JPP coupling constant observed by 31P{1H} NMR
spectroscopy (382 Hz), in a similar manner to the related
structures [Rh(2,20-biphenyl)Cl(PPh3)2]9 and [Rh(H)2Cl-
(36) Following the reaction of 4a with Na[BArF4] by 1H and 31P{1H}
NMR spectroscopy indicates rapid chloride abstraction and the presence of
intermediate species during the formation of 6 over ca. 20 h. Unfortunately
we have so far been unable to definitely assign these species, for example to
I-III (Scheme 6) or other potential alkene intermediates that could be
involved in this reaction. A partially refined, poor-quality, X-ray data set
for a single crystal obtained after shorter reaction times infers the presence
of an internal (E-) alkene compound during the formation of 6(seeSI). This
product could potentially form and isomerize to 6 (to minimize ring strain
in the chelating phosphine-olefin ligand) via the allyl-hydride intermediate
III. Complex 6 is stable in CD2Cl2 solution (under Ar) for extended periods
(days) of time, demonstrating that it is the thermodynamically preferred
product in this system.
i
t
(PR3)2] (R = Pr, Bu).35 In comparison to 1-3, there are
subtle changes in the coordination of the cyclometalated
phosphine ligand, with a slight contraction of the Rh-
˚
(C3 C4) distance [2.147(3) vs 2.219(7)-2.261(7) A] and
3 3 3
€
(34) Muller, T. W.; Mingos, D. M. P. Transition Met. Chem. 1995, 20,
533.
(35) (a) Harlow, R. L.; Thorn, D. L.; Baker, R. T.; Jones, N. L. Inorg.
Chem. 1992, 31, 993. (b) Yoshida, T.; Otsuka, S.; Matsumoto, M.; Nakatsu,
K. Inog. Chim. Acta 1978, 29, L257.

Article
Scheme 4. Reactivity of 4a; Preparation of 6 and 7
Organometallics, Vol. 29, No. 10, 2010 2337
three 1H (multiplet) coordinated alkene resonances at 4.35,
3.21, and 3.06 ppm in a 1:1:1 ratio. These signals are assigned
as H3 and the two vinyl E-H4 and Z-H4 atoms, respectively,
following HH-COSY and HSQC correlation experiments
(see Scheme 4 for NMR labeling). The corresponding 13C
signals, C3 (75.3 ppm) and C4 (48.7 ppm), both show large
one-bond coupling to rhodium of ca. 17 Hz, corroborating
coordination of the alkene. The 1H and 13C NMR spectra of
6 reveal two different methyl environments (C7 and C8) and a
diastereotopic methylene group (C5) for the triisobutylpho-
sphine ligand. In the 1H NMR spectrum, the isobutyl methyl
groups resonate at 1.10 (9H, H8) and 1.04 (9H, H7) ppm and
are observed as a doublet and doublet of doublets, respec-
tively. The principal splitting for both is readily attributed
to three-bond coupling with H6, with a magnitude of ca.
6.6 Hz, by HH-COSY and selective decoupling experi-
ments. The additional splitting of the upfield H7 resonance
(2.0 Hz) does not collapse on 31P decoupling, and no addi-
tional 1H correlations are apparent from HH-COSY experi-
ments. We correspondingly assign it to a time-averaged
one-bond coupling with 103Rh. Within resolution limits, no
additional coupling is seen to H8. Precedent for such cou-
pling has recently been demonstrated by Rourke in a Pt(II)
system (1JPtH = 15.5 Hz, 9H)37 and by Brookhart in
[(2,6-(tBu2PO)2C5H3N)Rh(CH4)][BArF4] (1JRhH = 6.3 Hz,
4H, 163 K).38 Overall, these observations for the isobutyl
signals are consistent with a fluxional process in solution at
room temperature involving rotation of the triisobutylpho-
sphine ligand about the Rh-P vector with time-averaged
agostic interaction of just one of the methyl groups on each
isobutyl substituent with the metal center. The compound
shows 31P resonances at 86.8 and 31.5 ppm with a large trans
coupling of 318 Hz, similar to the parent compound (396 Hz).
The solid-state structure of 6 has been determined by
X-ray crystallography and is depicted in Figure 5. The co-
ordinated alkene group [Rh1-C3 = 2.140(7); Rh1-C4 =
Figure 5. Solid-state structure of 6. Thermal ellipsoids are
drawn at 50%; minor disordered components (CH2CH2CHd
CH2, one iBu, and both tBu groups), anion, and most H atoms
˚
are omitted for clarity. Selected bond lengths (A) and angles
(deg): Rh1-P1, 2.3419(10); Rh1-P2, 2.3165(10); Rh1-C3,
2.140(7); Rh1-C4, 2.117(6); Rh1-C15, 2.410(4); Rh1-H15A,
1.88 (calc); Rh1-H15B, 2.15 (calc); C3-C4, 1.362(11); P1-
Rh1-P2, 179.36(4); P1-Rh1-Cg(C3,C4), 88.9(2); Cg(C3,C4)-
Rh1-C15, 167.2(2); Rh1-P1-C1, 101.5(3); Rh1-P2-C13,
105.77(13); P1-C1-C2, 110.0(7).
than those observed in the related rhodium(III) complex
[Rh(H)2(PiBu3)2][BArF4], F, where the agostic interactions
are trans to hydride ligands [ca. 2.90 A],41 but comparable to
˚
that found in the “T”-shaped rhodium(I) complex [((tBu2P)2-
t
CH2)Rh(CH2 Bu)] [2.491(4) A].
42
˚
Reaction of 6 with hydrogen (1 atm) results in the hydro-
genation of the tethered alkene group and formation of the
formally 14-electron dihydride complex [Rh(H)2(PiBu3)-
n
(PtBu2 Bu)][BArF4] (7, Scheme 4). This complex is identified
˚
by a broad hydride resonance at -22.8 ppm (fwhm = 65 Hz,
T1 = 0.89 ( 0.02 s), Cs symmetry in the 1H NMR spectrum,
high-field C3 and C4 13C resonances [27.5 and 14.9 ppm,
respectively], and 31P resonances at 76.1 and 32.2 ppm with
trans phosphine [2JPP = 297 Hz] and 103Rh coupling. Stabi-
lization of this complex by supporting agostic interactions
from a phosphine substituent(s), as is observed for the closely
related analogue F [δ(RhH) = -21.6 ppm],41 is likely and,
on the basis of the relatively low chemical shift value of the
2.117(6); C3-C4 = 1.362(11) A] and trans-coordinated
phosphines [P1-Rh1-P2 = 179.36(4)ꢀ] are readily appar-
ent, as is the adoption of a strong agostic interaction between
the metal center and an isobutyl phosphine substituent
(although the hydrogen atoms were not located), in line with
the solution characterization. The structure of 6 is essentially
square planar [Cg(C3,C4)-Rh1-C15 = 167.2(2)ꢀ]. The agos-
tic interaction is characterized by a short rhodium-carbon
˚
distance of 2.410(4) A [Rh1-C15], calculated hydrogen
H
3 1H resonance (2H, 0.75 ppm) compared to the other
˚
contacts of 1.88 and 2.15 A, and compression of the
n-butyl resonances, we suggest through the methylene C3
group of the n-butyl substituent. Complex 7 is stable only
for short periods of time in the absence of a hydrogen
Rh1-P2-C13 angle [105.77(13)ꢀ] compared to the other
two Rh1-P2-C angles [118.1(5)ꢀ and 120.79(13)ꢀ]. DFT
calculations (see Supporting Information) support the pre-
sence of an agostic interaction and favor a classical, M η2-
3 3 3
H2C,39 as opposed to a nonclassical, M η3-H2C, interac-
3 3 3
(39) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad.
Sci. 2007, 104, 6908.
tion.40 The rhodium-carbon distance is significantly shorter
(40) Baratta, W.; Mealli, C.; Herdtweck, E.; Lenco, A.; Mason, S. A.;
Rigo, P. J. Am. Chem. Soc. 2004, 126, 5549.
(41) Douglas, T. M.; Chaplin, A. B.; Weller, A. S. Organometallics
2008, 27, 2918.
(37) Crosby, S.; Clarkson, G. J.; Rourke, J. P. J. Am. Chem. Soc.
2009, 131, 14142.
(38) Bernskoetter, W. H.; Schauer, C. K.; Goldberg, K. I.; Brookhart,
€
(42) Urtel, H.; Meier, C.; Eisentrager, F.; Rominger, F.; Joschek, J.
M. Science 2009, 326, 553.
P.; Hofmann, P. Angew. Chem., Int. Ed. 2001, 40, 781.

2338 Organometallics, Vol. 29, No. 10, 2010
Chaplin and Weller
Scheme 5. [Rh(PPh3)3Cl]-Mediated Ring-Opening and
Hydrogenation of a Phosphite-Tethered Cyclopropane
Reported by Bart and Chirik4
Scheme 6. Proposed Mechanism for the formation of 6 from 4a
Figure 6. Solid-state structure of 5. Thermal ellipsoids are
drawn at 50%; H atoms are omitted for clarity. Only one of
the two independent molecules is shown. Selected bond lengths
˚
(A) and angles (deg): Rh1-P1, 2.3865(7); Rh1-Cl1, 2.3580(7);
Rh1-C1, 1.921(3); Rh1-C2, 1.827(3); C1-O1, 1.126(3);
C2-O2, 1.138(3); C5-C6, 1.483(5); P1-Rh1-Cl1, 94.67(3);
P1-Rh1-C1, 177.96(6); P1-Rh1-C2, 89.52(9); Cl1-Rh1-
C2, 174.99(9); Rh1-P1-C1, 101.5(3); P1-C1-C2, 110.0(7).
atmosphere, evolving to give a mixture of unidentified
products.
The selective isomerization of 4a on abstraction of chlor-
ide, resulting in the formation of 6, has direct relevance to the
transition-metal-mediated ring-opening reactions of cyclo-
propanes. In particular, this system represents a model for
the catalytic C-C bond activation and functionalization
(hydrogenation, hydrosilylation) of cyclopropanes mediated
by Willkinson’s catalyst, [Rh(PPh3)3Cl], reported by Bart
and Chirik.4 In this catalytic system, incorporation of a
coordinating phosphite tether to the cyclopropane ring
resulted in the regioselective activation of the most hindered
C-C bond, leading to terminal alkenyl or, in the presence of
hydrogen, n-alkyl groups, both as observed here (cf.
Scheme 5). Complexes 4a, 6, and 7, therefore, represent
well-characterized models for intermediates involved in this
process. The mechanism that we propose for the isomeriza-
tion of the metallocylobutane is outlined in Scheme 6.36 In
order to account for the formation of a terminal alkene,
activation of the more hindered C-C bond of the cyclopro-
prane is necessary. We suggest the first step in this process is
reductive elimination of the tethered cyclopropane group,
promoted by chloride abstraction from 4a and formation of
a less electron rich, cationic metal center (cf. reaction of 1
with CO, vide infra). Ring-opening, following γ-C-H acti-
vation (I f II) of the tethered cyclopropane, to afford the
allyl-hydride III is then proposed. In support of these
propositions, reaction of [Ir(C8H14)2Cl]2 with PtBu2CH2-
(C3H5) is known to give a cyclopropyl-hydride complex
closely related to II, [IrHCl(κ2-PtBu2CH2(C3H4))(PtBu2-
CH2(C3H5))]; this complex undergoes isomerization to the
vinyl-hydride complex [IrHCl(κ2-PtBu2CH2C(Me)dCH)-
(PtBu2CH2(C3H5))] in polar solvents.24 Related isomeriza-
tions of PtBu2CH2(C3H5) to σ-allyl complexes have been
shown by Ibers on Pd and Pt (with the loss of HCl).22,23
Periana and Bergman have similarly shown that [RhCp*-
(PMe3)I(η1-C3H5)] undergoes rearrangement to [RhCp*-
(PMe3)(η3-C3H5)]þ on iodine abstraction.14 Hydride inser-
tion into the allyl at Cβ in III could then lead to 6, as is
observed for [Ir(((C2F5)2PCH2)2)H(η3-C3H5)(OTf)], which
undergoes elimination of propylene on heating.43 Such a
mechanism avoids formation of strained intermediates, as
would be necessary for direct Cβ-Cγ activation in I, for
example.
resulted in the reductive elimination of the tethered cylcopropyl
group and quantitative, by NMR spectroscopy, formation of
cis-[RhCl(CO)2(PtBuCH2(C3H5))] (5, Scheme 2). This presum-
ably occurs via initial fragmentation to give [RhCl(CO)-
(κ3-PtBu2CH2CH(CH2)2)], as with the reaction of 1 with
phosphines, reductive elimination of the tethered cyclopro-
pane, as a consequence of reduced metal electron density on
coordination of CO, and coordination of a second CO ligand.
The reductive elimination0of the tethered cylcopropane group is
apparent from H3 and H3 1H resonances at 0.44 and 0.31 ppm,
comparable to those of free phosphine (0.53 and 0.11 ppm),
and a large upfield shift in the 31P{1H} NMR spectrum (58.1 vs
113.1 ppm). The structure of 5 is further substantiated by IR
spectroscopy with two strong absorption bands observed at
2089 and 1993 cm-1, supporting the cis configuration of the
carbonyl ligands, as observed in the closely related rhodium
compound cis-[RhCl(CO)2(PtBu2CH2CH2(2,6-Me2C6H3))]
(G, 2086 and 1999 cm-1).44 Similarly two carbonyl resonances
are observed by 13C NMR spectroscopy at 185.4 (dd, 1JRhC
=
70, 2JPC = 17) and 182.0 (dd, 2JPC = 114, 1JRhC = 58) ppm (cf.
184.8 and 181.1 ppm for G). These suggestions are upheld in the
solid-state structure (Figure 6), which verifies the reductive
elimination; the structural metrics about the rhodium center are
similar to those of G. Complex 5 is stable only for short periods
of time in the absence of a CO atmosphere.
Concluding Remarks
The selective rhodium-mediated C-C bond activation of a
cyclopropyl phosphine, PtBu2CH2(C3H5), has been achieved
by reaction with [Rh(C8H14)2Cl]2, and the structure of the
resulting tetrameric rhodacyclobutane, [RhCl(κ3-PtBu2CH2-
CH(CH2)2)]4, has been established in solution and the solid
state. This complex acts as a latent source of the [Rh(κ3-
PtBu2CH2CH(CH2)2)]þ fragment, forming a range of new
complexes by salt metathesis with NaCp, [RhCp(κ3-PtBu2-
CH2CH(CH2)2)], chloride abstraction in the presence of are-
nes, [Rh(η6-arene)(κ3-PtBu2CH2CH(CH2)2)][BArF ] (arene =
4
C6H5F, C6H3Me3), or fragmentation by addition of phosphine
ligands, trans-[RhCl(PR3)(κ3-PtBu2CH2CH(CH2)2)] (R =
iBu, Cy). This new family of rhodacyclobutanes has been fully
Relevant to this isomerization process is the reaction of the
tetrameric rhodacyclobutane 1 with carbon monoxide, which
(44) Canepa, G.; Brandt, C. D.; Werner, H. Organometallics 2004, 23,
1140.
(43) Schnabel, R. C.; Roddick, D. M. Organometallics 1996, 15, 3550.

Article
Organometallics, Vol. 29, No. 10, 2010 2339
Scheme 7
560 FTIR spectrometer. Microanalyses were performed at the
London Metropolitan University in all cases except for that of 6,
which was performed by Elemental Microanalysis Ltd.
Synthesis of New Complexes.
[RhCl(K3-PtBu2CH2CH(CH2)2)]4 (1). To a suspension of
[Rh(C8H14)2Cl]2 (0.686 g, 0.956 mmol) in heptane (10 mL) was
added a solution of PtBu2CH2(C3H5) in pentane (7.15 mL, 0.274
M, 1.96 mmol). The resulting suspension was heated at 80 ꢀC for
30 min and then cooled to -78 ꢀC. The product was isolated as a
pale yellow microcrystalline solid following filtration and wash-
ing with cold heptane (5 ꢁ 2 mL). Yield: 0.51 g (79%).
1H NMR (C6D6, 500 MHz): δ 2.76 (doublet of multiplets,
3JPH = 66.5, 1H, H2), 2.35 (br, 2H {δ 2.358, 1H, H3/4; δ 2.351,
characterized in solution by NMR spectroscopy and in the
solid state by X-ray diffraction (Table 2). Only small changes
in the coordination of the chelated phosphine ligand, which
binds with a bite angle of ca. 81ꢀ, comparable to dppe,25 are
observed within this series. In contrast to the aforementioned
reactions, where the metallocyclobutane ring remains intact,
reaction with carbon monoxide results in the reductive elim-
ination of the tethered cyclopropane, demonstrating reversible
C-C bond activation (Scheme 7).
0
0
0
0
1H, H4/3}), 2.14 (s, 1H, H3 /4 ), 1.71 (s, 1H, H4 /3 ), 1.54 (d, J =
3
t
6.9, 2H, H1), 1.49 (d, JPH = 12.1, 18H, Bu). 13C{1H} NMR
(C6D6, 126 MHz): δ 47.5 (dd, J = 9, J = 2, C2), 36.7 (dd, 1JPH
=
44, 2JRhH = 15, tBu{C}), 32.2 (d, 2JPH = 32, tBu{Me}), 29.0 (d,
1JPH = 23, C1), 12.1 (d, 1JRhH = 20, C3/4), 10.7 (d, 1JRh1H = 20,
C4/3). 31P{1H} NMR (C6D6, 202 MHz): δ 113.1 (d, JRhP
=
=
=
206). 31P{1H} NMR (CD2Cl2, 202 MHz): δ 111.5 (d, JRhP
1
200). 31P{1H} NMR (C6H5F, 202 MHz): δ 111.6 (d, JRhP
1
201). Anal. Calcd for C48H100Cl4P4Rh4 (1354.65 g mol-1): C,
42.56; H, 7.44. Found: C, 42.58; H, 7.52.
Reaction of the bis-phosphine complex trans-[RhCl-
(PiBu3)(κ3-PtBu2CH2CH(CH2)2)] with Na[BArF4] resulted
in chloride abstraction and selective isomerization of the
coordinated cyclopropane group to a terminal alkene. This
process is suggested to proceed via a mechanism involving
initial reductive elimination of the metallacyclobutane
group, followed by C-H activation and ring-opening of
the more hindered C-C bond, to account for the observed
selectivity. Addition of hydrogen to the product rhodium-
alkene compound, [Rh(PiBu3)(κ3-PtBu2CH2CH2CHdCH2)]-
[RhCp(K3-PtBu2CH2CH(CH2)2)] (2). To a Schlenk flask
charged with [RhCl(κ3-PtBu2CH2CH(CH2)2)]4 (0.050 g, 0.037
mmol) and NaCp (0.013 g, 0.147 mmol) was added CH2Cl2
(2 mL), and the mixture was stirred at room temperature for 1 h.
The solution was filtered and the solvent removed in vacuo. The
product recrystallized from heptane at -78 ꢀC. Yield: 0.037 g
(68%, pale yellow). This compound is prepared quantitatively in
situ by addition of a slight excess of NaCp to a suspension of
[RhCl(κ3-PtBu2CH2CH(CH2)2)]4 in CD2Cl2.
1H NMR (C6D6, 500 MHz): δ 5.13 (s, 5H, Cp), 3.77 (apparent
3
3
3
3
ddtt, JPH = 55.6, JRhH = 6, JHH = 4, JHH = 2, 1H, H2),
[BArF ], resulted in hydrogenation of the alkene group and
4
1.76-1.81 (m, 2H, H3), 1.52 (apparent dq, J = 7.7, J = 1.7, H1),
formation of a rhodium(III) dihydride complex, [Rh(H)2-
n
0
1.11 (d, 3JPH = 12.3, 18H, tBu), 1.02-1.07 (m, 2H, H3 ). 13C{1H}
NMR (C6D6, 126 MHz): δ 86.2 (apparent t, J = 3, Cp), 45.1 (dd,
J = 11, J = 4, C2), 36.6 (dd, 1JPC = 16, 2JRhC = 2, tBu{C}), 31.3
(d, 2JPC = 4, tBu{Me}), 28.0 (dd, 1JPC = 21, 2JRhH = C1), -0.9
(dd, 1JRhC = 21, 2JPC = 4, C3). 31P{1H} NMR (C6D6, 202 MHz):
δ 124.9 (d, 1JRhP = 196). Anal. Calcd for C17H30PRh (368.30 g
mol-1): C, 55.44; H, 8.21. Found: C, 55.49; H, 8.18.
(PiBu3)(PtBu2 Bu)][BArF ]. These steps overall correspond to
4
the selective C-C bond functionalization (hydrogenation) of
the tethered cyclopropane group (Scheme 7). The isolation of
these chelating compounds has direct significance to a related
catalytic process (ref 4) and, more generally, to the rhodium-
mediated transformation of alkanes.
[Rh(C6H5F)(K3-PtBu2CH2CH(CH2)2)][BArF
] (3a). To a
4
Schlenk flask charged with [RhCl(κ3-PtBu2CH2CH(CH2)2)]4
(0.0515 g, 0.038 mmol) and Na[BArF4] (0.1350 g, 0.152 mmol)
was added C6H5F (3 mL). After stirring for 1 h, the solution was
filtered, layered with pentane, and held at 5 ꢀC to afford the
product as pale yellow crystals. Yield: 0.146 (76%).
Experimental Section
All manipulations, unless otherwise stated, were performed
under an atmosphere of argon, using Schlenk and glovebox
techniques. Glassware was oven-dried at 130 ꢀC overnight and
flamed under vacuum prior to use. CH2Cl2 and pentane were
dried using a Grubbs-type solvent purification system (MBraun
SPS-800) and degassed by successive freeze-pump-thaw
cycles.45 Heptane was dried over sodium and vacuum distilled.
CD2Cl2, C6H5F, and 1,2-C6H4F2 were dried over CaH2, vacuum
1H NMR (CD2Cl2, 500 MHz): δ 7.70-7.74 (m, 8H, BArF4),
7.56 (br, 4H, BArF4), 6.98 (apparent td, 3JHH = 6.6, 4JFH = 4.2,
2H, m-C6H5F), 6.67 (apparent t, J = 6.1, 2H, o-C6H5F), 6.41 (t,
3JHH = 6.2, 1H, p-C6H5F), 3.10 (doublet of multiplets, 3JPH
=
66.7, 1H, H2), 1.90-1.93 (m, 4H H3), 1.80 (br d, 2JPH = 7.3, 2H,
H2), 1.34 (d, 3JPH = 14.0, 18H, tBu). 13C{1H} NMR (CD2Cl2,
126 MHz): δ 162.3 (q, 1JBC = 50, BArF4), 152.1 (d, 1JFC = 279,
˚
distilled, and stored over 3 A molecular sieves. C6D6 was dried over
˚
48
potassium, vacuum distilled, and stored over 3 A molecular sieves.
[Rh(C8H14)2Cl]2,46 PtBu2CH2(C3H5),22 NaCp,47 and Na[BArF
i-C6H5F), 135.4 (s, BArF4), 129.4 (qq, JFC = 32, JBC = 3,
2
3
]
4
BArF4), 125.2 (q, JFC = 273, BArF4), 118.0 (sept, JFC = 4,
BArF4), 111.0 (dt, J = 7, J = 2, m-C6H5F), 100.4 (m, p-C6H5F),
95.0 (dd, J = 20, J = 1, o-C6H5F), 45.7 (dd, J = 4, J = 3, C2),
1
3
were prepared by literature methods. All other chemicals are
commercial products and were used as received. NMR spectra
were recorded on a Varian Mercury VX 300 MHz, Varian Unity
Plus 500 MHz, or Bruker AVC 500 MHz spectrometer at room
temperature, unless otherwise stated. Chemical shifts are quoted in
ppm and coupling constants in Hz. NMR labeling is indicated in
Schemes 1, 2, and 4. Infrared spectra were measured on a Nicolet
1
2
t
2
38.5 (dd, JPC = 18, JRhC = 2, Bu{C}), 30.9 (d, JPC = 3,
tBu{Me}), 25.4 (dd, 1JPC = 25, 2JRhC = 2, C1), 10.2 (d, 1JRhC
=
18, C3). 19F NMR (CD2Cl2, 283 MHz): δ -62.9 (s, 24F, BArF4),
-110.8 (s, 1F, C6H5F). 31P{1H} NMR (CD2Cl2, 202 MHz): δ
1
133.2 (d, JRhP = 194). Anal. Calcd for C50H42BF25PRh
(1262.53 g mol-1): C, 47.57; H, 3.35. Found: C, 47.65; H, 3.26.
[Rh(C6H3Me3)(K3-PtBu2CH2CH(CH2)2)][BArF4] (3b). To a
Schlenk flask charged with [RhCl(κ3-PtBu2CH2CH(CH2)2)]4
(0.008 g, 0.0060 mmol) and Na[BArF4] (0.021 g, 0.0242 mmol)
was added C6H3Me3 (0.05 mL) and CH2Cl2 (0.5 mL). After
stirring for 10 min, the solution was filtered, layered with
(45) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(46) Van der Ent, A.; Onderdelinden, A. L. Inorg. Synth. 1990, 28, 90.
(47) Panda, T. K.; Gamer, M. T.; Roesky, P. W. Organometallics
2003, 22, 877.
(48) Buschmann, W. E.; Miller, J. S.; Bowman-James, K.; Miller, C.
N. Inorg. Synth. 2002, 33, 83.

2340 Organometallics, Vol. 29, No. 10, 2010
Chaplin and Weller
pentane, and held at 5 ꢀC to afford the product as pale yellow
crystals. Yield: 0.025 (81%).
1H NMR (CD2Cl2, 500 MHz): δ 7.70-7.74 (m, 8H, BArF4),
7.56 (br, 4H, BArF4), 4.30-4.39 (m, 1H, H3), 3.17-3.23 (m, 1H, E-
H4), 3.02-3.09 (m, 1H, Z-H4), 2.27-2.38 (m, 1H, H2), 2.15
1H NMR (CD2Cl2, 500 MHz): δ 7.70-7.74 (m, 8H, BArF4),
7.56 (br, 4H, BArF4), 6.11 (s, 3H, C6H3Me3), 3.38 (apparent ddtt,
3JPH = 64.4, 3JRhH = 6.2, 3JHH = 4.1, 3JHH = 2.0, 1H, H2), 2.36
(doublet of doublet of multiplets, 3JPH = 46.9,49 2JHH = 16, 1H,
0
H2 ), 2.00 (apparent decet, J = 7, 3H, H6), 1.71-1.80 (m, 1H, H1),
0
(s, 9H, C6H3Me3), 1.72-1.78 (m, 4H {δ1.766, 2H, H3;δ1.748, 2H,
1.47-1.63 (m, 6H {δ1.58, 3H, H5; δ1.51, 3H, H5 }), 1.31-1.43 (m,
0
0
3
t
H1}), 1.43-1.47 (m, 2H, H3 ), 1.31 (d, JPH = 13.7, 18H, Bu).
1H, H1 ), 1.29 (d, 3JPH = 12.8, 9H, tBu), 1.25 (d, 3JPH = 13.2, 9H,
13C{1H} NMR (CD2Cl2, 126 MHz): δ 162.3 (q, JBC = 50,
tBu0), 1.10 (d, 3JHH = 6.6, 9H, H8), 1.04 (dd, 3JHH = 6.6, 1JRhH
=
1
BArF4),135.4 (s, BArF4), 129.4 (qq, 2JFC = 32, 3JBC = 3, BArF4),
127.0 (dd, J = 2, J = 1, C6H3Me3{CMe}), 125.2 (q, 1JFC = 272,
BArF4), 118.0 (sept, 3JFC = 4, BArF4), 103.9 (apparent t, J =
2, C6H3Me3{CH}), 45.2 (dd, J = 5, J = 2, C2), 38.2 (dd,
1.6,† 9H, H7). 13C{1H} NMR (CD2Cl2, 126 MHz): δ 162.3 (q,
1JBC = 50, BArF4), 135.4 (s, BArF4), 129.4 (qq, 2JFC = 32, 3JBC
=
3, BArF4), 125.2 (q, JFC = 272, BArF4), 118.0 (sept, 3JFC = 4,
BArF4), 75.3 (dd, 1JRhC = 17, 2JPC = 4, C3), 48.7 (dt, 1JRhC = 17,
2JPC = 2, C4), 36.0 (dd, 1JPC = 13, 2JRhC = 3, tBu/tBu0{C}), 35.6
(dd, 1JPC = 14, 2JRhC = 3, tBu0/tBu{C}), 34.8 (br d, 1JPC = 21,
C5), 32.3 (dd, J = 8, J = 4, C2), 30.9 (d, 2JPC = 4, tBu{Me}), 29.7
(d, 2JPC = 4, tBu0{Me}), 27.4 (br, C6), 24.8 (apparent t {δ 24.85, d,
3JPC = 7, C7; δ 24.78, d, 3JPC = 7, C8}), 13.0 (br d, 1JPC = 19, C1).
1
1JPC = 18, JRhC = 2, Bu{C}), 30.9 (d, JPC = 3, Bu{Me}),
25.9 (dd, 1JPC = 25, 2JRhC = 2, C1), 20.7 (s, C6H3Me3), 12.8 (d,
1JRhC = 19, C3). 31P{1H} NMR (CD2Cl2, 202 MHz): δ 125.2 (d,
1JRhP = 194). Anal. Calcd for C53H49BF24PRh (1286.62 g mol-1):
C, 49.48; H, 3.84. Found: C, 49.55; H, 3.80.
2
t
2
t
[RhCl(PiBu3)(K3-PtBu2CH2CH(CH2)2)] (4a). To a suspension
of [RhCl(κ3-PtBu2CH2CH(CH2)2)]4 (0.150 g, 0.111 mmol) in
CH2Cl2 (2 mL) was added PiBu3 (0.113 mL, 0.453 mmol), and
the resulting orange solution stirred at room temperature for
10 min. The solvent was removed in vacuo and the product
recrystallized from heptane at -78 ꢀC. Yield: 0.14 g (58%,
yellow-orange). This compound is prepared quantitatively
in situ by addition of a slight excess of PiBu3 to a suspension
of [RhCl(κ3-PtBu2CH2CH(CH2)2)]4 in CD2Cl2.
31P{1H} NMR (CD2Cl2, 202 MHz): δ 86.8 (dd, JPP = 318,
2
1JRhP = 121, 1P, PtBu2), 31.5 (dd, 2JPP = 318, 1JRhP = 112, 1P,
PiBu3). Anal. Calcd for C56H64BF24P2Rh (1368.75 g mol-1): C,
49.14; H, 4.71. Found: C, 49.03; H, 4.88. †2.0 Hz, following
deconvolution analysis.
[Rh(H)2(PiBu3)(PtBu2 Bu)][BArF4] (7). A yellow solution of
n
[RhCl(PiBu3)(κ3-PtBu2CH2CH2CHdCH2)][BArF
] (0.012 g,
4
0.009 mmol) in CD2Cl2 (0.4 mL) in a J Young NMR tube was
placed under H2 (1 atm), resulting in rapid and quantitative
formation of [Rh(H)2(PiBu3)(PtBu2nBu)][BArF4] (pale yellow
solution) by NMR spectroscopy. The NMR tube was then
placed under argon and the product immediately analyzed in situ
by NMR spectroscopy. Characterization was carried out under
both conditions. The hydride ligands exchange with dissolved H2
under an atmosphere of H2 on the NMR time scale, resulting in a
ca. 2 ppm downfield shift of the hydride resonance and significant
1H NMR (C6D6, 500 MHz): δ 3.38 (doublet of multiplets,
3JPH = 56.5, 1H, H2), 1.87-1.98 (m, 9H, iBu {δ 1.933, 6H, CH2;
=
3
δ 1.925, 3H, CH}), 1.45 (obscured, 2H, H3), 1.43 (d, JPH
12.0, 18H, tBu), 1.40 (obscured, 2H, H1), 1.00 (d, 3JHH = 6.3,
0
i
18H, Bu{Me}), 0.79 (br, 2H, H3 ). 13C{1H} NMR (C6D6, 126
MHz): δ 44.1 (ddd, J = 17, J = 7, J = 4, C2), 35.6 (dd, 1JPC
=
10, 2JRhC = 4, tBu{C}), 32.5 (d, 1JPC = 20, iBu{CH2}), 31.5 (dd,
2JPC = 4, 3JRhC = 1, tBu{Me}), 26.0 (d, JPC = 7, iBu{Me}),
=
line broadening (fwhm = 500 Hz). The other H signals were
3
1
25.6 (s, iBu{CH}), 22.7 (br d, 1JPC = 15, C1), -2.3 (dd, 1JRhC
unchanged, as were 31P{1H} NMR spectra. The product has only
limited stability in the absence of H2.
19, 2JPC = 5, C3). 31P{1H} NMR (C6D6, 202 MHz): δ 83.4 (dd,
2JPP = 396, JRhP = 129, 1P, PtBu2), 14.4 (dd, JPP = 396,
1JRhP = 128, 1P, PiBu3). Anal. Calcd for C24H52ClP2Rh (540.98
g mol-1): C, 53.29; H, 9.69. Found: C, 53.35; H, 9.61.
1H NMR (CD2Cl2, 500 MHz): δ 7.70-7.74 (m, 8H, BArF4),
7.56 (br, 4H, BArF4), 1.79-1.98 (m, 11H {δ 1.92, 3H, iBu{CH};
δ 1.88, 2H, C1; δ 1.83, 6H, iBu{CH2}}), 1.54-1.66 (m, 2H, C2),
1
2
[RhCl(PCy3)(K3-PtBu2CH2CH(CH2)2)] (4b). To a Schlenk
flask charged with [RhCl(κ3-PtBu2CH2CH(CH2)2)]4 (0.100 g,
0.074 mmol) and PCy3 (0.084 g, 0.299 mmol) was added CH2Cl2
(2 mL); the resulting orange solution was stirred at room
temperature for 10 min. The solvent was removed in vacuo
and the product recrystallized from heptane at -78 ꢀC. Yield:
0.086 g (47%, yellow-orange). This compound is prepared
quantitatively in situ by addition of a slight excess of PCy3 to
a suspension of [RhCl(κ3-PtBu2CH2CH(CH2)2)]4 in CD2Cl2.
Crystals suitable for X-ray diffraction were grown from heptane
(with trace quantities of 1,2-C6H4F2) at -80 ꢀC.
1.25 (d, JPH = 13.7, 18H, tBu), 1.05 (t, JHH = 7.1, 3H, C4),
0.89 (d, 3JHH = 6.5, 18H, iBu{Me}), 0.75 (apparent sept, J = 7,
2H, H3), -22.78 (vbr, fwhm = 65 Hz, 2H, RhH, T1 = 0.89 (
0.02 s). 13C{1H} NMR (CD2Cl2, 126 MHz, 1 atm H2): δ 162.3 (q,
3
3
1JBC = 50, BArF4), 135.4 (s, BArF4), 129.4 (qq, JFC = 32,
2
3JBC = 3, BArF4), 125.2 (q, JFC = 272, BArF4), 118.0 (sept,
1
3JFC = 4, BArF4), 38.7 (br d, 1JPC = 25, iBu{CH2}), 35.4 (br d,
1JPC = 18, tBu{C}), 31.7(m, C2), 30.1 (d, 2JPC =4, tBu{Me}), 27.5
(d, J = 11, C3), 27.2 (br, iBu{CH}), 25.1 (d, 3JPC = 8, iBu{Me}),
23.4 (dd, 1JPC = 19, 2JRhC = 2, C1), 14.9 (s, C4). 31P{1H} NMR
2
1
(CD2Cl2, 202 MHz): δ 76.1 (dd, JPP = 297, JRhP = 110, 1P,
PtBu2), 32.2 (dd, 2JPP = 297, 1JRhP = 108, 1P, PiBu3).
1H NMR (C6D6, 500 MHz): δ 3.27 (doublet of multiplets,
3JPH = 58.7, 1H, H2), 2.54-2.65 (m, 3H, Cy{CH}), 2.02-2.11
(m, 6H, Cy), 1.55-1.79 (m, 17H {δ 1.74, 6H, Cy; δ 1.72. 6H, Cy;
δ 1.63. 3H, Cy; δ 1.59, 2H, H3}), 1.46 (d, 3JPH = 11.8, 18H, tBu),
cis-[RhCl(CO)2(PtBu2CH2(C3H5))] (5).
A suspension of
[RhCl(κ3-PtBu2CH2CH(CH2)2)]4 (0.070 g, 0.052 mmol) in hep-
tane (2 mL) was placed under CO (1 atm), then recrystallized
(under CO) by gentle heating and then cooling to 5 ꢀC. Yield:
0.015 (18%, yellow). This compound is prepared quantitatively
in situ by placing a solution/suspension of [RhCl(κ3-PtBu2-
CH2CH(CH2)2)]4 in CD2Cl2, C6D6, or heptane under CO
(1 atm). This compound is unstable in solution in the absence
of a CO atmosphere.
1.12-1.39 (m, 13H {δ 1.36, 2H, H1; δ 1.26, 6H, Cy; δ 1.20, 3H,
0
Cy; δ 1.17, 2H, H3 }). 13C{1H} NMR (C6D6, 126 MHz): δ 44.4
(ddd, J = 18, J = 7, J = 4, C2), 36.2 (dd, 1JPC = 9, 2JRhC = 3,
1
2
tBu{C}), 34.6 (d, JPC = 15, Cy{CH}), 31.8 (dd, JPC = 3,
3JRhC = 1, tBu{Me}), 31.2 (s, Cy), 28.5 (d, 2JPC = 10, Cy), 27.4
(s, Cy), 22.4 (br d, 1JPC = 15, C1), -2.1 (dd, 1JRhC = 19, 2JPC
=
1H NMR (C6D6, 500 MHz): δ1.92 (dd, 2JPH = 9.5, 3JHH = 6.1,
5, C3). 31P{1H} NMR (C6D6, 202 MHz): δ 83.8 (dd, 2JPP = 382,
1JRhP = 132, 1P, PtBu2), 27.1 (dd, 2JPP = 382, 1JRhP = 126, 1P,
PCy3). Anal. Calcd for C30H58ClP2Rh (619.10 g mol-1): C,
58.20; H, 9.44. Found: C, 58.23; H, 9.38.
2H, H1), 1.15 (d, 3JPH = 13.3, 18H, tBu), 0.83-0.93 (m, 1H, H2),
0
0.40-0.47 (m, 2H, H3), 0.28-0.33 (m, 2H, H3 ). 13C{1H} NMR
(C6D6, 126 MHz): δ 185.4 (dd, 1JRhC = 70, 2JPC = 17, CO), 182.0
(dd, 2JPC = 114, 1JRhC = 58, CO), 35.6 (dd, 1JPC = 17, 2JRhC = 1,
[RhCl(PiBu3)(K3-PtBu2CH2CH2CHdCH2)][BArF
] (6). A
4
suspension of [RhCl(PiBu3)(κ3-PtBu2CH2CH(CH2)2)] (0.025 g,
0.046 mmol) and Na[BArF4] (0.043 g, 0.049 mmol) in CH2Cl2
(1.5 mL) was stirred at room temperature for 20 h. The solution
was then filtered, layered with heptane, and held at 5 ꢀC to
afford the product as yellow crystals. Yield: 0.046 g (73% yield).
3
(49) This large JPH coupling constant (46.9 Hz) corresponds to a
0
P-C1-C2-H2 dihedral angle of 171.6ꢀ (average over two disordered
components) in the solid state, matching similar trends observed in 1-5
(Table 2).

Article
Organometallics, Vol. 29, No. 10, 2010 2341

2342 Organometallics, Vol. 29, No. 10, 2010
Chaplin and Weller
tBu{C}), 30.5 (d, 2JPC = 4, tBu{Me}), 24.2 (d, 1JPC = 20, C1), 9.3
(d, 2JPC = 2, C2), 8.9 (d, 3JPC = 6, C3). 31P{1H} NMR (C6D6, 202
MHz): δ 58.1 (d, 1JRhP = 127). IR (heptane, cm-1): ν(CO) 2089
(s), 1993 (s). Anal. Calcd for C14H25ClO2PRh (394.68 g mol-1): C,
42.60; H, 6.38. Found: C, 42.66; H, 6.35.
atoms were placed in calculated positions using the riding
model. Problematic solvent disorder in the structures of 1
and 2 was treated using the SQUEEZE algorithm.55 Further
details of disorder modeling are documented in the crystallo-
graphic information files under the heading _refine_special_
details. The overall quality of the data for 2 is poor, as evident
in the high value of 1.4 for the mosaicity. Crystal degrada-
tion, presumably as a result of solvent loss on warming from
-80 ꢀC, was observed during mounting. However, the model
has been carefully checked and is believed to be correct.
The structure is supported by correct microanalysis and
characterization in solution by NMR spectroscopy. In addi-
tion arene analogues (3) have been characterized in the
solid state and show similar structural metrics. The solution
of 2 contains three large Fourier peaks close to the heavy
Additional Experiments.
Reaction of 3a with [Ph3PNPPh3]Cl. To a J Young NMR tube
charged with 3a (0.0100 g, 0.008 mmol) and [Ph3PNPPh3]Cl
(0.0046 g, 0.0008 mmol) was added C6H5F (0.4 mL). The resulting
solution was immediately analyzed by 1H and 31P NMR spectros-
copy and indicated quantitative formation of 1.
Reaction of 1 with PtBu2CH2(C3H5). To a solution of 1 (0.005
g, 0.0037 mmol) in CD2Cl2 (0.4 mL) was added a pentane
solution of PtBu2CH2(C3H5) (0.070 mL, 0.274 M, 0.019 mmol).
The solution was monitored by 31P NMR spectroscopy at room
temperature (293 K), which indicated the formation of an equili-
brium mixture of 1:4c:PtBu2CH2(C3H5) in the ratio 1:18:10,
corresponding to an equilibrium constant of 10.5. 31P{1H}
-3
-3
˚
˚
˚
˚
atoms (3.9 e A , 0.97 A from Rh1; 3.3 e A , 0.94 A from
-3
˚
˚
Rh1; 2.3 e A , 1.00 A from P1) attributed to Fourier
truncation errors. If these peaks are excluded, the max./
min. residual density is 1.01/-1.23. Restraints to thermal
parameters were applied where necessary in order to main-
tain sensible values. Centroids (Cg) were calculated using
Platon.55 Graphical representations of the structures were
made using ORTEP3.56
2
1
NMR (CD2Cl2, 202 MHz): δ 82.1 [dd, JPP = 375, JRhP
=
=
2
1
130, 1P, PtBu2CH2CH(CH2)2], 45.6 [dd, JPP = 375, JRhP
126, 1P, PtBu2CH2(C3H5)].
Crystallography. Relevant details about the structure refine-
ments are given in Table 3. Data were collected on an Enraf
Nonius Kappa CCD diffractometer using graphite-monochro-
˚
Acknowledgment. We thank the EPSRC, University of
Oxford, and the John Fell Fund (University of Oxford)
for support. We also thank Dr. Amber Thompson for useful
advice on X-ray crystallography and Dr. Jon Rourke
(Universityof Warwick) forexploratory NMR experiments.
mated Mo KR radiation (λ = 0.71073 A) and a low-temperature
device;50 data were collected using COLLECT; reduction and
cell refinement was performed using DENZO/SCALEPACK.51
An empirical absorption correction was applied to the data set
of 2.52 The structures were solved by direct methods using
SIR2004 (1, 2, 3a, 3b, 5, and 6)53 or SHELXS-97 (4b)54 and
refined by full-matrix least-squares on F2 using SHELXL-97.54
All non-hydrogen atoms were refined anisotropically. Hydrogen
Supporting Information Available: NMR spectra of 6 and 7,
additional details about the isomeristion of [4a - Cl] to 6,
calculated structure of 6 using DFT, and CIF data. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(50) Cosier, J.; Glazer, A. M. J. Appl. Crystallogr. 1986, 19, 105.
(51) Otwinowski, Z.; Minor, W. Methods in Enzymology. In Macro-
molecular Crystallography, part A; Carter, C. W., Jr., Sweet, R. M., Eds.;
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