The reaction of triorganophosphorus diiodides, R3PI2, with zinc metal powder; Dependency of product on R; The X-ray crystal structures of dimeric {ZnI2[P(NMe2)3]}2 and monomeric ZnI2(PPh2Me)2

Article abstract of DOI:10.1016/S0020-1693(99)00197-8

Seventeen zinc(II) tertiary phosphine complexes have been synthesised directly from elemental zinc by reaction with the reagents R₃PI₂. The complexes have been characterised by elemental analysis and ³¹P{H} NMR spectroscopy. The present work represents the first comprehensive study of a wide variety of zinc(II) tertiary phosphine complexes containing different parent tertiary phosphines and the majority of the complexes are reported for the first time. In most cases, reaction of R₃PI₂ with zinc metal powder in diethyl ether in a 1:1 stoichiometric ratio, produces the dimeric complexes [ZnI₂(PR₃)]₂, analogous to the previously reported [ZnI₂(PEt₃)]₂. In contrast, reaction of R₃PI₂ (R=Ph₃, Ph₂Et, Ph₂Me) with zinc metal powder produces the monomeric bis complexes ZnI₂(PR₃)₂ and an equimolar quantity of zinc(II) iodide, the latter product being identified by X-ray powder diffraction. The X-ray crystal structures of dimeric {ZnI₂[P(NMe₂)₃]}₂ and monomeric ZnI₂(PPh₂Me)₂ are also described. The formation of the bis complexes ZnI₂(PR₃)₂ (R₃=Ph₃, Ph₂Me, Ph₂Et) is surprising and cannot be due to steric factors since complexes containing less bulky tertiary phosphines are shown to be dimeric and the adoption of a monomeric zinc(II) centre increases steric crowding at the metal atom. The existence of the bis complexes is therefore reasoned to be due to favourable Π-Π interactions on the ligands and crystal packing forces.

Full text of DOI:10.1016/S0020-1693(99)00197-8

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 292 (1999) 213–219
The reaction of triorganophosphorus diiodides, R3PI2, with zinc
metal powder; dependency of product on R; the X-ray crystal
structures of dimeric {ZnI2[P(NMe2)3]}2 and monomeric
ZnI2(PPh2Me)2
Stephen M. Godfrey *, Charles A. McAuliffe, Robin G. Pritchard, Joanne M. Sheffield
Department of Chemistry, Uni6ersity of Manchester Institute of Science and Technology, Manchester M60 1QD, UK
Received 4 November 1998; accepted 26 April 1999
Abstract
Seventeen zinc(II) tertiary phosphine complexes have been synthesised directly from elemental zinc by reaction with the reagents
R3PI2. The complexes have been characterised by elemental analysis and 31P{H} NMR spectroscopy. The present work represents
the first comprehensive study of a wide variety of zinc(II) tertiary phosphine complexes containing different parent tertiary
phosphines and the majority of the complexes are reported for the first time. In most cases, reaction of R3PI2 with zinc metal
powder in diethyl ether in a 1:1 stoichiometric ratio, produces the dimeric complexes [ZnI2(PR3)]2, analogous to the previously
reported [ZnI2(PEt3)]2. In contrast, reaction of R3PI2 (R=Ph3, Ph2Et, Ph2Me) with zinc metal powder produces the monomeric
bis complexes ZnI2(PR3)2 and an equimolar quantity of zinc(II) iodide, the latter product being identified by X-ray powder
diffraction. The X-ray crystal structures of dimeric {ZnI2[P(NMe2)3]}2 and monomeric ZnI2(PPh2Me)2 are also described. The
formation of the bis complexes ZnI2(PR3)2 (R3=Ph3, Ph2Me, Ph2Et) is surprising and cannot be due to steric factors since
complexes containing less bulky tertiary phosphines are shown to be dimeric and the adoption of a monomeric zinc(II) centre
increases steric crowding at the metal atom. The existence of the bis complexes is therefore reasoned to be due to favourable P–P
interactions on the ligands and crystal packing forces. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Zinc complexes; Phosphine complexes
believed that the steric demands of the tertiary phos-
phine may be fundamental in determining which struc-
1. Introduction
ture is formed, i.e. with less sterically demanding
tertiary phosphine ligands, the bis-phosphine complex
would be favoured, whereas bulky tertiary phosphines
would prefer the mono-ligand complex, thus relieving
steric crowding at the zinc(II) centre. Such a theory
seems reasonable and is in agreement with the cone-
angle theory first expounded by Tolman [5].
Thus, Fergusson and Heveldt [6] prepared the bis-
phosphine complexes ZnX2(R3P)2 (R3=Et3 or Et2Ph;
X=Cl, Br or I) and spectroscopically characterised
them as monomeric tetrahedral species. With the bulky
tricyclohexylphosphine, Moers and Langhout [7] re-
ported both ZnX2(Cy3P)2 and ZnX2(Cy3P) (X=Cl, Br,
I or NCS), concluding that the latter were dimeric.
However, whilst Goel and Ogini [8] were able to pre-
In contrast to that of divalent cadmium and mercury,
very little work has been carried out into the coordina-
tion chemistry of zinc(II) with Group 15 donors. Al-
though such complexes containing tertiary phosphine
ligands have been known for nearly 50 years [1,2], their
precise nature remains uncertain and has proved con-
troversial [3,4]. Nonetheless, in the case of the coordi-
nation compounds formed between zinc(II) halides and
tertiary phosphines, two structural types have been
identified, viz. the bis-phosphine complexes, ZnX2L2,
and the mono-ligand complexes, [ZnX2L]2. It has been
* Corresponding author. Tel.: +44-161-200 4516 ext. 4568; fax:
+44-161-228 1250.
E-mail address: stephen.m.godfrey@umist.ac.uk (S.M. Godfrey)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00197-8

214
S.M. Godfrey et al. / Inorganica Chimica Acta 292 (1999) 213–219
pare ZnX2(Cy3P), attempts to prepare the bis-phos-
phine complex ZnX2(Cy3P)2 claimed by Moers and
Langhout [7] resulted in the isolation of the mixed
phosphineꢀphosphine oxide complex ZnX2(Cy3P)(Cy3-
PO). These results seem to confirm Goel and Ogini’s
earlier conclusion [9] that bulky phosphines such as
tri(tertiarybutyl)phosphine will only form mono-ligand
complexes with zinc(II) halides.
In 1992, we reported, in a preliminary communica-
tion [10], the reaction of R3PI2 (R=Me, Et, Prn, Bun)
with zinc metal powder in diethyl ether solution to yield
the unexpected mono-ligand complexes [ZnI2(R3P)]2
(Eq. (1)) [10].
We now report a comprehensive study of the reaction
of R3PI2 (R3=Ph3, substituted triaryl, mixed aryl/
alkyl, trialkyl) with zinc metal powder. The motivation
for the present study is for the following reasons: firstly,
no comprehensive study of zinc(II) complexes contain-
ing a wide variety of tertiary phosphine ligands has so
far been reported; secondly, the use of a variety of
tertiary phosphine ligands may shed further light on
which structure (monomeric or dimeric) a given zinc(II)
phosphine complex adopts. Finally, we have already
reported the synthesis of novel products from the reac-
tion of our reagents R3PI2 with other metal powders
and there remains, therefore, the possibility that unex-
pected zinc complexes may be formed via this reaction
route.
EtO , N
2
2
R3PI2+Zn ꢀꢀꢀꢀꢀꢁ [ZnI2(R3P)]2
(1)
ca. 1 h, r.t.
(R=Me, Et, Prn, Bun)
The mono-ligand complex [ZnI2(PEt3)]2 was struc-
turally characterised by single crystal X-ray diffraction,
and was the first simple zinc(II) tertiary phosphine
complex to be crystallographically characterised. The
fact that this complex contains a tertiary phosphine
ligand of low steric requirements and has a mono-lig-
and stoichiometry casts further doubt on the existence
of the bis-phosphine complexes ZnX2(R3P)2, and sug-
gests that previous reports of such complexes are incor-
rect, and may represent the mixed ligand species
ZnX2(R3P)(R3PO) as originally proposed by Goel and
Ogini [8]. However, in 1996 Cotton and Schmidt [11]
characterised the monomeric tetrahedral complex
ZnCl2(PMe3)2, clearly establishing that monomeric
zinc(II) complexes can be prepared if ligands of suffi-
ciently small steric requirements are employed. In addi-
tion, the same workers also crystallographically
2. Results and discussion
Equimolar quantities of triorganophosphorus diio-
dide and zinc metal powder were reacted under anaero-
bic and anhydrous conditions in diethyl ether solution.
For the majority of R3PI2 compounds, a dimeric com-
plex results in quantitative yield (Eq. (2)):
Et O, N
2
2R3PI3+2Znꢀꢀꢀ2ꢀꢀꢀꢀꢀꢁ[ZnI2(PR3)]2
(2)
r.t., 1–20 days
The reaction times vary considerably and are dependent
upon R. In the case of trialkylphosphorus diiodides, all
the zinc metal is consumed within a matter of hours;
whereas, for substituted aryl derivatives reaction times
were in the region of 18–20 days. Additionally, the
reaction of R3PI2 (R3=Ph3, Ph2Et, Ph2Me) with zinc
metal powder does not produce a dimeric complex (Eq.
(2)), and this will be discussed later.
characterised Zn2Cl4(Me3P)3, in which
a
cationic
Analytical data and 31P{H} NMR shifts for the
dimeric complexes, [ZnI2(PR3)]2, are presented in Table
1. Clearly, from elemental analysis results in Table 1,
this stoichiometry is favoured for the majority of ter-
tiary phosphine complexes of zinc(II) iodide prepared
by this route. Interestingly, the reaction of Me3PI2 with
zinc metal powder also produces the dimeric complex
[ZnI2(PMe3)]2 which contrasts with the reaction of
Me3AsI2 with zinc powder [19], which produces the
monomeric complex ZnI2(AsMe3)2 and ZnI2. Clearly
the production of the zinc(II) complex formed (dimeric/
monomeric) results from a delicate balance of steric and
electronic factors
Only one compound of formula [ZnI2(PR3)]2 has
been crystallographically characterised [10], [ZnI2-
(PEt3)]2, which contains a tertiary phosphine of modest
steric requirements. It was therefore decided to crystal-
lographically characterise a second example of a com-
plex of this stoichiometry which contains a bulky
tertiary phosphine for comparative purposes. Recrys-
tallisation of {ZnI2[P(NMe2)3]}2 from dichloromethane
solution at room temperature yielded a large quantity
(Me3P)3Zn2+ moiety is linked via a Cl bridge to an
anionic ZnCl3− moiety.
We have investigated the reaction of R3PI2 com-
pounds with a number of unactivated course grain
metal powders and have produced a variety of unantic-
ipated metal complexes. The tremendous oxidising
powder of our R3PI2 reagents is illustrated by the
ability of Me3PI2 to oxidise cobalt [12–14], nickel [15]
and even gold [16] powders directly to the +3 oxida-
tion state in a single reaction step.
Additionally, our new synthetic procedure of reacting
R3PI2 with metal powders has led to unusual and, in
some cases, previously unobtainable metal complexes:
for example, CoI3(SbPh3)2 [17], In2I4(PPrn3)2 [18] and
AuI3(PMe3)2 [16]. Recently we have investigated [19]
the reaction of the related arsenic-containing reagents
R3AsI2 (R=Et, Me) with zinc metal powder and found
that where R=Et, a dimeric complex, [ZnI2(AsEt3)]2,
results, whereas, where R=Me, a monomeric complex
results, ZnI2(AsMe3)2. The reasons for this are assumed
to be steric [19].

S.M. Godfrey et al. / Inorganica Chimica Acta 292 (1999) 213–219
215
Table 1
Analytical and spectroscopic data for the complexes [ZnI2(PR3)]2
Complex
Colour
Analysis % Found (Calc.)
31P{H} a (ppm)
C
H
I
N
{ZnI2[P(NMe2)3]}2
{ZnI2[P(NEt2)3]}2
white
v. pale green
white
v. pale green
white
white
white
white
off-white
white
white
14.8(14.9)
25.6(25.4)
24.0(22.5)
21.6(21.1)
43.5(43.3)
35.9(36.1)
40.7(40.4)
39.9(38.3)
34.9(35.1)
35.0(34.0)
30.5(31.6)
36.2(37.6)
36.3(37.8)
36.4(38.1)
4.0(3.7)
5.6(5.3)
5.2(4.4)
2.4(2.3)
4.0(4.1)
5.7(5.5)
3.6(3.4)
3.3(2.9)
2.7(2.4)
2.3(1.9)
1.9(1.8)
3.4(3.1)
3.7(3.5)
3.8(3.9)
52.2(52.7)
44.4(44.9)
52.5(53.0)
48.4(49.6)
37.9(38.2)
42.9(42.4)
40.9(40.8)
42.3(42.7)
43.4(43.6)
39.9(40.0)
38.8(37.1)
36.7(37.9)
32.1(33.4)
29.3(29.8)
8.5(8.7)
7.2(7.4)
41.5b
38.6
42.8
[ZnI2(PPri3)]2
{ZnI2[P(CH2CH2CN)3]}2
{ZnI2[P(CH2CH2Ph)3]}2
[ZnI2(PCy3)]2
[ZnI2(PBz3)]2
[ZnI2(PPh2Bz)]2
7.8(8.2)
2.3(2.4)
11.8
40.0 b
77.3
24.0
10.1
−6.9
36.1
[ZnI2(PPh2Py)]2
{ZnI2[P(4-FC6H4)3]}2
{ZnI2[P(4-ClC6H4)3]}2
{ZnI2[P(4-CH3OC6H4)3]}2
{ZnI2[P(2,6-CH3OC6H3)3]}2
{ZnI2[P(2,4,6-CH3OC6H2)3]}2
38.4 b
−19.9
−59.4
−52.4
pale yellow
v. pale yellow
v. pale yellow
a All shifts are relative to 85% phosphoric acid standard.
b These shifts were recorded in CDCl3, the remainder were recorded in CD3CN.
,
of colourless crystals on standing at r.t. for approxi-
mately 5 days. From these, one suitable for analysis by
single crystal X-ray diffraction was chosen. The crystal
structure of {ZnI2[P(N Me2)3]}2 is illustrated in Fig. 1,
and selected bond lengths and angles are displayed in
Table 2. Predictably, this complex is also dimeric, simi-
lar to the only other crystallographically characterised
[10] simple zinc(II) iodide tertiary phosphine complex
[ZnI2(PEt3)]2. This result shows that the dimeric struc-
ture is available for zinc(II) iodide complexes containing
tertiary phosphine ligands of both modest and rather
greater steric requirements: d(ZnꢀP) for {ZnI2[P-
(N-Me2)3]}2, 2.372(3) A, is slightly longer than that
,
observed for [ZnI2(PEt3)]2, 2.361(5) A, whereas both the
terminal and bridging d(ZnꢀI) are similar for both
complexes, being 2.533(1) and 2.532(3), and 2.695(1)
and 2.689(3) A, for {ZnI2[P(NMe2)3]}2 and [ZnI2-
(PEt3)]2, respectively. Both complexes exhibit close to
regular tetrahedral geometries for the zinc(II) metal
centres.
,
The 31P{H} NMR shifts for the complexes
[ZnI2(PR3)]2 recorded in CDCl3 solution are shown in
Table 1. The spectra exhibit single chemical shifts,
similar to the limited number of spectra previously
recorded for other zinc complexes of formula
[ZnI2(PR3)]2, which have been shown not to ionise in
solution [8,9]. It therefore seems likely, by analogy to
these latter compounds, that the zinc(II) complexes
reported here also retain their molecular dimeric struc-
ture in solution.
2.1. The reaction of R3PI2 (R3=Ph3, Ph2Et, Ph2Me)
with zinc metal powder
Surprisingly, reaction of 1 equiv. of R3PI2 (R3=Ph3,
Ph2Et, Ph2Me) with zinc powder does not produce the
1:1 dimeric complex [ZnI2(PR3)]2. Instead, equimolar
quantities of the bis-phosphine monomeric complexes
ZnI2(PR3)2 (R3=Ph3, Ph2Et, Ph2Me) and zinc(II) io-
dide are produced, (Eq. (3)).
Et O, N
2
2
2R3PI2+2Zn ꢀꢀꢀꢀꢀꢁ ZnI2(PR3)2+ZnI2
(3)
2 days, r.t.
(R3=Ph3, Ph2Et, Ph2Me)
The slightly lower solubility of ZnI2(PR3)2 compared to
ZnI2 in diethyl ether solution means that separation of
Fig. 1. The X-ray crystal structure of dimeric {ZnI2[P(NMe2)3]}2.

216
S.M. Godfrey et al. / Inorganica Chimica Acta 292 (1999) 213–219
Table 2
Table 4
,
Selected bond lengths (A) and angles (°) for {ZnI2[P(NMe2)3]}2
Comparison of the X-ray powder diffraction patterns of experimen-
tally derived ZnI2 and the standard database entry
Zn(1)ꢀP(1)
Zn(1)ꢀI(2)
Zn(1)ꢀI(1)
Zn(1)ꢀI(1)
2.372(3)
2.5331(15)
2.6930(15)
2.6968(14)
Experimentally derived a ZnI2
ZnI2 JCPDS card no. 10-72
a
,
,
d (A)
Irel
d (A)
Irel
P(1)ꢀZn(1)ꢀI(2)
P(1)ꢀZn(1)ꢀI(1)
I(2)ꢀZn(1)ꢀI(1) a
P(1)ꢀZn(1)ꢀI(1) a
I(2)ꢀZn(1)ꢀI(1) a
I(1)ꢀZn(1)ꢀI(1) a
Zn(1)ꢀI(1)ꢀZn(1) a
123.55(8)
105.79(7)
110.06(5)
104.83(7)
109.89(5)
100.13(4)
79.87(4)
3.495
3.963
2.946
100
26
30
3.489
3.067
2.944
2.441
2.169
2.125
100
19
5
3
19
39
2.171
2.128
38
45
a Differences observed between the two patterns are due to trace
contamination of the experimentally derived ZnI2 with the complex
ZnI2(PR3)2 (see text).
a Symmetry transformations to generate equivalent atoms: −x+1,
−y, −z+1.
is very surprising and unequivocally shows that bis-
phosphine complexes of zinc(II) are not restricted to the
lighter halides nor to PR3 ligands with very small cone
angles, e.g. ZnCl2(PMe3)2, which had previously been
claimed by Goel and coworkers [8,9]. Indeed, the for-
mation of a mononuclear species from the reaction of
Ph2MePI2 with zinc metal powder is particularly sur-
prising since the reaction of Et3PI2, which contains a
parent tertiary phosphine of lower steric requirements,
produces the dimeric complex [ZnI2(PEt3)]2. It is also
interesting that, in the present study, the complexes
which appear to favour a monomeric structure contain
phenyl rings (but not substituted phenyl rings). It there-
fore occurred to us that the presence of these non-
substituted aromatic rings may be responsible for this
monomeric structure. A closer examination of the crys-
tal structure of ZnI2(PPh2Me)2 provides a possible ex-
planation. The nature of the crystal packing allows for
significant P–P interactions of the phenyl rings of the
tertiary phosphine ligands. This presumably imparts
greater stability to the complex, and, since such interac-
tions may not be possible in a dimeric complex, may
explain why zinc(II) complexes containing tertiary
the two products is possible, although difficult. Analyt-
ical data and 31P{H} NMR shifts for the complexes
ZnI2(PR3)2 (R3=Ph3, Ph2Et, Ph2Me) are given in Table
3. In the case of the reaction of Ph3PI2 with zinc,
gradual concentration of the filtrate from the reaction
led eventually to a relatively pure sample of ZnI2. This
was studied using X-ray diffraction, and the d-spacings
and relative intensities of experimentally derived ZnI2
and the standard database entry for ZnI2 are compared
in Table 4. Although there are some unassigned peaks
(which arise from trace contamination from the com-
plex, ZnI2(PPh2Me)2), the agreement unequivocally es-
tablishes zinc(II) iodide as a product from the reaction.
Acceptable X-ray powder diffraction patterns recorded
for experimentally derived ZnI2 from the other two
reactions were also obtained.
In the case of the reaction of Ph2MePI2 with zinc
metal powder, a sample of the complex ZnI2(PPh2Me)2
was carefully separated from ZnI2 and recrystallised
from diethyl ether solution at r.t. On standing for
approximately 7 days at r.t. a large number of colour-
less crystals formed, one of which was selected for
analysis by single crystal X-ray diffraction. The struc-
tural analysis confirms the monomeric structure of
ZnI2(PPh2Me)2 (Fig. 2). Selected bond lengths and an-
gles are displayed in Table 5. The fact that this com-
plex, which contains a tertiary phosphine of relatively
high steric requirements, adopts a monomeric structure
phosphine ligands with phenyl rings prefer
a
monomeric structure. The P–P interactions of the
phenyl rings in ZnI2(PPh2Me)2 is more clearly illus-
trated in its space-filling representation (Fig. 3). It is
presumed that such interactions are also present in the
monomeric complexes ZnI2(PR3)2 (R=Ph3, Ph2Et),
Table 3
Analytical and spectroscopic data for the complexes ZnI2(PR3)2
Complex
Colour
Analysis % Found (Calc.)
31P{H} a (ppm)
C
H
I
ZnI2(PPh2Me)2
ZnI2(PPh2Et)2
ZnI2(PPh3)2
white
white
white
42.1(43.4)
42.4(45.0)
49.7(51.2)
3.5(3.6)
4.1(4.0)
3.5(3.6)
36.5(35.3)
36.6(34.0)
29.0(30.1)
−4.5
2.7
−3.3
a All shifts are relative to 85% phosphoric acid standard.

S.M. Godfrey et al. / Inorganica Chimica Acta 292 (1999) 213–219
217
Fig. 2. The X-ray crystal structure of monomeric ZnI2(PPh2Me)2.
thus providing a possible explanation why this structure
Table 5
Selected bond lengths (A) and angles (°) for ZnI2(PPh2Me)2
,
is favoured rather than the dimeric structure,
[ZnI2(PR3)]2, exhibited by the majority of zinc(II) ter-
tiary phosphine complexes. For ZnI2(PPh2Me)2, both
Zn(1)ꢀP(1)
Zn(1)ꢀI(1)
2.416(5)
2.5702(2)
,
,
d(ZnꢀI), 2.570(2) A and d(ZnꢀP), 2.4165(5) A are
a
P(1)ꢀZn(1)ꢀP(1)
P(1)ꢀZn(1)ꢀI(1)
P(1) aꢀZn(1)ꢀI(1)
I(1)ꢀZn(1)ꢀI(1) a
103.9(3)
significantly longer than d(ZnꢀIt), and d(ZnꢀP) in
108.83(11)
109.05(11)
116.44(12)
,
{ZnI2[P(NMe2)3]}2 which are 2.533(1) and 2.372(3) A,
respectively. A likely explanation for this is the greater
basicity of P(NMe)3 compared to PPh2Me, and the
greater steric crowding around the mono-ligand, com-
pared to the bis-ligand, zinc(II) metal centre.
a Symmetry transformations to generate equivalent atoms: −x+1,
y, −z+2/3.
The 31P{H} NMR solution shifts for the complexes
ZnI2(PR3)2 recorded in CDCl3 solution are shown in
Table 3. The spectra exhibit single chemical shifts simi-
lar to those previously recorded for the analogous
cadmium(II) complexes CdI2(PR3)2 (R3=Ph3 [20],
Ph2Et [21], Ph2Me [22]). These cadmium(II) complexes
have been shown not to dissociate in CDCl3 solution
and, due to the similarity of the 31P{H} NMR values
for these complexes and the analogous zinc complexes
ZnI2(PR3)2, described herein, it is tentatively concluded
that these complexes also retain their molecular struc-
ture and do not dissociate in this solvent.
In conclusion, we would like to emphasise that the
complex {ZnI2[P(NMe2)3]}2 represents only the second
example of a simple zinc(II) compound containing ter-
tiary phosphine ligands to be characterised by single
crystal X-ray diffraction. Both this complex and
[ZnI2(PEt3)]2, the first crystallographically characterised
example of the mono-ligand complex, have been pre-
pared from the novel reaction of the reagents R3PI2
(R=NMe2, Et) with zinc metal powder. It has thus
been established that the dimeric 1:1 zinc:tertiary phos-
phine stoichiometry is available for zinc(II) complexes
regardless of the steric requirements of the tertiary
Fig. 3. A space-filling representation of the crystal structure of
ZnI2(PPh2Me)2.

218
S.M. Godfrey et al. / Inorganica Chimica Acta 292 (1999) 213–219
phosphine. The crystallographic characterisation of
ZnI2(PPh2Me)2 is important since it represents the first
crystal structure of a bis-phosphine complex of zinc(II)
iodide to be reported and, more importantly, illus-
trates that the nature of the zinc(II) complexes formed
from the reaction of R3PI2 reagents with zinc metal
powder is dependent on R, a phenomenon we have
previously observed in the reaction of R3PI2 with
manganese [23–25], cobalt [12–14], nickel [15], gallium
[26], and indium [18] metal powders. The reason why
the monomeric [ZnI2(PR3)], rather than the dimeric
[ZnI2(PR3)]2, complexes result from the reaction of
R3PI2 (R3 =Ph3, Ph2Et, Ph2Me) with zinc metal pow-
der may be due to favourable P–P interactions in the
ligand phenyl rings, illustrating the subtle structural
balance between mono- and bis-ligand complexes for
zinc(II) halide tertiary phosphine complexes. Synthesis
of the dimeric complexes, [ZnI2(PR3)]2, by the direct
reaction of zinc metal powder and the appropriate
R3PI2 reagent provides an excellent, even favourable
synthetic route, compared to conventional techniques
using ZnI2. Reaction times are fast (being only a few
hours in many cases) and the need for rigorous drying
of ZnI2 is obviated; additionally, yields are quantita-
tive in all cases. In contrast, however, synthesis of the
bis-ligand complexes, ZnI2(PR3)2, is, in fact, problem-
atic. Separation of the complex ZnI2(PR3)2 from an
equimolar quantity of ZnI2 in diethyl ether is difficult
and complete separation of the two products can be
rather time-consuming. The principal reason for this is
the similar solubilities of the two products. Neverthe-
less, isolation of a sufficient quantity of the pure com-
plex ZnI2(PR3)2 for characterisation is easily achieved
by removal of approximately half of the solvent from
which uncontaminated ZnI2(PR3)2 can then be ob-
tained. Removal of more solvent tends to lead to the
precipitation of some ZnI2. More importantly, since
previous workers [8,9] have claimed that the
monomeric complexes ZnI2(PR3)2 are only available
from conventional synthetic techniques (using ZnI2 as
starting material) when small tertiary phosphine lig-
ands are employed, the synthesis of the complexes
ZnI2(PR3)2 (R=Ph3, Ph2Et, Ph2Me) which contain
tertiary phosphine ligands of relatively large steric re-
quirements could possibly be attributed to our new
synthetic methodology starting from zinc metal pow-
der.
reagents, R3PI2, has been described elsewhere [27,28].
Diethyl ether (BDH) was dried over sodium wire for
approximately 1 day and then distilled over CaH2 in
an inert atmosphere prior to use. The dry diethyl ether
was then distilled directly into the reaction vessel.
Standard reagent grade zinc metal powder was found
in the laboratory, crudely labelled, and was used with-
out further purification. After isolation, any subse-
quent manipulation of the complexes was carried out
inside a Vacuum Atmospheres HE-493 glovebox.
3.1. Synthesis of the complexes [ZnI2(PR3)]2
All the complexes [ZnI2(PR3)]2 were synthesised in
quantitative yield from the direct stoichiometric 1:1
reaction of R3PI2 and zinc metal powder. The synthe-
sis of {ZnI2[P(NMe2)3]}2 is typical: I2P(NMe2)3 (0.895
g, 2.15 mmol) was suspended in diethyl ether (ca. 70
cm3) and subsequently zinc metal powder (0.142 g,
2.15 mmol) was added. After approximately 3 days,
the resultant white solid was isolated by standard
Schlenk techniques and dried in vacuo. The solid was
then transferred to pre-dried argon-filled ampoules
which were flame sealed.
Elemental analyses were performed by the analytical
laboratory of this department and the results are dis-
played in Tables 1 and 3. 31P{H} NMR spectra were
recorded as CDCl3 solutions on a Brucker AC200
high-resolution multiprobe spectrometer relative to
concentrated phosphoric acid as standard. X-ray pow-
der diffraction patterns were recorded on a Scintag
XRD2000 powder diffractometer using copper Ka ra-
,
diation of u=1.5418 A.
3.2. Crystallography
Crystals of {ZnI2[P(NMe2)3]}2 and ZnI2(PPh2Me)2
were independently mounted in Lindemann tubes un-
der an atmosphere of dry argon. All measurements
were performed on a Rigaku AFC 6S four-circle dif-
fractometer employing graphite monochromated Mo
,
Ka radiation (u=0.71069 A) and ꢀ–2q scans. Both
structures were solved by direct methods. Unit-cell
dimensions were derived from the setting angles of 25
accurately centred reflections. Lorentz polarisation
corrections were applied. Details of the X-ray mea-
surements and subsequent structure determinations are
presented in Table 6. Hydrogen atoms were confined
to chemically reasonable positions. Neutral atom scat-
tering factors were taken from Ref. [29]. Anomalous
dispersion effects were taken from Ref. [30]. All calcu-
lations were performed using the TEXSAN suite of
computer programs [31].
3. Experimental
All of the zinc(II) tertiary phosphine complexes de-
scribed herein are moisture sensitive, as are the
reagents R3PI2; therefore, strictly anaerobic and anhy-
drous conditions were adhered to during their synthe-
sis. The synthesis of the triorganophosphorus diiodide

S.M. Godfrey et al. / Inorganica Chimica Acta 292 (1999) 213–219
219
Table 6
[2] R.C. Cass, G.E. Coates, R.G. Hayter, J. Chem. Soc. (1955)
4007.
[3] M.N. Hughes, Coord. Chem. Rev. 37 (1981) 315.
[4] E.C. Constable, Coord. Chem. Rev. 58 (1984) 38.
[5] (a) C.A. Tolman, J. Am. Chem. Soc. 92 (1970) 2956. (b) C.A.
Tolman, Chem. Rev. 77 (1977) 313.
[6] J.E. Fergusson, P.F. Heveldt, Inorg. Chim. Acta 31 (1978) 145.
[7] F.G. Moers, J.P. Langhout, Recl. Trav. Chim. Pays-Bas 92
(1973) 996.
[8] R.G. Goel, W.O. Ogini, Inorg. Chem. 16 (1977) 1968.
[9] R.G. Goel, W.P. Henry, N.K. Jha, Inorg. Chem. 21 (1982) 2551.
[10] N. Bricklebank, S.M. Godfrey, C.A. McAuliffe, A.G.
Mackie, R.G. Pritchard, J. Chem. Soc., Chem. Commun. (1992)
944.
Crystal data and details of refinement for {ZnI2[P(NMe2)3]}2 and
ZnI2(PPh2Me)2
{ZnI2[P(NMe2)3]}2 ZnI2(PPh2Me)2
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C6H18I2N3PZn
482.37
C26H26I2P2Zn
359.79
293(2)
293(2)
,
0.71069
monoclinic
P21/c (no. 14)
0.71069
monoclinic
C2/c
Unit cell dimensions
,
a (A)
10.910(3)
10.094(3)
13.552(4)
95.08(2)
1486.6(7)
4
14.872(4)
13.130(9)
15.259(4)
109.32(3)
2812(2)
8
,
b (A)
[11] F.A. Cotton, G. Schmidt, Polyhedron 15 (1996) 4053.
[12] S.M. Godfrey, H.P. Lane, C.A. McAuliffe, R.G. Pritchard, J.
Chem. Soc., Dalton Trans. (1993) 1599.
[13] C.A. McAuliffe, S.M. Godfrey, A.G. Mackie, R.G. Pritchard,
Angew. Chem., Int. Ed. Engl. 31 (1992) 919.
,
c (A)
i (°)
3
,
Volume (A )
Z
Dcalc (Mg m−3
)
2.155
1.700
[14] N. Bricklebank, S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard,
J. Chem. Soc., Dalton Trans. (1996) 157.
[15] S.M. Godfrey, N. Ho, C.A. McAuliffe, R.G. Pritchard, J. Chem.
Soc., Dalton Trans. (1993) 2875.
[16] S.M. Godfrey, N. Ho, C.A. McAuliffe, R.G. Pritchard, Angew.
Chem., Int. Ed. Engl. 35 (1996) 2344.
[17] S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard, J. Chem. Soc.,
Chem. Commun. (1994) 45.
[18] S.M. Godfrey, K.J. Kelly, P. Kramkowski, C.A. McAuliffe,
R.G. Pritchard, J. Chem. Soc., Chem. Commun. (1997) 1001.
[19] S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard, J.M. Sheffield, J.
Chem. Soc., Dalton Trans. (1996) 3309.
[20] B.E. Mann, Inorg. Nucl. Chem. Lett. 7 (1971) 595.
[21] R.G. Goel, W.P. Henry, R.C. Srivastava, Inorg. Chem. 20
(1981) 1727.
Absorption coefficient
(mm−1
F(000)
58.84
31.95
)
904
1392
0.25×0.15×0.10
2408
2408
142
Crystal size (mm)
Reflections collected
Observed reflections
Parameters
0.30×0.20×0.20
2746
2602
124
Goodness-of-fit on F2
1.021
0.803
Final R indices [I\2|(I)] R1=0.0417,
wR2=0.1055
R indices (all data)
R1=0.0448,
wR2=0.1024
R1=0.3471,
wR2=0.1734
R1=0.0935,
wR2=0.1288
0.589 and −1.193 0.908 and −1.434
Largest difference peak
−3
,
and hole (e A
)
[22] J.M. Kessler, J.H. Reeder, R. Va, C. Yeung, J.H. Nelson, J.S.
Frye, N.W. Alcock, Magn. Reson. Chem. 29 (1991) 594.
[23] S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard, J. Chem. Soc.,
Dalton Trans. (1993) 371.
[24] S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard, J. Chem. Soc.,
Dalton Trans. (1991) 1447.
[25] S.M. Godfrey, A.G. Mackie, C.A. McAuliffe, R.G. Pritchard, J.
Chem. Soc., Chem. Commun. (1993) 2229.
[26] B. Beagley, S.M. Godfrey, K.J. Kelly, S. Kungwankunakorn,
C.A. McAuliffe, R.G. Pritchard, J. Chem. Soc., Chem. Com-
mun. (1996) 2179.
4. Supplementary material
Atomic coordinates, bond lengths and angles and
thermal parameters have been deposited with the Cam-
bridge Crystallographic Data Centre (CCDC). See in-
structions for Authors, J. Chem. Soc., Dalton Trans.
1997, Issue 1. Any request to the CCDC for this
material should quote the full literature citation and the
reference number.
[27] N. Bricklebank, S.M. Godfrey, A.G. Mackie, C.A. McAuliffe,
R.G. Pritchard, P.J. Kobryn, J. Chem. Soc., Dalton Trans.
(1993) 101.
Acknowledgements
[28] N. Bricklebank, S.M. Godfrey, H.P. Lane, C.A. McAuliffe,
R.G. Pritchard, J.M. Moreno, J. Chem. Soc., Dalton Trans.
(1995) 2521.
[29] International Tables for X-ray Crystallography, vol. 4, Kynoch
Press, Birmingham, 1974, Table 2.3.1.
We are grateful to the EPSRC for a research stu-
dentship (to J.M.S.).
References
[30] International Tables for X-ray Crystallography, vol. 4, Kynoch
Press, Birmingham, 1974, Table 2.2A.
[31] TEXSAN
–TEXRAY, Structure Analysis Package, Molecular
[1] W. Reppe, W.J. Schweckendiek, Liebigs Ann. Chem. 560 (1948)
104.
Structure Corporation, The Woodlands, Houston, TX, 1985.
.