Diversity of metal-ligand interactions in halide (X = I, Br, Cl, F) and halide-free ambiphilic ligand rhodium complexes

Article abstract of DOI:10.1021/ic902109p

Reaction of the neutral ambiphilic ligand 2,7-di-tert-butyl-5- diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB) with [{Rh(μ-Cl)(CO)₂}₂] yields [RhCl(CO)(TXPB)] (1) (Emslie et al. Organometallics 2006, 25, 5835). Complex 1 is square planar with the TXPB ligand bound to rhodium via the phosphine and thioether donors (these are features common to complexes 2-5, vide infra). Treatment of 1 with Me ₃SiBr and Me₃SiI allowed for halide substitution to afford [RhBr(CO)(TXPB)] (2) and [RhI(CO)(TXPB)] (3), respectively. The halide co-ligands in complexes 1 and 2 form a strong bridging interaction between rhodium and the borane group in TXPB. The presence of stronger borane-halide coordination in 1 is clearly illustrated by an ¹¹B NMR chemical shift of 12 ppm versus 27 ppm in 2. In contrast, the iodide ligand in 3 forms only a weak bridging interaction to boron, leading to a B...I distance of 3.125(7) A, and an ¹¹B NMR chemical shift of 56 ppm (versus 69 ppm for free TXPB). A lower carbonyl stretching frequency in 3 (2002 cm^-1) versus 1 or 2 (2008 and 2013 cm^-1, respectively) could be attributed to weakening of the Rh-X bond in 1 and 2 as a consequence of halide-borane coordination and/or a shorter Rh-S bond in complex 3. [Rh(CO)(TXPB-F)] (4) and the halide-free cation [Rh(CO)(TXPB)][PF₆] (5) were accessed by reaction of 1 with [NMe₄]F and Tl[PF₆], respectively. Complex 4 is zwitterionic with fluoride bound to boron [¹¹B NMR δ 4 ppm; B-F = 1.445(6) A; Rh...F = 3.261(3) A] and an η²-interaction between the cationic rhodium center and the ipso- and ortho-carbon atoms of a B-phenyl ring in TXPB-F. By contrast, rhodium in 5 engages in an η²-interaction with boron and the ipso-carbon of one B-phenyl ring; Rh-B and Rh-C_ipso bond lengths in 5 are 2.557(3) and 2.362(2) A, respectively. The long Rh-B distance and an ¹¹B NMR chemical shift of 57 ppm are consistent with only a weak Rh-B interaction in 5, and a CO stretching frequency of 2028 cm^-1 (Nujol), versus 2004-2013 cm^-1 for complexes 1-4, is indicative of greatly reduced electron density in 5, relative to 1-4.

Full text of DOI:10.1021/ic902109p

4060 Inorg. Chem. 2010, 49, 4060–4072
DOI: 10.1021/ic902109p
Diversity of Metal-Ligand Interactions in Halide (X = I, Br, Cl, F) and Halide-Free
Ambiphilic Ligand Rhodium Complexes
Bradley E. Cowie,† David J. H. Emslie,*,† Hilary A. Jenkins,‡ and James F. Britten‡
†Department of Chemistry and Chemical Biology and ‡McMaster Analytical X-ray Diffraction Facility,
McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4M1, Canada
Received October 27, 2009
Reaction of the neutral ambiphilic ligand 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene
(TXPB) with [{Rh(μ-Cl)(CO)2}2] yields [RhCl(CO)(TXPB)] (1) (Emslie et al. Organometallics 2006, 25, 5835). Complex
1 is square planar with the TXPB ligand bound to rhodium via the phosphine and thioether donors (these are features
common to complexes 2-5, vide infra). Treatment of 1 with Me3SiBr and Me3SiI allowed for halide substitution to afford
[RhBr(CO)(TXPB)] (2) and [RhI(CO)(TXPB)] (3), respectively. The halide co-ligands in complexes 1 and 2 form a strong
bridging interaction between rhodium and the borane group in TXPB. The presence of stronger borane-halide coordination
in 1 is clearly illustrated by an 11B NMR chemical shift of 12 ppm versus 27 ppm in 2. In contrast, the iodide ligand in 3 forms
11
˚
only a weak bridging interaction to boron, leading to a B I distance of 3.125(7) A, and an B NMR chemical shift of 56
3 3 3
ppm (versus 69 ppm for free TXPB). A lower carbonyl stretching frequency in 3 (2002 cm-1) versus 1 or 2 (2008 and 2013
cm-1, respectively) could be attributed to weakening of the Rh-X bond in 1 and 2 as a consequence of halide-borane
coordination and/or a shorter Rh-S bond in complex 3. [Rh(CO)(TXPB-F)] (4) and the halide-free cation [Rh(CO)-
(TXPB)][PF6] (5) were accessed by reaction of 1 with [NMe4]F and Tl[PF6], respectively. Complex 4 is zwitterionic with
11
2
˚
˚
fluoride bound to boron [ B NMR δ 4 ppm; B-F = 1.445(6) A; Rh F = 3.261(3) A] and an η -interaction between the
3 3 3
cationic rhodium center and the ipso- and ortho-carbon atoms of a B-phenyl ring in TXPB-F. By contrast, rhodium in 5
engages in an η2-interaction with boron and the ipso-carbon of one B-phenyl ring; Rh-B and Rh-Cipso bond lengths in 5
are 2.557(3) and 2.362(2) A, respectively. The long Rh-B distance and an 11B NMR chemical shift of 57 ppm are
˚
consistent with only a weak Rh-B interaction in 5, and a CO stretching frequency of 2028 cm-1 (Nujol), versus
2004-2013 cm-1 for complexes 1-4, is indicative of greatly reduced electron density in 5, relative to 1-4.
Introduction
[{PdCl(TXPB)}2] and [PdCl2(TXPB)]3 (D in Figure 1) are
rare, and most other examples have been reported by
Bourissou et al. These complexes include: [(p-cymene)RuCl2{N-
C5H4(CH2BCy2)-o}],5 [(η3-allyl)PdCl{PiPr2(C6H4)BCy2-o}],6
[(NBD)RhCl{PiPr2(C6H4)BCy2-o}] (NBD = norborna-
diene), [(PdCl2{PiPr2(C6H4)BCy2-o})2], and [PdCl2(PPh3)-
{PiPr2(C6H4)BCy2-o}] (Figure 2).7 Additional complexes
containing a metal-chloride-borane interaction are Boch-
mann et al.’s [{η5-C5H4B(C6F5)2}(L)TiCl2] [L = Cp, C5H4Si-
Me3, indenyl, and C9H6NMe2 {2-(dimethylamino)indenyl}],8
Mayer et al.’s [(κ3-Tp)OsCl2(NPhBPh2)],9 Fontaine et al.’s
The chemistry of ambiphilic borane-containing ligands has
seen a burst of activity over the past 10 years, providing a
diverse range of complexes, including those containing
direct metal-borane interactions.1 In this area, our research
has focused on 2,7-di-tert-butyl-5-diphenylboryl-4-diphenyl-
phosphino-9,9-dimethylthioxanthene (TXPB), a rigid phos-
phine/thioether/borane ligand,2 and complexes exhibit-
ing a range of metal-TXPB bonding modes have been
prepared (Figure 1).2-4 Metal-chloride-borane bridg-
ing interactions such as those in [RhCl(CO)(TXPB)] (1),4
*To whom correspondence should be addressed. E-mail: emslied@
mcmaster.ca. Phone: 905-525-9140. Fax: 905-522-2509.
(1) (a) Braunschweig, H.; Kollann, C.; Rais, D. Angew. Chem., Int. Ed.
2006, 45, 5254. (b) Fontaine, F.-G.; Boudreau, J.; Thibault, M.-H. Eur. J. Inorg.
Chem. 2008, 5439.
(2) Emslie, D. J. H.; Blackwell, J. M.; Britten, J. F.; Harrington, L. E.
Organometallics 2006, 25, 2412.
(5) Vergnaud, J.; Ayed, T.; Hussein, K.; Vendier, L.; Grellier, M.;
Bouhadir, G.; Barthelat, J.-C.; Sabo-Etienne, S.; Bourissou, D. Dalton
Trans. 2007, 2370.
(6) Bontemps, S.; Bouhadir, G.; Miqueu, K.; Bourissou, D. J. Am. Chem.
Soc. 2006, 128, 12056.
(7) Bontemps, S.; Bouhadir, G.; Aperley, D. C.; Dyer, P. W.; Miqueu, K.;
Bourissou, D. Chem. Asian J. 2009, 4, 428.
(3) Emslie, D. J. H.; Harrington, L. E.; Jenkins, H. A.; Robertson, C. M.;
Britten, J. F. Organometallics 2008, 27, 5317.
(4) Oakley, S. R.; Parker, K. D.; Emslie, D. J. H.; Vargas-Baca, I.;
Robertson, C. M.; Harrington, L. E.; Britten, J. F. Organometallics 2006, 25,
5835.
(8) Lancaster, S. J.; Al-Benna, S.; Thornton-Pett, M.; Bochmann, M.
Organometallics 2000, 19, 1599.
(9) Crevier, T. J.; Bennett, B. K.; Soper, J. D.; Bowman, J. A.; Dehestani,
A.; Hrovat, D. A.; Lovell, S.; Kaminsky, W.; Mayer, J. M. J. Am. Chem. Soc.
2001, 123, 1059.
r
pubs.acs.org/IC
Published on Web 03/30/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4061
Figure 1. Examples of different metal-TXPB bonding modes: (A) Triarylborane η3BCC-coordination. (B) Zwitterionic boratoxyallyl complex formation
induced through binding of an enone co-ligand (dba). (C) TXPB η1P-coordination induced by metal-diene coordination. (D) Chloride occupying a
bridging position between the metal and the borane.
Figure 2. Complexes exhibiting a metal-halide-borane bridging interaction, not including TXPB complexes. Xyl = 2,6-dimethylphenyl; C9H6NMe2 =
2-(dimethylamino)indenyl; IMes = 1,3-di(2,4,6-trimethylphenyl)imidazolin-2-ylidene.
Figure 3. Solid-state structure of [RhCl(CO)(TXPB)] hexane (1) hexane with ellipsoids at 50% probability. tert-Butyl and CMe2 methyl groups,
3
3
hydrogen atoms, and solvent are omitted for clarity.
[(IMes)2PtHCl{BC5H4(SiMe3)-o}],10 and Otero et al.’s [(η5-
C5H4SiMe3)2(L)NbCl{B(C6F5)3}] (L = CNXyl, CNCy, CO)
(Figure 2).11
have also been prepared.12 However, complexes containing
a metal-bromide-borane or metal-iodide-borane inter-
action appear to be unknown, presumably because of a
A wide range of complexes in which a fluoroborate anion
interacts with a cationic metal center via a M-F-B bridge
(12) For recent examples of complexes featuring M-F-BF3 bridging
interactions, see: (a) Frech, C. M.; Shimon, L. J. W.; Milstein, D. Organo-
metallics 2009, 28, 1900. (b) Tkach, V. S.; Myagmarsuren, G.; Suslov, D. S.;
Darjaa, T.; Dorj, D.; Shmidt, F. K. Catal. Commun. 2008, 9, 1501. (c) Majumdar,
M.; Patra, S. K.; Kannan, M.; Dunbar, K. R.; Bera, J. K. Inorg. Chem. 2008, 47,
2212. (d) 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. (e) Drabent,
K.; Clunlk, Z.; Ozarowskl, A. Inorg. Chem. 2008, 47, 3358.
ꢀ
ꢀ
(10) Languerand, A.; Barnes, S. S.; Belanger-Chabot, G.; Maron, L.;
Berrouard, P.; Audet, P.; Fontaine, F.-G. Angew. Chem., Int. Ed. 2009, 48,
6695.
~
ꢀ
(11) Antinolo, A. C.-H., F.; Fernandez-Baeza, J.; Garcıa-Yuste, S.;
´
ꢀ
~
Otero, A.; Sanchez-Prada, J.; Villasenor, E. J. Organomet. Chem. 2000,
609, 123.

4062 Inorganic Chemistry, Vol. 49, No. 9, 2010
Cowie et al.
decrease in B-X bond energies in the order F > Cl > Br > I.
This order was recently demonstrated in the reactivity of a series
of late transition metal tris(N-tert-butylimazolyl)borane com-
plexes; [{κ4-B(mttBu)3}NiCl] reacts with I2 or CHBr3 to form
[{κ3-ClB(mttBu)3}NiX] (X = I or Br) and with XeF2 to form
[{κ3-FB(mttBu)3}NiCl], [{κ4-B(mttBu)3}NiY] (Y = NCS or N3)
reacts with I2 to form [{κ3-YB(mttBu)3}NiI], and [{κ4-B-
(mttBu)3}Fe(CO)2] reacts with I2 in CHCl3 to form [{κ3-ClB-
(mttBu)3}Fe(CO)I].13 Furthermore, simple boron halides have
considerable precedent as reagents for halide metathesis, for
example, [{(Me2N)(EtO)C}AuCl3] reacts with BBr3 to yield
[{(Me2N)(EtO)C}AuBr3], which reacts with BI3 to form
[{(Me2N)(EtO)C}AuI3].14
An interesting but as yet unrealized possibility for com-
plexes exhibiting metal-halide-borane bridging interactions
is their application in C-X bond activation chemistry, for
example, in C-C bond forming catalysis. A typical cycle for
C-C bond formation at palladium (e.g., Suzuki-Miyaura,
Stille, or Negishi coupling) involves oxidative addition of an
aryl-halide substrate, followed by transmetalation and reduc-
tive elimination. For C-X bond oxidative addition, the order
of reactivity is generally Ar-I > Ar-Br > Ar-Cl > Ar-F,
consistent with substantial increases in Ar-X bond strength
as group 17 is ascended (fluorine forms the strongest of all
single bonds to carbon).15,16 A mismatch between hard
fluoride ligands (resulting from Ar-F oxidative addition)
and a soft palladium(II) metal center may also conspire to
reduce the thermodynamic driving force for Ar-F oxidative
addition, especially in the absence of strong π-acceptor co-
ligands.16,17 We are interested in exploring the potential for
strong M-X-BR3 interactions to increase the thermody-
namic favorability of aryl-chloride and aryl-fluoride oxidative
addition, with a view toward eventual applications in C-C
bond forming catalysis.18,19
Ph2P-NtBu-AlR2 (R = Me or Et) ligand,20 (2) rate en-
hancements for the dehydrogenative coupling of PhSiH3 by
[(Me-Ind)NiMe(PPh3)] in the presence of Me2PCH2AlMe2
(the proposed intermediate in this reactivity is [(Me-Ind)-
NiMe{Me2PCH2AlMe2}], and a related rhodium complex,
[Cp*RhMe2(κ1-Me2PCH2AlMe2-OSMe2)], has also been
prepared),21 and (3) reaction of Na[H2B(mt)2] with [RhCl-
(CS)(PPh3)2] to form [LRhH(PPh3)] [L = {H(mt)2B}(Ph3P)-
CdS], presumably via the intermediate [{κ3-HB(mt)2}RhH-
(CS)(PPh3)].22 Reactions of this type rely on the availability
of a free pendant group 13 Lewis acid, so we are interested to
probe whether like chloride, the heavier halides (bromide and
iodide) engage in metal-halide-bridging. Such interactions
would be deleterious to cooperative activation reactivity in
ambiphilic ligand complexes, and are of broad significance
given the ubiquitous nature of halide ligands in organome-
tallic chemistry.
We report here a series of rhodium(I) halide complexes,
[RhX(CO)(TXPB)] (X = Cl, Br, I and F), as well as halide-free
[Rh(CO)(TXPB)][PF6], all of which have been investigated by
X-ray crystallography and NMR and IR spectroscopy. [RhX-
(CO)(TXPB)] complexes were chosen for study in this work,
rather than [PdX2(TXPB)] complexes, for the following rea-
sons: (1) Neutral rhodium(I) complexes contain only one halide
co-ligand; in dihalide complexes, halide substitution/abstraction
reactions may be complicated by reactivity at different sites,
coupled with the presence of only one pendant borane in TXPB
to coordinate or abstract a halide from the metal. (2) The pro-
ducts of aryl halide oxidative addition at palladium(0) also
contain only one halide ligand. (3) Rhodium-103 is 100% abun-
dant with a nuclear spin of 1/2, so can provide an additional
NMR handle to probe the strength of metal-phosphine and/or
metal-fluoride interactions. (4) Carbonyl stretching frequen-
cies provide valuable insight into electronic changes occurring at
rhodium because of halide substitution or abstraction.
Beyond C-X bond activation, ambiphilic ligands offer a
more general possibility for cooperative reactivity involving
both a metal and a pendant borane. Rare examples of this
type of reactivity include: (1) CO insertion reactions at iron or
manganese promoted by the pendant alane group of an
Results and Discussion
Borane-Bearing Rhodium Chloro Carbonyl Complex. In
2006 we communicated the synthesis of [RhCl(CO)(TX-
PB)] (1) (Scheme 1; Figure 3) as a precursor to [(TXPB)-
Rh(μ-CO)2Fe(CO)Cp].4 Complex 1 adopts a distorted
square planar geometry [S-Rh-CO= 171.3(3)°; P-Rh-
Cl = 172.64(8)°] and contains an uncommon metal-halide-
borane bridging interaction. The Rh-Cl bond length of
2.381(2) A is in good agreement with the Rh-Cl distances
in related [RhCl(CO)(PAr3)(SR2)]23 complexes, indicating
that the Rh-Cl bond is not substantially weakened by
triarylborane coordination. However, the B-Cl bond length
of 1.995(9) A does indicate a strong bonding interaction
between boron and the bridging chloride, since this distance is
(13) (a) Pang, K.; Tanski, J. M.; Parkin, G. Chem. Commun. 2008, 1008.
(b) Figueroa, J. S.; Melnick, J. G.; Parkin, G. Inorg. Chem. 2006, 45, 7056.
(14) Fischer, E. O.; Bock, M. J. Organomet. Chem. 1985, 287, 279.
(15) (a) Kiplinger, J. L.; Richmond, T. G.; Osterberg, C. E. Chem. Rev.
1994, 94, 373. (b) Grushin, V. V.; Alper, H. Chem. Rev. 1994, 94, 1047. (c)
Torrens, H. Coord. Chem. Rev. 2005, 249, 1957. (d) Murphy, E. F.; Murugavel,
R.; Roesky, H. W. Chem. Rev. 1997, 97, 3425. (e) Amii, H.; Uneyama, K. Chem.
Rev. 2009, 109, 2119. (f) Perutz, R. N.; Braun, T. Transition Metal-mediated C-F
Bond Activation. In Comprehensive Organometallic Chemistry III; Parkin, G.,
Ed.; Elsevier Ltd.: Oxford, 2007; Vol. 3, Chapter 1.26, Compounds of Groups
13-15, p 725. (g) For a recent example of aryl-fluoride reductive elimination from
palladium(II), see: Watson, D. A.; Su, M.; Teverovskiy, G.; Zhang, Y.; García-
Fortanet, J.; Kinzel, T.; Buchwald, S. L. Science 2009, 325, 1661.
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145.
(17) Doherty, N. M.; Hoffman, N. W. Chem. Rev. 1991, 91, 553.
(18) In addition to thermodynamic challenges associated with C-F bond
oxidative addition, theoretical studies have in several cases identified sub-
stantial kinetic barriers for this process (see refs 15a-e and 16). Recently,
phosphine-assisted aryl fluoride oxidative addition has been reported as an
alternative pathway for C-F bond activation, involving a four-centered
transition state containing the metal, ipso-carbon, fluorine, and phosphorus
atoms (see ref 19). The borane group of an ambiphilic ligand could in
principle assume a similar role [differing in the absence of a metal-ER3 (E =
B or P) interaction], also leading to reduced kinetic barriers for Ar-F
oxidative addition.
(20) (a) Labinger, J. A.; Miller, J. S. J. Am. Chem. Soc. 1982, 104, 6856. (b)
Grimmett, D. L.; Labinger, J. A.; Bonfiglio, J. N.; Masuo, S. T.; Shearin, E.;
Miller, J. S. Organometallics 1983, 2, 1325. (c) Labinger, J. A.; Bonfiglio, J. N.;
Grimmett, D. L.; Masuo, S. T.; Shearin, E.; Miller, J. S. Organometallics 1983, 2,
733.
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Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4063
Scheme 1. Preparation of Complexes 1-3
metal-bromide-borane interaction. However, molecules A
and B differ in the position of the bromide anion with respect
to the thioxanthene backbone; the C(12)-C(5)-B-Br tor-
sion angle is 76.9(7)° in molecule A, and -43.3(9)° in
molecule B [cf. 78.7(8)° in 1]. Only one isomer was observed
1
in the solution H and 31P NMR spectra of 2 down to
-70 °C, and only one carbonyl stretch was observed in the
IR spectrum of 2 in CH2Cl2 and Nujol. However, different
orientations of the metal-halide bond relative to the TXPB
ligand backbone must be involved in the fluxional process
responsible for CMe2 methyl group exchange.
Because of the inequivalent metal-TXPB binding modes
in molecules A and B, key bond lengths and angles in the
two molecules are significantly different. For example, the
B-Br distance in molecule A is 2.190(8) A while that in
molecule B is 2.267(9) A. These distances are appreciably
different from one another (see below for discussion), but
are both approximately 0.2-0.3 A longer than B-Br in the
neutral Lewis acid-Lewis base adducts Ph3PBBr3 (1.978-
2.013 A),27 PyBBr3 (1.96-2.01 A),28 and LBBr2, where L =
2-(dimethylaminomethyl)phenyl (2.01 and 2.02 A),29 high-
lighting the presence of a significant B-Br interaction in
only 0.10-0.13 A longer than that in chloroborate anions24
and chloroborane Lewis base adducts.25 The presence of a
strong B-Cl interaction in 1 is also supported by consider-
both A and B. The 11B NMR signal for 2 (δ 27 ppm; ω1/2
≈
P
able pyramidalization at boron [ (C-B-C) = 340(1)°]
and a broad singlet in the 11B NMR spectrum at 12 ppm (ω1/2
≈ 700 Hz), characteristic of 4-coordinate boron. The B-Cl
bond length in 1 is 0.1-0.3 A shorter than those in Bour-
issou’s metal-chloride-borane complexes (Table 1), consis-
tent with the enhanced Lewis acidity of the ArBPh2 acceptor
in TXPB relative to an ArBCy2 group (see Table 2 for key
spectroscopic and crystallographic data for complexes 1-5).
Borane-Bearing Rhodium Bromo Carbonyl Complex.
Substitution of the chloride co-ligand in 1 to form [RhBr-
(CO)(TXPB)] (2) was achieved using bromotrimethylsilane
in CH2Cl2 (Scheme 1), providing complex 2 as an orange
powder in 74% isolated yield. A doublet was observed in the
31P NMR spectrum at 64.5 ppm (1JP,Rh = 164.0 Hz), shifted
4.5 ppm to higher frequency of complex 1. The CO stretching
frequency is 2013 cm-1 in Nujol and 2008 cm-1 in CH2Cl2 by
IR spectroscopy; very similar values were reported for
complex 1 [2010 cm-1(Nujol); 2013 cm-1(CH2Cl2)].4 Com-
plex 2, like complex 1, is fluxional in solution, giving a single
resonance in the room temperature 1H NMR spectrum for
the CMe2 group. At low temperature these methyl substit-
uents become inequivalent with a coalescence temperature
(Tc) of 211(2) K for 2 (ΔGq at Tc = 39.7(5) kJ/mol).26 For
comparison, Tc for 1 is 254(2) K, leading to a value of 47.7(6)
kJ/mol for ΔGq at this temperature.
900 Hz) is also closer to that of 1 (12 ppm) than free TXPB
(69 ppm),2 substantiating the presence in solution of a
significant B-Br interaction in 2.
The Rh-Br and Rh-S distances in molecules A and B of
2 are also notably different; Rh-Br is 2.4519(11) A in mole-
cule A and 2.5161(11) A in molecule B, while Rh-S is
2.380(2) A in molecule A and 2.304(2) A in molecule B. The
shorter Rh-Br distance in molecule A is similar to those in
closely related [RhBr(CO)(PPh3)2] (2.453 A)30 and [nBu4N]-
[RhBr(NBD)(iPr2P(C6H4)BPh3-p)] (NBD = norbornadi-
ene) (2.465 A).31 However, Rh-Br in molecule B is more
comparable with that in [RhBr(CO)(Me2carbox)] [Me2-
carbox=1-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-3-mesity-
limidazol-2-ylidene] (2.507 A)32 in which the bromo ligand
experiences the high trans-influence of an N-heterocyclic
carbene. By contrast, the Rh-S distance in molecule B is
more similar to that in closely related borane-free complexes,
while that in molecule A is significantly longer; Rh-S dis-
tances of 2.293 and 2.286 A were reported for [(nacnacXyl)-
Rh(κ1S-dbt)2] [nacnacXyl=CH{C(Me)NXyl}2;Xyl=C6H3-
Me2-2,6; dbt = dibenzo[b,d]thiophene],33 and Pd-S dis-
tances of 2.290 and 2.300 A were reported for [PdCl2(L)]
[L = 6-(4-hydroxy-2-phenylsulfanylphenoxy)-5,7-dioxa-6-
phosphadibenzo[a,c]cycloheptene]34 and [PdCl2{κ2-PhS-
(C6H4)CH2PPh2-o}],35 respectively (note: the covalent ra-
dius of Pd is 1.39 A versus 1.42 A for Rh).36
X-ray quality crystals of 2 hexane were grown from a
3
saturated solution of 2 in hexanes cooled to -30 °C for seve-
ral days (Figure 4, Tables 2-3). The X-ray crystal structure
contains two independent molecules of 2 (A and B) within
the unit cell. For both molecules, the geometry at rhodium
is distorted square planar with S-Rh-CO and P-Rh-Br
angles of 173.4(3)° and 176.34(6)° for molecule A, and
176.0(3)° and 169.56(5)° for molecule B; closely analog-
ous S-Rh-CO and P-Rh-X angles were observed for
complex 1. In addition, both molecules of 2 exhibit a unique
(27) Weller, F.; Mohlen, M.; Dehnicke, K. Z. Kristallogr. - New Cryst.
Struct. 1997, 212, 159.
(28) Lijima, K.; Oonishi, I.; Shibata, S. Chem. Lett. 1983, 251.
(29) Brown, D. S.; Carmalt, C. J.; Cowley, A. H.; Decken, A.; Isom, H. S.
Heteroatom Chem. 1998, 9, 79.
(30) Steyl, G.; Kirsten, L.; Muller, A.; Roodt, A. Acta Crystallogr. 2006,
E62, m1127.
(31) Thomas, C. M.; Peters, J. C. Inorg. Chem. 2004, 43, 8.
ꢀ
(32) Cesar, V.; Bellemin-Laponnaz, S.; Gade, L. H. Eur. J. Inorg. Chem.
2004, 3436.
(33) Willems, S. T. H.; Budzelaar, P. H. M.; Moonen, N. N. P.; Gelder,
R. D.; Smits, J. M. M.; Gal, A. W. Chem.;Eur. J. 2002, 8, 1310.
€
€
(24) Brauer, D. J.; Burger, H.; Chebude, Y.; Pawelke, G. Inorg. Chem.
(34) Kranich, R.; Eis, K.; Geis, O.; Muhle, S.; Bats, J. W.; Schmalz, H.-G.
1999, 38, 3972.
Chem.;Eur. J. 2000, 6, 2874.
(25) (a) Cross, W. I.; Lightfoot, M. P.; Mair, F. S.; Pritchard, R. G. Inorg.
(35) Dilworth, J. R.; W, C. A. M. v. B.; Pascu, S. I. Dalton Trans. 2005, 2151.
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ꢀ
(36) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.; Echeverrıa,
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Chem. 2000, 39, 2690. (b) Narula, C. K.; Noth, H. Inorg. Chem. 1985, 24, 2532.
(26) Gunther, H., NMR Spectroscopy; Thieme Verlag: Stuttgart, 1992.
ꢀ
J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008, 2832.

4064 Inorganic Chemistry, Vol. 49, No. 9, 2010
Cowie et al.
Table 1. Key Crystallographic and Spectroscopic Values for Structurally Characterized Literature Complexes Exhibiting a M-Cl-B Bridging Interactiona,b
P
Compound
M-Cl [A]
B-Cl [A]
M-Cl-B [deg]
(C-B-C) [deg]
11B NMR [δ, ppm]
Reference
[{PdCl(TXPB)}2]
[(p-cymene)RuCl2{NC5H4(CH2BCy2)-o}]d
2.362(2)
2.419(2)
2.419(2)
2.352(1)
2.344(1)
2.263(2)
2.280(1)
2.4641(9)
2.403(3)
N/A
1.981(8)
2.156(11)
2.103(9)
2.165(2)
2.117(2)
2.334(7)
2.109(4)
2.007(4)
2.078(14)
N/A
104.0(2)
111.0(3)
110.0(3)
101.10(6)
107.22(5)
NR
111.94(12)
88.38(11)
80.2(4)
N/A
336
346
2
22
3
5
[(η3-allyl)PdCl{PiPr2(C6H4)BCy2-o}]
[(NBD)RhCl{PiPr2(C6H4)BCy2-o}]
[PdCl2{PiPr2(C6H4)BCy2-o}]2
349
343
354
344
342
347
N/A
N/A
47
6
7
7
7
8
9
10
10
26c
ND
22
[PdCl2(PPh3){PiPr2(C6H4)BCy2-o}]
[{η5-C5H4B(C6F5)2}(Ind)TiCl2]
[(κ3-Tp)OsCl2(NPhBPh2)]
4.8
NR
36
[(IMes)2PtHCl{BC5H3(o-SiMe3)(p-iPr)}]
[(IMes)2PtHCl{BC5H4(SiMe3)-o}]
N/A
N/A
N/A
39
a See Table 2 for [RhCl(CO)(TXPB)]. b N/A = not applicable; ND = not detected; NR = not reported. c Solid-state NMR chemical shift. d Two
different orientations of the molecule were present in the asymmetric unit cell.
Table 2. Spectroscopic and Crystallographic Data for Complexes 1-5
2
5a
1
molecule A
molecule Bi
3
4
cation
metal and co-ligands
31P NMR [δ, ppm]
11B NMR [δ, ppm]
19F NMR [δ, ppm]
1JP,Rh [Hz]
Rh Cl CO
60.0
12
Rh Br CO
64.5
27
Rh I CO
67.2
56
Rh F CO
52.2
4
-186
166.2
75/19
6.2
Rh CO
64.9
57
161.3
77/18
164.0
77/15
166.8
74/14
166.8
72/13
1JC,Rh/2JC,P for CO [Hz]
2JP,F [Hz]
ν(CO)(CH2Cl2/Nujol) [cm-1
Tc for CMe2 exchange (K)b
]
2013/2010
254(2)
47.7(6)
2008/2013
211(2)
39.7(5)
2002/2004
210(2)
39.5(5)
2011/2008
274(2)
2038/2028
312(2)
61.2(8)
ΔG‡ at Tc (kJmol-1 b
)
51.5(7)
3.261(3)
2.564(5)
2.336(4)
3.231(5)
1.816(5)
2.2176(13)
2.4045(12)
1.445(6)
76.0(2)
168.02(17)
Rh-X [A]
Rh-Cortho [A]
Rh-Cipso [A]
2.381(2)
2.4519(11)
2.5161(11)
2.6640(7)
2.797(3)
2.362(2)
2.557(3)
1.870(3)
2.2394(7)
2.3234(6)
Rh B [A]
Rh-CO [A]
3.470
3.647(9)
1.829(8)
2.202(2)
2.3797(17)
2.190(8)
103.4(2)
173.4(3)
176.34(6)
3.316(9)
1.841(7)
2.196(2)
2.3044(17)
2.267(9)
87.6(2)
3.502(7)
1.855(7)
2.2237(14)
2.2997(14)
3.125(7)
73.96(12)
163.8(2)
169.58(4)
3 3 3
1.817(11)
2.205(2)
2.379(2)
1.995(9)
104.6(3)
171.3(3)
172.64(8)
Rh-P [A]
Rh-S [A]
B-X [A]
Rh-X-B [deg]
S-Rh-CO [deg]
P-Rh-X [deg]
P-Rh-CC(cent)/BC(cent)
176.0(3)
169.56(5)
172.48(9)
c
160.53(16)
1.226
331.2(7)
0.518
1.1(6)
154.20(9)
0.531
358.6(4)
0.110
4.9(3)
Rh-(PCCSplane) [A]d
1.023
340(1)
0.426
-13.3(10)
78.7(8)
42.8
0.988
342(1)
0.397
-14.8(9)
76.9(7)
42.4
0.271
339(1)
0.437
13.0(11)
-43.3(9)
47.9
0.144
356.8(9)
0.164
16.6(8)
-53.1(6)
52.9
P
(C-B-C) [deg]
B-(CCCplane) [A]e
S-C(12)-C(5)-B [deg]f,g
C(12)-C(5)-B-X [deg]f,g
Ligand Bend [deg]h
-46.5(6)
41.6
54.1
a NMR spectroscopic data for complex 5 is for the cation only. b Tc is the coalescence temperature and ΔGq is for CMe2 methyl exchange. c CC(cent) and
BC(cent) represent the centroid position between C(42)-C(43) and B(1)-C(42), respectively. d PCCSplane = P(1)-C(4)-C(11)-S(1). e CCCplane =
C(5)-C(36)-C(42). f Torsion angles are for the molecules as shown in Figures 3-6, and 8. g Positive torsion angles indicate that boron or the B-X bond
is oriented up into the fold of the thioxanthene backbone. h Ligand Bend = the angle between the C(1)-C(2)-C(3)-C(4)-C(10)-C(11) and
C(5)-C(6)-C(7)-C(8)-C(12)-C(13) planes (an angle of 0° would correspond to a planar thioxanthene backbone). i Molecule B of complex 2 uses a
different numbering scheme; substitute B(1), P(1), C(1)-C(13),C(36), C(42) and C(43) for B(2), P(2), C(49)-C(61), C(84), C(90) and C(91).
A final key structural parameter in the description of
complex 2 is the Rh-Br-B angle, which is 103.4(2)° in
molecule A, but only 87.6(2)° in molecule B (cf. 104.6(3)°
in 1). Both the acute Rh-Br-B angle and the short Rh-S
distance in molecule B are likely a consequence of the
alternative binding mode of the rigid TXPB ligand.
Elongation of both the Rh-Br and the B-Br bonds in
molecule B may perhaps be attributed to increased p-
character in Rh-Br and B-Br coordination because of a
Rh-Br-B angle constrained to less than 90°. For Al2X6
(X = Cl or Br), calculations have shown an ∼0.01 A
increase in the bridging Al-X bond lengths upon
narrowing of the Al-X-Al angle by only 4-5° (from
close to 90° by bending of the Al(Xterminal)2 groups out of
the plane with the two bridging halide ligands).37
Borane-Bearing Rhodium Iodo Carbonyl Complex.
Treatment of complex 1 with iodotrimethylsilane pro-
vided [RhI(CO)(TXPB)] (3) (Scheme 1) as a rust-red
powder in 83% isolated yield. The 31P NMR spectrum
of 3 consists of a doublet at 67.2 ppm (1JP,Rh = 166.8 Hz),
shifted 7.2 ppm to higher frequency of complex 1. A very
(37) Aarset, K.; Shen, Q.; Thomassen, H.; Richardson, A. D.; Hedberg,
K. J. Phys. Chem. A 1999, 103, 1644.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4065
Figure 4. Solid-state structure of [RhBr(CO)(TXPB)] hexane (2) hexane with ellipsoids at 50% probability. tert-Butyl and CMe2 methyl groups,
3
3
hydrogen atoms, and solvent are omitted for clarity.
Table 3. Crystallographic Data Collection and Refinement Parameters for Complexes 1-5
1 hexane
3
2 hexane
3
3 hexane
3
4 1.5CH2Cl2
3
5 CH2Cl2
3
formula
formula wt
T (K)
C54H62BClOPRhS
939.24
173(2)
C54H62BBrOPRhS
983.70
100(2)
C54H62BIOPRhS
1030.69
100(2)
C49.5H51BCl3FOPRhS
964.00
100(2)
C49H50BCl2F6OP2RhS
1047.51
173(2)
cryst. syst.
space group
a (A)
b (A)
c (A)
R [deg]
β [deg]
monoclinic
P2(1)/n
13.773(3)
20.799(5)
17.532(5)
90
103.832(5)
90
4877(2)
4
1.279
0.517
1968
0.35 ꢀ 0.04 ꢀ 0.03
1.70-18.15
13733
3396
98.9
analytical
0.9846, 0.8396
1.116
triclinic
P1
monoclinic
P2(1)/c
20.985(5)
10.931(2)
21.318(4)
90
94.691(4)
90
4873.7(18)
4
1.405
1.097
2112
0.17 ꢀ 0.10ꢀ 0.04
1.92-25.64
37759
9041
98.2
numerical
0.9575, 0.8355
0.936
triclinic
P1
triclinic
P1
13.784(4)
16.784(4)
22.340(6)
78.308(5)
72.860(5)
87.227(5)
4836(2)
4
1.351
1.293
2040
0.28 ꢀ 0.13 ꢀ 0.05
1.55-26.57
42443
10.480(2)
14.606(3)
15.417(3)
84.035(4)
81.671(4)
76.197(4)
2261.7(8)
2
1.416
0.677
994
0.22 ꢀ 0.16 ꢀ 0.03
1.34-26.5
26414
13.7285(11)
13.7787(10)
14.0510(11)
69.0590(10)
84.6330(10)
83.8570(10)
2463.7(3)
2
1.412
0.620
1072
0.58 ꢀ 0.22 ꢀ 0.08
1.55-30.57
36483
γ [deg]
volume [A3]
Z
density (calcd; mg/m3)
μ (mm-1
F(000)
)
crystal size (mm3)
θ range for collection [deg]
no. of reflns collected
no. of indep reflns
completeness to θ max (%)
absorption correction
max and min transmission
GOF on F2
19853
98.2
numerical
0.9382, 0.7135
0.885
9232
98.4
numerical
0.9800, 0.8653
0.970
14719
97.3
numerical
1.000, 0.712
1.027
final R1 [I > 2σ(I)] (%)
3.79
7.22
4.86
5.69
4.53
broad singlet at 56 ppm (ω1/2 ≈ 1800 Hz) was observed in
interaction. As with 2, complex 3 is fluxional in solution,
evidenced by chemically equivalent CMe2 methyl-substit-
uents in the H NMR spectrum at room temperature
the 11B NMR spectrum, which is shielded by only 13 ppm
1
relative to free TXPB, consistent with a weak B
I
3 3 3

4066 Inorganic Chemistry, Vol. 49, No. 9, 2010
Cowie et al.
Figure 5. Solid-state structure of [RhI(CO)(TXPB)] hexane (3) hexane with ellipsoids at the 50% probability level. tert-Butyl and CMe2 methyl groups,
3
3
hydrogen atoms, and solvent are omitted for clarity.
(coalescence temperature = 210(2) K). The ΔGq value for
CMe2 methyl group exchange at Tc is 39.5(5) kJ/mol,
which is equal within error to ΔGq for complex 2 (39.7(5)
kJ/mol at 211(2) K).
(2.237-2.272 A).43 The long B I distance in 3 may be
3 3 3
attributed to the incompatibility of a hard borane Lewis acid
with a soft iodide anion (B-X bond strengths decrease in the
order F > Cl > Br > I, and no iodoborate anions have been
structurally characterized to-date), in combination with an
extremely acute Rh-I-B angle. In keeping with the long
X-ray quality crystals of 3 hexane were obtained by
3
cooling a saturated solution of 3 in hexanes to -30 °C for
several days (Figure 5, Tables 2-3). The S-Rh-CO and
P-Rh-I bond angles are 163.8(2)° and 169.58(4)°, re-
spectively, highlighting a substantially distorted square
planar geometry. The Rh-P and Rh-CO bond distances
are 2.2237(14) and 1.855(7) A, respectively; Rh-P is
slightly longer in 3 than in 1 and 2 (Table 2), consistent
with the higher trans-influence of iodide relative to chlo-
ride and bromide,38 and the absence of a strong halide-
borane interaction in 3. The orientation of iodide relative
to the thioxanthene backbone of 3 is analogous to that in
molecule B in the unit cell of 2, with a C(12)-C(5)-B-I
torsion angle of -53.1(6)°. As a consequence, the Rh-S
distance is 2.2997(14) A, which is similar to that in
molecule B of complex 2, but much shorter than those
in complex 1 and molecule A of complex 2 (Table 2). The
Rh-I-B bond angle in 3 is also extremely acute
[73.96(12)°]. A similar situation was observed in molecule
B of 2 [Rh-I-B = 87.6(2)°], while the Rh-X-B angles
are 103-105° in complex 1 and molecule A of 2. The more
acute Rh-X-B angle in 3, relative to that in molecule B
of complex 2, is likely the result of a longer Rh-X bond
and the absence of a strong halide-borane interaction in 3.
The Rh-I bond distance of 2.6640(7) A compares well to
those in similar rhodium compounds, where an iodide is
bound trans to a phosphine. These compounds include [{(S)-
diop}Rh(PPh3)I] [(S)-diop = (S)-2-(diphenylphosphino)-
20-methoxy-1,10-binaphthyl]39 and [(BINAP)Rh(CO)I]
[BINAP = 2,20-bis(diphenylphosphino)-1,10-binaphthyl],40
with Rh-I bond distances of 2.704 and 2.686 A, respectively.
However, a key feature of complex 3 is the extremely long
B
I distance and the high frequency 11B NMR chemical
3 3 3
P
shift, boron in 3 is very nearly planar [ (C-B-C) =
356.8(9)°].
The CO stretching frequency for 3 (2004 cm-1 in Nujol
and 2002 cm-1 in CH2Cl2) is significantly lower than
those in complexes 1 and 2, indicating increased electron
density at the metal. In related series of d8 complexes with
cis-disposed halide and carbonyl ligands, the CO stretch-
ing frequency is effectively unchanged after substitution
of chloride for iodide; see for example [(BINAP)Rh-
(CO)X] (X = Cl or I)40 and [Rh(DTBPMB)X(CO)] [X =
Cl or I; DTBPMB = 1,2-(tBu2PCH2)2C6H4].44 The lower
CO stretching frequency for 3 relative to 1 and 2 is
therefore consistent with less effective donation from
the halide to the metal center in 1 and 2 as a result of
halide-borane coordination. However, all or part of the
shift in ν(CO) could also be due to predominance of a
different TXPB bonding mode in complex 3 with a short-
er Rh-S distance (as observed in the solid state struc-
ture). It is therefore not possible to draw any definite
conclusions from this data.
Zwitterionic [Rh(CO)(TXPB-F)]. Treatment of 1
with [NMe4]F in CH2Cl2 gave [Rh(CO)(TXPB-F)] (4)
[TXPB-F = {5-(2,7-di-tert-butyl-4-diphenylphosphino-
9,9-dimethylthioxanthenyl)}diphenylfluoroborate] as an
orange-red powder in an isolated yield of 72%
(Scheme 2). Reaction of 1 with [NBu4][Ph3SiF2] provided
an alternative route to complex 4, but because of the
formation of similarly soluble Ph3SiF as a reaction by-
product, isolation of pure 4 via this method proved
problematic. Complex 4, unlike 1-3 is not thermally
stable at room temperature, being substantially decom-
posed after 24 h in solution (CH2Cl2). A key spectroscopic
feature for complex 4 is a singlet in the 11B NMR
spectrum at 4 ppm (ω1/2 ≈ 350 Hz), characteristic of 4-
coordinate boron, and shifted 8 ppm to lower frequency
of 1, indicating the presence of a very strong B-F
interaction. Moreover, a broad singlet was observed in
B
I distance of 3.125(7) A, which is approximately
3 3 3
0.8-0.9 A longer than B-I distances in the Lewis acid-
Lewis base adducts Me2NCHO-BI3 (2.224-2.262 A),41
(IEtC=CEt)BI2-Py (2.275, 2.294 A)42 and Me3P-BI3
(38) Housecroft, C. E.; Sharpe, A. G., Inorganic Chemistry, 2nd ed.;
Pearson Education Limited: London, 2005.
(39) Brunner, H.; Zettler, C.; Zabel, M. Z. Anorg. Allg. Chem. 2003, 629,
1131.
(40) Lamb, G.; Clarke, M.; Slawin, A. M. Z.; Williams, B.; Key, L. Dalton
Trans. 2007, 5582.
(41) Corey, E. J.; Rohde, J. J.; Fischer, A.; Mihai, D. A. Tetrahedron Lett.
1997, 38, 33.
(43) Black, D. L.; Taylor, R. C. Acta Crystallogr., Sect. B: Struct.
Commun. 1975, 31, 1116.
(42) Nie, Y.; Schwiegk, S.; Pritzkow, H.; Siebert, W. Eur. J. Inorg. Chem.
2004, 1630.
(44) Jimenez-Rodriguez, C.; Pogorzelec, P. J.; Eastham, G. R.; Slawin,
A. M. Z.; Cole-Hamilton, D. J. Dalton Trans. 2007, 4160.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4067
Figure 6. Solid-state structure of[Rh(CO)(TXPB-F)] 1.5CH2Cl2 (4) 1.5CH2Cl2 with ellipsoids at50% probability. tert-Butyl and CMe2 methyl groups,
3
3
hydrogen atoms, and solvent are omitted for clarity.
Scheme 2. Preparation of Complexes 4 and 5
[Ar=1-(8-(trimethylammonio)methylnaphthalene)] (1.486
A),49 and K[FB(Ph)(CF3)2] (1.452 A).50 Boron in 4
P
also exhibits a greater degree of pyramidalization [ (C-
B-C) = 331.2(7)°] than that in compounds 1-3 (Table 2).
The Rh F distance of 3.261(3) A in complex 4 is well
3 3 3
outside of the sum of the atomic radii for the two elements
(1.99 A),36 and approaches the sum of the van der Waals
radii (3.51 A).51
To complete a highly distorted square planar geometry
at rhodium [S-Rh-CO = 168.02(17)°, P-Rh-cent =
160.53(16)°; cent = the centroid position between Cipso
and Cortho], a phenyl ring in the FBAr3 unit is η2-bound to
rhodium via the ipso- and ortho-carbon atoms. The
Rh-Cipso distance of 2.336(4) A in 4 is comparable with
those in other rhodium(I) complexes featuring an η2-
bound aryl ring, including [Rh(CO)(POPheph)][ClO4]
[POPheph = κ1-PPh2POCH(Ph)CH(Me)NMe{CH(Ph)-
(η2-Ph)}] (2.334 A)52 and [Rh(PEt3)2{κ1-OC(Ph2)(η2-
Ph)}] (2.350 A).53 By contrast, the Rh-Cortho distance
of 2.564(5) A in 4 is significantly longer (cf. 2.449 A and
2.398 A, respectively, in the literature complexes above),
indicative of a weaker interaction.
Fluxional NMR Behavior of [Rh(CO)(TXPB-F)]. De-
spite η2-arene coordination in the solid state, complex 4 is
fluxional in solution at room temperature; the CMe2 methyl
groups of the thioxanthene backbone are equivalent
[although a coalescence temperature of 274(2) K (ΔGq at
Tc = 51.5(7) kJ/mol) for CMe2 methyl group exchange does
suggest a higher activation barrier for this process in 4,
compared with complexes 1-3 (assuming that ΔSq is not
large and negative)], and the phenyl rings on both boron
and phosphorus undergo pairwise exchange. At -50 °C,
two distinct B-phenyl and P-phenyl rings are observed, but
the ortho and meta CH positions of each ring remain
equivalent down to -80 °C. Given the complexity of the
aryl region in complex 4, this assignment was verified by
low-temperature 2D COSY and DEPT-135 NMR spec-
troscopy of d10-4 in which both P-phenyl rings are perdeut-
erated (Figure 7). The exchange process responsible for
equivalence of the ortho and meta positions on each of the
the 19F NMR spectrum at -186 ppm (ω1/2 ≈ 180 Hz), char-
acteristic of fluorine bound to quadrupolar boron. These
NMR data compare well with the related triarylfluoroborate
compounds [FB(C6F5)2{C6F4(PiPr3)-p}] (11B NMR δ
-0.89 ppm; 19F NMR δ -191.37 ppm),45 [F(Tip)B(C6H4-
o)2PMe2] (Tip = 2,4,6-triisopropylphenyl) (11B NMR δ 3.7
ppm; 19F NMR δ -162.44 ppm),46 and [K{[2.2.2]-cryp-
tand}][FB(Ant)3] (Ant = 9-anthracenyl) (11B NMR δ 6.04
ppm; 19F NMR δ -133.32 ppm).47
X-ray quality crystals of 4 1.5CH2Cl2 were grown by
3
slow diffusion of hexanes into a solution of 4 in CH2Cl2 at
-30 °C. In the solid-state, as was observed spectroscopi-
cally in solution, the fluoride ligand does not form a strong
interaction with the metal center (Figure 6, Tables 2-3).
Rather, it binds preferentially to boron producing a zwit-
terionic complex containing a 4-coordinate anionic borate
and a cationic rhodium center. The B-F bond distance
in 4 is 1.445(6) A, which lies at the shorter end of the
range for B-F bond distances in fluoroborates such
as [CPh3][FB{C6F4(C6F5)-o}3] (1.472 A),48 [FB(Mes)2Ar]
(49) Chiu, C.-W.; Gabbaı, F. P. J. Am. Chem. Soc. 2006, 128, 14248.
(50) Brauer, D. J.; Burger, H.; Hubinger, R.; Pawelke, G. Z. Anorg. Allg.
Chem. 2001, 627, 679.
(51) (a) Bondi, A. J. Phys. Chem. 1964, 68, 441. (b) Nag, S.; Banerjee, K.;
Datta, D. New J. Chem. 2007, 31, 832.
(45) Welch, G. C.; Cabrera, L.; Chase, P. A.; Hollink, E.; Masuda, J. D.;
Wei, P.; Stephan, D. W. Dalton Trans. 2007, 3407.
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Chem. Lett. 2007, 36, 976.
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Horton, P. N.; Bochmann, M. Dalton Trans. 2006, 2415.
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metallics 1999, 18, 4706.
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128, 3124.

4068 Inorganic Chemistry, Vol. 49, No. 9, 2010
Cowie et al.
Figure 7. Aromatic regions of the 1H and DEPT-135 NMR spectra of 4 and d10-4 at -50 °C, aromatic region of the 2D COSY NMR spectrum for d10-4 at
-50 °C, and 31P NMR spectra for 4 at 25, -5, and -15 °C. All NMR spectra are in CD2Cl2.
two B-phenyl rings (while maintaining inequivalence of the
CMe2 methyl, B-phenyl and P-phenyl groups) in 4 must
involve rotation around the B-C bonds. This would require
loss of any η2-arene interaction, presumably with pivoting
about B(1)-C(5) (see Figure 8) to position the previously
coordinated B-phenyl ring further from rhodium and
bring fluorine into closer proximity with the metal. The
η2-arene interactions in [Rh(CO)(POPheph)][ClO4] and
[Rh(PEt3)2{κ1-OCPh2(η2-Ph)}] (vide supra) also are not
maintained on the NMR time scale in solution at room
temperature.52,53
For example, in various tetrakis(diphenylphosphino)-
ferrocene ligands, 31P-31P through-space coupling was
observed only at P P distances of 4.9 A and below.56,57
In addition, for a range of rigid fluorine-containing
3 3 3
compounds, 19F-19F through-space coupling was found
to decay exponentially with increasing F F distance,
3 3 3
falling to 2 Hz at an F F distance of 4.2 A.58 Similarly,
in triflone-bearing phosphoramidite ligands, through-
3 3 3
space 19F-31P coupling was calculated (using Me2NP-
(OH)2 F4C as a model) to be significant only at dis-
3 3 3
tances below 4.0-4.9 A,59 depending on the angle
between the interacting phosphorus lone pair and the
trifluoromethyl group.60
31P-19F NMR Coupling and ν(CO) in [Rh(CO)-
(TXPB-F)]. Interestingly, despite the long P F dis-
3 3 3
tance of 4.830(3) A in the X-ray crystal structure of 4,
31P-19F coupling is observed in the solution 31P NMR
spectrum at room temperature (δ52.2 ppm; 1JP,Rh = 166 Hz,
JP,F = 6.2 Hz; Figure 7). This small coupling could poten-
tially occur via a through-bond or a through-space
mechanism. For comparison, the trans-2JP,F coupling
constants in borane-free rhodium(I) fluoride complexes
such as [RhF(PPh3)3], [RhF(PPh3)2(PPh2F)], and [Rh2(μ-
F)2(PPh3)4] are 172, 217, and 196 Hz, respectively, and the
cis-2JP,F coupling constants for [RhF(PPh3)3] and
[RhF(PPh3)2(PPh2F)] are 28.5 and 27 Hz, respectively.54
Through-space coupling in solution (direct spin-spin
coupling) is a result of non-bonding interactions between lone
pairs, and decreases in strength rapidly as the distance between
coupling nuclei exceeds the sum of the van der Waals radii.55
These couplings represent an ideal situation involving
lone pair-lone pair interactions, but in compound 4, the
lone pair on phosphorus is bound to rhodium. Hierso
et al. have reported that in [(κ2P1P2-L)MX2] (M = Ni and
Pd; L = 1,10,2,20-tetrakis(diphenylphosphino)-4,40-di-
tert-butylferrocene; X = Cl or Br), through-space cou-
pling can be transmitted via an interaction between a free
phosphine lone pair and the metal-phosphine bonding
pair. However, the trans-annular through-space JPP cou-
plings in [(κ2P1P2-L)PdCl2] are only 24.0 and 6.4 Hz,
despite relatively short P P distances of 3.8 and 4.4 A,
respectively. On the basis of these and other trans-annular
3 3 3
(56) Hierso, J.-C.; Fihri, A.; Ivanov, V. V.; Hanquet, B.; Pirio, N.;
ꢁ
Donnadieu, B.; Rebiere, B.; Amardeil, R.; Meunier, P. J. Am. Chem. Soc.
2004, 126, 11077.
(57) Thomas, D. A.; Ivanov, V. V.; Butler, I. R.; Horton, P. N.; Meunier,
P.; Hierso, J.-C. Inorg. Chem. 2008, 47, 1607.
(58) Arnold, W. D.; Mao, J.; Sun, H.; Oldfield, E. J. Am. Chem. Soc. 2000,
122, 12164.
(54) (a) Grushin, V. V.; Marshall, W. J. J. Am. Chem. Soc. 2004, 126,
3068. (b) Macgregor, S. A.; Roe, D. C.; Marshall, W. J.; Bloch, K. M.;
Bakhmutov, V. I.; Grushin, V. V. J. Am. Chem. Soc. 2005, 127, 15304. (c)
(59) CF3 rotation averaged JP,F values were calculated as a function of
ꢀ
Marshall, W. J.; Aullon, G.; Alvarez, S.; Dobbs, K. D.; Grushin, V. V. Eur. J.
P
C distance. This was converted to a closest-approach P F distance by
3 3 3
3 3 3
Inorg. Chem. 2006, 3340.
subtraction of 1.32 A (the C-F distance in CF4).
(55) Mallory, F. B.; Mallory, C. W. Coupling Through Space in
Organic Chemistry. In Encyclopedia of Nuclear Magnetic Resonance; Wiley:
Chichester, 1996; Vol. 3, pp 1495-1497.
(60) Kruck, M.; Munoz, M. P.; Bishop, H. L.; Frost, C. G.; Chapman,
€
C. J.; Kociok-Kohn, G.; Butts, C. P.; Lloyd-Jones, G. C. Chem.;Eur. J.
2008, 14, 7808.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4069
Figure 8. Solid-state structure of [Rh(CO)(TXPB)][PF6] CH2Cl2 (5) CH2Cl2 with ellipsoids at the 50% probability level. tert-Butyl and CMe2 methyl
groups, the PF6 counteranion, hydrogen atoms, and solvent are omitted for clarity.
3
3
JPP coupling constants, Hierso et al. concluded that lone
pair-bonding pair interactions are less effective for
transmission of through-space coupling than lone
pair-lone pair interactions (because of reduced direc-
tionality in the former).57
A final important spectroscopic parameter for 4 is the
CO stretching frequency, which is 2008 cm-1 in Nujol and
2011 cm-1 in CH2Cl2. Zwitterionic 4 might be expected to
exhibit a significantly higher carbonyl stretching frequency
than neutral 1 and 2, but instead the frequencies are compar-
able (Table 2). The following factors must therefore compen-
sate for the increase in positive charge at rhodium: (1) the
η2-interaction between rhodium and a phenyl ring of the
fluoroborate group in TXPB-F, and (2) enhanced electron
donor properties of an anionic TXPB-F ligand relative to
neutral TXPB. Substantially more effective electron-donation
On the basis of the long P F distance in the X-ray
3 3 3
crystal structure of 4, the strong angular dependence of
through-space coupling,59-61 and the requirement for cou-
pling to occur via a lone pair-bonding pair interaction
rather than a lone pair-lone pair interaction, through-space
coupling in 4 seems unlikely. However, it is interesting to
note that the magnitude of the JP,F coupling decreases with
decreasing temperature (JP,F = 6.2, 5.1, 4.3, 3.5, 2.7, 1.4,
and 0 Hz at 25, 15, 10, 5, 0, -5, and -15 °C, respectively;
Figure 7). Significant temperature dependencies (positive
and negative) have been observed for through-space cou-
plings in molecules of intermediate rigidity, where the ob-
served coupling is a time-averaged value from all accessible
solution conformations. For example, positive temperature
dependencies were reported for through-space coupling in a
triflone-bearing phosphoramidite (JP,F = 6.5 Hz at 100 °C
and 1.7 Hz at -58 °C),60 P(C6H4CF3-o)xPh(3-x) (x = 1-3;
for x = 2, JP,F = 54.5 Hz at 117 °C and 51.1 Hz at
-43 °C),62 C6H4F(CF3)-o (JF,F = 13.7 Hz at 97 °C and
11.2 Hz at -62 °C)63 and C6H4(CF3)(SeCN)-o (JF,Se ≈ 51
Hz at 80 °C and 42 Hz at -40 °C),64 while a large negative
temperature dependency was reported for through-space
coupling in C6H4(CH2F)(SeCN)-o (JF,Se ≈ 77 Hz at 20 °C
and 104 Hz at -90 °C).64,65 The JP,F coupling in 4 could
therefore be assigned as a through-space coupling facilitated
-
has previously been reported for anionic R2B(CH2PR02)2
-
and m-Ph3B(C6H4)PiPr2 ligands relative to neutral R2Si-
(CH2PR02)2 and m-Ph3Si(C6H4)PiPr2 analogues.31,66
Cationic [Rh(CO)(TXPB)][PF6]. A halide-free rho-
dium-TXPB cation was targeted to gain additional in-
sight into the electronic environment in zwitterionic 4.
Treatment of 1 with Tl[PF6] in CH2Cl2 yielded [Rh(CO)-
(TXPB)][PF6] (5) as bright orange crystals in an isolated
yield of 92%. Complex 5 is the fluoride-free and formally
cationic cousin of zwitterionic 4, so sonication of 5 with
CsF and 18-Crown-6 in CH2Cl2 provides an alternative
route to 4 (Scheme 2). The 31P NMR spectrum of 5
shows a doublet at 64.9 ppm (1JP,Rh = 166.8 Hz), which
is shifted 12.7 ppm to higher frequency of complex 4
(Table 2). In solution, exchange of the CMe2 groups in 5 is
slow, as was observed for complex 4; the coalescence
temperature for CMe2 exchange in 5 is 312(2) K, leading
to a ΔGq of 61.2(8) kJ/mol at this temperature.
X-ray quality crystals of 5 (Figure 8, Tables 2-3)
were grown from CH2Cl2/hexane at -30 °C, and reveal a
T-shaped arrangement of the phosphine, thioether, and
carbonyl groups [S-Rh-CO = 172.48(9)°, P-Rh-
CO = 88.35(9)°, P-Rh-S = 84.84(2)°]. In addition, close
approach of boron and the ipso-carbon of one B-phenyl ring
to rhodium is observed [Rh-B = 2.557(3) A and Rh-
C(42) = 2.362(2) A]. A weak interaction between rhodium
and the ortho-carbon of the coordinated B-phenyl ring
is also plausible based on the Rh-C(43) distance of
2.797(3) A. However, pairwise equivalence of the ortho and
meta positions of each B-phenyl ring in the solution 1H and
13C NMR spectra, even at -80 °C, argues against a
significant Rh-Cortho interaction. For comparison, two
CHortho and two CHmeta environments were observed for
by solution conformations with P F distances significantly
3 3 3
shorter than that in the X-ray crystal structure of 4. However,
an alternative and perhaps more likely explanation is tighter
(entropically favored) η2-arene binding to rhodium at lower
temperatures, leading to an increase in the average Rh
F
3 3 3
distance (due to rotation about the C(5)-B bond)
and a reduction in the magnitude of through-bond JF,P
coupling.
2
€
(61) Tuttle, T.; Grafenstein, J.; Cremer, D. Chem. Phys. Lett. 2004, 394, 5.
(62) Miller, G. R.; Yankowsky, A. W.; Grim, S. O. J. Chem. Phys. 1969,
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(63) Jonas, J.; Gutowsky, H. S. J. Chem. Phys. 1965, 42, 140.
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4070 Inorganic Chemistry, Vol. 49, No. 9, 2010
Cowie et al.
1
the coordinated B-phenyl ring in the low temperature H
and 13C NMR spectra of the η3-arylborane complexes
[Pd(TXPB)], [Ni(TXPB)],3 and [(TXPB)Rh(μ-CO)2Fe-
(CO)Cp].4 The metal-arylborane interaction in 5 is there-
fore best considered to involve η2BC-coordination. This
assignment is supported by the observation of a broad
singlet at 57 ppm (ω1/2 ≈ 1800 Hz) in the 11B NMR
spectrum of 5, which is shifted 12 ppm to low frequency
of free TXPB, consistent with the presence of a significant,
albeit weak, Rh-B interaction (vide infra).
ambiphilic ligand complexes; a somewhat shorter M-B
distance was observed in cationic [({o-iPr2P(C6H4)}3B)-
Au][GaCl4] (Au-B = 2.448 A),73 and substantially shorter
M-B bonds were observed in the structurally rigid
B(mtR)3 and B(taz)3 complexes [Rh(CO)(PPh3){B(taz)3}]-
[PF6] (taz = 4-ethyl-3-methyl-5-thioxo-1,2,4-triazolyl) (Rh-
B = 2.155 A),74 [Co(PPh3){B(mttBu)3}][X] (X = BPh4,
PF6, or SbF6) (Co-B = 2.132 A),75 [Rh(CNtBu)(PPh3)-
{B(mt)3}]Cl (Rh-B = 2.155 A), [Rh(CNXyl)(PPh3)-
{B(mt)3}]Cl (Rh-B = 2.146 A), and [Rh(PMe3)2-
{B(mt)3}]Cl (Rh-B = 2.148 and 2.153 A).76
Both η1B- and η3BCC coordination modes have pre-
viously been reported in metal arylborane complexes
(vide supra), and the relationship between these arylbor-
ane coordination modes parallels that between η1-benzyl
and η3-benzyl coordination; examples of ηn-coordinated
triarylmethyl complexes are [(acac)M(η3-CPh3)] (M =
Pd, Pt),67 [(η5-CPh3)(ηn-CPh3)Yb(THF)2] (n = 1-2),68
The CO stretching frequency for 5 is 2028 cm-1 in
Nujol and 2038 cm-1 in CH2Cl2. These values are much
higher than those for complexes 1-4, indicating signifi-
cantly reduced electron density at the rhodium center.
The difference in ν(CO) between zwitterionic 4 and
cationic 5 can be attributed in large part to more effective
electron donation from the TXPB-F ligand in 4, relative
to the TXPB ligand in 5. This may be explained in terms of
the formal negative charge on the TXPB-F ligand,
combined with different arylborate/arylborane binding
modes; η2-arene binding in 4 versus η2BC-arylborane
coordination in 5. However, increasing positive charge
at a carbonyl ligated metal center has been shown to
reduce the extent to which the bonding orbitals of CO are
polarized toward oxygen, resulting in enhanced cova-
lency and an increase in the CO stretching force con-
stant.77 A portion of the increase in ν(CO) from 4 to 5 may
therefore arise from polarization effects due to the overall
positive charge on complex 5, rather than a decrease in the
extent of π-backdonation.
and [{κ4COO0O00-C(C6H2 Bu2O-o)3}Zr(THF)3].69 The
t
η2BC-coordination mode in 5 provides a link between
the η1B- and η3BCC-bonding extremes, much as η2-
benzyl coordination lies intermediate between the η1-
and η3-benzyl coordination modes. For comparison,
M-B bond distances of 2.320, 2.297, and 2.63 A, and
M-Cipso distances of 2.198, 2.019, and 2.33 A were
observed in the η3-arylborane complexes [Pd(TXPB)],
[Ni(TXPB)],3 and [(TXPB)Rh(μ-CO)2Fe(CO)Cp],4 re-
spectively. However, the M-Cortho distances of 2.325,
2.081, and 2.46 A in these complexes are much shorter
than the Rh-Cortho distance in 5.
An η2BC-coordination mode has also been reported
for the boratalkene complexes [(CO)Cp2Ta{η2-CH2B-
(C6F5)2}]70 and [(tBuNC)Cp2Ta{η2-CH2B(C6F5)2}],71
with Ta-C bond distances of 2.337 and 2.348 A, Ta-B
bond distances of 2.728 and 2.738 A, and B-C distances
of 1.508 and 1.525 A, respectively. However, the B-C
distance of 1.576(4) A in 5 is in the usual range for a
B-Csp2 single bond (e.g., 1.571-1.589 A in BPh3),72 and
C-C distances in the coordinated B-phenyl ring are not
obviously perturbed from typical values. The η2BC-inter-
action in complex 5 is therefore not significantly bora-
talkene-like, and presumably involves η1-arene coordina-
tion and a dative η1-borane interaction.
Summary and Conclusions
A series of ambiphilic ligand rhodium(I) halide complexes,
[RhX(CO)(TXPB)] [X = Cl (1), Br (2), I (3), and F (4);
TXPB = a phosphine-thioether-borane ligand], have been
prepared, as well as the halide-free cation [Rh(CO)(TXPB)]-
[PF6] (5). Complex 1 was accessed via reaction of TXPB with
[{Rh(μ-Cl)(CO)2}2] and was used as the starting material for
the preparation of complexes 2-5, either by halide substitu-
tion or halide abstraction. In all complexes, the TXPB ligand
binds to rhodium via the phosphine and thioether groups, as
well as an additional Rh-X-B, Rh-(η2CC-Ar3BF), or
Rh-(η2BC-BAr3) interaction. In complex 3, the iodide
proved to form a strong bonding interaction with rhodium,
but only a weak interaction with the borane in TXPB because
of the incompatibility of a hard borane Lewis acid with a soft
iodide ligand. By contrast, the bromide and chloride ligands
in 1 and 2 adopt bridging positions between rhodium and
boron, with a stronger halide-boron interaction in the
chloro complex. Bridging chloride interactions between a
metal and a Lewis acidic borane are rare, and to the best of
On the basis of this bonding description, the approximate
planarity of the borane, and the long Rh-B distance of
2.557(3) A in 5 is not unusual; boron remains planar in the
weakly coordinated η1-borane complexes [ClAu{PiPr2-
P
(C6H4)BFlu-o}] ( (C-B-C) = 356°) and [ClAu{PiPr2-
P
(C6H4)BCy2-o}] ( (C-B-C) = 359°),6 which also exhibit
long Au-B distances of 2.66 A and 2.90 A, respectively. The
borane is also approximately planar in the η3-coordinated
arylborane complexes [Pd(TXPB)], [Ni(TXPB)], and [(TX-
PB)Rh(μ-CO)2Fe(CO)Cp]. However, short metal-borane
distances have been shown to be accessible in cationic
(73) Sircoglou, M.; Bontemps, S.; Bouhadir, G.; Saffon, N.; Miqueu, K.;
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G. P. A.; Incarvito, C. D.; Rheingold, A. L.; Rabinovich, D. Dalton Trans.
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157.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4071
our knowledge, complex 2 is the first example of a bridging
metal-bromide-borane interaction. In the case of complex
4, fluoride binds to the borane to form an anionic TXPB-F
ligand, and the complex exhibits a weak 6.2 Hz JP,F coupling
in the room temperature 31P NMR spectrum. In contrast to
zwitterionic 4, the metal center in cationic 5 engages in η2BC-
coordination of the borane in TXPB. The metal-boron
interaction in this complex is weak, based on an 11B NMR
chemical shift of 57 ppm, which combined with an overall
positive charge on the complex, and less effective electron-
donation from neutral TXPB (relative to the anionic
TXPB-F ligand in 4), leads to a carbonyl stretching fre-
quency shifted 20-25 cm-1 to higher frequency of that in 4.
On the basis of these crystallographic and spectroscopic
data, it may be concluded that Rh-X coordination becomes
increasingly favorable, relative to B-X bond formation, as
group 17 is descended, consistent with the predictions of
hard-soft acid-base theory.78 However in this system, a
significant M-X-B bridging interaction is maintained for
bromide, and a weak interaction persists even in the case of
iodide. Nonetheless, iodide is by a wide margin the most
suitable choice for the preparation of halide-containing
ambiphilic ligand complexes in which a free pendant borane
is required for cooperative reactivity. These results also
confirm that in principle, it should be possible to use
ambiphilic borane-containing ligands to provide an addi-
tional thermodynamic driving force for oxidative addition of
less reactive aryl-chloride and aryl-fluoride substrates; either
by the formation of a bridging M-Cl-BR3 interaction or by
fluoride abstraction to yield an anionic fluoroborate and a
cationic metal center. However, preliminary reactions
(stoichiometric and catalytic conditions) of previously re-
ported [Pd(TXPB)]3 with aryl-chloride and aryl-fluoride
substrates have so far proved unsuccessful. This is perhaps
unsurprising given the nature of the donor atoms in TXPB,
and current efforts are focused on more electron-donating
and thioether-free ambiphilic ligands likely to result in group
10 metal complexes with higher inherent activities for Ar-X
oxidative addition and C-C bond forming catalysis.
proteo solvents were stored over an appropriate drying agent
(dme, toluene = Na/Ph2CO; hexanes = Na/Ph2CO/tetraglyme;
CH2Cl2 = CaH2) and introduced to reactions via vacuum
transfer with condensation at -78 °C. Deuterated solvents
(ACP Chemicals) were dried over CaH2 (CD2Cl2) or Na/Ph2CO
(C6D6). [{Rh(μ-Cl)(CO)2}2], Me3SiBr, Me3SiI, [NMe4]F, and
Tl[PF6] were purchased from Sigma-Aldrich and stored under
argon. Prior to use, [NMe4]F was heated to 120 °C for 3 days
under dynamic vacuum. The TXPB ligand,2 [RhCl(CO)-
81
(TXPB)] (1),4 Cl2P(NEt2),80 and ClP(C6D5)2 were prepared
according to literature procedures. The d10-TXPB ligand and
d10-1 were prepared using procedures identical to those for
TXPB and 1, but using ClP(C6D5)2 and d10-TXPB, respectively.
IR Spectra were recorded on a Thermo Scientific Nicolet 6700
FTIR spectrometer. Combustion elemental analyses were per-
formed on a Thermo EA1112 CHNS/O analyzer by Dr. Steve
Kornic of this department. NMR spectroscopy (1H, 13C{1H},
11B, 19F, 31P, DEPT-135, COSY, TOCSY, HSQC, HMBC) was
performed on Bruker DRX-500 and AV-600 spectrometers. All
1H NMR and 13C NMR spectra were referenced relative to
SiMe4 through a resonance of the employed deuterated solvent
or proteo impurity of the solvent; C6D6 (7.16 ppm) and CD2Cl2
(5.32 ppm) for 1H NMR; C6D6 (128.0 ppm) and CD2Cl2 (54.0
ppm) for 13C NMR. 11B, 31P, and 19F NMR spectra were
referenced using an external standard of BF3(OEt2) (0.0 ppm),
85% H3PO4 in D2O (0.0 ppm), and CFCl3 (0.0 ppm), respec-
tively. Temperature calibration was performed using a d4-
methanol sample, as outlined in the Bruker VTU user manual.82
Values of ΔG‡ for CMe2 methyl group exchange were calculated
using the equation ΔG‡ (kJ mol-1) = -RTc ln[(π h δν)/(21/2 kB
Tc)] = RTc [22.96 þ ln(Tc/δν)] where R is the ideal gas constant,
h is Planck’s constant, and kB is the Boltzmann constant. The
values of δν (NMR frequency difference in Hz) and Tc
(coalescence temperature) used were 364.8 Hz and 254 K for
1, 290.4 Hz and 211 K for 2, 278.0 Hz and 210 K for 3, 384.6 Hz
and 274 K for 4, and 165.0 Hz and 312 K for 5. Herein,
numbered proton and carbon atoms refer to the positions of
the xanthene backbone in the TXPB ligand (see Scheme 1).
X-ray crystallographic analyses were performed on suitable
crystals coated in Paratone oil and mounted on a SMART
APEX II diffractometer with a 3 kW Sealed tube Mo generator
in the McMaster Analytical X-ray (MAX) Diffraction Facility.
One of two molecules of hexane within the asymmetric unit cell
of 2 hexane, one molecule of hexane in 3 hexane, and a half
3
3
molecule of CH2Cl2 in 4 1.5CH2Cl2 were highly disordered and
3
Experimental Section
could not be modeled satisfactorily, so were treated using the
SQUEEZE routine.83 In addition, the following groups were
rotationally or positionally disordered over two positions: (a)
General Details. An argon-filled MBraun UNIlab glovebox
equipped with a -30 °C freezer was employed for the manipula-
tion and storage of all ligands and complexes, and reactions
were performed on a double-manifold high vacuum line using
standard techniques.79 Commonly utilized specialty glassware
includes the swivel frit assembly, J-Young NMR tubes, and
thick-walled flasks equipped with Teflon stopcocks. A Fisher
Scientific Ultrasonic FS-30 bath and a Branson 2510 Ultrasonic
bath was used to sonicate reaction mixtures where indicated,
and in some cases, a Fischer Scientific Model 228 centrific
centrifuge in combination with airtight Kimble-Kontes 15 mL
conical centrifuge tubes was used to remove insoluble byproduct
or to collect precipitated products. Residual oxygen and moist-
ure were removed from the argon stream by passage through an
Oxisorb-W scrubber from Matheson Gas Products.
both of the tert-butyl substituents for molecule B in 2 hexane,
(b) one of the tert-butyl substituents in 4 1.5CH2Cl2, (c) one
3
3
molecule of CH2Cl2 in 4 1.5CH2Cl2, and (d) the PF6 anion in
3
5 CH2Cl2. In all cases, disorder was modeled allowing occu-
3
pancy and positional parameters to refine freely. All tert-butyl
methyl groups (cases a and b above) were restrained to have
equivalent thermal parameters. However, (a) was refined iso-
tropically while (b) was refined anisotropically. For case (c),
carbon and chlorine atoms were restrained to have equivalent
thermal parameters, respectively, and were refined anisotropi-
cally. For case (d), all fluorine atoms were restrained to have
similar thermal parameters using the SIMU command, and
refinements were performed using the ISOR command.
Anhydrous CH2Cl2 was purchased from Aldrich. Hexanes and
toluene were initially dried and distilled at atmospheric pressure
from CaH2 and sodium, respectively. Unless otherwise noted, all
[RhBr(CO)(TXPB)] hexane (2). Me3SiBr (25 μL, 1.90 ꢀ
3
10-4 mol) was added dropwise at room temperature to
(80) Tollefson, M. B.; Li, J. J.; Beak, P. J. Am. Chem. Soc. 1996, 118, 9052.
(81) Yamashita, M.; Vicario, J. V. C.; Hartwig, J. F. J. Am. Chem. Soc.
2003, 125, 16347.
(82) Tyburn, J.-M. Bruker Variable Temperature Unit User Manual;
Bruker BioSpin SA: Wissembourg, France, 1998; Vol. 001, p 35.
(83) Sluis, P. V. D.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(78) Pearson, R. G. Science 1966, 151, 172.
(79) Burger, B. J.; Bercaw, J. E. Vacuum Line Techniques for Handling
Air-Sensitive Organometallic Compounds. In Experimental Organometallic
Chemistry - A Practicum in Synthesis and Characterization; American
Chemical Society: Washington, D.C., 1987; Vol. 357, p 79.

4072 Inorganic Chemistry, Vol. 49, No. 9, 2010
Cowie et al.
[RhCl(CO)(TXPB)] (160 mg, 1.88 ꢀ 10-4 mol) in CH2Cl2
(10 mL). The reaction mixture was stirred vigorously for 2 h
at room temperature before evaporation to dryness in vacuo.
The resulting tangerine-colored powder was left under dynamic
vacuum for 3 h to ensure removal of all solvent and Me3SiCl.
Further purification entailed washing with hexanes (ꢀ2) with
cooling to -30 °C for 1 h before decanting the mother liquors
during each washing, and subsequent drying in vacuo. Yield =
CH1), 7.66 (m, 2H, o-PPh2 A), 7.59 (broad s, 3H, p-PPh2
A þ o-BPh2 A), 7.55 (t, 2H, o-PPh2 A), 7.48-7.41 (m, 3H,
p-PPh2 B þ m-BPh2 A), 7.39 (s, 1H, CH8), 7.34 (broad s, 2H, m-
PPh2 B), 7.25 (m, 2H, o-PPh2 B), 7.21 (t, 3JH,H 7 Hz, 1H, p-BPh2
A), 7.13 (app t, 3JH,H 7 Hz, 2H, m-BPh2 B), 7.03 (s, 1H, CH6),
7.01 (t, 1H, p-BPh2 B), 6.96 (broad s, 2H, o-BPh2 B), 6.91 (d, 3JH,
P 11 Hz, 1H, CH3), 2.03, 1.26 (s, 2 ꢀ 3H, CMe2), 1.16, 1.13 (s,
9H, 2 ꢀ CMe3). 13C{1H} NMR (CD2Cl2, -50 °C): δ 186.8 (dd,
1JC,Rh 75, 3JC,P 19 Hz, RhCO), 151.9 (d, 3JC,P 7 Hz, C2CMe3),
125 mg (74%). X-ray quality crystals of 2 hexane were grown by
3
3
cooling a saturated solution of 2 in hexanes to -30 °C for several
days. 1H NMR (CD2Cl2, 20 °C): δ 7.78 (d, 4JH,H 2 Hz, 1H, CH1),
7.63 (d, 4JH,H 2 Hz, 1H, CH8), 7.47 (tt, 3JH,H 7, 4JH,H 1.8 Hz, 2H,
149.5 (s, C7CMe3), 141.1 (d, JC,P 14 Hz, C10), 138.1 (s, C13),
135.7 (d, 2JC,P 23 Hz, C11), 134.3 (d, 1JC,P 53 Hz, C4), 133.6 (d,
3JC,P 12 Hz, m-PPh2 A), 133.1 (broad s, ipso-BPh2 A), 132.6 (d,
2JC,P 12 Hz, o-PPh2 B), 131.9 (s, p-PPh2 A), 131.7 (s, o-BPh2 A þ
o-BPh2 B þ p-PPh2 B), 131.5 (app s, ipso-PPh2 A þ ipso-BPh2 B),
131.2 (d, 1JC,P 37 Hz, ipso-PPh2 B), 129.9 (broad s, C6), 129.4 (d,
2JC,P 12 Hz, m-PPh2 A), 129.2 (s, m-BPh2 A), 128.8 (d, 3JC,P 12
Hz, m-PPh2 B), 128.6 (s, p-BPh2 A), 128.1 (broad s, C5), 127.6 (s,
C3), 127.2 (s, m-BPh2 B), 126.2 (s, C12), 125.4 (s, C1), 125.1 (s, p-
BPh2 B), 119.7 (s, C8), 40.7 (s, CMe2), 35.1, 34.8 (s, 2 ꢀ CMe3),
31.2, 30.8 (s, 2 ꢀ CMe3), 27.8, 24.9 (s, 2 ꢀ CMe2). 31P {1H}
3
p-PPh2), 7.41-7.33 (m, 8H, o þ m-PPh2), 7.32 (dd, JH,H 8,
4JH,H 1 Hz, 4H, o-BPh2), 7.28 (dd, 3JH,P 9, 4JH,H 2 Hz, 1H, CH3),
7.07 (app t, 3JH,H 7 Hz, 4H, m-BPh2), 7.02 (d, 4JH,H 2 Hz, 1H,
CH6), 7.00 (t, 3JH,H 7 Hz, 2H, p-BPh2), 1.86 (s, 6H, CMe2), 1.25,
1.15 (s, 2 ꢀ 9H, CMe3). 13C{1H} NMR (CD2Cl2, 20 °C): δ 187.6
1
2
3
(dd, JC,Rh 77, JC,P 15 Hz, RhCO), 153.1 (d, JC,P 6 Hz,
C2CMe3), 150.0 (s, C7CMe3), 148.5 (broad s, ipso-BPh2), 148.0
(broad s, C5), 146.0 (d, 3JC,P 14 Hz, C10), 142.2 (s, C13), 137.3 (d,
2JC,P 27 Hz, C11), 136.5 (s, o-BPh2), 133.8 (d, 1JC,P 50 Hz, C4),
1
(CD2Cl2, 20 °C): δ þ52.2 (dd, JP,Rh 166, JP,F 6.2 Hz). 19F
2
133.7 (d, JC,P 12 Hz, o-PPh2), 133.5 (s, C6), 133.0 (d, 1JC,P 55
(CD2Cl2, 20 °C): δ -186 (broad s, ω1/2 ≈ 180 Hz). 11B (CD2Cl2,
20 °C): δ þ4 (broad s, ω1/2 ≈ 350 Hz). IR: ν(CO) = 2008 cm-1
(Nujol), 2011 cm-1 (CH2Cl2). Anal. Calcd. For C48H48-
OFPSBRh: C, 68.91; H, 5.78. Found: C, 69.27; H, 5.60%.
Hz, ipso-PPh2), 131.6 (s, p-PPh2), 130.2 (s, C12), 129.1 (d, 3JC,P
11 Hz, m-PPh2), 128.4 (s, C3), 127.4 (s, p-BPh2), 127.0 (m-BPh2),
125.8 (s, C1), 122.2 (s, C8), 42.9 (s, CMe2), 35.6, 35.2 (s, 2 ꢀ
CMe3), 31.5 (s, 2 ꢀ CMe3), 26.7 (s, CMe2). 31P {1H} (CD2Cl2,
20 °C): δ þ64.5 (d, 1JP,Rh 164 Hz). 11B (CD2Cl2, 20 °C): δ þ27 (v.
broad s, ω1/2 ≈ 900 Hz). IR: ν(CO) = 2013 cm-1 (nujol), 2008
cm-1 (CH2Cl2). Anal. Calcd. For C54H62OBrPSBRh: C, 65.93;
H, 6.35. Found: C, 66.17; H, 5.91%.
[Rh(CO)(TXPB)][PF6] 0.5CH2Cl2 (5). A mixture of [RhCl-
3
(CO)(TXPB)] (350 mg, 4.10 ꢀ 10-4 mol) and Tl[PF6] (350 mg,
1.00 ꢀ 10-3 mol) in CH2Cl2 (10 mL) was stirred vigorously for
4.5 h at room temperature. After allowing any solid to settle over
24 h at -30 °C, the mother liquors were carefully decanted,
layered with hexanes, and cooled to -30 °C for several days. The
resulting orange needles were washed with hexanes (ꢀ1) and
dried in vacuo. Yield = 363 mg (92%). X-ray quality crystals of
[RhI(CO)(TXPB)] 0.5hexane (3). A solution of Me3SiI (48.1
3
mg, 2.40 ꢀ 10-4 mol) in CH2Cl2 (2 mL) was added dropwise at
room temperature to [RhCl(CO)(TXPB)] (205 mg, 2.40 ꢀ 10-4
mol) in CH2Cl2 (10 mL). The reaction mixture was stirred
vigorously for 1 h before evaporation to dryness in vacuo. The
resulting rust-red powder was left under dynamic vacuum for
3 h to ensure all solvent and Me3SiCl had been removed. Further
purification entailed washing with hexanes (ꢀ2) with cooling to
-30 °C for 1 h before decanting the mother liquors during each
washing, and subsequent drying in vacuo. Yield = 187 mg
5 CH2Cl2 were grown by slow diffusion of hexanes into a
3
1
solution of 5 in CH2Cl2 at -30 °C. H NMR (CD2Cl2, -70
°C): δ 8.27 (d, 3JH,H 7 Hz, 2H, o-BPh2 A), 8.08 (t, 3JH,H 7 Hz, 1H,
p-BPh2 A), 7.81 (app t, 3JH,H 7 Hz, 2H, m-BPh2 A), 7.75 (s, 1H,
CH1), 7.71 (s, 1H, CH8), 7.66 (t, 3JH,H, 1H, p-BPh2 B), 7.60 (d,
3JH,H 7 Hz, 2H, o-BPh2 B), 7.56 (t, 3JH,H 8 Hz, 2H, 2 ꢀ p-PPh2),
7.54 (app t, 3JH,H 8 Hz, 2H, m-BPh2 B), 7.54-7.45 (m, 4H, o/m-
PPh2), 7.38-7.30 (m, 4H, o/m-PPh2), 7.21 (s, 1H, CH6), 7.13 (d,
3JH,P 10 Hz, 1H, CH3), 2.13, 1.80 (s, 2 ꢀ 3H, CMe2), 1.21, 1.14 (s,
9H, 2 ꢀ CMe3). 13C{1H} NMR (CD2Cl2, -70 °C): δ 183.3 (dd,
(83%). X-ray quality crystals of 3 hexane were grown by cool-
3
ing a saturated solution of 3 in hexanes to -30 °C for several
days. 1H NMR (C6D6, 20 °C): δ 7.83 (d, 3JH,H 7 Hz, 4H, o-BPh2),
1JC,Rh 72, JC,P 13 Hz, RhCO), 155.3 (s, C2CMe3), 152.0 (s,
3
3
7.80 (s, 1H, CH8), 7.69 (s, 1H, CH1), 7.56 (d, JH,P 8 Hz, 1H,
C7CMe3), 145.7 (d, JC,P 13 Hz, C10), 144.5 (s, C12), 142.3 (s,
3
3
CH3), 7.48-7.41 (m, 5H, CH6 þ o-PPh2), 6.95 (t, JH,H 7 Hz,
C13), 139.8 (s, p-BPh2 A), 139.3 (broad s, ipso-BPh2 B), 137.4 (s,
o-BPh2 B), 136.2 (s, o-BPh2 A), 135.9 (d, 2JC,P 24 Hz, C11), 133.3
(d, J 12 Hz, o/m-PPh2), 133.0 (s, C6), 132.8 (s, p-BPh2 B), 132.4 (s, 2
ꢀ p-PPh2), 132.3 (d, J 12 Hz, o/m-PPh2), 132.2 (s, C5), 130.0 (d,
1JC,P ∼60 Hz, C4 or ipso-PPh2), 129.7 (d, J12 Hz, o/m-PPh2), 129.4
(s, m-BPh2 A), 129.0 (d, J 12 Hz, o/m-PPh2), 128.9 (d, 1JC,P 59 Hz,
C4 or ipso-PPh2), 128.3 (s, m-BPh2 B), 127.4 (s, C1), 127.1 (s, C3),
125.60 (s, C8), 110.8 (broad s, ipso-BPh2 A), 43.3 (s, CMe2), 35.2,
35.0 (s, 2 ꢀ CMe3), 30.8, 30.6 (s, 2 ꢀ CMe3), 26.4, 25.0 (s, 2 ꢀ
2H, p-PPh2), 6.92-6.83 (m, 8H, m-PPh2 þ m-BPh2), 6.76 (t,
3JH,H 6 Hz, 2H, p-BPh2), 1.73 (s, 6H, CMe2), 1.18, 1.10 (s, 2 ꢀ
9H, CMe3). 13C{1H} NMR (C6D6, 20 °C): δ 189.7 (dd, 1JC,Rh 74,
3
3JC,P 14 Hz, RhCO), 152.5 (d, JC,P 5 Hz, C2CMe3), 149.7 (s,
C7CMe3), 147.6 (broad s, C5), 146.9 (d, 3JC,P 14 Hz, C10), 143.8
(broad s, ipso-BPh2), 143.7 (s, C13), 140.4 (d, 2JC,P 32 Hz, C11),
139.1 (s, o-BPh2), 134.2 (s, C6), 134.1 (d, 1JC,P 51 Hz, ipso-PPh2),
133.4 (d, 2JC,P 12 Hz, o-PPh2), 133.1 (s, C4), 132.4 (s, C12), 130.5(s,
p-PPh2), 129.0 (s, p-BPh2), 128.5 (d, 3JC,P 11 Hz, m-PPh2), 128.3 (s,
C3), 126.8 (s, m-BPh2), 125.1 (s, C1), 123.1 (s, C8), 43.3 (s, CMe2),
35.1, 35.0 (s, 2 ꢀ CMe3), 31.4, 31.3 (s, 2 ꢀ CMe3), 26.1 (s, CMe2).
31P {1H} (CD2Cl2, 20 °C): δ þ67.2 (d, 1JP,Rh 167 Hz). 11B (CD2Cl2,
20 °C): δ þ56 (v.broad s, ω1/2 ≈ 1800 Hz). IR: ν(CO) = 2004 cm-1
(Nujol), 2002 cm-1 (CH2Cl2).Anal. Calcd. For C51H55OBrPSBRh:
C, 62.02; H, 5.61. Found: C, 61.95; H, 5.79%.
CMe2). 31P{1H} (CD2Cl2, 20 oC): δ þ64.9 (d, 1JP,Rh 166.8 Hz). 11
B
(CD2Cl2, 20 oC): δ þ57 (broad s, ω1/2 ≈ 1800 Hz). IR: ν(CO) =
2028 cm-1 (Nujol), 2038 cm-1 (CH2Cl2). Anal. Calcd. for
C48H48P2SBF6Rh: C, 57.96; H, 4.91. Found: C, 57.73; H, 5.09%.
Acknowledgment. D.J.H.E. thanks NSERC of Canada for a
Discovery Grant, the Ontario Ministry of Resarch and Innova-
tion for an Early Researcher Award, and Canada Foundation
for Innovation (CFI) and Ontario Innovation Trust (OIT) for
New Opportunities Grants. B.E.C. thanks the Government of
Ontario for an Ontario Graduate Scholarship (OGS).
[Rh(CO)(TXPB-F)] (4). A mixture of [RhCl(CO)(TXPB)] (50
mg, 5.86 ꢀ 10-5 mol) and [NMe4]F (5.5 mg, 5.91 ꢀ 10-5 mol) in
CH2Cl2 (5 mL) was stirred vigorously for 1 h at room tempera-
ture. The resulting orange, opaque mixture was filtered through
a column of Celite, and the red/orange mother liquors were
evaporated to dryness in vacuo to yield a rust-red powder.
Supporting Information Available: X-ray crystallographic
data in PDF format and CIF files. This material is available
free of charge via the Internet at http://pubs.acs.org.
Yield = 35 mg (72%). X-ray quality crystals of 4 1.5CH2Cl2
were grown by slow diffusion of hexanes into a solution of 4 in
3
CH2Cl2 at -30 °C. 1H NMR (CD2Cl2, -50 °C): δ 7.68 (s, 2H,