514 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 514^515y
Coupling of Geminal Dihalides with Disodium
Tetracarbonyl Ferrate: a Novel Reactivity Pattern
for Collman's Reagenty
Kirstin F. Warner,* Atiq-ur Rehman, Salil K. Jha and
Wayne F. K. Schnatterz
Department of Chemistry, Polytechnic University Brooklyn, NY 11201, USA
The reaction of gem-dihalides with Na2FeꢀCO results in the formation of alkenes instead of the iron(0) carbene
4
complexes.
As part of our continuing e¡orts to determine the reactivity
pattern of iron(O) carbene complexes we undertook the
attempted synthesis of such complexes devoid of
heteroatom stabilization at the carbene carbon.1 Although
the tungsten analogues were ¢rst prepared via a protocol
involving modi¢cation of heteroatom stabilized complex
with aryllithium2 reagents or potassium triisopropoxy-
borohydride3 followed by treatment with acid; we know
of no account of similar procedures working with iron(O)
carbene complexes. It has been our experience that simple
modi¢cation of the iron(O) carbene complexes through
nucleophilic substitution does not follow the same
straightforward course as their chromium, molybdenum
and tungsten analogues. The chemistry of disodium
tetracarbonylferrate has been actively studied for over
twenty years4;5 but the synthesis of iron carbene complexes
by double displacement reactions is unprecedented.
materials including dihalides derived from enolizable
ketones as well as the possibility of preparing inorganic
derivatives and polymers.
Experimental
Disodium tetracarbonylferrate (1.2 g, 5.62 mmol) was transferred
in an argon ¢lled drybox to a 25 mL Schlenk £ask. 15 mL of THF
was added and the suspension was stirred at 25 8C for 10 min then
cooled in a dry ice±ethanol bath. 2,3-Diphenyldichlorocyclopropene
(1.33 g; 5.11 mmol) was added at 78 8C and gave 1. dc (75 MHz,
CDCl3) 213.4, 193.78, 192.10 (s, Fe^CO), 132.25, 129.58, 129.77,
128.78. IR (n/cm 1) 2071, 2042, 2001vs [Fe(CO)4], 2880s (CC.
General Preparation of Alkenes.öDisodium tetracarbonylferrate
(2.00 g, 9.35 mmol) was transferred in an argon ¢lled drybox to a
100 mL Schlenk £ask. 50 mL of THF was added and the suspension
was stirred at 25 8C for 10 min then cooled in a dry ice±ethanol
bath. 8.5 mmol of the gem-dihalide was added at 78 8C and the
reaction mixture was allowed to warm slowly to 25 8C. The mixture
was poured into benzene±hexanes (100 mL) and washed with water
(100 mL). The organic layer was dried over anhydrous magnesium
sulfate and concentrated on a rotary evaporator. The crude product
was puri®ed by column chromatography and eluted on silica gel in
hexanes and characterized by NMR and MS.
1,2-Diphenylcyclopropene and Na2FeꢀCO yield the novel
4
2,3-diphenylcyclopropene tetracarbonyliron(O) species 1 in
15% yield [eqn. (1)].
Ph
Ph
Ph
Ph
2a dH(300 MHz, CDCl3) 7.04^7.26 (5H, m). dC (75 MHz, CDCl3)
Cl
Cl
Na2Fe(CO)4
THF, –78 ˚C
126.47, 127.65, 131.38, 143.8. m/z 332 (100) [M ], 253(40), 255(20),
Fe(CO)4
(1)
178(6).
2b dH(300 MHz, CDCl3) 7.5 (2H, d, J 8.1 Hz), 7.7 (2H, d, J 8.1 Hz).
1
dC (75 MHz, CDCl3) 128.74, 131.4. m/z 460(0.8) [M ], 332(7),
250(38), 139(100), 111(50).
2c dH(300 MHz, CDCl3) 3.9 (3H, s), 7.7 (2H, d, J 8.1 Hz), 7.8 (2H,
d, J 8.1 Hz). dC (75 MHz, CDCl3) 55.51, 113.73, 128.51, 131.10,
132.38. m/z 604(1.5), 372(1.5), 246(42), 135(100).
Presumably, the strained 3,3-dichloro-1,2-diphenylcyclo-
propene binds strongly to iron because the rehybridization
on binding leads to the relief of strain and generation of
aromaticity which accounts for the stability of the carbene
complex 1 formed. The scope of this reaction was explored
using symmetrical diaryl gem-dichloromethanes;6 however,
the desired carbene complex was not isolated and low tem-
perature NMR provided no evidence of carbene formation.
Instead, coupling products were isolated (Table 1), and this
route has proven to be quite general for symmetrical diaryl
gem-dichloromethanes. This reaction is relatively insensitive
to the presence of strong electron donors or acceptors. For
example, 3,30-bis(tri£uoromethylphenyl) and 4,40-bis-
(methoxyphenyl) substitution gave the alkene in 34 and
37% yield, respectively. To date the best yield was obtained
with the 4,40-bis(methylphenyl) substituted derivative, which
gave a 96% yield of the alkene. Although much remains to
be established with respect to the scope of the reaction,
it is our hypothesis that this reaction proceeds via an
SN2 mechanism. Further study of this reaction pattern,
which to the best of our knowledge, has not been reported
2d dH(300 MHz, CDCl3) 7.1^7.3 (3H, m), 7.43 (1H, d, J 7.5 Hz). dC
(75 MHz, CDCl3) 124.33, 124.81, 127.87, 128.84, 131.30, 134.06,
142.28. m/z 604(100) [M ], 585(10), 302(16), 233(18), 145(2).
2e dH(300 MHz, CDCl3) 2.43 (3H, s), 7.24 (2H, d, J 8.1 Hz), 7.72
(2H, d, J 8.1 Hz). dC (75 MHz, CDCl3) 21.37, 128.73, 129.97, 135.23,
142.64. m/z 604(1.8), 402(100), 388(18) [M ], 195(24), 119(100),
57(70).
Table
1 Preparation of alkenes from symmetrical diaryl
gem-dichloromethanes with Na2FeꢀCO
4
Cl
Cl
Na2Fe(CO)4
THF
R
R
R
R
R
R
2a–e
for Na2FeꢀCO will involve unsymmetrical starting
4
Entry
Alkene
R
Yield(%)
* To receive any correspondence (e-mail: warnerk305@aol.com).
y This is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).
z Present address: Yeshiva University 500W l85 St., New York, NY
10033, USA.
1
2
3
4
5
2a
2b
2c
2d
2e
H
Cl
OMe
m-CF3
Me
63
54
37
34
96
Warner, Kirstin F.
