Studies on electrochemical and coordination behaviour of phosphiniminocyclotrithiazenes

Article abstract of DOI:10.1139/v02-140

Electrochemical (polarographic, cyclic voltammetric, and coulometric) and coordination behaviour of several symmetrically and unsymmetrically substituted phosphiniminocyclotrithiazenes have been studied. Polarograms of R₃PN-S₃N₃ R = C₆H₅, p-ClC₆H₄, p-H₃CC₆H₄, and (OC₄H₈N)), Ph₂OC₄H₈N)PN-S₃N₃, and Ph(OC₄H₈N)₂PN-S₃N₃ give two cathodic waves. Cyclic voltammograms of Ph₃PN-S₃N₃ (1) and (OC₄H₈N)₃PN-S₃N₃ (2) reveal nearly the same oxidation peak potential but different reduction potentials. Controlled potential electrolysis of 1 and 2 at +0.6 V indicates exocyclic cleavage and ring degradation. Cathodic reduction behaviour of Ph₃PN-S₃N₃ suggests the possibility for the) formation of 1,5-(Ph)₃(PN)₂S₄N₄ under electrochemical conditions. Reaction of nickel chloride hexahydrate with heterocycle 1 in 1:2 molar ratio in acetonitrile affords the complex, ([NiS₂N₂H₂] (A) (90% yield) and [Ph₃PNH₂]Cl salt as products. Analogous reactions with other ligands of this type (two symmetrical (sym.) and three unsymmetrical (unsym.)) except 2 also give A, while ligand 2 reacts with anhyd NiCl₂ in an equimolar ratio to afford a dark green, square-planar complex ((OC₄H₈N)₃(PN-S₃(N·NiCl ₂ (B)) whose ESCA results assist in providing its coordination details. The study reveals a high tendency of these heterocycles to different types of ring cleavage.

Full text of DOI:10.1139/v02-140

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1428
Studies on electrochemical and coordination
behaviour of phosphiniminocyclotrithiazenes
U. Swarnalatha, A. Sivaramakrishna, C.S. Venkatachalam, M.N. Sudheendra Rao,
Tomonori Inoue, Tadaharu Ueda, and Masashi Hojo
Abstract: Electrochemical (polarographic, cyclic voltammetric, and coulometric) and coordination behaviour of several
symmetrically and unsymmetrically substituted phosphiniminocyclotrithiazenes have been studied. Polarograms of
R3PN-S3N3 (R = C6H5, p-ClC6H4, p-H3CC6H4, and (OC4H8N)), Ph2(OC4H8N)PN-S3N3, and Ph(OC4H8N)2PN-S3N3 give
two cathodic waves. Cyclic voltammograms of Ph3PN-S3N3 (1) and (OC4H8N)3PN-S3N3 (2) reveal nearly the same oxi-
dation peak potential but different reduction potentials. Controlled potential electrolysis of 1 and 2 at +0.6 V indicates
exocyclic cleavage and ring degradation. Cathodic reduction behaviour of Ph3PN-S3N3 suggests the possibility for the
formation of 1,5-(Ph3PN)2S4N4 under electrochemical conditions. Reaction of nickel chloride hexahydrate with
heterocycle 1 in 1:2 molar ratio in acetonitrile affords the complex, [Ni(S2N2H)2] (A) (90% yield) and [Ph3PNH2]Cl
salt as products. Analogous reactions with other ligands of this type (two symmetrical (sym.) and three unsymmetrical
(unsym.)) except 2 also give A, while ligand 2 reacts with anhyd NiCl2 in an equimolar ratio to afford a dark green,
square-planar complex ((OC4H8N)3PN-S3N·NiCl2 (B)) whose ESCA results assist in providing its coordination details.
The study reveals a high tendency of these heterocycles to different types of ring cleavage.
Key words: phosphiniminocyclotrithiazenes, polarography and cyclic voltammetry, substituent effect, nickel complexes,
ESCA.
Résumé : On a étudié le comportement électrochimique (polarographique, voltampérométrie cyclique et coulométrique)
et de coordination de plusieurs phosphiniminocyclotrithiazènes substitués de façon symétrique et asymétrique. Les
polarogrammes des R3PN-S3N3 (R = C6H5, p-ClC6H4, p-H3CC6H4, OC4H8N) Ph2(OC4H8N)PN-S3N3 et Ph(OC4H8N)2PN-
S3N3 présentent deux vagues cathodiques. Les voltampérogrammes cycliques du Ph3PN-S3N3 (1) et (OC4H8N)3PN-S3N3
(2) présentent des potentiels d’oxydation maxima qui sont pratiquement les mêmes, mais les potentiels de réduction
sont différents. Une électrolyse du composé 1 à potentiel contrôlé, à 0,6 V, indique la présence de clivage exocyclique
et de dégradation de cycle. Le comportement du Ph3PN-S3N3 lors de la réduction cathodique suggère la possibilité de
formation du 1,5-(Ph3PN)2S4N4 dans les conditions électrochimiques. La réaction du chlorure de nickel hexahydraté
avec l’hétérocycle 1, dans un rapport molaire de 2:1 dans l’acétonitrile, conduit à la formation du complexe
[Ni(S2N2H)2] (A) (rendement de 90 %) et du [Ph3PNH2]Cl. Des réactions analogues (excepté celles avec le produit 2)
avec d’autres ligands de ce type (deux symétriques et trois non symétriques) conduisent aussi au produit à A. Le
composé 2 réagit avec le NiCl2 anhydre, dans un rapport moléculaire de 1:1, pour fournir un complexe plan carré, vert,
(OC4H8N)3PN-S3N·NiCl2 (B) dont les résultats de spectroscopie d’électrons pour analyse chimique (« ESCA »)
fournissent des détails relatifs à sa coordination. Cette étude révèle la grande tendance de ces hétérocycles à donner
lieu à des types différents de clivage de cycle.
Mots clés : phosphiniminocyclotrithiazènes, polarographie, voltampérométrie cyclique, effet de substituant, complexes
de nickel, ESCA.
[Traduit par la Rédaction] Swarnalatha et al. 1434
Introduction
the last couple of decades. Electrochemical studies have
helped in providing insight of chemical reactions and served
also as a preparative method for both known and new com-
pounds (3–9). Likewise, coordination studies have lead to
A variety of inorganic ring systems (1–2) have been the
subject of both coordination and electrochemical studies in
Received 14 February 2002. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 18 October 2002.
Dedicated to Professor Tristram Chivers for his contributions to Canadian chemistry.
U. Swarnalatha, A. Sivaramakrishna, C.S. Venkatachalam, and M.N.S. Rao.1,2 Department of Chemistry, Indian Institute of
Technology Madras, Chennai-600 036, India.
T. Inoue, T. Ueda, and M. Hojo.3 Department of Chemistry, Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520,
Japan.
1Corresponding author (e-mail: mns_rao@yahoo.com).
2Present address: Department of Chemistry, Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan.
3Corresponding author (e-mail: mhojo@cc.kochi-u.ac.jp).
Can. J. Chem. 80: 1428–1434 (2002)
DOI: 10.1139/V02-140
© 2002 NRC Canada

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Swarnalatha et al.
1429
realizing many interesting results and novel complexes of
transition metals (10–14).
clic voltammograms were recorded at 25 0.1°C with a mi-
crocomputer-controlled system at a scan rate of 100 mV s–1.
Glassy carbon electrode (Tokai Carbon GC-30S), freshly
polished with a 0.1 m diamond slurry was used as the
working electrode and a platinum wire served as the counter
electrode. Ag/AgNO3 (0.01 mol dm–3 in MeCN) was the ref-
erence electrode. Coulometric experiments were performed
on a GC fiber electrode using a potentiostat (Hokuto Denko
HA-151). Dichloromethane (Wako GR grade) was used as
the solvent. The electrolysis was followed by 31P NMR
spectroscopy using a JEOL JNM-LA400 instrument and (or)
Phosphiniminocyclotrithiazenes, R3PN-S3N3 are a class of
electron-rich inorganic heterocycles (15, 16) having a
phosphinimino moiety as the exocyclic substituent and have
served as stable derivatives of monosubstituted cyclotri-
thiazenes (-S3N3) (17–18). Ph3PN-S3N3, the first example in
this class (8 ꢀ system) to be reported in 1961 was subse-
quently obtained in an improved yield from a detailed rein-
vestigation study by Chivers and co-workers (19). Some of
its reactivity aspects have also been demonstrated (20–22).
Oakley and co-workers (20) have shown the usefulness of
the redox potential data in rationalizing its electronic absorp-
tion and some reactivity features. In an extension of this
work, we have prepared a variety of R3PN-S3N3 heterocycles
and studied their structural and reactivity aspects and have
obtained many interesting results (23–26). In addition to the
noticeable structural differences (27, 28), we have observed
substituent-dependent pyrolytic behaviour of these
heterocycles (29). We believe that the presence of a rela-
tively bulky phosphinimino moiety as an exocyclic part of
the S3N3 ring skeleton and the possibility of substituent vari-
ation on phosphorus render them as interesting examples for
further studies. Sometime ago, we observed the tendency of
these heterocyclic systems to nucleophilic attack by ammo-
nia, amines (30), and phosphines (31, 32) and recently to ox-
idative cleavage by mild oxidants such as iodine (33).4 The
results suggested the preferential cleavage of the trithiazene
ring skeleton over that of exocyclic substituent. These obser-
vations prompted us to undertake this study to probe the co-
ordination and electrochemical behaviour of R3PN-S3N3
ring systems for the first time. In this paper, we report
polarographic, cyclic voltammetric, and bulk electrolysis
studies as well as coordination behaviour with nickel chlo-
ride of many examples of symmetrically and unsymmetri-
cally substituted phosphiniminocyclotrithiazenes.
electronic spectroscopy using
photometer (Hitachi U-2000).
a double-beam spectro-
(a) Reaction of Ph3PN-S3N3 (1) with NiCl2·6H2O in
CH3CN (2:1)
To a stirred slurry of NiCl2·6H2O (0.40 g, 1.67 mmol) in
acetonitrile (25 mL), the red heterocyclic ligand 1 (1.39 g,
3.36 mmol) was added in batches over a 15 min interval at
room temperature. The colour of the solution changed grad-
ually to dark purple. After 20 h, it was filtered to isolate an
off-white precipitate (0.26 g) and a dark purple filtrate. The
CH3CN extract of the precipitate (4 × 3 mL) when cooled
gave a small amount of [Ph3PNH2]Cl (40 mg), mp 228 to
229°C (lit. (38) value mp 230–232°C). Its IR and 31P NMR
chemical shift agreed well with an authentic sample (38).
The acetonitrile insoluble residue (0.20 g) was metal free
(chemical test for Ni was negative) and found to be water
soluble.
The purple filtrate upon cooling for 36 h in the refrigera-
tor gave [Ph3PNH2]Cl (0.86 g). The residual mother liquor
was concentrated and cooled in the deep freezer for a day to
isolate purple crystals of [Ni(S2N2H)2] (A) (0.37 g, 90%),
mp 155 to 156°C (lit. (39) value mp 156–158°C). Its nickel
content, IR, and UV–Vis spectral data (552 nm (2.1 × 103);
399 nm (4.7 × 103); 305 nm (11.4 × 103)) agreed well with
the literature data (39).
Experimental
(b) Reaction of Ph3PN-S3N3 (1) with NiCl2 in CH3CN
(2:1)
All handling and manipulation of air-sensitive compounds
were done in a nitrogen or argon atmosphere. Solvents were
purified using standard procedures (34). NiCl2·6H2O,
NiSO4·7H2O, and NiI2 (s.d. Fine Chemicals), and Ph3P (Fluka)
were used as received. Anhydrous NiCl2 was prepared by
the literature method (35). S4N4 (caution: explosion sensi-
tive!) (36), (OC4H8N)3P (37), and different R3PN-S3N3 de-
rivatives employed in this study were synthesized by the
reported methods (19, 23, 26, 37). Various spectral and ana-
lytical facilities used for characterization have been pub-
lished elsewhere (26). Magnetic measurements were done in
a vibrating sample magnetometer (EG & G PARC VSM-
155) with 2 mg of the sample. Conductivity measurements
were done using a conductometer (Toshniwal CL01/02A)
with a glass electrode (cell constant: 1.2708 cm–1) on 1 mM
solution of the sample in CH3CN. ESCA measurements
were made using a VG ESCA LAB MK II X-ray photoelec-
tron spectrometer.
Anhydrous nickel chloride (0.10 g, 0.77 mmol) was added
in small amounts over a 15 min interval to a stirred slurry of
ligand 1 (0.64 g, 1.55 mmol) in CH3CN (25 mL) at room
temperature. The observations were same as in reaction (a).
After 16 h, it was worked up as in reaction (a) to isolate an
off-white crystalline material ([Ph3PNH2]Cl (0.23 g)) fol-
lowed by the purple crystals of [Ni(S2N2H)2] (80 mg, 42%).
An yellowish white insoluble residue (0.13 g) was also ob-
tained from the precipitate part of the reaction.
(c) Reaction of anhyd NiCl2 with Ph3P and S4N4 in
CH3CN
To a stirred solution of Ph3P (1.44 g, 5.50 mmol) in
CH3CN (25 mL) at room temperature, S4N4 (0.50 g,
2.72 mmol) was added as a solid in small amounts over a
20 min interval. When the reaction mixture had turned dark
red in colour (ca. 2 h), anhyd NiCl2 (0.18 g, 1.39 mmol) was
added in aliquots over a 15 min interval and stirred for 20 h.
The reaction mixture was filtered to obtain a dark purple
Direct-current polarograms were measured on a dropping
mercury electrode (DME) using a Yanagimoto polarograph
(P-1000) and a Graphtec X-Y recorder (WX-4410-L0). Cy-
4 A. Sivaramakrishna, B. Varghese, and M.N.S. Rao. Unpublished results.
© 2002 NRC Canada

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1430
Can. J. Chem. Vol. 80, 2002
Table 1. Reactions of R3PN-S3N3 heterocycles with nickel salts.a
Nickel salt
(g)
R3PNS3N3 ligands
Product isolatedb
(mmol)
2.31
(g)
(mmol)
Mol ratio
1:1
(g)
(%)
NiCl2
0.30
(1) 0.96
2.32
1.06
2.13
0.72
1.45
1.63
1.94
1.39
1.16
1.54
A
C
A
C
A
C
A
D
A
Ed
A
F
0.15
0.50
0.11
0.27
0.14
0.43
0.06
0.22
0.15
0.36
0.12
0.31
0.20
0.20
0.15
—
27
34
43
41
54
65
35
39
86
77
30
29
42
27
44
NiCl2·6H2O
NiCl2·6H2O
NiI2
0.25
0.25
0.22
0.20
0.21
0.25
0.18
0.15
0.20
1.05
1.05
0.70
0.71
1.62
1.93
1.39
1.16
1.54
(1) 0.44
(1) 0.88
(1) 0.30
(1) 0.60
(5) 0.71
(6) 0.93
(7) 0.59
(8) 0.50
(9) 0.66
1:1
1:2c
1:1
1:2
1:1
1:1
1:1
1:1
1:1
NiSO4·7H2O
NiCl2
NiCl2
A
Gd
NiCl2
A
e
NiCl2
A
0.12
—
0.12
—
42
32
e
NiCl2
A
e
Note: A = Ni(S2N2H)2; C = [Ph3PNH2]Cl; D = [Ph3PNH2]I; (40); E = [Ph3PNH2]2SO4; F = [(C5H10N)3PNH2]Cl (mp 147–150°C); 31P NMR: singlet at
36.0 ppm, gave satisfactory CHN analysis; G = [(H3C-NC4H8N)3PNH2]Cl.
aAll reactions were done in CH3CN at room temperature for ca. 18 h by adding the ligand to a stirred slurry of the nickel salt.
bIn all the reactions, an off-white insoluble residue was obtained in varying amounts. The ionic nature of this water soluble residue was revealed by its
broad IR absorptions in the ꢂNH and ꢂSO regions at 3345 and 1095 cm–1, respectively. It is possibly an ammonium salt of the SxOy anion.
cThis reaction was done by the addition of five drops of water.
dImpure samples, 31P NMR spectra showed strong singlets at 35.1 (E) and 35.6 ppm (G).
eNot isolated, 31P NMR spectrum showed a strong singlet at 41.1, 40.6, and 42.0 ppm for the purple coloured reaction mixtures of 7, 8, and 9,
respectively.
filtrate and a pale yellow precipitate which when worked up
as in reaction (a) gave [Ph3PNH2]Cl (0.10 g) and a residue
(0.11 g). The oily mass left after removal of the solvent
from the purple filtrate was chromatographed over a silica
gel column using benzene (caution: carcinogen!!) followed
by benzene–dichloromethane (1:1) eluants to isolate Ph3PS
(0.40 g), [Ph3PNH2]Cl (0.38 g), and [Ni(S2N2H)2] (0.20 g,
61%).
(N1s), 536.5 (O1s), 858.5 (Ni2p). Elemental anal. calcd. for
C12H24N5O3PS3NiCl2 (%): C 26.54, H 4.46, N 12.90, Cl
13.08, Ni 10.83; found: C 26.49, H 4.41, N 12.51, Cl 12.93,
Ni 10.73 (leaving behind a white insoluble residue (60 mg)).
A further quantity of B (0.12 g, 25%) was obtained when the
concentrated purple filtrate was cooled in the freezer for a day.
(e) Reaction of (OC4H8N)3PN-S3N3 (2) with NiCl2·6H2O
in CH3CN (1:1)
Nickel chloride hexahydrate (0.20 g, 0.84 mmol) stirred in
CH3CN (25 mL) at room temperature was added the ligand
2 (0.37 g, 0.84 mmol) in small amounts over a 15 min inter-
val. The reaction mixture, which turned gradually to dark
purple along with the formation of a green precipitate, was
filtered after 18 h. The acetonitrile extract (3 × 10 mL) of
the precipitate when cooled in the freezer for a day yielded a
lustrous dark-green solid B (0.13 g, 38%). The purple filtrate
was concentrated and cooled in the freezer to obtain a fur-
ther quantity of B (50 mg, 14%).
(d) Reaction of (OC4H8N)3PN-S3N3 (2) with anhyd
NiCl2 in CH3CN (1:1)
To a stirred slurry of anhyd NiCl2 (0.15 g, 1.16 mmol) in
acetonitrile (25 mL), was added the red ligand 2 (0.53 g,
1.20 mmol) as a solid in small amounts over a 15 min inter-
val at room temperature. The colour of the solution gradu-
ally changed to purple along with the formation of a green
precipitate. After 20 h, the green precipitate (0.32 g) was
separated by a filtration and extracted with CH3CN (8 ×
3 mL). This extract, on cooling in the refrigerator for 10 h,
gave a lustrous dark-green solid (0.22 g, 46%) which was
identified as (OC4H8N)3PNS3N·NiCl2 (B), mp 184–186°C.
IR (Nujol, cm–1): 1443 (m), 1344 (m), 1293 (w), 1251 (m),
1152 (s), 1126 (s), 1104 (vs), 1018 (s), 1014 (m), 960 (vs),
880 (w), 835 (w), 700 (vs), 662 (w), and 595 (w). UV–vis
(nm, L mol–1 cm–1): 580 (9.1 × 103), 420 (4.1 × 103), 300
(f) Reaction of anhyd NiCl2 with (OC4H8N)3P and S4N4
in CH3CN (1:1)
To a stirred solution of (OC4H8N)3P (1.05 g, 3.63 mmol)
in CH3CN (25 mL), S4N4 (0.33 g, 1.79 mmol) was added at
room temperature over a 20 min interval. When the reaction
mixture became dark red (ca. 2 h), anhyd NiCl2 (0.23 g,
1.77 mmol) was added in aliquots over a 15 min interval and
stirred for 15 h. The reaction mixture was then filtered to get
1
(1.9 × 103). H NMR ꢁ (ppm): 3.12 (m, 12H) and 3.60 (m,
12H). 31P NMR ꢁ (ppm): 33.7 (s,1P). XPE (B.E. in eV):
141.0 (P2p), 170.5 (S2p), 205.0 (Cl2p), 292.5 (C1s), 405.5
© 2002 NRC Canada

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Swarnalatha et al.
1431
Table 2. The cathodic half-wave potentials (E1/2) and the 31P
NMR chemical shifts of R3PN-S3N3 heterocycles and 1,5-
(Ph3PN)2S4N4.
Fig. 2. The polarograms of: (a) 0.5 mmol dm–3 Ph3PN-S3N3, and
(b) 0.5 mmol dm–3 1,5-(Ph3PN)2S4N4 in dichloromethane con-
taining 0.1 mol dm–3 n-Bu4NClO4.
31P NMR
chemical shift
E1/2 (V) vs. Ag/Ag+
Compound
Ph3PNS3N3
(4-ClC6H4)3PNS3N3
(4-MeC6H4)3PNS3N3
Ph2(OC4H8N)PNS3N3 –1.57
Ph(OC4H8N)2PNS3N3 ꢃ0.88
–1.59
–1.54
–1.58
–1.97
–1.90
–1.94
–1.94
–1.58
–2.07
–1.99
24.8
23.4
23.1
31.2
30.9
23.1
18.1 and 23.6
(OC4H8N)3PNS3N3
1,5-[Ph3PN]2S4N4
–1.62
–1.56
Fig. 1. Phosphiniminocyclotrithiazenes ((R)(R>)(R>>)PN-S3N3)
considered in this study.
The p-chlorophenyl derivative had the lowest value while
the morpholino derivative had the greatest. Unsymmetrical
ones showed very different E1/2 values to each other. Also,
no smooth trend in the E1/2 values was observed in the series
(C6H5)x(OC4H8N)3–xPN-S3N3 (x = 0, 1, 2, 3). Similar irregu-
larities have been observed in 31P NMR chemical shifts of
several unsymmetrically substituted tri-coordinate phospho-
rus(III) and tetra-coordinate phosphorus(V) compounds con-
taining amino substituents (42), which seem to suggest that
the unsymmetrical environment around phosphorus has a
more pronounced effect than the additive effects of the sub-
stituents attached (Table 2).
a green precipitate and dark purple filtrate. The CH3CN ex-
tract (6 × 5 mL) of the precipitate when cooled in the freezer
for a day gave the lustrous dark-green solid B (0.23 g, 31%).
A further quantity of B (0.12 g, 17%) was recovered from
the purple filtrate from which
a
slightly impure
(OC4H8N)3PS (0.38 g) was also isolated in two subsequent
crops.
All other reactions performed in this study are summa-
rized in Table 1.
Results and discussion
An interesting observation made in this study is that the
polarographic reduction of 1 at –1.6 V produced a reduction
wave at ca. –2.0 V that corresponded with the reduction
wave of 1,5-(Ph3PN)2S4N4 (–1.99 V) thereby suggesting the
possibility of the conversion of 1 to 1,5-(Ph3PN)2S4N4 under
electrochemical reduction. Such a ring conversion occurring
under the influence of a nucleophile has been previously ob-
served (23, 30, 32). Conceivably, the dimerization of
“Ph3PN-S2N2” arising from the cleavage of Ph3PN-S3N3
leads to the formation of this eight-membered heterocycle
(eqs. [1] and [2]).
The reported reactions of phosphiniminocyclotrithiazenes
include: (i) adduct formation (20, 37); (ii) thermolysis (21,
23); (iii) substituent exchange (22); (iv) ring conversions
(23); and (v) chemical and hydrolytic degradation (41). We
have now studied the first electrochemical and coordination
behaviour of several such heterocyclic systems carrying dif-
ferent substituents on phosphorus (Fig. 1) and the results are
described here.
Electrochemical behaviour
A polarographic investigation was carried out on R3PN-
S3N3 (R = phenyl (1), morpholino (2), p-chlorophenyl (3),
and p-tolyl (4)) (symmetrically substituted) and
Ph2(OC4H8N)PN-S3N3 (7) and Ph(OC4H8N)2PN-S3N3 (8)
(unsymmetrically substituted) to evaluate substituent effects
on redox potentials, if any, in this class of heterocycles. All
of them were found to give two cathodic waves (Fig. 2) with
significantly differing E1/2 values. A comparison (Table 2)
reveals that among the symmetrical ones, E1/2 for first and
second waves vary over a 80 to 170 mV range, respectively.
–•
[1]
Ph3PN-S3N3 + e– J Ph3PN-S3N3
J Ph3PN-S2N2 + NS•
[2]
2Ph3PN-S2N2 J 1,5-(Ph3PN)2S4N4
The fragment NS• possibly gets converted to S4N4.
Chivers and Hojo (4) have observed a similar dimerization
of “Ph2CNSNSO” under electrochemical reduction. The
polarograms of R3PNS3N3 in acetonitrile containing
© 2002 NRC Canada