9076 J. Am. Chem. Soc., Vol. 123, No. 37, 2001
Rybtchinski et al.
1H, 13C, and 31P NMR spectra were recorded at 400, 100, and 162
MHz, respectively, at 295 K, using a Bruker Avance-400 NMR
spectrometer. 1H NMR and 13C{1H} NMR chemical shifts are reported
in ppm downfield from tetramethylsilane. 1H NMR chemical shifts are
referenced to the residual hydrogen signal of the deuterated solvents,
and in 13C{1H} NMR the 13C signal of the deuterated solvents was
used as a reference. 31P NMR chemical shifts are reported in ppm
downfield from H3PO4 and referenced to an external 85% solution of
phosphoric acid in D2O. Abbreviations used in the description of NMR
data are as follows: Ar, aryl; br, broad; dist, distorted; s, singlet; d,
doublet; m, multiplet. Electrospray (ES) mass spectrometry was
performed using a MicroMass LCZ Detector 4000 with CV ) 43 V,
temperature ) 150 °C, and EE ) 4.2 V. Elemental analysis was
performed at the Hebrew University of Jerusalem.
integration is given only for 3b (major product)): 6.88 (s, Ar-H, 3a),
2
6.77 (s, 1H, Ar-H, 3b), 4.97 (d, JHH ) 12.5 Hz, 1H, Ar-CH2-O,
2
left part of AB-system, 3b), 4.61 (d, JHH ) 12.7 Hz, 1H, Ar-CH2-
O, right part of AB-system, 3b), 4.38 (s, Ar-CH2-O, 3a), 3.27 (s,
2
2
3H, O-CH3, 3b), 3.06 (dd, JHH ) 8.8 Hz, JPH ) 3.7 Hz, 1H, Ar-
CH2-P, left part of AB-system, 3b), 2.59 (br m, 4H, overlapping signals
of Ar-CH2-P and Ar-CH2-Rh, 3b), 2.42 (s, Ar-CH3, 3a), 2.36 (s,
3H, Ar-CH3, 3b), 2.34 (s, 3H, Ar-CH3, 3b), 2.28 (s, Ar-CH3, 3a),
1.62 (d, 3JPH ) 12.5 Hz, 9H, P-C(CH3)3, 3b), 1.48 (br s, P-C(CH3)3
3
of 3b), 1.07 (d, JPH ) 13.1 Hz, 9H, P-C(CH3)3, 3b), -24.70 (br m,
Rh-H, 3a), -24.89 (dd, 1JRhH ) 27.2 Hz, 2JPH ) 18.1 Hz, 1H, Rh-H,
1
3b). Selected 13C{1H} NMR (acetone-d6): 8.85 (d, JRhC ) 25.1 Hz,
Ar-CH2-Rh, 3b).
Complex 4 (4a:4b ) 1.5:1). 31P{1H} NMR (methanol-d4): 126.8
1
1
1
Synthesis of C6H(CH3)3(CH2OCH3)(CH2Br). A freshly prepared
methanol solution of NaOMe (0.53 g, 9.81 mmol) was added dropwise
to a THF solution of 1,3-bis(bromomethyl)-2,4,6-trimethylbenzene11
(3.00 g, 9.81 mmol) at 0 °C. The solution was stirred for 2 h at room
temperature, and the solvent was evaporated under vacuum. This yielded
the monomethoxy compound, 1-bromomethyl-3-methoxymethyl-2,4,6-
trimethylbenzene, which was purified by column chromatography (SiO2,
hexane:THF) to give 1.34 g (53.3% yield) of the pure product as a
white solid.
(d, JRhP ) 195.8 Hz, 4b), 126.3 (d, JRhP ) 194.8 Hz, 4a). H NMR
(methanol-d4, integration relates to 4a and 4b separately): 6.95 (s, 1H,
Ar-H, 4b), 6.76 (s, 1H, Ar-H, 4a), 4.61 (s, 2H, Ar-CH2-O, 4a),
4.44 (dd, J ) 9.1 Hz, J ) 9.0 Hz, 2H, Ar-CH2-O, 4b), 3.46 (s, 3H,
O-CH3, 4a), 3.34 (d, J ) 3.1 Hz, 3H, O-CH3, 4a), 2.83 (m, 2H,
Ar-CH2-Rh, 4b), 2.75 (m, 2H, Ar-CH2-Rh, 4a), 2.46 (s, 3H, Ar-
CH3, 4b), 2.42 (s, 3H, Ar-CH3, 4b), 2.37 (s, 3H, Ar-CH3, 4b), 2.32
(s, 3H, Ar-CH3, 4a), 2.31 (s, 3H, Ar-CH3, 4a), 2.29 (s, 3H, Ar-
CH3, 4a), 1.43 (d, 3JPH ) 12.5 Hz, 9H, P-C(CH3)3, 4b), 1.35 (d, 3JPH
1H NMR (CDCl3): 6.87 (s, 1H, Ar-H), 4.57 (s, 2H, Ar-CH2-Br),
4.44 (s, 2H, Ar-CH2-O), 3.39 (s, 3H, O-CH3), 2.41 (s, 3H, Ar-
CH3), 2.35 (s, 3H, Ar-CH3), 2.34 (s, 3H, Ar-CH3).
3
) 12.5 Hz, 9H, P-C(CH3)3, 4a), 1.17 (d, JPH ) 12.5 Hz, 9H,
P-C(CH3)3, 4b), 1.23 (d, 3JPH ) 13.1 Hz, 9H, P-C(CH3)3, 4a), -25.28
1
2
(dd, JRhH ) 27.4 Hz, JPH ) 21.2 Hz, 1H, Rh-H, 4a), -25.49 (dd,
1JRhH ) 28.0 Hz, JPH ) 20.9 Hz, 1H, Rh-H, 4b). ES-MS (methanol
2
Synthesis of C6H(CH3)3(CH2OCH3)(CH2P(t-Bu)2) (1). HP(t-Bu)2
(0.890 g, 6.09 mmol) was added to a solution of C6H(CH3)3(CH2-
OCH3)(CH2Br) (1.30 g, 5.06 mmol) in acetone. The resulting solution
was refluxed for 30 min, followed by solvent evaporation under vacuum.
The residue was washed with ether, and the resulting phosphonium
salt was dissolved in degassed water, treated with NaOAc, and extracted
with ether. Final purification of the phosphine 1 was accomplished by
column chromatography (SiO2, hexane:THF) to afford 1.14 g (70%
yield) of the PCO ligand 1, 1-methoxymethyl-3-(di-tert-butylphos-
phino)methyl-2,4,6-trimethylbenzene, as a colorless oil.
solution): M+ found 425.31, calcd for C20H35OPRh 425.37 (no solvent
molecules or BF4 are present); M- found 86.95, calcd for BF4 86.8.
Reaction of the C-H Activation Products 2-4 with Ethylene
Glycol. Ethylene glycol was added in a large excess (10 equiv) to a
solution of complexes 2-4 in THF, methanol, or acetone. The solution
was left at room temperature for 1 h, and then the solvent was evap-
orated under vacuum. The resulting residue was washed with pentane
and ether to remove excess of ethylene glycol and dried under vacuum.
1
31P{1H} NMR (methanol-d4): 127.1 (dd, JRhP ) 193.5 Hz), 126.7
31P{1H} NMR (benzene-d6): 26.38 (s). 1H NMR (benzene-d6): 6.80
(s, 1H, Ar-H), 4.35 (s, 2H, Ar-CH2-O), 3.15 (s, 3H, O-CH3), 2.81
(dd, 1JRhP ) 194.2 Hz). Selected 1H NMR signals (methanol-d4): 6.95
(s, 1H, Ar-H), 6.75 (s, 1H, Ar-H), 4.84 (s, 2H, Ar-CH2-O), 4.62 (s,
2H, Ar-CH2-O), 4.42 (d, J ) 1.6 Hz, 2H, Ar-CH2-O), 3.64 (s, 4H,
O-CH2CH2-O), 3.45 (s, 3H, O-CH3), 3.35 (s, 3H, O-CH3), -25.2
(dd, 1JRhH ) 39.2 Hz, 2JPH ) 27.6 Hz, Rh-H), -25.2 (d, 2JPH ) 27.1
Hz, Rh-H).
2
(d, JPH ) 2.0 Hz, 2H, Ar-CH2-P), 2.65 (s, 3H, Ar-CH3), 2.47 (s,
3
3H, Ar-CH3), 2.27 (s, 3H, Ar-CH3), 1.08 (d, JPH ) 10.3 Hz, 18H,
2 P-C(CH3)3). 13C{1H} NMR (benzene-d6): 137.05 (s, Ar), 136.07
(s, Ar), 136.05 (d, JPC ) 11.0 Hz, Ar), 134.76 (s, Ar), 133.34 (s, Ar),
130.8 (d, JPC ) 9.0 Hz, Ar), 69.46 (s, Ar-CH2-O), 57.45 (dd, J )
10.3 Hz, J ) 4.6 Hz, O-CH3), 32.32 (d, 1JPC ) 26.2 Hz, 2 P-C(CH3)3),
Formation of the C-C Activation Product 6. (a) Solutions of
complexes 2-4 in THF, methanol, or acetone were dried under vacuum
at room temperature for 3 days and redissolved in methanol to form
the C-C activation product 6 (70-80% yield). (b) Heating of a
methanol solution of 4 at 70 °C for 1 h leads to formation of 6 in 85%
yield (31P{1H}-NMR). Further heating leads to significant decomposi-
tion. Heating in acetone or THF also results in formation of C-C
activation products, but the reactions are not clean enough to character-
ize the products.
2
1
29.95 (d, JPC ) 13.0 Hz, 2 P-C(CH3)3), 24.17 (d, JPC ) 29.7 Hz,
Ar-CH2-P), 22.31 (d, J ) 8.4 Hz, Ar-CH3), 19.77 (d, J ) 6.1 Hz,
Ar-CH3), 17.73 (br s, Ar-CH3). 1H and 13C{1H} NMR signal
assignment was confirmed by 13C-1H correlation and 13C DEPT.
Reaction of [Rh(coe)2(solv)n]BF4 with the PCO Ligand 1. Forma-
tion of C-H Activation Products 2-4. A THF (3 mL) solution of
AgBF4 (12 mg, 0.062 mmol) was added to a THF solution (4 mL) of
[Rh(coe)2Cl]2 (22 mg, 0.031 mmol). Immediate precipitation of AgCl
took place, and the precipitate was removed by filtration after the
mixture was allowed to stand at room temperature for 15 min. The
resulting clear orange solution was evaporated under vacuum to yield
[Rh(coe)2(solv)n]BF4. This was then redissolved in THF, methanol, or
acetone to yield an orange solution in every solvent. To each of these
solutions was added a solution of 20 mg (0.062 mmol) of the PCO
ligand in the corresponding solvent. The color of the THF solution
changed to brown after a few minutes, whereas in methanol or acetone
there was no noticeable color change. The solution was kept at room
temperature for 1 h, resulting in formation of the C-H activation
products 3 and 4. Complex 2 was not sufficiently stable for spectro-
scopic characterization. Complexes 3 (in acetone) and 4 (in methanol)
exist in solution as a mixture of open-arm (3a, 4a) and closed-arm
(3b, 4b) forms. In the closed-arm form, the methoxy sidearm is
coordinated to the rhodium center. In the open-arm form this arm is
not coordinated and is replaced by a solvent molecule.
31P{1H} NMR (methanol-d4): 90.2 (d, 1JRhP ) 190.8 Hz). 1H NMR
(methanol-d4): 6.55 (s, 1H, Ar-H), 5.13 (d, 2JHH ) 12.9 Hz, 1H, Ar-
2
CH2-O, left part of AB-system), 5.00 (d, JHH ) 12.8 Hz, 1H, Ar-
CH2-O, right part of AB-system), 4.88 (s, 3H, O-CH3), 3.82 (br d,
2JPH ) 1.1 Hz, 2H, Ar-CH2-P), 2.25 (s, 3H, Ar-CH3), 2.11 (s, 3H,
3
3
Ar-CH3), 1.38 (d, JPH ) 13.5 Hz, 9H, P-C(CH3)3), 1.22 (d, JPH
)
2
12.8 Hz, 9H, P-C(CH3)3), 1.02 (d, JRhH ) 2.3 Hz, 3H, Rh-CH3).
13C{1H} NMR (methanol-d4): 157.02 (dd, 1JRhC ) 35.7 Hz, 2JPC ) 4.7
Hz, ipso CAr-Rh), 144.50 (dd, 2J ) 8.3 Hz, 2J ) 3.5 Hz, Ar), 140.25
(s, Ar), 133.21 (d, 2JRhC ) 15.9 Hz, Ar), 130.06 (s, Ar), 128.19 (s, Ar),
1
82.52 (s, Ar-CH2-O), 68.83 (s, O-CH3), 38.77 (d, JPC ) 21.9 Hz,
P-C(CH3)3), 36.92 (dd, 1JPC ) 19.5 Hz, 2JRhC ) 2.8 Hz, P-C(CH3)3),
1
2
31.68 (dd, JPC ) 31.0 Hz, JRhC ) 3.9 Hz, Ar-CH2-P), 31.07 (d,
2JPC ) 2.5 Hz, P-C(CH3)3), 29.74 (d, JPC ) 2.1 Hz, P-C(CH3)3),
2
1
20.94 (s, Ar-CH3), 19.16 (s, Ar-CH3), -4.55 (dd, JRhC ) 32.0 Hz,
2JPC ) 8.3 Hz, Rh-CH3). ES-MS (methanol solution): m/e 425.37,
M+ calcd for C20H35OPRh 425.37 (no solvent molecules are present).
ES-MS: M- found 86.96, calcd for BF4 86.80.
Complex 3 (3a:3b ) 1:4.4). 31P{1H} NMR (acetone-d6): 130.4 (d,
1
1JRhP ) 192.2 Hz, 3b), 126.5 (d, JRhP ) 191.5 Hz, 3a). 1H NMR
Elemental Analysis (after prolonged evaporation). Calcd for C20H35-
BF4OPRh (no solvent molecules present): C, 46.90; H, 6.89. Found:
C, 47.73; H, 7.81.
(acetone-d6, only selected signals of 3a (minor product) are given,
(19) Herde, J. L.; Senoff, C. V. Inorg. Nucl. Chem. Lett. 1971, 7, 1029.