Probing the steric limits of carbon-gold bond formation: (dialkylbiarylphosphine)gold(i) aryls

Article abstract of DOI:10.1021/om800746u

Aryl-group transfer from arylboronic acids to gold has emerged as a functionally tolerant alternative to classical lithiation- and magnesiation-based synthesis of arylgold(I) species. Here, the scope of the reaction is explored with attention to the steri

Full text of DOI:10.1021/om800746u

1666
Organometallics 2009, 28, 1666–1674
Probing the Steric Limits of Carbon-Gold Bond Formation:
(Dialkylbiarylphosphine)gold(I) Aryls
David V. Partyka,‡ James B. Updegraff III,‡ Matthias Zeller,† Allen D. Hunter,† and
Thomas G. Gray*,‡
Department of Chemistry, Case Western ReserVe UniVersity, CleVeland, Ohio 44106, and Department of
Chemistry, Youngstown State UniVersity, 1 UniVersity Plaza, Youngstown, Ohio 44555
ReceiVed August 1, 2008
Aryl-group transfer from arylboronic acids to gold has emerged as a functionally tolerant alternative
to classical lithiation- and magnesiation-based synthesis of arylgold(I) species. Here, the scope of the
reaction is explored with attention to the sterics of the boronic acid starting material and the supporting
ligand on gold. Dicyclohexylbiaryl phosphines are selected as supporting ligands on gold(I) because of
their substantial bulk. Aryl-group transfer is compatible with steric buildup on either reaction partner.
The structural preference of gold(I) for linear, two-coordinate geometries circumvents potential steric
clashes. The new organometallics likely gain added stability through dative interactions with the flanking
phosphine biaryl arm and, in three cases, through π-interactions with the aryl ligand σ-bonded to gold.
The new compounds are characterized by multinuclear NMR and optical spectroscopy, X-ray diffraction
crystallography, and combustion analysis. All compounds absorb ultraviolet light at wavelengths λ <
325 nm. Time-dependent density-functional theory calculations find that multiple singlet-singlet transitions
account for the absorption profile, which has both intraligand and (ligand-metal)-to-ligand charge-transfer
character.
analogues, which are isolobal with the proton,20-22 catalyze a
variety of reactions at unsaturated carbon centers. In broad
Introduction
Organogold chemistry1-4 is undergoing an impressive resur-
gence for its photophysical dimensions,5-13 for cancer therapy
and imaging,14-19 and not least for its catalytic applicability.
The (phosphine)gold(I) fragment and (N-heterocyclic carbene)
categories, these include nucleophilic additions across carbon-
carbon multiple bonds; activations of alcohols, carbonyl groups,
and carbon monoxide; and oxidation reactions.23-27 Gold(I) is
given to linear two-coordination, and the supporting ligands of
choice have been organophosphines and N-heterocyclic car-
benes, although phosphites,28 chelating nitrogen donors,29 and
other ligands30 have also been employed.
* Corresponding author. E-mail: tgray@case.edu.
† Case Western Reserve University.
‡ Youngstown State University.
In a number of these studies, steric girth about the supporting
ligand has been found to promote catalysis. For example,
Echavarren and co-workers31 have recently reported 1,3-enyne
and arylalkyne [4+2] cycloaddition reactions catalyzed by
cationic gold(I) species bearing hindered ligands. Sterically
imposing ligands were chosen in part because aryl-substituted
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10.1021/om800746u CCC: $40.75
2009 American Chemical Society
Publication on Web 02/27/2009

(Dialkylbiarylphosphine)gold(I) Aryls
Organometallics, Vol. 28, No. 6, 2009 1667
alkynes undergo alkoxycyclization and cycloisomerization reac-
tions with difficulty. Among the most active gold(I) catalysts
are complexes having bulky N-heterocyclic carbene ligands and
tris(2,6-di-tert-butyl)phosphite. In earlier work, the same group32
examined a diverse assortment of hindered phosphines as
supporting ligands in the gold(I)-catalyzed cyclization of enynes.
Here also, steric heft was necessary for efficient reaction. Bender
and Widenhoefer33 identified a hindered (N-heterocyclic car-
bene)gold(I) cation, generated by halide abstraction from the
chloro complex with Ag+, as an active catalyst in the intramo-
lecular hydroamination of N-alkenyl ureas. The carbene ligand
confers a higher catalytic activity than a similar complex bearing
a dialkybiarylphosphine ligand. Nolan and co-workers34 report
a bulky (N-heterocyclic carbene)gold(I) complex to be the
catalyst of choice for an indene synthesis. Arguably steric and
electronic effects combine in the case of [(p-CF3-C6H4)3P]AuCl,
which exceeds other gold(I) precursors in catalyzing the ring
expansion of propargyl cyclopropanols.35
Frequently, supporting phosphine ligands deriving from
palladium-catalyzed cross-coupling chemistry are applied to
investigations of gold(I). The ortho-biaryl phosphines of Buch-
wald and collaborators were originally developed for enhanced
reactivity of palladium in Suzuki-Miyaura cross-coupling36,37
and other reactions.38-45 These ligands are believed to stabilize
low-coordinate palladium intermediates, and thereby suppress
catalyst decomposition. Recent structural and theoretical studies
have examined dative interactions between palladium and the
flanking aryl group of the phosphine.46-50 X-ray diffraction
crystallography studies51,52 indicate similar π-interactions in
neutral and cationic gold(I) species.
acids. The new protocol’s tolerance of steric hindrance, on both
the (phosphine)gold(I) fragment and the organic transmetalating
partner, is emphasized. Products have been characterized by
multinuclear NMR, mass spectrometry, elemental analysis, and
X-ray diffraction crystallography. Dative interactions between
gold(I) and one or two carbon atoms of the flanking aryl moiety
are observed in the solid state. Excited-state properties of the
new compounds are interrogated with absorption and time-
resolved emission spectroscopy. Assignments of optical transi-
tions are made with the use of time-dependent density-functional
theory. A portion of this work has been communicated previ-
ously.53
Experimental Section
All solvents and reagents were used as received. Microanalyses
(C, H, and N) were performed by Quantitative Technologies Inc.,
Whitehouse, NJ. NMR spectra (1H, 31P) were recorded on a Varian
AS-400 spectrometer. UV-visible spectra were recorded on a Cary
5g UV-vis-NIR spectrophotometer. All UV-visible spectra were
similar, with a shoulder around the THF solvent cutoff (280 nm)
that tails off into the visible region, so all spectra report the molar
absorptivity at this wavelength at concentrations in the range (2-6)
× 10-5 M. Emission spectra were recorded (on a Cary Eclipse
fluorescence spectrometer) after solutions had been degassed with
argon for at least 20 min.
{[(PCy2)(2-biphenyl)]Au(phenyl)}, 4. In 5 mL of 2-propanol
were suspended Cs2CO3 (107 mg, 0.33 mmol) and phenylboronic
acid (39 mg, 0.32 mmol). To this suspension was added [(PCy2(2-
biphenyl))AuBr] (100 mg, 0.16 mmol), and the resultant mixture
was stirred at 50 °C for 30 h. After cooling, the mixture was stripped
of solvent in vacuo, extracted into benzene, and filtered through
Celite. The filtrate was taken to dryness and triturated with pentane
until a white solid formed, which was scraped into the pentane.
The pentane was decanted, the solid was extracted into benzene
and concentrated to saturation, and pentane was diffused into the
saturated solution. A colorless crystalline mass separated, which
was washed with cold methanol and pentane, dried, and collected.
Yield: 84 mg (84%). 1H NMR (C6D6): δ 7.81-7.86 (m, 2H, C6H5),
7.51-7.56 (m, 1H, C6H5), 7.49 (td, 2H, C6H5, J ) 1.6, 6.0 Hz),
7.17-7.28 (m, 6H, Cy2P(C12H9)), 7.00-7.08 (m, 3H, Cy2P(C12H9)),
0.82-2.00 (m, 22H, (C6H11)2P(2-biphenyl)) ppm. 31P NMR (C6D6):
δ 50.7 ppm. UV-vis (THF): λ (ꢀ, M-1 cm-1) 280 (6300) nm. Anal.
Calcd for C30H36AuP: C, 57.69; H, 5.81. Found: C, 57.56; H, 5.76.
{[PCy2(2-biphenyl)]Au(2-biphenyl)}, 5. In 5 mL of 2-propanol
were suspended Cs2CO3 (150 mg, 0.46 mmol) and 2-biphenylbo-
ronic acid (96 mg, 0.48 mmol). To this suspension was added
[(PCy2(2-biphenyl))AuBr] (144 mg, 0.23 mmol), and the mixture
was stirred at 50 °C for 30 h. After cooling, the mixture was stripped
of solvent in vacuo, extracted into benzene, filtered through Celite,
and taken to dryness by rotary evaporation. Pentane was added to
and thoroughly mixed with the white solid and removed via rotary
evaporation. The solid was dried, extracted into benzene, and filtered
through Celite. Slow evaporation gave colorless crystals; the crystals
were ground in and triturated with pentane. The pentane was
decanted, and the microcrystalline powder was washed with cold
Reported here are synthetic, structural, and spectroscopic
studies of (dialkylbiarylphosphine)gold(I) aryl complexes. The
compounds herein were prepared in base-induced arylation
reactions of the corresponding gold(I) bromides with boronic
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1
methanol and pentane and dried. Yield: 145 mg (90%). H NMR
(C6D6): δ 7.91 (dd, 2H, CH, J ) 1.6, 8.0 Hz), 7.84-7.88 (m, 1H,
CH), 7.66 (dt, 1H, CH, J ) 1.2, 8.0 Hz), 7.58-7.64 (m, 1H, CH),
7.48 (tt, 1H, CH, J ) 1.2, 7.6 Hz), 7.24-7.30 (m, 3H, CH),
7.12-7.19 (m, 5H, CH), 7.00-7.12 (m, 4H, CH), 0.85-1.86 (m,
22H, C6H11). 31P NMR (C6D6): δ 52.8 ppm. UV-vis (THF): λ (ꢀ,
M-1 cm-1) 280 (7710) nm. Anal. Calcd for C36H40AuP: C, 61.71;
H, 5.75. Found: C, 61.73; H, 5.72.
(52) Herrero-Go´mez, E.; Nieto-Oberhuber, C.; Lo´pez, S.; Benet-Bucholz,
J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2006, 45, 5455–5459.
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Chem., Int. Ed. 2006, 45, 8188–8191.

1668 Organometallics, Vol. 28, No. 6, 2009
Partyka et al.
{[PCy2(2′-methylbiphenyl)]Au(phenyl)}, 6. In 5 mL of 2-pro-
panol were suspended Cs2CO3 (95 mg, 0.29 mmol) and phenyl-
boronic acid (39 mg, 0.32 mmol). To this suspension was added
[(PCy2(2′-methylbiphenyl))AuBr] (94 mg, 0.15 mmol), and the
mixture was stirred at 50 °C for 30 h. After cooling, the mixture
was stripped of solvent in vacuo, extracted into benzene (∼20 mL),
filtered through Celite, and washed thoroughly with ethylene glycol
(3 × 8 mL) and water (2 × 10 mL). The organic layer was separated
and dried with MgSO4, filtered, and taken to a residue via rotary
evaporation. Pentane was added, thoroughly mixed, and removed
via rotary evaporation; this process was repeated. The sticky white
solid was extracted again into benzene, filtered, and taken to a
residue by rotary evaporation. Pentane was added, thoroughly
mixed, and removed via rotary evaporation; this process was
repeated. The white solid was collected and dried. Yield: 68 mg
(63%). 1H NMR (C6D6): δ 7.74-7.79 (m, 2H, C6H5), (td, 1H, C6H5,
J ) 1.2, 8.8 Hz), 7.11-7.28 (m, 6H, CH), 7.00-7.06 (m, 2H, CH),
6.93-6.98 (m, 1H, CH), 2.09 (s, 3H, CH3), 0.97-2.08 (m, 22H,
C6H11). 31P NMR (C6D6): δ 46.3 ppm. UV-vis (THF): λ (ꢀ, M-1
cm-1) 280 (6450) nm. Anal. Calcd for C31H38AuP: C, 58.31; H,
6.00. Found: C, 57.95; H, 6.01.
cooling, the mixture was stripped of solvent in vacuo, extracted
into benzene, filtered, and taken to dryness in vacuo. The solid
was washed with pentane and dried, re-extracted into benzene,
filtered, and concentrated to saturation, and pentane vapor was
diffused. The flaky white crystals that separated were washed with
cold methanol and pentane and dried. Yield: 83 mg (74%). 1H NMR
(C6D6): δ 7.60-7.64 (m, 2H, C6H5), 7.40 (td, 2H, C6H5, J ) 1.2,
8.0 Hz), 7.24 (s, 2H, XPhos), 7.11-7.22 (m, 3H, XPhos),
6.98-7.04 (m, 2H, Cy2P(2′,4′,6′-(Pri)3(C12H6))), 2.82 (sep, 1H,
CH(CH3)2, J ) 7.2 Hz), 2.56 (sep, 2H, CH(CH3)2, J ) 6.8 Hz),
1.57 (d, 6H, CH(CH3)2, J ) 7.2 Hz), 1.17 (d, 6H, CH(CH3)2, J )
7.2 Hz), 1.08 (d, 6H, CH(CH3)2, J ) 7.2 Hz), 0.91-2.02 (m, 22H,
C6H11). 31P NMR (C6D6): δ 43.7 ppm. UV-vis (THF): λ (ꢀ, M-1
cm-1) 280 (4170) nm. Anal. Calcd for C39H54AuP: C, 62.31; H,
7.37. Found: C, 62.30; H, 7.28.
[(XPhos)Au(2-biphenyl)], 10. In 5 mL of 2-propanol were
suspended Cs2CO3 (115 mg, 0.35 mmol) and 2-biphenylboronic
acid (74 mg, 0.37 mmol). To this suspension was added [(XPhos)-
AuBr] (133 mg, 0.18 mmol), and the mixture was stirred at 50 °C
for 30 h. After cooling, the mixture was stripped of solvent in vacuo,
extracted into benzene, filtered through Celite, and taken to dryness
in vacuo. The white solid was washed thoroughly with pentane,
dried, extracted into benzene, and filtered through Celite. Slow
evaporation gave wet-looking colorless crystals; the crystals were
ground in and triturated with pentane. The pentane was decanted,
and the microcrystalline powder was washed with cold methanol
{[PCy2(2′-methylbiphenyl)]Au(2-biphenyl)}, 7. In 5 mL of
2-propanol were suspended Cs2CO3 (102 mg, 0.31 mmol) and
2-biphenylboronic acid (62 mg, 0.31 mmol). To this suspension
was added [(PCy2(2′-methylbiphenyl))AuBr] (95 mg, 0.15 mmol),
and the mixture was stirred at 50 °C for 30 h. After cooling, the
mixture was stripped of solvent by rotary evaporation, extracted
into benzene (∼20 mL), and filtered through Celite. The benzene
solution was washed with ethylene glycol (3 × 10 mL) and water
(2 × 10 mL), dried with MgSO4, filtered, and concentrated by rotary
evaporation to a residue. Pentane was added to the residue, and
the residue was allowed to sit until crystals formed. The crystals
were collected, and the remaining pentane was concentrated by
rotary evaporation until a residue remained again. Pentane was
added and the mixture stored in a freezer to yield a second crop of
1
and pentane and dried. Yield: 116 mg (80%). H NMR (C6D6): δ
7.79 (dd, 2H, CH, J ) 1.2, 8.0 Hz), 7.62-7.68 (m, 1H, CH), 7.52
(d, 1H, CH, J ) 7.6 Hz), 7.44 (tt, 1H, CH, J ) 1.2, 8.0 Hz), 7.30
(t, 2H, CH, J ) 8.0 Hz), 7.23 (s, 2H, CH), 7.14-7.22 (m, 4H,
CH), 6.98-7.05 (m, 2H, CH), 2.78 (sep, 1H, (CH3)2CH, J ) 7.2
Hz), 2.51 (sep, 2H, (CH3)2CH, J ) 6.8 Hz), 1.47 (d, 6H, (CH3)2CH,
J ) 6.8 Hz), 1.12 (d, 6H, (CH3)2CH, J ) 6.8 Hz), 1.06 (d, 6H,
(CH3)2CH, J ) 7.2 Hz), 0.94-1.94 (m, 22H, C6H11). 31P NMR
(C6D6): δ 42.8 ppm. UV-vis (THF): λ (ꢀ, M-1 cm-1) 280 (8730)
nm. Anal. Calcd for C45H58AuP: C, 65.36; H, 7.07. Found: C, 64.98;
H, 7.12.
1
crystals. Yield: 65 mg (71%). H NMR (C6D6): δ 7.86 (dd, 2H,
CH, J ) 1.2, 8.4 Hz), 7.70-7.74 (m, 1H, CH), 7.63 (dt, 1H, CH,
J ) 1.2, 8.0 Hz), 7.47 (tt, 1H, CH, J ) 1.6, 8.4 Hz), 7.21-7.30
(m, 4H, CH), 7.15-7.19 (m, 1H, CH), 6.91-7.14 (m, 7H, CH),
2.00 (s, 3H, CH3), 0.81-2.08 (m, 22H, C6H11). 31P NMR (C6D6):
δ 46.1 ppm. UV-vis (THF): λ (ꢀ, M-1 cm-1) 280 (8350) nm. Anal.
Calcd for C36H40AuP: C, 62.18; H, 5.92. Found: C, 62.26; H, 5.63.
{[PCy2(2′-methylbiphenyl)]Au(mesityl)}, 8. To 6 mL of 2-pro-
panol were added mesitylboronic acid (80 mg, 0.49 mmol) and
Cs2CO3 (134 mg, 0.41 mmol). To this suspension was added
[(PCy2(2′-methylbiphenyl))AuBr] (104 mg, 0.16 mmol), and the
resultant mixture was stirred for 60 h at 50 °C. After cooling, the
mixture was stripped of solvent via rotary evaporation, extracted
into benzene, filtered through Celite, washed with ethylene glycol
(3 × 10 mL), washed with water (2 × 10 mL), and dried with
MgSO4. After filtration, the solution was taken to a residue via
rotary evaporation, triturated with pentane, and rotovapped to a
residue (the product slowly dissolves in pentane over time). The
residue was re-extracted into benzene, cooled to ∼0 °C, and filtered
again. The same pentane trituration procedure, repeated twice,
yielded a white solid, which had to be recrystallized (pentane/
benzene) to give an analytically pure material. Yield: 50 mg (45%).
1H NMR (C6D6): δ 7.34-7.40 (m, 1H, 2′-methylbiphenyl),
6.92-7.13 (m, 9H, 2′-methylbiphenyl + C6H2(CH3)3), 2.74 (s, 6H,
C6H2(CH3)3), 2.39 (s, 3H, C6H2(CH3)3), 2.08 (s, 3H, 2′-methylbi-
phenyl), 0.84-2.26 (m, 22H, C6H11). 31P NMR (C6D6): δ 48.1 ppm.
UV-vis (THF): λ (ꢀ, M-1 cm-1) 280 (6910) nm. Anal. Calcd for
C34H44AuP: C, 60.00; H, 6.52. Found: C, 60.11; H, 6.67.
[(XPhos)Au(mesityl)], 11. In 5 mL of 2-propanol were sus-
pended Cs2CO3 (118 mg, 0.36 mmol) and mesitylboronic acid (83
mg, 0.51 mmol). To this suspension was added [(XPhos)AuBr] (114
mg, 0.15 mmol), and the mixture was stirred at 55 °C for 60 h.
After cooling, the mixture was stripped of solvent in vacuo,
extracted into ∼20 mL of benzene, and filtered through Celite. The
benzene layer was washed three times with 10 mL of ethylene
glycol and twice with water (10 mL). After drying with MgSO4,
the benzene layer was filtered through Celite and taken to dryness
by rotary evaporation. Pentane was added to and thoroughly mixed
with the residue, and the pentane was removed with rotary
evaporation. The solid was extracted again into benzene, filtered,
and taken to dryness via rotary evaporation. Pentane was added
and subsequently removed by rotary evaporation to dry the
microcrystalline solid, which was collected. Yield: 104 mg (87%).
1H NMR (C6D6): δ 7.14-7.25 (m, 2H, XPhos), 7.19 (s, 2H, XPhos),
7.06 (s, 2H, C6H2(CH3)3), 7.01-7.05 (m, 2H, XPhos), 2.75 (sep,
1H, (CH3)2CH), 2.69 (s, 6H, C6H2(CH3)3), 2.59 (sep, 2H,
(CH3)2CH), 2.35 (s, 3H, C6H2(CH3)3), 1.56 (d, 6H, (CH3)2CH), 1.12
(d, 6H, (CH3)2CH), 1.05 (d, 6H, (CH3)2CH), 1.00-2.15 (m, 22H,
C6H11). 31P NMR (C6D6): δ 44.2 ppm. UV-vis (THF): λ (ꢀ, M-1
cm-1) 280 (6510) nm. Anal. Calcd for C42H60AuP: C, 63.79; H,
7.39. Found: C, 63.51; H, 7.68.
Computations. Spin-restricted density-functional theory com-
putations were performed within the Gaussian 03 program suite.54
Calculations employed the modified Perdew-Wang exchange
[(XPhos)Au(phenyl)], 9. In 5 mL of 2-propanol were suspended
Cs2CO3 (109 mg, 0.33 mmol) and phenylboronic acid (41 mg, 0.34
mmol). To this suspension was added [(XPhos)AuBr] (112 mg,
0.15 mmol), and the mixture was stirred at 50 °C for 30 h. After
(54) Frisch, M. J.; et al. Gaussian 03, ReVision D.01; Gaussian, Inc.:
Wallingford, CT, 2004.

(Dialkylbiarylphosphine)gold(I) Aryls
Organometallics, Vol. 28, No. 6, 2009 1669
functional of Adamo and Barone55 and the original Perdew-Wang
correlation functional.56 Nonmetal atoms were described with the
TZVP basis set of Godbelt, Andzelm, and co-workers.57 Gold
orbitals were described with the Stuttgart effective core potential
and the associated basis set,58 which was contracted as follows:
Au, (8s,7p,6d)f[6s,5p,3d]. Relativity with the Stuttgart ECP and
its associated basis set is introduced with a potential term (i.e., a
one-electron operator) that replaces the two-electron exchange and
Coulomb operators resulting from interaction between core electrons
and between core and valence electrons. In this way relativistic
effects, especially scalar effects, are included implicitly rather than
as four-component, one-electron functions in the Dirac equation.
We have previously found this combination of functional and basis
set to yield satisfactory comparisons with experiment.51,53,59 Test
computations run with the same basis and other functional yielded
qualitatively similar results. The geometries of 4 and 5 are those
of the crystal structures, except that hydrogen-atom positions were
optimized using the 6-31G(d,p) basis set on nonmetal atoms (gold
was treated with the Stuttgart ECP and basis).60 Vertical excitation
energies were calculated using a TDDFT implementation described
by Scuseria and co-workers.61 All calculated properties reported
here include implicit THF solvation (ε ) 7.58, 298.15 K), which
was incorporated in single-point calculations of the gas-phase
geometries with Tomasi’s polarizable continuum model (PCM). The
stability of each converged density was confirmed by calculation
of the eigenvalues of the A matrix.62,63 Percentage compositions
of molecular orbitals, overlap populations, and bond orders between
fragments were calculated using the AOMix program.64,65
X-ray Structure Determinations. All new products were
crystallized by diffusion of pentane into saturated benzene solutions.
Single-crystal X-ray data were collected on a Bruker AXS SMART
APEX or APEX II CCD diffractometer using monochromatic Mo
KR radiation with omega scan technique. The unit cells were
determined using SMART66 and SAINT+.67 Data collection for
all crystals was conducted at 100 K (-173.5 °C). All structures
were solved by direct methods and refined by full matrix least-
squares against F2 with all reflections using SHELXTL.68 All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were placed in standard calculated positions, and all hydrogen atoms
were refined with an isotropic displacement parameter 1.5 (methyl)
or 1.2 times (all others) that of the adjacent carbon.
Results and Discussion
Syntheses. Much previous organogold(I) chemistry predicates
on organolithium or Grignard reagents.1-4 In these instances,
(phosphine)- or (N-heterocyclic carbene)gold(I) halides trans-
metalate upon reaction with formal carbanions to produce the
corresponding arylgold(I) species and the corresponding lithium
or magnesium halides. These protocols can suffer from the
limited functional group tolerance of s-block organometallics,
although noteworthy progress has followed the low-temperature
synthesis of functionalized organomagesium reagents.69
Recently, we have disclosed a milder, functionally tolerant
means of arylgold(I) synthesis. (Phosphine)- or (N-heterocyclic
carbene)gold(I) bromides are reacted with arylboronic acids or
esters in alcohol solvents at 50-55 °C in the presence of a base,
eq 1.53
Cs2CO3,
LAuBr + ArB(OH)2
i-PrOH, 50-55 °C8 LAuAr + BBr(OH)2
(1)
L ) PR3, N-heterocyclic carbene; Ar ) aryl group
Cesium carbonate provides the best results. Arylation also
occurs in the presence of cesium fluoride, but in lower yields.
An attempted arylation reaction done with sodium carbonate
did not yield organogold product. Cesium carbonate is more
soluble in isopropyl alcohol at 50 °C than either CsF or Na2CO3;
this greater solubility may account for the higher yields of
gold(I) aryls. Aryl-group transfer here proceeds from boron to
gold in comparable or better yields, and in shorter time spans,
than with Grignard reagents at room temperature. Earlier
investigations by Fackler,70 Schmidbaur,71 and their respective
co-workers found phenyl-group transfer from BPh4- to gold(I)
under similarly mild conditions. Arylation from boron tolerates
the reducible and polar functional groups that react with formally
carbanionic reagents. The method employs only reagents and
yields only products that, when pure, are stable indefinitely to
air and moisture. We find the new method to be remarkably
forgiving of bulk: steric buildup in the (phosphine)gold(I) halide,
the boronic acid, or both affords crowded organogold products
in uncompromised yields.
The dialkylbiarylphosphines of Buchwald and collabora-
tors36-50 were selected as accessible (commercially obtainable)
extremes of steric encumbrance. Table 1 collects bromogold(I)
starting materials and the organometallic products derived from
them; a numbering system is indicated. The compounds are
isolated as white solids upon trituration of benzene solutions
with pentane in yields ranging from 45 to 90%.
Reaction times that afford optimal yields vary from 30-60
h and are similar to or somewhat longer than those for
(tricyclohexylphosphine)- or (N-heterocyclic carbene)gold(I)
products. None of the new compounds show any sensitivity to
air, moisture, or ambient light over a period of months in the
solid state.
(55) Adamo, C.; Barone, V. J. Chem. Phys. 1998, 108, 664–675.
(56) Perdew, J. P.; Wang, Y. Phys. ReV. B 1992, 45, 13244–13249.
(57) Godbout, N.; Salahub, D. R.; Andzelm, J.; Wimmer, E. Can.
J. Chem. 1992, 70, 560–571.
(58) Dolg, M.; Wedig, U.; Stoll, H.; Preuss, H. J. Chem. Phys. 1987,
86, 866–872.
(59) Partyka, D. V.; Robilotto, T. J.; Zeller, M.; Hunter, A. D.; Gray,
T. G. Proc. Natl. Acad. Sci., U.S.A. 2008, 105, 14293–14297.
(60) (a) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213–
222. (b) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon,
M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654–3665.
(c) Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.; Schleyer, P. v. R.
J. Comput. Chem. 1983, 4, 294–301. (d) Krishnam, R.; Binkley, J. S.;
Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650. (e) Gill, P. M. W.;
Johnson, B. G.; Pople, J. A.; Frisch, M. J. Chem. Phys. Lett. 1992, 197,
499–505.
(61) Stratman, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem. Phys. 1998,
109, 8218–8224.
(62) Seeger, R.; Pople, J. A. J. Chem. Phys. 1977, 66, 3045–3050.
(63) Bauernschmitt, R.; Alrichs, R. J. Chem. Phys. 1996, 104, 9047–
9052.
(64) Gorelsky, S. I. AOMix: Program for Molecular Orbital Analysis;
York University: Toronto, 1997; http://www.sg-chem.net.
(65) Gorelsky, S. I.; Lever, A. B. P. J. Organomet. Chem. 2001, 635,
187–196.
(66) SMART for WNT/2000 (Version 5.628),Bruker Advanced X-ray
Solutions; Bruker AXS Inc.: Madison, WI, 1997-2002.
(67) SAINT (Version 6.45), Bruker Advanced X-ray Solutions; Bruker
AXS Inc.: Madison, WI, 1997-2003.
(68) SHELXTL (Version 6.10),Bruker Advanced X-ray Solutions; Bruker
AXS Inc.: Madison, WI, 2000.
Phosphorus-31 NMR spectroscopy diagnoses aryl group
transfer to gold. Whereas 31P NMR resonances of the bromide
starting materials fall between 36.0 and 46.0 ppm, those of the
corresponding aryls are downfield-shifted. For the complexes
in Table 1, the range of 31P chemical shifts is 42.8 ppm (10) to
(69) Knochel, P.; Dohle, W.; Gommermann, N.; Kneisel, F. F.; Kopp,
F.; Korn, T.; Sapountzis, I.; Vu, V. A. Angew. Chem., Int. Ed. 2003, 42,
4302–4320.
(70) Forward, J. M.; Fackler, J. P., Jr.; Staples, R. J. Organometallics
1995, 14, 4194–4198.
(71) Sladek, A.; Hofreiter, S.; Paul, M.; Schmidbaur, H. J. Organomet.
Chem. 1995, 501, 47–51.

1670 Organometallics, Vol. 28, No. 6, 2009
Partyka et al.
Å for 11. As observed in gold(I) halide complexes,51,80 dative
interactions join gold to the ipso and ortho carbon atoms of the
flanking biaryl moieties bound to phosphorus. Au-Cipso separa-
tions range from 3.171(7) Å for one independent molecule of
10 to 3.357(6) Å for one independent molecule of 6; the sum
of the van der Waals radii for gold and carbon is 3.36 Å.81 The
corresponding range of Au-Cortho distances, where Cortho is the
nearer biarylphosphine ortho carbon, is 3.225(3) Å (for 9) to
3.462(6) Å for one crystallographically unique molecule of 6.
In four instances, a phosphine ortho carbon is nearer gold than
the neighboring ipso center: in 4 and 9 and in one independent
molecule each of 6 and 10.
Table 1. (Phosphine)gold(I) Reactants, Products, and Isolated Yields
Some years ago, Kochi and co-workers82 proposed a geo-
metric criterion of hapticity ηx that holds for atoms binding
asymmetrically across a carbon-carbon multiple bond:
d 2 - D2
√
1
x ) 1 + 2
(2)
d 2 - D2 + d 2 - D2
√
√
1
2
In this expression, D is the length of a normal vector that extends
from gold to the best-fit plane of the six pendant aryl-ring
carbons, and d1 and d2 are the nearest and second-nearest Au-C
distances, respectively (d1 e d2). Table 4 collects hapticity values
x calculated this way; they range from 1.41 for one crystallo-
graphically independent molecule of 10 to 1.93 for the other
independent molecule of 10. These values should be increased
by 1 if binding of the σ-carbon is to be included. The mean
hapticity is 1.67. However, in two instances a third biphe-
nylphosphine carbon penetrates within van der Waals contact
(e3.36 Å) of gold: in 7 and 8. For these, the hapticity of the
phosphine biphenyl arm may more accurately be said to exceed
2.
All gold centers approach a linear P-Au-Cσ-aryl geometry.
The corresponding bond angles centered about gold range from
169.13(16)° in one independent molecule of 6 to 175.85(17)°
in one molecule of 10.
The three compounds (5, 7, and 10) bearing o-biphenyl
ligands present additional gold-carbon π-interactions. Table 5
summarizes salient interatomic distances. In compound 5, gold
approaches the biphenyl ligand ipso carbon more closely
[3.289(2) Å] than any carbon of the flanking biphenyl substituent
of the phosphine ligand. In the structures of 7 and 10, similar
dative interactions with the σ-biphenyl ligand occur, but all
biphenyl ligand carbons are more distant from gold than the
ipso carbons of the phosphine ligands. In 5, 7, and 10, the ortho
carbon of the σ-biaryl ligand approaches within bonding reach
of gold. No evidence for aryl or benzylic carbon-hydrogen bond
activation has been found among the new compounds.84
Optical Spectroscopy. The new organometallics are colorless
or off-white solids, in common with their bromide precursors.
52.8 ppm (5). In all cases, the 31P NMR resonances shift
downfield 4.7-7.5 ppm from those of the starting bromide upon
arylation. This observation concurs with previous reports of the
sensitivity of bound-phosphorus resonances to the trans-situated
ligand opposite gold.72,73 1H NMR resonances of the phosphine
ligands are relatively insensitive to metal arylation.
Structures. All new organogold products have been crys-
tallographically characterized. Table 2 collects crystallographic
data. Figure 1 depicts thermal ellipsoid plots of two representa-
tives, 5 and 11. In no structure are aurophilic contacts
(gold-gold separations e 3.6 Å74-76) observed.
Table 3 compiles selected interatomic distances and angles.
Au-P bond lengths are similar to those encountered else-
where.77-79 Au-C σ-bond lengths range from 2.022(7) Å for
one crystallographically independent molecule of 10 to 2.065(2)
(79) Baenziger, N. C.; Bennett, W. E.; Soboroff, D. M. Acta Crystallogr.,
Sect. B 1976, 32, 962–963.
(80) Herrero-Go´mez, E.; Nieto-Oberhuber, C.; Lo´pez, S.; Benet-
Buchholz, J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2006, 45, 5455–
5459.
(81) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.
(82) Vasilyev, A. V.; Lindeman, S. V.; Kochi, J. K. Chem. Commun.
2001, 909–910.
(83) Kochi hapticities for the flanking phenyls of these σ-biphenyl
ligands bound directly to gold all hover near x ) 1.96. However, the
chemical significance of these values is doubtful. The side-on phenyl groups
are forced into greater proximity than for the flanking phosphine phenyls.
Therefore D in eq 1 ranges from 2.1 to 2.7. For phosphine biaryls, D falls
between 3.1 and 3.3. The Kochi hapticities for the phenyl groups of the
C-bound biphenyls are somewhat artificially compressed about x ) 2, and
skepticism about their meanings appears in order.
(72) Baker, L.-J.; Bott, R. C.; Bowmaker, G. A.; Healy, P. C.; Skelton,
B. W.; Schwerdtfeger, P.; White, A. H. J. Chem. Soc., Dalton Trans. 1995,
1341–1347.
(73) Bott, R. C.; Healy, P. C.; Smith, G. Polyhedron 2007, 26, 2803–
2809.
(74) Schmidbaur, H. Gold Bull. 2000, 33, 3–10.
(75) Balch, A. L. Struct. Bonding (Berlin) 2007, 123, 1–40.
(76) Pyykko¨, P. Chem. ReV. 1997, 97, 597–636.
(77) Partyka, D. V.; Updegraff, J. B., III; Zeller, M.; Hunter, A. D.;
Gray, T. G. Organometallics 2007, 26, 183–186.
(78) Partyka, D. V.; Robilotto, T. J.; Zeller, M.; Hunter, A. D.; Gray,
T. G. Organometallics 2008, 27, 28–32.

(Dialkylbiarylphosphine)gold(I) Aryls
Organometallics, Vol. 28, No. 6, 2009 1671
Figure 1. Thermal ellipsoid projections (50% probability, 100 K) of the representative compounds 5 and 11.
Table 2. Crystallographic Data for Compounds 4-11
4
5
6
7
8
9
10
11
formula
C30H36AuP
C36H40AuP
C31H38AuP ·
C37H42AuP
C34H44AuP
C39H54AuP ·
C45H58AuP ·
C42H60AuP
0.83C6H6
1/2C5H12
3/4C5H12
fw
624.52
700.62
645.05
714.64
680.63
786.83
880.96
792.84
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
ꢀ, deg
monoclinic
P21/n
11.1084(8)
15.4789(1)
14.9932(1)
monoclinic
P21/n
10.9514(7)
17.0221(1)
15.5282(1)
triclinic
P1
monoclinic
P21/n
10.9969(7)
15.7608(9)
17.9630(1)
monoclinic
P21/c
9.8061(2)
12.7470(2)
23.5452(5)
monoclinic
P21/c
10.6912(8)
15.6268(1)
22.5830(2)
triclinic
P1
monoclinic
P21/n
12.5649(1)
15.9222(1)
19.6846(2)
j
j
12.5163(2)
12.9094(2)
26.689(3)
85.599(2)
79.300(2)
71.929(2)
4027.5(8)
6
1.596
100(2)
5.556
1929
10.9277(4)
15.7120(5)
25.4351(9)
76.644(2)
87.555(2)
87.386(2)
4242.3(3)
4
1.379
173(2)
3.537
1814
94.074(1)
95.918(1)
100.147(1)
99.527(1)
101.010(1)
107.572(2)
γ, deg
cell volume, Å3
Z
2571.5(3)
4
1.613
100(2)
5.799
1240
2879.3(3)
4
1.616
100(2)
5.189
1400
3064.6(3)
4
1.549
100(2)
4.876
1432
2902.5(1)
4
1.558
273(2)
5.144
1368
3703.5(5)
4
1.411
100(2)
4.402
1612
3754.4(6)
4
1.403
100(2)
3.988
1624
Dcalcd, Mg, m3
T, K
µ, mm-1
F(000)
cryst size, mm3
0.060 × 0.042
0.65 × 0.49 ×
0.49 × 0.23 ×
0.63 × 0.12 ×
0.31 × 0.10 ×
0.58 × 0.36 ×
0.18 × 0.17 ×
0.57 × 0.51 ×
0.039
0.48
0.23
0.09
0.05
0.11
0.05
0.29
θ
min, θmax, deg
1.89, 28.28
26 019
6373
289
1.074
1.78, 28.28
29 650
7073
343
1.098
0.78, 30.63
47 860
24 370
923
1.73, 28.28
31 171
7606
353
1.062
4.36, 35.63
12 907
10 266
329
1.59, 28.28
29 907
8941
399
1.063
1.33, 27.50
67 306
18 752
903
1.58, 28.28
27 825
9038
406
1.046
no. of reflns collected
no. of indep reflns
no. of refined params
goodness-of-fit on F2
1.011
1.054
1.119
final R indices [I > 2σ(I)]
R1
0.0183
0.0218
0.0526
0.0196
0.0271
0.0304
0.0566
0.0253
wR2
0.0460
0.0190
0.0560
0.0229
0.1241
0.0790
0.0474
0.0229
0.0544
0.0440
0.0749
0.0349
0.1486
0.0764
0.0633
0.0290
R indices (all data)
R1
wR2
0.0463
0.0566
0.1365
0.0487
0.0652
0.0772
0.1625
0.0652
Table 3. Selected Interatomic Distances (Å) and Angles (deg) for
Figure 2 depicts absorption spectra of all new compounds in
THF. Absorption is confined within the ultraviolet region, with
an onset near 325 nm. An absorption shoulder is partly resolved
near 275 nm for all compounds.
4-11
compound Au-P Au-Cσ-aryl Au-Cipso Au-Cortho P-Au-Cσ-aryl
4
5
6
2.3048(5)
2.3043(6)
2.046(2) 3.306(2) 3.246 (2)
2.060(2) 3.296(2) 3.411(3)
174.18(6)
172.18(7)
169.44(17)
169.13(16)
167.20(19)
172.18(7)
172.76(6)
171.57(10)
175.85(17)
173.66(19)
174.78(6)
Absorption spectra of the free phosphine ligands exhibit a
broad, featureless transition near 280 nm that resembles the
absorption shoulders near the same wavelength in Figure 2.
Thus, the absorption shoulders near 280 nm for 4-11 are
assigned as a phosphine-based intraligand transition. At higher
energies (λ < 275 nm), absorption in 4-11 increases (not always
2.2938(15) 2.039(6) 3.313(7) 3.445(7)
2.2923(15) 2.048(6) 3.350(6) 3.462(6)
2.2981(16) 2.047(7) 3.357(6) 3.273(6)
2.3043(6)
2.2915(6)
2.3033(7)
2.2953(19) 2.022(7) 3.305(6) 3.283(6)
2.2911(16) 2.055(6) 3.171(7) 3.366(7)
2.3086(7)
7
8
9
10
2.060(2) 3.296(2) 3.411(2)
2.047(2) 3.195(2) 3.454(2)
2.048(3) 3.328(3) 3.225(3)
11
2.065(2) 3.267(2) 3.385(2)
(84) For a study of ortho-substituted biaryl ligands about nickel and
rhodium centers, see: Jones, G. D.; Anderson, T. J.; Chang, N.; Brandon,
R. J.; Ong, G. L.; Vicic, D. A. Organometallics 2004, 23, 3071–3074.
monotonically); molar absorptivities exceed 10 000 M-1 cm-1
at λ ) 250. No such increase is seen for the free phosphines;

1672 Organometallics, Vol. 28, No. 6, 2009
Partyka et al.
Table 4. Hapticities ηx Calculated for Phosphine Biaryl Moieties in
the Crystal Structures of 4-11
unoccupied Kohn-Sham orbitals (LUMOs) are primarily
(>88%) π* orbitals of the flanking biphenyl group on phos-
phorus. The calculated HOMO-LUMO gap is 3.30 eV. The
frontier orbitals of 5 are analogous, and its HOMO-LUMO
gap is 3.32 eV.
compound
x
4
1.82
1.64
1.73, 1.62, 1.57
1.69
5
6a
7
A natural bond order (NBO) analysis finds that the gold 5d
and 6s orbitals dominate its bonding. There is only a slight
participation of the gold 6p orbital in the bonding of 4 or 5
with a maximum occupation number of 0.005e. Similar obser-
vations have been made by DeKock,88 Schwerdtfeger,89 and
their respective co-workers. The natural atomic charge of gold
is calculated to be 0.255 for 4 and 0.273 for 5. This charge is
slightly positive of the mean natural atomic charges of all
hydrogens, which are 0.219 for 4 and 0.220 for 5. The charges
calculated for the σ-bonded aryl carbons are -0.350 for 4 and
-0.329 for 5, just negative of the average charge of all aromatic
carbon atoms (-0.217, 4; -0.203, 5). Together these results
indicate that the carbon-gold(I) σ-bond is modestly polar, as
anticipated by electronegativity arguments. The applicable
Pauling electronegativities are 2.4 for gold and 2.55 for carbon.90
Plots of the LUMO of the Lewis-acidic (phosphine)gold(I)
fragment and the HOMO of the Lewis-basic phenyl anion appear
in Figure S6, Supporting Information. These orbitals combine
to produce a C-Au bonding combination that is the HOMO of
4 and that carries mainly (phosphine)gold(I) character, cf. Figure
3.
8
1.58
1.67
1.41, 1.93
1.71
9
10b
11
a Three independent molecules per unit cell. b Two independent
molecules per unit cell.
Table 5. Close Approaches (Å) of Gold to the Non-σ-bonded Phenyl
Ring in Biphenyl Complexes 5, 7, and 10 (all measurements refer to
biphenyl ligands σ-bonded to gold)
compound
Au-Cipso
Au-Cortho
5
3.289(2)
3.317(2)
3.423(8)
3.454(7)
3.362(2)
3.225(2)
3.269(8)
3.336(7)
7
10a
a Two independent molecules per unit cell.
The present calculations do not make an accurate accounting
of dispersion and presumably underestimate dative gold-flanking
aryl group interactions. The Wiberg bond order in the orthogo-
nalized Lo¨wdin basis91 between gold and the ipso center and
the nearer ortho carbon in 4 is 0.071 (Au-Cipso) and 0.093
(Au-Cortho); Cortho is nearer gold than Cipso (Table 5). For
comparison, the bond order between gold and the bound carbon
of the phenyl ligand is 0.975. In ortho-biphenyl complex 5, the
crystal structure indicates dative interactions between gold and
both biphenyl moieties: that bound to phosphorus and that to
gold. For the gold-bound biphenyl ligand the Au-Cipso Wiberg
bond order (in the Lo¨wdin basis) is 0.064, and for the nearer
ortho carbon it is 0.082; the ortho carbon atom is closer to gold.
For the phosphorus-bound biphenyl in the same molecule, the
ipso carbon is nearer gold than either ortho neighbor. The
corresponding Wiberg bond orders are nearly the same: 0.074
(Au-Cipso) and 0.075 (Au-Cortho). These results indicate weak
carbon-gold interactions in the absence of dispersion.
Time-dependent density-functional theory calculations of the
lowest 10 singlet excited states of 4 afford fair agreement with
experiment. Table S1, Supporting Information, summarizes the
first 10 spin-allowed transitions. The computations find that the
absorption shoulder near 280 nm is composed of overlapping
optically allowed transitions. Some are nearly pure one-electron
promotions, while others are combinations of such transitions
intermixing through configuration interaction (CI). Two transi-
tions, calculated at 321.2 and 309.7 nm, bear significant
oscillator strength. That at 321.2 nm is 97% composed of a
LUMO+1 r HOMO-1 promotion. The transition calculated
Figure 2. Room-temperature absorption spectra of new compounds
in THF.
molar absorptivities at 250 nm are near 6000 M-1 cm-1. The
higher-energy optically allowed transitions of 4-11 are expected
to have some arylgold(I) character. The orbital origins of these
transitions have been investigated with density-functional theory
computations. At room temperature and 77 K, 4-11 are
nonluminescent.
Computations. Static and time-resolved density-functional
calculations were conducted on 4, which is representative of
the new arylgold(I) compounds. Compound 5 was also an object
of calculations because its σ-bonded ortho-biphenyl ligand
interacts datively with gold. The geometries are those of the
crystal structures, except that hydrogen-atom positions were
optimized.
Figure 3 depicts a partial Kohn-Sham orbital energy level
diagram. Contributions from the (phosphine)- and (phenyl)gol-
d(I) fragments appear in the figure, as do percentage contribu-
tions from Mulliken population analysis.85 Implicit THF sol-
vation is incorporated with the polarizable continuum model
of Tomasi and co-workers.86,87
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3093.
For compound 4, the highest-occupied Kohn-Sham orbital
(HOMO) is a σ-bonding combination centered between gold
and the phenyl-ligand carbon. The gold atom and the σ-bound
phenyl carbon atom contribute 67% and 11%, respectively, to
this orbital in terms of electron density. The first three lowest
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(Dialkylbiarylphosphine)gold(I) Aryls
Organometallics, Vol. 28, No. 6, 2009 1673
Figure 3. Kohn-Sham orbital correlation diagram for 4. Fragments are the (phosphine)gold(I) fragment (left) and the phenyl ligand, right
(mpwpw91/Stuttgart ECP and basis on Au; TZVP on nonmetal atoms); implicit THF solvation is included through a polarizable continuum
model. Right: plots of selected orbitals (contour level 0.03 au).
at 309.7 nm is primarily composed of four one-electron
excitations that undergo configuration interaction: LUMO r
HOMO-3 (60%), LUMO r HOMO-2 (16%), LUMO r
HOMO-4 (11%), and LUMO+1 r HOMO-2 (6%). Both the
LUMO and LUMO+1 are localized on the phosphine biaryl
substituent, as plotted in Figure 3, right. Diagrams of the
HOMOs-2, 3, and 4 appear in Figure S1, Supporting Informa-
tion. The HOMO-3 and HOMO-2 have extensive phenyl-
ligand π-character that derives from an eg orbital of free benzene.
The HOMO-4 has little phenyl-ligand character and is primarily
concentrated on gold and the phosphine ligand.
It is notable that no singlet-singlet transition involving the
C-Au σ-bond (i.e., the HOMO) carries substantial oscillator
strength. For example, the lowest-lying singlet excited state is
calculated at 373.4 nm; it consists (99%) of a LUMO r HOMO
excitation. Similarly, the LUMO+1 r HOMO promotion (97%)
affords the third singlet excited state, calculated at 343.1 nm.
The more intense of these transitions originating from the
HOMO has but 6.0% the oscillator strength of the intense
transition calculated at 309.7 nm. That is, the carbon-gold bond
is essentially nonchromophoric.
Crystallographic characterization reveals dative interactions
between gold and the flanking biaryl groups bound to the
phosphine ligands. In most compounds, the primary attractive
interaction is between the phosphine ipso carbon and gold,
although in a few structures, an ortho carbon has a closer
approach to gold. Kochi hapticities for 11 crystallographically
independent structures in eight distinct compounds are in the
range 1.41-1.93. Further, dative interactions prevail in three
gold complexes bearing σ-bonded ortho-biphenyl ligands (com-
pounds 5, 7, and 10). In these, the ipso and one ortho carbon
of the non-σ-bonded phenyl ring interact in a sidewise manner
with gold. Clearly, the proclivity of gold(I) to adopt two-
coordinate structures does not exclude higher coordination
numbers through π-interaction with available aromatic donors.
This finding concurs with recent demonstrations of tricoordinate
gold(I)92-96 and with an established tendency of linear gold(I)
to undergo associative ligand substitutions.97-100
Excited-state properties of dialkylbiarylphosphine metallo-
complexes are also reported, apparently for the first time. The
new compounds, which are white or pale yellow as solids,
absorb in the ultraviolet region, with absorption onsets near 350
nm in THF. Absorption features near 280 nm are visible in the
spectra of all complexes. Time-dependent density-functional
calculations on the representative complexes 4 and 5 indicate
these to be (ligand-metal)-to-ligand charge-transfer transitions
Conclusions
Aryl-group transfer from boron reagents has previously been
shown to tolerate reducible and polar functionalities in aryl-
gold(I) complex synthesis.53 The dicyclohexylbiarylphosphines
first popularized by Buchwald and co-workers36-49 were chosen
as sterically encumbrancing ancillary ligands. Compounds
bearing simultaneous bulk at the phosphorus center and in the
σ-aryl ligand are preparable in isolated yields ranging from 45
to 90%. Further, arylation from boron avoids pyrophoric
reactants such as aryllithium compounds and Grignard reagents.
The new compounds are indefinitely stable as solids to air,
moisture, and laboratory lighting.
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1674 Organometallics, Vol. 28, No. 6, 2009
Partyka et al.
between the arylgold(I) fragment and the biarylphosphine ligand.
The same computations find the carbon-gold σ-bond to be
nonchromophoric. Static DFT calculations indicate a weakly
polar C-Au bond, as expected from the small difference in
their Pauling electronegativities.
Western Reserve University for support. The diffractometer
at CWRU was funded by NSF grant CHE0541766; that at
YSU by NSF grant 0087210, by the Ohio Board of Regents
grant CAP-491, and by Youngstown State University. We
thank Mr. Thomas Teets, Massachusetts Institute of Technol-
ogy, for experimental assistance and Professor D. G. Nocera,
MIT, for access to instrumentation.
Acknowledgment. The authors thank the National Science
Foundation (grant CHE-0749086 to T.G.G.) and Case
Supporting Information Available: Thermal ellipsoid projec-
tions of 6, 7, 8, and 10; plots of selected orbitals of 4, first 10
calculated singlet-singlet transitions of 4; full citation of ref 54,
and crystallographic (CIF) data. This material is available free of
charge via the Internet at http://pubs.acs.org.
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