π-Complexes from acyl cyanides and lithium dimethylcuprate(i)

Article abstract of DOI:10.1039/c3cc40602d

Rapid injection of pyruvonitrile or benzoyl cyanide into solutions of Me₂CuLi in THF-d₈ at -100 °C gave complexes that were stable at this temperature. 1D NMR with multiply labelled substrates ( ¹³C/¹⁵N) and 2D

Full text of DOI:10.1039/c3cc40602d

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p-Complexes from acyl cyanides and lithium
dimethylcuprate(I)†
Cite this: Chem. Commun., 2013,
49, 3010
Steven H. Bertz,* Richard A. Hardin, Michael D. Murphy and Craig A. Ogle*
Received 24th January 2013,
Accepted 25th February 2013
DOI: 10.1039/c3cc40602d
www.rsc.org/chemcomm
Rapid injection of pyruvonitrile or benzoyl cyanide into solutions cuprate (À1.39 ppm) and substrate (2.45 ppm) disappeared.
of Me2CuLi in THF-d8 at À100 8C gave complexes that were stable Upon irradiation of the 1.40 ppm methyl hydrogens, those at
at this temperature. 1D NMR with multiply labelled substrates À0.08 ppm were enhanced by a NOE (cf. ESI†), which allowed us
(
13C/15N) and 2D NMR (1H/13C) identified them as the first cuprate– to assign them to Meb.
carbonyl p-complexes.
The 13C NMR spectrum of 2a had peaks at 124.83 ppm
(cyano carbon), 68.95 ppm (carbonyl carbon), 24.41 ppm
Organocuprates form p-complexes with activated alkenes and (substrate methyl), and À2.62 and À10.58 ppm (methyl groups
alkynes,1–3 which are well-characterized intermediates, thanks on copper). For the methyls on copper, an HMQC plot (cf. ESI†)
to mechanistic studies on the conjugate addition reactions of correlated the upfield 1H and 13C peaks (Mea) and likewise the
these useful reagents.4,5 We were able to extend our prepara- downfield ones (Meb).
tions of cuprate p-complexes from C–C to C–N double bonds by
Similar results were obtained upon injection of 1b, which
using isothiocyanates and azachalcones.4 In an attempt to afforded 2b (see Fig. 1 for chemical shifts). A p-complex was not
extend our studies to C–N triple bond complexes, we investi- observed from ethoxy derivative 1c under our conditions.
gated acyl cyanides and serendipitously discovered the title
compounds.‡
Rapid injection NMR has proven to be an outstanding methane (from enolate formation), ethane and acetone.
method for the preparation and characterization of thermally Complex 2b decomposed to ethane and acetophenone at
unstable and air sensitive compounds,6 for example, copper(I) À70 1C, when prepared from CuCN, or at À20 1C, when
reagents and copper(III) intermediates.7 Thus, injection of a prepared from CuI.
Complex 2a, prepared from either CuI or CuCN, decom-
posed at À70 1C to afford a mixture of products, including
solution of pyruvonitrile 1a in THF-d8 into a solution of
Triply-labelled 1b* was prepared starting from benzoic
Me2CuLiÁLiI in THF-d8–benzene-d6 (7 : 1), spinning at À100 1C acid-13C1 and K13C15N (cf. ESI†). Then, triply labelled 2b* and
under dry nitrogen in the probe of an NMR spectrometer, gave quintuply labelled 2b** were prepared from 1b* and
a new species 2a (Scheme 1), which had 1H peaks (1.40, À0.08, (CH3)2CuLi or (13CH3)2CuLi, respectively (Scheme 2). The
À0.92 ppm) that grew in rapidly (o10 s), while those for the 15N spectra were measured with a pyridine-15N1 external standard
(0.30 M in THF-d8, À100 1C) set at 318.26 ppm versus liquid
ammonia.8
Scheme 2 also lists the coupling constants that could
be measured directly from the 13C and 15N NMR spectra.
Scheme 1 Preparation of cuprate–carbonyl p-complexes 2.
Department of Chemistry, University of North Carolina at Charlotte, Charlotte,
NC 28223, USA. E-mail: sbertz1@uncc.edu, cogle@uncc.edu
Fig. 1 1H (red), 13C (blue) and 15N (magenta) NMR shifts for 1b and 2b from
CuI. (1H/13C shifts, ppm from TMS; 15N shifts for 2b**, see text.)
† Electronic supplementary information (ESI) available: Selected 1D and 2D NMR
plots. See DOI: 10.1039/c3cc40602d
c
3010 Chem. Commun., 2013, 49, 3010--3012
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Fig. 3 1H/13C HMBC plots for complex 2b. See text for explanations.
Furthermore, the 1-bond coupling for the CN group in 2b**
(1JCN = 15.1 Hz) is essentially unchanged (o10% difference in
magnitude) from its value in 1b* (1JCN = 14.1 Hz), which
indicates that the cyano group is not coordinated by copper.
Positive evidence that the carbonyl group is indeed coordi-
Scheme 2 Scalar coupling constants, JCC and JCN, measured for 2b**. (Note that
the phenyl ipso-C was not labelled, i.e., natural abundance.)
Several unresolved couplings appeared as shoulders or broad-
ening, and they were calculated by using spectral simulation nated by copper is provided by the observation of 2-bond
software (PERCH), which allowed us to estimate the 2-bond couplings between the carbonyl carbon and the carbon atoms
couplings between the carbonyl carbon and the cyano nitrogen, of Mea and Meb (2JCC = 12.7, 2.9 Hz, respectively).
2JCN E 3.7 Hz, between the carbonyl carbon and the cis-methyl
Further support is provided by the large upfield change in
group (Meb), 2JCC E 2.9 Hz, and between the two methyl groups the chemical shift of the carbonyl carbon upon complexation:
on copper (Mea–Meb), 2JCC E 4.8 Hz. As usual, this cis-coupling DCO = À106.52 ppm for 2a and DCO = À96.94 ppm for 2b. The
across Cu is much smaller than the trans-coupling.4
magnitudes (absolute values) are near the upper end of
Collecting the measured and calculated coupling constants, the range for C–C double bond complexes (DCC E À40 to
the carbonyl carbon resonance at 72 ppm for 2b** (Fig. 2) is a À120 ppm), but near the lower end of the range for complexes
complex pattern with one large (1JCC = 81.5 Hz), one medium of C–S double bonds (DCS E À95 to À180 ppm).4 In contrast,
2
(2JCC = 12.7 Hz) and two small (2JCC = 2.9 Hz, JCN = 3.7 Hz) the cyano carbon moves downfield by a relatively small amount
couplings to the cyano carbon, the trans-methyl (Mea) (DCN = 9.75, 8.88 ppm, respectively).
carbon, the cis-methyl (Meb) carbon and the cyano nitrogen,
The conclusions from the 1D NMR studies were confirmed
by 2D NMR experiments. 1H/13C HMBC mapped out the 3-bond
respectively.
The cyano 13C resonance at 123 ppm is a doublet of doublets couplings, as shown in Fig. 3. The 72 ppm 13C peak was
of doublets with coupling to the carbonyl carbon (1JCC
81.5 Hz), the cyano nitrogen (1JCN = 15.1 Hz), and the trans- phenyl ortho-hydrogens (7.29 ppm, left-hand plot). Finally,
=
assigned to the carbonyl carbon, owing to coupling with the
methyl (Mea) carbon (3JCC = 3.2 Hz, Scheme 2).
it was possible to establish that this carbon was bonded
The 15N resonance at 250 ppm for 2b** is a doublet of to copper, owing to coupling with the hydrogens of Mea
doublets with coupling to the cyano carbon (1JCN = 15.1 Hz) and (À0.66 ppm) and Meb (À0.25 ppm, right-hand plot).
carbonyl carbon (2JCN = 3.7 Hz). The magnitude of the former is
Major and minor species were not observed for 2a and 2b, as
much greater than the latter, which supports the assignment for some cuprate–enone p-complexes.4 Moreover, their
of the 123 ppm peak to the cyano carbon. (Note that there chemical shifts are independent of the copper salt (e.g., the
is no angular dependence, since the (O)C–CRN bonding 1H/13C shifts for 2b from CuCN are À0.64/À9.40 ppm for Mea
is linear).
and À0.25/2.36 ppm for Meb; see Fig. 1 for shifts from CuI).
Therefore, we believe that 2a and 2b are not aggregates in THF.9
By using rapid injection NMR, it has been possible to
prepare the first examples of organocuprate–carbonyl p-complexes,
which were characterized by using 1D and 2D NMR. These
results confirm theoretical predictions,10 and they open up
new possibilities for applications of organocopper reagents.
We thank the National Science Foundation (USA) for sup-
port of this research through grants 1012493 and 0321056.
Notes and references
‡ Our preliminary presentation discussed both possibilities, but
showed only the CN complex in the abstract: R. A. Hardin, S. H. Bertz,
M. D. Murphy, C. A. Ogle, J. D. Richter and A. A. Thomas, Abstracts of
Papers, 244th ACS National Meeting, August 19–23, 2012, ORGN-681.
Fig. 2 Measured (bottom) and calculated (top) 13C NMR resonances for the
carbonyl region of quintuply labelled 2b**. See text for J-values.
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1 G. Hallnemo, T. Olsson and C. Ullenius, J. Organomet. Chem., 1984,
265, C22–C24; B. Christenson, T. Olsson and C. Ullenius, Tetrahedron,
1989, 45, 523–534.
7 S. H. Bertz, S. Cope, M. Murphy, C. A. Ogle and B. J. Taylor, J. Am.
Chem. Soc., 2007, 129, 7208–7209; S. H. Bertz, S. Cope, D. Dorton,
M. Murphy and C. A. Ogle, Angew. Chem., Int. Ed., 2007, 46,
7082–7085; E. R. Bartholomew, S. H. Bertz, S. Cope,
M. Murphy and C. A. Ogle, J. Am. Chem. Soc., 2008, 130, 11244–
11245; E. R. Bartholomew, S. H. Bertz, S. Cope, D. C. Dorton,
M. Murphy and C. A. Ogle, Chem. Commun., 2008, 1176–1177;
E. R. Bartholomew, S. H. Bertz, S. K. Cope, M. D. Murphy,
C. A. Ogle and A. A. Thomas, Chem. Commun., 2010, 46,
1253–1254; S. H. Bertz, M. D. Murphy, C. A. Ogle and
A. A. Thomas, Chem. Commun., 2010, 46, 1255–1256; S. H. Bertz,
R. A. Hardin, M. D. Murphy, C. A. Ogle, J. D. Richter and
A. A. Thomas, J. Am. Chem. Soc., 2012, 134, 9557–9560.
2 S. H. Bertz and R. A. J. Smith, J. Am. Chem. Soc., 1989, 111,
¨
8276–8277; W. Henze, T. Gartner and R. M. Gschwind, J. Am. Chem.
Soc., 2008, 130, 13718–13726.
3 K. Nilsson, C. Ullenius and N. Krause, J. Am. Chem. Soc., 1996, 118,
4194–4195; K. Nilsson, T. Andersson and C. Ullenius, J. Organomet.
Chem., 1997, 545–546, 591–595; K. Nilsson, T. Andersson,
C. Ullenius, A. Gerold and N. Krause, Chem.–Eur. J., 1998, 4,
2051–2058.
4 S. H. Bertz, S. K. Cope, R. A. Hardin, M. D. Murphy, C. A. Ogle,
D. T. Smith, A. A. Thomas and T. N. Whaley, Organometallics, 2012,
31, 7827–7838.
5 J. Yang, D. F. Cauble, A. J. Berro, N. L. Bauld and M. J. Krische, J. Org.
Chem., 2004, 69, 7979–7984.
6 J. F. McGarrity, C. A. Ogle, Z. Brich and H. R. Loosli, J. Am. Chem.
Soc., 1985, 107, 1810–1815.
8 P. R. Srinivasan and R. L. Lichter, J. Magn. Reson., 1977, 28, 227–234.
9 R. M. Gschwind, Chem. Rev., 2008, 108, 3029–3053.
10 N. Yoshikai, R. Iida and E. Nakamura, Adv. Synth. Catal., 2008, 350,
1063–1072; N. Yoshikai and E. Nakamura, Chem. Rev., 2012, 112,
2339–2372.
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