Mononuclear Rh(II) PNP-type complexes. Structure and reactivity

Article abstract of DOI:10.1021/ic701044b

The Rh(II) mononuclear complexes [(PNP^tBu)RhCl][BF₄] (2), [(PNP^tBu)Rh(OC(O)CF₃)][OC(O)CF₃] (4), and [(PNP^tBu)Rh(acetone)][BF₄]₂ (6) were synthesized by oxidation of th

Full text of DOI:10.1021/ic701044b

Inorg. Chem. 2007, 46, 10479−10490
Mononuclear Rh(II) PNP-Type Complexes. Structure and Reactivity
Moran Feller,† Eyal Ben-Ari,† Tarkeshwar Gupta,† Linda J. W. Shimon,‡ Gregory Leitus,‡
Yael Diskin-Posner,‡ Lev Weiner,‡ and David Milstein*,†
Department of Organic Chemistry and Unit of Chemical Research Support,
The Weizmann Institute of Science, RehoVot 76100, Israel
Received May 29, 2007
The Rh(II) mononuclear complexes [(PNPtBu)RhCl][BF4] (2), [(PNPtBu)Rh(OC(O)CF3)][OC(O)CF3] (4), and [(PNPt-
Bu)Rh(acetone)][BF4]2 (6) were synthesized by oxidation of the corresponding Rh(I) analogs with silver salts. On
the other hand, treatment of (PNPtBu)RhCl with AgOC(O)CF3 led only to chloride abstraction, with no oxidation. 2
and 6 were characterized by X-ray diffraction, EPR, cyclic voltammetry, and dipole moment measurements. 2 and
6 react with NO gas to give the diamagnetic complexes [(PNPtBu)Rh(NO)Cl][BF4] (7) and [(PNPtBu)Rh(NO)(acetone)]-
[BF4]2 (8) respectively. 6 is reduced to Rh(I) in the presence of phosphines, CO, or isonitriles to give the Rh(I)
complexes [(PNPtBu)Rh(PR3)][BF4] (11, 12) (R
)
Et, Ph), [(PNPtBu)Rh(CO)][BF4] (13) and [(PNPtBu)Rh(L)][BF4]
(15, 16) (L tert-butyl isonitrile or 2,6-dimethylphenyl isonitrile), respectively. On the other hand, 2 disproportionates
)
to Rh(I) and Rh(III) complexes in the presence of acetonitrile, isonitriles, or CO. 2 is also reduced by triethylphosphine
and water to Rh(I) complexes [(PNPtBu)RhCl] (1) and [(PNPtBu)Rh(PEt3)][BF4] (11). When triphenylphosphine and
water are used, the reduced Rh(I) complex reacts with a proton, which is formed in the redox reaction, to give a
Rh(III) complex with a coordinated BF4, [(PNPtBu)Rh(Cl)(H)(BF4)] (9).
Introduction
(II) porphyrins exhibit diverse reactivity as metalloradicals
toward H2, CO, and hydrocarbons.6 Recently de Bruin et al.
reported a new family of Rh(II)(olefin)(N3) complexes, which
exhibit interesting reactivity in vinylic C-H activation and
in the oxygenation of the norbornadiene ligand to nor-
bornenone.3 Bergman, Tilley, and coworkers reported the
cyclopropanation of olefins with ethyl diazoacetate catalyzed
Whereas Rh(I) and Rh(III) complexes are ubiquitous and
have found many uses, Rh(II) complexes are less common.
In particular, mononuclear Rh(II) complexes are relatively
rare.1-5 Rh(II) monomers are mainly stabilized by sterically
crowded ligands. The most common Rh(II) monomers are
the porphyrin complexes, their stability being derived from
the sterically demanding substituted ligand, the chelating
effect, and the delocalized π system of the porphyrin. Rh-
(3) (a) Hetterscheid, D. G. H.; Smits, J. M. M.; de Bruin, B. Organome-
tallics 2004, 23, 4236-4246. (b) Hetterscheid, D. G. H.; de Bruin,
B.; Smits, J. M. M.; Gal, A. W. Organometallics 2003, 22, 3022-
3024. (c) Hetterscheid, D. G. H.; de Bruin, B. J. Mol. Catal. A: Chem.
2006, 251, 291-296. (d) Hetterscheid, D. G. H.; Klop, M.; Kicken,
R. J. N. A. M.; Smits, J. M. M.; Reijerse, E. J.; de Bruin, B. Chem.s
Eur. J. 2007, 13, 3386-3405.
* 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) For reviews on mononuclear rhodium (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.
(4) Krumper, J. R.; Gerisch, M.; Suh, J. M.; Bergman, R. G.; Tilley, T.
D. J. Org. Chem. 2003, 68, 9705-9710.
(5) (a) 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. (b) Dixon, F. M.; Farrell,
J. R.; Doan, P. E.; Williamson, A.; Weinberger, D. A.; Mirkin, C. A.;
Stern, C.; Incarvito, C. D.; Liable-Sands, L. M.; Zakharov, L. N.;
Rheingold, A. L. Organometallics 2002, 21, 3091-3093. (c) Singe-
wald, E. T.; Slone, C. S.; Stern, C. L.; Mirkin, C. A.; Yap, G. P. A.;
Liable-Sands, L. M.; Rheingold, A. L. J. Am. Chem. Soc. 1997, 119,
3048-3056.
(2) For recent examples, see (a) Collman, J. P.; Boulatov, R. J. Am. Chem.
Soc. 2000, 122, 11812-11821. (b) Connelly, N. G.; Emslie, D. J. H.;
Geiger, W. E.; Hayward, O. D.; Linehan, E. B.; Orpen, A. G.; Quayle,
M. J.; Rieger, P. H. J. Chem. Soc., Dalton Trans. 2001, 670-683. (c)
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. (d) Gerisch, M.; Krumper, J. R.; Bergman, R. G.; Tilley,
T. D. Organometallics 2003, 22, 47-58. (e) Doux, M.; Me´zailles,
N.; Ricard, L.; Le Floch, P.; Adkine, P.; Berclaz, T.; Geoffroy, M.
Inorg. Chem. 2005, 44, 1147-1152. (f) Hamazawa, R. T.; Nishioka,
T.; Kinoshita, I.; Takui, T.; Santo, R.; Ichimura, A. Dalton Trans.
2006, 1374-1376.
(6) For example, activation of various substrates by (TMP)Rh(II) (a)
dihydrogen: Wayland, B. B.; Ba, S.; Sherry, A. E. Inorg. Chem. 1992,
31, 148-150. (b) methane: Wayland, B. B.; Ba, S.; Sherry, A. E. J.
Am. Chem. Soc. 1991, 113, 5305-5311. (c) ethane and CO: Cui, W.;
Li, S.; Wayland, B. B. J. Organomet. Chem. 2007, 692, 3198-3206.
10.1021/ic701044b CCC: $37.00
Published on Web 09/29/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 25, 2007 10479

Feller et al.
by a stable monomeric bisoxazoline Rh(II) complex.4
Another example of stable Rh(II) monomers includes bis-
phosphinoalkylarene complexes with a two-legged piano-
stool geometry, which are stabilized by electron-rich and
sterically demanding arenes along with flexible tether arms.5
Late transition-metal complexes of electron donating and
bulky pincer ligands have found important applications in
synthesis, bond activation, and catalysis.7 Among these,
complexes of the ligand PNPtBu (PNPtBu ) 2,6-bis-(di-tert-
butyl phosphino methyl)pyridine)8 have recently shown
diverse reactivity. For example, the complex [(PNPtBu)Ir-
(COE)][BF4] (COE ) cyclooctene) selectively activates the
ortho C-H bonds of haloarenes9 and the sp3 C-H bonds of
ketones at the â position.10 It also demonstrates unusual C-H
and H2 activation via ligand-metal cooperativity, involving
dearomatization/aromatization of the ligand.11 PNPtBu ru-
thenium complexes exhibit high catalytic activity in the
acceptorless dehydrogenation of secondary alcohols to
ketones12 and primary alcohols to esters.13 Ruthenium PNN
complexes (PNN ) 2-di-tert-butylphosphinomethyl-6-di-
ethylaminomethyl-pyridine) are particularly efficient in the
latter reaction under neutral conditions13 and are also
exceptionally active in catalytic hydrogenation of esters to
alcohols under mild pressure and neutral conditions.14 PNPt-
Bu-Ru dihydrogen complexes15 catalyze the H/D exchange
of aromatic C-H bonds with D2O or C6D6 under mild
Figure 1. Molecular drawing of 2 (left) and 1 (right) at 50% probability
level. Hydrogen atoms were omitted for clarity.
Scheme 1
t
conditions.16 A palladium Bu-PNP system effectively
Herein, we report on the synthesis of (PNPtBu)Rh(II)
complexes and their characterization by X-ray diffraction,
EPR, cyclic voltammetry, and dipole moment measurements.
Their reactivity toward CO, acetonitrile, isonitriles, and
triphenylphosphine, including some unexpected observations,
is reported.
catalyzed the addition of amines to acrylic acid derivatives,17
t
and aryl C-H activation by Bu-PNP rhodium complexes
were reported.18
(7) Reviews, (a) Pugh, D.; Danopoulos, A. A. Coord. Chem. ReV. 2007,
251, 610-641. (b) Szabo´, K. J. Synlett 2006, 6, 811-824. (c)
Rybtchinski, B.; Milstein, D. ACS Symp. Ser. 2004, 885, 70-85. (d)
van der Boom, M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759-
1792. (e) Singleton, J. T. Tetrahedron 2003, 59, 1837-1857. (f)
Milstein, D. Pure Appl. Chem. 2003, 75, 445-460. (g) Albrecht, M.;
van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750-3781. (h)
Vigalok, A.; Milstein, D. Acc. Chem. Res. 2001, 34, 798-807. (i)
Jensen, C. M. Chem. Commun. 1999, 2443-2449. (j) Rybtchinski,
B.; Milstein, D. Angew. Chem., Int. Ed. 1999, 38, 871-883.
(8) Hermann, D.; Gandelman, M.; Rozenberg, H.; Shimon, L. J. W.;
Milstein, D. Organometallics 2002, 21, 812-818.
Results and Discussion
1. Synthesis and Characterization of (PNPtBu)Rh(II)
Complexes. We have recently reported the electron-rich,
neutral Rh(I) complex of 2,6-bis-(di-tert-butyl phosphino
methyl)pyridine, (PNPtBu)RhCl (1).8 Somewhat surprisingly,
the reaction of 1 with AgBF4 in acetone furnished a
mononuclear paramagnetic complex [(PNPtBu)RhCl][BF4]
(2) (Scheme 1) with no chloride abstraction being observed.
(9) (a) Ben-Ari, E.; Gandelman, M.; Rozenberg, H.; Shimon, L. J. W.;
Milstein, D. J. Am. Chem. Soc. 2003, 125, 4714-4715. (b) Ben-Ari,
E.; Gandelman, M.; Shimon, L. J. W.; Martin, J. M. L.; Milstein, D.
Organometallics 2006, 25, 3190-3210.
1
The H NMR spectrum of 2 exhibits only a solvent signal,
(10) Feller, M.; Karton, A.; Leitus, G.; Martin, J. M. L.; Milstein, D. J.
Am. Chem. Soc. 2006, 128, 12400-12401.
and no signals are observed in the 31P{1H} NMR spectrum.
The identity of 2 was confirmed by a single-crystal X-ray
analysis (Figure 1). The rhodium atom adopts a square-planar
geometry, which is consistent with reported four-coordinated
mononuclear Rh(II) X-ray structures.2d,19 The P-Rh-P angle
(168.33°) is distorted from linearity, as is typical for PNP
complexes.8-11 Selective bond lengths and bond angles are
given in Table 1. Neutral Rh(I) complex 1 was crystallized,
(11) Ben-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am. Chem.
Soc. 2006, 128, 15390-153901.
(12) Zhang, J.; Gandelman, M.; Shimon, L. J. W.; Rozenberg, H.; Milstein,
D. Organometallics 2004, 23, 4026-4033.
(13) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J. Am. Chem. Soc.
2005, 127, 10840-10841.
(14) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew. Chem., Int.
Ed. 2006, 45, 1113-1115.
(15) Prechtl, M. H. G.; Ben-David, Y.; Giunta, D.; Busch, S.; Taniguchi,
Y.; Wisniewski, W.; Gorls, H.; Mynott, R. J.; Theyssen, N.; Milstein,
D.; Leitner, W. Chem.sEur. J. 2007, 13, 1539-1546.
(16) Prechtl, M. H. G.; Ho¨lscher, M.; Ben-David, Y.; Theyssen, N.;
Loschen, R.; Milstein, D.; Leitner, W. Angew. Chem., Intl. Ed. 2007,
46, 2269-2272.
(19) (a) Garc´ıa, M. P.; Jime´nez, M. V.; Cuesta, A.; Siurana, C.; Oro, L.
A.; Lahoz. F. J.; Lo´pez, J. A.; Catala´n, M. P. Organometallics 1997,
16, 1026-1036. (b) Garc´ıa, M. P.; Jime´nez, M. V.; Oro, L. A.; Lahoz,
F. J.; Casas, J. M.; Alonso, P. J. Organometallics 1993, 12, 3257-
3263. (c) Hay-Motherwell, R. S.; Koschmieder, S. U.; Wilkinson, G.;
Hussain-Bates, B.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans.
1991, 2821-2830. (d) Ogle, C. A.; Masterman, T. C.; Hubbard, J. L.
J. Chem. Soc., Chem. Commun. 1990, 1733-1734.
(17) (a) Kawatsura, M.; Hartwig, J. F. Organometallics 2001, 20, 1960-
1964. (b) Stambuli, J. P.; Stauffer, S. R.; Shaughnessy, K. H.; Hartwig,
J. F. J. Am. Chem. Soc. 2001, 123, 2677-2678.
(18) Kloek, S. M.; Heinekey, D. M.; Goldberg, K. I. Angew. Chem., Int.
Ed. 2007, 46, 4736-4738.
10480 Inorganic Chemistry, Vol. 46, No. 25, 2007

Mononuclear Rh(II) PNP-Type Complexes
Table 1. Selected Bond Lengths (Angstroms) and Bond Angles
(Degrees) for [(PNPtBu)RhCl] (1) and [(PNPtBu)RhCl][BF4] (2)
[(PNPtBu)RhCl] (1) [(PNPtBu)RhCl][BF4] (2)
Rh(1)-P(1)
Rh(1)-P(2)a
Rh(1)-Cl(1)
Rh(1)-N(1)
2.271(1)
2.271(1)
2.381(1)
2.036(3)
2.322(1)
2.322(1)
2.332(1)
2.074(3)
P(1)-Rh(1)-Cl(1)
P(2)-Rh(1)-Cl(1)a
N(1)-Rh(1)-Cl(1)
N(1)-Rh(1)-P(2)a
N(1)-Rh(1)-P(1)
P(1)-Rh(1)-P(2)a
96.71(2)
95.74(4)
95.33(4)
178.65(8)
84.58(8)
84.26(8)
168.32(4)
96. 71(2)b
180.00(1)
83.29(2)b
83.29(2)
166.57(4)b
a P(2) in 1 is marked as P1A in Figure 1. b Symmetry transformations
used to generate equivalent atoms.
Scheme 2
Figure 2. Molecular drawing of 6 at 50% probability level. Hydrogen
atoms and the non-coordinating anion were omitted for clarity.
Table 2. Selected Bond Lengths (Angstroms) and Bond Angles
(Degrees) for [(PNPtBu)Rh(acetone)][BF4]2 (6)
Rh(1)-P(2)
O(1)-C(24)
Rh(1)-F(1)
F(1)-B(1)
2.351(1)
1.235(4)
2.523(9)
1.422(4)
Rh(1)-O(1)
Rh(1)-N(1)
Rh(1)-P(1)
2.088(2)
2.047(2)
2.363(3)
and its X-ray structure was determined also, providing an
opportunity to compare the two complexes, which have the
same atom connectivity and differ only in the metal oxidation
state. The structure of 1 (Figure 1, Table 1) reveals that the
Rh-N, Rh-P(1), and Rh-P(2) bonds of the PNP ligand
are shorter compared to the corresponding bonds of 2 (by
0.036 and 0.051 Å, respectively). Similar elongation due to
oxidation was described for Rh(I) and Rh(II) piano stool
complexes with bis(phosphinoalkyl)aryl ligands,5a complexes
(PEt3)2(C5H5)Co(I) and [(PEt3)2(C5H5)Co(II)][BF4],20 and
complexes (iPr3P)2RhCl2 and (iPr3P)2RhCl2H.21 However, the
Rh-Cl bond in 2 is shorter by 0.049 Å compared with 1.
The shortening of the Rh-Cl bond due to oxidation can be
explained by enhanced π donation of the chloride ligand in
2.22 The N-Rh-Cl angle in 1 is strictly linear and it is
almost linear in 2, whereas the P(1)-Rh-P(2) angle is
distorted from linearity to a similar degree in both complexes.
In 2, the phosphines P(1) and P(2) are above the pyridine
ring, whereas 1 adopts a propeller-type geometry with P(1A)
and P(1) above and below the pyridine plane, respectively.
1 was also oxidized by AgPF6 and AgBArf (BArf )
tetrakis{(3,5-trifluoromethyl)phenyl}borate)) in acetone to
give the paramagnetic 2. On the other hand, treatment of 1
with AgOC(O)CF3 in acetone resulted in chloride abstraction
rather than oxidation, exclusively yielding the diamagnetic
complex [(PNPtBu)Rh(OC(O)CF3)] (3) (Scheme 1). In the
31P{1H} NMR spectrum, 3 exhibits a sharp doublet at 61.27
ppm with a JRhP of 151.1 Hz in THF and a broad signal at
P(1)-Rh(1)-P(2)
N(1)-Rh(1)-O(1)
Rh(1)-O(1)-C(24)
N(1)-Rh(1)-P(1)
161.78(3)
173.71(9)
139.6(2)
82.81(7)
N(1)-Rh(1)-P(2)
O(1)-Rh(1)-P(1)
O(1)-Rh(1)-P(2)
81.88(7)
96.62(6)
97.51(6)
61 ppm in acetone due to fluxional coordination of the
trifluoroacetate in acetone. 3 was oxidized easily to the
paramagnetic complex [(PNPtBu)Rh(OC(O)CF3)][OC(O)-
CF3] (4) by the addition of an additional equiv of AgOC-
(O)CF3 (Scheme 1). Similarly, reaction of 3 with other AgX
(X ) BF4, PF6, BArf) led to [(PNPtBu)Rh(OC(O)CF3)][X].
Cationic Rh(I) complex [(PNPtBu)Rh(acetone)][BF4] (5)
was prepared in order to oxidize it to Rh(II). It was obtained
in quantitative yield by the addition of the free ligand PNPt-
Bu to an acetone solution of [Rh(COE)2(acetone)2][BF4].23
The acetone molecule in 5 is loosely bound and can be
replaced with other solvents such as THF or with N2 by
bubbling nitrogen through a THF solution of 5.18 5 is
oxidized easily by AgBF4 to the paramagnetic Rh(II)
complex [(PNPtBu)Rh(acetone)][BF4]2 (6) (Scheme 2). The
X-ray structure of 6 (Figure 2, Table 2) exhibits a Rh(II)
center in a square-pyramidal geometry with a loosely bound
BF4 at the apical position. Coordination of BF4 is rare,24 and
to the best of our knowledge, only two other crystal structures
containing a Rh-FBF3 bond were reported.24a,b The Rh-
F(1) bond in 6 (2.523 Å) is significantly longer than the
reported Rh-F bonds in other coordinated BF4 complexes24a,b
by about 0.37 Å, which indicates the very weak nature of
(20) Harlow, R. L.; McKinney, R. J.; Whitney, J. F. Organometallics 1983,
2, 1839-1842.
(21) Harlow, R. L.; Thorn, D. L.; Baker, R. T.; Jones, N. L. Inorg. Chem.
1992, 31, 993-997.
(23) Windmu¨ller, B.; Nu¨rnberg, O.; Wolf, J.; Werner, H. Eur. J. Inorg.
Chem. 1999, 613-619.
(22) For examples of stabilization by π donation of chloride see (a) Riehl,
J. F.; Jean, Y.; Eisenstein, O.; Pe´lissier, M. Organometallics 1992,
11, 729-737. (b) Blum, O.; Milstein, D. J. Am. Chem. Soc. 2002,
124, 11456-11467. (c) Bickford, C. C.; Johnson, T. J.; Davidson, E.
R.; Caulton, K. G. Inorg. Chem. 1994, 33, 1080-1086. (d) Bera, J.
K.; Nethaji, M.; Samuelson, A. G. Inorg. Chem. 1999, 38, 218-228.
(e) Werner, H.; Ho¨hn, A.; Dziallas, M. Angew. Chem., Int. Ed. Engl.
1986, 12, 1090.
(24) (a) Salem, H.; Ben-David, Y.; Shimon, L. J. W.; Milstein, D.
Organometallics 2006, 25, 2292-2300. (b) Rybtchinski, B.; Oevers,
S.; Montag, M.; Vigalok, A.; Rozenberg, H.; Martin, J. M. L.; Milstein,
D. J. Am. Chem. Soc. 2001, 123, 9064-9077. (c) Gandelman, M.;
Konstantinovski, L.; Rozenberg, H.; Milstein, D. Chem.sEur. J. 2003,
9, 2595-2602. (d) Beck, W.; Sunkel, K. Chem. Rev. 1988, 88, 1405-
1421. (e) Sutherland, B. R.; Cowie, M. Inorg. Chem. 1984, 23, 1290-
1297.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10481

Feller et al.
Bu)Rh(II) complexes are much more stable than (PNPiPr)-
Rh(II) because of steric shielding of the metal center.
The paramagnetic d7 Rh(II) complexes 2, 4 and 6 were
studied by X-band EPR spectroscopy in both fluid and frozen
acetone. For all three complexes in the frozen solution, an
EPR rhombic pattern was observed, and no hyperfine
structure was resolved for 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
1
the nuclear spin of 103Rh (I ) /2). The observed EPR
parameters of 2, 4 and 6 (Table 3) were found to be close to
the reported EPR parameters of other Rh(II) monomeric
complexes.2d,5a The EPR data implies an asymmetric coor-
dination environment around the metal center, which is in
correlation with the distorted square-planar X-ray structures
of 2 and 6. The EPR isotropic spectrum of 4 in solution at
ambient temperature is shown in Figure 4. The large line
width is likely caused by the slow reorientation of the bulky
complex and by unresolved coupling with the nuclear spin
of rhodium.
Figure 3. X-band EPR spectrum of 2 obtained at 125 K in frozen acetone.
Experimental conditions: microwave power 31 mW, modulation amplitude
0.8 G, time constant 0.65 s.
Electrochemical measurements of 1, 2, 5 and 6 were
t
carried out in acetone using Bu4NPF6 as a supporting
electrolyte. All of the measurements were performed using
Ag/AgCl as a reference electrode. The electrochemical data
for all of the complexes is given in Table 4. The cyclic
voltammetric data indicates that the oxidation and reduction
peaks of 1 are localized at values almost identical to those
observed for the redox waves of 2 and is the same for 5 and
6. This observation is similar to those found for related
rhodium compounds with the metal in different oxidation
states.19b,28 1, 2, 5 and 6 exhibit two redox processes in
positive potential, as illustrated in Figure 5. Analysis of the
first redox wave at scan rates of 100-900 mV s-1 gives clear
evidence that it involves a Rh(I)/Rh(II) couple. Each couple
is diffusion controlled, as evidenced by the constant current
function (ip vs ν-1/2) over scan rates of 100-900 mV s-1
(Supporting Information, Figure 1). The ∆E value for the
first redox process is in the range expected for fast one-
electron couples (Table 4). The ic/ia ration was found to be
unity for the first redox waves of 1, 2 and 5, 6 and second
redox waves of 5 and 6, indicating that this process is
reversible. The second redox wave of 5 and 6 can be assigned
to the Rh(II) to Rh(III) couple, whereas the second redox
waves of 1 and 2 show an irreversible process.
Figure 4. X-band EPR spectrum of 4 obtained at 293 K in acetone.
Experimental conditions: microwave power 39 mW, modulation amplitude
1 G, time constant 1.3 s.
Table 3. EPR Parameters of 2, 4, and 6
Complex
gx
gy
gz
A1G
2
4
6
2.5667
2.4851
2.5204
2.3124
2.3052
2.3231
1.9512
1.9654
1.9620
16.0
17.0
16.5
this bond. Because of BF4 disorder, it is impossible to
compare the F(1)-B bond length with the three other B-F
bond lengths, which should be shorter in the case of Rh-F
coordination. Although the Rh-F(1) bond is rather long, it
is shorter than the sum of the ionic radius in the crystal
structure of fluorine anion (1.33 Å)25 and the pseudopotential
radius of rhodium (2.52 Å).26
The distortion from planarity in 6 is much more extensive
compared to 2, with a P-Rh-P angle of 161.78° (168.32°
in 2) and a N-Rh-O angle of 173.67° (178.65° in 2 for
N-Rh-Cl). The phosphines are alternating above and below
the pyridine ring as in 1. The bond angle Rh-O-C(24) is
139.6°, which indicates that the acetone ligand is coordinated
through one of the lone pairs of electrons of the oxygen atom.
Oxidation of (PNPiPr)RhCl and [(PNPiPr)Rh(COE)]-
[BF4]27 gave mixtures of diamagnetic complexes according
to 31P{1H} NMR. It is likely that the mononuclear [(PNPt-
The presence of chloride in 1 and 2 may stabilize the Rh-
(III) state, resulting in an irreversible oxidation potential, in
contrast to 5 and 6. All of the complexes show an additional
irreversible reduction potential at ∼ -1.13 V, which can be
assigned to Rh(I)/Rh(0) reduction waves (Table 4).
Field dependences of magnetic moments (Figure 6) of 2
and 6, measured between T ) 5 and 300 K, were strictly
linear in the interval of -1 T < H < 1 T. The complexes do
not show any hysteresis phenomena. 6 exhibits clear Curie-
Weis behavior at the temperature interval of 2 K < T < 300
(25) Handbook of Chemistry and Physics, 85th ed.; Lide, D. R., Ed.; CRC
Press: Boca Raton, FL, 2004-2005; pp 12-14.
(26) Pseudopotential radii are calculated radii derived from first principles,
which can be used for predicting structure and compound formation.
International Tables For Crystallography, Kluwer Academic Publish-
ers: Norwell, MA, 1992; Vol. C, p 682.
(27) The complex [(PNPiPr)RhCl] was synthesized in a similar procedure
as 1. [(PNPiPr)Rh(COE)][BF4] was synthesized from [Rh(COE)2-
(acetone)2][BF4] and the free ligand in a similar procedure as [(PNP)-
Ir(COE)][BF4] (ref 9).
(28) (a) Haefner, S. C.; Dunbar, K. R.; Bender, C. J. Am. Chem. Soc. 1991,
113, 9540-9553. (b) Cooper, S. R.; Rawle, S. C.; Yagbasan, R.;
Watkin, D. J. J. Am. Chem. Soc. 1991, 113, 1600-1604.
10482 Inorganic Chemistry, Vol. 46, No. 25, 2007

Mononuclear Rh(II) PNP-Type Complexes
t
Figure 5. Cyclic voltammograms of 1 (a), 2 (b), 5 (c) and 6 (d) in acetone/0.1 M Bu4NPF6 at room temperature (υ ) 0.3 Vs-1; vs Ag/AgCl electrode).
Table 4. Formal Electrode Potentialsa (vs Ag/AgCl) of the Complexes
E1/2 (∆E); volts
Rh(I)/Rh(II)
E1/2 (∆E); volts
Rh(II)/Rh(III)
reduction wavesb
Rh(I)/Rh(0)
complex
1
2
5
6
0.19 (0.13)
0.17 (0.069)
0.19 (0.081)
0.17 (0.068)
0.77b
-1.12
-1.11
-1.12
-1.16
0.74b
0.67 (0.12)
0.65 (0.16)
t
a Acetone solution containing the complex (2 mM) and Bu4NPF6 (0.1
M); room temperature; ν ) 0.3 Vs-1 b Irreversible peak.
.
Figure 7. Zero field cooled and field cooled temperature dependences of
dc magnetic susceptibilities ø obtained at H ) 0.5 T for 2 and 6. Inlay:
The low-temperature part of the same dependences together with ac in-
phase magnetic susceptibilities ø′ for 2, obtained at the H ) 0.5 T, wave
frequency f ) 700 Hz, drive field amplitude HA ) 0.0003 T.
Figure 7 is clearly indicative of super-exchange interactions
at low temperatures in 2.
2. Reactivity of (PNPtBu)Rh(II) Complexes. Paramag-
netic (PNPtBu)Rh(II) complexes 2, 4 and 6 are stable and
can be kept at ambient temperature as solids or in solution
for months under nitrogen. No reaction was observed when
these complexes were treated with oxygen, hydrogen, or
ethylene. On the other hand, they exhibit rather unexpected
reactivity toward CO, acetonitrile, isonitriles and phosphines.
Reactions of paramagnetic 2 and 6 with an excess of NO
gas in acetone led to the formation of diamagnetic complexes
[(PNPtBu)Rh(NO)Cl][BF4] (7) and [(PNPtBu)Rh(NO)(ac-
etone)][BF4]2 (8), respectively (Schemes 4, 5). 7 was obtained
also by the addition of NOBF4 to a solution of 1 in acetone.
IR bands at 1675 and 1706 cm-1 for 7 and 8, respectively,
Figure 6. Field dependences of dc magnetic moments M at T ) 5 and
300 K for 2 and 6. Each graph displays results of measurements with
increasing and decreasing field (from -1 T to +1 T and backward).
K (Figure 7). Lack of coincidence is observed at T < 10 K
for 2. The fitting of dc temperature dependences by the
Curie-Weiss equation showed the values of effective
magnetic moment for 6, p ) 1.72(2) µB/molecule and for 2
(using T > 10 K), p ) 2.17(1) µB/molecule. Bergman, Tilley,
and co-workers report values in the range of 1.87 to 2.00 µB
for NCN bis(oxazoline) Rh(II) complexes.2d Our results for
2 and 6 show a broader interval of p values, which can be
explained by the presence of super-exchange interactions via
different anions. The in-phase ac susceptibility ø′ shown in
Inorganic Chemistry, Vol. 46, No. 25, 2007 10483

Feller et al.
Surprisingly, the addition of a half equiv of triphenyphos-
phine to a solution of Rh(II)Cl 2 in acetone yielded
diamagnetic Rh(III) hydride complex [(PNPtBu)Rh(Cl)(H)-
(BF4)] (9) (Scheme 3). The 31P{1H} NMR spectrum of this
complex exhibits a sharp doublet at 67.8 ppm (JPRh ) 99.9
Hz), in addition to singlet signals at 26 ppm, which
correspond to triphenylphosphine oxide. 9 was crystallized
by layering pentane over its acetone solution. It exhibits a
hydride signal at -21.71 ppm. The 19F NMR spectrum of
9 exhibits a broad signal at -150 ppm, whereas free BF4
gives a sharp signal at -151 ppm. Chemical shifts of
coordinated BF4 are reported in the range of -164 to -160
ppm, and the signal is usually broad because of fast rotation
of bound BF4.24 In the case of 9, the 19F chemical shift and
signal broadness indicate fast dissociative equilibrium of the
anion in solution, with the equilibrium shifted toward free
BF4.
Figure 8. Molecular drawing of 7 at 50% probability level. Hydrogen
atoms and counteranion were omitted for clarity.
A single-crystal X-ray analysis of 9 (Figure 9, Table 6)
confirmed the existence of a distorted octahedral structure
with BF4 coordinated through a fluorine atom (F(1)). F(1)
is trans to the hydride ligand with an angle of 173.8°, whereas
the chlorine atom is trans to the ipso nitrogen, with an
angle of 177.68°. The B-F(1) bond (1.437 Å) is longer
than the other B-F bonds (1.372-1.382 Å) as expected.
The Rh-F(1) bond in 9 (2.407 Å) is longer than the reported
Rh-F bonds in other coordinated BF4 complexes24a,b by
about 0.25 Å, which is consistent with the very weak nature
of this bond.
Table 5. Selected Bond Lengths (Angstroms) and Bond Angles
(Degrees) for [(PNPtBu)Rh(NO)Cl][BF4](7)
Rh(1)-N(1)
Rh(1)-N(2)
Rh(1)-P(1)
2.068(2)
1.943(3)
2.339(1)
Rh(1)-P(2)
Rh(1)-Cl(1)
N(2)-O(1)
2.351(1)
2.337(1)
1.163(3)
P(1)-Rh(1)-P(2)
P(1)-Rh(1)-N(2)
P(1)-Rh(1)-Cl(1)
N(1)-Rh(1)-N(2)
N(1)-Rh(1)-Cl(1)
N(1)-Rh(1)-P(1)
158.88(3)
97.77(8)
95.60(3)
89.62(10)
175.92(7)
83.94(7)
N(1)-Rh(1)-P(2)
P(2)-Rh(1)-N(2)
P(2)-Rh(1)-Cl(1)
Rh(1)-N(2)-O(1)
N(2)-Rh(1)-Cl(1)
83.73(7)
99.23(8)
95.48(3)
122.0(2)
94.46(8)
Scheme 3
Addition of acetonitrile to a solution of 9 in acetone
afforded the complex [(PNPtBu)Rh(H)(Cl)(CH3CN)][BF4]
(10) (Scheme 3), which exhibits a signal of free BF4 in the
19F NMR spectrum at -151 ppm and a triplet centered at
1
-16.48 (JHP ) 12 Hz) ppm in the H NMR spectrum.
A similar reaction was reported by Shaw and co-workers30
n
for the Rh(II) complex RhCl2(PtBuR2)2 (R)Me, Et, Pr),
which, upon heating in ethanol or methyl ethyl ketone in
the presence of excess of the phosphine ligand, gave Rh-
(III) complex RhCl2H(PtBuR2)2. No explanation for this
observation was given. The reduction of copper(II) chloride
by triethylphosphine was reported to give the copper(I)
complex CuClPEt3. The oxidation product has not been
characterized, although tertiary phosphine oxides have been
obtained in similar wet systems.31
The reaction rate of 2 with triphenylphosphine is dependent
on the amount of water in the solvent; in carefully dried
acetone the reaction time is 12 h, whereas in wet acetone,
obtained by the addition of a drop of water, the reaction
reaches completion in a minute. Moreover, in methylene
chloride, no reaction with triphenyphosphine takes place, but
upon addition of water to this solution, 9 is obtained
immediately. The formation of triphenyphosphine oxide and
the influence of water concentration on the reaction rate
indicate that Rh(II) complex 2 is reduced by Ph3P and water
indicate that they are best described as Rh(III) complexes
with a bent NO. A single-crystal X-ray analysis of 7 (Figure
8, Table 5) confirmed that it is a Rh(III) complex with a
square-pyramidal geometry and a bent nitrosyl ligand, the
O-N(2)-Rh angle being 122.0°. The chloride ligand is
located trans to the ipso nitrogen, whereas the NO is at an
apical position, which is typical for a bent NO ligand because
of its strong trans influence. Similar rhodium and iridium
nitrosyl complexes were reported.29 The P-Rh-P angle
(158.93°) is distorted from linearity, and the N(1)-Rh-Cl
angle is almost linear (175.96°).
(30) (a) Masters, C.; Shaw, B. L. J. Chem. Soc. A. 1971, 3679-3686. (b)
Masters, C.; McDonald, W. S.; Raper, G.; Shaw, B. L. Chem.
Commun. 1971, 210-211.
(31) Axtell, D. D.; Yoke, J. T. Inorg. Chem. 1973, 12, 1265-1268 and
references there in.
(29) (a) Goldberg, S. Z.; Kubiak, C.; Meyer, C. D.; Eisenberg, R. Inorg.
Chem. 1975, 14, 1650-1654. (b) Hodgson, D. J.; Ibers, J. A. Inorg.
Chem. 1968, 7, 2345-2352.
10484 Inorganic Chemistry, Vol. 46, No. 25, 2007

Mononuclear Rh(II) PNP-Type Complexes
Scheme 4
Scheme 5
(eq 1). Neutral Rh(I) thus formed undergoes protonation to
yield 9 (eq 2).
reaction mixture also reveals a broad signal at 26 ppm,
assignable to Ph3PO, which disappears with time and a sharp
signal at 44 ppm. 12 was also independently prepared like
11.
In the case of dicationic Rh(II) complex 6, reaction with
triphenylphosphine and water leads to a less electron-rich
cationic Rh(I) complex (eq 3), which does not undergo
protonation. Having a vacant coordination site, it reacts with
the excess triphenylphosphine to give 12 (eq 4).
[(PNP)RhII(Cl)]+ + 1/2Ph3P + 1/2H2O f
[(PNP)RhICl] + 1/2Ph3PO + H+ (1)
[(PNP)RhI(Cl)] + H+ f [(PNP)RhIII(H)(Cl)]+
(2)
Addition of the more-basic triethylposphine in excess to
a wet acetone solution of Rh(II) complex 2 yielded a mixture
of (PNPtBu)RhCl (1), [(PNPtBu)Rh(PEt3)][BF4] (11), and
[PEt3H][BF4], according to 31P NMR (Scheme 3).32 The 31P-
{1H} NMR spectrum of 11 exhibits a doublet of doublets at
67.87 ppm (JRhP ) 138.9, JPP ) 38.9 Hz) and a doublet of
triplets at 25.33 ppm (JRhP ) 159.2, JPP ) 38.9 Hz) with an
integration ratio of 2:1 respectively. 11 was also indepen-
dently prepared by heating an acetone solution of cationic
Rh(I) complex 5 with triethylphosphine at 55 °C for 1 h.
Dicationic Rh(II) complex 6 reacted slowly with 1.5 equiv
of triphenylphosphine and an excess of water in acetone at
ambient temperature to give Rh(I) complex [(PNPtBu)Rh-
(PPh3)][BF4] (12) after 48 h (Scheme 3). The 31P{1H} NMR
spectrum of 12 exhibits a doublet of doublets at 66.63 ppm
(JRhP ) 134.8, JPP ) 38.1 Hz) and a doublet of triplets at
35.43 ppm (JRhP ) 171.3, JPP ) 38.1 Hz) with an integration
ratio of 2:1 respectively. The 31P{1H} NMR spectrum of the
[(PNP)RhII]2+ + 1/2Ph3P + 1/2H2O f
[(PNP)RhI]+ + 1/2Ph3PO + H+ (3)
[(PNP)RhI] + + PPh3 f [(PNP)RhI(PPh3)]+
(4)
A similar reaction of Rh(II) complex 6 with excess
triethylphosphine and water in acetone gave 11.
Upon reaction of the Rh(II) complexes 2, 4 and 6 with
CO at ambient temperature, reduction to give cationic Rh(I)
complex [(PNPtBu)Rh(CO)][X] (13) (X ) Cl, BF4, BArf,
OC(O)CF3) took place (Schemes 4, 5).33 13 was also
prepared by reaction of CO with cationic Rh(I) complex 5.
The carbonyl ligand of this complex exhibits an IR band at
1982 cm-1, and the carbonyl carbon has a chemical shift of
(33) The presence of the non-coordinating BArf is significant in this
reaction. Reaction of 4, 6 and [(PNPtBu)RhCl][BArf] with CO gave
exclusively 13, whereas the reaction of [(PNPtBu)RhCl][BF4] with
CO afforded 13 as a major product (75% yield according to 31P NMR)
along with a new complex. Moreover, 4 and 6 react with one equiv
of CO, whereas the reaction of 2 with CO required an excess for
completion. The new complex exhibits, in the 31P{1H} NMR spectrum,
a doublet at 54.4 ppm (JRhP ) 84.5 Hz) and in the 19F NMR spectrum
a broad signal at -149 ppm (coordinated BF4). This complex is
transformed to 13 with time under CO. We assume that the complex
is [(PNPtBu)Rh(Cl)2(BF4)].
(32) (a) When less than one equiv of triethylphosphine was added to 2, a
mixture of [(PNPtBu)Rh(PEt3)][BF4] (11) and [(PNPtBu)Rh(Cl)(H)-
(BF4)] (9) was observed by 31P{1H} NMR. Addition of excess of
triethylphosphine led to the deprotonation of 9 to 1. (b) The 31P{1H}
NMR spectrum of the reaction mixture reveals also singlets at 44.41
and 52.35 ppm, but no signal for the moisture-sensitive OPEt3 was
detected. [PEt3H][OTf], formed by the addition of triflic acid to an
acetone solution of triethylphosphine, gave a signal at 44.41 ppm.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10485

Feller et al.
Table 7. Selected Bond Lengths (Anstroms) and Bond Angles
(Degrees) for [(PNPtBu)Rh(CO)][BF4] (13)
Rh(1)-P(1)
Rh(1)-P(2)
C(24)-O(1)
2.301(3)
2.303(3)
1.144(6)
Rh(1)-C(24)
Rh(1)-N(1)
1.818(5)
2.100(4)
N(1)-Rh(1)-C(24)
P(1)-Rh(1)-C(24)
P(2)-Rh(1)-C(24)
Rh(1)-C(24)-O(1)
175.19(18)
95.66(15)
96.24(15)
177.5(5)
N(1)-Rh(1)-P(1)
N(1)-Rh(1)-P(2)
P(1)-Rh(1)-P(2)
84.05(10)
84.00(10)
168.05(4)
portionation of a Rh(II) complex by CO was reported for
thecomplex[Rh(tmpp)2]2+(tmpp)tris(2,4,6-trimethoxyphenyl)-
phosphine).28a
Reaction of Rh(II) complex 2 with acetonitrile at room
temperature led to formation of a diamagnetic mixture of
two complexes in a ratio of 3:2, according to the 31P{1H}
NMR spectrum (Scheme 4). The major complex was
identified as the known [(PNPtBu)Rh(CH3CN)][BF4] (14).8
The second complex exhibits in the 31P{1H} NMR spectrum
a broad doublet at 60.2 ppm at 297 K, a sharp doublet at
61.36 ppm (JRhP ) 78.8) at 313 K, and an AB system at
55.24 and 63.54 ppm (JRhP ) 76.9 and JPP ) 479.8 Hz) at
230 K. The relatively small JRhP coupling constant and the
high field chemical shift of the minor complex suggest that
it is a Rh(III) complex, although we were not able to
determined its structure. To our knowledge, disproportination
of Rh(II) by acetonitrile was not reported. Reactions of Rh-
(II) with isonitriles include the cleavage of methyl isonitrile
by (TMP)Rh(II) (TMP ) tetrakis(2,4,6-trimethylphenyl)-
porphyrinato) to give (TMP)RhCN and (TMP)RhMe, re-
ported by Wayland and co-workers.35 Mirkin and co-workers
reported the reduction of Rh(II) to Rh(I) by tert-butyl
isonitrile.5a Wilkinson and co-workers reported the reduction
of Rh(2,4,6,-iPr3C6H2)(tht)2 (tht ) tetrahydrothiophene) by
tert-butyl isonitrile to give Rh(CNtBu)3(2,4,6,-iPr3C6H2CdNt-
Bu).36 This reduction was assumed to proceed via an aryl
radical, which abstracts a hydrogen atom from the solvent.
Disporprotonation of Rh(II) by methyl isonitrile was reported
by Dunbar and Haefner, although the diamagnetic complexes
were not identified.37
Figure 9. Molecular drawing of 9 at 50% probability level. Hydrogen
atoms (except hydride) were omitted for clarity.
Table 6. Selected Bond Lengths (Angstroms) and Bond Angles
(Degrees) for [(PNPtBu)Rh(Cl)(H)(BF4)] (9)
Rh(1)-N(1)
Rh(1)-P(1)
Rh(1)-P(2)
Rh(1)-Cl(1)
Rh(1)-H(1)
2.045(2)
2.327(1)
2.324(1)
2.345(1)
1.43(3)
Rh(1)-F(1)
B(1)-F(1)
B(1)-F(2)
B(1)-F(3)
B(1)-F(4)
2.407(1)
1.437(3)
1.375(3)
1.372(3)
1.382(3)
H(1)-Rh(1)-P(1)
H(1)-Rh(1)-P(2)
H(1)-Rh(1)-F(1)
H(1)-Rh(1)-Cl(1)
P(1)-Rh(1)-Cl(1)
P(1)-Rh(1)-P(2)
P(1)-Rh(1)-F(1)
Cl(1)-Rh(1)-F(1)
83.5(12)
82.8(12)
173.8(11)
89.9(11)
96.63(2)
162.10(2)
94.63(4)
96.16(3)
P(2)-Rh(1)-Cl(1)
P(2)-Rh(1)-F(1)
N(1)-Rh(1)-F(1)
N(1)-Rh(1)-Cl(1)
N(1)-Rh(1)-P(1)
N(1)-Rh(1)-P(2)
N(1)-Rh(1)-H(1)
94.84(2)
97.75(4)
81.59(6)
177.68(6)
84.13(6)
84.95(6)
92.3(11)
196.27 ppm (dt, JPC ) 13.4, JRhC ) 69.8 Hz) in the 13C NMR
spectrum. The X-ray structure of 13 (Figure 10) reveals a
distorted square-planar geometry with a P-Rh-P angle of
168.05° and an N-Rh-C(24) angle of 175.19° (Figure 10).
GC-MS measurements of the gas phase indicated the
formation of CO2 in the reaction of 2 and 6 with CO. It is
likely that a redox reaction involving CO and water, similar
to the one with phosphines, is involved.
Reduction of Rh(II) to Rh(I) complexes in the presence
of CO was observed with complexes [PBzPh3]2[Rh(C6-
Cl5)4]19a and with the two-legged piano-stool Rh(II) complex,
which was reported by Mirkin and co-workers.5a In the latter
case, the oxidation product was identified as CO2. Dispro-
Reaction of 2 with one equiv of tert-butyl isonitrile in
acetone also led to the formation of two diamagnetic
complexes in a ratio of 17:3, according to the 31P{1H} NMR
spectrum, of which the major product was identified as the
Rh(I) complex [(PNPtBu)Rh(CNC(CH3)3)][BF4] (15) (Scheme
4). 14 can be obtained also by the addition of tert-butyl
isonitrile to 5. The minor complex was not identified,
although the chemical shift and the coupling constant (54.3
ppm (JRhP ) 84 Hz)) imply a Rh(III) complex. A similar
reaction of 2 with 2,6-dimethylphenyl isonitrile also led to
(34) The X-ray diffraction of 13 was collected at 17° C because at lower
temperature the crystals cracked.
(35) (a) Wayland, B. B.; Sherry, A. E.; Bunn, A. G. J. Am. Chem. Soc.
1993, 115, 7675-7684. (b) Poszmik, G.; Carroll, P. J.; Wayland, B.
B. Organometallics 1993, 12, 3410-3417. For recent mechanistic
studies see Zhang, L.; Fung, C. W.; Chan, K. S. Organometallics 2006,
25, 5381-89.
(36) Hay-Motherwell, R. S.; Koschmieder, S. U.; Wilkinson, G.; Hussain-
Bates, B.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1991,
2821-2830.
Figure 10. Molecular drawing of 13 at 30% probability level.34 Hydrogen
atoms and counteranion were omitted for clarity.
(37) Dunbar, K. R.; Haefner, S. C. Organometallics 1992, 11, 1431-1433.
10486 Inorganic Chemistry, Vol. 46, No. 25, 2007

Mononuclear Rh(II) PNP-Type Complexes
1
mercially available reagents were used as received. H, 13C, 31P,
the formation of two diamagnetic complexes, one of them
being [(PNPtBu)Rh(CNC6H3(CH3)2)][BF4] (16).
and 19F NMR spectra were recorded using a Bruker DPX-250, a
Bruker AMX-400, and an Avance 500 NMR spectrometer. All of
the spectra were recorded at 23 °C, unless otherwise noted. 1H NMR
and 13C{1H} NMR chemical shifts are reported in ppm, downfield
from tetramethylsilane. In 1H NMR, chemical shifts were referenced
to the residual hydrogen signal of the deuterated solvents. In 13C-
{1H} NMR measurements, the signals of deuterated solvents were
used as a reference. 31P NMR chemical shifts are reported in parts
per million downfield from H3PO4 and referenced to an external
85% solution of phosphoric acid in D2O. 19F NMR chemical shifts
were referenced to C6F6 (-163 ppm). Abbreviations used in the
description of NMR data are as follows: br, broad; s, singlet; d,
doublet; t, triplet; q, quartet; m, multiplet; v, virtual.
In contrast to monocationic Rh(II)Cl complex 2, dicationic
Rh(II)(acetone) complex 6 does not react with acetonitrile.
It reacts with tert-butyl isonitrile and 2,6-dimethylphenyl
isonitrile in acetone to give exclusively Rh(I) complexes 14
and 15, respectively (Scheme 5).
Rh(II) chloride monocationic complex 2 and dicationic
complex 6 exhibit different reactivity. Whereas 6 is reduced
in the presence of triphenylphosphine, CO, and isonitriles,
2 undergoes disproportionation when reacted with CO,
acetonitrile, and isonitriles. Reaction of 2 with triphenylphos-
phine leads to the protonation product 9.38 Also, as demon-
strated by cyclic voltammetry, 6 exhibits a redox wave of
Rh(II)/Rh(III), whereas 2 is irreversibly oxidized to Rh(III).
Thus, the chloride ligand of 2 plays an important role in its
redox reactivity. It seems that the chloride stabilizes the
product Rh(III) complex, probably by π donation. The
shortening of the Rh-Cl bond length as a result of the
oxidation of Rh(I)Cl (1) to Rh(II)Cl (2), as evidenced from
the X-ray structures of 1 and 2, supports this assumption.
Cyclic voltammetric experiments were carried out using a CHI-
660A potentiostat. A three-electrode setup was used for measure-
ments consisting of a glassy-carbon working electrode, a platinum
wire counter electrode, and an Ag/AgCl, KCl (sat’d) reference
electrode. The measurements were performed using acetone solu-
tions of the compounds (2 × 10-3 M) under nitrogen at room
t
temperature (22 °C). Bu4NPF6 (0.1 M) was used as a supporting
electrolyte. Calibration was done with the ferrocenium/ferrocene
couple (observed at 0.47 V).
Electron Paramagnetic Resonance (EPR) spectra were recorded
on a ELEXSYS 500 spectrometer (Bruker, Germany) in 100 µL
quartz capillary. The g values of the complexes in glassy solutions
were determined using a 2,2-diphenyl-1-picrylhydrazyl (DPPH)
resonance signal (g ) 2.0037) as a standard. The variable
temperature EPR experiments were carried out using a temperature
unit (Euroterm, ER 4113VT, Bruker) with an accuracy of (1 K.
Magnetic moments (dc and ac) of the powdered samples of 2
and 6 were measured using a Quantum Design Co. SQUID MPMS2
field shielded magnetometer. The magnetic moment was measured
versus field at T ) 5 and 300 K at an increasing and decreasing
field strength with ∆H ) 0.01 T step inside of the interval -1 T
e H e +1 T. Temperature dependencies of dc and ac magnetic
susceptibility were taken at 0.5 T and with increasing the temper-
ature from 2 to 300 K with 1 K steps using zero field cooled and
field cooled modes. ac magnetic moment measurements were taken
at a frequency of 700 Hz and a drive field amplitude 3 Oe.
[(PNPtBu)RhCl] (1). Crystals suitable for X-ray analysis were
obtained by slow evaporation of the benzene solution of 1.
X-ray Structural Analysis of 1. Crystal Data. C23H43ClNP2-
Rh, red, 0.8 × 0.3 × 0.2 mm3, hexagonal; P6/5 2 2 (No. 179); a
) 16.275(2), b ) 16.275(2), c ) 19.222(4) Å; R ) 90, â ) 90, γ
) 120°, from 20 degrees of data; T ) 120(2) K; V ) 4409.3(12)
Conclusions
Paramagnetic monomeric (PNPtBu)Rh(II) complexes were
prepared by the oxidation of (PNPtBu)Rh(I) complexes with
AgX (X ) BF4, PF6, BArf), whereas with AgOC(O)CF3,
chloride abstraction without oxidation to Rh(II) was ob-
served. The Rh(II) complexes were characterized by X-ray
diffraction, EPR, cyclic voltammetry, and dipole moment.
The electron-rich, bulky tridentate PNPtBu ligand facilitates
the oxidation of Rh(I) complexes on one hand, and on the
other hand, the tert-butyl substituents stabilize the monomeric
Rh(II) d7 configuration by preventing dimerization. Although
the paramagnetic complexes are relatively stable, they exhibit
interesting reactivity. Mono- and dicationic Rh(II) complexes
[(PNPtBu)RhCl][BF4] (2) and [(PNPtBu)Rh(acetone)][BF4]2
(6) exhibit different reactivity patterns. Whereas 6 is reduced
to Rh(I) in the presence of isonitriles or CO, 2 dispropor-
tionates in the presence of acetonitrile, isonitriles, or CO. 2
and 6 are reduced in the presence of phosphines and water
to Rh(I) complexes. In the case of 2 and triphenylphosphine,
the reduced Rh(I) complex undergoes protonation to give a
Rh(III) complex with a coordinated BF4 [(PNPtBu)Rh(Cl)-
(H)(BF4)] (9).
Å3; Z ) 6; fw ) 533.88; Dc ) 1.206 Mg/m-3; µ ) 0.789 mm-1
.
Data Collection and Processing. Nonius KappaCCD diffrac-
tometer, Mo KR (λ ) 0.71073 Å), graphite monochromator; 20 191
reflections collected, 0 e h e 21, -17 e k e 0, -24 e l e 24,
frame scan width ) 1.0°, scan speed 1.0° per 60 s, typical peak
Experimental Section
General Procedures. All of the experiments with metal com-
plexes and phosphine ligands were carried out under an atmosphere
of purified nitrogen in a Vacuum Atmospheres glove box equipped
with a MO 40-2 inert gas purifier or using standard Schlenk
techniques. All of the solvents were reagent grade or better. All of
the non-deuterated solvents were refluxed over sodium/benzophe-
none ketyl and distilled under an argon atmosphere.
Deuterated solvents were used as received. All of the solvents
were degassed with argon and kept in the glove box over 4 Å
molecular sieves (acetone was kept over calcium sulfate). Com-
mosaicity 0.544°, 6717 independent reflections collected, (Rint
)
0.034). The data were processed with Denzo-Scalepack.
Solution and Refinement. The structure was solved by direct
methods with SHELXS-97. Full-matrix least-squares refinement
based on F 2 with SHELXL-97; 136 parameters with 0 restraints,
final R1 ) 0.0288 (based on F 2) for data with I >2σ(I), and R1 )
0.0347 on 3357 reflections, GOF on F 2 ) 1.006, largest electron
density peak ) 0.437 e Å-3
.
[(PNPtBu)RhCl][BF4] (2). An acetone solution (5 mL) of AgBF4
(21.8 mg, 0.112 mmol) was add to a red solution of (PNPtBu)-
RhCl (59.7 mg, 0.112 mmol) in 10 mL of acetone. The reaction
mixture turned to green immediately, and a black precipitate was
(38) In the case of added PEt3, the resulting deprotonation process masks
the difference in redox reactivity between 2 and 6.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10487

Feller et al.
formed. After stirring at ambient temperature for 30 min, the
reaction mixture was filtered over celite, and the solvent was
removed under a vacuum to give a green solid in quantitative yield.
Crystals suitable for X-ray analysis were obtained by layering a
concentrated acetone solution of 2 with pentane.
121.22 (bs, PNP aryl-CH), 135.14 (s, PNP aryl-CH), 166.35 (vt,
JPC)5.4 Hz, PNP aryl-C).
Acceptable elemental analysis results for 5 could not be obtained
due to the weakly coordinated acetone ligand.
[(PNPtBu)Rh(acetone)][BF4]2 (6). The same procedure as for
2 was followed with [(PNPtBu)Rh(acetone)][BF4](60 mg, 0.093
mmol) and AgBF4 (18.1 mg, 0.093 mmol), to give a brown oil in
quantitative yield. Crystals suitable for X-ray analysis were obtained
by layering a concentrated acetone solution of 6 with pentane.
Anal. for C26H49B2F8NOP2Rh, Calcd: C, 42.77; H, 6.76;
Found: C, 42.63; H, 6.75.
Anal. for C23H43BClF4NP2Rh, Calcd: C, 44.51; H, 6.98;
Found: C, 44.62; H, 7.08.
X-ray Structural Analysis of 2. Crystal Data. C23H43BClF4-
NP2Rh, green, 1.1 × 0.6 × 0.4 mm3, monoclinic, P21/c (No. 14);
a ) 14.643(3), b ) 12.744(3), c ) 15.677(3) Å; â ) 105.67(3)°
from 20 degrees of data; T ) 120(2) K; V ) 2815.0(10) Å3; Z )
4; fw ) 620.69; Dc ) 1.465 Mg/m-3; µ ) 0.854 mm-1
.
X-ray Structural Analysis of 6. Crystal Data. C26H49B2F8-
NOP2Rh, orange, 1.0 × 0.6 × 0.3 mm3, monoclinic, C2/c; a )
29.248(6), b ) 14.051(3), c ) 19.768(4) Å; â ) 125.59(3)°, from
20 degrees of data; T ) 120(2) K; V ) 6670(2) Å3; Z ) 8; fw )
Data Collection and Processing. Nonius KappaCCD diffrac-
tometer, Mo KR (λ ) 0.71073 Å), graphite monochromator, 28 923
reflections collected, -18 e h e 18, 0 e k e 16, 0 e l e 20,
frame scan width ) 1.0°, scan speed 1.0° per 20 s, typical peak
730.13; Dc ) 1.468 Mg/m-3; µ ) 0.680 mm-1
.
mosaicity 0.398°, 7430 independent reflections collected, (Rint
0.098). The data were processed with Denzo-Scalepack.
)
Data Collection and Processing. Nonius KappaCCD diffrac-
tometer, Mo KR (λ ) 0.71073 Å), graphite monochromator, 34 868
reflections collected, -39 e h e 31, 0 e k e 18, 0 e l e 26,
frame scan width ) 2.0°, scan speed 1.0° per 40 s, typical peak
Solution and Refinement. The structure was solved by direct
methods with SHELXS-97. Full-matrix least-squares refinement
based on F 2 and empirical absorption correction with SHELXL-
97; 310 parameters with 0 restraints, final R1 ) 0.0493 (based on
F 2) for data with I > 2σ(I), and R1 ) 0.0843 on 6426 reflections,
mosaicity 0.713°, 8683 independent reflections collected, (Rint
)
0.068). The data were processed with Denzo-Scalepack.
Solution and Refinement. The structure was solved by direct
methods with SHELXS-97. Full-matrix least-squares refinement
based on F 2 and empirical absorption correction with SHELXL-
97; 399 parameters with 0 restraints, final R1 ) 0.0401 (based on
F 2) for data with I > 2σ(I), and R1 ) 0.0462 on 8332 reflections,
GOF on F 2 ) 1.006, largest electron density peak ) 1.640 e Å-3
.
[(PNPtBu)Rh(OC(O)CF3)] (3). The same procedure as above
was followed with (PNPtBu)RhCl (50 mg, 0.094 mmol) and AgOC-
(O)CF3 (20.8 mg, 0.094 mmol) in acetone, to give a brown oil in
quantitative yield.
GOF on F 2 ) 0.986, largest electron density peak ) 1.531 e Å-3
.
31P{1H} NMR (101 MHz, THF-d8): 61.27 (d, JRhP ) 151.1 Hz).
19FNMR (235 MHz, THF-d8): -76.59. 1H NMR (400 MHz, THF-
d8): 1.38 (vt, 36H, JPH ) 5.6 Hz, C(CH3)3)), 3.13 (bs, 4H, CH2-
[(PNPtBu)Rh (NO)Cl][BF4] (7). A green solution of [(PNPt-
Bu)RhCl][BF4](2) (20 mg, 0.032 mmol) in acetone (2 mL) was
exposed to 1 atm of NO at ambient temperature. The solution turned
to light-green. The solvent was removed under a vacuum to give a
green solid as 7 in quantitative yield. Crystals suitable for X-ray
analysis were obtained by layering a concentrated acetone solution
of 7 with pentane.
3
3
P), 7.01 (d, 2H, JHH ) 6.8 Hz, PNP-aryl H), 7.46 (t, 1H, JHH
)
6.8 Hz, PNP-aryl H). 13C{1H} NMR (101 Hz, THF-d8): 29.52 (s,
C(CH3)3)), 35.03 (vt, JPC ) 6.0 Hz, C(CH3)3)) 36.06 (vt, JPC ) 6.0
Hz, CH2-P), 116.00 (q, 1JCF ) 292.8 Hz, C(O)CF3) 120.67 (vt, JPC
) 6.0 Hz, 5.1 Hz, PNP aryl-CH), 130.48 (s, PNP aryl-CH), 161.31
(q, 2JCF ) 33.2 Hz, C(O)CF3), 166.22 (vt, JPC ) 6.0 Hz, PNP aryl-
C).
7 was obtained also by the addition of NOBF4 (3.0 mg, 0.027
mmol) in acetone (5 mL) to a solution of (PNPtBu)RhCl (14.5 mg,
0.027 mmol) in acetone (5 mL). 31P{1H} NMR (101 MHz, acetone-
d6): 67.2 (d, JRhP ) 114 Hz). 1HNMR (500 MHz, acetone-d6): 1.33
(vt, 18H, JPH ) 7.5 Hz, C(CH3)3)), 1.43 (vt, 18H, JPH ) 7.3 Hz,
Anal. for C25H43F3NO2P2Rh, Calcd: C, 49.11; H, 7.09; Found:
C, 49.20; H, 6.95.
2
[(PNPtBu)Rh(OC(O)CF3)][OC(O)CF3] (4). The same proce-
dure as above was followed with [(PNPtBu)Rh(OC(O)CF3)] (30
mg, 0.049 mmol) and AgOC(O)CF3 (10.8 mg, 0.049 mmol) in
acetone to give a light-green solid in quantitative yield.
Anal. for C27H43F6NO4P2Rh, Calcd: C, 44.76; H, 5.98; Found:
C, 44.67; H, 6.08.
C(CH3)3)), 4.13(d of vt, 2H, JPH ) 3.7 Hz, JHH ) 18.4 Hz, CH2-
P), 4.30 (d of vt, 2H, JPH ) 5.5 Hz, 2JHH ) 18.4 Hz, CH2-P), 7.89
3
3
(d, 2H, JHH ) 7.6 Hz, PNP-aryl H), 8.13 (t, 1H, JHH ) 7.6 Hz,
PNP-aryl H). 13C{1H} NMR (126 Hz, acetone-d6): 28.20 (s,
C(CH3)3)), 34.43 (vt, JPC ) 9.5 Hz, CH2-P), 36.82 (vt, JPC ) 8.1
Hz, C(CH3)3)), 38.37 (vt, JPC ) 8.0 Hz, C(CH3)3)), 124.02 (vt, JPC
) 5.3 Hz, PNP aryl-CH), 141.20 (s, PNP aryl-CH), 165.69 (vt, JPC
[(PNPtBu)Rh(acetone)][BF4](5). An ether solution (5 mL) of
PNPtBu (134.0 mg, 0.339 mmol) was added dropwise to an acetone
solution (10 mL) of [Rh(COE)2 (acetone)2][BF4] (178.2 mg, 0.339
mmol). Upon the addition of the PNPtBu ligand, the solution color
turned from yellow to red. The reaction mixture was stirred for 5
min at ambient temperature, and then the solvent volume was
reduced using a vacuum to 2 mL. The solution was poured into
pentane, resulting in the precipitation of 5 as a red solid. The solid
was separated by decantation and dried under a vacuum (207 mg,
95% yield). 5 is poorly soluble in benzene and reacts with
chlorinated solvents.
) 2.9 Hz, PNP aryl-C). IR (νNO) ) 1675 cm-1
.
Anal. for C23H43BClF4N2OP2Rh, Calcd: C, 42.45; H, 6.66;
Found: C, 42.55; H, 6.75.
X-ray Structural Analysis of 7. Crystal Data. C23H43BClF4N2-
OP2Rh, orange, 0.8 × 0.6 × 0.2 mm3, monoclinic, P21/n; a )
12.526(3), b ) 7.8930(16), c ) 28.603(6) Å; â ) 93.36(3)°, from
20 degrees of data; T )120(2) K; V ) 2823.0(10) Å3; Z ) 4; fw
) 650.70; Dc ) 1.531 Mg/m-3; µ ) 0.859 mm-1
.
Data Collection and Processing. Nonius KappaCCD diffrac-
tometer, Mo KR (λ ) 0.71073 Å), graphite monochromator, 18 807
reflections collected, -16 e h e 16, 0 e k e 10, 0 e l e 37,
frame scan width ) 2.0°, scan speed 1.0° per 20 s, typical peak
31P{1H} NMR (162 MHz, acetone-d6): 64.20 (d, JRhP ) 144.0
1
Hz). H NMR (400 MHz, acetone-d6): 1.34 (vt, 36H, JPH ) 6.6
mosaicity 0.496°, 6842 independent reflections collected, (Rint
)
Hz, C(CH3)3)), 3.44 (vt, JPH ) 3.4 Hz, 4H, CH2-P), 7.27 (d, 2H,
3JHH ) 7.3 Hz, PNP-aryl H), 7.62 (t, 1H, 3JHH ) 7.3 Hz, PNP-aryl
H). 13C{1H} NMR (100 Hz, acetone-d6): 29.20 (s, C(CH3)3)), 34.77
(vt, JPC ) 7.0 Hz, CH2-P), 35.00 (vt, JPC ) 7.6 Hz, C(CH3)3)),
0.042). The data were processed with Denzo-Scalepack.
Solution and Refinement. The structure was solved by direct
methods with SHELXS-97. Full-matrix least-squares refinement
10488 Inorganic Chemistry, Vol. 46, No. 25, 2007

Mononuclear Rh(II) PNP-Type Complexes
based on F 2 and empirical absorption correction with SHELXL-
97; 328 parameters with 0 restraints, final R1 ) 0.0401 (based on
F 2) for data with I > 2σ(I), and R1 ) 0.0571 on 6379 reflections,
Hz, Rh-H), 1.37 (vt, 36H, JPH ) 7.3 Hz, C(CH3)3)), 3.61 (bd, 2H,
2JHH ) 16.5 Hz, CH2-P), 3.94 (bd, 2H, 2JHH ) 16.5 Hz, CH2-P),
7.59 (d, 2H, JHH ) 7.4 Hz, PNP-aryl H), 8.86 (t, 1H, JHH ) 7.4
Hz, PNP-aryl H). 13C{1H} NMR (125 Hz, acetone-d6): 1.95 (s,
CH3CN), 29.29 (vt, JPC ) 3.3 Hz C(CH3)3)), 36.53 (vt, JPC ) 8.2
3
3
GOF on F 2 ) 1.017, largest electron density peak ) 1.692 e Å-3
.
[(PNPtBu)Rh(acetone)(NO)][BF4]2 (8). The same procedure as
above was followed with [(PNPtBu)Rh(acetone)][BF4]2 (6).
31P{1H} NMR (101 MHz, acetone-d6): 67.73 (d, JRhP ) 122
Hz, CH2-P) 37.69 (vt, JPC ) 7.2 Hz, C(CH3)3)), 121.46 (vt, JPC
5.9 Hz, PNP aryl-CH), 139.42 (s, PNP aryl-CH), 165.56 (vt, JPC
3.6 Hz PNP aryl-C). A signal for CH3CN was not detected.
)
)
1
Hz). H NMR (400 MHz, acetone-d6): 1.17(vt, 18H, JPH ) 7.6
[(PNPtBu)Rh(PEt3)][BF4] (11). To an acetone solution (2 mL)
of 6 (20 mg, 0.027 mmol) a large excess of PEt3 and a drop of
water were added. The reaction mixture was stirred for 30 min at
ambient temperature, during which the color changed from brown
to light red. The solvent was removed under a vacuum to give 11
as an orange solid in quantitative yield. 11 can also be obtained by
heating a solution of 5 in acetone with PEt3 for 1 h at 50 °C.
Hz, C(CH3)3)), 1.38 (vt, 18H, JPH ) 7.6 Hz, C(CH3)3)), 4.11(d of
vt, 2H, JPH ) 4.4 Hz, JHH ) 18.6 Hz, CH2-P), 4.30 (d of vt, 2H,
2
2
3
JPH ) 4.4 Hz, JHH ) 18.6 Hz, CH2-P), 7.89 (d, 2H, JHH ) 7.7
Hz, PNP-aryl H), 8.17 (t, 1H, JHH ) 7.7 Hz, PNP-aryl H). 13C-
3
{1H} NMR (101 Hz, acetone-d6): 29.40 (s, C(CH3)3)), 34.26 (vt,
JPC ) 10.0 Hz, CH2-P), 39.11(vt, JPC ) 8.2 Hz, C(CH3)3)), 124.44
(vt, JPC ) 6.1 Hz, PNP aryl-CH), 142.17 (s, PNP aryl-CH), 165.10
(vt, JPC ) 3.0 Hz, PNP aryl-C). IR (νNO) ) 1706 cm-1
.
31P{1H} NMR (101 MHz, acetone-d6): 25.33 (1P, dt, JRhP
159.2 Hz, JPP ) 38.9 Hz), 67.87 (2P, dd, JRhp ) 138.9 Hz, JPP
)
)
Anal. for C26H49B2F8IrN2O2P2Rh, Calcd: C, 41.08; H, 6.50;
38.9 Hz). 1H NMR (400 MHz, acetone-d6): 1.21 (m, 9H,
P(CH2CH3)3), 1.34 (vt, 36H, JPH ) 4.0 Hz, C(CH3)3)), 2.03 (quin.,
6H, J ) 7.5 Hz, P(CH2CH3)3), 3.78 (bs, 4H, CH2-P), 7.61 (d, 2H,
3JHH ) 7.5 Hz, PNP-aryl H), 7.90 (t, 1H, 3JHH ) 7.5 Hz, PNP-aryl
H). 13C{1H} NMR (125 Hz, acetone-d6): 9.38 (bs, P(CH2CH3)3),
24.38 (b dd, J ) 2.1, 26.7 Hz, P(CH2CH3)3), 30.89 (vt, JPC ) 3.0
Hz C(CH3)3)), 36.60 (dvt, J ) 2.6, 5.9 Hz, C(CH3)3)) 38.51 (dvt,
J ) 1.9, 8.15 Hz, CH2-P), 121.37 (bs, PNP aryl-CH), 139.52 (s,
PNP aryl-CH), 162.33 (vt, JPC ) 7.5 Hz PNP aryl-C).
Anal. for C29H58BF4NP3Rh, Calcd: C, 49.52; H, 8.31; Found:
C, 49.36; H, 8.40.
[(PNPtBu)Rh(PPh3)][BF4] (12). To an acetone solution (2 mL)
of 6 (20 mg, 0.027 mmol) PPh3 (10.5 mg, 0.040 mmol) in acetone
(2 mL) and a drop of water were added. The reaction mixture was
stirred for 2 days at ambient temperature, during which the color
changed from brown to light yellow and finally to orange. The
solvent was removed under a vacuum to give 11 as a red oil in
quantitative yield. 11 can also be obtained by heating a solution of
5 in acetone with an equivalent amount of triphenylphosphine for
4 h at 50 °C.
Found: C, 41.17; H, 6.58.
[(PNPtBu)Rh(Cl)(H)(BF4)] (9). To an acetone solution (2 mL)
of 2 (20 mg, 0.032 mmol) was added PPh3 (8.4 mg, 0.032 mmol)
in acetone (2 mL). A drop of water was added to the reaction
mixture, and the color changed immediately from green to orange.
The solvent was removed under a vacuum, and the residue was
redissolved in 1 mL of acetone. 31P NMR indicated the disappear-
ance of the paramagnetic complex and the formation of 9 as the
only metal complex. Crystals of 9 were obtained by layering pentane
over the acetone solution. The crystals were washed with pentane
and redissolved in acetone for NMR analysis. Crystals for X-ray
analysis were produced in the same way.
31P{1H} NMR (101 MHz, acetone-d6): 67.23 (d, JRhP ) 99.9
1
Hz) H NMR (500 MHz, acetone-d6): -21.71 (m, 1H, Rh-H),
1.33(vt, 18H, JPH ) 6.8 Hz, C(CH3)3)), 1.36 (vt, 18H, JPH ) 6.7
2
Hz, C(CH3)3)), 3.87 (bd, 2H, JHH ) 17.6 Hz, CH2-P), 3.97 (bd,
2
3
2H, JHH ) 17.6 Hz, CH2-P), 7.59 (d, 2H, JHH ) 7.4 Hz, PNP-
aryl H), 8.86 (t, 1H, 3JHH ) 7.4 Hz, PNP-aryl H). 13C{1H} NMR-
(125 Hz, acetone-d6): 29.03 (s, C(CH3)3)) 29.14 (s, C(CH3)3)), 35.77
(vt, JPC ) 8.2 Hz, CH2-P), 36.28 (vt, JPC ) 9.4 Hz, C(CH3)3)),
36.90 (vt, JPC ) 7.5 Hz, C(CH3)3)), 122.78 (vt, JPC ) 4.4 Hz, PNP
aryl-CH), 140.09 (s, PNP aryl-CH), 166.02 (vt, JPC ) 3.1 Hz PNP
aryl-C).
31P{1H} NMR (101 MHz, acetone-d6): 35.43 (dt, 1P, JRhP
171.3 Hz, JPP ) 38.1 Hz), 66.63 (dd, 2P, JRhP ) 134.8 Hz, JPP
)
)
38.1 Hz). 1H NMR (400 MHz, acetone-d6): 0.9 (vt, 36H, JPH)6.6
Hz, C(CH3)3)), 3.77 (bt, 4H, JPH)3.9 Hz, CH2-P),7.4 (bs, 9H,
X-ray Structural Analysis of 9. Crystal Data. C23H44BClF4-
NP2Rh, orange, 0.4 × 0.3 × 0.2 mm3, monoclinic, P21/c (No. 2);
a ) 18.5010(3), b ) 10.9900(4), c ) 15.2180(7) Å; â ) 111.949-
(2)°, from 20 degrees of data; T )120(2) K; V ) 2869.9(2) Å3; Z
3
RhPPh3), 7.66 (d, 2H, JHH )7.9 Hz, PNP-aryl H), 7.95 (t, 1H,
3JHH)7.9 Hz, PNP-aryl H), 8.12-8.08 (m, 6H, RhPPh3). 13C{1H}
NMR (125 Hz, acetone-d6): 30.07 (s, C(CH3)3)) 30.09 (s, C(CH3)3)),
36.57 (vt, JPC ) 6.5 Hz, C(CH3)3)) 38.05 (vt, JPC ) 7.0 Hz, CH2-
P), 121.48 (s, PNP aryl-CH), 128.70 (d, JPC ) 9.0 Hz, RhPPh3),
131.16 (d, JPC ) 2.0 Hz, RhPPh3), 136.57 (d, JPC ) 12.1 Hz,
RhPPh3), 139.68 (s, PNP aryl-CH), 141.01 (d, JPC ) 39.2 Hz,
RhPPh3), 162.67 (bs, PNP aryl-C).
) 4; fw ) 621.70; Dc ) 1.439 Mg/m-3; µ ) 0.838 mm-1
.
Data Collection and Processing. Nonius KappaCCD diffrac-
tometer, Mo KR (λ ) 0.71073 Å), graphite monochromator, 25 884
reflections collected, -24 e h e 22, 0 e k e 14, 0 e l e 19,
frame scan width ) 2.0°, scan speed 1.0° per 20 s, typical peak
mosaicity 0.59°, 6895 independent reflections collected, (Rint
0.053). The data were processed with Denzo-Scalepack.
)
Anal. for C41H58BF4NP3Rh, Calcd: C, 58.10; H, 6.90; Found:
C, 57.94; H, 6.82.
[(PNPtBu)Rh(CO)][X] (X ) BF4, BArf, OC(O)CF3, Cl) (13).
To an acetone solution (0.5 mL) of 2, 5 and 6 (20 mg, 0.032, 0.031
and 0.027 mmol respectively) in a septum-capped NMR tube was
bubbled CO. The color changed to yellow, and 13 was immediately
formed. The solvent was removed under a vacuum, resulting in a
yellow solid in quantitative yield. Crystals suitable for X-ray
analysis were obtained by layering a concentrated acetone solution
of 13 with pentane.
Solution and Refinement. The structure was solved by direct
methods with SHELXS-97. Full-matrix least-squares refinement
based on F 2 and empirical absorption correction with SHELXL-
97; 302 parameters with 0 restraints, final R1 ) 0.0345 (based on
F 2) for data with I > 2σ(I), and R1 ) 0.0561 on 6554 reflections,
GOF on F 2 ) 1.015, largest electron density peak ) 1.081 e Å-3
.
[(PNPtBu)Rh(Cl)(H)(CH3CN)][BF4] (10). To a solution of 9
in acetone (15 mg, 0.024 mmol) in a NMR tube was added
acetonitrile (1.26µL, 0.024 mmol). The color changed from orange
to yellow.
31P{1H} NMR (101 MHz, acetone-d6): 79.84 (d, JRhP ) 120.0
1
Hz). H NMR (400 MHz, acetone-d6): 1.40 (vt, 36H, JPH ) 7.3
31P{1H} NMR (101 MHz, acetone-d6): 68.61 (d, JRhP ) 99.3
Hz, C(CH3)3)), 4.11 (vt, 4H, JPH ) 3.8 Hz, CH2-P), 7.70 (d, 2H,
Hz) 1H NMR (500 MHz, acetone-d6): -16.48 (bd, 1H, JRhP ) 12
3JHH ) 7.6 Hz, PNP-aryl H), 7.97 (t, 1H, 3JHH ) 7.6 Hz, PNP-aryl
Inorganic Chemistry, Vol. 46, No. 25, 2007 10489

Feller et al.
H). 13C{1H} NMR (101 Hz, acetone-d6): 29.42 (s, C(CH3)3)), 43.29
(vt, JPC ) 6.5 Hz, CH2-P), 43.29 (vt, JPC ) 6.5 Hz, C(CH3)3)),
122.69 (vt, JPC ) 4.5 Hz, PNP aryl-CH), 141.57 (s, PNP aryl-CH),
166.43 (vt, JPC ) 7.5 Hz, PNP aryl-C) 196.27 (dt, JPC ) 13.4 Hz,
JRhC ) 69.8 Hz, RhCO). IR (νCO) ) 1982 cm-1
Hz, C(CH3)3)), 36.61(vt, JPC ) 8.0 Hz, CH2-P), 58 (s, NC(CH3)3),
121.73 (vt, JPC ) 6.5 Hz, PNP aryl-CH), 139.10 (s, PNP aryl-CH),
145.8 (bd, JRhC ) 75 Hz, RhC), 165.87 (vt, JPC ) 5.0 Hz, PNP
aryl-C). IR (νCtN) ) 2104 cm-1
.
Anal. for C28H52BF4N2P2Rh, Calcd: C, 50.32; H, 7.84; Found:
C, 49.86; H, 7.67.
Anal. for C24H43BF4NOP2Rh, Calcd: C, 47.00; H, 7.07; Found:
C, 48.08; H, 7.18.
[(PNPtBu)Rh(CNC6H3(CH3)2)][BF4] (16). The same procedure
as above was followed with 2, 5 and 6, and 2,6-dimethylphenyl
isonitrile.
X-ray Structural Analysis of 13. Crystal Data. C24H43BF4-
NOP2Rh, yellow, 0.1 × 0.1 × 0.05 mm3, triclinic, P1h; a ) 8.0990-
(2), b ) 12.3870(2), c ) 15.5640(3) Å; R )107.840(1), â )
102.825(1), γ ) 91.456(1)°, from 20 degrees of data; T ) 290(2)
31P{1H} NMR (161 MHz, acetone-d6): 78.05 (d, JRhP ) 128.2
1
Hz). H NMR (400 MHz, acetone-d6): 1.40 (vt, 36H, JPH ) 7.3
K; V ) 1441.90(5) Å3; Z ) 2; fw ) 613.26; Dc ) 1.412 Mg/m-3
;
Hz C(CH3)3)), 2.42 (s, 6H, CN(C6H3(CH3)2)), 3.94 (vt, 4H, JPH )
µ ) 0.746 mm-1
.
4.0 Hz, CH2-P), 7.17 (bs, 3H, CN(C6H3(CH3)2)), 7.62 (d, 2H, 3JHH
3
Data Collection and Processing. Nonius KappaCCD diffrac-
tometer, Mo KR (λ ) 0.71073 Å), graphite monochromator, 16 163
reflections collected, -10 e h e 10, -16 e k e 15, 0 e l e 20,
frame scan width ) 1.0°, scan speed 1.0° per 60 s, typical peak
mosaicity 0.842°, 6282 independent reflections collected, (Rint
0.040). The data were processed with Denzo-Scalepack.
) 7.3 Hz, PNP-aryl H), 7.90 (t, 1H, JHH ) 7.3 Hz, PNP-aryl H).
13C{1H} NMR (101 Hz, acetone-d6): 18.88 (s, CN(C6H3(CH3)2)),
29.40 (vt, JPC ) 3.0 Hz C(CH3)3)), 36.08 (vt, JPC ) 8.5 Hz,
C(CH3)3)), 36.40 (vt, JPC ) 8.4 Hz, CH2-P), 122.01 (vt, JPC ) 5.1
Hz, PNP aryl-CH),128.34 (s, C4 - NC(C6H3(Me)2)), 128.98 (s, C3,
C5 - CN(C6H3(CH3)2)), 129.57 (s, C1 - CN(C6H3(CH3)2)), 134.02
(s, C2, C6 - CN(C6H3(CH3)2)), 139.80 (s, PNP aryl-CH), 165.96
)
Solution and Refinement. The structure was solved by the
Patterson method with SHELXS-97. Full-matrix least-squares
refinement based on F 2 and empirical absorption correction with
SHELXL-97; 284 parameters with 2 restraints, final R1 ) 0.0582
(based on F 2) for data with I > 2σ(I), and R1 ) 0.0653 on 6273
reflections, GOF on F 2 ) 1.069, largest electron density peak )
(vt, JPC ) 6.0 Hz, PNP aryl-C). IR (νCtN) ) 2077 cm-1
.
Anal. for C33H56BF4N2P2Rh, Calcd: C, 54.11; H, 7.71; Found:
C, 53.88; H, 7.66.
Acknowledgment. This work was supported by the Israel
Science Foundation, by the DIP program for German-Israeli
cooperation, by the MINERVA foundation, and by The
Helen and Martin Kimmel Center for Molecular Design.
D.M. holds the Israel Matz Professorial Chair of Organic
Chemistry.
1.090 e Å-3
.
[(PNPtBu)Rh(CNC(CH3)3)][BF4] (15). To an acetone solution
of 2, 5 and 6 (20 mg, 0.032, 0.031 and 0.027 mmol respectively)
one equiv of tert-butyl isocyanide was added, and the color changed
to orange. The solvent was removed under a vacuum, resulting in
a yellow solid in quantitative yield (in case of 5 and 6).
Supporting Information Available: CIF files containing X-ray
crystallographic data for 1, 2, 6, 7, 9, and 13. Correlation of
peak current versus scan rate for first reversible redox process of
1, 2, 5 and 6. This material is available free of charge via the
Internet at http://pubs.acs.org.
31P{1H} NMR (101 MHz, acetone-d6): 73.91 (d, JRhP ) 131.1
1
Hz). H NMR (400 MHz, acetone-d6): 1.45 (bs, 36, C(CH3)3)),
1.52 (s, 9H, CNC(CH3)3)), 3.85 (vt, 4H, JPH ) 3.7 Hz, CH2-P),
3
3
7.58 (d, 2H, JHH ) 7.8 Hz, PNP-aryl H), 7.86 (t, 1H, JHH ) 7.8
Hz, PNP-aryl H). 13C{1H} NMR (101 Hz, acetone-d6): 29.43 (vt,
JPC ) 3.4 Hz C(CH3)3)), 30.57 (s, NC(CH3)3), 35.87 (vt, JPC ) 8.5
IC701044B
10490 Inorganic Chemistry, Vol. 46, No. 25, 2007