Article
Platinabenzene 7. Cyclopropene 1 (688 mg, 2.0 mmol) was
Organometallics, Vol. 28, No. 17, 2009 5189
3JHH=7.8 Hz, 4JHH=1.8 Hz, 1H, H3), 12.09 (dd, 3JHH=7.5 Hz,
2
dissolved in dry Et2O (20 mL) under Ar and cooled to -78 °C.
BuLi (0.8 mL, 2.5 M in hexanes, 2.0 mmol) was added dropwise,
and the resulting yellow solution was stirred at -78 °C for
15 min. This solution was added dropwise to a stirred, ice-cooled
suspension of (cod)PtCl2 (374 mg, 1.0 mmol) in Et2O (5 mL).
The resulting dark brown suspension was allowed to warm to
room temperature and stirred for 12 h before filtration. The
filtrate was evaporated to give a dark brown solid that was
chromatographed twice on silica (30:1 hexanes/EtOAc). Eva-
poration of the red band afforded 7 (45 mg, 7%) as a red solid.
4JHH=1.8 Hz, JPtH=50 Hz, 1H, H5). 13C NMR (125 MHz,
2
C6D6): δ 9.03 (s, JPtC=17 Hz, CH3), 107.5 (s, CCH3), 124.6,
124.9, 125.09, 125.5 (C6H5 and C4), 127.1, 127.7, 131.6 (C6H5),
137.2 (s, 2JPtC=43 Hz), 135.1 (s, 3JPtC=163 Hz, C3), 146.40 (s,
3JPtC=73 Hz), 159.4 (s, 2JPtC=24 Hz, C2), 188.7 (s, 1JPtC=1330
1
Hz, C5), 200.6 (s, JPtC = 1370 Hz, C1). Anal. Calcd for
C27H28Pt: C, 59.22; H, 5.15; Pt, 35.62. Found: C, 59.11; H,
5.10; Pt, 35.74.
Platinabenzene 9 and σ-Vinyl Complex 15. Using the condi-
tions described above, reaction of (Z)-1-tert-butyl-3-(2-
iodoethenyl)-2-phenylcyclopropene (309 mg, 0.95 mmol), BuLi
(0.41 mL, 2.5 M in hexanes, 1.03 mmol), and Cp*Pt(CO)I
(420 mg, 0.86 mmol) afforded a red-brown semisolid, which
was chromatographed on silica beginning with hexanes and
gradually increasing in polarity to 9:1 hexanes/Et2O. Isolation
of a yellow band and evaporation gave 15 (78 mg, 16%) as a
Mp: 168 °C (dec). 1H NMR (500 MHz, C6D6): δ 5.09 (t, 3JHH
=
2.7 Hz, 1H, CpH), 5.36 (d, 3JHH=2.7 Hz, 2H, CpH), 6.74 (br t,
3JHH=7.5 Hz, 1H, C6H5), 6.85-6.94 (m, 3H, C6H5), 6.94-6.98
=
(m, 6H, C6H5), 6.99 (t, 3JHH=7.7 Hz, 2H, C6H5), 7.07 (d, 3JHH
7.3 Hz, 2H, C6H5), 7.13 (d, 3JHH=7.3 Hz, 2H, C6H5), 7.25-7.30
(m, 4H, C6H5), 7.42 (t, 3JHH=7.7 Hz, 3JPtH=150 Hz, 1H, H4),
8.20 (dd, JHH =8.1 Hz, JHH =1.7 Hz, 1H, H3), 12.76 (dd,
3
4
1
viscous yellow oil. H NMR (500 MHz, C6D6): δ 1.32 (s, 9H,
3JHH=7.7 Hz, 4JHH=1.7 Hz, 2JPtH=65 Hz, 1H, H5). 13C NMR
CH3), 1.83 (s, 2JPtH=16 Hz, 15H, CH3), 3.02 (d, 3JHH=8.2 Hz,
1H, CHCpr), 6.10 (pseudo t, 3JHH=8.2 Hz, 2JPtH=167 Hz, 1H,
CHdCH), 6.57 (d, 3JHH=8.3 Hz, 2JPtH=10.4 Hz, 1H, PtCH),
0
(125 MHz, C6D6): δ 96.09 (s, CHCp ), 97.83 (s, CHCp’), 114.97 (s,
0
CPhCp ), 124.51, 125.00, 125.46, 125.72, 126.19, 128.51, 130.54,
130.92, 132.22 (s each; C6H5 and C4), 135.73 (s), 140.99 (s,
3
4
7.04 (tt, JHH = 7.5 Hz, JHH = 1.8 Hz, 1H), 7.22 (pseudo t,
3JHH=7.6 Hz, 2H), 7.77 (dd, 3JHH=8.3 Hz, 4JHH=1.3 Hz, 2H).
13C NMR (75 MHz, C6D6): δ 9.9, 29.0, 29.4, 32.9, 104.1, 104.2,
111.5, 127.9, 129.0, 130.0, 130.9, 145.7, 167.0 (s, JPtC=1190 Hz).
IR (toluene): ν 2002 cm-1. HRMS (MALDI) for C26H32OPt
[M]þ: calcd 555.2101, found 555.2087.
3JPtC ≈ 150 Hz, C3), 144.17 (s), 161.74 (s, C2), 194.96 (s, 1JPtC
=
1330 Hz, C5), 204.01 (s, 1JPtC =1400 Hz, C1) (2 signals obscured
by solvent peaks). Anal. Calcd for C34H26Pt: C, 64.86; H, 4.16.
Found: C, 64.95; H, 4.29.
η5-Cp*Pt(CO)I (13). [(η5-Cp*)Pt(CO)]2 (450 mg, 0.63 mmol)
was dissolved in dry toluene (15 mL) under Ar and cooled to
-30 °C. Solid I2 (168 mg, 0.66 mmol) was added, and the
reaction mixture was allowed to warm slowly to room tempera-
ture. After stirring for 10 min at room temperature, the brown
solution was evaporated to a volume of ca. 5 mL and chroma-
tographed on silica (toluene). The violet band (Rf ≈ 0.6) was
collected and evaporated to give 13 (410 mg, 67%) as a purple
solid. Mp: 118 °C (dec). 1H NMR (300 MHz, C6D6): δ 1.63 (s,
2JPtH=17 Hz, 15H, CH3). 13C NMR (75 MHz, C6D6): δ 10.61 (s,
CH3), 108.98 (s, 2JPtC=28 Hz, CCH3), 166.13 (s, 1JPtC=2440
Hz, CO). IR (toluene): ν 2029 cm-1. Anal. Calcd for
C11H15IOPt: C, 27.23; H, 3.12; Pt, 40.20. Found: C, 27.42; H,
2.93; Pt, 40.09.
A red band (Rf ≈ 0.4 using 9:1 hexanes/Et2O) was collected
next and evaporated to afford arene 9 (72 mg, 14%) as an
orange-red solid. Mp: 150 °C. 1H NMR (500 MHz, C6D6):
δ 1.23 (s, 9H, CH3), 1.56 (s, 3JPtH=9 Hz, 15H, CH3), 6.83 (tt,
4
3JHH = 7.3 Hz, JHH = 1.8 Hz, 1H), 7.01-7.08 (m, 2H),
7.08-7.16 (m, 3H), 7.60 (pseudo t, 3JHH=7.9 Hz, 3JPtH=151
Hz, 1H, H4), 8.54 (dd, 3JHH=8.3 Hz, 4JHH=1.6 Hz, 1H, H3),
11.83 (dd, 3JHH=7.5 Hz, 4JHH=1.6 Hz, 2JPtH=41 Hz, 1H, H5).
13C NMR (125 MHz, C6D6): δ 8.9 (s, CH3), 35.1 (s, C(CH3)3),
38.8 (s, C(CH3)3), 107.9 (s, CCH3), 124.5, 124.7, 126.3,
3
126.8 (C6H5 and C4), 134.1 (s, JPtC =134 Hz, C3), 139.9 (s,
2JPtC=43 Hz, C2), 161.2 (s, 2JPtC=48 Hz), 187.8 (s, 1JPtC=1338
Hz, C5), 203.7 (s, JPtC = 1370 Hz, C1). Anal. Calcd for
1
Platinabenzene 8 and σ-Vinyl Complex 14. (Z)-1,2-Diphenyl-
3-(2-iodoethenyl)cyclopropene (1, 167 mg, 0.485 mmol) was
dissolved in dry Et2O (20 mL) under Ar and cooled to
-78 °C. BuLi (0.20 mL, 2.5 M in hexanes, 0.50 mmol) was
added dropwise, and the resulting yellow solution was stirred at
-78 °C for 15 min. The lithiate solution was transferred into a
-50 °C cooled Schlenk flask containing Cp*Pt(CO)I (13,
195 mg, 0.40 mmol). A clear light red solution formed immedi-
ately. The solution was allowed to warm to -20 °C and stirred
for 12 h at this temperature to give a dark brown suspension.
The mixture was evaporated and chromatographed on silica
(30:1 hexanes/EtOAc). Concentration of a yellow fraction (Rf ≈
0.7 using 9:1 hexanes/EtOAc) furnished 14 (71 mg, 24%) as a
C25H32Pt: C, 56.91; H, 6.11; Pt, 36.97. Found: C, 56.79;
H, 6.35; Pt, 36.54.
Platinabenzene 10. Using the conditions described above,
reaction of (Z)-1-methyl-3-(2-iodoethenyl)-2-phenylcyclopro-
pene (180 mg, 0.64 mmol), BuLi (0.28 mL, 2.5 M in hexanes,
0.70 mmol), and Cp*Pt(CO)I (281 mg, 0.58 mmol) afforded a
red-brown semisolid, which was chromatographed on silica
beginning with hexanes and gradually increasing in polarity to
9:1 hexanes/Et2O. A red band was collected and evaporated to
give platinabenzene 10 (11 mg, 4%). 1H NMR (500 MHz,
C6D6): δ 1.61 (s, 3JPtH=8.3 Hz, 15H, CH3), 2.29 (s, 3H, CH3),
6.97 (d, 3JHH=8.2 Hz, 2H), 7.20 (d, 3JHH=8.2 Hz, 1H), 7.26 (t,
3JHH=8.2 Hz, 2H), 7.57 (pseudo t, 3JHH=7.6 Hz, 3JPtH=147.1
1
yellow solid. Mp: 116 °C (dec). H NMR (500 MHz, C6D6):
Hz, 1H, H4), 8.10 (d, 3JHH=7.6 Hz, 1H, H3), 11.93 (dd, 3JHH
=
δ 1.84 (s, 2JPtH=14 Hz, 15H, CH3), 3.38 (d, 3JHH=8.1 Hz, 1H,
CHCpr), 6.20 (pseudo t, JHH = 8.1 Hz, JPtH = 150 Hz, 1H,
7.6 Hz, 4JHH=1.5 Hz, 2JPtH=48.0 Hz, 1H, H5). MS (APCI): m/z
(%) 486.2 (Mþ þ H, 100). Anal. Calcd for C22H26Pt: C, 54.42;
H, 5.40; Pt, 40.18. Found: C, 54.59; H, 5.35; Pt, 39.97.
Transformation of 14/15 into 8/9. σ-Vinyl complex 14 or 15 (30
mg) was dissolved in C6D6 (0.6 mL) and stored at room
temperature under Ar in an NMR tube. The conversion was
monitored by proton NMR spectroscopy and proved to be
complete after 36-48 h. During the course of this conversion
identifiable side products were not formed, nor was significant
decomposition observed. Platinabenzene 8 or 9 was obtained in
>95% yield.
3
3
3
CHdCH), 6.69 (d, JHH=8.1 Hz, JPtH=14 Hz, 1H, PtCH),
2
3
4
7.07 (tt, JHH = 7.5 Hz, JHH = 1.2 Hz, 2H), 7.25 (pseudo t,
3JHH=7.7 Hz, 4H), 7.88 (dd, 3JHH=8.0 Hz, 4JHH=1.2 Hz, 4H).
13C NMR (75 MHz, C6D6): δ 9.7, 28.9, 103.9, 106.5, 117.3,
128.5, 129.0, 130.0, 137.0, 143.7, 167.1 (s, JPtC=1180 Hz). IR
(toluene): ν 2001 cm-1. Anal. Calcd for C28H28OPt: C, 58.43; H,
4.90; Pt, 33.89. Found: C, 58.73; H, 4.89; Pt, 33.47.
A red band (Rf ≈ 0.4 using 9:1 hexanes/EtOAc) was collected
next and evaporated to afford arene 8 (31 mg, 14%) as an
orange-red solid. Mp: 186 °C (dec). 1H NMR (500 MHz, C6D6):
Cycloadduct 16. Platinabenzene 8 (20 mg, 0.036 mmol) and
maleic anhydride (5.5 mg, 0.056 mmol) were dissolved in dry
Et2O (2 mL). This mixture was stirred overnight at room
temperature and then cooled to -30 °C. The solvent was
removed via cannula, leaving behind 16 (15 mg, 63%) as a light
δ 1.59 (s, 3JPtH=8 Hz, 15 H, CH3), 6.74 (tt, 3JHH=9.0 Hz, 4JHH
=
3
4
1.8 Hz, 1H), 6.86 (tt, JHH = 7.2 Hz, JHH = 1.5 Hz, 1H),
6.95-7.01 (m, 4H), 7.02-7.07 (m, 2H), 7.13-7.17 (m, 2H),
7.63 (pseudo t, 3JHH=7.8 Hz, 3JPtH=143 Hz, 1H, H4), 8.25 (dd,