C-H activation via carbodiimide insertion into yttrium-carbon alkynide bonds: An organometallic Alder-ene reaction

Article abstract of DOI:10.1021/om200419k

The yttrium alkynide (C₅Me₅)₂Y(C≡ CPh)(THF), 1, and the related trienediyl [(C₅Me₅) ₂Y₂(μ-η²:η²-PhC=C=C=CPh), 2, can be isolated from the reaction of (C₅Me₅) ₂Y(η³-CH₂CHCH₂)(THF) with phenylacetylene in THF and hexane, respectively. Complex 1 reacts with ^tBuN=C=N^tBu to afford the conventional amidinate insertion product (C₅Me₅)₂Y[^tBuNC(C≡ CPh)N^tBu-κ²N,N′, 3. However, the analogous reaction with iso-propyl and cyclohexyl carbodiimides involves C-H activation and forms the iminovinyl complexes (C₅Me₅) ₂Y[C(=CHPh)C(N=CMe₂)=NⁱPr-κ²C, N, 4, and (C₅Me₅)₂Y{C(=CHPh)C[N=C(CH ₂)₅=NCH(CH₂)₅-κ²C, N}, 5, respectively. The reaction is formally a variation of the Alder-ene reaction in which a C-H bond of the carbodiimide (ene) is activated and transferred to the alkynide ligand (enophile) bound to yttrium. The trienediyl 2 reacts with iso-propyl carbodiimide via conventional insertion to form a bis(amidinate) product with a trienediyl linker, namely, (C₅Me ₅)₂Y[μ-κ²-(ⁱPrN) ₂C-C(Ph)=C=C=C(Ph)-C(NⁱPr)₂Y(C ₅Me₅)₂, 6. The alkynide ligand in 1 is also modified in the reaction with benzylcyanide that forms an unusual insertion product, the amidonitrile complex [(C₅Me₅) ₂Y{μ-N(H)C(CH₂Ph)=C[C(Ph)=CHPhC≡N}₂, 7.

Full text of DOI:10.1021/om200419k

ARTICLE
pubs.acs.org/Organometallics
CꢀH Activation via Carbodiimide Insertion into YttriumꢀCarbon
Alkynide Bonds: An Organometallic Alder-ene Reaction
Ian J. Casely, Joseph W. Ziller, and William J. Evans*
Department of Chemistry, University of California, Irvine, California 92697-2025, United States
S Supporting Information
b
ABSTRACT:
The yttrium alkynide (C5Me5)2Y(CtCPh)(THF), 1, and the related trienediyl [(C5Me5)2Y]2(μ-η2:η2-PhCdCdCdCPh), 2,
can be isolated from the reaction of (C5Me5)2Y(η3-CH2CHCH2)(THF) with phenylacetylene in THF and hexane, respectively.
Complex 1 reacts with tBuNdCdNtBu to afford the conventional amidinate insertion product (C5Me5)2Y[tBuNC(CtCPh)NtBu-
k2N,N0], 3. However, the analogous reaction with iso-propyl and cyclohexyl carbodiimides involves CꢀH activation and forms the
iminovinyl complexes (C5Me5)2Y[C(dCHPh)C(NdCMe2)dNiPr-k2C,N], 4, and (C5Me5)2Y{C(dCHPh)C[NdC(CH2)5]d
NCH(CH2)5-k2C,N}, 5, respectively. The reaction is formally a variation of the Alder-ene reaction in which a CꢀH bond of the
carbodiimide (ene) is activated and transferred to the alkynide ligand (enophile) bound to yttrium. The trienediyl 2 reacts with iso-
propyl carbodiimide via conventional insertion to form a bis(amidinate) product with a trienediyl linker, namely, (C5Me5)2Y-
[μ-k2-(iPrN)2CꢀC(Ph)dCdCdC(Ph)ꢀC(NiPr)2]Y(C5Me5)2, 6. The alkynide ligand in 1 is also modified in the reaction with
benzylcyanide that forms an unusual insertion product, the amidonitrile complex [(C5Me5)2Y{μ-N(H)C(CH2Ph)dC[C(Ph)d
CHPh]CtN}]2, 7.
Scheme 1. Insertion with CO2 and Isoelectronic Analogues
’ INTRODUCTION
Recent studies in f element chemistry have shown that
insertion of carbodiimides, RNdCdNR, into metal carbon
bonds is a useful method to change the coordination environ-
ment of organometallic complexes.1ꢀ8 Although carbodiimides
are isoelectronic versions of common insertion substrates, such
as CO29ꢀ14 and RNCO,11,12,15 they offer important alternatives
in that the amidinate ligand has substituents on both donor
atoms in the products (Scheme 1). In addition to this increased
steric control compared to CO2 or PhNCO insertion products,
carbodiimides deliver two strongly donating nitrogen atoms.
Formation of amidinate complexes by insertion of a carbodii-
mide into a metal alkynide bond is less common. However,
reactions have been reported for Li,16 Ca,17 Y,18,19 Sm,20 and U4
complexes, and in some cases, catalytic formation of the corre-
sponding amidines has been observed.17ꢀ19 For example, Hou
and co-workers18 reported carbodiimide insertion with the bridged
yttrium alkynide, {[Me2Si(C5Me4)(NPh)]Y(μ-CtCPh)(THF)}2,
to form [Me2Si(C5Me4)(NPh)]Y[tBuNC(CtCPh)NtBu-k2N,
N0](THF). Subsequent addition of phenylacetylene liberated the
of (C5Me5)2Y(CtCPh)(Et2O), previously prepared from
(C5Me5)2Y[CH(SiMe3)2] and phenylacetylene.21 Surprisingly,
the course of the reaction was highly dependent upon the nature
of R in the RNdCdNR substrate. Specifically, CꢀH bond
activation and reduction of the alkynide CtC bond was ob-
served when the R group was a secondary alkyl. Analysis of the
reaction chemistry indicated that this was an organometallic
version of the Alder-ene reaction (Scheme 2).22
Two examples of the organometallic Alder-ene reaction are
described as well as the synthesis and structure of the solvated
alkynide precursor, 1, and the related trienediyl complex,
[(C5Me5)2Y]2(μ-η2:η2-PhCdCdCdCPh), 2, obtained by
formal coupling of two alkynide ligands in unsolvated
t
alkynylamidine, BuNdC(CtCPh)N(H)tBu, with concomitant
formation of the starting alkynide. Catalysis was possible with a range
of substituents on both the carbodiimide and the alkyne components.
We report here on yttrium alkynide carbodiimide inser-
tion chemistry examined as part of a study of the reaction
chemistry of (C5Me5)2Y(CtCPh)(THF), 1, the THF analogue
Received: May 18, 2011
Published: August 23, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/om200419k Organometallics 2011, 30, 4873–4881
|

Organometallics
ARTICLE
Scheme 2. General Examples of the Alder-ene Reaction
617 w, 592 w, 532 m, 519 m cmꢀ1. Anal. Calcd for C32H43OY: C, 72.15;
H, 8.15. Found: C, 71.51; H, 7.97.
[(C5Me5)2Y]2(μ-η2:η2-PhCdCdCdCPh), 2. A solution of
HCtCPh (22 mg, 0.21 mmol) in hexane (5 mL) was added to a stirred
yellow solution of (C5Me5)2Y(η3-CH2CHCH2)(THF) (100 mg, 0.21
mmol) in hexane (5 mL) with stirring. Within 1 min, gas evolution was
observed (presumably propene) and a transient colorless solution
formed, which proceeded to turn yellow, then orange, with stirring for
16 h. Volatiles were removed under reduced pressure, affording an
orange solid. This was dissolved in hot benzene (3 mL), and X-ray
quality single crystals formed by slow cooling to ambient temperature
overnight. Decantation of the mother liquor, washing with benzene
(2 mL), and drying under reduced pressure afforded orange crystalline 2
(33 mg, 34%). 1H NMR (C6D6): δ 7.30 (t, 4H, 3JHH = 7.5 Hz, m-Ph),
7.08 (t, 2H, 3JHH = 7.5 Hz, p-Ph), 6.75 (d, 4H, 3JHH = 7.5 Hz, o-Ph), 2.08
(s, 60H, C5Me5). 13C NMR (C6D6): δ 197.9 (d, 1JCY = 37.7 Hz, YꢀC),
“(C5Me5)2Y(CtCPh)”.21,23 An additional reaction in which
insertion leads to an unexpected product and reduction of the
triple bond in 1 is also reported: the formation of an amidonitrile
complex from 1 and benzylnitrile.
2
’ EXPERIMENTAL SECTION
155.2 (d, JCY = 3.8 Hz, YꢀCdC), 141.4 (i-Ph), 131.1, 128.5, 128.2
(PhꢀCH), 119.2 (C5Me5), 11.7 (C5Me5). IR: 3064 w, 3028 w, 2900 m,
2857 m, 2725 w, 1588 w, 1551 m, 1472 m, 1438 m, 1379 m, 1278 w,
1181 w, 1155 w, 1123 w, 1066 w, 1023 w, 990 w, 810 w, 759 m, 681 s, 628
m, 609 m, 593 w, 544 w, 463 w cmꢀ1. Anal. Calcd for C56H70Y2: C,
73.02; H, 7.68. Found: C, 74.31; H, 7.76. The 1H NMR spectrum of the
mother liquor showed the presence of 1 as a byproduct.
All manipulations and syntheses described below were conducted
with the rigorous exclusion of air and water using standard Schlenk line,
high-vacuum line, and glovebox techniques under an argon atmosphere.
Solvents were sparged with UHP argon and dried by passage through
columns containing Q-5 and molecular sieves prior to use. Deuterated
NMR solvents were purchased from Cambridge Isotope Laboratories,
dried over NaK alloy, degassed by three freezeꢀpumpꢀthaw cycles, and
vacuum-transferred before use. (C5Me5)2Y(η3-CH2CHCH2)(THF)
was prepared according to the literature procedure.24 Cyclohexylcarbo-
diimide was sublimed (10ꢀ5 Torr) and iso-propyl- and tert-butylcarbo-
diimide, phenylacetylene, and benzylnitrile were stored over molecular
sieves overnight and freezeꢀpumpꢀthaw degassed three times prior to
use. All other reagents were purchased from Aldrich and used as
(C5Me5)2Y[tBuNC(C;CPh)NtBu-k2N,N0], 3. Toluene solutions
t
of 1 (100 mg, 0.19 mmol in 5 mL) and BuNdCdNtBu (30 mg,
0.19 mmol in 5 mL) were combined in a Schlenk tube equipped with a
greaseless stopcock. The colorless reaction mixture turned yellow after
heating at 110 °C for 2 h. The solvent was removed under reduced
pressure to afford a yellow solid. X-ray quality single crystals were
obtained overnight from a concentrated hexane solution at ꢀ30 °C.
Separation of the mother liquor, followed by washing with cold hexane
(3 mL) and drying under reduced pressure, afforded 3 as a yellow
crystalline solid (79 mg, 68%). 1H NMR (C6D6): δ 7.45 (m, 2H,
1
received. The H and 13C NMR spectra were recorded on a Bruker
GN500 or CRYO500 MHz spectrometer at 298 K, unless otherwise
stated, and referenced internally to residual protio-solvent resonances.
89Y NMR spectra were recorded on an AVANCE600 MHz spectrometer
PhꢀCH), 6.98 (m, 3H, PhꢀCH), 2.10 (s, 30H, C5Me5), 1.60 [bs v1/2
=
28.5 Hz, 18H, C(CH3)3]. 13C NMR (C6D6): δ 152.5 (NCN), 130.8,
129.1, and 128.5 (PhꢀCH), 122.5 (i-Ph), 117.9 (C5Me5), 97.8
operating at 29.4 MHz and referenced externally to Y(NO3)3 6H2O in
3
D2O. HMQC and HMBC experiments were performed to aid in the
assignment of spectral resonances. Infrared spectra were recorded as
KBr pellets on a Varian FTS 1000 FT-IR spectrometer. Elemental
analyses were recorded on a PerkinElmer 2400 Series CHNS elemental
analyzer.
3
(CtCPh), 84.5 (d, JCY = 6.3 Hz, CtCPh), 52.8 [C(CH3)3], 31.8
[broad, C(CH3)3], 12.3 (C5Me5). IR: 3068 w, 2977 m, 2903 m, 2859 m,
2723 w, 2210 m, 1617 w, 1597 w, 1574 w, 1492 m, 1421 s, 1384 s, 1356 s,
1226 m, 1197 s, 1072 m, 1025 w, 915 w, 892 w, 870 w, 797 w, 755 m, 705
m, 688 m, 593 w, 549 w, 530 w, 464 w cmꢀ1. Anal. Calcd for C37H53N2Y:
C, 72.28; H, 8.71; N, 4.56. Found: C, 71.75; H, 8.99; N, 4.47.
(C5Me5)2Y(C;CPh)(THF), 1. Complex 1 was made by a variation
of the synthesis of (C5Me5)2Y(CtCPh)(Et2O) from (C5Me5)2Y-
[CH(SiMe3)2] and phenylacetylene.21 A solution of HCtCPh (128 mg,
1.25 mmol) in THF (5 mL) was added to a stirred yellow solution of
(C5Me5)2Y(η3-CH2CHCH2)(THF) (500 mg, 1.25 mmol) in THF
(10 mL). Within 1 min, gas evolution was observed (presumably
propene) and the yellow color faded from the reaction mixture. After
the mixture was stirred for 16 h, volatiles were removed under reduced
pressure to afford an off-white crystalline solid. This was washed quickly
with hexane (3 mL) and the yellow solution saved. The bulk solid was
dissolved in hot hexane (3 mL) from which X-ray quality single crystals
formed by slow cooling to ambient temperature overnight. Decantation
of the mother liquor and drying of the crystals under reduced pressure
afforded white 1 (307 mg, 46%). Combination of the mother liquor and
original hexane washings, followed by concentration and overnight
storage at ꢀ30 °C, afforded a second crop of crystalline material (200 mg,
(C5Me5)2Y[C(dCHPh)C(NdCMe2)dNiPr-k2C,N], 4. Portion-
wise addition of a THF solution of iPrNdCdNiPr (24 mg, 0.19 mmol in
5 mL) to a stirred THF solution of 1 (100 mg, 0.19 mmol in 5 mL)
elicited an immediate color change to bright yellow. After stirring at
room temperature for 16 h, volatiles were removed under reduced
pressure to afford a yellow solid (108 mg), which was dissolved in hot
hexane (2 mL) and stored overnight at ꢀ30 °C. An amorphous yellow
solid was isolated after decantation of the mother liquor. Washing in cold
hexane (2 mL) and drying under reduced pressure afforded yellow 4 (76
mg, 69%). 1H NMR (C6D6): δ 7.44 (d, 1H, 3JHY = 5.6 Hz, YCdCH),
7.41 (d, 2H, 3JHH = 7.5 Hz, o-Ph), 7.27 (m, 2H, m-Ph), 7.16 (t, 1H, 3JHH
= 7.5 Hz, p-Ph) partially obscured by solvent, 3.49 [sept, 1H, 3JHH = 6.5
Hz, NCH(CH3)2], 2.05 (s, 30H, C5Me5), 1.71 [s, 6H, NdC(CH3)2],
1.16 [d, 6H, 3JHH = 6.5 Hz, NCH(CH3)2]. 13C NMR (C6D6): δ 180.3
(d, 1JCY = 42.8 Hz, YꢀC), 174.9 (NCN), 163.5 [NdC(CH3)2], 143.7
(YCdCH), 141.7 (d, 3JCY = 1.2 Hz, i-Ph), 128.4 (o-Ph), 127.8 (m-Ph),
127.3 (p-Ph), 117.3 (C5Me5), 48.2 [NCH(CH3)2], 25.4 [NdC-
(CH3)2], 23.1 [NCH(CH3)2], 11.7 (C5Me5). 89Y (C6D6): δ ꢀ24.2.
1H{89Y} (C6D6): δ 7.44 (s, 1H, YCdCH), 7.41 (d, 2H, 3JHH = 7.5 Hz,
o-Ph), 7.27 (m, 2H, m-Ph), 7.16 (t, 1H, 3JHH = 7.5 Hz, p-Ph) partially
obscured by solvent, 3.49 [sept, 1H, 3JHH = 6.5 Hz, NCH(CH3)2], 2.05
(s, 30H, C5Me5), 1.71 [s, 6H, NdC(CH3)2], 1.16 [d, 6H, 3JHH = 6.5 Hz,
1
3
30%). H NMR (C6D6): δ 7.70 (d, 2H, JHH = 7.7 Hz, o-Ph), 7.14
(m, 2H, m-Ph), 7.03 (t, 1H, 3JHH = 7.5 Hz, p-Ph), 3.53 (bs, 4H, THF),
2.10 (s, 30H, C5Me5), 1.16 (bs, 4H, THF). 13C NMR (C6D6): δ 147.3
1
(d, JCY = 70.4 Hz, YꢀCtCPh), 131.4 (m-Ph), 128.6 (i-Ph), 128.0
2
(o-Ph), 125.3 (p-Ph), 116.9 (C5Me5), 109.6 (d, JCY = 12.6 Hz,
YꢀCtCPh), 70.9 and 24.8 (THF), 11.5 (C5Me5). IR: 2969 s, 2895 s,
2855 s, 2722 w, 1974 m, 1593 m, 1483 s, 1439 m, 1377 m, 1244 w, 1196
m, 1171 w, 1066 w, 1016 s, 929 s, 875 m, 775 m, 757 s, 694 s, 670 w,
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Organometallics
ARTICLE
1
NCH(CH3)2]. A 89Yꢀ H HMQC experiment confirmed the coupling
between yttrium and (CdCH) and revealed the presence of weak
coupling to [NCH(CH3)2] and (C5Me5). IR: 2971 m, 2906 s, 2859 s,
2724 w, 1677 s, 1596 w, 1509 s, 1440 m, 1371 m, 1329 w, 1279 w,
1228 m, 1212 m, 1170 w, 1121 w, 1068 w, 1023 w, 969 w, 924 w, 894 w,
853 w, 793 w, 755 m, 692 s, 618 w, 589 w, 516 w, 502 m, 487 m,
474 m cmꢀ1. Anal. Calcd for C35H49N2Y: C, 71.64; H, 8.43; N, 4.78.
Found: C, 71.43; H, 9.18; N, 4.72.
1378 m, 1256 w, 1180 m, 1156 m, 1077 w, 1022 w, 949 w, 925 w, 774 m,
756 m, 730 m, 697 s, 605 w, 560 w, 538 w, 464 w cmꢀ1. Anal. Calcd for
C44H47N2Y: C, 76.05; H, 6.83; N, 4.03. Found: C, 75.72; H, 7.23;
N, 3.88.
X-ray Crystallographic Data. Information on X-ray data collec-
tion, structure determination, and refinement for 1ꢀ3 and 5ꢀ7 are
given in the Supporting Information.
(C5Me5)2Y{C(dCHPh)C[NdC(CH2)5]dN(Cy)-j2C,N}, 5. Por-
tionwise addition of a THF solution of CyNdCdNCy (39 mg, 0.19
mmol in 5 mL) to a stirred THF solution of 1 (100 mg, 0.19 mmol in
5 mL) elicited an immediate color change to bright yellow. After stirring
at room temperature for 16 h, volatiles were removed under reduced
pressure to afford a yellow solid (125 mg). This was dissolved in hot
hexane (2 mL) and stored overnight at ambient temperature. The X-ray
quality yellow single crystals of 5 were isolated from solution by
decantation of the mothor liquor, washed in cold hexane (2 mL), and
dried under reduced pressure (85 mg, 68%). 1H NMR (C6D6): δ 7.55
(d, 1H, 3JHY = 5.6 Hz, YCdCH), 7.45 (d, 2H, 3JHH = 7.5 Hz, o-Ph), 7.29
(m, 2H, m-Ph), 7.17 (t, 1H, 3JHH = 7.5 Hz, p-Ph) partially obscured by
solvent, 3.32 [m, 1H, NCH(CH2)5], 2.08 (s, 30H, C5Me5), 2.30ꢀ1.10
(m, 20H, CH2). 13C (C6D6): δ 180.6 (d, 1JCY = 42.8 Hz, Y-C), 174.7
(NCN), 169.5 [NdC(CH2)5], 143.9 (YCdCH), 141.7 (d, 3JCY = 1.2 Hz,
i-Ph), 128.5 (o-Ph), 127.9 (m-Ph), 127.4 (p-Ph), 117.3 (C5Me5), 57.7
[NCH(CH2)5], 36.7, 33.0, 27.8, 26.0, 25.7, and 25.1 (CH2), 11.8
(C5Me5). 89Y (C6D6): δ ꢀ23.8. 1H{89Y} (C6D6): δ 7.55 (s, 1H,
’ RESULTS
Reactivity of (C5Me5)2Y(η3-CH2CHCH2)(THF) and HC;
CPh. Complex 1 was made by a variation of the syntheses of
(C5Me5)2Y(CtCPh)(Et2O)21 and {[Me2Si(C5Me4)(NPh)]Y-
(μ-CtCPh)(THF)}218 from phenylacetylene with (C5Me5)2Y-
[CH(SiMe3)2] and [Me2Si(C5Me4)(NPh)]Y[CH2SiMe3], re-
spectively, using the allyl precursor (C5Me5)2Y(η3-CH2CHCH2)-
(THF). Bis(pentamethylcyclopentadienyl) rare earth allyl com-
plexes have previously been shown to be convenient reagents to
deliver the reactivity of a metal alkyl bond.11,25,26
Addition of 1 equiv of phenylacetylene to a bright yellow THF
solution of (C5Me5)2Y(η3-CH2CHCH2)(THF) resulted in fast
evolution of propene and fading of the color to pale yellow. The
monomeric terminal alkynide (C5Me5)2Y(CtCPh)(THF), 1,
was isolated in 76% yield (Scheme 3).
The NMR and IR spectra of 1 were consistent with those of
(C5Me5)2Y(CtCPh)(Et2O).21 Because the latter complex had
not been characterized by X-ray crystallography, complete
structural data were obtained for 1; see Figure 1 and Table S2
in the Supporting Information.
3
YCdCH), 7.45 (d, 2H, JHH = 7.5 Hz, o-Ph), 7.29 (m, 2H, m-Ph),
7.17 (t, 1H, 3JHH = 7.5 Hz, p-Ph) partially obscured by solvent, 3.32 [m,
1H, NCH(CH2)5], 2.08 (s, 30H, C5Me5), 2.30ꢀ1.10 (m, 20H, CH2). A
1
89Yꢀ H HMQC experiment also confirmed the coupling between
yttrium and (CdCH) and revealed the presence of weak coupling to
[NCH(CH2)5] and (C5Me5). IR: 3057 w, 3020 w, 2934 s, 2854 s, 2723
w, 1670 s, 1597 w, 1514 s, 1443 m, 1364 w, 1347 w, 1280 w, 1254 w, 1229
w, 1200 m, 1178 m, 1127 w, 1107 w, 1074 w, 1024 w, 994 w, 972 w, 922
In contrast to the formation of 1 in THF, treatment of
(C5Me5)2Y(η3-CH2CHCH2)(THF) with 1 equiv of phenylace-
tylene in hexane results in transient formation of a colorless
solution that became dark orange with overnight stirring. Crystalliza-
tion from hot benzene affords trienediyl complex [(C5Me5)2Y]2-
(μ-η2:η2-PhCdCdCdCPh), 2, as orange crystals in low yield
(Scheme 3) (Figure 2 and Table S3 in the Supporting In-
formation). This complex arises from the formal coupling of
two unsolvated (C5Me5)2Y(CtCPh) units. Similar complexes
have been previously reported and structurally characterized.23,28ꢀ31
NMR studies show that 1 is also a product of this reaction and the
less soluble 2 is readily separated by precipitation from benzene.
The dark, intense color of 2 is unusual for an Y3+ complex, but
it is consistent with butatrienediyl formation.28ꢀ31 The spectro-
scopic profile of 2 is similar to that of [(DAC)Y]2(μ-PhCd
CdCdCPh) (DAC = deprotonated 4,13-diaza-18-crown-6),28
with the 13C NMR spectrum showing doublets at 197.9 ppm -
(1JCY = 37.7 Hz, terminal carbon) and 155.2 ppm (2JCY = 3.8 Hz,
internal carbon) and an IR spectrum with ν(CdC) absorptions
at 1588 and 1551 cmꢀ1. The facile formation of 2 contrasts with
the analogous reaction with (C5Me5)2Sm(CtCPh)(THF),
which required >120 °C for 3 days to get 40% of the coupled
product.23
w, 887 w, 845 w, 780 m, 750 m, 693 s, 591 w, 578 w, 508 m, 470 m cmꢀ1
.
Anal. Calcd for C41H57N2Y: C, 73.83; H, 8.63; N, 4.20. Found: C, 73.62;
H, 8.79; N, 4.20.
NMR Scale Synthesis of (C5Me5)2Y[μ-j2-(iPrN)2CꢀC-
(Ph)dCdCdC(Ph)ꢀC(NiPr)2]Y(C5Me5)2, 6. Neat iPrNdCdNiPr
(3.3 μL, 0.02 mmol) was added to an NMR tube fitted with a Young’s tap
containing an orange C6D6 (1 mL) solution of 2 (10 mg, 0.01 mmol).
The tube was sealed and heated at 100 °C for 7 days, over which time the
color of the solution faded and a few X-ray quality orange crystals
formed.
[(C5Me5)2Y{μ-N(H)C(CH2Ph)dC[C(Ph)dCHPh]C;N}]2, 7.
Portionwise addition of a toluene solution of PhCH2CtN (66 mg,
0.56 mmol in 5 mL) to a stirred toluene solution of 1 (150 mg, 0.28
mmol in 5 mL) elicited an immediate color change to bright orange.
After stirring at room temperature for 3 h, volatiles were removed under
reduced pressure to afford an orange residue (196 mg), which was
dissolved in warm toluene (3 mL) and stored for 4 days at ꢀ30 °C. A
pale yellow solid formed, which was isolated from solution by decanta-
tion of the mother liquor, washed in cold hexane (2 mL), and dried
under reduced pressure (62 mg). A second crop of solid (38 mg) was
isolated after storing the mother liquor at ꢀ30 °C overnight (combined
yield of 7: 100 mg, 51%). 1H NMR (C6D6): δ 7.62 (d, 2H, 3JHH = 7.0
Hz, Ph), 7.15ꢀ6.80 (m, 13H, Ph), 6.75 (s, 1H, CH), 4.84 (s, 1H, NH),
3.50 (s, 2H, CH2), 1.93 (s, 30H, C5Me5). 13C NMR (C6D6): δ 182.6 (d,
2JCY = 2.5 Hz, CtN), 141.0, 138.3, 136.8, 136.3 (q-Ph/CdC) the
remaining two phenyl or alkene quaternary carbons could not be
resolved, 130.6, 130.3, 130.2, 129.4, 129.2, 129.1, 128.7, 128.6, 128.5,
128.2, 128.0, 127.8, 127.1, 126.9 (o-, m-, p-Ph), 124.1 (CdCH), 117.7
(C5Me5), 43.3 (CH2), 10.7 (C5Me5). IR: 3430 w, 3378 w, 3325 w, 3058
w, 3023 w, 2902 m, 2857 m, 2725 w, 2122 s, 1599 w, 1501 s, 1444 m,
Carbodiimide Reactivity. Reactions of (C5Me5)2Y(CtCPh)-
(THF), 1, with alkyl-substituted carbodiimides follow two different
t
reaction pathways depending on the alkyl substituent. BuNd
CdNtBu does not react at ambient temperature with 1, but heating
at 110 °C for 2 h affords the anticipated amidinate insertion product
(C5Me5)2Y[tBuNC(CtCPh)NtBu-k2N,N0], 3, as a yellow solid in
68% yield (eq 1). The solid-state structure of 3 is shown in Figure 1,
and the metrical parameters are listed in Table S2 (Supporting
Information). The NMR spectra of 3 are consistent with its
structure, and the IR spectrum displays a distinctive ν(CtC)
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Scheme 3. Yttrium Allyl Reactivity with Phenylacetylene
Figure 1. ORTEP27 representation of (C5Me5)2Y(CtCPh)(THF), 1, (left) and (C5Me5)2Y[tBuNC(CtCPh)NtBu-k2N,N0], 3, (right) drawn at the
50% probability level. Hydrogen atoms are omitted for clarity, and only one molecule of 3 present in the asymmetric unit is shown. Selected bond lengths
(Å) and angles (deg): For 1, Y1ꢀO1 2.3988(12), Y1ꢀC21 2.4071(18), C21ꢀC22 1.206(2), (cnt)ꢀY1ꢀ(cnt) 137.7, O1ꢀY1ꢀC21 91.10(5),
Y1ꢀC21ꢀC22 169.04(15). For 3, Y1ꢀN1 2.3643(14), Y1ꢀN2 2.3811(14), N1ꢀC21 1.338(2), N2ꢀC21 1.336(2), C21ꢀC22 1.453(2), C22ꢀC23
1.195(3), (cnt)ꢀY1ꢀ(cnt) 132.1, N1ꢀY1ꢀN2 57.15(5), N1ꢀC21ꢀN2 116.20(15), C21ꢀC22ꢀC23 176.52(19).
In contrast, the reaction of 1 with RNdCdNR, where R = iPr
or cyclohexyl, occurs within minutes at ambient temperature to
afford the iminovinyl complexes (C5Me5)2Y[C(dCHPh)C-
(NdCMe2)dNiPr-k2C,N], 4, and (C5Me5)2Y{C(dCHPh)C-
[NdC(CH2)5]dN(Cy)-k2C,N}, 5, respectively (Scheme 4).
Complex 5 was identified by X-ray crystallography (Figure 3 and
Table S4 in the Supporting Information), and the identity of 4 was
established by analytical and spectral means in comparison with 5.
The IR spectra of 4 and 5 are consistent with reduction of the
alkyne bond during the reaction. No absorptions are observed in
the ν(CtC) stretching region. Instead, absorptions at 1677 and
1509 cmꢀ1 for 4 and at 1670 and 1514 cmꢀ1 for 5 are observed
and assigned to ν(CdN) and ν(CdC), respectively. These
values are close to those observed in the cyclic iminiumazetidi-
Figure 2. ORTEP representation of [(C5Me5)2Y]2(μ-η2:η2-
PhCdCdCdCPh), 2, drawn at the 50% probability level. Hydrogen
nylidenemethyl complex [(C5H5)Ru{CHdCCPh2N(Cy)CNd
C(CH2)4CH2}(CO)(PiPr3)][BF4], which has similar func-
atoms and solvent are omitted for clarity, and only one component of the
tionality [ν(CdN) 1679 cmꢀ1 and ν(CdC) 1528 cmꢀ1 32
]
(C5Me5)1ꢀ disorder is shown.
(Figure 4).
stretch at 2210 cmꢀ1, comparable to that observed by Hou at
2205 cmꢀ1 in [Me2Si(C5Me4)(NPh)]Y[tBuNC(CtCPh)NtBu-
k2N,N0](THF).18
The NMR spectra of 4 and 5 are similar. Both have the
expected phenyl and (C5Me5)1ꢀ resonances, as well as reso-
nances for the two different substituents on the nitrogen atoms.
Each 1H NMR spectrum also contains a doublet with J = 5.6 Hz
attributable to the YCdCH vinyl proton: at 7.44 ppm in 4 and
7.55 ppm in 5. Few rare earth vinyl complexes are available for
comparison,33 but (C5Me5)2Y[CHdCHCH(Me)Et] has an
analogous vinyl resonance with 3JHY = 4 Hz.34
The 5.6 Hz 3JHY coupling in 4 and 5 was confirmed by a 1H{89Y}
NMR experiment in which the YCdCH doublet collapsed to a
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Scheme 4. Alder-ene Reactivity With Carbodiimides
Figure 5. ORTEP drawing of (C5Me5)2Y[μ-k2-(iPrN)2CꢀC(Ph)d
CdCdC(Ph)ꢀC(NiPr)2]Y(C5Me5)2, 6, drawn at the 50% probability
level. Hydrogen atoms are omitted for clarity.
i
In contrast to the reaction of PrNdCdNiPr with 1, the
trienediyl [(C5Me5)2Y]2(μ-η2:η2-PhCdCdCdCPh), 2, reacts
in a conventional way with the isopropyl carbodiimide (eq 2).
Figure 3. ORTEP representation of (C5Me5)2Y{C(dCHPh)C[Nd
C(CH2)5]dNCH(CH2)5-k2C,N}, 5, drawn at the 50% probability
level. Hydrogen atoms are omitted for clarity, except H29a and H35a.
Selected bond lengths (Å) and angles (deg): Y1ꢀC21 2.4291(12),
Y1ꢀN1 2.4365(10), C21ꢀC22 1.4782(17), C21ꢀC35 1.3458(17),
N1ꢀC22 1.3063(16), N1ꢀC29 1.4739(16), N2ꢀC22 1.4003(16),
N2ꢀC23 1.2736(17), (cnt)ꢀY1ꢀ(cnt) 137.2, Y1ꢀC21ꢀC22 91.34(7),
Y1ꢀC21ꢀC35 150.52(10), Y1ꢀN1ꢀC22 95.51(8), Y1ꢀN1ꢀC29
144.22(8), C22ꢀC21ꢀC35 118.11(11), C21ꢀC22ꢀN1 115.26(11),
C21ꢀC22ꢀN2 121.12(11), N1ꢀC22ꢀN2 123.23(11), C22ꢀN2ꢀC23
124.43(11).
Carbodiimide insertion occurs at each YꢀC bond to make a
bimetallic complex containing a bridging ligand composed of two
amidinates connected by a trienediyl linker (C5Me5)2Y[μ-
k2-(iPrN)2CꢀC(Ph)dCdCdC(Ph)ꢀC(NiPr)2]Y(C5Me5)2,
6. Crystals were obtained from an NMR scale reaction (Figure 5
and Table S5 in the Supporting Information).
1
The H NMR spectrum of the solution showed a small
amount of unreacted starting material and multiple aromatic
and (C5Me5) resonances that could not be satisfactorily assigned.
Because only a small number of crystals formed and this indi-
cated straightforward carbodiimide insertion, the system was not
pursued further.
Benzylnitrile Reactivity. The reaction of 1 with 2 equiv
of benzylnitrile did not give simple substitution of the THF,
but instead led to the isolation of the amidonitrile complex
[(C5Me5)2Y{μ-N(H)C(CH2Ph)dC[C(Ph)dCHPh]CtN}]2,
7 (eq 3), identified by X-ray crystallography (Figure 6 and Table
S6intheSupportingInformation). Inthisreaction,asinScheme4
above, insertion is accompanied by transfer of substitutents to the
alkynide moiety in 1.
Figure 4. Comparison ruthenium complex.
89
singlet upon decoupling. A 1Hꢀ Y HMQC experiment also showed
coupling between yttrium and the vinyl proton and, in addition,
revealed the presence of weak coupling with the “NCH” and
(C5Me5)ꢀ protons. The 13C NMR spectra of 4 and 5 are consistent
with the formulation of these complexes, although the resonance
assigned to the YCdCH vinyl carbon (confirmed by HMQC) does
not appear as the expected yttrium coupled doublet, but rather as a
singlet. The 89Y NMR spectra of 4 and 5 are also similar, with
resonances at ꢀ24.2 and ꢀ23.8 ppm, respectively. These are within
the wide range of values observed for yttrium metallocenes.35
Complex 7 is similar to the dimeric crotononitrileamido com-
plex {[Me2Si(NCMe3) (OCMe3)]2Y[(μ-N,N0)-N(H)C(Me)d
C(H)CtN]}2, prepared from [Me2Si(NCMe3)(OCMe3)]2-
Y[CH(SiMe3)2] and MeCN.36
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The 2.407(2) Å Y1ꢀC21(CtCPh) length in eight coordi-
nate (C5Me5)2Y(CtCPh)(THF), 1, can be compared to the
2.448(4) Å analogue in six coordinate [Me2Si(NCMe3)-
(OCMe3)]2Y(CtCPh)(THF)39 and the 2.38(2) Å length in
the eight coordinate “ate” complex (C5Me5)2Y(μ-CtCCMe3)2-
Li(THF).40 The 1.206(2) Å C21ꢀC22 bond distance in 1 is
similar to the 1.217(5) and 1.24(2) Å lengths in these latter
complexes.
In the trienediyl [(C5Me5)2Y]2(μ-η2:η2-PhCdCdCdCPh),
2 (Figure 2), the 151.3(6)° C12ꢀC11ꢀC110 angle (Table S3 in
the Supporting Information) is similar to that in the analogous
[(C5Me5)2Ln]2(μ-η2:η2-PhCdCdCdCPh) (Ln = Sm,41 La29)
complexes of 146.9(10)° and 148.6(13)°, respectively. The
1.367(6) Å C11ꢀC12 and 1.276(8) Å C11ꢀC110 distances
are indicative of double bonds and are also similar to those in the
other complexes, 1.363(17) and 1.298(19) Å for Sm and 1.36(2)
and 1.26(2) Å for La. After insertion of diisopropylcarbodiimide
into each of the YꢀC bonds in 2, the C22ꢀC23ꢀC230 angle in
(C5Me5)2Y[μ-k2-(iPrN)2CꢀC(Ph)dCdCdC(Ph)ꢀC(NiPr)2]-
Y(C5Me5)2, 6 (Figure 5), is now much closer to linear,
174.28(16)°. The carbon carbon multiple bonds in the tri-
enediyl linker are 1.261(3) and 1.331(2) Å (Table S5, Support-
ing Information).
Figure 6. ORTEP representation of [(C5Me5)2Y{μ-N(H)C-
(CH2Ph)dC[C(Ph)dCHPh]CtN}]2, 7, drawn at the 50% probabil-
ity level. Hydrogen atoms are omitted for clarity, except H1 and H38a.
Selected bond lengths (Å) and angles (deg): Y1ꢀN1 2.366(2),
N1ꢀC21 1.326(3), C21ꢀC24 1.514(4), C21ꢀC22 1.417(4),
C22ꢀC31 1.489(4), C31ꢀC38 1.334(4), C22ꢀC23 1.398(4),
C23ꢀN2 1.162(3), N2ꢀY10 2.351(2), (cnt)ꢀY1ꢀ(cnt) 138.7,
N1ꢀY1ꢀN20 82.05(8), Y1ꢀN1ꢀC21 149.9(2), N1ꢀC21ꢀC22
124.2(3), N1ꢀC21ꢀC24 115.9(2), C24ꢀC21ꢀC22 119.8(2),
C21ꢀC22ꢀC31 128.4(2), C22ꢀC23ꢀN2 179.0(3), C22ꢀC31ꢀC38
121.3(3), C31ꢀC22ꢀC23 115.7(2), C23ꢀN2ꢀY10 172.1(2).
In (C5Me5)2Y[tBuNC(CtCPh)NtBu-k2N,N0], 3 (Figure 1),
the 2.364(1) Å Y1ꢀN1 and 2.381(1) Å Y1ꢀN2 distances are
similar and more symmetric than those in seven coordinate
[Me2Si(C5Me4)(NPh)]Y[tBuNC(CtCPh)NtBu-k2N,N0](THF)18
(2.393(5) and 2.339(5) Å), which has differing lengths presum-
ably because it has an extra ligand in the metallocene wedge. The
metrical parameters in the amidinate ligands in both complexes
are similar, with 1.195(3) Å C22ꢀC23 and 1.182(8) Å alkyne
lengths, respectively. The trienediyl bis(amidinate) (C5Me5)2Y-
[μ-k2-(iPrN)2CꢀC(Ph)dCdCdC(Ph)ꢀC(NiPr)2]Y(C5Me5)2,
6, has similar 2.378(1) and 2.385(2) Å YꢀN distances; that is,
the nature of the substituent on the central carbon does not seem
to change the coordination to yttrium to a great extent.
In eight coordinate (C5Me5)2Y{C(dCHPh)C[NdC-
(CH2)5]dNCH(CH2)5-k2C,N}, 5 (Figure 3), the 2.429(1) Å
yttriumꢀvinyl Y1ꢀC21 bond length is identical to the 2.422(5)
Å LuꢀC(vinyl) length in (C5Me5)2Lu(CHdC5Me4).33 Given
the larger size of yttrium (8-coordinate ionic radius, Y3+ = 1.019 Å;
Lu3+ = 0.977 Å)42 and the larger coordination number in 5, a
longer distance would be expected. The 1.346(2) Å C21ꢀC35
(alkene) length in 5 is also shorter than the 1.380(5) Å analogue
in the lutetium complex, although both of these are longer than
the typical 1.326 Å length for trisubstituted alkenes of the type
(C)2ꢀCdCHꢀC.43
The IR spectrum of 7 contains ν(CtN) at 2122 cmꢀ1 and
additional absorptions at 3300ꢀ3450 and 1500 cmꢀ1 due to the
NꢀH and CdC stretches, respectively, similar to those observed
for the crotononitrileamido complex above. The 1H NMR
spectrum shows single (C5Me5)1ꢀ and methylene resonances,
as well as a complicated aromatic region consistent with the
composition of 7. Singlets at 6.75 and 4.84 ppm are assigned to
the CdCH proton (confirmed by HMQC) and NH proton,
respectively. The 13C NMR spectrum is consistent with this and
additionally shows a doublet at 182.6 ppm (2JCY = 2.5 Hz) for the
nitrile CtN carbon.
Structural Features. Because most of the structural features in
1ꢀ3 and 5ꢀ7 are in the normal range (Tables S2ꢀS6 in the
Supporting Information), only a few select data will be discussed.
For all of these complexes, the metallocene units have structural
parameters within previously reported ranges.37,38 For example,
complex 1 (Figure 1) displays typical 2.367 and 2.377 Å Yꢀ
(C5Me5 ring centroid) lengths and a 137.7° (C5Me5 ring
centroid)ꢀYꢀ(C5Me5 ring centroid) bond angle.
The central YC3N2 core in 5 has Y1/C35/C21/C22/N1/N2
bond angles within the range of 115.26(11)ꢀ124.43(11)° and a
planar arrangement of these atoms, indicative of sp2-hybridized
carbon and nitrogen atoms. Along with the 1.346(2) Å C21ꢀ
C35 and 1.306(2) Å C22ꢀN1 double bonds, the 1.478(2) Å
C21ꢀC22 and 1.400(2) Å C22ꢀN2 lengths are consistent with
single bonds and are indicative of the localized structure shown in
Scheme 4 for the iminovinyl ligand. The shorter than expected
2.429(1) Å Y1ꢀC21 length and long 2.436(1) Å Y1ꢀN1 value
support this assignment and suggest that the negative charge
of the ligand resides more on C21 than N1. This situation is
in contrast to the delocalized azaallyl ligand in (C5H5)2Y-
[tBuNC(Me)CHPh](THF),44 which has a similar YCCN core
motif with 2.366(4) Å YꢀN and 2.613(6) Å YꢀC bonds. These
distances can also be compared with the YꢀN lengths of the
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Scheme 5. One Possible Mechanism for the Formation of 4 and 5
Scheme 6. Possible Mechanism for the Formation of 7
amidinate ligand in 3, which are in the range of 2.364(1)ꢀ2.384(1) Å.
The C6 ring of 5 derived from deprotonation of the cyclo-
hexyl group on the carbodiimide substrate now contains an sp2-
hybridized carbon atom bound to nitrogen, as evidenced by the
125.77(12)° and 119.69(12)° angles defined by N2ꢀC23ꢀC24
and N2ꢀC23ꢀC28, respectively, and the shorter 1.274(2) Å
N2ꢀC23 bond length, compared to the 1.474(2) Å N1ꢀC29
length.
Y1ꢀN1 amido and 1.162(3) Å C23ꢀN2 nitrile lengths in 7 are
similar to those in the crotononitrile complex (2.344(4) and
1.156(6) Å). In 7, the 2.351(2) Å N2ꢀY10 length is shorter and
the 149.9° Y1ꢀN1ꢀC21 angle larger than those observed in the
crotononitrile complex of 2.460(4) Å and 143.1(3)°, respec-
tively, which could be due to the differing steric bulk of the
ligands in the two complexes.
The X-ray structure of [(C5Me5)2Y{μ-N(H)C(CH2Ph)dC-
[C(Ph)dCHPh]CtN}]2, 7 (Figure 6), revealed that the newly
formed amidonitrile ligand bridged two yttrium metallocene
units to form a dimer with a crystallographically imposed inver-
sion center. The YC3N2 core bears the hallmarks of the croto-
nonitrile ligand in the yttrium complex {[Me2Si(NCMe3)-
(OCMe3)]2Y[(μ-N,N0)-N(H)C(Me)dC(H)CtN]}2.36 The
short 1.326(3) Å N1ꢀC21 and 1.398(4) Å C22ꢀC23 (typical
Csp2ꢀN and Csp2ꢀCsp lengths are 1.36ꢀ1.38 and 1.43 Å,
respectively) and long 1.417(4) Å C21ꢀC22 bond lengths
(a typical Csp2dCsp2 length is 1.33 Å)43 are indicative of charge
delocalization across the central ligand core. This is similar to the
crotononitrile complex, which displays comparable lengths of
1.331(6), 1.393(7), and 1.375(7) Å, respectively. The 2.366(2) Å
’ DISCUSSION
The allyl complex (C5Me5)2Y(η3-CH2CHCH2)(THF) func-
tions as an effective alkyl synthon in Scheme 3 to deprotonate
HCtCPh to make the alkynide (C5Me5)2Y(CtCPh)(THF), 1.
Surprisingly, when the reaction is done in hexane, the unsolvated
trienediyl, [(C5Me5)2Y]2(μ-η2:η2-PhCdCdCdCPh), 2, can
be isolated, despite the presence of THF. Formation of trienediyl
complexes from unsolvated “[(C5Me5)2LnCtCPh]” precursors
is well-known, but usually the presence of an equivalent of THF
inhibits this conversion.23
The reactions of tBuNdCdNtBu with 1 and iPrNdCdNiPr
with 2, eqs 1 and 2, respectively, involve conventional insertions
to form amidinates, which require heating as previously reported.18
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However, in the case of isopropyl and cyclohexyl carbodiimide
reactions with 1 (Scheme 4), an unexpected CꢀH activation
occurs upon mixing at room temperature and the iminovinyl
products (C5Me5)2Y[C(dCHPh)C(NdCMe2)dNiPr-k2C,N],
4, and (C5Me5)2Y{C(dCHPh)C[NdC(CH2)5]dN(Cy)-k2-
C,N}, 5, are obtained. The reaction is formally an organometallic
version of the Alder-ene reaction (Scheme 2). Because typical
CdN insertion has been observed with less substituted cyclo-
pentadienyl complexes, it is possible that the steric profile of the
pentamethylcyclopentadienyl auxiliary ligands allows the ob-
served CꢀH activation to occur.
’ ACKNOWLEDGMENT
We thank the Chemical Sciences, Geosciences, and Bio-
sciences Division of the Office of Basic Energy Sciences of the
Department of Energy for support, Dr. Katy L. Bridgwood for
helpful discussions, and Dr. Phil Dennison for help with NMR
experiments.
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One scenario by which the product could form is shown in
Scheme 5. Initial displacement of the coordinated THF in 1 by
the carbodiimide seems plausible. If the carbodiimide aligns with
the alkynide as shown, the intermediate is set up for an Alder-ene
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(Ph)dCHPh]CtN}]2, 7, from the reaction of 1 with benzylni-
trile (eq 3) can be explained along similar lines, and one possible
mechanism is shown in Scheme 6. Although there are many
pathways by which complex 7 could be formed in this fast
reaction, displacement of THF by the nitrile and insertion seem
most likely for the initial steps. Subsequent alignment of a second
benzylnitrile with the iminoalkyne ligand formed by the initial
insertion could lead to benzylcyanide addition across the alkyne.
A subsequent 1,5-hydrogen shift and dimerization would give the
observed product. The insertion step and a 1,3-H shift are
components in the previously observed formation of the croto-
nonitrile-containing complex {[Me2Si(NCMe3)(OCMe3)]2Y-
[(μ-N,N0)-N(H)C(Me)dC(H)CtN]}2.36
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’ CONCLUSIONS
Carbodiimide insertion into rare earthꢀcarbon bonds of rare
earth metallocene alkynide complexes can take an unexpected
turn when reagents with secondary alkyl groups are present. As
shown with (C5Me5)2Y(CtCPh)(THF), 1, CꢀH activation
can occur in an organometallic Alder-ene reaction to make
iminovinyl products. Alkynide 1 can also display reactivity
beyond conventional insertion with nitriles, as shown by the for-
mation of the amido nitrile, [(C5Me5)2Y{μ-N(H)C(CH2Ph)d
C[C(Ph)dCHPh]CtN}]2, 7. In each of these reactions, the
yttrium metallocene unit functions as an anchor point to facilitate
the reactivity between the unsaturated organic ligands.
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’ ASSOCIATED CONTENT
(24) Evans, W. J.; Kozimor, S. A.; Brady, J. C.; Davis, B. L.; Nyce,
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S
Supporting Information. X-ray data collection (Table
b
S1), selected metrical parameters (Tables S2ꢀS6), and structure
determination and refinement parameters for 1ꢀ3 and 5ꢀ7.
This material is available free of charge via the Internet at http://
pubs.acs.org. CCDC 824449-824454 contains the supplemen-
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obtained free of charge from the Cambridge Crystallographic
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’ AUTHOR INFORMATION
Corresponding Author
*E-mail: wevans@uci.edu.
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