Studies in Boron Hydrides-V

STUDIES IN BORON HYDRIDES- V* ASSIGNMENT OF ТНЕ 11 В NMR SPECTRUM OF ТНЕ TRIDECAHYDRO DECABORATE(l-) ION Abstract- The 70·6 MHz 1 18 NMR spectrum of 810Н13- consists of four douЫets of relative inten­ sities 2: 1: 5: 2 which аге assigned to 8(6, 9); 8(1 ог 3): 8(5, 7, 8, 1 О and I ог 3); and 8(2, 4) respec­tively. This data is consistent with а 3630 model for the solution structure. INTRODUCTION IN А v ARIETY of donor solvents, decaborane behaves as а monoprotic acid and, upon treatment with suitaЫe bases such as amines or ylides, affords the trideca­ hydrodecaborate(l-) ion, B 10H13-[ l ]. Previous 11В NMR studies[2], done at lower field strengths, did not allow an interpretation of these spectra. In this communication, spectra of В 10Н 13- and some of its derivatives, recorded at 70·6 MHz, are reported. They are sufficient to allow an assignment of the 11 В NMR spectrum. The 70·6 MHz 11 В spectrum of (C2H5)3NH+B10H 13 - in acetonitrile, Fig. 1а, is substantially more complex than the 32 MHz 11 В spectrum reported Ьу Norman et al. [3]. It consists of four douЫets of relative intensity 2: 1: 5: 2 in order of increasing field. The spectrum of this salt is relatively insensitive to solvent: in acetonitrile-diethyl sulfide, the two douЫets at lowest field begin to merge, while in benzene-dichloromethane, there is in addition а loss of apparent splitting in the douЬlet of relative intensity 5. Similar effects, although smaller in degree, are seen in dichloromethane solvent. The similarity of the spectra in both non­ coordinating and donor solvents strongly indicates that one is not observing а species of the type B 10H 13 ·L-, where L is а coordinated solvent. The spectrum of (C2H5)3NH+ 1,2,3,4-B 10D4H9- is shown in Fig. l b. Deutera­ tion in these positions causes collapse of the douЫets at -2·О and 35 ·4 ppm. The collapse is complete. and there is no alteration of the douЫets at -6·8 and 5 ·О *Part IV., L. А. Kaplan and А. R. Siedle,J. Org. Chem. 36, (1971). tTo whom correspondence may Ье addressed at Indiana University, Department of Chemistry, 8loomington, Ind. 47401. 1. М. F. Hawthorne, А. R. Pitochelli, R. D. Strahm and J. J. Miller, J. Ат. chem. Soc. 82, 1825 (1960). 2. G. R. Eaton and W. N. Lipscomb, N.M.R. Studies oj'Boron Hydrides and Related Compounds р. 186. 8enjamin, New York, (1969). 3. J. Q. Chambers, А. D. Norman, М. R. 8ickell and S. Н. Cadle,J. Ат. chem. Soc. 90, 6056 (1968). +5.0 -6.8 6,9 1 1,(з) 1 1 -----__,2, 4 ...,....,---- 5,7. s,1r.-з,(1) Fig. l(a). Fig. 1(Ь). Fig. 1(с). Studies in boron hydrides - V Fig. l(d). Fig. l(e). Fig. l(f). Fig. 1. The 70·6 MHz 11 В NMR spectra in acetonitrile of: (а) (C2H5)3NH+ В 10Н13-; (Ь) (C2H,)3 NH+ l,2,3,4-B,0D4H9-; (с) (C2H5)3NH+ 2,4-B10I2H11-; (d) (C2H5)3NH+ 6-PhCH2B,oH12-; (е) (C2H5)3NH+ µ3-5,6,7,8,9, 1O-B10D9H4-; (f) (C2H5)3NH+ В,оН, 3-, ' Н decoupled. А. R. SIEDLE, G. М. BODNER and L. J. TODD pprn, which irnplies that the deuteriurn label has not been scrarnЫed. The assign­ rnent of the high field douЫet to В(2, 4) сап then Ье rnade оп the basis of the spectrurn of (C2H5)3NH+ 2,4-B10 l2H11 -, shown in Fig. lc, since the positions of iodination in the parent decaborane have been elucidated Ьу а X-ray crystal structure deterrnination[4]. The douЫet of relative intensity one at -2·5 pprn in the structure of В 10Н13 - apparently has shifted to -6•5 pprn in the spectrurn of the diiodo derivative. А second douЫet of relative intensity one appears at + 1·3 pprn in the spectrurn of 2,4-B10l2H11 -. These two douЫets of unit area are as­ signed to B( l ) and В(З) but which is which is not known. The spectrurn of (C2H5)3NH+ 6-PhCH2 B10H12 - is shown in Fig. ld. In this spectrurn, the low field douЫet has been halved in intensity and in addition а singlet due to В(6) appears at -16·5 pprn. This indicates that the douЫet at lowest field, of area 2, is due to В(6, 9). Since В(2, 4) по longer lie оп а rnirror plane they now appear as two overlapping douЬlets, which gives added credence to the assignrnent of these two positions. This effect has also been observed in the 11В NMR spectrurn of 6-PhCH2 B10H 1з• Further confirrnation of this assignrnent was provided Ьу the spectrurn of (C2H5)3NH+ µ,3,5,6,7,8,9,1O-В10DэН4-, Fig. le, in which the expected collapse of the douЫets at -6·8 pprn and 5·0 pprn, with relative intensities 2: 5, occurs. The distorted line shape of the low field portion of the resonance at 5 ·О pprn is suggestive of а douЫet of area one due to either B(l) or В(3) superirnposed оп the В(5, 7, 8, 10) resonance. In Fig. lf is shown the spectrurn of (C2H5)3NH+ В10Н1з-, in which а wide band, white noise 1Н decoupling experirnent was perforrned. Unfortunately, it was not possiЫe to conclusively dernonstrate the existence of two distinct boron environrnents beneath this resonance at 5·0 pprn. А disturЬing feature of the 11В NMR spectrurn of В10Н13- is the gross non­ equivalence of B(l) and В(3), while В(2, 4), and В(5, 7, 8, 10) are apparently rnagnetically equivalent. In the 1 1В spectrurn of NaB10H13 in diethyl ether, the +5 pprn region consists of two overlapping douЫets of relative areas 2: 3. The reson­ ances due to В(5, 1О) and В(7, 8) rnay Ье resolved in this case. These results are inconsistent with the various structures suggested Ьу Lipscornb [5]. А study of the PMR of (C2H5)3 NH+ В10Н13- at 220 MHz in various solvents has dernonstrated the existence of two distinct bridge resonances, which were rnarkedly solvent dependent[6]. In acetonitrile, these resonances occurred at 3·2 and 3·61 pprn upfield frorn TMS, with relative intensities that appeared to Ье 1: 2. In а diethyl ether solution of Na+ В10Н 1з-, the bridge resonances becarne sufficiently well resolved to allow confirrnation of their relative intensities as 1: 2. There was по evidence of collapse in these two resonances, upon cooling to -3O°С. These observations along with the 11В NMR data, leads us to postulate а static 3630 structure, оп an NMR tirne scale. This structure, shown in Fig. 2, appears to fit all the presently availaЫe data. The nurnbering of this structure has been rnade identical to that of В10Н 14 for convenience. Alternatively, а nonstatic 4. R. О. Schaeffer,J.Am. Chem. Soc. 79, 2726 (1957). 5. W. N. Lipscomb, Boron Hydrides р. 182. Benjamin, New York (1963). 6. Similar results were obtained for the bridge resonance in В,0Н,,; G. М. Bodner and L. G. Sneddon, lnorg. Chem. 9, 1421 (1970). Studies in boron hydrides - V Fig. 2. The proposed structure for the B 10His- ion in solution. ТаЫе 1. 70·6 MHz 1 1В chemical shifts" Compound (C2 H,)3NH [В 10Н,з] (С 2Н5)зNН [ l .2.3,4-B I0D ,H9] (C2 H5)3NH [2.4-B 1 ol 2H11 J (C2H5)3NH [J.t:3,5,6,7 ,8,9,1 0-B 10D9H.] (С2Н 5) зNН [6-PhCH2B I0H 12] 8(6, 9) B(l )b 8(5, 7, 8,10) В(З)с 8(2. 4) -6·8 (140) -6·8 -6·5 -6·5 (-16·5'1 ,-8·8) -2·5 ( 135) -2-2 -6·5 -2·6 -1·9 +5·0 (135) +5·0 (+1·3.+3·6) +5·0 (+4·4. +6·5) +35·2 (150) +35·4 +40·4 +35·2 (+33·8,+35·8) "ln acetonitrile; relative to ВFз . О(С,Н5 )2 = О ppm. Ьоr В(З). "or B(I). 1 ' 8(6). structure may Ье envisioned in which rapid hydrogen exchange occurs on only one side of the ion such that B(l) and В(З) remain non equivalent. А single crystal X-ray study of В 10Н 13- is now underway in this department in ап attempt to elucidate the solid state structure ofthis ion. EXPERIMENTAL NMR spectra were recorded on а Varian HR-220 spectrometer with digitized frequency sweep. Chemical shifts were calibrated with an extemal capillary and are reported in ppm from BF3 ·O(C2H5) 2 , ±О·15 ppm. 6-Benzyldecaborane[7], l .2,3,4-B 10 D4 H10[8], J,t4 -5,6,7,8,9. I0-B10D10 H4 [8] and 2,4-B10 J2 H12 [9] were prepared Ьу literature methods and converted to the corresponding В10Н 13- salts with triethyl­ amine[I J. 11В (С2Н,)зNН+ 6-C6HsCH2B ,oH12То 1 ·05 m-mole 6-benzyldecaborane in 8 ml dry benzene was added under nitrogen with stirring 1 ·О m-mole triethylamine in 2 ml benzene, whereupon а yellow oil separated. Cooling and trituration with benzene-heptane induced the formation of nearly white, air sensitive crystals which were collected on а filter and dried in vacuo, wt. 0·27 gm, m.p. 97° (dec.), Лmах (CH3CN) 326 nm (7700). Апа/. Calcd. for C1 3H35 NB 1 0: С, 49·84; Н, 11 ·18. Found: С, 49·15; Н, 1158. А sample of this salt was dissolved in dichloromethane and treated with anhydrous hydrogen 7. R. J. F. Palchak,J. Н. Norman and R. Е. Williams,J. Ат. chem. Soc. 83, 3380 ( 1961 ). 8. J. А. Dupont and М. F: Hawthorne,J. Ат. chem. Soc. 84, 1804 (1962). 9. М. Hilman.J. Ат. chem. Soc. 82, 1096 (1960). chloride. А white precipitate formed and was removed Ьу filtration. Evaporation of the filtrate under nitrogen afforded а white solid which was suЫimed in vacuo (50°/0·001 mm). The melting point and infrared spectrum of this recovered benzyldecaborane were identical with that of the starting material. (C2Hs)зNH+ 2,4-B,0H11 I2To 0· 187 g (0·5 m-mole) 2,4-В10 Н 12 12 suspended in 2·5 ml acetonitrile was added with stirring 0·05 g (0·5 m-mole) triethylamine in 0·5 ml acetonitrile. The iododecaborane dissolved and the solution became yellow. Concentration of this solution and addition of cyclohexane produced 0·22 g of yellow oil which was separated and dried in vacuo for 24 hr. The product was very sensitive to moisture. All attempts to induce crystallization failed. Anal: Calcd. for C6H27Nl2B10: С, 15·16; Н, 5·68; В 22·73. Found: С, 15·33; Н, 5·95; В, 23·29. Acknowledgements-We are grateful to W. С. Jankowski for preliminary 32 MHz "В spectra, to Professor А. D. Norman for communicating some of his results prior to puЬlication, and to А. О. Clouse for help in oЬtaining the spectra. The "В NMR probe for the HR-220 spectrometer was made availaЫe through Grant GP-10483 from the National Science Foundation. This work was supported in part Ьу the Office of Naval Research.