A singly bonded amido-distannyne: H2 activation and isocyanide coordination

Article abstract of DOI:10.1039/c3cc49651a

The first amido-distannyne, L^?SnSnL^? (L^? = -N(Ar^?)(SiPrⁱ₃), Ar^? = C₆H₂{C(H)Ph₂} ₂Prⁱ-2,6,4), has been prepared and shown to possess a very long Sn-Sn single bond; the compound activates dihydrogen under ambient conditions to give L^?Sn(μ-H)₂SnL ^?, and reacts with Bu^tNC to give a stable adduct complex, L^?(Bu^tNC)SnSn(CNBu^t)L ^?. The Royal Society of Chemistry 2014.

Full text of DOI:10.1039/c3cc49651a

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A singly bonded amido-distannyne: H2 activation
and isocyanide coordination†
Cite this: Chem. Commun., 2014,
50, 2321
Terrance J. Hadlington and Cameron Jones*
Received 20th December 2013,
Accepted 14th January 2014
DOI: 10.1039/c3cc49651a
www.rsc.org/chemcomm
The first amido-distannyne, L†SnSnL† (L† = –N(Ar†)(SiPri3), Ar†
=
We have recently developed a series of extremely bulky
C6H2{C(H)Ph2}2Pri-2,6,4), has been prepared and shown to possess amides9 and have begun to explore their utility for the stabilisa-
a very long Sn–Sn single bond; the compound activates dihydrogen tion of low oxidation state p-block compounds.10 As part of that
under ambient conditions to give L†Sn(l-H)2SnL†, and reacts with study, the first amido-digermynes, LGeGeL (L = –N(Ar*)(SiMe3)
ButNC to give a stable adduct complex, L†(ButNC)SnSn(CNBut)L†.
L*, or –N(Ar†)(SiPri3) L†, Ar* = C6H2{C(H)Ph2}2Me-2,6,4; Ar†
C6H2{C(H)Ph2}2Pri-2,6,4) have been prepared and shown to possess
=
The chemistry of the heavier group 14 alkyne analogues, REER either a very long Ge–Ge single bond (ca. 2.71 Å, L*GeGeL*),11 or a
(E = Si, Ge, Sn or Pb; R = bulky aryl or silyl), has rapidly expanded short Ge–Ge multiple bond (ca. 2.36 Å, L†GeGeL†).12 The suppres-
since the first example was reported in 2000.1 The interest sion of any Ge–Ge p-bonding character in L*GeGeL* is thought to
in these compounds was initially derived from their unusual result from significant N-Ge p-donation within the planar SiCNGe2
structure and bonding. That is, they possess trans-bent struc- fragments of that compound. In contrast, the greater bulk of
tures, as opposed to linear alkynes, and their E–E bond orders the amide ligands in L†GeGeL† prevents planarity of its SiCNGe2
can range from near three (E = Si) to one (E = Pb).2 All examples fragments, thereby circumventing N-Ge p-overlap, and promoting
of digermynes, RGeGeR, have intermediate Ge–Ge bond orders, Ge–Ge p-bonding. Despite the electronic differences between the two
and some are thought to possess significant singlet biradical compounds, solutions of both were found to facilely activate H2 at
character, which has been proposed to lead to the unusual temperatures as low as ꢀ10 1C in solution, while H2 activation also
‘‘transition metal-like’’ reactivity displayed by these species.2a,3 occurs for L*GeGeL* in the solid state.11
The most high profile manifestation of this was the first
To date, efforts to prepare the distannyne analogues of L*GeGeL*
ambient temperature activation of H2 by a main group complex, and L†GeGeL† have not been successful, though this would be of
Ar0GeGeAr0 (Ar0 = C6H3(C6H3Pri2-2,6)2-2,6), reported by Power interest as amido-distannynes are unknown. Moreover, a recent
and co-workers in 2005.4 More recently, several distannynes, theoretical study has suggested that they should possess Sn–Sn
e.g. Ar0SnSnAr0, have also been shown to activate H2 at room single bonds, and should activate H2 via a similar mechanism to
temperature.5 Although these distannynes have either Sn–Sn that calculated for amido-digermynes, albeit in a less thermo-
single or multiple bonds in the solid state, calculations indicate dynamically and kinetically favourable fashion.13 Here, we report
that their electronic ground state is the multiply bonded form,6 the synthesis of the first amido-distannyne, L†SnSnL†,14 and
and therefore that they exist in this form in solution.7 Consequently, reveal that it does, indeed, activate H2 slowly under ambient
the activation of H2 by distannynes in solution is thought to conditions to give the known tin(II) hydride, L†Sn(m-H)2SnL†.12 In
involve multiply bonded species, in all cases. A recent theoretical addition, the irreversible formation of an adduct of L†SnSnL†
study supports this view, but does show that the mechanism with the isocyanide, ButNC, is described.
of activation by distannynes (and digermynes) may be more
complex than originally thought.8
Previous attempts to prepare amido-distannynes via the
reduction of LSnCl (L = L* or L†) with the magnesium(I) dimer,
{(MesNacnac)Mg}2 (MesNacnac = [(MesNCMe)2CH]ꢀ, Mes = mesityl)
led only to tin deposition and formation of LH.11,12 It was postulated
that related reductions with LSnBr would proceed at lower tempera-
tures, which might allow for the isolation of distannyne products.
This proved to be the case for the reduction of L†SnBr (see ESI† for
full synthetic and structural details) with {(MesNacnac)Mg}2,15 which
afforded the amido-distannyne, L†SnSnL† 1, in a moderate isolated
School of Chemistry, PO Box 23, Monash University, Melbourne, VIC, 3800,
Australia. E-mail: cameron.jones@monash.edu;
Web: http://monash.edu/science/jonesgroup/
† Electronic supplementary information (ESI) available: Full synthetic, spectro-
scopic and crystallographic details for new compounds. CCDC 977193–977197.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3cc49651a
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Scheme 1 Reagents and conditions: (i) {(MesNacnac)Mg}2, –{(MesNac-
nac)Mg(m-Br)}2; (ii) H2; (iii) ButNC.
Fig. 1 Molecular structure of 1 (25% thermal ellipsoids; hydrogen atoms
omitted). Selected bond lengths (Å) and angles (1): Sn(1)–N(1) 2.128(4),
Sn(1)–Sn(2) 3.1434(5), Sn(2)–N(2) 2.118(4), N(1)–Sn(1)–Sn(2) 104.53(10),
N(2)–Sn(2)–Sn(1) 103.48(11).
yield as dark green/orange dichroic crystals (Scheme 1). The
compound is thermally stable in the solid state, though it
decomposes in solution at ambient temperature over the course of
two days, depositing tin metal and yielding L†H. The 1H and 13C{1H}
NMR spectra of 1 both display one set of amide signals, which
implies the compound has a symmetrical structure in solution. No ca. 70% complete, though because of the low thermal stability
signal was observed in the 119Sn{1H} NMR spectrum, presumably as of both 1 and 2, small amounts of L†H and tin metal were
a result of large chemical shift anisotropies arising from the two- also present in the reaction mixture at that time. Points to note
coordinate tin environments.7 Only one distinguishable absorption about this experiment are, firstly, that the hydrogenation of 1 is
band (lmax 409 nm, e = 6500 L molꢀ1 cmꢀ1) was observed in the considerably slower than that of the corresponding digermyne,
UV/visible spectrum of 1, which contrasts with organo- L†GeGeL† (which is complete after 20 min), and that the product
distannynes, all of which display moderately intense p - p* of the digermyne reaction exists in a different isomeric form in
absorption bands at ca. lmax 600 nm, and are, therefore, the solid state, viz. L†(H)GeQGe(H)L†, than does 2. Both of these
thought to possess Sn–Sn multiple bonds in solution.7 This facts were predicted by the prior theoretical study of the hydro-
difference may indicate that 1 does not exhibit Sn–Sn multiple genation of L0EEL0 (E = Ge or Sn).13 That study also suggested
bond character in solution or the solid state, a situation which that unlike hydrogenations of aryl-distannynes (which likely all
is consistent with the results of DFT calculations on the model occur via their multiply bonded forms), the mechanism of hydro-
compound, L0SnSnL0 (L0 = –NMe2), the electronic ground state genation of L0SnSnL0 (and by implication, 1) involves an initial
structure of which has a Sn–Sn single bond.13
donation of H2 s-bond electron density into the Sn–Sn p-bonded
In order to shed light on the nature of the Sn–Sn bonding in LUMO of L0SnSnL0, with concomitant back-donation of high
1 in the solid state, its X-ray crystal structure was determined p-character Sn–Sn s-bond HOMO density into the s* orbital of H2.
(Fig. 1). The compound displays a trans-bent structure with a Moreover, as the hydrogenation of L0SnSnL0 to give L0Sn(m-H)2SnL0
13
Sn–Sn bond (3.1429(7) Å, cf. 3.038 Å calculated for L0SnSnL0
)
is essentially thermo-neutral (DG = 0.7 kcal molꢀ1),13 the possibility
that is longer than in any previously reported distannyne. This, exists that the hydrogenation of 1 might be reversible under mild
combined with the rather narrow N–Sn–Sn angles (104.001 conditions. We have, however, seen no experimental evidence for
mean, cf. 94.41 calculated for L0SnSnL013), clearly signifies that such reversibility.
1 possesses a Sn–Sn single bond.16 It is likely that Sn–Sn multiple
To further explore analogies between the reactivity of 1 and
bonding in the distannyne is frustrated by its essentially planar aryl-distannynes, the former was generated in situ and treated
Sn2NSiC fragments, which presumably allows for a degree of with two equiv. of the isocyanide, ButNC. Upon work-up, the
N - Sn p-donation (cf. singly bonded L*GeGeL*11). A similar adduct complex, 3, was obtained in moderate isolated yield as
planarization of the Ge2NSiC fragments in the multiply bonded dichroic orange/green crystals (Scheme 1). Unlike the corre-
digermyne analogue of 1, viz. L†GeGeL†, is doubtless prevented sponding aryl-distannyne complex, Ar0(ButNC)SnSn(CNBut)Ar0,
by greater steric buttressing between the amide ligands, which which fully dissociates to Ar0SnSnAr0 and ButNC in solution
occurs because of the smaller covalent radius of Ge (1.20 Å) vs. Sn at 25 1C,18 compound 3 is stable in C6D6 solutions at room
(1.39 Å).17 Despite this, there is still significant steric crowding temperature (119Sn{1H} NMR: d 241 ppm; cf. d 181 ppm for
in 1, as evidenced by the marked twisting of its N2Sn2 fragment Ar0(ButNC)SnSn(CNBut)Ar0), and is returned when volatiles are
away from planarity (torsion angle: 148.61).
removed from those solutions in vacuo. This is perhaps surprising,
With the amido-distannyne, 1, in hand, its reactivity towards as it might be thought that the isocyanide–Sn interactions in 3
H2 was investigated by placing a solution of the compound in would be weak, given the crowding around the tin centres of 1,
C6D6 under an atmosphere of dihydrogen at ambient temperature and the fact that the infrared spectrum of crystals of 3 exhibit a
and pressure. Monitoring the reaction by NMR spectroscopy CRN stretching mode at 2138 cmꢀ1 (cf. 2162/2175 cmꢀ1 for
showed that ca. 30% of 1 had converted to the previously reported Ar0(ButNC)SnSn(CNBut)Ar0) which is only slightly shifted relative
tin(II) hydride complex, 2,12 after 3 h. After 24 h the reaction was to that for free ButNC (2134 cmꢀ1).18,19 It is also noteworthy that
2322 | Chem. Commun., 2014, 50, 2321--2323
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stable adduct, L†(ButNC)SnSn(CNBut)L† 3. We are currently
exploring the further chemistry of 1.
CJ gratefully acknowledges financial support from the Australian
Research Council (DP120101300), and the U.S. Air Force Asian Office
of Aerospace Research and Development (FA2386-11-1-4110).
Notes and references
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2 Selected reviews on ditetrelyne chemistry: (a) P. P. Power, Acc. Chem.
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(c) P. P. Power, Organometallics, 2007, 26, 4362.
3 P. P. Power, Nature, 2010, 463, 171.
4 G. H. Spikes, J. C. Fettinger and P. P. Power, J. Am. Chem. Soc., 2005,
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5 Y. Peng, M. Brynda, B. D. Ellis, J. C. Fettinger, E. Rivard and
P. P. Power, Chem. Commun., 2008, 6042.
6 N. Takagi and S. Nagase, Organometallics, 2007, 26, 469.
7 (a) Y. Peng, R. C. Fischer, W. A. Merrill, J. Fischer, L. Pu, B. D. Ellis,
J. C. Fettinger, R. H. Herber and P. P. Power, Chem. Sci., 2010, 1, 461;
(b) R. C. Fischer, L. Pu, J. C. Fettinger, M. A. Brynda and P. P. Power,
J. Am. Chem. Soc., 2006, 128, 11366.
Fig. 2 Molecular structure of 3 (25% thermal ellipsoids; hydrogen atoms
omitted). Selected bond lengths (Å) and angles (1): Sn(1)–N(1) 2.202(3),
Sn(1)–C(45) 2.325(4), Sn(1)–Sn(1)0 3.0759(6), N(2)–C(45) 1.149(6), N(1)–
Sn(1)–Sn(1)0 105.76(10), C(45)–Sn(1)–Sn(1)0 92.23(12), N(1)–Sn(1)–C(45)
0
89.39(14). Symmetry operation: ꢀx + 1, ꢀy, ꢀz + 2.
8 L. L. Zhao, F. Huang, G. Lu, Z.-X. Wang and P. v. R. Schleyer, J. Am.
Chem. Soc., 2012, 134, 8856.
9 (a) E. W. Y. Wong, D. Dange, L. Fohlmeister, T. J. Hadlington and
C. Jones, Aust. J. Chem., 2013, 66, 1144; (b) J. Hicks, T. J. Hadlington,
C. Schenk, J. Li and C. Jones, Organometallics, 2013, 32, 323; (c) J. Li,
A. Stasch, C. Schenk and C. Jones, Dalton Trans., 2011, 40, 10448.
reaction of the related singly bonded digermyne, L*GeGeL*,
with ButNC did not give a stable adduct complex, but instead
led to facile reductive coupling of two ButNC molecules.20 This
indicates that L*GeGeL* is more reducing than L†SnSnL†.
The apparent weakness of the isocyanide–Sn interactions 10 (a) J. Li, C. Schenk, F. Winter, H. Scherer, N. Trapp, A. Higelin,
¨
S. Keller, R. Pottgen, I. Krossing and C. Jones, Angew. Chem., Int. Ed.,
in 3 is borne out by its X-ray crystal structure (Fig. 2), which
reveals NC-Sn distances (2.325(4) Å) that are longer than
those in Ar0(ButNC)SnSn(CNBut)Ar0 (2.301 Å mean).18 Moreover,
the purely dative nature of those interactions is evidenced
by the isocyanide CN bond lengths, 1.149(6) Å (cf. 1.159 Å mean
2012, 51, 9557; (b) A. V. Protchenko, K. Birjkumar, D. Dange,
A. D. Schwarz, D. Vidovic, C. Jones, N. Kaltsoyannis, P. Mountford
and S. Aldridge, J. Am. Chem. Soc., 2012, 134, 6500; (c) D. Dange, J. Li,
¨
C. Schenk, H. Schnockel and C. Jones, Inorg. Chem., 2012, 51, 13050.
11 J. Li, C. Schenk, C. Goedecke, G. Frenking and C. Jones, J. Am. Chem.
Soc., 2011, 133, 18622.
in Ar0(ButNC)SnSn(CNBut)Ar0), which are typical for triple bonds.21 12 T. J. Hadlington, M. Hermann, J. Li, G. Frenking and C. Jones,
Angew. Chem., Int. Ed., 2013, 52, 10199.
It is interesting to note that the Sn–Sn bond in 3 (3.0759(6) Å) is
13 M. Hermann, C. Goedecke, C. Jones and G. Frenking, Organometallics,
significantly shorter than that in 1, presumably because the
2013, 32, 6666.
bond takes on more s-character (S angles at Sn(1) = 287.41) 14 As L†SnSnL† possesses a Sn–Sn single bond it could be regarded
as a 1,2-distannylene. We use the term distannyne to describe
upon isocyanide coordination. This differs to coordination of
the compound, in line with nomenclature established for both
Ar0SnSnAr0 by ButCN, which leads to a lengthening of its Sn–Sn
single and multiply bonded heavier analogues of alkynes, viz. the
bond by 0.374 Å, due to loss of multiple bond character for that
bond.18 Somewhat related is the likelihood that any N–Sn
p-character in 1 must be lost upon isocyanide coordination,
as the planar NSiC fragments of 3 are essentially orthogonal
to the Sn2N2 plane in that compound. Although the increased
Sn–N bond lengths in 3 (Sn–N 2.202(3) Å), relative to those in 1
ditetrelynes, see ref. 2 and 7.
15 S. J. Bonyhady, C. Jones, S. Nembenna, A. Stasch, A. J. Edwards and
G. J. McIntyre, Chem.–Eur. J., 2010, 16, 938.
16 Two structurally characterised three-coordinate amido-tin(I) dimers
have been reported. (a) S. L. Choong, C. Schenk, A. Stasch, D. Dange
and C. Jones, Chem. Commun., 2012, 48, 2505; (b) C. Jones,
S. J. Bonyhady, N. Holzmann, G. Frenking and A. Stasch, Inorg.
Chem., 2011, 50, 12315.
(Sn–N 2.123 Å mean), might support this proposal, this difference 17 B. Cordero, V. Gomez, A. E. Platero-Prats, M. Reves, J. Echeverria,
E. Cremades, F. Barragan and S. Alvarez, Dalton Trans., 2008, 2832.
18 Y. Peng, X. Wang, J. C. Fettinger and P. P. Power, Chem. Commun.,
could also be due to the increased coordination number in the
former. Indeed, the observed values are close to the mean Sn–N
2010, 46, 943.
distances for all crystallographically characterised 2- and 3-coordinate 19 For a discussion on the factors affecting CN stretching frequencies
in isocyanide–SnII adducts, see: A. Mansikkamaki, P. P. Power and
tin(II) amides, viz. 2.10 Å and 2.20 Å respectively.22
¨
H. M. Tuononen, Organometallics, 2013, 32, 6690.
20 J. Li, M. Hermann, G. Frenking and C. Jones, Angew. Chem., Int. Ed.,
In summary, the first example of an amido-distannyne,
L†SnSnL† 1, has been prepared and shown to possess a very
long Sn–Sn single bond. The compound activates dihydrogen
under ambient conditions to give the known tin(II) hydride
complex, L†Sn(m-H)2SnL† 2, and reacts with ButNC to give the
2012, 51, 8611.
21 J. A. Green and P. T. Hoffmann, Isonitrile Chemistry, in Org. Chem.,
ed. I. Ugi, Academic Press, New York, 1971, vol. 20, p. 1.
22 As determined by a survey of the Cambridge Crystallographic
Database, December 2013.
This journal is ©The Royal Society of Chemistry 2014
Chem. Commun., 2014, 50, 2321--2323 | 2323