Synthesis and characterization of a gold vinylidene complex lacking π-conjugated heteroatoms

Article abstract of DOI:10.1002/anie.201501474

Abstract Hydride abstraction from the gold (disilyl)ethylacetylide complex [(P)Au{η¹-C≡CSi(Me)₂CH₂CH₂SiMe₂H}] (P=P(tBu)₂o-biphenyl) with triphenylcarbenium tetrakis(pentafluorophenyl)borate at -20 °C formed the cationic gold (β,β-disilyl)vinylidene complex [(P)Au=C=CSi(Me)₂CH₂CH₂Si(Me)₂]⁺B(C₆F₅)₄^- with ≥90% selectivity. ²⁹Si NMR analysis of this complex pointed to delocalization of positive charge onto both the β-silyl groups and the (P)Au fragment. The C1 and C2 carbon atoms of the vinylidene complex underwent facile interconversion (ΔG^≠=9.7 kcal mol^-1), presumably via the gold π-disilacyclohexyne intermediate [(P)Au{η²-C≡CSi(Me)₂CH₂CH₂Si(Me)₂}]⁺B(C₆F₅)₄^-. Good as gold: Cationic gold (β,β-disilyl)vinylidene complex 1 was generated by addition of a pendant silylium ion to the C≡C bond of a gold acetylide complex (see scheme, P=PtBu₂(o-biphenyl)). The vinylidene C1 and C2 atoms of 1 undergo facile interconversion, presumably via a π-disilacyclohexyne intermediate. ²⁹Si NMR analysis of 1 indicates delocalization of positive charge onto both the β-silyl groups and the (P)Au fragment.

Full text of DOI:10.1002/anie.201501474

Angewandte
Chemie
International Edition: DOI: 10.1002/anie.201501474
German Edition: DOI: 10.1002/ange.201501474
Gold Complexes
Synthesis and Characterization of a Gold Vinylidene Complex Lacking
p-Conjugated Heteroatoms**
Robert J. Harris and Ross A. Widenhoefer*
Abstract: Hydride abstraction from the gold (disilyl)ethylace-
1
ꢀ
tylide complex [(P)Au{h -C CSi(Me)2CH2CH2SiMe2H}]
(P = P(tBu)2o-biphenyl) with triphenylcarbenium tetrakis-
(pentafluorophenyl)borate at À208C formed the cationic
= =
[(P)Au C
gold
(b,b-disilyl)vinylidene
complex
CSiK(Me)2CH2CH2SiL(Me)2]+B(C6F5)4 with ꢁ 90% selectivity.
29Si NMR analysis of this complex pointed to delocalization of
positive charge onto both the b-silyl groups and the (P)Au
fragment. The C1 and C2 carbon atoms of the vinylidene
complex underwent facile interconversion (DG° = 9.7 kcal
molÀ1), presumably via the gold p-disilacyclohexyne inter-
À
Scheme 1. Recent examples of gold carbenoid complexes (L=N-heter-
ocyclic carbene or tertiary phosphine).[5–9]
Cy = cyclohexyl), which are significantly biased toward the
oxonium/iminium contributor E’ owing to the presence of two
p-conjugated heteroatoms (Scheme 1).[16] Herein we report
the synthesis and characterization of a cationic gold vinyli-
dene complex that lacks p-conjugated heteroatoms.
Toward the generation of a cationic gold vinylidene
complex lacking p-conjugated heteroatoms, we targeted gold
(b,b-disilyl)vinylidene complexes generated by addition of
2
+
À
ꢀ
mediate [(P)Au{h -CK CSi(Me)2CH2CH2SiL(Me)2}] B(C6F5)4
.
C
ationic gold carbene complexes are widely invoked as
intermediates in a range of gold-catalyzed transformations
including enyne[1] and propargyl carboxylate cycloaddition,[2]
alkyne oxidation,[3] and alkene cyclopropanation.[4,5]
Although the intermediacy of gold carbenes in these trans-
formations is generally accepted, there remains considerable
ꢀ
a pendant silylium ion to the C C bond of a gold acetylide
complex. This approach was inspired by studies from the
research groups of Lambert,[17] Siehl,[18,19] and Müller,[19–23]
who have both documented and exploited the stabilization of
alkyl and vinyl carbenium ions by b-SiC hyperconjugation.[24]
To this end, treatment of disilylethylacetylene 1 with nBuLi
followed by auration of the resulting lithium acetylide with
À
debate regarding the electronic structure of the Au C
bond,[6–9] due in large part to the dearth of suitable model
complexes for structural and/or spectroscopic interrogation.
It is therefore significant that within the past year well-
defined gold carbene complexes that 1) lack p-conjugated
heteroatoms (A, B),[7,10] 2) display alkylidene transfer behav-
ior (C),[8] or 3) contain a cyclopropyl group at C1 (D)[9] have
been reported (Scheme 1), which provide new insight into the
electronic structure and behavior of gold carbene com-
[(P)AuCl] (P = P(tBu)2o-biphenyl) led to isolation of the gold
1
ꢀ
(disilylethyl)acetylide
complex
[(P)Au{h -C CSi(Me)2-
CH2CH2SiMe2H}] (2) in 36% yield (Scheme 2). Treatment
of 2 with triphenylcarbenium tetrakis(pentafluorophenyl)bo-
rate in CD2Cl2 at À208C for 10 min led to hydride abstraction
and cyclization, presumably via the transient silylium ion
species I, to form the (b,b-disilyl)vinylidene complex 3 with
ꢁ 90% selectivity, as determined by 31P NMR analysis.[25]
Although 3 was stable in solution for short periods
(ꢂ 5 min) at room temperature, concentration or attempted
precipitation at À208C led to rapid decomposition, and 3 was
therefore characterized in solution by spectroscopy. The low-
temperature (À808C) 31P and 29Si NMR spectra of 3 displayed
single resonances at d = 58.3 and d = 33.5, respectively, and
plexes.[11,12]
+
= =
Gold vinylidene complexes of the form [(L)Au C CR2]
constitute a particularly intriguing class of gold carbene
complexes that have attracted considerable recent interest.
These species have been invoked as intermediates in
a number of transformations,[13] most notably the gold-
catalyzed polycyclization of o-dialkynyl arenes.[14] Although
the existence of gold vinylidene complexes is supported by
both indirect experimental evidence and computation,[14]
direct experimental evidence for these complexes is
absent.[15] The only relevant model complexes are the
Fischer-type gold allenylidene complexes E (L = IPr or
PCy3; IPr= 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene,
[*] R. J. Harris, Prof. R. A. Widenhoefer
French Family Science Center, Duke University
Durham, NC 27708-0346 (USA)
E-mail: rwidenho@chem.duke.edu
[**] We acknowledge the NSF (CHE-1213957) for support of this
research.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201501474.
Scheme 2. Synthesis of gold (b,b-disilyl)vinylidene complex 3.
Angew. Chem. Int. Ed. 2015, 54, 6867 –6869
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6867

.
Angewandte
Communications
Scheme 4. Fluxional behavior of gold vinylidene isotopomer [1,2-13C2]-
3.
vinylidene carbon atoms of 3 involves 1,2-silyl migration to
generate the unobserved gold h2-disilacyclohexyne intermedi-
2
+
À
ꢀ
ate [(P)Au{h -CK CSi(Me)2CH2CH2SiL(Me)2}] B(C6F5)4 (II;
Scheme 4).[28] Similar fluxional behavior has been documented
for b,b-disilylvinyl cations possessing an a-SiR3 or a-GeR3
group.[23]
Scheme 3. Resonance contributors to gold vinylidene complex 3 along
with vinyl cations 4 and 5.
the 1H NMR spectrum of 3 at À808C displayed a 9:2:6 ratio of
resonances at d = 1.31 (d, JPH = 15.5 Hz), 1.14 (s), and 0.47 (s)
corresponding to the tert-butyl, Si-CH2, and Si-CH3 protons,
respectively. Together, these spectroscopic features estab-
lished both the cyclization of 2 and the high symmetry (static
or time-averaged) of gold vinylidene complex 3. The signifi-
cant downfield shift of the 29Si NMR resonance of 3 relative to
the C(sp)-Si resonance of neutral acetylide precursor 2 (d =
À20.6; Dd =+ 54) points to accumulation of positive charge
on the b-silicon atoms of 3, as represented by resonance
structures 3c and 3d (Scheme 3). A number of studies have
shown that b-SiC hyperconjugation in b-silyl-substituted
carbenium ions increases with the increasing electron
demand of the electron-deficient carbon atom.[26] Müller
et al. extended and quantified this relationship by establishing
a correlation between the downfield shift of the 29Si NMR
chemical shift (Dd) of the a-aryl-b,b-disilylvinyl cations 4
relative to their neutral arylacetylene precursors versus the
Hammett s+ parameter.[22] It is therefore worth noting that
the Dd value for 3 is significantly less than that of the
analogous a-tert-butyl-b,b-disilylvinyl cation 5 (Dd = 86),[23,27]
which suggests that the electron-donor ability of the (P)Au
fragment in 3 significantly exceeds that of a tert-butyl group,
in accord with our previous analysis of Au !C electron
donation in the cyclopropyl carbene complex D.[9] The IR
spectrum of 3 displayed an absorbance at 1955 cmÀ1 assigned
In summary, we have synthesized the gold (b,b-disilyl)vi-
nylidene complex 3 by hydride abstraction/cyclization of
neutral gold acetylide complex 2. Complex 3 represents the
first example of a gold vinylidene complex and a rare example
of a gold carbene complex that lacks p-conjugated heter-
oatoms.[7,10] The C1 and C2 vinylidene atoms of 3 undergo
facile interconversion (DG°183K = 9.7 kcalmolÀ1), presumably
via the gold p-disilacyclohexyne intermediate II. 29Si NMR
analysis of 3 points to delocalization of positive charge onto
both the b-silyl groups and the (P)Au fragment. Ongoing
efforts are directed toward further quantifying the extent of
Au!C electron donation in these complexes.
Keywords: bonding modes · carbene ligands · carbenoids ·
gold · vinylidenes
How to cite: Angew. Chem. Int. Ed. 2015, 54, 6867–6869
Angew. Chem. 2015, 127, 6971–6973
[1] a) C. Obradors, A. M. Echavarren, Acc. Chem. Res. 2014, 47,
902 – 912; b) A. Fürstner, Acc. Chem. Res. 2014, 47, 925 – 938;
c) P. Y. Toullec, V. Michelet, Top. Curr. Chem. 2011, 302, 31 – 80;
d) A. M. Echavarren, E. JimØnez-NfflÇez, Top. Catal. 2010, 53,
924 – 930; e) A. Fürstner, Chem. Soc. Rev. 2009, 38, 3208 – 3221;
f) E. JimØnez-NfflÇez, A. M. Echavarren, Chem. Rev. 2008, 108,
3326 – 3350; g) V. Michelet, P. Y. Toullec, J. P. GenÞt, Angew.
Chem. Int. Ed. 2008, 47, 4268 – 4315; Angew. Chem. 2008, 120,
4338 – 4386.
[2] A. Correa, N. Marion, L. Fensterbank, M. Malacria, S. P. Nolan,
L. Cavallo, Angew. Chem. Int. Ed. 2008, 47, 718 – 721; Angew.
Chem. 2008, 120, 730 – 733.
[3] D. Qian, J. Zhang, Chem. Soc. Rev. 2015, 44, 677 – 698.
[4] a) L. Zhang, Acc. Chem. Res. 2014, 47, 877 – 888; b) H.-S. Yeom,
S. Shin, Acc. Chem. Res. 2014, 47, 966 – 977.
=
to the vinylidene C C stretch, which is similar to those
observed for cations 4.[21]
Although the 13C NMR spectrum of 3 at À908C was
likewise consistent with a highly symmetric structure, the key
C1 and C2 vinylidene resonances could not be detected, even
upon extended acquisition. However, 13C NMR analysis of
the doubly labeled isotopomer [1,2-13C2]-3 at À908C dis-
[5] For general reviews of gold catalysis, see a) M. Bandini, Chem.
´
Soc. Rev. 2011, 40, 1358 – 1367; b) A. Corma, A. Leyva-Perez,
played broad multiplets at d = 206 (dd, JCP = 110 Hz, JCC
=
M. J. Sabater, Chem. Rev. 2011, 111, 1657 – 1712; c) M. Rudolph,
A. S. K. Hashmi, Chem. Commun. 2011, 47, 6536 – 6544; d) N.
Krause, C. Winter, Chem. Rev. 2011, 111, 1994 – 2009; e) T. C.
Boorman, I. Larrosa, Chem. Soc. Rev. 2011, 40, 1910 – 1925; f) A.
Pradal, P. Y. Toullec, V. Michelet, Synthesis 2011, 1501 – 1514.
[6] a) A. S. K. Hashmi, Angew. Chem. Int. Ed. 2008, 47, 6754 – 6756;
Angew. Chem. 2008, 120, 6856 – 6858; b) A. Fürstner, L.
Morency, Angew. Chem. Int. Ed. 2008, 47, 5030 – 5033; Angew.
Chem. 2008, 120, 5108 – 5111; c) A. M. Echavarren, Nat. Chem.
2009, 1, 431 – 433; d) G. Seidel, R. Mynott, A. Fürstner, Angew.
Chem. Int. Ed. 2009, 48, 2510 – 2513; Angew. Chem. 2009, 121,
2548 – 2551; e) D. Benitez, N. D. Shapiro, E. Tkatchouk, Y.
Wang, W. A. Goddard, F. D. Toste, Nat. Chem. 2009, 1, 482 – 486;
60 Hz) and d = 112 (d, JCC = 60 Hz) corresponding to the
vinylidene C1 and C2 atoms, respectively (Scheme 4). As the
temperature was raised, these resonances broadened further
and disappeared into the baseline between À70 and À508C.
Although these resonances did not coalesce at 258C, they
reappeared unchanged when the solution was again cooled to
À908C. 13C-Spin saturation transfer analysis of [1,2-13C2]-3 at
À908C confirmed interconversion of the C1 and C2 vinyli-
dene carbon atoms and established an energy barrier of
DG°183K = 9.7 kcalmolÀ1 for this process. The simplest mech-
anism that accounts for interconversion of the C1 and C2
6868 www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 6867 –6869

Angewandte
Chemie
f) G. Seidel, B. Gabor, R. Goddard, B. Heggen, W. Thiel, A.
Fürstner, Angew. Chem. Int. Ed. 2014, 53, 879 – 882; Angew.
Chem. 2014, 126, 898 – 901; g) G. Ciancaleoni, L. Biasiolo, G.
Bistoni, A. Macchioni, F. Tarantelli, D. Zuccaccia, L. Belpassi,
Chem. Eur. J. 2015, 21, 2467 – 2473.
Mader, S. Moghimi, M. Rudolph, I. Braun, F. Rominger, A. S. K.
Hashmi, Adv. Synth. Catal. 2015, 357, 500 – 506; p) J. Bucher, T.
Stçßer, M. Rudolph, F. Rominger, A. S. K. Hashmi, Angew.
Chem. Int. Ed. 2015, 54, 1666 – 1670; Angew. Chem. 2015, 127,
1686 – 1690; q) P. Morµn-Poladura, E. Rubio, J. M. Gonzµlez,
Angew. Chem. Int. Ed. 2015, 54, 3052 – 3055; Angew. Chem.
2015, 127, 3095 – 3098.
[7] M. W. Hussong, F. Rominger, P. Krämer, B. F. Straub, Angew.
Chem. Int. Ed. 2014, 53, 9372 – 9375; Angew. Chem. 2014, 126,
9526 – 9529.
[8] G. Seidel, A. Fürstner, Angew. Chem. Int. Ed. 2014, 53, 4807 –
4811; Angew. Chem. 2014, 126, 4907 – 4911.
[15] For recent reviews of transition-metal vinylidene complexes, see
a) J. M. Lynam, Chem. Eur. J. 2010, 16, 8238 – 8247; b) B. M.
Trost, A. McClory, Chem. Asian J. 2008, 3, 164 – 194.
[16] a) M. M. Hansmann, F. Rominger, A. S. K. Hashmi, Chem. Sci.
2013, 4, 1552 – 1559; b) X.-S. Xiao, W.-L. Kwong, X. Guan, C.
Yang, W. Lu, C.-M. Che, Chem. Eur. J. 2013, 19, 9457 – 9462.
[17] a) J. B. Lambert, Y. Zhao, H. Wu, J. Org. Chem. 1999, 64, 2729 –
2736; b) J. B. Lambert, Y. Zhao, J. Am. Chem. Soc. 1996, 118,
7867 – 7868.
[18] a) H.-U. Siehl, F.-P. Kaufmann, Y. Apeloig, V. Braude, D.
Danovich, A. Berndt, N. Stamatis, Angew. Chem. Int. Ed. Engl.
1991, 30, 1479 – 1482; Angew. Chem. 1991, 103, 1546 – 1549;
b) H.-U. Siehl, F.-P. Kaufmann, J. Am. Chem. Soc. 1992, 114,
4937 – 4939; c) H.-U. Siehl, F.-P. Kaufmann, K. Hori, J. Am.
Chem. Soc. 1992, 114, 9343 – 9349; d) H.-U. Siehl, Pure Appl.
Chem. 1995, 67, 769 – 775; e) H.-U. Siehl, S. Brixnera, C. Coletti,
N. Reb, B. Chiavarinoc, M. E. Crestonic, A. De Petris, S.
Fornarini, Int. J. Mass Spectrom. 2013, 334, 58 – 66.
[9] R. E. M. Brooner, R. A. Widenhoefer, Chem. Commun. 2014,
50, 2420 – 2423.
[10] R. J. Harris, R. A. Widenhoefer, Angew. Chem. Int. Ed. 2014, 53,
9369 – 9371; Angew. Chem. 2014, 126, 9523 – 9525.
[11] For gas-phase studies of gold carbene complexes, see a) A.
Fedorov, M.-E. Moret, P. Chen, J. Am. Chem. Soc. 2008, 130,
8880 – 8881; b) A. Fedorov, P. Chen, Organometallics 2009, 28,
1278 – 1281; c) L. Batiste, A. Fedorov, P. Chen, Chem. Commun.
2010, 46, 3899 – 3901; d) A. Fedorov, L. Batiste, A. Bach, D. M.
Birney, P. Chen, J. Am. Chem. Soc. 2011, 133, 12162 – 12171;
e) D. H. Ringger, P. Chen, Angew. Chem. Int. Ed. 2013, 52, 4686 –
4689; Angew. Chem. 2013, 125, 4784 – 4787; f) D. H. Ringger, I. J.
Kobylianskii, D. Serra, P. Chen, Chem. Eur. J. 2014, 20, 14270 –
14281; g) L. Batiste, P. Chen, J. Am. Chem. Soc. 2014, 136, 9296 –
9307.
[19] T. Müller, R. Meyer, D. Lennartz, H.-U. Siehl, Angew. Chem. Int.
Ed. 2000, 39, 3074 – 3077; Angew. Chem. 2000, 112, 3203 – 3206.
[20] a) H.-U. Steinberger, T. Müller, N. Auner, C. Maerker, P. von R.
Schleyer, Angew. Chem. Int. Ed. Engl. 1997, 36, 626 – 628;
Angew. Chem. 1997, 109, 667 – 669; b) A. Klaer, W. Saak, D.
Haase, T. Müller, J. Am. Chem. Soc. 2008, 130, 14956 – 14957;
c) T. Müller, C. Bauch, M. Ostermeier, M. Bolte, N. Auner, J.
Am. Chem. Soc. 2003, 125, 2158 – 2168; d) T. Müller, M. Juhasz,
C. A. Reed, Angew. Chem. Int. Ed. 2004, 43, 1543 – 1546; Angew.
Chem. 2004, 116, 1569 – 1572.
[21] A. Klaer, T. Müller, J. Phys. Org. Chem. 2010, 23, 1043 – 1048.
[22] T. Müller, D. Margraf, Y. Syha, J. Am. Chem. Soc. 2005, 127,
10852 – 10860.
[23] A. Klaer, Y. Syha, H. R. Nasiri, T. Müller, Chem. Eur. J. 2009, 15,
8414 – 8423.
[12] For additional examples of heteroatom-stabilized gold carbenes,
see a) L.-P. Liu, B. Xu, M. S. Mashuta, G. B. Hammond, J. Am.
Chem. Soc. 2008, 130, 17642 – 17643; b) M. N. FaÇanµs-Mastral,
F. Aznar, Organometallics 2009, 28, 666 – 668; c) U. Schubert, K.
Ackermann, R. Aumann, Cryst. Struct. Commun. 1982, 11, 591 –
594; d) G. Ung, G. Bertrand, Angew. Chem. Int. Ed. 2013, 52,
11388 – 11391; Angew. Chem. 2013, 125, 11599 – 11602.
[13] a) Y. Xia, A. S. Dudnik, Y. Li, V. Gevorgyan, Org. Lett. 2010, 12,
5538 – 5541; b) V. Lavallo, G. D. Frey, S. Kousar, B. Donnadieu,
G. Bertrand, Proc. Natl. Acad. Sci. USA 2007, 104, 13569 –
13573; c) H. Rabaâ, B. Engels, T. Hupp, A. S. K. Hashmi, Int.
J. Quantum Chem. 2007, 107, 359 – 365; d) V. Mamane, P.
Hannen, A. Fürstner, Chem. Eur. J. 2004, 10, 4556 – 4575; e) E.
Soriano, J. Marco-Contelles, Organometallics 2006, 25, 4542 –
4553; f) I. V. Seregin, V. Gevorgya, J. Am. Chem. Soc. 2006, 128,
12050 – 12051.
[14] a) A. Gómez-Suµrez, S. P. Nolan, Angew. Chem. Int. Ed. 2012,
51, 8156 – 8159; Angew. Chem. 2012, 124, 8278 – 8281; b) L. Ye,
Y. Wang, D. H. Aue, L. Zhang, J. Am. Chem. Soc. 2012, 134, 31 –
34; c) A. S. K. Hashmi, M. Wieteck, I. Braun, M. Rudolph, F.
Rominger, Angew. Chem. Int. Ed. 2012, 51, 10633 – 10637;
Angew. Chem. 2012, 124, 10785 – 10789; d) A. S. K. Hashmi, M.
Wieteck, I. Braun, P. Nçsel, L. Jongbloed, M. Rudolph, F.
Rominger, Adv. Synth. Catal. 2012, 354, 555 – 562; e) M. M.
Hansmann, M. Rudolph, F. Rominger, A. S. K. Hashmi, Angew.
Chem. Int. Ed. 2013, 52, 2593 – 2598; Angew. Chem. 2013, 125,
2653 – 2659; f) I. Braun, A. M. Asiri, A. S. K. Hashmi, ACS
Catal. 2013, 3, 1902 – 1907; g) P. Nçsel, T. Lauterbach, M.
Rudolph, F. Rominger, A. S. K. Hashmi, Chem. Eur. J. 2013,
19, 8634 – 8641; h) M. M. Hansmann, S. Tsupova, M. Rudolph, F.
Rominger, A. S. K. Hashmi, Chem. Eur. J. 2014, 20, 2215 – 2223;
i) A. S. K. Hashmi, Acc. Chem. Res. 2014, 47, 864 – 876; j) J.
Bucher, T. Wurm, K. S. Nalivela, M. Rudolph, F. Rominger,
A. S. K. Hashmi, Angew. Chem. Int. Ed. 2014, 53, 3854 – 3858;
Angew. Chem. 2014, 126, 3934 – 3939; k) H. M. Vilhelmsen,
A. S. K. Hashmi, Chem. Eur. J. 2014, 20, 1901 – 1908; l) J. Xie, C.
Pan, A. Abdukadera, C. Zhu, Chem. Soc. Rev. 2014, 43, 5245 –
5256; m) O. J. S. Pickup, I. Khazal, E. J. Smith, A. C. Whitwood,
J. M. Lynam, K. Bolaky, T. C. King, B. W. Rawe, N. Fey,
Organometallics 2014, 33, 1751 – 1761; n) Y. Tokimizu, M.
Wieteck, M. Rudolph, S. Oishi, N. Fujii, A. S. K. Hashmi, H.
Ohno, Org. Lett. 2015, 17, 604 – 607; o) P. Nçsel, V. Müller, S.
[24] J. B. Lambert, Tetrahedron 1990, 46, 2677 – 2689.
[25] The length of the alkyl chain connecting the two silicon atoms
was critical to successful formation of a stable gold vinylidene
complex. For example, hydride abstraction from the (disilylme-
1
ꢀ
thyl)acetylide complex [(P)Au{h -C CSi(Me)2CH2SiMe2H}]
formed no detectable vinylidene complex, whereas preliminary
investigation of hydride abstraction from the corresponding
(disilylpropyl)acetylide
complex
[(P)Au{h1-C ꢀ CSi(Me)2-
(CH2)3SiMe2H}] suggested formation of
a ground-state p-
disilacycloheptyne complex.[28]
[26] a) W. Zhang, J. A. Stone, M. A. Brook, G. A. McGibbon, J. Am.
Chem. Soc. 1996, 118, 5764 – 5771; b) X. Li, J. A. Stone, J. Am.
Chem. Soc. 1989, 111, 5586 – 5592; c) H.-U. Siehl in Dicoordi-
nated Carbocations (Eds.: Z. Rappoport, P. J. Stang), Wiley, New
York, 1997, p. 189.
[27] Unfortunately, no correlation between the Dd and s+ values has
been established for a-aryl-b,b-disilylvinyl cations in which the
b-silicon atoms are part of a five-membered ring, such as in 3 and
5. As such, no definitive assignment of the electron-donor ability
of the (P)Au fragment of 3 can be determined from these data.
[28] For an example of a neutral gold p-cycloheptyne complex and
a cationic p-bis(tert-butyldimethylsilyl)acetylene complex, see
a) P. Schulte, U. Behrens, Chem. Commun. 1998, 1633 – 1634;
b) D. Zhu, X. Cao, B. Yu, Org. Chem. Front. 2015, 2, 369 – 365.
Received: February 14, 2015
Published online: April 23, 2015
Angew. Chem. Int. Ed. 2015, 54, 6867 –6869
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 6869