A study of M-X-BR3 (M = Pt, Pd or Rh; X = Cl or I) interactions in square planar ambiphilic ligand complexes: Structural, spectroscopic, electrochemical and computational comparisons with borane-free analogues

Article abstract of DOI:10.1039/c2dt11991a

Reaction of [PtCl₂(COD)] and [PtI₂(COD)] with 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB) afforded square planar [PtCl₂(TXPB)] (1B) and [PtI ₂(TXPB)] (4B), both of which were crystallographically characterized. Single-crystal X-ray quality crystals were also obtained for [PdCl ₂(TXPB)] (2B; Emslie et al., Organometallics, 2008, 27, 5317) as 2B·2CH₂Cl₂ and solvent-free 2B. Both the chloro and iodo TXPB complexes exhibit metal-halide-borane bridging interactions similar to those in previously reported [RhCl(CO)(TXPB)] (3B) and [RhI(CO)(TXPB)] (5B) (Emslie et al., Organometallics, 2006, 25, 583 and Inorg. Chem., 2010, 49, 4060). To facilitate a more detailed analysis of M-X-BR₃ (X = Cl and I) interactions, a borane-free analogue of the TXPB ligand, 2,7-di-tert-butyl-4- diphenylphosphino-9,9-dimethylthioxanthene (TXPH), was prepared. Reaction with [PtX₂(COD)] (X = Cl or I), [PdCl₂(COD)] and 0.5 [{RhCl(CO)₂}₂] provided square planar [PtCl ₂(TXPH)] (1H), [PdCl₂(TXPH)] (2H), [RhCl(CO)(TXPH)] (3H) and [PtI₂(TXPH)] (4H). M-Cl-BR₃ and M-I-BR₃ bonding in 1B-5B was then probed through the use of structural comparisons, IR and NMR spectroscopy, cyclic voltammetry, and DFT calculations (Slater-type orbitals, Mayer bond orders, Hirshfeld charges, fragment analysis, SCF deformation density isosurfaces, and energy decomposition analysis). The Royal Society of Chemistry 2012.

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PAPER
A study of M–X–BR3 (M = Pt, Pd or Rh; X = Cl or I) interactions in
square planar ambiphilic ligand complexes: structural, spectroscopic,
electrochemical and computational comparisons with borane-free analogues†
David J. H. Emslie,*a Bradley E. Cowie,a Simon R. Oakley,a Natalie L. Huk,a Hilary A. Jenkins,b
Laura E. Harringtonb and James F. Brittenb
Received 20th October 2011, Accepted 23rd December 2011
DOI: 10.1039/c2dt11991a
Reaction of [PtCl2(COD)] and [PtI2(COD)] with 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-
9,9-dimethylthioxanthene (TXPB) afforded square planar [PtCl2(TXPB)] (1B) and [PtI2(TXPB)] (4B),
both of which were crystallographically characterized. Single-crystal X-ray quality crystals were also
obtained for [PdCl2(TXPB)] (2B; Emslie et al., Organometallics, 2008, 27, 5317) as 2B·2CH2Cl2 and
solvent-free 2B. Both the chloro and iodo TXPB complexes exhibit metal–halide–borane bridging
interactions similar to those in previously reported [RhCl(CO)(TXPB)] (3B) and [RhI(CO)(TXPB)] (5B)
(Emslie et al., Organometallics, 2006, 25, 583 and Inorg. Chem., 2010, 49, 4060). To facilitate a more
detailed analysis of M–X–BR3 (X = Cl and I) interactions, a borane-free analogue of the TXPB ligand,
2,7-di-tert-butyl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPH), was prepared. Reaction with
[PtX2(COD)] (X = Cl or I), [PdCl2(COD)] and 0.5 [{RhCl(CO)2}2] provided square planar
[PtCl2(TXPH)] (1H), [PdCl2(TXPH)] (2H), [RhCl(CO)(TXPH)] (3H) and [PtI2(TXPH)] (4H). M–Cl–
BR3 and M–I–BR3 bonding in 1B–5B was then probed through the use of structural comparisons, IR and
NMR spectroscopy, cyclic voltammetry, and DFT calculations (Slater-type orbitals, Mayer bond orders,
Hirshfeld charges, fragment analysis, SCF deformation density isosurfaces, and energy decomposition
analysis).
Lewis acid have also been reported. These include: (1) pendant
Introduction
borane facilitated delivery of multiple hydride equivalents to a
carbonyl ligand in [Re(CO)4{PPh2(CH2)2B(C8H14)}2]+ (I in
Ambiphilic ligands are defined as those containing a Lewis
acidic group in addition to one or more conventional donors
capable of σ-donation to the metal (e.g. a phosphine or an
amine). These ligands may be generated in situ on a metal, as is
typically the case for tris(N-alkylimazolyl)boranes, or they may
be isolated prior to metal coordination. The transition metal
chemistry of group 13 Lewis acid-containing ambiphilic ligands
has seen a surge of activity over the past decade, much of it
directed towards the isolation and study of unusual metal–Lewis
acid bonds where the Lewis acid is considered a zero-electron
donor Z-type ligand.1 However, studies focused on the develop-
ment of cooperative reactivity involving a pendant group 13
Fig. 1), followed by spontaneous alkyl migration to form a C–C
bond,2 (2) rate enhancements for the dehydrogenative coupling
of PhSiH3 by [(Me-Ind)NiMe(PPh3)] in the presence of Me2P-
CH2AlMe2; the proposed intermediate in this reactivity is [(Me-
Ind)NiMe(PMe2CH2AlMe2)] (II in Fig. 1),3 (3) propene and
methane formation upon reaction of [Cp*RhMe2(PMe2-
CH2AlMe2)] with ethylene at 50 °C; [Cp*Rh+Me(C2H4)(PMe2-
CH2AlMe3−)] (III in Fig. 1) was identified as an intermediate in
this reaction,4 (4) reaction of Na[H2B(mt)2] (mt = N-methylima-
zolyl) with [RhCl(CS)(PPh3)2] to form [LRhH(PPh3)] [IV in
Fig. 1; L = {H(mt)2B}(Ph3P)CvS], presumably via the inter-
mediates [{κ3-H2B(mt)2}Rh(CS)(PPh3)] (V in Fig. 1) and [{κ3-
HB(mt)2}RhH(CS)(PPh3)],5 (5) reaction of [{κ4-B(mttBu)3}
NiCl] (VI in Fig. 1; mttBu = N-tert-butylimazolyl)) with I2 or
CHBr3 to form [{κ3-ClB(mttBu)3}NiX] (VII in Fig. 1; X = I or
Br), and with XeF2 to produce [{κ3-FB(mttBu)3}NiCl],6 and (6)
reaction of [Pd(TXPB)] (VIII in Fig. 1; TXPB = 2,7-di-tert-
butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthiox-
anthene) with dibenzylidene-acetone (dba) to afford [Pd(dba)
(TXPB)] (IX in Fig. 1); a zwitterionic palladium(II) η3-boratoxy-
allyl complex.7
aDepartment of Chemistry, McMaster University, 1280 Main Street West,
Hamilton, ONL8S 4M1, Canada. E-mail: emslied@mcmaster.ca;
Fax: +(905)-522–2509; Tel: +(905)-525-9140(23307)
bMcMaster Analytical X-Ray Diffraction Facility, Department of
Chemistry, McMaster University, 1280 Main Street West, Hamilton,
ONL8S 4M1, Canada
†Electronic supplementary information (ESI) available: Calculated
structures for 1B–5B, 1H–5H, TXPB and [TXPB–I]−, and X-Ray crys-
tallographic data. CCDC 849792–849797. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c2dt11991a
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 3523–3535 | 3523

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Fig. 1 Selected reactants, proposed intermediates and products from reactions involving a pendant group 13 Lewis acid (the group 13 element is
highlighted).
Previous research in the Emslie group has focused on late
transition metal complexes of the phosphine–thioether–borane
ambiphilic ligand, TXPB, and a range of complexes containing
direct metal–borane or metal–ligand–borane interactions have
been prepared, including compounds VIII and IX in Fig. 1.7–9
The current work probes the nature of halide ligand coordination
by a pendant borane; in particular the extent to which the
strength of metal–halide–borane (M–X–BR3) interactions vary
between chloro and iodo complexes, and the effect that borane
coordination has on the metal–halide bond. Our interest in these
features is twofold: (1) for late transition metal catalysis invol-
ving halide ligands, it is possible to envisage modified reaction
cycles involving halide coordination or abstraction by a pendant
borane. However, to allow rational progress in this direction, a
more detailed understanding of metal–halide–borane interactions
is desirable. (2) The potential exists for a pendant borane to
effect pre-coordination or cooperative activation of organic sub-
strates. However, due to the ubiquitous nature of chloro, bromo
and iodo ligands throughout much of transition metal chemistry,
it is desirable to determine the extent to which coordination of
halide co-ligands is likely to take place, potentially sequestering
the pendant borane.
Results and discussion
Platinum dichloro and diiodo complexes of TXPB
Reaction of [PtCl2(COD)] with 2,7-di–tert-butyl-5-diphenyl-
boryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB)7
afforded colourless [PtCl2(TXPB)] (1B) in moderate yield
(Scheme 1). The 31P NMR signal at 32.5 ppm (1JP,Pt = 3836 Hz)
demonstrates platinum–phosphine coordination and the 11B
NMR signal at 3 ppm is characteristic of 4-coordinate boron.
These data are consistent with square planar platinum ligated by
the phosphine and thioether groups of TXPB and two chloride
anions, with one chloride forming a strong bridging interaction
to the borane unit of TXPB. Analogous M–Cl–B bridging inter-
actions have been observed in [RhCl(CO)(TXPB)] (3B) and
[{PdCl(TXPB)}2].9
X-ray quality crystals of 1B·2CH2Cl2 were obtained by slow
diffusion of hexanes into a CH2Cl2 solution at −30 °C (Table 1,
Fig. 2). Crystals of the previously reported 2B were also
obtained from CH2Cl2/hexanes or toluene/hexanes at −30 °C;
the resulting crystals, 2B·2CH2Cl2 and solvent-free 2B, differ in
the orientation of the Pd–Cl bond with respect to the bend of the
ligand backbone (Table 1, Fig. 2; vide infra).
A previous publication reported the synthesis and structural
characterization of [RhX(CO)(TXPB)] (X = F, Cl, Br and I)
complexes, revealing short B–X distances in the chloro and
bromo complexes, a long B–I interaction in the iodo complex,
and halide abstraction by the borane in the fluoro complex.8 This
trend is in keeping with the soft nature of rhodium(I), the classifi-
cation of organoboranes as moderately hard Lewis acids, and the
decrease in halide hardness as group 17 is descended.10 Herein
we provide a more detailed analysis of M–X–BR3 (M = Pt, Pd
or Rh; X = Cl or I) bonding in [MX2(TXPB)] and [MX(CO)
(TXPB)] complexes through the use of crystallographic, spectro-
scopic, electrochemical and computational comparisons with
borane-free TXPH ligand analogues (TXPH = 2,7-di-tert-butyl-
4-diphenylphosphino-9,9-dimethylthioxanthene).
In 1B·2CH2Cl2, as well as 2B and 2B·2CH2Cl2, the M–Cl(1)
bond is considerably longer than M–Cl(2) (Table 2), which can
be rationalized as a consequence of the chloro ligand–borane
interaction and/or the greater trans influence of PAr3 vs. SAr2
(vide infra).11 In all chloro complexes in Table 1, the B–Cl(1)
Scheme 1 Preparation of [PtCl2(TXPB)] (1B).
3524 | Dalton Trans., 2012, 41, 3523–3535
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Table 1 Crystallographic data collection and refinement parameters for TXPB complexes 1B, 2B, and 4B, and TXPH complexes 2H and 4H
Structure
1B·2CH2Cl2
2B
2B·2CH2Cl2
4B·1.31CH2Cl2
2H·2CH2Cl2
4H·1.5CH2Cl2
Formula
Formula wt
T [K]
Cryst. syst.
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C49H52BCl6PPtS C47H48BCl2PPdS
C49H52BCl6PPdS C48.31H50.62BCl2.62I2PPtS C37H43Cl6PPdS
C36.5H42Cl3I2PPtS
1098.97
173(2)
1122.54
173(2)
863.99
173(2)
1033.85
173(2)
1246.93
173(2)
869.84
173(2)
Orthorhombic
Pna2(1)
21.373(2)
8.9593(9)
25.330(3)
90
Monoclinic
P2(1)/c
11.2575(5)
27.0326(13)
13.7991(7)
90
Orthorhombic
Pna2(1)
21.3801(14)
8.9678(6)
25.2512(17)
90
Orthorhombic
Pna2(1)
22.18(2)
9.043(8)
24.75(2)
90
Triclinic
Triclinic
ˉ
ˉ
P1
P1
12.1463(18)
12.547(2)
13.883(2)
76.402(10)
74.583(10)
81.960(10)
1975.7(5)
2
12.451(2)
12.803(2)
13.852(2)
75.815(2)
74.648(2)
80.524(4)
2052.7(6)
2
90
90
97.258(3)
90
90
90
90
90
γ [°]
Volume [Å3]
Z
4850.4(8)
4
4165.7(3)
4
4841.5(6)
4
4964(8)
4
Crystal size
0.24 × 0.18 ×
0.01
0.17 × 0.12 × 0.02 0.32 × 0.28 ×
0.12
0.25 × 0.13 × 0.03
0.30 × 0.30 ×
0.15
0.06 × 0.05 ×
0.03
[mm3]
No. of reflns
collected
No. of indep.
reflns
θ range for
collection [°]
Completeness
to θ max. [%]
Absorption
correction
GOF on F2
Final R1
27 401
25 320
72 714
34 768
9159
13 584
17 425
6568
5445
14 333
6736
9987
2.07–26.48
99.3
1.49–22.50
100.0
1.61–30.67
99.5
1.65–26.36
99.8
1.56–24.75
99.4
2.02–28.35
97.3
Numerical
Semi-empirical
from equivalents
1.218
Numerical
Semi-empirical from
equivalents
1.021
Semi-empirical
from equivalents
1.044
Numerical
1.011
4.51
1.031
4.21
0.868
6.73
9.61
6.52
8.77
[I>2σ(I)] [%]
bond distances (1.98–2.15 Å) are only 0.04–0.22 Å longer than
B–Cl in the chloroborate anions [CPh3][ClB(C6F5)3] (1.928(2)
Å)12 and [{ClPhB(η5-C5H4)2}ZrCl2]− (1.937(5) Å),13 and boron
is strongly pyramidalized [Σ(C–B–C) = 337–342°]. These data,
in keeping with the 11B NMR chemical shifts (Table 2), are
indicative of strong B–Cl interactions. Similar B–Cl distances
and boron pyramidalizations have also been reported for borane
functionalized [(η3-allyl)Pd(μ-Cl){PiPr2(C6H4)BCy2-o}] (B–Cl
= 2.16 Å; Σ(C–B–C) = 349°),14 [(Ph3P)PdCl(μ-Cl){PiPr2(C6H4)
BCy2-o}] (B–Cl = 2.11 Å; Σ(C–B–C) = 343°),15 [(η2:η2-nbd)Rh
(μ-Cl){PiPr2(C6H4)BCy2-o}] (B–Cl = 2.12 Å; Σ(C–B–C) =
343°),15 [(p-cymene)RuCl(μ-Cl)(NC5H4(CH2BCy2)-o}] (B–Cl
= 2.11 Å; Σ(C–B–C) = 347°),16 [(κ3-Tp)OsCl(μ-Cl){NPh
(BPh2)}] (B–Cl = 2.11 Å; Σ(C–B–C) = 347°),17 [(η5-Ind)TiCl
(μ-Cl){C5H4B(C6F5)2}] (B–Cl = 2.01 Å; Σ(C–B–C) = 342°),18
and a B–Cl distance of 1.93 Å was calculated for the un-
complexes in Table 1, resulting in equivalent CMe2 groups at
room temperature or slightly above.
Reaction of [PtI2(COD)] with TXPB gave bright yellow
[PtI2(TXPB)] (4B) in 73% isolated yield (Scheme 2). The 11B
NMR signal at 50 ppm is indicative of a weaker PtX⋯B inter-
action than in related chloro TXPB complexes (cf. 69 ppm for
the free TXPB ligand7 and 3–13 ppm for 1B–3B). An analogous
situation was observed for previously prepared [RhI(CO)
(TXPB)] (5B; 11B NMR δ 56 ppm).8
Single-crystal X-ray quality crystals of 4B·1.31CH2Cl2 were
grown from CH2Cl2/hexanes at −30 °C. The solid state structure
of 4B (Tables 1–2, Fig. 2) revealed approximate square planarity
at platinum [P–Pt–I(1) = 175.0(1)° and S–Pt–I(2) = 171.8(1)°]
and an M–X–BR3 bridging interaction directed towards the
outside of the fold of the ligand backbone; an analogous arrange-
ment was observed in the platinum chloro analogue 1B. The
B⋯I distance20 in 4B is 2.75(2) Å. Structurally characterized
iodoborates (BR3I−) are not available for comparison, but this
distance is approximately 0.5 Å longer than the B–I bond in
crystallographically characterized iodoboranes (cf. 2.15–2.17 Å
in 1,3,5-triiodo-1,3,5-triborocyclohexane,21 and 2.22–2.25 Å in
Me3PBI3).22 The boron atom in 4B is also pyramidalized to a
much lesser extent [Σ(C–B–C) = 353(3)°] than in 1B, 2B or 3B
[Σ(C–B–C) = 337–342°]. For comparison, the B–I distance in
the rhodium iodo complex 5B is 3.125(7) Å and the sum of the
C–B–C angles is 357(1)°.8 The Pt–I(1) bond (trans to PAr3;
2.637(2) Å) in 4B is significantly longer than Pt–I(2) (trans to
SAr2; 2.590(2) Å), presumably as a consequence of the iodo
ligand–borane interaction and/or the greater trans influence of
PAr3 vs. SAr2;11 the latter effect is expected to dominate given
the long B–I distance in 4B.
supported
M–Cl–B
bridge
in
[(IMes)2HPt(μ-Cl)
{BC5H4(SiMe3)}].19
In 1B·2CH2Cl2 and 2B·2CH2Cl2, the M–Cl–B bridge is
directed towards the outside of the fold of the ligand backbone,
resulting in a C(9)⋯S–M angle of 160–161° and an acute
M–Cl–B angle of 95–96°. By contrast, in solvent-free 2B and
3B·hexane, the M–Cl–B bridge is directed into the fold of the
ligand backbone, leading to a more acute C(9)⋯S–M angle of
146°, but allowing for an expanded M–Cl–B angle of 105–108°
(Table 2). Observation of both possible M–Cl–B bridge orien-
tations in the crystals of complex 2B obtained under different
conditions highlights the absence of a strong thermodynamic
preference for one particular orientation in the chloro complexes.
Furthermore, static structures are not preserved in solution;
fluxional behaviour is observed for all of the chloro and iodo
This journal is © The Royal Society of Chemistry 2012
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Fig. 2 Solid state structures of (a) [PtCl2(TXPB)]·2CH2Cl2 (1B·2CH2Cl2), (b) [PdCl2(TXPB)]·2CH2Cl2 (2B·2CH2Cl2), (c) [PdCl2(TXPB)] (2B), (d)
the previously reported [RhCl(CO)(TXPB)]·hexane (3B·hexane), (e) [PtI2(TXPB)]·1.31CH2Cl2 (4B·1.31CH2Cl2), and (f) the previously reported [RhI
(CO)(TXPB)]·hexane (5B·hexane). Ellipsoids are at 50% probability. One CMe3 group in 1B·2CH2Cl2 and 2B·2CH2Cl2 is disordered over two pos-
itions; only one orientation is shown. Hydrogen atoms and lattice solvent are omitted for clarity.
2JC,P coupling of 16 Hz.23 Sharp CO stretches at 2010 and
Complexes of a borane-free analogue of TXPB
2001 cm−1 were observed for 3B and 3H respectively in Nujol,
To probe in more detail the factors responsible for differences in
the M–X(1) and M–X(2) bond lengths in 1B, 2B, and 4B, and
the nature of M–X–BR3 interactions, complexes of a borane-free
analogue of TXPB, 2,7-di-tert-butyl-4-diphenylphosphino-9,9-
dimethylthioxanthene (TXPH), were prepared.
The TXPH ligand was accessed by lithiation of 2,7-di-tert-
butyl-4-bromo-5-diphenylphosphino-9,9-dimethylthioxanthene
(TXPBr)7 followed by quenching with deoxygenated MeOH.
Reaction of [PtCl2(COD)], [PdCl2(COD)], 0.5[{RhCl(CO)2}2]
and [PtI2(COD)] with TXPH then provided [PtCl2(TXPH)]
(1H), [PdCl2(TXPH)] (2H), [RhCl(CO)(TXPH)] (3H) and
[PtI2(TXPH)] (4H), respectively (Scheme 3). As in complex 3B,
the CO ligand in 3H is cis to the phosphine donor, based on a
indicative of decreased electron density at the metal centre in 3B.
However, a very broad carbonyl stretch at 2013 cm−1 was
observed for both complexes in CH2Cl2.
X-ray quality crystals of 2H·2CH2Cl2 and 4H·1.5CH2Cl2
were grown by slow diffusion of hexanes into CH2Cl2 solutions
of each complex at −30 °C (Table 1, Fig. 3). Both complexes are
square planar with M–P, M –S, M–X(1) and M–X(2) bond dis-
tances (Table 3) very close to those in the TXPB analogues
(Table 2). These data highlight that in complexes 2B and 4B
(and by extrapolation, 1B), the greater trans-influence of PAr3
vs. SAr2 donors11 is the major factor responsible for elongation
of the M–X(1) bond relative to M–X(2). In both 2H·2CH2Cl2
and 4H·1.5CH2Cl2, C9⋯S–M angles of 158° were observed,
3526 | Dalton Trans., 2012, 41, 3523–3535
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Table 2 Crystallographic, spectroscopic and electrochemical data for late transition metal TXPB chloro and iodo complexesa
Complex
1B
2B
3B
4B
5B
Metal and co-ligands
PtCl2
PdCl2
RhCl(CO)
PtI2
RhI(CO)
31P NMR [δ, ppm]
1JP, Pt or 1JP, Rh [Hz]
1JC,Rh/2JC,P for CO [Hz]
11B NMR [δ, ppm]
32.5
3836
—
58.4
—
—
13
63.8
161
77/18
12
41.6
3517
—
67.2
167
74/14
56
3
50
Ep vs. SCE (CH2Cl2, 200 mV s−1
)
Epc = −1.55
Epc = −0.81
Epa = 0.97
Epc = −1.43
Epa = 0.79
ν(CO)(CH2Cl2/Nujol) [cm−1
]
—
—
2013/2010
—
2002/2004
X-ray crystal structure reference
Lattice solvent in crystal
M–X(1) [Å]
M–X(2) or M–CO [Å]
M–P [Å]
M–S [Å]
B–X(1) [Å]
This work
2 CH2Cl2
2.391(2)
2.321(2)
2.213(2)
2.243(2)
2.14(1)
95.9(3)
342(2)
20(2)
160
0.54
0.46
51
This work
2 CH2Cl2
2.396(1)
2.313(1)
2.226(1)
2.256(1)
2.101(4)
94.6(1)
340(1)
19.6(4)
161
This work
None
8
This work
1.31 CH2Cl2
2.637(2)
2.590(2)
2.222(5)
2.246(5)
2.75(2)
82.7(5)
352(2)
26(3)
163
0.45
0.26
53
8
Hexane
2.381(2)
1.82(1)
2.205(2)
2.379(2)
2.00(1)
104.6(3)
340(1)
–13(1)
146
Hexane
2.664(1)
1.855(7)
2.224(1)
2.300(1)
3.125(7)
74.0(1)
357(1)
17(1)
165
0.14
0.16
53
2.352(3)
2.290(3)
2.219(3)
2.320(3)
1.98(1)
107.7(4)
337(1)
–5(2)
146
1.05
0.45
47
M–X(1)–B [°]
Σ(C–B–C) [°]
S–C(12)–C(5)–Bb [°]
C(9)⋯S–M [°]
M–(PCCSplane)c [Å]
B–(CCCplane)d [Å]
Ligand bende [°]
0.57
0.42
51
1.02
0.43
43
a In the X-ray crystal structures of 1B–5B, atoms C(1)–C(13) of the xanthene ligand backbone are numbered as shown in Scheme 1. b Positive S–C
(12)–C(5)–B torsion angles indicate that boron is oriented up into the fold of the thioxanthene backbone. c PCCS plane = P–C4–C11–S. d CCC plane
= C5–C36–C42. e Ligand bend = the angle between the two aromatic rings in the thioxanthene backbone of the ligand [i.e. 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].
Scheme 2 Preparation of [PtI2(TXPB)] (4B).
and the M–X(1) bond is directed towards the outside of the fold
of the ligand backbone, leading to C9⋯S–M angles in the
157–165° range. This M–X(1) bond orientation is analogous
to that in 1B·2CH2Cl2, 2B·2CH2Cl2, 4B·1.31CH2Cl2, and
5B·hexane, but not 2B or 3B·hexane.
Scheme 3 Preparation and complexation of the TXPH ligand.
Electrochemistry of chloro and iodo complexes
of irreversible peak potentials to parameters such as uncompen-
sated resistance, diffusion coefficients and test complex concen-
tration (E1/2 values are insensitive to these parameters).24 More
reversible redox behaviour was not observed in a CV of 2H in
CH2Cl2 at −78 °C using [NBu4][B(C6F5)4] as the base
electrolyte.
All TXPB complexes and their TXPH analogues were investi-
gated by cyclic voltammetry (CV) in CH2Cl2 (platinum disk
electrode, [NBu4][PF6] base electrolyte, FeCp*2 calibrant; Tables
2 and 3). Palladium and platinum complexes exhibited an ir-
reversible reduction peak while rhodium complexes 3B and 5B
gave rise to an irreversible oxidation peak. At a scan rate of
200 mV s−1, the Epc values for 4B and 4H are equal within
error. By contrast, the Epc values for the Pd and Pt chloro TXPB
complexes are less negative, by 80–300 mV, than those for
TXPH analogues, suggesting decreased electron density at the
metal centre in chloro TXPB complexes. However, these differ-
ences should be viewed with some caution given the sensitivity
DFT calculations
To further investigate the strength and consequences of halide
ligand–borane coordination, DFT calculations (ADF, all-electron,
TZ2P, ZORA, VWN, PW91) were carried out on 1B–5B (for
This journal is © The Royal Society of Chemistry 2012
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Fig. 3 Solid state structures for: (a) [PdCl2(TXPH)]·2CH2Cl2 (2H·2CH2Cl2) and (b) [PtI2(TXPB)]·1.5CH2Cl2 (4H·1.5CH2Cl2) with ellipsoids at
50% probability. Both CMe3 groups in 2H·2CH2Cl2 and one CMe3 group in 2B·2CH2Cl2 are disordered over two positions; only one orientation is
shown. Hydrogen atoms and lattice solvent are omitted for clarity.
Table 3 Spectroscopic, crystallographic and electrochemical data for
TXPH complexes
be a consequence of a particularly shallow potential energy
surface associated with changes in the B–X bond length in iodo
complexes.
Complex
1H
2H
3H
4H
At least one molecular orbital involved in B–X(1) bonding
was observed for all TXPB complexes (Fig. 4), and selected
Mayer bond orders25 and Hirshfeld charges26 are listed in
Table 5. The B–X(1) Mayer bond orders are 0.626, 0.654, 0.639,
0.585 and 0.337 in 1B, 2B, 3B, 4B and 5B (the B–I(1) Mayer
bond order is 0.509 for the TZ2P geometry optimized structure
of 4B with the B–X(1) bond constrained to the crystallographi-
cally determined bond distance). These data are indicative of
greater covalency in B–Cl bonds relative to B–I bonds, despite
the higher electronegativity of chlorine. However, they do not
provide direct insight into the strength of B–Cl vs. B–I bonding.
Now comparing TXPB complexes with their TXPH ana-
logues, the differences in M–P, M –S and M–X(2) Mayer bond
orders are never more than 4%. By contrast, the M–X(1) Mayer
bond orders for 1B–5B are 19, 27, 20, 10 and 8% lower than the
corresponding bond orders for 1H–5H, indicating that the M–X
(1) bonds in all five TXPB complexes are weakened as a result
of borane complexation; to a greater extent in chloro complexes
1B–3B. Calculated M–X(1) bond distances are also elongated
(by 0.049, 0.070 and 0.030 Å) in chloro TXPB complexes 1B–
3B, relative to their TXPH analogues. By contrast, the M–X(1)
bonds in 4B and 5B lie within 0.01 Å of the M–X(1) distances
in their TXPH analogues.
RhCl
(CO)
Metal and co-ligands PtCl2
PdCl2
PtI2
31P NMR [δ, ppm]
1JC,Rh/2JC,P for CO
[Hz]
38.6
—
61.4
—
69.5
78/16
43.6
—
1JP, Pt or 1JP, Rh [Hz]
3458
—
148
3251
Ep vs. SCE (CH2Cl2,
Epc
−1.63
=
Epc
=
Ill
defined
Epc =
−1.45
200 mV s−1
)
−1.11
ν(CO)(CH2Cl2/Nujol)
[cm−1
Lattice solvent in
crystal
—
—
—
2013/
2001
—
—
]
2CH2Cl2
1.5CH2Cl2
M–X(1) [Å]
M–X(2) or M–CO
[Å]
M–P [Å]
M–S [Å]
—
—
2.369(3)
2.308(3)
—
—
2.658(1)
2.607(1)
—
—
—
—
2.216(3)
2.260(3)
158
—
—
—
—
2.232(3)
2.258(3)
158
C(9)⋯S–M [°]
Ligand benda [°]
48
49
a Ligand bend = the angle between the two aromatic rings in the
thioxanthene backbone of the ligand [i.e. the angle between the C(1)/C
C(5)/C(6)/C(7)/C(8)/C(12)/C(13)
planes]. In the X-ray crystal structures of 2H and 4H, atoms C(1)–C(13)
(2)/C(3)/C(4)/C(10)/C(11)
and
of the xanthene ligand backbone are numbered as shown in Scheme 3.
Borane coordination in TXPB complexes also results in less
negative Hirshfeld charges on X(1), relative to TXPH com-
plexes; Hirshfeld charges on X(1) lie in the −0.01 to −0.14
range for 1B–5B, compared with −0.27 to −0.37 in 1H–5H.
These changes as a result of boron–halide coordination are
accompanied by a slight reduction in the positive charge on
boron; Hirshfeld charges on boron are 0.02–0.04 in 1B–4B and
0.08 in 5B, compared with 0.12 in the free TXPB ligand (for
comparison, the Hirshfeld charges on boron and iodine are 0.01
and −0.25 in the [TXPB–I]− anion calculated at the same level
of theory; B–I = 2.456 Å; Σ(C–B–C) = 339.1°; B–I Mayer bond
order = 0.793).
complex 2B, the geometry in 2B·2CH2Cl2 was used as the start-
ing point for geometry optimization), 1H–4H, and [RhI(CO)
(TXPH)] (5H). The geometry optimized structures for crystallo-
graphically characterized 1B–5B, 2H and 4H match closely with
experimental values (Table 4). For example, calculated M–P,
M–S, M–X bond lengths lie within 0.05 Å (2%) of the exper-
imental values, and the calculations satisfactorily reproduced the
bond angles at the metal (<1.5% deviation for TXPB complexes
and <3.5% deviation for TXPH complexes). M–X–B bond
angles were also reproduced to within 6% of crystallographic
values, and calculated B–X bond distances in the TXPB com-
plexes differed from crystallographically determined values by
1.5–3% in 1B–3B and 5B and 5% in 4B. The larger difference
between calculated and crystallographic bond lengths in 4B may
All TXPB and TXPH complexes were further investigated
through a fragment approach that considered the interaction of
an uncharged MX2 (M = Pt or Pd) or RhX(CO) fragment with a
neutral TXPB or TXPH ligand (fragments were generated from
3528 | Dalton Trans., 2012, 41, 3523–3535
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Table 4 Calculated bond lengths (Å) and angles (°) for complexes 1B–5B and 1H–5H [Y = X(2) or CO]. Where available, crystallographic valuesa
are shown in square brackets27
Compound 1B
1H
2B
2H
3B
3H
RhCl
(CO)
4B
4H
5B
5H
RhI
(CO)
MXY
M–P
PtCl2
PtCl2 PdCl2
PdCl2
RhCl(CO)
PtI2
PtI2
RhI(CO)
2.222
[2.213(2)]
2.248
2.224 2.233
2.239
[2.216(3)]
2.286
[2.260(3)]
2.358
[2.369(3)]
2.320
2.225
[2.205(2)]
2.394
[2.379(2)]
2.399
[2.381(2)]
1.841
[1.82(1)]
2.040
[2.00(1)]
170.6
[172.6(1)]
169.2
[171.3(3)]
105.0
2.229
2.379
2.369
1.841
—
2.243
[2.222(5)]
2.276
[2.246(5)]
2.689
[2.637(2)]
2.643
[2.590(2)]
2.614
[2.75(2)]
174.4
[175.0(1)]
172.2
[171.8(1)]
87.7
2.243
[2.232(3)]
2.279
[2.258(3)]
2.690
[2.658(1)]
2.640
2.241
[2.224(1)]
2.320
[2.300(1)]
2.699
[2.664(1)]
1.845
[1.855(7)]
3.043
[3.125(7)]
170.5
[169.58(4)]
166.1
[163.8(2)]
78.0
2.236
2.383
2.690
1.839
—
[2.226(1)]
2.257 2.258
[2.256(1)]
2.365 2.428
[2.396(1)]
2.323 2.319
[2.313(1)]
2.065
[2.101(4)]
177.5 171.9
[173.35(3)]
178.1 173.2
[171.80(3)]
98.6
M–S
[2.243(2)]
2.414
[2.391(2)]
2.324
M–X(1)
M–Y
[2.321(2)]
2.107
[2.308(3)]
—
[2.607(1)]
—
B–X(1)
—
[2.14(1)]
P–M–X(1) 173.9
[174.8(1)]
172.5
[173.4(1)]
M–X(1)–B 98.3
[95.9(3)]
Σ(C–B–C) 340.8
[342(2)]
176.8
[171.1(1)]
175.6
[175.7(1)]
—
175.9
172.5
—
173.3
[169.3(1)]
179.8
[178.3(1)]
—
173.2
174.1
—
S–M–Y
—
—
[94.6(1)]
338.9
[340(1)]
[104.6(3)]
339.0
[340(1)]
[82.7(5)]
346.6
[352(2)]
[74.0(1)]
353.9
[357(1)]
—
—
—
—
a For complex 2B, crystallographic values are from 2B·2CH2Cl2.
analysis of 1B–5B and 1H–5H (Table 5, Fig. 6), which par-
titions the total interaction energy (ΔEint) between two prepared
fragments into three major components: (1) orbital mixing
(ΔEorb), which includes electron pair bonding, charge-transfer,
donor–acceptor interactions, and intrafragment polarization, (2)
the electrostatic interaction energy (ΔEelec), which is typically
dominated by nucleus–electron attractions, and (3) Pauli repul-
sion (ΔEPauli) which arises from destabilizing interfragment inter-
actions between electrons with the same spin.
The orbital mixing contribution is substantially more negative
in TXPB complexes relative to their TXPH analogues; by
274–322 kJ mol−1 in 1B–3B, 163 kJ mol−1 in 4B, and 102 kJ
mol−1 in 5B. These data support the presence of a strong
covalent contribution to B–Cl(1) bonding, and a weaker but still
significant covalent contribution to B–I(1) bonding. In TXPB
complexes, the electrostatic contribution to bonding is also more
negative than that in TXPH analogues, and this difference is
markedly more pronounced in chloro complexes than iodo com-
plexes; ΔEelec(TXPB_complex)–ΔEelec(TXPH_complex) is −192
to −233 kJ mol−1 in 1B–3B, compared with −101 and −85 kJ
mol−1 in 4B and 5B. These data are commensurate with the
greater electronegativity of chlorine vs. iodine, and the shorter
B–X distances in chloro vs. iodo complexes. In contrast to the
orbital mixing and electrostatic terms, the Pauli repulsion term is
more positive in TXPB complexes relative to TXPH analogues;
by approx. 400 kJ mol−1 in 1B–3B and approx. 200 kJ mol−1 in
4B and 5B. The larger Pauli repulsion term in chloro vs. iodo
TXPB complexes presumably arises due to closer approach of
the borane and the chloro ligand.
Fig. 4 Slater-type molecular orbitals involved in B–X(1) bonding in
chloro complex 1B and iodo complex 4B: (a) HOMO–13 in 1B, (b)
HOMO–17 in 1B, (c) HOMO–28 in 1B, (d) HOMO–21 in 4B. Iso-
surfaces are set to 0.03.
the TZ2P geometry optimized structures of each complex). For
each TXPB complex and TXPH analogue, the Hirshfeld charge
on the TXPB fragment is less positive than the Hirshfeld charge
on the TXPH fragment by 0.06–0.15 electrons, consistent with
donation of electron density from X(1) to boron. Regions in
which electron density is depleted or increased upon combi-
nation of each MX2 or MX(CO) fragment with TXPB or TXPH
are illustrated in the SCF deformation density (SCF electron
density for the molecule minus the sum of the SCF electron
density for the two fragments) isosurfaces in Fig. 5. These iso-
surfaces clearly show electron donation from the halide to the
borane in both the chloro and iodo TXPB complexes.
Overall, the total interaction energy (ΔEint) for combination of
an MX2 or MX(CO) fragment with a TXPB or TXPH fragment
is more positive in TXPB complexes than in TXPH analogues,
and this difference is more pronounced in chloro complexes than
iodo complexes; ΔEint(TXPB_complex)–ΔEint(TXPH_complex)
is −80 to −110 kJ mol−1 in 1B–3B, compared with −30 and
Particularly valuable insight into the bonding situation in
TXPB complexes was gained through energy decomposition
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Table 5 Mayer bond orders (MBO), Hirshfeld charges, and energy decomposition analysis data for complexes 1B–5B and 1H–5H. Hirshfeld
charges for MXY and L are from fragment analysis [X = X(1), Y = X(2) or CO, L = TXPB or TXPH]27
Compound
MXY
1B
PtCl2
1H
PtCl2
2B
PdCl2
2H
PdCl2
3B
RhCl(CO)
3H
RhCl(CO)
4B
PtI2
4H
PtI2
5B
RhI(CO)
5H
RhI(CO)
M–P MBO
M–S MBO
M–X(1) MBO
Δ[M–X(1)]a
M–Y MBO
B–X(1) MBO
1.211
1.040
0.645
19%
0.849
0.626
1.212
1.023
0.766
1.098
0.922
0.569
27%
0.794
0.654
1.068
0.884
0.723
1.1774
0.7447
0.6047
20%
1.3126
0.6387
1.152
0.7695
0.7234
1.170
0.983
0.729
10%
0.904
0.5850
1.165
0.980
0.804
1.1609
0.8590
0.6889
8%
1.2875
0.3368
1.1293
0.7660
0.7466
0.839
—
0.777
—
1.289
—
0.905
—
1.2611
—
M Hirshfeld
0.1330
−0.0497
0.2606
−0.2529
0.0347
0.103
−0.3103
0.3238
−0.0825
0.2846
−0.3118
0.0230
0.2960
−0.3671
0.0410
−0.0319
0.2885
—
0.0080
−0.3204
0.0668
−0.0114
0.2546
−0.1931
0.0430
0.0394
−0.2660
0.0180
−0.1448
0.1262
—
–0.0221
−0.2710
X(1) Hirshfeld
Δ[X(1) Hirsh]b
X(2) Hirshfeld
B Hirshfeld
−0.2629
—
−0.3099
—
—
—
−0.2027
—
—
—
0.0231
0.0847
MXY Hirshfeld
L Hirshfeld
−0.2076
0.2077
−0.1462
−0.3537
0.3539
−0.2107
0.2112
−0.1427
−0.3537
0.3539
−0.0449
0.0449
−0.1207
−0.1652
0.1656
−0.2412
0.2418
−0.1533
−0.3949
0.3951
−0.1231
0.1238
−0.0600
−0.1832
0.1838
Δ[L Hirsh]c
ΔEint
Δ(ΔEint
ΔEorb
Δ(ΔEorb
ΔEelec
Δ(ΔEelec
ΔEPauli
−573
−80
−493
−756
−1152
1414
−491
−108
−905
−322
−1102
−233
1516
448
−383
−583
−869
1068
−477
−110
−810
−294
−982
−198
1315
382
−367
−516
−784
933
−455
−30
−425
−718
−1157
1450
−368
−19
−605
−102
−877
−85
−348
−503
−792
947
)
−1030
−274
−1344
−192
1801
387
−880
−163
−1258
−101
1684
234
)
)
1115
168
Δ(ΔEPauli
)
ΔEx in kJ mol−1. ΔEint = total interaction energy; ΔEorb = orbital mixing energy; ΔEelec = electrostatic interaction energy; ΔEPauli = Pauli repulsion
energy; Δ(ΔEx) = ΔEx (TXPB_complex) − ΔEx(TXPH_analogue). a Δ[M–X(1)] = [(M–X(1) distance in TXPH complex/M–X(1) distance in TXPB
analogue)*100] − 100. b Δ[X(1) Hirsh] = ‘X(1) Hirshfeld’ for TXPB complex–‘X(1) Hirshfeld’ for TXPH analogue. c Δ[L Hirsh] = ‘L Hirshfeld’ for
TXPB complex–‘L Hirshfeld’ for TXPH analogue.
−19 kJ mol−1 in 4B and 5B. In chloro TXPB complexes, the
larger contribution (relative to iodo TXPB complexes) from B–X
bonding to the total interaction energy arises from significantly
more negative orbital mixing and electrostatic terms, which are
partially offset by a larger Pauli repulsion term. The presence of
a significantly stronger B–X interaction in the chloro complexes
relative to the iodo complexes is commensurate with the exper-
imentally determined 11B NMR chemical shifts, B–X distances,
and C–B–C angles. The relative weakness of the B–I interactions
in 4B and 5B is consistent with the poor match between a fairly
hard borane Lewis acid and a soft iodide anion. Indeed, [NBu4]
[BI4] is reported to be extremely labile,28 [NEt4][BI4] is pro-
posed to ionize to [NEt4]+, [BI2(NCMe)2]+ and I− (2 equiv.)
upon dissolution in acetonitrile,29 in the reaction of BPh3 with
[NEt4]I in CH2Cl2, the equilibrium lies towards the reactants
rather than the iodoborate salt, and [Co(C5H4BiPr2I)
frequency than free TXPB. By contrast, TXPB iodo complexes
4B and 5B display B–I(1) distances that are roughly 0.5 Å
longer than those reported for iodoboranes, only slight pyramida-
lization at boron, and 11B NMR signals that are shifted
10–20 ppm to lower frequency than free TXPB. Structural, spec-
troscopic and/or computational comparison of TXPB complexes
1B–5B with TXPH complexes 1H–5H allowed for more detailed
analysis of the M–X(1)–BR3 interactions in TXPB complexes.
Crystallographically and computationally determined M–X(1)
and M–X(2) bond lengths revealed that the differing trans-
influence of PAr3 and SAr2 donors plays a major role in the
elongation of M–X(1) bonds relative to M–X(2) bonds.
However, in all the TXPB complexes, borane-coordination does
result in reduced M–X(1) Mayer bond orders and smaller Hirsh-
feld charges on X(1) relative to the TXPH analogues. Energy
decomposition analysis using MX2 or MX(CO) and TXPB or
TXPH fragments revealed a larger contribution from B–X
bonding to the total interaction energy in chloro TXPB com-
plexes, relative to iodo TXPB complexes; ΔEint(TXPB_com-
plex)–ΔEint(TXPH_complex) is −80 to −110 kJ mol−1 in 1B–
3B vs. −30 and −19 kJ mol−1 in 4B and 5B. The larger contri-
bution in chloro complexes arises from significantly more nega-
tive orbital mixing and electrostatic terms, which are partially
offset by a larger Pauli repulsion term. The presence of a signifi-
cantly stronger B–X interaction in the chloro complexes relative
to the iodo complexes is consistent with the trends in B–X Mayer
bond order, 11B NMR chemical shift, irreversible peak potentials
from cyclic voltammetry, B–X distance, and C–B–C angle.
(C5H4BiPr2)] is substantially dissociated to [Co(C5H4BiPr2)2]I in
−
CH2Cl2.30 However, BI4
salts of [C7H7]+, [CPh3]+,31
[C5Me5BI]+,32 and [{Si(SitBu3)}4I]+ cations33 have been
reported, as has [C7H7][PhBI3].34
Conclusions
The chloro TXPB complexes 1B, 2B and 3B exhibit strong
M–Cl(1)–BR3 bridging interactions, resulting in B–Cl(1) dis-
tances that are only 0.04–0.22 Å longer than those reported for
chloroborate complexes, significant pyramidalization at boron,
and approx. 60 ppm shifts in the 11B NMR signal to lower
3530 | Dalton Trans., 2012, 41, 3523–3535
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standard techniques.35 A Fisher Scientific Ultrasonic FS-30 bath
was used to sonicate reaction mixtures where indicated. Residual
oxygen and moisture was removed from the argon stream by
passage through an Oxisorb-W scrubber from Matheson Gas
Products.
Anhydrous CH2Cl2 was purchased from Aldrich. Hexanes and
toluene were initially dried and distilled at atmospheric pressure
from CaH2 and Na, respectively. Unless otherwise noted, all
proteo solvents were stored over an appropriate drying agent
(toluene, benzene = Na/Ph2CO; hexanes = Na/Ph2CO/tetra-
glyme; CH2Cl2 = CaH2) and introduced to reactions via vacuum
transfer with condensation at −78 °C. The deuterated solvents
CD2Cl2 and C6D5Br (ACP Chemicals) were dried over CaH2.
[PdCl2(COD)], [PtCl2(COD)] and [PtI2(COD)] were purchased
t
from Strem Chemicals. [{RhCl(CO)2}2] and BuLi (1.7 M in
pentane) were purchased from Sigma-Aldrich. Prior to use,
tBuLi solutions were titrated with N-benzylbenzamide (Aldrich)
at −45 °C.36 The compounds TXPBr and TXPB were prepared
as previously described.7
NMR spectroscopy (1H, 13C{1H}, DEPT-135, DEPTq, COSY,
HSQC, HMBC) was performed on Bruker DRX-500 and
1
AV-600 spectrometers. All H NMR and 13C NMR spectra were
referenced relative to SiMe4 through a resonance of the
employed deuterated solvent or proteo impurity of the solvent;
1
CD2Cl2 (5.32 ppm), C6D5Br (δ 7.30, 7.02, 6.94 ppm) for H
NMR, and CD2Cl2 (54.0 ppm), C6D5Br (δ 130.9, 129.3, 126.1,
122.3 ppm) for 13C NMR. Herein, numbered proton and carbon
atoms refer to the positions of the xanthene backbone in the
TXPB or TXPH ligands (see Schemes 1 and 3).
Fig. 5 SCF deformation density isosurfaces from fragment analysis of
(a) chloro complex 1B and (b) iodo complex 4B. Blue represents
increased electron density and red represents depleted electron density,
relative to the constituent MX2 and TXPB fragments (isosurfaces are set
to 0.003).
Combustion elemental analyses were performed on a Thermo
EA1112 CHNS/O analyser and IR spectra were recorded on a
Bio-Rad FTS-40 FTIR instrument. Cyclic voltammetry (CV)
studies were carried out using a PAR (Princeton Applied
Research) model 283 potentiostat (using PAR PowerCV soft-
ware) in conjunction with a three-electrode cell under an argon
atmosphere. The auxiliary electrode was a platinum wire, the
pseudo-reference electrode a silver wire, and the working elec-
trode a platinum disc (1.6 mm diameter, Bioanalytical Systems).
Solutions were 1 × 10–3 M in test compound and 0.1 M in
[NnBu4][PF6] as the supporting electrolyte in CH2Cl2. In all
Experimental section
General details
An argon-filled MBraun UNIlab glove box equipped with a
−30 °C freezer was employed for the manipulation and storage
of the TXPB ligand and its complexes, and reactions were
performed on a double manifold high vacuum line using
Fig. 6 Graphs of (a) ΔEint, (b) ΔEorb, (c) ΔEelec, and (d) ΔEPauli from energy decomposition analysis of complexes 1B–5B and 1H–5H using MX2,
MX(CO), TXPB and TXPH fragments in conformations corresponding to those in each complex. Double headed arrows are provided for graphical
comparison of the magnitude of ΔEx(TXPB_complex)–ΔEx(TXPH_complex) (x = int, orb, elec or Pauli) between chloro and iodo complexes.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 3523–3535 | 3531

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experiments, potentials were calibrated by addition of [FeCp*2];
the E1/2 value for [FeCp*2]0/+1 is −0.07 V vs. the SCE.37
stirred at room temperature for 1 h. The resulting solution was
evaporated to dryness in vacuo leaving an oily orange solid to
which hexanes (15 mL) was added. After sonication for 30 min,
the mixture was filtered to collect a peach solid, which was
washed with hexanes (×1) and dried in vacuo. Yield = 78 mg
Single-crystal X-ray crystallographic analyses were performed
on suitable crystals coated in Paratone oil and mounted on
either: (a) a P4 diffractometer with a Bruker Mo rotating-anode
generator and a SMART1K CCD area detector, or (b) a SMART
APEX II diffractometer with a 3 kW sealed tube Mo generator,
both in the McMaster Analytical X-Ray (MAX) Diffraction
Facility. In all cases, non-hydrogen atoms were refined anisotro-
pically and hydrogen atoms were generated in ideal positions
and then updated with each cycle of refinement. The following
groups were rotationally or positionally disordered over two pos-
itions: (a) one of the tert-butyl substituents in 1B·2CH2Cl2, (b)
both molecules of CH2Cl2 in 1B·2CH2Cl2, (c) one of the tert-
butyl substituents in 2B·2CH2Cl2, (d) both molecules of CH2Cl2
in 2B·2CH2Cl2, (e) both of the tert-butyl substituents in
2H·2CH2Cl2, (f) one of the tert-butyl substituents in
4H·1.5CH2Cl2, and (g) one molecule of CH2Cl2 in
4H·1.5CH2Cl2; the other half molecule of CH2Cl2 was
SQUEEZED from this lattice due to unresolvable disorder.38
In all cases, disorder was modelled allowing occupancy and
positional parameters to refine freely. All tert-butyl methyl
groups in cases (a), (c), (e) and (f) above were restrained to have
equivalent thermal parameters, and were refined anisotropically.
The quaternary carbon–methyl carbon bond distances within the
disordered tert-butyl substituents in 1B·2CH2Cl2, 2B·2CH2Cl2,
2H·2CH2Cl2, and 4H·1.5CH2Cl2 were restrained to approxi-
mately 1.54 Å. In addition, the Cmethyl–C–Cmethyl bond angles in
the disordered tert-butyl substituent in 1B·2CH2Cl2 were
restrained to approximately 109.5°. For cases (a), (c), and (f),
the disorder found within each of the modelled tert-butyl substi-
tuents was equal to 0.59(1), 0.637(5), and 0.41(1), respectively.
For case (e), the disorder found within the tert-butyl substituents
was 0.46(3) (C16–C19) and 0.14(1) (C20–C23). The carbon–
chlorine bond distances in molecules of CH2Cl2 found in
1B·2CH2Cl2, 2B·2CH2Cl2, 4B·1.31CH2Cl2 and 4H·1.5CH2Cl2
were restrained to approximately 1.77 Å. For cases (b), (d) and
(g), CH2Cl2 carbon and chlorine atoms were restrained to have
equivalent thermal parameters, respectively. For case (b),
CH2Cl2 carbon and chlorine atoms were refined using the ISOR
command; unrestrained anisotropic refinement of the CH2Cl2
molecules resulted in unstable refinement of the carbon atoms.
The disorder for each molecule of CH2Cl2 in case (b) is 0.56(2)
(C48, Cl3, Cl4) and 0.60(3) (C49, Cl5, Cl6). For case (d), the
CH2Cl2 carbon and chlorine atoms were refined anisotropically,
and the disorder for each molecule of CH2Cl2 is 0.46(6) (C48,
Cl3, Cl4) and 0.43(1) (C49, Cl5, Cl6). For case (g), one mol-
ecule of CH2Cl2 [disorder = 0.39(1)] was refined using the ISOR
command because unrestrained anisotropic refinement resulted
in unstable refinement for the carbon atom. Both molecules of
CH2Cl2 in 4B·1.31CH2Cl2 were refined with partial occupancy
[0.60(1) for C48, Cl1, Cl2; 0.70(1) for C49, Cl3, Cl4]. Positional
disorder throughout 4B·1.31CH2Cl2 and 4H·1.5CH2Cl2 was re-
solved by applying similar constraints to the thermal parameters.
1
(59%). H NMR (CD2Cl2): δ 7.83 (s, 1H, CH1), 7.77 (m, 1H,
Ph), 7.63–7.59 (broad m, 1H, Ph), 7.60 (m, 1H, CH8),
7.57–7.48 (m, 3H, Ph), 7.38–7.12 (m, 15 H, Ph), 7.25 (d, J 11
Hz, 1H, CH3), 7.13 (s, CH6), 2.17, 1.55 (broad s, 2 × 3H,
CMe2), 1.25 (s, 9H, C2CMe3), 1.17 (s, 9H, C7CMe3). 13C{1H}
NMR (CD2Cl2): δ 155.05 (s, C2CMe3), 151.58, 149.43 (broad s,
C5 & ipso-BPh2), 151.01 (s, C7CMe3), 150.50 (s, C12), 145.84
(d, J 12 Hz, C10), 140.96 (s, C13), 137.86 (s, C11), 135.9, 135.2,
134.6, 134.1, 133.0, 132.9, 129.7, 129.2, 127.5, 127.4, 127.4,
126.7 (s, 12 × Ph), 133.97 (s, CH6), 131.65 (d, J 66 Hz, C4),
129.20 (s, CH3), 127.11 (s, CH1), 121.17 (s, CH8), 43.03 (s,
CMe2), 35.64 (s, C2CMe3), 35.28 (s, C7CMe3), 31.42 (s, 2 ×
CMe3), 28.36, 26.19 (s, 2 × CMe2). 31P{1H} (CD2Cl2): δ +
1
32.48 (s, JP,195Pt 3836 Hz). 11B (CD2Cl2): δ 3 (broad s). Anal.
calcd for C53H62PSBCl2Pt: C, 61.27; H, 6.01. Found: C, 61.33;
H, 5.47%.
[PtI2(TXPB)] (4B)
A solution of [PdI2(COD)] (37 mg, 6.64 × 10−4 mol) and TXPB
(55 mg, 8.01 × 10−5 mol) in CH2Cl2 (10 mL) was stirred at
room temperature for 30 min. The resulting solution was evapor-
ated to dryness in vacuo leaving an orange solid to which
hexanes (10 mL) was added. After sonication, the mixture was
filtered to collect an orange solid, which was washed with
1
hexanes and dried in vacuo. Yield = 55 mg (73%). H NMR
(CD2Cl2): δ 7.84 (s, 1H, CH1), 7.78 (d, J 2 Hz, 1H, CH8),
7.54–7.45 (m, 6H, p-PPh2 & m-PPh2), 7.43–7.36 (m, 8H, o-
PPh2 and BPh2), 7.25 (dd, J = 9, 2 Hz, 1H, CH3), 7.05–6.97 (m,
6H, BPh2), 6.98 (d, J 2 Hz, CH6), 2.03 (broad s, 6H, CMe2),
1.25 (s, 9H, C2CMe3), 1.16 (s, 9H, C7CMe3). 13C{1H} NMR
(CD2Cl2): δ 154.98 (s, C2CMe3), 150.26 (s, C7CMe3), 146.92
(broad s, C5), 146.35 (d, J 12 Hz, C10), 145.99 (broad s, ipso-
BPh2), 143.36 (s, C13), 139.71 (d, J 22 Hz, C11), 138.70 (s,
BPh2), 134.95 (d, J 11 Hz, m-PPh2), 134.00 (CH6), 132.30 (d, J
61 Hz, ipso-PPh2), 132.23 (s, p–PPh2), 129.64 (s, C12), 129.09
(s, BPh2), 129.01 (s, CH3), 128.77 (d, J 12 Hz, m-PPh2), 127.41
(s, BPh2), 126.88 (s, CH1), 123.41 (s, CH8), 44.01 (s, CMe2),
35.58 (s, C2CMe3), 35.27 (s, C7CMe3), 31.48 (s, C2CMe3),
31.40 (s, C7CMe3), 27.01 (s, CMe2). 31P{1H} (CD2Cl2): δ 41.61
(1JP,195Pt 3517 Hz). 11B (CD2Cl2): δ 50 ppm (broad s). Anal.
calcd for C47H48PSBI2Pt: C, 49.72; H, 4.26. Found: C, 49.43;
H, 4.51%.
TXPH ligand
A 1.81 M solution of tert-butyl lithium in pentane (1.8 mL,
3.32 mmol) was added to a solution of TXPBr (1.00 g,
1.66 mmol) in toluene (60 mL) at −78 °C, and the mixture was
allowed to warm to room temperature over 12 h. The resulting
yellow solution was cooled to −78 °C and N2-saturated MeOH
(0.2 mL, 4.9 mmol) was added dropwise. After stirring for
10 min at −78 °C and 20 min at room temperature, the mixture
[PtCl2(TXPB)]·hexane (1B)
A solution of [PtCl2(COD)] (52 mg, 1.39 × 10–4 mol) and
TXPB (100 mg, 1.46 × 10–4 mol) in CH2Cl2 (10 mL) was
3532 | Dalton Trans., 2012, 41, 3523–3535
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was evaporated to dryness in vacuo. Hexanes (30 mL) was then
added, and the mixture was sonicated before filtration to collect
a white solid, which was washed with hexanes (×1) and evapor-
ated to dryness in vacuo. Yield 765 mg (88%). 1H NMR
(CD2Cl2): δ 7.55 (m, 2H, CH1 & CH8), 7.38–7.35 (m, 6H, o–
PPh2 and p–PPh2), 7.31 (app. t d, J 7, 2 Hz, 4H, m–PPh2), 7.29
(d, J 8 Hz, 1H, CH5), 7.19 (dd, J 8, 2 Hz, 1H, CH6), 6.72 (dd, J
1.69 (s, 6H, CMe2), 1.18 (s, 9H, C7CMe3), 1.08 (s, 9H,
C2CMe3). 13C{1H} NMR (C6D5Br, 60 °C): δ 154.29 (s,
C2CMe3), 152.82 (s, C7CMe3), 146.46 (d, J 12 Hz, C10), 142.11
(s, C13), 137 (C11), 133.85 (d, J 11 Hz, o-PPh2), 131.89 (s, p-
PPh2), 130.82 (s, CH5), 128.5 (CH3 & m-PPh2), 126.40 (s,
CH1), 125.23 (s, C12), 124.69 (s, CH6), 122.06 (s, CH8), 42.63
(s, CMe2), 34.88 (s, C2CMe3), 34.70 (s, C7CMe3), 31.04 (s,
C7CMe3), 30.85 (s, C2CMe3), 26.60 (s, CMe2). 31P{1H}
(CD2Cl2): δ + 61.42 (s). Anal. calcd for C38H42PSCl2Pd: C,
62.77; H, 5.82. Found: C, 63.11; H, 5.67%.
2
4, 2 Hz, 1H, CH3), 1.72 (s, 6H, CMe2), 1.27 (d, JH,P 8 Hz, 9H,
PMe3), 1.32 (s, 9H, C7CMe3), 1.12 (s, 9H, C2CMe3). 13C{1H}
NMR (CD2Cl2): δ 150.38 (s, C7CMe3), 149.49 (s, C2CMe3),
143.03 (s. C10), 142.82 (s, C13), 137.21 (d, J 11 Hz, ipso-PPh2),
135.99 (d, J 28 Hz, C11), 135.24 (d, J 9 Hz, C4), 134.52 (d, J 20
Hz, m-PPh2), 130.34 (d, J 9 Hz, C12), 129.4–129.0 (s, p-PPh2 &
d, o-PPh2), 128.74 (s, CH3), 127.52 (s, C5), 123.69 (s, CH6),
122.76 (s, CH1), 121.97 (s, CH8), 41.50 (s, CMe2), 35.27 (s, 2 ×
CMe3), 31.74 (s, C7CMe3), 31.45 (s, C2CMe3), 25.32 (s, CMe2).
31P{1H} (CD2Cl2): δ −8.26 (s). Anal. calcd for C35H39PS: C,
80.42; H, 7.52. Found: C, 80.18; H, 7.50%.
[RhCl(CO)(TXPH)] (3H)
A mixture of [{Rh(μ-Cl)(CO)2}2] (35 mg, 9.00 × 10−5 mol) and
TXPH (100 mg, 1.91 × 10−4 mol) in CH2Cl2 (15 mL) was
stirred at room temperature for 1 h. At this temperature, CO was
evolved, and the mixture was then warmed to room temperature
and stirred for 1 h. The resulting orange solution was evaporated
to dryness in vacuo to give an orange solid to which hexanes
(15 mL) was added. After sonication, the mixture was filtered to
give a mustard yellow solid which was washed with hexanes and
dried in vacuo. Yield = 98 mg (79%). 1H NMR (CD2Cl2): δ 8.85
(d, J 8 Hz, 1H, CH5), 7.79 (s, 1H, CH1), 7.67 (dd, J 12, 8 Hz,
4H, o-PPh2), 7.62 (s, 1H, CH8), 7.50 (t, J 7 Hz, 2H, p-PPh2),
7.44 (app. t, J 8 Hz, 4H, m-PPh2), 7.40 (d, J 9 Hz, 1H, CH3),
7.35 (d, J 8 Hz, 1H, CH6), 1.86 (s, 6H, CMe2), 1.33, 1.24 (s, 2 ×
[PtCl2(TXPH)] (1H)
A solution of [PtCl2(COD)] (72 mg, 1.91 × 10−4 mol) and
TXPH (100 mg, 1.91 × 10−4 mol) in CH2Cl2 (15 mL) was
stirred at room temperature for 1 h. The resulting yellow solution
was evaporated to dryness in vacuo leaving a yellow solid to
which benzene (15 mL) was added. After sonication, the mixture
was filtered to give a pale yellow solid which was washed with
1
9H, CMe3). 13C{1H} NMR (CD2Cl2): δ 185.99 (dd, JC,Rh 78,
1
benzene and dried in vacuo. Yield = 70 mg (43%). H NMR
2JC,P 16 Hz, RhCO), 153.58 (s, C2CMe3), 152.77 (s, C7CMe3),
146.11 (d, J 13 Hz, C10), 143.24 (s, C13), 136.85 (d, J 27 Hz,
C11), 134–133 (C4 & ipso-PPh2), 133.57 (d, J 12 Hz, o-PPh2),
131.70 (s, p-PPh2), 129.67 (s, C5), 129.39 (d, J 11 Hz, m-PPh2),
128.33 (s, CH3), 127.33 (s, C12), 126.36 (s, CH1), 124.70 (s,
CH6), 122.75 (s, CH8), 42.86 (s, CMe2), 35.65 (s, C2CMe3),
35.48 (s, C7CMe3), 31.62 (s, C7CMe3), 31.49 (s, C2CMe3),
(CD2Cl2): δ 8.78 (d, J 8 Hz, 1H, CH5), 7.88 (dd, J 12, 8 Hz, 2H,
o-PPh2 A), 7.80 (s, 1H, CH1), 7.67 (dd, J 13, 8 Hz, 2H, o-PPh2
B), 7.64 (s, 1H, CH8), 7.63 (t, J 8 Hz, 1H, p-PPh2 A), 7.56 (app.
t, J 6 Hz, 2H, m-PPh2 A), 7.50 (t, J 7 Hz, 1H, p-PPh2 B), 7.43
(d, J 10 Hz, 1H, CH6), 7.40 (d, J 9 Hz, 1H, CH3), 2.13, 1.74 (s,
2 × 3H, CMe2), 1.35, 1.26 (s, 2 × 9H, CMe3). 13C{1H} NMR
(CD2Cl2): δ 155.45 (d, J 7 Hz, C2CMe3), 152.78 (s, C7CMe3),
146.53 (d, J 12 Hz, C10), 143.35 (s, C13), 139.09 (d, J 20 Hz,
C11), 134.55 (d, J 12 Hz, o-PPh2 B), 134.43 (d, J 11 Hz, o-PPh2
A), 132.79 (s, p-PPh2 A & B), 131.69 (d, J 65 Hz, C4 or ipso-
PPh2), 130.22 (s, CH5), 129.49 (d, J 12 Hz, m-PPh2 A), 129.30
(d, J 12 Hz, m-PPh2 B), 128.55 (s, CH3), 127.59 (s, CH1),
125.86 (s, C12), 125.00 (s, CH6), 123.15 (s, CH8), 43.71 (s,
CMe2), 35.68 (s, C2CMe3), 35.55 (s, C7CMe3), 31.58 (s,
C7CMe3), 31.45 (s, C2CMe3), 26.56, 26.05 (s, 2 × CMe2). 31P
1
25.91 (s, CMe2). 31P{1H} (CD2Cl2): δ + 69.52 (d, JP,Rh 148
Hz). Anal. calcd for C36H39OPSClRh: C, 62.75; H, 5.70. Found:
C, 62.70; H, 5.99%.
[PtI2(TXPH)]·0.5 toluene (4H·0.5 toluene)
A solution of [PtI2(COD)] (128 mg, 2.30 × 10−4 mol) and
TXPH (120 mg, 2.30 × 10−4 mol) in CH2Cl2 (10 mL) was
stirred at room temperature for 1 h and then evaporated to
dryness in vacuo. The residue was then sonicated in toluene
(5 mL), and filtered to collect a pale yellow powder. Yield =
141 mg (60%). 1H NMR (CD2Cl2): δ 8.66 (d, J 8 Hz, 1H, CH5),
7.86, 7.70 (v. broad s, 2 × 2H, o-PPh2), 7.75 (s, 1H, CH1), 7.61
(s, 1H, CH8), 7.59, 7.47 (v. broad s, 2 × 1H, p-PPh2), 7.49 (v.
broad s, 4H, m-PPh2), 7.39–7.33 (m, 2H, CH3 & CH6), 2.12,
1.81 (s, 2 × 3H, CMe2), 1.34 (s, 9H, C7CMe3), 1.22 (s, 9H,
C2CMe3). 13C{1H} NMR (CD2Cl2): δ 155.50 (s, C2CMe3),
153.43 (s, C7CMe3), 146.2 (s, C10), 143.58 (s, C13), 139.77 (d, J
23 Hz, C11), 134.91 (d, J 11 Hz, o-PPh2), 133.13 (d, J 60 Hz, C4
or ipso-PPh2), 132.60 (s, p-PPh2), 132.36 (s, CH5), 129.09 (d, J
12 Hz, m-PPh2), 128.30 (s, CH3), 127.44 (s, CH1), 126.01 (s,
C12), 124.66 (s, CH6), 123.28 (s, CH8), 43.81 (s, CMe2), 35.62
(s, C2CMe3), 35.54 (s, C7CMe3), 31.58 (s, C7CMe3), 31.46 (s,
C2CMe3), 26.28 (s, 2 × CMe2). 31P{1H} (CD2Cl2): δ + 47.36
1
{1H} (CD2Cl2): δ + 38.60 (s, JP,195Pt 3458 Hz). Anal. calcd for
C35H39PS: C, 53.30; H, 4.98. Found: C, 53.05; H, 5.27%.
[PdCl2(TXPH)]·0.5C6H6 (2H·0.5C6H6)
A solution of [PdCl2(COD)] (52 mg, 1.82 × 10−4 mol) and
TXPH (100 mg, 1.91 × 10−4 mol) in CH2Cl2 (10 mL) was
stirred at room temperature for 1 h. The resulting orange solution
was evaporated to dryness in vacuo leaving a bright yellow solid
to which benzene (10 mL) was added. After sonication, the
mixture was filtered to give a pale yellow solid, which was
washed with benzene and dried in vacuo. Yield = 98 mg (77%).
1H NMR (C6D5Br, 60 °C): δ 9.38 (d, J 7 Hz, 1H, CH5), 7.74
(broad s, 5H, CH1 & o-PPh2), 7.53 (s, 1H, CH8), 7.29 (s, 1H,
CH3), 7.14 (m, 3H, CH6 & p-PPh2), 7.04 (broad s, m-PPh2),
This journal is © The Royal Society of Chemistry 2012
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1
3 F.-G. Fontaine and D. Zargarian, J. Am. Chem. Soc., 2004, 126, 8786.
4 J. Boudreau and F.-G. Fontaine, Organometallics, 2011, 30, 511.
5 I. R. Crossley, A. F. Hill and A. C. Willis, Organometallics, 2007, 26,
3891.
(s, JP,195Pt 3249 Hz). Anal. calcd for C38.5H43PSI2Pt: C, 45.44;
H, 4.26. Found: C, 45.45; H, 4.33%.
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DFT calculations
All structures were fully optimized with the ADF DFT package
(SCM, version 2010.02).39 The adiabatic local density approxi-
mation (ALDA) was used for the exchange-correlation kernel40
and the differentiated static LDA expression was used with
Vosko–Wilk–Nusair (VWN) parameterization.41 All geometry
optimizations were conducted using the zero-order regular
approximation (ZORA)42 for relativistic effects, and were gradi-
ent corrected using the exchange and correlation functionals of
Perdew and Wang (PW91).43 Geometry optimizations were
initially conducted using a double-ζ basis set with one polariz-
ation function (DZP) and a medium core, followed by a triple-ζ
all-electron basis set with two polarization functions (TZ2P).
Crystallographically determined geometries were used as the
starting point for calculations on 1B–5B, 2H and 4H (for 2B,
the structure from 2B·2CH2Cl2 was used). Geometry optimized
structures of 1B and 3B were used as the starting point for calcu-
lations on 1H and 3H (after replacement of the BPh2 group in
the TXPB complexes with a hydrogen atom).
Bonding was analysed in more detail using a fragment
approach that considered the interaction of an uncharged MXY
[MXY = PtCl2, PdCl2, RhCl(CO), PtI2 or RhI(CO)] fragment
with a neutral TXPB or TXPH ligand (fragments were generated
from the TZ2P geometry optimized structures of each complex).
Hirshfeld charges,26 SCF deformation density isosurfaces and
energy decomposition analyses44 were employed to further
probe the nature of metal–ligand and boron–halide bonding.
Deformation density maps were computed by subtracting the
sum of the SCF electron density for the two fragments (main-
tained at their optimized positions) from the SCF electron
density for the complex. The resulting isosurfaces illustrate the
electronic reorganization that occurs upon interaction between
the two fragments to form the complex. Mayer bond orders25,45
were obtained using the ADF keyword EXTENDEDPOPAN.
Visualization of the computational results was performed using
the ADF-GUI (SCM) or Discovery Studio Visualizer (Accelrys).
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Soc., Dalton Trans., 2001, 2095.
26 (a) F. L. Hirshfeld, Theor. Chim. Acta, 1977, 44, 129; (b) E. R. Davidson
and S. Chakravorty, Theor. Chim. Acta, 1992, 83, 319; (c) K. B. Wiberg
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27 The following bond lengths and angles, Mayer bond orders, Hirshfeld
charges, and energy decomposition analysis data were calculated for
complex 4B after geometry optimization with the B–X(1) bond distance
constrained to that observed by single-crystal X-ray crystallography: M–P
= 2.243 Å, M–S = 2.276 Å, M–X(1) = 2.690Å, M–Y = 2.641 Å, B–X(1)
= 2.758 Å, P–M–X(1) = 173.3°, S–M–Y = 174.0°, M–X(1)–B = 85.9°,
Σ(C–B–C) = 349.1°, M–P MBO = 1.175, M–S MBO = 0.979, M–X(1)
MBO = 0.734, M–Y MBO = 0.905, B–X(1) MBO = 0.509, M Hirshfeld
= 0.0660, X(1) Hirshfeld = −0.0503, X(2) Hirshfeld = −0.1909, B Hirsh-
Acknowledgements
D. J. H. E. thanks NSERC of Canada for a Discovery Grant,
Canada Foundation for Innovation and Ontario Innovation Trust
for New Opportunities Grants, and Ontario Centers of Excel-
lence for an Early Researcher Award. B. E. C. thanks the Gov-
ernment of Ontario for an Ontario Graduate Scholarship and
NSERC of Canada for a PGS-D award.
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