PNacPNacE: (E = Ga, In, Tl) – monomeric group 13 metal(I) heterocycles stabilized by a sterically demanding bis(iminophosphoranyl)methanide

Christian P. Sindlinger ab, Samuel R. Lawrence c, Shravan Acharya a, C. André Ohlin d and Andreas Stasch *ac
aSchool of Chemistry, Monash University, 17 Rainforest Walk, Melbourne, Victoria 3800, Australia
bInstitut für Anorganische Chemie, Universität Göttingen, Tammannstr. 4, 37077 Göttingen, Germany
cEaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY16 9ST, UK. E-mail: as411@st-andrews.ac.uk
dDepartment of Chemistry, Umeå University, Linnaeus väg 10, Umeå, 907 36, Sweden

Received 27th October 2017 , Accepted 23rd November 2017

First published on 23rd November 2017


The salt metathesis reaction of the sterically demanding bis(iminophosphoranyl)methanide alkali metal complexes LM (L = HC(Ph2P[double bond, length as m-dash]NDip)2, Dip = 2,6-iPr2C6H3; M = Li, Na, K) with “GaI”, InBr or TlBr afforded the monomeric group 13 metal(I) complexes LE:, E = Ga (1), In (2) and Tl (3) in moderate yields, and small quantities of LGaI24 in the case of Ga, respectively. The molecular structures of LE: 1–3 from X-ray single crystal diffraction show them to contain puckered six-membered rings with N,N’-chelating methanide ligands and two-coordinated metal(I) centres. Reduction reactions of LAlI25, prepared by iodination of LAlMe2, were not successful and no aluminium(I) congener could be prepared so far. DFT studies on LE:, E = Al–Tl, were carried out and support the formulation as an anionic, N,N’-chelating methanide ligand coordinating to group 13 metal(I) cations. The HOMOs of the molecules for E = Al–In show a dominant contribution from a metal-based lone pair that is high in s-character.


Introduction

For the heavier elements of groups 13 and 14, the most stable and common oxidation states in compounds change from +3 or +4 (e.g. period 3 and 4) to +1 and +2 (period 6), respectively, when descending a group.1,2 Especially for the period 6 elements, a low oxidation state with a nonbonding s2 lone pair is stabilised and does not significantly engage in bonding and hybridisation (inert pair effect).1,3 For the lighter elements of groups 13 and 14, however, this electronic configuration is increasingly difficult to stabilise and molecular low oxidation state compounds are in turn less stable and undergo numerous redox reactions, with a tendency to revert to compounds with the main group element in a more stable high oxidation state, i.e. +3 and +4, respectively.2,4 Especially over the past few decades numerous compound classes with the lighter group 13 metals in low oxidation states have been reported.2,5 For gallium, for example, stable and well-defined complexes with Ga centres in the +1 oxidation state have been reported that range from simple species such as weakly coordinated Ga+ cations6 and mononuclear one-coordinate complexes7 to huge metalloid5d,8 cluster compounds.2,5 Several heterocyclic molecules that incorporate a group 13 metal(I) ion of Al–In by coordination to N,N’-chelating anionic ligands to form six-membered (β-diketiminate complexes I of Al,9 Ga,10 and In11), five-membered (anionic complexes II of Ga12) and four-membered (guanidinate III13 and diiminophosphinate IV14 complexes of Ga and In) ring systems are known, see Fig. 1, as well as a related monomeric tris(pyrazolylborate) complex.15 In the solid state structures of several of these GaI and InI heterocycles, metal–metal bonding interactions11a,b,d,14 from metal-based orbital overlaps exist that are weak in nature, do not persist in solution, and typically compare in strength with those of closed-shell interactions16 and London dispersion forces.17 Because of their heterocyclic nature with typically two-coordinate metal(I) centres carrying a non-bonding metal-based lone pair, these species have been coined carbene analogues which highlights parallels that these molecules can serve as donor ligands in (transition) metal complexes.2,18
image file: c7dt04048b-f1.tif
Fig. 1 Heterocyclic N,N’-coordinated metal(I) complexes of Al, Ga and In.

Substitution of the imine carbon centres in β-diketiminates19 (NacNac) by phosphoranyl moieties leads to structurally and electronically related bis(iminophosphoranyl)methanides20 (PNacPNac) of which we expected similar successful applicability in low-valent group 13 chemistry as is known for the iconic NacNacs (see Fig. 2).2c,4a Here we report a series of related monomeric group 13 metal(I) complexes bearing monoanionic bis(iminophosphoranyl)methanide ligands.


image file: c7dt04048b-f2.tif
Fig. 2 NacNacE: vs. PNacPNacE:, E = heavier group 13 element, Dip = 2,6-iPr2C6H3.

Results and discussion

The sterically demanding iminophosphorane H2C(Ph2P[double bond, length as m-dash]NDip)2, Dip = 2,6-iPr2C6H3 (=[thin space (1/6-em)]LH)21 is readily deprotonated at its central carbon atom by strong alkali metal bases to various bis(iminophosphoranyl)methanide complexes LM (M = Li, Na, K) and their solvates.22 The salt metathesis reaction of these complexes with a variety of group 13 metal(I) halide sources such as “GaI”,23 InBr and TlBr in toluene (Ga) or THF (In, Tl) afforded the new monomeric complexes LE:, E = Ga (1), In (2) Tl (3) in moderate isolated yields, see Scheme 1. Reagent additions were performed at low temperatures and the reaction mixtures were typically vigorously stirred for up to two days at room temperature. The reactions appear to proceed slower than those forming the recently reported complexes Ph2P(NDip)2E: (E = Ga, In, Tl) having a comparable monoanionic iminophosphorane ligand system,14 which is likely due to the greater steric demand of the bis(iminophosphoranyl)methanide system in 1–3.
image file: c7dt04048b-s1.tif
Scheme 1 Synthesis of compounds 1–3.

The new complexes were isolated as colourless crystals and could be structurally characterised, see Fig. 3 and Table 1 for selected bond lengths and angles. Common reaction by-products were identified by NMR spectroscopy as the neutral iminophosphorane LH and in the case for Ga, the gallium(III) complex LGaI24 that was also structurally characterised (Fig. 3). Previously, higher oxidation state by-products have been found for example in the synthesis of β-diketiminate gallium(I) complexes10 using the mixed oxidation state species “GaI”.23 In addition, varying small quantities of the respective group 13 metals could be found at the end of the salt metathesis reactions likely from disproportionations. Complex LGa: 1 could also be rapidly converted to LGaI24 with one equivalent of I2 in deuterated benzene.


image file: c7dt04048b-f3.tif
Fig. 3 Molecular structures of compounds 1–4 (30% thermal ellipsoids). Hydrogen atoms except on C1 are omitted for clarity.
Table 1 Selected interatomic distances (Å) and angles (°) for complexes 1–4
  LGa: 1 LIn: 2 LTl: 3 LGaI24
E–N/Å Ga(1)–N(1) 2.030(4) In(1)–N(1) 2.3578(17) Tl(1)–N(1) 2.463(2) Ga(1)–N(1) 1.943(5)
Ga(1)–N(2) 2.067(4) In(1)–N(2) 2.3092(18) Tl(1)–N(2) 2.416(2) Ga(1)–N(2) 1.948(5)
P–N/Å P(1)–N(1) 1.618(4) P(1)–N(1) 1.6264(17) P(1)–N(1) 1.617(2) P(1)–N(1) 1.651(5)
P(2)–N(2) 1.629(4) P(2)–N(2) 1.6147(18) P(2)–N(2) 1.611(2) P(2)–N(2) 1.652(5)
P–C/Å P(1)–C(1) 1.702(5) P(1)–C(1) 1.708(2) P(1)–C(1) 1.711(2) P(1)–C(1) 1.717(6)
P(2)–C(1) 1.698(5) P(2)–C(1) 1.714(2) P(2)–C(1) 1.712(2) P(2)–C(1) 1.697(6)
Ga–I/Å Ga(1)–I(1) 2.5395(9)
Ga(1)–I(2) 2.5919(9)
N–E–N/° N(1)–Ga(1)–N(2) 96.92(15) N(2)–In(1)–N(1) 91.90(6) N(2)–Tl(1)–N(1) 89.98(7) N(1)–Ga(1)–N(2) 108.3(2)
P–C–P/° P(2)–C(1)–P(1) 129.9(3) P(1)–C(1)–P(2) 125.19(12) P(1)–C(1)–P(2) 126.37(15) P(2)–C(1)–P(1) 130.9(3)
I–Ga–I/° I(1)–Ga(1)–I(2) 102.65(4)


The complexes LE:, E = Ga (1), In (2) and Tl (3), are isostructural and all crystallise with a full molecule in the asymmetric unit; complexes 2 and 3 are isomorphous. The compounds contain central six-membered NPCPNE chelate rings with two-coordinate metal centres (cf. related β-diketiminate complexes).9–11 The Ga congener 1 is the most planar molecule of the series with slight distortion to a boat conformation, whereas the central ring in the heavier homologues is more puckered and distorted. The β-diketiminate examples I do largely show essentially perfect planarity of the six-membered rings in their solid state structures.9–11 Each complex 1–3 shows two slightly different E–N distances (see Table 1) that generally compare well to those of the β-diketiminate complexes. The N–E–N angles in 1–3 reduce from ca. 97° for Ga to 90° for Tl; an expected value if no s–p hybridisation occurs. This is in contrast to those of the β-diketiminate derivatives I with R = Me and Ar = Dip that show a decreasing N–E–N angle from Al to Tl (approximate angles, E = Al: 90°, Ga: 88°, In: 81°, Tl: 77°) that is likely caused by the different steric profiles of the two ligand classes and the facile delocalisation of electron density for the β-diketiminate backbones. No large differences are found for P–N or P–C bond lengths within the series 1–3. The molecular structure of LGaI24 contains a six-membered chelate ring in a twist-boat configuration that is folded along the Ga⋯C vector. The Ga centre is in a distorted tetrahedral coordination mode showing shorter Ga–N distances compared to those in the GaI complex 1 due to the smaller GaIII ion in 4.

NMR spectra of compounds 1–3 in deuterated benzene are consistent with a highly symmetric average solution structure of the molecules. The 1H NMR spectra show one doublet and one septet only for the resonances of the isopropyl groups. For LGa: 1, however, the 1H NMR resonance for the methyl groups is extremely broad at room temperature, sharpens at elevated temperature and resolves to one doublet at around 65 °C. The likely reason for this is that the comparatively small Ga centre causes the shortest approach of the two Dip substituents and contributes to hindered rotation of the iPr groups. The 31P{1H} NMR signals for LE: show sharp singlets for E = Ga (δ 20.4 ppm) and In (δ 17.0 ppm), and a broad doublet of 109 Hz for LTl: 3 (δ 11.0 ppm) from coupling to the combined 203/205Tl nuclei (both I = ½). The latter Tl–P coupling constant is significantly smaller than that found for another iminophosphorane-based complex Ph2P(NDip)2Tl (416 Hz).14 Previously, a bis(iminophosphoranyl)methanediide dithallium(I) complex had been prepared that crystallised as a dimer via Tl⋯Tl interactions.24 This complex shows a broad triplet in its 31P{1H} NMR spectrum at δ −0.3 ppm with a coupling constant of 407 Hz. Complex LGaI24 shows two broad resonances and one sharp septet for the protons of the isopropyl groups in its 1H NMR spectrum that merge at elevated temperatures (approximately above 50 °C) to one broad methyl resonance and a sharp methine septet.

To access a potential starting material to an aluminium(I) complex LAl:, we have synthesised the aluminium(III) iodide complex LAlI25 from LAlMe2[thin space (1/6-em)]25 and elemental iodine, see Scheme 2, in analogy to the synthetic pathway to yield the β-diketiminate aluminium(I) examples I.9 Alternatively, we have obtained LAlI25 from the iodination of LAlH2[thin space (1/6-em)]26 with approximately one equivalent of I2 and the salt metathesis of LK and AlI3, respectively, though materials from these reactions have been significantly less pure. Complex LAlI25 was obtained as a colourless crystalline material. Once crystallised, the complex shows a relatively poor solubility in hydrocarbon solvents at room temperature.


image file: c7dt04048b-s2.tif
Scheme 2 Synthesis of compound 5.

We have found the molecular structure of LAlI25 from single crystal X-ray diffraction to be isostructural and isomorphous to LGaI24, though the data quality was too poor for inclusion in here and only an image is presented in the ESI (Fig. S1). The 1H NMR spectroscopic data for LAlI25 shows two doublets and one septet for the protons of the isopropyl groups with similar chemical shifts to those of LGaI24 and LAlR2 (R = H, Me),25,26 and similar properties to related complexes bearing different N-substituents.27 Reduction reactions of LAlI25 under varying conditions, e.g. using two equivalents or an excess of potassium metal, so far only led to intractable product mixtures with no support for the formation of a stable LAl: complex. The use of dimeric magnesium(I) compounds as reducing agents28 provided very poor consumption only, even at elevated temperatures, likely due to the large steric profile of the L ligand.

Density functional theory calculations at the pbe0/def2-tzvp (P, N, C(1) and E atoms) + def2-svp (all other atoms) level were carried out to optimize the full molecules LE: (E = Al, Ga 1, In 2, Tl 3) in their singlet ground state, see Table 2 for data. These accurately reproduced the molecular geometries for 1–3, including key bond lengths. Selected NBO and DFT orbitals are shown in Fig. 4. The HOMOs for the LE: molecules with E = Al–In show a dominant contribution of a metal-based lone pair that is high in s-character (see Table 2). For Tl, this lone pair contribution is found in lower lying orbitals, mainly the HOMO−7 together with a smaller contribution to the HOMO−14 (not shown) with 99% s-character. Instead, the HOMO for E = Tl is associated with a central carbon p-orbital of the ligand backbone forming a π-type interaction towards the two adjacent P centres. For E = Al–In, a similar delocalised orbital is found in the HOMO−1. Higher lying relevant virtual orbitals show significant contributions of empty metal p-orbitals. For Al, the LUMO+8 and LUMO+12, for Ga, the LUMO+8 with a smaller contribution in the LUMO+3, for In, the LUMO+3 (plus minor contributions in the LUMO+5 and +6) and for Tl, the LUMO show a metal p-orbital orthogonal to the metal-chelate plane. Higher lying orbitals can show contributions of in-plane metal p-orbitals orthogonal to the E⋯C vector (LUMO+14 for Al and Ga, LUMO+13 for In and Tl) and even contributions of in-plane metal p-orbitals in line with the E⋯C vector (LUMO+14 for In, LUMO+9 for Tl). What little ligand-based contribution there is to these virtual orbitals shows an anti-bonding combination to the metal-based content. Accordingly, ligand-based orbitals which suggest bonding interactions with very small-to-negligible contributions from metal-based orbitals can be detected in lower lying occupied molecular orbitals. These may further corroborate the relatively ionic coordination interaction of the anionic ligand donor system to empty metal p-orbitals of E+. The remaining orbitals in LE: can be mainly attributed to ligand-based orbitals from the multiple aromatic groups of the molecule.


image file: c7dt04048b-f4.tif
Fig. 4 Selected orbitals for the optimised molecules LE: (E = Al, Ga, In, Tl) shown in two views each (isovalue 0.04 e Å−3). The orbital energies are given relative to the respective HOMO.
Table 2 Selected data for the DFT (pbe0/def2-tzvp + def2-svp) optimized compounds LE
  E = Al E = Ga E = In E = Tl
E–N/Å 1.977 2.088 2.340, 2.347 2.456, 2.501
P–N/Å 1.636 1.625 1.616, 1.621 1.608, 1.616
P–C/Å 1.698 1.699 1.703, 1.712 1.707, 1.717
ΔEHOMO–LUMO/kJ mol−1 (eV) 299 (3.10) 399 (4.13) 437 (4.53) 445 (4.61)
ΔEE-s–E-p/kJ mol−1 (eV) 415 (4.30) 493 (5.11) 462 (4.79) 601 (6.23)
HOMO to LUMO+8 HOMO to LUMO+8 HOMO to LUMO+3 HOMO−7 to LUMO
438 (4.54)
HOMO to LUMO+3
LP hybridization on E 90% s, 10% p 93% s, 7% p 98% s, 2% p 99% s, 1% p
Charges (natural), E +0.856 +0.785 +0.892 +0.872
Charges (natural), P +1.92 +1.92 +1.90 1.89
Charges (natural), N −1.34 −1.27 −1.30 −1.27
Charges (natural), C −1.55 −1.51 −1.54 −1.54


The HOMO–LUMO gaps (Table 2) involve different types of orbitals across the series with the HOMO–LUMO gaps increasing down the group. The values are very close to those computed for the related diiminophosphinate group 13 metal(I) complexes IV.14 The gaps between the dominant metal lone pair orbital to the first empty metal p-orbital is also comparable to those determined for the diiminophosphinate metal(I) complexes with the exception of the value for Tl, which is significantly larger for LTl (6.23 eV versus 4.62 eV for Ph2P(NDip)2Tl). Overall, these results support that the compounds LE: can be described as coordination compounds of an anionic bis(iminophosphoranyl)methanide ligand to monovalent group 13 metal cations having a predominantly s-orbital lone pair where the metal–ligand bonding involves some interaction with “empty” E+ metal p-orbitals. These findings are in line with the general features found for related heterocyclic group 13 metal(I) compounds.2c

Conclusions

We have prepared and characterised the monomeric bis(iminophosphoranyl)methanide metal(I) complexes LGa: 1, LIn: 2 and LTl: 3, and the heteroleptic iodide complexes LGaI24 and LAlI25. The aluminium(I) congener LAl: could not be prepared so far from reductions of LAlI25. The metal(I) complexes LE: show puckered six-membered ring systems with N,N’-chelating bis(iminophosphoranyl)methanide ligands that are more folded and twisted down the group. DFT studies support that the metal(I) compounds with anionic N,N’-chelating methanide ligands show largely unhybridised E+ cations having a metal-based lone pair that is high in s-character as part of the HOMO for E = Al–In. Higher lying virtual orbitals show significant contributions from metal-based p-orbitals. These compounds generally mimic the overall features found for the β-diketiminate examples I of Al–Tl although the latter compound classes contain planar chelate rings and show somewhat different N–E–N angles compared with 1–3. β-Diketiminate ligands19 have been highly successful in stabilising a wide variety of unusual low oxidation state metal complexes2c,4a,28 and the use of related bis(iminophosphoranyl)methanides20 may further advance this area.29 The presented iminophosphorane-based complexes LE:, or “PNacPNacE:”, show some similarities to the β-diketiminate heterocycles I with respect to their overall connectivity and nitrogen-group 13 metal(I) coordination.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

A. S. and C. A. O. are grateful to the Australian Research Council for support. A. S. thanks the University of St Andrews. CAO is grateful for a grant from the Kempe foundation (JCK-1719). Part of this research was undertaken on the MX1 and MX2 beamlines at the Australian Synchrotron, Victoria, Australia.

References

  1. C. E. Housecroft and A. G. Sharpe, Inorganic Chemistry, Pearson Prentice Hall, Harlow, 2nd edn, 2005 Search PubMed .
  2. (a) R. J. Wehmschulte, Top. Organomet. Chem., 2013, 41, 91–124 CrossRef CAS ; (b) S. S. Sen, S. Khan, P. P. Samuel and H. W. Roesky, Chem. Sci., 2012, 3, 659–682 RSC ; (c) M. Asay, C. Jones and M. Driess, Chem. Rev., 2011, 111, 354–396 CrossRef CAS PubMed ; (d) S. Yao, Y. Xiong and M. Driess, Organometallics, 2011, 30, 1748–1767 CrossRef CAS ; (e) R. C. Fischer and P. P. Power, Chem. Rev., 2010, 110, 3877–3923 CrossRef CAS PubMed ; (f) Y. Mizuhata, T. Sasamori and N. Tokitoh, Chem. Rev., 2009, 109, 3479–3511 CrossRef CAS PubMed ; (g) S. Nagendran and H. W. Roesky, Organometallics, 2008, 27, 457–492 CrossRef CAS ; (h) E. Rivard and P. P. Power, Inorg. Chem., 2007, 46, 10047–10064 CrossRef CAS PubMed ; (i) H. W. Roesky and S. S. Kumar, Chem. Commun., 2005, 4027–4038 RSC ; (j) R. J. Baker and C. Jones, Coord. Chem. Rev., 2005, 249, 1857–1869 CrossRef CAS ; (k) O. Kühl, Coord. Chem. Rev., 2004, 248, 411–427 CrossRef .
  3. (a) J. S. Thayer, J. Chem. Educ., 2005, 82, 1721–1727 CrossRef CAS ; (b) D. R. McKelvey, J. Chem. Educ., 1983, 60, 112–116 CrossRef CAS .
  4. (a) Y.-C. Tsai, Coord. Chem. Rev., 2012, 256, 722–758 CrossRef CAS ; (b) S. Schulz, Chem. – Eur. J., 2010, 16, 6416–6428 CrossRef CAS PubMed ; (c) C. Jones, Coord. Chem. Rev., 2010, 254, 1273–1289 CrossRef CAS .
  5. (a) W. Uhl and M. Layh, in The Group 13 Metals Aluminium, Gallium, Indium and Thallium. Chemical Patterns and Peculiarities, ed. A. J. Downs and S. Aldridge, Wiley-Blackwell, Chichester, 2011, ch. 4, pp. 246–284 Search PubMed ; (b) C. Jones and A. Stasch, in The Group 13 Metals Aluminium, Gallium, Indium and Thallium. Chemical Patterns and Peculiarities, 2011, ch. 5, pp. 285–341 Search PubMed ; (c) B. F. T. Cooper and C. L. B. Macdonald, in The Group 13 Metals Aluminium, Gallium, Indium and Thallium. Chemical Patterns and Peculiarities, 2011, ch. 6, pp. 342–401 Search PubMed ; (d) H. Schnöckel and A. Schnepf, in The Group 13 Metals Aluminium, Gallium, Indium and Thallium. Chemical Patterns and Peculiarities, 2011, ch. 7, pp. 402–487 Search PubMed .
  6. (a) M. R. Lichtenthaler, S. Maurer, R. J. Mangan, F. Stahl, F. Mönkemeyer, J. Hamann and I. Krossing, Chem. – Eur. J., 2015, 21, 157–165 CrossRef PubMed ; (b) J. M. Slattery, A. Higelin, T. Bayer and I. Krossing, Angew. Chem., Int. Ed., 2010, 49, 3228–3231 CrossRef CAS PubMed .
  7. (a) M. K. Thomsen, D. Dange, C. Jones and J. Overgaard, Chem. – Eur. J., 2015, 21, 14460–14470 CrossRef CAS PubMed ; (b) D. Dange, J. Li, C. Schenk, H. Schnöckel and C. Jones, Inorg. Chem., 2012, 51, 13050–13059 CrossRef CAS PubMed ; (c) Z. Zhu, R. C. Fischer, B. D. Ellis, E. Rivard, W. A. Merrill, M. M. Olmstead, P. P. Power, J. D. Guo, S. Nagase and L. Pu, Chem. – Eur. J., 2009, 15, 5263–5272 CrossRef CAS PubMed ; (d) R. J. Wright, M. Brynda, J. C. Fettinger, A. R. Betzer and P. P. Power, J. Am. Chem. Soc., 2006, 128, 12498–12509 CrossRef CAS PubMed .
  8. (a) H. Schnöckel, Chem. Rev., 2010, 110, 4125–4163 CrossRef PubMed ; (b) H. Schnöckel, Dalton Trans., 2008, 4344–4362 RSC ; (c) A. Schnepf and H. Schnöckel, Angew. Chem., Int. Ed., 2002, 41, 3532–3552 CrossRef CAS .
  9. (a) X. Li, X. Cheng, H. Song and C. Cui, Organometallics, 2007, 26, 1039–1043 CrossRef CAS ; (b) C. Cui, H. W. Roesky, H.-G. Schmidt, M. Noltemeyer, H. Hao and F. Cimpoesu, Angew. Chem., Int. Ed., 2000, 39, 4274–4276 CrossRef CAS .
  10. (a) D. Dange, S. L. Choong, C. Schenk, A. Stasch and C. Jones, Dalton Trans., 2012, 41, 9304–9315 RSC ; (b) S. L. Choong, W. D. Woodul, A. Stasch, C. Schenk and C. Jones, Aust. J. Chem., 2011, 64, 1173–1176 CrossRef CAS ; (c) N. J. Hardman, B. E. Eichler and P. P. Power, Chem. Commun., 2000, 1991–1992 RSC .
  11. (a) M. E. Desat, S. Gärtner and R. Kretschmer, Chem. Commun., 2017, 53, 1510–1513 RSC ; (b) M. S. Hill, P. B. Hitchcock and R. Pongtavornpinyo, Dalton Trans., 2007, 731–733 RSC ; (c) M. S. Hill, P. B. Hitchcock and R. Pongtavornpinyo, Dalton Trans., 2005, 273–277 RSC ; (d) M. S. Hill, P. B. Hitchcock and R. Pongtavornpinyo, Angew. Chem., Int. Ed., 2005, 44, 4231–4235 CrossRef CAS PubMed ; (e) M. S. Hill and P. B. Hitchcock, Chem. Commun., 2004, 1818–1819 RSC .
  12. (a) Y. Liu, S. Li, X.-J. Yang, Q.-S. Li, Y. Xie, H. F. Schaefer and B. Wu, J. Organomet. Chem., 2011, 696, 1450–1455 CrossRef CAS ; (b) I. L. Fedushkin, A. N. Lukoyanov, A. N. Tishkina, G. K. Fukin, K. A. Lyssenko and M. Hummert, Chem. – Eur. J., 2010, 16, 7563–7571 CrossRef CAS PubMed ; (c) R. J. Baker, C. Jones, D. P. Mills, G. A. Pierce and M. Waugh, Inorg. Chim. Acta, 2008, 361, 427–435 CrossRef CAS ; (d) I. L. Fedushkin, A. N. Lukoyanov, G. K. Fukin, S. Y. Ketkov, M. Hummert and H. Schumann, Chem. – Eur. J., 2008, 14, 8465–8468 CrossRef CAS PubMed ; (e) R. J. Baker, R. D. Farley, C. Jones, M. Kloth and D. M. Murphy, J. Chem. Soc., Dalton Trans., 2002, 3844–3850 RSC ; (f) E. S. Schmidt, A. Schier and H. Schmidbaur, J. Chem. Soc., Dalton Trans., 2001, 505–507 RSC ; (g) E. S. Schmidt, A. Jockisch and H. Schmidbaur, J. Am. Chem. Soc., 1999, 121, 9758–9759 CrossRef CAS .
  13. (a) J. Overgaard, C. Jones, D. Dange and J. A. Platts, Inorg. Chem., 2011, 50, 8418–8426 CrossRef CAS PubMed ; (b) G. Jin, C. Jones, P. C. Junk, A. Stasch and W. D. Woodul, New J. Chem., 2008, 32, 835–842 RSC ; (c) C. Jones, P. C. Junk, J. A. Platts and A. Stasch, J. Am. Chem. Soc., 2006, 128, 2206–2207 CrossRef CAS PubMed .
  14. A. L. Hawley, C. A. Ohlin, L. Fohlmeister and A. Stasch, Chem. – Eur. J., 2017, 23, 447–455 CrossRef CAS PubMed .
  15. M. C. Kuchta, J. B. Bonanno and G. Parkin, J. Am. Chem. Soc., 1996, 118, 10914–10915 CrossRef CAS .
  16. P. Pyykkö, Chem. Rev., 1997, 97, 597–636 CrossRef .
  17. D. J. Liptrot and P. P. Power, Nat. Rev. Chem., 2017, 1, 0004 CrossRef CAS .
  18. (a) S. Gonzalez-Gallardo, T. Bollermann, R. A. Fischer and R. Murugavel, Chem. Rev., 2012, 112, 3136–3170 CrossRef CAS PubMed ; (b) S. Gonzalez-Gallardo, G. Prabusankar, T. Cadenbach, C. Gemel, M. von Hopffgarten, G. Frenking and R. A. Fischer, Struct. Bonding, 2010, 136, 147–188 CrossRef CAS .
  19. L. Bourget-Merle, M. F. Lappert and J. R. Severn, Chem. Rev., 2002, 102, 3031–3065 CrossRef CAS PubMed .
  20. (a) T. Chivers, J. Konu and R. Thirumoorthi, Dalton Trans., 2012, 41, 4283–4295 RSC ; (b) S. T. Liddle, D. P. Mills and A. J. Wooles, Organomet. Chem., 2010, 36, 29–55 CAS ; (c) T. K. Panda and P. W. Roesky, Chem. Soc. Rev., 2009, 38, 2782–2804 RSC .
  21. S. Al-Benna, M. J. Sarsfield, M. Thornton-Pett, D. L. Ormsby, P. J. Maddox, P. Brès and M. Bochmann, J. Chem. Soc., Dalton Trans., 2000, 4247–4257 RSC .
  22. (a) C. P. Sindlinger, A. Stasch and L. Wesemann, Organometallics, 2014, 33, 322–328 CrossRef CAS ; (b) A. J. Wooles, M. Gregson, S. Robinson, O. J. Cooper, D. P. Mills, W. Lewis, A. J. Blake and S. T. Liddle, Organometallics, 2011, 30, 5326–5337 CrossRef CAS ; (c) O. J. Cooper, A. J. Wooles, J. McMaster, W. Lewis, A. J. Blake and S. T. Liddle, Angew. Chem., Int. Ed., 2010, 49, 5570–5573 CrossRef CAS PubMed .
  23. (a) R. J. Baker and C. Jones, Dalton Trans., 2005, 1341–1348 RSC ; (b) M. L. H. Green, P. Mountford, G. J. Smout and S. R. Speel, Polyhedron, 1990, 9, 2763–2765 CrossRef CAS .
  24. G. Ma, M. J. Ferguson and R. G. Cavell, Chem. Commun., 2010, 46, 5370–5372 RSC .
  25. C. P. Sindlinger and A. Stasch, Aust. J. Chem., 2012, 66, 1219–1225 Search PubMed .
  26. C. P. Sindlinger, S. R. Lawrence, D. B. Cordes, A. M. Z. Slawin and A. Stasch, Inorganics, 2017, 5, 29 CrossRef .
  27. (a) M. S. Hill, P. B. Hitchcock and S. M. A. Karagouni, J. Organomet. Chem., 2004, 689, 722–730 CrossRef CAS ; (b) C. M. Ong, P. McKarns and D. W. Stephan, Organometallics, 1999, 18, 4197–4204 CrossRef CAS .
  28. (a) C. Jones, Nat. Rev. Chem., 2017, 1, 0059 CrossRef ; (b) A. Stasch and C. Jones, Dalton Trans., 2011, 40, 5659–5672 RSC .
  29. S. Schulz, S. Gondzik, D. Schuchmann, U. Westphal, L. Dobrzycki, R. Boese and S. Harder, Chem. Commun., 2010, 46, 7757–7759 RSC .

Footnote

Electronic supplementary information (ESI) available. CCDC 1580479–1580482. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7dt04048b

This journal is © The Royal Society of Chemistry 2017