B-C bond cleavage of BArF anion upon oxidation of rhodium(I) with AgBArF. Phosphinite rhodium(I), rhodium(II), and rhodium(III) pincer complexes

Article abstract of DOI:10.1021/om800034t

A rare case of BAr_F anion cleavage (BAr_F^- = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) by a metal complex is described. Reaction of the Rh(I) dinitrogen complexes 5a,b and 6a,b, based on the phosphinite pincer ligands {C₆H₄[OP( _tBu)₂]₂} (2), with 2 equiv of AgBAr_F at room temperature resulted in B-C bond cleavage of one of the BAr_F anions and aryl transfer to afford the Rh(III) aryl complexes 7 and 8, respectively. The X-ray structure of 8 revealed a square-pyramidal geometry with a coordinated acetone molecule. The aryl transfer occurred as a result of electrophilic attack by unsaturated Rh(III) on one of the aryl rings of the BAr_F anion. Utilizing different solvents yielded the same product, except when CH₃CN was used, in which case one-electron oxidation took place, yielding complex 9. Treatment of 6a,b with 1 equiv of AgX (X = BAr _F, BF₄, PF₆) resulted in a one-electron oxidation to yield the paramagnetic Rh(II) complexes 9-11, respectively. Complex 11 was characterized by X-ray diffraction, revealing a mononuclear square-planar Rh(II) complex.

Full text of DOI:10.1021/om800034t

Organometallics 2008, 27, 2293–2299
2293
B-C Bond Cleavage of BArF Anion Upon Oxidation of Rhodium(I)
with AgBArF. Phosphinite Rhodium(I), Rhodium(II), and
Rhodium(III) Pincer Complexes
Hiyam Salem,† Linda J. W. Shimon,‡ Gregory Leitus,‡ Lev Weiner,‡ and David Milstein*,†
Department of Organic Chemistry and Unit of Chemical Research Support, The Weizmann Institute of
Science, RehoVot 76100, Israel
ReceiVed January 14, 2008
-
A rare case of BArF anion cleavage (BArF ) tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) by a
metal complex is described. Reaction of the Rh(I) dinitrogen complexes 5a,b and 6a,b, based on the
phosphinite pincer ligands {C6H4[OP(tBu)2]2} (2), with 2 equiv of AgBArF at room temperature resulted
in B-C bond cleavage of one of the BArF anions and aryl transfer to afford the Rh(III) aryl complexes
7 and 8, respectively. The X-ray structure of 8 revealed a square-pyramidal geometry with a coordinated
acetone molecule. The aryl transfer occurred as a result of electrophilic attack by unsaturated Rh(III) on
one of the aryl rings of the BArF anion. Utilizing different solvents yielded the same product, except
when CH3CN was used, in which case one-electron oxidation took place, yielding complex 9. Treatment
of 6a,b with 1 equiv of AgX (X ) BArF, BF4, PF6) resulted in a one-electron oxidation to yield the
paramagnetic Rh(II) complexes 9-11, respectively. Complex 11 was characterized by X-ray diffraction,
revealing a mononuclear square-planar Rh(II) complex.
preceded by a paramagnetic mononuclear Rh(II) complex. While
dinuclear Rh(II) complexes are well-known, the normally less
stable mononuclear Rh(II) complexes7 are less common. Mono-
nuclear Rh(II) complexes can be stabilized by bulky ligands or
by electronic effects involving delocalization of the unpaired
electron.8 The most common mononuclear Rh(II) complexes
are porphyrin complexes.7i,8b Stable pincer-type Rh(II) bis(ox-
azoline) monomeric complexes were reported by Bergman and
Tilley.7f Recently, monomeric Rh(II) PNP-type complexes,7a
Introduction
Noncoordinating or weakly coordinating anions play major
roles in bond activation and catalysis by cationic transition-
metal complexes,1 including C-H activation and polymerization
-
reactions. The BArF anion (BArF ) tetrakis(3,5-bis(trifluo-
romethyl)phenyl)borate) has been widely used in this context.2
It was synthesized by Kobayashi and co-workers3 as its sodium
salt and was shown to be an excellent stable noncoordinating
anion. However, recently two reports revealed that the BArF
anion can be reactive. Saeed et al. reported4 a complex in which
the BArF anion is coordinated to silver and rhodium metal
centers through η3, η4, and η6 modes. Kubas reported5 the only
example of B-C bond cleavage of the BArF anion; this reaction
took place with the cationic complex trans-[(Ph3P)2Pt(Me)-
(OEt2)][BArF] at room temperature or upon refluxing in benzene.
The analogous, generally weakly coordinating BPh4 anion can
exhibit η6 coordination to metal centers,6 and it is susceptible
to attack by electrophilic transition-metal complexes, leading
to phenyl group transfer.6
(6) (a) Fachinetti, G.; Funaioli, T.; Zanazzi, P. F. J. Chem. Soc., Chem.
Commun. 1988, 1100. (b) Morris, J. H.; Gysling, H. J.; Reed, D. Chem.
ReV. 1985, 85, 51. (c) Ananias de Carvalho, L. C.; Dartiguenave, M.;
Dartiguenave, Y.; Beauchamp, A. L. J. Am. Chem. Soc. 1984, 106, 6848.
(d) Albano, P.; Aresta, M.; Manassero, M. Inorg. Chem. 1980, 19, 1069.
(e) Bancroft, E. E; Blount, H. N.; Janzen, E. G. J. Am. Chem. Soc. 1979,
101, 3692. (f) Ashworth, T. V.; Nolte, M. J.; Reimann, R. H.; Singleton,
E. J. Chem. Soc., Chem. Commun. 1977, 937. (g) Eisch, J. J.; Wilcsek,
R. J. J. Organomet. Chem. 1974, 71, C21. (h) Kruger, G. J.; duPreez, A. L.;
Haines, R. J. J. Chem. Soc., Dalton Trans. 1974, 1302. (i) Abley, P.;
Halpern, J. J. Chem. Soc., Chem. Commun. 1971, 1238. (j) Nolte, M. J.;
Gafner, G.; Haines, L. M. J. Chem. Soc., Chem. Commun. 1969, 1406. (k)
Williams, J. L. R.; Doty, J. C.; Grisdale, P. J.; Regan, T. H.; Borden, D. G.
J. Chem. Soc., Chem. Commun. 1967, 109.
Here we report the second example of B-C bond cleavage
of the BArF anion. This reaction takes place upon two-electron
oxidation of a phosphinite pincer Rh(I) complex, and it is
(7) For recent examples see: (a) Feller, M.; Ben-Ari, E.; Gupta, T.;
Shimon, L. J. W.; Leitus, G.; Diskin-Posner, Y.; Weiner, L.; Milstein, D.
Inorg. Chem. 2007, 46, 10479–10490. (b) Hetterscheid, D. G. H.; Klop,
M.; Kicken, R. J. N. A. M.; Smits, J. M. M.; Reijerse, E. J.; de Bruin, B.
Chem. Eur. J. 2007, 13, 3386–3405. (c) Hamazawa, R. T.; Nishioka, T.;
Kinoshita, I.; Takui, T.; Santo, R.; Ichimura, A. Dalton Trans. 2006, 1374–
1376. (d) Doux, M.; Mézailles, N.; Ricard, L.; Le Floch, P.; Adkine, P.;
Berclaz, T.; Geoffroy, M. Inorg. Chem. 2005, 44, 1147–1152. (e) Hetter-
scheid, D. G. H.; de Bruin, B.; Smits, J. M. M.; Gal, A. W. Organometallics
2003, 22, 3022–3024. (f) Gerisch, M.; Krumper, J. R.; Bergman, R. G.;
Tilley, T. D. Organometallics 2003, 22, 47–58. (g) Willems, S. T. H.;
Russcher, J. C.; Budzelaar, P. H. M.; de Bruin, B.; de Gelder, R.; Smits,
J. M. M.; Gal, A. W. Chem. Commun. 2002, 148–149. (h) Gerisch, M.;
Krumper, J. R.; Bergman, R. G.; Tilley, T. D. J. Am. Chem. Soc. 2001,
123, 5818. (i) Collman, J. P.; Boulatov, R. J. Am. Chem. Soc. 2000, 122,
11812–11821.
* To whom correspondence should be addressed. E-mail: david.milstein@
weizmann.ac.il. Fax: 972-8-9344142.
† Department of Organic Chemistry.
‡ Unit of Chemical Research Support.
(1) Strauss, S. H. Chem. ReV. 1993, 93, 927.
(2) (a) Holtcamp, M. W.; Henling, L. M.; Day, M. W.; Labinger, J. A.;
Bercaw, J. E. Inorg. Chim. Acta 1998, 270, 467. (b) Alaimo, P. J.; Arndtsen,
B. A.; Bergman, R. G. J. Am. Chem. Soc. 1997, 119, 5269. (c) Butts, M. D.;
Scott, B. L.; Kubas, G. J. J. Am. Chem. Soc. 1996, 118, 11831. (d)
Brookhart, M.; Grant, B.; Volpe, A. F. Organometallics 1992, 11, 3920.
(3) Nishida, H.; Takada, N.; Yoshimura, M.; Sonoda, T.; Kobayashi,
H. Bull. Chem. Soc. Jpn. 1984, 57, 2600–2604.
(4) Powell, J.; Lough, A.; Saeed, T. J. Chem. Soc., Dalton Trans. 1997,
4137, 4138.
(8) For reviews on mononuclear Rh(II) complexes see: (a) de Bruin,
B.; Hetterscheid, D. G. H. Eur. J. Inorg. Chem. 2007, 211–230. (b) DeWit,
D. G. Coord. Chem. ReV. 1996, 147, 209–246. (c) Pandey, K. K. Coord.
Chem. ReV. 1992, 121, 1–42.
(5) Konze, W. V.; Scott, B. L.; Kubas, G. J. Chem. Commun. 1999,
1807–1808.
10.1021/om800034t CCC: $40.75
2008 American Chemical Society
Publication on Web 04/18/2008

2294 Organometallics, Vol. 27, No. 10, 2008
Salem et al.
Scheme 1
Figure 1. ORTEP drawing of complex 4. Hydrogen atoms, except
for hydride, are omitted for clarity. Ellipsoids are given at the 50%
probability level.
as well as PC-type Rh(II) complexes,9 were prepared in our
group. To the best of our knowledge, Rh(II) complexes of the
common PCP pincer type systems are not known.
Table 1. Selected Bond Lengths (Å) and Angles (deg) of Complex 4
Rh(1)-C(11)
1.998(2)
2.299(1)
2.301(1)
2.405(1)
179.52(5)
82(1)
Rh(1)-H(1)
P(2)-O(21)
P(3)-O(31)
1.57(3)
1.659(2)
1.657(2)
Results and Discussion
Rh(1)-P(2)
Rh(1)-P(3)
Rh(1)-Cl(1)
C(11)-Rh(1)-Cl(1)
C(11)-Rh(1)-H(1)
C(11)-Rh(1)-P(2)
C(11)-Rh(1)-P(3)
Synthesis of Hydrido Chloride Rh(III) and Dinitrogen
Rh(I) Phosphinite Complexes. We have recently reported the
selective C-C bond activation of the phosphinite pincer ligand
C6H3(CH3)[OP(iPr)2]2 at room temperature, upon reaction with
the cationic complex [Rh(COE)2(THF)2]BF4 (COE ) cy-
clooctene), yielding the phosphinite Rh(III) complex [(iPr-
POCOP)Rh(Me)]BF4 (iPr-POCOP ) C6H4[OP(iPr)2]2).10 This
complex underwent an apparent R-H elimination to give the
hydrido complex [(iPr-POCOP)Rh(H)]BF4 and ethylene gas. We
have now utilized the previously reported bulky ligands 111 and
212 to prepare the phosphinite complexes 3 and 4 by their
reaction with the alkene complexes [Rh(COE)2Cl]2 and [Rh-
(COD)Cl]2, respectively, in toluene at 150 °C (Scheme 1). The
P(2)-Rh(1)-P(3)
P(2)-Rh(1)-Cl(1)
P(3)-Rh(1)-Cl(1)
160.34(2)
99.44(4)
100.18(4)
80.35(6)
80.03(6)
weakening of the N-N bond. While several PCP-based dini-
trogen complexes are known, only a small number of POCOP-
based complexes have been reported.9,13
An X-ray diffraction study of crystals of 4 grown from toluene
reveals the expected square-pyramidal geometry (Figure 1, Table
1). The hydride ligand is located at the apical position, in line
with its high-field chemical shift value in the 1H NMR spectrum
31P{1H} NMR of 3 exhibits a doublet at δ 188.41 (1JRh,P
)
1
(-27.13, JRh,H ) 48.9 Hz). The chloride atom is trans to the
122.2 Hz), while the 31P{1H} NMR of 4 exhibits two over-
lapping doublets (in a ratio of 1:1) at δ 190.08 and 201.08 (1JRh,P
) 120.8 Hz), probably due to the presence of square-pyramidal
and trigonal-bipyramidal isomers. In the 1H NMR, the hydride
ipso carbon. The Rh-Cl and Rh-Cipso bond lengths are 2.405(1)
and 1.998(2) Å, respectively, the latter being in the range of
Rh-Cipso bond lengths in the POCOP rhodium systems reported
by us.10 X-ray structures of two PCP-type hydrido chloride
rhodium complexes14 and two such iridium complexes were
reported.8,15
1
appears as a broad doublet at δ -25.19 with JRh,H ) 39.4 Hz
for complex 3 and as a double of triplets at δ -27.13 with 1JRh,H
) 48.9 Hz for complex 4. Deprotonation of complexes 3 and 4
with 1 equiv or an excess of KOtBu led to formation of the
dinitrogen complexes 5a,b and 6a,b, respectively (Scheme 1).
Complexes 5a,b were previously prepared by us by a different
Reaction of the Dinitrogen Complexes 5a,b and 6a,b
with AgBArF. Formation of BArF Cleavage Products. Reac-
tion of the dinitrogen Rh(I) complexes 5a,b and 6a,b with 2
equiv of AgBArF at room temperature led to formation of
complexes 7 and 8, respectively, accompanied by metallic silver
(Scheme 2). The 31P{1H} NMR spectrum exhibits new doublets
at δ 171.66 for 7 (1JRh,P ) 119.3 Hz) and at δ 179.56 for 8
(1JRh,P ) 112.0 Hz). No frequency suitable for a terminal N2
molecule was detected in the IR spectrum, the absence of which
route.10 Complex 6b exhibits a doublet at δ 202.68 (1JRh,P
)
172.7 Hz) in the 31P{1H} NMR spectrum. Complexes analogous
to 6a,b with iridium were reported.13 The νN bands in the IR
2
spectra of complex 6a and the reported iridium analogue13 are
quite similar (2143 vs 2118 cm-1). The νN band of complex
2
5a is slightly higher (2162 cm-1). This trend can be attributed
1
was confirmed by elemental analysis. However, the H and
t
13C{1H} NMR spectra were not sufficiently informative for
conclusive structure elucidation. Crystals suitable for X-ray
diffraction analysis were grown by vapor diffusion of diethyl
ether into an acetone solution of complex 8 at -35 °C.
Surprisingly, the crystal structure revealed that B-C bond
to the higher basicity of the Bu groups, which results in more
back-bonding to the dinitrogen ligand, with a corresponding
(9) Montag, M.; Leitus, G.; Shimon, L. J. W.; Ben-David, Y.; Milstein,
D. Chem. Eur. J. 2007, 13, 9043–9055.
(10) Salem, H.; Ben-David, Y.; Shimon, L. J. W.; Milstein, D.
Organometallics 2006, 25, 2292–2300.
(11) Morales-Morales, D.; Grause, C.; Kasaoka, K.; Redon, R.; Cramer,
R. E.; Jensen, C. M. Inorg. Chim. Acta 2000, 300–302, 958.
(12) Gottker-Schnetmann, I.; White, P.; Brookhart, M. J. Am. Chem.
Soc. 2004, 126, 1804–1811.
(14) (a) Nemeh, S.; Jensen, C.; Binamira-Soriaga, E.; Kaska, W. C.
Organometallics 1983, 2, 1442–1447. (b) Crocker, C.; Errington, J.;
McDonald, W. S.; Odell, K. J.; Shaw, B. L. J. Chem. Soc., Chem. Commun.
1979, 498.
(13) Gottker-Schnetmann, I.; White, P. S.; Brookhart, M. Organome-
tallics 2004, 23, 1766–1776.
(15) Grimm, J. C.; Nachtigal, C.; Mack, H.-G.; Kaska, W. C.; Mayer,
H. A. Inorg. Chem. Commun. 2000, 3, 511–514.

Phosphinite Rh Pincer Complexes
Scheme 2a
Organometallics, Vol. 27, No. 10, 2008 2295
a
For simplicity we depict complexes 5a,b and 6a,b as monomeric
(5a and 6a) in all schemes.
Figure 3. EPR spectra of complexes 9 (upper spectrum) and 11
(lower spectrum) obtained at 125 K in frozen acetone. Experimental
conditions: microwave power 31 mW, modulation amplitude 0.8
G, time constant 0.65 s.
The cleaved ArF protons exhibit in the 1H NMR spectrum a
downfield shift and a change in the relative ratios of the peaks,
as observed in the previously reported example.2b The ortho
protons of the coordinated ArF ring are shifted upfield relative
to its para proton, whereas the order is opposite for the BArF
anion protons. The ipso carbons of the cleaved ArF groups could
not be located in the 13C{1H} NMR spectra of complexes 7
and 8. We assume that their chemical shifts overlap with those
of the ipso carbons of the POCOP ligands.
Mechanistic Aspects of the B-C Cleavage of the BArF
Anion. Characterization of Rh(II) Species. We believe that
the unexpected, room-temperature cleavage of the BArF anion
occurs as a result of an electrophilic attack of an unsaturated
Rh(III) cationic center (obtained by two-electron oxidation of
the Rh(I) precursor) on the ipso carbon of one of the aryl rings
of the BArF anion.
Figure 2. ORTEP drawing of complex 8. The hydrogen atoms and
BArF anion are omitted for clarity. Ellipsoids are given at the 50%
probability level.
Table 2. Selected Bond Lengths (Å) and Angles (deg) of Complex 8
Rh(1)-C(6)
1.975(5)
2.000(5)
2.186(4)
88.8(2)
167.2(2)
104.0(2)
Rh(1)-P(1)
P(1)-O(1)
2.355(1)
1.647(3)
As the reaction was observed in several solvents, none of
which is acidic (see Influence of Solvents on the B-C Bond
Cleavage), a mechanism in which the B-C cleavage is promoted
by protonation of the ipso carbon of the phenyl ring is unlikely.
Rh(1)-C(15)
Rh(1)-O(2)
C(6)-Rh(1)-C(15)
C(6)-Rh(1)-O(2)
C(15)-Rh(1)-O(2)
C(6)-Rh(1)-P(1)
C(15)-Rh(1)-P(1)
O(2)-Rh(1)-P(1)
80.64(3)
92.16(4)
98.60(3)
Treatment of the Rh(I) complexes 5a,b and 6a,b with 2 equiv
of NaBArF did not lead to any reaction, indicating that Rh(I)
species are probably not involved in the B-C bond cleavage
reaction. In order to check if the reaction proceeds through an
electrophilic attack of a Rh(II) center (i.e., one-electron oxidation
of the metal and the BArF cleavage take place initially, followed
by a second oxidation to afford the Rh(III) center) only 1 equiv
of AgBArF was utilized. Under these conditions, reaction of
5a,b resulted in a mixture of complexes. Reaction of complexes
6a,b led to a solution that exhibited two doublets in the 31P{1H}
NMR spectrum, which turned out to be minor products after
their extraction with pentane. The major product was a
paramagnetic complex, according to an EPR measurement
(Figure 3).
cleavage of one of the two BArF anions took place, resulting in
an aryl transfer to afford a cationic Rh(III) metal center (Figure
2, Table 2).16
The rhodium atom in complex 8 is in the center of a distorted
square pyramid. The σ-coordinated C6H3-(3,5-CF3) ring is at
the axial position and is trans to the vacant site, as expected
(Figure 2), whereas the position trans to the ipso carbon of the
tBu-POCOP ligand is occupied by an acetone molecule.
(16) The presumed cleaved product B(C6H3(3,5-CF3)3 could not be
detected by 19F NMR of the reaction mixture, perhaps as a result of reaction
with adventitious water forming an insoluble compound (a precipitate was
observed).

2296 Organometallics, Vol. 27, No. 10, 2008
Salem et al.
Scheme 3
Since attempts to crystallize the paramagnetic product (which
was eventually characterized as complex 9)17 were not suc-
cessful, other oxidants with anions potentially better suited for
crystallization were applied. The dinitrogen complexes 6a,b
were treated with 1 equiv of AgBF4 or [Cp2Fe][BF4], resulting
in an oxidation product similar to that for AgBArF according
to EPR measurements. Treatment of those products with 1 equiv
of NaBArF resulted in a color change from reddish brown to
violet, but the product remained paramagnetic and only anion
exchange took place, as confirmed by an EPR measurement,
which exhibited the same spectrum as for 9 (Scheme 3).
Moreover, treatment of complex 9 with 1 equiv of NaBArF did
not lead to any reaction. On the other hand, treatment of those
products with 1 equiv of AgBArF resulted in the formation of
the BArF cleavage product 8 (with BF4- as a counterion). These
results support a mechanism of electrophilic attack at the aryl
ring by a Rh(III) center and not by Rh(II).
complex [(tBu-POCOP)RhII][BF4] (10) (Scheme 3). Crystals of
this complex were grown by diffusion of pentane into its
fluorobenzene solution, but the structure obtained by X-ray
diffraction was disordered, although it did indicate the con-
nectivity of this structure.
Reaction of AgPF6 as with 6a,b resulted in the paramagnetic
product 11 (Scheme 3), and crystals of it were grown by pentane
diffusion into its fluorobenzene solution. X-ray diffraction of
these crystals showed a Rh(II) product with [PF2O2]- as a
coordinated counteranion (Figure 4), which was probably formed
–
by Rh(II)- or Ag+-catalyzed18 hydrolysis of PF6 with traces
of water. Transition-metal complexes containing [PO2F2]- as a
ligand or counteranion, resulting from PF6- hydrolysis, probably
promoted by the Lewis-acidic metal center, were reported.19
The product of the oxidation of 6a,b with AgBF4 described
above was the analogue of 9 with a BF4 anion, the paramagnetic
(17) Crystals of complex 9 (Scheme 3) were grown by vapor diffusion
of pentane into its dichloromethane solution. However, the structure was
disordered, although it revealed a Rh(II) product with a coordinated acetone
molecule and the BArF counteranion.
-
(18) Catalysed hydrolysis of PF6 by Ag+ was reported: Fernandez-
Galan, R.; Manzano, B. R.; Otero, A.; Lanfranchi, M.; Pellinghelli, M. A.
Inorg. Chem. 1994, 33, 2309. The adventitious water in the reaction leading
to complex 11 might be derived from the solvent.
(19) (a) Lemattre, F.; Lucas, D.; Groison, K.; Ricard, P.; Mugnier, Y.;
Harvey, P. D. J. Am. Chem. Soc. 2003, 125, 5511. (b) Connelly, N. G.;
Einig, T.; Garcia Herbosa, G.; Hopkins, P. M.; Mealli, C.; Orpen, A. G.;
Rosair, G. M.; Viguri, F. J. Chem. Soc., Dalton Trans. 1994, 2025. (c)
Bauer, H.; Nagel, U.; Beck, W. J. Organomet. Chem. 1985, 290, 219. (d)
Wimmer, F. L.; Snow, M. R. Aust. J. Chem. 1978, 31, 267. (e) White, C.;
Thompson, S. J.; Maitlis, P. M. J. Organomet. Chem. 1977, 134, 319. (f)
Thompson, S. J.; Bailey, P. M.; White, C.; Maitlis, P. M. Angew. Chem.,
Int. Ed. Engl. 1976, 15, 490.
Figure 4. ORTEP drawing of complex 11. Hydrogen atoms are
omitted for clarity. Ellipsoids are given at the 50% probability
level.

Phosphinite Rh Pincer Complexes
Organometallics, Vol. 27, No. 10, 2008 2297
Table 3. Selected Bond Lengths (Å) and Angles (deg) of Complex 11
Thus, only one -electron oxidation takes place in CH3CN, even
when 2 equiv of AgBArF is used. The effect of different solvents
on the redox potential of Ag+/Ag has been described in the
literature.23 It was shown that the lowest redox potential among
the tested solvents was in CH3CN, which is probably why the
second oxidation did not take place.
C(1)-Rh(1)
1.980(3)
2.148(2)
2.304(1)
2.3176(1)
170.78(11)
160.16(3)
P(3)-F(2)
P(3)-F(1)
1.549(3)
1.550(2)
1.449(3)
1.469(3)
137.19(15)
Rh(1)-O(3)
Rh(1)-P(2)
P(3)-O(4)
Rh(1)-P(1)
C(1)-Rh(1)-O(3)
P(1)-Rh(1)-P(2)
P(3)-O(3)
P(3)-O(3)-Rh(1)
On the other hand, when the less bulky complexes 5a,b were
oxidized in CH3CN, a mixture containing two major complexes
(in a ratio of 1:1.4) was obtained. The minor complex exhibits
in 31P{1H} NMR a doublet and a coupling constant similar to
the BArF cleaved product (7). It seems that the combination of
the bulkier tBu substituents in 6a,b and the use of CH3CN as a
solvent prevents a second oxidation from taking place and
therefore the B-C cleavage of BArF does not occur.
Table 4. EPR Parameters of Complexes 9-11a
complex
gx
gy
gz
A1 (G)
9b
2.536
2.531
2.532
2.540
2.525
2.331
2.328
2.233
2.332
2.324
1.954
1.956
1.953
1.955
1.956
17.5
17
17
17.5
17
9c
10d
10e
11
Complexes 7 and 8 are probably solvent-stabilized, even in
the case of the weakly coordinating CH2Cl2.24 In the case of
the noncoordinating solvent PhF, agostic interactions with the
C-H bonds of the tBu substituents might be involved, although
we have no evidence for such interactions with the metal center.
Repeated attempts to crystallize complexes 7 and 8 in CH2Cl2
or PhF were not successful.
a Repetition is due to different synthesis pathways. b Obtained from
6a,b. c Obtained from 10. d Obtained from AgBF4. e Obtained from
[Cp2Fe][BF4].
The rhodium atom in complex 11 is in the center of a slightly
distorted square plane. The Rh-C(1) bond length (1.980(3) Å)
is similar to that of the Rh(III) complex 8 (1.975(5) Å)
(Table 3).
Formation of the Rh(II) complex 9 upon one-electron
oxidation of 6a,b, without B-C cleavage taking place, indicates
that Rh(II) is not active in the cleavage of the BArF anion. Thus,
the likely mechanism of B-C cleavage involves elecrophilic
attack of an unsaturated Rh(III) center on the ipso carbon of
the anion.20
Summary
Treatment of the phosphinite dinitrogen Rh(I) complexes
(5a,b and 6a,b) with 2 equiv of AgBArF leads unexpectedly to
the cleavage of one of the B-C bonds of the BArF anion
and the transfer of the cleaved aryl group to the rhodium center.
The reaction takes place at room temperature via an electrophilic
attack of the Rh(III) center on the B-C bond. The reaction of
only 1 equiv of AgBArF with the dinitrogen complexes 6a,b
leads to 1-electron oxidation, affording a 15-electron, square-
planar Rh(II) complex (the fourth coordination site being
occupied by a solvent molecule or a coordinating anion), with
no aryl ring transfer being observed. The reaction of the Rh(II)
intermediate 9 with 1 equiv of NaBArF does not lead to any
reaction, proving that a second oxidation to afford the Rh(III)
complex is necessary for the cleavage process to take place.
Moreover, the reaction of 2 equiv of NaBArF with Rh(I)
complexes 6a,b does not lead to any reaction, confirming that
metal oxidation to Rh(III) is necessary for the cleavage process
to take place. The B-C cleavage product 8 and the Rh(II)
intermediate 11 were characterized by X-ray diffraction analysis.
Utilization of different solvents resulted in the formation of the
same product (7 and 8), except in the case of CH3CN, in which
case only one-electron oxidation was possible due to the lower
redox potential of silver salts in it.
The paramagnetic d7 Rh(II) complexes 9-11 were studied
by X-band EPR spectroscopy in frozen acetone solutions. For
all complexes an EPR rhombic pattern was observed and no
hyperfine structure was resolved for the central- and low-field
components gx and gy (Figure 3). For the gz component the
observed doublet hyperfine splitting can be explained by
coupling with the nuclear spin of 103Rh (I ) 1/2). The EPR
data obtained can reflect asymmetric coordination of ligands
around the metal center which correspond to the slight distortion
of the square-planar geometry exhibited in the X-ray structure
of complex 11. For Rh(II) complexes with bis(phosphinoalkyl)-
arene21 and bis(oxazoline)7e ligands, spectra in frozen solutions
with EPR parameters close to those obtained by us were
observed. The EPR parameters of complexes 9-11 are outlined
in Table 4.
Influence of Solvents on the B-C Bond Cleavage. The
oxidation of complexes 5a,b and 6a,b with 2 equiv of AgBArF,
when carried out in coordinating (acetone, diethyl ether) or
noncoordinating (PhF, CH2Cl2)22 solvents, afforded the same
red products, complexes 7 and 8, respectively. However, when
the reaction of complexes 6a,b was carried out in the strongly
coordinating solvent CH3CN, a green product was obtained,
which showed no signals in the 31P{1H} NMR spectrum. When
the solvent was removed, the color of the residue became violet.
The violet product was identified as the Rh(II) complex 9
(Scheme 3), as evidenced by its EPR analysis and confirmed
by the reaction of 1 equiv of AgBArF with 6a,b in CH3CN.
Experimental Section
General Procedures. All experiments with metal complexes and
the phosphinite ligand were carried out under an atmosphere of
purified nitrogen in a Vacuum Atmospheres glovebox equipped with
a MO 40-2 inert gas purifier, or using standard Schlenk techniques.
All solvents were reagent grade or better. All nondeuterated solvents
were refluxed over sodium/benzophenone ketyl and distilled under
an argon atmosphere. Deuterated solvents were dried over 4 Å
molecular sieves. Commercially available reagents were used as
received. [Rh(COE)Cl]2,25 [Rh(COD)Cl]2,26 NaBArF,27 and Ag-
(20) Attempts to explore the reactivity of unsaturated Rh(III) complexes
toward electrophilic attack on the B-C bond were hampered by the lack
of such suitable complexes; the oxidation of the Rh(II) complexes 10 and
11 to Rh(III) by treating them with another 1 equiv of AgBF4 or AgPF6,
respectively, did not occur.
(21) Dixon, F. M.; Masar, M. S., III; Doan, P. E.; Farrell, J. R.; Arnold,
F. P., Jr.; Mirkin, C. A.; Incarvito, C. D.; Zakharov, L. N.; Rheingold, A. L.
Inorg. Chem. 2003, 42, 3245–3255.
(23) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877–910.
(24) Examples of such coordination: Zhang, J.; Barakat, K. A.; Cundari,
T. R.; Gunnoe, T. B.; Boyle, P. D.; Petersen, J. L.; Day, C. S. Inorg. Chem.
2005, 44, 8379–8379.
(22) Excluding complexes 5a,b in the case of CH2Cl2, in which they
are not stable. However, complex 7, obtained in the other solvents, is stable
in CH2Cl2.
(25) Herde, J. L.; Senoff, C. V. Inorg. Nucl. Chem. Lett. 1971, 7, 1029.
(26) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88–90.

2298 Organometallics, Vol. 27, No. 10, 2008
Salem et al.
BArF28 were prepared according to literature procedures. 1H, 13C,
31P, and 19F NMR spectra were recorded at 400, 100, 162, and
376 MHz, respectively, using a Bruker AMX-400 NMR spectrom-
eter and at 500, 125, and 202 MHz, respectively, for 1H, 13C, and
31P, using a Bruker Avance-500 NMR spectrometer. All spectra
were recorded at 23 °C unless stated otherwise. NMR measurements
were performed in CDCl3, CD2Cl2, and C6D6. 1H and 13C{1H}
NMR chemical shifts are reported in ppm downfield from tetram-
ethylsilane. 1H NMR chemical shifts are referenced to the residual
hydrogen signal of the deuterated solvent (7.15 ppm for benzene,
5.32 ppm for dichloromethane, and 7.24 ppm for chloroform). In
13C{1H} NMR measurements the signals of deuterated benzene
(128.0 ppm), deuterated dichloromethane (53.8 ppm), and deuterated
chloroform (77.0 ppm) were used as a reference. 31P NMR chemical
shifts are reported in ppm downfield from H3PO4 and referenced
to an external 85% solution of phosphoric acid in D2O. Abbrevia-
tions used in the description of NMR data are as follows: b, broad;
s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; v, virtual,
dist, distorted. X-band electron spin resonance (ESR) spectra were
recorded on a ELEXSYS 500 spectrometer (Bruker, Karlsruhe,
Germany). g values of the complexes in glassy solutions were
determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) reso-
nance signal (g ) 2.0037) as a standard. The variable-temperature
ESR experiments were carried out using a temperature unit
(Euroterm, ER 4113VT, Bruker) with an accuracy of (1 K.
(t, 1JP,C ) 9.4 Hz, 2JRh,C ) 2.3 Hz, PC(CH3)3), 27,65 (dist dd, 2JP,C
3
) 6.4 Hz, JRh,C ) 2.8 Hz, PC(CH3)3). Anal. Calcd for C22H40-
ClO2P2Rh: C, 49.22; H, 7.51. Found: C, 49.37; H, 7.31.
X-ray Structural Analysis of 4. Crystal data: C22H40ClO2P2Rh,
3
j
orange prisms, 0.7 × 0.5 × 0.3 mm , triclinic, P1 (No. 2), a )
8.176(2) Å, b ) 12.184(2) Å, c ) 13.351(3) Å, R ) 100.49(3)°, ꢀ
) 95.71(3)°, γ ) 103.91(3)°, from 20° of data, T ) 120(2) K, V
) 1255.1(5) Å3, Z ) 2, fw 536.84, Dc ) 1.421 Mg/m3, µ ) 0.929
mm-1. Data collection and processing: Nonius KappaCCD dif-
fractometer, Mo KR (λ ) 0.71073 Å), graphite monochromator,
-10 e h e 10, -15 e k e 15, 0 e l e 17, frame scan width 1.0°,
scan speed 1.0° per 30 s, typical peak mosaicity 0.47°, 26 574
reflections collected, 5733 independent reflections (Rint ) 0.027).
The data were processed with Denzo-Scalepack. Solution and
refinement: structure solved by direct methods with SHELXS-97,
full-matrix least-squares refinement based on F2 with SHELXL-
97, 301 parameters with 213 restraints, final R1 ) 0.0261 (based
on F2) for data with I > 2σ(I) and R1 ) 0.0286 on 5361 reflections,
goodness of fit on F2 1.073, largest electron density peak 0.696 e
Å-3
.
Reaction of (tBu-POCOP)Rh(H)(Cl) (4) with KOtBu. For-
mation of (tBu-POCOP)Rh(N2) (6a) and [(tBu-POCOP)Rh]2-
(µ-N2) (6b). To a THF solution (5 mL) of 4 (200 mg, 0.37 mmol)
was added a slight excess (1.2 equiv, 50.2 mg, 0.44 mmol) of
KOtBu as a solid, leading to a color change to brownish yellow
and the immediate formation of the dinitrogen complexes 6a,b. The
solvent was removed under vacuum, the residue was extracted with
benzene, and the extract was filtered through a cotton pad. The
solvent was removed from the filtrate under vacuum, resulting in
a yellow powder in 96.9% (190.7 mg) yield. Upon bubbling argon
through a C6D6 solution of 6a,b in a septum-capped NMR tube for
30 min, complex 6a was quantitatively converted to complex 6b.
i
Reaction of [Rh(COE)2Cl]2 with Pr-POCOP-H (1). For-
mation of (iPr-POCOP)Rh(H)(Cl) (3). To a toluene solution (2
mL) of [Rh(COE)2Cl]2 (50 mg, 0.07 mmol) was added ligand 1
(47.7 mg, 0.14 mmol). The reaction mixture was transferred to a
pressure vessel and heated at 150 °C for 8 h. The color changed
from orange to brown, and a black fine solid was also formed. The
product was filtered in order to remove the black solid through a
cotton pad, and the solvent was removed from the filtrate under
vacuum, resulting in a 90% pure oily complex in 97.2% (65.0 mg)
yield.
31P{1H} NMR (C6D6): 202.68 (d, 1JRh,P ) 172.7 Hz). 1H NMR
3
3
(C6D6): 6.92 (t, JH,H ) 7.6 Hz, 1H, Ar), 6.80 (d, JH,H ) 7.6 Hz,
2H, Ar), 1.38 (vt, 3JP,H ) 7.6 Hz, 36H, PC(CH3)3). 13C{1H} NMR
(C6D6): 169.30 (t, 2JP,C ) 8.7 Hz, Cipso, Rh-Ar), 138.95 (dt, 2JP,C
) 9.7 Hz, 2JRh,C ) 34.5 Hz), 126.18 (s, Ar), 104.44 (t, 2JP,C ) 6.7
31P{1H} NMR (C6D6): 188.41 (d, 1JRh,P ) 122.2 Hz). 1H NMR
3
3
(C6D6): 6.84 (t, JH,H ) 7.6 Hz, 1H, Ar), 6.68 (d, JH,H ) 7.6 Hz,
2H, Ar), 2.49 (m, 2H, PCH(CH3)2), 2.12 (m, 2H, PCH(CH3)2), 1.13
(overlapping double of doublets, 24H, PCH(CH3)2), -25.19 (br d,
1JRh,H ) 39.4 Hz, 1H, Rh-H). 13C{1H} NMR (C6D6): 166.91 (t,
2JP,C ) 6.9 Hz, Cipso, Rh-Ar), 128.53 (s, Ar), 126.78 (s, Ar), 106.38
1
2
Hz, Ar), 39.36 (td, JP,C ) 2.2 Hz, JRh,C ) 7.2 Hz, PC(CH3)3),
38.60 (t, 1JP,C ) 9.4 Hz, 2JRh,C ) 2.3 Hz, PC(CH3)3), 27.65 (t, 2JP,C
) 6.4 Hz, PC(CH3)3). IR (6a): νN 2143 cm-1. Anal. Calcd for
2
C22H39N2O2P2Rh: C, 50.01; H, 7.44. Found: C, 49.82; H, 7.22.
Reaction of 5a,b with 2 Equiv of AgBArF. Formation of
[(iPr-POCOP)Rh(C6H3(CF3)2)][BArF] (7). To a fluorobenzene
solution (1 mL) of 5a,b (20.0 mg, 0.04 mmol) was slowly added
2 equiv of AgBArF (82.2 mg, 0.08 mmol) in fluorobenzene (1 mL),
resulting in a color change from yellow to orange-red, and metallic
silver was immediately massively formed. The reaction mixture
was kept at room temperature overnight with protection from light
until the reaction was complete. The metallic silver was removed
by filtration through a cotton and Celite pad, and the solvent was
removed from the filtrate under vacuum, resulting in a red oil. The
residue was washed with pentane (3 × 2 mL) and dried again,
resulting in a red solid in 96.9% (61.9 mg) yield.
2
1
(t, JP,C ) 5.7 Hz, Ar), 29.91 (t, JP,C ) 11.0 Hz, PCH(CH3)2),
28.44 (t, 1JP,C ) 13.5 Hz, PCH(CH3)2), 17.45 (s, 6H, PCH(CH3)2),
17.34 (s, 6H, PCH(CH3)2), 16.94 (s, 6H, PCH(CH3)2), 16.45 (s,
6H, PCH(CH3)2). IR: νRh-H 2150 cm-1. MS: m/z 479 (M+, calcd
m/z 480).
t
Reaction of [Rh(COD)Cl]2 with Bu-POCOP-H (2). Forma-
tion of (tBu-POCOP)Rh(H)(Cl) (4). To a toluene solution (10 mL)
of [Rh(COD)Cl]2 (600 mg, 1.2 mmol) was added ligand 2 (970
mg, 2.4 mmol) in toluene (5 mL). The reaction mixture was
transferred to a pressure vessel and heated at 150 °C for 18 h.
Complex 4 was obtained as an orange precipitate. The vessel was
cooled, and the solvent was removed under vacuum, resulting in
an orange solid in 83.9% (1096 mg) yield.
31P{1H} NMR (CD2Cl2): 171.66 (d, 1JRh,P ) 119.3 Hz). 1H NMR
(CD2Cl2): 7.58 (br s, 1H, p-H of ArF), 7.50 (br s, 2H, o-H of ArF),
7.38 (br s, 8H, o-H of BArF), 7.22 (br s, 4H, p-H of BArF), 6.92 (t,
31P{1H} NMR (CDCl3): 190.08 (dd (two isomers), 1JRh,P ) 120.8
1
3
3
3JH,H ) 7.6 Hz, 1H, Ar), 6.49 (d, JH,H ) 7.6 Hz, 2H, Ar), 2.28
Hz). H NMR (CDCl3): 6.89 (t, JH,H ) 7.8 Hz, 1H, Ar), 6.54 (d,
3JH,H ) 7.8 Hz, 2H, Ar), 1.37 (dd, 3JP,H ) 7.8 Hz, 36H, PC(CH3)3),
3
(m, 2H, PCH(CH3)2), 1.8 (br m, 2H, PCH(CH3)2), 0.88 (dd, JH,H
1
2
) 7.6 Hz, 3JH,P ) 13.9 Hz, 6H, PCH(CH3)2), 0.7–0.8 (overlapping
-27.13 (dt, JRh,H ) 48.9 Hz, JP,H ) 10.8 Hz, 1H, Rh-H).
13C{1H} NMR (CDCl3): 167.51 (t, 2JP,C ) 6.2 Hz, Cipso, Rh-Ar),
129.36 (dq, 2JP,C ) 5.0 Hz, 2JRh,C ) 31.3 Hz), 126.22 (s, Ar), 105.66
(t, 2JP,C ) 5.5 Hz, Ar), 40.88 (t, 1JP,C ) 8.3 Hz, PC(CH3)3), 38.60
3
double of doublets, 12H, PCH(CH3)2), 0.35 (dd, JH,H ) 8.9 Hz,
3JH,P ) 16.5 Hz, 6H, PCH(CH3)2). 13C{1H} NMR (CD2Cl2): 164.92
2
1
(t, JP,C ) 5.5 Hz, Cipso, Rh-Ar), 162.11 (q, JB,C ) 49.73 Hz,
Cipso of BArF), 135.17 (br s, o-C of BArF), 134.58 (br s, p-C of
ArF), 131.02 (s, Ar of POCOP), 129.24 (qq, -C of BArF), 129.03
(s, Ar of POCOP), 126.33 (s, -C of BArF), 123.62 (s, p-C of ArF),
121.53 (s, CF3 of ArF), 119.44 (dd or m, p-C of ArF), 117.84 (br s,
(27) Yakelis, N. A.; Bergman, R. G. Organometallics 2005, 24, 3579–
3581.
(28) Hayashi, Y.; Rohde, J. J.; Corey, E. J. J. Am. Chem. Soc. 1996,
118, 5502–5503.
3
p-C of BArF), 109.55 (t, JP,C ) 5.8 Hz, Ar of POCOP), 31.26

Phosphinite Rh Pincer Complexes
Organometallics, Vol. 27, No. 10, 2008 2299
1
1
(t, JP,C ) 10.7 Hz, PCH(CH3)2), 28.39 (t, JP,C ) 13.7 Hz,
PCH(CH3)2), 19.17 (s, PCH(CH3)2), 17.72 (s, PCH(CH3)2),
15.65 (s, PCH(CH3)2), 15.45 (s, PCH(CH3)2). 19F NMR (CD2Cl2):
-62.93 (s, 24F, CF3 of BArF anion), -63.32 (s, 3F, CF3 of ArF),
-63.80 (s, 3F, CF3 of ArF). Anal. Calcd for C58H46BF30O2P2Rh:
C, 45.81; H, 3.05. Found: C, 45.96; H, 3.15.
kept for overnight at room temperature for reaction completion.
The solvent was removed under vacuum, and the residue was
washed with pentane to remove the formed ferrocene and then
extracted with fluorobenzene and filtered through a cotton pad. The
solvent was removed from the filtrate under vacuum, resulting in
an 89.2% (14.9 mg) yield of complex 10. Anal. Calcd for
C22H39BF4O2P2Rh: C, 45.0; H, 6.69. Found: C, 45.12; H, 6.76.
Reaction of 6a,b with 1 Equiv of AgBF4. Formation of [(tBu-
POCOP)RhII][BF4] (10). To a fluorobenzene solution (1 mL) of
6a,b (20 mg, 0.04 mmol) was added 1 equiv of AgBF4 (7.4 mg,
0.04 mmol) in fluorobenzene, leading to an immediate formation
of metallic silver and a color change to violet. The reaction mixture
was kept for additional 2 h at room temperature for reaction
completion and then filtered through a cotton and Celite pad for
metallic silver removal, and the solvent was removed from the
filtrate under vacuum, giving a brown solid in 92.8% (20.6 mg)
yield. Anal. Calcd for C22H39BF4O2P2Rh: C, 45.0; H, 6.69. Found:
C, 45.65; H, 6.75.
Reaction of Complex 10 with NaBArF. Formation of [(tBu-
POCOP)RhII][BArF] (9). Upon addition of 1 equiv of NaBArF
(30.2 mg, 0.034 mmol) to complex 10 (20 mg, 0.034 mmol) in
acetone, the color changed immediately to violet. The solvent was
removed after 1 h, the residue was extracted with acetone, and the
extract was filtered in order to remove the formed NaBF4. The
solvent was removed from the filtrate under vacuum, giving a violet
solid in 98% (45.4 mg) yield. Anal. Calcd for C54H51BF24O2P2Rh:
C, 47.56; H, 3.77. Found: C, 47.69; H, 3.85.
Reaction of 6a,b with 1 Equiv of AgPF6. Formation of [(tBu-
POCOP)RhII][PO2F2] (11). To a fluorobenzene solution (1 mL)
of 6a,b (20 mg, 0.04 mmol) was added 1 equiv of AgPF6 (10.7
mg, 0.04 mmol) in fluorobenzene, leading to an immediate
formation of metallic silver and a color change to violet. The
reaction mixture was kept for an additional 2 h at room tempera-
ture for reaction completion and then filtered through a cotton and
Celite pad for metallic silver removal. The solvent was removed
from the filtrate under vacuum, giving a brown solid in 30.7% (7.5
mg) yield. Anal. Calcd for C22H39F2O4P3Rh: C, 43.94; H, 6.54.
Found: C, 42.85; H, 6.14.
Reaction of 6a,b with 2 Equiv of AgBArF. Formation of [(tBu-
POCOP)Rh(C6H3(CF3)2)][BArF] (8). To a fluorobenzene solution
(1 mL) of 6a,b (15 mg, 0.03 mmol) was added 2 equiv of AgBArF
(55.1 mg, 0.06 mmol) in a fluorobenzene solution (1 mL), leading
to an immediate color change to violet and formation of metallic
silver. The reaction mixture was stirred at room temperature for a
few hours, resulting in a color change to red. The solution was
filtered through a cotton and Celite pad to remove the metallic silver,
and the solvent was removed from the filtrate under vacuum. The
residue was washed with pentane (3 × 2 mL) and dried again,
resulting in a red solid in 95.8% (42.9 mg) yield.
31P{1H} NMR (CD2Cl2): 179.56 (d, 1JRh,P ) 112.0 Hz). 1H NMR
(CD2Cl2): 7.58 (br s, 1H, p-H of ArF), 7.50 (br s, 2H, o-H of ArF),
7.38 (br s, 8H, o-H of BArF), 7.22 (br s, 4H, p-H of BArF), 6.92 (t,
3JH,H ) 7.6 Hz, 1H, Ar), 6.49 (d, JH,H ) 7.6 Hz, 2H, Ar), 2.28
3
3
(m, 2H, PCH(CH3)2), 1.8 (br m, 2H, PCH(CH3)2), 0.88 (dd, JH,H
) 7.6 Hz, 3JH,P ) 13.9 Hz, 6H, PCH(CH3)2), 0.7–0.8 (overlapping
3
double of doublets, 12H, PCH(CH3)2), 0.35 (dd, JH,H ) 8.9 Hz,
3JH,P ) 16.5 Hz, 6H, PCH(CH3)2). 13C{1H} NMR (CD2Cl2): 165.92
(t, 2JP,C ) 5.5 Hz, Cipso, Rh-Ar), 162.0 (q, 1JB,C ) 49.73 Hz, Cipso
of BArF), 135.0 (br s, o-C of BArF), 134.17 (br s, p-C of ArF),
131.20 (s, Ar of POCOP), 129.10 (qq, -C of BArF), 128.84 (s, Ar
of POCOP), 126.13 (s, -C of BArF), 123.42 (s, p-C of ArF), 120.71
(s, CF3 of ArF), 119.22 (dd or m, p-C of ArF), 117.72 (br s, p-C of
BArF), 109.36 (t, 3JP,C ) 5.8 Hz, Ar of POCOP), 43.63 (t, 1JP,C
)
1
7.6 Hz, PC(CH3)3), 41.47 (td, JP,C ) 7.6 Hz, PC(CH3)3), 29.21
(m, PC(CH3)3), 27.35 (br s, PC(CH3)3). 19F NMR (CD2Cl2): -63.01
(s, 24F, CF3 of BArF anion), -63.65 (s, 3F, CF3 of ArF), -64.29
(s, 3F, CF3 of ArF). Anal. Calcd for C63H58BF30O2P2Rh: C, 47.51;
H, 3.67. Found: C, 47.45; H, 3.86.
X-ray Structural Analysis of 8. Crystal data: C33H48F6O3P2Rh
+ C32H12BF24, red, 0.4 × 0.3 × 0.3 mm3, monoclinic, P21/m (No.
11), a ) 13.190(3) Å, b ) 19.765(4) Å, c ) 13.373(3) Å, ꢀ )
97.16(3)°, from 20° of data, T ) 120(2) K, V ) 3459(1) Å3, Z )
2, fw 1634.79, Dc ) 1.570 Mg/m3, µ ) 0.419 mm-1. Data
collection and processing: Nonius KappaCCD diffractometer, Mo
KR (λ ) 0.710 73 Å), graphite monochromator, -14 e h e 14, 0
e k e 21, -14 e l e 0, frame scan width 1.0°, scan speed 1.0°
per 400 s, typical peak mosaicity 0.97°, 16 307 reflections collected,
5074 independent reflections (Rint ) 0.066). The data were pro-
cessed with Denzo-Scalepack. Solution and refinement: structure
solved by direct methods with SHELXS-97, full-matrix least-
squares refinement based on F2 with SHELXL-97, 524 parameters
with 0 restraints, final R1 ) 0.0497 (based on F2) for data with I
> 2σ(I) and R1 ) 0.0610 on 5018 reflections, goodness of fit on
X-ray Structural Analysis of 11. Crystal data: C22H39F2O4P3Rh,
3
j
red, 0.3 × 0.2 × 0.1 mm , triclinic, P1 (No. 2), a ) 8.404(2) Å,
b ) 16.600(3) Å, c ) 20.931(4) Å, R ) 102.71(3)°, ꢀ ) 95.99(3)°,
γ ) 104.26(3)° from 20° of data, T ) 120(2) K, V ) 2721.6(11)
Å3, Z ) 4, fw 601.35, Dc ) 1.468 Mg/m3, µ ) 0.842 mm-1. Data
collection and processing: Nonius KappaCCD diffractometer, Mo
KR (λ ) 0.71073 Å), graphite monochromator, -10 e h e 10,
-21 e k e 21, 0 e l e 27, frame scan width 1.0°, scan speed 1.0°
per 30 s, typical peak mosaicity 0.419°, 49 652 reflections collected,
13 354 independent reflections (Rint) 0.069). The data were
processed with Denzo-Scalepack. Solution and refinement: structure
solved by direct methods with SHELXS-97, full-matrix least-
squares refinement based on F2 with SHELXL-97, 601 parameters
with 0 restraints, final R1 ) 0.0461 (based on F2) for data with I
> 2σ(I) and R1 ) 0.0791 on 12 436 reflections, goodness of fit on
F2 ) 1.125, largest electron density peak 0.419 e Å-3
.
Reaction of 6a,b with 1 Equiv of AgBArF. Formation of [(tBu-
POCOP)RhII][BArF] (9). To a fluorobenzene solution (1 mL) of
6a,b (20 mg, 0.04 mmol) was added 1 equiv of AgBArF (36.7 mg,
0.04 mmol) as a solid, leading to an immediate formation of metallic
silver and a color change to violet. The reaction mixture was kept
for additional 2 h at room temperature for reaction completion and
then filtered through a cotton and Celite pad for metallic silver
removal. The solvent was removed from the filtrate under vacuum,
giving a violet solid in 85.3% (44 mg) yield. Anal. Calcd for
C54H51BF24O2P2Rh: C, 47.56; H, 3.77. Found: C, 48.29; H, 3.87.
Reaction of 6a,b with 1 Equiv of [(CP)2Fe][BF4]. Forma-
tion of [(tBu-POCOP)RhII][BF4] (10). To a fluorobenzene solution
(1 mL) of 6a,b (15 mg, 0.03 mmol) was added [(CP)2Fe][BF4] (7.7
mg, 0.03 mmol) as a solid, leading to a color change to reddish
brown. 31P{1H} NMR showed no signals; the reaction mixture was
F2 ) 1.213, largest electron density peak 1.423 e Å-3
.
Acknowledgment. This work was supported by the Israel
Science Foundation, by the program for German-Israeli
Cooperation (DIP), and by the Helen and Martin Kimmel
Center for Molecular Design. D.M. holds the Israel Matz
Professorial Chair of Organic Chemistry.
Supporting Information Available: CIF files containing X-ray
crystallographic data for complexes 4, 8, and 11. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM800034T