Organometallics
Article
vacuum. The crude dark red solid was recrystallized from toluene
layered with pentane at −35 °C (83 mg, 0.102 mmol, 78% yield).
Crystals suitable for X-ray crystallography were collected by slow
diffusion of pentane vapors into a concentrated toluene solution.
Anal. Calcd for C47H59Cl2NOP2Ru [M + THF]: C, 63.58; H, 6.70;
N, 1.58. Found: C, 63.24; H, 6.85; N, 1.46. HRMS: m/z calcd for
C48H51N2O2P2Ru [M]+, 815.1917; found, 815.2510. 31P{1H} NMR
EXPERIMENTAL SECTION
■
General Experimental Details. Unless otherwise specified, all
reactions and manipulations were performed under a nitrogen
atmosphere in a MBraun glovebox or using standard Schlenk
techniques. All glassware was oven-dried overnight (at minimum) at
140 °C prior to use. Anhydrous solvents were purchased directly from
chemical suppliers (Aldrich or Acros), pumped directly into the
glovebox, and stored over oven-activated 4 or 5 Å molecular sieves
(Aldrich). RuCl2(PPh3)3 and Zn dust were purchased from Strem and
used as is; PMe3 was also bought from Strem and stored over
molecular sieves prior to use. The 6-substituted pyridine-2-
carboxyaldehyde derivatives were obtained from Sigma-Aldrich, and
Mes*PCl2 was prepared via a literature protocol.56 NMR spectra were
obtained on Varian spectrometers operating at 300, 400, or 500 MHz;
chemical shifts are reported as ppm relative to tetramethylsilane and
are referenced to the residual proton or 13C signal of the solvent (1H
1
(CDCl3): δ 290.7 (d, J = 36.4, CP), 36.0 (d, J = 36.4, PPh3). H
NMR (CDCl3): δ 7.56 (t, J = 8.0 Hz, 1H, Ar), 7.46−7.39 (m, 8H,
Ar), 7.38−7.32 (m, 3H, Ar), 7.26−7.22 (m, 6H, Ar), 6.92 (d, J = 7.5
Hz, 1H, Ar), 6.54 (d, J = 4.1 Hz, 1H, Ar), 2.85 (s, 3H, Me), 1.33 (s,
9H, t-Bu), 1.23 (s, 18H, t-Bu).13C{1H} NMR (125 MHz, CDCl3): δ
163.3 (Ar), 159.5 (Ar), 155.2 (Ar), 153.4 (Ar), 136.0 (Ar), 134.7 (d, J
= 10.0 Hz, Ar), 133.2 (Ar), 132.9 (Ar), 129.5 (Ar), 127.8 (d, J = 10.0
Hz, Ar), 125.6 (d, J = 26.0 Hz, Ar), 123.8 (d, J = 10.0 Hz, Ar), 119.2
(d, J = 25.0 Hz, CP), 119.0 (Ar), 39.8 (CMe3), 35.2 (CMe3), 33.9
(t-Bu), 31.0 (t-Bu), 24.7 (Me).
Due to its similarity to that for 3b, the synthesis of 3d is included in
1
CDCl3, 7.27 ppm; H C6D6, 7.16 ppm; 13C CDCl3, 77.16 ppm; 13C
C6D6, 128.06 ppm). Mass spectroscopic data were collected on an
Agilent 6545 Accurate-Mass Q-TOF LC/MS instrument (NSF CHE-
1532310). Analytical data were obtained from the CENTC Elemental
Analysis Facility at the University of Rochester, funded by NSF CHE-
065-456. All X-ray-quality crystals were analyzed at the Small
Molecular X-ray Crystallography Facility located at the University
of California, San Diego.
Synthesis of Pyridine-Phosphaalkenes of Type 2. Derivative
2a was previously prepared as an E/Z mixture by Geoffroy10 and
selectively (at low temperature) as the E isomer by Bickelhaupt22
using a phospha-Peterson methodology.17 Its full spectroscopic
characterization is reported in ref 22. Using a phospha-Wittig
methodology, in a manner as described below for 2b, parent 2a was
isolated in 83% yield.
Cyclized (Pyridine-Phospholane) Complex 4b. A solution of 3b
(15 mg, 0.019 mmol) in 1 mL of THF was heated at 80 °C for 48 h,
at which time the phosphaalkene resonance was no longer observed
by 31P NMR spectroscopy. The cyclized complex (31P NMR: δ 91.1,
46.7) was filtered through a pad of Celite, and the filtrate was
concentrated under vacuum. The crude solid was recrystallized from a
1/3 solution of THF/pentane at −35 °C to give dark green crystals
(12 mg, 0.015 mmol, 80% yield). Crystals suitable for X-ray
crystallography were collected by slow diffusion of pentane vapors
into a concentrated THF solution.
HRMS: m/z calcd for C45H54ClN2P2Ru [M − (Cl−) + NCMe]+,
821.2494; found, 821.2516. 31P{1H} NMR (202 MHz, CDCl3): δ
1
91.1 (br, CH2P), 48.7 (d, J = 36.4 Hz, PPh3). H NMR (500 MHz,
CDCl3): δ 7.61−7.56 (m, 2H, Ar), 7.40 (t, J = 9.0 Hz, 6H, Ar), 7.31
(t, J = 8.5 Hz, 4H, Ar), 7.21−7.14 (m, 7H, Ar), 6.96 (d, J = 1.5 Hz,
1H, Ar), 4.23 (dd, J = 17.0, 11.0 Hz, 1H, benzylic NAr), 3.99 (dd, J =
17.0, 10.0 Hz, 1H, benzylic NAr), 2.80 (s, 3H, Me), 2.17−1.96 (m,
2H, CH2P), 1.38 (s, 9H, t-Bu), 1.23 (s, 9H, t-Bu), 1.10 (s, 3H,
CMe2), 0.79 (s, 3H, CMe2). 13C{1H} NMR (125 MHz, CDCl3): δ
162.1 (Ar), 160.4 (Ar), 157.3 (d, J = 21.3, Ar), 156.7 (d, J = 7.5 Hz,
Ar), 153.6 (Ar), 136.2 (Ar), 134.6 (d J = 10.0 Hz, Ar), 133.7 (d, J =
42.5 Hz, Ar), 129.3 (Ar), 129.0 (Ar), 128.3 (d, J = 12.5 Hz, Ar), 127.9
(d, J = 8.8 Hz, Ar), 126.8 (d, J = 10.0 Hz, Ar), 123.8 (Ar), 119.2 (d, J
= 10.0 Hz, Ar), 117.9 (d, J = 10.0 Hz, Ar), 50.9 (d, J = 22.5 Hz,
benzylic), 47.6 (d, J = 43.8 Hz, PCH2CMe2), 43.2 (CMe2), 37.9
(CMe3), 35.4 (t-Bu), 35.0 (CMe3), 34.1 (t-Bu), 31.3 (t-Bu), 28.6 (d, J
= 10.0 Hz, CMe2), 25.0 (Me).
E-Selective Synthesis of 2b using a Phospha-Wittig
Methodology. Mes*PCl2 (1.00 g, 2.88 mmol) and Zn dust (940
mg, 14.4 mmol, 5 equiv) were combined in a vial, and 4 mL of THF
was added. Treatment of the suspension with a room-temperature
solution of PMe3 (560 mg, 7.36 mmol, 2.6 equiv) in THF resulted in
a yellow reaction mixture. The reaction mixture was stirred at room
temperature for 1 h and filtered through a Celite plug directly into a
solution of 6-methylpyridine-2-carboxaldehyde (262 mg, 2.16 mmol,
0.75 equiv) in 3 mL of THF to afford a homogeneous yellow-orange
solution. After it was stirred for 10 min, the reaction mixture was
concentrated under vacuum. The yellow residue was extracted with 5
mL of pentane and filtered through a Celite plug. The filtrate was
concentrated under vacuum and recrystallized from 5 mL of a 50/50
solution of THF and acetonitrile at −35 °C to give a yellow solid (700
mg, 1.84 mmol, 85% yield).
Anal. Calcd for C25H36NP: C, 78.70; H, 9.51; N, 3.67. Found: C,
78.42; H, 9.54; N, 3.59. HRMS: m/z calcd for C25H36NP [M]+,
381.2585; found, 381.2591. 31P{1H} NMR (CDCl3): δ 280.4. 1H
NMR (CDCl3): δ 8.10 (d, J = 25.0 Hz, 1H, PCH), 7.51 (m, 2H,
Ar), 7.43 (s, 2H, Ar), 6.97 (br m, 1H, Ar), 2.53 (s, 3H, Me), 1.52 (s,
18H, t-Bu), 1.35 (s, 9H, t-Bu). 13C{1H} NMR (CDCl3): δ 175.6 (d, J
= 33.8, PC), 158.2 (Ar), 157.5 (d, J = 15.0 Hz, Ar), 153.9 (Ar),
149.7 (Ar), 148.5 (Ar), 139.0 (d, J = 52.5 Hz, Ar), 136.4 (Ar), 123.7
(Ar), 121.6 (Ar), 119.4 (Ar), 117.0 (d, J = 20.0 Hz, Ar), 38.2 (CMe3),
34.0 (t-Bu), 33.9 (t-Bu), 31.8 (CMe3), 31.6 (CMe3), 31.4 (t-Bu), 30.9
(Me).
The closely related thermally induced cyclization of 3d to 4d can
be found in the Supporting Information.
Cyclization of 2e to 4e. RuCl2(PPh3)3 (197 mg, 0.205 mmol) was
loaded into a vial and treated with a solution of 2e (100 mg, 0.205
mmol) in 2 mL of benzene at room temperature. The dark reaction
mixture was transferred to a J. Young tube and monitored by 31P{1H}
NMR spectroscopy. After it was heated at 80 °C for 72 h, the reaction
mixture turned dark green, and the 31P{1H} NMR spectrum showed
two doublets at 90.3 and 48.6 ppm. The mixture was subsequently
filtered through Celite, and the filtrate was concentrated under
vacuum. The dark green residue was recrystallized from a 5 mL
solution of THF layered with pentane at −35 °C (185 mg, 0.201
mmol, 98% yield). Crystals suitable for X-ray crystallography were
collected by slow diffusion of pentane vapors into a concentrated
THF solution.
Ligands 2c−e were prepared in an analogous fashion to 2b using a
phospha-Wittig methodology. Full experimental details are included
Anal. Calcd for C48H52Cl2N2O2P2Ru was consistently low (three
attempts) in carbon, for example: C, 62.47; H, 5.68; N, 3.04. Found:
C, 61.83; H, 5.69; N, 2.69. HRMS: m/z calcd for
C48H52Cl2N2O2P2Ru [M]+, 922.1925; found, 922.1906. 31P{1H}
NMR (CDCl3): δ 90.3 (d, J = 36.4 Hz, P-Mes*), 48.6 (d, J = 36.4
Hz, PPh3). 1H NMR (CDCl3): δ 8.57 (s, 1H, Ar), 8.11 (d, J = 7.0 Hz,
1H, Ar), 8.03 (d, J = 9.5 Hz, 1H, Ar), 7.87 (t, J = 8.0 Hz, 1H, Ar),
7.58−7.54 (m, 3H, Ar), 7.27 (m, J = 7.0 Hz, 9H, Ar), 7.08 (t, J = 6.5
Hz, 6H, Ar), 6.95 (s, 1H, Mes*), 6.89 (t, J = 8.0 Hz, 1H, Ar), 4.25
Syntheses of Ru(II) Complexes 3−6. Pyridine-Phosphaalkene
Complex 3b. RuCl2(PPh3)3 (126 mg, 0.131 mmol) was loaded into a
vial and treated with a solution of 2b (50 mg, 0.131 mmol) in 1 mL of
benzene at room temperature. The dark reaction mixture was
transferred to a J. Young tube and monitored by 31P{1H} NMR
spectroscopy. After it was heated at 60 °C for 120 h, the solution
turned dark red, and the 31P{1H} NMR spectrum showed two
doublets at 290.7 and 36.0 ppm. The mixture was subsequently
filtered through Celite, and the filtrate was concentrated under
H
Organometallics XXXX, XXX, XXX−XXX