Metal-only Lewis pairs featuring unsupported Pt→M (M = Zn or Cd) dative bonds

Article abstract of DOI:10.1039/c2cc37442k

Reactions of [Pt(PCy₃)₂] (Cy = cyclohexyl) with group 12 metal dihalides have afforded the novel metal only Lewis pair (MOLP) complexes, [(Cy₃P)₂Pt→MX₂] (M = Zn or Cd, X = Br or I), or the oxidative a

Full text of DOI:10.1039/c2cc37442k

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Metal-only Lewis pairs featuring unsupported Pt-M
(M = Zn or Cd) dative bonds†
Cite this: Chem. Commun.,
2013, 49, 48--50
Mengtao Ma,z Anastas Sidiropoulos, Lalrempuia Ralte, Andreas Stasch* and
Received 12th October 2012,
Accepted 2nd November 2012
Cameron Jones*
DOI: 10.1039/c2cc37442k
www.rsc.org/chemcomm
Reactions of [Pt(PCy3)2] (Cy = cyclohexyl) with group 12 metal of these adducts have indicated that [Pt(PCy3)2] can act as a
dihalides have afforded the novel metal only Lewis pair (MOLP) relatively strong Lewis base. Moreover, the oxidative addition of
complexes, [(Cy3P)2Pt-MX2] (M = Zn or Cd, X = Br or I), or the metal and non-metal halide bonds to its Pt0 centre has been
oxidative addition product, trans-[(Cy3P)2(I)PtHgI]. The zinc demonstrated in some instances.5b,7 It is surprising that
complex represents the first MOLP to contain an unsupported there have been no reports of adducts between [Pt(PCy3)2]
Pt-Zn linkage.
and group 12 metal halides, and to the best of our knowledge,
unsupported Pt-Zn MOLPs of any kind are unknown. Here we
The chemistry of heterobimetallic complexes featuring metal– report the preparation of the thermally stable complexes,
metal bonds is of considerable importance, both for funda- [(Cy3P)2Pt-MX2] (M = Zn or Cd; X = Br or I), and show that
mental reasons, and because such systems have found a variety related mercury halide adducts are not easily accessible.
of applications in synthesis, catalysis, materials chemistry etc.1
Treatment of toluene solutions of [Pt(PCy3)2] with either
While the majority of such compounds are stabilised by ligands ZnBr2 or CdI2 led to high isolated yields of the yellow-orange
that bridge their metal–metal bonds, compounds with unsup- crystalline products, 1 and 2, upon work-up (Scheme 1). Both
ported metal–metal bonds are generally considered as being more compounds are thermally robust and show no tendency to
reactive species.1,2 There are a variety of methodologies available convert to oxidative addition products, [(Cy3P)2(X)PtMX2], in
for the construction of metal–metal bonded complexes, though solution or the solid state at ambient temperature. In contrast,
the formation of heteronuclear M-M0 dative linkages from Lewis treatment of [Pt(PCy3)2] with HgI2 afforded a high yield of
basic and Lewis acidic metal fragments is increasingly employed the yellow addition product, trans-[(Cy3P)2(I)PtHgI] 3, with no
in this field.3 The popularity of this synthetic approach is derived evidence of adduct formation (though the reaction likely proceeds
from its simplicity, but also from the wide array of supported and via [(Cy3P)2Pt-HgI2]). Similar oxidative addition processes have
unsupported M-M0 combinations that it offers the synthetic been previously described for reactions of [Pt(PCy3)2] with, for
chemist. Compounds bearing such bonds have been termed example, GaX3 (X = Br or I), BiCl3 and group 11 metal halides.5b,7
metal-only Lewis pairs, or MOLPs.3a
However, the outcome of these reactions can be dependent on the
One of the more important metal donor Lewis bases that nature of the halide as much as the metal, as evidenced by the fact
have been examined in recent years is the linear platinum(0) that GaCl3 forms a stable adduct with the Pt0 Lewis base.5b As a
complex, [Pt(PCy3)2] (Cy = cyclohexyl). This has been employed result, we investigated the reaction of HgCl2 with [Pt(PCy3)2], and
to great effect, largely by Braunschweig and co-workers, in the found that this led to deposition of mercury metal and the
formation of novel complexes with unsupported dative bonds formation of the known complex, trans-[PtCl2(PCy3)2],8 in addition
between platinum and an array of s-,4 p-5 and d-block6 metal to small amounts of trans-[(Cy3P)2(Cl)PtHgCl] (see ESI†). It is
fragments.5b,7 Structural and computational studies of several
School of Chemistry, Monash University, PO Box 23, Melbourne, VIC 3800,
Australia. E-mail: cameron.jones@monash.edu, andreas.stasch@monash.edu;
Fax: +61-3-9905-4597; Tel: +61-3-9902-0391
† Electronic supplementary information (ESI) available: Further details and
references for synthetic and crystallographic studies. CCDC 905516–905520. For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c2cc37442k
‡ Current address: Department of Chemistry, College of Science, Nanjing
Scheme 1 Reagents and conditions: i, ZnBr2 or CdI2; ii, HgI2 (Cy = cyclohexyl).
Forestry University, Jiangsu 210037, China.
c
48 Chem. Commun., 2013, 49, 48--50
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Fig. 1 Molecular structure of 1 (25% thermal ellipsoids; hydrogen atoms
omitted). Selected bond lengths (Å) and angles (8) for 1: Pt(1)–P(1) 2.2760(6),
Pt(1)–Zn(1) 2.4040(6), Br(1)–Zn(1) 2.3305(5), P(1)0–Pt(1)–P(1) 176.28(3), Br(1)–
Zn(1)–Br(1)0 118.75(3), Br(1)–Zn(1)–Pt(1) 120.626(15), Br(1)0–Zn(1)–Pt(1)
120.626(15); symmetry operation: 0ꢀx + 1, y, ꢀz + 1/2. Selected bond lengths (Å)
and angles (8) for 2 (see ESI† for ORTEP diagram): Pt(1)–P(1) 2.2799(13), Pt(1)–
P(2) 2.2920(13), Pt(1)–Cd(1) 2.5867(6), I(1)–Cd(1) 2.6974(8), I(2)–Cd(1) 2.6997(8),
P(1)–Pt(1)–P(2) 176.92(3), Pt(1)–Cd(1)–I(1) 122.176(19), Pt(1)–Cd(1)–I(2)
117.531(19), I(1)–Cd(1)–I(2) 120.21(2).
Fig. 2 Molecular structure of 3 (25% thermal ellipsoids; hydrogen atoms
omitted). Selected bond lengths (Å) and angles (8): Hg(1)–Pt(1) 2.5250(2), Hg(1)–
I(2) 2.6764(16), Pt(1)–P(1) 2.3304(10), Pt(1)–P(2) 2.3403(10), Pt(1)–I(1) 2.6542(3),
Pt(1)–Hg(1)–I(2) 173.05(3), P(1)–Pt(1)–P(2) 168.10(4), Hg(1)–Pt(1)–I(1)
178.850(11), P(1)–Pt(1)–Hg(1) 85.99(2), P(2)–Pt(1)–Hg(1) 87.17(3).
Furthermore, the Pt–Cd bond in 2 (2.5867(6) Å) is shorter than
all of the more than 50 other reported examples of such
interactions (range: 2.606–3.129 Å).9 This, combined with the
fact that 1 and 2 possess very rare examples of terminal MX2
fragments, could indicate that [Pt(PCy3)2] acts as a strong
nucleophile to those fragments.11
The molecular structure of 3 (Fig. 2) confirms it to be an
oxidative addition product. The compound is monomeric and
its Pt center has a square planar coordination environment,
with the two phosphine ligands trans- to each other. The Pt–Hg
bond length is at the low end of the reported range for
unsupported interactions of this nature (2.509–2.808 Å),9 while
the terminal Hg–I and Pt–I distances are unexceptional. It is of
note that several reports have detailed the oxidative addition of
mercury(II) dihalides to platinum(II) centres,12 though we are
not aware of any prior structurally authenticated examples of
such additions to platinum(0) complexes.
In conclusion, the first examples of adducts between the
widely used metal donor Lewis base, [Pt(PCy3)2], and group 12
metal fragments have been prepared and structurally characterised.
One synthesised complex, [(Cy3P)2Pt-ZnBr2], represents the first
MOLP containing an unsupported Pt-Zn linkage, while attempts
to prepare a related Pt-Hg adduct, instead lead to an oxidative
addition reaction. We are currently exploring the controlled
reduction of 1–3 and related compounds with the aim of forming
well defined, low valent bimetallic cluster compounds. Our results
in this direction will be reported in due course.
noteworthy that a similar result was obtained from the reaction of
Hg2Cl2 with [Pt(PCy3)2].
The NMR spectroscopic data for 1 and 2 are similar and
suggest both retain their solid state structures in solution.§
Their 31P{1H} NMR spectra display singlet resonances at d =
53.0 and 51.6 ppm respectively, each of which exhibits 195Pt
satellites (1JPtP = 2982 Hz 1; 2978 Hz 2). These values are
comparable to those for the isostructural adduct, [(Cy3P)2Pt-
BeCl2] (d = 53.6 ppm, 1JPtP = 3240 Hz),4 but lower in magnitude
than the values for the precursor complex, [Pt(PCy3)2]
1
(d = 62.2 ppm, JPtP = 4155 Hz).7a Furthermore, 111/113Cd
satellites (2JCdP = 36 Hz) flank the signal for 2. Triplet reso-
nances were observed in the 195Pt{1H} NMR spectra of the
compounds (1: d = ꢀ5425 ppm, 2: d = ꢀ5260 ppm), which
are significantly downfield of that for [Pt(PCy3)2] (d
=
ꢀ6505 ppm).7a The NMR spectroscopic data for the insertion
product 3 (31P{1H}: d = 31.0 ppm, 1JPtP = 2448 Hz, 2JHgP = 299 Hz;
195Pt{1H}: d = ꢀ5052 ppm) compare well with data for similar
compounds, e.g. trans-[(Cy3P)2(I)PtGaI2] (31P{1H}: d = 23.1 ppm,
1JPtP = 2281 Hz).5b
X-ray crystallographic studies determined 1 and 2 to be
monomeric and isostructural in the solid state. Therefore only
the molecular structure of 1 is depicted in Fig. 1 (see ESI† for an
ORTEP diagram of 2).¶ Both compounds are also broadly
isostructural with [(Cy3P)2Pt-BeCl2] in that their Lewis acidic
metal centres all possess trigonal planar geometries, while their
Pt centres have T-shaped coordination environments with close
to linear P–Pt–P fragments. In fact, this unit in 1 and 2 is more
obtuse than in any other metal adduct of [Pt(PCy3)2]. The PtMX2
and P2PtM least squares planes of 1 and 2 bisect each other at
angles of 71.81 1 and 69.71 2 (cf. 71.81 in [(Cy3P)2Pt-BeCl2]4).
With regard to the Pt–M distances in the compounds, that in 1
(2.4040(6) Å) is at the short end of the known range (2.343–
3.003 Å),9 with only covalently bonded two-coordinate zinc
CJ and AS gratefully acknowledge financial support from the
Australian Research Council (fellowships for MM and LR). The
EPSRC is also thanked for access to the UK National Mass
Spectrometry Facility.
Notes and references
§ [(Cy3P)2Pt-ZnBr2] (1): ZnBr2 (0.039 g, 0.173 mmol) was added to a
solution of [Pt(PCy3)2] (0.131 g, 0.173 mmol) in toluene (80 cm3) at
ꢀ70 1C. The mixture was warmed to room temperature overnight, then
compounds, e.g. [Cp*Pt(ZnCp*)3],10 having shorter Pt–Zn bonds. concentrated to ca. 25 cm3 in vacuo. Yellow-orange crystals of 1
c
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Chem. Commun., 2013, 49, 48--50 49

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deposited from this solution over 1 week (0.14 g, 0.143 mmol, 83%). (on F2) 0.0413 (all data); Crystal data for 3: C36H66HgI2P2PtZn, M = 1210.31,
N.B. Crystals for the X-ray experiment were grown from benzene. M.p. monoclinic, space group P21/c, a = 13.4975(5) Å, b = 13.4310(3) Å, c =
258–260 1C; 1H NMR (300 MHz, 303 K, C6D6): d = 1.29 (br., 18H, Cy- 23.4845(8) Å, b = 107.180(3)1, V = 4067.4(2) Å3, Z = 4, Dc = 1.976 g cmꢀ3
,
CH2), 1.60–1.73 (m, 30H, Cy-CH2), 2.06–2.12 (m, 12H, Cy-CH2), 2.28 (m, F(000) = 2304, m(Mo-Ka) = 8.825 mmꢀ1, 123(2) K, 26 184 collected reflec-
6H, Cy-CH); 13C{1H} NMR (75.5 MHz, 303 K, C6D6): d = 26.4 (s, C4, Cy), tions, 7991 unique reflections [R(int) 0.0245], R (on F) 0.0233 (I > 2sI), wR
27.6 (virtual triplet, JPC = 11 Hz, C2,6, Cy), 31.6 (s, C3,5, Cy), 35.7 (virtual t, (on F2) 0.0481 (all data).
JPC = 27 Hz, C1, Cy); 31P{1H} NMR (121.5 MHz, 303 K, C6D6): d = 53.0 (s,
1JPt-P = 2982 Hz); 195Pt{1H} NMR (85.6 MHz, 300 K, C6D6): d = ꢀ5425 (s,
1 See for example: (a) C. M. Thomas, Comments Inorg. Chem., 2011,
1JPt-P = 2980 Hz); IR (Nujol) n (cmꢀ1): 1601s, 1006s, 889s, 851s, 814s,
32, 14; (b) M. Asay, C. Jones and M. Driess, Chem. Rev., 2011,
748s, 698s; MS (ꢀve CI/CH4) m/z (%): 981.2 (Mꢀ, 6), 898.0 (Mꢀ-Br, 1);
111, 354; (c) S. T. Liddle and D. P. Mills, Dalton Trans., 2009, 5592;
(d) L. Gade, Angew. Chem. Int. Ed., 2000, 39, 2658; (e) N. Wheatley
and P. Kalck, Chem. Rev., 1999, 99, 3379; ( f ) D. W. Stephan, Coord.
Chem. Rev., 1989, 95, 41, and references therein.
2 See for example: H. Lei, J.-D. Guo, J. C. Fettinger, S. Nagase and
P. P. Power, J. Am. Chem. Soc., 2010, 132, 17399, and references
therein.
3 See for example: (a) J. Bauer, H. Braunschweig and R. D. Dewhurst,
Chem. Rev., 2012, 112, 4329; (b) A. Amgoune and D. Bourissou,
Chem. Commun., 2011, 47, 859, and references therein.
4 H. Braunschweig, K. Gruss and K. Radacki, Angew. Chem. Int. Ed.,
2009, 48, 4239.
5 See for example: (a) H. Braunschweig, A. Damme, R. D. Dewhurst,
F. Hupp, J. O. C. Jiminez-Halla and K. Radacki, Chem. Commun.,
2012, 48, 10410; (b) H. Braunschweig, K. Gruss and K. Radacki,
Inorg. Chem., 2008, 47, 8595; (c) H. Braunschweig, K. Gruss and
K. Radacki, Angew. Chem. Int. Ed., 2007, 46, 7782.
anal. calcd for C36H66Br2P2PtZn: C 44.07%, H 6.78%; found: C 44.10%,
H 6.87%. [(Cy3P)2Pt-CdI2] (2): A similar procedure to that used to
prepare 1 was employed for the synthesis of 2 (yield: 74%). M.p. 229–
231 1C; 1H NMR (300 MHz, 303 K, C6D6): d = 1.30 (br., 18H, Cy-CH2),
1.61–1.74 (m, 30H, ꢀCH2), 2.06 (m, 12H, ꢀCH2), 2.22 (m, 6H, ꢀCH);
13C{1H} NMR (75.5 MHz, 303 K, C6D6): d = 26.4 (s, C4, Cy), 27.7 (virtual t,
JPC = 11 Hz, C2,6, Cy), 31.8 (s, C3,5, Cy), 36.0 (virtual t, JPC = 27 Hz, C1, Cy);
1
31P{1H} NMR (121.5 MHz, 303 K, C6D6): d = 51.6 (s, JPt-P = 2978 Hz,
2JCd-P = 36 Hz); 195Pt{1H} NMR (85.6 MHz, 300 K, C6D6): d = ꢀ5260
1
(s, JPt-P = 2974 Hz); IR (Nujol) n (cmꢀ1): 1494w, 1027s, 914m, 887m,
851m, 799s, 732s, 695m; MS (ꢀve CI/CH4) m/z (%): 1122.1 (Mꢀ, 1), 754.3
(Mꢀ-CdI2, 1), 367.6 (CdI2ꢀ, 2); anal. calcd for C36H66CdI2P2Pt: C 38.53%,
H 5.93%; found: C 38.42%, H 5.90%. trans-[(Cy3P)2(I)PtHgI] (3): HgI2
(0.101 g, 0.222 mmol) was added to a solution of [Pt(PCy3)2] (0.167 g,
0.221 mmol) in toluene (20 cm3) at ꢀ65 1C. The mixture was warmed to
room temperature over 2 h, then concentrated to ca. 8 cm3 in vacuo.
Hexane (20 cm3) was added to this solution and the mixture allowed
to stand in the absence of light for 1 day, yielding yellow crystals of 3
(0.24 g, 0.198 mmol, 90%). M.p. 270–272 1C; 1H NMR (300 MHz, 303 K,
C6D6): d = 1.22 (m, 6H, Cy-CH2), 1.37 (m, 12H, Cy-CH2), 1.60–1.73
(m, 30H, Cy-CH2), 2.14 (d, 12H, Cy-CH2), 2.89 (br., 6H, Cy-CH); 13C{1H}
6 H. Braunschweig, K. Radacki and K. Schwab, Chem. Commun., 2010,
46, 913.
7 See for example: (a) J. Bauer, H. Braunschweig, A. Damme and
K. Radacki, Angew. Chem. Int. Ed., 2012, 51, 10030; (b) J. Bauer,
H. Braunschweig, K. Kraft and K. Radacki, Angew. Chem. Int. Ed.,
2011, 50, 10457; (c) H. Braunschweig, P. Brenner, P. Cogswell,
K. Kraft and K. Schwab, Chem. Commun., 2010, 46, 7894.
8 A. Del Pra and G. Zanotti, Inorg. Chim. Acta, 1980, 39, 137.
9 As determined from a survey of the Cambridge Crystallographic
Database, October, 2012.
10 T. Bollermann, K. Freitag, C. Gemel, R. W. Seidel and R. A. Fischer,
Organometallics, 2011, 30, 4123, and references therein.
11 N.B. In order to draw structural comparisons with other adducts
between sterically bulky and strongly nucleophilic Lewis bases and
the ZnBr2 and CdI2 fragments, the N-heterocyclic carbene, IPr
(:C{N(Dip)C(H)}2, Dip = C6H3Pri2-2,6), was reacted with the metal
halides. However, instead of monomeric adducts, the dimeric, halide
bridged complexes, [{(IPr)MX(m-X)}2] (M = Zn or Cd, X = Br or I), were
formed, thus discounting the proposed comparisons. See ESI† for
synthetic, spectroscopic and structural details of these adducts.
12 See for example: (a) M. C. Janzen, M. C. Jennings and R. J. Puddephatt,
Inorg. Chim. Acta, 2005, 358, 1614; (b) M. C. Janzen, M. C. Jennings and
R. J. Puddephatt, Inorg. Chem., 2001, 40, 1728.
NMR (75.5 MHz, 303 K, C6D6): d = 26.9 (s, C4, Cy), 27.7 (virtual t, JPC
=
11 Hz, C2,6, Cy), 31.1 (virtual t, JPC = 22 Hz, C3,5, Cy), 39.0 (virtual t,
JPC = 29 Hz, C1, Cy). 31P{1H} NMR (121.5 MHz, 303 K, C6D6): d = 31.0
1
2
(s, JPt-P = 2448 Hz, JHg-P = 299 Hz); 195Pt{1H} NMR (85.6 MHz, 300 K,
C6D6): d = ꢀ5052 (s, 1JPt-P = 2446 Hz); IR (Nujol) n (cmꢀ1): 1445s, 1050m,
1002s, 916m, 891s, 848s, 816m, 733s; MS (EI/70 eV) m/z (%): 1082.3
(M+-I, 1), 755.4 (M+-HgI2, 75); anal. calcd for C36H66HgI2P2Pt: C 35.72%,
H 5.50%; found: C 35.63%, H 5.38%.
¶ Crystal data for 1ꢁ(benzene): C42H72Br2P2PtZn, M = 1059.22, mono-
clinic, space group C2/c, a = 16.7915(8) Å, b = 10.9089(17) Å, c =
23.5671(14) Å, b = 93.615(5)1, V = 4308.4(7) Å3, Z = 4, Dc = 1.633 g cmꢀ3
,
F(000) = 2128, m(Mo-Ka) = 5.757 mmꢀ1, 123(2) K, 19036 collected reflec-
tions, 6274 unique reflections [R(int) 0.0240], R (on F) 0.0251 (I > 2sI),
wR (on F2) 0.0523 (all data); Crystal data for 2ꢁ(toluene): C43H74CdI2P2PtZn,
M = 1214.25, monoclinic, space group C/c, a = 17.011(3) Å, b = 11.399(2) Å,
c = 23.647(5) Å, b = 92.39(3)1, V = 4581.2(16) Å3, Z = 4, Dc = 1.761 g cmꢀ3
,
F(000) = 2376, m(Mo-Ka) = 4.959 mmꢀ1, 123(2) K, 20129 collected reflec-
tions, 8275 unique reflections [R(int) 0.0253], R (on F) 0.0192 (I > 2sI), wR
c
50 Chem. Commun., 2013, 49, 48--50
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