was oxidized to a mixture of 2-octanone and 4-octanone (entry
12), cyclohexane to cyclohexanol and cyclohexanone (entry 13),
and adamantane to adamanta-1-ol and 2-adamantone (entry
15). The fact that oxidation of octane occurred at the secondary
C–H bond exclusively, with no detectable products from
primary C–H bond oxidation, and adamantane preferentially
at the tertiary C–H bond suggests that the alkane oxidations
probably proceed via a H-atom abstraction pathway with rapid
radical recombination. This is further supported by the oxid-
ation of cyclohexane in a 9 : 1 benzene–CCl4 mixture (entry 14),
which gave cyclohexanol and cyclohexanone, as well as cyclo-
hexyl chloride. A similar mechanism has been proposed for
ruthenium-catalyzed oxidation of alkanes with TBHP.24 How-
ever, the conversions for aryl-substituted alkanes were much
higher, ranging from 18 to 70%. Under the same conditions,
n-propylbenzene was oxidized to 1-phenyl-1-propanone (entry
16), ethylbenzene to acetophenone (entry 17), diphenylmethane
to benzophenone (entry 18), cumene to a mixture of 2-phenyl-
2-propanol and acetophenone (entry 19), and 1,3-diiso-
propylbenzene to 2,4-diisopropylphenol (entry 20). The sub-
stantial increase in the oxidation reactivity of 2 from octane
to 1,3-diisopropylbenzene is consistent with the stability of
the radicals generated through H-atom abstraction, i.e. aryl-
substituted radicals are more stable than unsubstituted radicals.
Experimental evidence suggests that free radicals are probably
involved in the catalytic oxidation processes.
m, PhCH2–), 3.61 (2H, m, –NCH2CH2N–), 3.30 (2H, m,
–NCH2CH2N–), 2.80 (1H, m, NH), 2.51 (1H, m, NH) and 7.21
(0.75H, s, CHCl3). Found (calc. for C58H53N2P3Cl2Ruؒ
0.75CHCl3): C, 61.96 (62.27); H, 5.03 (4.75); N, 2.65 (2.47)%.
LRMS (positive FAB) m/z: 1042 (M ϩ 1)ϩ for 102Ru and 35Cl.
Synthesis of trans-RuCl2(ꢀ4-L2) 3. A solution of 2 (0.035 g,
0.034 mmol) in toluene (20 cm3) was heated under reflux in air
for 6 h. After cooling to room temperature, the solution was
filtered and evaporated to dryness in in vacuo to give an orange
residue. The residue was washed with diethyl ether (2 × 5 cm3)
and crystallized in a dichloromethane–n-hexane mixture to give
orange crystals of 3. Yield: 0.024 g, 92%. The identity of 3 was
confirmed by comparing its IR, 31P{1H} and 1H NMR, and MS
(positive FAB) data with those of an authentic sample of trans-
RuCl2(κ4-L2).5
Synthesis of trans-RuCl2(PPh3)(ꢀ3-L3) 4. A 30% solution of
H2O2 (0.024 g, 0.212 mmol) was added dropwise to a solution
of 2 (0.210 g, 0.202 mmol) in chloroform (30 cm3). The reaction
mixture was stirred at room temperature for 12 h before it was
filtered. The filtrate was evaporated to dryness in vacuo to give a
red residue, which was washed with diethyl ether (2 × 5 cm3).
Crystallization of the red residue in a chloroform–diethyl ether
mixture gave red crystals of 4. Yield: 0.198 g, 93%; m.p 195–
196 ЊC (dec). IR (cmϪ1, in KBr): 3053m, 1481m, 1434s, 1197s.,
1093m, 974m, 747s, 705s and 540s. NMR (CDCl3): 31P{1H},
δ 47.4 (d, 2JP–P = 28.5 Hz, PPh2), 38.5 (d, 2JP–P = 28.5 Hz, PPh3)
and 29.2 [s, P(O)Ph2]; 13C{1H}, 126.4–133.6 (m), 49.9 (s), 45.4
Experimental
1
(s), 31.4 (s) and 22.5 (s); H, δ 6.21–7.70 (43H, m, Ph-H), 4.71
General procedures
(2H, m, PhCH2–), 4.38 (2H, m, PhCH2–), 3.60 (2H, m,
–NCH2CH2N–), 3.12 (2H, m, –NCH2CH2N–), 2.60 (1H, m,
NH), 2.30 (1H, m, NH), 7.21 (1H, s, CHCl3), 3.46 (4H, q, J =
6.8 Hz, CH3CH2O) and 1.15 (6H, t, J = 6.8 Hz, CH3CH2O).
Found (calc. for C58H53Cl2N2OP3RuؒCHCl3ؒC4H10O): C, 60.33
(60.38); H, 5.13 (5.11); N, 2.31 (2.24)%. LRMS (positive FAB)
m/z: 1058 (M ϩ 1)ϩ for 102Ru and 35Cl.
Unless otherwise stated, all reactions were carried out in an
atmosphere of dry nitrogen or in vacuo. Solvents were dried by
standard procedures, distilled and deaerated prior to use. All
chemicals used were of reagent grade, obtained from the
Aldrich Chemical Company and, where appropriate, degassed
before use. Melting points were taken in sealed capillaries and
25
are uncorrected. The compounds L1, L2,7 and RuCl2(PPh3)3
were prepared according to literature methods. Microanalyses
were performed by the Shanghai Institute of Organic Chem-
istry, Chinese Academy of Sciences. The IR spectra (KBr
pellets) were recorded on a Nicolet Nagna-IR 550 spectrometer
Synthesis of trans-RuCl2(PPh3)(ꢀ3-L4) 5. A 30% solution of
H2O2 (0.027 g, 0.238 mmol) was added dropwise to a solution
of 4 (0.210 g, 0.198 mmol) in chloroform (30 cm3). The reaction
mixture was stirred at room temperature for 12 h before it was
filtered. The filtrate was evaporated to dryness in vacuo to give a
red residue, which was washed with diethyl ether (2 × 5 cm3).
Crystallization of the red residue in a chloroform–pentane mix-
ture gave red crystals of 5. Yield: 0.199 g, 95%; m.p. 200–201 ЊC
(dec). IR (cmϪ1, in KBr): 3048m, 1631m, 1481m, 1434s, 1186s,
1093m, 757s, 695s and 545s. NMR (CDCl3): 31P{1H}, δ 55.4
1
and NMR spectra on a JEOL EX270 spectrometer. H and
13C{1H} NMR chemical shifts were referenced to internal
deuteriated solvents and then recalculated to TMS (δ 0.00),
31P{1H} NMR spectra were referenced to external 85%
H3PO4. Low resolution mass spectra (LRMS) were obtained on
Finnigan MAT SSQ-710 and MAT 95 spectrometers in FAB
(positive ion) mode and reported as m/z. Gas chromatograms
were obtained on a HP 5890 GC system or a HP 6890-
5972 GC-MSD system. The progress of all the reactions was
monitored by 31P{1H} NMR spectroscopy.
2
2
(d, JP–P = 29.1 Hz, PPh2), 32.2 (d, JP–P = 29.1 Hz, PPh3) and
30.1 [s, P(O)Ph2]; 13C{1H}, 169.9 (s), 126.9–134.6 (m), 59.8 (s),
1
30.9 (s) and 21.6 (s); H, δ 8.60 (1H, s, –CH᎐N–), 6.21–7.52
᎐
(43H, m, Ph-H), 4.61 (2H, m, PhCH2–), 4.40 (1H, m,
–NCH2CH2N–), 3.60 (1H, m, –NCH2CH2N–), 3.31 (2H, m,
–NCH2CH2N–), 2.60 (1H, m, NH), 7.22 (1H, s, CHCl3) and
0.78–1.32 [12H, m(br), C5H12]. Found (calc. for C58H51Cl2-
N2OP3RuؒCHCl3ؒC5H12): C, 61.16 (61.51); H, 5.49 (5.14); N,
2.31 (2.25)%. LRMS (positive FAB) m/z: 1056 (M ϩ 1)ϩ for
102Ru and 35Cl.
Preparations
Synthesis of trans-RuCl2(PPh3)(ꢀ3-L2) 2. A solution of L2
(0.060 g, 0.1 mmol) and RuCl2(PPh3)3 (0.096 g, 0.1 mmol) in
dichloromethane (30 cm3) was stirred at room temperature for
4 h, then the solvent was removed in vacuo to give an orange
residue which was washed with n-hexane (2 × 5 cm3). The resi-
due was purified by column chromatography. When eluting
with chloroform, an orange band was obtained from the silica
gel column. Removal of the solvent from the orange band gave
an orange solid which, upon crystallization in a chloroform–
hexane mixture, gave orange crystals of 2. Yield: 0.087 g, 84%;
m.p. 190–191 ЊC (dec). IR (cmϪ1, in KBr): 3057m, 1568m,
1481m, 1432s, 1188m, 1087m, 975m, 746vs, 695vs and 520vs.
NMR (CDCl3): 31P{1H}, δ 48.6 (d, 2JP–P = 28.9 Hz, PPh2), 38.9
(d, 2JP–P = 28.9 Hz, PPh3) and Ϫ13.3 (s, pendant PPh2); 13C{1H},
Synthesis of trans-RuCl2(ꢀ4-L5) 6. To a yellow solution of 3
(0.180 g, 0.230 mmol) in a chloroform–ethanol mixture(20 cm3,
1 : 10), an excess of H2O2 (0.078 g, 0.617 mmol) was added. The
progress of the reaction was monitored by 31P{1H} NMR spec-
troscopy. After stirring at room temperature for 20 h, the reac-
tion mixture turned purple. The solvent was removed to give a
purple solid, which was re-dissolved in acetone and chromato-
graphed on a silica gel column. A bright red band and a deep
blue band were obtained when eluting with n-hexane–ethyl
acetate (1 : 1) and ethyl acetate, respectively. Removal of the
solvent from the red band gave a small amount of a red solid,
1
δ 126.7–141.5 (m), 57.0 (s), 49.2 (s), 31.9 (s) and 22.8 (s); H,
δ 6.41–7.99 (43H, m, Ph-H), 4.70 (2H, m, PhCH2–), 4.32 (2H,
1144
J. Chem. Soc., Dalton Trans., 2002, 1139–1146
Wong, Wai-Kwok
