Silylene Complexes of Late 3 d Transition Metals Supported by tris-Phosphinoborate Ligands

Article abstract of DOI:10.1021/acs.organomet.8b00635

The complexes [BP₃^R]MX ([BP₃^R] = PhB(CH₂PR₂)₃^-, R = Ph, ⁱPr; M = Ni, Co, Fe; X = halide) were explored as platforms for generation of first-row metal silylene complexes. Direct silylation of [BP₃^Ph]NiCl or [BP₃^iPr]CoCl with (THF)₂LiSiHMes₂ resulted in formation of the silylene complexes [BP₃^Ph]Ni(μ-H)(SiMes₂) and [BP₃^iPr]Co(μ-H)(SiMes₂), respectively. In contrast, [BP₃^iPr]FeBr reacted with (THF)₂LiSiHMes₂ to produce the iron-alkyl [BP₃^iPr]Fe(CH₂-2-(SiH₂Mes)-3,5-Me₂C₆H₂), a constitutional isomer of the expected silyl or silylene complex. Preparation of the nickel benzyl complex [BP₃^Ph]Ni(η²-Bn) allowed for exploration of addition-elimination chemistry for access to silylene complexes from simple primary and secondary silanes. Heating toluene solutions of [BP₃^Ph]Ni(η²-Bn) in the presence of CySiH₃ resulted in the formation of a dimeric μ-silylene complex [Ni(μ-BP₂^Ph)(μ-SiHCy)]₂. In the presence of 4-dimethylaminopyridine (DMAP), these conditions led to exclusive formation of the base-stabilized silylene complex [BP₃^Ph]Ni(μ-H)[SiHCy(DMAP)].

Full text of DOI:10.1021/acs.organomet.8b00635

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Silylene Complexes of Late 3d Transition Metals Supported by tris-
Phosphinoborate Ligands
Rex C. Handford, Patrick W. Smith, and T. Don Tilley*
Department of Chemistry, University of California, Berkeley, Berkeley, California 94720-1460, United States
S
* Supporting Information
R
R
ABSTRACT: The complexes [BP3 ]MX ([BP3 ] = PhB-
−
i
(CH2PR2)3 , R = Ph, Pr; M = Ni, Co, Fe; X = halide) were
explored as platforms for generation of first-row metal silylene
complexes. Direct silylation of [BP3Ph]NiCl or [BP3iPr]CoCl
with (THF)2LiSiHMes2 resulted in formation of the silylene
complexes [BP3Ph]Ni(μ-H)(SiMes2) and [BP3iPr]Co(μ-H)-
(SiMes2), respectively. In contrast, [BP3iPr]FeBr reacted with
(THF)2LiSiHMes2 to produce the iron-alkyl [BP3iPr]Fe(CH2-
2-(SiH2Mes)-3,5-Me2C6H2), a constitutional isomer of the
expected silyl or silylene complex. Preparation of the nickel benzyl complex [BP3Ph]Ni(η2-Bn) allowed for exploration of
addition−elimination chemistry for access to silylene complexes from simple primary and secondary silanes. Heating toluene
solutions of [BP3Ph]Ni(η2-Bn) in the presence of CySiH3 resulted in the formation of a dimeric μ-silylene complex [Ni(μ-
BP2Ph)(μ-SiHCy)]2. In the presence of 4-dimethylaminopyridine (DMAP), these conditions led to exclusive formation of the
base-stabilized silylene complex [BP3Ph]Ni(μ-H)[SiHCy(DMAP)].
promotes silicon-centered hydrosilylation catalysis by silylene
complexes.1,12,15,16
INTRODUCTION
■
To date, most reported silylene (SiR2) complexes bear 4d and
5d transition-metal centers, while few 3d-metal silylene
complexes have been reported.1 These heavier-metal silylene
complexes have served to develop synthetic methods to access
MSi linkages and have been instrumental in elucidating the
electronic structures and reactivity patterns associated with
multiple bonding between transition-metal centers and
silicon.2−6 The MSi linkage in these complexes can be
accessed by abstraction of suitable leaving groups “X” bound to
a silyl substituent,7,8 by α-H migration of a nearby Si−H bond
to the metal center,9 or by extrusion of a silylene by direct
reaction with a silane,3−5,10,11 among other methods (Scheme
1).1,6 The reactions of silylene complexes reflect substantial
electrophilic character at silicon,12 which in turn renders them
prone to coordination by nucleophiles to generate base-
stabilized silylene ligands.13,14 This electrophilicity also
In contrast to the well-known 4d- and 5d-metal silylenes,1
there is a paucity of analogous compounds based on first-row
metals. This difference might be in part due to the diminished
ability of 3d-metal centers to stabilize silylene fragments,
whereas the valence 4d and 5d orbitals have a large radial
extension and can therefore participate in significant π-bonding
stabilization of the SiR2 fragment. The smaller 3d orbitals are
less available to engage in this interaction. One consequence of
this effect is the tendency of documented 3d-metal silylenes to
undergo further stabilization by interaction of M−H bonds
with the electrophilic silicon center, as demonstrated in
complexes such as [BP3iPr]FeH(η3-H2SiMeR),17 [(dtbpe)Ni-
(μ-H)(SiMes2)]+,18 and Cp*Fe(iPr2PMe)(H)(μ-H)(SiRR′).19
Such stabilizing interactions have also been demonstrated for
4d-metal complexes (e.g., [Cp*Ru(iPr3P)(μ-H)2(SiRR′)]+),15
albeit to a lesser extent, and such interactions are further
diminished in related 5d-metal complexes (e.g., Cp*Os(iPr3P)-
(H)(SiHTrip); Trip = 2,4,6-triisopropylphenyl).19−21 Both
IR and NMR spectroscopies are consistent with the
interpretation that (M)H−Si bonding decreases as Fe > Ru
> Os. The lower ability of 3d metals to stabilize SiR2 fragments
might result in enhanced electrophilicity at silicon that may be
exploited to promote more facile coordination of hydro-
silylation substrates to the silylene ligand.
Scheme 1. Some Methods To Access Transition-Metal
Silylene Complexes
Silylene complexes of the late 3d transition metals were
targeted in order to develop further insight into their
Received: August 31, 2018
© XXXX American Chemical Society
A
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properties and potential reactivity; late, low-valent transition
metals appear to be effective in supporting the reactive MSi
linkage.1,12 Our investigations therefore focused on iron-,
R
R
cobalt-, and nickel-based complexes of [BP3 ] ligands ([BP3
=
−
i
PhB(CH2PR2)3 ; R = Ph, Pr). The preparation of silylene
complexes based on these [BP3 ]M scaffolds, as well as their
R
unique structural and spectroscopic properties, is detailed
herein.
RESULTS AND DISCUSSION
■
R
First-row metal complexes stabilized by the [BP3 ] ligand
Figure 1. Solid-state molecular structure of 1. Thermal ellipsoids are
drawn at 50% probability. Most H atoms and all carbon atoms of the
molecule’s arene rings, with the exception of the ipso-C atoms, are
omitted for clarity. Selected bond distances (Å) and angles (deg):
Fe1−Si1: 2.1415(5), Fe1−H1: 1.58(2), Si1−H1: 1.56(2), Fe1−P1:
2.2564(4), Fe1−P2: 2.1773(5), Fe1−P3: 2.2866(4), Ni1−H1−Si1:
85.7(12), Ni1−Si1−C1: 120.33(5), Ni1−Si1−C2: 126.69(5), C1−
Si1−C2: 112.38(7), B1−Ni1−Si1: 164.66(3).
scaffold were selected as convenient starting materials for
derivatization with silyl anion sources and silanes. The
sterically encumbering and strongly electron-donating coordi-
R
nation environment provided by the [BP3 ] ligand stabilizes
reactive, low-valent 3d-metal complexes.22 Also, the readily
R
prepared [BP3 ]MX (M = Mn, Fe, Co, Ni; X = halide) starting
materials have served as useful precursors to an array of
unusual late first-row metal complexes in a variety of oxidation
states.22−25
R
at 192.2 ppm; this chemical shift is similar to those of silylene
and η3-silane complexes reported in the literature.1,13,17−19
While the solid-state and solution spectroscopic properties of 1
are consistent with silylene character in the Ni−Si linkage, a
Si−H bonding interaction is still clearly present. Thus, 1 is also
an example of “arrested” α-migration of the hydride from the
silicon atom to the metal center, as observed in [(dtbpe)Ni(μ-
H)(SiMes2)]+.18 The singlet observed in the 31P{1H} NMR
spectrum at 20.0 ppm indicates that the three phosphorus
donor atoms of the [BP3Ph] ligand are equivalent in solution at
room temperature, likely as the result of an intramolecular
dynamic process.
Direct Silylation of [BP3 ]MX Complexes. Reactions
with [BP3Ph]NiCl were initially explored with the goal of
forming closed-shell 18 electron compounds that would be
amenable to NMR characterization and analysis. The silyl
26
anion reagent (THF)2LiSiHMes2 was employed for con-
R
venient installation of −SiHMes2 into [BP3 ]M platforms,
where α-H-migration or hydride abstraction chemistry might
be expected to generate a silylene ligand. Thus, addition of
(THF)2LiSiHMes2 to a toluene solution of [BP3Ph]NiCl
resulted in a color change from green to dark purple, and
the 31P{1H} NMR spectrum of the reaction mixture indicated
the formation of a single major product (δP = 20.0 ppm).
Single-crystal X-ray diffraction analysis of crystals of this
complex grown from a saturated toluene solution layered with
pentane at −30 °C reveals the product to be [BP3Ph]Ni(μ-
H)(SiMes2) (1; eq 1).
Given this success with the [BP3Ph]NiCl system and its
silylation with (THF)2LiSiHMes2, silylations of the corre-
R
sponding [BP3 ]MX (M = Fe, Co) complexes were examined.
Initial investigations focusing on reactions of [BP3Ph]MX (M =
Fe, X = Br; M = Co, X = I) with (THF)2LiSiHMes2 were not
fruitful, and in all cases resulted in complex, intractable product
mixtures. Suspecting that this may be a result of the relatively
diminished electron-donating ability of [BP3Ph] and the
resulting instability of electronically unsaturated [BP3Ph]FeII
and [BP3Ph]CoII complexes, attention was turned to complexes
of [BP3iPr]. In the past, this more donating trisphosphinoborate
ligand has been observed to stabilize highly electronically and
coordinatively unsaturated metal complexes that were
inaccessible using the [BP3Ph] congener.22,23,25 Also, the
The solid-state molecular structure reveals the coordinated P
and Si atoms in an approximately tetrahedral arrangement
about the Ni center (Figure 1). A hydride bridging the Ni and
Si centers was located in the Fourier difference map and freely
refined. Complex 1 possesses a Ni−Si bond distance of
i
greater steric protection afforded by the Pr groups over Ph
should help stabilize reactive metal centers containing silylene
ligands.22
2.1415(5) Å, (cf. [(dtbpe)Ni(μ-H)(SiMes2)]+; d(Ni−Si)
=
Treatment of a pentane suspension of [BP3iPr]CoCl with 1
equiv of (THF)2LiSiHMes2 at −30 °C resulted in a gradual
color change from aquamarine to purple (eq 2). The 1H NMR
spectrum of the product mixture indicated formation of a
paramagnetic product, along with trace amounts of Mes2SiH2
and (Mes2SiH)2. Maintenance of (Me3Si)2O solutions of the
reaction mixture at −30 °C for 2 weeks resulted in
precipitation of the silane byproducts, leaving behind a dark
purple complex in solution in spectroscopically pure form. The
1H NMR spectrum of this species revealed 11 broadened and
shifted resonances consistent with a paramagnetic complex
formulated as [BP3iPr]Co(SiHMes2) or [BP3iPr]Co(μ-H)-
(SiMes2) (2). The low isolated yield (28%) of 2 could be
the result of various 1-electron processes resulting in
2.147(2) Å).18 The Ni, Si, and ipso-C atoms of the Mes
groups lie in a plane (∑(∠) = 359° about Si), while the
bridging hydride lies above this plane along the Ni−Si bond
vector.
1
The H NMR resonance for the bridging hydride of 1 in
benzene-d6 (at −6.22 ppm) is a quartet due to coupling to
phosphorus (2JHP = 11.7), with satellites for coupling to silicon
(1J(Ni)H−Si = 70 Hz). The latter coupling constant is larger than
that for [(dtbpe)Ni(μ-H)(SiMes2)]+ (1J(Ni)H−Si = 43 Hz; dtpbe
=
tBu2PCH2CH2PtBu2), indicative of a greater bonding
interaction between Si and the bridging hydride. The
29Si−1H HMBC NMR spectrum of 1 shows correlation
between the upfield hydride resonance and a silicon resonance
B
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disproportionation of the starting materials, as indicated by the
formation of Mes2SiH2 and (Mes2SiH)2. An Evans method
measurement of 2 revealed a magnetic moment of 1.5 μB,
which is closest to that expected for an S = 1/2 complex and
most consistent with the 17-electron silylene complex
[BP3iPr]Co(μ-H)(SiMes2) (2), since all reported 15-electron
complexes of the type [BP3iPr]CoX (X = Cl, I) have been
found to possess quartet ground states at room temperature,22
likely the spin state that would be adopted by the hypothetical
silyl complex [BP3iPr]Co(SiHMes2). The IR spectrum of 2
contains a medium-intensity absorption band at 1604 cm−1,
which is similar in frequency to the Ni(μ-H)Si band in the IR
spectrum of 1 (ν = 1602 cm−1). This suggests closely related
M(μ-H)Si bonding for both complexes (M = Co, Ni).
Unfortunately, crystals suitable for X-ray diffraction analysis
were not obtained, due to the extremely high solubility of 2 in
all solvents tested. In the absence of such data, the molecular
structure assigned to 2 must remain somewhat tentative.
Figure 2. Solid-state molecular structure of 3. Most H atoms have
been omitted, and isopropyl- and phenyl-groups of the [BP3iPr] ligand
have been truncated for clarity. Fe1−C1: 2.062(3), Fe1−Si1:
4.5503(10), C1−H1: 0.91(3), C1−H2: 0.93(3), Si1−H3: 1.40(3),
Si1−H4: 1.42(3), Fe1−P1: 2.4733(8), Fe1−P2: 2.4257(8), Fe1−P3:
2.4806(7), B1−Fe1−C1: 167.99(10).
literature.28 At present, it remains unclear what the driving
force for this transformation is, though it is possible that the
reduction in steric interactions during the conversion of
“[BP3iPr]Fe(SiHMes2)” into 3 is a major factor.
Reactions of [BP3 ]NiII Complexes with Silanes.
R
R
[BP3 ]MR complexes (R = alkyl, aryl) were examined to
As for the [BP3 ]FeII systems, previous investigations of
R
evaluate whether silyl and silylene complexes could be
generated by direct reaction with primary and secondary
silanes through the release of R-H with formation of a new M−
Si bond. Initially, [BP3Ph]Ni(Bn) (4; Bn = benzyl) was
targeted, envisioning its use in addition−elimination reactivity
with silanes. Treatment of [BP3Ph]NiCl with 0.5 equiv of
Bn2Mg(THF)2 afforded a magenta-colored solid following
precipitation from a saturated THF solution of the reaction
mixture with pentane. Multinuclear NMR spectroscopy of
benzene-d6 solutions of the solid indicated the formation of a
diamagnetic complex whose spectroscopic features are
consistent with those expected for complex 4 (eq 4).
these complexes have concluded that species of the type
[BP3iPr]FeSiR3 (R = SiMe3, Ph) can be readily prepared by
metathesis of the Fe−Br bond in [BP3iPr]FeBr with KSi-
(SiMe3)3 or [(THF)3Li]SiPh3, respectively.27 A complex
originally formulated as [BP3iPr]Fe(SiHMes2) was also
prepared, but its solid-state molecular structure was not
determined. To interrogate the nature of the Fe−Si bond, and
to compare its bonding metrics relative to the nickel congener
1, this complex was again prepared with the goal of obtaining
crystalline material suitable for single-crystal X-ray diffraction
analysis. Surprisingly, the structure obtained from X-ray studies
of single crystals of “[BP3iPr]Fe(SiHMes2)” was not that of the
expected iron silyl complex, but rather that of the isomeric iron
benzyl complex [BP3iPr]Fe(CH2-2-(SiH2Mes)-3,5-Me2C6H2)
(3, eq 3; Figure 2).
As with 1, the 31P{1H} NMR spectrum of 4 at room
temperature contains only a sharp singlet corresponding to the
three phosphorus nuclei of the [BP3Ph] ligand, indicative of
approximate C3v symmetry in solution. The η2-coordination of
the benzyl ligand in 4, with net donation of three electrons, has
been documented in the literature,29 and in this case likely
results from steric crowing about the metal center resulting
from the Ph-substituents of the [BP3Ph] ligand which precludes
η3-coordination. Consistent with this, the solid-state structure
of 4 (Figure 3) shows Ni−CH2 and Ni−Cipso distances of
1.982(2) and 2.226(3) Å, while the nonbonding Ni−Cortho
distances are 2.644(3) and 3.149(3) Å.
No Fe−Si bond is apparent in the solid-state structure of 3
(d(Fe−Si) = 4.5503(10) Å), and both hydrogen atoms bound to
the Si atom were located in the Fourier difference map and
isotropically refined. On the basis of this structure, the original
spectroscopic data reported for “[BP3iPr]Fe(SiHMes2)” can be
better rationalized. The solution magnetic moment of 4.81 μB
corresponding to an S = 2 ground state is consistent with a
tetrahedrally coordinated high-spin d6 metal center, and the
Si−H stretching frequency of 2151 cm−1 is typical for silanes.
The rearrangement of the initial Fe−Si bond to the Fe−C
bond present in 3 is unexpected, given that bond strengths for
the former are typically greater than for the latter, though Fe−
Si to Fe−C rearrangements have been observed in the
Mixtures of 4 and a secondary silane (1 equiv of Ph2SiH2,
Mes2SiH2, or Cy2SiH2) in benzene-d6 underwent no reaction,
even after several hours at temperatures up to 100 °C. In
contrast, the primary silanes PhSiH3 and CySiH3 reacted with
4 at 65 °C in benzene-d6 to produce 1 equiv of toluene, as
1
indicated by H NMR spectroscopy. In the case of PhSiH3,
C
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Figure 3. Solid-state molecular structure of 4. Thermal ellipsoids are
drawn at 50% probability. Most H atoms and all carbon atoms of the
Ph rings on the [BP3Ph] ligand, with the exception of the ipso-C
atoms, are omitted for clarity. Selected bond distances (Å) and angles
(deg): Ni1−C1: 1.982(2), Ni1−C2: 2.226(3), C1−C2: 1.455(4),
Ni1−C3: 2.644(3), Ni1−C7: 3.149(3), C1−H1: 0.91(3), C1−H2:
0.94(3), Ni1−P1: 2.2302(8), Ni1−P2: 2.2325(8), Ni1−P3:
2.2490(7). Ni1−C1−C2: 79.10(15), Ni1−C2−C1: 60.95(14), B1−
Ni1−C1: 135.80(9), B1−Ni1−C2: 175.74(8).
Figure 4. Solid-state molecular structure of 5. Thermal ellipsoids are
drawn at 50% probability. Most H atoms and all carbon atoms of the
Ph rings on the [BP2Ph] ligands, with the exception of the ipso-C
atoms, are omitted for clarity. Selected bond distances (Å) and angles
(deg): Ni1−Si1: 2.1800(8), Si1−Ni1′: 2.2104(8), Ni1−H1: 1.53(3),
H1−Si1′: 1.73(3), Ni1−P1: 2.1753(7), Ni1−P2′: 2.2277(7), Ni1−
Ni1′: 2.6825(6), Ni1−Si1−Ni1′: 75.33(3), Ni1−Si1−H1′: 118.2(9),
Ni1′-H1′-Si1: 85.7(13), P1−Ni1−P2′: 127.89(3).
consistent with a Ci-symmetric complex, suggesting that the
dimeric structure is conserved in solution. The 1H NMR
spectrum of 5 contains a multiplet corresponding to the
bridging hydride ligand at −7.17 ppm and another resonance
belonging to the cyclohexyl methine proton at 2.03 ppm. A
cross-peak between both resonances and a 29Si nucleus is
observed at 220.9 ppm in the 29Si−1H HMBC NMR spectrum.
The moderate coupling constant (1J(Ni)H−Si = 52 Hz) for the
bridging hydride indicates a diminished H−Si interaction
relative to 1, possibly indicating that 5 has progressed further
along the reaction coordinate for the α-H migration. Thus, the
degree of Si−H bond activation in 5 suggests that the complex
is intermediate between μ-silylene and μ-silylyne descriptions.
The 31P{1H} NMR spectrum of 5 exhibits resonances
consistent with an AA′BB′ spin system (Figure S1); using
the same numbering scheme presented in Figure 4, nuclei P1/
P1′ and P2/P2′ comprise the two sets of nuclei that are
mutually chemically inequivalent, thereby giving rise to the
observed coupling.
1
monitoring of the reaction mixture by H NMR spectroscopy
indicated intermediate formation of hydride-containing prod-
ucts, as evidenced by the appearance of several upfield
multiplets. Unfortunately, these species decayed over time
1
even as the amount of evolved toluene increased. The H
NMR spectrum of the dark-brown colored final reaction
mixture after 4 h at 65 °C indicated a complex mixture, with
small quantities of the redistribution products Ph2SiH2 (27%
yield) and trace PhSiH3 1being the only tractable species (no
SiH4 was evident in the H NMR spectrum).
In contrast, the reaction of 4 with an excess of CySiH3 at 65
°C for 5 h (eq 5) produced a dark brown solution which,
following removal of the solvent and subsequent ether washes,
yielded a purple powder whose H and 31P{1H} NMR spectra
1
in benzene-d6 indicated the presence of a single diamagnetic
product bearing a hydride resonance at −7.17 ppm.
Recrystallization of the complex from THF layered with
pentane at −30 °C provides small single-crystals suitable for X-
ray diffraction analysis. The molecular structure (Figure 4)
reveals a dinuclear nickel silylene complex, [Ni(μ-BP2Ph)(μ-
SiHCy)]2 (5; [BP2Ph] = PhB(CH2PPh2)2) wherein the metal
centers are bridged by SiHCy and [BP2Ph] ligands.
Given the moderate isolated yield of 5 (46%), the reaction
1
of 4 with CySiH3 was monitored by H NMR spectroscopy.
Integration against an internal standard of Si(SiMe3)4 showed
formation of 1 equiv of toluene relative to the starting material,
which was consumed after 5 h at 65 °C, indicating that the
addition−elimination reaction to form toluene is quantitative.
However, the fate of the CH2PPh2 side arm formally lost in the
conversion of 4 to 5 remains unknown, and no MePPh2 was
observed in the 31P{1H} NMR spectrum of the reaction
mixture at any point during the thermolysis. Any MePPh2
generated in the reaction mixture may have been quickly
consumed by other reactive species, contributing to the low
yield of 5.
Complex 5 possesses a diamond-shaped Ni2Si2 core, with
two of the opposing Ni−Si bonds being bridged by hydride
ligands. The Ni−Si distances (d(Ni(μ‑H)Si) = 2.2104(8) Å and
d(Ni−Si) = 2.1800(8) Å) are shorter than those found in the
related nickel μ-silylene [(depe)Ni(HSi(2-H2Si−C6H4))]2
(d(Ni−Si) = 2.210(1) Å; depe = 1,2-bis(diethylphosphino)-
ethane).30 Solution NMR spectra of 5 in benzene-d6 are
The thermolysis of complex 4 in the presence of CySiH3 and
4-dimethylaminopyridine (DMAP) was examined, to poten-
tially trap a coordinatively unsaturated monomeric complex.
Maintenance of a mixture containing 4, an arbitrary excess of
CySiH3 (6 equiv), and 1 equiv DMAP in toluene at 80 °C for 6
h resulted in precipitation of a bright yellow flocculent solid.
1
The H NMR spectrum of the final reaction mixture in the
D
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presence of an internal standard (Si(SiMe3)4) indicated that 1
equiv of CySiH3 was consumed with concomitant evolution of
1 equiv of toluene. Though the yellow powder isolated from
the reaction mixture was insoluble in pentane, ether, and
arenes, it was highly soluble in THF. Thus, single-crystal X-ray
diffraction analysis of crystals of the complex grown by vapor
diffusion of ether into a concentrated THF solution at −30 °C
over several days reveals that this complex can be formulated as
the base-stabilized silylene complex [BP3Ph]Ni(μ-H)[SiHCy-
(DMAP)] (6, eq 6).
related parameters for 1 and 5 (1J(Ni)H−Si = 70, 52 Hz,
respectively) suggests that the strength of the bridging
hydride−silicon interaction is diminished in 6.
A probable mechanism for the formation of 6 (Scheme 2)
involves oxidative addition of a Si−H bond in CySiH3 to give
Scheme 2. Possible Mechanism for the Formation of
Proposed Intermediate C, and Further Reactivity of C To
Form Complexes 5 and 6 ([Ni] = [BP3Ph]Ni)
The solid-state molecular structure of 6 (Figure 5) possesses
a Ni−Si distance of 2.173(2) Å, which is between the
[BP3Ph]Ni(H)(Bn)(SiH2Cy) (A). As thermolysis of a C6D6
solution containing only 4 and DMAP did not result in the
consumption of either species, it is likely that Si−H activation
in the presence of CySiH3 initiates the reaction leading to 6.
Next, elimination of toluene from A leads to the transient
generation of {[BP3Ph]Ni(SiH2Cy)} (B), which then rapidly
isomerizes via partial α-migration to [BP3Ph]Ni(μ-H)(SiHCy)
(C). The evolution of toluene during the course of this
1
reaction is quantitative, as determined by H NMR spectros-
Figure 5. Solid-state molecular structure of 5. Thermal ellipsoids are
drawn at 50% probability. All carbon atoms of the Ph rings on the
[BP3Ph] ligand, with the exception of the ipso-C atoms, are omitted for
clarity. Selected bond distances (Å) and angles (deg): Ni1−Si1:
2.1731(15), Si1−H1: 1.51(5), Si1−N1: 1.908(5), Ni1−P1:
2.2016(13), Ni1−P2′: 2.2235(13), Ni1−P3: 2.1694(11), B1−Ni1−
Si1: 149.13(9).
copy in the presence of an internal standard (Si(SiMe3)4). The
electrophilic silylene moiety of C is trapped in the presence of
DMAP to give 6 as the final product. In the absence of DMAP,
C is a potential intermediate for the formation of 5, though the
mechanism of the remaining steps leading to 5 remain elusive.
An examination of the reactivity of 6 with several
unsaturated organic substrates demonstrated that the Si−H
bond is not prone toward direct insertions. Thermolysis of
THF solutions of 6 in the presence of 1-octene, 3-hexyne,
benzophenone, or benzaldehyde at 40−50 °C for 1 h did not
result in any consumption of the starting materials. Evidently,
the strong binding of DMAP inhibits the coordination of an
unsaturated substrate, a step that precedes Si−H insertion in
related complexes.12 The lack of electrophilic character at
silicon is also consistent with the 29Si chemical shift of 6 (53.4
ppm), which is substantially upfield from the region commonly
observed for silylene complexes (∼150−400 ppm),1 and is
similar to those commonly observed for metal-silyl complexes
(−100 to 100 ppm).10 Previous reports of base-stabilized
silylene complexes have indicated substantial sp3 (i.e., silyl)
character at silicon and M−Si single-bond character;1 the
aforementioned properties of 6 are consistent with this
characterization.
corresponding values found in complexes 1 and 5. The Ni−Si
linkage in 6 is highly distorted away from the Ni−B axis
(θ(Si−Ni−B) = 149.13(9)°), in contrast to the nearly linear Si−
Ni−B unit observed in 1. This distortion is due to steric
interactions between the silicon-bound DMAP and the Ph
substituents of the [BP3Ph] ligand, which would be brought
into close contact for Si−Ni−B angles approaching 180°.
Though the presence of a nickel-bound hydride ligand could
1
not be confirmed crystallographically, the H NMR spectrum
of 6 in THF-d8 exhibits a resonance at −7.85 ppm (1J(Ni)H−Si
=
28 Hz) corresponding to the Ni−H nucleus. This spectrum
also displays a Si−H resonance at 5.10 ppm (1JSiH = 173.0 Hz).
Both Ni−H and Si−H nuclei exhibit coupling to a silicon
nucleus at 53.4 ppm in the 29Si−1H HMBC NMR spectrum of
6, indicating that the hydride ligand interacts with the silicon
center in a manner similar to those in complexes 1 and 5.
However, the diminished value of the (Ni)H−Si coupling
constant for this interaction (1J(Ni)H−Si = 28 Hz) relative to
A closely related complex to 6 bearing a Si-coordinated 4-
morpholinopyridine (MorPy) ligand, [BP3Ph]Ni(μ-H)[SiHCy-
(MorPy)] (6′), was also prepared. As DMAP is more basic
E
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Article
than MorPy (pKa = 10.06, 9.01, respectively),31 thermolysis of
6′ in the presence of DMAP might be expected to furnish 6.
However, heating of a benzene-d6 solution containing 6′ and 1
equiv of DMAP at 70 °C for 1 h did not result in any
conversion of 6′ to 6; heating to 100 °C resulted only in the
partial decomposition of 6′ to release unbound MorPy as the
only tractable product, with no consumption of DMAP.
Likewise, no reaction was observed following thermolysis of a
THF-d8 solution of 6 in the presence of MorPy (3 equiv) at 70
°C for 1 h. The substantial silyl characters of 6 and 6′ are likely
responsible for the substitutional inertness of the coordinated
Lewis bases.
combined filtrate were removed in vacuo to produce 1 as an
analytically pure purple solid. Yield: 0.027 mg; 46%. Crystals of 1
suitable for single-crystal X-ray diffraction analysis were grown by
layering a concentrated toluene solution of the complex with pentane,
and maintaining the mixture at −30 °C for 18 h. 1H NMR (400 MHz,
2
benzene-d6): δ −6.22 (q, JHP = 12 Hz, 1J(Ni)H−Si = 70 Hz, 1H, μ-H),
2
1.95 (d, JHP = 3.50, 6H, PhB(CH2PPh2)3), 2.07 (s, 6H, Mes para-
CH3), 2.28 (s, 12H, Mes ortho-CH3), 6.65 (s, 4H, Mes meta-H), 6.75
3
3
(t, JHH = 7.2 Hz, 12H, PPh2 meta-H), 6.84 (t, JHH = 7.4 Hz, 6H,
PPh2 para-H), 7.24 (m, 1H, BPh para-H), 7.36 (t, J = 7.2 Hz, 12H,
PPh2 ortho-H), 7.66 (t, 3JHH = 7.4 Hz, 2H, BPh meta-H), 8.18 (d, 3JHH
= 6.4 Hz, 2H, BPh ortho-H). 13C NMR (151 MHz, benzene-d6) δ
20.2 (m, PhB(CH2PPh2)3) 21.0 (Mes para-CH3), 24.6 (Mes ortho-
CH3), 124.1 (s), 125.5 (s), 128.2 (s), 128.4 (s), 129.4 (s), 132.1 (s),
2
2
132.5 (d, JCP = 4.2 Hz), 132.5 (d, JCP = 4.9), 137.7 (s), 139.8 (s),
140.5 (m), 141.0 (m), 141.5 (s), 145.1 (s). 31P{1H} NMR (160 MHz,
benzene-d6): δ 20.0 (s). 11B NMR (193 MHz, benzene-d6): δ −13.6
(s). 29Si−1H HMBC NMR (500 MHz; 99 MHz, benzene-d6): δ
192.2. Anal. Calcd for C63H64BNiP3Si: C, 74.79; H, 6.40. Found: C,
74.46; H, 6.40. IR (cm−1): 1602 (m), 1584 (m), 1433 (s), 1307 (w),
1263 (w), 1158 (m), 1091 (s), 1027 (m), 919 (m), 891 (m), 861
(m), 740 (s), 697 (s), 619 (m), 603 (m).
CONCLUDING REMARKS
■
The complexes described here illustrate the general utility of α-
H migration steps in forming first-row metal-silylene
complexes, even with high-spin metal centers. Both an anionic
silyl source and a hydrosilane have proven to be useful
precursors for introduction of silylene-type ligands. The
residual M−H···Si interactions observed in some of these
complexes further emphasize a growing theme for 3d-metal
silylene complexes, in that hydride ligands can be important for
stabilization of reactive silylene moieties. With respect to the
[BP3iPr]CoCl. In a glovebox, (THF)Li[BP3iPr] (0.181 g; 0.32
mmol) was loaded into a 20 mL vial and dissolved in THF (5 mL).
Separately, another 20 mL vial was charged with CoCl2 (0.043 g; 0.33
mmol), THF (2 mL), and a stir bar. Both mixtures were chilled to
−30 °C, and at this temperature, the clear, colorless solution of
(THF)Li[BP3iPr] was added dropwise to the rapidly stirred
suspension of CoCl2. Over the course of 4 h, the mixture became a
dark, clear aquamarine color with some suspended CoCl2 settling out
of solution. The reaction mixture was dried in vacuo to produce a
dark blue paste, which was subsequently extracted into toluene (3 × 2
mL) and filtered through Celite (0.5 × 2 cm). The filtrate was dried
in vacuo, and the resulting solid was crystallized by layering a
saturated toluene solution with pentane, and maintaining the mixture
at −30 °C for 18 h, depositing dark blue blocks of [BP3iPr]CoCl.
Yield: 0.147 g; 87%. The spectroscopic properties of this complex are
consistent with those reported in the literature.22
R
[BP3 ] scaffolds, investigations targeting cobalt and iron
complexes indicate that the [BP3iPr] ligand enables access to
silylene and alkyl complexes that could not be generated with
the less sterically protecting [BP3Ph] ligand. Future efforts will
focus on the influence of such ancillary ligands on 3d-metal
silylene reactivity.
EXPERIMENTAL SECTION
■
All manipulations were carried out using standard Schlenk techniques
or in inert atmosphere gloveboxes filled with dry dinitrogen. Solvents
were stored over molecular sieves (4 Å) after collection from a JC
Meyers Phoenix solvent purification system. Benzene-d6 was degassed
with 3 freeze−pump−thaw cycles and stored over activated molecular
sieves (4 Å) for 1 d prior to use. The compounds Tl[BP3Ph],32
(THF)Li[BP3iPr],27 [BP3Ph]NiCl,24 [BP3iPr]FeBr,27 Bn2Mg(THF)2,33
(THF)2LiSiHMes2,26 CySiH3,34 and [BP3iPr]Fe(CH2-2-(SiH2Mes)-
3,5-Me2C6H2)27 (3) were prepared according to literature proce-
dures. The purity of 3 following purification via recrystallization was
verified by 1H NMR spectroscopy, which indicated the exclusive
formation of one species (3) whose spectroscopic features are
identical to those reported previously.27 The NMR spectra were
recorded on Bruker Avance 400, 500, and 600 MHz spectrometers,
and spectra were referenced to solvent residual signals (1H, 13C),35 or
to external references (31P, 11B, 29Si). The IR spectra were collected
on a Bruker Vertex spectrometer, with samples prepared as Nujol
mulls sandwiched between NaCl plates; absorption bands in spectra
that are masked by peaks for Nujol are not reported.
[BP3iPr]Co(μ-H)(SiMes2) (2). In a glovebox, a 20 mL vial was
charged with [BP3iPr]CoCl (0.028 g; 0.048 mmol) and a stir bar. The
powder was suspended in pentane (5 mL), and the resulting
aquamarine suspension was chilled to −30 °C. At this temperature,
solid (THF)2LiSiHMes2 (0.020 g; 0.048 mmol) was added to the
suspension, causing the reaction mixture to change to a purple color
with suspended brown solids after 3 min. The reaction mixture was
stirred for a further 30 min, and then filtered through Celite (0.5 × 2
cm) to afford a clear purple filtrate, which was dried in vacuo to give a
sticky purple solid. The residue was again extracted in pentane (5
mL), and filtered through Celite (0.5 × 1 cm). The clear purple
filtrate was dried in vacuo, and the sticky purple oil was redissolved in
(Me3Si)2O (2 mL). The resulting solution was maintained at −30 °C
for 2 weeks to induce the deposition of small colorless crystals,
presumably the silane byproducts (Mes2SiH2 and (Mes2SiH)2). A
final filtration of the purple solution through a glass wool plug
afforded 2 as a sticky purple oil after drying in vacuo. Yield: 0.011 g;
28%. 1H NMR (500 MHz; benzene-d6): δ −2.68 (v br), 2.16 (s), 2.20
(s), 2.38 (s), 3.14 (s), 6.05 (s), 6.36 (s), 7.64 (s), 8.04 (s), 8.81 (br),
13.6 (br). μeff (Evans method; benzene-d6): 1.5 μB. Anal. Calcd for
C45H76BCoP3Si: C, 66.91; H, 9.48. Found: C, 68.51; H, 9.08. The
inaccurate elemental analysis of oily samples of 4 is presumably due to
the tenacious retention of (Me3Si)2O solvent molecules, as indicated
by 1H NMR analysis of samples of the complex. IR (cm−1): 1604 (m),
1551 (w), 1412 (w), 1288 (w), 1261 (w), 1241 (w), 1154 (w).
[BP3Ph]Ni(η2-Bn) (4). In a glovebox, a 20 mL vial was charged with
[BP3Ph]NiCl (0.097 g; 0.12 mmol), a stir bar, and toluene (5 mL).
The contents of the vial were then rapidly stirred to afford a clear
emerald solution of [BP3Ph]NiCl. To this was added a toluene (1 mL)
solution of Bn2Mg(THF)2 (0.022 g; 0.063 mmol) dropwise over 2
min. A clear magenta-colored reaction mixture resulted, which
became cloudy after 2 min. After being allowed to stir for another
[BP3Ph]Ni(μ-H)(SiMes2) (1). In a glovebox, a 20 mL vial was
charged with [BP3Ph]NiCl (0.045 g; 0.058 mmol), a stir bar, and
toluene (2 mL). The contents of the vial were then rapidly stirred to
afford a clear emerald solution, and then chilled to −30 °C.
Separately, a solution of (THF2)LiSiHMes2 (0.024 g; 0.058 mmol) in
toluene (1.5 mL) was prepared, and also chilled to −30 °C. At this
temperature, the (THF2)LiSiHMes2 solution was added to the stirred
[BP3Ph]NiCl solution dropwise over 2 min, resulting in a color change
to dark purple. The mixture was stirred for a further 5 min, and then
the volatile components were removed in vacuo. The dark purple
paste was suspended in pentane (4 mL), affording a purple solution
containing suspended brown solids. Toluene (1.5 mL) was added to
increase the solubility of 1 in the extracts. The mixture was filtered
through Celite (0.5 × 3 cm) to afford a dark purple solution, and the
reaction mixture was washed further with pentane (3 × 2 mL). The
clear purple washes were also filtered. The volatile components of the
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5 min, the volatile components of the reaction mixture were removed
in vacuo to produce a shiny magenta solid. The solid was redissolved
in THF (3 mL) and rapidly stirred to give a clear magenta solution. A
THF (1 mL) solution of 1,4-dioxane (0.023 g; 0.26 mmol) was added
in one portion to the reaction mixture, which was stirred for a further
30 min and then filtered through Celite (0.5 × 3 cm) to give a clear
magenta filtrate. The volume of the filtrate mixture was reduced in
vacuo to 3 mL and subsequently layered with pentane (9 mL). This
mixture was maintained at −30 °C for 1 d to induce the deposition of
4 as an analytically pure microcrystalline magenta solid. Yield: 0.084
g; 73%. Crystals of 4 were grown from a saturated toluene solution of
4 which was layered with pentane and stored at room temperature for
2 d. 1H NMR (400 MHz, benzene-d6): δ 1.95 (br s, 6H,
color change to bright yellow-orange. After this time, the vessel was
returned to a glovebox and the volatile components of the reaction
mixture were removed in vacuo, producing a yellow-orange powder.
The powder was redissolved in THF (4 mL) and layered with Et2O
(10 mL). Maintenance of the mixture at −30 °C for 18 h resulted in
deposition of 6 as an analytically pure microcrystalline powder. Yield:
0.058 g; 91%. Crystals of 6 suitable for X-ray diffraction analysis were
1
grown by slow vapor diffusion of Et2O into a THF solution of 6. H
NMR (600 MHz, THF-d8): δ −7.85 (qd, 2JHP = 26 Hz, 3JHH = 12 Hz,
1J(Ni)H−Si = 28 Hz, 1H, Ni-H), 0.83 (pentet d, J = 12.6, 3.2, 1H, Cy-
H), 0.91 (tt, J = 13, 2.4 Hz, 1H, Cy-H), 0.98 (qd, J = 13, 3.3 Hz, 1H,
Cy-H), 1.04 (tt, J = 13, 3.7 Hz, 1H, Cy-H), 1.15 (qt, J = 13, 3.3 Hz,
1H, Cy-H), 1.25 (qt, J = 13, 3.6 Hz, 1H, Cy-H), 1.33 (m, 6H,
PhB(CH2PPh2)3), 1.58 (d, J = 14 Hz, 1H, Cy-H), 1.62 (d, J = 12 Hz,
1H, Cy-H), 1.74 (overlapping with solvent residual, 2H, Cy-H), 2.36
(d, J = 13 Hz, 1H, Cy-H), 3.23 (s, 6H, N(CH3)2), 5.10 (qd, 3JHP = 21
Hz, 3JHH = 12 Hz, 1JSiH = 173.0, 1H, Si-H), 6.77 (q, J = 8.2 Hz, 12H,
PPh2 meta-H), 6.77 (overlapping, 2H, DMAP meta-H), 6.83 (t, J = 7.5
Hz, 1H, BPh para-H), 6.87 (q, J = 6.7 Hz, 6H, PPh2 para-H), 7.05 (t, J
= 7.5 Hz, 2H, BPh meta-H), 7.15 (dt, J = 29, 7.4 Hz, 12H, PPh2 ortho-
3
PhB(CH2PPh2)3), 2.48 (q, JHP = 4.8 Hz, 2H, η2-CH2Ph), 6.85−
6.94 (m, 13H, Ar-H), 6.85−6.94 (m, 7H, Ar-H), 7.11−7.23 (obscured
m, 11H, Ar-H), 7.27−7.52 (m, 5H, Ar-H), 7.62 (t, 3JHH = 7.4 Hz, 2H,
3
B-Ph meta-H), 8.10 (d, JHH = 7.4 Hz, 2H, B-Ph ortho-H). 13C{1H}
NMR (150 MHz, 1.0 mL 9:1 THF: benzene-d6): δ 20.8 (m,
2
PhB(CH2PPh2)3), 34.6 (q, JCP = 5.9 Hz, η2-CH2Ph), 119.2, 123.4,
127.4, 128.3, 129.3, 129.5, 131.7, 132.5 (m), 140.1 (m). 31P{1H}
NMR (162 MHz, benzene-d6): δ 15.0. 11B{1H} NMR (193 MHz, 1.0
mL 9:1 THF: benzene-d6): δ −14.5. Anal. Calcd for C52H48BNiP3: C,
74.76; H, 5.79. Found: C, 74.39; H, 5.96. IR (cm−1): 1305 (m), 1154
(m), 1087 (m), 1068 (w), 1025 (w), 907 (m), 860 (m), 765 (s), 748
(s), 730 (s).
3
H), 7.56 (d, J = 7.3 Hz, 2H, BPh ortho-H), 8.42 (d, J = 7.1 Hz, 2H,
DMAP ortho-H). 13C{1H} NMR (151 MHz, THF-d8): 21.4 (1:1:1:1
q, 1JCB = 41.5, PhB(CH2PPh2)3), 28.0 (Cy-C), 29.4 (Cy-C), 29.7 (Cy-
3
C), 30.3 (Cy-C), 32.0 (Cy-C), 34.7 (q, JCP = 4.2 Hz, Cy-C-Si), 39.6
(N(CH3)2), 107.6 (s), 123.0 (s), 127.1 (s), 127.3 (d, J = 6.8), 127.6
(m), 132.5 (s), 133.2 (m), 144.8 (m), 146.6 (s), 157.5 (s). 11B{1H}
NMR (193 MHz, THF-d8): δ −14.2 (s). 31P{1H} NMR (243 MHz,
THF-d8): δ 25.0 (s). 29Si−1H HMBC NMR (600 MHz; 120 MHz,
THF-d8): δ 53.4. Anal. Calcd for C58H64BN2NiP3Si: C, 71.11; H,
6.59; N, 2.86. Found: C, 70.73; H, 6.72; N, 2.95. IR (cm−1): 2048
(m), 1768 (w), 1624 (s), 1556 (m), 1301 (w), 1205 (m), 1157 (w),
1089 (w), 1064 (s), 1024 (s), 917 (m), 857 (m), 733 (s), 696 (s).
[BP3Ph]Ni(μ-H)[SiHCy(MorPy)] (6′). A J. Young NMR tube was
charged with a benzene suspension containing 4 (0.011 g; 0.013
mmol), MorPy (0.002 g; 0.012 mmol), and CySiH3 (0.004 g; 0.035
mmol). Thermolysis of the mixture at 70 °C for 1 h resulted in a color
change from magenta to clear orange-brown. The mixture was
brought to a glovebox, and the volatile components were removed in
vacuo, giving a dark orange powder. The powder was redissolved in
toluene (1 mL) and layered with pentane (3 mL). Maintenance of the
mixture at −30 °C for 18 h resulted in the precipitation of a yellow
powder. The supernatant was decanted from the solids, which were
then washed with pentane (3 × 1 mL) to afford 6′ as a
spectroscopically pure yellow powder. Yield: 0.010 g; 73%. 1H
NMR (600 MHz, benzene-d6): δ −7.95 (qd, 2JHP = 26 Hz, 3JHH = 12
Hz, J(Ni)Si−H = 51 Hz, 1H, Ni-H), 1.13 (dq, J = 14, 3 Hz, 1H, Cy-H),
1.24 (qm, J = 13, 2H, Cy-H), 1.37 (tm, J = 13 Hz, 1H, Cy-H), 1.41
(tt, J = 13, 4 Hz, 1H, Cy-H), 1.52 (qt, J = 13, 4 Hz, 1H, Cy-H), 1.80
(tm, J = 16, 2H, Cy-H), 1.91−2.04 (overlapping m, 7H = 6H,
PhB(CH2PPh2)3 and 1H, Cy-H), 2.15 (dm, J = 14 Hz, 1H, Cy-H),
2.23 (dd, J = 6, 4 Hz, 4H, Mor CH2), 3.01 (t, J = 5 Hz, 4H, Mor
CH2), 5.54 (qd, JHP = 21 Hz, JHH = 12 Hz, JHSi = 169 Hz, 1H, Si-
H), 5.63 (d, J = 7 Hz, 2H, Py meta-H), 6.88 (tm, J = 8 Hz, 12 H, PPh2
meta-H), 6.91 (dd, J = 7, 5 Hz, 6H, PPh2 para-H), 7.43 (tt, J = 7, 1
Hz, 1H, BPh para-H), 7.52 (dt, J = 32, 8 Hz, 12 H, PPh2 ortho-H),
7.69 (t, J = 7 Hz, 2H, BPh meta-H), 8.30 (d, J = 7 Hz, 2H, Py ortho-
H), 8.32 (br d, J = 7 Hz, 2H, BPh ortho-H). 13C{1H} NMR (126
MHz, benzene-d6): δ 22.1 (m, PhB(CH2PPh2)3), 27.6 (Cy-C), 28.9
(Cy-C), 29.1 (Cy-C), 30.1 (Cy-C), 31.8 (Cy-C), 34.3 (m, Cy-C), 45.0
(Mor CH2), 65.4 (Mor CH2), 106.7 (Py meta-C), 123.7, 127.1 (d, J =
8 Hz), 127.5 (m), 132.9 (m), 137.9, 144.4, 146.5, 155.8. 11B{1H}
NMR (193 MHz, THF-d8): δ −13.5 (s). 31P{1H} NMR (243 MHz,
THF-d8): δ 26.3 (s). 29Si−1H HMBC NMR (600 MHz; 120 MHz,
THF-d8): δ 56.1.
{Ni(μ-BP2Ph)(μ-SiHCy)}2 (5). In a glovebox, a 50 mL reaction
vessel was charged with 4 (0.063 g; 0.075 mmol), CySiH3 (0.024 g;
0.21 mmol), and a stir bar. To this mixture was added toluene (10
mL) to afford a magenta-colored mixture. The vessel was sealed with
a Teflon stopcock and then immersed in an oil bath heated to 65 °C.
The rapidly stirred contents were maintained at this temperature for 5
h, in which time the reaction mixture became a dark-brown color. In a
glovebox, the volatile components of the reaction mixture were
removed in vacuo to afford a dark brown paste. Washing the paste
with ether (5 × 1 mL) produced a dark purple solid, which was dried
in vacuo to afford 5 as a purple powder. Yield: 0.023 g; 46%. Crystals
of 5 suitable for X-ray diffraction analysis were grown from a saturated
THF solution of 5 layered with pentane, which was maintained at
1
−30 °C for 4 d. H NMR (600 MHz, benzene-d6): δ −7.17 (m, 2H,
Si-H), 0.58 (m, 2H, Cy-H), 1.13 (m, 4H, Cy-H), 1.36 (m, 6H, Cy-H),
1.43−1.51 (overlapping m, 1H, Cy-H), 1.43−1.51 (overlapping m,
2H, CH2PPh2), 1.55−1.62 (overlapping m, 1H, Cy-H), 1.55−1.62
(overlapping m, 2H, CH2PPh2), 1.71 (m, 2H, Cy-H), 2.03 (m, 2H, Si-
C-H), 2.08 (br d, J = 13.1 Hz, 2H, Cy-H), 2.24 (m, 2H, CH2PPh2),
2.45 (br d, J = 15.4 Hz, 2H, CH2PPh2), 6.79 (t, J = 7.5 Hz, 4H, B-Ph
meta-H), 6.90 (t, J = 7.4 Hz, 2H, B-Ph para-H), 6.96 (d, J = 7.1 Hz,
2H, CH2PPh2), 6.97−7.03 (m, 16H, CH2PPh2), 7.04−7.07 (m, 6H,
CH2PPh2), 7.08−7.12 (overlapping m, 4H, CH2PPh2), 7.28 (t, J = 7.7
Hz, 4H, B-Ph ortho-H), 7.61 (tm, J = 7.6 Hz, 4H, CH2PPh2), 7.86
(tm, J = 8.9 Hz, 4H, CH2PPh2), 8.09 (tm, J = 8.3 Hz, 4H, CH2PPh2).
13C{1H} NMR (150 MHz, benzene-d6): δ 26.9 (Cy-C), 28.2 (Cy-C),
29.0 (Cy-C), 29.4 (Cy-C), 31.1 (Cy-C), 38.6 (Cy-C), 125.6, 126.9,
127.5 (m), 127.6, 128.5 (d, J = 10.2), 128.9 (d, J = 13.2), 129.3, 131.9
(m), 132.9 (m), 133.1 (m), 133.2, 134.9 (m). Note: a resonance for
the carbon nucleus in each PCH2B unit was not found by direct or
indirect detection methods. 31P{1H} NMR (160 MHz, benzene-d6): δ
28.6 (AA′BB′ m), 31.9 (AA′BB′ m). 29Si−1H HMBC NMR (500
MHz; 99 MHz, benzene-d6): δ 220.8 (1J(Ni)H−Si = 52 Hz). Anal. Calcd
for C76H82B2Ni2P4Si2: C, 69.44; H, 6.29. Found: C, 65.55; H, 6.64.
Repeated combustion analyses of spectroscopically pure samples of 5
gave consistently low carbon content, possibly due to the formation of
nickel carbides during combustion. IR (cm−1): 1886 (w), 1744 (w),
1649 (m), 1584 (w), 1263 (w), 1180 (w), 1087 (m), 1025 (m), 977
(w), 884 (w), 794 (m), 757 (m), 738 (m), 721 (m).
3
3
1
[BP3Ph]Ni(μ-H)[SiHCy(DMAP)] (6). In a glovebox, a 25 mL vessel
was charged with a magenta-colored toluene suspension (10 mL)
containing 4 (0.055 g; 0.065 mmol), 4-dimethylaminopyridine
(DMAP) (0.008 g; 0.065 mmol), CySiH3 (0.045 g; 0.39 mmol),
and a stir bar. The vessel was sealed with a Teflon stopcock and
immersed in an oil bath maintained at 80 °C for 6 h, resulting in a
X-ray Crystallography. Data for 3 and 4 were collected at the
UC Berkeley CheXRay crystallographic facility on a Bruker APEX-II
CCD area detector using Mo Kα (λ = 0.7107 Å) monochromated
using QUAZAR multilayer mirrors. Data for 1, 5, and 6 were
collected at the Advanced Light Source beamline 12.2.1 using a
Bruker D85 three-circle diffractometer equipped with an PHOTON II
G
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CCD area detector using synchrotron radiation (λ = 0.7288 Å)
monochromated by channel-cut Si(111). Structure solution, model-
ing, and refinement was performed using OLEX236 with the
SHELX37,38 suite of programs.
Molecular Structure of [Cp*(PMe3)2Ru = SiMe2][B(C6F5)4]. J. Am.
Chem. Soc. 1994, 116, 5495−5496.
(8) Fasulo, M. E.; Glaser, P. B.; Tilley, T. D. Cp*(PiPr3)RuOTf: A
Reagent for Access to Ruthenium Silylene Complexes. Organometallics
2011, 30, 5524−5531.
(9) Mitchell, G. P.; Tilley, T. D. Generation of a Silylene Complex
by the 1,2-Migration of Hydrogen from Silicon to Platinum. Angew.
Chem., Int. Ed. 1998, 37, 2524−2526.
(10) Corey, J. Y.; Braddock-Wilking, J. Reactions of Hydrosilanes
with Transition-Metal Complexes: Formation of Stable Transition-
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00635.
31P{1H} NMR spectrum of 5 and details of X-ray
crystallography (PDF)
Accession Codes
CCDC 1864939−1864943 contain the supplementary crys-
tallographic 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.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tdtilley@berkeley.edu.
■
(15) Fasulo, M. E.; Lipke, M. C.; Tilley, T. D. Structural and
Mechanistic Investigation of a Cationic Hydrogen-Substituted
Ruthenium Silylene Catalyst for Alkene Hydrosilation. Chem. Sci.
2013, 4, 3882−3887.
ORCID
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[{PhB(CH2PiPr2)3}FeIIH]. Angew. Chem., Int. Ed. 2006, 45, 776−
780.
Rex C. Handford: 0000-0002-3693-1697
Patrick W. Smith: 0000-0001-5575-4895
T. Don Tilley: 0000-0002-6671-9099
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
This work was funded by the National Science Foundation
under grant no. CHE-1566538. UC Berkeley ChexRay is
funded by the National Institutes of Health under grant no.
S10-RR027172. We thank Simon J. Teat and Laura J.
McCormick of the Advanced Light Source for their expertise
and assistance. This research used resources of the Advanced
Light Source, which is a DOE Office of Science User Facility
under contract no. DE-AC02-05CH11231.
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