A R T I C L E S
Partyka et al.
Scheme 1. Syntheses of Aurated Diphosphenes 2 and 3
2 and 3 were prepared under nitrogen within an MBraun Unilab
2000 inert atmospheres drybox. Microanalyses (C, H, and N) were
performed by Quantitative Technologies Inc. All NMR spectra (1H
and 31P{1H}) were recorded in CDCl3 on a Varian AS-400
spectrometer operating at 399.7 and 161.8 MHz, respectively.
Raman spectra of 2 and 3 were generated using a 532 nm compact
diode laser source at Cleveland State University. UV-vis and
fluorescence data were recorded using a Cary 5G UV-vis-NIR
spectrometer and a Cary Eclipse spectrometer, respectively.
[Mes*PdP{AuCl}Mes*] (2). An orange solution of 1 (23.3 mg,
0.042 mmol) in 1.5 mL of dichloromethane was added dropwise
to a solution of tetrahydrothiophenegold(I) chloride (13.5 mg, 0.042
mmol) in 1.5 mL of dichloromethane. The mixture became yellow
and was stirred 1 h. The solvent was then removed by rotary
evaporation. The resulting yellow solid 2 was washed with cold
(-25 °C) pentane and then collected and dried. Yield: 31 mg (94%).
1H NMR: δ 7.48 (s br, 2H, aromatic), 7.46 (s br, 2H, CH aromatic),
1.60 (s, 18H, o-C(CH3)3), 1.48 (s, 18H, o-C(CH3)3), 1.40 (s, 9H,
p-C(CH3)3), 1.35 (s, 9H, p-C(CH3)3). 31P{1H} NMR: δ 386.0 (d,
1P, J(P-P) ) 538 Hz), 338.8 (d, 1P, J(P-P) ) 539 Hz). IR
(KBr): 648 (m, υPdP) cm-1. Raman (neat powder, 532 nm
excitation): 645 (υPdP) cm-1. UV-vis (CH2Cl2, 1.88 × 10-5 M): λ
(ε, M-1 cm-1) 277 (18 600), 338 (4800), 427 (800) nm. MP: Slow
decomposition (turns brown) ∼80-160 °C. A recrystallized sample
(chlorobenzene/pentane) gave a satisfactory microanalysis. Anal.
Calcd for C36H58AuClP2: C, 55.07; H, 7.45. Found: C, 55.37; H,
7.31.
diphosphene for an array of studies involving multiply bonded
main group compounds.4 More recent studies particularly
relevant to our work include a combined high-level computa-
tional and EDD analysis by Cowley to examine the electronic
structure of 1.19 In this investigation, a long-standing question
on the ordering of the HOMO and HOMO-1 was addressed for
1. In the UV-vis spectra, two transitions are noted, a n+fπ*
and a πfπ*, with the latter proposed as the higher energy
transition owing to its greater intensity. The EDD/DFT study
indicated that the lone pairs on phosphorus make a major
contribution to the HOMO, and that the phosphorus-phosphorus
π-bond is slightly lower in energy than the n+ combination of
the lone pairs. Another recent computational study indicates that
the ordering of these levels is dependent on the extent of
conjugation of the aromatic groups with the PdP π system may
also be important.14
As the lone pairs of electrons are clearly positioned to be
involved in the photochemistry of diphosphenes, one might
suspect that they could play a role in influencing photolumi-
nescence properties. Azobenzenes (RNdNR) are also structur-
ally related to diphosphenes, and have been extensively studied
for their photochemical properties. A recent report has demon-
strated that introduction of an ortho-B(C6F5)2 group onto
azobenzene increases fluorescence intensity by a factor of
30 000.20
1
1
[Mes*{AuCl}PdP{AuCl}Mes*] (3). An orange solution of 1
(30 mg, 0.054 mmol) in 1.5 mL of dichloromethane was added
dropwise to a solution of tetrahydrothiophenegold(I) chloride (34.7
mg, 0.11 mmol) in 1.5 mL of dichloromethane. The solution became
yellow and was stirred 1 h. The solvent was removed by rotary
evaporation. Analytically pure yellow solid 3 was obtained after
trituration with pentane and drying. Yield: 48 mg (87%). 1H NMR:
δ 7.55 (s, 4H, aromatic CH), 1.60 (s, 36H, o-C(CH3)3), 1.40 (s,
18H, o-C(CH3)3). 31P{1H} NMR: δ 291.3 (s, 2P). Raman (neat
powder, 532 nm excitation): 683 (υPdP) cm-1. UV-vis (CH2Cl2,
2.9 × 10-5 M): λ (ε, M-1 cm-1) 266 (21 000), 350 (8010), 410
(sh, 3530) nm. MP: Slow decomposition (turns brown) 110-161
°C. Anal. Calcd for C36H58Au2Cl2P2: C, 42.49; H, 5.74. Found: C,
42.18; H, 5.52.
While diphosphenes bearing one or more transition metal
complexes are known, the impact on fluorescence properties
does not appear to have been noted. In addition, owing to the
immense size of the Mes* groups in 1, creating materials having
two P-bound transition metal groups is difficult. Diphosphenes
having smaller R groups allow coordination of two transition
metal centers but often at the expense of being unable to isolate
monoadducts. In this article, we report the synthesis and isolation
of both monoaurated (Mes*{AuCl}PdPMes*, 2) and diaurated
(Mes*{AuCl}PdP{AuCl}Mes*, 3) adducts of 1. While no
significant increases in fluorescence properties was found, these
studies instead reveal unusual phosphorus-phosphorus bond
shortening. Possible explanations for the structural impacts of
these Lewis acids on a diphosphene are explicated. Such effects
do not appear to have been reported for aurated phosphaalkenes
that are receiving increased attention.21-27
Computational Analyses. Spin-restricted density-functional
theory (DFT) computations were performed within the Gaussian03
(21) Bedford, R. B.; Hill, A. F.; Jones, C.; White, A. J. P.; Williams, D. J.;
Wilton-Ely, J. D. E. T. J. Chem. Soc., Chem. Commun. 1997, 179–
180.
Experimental Section
(22) Weber, L.; Dembeck, G.; Loenneke, P.; Stammler, H.-G.; Neumann,
B. Organometallics 2001, 20, 2288–2293.
All solvents and reagents were used as received. Diphosphene 1
was prepared according to the literature procedure.18 Compounds
(23) Weber, L.; Lassahn, U.; Stammler, H.-G.; Neumann, B.; Karaghiosoff,
K. Eur. J. Inorg. Chem. 2002, 327, 2–3277.
(18) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T. J. Am.
Chem. Soc. 1981, 103, 4587–4589.
(24) Deschamps, E.; Deschamps, B.; Dormieux, J. L.; Ricard, L.; Mezailles,
N.; Le Floch, P. Dalton Trans. 2006, 594–602.
(19) Cowley, A. H.; Decken, A.; Norman, N. C.; Kru¨ger, C.; Lutz, F.;
Jacobsen, H.; Ziegler, T. J. Am. Chem. Soc. 1997, 119, 3389–3390.
(20) Yoshino, J.; Kano, N.; Kawashima, T. J. Chem. Soc., Chem. Commun.
2007, 559–561.
(25) Freytag, M.; Ito, S.; Yoshifuji, M. Chem. Asian J. 2006, 1, 693–700.
(26) Ito, S.; Freytag, M.; Yoshifuji, M. Dalton Trans. 2006, 710–713.
(27) Ito, S.; Freytag, M.; Liang, H.; Nishide, K.; Yoshifuji, M. Phosphorus,
Sulfur Silicon Relat. Elem. 2008, 183, 555–557.
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10042 J. AM. CHEM. SOC. VOL. 131, NO. 29, 2009