Partially Shielded Fe(CO)3 Rotors: Syntheses, Structures, and Dynamic Properties of Complexes with Doubly trans Spanning Diphosphines, trans- Fe(CO)3(PhP((CH2)n)2 PPh)

Article abstract of DOI:10.1021/acs.organomet.7b00330

Reactions of Fe(CO)₃(n⁴-benzylideneacetone) and PhP((CH₂)_mCH=CH₂)₂ (m = a, 4; b, 5; c, 6) give trans-Fe(CO)₃(PhP((CH₂)_mCH=CH₂)₂)₂ (2a-c, 28-70%), which are treated with Grubbs' catalyst (15 mol %; refluxing CH₂Cl₂). NMR analyses of the crude interligand metathesis products trans-Fe(CO)₃(PhP((CH₂)_mCH=CH(CH₂)_m)₂PPh) (3a-c, 30-31%) suggest Z/E C=C mixtures and/or byproducts from intraligand metathesis or oligomers. Subsequent hydrogenations (5 bar/cat. Rh(Cl)(PPh₃)₃ or PtO₂) afford trans-Fe(CO)₃(PhP((CH₂)_n)₂PPh) (4a-c, 69-77%; n = 2m + 2, synperiplanar phenyl groups), which density functional theory calculations show to be more stable than isomers derived from other metathesis modes. Crystallizations give (E,E)-3a and 4b, the X-ray structures of which are determined and analyzed. Variableerature ¹³C{¹H} NMR experiments show that rotation of the Fe(CO)₃ moiety in 4b is rapid on the NMR time scale (RT to 0 °C; δG^?_{273 K} ≤ 12.8 kcal/mol), but that in 4a is not (RT to 105 °C; δG^?_{378 K} ≥ 17.9 kcal/mol). These data indicate rotational barriers lower than those in analogues in which three methylene chains connect the phosphorus atoms, trans-Fe(CO)₃(P((CH₂)_n)₃P).

Full text of DOI:10.1021/acs.organomet.7b00330

Article
pubs.acs.org/Organometallics
Partially Shielded Fe(CO)3 Rotors: Syntheses, Structures, and
Dynamic Properties of Complexes with Doubly trans Spanning
Diphosphines, trans-Fe(CO)3(PhP((CH2)n)2PPh)
Esther Steigleder,† Takanori Shima,† Georgette M. Lang,‡ Andreas Ehnbom,‡ Frank Hampel,†
and John A. Gladysz*,†,‡
†Institut fur Organische Chemie and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander-Universitat
̈
̈
Erlangen-Nurnberg, Henkestraße 42, 91054 Erlangen, Germany
̈
‡Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77843-3012, United States
S
* Supporting Information
ABSTRACT: Reactions of Fe(CO)3(η4-benzylideneacetone)
and PhP((CH2)mCHCH2)2 (m = a, 4; b, 5; c, 6) give trans-
Fe(CO)3(PhP((CH2)mCHCH2)2)2 (2a−c, 28−70%),
which are treated with Grubbs’ catalyst (15 mol %; refluxing
CH2Cl2). NMR analyses of the crude interligand metathesis
products trans-Fe(CO)3(PhP((CH2)mCHCH(CH2)m)2PPh)
(3a−c, 30−31%) suggest Z/E CC mixtures and/or byprod-
ucts from intraligand metathesis or oligomers. Subsequent
hydrogenations (5 bar/cat. Rh(Cl)(PPh3)3 or PtO2) afford
trans-Fe(CO)3(PhP((CH2)n)2PPh) (4a−c, 69−77%; n = 2m + 2,
synperiplanar phenyl groups), which density functional theory
calculations show to be more stable than isomers derived from
other metathesis modes. Crystallizations give (E,E)-3a and 4b, the X-ray structures of which are determined and analyzed.
Variable-temperature 13C{1H} NMR experiments show that rotation of the Fe(CO)3 moiety in 4b is rapid on the NMR
time scale (RT to 0 °C; ΔG⧧
≤ 12.8 kcal/mol), but that in 4a is not (RT to 105 °C; ΔG⧧
≥ 17.9 kcal/mol). These
273 K
378 K
data indicate rotational barriers lower than those in analogues in which three methylene chains connect the phosphorus atoms,
trans-Fe(CO)3(P((CH2)n)3P).
bonds and a resulting increase in vertical (top/bottom) free
van der Waals space within the cage-like assembly.
INTRODUCTION
■
The intersection of alkene metathesis and inorganic or
organometallic synthesis has proved to be a rich area, allowing
targeted approaches to a variety of complex metal-containing
molecules.1,2 We evolved initial interests in metallomacrocycle
and metallamacrocycle syntheses (I and II in Scheme 1)3,4 into a
program involving gyroscope-like complexes of the general type
IIIa.5−11 These are distinguished by three methylene chains that
span two trans-phosphorus donor atoms and are assembled by
alkene metathesis/hydrogenation sequences. Some of the most
interesting and intensively studied species have trigonal planar
iron carbonyl cores or “rotators” (Fe(CO)3, Fe(CO)2(NO)+,
Fe(CO)(NO)(X))5 within the dibridgehead diphosphine
“stators”. Many crystal structures and barriers to Fe(CO)(L)(L′)
rotation have been determined.
As such, another goal became the synthesis of related trigonal
bipyramidal complexes with two instead of three trans spanning
methylene chains. These would have fewer impediments in a
horizontal dimension to rotator rotation. Also, their lower
symmetries cansimplify the determinationof activation parameters
by variable-temperature NMR. Accordingly, in this paper, we
describe the syntheses, structures, and dynamic properties of a
series of iron tricarbonyl bis(phenyldialkylphosphine) complexes of
the formula trans-Fe(CO)3(PhP((CH2)n)2PPh) (n = 10, 12, 14).
A number of characteristics are carefully compared to those of
related species IIIa, affording new insights regarding the various
factors contributing to Fe(CO)(L)(L′) rotational barriers.
RESULTS
■
The interpretation of the rotational barriers has required a
variety of supporting synthetic and physical studies. For example,
analogous dibridgehead diarsine complexes have been prepared
(IIIb).12 Their distinctly lower barriers have been analyzed in the
context of the longer iron−arsenic versus iron−phosphorus
Syntheses of Title Complexes. The monophosphine ligands
needed for the precursor iron complexes, PhP((CH2)mCHCH2)2
Received: May 8, 2017
© XXXX American Chemical Society
A
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adducts trans-Fe(CO)3(PhP((CH2)mCHCH2)2)2 (2a−c) as
yellow-brown oils in 28−70% yields. These and all other iso-
merically homogeneous new complexes described below were
characterized by IR and NMR (1H, 13C{1H}, 31P{1H}) spec-
troscopy, and often by mass spectrometry and microanalyses, as
summarized in the Experimental Section. Key NMR data are
presented in Table 1.
Scheme 1. Typical Metal-Containing Macrocycles
Constructed via Alkene Metathesis (i = Grubbs’ Catalyst;
ii = H2, Hydrogenation Catalyst)
Next, dilute CH2Cl2 solutions of 2a−c (0.0009−0.0010 M)
were treated with Grubbs’ first generation catalyst (7.5 mol %, or
3.75%/new CC linkage). The samples were stirred at 45 °C,
and aliquots were monitored by 1H and 31P{1H} NMR. The data
were consistent with the formation of the target interligand
metathesis products trans-Fe(CO)3(PhP((CH2)mCHCH-
(CH2)m)2PPh) (3a−c). However, a second catalyst charge
(7.5 mol %) was necessary for the complete consumption of all
terminal alkene moieties. Workups gave crude 3a−c in 30−31%
yields.
The NMR data suggested that 3a−c were mixtures of CC
geometric isomers (e.g., EE, EZ, ZZ). The 31P NMR spectra
showed more than three signals, suggesting the presence of
oligomers or other types of isomers, one possibility being 3′a−c
(Scheme 2), derived from intraligand metathesis. In any case,
3a−c were hydrogenated (5 bar, 15 h) using either Wilkinson’s
catalyst or PtO2. Chromatographic workups gave the title com-
(1; m = a, 4; b, 5; c, 6), were accessed by one of two methods.
The first, a published procedure,3a,c involved the initial addition
of PhPH2 and n-BuLi (2.0 equiv) to give the dilithiated
phosphorus nucleophile PhPLi2. Subsequent reactions with
α,ω-bromoalkenes Br(CH2)mCHCH2 (2.0 equiv) afforded
1a−c in 51−59% yields. The second, new to this work, involved
initial conversions of Br(CH2)mCHCH2 to the corresponding
Grignard reagents, followed by additions of PhPCl2 (0.5 equiv).
Workups gave 1a−c in 78−90% yields.
plexes trans-Fe(CO)3(PhP((CH2)n)2PPh) (4a−c; n = 2m + 2) as
white-yellow gums or waxes in 69−77% yields (21−24% from
2a−c). These feature 13-, 15-, and 17-membered macrocycles,
respectively. No significant amounts of the isomeric species
trans-Fe(CO)3(PhP(CH2)n)2 (4′a−c; Scheme 2) were detected.
Relevant to an analysis below, note that conformations in which
the phenyl groups are anticlinal (Ph−P−P−Ph dihedral angle
120°, as opposed to the 0° depicted) are available to 4′a−c but
not 4a−c.
The corresponding bis(phosphine) iron tricarbonyl com-
plexes were prepared analogously to the similar precursors to
IIIa (Scheme 1).5 As shown in Scheme 2, the substitution
Several NMR properties of 4a−c (see Table 1) deserve
emphasis. First, the PCH2CH2CH2 13C{1H} signals could be
assigned by analogy to those of iron tricarbonyl complexes of the
type IIIa. The PCH2 and the PCH2CH2CH2 signals were either
virtual triplets14 or apparent (second-order) doublets of doublets
with comparable coupling constants. The PCH2CH2 signals did
not exhibit detectable phosphorus couplings. The PC6H5
13C{1H} signals of 4a−c as well as 2a−c were assigned by
standard protocols.15 The o-Ph and m-Ph signals were virtual
triplets.14 However, some i-Ph signals were virtual triplets, and
others were apparent doublets of doublets. The p-Ph signals did
not show detectable phosphorus couplings.
Scheme 2. Syntheses of the Title Complexes
The CO 13C{1H} NMR signals of 4a−c were phosphorus
2
coupled triplets with JCP values ranging from 26.8 to 29.1 Hz.
Depending on the macrocycle size, either one triplet or two
(ca. 2:1 area ratio) were observed. These data are interpreted in
the context of variable-temperature NMR experiments below.
The noncyclized complexes 2a−c always exhibited a single CO
signal (t, 2JCP = 28.5−28.7 Hz), as would the isomers 4′a−c.
Molecular Structures. Attempts were made to crystallize
the preceding samples. These were successful in the cases of 3a
and 4b, which have 13- and 15-membered macrocycles. With the
former, crystals of the trans,trans CC isomer (E,E)-3a were
obtained. In other alkene metatheses of complexes with trans-
H2CCH(CH2)4P-M-P(CH2)4CHCH2 linkages, marked
preferences for trans (E) isomers have been observed,3b,c,5a,b,12
and rationales have been suggested.5b
labile precursor Fe(CO)3(η4-benzylideneacetone)13 and 1a−c
(2.0 equiv) were combined in THF. Workups gave the expected
B
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a
Table 1. Selected 31P{1H} and 13C{1H} NMR Data for 2a−c and 4a−c
13C{1H} (δ/ppm)
31P{1H}
(δ/ppm)
PCH2CH2CH2
o-Ph
m-Ph
complex
CO [2JPC, Hz]
PCH2 [1JPC, Hz] PCH2CH2
[3JPC, Hz]
i-Ph [1JPC, Hz]
[2JPC, Hz]
p-Ph
[4JPC, Hz]
b
c
e
e
e
e
e
e
e
2a
70.1
69.0
69.8
78.0
72.6
72.0
215.6 [28.6]
33.0 [15.3],
24.1
24.4
24.6
24.1
23.2
24.7
30.6 [6.6]
f
131.9
e
130.0 128.7 [4.3]
130.2 128.7 [4.4]
129.9 128.7 [4.5]
130.1 128.8 [4.5]
130.0 128.8 [4.6]
130.2 128.9 [4.2]
d
[13.3]
[4.6]
c
e
2b
2c
4a
4b
4c
215.6 [28.6]
33.1 [15.4],
30.8 [6.6]
136.4 [21.5],
131.9
[4.7]
d
d
e
[13.5]
[17.4]
c
e
215.7 [28.5]
33.2 [15.9],
31.4 [6.6]
136.5 [21.4],
131.8
[4.6]
d
d
e
[12.5]
[17.6]
g
c
g
e
216.5 [28.5]; 215.1
32.4 [15.5],
29.0 [6.2]
136.5 [20.3],
132.1
[5.1]
c
d
d
e
[26.8]
[13.6]
[17.3]
c
e
215.4 [29.1]
34.0 [15.7],
29.7 [7.3]
136.8 [21.0],
132.1
[5.0]
d
d
e
[13.7]
[17.1]
c
e
e
214.1 [28.8]
34.0 [13.6]
31.1 [6.9]
136.9 [21.0],
132.2
[4.6]
d
e
[16.9]
a
b
NMR spectra were recorded on a 400 MHz instrument in C6D6. Signals for which no J values are indicated are singlets. The data for 2a are taken
c
d
from the NMR spectra in the Supporting Information, for which some couplings were better resolved. These J values are for triplets. These J values
are for apparent doublet of doublets. These J values are for virtual triplets. The expected signal was not observed. The upfield signal is more
e
f
g
intense (ca. 2:1 ratio per Figure 4).
Figure 1. Thermal ellipsoid (left) and space-filling (right) representa-
Figure 2. Thermal ellipsoid (left) and space-filling (right) representa-
tions of the molecular structure of (E,E)-3a; views with the P−Fe−P axis
tions of the molecular structure of 4b; views with the P−Fe−P axis in the
plane (top) and perpendicular to the plane (bottom) of the paper.
in the plane (top) and perpendicular to the plane (bottom) of the paper.
The crystal structures of (E,E)-3a and 4b were determined
as outlined in Table S1 (Supporting Information) and the
Experimental Section. Thermal ellipsoid plots and space-filling
models are depicted in Figures 1 and 2. Key metrical parameters are
listed in Table 2. The Cipso−P1−P2−Cipso torsion angles of (E,E)-3a
and 4b provide measures of the relative dispositions of the phenyl
rings. The values are close to zero (−36.22 and 3.67°, respectively),
indicative of synperiplanar orientations. The Fe−P−Cipso−Cortho
torsion angles are also close to zero (Table 2), indicating roughly
parallel dispositions of the phenyl rings and P−Fe−P axes.
Figure 3 shows the unit cells of (E,E)-3a and 4b, each of which
contains four molecules. In all neutral trigonal bipyramidal
complexes of the type IIIa that have been crystallized to date, the
P−M−P axes are parallel (MLy = Fe(CO)3,5a,b,12 Os(CO)3,10a
Fe(CO)(NO)(X)5c).16 In contrast, the P−Fe−P axes in
crystalline (E,E)-3a and 4b clearly orient in more than one
direction. In the latter, there are two sets of molecules with
parallel axes (such that an axis from one set would not be parallel
to an axis from the other set). Thus, least-squares planes are
defined using six atoms from two P−Fe−P axes from each set
(planes defined by only three nearly collinear experimental
points have large error limits). These intersect at an 89° angle,
consistent with the near perpendicular orientation that is visually
apparent in Figure 3 (bottom). With (E,E)-3a, there are four
such sets, and the angles involving all six possible combinations
are given in Table 2 (48−82°).
The radii of the Fe(CO)3 rotators of (E,E)-3a and 4b were
estimated by taking the average FeCO distances (2.92−2.93 Å;
Table 2) and adding the van der Waals radius of an oxygen atom
(1.52 Å;17 sums = 4.44−4.45 Å). The average distances from the
iron atoms to the two carbon atoms of each macrocycle closest
to the planes of the Fe(CO)3 rotators were also calculated
(Table 2), and the van der Waals radius of a carbon atom (1.70 Å)17
was subtracted. This can be viewed as one measure of the
horizontal free van der Waals space or “clearance” within the
C
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Table 2. Key Distances (Å) and Angles (deg) for Crystalline (E,E)-3a and 4b
(E,E)-3a
4b
distances
Fe−P1/Fe−P2
P1−P2
2.2153(10)/2.2239(10)
2.2097(7)/2.2108(7)
4.4205(14)
4.4543(20)
Fe−C1/Fe−C2/Fe−C3
C1−O1/C2−O2/C3−O3
avg FeCO
1.761(4)/1.760(4)/1.772(4)
1.766(3)/1.770(2)/1.777(2)
1.163(4)/1.158(4)/1.162(4)
1.156(3)/1.163(3)/1.156(3)
2.924
2.929
a
avg FeCO + O vdW
4.44
4.45
b
Fe−Cd
5.385/5.407/5.540/5.525
6.047/5.849/6.011/5.936
avg Fe−Cd
avg Fe−Cd − C vdW
Fe−Cneighbor
Fe−Cneighbor − C vdW
5.464
3.76
5.961
4.26
a
c
5.175
3.48
5.503
3.80
a
bond angles
P1−Fe−P2
171.82(4)
176.48(3)
Fe−C1−O1/Fe−C2−O2/Fe−C3−O3
P1−Fe−C1/P1−Fe−C2/P1−Fe−C3
P2−Fe−C1/P2−Fe−C2/P2−Fe−C3
178.2(3)/178.9(4)/176.9(3)
85.34(11)/91.42(12)/89.29(12)
86.68(11)/91.42(12)/96.08(12)
118.24(11)/120.69(11)
114.26(12)/114.88(11)/
114.10(14)/113.46(12)
179.3(2)/176.9(2)/179.1(2)
89.35(8)/91.63(8)/89.94(7)
89.47(8)/91.87(8)/88.10(7)
116.37(8)/116.04(7)
116.14(7)/116.13(8)
116.38(8)/116.30(8)
d
Fe−P1−Ci/Fe−P2−Ci
e
Fe−P1−Ca/Fe−P2−Ca
torsion and other angles
d
Ci−P1−P2−Ci
−36.22
17.0(3)
3.67
df
,
Fe−P1−Ci−Co
Fe−P2−Ci−Co
4.6(2)
−16.6(2)
89
df
,
−20.9(5)
82.1/75.8/62.9/56.2/56.0/48.3
g
[P−Fe−P + P−Fe−P]/[P′−Fe′−P′ + P′−Fe′−P′]
a
b
vdW = van der Waals. The subscript d (distal) denotes the two carbon atoms of each macrocycle that are closest to the plane of the rotator. For
(E,E)-3a: C5a/C6a/C5b/C6b. For 4b: C16/C17/C36/C37. Cneighbor denotes the closest atom (always carbon) of a neighboring molecule. For
(E,E)-3a, C8A. For 4b, C65, with C33 only slightly more distant (5.527 Å). Ci denotes an ipso C6H5 carbon atom. Ca denotes a macrocyclic
carbon atom bound to a phosphorus atom. Co denotes an ortho C6H5 carbon atom. Least-squares planes are defined using the six atoms of two
c
d
e
f
g
P−Fe−P axes of all molecules with parallel axes in the lattice. These values represent the angles between all such planes.
macrocycles. In (E,E)-3a, this value is much shorter than the
radius of the rotator (3.76 Å), whereas in 4b, it is nearly
comparable (4.26 Å).
the coalescence formula18 allows the ΔG⧧378 K value for Fe(CO)3
rotation to be bounded as greater than 17.9 kcal/mol, as derived
in the Supporting Information.
The non-hydrogen atoms of neighboring molecules nearest to
the iron atoms in (E,E)-3a and 4b were identified, and the
van der Waals radii of these nearby atoms were subtracted from
the distances. As summarized in Table 2, these intermolecular
“clearances” are significantly less than the radius of the rotators
(3.48−3.80 Å vs 4.44−4.45 Å). Hence, there should be additional
impediments to Fe(CO)3 rotation in the solid state.
Complex 4b features 15-membered macrocycles with 12 CH2
groups, and variable-temperature 13C{1H} NMR spectra were
recorded in CD2Cl2, as depicted Figure S1 (signal/noise similar
to that in Figure 4) in the Supporting Information. As noted
above, only one signal was observed at 25 °C. However, the
results upon cooling were ambiguous. New signals seemed to
appear below 0 °C, but there was not a clear-cut decoalescence, in
part due to the signal/noise. Nonetheless, an upper limit on the
rotational barrier could be estimated, as described below.
During the review phase of this paper, a referee inquired about
the relative stabilities of isomers of the types 3/4 and 3′/4′ in
Scheme 2 as well as variants of the former in which the phenyl
groups are antiperiplanar as opposed to synperiplanar (3″/4″;
vide infra). Hence, a computational investigation was conducted,
focusing on the saturated systems 4, 4′, and 4″ to avoid the
complication of multiple CC isomers. With 4′, conformations
with synperiplanar and anticlinal phenyl groups were both
examined. Density functional theory (DFT) calculations were
carried out as described in the Experimental Section, and the
relative energies found with one functional (CAM-B3LYP) are
presented in Figure 5. Similar data were obtained with other
functionals, as summarized in Table S2 (Supporting Information).
The results were further validated by the excellent agreement
of the computed structure of 4b with the crystal structure
(Figure S2). The trends evident in Figure 5 are analyzed below.
Dynamic Properties and Computations. The barriers
to Fe(CO)3 rotation in the title molecules were probed by
variable-temperature 13C{1H} NMR. Various limiting situations
were anticipated. In one, the macrocycles would be too small to
allow Fe(CO)3 rotation under any conditions. This would be
evidenced by two CO 13C signals in a ca. 2:1 area ratio at all
accessible temperatures. In another, the macrocycles would be
sufficiently large for facile Fe(CO)3 rotation, even at very low
temperatures. This would be evidenced by a single CO 13C signal.
In a more informative scenario, both limits could be observed
depending upon temperature, and activation parameters could
be calculated from signal coalescence or line shape data.
Complex 4a features 13-membered macrocycles with 10 CH2
groups, and variable-temperature 13C{1H} NMR spectra were
recorded in toluene-d8, as depicted in Figure 4. Although the
signal/noise ratio was not optimal, two CO 13C NMR signals
(each phosphorus coupled triplets as noted above) were plainly
visible at 25 °C. Spectra at higher temperatures showed no hint of
any onset of coalescence, even at 105 °C (378 K). Application of
D
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Figure 4. Partial 13C{1H} NMR spectra of 4a in toluene-d8 as a function
of temperature.
phenyl rings have an antiperiplanar arrangement. This
corresponds to the structures 4″a−c in Figure 5.
Hence, intermolecular alkene metatheses, such as oligomeriza-
tion, or intraligand metatheses to give species of the type 4′a−c
should be able to better compete with reactants of the type 2a−c.
Accordingly, the yields of crude 3a−c (30−31%) are low com-
pared to those of analogues in which three methylene chains span
the trans phosphorus atoms (60−81%).5a,b Alternatively, the
overall yields after hydrogenation can be compared (21−24% vs
34−51%).
Alkene metatheses have also been carried out using square
planar platinum complexes with trans-phosphine ligands 1a−c,
as shown in Scheme 4.3c With this coordination geometry, no
conformation is possible that preorganizes the reactants for
three-fold interligand metathesis. Accordingly, the yields of
monoplatinum metathesis/hydrogenation products 6a−c are
low (5−38%). With 6c, which has the largest macrocycles
(17-membered), diastereomers with synperiplanar and antiper-
iplanar phenyl rings are both produced (31:7; cf. IV and V in
Scheme 3). No products involving intraligand metathesis have
been detected. However, when the alkyl chains of the phosphines
are reduced to two methylene groups, this becomes the exclusive
reaction mode (86% isolated). Other experiments show that the
larger pentafluorophenyl ligand constitutes an additional
impediment to interligand metathesis.6b,19
Figure 3. Unit cells of (E,E)-3a (top) and 4b (bottom).
DISCUSSION
■
Syntheses. The lower symmetries of the title complexes
4a−c versus the analogous gyroscope-like species IIIa (MLy =
Fe(CO)3) carry subtle implications regarding their syntheses.
Consider first the structure VIII in Scheme 3 (top), which
represents a precursor to IIIa. As noted in previous papers,5 the
phosphorus atom substituents will prefer to be staggered relative
to the carbonyl groups on iron. This preorganizes the reactants
for three-fold intramolecular interligand ring-closing alkene
metatheses. After the first trans spanning linkage is generated
(IX), the remaining (CH2)mCHCH2 groups are locked into
place for analogous couplings, which result in X. For simplicity,
each cyclization in Scheme 3 incorporates a hydrogenation step.
Contrast this to the scenario with 2a−c. As shown in Scheme 3
(bottom), two inequivalent conformations are now possible
in which the phosphorus atom substituents are staggered rela-
tive to the carbonyl groups on iron, XI (idealized C2v symmetry,
synperiplanar phenyl groups) and XIII (C2, anticlinal phenyl
groups). With XI, after the first trans spanning linkage is
generated (XII), the two remaining (CH2)mCHCH2 groups
are locked into place for coupling to the product IV (4a−c)
However, with XIII, only a single trans spanning linkage can
readily be generated (XIV). To form a second, (CH2)mCH
CH2 groups from different OC−Fe−CO interstices must couple.
As can be seen in XIV and XV, a carbonyl ligand provides
considerable interference. Furthermore, the product XV is not
topologically equivalent to IV but is rather a distorted form of V
(idealized Cs symmetry), a diastereomer of IV in which the two
Although this study was not designed to explore the reactivity
of 2a−c or 4a−c, NMR tube experiments show that they can be
protonated at iron with strong acids or one CO ligand displaced
−
upon addition of NO+ BF4 , affording tetrafluoroborate salts of
the isosteric and isoelectronic Fe(CO)2(NO)+ species. Both
types of reactions have abundant precedent with IIIa (MLy =
Fe(CO)3) or their acyclic precursors.5,20
Physical Properties. As shown in Figures 1 and 2, crystalline
(E,E)-3a and 4b exhibit approximately staggered arrangements
E
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Article
Figure 5. Relative energies (kcal/mol) of the isomers 4, 4″, 4′synperiplanar, and 4′anticlinal as computed by DFT.
Scheme 3. Conformations of 2a−c (XI, XIII) and Implications
for Alkene Metathesis/Hydrogenation Products
Scheme 4. Alkene Metathesis/Hydrogenation Sequences
Using Square Planar Platinum Complexes with trans-
Phosphine Ligands P(CH2)mCHCH2 (1a−c)
Figure 6. Conformational minima and maxima for the title complexes
(left) and analogues with three trans spanning linkages (right).
In contrast, 4b represents a new macrocycle size for crystallo-
graphically characterized Fe(CO)3 adducts of trans spanning
diphosphine ligands. However, the structure of the diarsine
analogue with three (CH2)12 linkages has been determined.12
The dimensions of the 13- and 15-membered macrocycles in
(E,E)-3a and 4b are in the range of those found earlier in the
of the phosphorus atom substituents and carbonyl ligands on iron,
as posited for the precursors in Scheme 3. The crystal structure of
the analogue of (E,E)-3a with three as opposed to two
(E)-(CH2)4CHCH(CH2)4 linkages spanning the trans-phos-
phorus atoms has also been determined (two different solvates).5a,b
F
DOI: 10.1021/acs.organomet.7b00330
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Organometallics
Article
diphosphine or diarsine analogues with three identical link-
ages.5,12 For example, as noted above, the distances from iron to
the two carbon atoms of each macrocycle closest to the plane of
the rotator are given in Table 2 (5.39−5.54 Å for (E,E)-3a;
5.85−6.05 Å for 4b). The corresponding distances for the
analogues with three identical linkages are 5.34−5.35 and
5.62−6.38 Å, respectively. Probably the average values (5.46 vs
5.34 Å and 5.96 vs 5.94 Å) best reflect the typical horizontal
extensions of the macrocycles in solution.
All of the iron complexes described in this paper, as well as
IIIa,b with LyM = Fe(CO)3, Fe(CO)2(NO)+, or Fe(CO)(NO)-
(X), possess three-fold barriers to Fe(CO)(L′)(L″) rotation
that is, three degenerate minima and maxima over the course of a
360° rotation.21 These are depicted in Figure 6, with XVI and
XVIII representing 3a−c/4a−c and XVII and XIX representing
IIIa,b. The maxima feature three-fold eclipsing interactions of
the phosphorus substituents and iron carbonyl ligands. With
IIIa,b, all three carbonyl ligands must simultaneously pass
through the restricted space associated with the interior of the
macrocycles (XIX). With the title compounds, only two carbonyl
ligands must so transit (XVIII). Hence, given that macrocycles of
the same sizes have roughly the same dimensions (vide supra),
somewhat lower rotational barriers would be expected with
XVIII.
methylene chains should afford lower activation barriers and less
strained products. Accordingly, for the platinum complexes in
Scheme 4, isomers with antiperiplanar phenyl groups did form
(as minor products) in the case of 17-membered macrocycles.
Interestingly, both conformers of 4′a−c are also much less
stable than 4a−c. The difference is marked for the smaller
13-membered macrocycles (4′a, 20.0−19.0 kcal/mol), suggest-
ing greater ring strain as compared that for 4a, in which
the macrocycles are two atoms larger. In the conformers of 4′c,
the energy differences versus that of 4c are nearly halved
(9.9−9.8 kcal/mol). Although the selectivities in the metathesis
reactions in Scheme 2 remain a function of the correspond-
ing alkenes, one would expect stability trends analogous to
those in Figure 5 for the more stable CC isomers. Hence,
the high selectivity for 4a−c as opposed to that of other
isomeric monoiron products tracks the relative thermodynamic
stabilities.23
CONCLUSION
■
Iron tricarbonyl complexes with doubly trans spanning
diphosphine ligands of the formula PhP((CH2)n)2PPh (n = 10,
12, 14) are easily synthesized by metathesis/hydrogenation
sequences from precursors with trans-PhP((CH2)mCHCH2)2
ligands (m = 4, 5, 6). However, the yields are somewhat lower
than for those of analogous complexes with triply trans spanning
P((CH2)n)3P ligands, and rationales for increased amounts of
byproducts have been presented. The doubly bridged complexes
feature lower Fe(CO)3 rotational barriers, as only two, as
opposed to three, CO ligands must pass through macrocycles
during the transition state. While these findings may not be
highly surprising, they provide welcome confirmation of the
physical models that have been proposed to govern dynamic
behavior. Other approaches to reducing rotational barriers in
trans-diphosphine complexes, in which multiple methylene
chains connect the phosphorus atoms, will be described in the
near future.
This expectation is fulfilled, albeit with the proviso that the
isosteric and isoelectronic rotator Fe(CO)2(NO)+ has been used
as a surrogate for Fe(CO)3 in complexes of the type III. This
desymmetrization is required in order for two sets of P(CH2)n/2
13C NMR signals to be observed. Thus, variable-temperature
13C{1H} NMR spectra of trans-[Fe(CO)2(NO)(P((CH2)12)3P)]+
−
BF4 (three 15-membered macrocycles) exhibit two sets of
P(CH2)6 signals at room temperature but only one at 100 °C
(typical Tcoal = 70 °C).5b The data allow ΔG⧧ values of
T
19.0 kcal/mol (378 K), 16.7 kcal/mol (298 K), or 16.1 kcal/mol
(273 K) to be calculated. In contrast, 4b gives one set of Fe(CO)3
13C NMR signals at room temperature, and per Figure S1, Tcoal is
likely less than 0 °C. If one approximates the Δν of the two 13CO
signals as the same as 4a and assumes a Tcoal of 0 °C,22 an upper
EXPERIMENTAL SECTION
■
limit of 12.8 kcal/mol is obtained for the ΔG⧧
value,
General. Reactions were carried out under dry N2 except for
hydrogenations. Chemicals were treated as follows: THF and hexanes,
distilled from Na/benzophenone; CH2Cl2, distilled from CaH2; MeOH,
distilled by rotary evaporation; Br(CH2)4CHCH2 (97%, Acros),
Br(CH2)5CHCH2 (96%, Acros), Br(CH2)6CHCH2 (90%, Fluka),
n-BuLi (2.5 M in hexanes, Acros), 1,2-dibromoethane (99%, Acros),
PhPCl2 (98%, Fluka), PhPH2 (98%, Aldrich), Mg powder (99%, Fluka),
NH4Cl (Fluka), neutral alumina 507 C (Fluka), PtO2 (83% Pt, Acros),
Rh(Cl)(PPh3)3 (97%, Lancaster), and Grubbs’ first generation catalyst
Ru(CHPh)(PCy3)2(Cl)2 (Aldrich), used as received. NMR spectra
were recorded on standard FT 400 MHz instruments at ambient probe
temperatures unless noted, with solvents used as received and
273 K
as illustrated in the Supporting Information. This is several
kcal/mollower than thatof the analogouscomplexof thetype IIIa.
This limit can also be compared to the barrier for Fe(CO)2(NO)+
rotation in trans-[Fe(CO)2(NO)(P((CH2)14)3P)]+ BF4
−
(three 17-membered macrocycles), which has a ΔG⧧273 K value of
11.3 kcal/mol. We therefore suggest that the barriers to rotator
rotation in 4a−c are comparable to those in homologous
complexes IIIa with two additional methylene groups in each
macrocycle. In the case of 4a (two 13-membered macrocycles), a
lower limit of 17.9 kcal/mol for the ΔG⧧378 K value can be derived
from Figure 4 without any chemical shift assumptions
(Supporting Information). However, this affords little insight,
as no evidence has been obtained to date that a CO ligand can
pass through a 13-membered macrocycle in any complex of the
types IIIa,b.
1
referenced as follows (δ, ppm): H, residual internal CHCl3 (7.24) or
C6D5H (7.15); 13C, internal CDCl3 (77.0) or C6D6 (128.0); 31P{1H}
NMR, internal H3PO4 capillary (δ 0.00). IR and MS spectra were
recorded on ASI React-IR 1000 and Micromass Zabspec instruments,
respectively.
PhP((CH2)4CHCH2)2 (1a). A. A Schlenk flask was charged
with Mg powder (0.9539 g, 39.25 mmol), THF (40 mL), and
1,2-dibromoethane (0.2 g, 0.1 mL, 1.2 mmol) and cooled to 0 °C. Then,
Br(CH2)4CHCH2 (4.00 g, 3.29 mL, 24.5 mmol) was added dropwise
with stirring, and the cold bath was removed. After 2 h, the mixture was
cooled to 0 °C, and PhPCl2 (2.20 g, 1.67 mL, 12.3 mmol) was added
over 5 min. After 2 h, saturated aqueous NH4Cl (30 mL) was added. The
aqueous phase was removed by syringe. The organic phase was removed
by oil pump vacuum. The residue was extracted with CH2Cl2. The
extracts were filtered through a plug of neutral alumina (2 × 2 cm). The
Finally, we return to Figure 5 and the energies of the two
isomers derived from interligand metathesis, 4a−c and 4″a−c.
The latter are computed to be much less stable, but the difference
is greatest for 4a/4″a (19.0 kcal/mol), which have the shortest
methylene chains and 13-membered macrocycles. With 4c/4″c,
which have 17-membered macrocycles, the difference is nearly
cut in half (10.9 kcal/mol). Indeed, considering the steric
interactions en route to 4″a−c outlined in Scheme 3, longer
G
DOI: 10.1021/acs.organomet.7b00330
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Article
solvent was removed from the combined filtrates by oil pump vacuum to
give 1a as a colorless oil (2.64 g, 9.62 mmol, 78%). B.24 A Schlenk flask
was charged with PhPH2 (1.028 g, 9.337 mmol) and THF (40 mL) and
cooled to 0 °C. Then, n-BuLi (2.5 M in hexanes, 7.5 mL, 18.70 mmol)
was added dropwise with stirring over 15 min. The colorless solution
turned first orange and then bright yellow and became cloudy. After
10 min, Br(CH2)4CHCH2 (3.05 g, 2.50 mL, 18.7 mmol) was added.
The cold bath was removed. After 4 h, the solvent was removed by oil
pump vacuum. Vacuum distillation gave 1a as a colorless oil (1.38 g,
5.01 mmol, 54%). NMR (CDCl3, δ in ppm): 1H (400 MHz) 7.57−7.46
2.06−1.96 (m, 8H, CH2) 1.88−1.50 (m, 12H, CH2), 1.46−1.18 (m,
4H, CH2, 4H, C6H14 solvate), 1.15−0.82 (m, 3H, C6H14); 13C{1H}
(100 MHz)15,26,27 215.3 (t, 2JCP = 28.7 Hz, CO), 138.5 (s, CH), 131.8
(virtual t,14 JCP = 4.4 Hz, o-Ph), 130.0 (s, p-Ph), 128.7 (virtual t,14 JCP
=
2
3
4.2 Hz, m-Ph), 114.9 (s, CH2), 33.5 (s, CH2), 33.1−32.8 (m, PCH2), 30.5
(virtual t,14 JCP = 6.6 Hz, PCH2CH2CH2), 24.0 (s, PCH2CH2); 31P{1H}
3
(162 MHz) 70.2 (s). IR (cm−1, oil film): 2940 (m), 2875 (w), 1861 (s, νCO),
1873 (m), 1475 (m), 953 (m). MS:28 630 ([M − 3CO]+, 1%).
trans-Fe(CO)3(PhP((CH2)5CHCH2)2)2 (2b). Fe(CO)3(η4-benzy-
lideneacetone) (0.8024 g, 2.805 mmol),13 THF (40 mL), and 1b
(1.6964 g, 5.609 mmol) were combined in a procedure analogous to that
for 2a. An identical workup gave 2b·(C6H14)0.5 as a yellow-brownish oil
(1.539 g, 1.953 mmol, 70%). Anal. Calcd for C43H62FeO3P2·(C6H14)0.5
(787.85): C 70.13, H 8.83. Found: C 70.03, H 7.96.29 NMR (C6D6, δ in
ppm): 1H (400 MHz) 8.03−7.99 (m, 4H, Ph), 7.34−7.20 (m, 6H, Ph),
(m, 2H, Ph), 7.40−7.29 (m, 3H, Ph), 5.79 (tdd, 3JHH = 6.7 Hz, 3JHHcis
=
10.2 Hz, 3JHHtrans = 16.9 Hz, 2H, CH), 5.06−4.87 (m, 4H, CH2),
2.10−1.96 (m, 4H, CH2), 1.80−1.54 (m, 4H, CH2), 1.54−1.28 (m, 8H,
15
1
CH2); 13C{1H} (100 MHz) 138.9 (d, JCP = 15.2 Hz, i-Ph), 138.6
(s, CH), 132.2 (d, 2JCP = 18.6 Hz, o-Ph), 128.5 (s, p-Ph), 128.2 (d,
3JCP = 6.8 Hz, m-Ph), 114.3 (s, CH2), 33.3 (s, CH2), 30.4 (d, 3JCP
=
3
3
3
5.82 (tdd, JHH = 6.7 Hz, JHHcis = 10.1 Hz, JHHtrans = 16.9 Hz, 4H,
CH), 5.12−5.04 (m, 8H, CH2), 2.32−2.10 (m, 8H, CH2),
2.10−1.92 (m, 8H, CH2), 1.90−1.64 (m, 8H, CH2), 1.48−1.27 (m, 16H,
CH2, 4H, C6H14), 0.98−0.86 (m, 3H, C6H14); 13C{1H} (100 MHz)15,27
215.6 (t, 2JCP = 28.6 Hz, CO), 138.9 (s, CH), 136.4 (apparent dd, 1JCP,
11.6 Hz, CH2), 28.1 (d, JCP = 11.3 Hz, CH2), 25.4 (d, 1JCP = 13.9 Hz,
PCH2);25 31P{1H} (162 MHz) −23.7 (s).
PhP((CH2)5CHCH2)2 (1b). A. Mg powder (0.5490 g, 22.59 mmol),
THF (30 mL), 1,2-dibromoethane (0.2 g, 0.1 mL, 1.2 mmol),
Br(CH2)5CHCH2 (2.50 g, 2.15 mL, 14.1 mmol), PhPCl2 (1.26 g,
0.96 mL, 7.06 mmol), and saturated aqueous NH4Cl (25 mL) were
combined in a procedure analogous to A for 1a. An identical workup
gave 1b as a colorless oil (1.70 g, 5.61 mmol, 79%). B.24 PhPH2 (1.028 g,
9.337 mmol), THF (40 mL), n-BuLi (2.5 M in hexanes, 7.50 mL,
18.7 mmol), and Br(CH2)5CHCH2 (3.31 g, 2.85 mL, 18.7 mmol)
were combined in a procedure analogous to B for 1a. An identical
workup gave 1b as a colorless oil (1.44 g, 4.76 mmol, 51%). NMR
3JCP = 21.5, 17.4 Hz, i-Ph), 131.9 (virtual t,14 JCP = 4.7 Hz, o-Ph), 130.2 (s,
2
p-Ph), 128.7 (virtual t,14 JCP = 4.4 Hz, m-Ph), 114.7 (s, CH2), 33.8 (s,
3
CH2), 33.1 (apparent dd, 1JCP, 3JCP = 15.4, 13.5 Hz, PCH2), 30.8 (virtual t,14
3JCP = 6.6 Hz, PCH2CH2CH2), 28.7 (s, CH2), 24.4 (s, PCH2CH2); 31P{1H}
(162 MHz) 69.0 (s). IR (cm−1, oil film): 2943 (m), 2878 (w), 1864
(s, νCO), 1477 (m), 957 (m). MS:28 743 ([M]+, 8%), 689 ([M − 2CO]+,
1%), 660 ([M − 3CO]+, 358 ([Fe + 1b]+, 100%), 303 ([1b]+, 17%).
trans-Fe(CO)3(PhP((CH2)6CHCH2)2)2 (2c). Fe(CO)3(η4-benzy-
lideneacetone) (0.6297 g, 2.201 mmol),13 THF (40 mL), and 1c (1.455 g,
4.402 mmol) were combined in a procedure analogous to that for 2a.
An identical workup gave 2c·(C6H14)2 as a yellow-brownish oil (0.7892 g,
0.8109 mmol, 37%). Anal. Calcd for C47H70FeO3P2·(C6H14)2 (973.22):
C 72.81, H 10.15. Found: C 73.15, H 9.46.29 NMR (C6D6, δ in ppm): 1H
(400 MHz) 8.01−7.92 (m, 4H, Ph), 7.26−7.02 (m, 6H, Ph), 5.75 (tdd,
(CDCl3, δ in ppm): 1H (400 MHz) 7.50 (dt, JHH3 = 1.8 Hz, JHH = 7.4 Hz,
3
2H, Ph), 7.37−7.30 (m, 3H, Ph), 5.77 (tdd, JHH = 6.7 Hz, JHHcis
=
10.2 Hz, 3JHHtrans = 16.9 Hz, 2H, CH), 4.95−4.88 (m, 4H, CH2),
2.03−1.92 (m, 4H, CH2), 1.73−1.60 (m, 4H, CH2), 1.50−1.24 (m, 12H,
15
CH2); 13C{1H} (100 MHz) 139.0 (d, JCP = 18.0 Hz, i-Ph), 138.9
1
2
(s, CH), 132.3 (d, JCP = 18.5 Hz, o-Ph), 128.5 (s, p-Ph), 128.2
(d, 3JCP = 6.8 Hz, m-Ph), 114.2 (s, CH2), 33.6 (s, CH2), 30.7 (d, JCP
=
3
3
3JHH = 6.7 Hz, JHHcis = 10.1 Hz, JHHtrans = 16.9 Hz, 4H, CH),
5.09−4.92 (m, 8H, CH2), 2.29−2.08 (m, 8H, CH2), 2.02−1.88
(m, 8H, CH2), 1.86−1.62 (m, 8H, CH2), 1.38−1.15 (m, 24H, CH2,
22 H, C6H14), 0.98−0.86 (m, 6H, C6H14); 13C{1H} (100 MHz)15,27
11.5 Hz, CH2), 28.5 (s, CH2), 28.2 (d, JCP = 11.1 Hz, CH2), 25.8
(d, 1JCP = 13.7 Hz, PCH2);25 31P{1H} (162 MHz) −23.4 (s).
PhP((CH2)6CHCH2)2 (1c). A. Mg powder (0.7083 g, 29.14 mmol),
THF (40 mL), 1,2-dibromoethane (0.2 g, 0.1 mL, 1.2 mmol),
Br(CH2)6CHCH2 (3.99 g, 3.50 mL, 20.9 mmol), PhPCl2 (1.86 g,
1.20 mL, 10.4 mmol), and saturated aqueous NH4Cl (25 mL) were
combined in a procedure analogous to A for 1a. An identical workup
gave 1c as a colorless oil (3.12 g, 9.43 mmol, 90%). B.24 PhPH2 (1.028 g,
9.337 mmol), THF (40 mL), n-BuLi (2.5 M in hexanes, 7.50 mL,
18.70 mmol), and Br(CH2)6CHCH2 (3.59 g, 3.15 mL, 18.7 mmol)
were combined in a procedure analogous to B for 1a. An identical
workup gave 1c as a bright yellow oil (1.82 g, 5.51 mmol, 59%). NMR
215.7 (t, 2JCP = 28.5 Hz, CO) 139.1 (s, CH), 136.5 (apparent dd, 1JCP
,
3JCP = 17.6, 21.4 Hz, i-Ph), 131.8 (virtual t,14 JCP = 4.6 Hz, o-Ph), 129.9
2
(s, p-Ph), 128.7 (virtual t,14 JCP = 4.5 Hz, m-Ph), 114.5 (s, CH2), 34.1
3
1
3
(s, CH2), 33.2 (apparent dd, JCP, JCP = 15.9, 12.5 Hz, PCH2), 31.4
(virtual t,14 JCP = 6.6 Hz, PCH2CH2CH2), 29.1 (s, CH2), 29.0 (s, CH2),
3
24.6 (s, PCH2CH2); 31P{1H} (162 MHz) 69.8 (s). IR (cm−1, oil film):
2927 (s), 2858 (m), 1869 (m, νCO), 1437 (m), 1174 (s), 911 (s). MS:28
800 ([M]+, 3%), 716 ([M − 3CO]+, 24%), 368 ([Fe + 1c]+, 100%), 331
([1c]+, 16%).
(CDCl3, δ in ppm): 1H (400 MHz) 7.50 (dt, JHH3 = 1.8 Hz, JHH = 7.5 Hz,
3
trans-Fe(CO)3(PhP((CH2)4CHCH(CH2)4)2PPh) (3a). A Schlenk
flask was charged with 2a (0.2241 g, 0.3254 mmol) and CH2Cl2
(325 mL; the resulting solution was 0.00099 M in 2a) and heated to
45 °C. Then, Grubbs’ first generation catalyst (0.0201 g, 0.0244 mmol)
was added with stirring. After 2 h, another charge of Grubbs’ catalyst
(0.0201 g, 0.0244 mmol) was added. After 15 h, the mixture was cooled
and the solvent was removed by oil pump vacuum. The residue was
extracted with hexanes. The extracts were filtered through neutral
alumina (7 × 2.5 cm), which was rinsed with additional hexanes. The
solvent was removed from the filtrate by oil pump vacuum to give a
mixture of 3a and oligomers as a yellow solid (0.0625 g, 0.0988 mmol,
30%). NMR (C6D6, δ in ppm): 1H (400 MHz) 8.06−8.01 (m, 4H, Ph),
7.52−7.03 (m, 6H, Ph), 5.59−5.30 (m, 4H, CH), 2.53−0.82 (m, 32H,
CH2); 13C{1H} (100 MHz)30 214.44 (t, 2JCP = 26.4 Hz, 2CO), 214.38
2H, Ph), 7.37−7.29 (m, 3H, Ph), 5.78 (tdd, JHH = 6.7 Hz, JHHcis
=
10.2 Hz, 3JHHtrans = 16.9 Hz, 2H, CH), 5.03−4.89 (m, 4H, CH2),
1.98−1.90 (m, 4H, CH2), 1.75−1.60 (m, 4H, CH2), 1.55−1.22 (m, 16H,
15
CH2); 13C{1H} (100 MHz) 139.1 (d, JCP = 14.6 Hz, i-Ph), 139.0
(s, CH), 132.2 (d, 2JCP = 18.5 Hz, o-Ph), 128.5 (s, p-Ph), 128.2 (d, 3JCP
= 6.8 Hz, m-Ph), 114.1 (s, CH2), 33.7 (s, CH2), 31.1 (d, JCP = 11.4 Hz,
1
3
1
CH2), 28.4 (s, 2CH2), 28.3 (d, JCP = 12.8 Hz, CH2), 25.9 (d, JCP
=
13.6 Hz, PCH2);25 31P{1H} (162 MHz) −23.3 (s).
trans-Fe(CO)3(PhP((CH2)4CHCH2)2)2 (2a). A Schlenk flask
was charged with Fe(CO)3(η4-benzylideneacetone) (0.6234 g,
2.179 mmol),13 THF (40 mL), and 1a (1.375 g, 5.012 mmol). The
red-brown mixture was stirred for 15 h and turned yellow. The solvent
was removed by oil pump vacuum. The residue was extracted with
hexanes. The extracts were filtered through neutral alumina (7 ×
3.5 cm), which was washed with hexanes and then hexanes/CH2Cl2
(67:33 v/v). The solvent was removed from the combined filtrates by oil
pump vacuum to give 2a·(C6H14)0.5 as a yellow-brownish oil (0.4482 g,
0.6125 mmol, 28%). Anal. Calcd for C39H54FeO3P2·(C6H14)0.5
(731.74): C 68.95, H, 8.40. Found: C 69.19, H, 8.49. NMR (C6D6, δ
(t, JCP = 33.2 Hz, CO), 132.0 (s, CH), 131.7 (virtual t,14 JCP
=
2
2
5.1 Hz, o-Ph), 130.8 (obscured dd, one of two central peaks, i-Ph), 130.8
(s, p-Ph), 128.8 (virtual t,14 JCP = 4.6 Hz, m-Ph), 33.1 (s, CH2), 33.5
3
(apparent dd, 1JCP, 3JCP = 15.5, 13.3 Hz, PCH2), 30.9 (virtual t,14 JCP
=
3
7.7 Hz, PCH2CH2CH2), 24.6 (s, PCH2CH2); 31P{1H} (162 MHz) 79.3
(s, 53%), 75.9 (s, 6%), 73.8−72.6 (overlapping signals, 41%). MS:28 632
([M]+, 25%), 606 ([M − CO]+, 13%), 576 ([M − 2CO]+, 20%), 548
([M − 3CO]+, 100%).
1
in ppm): H (400 MHz) 8.05−8.03 (m, 4H, Ph), 7.34−7.13 (m, 6H,
Ph), 5.79 (tdd, 3JHH = 6.6 Hz, 3JHHcis = 10.0 Hz, 3JHHtrans = 13.4 Hz, 4H,
CH), 5.15−4.98 (m, 8H, CH2), 2.33−2.06 (m, 8H, CH2),
H
DOI: 10.1021/acs.organomet.7b00330
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(100 MHz)15 214.1 (t, 2JCP = 28.8 Hz, CO), 136.9 (apparent dd, 1JCP
,
trans-Fe(CO)3(PhP((CH2)5CHCH(CH2)5)2PPh) (3b). Complex
2b (0.5213 g, 0.6999 mmol), CH2Cl2 (700 mL; the resulting solution
was 0.00089 M in 2b), and Grubbs’ first generation catalyst (0.0431 g,
0.0525 mmol and then 0.0432 g, 0.0525 mmol) were combined in a
procedure analogous to that for 3a. A similar workup (neutral alumina
10 × 2.5 cm) gave a mixture of 3b and oligomers as a yellow solid
(0.1494 g, 0.2170 mmol, 31%). NMR (C6D6, δ in ppm): 1H (400 MHz)
8.19−8.01 (m, 4H, Ph), 7.37−7.18 (m, 6H, Ph), 5.99−5.48 (m, 4H,
CH), 2.55−1.12 (m, 40H, CH2); 31P{1H} (162 MHz) 73.5 (s, 35%),
73.1 (s, 31%), 72.7 (s, 8%), 71.5 (s, 15%), 71.3 (s, 11%).
3JCP = 21.0, 16.9 Hz, i-Ph), 132.2 (virtual t,14 JCP = 4.6 Hz, o-Ph), 130.2
2
(s, p-Ph), 128.9 (virtual t,14 JCP = 4.2 Hz, m-Ph), 34.0 (virtual t,14 JCP
=
3
1
13.6 Hz, PCH2),31 31.1 (virtual t,14 JCP = 6.9 Hz, PCH2CH2CH2),31
28.3 (s, CH2), 28.1 (s, CH2), 27.4 (s, CH2), 26.7 (s, CH2), 24.7
(s, PCH2CH2);31 31P{1H} (162 MHz) 72.0 (s). IR (cm−1, oil film): 2927
(s), 2858 (m), 1869 (s, νCO), 1259 (s), 1089 (s), 1020 (s). MS:28 748
([M]+, 7%), 692 ([M − 2CO]+, 4%), 664 ([M − 3CO]+, 100%).
Crystallography. A. Crude 3a was suspended in methanol and
warmed. THF was added until the sample was homogeneous. After
1 day, colorless prisms of (E,E)-3a had formed. Data were collected
using a Nonius Kappa CCD area detector as outlined in Table S1. Cell
parameters were obtained from 10 frames using a 10° scan and refined
with 3445 reflections. Lorentz, polarization, and absorption correc-
tions32 were applied. The space group was determined from systematic
absences and subsequent least-squares refinement. The structure was
solved by direct methods. The parameters were refined with all data
by full-matrix least-squares on F2 using SHELXL-97 (racemic twin,
56:44).33 Non-hydrogen atoms were refined with anisotropic thermal
parameters. The hydrogen atoms were fixed in idealized positions using
a riding model. Scattering factors were taken from the literature.34
B. Complex 4b was dissolved in hexanes. After 4 days, colorless needles
had formed. Data were collected as with 3a. Cell parameters were
obtained from 10 frames using a 10° scan and refined with 8473
reflections, and the structure was solved identically to 3a.
3
trans-Fe(CO)3(PhP((CH2)6CHCH(CH2)6)2PPh) (3c). Complex
2c (0.4025 g, 0.5025 mmol), CH2Cl2 (503 mL; the resulting solution
was 0.00099 M in 2c), and Grubbs’ first generation catalyst (0.0310 g,
0.0377 mmol and then 0.0310 g, 0.0377 mmol) were combined in a
procedure analogous to that for 3a. The residue was extracted with
hexanes/CH2Cl2 (84:16 v/v). The extracts were filtered through neutral
alumina (12 × 2.5 cm), which was rinsed with additional hexanes/
CH2Cl2. The solvent was removed from the filtrate by oil pump vacuum
to give a mixture of 3c and oligomers (0.1160 g, 0.1558 mmol, 31%).
1
NMR (C6D6, δ in ppm): H (400 MHz) 8.21−8.06 (m, 4H, Ph),
7.46−7.11 (m, 6H, Ph), 5.62−5.21 (m, 4H, CH), 2.49−0.98 (m, 48H,
CH2); 31P{1H} (162 MHz) 73.9 (s, 63%), 73.3 (s, 13%), 73.1 (s, 14%),
72.5 (s, 4%), 72.3 (s, 6%).
trans-Fe(CO)3(PhP((CH2)10)2PPh) (4a). A Fisher−Porter bottle
was charged with 3a (0.2164 g, 0.3421 mmol), Rh(Cl)(PPh3)3 (0.0633 g,
0.0648 mmol), THF (20 mL), and H2 (5 bar). The mixture was stirred.
After 15 h, the solvent was removed by oil pump vacuum. The residue
was extracted with hexanes/CH2Cl2 (92:8 v/v). The extract was filtered
through neutral alumina (12 × 2.5 cm), which was rinsed with hexanes/
CH2Cl2 (92:8 v/v). The solvent was removed from the filtrate by oil
pump vacuum to give 4a as a white-yellow gum (0.1502 g, 0.2360 mmol,
69%). NMR (C6D6, δ in ppm): 1H (400 MHz) 8.11−7.89 (m, 4H, Ph),
7.31−6.95 (m, 6H, Ph), 2.22−1.68 (m, 12H, CH2), 1.58−1.38 (m, 20H,
Calculations. Computations were performed using the Gaussian09
program package, employing the ultrafine grid (99 590) to enhance
accuracy.35 Geometries were optimized using density functional theory
and the B3LYP,36 TPSS,37 and CAM-B3LYP38 functionals with an
all-electron 6-311+G(d,p)39 basis set on all atoms except iron, which
was treated with a pseudopotential.40 Frequency calculations were
performed at the same level to characterize the optimized geometries.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.organomet.7b00330.
■
CH2), 1.37−0.85 (m, 8H, CH2); 13C{1H} (100 MHz)15 216.5 (t, 2JCP
=
,
S
28.5 Hz, CO), 215.1 (t, 2JCP = 26.8 Hz, 2CO), 136.5 (apparent dd, 1JCP
3JCP = 20.3, 17.3 Hz, i-Ph), 132.1 (virtual t,14 JCP = 5.1 Hz, o-Ph), 130.1
2
(br s, p-Ph), 128.8 (virtual t,14 JCP = 4.5 Hz, m-Ph), 32.4 (apparent dd,
3
Table of crystallographic data, additional preparative and
spectroscopic data, calculations of ΔG⧧ values, and data
from DFT computations (PDF)
Molecular structure file that can be read by the program
Mercury41 and contains the optimized geometries of all
computed structures42 (MOL)
1JCP, JCP = 15.5, 13.6 Hz, PCH2),31 29.0 (virtual t,14 JCP = 6.2 Hz,
PCH2CH2CH2),31 27.6 (s, CH2), 25.4 (s, CH2), 24.1 (s, PCH2CH2);31
31P{1H} (162 MHz) 78.0 (s). MS:28 636 ([M]+, 5%), 552 ([M −
3CO]+, 100%).
3
3
trans-Fe(CO)3(PhP((CH2)12)2PPh) (4b). A Fisher−Porter bottle
was charged with 3b (0.3051 g, 0.2443 mmol), PtO2 (0.0194 g,
0.0855 mmol), THF (20 mL), and H2 (5 bar). The mixture was stirred.
After 15 h, the solvent was removed by oil pump vacuum. The residue
was extracted with hexanes/CH2Cl2 (75:25 v/v). The extract was
filtered through neutral alumina (12 × 2.5 cm), which was rinsed with
hexanes/CH2Cl2. The solvent was removed from the filtrate by oil pump
vacuum to give 4b as a white wax (0.133 g, 0.1881 mmol, 77%). Anal.
Calcd for C39H58FeO3P2 (692.68): C 67.63, H 8.44. Found: C 67.60, H,
Accession Codes
CCDC 1546130−1546131 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033.
10.20.29 NMR (C6D6, δ in ppm): H (400 MHz) 8.12−7.98 (m, 4H,
1
Ph), 7.36−7.11 (m, 6H, Ph), 2.18−1.14 (m, 48H, CH2); 13C{1H}
(100 MHz)15 215.4 (t, 2JCP = 29.1 Hz, CO), 136.8 (apparent dd, 1JCP
,
AUTHOR INFORMATION
Corresponding Author
*E-mail: gladysz@mail.chem.tamu.edu.
■
3JCP = 21.0, 17.1 Hz, i-Ph), 132.1 (virtual t,14 JCP = 5.0 Hz, o-Ph), 130.0
2
(br s, p-Ph), 128.8 (virtual t,14 JCP = 4.6 Hz, m-Ph), 34.0 (apparent dd,
3
1JCP, JCP = 15.7, 13.7 Hz, PCH2),31 29.7 (virtual t,14 JCP = 7.3 Hz,
PCH2CH2CH2),31 27.7 (s, CH2), 27.4 (s, CH2), 26.4 (s, CH2), 23.2
(s, PCH2CH2);31 31P{1H} (162 MHz) 72.6 (s). IR (cm−1, oil film): 2927
(m), 2858 (m), 1861 (s, νCO), 1460 (w), 1097 (m), 1020 (m). MS:28
692 ([M]+, 6%), 636 ([M − 2CO]+, 7%), 608 ([M − 3CO]+, 100%).
3
3
ORCID
John A. Gladysz: 0000-0002-7012-4872
Notes
The authors declare no competing financial interest.
trans-Fe(CO)3(PhP((CH2)14)2PPh) (4c). Complex 3c (0.4025 g,
0.5404 mmol), Rh(Cl)(PPh3)3 (0.0749 g, 0.0811 mmol), THF
(20 mL), and H2 (5 bar) were combined in a procedure analogous to
that for 4a. An identical workup gave 4c as a white-yellow gum (0.2953 g,
0.3945 mmol, 73%). NMR (C6D6, δ in ppm): 1H (400 MHz)
8.21−8.08 (m, 4H, Ph), 7.47−7.18 (m, 6H, Ph), 2.21−2.10 (m, 8H,
CH2), 2.10−1.82 (m, 8H, CH2), 1.82−1.21 (m, 40H, CH2); 13C{1H}
ACKNOWLEDGMENTS
■
The authors thank the U.S. National Science Foundation (CHE-
1153085, CHE-156601) and Deutsche Forschungsgemeinschaft
(DFG, GL 300/9-1) for support, the Laboratory for Molecular
Simulation and Texas A&M High Performance Research
I
DOI: 10.1021/acs.organomet.7b00330
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
chemical shift closest to benzene was attributed to the meta carbon, and
the least intense to the ipso carbon. See also Jolly, P. W.; Mynott, R. Adv.
Organomet. Chem. 1981, 19, 257−304.
Computing for resources, Prof. Michael B. Hall for helpful
discussions, and Dr. Tobias Fiedler for assistance in preparing the
manuscript.
(16) Among three diarsine analogues IIIb, there is one exception.12
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