Alkali and alkaline-earth metal ketyl complexes: Isolation, structural diversity, and hydrogenation/protonation reactions

Article abstract of DOI:10.1002/1521-3765(20000818)6:16<2994::AID-CHEM2994>3.0.CO;2-E

The use of hexamethylphosphoric triamide (HMPA) as a stabilizing ligand allowed successful isolation of a series of structurally characterizable alkali metal and calcium ketyl complexes. Reaction of lithium and sodium with one equivalent of fluorenone and reaction of sodium with one equivalent of benzophenone in THF, followed by addition of two equivalents of HMPA, yielded the corresponding ketyl complexes 1, 2, and 11, respectively, as μ-ketyl-bridged dimers. If one equivalent of HMPA was used in the reaction of sodium with fluorenone, a further aggregated complex, the μ₃-ketyl-bridged tetramer 3, was isolated, whereas analogous reaction of benzophenone with sodium afforded the trimeric ketyl complex 13, rather than a simple benzophenone analogue of 3. In the reaction of potassium with fluorenone, the use of two equivalents of HMPA gave the tetramer 4, rather than a dimeric complex analogous to 1 or 2. Compared to the tetrameric sodium complex 3, there is an extra HMPA ligand that bridges two of the four K atoms in 4. When 0.5 equiv of HMPA was used in the above reaction, complex 5, a THF-bridged analogue of 4, was isolated. In the absence of HMPA, the reaction of sodium with an excess of fluorenone yielded the tetrameric ketyl complex 6, in which two of the four Na atoms are each terminally coordinated by a fluorenone ligand, and the other two Na atoms are coordinated by a THF ligand. Two bridging THF ligands are also observed in 6. Reaction of 1,2-bis(biphenyl-2,2′-diyl)ethane-1,2-diol (7) with two equivalents of LiN(SiMe₃)₂ or NaN(SiMe₃)₂ in the presence of four equivalents of HMPA easily afforded 1 or 2, respectively, via C-C bond cleavage of a 1,2-diolate intermediate. The reaction of calcium with two equivalents of fluorenone or benzophenone in the presence of HMPA gave the corresponding complexes that bear two independent ketyl ligands per metal ion. In the presence of 3 or four equivalents of HMPA, the fluorenone ketyl complex was isolated in a six-coordinate octahedral form (10), while the benzophenone ketyl complex was obtained as a five-coordinate trigonal bipyramid (13). The radical carbon atoms in both benzophenone ketyl and fluorenone ketyl complexes are still in an sp²-hybrid state. However, in contrast with the planar configuration of the whole fluorenone ketyl unit, the radical carbon atom in a benzophenone ketyl species is not coplanar with any of the phenyl groups; this explains why benzophenone ketyl is more reactive than fluorenone ketyl. Hydrolysis of 2 or 11 with 2 N HCl yielded the corresponding pinacol-coupling product, while treatment of 2 or 11 with 2-propanol, followed by hydrolysis, gave the pairs fluorenone and fluorenol or benzophenone and benzhydrol, respectively. A possible mechanism for these reactions is proposed.

Full text of DOI:10.1002/1521-3765(20000818)6:16<2994::AID-CHEM2994>3.0.CO;2-E

FULL PAPER
Alkali and Alkaline-Earth Metal Ketyl Complexes: Isolation, Structural
Diversity, and Hydrogenation/Protonation Reactions
[
a]
[a]
[b]
[b]
[b]
Zhaomin Hou,* Xueshun Jia, Akira Fujita, Hiroaki Tezuka, Hiroshi Yamazaki,
and Yasuo Wakatsuki*[
a]
Abstract: The use of hexamethylphos-
phoric triamide (HMPA) as a stabilizing
ligand allowed successful isolation of a
series of structurally characterizable al-
kali metal and calcium ketyl complexes.
Reaction of lithium and sodium with
one equivalent of fluorenone and reac-
tion of sodium with one equivalent of
benzophenone in THF, followed by
addition of two equivalents of HMPA,
yielded the corresponding ketyl com-
plexes 1, 2, and 11, respectively, as m-
ketyl-bridged dimers.If one equivalent
of HMPA was used in the reaction of
sodium with fluorenone, a further ag-
two of the four K atoms in 4.When
0.5 equiv of HMPA was used in the
above reaction, complex 5, a THF-
bridged analogue of 4, was isolated.In
the absence of HMPA, the reaction of
sodium with an excess of fluorenone
yielded the tetrameric ketyl complex 6,
in which two of the four Na atoms are
each terminally coordinated by a fluo-
renone ligand, and the other two Na
atoms are coordinated by a THF ligand.
Two bridging THF ligands are also
observed in 6.Reaction of 1,2-bis(bi-
phenyl-2,2'-diyl)ethane-1,2-diol (7) with
two equivalents of LiN(SiMe3)2 or
NaN(SiMe3)2 in the presence of four
equivalents of HMPA easily afforded 1
or 2, respectively, via CÀC bond cleav-
sponding complexes that bear two in-
dependent ketyl ligands per metal ion.
In the presence of 3 or four equivalents
of HMPA, the fluorenone ketyl complex
was isolated in a six-coordinate octahe-
dral form (10), while the benzophenone
ketyl complex was obtained as a five-
coordinate trigonal bipyramid (13).The
radical carbon atoms in both benzophe-
none ketyl and fluorenone ketyl com-
2
plexes are still in an sp -hybrid state.
However, in contrast with the planar
configuration of the whole fluorenone
ketyl unit, the radical carbon atom in a
benzophenone ketyl species is not co-
planar with any of the phenyl groups;
this explains why benzophenone ketyl is
more reactive than fluorenone ketyl.
Hydrolysis of 2 or 11 with 2n HCl
yielded the corresponding pinacol-cou-
pling product, while treatment of 2 or 11
with 2-propanol, followed by hydrolysis,
gave the pairs fluorenone and fluorenol
or benzophenone and benzhydrol, re-
spectively.A possible mechanism for
these reactions is proposed.
gregated complex, the m -ketyl-bridged
3
tetramer 3, was isolated, whereas anal-
ogous reaction of benzophenone with
sodium afforded the trimeric ketyl com-
plex 13, rather than a simple benzophe-
none analogue of 3.In the reaction of
potassium with fluorenone, the use of
two equivalents of HMPA gave the
tetramer 4, rather than a dimeric com-
plex analogous to 1 or 2.Compared to
the tetrameric sodium complex 3, there
is an extra HMPA ligand that bridges
age of a 1,2-diolate intermediate.The
reaction of calcium with two equivalents
of fluorenone or benzophenone in the
presence of HMPA gave the corre-
Keywords: alkali metals ´ calcium ´
ketones ´ radical anions ´ reduc-
tions
istry.[1, 2] These highly reactive and synthetically useful species
have received continuous attention from a broad range of
chemists since their discovery more than 100 years ago.
Although extensive studies have been carried out so far in this
area, structurally characterized examples of metal ketyls
remain rare owing to their extremely high reactivity, which
makes them difficult to isolate.[ Isolation and structural
characterization of new metal ketyl complexes continue to be
of great importance and interest for understanding the nature
of this important class of species.
Introduction
Metal ketyl species, formed by one-electron reduction of
ketones or aldehydes with reducing metals, represent one of
the most important kinds of intermediates in organic chem-
3]
[
a] Dr.Z.Hou, Dr.Y.Wakatsuki, Dr.X.Jia
RIKEN (The Institute of Physical and Chemical Research)
Hirosawa 2-1, Wako, Saitama 351-0198 (Japan)
Fax : (‡48)462-4665
E-mail: houz@postman.riken.go.jp
Alkali and alkaline-earth metal ketyls are among the best
[
b] A.Fujita, H.Tezuka, Prof.Dr.H.Yamazaki
known and most widely used ketyls.[
1, 2f,g, 3c, 4]
Because they are
Department of Applied Chemistry, Chuo University
Kasuga 1-13-27, Bunkyo, Tokyo 112-0003 (Japan)
so well known and synthetically very useful, we carried out a
2994
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Chem. Eur. J. 2000, 6, No. 16

2
994±3005
systematic study on the isolation and structures of a series of
alkali and alkaline-earth metal ketyl complexes, as part of our
recent research project on structurally well-defined metal ±
Table 1.Selected bond lengths [Š] and angles [ 8] of 1.
Li(1) O(1)
Li(1)ÀO(2)
O(1)ÀC(1)
À
1.953(12)
1.972(12)
1.288(8)
90.6(5)
114.0(6)
114.1(6)
89.4(5)
Li(1) O(1')
Li(1)ÀO(3)
À
1.976(12)
1.925(12)
ketyl complexes.[
3a±e,h±j]
Herein, we report on lithium, sodium,
O(1)-Li(1)-O(1')
O(1)-Li(1)-O(3)
O(1')-Li(1)-O(3)
Li(1)-O(1)-Li(1')
Li(1')-O(1)-C(1)
Li(1)-O(3)-P(2)
O(1)-Li(1)-O(2)
O(1')-Li(1)-O(2)
O(2)-Li(1)-O(3)
Li(1)-O(1)-C(1)
Li(1)-O(2)-P(1)
114.4(6)
115.6(6)
107.7(6)
134.3(6)
146.2(5)
potassium, and calcium benzophenone and fluorenone ketyl
complexes (benzophenone ketyl ˆ diphenyl ketyl, fluorenone
ketyl ˆ biphenyl-2,2'-diyl ketyl).X-ray analyses of these
complexes have revealed unprecedented structural features
of metal ketyl complexes.Hydrogenation/protonation of
some of these ketyl complexes have shed new light on the
mechanistic aspects of the reduction of ketones with dissolv-
ing metals.A portion of this work has been communicated
previously.[
135.7(6)
168.1(5)
3e,i]
favorable form for the HMPA-coordinated lithium fluore-
none ketyl complex.The use of one equivalent of HMPA also
yielded the bis(HMPA)-coordinated dimeric complex 1 as the
only isolable product, while further addition of HMPA to a
THF solution of 1 did not give a monomeric complex.The
C(1)ÀO(1) bond length in 1 (1.288(8) Š) is in the 1.27 ± 1.32 Š
range of the CÀO (ketyl) bond lengths found in other metal
ketyl complexes,[ which is longer than the CÀO double bond
Results and Discussion
Alkali metal fluorenone ketyl complexes: Reaction of one
equivalent of lithium chips with fluorenone in THF, followed
by addition of two equivalents of hexamethylphosphoric
triamide (HMPA), easily afforded the lithium fluorenone
ketyl complex 1 as brown crystals (Scheme 1).[ An X-ray
3]
[6]
of free fluorenone (1.220(4) Š) and shorter than the CÀO
single bond found in a samarium fluorenoxide complex,
5]
[
(
Sm(OC H )(OC H tBu -2,6-Me-4) (HMPA) ]
13 9 6 2 2 2 2
1.404(8) Š).[
7]
Similar reaction of sodium chips with one equivalent of
fluorenone and two equivalents of HMPA yielded the
analogous dimeric sodium fluorenone ketyl complex 2 as
brown crystals (Scheme 2), which is isostructural with the
THF
2 equiv HMPA HMPA
O
HMPA
HMPA
Li
+
Li
room temp., 7 h
73%
Li
HMPA
O
O
1, brown
Scheme 1.Isolation of the dimeric lithium fluorenone ketyl complex 1.
HMPA
HMPA
O
2
equiv HMPA
1%
HMPA
HMPA
Na
Na
8
O
analysis has shown that 1 adopts a centrosymmetric dimeric
structure, in which the two Li atoms are bridged by two
identical fluorenone ketyl ligands and each of the two Li
atoms is also coordinated by two HMPA ligands (Figure 1 and Na +
Table 1).This dimeric structure seemed to be the most
2, brown
THF
room temp., 4 h
HMPA
O
HMPA
Na
O
HMPA
1
equiv HMPA
8%
O
O
Na
Na
7
HMPA
Na
O
HMPA
3, greenish-brown
Scheme 2.Isolation of dimeric ( 2) and tetrameric (3) sodium fluorenone
ketyl complexes.
lithium complex 1 (Figure 2 and Table 2).When one equiv-
alent of HMPA was used in this reaction, the tetrameric, m3-
ketyl-bridged sodium complex 3 was isolated as greenish-
brown crystals in 78% yield (Scheme 2).Complex 3 possesses
an Na O cubane core, in which each Na atom is coordinated
4
4
by one terminal HMPA ligand (Figure 3 and Table 3).The
formation of 3 can formally be viewed as dimerization of two
molecules of 2 by removal of one of the two HMPA ligands on
Figure 1.X-ray crystal structure of 1 (with 30% thermal ellipsoids).
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Z.Hou, Y.Wakatsuki et al.
FULL PAPER
Table 3.Selected bond lengths [Š] and angles [ 8] of 3.
Na(1)ÀO(1)
2.290(14)
2.418(17)
2.453(18)
2.290(16)
1.27(3)
Na(1)ÀO(1')
2.315(15)
2.129(19)
2.328(15)
2.171(19)
1.30(3)
90.0(6)
90.0(6)
120.0(7)
89.8(6)
89.7(6)
Na(1)ÀO(2)
Na(1)ÀO(3)
Na(2)ÀO(1)
Na(2)ÀO(2)
Na(2)ÀO(2')
Na(2)ÀO(4)
O(1)ÀC(1)
O(2)ÀC(14)
O(1)-Na(1)-O(1')
O(1)-Na(1)-O(3)
O(1')-Na(1)-O(3)
O(1)-Na(2)-O(2)
O(1)-Na(2)-O(4)
O(2)-Na(2)-O(4)
Na(1)-O(1)-Na(1')
Na(1')-O(1)-Na(2)
Na(1)-O(2)-Na(2)
Na(1)-O(1)-C(1)
Na(2)-O(1)-C(1)
Na(2)-O(2)-C(14)
Na(1)-O(3)-P(1)
89.6(5)
O(1)-Na(1)-O(2)
O(1')-Na(1)-O(2)
O(2)-Na(1)-O(3)
O(1)-Na(2)-O(2')
O(2)-Na(2)-O(2')
O(2')-Na(2)-O(4)
Na(1)-O(1)-Na(2)
Na(2)-O(2)-Na(2')
Na(1')-O(2)-Na(2)
Na(1')-O(1)-C(1)
Na(1)-O(2)-C(14)
Na(2')-O(2)-C(14)
Na(2)-O(4)-P(2)
135.7(7)
119.5(7)
88.3(6)
130.7(7)
118.7(7)
90.4(5)
89.4(6)
90.8(6)
136.3(12)
100.7(13)
126.0(12)
163.5(12)
127.4(7)
90.9(6)
90.3(6)
90.8(6)
131.3(12)
102.2(12)
140.5(12)
150.1(11)
each Na atom.It is noteworthy that this dimerization is not
pinacol-coupling of the ketyls[
3d,j]
but further aggregation of
the ketyls through Na ± O(ketyl) interactions.Addition of
four equivalents of HMPA to the tetrameric complex 3 in
THF easily gave the dimeric complex 2.But further addition
of HMPA to a THF solution of 2 did not afford a monomeric
ketyl complex.The HMPA-dependence of the reaction,
leading to formation of either dimeric complex 2 or tetrameric
complex 3, is in sharp contrast with what was observed in the
case of lithium fluorenone ketyl.This difference may result
from the different ion sizes of lithium and sodium.
In contrast with lithium and sodium fluorenone ketyls,
potassium fluorenone ketyl always adopted a tetrameric
structure.A bis(HMPA)-coordinated dimeric potassium com-
plex analogous to 1 and 2 was not obtained when two
equivalents of HMPA was added to a THF solution of
potassium fluorenone ketyl, but instead the tetrameric com-
plex 4, which bears one terminal HMPA ligand on each K
atom, was isolated in 75% yield (Scheme 3).Furthermore,
Figure 2.X-ray crystal structure of 2 (with 30% thermal ellipsoids).
Table 2.Selected bond lengths [Š] and angles [ 8] of 2.
Na(1)ÀO(1)
2.292(5)
2.236(4)
1.275(7)
91.9(2)
Na(1)ÀO(1')
Na(1)ÀO(3)
2.316(5)
2.199(5)
Na(1)ÀO(2)
O(1)ÀC(1)
O(1)-Na(1)-O(1')
O(1)-Na(1)-O(3)
O(1')-Na(1)-O(3)
Na(1)-O(1)-Na(1')
Na(1')-O(1)-C(1)
Na(1)-O(3)-P(3)
O(1)-Na(1)-O(2)
O(1')-Na(1)-O(2)
O(2)-Na(1)-O(3)
Na(1)-O(1)-C(1)
Na(1) -O(2)-P(1)
123.3(2)
106.9(2)
108.9(2)
88.1(2)
133.4(4)
163.0(4)
112.6(2)
111.2(2)
134.7(4)
151.5(3)
HMPA
K
O
K
HMPA
K
HMPA
HMPA
O
K
2
equiv HMPA
5%
O
7
O
HMPA
4, brown
THF
K
+
room temp., 4 h
O
HMPA
K
O
K
HMPA
K
O
O
O
0.5 equiv HMPA
HMPA
K
O
HMPA
5
, dark brown
2% based on HMPA
36 % based on K)
7
(
Figure 3.X-ray crystal structure of 3.
Scheme 3.Isolation of potassium fluorenone ketyl complexes 4 and 5.
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Alkali and Alkaline-Earth Metal Ketyl Complexes
2994±3005
reflecting the larger ion size of potassium, an additional
bridging HMPA ligand is also bonded to two of the four
potassium atoms, and the K O cubane core in 4 is thus more
4
4
distorted than the Na O core in 3 (Figure 4 and Table 4).This
4
4
Figure 5.X-ray crystal structure of 5.
coordinatedtetrameric complexes 3 ± 5, two of the four Na
atoms in 6 are each terminally coordinated by a fluorenone
and the other two Na atoms are coordinated by a THF ligand
(
Figure 6 and Table 6).In addition, the Na atoms in 6 are also
Figure 4.X-ray crystal structure of 4.
bridged in pairs by a THF ligand whose oxygen atom is sitting
on a crystallographic C axis.As far as we are aware, complex
2
K O cubic skeleton was obtained even when less than one
6 represents the first example of a ketone-coordinated ketyl
complex, and is also a rare example of a complex bearing
bridging THF ligands.[
4
4
equivalent of HMPA was employed.As shown in Scheme 3,
addition of 0.5 equiv of HMPA to a THF solution of
potassium fluorenone ketyl afforded 5, a THF-bridged
analogue of 4 (Figure 5 and Table 5), whereas formation of
a further aggregated complex was not observed.
8]
Deprotonation of an appropriate 1,2-diol, followed by CÀC
bond cleavage of the resultant diolate, the reverse process of a
normal pinacol-coupling reaction,[
3d,j]
could also be used for
Although the use of HMPA as a stabilizing ligand was
essential to isolate a structurally characterizable metal ketyl
complex in most of the above reactions, single crystals of the
HMPA-free, tetrameric ketyl complex 6 could also be isolated
when an excess of fluorenone was employed in the reaction
with sodium in THF (Scheme 4).In contrast to the HMPA-
the synthesis of a ketyl complex.As shown in Scheme 5,
reaction of 1,2-bis(biphenyl-2,2'-diyl)ethane-1,2-diol (7) with
two equivalents of LiN(SiMe3)2 or NaN(SiMe3)2 in the
presence of four equivalents of HMPA easily afforded the
ketyl complex 1 or 2, respectively, through CÀC bond
cleavage of the 1,2-diolate intermediate 8.[
3d,j]
Although this
Table 4.Selected bond lengths [Š] and angles [ 8] of 4.
K1ÀO1
K2ÀO2
K3ÀO4
K4ÀO4
O3ÀC27
O1-K1-O2
O2-K1-O5 120.9(4)
O1-K2-O2 98.7(3)
O2-K2-O6 118.8(4)
O2-K3-O4 86.5(3)
2.837(10) K1ÀO2
2.740(9) K2ÀO3
2.774(10) K3ÀO7
2.688(11) K4ÀO8
1.286(16) O4ÀC40
2.715(9) K1ÀO4
2.830(10) K2ÀO6
2.541(11) K4ÀO1
2.511(11) O1ÀC1
1.285(16)
2.785(10) K1ÀO5
2.574(10) K2ÀO9
2.587(10) K4ÀO3
1.276(16) O2ÀC14
2.576(11) K1ÀO9
2.744(10) K3ÀO2
2.727(10)
2.778(10) K2ÀO1 2.714(10)
2.678(10) K3ÀO3 2.629(10)
1.278(16)
96.3(3)
O1-K1-O4
O2-K1-O9
O1-K2-O3
O2-K2-O9
80.0(3)
78.2(3)
79.6(3)
78.4(3)
O1-K1-O5 142.8(4)
O1-K1-O9
70.4(3)
O2-K1-O4
85.6(3)
O4-K1-O5 101.7(3)
O1-K2-O6 142.6(4)
O3-K2-O6 105.0(4)
O4-K1-O9 144.1(3)
O1-K2-O9 72.8(3)
O3-K2-O9 142.1(3)
O2-K3-O3 85.7(3)
O1-K4-O8 112.6(4)
K1-O1-K4
K2-O3-K3
K3-O4-K4
O5-K1-O9 114.1(4)
O2-K2-O3 80.7(3)
O6-K2-O9 112.7(4)
O3-K3-O7 113.7(4)
O2-K3-O7 126.5(4)
O1-K4-O3 83.8(3)
O4-K4-O8 134.1(4)
O3-K3-O4
O1-K4-O4
K1-O1-K2
K2-O2-K3
K1-O4-K4
89.0(3)
86.4(3)
77.8(3)
97.1(3)
96.0(4)
O4-K3-O7 139.4(4)
O3-K4-O8 132.7(4)
K1-O2-K2
K3-O3-K4
O3-K4-O4
88.8(3)
97.1(3)
96.0(3)
88.3(3)
K2-O1-K4 101.2(4)
K2-O3-K4
K1-O9-K2
79.4(3)
90.5(3)
K1-O2-K3
K1-O4-K3
95.7(3)
92.0(3)
95.0(3)
78.3(3)
K1-O5-P1 164.1(7)
K2-O2-C14 131.1(8)
K1-O4-C40 125.9(9)
K4-O8-P4 158.5(8)
K1-O1-C1 111.0(8)
K3-O2-C14 98.9(8)
K3-O4-C40 119.2(9)
K1-O9-P5 127.7(6)
K2-O1-C1 131.5(9)
K2-O3-C27 112.3(8)
K4-O4-C40 125.3(9)
K2-O9-P5 144.9(6)
K4-O1-C1 123.5(8)
K3-O3-C27 141.0(8)
K2-O6-P2 168.0(7)
K1-O2-C14 143.4(9)
K4-O3-C27 112.1(8)
K3-O7-P3 160.2(7)
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Table 5.Selected bond lengths [Š] and angles [ 8] of 5.
K1ÀO1
K2ÀO2
K3ÀO4
O1ÀC1
2.643(10) K1ÀO3
2.804(10) K2ÀO3
2.668(10) K3ÀO7
1.291(16) O2ÀC14
2.776(11) K1ÀO4
2.687(10) K2ÀO6
2.566(11) K4ÀO2
1.285(17) O3ÀC27
2.839(10) K1ÀO5
2.547(13) K2ÀO9
2.726(10) K4ÀO3
1.281(16) O4ÀC40
O1-K1-O9
2.539(12) K1ÀO9
2.922(15) K3ÀO1
2.678(9) K4ÀO4
1.299(17)
3.007(15) K2ÀO1 2.758(10)
2.769(10) K3ÀO2 2.656(10)
2.618(10) K4ÀO8 2.511(11)
O1-K1-O3
96.1(4)
O1-K1-O4
O3-K1-O9
O1-K2-O3
84.3(3)
73.3(4)
95.5(4)
O1-K1-O5 119.4(4)
71.8(4)
O3-K1-O4
80.3(3)
83.7(4)
85.4(3)
85.4(4)
O3-K1-O5 128.9(4)
O1-K2-O2 83.3(3)
O2-K2-O6 127.7(4)
O1-K3-O2 85.9(3)
O4-K3-O7 120.6(4)
O3-K4-O8 111.8(4)
K2-O2-K3
K2-O3-K4
K1-O1-C1 137.5(9)
K4-O2-C14 125.7(9)
K3-O4-C40 130.7(8)
K4-O8-P4 173.5(8)
O4-K1-O5 134.4(4)
O1-K2-O6 129.1(4)
O3-K2-O6 122.7(4)
O1-K3-O7 134.8(4)
O2-K4-O4
K1-O1-K2
K3-O2-K4
K1-O4-K4
K3-O1-C1
O4-K1-O9 141.8(4)
O5-K1-O9
O2-K2-O3
O6-K2-O9
O1-K2-O9
O3-K2-O9
O2-K3-O4
71.7(4)
76.0(4)
88.6(3
O2-K2-O9 146.9(4)
O1-K3-O4
O2-K4-O3
85.2(3)
87.2(3)
O2-K3-O7 127.2(4)
88.2(3)
82.7(3)
89.4(3)
96.5(3)
99.6(8)
O2-K4-O8 140.1(4)
O3-K4-O4
K2-O1-K3
K1-O3-K4
K1-O9-K2
86.2(3)
94.4(3)
96.7(3)
74.0(4)
O4-K4-O8 126.3(4)
K1-O1-K3
K1-O3-K2
K3-O4-K4
K2-O2-C14 98.8(8)
K4-O3-C27 106.1(8)
K2-O6-P2 153.1(8)
K2-O9-C77 106.4(13)
96.4(3)
81.6(3)
91.5(4)
95.9(4)
95.5(3)
K2-O2-K4
K1-O4-K3
91.8(3)
94.2(3)
K2-O1-C1 134.4(9)
K1-O3-C27 118.9(9)
K4-O4-C40 133.2(9)
K1-O9-C77 125.5(13)
K3-O2-C14 141.1(9)
K1-O4-C40 99.0(8)
K3-O7-P3 150.6(7)
K2-O9-C80 131.0(13)
K2-O3-C27 147.2(9)
K1-O5-P1 151.3(7)
K1-O9-C80 107.5(14)
O
Na
O
O
THF
Na
+
O
Na
O
O
O
room temp., 4 h
0.67 equiv
O
Na
85%
O
O
Na
O
6, dark-green
Scheme 4.Isolation of an HMPA-free sodium fluorenone ketyl complex 6.
approach does not offer an advantage over the reduction
method for the synthesis of an alkali metal ketyl complex such
as 1 or 2, it may provide a particularly useful route to metal
ketyls whose metal species are not good electron-transfer
[3c]
6 6
Figure 6.X-ray crystal structure of 6 (the lattice solvent C H is omitted
for clarity).
agents but are available as deprotonation agents (or bases).
Calcium fluorenone ketyl complexes: In contrast to the one-
electron reducing alkali metals, the reaction of calcium metal,
a two-electron transfer agent, with two equivalents of
fluorenone and two equivalents of HMPA in THF gave the
monomeric bis(ketyl) complex 9 in 79% yield (Scheme 6).
Complex 9 possesses an octahedral structure, in which the
central Ca ion is coordinated in trans form by two fluorenone
ketyl, two THF, and two HMPA ligands (Figure 7 and
II
Table 6.Selected bond lengths [Š] and angles [ 8] of 6.
Na(1)ÀO(1)
2.413(10)
2.556(11)
2.330(15)
1.286(17)
86.4(4)
97.0(4)
75.1(3)
131.5(5)
75.4(3)
96.1(4)
Na(1)ÀO(2)
2.298(10)
2.327(10)
2.667(14)
1.294(18)
82.3(4)
116.6(4)
78.7(4)
77.5(3)
110.9(5)
91.8(4)
72.6(4)
117.3(8)
146.0(11)
118.2(7)
114.0(12)
Na(1)ÀO(2')
Na(2)ÀO(1')
2.434(10)
2.452(10)
Na(1)ÀO(3)
Na(2)ÀO(2')
2.335(11)
2.376(10)
Na(1)ÀO(4)
Na(2)ÀO(1)
Na(2)ÀO(5)
Na(2)ÀO(6)
O(1)ÀC(1)
O(2)ÀC(14)
O(3)ÀC(27)
1.22(3)
131.1(4)
O(1)-Na(1)-O(2)
O(2)-Na(1)-O(2')
O(2')-Na(1)-O(4)
O(1)-Na(2)-O(5)
O(1')-Na(2)-O(6)
Na(1)-O(1)-Na(2)
Na(1)-O(2)-Na(2')
Na(2)-O(1)-C(1)
Na(1')-O(2)-C(14)
Na(1)-O(4)-C(40)
Na(2)-O(6)-C(46)
O(1)-Na(1)-O(2')
O(2)-Na(1)-O(3)
O(3)-Na(1)-O(4)
O(1)-Na(2)-O(6)
O(2')-Na(2)-O(5)
Na(1)-O(1)-Na(2')
Na(1)-O(4)-Na(1')
Na(2')-O(1)-C(1)
Na(1)-O(3)-C(27)
Na(1)-O(4)-C(40')
Na(2)-O(6)-C(46')
O(1)-Na(1)-O(3)
O(2)-Na(1)-O(4)
O(1)-Na(2)-O(1')
O(1)-Na(2')-O(2)
O(2')-Na(2)-O(6)
Na(2)-O(1)-Na(2')
Na(2)-O(6)-Na(2')
Na(1)-O(2)-C(14)
O(1)-Na(1)-O(4)
O(2')-Na(1)-O(3)
O(1)-Na(2)-O(2')
O(1')-Na(2)-O(5)
O(5)-Na(2)-O(6)
Na(1)-O(2)-Na(1')
Na(1)-O(1)-C(1)
Na(1')-O(2)-Na(2')
150.2(4)
77.5(3)
97.6(4)
83.9(4)
150.9(4)
79.4(4)
69.9(4)
142.9(9)
131.1(4)
85.4(4)
128.4(5)
98.0(5)
79.4(3)
118.0(8)
94.3(4)
96.8(4)
139.8(8)
122.1(9)
116.1(7)
120.8(12)
Na(2)-O(5)-C(42)
129.9(16)
Na(2)-O(5)-C(45)
127.7(18)
2998
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Chem. Eur. J. 2000, 6, No. 16

Alkali and Alkaline-Earth Metal Ketyl Complexes
2994±3005
Benzophenone ketyl com-
plexes: The reaction of benzo-
phenone with one equivalent of
sodium and two equivalents of
HMPA yielded the sodium ben-
zophenone ketyl complex 11 as
blue crystals; it adopts a dimer-
ic structure similar to its fluor-
enone analogue 2 (Scheme 7,
Figure 9 and Table 9).Howev-
(
THF)xM
O
HMPA
HMPA
O
OH
HO
MN(SiMe3)2
THF
4 HMPA
80%
HMPA
HMPA
M
M
O
–
HN(SiMe3)2
O
M(THF)x
7
8
M = Li (1), Na (2)
Scheme 5.Formation of ketyl complexes 1 and 2 by C ± C bond cleavage of the pinacol compound 7 via 8.
er, when one equivalent of HMPA was used in this reaction,
the trimeric complex 12, rather than a simple benzophenone
analogue of the tetrameric complex 3, was obtained
O
2
equiv HMPA
THF
HMPA
THF
[10]
Ca
(Scheme 7 and Figure 10). Similarly, the reaction of calcium
THF, room temp.
overnight
HMPA
O
79%
Table 7.Selected bond lengths [Š] and angles [ 8] of 9.
9
, dark brown
Ca(1)ÀO(1)
2.208(15)
2.447(18)
1.33(3)
Ca(1)ÀO(2)
2.323(15)
2.221(16)
Ca
+
2
À
À
Ca(1) O(3)
Ca(2) O(4)
HMPA
O(1)ÀC(1)
O
O(1)-Ca(1)-O(1')
O(1)-Ca(1)-O(2')
O(1)-Ca(1)-O(3')
O(2)-Ca(1)-O(3)
O(3)-Ca(1)-O(3')
Ca(1)-O(2)-P(1)
Ca(1)-O(3)-C(23)
180.0
O(1)-Ca(1)-O(2)
O(1)-Ca(1)-O(3)
O(2)-Ca(1)-O(2')
O(2)-Ca(1)-O(3')
Ca(1)-O(1)-C(1)
Ca(1)-O(3)-C(20)
89.2(6)
88.7(6)
180.0
90.8(6)
171.9(13)
125.1(17)
90.8(6)
91.3(6)
89.2(6)
180.0
165.7(10)
121.2(18)
O
3
or 4 equiv HMPA HMPA
HMPA
THF
Ca
O
THF, room temp. HMPA
overnight
84%
10, dark brown
Scheme 6.Isolation of calcium complexes 9 and 10 bearing two independ-
ent fluorenone ketyl ligands.
Figure 7.X-ray crystal structure of 9 (only one of the two independent
molecules is shown for clarity)
Figure 8.X-ray crystal structure of 10.
Table 7).Upon further reaction with HMPA, one of the two
THF ligands in 9 was replaced by an HMPA ligand, leading to
formation of 10 (Scheme 6, Figure 8 and Table 8).Complex 10
could also be prepared in 84% yield by direct reaction of
calcium with two equivalents of fluorenone and three
equivalents of HMPA in THF.Further replacement of the
THF ligand in 10 by HMPA did not occur when four or more
equiv of HMPA was used, apparently owing to steric
hindrance of the HMPA ligand.[
with two equivalents of benzophenone in the presence of 3 or
four equivalents of HMPA in THF yielded the five-coordinate
trigonal bipyramidal complex 13 (Scheme 8, Figure 11 and
Table 10), instead of a simple benzophenone analogue of the
octahedral complex 9 or 10.The radical carbon atoms in 11
2
and 13 are still in an sp -hybrid state, as in fluorenone ketyl
complexes.[ However, the CO groups in 11 and 13 are not
coplanar with any of the phenyl rings (Tables 9 and 10).The
structural differences between 12 and 3 and between 13 and 10
3d]
9]
Chem. Eur. J. 2000, 6, No. 16
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2999

Z.Hou, Y.Wakatsuki et al.
FULL PAPER
Table 8.Selected bond lengths [Š] and angles [ 8] of 10.
Table 9.Selected bond lengths [Š] and angles [ 8] of 11.
Ca(1)-O(1)
Ca(1)-O(3)
Ca(1)-O(5)
O(1)-C(1)
2.281(10)
2.324(10)
2.334(10)
1.286(17)
Ca(1)-O(2)
Ca(1)-O(4)
Ca(1)-O(6)
O(2)-C(14)
2.234(11)
2.328(8)
2.487(11)
1.280(18)
92.6(4)
86.6(4)
89.6(4)
89.7(4)
92.9(4)
Na(1)ÀO(1)
2.317(6)
2.260(6)
1.299(10)
87.8(2)
110.3(3)
115.7(3)
92.2(2)
Na(1)ÀO(1')
Na(1)ÀO(3)
2.269(6)
2.261(8)
Na(1)ÀO(2)
O(1)ÀC(1)
O(1)-Na(1)-O(1')
O(1)-Na(1)-O(3)
O(1')-Na(1)-O(3)
Na(1)-O(1)-Na(1')
Na(1')-O(1)-C(1)
Na(1)-O(3)-P(2)
O(1)-Na(1)-O(2)
O(1')-Na(1)-O(2)
O(2)-Na(1)-O(3)
Na(1)-O(1)-C(1)
Na(1)-O(2)-P(1)
123.2(3)
121.3(3)
99.4(3)
131.8(5)
150.8(4)
O(1)-Ca(1)-O(2)
O(1)-Ca(1)-O(4)
O(1)-Ca(1)-O(6)
O(2)-Ca(1)-O(4)
O(2)-Ca(1)-O(6)
O(3)-Ca(1)-O(5)
O(4)-Ca(1)-O(5)
O(5)-Ca(1)-O(6)
Ca(1)-O(2)-C(14)
Ca(1)-O(4)-P(2)
Ca(1)-O(6)-C(45)
168.5(4)
O(1)-Ca(1)-O(3)
O(1)-Ca(1)-O(5)
O(2)-Ca(1)-O(3)
O(2)-Ca(1)-O(5)
O(3)-Ca(1)-O(4)
O(3)-Ca(1)-O(6)
O(4)-Ca(1)-O(6)
Ca(1)-O(1)-C(1)
Ca(1)-O(3)-P(1)
Ca(1)-O(5)-P(3)
Ca(1)-O(6)-C(48)
97.6(4)
86.5(4)
93.5(4)
82.6(4)
172.1(4)
95.0(4)
89.4(4)
169.7(10)
159.3(6)
122.0(9)
135.8(5)
165.6(5)
82.7(4)
O(1)-C(1)-C(2)-C(8)/Ph(C2±7) dihedral angle: 24
O(1)-C(1)-C(2)-C(8)/Ph(C8±13) dihedral angle: 15
174.1(4)
158.4(10)
171.4(7)
174.5(6)
123.3(11)
Ph
Ph
C
O
HMPA
HMPA
HMPA
HMPA
2
equiv HMPA
Na
Na
room temp., 4 h
O
80%
C
Ph
Ph
1
1, blue
O
THF
Na
+
C
HMPA
Ph
Ph
Ph
C
HMPA
Na
Ph
O
HMPA
O
1
equiv HMPA
Ph
C
Na
Na HMPA
room temp., 4 h
Ph
HMPA
O
C
Ph
Ph
12, blue
84% based on HMPA
(63% based on Na)
Figure 10.X-ray crystal structure of 12.
Scheme 7.Isolation of sodium benzophenone ketyl complexes 11 and 12.
Ph
HMPA
C
O
O
O
Ph
Ph
3
or 4 equiv HMPA
Ca
+
2
C
HMPA Ca
HMPA
THF, room temp.
overnight
Ph
Ph
C
77%
Ph
13, blue
Scheme 8.Isolation of the calcium complex 13 bearing two independent
benzophenone ketyl ligands.
sterically more demanding than a fluorenone ketyl unit.On
the other hand, the lack of planarity in the whole benzophe-
none ketyl unit also explains why benzophenone ketyl is more
reactive than fluorenone ketyl:[ stabilization of the radical
3d]
through p ± p orbital interactions with the phenyl groups
z
becomes more difficult in benzophenone ketyl than in the
planar fluorenone ketyl.
Hydrogenation/protonation of ketyl complexes: The reac-
tions of sodium fluorenone ketyl complex 2 and benzophe-
none ketyl complex 11 with 2-propanol and aqueous HCl
were investigated, so that information on the elemental steps
of the reduction of ketones by dissolving metals could be
obtained.[ The typical reactivity of a ketyl species is
reflected in the treatment of 2 with 2n HCl which yielded
Figure 9.X-ray crystal structure of 11.
must result from the structural difference between benzophe-
none ketyl and fluorenone ketyl; because the phenyl groups in
a benzophenone ketyl unit can rotate, this unit may become
2f]
3000
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Alkali and Alkaline-Earth Metal Ketyl Complexes
2994±3005
OH
HO
, 100%
2
–
N HCl
NaCl
7
HMPA
HMPA
O
HMPA
HMPA
5
5
equiv i PrOH 2N HCl
0 min
Na
Na
+
3
O
H
5
OH
0%
O
50%
2
equiv i PrOH 2N HCl
min
+
+
7
5
H
OH
O
23%
23%
54%
Scheme 9.Hydrogenation/protonation of sodium fluorenone ketyl com-
plex 2.
HO OH
2
N HCl
NaCl
Ph
C
C Ph
–
Ph Ph
00%
1
Ph
Ph
Na
Ph
C
O
Figure 11.X-ray crystal structure of 13.
OH
C
O
C
HMPA
HMPA
HMPA
HMPA
5
equiv i PrOH 2N HCl
Na
Ph
Ph
Ph
+
+
30 min
O
C
Ph
Ph
Ph
H
51%
Table 10.Selected bond lengths [Š] and angles [ 8] of 13.
49%
Ca(1)-O(1)
Ca(1)-O(3)
Ca(1)-O(5)
O(1)-C(1)
2.187(9)
2.315(9)
2.314(10)
1.313(14)
Ca(1)-O(2)
Ca(1)-O(4)
P(1)-O(3)
2.206(10)
Ph
2.286(8)
1.446(9)
1.308(16)
11
OH
O
C
5 equiv i PrOH 2N HCl
min
C
H
Ph
5
O(2)-C(14)
Ph
O(1)-Ca(1)-O(2)
O(1)-Ca(1)-O(4)
O(2)-Ca(1)-O(3)
O(2)-Ca(1)-O(5)
O(3)-Ca(1)-O(5)
Ca(1)-O(1)-C(1)
Ca(1)-O(3)-P(1)
Ca(1)-O(5)-P(3)
114.2(4)
110.2(4)
89.4(4)
O(1)-Ca(1)-O(3) 95.0(4)
O(1)-Ca(1)-O(5) 94.5(4)
O(2)-Ca(1)-O(4) 135.6(4)
O(3)-Ca(1)-O(4) 86.2(3)
O(4)-Ca(1)-O(5) 87.1(4)
Ca(1)-O(2)-C(14)160.0(10)
Ca(1)-O(4)-P(2) 171.9(7)
50%
50%
Scheme 10.Hydrogenation/protonation of sodium benzophenone ketyl
complex 11.
90.0(4)
169.8(4)
162.5(8)
165.6(6)
154.3(6)
product.On the other hand, the formation of benzhydrol or
fluorenol must proceed through hydrogen radical abstraction
from 2-propanol by a ketyl radical species,[
O(1)-C(1)-C(2)-C(8)/Ph(C2±7) dihedral angle:
O(1)-C(1)-C(2)-C(8)/Ph(C8±13) dihedral angle:
16
30
3d,h]
while the
formation of benzophenone or fluorenone obviously requires
oxidation of the corresponding ketyl species.As shown in
Scheme 11, hydrogen radical abstraction from 2-propanol by
one of the two ketyl radicals in a dimeric ketyl complex such
as 11 or 2 would yield the mixed ketyl/diarylmethoxide 15 and
the iPrO ´ radical.Subsequent oxidation of the ketyl unit in 15
by the inner-sphere radical iPrO ´ could afford the ketone
O(2)-C(14)-C(15)-C(21)/Ph(C15±20) dihedral angle: 20
O(2)-C(14)-C(15)-C(21)/Ph(C21±26) dihedral angle: 30
quantitatively the pinacol-coupling product 7 (Scheme 9).
However, when 2 was stirred with 5 equiv of 2-propanol in
THF for 30 min and then hydrolyzed with 2n HCl, fluorenol
and fluorenone were obtained in a 1:1 molar ratio, whereas 7
did not form (Scheme 9).Similarly, hydrolysis of 11 afforded
only benzopinacol, while the reaction of 11 with 2-propanol
followed by hydrolysis with 2n HCl exclusively yielded
benzhydrol and benzophenone in a 1:1 molar ratio (Scheme 10).
If the reaction of fluorenone ketylcomplex 2 with 2-propanol
was carried out for a shorter time (5 min), followed by
hydrolysis with 2n HCl, a mixture of fluorenol, fluorenone,
and 7 was obtained, in which the molar ratio of fluorenol to
fluorenone was still 1:1 (Scheme 9).The higher reactivity of
benzophenone ketyl is reflected in the analogous reaction of
(
benzophenone or fluorenone) and 16, which, after hydrolysis,
gives the alcohol (benzhydrol or fluorenol).The formation of
benzophenone and benzhydrol, as well as that of fluorenone
and fluorenol, in an approximately 1:1 molar ratio strongly
suggests that the oxidation of the ketyl radical species in 15 by
the inner-sphere radical iPrO ´ should be much faster than the
hydrogen radical abstraction from 2-propanol by a ketyl
radical species.Similarly, the reaction of the calcium bis(ben-
zophenone ketyl) complex 13 with 2-propanol, followed by
hydrolysis with 2n HCl, afforded benzhydrol and benzophe-
none, possibly through the intermediates 17 and 18, as shown
in Scheme 12.
11 with 2-propanol under the same conditions (5 min) which
afforded only benzhydrol and benzophenone without forma-
tion of a coupling product (Scheme 10).These results suggest
that the first step in the pinacol-coupling reaction of 2 or 11 is
Conclusion
‡
À
that of a proton (H ) attacking the oxygen anion (O ) of the
ketyl unit, leading to formation of a hydroxymethyl radical
species such as 14 (Scheme 11).Subsequent rapid dimeriza-
tion of the hydroxymethyl radical yields the final 1,2-diol
By using HMPA as a stabilizing ligand, we successfully
isolated and structurally characterized a series of alkali and
alkaline-earth metal ketyl complexes, including those of the
Chem. Eur. J. 2000, 6, No. 16
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Z.Hou, Y.Wakatsuki et al.
FULL PAPER
OH
C
HO OH
octahedral structures (9 and 10), while calcium benzophenone
ketyl favors a five-coordinate, trigonal-bipyramidal form (13).
On the other hand, the formation of the ketyl complexes 1 and
2 from the 1,2-diol 7 demonstrates that deprotonation of a
pinacol followed by C À C bond cleavage of the resultant
pinacolate can constitute a new method for the synthesis of
metal ketyls.The reactions of the ketyl complexes 2, 11, and
13 with 2-propanol and/or aqueous HCl have provided
unprecedented insights into the elemental steps of the
reduction of ketones by dissolving metals.
HCl
MCl
Ar
C
C
Ar
–
Ar
Ar
Ar
Ar
Ar Ar
C
O
14
HMPA
HMPA
HMPA
HMPA
M
M
O
C
Ar
M
Ar
C
O
Ar
Ar
HMPA
HMPA
i PrOH
HMPA
HMPA
M = an alkali metal
Ar = Ph or
Ar, Ar = biphenyl-2,2'-diyl
M
+ i PrO
slow
O
H
C
Ar
Ar
15
O
C
fast
Ar
Ar
Experimental Section
iPr
OH
HMPA
HMPA
O
General methods: All reactions were carried out under a dry and oxygen-
free argon atmosphere by Schlenk techniques or under a nitrogen
atmosphere in an Mbraun glovebox.The argon was purified by being
passed through a Dryclean column (4-Š molecular sieves, Nikka Seiko Co.)
and a Gasclean GC-XR column (Nikka Seiko Co.). The nitrogen in the
glovebox was constantly circulated through a copper/molecular sieves
(4 Š) catalyst unit.The oxygen and moisture concentrations in the
glovebox atmosphere were monitored by an O /H O Combi-Analyzer
HMPA
HMPA
HCl
M
M
Ar
C
H
Ar
–
–
MCl
i PrOH
O
C
H
Ar
Ar
16
Scheme 11.A plausible mechanism for the hydrogenation/protonation of
dimeric ketyl complexes.
2
2
(
Mbraun) to ensure both were always below 1 ppm.Samples for spectro-
scopic studies were prepared in the glovebox, and J.Young valve cells were
used for measurements.UV/Vis spectra were recorded on a Shimadzu UV-
2400PC spectrometer.ESR spectra were obtained on a Jeol JES FE 3AX
X-band spectrometer and the g value was calibrated with DPPH (2,2-
diphenyl-1-picrylhydrazyl).Elemental analyses were performed by the
Chemical Analysis Laboratory of RIKEN.Solvents were distilled from
sodium/benzophenone ketyl, degassed by the freeze ± thaw method (three
times) and dried over fresh Na chips in the glovebox.HMPA was distilled
from sodium chips under reduced pressure, degassed by the freeze ± thaw
method (three times) and dried over molecular sieves (4 Š).2-Propanol
was degassed by the freeze ± thaw method (three times) and dried over
molecular sieves (4 Š).Benzophenone and fluorenone were purchased
from Tokyo Kasei Co.and recrystallized from MeOH.
OH
C
HO OH
Ph
2
N HCl
CaCl2
Ph
2
Ph
C
C
–
Ph
Ph
HMPA
Ph Ph
C
O
O
Ph
Ph
14a
9
8% (isolated)
HMPA Ca
HMPA
C
OH
C
O
2
equiv i PrOH 2N HCl
Ph
Ph
Ph
+
C
13
25 min
Ph
Ph
H
5
0% (isolated) 46% (isolated)
slow
i PrOH
–
–
CaCl2
i PrOH
2N HCl
[Li(C
8 2 2
13H O)(HMPA) ] (1): A solution of fluorenone (366 mg, 2.03 mmol)
Ph
in THF (20 mL) was added to lithium shots (4 ± 16 mesh, 14 mg,
2.03 mmol). A brown mixture was initially obtained, which changed to
dark green after being stirred at room temperature for 7 h.Addition of
HMPA (0.71 mL, 4.06 mmol) yielded a dark brown solution, which was
then stirred for 20 min.After filtration and concentration under reduced
pressure, diethyl ether was layered, to give 1 as brown crystals (808 mg,
HMPA
HMPA
C
O
C
O
O
Ph
Oi Pr
HMPA Ca
HMPA
+
HMPA Ca
HMPA
+
i PrO
fast
O
C
Ph
Ph
Ph
H
Ph
H
C
Ph
Ph
18
17
0
3 2
.74 mmol, 73%). Reaction of 7 with two equivalents of LiN(SiMe ) in
Scheme 12.Hydrogenation/protonation of bis(benzophenone ketyl) com-
plex 13.
THF, followed by addition of four equivalents of HMPA, also afforded 1 in
3
À1 À1
75% yield.UV/Vis (THF, 22 8C): l ˆ 453 nm (e ˆ 6.3  10 cm
m
),
3
À1 À1
3
À1 À1
5
00 nm (e ˆ 4.6  10 cm
m
), 518 nm (e ˆ 4.7  10 cm
m
); ESR
(
THF, 228C): g ˆ 2.0030; elemental analysis calcd (%) for C50
88 12 6-
H N O
well-known sodium benzophenone ketyl.The structures of
4 2
P Li : C 55.04, H 8.13, N 15.40; found: C 55.08, H 8.20, N 15.58.
these ketyl complexes are dependent on both the ion size of
the metals and the structure of the ketones.Lithium
fluorenone ketyl favors a dimeric structure (1), while potas-
sium fluorenone ketyl prefers to form tetrameric aggregations
[Na(C H O)(HMPA) ] (2):
A
solution of fluorenone (360 mg,
2.00 mmol) in THF (20 mL) was added to fresh sodium chips (46 mg,
.00 mmol). The color of the mixture changed immediately to brown and
1
3
8
2 2
2
finally to dark green after being stirred at room temperature for 4 h.
Addition of HMPA (0.70 mL, 4.02 mmol) yielded a red-brown solution,
which was then stirred for 20 min.After filtration and concentration under
reduced pressure, hexane was layered to give 2 as brown crystals (910 mg,
(
4 and 5).In the case of sodium, both dimeric ( 2) and
tetrameric (3) fluorenone ketyl complexes can be isolated
through adjustment of the ligand-to-substrate ratios.For
sodium benzophenone ketyl, a trimeric complex (12), rather
than a simple benzophenone analogue of the tetrameric 3, is
preferred, while a dimeric complex (11) is also isolable.In
contrast to the one-electron reducing alkali metals, which
yield ketyl complexes bearing one ketyl ligand per metal ion,
the reactions of calcium metal with two equivalents of ketones
afford the corresponding bis(ketyl) complexes, in which two
independent ketyl ligands are bonded to one metal ion.
Calcium fluorenone ketyl tends to form six-coordinated,
0
.81 mmol, 81%). Reaction of 1,2-bis(biphenyl-2,2'-diyl)ethane-1,2-diol (7)
with two equivalents of NaN(SiMe in THF followed by addition of four
equivalents of HMPA also afforded 2 in 80% yield.UV/Vis (THF, 22 8C):
3 2
)
3
À1 À1
3
À1 À1
l ˆ 460 nm (e ˆ 4.4  10 cm
m
), 530 nm (e ˆ 6.1  10 cm
m ); ESR
(THF, 228C): g ˆ 2.0030; elemental analysis calcd (%) for C H N O P
5
0
88 12
6
4-
Na
2
: C 53.47, H 7.90, N 14.96; found: C 53.00, H 8.06, N 14.78.
O)(HMPA)] (3): A solution of fluorenone (360 mg, 2.00 mmol)
[Na(C13
H
8
4
in THF (20 mL) was added to fresh sodium chips (46 mg, 2.00 mmol). The
color of the mixture changed immediately to brown and finally to dark
green after being stirred at room temperature for 4 h.Addition of HMPA
(
0.35 mL, 2.01 mmol) yielded a brown solution, which was then stirred for
20 min.After filtration and concentration under reduced pressure, hexane
3002
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Chem. Eur. J. 2000, 6, No. 16

Alkali and Alkaline-Earth Metal Ketyl Complexes
2994±3005
was layered to give 3 as greenish-brown crystals (597 mg, 0.39 mmol, 78%).
added to fresh sodium chips (20 mg, 0.87 mmol). The resultant blue mixture
was stirred at room temperature for 4 h, during which all sodium chips
disappeared.After filtration and concentration under reduced pressure,
hexane was layered to yield 12 as blue blocks (242 mg, 0.18 mmol, 63%
based on Na, 84% based on HMPA).UV/Vis (THF, 22 8C): l ˆ 675 nm
3
À1 À1
UV/Vis (THF, 228C): l ˆ 460 nm (e ˆ 10.2  10 cm
m
), 530 nm (e ˆ
3
À1 À1
1
6.0 Â 10 cm
m
); ESR (THF, 228C): g ˆ 2.0030; elemental analysis
calcd (%) for C76
H 6.89, N 10.59.
104 12 8 4 4
H N O P Na : C 59.68, H 6.85, N 10.99; found: C 58.82,
3
À1 À1
(
e ˆ 6.5  10 cm
m
); ESR (THF, 228C): g ˆ 2.0030; elemental analysis
Na : C 56.79, H 7.72, N 12.61; found: C 56.40,
[
1
1
K(C13
H
8
O)(HMPA)]
.00 mmol) in THF (15 mL) was added to fresh potassium chips (39 mg,
.00 mmol). The resultant brown mixture was stirred at room temperature
4
(m-HMPA) (4): A solution of fluorenone (180 mg,
calcd (%) for C63
H
102
N
12
O
7
P
4
3
H 7.93, N 12.68.
for 4 h, and HMPA (0.35 mL, 2.01 mmol) was then added. After being
stirred for 20 min, the red-brown solution was filtered and concentrated
under reduced pressure.Layering of diethyl ether and hexane yielded 4 as
brown crystals (332 mg, 0.19 mmol, 75%). UV/Vis (THF, 228C): l ˆ
2 3 2 2
Ca(C13H10O) (HMPA) (13): CH I (2% mol) in THF (1 mL) was added to
calcium chips (28 mg, 0.7 mmol). After the mixture was stirred for 2 h at
room temperature to activate the metal surface, HMPA (0.36 mL,
2.08 mmol) was added. Addition of a solution of benzophenone (255 mg,
1.40 mmol) in THF (10 mL) yielded a blue mixture within a few minutes.
After being stirred at room temperature overnight, the blue solution was
filtered and concentrated under reduced pressure.Addition of hexane
precipitated 13 as blue blocks (510 mg, 0.54 mmol, 77%). UV/Vis (THF,
3
À1 À1
3
À1 À1
4
65 nm (e ˆ 10.2  10 cm
m
), 535 nm (e ˆ 19.6  10 cm
m ); ESR
(
C
THF, 228C): g ˆ 2.0032; elemental analysis calcd (%) for
82
H
122
N
15
O
9
P
5
K
4
: C 55.54, H 6.93, N 11.85; found: C 55.07, H 6.99, N 11.65.
O)(HMPA)] (m-THF) (5): A solution of fluorenone (184 mg,
.02 mmol) in THF was added to fresh potassium chips (40 mg, 1.02 mmol).
[
K(C13
H
8
4
3
À1 À1
2
28C): l ˆ 635 nm (e ˆ 3.8  10 cm
m
); ESR (THF, 228C): g ˆ 2.0028;
1
elemental analysis calcd (%) for C44
found: C 55.81, H 8.03, N 13.33.
74 9 5 3
H N O P Ca: C 56.09, H 7.92, N 13.38;
The resultant brown mixture was stirred at room temperature for 4 h, and
HMPA (0.089 mL, 0.51 mmol) was then added. After being stirred for
2
0 min, the brown solution was filtered and concentrated under reduced
A typical procedure for alcoholysis/hydrolysis of ketyls: To a solution of a
ketyl complex in THF was added 2 ± 5 equivalents of 2-propanol.Usually,
the typical color of a ketyl species faded gradually.then 2 n HCl was added.
The mixture was extracted with diethyl ether and dried over Na SO .The
pressure.Layering of hexane yielded 5 as dark brown crystals (152 mg,
0
.09 mmol; 36% based on K, 72% based on HMPA). UV/Vis (THF, 228C):
3
À1 À1
3
À1 À1
l ˆ 465 nm (e ˆ 7.3  10 cm
m
), 535 nm (e ˆ 13.0  10 cm
m
); ESR
2
4
(
C
THF, 228C): g ˆ 2.0032; elemental analysis calcd (%) for
organic products were separated by chromatography (silica gel) and
1
1
80
H
112
N
12
O
9
P
4
K
4
: C 57.67, H 6.78, N 10.09; found: C 56.89, H 6.81, N 10.31.
O) (THF) (m-THF) (6): A solution of fluorenone
400 mg, 2.22 mmol) in THF was added to fresh sodium chips (34 mg,
.48 mmol). The color of the mixture changed immediately to brown and
identified by H NMR comparison with authentic samples.The H NMR
spectra of the product mixture could also be easily assigned by comparison
with authentic samples.
Na
(
1
4
(m
3
-C13
H
8
O)
4
(C13H
8
2
2
2
X-ray crystallographic studies: Crystals for X-ray analyses were obtained as
described in the preparations.The crystals were manipulated in the
glovebox under a microscope mounted on the glovebox window, and were
sealed in thin-walled glass capillaries.Data were collected on a Mac
Science MXC3 K diffractometer (208C, MoKa radiation, graphite mono-
chromator, l ˆ 0.71073 Š, w-2q scan), and were corrected for Lorentzian
and polarization effects and X-ray absorption effects.Lattice constants and
orientation matrices were obtained by least-squares refinement of 25
reflections with 258 ꢀ 2q ꢀ 358.Three reflections were monitored periodi-
cally as a check for crystal decomposition or movement; no significant
decay or movement was observed.The observed systematic absences were
consistent with the space groups given in Table 11.The structures were
solved by direct methods with SIR92 in the Crystan-GM software package.
Hydrogen atoms in 1 and 2 were either located from the difference Fourier
maps, or placed at calculated positions.Attempts to locate the hydrogen
atoms in other complexes were not made.Refinements against jF j were
performed anisotropically for non-hydrogen atoms and isotropically for
hydrogen atoms by the block-diagonal least-squares method.Neutral
atomic scattering factors were taken from the International Tables for
finally to dark-green after being stirred at room temperature for 4 h.After
filtration, the solvent was evaporated to give a green crystalline product
which after recrystallization from diethyl ether afforded 6 as green crystals
(
1
460 mg, 0.31 mmol, 85%). UV/Vis (THF, 228C): l ˆ 460 nm (e ˆ 13.6 Â
3
À1 À1
3
À1 À1
0 cm
m
), 530 nm (e ˆ 16.0  10 cm
m
); ESR (THF, 228C): g ˆ
À1
2
.0030; IR (THF, 228C): nÄ CO ˆ 1720 cm ; elemental analysis calcd (%)
for C94
H
80
O
10Na
4
: C 77.25, H 5.52; found C 77.46, H 5.75.
Ca(C13
H
8
O)
2
(HMPA) (THF) (9): CH (2% mol) in THF (1 mL) was
2
2
2 2
I
added to calcium chips (31 mg, 0.77 mmol). After the mixture was stirred
for 2 h at room temperature to activate the metal surface, HMPA (0.27 mL,
1.54 mmol) was added. Addition of a solution of fluorenone (279 mg,
1.4 mmol) in (10 mL) yielded a brown mixture within a few minutes. After
being stirred at room temperature overnight, the brown solution was
filtered and concentrated under reduced pressure.Addition of hexane
precipitated 9 (549 mg, 0.61 mmol, 79%) as dark brown blocks. UV/Vis
3
À1 À1
(
1
THF, 228C): l ˆ 453 nm (e ˆ 4.5  10 cm
m
), 490 nm (e ˆ 2.6 Â
3
À1 À1
0 cm
m
); ESR (THF, 228C): g ˆ 2.0030; elemental analysis calcd (%)
for C46
H
68
N
6
O
6
P
2
Ca: C 61.18, H 7.59, N 9.31; found C 60.65, H 7.53, N 9.76.
X-Ray Crystallography.[ The residual electron densities (<1e Š ) were
of no chemical significance.Crystal data, data collection and processing
parameters are given in Table 11.Crystallographic data (excluding
structure factors) for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as supple-
mentary publication nos.CCDC-139185 ± CCDC-139194.Copies of the
data can be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit
11]
À3
Ca(C13
H
8
O)
2
(HMPA) (THF) (10): CH (2% mol) in THF (1 mL) was
3
2 2
I
added to calcium chips (21 mg, 0.52 mmol). After the mixture was stirred
for 2 h at room temperature (to activate the metal surface), HMPA
(
(
0.36 mL, 2.08 mmol) was added. Addition of a solution of fluorenone
189 mg, 1.05 mmol) in THF (10 mL) yielded a brown mixture within a few
minutes.After being stirred at room temperature overnight, the brown
solution was filtered and concentrated under reduced pressure.Addition of
hexane precipitated 10 (440 mg, 0.44 mmol, 84%) as dark brown blocks.
@ccdc.cam.ac.uk).
3
À1 À1
UV/Vis (THF, 228C): l ˆ 453 nm (e ˆ 4.2  10 cm
m
), 490 nm (e ˆ
3
À1 À1
2
.4 Â 10 cm
m
); ESR (THF, 228C): g ˆ 2.0030; elemental analysis calcd
(
78 9 6 3
%) for C48H N O P Ca: C 57.07, H 7.78, N 12.48; found: C 56.94, H 7.82, N
1
2.73.
Acknowledgements
[
Na(C13H10O)(HMPA) ] (11): HMPA (0.42 mL, 2.42 mmol) and a solu-
2 2
This work was partly supported by a grant-in-aid from the Ministry of
Education of Japan.We are grateful to Drs.M.Hoshino and Q.Meng for
ESR measurements.
tion of benzophenone (221 mg, 1.21 mmol) in THF (10 mL) were
successively added to fresh sodium chips (28 mg, 1.21 mmol). The resultant
blue mixture was stirred at room temperature for 4 h, during which all
sodium chips disappeared.After filtration and concentration under
reduced pressure, hexane was layered to give 11 as blue blocks (545 mg,
0
1
.48 mmol, 80%). UV/Vis (THF, 228C): l ˆ 675 nm (e ˆ 5.7 Â
[
1] For early examples of the formation of ketyl species, see: a) F.
Bechman, T.Paul, Justus Liebigs Ann. Chem. 1891, 266, 1; b) W.
Schlenk, T.Weichel, Ber. Dtsch. Chem. Ges. 1911, 44, 1182; c) W.
Schlenk, A.Thal, Ber. Dtsch. Chem. Ges. 1913, 46, 2840.
3
À1 À1
0 cm
m
); ESR (THF, 228C): g ˆ 2.0030; elemental analysis calcd (%)
Na : C 53.28, H 8.23, N 14.91; found: C 53.01, H 8.29, N
for C50
5.17.
Na
of benzophenone (158 mg, 0.87 mmol) in THF (10 mL) were successively
H
92
N
12
O
6
P
4
2
1
3
(C13
H
10O)
3
(HMPA)
4
(12): HMPA (0.15 mL, 0.87 mmol) and a solution
[2] For recent reviews on metal ketyl-mediated organic synthesis, see:
a) G.A.Molander, Acc. Chem. Res. 1998, 31, 603; b) T.Skrydstrup,
Chem. Eur. J. 2000, 6, No. 16
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0616-3003 $ 17.50+.50/0
3003

Z.Hou, Y.Wakatsuki et al.
FULL PAPER
Table 11.Summary of crystallographic data for 1 ± 6, 9 ± 11, and 13.
1
2
3
4
5
formula
C
50
H
88
N
12
O
6
P
4
Li
2
C
50
H
88
N
12
O
6
P
4
Na
2
C
76
H
104
N
12
O
8
P
4
Na
4
C
82
H
122
N
15
O
9
P
5
K
4
80 112 12 9 4 4
C H N O P K
f
w
1091.11
triclinic
1123.21
triclinic
1529.61
1773.24
monoclinic
P2 /n (no.14)
18.428(5)
24.208(7)
23.894(8)
1666.15
monoclinic
P2 /a (no.14)
22.010(5)
24.275(5)
17.462(4)
cryst syst
space group
a [Š]
b [Š]
c [Š]
a [8]
b [8]
g [8]
V [Š ]
monoclinic
C2/c (no.15)
29.195(7)
11.938(4)
27.942(7)
Å
Å
P1 (no.2)
10.929(1)
11.480(3)
13.799(2)
113.38(1)
102.68(1)
87.01(2)
1549.2(5)
1
P1 (no.2)
11.152(5)
12.398(2)
12.492(2)
107.56(1)
103.11(2)
95.53(2)
1598.1(7)
1
1
1
117.99(2)
112.64(2)
102.19(2)
3
8599(4)
4
1.20
9838(5)
4
1.21
9120(4)
4
Z
1
À3
calcd [gcm ]1.17
1.17
1.18
2
q range [8]
3 ± 55
1.688
6903
6395
3 ± 55
1.774
10413
7351
3 ± 55
1.585
8404
3 ± 55
3.374
18639
17192
8284 (x ˆ 3)
1036
3 ± 55
3.150
17448
16055
7061 (x ˆ 2)
982
À1
m [m
no.of reflns collcd
no.of unique reflns
no.of reflns for refinement ( I
no.of variables
]
7581
o
ꢁx s(I
o
))
3061 (x ˆ 3)
3864 (x ˆ 3)
1640 (x ˆ 3)
447
366
267
R
int
0.03
0.07
0.10
0.08
0.08
R [%]
[%]
5.60
5.64
6.64
6.68
10.49
11.79
7.93
8.59
8.58
9.39
R
w
6
´ C
6
H
6
2[9]
10
11
13
formula
C
100
H
86
O
10Na
4
C
92
H
136
N
12
O
12
P
4
Ca
2
C
48
H
78
N
9
O
6
P
3
Ca
C
50
H
92
N
12
O
6
P
4
Na
2
44 74 9 5 3
C H N O P Ca
f
w
1539.75
1806.24
triclinic
1010.22
monoclinic
P2 /n (no.14)
18.771(4)
13.876(3)
21.883(5)
1127.24
triclinic
942.14
triclinic
cryst syst
space group
a [Š]
b [Š]
c [Š]
a [8]
b [8]
g [8]
V [Š ]
monoclinic
C2/c (no.15)
20.279(5)
18.718(5)
21.814(6)
Å
Å
Å
P1 (no.2)
10.248(2)
13.846(8)
18.268(6)
94.33(4)
97.73(2)
93.96(3)
2553(2)
1
1
P1 (no.2)
10.960(2)
12.867(3)
13.416(5)
113.95(3)
107.96(2)
73.04(2)
1614.3(9)
1
P1 (no.2)
10.953(2)
11.812(2)
22.360(5)
93.09(2)
93.36(2)
108.92(2)
2724
93.33(2)
90.22(2)
3
8266(4)
4
1.24
5700(2)
4
1.18
Z
1
2
1.15
À3
calcd [g cm
]
1.18
1.16
2
q range [8]
3 ± 55
0.908
8003
5529
3556 (x ˆ 2)
510
3 ± 55
2.149
9690
8994
3 ± 55
2.628
11126
10046
4269 (x ˆ 2.5)
604
3 ± 50
1.758
6112
4387
3 ± 55
2.432
10383
9566
À1
m [cm
no.of reflns collcd
no.of unique reflns
no.of reflns for refinement ( I
no.of variables
]
o
ꢁx s(I
o
))
3114 (x ˆ 2)
2731 (x ˆ 3)
3929 (x ˆ 2)
448
334
559
R
int
0.06
0.10
0.08
0.05
0.06
R [%]
[%]
8.71
9.70
11.57
12.86
7.76
8.53
8.40
9.11
8.67
8.90
R
w
Angew. Chem. Int. Ed. Engl. 1997, 36, 345. Angew. Chem. 1997, 109,
55; c) G.A.Molander, C.R.Harris, Chem. Rev., 1996, 96, 307; d) T.
Wirth, Angew. Chem. Int. Ed. Engl., 1996, 35, 61; e) A.Fürstner,
Angew. Chem. Int. Ed. Engl., 1993, 32, 164. Angew. Chem. 1993, 105,
Chem. Int. Ed. Engl. 1997, 36, 2815; Angew. Chem. 1997, 109, 2925;
g) J.Takats, J. Alloys Compd. 1997, 249, 51; h) Z.Hou, A.Fujita, H.
Yamazaki, Y.Wakatsuki, J. Am. Chem. Soc. 1996, 118, 7843; i) Z.Hou,
A.Fujita, H.Yamazaki, Y.Wakatsuki, J. Am. Chem. Soc. 1996, 118,
2503; j) Z.Hou, T.Miyano, H.Yamazaki, Y.Wakatsuki, J. Am. Chem.
Soc. 1995, 117, 4421; k) H.Bock, H.-F.Herrmann, D.Fenske, H.
Goesmann, Angew. Chem. Int. Ed. Engl. 1988, 27, 1067; Angew. Chem.
1988, 100, 1125.
3
1
(
1
(
71.f) J W. .Huffman in
Eds.: B. M. Trost, I. Fleming), Pergamon, New York, 1991, chapter
.4; g) G. M. Robertson in Comprehensive Organic Synthesis, Vol. 3
Eds.: B. M. Trost, I. Fleming), Pergamon, New York, 1991, chapter
.6; h) J. E. McMurry, Chem. Rev. 1989, 89, 1513.
3] For structurally characterized ketyl complexes, see: a) Z.Hou, Y.
,
Comprehensive Organic Synthesis Vol. 8
2
[4] For example, sodium benzophenone ketyl is familiar to almost every
chemist for its use in dehydration and deoxygenation of ethereal
solvents.
[5] All alkali and alkaline-earth metal ketyl complexes reported in this
paper showed well-resolved X-band ESR spectra and UV/Vis spectra
(see Experimental Section), which were similar to those previously
reported for the corresponding ketyl species generated in situ.For
examples of spectroscopic studies on alkali and alkaline-earth metal
ketyl species, see: a) P.H.Rieger, G.K.Fraenkel, J. Chem. Phys. 1962,
[
Wakatsuki, Chem. Eur. J. 1997, 3, 1005; b) Z.Hou, Y.Wakatsuki, Top.
Organomet. Chem. 1999, 2, 233; c) Z.Hou, A.Fujita, T.Koizumi, H.
Yamazaki, Y.Wakatsuki, Organometallics 1999, 18, 1979; d) Z.Hou,
A.Fujita, Y.Zhang, T.Miyano, H.Yamazaki, Y.Wakatsuki,
J. Am.
Chem. Soc. 1998, 120, 754; e) Z.Hou, X.Jia, Y.Wakatsuki, Angew.
Chem. Int. Ed. Engl. 1997, 36, 1292; Angew. Chem. 1997, 109, 1348;
f) W.Clegg, C.Eaborn, K.Izod, P.O 'Shaughnessy, J.D.Smith, Angew.
3004
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Chem. Eur. J. 2000, 6, No. 16

Alkali and Alkaline-Earth Metal Ketyl Complexes
2994±3005
3
7, 2811; b) N.Hirota, S .I .Weissman,
J. Am. Chem. Soc. 1964, 86,
[9] a) Z.Hou, Y.Wakatsuki, J. Chem. Soc., Chem. Commun. 1994, 1205;
2
538; c) N.Hirota, J. Am. Chem. Soc. 1967, 89, 32; d) K.Nakamura, N.
b) Z.Hou, Y.Zhang, Y.Wakatsuki,
149.
Bull. Chem. Soc. Jpn. 1997, 70,
Hirota, Chem. Phys. Lett. 1969, 3, 134; e) S.W.Mao, N.Hirota, Chem.
Phys. Lett. 1973, 22, 26; f) S.W.Mao, K.Nakamura, N.Hirota, J. Am.
Chem. Soc. 1974, 96, 5341.
[10] Crystal data for 12: C63
H
102
N
12
O
7
P
4
Na , F
3
w
ˆ 1332.46, monoclinic,
space group P2 /c (No.14),
1
a ˆ 12.2681(6), b ˆ 25.389(2), c ˆ
3
[
[
[
6] H.R.Luss, D.L.Smith, Acta Crystallogr. Sect. B 1972, 28, 884.
7] T.Yoshimura, Z.Hou, Y.Wakatsuki, Organometallics 1995, 14, 5382.
8] For previous examples of complexes bearing bridging THF ligands,
25.032(1) Š, b ˆ 93.445(4)8, Vˆ 7782.9(7) Š , Z ˆ 4,
1
calcd
ˆ
À3
1.14 gcm .Since the crystal was very small, the diffraction data
(collected on an Enraf-Nonius CAD4 diffractometer with a rotating
Cu anode) were not good enough for satisfactory full refinement of
the structure.Nevertheless, the connectivity of the whole molecule
was unequivocally determined.
see: a) Z.Hou, A.Fujita, H.Yamazaki, Y.Wakatsuki,
Commun. 1998, 669; b) S.Brooker, F.T.Edelmann, T.Kottke, H.W.
Roesky, G.M.Scheldrick, D.Stalke, K.H.Whitmire,
Chem. Commun. 1991, 144; c) Q.Shen, M.Qi, Y.Lin, J. Organomet.
Chem. 1990, 399, 247.
Chem.
J. Chem. Soc.
[11] D.T.Cromer, J.T.Waber,
International Tables for X-Ray Crystallog-
raphy, Kynoch, Birmingham, 1974.
Received: January 24, 2000 [F2257]
Chem. Eur. J. 2000, 6, No. 16
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0947-6539/00/0616-3005 $ 17.50+.50/0
3005