Transition-metal-promoted or -catalyzed exocyclic alkyne insertion via zirconacyclopentene with carborane auxiliary: Formation of symmetric or unsymmetric benzocarboranes

Article abstract of DOI:10.1021/ja211485t

Reactions of Cp₂Zr(μ-Cl)(μ-C₂B ₁₀H₁₀)Li(OEt₂)₂ with alkynes R ¹C≡CR² gave as insertion products zirconacyclopentenes incorporating a carboranyl unit, 1,2-[Cp ₂ZrC(R¹)=C(R²)]-1,2-C₂B ₁₀H₁₀ (1). Treatment of 1 with another type of alkyne R³C≡CR⁴ in the presence of stoichiometric amounts of NiCl₂ and FeCl₃ or a catalytic amount of NiCl₂ afforded symmetric or unsymmetric benzocarboranes. The regioselectivity was dominated by the polarity of the corresponding alkynes. These reactions could also be carried out in one pot, leading to the equivalent of a three-component [2 + 2 + 2] cycloaddition of carboryne and two different alkynes promoted by transition metals. A reaction mechanism was proposed after the isolation and structural characterization of the key intermediate nickelacycle. These results show that nickel complexes are more reactive than the iron ones toward the insertion of alkynes but that the latter do not initiate the trimerization of alkynes, making the insertion of activated alkynes possible. This work also demonstrates that a catalytic amount of nickel works as well as a stoichiometric amount of nickel in the presence of excess FeCl₃ for the reactions. Such a catalytic reaction may shed some light on the development of zirconocene-based catalytic reactions.

Full text of DOI:10.1021/ja211485t

Transition Metal Promoted or Catalyzed Exo-cyclic Alkyne Insertion via
Zirconacyclopentene with Carborane Auxillary: Formation of Symmetric
or Unsymmetric Benzocarboranes
Shikuo Ren, Zaozao Qiu, and Zuowei Xie*
Department of Chemistry and State Key Laboratory on Synthetic Chemistry, The Chinese University of Hong Kong, Shatin, New
Territories, Hong Kong, People’s Republic of China; zxie@cuhk.edu.hk
Table S1. Crystal Data and Summary of Data Collection and Refinement for 3h, 3m, 3n, 3p, 3q, 3v and 5
compd
3e
3h
3m
3n
3p
3q
3v
5·toluene
C49H52B10NiP2
0.50x0.40x0.30
869.7
formula
cryst size (mm)
fw
C17H28B10
C18H38B10
C18H30B10O
0.50x0.40x0.30
370.5
C19H30B10
0.40x0.30x0.20
366.5
C17H38B10Si
0.50x0.40x0.30
378.7
C19H34B10Si
0.50x0.40x0.30
398.7
C23H32B10
0.40x0.30x0.20
416.6
0.50x0.40x0.30 0.30x0.30x0.20
340.5
362.6
cryst syst
space group
a, Å
triclinic
P(-1)
triclinic
P(-1)
monoclinic
P21/c
monoclinic
P21/c
hexagonal
P65
monoclinic
P21/c
monoclinic
P21/n
monoclinic
P21/n
9.726(2)
14.740(2)
9.777(2)
10.179(2)
11.337(2)
10.624(2)
9.533(2)
18.412(4)
10.693(3)
10.693(3)
13.579(2)
13.033(2)
11.829(2)
16.137(2)
11.07(2)
b, Å
21.30(3)
S1

c, Å
14.927(2)
79.45 (1)
81.49(1)
81.42(1)
2064.1(5)
4
13.111(2)
82.25(1)
81.31(1)
62.98(1)
1145.8(3)
2
19.108(3)
90
13.318(3)
90
37.114(11)
14.930(2)
90
14.117(2)
90
20.99(3)
90
, deg
β, deg
, deg
V, Å3
Z
90
106.54(1)
90
102.60(1)
90
90
113.18(1)
90
108.30(1)
90
90.45(3)
90
120
2206.0(6)
4
2281.5(8)
4
3675.1(18)
2428.8(7)
4
2558.4(7)
4
4948(13)
4
6
D
calcd, Mg/m3
1.096
1.051
1.116
1.067
1.027
1.090
1.082
1.167
Mo Kα
Mo Kα
Mo Kα
Mo Kα
Mo Kα
Mo Kα
Mo Kα
Mo Kα
radiation (λ), Å
(0.71073)
2.8 to 50.5
(0.71073)
3.2 to 50.0
(0.71073)
3.7 to 50.0
(0.71073)
3.8 to 55.9
(0.71073)
4.4 to 50.0
(0.71073)
3.6 to 50.0
(0.71073)
3.6 to 50.0
(0.71073)
2.7 to 50.0
2θ range, deg
μ, mm-1
0.054
720
0.052
392
0.059
784
0.053
776
0.097
1224
4322
0.101
848
0.055
880
0.489
1816
8543
F(000)
no. of obsd reflns
4007
3885
5475
4285
4506
7425
505
no. of params refnd
253
262
262
254
271
298
559
goodness of fit
1.059
0.071
0.191
1.004
0.065
0.156
1.026
0.052
0.133
1.001
0.055
0.138
1.066
0.055
0.136
1.062
0.054
0.140
1.016
0.062
0.159
1.008
0.058
0.148
R1
wR2
S2