COMMUNICATIONS TO THE EDITOR
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(Fig. 1) was performed, which confirmed the 1 : 1 paired type.' A rigorously square-planar and spin-free stoichiometry. The compound may be conveniently cobaltous anionic complex has been described only very prepared in benzene or toluene since biscyclopentarecently. dienyltungsten dihydride is soluble in such hydroThe "pure" square-planar complexes of nickel(1I) carbons but the BF:j adduct is not. This adduct does so far investigated are only of the spin-paired type and not have an appreciable BFa dissociation pressure. the paramagnetic complexes are either tetrahedral or Infrared spectra were obtained on Kujol mulls using octahedral. On the other hand, the existence in solu(311 (m), tion of the equilibrium square-planar (diamagnetic) a prism-grating Becknian I KR : (C5H5)S\2'HI, 776 (s), 822 (s), S i 6 (w), 906 ( m ) , 9% (s), 1o(iJ (s), tcfralzedral (paramagnetic) has clearly been established. IO53 (w), 1097 (m), 125%(w), 1415 (m), 1921 (In)c m . ; Lye wish to report some results which seem to us to (C~H~)~WH*.O BFa, . % 602 ? J (m), 777 (s), 823 (s), 906 (m), be both novel and important, becailse they suggest the 1005 (s), 1053 (s), 1093 (s), 1286 (w), 1917 ( m ) , 1922 existence of a similar equilibrium in the tetracoordinate (sh) cm.-'. The 12'-H stretching frequency 1921 cobalt (11) complex compound [Co(PEts)z(NCS)?]. cm.-l is shifted to 1917 cm.-I upon complex formation Anhydrous cobaltous thiocyanate in absolute ethanol (the shoulder a t 1022 em.-' is attributed to the small reacted with P(C2H6)3to give a red crystalline product, amount of parent compound present in the sample). which was washed with ice-cold ethanol and dried in an The very small frequency shift and negligible change in dec. atmosphere of pure nitrogen, m . p . 72-74' relative intensity of this band renders unlikely a single .Ana/. Calcd. for C O ( P E ~ ~ ) ~ ( N C SC,) ~40.9; : H, hydrogen bridge such as t h a t found in B2H7- (HeB-H7.35; N , 6.8; Co, 14.3. Found: C, 40.5; H , 7.4; N , 6.75; Co, 14.3. BHZ-).: In the case of (C5Hb)212'H2.BF3 a broad absorption appears to underlie the bands in the 1100 The solid compound, stable a t room temperature for to 1000 cm. - l region. This broad band is in the correct months in the absence of oxygen, decomposes in a few region for the asymmetric BFa stretching frequency of seconds in contact with air. Preparation and measurecoordinated BFa.' The symmetric BF:l stretch, which ments were carried out in an atmosphere of nitrogen to is expected to be less intense, cannot be located with avoid oxidation. certainty, b u t , judging from band shapes, i t may fall The solid compound dissolves in alcohols giving in the region of the 823 cm.-' absorption. Due to lack solutions which initially are yellow-brown. Solutions of a suitable solvent it was not possible to obtain n.m.r. in aprotic solvents (acetone, dimethylformamide, dispectra for the adduct. chloromethane, and benzene) are deep blue or green. In order to rule out the rather unlikely possibility of The spectrum in benzene or dichloromethane solution BFa interaction with C5H5groups a comparable tensioin the 500-1800-mp region is extremely similar to the metric titration was performed with ferrocene and BF3, spectra of tetrahedral complexes such as [Co(PCy3)2but a complex did not r e ~ u l t . ~As noted previously, (iYCS)2] and [ C O ( P P ~ ~ ) ~ ( C N SIn) ~the ] . ~ 500-700mp region the solution spectra exhibit the characteristic boron trifluoride coordinated through a hydrogen multicomponent band associated with the 4A2 + 4T1 bridge can also be discounted. The remaining alter(P) transition in tetrahedral (or pseudo-tetrahedral) native is a metal-boron bond analogous to (CbH5)2\2'Ha+. Like the protonated species the BF3 adduct probably complexes.4 , 5 The spectrum of the crystalline complex involves bonding with a lone pair in a hybrid orbital does not show absorption bands in this region. Thus, directed along the twofold axis of the parent molecule the electronic spectra indicate t h a t the compound is not (Fig. 2) . 3 , 8 The similar molecules ( C ~ H ~ ) ~ ~ and I O H ? tetrahedral in the solid, whereas the tetrahedral species predominates in solution. We say predominates, (CbH5)KeH are also known to protonate with relative because there are distinctive features in the 400--500ease and may prove to have substantial affinities for mp region which strongly suggest the presence of nonLewis acids. tetrahedral species in CH2C12solution. In this region Acknowledgment.-The author is indebted to Prothe extinction coefficient of the solution is greater than fessor A . L. Allred for obtaining n.m.r. spectra and to 150; whereas i t is less than 30 for solutions of [COProfessors Allred and Basolo for helpful discussion. PCy3),(NCS)2], [Co(PEt3)2Cl?],and [ C O ( P E ~ ~ )a ~t R ~ ~ ] This work was partially supported by the Advanced the same concentration. The occurrence of both tetraResearch Projects of the Department of Defense hedral and nontetrahedral species in CH*Cl$solution is through the Northwestern llaterials Research Center. supported by magnetic and infrared measurements. ( 5 ) H C B r o w n , a n d P A . 'I'ierney, J A m Chem .Cor., 80, 1352 ( 1 9 3 8 ) . The average magnetic moment a t 25' of solid [ c o I ) F G a i n e i , I,ioi.# C'liai,r , 2 , 5 2 3 ( l g I i , j ) ,a n d references therein (PEta)a(NCS)%]corrected for diamagnetism is 2 . 3 B.M., ( ( i ) A K K a t r i t z k y , J ( . ~ P I I ? .Cor , 2049 ( I Q Z g ) , G I..CiBle a n d H. W in agreement with a low spin square-planar structure. ?'hnrni,sr,n, Pror Roq .So( ( l . o n d o n j , A810, 217 t I % : l ) , G . hl Begun a n d An octahedral spin-paired coordination would require a A A Palkr,. J . C h a i n P h y s , 38, 2 1 1 2 (19fi3) 17) In thi.: iaintl connecti9YcZ lrairs in reactions described herein as ionic, b u t up t o 4 % cis in those described as radical. (8) Suggested as a product without isolation or positive identification by G. F. Bloomfield, J . Chem. SOL., 114 (1944).
