Metallacrown ethers with trans-tetracarbonylmolybdenum(0) centers

Article abstract of DOI:10.1016/S0020-1693(01)00350-4

Photolysis of the cis-Mo(CO)₄{Ph₂P(CH₂CH₂O) _nCH₂CH₂PPh₂-P,P′}, (1, n = 3; 2, n = 4; 3, n = 5) metallacrown ethers in tetrahydrofuran under nitrogen gives moderate yiel

Full text of DOI:10.1016/S0020-1693(01)00350-4

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 317 (2001) 199–210
Metallacrown ethers with trans-tetracarbonylmolybdenum(0)
centers. X-ray crystal structures of
trans-Mo(CO)4{Ph2P(CH2CH2O)nCH2CH2PPh2-P,P%} (n=3, 5)
and trans-Mo(CO)4{Ph2P(CH2CH2O)2-1-C6H4-2-
(OCH2CH2)2PPh2-P,P%}
Christina H. Duffey a, Charles H. Lake b, Gary M. Gray c,*
a Department of Chemistry, Samford Uni6ersity, Birmingham, AL 35229, USA
b Department of Chemistry, Indiana Uni6ersity of Pennsyl6ania, Indiana, PA 15701, USA
c Department of Chemistry, The Uni6ersity of Alabama at Birmingham, CHEM201, 1530 3rd A6e. Street, Birmingham, AL 35294-1240, USA
Received 2 November 2000; accepted 24 January 2001
Abstract
Photolysis of the cis-Mo(CO)4{Ph2P(CH2CH2O)nCH2CH2PPh2-P,P%}, (1, n=3; 2, n=4; 3, n=5) metallacrown ethers in
tetrahydrofuran under nitrogen gives moderate yields of the corresponding trans-Mo(CO)4{Ph2P(CH2CH2O)nCH2CH2PPh2-P,P%}
(4, n=3; 5, n=4; 6, n=5) metallacrown ethers. The trans-metallacrown ethers are also obtained when catalytic amounts of
HgCl2 are added to chloroform solutions of the cis-metallacrown ethers. The 1 ? 4 and 2 ? 5 equilibria are established within
3 min at ambient temperature and approximately equal amounts of the cis- and trans-metallacrown ethers are present in the
equilibrium mixtures. The 3 ? 6 equilibrium is more complicated because HgCl2 complexation by 3 also occurs in these solutions.
Addition of excess HgCl2 to the equilibrium mixture of 3 and 6 results in the formation of the previously reported
cis-Mo(CO)4{m-Ph2P(CH2CH2O)5CH2CH2PPh2-P,P%,O,O%,O¦,O§,O¨}HgCl2. Comparison of the X-ray crystal structures of the
trans-metallacrown ethers 4–6 and trans-Mo(CO)4{Ph2P(CH2CH2O)2-1-C6H4-2-(OCH2CH2)2PPh2-P,P%} (7) indicates that both
ring size and flexibility affect the conformations of the metallacrown ether rings. The larger oxygen–oxygen distances in the
trans-metallacrown ethers, compared with those in the corresponding cis-metallacrown ethers 1,
3
and cis-
Mo(CO)4{Ph2P(CH2CH2O)2-1-C6H4-2-(OCH2CH2)2PPh2-P,P%} (8), may explain why the trans-metallacrown ethers have not been
observed to bind strongly the hard metal cations. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Molybdenum complexes; Carbonyl complexes; Crown ethers complexes
temperature even though the HgCl2 is in a separate
phase (solid or aqueous) from that containing the cis-
metallacrown ether (chloroform-d).
1. Introduction
Cis–trans isomerizations of the cis-tetracarbonyl-
molybdenum(0) complexes of a,v-bis(phosphorus-
donor)polyether ligands (cis-metallacrown ethers) occur
when these complexes are either exposed to UV light
[1,2] or treated with catalytic amounts of HgCl2 [2,3].
All of the HgCl2-catalyzed reactions that have been
studied to date are complete within 3 min at ambient
The trans-metallacrown ethers are unusual in that
the chelating bis(phosphorus-donor) ligands bridge the
trans positions of the octahedral metal centers. Only
three complexes of this type [4,5] were known prior to
our initial report [1] and these complexes either con-
tained a bis(phosphine) ligand either with a rigid back-
bone that prevented cis coordination [4] or were
prepared by ring closure after monodentate phosphine
ligands were trans-coordinated to the metal center [5].
Unlike the cis-metallacrown ethers [6], the trans-metal-
* Corresponding author. Tel.: +1-205-9344747; fax: +1-205-
9342543.
E-mail address: gmgray@uab.edu (G.M. Gray).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00350-4

200
C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
To gain more insight into the manner in which the
unusual coordination mode of the a,v-bis(phosphorus-
donor)polyether ligands in trans-metallacrown ethers
affects the properties of these complexes, we have stud-
lacrown ethers do not appear to coordinate metal
cations. Consistent with this observation, the carbonyl
ligands in the trans-metallacrown ethers are not acti-
vated towards attack by organolithium reagents [3,7].
Table 1
31P and phenyl 13C NMR data a
No. P (31P) (ppm)
ipso
ortho
meta
para l(13C)
(ppm)
l(13C) (ppm)
ꢀJ(PC)ꢀ (Hz)
l(13C) (ppm)
ꢀJ(PC)ꢀ (Hz)
l(13C) (ppm)
ꢀJ(PC)ꢀ (Hz)
1 b
2 b
3 b
4
20.36s
20.11s
20.44s
35.24s
32.32s
32.53s
137.48aq
136.94aq
136.17aq
139.90t
139.48t
139.05t
57 c
56 c
62 c
16 f
132.14aq
132.13aq
132.12aq
131.77t
131.70t
131.56t
9 d
9 d
8 d
6 g
6 g
6 g
128.30
129.30s
129.32s
129.46s
128.30s
129.16s
129.08s
128.35aq
128.33bs
128.23t
128.28bs
128.18
8 e
5 h
f
5 i
6
17
16 f
a b=broad, s=singlet, t=triplet, aq=apparent quintet.
b Data from Ref. [8].
c
d
e
f
1
ꢀ J(PC)+3J(PC)ꢀ.
2
ꢀ J(PC)+4J(PC)ꢀ.
3
ꢀ J(PC)+5J(PC)ꢀ.
1
ꢀ J(PC)ꢀ.
g
h
2
ꢀ J(PC)ꢀ.
3
ꢀ J(PC)ꢀ.
i Data from Ref. [1].
Table 2
Aliphatic and carbonyl 13C NMR data a
No. C1
C2
C3, C4, C5, CO cis
C6 (l(13C))
CO trans
(ppm)
l(13C) (ppm) ꢀJ(PC)ꢀ (Hz) l(13C) (ppm) ꢀJ(PC)ꢀ (Hz)
l(13C) (ppm) ꢀJ(PC)ꢀ (Hz) l(13C) (ppm) ꢀJ(PC)ꢀ (Hz)
1 b
2 b
31.83aq
31.31aq
14 c
67.71bs
66.95bs
70.66s,
71.54s
70.16s,
70.25s,
70.65s
69.96s,
70.34s,
70.47s,
70.47s
70.02s,
72.82s
70.24s,
71.03s,
71.07s
70.34s,
70.43s,
70.57s,
70.62s
214.96aq
215.08aq
14 d
209.79t
209.69t
9 e
15 c
16 d
8 e
3 b
31.34aq
20 c
66.94bs
215.05aq
14 d
209.55t
9 e
4
34.22aq
34.37aq
11 c
11 c
66.91aq
66.96aq
6 d
210.35w
210.59t
5 f
12 d
8 c
6
NO g
67.60bs
NO
a b=broad, s=singlet, t=triplet, aq=apparent quintet, w=weak.
b Data from Ref. [8].
c
d
e
1
ꢀ J(PC)+3J(PC)ꢀ.
2
ꢀ J(PC)ꢀ.
2
ꢀ J(PC)+2J(P%C)ꢀ.
f Data from Ref. [5].
g NO=not observed.

C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
201
Table 3
Data collection and structure solution and refinement parameters for 4, 6 and 7 a
4
6
7
Formula
MW
C36H36Mo1O7P2
738.57
C40H44Mo1O9P2
826.68
C42H40MoO8P2
830.19
(
(
(
Space group
P1
P1
P1
,
a (A)
10.032(2)
11.792(2)
16.776(2)
103.13(1)
99.11(1)
109.02(1)
1765.8
12.112(1)
13.350(2)
14.215(2)
63.50(1)
74.16(1)
83.39(1)
1978.8
8.834(1)
13.947(2)
17.440(3)
71.79(1)
76.13(1)
80.50(1)
1972.0
2
,
b (A)
,
c (A)
h (°)
i (°)
g (°)
3
,
V (A )
Z
2
2
dcalc (g cm−3
)
1.389
1.387
1.399
0.3×0.3V0.2
0, 9
−14, 14
−18, 18
0.71073
23
4.6
1.0–22.5
none
Crystal dimensions (mm3)
hmax, hmin
1.0×0.5×0.2
13, −12
1, −15
21, −21
0.71073
23
4.9
1.0–27.5
−1.3
0.6×0.6×0.2
0, −15
17, −17
17, −18
0.71073
23
4.5
1.0–27.5
−5.1
kmax, kmin
lmax, lmin
,
u (A)
Temperature (°C)
Absorption coefficient (cm−1
q limits (°)
)
Decay (%)
Decay corr.
Abs. corr.
Tmax, Tmin (%)
Reflections measured
Scan type
linear
linear
not applicable
„ scan
93.08, 84.14
5536
„ scan
99.91, 96.02
9266
„ scan
99.77, 82.46
9077
ꢀ–2q
ꢀ–2q
ꢀ
Reflections [I\2|(I)]
No. of variables
Function min.
Weighting scheme
Inst. uncert. fact.
Extinction corr.
Extinction coeff.
R (%) a
6760
416
4110
470
3206
478
w(ꢀFoꢀ−ꢀFcꢀ)2
non-Poisson
0.03
w(ꢀFoꢀ−ꢀFcꢀ)2
non-Poisson
0.05
w(ꢀFoꢀ−ꢀFcꢀ)2
w
-1=|2+0.0039F2
not applicable
not applicable
Zachariesen
9.0169×10−7
4.1
5.0
1.581
Zachariesen
1.0160×10−7
7.9
8.4
1.385
5.47
5.99
0.91
1.27, −0.68
0.00
Rw (%) b
GOF c
−3
,
Max., min. residual elect. den. (e A
Max. shift/error
)
0.651, −0.116
0.00
0.998, −0.274
0.00
a R=ꢁ(ꢀ Fo ꢀ−ꢀFc ꢀ)/ꢁ(ꢀ Fo ꢀ).
2 0.5
b Rw=ꢁ w(ꢀ Fo ꢀ−ꢀFcꢀ)2/ꢁ(ꢀ Fo ꢀ )
.
c GOF=[ꢁ w(ꢀ Fo ꢀ−ꢀFcꢀ)2/(nobsv−nvar)]0.5
.
2. Experimental section
ied the isomerizations of cis-Mo(CO)4{Ph2P-
(CH2CH2O)nCH2CH2PPh2-P,P%} (n=3 (1); 4 (2); 5 (3))
metallacrown ethers to the corresponding trans-
Mo(CO)4{Ph2P(CH2CH2O)nCH2CH2PPh2-P,P%} (n=3
(4); 4 (5); 5 (6)) metallacrown ethers using both UV
light and HgCl2. X-ray crystal structures of 4, 6 and the
previously reported trans-Mo(CO)4{Ph2P(CH2CH2O)2-
1-C6H4-2-(OCH2CH2)2PPh2-P,P%} (7) have also been
determined and are compared to that of 5, which was
previously reported [1].
All NMR spectra were recorded at 21°C on a Bruker
ARX 300 MHz NMR spectrometer with a quad (1H,
13C, 19F, 31P) 5 mm probe. The 31P{1H} NMR spectra
were referenced to external 85% H3PO4 and the
13C{1H} spectra were referenced to internal TMS. The
31P and 13C data for the complexes are given in Tables
1 and 2 with positive chemical shifts downfield from
those of the references. Quantitative 31P(1H} NMR

202
C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
Table 5
spectra were run using a 30° inverse-gated pulse se-
quence with a 20 s pulse delay. Infrared spectra of
dilute dichloromethane solutions of the carbonyl com-
plexes in a 0.2 mm KBr solution cell were run on either
a Perkin–Elmer Paragon 1000 FTIR or a Nicolet IR44
FTIR spectrometer. The background for these mea-
surements was pure dichloromethane in the same cell.
Elemental analyses of the compounds were performed
by Atlantic Microlab, Inc., Norcross, GA.
All the solvents and HgCl2 were of reagent grade and
were used as received. The water was deionized. Te-
trahydrofuran (THF) was dried over MgSO4 before
use. Chloroform-d1 was opened and handled under a
dry nitrogen atmosphere at all times. The cis-
Mo(CO)4{Ph2P(CH2CH2O)nCH2CH2PPh2-P,P%} (n=3
(1), 4 (2), 5 (3)) metallacrown ethers [8,9] and trans-
Mo(CO)4{Ph2P(CH2CH2O)2 - 1 - C6H4 - 2 - (OCH2CH2)2-
PPh2-P,P%} (7) metallacrown ether [2b] were prepared
using the literature procedures.
,
Selected bond distances (A) and angles (°) for 6
MoꢀP1
MoꢀP2
MoꢀC37
MoꢀC38
MoꢀC39
MoꢀC40
P1ꢀC1
P1ꢀC13
P1ꢀC19
P2ꢀC12
P2ꢀC25
P2ꢀC31
O1ꢀC2
2.487(2)
2.471(2)
2.019(9)
2.01(1)
2.03(1)
2.02(1)
1.82(1)
1.82(1)
1.839(7)
1.84(1)
1.83(1)
1.829(8)
1.40(1)
1.40(1)
1.38(1)
1.41(1)
O3ꢀC6
O3ꢀC7
O4ꢀC8
O4ꢀC9
O5ꢀC10
O5ꢀC11
O6ꢀC40
O7ꢀC37
O8ꢀC38
O9ꢀC39
C1ꢀC2
C3ꢀC4
C5ꢀC6
C7ꢀC8
C9ꢀC10
C11ꢀC12
1.39(1)
1.36(2)
1.43(1)
1.41(1)
1.41(1)
1.44(1)
1.14(2)
1.14(1)
1.15(1)
1.14(1)
1.52(1)
1.46(2)
1.51(2)
1.46(1)
1.51(2)
1.50(1)
O1ꢀC3
O2ꢀC4
O2ꢀC5
P1ꢀMoꢀP2
P1ꢀMoꢀC37
P1ꢀMoꢀC38
P1ꢀMoꢀC39
P1ꢀMoꢀC40
P2ꢀMoꢀC37
P2ꢀMoꢀC38
P2ꢀMoꢀC39
P2ꢀMoꢀC40
MoꢀP1ꢀC1
MoꢀP1ꢀC13
MoꢀP1ꢀC19
MoꢀP2ꢀC12
MoꢀP2ꢀC25
MoꢀP2ꢀC31
C2ꢀO1ꢀC3
173.77(9)
94.7(3)
88.0(3)
87.9(3)
91.6(3)
91.2(3)
89.9(3)
86.2(3)
90.6(3)
118.8(3)
113.0(3)
119.3(3)
117.5(4)
115.1(3)
119.6(3)
115.8(7)
113.7(8)
117.(1)
C8ꢀO4ꢀC9
C10ꢀO5ꢀC11
P1ꢀC1ꢀC2
113.5(9)
113.6(7)
113.8(6)
108.9(7)
117.3(9)
113(1)
108.6(9)
109(1)
117(1)
111(1)
108.1(9)
113(1)
108.9(7)
112.9(6)
178(1)
177.4(8)
179(1)
O1ꢀC2ꢀC1
O1ꢀC3ꢀC4
O2ꢀC4ꢀC3
O2ꢀC5ꢀC6
O3ꢀC6ꢀC5
O3ꢀC7ꢀC8
O4ꢀC8ꢀC7
O4ꢀC9ꢀC10
O5ꢀC10ꢀC9
O5ꢀC11ꢀC12
P2ꢀC12ꢀC11
MoꢀC37ꢀO7
MoꢀC38ꢀO8
MoꢀC39ꢀO9
MoꢀC40ꢀO6
2.1. UV photoisomerizations
Dry THF (150 ml) was poured into an Ace concen-
tric photochemical reactor and purged for 10 min with
dry nitrogen. The solid cis-metallacrown ether was then
added to the THF. This solution was irradiated with a
350 W mercury vapor lamp for 20 min. Water was
Table 4
C4ꢀO2ꢀC5
C6ꢀO3ꢀC7
,
Selected bond distances (A) and angles (°) for 4
177.9(9)
MoꢀP1
MoꢀP2
MoꢀC33
MoꢀC34
MoꢀC35
MoꢀC36
P1ꢀC1
P1ꢀC21
P1ꢀC27
P2ꢀC8
2.472(2)
2.472(2)
2.031(9)
2.025(5)
2.019(6)
2.014(8)
1.839(7)
1.837(7)
1.837(6)
1.845(8)
1.844(8)
1.830(5)
1.42(1)
O1ꢀC3
O2ꢀC4
O2ꢀC5
O3ꢀC6
O3ꢀC7
O4ꢀC33
O5ꢀC34
O6ꢀC35
O7ꢀC36
C1ꢀC2
C3ꢀC4
C5ꢀC6
C7ꢀC8
1.409(9)
1.43(1)
1.42(1)
1.413(7)
1.41(1)
1.13(1)
1.143(7)
1.150(8)
1.15(1)
1.493(9)
1.50(1)
1.50(1)
1.525(9)
circulated through a jacket located between the lamp
and solution chambers to cool the solution. The irradi-
ation time was chosen to maximize the production of
the trans-metallacrown ether and minimize photochem-
ical decomposition. After the irradiation was com-
pleted, the solution was evaporated to dryness. The
residue was dissolved in methylene chloride and filtered
through silica gel. The filtrate was concentrated on a
rotary evaporator to 5–10 ml and streaked on to a
silica gel prep TLC plate. A 2:5 ethyl acetate:hexanes
solvent system was used to develop the plate. The
bands containing the cis- and trans-metallacrown
ethers were scraped off and the complexes were eluted
from the silica gel with methanol. The methanol solu-
tions were evaporated to dryness on a rotary evapora-
tor and the solid products were dried for 2 h under high
vacuum (0.5 mm Hg).
P2ꢀC9
P2ꢀC15
O1ꢀC2
P1ꢀMoꢀP2
P1ꢀMoꢀC33
P1ꢀMoꢀC34
P1ꢀMoꢀC35
P1ꢀMoꢀC36
P2ꢀMoꢀC33
P2ꢀMoꢀC34
P2ꢀMoꢀC35
P2ꢀMoꢀC36
MoꢀP1ꢀC1
MoꢀP1ꢀC21
MoꢀP1ꢀC27
MoꢀP2ꢀC8
MoꢀP2ꢀC9
MoꢀP2ꢀC15
177.01(7)
88.6(3)
89.5(2)
91.3(2)
91.3(3)
88.5(3)
89.8(2)
89.5(2)
91.6(3)
116.5(3)
119.0(3)
114.6(2)
118.5(3)
120.9(3)
110.9(2)
C2ꢀO1ꢀC3
C4ꢀO2ꢀC5
C6ꢀO3ꢀC7
P1ꢀC1ꢀC2
O1ꢀC2ꢀC1
O1ꢀC3ꢀC4
O2ꢀC4ꢀC3
O2ꢀC5ꢀC6
O3ꢀC6ꢀC5
O3ꢀC7ꢀC8
P2ꢀC8ꢀC7
MoꢀC33ꢀO4
MoꢀC34ꢀO5
MoꢀC35ꢀO6
MoꢀC36ꢀO7
113.0(7)
111.6(7)
112.5(6)
112.1(6)
109.0(7)
114.1(6)
110.6(7)
110.5(8)
110.8(7)
109.4(7)
114.1(6)
175.2(5)
179.3(7)
178.2(7)
176.4(6)
2.2. trans-Mo(CO)4{Ph2P(CH2CH2O)3CH2CH2PPh2-
P,P%} (4)
Using the above procedure 0.122 g (0.165 mmol) of 1
yielded 0.030 g (24%) of 4 and 0.020 g (16%) of 1 was

C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
203
recovered. Anal. Found: C, 52.20; H, 4.99. Calc. for
C36H36MoO7P2 (4). 1.5 CH2Cl2: C, 52.01; H, 4.54%. IR
(CH2Cl2) (4) (cm−1): w(s, CO) 1895.
ether of known concentration was prepared in an NMR
tube. The headspace of the tube was then flushed with
nitrogen and the tube was carefully sealed with a
septum cap. Both the 13C{1H} and 31P{1H} NMR
spectra of this solution were recorded. Then, an aliquot
of a 45 mg ml−1 aqueous solution of HgCl2 was in-
jected under the surface of the chloroform-d1 solution
and dispersed by vigorous shaking. A 31P{1H} NMR
spectrum was run as quickly as possible and then
31P{1H} NMR spectra were taken at regular intervals
until no change was observed in the ratio of the inte-
grals of the resonances due to the cis- and trans-metal-
lacrown ethers. At this point a quantitative 31P{1H}
NMR spectrum was run and the resonances due to the
cis- and trans-metallacrown ethers were integrated to
determine accurately the concentrations of both
complexes.
A 0.60 ml solution of 1 was made for the NMR study
with 0.093 g (0.13 mmol) of 1 dissolved in chloroform-
d1. A volume of 10.0 ml of the 45 mg ml−1 aqueous
HgCl2 (0.0018 mmol) was added to this solution.
A 0.66 ml solution of 2 was made for the NMR study
with 0.020 g (0.024 mmol) of 2 dissolved in chloroform-
d1. A volume of 1.5 ml of the 45 mg ml−1 aqueous
HgCl2 (0.00024 mmol) was added to this solution.
A 0.66 ml solution of 3 was made for the NMR study
with 0.089 g (0.11 mmol) of 3 dissolved in chloroform-
d1. A volume of 37.3 ml of 45 mg ml−1 aqueous HgCl2
(0.0062 mmol) was added to this solution.
2.3. trans-Mo(CO)4{Ph2P(CH2CH2O)4CH2CH2-
PPh2-P,P%} (5)
Using the above procedure 0.129 g (0.165 mmol) of 2
yielded 0.030 g (23%) of 5 and 0.060 g (47%) of 2 was
recovered. Anal. Found: C, 57.82; H, 5.33. Calc. for
C38H40MoO8P2 (5): C, 58.32; H, 5.15%. IR (CH2Cl2) (5)
(cm−1): w(s, CO) 1896.
2.4. trans-Mo(CO)4{Ph2P(CH2CH2O)5CH2CH2-
PPh2-P,P%} (6)
Using the above procedure 0.136 g (0.165 mmol) of 3
yielded 0.040 g (29%) of 6 and 0.050 g (37%) of 3 was
recovered. Anal. Found: C, 58.22; H, 5.37. Calc. for
C40H44MoO9P2 (6): C, 58.12; H, 5.36%. IR (CH2Cl2) (6)
(cm−1): w(s, CO) 1895.
2.5. 31P NMR studies of isomerizations catalyzed by
HgCl2
A chloroform-d1 solution of the cis-metallacrown
Table 6
,
Selected bond distances (A) and angles (°) for 7
MoꢀP1
MoꢀP2
MoꢀC39
MoꢀC40
MoꢀC41
MoꢀC42
P1ꢀC1
P1ꢀC15
P1ꢀC21
P2ꢀC14
P2ꢀC27
P2ꢀC33
O1ꢀC2
2.468(2)
2.483(2)
2.039(8)
2.024(9)
2.022(8)
2.013(8)
1.859(7)
1.840(7)
1.828 (9)
1.858(7)
1.852(9)
1.834(7)
1.412(11)
1.422(9)
1.307(11)
O2ꢀC5
1.424(14)
1.345(19)
1.411(24)
1.433(11)
1.396(10)
1.131(10)
1.144(10)
1.133(10)
1.155(10)
1.514(10)
1.563(15)
1.366(22)
1.385(21)
1.504(10)
O3ꢀC10
O3ꢀC11
O4ꢀC12
O4ꢀC13
O5ꢀC39
O6ꢀC40
O7ꢀC41
O8ꢀC42
C1ꢀC2
2.6. Collection of the X-ray diffraction data and solution
of the crystal structures 4, 6 and 7
Crystals of each compound were grown at room
temperature by the diffusion of methanol into a
dichloromethane solution of the complex. All the crys-
tals were mounted and aligned on an Enraf–Nonius
CAD4 diffractometer with k-geometry. All the data
were collected at 23°C with Mo Ka radiation (u=
C3ꢀC4
C5ꢀC10
C11ꢀC12
C13ꢀC14
O1ꢀC3
O2ꢀC4
,
0.71073 A), and corrected for Lorentz and polarization
effects as well as for absorption. Cell constants were
determined by the least-squares refinement of 25 reflec-
tions with sin q/u between 0.30 and 0.36. Details of the
data collections are given in Table 3.
P1ꢀMoꢀP2
172.0(1)
91.7(3)
89.6(2)
93.3(3)
82.8(3)
95.9(3)
83.2(2)
90.3(3)
94.7(3)
118.6(3)
113.1(3)
119.6(2)
113.9(3)
121.6(2)
112.0(3)
111.4(7)
C4ꢀO2ꢀC5
107.8(8)
113.4(11)
110.2(7)
115.9(5)
110.2(7)
113.1(9)
108.9(8)
120.0(11)
115.7(11)
107.5(13)
113.3(11)
109.3(6)
178.0(7)
174.3(6)
177.8(7)
174.4(7)
P1ꢀMoꢀC39
P1ꢀMoꢀC40
P1ꢀMoꢀC41
P1ꢀMoꢀC42
P2ꢀMoꢀC39
P2ꢀMoꢀC40
P2ꢀMoꢀC41
P2ꢀMoꢀC42
MoꢀP1ꢀC1
MoꢀP1ꢀC15
MoꢀP1ꢀC21
MoꢀP2ꢀC14
MoꢀP2ꢀC27
MoꢀP2ꢀC33
C2ꢀO1ꢀC3
C10ꢀO3ꢀC11
C12ꢀO4ꢀC13
P1ꢀC1ꢀC2
O1ꢀC2ꢀC1
O1ꢀC3ꢀC4
All the three compounds crystallized in the triclinic
crystal system with the possible space groups being the
O2ꢀC4ꢀC4
(
centrosymmetric space group P1 (No. 2) or the non-
O2ꢀC5ꢀC10
O3ꢀC10ꢀC5
O3ꢀC11ꢀC12
O4ꢀC12ꢀC11
O4ꢀC13ꢀC14
MoꢀC39ꢀO5
MoꢀC40ꢀO6
MoꢀC41ꢀO7
MoꢀC42ꢀO8
centrosymmetric space group P1 (No. 1). In all cases,
the intensity statistics clearly favored the centrosymmet-
ric space group. This was later confirmed by the suc-
cessful solution and refinement of each of the crystal
structures. All the structures were solved with Patterson
methods. All the hydrogen atoms were placed at calcu-
lated positions with the appropriate staggered
geometry.

204
C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
Fig. 1. ORTEP drawing of the molecular structure of trans-Mo(CO)4{Ph2P(CH2CH2O)3CH2CH2PPh2-P,P%} (4). Thermal ellipsoids are drawn at
the 50% probability level and hydrogen atoms are omitted for clarity.
In all cases, refinement converged with no parameter
varying by more than 0.01|. The final difference-
Fourier maps possessed no unexplained anomalous
peaks. Selected bond distances and angles for structures
4, 6 and 7 are presented in Tables 4–6, respectively.
cement. The crystal was then mounted and aligned
upon the diffractometer. Data (9077) were collected by
means of an ꢀ–2q scan out to sin q/u=0.65. This data
set contained 4110 unique reflections with I\3|(I).
Analysis of the three standard reflections revealed a
5.1% decay during the data collection. This was cor-
rected by a linear decay correction. Structure solution
2.7. trans-Mo(CO)4{Ph2P(CH2CH2O)3CH2CH2PPh2-
P,P%} (4)
and refinement were accomplished using the MOlEN
program package. The structure converged with R=
7.9% and Rw=8.4%. The final difference-Fourier map
A colorless blocky crystal (dimensions=1.0×0.5×
0.2 mm3) was glued to the tip of a glass fiber with
epoxy cement. Data (9266) were collected by means of
an ꢀ–2q scan out to sin q/u=0.65. This data set
contained 6760 unique reflections with I\3|(I). No
appreciable decay was noted during the data collection.
Structure solution and refinement were accomplished
showed residual electron density in the range −0.274
−3
e A –0.998 e A−3. The final labeling of the atoms is
,
,
presented in Fig. 2.
2.9. trans-Mo(CO)4{Ph2P(CH2CH2O)2-1-C6H4-2-
(OCH2CH2)2PPh2-P,P%} (7)
using the MOlEN program package. The structure con-
verged with R=4.1% and Rw=5.0%. The final differ-
A colorless blocky crystal (dimensions=0.3×0.3×
0.2 mm3) was placed in a thin-walled glass capillary
under aerobic conditions. The crystal was then
mounted and aligned upon the diffractometer. Data
(5536) were collected by means of an ꢀ scan out to
sin q/u=0.54. This data set contained 3206 unique
reflections with I\3|(I). No appreciable decay was
noted during the data collection. Structure solution and
refinement were accomplished using the SHELXTL-PC
ence-Fourier map showed residual electron density in
the range −0.116 e A –0.651 e A−3. The final label-
−3
ing of the atoms is presented in Fig. 1.
,
,
2.8. trans-Mo(CO)4{Ph2P(CH2CH2O)3CH2CH2PPh2-
P,P%} (6)
A yellow blocky crystal (dimensions=0.6×0.6×0.2
mm3) was glued to the tip of a glass fiber with epoxy

C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
205
program package. The structure converged with
R=5.5% and Rw=6.0%. The final difference-Fourier
map showed no anomalous features after refinement,
We have now carried out photolyses of 1–3 under
identical conditions to determine if the size of the
metallacrown ether ring influences the reaction. Irradia-
tion of 0.0011 M solutions of the cis-metallacrown
ethers 1–3 with UV light for 20 min resulted in
complex reaction mixtures in which the primary
components were the cis- and trans-metallacrown
ethers. The cis:trans ratio in each of the crude reaction
mixtures is nearly the same, based on the integration of
the 31P NMR resonances (1:4=60:40, 2:5=57:43,
3:6=56:44). This suggests that the ring size does not
have a significant effect upon the extent of the isomeri-
zation. The isolated yields of trans- and cis-metalla-
crown ethers from thin layer chromatography were not
consistent with the 31P NMR data (a 24% yield for 4, a
23% yield for 5 and a 29% yield for 6 with a 16%
reclamation of 1, a 47% reclamation of 2 and a 37%
reclamation of 3) because the two isomers were not
totally resolved by chromatography. It is interesting to
note, however, that the total metallacrown ether
recovery for the n=3 metallacrown ethers (40%) was
significantly lower than for the n=4 (70%) and n=5
(66%) metallacrown ethers. This suggests that, although
the smaller ring does not appear to affect the cis:trans
ratio, it does allow more side reactions to occur.
with the residual electron density in the range −0.68
−3
,
e A
to 1.27 e A−3. The final labeling of the atoms is
,
presented in Fig. 3.
3. Results and discussion
3.1. UV photoisomerizations
In a recent communication [1] we reported the
isomerization of the cis-metallacrown ether 2 into the
trans-metallacrown ether 5 upon exposure to UV
radiation for 12 min, as shown in (Eq. (1)).
(1)
Fig. 2. ORTEP drawing of the molecular structure of trans-Mo(CO)4{Ph2P(CH2CH2O)5CH2CH2PPh2-P,P%} (6). Thermal ellipsoids are drawn at
the 50% probability level and hydrogen atoms are omitted for clarity.

206
C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
Fig. 3. ORTEP drawing of the molecular structure of trans-Mo(CO)4{Ph2P(CH2CH2O)2-1-C6H4-2-(OCH2CH2)2PPh2-P,P%} (7). Thermal ellipsoids
are drawn at the 25% probability level and hydrogen atoms are omitted for clarity.
3.2. HgCl2-catalyzed isomerizations
Keq=[trans]/[cis]
(2)
The HgCl2-catalyzed isomerization of 2–5 was nearly
identical to that of 1–4. With a 100:1 mole ratio of 2 to
HgCl2 the equilibrium was established within 3 min and
gave equimolar amounts of 2 and 5. The equilibrium
constant for the reaction at 21°C, calculated using Eq.
(2), was 1.0. The results for the HgCl2-catalyzed
isomerizations of 1–4 and 2–5 are consistent with those
of the UV photoisomerizations in which nearly
equimolar amounts of the cis- and trans-metallacrown
ethers are observed in the crude reaction products after
20 min of photolysis.
We have also recently reported that HgCl2 serves as
a catalyst for the isomerization of 2–5, but forms a 1:1
adduct with 3 [2a]. To rationalize these seemingly
contradictory results and to determine if HgCl2
catalysis is a better route to the trans-metallacrown
ethers than UV photolysis, we have studied the
reactions of the three cis-metallacrown ethers 1–3 with
HgCl2 under identical conditions. These studies were
carried out in mixtures of chloroform-d and water to
test the phase transfer abilities of the cis-metallacrown
ethers and the reactions were followed by 31P{1H}
NMR spectroscopy.
For 1 the cis–trans equilibrium is established in less
than 3 min, which is the time needed to add the
aqueous HgCl2 solution to the chloroform-d solution of
1, shake the two layers vigorously and record
qualitative 31P{1H} NMR spectra. No change in this
ratio is observed if the mixture is allowed to stand for
several hours. The reaction is obviously catalytic, based
on the fact that a 100:1 mole ratio of 1 to HgCl2 was
used. Equimolar amounts of 1 and 4 were present in the
equilibrium mixture and the equilibrium constant for
the reaction at 21°C, calculated using Eq. (2), was 1.0.
The HgCl2-catalyzed isomerization of 3–6 was quite
different from those of 1–4 and 2–5. No isomerization
was observed with a 100:1 mole ratio of 3 to HgCl2.
Table 7
Effect of HgCl2 on the equilibrium between 3·HgCl2 and 6
HgCl2:metallacrown ether
mol% 3·HgCl2
mol% 6
1:1
2:1
3:1
4:1
77.5
86.3
92.3
96.4
22.5
13.7
7.7
3.6

C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
207
shift the equilibrium towards the complexed cis-metal-
lacrown ether 3·HgCl2. To determine if this was indeed
the case, aqueous solutions containing varying amounts
of HgCl2 were added to a chloroform-d solution of 3.
As shown in Table 7, at a HgCl2 to metallacrown ether
ratio of 4:1 essentially all of the metallacrown ether is
in the cis-form and is complexed to the HgCl2.
3.3. Cis–trans isomerizations in Mo(CO)4-containing
metallacrown ethers
As shown in Fig. 4, changing the steric constraints in
Mo(CO)4-containing metallacrown ether rings has a
significant effect on the cis–trans equilibrium constants.
As might be expected, steric bulk next to the phospho-
rus-donor group (10 and 11) shifts the equilibrium
towards the trans isomer. Surprisingly, replacing the
central ethylene in 2 with a 1,2-phenylene group in 8
has an equally strong effect in the opposite direction in
spite of the fact that the steric requirements of the
1,2-phenylene group are transmitted to the cis-
Mo(CO)4 center through the flexible oxyethylene
groups. This suggests that there are a limited number of
Fig. 4. Cis–trans equilibrium constants for various metallacrown
ethers.
Table 8
Bond angles (°) around the Mo in the trans-metallacrown ethers
4
5
6
7
P1ꢀMoꢀP2
Avg. PꢀMoꢀC towards
177.01
89.56
175.69
90.32
173.77
92.02
172.0
87.6
ring (ÚPMoCsyn
Avg. PꢀMoꢀC away from
ring (ÚPMoCanti
)
90.55
89.65
88.00
92.8
)
Difference between ideal
+2.99
−4.31
−6.23
+8.0
and observed a
a (+) indicates that the P1ꢀMoꢀP2 angle is directed towards the
same side of the molybdenum as the metallacrown ether ring; (−)
indicates that the P1ꢀMoꢀP2 angle that is B180° is directed towards
the opposite side of the molybdenum from the metallacrown ether
ring.
When the mole ratio of 3 to HgCl2 was changed to
20:1, the isomerization occurred slowly and, after 7 h,
the 3:6 ratio was 64:36. With a 10:1 mole ratio of 3 to
HgCl2 the rate of the isomerization increased and, after
2 h, the 3:6 ratio was 56:44. No attempts were made to
calculate the equilibrium constants for this isomeriza-
tion because the HgCl2 not only serves as a catalyst but
also binds to 3 to form a bimetallic complex 3·HgCl2.
This suggests that coordination of the HgCl2 by 3
inhibits its ability to catalyze the isomerization of 3–6,
perhaps by saturating all of the coordination sites on
the Hg2+ cation.
Because HgCl2 does not bind strongly to the trans-
metallacrown ether 6 but does bind strongly to the
cis-metallacrown ether 3, it seemed likely that the addi-
tion of excess of HgCl2 to the reaction mixture should
Fig. 5. Ball and stick drawings of the trans-metallacrown ethers with
oxyethylene bridges 4–6, in equivalent orientations.

208
C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
Table 9
Selected torsion angles (°) for 4–7
4
5
6
7
MoꢀP1ꢀC1ꢀC2
P1ꢀC1ꢀC2ꢀO1
C1ꢀC2ꢀO1ꢀC3
C2ꢀO1ꢀC3ꢀC4
O1ꢀC3ꢀC4ꢀO2
C3ꢀC4ꢀO2ꢀC5
60.2
178.1
165.7
−80.6
77.0
MoꢀP1ꢀC1ꢀC2
P1ꢀC1ꢀC2ꢀO1
C1ꢀC2ꢀO1ꢀC3
C2ꢀO1ꢀC3ꢀC4
O1ꢀC3ꢀC4ꢀO2
C3ꢀC4ꢀO2ꢀC5
C4ꢀO2ꢀC5ꢀC6
O2ꢀC5ꢀC6ꢀO3
65.5
−173.4
−166.4
−61.5
−50.5
157.9
MoꢀP1ꢀC1ꢀC2
P1ꢀC1ꢀC2ꢀO1
C1ꢀC2ꢀO1ꢀC3
C2ꢀO1ꢀC3ꢀC4
O1ꢀC3ꢀC4ꢀO2
C3ꢀC4ꢀO2ꢀC5
C4ꢀO2ꢀC5ꢀC6
O2ꢀC5ꢀC6ꢀO3
C5ꢀC6ꢀO3ꢀC7
C6ꢀO3ꢀC7ꢀC8
O3ꢀC7ꢀC8ꢀO4
C7ꢀC8ꢀO4ꢀC9
C8ꢀO4ꢀC9ꢀC10
O4ꢀC9ꢀC10ꢀO5
C9ꢀC10ꢀO5ꢀC11
C10ꢀO5ꢀC11ꢀC12
O5ꢀC11ꢀC12ꢀP2
C11ꢀC12ꢀP2ꢀMo
65.8
172.0
179.8
−76.2
73.7
−158.8
−174.2
74.7
−174.1
−67.9
82.9
−156.7
−172.7
−65.9
91.5
130.4
−173.7
−69.9
MoꢀP1ꢀC1ꢀC2
P1ꢀC1ꢀC2ꢀO1
C1ꢀC2ꢀO1ꢀC3
C2ꢀO1ꢀC3ꢀC4
O1ꢀC3ꢀC4ꢀO2
C3ꢀC4ꢀO2ꢀC5
C4ꢀO2ꢀC5ꢀC10
O2ꢀC5ꢀC10ꢀO3
−66.6
95.4
−179.6
179.1
82.9
164.1
84.4
−16.2
177.1
−177.8
142.4
C5ꢀC6ꢀO3ꢀC7
C6ꢀO3ꢀC7ꢀC8
O3ꢀC7ꢀC8ꢀO4
C7ꢀC8ꢀO4ꢀC9
C8ꢀO4ꢀC9ꢀC10
O4ꢀC9ꢀC10ꢀP2
C9ꢀC10ꢀP2ꢀMo
168.9
173.9
−79.6
82.8
178.4
−173.5
−65.3
C5ꢀC10ꢀO3ꢀC11
C10ꢀO3ꢀC11ꢀC12
O3ꢀC11ꢀC12ꢀO4
C11ꢀC12ꢀO4ꢀC13
C12ꢀO4ꢀC13ꢀC14
O4ꢀC13ꢀC14ꢀP2
C13ꢀC14ꢀP2ꢀMo
−174.7
170.9
−70.3
−145.4
178.4
C4ꢀO2ꢀC5ꢀC6
O2ꢀC5ꢀC6ꢀO3
C5ꢀC6ꢀO3ꢀC7
C6ꢀO3ꢀC7ꢀC8
O3ꢀC7ꢀC8ꢀP2
C7ꢀC8ꢀP2ꢀMo
−172.2
−82.0
−172.6
178.1
85.6
−66.4
−178.5
−60.0
Table 10
,
Distances (A) between the ether oxygens in the trans-metallacrown ethers
Bonds between oxygens
3
4
5
6
7
O1ꢀO2
O2ꢀO3
3.047
3.040
O1ꢀO2
O2ꢀO3
O3ꢀO4
2.864
3.372
3.057
O1ꢀO2
O2ꢀO3
O3ꢀO4
O4ꢀO5
3.035
O1ꢀO2
O2ꢀO3
O3ꢀO4
3.050
2.683
2.826
2.898
3.087
2.882
6
O1ꢀO3
5.527
O1ꢀO3
O2ꢀO4
5.633
6.083
O1ꢀO3
O2ꢀO4
O3ꢀO5
5.861
5.374
5.167
O1ꢀO3
O2ꢀO4
4.476
4.491
9
O1ꢀO4
7.619
O1ꢀO4
O2ꢀO5
7.976
6.368
O1ꢀO4
5.332
12
O1ꢀO5
8.314
conformations for the metallacrown ether rings, most
likely due to the steric bulk of the phosphorus-donor
groups.
the ideal (180°) and observed P1ꢀMoꢀP2 bond angles.
The direction of the ring strain, either towards or away
from the metallacrown ether ring, is more difficult to
determine. Perhaps the best means of estimating this is
to compare the average of the PꢀMoꢀC angles for the
two carbonyls that point towards the metallacrown
ether ring (ÚPMoCsyn) with the average of the
PꢀMoꢀC angles for the two carbonyls that point away
from the metallacrown ether ring (ÚPMoCanti). If
ÚPMoCsyn is smaller than ÚPMoCanti, the P1ꢀMoꢀP2
angle is distorted towards the metallacrown ether ring,
suggesting that the ligand is too small to span the trans
positions. If ÚPMoCsyn is larger than ÚPMoCanti, the
P1ꢀMoꢀP2 angle is distorted away from the metal-
lacrown ether ring, suggesting that the ligand easily
spans the trans positions and pushes the phosphines
away from the metallacrown ether ring. From the data
summarized in Table 8 the least distortion is observed
3.4. Solid state conformations
The molecular structures of 4,
6 and trans-
Mo(CO)4{Ph2P(CH2CH2O)2 - 1 - C6H4 - 2 - (OCH2CH2)2-
PPh2-P,P%} (7) have been determined, and are com-
pared to that of 5, which was previously reported [1].
The coordination environment about the molybdenum
in each of the complexes is a distorted octahedron with
the phosphines occupying trans coordination sites.
One of the most interesting aspects of these struc-
tures is the insight that they provide into ring strain in
the trans-metallacrown ethers. The magnitude of the
ring strain is easily measured by the difference between

C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
209
in 4 and is towards the metallacrown ether ring. The
distortion in 5 is slightly larger than in 4 but is away
from the metallacrown ether ring. The distortion in 6 is
in the same direction as in 5 but is significantly greater
while the distortion in 7 is even larger than in 6 but is
directed towards the metallacrown ether ring as is that
in 4. These data indicate that the ligands with only
oxyethylene groups can readily span the trans positions
of the octahedral metal center (in 4–6), and that the
difficulty in packing these ligands on one side of the
trans-Mo(CO)4 group increases as the number of
oxyethylene groups increases (4B5B6). In contrast,
the metallacrown ether ring in 7, which contains a
sterically constraining 1,2-phenylene group, has
difficulty bridging the trans positions of the octahedral
metal center. These inferences about the ring strain in
the trans-metallacrown ethers are consistent with the
values of Kct that were discussed above. The Kct values
for 1 ? 4 and 2 ? 5 are identical, as expected from the
lack of significant ring strain in either trans-metal-
lacrown ether. In contrast, the Kct value for 8 ? 7 is
much smaller than for 1 ? 4 and 2 ? 5, consistent with
the greater ring strain in 7.
The conformations of the metallacrown ether rings in
the trans-metallacrown ethers are also of interest. As
shown in Fig. 5, the conformations near the metal
center for the trans-metallacrown ethers with
oxyethylene bridges (4–6) are nearly identical. This is
apparently due to the steric constraints imposed by the
carbonyl ligands and the diphenylphosphino groups on
the molybdenum. Thus the torsion angles about both
PꢀC bonds and about the CꢀC and CꢀO bonds of one
Ph2PCH2CH2O group in 4–6 are nearly identical. In
contrast, the steric constraints imposed by the 1,2-phen-
ylene group in 7 result in a significantly different ring
conformation as shown by the different torsion angles
in Table 9.
(O2ꢀO3 for 5) because all the ethylene groups, except
the one bridging the O2 and O3 oxygens in 5, are
gauche. The distances between the other oxygens are
more variable, but are significantly smaller in 7 with the
sterically constraining 1,2-phenylene group than in the
trans-metallacrown ethers with oxyethylene bridges. It
is also interesting that the sterically constraining 1,2-
phenylene group in 7 causes the O1ꢀO4 distance (5.332
,
A) to be much smaller than the O1ꢀO4 distance in 5
,
(7.619 A), and even slightly smaller than the O1ꢀO3
,
distance in 4 (5.527 A). This is further support for the
suggestion that the introduction of the sterically con-
straining groups into metallacrown ethers may greatly
affect the abilities of these complexes to bind the alkali
metal cations [2b,6].
As expected, the distances between the ether oxygens
separated by more than one ethylene group are signifi-
cantly larger in the trans-metallacrown ethers than in
the cis-metallacrown ethers containing the same a,v-
bis(phosphine)polyether ligands. This is most easily ob-
served for the distance between the first and last
oxygens in the metallacrown ether ring (O1ꢀO3: 4.481
,
,
,
A for 1 [8] versus 5.527 A for 4; O1ꢀO5: 7.445 A for 3
,
[10] versus 8.314 A for 6). The longer OꢀO distances in
the trans-metallacrown ethers may explain why these
complexes, unlike the cis-metallacrown ethers, do not
bind the alkali metal cations strongly.
1
3.5. 31P, H, and 13C NMR spectroscopic studies
The 31P{1H} NMR chemical shifts for the trans-
metallacrown ethers are downfield of those in the cis-
metallacrown ethers, indicating that the phosphorus is
more deshielded in the trans-metallacrown ethers [1,3].
The 13C{1H} NMR chemical shifts of the Cipso and C1
carbons in the trans-metallacrown ethers are also
downfield of those in the cis-metallacrown ethers, con-
sistent with the 31P{1H} NMR data. There is some
variation in the differences in the chemical shifts for the
three pairs of cis- and trans-metallacrown ethers (Dl:
4–1=14.88 ppm, 5–2=12.21 ppm, 6–3=12.09 ppm).
The larger difference between the 31P{1H} NMR chem-
ical shifts of 4 and 1 is consistent with the smaller
metallacrown ether rings in these complexes. The
smaller metallacrown ether ring in 4 may also explain
why the 13C{1H} NMR resonance of either the C3 or
C4 methylene of 4 is found 1.5 ppm farther downfield
than any of the other 13C resonances of the ring
methylenes in the metallacrown ethers.
The major conformational differences between the
metallacrown ether rings in 4–6 occur after the first
oxygens (O1 and O3 in 4, O1 and O4 in 5, and O1 and
O5 in 6). The angle between the least-squares plane
through the ether oxygens and the least-squares plane
through Mo, P1, P2 and the centroids of the carbonyl
carbons group on each side of the metallacrown ether
ring (C33/C34 and C35/C36 for 4, C35/C37 and C36/
C38 for 5 [1] and C37/C38 and C39/C40 for 6) is quite
dependent on the size of the trans-metallacrown ether
ring. This angle is significantly larger for 4 (68°) and 5
(72°) than for 6 (39.2°), suggesting that the large metal-
lacrown ether ring in 6 folds to minimize the crystal
packing forces.
The distances between the ether oxygens in trans-
metallacrown ethers should affect their abilities to bind
the alkali metal cations. These distances are summa-
rized in Table 10 for the four trans-metallacrown
ethers. Distances between the oxygens separated by a
single ethylene group are similar with one exception
4. Summary
Cis–trans isomerization of metallacrown ethers oc-
curs when the cis-metallacrown ethers are irradiated
with UV light, and is also efficiently catalyzed by

210
C.H. Duffey et al. / Inorganica Chimica Acta 317 (2001) 199–210
References
HgCl2. The HgCl2-catalyzed isomerizations of 1–4 and
2–5 are very rapid. In contrast, the HgCl2-catalyzed
isomerization of 3–6 is significantly slower, probably
because 3 strongly coordinates HgCl2. The equilibrium
constants for the cis–trans isomerization of Mo(CO)4-
containing metallacrown ethers are very sensitive to the
nature of the metallacrown ether ring. Sterically bulky
groups adjacent to the phosphine favor the trans-iso-
mer and sterically constraining groups in the metal-
lacrown ether ring favoring the cis-isomer. Sterically
constraining groups in the metallacrown ether ring also
affect the solid state conformation of the trans-metal-
lacrown ether, as indicated by the smaller distances
between the ether oxygens separated by more than one
ethylene group.
[1] G.M Gray, C.H. Duffey, Organometallics 13 (1994) 1542.
[2] (a) G.M Gray, C.H. Duffey, Organometallics 14 (1995) 245. (b)
C.H. Duffey, C.H. Lake, G.M. Gray, Organometallics 17 (1998),
3550.
[3] M. Hariharasarma, C.H. Lake, C.L. Watkins, G.M. Gray, J.
Organomet. Chem. 580 (1999) 328.
[4] E. Baumgartner, F.J.S. Reed, L.M. Venanzi, F. Bachechi, P.
Mura, L. Zambonelli, Helv. Chim. Acta 66 (1983) 2752.
[5] R.A. Leising, J.L. Grzybowski, K.J. Takeuchi, Inorg. Chem. 27
(1988) 1020.
[6] G.M. Gray, F.P. Fish, C.H. Duffey, Inorg. Chim. Acta 246 (1996)
229 (Special edition on Macrocyclic Complexes).
[7] (a) J. Powell, A. Kuksis, C.J. May, S.C. Nyberg, S.J. Smith, J. Am.
Chem. Soc. 103 (1981) 5941. (b) J. Powell, S.C. Nyberg, S.J. Smith,
Inorg. Chim. Acta 76 (1983) L75. (c) J. Powell, K.S. Ng, W.W. Ng,
S.C. Nyberg, J. Organomet. Chem. 243 (1983) C1. (d) J. Powell, M.
Gregg, A. Kuskis, P. Meindl, J. Am. Chem. Soc. 105 (1983) 1064.
(e) J. Powell, M.R. Gregg, A. Kuksis, C.J. May, S.J. Smith,
Organometallics 8 (1989) 2918. (f) J. Powell, A. Kuskis, C.J. May,
P.E. Meindl, S.J. Smith, Organometallics 8 (1989) 2933. (g) J. Pow-
ell, M.R. Gregg, P.E. Meindl, Organometallics 8 (1989) 2942.
[8] A. Varshney, G.M. Gray, Inorg. Chem. 30 (1991) 1748.
[9] A. Varshney, M.L. Webster, G.M. Gray, Inorg. Chem. 31 (1992)
2580.
Acknowledgements
The authors thank the Chemistry Department of the
University of Alabama at Birmingham and the ACS
Petroleum Research Fund (grant 35349-AC3) for sup-
port of this work.
[10] G.M. Gray, D.C. Smith Jr., C.H. Duffey, Inorg. Chim. Acta 300–
302 (2000) 581.
.