Base-Free and Bisphosphine Ligand Dialkylmanganese(II) Complexes as Precursors for Manganese Metal Deposition

Article abstract of DOI:10.1021/acs.organomet.5b00907

The solid-state structures and the physical, solution magnetic, solid-state magnetic, and spectroscopic (NMR and UV/vis) properties of a range of oxygen- and nitrogen-free dialkylmanganese(II) complexes are reported, and the solution reactivity of these complexes toward H₂ and ZnEt₂ is described. The compounds investigated are [{Mn(μ-CH₂SiMe₃)₂}₈] (1), [{Mn(CH₂CMe₃)(μ-CH₂CMe₃)₂}₂{Mn(μ-CH₂CMe₃)₂Mn}] (2), [Mn(CH₂SiMe₃)₂(dmpe)] (3; dmpe = 1,2-bis(dimethylphosphino)ethane), [{Mn(CH₂CMe₃)₂(μ-dmpe)}₂] (4), [{Mn(CH₂SiMe₃)(μ-CH₂SiMe₃)}₂(μ-dmpe)] (5), [{Mn(CH₂CMe₃)(μ-CH₂CMe₃)}₂(μ-dmpe)] (6), [{Mn(CH₂SiMe₃)(μ-CH₂SiMe₃)}₂(μ-dmpm)] (7; dmpm = bis(dimethylphosphino)methane), and [{Mn(CH₂CMe₃)(μ-CH₂CMe₃)}₂(μ-dmpm)] (8). Syntheses for 1-4 have previously been reported, but the solid-state structures and most properties of 2-4 had not been described. Compounds 5 and 6, with a 1:2 dmpe/Mn ratio, were prepared by reaction of 3 and 4 with base-free 1 and 2, respectively. Compounds 7 and 8 were accessed by reaction of 1 and 2 with 0.5 equiv or more of dmpm per manganese atom. An X-ray structure of 2 revealed a tetrametallic structure with two terminal and six bridging alkyl groups. In the solid state, bisphosphine-coordinated 3-8 adopted three distinct structural types: (a) monometallic [LMnR₂], (b) dimetallic [R₂Mn(μ-L)₂MnR₂], and (c) dimetallic [{RMn(μ-R)}₂(μ-L)] (L = dmpe, dmpm). Compound 3 exhibited particularly desirable properties for an ALD or CVD precursor, melting at 62-63 °C, subliming at 60°C (5 mTorr), and showing negligible decomposition after 24 h at 120°C. Comparison of variable-temperature solution and solid-state magnetic data provided insight into the solution structures of 2-8. Solution reactions of 1-8 with H₂ yielded manganese metal, demonstrating the thermodynamic feasibility of the key reaction steps required for manganese(II) dialkyl complexes to serve, in combination with H₂, as precursors for metal ALD or pulsed CVD. In contrast, the solution reactions of 1-8 with ZnEt₂ yielded a zinc-manganese alloy with an approximate 1:1 Zn/Mn ratio.

Full text of DOI:10.1021/acs.organomet.5b00907

Article
pubs.acs.org/Organometallics
Base-Free and Bisphosphine Ligand Dialkylmanganese(II) Complexes
as Precursors for Manganese Metal Deposition
Jeffrey S. Price, Preeti Chadha, and David J. H. Emslie*
Department of Chemistry and Chemical Biology, McMaster University, Hamilton, Ontario L8S 4M1, Canada
*
S Supporting Information
ABSTRACT: The solid-state structures and the physical,
solution magnetic, solid-state magnetic, and spectroscopic
(
NMR and UV/vis) properties of a range of oxygen- and
nitrogen-free dialkylmanganese(II) complexes are reported, and
the solution reactivity of these complexes toward H and ZnEt2
2
is described. The compounds investigated are [{Mn(μ-
CH SiMe ) } ] (1), [{Mn(CH CMe )(μ-CH CMe ) } {Mn-
2
3 2
∞
2
3
2
3 2 2
(
μ-CH CMe ) Mn}] (2), [Mn(CH SiMe ) (dmpe)] (3; dmpe
2 3 2 2 3 2
=
1,2-bis(dimethylphosphino)ethane), [{Mn(CH CMe ) (μ-
2 3 2
dmpe)} ] (4), [{Mn(CH SiMe )(μ-CH SiMe )} (μ-dmpe)]
2
2
3
2
3
2
(
(
(
5), [{Mn(CH CMe )(μ-CH CMe )} (μ-dmpe)] (6), [{Mn-
2 3 2 3 2
CH SiMe )(μ-CH SiMe )} (μ-dmpm)] (7; dmpm = bis-
2
3
2
3
2
dimethylphosphino)methane), and [{Mn(CH CMe )(μ-
2
3
CH CMe )} (μ-dmpm)] (8). Syntheses for 1−4 have previously been reported, but the solid-state structures and most
2
3
2
properties of 2−4 had not been described. Compounds 5 and 6, with a 1:2 dmpe/Mn ratio, were prepared by reaction of 3 and 4
with base-free 1 and 2, respectively. Compounds 7 and 8 were accessed by reaction of 1 and 2 with 0.5 equiv or more of dmpm
per manganese atom. An X-ray structure of 2 revealed a tetrametallic structure with two terminal and six bridging alkyl groups. In
the solid state, bisphosphine-coordinated 3−8 adopted three distinct structural types: (a) monometallic [LMnR ], (b) dimetallic
2
[
R Mn(μ-L) MnR ], and (c) dimetallic [{RMn(μ-R)} (μ-L)] (L = dmpe, dmpm). Compound 3 exhibited particularly desirable
2 2 2 2
properties for an ALD or CVD precursor, melting at 62−63 °C, subliming at 60 °C (5 mTorr), and showing negligible
decomposition after 24 h at 120 °C. Comparison of variable-temperature solution and solid-state magnetic data provided insight
into the solution structures of 2−8. Solution reactions of 1-8 with H yielded manganese metal, demonstrating the
2
thermodynamic feasibility of the key reaction steps required for manganese(II) dialkyl complexes to serve, in combination with
H , as precursors for metal ALD or pulsed CVD. In contrast, the solution reactions of 1−8 with ZnEt yielded a zinc−manganese
2
2
alloy with an approximate 1:1 Zn/Mn ratio.
INTRODUCTION
gas or vacuum purge steps, and the precursor pulse/purge/
■
coreactant pulse/purge sequence is repeated until a film of the
Prominent methods for thin film deposition include electro-
plating, electroless deposition, physical vapor deposition
2
desired thickness is obtained.
Of the thin film deposition methods described above,
thermal ALD is uniquely well suited to deposit the highly
uniform and conformal ultrathin films required in future
microelectronic devices. For this reason, ALD is currently used
to deposit HfO in microprocessors, Al O in dynamic random
(
PVD), chemical vapor deposition (CVD), and atomic layer
1
deposition (ALD). Electroplating and electroless deposition
are conducted in solution or a melt, whereas PVD relies upon
evaporation or sputtering of the target material under vacuum,
often using resistive or electron beam heating or bombardment
by high-energy particles, respectively. In contrast, CVD and
ALD are vapor-phase deposition techniques requiring at least
one volatile molecular precursor as a source of elements in the
target thin film. In CVD, the target material is formed by
thermal decomposition of the volatile molecular precursor
upon contact with a heated substrate. In contrast, in ALD, a
volatile molecular precursor is adsorbed on the surface of a
heated substrate and the resulting monolayer is reacted with a
volatile coreactant (a molecular coreactant in the case of
thermal ALD or plasma-generated atoms in the case of plasma-
enhanced ALD) to produce a submonolayer of the target
material. Precursor and coreactant pulses are separated by inert
2
2
3
3
access memory, and ZnS in electroluminescent displays.
Thermal metal ALD has been reported for the following late4
transition metals: Cu, Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, and Os.
However, reports of more electropositive early- or mid-
transition-metal ALD are scarce (vide infra), given that most
ALD precursors contain a metal in a positive oxidation state,
which must be reduced to the 0 oxidation state for metal film
deposition. ALD of moderately electropositive tungsten has
5
6
been achieved using WF in combination with Si H , SiH , or
6
2
6
4
Received: October 29, 2015
Published: December 30, 2015
©
2015 American Chemical Society
168
DOI: 10.1021/acs.organomet.5b00907
Organometallics 2016, 35, 168−180

Organometallics
Article
6
b,7
B H .
Furthermore, ALD of elemental chromium, which is
Scheme 1. Possible Pathways for Mn(s) Deposition Using
Dialkylmanganese(II) Complexes in Combination with H2
2
6
8
significantly more electropositive (χPauling = 1.66) than
tungsten, was recently reported by Winter using [Cr-
or ZnEt Coreactants
2
t
t
(
OCMe BuCHN Bu) ] and BH (NHMe ). However, film
2
3
2
growth was only observed on Ru/SiO /Si substrates, a lengthy
2
nucleation process was required, and the film thickness
9
plateaued at approximately 10 nm. Manganese ALD was also
t
t
likely achieved using [Mn (OCMe BuCHN Bu) ] and
2
4
BH (NHMe ), although only MnO was observed after air
3
2
x
exposure, and the same substrate, nucleation, and film growth
10
restrictions that applied to Cr also applied to Mn. Cu−Mn
alloy ALD has recently been reported using a combination of
t
t
[
(
Mn (OCMe BuCHN Bu) ]/BH (NHMe ) and [Cu-
2
4
3
2
dmap) ]/BH (NHMe ) cycles (dmap = 1-dimethylamino-2-
2 3 2
1
1
propoxide). Additionally, titanium ALD was recently
accomplished using TiCl in combination with 2-methyl-1,4-
4
elimination to form manganese metal, or β-hydride elimination
bis(trimethylsilyl)-2,5-cyclohexadiene or 1,4-bis(trimethylsilyl)-
to form MnH ; an unstable species observed only in low-
2
12
26
1,4-dihydropyrazine.
temperature matrices. While HR (R = CH EMe ) is the only
2
3
We have previously investigated the use of metal alkyl
byproduct expected in reactions with H , byproducts in the
2
13
complexes (e.g., ZnEt ) as coreactants for copper metal ALD,
2
reactions with ZnEt can include ZnEtR (or ZnR ; not shown
2
2
and in this work we set out to determine whether highly
reactive electropositive transition-metal alkyl complexes could
exhibit the reactivity, volatility, and thermal stability suitable to
effect electropositive metal deposition in combination with
in Scheme 1), ethylene, HR, HEt, and H2.
The aforementioned reactivity can only be utilized for
manganese ALD or pulsed CVD if a dialkylmanganese(II)
precursor with an appropriate balance of thermal stability,
volatility, and reactivity can be identified. The first neutral
reagents such as H and ZnEt (hydrogen gas has previously
2
2
14
15
14
16
been used as a coreactant for ALD of Fe, Ru, Co, Ir,
dialkylmanganese(II) complex, MnMe , was reported by
2
1
4,17
18
14,19
Ni,
Pd, and Cu;
ZnEt has been used as a coreactant
2
Beermann and Clauss over a half century ago, although the
20
for the ALD of Cu ).
structure this compound, which explodes under the influence of
27
As ALD precursors, electropositive metal alkyl complexes
offer several potential advantages relative to coordination or
cyclopentadienyl complexes: (a) the high reactivity of polar
metal−alkyl bonds may provide access to low-temperature
shock or friction, remains unknown. In contrast, Wilkinson et
al. prepared homoleptic trimethylsilylmethyl, neopentyl, neo-
28
29
phyl (CH CMe Ph), and 1-adamantylmethyl manganese-
2
2
(
II) complexes with much greater stability due to increased
23
reaction pathways for elemental metal deposition, (b) the
metal−nitrogen and metal−oxygen bonds typically encoun-
tered in coordination complexes can be avoided, precluding
metal oxide or nitride formation, and (c) in reactions with H2,
the byproducts are highly unreactive and volatile alkanes which
should be readily eliminated from the growing film. Transition-
metal alkyl complexes have rarely been used as precursors for
pulsed CVD or ALD, although notable exceptions are
steric bulk. X-ray crystal structures were reported for the
trimethylsilylmethyl and neophyl complexes, which are
polymeric and dimeric, respectively.
homoleptic benzyl, o-CH C H NMe , bis(trimethylsilyl)-
methyl,
2
8b,30
32
More recently,
31
2
6
4
2
3
3
3 4
tris(trimethylsilyl)methyl,
and C-
35
(SiMe ) (SiMe NMe ) manganese(II) complexes have also
3
2
2
2
been crystallographically characterized.
Dialkylmanganese(II) complexes have been coordinated to a
wide variety of Lewis bases, including PMe , PEt , PMe Ph,
2
1
22
36
[
PtMe (COD)] and [Cp′PtMe ] (COD = 1,5-cyclo-
2
3
3
3
2
3
7
octadiene, Cp′ = methylcylcopentadienyl).
Manganese was selected as the metal of choice in the current
work due to a Pauling electronegativity (χPauling = 1.55) lower
PMePh , PCy ,
ethane),
dmpe (1,2-bis(dimethylphosphino)-
2
3
3
6b,38
31,39 31
pyridine,
2,2′-bipyridine (bipy), TMEDA
28
(N,N,N′,N′-tetramethylethylenediamine), a bidentate diimine
than that of all transition metals in groups 5−12, with the
ligand (N,N′-bis(mesitylmethylene)-1,2-cyclohexanedi-
9
40
41
31,38b,42
i
43
exception of tantalum (χ
= 1.5). Furthermore, manganese
amine), sparteine, THF,
Pr NC(O)CH Ph, 1,4-
2 2
Pauling
3
9
ALD is of interest since copper−manganese alloys can be used
dioxane, and a carbene (1,3-bis(2,6-diisopropylphenyl)-
imidazole-2-ylidene), although many of these complexes
have not been structurally characterized. Dialkylmanganese(II)
44
for self-formation of a MnSi O diffusion barrier at the interface
x
y
between copper interconnect wiring and dielectric materials
24
2− 36b
rich in silicon and oxygen.
complexes with o-phenylenedimethylene (o-C H (CH ) ),
6
4
2 2
45
The reactivity envisaged between a dialkylmanganese
cyclohexyl, and tert-butyl alkyl groups have also been isolated
in combination with supporting dmpe ligands.
precursor and H or ZnEt is shown in Scheme 1. With H , a
2
2
2
mixed alkyl hydride complex (MnHR) should be accessible by
Herein we describe the synthesis of both new and previously
reported dialkylmanganese(II) complexes (eight in total),
detailed solution and solid-state characterization, including
single-crystal X-ray diffraction, PXRD, NMR and UV−visible
spectroscopy, and variable-temperature solution state (Evans)
and solid-state (SQUID) magnetic measurements, evaluation of
thermal stability and volatility, and solution reactivity studies
with H2 and ZnEt2 leading to manganese metal and
manganese−zinc alloy electroless deposition. This work targets
base-free as well as dmpe and dmpm (bis(dimethylphosphino)-
methane) coordinated bis(trimethylsilylmethyl) and dineopen-
σ-bond metathesis or oxidative addition of H followed by
2
reductive elimination of HR. This mixed alkyl hydride complex
can be expected to be particularly susceptible to HR reductive
25
elimination for both thermodynamic and kinetic reasons,
leading to manganese metal deposition. With ZnEt , stepwise
2
alkyl exchange with MnR would provide Mn(Et)R and then
2
MnEt , which can be expected to undergo rapid β-hydride
2
elimination to form either MnHR or MnHEt, respectively.
MnHR is the same intermediate targeted in reactions with H2,
and MnHEt will decompose via either HEt reductive
1
69
DOI: 10.1021/acs.organomet.5b00907
Organometallics 2016, 35, 168−180

Organometallics
Article
4
6
tyl manganese(II) complexes, since (a) they have fairly low
molecular weights and do not contain aromatic groups,
maximizing the potential for appreciable volatility, (b) they
do not contain β-hydrogen atoms, imparting thermal stability,
analysis, single-crystal X-ray diffraction (except 1), PXRD on
1
the bulk sample, H NMR spectroscopy (except nearly
insoluble 1), UV/vis spectroscopy (except nearly insoluble 1
and colorless 4), and both SQUID and Evans solution magnetic
measurements (except 1) (vide infra). Additionally, melting
points and sublimation temperatures were determined, and the
thermal stability was assessed.
An X-ray structure has not previously been reported for base-
free dineopentylmanganese(II) (2). However, Wilkinson et al.
(
c) they are free from oxygen or nitrogen donors, precluding
manganese oxide or nitride deposition, and (d) the chelate
effect will help to prevent phosphine ligand dissociation during
28
sublimation. The base-free compounds and the 1:1 MnR2/
3
6b
dmpe adducts have previously been reported, but an X-ray
2
8b
crystal structure has only been reported for [{Mn(μ-
noted in 1976 that 2 is a tetramer in the solid state, citing a
CH SiMe ) } ].
personal communication from M. B. Hursthouse and P.
2
3 2 ∞
30
Raithby. Additionally, an electron diffraction study was
reported for 2, revealing a monometallic structure in the
RESULTS AND DISCUSSION
Synthesis and X-ray Crystal Structures. Base-free
bis(trimethylsilylmethyl)manganese(II) (1) and
dineopentylmanganese(II) (2) were prepared via the reactions
of MnCl with MgR (dioxane) (R = CH SiMe , CH CMe ; x
■
47
vapor phase. In this work, dark brown X-ray-quality crystals of
2
were obtained from hexanes at −30 °C, confirming a
tetrametallic structure (Figure 1), with the two outer
2
2
x
2
3
2
3
=
0.25−0.8), following modifications of the literature
28b
procedures (Scheme 2). The 1:1 Mn/dmpe (dmpe = 1,2-
Scheme 2. Synthesis of Compounds 1−8
Figure 1. X-ray crystal structure for [{Mn(CH CMe )(μ-
2
3
CH CMe ) } {Mn(μ-CH CMe ) Mn}] (2). Hydrogen atoms are
2
3
2
2
2
3 2
omitted for clarity, and ellipsoids are set to 60% (C) and 80%
probability (Mn). Bond distances (Å) and angles (deg): Mn(1)···
Mn(2) 2.7022(4), Mn(2)···Mn(2′) 2.7165(4), Mn(1)−C(1)
2
.1211(9), Mn(1)−C(6) 2.2322(9), Mn(2)−C(16) 2.232(1),
Mn(2)−C(11) 2.213(1), Mn(1)−C(16) 2.3265(7), Mn(2)−C(6)
2.3939(7), Mn(2)−C(11′) 2.4092(9); Mn(1)−C(6)−Mn(2)
71.38(3), Mn(1)−C(16)−Mn(2) 72.67(3), Mn(2)−C(11)−Mn(2′)
71.85(3), C(1)−Mn(1)−C(6) 132.04(4), C(1)−Mn(1)−C(16)
122.62(3), C(6)−Mn(1)−C(16) 105.16(3).
manganese atoms in a distorted-trigonal-planar geometry
∑(C−Mn(1)−C) = 359.82(6)°; C−Mn(1)−C = 105.16(3),
22.62(3), and 132.04(4)°) and the inner manganese atoms in
a distorted-tetrahedral geometry (C−Mn(2)−C = 100.06(3)−
(
1
1
22.50(3)°). The only other neutral and homoleptic
dialkylmanganese(II) complex known to contain a trigonal-
planar manganese center is [{Mn(CH CMe Ph)(μ-
2
2
2
8b,30,31
bis(dimethylphosphino)ethane) complexes [Mn-
CH CMe Ph)} ],
though it deviates more from
2
2
2
(
CH SiMe ) (dmpe)] (3) and [{Mn(CH CMe ) (μ-
planarity (∑(C−Mn−C) = 354.7(1)°) than complex 2, likely
2
3
2
2
3 2
2
dmpe)} ] (4) were also prepared as previously reported
due to an η interaction between each manganese atom and the
2
3
6b
(
(
(
Scheme 2),
while the 2:1 Mn/dmpe complexes [{Mn-
phenyl ring of a bridging CH CMe Ph group. The tetrametallic
2
2
CH SiMe )(μ-CH SiMe )} (μ-dmpe)] (5) and [{Mn-
structure of 2 presumably differs from the polymeric structure
2
3
2
3
2
28b
CH CMe )(μ-CH CMe )} (μ-dmpe)] (6) were synthesized
of 1 due to the increased steric demands of neopentyl versus
trimethylsilylmethyl ligands.
2
3
2
3
2
by addition of 1 equiv of the corresponding base-free
dialkylmanganese(II) precursor to 3 and 4, respectively
Compound 2 has an inversion center between the central
manganese atoms, and the terminal Mn(1)−C(1) bond
distance of 2.1211(9) Å is significantly shorter than the Mn−
C bonds to the bridging neopentyl ligands. For each bridging
neopentyl group, one Mn−C bond is approximately 0.1−0.2 Å
shorter than the other, with the short Mn−C distances ranging
from 2.213(1) to 2.232(1) Å and long Mn−C distances of
2.3265(7) Å to three-coordinate Mn(1) and 2.3939(7) and
2.4092(9) Å to four-coordinate Mn(2). Bridging alkyl groups in
multimetallic manganese alkyl complexes in the literature also
(
(
Scheme 2). Compounds 1 and 2 reacted with bis-
dimethylphosphino)methane (dmpm) to form exclusively
[
(
{Mn(CH SiMe )(μ-CH SiMe )} (μ-dmpm)] (7) and [{Mn-
2 3 2 3 2
CH CMe )(μ-CH CMe )} (μ-dmpm)] (8), even when an
2
3
2
3
2
excess of dmpm was added (Scheme 2).
Compound 4 is colorless, 3 is yellow, and 2 is dark brown,
whereas 1 and 5−8 are red or black when crystalline and pale
pink when powdered. All eight compounds display high oxygen
sensitivity and were characterized by combustion elemental
1
70
DOI: 10.1021/acs.organomet.5b00907
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Organometallics
Article
4
8
exhibit one short and one long Mn−C bond, as do all μ-alkyl
manganese complexes in this work (vide infra). The Mn(1)−
Mn(2) and Mn(2)−Mn(2′) distances in 2 are 2.7022(4) and
X = 94.79(2)−122.20(9)°; X = C, P) and a central 10-
membered ring with a boat−chair−boat conformation, which is
51,52
the dominant conformation of cyclodecane.
An organo-
2
.7165(4) Å, which are almost 0.2 Å shorter than the Mn−Mn
metallic complex featuring a similar M (μ-dppe) core (dppe =
2 2
distances previously reported for [{Mn(CH SiMe ) } ] (1).
bis(diphenylphosphino)ethane) has been structurally charac-
53
2
3 2 ∞
Furthermore, the Mn−C−Mn angles in 2 (71.38(3)−
terized for Mo. The Mn−P and Mn−C distances in 3 and 4
are unremarkable, ranging from 2.6241(9) to 2.6541(5) Å
(Mn−P) and from 2.1320(14) to 2.160(2) Å (Mn−C), similar
7
2.67(3)°) are approximately 5° more acute than those in 1,
3
1
while the Mn−C distances are comparable. The Mn−Mn
distances in 2 lie between the sum of ionic (2.58 Å) and van der
to the Mn−P and Mn−C
bond lengths in 1, 2,
and [Mn(CH SiMe ) (tmeda)]
2 3 2
39
terminal
49
36b
Waals radii (4.10 Å) and are within the range previously
reported (2.5−3.2 Å) for single Mn−Mn bonds in the vast
majority of coordination and organometallic complexes.
However, they are longer than the shortest Mn−Mn distances
in elemental manganese (2.26, 2.37, and 2.47 Å for α-, β-, and
[Mn(CH Ph) (PMe ) ],
2
2
3
2
(tmeda = N,N,N′,N′-tetramethylethylenediamine). In con-
trast, significantly longer Mn−P and Mn−C distances were
48
38b
reported for [Mn{CH(SiMe ) } (dmpe)], presumably due
3 2 2
to greatly increased steric hindrance at the metal center.
50
γ-Mn, respectively).
Bright red X-ray-quality crystals of [{Mn(CH SiMe )(μ-
2
3
X-ray-quality crystals of the 1:1 Mn/dmpe complexes
CH SiMe )} (μ-dmpe)] (5) were obtained at −30 °C from
2
3
2
[
Mn(CH SiMe ) (dmpe)] (3) and [{Mn(CH CMe ) (μ-
both toluene and hexanes. The unit cell for the structure
obtained from toluene (Figure 4) contains three independent
2
3
2
2
3 2
dmpe)} ] (4) were obtained from hexanes at −30 °C.
2
Compound 3 (Figure 2) is monometallic with a tetrahedral
Figure 4. X-ray crystal structure for [{Mn(CH SiMe )(μ-
2
3
Figure 2. X-ray crystal structure for [Mn(CH SiMe ) (dmpe)] (3).
Hydrogen atoms are omitted for clarity, and ellipsoids are set to 50%
CH SiMe )} (μ-dmpe)] (5) obtained by crystallization from toluene.
2
3
2
2 3 2
Hydrogen atoms are omitted for clarity, and ellipsoids are set to 50%
(C, P, Si) and 70% probability (Mn). The unit cell contains three
independent and essentially isostructural molecules (A−C), and only
molecule A is shown. Bond distances (Å) and angles (deg): Mn(1A)···
Mn(1A′) 2.7202(6), Mn(1B)···Mn(1B′) 2.7177(6), Mn(1C)···Mn-
(1C′) 2.7322(6), Mn(1A)−P(1A) 2.6007(9), Mn(1B)−P(1B)
2.5909(9), Mn(1C)−P(1C) 2.6020(9), Mn(1A)−C(1A) 2.123(2),
Mn(1B)−C(1B) 2.137(2), Mn(1C)−C(1C) 2.136(2), Mn(1A)−
C(6A) 2.183(2), Mn(1B)−C(6B) 2.200(2), Mn(1C)−C(6C)
(
C, P, Si) and 70% probability (Mn). All carbon atoms in the dmpe
ligand are disordered over two positions, and only the dominant
conformation (69%) is shown above. Bond distances (Å) and angles
(
deg): Mn−C 2.1320(14), Mn−P 2.6541(5); P−Mn−P 78.76(2), C−
Mn−C 144.34(9), P(1)−Mn−C(1) 108.59(5), P(1)−Mn−C(1′)
8.89(4).
9
geometry that is distorted due to the small bite angle of dmpe
78.76(2)° in 3). In contrast, 4 (Figure 3) is dimetallic with
2
.208(2), Mn(1A)−C(6A′) 2.366(2), Mn(1B)−C(6B′) 2.370(2),
(
Mn(1C)−C(6C′) 2.362(2); Mn(1A)−C(6A)−Mn(1A′) 73.34(7),
Mn(1B)−C(6B)−Mn(1B′) 72.88(7), Mn(1C)−C(6C)−Mn(1C′)
73.35(8). See the Supporting Information for bond distances and
angles in the structure of 5 obtained from hexanes.
bridging dmpe ligands and a Mn−Mn distance of 6.756(2) Å,
which is far greater than the sum of the van der Waals radii.
Compound 4 features tetrahedral manganese centers (X−Mn−
molecules, while the structure obtained from hexanes (Figure
S36 in the Supporting Information) has only one independent
molecule in the unit cell. Black X-ray-quality crystals of the
neopentyl analogue [{Mn(CH CMe )(μ-CH CMe )} (μ-
2
3
2
3
2
dmpe)] (6) (Figure 5) were obtained from toluene at −30
°
C. Both 5 and 6 are dimetallic with tetrahedral manganese
centers (C−Mn−X = 94.4(1)−131.4(4)°; X = C, P)
coordinated to one terminal alkyl group, two bridging alkyl
groups, and one phosphorus atom of a bridging dmpe ligand.
The terminal Mn−C distances in 5 and 6 (2.123(2)−2.141(5)
Å in 5; 2.160(6) and 2.18(1) Å in 6) are shorter than the
bridging Mn−C distances, and as in base-free 1 and 2, each of
the bridging alkyl groups is closer to one manganese atom than
Figure 3. X-ray crystal structure for [{Mn(CH CMe ) (μ-dmpe)} ]
2
3
2
2
(
6
(
2
4). Hydrogen atoms are omitted for clarity, and ellipsoids are set to
0% (C, P) and 80% probability (Mn). Bond distances (Å) and angles
deg): Mn···Mn 6.756(2), Mn(1)−P(1) 2.6241(9), Mn(1)−P(2′)
the other; the short Mn−C
distances range from 2.183(2)
to 2.211(4) Å in 5 and from 2.252(5) to 2.27(1) Å in 6,
whereas the long Mn−C distances range from 2.362(2) to
.643(1), Mn(1)−C(1) 2.160(2), Mn(1)−C(6) 2.160(2); P(1)−
bridging
Mn(1)−P(2) 94.79(2), C(1)−Mn(1)−C(6) 122.20(9), C(1)−
Mn(1)−P(1) 104.25(7), C(6)−Mn(1)−P(1) 106.94(7), C(1)−
Mn(1)−P(2) 119.20(7), C(6)−Mn−P(2) 105.25(7).
bridging
2.379(4) Å in 5 and from 2.300(9) to 2.342(6) Å in 6.
1
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Mn−Mn, Mn−C, and Mn−P distances and Mn−C−Mn angles
in 7 are very similar to those in 5, although the dmpm ligand in
7
is bound less symmetrically than the dmpe ligand in 5 (the
Mn−P distances in 7 differ by approximately 0.06 Å, in
comparison with approximately 0.02 Å in 5). The solid-state
structure of [{Mn(CH CMe )(μ-CH CMe )} (μ-dmpm)] (8)
2
3
2
3
2
was also determined using crystals obtained (a) from hexanes at
30 °C and (b) by slow evaporation of a hexanes solution at 20
C (Figure S37 in the Supporting Information). However, the
−
°
Figure 5. X-ray crystal structure for [{Mn(CH CMe )(μ-
2
3
CH CMe )} (μ-dmpe)] (6). Hydrogen atoms are omitted for clarity,
and ellipsoids are set to 50% (C, P) and 70% probability (Mn).
Positions of all carbon atoms in three of the four neopentyl groups
quality of both data sets was only suitable to establish
connectivity, which is analogous to that of 7.
2
3
2
The structures of 5 and 7 can also be compared with
(
C(1)−C(15)) are disordered over two positions. The figure shows
36a
[
{Mn(CH SiMe )(μ-CH SiMe )(PMe )} ], and an isostruc-
2 3 2 3 3 2
only one position for each of the disordered groups (occupancy: 50%
for C1−C5, 82% for C6−C10, and 87% for C11−C15). Bond
distances (Å) and angles (deg): Mn(1)···Mn(2) 2.685(1), Mn(1)−
P(1) 2.605(1), Mn(2)−P(2) 2.641(1), Mn(1)−C(1) 2.160(6),
Mn(2)−C(11) 2.18(1), Mn(1)−C(16) 2.252(5), Mn(2)−C(6)
tural PEt3 complex, [{Mn(CH SiMe )(μ-CH SiMe )-
2
3
2
3
37
(
PEt )} ], which was structurally characterized in this work
3 2
(
Figure S35 in the Supporting Information). Key differences
are that the phosphine ligands in the PR (R = Me, Et)
3
2
.27(1), Mn(1)−C(6) 2.300(9), Mn(2)−C(16) 2.342(6); Mn(1)−
complexes are trans to one another across the Mn−Mn axis,
C(6)−Mn(2) 72.0(3), Mn(1)−C(16)−Mn(2) 71.5(2).
and the Mn−Mn distances (2.772(1) Å (R = Me) and
2
.7937(3) Å (R = Et)) are 0.05−0.07 Å longer than those in 5
The Mn−P distances in 5 and 6 are similar and
unexceptional. However, the Mn−Mn distances of
and 7. Furthermore, the Mn−C−Mn angles in the mono-
phosphine complexes (74.5(1)° for R = Me and 75.21(3)° for
R = Et) are less acute than those in 5 and 7 (∼73°), while Mn−
P and Mn−C distances are comparable. These data highlight
the substantial influence of the bidentate dmpe ligand on the
relative orientation of the phosphorus donors, the Mn−Mn
2
.7177(6)−2.7322(6) Å in 5 are shorter than those in base-
free 1 by over 0.15 Å, likely due to the tethering influence of
the bridging bisphosphine ligand. The Mn−C−Mn angles in 5
(
72.88(7)−73.35(8)°) are also more acute than those in base-
free 1 (76.82(4) and 77.19(5)°), consistent with the shorter
Mn−Mn distance in the former compound. The Mn−Mn
distance of 2.685(1) Å in 6 is less than 0.05 Å shorter than the
corresponding distance in base-free 2, but it is significantly
distance, and the Mn−C−Mn angle. The neopentyl complex
37
[
{Mn(CH CMe )(μ-CH CMe )(PMe )} ] has also been
2 3 2 3 3 2
reported, featuring an elongated Mn−Mn distance (2.718(3)
Å) and statistically equivalent Mn−C−Mn angles (69.6(6)°
and 71.0(6)°) relative to 6.
shorter than the Mn−Mn distance in 5. The Mn−C
and
terminal
average Mn−C
distances (vide supra) are slightly longer
bridging
NMR Spectroscopy and Magnetic Measurements. The
in 6 than in 5, and the Mn−C−Mn angles in 6 (71.5(2)−
1
H NMR spectra of complexes 2−8 (Figure 7; C D , 500
6
6
72.0(3)°) are slightly more acute than those in 5 (vide supra).
MHz) show paramagnetically broadened and shifted peaks,
between 5 and 60 ppm, with full width at half-maximum values
from 1150 to 8200 Hz. Further spectra were collected in d8-
These geometric trends mirror those observed for base-free 1
and 2. An even shorter Mn−Mn distance of 2.616(5) Å and a
particularly acute Mn−C−Mn angle of 69.6(4)° were
previously reported for isostructural [{MnCy(μ-Cy)} (μ-
2
45
dmpe)] (Cy = cyclohexyl), which features more sterically
demanding and electron donating secondary alkyl groups.
Bright red X-ray-quality crystals of [{Mn(CH SiMe )(μ-
2
3
CH SiMe )} (μ-dmpm)] (7) were obtained from hexanes at
2
3
2
−
30 °C (Figure 6), revealing a dimetallic structure analogous to
the structures of the 2:1 MnR :dmpe complexes 5 and 6. The
2
Figure 6. X-ray crystal structure for [{Mn(CH SiMe )(μ-
2
3
CH SiMe )} (μ-dmpm)] (7). Hydrogen atoms are omitted for clarity,
2
3
2
and ellipsoids are set to 50% (C, P, Si) and 70% probability (Mn).
Bond distances (Å) and angles (deg): Mn(1)···Mn(2) 2.7243(5),
Mn(1)−P(1) 2.6584(5), Mn(2)−P(2) 2.6016(6), Mn(1)−C(1)
1
Figure 7. Room-temperature H NMR spectra for 2−8 (500 MHz,
2
.134(1), Mn(2)−C(11) 2.121(1), Mn(1)−C(6) 2.220(2), Mn(2)−
C D ). Black tick marks indicate broad peaks associated with
organomanganese(II) complexes, while the sharp signals are due to
residual C D H in the NMR solvent and trace hexanes.
6
6
C(16) 2.233(1), Mn(1)−C(16) 2.340(1), Mn(2)−C(6) 2.337(1),
Mn(1)−C(6)−Mn(2) 73.38(5), Mn(1)−C(16)−Mn(2) 73.08(4).
6
5
1
72
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Article
toluene between 186 K and room temperature (Figure 8 for 6;
Supporting Information for 2−5, 7, and 8). A spectrum was not
collected for 1 due to insolubility in noncoordinating solvents.
Solid-state and solution magnetic measurements were carried
out on complexes 2−8 (Table 1). SQUID magnetic measure-
Table 1. Room-Temperature Solution and Solid-State
Magnetic Data for 2−8
χM(corr) per Mn center (10−3 cm /mol)
a
3
complex
in C D at 298 K in the solid state at 300 K
6
6
d
2
3
4.2 ± 0.1
13.6 ± 0.5
μ = 5.71 μ ± 0.11)
2.82 ± 0.03
14.0 ± 1.2 (μ = 5.8 μ ± 0.2)
b
B
B
e
(
B
B
4
14.4 ± 0.5
μ = 5.87 μ ± 0.10)
14.1 ± 0.1
c
(
(μ = 5.83 μ ± 0.03)
B
B
B
B
5
6
7
8
3.5 ± 0.3
6.5 ± 0.3
3.0 ± 0.2
3.4 ± 0.1
3.48 ± 0.04
3.30 ± 0.03
3.24 ± 0.03
3.35 ± 0.03
a
χM(corr) = corrected molar magnetic susceptibility; μ = effective
B
b
magnetic moment; Θ = Weiss temperature. Θ = −0.6 ± 0.1 K for 3.
c
d
28b
e
36b
Θ = 0.04 ± 0.06 K for 4. Lit: 3.9 μ .
Lit: 5.6 μ .
B
B
1
Figure 8. (left) H NMR spectra for [{Mn(CH CMe )(μ-
2
3
CH CMe )} (μ-dmpe)] (6) from 186 to 298 K (500 MHz, d -
toluene). Broad signals (|) are due to 6, while sharp signals are due to
ments have previously been reported for 1 and show
2
3
2
8
antiferromagnetic coupling/exchange between the manganese
39
residual d -toluene solvent impurity (≠) and hexanes (*). (right)
atoms. SQUID magnetic measurements on 3, which is
monometallic, and 4, which is a dimer with spatially separated
manganese centers, show that both complexes obey the Curie−
Weiss law (Figure 9; 300 to 5 K), leading to effective magnetic
7
1
Region of the H NMR spectra used for Evans measurements between
1
86 and 298 K (500 MHz, 40:1 d -toluene/toluene). The methyl
8
group from external toluene (†) is calibrated to 2.11 ppm, and the
methyl group of internal toluene (‡) is observed to shift with
temperature. Shoulders to the right of the two toluene (C H ) signals
7
8
are the residual solvent signals due to d -toluene, C D (CHD ).
7
6
5
2
On the basis of the solid-state structure of phosphine-free 2,
1
six H NMR signals are predicted with integrations of 36H,
1
8H, 18H, 8H, 4H, and 4H. However, it is not unreasonable to
expect that the MnCH signals would be broadened to the
2
point at which they cannot be located, due to their proximity to
5
1
the high-spin d metal centers; in this case, a total of three H
1
NMR signals would be observed. At room temperature, the H
NMR spectrum of 2 shows only a single broad H NMR
1
resonance, but at −32 °C this peak splits into the expected
three signals.
1
54
The H NMR spectra for dmpe complexes 3 and 4, which
do not contain bridging alkyl groups, would be expected to give
rise to three signals (18H, 12H, and 4H, not including MnCH2
1
signals), whereas the H NMR spectra for 5−8 should give rise
to four signals (18H, 18H, 12H, and 2H, not including MnCH2
signals). The expected number of signals was observed for 3, 4,
and 7 at 25 °C, below 10 °C for 5, and below −28 °C for 8. For
1
Figure 9. SQUID magnetic susceptibility data from 5 to 300 K: (top)
χ (corr) vs T (solid lines) and (1/χ (corr)) vs T (dashed lines) for
compound 6, just two H NMR signals were observed at room
M
M
temperature, and at −15 °C the largest of these signals split
into two, yielding three broad peaks; the observation of just
three signals (−15 to −80 °C) in the spectrum for 6 is likely
due to coincidental overlap of two signals (Figure 8). The
paramagnetic 3 (red) and 4 (blue); (bottom) χ (corr) vs T (solid
M
lines) and [χ (corr)]T vs T (dashed lines) for 2 (red), 5 (blue), 6
M
(purple), 7 (orange), and 8 (green), which feature antiferromagnetic
interactions.
1
increased number of signals in the low-temperature H NMR
spectra of 2, 5, 6, and 8 may be attributed to (a) different
temperature dependencies for overlapping paramagnetically
shifted signals or (b) decoalescence of signals that are averaged
at room temperature due to exchange processes. For
compound 8, explanation (a) is most likely on the basis of
solution magnetic measurements (vide infra). In contrast, for
compounds 2, 5, and 6, explanation (b) seems likely, given that
solution magnetic measurements indicate that these tetrame-
tallic or dimetallic complexes exist in equilibrium with other
manganese-containing species in solution (vide infra).
moments (μ ) of 5.8 ± 0.2 and 5.83 ± 0.03 μ , respectively,
B
B
−3
and magnetic susceptibilities (χ
) of (14.0 ± 1.2) × 10
M(corr)
and (14.08 ± 0.13) × 10− cm /mol of Mn at room
3
3
5
temperature (for a high-spin d metal center, the ideal values
−3
3
for μ and χ (corr) are 5.92 μ and 14.6 × 10 cm /mol,
B
M
B
respectively). Compounds 3 and 4 are therefore paramagnetic
with no antiferromagnetic exchange.
In contrast, the SQUID magnetic data (Figure 9) for
complexes 2 and 5−8, which feature Mn−Mn distances
1
73
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Organometallics
Article
between 2.685(1) and 2.7322(6) Å, do not obey the Curie law
and are indicative of significant antiferromagnetic exchange/
coupling between neighboring manganese centers (with
paramagnetic impurity tails at low temperature). At room
temperature, the magnetic susceptibility per manganese center
susceptibility values that are statistically equivalent to those
from SQUID measurements over the same temperature range.
−3
3
is 2.82 × 10 cm /mol for tetrametallic 2 and ranges from 3.24
−
3
−3
3
×
10 to 3.48 × 10 cm /mol for bimetallic 5−8; these values
are far lower than that expected for a paramagnetic metal center
−3
3
with five unpaired d electrons (14.6 × 10 cm /mol). The
variable-temperature magnetic behavior of 2 and 5−8 is
qualitatively similar to that reported for polymeric 1 and
39
42
dimetallic [{Mn(CH SiMe ) (THF)} ], and for the latter
2
3 2
2
compound, Thompson et al. concluded that the significant
magnetism observed at low temperatures indicates an absence
of Mn−Mn bonding, despite the short Mn−Mn distance of
Figure 10. Solution magnetic susceptibilities per mole of Mn
calculated from Evans measurements at various temperatures for
[{Mn(CH CMe )(μ-CH CMe ) } {Mn(μ-CH CMe ) Mn}] (2)
4
2
2
3
2
3
2
2
2
3 2
2.7878(9) Å.
(
blue ⧫), [{Mn(CH SiMe )(μ-CH SiMe )} (μ-dmpe)] (5) (green
2 3 2 3 2
The SQUID magnetic susceptibility data for dinuclear 5−8
and tetranuclear 2 were fitted to an exchange expression
Supporting Information) for simple high-spin Mn(II) systems
▲
), [{Mn(CH CMe )(μ-CH CMe )} (μ-dmpe)] (6) (red ■), and
2 3 2 3 2
[
{Mn(CH SiMe )(μ-CH SiMe )} (μ-dmpm)] (7) (purple ×).
2 3 2 3 2
(
55
using MAGMUN-4.1, and the resulting fits (Table 2 and
In contrast, the solution magnetic susceptibilities for base-
Table 2. Magnetic Parameters Determined by Fitting an
Exchange Expression to the SQUID Magnetic Susceptibility
Data for Compounds 2 and 5−8
free 2 and dimetallic 6 are significantly higher than the solid-
state values (although they are still much lower than those
expected in the absence of antiferromagnetic exchange). For
dimetallic 6, the solution magnetic susceptibility values
decreased as the temperature was lowered, until an asymptote
was reached at a value corresponding to that from solid-state
SQUID measurements; compound 5 showed analogous
behavior, but with a much less pronounced change in magnetic
susceptibility (Figures 9 and 10). This behavior is consistent
with a solution equilibrium (significant above 245 K for 5 and
above 210 K for 6) between the dimetallic solid-state structures
and entropically favored paramagnetic species; most likely
mononuclear [Mn(CH EMe ) (dmpe)] (E = Si (3), C (4))
a
b
mean g value intradimer J (cm‑1)
compound
ρ
Θ (K) 100R
c
2
2.07 ± 0.01
2.12 ± 0.02
2.10 ± 0.02
2.07 ± 0.01
2.04 ± 0.03
−117 ± 1
−112 ± 2
−112 ± 2
−109 ± 1
−107 ± 2
0.005
0.02
2.4
4.9
1.1
3.4
5.1
0.71
1.47
1.03
0.82
1.06
5
6
7
8
0.01
0.007
0.011
a
J = exchange coupling constant; ρ = fraction paramagnetic impurity;
2
Θ = Weiss-like temperature correction; R = [(∑χ − χ ) /
obs
calc
2
1/2
b
(
∑χ ) ]
.
The calculated temperature independent paramagnet-
obs
3
−5
3
2
3 2
ism (TIP) is 0 cm /mol for 2, 6, and 7, 4 × 10 cm /mol for 5, and 3
−5
3
c
and base-free “Mn(CH EMe ) ”. Our inability to directly
2 3 2
×
10 cm /mol for 8. For 2, J is an average over the three Mn−Mn
observe the proposed minor solution species by variable-
interactions present.
1
temperature H NMR spectroscopy is consistent with the low
concentrations of these species in solution, the broadness of the
1
observed H NMR signals, and the likelihood of rapid exchange
between these species and 5 and 6, especially at the upper end
of the temperature range.
Figures S29−S33 in the Supporting Information) are in good
agreement with the experimental data. The resulting calculated
g factors are close to 2.0, as expected for high-spin
organomanganese(II) complexes which lack an orbital
contribution to the magnetic moment, and the exchange
coupling constants (J) for 2 and 5−8 range from −107 to −117
Unlike the solution magnetic susceptibility data for
complexes 5 and 6, the solution magnetic susceptibility of
base-free 2 increased as the temperature was reduced and did
not reach a plateau (Figure 10), moving increasingly further
−1
−3
cm , indicative of strong antiferromagnetic coupling (J is an
averaged value for compound 2).
from the solid-state magnetic susceptibility value of 2.82 × 10
3
cm /mol of Mn. This increase in magnetic susceptibility is
Solution-state magnetic measurements were conducted using
the Evans NMR method (Figure 8 and Supporting
indicative of an equilibrium that shifts at lower temperature
toward species with weaker antiferromagnetic coupling in
comparison to that observed in tetrametallic 2. Above room
temperature, the magnetic susceptibility of the solution (per
manganese atom) continued to decrease toward the solid-state
value, but magnetic measurements were not accessible above 60
5
6
Information). Measurements were taken at room temperature
for all complexes (in a 40:1 C D /C H mixture) and between
6
6
6
6
2
98 and 186 K for 2 and 5−7 (in a 40:1 d -toluene/toluene
8
mixture). Complexes 3 and 4, which are monometallic or
feature well-separated manganese centers, have room-temper-
ature solution effective magnetic moments of 5.71 and 5.87 μB,
respectively, which are very close to the theoretical value of
−
3
3
°C (χ (corr) = 3.8 × 10
cm /mol) due to slow
M
decomposition of solutions of 2 above this temperature.
Physical Properties of 1−8. Melting points ranging from
62 to 176 °C were measured for 1−8 in a flame-sealed glass
capillary under an atmosphere of argon (Table 3). All
complexes were found to melt without noticeable decom-
5
.92 μ and are statistically equivalent to the solid-state effective
B
magnetic moments. dmpm complexes 7 and 8 gave rise to
statistically identical solution and solid-state magnetic suscepti-
bilities at room temperature, indicating that the solid-state
structures of 7 and 8 remain intact in solution. Additionally,
variable-temperature Evans magnetic measurements on com-
pound 7 (Figure 10; 298 to 186 K) yielded magnetic
1
position (determined visually and by H NMR spectroscopy
and/or PXRD after cooling to room temperature) if the
temperature was reached quickly (5 °C/min), with the
exception of 6, which showed minor decomposition.
1
74
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Table 3. Physical Properties of Complexes 1−8
a
complex
mp (°C)
sublimation temp at 5 mTorr (°C)
39
thermal dec data (°C)
2
8b
1
2
3
4
5
6
7
8
151−153 (lit. 98)
99−102
62−63 (lit. 62−64)
132 (lit. 132−133)
145−146
149−151.5 (partial dec)
150−160 (lit. 150)
195 (rapid dec)
28b
90 (lit. 100)
110 (>50% after 24 h)
120 (v. little over 24 h)
3
6b
60
80
3
6b
120 (complete after 5−6 h)
120 (complete after 5−6 h)
110 (visible after 2−3 h)
120 (very little over 24 h)
110 (very little over 24 h)
115−135 (dec products sublime)
110
176
100
161.5−165
100−120
a
1
Amount of decomposition assessed visually and by H NMR spectroscopy and/or PXRD after cooling to room temperature.
Importantly, the melting points of 3 and 4 match those
Table 4. Reaction Conditions and Byproducts for (i) the
36b
reported by Wilkinson et al., confirming that the originally
reported complexes were 1:1 Mn/dmpe complexes as
proposed, rather than 2:1 complexes.
Solution Reactions of 1−8 with H Yielding Mn Metal
2
(Determined by PXRD) and (ii) Solution Reactions of 1−8
with ZnEt To Deposit a 1:1 Mn/Zn Alloy (Determined by
2
Base-free [{Mn(μ-CH SiMe ) } ] (1), though very ther-
PXRD and in Some Cases XPS; Accompanied by Zn Metal
Deposition in the Reaction of 2 with ZnEt2)
2
3 2 ∞
mally stable (rapid decomposition at 195 °C), is not especially
volatile (sublimation at 150−160 °C; 5 mTorr). This low
volatility can be explained by the polymeric nature of 1 in the
solid state. In contrast, [{Mn(CH CMe )(μ-
Treaction with
2
Treaction with
H (°C)/time H reaction
ZnEt (°C)/
ZnEt reaction
2
,
ab
2
2
b
complex
(h)
byproducts
time (h)
byproducts
2
3
CH CMe ) } {Mn(μ-CH CMe ) Mn}] (2), which exists as a
1
120/48
SiMe4
25/12
C H , C H ,
2 6 2 4
2
3 2
2
2
3 2
47
SiMe , ZnRX
monomer in the vapor phase, sublimed at 90 °C (5 mTorr)
but was more than 50% decomposed after 24 h at 110 °C. The
remaining complexes, 3−8, sublimed between 60 and 135 °C at
4
2
3
4
5
25/72
CMe4
25/12
60/1
C H , C H ,
2
6
2
4
CMe , ZnRX
4
120/24
SiMe4,
dmpe
C H , C H , 9,
2
6
2
4
5
mTorr, although 5 underwent extensive decomposition
d
c
SiMe , u.p.
4
during sublimation and 6 and 8 decomposed slowly at the
70/216 (or
100/24)
CMe4,
dmpe
25/72
25/48
C H , C H ,
2 6 2 4
d
sublimation temperature (Table 3). The 1:1 MnR /dmpe
9, ZnRX
2
complexes, monometallic 3 and dimetallic 4, exhibited the most
promising volatility/thermal stability characteristics for possible
applications in ALD or CVD, subliming at 60 and 80 °C,
respectively, with negligible decomposition after 24 h at 120
and 110 °C, respectively. Furthermore, 3 has a melting point of
120/4
SiMe
, 3
4
C
2
9
H
6
, C
2
H
4
,
d
, SiMe4,
ZnRX,
6
7
8
25/168 (or
60/1)
CMe , 4
25/12
90/0.5
95/1
C H , C H ,
2 6 2 4
d
4
9, cZnRX,
u.p.
120/4
100/4
SiMe4,
C H , C H ,
6
2−63 °C and thus would be a liquid at the delivery
2
6
2
4
dmpm,
ZnRX, dmpm
temperature in a typical ALD or CVD experiment.
c
u.p.
Reactions with Hydrogen and Diethylzinc. Solutions of
CMe4,
dmpm
C H , C H ,
2
6
2
4
complexes 2−8, or a slurry of 1, were placed under 2 atm of H
ZnRX, dmpm
2
1
a
b
1
in an aromatic solvent, the reactions were monitored by H
R = CH EMe ; X = Et, R; E = C, Si. Byproducts identified by H
NMR spectroscopy. u.p. = unidentified product. Compound 9 is
[MnH(C H )(dmpe) ].
2 4 2
2
3
c
d
NMR spectroscopy (Figures S46−S55 in the Supporting
Information), and insoluble products were characterized using
PXRD (Figures S64−S65 in the Supporting Information).
Reactions took place between 25 and 120 °C (Table 4), and in
each case, a clear colorless or very pale beige solution was
formed with a metallic-looking silver-gray mirror on the walls of
the NMR tube (Scheme 3), or in one case (complex 1) a
precipitate of black powder. The diamagnetic reaction by-
products were tetramethylsilane or neopentane, accompanied
by dmpe or dmpm in the case of compounds 3−8 (Scheme 3).
The deposited solid was identified as manganese metal by
PXRD. Additionally, conducting the reactions of 3 and 5 with
60
manganese center, showed low reactivity toward H ; the
2
reaction with 3 was only complete after 12 h at 120 °C, and the
reaction with 4 was complete after 24 h at 100 °C. Dimetallic 5
and 6, which contain 1/2 equiv of dmpe per manganese center,
reacted with H2 to form 3 or 4, accompanied by
tetramethylsilane or neopentane and manganese metal.
Complete consumption of 5 required 4.5 h at 120 °C, and
the analogous reaction with 6 proceeded over 1 week at room
temperature. The similarity in the reaction conditions required
for consumption of 6 and 2 supports the proposal (vide supra)
that, in solution, 6 exists in equilibrium with 2 and 4 (i.e., H2
likely reacts with 2 that is in equilibrium with 6 in solution,
leaving unreacted 4). Compounds 7 and 8 reacted with H over
the course of 4 h at 120 and 100 °C, respectively. However,
unlike the dmpe analogues (5 and 6), compounds 7 and 8
reacted with H to provide manganese metal without formation
of an observable monometallic intermediate. A general trend
for 1−8 is the greater reactivity of the neopentyl complexes
toward H .
58
H in the presence of hexaethylbenzene as an internal NMR
2
57
standard yielded exactly 2 and 4 equiv of SiMe , respectively,
4
illustrating complete removal of the alkyl groups from
manganese. The appearance of the deposited films is also
consistent with metallic manganese.
Polymeric complex 1 was the least reactive toward hydrogen,
requiring several days at 120 °C to react completely, most likely
due to very low solubility. In contrast, highly soluble
tetrametallic 2 reacted to completion within 3 days at room
temperature; 2 is far more reactive than 1 and 3−8, likely due
to the presence of three-coordinate manganese centers.
Complexes 3 and 4, which contain 1 equiv of dmpe per
2
2
2
Overall, the reactions of the dialkylmanganese(II) complexes
and their bisphosphine adducts with H highlight the utility of
2
1
75
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Article
Scheme 3. Reactions of 1−8 with H in Benzene or Toluene
The reactivities of 5 and 6 with ZnEt are greater than those
of 3 and 4, respectively, implying that 3 and 4 are not formed as
2
2
intermediates in the reactions of 5 and 6 with ZnEt , in contrast
2
to the analogous reactions with H2 (vide supra). The
aforementioned manganese(I) hydride compound, diamagnetic
[
MnH(C H )(dmpe) ] (9), was first prepared by Wilkinson et
2 4 2
45
al. via the reactions of manganese dihalides with MgEt2 and
may be formed in this work by bimolecular HR reductive
elimination from manganese dihydride and manganese
hydrido/alkyl centers or comproportionation between a
manganese dihydride species and elemental manganese (or
an unobserved zerovalent manganese species formed en route
to manganese metal).
By PXRD, the insoluble product from the reactions of 1−8
61
with ZnEt was a 1:1 manganese/zinc alloy, accompanied by
2
zinc metal in the case of 2. The presence of both zinc and
manganese was further confirmed by XPS on representative
samples (Zn/Mn = 0.68:1 for 2 and 1.32:1 for 7). Elemental
zinc deposition could potentially occur via hydride transfer
from a manganese hydride intermediate to a dialkyl zinc
compound, leading to a zinc hydrido/alkyl species with very
limited thermal stability; the only isolated zinc hydrido
hydrocarbyl compounds contain extremely large aryl groups
6
2
(
e.g. R = C H -2,6-(C H -2,6-iPr ) , C H ,-2,6-(C H -2,4,6-
6 3 6 3 2 2 6 3 6 2
63
iPr ) , C H -2,6-(C H -2,4,6-iPr ) -4-SiMe ) ), although
3
2
6
2
6
2
3
2
3
64
metal alkyl complexes for electropositive metal deposition,
demonstrating the thermodynamic feasibility of key reaction
steps en route to manganese deposition. In solution, base-free 2
and dmpe complex 6 displayed the highest reactivity. However,
solution reaction temperatures may not be of direct relevance
to thermal ALD, given that adsorption to the surface of the
growing thin film during ALD is likely to result in phosphine
dissociation and/or formation of surface-bound species with
coordination geometries and steric environments which differ
significantly from those in the intact precursor complex.
Complexes 1−8 were also reacted with 1−3 equiv of ZnEt2
ZnHMe has been observed in an argon matrix and by
65,66
spectroscopy in the gas phase.
SUMMARY AND CONCLUSION
■
In the solid state, dineopentylmanganese(II) (2) is tetrametallic
with two terminal alkyl groups and six bridging alkyl groups.
The outer manganese centers are trigonal planar, whereas the
inner manganese centers are tetrahedral. dmpe complexes of
b i s ( t r i m e t h y l s i l y l m e t h y l ) m a n g a n e s e ( I I ) a n d
dineopentylmanganese(II) adopt three distinct structural
(per Mn) in C D (2-8) or d -toluene (1) in a sealed NMR
types: monometallic [LMnR
L) MnR ] (4), and dimetallic [{RMn(μ-R)}
6). In contrast, dmpm only yielded [{RMn(μ-R)}
2
] (3), dimetallic [R
(μ-L)] (5 and
(μ-L)]
2
Mn(μ-
6
6
8
1
31
tube; the reactions were monitored by H and/or P NMR
spectroscopy (Figures S56−S63 in the Supporting Informa-
tion), and precipitated solids were characterized by PXRD and
in some cases XPS (Figures S66−S71 in Supporting
Information). Complexes 1, 2, and 4−6 reacted completely
over 12−72 h at room temperature, whereas 3 required heating
for 1 h at 60 °C and dmpm complexes 7 and 8 required heating
at 90−95 °C for 30−60 min. In each of these reactions, a silver-
colored mirror was deposited onto the walls of the NMR tube,
and ethane, ethylene, and ZnX(CH EMe ) (X = Et, CH EMe ;
2
2
2
2
complexes (7 and 8). All polymetallic complexes with doubly
bridging alkyl groups feature one long and one short Mn−C
bond, and the neopentyl complexes exhibit more acute Mn−
C−Mn angles and shorter Mn−Mn distances than trimethylsi-
lylmethyl analogues.
All complexes have nonzero magnetic susceptibilities
between 300 and 5 K. Both [Mn(CH SiMe ) (dmpe)] (3)
2
3 2
and [{Mn-(CH CMe ) (μ-dmpe)} ] (4) obey the Curie−
2
3
2
3
2
3 2
2
E = Si, C) were released, accompanied in some cases by a small
amount of EMe (E = Si, C); H formation was not observed.
Weiss law, whereas tetrametallic dineopentylmanganese(II) (2)
and [{RMn(μ-R)} (μ-L)] (L = dmpe (5 and 6), dmpm (7 and
4
2
2
59
Compounds 7 and 8 released free dmpm, whereas dmpe
compounds 3−6 formed [MnH(C H )(dmpe) ] (9) (0.5
equiv per Mn in 3 and 4 and 0.25 equiv per Mn in 5 and 6;
8)) engage in strong antiferromagnetic coupling with J values
60
−1
from −107 to −117 cm . A comparison of solution and solid-
2
4
2
state magnetic data indicates that the structures of the dmpm
Scheme 4), and free dmpe was not liberated.
complexes (7 and 8) are maintained in solution, whereas the
[
{RMn(μ-R)} (μ-dmpe)] complexes (5 and 6) exist in
2
Scheme 4. Reactions of Dmpe Complexes 3−6 with ZnEt
equilibrium at 25 °C with species with a higher average
2
(
R = CH EMe ; X = Et, R; E = C, Si) in Benzene
magnetic susceptibility: most likely [(dmpe)MnR ] and
2
3
2
“
MnR ”. However, the solution magnetic susceptibilities of 5
2
and 6 decreased with decreasing temperature until an
asymptote was reached, consistent with the presence of only
5
or 6 in solution at low temperature. In contrast, the magnetic
susceptibility (per Mn) of dineopentylmanganese(II) (2)
almost doubled as the temperature was reduced from 335 to
1
85 K, implying that the tetrametallic solid-state structure is in
1
76
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Article
equilibrium with species which exhibit less effective anti-
ferromagnetic coupling and are favored at lower temperatures.
The two compounds without bridging alkyl groups (3 and 4)
exhibited the most desirable thermal stability and volatility for
ALD or CVD applications, and all CH SiMe derivatives
magnesium contained 0.25 equiv of 1,4-dioxane. [{Mn(CH
2
S7iMe )(μ-
3
3
CH SiMe )(PEt )} ] was prepared as previously described.
2
3
3
2
1
13
31
1
NMR spectroscopy ( H, C, and P{ H}) was performed on
Bruker DRX-500, AV-200, and AV-600 spectrometers. Spectra were
obtained at 298 K unless otherwise indicated. All H NMR spectra
1
2
3
were referenced relative to SiMe through a resonance of the proteo
4
exhibited slightly increased thermal stability relative to
impurity of the solvent used: C D (δ 7.16 ppm) and toluene-d (δ
6
6
8
CH CMe analogues; monometallic 3 was the most promising,
13
2
3
2
.08, 6.97, 7.01, and 7.09 ppm). In addition, all C NMR spectra were
melting at 62−63 °C, subliming at 60 °C (5 mTorr), and
undergoing negligible decomposition after 24 h at 120 °C.
13
referenced relative to SiMe through a resonance of the trace C in
4
the solvents: C D (δ 128.06 ppm) and toluene-d (δ 20.43, 125.13,
6
6
8
31
Solution reactions of 1−8 with H yielded manganese metal
127.96, 128.87, and 137.48 ppm). The P NMR spectra were
referenced using an external standard of 85% H PO in D O (0.0
2
with elimination of 2 equiv of HR (R = CH EMe ; in all cases,
2
3
3
4
2
neopentyl complexes displayed higher reactivity toward H than
ppm). Various impurities (normally solvents) were identified by
2
comparing to the tables of NMR chemical shifts of common impurities
trimethylsilylmethyl analogues), demonstrating the thermody-
namic feasibility of the key reaction steps required for
manganese(II) dialkyl complexes to serve, in combination
7
0
prepared by Goldberg et al. Evans NMR measurements were
conducted on the Bruker DRX-500 spectrometer in a manner
described in the Supporting Information, and values are the average
with H , as precursors for metal ALD or pulsed CVD. In
2
of two independent experiments. For 2, χ (corr) values above and
M
contrast, the solution reactions of 1−8 with ZnEt yielded a
2
below room temperature were collected using two different sets of
samples; the values from 298 to 335 K were adjusted to give the same
room-temperature value by correcting the mass used from 8.3 to 8.6
mg, which is within the error of the mass balance.
zinc/manganese alloy with an approximate 1:1 Zn/Mn ratio,
eliminating ethane and ethylene, accompanied by dmpm,
[
MnH(C H )(dmpe) ] (9), EMe , and/or ZnXR (R =
2 4 2 4
CH EMe ; X = Et, R). ALD/pulsed CVD studies using 3, 4,
and the recently reported [(allyl
(
Combustion elemental analyses were performed on a Thermo
EA1112 CHNS/O analyzer. Samples for elemental analysis (typically
1−4 mg) were packed and sealed in preweighed 3 × 6 mm smooth
wall tin capsules inside the glovebox. After removal from the glovebox,
these capsules were packed into 5 × 8 mm pressed aluminum capsules
containing approximately 10 mg of V O .
2
3
TMS2
)Mn{C(SiMe ) }-
PMe )] in combination with H are in progress and will
3 3
6
7
3
2
be reported in due course.
2
5
EXPERIMENTAL SECTION
■
Single-crystal X-ray crystallographic analyses were performed on
crystals coated in Paratone oil and mounted on a SMART APEX II
diffractometer with a 3 kW sealed-tube Mo generator and
SMART6000 CCD detector in the McMaster Analytical X-ray
General Details. An argon-filled MBraun UNIlab glovebox
equipped with a −30 °C freezer was employed for the manipulation
and storage of all oxygen- and moisture-sensitive compounds. Air-
sensitive preparative reactions were performed on a double-manifold
high-vacuum line equipped with a two-stage Welch 1402 belt-drive
(MAX) Diffraction Facility. Numerical absorption corrections were
applied by face indexing, and a further semiempirical absorption
correction was applied using redundant data. Raw data were processed
using XPREP (as part of the APEX v2.2.0 software) and solved by
−4
vacuum pump (ultimate pressure 1 × 10 Torr) using standard
68
techniques. The vacuum was measured periodically using a Kurt J.
Lesker 275i convection enhanced Pirani gauge, and residual oxygen
and moisture were removed from the argon stream by passage through
an Oxisorb-W scrubber from Matheson Gas Products. Commonly
utilized specialty glassware included a swivel frit assembly, thick-walled
flasks equipped with Teflon stopcocks, J. Young or Wilmad-LabGlass
LPV NMR tubes, Wilmad-LabGlass LPV EPR tubes, and Starna 1-Q-
71
direct methods (SHELXS-97). The structure was completed by
difference Fourier synthesis and refined with full-matrix least-squares
2
procedures based on F . In all cases, non-hydrogen atoms were refined
anisotropically and hydrogen atoms were generated in ideal positions
and then updated with each cycle of refinement. Powder X-ray
diffraction experiments were performed on a Bruker D8 Advance
powder diffractometer with Cu Kα radiation (λ = 0.154 nm) operated
at 40 kV and 40 mA. Powders were packed in 0.5 mm o.d. special glass
1
0/GS UV−vis−NIR cells with Spectrosil far-UV quartz windows
(
transparent from 170 to 2700 nm), quartz to Pyrex graded seals, and
Teflon stopcocks. Where indicated, a Branson 2510 ultrasonic bath
was used to sonicate reaction mixtures. A VWR Clinical 200 Large
Capacity Centrifuge (with 28° fixed-angle rotors that hold 12 × 15 mL
or 6 × 50 mL tubes, in combination with VWR high-performance
polypropylene conical centrifuge tubes) located within a glovebox was
used where indicated.
(
(
SG; wall thickness 0.01 mm) capillary tubes for X-ray diffraction
purchased from Charles Supper Co.) and sealed by inverting to
submerge the open end in a pool of Apiezon H-grease within the
glovebox. Calculated powder patterns were generated from the low-
temperature single-crystal data (for complexes 2−8) and a file
downloaded from the Cambridge Crystallographic Database (for
Anhydrous diethyl ether was purchased from Aldrich, hexanes and
toluene were purchased from Caledon, and deuterated solvents were
purchased from ACP Chemicals. Hexanes and toluene were initially
dried and distilled at atmospheric pressure from sodium/benzophe-
none and sodium, respectively. All solvents were stored over an
appropriate drying agent (diethyl ether, toluene, d -toluene, C D =
3
9
complex 1) using Mercury. Experimental powder diffractograms
were generated and viewed using Gadds, Powdercell, Crystal Sleuth,
Diffrac.eva, Topaz, and PANalytical HighScore.
UV/vis spectra were obtained on a Cary 50 UV/visible
spectrometer using 10 mM to 10 μM solutions in hexanes. Melting
points were measured on a DigiMelt SRS MPA 160 melting point
apparatus; between 1 and 2 mg of each sample was flame-sealed in a
thin glass tube under an atmosphere of argon. X-ray photoelectron
spectra were collected on either a Thermo Scientific Thetaprobe or a
K-Alpha instrument (Thermo Scientific, East Grinstead, U.K.), both of
which are located at the University of Toronto. A monochromated Al
K-Alpha was used with a spot size of 400 μm. An initial survey
spectrum was collected at low-energy resolution for composition, as
well as the high-energy resolution spectrum of the Zn 2p, Zn Aug, and
Mn 2p regions. SQUID measurements were collected on a Quantum
Design MPMS instrument between 5 and 300 K at applied fields
ranging from 100 Oe (for most) to 10000 Oe (for complexes 3 and 6).
Roughly 50 mg of sample was placed in a sealed sample rod assembly
for transport of air-sensitive samples into the magnetometer (with the
8
6
6
Na/Ph CO; hexanes = Na/Ph CO/tetraglyme) and introduced to
2
2
reactions or solvent storage flasks via vacuum transfer with
condensation at −78 °C.
dmpe, dmpm, trimethylsilylmethylmagnesium chloride solution (1.0
M in diethyl ether), and 1,4-dioxane were purchased from Sigma-
Aldrich. Manganese dichloride, neopentyl chloride, and diethylzinc
(
minimum 95% in a Sure-Pak cylinder) were purchased from Strem
Chemicals. Argon and hydrogen gas were purchased from PraxAir.
28b
69
Bis(trimethylsilylmethyl)magnesium and dineopentylmagnesium
were prepared according to the literature, though a slight excess of 1,4-
dioxane was used, leading to between 0.25 (trimethylsilylmethyl) and
0
.8 equiv (neopentyl) of 1,4-dioxane in the products. Bis-
39
(trimethylsilylmethyl)manganese(II) was prepared according to
literature procedures, though the reactant bis(trimethylsilylmethyl)
1
77
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Article
exception of 3, where between 2.9 and 3.4 mg of sample was placed in
a flame-sealed glass capillary).
crystals, leading to a total yield of 92% (279 mg). The product
sublimed at 110 °C at 5 mTorr and melted with some decomposition
1
Thermal stability data were obtained by sealing approximately 10
mg of powder under argon in a flask with a Teflon valve. This flask was
heated to the desired temperature for 24 h and then cooled to room
between 149 and 151.5 °C. H NMR: (C D ) 12.8, 26 (v broad) ppm;
6
6
(d -toluene, 298 K) 12.2, 25 (v broad) ppm; (d -toluene, 233 K) 4.0,
8
8
11.3, 31 (v broad) ppm. Vis: λmax 486 nm. Anal. Found (calcd): C,
57.06 (57.34); H, 11.23 (11.11).
1
temperature for visual inspection as well as PXRD and/or H NMR
spectroscopy. When “very little” is used to describe the extent of
[{Mn(CH
[{Mn(μ-CH
2
SiMe )(μ-CH
SiMe ) } ] (1; 119 mg, 0.52 mmol per Mn) in toluene
3 2 ∞
3
2 3 2
SiMe )} (dmpm)] (7). A suspension of
decomposition, this indicates that the compound darkened in color
2
1
but that decomposition was not observed by PXRD or H NMR
(20 mL) was cooled to −78 °C. A solution of dmpm (180 mg, 1.3
mmol) in toluene (2 mL) was then added dropwise, and after the
suspension was stirred for 30 min at −78 °C and 1.5 h at room
temperature, it turned to a clear orange solution. The solvent was then
removed in vacuo, and the solid was extracted with hexanes. After the
extract was centrifuged to remove residual solid, the clear red hexanes
solution was maintained at −30 °C for several days. The resulting red
crystals were of X-ray quality. Crushing the crystals afforded a light
pink powder (99 mg; 52% yield). Complex 7 sublimed cleanly at 100
°C (5 mTorr) and melted without significant decomposition when
spectroscopy.
Complexes 1−8 are exceptionally air sensitive, as is diethylzinc, and
the phosphines dmpm and dmpe are malodorous. Therefore, all
syntheses were conducted under an atmosphere of argon, in a fume
hood where necessary.
[
{Mn(CH CMe )(μ-CH CMe ) } {Mn(μ-CH CMe ) Mn}] (2).
2 3 2 3 2 2 2 3 2
MnCl (2 g, 15.9 mmol) was suspended in 20 mL of diethyl ether.
2
Mg(CH CMe ) (1,4-dioxane) (4.9 g, 20.7 mmol) was dissolved
2
3
2
0.8
separately in 40 mL of diethyl either and added dropwise to the MnCl2
suspension over 20 min. The reaction was stirred at room temperature
for 4 days with regular sonication. The resulting yellow/light brown
heated rapidly to 176 °C (note: partial melting commenced at 160
1
°C). H NMR: (C
D
6
) 3.1, 7.9, 15.5, 24 (v broad) ppm; (d
-toluene,
6
8
suspension was centrifuged to remove MgCl , and the solvent was
298 K) 3.1, 7.7, 15.4, 25 (v broad) ppm; (d
8
-toluene, 233 K) 2.5, 8.4,
2
removed from the resulting solution in vacuo. Crude 2 was extracted
into toluene, forming a dark brown solution, and the solvent was again
removed in vacuo. The remaining solid was recrystallized from hexanes
15.4, 25 (v broad) ppm. Vis: λmax 476 nm. Anal. Found (calcd): C,
42.24 (42.40); H, 9.86 (9.83).
[{Mn(CH CMe )(μ-CH CMe )} (dmpm)] (8). dmpm (220 mg,
2 3 2 3 2
(
∼10 mL) at −30 °C to afford large brown crystals. The mother
liquors were then concentrated and maintained for several days at −30
C to afford a second batch of crystals; the total yield was 60% (1.88
1.61 mmol) was added to a solution of tetrametallic 2 (310 mg, 0.39
mmol) in a 4:1 mixture of hexanes and toluene (10 mL total). The
reaction mixture was stirred for 24 h, after which time the solvent was
removed in vacuo to give a brown powder (70% yield). Both
recrystallization over days at −30 °C from saturated hexanes, and slow
evaporation of hexanes yielded thin red needles. The product sublimed
°
g). Note that, on one occasion, a white solid was obtained rather than
the expected dark brown solid. This solid was likely the Et O or 1,4-
dioxane adduct of dineopentylmanganese(II) and was converted to
pure 2 by extended exposure to dynamic vacuum. Compound 2 was
2
between 100 and 120 °C at 5 mTorr and melted without
1
decomposition between 161 and 165 °C. H NMR: (C D ) 8.1,
found to sublime at 90 °C (5 mTorr) and to melt between 99 and 102
6
6
1
1
3.8, 21 (v broad) ppm; (d -toluene, 298 K) 8.1, 13.8, 21 (v broad)
°
C. X-ray-quality crystals were obtained from hexanes at −30 °C. H
8
ppm; (d -toluene, 233 K) 4.9, 11.4, 12.9, 19 (v. broad) ppm. Vis: λ
NMR: (C D ) 32.6 ppm; (d -toluene, 298 K) 28.2; (d -toluene, 233
8
max
6
6
8
8
4
81 nm. Anal. Found (calcd): C, 56.16 (56.60); H, 11.34 (11.02).
Reactions with H (g). Approximately 10 mg of each complex was
K) 14.9, 28.9, 65.9 ppm. Vis: λmax 464 nm. Anal. Found (calcd): C,
0.18 (60.90); H, 10.75 (11.24).
Mn(CH SiMe ) (dmpe)] (3) and [{Mn(CH CMe ) (μ-dmpe)} ]
6
2
dissolved in approximately 1 mL of C D (with the exception of
[
6
6
2
3 2
2
3 2
2
(
4). The 1:1 dialkylmanganese(II)/dmpe adducts were prepared
[{Mn(μ-CH
SiMe ) } ], which was suspended in approximately 1
2 3 2 ∞
36b
according to literature procedures.
Complex 3 was purified by
mL of d -toluene). The resulting solution (or suspension) was placed
8
sublimation (60 °C at 5 mTorr) to give a bright yellow powder, and
complex 4 was purified by recrystallization from hexanes to afford a
white powder (4 also sublimed cleanly between 80 and 100 °C at 5
mTorr). X-ray-quality crystals of 3 and 4 were obtained from hexanes
in a thick-walled NMR tube with a J. Young Teflon valve and was
freeze−pump−thawed (×3). The NMR tube was then placed under
an atmosphere of hydrogen gas, cooled to −95 °C using a liquid
nitrogen/acetone bath, sealed at this low temperature, and warmed to
room temperature to provide approximately 1.7 atm of hydrogen gas.
1
at −30 °C. Data for complex 3 are as follows. H NMR: (C D ) 20.6,
6
6
1
4
2
4.0, 58.1 ppm; (d -toluene, 298 K) 20.6, 43.4, 56.4 ppm; (d -toluene,
Reactions were then observed by H NMR spectroscopy as a function
8
8
of time and temperature. Upon reaction completion, gases were
removed by exposing to dynamic argon and solutions were decanted.
Shiny metallic mirrors on the walls of the NMR tubes were sonicated
into around 2 mL of toluene (rarely, the mirrors were physically
scratched into suspension). The resulting silver-black powder was then
washed twice with 5 mL of toluene and once with 5 mL of hexanes,
dried in vacuo, and examined by PXRD.
33 K) 26.2, 76 (v broad) ppm. Anal. Found (calcd): C, 44.16
1
(
44.31); H, 10.36 (10.09). Data for complex 4 are as follows. H
NMR: (C D ) 25.2, 46.3, 59.1 ppm; (d -toluene, 298 K) 25.1, 45.6,
6
6
8
5
6.5 ppm; (d -toluene, 233 K) 30.6, 67 (v broad) ppm. Anal. Found
8
(
calcd): C, 56.02 (55.32); H, 11.11 (11.03).
{Mn(CH SiMe )(μ-CH SiMe } (μ-dmpe)] (5). [{Mn(μ-
[
2
3
2
3 2
CH SiMe ) } ] (1; 67.1 mg, 0.294 mmol of Mn) and [Mn-
2
3 2 ∞
Reactions with Diethylzinc. These reactions were conducted in a
(
CH SiMe ) (dmpe)] (3; 110.9 mg, 0.292 mmol) were dissolved in
2 3 2
manner analogous to those with H , with the following modifications:
toluene at −78 °C. The resulting light orange solution was stirred for 1
h at −78 °C and 3 h at room temperature before solvent was removed
in vacuo. The resulting powder was dissolved in 1 mL of hexanes,
centrifuged to remove a white solid impurity, and maintained at −30
2
approximately 10−15 mg of each manganese complex was used, and
rather than addition of H , 1−3 equiv of neat diethylzinc was added to
2
the solution (or suspension) in the NMR tube within the glovebox,
and the Teflon valve was immediately closed to ensure that volatile
reaction byproducts did not escape. The resulting silver mirrors were
sonicated to yield silver-black powders (in most cases pyrophoric)
which were examined by PXRD as well as XPS in some cases.
°
C for several days to produce orange-red crystals, which when
crushed yielded an orange powder (87.2 mg; 49% yield). The product
was found to melt cleanly between 145 and 146 °C when heated
1
quickly. H NMR: (C D ) 5.2, 12.7, 19 (v broad) ppm; (d -toluene,
6
6
8
2
1
98 K) 5.2, 12.7, 19 (v broad) ppm; (d -toluene, 233 K) 2.5, 7.6, 12.1,
9 (v broad) ppm. Vis: λmax 477 nm. Anal. Found (calcd): C, 43.01
8
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00907.
■
(
43.40); H, 9.58 (9.93).
{Mn(CH CMe )(μ-CH CMe )} (μ-dmpe)] (6). Tetrametallic 2
S
*
[
2
3
2
3
2
(
110 mg, 0.14 mmol) and dimetallic 4 (200 mg, 0.29 mmol) were
dissolved in 5 mL of toluene. The solution was stirred overnight at
room temperature and then maintained at −30 °C for several days to
obtain black crystals. The mother liquor was concentrated and
maintained at −30 °C for several days to obtain a second batch of
Crystallographic details, X-ray structures of 5 (crystal-
lized from toluene), 8, and [{Mn(CH SiMe )(μ-
2
3
1
78
DOI: 10.1021/acs.organomet.5b00907
Organometallics 2016, 35, 168−180

Organometallics
CH SiMe )(PEt )} ], UV/visible spectra, SQUID data
Article
(9) Thompson, D.; Anthis, J. W. Precursors and methods for the
atomic layer deposition of manganese. WO2012125439A2, 2012.
10) Kalutarage, L. C.; Martin, P. D.; Heeg, M. J.; Winter, C. H. J.
Am. Chem. Soc. 2013, 135, 12588−12591.
11) Kalutarage, L. C.; Clendenning, S. B.; Winter, C. H. ECS Trans.
014, 64, 147−157.
12) Klesko, J. P.; Thrush, C. M.; Winter, C. H. Chem. Mater. 2015,
2
3
3
2
1
and fits, Evans magnetic measurement data, H NMR
(
spectra of pure products and reactions with H and
2
ZnEt , and PXRD and XPS data (PDF)
2
(
2
(
Crystallographic data (CIF)
AUTHOR INFORMATION
Corresponding Author
D.J.H.E.: tel, 905-525-9140; fax, 905-522-5209; e-mail,
■
*
27, 4918−4921.
(13) (a) Vidjayacoumar, B.; Emslie, D. J. H.; Clendenning, S. B.;
Blackwell, J. M.; Britten, J. F.; Rheingold, A. Chem. Mater. 2010, 22,
844−4853. (b) Vidjayacoumar, B.; Ramalingam, V.; Emslie, D. J. H.;
Blackwell, J.; Clendenning, S. ECS Trans. 2013, 50, 53−66.
14) (a) Lim, B. S.; Rahtu, A.; Gordon, R. G. Nat. Mater. 2003, 2,
4
emslied@mcmaster.ca.
Notes
(
7
The authors declare no competing financial interest.
49−754. (b) Lim, B. S.; Rahtu, A.; Park, J.-S.; Gordon, R. G. Inorg.
Chem. 2003, 42, 7951−7958.
ACKNOWLEDGMENTS
■
(15) Igumenov, I. K.; Semyannikov, P. P.; Trubin, S. V.; Morozova,
N. B.; Gelfond, N. V.; Mischenko, A. V.; Norman, J. A. Surf. Coat.
Technol. 2007, 201, 9003−9008.
D.J.H.E. thanks Intel Corporation for funding through
Semiconductor Research Corporation (SRC). We are grateful
to Paul Dube and Dr. Yurij Mozharivskyj for assistance with
SQUID operation and analysis, Dr. Hilary Jenkins, Dr. Jim
Britten, and Victoria Jarvis for assistance with single-crystal and
powder X-ray diffraction, Megan Fair for running combustion
elemental analysis, Allen Pauric for assistance in determining T1
relaxation times and attempting DOSY NMR spectroscopy, and
Dr. Rana Sodhi (Surface Interface Ontario) for running XPS on
selected samples.
(16) Dussarrat, C.; Gatineau, J. Proc. Electrochem. Soc. 2005, 2005-05,
3
(
54−359.
17) Utriainen, M.; Kroger-Laukkanen, M.; Johansson, L. S.; Niinisto,
L. Appl. Surf. Sci. 2000, 157, 151−158.
18) (a) Senkevich, J. J.; Tang, F.; Rogers, D.; Drotar, J. T.; Jezewski,
C.; Lanford, W. A.; Wang, G.; Lu, T. Chem. Vap. Deposition 2003, 9,
58−264. (b) Ten Eyck, G. A.; Pimanpang, S.; Bakhru, H.; Lu, T.-M.;
Wang, G.-C. Chem. Vap. Deposition 2006, 12, 290−294.
19) (a) Martensson, P.; Carlsson, J. O. Chem. Vap. Deposition 1997,
, 45−50. (b) Martensson, P.; Carlsson, J.-O. J. Electrochem. Soc. 1998,
145, 2926−2931. (c) Li, Z.; Rahtu, A.; Gordon, R. G. J. Electrochem.
Soc. 2006, 153, C787−C794. (d) Li, Z.; Barry, S. T.; Gordon, R. G.
Inorg. Chem. 2005, 44, 1728−1735.
(20) Lee, B. H.; Hwang, J. K.; Nam, J. W.; Lee, S. U.; Kim, J. T.; Koo,
S.-M.; Baunemann, A.; Fischer, R. A.; Sung, M. M. Angew. Chem., Int.
Ed. 2009, 48, 4536−4539.
21) Hierso, J.-C.; Feurer, R.; Kalck, P. Chem. Mater. 2000, 12, 390−
99.
22) (a) Aaltonen, T.; Ritala, M.; Sajavaara, T.; Keinonen, J.;
(
2
(
3
REFERENCES
■
(
1) (a) Smith, D. L. Thin Film Deposition: Principles and Practice;
McGraw-Hill: New York, 1995. (b) Modern Electroplating, 5th ed.;
Schlesinger, M., Ed.; Wiley: Hoboken, NJ, 2014.
(
2) (a) So long as the amount of precursor and coreactant delivered
to the surface is sufficient to ensure complete reaction and maximum
surface coverage, the film thickness will depend only on the number of
precursor/purge/coreactant/purge cycles, even within high aspect
ratio features. This is termed self-limiting growth, and if self-limiting
growth cannot be achieved, the deposition method is pulsed CVD,
rather than ALD. (b) For the remainder of this paper, ALD will refer
exclusively to thermal ALD.
(
3
(
Leskelae, M. Chem. Mater. 2003, 15, 1924−1928. (b) Aaltonen, T.;
Ritala, M.; Tung, Y.-L.; Chi, Y.; Arstila, K.; Meinander, K.; Leskelae,
M. J. Mater. Res. 2004, 19, 3353−3358.
(
̈
3) (a) Ritala, M.; Niinisto, J. Atomic Layer Deposition. In Chemical
(
23) Alkyl complexes of more electropositive metals are typically
Vapour Deposition: Precursors, Processes and Applications; Jones, A. C.,
more reactive towards σ-bond metathesis reactions: Waterman, R.
Organometallics 2013, 32, 7249−7263.
24) (a) Koike, J.; Wada, M. Appl. Phys. Lett. 2005, 87, 041911.
Hitchman, M. L., Eds.; Royal Society of Chemistry: London, 2009;
̈ ̈ ̈ ̈ ̈ ̈
Chapter 4, pp 158−271. (b) Kaariainen, T.; Cameron, D.; Kaariainen,
M.-L.; Sherman, A. Atomic Layer Deposition: Principles, Characteristics
and Nanotechnology Applications; Scrivener Publishing: Salem, MA,
(
(
b) Usui, T.; Nasu, H.; Takahashi, S.; Shimizu, N.; Nishikawa, T.;
Yoshimaru, M.; Shibata, H.; Wada, M.; Koike, J. IEEE Trans. Electron
Devices 2006, 53, 2492−2499. (c) Haneda, M.; Iijima, J.; Koike, J.
Appl. Phys. Lett. 2007, 90, 252107. (d) Au, Y.; Lin, Y.; Kim, H.; Beh,
E.; Liu, Y.; Gordon, R. G. J. Electrochem. Soc. 2010, 157, D341−D345.
e) Lozano, J. G.; Lozano-Perez, S.; Bogan, J.; Wang, Y. C.; Brennan,
B.; Nellist, P. D.; Hughes, G. Appl. Phys. Lett. 2011, 98, 123112.
25) Hartwig, J. Organotransition Metal Chemistry: From Bonding to
Catalysis; University Science Books: Sausalito, CA, 2010.
26) (a) Ozin, G. A.; McCaffrey, J. G. J. Am. Chem. Soc. 1984, 106,
2013. (c) Atomic Layer Deposition for Semiconductors; Hwang, C. S.,
Ed.; Springer: New York, 2014. (d) Atomic Layer Deposition of
Nanostructured Materials; Pinna, N., Knez, M., Eds.; Wiley-VCH:
Weinheim, Germany, 2012. (e) Johnson, R. W.; Hultqvist, A.; Bent, S.
F. Mater. Today 2014, 17, 236−246.
(
(
4) (a) Knisley, T. J.; Kalutarage, L. C.; Winter, C. H. Coord. Chem.
(
Rev. 2013, 257, 3222−3231. (b) Emslie, D. J. H.; Chadha, P.; Price, J.
S. Coord. Chem. Rev. 2013, 257, 3282−3296.
(
8
(
5) (a) Klaus, J. W.; Ferro, S. J.; George, S. M. Thin Solid Films 2000,
07−809. (b) Wang, X.; Andrews, L. J. Phys. Chem. A 2003, 107,
3
60, 145−153. (b) Grubbs, R. K.; Steinmetz, N. J.; George, S. M. J.
Vac. Sci. Technol., B: Microelectron. Process. Phenom. 2004, 22, 1811−
821.
6) (a) Kim, S.-H.; Hwang, E.-S.; Kim, B.-M.; Lee, J.-W.; Sun, H.-J.;
4
(
081−4091.
27) Clauss, K.; Beermann, C. Angew. Chem. 1959, 71, 627.
28) (a) Andersen, R. A.; Carmona-Guzman, E.; Mertis, K.;
1
(
(
Sigurdson, E.; Wilkinson, G. J. Organomet. Chem. 1975, 99, C19−
C20. (b) Andersen, R. A.; Carmona-Guzman, E.; Gibson, J. F.;
Wilkinson, G. J. Chem. Soc., Dalton Trans. 1976, 2204−2211.
(29) Bochmann, M.; Wilkinson, G.; Young, G. B. J. Chem. Soc.,
Dalton Trans. 1980, 1879−1887.
(30) Personal communication (ref 6) within ref 28b.
(31) Campora, J.; Palma, P.; Perez, C. M.; Rodriguez-Delgado, A.;
Alvarez, E.; Gutierrez-Puebla, E. Organometallics 2010, 29, 2960−2970.
(32) Manzer, L. E.; Guggenberger, L. J. J. Organomet. Chem. 1977,
139, C34−C38.
Hong, T. E.; Kim, J.-K.; Sohn, H.; Kim, J.; Yoon, T.-S. Electrochem.
Solid-State Lett. 2005, 8, C155−C159. (b) Kim, S.-H.; Kwak, N.; Kim,
J.; Sohn, H. J. Electrochem. Soc. 2006, 153, G887−G893.
(
7) Yang, M.; Chung, A.; Yoon, A.; Fang, H.; Zhang, A.; Knepfler, C.;
Jackson, R.; Byun, J. S.; Mak, A.; Eizenberg, M.; Xi, M.; Kori, M.;
Sinha, A. K. In Conference Proceedings ULSI, XVII; Materials Research
Society: Conshohocken, PA, 2002; p 655.
(
8) CRC Handbook of Chemistry and Physics, 92nd ed.; Haynes, W.
M., Ed.; CRC Press: Boca Raton, FL, 2011−2012; pp 5−80 and 85−
9.
8
1
79
DOI: 10.1021/acs.organomet.5b00907
Organometallics 2016, 35, 168−180

Organometallics
Article
(
33) Andersen, R. A.; Berg, D. J.; Fernholt, L.; Faegri, K., Jr.; Green,
(60) A small amount of an unidentified phosphorus-containing
J. C.; Haaland, A.; Lappert, M. F.; Leung, W. P.; Rypdal, K. Acta Chem.
Scand. 1988, 42a, 554−562.
product was observed in the reaction of 3 with ZnEt at 60 °C. This
2
product was not observed in the reaction of 5 with ZnEt , most likely
2
(
34) Buttrus, N. H.; Eaborn, C.; Hitchcock, P. B.; Smith, J. D.;
due to milder reaction conditions.
Sullivan, A. C. J. Chem. Soc., Chem. Commun. 1985, 1380−1381.
35) Al-Juaid, S. S.; Eaborn, C.; El-Hamruni, S. M.; Hitchcock, P. B.;
Smith, J. D.; Sozerli Can, S. E. J. Organomet. Chem. 2002, 649, 121−
27.
36) (a) Davies, J. I.; Howard, C. G.; Skapski, A. C.; Wilkinson, G. J.
(61) Nakagawa, Y.; Hori, T. Trans. Jpn. Inst. Met. 1972, 13, 167−170.
(62) (a) Zhu, Z.; Wright, R. J.; Olmstead, M. M.; Rivard, E.; Brynda,
M.; Power, P. P. Angew. Chem., Int. Ed. 2006, 45, 5807−5810. (b) Zhu,
Z.; Brynda, M.; Wright, R. J.; Fischer, R. C.; Merrill, W. A.; Rivard, E.;
Wolf, R.; Fettinger, J. C.; Olmstead, M. M.; Power, P. P. J. Am. Chem.
Soc. 2007, 129, 10847−10857.
(
1
(
Chem. Soc., Chem. Commun. 1982, 1077−1078. (b) Howard, C. G.;
Girolami, G. S.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B.
J. Chem. Soc., Dalton Trans. 1983, 2631−2637.
(63) Zhu, Z.; Fettinger, J. C.; Olmstead, M. M.; Power, P. P.
Organometallics 2009, 28, 2091−2095.
(
37) Howard, C. G.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse,
(64) Greene, T. M.; Andrews, L.; Downs, A. J. J. Am. Chem. Soc.
1995, 117, 8180−8187.
M. B. J. Chem. Soc., Dalton Trans. 1983, 2025−2030.
38) (a) Girolami, G. S.; Wilkinson, G.; Galas, A. M. R.; Thornton-
Pett, M.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1985, 1339−
348. (b) Hitchcock, P. B.; Lappert, M. F.; Leung, W. P.; Buttrus, N.
H. J. Organomet. Chem. 1990, 394, 57−67.
39) Alberola, A.; Blair, V. L.; Carrella, L. M.; Clegg, W.; Kennedy, A.
(
(65) Flory, M. A.; Apponi, A. J.; Zack, L. N.; Ziurys, L. M. J. Am.
Chem. Soc. 2010, 132, 17186−17192.
(
66) ZnH is reported to decompose to Zn and H at 90 °C: Ashby,
1
2
2
E. C.; Watkins, J. J. Inorg. Synth. 1977, 17, 6−9.
67) Chadha, P.; Emslie, D. J. H.; Jenkins, H. A. Organometallics
014, 33, 1467−1474.
68) Burger, B. J.; Bercaw, J. E. Vacuum Line Techniques for
(
2
(
(
R.; Klett, J.; Mulvey, R. E.; Newton, S.; Rentschler, E.; Russo, L.
Organometallics 2009, 28, 2112−2118.
Handling Air-Sensitive Organometallic Compounds. In Experimental
Organometallic Chemistry-A Practicum in Synthesis and Characterization;
American Chemical Society: Washington, DC, 1987; Vol. 357, pp 79−
(
40) Riollet, V.; Coperet, C.; Basset, J.-M.; Rousset, L.; Bouchu, D.;
Grosvalet, L.; Perrin, M. Angew. Chem., Int. Ed. 2002, 41, 3025−3027.
41) Bart, S. C.; Hawrelak, E. J.; Schmisseur, A. K.; Lobkovsky, E.;
Chirik, P. J. Organometallics 2004, 23, 237−246.
42) Crewdson, P.; Gambarotta, S.; Yap, G. P. A.; Thompson, L. K.
Inorg. Chem. 2003, 42, 8579−8584.
43) Blair, V. L.; Clegg, W.; Conway, B.; Hevia, E.; Kennedy, A.;
Klett, J.; Mulvey, R. E.; Russo, L. Chem. - Eur. J. 2008, 14, 65−72.
44) Kennedy, A. R.; Klett, J.; Mulvey, R. E.; Robertson, S. D. Eur. J.
Inorg. Chem. 2011, 2011, 4675−4679.
45) Girolami, G. S.; Howard, C. G.; Wilkinson, G.; Dawes, H. M.;
(
9
(
(
8.
69) Andersen, R. A.; Wilkinson, G. Inorg. Synth. 1979, 19, 262−265.
70) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
(
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I.
(
Organometallics 2010, 29, 2176−2179.
(71) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
(
2
008, 64, 112−122.
(
Thornton-Pett, M.; Motevalli, M.; Hursthouse, M. B. J. Chem. Soc.,
Dalton Trans. 1985, 921−929.
(
46) Complex 1 has previously been characterized crystallographi-
28b,39
cally.
(
47) Andersen, R. A.; Haaland, A.; Rypdal, K.; Volden, H. V. J. Chem.
Soc., Chem. Commun. 1985, 1807−1808.
48) Meier, R. M.; Hanusa, T. P. In Structural Organomanganese
Chemistry; Wiley: Chichester, U.K., 2011; pp 43−169.
49) CRC Handbook of Chemistry and Physics, 95th ed.; Haynes, W.
(
(
M., Ed.; CRC Press: Boca Raton, FL, 2014−2015; Section 9:
Molecular Structure and Spectroscopy-Atomic Radii of the Elements.
(
50) (a) Oberteuffer, J. A.; Ibers, J. A. Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem. 1970, 26, 1499−1504. (b) Preston, G. D.
Philos. Mag. 1928, 5, 1207−1225. (c) Haglund, J.; Fernandez
Guillermet, F.; Grimvall, G.; Korling, M. Phys. Rev. B: Condens. Matter
Mater. Phys. 1993, 48, 11685−11691.
(
51) Dunitz, J. D. Perspectives in Structural Chemistry; Wiley: New
York, 1968; Vol. II.
52) Hilderbrandt, R. L.; Wieser, J. D.; Montgomery, L. K. J. Am.
Chem. Soc. 1973, 95, 8598.
53) Dumke, A. C.; Pape, T.; Ko
Brinke, C.; Hahn, F. E. Organometallics 2013, 32, 289−299.
54) Attempts to determine whether the dimeric structure of
(
(
̈
sters, J.; Feldmann, K.-O.; Schulte to
(
complex 4 (Figure 3) remained intact in solution or dissociated into
monometallic species using DOSY NMR failed due to very short T1
relaxation times (the average for the three signals in complex 4 is 0.282
ms at 0.03 g/mL).
(
55) Xu, Z.; Thompson, L. K.; Waldmann, O. MAGMUN4.1.
(
56) (a) Evans, D. F. J. Chem. Soc. 1959, 2003−2005. (b) Schubert,
E. M. J. Chem. Educ. 1992, 69, 62.
(
57) For 5, 4 equiv of SiMe was observed after the intermediate (3)
4
had reacted with excess H at 120 °C for 12 h.
2
(
58) Complex 5 slowly decomposed to 3 at 120 °C in solution.
However, this decomposition proceeded much more slowly than the
reaction to form 3 in the presence of H2.
1
(
59) NMR signals for free dmpm were shifted by 0.05−0.1 ppm ( H
31
NMR) and 1−3 ppm ( P NMR) relative to a reference sample.
1
80
DOI: 10.1021/acs.organomet.5b00907
Organometallics 2016, 35, 168−180