Journal of the American Chemical Society
Communication
a
Scheme 2. Formation of 6 and 7
ACKNOWLEDGMENTS
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We thank the Leverhulme Trust, the OUP John Fell Fund, the
ARC, the EPSRC (EP/L025000/1 and EP/K014714/1, and
the NMSF, Swansea University).
REFERENCES
■
(
1) Downs, A. J.; Himmel, H.-J. In The Group 13 Metals Aluminium,
Gallium, Indium and Thallium: Chemical Patterns and Peculiarities;
Aldridge, S., Downs, A. J., Eds.; Wiley: Chichester, 2011; Chap. 1.
(2) Uhl, W.; Layh, M. In The Group 13 Metals Aluminium, Gallium,
Indium and Thallium: Chemical Patterns and Peculiarities; Aldridge, S.,
Downs, A. J., Eds.; Wiley: Chichester, 2011; Chap. 1.
(
3) See, for example: Knight, L. B., Jr.; Banisaukas, J. J., III; Babb, R.;
Davidson, E. R. J. Chem. Phys. 1996, 105, 6607.
4) (a) Protchenko, A. V.; Dange, D.; Harmer, J. R.; Tang, C. Y.;
(
Schwarz, A. D.; Kelly, M. J.; Phillips, N.; Tirfoin, R.; Birjkumar, K. H.;
Jones, C.; Kaltsoyannis, N.; Mountford, P.; Aldridge, S. Nat. Chem.
2014, 6, 315. (b) This synthetic route utilizes a boryllithium reagent:
Segawa, Y.; Yamashita, M.; Nozaki, K. Science 2006, 314, 113.
(5) For reviews of Main Group radical chemistry, see, for example:
(a) Power, P. P. Chem. Rev. 2003, 103, 789. (b) Lee, V. Y.; Sekiguchi,
A. Acc. Chem. Res. 2007, 40, 410. For a review of singlet diradicaloid
chemistry, see: (c) Rodriguez, A.; Prasang, C.; Gandon, V.; Bourg, J.-
B.; Bertrand, G. A.C.S. Sym. Ser. 2007, 917, 81.
a
Key reagents and conditions: (i) 2,3-dimethylbutadiene (2 equiv),
C D , 50 °C, 4 h, 69% yield of 6, (7% of 7). Molecular structures of 6
6
6
and 7 as determined by X-ray crystallography. Key bond lengths (Å)
and angles (°): for 6, Tl(1)−B 2.259(1) and 2.262(3), Tl(1)−C(79)
2
.299(3), B(3)−C(82) 1.570(4), B(42)−Tl(1)−B(75) 150.9(1); for
, B(1)−N 1.434(1) and 1.429(1), B(1)−C(27) 1.579(1).
7
times. The facts that (i) 6 and 7 both feature trans-
functionalized alkene cores similar to 4-Ga and 4-In and (ii)
B−C bond formation between adjacent (nucleophilic) alkyl and
electrophilic boron-based ligands is known to be facile at
transition metal centers suggest a mechanism for the formation
of 6/7 involving initial generation of doubly metalated 4-Tl,
followed by successive B−C reductive elimination steps.
(
6) Radical anions centered on the non-metal boron, such as
•−
[
BH3] , have been known for more than 30 years: Sprague, E. D.;
Williams, F. Mol. Phys. 1971, 20, 375.
(7) Other examples of Group 13 metal radicals: (a) Pluta, C.;
Po
988, 32, 388. (b) He, X.; Bartlett, R. A.; Olmstead, M. M.; Ruhlandt-
Senge, K.; Sturgeon, B. E.; Power, P. P. Angew. Chem., Int. Ed. Engl.
1993, 32, 717. (c) Dohmeier, C.; Mocker, M.; Schnockel, H.; Lotz, A.;
Schneider, U.; Alrichs, R. Angew. Chem., Int. Ed. Engl. 1993, 32, 1428.
d) Wehmschulte, R. J.; Ruhlandt-Senge, K.; Olmstead, M. M.; Hope,
̈
̈
rschke, K.-R.; Kruger, C.; Hildebrand, K. Angew. Chem., Int. Ed. Engl.
1
I
̈
̈
Decomposition of the extruded [Tl (boryl)] unit is presumably
responsible for the observed formation of thallium metal; the
occurrence of similar reductive elimination chemistry for
indium system 4-In (although clearly less facile, presumably
due to the differing redox properties of In vs Tl ) offers a
source of the [In (boryl)] units found in 5. Thus, the diene
effectively acts as a boryl ligand sink in the formation of this
cluster.
(
H.; Sturgeon, B. E.; Power, P. P. Inorg. Chem. 1993, 32, 2983. (e) Uhl,
W.; Vester, A.; Kaim, W.; Poppe, J. J. Organomet. Chem. 1993, 454, 9.
III
III
(
f) Uhl, W.; Schu
1995, 501, 79. (g) Haaland, A.; Martinsen, K.-G.; Volden, H. V.; Kaim,
W.; Waldhor, E.; Uhl, W.; Schutz, U. Organometallics 1996, 15, 1146.
̈
̈
tz, U.; Kaim, W.; Waldhor, W. J. Organomet. Chem.
I
̈
̈
(h) Uhl, W.; Cuypers, L.; Kaim, W.; Schwederski, B.; Koch, R. Angew.
Chem., Int. Ed. 2003, 42, 2422. (i) Nakamoto, M.; Yamasaki, T.;
Sekiguchi, A. J. Am. Chem. Soc. 2005, 127, 6954.
In conclusion, we report a first exploration of the reactivity of
monomeric, five-valence-electron MX radicals (M = Ga−Tl) in
bond formation processes. Bis(boryl)gallium, -indium, and
2
(
̈
8) Wiberg and Noth note that solutions of the dithallium(IV)
t
t
species, ( Bu Si) TlTl(SiBu ) , in C D are EPR active, and they make
the comment, “( Bu Si) Tl radicals?”, although no data relating to this
3
2
3
2
6
6
-
thallium systems all undergo oxidative M−C bond formation
t
•
3
2
with 2,3-dimethylbutadiene, in a manner consistent both with
putative monomeric species have been reported: Wiberg, N.;
II
the redox properties expected for M species, and with their
Amelunxen, K.; Noth, H.; Schmidt, M.; Schwenk, H. Angew. Chem.,
̈
metal-centered radical character. The weaker nature of the M−
C bond for the heavier two elements leads to the observation of
reversibility in M−C bond formation (for indium) and to the
isolation of products resulting from subsequent B−C reductive
elimination (for both indium and thallium). Further studies of
the reactivity of these radical species are in progress and will be
reported in due course.
Int. Ed. Engl. 1996, 35, 65.
(9) See, for example: Hartwig, J. F. Organotransition Metal Chemistry:
From Bonding to Catalysis; University Science Books: Mill Valley, CA,
2010.
(
10) For a recent review of carbenoid [4+1] cycloaddition chemistry,
see, for example: Tobisu, M.; Chatani, N. Chem. Lett. 2011, 40, 330.
11) (a) For a recent example in Group 13 carbenoid chemistry, see,
(
for example: Zhao, Y.; Lei, Y.; Dong, Q.; Wu, B.; Yang, X.-J. Chem.
Eur. J. 2013, 19, 12059. (b) Larger metallacycles have also been
reported from reactions with 2,3-dimethylbutadiene, e.g.: Hardman, N.
J.; Wright, R. J.; Phillips, A. D.; Power, P. P. J. Am. Chem. Soc. 2003,
125, 2667.
(12) Protchenko, A. V.; Birjkumar, K. H.; Dange, D.; Schwarz, A. D.;
Vidovic, D.; Jones, C.; Kaltsoyannis, N.; Mountford, P.; Aldridge, S. J.
Am. Chem. Soc. 2012, 134, 6500.
ASSOCIATED CONTENT
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*
S
Supporting Information
Complete data for 3, 4-Ga, 4-In, 5, 6, and 7; all CIFs. This
(
13) The corresponding SnB angle measured, for example, for the
AUTHOR INFORMATION
Notes
2
dichlorotin(IV) species Cl Sn{B(NDippCH) } is 136.3(1)°: Saleh, L.
M. A.; Protchenko, A. V.; Mountford, P.; Aldridge. S., unpublished
results.
2
2 2
(14) 4-In: To a solution of 2-In (0.030 g, 0.032 mmol) in C D (0.5
6
6
The authors declare no competing financial interest.
mL) was added 2,3-dimethylbutadiene (30 μL, 0.022 g, 0.265 mmol)
1
0904
dx.doi.org/10.1021/ja5062467 | J. Am. Chem. Soc. 2014, 136, 10902−10905