V d . 1, No. 4, November, 1962
CORRESPONDENCE971
quite reasonable. The value of p4 is clo$er to that for NiBr,-2, 4560 cm,-', than would have been expected if the distortion were neglected. However, it is still rather high, a fact that we must ascribe to the larger covalency of the more electronegative copper ion. The ratio is 0.9, in consonance with previous experimental determinations which suggest this ratio is considerably smaller than the value of 2 or 3 predicted by Hartree-Fock metal ion functions.6 The predicted splitting of the Ta state is very large and the ground state is non-degenerate as required by the Jahn-Teller theorem. Ballhausen and Liehre have correctly pointed out that even tetrahedral CuBr4-2is strictly not a case to which this theorem applies since the spin-orbit splitting alone (m. 1000 an.-') provides a non-degenerate ground state. Comparison with the but slightly distorted ZnBr*-2 ion suggests that spin-orbit coupling is insufficient to stabilize the CuBrd-' ion against further distortion than already is provided by the lattice.
In agreement with the formulation Nb(OCH$C~S'~,the infrared spectrum reveals no absorption characteristic of the OH group, but does show an intense band at 1095 an.-' which is not due to pyridinium ion, but is typical of the C-0 stretching mode in &oxides. Furthermore, the spectrum indicates the presence of pyridinium ion and not ligand pyridine.' Magnetic studies indicate Curie-Weiss paramagnetism (Table I) and verify the presence of the niobium(1V) ion, with 4d1configuration.
Sir:
RUPERT A. D. WENTWORTH KEDZIECHEMICAL LABORATORY CARLH. BRUBAKER, JR. MICHIGAN STATEUNIVTERSITY EASTLANSING, MICHIGAN
TABLE I Ttmp.,
x'm X
OK.
loa
299 196 77
1020 1425 2700
0
61
c.rr
1.72
The compound is extremely sensitive to air, turning blue and then white. It is soluble in water and gives an immediate brown coloration and then slowly deposits a brown hydrous oxide. It is soluble with decomposition in alcohols. In dimethylformamide, solution is accompanied by a Acknowledgment.-This research was supviolet color which changes quickly to blue. It is ported by the National Science Foundation. insoluble in dimethyl sulfoxide and common or(6) H. A. Weakliem, J . Chem. Phys., 36, 2117 (1962). ganic solvents, such as benzene, ethers, and (6) C. J. Ballhausen and A. D. Liehr, J . Md. Spectry., 4, 190 ketones. (1960). By varying the organic base and the solvent, a NOYES LABORATORY OF CHEMISTRY A. G. KARIPIDES series of methoxy, ethoxy, and isopropoxy comT. S. PIPER UNIVERSITY OF ILLINOIS pounds has been obtained. They are similar, exURBANA, ILLINOIS and will cept in color, to (~y)~[Nb(0CH~)Clb], RECEIVEDJUNE25, 1962 be described in detail in a later publication. Further work will include an investigation of the distinct color differences in these compounds and the preparation of the analogous bromides, iodides, and thiocyanates. The Preparation of a Series of Compounds Containing the (1) N. S. Gill, R. H. Nuttall, D. E. Scaife, and D. W. A. Sharp Pentachloroalkoxoniobate(IV)Anion J . Inorg. Nucl. Chem., 18, 79 (1961).
We wish to report the preparation of a new class of niobium(1V) compounds. In particular, pyridinium pentachloromethoxoniobate(IV), ( p y ) ~ RECEIVED JULY 25,1962 [Nb(OCHa)Cls], has been prepared by the electrolytic reduction of NbC16 dissolved in anhydrous methanol (saturated with anhydrous H a ) , folMechanism of Alkylborane Isomerization' lowed by the addition of a hot methanol solution of pyridinium chloride. The compound, which reSir: sults after cooling for several hours, is obtained as I wish to present evidence which suggests that a red-brown, spiny, crystalline agglomerate. an intramolecular bridge hydrogen tautomerism Anal. Calcd. for (pyH)2Nb(OCHs)Clrr: C, 28.61; H, 3.27; C1, 38.45; Nb, 20.13. Found: (1) Presented at the American Chemical Society Regional Meeting, Los Angeles, Calif., December, 1960. C, 28.67; H, 3.30; Ck38.21; Nb, 20.21.
Imrganic Chemistry
972 CORRESPONDENCE
mechahism was consid&ed to accotrnt for the mechanism accounts for alkylborane isemeibaalkylisomerization. tioa more satisfactorily th&B the previously sugThe bridge hydrogen tautomerism mechanism gested dissociation-association mechanism. explains several observations with respect to Hydrogen tau torne‘rism and intramolecular realkylborane isomerization which are not satisarrangement have been observed to take place in factorily explained by the dissociation-association many electrob-deficient borm containing commechanism. pounds. Examples are: A1(8H&,2 BQ&-,’ BSH , : O ( C Z H ~ )B6H10,394 ~,~ B z H ~ - , ~BJ~ H ~ : N ( C H S ) ~ , ~(1) The bridge hydrogen tautomerism mechand 3310H14:cineo1e5~6; the Bl1n.rtl.t. spectra of 1310- anism requires that RzBH be present. UnusWlly rapid isomerization has been reported“ in cases HI$-’ and (CH3)2NBzHs.s where the olefin is too bulky to allow the forrnaWe suggest that the bridge hydrogen tauto’tion of the trialkylborane. merism mechanism in B3H8- and (CH&NBZHE,is relevant to alkylborane isomerization. (2) The addition of a small amount of diborane should increase (Zr;a rapid alkyl-hydrogen exThe hydrogens in B3HS- may be considered to change12) the concentration of R2BH present in migrate about the molecule ion in the following the system. Subsequent rapid alkyl-hydrogen manner exchange would allow all alkyl groups to exist K .HH. .H“part time” in R2BH molecules and dkylborane isomerization consequently should bq speeded up. Such atl effect for diboratle has been reporkd.lg (3) Alkylborane isomerhation proceeds a t I H H 160’ (ca. 1 hr-)in diglyme, whereas 215’ ( W W H .----.a hr.) is necessary’* in the absence of diglyme. I Diborane and diglyme react reversibly to form The B” n.m.r. spectra o€ p-dimethylamhodidiglyme:BH2+ and B s H ~ - . ~ ~ ’ ~ borane at several temperatures are compatible It is probable that the diglyme-dibrane equilwith the bridge hydrogen tautomerism mechanism ibrium is such that the last traces of diborane are about the bomn-boron-nitrogen skeleton d t h u g h not easily removed, therefore a small amount of other processes also have been suggestdS diborane is retained which catalyzed the isonlefiOne might speculate that an electron-deficient zation reaction as in (2) above. (and isoelectronic) system of boron, carbon, and It is probable that alkylalurnkane isomerizahydrogen atoms also could tautornerize. For tionl6vl7 and certain rearrangements and hydrogen exampk, di-Bbutylborane could rearrange via a migration in carbonium ions also take place vk a tautomeric process. bridge hydrogen tautomerism mechanism.
This intermediate structure was suggested previously to account for the cis addition of BH3 groups to the double bond in the hydroboration of olefin^.^ However, the dissociation-association (2) R. A Ogg and J. n. Ray, Discussions Faraday Soc., 19, 239 (1955). (3) W. N. Lipscomb, Advan. Inwg. Chcm., 1, 139 (1959). (4) R. E.Williams, J. Inorg. Nucl. Chcm., 20, 198 (1961). (5) R. E. Williams, 140th National Meeting of the American Chemical Society, Chicago, Illinois, September, 1960. (6) R. 3. F. PalchbTt, J. H.Namaf~,ah6 R. E. Wikiams, Y. Am. C h m . Soc., 88, 3380 (1961). (7) This conclusion also was made independentIy by Dr. R. L. Williams, Admiralty Materials Laboratory, Dorset. England. (8) W. D. Phrtlps, € C. I. M i l k , and E. L. Mu&r€ies, J . Am. Chew SOG.,81, 4496 (1959).
(9) H.C Brown and G . Zweifel, ibid., 81, 247 (1959). (10) H.C. Brown and B. C. Suba Rao, iMd., S I , 6434 (1959). (11) H.C. Brown and G. Zweifel, ibid., $2, 4708 (1960). (12) H.I. Schlesinger and A. A. Walker, ibid., 67, 621 (1935). (13) G. Zweifel, Tetrahedron, Z, 117 (1961). (14) G. F. Hennion, P. A. McCusker, E. C. Ashby, and A. J. Rutkowsky, J . A m . Chem. Sod., 79, 5190 (1957). C. I. Brown and P. E. Tierney, i b i d . , 80, 1552 (1958). (15) € (16)R.Ziegler, Brennstof-Chcm.,SQ, 321 (1954). (17) K. Ziegler, “Metal-Organic Syntheses,” in “Perspec~vesin Organic Cbemistry,” A. Todd, ed., rntersdence Publ., New York, N. Y.,1956.
SPACE-GENERAL CORPORATION ROBERT E. WILLIAMS EL MONTE,CALIFORNIA RECEIVED FEBRUARY 23, 1962
The Reaction of Dioxygen Difluoride with Tetmfluoroethylene Sir: Bbrygen difluoride, OzFz, discovaed by Ruff and Menzel,’ melts at - 163.5’ to a red liquid; it
