Novel binuclear copper(I) complexes with unusual azide and thiocyanate bridges. Crystal structures of [Cu2(μ-Ph2Ppypz)2(μ-1,1-N 3)]-[ClO4]·Et2O and [Cu2(μ-Ph2Ppypz)2(μ-1,1-SCN)][ClO 4] [Ph2Ppypz = 2-(diphenylphosphino)-6-(pyrazol-1-yl)pyridine]

Article abstract of DOI:10.1039/a706986c

The first binuclear copper(I) complex with a μ-1,1-N₃ bridge, [Cu₂(μ-Ph₂Ppypz)₂(μ-1,1-N ₃)][ClO₄]·Et₂O and [Cu₂(μ-Ph₂-Ppypz)₂(μ-1,1-SCN)][ClO ₄][Ph₂Ppypz = 2-(diphenylphosphino)-6-(pyrazol-1-yl)pyridine], which exhibits an unusual thiocyanate (μ-1,1-SCN) bridge, have been synthesised and characterised.

Full text of DOI:10.1039/a706986c

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Novel binuclear copper(I) complexes with unusual azide and thiocyanate
bridges. Crystal structures of [Cu2(ì-Ph2Ppypz)2(ì-1,1-N3)]-
[ClO4]ؒEt2O and [Cu2(ì-Ph2Ppypz)2(ì-1,1-SCN)][ClO4]
[Ph2Ppypz ؍ 2-(diphenylphosphino)-6-(pyrazol-1-yl)pyridine]
Shan-Ming Kuang,a Zheng-Zhi Zhang,*,b Qi-Guang Wanga and Thomas C. W. Mak*,†,a
a The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
b Elemento-Organic Chemistry Laboratory, Nankai University, Tianjin, China
and LiBun), with 2,6-dichloropyridine at low temperature
The first binuclear copper() complex with a µ-1,1-N3 bridge,
[Cu2(µ-Ph2Ppypz)2(µ-1,1-N3)][ClO4]ؒEt2O and [Cu2(µ-Ph2-
Ppypz)2(µ-1,1-SCN)] [ClO4] [Ph2Ppypz = 2-(diphenylphos-
phino)-6-(pyrazol-1-yl)pyridine], which exhibits an unusual
thiocyanate (µ-1,1-SCN) bridge, have been synthesised and
characterised.
yielded the mono-substituted product 2-diphenylphosphino-
6-chloropyridine, which in turn reacted with potassium
pyrazolate to give Ph2Ppypz. Reaction of Ph2Ppypz with 1
equivalent of [Cu(MeCN)4][ClO4] resulted in the formation of
[Cu2(µ-Ph2Ppypz)2(MeCN)2][ClO4]2,6 which reacted with NaN3
or KSCN in MeCN at room temperature to afford [Cu2-
(µ-Ph2Ppypz)2(µ-1,1-N3)][ClO4] 1 or [Cu2(µ-Ph2Ppypz)2(µ-1,1-
SCN)][ClO4] 2 in high yield.‡ Subsequent diffusion of Et2O into
their MeCN solutions gave crystals of 1ؒEt2O or 2 suitable for
X-ray crystallography.§
The IR spectrum of [Cu2(µ-Ph2Ppypz)2(µ-1,1-N3)][ClO4]ؒ
Et2O shows the characteristic asymmetric N3 stretching vibra-
tion at 2037 cmϪ1, which is in good agreement with the exist-
ence of the end-on bonded azide group, but a little lower than
that (about 2070 cmϪ1) of binuclear copper() complexes with
a (µ-1,1-N3) bridge.2c,d,7–9 The IR spectrum of [Cu2(µ-Ph2-
Ppypz)2(µ-1,1-SCN)][ClO4] shows the symmetric SCN stretch-
ing vibrations at 2091 (mainly CN) and 693 cmϪ1 (mainly CS),
which are comparable to those (2105 and 700 cmϪ1) of the
complex [Cu2L(µ-1,1-SCN)2] (L = macrocyclic Schiff base).5
The 31P-{1H} NMR spectra of 1ؒEt2O and 2 show a singlet at
δ 18.51 and 20.57, respectively.
The molecular structure of the cation [Cu2(µ-Ph2Ppypz)2-
(µ-1,1-N3)]ϩ in 1ؒEt2O is depicted in Fig. 1. The two copper()
centres are bridged by two Ph2Ppypz ligands and a disordered
µ-1,1-azide§ (see legend to Fig. 1). The geometry at each copper
centre is highly distorted but, despite the large N(6)᎐Cu(1)᎐P(1)
and N(3)᎐Cu(2)᎐P(2) angles of 130.4(1) and 139.9(1)Њ, better
described as a distorted square pyramid with the azide bridge
in the axial position, rather than as a trigonal bipyramid. The
Cu(1)᎐Cu(2) distance of 2.773(1) Å is significantly shorter than
The pseudo-halides N3Ϫ and NCSϪ are known to co-ordinate to
metals in both the terminal and bridging modes. As bridging
ligands, they can link a pair of metal centres in either an end-on
(µ-1,1) or a side-on (µ-1,3) bonded fashion (see below).
N
N
N
N
C
S
M
M
M
M
µ-1,3-N3
µ-1,3-NCS
N
N
N
S
C
N
N
C
S
M
M
M
M
M
M
µ-1,1-N3
µ-1,1-NCS
µ-1,1-SCN
Binuclear copper azide systems are of considerable interest
due to the broad range of their structural and magnetic proper-
ties, and they have been widely explored as structural models
for copper-containing enzymes involved in the reversible bind-
ing and activation of dioxygen, e.g. hemocyanin.1 However, the
vast majority of studies have focused on binuclear copper()
azide complexes.2 On the other hand, reports on binuclear
copper() complexes are scarce and only one structure, namely
that of [(Ph3P)2Cu(µ-1,3-N3)Cu(PPh3)2] which exhibits a µ-1,3-
N3 bridge,3 has been established. To our knowledge, there is as
yet no known example of a binuclear copper() with a µ-1,1-N3
bridge. We report here the first structure of this kind in the
binuclear copper() complex [Cu2(µ-Ph2Ppypz)2(µ-1,1-N3)]-
[ClO4]ؒEt2O [Ph2Ppypz = 2-(diphenylphosphino)-6-(pyrazol-1-
yl)pyridine].
Analogous binuclear copper thiocyanate complexes usually
exhibit the µ-1,3-NCS co-ordination mode.4 Only one binuclear
copper() compound with the µ-1,1-SCN co-ordination mode,
namely [Cu2L(µ-1,1-SCN)2] (L = macrocyclic Schiff base),5 has
been structurally characterised. Herein we describe a second
example of this type in the binuclear copper() complex [Cu2-
(µ-Ph2Ppypz)2(µ-1,1-SCN)][ClO4].
‡ Preparation of [Cu2(µ-Ph2Ppypz)2(µ-1,1-N3)][ClO4]ؒEt2O and [Cu2-
(µ-Ph2Ppypz)2(µ-1,1-SCN)][ClO4]. Solid NaN3 or KSCN (0.30 mmol)
was added to a solution of [Cu2(µ-Ph2Ppypz)2(MeCN)2][ClO4]2 (0.32 g,
0.30 mmol) in MeCN (20 mL), and the mixture was stirred at room
temperature for 48 h. Filtration followed by vapour diffusion of Et2O
into their concentrated solutions afforded yellow crystals. Complex
1ؒEt2O (0.25 g, 83%): IR (KBr disc) ν(N3) 2037 cmϪ1; 1H NMR δ 8.63
(d, J = 0.6, 2 H), 8.23 (m, 4 H), 7.34 (m, 20 H), 7.02 (m, 4 H), 6.63 (t,
J = 0.6), 3.45 (t, J = 0.4, 2 H), 1.21 (t, J = 0.4 Hz, 3 H); 31P-{1H} NMR δ
18.51. Complex 2: (0.23 g, 72%): IR (KBr disc) ν(SCN) 2091, 693 cmϪ1
;
1H NMR δ 8.58 (d, J = 0.5, 2 H), 8.17 (m, 4 H), 7.31 (m, 20 H), 7.07
(m, 4 H), 6.55 (t, J = 0.5 Hz); 31P-{1H} NMR δ 20.57.
§ Crystal data. [Cu2(µ-Ph2Ppypz)2(µ-1,1-N3)][ClO4]ؒEt2O, C40H32Cl-
Cu2N9O4P2ؒEt2O, M = 1001.34, monoclinic, space group P2/c (no. 13),
a = 25.124(2), b = 12.824(1), c = 14.796(1) Å, β = 104.62(10)Њ, Z = 4,
µ(Mo-Kα) = 1.104 mmϪ1; 6526 observed data [|Fo| > 4σ(Fo)] out of
᎐
7305 unique reflections converged to RF ᎐᎐ Σ(|Fo| Ϫ |Fc|)/Σ|Fo| = 0.064
¹
2
2
2
᎐
and RwF ᎐ {[Σw(|Fo| Ϫ |Fc|) ]/[Σw|Fo| ]}² = 0.079.
᎐
We have recently prepared a new tridentate phosphine ligand,
2-(diphenylphosphino)-6-(pyrazol-1-yl)pyridine (Ph2Ppypz) in
two steps.6 Reaction of Ph2PLi (generated in situ from Ph2PH
[Cu2(µ-Ph2Ppypz)2(µ-1,1-SCN)][ClO4], C41H32ClCu2N7O4P2S, M =
¯
943.30, triclinic, space group P1 (no. 2), a = 10.919(2), b = 13.535(3),
c = 14.882(3) Å, α = 71.86(3), β = 83.06(3), γ = 87.94(3)Њ, Z = 2, µ(Mo-
Kα) = 1.267 mmϪ1; 5604 observed data out of 6269 unique reflections
converged to RF = 0.054 and RwF2 = 0.060. CCDC reference number
186/778.
† E-Mail: tcwmak@cuhk.edu.hk
J. Chem. Soc., Dalton Trans., 1997, Pages 4477–4478
4477

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those of binuclear copper() complexes with µ-1,1-azide
bridges, which are usually over 3.0 Å.2,7–9 Since the Cu ؒ ؒ ؒ Cu
distances of two independent cations in [Cu2(µ-Ph2Ppypz)2-
(MeCN)2][ClO4]2 are 3.625(1) and 3.587(1) Å,6 the short
Cu(1)᎐Cu(2) distance is mainly caused, not by the rigidity of
the bridging phosphine ligand, but by the desire for both CuI
atoms to maximize σ bonding with the sp orbital of the azide
ligand, which is indicated by the very acute angles N(7)᎐Cu(1)᎐
Cu(2) {52.1(4) [44.1(4)]} and N(7)᎐Cu(2)᎐Cu(1) {48.1(4)
[48.8(6)]Њ}. This is the probable reason for the stabilisation of
the CuI state. The azide bridge angle Cu(1)᎐N(7)᎐Cu(2) is
79.8(4) [87.1(5)]Њ, and such a small angle has never been found
in binuclear copper() complexes with µ-1,1-azide bridges.2,7–9
The Cu᎐N (pypz) bond lengths of 2.150(4) and 2.030(5) Å for
Cu(1), and 2.084(4) and 2.084(4) Å for Cu(2) are typical for
a copper() centre chelated by nitrogen heterocycles.10 The
N᎐Cu᎐N ‘bite angles’ of 78.0(2) for Cu(1) and 78.5(2)Њ for
Cu(2) for the bidentate pyridylpyrazole fragments are usual for
relatively rigid bidentate diamine ligands, and the values are
very similar to that [78.9(3)Њ] found in [Cu3LЈ2(MeCN)2][PF6]3
[LЈ = 2,6-bis(5-methylpyrazol-3-yl)pyridine]11 and those [78.9(2)
and 78.6(2)Њ] found in [Cu2(µ-Ph2Ppypz)2(MeCN)2][ClO4]2.6
Fig. 2 shows a perspective drawing of the cation [Cu2(µ-Ph2-
Ppypz)2(µ-1,1-SCN)]ϩ in 2 with the atom numbering scheme.
The molecular structure is very similar to that in 1ؒEt2O except
that the µ-1,1-azide bridge is replaced here by a µ-1,1-
thiocyanate bridge. The choice of sulfur rather than nitrogen as
the bridge atom is presumably associated with the class b or
‘soft’ nature of CuI. The bond length of 2.766(1) Å for
Cu(1)᎐Cu(2) is similar to that in 1ؒEt2O, but shorter than that
[2.796(8) Å] of [Cu2L(µ-1,1-SCN)2] (L = macrocyclic Schiff
base).5 The Cu᎐S distances of 2.374(1) and 2.412(1) Å are in
good agreement with the corresponding distances [2.37(1) and
2.39(1) Å] in [Cu2L(µ-1,1-SCN)2].5 The Cu᎐S᎐Cu angle of
70.6(1)Њ is smaller than the azide angle in 1ؒEt2O, which is a
consequence of the longer Cu᎐S distances compared to Cu᎐N.
Fig. 1 Perspective view (35% thermal ellipsoids) of the [Cu2(µ-
Ph2Ppypz)2(µ-1,1-N3)]ϩ cation in 1ؒEt2O. For clarity the disordered
azide ligand is shown in only one of its two populated locations; dimen-
sions relating to the N(7Ј) atom of the alternative location are enclosed
in square brackets. Pertinent bond lengths (Å) and angles (Њ):
Cu(1)᎐Cu(2) 2.773(1), Cu(1)᎐P(1) 2.192(2), Cu(2)᎐P(2) 2.173(1), Cu(1)᎐
N(7) 2.10(2) [2.09(2)], Cu(1)᎐N(4), 2.030(5), Cu(1)᎐N(6), 2.150(4),
Cu(2)᎐N(7) 2.22(1) [1.93(1)], Cu(2)᎐N(1), 2.084(4), Cu(2)᎐N(3)
2.084(4); Cu(1)᎐N(7)᎐Cu(2) 79.8(4) [87.1(5)], N(7)᎐Cu(1)᎐Cu(2)
52.1(4), [44.1(4)], N(7)᎐Cu(2)᎐Cu(1) 48.1(4) [48.8(6)], N(6)᎐Cu(1)᎐P(1)
130.4(1), N(4)᎐Cu(1)᎐Cu(2) 152.4(2), N(1)᎐Cu(2)᎐Cu(1) 154.7(1),
N(3)᎐Cu(2)᎐P(2) 139.9(1), N(4)᎐Cu(1)᎐N(6) 78.0(2), N(1)᎐Cu(2)᎐N(3)
78.5(2)
Acknowledgements
This work is supported by the Hong Kong Research Grants
Council Earmarked Grant Ref. No. CUHK 311/94P and the
National Natural Science Foundation of China.
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Fig. 2 Perspective view (35% thermal ellipsoids) of the [Cu2(µ-
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Received 29th September 1997; Communication 7/06986C
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J. Chem. Soc., Dalton Trans., 1997, Pages 4477–4478