Complexes with dative bonds between d- and s-block metals: Synthesis and structure of [(Cy3P)2Pt-Be(Cl)X] (X = Cl, Me)

Full text of DOI:10.1002/anie.200900521

Angewandte
Chemie
DOI: 10.1002/anie.200900521
Beryllium Ligands
Complexes with Dative Bonds between d- and s-Block Metals:
ꢀ
Synthesis and Structure of [(Cy3P)2Pt Be(Cl)X] (X = Cl, Me)**
Holger Braunschweig,* Katrin Gruss, and Krzysztof Radacki
Dedicated to Professor Helmut Werner on the occasion of his 75th birthday
The chemistry of beryllium has developed in parallel with the
awareness of the toxicity of beryllium compounds.[1] There-
fore, investigations on beryllium are severely limited, in
contrast to its neighboring elements. Recent research has
focused on applications in material sciences, owing to the
unique properties of beryllium-containing materials,[2] and on
the coordination chemistry of BeII in aqueous solutions with
regard to its toxicity.[3] The coordination of ligands with
neutral main-group donor substituents to Be, which mostly
results in the formation of tetrahedral, four-coordinate
species, is well-established.[4] Tricoordinate beryllium com-
plexes were discovered as early as their tetracoordinate
counterparts, but they are far less numerous.[5] In addition to
resonance at d = 53.6 ppm (1JPt,P = 3240 Hz) is shifted slightly
upfield with respect to the starting material (d = 62.3 ppm,
1JPt,P = 4160 Hz). The upfield shift is not large enough to
suggest formation of a square-planar PtII complex but fits
more comfortably in the range of known Pt0 adducts of
Group 13 compounds.[9] Single crystals suitable for X-ray
analysis confirmed the formation of the Pt0–BeII adduct
ꢀ
[(Cy3P)2Pt BeCl2] (1, Figure 1).
ꢀ
these species with dative Be E bonds (E = main-group
element), beryllium-containing clusters have attracted further
interest.[6] While some of these clusters contain transition
metals, in particular Zr, electron-precise bonds between
beryllium and transition metals are unknown to date.
Recently, we initiated studies on the behavior of Lewis
basic, low-valent Pd and Pt complexes towards Group 13
element halides and their derivatives and consequently
elucidated two different reactivity patterns. Boron–bromide
and boron–iodide bonds display a propensity to add oxida-
tively to Pt0 and Pd0 centers, respectively, thus furnishing a
wide range of boryl and heterodinuclear borylene com-
plexes.[7] Conversely, metal-coordinated boryl and borylene
ligands show a unique tendency to form adducts in which the
Figure 1. Molecular structure of 1 (thermal ellipsoids are set at the
50% probability level; hydrogen atoms are omitted for clarity).
Selected bond lengths [ꢀ] and angles [8]: Pt–Be 2.168(4), Be–Cl1
1.923(4), Be–Cl2 1.921(4); P1-Pt1-P2 172.63(2), Cl1-Be-Cl2 118.61(18).
transition metal acts as the Lewis base, with formation of a
[8]
ꢀ
dative M B bond (M = Pd, Pt). Likewise, the heavier
Group 13 analogues AlCl3 and GaCl3 were found to form
similar platinum–base adducts,[9] thus inspiring us to extend
this field to strongly Lewis acidic beryllium compounds such
as BeCl2. Herein, we report the synthesis and characterization
of the first complex with an electron-precise beryllium–
transition-metal bond.
Monitoring the reaction of [Pt(PCy3)2] (Cy = cyclohexyl)
with a slight excess of BeCl2 in benzene by 31P{1H} NMR
spectroscopy revealed the formation of a new species, and
conversion was complete after 18 h at 808C. The new
Despite the close relation of 1 to platinum alane and
gallane adducts, the P1-Pt-P2 unit in 1 is nearly linear. The P1-
Pt-P2 angle (172.63(2)8) is significantly larger than in the
former complexes (162.07(2) and 162.21(2)8, respectively).
The Cl1-Be1-Cl2 angle (118.61(18)8) indicates almost trigo-
nal-planar coordination of the Be atom, and the BeCl2
fragment is rotated by 71.828 with respect to the P1-Pt-P2
ꢀ
moiety. The average Be Cl bond length of 1.922 ꢀ is similar
ꢀ
to that observed in the Be N adduct [Cl2Be(N(SiMe3)PEt3)]
(1.927 ꢀ), a rare example of a three-coordinate beryllium–
base adduct reported by Neumueller and Dehnicke in 2004.[10]
ꢀ
The Pt Be bond (2.168(4) ꢀ) is the first example of a classical
[*] Prof. Dr. H. Braunschweig, K. Gruss, K. Radacki
Institut fꢁr Anorganische Chemie
transition-metal–beryllium bond. Dative interactions from d-
block metals to alkaline earth metals have a modicum of
precedent: Bergman and co-workers published a complex in
which two [(h5-C5Me5)Ir(PMe3)H] fragments are bridged by
two MgPh groups. The transition-metal–magnesium bonds
are of different lengths, thus suggesting dative-bond charac-
ter, but no further details were given.[11]
Julius-Maximilians-Universitꢂt Wꢁrzburg
Am Hubland, 97074 Wꢁrzburg (Germany)
Fax: (+49)931-888-4623
E-mail: h.braunschweig@mail.uni-wuerzburg.de
[**] Financial support from the Fonds der Chemischen Industrie is
gratefully acknowledged.
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4239

Communications
Formation of a Pt0!BeII adduct, although unprece-
In comparison to 1 (2.168(4) ꢀ), the Pt Be bond in 2 is
slightly elongated (2.195(3) ꢀ), and the Cl-Be-C angle of 2
(123.70(17)8) is wider than the Cl1-Be-Cl2 angle of 1
ꢀ
dented, is consistent with theoretical work of Frenking and
co-workers on beryllium chloro complexes with nitrogen
donors in which BeCl2 was determined to be strongly Lewis
acidic.[12] To gain an estimation of the bond strength, we
treated 1 with 4-methylpyridine, which led to abstraction of
the BeCl2 moiety as a 4-methylpyridine adduct and to
liberated [Pt(PCy3)2]. The monopyridine adduct was con-
firmed by 9Be NMR spectroscopy in which a single resonance
was found at d = 7.08 ppm (in C6D6). When the reaction of
[Pt(PCy3)2] and BeCl2 was performed in diethyl ether, no
formation of 1 was observed by NMR spectroscopy, and
treatment of preformed 1 with diethyl ether led to liberation
of [Pt(PCy3)2], as with 4-methylpyridine.
ꢀ
(118.61(18)8). The assumption that a shorter Pt Be bond
and a smaller Cl-Be-Cl angle are indicative of a stronger
platinum–beryllium interaction in 1 was supported by DFT
ꢀ
calculations on model compounds [(H3P)2Pt Be(Cl)X] (X =
Cl, Me).[14] The use of smaller phosphane ligands in compu-
ꢀ
tations leads to shortening of the Pt Be bonds by approx-
imately 0.1 ꢀ and to wider (by 158) Cl-Be-X angles for both
ꢀ
molecules. The Pt Be bond dissociation energies (D0) are
77.6 and 47.8 kJmolꢀ1 for X = Cl and Me, respectively, and
ꢀ
thus corroborate stronger Pt Be interactions for the more
Lewis acidic BeCl2.
To gain further information about the new species, 1 was
treated with a slight excess of methyllithium, which resulted in
a new resonance at d = 54.2 ppm (1JPt,P = 3460 Hz) in the
In conclusion, the platinum–beryllium adducts
ꢀ
[(Cy3P)2Pt Be(Cl)X] (X = Cl, Me) reported herein display
unprecedented two-center two-electron transition-metal–ber-
yllium bonds. The reactivity of the beryllium dichloride
adduct was investigated, and X-ray structure analyses and
theoretical calculations of both complexes allow a deeper
1
31P{1H} NMR spectrum. In the H NMR spectrum, a charac-
teristic resonance was detected at d = 0.14 ppm, in accordance
with a new broad singlet at d = 0.6 ppm in the 13C{1H} NMR
spectrum. Filtration of the reaction mixture and layering of
ꢀ
insight into the Pt Be bond strength.
ꢀ
the filtrate with hexane yielded [(Cy3P)2Pt Be(Cl)CH3] (2) as
cubic crystals (Scheme 1, Figure 2).
Experimental Section
Safety note: In view of the toxicity of beryllium and its compounds, all
necessary safety measures were undertaken. All reactions were
carried out on a small scale, and for NMR spectroscopy we used
exclusively J. Young NMR tubes. The glassware was cleaned
separately, and all waste was collected in suitable containers.
All manipulations were performed in an inert atmosphere of dry
argon using standard Schlenk and glovebox techniques. C6D6 was
dried over molecular sieves and degassed by three freeze-pump-thaw
cycles before use. Anhydrous BeCl2 was purchased from Aldrich, and
[Pt(PCy3)2] was prepared according to known methods.[15] The NMR
spectra were recorded on a Bruker Avance 500 (1H: 500.13 MHz; 13C:
Scheme 1. Formation of 1 and 2.
9
125.76 MHz; 31P: 202.45 MHz; Be: 70.28 MHz) FT-NMR spectrom-
eter. NMR spectra of reaction controls were recorded on a Bruker
Avance 200 (1H: 200.13 MHz; 31P: 81.01 MHz) FT-NMR spectrom-
1
eter. H and 13C{1H} NMR spectra were referenced to external TMS
using the residual protio signal of the solvent (1H) or the solvent itself
(13C). 31P{1H} NMR spectra were referenced to 85% H3PO4;
9Be NMR spectra were referenced to an aqueous solution of BeCl2.
The 9Be NMR resonances of 1 and 2 were significantly broadened
owing to unresolved coupling to platinum and phosphorus nuclei such
that no definitive signal was observed.[7c] Microanalyses were
performed on an Elementar vario MICRO cube elemental analyzer.
1: BeCl2 (5.4 mg, 0.068 mmol) was added to a pale yellow solution
of [Pt(PCy3)2] (0.030 g, 0.040 mmol) in C6D6 (0.5 mL). The reaction
was heated for 18 h at 808C. The light yellow solution was layered
with hexane and allowed to evaporate slowly in a glovebox at room
1
temperature to yield 1 as colorless crystals (0.029 g, 87%). H NMR
Figure 2. Molecular structure of 2 (thermal ellipsoids are set at the
50% probability level; hydrogen atoms are omitted for clarity).
Selected bond lengths [ꢀ] and angles [8]: Pt–Be 2.195(3), Be–Cl
1.933(3), Be–C 1.788(4); P1-Pt-P2 167.34(2), Cl-Be-C 123.70(17),
Pt-Be-Cl 116.12(15), Pt-Be-C 120.18(18).
(500.1 MHz, C6D6): d = 2.31–2.26 (m, 6H, Cy), 2.12–2.09 (m, 12H,
Cy), 1.76–1.60 (m, 30H, Cy), 1.27–1.21 ppm (m, 18H, Cy); 13C{1H}
NMR (125.8 MHz, C6D6): d = 35.3 (virtual triplet, N[16] = 21 Hz, C1,
Cy), 31.1 (s, C3,5, Cy), 27.7 (virtual triplet, N[17] = 9 Hz, C2,6, Cy),
26.5 ppm (s, C4, Cy); 31P{1H} NMR (202.5 MHz, C6D6): d = 53.6 ppm
(1JPt,P = 3240 Hz); elemental analysis (%) calcd for C36H66BeCl2P2Pt:
C 51.73, H 7.96; found: C 52.44, H 7.92.
2: Compound 1 was used without prior isolation and treated with
2.4 equivalents methyllithium (2.1 mg, 0.096 mmol) in a sealable
NMR tube. The reaction mixture became lighter in color, and a fine
white solid precipitated immediately. The NMR tube was placed in an
ultrasonic bath for 1 min and heated for 18 h at 808C to complete the
reaction. The dark precipitate was filtered off and discarded, and the
The facile substitution of chloride upon treatment with
methyllithium has also been observed for the half-sandwich
complex [(h5-C5Me5)BeCl].[13] Nevertheless, to our knowl-
edge no complexes of the heteroleptic Cl-Be-CH3 fragment
with a donor ligand exist.
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Angewandte
Chemie
resulting orange solution was layered with hexane and allowed to
[6] a) R. P. Ziebarth, J. D. Corbett, J. Am. Chem. Soc. 1985, 107,
evaporate slowly in a glovebox at room temperature to yield 2 as
colorless cubic crystals (0.020 g, 71%). H NMR (500.1 MHz, C6D6):
4571 – 4573; b) J. B. Willems, H. W. Rohm, C. Geers, M. Koe-
ckerling, Inorg. Chem. 2007, 46, 6197 – 6203.
1
d = 2.22–2.17 (m, 6H, Cy), 2.14–2.12 (m, 12H, Cy), 1.78–1.62 (m,
30H, Cy), 1.26 ppm (m, 18H, Cy), 0.14 ppm (s, 3H, Be-CH3); 13C{1H}
NMR (125.8 MHz, C6D6): d = 35.5 (virtual triplet, N[16] = 27 Hz, C1,
Cy), 31.2 (s, C3,5, Cy), 27.8 (virtual triplet, N[17] = 11 Hz, C2,6, Cy),
26.7 ppm (s, C4, Cy), 0.6 (br s, CH3); 31P{1H} NMR (202.5 MHz, C6D6):
d = 54.2 ppm (1JPt,P = 3460 Hz); elemental analysis (%) calcd for
C37H69BeClP2Pt: C 54.50, H 8.53; found: C 54.93, H 8.45.
The crystal data of 1 and 2 were collected on a Bruker D8
diffractometer with an Apex CCD area detector and graphite-
monochromated MoKa radiation. The structures were solved using
direct methods, refined with the Shelx software package (G. M.
Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112–122), and expanded
using Fourier techniques. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were assigned idealized positions
and were included in structure factor calculations.
[7] a) H. Braunschweig, K. Radacki, D. Rais, F. Seeler, Organo-
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4461; Angew. Chem. Int. Ed. 2006, 45, 4352 – 4355. Further
Crystal data for 1: C42H72BeCl2P2Pt, Mr = 913.94, colorless block,
0.23 ꢁ 0.14 ꢁ 0.11 mm3, monoclinic space group P21/c, a =
14.8648(18) ꢀ, b = 16.0483(19) ꢀ, c = 18.741(2) ꢀ, b = 104.196(2)8,
V= 4334.2(9) ꢀ3, Z = 4, 1calcd = 1.401 gcmꢀ3
, , F-
m = 3.462 mmꢀ1
(000) = 1880, T= 168(2) K, R1 = 0.0262, wR2 = 0.0564, 8619 independ-
ent reflections [2q ꢁ 52.228] and 433 parameters.
ꢀ
examples of dative Pt B bonds: I. R. Crossley, A. F. Hill,
Crystal data for 2: C37H69BeClP2Pt, Mr = 815.41, colorless block,
0.48 ꢁ 0.28 ꢁ 0.26 mm3, monoclinic space group P21/n, a =
Organometallics 2004, 23, 5656 – 5658; S. Bontemps, M. Sirco-
glou, G. Bouhadir, H. Puschmann, J. A. K. Howard, P. W. Dyer,
K. Miqueu, D. Bourissou, Chem. Eur. J. 2008, 14, 731 – 740. For a
review on boryl and borane complexes, see: H. Braunschweig, C.
Kollann, D. Rais, Angew. Chem. 2006, 118, 5380 – 5400; Angew.
Chem. Int. Ed. 2006, 45, 5254 – 5274.
12.1749(13) ꢀ,
b = 17.1299(18) ꢀ,
c = 19.111(2) ꢀ,
b =
m =
107.3470(10)8, V= 3804.4(7) ꢀ3, Z = 4, 1calcd = 1.424 gcmꢀ3
,
3.866 mmꢀ1, F(000) = 1680, T= 169(2) K, R1 = 0.0218, wR2 = 0.0508,
9552 independent reflections [2q ꢁ 56.98] and 380 parameters.
CCDC 717995 (1) and 717996 (2) contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[9] a) H. Braunschweig, K. Gruss, K. Radacki, Angew. Chem. 2007,
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47, 8595 – 8597.
[10] B. Neumꢂller, K. Dehnicke, Z. Anorg. Allg. Chem. 2004, 630,
369 – 376.
Received: January 28, 2009
[11] J. T. Golden, T. H. Peterson, P. L. Holland, R. G. Bergman, R. A.
Andersen, J. Am. Chem. Soc. 1998, 120, 223 – 224.
Published online: May 4, 2009
[12] S. Metz, M. C. Holthausen, G. Frenking, Z. Anorg. Allg. Chem.
2006, 632, 814 – 818.
[13] a) M. Mar Conejo, R. Fernandez, E. Carmona, R. A. Andersen,
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[14] All computations were performed on a cluster of Linux work-
stations using Gaussian03, Revision E.01, M. J. Frisch et al.,
Gaussian, Inc., Pittsburgh PA, 2003. Calculations were per-
formed using DFT methods, applying the three hybrid functional
B3LYP using 6-31G(d,p) basis function sets for nonmetals and
the Stuttgart relativistic, small core ECP basis set for Pt. The
Keywords: adduct formation · beryllium · coordination modes ·
metal–metal interactions · platinum
.
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ꢀ
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1
[16] N = j JP, C + 3JP, C j .
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Angew. Chem. Int. Ed. 2009, 48, 4239 –4241
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
4241