Synthesis of new mer,trans-rhodium(III) hydrido-bis(acetylide) complexes: Structure of mer,trans-[(PMe3)3Rh(C{triple bond, long}C-C6H4-4-NMe2)2H]

Article abstract of DOI:10.1016/j.ica.2005.11.030

Terminal alkynes (R-C{triple bond, long}C-H, R = 1-naphthyl, 9-anthryl, 4-Me₂N-C₆H₄-, or the longer analogue, 4-(4-Me₂N-C₆H₄-C{triple bond, long}C-)-C₆H₄-) react with

Full text of DOI:10.1016/j.ica.2005.11.030

Inorganica Chimica Acta 359 (2006) 2859–2863
www.elsevier.com/locate/ica
Synthesis of new mer,trans-rhodium(III)
hydrido-bis(acetylide) complexes: Structure of
mer,trans-[(PMe3)3Rh(C„C–C6H4-4-NMe2)2H]
a,b
a
a
a
´
Xunjin Zhu , Richard M. Ward , David Albesa-Jove , Judith A.K. Howard ,
a
a
a
b
a,
*
`
Laurent Porres , Andrew Beeby , Paul J. Low , Wai-Kwok Wong , Todd B. Marder
a
Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Kowloon, PR China
b
Received 18 October 2005; received in revised form 18 November 2005; accepted 23 November 2005
Available online 4 January 2006
Dedicated to Professor Brian James on the occasion of his 70th birthday, in recognition of his extensive contributions to inorganic chemistry and catalysis.
Abstract
Terminal alkynes (R–C„C–H, R = 1-naphthyl, 9-anthryl, 4-Me2N–C6H4–, or the longer analogue, 4-(4-Me2N–C6H4–C„C–)–
C6H4–) react with [Rh(PMe3)4Me] at ambient temperature, with loss of methane and one PMe3 ligand, to form the corresponding
mer, trans-[(PMe3)3Rh(C„CR)2H] compounds in excellent yield. In this preliminary study, the synthesis and spectroscopic character-
ization of the four new compounds are reported, along with the single-crystal structure of the R = 4-Me2N–C6H4 derivative.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Acetylide; Alkynyl; Luminescent; Hydride; Crystal structure
1. Introduction
delocalization and ability to interact with metal centers
via dp–pp overlap make metal alkynyls versatile structural
motifs for molecular wires [2–5], polymeric systems [6,7],
catalysts for polymerisation [8–10], liquid crystals [11–14],
organometallic catenanes [15], dendrimers [16,17], molecu-
lar scaffolds [18], luminescent materials [19–22], and as
materials for nonlinear optics (NLO) [23–28]. Some
systems have received more study than others and, in par-
ticular, those containing platinum or palladium [11,12,20,
21,27,29–33], rhodium [13,34–36], iron and ruthenium
[37–41], rhenium [5,19,42,43] and osmium [44] have
received the bulk of the attention.
Some time ago, we reported the synthesis of rhodium acet-
ylide complexes of the form cis-[Rh(PMe3)4(H)(C„CR)]Cl
[45], [Rh(PMe3)4(C„CR)] [46], [Rh(PMe3)4(C„C-p-
C6H4-C„C)Rh(PMe3)4] [47,48], mer,trans-[(PMe3)3Rh-
(C„CR)2H] [49] and related polyyne polymers [47].
Whereas we were previously able to prepare the unsymmet-
The search for advanced materials with interesting prop-
erties has led to numerous investigations into inorganic and
organometallic molecular materials [1]. A wide variety of
transition metals with different nature, coordination geom-
etry, coordination numbers, and oxidation states, and
hence the number of d-electrons, can be employed. These,
together with the diversity of ligand systems provide an
extremely important and rich area of research in the field
of materials science. The chemistry of transition metal acet-
ylide complexes and polymers, in particular those with long
sp carbon chains, has been the subject of much interest in
recent years [1d,1e,1f], The linear geometry of the alkynyl
unit, the rigidity of its structure, its extended p-electron
*
Corresponding author. Tel.: +44 191 334 2037; fax: +44 191 384 4737.
E-mail address: todd.marder@durham.ac.uk (T.B. Marder).
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.11.030

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X. Zhu et al. / Inorganica Chimica Acta 359 (2006) 2859–2863
rically substituted donor–acceptor trans-[(PR3)2Pt(–C„C–
D)(–C„C–A)] complexes necessary for useful second-order
NLO effects [27,28] (others have recently investigated the
mechanism of alkynyl exchange in these systems [50]), we
were unsuccessful in synthesizing related unsymmetrical
octahedral Rh(III) bis(alkynyls) in the absence of their sym-
metrical counterparts [47–49]. We therefore studied in detail
the mechanism of formation of [(PMe3)3Rh(C„CR)2H] via
C–H oxidative addition including isomerization, alkynyl
exchange, and hydride replacement by chloride [51]. In the
process of this work, we discovered an unusual regioselective
coupling of diynes to form luminescent 2,5-bis(arylethynyl)-
3,4-bis(aryl)rhodacyclopentadienes [52]. This prompted us
to re-explore the chemistry of the rhodium hydrido-bis(acet-
ylide) complexes. In our previous studies, we had not
observed luminescent behavior in such complexes. To this
end, we prepared several new mer,trans-[(PMe3)3Rh-
(C„CR)2H] complexes with aromatic substituents on the
alkynyl groups. Although detailed studies of the photophys-
ical properties (e.g., luminescence) of the new compounds
are in progress, and will form the basis for a future paper,
we report herein the synthesis and characterization of four
new compounds in this series.
tion of methane and the formation of the trigonal bipyra-
midal complex [(PMe3)4Rh(–C„CR)], a reaction that has
been shown to take place at temperatures as low as
ꢀ78 °C [51]. This intermediate reacts with a second
equivalent of alkyne via oxidative addition of the „CH
bond with loss of one PMe3 ligand to give the thermody-
namic product mer,trans-[(PMe3)3Rh(–C„CR)2H]. Once
formed, mer,trans-[(PMe3)3Rh(–C„CR)2H] complexes
are configurationally stable [51].
2.2. Characterization
The 1H NMR spectra of the complexes show the
expected virtual triplet and doublet resonances respectively
at ca. 1.4–1.5 and 1.1–1.3 ppm for the mutually trans PMe3
groups and the one trans to H, aromatic resonances for
naphthyl, anthryl and para-phenylene fragments and a
hydride at ca. ꢀ9 ppm which is split into a doublet with
a large coupling (2JH–P(trans) = 194 Hz) and then further
split into two apparent quartets with a smaller coupling
(2JH–P(cis) = 1JH–Rh = 18 Hz) confirming the geometry of
this species as the mer,trans-isomer. In the 31P NMR, the
PMe3 groups thus give rise to a doublet of doublets and
1
a doublet of triplets with JRh–P values of ca. 93 and
2
2. Results and discussion
76 Hz, and JP–P values are 26–27 Hz for P trans to P
and P trans to H, respectively. The IR spectra of the
complexes 1–4 show tC„C bands in the range 2087–2066
and tRh–H in the range 1978–1930 cmꢀ1. Interestingly,
while most samples for elemental analyses were prepared
and sealed in a glove box, compound 3 was also submitted
in air, and a relatively reasonable analysis on that sample
was obtained indicating that, in the solid state, it is not very
air-sensitive.
2.1. Synthesis
The complexes mer,trans-[(PMe3)3Rh(–C„CR)2H]
(R = 1-naphthyl, 9-anthryl, 4-Me2N–C6H4 or (4-Me2N–
C6H4–C„C–)–C6H4–) were formed cleanly from reaction
of [(PMe3)4RhMe] with the corresponding terminal alkynes
(Scheme 1). The initial step of the reaction is the elimina-
Me
H
2 equiv.
R.T.
PMe3
PMe3
PMe3
R
H
Me3P
Rh
R
R
Rh
Me3P
PMe3
PMe3
Me
N
N
1
2
Me
Me
Me
3
4
Scheme 1.

X. Zhu et al. / Inorganica Chimica Acta 359 (2006) 2859–2863
2861
˚
Fig. 1. Molecular structure of 1 with ellipsoids shown at 50% probability. Selected distances (A) and angles (°): Rh(1)–C(10) 2.034(4), Rh(1)–C(11)
2.034(4), Rh(1)–P(1) 2.3750(12), Rh(1)–P(2) 2.3039(11), Rh(1)–P(3) 2.2933(11), Rh(1)–H(1) 1.66(4), C(9)–C(10) 1.215(6), C(11)–C(12) 1.208(6), C(10)–
Rh(1)–C(11) 177.53(15), P(2)–Rh(1)–P(3) 160.90(4).
2.3. Molecular structure of 1
4.2. Synthesis of mer,trans-[(PMe3)3Rh(–C„C–C6H4-4-
NMe2)2H] (1)
The molecular structure of 1 has been determined by
single-crystal X-ray diffraction and a diagram with selected
distances and angles is presented in Fig. 1. The crystals
could not be cooled to very low temperatures due to a
destructive phase change, so the diffraction data were
collected at 255 K. The structure is very similar to that of
the parent (R = Ph) compound [49], indicating that the
presence of the strong Me2N donors does not have a
significant influence on geometric parameters at the Rh
center. The alkynyl moieties are trans to one another with
an angle of C(10)–Rh(1)–C(11) 177.53(15)°, whereas the
smaller trans P(2)–Rh(1)–P(3) angle of 160.90(4)° is indica-
tive of some steric interactions. As expected, the hydride
exerts a strong trans-influence, lengthening the Rh–P(1)
A solution of p-dimethylaminophenylethyne (69 mg,
0.474 mmol) in THF (2 ml) was added to a solution of
[(PMe3)4RhMe] (100 mg, 0.237 mmol) in THF (2 ml), and
the mixture was stirred for 4 h under a N2 atmosphere.
The solvent was removed in vacuo and the product was
crystallized from THF/hexane (yield: 125 mg, 85%). 1H
NMR (500 MHz, C6D6): d 7.52 (4H, (AB)0, Ar), 6.63 (4H,
(AB)0, Ar), 2.51 (12H, s, Me2N), 1.51 (18H, vt, J = 3 Hz,
PMe3 trans to PMe3), 1.28 (9H, d, J = 7.5 Hz, PMe3 trans
1
2
to H), ꢀ9.09 (1H, dq, JRh–H = 2JPcis-H = 17, JPtrans-H
= 195 Hz). 31P{1H} NMR (161.9 MHz): d ꢀ5.77 (2P, dd,
2
1JRh–P = 93 Hz, JP–P = 27 Hz, P trans to P), ꢀ23.23 (1P,
1
2
dt, JRh–P = 76 Hz, JP–P = 27 Hz, P trans to H). Anal.
˚
bond by ca. 0.07–0.08 A with respect to that of Rh–P(2)
and Rh–P(3).
Found (C29H48N2P3Rh requires): C, 56.24 (56.13); H,
8.00 (7.80); N, 4.02 (4.51). IR (KBr): t(C„C) = 2087 cmꢀ1
,
t
(Rh–H) = 1961 cmꢀ1. Single crystals of 1 were grown by
3. Conclusions
very slow evaporation of a THF/hexane solution.
A series of rhodium hydrido-bis(acetylide) complexes
have been synthesized and characterized, some of which
display luminescent behavior which is the subject of ongo-
ing investigations.
4.3. Synthesis of mer,trans-[(PMe3)3Rh(–C„C–
C18H14N)2H] (2)
A
solution of [4-(4-ethynyl-phenylethynyl)-phenyl]-
dimethylamine [53] (23 mg, 0.095 mmol) in THF (1 ml)
was added to a solution of [(PMe3)4RhMe] (20 mg,
0.048 mmol) in THF (1 ml), and the mixture was stirred
for 4 h under a N2 atmosphere. The solvent was removed
in vacuo and the product was crystallized from THF/
hexane (yield: 32 mg, 79%). 1H NMR (400 Hz, C6D6):
d 7.64 (4H, J = 8.5 Hz, Ar), 7.59 (4H, J = 9.1 Hz, Ar),
7.41 (4H, J = 8.5 Hz, Ar), 6.36 (4H, J = 9.1 Hz, Ar),
2.35 (12H, N(CH3)2), 1.39 (18H, vt, J = 4 Hz, PMe3
trans to PMe3), 1.13 (9H, d, J = 8 Hz, PMe3 trans to
4. Experimental
4.1. General
All reagents were used as supplied, unless noted other-
wise. Solvents were distilled under nitrogen from appropri-
ate drying agents. NMR spectra were obtained on either
Varian Inova 500 or Bruker AC 400 spectrometers and
are referenced to external TMS (1H) and 85% H3PO4
(31P). IR spectra were recorded on solid samples on a Per-
kin–Elmer Paragon 1600 FTIR spectrophotometer. Ele-
mental analyses were performed in the department of
Chemistry, University of Durham. Reactions were carried
out, and NMR samples were prepared in Innovative Tech-
nology Inc. gloveboxes under an atmosphere of dry
nitrogen.
1
2
H), ꢀ9.12 (1H, dq, JRh–H = 2JPcis-H = 18, JPtrans-H
=
194 Hz). 31P{1H} NMR (161.9 MHz): d ꢀ6.30 (2P, dd,
1JRh–P = 92 Hz, JP–P = 26 Hz, P trans to P), ꢀ23.74
2
1
2
(1P, dt, JRh–P = 76 Hz, JP–P = 27 Hz, P trans to H).
Anal. Found (C45H56N2P3Rh requires): C, 65.64
(65.85); H, 6.83 (6.88); N, 3.49 (3.41)%. IR (KBr):
t
(C„C) = 2083 cmꢀ1, t(Rh–H) = 1978 cmꢀ1
.

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X. Zhu et al. / Inorganica Chimica Acta 359 (2006) 2859–2863
4.4. Synthesis of of mer,trans-[(PMe3)3Rh(–C„C–
C10H7)2H] (3)
Mr. A.C. Parsons and Dr. J.C. Collings for a sample of
4-(4-Me2N–C6H4–C„C–)C6H4–C„CH.
A
solution
of
1-ethynylnaphthalene
(72 mg,
Appendix A. Supplementary data
0.474 mmol) in THF (2 ml) was added to a solution of
[(PMe3)4RhMe] (100 mg, 0.237 mmol) in THF (2 ml),
and the mixture was stirred for 4 h under a N2 atmo-
sphere. The solvent was removed in vacuo and the prod-
uct crystallized from THF/hexane (yield: 128 mg, 83%).
1H NMR (500 MHz, C6D6): d 9.00 (2H, d, J = 8.8 Hz,
Ar), 7.69 (4H, m, Ar), 7.45 (4H, m, Ar), 7.30 (4H, m,
Ar), 1.50 (18H, vt, J = 4 Hz, PMe3 trans to PMe3), 1.06
(9H, d, J = 8 Hz, PMe3 trans to H), ꢀ9.22 (1H, dq,
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 286527. Copies of this information
may be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge, CB2 1EZ, UK, fax: +44 1223
366 033, e-mail: deposit@ccdc.ac.uk or on the web www:
http://www.ccdc.cam.ac.uk. Supplementary data associ-
ated with this article can be found, in the online version,
at doi:10.1016/j.ica.2005.11.030.
1JRh–H = 2JPcis-H = 17,
2JPtrans-H = 194 Hz).
31P{1H}
1
NMR (161.9 MHz): d ꢀ5.90 (2P, dd, JRh–P = 92 Hz,
1
2JP–P = 26 Hz, P trans to P), ꢀ24.22 (1P, dt, JRh–P
=
References
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76 Hz, JP–P = 26 Hz, P trans to H). Anal. Found
(C33H42P3Rh requires): C 61.78 (in air), 62.59 (under
N2) (62.47); H 6.65 (in air), 6.72 (under N2) (6.67)%. IR
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.
4.6. Crystal data and structure refinement for 1
C29H48N2P3Rh, MW = 620.51, monoclinic, space group
˚
˚
P21/n (No. 14), a = 12.660(2) A, b = 13.189(2) A, c =
3
˚
˚
19.968(4) A, b = 102.442(3)°, V = 3255.6(10) A , Z = 4,
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