Rh-Pt heterobimetallic complexes with unsymmetrically bridging organosilyl ligands: Crystal structure and dynamic behavior in solution

Article abstract of DOI:10.1246/cl.2001.962

Pt{SiH(C₆H₄F-4)₂}₂(PMe ₃)₂ reacts with Rh (I) complexes to afford new Rh-Pt heterobimetallic complexes with bridging hydrido and diarylsilyl ligands. These complexes were characterized by X

Full text of DOI:10.1246/cl.2001.962

962
Chemistry Letters 2001
Rh–Pt Heterobimetallic Complexes with Unsymmetrically Bridging Organosilyl Ligands:
Crystal Structure and Dynamic Behavior in Solution
Makoto Tanabe and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta, Yokohama 226-8503
(Received July 8, 2001; CL-010601)
Pt{SiH(C6H4F-4)2}2(PMe3)2 reacts with Rh (I) complexes
to afford new Rh–Pt heterobimetallic complexes with bridging
hydrido and diarylsilyl ligands. These complexes were charac-
terized by X-ray crystallography. The NMR spectra exhibit
dynamic behavior of hydrogen atoms and three PMe3 ligands
bonded to Rh center in solution.
There have been a number of dinuclear complexes with
bridging organosilyl groups such as µ-SiHR2 and µ-SiH2R lig-
ands which form both stable M–Si σ-bond and structurally
favorable M–H–Si three center two electron (3c-2e) bond.1 The
structure and dynamic behavior of the bridging-coordinated
SiHR2 group in bimetallic systems are of significant interest.
Although much attention has been paid to such complexes com-
posed of the same two metal centers (Scheme 1, M = M'), anal-
ogous heterobimetallic complexes bridged by organosilyl lig-
ands (M ≠ M') were reported only in a limited number.2 In this
paper we report the synthesis of new Rh–Pt heterobimetallic
complexes with bridging diarylsilyl and hydrido ligands as well
as unique dynamic behavior in solution.
Figure 1 depicts the molecular structures of complexes 1 and
2 containing Rh and Pt centers bridged by hydrido and diarylsilyl
ligands.9 The Pt center is bonded also to ClSiAr2 or HSiAr2 ligand
and a PMe3 ligand, while the Rh center contains three PMe3 lig-
ands situated at facial coordination sites. The Rh–Si bonds longer
(2.368(5) Å for 1, 2.378(8) Å for 2) than the Pt–Si bonds (2.323(4)
Å for 1, 2.324(8) Å for 2) indicate the presence of a hydrogen atom
close to Si and Rh to form a Rh–H–Si 3c-2e bond. The bond dis-
tances of Pt–Rh (2.934(2) Å for 1, 2.945(3) Å for 2) may suggest
an elongated metal–metal bond in a Pt–H–Rh 3c-2e bond.
3
Pt{SiH(C6H4F-4)2}2(PMe3)2 reacts with an equimolar
amount of RhMe(PMe3)44 at room temperature to produce a new
Rh–Pt heterobimetallic complex {(4-FC6H4)2HSi}(Me3P)Pt(µ-
H){µ-SiH(C6H4F-4)2}Rh(PMe3)3 (1) in 48% yield (eq 1).5
1H and 31P{1H} NMR spectra of 1 and 2 are similar to each
other, and provided detailed information on the structure of these
complexes in solution. Figure 2 depicts the variable temperature
1H NMR spectra of 2. Two 1H NMR signals of 2 are observed in
the hydrido region (δ –7.47, –13.1) at –90 °C in CD2Cl2. The
doublet (J(RhH) = 63 Hz) at δ –7.47 is flanked by the 195Pt satel-
lite signals (J(PtH) = 358 Hz), and the signal at a higher magnetic
field (δ –13.1) appears as doublet (J(RhH) = 143 Hz). They are
assigned to the hydrido ligand bonded to both Rh and Pt centers
and to the hydrogen in the Rh–H–Si 3c-2e bond, respectively.
On raising the temperature, the two hydrido signals coalesce to
give a single broad doublet at δ –10.1, indicating exchange of the
hydrogen atoms on the NMR time scale. The four signals of
PMe3 hydrogen atoms at –90 °C are also consistent with the
molecular structure obtained from X-ray crystallography. At –30
°C, two of the three PMe3 hydrogen signals bonded to Rh center
A similar reaction of Pt{SiH(C6H4F-4)2}2(PMe3)2 with
RhCl(PMe)3 requires heating for 24 h at 50 ºC to give a mix-
ture of complexes including {(4-FC6H4)2ClSi}(Me3P)Pt(µ-H)
{µ-SiH(C6H4F-4)2}Rh(PMe3)3 (2 : 58%) and fac-RhH2
{SiCl(C6H4F-4)2}(PMe3)37 (3 : 5%) (eq 2).8
6
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
963
References and Notes
1
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undergo coalesence to give a sharp signal at δ 0.97. The above
coalesence phenomena and those observed in the 31P{1H} NMR
spectra indicate fast exchange of two PMe3 ligands. This
exchange of hydrido and PMe3 ligands bonded to Rh is interpret-
ed by assuming a mechanism involving rotation of two PMe3 lig-
ands (PX, PY) and two hydrogen atoms (HA, HB) around the axis
of Si–Rh–PZ bond caused by cleavage of the Si–H interaction of
the 3c-2e bond (Scheme 2). All the hydrogen signals of PMe3
bonded to Rh are observed as a very broad single peak at room
temperature.
5
Data of 1. Anal. Calcd (%) for C36H55F4P4PtRhSi2·0.5 C7H8: C,
43.61; H, 5.47; F, 6.99. Found: C 43.23, H 5.76, F 6.73. 1H NMR
(400 MHz, THF-d8, –90 °C): δ = 7.89 (br, 2H, C6H4), 7.76 (t, 2H,
C6H4, J = 7 Hz), 7.67 (t, 2H, C6H4, J = 7 Hz), 7.08 (t, 2H, C6H4, J
= 7 Hz), 7.00 (t, 2H, C6H4, J = 7 Hz), 6.79 (br, 2H, C6H4), 6.60 (d,
4H, C6H4, J = 7 Hz), 4.47 (d, 1H, SiH, J(PH) = 12 Hz, J(PtH) =
151 Hz), 1.65 (d, 9H, Rh–P–CH3, J(PH) = 6 Hz), 1.51 (d, 9H,
Pt–P–CH3, J(PH) = 6 Hz), 1.39 (d, 9H, Rh–P–CH3, J(PH) = 7
Hz), 0.78 (d, 9H, Rh–P–CH3, J(PH) = 7 Hz), –7.69 (d, 1H,
Pt–H–Rh, J(RhH) = 70 Hz, J(PtH) = 356 Hz), –12.9 (d, 1H,
Si–H–Rh, J(RhH) = 148 Hz). 31P{1H} NMR (162 MHz, THF-d8,
–90 °C, referenced to 85% H3PO4): δ = –7.9 (m, Rh–P, J(RhP) =
115 Hz), –11.8 (dt, Rh–P, J(PP) = 31 Hz, J(RhP) = 98 Hz), –15.6
(apparent triplet, Pt–P, J(PP) = 27 Hz, J(PSi) = 118 Hz, J(PtP) =
2220 Hz), –23.6 (m, Rh–P, J(RhP) = 90 Hz).
6
A. J. Richard, M. R. Fernando, G. Wilkinson, A. M. R. Galas, M.
B. Hursthouse, and K. M. A. Malik, J. Chem. Soc., Dalton Trans.,
1980, 511.
7
8
K. Osakada, S. Sarai, T. Koizumi, and T. Yamamoto,
Organometallics, 16, 3973 (1997).
Data of 2. Anal. Calcd. (%) for C36H54ClF4P4PtRhSi2·0.5 C7H8:
C, 42.27; H, 5.21; Cl, 3.16, F, 6.77. Found: C, 43.04, H, 5.17, Cl,
3.03, F, 6.28. 1H NMR (400 MHz, CD2Cl2, –90 °C): δ = 7.75 (br,
2H, C6H4), 6.95–6.89 (br, 6H, C6H4), 6.81 (t, 2H, C6H4, J = 7 Hz),
6.60 (t, 6H, C6H4, J = 7 Hz), 1.51 (d, 9H, Rh–P–CH3, J(PH) = 6
Hz), 1.33 (d, 9H, Pt–P–CH3, J(PH) = 7 Hz), 1.21 (d, 9H,
Rh–P–CH3, J(PH) = 6 Hz), 0.65 (d, 9H, Rh–P–CH3, J(PH) = 6
Hz), –7.47 (d, 1H, Pt–H–Rh, J(RhH) = 63 Hz, J(PtH) = 358 Hz),
–13.1 (d, 1H, Si–H–Rh, J(RhH) = 143 Hz). 31P{1H} NMR (162
MHz, CD2Cl2, –90 °C, referenced to 85% H3PO4): δ = –10.2 (m,
Rh–P, J(RhP) = 137 Hz), –14.4 (dt, Rh–P, J(PP) = 31 Hz, J(RhP)
= 98 Hz), –17.0 (apparent triplet, Pt–P, J(PP) = 29 Hz, J(PSi) =
136 Hz, J(PtP) = 1995 Hz), –25.7 (m, Rh–P, J(RhP) = 90 Hz).
Crystallographic data for 1 : C36H55F4P4PtRhSi2, Mr = 1041.89,
These results indicate that the activation and formation of
Si–H bond takes place at the Rh center only. It contrasts with
the mechanism to account for the dynamic NMR spectra of
[(dippe)Rh]2(µ-H)(µ-η2-HSiR2) in which both Rh centers par-
ticipate in Si–H bond activation and formation of the ligands.10
This study provided new Pt–Rh dinuclear complexes with
bridging organosilyl ligands which formed the Si–Pt σ-bond and
the Si–H–Rh 3c-2e bond. The unsymmetrical organosilyl ligand
caused smooth and reversible dynamic motion of Si–H–Rh and
Pt–H–Rh hydrogen atoms and three PMe3 ligands bonded to Rh
center.
9
¯
triclinic, space group P1(No. 2), a =12.097(3) Å, b = 19.705(7) Å,
c = 11.002(2) Å, α = 98.25(2)°, β = 109.71(1)°, γ = 79.04(2)°, V
= 2415(1) Å3, Z = 2, µ(Mo Kα) = 3.441 mm–1, Dc = 1.433 g cm–3,
11105 unique reflections, 433 variables, R = 0.050, Rw = 0.073,
for 6125 reflections with I > 3σ(I). CCDC-162856. For 2·THF :
C36H52ClF4P4PtRhSi2·C4H8O, Mr = 1146.42, triclinic, space
¯
group P1(No. 2), a = 12.189(5) Å, b = 18.547(8) Å, c = 11.536(4)
Å, α = 90.72(4)°, β = 104.31(3)°, γ = 94.63(4)°, V = 2517(2) Å3, Z
= 2, µ(Mo Kα) = 3.362 mm–1, Dc = 1.512 g cm–3, 9664 unique
reflections, 487 variables, R = 0.060, Rw = 0.067, GOF = 1.67 for
2838 reflections with I > 3σ(I). CCDC-162857.
This work was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
10 a) M. D. Fryzuk, L. Rosenberg, and S. J. Retting,
Organometallics, 10, 2537 (1991). b) M. D. Fryzuk, L.
Rosenberg, and S. J. Retting, Organometallics, 15, 2871 (1996).
Dedicated to Prof. Hideki Sakurai on the occasion of his
70th birthday.