An unusual palladium complex involved in an unusual rearrangement of ortho-palladated aryldithioacetals

Article abstract of DOI:10.1021/ja0175035

The reaction of 1 with Pd(dba)₂, Tl(TfO) and PPh₃ in 1:1:1:2 molar ratios to give 3 implicates (i) an oxidative addition reaction, (ii) a rearrangement involving the cleavage of one HC-S bond and formation of an aryl-S bonds, and (iii) coordination of the Pd(PR₃)₂ group with a ligand intermediate between η²-[ArCH=S⁽⁺⁾To] and κ²-C,S-ArCH^(-)STo, which requires the consideration of 3 as intermediate between a Pd(0) and a Pd(II) complex. The coordination of the ligand as a chelating three-membered ring, instead of the expected five-membered ring involving C(10) and S(1), and the partial intramolecular redox process are explained as a consequence of the transphobia of the pair of ligands Ph₃P/CH(STo)Ar. Copyright

Full text of DOI:10.1021/ja0175035

Published on Web 03/23/2002
An Unusual Palladium Complex Involved in an Unusual Rearrangement of
Ortho-Palladated Aryldithioacetals
Jose´ Vicente,*,† Jose´-Antonio Abad,*,† Francisco S. Herna´ndez-Mata,† and Peter G. Jones‡
Grupo de Qu´ımica Organometa´lica, Departamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica, UniVersidad de
Murcia Apto. 4021, E-30071 Murcia, Spain, and Institut fu¨r Anorganische und Analytische Chemie, Technische
UniVersita¨t Braunschweig Postfach 3329, Braunschweig, Germany
Received November 9, 2001; Revised Manuscript Received March 4, 2002
Scheme 1
We have recently reported that IC6(OMe)3-2,3,4-CH(STo)2-6 (1,
To ) 4-tolyl) adds to Pd(dba)2 [dba ) dibenzylideneacetone],
resulting in the formation of 2 (Scheme 1) through an unexpected
rearrangement involving the cleavage of aryl-I and HC-S bonds
and formation of aryl-S, HC-Pd, I-Pd, and S-Pd bonds. We
proposed the reaction pathway depicted in Scheme 1 to explain
this rearrangement.1 We isolated an adduct of the intermediate A
[Pd{κ1-C-CH(STo)Ar}(I)(bpy)] (Ar ) C6H(STo)-2-(OMe)3-3,4,5;
bpy ) 2,2′-bipyridine), and in this communication we report the
synthesis of a new complex whose structure can be related to the
intermediate C.
The reaction of 1 with Pd(dba)2, Tl(TfO) and PPh3 in 1:1:1:2
molar ratios results in the formation of the complex [Pd{κ2-C,S-
CH(STo)Ar}(PPh3)2]TfO (3, 39% yield, Scheme 1) that can also
be obtained by reacting 2 with PPh3 and Tl(TfO) (1:2:1, 98% yield).
The crystal and molecular structure of 3 has been determined by
X-ray diffraction studies and shows great differences from the
homologous complex 4 (Scheme 1).1 Thus, in 4, the Pd-S(1) bond
length is 2.2743(10) Å, while that in 3 is much longer [2.8648(7)
Å]. Distances in the range 2.877(3)-3.140(2) Å have been
considered as corresponding to weak Pd-S interactions.2 In
addition, the Pd-S(2) distance in 3 [2.3843(6) Å] is much shorter
than that in 4 [2.9755(5) Å]. The C(10)-S(2) distance in 3 [1.781(2)
Å] is significantly shorter than that in 4 [1.8163(15) Å] and lies
between the latter value, corresponding to a single bond, and that
corresponding to a CdS bond [1.66-1.68 Å].3 The C(12)-C(10)-
S(2) angle in 3 [117.36(17)°] is significantly wider than that in 4
[107.14(10)°], the values being in accordance with C(sp2) and
C(sp3), respectively. However, the angles H-C(10)-S(2) and
H-C(10)-C(12) are similar in both compounds, at 113 and 112°
(the H atom was fixed as for an sp3 system, but a free refinement
led to an almost identical position). These data suggest that the
sulfur ligand in 3 can be viewed as intermediate between the cation
η2-[ArCHdS(+)To], postulated in the intermediate C, and the anion
κ2-C,S-ArCH(-)STo. The same intermediate role of the ligand
CH2SMe has been proposed in [Mo(η5-Cp)(κ2-C,S-CH2SMe)(CO)2]4
and [PdCl(κ2-C,S-CH2SMe)(PPh3)].5 Therefore, 3 can be viewed
as intermediate between a tricoordinate Pd(0) complex and a square-
102-104° (R factors e5%). The angles P(1 or 2)-Pd-X (X )
midpoint C-S) are 133° for P1 and 119° for P2. Alternatively, 3
can be viewed, assuming coordination of S(1) to palladium, as
planar Pd(II) complex. Thus, the P-Pd-P angle [105.04(2)°]
is in the range 101-110° found in Pd(0) complexes [Pd0(PPh3)2-
intermediate between a tetrahedral Pd(0) complexsthe dihedral
(η2-ligand)],6 but [PdII(η3-ligand)(PPh3)2]7 and the only Pd(II)
angle formed by the planes X-Pd-S(1) and P(1)-Pd-P(2) is 83.8°
complex related with 3 whose crystal structure has been reported,
and that between X-Pd-P(1) and S(1)-Pd-P(2), 74.8°sand a
flattened square pyramid with S(1) at the appex. Magnetic measure-
[PdII{κ2-P,S-P(S)Ph2}(PPh3)2]+,8 show P-Pd-P angles in the range
ments indicate that 3 is diamagnetic in the solid state.
* To whom correspondence should be addressed. (J.V.) E-mail: jvs@um.es.
The structures of some palladium complexes with a chelating
ligand κ2-C,S-RCHSR′ show CH-S distances similar to those in
3,9,10 whereas those with a bridging µ2-κ2-C,S-RCH(-)SR′ or a
WWW: http://www.scc.um.es/gi/gqo/. (J.-A.A.) E-mail: jaab@um.es. (P.G.J.)
E-mail: jones@xray36.anchem.nat.tu-bs.de.
† Universidad de Murcia.
‡ Technische Universita¨t Braunschweig.
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J. AM. CHEM. SOC. 2002, 124, 3848-3849
10.1021/ja0175035 CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
terminal κ1-C-RCH(-)SR′ ligand show CH-S distances correspond-
ing to a C-S single bond, similar to that in 4.10-12
lengths and angles, and figure with atom numbering, for compound 3
(PDF). This material is available free of charge via the Internet at http://
pubs.acs.org.
The 31P NMR spectrum of 3 shows two doublets at 27.13 and
20.38 ppm with 2JPP ) 37 Hz. This coupling constant is within the
expected range for a cis bis(arylphosphine)palladium(II) complex
(30-58 Hz).8,13,14 In palladium(0) complexes [Pd(PR3)2(olefin)],
2JPP is in the range 5-17 Hz.13,15-17 Complex 3 does not react
with PPh3 (1:2 molar ratio) which contrasts with the behavior of
[PdCl(κ2-C,S-CH2SMe)(PPh3)] which reacts with PPh3 to give
trans-[PdCl(κ1-C-CH2SMe)(PPh3)2].12 In its reactivity complex 3
bears more resemblance to the related Pd(0) complex [Pd(PR3)2-
(PhCHdCHP(+)Ph3)] so that neither reacts with PPh3.16 However,
the nature of 3 in solution could be different than that in the solid
state.
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The most striking feature of our result is that changing XyNC
in 4 for PPh3 to give 3 induces an important change of the
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(STo)Ar is greater than that between the pair XyNC/CH(STo)Ar.
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Acknowledgment. We thank Direccio´n General de Investiga-
cio´n Cient´ıfica y Te´cnica (PB97-1047), INTAS (97-166), and the
Fonds der Chemischen Industrie for financial support. F.S.H.-M.
is grateful to Fundacio´n Se´neca (Murcia).
Supporting Information Available: Methods of synthesis, spec-
troscopic and analytical data, a listing of all refined and calculated
atomic coordinates, all the anisotropic thermal parameters, full bond
JA0175035
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