Activation of heteroallenes by coordinatively unsaturated nickel(II) alkyl complexes supported by the hydrotris(3-phenyl-5-methyl)pyrazolyl borate (TpPh,Me) ligand

Article abstract of DOI:10.1039/c6dt01585a

Activation of sulfur containing heteroallenes by nickel(ii) alkyl complexes supported by the bulky hydrotris(3-phenyl-5-methylpyrazolyl)borate (Tp^Ph,Me) ligand is described. Exposure of Tp^Ph,MeNiCH₂Ph (1a) and Tp^Ph,MeNiCH₂Si(CH₃)₃ (1b) to CS₂ resulted in formation of the insertion products Tp^Ph,MeNi(η²-CS₂)CH₂Ph (2a) and Tp^Ph,MeNi(η²-CS₂)CH₂Si(CH₃)₃ (2b) in moderate yields. Reaction of 1a and MeNCS produced two species in a 1:1 ratio, identified as Tp^Ph,MeNi(η²-MeNC)CH₂Ph (3) and Tp^Ph,MeNi(η²-MeNCS)SCH₂Ph (4). Isolation of the unexpected insertion product (3) prompted an investigation into the activity of 1a-b in the presence of isocyanides (i.e.^tBuNC), which resulted in isolation of Tp^Ph,MeNi(η^2-tBuNC)CH₂Ph (5a) and Tp^Ph,MeNi(η^2-tBuNC)CH₂Si(CH₃)₃ (5b). Similarly, reaction of 1a with OCS led to the isolation of a rare example of a Ni(i) carbonyl species Tp^Ph,MeNiCO (6). Alternatively, complex 6 was also formed by exposure of 1a-b to an atmosphere of CO. Isolation of the intermediate species (Tp^Ph,MeNi(η²-CO)CH₂TMS (7b) and Tp^Ph,MeNi(CO)(C(O)R, (8a-b) with R = Ph, TMS)) shed light on the formation of such species.

Full text of DOI:10.1039/c6dt01585a

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Activation of heteroallenes by coordinatively
unsaturated nickel(II) alkyl complexes supported
by the hydrotris(3-phenyl-5-methyl)pyrazolyl
borate (TpPh,Me) ligand†
Cite this: DOI: 10.1039/c6dt01585a
Mark Abubekerov, Léonard Y. M. Eymann, Thomas L. Gianetti and John Arnold*
Activation of sulfur containing heteroallenes by nickel(II) alkyl complexes supported by the bulky hydrotris-
(3-phenyl-5-methylpyrazolyl)borate (TpPh,Me) ligand is described. Exposure of TpPh,MeNiCH2Ph (1a) and
TpPh,MeNiCH2Si(CH3)3 (1b) to CS2 resulted in formation of the insertion products TpPh,MeNi(η2-CS2)CH2Ph
(2a) and TpPh,MeNi(η2-CS2)CH2Si(CH3)3 (2b) in moderate yields. Reaction of 1a and MeNCS produced two
species in a 1 : 1 ratio, identified as TpPh,MeNi(η2-MeNC)CH2Ph (3) and TpPh,MeNi(η2-MeNCS)SCH2Ph (4).
Isolation of the unexpected insertion product (3) prompted an investigation into the activity of 1a–b in
t
the presence of isocyanides (i.e. BuNC), which resulted in isolation of TpPh,MeNi(η2-tBuNC)CH2Ph (5a)
and TpPh,MeNi(η2-tBuNC)CH2Si(CH3)3 (5b). Similarly, reaction of 1a with OCS led to the isolation of a rare
example of a Ni(I) carbonyl species TpPh,MeNiCO (6). Alternatively, complex 6 was also formed by exposure
of 1a–b to an atmosphere of CO. Isolation of the intermediate species (TpPh,MeNi(η2-CO)CH2TMS (7b)
and TpPh,MeNi(CO)(C(O)R, (8a–b) with R = Ph, TMS)) shed light on the formation of such species.
Received 23rd April 2016,
Accepted 13th June 2016
DOI: 10.1039/c6dt01585a
www.rsc.org/dalton
Based on our interest in utilizing reactive metal–carbon
Introduction
bonds for activation of small molecules,36–42 we investigated
Reduction of carbon dioxide (CO2) to liquid fuels, organic reactions of sulfur containing heteroallenes toward coordina-
chemicals, and carbohydrates has attracted much attention in tively unsaturated hydrotris(pyrazolyl)borate nickel(II) alkyl
the past few decades.1–5 Apart from CO2, other unsaturated complexes.43 Here we present the insertion of CS2 into the
small molecules, such as sulfur containing heteroallenes (CS2, square planar TpPh,MeNiCH2Ph, which resulted in the for-
RNCS, and OCS), can serve as potential building blocks for C1 mation of a square planar insertion product TpPh,MeNi(η2-
chemistry.6,7 These molecules are often more reactive than CS2)CH2Ph with an η2-C,S bonding motif. Contrastingly,
CO2 but often display similar bonding mode making them a insertion of CS2 into the tetrahedral complex TpPh,MeNiCH2Si-
useful model for CO2 activation. The activation of these com- (CH3)3 results in a trigonal bipyramidal insertion product
pounds by transition metal complexes with M–C and M–H TpPh,MeNi(η2-CS2)CH2Si(CH3)3 with an κ2-S,S arrangement. We
bonds frequently results in the formation of insertion also show that addition of MeNCS to TpPh,MeNiCH2Ph leads
products.8–18 Further transformations of these substrates can to the formation of an imidoyl complex TpPh,MeNi(η2-MeNC)-
be achieved via cleavage of the carbon–sulfur bond, similar to CH2Ph as a product of carbon–sulfur bond cleavage in
sulfur abstraction observed in low valent transition metal MeNCS. Similarly, activation of carbonyl sulfide by the TpPh,
complexes.19–21 Such reactivity has been observed for RNCS MeNiCH2Ph complex yielded a rare example of a nickel(I) car-
and OCS, which are known to undergo carbon–sulfur bond bonyl complex via sulfur abstraction. Monovalent nickel com-
cleavage by transition metal complexes.22–29 The carbon–sulfur plexes are postulated to be the active species in catalytic C–C
bonds in CS2 are less susceptible to metal-mediated bond formation in the presence of appropriate organic
cleavage,30–33 however, and the reactivity of the insertion pro- substrates.44–47 Due to the “rarity” of these species their reac-
ducts is a function of their structures.34,35
tivity is poorly understood and largely unexplored.48 Alterna-
tively, the preparation of the TpPh,MeNiCO complex was
achieved by exposing the nickel benzyl complex to carbon
monoxide under elevated temperatures. Additionally, we
report the reactivity of nickel alkyl complexes, supported by
the hydrotris(pyrazolyl) borate ligand, towards other un-
saturated small molecules.
Department of Chemistry, University of California, Berkeley, CA 94720, USA.
E-mail: arnold@berkeley.edu
†CCDC 1476054–1476061, 1476064 and 1476065. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c6dt01585a
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0.33 mmol) in 30 mL of diethyl ether at room temperature.
The reaction mixture was stirred for 12 hours. Filtration,
removal of volatile substances under reduced pressure, and
Experimental section
General considerations
All reactions were performed using standard Schlenk tech- crystallization from diethyl ether at −40 °C gave 2a as dark red
niques or in an MBraun drybox (<1 ppm O2/H2O) unless noted crystals (137 mg, 58% yield). X-ray quality crystals were
otherwise. All glassware, cannulae, and Celite were stored in obtained from a toluene/hexanes layering. 1H NMR (C6D6,
an oven at >425 K. All chemicals were used as received after 400 MHz, 298 K): δ (ppm) 2.32 (9H, s, –CH3), 3.34 (2H, s,
being dried over 4 Å sieves for 48 hours and degassed with –CH2–), 6.15 (3H, s, –CH–), 6.55 (2H, d, o-Ph), 6.88–6.90 (3H,
nitrogen. Toluene, hexanes, and diethyl ether were purified by m, m-Ph, p-Ph), 7.09 (3H, t, p-Ph), 7.20 (6H, t, m-Ph), 8.13 (6H,
passage through a column of activated alumina and degassed d, o-Ph). 13C NMR (C6D6, 151 MHz, 298 K): δ (ppm) 12.6
with nitrogen prior to use. Hexamethyldisiloxane was dried (s, –CH3), 47.4 (br s, –CH2–), 105 (s, –CH–), 127–136 (aromatic
with P2O5. Deuterated benzene was vacuum transferred from region), 145 (s, –CPh), 154 (s, –CMe). IR (cm−1): 2502 (BH, m),
sodium/benzophenone. NMR spectra were recorded at 1602 (w), 1542 (m), 1507 (w), 1476 (w), 1452 (m), 1411 (m),
ambient temperature on Bruker AVQ-400, AVB-400, DRX-500, 1370 (m), 1355 (m), 1342 (m), 1304 (w), 1283 (w), 1231 (w),
1
or AV-600 spectrometers. H chemical shifts are given relative 1180 (s), 1126 (s), 1083 (m), 1058 (m), 1031 (w), 987 (w),
to residual solvent peaks. Infrared samples were prepared as 958 (w), 910 (w), 846 (w), 753 (s), 690 (s), 657 (w), 645 (w),
Nujol mulls. Magnetic susceptibility measurements were per- 631 (m), 568 (w). Anal. Calcd: TpPh,MeNi(CS2)CH2Ph
formed in C6D6 using the Evans NMR method. Uncorrected (C38H35BN6NiS2) C, 64.34; H, 4.97; N, 11.85. Found: C, 64.01;
melting points were determined using sealed capillaries H, 4.83; N, 11.59. Mp: 155–155.9 °C.
prepared under static vacuum on an Optmelt SRS.
TpPh,MeNi(η2-CS2)CH2Si(CH3)3 (2b). Carbon disulfide
TpPh,MeNiCH2Ph (1a) and TpPh,MeNiCH2Si(CH3)3 (1b)43 were (0.20 mL, 3.3 mmol) was added via syringe to a solution of 1b
prepared using literature procedures, and unless otherwise (190 mg, 0.3 mmol) in 30 mL of diethyl ether at room tempera-
noted, all reagents were acquired from commercial sources. ture. The reaction mixture was stirred for 12 hours. Filtration,
Elemental analyses were performed at the College of Chemistry removal of volatile substances under reduced pressure, and
Microanalytical Laboratory, University of California, Berkeley. crystallization from hexanes at −40 °C gave 2b as lime-green
X-ray structural determinations were performed at the crystals (76 mg, 36% yield). 1H NMR spectroscopy shows an
CHEXRAY facility at UC Berkeley using Bruker SMART 1000 or average of 0.5 molecules of hexanes per molecule of 2b. X-ray
SMART APEX diffractometers.
quality crystals were obtained from hexamethyldisiloxane at
−40 °C. H NMR (C6D6, 400 MHz, 298 K): δ (ppm) −6.3 (br s),
1.29 (s), 1.54 (s), 3.02 (s), 4.18 (br s), 6.14 (s), 6.99 (s), 56.4
1
Crystallographic analyses
X-ray structural determinations were performed on a Bruker (br s). IR (cm−1): 2546 (BH, w), 1546 (m), 1506 (w), 1474 (w),
SMART 1000 or SMART APEX diffractometer. Both are 3-circle 1436 (m), 1415 (m), 1368 (m), 1346 (m), 1248 (m), 1220 (w),
diffractometers that couple a CCD detector49 with a sealed- 1190 (s), 1148 (m), 1089 (m), 1064 (s), 982 (m), 928 (s), 842 (s),
tube source of monochromated Mo Kα radiation (λ
=
782 (s), 760 (s), 694 (s), 659 (w), 638 (m), 614 (w), 542 (w).
0.71073 Å). A crystal of appropriate size was coated in Para- Anal. Calcd: TpPh,MeNi(CS2)CH2Ph + 1C6H14 (C41H42BN6NiS2)
2
tone-N oil and mounted on a Kaptan® loop. The loop was C, 60.97; H, 6.19; N, 11.23. Found: C, 60.96; H, 6.18; N, 10.89.
transferred to the diffractometer, centered in the beam, and Mp: 175–176 °C (dec). μeff = 2.7(7)μB.
cooled by a nitrogen flow low-temperature apparatus that had
TpPh,MeNi(η2-MeNC)CH2Ph (3)
&
TpPh,MeNi(η2-MeNCS)-
been previously calibrated by a thermocouple placed at the SCH2Ph (4). Methyl isothiocyanate (16 mg, 0.22 mmol, 1.2
same position as the crystal. Preliminary orientation matrices equiv.) in 2 mL of toluene was added drop-wise to 1a (114 mg,
and cell constants were determined by collection of 60 × 10 s 0.18 mmol, 1 equiv.) in 8 mL of toluene. The reaction mixture
frames, followed by spot integration and least-squares refine- was stirred for 12 hours. Volatile substances were removed
ment. The reported cell dimensions were calculated from all under reduced pressure. Extraction from the reaction solids
reflections with I > 10σ. The data was corrected for Lorentz and with hexanes and crystallization at −40 °C gave 4 as green crys-
polarization effects; no correction for crystal decay was tals (34%). X-ray quality crystals were obtained from hexanes at
applied. An empirical absorption correction based on compari- −40 °C. Remaining solids were dissolved in toluene, filtered
son of redundant and equivalent reflections was applied using and layered with hexanes to yield 3 as yellow crystals (27%).
SADABS.50 All software used for diffraction data processing X-ray quality crystals were obtained from toluene/hexanes
and crystal-structure solution and refinement are contained in vapor diffusion.
the APEX2 program suite (Bruker AXS, Madison, WI).51
For 3: 1H NMR (C6D6, 500 MHz, 298 K): δ (ppm) 1.73 (3H, s,
Thermal parameters for all non-hydrogen atoms were refined NCH3), 2.38 (11H, s, –CH3, –CH2–), 6.20 (3H, s, –CH–), 6.54
anisotropically. For all structures, R1 = ∑(|Fo|−|Fc|)/∑(|Fo|); (2H, d, o-Ph), 6.84–6.85 (3H, m, m-Ph, p-Ph), 7.06 (3H, t, p-Ph),
wR2 = [∑{w(Fo − Fc ) ]/∑{w(Fo ) }]1/2. ORTEP diagrams were 7.19 (6H, t, m-Ph), 8.26 (6H, d, o-Ph). 13C NMR (C6D6,
2
2 2
2 2
created using the ORTEP-3 software package and POV-ray.52
126 MHz, 298 K): δ (ppm) 13.5 (s, –CH3), 29.5 (s, NCH3),
TpPh,MeNi(η2-CS2)CH2Ph (2a). Carbon disulfide (0.2 mL, 30.9 (s, –CH2–), 105 (s, –CH–), 126–137 (aromatic region), 146
3.3 mmol) was added via syringe to a solution of 1a (210 mg, (s, –CMe), 154 (s, –CPh), 172 (s, CN). IR (cm−1): 2519 (BH, w),
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1743 (CN, m), 1603 (w), 1544 (m), 1509 (m), 1494 (w), 1453 (w),
1413 (m), 1371 (m), 1357 (m), 1344 (m), 1305 (w), 1282 (w),
Synthesis of TpPh,MeNiCO (6)
Method a. OCS (1 atm) was added to a degassed solution of
1201 (m), 1179 (s), 1085 (m), 1068 (m), 1028 (w), 986 (w), 1a (150 mg, 0.24 mmol) in 20 ml of diethyl ether. The reaction
958 (w), 917 (w), 885 (w), 830 (w), 785 (s), 765 (s), 713 (s), mixture was stirred for 24 hours at room temperature.
693 (s), 656 (m), 631 (m), 616 (m), 571 (w), 542 (m). Anal. Filtration, removal of volatile substances under reduced
Calcd: TpPh,MeNi(MeNC)CH2Ph (C39H38BN7Ni) C, 69.47; pressure, and crystallization from hexane at −40 °C gave 6 as
H, 5.68; N, 14.54. Found: C, 69.19; H, 5.32; N, 14.83. Mp: yellow crystals (22 mg, 18% yield). X-ray quality crystals were
160 °C (dec).
obtained from hexane at −40 °C. 1H NMR (C6D6, 400 MHz,
For 4: IR (cm−1): 2543 (BH, w), 1545 (m), 1511 (w), 1425 (w), 298 K): δ (ppm) −9.26 (br s), 0.31 (s), 7.33 (s), 8.03 (s), 17.2 (s),
1416 (m), 1411 (m), 13 128 (m), 1346 (m), 1248 (m), 1220 (w), 19.2 (s). IR (cm−1): 2526 (BH, m), 2003 (CO, m), 1543 (m),
1190 (s), 1148 (m), 1089 (m), 1064 (s), 982 (m), 928 (s), 842 (s), 1505 (w), 1475 (w), 1437 (m), 1415 (m), 1370 (m), 1346 (m),
782 (s), 760 (s), 694 (s). Anal. Calcd: TpPh,MeNi(η2-MeNCS) 1173 (s), 1095 (w), 1056 (s), 1030 (w), 982 (m), 912 (w), 839 (w),
SCH2Ph (C39H38BN7NiS2) C, 63.44; H, 5.19; N, 13.28. Found: 793 (m), 774 (s), 759 (s), 693 (s), 663 (m), 632 (s), 617 (m).
C, 63.22; H, 5.01; N, 13.08. Mp: 196 °C (dec). μeff = 2.8(7)μB.
Anal. Calcd: TpPh,MeNiCO (C31H28BN6NiO) C, 65.14; H, 4.95;
TpPh,MeNi(η2-tBuNC)CH2Ph (5a). tert-Butyl isocyanide N, 14.74. Found: C, 65.14; H, 4.95; N, 14.46. Mp: 190 °C (dec).
(0.045 mL, 0.40 mmol) was added via syringe to a solution of μeff = 2.2(8)μB.
1a (250 mg, 0.40 mmol) in 30 mL of diethyl ether at room
Characterization of (PhCH2S)2. 1H NMR (C6D6, 400 MHz,
temperature. The reaction mixture was stirred for 12 hours. 298 K): δ (ppm) 1.40 (1H, t, –SH–), 3.26 (2H, d,–CH2–),
Filtration, removal of volatile substances under reduced 6.95–7.10 (aromatic region); GC-MS (m/z): 91, 124.
pressure, and crystallization from hexanes at −40 °C gave 5a as
Method b. CO (1 atm) was added to a degassed solution of 1a
yellow-orange crystals (159 mg, 56%). X-ray quality crystals (177 mg, 0.28 mmol) in 20 ml of benzene. The reaction
were obtained from diethyl ether at −40 °C. 1H NMR (C6D6, mixture was stirred for 24 hours at 60 °C. Filtration, removal of
400 MHz, 298 K): δ (ppm) 0.331 (9H, s, tBu), 2.27 (9H, br s, volatile substances under reduced pressure, and crystallization
–CH3), 2.66 (2H, s, –CH2–), 6.22 (3H, br s, –CH–), 6.478 (1H, d, from ether at −40 °C gave 6 as yellow crystals (64 mg, 40%
o-Ph), 6.483 (1H, d, o-Ph), 6.90–6.94 (3H, m, m-Ph, p-Ph), 7.10 yield).
(3H, t, p-Ph), 7.26 (6H, t, m-Ph), 8.42 (6H, d, o-Ph). 13C NMR
Method c. CO (1 atm) was added to a degassed solution of 1b
(C6D6, 100 MHz, 298 K): δ (ppm) 12.7 (s, –CH3), 28.0 (s, (50 mg, 0.28 mmol) in 20 ml of diethyl ether after one freeze–
NC(CH3)3), 31.7 (s, –CH2–), 53.9 (s, NC(CH3)3), 105 (s, –CH–), pump–thaw cycle. Quick color change from dark green to dark
126–136 (aromatic region), 170 (s, CN). IR (cm−1): 2472 orange upon addition of CO was observed. Mixture was stirred
(BH, w), 1712 (CN, m), 1605 (w), 1544 (m), 1510 (m), 1474 (w), overnight at room temperature without further color change.
1453 (m), 1410 (m), 1371 (m), 1345 (m), 1283 (w), 1223 (m), Removal of the volatiles and further heating at 60 °C in
1175 (s), 1069 (s), 1056 (s), 985 (w), 957 (w), 908 (w), 827 (w), hexanes was carried for 24 h. Color turned from orange to
783 (s), 759 (s), 733 (m), 693 (s), 667 (w), 638 (m). Anal. Calcd: yellow. Removal of the volatiles and crystallization from ether
TpPh,MeNi(tBuNC)CH2Ph (C42H44BN7Ni) C, 70.42; H, 6.19; gave 6 as yellow crystals (18 mg, 30% yield).
N, 13.69. Found: C, 70.31; H, 6.33; N, 13.53. Mp: 175.2–176.5 °C.
TpPh,MeNi(CO)CH2Si(CH3)3 (7b). CO (1 atm) was added to a
TpPh,MeNi(η2-tBuNC)CH2Si(CH3)3 (5b). tert-Butyl isocyanide degassed solution of 1b (110 mg, 0.28 mmol) in 20 ml of
(0.054 mL, 0.48 mmol) was added via syringe to a solution of diethyl ether. The reaction mixture was stirred overnight at
1b (300 mg, 0.48 mmol) in 30 mL of diethyl ether at room room temperature. Removal of volatile substances under
temperature. The reaction mixture was stirred for 12 hours. reduced pressure, and crystallization from hexanes and THF at
Filtration, removal of volatile substances under reduced −40 °C gave 7b as orange crystals (95 mg, 82% yield). X-ray
pressure, and crystallization from hexanes at −40 °C gave 5b as quality crystals were obtained from a 3 : 1 mixture hexane/THF
yellow-orange crystals (115 mg, 34%). X-ray quality crystals at −40 °C. 1H NMR (C6D6, 400 MHz, 298 K): δ (ppm) −0.52
were obtained from hexanes at −40 °C. 1H NMR (C6D6, (9H, s, –Si(CH3)3), 0.64 (2H, s, –CH2–), 2.31 (9H, br s, –CH3–),
500 MHz, 350 K): δ (ppm) −0.424 (9H, s, NC(CH3)3), 0.511 (9H, 6.17 (3H, s, –CH–), 7.09 (3H, t, p-Ph), 7.24 (6H, t, m-Ph), 8.23
s, Si(CH3)3), 0.708 (2H, s, –CH2–), 2.35 (9H, br s, –CH3), 6.25 (6H, br s, o-Ph) 13C NMR (C6D6, 400 MHz, 298 K): δ (ppm)
(3H, s, –CH–), 7.14 (3H, t, p-Ph), 7.31 (6H, t, m-Ph), 8.43 (6H, −1.52 (s, –Si–(CH3)3), 13.43 (s, –CH3), 55 (s, –CH2–) 105 (s, –
br s, o-Ph). 13C NMR (C6D6, 125 MHz, 350 K): δ (ppm) −0.95 (s, CH–), 127–136 (aromatic region), 145 (s, –CPh), 154 (s, –CMe).
–CH3), 17.9 (s, –CH2–), 29.4 (s, NC(CH3)3), 53.6 (s, NC(CH3)3), IR (cm−1): 2514 (BH, br m), 2159 (w), 2047 (w), 1684 (CO, m),
105 (s, –CH–), 127–136 (aromatic region), 169 (s, CN). IR 1585 (w), 1543 (w), 1508 (w), 1413 (w), 1369 (w), 1347 (w), 1181
(cm−1): 2487 (BH, w), 1715 (CN, m), 1605 (w), 1544 (m), 1507 (s), 1068 (m), 1056 (m), 1025 (m), 982 (w), 915 (w), 840 (s), 783
(m), 1410 (m), 1345 (m), 1303 (w), 1246 (m), 1224 (w), 1198 (m), 759 (s), 694 (s), 633 (m), 582 (w), 538 (w). Anal.
(m), 1177 (s), 1163 (s), 1123 (m), 1078 (m), 1066 (w), 1055 (s), Calcd: TpPh,MeNi(CO)CH2Si(CH3)3 (C35H39BN6NiSiO) C, 63.95;
984 (w), 956 (w), 913 (w), 849 (s), 784 (s), 760 (s), 713 (w), 697 H, 5.98; N, 12.79. Found: C, 63.58; H, 5.65; N, 12.84. Mp:
(s), 636 (w), 625 (w). Anal. Calcd: TpPh,MeNi(tBuNC)CH2Si- 150–151.5 °C.
(CH3)3 (C39H48BN7NiSi) C, 65.75; H, 6.79; N, 13.76. Found:
C, 66.0; H, 6.98; N, 13.39. Mp: 205.7–206.7 °C.
TpPh,MeNi(CO)(COCH2Ph) (8a). CO (1 atm) was added to a
degassed solution of 1a (120 mg, 0.19 mmol) in 20 ml of
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diethyl ether. The reaction mixture was further concentrated formation of TpPh,MeNiCl, and the coupling product, which
by bubbling CO through the solution and the reaction flask was further confirmed by GC-MS analysis.
was crystallized from diethyl ether at −40 °C gave 8a as dark
Bibenzyl. 1H NMR (C6D6, 400 MHz, 298 K): δ (ppm) 2.91 (4H,
red X-ray quality crystals (12 mg, 10% yield). 1H NMR (C6D6, s, –CH2–), 7.12–7.42 (aromatic region); 13C NMR (C6D6,
600 MHz, 298 K): δ (ppm) 2.27 (9H, br s, –CH3–), 3.27 (2H, s, 400 MHz, 298 K): 38 (–CH2–), 125.92 (p-Ph), 128.34 (m-Ph),
–CH2–), 6.03 (3H, s, –CH–), 6.20 (2H, br d, m-Ph), 6.85 (3H, s, 128.45 (o-Ph), 141.80 (i-Ph). GC-MS (m/z): 91, 182.
1
o-Ph), 7.11 (3H, t, p-Ph), 7.25 (6H, t, m-Ph), 7.99 (6H, d, o-Ph).
4-Phenyl-1-butene. H NMR (C6D6, 400 MHz, 298 K): δ (ppm)
13C NMR (tol-d8, 600 MHz, 298 K): δ (ppm) 12.73 (s, –CH3), 2.37 (q, 2 H), 2.69 (t, 2 H), 4.98 (m, 2 H), 5.49 (m, 1 H), 7.1
55 (s, –CH2), 106 (s, –CH–), 127–136 (aromatic region), 145 (m. 5 H). GC-MS (m/z): 125, 132.
(s, –CPh), 154 (s, –CMe), 184 (s, –NiCOCH2), 214 (s, NiCO). IR
1a + Ph3CCl. On the other hand, trityl chloride (119.6 mg,
(cm−1): 2926 (m), 2523 (BH, m), 2033 (terminal CO, m), 0.43 mmol, 3 equiv.) was added to a solution of 1a (100 mg,
1724 (CO, m), 1539 (m), 1504 (m), 1414 (w), 1372 (w), 1345 (w), 0.16 mmol, 1 equiv.) in toluene at room temperature. The
1177 (w), 1055 (w), 1029 (m), 981 (m), 916 (m), 884 (w), mixture was stirred 1 h. Removal of the volatiles, trituration in
841 (m), 782 (w), 763 (w), 696 (w), 634 (w), 554 (m), 539 (w). diethyl ether and extraction in hexanes yield to 1,1,1,2-tetra-
Anal. Calcd: TpPh,MeNi(CO)(COCH2Ph) (C39H35BN6NiO2) phenylethane as pale yellow powder. 1H NMR (C6D6, 400 MHz,
C, 67.96; H, 5.12; N, 12.19. Found: C, 68.29; H, 5.41; N, 12.34. 298 K): δ (ppm) 3.81 (2H, s, –CH2), 6.91–7.7.36 (aromatic
Mp: 112–114 °C.
region); 13C NMR (C6D6, 400 MHz, 298 K): δ (ppm) −47
TpPh,MeNi(CO)(COCH2Si(CH3)3) (8b). CO (1 atm) was added (–CH2–), 59 (–C–), 125–131 (aromatic region), 145 (s, –CPh),
to a degassed solution of 1b (150 mg, 0.24 mmol) in 20 ml of 154 (s, –CMe); DEPT-135 (C6D6, 400 MHz, 298 K): 47 (–CH2–).
diethyl ether. The reaction mixture was further concentrated Extraction of the remaining solid and crystallization from
by bubbling CO through the solution and the reaction flask CH2Cl2 yield to 9 as pink crystals (62 mg, 67%).
was crystallization from diethyl ether at −40 °C gave 8b as dark
1
orange X-ray quality crystals (20 mg, 12% yield). H NMR (tol-
d8, 600 MHz, 298 K): δ (ppm) −0.57 (9H, s, –Si(CH3)3–), 1.79
Results and discussion
Carbon disulfide activation
(2H, s, –CH2–), 2.27 (9H, br s, –CH3–), 6.01 (3H, s, –CH–), 7.15
(3H, t, p-Ph), 7.29 (6H, t, m-Ph), 8.08 (6H, d, o-Ph) 13C NMR
Addition of CS2 to a diethyl ether solution of TpPh,MeNiCH2Ph
(1a) at room temperature resulted in a color change from light
red to dark red (Scheme 1a). Following evaporation of the
solvent under reduced pressure, extraction with diethyl ether
and cooling to −40 °C, the TpPh,MeNi(η2-CS2)CH2Ph complex
2a was isolated as dark red crystals in moderate yield. Results
of an X-ray diffraction study are shown in the ORTEP diagram
(Fig. 1, left). Consistent with the diamagnetic solution behav-
ior of 2a, the coordination environment around the nickel is in
a distorted square planar geometry in which only two arms of
the Tp ligand are bound to the metal center. Surprisingly, the
coordination of CS2 moiety is in an η2-C,S arrangement, result-
(tol-d8, 600 MHz, 298 K): δ (ppm) −1.63 (s, –Si–(CH3)3), 12.73
(s, –CH3), 15.62 (s, –CH2–), 105 (s, –CH–), 127–136 (aromatic
region), 145 (s, –CPh), 154 (s, –CMe), 184 (s, –NiCOCH2), 220
(s, NiCO). IR (cm−1): 2920, 2522 (BH, m), 2047 (terminal CO,
m), 1683 (CO, m), 1545 (m), 1507 (m), 1438 (m), 1413 (w), 1367
(m) 1349 (m), 1304 (m), 1282 (s), 1243 (m), 1186 (w), 1173 (w),
1098 (s), 1058 (w), 1028 (m), 981 (m), 961 (s), 917 (m), 842 (w),
784 (w), 759 (w), 695 (w), 658 (m), 634 (w), 617 (m), 582 (m),
536 (m). Anal. Calcd: TpPh,MeNi(CO)(COCH2Si(CH3)3)
(C36H39BN6NiSiO2) C, 63.09; H, 5.74; N, 12.26. Found: C, 62.88;
H, 5.48; N, 12.51. Mp: 115–116 °C.
NMR spectroscopic monitoring
Complexes 1a or 1b (0.02 mmol) were dissolved in 0.45 mL of
C6D6 and added to a J-Young NMR tube under N2 atmosphere.
The J-Young NMR tube was connected to Schlenck line and
freeze–pump–thaw three times, after which CO (1 atm) was
added to the degassed solution. The reactions were heated at
60 °C and were followed by 1H NMR spectroscopy.
9,10-Dihydro-anthracene. Using the same condition as
described, the reaction between 1a and CO was carried in
presence of 10 equiv. of 9,10-dihydro-anthracene (0.2 mmol,
36.1 mg).
Radical trap experiment
1a + RCl. These reactions have been performed following a
standard procedure in which 10 mg of 1a and 3 equivalents of
the halide species (benzyl chloride or allyl chloride) were dis-
solved in 0.45 mL of C6D6 and added to a J-Young NMR tube
under N2 atmosphere. 1H NMR spectroscopy revealed the
Scheme 1
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Methyl isothiocyanate activation
The insertion chemistry of 1a was further studied using other
sulfur containing saturated small molecules. Dropwise
addition of methyl isothiocyanate in toluene to a solution of
1a in toluene resulted in a color change from red to green.
Evaporation of solvent under reduced pressure, extraction in
hexanes and cooling to −40 °C resulted in isolation of TpPh,
MeNi(η2-MeNCS)SCH2Ph (4) as green crystals in low yield. Dis-
solving the remaining reaction solids in toluene, followed by
filtration and layering with hexanes allowed for the isolation of
TpPh,MeNi(η2-MeNC)CH2Ph (3) as yellow crystals in moderate
yield (Scheme 2). X-ray quality crystals for 3 were obtained
from toluene/hexanes vapor diffusion while 4 was obtained
from hexanes at −40 °C. The results of X-ray diffraction studies
are shown in the ORTEP diagram (Fig. 2). The coordination
environment around nickel is distorted square planar geome-
try in 3 (τ = 0.38) and distorted trigonal bipyramidal in 4 (τ =
0.64). 1H NMR spectroscopy of 3 shows well-resolved and
sharp ligand resonances, this diamagnetic behavior being con-
sistent with the solid-state geometry determination. As for the
other square panar complex 1a, the high symmetry observed in
solution indicates fast κ2 and κ3 interconversion on the NMR
time scale.
Fig. 1 ORTEP diagrams of compound 2a (left) and 2b (right). For 2a (Å):
Ni(1)–C(1) 1.7971(16), Ni(1)–S(1) 2.1971(4), C(1)–S(1) 1.6352(16), C(1)–S(2)
1.6802(16), Ni(1)–N(1) 2.885, Ni(1)–N(2) 1.9017(13), Ni(1)–N(3)
1.9320(13). For 2b (Å): Ni(1)–S(1) 2.3567(20), Ni(1)–S(2) 2.4604(10), C(1)–
S(1) 1.674(3), C(1)–S(2) 1.689(3), Ni(1)–N(av) 2.061.
ing from a C–S bond formation rather than a C–C bond as
observed in classical insertion chemistry. The Ni–S and Ni–C
distances of 2.1971(4) Å (Ni(1)–S(1)), 1.797(2) Å (Ni(1)–C(1))
and the S(1)–C(1)–S(2) angle of 135.8(1)° are similar to the pre-
viously reported values.53,54 Proton NMR spectroscopy analysis
reveals the presence of a diamagnetic species suggesting that
2a retains its square planar geometry in solution. The high
symmetry observed in solution (all three methyl groups are
equivalent) suggests that a dynamic process renders each TpPh,
Me
arm equivalent at room temperature, consistent with a fast
κ2 and κ3 interconversion on the NMR time-scale. The ligand
resonance signals in the H NMR are clearly defined with the
1
exception of the boron bound hydrogen, which could not be
resolved. The νBH at 2502 cm−1 is in agreement with the κ2
binding mode of TpPh,Me
.
Scheme 2
In order to understand the unusual insertion chemistry
observed with 1a, the reaction of TpPh,MeNiCH2Si(CH)3 (1b)
with CS2 was also performed, which resulted in a slight color
change of the solution to a lighter green (Scheme 1). After
evaporation of the solvent under reduced pressure, extraction
in hexanes, and cooling to −40 °C, TpPh,MeNi(η2-CS2)CH2Si-
(CH3)3 (2b) was isolated as lime-green crystals in moderate
yield (Scheme 1b). X-ray quality crystals were obtained from
hexamethyldisiloxane at −40 °C. An ORTEP diagram shows the
molecular structure (Fig. 1, right). Classical insertion of
carbon disulfide into the metal–carbon bond is observed
leading to CS2 moiety bound to the Ni metal center in κ2-S,S
fashion. The coordination environment around the nickel
atom is in a distorted square pyramidal (τ = 0.38).55 The
nickel–sulfur distances, Ni(1)–S(1) 2.357(1) Å, Ni(1)–S(2)
2.460(1) Å and S(1)–C(1)–S(2) angle of 117.4(2)° are similar to
previously reported values. The solution state magnetic
moment was determined to be 2.7(7)μB and is consistent with
an S = 1 electronic configuration.
Fig. 2 ORTEP diagrams of compound 3 (left) and 4 (right). For 3 (Å):
Ni(1)–C(1) 1.8271(16), Ni(1)–N(4) 1.8554(13), C(1)–N(4) 1.247(2), Ni(1)–
N(1) 3.037, Ni(1)–N(2) 1.8932(13), Ni(1)–N(3) 1.9392(13). For 4 (Å): Ni(1)–
S(1) 2.4045(8), Ni(1)–N(4) 2.040(2), C(1)–S(1) 1.739(3), C(1)–S(2) 1.758(3),
C(1)–N(4) 1.280(3), Ni(1)–N(av) 2.032.
The effects of the paramagnetic shift on ligand resonance
signals in the 1H NMR renders them uninformative. The νBH at
2546 cm−1 is in accord with a κ3-TpPh,Me ligand.
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1
On the other hand, broad signals in the H NMR spectrum
of complex 4 were observed and the solution-state magnetic
moment was found to be 2.8(7)μB. The νBH of 2519 cm−1 and
2549 cm−1 of complexes 3 and 4 are consistent with a κ2 and
κ3-TpPh,Me ligand respectively.
Intrigued by the formation of complex 3, the reaction of
tert-butyl isocyanide with both 1a and 1b (Scheme 3) was inves-
t
tigated. Addition of BuNC to a solution of 1a–b in diethyl
ether resulted in a rapid color change. Filtration, removal of
volatile substances under reduced pressure and crystallization
from hexanes at −40 °C yielded both 5a and 5b as yellow-
orange crystals in moderate yields (56% and 34% respectively).
X-ray quality crystals were obtained from diethyl ether at
−40 °C for 5a and from hexanes at −40 °C for 5b. Results of an
X-ray diffraction study are shown in the ORTEP diagrams in
Fig. 3. The coordination environment around the nickel center
is in both cases distorted square planar. The Ni(1)–C(1) bond
distances (5a: 1.831(2) Å and 5b: 1.823(2) Å) and Ni(1)–N(1)
bond distances (5a: 1.849(1) Å and 5b: 1.871(2) Å) between the
metal center and the iminyl moiety are in agreement with pre-
viously reported distances for other nickel η2-bound imine
complexes.56,57 Additionally, the long carbon–nitrogen bond of
the imine bound moiety C(1)–N(1) of 1.254(2) Å or 5a and
Scheme 4
η2 coordination mode and the interaction between the
π-system of the iminyl moiety and the metal center. H NMR
1
spectroscopy of 5a–b reveals the presence of diamagnetic
species, suggesting that 5a–b retain their square planar geome-
try in solution. Interestingly, the 1H NMR spectrum of 5a
shows that all three arms of the ligand are equivalent on the
NMR timescale at room temperature, whereas a 2 : 1 ratio both
at room temperature and 350 K is observed for 5b. The νBH at
2472 cm−1 and 2487 cm−1 for 5a and 5b respectively are in
accord with a κ2-TpPh,Me ligand.
t
1.248(2) Å for 5b, as well as the BuNC angle (C(1)–N(4)–C(2))
of 138.0(1)° for 5a and 134.8(2)° for 5b, further confirm the a
Based on the structure of 4 and the resemblance of
complex 3 to an isocyanide insertion product with complex 1a
we propose the reaction profile shown in Scheme 4. Interaction
of 1a with the first equivalent of the methyl isothiocyanate pro-
ceeds with the cleavage of the sulfur–carbon bond, release of
methyl isocyanide and formation of
a
TpPh,MeNiSCH2Ph
complex. The methyl isocyanide reacts with complex 1a in
solution to yield the reaction product 3 while an insertion of a
second equivalent of the methyl isothiocyanated into the thio-
benzyl complex result in the formation of 4. To further solidify
our proposed pathway, both complexes 1a–b were exposed to
tert-butyl isocyanide and the resulting reaction products 5a–b
were isolated and characterized.
Scheme 3
Activation of OCS
To further understand the chemistry of 1a toward CvS con-
taining small molecules, 1 atm of OCS was added to a solution
of 1a in diethyl ether (Scheme 5). Compound 6 was isolated as
yellow crystals from hexane; benzyl disulfide was obtained by
sublimation of the residue from the reaction. There are only
Fig. 3 ORTEP diagrams of 5a (left) and 5b (right). Selected bond dis-
tances for 5a (Å): Ni(1)–C(1) 1.8312(16), Ni(1)–N(4) 1.8487(13), C(1)–N(4)
1.248(2), Ni(1)–N(1) 3.410, Ni(1)–N(2) 1.9066(13), Ni(1)–N(3) 1.9468(13).
5b (Å): Ni(1)–C(1) 1.8228(18), Ni(1)–N(4) 1.8708(15), C(1)–N(4) 1.254(2),
Ni(1)–N(1) 3.108, Ni(1)–N(2) 1.8950(15), Ni(1)–N(3) 1.9604(15).
Scheme 5
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few examples in the literature of such terminal carbonyl Ni(I) Activation of CO
species. Riordan has reported activation of dioxygen and
To probe this hypothesis, 1 atm of CO was added at room
temperature to a degassed solution of 1a in benzene. No color
change was observed after 2 hours; however, the solution
turned from dark red to yellow when the mixture was heated to
60 °C overnight. After removal of volatiles under reduced
pressure, bibenzyl was isolated by sublimation and character-
ability of the resulting complex to oxidize nitric oxide into
nitrites and nitrates.58 The X-ray structure of 6 is depicted in
Fig. 4. The Ni(1)–C(1) bond (1.766(4) Å) is comparable to other
nickel 4-coordinate terminal CO compounds, such as the tetra-
hedral PhTttBuNiCO (1.754(7) Å, TttBu
= phenyltris(tert-
butyltho)methyl)borate).58,59 Similarly, the C(1)–O(1) of 1.141(4)
Å and νCO of 2003 cm−1 are also within values reported in
the literature for the few example of Ni(I) terminal CO, and
suggest little π-back donation. The broad, shifted resonances
1
ized by H, 13C NMR spectroscopy and by GC/MS (Scheme 7).
Extraction and crystallization at −40 °C from diethyl ether of
the remaining yellow powder afforded 6 (Scheme 7, 40% yield).
On the other hand, when 1 atm of CO was added to a solution
of 1b in diethyl ether, a rapid color change from red to orange
was observed. After two hours the volatiles were removed
under reduced pressure resulted in an orange powder which
was extracted with THF and crystalized with a 3 : 1 mixture
THF/hexane at −40 °C yielding orange crystals of 7b. X-ray
quality crystals were grown from a similar mixture and
revealed the formation of a square-planar η2-acyl nickel
complex with a κ2-Tp ligand (Scheme 7 and Fig. 4).
The long CO bond (C(1)–O(1) = 1.235(3) Å) along with the
low vibrational frequency (ν = 1684 cm−1) observed in the
solid-state are consistent with an η2-acyl complex. The only
reported TMSCH2 acyl nickel example in the literature shows
η1-coordination to the metal.60 1H and 13C NMR spectroscopy
reveal the presence of a diamagnetic compound implying that
the square planar geometry and κ2-coordination of the Tp
ligand observed in the solid state is retained in solution. The
–SiMe3 group appears at −0.53 ppm and the Ni–C(O)–
CH2(TMS) methylene group at 1.85 ppm, which is slightly
upfielded, yet comparable to related organic species (e.g.
3-chloro-1-(trimethylsilyl)propane-2-one: δ = 0.1 ppm for the
–SiMe3 and δ = 2.3 ppm for the –CH2).61 Interestingly, when 8b
was dissolved in hexane and heated at 60 °C for several hours,
a color change from orange to yellow was observed. Spectro-
scopic analysis as well as unit cell determination confirmed
the formation of complex 6 in low yield (Scheme 7). The
organic byproduct (i.e. 1,2-ethanebistrimethylsilane) of the
1
observed by H NMR spectroscopy, along with a magnetism of
μeff = 2.2(8)μB are consistent with a paramagnetic species,
however the μeff obtained is rather surprising and suggest an
electronic configuration between a S = 1/2 and S = 1.
Based on the isolated products, a mechanism can be pro-
posed in which the first step is analogous to the CS2 and RNCS
insertions, resulting in a S–C bond formation (Scheme 6, inter-
mediate C). Then, extrusion of CO to a terminal position
(intermediate D), would generate the final products by homo-
lytic cleavage of the Ni–S bond to release 6 and a benzyl di-
sulfide radicals, the latter coupling form the disulfide species.
Fig. 4 ORTEP diagrams of compound 6 (left) and 7b (right). Selected
bond distances for 6 (Å): Ni(1)–C(1) 1.766(4), C(1)–O(1) 1.141(4), Ni(1)–
Nav 2.021. Selected bond distances for 7b (Å): Ni(1)–C(1) 1.776(3), Ni(1)–
O(1) 1.9765(19), C(1)–O(1) 1.235(3), Ni(1)–N(1) 2.710(2), Ni(1)–N(2)
1.878(2), Ni(1)–N(3) 1.970 (2).
Scheme 6
Scheme 7 Reaction of TpPh,MeNiCH2R 1a–b with CO.
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reaction was isolated by vacuum-transfer of the hexane solu-
tion and was characterized by NMR spectroscopy and GC/MS.
1
Monitoring of the reaction between 1b and CO by H NMR
reveals the rapid formation of 7b, identified by its character-
istic methylene and TMS resonances (δ = 1.85 ppm and
−0.53 ppm, respectively). Complex 7b further reacts over
time and is quantitatively converted to a new diamagnetic
species, complex 8b. This new species does not undergo
further transformations after several hours at room tempera-
ture; however, 8b was found to be unstable under prolonged
period of heating and dynamic vacuum, and slowly converts to
Fig. 5 ORTEP diagrams of compound 8a (left) and 8b (right). Selected
bond distances for 8a (Å): Ni(1)–C(1) 1.9518(15), Ni(1)–C(2) 1.7848(16),
C(1)–O(1) 1.186(2), C(2)–O(2) 1.138(2), Ni(1)–Nav 2.045. Selected bond
distances for 8b (Å): Ni(1)–C(1) 1.951(3), Ni(1)–C(2) 1.764(3), C(1)–O(1)
1.198(4), C(2)–O(2) 1.146(4), Ni(1)–N(1) 2.346(2), Ni(1)–N(2) 2.055(2),
Ni(1)–N(3) 1.999 (3).
1
complex 6. A H NMR monitoring experiment was conducted
to explore the reaction between 1a and CO. As observed with
complex 1b, 1a reacts quickly with CO and forms a short live
diamagnetic intermediate, 7a, with a signal at δ = 2.96 ppm,
assigned to –CH2Ph group in the 1H NMR spectrum. This
characteristic resonance quickly disappears and a new dia-
magnetic complex was formed with a more upfield methylene
peak (δ = 3.27 ppm). No further reactivity of the new complex,
8a, was observed at room temperature. However, 8a was also
found to be unstable under prolonged period of heating at
60 °C even under CO atmosphere, or dynamic vacuum, and
like 8b, converts to the terminal carbonyl complex 6 and the
dibenzyl organic product.
Unlike complex 7b, which was persistent enough to be iso-
lated, attempts to obtain 7a were unsuccessful due its conver-
sion to either 8a or 2. However, both complexes 8a–b were
successfully isolated and crystalized by bubbling CO through a
solution of 1a or 1b in diethyl ether (Scheme 8). Dark red X-ray
suitable crystals were obtained after 24 hours (10% for 8a and
12% for 8b). In both cases, crystallographic analyses revealed
the formation of a nickel complex with both a terminal CO
and terminal acyl ligands (Fig. 5). The geometry of 8a is
between trigonal bipyramidal and square pyramidal, with a τ
factor of 0.56, while 8b has τ factor of 0.25, indicating a dis-
torted square pyramidal geometry. In both complexes the
three arms of the scorpionate ligand are coordinated to the
metal center in a κ3 fashion, however the Ni–N distances differ
slightly in the two complexes (see Fig. 5). The Ni–C bond dis-
tances of the terminal carbonyl are similar, 8a: 1.785(4) Å and
8b: 1.764(3) Å, and comparable to other set of nickel carbonyl
bond found in the literature as well as the value found for 6
(between 1.65 Å and 1.80 Å, Ni–C of 6 is 1.766(4) Å). Similarly,
the short C(2)–O(2) bond distance of the terminal carbonyl of
8a: 1.138(4) Å and 8b: 1.146(3) Å, is comparable to literature
data (between 1.12 Å and 1.19 Å).62 The C(1)–O(1) bond length
of the acyl ligand, 8a: 1.186(5) Å and 8b: 1.198(4) Å, is shorter
compared to typical sp2 carbonyl groups (e.g. acetone, 1.213 Å)
or that in 7a (1.235(3) Å) but comparable to the already cited
acyl nickel (1.191 Å).62 Two signals were observed in solid state
IR (8a: 2033 and 1724 cm−1 and 8b: 2047 and 1683 cm−1). The
vibrational frequencies (ν = 1724 and 1683 cm−1) are typical of
an sp2 CvO stretch and are assigned to the COacyl moiety. The
high frequency of the terminal CO (ν = 2033 cm−1 for 8a and
2047 cm−1 for 8b) indicates weak π back-bonding from the
nickel to CO, which is consistent with the short C–O bond
length observed in the solid state, and further explains the
instability of 8a–b to dynamic vacuum or heating. Finally, 13C
NMR data for the two CO moiety of 8a–b are also consistent
with values of other terminal and acyl nickel complexes (8a:
215 ppm and 8b: 219 ppm for the terminal CO; 8a: 184 ppm
and 8b: 182 ppm for the acyl CO moiety).63
Based on these data, a mechanism for the reductive coup-
ling of alkyl induced by CO can be proposed (Scheme 9). Upon
addition of CO, coordination to the metal center results in the
formation of a terminal carbonyl. There is an equilibrium
between the terminal/inserted CO that is mainly shifted to the
acyl complexes 7a–b. In the presence of excess CO, 7a–b con-
verts quickly to the carbonyl acyl complexes 8a–b. By applying
Scheme 8
Scheme 9
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Scheme 10
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vacuum, the terminal CO decoordinates from 8a–b reforming
the η2-acyl 7a–b. The final step is the formation of 6 and the
organic byproduct, which based on the radical trap experi-
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6 and the organic radical.
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of 9,10-dihydroanthracene (DHA) while the reaction was moni-
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revealed the conversion of 6 and bibenzyl, however both
toluene and 9,9′,10,10′-tetrahydro-9,9′-bianthracene were
detected by NMR and GC/MS analyses, suggesting a radical
process in which benzyl radical is involved. Additionally,
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ence of organic halides known to generate persistent radicals
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coupling product between the benzyl moiety and the organic
fragment as well as formation of the TpPh,MeNiCl complex 9.
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Conclusions
We have described the activation of several unsaturated small
molecules by nickel(II) alkyl complexes supported by the hydro-
tris(3-phenyl-5-methylpyrazolyl) borate ligand. The addition of
CS2 to the nickel alkyl complexes 1a and 1b resulted in the for-
mation of the insertion products 2a and 2b. In the presence of
COS and MeNCS sulfur abstraction by complexes 1a and 1b
was observed yielding the carbonyl and imidoyl complexes 3
and 6 respectively. Alternatively, complex 6 and an analogous
complex to 3 were prepared using tBuNC and CO directly.
Additional insertion products based on TpPh,MeNi complexes
are also reported.
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Acknowledgements
We thank the NSF (CHE-1465188) for funding and the NIH
(S10-RR027172) for support of our X-ray facility. We thank the
NSF (CHE-1465188) for funding this work.
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