Photochemistry of Substituted Benzyldiphenylphosphine Oxides

Article abstract of DOI:10.1021/jo991761r

Photochemical reactions (λ _irr = 54 nm) of substituted benzyldiphenylphosphine oxides 1a-e have been investigated in benzene and acetonitrile. α-Cleavage from the singlet excited state is proposed as the primary process, and products formed bot

Full text of DOI:10.1021/jo991761r

J . Org. Chem. 2000, 65, 2145-2150
2145
P h otoch em istr y of Su bstitu ted Ben zyld ip h en ylp h osp h in e Oxid es
Ningning Zhao and Douglas C. Neckers*,1
Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403
Received November 11, 1999
Photochemical reactions (λ irr ) 254 nm) of substituted benzyldiphenylphosphine oxides 1a -e have
been investigated in benzene and acetonitrile. R-Cleavage from the singlet excited state is proposed
as the primary process, and products formed both before and after escape of the primary
intermediates from the solvent cage result. Radicals 2 and 3 are observed by nanosecond flash
photolysis following excitation of 1a at 266 nm in acetonitrile. Acetone sensitization of 1a ,b fails
to improve the efficiency of product formation. The quantum yields of disappearance of 1a ,b are
unaffected by O2, and mechanisms for product formation from 1a in the presence of oxygen are
proposed.
In tr od u ction
Acyl- and bis(acyl)phosphine oxides are efficient photo-
initiators of radical polymerization.2-7 Such compounds,
the critical differentiating feature of which is formation
of highly reactive phosphorus-centered radicals, are quite
important commercially.8-14 Time-resolved ESR experi-
ments have shown that diphenylphosphinoyl radical has
a large 31P hyperfine coupling constant [(hfcc) ≈ 370 G15],
indicating a high degree of σ character and significant
spin localization on phosphorus. In some measure, this
is proposed to account for its reactivity.
Resu lts a n d Discu ssion
P h otoch em istr y of 1a -e. Phosphine oxides 1a -e
were irradiated (λ irr ) 254 nm) in acetonitrile or benzene.
In a typical experiment, a 5 × 10-3 M degassed solution
of 1a in acetonitrile gave bibenzyl 10 as a major product,
along with minor products 4-9 and trace amounts of
2-phenylpropionitrile, 15, Scheme 1. Similar results were
obtained for 1b-e. Product yields as a function of
irradiation time are shown in Table 1.
Benzyldiphenylphosphine oxides 1a -e incorporate the
phosphinoyl group but absorb shorter wavelength UV
irradiation. Quantum yields for the disappearance of
1a -e in both benzene and acetonitrile, and for the
appearance of product 10, in benzene are reported in this
paper. We also examined the role of oxygen in the
photoreaction of 1a .
Product distributions suggest radical pairs 2 and 3 are
generated from 1a and undergo both solvent cage and
diffusion processes, Scheme 1. Compound 10 is formed
by radical recombination in significant yields (e.g., 80%
at 15-94% conversion), while modest yields of products
from cross-radical recombination (∼10%) are also de-
tected. Benzyldiphenyl phosphinite 4 and product 5,32b
intermediates isomers 6 and 8, and the secondary
products of tautormerization 7 and 9 account for about
10% of the benzyl radical generated.
Products resulting from the dimerization of 2, tetra-
phenylphosphine dioxide 11, and the product of its
decomposition, diphenylphosphinic acid 22, can be identi-
fied using 31P NMR. Since 11 decomposes under the
conditions of gas chromatography, its structure and those
of its decomposition products were confirmed by com-
parison with authentic compounds. Hydrogen abstraction
from solvent produces diphenylphosphine oxide and
toluene. These are potentially formed in minor amounts
in acetonitrile and not detected.
* To whom correspondence should be addressed. Phone: (419) 372-
2034. Fax: (419) 372-0366. E-mail: neckers@photo.bgsu.edu.
(1) Contribution no. 393 from the Center for Photochemical Sciences.
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(3) J acobi, M.; Henne, A. Polym. Paint Color J . 1985, 175, 636.
(4) Oldering, P. K. T. Chemistry and Technology of UV and EB
Formulation for Coatings, Inks and Paints; SITA Technology Ltd.:
London, 1991; Vol. 3, 168.
(5) Rees, M. T. L.; Russell, G. T. Macromolecules 1998, 31, 1763.
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1999, 264, 88.
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1985, 26, 141.
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N, J . J . Am. Chem. Soc. 1995, 117, 5148.
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1996, 118, 6477.
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Turro, N, J . J . Am. Chem. Soc. 1996, 118, 7367.
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Turro, N. J .; Watkins, D. M. J . Am. Chem. Soc. 1997, 119, 11495.
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11773.
(15) (a) Roberts, B. P.; Singh, K. J . J . Organomet. Chem. 1978, 159,
31. (b) Kamachi, M.; Kuwata, K.; Sumiyoshi, T.; Schnabel, W. J . Chem.
Soc., Perkin Trans. 2 1988, 961. (c) Turro, N. J .; Khudyakov, I. V.
Chem. Phys. Lett. 1992, 193, 546. (d) Kajwara, A.; Konishi, Y.;
Schnabel, W.; Kuwata, K.; Kamachi, M. Macromolecules 1993, 26,
1656. (e) Kamachi, M.; Kajiwara, A.; Saegusa, K.; Morishiwa, Y.
Macromolecules 1993, 26, 7369.
The products formed from irradiations of 1a in benzene
develop at different rates and in different distributions,
Table 1. At 30% conversion, the yield of 4-9 (∼20%)
formed from the solvent cage process is obviously higher
than is the yield formed from radicals escaping the
10.1021/jo991761r CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/14/2000

2146 J . Org. Chem., Vol. 65, No. 7, 2000
Zhao and Neckers
Sch em e 1. P h otoch em istr y of 1a in Ben zen e a n d Aceton itr ile in th e Absen ce a n d P r esen ce of Oxygen
Ta ble 1. P r od u cts of th e Ir r a d ia tion of 1a (5 × 10-3 M) in Aceton itr ile/Ben zen e
product accountability %a
convn of 1c
solvent
CH3CN
(%)
4
[6] + 5 + 7
[8] + 9
10b
12
13
14
15
15
36
81
95
1.3
8.5
6.2
8.7
0.19
2.6
13.4
24.6
74
trace
82.5
trace
benzene
15
30
45
73
83
98
0.12
0.52
1.2
1.3
1.9
4.2
5.5
8.0
7.4
10.6
8.9
8.3
15
20.4
14.6
13.6
4.4
1.7
7.6
13
47
52
0.20
1.3
2.3
4.4
5.8
1.2
74
trace
trace
a
b
Based on the consumed 1. The GC factors are predetermined, using decane as internal standard. Product 11 is not included. Yield
of 10 doubled account for the stoichiometry of its formation from 1. c Total irradiation time is 2 h.
solvent cage (∼7%). At higher conversions, 10 and 11,
both products of cage escape, remain major though trace
amounts of photoproducts 12-14 are also formed. These
likely come from the addition of the phosphinoyl radical
2 to benzene forming the cyclohexadienyl adduct,16
Scheme 2.
though 4 undergoes further oxidation to form 5, Table 2.
Oxygen dramatically affects the yield of bibenzyl with
16, 17, and 21 being formed instead. Similarly, product
11 resulting from phosphinoyl radical coupling is not
observed. Instead, diphenylphosphinic acid 22 with a
known 31P NMR resonance at 34.07 ppm can be detected.
Irradiation of 1a in benzene leads to products and
distributions differing from those obtained in acetonitrile.
The yield of benzaldehyde, 16 (∼34%), decreases from
∼84% in acetonitrile while that of 21 increases from <1%
to ∼15%. Secondary products 17, 18, and 21 are formed
in significant amounts while benzoic acid is formed in
trace amounts during the entire irradiation. Photoprod-
ucts 12-14 are formed in benzene but not in acetonitrile.
In the presence of O2, 12 disappears and 13 is obtained
instead.
Mech a n ism . Proposed mechanisms that account for
all photoproducts are shown in Schemes 3 and 4, respec-
tively. R-Cleavage of the benzyl carbon/phosphorus bond
produces the phosphinoyl radical 2, which is known to
have two spin density distributions,17 and the benzyl
radical 3, which can be thought of as a hybrid of several
resonance contributors. As a result, multiple products
from geminate radical recombination between phos-
The 31P NMR spectrum of the photolysis mixture
formed from 1a in benzene clearly shows resonances of
all the major photoproducts that contain phosphorus 7,
8, 9, and 11, though the resonance at 29.378 ppm,
corresponding to isomer 8, overlaps with that at 29.113
ppm corresponding to isomer 9. The individual isomers
7 and 9 have been identified by co-injection of authentic
compounds on GC/MS. Since both 1a and most of the
photoproducts absorb at 254 nm, secondary reactions
from primary photoproducts likely occur, and minor
amounts of several secondary products are formed.
P h otoch em istr y of 1a -e w ith O2 P r esen t. Irradia-
tion (λ ) 254 nm) of 5 × 10-3 M solution of 1a in an
irr
O2-saturated solution in acetonitrile yields benzaldehyde
16, benzoic acid 17, and 2-(diphenylphosphinoyl)benz-
aldehyde 21.
Solvent cage recombination products are formed in
approximately the same amounts in the presence of O2,
(16) Griller, D.; Marriott, P. R.; Nonhebel, D. C.; Perkins, M. J .;
Wong, P. C. J . Am. Chem. Soc. 1981, 103, 7761.
(17) Kolezak, U.; Rist, G.; Dietliker, K.; Wirz, J . J . Am. Chem. Soc.
1996, 118, 6477.

Photochemistry of Benzyldiphenylphosphine Oxides
J . Org. Chem., Vol. 65, No. 7, 2000 2147
Ta ble 2. P r od u cts of th e Ir r a d ia tion of 1a (5 × 10-3 M) w ith O2 P r esen t in Aceton itr ile/Ben zen e
product accountabilitya (%)
convn of 1b
solvent
CH3CN
(%)
[6] + 5 + 7
[8] + 9
13
14
16
17
18
19
20
21
8
15
52
87
98
1.9
4.0
12.5
12.3
3.8
2.0
3.4
trace
2.5
2.0
11.0
14.4
5.3
trace
16
19
50
83.6
0.2
0.6
trace
9.0
10.5
5.2
benzene
15
30
60
81
90
95
3.6
7.4
9.1
10.7
10.6
8.7
4.3
8.8
10.8
8.7
6.1
4.5
2.2
1.7
1.2
4.5
13
15.4
15.5
14.1
12.6
trace
13.3
22.8
28.2
33.6
trace
4.9
15.6
20.7
23
trace
2.4
5.6
7.6
10
1.0
1.2
2.7
4.2
trace
trace
a
b
Based on the consumed 1. The GC factors are predetermined, using decane as internal standard. Product 22 is not included. Total
irradiation time is 2 h.
Sch em e 2. Mech a n ism of Ben zen e Sca ven gin g of
P h osp h in oyl Ra d ica l 2
constant of hydrogen abstraction, Ph2CHOH (87 kcal/mol)
< CH3CN (93 kcal/mol),18 the rate constant of hydrogen
abstraction from acetonitrile must be much lower than
5 × 105 M-1 s-1. When compared to the coupling rate
constant of phosphinoyl radical ∼1.3 × 1010 M-1 s-1 19
,
formation of diphenylphosphine oxide is not a favorable
process.
It is well-established that the rate constant for reaction
of the benzyl radical with O2 is in the range of 3.0 × 109
M-1 s-1 20
. Since this is at least 1 order of magnitude faster
than the recombination rate constant of two benzyl
radicals (3-20) × 108 M-1 s-1 21,27b
,
benzylperoxy radical
formation is more favorable than benzyl radical coupling.
In addition, the rate constant for reaction of the
12,19
phosphinoyl radical with O2 (5.3 × 108 M-1 s-1
)
is
slower than that of phosphinoyl radical recombination
(1.3 × 1010 M-1 s-1.)19 Since reaction of 1a is carried out
with atmospheric O2, moisture may also be inadvertently
introduced during irradiation. Some hydrolysis of 11 may
occur forming diphenylphosphinic acid 22.
Solvent affects the formation and distribution of photo-
oxidized products, Table 2. The proposed reaction of
benzyl radical with O2 leading to formation of benzyl-
peroxy radical results in a situation where cross-radical
recombination and inter- and intramolecular hydrogen
abstraction processes compete, Scheme 4. Though aceto-
nitrile is a poor hydrogen donor, intermolecular hydrogen
abstraction processes may occur, and the resulting
benzyl peroxide subsequently is converted to benzalde-
hyde 16. Self-coupling of peroxy radicals may result in
benzaldehyde and phenylmethyl alcohol.22 Benzoic acid
17 is a secondary product resulting from oxidation of
benzaldehyde.23
In non-hydrogen-donating solvents such as benzene,
intramolecular hydrogen abstraction processes may oc-
cur. The putatively formed four-center intermediate is
followed by the formation of benzylperoxide radical,
Scheme 3. Such internal hydrogen abstraction is very
likely for a resonance-weakened C-H bond such as allylic
and benzylic -H. Energetically, the overall reaction has
phinoyl radicals 2, 2′ and the benzyl radical can occur.
4, which results from recombination of 2′ and 3, may be
further oxidized to 5. 6 and 8 result from the recombina-
tion of 2 and 3′, 3′′ respectively. Subsequent 1,3 and 1,5
H-atom shifts of 6 and 8 to more stable products 7 and
9, respectively, are expected to be facile photochemical
processes. An attempt to isolate these products by column
chromotography was not successful, so comparison samples
of 4, 7, and 9 were synthesized. Cross-radical recombina-
tion products 5-9 would not have formed in the presence
of O2, were there no solvent-cage processes occurring.
In acetonitrile, hydrogen abstractions between either
radical 2 or 3 and the solvent may occur. Toluene likely
elutes with solvent and was not detected. As for phos-
phinoyl radical 2, the rate constant of hydrogen abstrac-
tion with benzhydrol (Ph2CHOH) in hexane has been
calculated to be less than 5 × 105 M-1 s-1.9 Since the
bond strength of the H-atom donor dictates the rate
(18) Murov, S. L.; Carmichael, I.; Hug, G. L. Handbook of Photo-
chemistry; 2nd ed.; Marcel Dekker: New York, 1993.
(19) Zhao, N.; Strehmel, B.; Gorman, A. A.; Hamblett, I.; Neckers,
D. C. J . Phys. Chem. A. 1999, 103, 7757.
(20) Tokumura, K.; Nosaka, H.; Ozaki, T. Chem. Phys. Lett. 1990,
169, 321.
(21) Meiggs, T. O.; Miller, S. I. J . Am. Chem. Soc. 1972, 94, 1989.
(22) (a) Russell, G. A. J . Am. Chem. Soc. 1957, 79, 3871. (b) Zaikov,
G. E.; Howard, J . A.; Ingold, K. U. Can. J . Chem. 1969, 47, 3017. (c)
Ingold, K. U. Acc. Chem. Res. 1969, 2, 1.
(23) Niclause, M.; Lemaire, J .; Letort, M. Advan. Photochem. 1966,
4, 25.

2148 J . Org. Chem., Vol. 65, No. 7, 2000
Sch em e 3. Mech a n ism for th e P r ocess in th e Solven t Ca ge
Zhao and Neckers
Sch em e 4. Mech a n ism in Ben zen e a n d Aceton itr ile in th e Absen ce a n d P r esen ce of Oxygen for
F or m a tion of P r od u cts ou tsid e th e Solven t Ca ge
been calculated to be exothermic by 51-57 kcal/mol in
gas phase.24 The subsequent secondary reactions of the
benzylperoxy radicals lead to formation of 18, 19,25 and
21.
Qu a n tu m Yield s a n d th e Na tu r e of th e Excited
Sta tes. The quantum yields of disappearance of the
phosphine oxides 1a -e and of the appearance of bibenzyl
10 are reported in Table 3. 1a turns out to be relatively
more reactive than the p- and o-methoxybenzyldiphenyl-
phosphine oxides 1c and 1e.
disappearance, though reaction with O2 accounts for the
formation of products 16, 17, 20, and 21 and subsequent
secondary products. There are other literature examples
where oxygen apparently has no affect on the photoeffi-
ciency of reaction of benzylic compounds.26
Sensitization studies of 1a -e are difficult because
there are few sensitizers with triplet energies high
enough to enable energy transfer. Attempted sensitiza-
tion of the reactions of 1a ,b using acetone (ET ∼78 kcal/
mol) leads to substantially lower efficiencies. A suffi-
ciently high acetone concentration (OD > 2 at 313 nm)
in benzene ensures minimal competitive absorption of
1a ,b. Since the photoproducts form but at much lower
Quenching of the photoreactions of either 1a or b with
O2 results in no decrease in the quantum efficiency of
(24) Benson, S. W. J . Am. Chem. Soc. 1965, 87, 972.
(25) (a) Chateauneuf, J .; Lusztyz, J .; Ingold, K. U. J . Am. Chem.
Soc. 1988, 110, 2877. (b) Chateauneuf, J .; Lusztyz, J .; Ingold, K. U. J .
Am. Chem. Soc. 1988, 110, 2886. (c) Yamauchi, S.; Hirota, N.;
Takahara, S.; Misawa, H.; Sawabe, K.; Sakuragi, H.; Tokumaru, K. J .
Am. Chem. Soc. 1989, 111, 4402.
(26) (a) Givens, R. S.; Matuszewski, B.; Athey, P. S.; Stoner, M. R.
J . Am. Chem. Soc. 1990, 112, 6016. (b) Fleming, S. A.; J ensen, A. W.
J . Org. Chem. 1996, 61, 7040. (c) Ganapathy, S.; Sekhar, B. B. V. S.;
Cairns, S. M.; Akutagawa, K.; Bentrude, W. G. J . Am. Chem. Soc. 1999,
121, 2085.

Photochemistry of Benzyldiphenylphosphine Oxides
J . Org. Chem., Vol. 65, No. 7, 2000 2149
Ta ble 3. Qu a n tu m Yield s of Disa p p ea r a n ce of Su bstitu ted Ben zyld ip h en ylp h osp h in e Oxid es 1a -e in Ben zen e
1a
1b
1c
1d
1e
a
φdis
φapp(10)a
0.3 ( 0.03
0.0005
0.27 ( 0.04
0.0001
0.29 ( 0.04
0.06 ( 0.05
0.27 ( 0.04
0.07 ( 0.008
φdis(O2)a
0.2 ( 0.03
0.0007
φdis(acetone)b
a
Quantum yields are measured within 5% conversion at 254 nm irradiation (actinometer: cyclohepta-1,3-diene φ ) 4.6 ( 0.01 at 10-2
M in ethanol);37 decane is used as an internal standard; φdis is the disappearance of 1a -e; φapp(10) is the appearance of bibenzyl;
b
φdis(O2)disappearance of 1a ,b with O2 saturated solutions. φdis(acetone) is the disappearance of 1a ,b with addition of acetone (OD > 2
at 313 nm) using 2-hexanone as an actinometer (φd ) 0.327 at 1 M in pentane).38
6020 FTIR spectrometer. Thin-layer chromotography was
performed with Whatman silica gel coated TLC plates. Ab-
sorption spectra were recorded using a Hewlett-Packard 8452A
diode array UV-vis spectrophotometer.
efficiencies (Table 3), this result suggests a less reactive
triplet excited state.
Na n osecon d La ser F la sh P h otolysis. Laser flash
photolysis of 1a -e using 266 nm excitation gives similar
transient absorption spectra in acetonitrile and cyclo-
hexane. The transient absorption between 280 and 400
nm has been assigned to the overlap of the absorptions
of the benzyl and phosphinoyl radicals. The decay of this
transient, monitored at 320 nm, follows clean biexponen-
tial kinetics on the microsecond scale. The fast component
is phosphinoyl radical with a lifetime of ∼6 µs. The slow
component is a long-lived species that does not decay
completely over 1 ms; the longest time scale of our
analyzing light and laser system. It is assigned to the
benzyl radical that has a lifetime of ∼139 µs. Similar
transient absorptions and lifetimes of benzyl and phos-
phinoyl radicals have been reported.8,12,19,27
The lifetimes of the radicals change with concentration
of 1a -e. In addition, triplet absorption is not detected
on the nanosecond scale. As a result, it is very likely that
radicals are generated from the singlet excited state.
Con clu sion . The photoreactions of phosphine oxides
1a -e proceed primarily via singlet excited states with
the resulting photoproducts deriving from both solvent
cage and cage escape processes. The presence of oxygen
does not seriously affect the reaction efficiency though
some oxidized products are obtained.
Ben zyld ip h en ylp h osp h in e Oxid e (1a ).28 Diphenylmethyl
phosphinite (0.005 mol) was added dropwise to benzyl chloride
(0.005 mol). The reaction mixture was then heated to 100 °C
and stirred at that temperature for 30 min. After the solution
was cooled, a white solid appeared. The crude product was
purified by crystallization from ethanol affording 1.4 g (97%
yield) of 1a : white needles; mp 189-190 °C (lit.29 mp 192-
193 °C); 1H NMR (200 MHz, CDCl3) δ 3.689-3.619 (d, J ) 14
Hz, 2 H), 7.101-7.2 (m, 5 H), 7.393-7.517 (m, 6 H), 7.642-
7.746 (m, 4 H); 13C NMR (50 Hz, CDCl3) δ 38.750-37.421 (d,
J ) 66.45 Hz), 126.769-126.697 (d, J ) 3.6 Hz), 128.334,
128.553, 130.045-130.154 (d, J ) 5.45 Hz), 131.046-131.226
(d, J ) 9.1 Hz), 131.282, 131.710-131.774 (d, J ) 2.75 Hz),
133.248-134.430 (d, J ) 59.1 Hz); 31P NMR (162 MHz, CDCl3)
δ 30.430; MS m/e 292 (16.2, M+), 291 (30.4), 202 (14.2), 201
(100), 183 (4.2), 152 (4.7), 91 (10.6), 77 (29.6).
p-Meth ylben zyl ip h en ylp h osp h in e Oxid e (1b).28 A pro-
cedure similar to that described for 1a produced 1b in 87%
yield: white needles; mp 198-199 °C (lit.30 196 °C); 1H NMR
(200 MHz, CDCl3) δ 2.251 (s, 3 H), 3.583-3.651 (d, J ) 13.6
Hz, 2 H), 6.988 (s, 4 H), 7.422-7.7 (m, 10 H); 31P NMR (162
MHz, CDCl3) δ 30.412; MS m/e 306 (18.6, M+), 305 (36.6),
202 (13.8), 201 (100), 183 (4.5), 181 (6.7), 123 (2), 105 (17.5),
77 (46).
p-Meth oxyben zyld ip h en ylp h osp h in e oxid e (1c).28
A
procedure similar to that described for 1a produced 1c in 92%
1
yield: white needles; mp 227-228 °C (lit.31 228-229 °C); H
A complete mechanism for the photoreaction of benzyl
diphenylphosphine oxide based on extensive studies of
various phosphine oxides has been proposed. Further
exploitation of benzyldiphenylphosphine oxide photo-
chemistry both in photoinitiation and protecting group
applications is vigorously underway in this laboratory.
NMR (200 MHz, CDCl3) δ 3.564-3.632 (d, J ) 13.6 Hz, 2 H),
3.748 (s, 3 H), 6.709-6.752 (q, J ) 8.6 Hz, J ) 2.2 Hz, 2 H),
6.992-7.036 (q, J ) 8.8 Hz, J ) 2.2 Hz, 2 H), 7.429-7.737 (m,
10 H); 31P NMR (162 MHz, C6D6) δ 29.298; MS m/e 322 (10.5,
M+), 321 (9.7), 202 (3.5), 201 (25.6), 197 (6.5), 152 (2.2), 121
(100), 122 (8.9), 77 (26.5).
o-Meth ylben zyld ip h en ylp h osp h in e Oxid e (1d ).28 A pro-
cedure similar to that described for 1a produced 1d in 59%
yield: white needles; mp 122-123 °C; 1H NMR (200 MHz,
CDCl3) δ 2.113 (s, 3 H), 3.667-3.702 (d, J ) 14 Hz, 2 H), 6.9
(m, 2 H), 7.0 (m, 2 H), 7.4-7.7 (m, 10 H); 31P NMR (162 MHz,
CDCl3) δ 31.803; MS m/e, 306 (42.5, M+), 291 (3.6), 215 (3.8),
201 (100), 183 (5.3), 181 (8.1), 165 (4.7), 152 (3.8), 105 (9.1),
91 (1.8), 77 (45.3); HRMS m/e measured 306.1171, calcd
306.1167.
Exp er im en ta l P a r t
Ma ter ia ls a n d Solven ts. Benzene (Aldrich) was dried over
sodium under Argon. Chlorodiphenylphosphine was obtained
from Lancaster. Unless mentioned, all other chemicals and
solvents (anhydrous grade) were obtained from Aldrich and
used as received.
Gen er a l Meth od s. Melting points were determined with
a Thomas-Hoover capillary melting point apparatus and are
uncorrected. NMR spectra were obtained either with a Varian
Gemini 200 NMR spectrometer or Varian Unity Plus 400 NMR
spectrometer. Chemical shifts are in ppm with TMS as the
internal standard (1H NMR and 13C NMR) or H3PO4 as the
external standard (31P NMR). GC/MS and MS spectra were
obtained on a Shimadzu GC/MS-QP5050 mass spectrometer
coupled to a GC-17A (Restek ST1-5 column 30 m × 0.25 mm
× 0.25 µm). Quantitative GC analysis utilized decane as an
internal standard against which all other peaks were cali-
brated for sensitivity (response factor), except as mentioned
otherwise. Infrared spectra were taken with a Galaxy series
o-Meth oxyben zyld ip h en ylp h osp h in e Oxid e (1e).28
A
procedure similar to that described for 1a produced 1e in 71%
yield: white solid; mp 107-108 °C; 1H NMR (200 MHz, CDCl3)
δ 3.450(s, 3 Η), 3.735-3.771 (d, J ) 13.6 Hz, 2 H), 6.649-
6.670 (d, J ) 8.4 Hz, 1 H), 6.850-6.887 (t, J ) 7.6 Hz, 7.2 Hz,
1 H), 7.123-7.163 (t, J ) 7.2 Hz, 1 H), 7.356-7.727 (m, 11
H); 31P NMR (162 MHz, CDCl3) δ 31.052; MS m/e 322 (35.8,
M+), 304 (19.1), 291 (6.4), 201 (100), 183 (6.4), 165 (4), 152
(5.2), 121 (25.3), 91 (57.8), 77 (37.9); HRMS m/e measured
322.1228, calcd 322.1227.
(28) Brown, K. M.; Lawrence, N. J .; Liddle, J .; Muhammad, F.
Tetrahedron Lett. 1994, 35, 6733.
(29) Michaelis, A.; La Coste, W. Ber. 1885, 18, 2109.
(30) Horner, L.; Klink, W.; Hoffmann, H. Chem. Ber. 1963, 96, 3133.
(31) Davidson, R. S.; Sheldon, R. A.; Trippett, S. J . Chem. Soc. C
1967, 1547.
(27) (a) Tokumura, K.; Tomomi, O.; Nosaka, H.; Saigusa, Y. Itoh,
M. J . Am. Chem. Soc. 1991, 113, 4974. (b) Meiggs, T. O.; Grossweiner,
L. I.; Miller, S. I. J . Am. Chem. Soc. 1972, 94, 7896.

2150 J . Org. Chem., Vol. 65, No. 7, 2000
Zhao and Neckers
Ben zyld ip h en yl p h osp h in ite (4):32 crude yield 83%; bp
220-30 °C,32a characterized without purification; 31P NMR
(162 MHz, C6D6) δ 118.1; MS m/e 292 (5, M+), 291 (15.2), 201
(100), 183 (6.5), 152 (3.7), 107 (3.1), 91 (17.3), 77 (26.7).
o-Meth ylp h en yld ip h en ylp h osp h in e oxid e (7):33 86%
a Rayonet RPR 100 photoreactor, equipped with 16 254 nm
F8T5-BLB UV lamps. The products were identified by com-
parison with authentic samples, which were synthesized or
purchased.
Qu a n tu m Yield Mea su r em en ts. Light intensity was
determined using the reaction of cyclohepta-1,3-diene in
ethanol (φ ) 0.46 ( 0.01 at 0.01 M) at 254 nm.37 The progress
of the reaction was monitored by GC/MS analysis. Decane was
used as an internal standard in GC calibration and for
quantitative measurements. The values reported in Table 3
are the average of three experiments.
Aceton e-Sen sitized P h otolysis of 1a ,b in Ben zen e.
Each sample solution in benzene with high acetone concentra-
tion (OD > 2 at 313 nm) was irradiated with 200W mercury
lamp at 313 nm using 313 ( 10 nm band glass filter.
2-Hexanone in pentane solution (1 mol/L, φd ) 0.327, λex ) 313
nm)38 was used as an actinometer. Decane was used as an
internal standard in GC calibration and quantitative measure-
ments.
La ser F la sh P h otolysis. Nanosecond laser flash photolysis
experiments were carried out on a setup described by Ford
and Rodgers using a Q-switched Nd:YAG laser as a pump light
(355 nm; 60 mJ /pulse; 8 ns pulse or 266 nm; 5 mJ /pulse; 8 ns
pulse).39 Argon, oxygen, or air was bubbled continuously
through the sample solution during the measurements.
1
yield; white solid; mp 120-121 °C (lit.33 mp 122-123 °C); H
NMR (200 MHz, C6D6) δ 2.581 (s, 3 H), 7.0-7.3 (m, 3 H), 7.4-
7.7 (m, 11 H); 31P NMR (162 MHz, C6D6) δ 32.149; MS m/e
292 (49, M+), 291 (100), 213 (16), 199 (7.5), 183 (6), 166 (14.4),
165 (27.4), 152 (8.4), 91 (5.5), 77 (11.8).
p-Meth ylp h en yld ip h en ylp h osp h in e oxid e (9):34 95%
1
yield; white solid; mp 129-130 °C (lit.34 mp 129-130 °C); H
NMR (200 MHz, C6D6) δ 1.957 (s, 3 H), 6.827-6.880 (q, J )
8.4 Hz, J ) 2.2 Hz, 2 H), 6.992-7.052 (m, 6 H), 7.651-7.851
(m, 6 H); 31P NMR (162 MHz, C6D6) δ 29.094; MS m/e 292 (50.8,
M+), 291 (100), 215 (15.6), 213 (14), 201 (4.3), 199 (20), 183
(11.9), 165 (8.7), 152 (9.8), 91 (11.2), 77 (21).
Tetr a p h en ylp h osp h in e d ioxid e (11):35 mp 167-168 °C
(lit.35 mp 168-169 °C); 31P NMR (162 MHz, CDCl3) δ 22.8; MS
m/e 402 (0.07, M+), 277 (3.7), 217 (17.8), 202 (58), 201 (100),
183 (16.6), 152 (9.8), 124 (14.5), 77 (68.4).
2-(Diph en ylph osph in oyl)ben zaldeh yde (21):36 95% yield;
mp 146-7 °C (lit.36 mp 120-121 °C); 1H NMR (200 MHz,
CDCl3) δ 7.487-7.683 (m, 14 H), 10.733 (s, 1 H); 31P NMR (162
MHz, CDCl3); δ 32.141; MS m/e 306 (34.4, M+), 278 (23), 277
(100), 199 (53.4), 183 (12.1), 152 (30), 77 (29.4); IR (cm-1) 2940
(CHO), 1689 (CdO), 1189 (PdO).
Ack n ow led gm en t. We thank the National Science
Foundation Division of Materials Research (NSF
9526755) and the Office of Naval Research Polymers
Program (N00014-97-1-0834) for financial support
P h otolysis of 1a -e. The benzyldiphenylphosphine oxides
were dissolved in benzene or acetonitrile in a quartz cuvette
and sealed with a rubber septum bound by sticky Parafilm,
and the solution was degassed by bubbling with dry argon gas
for 10-15 min. The solution was irradiated for 3-120 min in
of this work.
A research fellowship granted by
the McMaster Endowment to N.Z. is also gratefully
acknowledged.
(32) (a) Arbuzov, A. E.; Nikonorov, K. V. Zh. Obshch. Khim. J . Gen.
Chem. 1948, 18, 2008. (b) Since product 4 is very sensitive to oxygen,
only trace amount of oxygen will oxidize 4 to 5.
(33) Griffin, C. E.; Davison, R. B.; Gordon, M. Tetrahedron 1966,
22, 561.
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(34) Streitwieser, A., J r.; J uaristi, E. J . Org. Chem. 1982, 47, 768.
(35) Spanier, E. J .; Caropreso, F. E. J . Am. Chem. Soc. 1970, 92,
3348.
(37) Numao, N.; Hamada, T.; Yonemitsu, O. Tetrahedron Lett. 1977,
19, 1661.
(38) Coulson, D. R.; Yang, N. C. J . Am. Chem. Soc. 1966, 85, 451.
(39) Ford, W. E.; Rodgers, M. A. J . J . Phys. Chem. 1994, 98, 3822.
(36) Schiemenz, G. P.; Kaack, H. Liebigs. Ann. Chem. 1973, 1, 1480.