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Perspectives in Organometallic Chemistry


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Perspectives in Organometallic
Chernistry

Edited by
C. G. Screttas and B. R. Steele
National Hellenic Research Foundation, Athens, Greece

advancing the chemical sciences


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The proceedings of the 20th International Conference on OrganometallicChemistry held in
Corfu, Greece on 7-12 July 2002.

Special Publication No. 287
ISBN 0-85404-876-6

A catalogue record for this book is available from the British Library
0 The Royal Society of Chemistry 2003

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this publication may not be reproduced, stored or transmitted, in any form or by any means,
without the prior permission in writing of The Royal Society of Chemistry, or in the case of
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issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries
concerning reproduction outside the terms stated here should be se. to The Royal Society of
Chemistry at the address printed on this page.
A

Published by The Royal Society of Chemistry,
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Cambridge CB4 OWF, UK
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For further information see our web site at www.rsc.org
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Preface
The 20* International Conference on Organometallic Chemistry, which was held in
Corfu, Greece in July 2002, provided an opportunity for organometallic chemists
from all over the world to learn about the latest developments in the field from
young and senior researchers alike. This series of conferences dates back to 1963

and has become a major event in the calendar of those who have an interest in this
important area. Prominent organometallic chemists were specially invited to make
presentations at the conference and a number of them kindly agreed to submit
written accounts of their recent work to be published in this special volume. The
chapters in this book are thus intended to reflect state-of-the-art developments in
organometallic chemistry by some of the foremost groups in the field.
The aim of the conference was to provide a forum for the presentation of the
latest results in all areas of interest to organometallic chemists. Organometallic
chemistry is an area which touches on and plays an active role in all of the
traditional divisions of chemistry, inorganic, organic, physical and theoretical,
while the field of bio-organometallic chemistry is also now attracting substantial
interest and it was particularly pleasing that all of these areas were represented at
the meeting. It is intended that the present volume should also reflect the many
facets of organometallic chemistry and, in the knowledge that an organometallic
chemist is required to have a broad knowledge of most, if not all of these areas, we
hope that the contents of this volume will be of wide appeal.
We are grateful to all the authors for preparing their contributions within a rather
strict time schedule and hope that this book will constitute a useful source of
information and ideas.
C.G. Screttas
B.R. Steele

V


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Contents
Group 15 element imido and phosphido cages; Coordination chemistry and
synthetic applications
E L Doyle, A.D. Hopkins, G.T. Luwson, M.McPartlin, A.D. Woods and
D.S. Wright
Neutral clusters EnRn of the monovalent elements gallium and indium.
Recent results in synthesis and reactivity
W. Oh1

1

16

New titanium imido chemistry with polydentate N-donor ligands
P. Mounford

28

Organometallic complexes with 1,2-dichalcogenolate-o-carboranes
Guo-Xin Jin

47

Synthesis and reactivities of multinuclear sulfur-bridged metal
complexes ranging from dinuclear to hexanuclear cores
M. Hidai

62

a,o-Bis [(triphenylphosphine)gold(I)] hydrocarbons

K.A. Porter, A. Schier and H. Schmidbaur

74

Researches on non-classical organolanthanide chemistry
P.B. Hitchcock, A. G. Hulkes, A. V. Khvostov, M.F. Lappert and
A. K Protchenko

86

Hyper-structured alkynylruthenium complexes: Effect of dimensional
evolution on NLO properties
M.G. Humphrey, M.P. Cijientes, M. Samoc, T. Isoshimu and A. Persoons
Cycloaddition of alkynes mediated by [RuCp(L)]+ (L = CO, NCH, PH3)
and RuCpCl complexes - Metallacyclopentatrienes as key intermediates A DFT study
M.J. Calhorda, K. Kirchner and L F. Veiros
Selective C-C coupling reactions of Me2N-bC-NMe2 at iron(0) centers
A.C. Filippou, T. Rosenauer and G. Schnaknburg
Routes to fluorinated organic derivatives by nickel mediated C-Factivation
of heteroaromatics
T. Braun and R.N.Perutz

Vii

100

111

120


136

'


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Viii

Contents

Novel q5 - q6 rearrangement of bis(fluoreny1)lanthanide complexes
by the addition of A l R 3
H. Yasuda
Results and perspectives of high oxidation state organomolybdenum
chemistry in water
E. Collange, F. Demirhan, J. Gun, 0.Lev, A. Modestov, R. Poli,
P. Richard and D. Saurenz
Modulation of electronic behaviour of metal carbonyl clusters
D. Collini, C. Femoni, M.C. Iapalucci, G. Longoni and P. Zunello
Interionic and intermolecular solution structure of transition metal
complexes by N M R
A. Macchioni
Synthetic and mechanistic pathways in platinum(I1) chemistry
R. Romeo and L. Monsu Scolaro
New perspectives for olefin complexes: Synthesis and characterisation
of stable rhodium(0)and iridium(0) complexes
J. Harmer, G. Frison, M. Rudolph, H. Schonberg, S. Deblon, P. Maire,
S. Boulmiiaz, F. Breher, C. Bohler, H. Riiegger, A. Schweiger and
H. Griitzmacher
Substitution and addition reactions catalyzed by transition metal complexes

I. P. Beletskuya
Late transition metal (CoyRh,Ir)-siloxide complexes - Synthesis,
structure and application to catalysis
B. Marciniec, I. Kownacki, M. Kubicki, P. Krzyzanowski, E. Walczuk
and P. Btazejewska-Chadyniak

152

167

183

196

208

222

240

253

Cheap chiral ligands for asymmetric transition metal catalyzed reactions
M.T. Reetz

265

Chiral metal complexes in asymmetric catalysis
C.Moberg, 0.Belda, K.Hallrnan, R. Stranne, M. Svensson, J.L. Vasse,
T. Wondirnagegn and R. Zalubovskis


275

In search of asymmetric propargylic substitution reactions mediated by
optically active indenyl-ruthenium(II) allenylidene complexes
V. Cadierno, S. Conejero, M. P. Gamasa and J. Gimeno

285

Recent developments on hydride iridium triisopropylphosphine complexes:
[IrH2(NCCH3)3(PiPr3)]BF4as hydrogenation catalyst
LA. Oro, E. Sola and J. Navarro

297


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Contents

ix

Pd complex-catalyzed ring-opening polymerisation of 2-aryl- 1-methylenecyclopropanes
S. Kim, D. Takeuchi and K. Osakada

306

Subject Index

3 17



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GROUP 15 ELEMENT IMIDO AND PHOSPHIDO CAGES; COORDINATION
CHEMISTRY AND SYNTHETIC APPLICATIONS

Emma L. Doyle,' Alexander D. Hopkins,' Gavin T. Lawson,' Mary McPartlin? Anthony
D. Woods,' Dominic S. Wright

'

'

Chemistry Department, University of Cambridge, Lensfield Road, Cambridge CB2 1EW,
UK; e-mail dsw 1OOO@,cus.cam.ac.uk.
School of Chemistry, University of North London, London N7 8DB, UK

1 INTRODUCTION
This review details recent developments in the synthesis and coordination chemistry
primarily of Group 15 imido and phosphido cages containing a variety of anionic
arrangements. The review will concentrate on the applications of these Group 15 anionic
ligands in organometallic chemistry, and essentially follows the theme of the lecture given
at the XXth International Conference on Organometallic Chemistry (Corfu, 2002). Further
aspects of this work have been published in separate review articles."2
2 MIXED (OR STEP-WISE) METALLATION
In contrast to the alkali metal organometallics (such as the ubiquitous "BuLi), the

organometallics of the later p block elements (E= Group 14, Sn, Pb; Group 15, As-Bi) are
significantly less polar. As a consequence previous synthetic strategies to imido (RN2-)
complexes of the later main group metals had been mainly limited to procedures involving
condensation with Group 15 halides (eqn. l), desilylation with SiR3 reagents (eqn. 2), or
(in rare cases) reactions of alkali metal RN2- reagents with p block element salts (eqn. 3).
In view of this background it is perhaps not surprising that until fairly recently very few
imido complexes of the later p-block metals had been structurally characterised.
EX3

+

EX3

+

EX3

+


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2

Perspectives in Organometallic Chemistry

The aim at the beginning of our studies in this area was to develop a range of p- block
metal reagents which were strong enough bases to effect smooth deprotonation of primary
amines, allowing direct access to complexes containing the RN2- dianion. We showed in
preliminary studies that Sb(NMe2)3, which is readily prepared in high yield via the reaction
of LiNMe2 with SbC13 (eqn. 4); will doubly-deprotonate a broad range of primary amines

even at low temperature (eqn. 5): Similar dimers of the type [Me2NSb@-NR)]2 are
isolated from these high-yielding reactions.
-3LiCl

SbC13

+ 3Me2NLi

Sb(NMe&

A

(4)

-4Me2NH

2Sb(NMe2)3 + 2RNH2

A

[MezNSb(p - NR)]2

(5)

The key point as regards further developments in this field to p-block metal anion
arrangements is that the extremely basic nature of reagents like Sb(NMe& contrasts with
the lower basicity generally observed for alkali metal organometallics (RM). In the
absence of conjugation within the organic group of the primary amine only single
deprotonation will follow (giving RNHM). Thus, there was the possibility that step-wise
deprotonation of the primary amine, first with R'M then with Sb(NMe2)3, would lead to

mixed alkali metal/p-block element imido complexes. This scenario is shown in Scheme 1.

[MI= Alkali metal Reagent; [El= Group 15 Reagent

Scheme 1

In practice the strategy of step-wise (or mixed-) metallation of primary amines (and,
indeed, of primary phosphines) employing Group 15 bases of the type E Me2 3 works
the
very well.' Alkali metal cage compounds containing the trianions [E(NR)3] - (type

P )3.'

dianions [E2(NR)4I2- (type ZI),6 and the monoanions [Me2NE(pu-NR))2E]-(type ZZI) can
be readily obtained (Figure 1). A significant point in regard to the selection of a particular
anion type is that the precise anion unit obtained by these reactions (the syntheses of which
are discussed in more detail later) depends on the synthetic route used. In this sense, the
reaction products are kinetically controlled and a particular desired ligand grouping can be
targeted by the choice of reaction conditions.


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Group 15 element imido and phosphido cages
TYPE I

r -I3-

3

TYPE I1


TYPE 111

1

/\ / \

2-

iR'

""\

R E /E\ER

MQN,

/N\ R\

E\N/E

E\
R
'

/E\

N
,M,


1-

/E

i

7

R

E = N; E= Sb
R= Cy, 'Bu, 2,5-(MeO)2C6H3.
CHzPh.
E = N; E= As
R= 'Bu, 2-pyridyl, CHzPh,
2-MeOC6H4.
E'= P; E= Sb
R= 'Bu, Cy.

N

R

E= Sb, A0

E= Sb

R= Cy
E= Bi
R= 'Bu


R= Cy

Figure 1 Principal Group 15 imido anion types.

3 STRUCTURE AND ORGANOMETALLIC REACTIONS OF IMIDO
COMPLEXES
The synthesis of trianionic frameworks of type Z is the most obvious reaction sequence,
involving the 3:l reaction of a primary amido alkali metal precursor (RNHM) with
Sb(NMe2)3 (eqn. 6a).5"bIn the case of the As(II1) analogues, a modified reaction sequence
is required owing to the lower basicity of As(NMe2)3, involving reaction of the amine with
As(NMe2)3 followed by deprotonation with "BuLi (eqn. 6b)." Several structurally
characterised examples containing Li' have been ~ r e p a r e d .All
~ of these have similar
structures in which two [E(NR)3I3- anions are associated by six Li' cation^,^ e.g.,
[ { Sb(NCy)3}2Li6.2Me2NH] (1) (Figure
In most cases the central N6Li6 'stack'
arrangement within these complexes is retained even in the presence of extensive Lewis
base solvation. The [E(NR)3I3-anions(E= Sb, As) are valence isoelectronic with the Group
16 dianions [E(NR)3]2-.7

-3Me2NH

As(NMe2)3 + 3RNH2

---+

+3"BuLi

[As(NHR)3]


[As(NR)~]~- (6a)

Bearing out the view that the [Sb(NR)3I3- trianions are the robust chemical
constituents of alkali metal cages of this type, these anions are transferred intact in
reactions with a range of main group and transition metal precursors.' For example, the
reaction of [Cp2Pb.TMEDA] (2) with 1 gives the heterometallic cage [{ Sb(NCy)3}2Pb3]
(3) (eqn. 7) (Figure 3), in which the three Pb" centres replace the six Li' cations at the
centre of the cage structure.* The predominant bonding within the SbzNbPb3 core of 3 is
undoubtedly between the N and Sb and Pb centres. However, it is of value to note here, in
relation to the later discussion of the behaviour of phosphide analogues, that the Pb3Sbz
metal core of the complex would (if an isolated fragment) conform to Wade's rules (an
n+l ,closo polyhedron).


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Perspectives in Organometallic Chemistry

4

Figure 2

Structure of the trianion complex I .

Figure 3

Structure of 3

Dianions can be accessed via the 1:2 stoichiometric reactions of dimers of the type
[Me2NE@-NR)]2 (E= As, Sb, Bi) with RNHM (eqn. 8).6 The structures of

[{E2(NCy)4}2L&](E= Sb,6aAs6c) (4) (Figure 4) consist of two [E2(NCy)4I2- dianions that
are associated by four Li' cations (adopting a tetrahedral Li4 arrangement at the centre of
the cage). This arrangement can be described as arising from the association of two
E2N4Li2 cubane units, a view that is supported by the dissociation of the com lexes into
these units in arene solutions.6dUnlike the alkali metal complexes of [Sb(NR)3] trianions,
Lewis base solvation of the Li' cations results in dissociation of the cubane constituents.
This is seen in the formation of the discrete cubane [Bi2(NfBu)4Li2.2thfl(5) from the
reaction of Bi(NMe2)3 with 'BuNHLi in thf as the solvent.6d

P


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Group 15 element imido and phosphido cages

Figure 4

5

Structure of the dianion complexes 4.

The reactivity patterns of alkali metal cages containing [E2(NR)4I2- dianions mirror
that of the trianion counterparts, the dianions being transferred intact to other metal ions.
This is illustrated here by the organometallic example of the reactions of the complexes 4
with Cp2Mn leading to the cubanes [E2(NtBu)4(MnCp)2] (5) (Figure 5).' Investigation of
the magnetic behaviour of these complexes reveals that they are predominantly high-spin,
with the magnetic properties being subtly dependent on the Group 15 element (E). The
origin of this dependence stems from the geometric constraints within the [E2(NCy)4I2ligands which effect the Mn.. .Mn separation and therefore the communication between the
two Mn" centres.


Figure 5 Structure of 5
The ability for ligands of this type to influence the architecture of coordinated metal
cores is illustrated most dramatically by the comparison of the structures of the two Cu
complexes [{ Sb2(NtBu)4}2Cuq]
and [{As2(NtBu)4}2C~](7)'Ob (Figure 6). The more
compact As2N2 ring of the [AS~(NCY)~]~dianion leads to a different ligand coordination
mode than in the Sb analogue, in which unfavourably close Cu.. .Cu contacts are avoided.
Consequently, 7 has an unusual CQ butterfly arrangement at its centre whereas 6 has a
square-planar CQ core.


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Perspectives in Organometallic Chemistry

6

Figure 6

Structure of (a) 6 and (3) 7.

Monoanions of type IZI can be repared by the reaction of the salt Sb(NHR)4Li with
the result is a bicyclic, spiro arrangement in which
Sb(NMe2)3 (1 :2 molar equivalents)!
the central Sb(II1) atom has a 10e, pseudo-trigonal bipyramidal geometry with the two
terminal Sb(II1) centres being 8e, pyramidal (eqn. 9). The normal coordination mode
observed in these species is illustrated in the structure of [{Me2NSb(NCy)2}2Sb]Li (8)
(Figure 7), in which the alkali metal ion is coordinated by two bridging NCy groups and by
the terminal Me2N groups of the monoanion ligand.5a The reactivity of the parent
[{Me2NSb(NCy)2}2Sb]- anion is of some interest. Reaction with primary amines leads to
replacement of the Me2N groups by RNH groups, with retention of the spiro structure of

the original monoanion.* In the structure of [{CyNHSb(NCy)2)2Sb]K.toluene (9) (Figure
8) the low coordination number of the K' ion is made up for by agostic interactions with
the Me groups of two toluene ligands.*
-4Me2NH

[Sb(NHR)4]- Li'

Figure 7

+ 2Sb(NMe2)3

Structure of the monoanion complex 8.

[{Me2NSb(p -NR)2)2Sb]

-

(9)


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Group 15 element imido and phosphido cages

Figure 8

7

Structure of 9.

However, the reaction of the [{Me2NSb(NCy)2}2Sb] - monoanion with 'BuOH leads to

rearrangement of the spiro structure into a nido isomer." The structure of the product
[{ Sb(,~-NCy)}3(p3-NCy)(O'Bu)2]K.toluene(10) is illustrated in Figure 9. One of the major
reasons for this rearrangement is the greater Lewis acidity of the Sb(II1) centres in 10
compared to those in 9, leading to an overall desire to increase the coordination numbers of
the Sb centres.

T27
Figure 9

Structure of the spiro-anion complex (10).

4 PHOSPHIDE ANALOGUES

As can be concluded from the previous section, the chemically robust nature of Group 15
imido systems gives them some potentially broad applications in various aspects of
coordination chemistry. There is, however, a striking difference between these systems and
their phosphide analogues2 Such phosphide cages decompose into Zintl compounds
containing -E: anions at relatively low temperatures, via an apparent step-wise mechanism
involving heterocyclic intermediates of the type [(RP)nE]- (Scheme 2). The extent of this
decomposition process and whether or not it can be limited to the intermediate
heterocycles depends on a number of factors, which include,


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Perspectives in Organometallic Chemistry

the organic group (R) present within the phosphide groups (d9;
aromatic groups
accelerate the formation of Zintl compounds, whereas aliphatic groups result in the
stabilisation of the [(RPbE] - heterocycles.

the presence of Me2NH in the reaction, which encourages formation of the Zintl
compound.
the alkali metal present in the Group 15 cage; as Group 1 is descended the
decomposition of the cage is encouraged.
the Group 15 element present; as the group is descended (from As to Bi) formation of
the Zintl phase becomes more favourable.

Scheme 2

Underlying the thermolability of the phosphide cages is the strength of single P-P
bonds, which are the strongest homoatomic bond energies of all the Group 15 elements.
The latter provides the thermodynamic driving force for the conversion of the Group
1Yalkali metal cages to (effectively) an alloy phase (the Zintl phase). The ultimate
formation of cylophosphazanes, [RP],,, together with the Zintl compound suggests that the
[(RP) ,,El - intermediates play the role of metal atom deliverers.
Although the phosphide cage C ( S ~ ( P C Y ) ~ ) ~ L ~ ~ . ~(11)
M ~(Figure
~ N H ] 1Oa) can be
obtained from the reaction of Sb(NMez)3 with CyPHLi (eqn. 10),l2the complex is unstable
above ca. 0°C. At 30-40°C 11 undergoes thermal decomposition into the Zintl compound
[Sb7Li~.6Me2NH](12) (Figure 10b).13 Interestingly, if 11 is held under vacuum and the
Me2NH solvation removed then the decomposition process no longer takes place (if
MezNH is bubbled through a solution of the complex rapid decomposition to 12 ensues)?
2Sb(NMe2)3

Figure 10

+ 6CyPHLi

-


[(Sb(PCy)3}2Li6.6Me2NH]

(10)

11

(a) The cage 11 and (b) the Zintl compound 12.

The decomposition of 11 can be compared to that of the related complex
[ { Sb(P'Bu)}zLi6.6thfJ (13) in which the final product isolated is the bicyclic, distibane
[('BuP)3Sb]z (14) (Figure 1l), together with ['BuP]~.'~
This reaction can be monitored by


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Group 15 element imido andphosphido cages

9

31

P NMR spectroscopy and occurs via the heterocyclic anion [(‘BuP)3Sb] -.14 The
significance of the different reactivity of 13 to that of 11 is the suggestion that coupling of
the heterocyclic [(RP)nSb]- anions via an oxidative process is probably the key metalmetal bond forming process in the ultimate formation of the Sb-:
anion. The fact that the
decomposition of 13 stops at 14 provides some circumstantial evidence for the importance
of the presence of Me2NH bonded to the alkali metal within the cage precursor and
intermediates (as implied by the activation and deactivation of 11, mentioned previously).


d
Figure 11

Structure of the bicyclic distibane 14.

The in situ reaction of the dimer [Me2NSb@-PCy)]z (15) with CyPHNa was carried
out in an attempt to obtain the phosphide analogue of the imido cage [{Sb2(NCy)4)2Na]
(16), containing the Sb2(NCy)4I2- dianion and having a structure similar to the Cu
complex 6 (Figure 6)J5 If the reaction mixture is heated to 6OoC in the presence of the
Lewis base donor TMEDA (= Me2NCHzCH2NMe2) the Zintl compound
[Sb7Na3.3thf.3TMEDA] (17) is isolated in almost quantitative yield (together with
[CyP]4).’5 However, if held at 10°C then the product is [{ (CyP)4Sb)Na.TMEDA.Me2NH]2
(18) (Figure 12), containing the heterocyclic anion [(CyP)4Sb]-.I5 The different ring size
of this heterocyclic intermediate to that involved in the formation of 14 suggests that the
organic substituent present in the phosphine has the major influence over ring size in these
species.

Figure 12 Structure of 18.
Although the Sb(II1) heterocycles are thermally unstable and therefore cannot be used
readily as ligands in their own right, the greater bond energy of As-P bonds compared to
Sb-P bonds leads to greater thermodynamic stability of analogous [(RP)nAs]- anions.’’-”
For reactions involving aliphatic phosphines (containing R-groups like ‘Bu,Cy or 1adamantyl), the heterocyclic anions are stable at room temperature and only decompose


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10

Perspectives in Organometallic Chemistry

into Zintl compounds containing As-:

anions on prolonged reflux in toluene. As with the
Sb(II1) systems, the ring sizes of the heterocycles isolated depend on the organic
substituent. This is seen most obviously in the formation of [(CyP)4AsLi.TMEDA.thfJ(19)
(Figure 13a), containing the five-membered [(CyP)4As]- heterocycle, in the 3: 1
stoichiometric reaction of CyPHLi with As(NMe2)3 in TMEDA/thf.’5”6 In contrast, the
reaction of ‘BuPHLi with As(NMe& under the same conditions gives
[(‘BuP),AsLi.TMEDA.thfl (20) (Figure 13b), in which a four-membered heterocyclic ring
is formed.17

Figure 13

Structures of the [(RP),,As]-- complexes (a) 19 and (b) 20.

For aromatic organic substituents we have so far been unable to isolate stable
heterocycles. For example, the reaction of MesPHLi (Mes= 2,4,6-Me3C&) with
As(NMe2)3 in the presence of TMEDA gives the Zintl compound [As7Li3.3TMEDA](21)
after stirring at room temperature for only one hour.I6 Analogous reactivity is also seen in
reactions involving arsines, the reaction of PhAsHLi giving 21 in the presence of TMEDA
(22) (isostructural with 14) is obtained in
whereas the bicyclic compound [(‘BuAs)~As]~
the analogous reaction of ‘BuPHLi with As(NMe2)3.I6 Another observation relating to the
stability of [(RP)nE]- heterocycles is their increased tendency to decompose into Zintl
compounds as the size of the Group 1 counter-cation is increased. For example, the Na
complex [(CyP)4AsNa.TMEDA]z (23) (whose structure is related to the Sb complex 18) is
considerable less thermally stable than the Li complex 19.17
Interestingly, the reactivity patterns found for related Group 14 phosphide compounds
mirror those described above for the Group 15 systems. The reactions of Sn(NMez)2 with
RPHLi (R= ‘Bu, Cy) give the cages [ { Sn(p-PR)}2(p-PR)}2Li4’4thfJ(24), containing
metallacyclic [ { Sn(p-PR)}2(p-PR)}2]” tetraanions (Figure 14).18 The latter can be
regarded as the Group 14 analogues of precursor cages such as 11 and 13.

If the same reaction is undertaken using MesPHLi in the presence of TMEDA then
coupling of two of the MesP groups occurs in the product [(Sn(pPMes)}2(MesPPMes)](Li.TMEDA)2 (25) (Figure 15), containing a [{ Sn(pPMes))2(MesPPMes)l2- dianion.18Further coupling of the phosphide groups ensues in the
reaction of CyPHK with Sn(NMe2)2, giving [Sn2(CyPPCy)2(pu-PCy)](K.2thf)2(26) (Figure
16), containing the [Sn2(CyPPCy)2@-PCy)14-dianion. l 9


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Group 15 element imido andphosphido cages

11

Figure 14 Structure of 24, and the metallacyclic [{Sn(p-PR))2(p-PR)}2J4 tetraanion.

2Mes,

P

1-p

/Mes

Figure 1$ Structure of 25, and the [{Sn(p-PMes}}2(MesPPMe~)]~
dianion.

1*I

Figure 16 Structure of 26, and the [Sn,(CyPPCy)2(p-PCy)/” dianion.


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Perspectives in Organometallic Chemistry

12

5 LIGAND CHARACTERISTICS AND REACTIVITY OF [(RP),As]- ANIONS
The stable As(II1) heterocyclic anions [(RP),As] - are of interest as new ligands to a range
of main group and transition metals. Of particular interest is the potential for these
heterocycles to behave as sources of As atoms, as illustrated in the above section in regard
to the formation of Zintl compounds.
The characteristics of [(RP),As]- anions as ligands are unusual, and appear to be
dominated by their large steric demands. The reaction of [(‘BuP),As] - with [CpFe(C0)2Cl]
leads to the expected substitution of the metal-bonded C1 ligand, the product being
[CpFe(CO)2As(‘BuP)3] (27)?’ However, reaction with [CpM(C0)3Cl] (M= Mo, W) results
(28) (Figure 1 7).21
in [ ((‘BuP)3AsC~H~>M(CO>~Cl]

9

Figure 17 Structure of 28.
This formal H- substitution reaction of the Cp ring probably occurs via a mechanism
involving addition of the [(‘BuP)3As] - anion to the metal centres, generating a $ecies like
27, followed by transfer of the ligand to the C ring. The high steric demands of the
[(‘BuP)3As] group in 28 are also apparent in the P NMR spectrum of the complex which
reveals restricted rotation of the [(‘BuP)3As] ring about the As-C bond of the
[(‘BuP)3AsCJ&] ligand.2’
The reactivity of [(RP)nAs]- anions with electrophiles is also worthy of mention. The
reactions of H20 or organic halides (RX) with the [(‘BuP)3As]- anion provide a very
simple and highly efficient route to terminally substituted triphosphines of the type
[(‘BuP)~R~]
(R= H, or organic group) (29) (scheme 3). This reaction clearly relies on the

polarity of the As-P bonds in the [(‘BuP)3As] - anion. Ab initio MO calculations reveal that
this reaction is enthalpically driven. We have recently shown that new heterocycles can
also be generated using this method. For example, the reaction of the five-membered
[(CyP)4As]- anion with excess MezSiC12 gives the four-membered heterocycle
[(CyP)3SiMez] (30).l7

P


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Group 15 element imido and phosphido cages

i““

13

1-

‘Bu-

+

M

2

I

I


‘Bu

‘Bu

Scheme 3
Terminally substituted triphosphines like 29 are of some interest since there are few
simple routes available to this class of ligands and their coordination chemistry has
therefore not been studied extensively. The reaction of a solution of the triphosphine
[(‘BuP)3H2] (generated in the above manner) with \W(CO)4.2thq give the simple
(31) (Figure 18).
phosphine complex [(‘BuP)~H~.W(CO)~]

Figure 18 Structure of the triphosphine complex 31
5 CONCLUSIONS AND CLOSING REMARKS
The results presented in this short review show the breadth of new chemistry that can be
accessed using Group 15 reagents of the type E(NMe2)3. Imido anions (like the tripodal
[E(NR),]” trianion) are stable and have broad applications as ligands to a range of main
group and transition metals. However, the analogous phosphide species are thermally
unstable, decomposing via heterocyclic intermediates [(RP)nE]- into Zintl compounds. The
As(II1) heterocycles are stable enough to be used as new ligands or reaction precursors in
their own right, exhibiting unusual reactivity and coordination chemistry.
References
1
2
3
4

M.A. Beswick and D.S. Wright, Coord. Chem. Rev., 1998,176,373; M. A. Beswick,
Dalton Trans., 1998,2437.
M.E.G. Mosquera and D.S. Wright, J. Chem. SOC.

A.D. Hopkins, J.A. Wood and D.S. Wright, Coord. Chem. Rev., 2001,216, 155.
A. Kiennemann, G. Levy, F. SchuC and C. Tanielian, J. Organomet. Chem., 1972,35,
143.
A.J. Edwards, M.A. Paver, M.-A. Rennie, P.R. Raithby, C.A. Russell and D.S.
Wright, .
I
Chem. SOC.,Dalton Trans., 1994,2963.