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1,1′-Bis(ortho-carborane) as a κ2 co-ligand
Journal of Organometallic Chemistry 798 (2015) 36e40
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Communication
1,10 -Bis(ortho-carborane) as a k2 co-ligand Maria J. Martin, Wing Y. Man, Georgina M. Rosair, Alan J. Welch* Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 March 2015 Accepted 10 April 2015 Available online 2 May 2015
The compounds (dmpe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-C2B10H10]} (1) and (dppe)Ni{k22,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-C2B10H10]} (2) have been synthesised and fully characterised, including crystallographic studies. In all three structures studied (1, 2 and 2$2THF) the metal atom is slightly distorted from square-planar towards tetrahedral (t4 values [Houser et al., 2007] of 0.30, 0.33 and 0.11, respectively). Consideration of these molecular structures together with those of related species in the literature allows us to tentatively conclude that, in square-planar NiII compounds, the structural trans effect (trans influence) of s-bonded carborane is greater than that of Cl and sp2 N but less than that of sp2 C and sp3 C. Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.
Dedicated to Professor Russell Grimes with very best wishes on the occasion of his 80th birthday and in recognition of his many outstanding contributions to carborane and heterocarborane chemistry. Keywords: Carborane 1,10 -Bis(ortho-carborane) Nickel Synthesis Structure Structural trans effect
Introduction
Results and discussion
1,10 -bis(ortho-carborane) (Fig. 1) is the trivial name for [1-(10 10,20 -closo-C2B10H11)-1,2-closo-C2B10H11], the simplest bis(carborane) composed of two ortho-carborane units connected by a CeC bond [1]. Although 1,10 -bis(o-carborane) has been known for many years [2], its chemistry remains largely underdeveloped. Double deprotonation of 1,10 -bis(o-carborane) gives a dianionic chelating ligand which has been used to complex a variety of transitionmetal cations [3], an {(AuPPh3)2} fragment [4] and also an {AsMe} fragment [5]. The compound has also been reduced with both 2e and 4e [6] and the 4e-reduced species metallated [7]. Moreover, 1,10 -bis(o-carborane) has been both singly- and doublydeboronated [8] and these anions subsequently metallated [9]. In this contribution we return to the chelating properties of double-deprotonated 1,10 -bis(o-carborane) and extend the use of this unit as a k2 ligand, reporting the syntheses and spectroscopic and structural characterisation of two nickel complexes with 1,10 bis(o-carborane) and chelating diphosphines as co-ligands.
The reaction between 1,10 -bis(o-carborane), previously doubledeprotonated by n-BuLi, with (dmpe)NiCl2 in THF affords, following work-up involving thin-layer chromatography (TLC) on silica, the compound (dmpe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)1,2-closo-C2B10H10]} (1) as a bright yellow solid in moderate (38%) yield. Compound 1 was initially characterised by elemental analysis, mass-spectrometry, and 1H, 11B and 31P NMR spectroscopies. Microanalysis and mass spectrometry are both fully consistent with the molecular composition C10H36B20NiP2. The 31P NMR spectrum reveals a singlet, d 37.5 ppm, consistent with the expected C2 molecular symmetry. In the 1H spectrum are two integral-2 singlets for the axial and equatorial protons of the eCH2CH2e bridge in the chelating diphosphine and a multiplet for the 12 protons of the methyl groups. The 11B{1H} NMR spectrum reveals a 2:2:4:8:4 pattern of resonances, from d 2.7 to d 10.2 ppm. Similarly, using (dppe)NiCl2 as the source of the nickel diphosphine fragment affords (dppe)Ni{k2-2,20 -[1-(10 -10,20 -closoC2B10H10)-1,2-closo-C2B10H10]} (2) in 33% yield after work-up. After satisfactory elemental analysis and mass spectrometry, NMR spectroscopy of 2 revealed a singlet (d 49.1) in the 31P spectrum, a 2:2:12:4 pattern from d 2 to 10.5 in the 11B{1H} spectrum, and a
* Corresponding author. Tel.: þ44 131 451 3217; fax: þ44 131 451 3180. E-mail address: [email protected] (A.J. Welch). http://dx.doi.org/10.1016/j.jorganchem.2015.04.011 0022-328X/Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.
M.J. Martin et al. / Journal of Organometallic Chemistry 798 (2015) 36e40
Fig. 1. 1,10 -bis(ortho-carborane).
multiplet for the aromatic protons and two singlets for the two pairs of dppe bridge protons in the 1H spectrum. As far as we are aware, compounds 1 and 2 are the first reported compounds with double-deprotonated 1,10 -bis(o-carborane) and another ligand co-ligating a single transition metal centre. As such we have undertaken crystallographic studies of 1, 2 and 2$2THF, and the molecular structures determined are shown, together with the atomic numbering schemes used and selected interatomic distances, in Figs. 2e4 respectively. Compounds 1 and 2 are 4-co-ordinate NiII species with idealised C2 molecular symmetry and metal centre geometries intermediate between the extremes of square-planar and tetrahedral. A convenient method of quantifying the extent of the “distortion” from square-planar to tetrahedral is the index t4 [10], defined as
t4 ¼
360 ða þ bÞ 141
where a and b are the two largest angles at the metal centre, and t4 ¼ 0.00 for a perfect square-planar metal and 1.00 for a perfect tetrahedron. In Table 1 we list t4 values for 1 (two crystallographically-independent molecules), 2 and 2$2THF
37
together with NieCcage and NieX (X ¼ other ligand) distances for the structures determined herein and closely related structures taken from the Cambridge Structural Database [11]. Of these, NUMCAZ is the only species containing bis(carborane). The others have either one or two single carborane ligands co-ordinated to the metal atom. As can be seen from the t4 values, the NiII centre in all these compounds is approximately square-planar. Given this, we can use the data in Table 1 to comment tentatively on the trans influence (or Structural Trans Effect, STE [12]) of carborane versus other ligands, at least in essentially square-planar NiII compounds, as follows: When a carborane ligand is trans to another carborane (NUMCAZ [3c], FAMHEH [13] and UCUJIN [14]), the NieC distances span the range 1.972(5)e2.013(10) Å. When, however, Cl is the trans ligand (BUBSIB [15]) the NieC distances are considerably shorter, 1.880(6)e1.884(5) Å, confirming that carborane has a greater STE than Cl. A similar situation exists when sp2 N is the first atom of the trans ligand (BEKRIU [16] and BEKROA [16]) in that NieC is now 1.903(3)e1.905(4) Å, showing that carborane also has a greater STE than sp2 N. In cases where the chelating phosphine dppm or dppe is trans to the carborane (1, 2, 2$2THF, GATXOQ [17] and HAPCUY [18]) the NieCcage distances are found to lie in the relatively narrow range 1.935(3)e2.004(6) Å, suggesting that the STEs of carborane and these phosphines are approximately equal. However, close inspection of the data for GATXOQ and HAPCUY provides more information, since in these compounds the other arm of the diphosphine chelate is trans to a different type of C atom, sp3 in the case of GATXOQ (italicised entries in Table 1) and sp2 in the case of HAPCUY (bold entries). For both molecules the NieP distances trans to these non-carborane C atoms are significantly longer than those trans to carborane C atoms, 2.2141(8) vs 2.1542(10) Å for GATXOQ and 2.230(2) vs 2.214(2) Å for HAPCUY, showing that the STE of carborane is less than that of both sp2 and sp3 C atoms. Conclusions Two new compounds have been synthesised and characterised in which doubly-deprotonated 1,10 -bis(o-carborane) bonds as a k2 co-ligand, together with a chelating diphosphine, to a NiII centre. Structural studies reveal metal geometries nearer to square-planar than tetrahedral. Consideration of the metal-ligand distances in these and related species has enabled us to tentatively position the structural trans effect (trans influence) of s-bonded carborane as lying between that of Cl and sp2 N on the one hand, and sp2 C and sp3 C on the other, in essentially square-planar NiII complexes. Experimental Synthesis
Fig. 2. View of one of the two crystallographically-independent molecules of compound 1 projected onto the least-squares plane defined by Ni1A, P1A, P2A, C1A, C2A, C1B and C2B. Displacement ellipsoids are drawn at the 50% probability level except for H atoms. Selected interatomic distances (Å): Ni1AeC2A 1.980(4), Ni1AeC2B 1.977(4), Ni1AeP1A 2.1812(12), Ni1AeP2A 2.1724(12), C1AeC1B 1.517(6). For the other independent molecule: Ni1CeC2C 1.976(4), Ni1CeC2D 1.975(4), Ni1CeP1C 2.1734(12), Ni1CeP2C 2.1711(12), C1CeC1D 1.518(6).
All experiments were performed under dry, oxygen-free, N2 using standard Schlenk techniques, with some subsequent manipulation in the open laboratory. Solvents were freshly distilled over Na wire [tetrahydrofuran (THF), petroleum ether (petrol, bp 40e60 C)] or CaH2 [dichloromethane (DCM)] or stored over 4 Å molecular sieves (CDCl3) and were degassed (3 freeze-pumpthaw cycles) before use. Preparative TLC employed 20 20 cm Kieselgel F254 glass plates. NMR spectra at 400.1 MHz (1H), 162.0 MHz (31P) or 128.4 MHz (11B) were recorded on a Bruker AVIII-400 spectrometer at ambient temperature from CDCl3 or (CD3)2CO solutions at Heriot-Watt University (HWU). Electron ionisation mass spectrometry (EIMS) was carried out using a Finnigan (Thermo) LCQ Classic ion trap mass spectrometer at the
38
M.J. Martin et al. / Journal of Organometallic Chemistry 798 (2015) 36e40
Fig. 3. View of compound 2 projected onto the least-squares plane defined by Ni1, P1, P2, C1, C2, C10 and C20 . Displacement ellipsoids as in Fig. 2. Selected interatomic distances (Å): Ni1eC2 2.003(5), Ni1eC20 1.994(4), Ni1eP1 2.2436(13), Ni1eP2 2.2327(14), C1eC10 1.515(6).
University of Edinburgh. Elemental analyses were carried out using an Exeter CE-440 elemental analyser at HWU. 1,10 -Bis(o-carborane) [19], (dmpe)NiCl2[20] and (dppe)NiCl2[20] were prepared by literature methods or slight variants thereof. All other reagents were supplied commercially. (dmpe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-C2B10H10]} (1) 1,10 -Bis(o-carborane) (0.20 g, 0.70 mmol) was dissolved in dry, degassed, THF (12 mL) and cooled to 0 C. n-BuLi in hexanes
(0.69 mL of a 2.24 M solution, 1.54 mmol) was added and the solution was stirred under N2 for 30 min. The solution was then frozen at 196 C and (dmpe)NiCl2 (0.195 g, 0.70 mmol) added. The mixture was allowed to thaw and was stirred overnight. Solvent was removed in vacuo to afford a dark orange solid. This was dissolved in DCM and filtered through a short silica plug, eluting with DCM:petrol (1:1). Further purification by thin-layer chromatography (TLC) on silica (eluting with DCM:petrol, 1:1) yielded one mobile band at Rf 0.30 which, on removal of solvent, afforded the product (dmpe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-
Fig. 4. View of compound 2 (from crystallographic study of 2$2THF) projected onto the least-squares plane defined by Ni1, P1, P2, C1, C2, C10 and C20 . Displacement ellipsoids as in Fig. 2. Selected interatomic distances (Å): Ni1eC2 1.994(3), Ni1eC20 1.996(4), Ni1eP1 2.1956(9), Ni1eP2 2.2100(9), C1eC10 1.515(5).
M.J. Martin et al. / Journal of Organometallic Chemistry 798 (2015) 36e40 Table 1 t4 values and Nieligand distances (Å) in 4-co-ordinate NiII carboranyl compounds in the CSD. Ligands 1 and 2 are mutually trans. Compound/ refcode
t4
Ligand 1
NieL1
Ligand 2
NieL2
1 (NiA)
0.30
1 (NiC)
0.33
2
0.11
2$2THF
0.39 0.26
FAMHEH
0.23
UCUJIN BUBSIB (Ni1) BUBSIB (Ni2) BUBSIB (Ni3) BEKRIU
0.00a 0.13 0.15 0.10 0.33
BEKROA
0.34
GATXOQ
0.16
HAPCUY
0.12
1.980(4) 1.977(4) 1.976(4) 1.975(4) 2.003(5) 1.994(4) 1.994(3) 1.996(4) 2.002(10) 2.001(10) 1.998(11) 2.013(10) 1.973(5) 1.972(5) 1.989(3) 1.885(5) 1.884(5) 1.880(6) 1.903(3) 1.903(3) 1.905(4) 1.904(4) 1.935(3) 1.953(2) 1.950(4) 1.963(4)
dmpe dmpe dmpe dmpe dppe dppe dppe dppe Carborane Carborane Carborane Carborane Carborane Carborane Carborane Cl Cl Cl N sp2 N sp2 N sp2 N sp2 dppe dppe dppe dppe
2.1812(13) 2.1724(13) 2.1734(12) 2.1722(13) 2.2327(14) 2.2436(13) 2.2100(9) 2.1956(9)
NUMCAZ
Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane C sp3 Carborane C sp2
a
2.2920(14) 2.3072(15) 2.2854(14) 1.951(3) 1.947(2) 1.959(3) 1.967(4) 2.1542(10) 2.2141(8) 2.214(2) 2.230(2)
Ni atom located at inversion centre so t4 required to be 0.
C2B10H10]} (1) as a bright yellow solid (0.13 g, 38%). C10H36B20NiP2 requires: C 24.4, H 7.36. Found: C 24.6, H 7.40%. 11B NMR [(CD3)2CO] d 2.7(2B), 3.4(2B), 7.4(4B), 8.4(8B), 10.2(4B). 1H NMR [CDCl3] d 1.74 (s, 2H, PMe2CHHCHHPMe2), 1.69 (s, 2H, PMe2CHHCHHPMe2), 1.67e1.64 (m, 12H, PMe2CH2CH2PMe2). 31P {1H} NMR [(CD3)2CO] d 37.5. EIMS: envelope centred on m/z 493 (Mþ). (dppe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-C2B10H10]} (2) Similarly, from the reaction between 1,10 -bis(o-carborane) (0.20 g, 0.70 mmol) in THF (12 mL), n-BuLi (0.69 mL of a 2.24 M solution, 1.54 mmol) and (dppe)NiCl2 (0.37 g, 0.70 mmol), was prepared (dppe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closoC2B10H10]} (2) as a yellow solid (0.164 g, 32%) after column chromatography on silica (DCM: petroleum ether, 1:1, Rf ¼ 0.57). C30H44B20NiP2 requires C 48.6, H 5.98. Found for 1: C 47.0, H 5.75%. 11 1 B{ H} NMR [(CD3)2CO] d 2.0 (2B), 3.6 (2B), 8.1 (12B), 10.5 (4B). 1H NMR [(CD3)2CO] d 7.88e7.59 (m, 20H, PPh2CH2CH2PPh2), 2.36 (s, 2H, PPh2CHHCHHPPh2), 2.32 (s, 2H, PPh2CHHCHHPPh2). 31P {1H} NMR [(CD3)2CO] d 49.1. EIMS: envelope centred on m/z 741 (Mþ). Crystallography Diffraction-quality yellow crystals of both 1 (needle) and 2 (plate) were grown by diffusion of a DCM solution of the compound and petrol at 30 C. In addition 2 was also grown by diffusion of a THF solution and petrol, affording red plate crystals of the solvate 2$2THF. Intensity data for 1, 2 and 2$2THF were collected on a Bruker X8 APEX2 diffractometer using Mo-Ka X-radiation, with crystals mounted in inert oil on a cryoloop and cooled to 100 K by an Oxford Cryosystems Cryostream. Indexing, data collection and absorption correction were performed using the APEXII suite of programs [21]. Structures were solved by direct methods (SHELXS
39
Table 2 Crystallographic data.
Formula M Crystal system Space group a/Å b/Å c/Å a ( ) b ( ) g ( ) U/Å3 Z, Z0 F(000)/e Dcalc/Mg m3 m(Mo-Ka)/mm1 qmax ( ) Data measured Unique data, n Rint R, wR2 (obs. data) S Variables Emax, Emin/e Å3 Abs. str. parameter
1
2
2$2THF
C10H36B20NiP2 493.24 Monoclinic P21/c 18.9628(7) 23.5990(8) 11.6114(4) 90 90.488(2) 90 5195.9(3) 8, 2 2032 1.261 0.871 28.32 91,707 12,912 0.0681 0.0669, 0.1465 1.188 603 1.23, 0.81 e
C30H44B20NiP2 741.50 Triclinic Pbar1 11.1226(12) 13.2200(15) 15.1663(18) 101.186(7) 107.372(6) 110.895(6) 1872.1(4) 2, 1 764 1.315 0.630 24.89 18,568 6320 0.0834 0.0615, 0.1328 0.980 478 0.90, 0.90 e
C30H44B20NiP2$2C4H8O 885.71 Triclinic P1 10.7292(4) 11.0036(4) 11.5632(4) 68.403(2) 88.584(2) 65.786(2) 1144.70(7) 1, 1 462 1.285 0.530 27.05 17,212 9269 0.0250 0.0431, 0.1021 1.016 606 0.87, 0.51 0.012(11)
[22] or OLEX2 [23]) and refined by full-matrix least-squares (SHELXL) [22]. Structure solution for 1 and 2 was straightforward, but in 2$2THF there is partial disorder of both the THF molecules of solvation; in one case one C atom is disordered over two sites [SOFs 0.703(13) and 0.297(13)] and in the other case three C atoms are disordered over two sites [SOFs 0.604(11) and 0.396(11)]. In all cases H atoms were set in idealised (riding) positions with BeH 1.12 Å, CeH (CH2) 0.99 Å, CeH (CH3) 0.98 Å and CeH (C6H5) 0.95 Å. All H displacement parameters, Uiso, were constrained to be 1.2 Ueq (bound B or C) except those in methyl groups [1.5 Ueq (C)]. Table 2 contains further experimental details.
Acknowledgements We thank the EPSRC for support in the form of grant EP/I031545/ 1 (WYM). MJM is an Erasmus exchange student from the Universidad de Zaragoza.
Appendix A. Supplementary material CCDC 1053065, 1053066 and 1053067 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.
References [1] W.Y. Man, G.M. Rosair, A.J. Welch, Acta Cryst. Sect. E Struct. Rep. 70 (2014) 462. [2] J.A. Dupont, M.F. Hawthorne, J. Am. Chem. Soc. 86 (1964) 1643. [3] (a) D.A. Owen, M.F. Hawthorne, J. Am. Chem. Soc. 92 (1970) 3194; (b) D.A. Owen, M.F. Hawthorne, J. Am. Chem. Soc. 93 (1971) 873; (c) D.E. Harwell, J. McMillan, C.B. Knobler, M.F. Hawthorne, Inorg. Chem. 36 (1997) 5951. [4] D.E. Harwell, M.D. Mortimer, C.B. Knobler, F.A.L. Anet, M.F. Hawthorne, J. Am. Chem. Soc. 118 (1996) 2679. [5] A.I. Yanovsky, N.G. Furmanova, Yu.T. Struchkov, N.F. Shemyakin, L.I. Zakharkin, Izv. Akad. Nauk SSSR Ser. Khim. (1979) 1523. [6] (a) T.D. Getman, C.B. Knobler, M.F. Hawthorne, Inorg. Chem. 31 (1992) 101; (b) T.D. Getman, C.B. Knobler, M.F. Hawthorne, J. Am. Chem. Soc. 112 (1990) 4594.
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M.J. Martin et al. / Journal of Organometallic Chemistry 798 (2015) 36e40
[7] (a) D. Ellis, D. McKay, S.A. Macgregor, G.M. Rosair, A.J. Welch Angew, Chem. Int. Ed. 49 (2010) 4943; (b) D. Ellis, G.M. Rosair, A.J. Welch, Chem. Commun. 46 (2010) 7394. [8] M.F. Hawthorne, D.A. Owen, J.W. Wiggins, Inorg. Chem. 10 (1971) 1304. [9] (a) J.A. Doi, E.A. Mizusawa, C.B. Knobler, M.F. Hawthorne, Inorg. Chem. 23 (1984) 1482; (b) J.A. Long, T.B. Marder, P.E. Behnken, M.F. Hawthorne, J. Am. Chem. Soc. 106 (1984) 2979; (c) P.E. Behnken, T.B. Marder, R.T. Baker, C.B. Knobler, M.R. Thompson, M.F. Hawthorne, J. Am. Chem. Soc. 107 (1985) 932; (d) G. Thiripuranathar, W.Y. Man, C. Palmero, A.P.Y. Chan, B.T. Leube, D. Ellis, D. McKay, S.A. Macgregor, L. Jourdan, G.M. Rosair, A.J. Welch Dalton Trans. 44 (2015) 5628. [10] L. Yang, D.R. Powell, R.P. Houser Dalton Trans. (2007) 955. [11] C.R. Groom, F.H. Allen, Angew. Chem. Int. Ed. 53 (2014) 662. For this study we used the 2015 version of the Cambridge Structural Database.
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B.J. Coe, S. Glenwright, Coord. Chem. Rev. 203 (2000) 5. X. Wang, G.-X. Jin, Organometallics 23 (2004) 6319. P. Hu, Z.-J. Yau, J.-Q. Wang, G.-X. Jin, Organometallics 30 (2011) 4935. Z. Qiu, Z. Xie, J. Am. Chem. Soc. 131 (2009) 2084. Z.-J. Yao, G.-X. Jin, Organometallics 31 (2012) 1767. S. Ren, Z. Qiu, Z. Xie, Angew. Chem. Int. Ed. 51 (2012) 1010. S. Ren, Z. Qiu, Z. Xie, J. Am. Chem. Soc. 134 (2012) 3242. S. Ren, Z. Xie, Organometallics 27 (2008) 5167. G. Booth, J. Chatt, J. Chem. Soc. (1965) 3238. A.X.S. Bruker, APEX2, Version 2011, Bruker AXS Inc., Madison, Wisconsin, USA, 2011. [22] G.M. Sheldrick, Acta Cryst. A64 (2008) 112. [23] (a) O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl. Cryst. 42 (2009) 339; (b) O.V. Dolomanov, R.J. Gildea, J.A.K. Howard, H. Puschmann, L.J. Bourhis, Acta Cryst. A71 (2015) 59.
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Communication
1,10 -Bis(ortho-carborane) as a k2 co-ligand Maria J. Martin, Wing Y. Man, Georgina M. Rosair, Alan J. Welch* Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 March 2015 Accepted 10 April 2015 Available online 2 May 2015
The compounds (dmpe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-C2B10H10]} (1) and (dppe)Ni{k22,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-C2B10H10]} (2) have been synthesised and fully characterised, including crystallographic studies. In all three structures studied (1, 2 and 2$2THF) the metal atom is slightly distorted from square-planar towards tetrahedral (t4 values [Houser et al., 2007] of 0.30, 0.33 and 0.11, respectively). Consideration of these molecular structures together with those of related species in the literature allows us to tentatively conclude that, in square-planar NiII compounds, the structural trans effect (trans influence) of s-bonded carborane is greater than that of Cl and sp2 N but less than that of sp2 C and sp3 C. Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.
Dedicated to Professor Russell Grimes with very best wishes on the occasion of his 80th birthday and in recognition of his many outstanding contributions to carborane and heterocarborane chemistry. Keywords: Carborane 1,10 -Bis(ortho-carborane) Nickel Synthesis Structure Structural trans effect
Introduction
Results and discussion
1,10 -bis(ortho-carborane) (Fig. 1) is the trivial name for [1-(10 10,20 -closo-C2B10H11)-1,2-closo-C2B10H11], the simplest bis(carborane) composed of two ortho-carborane units connected by a CeC bond [1]. Although 1,10 -bis(o-carborane) has been known for many years [2], its chemistry remains largely underdeveloped. Double deprotonation of 1,10 -bis(o-carborane) gives a dianionic chelating ligand which has been used to complex a variety of transitionmetal cations [3], an {(AuPPh3)2} fragment [4] and also an {AsMe} fragment [5]. The compound has also been reduced with both 2e and 4e [6] and the 4e-reduced species metallated [7]. Moreover, 1,10 -bis(o-carborane) has been both singly- and doublydeboronated [8] and these anions subsequently metallated [9]. In this contribution we return to the chelating properties of double-deprotonated 1,10 -bis(o-carborane) and extend the use of this unit as a k2 ligand, reporting the syntheses and spectroscopic and structural characterisation of two nickel complexes with 1,10 bis(o-carborane) and chelating diphosphines as co-ligands.
The reaction between 1,10 -bis(o-carborane), previously doubledeprotonated by n-BuLi, with (dmpe)NiCl2 in THF affords, following work-up involving thin-layer chromatography (TLC) on silica, the compound (dmpe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)1,2-closo-C2B10H10]} (1) as a bright yellow solid in moderate (38%) yield. Compound 1 was initially characterised by elemental analysis, mass-spectrometry, and 1H, 11B and 31P NMR spectroscopies. Microanalysis and mass spectrometry are both fully consistent with the molecular composition C10H36B20NiP2. The 31P NMR spectrum reveals a singlet, d 37.5 ppm, consistent with the expected C2 molecular symmetry. In the 1H spectrum are two integral-2 singlets for the axial and equatorial protons of the eCH2CH2e bridge in the chelating diphosphine and a multiplet for the 12 protons of the methyl groups. The 11B{1H} NMR spectrum reveals a 2:2:4:8:4 pattern of resonances, from d 2.7 to d 10.2 ppm. Similarly, using (dppe)NiCl2 as the source of the nickel diphosphine fragment affords (dppe)Ni{k2-2,20 -[1-(10 -10,20 -closoC2B10H10)-1,2-closo-C2B10H10]} (2) in 33% yield after work-up. After satisfactory elemental analysis and mass spectrometry, NMR spectroscopy of 2 revealed a singlet (d 49.1) in the 31P spectrum, a 2:2:12:4 pattern from d 2 to 10.5 in the 11B{1H} spectrum, and a
* Corresponding author. Tel.: þ44 131 451 3217; fax: þ44 131 451 3180. E-mail address: [email protected] (A.J. Welch). http://dx.doi.org/10.1016/j.jorganchem.2015.04.011 0022-328X/Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.
M.J. Martin et al. / Journal of Organometallic Chemistry 798 (2015) 36e40
Fig. 1. 1,10 -bis(ortho-carborane).
multiplet for the aromatic protons and two singlets for the two pairs of dppe bridge protons in the 1H spectrum. As far as we are aware, compounds 1 and 2 are the first reported compounds with double-deprotonated 1,10 -bis(o-carborane) and another ligand co-ligating a single transition metal centre. As such we have undertaken crystallographic studies of 1, 2 and 2$2THF, and the molecular structures determined are shown, together with the atomic numbering schemes used and selected interatomic distances, in Figs. 2e4 respectively. Compounds 1 and 2 are 4-co-ordinate NiII species with idealised C2 molecular symmetry and metal centre geometries intermediate between the extremes of square-planar and tetrahedral. A convenient method of quantifying the extent of the “distortion” from square-planar to tetrahedral is the index t4 [10], defined as
t4 ¼
360 ða þ bÞ 141
where a and b are the two largest angles at the metal centre, and t4 ¼ 0.00 for a perfect square-planar metal and 1.00 for a perfect tetrahedron. In Table 1 we list t4 values for 1 (two crystallographically-independent molecules), 2 and 2$2THF
37
together with NieCcage and NieX (X ¼ other ligand) distances for the structures determined herein and closely related structures taken from the Cambridge Structural Database [11]. Of these, NUMCAZ is the only species containing bis(carborane). The others have either one or two single carborane ligands co-ordinated to the metal atom. As can be seen from the t4 values, the NiII centre in all these compounds is approximately square-planar. Given this, we can use the data in Table 1 to comment tentatively on the trans influence (or Structural Trans Effect, STE [12]) of carborane versus other ligands, at least in essentially square-planar NiII compounds, as follows: When a carborane ligand is trans to another carborane (NUMCAZ [3c], FAMHEH [13] and UCUJIN [14]), the NieC distances span the range 1.972(5)e2.013(10) Å. When, however, Cl is the trans ligand (BUBSIB [15]) the NieC distances are considerably shorter, 1.880(6)e1.884(5) Å, confirming that carborane has a greater STE than Cl. A similar situation exists when sp2 N is the first atom of the trans ligand (BEKRIU [16] and BEKROA [16]) in that NieC is now 1.903(3)e1.905(4) Å, showing that carborane also has a greater STE than sp2 N. In cases where the chelating phosphine dppm or dppe is trans to the carborane (1, 2, 2$2THF, GATXOQ [17] and HAPCUY [18]) the NieCcage distances are found to lie in the relatively narrow range 1.935(3)e2.004(6) Å, suggesting that the STEs of carborane and these phosphines are approximately equal. However, close inspection of the data for GATXOQ and HAPCUY provides more information, since in these compounds the other arm of the diphosphine chelate is trans to a different type of C atom, sp3 in the case of GATXOQ (italicised entries in Table 1) and sp2 in the case of HAPCUY (bold entries). For both molecules the NieP distances trans to these non-carborane C atoms are significantly longer than those trans to carborane C atoms, 2.2141(8) vs 2.1542(10) Å for GATXOQ and 2.230(2) vs 2.214(2) Å for HAPCUY, showing that the STE of carborane is less than that of both sp2 and sp3 C atoms. Conclusions Two new compounds have been synthesised and characterised in which doubly-deprotonated 1,10 -bis(o-carborane) bonds as a k2 co-ligand, together with a chelating diphosphine, to a NiII centre. Structural studies reveal metal geometries nearer to square-planar than tetrahedral. Consideration of the metal-ligand distances in these and related species has enabled us to tentatively position the structural trans effect (trans influence) of s-bonded carborane as lying between that of Cl and sp2 N on the one hand, and sp2 C and sp3 C on the other, in essentially square-planar NiII complexes. Experimental Synthesis
Fig. 2. View of one of the two crystallographically-independent molecules of compound 1 projected onto the least-squares plane defined by Ni1A, P1A, P2A, C1A, C2A, C1B and C2B. Displacement ellipsoids are drawn at the 50% probability level except for H atoms. Selected interatomic distances (Å): Ni1AeC2A 1.980(4), Ni1AeC2B 1.977(4), Ni1AeP1A 2.1812(12), Ni1AeP2A 2.1724(12), C1AeC1B 1.517(6). For the other independent molecule: Ni1CeC2C 1.976(4), Ni1CeC2D 1.975(4), Ni1CeP1C 2.1734(12), Ni1CeP2C 2.1711(12), C1CeC1D 1.518(6).
All experiments were performed under dry, oxygen-free, N2 using standard Schlenk techniques, with some subsequent manipulation in the open laboratory. Solvents were freshly distilled over Na wire [tetrahydrofuran (THF), petroleum ether (petrol, bp 40e60 C)] or CaH2 [dichloromethane (DCM)] or stored over 4 Å molecular sieves (CDCl3) and were degassed (3 freeze-pumpthaw cycles) before use. Preparative TLC employed 20 20 cm Kieselgel F254 glass plates. NMR spectra at 400.1 MHz (1H), 162.0 MHz (31P) or 128.4 MHz (11B) were recorded on a Bruker AVIII-400 spectrometer at ambient temperature from CDCl3 or (CD3)2CO solutions at Heriot-Watt University (HWU). Electron ionisation mass spectrometry (EIMS) was carried out using a Finnigan (Thermo) LCQ Classic ion trap mass spectrometer at the
38
M.J. Martin et al. / Journal of Organometallic Chemistry 798 (2015) 36e40
Fig. 3. View of compound 2 projected onto the least-squares plane defined by Ni1, P1, P2, C1, C2, C10 and C20 . Displacement ellipsoids as in Fig. 2. Selected interatomic distances (Å): Ni1eC2 2.003(5), Ni1eC20 1.994(4), Ni1eP1 2.2436(13), Ni1eP2 2.2327(14), C1eC10 1.515(6).
University of Edinburgh. Elemental analyses were carried out using an Exeter CE-440 elemental analyser at HWU. 1,10 -Bis(o-carborane) [19], (dmpe)NiCl2[20] and (dppe)NiCl2[20] were prepared by literature methods or slight variants thereof. All other reagents were supplied commercially. (dmpe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-C2B10H10]} (1) 1,10 -Bis(o-carborane) (0.20 g, 0.70 mmol) was dissolved in dry, degassed, THF (12 mL) and cooled to 0 C. n-BuLi in hexanes
(0.69 mL of a 2.24 M solution, 1.54 mmol) was added and the solution was stirred under N2 for 30 min. The solution was then frozen at 196 C and (dmpe)NiCl2 (0.195 g, 0.70 mmol) added. The mixture was allowed to thaw and was stirred overnight. Solvent was removed in vacuo to afford a dark orange solid. This was dissolved in DCM and filtered through a short silica plug, eluting with DCM:petrol (1:1). Further purification by thin-layer chromatography (TLC) on silica (eluting with DCM:petrol, 1:1) yielded one mobile band at Rf 0.30 which, on removal of solvent, afforded the product (dmpe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-
Fig. 4. View of compound 2 (from crystallographic study of 2$2THF) projected onto the least-squares plane defined by Ni1, P1, P2, C1, C2, C10 and C20 . Displacement ellipsoids as in Fig. 2. Selected interatomic distances (Å): Ni1eC2 1.994(3), Ni1eC20 1.996(4), Ni1eP1 2.1956(9), Ni1eP2 2.2100(9), C1eC10 1.515(5).
M.J. Martin et al. / Journal of Organometallic Chemistry 798 (2015) 36e40 Table 1 t4 values and Nieligand distances (Å) in 4-co-ordinate NiII carboranyl compounds in the CSD. Ligands 1 and 2 are mutually trans. Compound/ refcode
t4
Ligand 1
NieL1
Ligand 2
NieL2
1 (NiA)
0.30
1 (NiC)
0.33
2
0.11
2$2THF
0.39 0.26
FAMHEH
0.23
UCUJIN BUBSIB (Ni1) BUBSIB (Ni2) BUBSIB (Ni3) BEKRIU
0.00a 0.13 0.15 0.10 0.33
BEKROA
0.34
GATXOQ
0.16
HAPCUY
0.12
1.980(4) 1.977(4) 1.976(4) 1.975(4) 2.003(5) 1.994(4) 1.994(3) 1.996(4) 2.002(10) 2.001(10) 1.998(11) 2.013(10) 1.973(5) 1.972(5) 1.989(3) 1.885(5) 1.884(5) 1.880(6) 1.903(3) 1.903(3) 1.905(4) 1.904(4) 1.935(3) 1.953(2) 1.950(4) 1.963(4)
dmpe dmpe dmpe dmpe dppe dppe dppe dppe Carborane Carborane Carborane Carborane Carborane Carborane Carborane Cl Cl Cl N sp2 N sp2 N sp2 N sp2 dppe dppe dppe dppe
2.1812(13) 2.1724(13) 2.1734(12) 2.1722(13) 2.2327(14) 2.2436(13) 2.2100(9) 2.1956(9)
NUMCAZ
Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane Carborane C sp3 Carborane C sp2
a
2.2920(14) 2.3072(15) 2.2854(14) 1.951(3) 1.947(2) 1.959(3) 1.967(4) 2.1542(10) 2.2141(8) 2.214(2) 2.230(2)
Ni atom located at inversion centre so t4 required to be 0.
C2B10H10]} (1) as a bright yellow solid (0.13 g, 38%). C10H36B20NiP2 requires: C 24.4, H 7.36. Found: C 24.6, H 7.40%. 11B NMR [(CD3)2CO] d 2.7(2B), 3.4(2B), 7.4(4B), 8.4(8B), 10.2(4B). 1H NMR [CDCl3] d 1.74 (s, 2H, PMe2CHHCHHPMe2), 1.69 (s, 2H, PMe2CHHCHHPMe2), 1.67e1.64 (m, 12H, PMe2CH2CH2PMe2). 31P {1H} NMR [(CD3)2CO] d 37.5. EIMS: envelope centred on m/z 493 (Mþ). (dppe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closo-C2B10H10]} (2) Similarly, from the reaction between 1,10 -bis(o-carborane) (0.20 g, 0.70 mmol) in THF (12 mL), n-BuLi (0.69 mL of a 2.24 M solution, 1.54 mmol) and (dppe)NiCl2 (0.37 g, 0.70 mmol), was prepared (dppe)Ni{k2-2,20 -[1-(10 -10,20 -closo-C2B10H10)-1,2-closoC2B10H10]} (2) as a yellow solid (0.164 g, 32%) after column chromatography on silica (DCM: petroleum ether, 1:1, Rf ¼ 0.57). C30H44B20NiP2 requires C 48.6, H 5.98. Found for 1: C 47.0, H 5.75%. 11 1 B{ H} NMR [(CD3)2CO] d 2.0 (2B), 3.6 (2B), 8.1 (12B), 10.5 (4B). 1H NMR [(CD3)2CO] d 7.88e7.59 (m, 20H, PPh2CH2CH2PPh2), 2.36 (s, 2H, PPh2CHHCHHPPh2), 2.32 (s, 2H, PPh2CHHCHHPPh2). 31P {1H} NMR [(CD3)2CO] d 49.1. EIMS: envelope centred on m/z 741 (Mþ). Crystallography Diffraction-quality yellow crystals of both 1 (needle) and 2 (plate) were grown by diffusion of a DCM solution of the compound and petrol at 30 C. In addition 2 was also grown by diffusion of a THF solution and petrol, affording red plate crystals of the solvate 2$2THF. Intensity data for 1, 2 and 2$2THF were collected on a Bruker X8 APEX2 diffractometer using Mo-Ka X-radiation, with crystals mounted in inert oil on a cryoloop and cooled to 100 K by an Oxford Cryosystems Cryostream. Indexing, data collection and absorption correction were performed using the APEXII suite of programs [21]. Structures were solved by direct methods (SHELXS
39
Table 2 Crystallographic data.
Formula M Crystal system Space group a/Å b/Å c/Å a ( ) b ( ) g ( ) U/Å3 Z, Z0 F(000)/e Dcalc/Mg m3 m(Mo-Ka)/mm1 qmax ( ) Data measured Unique data, n Rint R, wR2 (obs. data) S Variables Emax, Emin/e Å3 Abs. str. parameter
1
2
2$2THF
C10H36B20NiP2 493.24 Monoclinic P21/c 18.9628(7) 23.5990(8) 11.6114(4) 90 90.488(2) 90 5195.9(3) 8, 2 2032 1.261 0.871 28.32 91,707 12,912 0.0681 0.0669, 0.1465 1.188 603 1.23, 0.81 e
C30H44B20NiP2 741.50 Triclinic Pbar1 11.1226(12) 13.2200(15) 15.1663(18) 101.186(7) 107.372(6) 110.895(6) 1872.1(4) 2, 1 764 1.315 0.630 24.89 18,568 6320 0.0834 0.0615, 0.1328 0.980 478 0.90, 0.90 e
C30H44B20NiP2$2C4H8O 885.71 Triclinic P1 10.7292(4) 11.0036(4) 11.5632(4) 68.403(2) 88.584(2) 65.786(2) 1144.70(7) 1, 1 462 1.285 0.530 27.05 17,212 9269 0.0250 0.0431, 0.1021 1.016 606 0.87, 0.51 0.012(11)
[22] or OLEX2 [23]) and refined by full-matrix least-squares (SHELXL) [22]. Structure solution for 1 and 2 was straightforward, but in 2$2THF there is partial disorder of both the THF molecules of solvation; in one case one C atom is disordered over two sites [SOFs 0.703(13) and 0.297(13)] and in the other case three C atoms are disordered over two sites [SOFs 0.604(11) and 0.396(11)]. In all cases H atoms were set in idealised (riding) positions with BeH 1.12 Å, CeH (CH2) 0.99 Å, CeH (CH3) 0.98 Å and CeH (C6H5) 0.95 Å. All H displacement parameters, Uiso, were constrained to be 1.2 Ueq (bound B or C) except those in methyl groups [1.5 Ueq (C)]. Table 2 contains further experimental details.
Acknowledgements We thank the EPSRC for support in the form of grant EP/I031545/ 1 (WYM). MJM is an Erasmus exchange student from the Universidad de Zaragoza.
Appendix A. Supplementary material CCDC 1053065, 1053066 and 1053067 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.
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