Reactivity of [TismPriBenz]MgMe towards secondary amines and terminal alkynes: Catalytic dehydrocoupling with hydrosilanes to afford Si–N and Si–C bonds

Article abstract of DOI:10.1016/j.ica.2019.03.015

The magnesium hydride and methyl compounds, [Tism^PriBenz]MgX (X = H, Me), react with diphenylamine (Ph₂NH)and pyrrolidine (C₄H₈NH)to afford the amide derivatives, [Tism^PriBenz]MgNPh₂ and [Tism^PriBenz]MgNC₄H₈, while reactions with the terminal alkynes, PhC[tbnd]CH and BuⁿC[tbnd]CH, afford the corresponding acetylide derivatives, [Tism^PriBenz]MgC[tbnd]CPh and [Tism^PriBenz]MgC[tbnd]CBuⁿ. The Mg[sbnd]N bond of [Tism^PriBenz]MgNR₂ may be cleaved by hydrosilanes, such that [Tism^PriBenz]MgMe is an effective precatalyst for the dehydrocoupling of hydrosilanes and amines. For example, [Tism^PriBenz]MgMe enables the conversion of a 1:1 mixture of Ph₂SiH₂ and C₄H₈NH at room temperature to the silazane, Ph₂SiH(NC₄H₈). [Tism^PriBenz]MgH and [Tism^PriBenz]MgMe are also capable of dehydrocoupling PhC[tbnd]CH and PhSiH₃ to form PhSiH₂C[tbnd]CPh. In addition to dehydrocoupling of terminal alkynes, [Tism^PriBenz]MgMe is also capable of achieving the isomerization 3-phenyl-1-propyne to phenylallene.

Full text of DOI:10.1016/j.ica.2019.03.015

Accepted Manuscript
Research paper
i
Reactivity of TismPr Benz MgMe towards Secondary Amines and Terminal
Alkynes: Catalytic Dehydrocoupling with Hydrosilanes to Afford Si–N and
Si–C Bonds
Michael Rauch, Renee C. Roberts, Gerard Parkin
PII:
S0020-1693(19)30044-1
https://doi.org/10.1016/j.ica.2019.03.015
ICA 18820
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
10 January 2019
6 March 2019
12 March 2019
i
Please cite this article as: M. Rauch, R.C. Roberts, G. Parkin, Reactivity of TismPr Benz MgMe towards Secondary
Amines and Terminal Alkynes: Catalytic Dehydrocoupling with Hydrosilanes to Afford Si–N and Si–C Bonds,
Inorganica Chimica Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.03.015
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i
Reactivity of [TismPr Benz]MgMe towards Secondary Amines and
Terminal Alkynes: Catalytic Dehydrocoupling with Hydrosilanes to
Afford Si–N and Si–C Bonds‡
Michael Rauch, Renee C. Roberts and Gerard Parkin,*
Department of Chemistry,
Columbia University,
New York, New York 10027, USA.
‡
In celebration of the distinguished and inspirational career of Malcolm L. H Green.
Congratulations Malcolm!
i
Abstract: The magnesium hydride and methyl compounds, [TismPr Benz]MgX (X = H,
Me), react with diphenylamine (Ph2NH) and pyrrolidine (C4H8NH) to afford the amide
i
i
derivatives, [TismPr Benz]MgNPh2 and [TismPr Benz]MgNC4H8, while reactions with the
terminal alkynes, PhCCH and BunCCH, afford the corresponding acetylide
i
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derivatives, [TismPr Benz]MgCCPh and [TismPr Benz]MgCCBun. The Mg–N bond of
i
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[TismPr Benz]MgNR2 may be cleaved by hydrosilanes, such that [TismPr Benz]MgMe is an
effective precatalyst for the dehydrocoupling of hydrosilanes and amines. For example,
i
[TismPr Benz]MgMe enables the conversion of a 1:1 mixture of Ph2SiH2 and C4H8NH at
i
room temperature to the silazane, Ph2SiH(NC4H8). [TismPr Benz]MgH and
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[TismPr Benz]MgMe are also capable of dehydrocoupling PhCCH and PhSiH3 to form
i
PhSiH2CCPh. In addition to dehydrocoupling of terminal alkynes, [TismPr Benz]MgMe
is also capable of achieving the isomerization 3-phenyl-1-propyne to phenylallene.

2
INTRODUCTION
Dehydrocoupling reactions involving molecules with Si–H and X–H bonds provide a
valuable method for the synthesis of compounds with Si–X bonds,1 which complements
that of hydrosilylation in which Si–X bond formation is achieved by the addition of an
Si–H bond across an X≈Y multiple bond.2 For example, the formation of Si–N bonds by
the dehydrocoupling of hydrosilanes with either primary or secondary amines is an
important transformation for the synthesis of silazanes, which are a useful class of
molecules with respect to their function as chemical reagents (e.g. bases and silylating
agents).3,4 Such compounds, however, are traditionally obtained by the net
dehydrohalogenation of amines and halosilanes,5 a transformation that is less appealing
than one involving dehydrogenation, from the perspective of both functional group
tolerance and the nature of the byproducts.3 Likewise, alkynylsilanes are of use for the
formation of C–C and C–X bonds, and are also traditionally obtained by employing
halosilanes.6 Efforts to obtain improved syntheses of alkynylsilanes have, therefore,
also focused on the dehydrocoupling of terminal alkynes and hydrosilanes.7 Despite
these advances in the formation of Si–X bonds by dehydrocoupling, however, there is
much current interest in developing catalytic systems that feature nonprecious metals.3,8
Therefore, we report here the ability of the tris[(1-isopropylbenzimidazol-2-
i
yl)dimethylsilyl]methyl magnesium compounds, [TismPr Benz]MgMe9 and
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[TismPr Benz]MgH,10 to enable the catalytic formation of Si–N and Si–C bonds.
RESULTS AND DISCUSSION
We have recently demonstrated that the magnesium hydride and magnesium methyl
i
i
compounds, [TismPr Benz]MgH10 and [TismPr Benz]MgMe,9 provide access to a series of
i
[TismPr Benz]MgX derivatives by either metathesis or insertion of X–Y into the Mg–H and
Mg–Me bonds.10,11,12 For example, protolytic cleavage of the Mg–Me bond by PhNH2
i
i
and by H2S affords [TismPr Benz]MgN(H)Ph and [TismPr Benz]MgSH, respectively. We now
report that protolytic cleavage of the Mg–H and Mg–Me bonds can also be achieved by

3
i
secondary amines and terminal alkynes. Thus, [TismPr Benz]MgMe reacts with
i
diphenylamine (Ph2NH) and pyrrolidine (C4H8NH) to form [TismPr Benz]MgNPh2 and
i
[TismPr Benz]MgNC4H8 (Scheme 1), while reactions with the terminal alkynes, PhCCH
and BunCCH, afford the corresponding magnesium acetylide derivatives,
i
i
[TismPr Benz]MgCCPh and [TismPr Benz]MgCCBun (Scheme 2). The hydride complex,
i
i
[TismPr Benz]MgH, reacts similarly to [TismPr Benz]MgMe, but with enhanced reactivity.
i
For example, [TismPr Benz]MgH reacts immediately with PhCCH at room temperature,
i
whereas the corresponding reaction of [TismPr Benz]MgMe occurs over a period of several
hours under comparable conditions.
Scheme 1.

4
Scheme 2.
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The molecular structures of [TismPr Benz]MgNPh2, [TismPr Benz]MgNC4H8,
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[TismPr Benz]MgCCPh and [TismPr Benz]MgCCBun have been determined by X-ray
i
diffraction, as illustrated in Figures 1–4. Interestingly, while [TismPr Benz]MgX (X = NPh2,
CCPh and CCBun) exhibit a distorted trigonal bipyramidal geometry in which the X
i
substituent resides in an axial site, the pyrrolidinide ligand of [TismPr Benz]MgNC4H8
i
resides in an equatorial site.13 In this regard, previous studies on other [TismPr Benz]MgX
derivatives indicate that H, Me, F, Cl, Br, N(H)Ph, and OC(H)OB(C6F5)3 substituents
reside in axial sites, whereas SH, I and C(H)(Me)Ph substituents reside in equatorial
sites.9,10,11

5
Density functional theory (DFT) calculations indicate that there is a preference
for the pyrrolidinide ligand to reside in an equatorial location as compared to an axial
position (Figure 5), although the difference in energies is not large (2.4 kcal mol–1). In
contrast, DFT calculations indicate that the diphenylamide ligand prefers to occupy the
axial site (Figure 6).
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Figure 1. Molecular structure of [TismPr Benz]MgNPh2.

6
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Figure 2. Molecular structure of [TismPr Benz]MgNC4H8.

7
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Figure 3. Molecular structure of [TismPr Benz]MgCCPh (only one of the
crystallographically independent molecules is shown).

8
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Figure 4. Molecular structure of [TismPr Benz]MgCCBun.
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Figure 5. Geometry optimized structures of [TismPr Benz]MgNC4H8 with axial (left) and
equatorial (right) locations of the pyrrolidinide ligand. Hydrogen atoms are omitted for
clarity.

9
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Figure 6. Geometry optimized structures of [TismPr Benz]MgNPh2 with axial (left) and
equatorial (right) locations of the diphenylamide ligand. Hydrogen atoms are omitted
for clarity.
Although magnesium amide compounds are precedented,14 there are relatively
few examples of structurally characterized diphenylamide and pyrrolidinide
derivatives listed in the Cambridge Structural Database (CSD),15 of which a selection are
presented in Table 1.16-19 In particular, there is only one example of a magnesium
pyrrolidinide complex, namely {[HC{C(Me)NAr}2]Mg(–NC4H8)}2 (Ar = 2,5-Pri2C6H3),14a
and the pyrrolidinide ligand in this complex bridges two magnesium centers rather
than serve as a terminal ligand. Accordingly, the Mg–N bond length of
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[TismPr Benz]MgNC4H8 [1.970(5) Å] is shorter than those in {[HC{C(Me)NAr}2]Mg(–
NC4H8)}2 [2.088(2) Å and 2.117(2) Å].14a It is also pertinent to note that the Mg–N bond
length is shorter than the values observed for the pyrrolidine derivative, (dpp-
bian)Mg(HNC4H8)3 [2.090(2) Å, 2.196(2) Å and 2.221(2) Å],20 a difference which is in
accord with the L versus X nature of the ligands.21

Table 1. Bond lengths of terminal magnesium diphenylamido and related derivatives.
d(Mg–
N)/ Å
1.970
2.100
2.013
2.020
2.055
2.056
2.035
2.037
2.084
2.043
2.061
Mg-N-R1/ ˚ Mg-N-R2/ ˚ R1-N-R2/ ˚
(X–N–Y)
Ref.
i
[TismPr Benz]MgNC4H8
126.8
115.1
113.4
113.5
116.5
117.9
115.1
115.6
118.6
113.2
111.4
129.3
125.7
124.3
123.3
123.7
123.4
126.2
125.7
120.3a
128.4
127.9
102.6
118.5
119.3
118.5
119.2
118.7
118.6
118.7
121.0a
118.3
118.7
358.7
359.3
357.0
355.3
359.4
360.0
359.9
360.0
359.9
359.9
358.0
this work
this work
16
i
[TismPr Benz]MgNPh2
(THF)2Mg(NPh2)2
[(HMPA)2Mg(NPh2)2]
17
EtMgNPh2(THF)2
17
17
18
19
PriMgNPh2(THF)2
[Na(THF)5][{(CyN)2C(NPh2)}2Mg(NPh2)]
[(PMDETA)K][Mg(THF)(NPh2)3]b
(a) Average values for disordered structure.
(b) Two of the NPh2 ligands interact with the [K(PMDETA)] moiety.

Magnesium diphenylamide compounds are more common than pyrrolidinide
derivatives, and complexes that feature both terminal and bridging diphenylamide
ligands have been reported. In this regard, the Mg–N bond length of
i
[TismPr Benz]MgNPh2 [2.100(2) Å] is comparable to that of the pyrrolidinide derivative,
i
i
[TismPr Benz]MgNC4H8 [1.970(5) Å], and also [TismPr Benz]MgN(H)Ph [2.058(4) Å and
2.049(4) Å for two crystallographically independent molecules],10 but is distinctly
longer than the values for the terminal diphenylamide compounds listed in Table 1,
which range from 2.01 Å to 2.08 Å. Interestingly, the Mg–N bond length of
i
[TismPr Benz]MgNPh2 is actually comparable to those in the bridging diphenylamide
compounds, namely [(PhNpy)Mg(–NPh2)]2 [2.080(5) Å and 2.119(5) Å]22 and [CpMg(–
NPh2)]2 [2.0934(16) Å, 2.1050(16) Å, 2.1092(17) Å and 2.1153(17) Å].23 As such, it is
i
evident that the Mg–N bond lengths in [TismPr Benz]MgNR2 are longer than anticipated.
Also of note, the geometry about the nitrogen atom in each of the terminal amido
compounds listed in Table 1 is close to planar, with the sum of bond angles at nitrogen
being in the range 355.3˚ – 360.0˚.
With respect to the acetylide compounds, the Mg–C2R bond lengths of
i
i
[TismPr Benz]MgCCPh [2.166(4) Å] and [TismPr Benz]MgCCBun [2.1700(19) Å] are
i
comparable to the Mg–Me bond length of [TismPr Benz]MgMe [2.1781(13) Å],9 but
distinctly shorter than the corresponding Mg–Calkyl bond length of
i
[TismPr Benz]MgC(H)(Me)Ph [2.231(2) Å].10 For further comparison, several other
LnMgCCPh derivatives have been structurally characterized (Table 2),24-30 although
there is only one other structurally characterized LnMgCCBun derivative listed in the
CSD, namely [HC{C(Me)NAr}2]MgCCBun (Ar = 2,6-Ph2CH-4-Me-C6H2).31 Most
magnesium acetylide compounds possess terminal ligands, but bridging derivatives are
also known. For example, [{2-Me2NC2H4NHCH(Ph)CH2Ph}Mg(C2Ph)(–C2Ph)]2
possesses a symmetrically bridging phenylacetylide ligand with Mg–C bond lengths of
i
2.127(4) Å and 2.181(4) Å,26,32 which are comparable to that for [TismPr Benz]MgCCPh

12
and other terminal magnesium acetylide compounds, for which the mean value is 2.16
Å.
i
i
Spectroscopically, [TismPr Benz]MgCCPh and [TismPr Benz]MgCCBun are
characterized by two signals in the 13C{1H} NMR spectrum attributable to the acetylide
moiety. These values are within the range for other magnesium acetylide compounds
that have been reported in the literature (Table 3).24,31,33,34

Table 2. Structural data for terminal magnesium phenylacetylide and n-butylacetylide compounds.
d(Mg–C)/ Å
2.166
d(C–C) / Å
1.216
1.215
1.213
1.209
1.239
1.195
1.219
1.213
1.224
1.220
1.223
1.210
Mg-C-C/ ˚
175.0
177.7
175.0
174.7
174.2
172.8
180.0
180.0
180.0
180.0
168.8
168.4
Ref
i
[TismPr Benz]MgCCPha
this work
i
[TismPr Benz]MgCCBun
2.170
this work
[F12-Tp4Bo,3Ph]MgCCPha
2.045
24
25
26
17
27
[dpp-bian(H)]Mg(CCPh)(THF)2
[{2-Me2NC2H4NHCH(Ph)CH2Ph}Mg(C2Ph)]2
[(PhCC)Mg(μ-NPri2)(THF)]2
(tmeda)2Mg(CCPh)2b
2.124
2.104
2.134
2.176
2.200
(THF)4Mg(CCPh)2b
2.187
28
2.191
[{(dpp-mian)(PhCCH2)}Mg(CCPh)2(THF)]2•(toluene)
[{(dpp-mian)(PhCCH2)}Mg(CCPh)2(THF)]2•(THF)
2.151
29
29
2.138
(a) Average for crystallographically independent molecules in the asymmetric unit
(b) Data for independent CCPh moieties in the same molecule

Table 3. 13C NMR spectroscopic data for terminal magnesium acetylide compounds.
 13C/ ppm
112.2, 142.0
109.7, 126.0
113.6, 121.8
120.0, 146.7
110.6, 117
Ref.
i
[TismPr Benz]MgCCPh
This work
i
[TismPr Benz]MgCCBun
This work
t
[TpBu ]MgCCPh
33
33
24
31
t
[TpBu ]MgCCSiMe3
[F12-Tp4Bo,3Ph]MgCCPh
[HC{C(Me)NAr}2]MgCCBun (Ar = 2,6-
103.5, 111.9
Ph2CH-4-Me-C6H2)
{[HC{C(Me)NAr}2]Mg(–CCBun)}2 (Ar
= 2,6-Pri2C6H3)
112.2, 121.0
111.2, 122.0
103.5, 120.1
34
34
34
{[HC{C(Me)NAr}2]Mg(–CCPh)}2 (Ar =
2,6-Pri2C6H3)
{[HC{C(Me)NAr}2]Mg(–CCBut)}2 (Ar
= 2,6-Pri2C6H3)
i
Significantly, the Mg–N bond of [TismPr Benz]MgNR2 may be cleaved by
hydrosilanes, which provides a means to achieve catalytic Si–N bond formation by the
dehydrocoupling of hydrosilanes and amines (Scheme 3). For example,
i
[TismPr Benz]MgMe is an effective precatalyst for the dehydrocoupling of a 1:1 mixture of
Ph2SiH2 and C4H8NH at room temperature to afford the silazane, Ph2SiH(NC4H8), with a
i
turnover frequency of 200 h–1. [TismPr Benz]MgMe also achieves the dehydrocoupling of a
1:1 mixture PhSiH3 and C4H8NH, to afford a mixture of PhSiH2(NC4H8) and
PhSiH(NC4H8)2.35 Although catalysts for the dehydrocoupling of silanes and amines are
long known, it is only recently that they have become the subject of intense attention.4

15
In this regard, there are very few magnesium systems,3,36,37 of which the first reported
employs the tris(4,4-dimethyl-2-oxazolinyl)phenylborate complex, [ToM]MgMe, as
described by Sadow.3 The proposed mechanism for the catalytic cycle is illustrated in
Scheme 3 and is based on that suggested for [ToM]MgMe, which involves the
intermediacy of the magnesium hydride complex [ToM]MgH, albeit not observed.38,39
Support for the catalytic cycle presented in Scheme 3 is provided by the observations
i
i
that (i) [TismPr Benz]MgH reacts with R2NH to afford [TismPr Benz]MgNR2 and (ii)
i
i
[TismPr Benz]MgNC4H8 reacts with PhSiH3 or Ph2SiH2 to regenerate [TismPr Benz]MgH.
i
Furthermore, [TismPr Benz]MgNR2 is observed as the resting state during the catalytic
transformation.
Scheme 3.
i
i
[TismPr Benz]MgH and [TismPr Benz]MgMe are also capable of dehydrocoupling
PhCCH and PhSiH3 at 130˚C to form PhSiH2CCPh (Scheme 4). Although the activity
is lower than that for the dehydrocoupling of R2NH and silanes, this transformation is,

16
nevertheless, of interest because there are no reports of well-defined mononuclear
magnesium compounds that have been employed for this transformation.40,41,42 The
mechanism for the dehydrocoupling of PhCCH and PhSiH3 is proposed to occur via a
similar mechanism to that for R2NH (Scheme 4), with the acetylide species being the
resting state.
Scheme 4.
i
[TismPr Benz]MgMe is also capable of achieving the isomerization of a terminal
alkyne to an allene. Specifically, 3-phenyl-1-propyne, PhCH2CCH, isomerizes to
phenylallene at elevated temperature (100 – 130˚C), as illustrated in Scheme 5. In
addition, small quantities of 3-phenyl-2-propyne, PhCCMe, and a cyclobutane
derivative resulting from the dimerization of phenylallene are also observed by NMR
spectroscopy.

17
Scheme 5.
Metal catalyzed isomerization of terminal alkynes to allenes and 2-alkynes is
precedented,43 as illustrated by organomagnesium compounds that feature N,N-
dialkylamineimine ligands.26 On the basis of that proposed for the aforementioned
magnesium system,26 a potential mechanism for the isomerization is illustrated in
Scheme 6. Specifically, key steps in this mechanism involve 1,3-hydrogen shifts to
i
i
isomerize the acetylide [TismPr Benz]MgCCCH2Ph to [TismPr Benz]MgCH=C=CHPh and
i
[TismPr Benz]MgCH2CCPh. Sigma-bond metathesis44 between
i
[TismPr Benz]MgCH=C=CHPh and PhCH2CCH releases PhCH=C=CH2 and regenerates
i
[TismPr Benz]MgCCCH2Ph. Correspondingly, the metathesis between
i
[TismPr Benz]MgCH2CCPh and PhCH=C=CH2 releases PhCCCH3,26 but it is also
i
possible that PhCCCH3 is formed by reaction between [TismPr Benz]MgCH2CCPh and
PhCH2CCH (not shown).

18
Scheme 6.
CONCLUSIONS
i
In summary, the magnesium hydride and methyl compounds, [TismPr Benz]MgX (X = H,
Me), react with diphenylamine and pyrrolidine to afford the amide derivatives,
i
i
[TismPr Benz]MgNPh2 and [TismPr Benz]MgNC4H8, while reactions with the terminal
alkynes, PhCCH and BunCCH, form the corresponding magnesium acetylide
i
i
derivatives, [TismPr Benz]MgCCPh and [TismPr Benz]MgCCBun. The molecular structures
i
of [TismPr Benz]MgX (X = NPh2, NC4H8, CCPh, CCBun) have been determined by X-ray

19
diffraction, thereby demonstrating that each complex adopts a distorted trigonal
i
bipyramidal geometry. However, while the X substituent of [TismPr Benz]MgX (X = NPh2,
CCPh and CCBun) resides in an axial site, the pyrrolidinide ligand of
i
[TismPr Benz]MgNC4H8 resides in an equatorial site. The Mg–N bond of
i
[TismPr Benz]MgNR2 may be cleaved by hydrosilanes, thereby providing a means to
achieve catalytic Si–N bond formation by dehydrocoupling of hydrosilanes and amines.
i
For example, [TismPr Benz]MgMe is an effective precatalyst for the dehydrocoupling of a
1:1 mixture of Ph2SiH2 and C4H8NH at room temperature to afford the silazane,
i
i
Ph2SiH(NC4H8). [TismPr Benz]MgH and [TismPr Benz]MgMe are also capable of
dehydrocoupling PhCCH and PhSiH3 to form PhSiH2CCPh. In addition to
i
dehydrocoupling of a terminal alkyne and hydrosilane, [TismPr Benz]MgMe is also
capable of achieving the isomerization of a terminal alkyne, namely, 3-phenyl-1-
propyne to phenylallene.
EXPERIMENTAL SECTION
General considerations
All manipulations were performed using a combination of glovebox, high vacuum, and
Schlenk techniques under an argon atmosphere.45 Solvents were purified and degassed
by standard procedures. NMR spectra were recorded on Bruker AVIII 300, Bruker
1
AVIII 400SL and Bruker AVIII 500 spectrometers. H NMR chemical shifts are reported
in ppm relative to SiMe4 ( = 0), and were referenced with respect to the protio solvent
impurity ( = 7.16 for C6D5H).46 13C NMR spectra are reported in ppm relative to SiMe4
( = 0) and were referenced internally with respect to the solvent ( = 128.06 for C6D5H).
Coupling constants are given in hertz. NMR spectra are provided in the Supporting
Information. Infrared spectra were recorded on a Perkin Elmer Spectrum Two
spectrometer in attenuated total reflectance (ATR) mode and are reported in reciprocal
i
i
centimeters. [TismPr Benz]MgMe9 and [TismPr Benz]MgH10 were obtained by literature

20
methods, and phenylsilane, diphenylsilane, phenylacetylene, 1-hexyne, pyrrolidine,
diphenylamine, and 3-phenyl-1-propyne were obtained commercially and used as
received.
X-ray Structure Determinations
X-ray diffraction data were collected on a Bruker Apex II diffractometer. The structures
were solved by using direct methods and standard difference map techniques, and
were refined by full-matrix least-squares procedures on F2 with SHELXTL (Version
2014/7).47 Crystallographic data have been deposited with the Cambridge
Crystallographic Data Centre (CCDC 1889843-1889846).
Computational Details
Calculations were carried out using DFT as implemented in the Jaguar 8.9 (release 15)
suite of ab initio quantum chemistry programs.48 Geometry optimizations were
performed with the B3LYP density functional using the LACVP** basis sets and
Cartesian coordinates are provided in the Supporting Information.
i
Synthesis of [TismPr Benz]MgNPh2
i
(i) A solution of [TismPr Benz]MgMe (15 mg, 0.021 mmol) in C6D6 was added to a solution
of diphenylamine (4.5 mg, 0.027 mmol) in C6D6 (0.7 mL total). The mixture was allowed
to stand at room temperature for one hour and crystals suitable for X-ray diffraction
were obtained via vapor diffusion of pentane into the benzene solution. The crystals
i
were isolated and washed with pentane to afford [TismPr Benz]MgNPh2 as a white solid (8
i
mg, 44% yield). Anal. calcd. for [TismPr Benz]MgNPh2: C, 68.7%; H, 7.2%; N, 11.5%.
1
Found: C, 66.8%; H, 7.3%; N, 11.0%. H NMR (C6D6): 0.48 [s, 18H, Si(CH3)2], 1.17 [d, J =
7, 18H, CH(CH3)2], 4.61 [sep, J = 7, 3H, CH(CH3)2], 6.43 [t, J = 7, 2H, MgNPh2], 6.84 [t, J =
8, 4H, MgNPh2], 6.90 [m, 6H, C6H4], 7.07 [m, 3H, C6H4], 7.33 [d, J = 8, 4H, MgNPh2], 8.43
[m, 3H, C6H4]. 13C{1H} NMR (C6D6): 4.92 [s, 6C, Si(CH3)2], 21.11 [s, 6C, CH(CH3)2], 50.27

21
[s, 3C, CH(CH3)2], 111.97 [s, 3C, C6H4], 115.04 [s, 2C, MgNPh2], 121.58 [s, 4C, MgNPh2],
122.53 [s, 3C, C6H4], 122.91 [s, 3C, C6H4], 122.94 [s, 3C, C6H4], 128.66 [s, 4C, MgNPh2],
134.07 [s, 3C, C6H4], 143.86 [s, 3C, C6H4], 157.22 [s, 2C, MgNPh2], 166.42 [s, 3C,
N2CSi(CH3)2], not observed [CMg]. IR Data (ATR, cm-1): 3070 (w), 2973 (w), 2942 (w),
2898 (w), 2880 (w), 1576 (w), 1478 (m), 1463 (m), 1388 (w), 1357 (m), 1298 (m), 1253 (m),
1171 (w), 1064 (w), 989 (w), 950 (s), 929 (s), 824 (m), 791 (m), 738 (s), 693 (m), 648 (w), 558
(w), 527 (m), 502 (m), 438 (m).
i
(ii) A solution of [TismPr Benz]MgH (5 mg, 0.007 mmol) in C6D6 was added to a solution of
diphenylamine (1.5 mg, 0.009 mmol) in C6D6 (0.7 mL total). The sample was monitored
by 1H NMR spectroscopy, thereby indicating the immediate formation of
i
[TismPr Benz]MgNPh2.
i
Synthesis of [TismPr Benz]MgNC4H8
i
(i) A solution of [TismPr Benz]MgMe (15 mg, 0.021 mmol) in C6D6 was added to a solution
of pyrrolidine (2 mg, 0.028 mmol) in C6D6 (0.7 mL total). The mixture was allowed to
stand at room temperature for one hour, during which time crystals suitable for X-ray
diffraction were deposited. The crystals were isolated and washed with pentane to give
i
1
[TismPr Benz]MgNC4H8 as a white solid (8 mg, 49% yield). H NMR (C6D6; due to low
solubility following isolation, data is reported for the in situ generated compound): 0.65
[s, 18H, Si(CH3)2], 1.07 [d, J = 7, 18H, (CH(CH3)2], 1.91 [m, 4H, MgNC4H8], 3.74 [m, 4H,
MgNC4H8], 4.64 [sep, J = 7, 3H, CH(CH3)2], 6.91 [t, J = 8, 3H, C6H4], 7.04 [d, J = 8, 3H,
C6H4], 7.14 [m, 3H, C6H4], 8.51 [d, J = 8, 3H, C6H4]. 13C{1H} NMR (C6D6): 6.42 [s, 6C,
Si(CH3)2], 21.04 [s, 6C, CH(CH3)2], 28.19 [s, 2C, MgNC4H8], 49.65 [s, 3C, CH(CH3)2], 55.04
[s, 2C, MgNC4H8], 112.50 [s, 3C, C6H4], 120.91 [s, 3C, C6H4], 122.34 [s, 3C, C6H4], 122.44
[s, 3C, C6H4], 133.83 [s, 3C, C6H4], 144.05 [s, 3C, C6H4], 165.66 [s, 3C,
(C6H4N2CH(CH3)2CSi(CH3)2)3CMgNC4H8], not observed [CMg]. IR Data (ATR, cm-1):
3056 (w), 2973 (w), 2942 (w), 2902 (w), 2882 (w), 1462 (m), 1391 (w), 1340 (m), 1250 (m),

22
1158 (w), 1132 (w), 1061 (m), 1011 (m), 951 (m), 913 (m), 824 (s), 787 (m), 739 (vs), 686
(m), 531 (w), 430 (m).
i
(ii) A solution of [TismPr Benz]MgH (5 mg, 0.007 mmol) in C6D6 was added to a solution of
pyrrolidine (0.7 mg, 0.010 mmol) in C6D6 (0.7 mL total). The mixture was monitored by
1H NMR spectroscopy, thereby indicating the immediate formation of
i
[TismPr Benz]MgNC4H8.
i
Synthesis of [TismPr Benz]MgCCPh
i
(i) A solution of [TismPr Benz]MgMe (15 mg, 0.021 mmol) in C6D6 was added to a solution
of phenylacetylene (2.7 mg, 0.026 mmol) in C6D6 (0.7 mL total). The mixture was
allowed to stand at room temperature for 16 hours, after which period, crystals of
i
[TismPr Benz]MgCCPh suitable for X-ray diffraction were deposited and isolated. Vapor
diffusion of pentane into the remaining benzene solution resulted in a second crop of
crystals. The samples were combined and washed with pentane to give
i
1
[TismPr Benz]MgCCPh as a white solid (9 mg, 53% yield). H NMR (C6D6): 0.39 [s, 18H,
Si(CH3)2], 1.16 [d, J = 7, 18H, CH(CH3)2], 4.63 [sep, J = 7, 3H, CH(CH3)2], 7.04 [m, 4H,
(C6H4N2CH(CH3)2CSi(CH3)2)3CMgCCPh], 7.20 [m, 9H,
(C6H4N2CH(CH3)2CSi(CH3)2)3CMgCCPh], 7.96 [m, 2H, MgCCPh], 10.08 [d, J = 8, 3H,
C6H4]. 13C{1H} NMR (C6D6): 4.43 [s, 6C, Si(CH3)2], 21.03 [s, 6C, CH(CH3)2], 50.13 [s, 3C,
CH(CH3)2], 111.97 [s, 3C, C6H4], 112.22 [s, 1C, MgCCPh], 122.58 [s, 3C, C6H4], 122.92 [s,
3C, C6H4], 124.11 [s, 3C, C6H4], 124.67 [s, 2C, MgCCPh], 131.22 [s, 1C, MgCCPh], 131.63
[s, 2C, MgCCPh], 132.40 [s, 1C, MgCCPh], 134.39 [s, 3C, C6H4], 142.03 [s, 1C, MgCCPh],
144.82 [s, 3C, C6H4], 166.94 [s, 3C, N2CSi(CH3)2], not observed [CMgCCPh]. IR Data
(ATR, cm-1): 3054 (w), 2973 (w), 2946 (w), 2904 (w), 2886 (w), 1462 (w), 1391 (w), 1341
(w), 1253 (w), 1160 (w), 1133 (w), 1062 (w), 1012 (w), 946 (m), 825 (s), 790 (m), 741 (s),
693 (w), 531 (w), 433 (w).

23
i
(ii) A solution of [TismPr Benz]MgH (5 mg, 0.007 mmol) in C6D6 was added to a solution of
phenylacetylene (1 mg, 0.010 mmol) in C6D6 (0.7 mL total). The mixture was monitored
i
by 1H NMR spectroscopy, indicating the immediate formation of [TismPr Benz]MgCCPh.
i
Synthesis of [TismPr Benz]MgCCBun
i
(i) A solution of [TismPr Benz]MgMe (15 mg, 0.021 mmol) in C6D6 was added to a solution
of 1-hexyne (2.3 mg, 0.027 mmol) in C6D6 (0.7 mL total). The mixture was heated at 60˚C
for 16 hours, after which period, crystals suitable for X-ray diffraction were obtained via
vapor diffusion of pentane into the benzene solution. The crystals were isolated and
i
washed with pentane to afford [TismPr Benz]MgCCBun as a white solid (4 mg, 24%
i
yield). Anal. calcd. for [TismPr Benz]MgCCBun: C, 67.1%; H, 7.9%; N, 10.9%. Found: C,
67.1%; H, 8.0%; N, 10.8%. 1H NMR (C6D6): 0.38 [s, 18H, Si(CH3)2)], 1.01 [t, J = 7, 3H,
MgCC(C4H9)], 1.14 [d, J = 7, 18H, CH(CH3)2], 1.79 [m, 2H, MgCC(C4H9)], 1.92 [m, 2H,
MgCC(C4H9)], 2.79 [t, J = 7, 2H, MgCC(C4H9)], 4.61 [sep, J = 7, 3H, CH(CH3)2], 7.10 [m,
3H, C6H4], 7.19 [m, 3H, C6H4], 7.34 [m, 3H, C6H4], 10.23 [d, J = 8, 3H, C6H4]. 13C{1H} NMR
(C6D6): 4.45 [s, 6C, Si(CH3)2], 14.38 [s, 1C, MgCC(C4H9)], 21.01 [s, 6C, CH(CH3)2], 22.32 [s,
1C, MgCC(C4H9)], 22.82 [s, 1C, MgCC(C4H9)], 33.47 [s, 1C, MgCC(C4H9)], 50.05 [s, 3C,
CH(CH3)2], 109.73 [s, 1C, MgCC(C4H9)], 111.89 [s, 3C, MgCC(C4H9)], 122.18 [s, 3C,
MgCC(C4H9)], 122.78 [s, 3C, MgCC(C4H9)], 124.63 [s, 3C, C6H4)], 126.04 [s, 1C,
MgCC(C4H9)], 134.41 [s, 3C, C6H4], 144.97 [s, 3C, C6H4], 166.93 [s, 3C, N2CSi(CH3)2], not
observed [CMgCC(C4H9)]. IR Data (ATR, cm-1): 3066 (w), 2972 (w), 2946 (w), 2904 (w),
2892 (w), 1463 (w), 1391 (w), 1353 (w), 1252 (w), 1160 (w), 1133 (w), 1105 (w), 1063 (w),
1013 (w), 947 (s), 825 (s), 790 (m), 740 (vs), 695 (w), 559 (w), 530 (w), 460 (w), 436 (m).
i
(ii) A solution of [TismPr Benz]MgH (5 mg, 0.007 mmol) in C6D6 was added to a solution of
1-hexyne (0.8 mg, 0.009 mmol) in C6D6 (0.7 mL total). The mixture was heated at 60˚C
overnight, and monitored by 1H NMR spectroscopy, indicating the formation of
i
[TismPr Benz]MgCCBun.

24
Dehydrocoupling of Ph2SiH2 and C4H8NH
A solution of Ph2SiH2 (0.284 mmol) and C4H8NH (0.284 mmol) in C6D6 (0.7 mL),
i
containing mesitylene as an internal standard, was treated with [TismPr Benz]MgMe (2
mg, 0.003 mmol). The reaction was monitored by 1H NMR spectroscopy, thereby
indicating the formation of Ph2SiH(NC4H8)49 (TON50 = 200) within a period of 30
minutes.
Dehydrocoupling of PhSiH3 and C4H8NH
A solution of PhSiH3 (0.085 mmol) and C4H8NH (0.085 mmol) in C6D6 (0.7 mL),
i
containing mesitylene as an internal standard, was treated with [TismPr Benz]MgMe (3
mg, 0.004 mmol). The reaction was monitored by 1H NMR spectroscopy, thereby
indicating the formation of PhSiH2(NC4H8) and PhSiH(NC4H8)249 (TON50 = 20) within a
period of 30 minutes.
Dehydrocoupling of PhSiH3 and Ph2NH
(a) A solution of PhSiH3 (0.085 mmol) and Ph2NH (0.085 mmol) in C6D6 (0.7 mL),
i
containing mesitylene as an internal standard, was treated with [TismPr Benz]MgMe (3
mg, 0.004 mmol). The sample was heated at 100˚C and monitored by 1H NMR
spectroscopy, thereby indicating the formation of PhSiH2(NPh2)51 (TON50 = 4) after a
period of 21 days.
i
(b) A solution of [TismPr Benz]MgH (2 mg, 0.003 mmol) was treated with diphenylamine
(5 mg, 0.030 mmol) and phenylsilane (3 mg, 0.028 mmol). The reaction mixture was
heated at 100˚C for 3 days, resulting in the formation of PhH2Si(NPh2).
i
Reactivity of [TismPr Benz]MgNC4H8 towards Ph2SiH2
i
A solution of [TismPr Benz]MgNC4H8 (3 mg, 0.004 mmol) in C6D6 (ca 0.7 mL) was treated
with Ph2SiH2 (ca 3 equivs) and monitored by 1H NMR spectroscopy, thereby

25
i
demonstrating the formation of [TismPr Benz]MgH as the major magnesium-containing
species, together with Ph2SiH(NC4H8).
i
Reactivity of [TismPr Benz]MgNC4H8 towards PhSiH3
i
A solution of [TismPr Benz]MgNC4H8 (3 mg, 0.004 mmol) in C6D6 (0.7 mL) was treated
with PhSiH3 (ca 3 equivs) and monitored by 1H NMR spectroscopy, thereby
i
demonstrating the formation of [TismPr Benz]MgH as the major magnesium-containing
species, together with PhSiH2(NC4H8) and PhSiH(NC4H8)2.
Dehydrocoupling of PhSiH3 and PhCCH
(a) A solution of PhSiH3 (0.063 mmol) and PhCCH (0.021 mmol) in C6D6 (0.7 mL),
i
containing mesitylene as an internal standard, was treated with [TismPr Benz]MgMe (3
mg, 0.004 mmol). The sample was heated at 130˚C and was monitored by 1H NMR
spectroscopy, thereby demonstrating the formation of PhSiH2CCPh52 (TON50 = 4.5)
after a period of 21 days.
i
(b) A solution of [TismPr Benz]MgH (2 mg, 0.003 mmol) in C6D6 (0.7 mL) was treated with
PhCCH (3 mg, 0.020 mmol) and PhSiH3 (3 mg, 0.028 mmol). The sample was heated at
130˚C for 7 days, resulting in the formation of PhSiH2CCPh.
Isomerization of PhCH2CCH
A solution of 3-phenyl-1-propyne (0.043 mmol) in C6D6 (ca 0.7 mL) was treated with
i
[TismPr Benz]MgMe (3 mg, 0.004 mmol). The mixture was heated at 100˚C for 4 days and
monitored by 1H NMR spectroscopy, thereby demonstrating 32% conversion and the
formation of PhCH=C=CH2, PhCCMe and C4H2Ph2(CH2)253 in a 94:3:3 ratio.
Subsequent heating at 130˚C for 9 days results in 90% conversion and the formation of
PhCH=C=CH2, PhCCMe and C4H2Ph2(CH2)2 in a 81:8:11 ratio with an overall TON50 =
9.

26
Acknowledgements. We thank the National Science Foundation (CHE-1465095) for
support of this research. M. R. acknowledges the National Science Foundation for a
Graduate Research Fellowship under Grant No. DGE-16-44869.
APPENDIX A. Supplementary Data
Crystallographic data in CIF format (CCDC #1889843-1889846). These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
https://dx.doi.org/10.1016/j.ica.xxxxxx.

27
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