Interaction between d- and p-block metals: Synthesis and structure of platinum-alane adducts

Article abstract of DOI:10.1002/anie.200702726

(Figure Presented) You'll never walk alane: An intriguing T-shaped platinum-alane adduct results from the almost quantitive reaction of [Pt(PCy₃)₂] with AlX₃ (X = Cl, Br, I). The compound [(Cy₃P)₂Pt-A

Full text of DOI:10.1002/anie.200702726

Communications
DOI: 10.1002/anie.200702726
Platinum Complexes
Interaction between d- and p-Block Metals: Synthesis and Structure of
Platinum–Alane Adducts**
Holger Braunschweig,* Katrin Gruss, and Krzysztof Radacki
Dative bonds between transition metals and the archetypal
Lewis acid BF3 were proposed as early as 1966,[1] but were
called into question 30years later. [2] However, more recent
work by Hill,[3] Parkin,[4] Bourissou,[5] and Rabinovich[6] and
respective co-workers has demonstrated that borane com-
herein provided a strong indication that the reaction takes a
different course.
After workup,
a colorless crystalline material was
obtained in almost quantitative yield, for which the elemental
analysis revealed a 1:1 composition with respect to the
starting materials. The formulation of this compound as the
plexes of the type [LnM BR3][7] can be obtained from a range
ꢀ
ꢀ
of late Lewis basic transition metals, and the nature of the
dative metal–boron bond has been elucidated by experimen-
tal and computational studies. In addition, the metal–phos-
phine fragments {M(PCy3)} (M = Pd, Pt) have proven to act as
versatile metal bases towards a range of coordinated boryl[8]
and borylene ligands.[9]
platinum alane complex trans-[(Cy3P)2Pt AlCl3] (2) was
shown by
a
single-crystal X-ray diffraction study
(Figure 1).[15] Complex 2 crystallizes in the triclinic space
The heavier Group 13 elements are also known to form a
variety of transition-metal complexes, in analogy to boron.[10]
Despite the plethora of complexes with transition-metal–
aluminum bonds, however, corresponding alane complexes
ꢀ
[LnM AlR3] are exceptionally rare. Structural evidence for an
unsupported dative transition-metal–aluminum bond is to our
knowledge restricted to the ionic species [NEt4][(h5-
C5H5)(OC)2Fe AlPh3].[11] Bergman and co-workers reported
ꢀ
the synthesis of [(h5-C5Me5)(Me3P)IrH2(AlPh3)], which,
according to structural data, has a certain amount of Ir–Al
interaction. This metal–metal bond, however, is supported by
two bridging hydrogen atoms.[12] Given the pronounced
propensity of zerovalent platinum to add to three-coordinate
boron centers, we initiated studies to extend this chemistry to
the higher homologue, aluminum. Herein we report the first
neutral alane complexes with an unsupported dative bond.
The reaction of AlCl3 with an equimolar amount of
[Pt(PCy3)2] (1) in C6D6 was monitored by 31P{1H} NMR
Figure 1. Molecular structure of 2 (hydrogen atoms omitted; thermal
ellipsoids are set at 50% probability). Selected bond lengths [Š] and
angles [8]: Pt1-Al1 2.3857(7), Al1-Cl1 2.1548(10), Al1-Cl2 2.1511(10),
Al1-Cl3 2.1576(9); P1-Pt1-P2 162.07(2).
spectroscopy. A new resonance at d = 53.5 ppm (1JPtP
=
group P1, and the platinum center adopts an unusual T-
¯
3032 Hz) was observed that is shifted only marginally upfield
shaped geometry with a P-Pt-P angle of 162.07(2)8. Similar
1
with respect to that of 1 (d = 62.3 ppm, JPtP = 4161 Hz).[13]
geometries have only been reported for the related SO2
Corresponding reactions between Pt0 species and BCl3 or
other boron halides usually proceed by oxidative addition of
the boron–halogen bond to the platinum center, which is
accompanied by a significant upfield shift of the 31P{1H} NMR
spectroscopic resonances.[14] Thus, the chemical shift observed
complex trans-[(Cy3P)2Pt SO2] (P-Pt-P 165.72(4)8)
and
[16]
ꢀ
the platinum(II) boryl complex trans-[(Cy3P)2Pt{B(Fc)Br}]-
[BArF ] (Fc = [(h5-C5H4)Fe(C5H5)], ArF = 3,5-C6H3(CF3)2; P-
4
Pt-P 162.96(3)8).[17] The most prominent structural feature of
2 is the presence of an unsupported platinum–aluminum bond
with a Pt–Al separation of 2.3857(7) Š, which only slightly
exceeds that of zerovalent platinum alanediyl complexes, for
example, [(dcpe)Pt(AlCp*)2] (dcpe = 1,2-bis(dicyclohexyl-
phosphanyl)ethane, Cp* = Me5C5; 2.327(2) and 2.335(2) Š).
[*] Prof. Dr. H. Braunschweig, K. Gruss, K. Radacki
Institut für Anorganische Chemie
ꢀ
The diyl complex, however, has an additional Pt Al p
Julius-Maximilians-Universität Würzburg
Am Hubland, 97074 Würzburg (Germany)
Fax: (+49)931-888-4623
backdonation, thus resulting in a short Pt–Al bond.[18]
Since the compound 2 represents the first example of a
platinum–alane complex, it is instructive to compare the
geometry of the AlCl3 moiety with that of corresponding
E-mail: h.braunschweig@mail.uni-wuerzburg.de
[**] Financial support from the Fonds der Chemischen Industrie is
gratefully acknowledged.
ꢀ
adducts [Cl3Al D] (D = main-group-element base). For these
ꢀ
systems, a correlation of the Cl-Al-Cl angles and Al Cl bond
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
lengths with the stability of the appropriate adducts has been
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Angew. Chem. Int. Ed. 2007, 46, 7782 –7784

Angewandte
Chemie
established from computational[19] and experimental studies.
Although monomeric AlCl3 has trigonal-planar geometry,
formation of the adduct [AlCl3(C3N3Cl3)] imposes a signifi-
cant decrease of the Cl-Al-Cl angles (113.28) associated with
[1] M. P. Johnson, D. F. Shriver, J. Am. Chem. Soc. 1966, 88, 30 1 –
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[2] a) H. Braunschweig, T. Wagner, Chem. Ber. 1994, 127, 1613 –
1614; b) H. Braunschweig, T. Wagner, Z. Naturforsch. B 1996,
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B 1999, 54, 839 – 842.
ꢀ
an increase of the Al Cl bond lengths (from 2.06 to
2.107 Š).[20] Similar trends were also observed for [AlCl3-
(dmap)]
(dmap = 4-(dimethylamino)pyridine;
111.68,
[3] a) A. F. Hill, G. R. Owen, A. J. P. White, D. J. Williams, Angew.
Chem. 1999, 111, 2920– 2923; Angew. Chem. Int. Ed. 1999, 38,
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metallics 2006, 25, 289 – 299.
[4] a) V. K. Landry, J. G. Melnick, D. Buccella, K. Pang, J. C.
Ulichny, G. Parkin, Inorg. Chem. 2006, 45, 2588 – 2597; b) K.
Pang, S. M. Quan, G. Parkin, Chem. Commun. 2006, 5015 – 5017.
[5] a) S. Bontemps, H. Gornitzka, G. Bouhadir, K. Miqueu, D.
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Miqueu, D. Bourissou, J. Am. Chem. Soc. 2006, 128, 12056 –
12057.
2.116 Š).[21] In comparison, complex 2 displays even more
acute Cl-Al-Cl angles (105.918 mean) and notably elongated
ꢀ
Al Cl bonds (2.1545 Š mean), thus suggesting a strong dative
ꢀ
Pt Al bond.
Analogous reactions of 1 with AlBr3 and AlI3 resulted in
the formation of the related alane complexes trans-
ꢀ
ꢀ
[(Cy3P)2Pt AlBr3] (3) and trans-[(Cy3P)2Pt AlI3] (4;
Scheme 1), which were isolated in almost quantitative yields
[6] D. J. Mihalcik, J. L. White, J. M. Tanski, L. N. Zakharov, G. P. A.
Yap, C. D. Incarvito, A. L. Rheingold, D. Rabinovich, Dalton
Trans. 2004, 1626 – 1634.
[7] For a recent review covering aspects of borane complexes, see:
H. Braunschweig, C. Kollann, D. Rais, Angew. Chem. 2006, 118,
5380– 5400; Angew. Chem. Int. Ed. 2006, 45, 5254 – 5274.
[8] H. Braunschweig, K. Radacki, D. Rais, G. R. Whittell, Angew.
Chem. 2005, 117, 1217 – 1219; Angew. Chem. Int. Ed. 2005, 44,
1192 – 1194.
[9] a) H. Braunschweig, D. Rais, K. Uttinger, Angew. Chem. 2005,
117, 3829 – 3832; Angew. Chem. Int. Ed. 2005, 44, 3763 – 3766;
b) H. Braunschweig, K. Radacki, D. Rais, F. Seeler, Angew.
Chem. 2006, 118, 1087 – 1090; Angew. Chem. Int. Ed. 2006, 45,
1066 – 1069; c) H. Braunschweig, C. Burschka, M. Burzler, S.
Metz, K. Radacki, Angew. Chem. 2006, 118, 4458 – 4461; Angew.
Chem. Int. Ed. 2006, 45, 4352 – 4355; d) H. Braunschweig, K.
Radacki, D. Rais, K. Uttinger, Organometallics 2006, 25, 5159 –
5164; e) H. Braunschweig, K. Radacki, K. Uttinger, Eur. J. Inorg.
Chem. 2007, DOI: 10.1002/ejic.200700356.
Scheme 1. Synthesis of platinum alane complexes 2–4.
as pale orange (3) or red-brown (4) solids. The formulations
were supported by 31P{1H} NMR spectroscopy data (3: d =
51.2 ppm, 1JPPt = 3046 Hz; 4: d = 46.8 ppm, 1JPPt = 3062 Hz).
Alane complexes 2–4 are all extremely sensitive towards air
and moisture. Although all the compounds are stable in the
solid state, 3 and 4 tend to decompose after 1–2 days in
solution
to
yield
trans-[(Cy3P)2PtX2]
and
trans-
[10] For a comprehensive review, see: R. A. Fischer, J. Weiss, Angew.
Chem. 1999, 111, 3002 – 3022; Angew. Chem. Int. Ed. 1999, 38,
2830– 2850.
[(Cy3P)2Pt(H)X] (X = Br, I), as indicated by 31P{1H} NMR
spectroscopy.[22]
In conclusion, the first platinum alane complexes are
reported, which display an unsupported bond between a d-
block and a p-block metal. From the structural data of trans-
[11] J. M. Burlitch, M. E. Leonowicz, R. B. Petersen, R. E. Hughes,
Inorg. Chem. 1979, 18, 1097 – 1105.
[12] J. T. Golden, T. H. Peterson, P. L. Holland, R. G. Bergman, R. A.
Andersen, J. Am. Chem. Soc. 1998, 120, 223 – 224.
[13] S. Otsuka, T. Yoshida, M. Matsumoto, K. Nakatsu, J. Am. Chem.
Soc. 1976, 98, 5850– 5858; the significantly reduced Pt–P
coupling observed for 2–4 is presumably due to the increased
coordination number of the platinum center.
ꢀ
[(Cy3P)2Pt AlCl3] (2) the presence of a strong dative Pt–Al
bond can be concluded.
Experimental Section
[14] a) Recently, trans-[PtCl(BCl2)(PPh3)2] was obtained by oxida-
tive addition of BCl3; 31P{1H} NMR: d = 23 ppm, 1JPPt = 3046 Hz:
J. P. H. Charmant, C. Fan, N. C. Norman, P. G. Pringle, Dalton
Trans. 2007, 114 – 123; For further examples of boron–halogen
addition to Pt0, see reviews: b) G. J. Irvine, G. Lesley, T. B.
Marder, N. C. Norman, C. R. Rice, E. G. Robins, W. R. Roper,
G. R. Whitell, L. J. Wright, Chem. Rev. 1998, 98, 2685 – 2722;
c) S. Aldridge, D. L. Coombs, Coord. Chem. Rev. 2004, 248, 535 –
559; d) H. Braunschweig, M. Colling, Coord. Chem. Rev. 2001,
223, 1 – 51; e) H. Braunschweig, Angew. Chem. 1998, 110, 1882 –
1898; Angew. Chem. Int. Ed. 1998, 37, 1786 – 1801.
2: AlCl3 (0.004 g, 0.026 mmol) was added to a pale yellow solution of
1 (0.020 g, 0.026 mmol) in benzene (1 mL) in a NMR tube fitted with
a Youngꢀs stopcock. The solution was kept at room temperature for
24 h to yield
2
as colorless crystals (0.021 g, 93%). 1H NMR
(500.1 MHz, C6D6, 258C): d = 2.60–0.92 ppm (m, 66H, Cy); 13C{1H}
NMR (125.8 MHz, C6D6, 258C): d = 36.3 (virtual triplet, N[23] = 26 Hz,
C1, Cy), 31.6 (s, C3, C5, Cy), 27.9 (m, C2, C6, Cy), 26.6 ppm (s, C4, Cy);
31P{1H} NMR (202.5 MHz, C6D6, 258C): d = 53.5 ppm (1JPtP
=
3032 Hz). Elemental analysis (%) calcd for C36H66AlCl3P2Pt: C
48.62, H 7.48; found: C 48.34, H 7.14.
[15] The crystal data of 2 were collected at a Bruker x8apex
diffractometer with a CCD area detector and multi-layer
mirror monochromated MoKa radiation. The structure was
solved using direct methods, refined with the SHELX software
package (G. Sheldrick, University of Göttingen, 1997) and
expanded using Fourier techniques. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were assigned
Received: June 21, 2007
Published online: September 5, 2007
Keywords: alanes · aluminum · coordination modes ·
.
Lewis bases · platinum
Angew. Chem. Int. Ed. 2007, 46, 7782 –7784
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7783

Communications
idealized positions and were included in structure factor
[18] D. Weiss, T. Steinke, M. Winter, R. A. Fischer, Organometallics
2000, 19, 4583 – 4588.
[19] A. Y. Timoshkin, A. V. Suvorov, H. F. Bettinger, H. F. Schaefer
III, J. Am. Chem. Soc. 1999, 121, 5687 – 5699.
[20] S. Tragl, K. Gibson, H.-J. Meyer, Z. Anorg. Allg. Chem. 2007,
633, 470– 472.
[21] F. Thomas, T. Bauer, S. Schulz, M. Nieger, Z. Anorg. Allg. Chem.
2003, 629, 2018 – 2027.
calculations. Crystal data for 2: C51H81AlCl3P2Pt, Mr = 1084.52,
3
¯
colorless plates, 0.35 ” 0.25 ” 0.08 mm , triclinic space group P1,
a = 11.0306(5), b = 19.0585(9), c = 24.4351(12) Š, a = 86.181(2),
b = 84.304(2), g = 87.857(2)8, V= 5097.7(4) Š3, Z = 4, 1calcd
=
1.413 gcmꢀ3, m = 3.023 mmꢀ1, F(000) = 2236, T= 100(2) K, R1 =
0.0365, wR2 = 0.0755, 29252 independent reflections (2q =
64.068) and 1195 parameters. CCDC-651210contains the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[16] J. M. Ritchey, D. C. Moody, R. R. Ryan, Inorg. Chem. 1983, 22,
2276 – 2280.
[22] For 31P{1H} NMR of trans-[(Cy3P)2Pt(H)X] (X = Br, I) see:
a) N. A. Jasmin, R. N. Perutz, J. Am. Chem. Soc. 2000, 122,
8685 – 8693; for 31P{1H} NMR of trans-[(Cy3P)2PtX2] (X = Br, I),
see b) T. S. Cameron, H. C. Clark, A. Linden, A. M. Nicholas,
Polyhedron 1990, 9, 1683 – 1688; c) I. M. Al-Najjar, Inorg. Chim.
Acta 1987, 128, 93 – 104.
[17] H. Braunschweig, K. Radacki, D. Rais, D. Scheschkewitz,
Angew. Chem. 2005, 117, 5796 – 5799; Angew. Chem. Int. Ed.
2005, 44, 5651 – 5654.
1
[23] N = j JPC + 3JPC j ; for details on the virtual coupling constant N
see J. P. Fackler, Jr., J. A. Fetchin, J. Mayhew, W. C. Seidel, T. J.
Swift, M. Weeks, J. Am. Chem. Soc. 1969, 91, 1941 – 1947.
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