Synthesis, Structure, and Optical Properties of Pt(II) and Pd(II)
Complexes with Oxazolyl- and Pyridyl-Functionalized DPPM-Type
Ligands: A Combined Experimental and Theoretical Study
Shuanming Zhang,
†
Roberto Pattacini,
†
Pierre Braunstein,*
,†
Luisa De Cola,*
,‡
Edward Plummer,
‡
Matteo Mauro,
‡,§
Christophe Gourlaouen,
∥
and Chantal Daniel*
,∥
†
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS/UdS), Universite ́ de Strasbourg, 4 rue Blaise Pascal,
F-67081 Strasbourg, France
‡
Laboratoire de Chimie et des Biomate ́ riaux Supramole ́ culaires ISIS, 8 rue Gaspard Monge, BP 70028, F-67083 Strasbourg Cedex,
France
§
University of Strasbourg Institute for Advanced Study (USIAS), 5 allé e du Ge ́ ne ́ ral Rouvillois, 67083 Strasbourg, France
∥
Laboratoire de Chimie Quantique, Institut de Chimie (UMR 7177 CNRS/UdS), Universite ́ de Strasbourg, 1 rue Blaise Pascal,
BP 296/R8, F-67008 Strasbourg Cedex, France
* S Supporting Information
ABSTRACT: New square-planar complexes [Pt(1
−H
)
2
](2a)
[1
−H
= (oxazolin-2-yl)bis(diphenylphosphino)methanide]
and [Pd(1
−H
)
2
](2b), of general formula [M{(Ph
2
P)
2
C ---
C ---NCH
2
CH
2
O }
2
] (M = Pt, 2a; M = Pd, 2b), result from
deprotonation of 2-{bis(diphenylphosphino)methyl}oxazoline
(1) at the PCHP site. The new, functionalized dppm-type
ligand 4-{bis(diphenylphosphino)methyl}pyridine,
(Ph
2
P)
2
CH(4-C
5
H
4
N) (4), was prepared by double lithiation
and phosphorylation of 4-picoline. In the presence of NEt
3
, the
reactions of 2 equiv of 4 with [PtCl
2
(NCPh)
2
] and
[Pd(acac)
2
] (acac = acetylacetonate) afforded [Pt(4
−H
)
2
](5a)[4
−H
= bis(diphenylphosphino)(pyridin-4-yl)methanide] and
[Pd(4
−H
)
2
](5b), of general formula [M{(Ph
2
P)
2
C(4-C
5
H
4
N)}
2
] (M = Pt, 5a; M = Pd, 5b), respectively. In the absence of base,
the reactions of 2 equiv of 4 with [PtCl
2
(NCPh)
2
] and [PdCl
2
(NCPh)
2
]afforded (5a·2HCl) (6a) and (5b·2HCl) (6b),
respectively, in which the PCHP proton of 4 has migrated from carbon to nitrogen to give a pyridinium derivative of general
formula [M{(Ph
2
P)
2
C(4-C
5
H
4
NH)}
2
]Cl
2
(M = Pt, 6a; M = Pd, 6b). The complexes 3a, 5a·2MeOH, and 6b·4CH
2
Cl
2
have been
structurally characterized by X-ray diffraction. The absorption/emission properties of the Pt(II) complexes 2a and 5a and the
Pd(II) complexes 2b and 5b have been investigated by UV−vis spectroscopy and theoretical analysis based on density functional
theory. The UV−vis absorption spectra of the neutral complexes recorded in dilute N,N′-dimethylformamide solutions are
dominated by intense spin-allowed intraligand transitions in the region below 350 nm. The complexes exhibit charge-transfer
bands between 350 and 500 nm. The experimental and theoretical absorption spectra agree qualitatively and point to two
low-lying ligand-to-metal charge transfer states that contribute to the bands observed between 350 and 500 nm. The complexes
are emissive in frozen solutions at 77 K, in the pure solid state, and when doped into films of poly(methyl methacrylate) but are
nonemissive in solution. A red shift is observed when Pt(II) is replaced by Pd(II).
■
INTRODUCTION
The synthesis and study of heterotopic ligands bearing
phosphorus and nitrogen donor atoms represent increasingly
active fields of research because of the sometimes unexpected
structural features associated with their metal complexes and the
often unique properties of the latter, in particular for
stoichiometric or catalytic transformations, that originate from
the different stereoelectronic properties of the P and N donor
groups.
1,2
Because of our combined interest in the synthesis
and applications of such P,N ligands in coordination chemistry
and catalysis
2−4
and in short-bite diphosphine ligands such
as bis(diphenylphosphino)methane, Ph
2
PCH
2
PPh
2
(dppm),
bis(diphenylphosphino)amine, Ph
2
PNHPPh
2
(dppa), and their
derivatives, which are well-known for their ability to stabilize di- or
polynuclear complexes and clusters
5
and allow, e.g., their anchoring
inside nanoporous membranes,
6
we decided to introduce an
oxazoline moiety as a substituent on the PCP carbon of the dppm
ligand.
3
The coordination behavior of 2-{bis(diphenylphosphino)-
methyl}oxazoline, (Ph
2
P)
2
CHC NCH
2
CH
2
O (1) (Scheme 1),
has barely been examined.
4
Received: July 4, 2014
Published: November 24, 2014
Article
pubs.acs.org/IC
© 2014 American Chemical Society 12739 dx.doi.org/10.1021/ic501566u | Inorg. Chem. 2014, 53, 12739−12756