H2 binding to and silane alcoholysis on an electrophilic Mn(I) fragment with tied-back phosphite ligands. X-ray structure of a Mn-CH2Cl2 complex

Article abstract of DOI:10.1016/S0022-328X(00)00230-8

The solvent-coordinated cationic complex [mer-Mn(CO)₃{P(OCH₂)₃CMe}₂(ClCH ₂Cl)][BAr_F] (4), has been prepared by the reaction of the methyl precursor mer-Mn(Me)(CO)₃{P(OCH₂)₃CMe}₂ with [Ph₃C][BAr_F]. The coordinated solvent, CH₂Cl₂, binds to Mn through one chloride atom in the X-ray crystal structure, which also exhibits novel interligand hydrogen bonding between an acidic hydrogen on CH₂Cl₂ and an oxygen of the phosphite. 4 binds H₂ in equilibrium fashion, and the η²-H₂ complex has a very high J_HD of 34.5 Hz indicative of the high electrophilicity of the metal center. Silanes also displace the bound CH₂Cl₂ at low temperature, although the η²-Si-H bond undergoes heterolytic cleavage on warming. 4 catalyzes reaction of SiHEt₃ with phenol to give Et₃SiOPh and H₂. The bound CH₂Cl₂ in 4 is displaced irreversibly by olefins, ethers, and amines, to form stable adducts. The cationic [Mn(CO)₃(P(OCH₂)₃CMe)₂]⁺ fragment is more electrophilic than phosphine analogues, and the tied-back phosphites give less steric congestion and, importantly, cannot engage in agostic interactions that would compete with external ligand binding. The results in these and other related systems bring to the forefront the subtle balance between electronic and steric forces that occur on addition of sixth ligands to 16 e^- metal fragments.

Full text of DOI:10.1016/S0022-328X(00)00230-8

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Journal of Organometallic Chemistry 609 (2000) 95–103
H2 binding to and silane alcoholysis on an electrophilic Mn(I)
fragment with tied-back phosphite ligands. X-ray structure of a
Mn–CH2Cl2 complex
Xinggao Fang, Jean Huhmann-Vincent, Brian L. Scott, Gregory J. Kubas *
Chemical Science and Technology Di6ision, MS J514, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Received 20 January 2000; received in revised form 16 April 2000
Abstract
The solvent-coordinated cationic complex [mer-Mn(CO)3{P(OCH2)3CMe}2(ClCH2Cl)][BArF] (4), has been prepared by the
reaction of the methyl precursor mer-Mn(Me)(CO)3{P(OCH2)3CMe}2 with [Ph3C][BArF]. The coordinated solvent, CH2Cl2, binds
to Mn through one chloride atom in the X-ray crystal structure, which also exhibits novel interligand hydrogen bonding between
an acidic hydrogen on CH2Cl2 and an oxygen of the phosphite. 4 binds H2 in equilibrium fashion, and the h2-H2 complex has
a very high JHD of 34.5 Hz indicative of the high electrophilicity of the metal center. Silanes also displace the bound CH2Cl2 at
low temperature, although the h2-SiꢀH bond undergoes heterolytic cleavage on warming. 4 catalyzes reaction of SiHEt3 with
phenol to give Et3SiOPh and H2. The bound CH2Cl2 in 4 is displaced irreversibly by olefins, ethers, and amines, to form stable
adducts. The cationic [Mn(CO)3(P(OCH2)3CMe)2]+ fragment is more electrophilic than phosphine analogues, and the tied-back
phosphites give less steric congestion and, importantly, cannot engage in agostic interactions that would compete with external
ligand binding. The results in these and other related systems bring to the forefront the subtle balance between electronic and
steric forces that occur on addition of sixth ligands to 16 e− metal fragments. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Manganese; Dichloromethane; Dihydrogen; Silane; Phosphite; Cyclooctene
1. Introduction
of which contain agostic CꢀH interactions (Scheme 1),
were recently reported to reversibly weakly bind H2 in
place of the CꢀH.
The coordination and activation of small molecules
such as H2 and silanes by formally 16 e− electrophilic
transition metal complexes has drawn considerable re-
cent attention [1–5]. The binding properties of H2 s
ligands are dependent primarily upon the electronic
environment of the metal complexes, but steric factors
can be critical for larger s ligands such as silanes
(SiHnR4−n; n=1–3), olefins, and alkanes. Generally,
cationic electrophilic metal centers with CO ligands
favor formation of s complexes of H2 and silanes over
oxidative addition to hydrides and silyl(hydrides) be-
cause the weak M“L backdonation cannot promote
XꢀH bond cleavage. In particular, electrophilic man-
ganese complexes, [Mn(CO)(dppe)2]+ (1) [6,7], and
[Mn(CO)3(PCy3)2]+ (2) [8], and its Re analogue [9], all
(1)
Such cationic agostic complexes, which of necessity
contain low-coordinating BAr−F (B[C6H3(3,5-CF3)2]4−)
anions, can be prepared according to Eq. (1) by
metathesis of a metal halide with NaBArF [6–8]. They
can possess multiple internal CꢀH interactions as in 1,
and are valuable synthetic precursors for coordination
of relatively weak ligands such as H2. However, other
weak ligands, including both p-acceptors such as
SiH3Ph, and s bases such as Et2O or CH2Cl2 do not
coordinate (silane reactions with the Re species were
not reported [9]). Presumably organosilane binding
does not occur for steric reasons because SiH3Ph does
* Corresponding author. Fax: +1-505-6673314.
E-mail address: kubas@lanl.gov (G.J. Kubas).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00230-8

96
X. Fang et al. / Journal of Organometallic Chemistry 609 (2000) 95–103
where the water from the acid binds to the metal center
instead of the anion. Similarly, protonation of mer-Mn-
H(CO)3(PP) (PP=dppe or depe) with HBF4·Et2O in
CHCl3 at r.t. afforded [Mn(CO)3(PP)(H2O)]BF4 [15],
where the water is from adventitious sources (H2O is
clearly a stronger ligand here than BF4, a known coor-
dinating anion). Thus there are four different synthetic
routes to four possible reaction products in these sys-
tems: (a) a solvento complex, (b) an anion-coordinated
species, (c) an agostic complex or (d) an H2 complex.
The trends for (a)–(d) formation cannot be predicted
and depend on several factors including the elec-
trophilicity of the metal center, sterics and relative
binding strengths of the sixth ligand. Entropy effects
play a large role here, and agostic binding can be
favored by up to 10 kcal mol−1 over external ligand
coordination
Scheme 1.
bind to isoelectronic, neutral W(CO)3(PCy3)2 and is
activated towards oxidative addition [10]. Third row
metals such as W have a larger coordination sphere and
less steric congestion than first row metal such as Mn.
Possibly because of steric effects, weak bases such as
Et2O and CH2Cl2 do not displace the agostic interac-
tion in M(CO)3(PCy3)2 (M=W, Mn+, Re+), but they
do form isolatable adducts with a more electrophilic 16
e− fragment with four electron-withdrawing CO lig-
ands and only one phosphine, [Re(CO)4(PR3)]+ (R=
Cy, i-Pr, Ph). The latter has been isolated only as six
coordinate solvento species, [Re(CO)4(PR3)(S)]+ (S=
Et2O, CH2Cl2, pentafluoropyridine) [11,12], and an
agostic precursor complex has not been observed, al-
though the weakly-bound CH2Cl2 is displaceable by H2
Eq. (2) [11,13].
It would be of interest to further tune the steric and
electronic properties of analogous Mn(I) complexes
with phosphorus donor ligands and low-coordinating
anions. The tied-back phosphite ligand, P(OCH2)3CMe
in 4 is of interest here for several reasons. It is both a
weaker s-donor and
a stronger p-acceptor than
analogous phosphines, and should increase the elec-
trophilicity of the metal center. Most importantly, un-
like 2, it lacks accessible CꢀH bonds to form agostic
interactions that would compete with binding of very
weak external ligands, e.g. alkanes.
S
H
LnRe−CH3+HA ꢀꢀꢀꢁ [LnRe−S]A“2 [LnRe−H2]A+S
−CH
4
(2)
The above Re solvento [11,12] or agostic [9] com-
plexes were prepared by treatment of the methyl com-
plexes with acids (Eq. (2)), or alternately for the former,
with
[Ph3C][BArF]
to
give
Ph3CMe
and
[Re(CO)4(PCy3)(S)]+.
Another synthetic option for preparing such precur-
sors or H2 complexes is protonation of a hydride to
directly give the H2 complex or a precursor complex via
rapid H2 elimination, if the H2 complex is very labile.
For example, the protonation of the phosphite com-
plex, mer-MnH(CO)3P2 (P=P(OEt)3), with CF3SO3H
at low temperature afforded in this case a neutral
anion-coordinated complex, Mn(CO)3P2(h1-OSO2CF3)
(3) (Scheme 1), without detection of the cationic H2
complex formed initially [14].
Such s complexes are being highly sought for studies
of CꢀH activation, but DH of binding is at best only
10–15 kcal mol−1, which is not enough to overcome
the entropic advantage for internal agostic CꢀH coordi-
nation. A stable (or even transient) 16 e− fragment that
cannot possess competing agostic interactions is neces-
sary for observing s-alkane coordination, which is an
intermediate in alkane activation on for example highly
electrophilic cationic platinum complexes [16–18]. Also,
CpRe(CO)2(cyclopentane) has been observed by NMR
at low temperature [19], so Group 7 carbonyl com-
plexes are appropriate targets for isolation of alkane
complexes.
Et O
2
MnH(CO)3P2CF3SO3Hꢀꢀꢁ[Mn(CO)3P2(H2)]
−H
CF3SO3 “2Mn(CO)3P2(h1-OSO2CF3)
(3)
The tied-back phosphite is also sterically more com-
pact than phosphines and may accommodate alkanes,
silanes, olefins, and other more sterically demanding
ligands in first-row metals. Here we would like to report
the synthesis of 4 and other adducts of a highly elec-
trophilic cationic 16 e− Mn(I) fragment with tied-back
phosphite ligands and a weakly coordinating BArF
The failure in detecting H2 complexation in Eq. (3) is
presumably due to the immediate coordination of
CF3SO−3 , which unlike BArF is not a low-coordinating
anion. The same type of reaction carried out in ethanol
using aqueous HBF4 as the acid yielded the aquo
complex [Mn(CO)3(P)(H2O)]BF4 (P=PPh(OEt)2),
which can be considered a ‘solvento-type’ complex,

X. Fang et al. / Journal of Organometallic Chemistry 609 (2000) 95–103
2. Results and discussion
97
2.1. Dichloromethane complex (4)
The cationic dichloromethane complex 4 is prepared
in high yield as outlined in Scheme 2. Treatment of
Mn(CO)5Me
[21]
with
two
equivalents
of
P(OCH2)3CMe (1-methyl-4-phospha-3,5,8-trioxabicy-
clo[2.2.2]octane) [22] in refluxing toluene yields the
tricarbonyl methyl complex 5. The mer-configuration of
5 is shown by the IR CO stretching (wCO) pattern: 2035
w, 1952 s, 1926 s. Reaction of 5 with [Ph3C][BArF] [23]
in CH2Cl2 leads to the CH2Cl2 complex 4 as yellow
crystals in 82% yield. The wCO values for 4 (in CD2Cl2),
2096 w, 2025 s and 2004 s, are much higher than those
(2048 w, 1962 s, and 1942 s) of the phosphine analogue
2 (where an agostic interaction takes the place of
CH2Cl2). This is a result of weaker backdonation from
Mn to the CO ligands in 4 and suggests that the Mn(I)
center in 4 is significantly more electrophilic than that
Scheme 2.
Table 1
Crystal data and structure refinement for complex 4
Empirical formula
Crystal size (mm3)
Temperature (K)
C46H32BCl2F24MnO9P2
0.04×0.08×0.25
203(2)
,
Wavelength (A)
Space group
0.71073
(
Triclinic, P1
Unit cell dimensions
,
a (A)
13.0850(7)
14.5411(7)
15.0947(8)
93.482(1)
104.105(1)
98.799(1)
2
1.4–26.4
14 134
10 116 [Rint=0.0196]
R1=0.0716, wR2=0.2035
R1=0.0964, wR2=0.2217
1
in 2. The H-NMR spectrum of 4 shows a resonance at
,
b (A)
,
c (A)
5.33 ppm corresponding to the free CH2Cl2 (free ex-
change with the solvent, CD2Cl2, occurs). In contrast,
the less electrophilic and more sterically demanding 2
does not bind CH2Cl2 [8]. The bound CH2Cl2 cannot be
removed from solid 4 by exposure to high vacuum for
hours, but can be displaced in solution by H2 and other
ligands as will be shown below. As for 1 and 2, N2 does
not react with 4, presumably because N2 is a very poor
s donor, weaker even than CH2Cl2. In contrast to 4,
the analogue 3 with non tied-back phosphites is found
to coordinate the CF3SO−3 anion instead of CH2Cl2
solvent [14]. This demonstrates the importance of using
the low-coordinating BArF anion because anions such
as CF3SO−3 are stronger ligands than CH2Cl2 and
perhaps other small molecules of interest here, e.g. H2.
Also in this regard, all mononuclear dichloromethane
complexes are cationic because CH2Cl2 is a very poor
base and coordinates only to strong metallo Lewis
acids.
h (°)
i (°)
k (°)
Z
Theta range for data collection (°)
Reflections collected
Independent reflections
Final R indices [I\2|(I)]
R indices (all data)
anion. The labile dichloromethane ligand in the valu-
able synthon 4 can be displaced by H2, ethers, amines,
olefins and silanes, which undergo heterolytic cleavage.
Facile heterolytic cleavage of both H2 and silanes are
observed on the cationic system [Re(CO)4(PR3)(L)]+
[11,13].
Only a handful of dichloromethane complexes have
been structurally characterized, and coordination can
be monodentate [11,12,24], bidentate as in the first
CH2Cl2 complex characterized by X-ray diffraction by
Strauss and coworkers [25,26], or bridging via both Cl
in a Ru3 cluster [27]. In order to determine the geome-
try in 4, single crystals were grown from mixed CH2Cl2
and hexane solvents and were subjected to X-ray struc-
tural analysis (Table 1 and Fig. 1). The complex shows
typical octahedral configuration with trans-phosphite
ligands. The CH2Cl2 molecule is bound to Mn through
one chlorine atom Cl(1) with a MnꢀCl(1) distance of
(4)
Bound H2 can be highly acidic on cationic systems
(pKa near zero or less) and can readily protonate ethers
or other weak bases B as in Eq. (4) [1]. Cationic silane
s complexes can be observed at low temperature but
are nearly always unstable towards heterolytic cleavage
at room temperature (r.t.) [13,20]. The Mn–phosphite
system offers an opportunity for further study of these
types of reactions, which in principle may occur for
alkane activation.
,
2.4109(13) A. The average MnꢀP distance, 2.2281(12)
,
,
A, is shorter than that found in 2, 2.354 A. Regarding
the metalꢀCO bonding, the distance for MnꢀC(2) trans
,
to the bound CH2Cl2, 1.803(3) A, is much shorter than

98
X. Fang et al. / Journal of Organometallic Chemistry 609 (2000) 95–103
,
,
the bound Cl, 1.804(5) A, is longer than the 1.720(7) A
distance for the terminal C(4)ꢀCl(2), as has been ob-
served in similar octahedral Re(I) complexes,
[Re(CO)4(PR3)(CH2Cl2)]+ [11,12] and other monoden-
tate CH2Cl2 complexes [24]. The C(1)ꢀMn(1)ꢀC(3) an-
gle 179.0(2)° is very close to linear while that for
C(2)ꢀMn(1)ꢀCl(1), 173.96(16)°, shows the two bonds
C(2)ꢀMn(1) and Cl(1)ꢀMn(1) to be slightly bent away
from linearity.
the MnꢀC(1) and MnꢀC(3) distances of 1.867(5) and
,
1.880(5) A, respectively. This reflects a strong trans
effect: the nearly pure base CH2Cl2 does not compete
for backdonation with the CO trans to it unlike the
situation for the other two CO ligands that are trans to
one another. Hence the MnꢀC(2) bond is stronger than
the other MꢀCO bonds, and MꢀC distances generally
decrease as the p-acceptor strength of the ligand trans
to CO decreases. Several closely-related Group 6 and 7
complexes show this behavior [7], especially 2 where the
weak agostic interaction (with virtually no p-acceptor
strength) is trans to the CO and the MnꢀC distance is
A weak interligand hydrogen bonding interaction
appears to occur in 4 between an acidic hydrogen on
CH2Cl2 and an oxygen atom on the phosphite ligand.
The distance between O(9) and an idealized hydrogen
,
even shorter, 1.761(7) A [8]. The C(4)ꢀCl(1) distance for
,
position H(4B) is calculated to be 2.418 A, well within
the general range for CꢀH···O hydrogen bonds [28,29],
which for example can involve the oxygen of CO
ligands in metal complexes [30]. The distance between
,
C(4) and O(9), 3.185(6) A, is within the short end of the
,
range (3.0–4.0 A) for such an interaction, although the
CꢀH···O angle, 135.7°, is more acute than normal.
Hydrogen bonding involving haloalkanes is common,
and the hydrogens on the CH2Cl2 ligand might be
expected to be more acidic than in free dichloro-
methane because the electrophilic metal is withdrawing
electrons from Cl. The coordination geometry of the
CH2Cl2 ligand is not distorted from that in related
complexes. A precedent for any type of hydrogen bond-
ing to an oxygen atom of a phosphite ligand was not
located in a literature search. The hydrogen bonding
interaction energy in 4 can be estimated to be several
kcal mol−1, which may help stabilize the CH2Cl2 coor-
dination.
,
Fig. 1. Ortep diagram for complex 4. Selected bond distance (A) and
bond angles (°): MnꢀC(1)=1.867(5), MnꢀC(2)=1.803(3),
MnꢀC(3)=1.880(5), MnꢀP(1)=2.2328(12), MnꢀP(2)=2.2234(12),
MnꢀCl(1)=2.4109(13), Cl(1)ꢀC(4)=1.804(5), Cl(2)ꢀC(4)=1.720(7),
C(4)ꢀO(9)=3.185(6),
C(1)ꢀMnꢀC(3)=179.0(2), C(2)ꢀMnꢀCl(1)=173.69(16), P(1)ꢀMnꢀ
P(2)=176.97(5), C(3)ꢀMnꢀCl(1)=93.59(15), C(1)ꢀMnꢀCl(1)=
86.52(16), P(1)ꢀMnꢀCl(1)=86.47(4), P(2)ꢀMnꢀCl(1)=94.53(5),
2.2. Dihydrogen complex (6)
H(4B)ꢀO(9)=2.418
(idealized
H),
Exposure of a yellow solution of 4 in CD2Cl2 to ca.
3 atm of H2 gave a similarly colored solution that
showed a broad signal at −9.19 ppm in the tempera-
ture range of −60 to 25°C. The peak is attributed to
the s-bound H2 ligand in 6 that is presumably undergo-
ing equilibrium exchange with CH2Cl2–CD2Cl2
(Scheme 3). Integration showed that only about 2–3%
H2 complex was present, but this merely reflects the
much greater concentration of CD2Cl2 over H2 rather
than relative ligand binding strengths (H2 may actually
be the stronger ligand). The 31P-NMR chemical shifts
for 6 and 4 are virtually identical, l 155.1 and 155.2,
respectively, indicating similar net ligand effects for H2
and CH2Cl2 (although these ligands are not electroni-
cally similar because H2 is a moderate p-acceptor).
Replacement of H2 with HD gas afforded the h2-HD
complex, [mer-Mn(CO)3{P(OCH2)3CMe}2(HD)][BArF],
which showed a JHD coupling of 34.5 Hz (JPH is not
seen because the peaks are too broad, as for most HD
or H2 complexes). As can be seen in Table 2, this is the
highest value found for any Mn–Re phosphite–phos-
Cl(1)ꢀC(4)ꢀCl(2)=112.1(3), MnꢀCl(1)ꢀC(4)=118.2(2).
Scheme 3.

X. Fang et al. / Journal of Organometallic Chemistry 609 (2000) 95–103
99
Table 2
The H2 ligand in 6 does not appear to be as prone
towards heterolytic cleavage as that in [Re(CO)4(PR3)-
(H2)]+ (Eq. (4)), where protonation of ethers such as
iPr2O readily occurs [11]. An analogous experiment was
performed in which H2 was added to a solution of 4 in
CD2Cl2 at liquid nitrogen temperature to form 6, which
was then warmed to −78° and treated with ca. 1.5 ml
JHD coupling constants and HꢀH distances for H2 complexes of
Group 7 fragments with trans-CO ligands
a
,
Metal fragment
JHD (Hz) HꢀH (A)
Reference
[Mn(CO)(dppe)2]+ (1)
[Mn(CO)(depe)2]+
32
33
32
32.5
33
34.5
33
33.8
32
33
30
0.89–0.90
0.87–0.89
0.89–0.90
0.88–0.89
0.87–0.89
0.84–0.86
0.87–0.89
0.85–0.87
0.89–0.90
0.87–0.89
0.92–0.94
0.90–0.92
0.87–0.89
0.87–0.89
[6]
[7]
[Mn(CO){P(OEt)3}4]+
[Mn(CO){PPh(OEt)2}4]+
[Mn(CO)2{P(OEt)3}3]+
[Mn(CO)3(L)2]+ b (6)
[Mn(CO)3(PCy3)2]+ (2)
[Re(CO)4(PCy3)]+
[14]
[14]
[14]
This work
[8]
[11]
[9]
[9]
[37]
[20]
[37]
[37]
i
of Pr2O (ca. three equivalents). 1H- and 31P-NMR
spectra were recorded from −80 to 25°, but only the
iPr2O complex 9 (see below) and free H2 were observed
i
at all temperatures. Similarly, reaction of 4 with Pr2O
followed by addition of H2 (3 atm) at −198°C and
warming gave only 9. Although the stronger binding of
the ether than H2 may interfere with a potential H2
heterolytic cleavage process, the acidity of the bound
H2 is probably lower than that in [Re(CO)4(PR3)(H2)]+.
In the latter, formation of a hydride-bridged dinuclear
species on deprotonation as in Eq. (4) is thermodynam-
ically very favorable, but such a complex (or a
mononuclear hydride) is not seen for the Mn system
here.
[Re(CO)3(PCy3)2]+
[Re(CO)3(PPri3)2]+
[Re(CO)3{P(OEt)3}2]+
[Re(CO)2(PMe2Ph)3]+ c
[Re(CO)2{P(OEt)3}3]+
[Re(CO){P(OEt)3}4]+ c
31
33
33
a Except where noted, calculated from and bracketed by the empir-
ical relationships, rHH=1.42−0.0167; JHD [32] and rHH=1.44−
0.0168; JHD [33].
b L=P(OCH2)3CMe.
c In equilibrium with dihydride tautomer in solution.
2.3. Binding, heterolytic clea6age, and alcoholysis of
silanes
phine complex with varying numbers of CO ligands and
is among the highest ever reported (35 Hz for
i
,
Cr(CO)3(P Pr3)2(HD) is the highest; HꢀH=0.85 A
When a CD2Cl2 solution of 4 was treated with 1.2
equivalents of Et3SiH at −78°C, a yellow solution was
generated which showed a triplet at high field, l= −
16.1 (JHP=15.9 Hz), corresponding to one proton.
When PhSiH3 was used in place of Et3SiH, a similar
1H-NMR signal appeared at l −15.3 (JHP=15.5 Hz)
corresponding to ca. 0.2 proton, i.e. about 20% com-
plexation by the silane (recorded at −60°C; no reac-
tion occurs at −80°C here). In addition, the 31P-NMR
spectra showed a new signal at 159.3 ppm along with
the 155.6 ppm peak from the starting 4. These new
signals presumably represent an h2-bound R3SiꢀH com-
plex 7 similar to structurally-characterized Mo(CO)(h2-
HꢀSiR3)(diphosphine)2 [34] and [Re(CO)4(PR3)-
(h2-HꢀSiEt3)]+ observed by low-temperature NMR
[13]. As in the latter, the JHP coupling constants are too
small for a Mn–H complex (typical JHP=40–60 Hz
[14,35]). JSiH could not be measured due to the Mn
quadruplar broadening. When the mixtures were raised
to r.t., the high field proton signal disappeared, and the
1H-NMR spectra indicated the formation of a mixture
of several unidentified products that were likely formed
by heterolytic cleavage of the h2-SiꢀH bond as for the
Re complex [13]. No clear evidence was present for
formation of a Mn hydride complex, either as an
intermediate or a final product. GC–MS analysis of the
volatiles released from 7a showed (Et3Si)2O to be the
major component, which is presumably generated from
reaction of the silyl cation with adventitious mois-
ture as for [Re(CO)4(PR3)(HSiEt3)]+ as well as a
[CpFe(CO)(PPh3)(HSiR3)]+ system [36].
[31]). This is consistent with h2-H2 binding to a highly
electrophilic metal center with a relatively short HꢀH
,
distance (calculated [32,33] to be 0.84–0.86 A from
JHD). In all cases CO is trans to H2 in Table 2, and the
nature of the trans ligand exerts by far the greatest
influence on properties such as JHD and HꢀH distance
[7]. However, the cis ligands do have some effect,
although not always according to the expected trends,
e.g. JHD might have been expected to be reversed for
the dppe versus the more electron-rich depe Mn com-
plex (which should elongate the HꢀH bond more). Also
the trends for Re phosphite and phosphine complexes
are the reverse of what might have been expected
electronically, e.g. [Re(CO)3{P(OEt)3}2]+ has a lower
JHD than that for [Re(CO)3(PCy3)2]+. Thus the very
high JHD for 6 might be somewhat anomalous, al-
though it is not contrary to expected trends.
Regarding the lability of the H2 ligand in 6 in solu-
tion, the bound H2 is readily displaced by CH2Cl2 when
the H2 atmosphere is released by exposure of the solu-
tion to a He atmosphere. This is similar to the behavior
for Cr(CO)3(PiPr3)2(H2) and other highly labile H2 com-
plexes, and it appears that the H2 in 6 is more weakly
bound than the H2 coordinated to the less electrophilic
Mn fragments 1 and 2. For example, 95% of complex 2
was found to be bound to H2 at −10°C under similar
conditions. A possible explanation is that the bulky
phosphine groups in [Mn(CO)3(PCy3)2(H2)]+ inhibit
displacement of the H2 by the solvent, CH2Cl2.

100
X. Fang et al. / Journal of Organometallic Chemistry 609 (2000) 95–103
H O
2
2[Mn(Et3SiH)]+“2Et3Si+ꢀꢀꢁ(Et3Si)2O+2H+
(5)
2.4. Olefin, ether, and amine complexes (8–10) and
summary
As mentioned in Section 1, this is typical behavior
for a cationic silane complex because the Si atom of the
SiꢀH bond is highly activated toward nucleophilic at-
tack on account of depletion of the electron density of
the SiꢀH bond on coordination to cationic metal
centers.
The fate of the Mn fragment is not shown in Eq. (5)
but it is conceivable that if a MnꢀH species forms it
could be immediately protonated to the H2 complex 6
by the protons released from silane hydrolysis in Eq.
(5). The labile H2 in 6 could then be displaced by
CH2Cl2 solvent, to regenerate 4 in the absence of excess
Reaction of 4 with cis-cyclooctene (cco) afforded 8 as
a yellow solid in 65% yield. The olefinic protons show a
1H-NMR signal at 4.81 ppm, upfield shifted from the
5.67 ppm found for free cco. The cco cannot be re-
moved under prolonged vacuum. Lastly, addition of
iPr2O or Et3N to CD2Cl2 solutions of 4 resulted in the
respective ether or amine complexes 9 and 10. All of
these molecules appear tightly bound to the metal Mn,
and none were in equilibrium with CD2Cl2 or H2 under
three atmospheres of hydrogen gas. The formation of
i
i
the Pr2O complex is somewhat surprising since Pr2O
does not bind to the [Re(CO)4(PPh3)]+ fragment, al-
though the latter does coordinate Et2O [11,12]. That
could mean the bis(phosphite) Mn complex is either
more electrophilic than the Re monophosphine species,
or has more room for coordination (or both electronic
and steric factors are more favorable). There may be
H2.
+
[Mn(Et3SiH)]+“[Mn(H)]H“[Mn(H2)]+
unobserved
7a
2
6
CH Cl
2
ꢀꢀꢀꢀꢁ[Mn(CH2Cl2)]+
(6)
−H
2
4
Such formation of [CpFe(CO)(PPh3)(H2)]+ from hy-
drolysis of [CpFe(CO)(PPh3)(HSiR3)]+ has previously
been observed and employed for catalytic silane alco-
holysis [36]. The Mn system also catalyzes reaction of
phenol with triethylsilane, presumably by a mechanism
similar to that proposed for the Fe system (Scheme 4).
The ratio of silane (0.307 mmol) to the precatalyst 4
was about 24:1, and a slight deficiency of phenol (0.287
mmol) was added at −78°C in a NMR tube reaction.
1H-NMR spectra recorded from −80°C to 25°C all
showed a broad signal at −9.23 ppm presumably due
to the H2 complex formed according to Scheme 4.
Upon exposure of the solution in the NMR tube to a
He atmosphere after reaction was complete, the 1H-
NMR spectrum showed a triplet at −16.75 ppm corre-
sponding to the silane s complex, 7a. The latter would
be expected according to Scheme 4 since unreacted
silane was present (stoichiometric excess over phenol
reactant) and is a stronger ligand than either H2 or
CH2Cl2. The expected product of silane alcoholysis,
PhOSiEt3, was isolated in ca. 50% yield, demonstrating
that the reaction is catalytic. Manganese carbonyl spe-
cies such as Mn(CO)5(CH3) and [Mn(CO)4Br]2 are also
effective precatalysts for alcoholysis of silanes [38] and
may operate via a similar pathway, i.e. the true catalyst
is an electrophilic unsaturated Mn fragment that het-
erolytically cleaves an intermediate silane s complex.
i
more steric interference of the Pr groups with the
phenyl groups on the single cis phosphine on Re than
with the two tied-back phosphites on Mn.
In summary, the highly electrophilic [Mn(CO)3-
(P(OCH2)3CMe)2]+ fragment with trans tied-back
phosphite ligands binds dichloromethane solvent to
form the structurally characterized complex 4, isolated
as a BArF salt. The latter contains novel interligand
hydrogen bonding between an acidic hydrogen on the
CH2Cl2 ligand and an oxygen of the phosphite. The
coordination of CH2Cl2 is in direct contrast to the lack
of binding by the phosphine analogues [M(CO)3-
(PCy3)2]+ (M=Mn, Re) that contain agostic interac-
tions. Presumably the tied-back phosphites give less
steric congestion and more electrophilic metal centers,
and of course cannot engage in agostic interactions that
would compete with external ligand binding. Under a
hydrogen atmosphere, 4 is in equilibrium with the
h2-H2 complex (6), and the very high JHD for 6 points
to the high electrophilicity of the metal center. Silanes
also displace the bound CH2Cl2 at low temperature, but
the h2-SiꢀH bond undergoes heterolytic cleavage on
warming. 4 catalyzes reaction of SiHEt3 with phenol to
give Et3SiOPh and H2. The CH2Cl2 ligand in 4 is
irreversibly displaced by olefins, ethers and amines to
form stable adducts. The results in these and other
related systems bring to the forefront the subtle balance
between electronic and steric forces that occur on addi-
tion of sixth ligands to 16 e− metal fragments.
3. Experimental
All manipulations were performed either under a
helium atmosphere in a Vacuum Atmospheres drybox
or under an argon atmosphere using standard Schlenk
Scheme 4.

X. Fang et al. / Journal of Organometallic Chemistry 609 (2000) 95–103
101
techniques unless otherwise specified. CH2Cl2 was dis-
3.3. Reaction of 4 with H2 to gi6e 6
tilled under Ar from P2O5. Toluene and hexane were
purified by passing through an alumina column. Hy-
drogen gas was obtained from an in-house gas plant
and was of UHP grade. HD gas was purchased from
Isotec Inc. Other reagents were purchased from
Aldrich, Acros or Strem Chemical Co. and used as
received. 1H-, 31P-, 13C- and 11B-NMR spectra were
recorded on a Varian Unity 300 spectrometer with field
A J-Young NMR tube was charged with 4 (0.020 g)
and CD2Cl2. On a vacuum line, the yellow solution was
frozen and evacuated, then backfilled at liquid N2
temperature with H2 (ca. 3 atm). The tube was closed
off and warmed to r.t. to give a yellow solution.
1H-NMR (CD2Cl2), l −9.19 (br, s), 0.88 (s, 6H), 4.40
(t, 12H, J=2.2 Hz), 7.56 (s, 4H), 7.72 (t, 8H, J=2.4
Hz). 31P-NMR (CD2Cl2), l 155.1. The NMR spectrum
obtained at −60°C was identical. However the com-
plex partially decomposed while left standing at r.t. for
ca. 16 h.
1
strengths of 300, 121, 75 and 96 MHz, respectively. H
and 13C chemical shifts were referenced to the residual
solvent resonance relative to TMS; 31P and 11B chemi-
cal shifts were referenced to external 85% H3PO4 and
BF3–Et2O, respectively. Infrared spectra were recorded
on a Nicolet Avator 360 FTIR spectrometer. Elemental
analyses were performed in house on a Perkin–Elmer
Series II CHNS/O model 2400 analyzer.
3.4. Reaction of 4 with silanes to gi6e 7 and heterolytic
clea6age
Et3SiH (7.3 ml, 0.046 mmol) was injected into a 5 mm
NMR tube containing 4 (49.4 mg, 0.038 mmol) in
CD2Cl2 (0.5 ml) at −78°C to give a yellow solution.
NMR spectra were recorded at −60°C. 1H-NMR
(CD2Cl2), l −16.81 (t, JHP=15.9 Hz, Et3SiꢀH), 0.87
(s, 6H), 1.06 (m, 15H), 4.37 (s, 12H), 7.62 (s, 4H), 7.78
(s, 12H). 31P-NMR (CD2Cl2), l 161.2. The NMR spec-
tra recorded at progressively elevated temperatures of
−40°C, −20°C and 0°C showed no apparent change.
However at r.t. the complex decomposed to several
unidentified products within 10 min.
3.1. Preparation of mer-Mn(P(OCH2)3CMe)2-
(CO)3(Me) (5)
A mixture of Mn(CO)5Me (0.210 g, 1.00 mmol) and
P(OCH2)3CMe (0.311 g, 2.10 mmol) in toluene (ca. 10
ml) was refluxed for ca. 16 h under Ar atmosphere to
give a yellowish suspension. The mixture was then
filtered and the solid washed with toluene (2×) and
hexane (2×) to give an off-white solid. The solid was
purified in air by flash silica-gel column chromatogra-
phy eluting with CH2Cl2 to give the product (0.390 g,
87%) as a white solid. Anal. Calc. for C14H21O9P2Mn:
C, 37.35; H, 4.70. Found: C, 37.16; H, 4.77%. FTIR
(CD2Cl2, cm−1) 2035 w, 1952 vs. 1926 s. 1H-NMR
(CD2Cl2), l 4.20 (t, JHP=2.2 Hz, 12H, P(OCH2)3-
On analogy, reaction of
4
with PhSiH3 at
−60°C gave a similar silane complex which decom-
1
posed at r.t. Relevant NMR data: H-NMR l −15.3
(t, J=15.3 Hz, ca. 0.2 H). 31P-NMR, l 159.3, 155.6
(major).
CMe), 0.76 (s, 6H, P(OCH2)3CCH3), −0.62 (t, JHP
8.0 Hz, 3H, MnCH3). 31P-NMR (CD2Cl2),
167.7.
=
l
3.5. Reaction of 4 with Et3SiH and phenol
Et3SiH (49 ml, 0.307 mmol) was injected into a 5 mm
NMR tube containing 4 (17.0 mg, 0.013 mmol) at
−78°C. Then a solution of phenol (27.0 mg, 0.287
mmol) in CD2Cl2 (ca. 0.6 ml) at ca. −40°C was
3.2. Preparation of [mer-Mn(P(OCH2)3CMe)2(CO)3-
(ClCH2Cl)][BArF] (4)
1
A yellow solution of 5 (0.101 g, 0.224 mmol)
and [Ph3C][BArF] (0.248 g, 0.224 mmol) in CH2Cl2
(5 ml) was stirred at r.t. for 20 min. Hexane (15 ml)
was then layered on top of the CH2Cl2 solution and
the mixture was cooled at −30°C to give the pro-
duct (0.238 g, 82%) as yellow crystals. Anal. Calc.
for C46H32BCl2F24O9P2Mn: C, 39.91; H, 2.31. Found:
C, 40.06; H, 2.52%. FTIR (CD2Cl2, cm−1) 2096
w, 2025 vs. 2004 s. 1H-NMR (CD2Cl2) l 7.74 (s,
8H, BArF), 7.58 (s, 4H, BArF), 4.39 (t, JHP=2.2
Hz, 12H, P(OCH2)3CCH3), 0.86 (s, 6H, P(OCH2)3-
transferred via cannula to give a yellow solution. H-
NMR spectra recorded from −80°C to 25°C all
showed a broad signal at −9.23 ppm presumably due
to the H2 complex, 6. 31P-NMR (−80°C): l 160.0
(major), 155.0 (minor); (−40°C) 160.3; (0°C) 160.5;
(25°C) 161.0. After the solution in the NMR tube was
exposed to a He atmosphere, NMR spectra were
1
recorded immediately at RT. The H-NMR spectrum
showed a triplet at −16.75 ppm with a coupling con-
stant of 15.5 Hz, and the 31P-NMR showed a singlet at
161.4 ppm. These signals correspond to the silane s
complex (7a). PhOSiEt3 was isolated in ca. 50% yield by
chromatography on a silica gel column and identified
by GC–MS and NMR data.
CCH3). 13C-NMR (CD2Cl2),
l 15.1, 34.1, 77.6.
11B-NMR (CD2Cl2), l −12.1. 31P-NMR (CD2Cl2), l
155.2.

102
X. Fang et al. / Journal of Organometallic Chemistry 609 (2000) 95–103
3.9. X-ray structure determination of 4
3.6. Preparation of [mer-Mn(P(OCH2)3CMe)2(CO)3-
(cis-cyclooctene)][BArF] (8)
A yellow, needle-shaped crystal of 4 was attached to
a glass fiber using a spot of silicone grease. The air-sen-
sitive crystal was mounted from a matrix of mineral oil
under argon gas flow. The crystal was immediately
placed on a Bruker P4/CCD/PC diffractometer, and
cooled to 203 K using a Bruker LT-2 temperature
device. The data were collected using a sealed, graphite
monochromatized Mo–Ka X-ray source. A hemisphere
of data was collected using a combination of € and ꢀ
scans, with 20 s frame exposures and 0.3° frame widths.
Data collection and initial indexing and cell refinement
were handled using SMART software [39]. Frame inte-
gration and final cell parameter calculation were carried
out using SAINT software [40]. The data were corrected
for absorption using the SADABS program [41]. Decay
of reflection intensity was not observed.
To a mixture of 5 (74.3 mg, 0.165 mmol) and
[Ph3C][BArF] (182.6 mg, 0.165 mmol) was added cis-cy-
clooctene (0.1 ml, 0.768 mmol) followed by CH2Cl2 (2
ml) at 25°C. The resulting yellow solution was stirred
for 30 min. Hexane (12 ml) was layered on top of the
CH2Cl2 solution, and the mixture was cooled to −
30°C to give the product (0.151 g, 65%) as a light
yellow solid. Anal. Calc. for C53H44BF24O9P2Mn·
0.5CH2Cl2: C, 44.26; H, 3.10. Found: C, 44.60; H,
3.33%. FTIR (CD2Cl2, cm−1) 2083 w, 2013 vs. (br).
1H-NMR (CD2Cl2), l 0.79 (s, 6H), 1.53 (m, 6H), 1.85
(m, 2H), 2.05 (m, 2H), 2.35 (dd, 2H, J=13.4, 3.4 Hz),
4.25 (t, 12H, J=2.2 Hz), 4.81 (m, 2H, CHCH2), 7.57
(s, 4H), 7.73 (s, 12H). 13C-NMR (CD2Cl2) l 15.0, 26.2,
28.3, 31.5, 33.6 (CMe), 77.3 (OCH2), 101.6 (CHCH2).
31P-NMR (CD2Cl2), l 157.2.
(
The structure was solved in space group P1 using
direct methods and difference Fourier techniques. The
initial solution revealed the manganese, and the major-
ity of all non-hydrogen atom positions. The remaining
atomic positions were determined from subsequent
Fourier synthesis. Hydrogen atom positions were fixed
in ideal geometries (CꢀH=0.93 for aromatic, 0.97 for
3.7. Reaction of 4 with isopropyl ether and H2 to gi6e
9
To a solution of 4 (20 mg) in CD2Cl2 (0.5 ml) in a
,
methylene and 0.96 A for methyl). The hydrogen atoms
i
J-Young NMR tube at 25°C was added Pr2O (ca. 4 ml,
were refined using the riding model, with isotropic
temperature factors fixed to 1.5 (methyl) or 1.2 (methyl-
ene and aromatic) times the equivalent isotropic U of
the carbon atom they were bound to. The final refine-
ment [42] included anisotropic temperature factors on
all non-hydrogen atoms, and converged with final resid-
uals of R1=0.0716 and R2w=0.2035. Structure solu-
tion, refinement, graphics, and creation of publication
materials were performed using SHELXTL NT [43].
1.2 equivalent) to give a yellow solution. The mixture
was then charged with H2 under liquid N2 temperature
(ca. 3 atm), and NMR spectra were recorded at temper-
atures progressively from −60 to 25°C. Neither the H2
complex 6 nor a hydride complex was observed within
the chemical shift ranges of 20 to −30 ppm. H2 was
then released and NMR spectra were recorded at 25°C
showing the presence of the ether complex 9. FTIR
(CD2Cl2, cm−1) 2092 w, 2017 vs., 1982 s. 1H-NMR
(CD2Cl2), l 0.88 (s, 6H), 1.10 (d, 12H, J=6.1 Hz, ether
OCHCH3), 3.68 (hept, 2H, J=6.1 Hz, ether OCH),
4.38 (t, 12H, J=2.2 Hz), 7.57 (s, 4H), 7.73 (s, 8H).
13C-NMR (CD2Cl2), l 22.6, 22.8, 69.3 (ether OCH),
76.9 (OCH2). 31P-NMR (CD2Cl2), l 156.5. Data for
free (Me2CH)2O: 1H: 3.63 ppm (OCH, same pattern
and J as bound ether); 13C: 68.0 (OCH).
4. Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 139109 for compound 4.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
3.8. Reaction of 4 with triethylamine and H2 to gi6e 10
Same procedures were followed as for the reaction
with isopropyl ether. FTIR (CD2Cl2, cm−1),
2092w, 1999s, 1957s. 1H-NMR (CD2Cl2), l 0.82
(s, 6H), 0.98 (t, J=7.1 Hz, NCH2CH3, free Et3N), 1.34
(t, 9H, J=7.3 Hz, coordinated NCH2CH3), 2.48 (quar-
tet, J=7.1 Hz, NCH2, free Et3N), 3.30 (quartet, 6H,
J=7.3 Hz, coordinated NCH2), 4.30 (t, 12H, J=2.2
Hz), 7.56 (s, 4H), 7.72 (s, 8H). 31P-NMR (CD2Cl2), l
156.2.
Acknowledgements
This work was supported by the Department of
Energy, Office of Basic Energy Sciences, Chemical Sci-
ences Division. J.H.V. is grateful to the Director of the
Los Alamos National Laboratory for postdoctoral
funding.

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