Role of N-donor groups on the stability of hydrazide based hypercoordinate silicon(IV) complexes: Theoretical and experimental perceptions

Article abstract of DOI:10.1016/j.poly.2015.08.011

A triphenylphosphinimino donor group is illustrated as a ligand in pentacoordinate siliconium halide dichelates, [YSiL₂]⁺X^-, where L is the bidentate ligand -OC(R)=NN=PPh₃)- (R = t-Bu-Ph or Ph), Y = Me, Ph, CH₂Cl, CHCl₂, Cl or Br, and X = Cl or Br. All the new complexes were characterized by NMR spectroscopy and elemental analysis. The remote substituent, the t-Bu-phenyl or phenyl group, imparts more pentacoordinate character, i.e. more ionization to the complexes, compared to the PhCH₂ group. DFT calculations indicate that the central silicon atom, due to the more positive charge, demands greater electron density. As a result of this, shorter Si-O, Si-N and Si-Cl bonds were observed. Both theoretical and experimental analysis indicate that the phosphinimino ligand is a stronger donor than the previously studied dimethylamino and isopropylidenimino ligands, causing all of the complexes to be pentacoordinate siliconium-halide salts in solution. The hypercoordinate silicon dichelates undergo unique intermolecular chelate exchange reactions: (i) complete ligand transfer from the dichelates to PhSiCl₃ by a ligand priority order and (ii) bidentate ligand interchange between the dichelates and a trimethylsilyl-hydrazide precursor. Thermolysis of some selected hypercoordinated silicon(IV) complexes containing a silicon-carbon σ-bond significantly undergo a two step decomposition, while other complexes with silicon-halogen σ-bonds follow three steps. The thermal decomposition strongly depends on the nature of the substituents directly attached to the central silicon atom.

Full text of DOI:10.1016/j.poly.2015.08.011

Polyhedron 99 (2015) 266–274
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Role of N-donor groups on the stability of hydrazide based
hypercoordinate silicon(IV) complexes: Theoretical and experimental
perceptions
a
a
b
b
a
Pothini Suman , Sannapaneni Janardan , Mohsin Y. Lone , Prakash Jha , Kari Vijayakrishna ,
a,
⇑
Akella Sivaramakrishna
a
Department of Chemistry, School of Advanced Sciences, VIT University, Vellore 632 014, TN, India
School of Chemical Sciences, Central University of Gujarat, Sector-30, Gandhinagar, Gujarat, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A triphenylphosphinimino donor group is illustrated as a ligand in pentacoordinate siliconium halide
Received 17 April 2015
Accepted 5 August 2015
Available online 24 August 2015
+ ꢀ
dichelates, [YSiL
Ph, CH Cl, CHCl
troscopy and elemental analysis. The remote substituent, the t-Bu-phenyl or phenyl group, imparts more
pentacoordinate character, i.e. more ionization to the complexes, compared to the PhCH group. DFT
2
] X , where L is the bidentate ligand –OC(R)@NN@PPh
3
)– (R = t-Bu-Ph or Ph), Y = Me,
2
2
, Cl or Br, and X = Cl or Br. All the new complexes were characterized by NMR spec-
2
Keywords:
Pentacoordinate siliconium salts
Thermal stability
Phosphinimino ligand
DFT calculations
Ligand crossover reaction
calculations indicate that the central silicon atom, due to the more positive charge, demands greater
electron density. As a result of this, shorter Si–O, Si–N and Si–Cl bonds were observed. Both theoretical
and experimental analysis indicate that the phosphinimino ligand is a stronger donor than the previously
studied dimethylamino and isopropylidenimino ligands, causing all of the complexes to be pentacoordi-
nate siliconium-halide salts in solution. The hypercoordinate silicon dichelates undergo unique
intermolecular chelate exchange reactions: (i) complete ligand transfer from the dichelates to PhSiCl
3
by a ligand priority order and (ii) bidentate ligand interchange between the dichelates and a trimethylsi-
lyl-hydrazide precursor. Thermolysis of some selected hypercoordinated silicon(IV) complexes
containing a silicon–carbon
complexes with silicon–halogen
depends on the nature of the substituents directly attached to the central silicon atom.
Ó 2015 Elsevier Ltd. All rights reserved.
r
-bond significantly undergo a two step decomposition, while other
r-bonds follow three steps. The thermal decomposition strongly
1
. Introduction
toxicity and are environmental friendly reagents [6,7] which
makes them ideal to develop organocatalyzed enantio-selective
reactions [8], similar to other organosilicon compounds [9]. Stere-
oselective reactions catalyzed by hypercoordinate silicate
compounds have been very well-reviewed in the recent past [10].
Investigations on the effect of ligands upon the reactivity pat-
terns of hypercoordinate silicon complexes led to the preparation
and study of a new class of silicon complexes: those with a triph-
enylphosphinimino-N ligand group with the t-Bu–Ph substituent,
which are the subject of the present work [11]. The new ligand
was expected, and indeed was found, to be superior in terms of
donor strength in comparison to other nitrogen-donor ligands (in
1, 2 and 3), due to its ylide character [12,13] and the resulting
excess electron density on the nitrogen atom. The strength of the
coordination also depends on the nature of the remote substituent
The chemistry of hypercoordinate compounds has been acquir-
ing wider and deeper attention both by organic chemists and by
inorganic chemists due to their potential in developing pathways
for the synthesis of chemicals which may otherwise be difficult
to prepare or even be inaccessible [1]. Hypercoordinate silicon
(
IV) complexes are highly flexible molecular systems, undergoing
a variety of chemical and geometrical transformations [2], includ-
ing ionic dissociation, an alternative neutral dissociation of the
N ? Si dative bond [3,4], thermal and photochemical molecular
rearrangements as well as flexible intramolecular ligand exchange
reactions controlled by priority rules [5]. Apart from the rich chem-
istry of these penta and/or hexacoordinate silicon compounds, it
has been found that these species are relatively cheap, have low
‘
R’. The evidence for complete intermolecular bidentate ligand
⇑
Corresponding author. Tel.: +91 416 2202351; fax: +91 416 2243092.
E-mail address: asrkrishna@vit.ac.in (A. Sivaramakrishna).
crossover among different dichelate complexes is also discussed,
further extending the flexible nature of these compounds, and this
http://dx.doi.org/10.1016/j.poly.2015.08.011
277-5387/Ó 2015 Elsevier Ltd. All rights reserved.
0

P. Suman et al. / Polyhedron 99 (2015) 266–274
267
ligand crossover is controlled by priority rules. However, it has
been widely unexplored whether there are some significant influ-
ences of the hypercoordinate Si atom’s coordination environment
through theoretical and experimental studies.
CCl
then the precipitate which formed was filtered off and dissolved
in CHCl ; Et
NꢁHBr was washed out with cold water in a separating
funnel. The solid isolated on evaporation of CHCl was dried under
vacuum to yield 13.85 g (67%) of 6. M.p.: 186–188 °C. H NMR
CDCl , 300 K) d, ppm: 1.239 (s, 9H, CH ), 7.35–7.60 (m, 19H, Ph);
C NMR (CDCl , 300 K) d, ppm: 31.14 (CH ), 34.95 (C-Me ),
25.60–132.15 (Ph), 168.63 (C@O); P NMR (CDCl , 300 K) d,
ppm: 29.6.
4
. The mixture was stirred for 14 h at room temperature and
3
3
3
1
(
3
3
2
. Experimental section
1
3
3
3
3
3
1
1
3
The reactions were carried out under dry argon using Schlenk
techniques. Solvents were dried and purified by standard methods.
Reagents (including polyhalosilanes) were purchased from
Sigma–Aldrich. The halosilanes were distilled and kept in sealed
ampules prior to use. NMR spectra were recorded on a Bruker
Avance DMX-500 spectrometer operating at 500.13, 202.46,
2
.3.2. O-Trimethylsilyl-N-(triphenylphosphinimino)-4-(t-butyl)
benzohydrazide (7)
To a mixture of 8.04 g (17.7 mmol) of 6 and 2.24 g (22.2 mmol)
of triethylamine in 100 mL of diethyl ether, Me SiCl (2.74 g,
5.2 mmol) in 10 mL of diethyl ether was added dropwise. After
1
13
29
1
25.76 and 99.36 MHz, respectively, for H, 31P, C and Si spec-
3
tra. Spectra are reported in d (ppm) relative to TMS, as determined
2
1
from standard residual solvent-proton (or carbon) signals for
H
refluxing for 10 h, the mixture was cooled and Et
tered off, followed by the removal of volatiles at low pressure.
3
NꢁHCl was fil-
1
3
31
3 4
and C, relative to external (capillary) H PO for P, and directly
2
9
from TMS for Si. Melting points were measured in sealed capillar-
ies using a Büchi melting point instrument and are uncorrected. TG
curves in the range 25–900 °C were recorded using an EXSTAR
The white powder that formed was washed with 15 mL of n-hex-
1
ane and filtered, yielding 3.94 g (42%) of 7. H NMR (CDCl
3
,
3
00 K) d, ppm: 0.57 (s, 9H, SiCH
3
), 1.23 (s, 9H, CCH
3
), 7.33–7.86
ꢀ
1
TG/DTA 6300 instrument at a heating rate of 10 °C min
in a
31
29
(
m, Ph); P NMR (CDCl
3
, 300 K) d, ppm: 16.2; Si NMR (CDCl
3
,
dynamic nitrogen atmosphere. In each experiment, solid samples
having masses ranging from 9 mg to 10 mg were used.
3
00 K) d, ppm: 7.2.
0
2.1. Computational methodology
2.3.3. Bis[N-(triphenylphosphinimino)-4-t-butyl-phenyl-N ,O]
methylsiliconium chloride (8)
All the quantum chemical calculations of the Si complexes have
To a mixture of 0.494 g (0.93 mmol) of 7 in 10 mL of chloroform,
MeSiCl (0.31 g, 2.11 mmol) was added, followed by stirring at
room temperature for 30 min. The residue left after removal of
volatiles under reduced pressure was recrystallized from a solvent
been calculated using the Gaussian 09 program package [16]. The
spin multiplicity of all the studied molecules is singlet, while the
charge for 1 and 2 is zero and for 3, 8, 11 and 13 it is +1. Geometry
minimization was carried out by employing Becke’s three parame-
ter hybrid density functional B3LYP [17–19] and valance triple-f
3
2 2
mixture of 1:2 CH Cl –n-hexane. The product was washed with
10 mL of n-hexane. The yield was 0.43 g (93%) of a white powder.
1
6
-311G (d,p) as a basis set for all the atoms. Frequency calculations
M.p.: 106–108 °C. H NMR (CDCl
CH ), 1.16 (s, 18H, CH ), 7.38–7.90 (m, 38H, Ph); C NMR (CDCl
300 K) d, ppm: 8.47 (Si–CH ), 25.68 (Me ), 31.95 (C-Me
126.83–132.94 (Ph), 155.33 (C@N); P NMR (CDCl , 300 K) d,
3
, 300 K) d, ppm: 0.794 (s, 3H, Si–
1
3
were exercised to ascertain the stationary structures. Natural bond
orbital (NBO) [20,21] analysis was carried out at the B3LYP/6-311G
3
3
3
,
3
3
3
),
2
9
31
(
d,p) level by the NBO 3.1 version of Gaussian 09 [16]. Si NMR
3
2
9
shielding constants were computed at the DFT level by using the
gauge independent atomic orbitals (GIAO) [22] method in conjunc-
tion with the meta-GGA functional HCTH. The choice of functional
was made from the literature [23]. The effect of solvent on shield-
ing constants was accounted for by using the polarizable contin-
uum model (PCM) of Tomasi and co-workers [24]. Pople’s triple
zeta, split valance basis set 6-311 + G(2d) was employed for the
calculation of shielding constants.
ppm: 41.2; Si NMR (CDCl
3
, 300 K) d, ppm: ꢀ77.1.
0
2
(
.3.4. Bis[N-(triphenylphosphinimino)-4-t-butyl-phenyl-N ,O]
chloromethyl)siliconium chloride (9)
In a Schlenk flask, CH ClSiCl (0.28 g, 1.30 mmol) was added to a
2
3
mixture of 0.373 g (0.70 mmol) of 7 in 10 mL of chloroform, fol-
lowed by stirring at room temperature for 30 min. The same proce-
dure as mentioned above for 2.3.3 was used for the work-up of the
reaction mixture and further purification of the product. The yield
2
.2. Materials and methods
1
was 0.32 g (88%) of a white powder. M.p.: 114 °C. H NMR (CDCl
3
,
2
3
2
00 K) d, ppm: 0.81 (s, 18H, CH
H, CH Cl), 6.28–7.72 (m, 38H, Ph); C NMR (CDCl
), 31.29 (C-Me ), 64.96 (CH), 121.94–121.24 (Ph),
3
), 2.11, 2.38 (ABq,
J
AB = 14.4 Hz,
All reactions were carried out under an inert atmosphere of dry
13
2
3
, 300 K) d,
nitrogen using standard Schlenk and vacuum line techniques. The
polyhalosilanes, Me SiCl, 4-(t-butyl)benzohydrazide and benzohy-
drazide were purchased from Sigma Aldrich and used as such. The
solvents were purchased from Sd fine chemicals purified and
distilled according to standard procedures prior to use.
ppm: 27.48 (CH
3
31
3
3
29
1
58.67 (C@N); P NMR (CDCl
3
, 300 K) d, ppm: 52.2; Si NMR
(
3
CDCl , 300 K) d, ppm: ꢀ94.1.
0
2
.3.5. Bis[N-(triphenylphosphinimino)-4-t-butyl-phenyl-N ,O]
2
2
.3. Preparation of compounds
(dichloromethyl)siliconium chloride (10)
A Schlenk flask was charged with 0.512 g (0.97 mmol) of 7 in
3
10 mL of chloroform and SiCl (0.29 g, 1.62 mmol) and the mixture
.3.1. 4-(t-Butyl)-N-(triphenylphosphoranylidene)benzohydrazide (6)
At ice-cold temperature, 8.01 g (50.3 mmol) of Br
CCl was added dropwise to a solution of 12.02 g (45.7 mmol) of
Ph P in 100 mL of CCl and the mixture was allowed to stir for
h. The resultant product (Ph PBr ) which formed was is in the
form of a pale yellow precipitate and this was used for further reac-
tion without isolation. 4-(t-Butyl)benzohydrazide (8.79 g,
2
in 50 mL of
was then stirred at room temperature for 30 min. The same proce-
dure as mentioned above for 2.3.3 was used for the work-up of the
reaction mixture and further purification of the product. The yield
4
3
4
1
4
3
2
was 0.45 g (92%) of a white powder. M.p.: 72–74 °C (dec). H NMR
(CDCl
NMR (CDCl
(CH ), 122.60–129.89 (Ph), 156.80 (C@N); P NMR (CDCl
d, ppm: 47.6; Si NMR (CDCl
3
, 300 K) d, ppm: (s, 18H, CH
3
), 7.35–7.60 (m, 38H, Ph); 13
C
3
, 300 K) d, ppm: 28.14 (CH
3
), 31.95 (C-Me
3
), 48.78
3
, 300 K)
3
1
2
3.6 mmol) was added to the reaction mixture, followed by drop-
2
2
9
wise addition of 10.62 g (105.2 mmol) of triethylamine in 80 mL of
3
, 300 K) d, ppm: ꢀ88.6.

2
68
P. Suman et al. / Polyhedron 99 (2015) 266–274
0
2
.3.6. Bis[N-(triphenylphosphinimino)-4-t-butyl-phenyl-N ,O]
of volatiles at low pressure. The white precipitate that formed was
washed with 15 mL of n-hexane and filtered, yielding 4.24 g (68%)
phenylsiliconium chloride (11)
PhSiCl (0.301 g, 1.42 mmol) was added to a solution of 0.375 g
0.71 mmol) of 7 in 10 mL of chloroform, followed by stirring at
room temperature for 30 min. The same procedure as mentioned
above for 2.3 was used for the work-up of the reaction mixture
and further purification of the product. The yield was 0.32 g
87%) of a colourless solid. M.p.: 94–96 °C (dec). H NMR (CDCl
1
3
of 15, consisting of a 2:1 mixture of E, Z isomers. H NMR (CDCl
300 K) d, ppm: major isomer 0.08 (s, 9H, Si–CH ), 7.12–7.78 (m,
Ph); minor isomer 0.16 (s, 9H, Si–CH ), 7.12–7.78 (m, Ph).
NMR (CDCl 300 K) d, ppm: major isomer 0.12 (Si–CH
122.5–136.8 (Ph), 159.4 (N@C–O); minor isomer 1.9 (Si–CH
3
,
(
3
13
3
C
),
),
3
,
3
3
1
31
(
3
,
122.5–136.8 (Ph), 147.3 (N@C–O). P NMR (CDCl
3
, 300 K) d,
ppm: major isomer 17.2; minor isomer 19.4. Si NMR (CDCl
300 K) d, ppm: major isomer 17.4; minor isomer 15.3. Anal. Calc.
for C28 OPSi: C, 77.77; H, 6.24; N, 5.98. Found: C, 77.82; H,
6.33; N, 6.04%.
2
9
3
00 K) d, ppm: 1.76 (s, 18H, CH
3
), 6.90–7.74 (m, 38H, Ph);
, 300 K) d, ppm: 25.66 (CH ), 30.37 (C-Me ),
25.58–134.32 (Ph), 157.26 (C@N); P NMR (CDCl , 300 K) d,
3
,
1
3
C NMR (CDCl
3
3
3
31
1
3
29 2
H N
2
9
ppm: 45.8; Si NMR (CDCl
3
, 300 K) d, ppm: ꢀ92.7.
0
2
.3.7. Bis[N-(triphenylphosphinimino)-4-t-butyl-phenyl-N ,O]
0
2
.3.11. Bis[N-(triphenylphosphinimino)-phenyl-N ,O]methylsiliconium
chlorosiliconium chloride (12)
To a mixture of 0.71 g (1.36 mmol) of 7 in 10 mL of chloroform,
SiCl (0.32 g, 1.89 mmol) was added, followed by stirring at room
temperature for 30 min. The same procedure as mentioned above
for 2.3.3 was used for the work-up of the reaction mixture and fur-
chloride (16)
MeSiCl
(
3
(0.11 g, 0.75 mmol) was added to a solution of 15
0.286 g, 0.61 mmol) in 10 mL of chloroform, followed by stirring
at room temperature for 30 min. The same procedure as mentioned
above for 2.2.3 was used for the work-up of the reaction mixture
and further purification of the product. The yield was 0.254 g
4
ther purification of the product. The yield was 0.55 g (82%) of a
1
white solid. M.p.: 88–90 °C (dec). H NMR (CDCl
3
, 300 K) d, ppm:
), 6.57–7.02 (m, 38H, Ph); C NMR (CDCl
1
1
3
(95%) of a white powder. M.p.: 154–56 °C. H NMR (CDCl
3
, 300 K)
1
3
1
.11 (s, 18H, CH
3
3
,
), 7.22–7.98 (m, 40H, Ph); 1 C NMR
3
d, ppm: 0.82 (s, 3H, Si–CH
(CDCl , 300 K) d, ppm: 8.54 (Si–CH
3
00 K) d, ppm: 26.95 (CH
57.78 (C@N); P NMR (CDCl
, 300 K) d, ppm: ꢀ99.2.
3
), 30.75 (C-Me ), 121.40–128.75 (Ph),
3
3
1
29
3
3
), 123.1–134.8 (Ph), 156.4
, 300 K) d, ppm: 40.6; Si NMR (CDCl
3
, 300 K) d, ppm: 49.8; Si NMR
3
1
29
(
O–C@N); P NMR (CDCl
3
3
,
(
CDCl
3
3
00 K) d, ppm: ꢀ76.2. Anal. Calc. for C51
43 4 2 2
H N O P
SiCl: C, 70.46;
0
H, 4.99; N, 6.44. Found: C, 70.52; H, 5.08; N, 6.52%.
2
.3.8. Bis[N-(triphenylphosphinimino)-4-t-butyl-phenyl-N ,O]
bromosiliconium bromide (13)
To a mixture of 0.33 g (0.63 mmol) of 7 in 10 mL of chloroform,
SiBr (0.300 g, 0.86 mmol) was added, followed by stirring at room
4
temperature for 30 min. The same procedure as mentioned above
for 2.3.3 was used for the work-up of the reaction mixture and fur-
ther purification of the product. The yield was 0.29 g (91%) of a
0
2
.3.12. Bis[N-(triphenylphosphinimino)-phenyl-N ,O]phenylsiliconium
chloride (17)
PhSiCl (0.1802 g, 0.85 mmol) was added to a solution of 15
0.304 g, 0.65 mmol) in 10 mL of chloroform, followed by stirring
at room temperature for 30 min. The same procedure was followed
to work-up the reaction mixture as mentioned above. The yield
3
(
1
colourless solid. M.p.: 78–80 °C (dec). H NMR (CDCl
3
, 300 K) d,
ppm: 1.04 (s, 18H, CH
3
), 6.707–7.60 (m, 38H, Ph); 13C NMR (CDCl
00 K) d, ppm: 27.13 (CH ), 30.93 (C-Me ), 121.58–128.90 (Ph),
58.63 (C@N); P NMR (CDCl , 300 K) d, ppm: 53.1; Si NMR
, 300 K) d, ppm: ꢀ106.2.
3
,
1
was 0.28 g (93%) of a pale yellow solid. M.p.: 134–36 °C (dec).
H
3
1
(
3
3
13
NMR (CDCl
CDCl , 300 K) d, ppm: 122.5–136.2 (Ph), 157.6 (O–C@N);
NMR (CDCl
ppm: ꢀ94.3. Anal. Calc. for C56
N, 6.01. Found: C, 72.36; H, 5.01; N, 6.08.
3
, 300 K) d, ppm: 6.90–7.74 (m, 45H, Ph); C NMR
3
1
29
3
31
(
3
P
CDCl
3
29
3
, 300 K) d, ppm: 47.3; Si NMR (CDCl
3
, 300 K) d,
45 4 2 2
H N O P
SiCl: C, 72.21; H, 4.87;
2
.3.9. N-(Triphenylphosphoranylidene)benzohydrazide (14)
In a 2-necked 500 mL RB flask, 6.47 g (40.6 mmol)of Br in
2
The other complexes, bis[N-(dimethylamino) benzoimidato-N,
O]phenylsiliconium chloride (18) [14] and bis[N-isopropyli-
deneimino)benzoimidato-N ,O]phenylsiliconium chloride (19)
15], were prepared from the corresponding precursors N-(iso-
propylideneimino)benzoimidate and N-(isopropylideneimino)-O-
trimethylsilyl)benzoimidate as per the literature reports.
8
(
0 mL of CCl
36.2 mmol) of Ph
4
was added dropwise to a solution of 9.52 g
P in 120 mL of CCl at 0 °C and the mixture
was then stirred for 4 h. The resultant pale yellow precipitate,
Ph PBr was used as such in the subsequent reaction.
3
4
0
[
3
2
,
Benzohydrazide (2.7 g, 36.3 mmol) was added to the reaction
mixture followed by dropwise addition of 10.18 g (100.5 mmol)
(
4
of triethylamine in 80 mL of CCl . The mixture was stirred for 2 h
at room temperature and then heated for 2 h at 70 °C. After cooling
2.4. General procedure for ligand crossover reactions
the precipitate that formed, it was filtered off and dissolved in
CHCl
separating funnel. The solid isolated on evaporation of CHCl
was dried under vacuum to yield 6.45 g (83%) of 14. M.p.:
3
, and Et
3
NꢁHBr was washed out with ice-cold water in a
The reaction of Eq. (1) was carried out by the addition of a
3
3 3
10–20% molar excess of PhSiCl to a CDCl solution of 16 with stir-
ring under N atm. at ambient temperature for 15 min. The disap-
2
1
29
2
06–208 °C. H NMR (CDCl
Ph), 8.72 (s (broad), 1H, NH); C NMR (CDCl
1.14 (CH ), 34.95 (C-Me ), 119.60–132.15 (Ph), 171.6 (NC@O);
P NMR (CDCl , 300 K) d, ppm: 29.2. Anal. Calc. for C25 OP:
C, 75.74; H, 5.34; N, 7.07. Found: C, 75.78; H, 5.41; N, 7.1%.
3
, 300 K) d, ppm: 7.12–7.94 (m, 20H,
pearance of the Si NMR signal of 16, accompanied by the growth
of the corresponding crossover product 17, was monitored by
13
3
, 300 K) d, ppm:
3
3
3
NMR. MeSiCl
PhSiCl . To ensure that the exchange was complete and irre-
versible, this procedure was followed by the addition of a large
excess of MeSiCl . No reversal of the reaction was detected. These
3
was formed, along with an excess of unreacted
3
1
3
H
21
N
2
3
3
1
13
29
31
2.3.10. O-Trimethylsilyl-N-(triphenylphosphinimino)benzohydrazide
complexes were characterized by their H, C, Si and P NMR
spectra, but could not be isolated because of rapid equilibration
with their precursors.
(15)
5
.24 g (13.22 mmol) of 14 and 1.52 g (15.02 mmol) of triethy-
lamine in 100 mL of diethylether were added to a 3-necked RB
flask. To this mixture, Me SiCl (1.63 g, 15.02 mmol) in 20 mL of
diethyl ether was added dropwise. After refluxing for 8 h, the mix-
ture was cooled and Et
NꢁHCl was filtered off, followed by removal
In a similar way, the reactions of Eqs. (2) and (3) were moni-
2
9
3
tored by Si NMR spectral data on reacting 18 or 19 with 15 in
CDCl solution. In both the cases, the appearance of a new signal
at d ꢀ94.3 indicates the formation of 17.
3
3

P. Suman et al. / Polyhedron 99 (2015) 266–274
269
Table 3
3
. Results and discussion
In a recent note, the introduction of a new chelating ligand sys-
Bond lengths, NPA [20] charge distribution and Wiberg index [21] of 3.
Atoms
1-Si
2-Cl
3-O
4-O
5-N
6-N
tem based on N-cyclohexylidene hydrazides was described [15b].
In the present study, we have prepared several new silicon
compounds (6–19) based on the phosphinimino donor group
NPA charge
Bond length (Å)
Wiberg index
2.028
ꢀ0.414
2.130
0.773
ꢀ0.847
1.716
0.547
ꢀ0.847
1.716
0.547
ꢀ0.987
1.875
0.489
ꢀ0.987
1.875
0.489
(
–N@PPh
3
)
and have studied their donor properties in
comparison with the former chelates (1 and 2). In particular, we
were interested in comparing the donor strengths of the two
nitrogen-ligand systems (NMe , N@CMe and N@PPh ), as given
2 2 3
in Chart 1, and their effects on siliconium ion formation and
stability. Four criteria for donor strength have been studied: the
N–Si bond length by DFT calculations, the 29Si chemical shifts,
the ligand crossover behavior and thermal stability.
in turn increases the overlap of the metal–ligand orbitals and
decreases the bond length. Moreover, the magnitude of the
covalent bond interactions between the central metal atom and
the ipso atoms of the ligands can be envisaged from the quantum
chemistry wave function based Wiberg bond index (Tables 1–3). In
other words, the electrophilicity of the central metal atom dimin-
ishes with the decrease in charge and the nucleophilic inclination
of the ligands towards the center also drops thus, augmenting
the bond length.
3.1. DFT calculations
It is very clear from Tables 1–3 that the central silicon atom, due
to a greater positive charge (2.028), demands greater electron
density. As a result of this, shorter Si–O, Si–N and Si–Cl bonds
are observed. The DFT optimized structures of 1, 2 and 3 are given
in Figs. 1–3 respectively.
The two factors that can potentially explain the differences in
bond lengths are coordination number and charge on a metal atom.
It is well documented in the literature that an increase in ligand
coordination increases the bond lengths of Si–O and Si–N covalent
and dative bonds, which could be seen by comparing the Wiberg
index, reported in Tables 1–3 respectively. This can be further elu-
cidated in that an increase in coordination number increases the
electron density around the silicon atom, leading to a decrease in
the overlap of the metal–ligand orbitals and hence changes in
the bond lengths. On the other hand, there is an inverse trend of
charge and bond length followed by the complexes of interest.
For the same coordination number, the decrease in the NPA [20]
charge on the metal atom decreases the bond length, with a nota-
ble effect on axially directed bonds (Tables 1 and 2). This fact can
be supported by the reason that the decrease in charge on the
silicon atom leads to an expansion of the valance orbital, which
3.2. Synthesis and characterization of products
The N-triphenylphosphinimines 6 and 14 were prepared from
the corresponding phenyl-benzohydrazide (5) and triphenylphos-
phine dibromide (4) as described previously for the benzhydrazide
analogue [25]. They were then converted to the corresponding
O-trimethylsilyl derivatives (7 and 15) by the reaction with
trimethylsilyl chloride in the presence of Et
The transsilylation reaction of 7 with excess YSiX
Cl/CHCl /Cl/Br and X = Cl/Br) afforded exclusively ionic
3
N (Schemes 1 and 2).
3
(Y = Me/Ph/
CH
2
2
Ph
N
N
+
N
N
NMe2
N=PPh3
Ph
Ph
Ph
O
CMe
2
Cl
O
O
O
Cl
Si
Si
Cl
X
Si
X
O
Cl
Me
2
C
N
N
O
Ph
NMe2
N
N=PPh3
N
Ph
1
3
2
Chart 1.
Table 1
Bond lengths, NPA [20] charge distribution and Wiberg index [21] of 1.
Atoms
1-Si
2-Cl
3-Cl
5-O
6-O
7-N
18-N
NPA charge
Bond length (Å)
Wiberg index
1.819
ꢀ0.447
2.207
0.723
ꢀ0.447
2.207
0.723
ꢀ0.837
1.783
0.429
ꢀ0.837
1.783
0.429
ꢀ0.432
2.061
0.353
ꢀ0.432
2.061
0.353
Table 2
Bond lengths, NPA [20] charge distribution and Wiberg index [21] of 2.
Atoms
1-Si
4-Cl
5-Cl
6-O
7-O
8-N
9-N
NPA charge
Bond length (Å)
Wiberg index
1.779
ꢀ0.476
2.252
0.669
ꢀ0.464
2.220
0.692
ꢀ0.823
1.764
0.448
ꢀ0.823
1.764
0.448
ꢀ0.422
1.973
0.416
ꢀ0.422
1.973
0.416

2
70
P. Suman et al. / Polyhedron 99 (2015) 266–274
Fig. 1. DFT optimized structure of 1.
Fig. 3. DFT optimized structure of 3.
and 17 is further supported by the fact that they are insoluble in
toluene, whereas essentially all of the neutral hexacoordinate sili-
con compounds studied to date are soluble in this solvent, as long
as they do not ionize [27].
This interaction increases gradually in the compounds with the
more electron-withdrawing ligands, 11–13. It appears that in the
presence of electron-withdrawing ligands coordination is stronger
than in the alkyl complexes (8–10), as shown in Fig. 4. The effect of
2 2
the Y ligands (Y = Me, Ph, CH Cl, CHCl , Cl, Br and X = Cl or Br) on
2
9
31
13
the Si, P and C NMR chemical shifts is comparable with sim-
ilar reported complexes [28].
3
The chemical shifts for YSiCl were compared for the change in
the 2 Si chemical shift of the complexes caused by coordination.
The halogeno ligands attached directly to silicon (12, 13) generate
greater spin–spin interactions than the chloro- and dichloro-
methyl ligands (in 9 and 10, respectively), in which carbon, and
not halogen, is attached to silicon. It is interesting to note that
the two-bond spin–spin interactions discussed above are of the
same order of magnitude as those reported for similar interactions
through covalent P–N–Si bonds [29].
9
Fig. 2. DFT optimized structure of 2.
pentacoordinated silicon dichelate chloride (or bromide) salts,
where Y = alkyl (8–10, 16), phenyl (11, 17) or halide (12, 13), in
high yield. All these products were characterized by their H, C,
Si and P NMR spectral data. The structures of 8–13, 16 and
1
13
2
9
31
It is worth determining the 29Si NMR chemical shift because of
its immense significance in expounding the identity of silicon pos-
sessing complexes. For this purpose the vapour and solvent phase
1
7 were likewise obtained from their NMR spectral analyses and
from the obvious analogy with the literature reports [26]. It is pre-
dicted that the geometry of 8–13, 16 and 17 corresponds to a
slightly distorted trigonal bipyramid (TBP), with nitrogen atoms
occupying the axial positions.
2
9
Si NMR chemical shifts of three pentacoordinated complexes
were calculated, compared and contrasted with experimental val-
ues (Table 5). The experimentally observed chemical shift relative
to TMS varies from ꢀ77 ppm to ꢀ106 ppm, however, the computed
isotropic shifts range from ꢀ72 ppm to ꢀ84 ppm. It is obvious from
the calculated results that there is a slight increase in the values of
shielding constants in the presence of solvent. Although, the theo-
retical chemical shifts values mimic the experimental trend, a large
deviation was observed depending upon various factors. One of the
prime factors is the huge conformational flexibility and fluxionality
of the complexes of interest (8, 11 and 13). For complex 13, the
cumulative effect of conformational flexibility, fluxionality and
spin orbit effects of the heavy atom for nuclear magnetic shifts of
group 14 halides is accountable for the prevalent deviation of the
studied complexes.
Table 4 lists selected the multinuclear NMR data from the var-
2
9
ious spectra of the triphenylphosphinimino complexes. The Si
chemical shifts for the alkyl-substituted compounds (8–13, 16
and 17) are all in the range ꢀ76 to ꢀ107 ppm, and they shift grad-
ually to higher field as the ligands become more electron-with-
2
9
drawing. All of these Si chemical shifts are well within the
range of characteristic pentacoordination and hence support the
proposed ionic structures (Schemes 1 and 2).
The fact that all of these new triphenylphosphinimino com-
plexes are pentacoordinate in solution indicates that the donor
ability of the new ligand is greater than those of the previously
reported ligand systems 1 and 2. The ionic nature of 8–13, 16

P. Suman et al. / Polyhedron 99 (2015) 266–274
271
O
O
N=PPh3
NH2
Et N, CCl
R.T, 14hrs
N
H
3
4
N
H
Ph PBr
3
2
-
Et N.HBr
tBu
3
tBu
6
4
5
Me SiCl,
3
R.T, 12hrs
Et N,
3
-
Et N.HCl
Dry Ether
3
+
N
N=PPh3
tBu
tBu
YSiX3,
CHCl3
N
O
N=PPh3
X
tBu
Si
Y
O
-2Me SiX
O
SiMe3
3
N
N=PPh3
E,Z-7
8
9
1
1
1
1
, X= Cl, Y= Me
, X= Cl,Y= CH Cl
2
0, X= Cl,Y= CHCl
1, X= Cl, Y= Ph
2. X= Y = Cl
2
3, X= Y = Br
Scheme 1.
Ph
O
N
N
PPh3
MeSiCl3
Chloroform
Me Si Cl
Ph
P
N
O
3
N
Ph
SiMe3
O
Me SiCl
O
16
3
N
N
N
Ph
N
H
PPh3
Et N,
Ph
PPh3
3
Et O
2
15
Ph
1
4
N
PhSiCl3
O
N
PPh3
Ph Si Cl
Chloroform
Ph3P
N
O
N
Ph
1
7
Scheme 2.
Table 4
Significant NMR data of the complexes 8–13, 16 and 17.
Monodentate
ligand (Y)
29Si NMR (d in
ppm)
31P NMR (d in
ppm)
13C NMR (d in ppm)
(C@N)
–
6
7
8
9
1
1
1
1
1
1
1
1
(free ligand)
(O-silylated)
, Me
29.57
16.24
36.43
47.57
53.20
45.83
49.80
53.14
29.22
17.2
168.63 (C@O)
151.23
155.33
156.80
158.67
157.26
157.78
158.03
171.6
7.6
ꢀ77.07
ꢀ88.61
ꢀ94.09
ꢀ92.73
ꢀ99.02
2
, CH Cl
0, CHCl
1, Ph
2, Cl
2
3, Br
ꢀ106.24
–
4 (free ligand)
5 (O-silylated)
6, Me
17.4
ꢀ76.2
ꢀ94.3
147.3
156.4
157.6
40.6
47.3
7, Ph
Fig. 4. Effect of Y group on the 29Si NMR chemical shifts.

2
72
P. Suman et al. / Polyhedron 99 (2015) 266–274
Table 5
3.3. Ligand exchange reactions
Comparison of 29Si NMR data for selected complexes.
Complex
Experimental 29Si
NMR (d in ppm)
Calculated 29Si-NMR
(d in ppm) Gs Phase
Hypercoordinate silicon dichelates undergo two unique inter-
molecular chelate exchange reactions: (i) complete ligand transfer
8
1
1
ꢀ77.07
ꢀ92.73
ꢀ72.06
ꢀ79.28
ꢀ83.69
ꢀ74.08
3
from dichelates to trichlorosilanes (PhSiCl ) by a ligand priority
1
3
ꢀ82.90
ꢀ84.96
order and (ii) bidentate ligand interchange between dichelates
and a trimethylsilyl-hydrazide precursor. Evidence for complete
intermolecular ligand crossover among different silicon(IV) com-
plexes, further extending the flexible nature of these ligands and
understanding the degree of coordination strength, is obtained.
ꢀ106.24
3
.3.1. Complete ligand transfer from the dichelates to PhSiCl
ligand priority order
The ligand crossover reactions were monitored in chloroform
3
by a
2
9
31
solutions by Si and P NMR (wherever necessary) spectral data.
As shown in Eq. (1), addition of PhSiCl to complex 16 readily gave
a new complex (17) in chloroform solution. The data showed that
PhSiCl can easily attract the ligands from the silicon complex
where X = Me. This was confirmed by obtaining two new signals
in the Si NMR spectrum at d ꢀ12.4 and ꢀ94.3 ppm for MeSiCl
and 17 respectively (Fig. 5). Subsequently the signals due to com-
plex 16 and PhSiCl disappeared. This could be due to the fact that
3
3
2
9
3
3
the electron withdrawing Ph ring directly attached to silicon atom
demands more electrons than the Me counterpart (16). This ligand
crossover was not affected by the addition of neutral phosphine
oxide or 1,10-phenanthroline ligands.
Fig. 5. 29Si NMR spectral evidence for the formation of a new complex (17) by
complete ligand transfer from 16 on addition of PhSiCl .
3
Ph
N
Ph
N
O
N
Cl
O
PPh3
O
N
Cl
O
PPh3
+
PhSiCl3
Me Si
Ph Si
Ph3P
N
+
MeSiCl3
ð1Þ
Ph3P
N
N
N
Ph
Ph
17
1
6
Fig. 6. TGA curves of hypercoordinated silicon(IV) complexes having Si-Me (a), Si-Ph (b), Si-Cl (c) and Si–Br (d)
r-bonds.

P. Suman et al. / Polyhedron 99 (2015) 266–274
273
3
.3.2. Bidentate ligand interchange between the dichelates and the
The thermal curve of compound 11 (Fig. 6(b)) was found to be
similar to 8 within the temperature range 270–583 °C. The initial
decomposition was observed in the temperature range 270–
442 °C, due the loss of two molecules of triphenylphosphine with
a mass loss of 51.4% (calc. 50.26%). The next stage of decomposition
in the temperature range 442–583 °C was observed due to the
removal of the remaining fragments of the ligand (Table 6), with a
trimethylsilyl-hydrazide precursor
3
When the ligand with the N@PPh group (15) was added to 18,
2
containing –NMe donor groups, the formation of 17 was observed
immediately together with O-trimethylsilyl-N-(dimethylamino)
benzohydrazide. This reaction is not reversible even with a large
excess of O-trimethylsilyl-N-(triphenylphosphinimino)benzohy-
drazide. In a similar way, a noticeable exchange of two sub-
stituents involves complete removal of the bidentate chelating
ligand from 19, and its replacement by the ligand 15. This clearly
2
mass loss of 42.4% (calc. 43.98%), leaving the residue of 6.7% for SiO .
Complex 12 shows three major stages of thermal decomposi-
tion, as shown in the TG curve (Fig. 6(c)). The first stage could be
due to the removal of two Cl atoms in the temperature range
80–120 °C, with a corresponding endothermic peak shown in the
indicates the better donor ability of –N@PPh
supported by DFT calculations.
3
ligand systems, as
Ph
N
Ph
N
SiMe
3
O
O
N
PPh
SiMe
3
O
NMe2
Ph Si+ Cl
Me2N
Chloroform
3
O
+
N
N
Ph Si Cl
Ph
PPh
3
+
NMe2
Ph
3
P
N
O
Ph
N
ð2Þ
ð3Þ
O
N
N
Ph
15
Ph
1
7
18
Ph
Ph
CH
3
N
N
N
N
SiMe
3
O
SiMe3
O
CH3
Chloroform
O
PPh
3
O
Ph Si+ Cl
+
N
Ph Si+ Cl
Ph
N
PPh3
N
H
3
C
+
Ph
N
CH
3
3
N
O
Ph P
N
O
3
CH
H C
N
N
3
Ph
15
Ph
1
7
1
9
3
.4. Thermal analysis
DTA curve. The second step indicates the loss of two triph-
enylphosphine moieties in the temperature range 120–380 °C.
The third step, in the relatively high temperature range 380–
590 °C, corresponds to the thermal decomposition of the remaining
fragment of the ligand into fragments (Table 2) .Silicon dioxide was
identified as the final residue. The proposed decomposition mech-
anism is shown in Scheme 4. The results of the thermal decompo-
sition patterns of 13 (Fig. 6(d)) are similar to complex 12.
The thermal behavior of the synthesized silicon(IV) complexes
8, 11–13) at different temperatures was studied on the basis of
(
TG/DTG and DTA data. Two stage thermal decomposition processes
were observed on the TG curve for compound 8 (Fig. 6(a)). The first
step of thermal decomposition was seen in the temperature range
1
58–300 °C with the release of two triphenylphosphine molecules
in an exothermic effect, as shown in the DTA curve. The second
step of the thermal decomposition, in the temperature range
It is predicted that the TG curves of 12 and 13 reveal the loss of
the ligand (XY) in the first step, with probable formation of an
intermediate tetracoordinated silicon complex. The residual
4-(t-butyl)-N-(triphenylphosphoranylidene)benzohydrazide sili-
3
00–370 °C, was found to be due to the removal of the remaining
fragments of the ligand, as shown in Table 6. This was accompa-
nied by an endothermic effect in the DTA curve. The final residual
2
con compound decomposes finally to give SiO . Thermal stability
product of the thermal decomposition was found to be SiO
proposed mechanism for the thermal decomposition of 8 is given
2
. The
follows the order: 8 (DTA 90 °C) < 11 (DTA 130 °C) < 12 (DTA
170 °C) < 13 (DTA 400 °C). In all the cases, the final residue was
in Scheme 3.
SiO
2
and it exactly matched the powder X-ray diffraction patterns
of the literature reports.
Table 6
Thermolysis data of some selected hypercoordinate silicon(IV) complexes.
Compound
Stages of decomposition
TG temperature ranges/°C
Mass loss%
Calc.
DTA curve
DTG max/°C
Assignment
Exp.
8
First stage
Second stage
158–300
300–372
50.4
42.8
52.1
40.8
Exo
Endo
124
275
2PPh
3
2( Bu–C
t
6
H
H
5
C), N
2
, Me, Cl
,Ph, Cl
1
1
1
2
First stage
Second stage
270–442
442–583
50.2
43.9
51.4
42.4
Exo
Exo
399
473
2PPh
2( Bu–C
3
t
6
5
C), N
2
First stage
Second stage
Third stage
82–118
120–381
381–592
7.07
52.4
34.6
6.96
50.2
35.4
91
187
582
2Cl
Endo
Endo
3
2PPh ,
t
2( Bu–C
6
H
5
C), N
2
1
3
First stage
Second stage
Third stage
114–128
180–304
304–572
14.6
48.0
31.7
15.0
50.0
29.8
Endo
Endo
Endo
124
275
492
2Br
2PPh
3
t
2( Bu–C
6
C
H5 ), N
2

2
74
P. Suman et al. / Polyhedron 99 (2015) 266–274
-
2PPh3
[2] (a) J. Wagler, U. Böhme, E. Brendler, G. Roewer, Organometallics 24 (2005)
1348;
t
-
t
[
(Ph P=NN=( Bu-C H )CO-) SiMe]Cl
[-NN=( Bu-C H )CO] Si
6 5 2
3
6
5
2
°
1
58-300 C
(
(
b) D. Kost, I. Kalikhman, Adv. Organomet. Chem. 50 (2004) 1;
c) D. Kost, V. Kingston, B. Gostevskii, A. Ellern, D. Stalke, B. Walfort, I.
Kalikhman, Organometallics 21 (2002) 2293;
(d) D. Kost, B. Gostevskii, N. Kocher, D. Stalke, I. Kalikhman, Angew. Chem., Int.
Ed. 42 (2003) 1023;
t
°
-2( Bu-C H C),
6 5
-
3
00-370 C
N ,-Me, -Cl
2
(
(
e) D. Stalke, S. Deuerlein, N. Kocher, I. Kalikhman, D. Kost, Organometallics 24
2005) 2913.
[
3] J. Wagler, T. Doert, G. Roewer, Angew. Chem. Int. Ed. 43 (2004) 2441.
SiO2
[4] J. Wagler, U. Böhme, G. Roewer, Organometallics 23 (2004) 6066.
[
5] S. Sergani, I. Kalikhman, S. Yakubovich, D. Kost, Organometallics 26 (2007)
5799.
Scheme 3.
[6] S. Rendler, M. Oestreich, Synthesis 11 (2005) 1727.
[7] Y. Orito, M. Nakajima, Synthesis 9 (2006) 1391.
[8] (a) Reviews about the formation and structure of hypercoordinate silicon
compounds S.N. Tandura, M.G. Voronkov, N.V. Alekseev, Top. Curr. Chem. 131
(1986) 99;
-
2Cl
t
SiCl]Cl-
t
[(Ph
3
P=NN=( Bu-C
6
H )CO)
5
2
[Ph
3
P=NN=( Bu-C
6
H
5
)CO]
2
Si
°
8
0-120 C
(b) V.E. Shklover, Y.T. Struchov, M.G. Voronkov, Russ. Chem. Rev. 58 (1989)
2
11;
t
-
2PPh
3
-2( Bu-C
6
H
5
C), -N
2
(c) E. Lukevics, O. Pudova, R. Sturkovich (Eds.), Molecular Structure of
Organosilicon Compounds, Ellis Horwood, Chichester, 1989;
(d) R.R. Holmes, Chem. Rev. 96 (1996) 927.
t
[
-NN=( Bu-C
6
H
5
2
)CO] Si
SiO2
°
°
1
20-380 C
380-590 C
[
9] (a) A. Hosomi, Acc. Chem. Res. 21 (1988) 200;
(
4
b) G.G. Furin, O.A. Vyazankina, B.A. Gostevsky, N.S. Vyazankin, Tetrahedron
4 (1988) 2675.
10] M. Benaglia, S. Guizzetti, L. Pignataro, Coord. Chem. Rev. 252 (2008) 492.
[11] (a) H.H. Karsch, R. Richter, E. Witt, J. Organomet. Chem. 521 (1996) 185;
b) H.H. Karsch, R. Richter, E. Witt, in: N. Auner, J. Weis (Eds.), In Organosilicon
Chemistry III, Wiley-VCH, Weinheim, Germany, 1997, p. 460;
Scheme 4.
[
4
. Conclusions
Novel hypercoordinate silicon bis-chelate complexes with the
(
(
(
c) U.-H. Berlekamp, P. Jutzi, Angew. Chem. Int. Ed. 38 (1999) 2048;
d) U.-H. Berlekamp, A. Mix, B. Neumann, H.-G. Stammler, P. Jutzi, J.
phosphinimino-N ligand group have been prepared and character-
ized by multinuclear NMR spectroscopy. The phosphinimino-N
ligand group is found to be superior in terms of strength of coordi-
nation to silicon through the formation of pentacoordinate silicon
Organomet. Chem. 667 (2003) 167;
e) G. Muller, M. Waldkircher, A. Pape, in: N. Auner, J. Weis (Eds.), In
(
Organosilicon Chemistry III, Wiley-VCH, Weinheim, Germany, 1997, p. 452.
12] C.C. Walker, H. Shechter, J. Am. Chem. Soc. 90 (1968) 5626.
[
(
IV) complexes relative to previously reported dimethylamino-
[13] G.B. Merrill, H. Shechter, Tetrahedron Lett. (1975) 4527.
[
14] (a) D. Kost, I. Kalikhman, M. Raban, J. Am. Chem. Soc. 117 (1995) 11512;
b) V. Kingston, B. Gostevskii, I. Kalikhman, D. Kost, Chem. Commun. (2001)
272;
and isopropylideneimino-coordinated analogous complexes. This
superiority was further confirmed by ligand crossover reactions.
The optimized DFT structures of some selected complexes closely
agree with the experimental results through the bond lengths
and bond angles of the respective silicon(IV) complexes. On ther-
molysis, the hypercoordinate silicon(IV) complexes containing a
(
1
(c) D. Kost, B. Gostevskii, N. Kocher, D. Stalke, I. Kalikhman, Angew. Chem. Int.
Ed. 40 (2003) 1023;
(
d) B. Gostevskii, K. Adear, A. Sivaramakrishna, G. Silbert, D. Stalke, N. Kocher,
I. Kalikhman, D. Kost, Chem. Commun. (2004) 1644;
(e) Janardan, P. Suman, K. Vijayakrishna, A. Sivaramakrishna, Synthesis and
Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, (2015) (in
press).;
silicon–carbon
sition, while the other complexes with silicon–halogen
r
-bond significantly undergo a two step decompo-
-bonds
r
(
f) I. Kalikhman, B. Gostevskii, A. Sivaramakrishna, D. Kost, N. Kocher, D.
follow three steps. This clearly indicates the thermal decomposi-
tion strongly depends on the nature of the substituents directly
attached to the central silicon atom. The controlled thermolysis
of these complexes may give unusual transformations, leading to
the preparation of novel silicon materials depending on the nature
of ligand systems which are otherwise difficult to make. We are
currently working on the bond making and bond breaking transfor-
mations of hypercoordinate silicon complexes.
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Acknowledgments
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Appendix A. Supplementary data
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