Reversible sulfur dioxide reactions with cyclopentadienylnickel(II) organochalcogenide complexes

Article abstract of DOI:10.1016/S0022-328X(98)00604-4

A series of cyclopentadienylnickel(II) organochalcogenides containing different phosphines have been prepared by either reacting [CpNi(μ-SC₆H₄X-4)]₂ (Cp^#=η⁵-C₅H₅,(Cp), η⁵-C₅H₅Me, (Cp′); X=Cl, Br) with phosphines or Cp^#Ni(PR₃)Br with HSC₆H₄X-4 and Et₃N or NaSeC₆H₄Cl-4. The complexes that were isolated have the general formula CpNi(PR₃)(EC₆H₄X-4) {E=S, X=Cl, R=Ph (1a), Bu (2a), OPh (3a), OEt (4a), OMe (5a); X=Br, R=Bu (6a), Ph (7a)}. In addition to spectroscopic characterisation, the complexes CpNi(PBu₃)(SC₆H₄Cl-4) (2a) and Cp'Ni(PPh₃)(SeC₆H₄Cl-4) (9a) were subjected to single-crystal X-ray diffraction studies. While the solution and solid state structures of CpNi(PBu₃)(SC₆H₄Cl-4) were found to be the same, that of Cp'Ni(PPh₃)(SeC₆H₄Cl-4) were different. The orientation of the methyl group of 9a in the solid state is almost trans to the phosphine, but solution NMR data indicate that the methyl substituent on the cyclopentadienyl ligand is cis to the phosphorus. All the complexes, 1a-9a, were found to react reversibly with SO₂ to form SO₂ adducts and the reversibility could be monitored by visible and ¹H-NMR spectroscopy. Electrochemical studies show that 2a and 6a have reversible couples whereas 1a and 7a are only quasi-reversible. The PBu₃ complexes are easier to oxidise as compared with the PPh₃ analogues.

Full text of DOI:10.1016/S0022-328X(98)00604-4

Journal of Organometallic Chemistry 564 (1998) 37–45
Reversible sulfur dioxide reactions with cyclopentadienylnickel(II)
organochalcogenide complexes
James Darkwa 1,a,b,*, Richard M. Moutloali b, Tebello Nyokong c
a Department of Chemistry, Uni6ersity of the Western Cape, Pri6ate Bag X17, Bell6ille 7535, South Africa
b Department of Chemistry, Uni6ersity of the North, Pri6ate Bag X1106, So6enga 0727, South Africa
c Department of Chemistry, Rhodes Uni6ersity, Grahamstown 6140, South Africa
Received 13 January 1998
Abstract
A series of cyclopentadienylnickel(II) organochalcogenides containing different phosphines have been prepared by either
reacting [CpNi(v-SC6H4X-4)]2 (Cpc =p5-C5H5,(Cp), p5-C5H5Me, (Cp%); X=Cl, Br) with phosphines or CpcNi(PR3)Br with
HSC6H4X-4 and Et3N or NaSeC6H4Cl-4. The complexes that were isolated have the general formula CpNi(PR3)(EC6H4X-4)
{E=S, X=Cl, R=Ph (1a), Bu (2a), OPh (3a), OEt (4a), OMe (5a); X=Br, R=Bu (6a), Ph (7a)}. In addition to spectroscopic
characterisation, the complexes CpNi(PBu3)(SC6H4Cl-4) (2a) and Cp’Ni(PPh3)(SeC6H4Cl-4) (9a) were subjected to single-crystal
X-ray diffraction studies. While the solution and solid state structures of CpNi(PBu3)(SC6H4Cl-4) were found to be the same, that
of Cp’Ni(PPh3)(SeC6H4Cl-4) were different. The orientation of the methyl group of 9a in the solid state is almost trans to the
phosphine, but solution NMR data indicate that the methyl substituent on the cyclopentadienyl ligand is cis to the phosphorus.
All the complexes, 1a–9a, were found to react reversibly with SO2 to form SO2 adducts and the reversibility could be monitored
1
by visible and H-NMR spectroscopy. Electrochemical studies show that 2a and 6a have reversible couples whereas 1a and 7a are
only quasi-reversible. The PBu3 complexes are easier to oxidise as compared with the PPh3 analogues. © 1998 Elsevier Science
S.A. All rights reserved.
Keywords: Cyclopentadienylnickel(II); Organochalcogenide; Reversible; Sulfur dioxide
1. Introduction
seldom leads to reversible absorption, whereas the latter
almost invariably gives products that easily release sul-
fur dioxide; presumably because the ligand–SO2 inter-
action is generally weak. Most of these ligand based
adducts are thiolato complexes [2](a), [3–5], with the
sulfur of the thiolato ligand behaving as a Lewis
base—though this behaviour is not restricted to sulfur
containing ligands. One of the earliest known ligand
bound SO2 complexes is Pt(PPh3)2(CH3)I·SO2 [6],
where the SO2 is bound to the iodo ligand. Other
examples are oxygen and selenium organochalcogenide
compounds which form adducts that are less stable
than their sulfur analogues [2](a), due to their poorer
Lewis base character.
Interest in the chemistry of sulfur dioxide is primarily
driven by environmental concerns about this gas. A
potential solution for this problem lies in the ability to
trap the gas before it gets to the atmosphere. Efforts
directed towards solving this problem have led to the
reactions of metal complexes with sulfur dioxide. Two
main reaction types have been identified in this regard.
First, reactions in which the sulfur dioxide binds to the
metal centre [1]; and secondly, those where the gas is
bound to a ligand in a metal complex [2–5]. The former
* Corresponding author.
1 Present address: Department of Chemistry, University of the
Western Cape, Private Bag X17, Bellville 7535, South Africa.
In this paper we describe the synthesis of cyclopenta-
dienylnickel(II) organochalcogenide compounds, some
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00604-4

38
J. Darkwa et al. / Journal of Organometallic Chemistry 564 (1998) 37–45
Fig. 1. ORTEP plot for CpNi(PBu3)(SC6H4Cl-4).
[9] were prepared by the literature procedure. Infrared
spectra were recorded on a Nicolet 205 FT-IR as KBr
pellets. The 1H, 13C, 31P-NMR spectra were on a
Varian Gemini 2000 and referenced to residual CHCl3
of which are known, and their reversible reactions with
SO2. The SO2 adducts have the SO2 bound to the
chalcogen of the ligands.
1
for H (l 7.26), 13C (l 77.0) and to 85% H3PO4 for 31P.
Elemental analyses were performed by the microanalyt-
ical laboratory at the University of Cape Town, South
Africa, as a service.
2. Experimental section
2.1. Materials and instrumentation
Cyclic voltammetric studies were carried out on a
Bio-Analytical Systems CV-50W electrochemical analy-
ser, at a glassy carbon electrode (area=0.07 cm2). The
reference electrode was a silver wire coated with silver
chloride. A platinum wire was used as a counter elec-
trode. All experiments were carried out under pre-
purified and dry nitrogen atmosphere. Samples were
measured in dichloromethane solution (10−3 M) with
[n-Bu4N[ClO4] as supporting electrolyte (0.1 M). Poten-
tials were referenced internally to the potential for the
oxidation of ferrocene (0.44 V) versus the saturated
calomel electrode (SCE), as described in an earlier
report [10].
All reactions were performed under a nitrogen atmo-
sphere but products were air-stable and could be
worked-up in air. Solvents were of analytical grade but
THF was dried and distilled over sodium benzophe-
none ketyl. The phosphines, 4-chlorothiophenol and
bis(4-chlorophenyl)diselenide (Aldrich) were used as re-
ceived. Nickelocene (Cp2Ni) [7], CpNi(PR3)Br [7], Cp’-
Ni(PR3)Br [8] and [CpNi(v-SC6H4X-4)]2 (X=Cl, Br)
Table 1
Selected bond distances and bond angles for Cp%Ni(PBu3)(SC6H4Cl-4)
˚
Bond distances (A)
Ni–S(1)
2.194(9)
1.754
1.824(3)
1.762(3)
Ni–P(1)
2.140(8)
1.841(3)
1.829(3)
1.767(3)
2.2. One pot synthesis of CpNi(PPh3)(SC6H4Cl-4) (1a)
Ni–Cpa
P(1)–C(11)
P(1)–C(31)
Cl(1)–C(44)
P(1)–C(21)
S(1)–C(41)
A mixture of Cp2Ni (1.00 g, 5.29 mmol) and 4-
chlorothiophenol (0.79 g, 5.46 mmol) was stirred in
CH2Cl2 (50 ml) for 2 h. The green solution turned dark
brown and PPh3 (1.09 g, 4.16 mmol) was added and the
solution stirred for a further 20 h. The mixture was
filtered, concentrated to about 20 ml and an equal
volume of hexane was added and stored at −15°C to
yield green crystals of CpNi(PPh3)(SC6H4Cl-4) (1.17 g,
Bond angles (°)
Cp–Ni–P(1)
P(1)–Ni–S(1)
C(21)–P(1)–Ni
C(21)–P(1)–C(11) 104.45(14)
C(21)–P(1)–C(31) 104.80(13)
134.9
92.48(4)
111.94(11)
Cp–Ni–S(1)
C(11)–P(1)–Ni
C(31)–P(1)–Ni
C(31)–P(1)–C(11) 103.76(13)
—
132.0
115.58(9)
115.13(11)
—
a The distance from the centroid of the C5H5 ring to the nickel atom.

J. Darkwa et al. / Journal of Organometallic Chemistry 564 (1998) 37–45
39
Fig. 2. ORTEP plot for Cp’Ni(PPh3)(SeC6H4Cl-4).
2.3. Reactions of [CpNi(v-SC6H4Cl-4)]2 with PPh3:
formation of CpNi(PPh3)(SC6H4Cl-4) (1a)
56%). Anal. Calcd. for C29H24ClPSNi: C, 65.76; H,
4.57%. Found: C, 65.88; H, 4.67%. H-NMR (CDCl3):
1
l 7.68–7.62 (m, 6H, PPh3), 7.38–7.30 (m, 9H, PPh3),
7.25 (d, 2H, JHH=8.50 Hz, SC6H4Cl-4), 6.82 (d, 2H,
A mixture of [CpNi(v-SC6H4Cl-4)]2 (1.00 g, 3.74
mmol) and PPh3 (1.96 g, 7.48 mmol) in CH2Cl2 (50 ml)
was stirred for 18 h. The colour of the solution re-
mained brown–black without much change. After
filtration the solution was concentrated to about 15 ml
and an equal volume of hexane added. Upon cooling at
−15°C overnight green crystals of pure Cp-
Ni(PPh3)(SC6H4Cl-4) were obtained. Yield=1.58 g,
80%. The rest of the phosphine reactions were per-
formed with two equivalents of the appropriate phos-
phine and 0.30 g (0.56 mmol) of [CpNi(v-SC6H4Cl-4)]2.
The yields and analytical data are given below for each
reaction.
JHH=8.50 Hz, SC6H4Cl-4), 5.11 (s, 5H, C5H5).
31P{1H}-NMR: l 35.8 (s, PPh3). IR (nujol mull cm−1):
1586(m), 1570(m), 1543(m), 1480(s), 1466(vs), 1433(vs),
1400(m), 1387(m), 1348(m), 1313(m), 1283(m), 1266(w)
1228(w), 1182(m), 1168(w), 1157(w), 1116(w), 1091(vs),
1069(m), 1045(m), 1009(s), 998(m), 971(w), 903(w),
848(w), 834(w), 810(s), 785(vs), 766(w), 750(s), 740(s),
698(vs), 692(vs), 618(w), 533(vs), 509(vs), 492(s), 482(s),
454(m), 441(w), 427(m).
Table 2
Selected bond distances and bond angles for Cp%Ni(PPh3)(SeC6H4Cl-
4)
2.4. CpNi(PBu3)(SC6H4Cl-4) (2a)
˚
Yield=0.42 g, 80%. Anal. Calcd. for C23H36ClPSNi:
Bond distances (A)
Ni–Se(1)
2.317(6) Ni–P(1)
2.136(10)
1.822(4)
1.825(4)
1.74 9(5)
C, 58.81; H, 7.70; S, 6.83%. Found: C, 58.91; H, 8.00;
S, 6.58%. H-NMR (CDCl3): l 7.53 (d, 2H, JHH=8.60
Hz, SC6H4Cl-4), 6.94 (d, 2H, JHH=8.60 Hz, SC6H4Cl-
Ni–Cpa
1.746
P(1)–C(11)
1
P(1)–C(21)
Se(1)–C(41)
1.835(4) P(1)–C(31)
1.912(4) Cl(1)–C(44)
4); 5.25 (s, 5H, C5H5); 1.48 (m, 18H, PBu3); 0.91 (t, 9H,
Bond angles (°)
Cp–Ni–P(1)
P(1)–Ni–Se(1)
C(21)–P(1)–Ni
C(21)–P(1)–C(11) 103.1(2)
C(21)–P(1)–C(31) 102.9(2)
J
HH=7.00 Hz, PBu3). 31P{1H}-NMR: l (s, 22.4, PBu3).
137.0
91.24(3)
Cp–Ni–Se(1)
C(11)–P(1)–Ni
130.7
114.45(11)
112.55(13)
IR (KBr pellet cm−1): 3036(m), 2931(vs), 2868(vs),
1567(m), 1546(m), 1475(vs), 1412(s), 1377(s), 1342(s),
1278(m), 1257(m) 1222(m), 1201(s), 1180(m), 1082(vs),
1018(m), 1004(s), 976(m), 962(m), 906(m), 857(w),
835(w), 814(vs), 786(vs), 737(m), 716(s), 688(m),
540(m), 484(s), 463(m), 435(m).
115.07(13) C(31)–P(1)–Ni
C(31)–P(1)–C(11) 107.7(2)
—
—
a The distance from the centroid of the C5H4Me ring to the nickel
atom.

40
J. Darkwa et al. / Journal of Organometallic Chemistry 564 (1998) 37–45
Table 3
1H-NMR chemical shifts (ppm) for CpcNi(PR3)(EC6H4X-4) and CpcNi(PR3)(E(SO2)C6H4X-4)
CpcNi(PR3)(EC6H4X-4)
Cpc
CpcNi(PR3)(E(SO2)C6H4X-4)
Cpc
EC6H4X-4
(E(SO2)C6H4X-4)
1a
2a
3a
4a
5a
6a
7a
8a
9a
5.13
5.25
4.98
5.30
5.33
5.24
5.14
5.07
—, 6.83(d)
7.53(d), 6.93(d)
—, 6.85(d)
7.52(d), 6.94(d)
7.52(d), 6.96(d)
7.23(d), 6.96(d)
—, 6.98(d)
1b
2b
3b
4b
5b
6b
7b
8b
9b
5.38
5.48
5.16
5.53
5.51
5.43
5.39
5.30
—, 6.96(d)
7.44(d), 7.12(d)
—, 7.01(d)
7.52(d), 7.20(d)
7.40(d), 7.20(d)
7.43(d), 7.19(d)
—, 7.10(d)
—, 6.87(d)
—, 6.83(d)
—, 7.05(d)
—, 6.98(d)
5.15, 4.70
5.25, 5.00
2.5. CpNi(P(OPh)3)(SC6H4Cl-4) (3a)
Yield=0.22 g, 68%. Anal.
799(s, br), 755(s), 698(w), 667(w), 629(w), 569(w),
539(s), 487m), 465(w), 449(w).
Calcd.
for
C29H24ClO3PSNi: C, 60.30; H, 4.19; S, 5.62%. Found:
C, 60.15; H, 4,20; S, 5.32%. 1H-NMR (CDCl3): l
7.37–7.18 (m, P(OPh)3); 6.85 (d, 2H, JHH=8.20 Hz,
SC6H4Cl-4); 4.98 (s, 5H, C5H5); 1.48 31P{1H}-NMR: l
(s, 63.6, P(OPh)3). IR (KBr pellet cm−1): 3086(m),
3071(m), 1635(w), 1589(m), 1567(m), 1548(w), 1491(s),
1485(vs, sh), 1466(vs), 1455(s), 1419(m), 1400(m),
1386(m), 1348(w), 1332(w), 1302(w), 1286(m), 1231(m,
sh) 1195(vs), 1184(vs), 1171(vs), 1110(w), 1086(vs),
1075(m), 1045(s), 1026(s), 1007(m), 976(w), 914(vs),
897(vs, sh), 864(m, sh), 834(m), 810(s), 796(s), 777(vs),
760(vs), 744(vs), 717(s), 689(s), 618(s), 596(s), 561(w),
536(m), 498(m), 479(s), 465(s), 432(w), 422(w).
2.8. Reaction of [CpNi(v-SC6H4Br-4)]2 with PPh3 and
PBu3: formation of CpNi(PR3)(SC6H4Br-4)
In a typical reaction [CpNi(v-SC6H4Br-4)]2 (0.30 g,
0.48 mmol) in CH2Cl2 (50 ml) was reacted with PBu3
(0.19 ml, 0.96 mmol). The mixture was stirred at room
temperature for 18 h. A green solution was obtained,
which was filtered and the solvent removed on a rotary
evaporator to give an oil residue. This was dissolved in
a minimum amount of hexane and cooled at −15°C
for several days, forming green crystals of Cp-
Ni(PBu3)(SC6H4Br-4) (6a). Yield=0.31 g, 63%. Anal.
Calcd. for C23H36BrPSNi: C, 53.73; H, 7.06; S, 6.24%.
1
Found: C, 53.57; H, 7.25; S, 6.46%. H-NMR (CDCl3):
2.6. CpNi(P(OEt)3)(SC6H4Cl-4) (4a)
l 7.48 (d, 2H, JHH=8.60 Hz, SC6H4Br-4), 7.06 (d, 2H,
JHH=8.60 Hz, SC6H4Br-4); 5.24 (s, 5H, C5H5); 1.47
1
Yield=0.35 g, 72%. H-NMR (CDCl3): l 7.52 (d,
(m, 18H, PBu3); 0.90 (t, 9H, JHH=7.00 Hz, PBu3).
31P{1H}-NMR: l (s, 22.5 PBu3). IR: (KBr pellet cm−1):
2951(vs), 2921(vs), 2865(s), 1571(m), 1556(s), 1462(vs),
1415(s), 1403(s), 1375(s), 1346(s), 1303(m), 1278(m),
1265(m) 1255(w), 1206(m), 1168(m), 1087(s), 1078(vs),
1050(s), 1000(s), 934(w), 903(s), 887(s), 836(m), 823(s),
810(s), 781(vs), 761(s, sh), 740(m), 719(s), 625(w),
590(w), 493(s), 482(s), 459(m), 432(w), 402(m).
2H, JHH=8.60 Hz, SC6H4Cl-4), 6.94 (d, 2H, JHH
=
8.60 Hz, SC6H4Cl-4); 5.30 (s, 5H, C5H5); 4.09 (q, 6H,
P(OEt)3); 1.22 (t, 9H, P(OEt)3). 31P{1H}-NMR: l (s,
65.4, P(OEt)3). IR (nujol mull cm−1): 3064(m), 2980(s),
2931(s), 2896(m), 2875(m), 1573(s), 1553(w), 1474(s),
1441(m), 1389(s), 1370(m), 1348(w), 1294(m), 1258(s),
1179(m), 1162(s), 1097(s), 1075(s, sh), 1034(s, br),
1012(s), 975(s), 894(w), 815(s), 744(m), 681(w), 569(m),
550(m), 495(m).
2.9. CpNi(PPh3)(SC6H4Br-4) (7a)
2.7. CpNi(P(OMe)3)(SC6H4Cl-4) (5a)
This compound was prepared using the same proce-
dure for 6a, using [CpNi(v-SC6H4Br-4)]2 (0.20 g, 0.32
mmol) and PPh3 (0.16 g, 0.64 mmol). Yield=0.14 g,
77.3%. Anal. Calcd. for C29H24BrPSNi: C, 60.67; H,
4.21; S, 5.58%. Found: C, 60.82; H, 4.30; S, 5.37%.
1H-NMR (CDCl3): l 7.66 (m, 6H, PPh3), 7.37 (m, 9H,
PPh3); 7.23 (d, 2H, JHH=8.60 Hz, SC6H4Br-4), 6.96 (d,
2H, JHH=8.60 Hz, SC6H4Br-4); 5.30 (s, 5H, C5H5).
31P{1H}-NMR: l (s, 35.2 PPh3). IR: (nujol mull cm−1):
1569(m), 1559(m), 1498(m), 1477(s), 1461(s), 1431(m),
1
Yield=0.30 g, 63%. H-NMR (CDCl3): l 7.52 (d,
2H, JHH=8.60 Hz, SC6H4Cl-4), 6.95 (d, 2H, JHH
=
8.60 Hz, SC6H4Cl-4); 5.33 (s, 5H, C5H5); 3.67 (s, 9H,
P(OMe)3). 31P{1H}-NMR: l (s, 67.2, P(OMe)3). IR
(nujol mull cm−1): 3064(m), 2945(s), 2839(m), 1570(m),
1548(w), 1469(s), 1441(m, sh), 1400(m), 1387(s),
1351(m), 1283(s), 1266(s), 1175(s), 1143(m), 1091(s),
1024(s, br), 935(w), 900(w), 853(m, sh), 834(s, sh),

J. Darkwa et al. / Journal of Organometallic Chemistry 564 (1998) 37–45
41
Fig. 3. 1H-NMR spectra of CpNi(PBu3)(SC6H4Cl-4) (2a) and its SO2 adduct (2b). * Represents residual CH2Cl2 in each of the complexes.
1397(s), 1380(m), 1306(m), 1180(m), 1093(s), 1080(s),
1019(m), 1005(s), 995(s), 971(m), 902(m), 834(m),
806(s), 784(s), 748(s), 740(s), 691(s), 617(w), 533(s),
509(s), 492(s), 479(s), 454(m), 426(m).
diselenide. A solution of CpNi(PPh3)Br (1.04 g, 2.23
mmol) in CH2Cl2 (40 ml) was added via a pressure
equalising dropping funnel to give a dark brown mix-
ture. The mixture was stirred at room temperature for
24 h, filtered and the filtrate evaporated on a rotary
evaporator. The resultant green residue was recrys-
tallised from CH2Cl2/hexane to give crystalline Cp-
Ni(PPh3)(SeC6H4Cl-4). Yield=0.37 g, 43%. Anal.
Calcd. for C29H24ClPSeNi: C, 60.31; H, 4.36%. Found:
2.10. Synthesis of CpNi(PPh3)(SeC6H4Cl-4) (8a)
To a mixture of bis(4-chlorophenyl)diselenide (0.95 g,
3.04 mmol) and sodium borohydride (0.19 g, 5.02
mmol) was added methanol (30 ml). After vigorous
evolution of gas the resultant yellow solution was
stirred for 2 h to allow the complete dissolution of the
1
C, 61.96; H, 4.36%. H-NMR (CDCl3): l 7.69 (t, 6H,
PPh3), 7.61–7.35 (m, 9H, PPh3), 6.86 (d, 2H, JHH
=
8.40 Hz, SC6H4Cl-4), 5.06 (s, 5H, C5H5). 31P{1H}-

42
J. Darkwa et al. / Journal of Organometallic Chemistry 564 (1998) 37–45
Fig. 4. Packing diagram for Cp’Ni(PPh3)(SeC6H4Cl-4) viewed down the a axis.
NMR: l (s, 39.0 PPh3). IR (nujol mull cm−1): 1589(m),
1570(m), 1477(s), 1464(vs), 1433(vs), 1400(m), 1381(s),
1346(m), 1310(m), 1285(m), 1264(m), 1184(m), 1157(m),
1119(s), 1097(vs), 1086 (vs), 1069(s), 1059(m), 1048(m),
1026(m), 1009s), 996(s), 971(m), 927(m), 900(m),
862(w), 848(m), 834(m), 810(s), 788(s), 750(s), 736(s),
722(s), 695(vs), 618(w), 533(vs), 509(s), 492(s), 479(s),
454(s), 441(m), 424(m), 408(m).
PPh3), 7.59–7.35 (m, 11H, PPh3 and SeC6H4Cl-4), 6.84
(d, 2H, JHH=8.40 Hz, SeC6H4Cl-4), 5.13 (s, 2H,
C5H4Me), 4.69 (s, 2H, C5H4Me). 31P{1H}-NMR: l (s,
39.5, PPh3). IR (nujol mull cm−1): 3142(w), 3071(m),
3001(w), 2959(s), 2924(m), 2868(m), 1584(w), 1573(w),
1559(w), 1471(s), 1433(vs), 1384(m), 1351(w), 1326(w),
1307(w), 1264(m), 1198(m), 1182(m), 1160(m), 1116(s),
1089(s), 1069(m), 1056(m), 1026(m), 1009(s), 914(w),
862(m), 810(s), 744(s), 722(s), 695(s), 618(w), 457(w),
424(m).
2.11. Synthesis of Cp’Ni(PPh3)(SeC6H4Cl-4) (9a)
To a mixture of bis(4-chlorophenyl)diselenide (0.30 g,
1.02 mmol) and NaBH4 (0.08 g, 2.04 mmol) was added
methanol (50 ml) to generate NaSeC6H4Cl-4. After the
evolution of gas had ceased, a toluene (50 ml) solution
of Cp’Ni(PPh3)Br (0.25 g, 0.51 mmol) was added via a
pressure equalising dropping funnel to the solution,
NaSeC6H4Cl-4. The solution changed from yellow to
green and was stirred for 2 h. After filtration, the
solvent was removed in vacuo and the residue recrys-
tallised from CH2Cl2/hexane at −15°C to give pure
Cp’Ni(PPh3)(SeC6H4Cl-4). Yield=0.14 g, 58%. Anal.
Calcd. for C30H26ClPSeNi: C, 60.91; H, 4.60%. Found:
2.12. Reactions of CpNi(PR3)(EC6H4Cl-4) with sulfur
dioxide NMR tube generation of
CpNi(PBu3)(S(SO2)C6H4Cl-4)
In a typical reaction CpNi(PBu3)(SC6H4Cl-4) was
1
dissolved in an NMR tube in CDCl3 and the H-NMR
of the solution was run. Sulfur dioxide was slowly
bubbled through the solution for about 5 min and the
1H-NMR of the solution re-run. The two spectra are
shown in Fig. 3. All other reactions with SO2 were
performed using the same procedure. The NMR data is
summarised in Table 3.
1
C, 61.13; H, 4.37%. H-NMR (CDCl3): l 7.63 (t, 6H,

J. Darkwa et al. / Journal of Organometallic Chemistry 564 (1998) 37–45
43
2.13. Crystal Structure determination of 2a and 9a
3. Results and discussion
3.1. Synthesis of complexes
Single crystals of 2a and 9a suitable for structural
determination were obtained from a CH2Cl2/hexane
mixture at −15°C. A dark green crystal of 2a (0.58×
0.52×0.36 mm) and 9a (0.58×0.52×0.36 mm) were
mounted in sealed capillary tube for data collection. All
geometric and intensity data were collected on a
Siemens SMART diffractometer with a CCD detector.
The structures were solved by the Patterson method for
primary atom sites and by difference map for atoms in
secondary sites [11]. All non-hydrogen atoms were
refined anisotropically and hydrogen atoms were
refined without restraints. The structures were refined
by full-matrix least-squares on F2 with a weighting
scheme of w−1=|2(Fo2)+(0.100P)2+0.00P, where
P=(F2o+2F2c)/3 using SHELX-93 [12]. An absorption
correction based on multiple redundant data analysis
was applied [13]. Crystal data and structure refinement
details are listed in Table 4.
The general synthetic route to the CpcNi(PR3)
(SC6H4X-4) complexes is via the method of Taube et al.
[14]. When the dimer, [CpNi(v-SC6H4X-4)]2, (Cp=p5-
C5H5, X=Cl, Br) is treated with phosphines, PR3
(R=Bu, Ph, OPh, OEt, OMe), it is cleaved to form
complexes of the type CpNi(PR3)(SC6H4X-4) in moder-
ate to high yields (Eq. (1)). The 4-bromo complexes
were isolated for only PPh3 and PBu3 to determine if
the change of halogen would have any electronic ef-
1
fects. Based on the H-NMR data (Table 3); there was
no significant electronic effect between the Cl and Br
compounds. The products from PPh3, P(OPh)3 and
PBu3 were brown in solution but green to dark green in
the solid state; whereas the products from P(OEt)3 and
P(OMe)3 were both green oils. The brown–green colour
changes in solution and in the solid state is similar to
that observed for PPh3 complexes of SC6H5 and
SC6H4Me-4 [15].
Table 4
Crystal data and structural refinement for 2a and 9a
[CpNi(v-SC6H4X-4)]2+2PR3
2a
9a
“2CpNi(PR3)(SC6H4X-4)
(1)
Formula
FW
T (K)
C23H36ClPSNi
469.71
293(2)
0.71073
Monoclinic
P21/c
12.950(3)
9.839(2)
20.274(4)
108.60(3)
2448.3(9), 4
1.274
C30H26ClPSeNi
580.60
296(2)
0.71073
Monoclinic
P21/c
The PBu3 complex, CpNi(PBu3)(SC6H4Cl-4), has pre-
viously been prepared by Sato and Yoshida when they
reacted [CpNi(PBu3)2]+Cl− with NaSC6H4Cl-4 [16];
but the route described in equation (1) is much simpler
and represents a one-pot reaction if [CpNi(v-SC6H4X-
4)]2 is generated in situ from Cp2Ni and HSC6H4X-4,
followed by the addition of phosphine. All products
from reaction (1) were characterised by IR and NMR
spectroscopy and by elemental analyses. In addition,
the structure of 2a was determined by X-ray crystallog-
raphy as shown in Fig. 1 and some selected parameters
are shown in Table 1.
˚
Wavelength (A)
Crystal system
Space group
˚
a (A)
9.579(4)
˚
b (A)
11.239(5)
24.395(11)
95.601(10)
2613.9(2), 4
1.501
˚
c (A)
i (°)
Volume (A ), Z
3
˚
Density (calcd.)
(Mg m−3
)
Absorption coefficient
(mm−1
F(000)
Crystal size (mm)
q-range for data
collected (°)
1.058
1000
2.315
1200
)
In order to compare the behaviour of the Se ana-
logues to the
S
ones, we prepared Cp-
0.58×0.52×0.360 58×0.38×0.25
1.66–23.28
1.68–28.30
Ni(PPh3)(SeC6H4Cl-4) via a route similar to that
employed for CpNi(PBu3)(SeC6H4Cl-4) (Eq. (2)) [16].
CpcNi(PPh3)Br+NaSeC6H4Cl-4
“CpcNi(PPh3)(SeC6H4Cl-4)
Limiting indices
−145h]13
−105k]8
−225l]22
9033
−125h]12
−125k]14
−305l]25
15595
No. of reflections col-
lected
No. of independent
reflections
R(int.)
Refinement method
+NaBr (Cpc =p5-C5H5, p5-C5H4Me)
(2)
3497
5873
The colours of these compounds in solution and in
the solid state were also brown and green respectively
like those of the sulfur analogues. Spectroscopic charac-
terisation by IR, NMR and elemental analyses confi-
rmed the formulation as in equation (2); and the
structure of 9a established by X-ray crystallography is
shown in Fig. 2 and selected parameters are shown in
Table 2. Our attempts so far to prepare Cp’-
Ni(PPh3)(SC6H4Cl-4) (Cp’=p5-C5H4Me) have been
unsuccessful.
0.0239
0.0318
Full-matrix least-squares on F2
Data/restraints/parameters 3497/0/388
5873/0/411
1.113
0.0483
0.1436
0.0647
0.1559
Goodness of fit on F2
1.078
Final R indices [I\2|(I)] R1=0.0329
wR2=0.1195
R indices (all data)
R1=0.0364
wR2=0.1248
0.322 and −0.305 0.588 and −0.403
Largest difference peak
and hole (e A
−3
˚
)

44
J. Darkwa et al. / Journal of Organometallic Chemistry 564 (1998) 37–45
3.2. Spectroscopic characterisation of complexes and
their SO2 adducts
downfield shifts are observed for complexes containing
more basic phosphines. The 31P-NMR spectra of all the
SO2 adducts shifted downfield by 1.0 ppm or less from
the non-SO2 adducts.
Infrared spectra of all complexes displayed strong
bands in the 800 cm−1 region, characteristic of Cp and
at 690–780 cm−1 for the phenyl containing phosphines.
However, attempts to determine the mode of SO2 bind-
ing by the w(SO) of the infrared spectra of the SO2
adducts were unsuccessful. This was due to the over-
whelming excess of free SO2 in solution, after bubbling
the gas, compared with the presence of bound SO2. In
the NMR spectra of 1a–8a, the peaks due to the Cp
were in the range 4.98–5.25 ppm and that of Cp’ (9a)
at 4.70 and 5.15 ppm. Treatment of CH2Cl2 solutions
of complexes 1a–9a with SO2 resulted in shifts of the
peaks observed for the compounds prior to the addition
of SO2. The SO2 reactions could be monitored by
Based on the spectroscopic data, the SO2 adducts
could be formulated as CpNi(PR3)(S(SO2)C6H4X-4)
(X=Cl, Br) which would be similar to the structurally
characterised ruthenium compound, CpRu(PPh3)2
(S(SO2)C6H4Me-4) [4]. It must be noted that the ruthe-
nium complex can absorb a further one mole of SO2 to
form CpRu(PPh)(SO2)(S(SO2)C6H4Me-4) [4] by substi-
tuting one of the PPh3 ligands. This would offer a
second binding site option for the nickel complexes;
namely PPh3 substitution. From the 31P-NMR data of
the SO2 adducts, phosphine substitution do not occur
for nickel as this would leave free phosphine in solu-
tion. In the case of PPh3 complexes a peak at −5.0
ppm for free PPh3 would have been observed, but this
was not the case. Unfortunately our products are too
labile for us to obtain solid materials for either elemen-
tal analyses or crystal structure determination; but the
characteristic shifts in the NMR are consistent with a
ligand based SO2 adduct. The highly labile nature of
the SO2 compound could be attributed to the low
basicity of nickel compounds as compared with those
of its congeners [18].
1
UV-visible, H and 31P-NMR spectroscopy. The visible
spectra generally shifted from a distinct umax for the
starting material to featureless spectra for the SO2
adducts. When solutions of the SO2 adducts were sub-
jected to reduced pressure, even on a rotary evaporator,
they reverted back to the spectra of the original solu-
tion before SO2 was added. These observation are
similar to that made for (dppe)Ni(S2C6H3R) (R=H,
Me) [17]. When the reactions with SO2 were monitored
1
by H-NMR, a general shift of the Cp peaks downfield
was observed (Table 3), which is consistent with the
observation made by Shaver and Plouffe for the reac-
tion of CpRu(PPh3)2(SC6H4Me-4) with SO2 [4]. Similar
downfield shifts of the m-protons to the sulfur in
SC6H4Cl-4 and SC6H4Br-4 were also observed. But the
general trend of doublets from the protons next to the
sulfur in the ligands is difficult to establish since some
of the peaks are obscured by the phenyl peaks of PPh3
and P(OPh)3 of 1b and 3b. However, a clearer picture
can be seen when the spectrum of 2a is compared with
that of 2b (Fig. 3) and that of 7a with 7b (Table 3),
respectively. In these complexes, the downfield doublets
could be assigned to the protons close to the more
electronegative halogen atoms and the upfield doublets
to the protons next to the sulfur. The protons near the
sulfur atom have upfield shifts in the SO2 adducts. This
implies that the SO2 is bound to the sulfur of the ligand
and draws electron density from this sulfur and hence
from the nearest protons. On the other hand the pro-
tons nearest to the halogens experience very little elec-
tron density changes, resulting in only slight changes in
chemical shifts (Fig. 3). The general trends in the
1H-NMR chemical shifts are strongly related to the
donor ability of the phosphines. Thus alkyl phosphines
that are better |-donors increase the electron density of
the nickel centre. This improved electron density on the
nickel results in better y-backbonding between the Ni
and S or Se and leads to the Ni reducing electron
density on the cyclopentadienyl ligand; hence larger
3.3. Electrochemical properties
Preliminary cyclic voltammetric studies of complexes
1a (0.48 V), 2a (0.36 V), 6a (0.32 V) and 7a (0.42 V),
with their oxidation potentials, show that the PBu3
complexes are easier to oxidise than their PPh3 ana-
logues. This suggests that 2a and 6a, which contain the
more electron donating PBu3, probably have their
highest occupied molecular orbitals lower in energy
compared with the corresponding PPh3 complexes 1a
and 7a. Also when the halide in the para position of the
thiolato ligand was changed from Cl (1a, 2a) to Br (6a,
7a), the less electron withdrawing Br had complexes
that were easier to oxidise, since the Ni centre in bromo
complexes would be more electron rich than the chloro
analogue. In addition oxidation couples of the PBu3
showed more reversible behaviour than the PPh3 com-
plexes. A similar observation has been made by
Gladysz et al. on (p5-C5Me5)Re(NO)(PR3) [19], where
reversibility improves as the |-donor property of the
phosphine increases. This observation corroborates the
1H-NMR downfield shifts observed for complexes 1a,
2a, 6a and 7a as the phosphine becomes more basic.
3.4. Molecular structures of 2a and 9a
Both complexes show a trigonal geometry around the
nickel if the centriod of the cyclopentadienyl ligand is
considered to occupy a co-ordination site. This is simi-

J. Darkwa et al. / Journal of Organometallic Chemistry 564 (1998) 37–45
45
lar to other cyclopentadienylnickel(II) complexes con-
5. Supplementary material
taining phosphines and organochalcogenide ligands
[8,15,20]. A comparison of the Ni–P distances in 2a
Further crystallographic details can be obtained on
request from the Director of the Cambridge Data Cen-
tre, University Chemical Laboratory, Lensfield Road,
Cambridge CB2 1EW, UK.
˚
˚
(2.140(8) A) and 9a (2.136(10) A) with similar com-
pounds show that the Ni–P bonds lie within the accept-
able range. The longest for such bonds is found in
˚
CpNi(PPh3)(SC6H4Cl-4) (2.144(1) A) [20] and the short-
˚
est is 2.136(1) A for CpNi(PPh3)(SeC6H5) [8]. No sig-
Acknowledgements
nificant changes in the nickel–chalcogen distances were
also observed when compared with the same types of
bonds in other compounds, CpNi(PPh3)(SC6H4Cl-4)
Financial support by the Foundation for Research
Development (South Africa) and the University of the
North is gratefully acknowledged. We thank Prof.
J.C.A. Boeyens and Ms Leanne Cook, University of the
Witwatersrand, South Africa, who determined the
structures as a service.
˚
˚
(2.190(1) A) [20], CpNi(PPh3)(SeC6H5) (2.303(1) A) [8]]
and [Cp*Ni(v-SeC6H5)]2 (Cp*=p5-C5Me5) (2.301(1)
˚
A) [21]. One significant observation is the difference in
the structure of 9a in solution and that in the solid
state. This is mainly in the orientation of the methyl
group on the cyclopentadienyl ligand with respect to
1
that of the phosphine. From the H-NMR spectrum of
References
9a, it is clear that there is long range coupling between
the phosphorus and the methyl protons, but in the solid
state the nearest carbon to the phosphorus is C(2). A
good illustration of this is provided by the packing
diagram of 9a (Fig. 4). Similar through space coupling
have been observed for Cp’Ni(PPh3)(SC6H5) and Cp’-
Ni(PPh3)(SeC6H5) [8], as well as Cp’Ni(PPh3)X (X=Cl,
Br, CN) [22] in solution. It is noteworthy that the
maximum deviation of the methyl group from the plane
of the C5H4 ring is 0.005 and therefore shows no close
proximity to the phosphorus. Thus the solid state struc-
ture is different from that in solution, unlike Cp’-
Ni(PPh3)I where the lack of coupling of the methyl
protons to the phosphorus of PPh3 in solution is sup-
ported by a solid state structure with the methyl group
almost trans to the phosphorus [22]. The orientation of
the methyl group, nearly trans to the phosphorus in 9a,
appears to minimise steric repulsion with the
triphenylphosphine ligand in the solid state compared
to its structure in solution. Crystal data and structure
refinement details are listed in Table 4.
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4. Conclusion
A
number
of
cyclopentadienylnickel(II)
organochalcogenide phosphine complexes can be pre-
pared by the very simple procedure of reacting the
dimer, [CpNi(v-SC6H4X-4)]2, with a phosphine. The
more basic phosphines increases the electron density on
the nickel, but it appears the halogen on the chalcogen
containing ligand has very little effect on the electrons
at the metal centre. A very facile reversible reaction of
these complexes with SO2 makes them potential scrub-
bers of SO2. The electron count for the compounds,
Cp’Ni(PPh3)(EC6H4X-4), imply that the SO2 is bound
to the chalcogen, instead of the nickel, and this could
be a factor in making the SO2 so labile.
[19] J.A. Gladysz, Private communication.
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