Mechanistic Studies of Ethylene Hydrophenylation Catalyzed by Bipyridyl Pt(II) Complexes Page: 19,149
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Journal of the American Chemical Society
(d, 1H, 4JHH = 1.9 Hz, H3-tbpy), 8.73 (d, 1H, 4JHH = 2.1 Hz, H3-tbpy),
8.25 (d, 1H, 3JHH = 6.3 Hz, H6-tbpy), 7.93 (dd, 1H, JHH = 5.8, 4JHH = 1.9
Hz, HS-tbpy), 7.80 (br s, 8H, Ho(Ar')), 7.72 (dd, 1H, 3JHH = 6.3, 4JHH =
2.1, HS-tbpy), 7.68 (br s, 4H, Hp(Ar')), 7.39 (m, 2H, Ho(Ph)), 7.10 (m,
3H, Hm(Ph) and H,(Ph)), 2.81 (s, 3H, NCMe), 1.48 (s, 9H, tert-butyl
tbpy), 1.43 (s, 9H, tert-butyl tbpy). 13C NMR (75 MHz, acetone-d6)
167.0, 166.9, 158.8, 155.2, 152.4, 149.7, 137.5, 128.9, 126.1, 125.9, 125.5,
122.8, 122.2, 120.9 (tbpy and Ph aromatic), 69.5 (tert-butyl, quaternary,
tbpy), 68.2 (tert-butyl, quaternary, tbpy), 37.0 (tert-butyl-CH3, coin-
cidental overlap), 4.2 (NCMe, CH3); 162.8 (q, Ar', IJB-Cipso = 50 Hz),
135.7 (Ar'), 130.2 (q, m-Ar', 2JC_F = 31 Hz), 125.5 (q, CF3-Ar', Jc-_F =
272 Hz), 118.6 (Ar'). 19F NMR (282 MHz, acetone-d6) 6 -60.6
(s, CF3-Ar'). Anal. Calcd for PtBN3F24C58H44 (%): C 48.21, H 3.08,
N 2.91; found: C 48.43, H 3.05, N 3.03.
[(tbpy)Pt(CH2CH2Ph)(9]2-C2H4)][BAr'4] (4). Complex 1 (0.033
g, 0.019 mmol) was dissolved in dichloromethane (-5 mL). The
reaction mixture was transferred to a stainless steel pressure reactor
and pressurized with ethylene (0.3 MPa) for 16 h. The volatiles were
removed and pentane (-2 mL) was added to the crude solid. The
pentane was removed under vacuum to afford an orange solid. The solid
was collected and dried in vacuo (0.027 g, 97%). 1H NMR (CD2Cl12)
8.67 (d, 1H, 3JHH = 6 Hz, H6-tbpy), 8.21 (s, 1H, H3-tbpy), 8.16 (s, 1H,
H3-tbpy), 7.93 (d, 1H, 3JHH = 6 Hz, H6-tbpy), 7.79 (d, 1H, 3JHH = 6 Hz,
Hs-tbpy), 7.72 [br s, 9H, Ho(Ar') and HS-tbpy], 7.55 [br s, 4H, Hp(Ar')],
7.28-7.12 (m, SH, Ph), 4.14 (br s with doublet ("33%) due to 2Jpt-H,
4H, 2JPt-H = 69 Hz, C2H4), 2.70 (t, 2H, 3JHH = 8 Hz, Pt-CH2CH2Ph),
1.48 and 1.43 (overlapping resonances, 20H, tert-butyl tbpy and
PtCH2CH2Ph). 13C NMR (75 MHz, CD2C12) 169.4, 167.0, 157.7,
154.5, 148.1, 145.5, 144.0, 129.2, 126.7, 126.5, 125.8, 121.0, 120.9 (tbpy
and Ph aromatic), 70.2 (C2H4), 37.7 (PtCH2CH2Ph, 2Jpt_C = 28 Hz, Pt
satellites), 36.9 (tert-butyl, quaternary, tbpy), 36.6 (tert-butyl, quaternary,
tbpy), 30.3 (tert-butyl-CH3, tbpy, coincidental overlap), 17.0 (PtCH2-
CH2Ph, 1Jpt_c = 674 Hz, Pt satellites); 162.3 (q, Ar', 1JB-Cipso = 49 Hz),
135.4 (Ar'), 129.5 (q, m-Ar', 2JCF = 32 Hz), 125.2 (q, Ar', 2JC_F = 272
Hz), 118.1 (Ar'). Remaining three tbpy and Ph aromatic resonances are
obscured due to broadening or coincidental overlap. 19F NMR (282 MHz,
CD2Cl2) 6 -63.1 (s, CF3-Ar'). Anal. Calcd for PtBN2F24C60H49 (%): C
49.36, H 3.39, N 1.92; found: C 49.28, H 3.27, N 1.89.
[(tbpy)Pt(CH2CH2Ph-d5)(y2-C2H4)][BAr'4] (4-ds). This com-
plex was synthesized by the procedure used for 4. In the preparation of
the initial starting material, PhLi was substituted with PhLi-ds to produce
(tbpy)Pt(Ph-ds)2. 1H and 13C NMR spectra were consistent with the
spectra of the all-protio analogue minus the resonances for the phenyl
ring in the 1H NMR spectrum.
[(tbpy)Pt(Et)(NCMe)][BAr'4] (10). Method A: Complex 4 (0.060 g,
0.040 mmol) was dissolved in nitromethane-d3 (0.4 mL) and transferred
to a high pressure NMR tube. The NMR tube was then degassed,
pressurized with ethylene (0.3 MPa), and heated at 80 OC for 16 h. To
the solution was added NCMe (200 L). After 2 h, the solution was filtered
through Celite using dichloromethane. The volatiles were removed from
the filtrate in vacuo, and the resulting solid was collected (0.039 g, 70%).
The identity of the product was confirmed by comparison to a sample
prepared by Method B. Method B: To a cooled solution of (tbpy)Pt(Et)2
(0.017 g, 0.030 mmol) in THF (-15 mL, -60 oC), [H(Et2O)2] [BAr'4]
(0.033 g, 0.030 mmol) in THF (~5 mL, -60 oC) was added. After the
addition, the solution immediately changed from red-orange to pale yellow.
The solvent volume was reduced by ~50% under vacuum. Acetonitrile
(1 mL) was added. All volatiles were removed in vacuo. The crude solid was
treated with n-pentane (~I1 mL), which was subsequently removed under
vacuum to afford a fluffy, yellow powder. The resulting product was dried in
vacuo (0.040 g, 92%). 1H NMR (CD2C12) & 8.79 (d, 1H, 3JHH = 6 Hz,
H6-tbpy), 8.57 (d, 1H, JHH = 6 Hz, H6-tbpy), 8.10 (d, 1H, 4JHH = 2 Hz,
H3-tbpy), 8.07 (d, 1H, 4JHH = 2 Hz, H-tbpy), 7.74 [s, 8H, Ho(Ar')l, 7.70(dd, 1H, 3JHH= 6 Hz, 4JHH = 2 Hz, HS-tbpy), 7.67 (dd, 1H, 3JHH = 6 Hz,
4JHH = 2 Hz, HS-tbpy), 7.57 [s, 4H, Hp(Ar')], 2.61 (s, 3H, NCMe), 1.73
(q, 2H, 3JHH = 8 Hz, CH2-Et), 1.45 (s, 9H, tert-butyl tbpy), 1.44 (s, 9H,
tert-butyl tbpy), 1.00 (t, 3H, 3JHH = 8 Hz, CH3-Et). 13C NMR (125 MHz,
CD2Cl2) 166.3, 165.9, 158.6, 153.6, 149.1, 147.8, 125.9, 125.4, 120.9,
120.3 (tbpy aromatic), 36.5 (tert-butyl, quaternary, tbpy), 30.3 (tert-butyl-
CH3, tbpy, coincidental overlap), 16.7 (NCCH3), 4.8 (CH2-Et),
1.8 (CH3-Et); 162.3 (q, Ar', IJB-Cipso = 49 Hz), 135.4 (Ar'), 129.2
(q, m-Ar', 2JCF = 30 Hz), 125.2 (q, Ar', 2JcF = 272 Hz), 118.1 (Ar').
19F NMR (282 MHz, CD2Cl2) 6 -64.86 (s, CF3-Ar'). Anal. Calcd
for PtBN2F24C60H41D3 (%): C 46.43, H 3.18, N 3.00; found: C 47.06,
H 3.29, N 2.86.
Catalytic Ethylene Hydrophenylation. A representative cata-
lytic reaction is described. [(tbpy)Pt(Ph)(THF)] [BAr'4] (1) (0.049 g,
0.033 mmol) was dissolved in 12.0 mL of benzene containing
0.025 mol % hexamethylbenzene (HMB) relative to benzene as an inter-
nal standard. The reaction mixture was placed in a stainless steel pressure
reactor, charged with ethylene, and heated to 100 OC. After 4 and 16 h,
the reaction mixture was cooled to room temperature and analyzed by
GC/MS. Peak areas of the products and the internal standard were used
to calculate product yields. Ethylbenzene production was quantified
using linear regression analysis of gas chromatograms of standard
samples. A set of five known standards were prepared consisting of
2:1, 3:1, 4:1, 5:1, and 6:1 molar ratios of ethylbenzene to hexamethyl-
benzene in benzene. A plot of the peak area ratios versus molar ratios
gave a regression line. For the GC/MS system, the slope and correlation
coefficient (R2) for ethylbenzene were 0.53 and 0.98, respectively.
Identical procedures were used to quantify the production of 1,3-
diethylbenzene, 1,4-diethylbenzene, and 1,2-diethylbenzene. The slope
and correlation coefficients (R2) for these species are 0.56, 0.99; 0.56,
0.99; 0.52, 0.99, respectively. At a minimum, reactions were performed
in triplicate for a given set of conditions.
Determination of Percent Yield for Catalytic Ethylene
Hydrophenylation. Complex 1 (0.040 g, 0.027 mmol) was dissolved
in 12.0 mL of benzene containing 0.02 mol % HMB relative to benzene
as an internal standard. The reaction mixture was placed inside a stainless
steel pressure reactor with a gas buret (300 mL) attached. The buret was
evacuated and backfilled with N2 (three times), evacuated, and pressur-
ized with C2H4 (0.4 MPa). From the buret, the pressure reactor was
charged with ethylene (0.03 MPa). The buret was then evacuated and
backfilled with N2 (three times) and pressurized, along with the pressure
reactor, with N2 (0.8 MPa). The solution was then heated for 4 h at
120 OC, cooled to room temperature, and analyzed by GC/MS.
Kinetic Isotope Effect for Catalysis. A representative catalytic
reaction is described. [(tbpy)Pt(Ph)(THF)] [BAr'4] (1) (0.021 g, 0.014
mmol) was dissolved in 5.0 mL of C6D6 containing 0.025 mol %
hexamethylbenzene (HMB) relative to C6D6 as an internal standard.
The reaction mixture was placed in a stainless steel pressure reactor,
charged with ethylene (0.1 MPa), and heated to 100 OC. After 4 and 16 h,
the reaction mixture was cooled to room temperature and analyzed by
GC/MS. Peak areas of the products and the internal standard were used
to calculate product yields. The reaction was performed five times,
and the average TOs of ethylbenzene, diethylbenzenes, and styrene
were determined. The catalytic KIE was determined from the ratio of
total alkylbenzene TO after 4 h produced from reaction in C6H6
versus C6D6. The reported error is the deviation from multiple
experiments.
Kinetics of Benzene C-D Activation as a Function of C6D6
Concentration. A representative kinetic experiment is described.
Complex 1 (0.071 g, 0.048 mmol) and hexamethyldisilane (HMDS, 2 L)
an internal standard, were dissolved in 1.3 mL of CD2C12. The solution
was then divided (0.38 mL for each sample) and added to three NMR
tubes. To each tube was added C6D6 (0.040 mL, 0.42 mmol). The
sample was then placed into a temperature-equilibrated (30 oC) NMRprobe. The kinetic runs were performed in triplicate. 1H NMR spectra
dx.doi.org/10.1021/ja206064v IJ. Am. Chem. Soc. 2011, 133, 19131-19152
19149
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McKeown, Bradley A.; Gonzalez, Hector Emanuel; Friedfeld, Max R.; Gunnoe, T. Brent; Cundari, Thomas R., 1964- & Sabat, Michal. Mechanistic Studies of Ethylene Hydrophenylation Catalyzed by Bipyridyl Pt(II) Complexes, article, November 8, 2011; [Washington, DC]. (https://digital.library.unt.edu/ark:/67531/metadc107788/m1/19/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.