Halide abstraction by Na[B{C6H3(CF3) 2-3,5}4]: Synthesis and structural characterization of the rhodium(I) cations [(η6-arene)Rh(PPh3) 2]+ (Arene = benzene, toluene)

Article abstract of DOI:10.1002/zaac.200600165

Halide abstraction from [(Ph₃P)₂Rh(μ-Cl)] ₂ by the sodium salt of the weakly coordinating [BAr^f ₄]^- anion [Ar^f = C₆H ₃(CF₃)₂-3,5] in the presence of excess arene offers a convenient, high-yielding route to the half-sandwich cations [(arene)Rh(PPh₃)₂]⁺[BAr^f ₄]^- [arene = benzene (1), toluene (2)]. Crystalline samples of 1 and 2 are isomorphous [a = 13.1270(2), b = 15.3030(2), c = 17.5760(3) A, α = 74.620(1), β = 81.533(1), γ = 88.540(1)° for 1] and feature the arene ligand bound to the rhodium atom in η⁶ fashion.

Full text of DOI:10.1002/zaac.200600165

DOI: 10.1002/zaac.200600165
Halide Abstraction by Na[B{C6H3(CF3)2-3,5}4]: Synthesis and Structural
Characterization of the Rhodium(I) Cations [(η6-arene)Rh(PPh3)2]؉
(Arene ؍ benzene, toluene)
Oliver Buttler, Amal Al-Fawaz, Deborah L. Kays, Joanna K. Day, Li-Ling Ooi and Simon Aldridge*
Cardiff / UK, Centre for Fundamental and Applied Main Group Chemistry, Cardiff School of Chemistry
Received June 1st, 2006.
˚
Abstract. Halide abstraction from [(Ph3P)2Rh(µ-Cl)]2 by the
sodium salt of the weakly coordinating [BArf4]Ϫ anion [Arf
C6H3(CF3)2-3,5] in the presence of excess arene offers a convenient,
b ϭ 15.3030(2), c ϭ 17.5760(3) A, α ϭ 74.620(1), β ϭ 81.533(1),
γ ϭ 88.540(1)° for 1] and feature the arene ligand bound to the
rhodium atom in η6 fashion.
ϭ
high-yielding
route
to
the
half-sandwich
cations
[(arene)Rh(PPh3)2]ϩ[BArf4]Ϫ [arene ϭ benzene (1), toluene (2)].
Crystalline samples of 1 and 2 are isomorphous [a ϭ 13.1270(2),
Keywords: Rhodium; Phosphine; Halide abstraction
Cationic rhodium(I) complexes are known to be active homogen-
ous catalysts for a range of organic transformations [1]. Thus, for
example, the Schrock-Osborn diene system [(Ph3P)2Rh(nbd)]ϩ
(nbd ϭ norbornadiene) represents a benchmark in hydrogenation
catalysis [2], and more recent work has demonstrated that com-
plexes of the type [(arene)RhL2]ϩ (arene ϭ benzene, toluene; L2 ϭ
a chiral chelating phosphine such as 1,2-bis(2,5-diethylphospholan-
yl)benzene (Et-DuPHOS)) are effective catalysts for asymmetric
hydrogenation reactions [3]. Synthetic routes to a range of arene-
stabilized rhodium(I) bis(phosphine) cations have therefore been
demonstrated [3Ϫ9] including complexes in which the π-system is
provided by an aryl-containing borate counterion (e.g. [BPh4]Ϫ) [8],
or by ancillary coordination of one of the phosphine ligands {as
in [(Ph3P)(Ph2P-η6C6H5)Rh]22ϩ} [9].
Scheme
1 Syntheses of the cationic bis(triphenylphosphine)-
rhodium arene complexes 1 and 2:. Reagents and conditions: (i)
Na[BArf4] (2 equiv.), arene (ca. 300 equiv.), dichloromethane,
20 °C, 90 min, ca. 85 % isolated yield.
Reaction of [(Ph3P)2Rh(µ-Cl)]2 with two equivalents of Na[BArf4]
and a vast excess of benzene or toluene (ca. 300 equivalents) using
dichloromethane as the solvent (Scheme 1) leads to the formation
of [(arene)Rh(PPh3)2]ϩ[BArf4]Ϫ [arene ϭ benzene (1), toluene (2)]
in good yields (ca. 85 %). 1 and 2 have been characterized by multi-
nuclear (1H, 11B, 13C, 19F and 31P) NMR, and IR spectroscopies
and by elemental analysis. Particularly diagnostic among the spec-
Recent investigation of the reactivity of late transition metal com-
plexes such as [(Ph3P)2Rh(µ-Cl)]2 towards the strongly Lewis acidic
boranes [(C6F5)2BCl] and [(C6F5)2BH]2 in arene solvents (benzene
or toluene) reveals the formation of products due to halide or phos-
phine abstraction from the metal atom [10]. Given the widespread
application of cationic rhodium(I) bis(phosphine) systems we were
surprised to find, however, that reports concerning the synthesis
and spectroscopic characterization of the parent system
[(benzene)Rh(PPh3)2]ϩ (1) were lacking, at that crystallographic
studies of 1 (and its toluene analogue, 2) were similarly absent.
Therefore we report herein a straightforward synthesis of com-
plexes 1 and 2, as the [BArf4]Ϫ salts [Arf ϭ C6H3(CF3)2-3,5], and
their structural characterization in the solid state.
1
troscopic signatures are the extremely high JRhP coupling con-
stants, typical of Rh(I) arene and cyclopentadienyl systems (ca.
205 Hz for both 1 and 2) [3Ϫ5, 9a, 9b, 10], and aromatic 1H reson-
ances for the coordinated arene (δH 5.78 for 1; δH 5.20, 5.55, 6.64
for 2) shifted upfield from the corresponding free species [3Ϫ5, 9b,
10]. Single crystals of 1 and 2 suitable for study by X-ray crystal-
lography could also be obtained, with the results shown in Figure
1 and Table 1.
The principal point of interest concerning the structures of the cat-
ionic components of 1 and 2 concerns the mode of interaction of
the arene ligand with the bis(phosphine)rhodium(I) fragment. Ex-
amples of both 16-electron species containing η4 arenes and 18-
electron complexes featuring η6 binding have previously been re-
ported [3Ϫ7]. In the case of 1 and 2, the metric parameters (notably
the Rh-C and C-C distances) do reflect slight asymmetry in the
arene binding, but the range of Rh-C and C-C distances [e.g.
* Dr Simon Aldridge
Cardiff University, Cardiff School of Chemistry
Centre for Fundamental and Applied Main Group Chemistry
Main Building, Park Place
Cardiff, CF10 3AT / UK
Tel: (029) 20875495
Fax: (029) 20874030
AldridgeS@cardiff.ac.uk
Z. Anorg. Allg. Chem. 2006, 632, 2187Ϫ2189
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2187

O. Buttler, A. Al-Fawaz, D. L. Kays, J. K. Day, L.-L. Ooi, S. Aldridge
Figure 1 Structure of the cationic component of [(η6-C6H6)Rh(PPh3)2]ϩ[BArf4]Ϫ (1, left) and [(η6-C6H5CH3)Rh(PPh3)2]ϩ[BArf4]Ϫ (2,
right); hydrogen atoms omitted for clarity and ORTEP ellipsoids shown at the 50 % probability level.
˚
Key bond lengths /A and angles /°: for 1 Rh(1)-P(1) 2.243(1), Rh(1)-P(2) 2.272(1), Rh(1)-C6H6 centroid 1.864(5), Rh(1)-C(1) 2.340(4),
Rh(1)-C(2) 2.298(4), Rh(1)-C(3) 2.366(4), Rh(1)-C(4) 2.357(4), Rh(1)-C(5) 2.283(4), Rh(1)-C(6) 2.320(4), C(1)-C(2) 1.413(7), C(2)-C(3)
1.392(7), C(3)-C(4) 1.380(7), C(4)-C(5) 1.410(7), C(5)-C(6) 1.403(7), C(1)-C(6) 1.367(7), P(1)-Rh(1)-P(2) 93.42(4); for 2 Rh(1)-P(1) 2.280(1),
Rh(1)-P(2) 2.237(1), Rh(1)-C6H5 centroid 1.889(5), Rh(1)-C(2) 2.401(3), Rh(1)-C(3) 2.379(3), Rh(1)-C(4) 2.307(4), Rh(1)-C(5) 2.259(4),
Rh(1)-C(6) 2.341(4), Rh(1)-C(7) 2.380(4), C(2)-C(3) 1.382(5), C(3)-C(4) 1.362(6), C(4)-C(5) 1.393(7), C(5)-C(6) 1.422(8), C(6)-C(7) 1.391(7),
C(2)-C(7) 1.387(5), P(1)-Rh(1)-P(2) 92.84(3).
Table 1 Details of data collection, structure solution and refinement for compounds 1 and 2.
Compound
1
2
Empirical formula
Formula weight
Temperature /K
C74H48BF24P2Rh
1568.78
150(2)
C75H50BF24P2Rh
1582.81
150(2)
CCDC deposit number
Wavelength /A
609304
0.71073
609305
0.71073
˚
Crystal system
Space group
Unit cell dimensions /A, °
Triclinic
P1
13.1270(2)
15.3030(2)
triclinic
P1
13.1761(2)
15.5566(2)
¯
¯
˚
a
b
c
17.5760(3)
17.5140(3)
α
β
γ
74.620(1)
81.533(1)
88.540(1)
3366.8(1)
1.547
2
0.412
1576
0.43 x 0.30 x 0.15
3.06 to 27.56
Ϫ17 to 17
Ϫ19 to 19
Ϫ22 to 22
74.806(1)
81.553(1)
88.517(1)
3426.6(1)
1.534
2
0.405
1592
0.38 x 0.35 x 0.25
3.52 to 26.37
Ϫ16 to 16
Ϫ19 to 19
Ϫ21 to 21
3
˚
Volume /A
Density (calcd), /Mg mϪ3
Z
Absorption coefficient /mmϪ1
F(000)
Crystal size /mm3
Theta range /°
Index ranges
h
k
l
Reflections collected
59933
51378
Independent reflections
Completeness to theta max
Absorption correction
Max. and min. transmission
Refinement method
15395 [R(int) ϭ 0.1508]
99.1 %
Semi-empirical from equivs
0.941 and 0.843
Full-matrix least-squares (F2)
15395 / 144 / 994
1.033
13980 [R(int) ϭ 0.0700]
99.6 %
Semi-empirical from equivs
0.905 and 0.861
Full-matrix least-squares (F2)
13980 / 144 / 1038
1.026
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. pk and hole /e A
R1 ϭ 0.0623, wR2 ϭ 0.1409
R1 ϭ 0.1030, wR2 ϭ 0.1608
0.806 and Ϫ0.947
R1 ϭ 0.0490, wR2 ϭ 0.1058
R1 ϭ 0.0690, wR2 ϭ 0.1154
0.976 and Ϫ0.845
Ϫ3
˚
˚
˚
2.283(4)-2.366(4) and 1.367(7)-1.413(7) A, respectively for the par-
fragment [d(Rh-P) ϭ 2.243(1), 2.272(1) A; ՄP-Rh-P ϭ 93.42(4)°]
is similar to that of related systems, and shows the expected length-
ening of the Rh-P bonds compared to the analogous bis(triphenyl-
ent benzene system 1] are within the bounds expected for η6 coordi-
6
˚
nation {e.g. 2.277-2.343 and 1.365-1.416 A for [(η -C6H6)Rh(S,S-
Me-DuPHOS)]ϩ} [3]. The geometry of the rhodium bis(phosphine)
phosphite) system [2.184 A (mean)] [6].
˚
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 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 2187Ϫ2189

Halide Abstraction by Na[B{C6H3(CF3)2-3,5}4]
97, respectively; absorption corrections were performed using
SORTAV [12]. Details of each data collection, structure solution
and refinement can be found in Table 1. Relevant bond lengths and
angles are included in the figure captions and complete details of
each structure have been deposited with the CCDC (numbers as
listed in Table 1).
Experimental Section
Syntheses of [(η6-arene)Rh(PPh3)2]؉[BArf4]؊
[arene ؍ benzene (1), toluene (2)]
The two compounds were synthesized using a common method
exemplified for 1. All manipulations were carried out using stand-
ard Schlenk line techniques, employing dried degassed solvents;
precursors were prepared by standard literature methods [11]. A
mixture of [(Ph3P)2Rh(µ-Cl)]2 (0.155 g, 0.117 mmol), Na[BArf4]
(0.207 g, 0.234 mmol) and benzene (6 ml) in dichloromethane
(40 ml) was stirred for 90 min at 20 °C, after which time the reac-
tion was judged to be complete by 31P NMR. Concentration of the
reaction mixture (to ca. 10 ml), addition of hexanes (50 ml) and
cooling to Ϫ30 °C for 12 h led to the formation of 1 as a beige solid
(yield: 0.361 g, 86 %). Recrystallization by layering a concentrated
solution in dichloromethane with hexanes at Ϫ30 °C led to the for-
mation of crystals suitable for X-ray diffraction. Elemental analy-
sis: calc. for C74H48BF24P2Rh (1), C 56.65 %, H 3.08 %; found C
56.21 %, H 2.88 %. Elemental analysis: calc. for C75H50BF24P2Rh
(2), C 56.91 %, H 3.18 %; found C 56.63 %, H 3.06 %.
[1] See, for example, J. P. Collman, L. S. Hegedus, J. R. Norton,
R. G. Finke, Principles and Applications of Organotransition
Metal Chemistry, University Science Books, Sausalito, Cali-
fornia, 1987, chp 10.
[2] R. R. Schrock, J. A. Osborn, J. Am. Chem. Soc. 1976, 98,
2134.
[3] D. Heller, H.-J. Drexler, A. Spannenberg, B. Heller, J. You, W.
Baumann, Angew. Chem. 2002, 114, 814; Angew. Chem. Int.
Ed. 2002, 41, 777.
[4] J. Wolf, M. Manger, U. Schmidt, G. Fries, D. Barth, B.
Weberndörfer, D. A. Vicic, W. D. Jones, H. Werner, Dalton
Trans. 1999, 1867.
Characterizing data for 1: 1H NMR (CD2Cl2, 300 MHz): δ 5.87 (s,
6H, η6-C6H6), 7.15-7.30 (m, 30H, PPh3), 7.46 (s, 4H, para-CH of
[BArf4]Ϫ), 7.63 (s, 8H, ortho-CH of [BArf4]Ϫ). 13C NMR (CD2Cl2,
76 MHz): δ 103.5 (CH of η6-C6H6), 117.5 (para-CH of BArf4Ϫ),
[5] E. T. Singewald, C. S. Slone, C. L. Stern, C. A. Mirkin, G. P.
A. Yap, L. M. Liable-Sands, A. L. Rheingold, J. Am. Chem.
Soc. 1997, 119, 3048.
[6] R. Uson, P. Lahuerta, J. Reyes, L. A. Oro, C. Foces-Foces, F.
H. Cano, S. Garcia-Blanco, Inorg. Chim. Acta 1980, 42, 75.
[7] P. Marcazzan, B. O. Patrick, B. R. James, Organometallics
2003, 22, 1177.
[8] (a) Z. Zhou, G. Facey, B. R. James, H. Alper, Organometallics
1996, 15, 2496; (b) C. Dai, E. G. Robbins, A. J. Scott, W.
Clegg, D. S. Yufit, J. A. K. Howard, T. B. Marder, Chem.
Commun. 1998, 1983.
[9] (a) A. Rifat, N. J. Patmore, M. F. Mahon, A. S. Weller, Or-
ganometallics 2002, 21, 2856; (b) P. Marcazzan, M. B. Ezhova,
B. O. Patrick, B. R. James, C. R. Chimie 2002, 5, 373; (c) X.-
Y. Yu, M. Maekawa, T. Morita, H.-C. Chang, S. Kitagawa,
G.-X. Jin, Bull. Chem. Soc. Jpn. 2002, 75, 267.
[10] A. Al-Fawaz, S. Aldridge, D. L. Coombs, A. A. Dickinson,
D. J. Willock, L.-L. Ooi, M. E. Light, S. J. Coles, M. B. Hurst-
house, Dalton Trans. 2004, 4030.
[11] (a) J. A. Osborn, F. H. Jardine, J. F. Young, G. Wilkinson, J.
Chem. Soc. A 1966, 1711; (b) D. L. Reger, T. D. Wright, C.
A. Little, J. J. S. Lamba, M. D. Smith, Inorg. Chem. 2001,
40, 3810.
[12] (a) Denzo: Z. Otwinowski, W. Minor, in: Methods in Enzy-
mology, C. W. Carter, R. M. Sweet (eds), Academic Press, New
York. 1996, vol. 276, p. 307; (b) Sir-97: A. Altomare, M. C.
Burla, M. Camalli, G. L. Cascarano, C. Giocavazzo, A.
Guagliardi, A. G. G. Moliterni, G. Polidori, R. Spagna, J.
Appl. Cryst. 1999, 32, 115. (c) Dirdiff-99: P. T. Beurskens, G.
Peurskens, W. P. Bosman, R. de Gelder, S. Garcia-Granda, R.
O. Gould, R. Israel, J. M. M. Smits, University of Nijmegen,
Netherlands, 1996; (d) G. M. Sheldrick, Acta Crystallogr.
1990, A46, 467; (e) Sortav: R. H. Blessing, Acta Crystallogr.
1995, A51, 33.
1
2
124.6 (q, JCF ϭ 272 Hz, CF3 of BArf4Ϫ), 128.8 (q, JCF ϭ 32 Hz,
meta-C of BArf4Ϫ), 134.8 (ortho-CH of BArf4Ϫ), 161.8 (q, JCB
ϭ
1
50 Hz, ipso-C of BArf4Ϫ), 128.3, 130.8, 133.7 (CH of Ph). 11B NMR
(CD2Cl2, 96 MHz): δ Ϫ7.6. 19F NMR (CD2Cl2, 283 MHz): δ
1
Ϫ62.8. 31P NMR (CD2Cl2, 122 MHz): δ 44.1 (d, JRhP
ϭ
205.6 Hz). IR (CCl4 solution, cmϪ1): 1549 m, 1354 w, 1217 w, 792 s.
Characterizing data for 2: 1H NMR (CD2Cl2, 300 MHz): δ 2.19 (s,
3
3H, CH3 of η6-C6H5CH3), 5.20 (d, JHH ϭ 6.4 Hz, 2H, ortho-CH
3
of η6-C6H5CH3), 5.55 (t, JHH ϭ 6.4 Hz, 2H, meta-CH of η6-
C6H5CH3), 6.64 (t, 3JHH ϭ 6.4 Hz, 1H, para-CH of η6-C6H5CH3),
7.19-7.32 (m, 30H, PPh3), 7.50 (s, 4H, para-CH of [BArf4]Ϫ), 7.67
(s, 8H, ortho-CH of [BArf4]Ϫ). 13C NMR (CD2Cl2, 76 MHz): δ 19.9
(CH3 of η6-C6H5CH3), 100.8, 104.8, 119.3 (CH of η6-C6H5CH3),
1
117.5 (para-CH of BArf4Ϫ), 124.6 (q, JCF ϭ 272 Hz, CF3 of
2
BArf4Ϫ), 128.9 (q, JCF ϭ 32 Hz, meta-C of BArf4Ϫ), 134.8 (ortho-
1
CH of BArf4Ϫ), 161.8 (q, JCB ϭ 50 Hz, ipso-C of BArf4Ϫ), 128.3,
130.8, 133.7 (CH of Ph). 11B NMR (CD2Cl2, 96 MHz): δ Ϫ7.6. 19
Ϫ62.8. 31P NMR (CD2Cl2,
F
NMR (CD2Cl2, 283 MHz):
δ
122 MHz): δ 44.4 (d, 1JRhP ϭ 205.4 Hz). IR (CCl4 solution, cmϪ1):
1550 m, 1353 w, 1217 w, 782 s. 1H and 31P NMR data for com-
pounds thought to contain the [(η6-toluene)Rh(PPh3)2]ϩ cation
have been noted previously by James [9b] and by Weller [9a].
Crystallographic method
Data for compounds 1 and 2 were collected on a Bruker Nonius
Kappa CCD diffractometer. Data collection and cell refinement
were carried out using DENZO and COLLECT; structure solution
and refinement used SIR-92 (1) or DIRDIFF-99 (2) and SHELXL-
Z. Anorg. Allg. Chem. 2006, 2187Ϫ2189
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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