July 5, 1958
COMMUNICATIONS TO THE EDITOR
3479
analog of the substitution reactions a t the saturated carbon atom in the P-branched alkyl series (Et, Pr, i-Bu and neopentyl) where the decrease in rate along the series invariably is attributed to a steric effect. I n the latter series the relative rates of substitution (bromide for isotopic bromide) are6: 100, 65, 3.3 and 0.0015. The comparison between the two series provides striking evidence of the similarity of the geometrical arrangement of the transition states for substitution a t carbon and a t sulfur. Just as in the carbon analog, it is seen easily that steric hindrance, and the consequent drop in reactivity, is justified only if the entering group attacks the central atom from the back side. If attack were possible from other directions, either making an angle of 90" or 120°, no such decrease could be justified. It must then be concluded that the linear arrangement is quite strongly favored. It may be observed that this arrangement is also the most favorable from the viewpoint of electrostatics. However, elementary considerations show that electrostatics alone would provide but a minor contribution to the total free energy difference between the various arrangements.
served by Klemm and Bommer in the rare earth elements is duplicated in the hexaborides. Efforts also were made to prepare EuB4, but, although preparative conditions (including reaction temperatures and specimen compositions) were varied over wide ranges, these were uniformly unsuccessful. When reaction occurred, the product invariably contained large amounts of EuBBwith no signs of a tetraboride. It appeared likely that the failure to prepare EuB4 is related to the large effective size of the metal atom. As a check on this hypothesis, efforts were made to prepare LaB4.. After a number of failures, it was found possible to prepare LaB4 of a satisfactory purity by reaction of lanthanum metal with boron in vacuum a t about 1300". The LaB4 phase, like EuBe, appears to have a wide range of homogeneity. Compositions containing from two to four parts of boron per metal atom yielded products containing the LaB4 phase as a major component. When the boron content was less than that corresponding to L'LaB2,''or when lanthanum oxide was used as a starting material, no LaB4 was formed. Lattice dimensions of LaB4 did not appear to vary significantly with composition. The unit cell (13) P. D . B. d e l a Mare, J . Chem. Soc ,3180 (1955). DEPARTMENTS OF GENERAL AND OF is tetragonal with a = 7.30 A. and c = 4.17A. It is ORGANIC CHEMISTRY, AND CENTER ANTOSINO FAVA isomorphous with CeB4 and other rare earth tetraOF NUCLEAR CHEMISTRY ANTONIOILICETO borides3 UNIVERSITY OF PADUA,ITALY I t appears in view of our experience with LaB4, RECEIVED MAY16, 1958 that it may be possible to prepare EuB4 by direct reaction of boron with metal; the latter, unforEUROPIUM HEXABORIDE AND LANTHANUM tunately, is not presently available to us. TETRABORIDEI DIVISIONO F APPLIED PHYSICS EDWARD J. FELTEN Sir: BROOKLYN POLYTECHNIC INSTITUTE IRABIXDER It is well known2 that the effective atomic radii BROOKLYN, N. Y. BES POST of the rare earth elements decrease regularly with RECEIVED MAY16, 1958 increasing atomic number, with the exceptions of Eu and Yb. SIMULTANEOUS REDUCTION OF DIPHOSPHOPYRIIn a recent paper3 i t was pointed out that the lat- DINE NUCLEOTIDE AND OXIDATION OF REDUCED tice constants of the cubic rare earth hexaborides FLAVIN MONONUCLEOTIDE BY ILLUMINATED BACTERIAL CHROMATOPHORES1 also decrease with increasing atomic number of the metal atoms, with the significant exception of YbBe. Sir: No data for europium borides were then available. The direct spectroscopic observation of light inI t was also noted that the rare earth tetraborides duced reduction of pyridine nucleotides by chloroshowed no such anomalies; the lattice constants of plasts has been de~cribed.5~A similar reduction of these compounds, including YbB4, decrease mono- DPN* can be observed with chromatophores from tonically with increasing atomic number of the Rhodospirillum rubrum under highly anaerobic metal atom. conditions on illumination with red light. PuriRecently a quantity of Euz03 of high purity was fied chromatophores5 were used in this study to made available to us and efforts were made to pre- minimize dark reduction of DPN or T P N which pare EuB6 and EuB4. The former was readily pre- may occur in crude preparations. It can be seen pared by heating the metal oxide with the appro- from Table I, 4, that in the reaction system depriate amount of boron; BzOZ was evolved and the scribed there is a close molar equivalence of DPN hexaboride remained in the reaction chamber. reduced and of FRZNH2 oxidized; furthermore, Reaction products were studied primarily by X-ray this equivalence holds for the much slower reverse diffraction methods. The compound exhibited a reaction in the dark. FMNH2 also can be reconsiderable range of homogeneity; the lattice ( 1 ) T h i s investigation was supported by the Graduate School of t h e constant ranged from 4.170A. for preparations University of Minnesota a n d by the National Science Foundation G-1922). somewhat deficient in boron, to 4.184A. for prep- (Grant (2) A. San Pietro and H . hf. Lang, Science, 124, 118 (1956); J . Biol. arations containing excess boron. The lattice con- Chem., 281, 211 (1933). (3) D. I. Arnon, F. R. Whatley and M. B. Allen, Koture, 180, stant of apparently stoichiometric preparations Science, 127, 1026 (1958). was 4.178A. I t is clear that the size anomaly ob- 182(4)(1957); Abbreviations used: D P N , D P N H , respectively, for oxidized (1) S t u d y supported by the Ofice of Naval Research. (2) W Klemm and H. Bommer, Z . anorg. Chem ,231, 138 (1937). (3) B Post, D Moskowitz and F. W. Glaser, THIS J O U R N A L , 78, 1800 (1950).
and reduced diphosphopyridine nucleotide; T P N for oxidized triphosphopyridine nucleotide; FMN, FMNHz, respectively, for oxidized and reduced flavin mononucleotide. (5) A. W. Frenkel, J. B i d . Chenz., 222, 823 (19.X).
COMMUNICATIONS TO THE EDITOR
3480
placed by succinate, in which case photoreduction of DPN proceeds several times faster than in the presence of F M N H z ; here again T P N cannot replace DPN.
Vol. 80
THE REACTION OF PHOSPHINE METHYLENES WITH BORON HYDRIDES
Sir: Triphenylphosphine methylene (I, (CsHs)3PfCH2-) may be regarded as a carbanion stabilized by T TABLE I bonding of the unshared pair with adjacent phosRATESAND REQUIREMENTS OF LIGHTINDUCED OXIDATION- phorus orbitals. It therefore appeared probable REDUCTION REACTIONS that this material would interact with electron(Rates in pmoles per hr. per pmole chlorophylla) deficient boron hydrides such as diborane and deAll preparations made up to 3.0 ml. in 0.1M glycylglycine caborane to produce compounds containing P-C-I3 (pH 7.5) (chlorophyll content of chromatophores from 0.02 bonding. to 0.025 pM.). Further additions as indicated: DPN, Diborane Reactions.-Addition of gaseous diTPIV 0.7 p M . DPNH, 0.1 pM. FMIV, 0.15 p M . FMSHz (catalytically reduced with Hz), 0.05-0.15 pM. Samples borane to an ethereal solution of I in diethyl ether degassed in anaerobic cuvettes. a t room temperature resulted in rapid decolorizaDark period following tion and the deposition of triphenylphosphine -Light-illuminationSubs. Re- OxiSulis. Re0 methylene boron trihydride (11, (CsHs)aP+CHzAdditions meas. duced dized mens. duper1 dizel BHa-). The product, 11, proved to be stable 1 FMN FMN 0.0 toward water and was recrystallized easily from 2 FMNHz FMiYH2 . . . 0 . 3 FM.INH? . . . 0 . 3 methylene chloride-diethyl ether solution. Hy3 DPN + drolysis with aqueous hydrobromic or hydroDPNH DPNH . . . 0 . 2 DPSH . . . 0.2 chloric acids afforded three moles of hydrogen per DPX 9 . 1 . . . DPXH . . 0.6 4 DPN + mole of boron trihydride and the corresponding FMNHz FMNHz . . . 9 . 5 FMS 0.6 . . . triphenylmethylphosphonium halide. 5 4(+ D P S H DPNH . . . 0 . 6 DPYH . . . 0 . 6 ,
+
FMN FMN 0 . 6 . . . FMN 0.6 . . . formed in the light) heated 2 min. at 60" 6 TPN TPhT 0.0 FMKHz FMSHz . . . 0 . 3 FMKH? , . , 0 . 3 a Concentration changes measured a t 15-20' with a Reckman DU Spectrophotometer. Actual changes in optical density a t 340 mp of the order of 0.1 zt 0.005 unit for an initial 10 min. period of illumination (initial o.d. 0.5-0.8); dark values of the order of 0.01 j=0.002 unit per hour. F M K measured a t 455 nip, Difference spectra kindly measured by Dr. V. Lorber.
+
C B H ~ 'CH3BHaSP
+ 4HX
Hz0 ------f
+
(CGH~)BP+CHBX-3H2
+ BX?
Iodine was reduced to iodide ion and silver ion was reduced to silver metal by I1 in alcoholic solution. Table I presents the preparation data and properties of I1 and two other triphenylphosphine methylene boron trihydrides which have substituents on the methylene carbon. Each of these compounds displayed strong B-H stretching bands a t 4.40 and 4 . 5 0 ~ . TABLE I PROPERTIES O F TRIPHESYLPHOSPHINEMETHYLENE BOROSTRIHVDRIDES
The purified chromatophores, without any added enzymes, can carry out either photophosphorylations or photoreduction of DPN or both reactions simultaneously; photoreduction of DPN is partially inhibited when photophosphorylation occurs a t the same time. Vernon6 has described a system from R. rubrum, fortified with a number of enzymes, which preferentially photoreduces T P N (as indicated by suitable trapping agents); it is hoped that the basis for this difference in pyridine nucleotide specificity can be ascertained soon. The pyridine nucleotide specificity and the high lability of the system make i t plausible that one is dealing with an enzymatic reaction and not simply with a non-enzymatic, chlorophyll sensitized reaction.' Thus, the simultaneous stoichiometric reduction of DPN and oxidation of FMNHz in the light represent a reaction in bacterial preparations analogous to the Hill reaction of illuminated chloroplasts1t2(cf. 8).
PREP.4R.4TION
AND
A c a d . Sci. U S . S . R . ,6 7 , 32.5 (1949). ( 8 ) L. P . Vernon and hZ. D. Kamen, A r c h . Aiochem. Biobhys., S1,
(1) E. LViberg and P. Strebel. A n i $ . ,607, Y (1937). ( 2 ) Obtained from American Potash and Chemical Co , Henderson, Pievada.
R in (CsHs)rP*CHRBHa
hl.p., OC.
H CHB CbHs
191-192' 171-1 72" 143-li-L0 C
H CH3 CeHj
Vo Yield from Moles Hz (CsHa)aP+CHzRBr M o l e Compd.
Calculated, 5% H B
78.65 6 . 9 5 3.72 78.97 7 . 2 9 3 . 5 6 81.98 6 . 6 1 2 . 9 3
45 38 42
3 02
2 98 2 90 C
F o u nH d . "0
B
78.40 7.16 3.50 78.80 7 . 2 1 3.71 81.62 6 . 6 8 3 . 1 8
The formation of I1 from I and diborane is in sharp contrast to the results of Wiberg and Strebell who reported the reaction of ethylmagnesium halides and diborane to produce triethylborane and magnesium halohydrides, HXgX. Decaborane Reactions.-The addition of an ethereal solution of decaborane2 to a similar solution of I produced an oil which crystallized 011 standing to give a 35y0 yield of bright yellow DEPARTMENT OF BOTANY rhombs (111). The product was recrystallized easily VSIVERSITY OF MINSESOTA ALBERTU'. FRESKEL from methylene chloride-diethyl ether. m.p. 127hIINSEAPOLIS 14, MINNESOTA 129'; C19HelBloP(found: C, 56.8; H , S.01: I), RECEIVED M A Y 8, 1958 25.9; P, 7.GO. Calculated: C, 57.23; 11, 7.S4; ( 6 ) L. P . Vernon. THISJ O U R N A L , 80, 2.46 (1858); F e d e r a t i o ~Proc., B, 27.11; P, 7 . 7 ) . The infrared spectrum of I11 17,3 2 8 (19B8). contained B-H stretching a t 4 . 0 5 ~(terminal) and ( 7 ) A. A. Krasnovskii and G. P . Brin, Compl. Rend. ( D o k l n d y ) 1 2 2 (185.4).
