1448 Inorganic Chemistry, Vol. 12, No. 6, 1973 c F 3 - y ~ f-CF3
CF3-
7 ‘7-
Notes C F,
Acknowledgment. The authors are grateful to the National Science Foundation (Grant GP-28634) and the Robert A. Welch Foundation for generous financial support.
Contribution from the Department of Chemistry, University of Southern California, Los Angeles, California 90007
4b
4a
tene ring and an iron-iron bond as indicated in 4b. The electronic spectrum of 4 (Table 11) displays pronounced shifts compared with free 1 ;6 however, this evidence per se is not sufficient to establish the scission of the P-P bond. On the basis of these initial observations it would appear that the ligand behavior of 1 is quite different from that of 1,2-bis(trifluoromethy1)dithietene since there are no sulfur analogs of 3 or 4.2 Compound 4 is also noteworthy from the standpoint that all previously reported Fe3(CO) complexes involve bridging CO groups.’ The reaction of the cyclotetraphosphine, (CF3P)4, with Fe2(C0)9 results in a product of empirical composition (CF3P)2Fe(C0)3. If the intense mass spectral peak at m/e 680 (Table I) is assigned to the parent ion. the molecular formula of 5 is (CF3P)4Fe2(C0)6. The m/e 680 peak is considered t o be the parent peak because West, et ~ l . , have ~ ’ ~ demonstrated that several other compounds of the general type (Khf)4Fe2(C0)6 (M = P, As; R = alkyl, aryl) exhibit intense molecular ion peaks. The correctness of these mass spectral assignments was confirmed by a subsequent X-ray crystallographic study” of (CH3As)4Fe2(C0)6. One additional mass spectral feature which 5 shares in common with other (RM)4Fez(C0)6 corn pound^^'^ is a fragment corresponding to the species (RM)4Fe2+. Furthermore, like the compounds reported by West, et a1.,3’9 5 exhibits four intense ir bands in the C-0 stretching region. The latter observation appears to be a characteristic feature of phosphido and arsenido bridging” and may be due to coupling between the two Fe(CO)3 groups. By analogy with the bis(arsenid0)bridged structure of (CH3A~)4Fe2(C0)6the most reasonable structure for 5 is
Displacement of Diborane from Bentaborane(9) by Strong Molecular Bases Anton B. Burg
Received November 15, 1972
It has been demonstrated that the weak base dimethyl sulfide can act upon B5H9 to displace a BH3 group as diborane or (CH3)2SBH3.1 It appeared that the driving force of the reaction was the attachment of (CH3)2S to the remarkably strong Lewis acid B4H6 (through cleavage of two B-H-B bridges to remove one BH3 from B5H9);then the resulting (CH3)2S-B4H6 complex would rapidly convert to unintelligible resins. The reaction thus was related to earlier work on the action of (CH3)2NBH2 upon B5M9,whereby the displaced BH3 group appeared as (CH3)2NB2Hs.2 More generally, it was assumed that any strong molecular base would capture each BH3 group as soon as it was free, so that proof of the initial displacement of BH3 from B5H9 would be more difficult than in the dimethyl sulfide case. It now is found, however, that the relatively strong bases ammonia and methylamine, reacting with B5H9 during sudden heating at 160-180”, can displace as much as 0.25 B2H6 per B5H9 consumed. Thus we have interesting reactions in which strong bases act to liberate the strong Lewis acid diborane; that is, bases strong enough for irreversible attachment t o BH3 actually liberate this Lewis acid by action upon B5H9. The final volatile products of these reactions included the borazine (HNBH)3 or (CH3NBM)3 and the unstable p-aminodiborane H2NB2H5or CH3NHB2H5.3’4 Thus steps such as the following may be suggested for all such reactions
+ B,H, BH, + B,H,.nNH, +resins + H, NH, + BH, H,NBH, H, t H,NBH, H,NBH, + BH, H,NB,H, 6H,NB,H, 3B,H, + 2(H,NBH,), 3(H,NBH,), 3H, + (HNBH),
nNH,
+
-+
-+
oc’
‘co 5
+
+
-+
The above structure is also consistent with the fact that two equally intense resonances are observed in the 19F nmr spectrum of 5 . The “deceptively simple” appearance12 of these resonances is due to the second-order nature of the nuclear spin coupling within the (CF3P)4 moiety. Registry No. Fe2(C0)9, 15321-51.4; (CF&CZPZ(CF~)ZFe(C0)4, 39262-37-8; (CF3)2C~P~(CF3)2Fe3(CO)lo, 391 5336-1 ;(CF3P)4Fe2(C0)6,391 53-37-2. (8) W. R. Cullen, D. A. Harbourne, B. V. Liengme, and J . R. Sams, Inorg. Chem., 9, 702 (1970); P. J. Pollick and A. Wojcicki, J. Organometal. Chem., 14, 469 (1968). (9) P. s. Elmes and B. 0. West, Coord. Chem. Rev., 3, 279 ( 196 8). (10) B. M. Gatehouse, Chem. Commun., 948 (1969). (11) J. Chatt and D. A. Thornton, J. Chem. Soc., 1005 (1964). (1 2) R. J. Abraham and 13. J . Bernstein, Can. J. Chem., 39, 2 1 6 (1961); R. K. Harris, ibid., 42, 2275 (1964).
(1) (2)
(3)
(4) (51
Steps 1-3 would be fast and irreversible, leading to products known t o be unstable in the sense of steps 4 and 5. On the assumption that these are the only processes which occur and that step 4 is complete, one would predict the formation of 0.25 B2H6 per B5H9 consumed, in good agreement with the results for the ammonia reaction. For methylamine, however, step 4 is far from complete (because the p-aminodiborane is more stable), but the yield of diborane still can ( 1 ) I. B. Mishra and A. B. Burg, Inorg. Chem., 9 , 2188 (1470). (2) A. B. Burg and J . S. Sandhu, J. Amer. Chem. SOC., 89, 1 6 2 6
(1967). (3) A. B. Burg and C. L. Randolph, Jr., J. Amer. Chem. SOC.,71, 3451 (1949). (4) C. L. Bramlett and A. T. Tabereaux, Inorg. Chem., 9 , 978 (1970), reported CH,NHB,H, as a product o f the CH,NH,-BSH, reaction at far lower temperatures (25-100’) but mentioned diborane only as a trace product of their l Q O o pyrolysis of this aminodiboratie.
Notes
Inorganic Chemistry, Vol. 12,No. 6, 1973 1449
Table I. Base-Pentaborane(9) Flash Reactions mmol of reactantsa B,H,
Base
3.362 -1.600 1.762 2.454 -1.291 1.163 2.717 -0.915 1.802 2.072 -0.210 1.862 0.847 -0.619 0.228 0.981 -0.177 0.804 3.310 -0.773 2.537 5.230 -2.083 3.147 2.352 -0.107 2.245 2.341 -1.334 1.007 2.124 -1.130 0.994 1.892 -0.262 1.630 2.811 -1.390 1.421 1.497 -0.361 1.136 0.395 -0.275 0.120 -
_
_
Time, min
Ttmp, C
Tube vol, ml
H,
BzH,
mmol of products Others
6.56 NH,
4
180
80
10.756
0.184
1.07 (HNBH), , etc.
4.539 NH,
5
163
80
6.634
0.292
5.371 CH,NH,
10
160
80
(Lost)
0.460
0.596 (HNBH), 0.067 H,NB,H, 0.09 B in X 1.065 (CH,NBH), 1.053 CH,NHB,H,
5.635 CH,NH,
5
170
70
4.707
0.296
1.052 (CH,NBH), 1.851 CH,NHB,H,
0.872 CH,NH,.BH, 0.029 CH,NH,
4
167
50
0.928
0.058
0.060 (CH,NBH), 0.506 CH,NHB,H,
2.101 CH,NH, (combined
