935
Chemistry of Boranes. XXW.' Inner Diazonium Salts 1910-B10H6(N2)29
and -B1016(N2)2
-B10c18(N2)29
W. H. Knoth
Contribution No. 1145f r o m the Central Research Department, Experimental Station, E. I . du Pont de Nemours and Company, Wilmington, Delaware 19898. Received October 4, 1965 Abstract: Reaction of B,oHlo2-with excess nitrous acid followed by reduction gives 1,10-BloHs(Nz)2.This inner
diazonium salt is a useful synthetic intermediate because the nitrogen can be replaced by a variety of nucleophiles. The halogenated analogs l,10-BloC18(N2)z and 1,10-Blo18(N2)2 have also been prepared. Evidence is presented for apical-apical conjugation in certain BloHlo2-derivatives.
A
romatic diazonium salts have long been of interest principally because of their synthetic versatility. Inorganic counterparts, species in which molecular nitrogen is bonded to an element other than carbon, have not been known except for the special case of azides. In a preliminary communication,2 we outlined the synthesis and chemistry of the first inorganic diazonium compound, 1,10-BloHs(Nz)z,a species which is actually an inner salt, +NzBlo2-HsN2+. Succeeding article^^-^ from this laboratory have described other inorganic diazonium compounds and cations such as I , ~ - N Z B I O H ~ N ( C H1,10-N2BloHaS(CH3)2,4 ~)~,~ and 1(CH3)2SB10H7-6-NH310-Nz+,jall of which are also derivatives of BloHloZ-. Their article reports in detail the chemistry of 1,10-BloHs(N2)2and of its halogenated analogs 1,10-BloCIE(Nz)z and 1,10-Blo18(Nz)z and discusses correlations between their chemistry and that reported for the other inner diazonium salts of BloHlo2-. Preparation and Characterization. The reaction of an aqueous solution of (NH4)2B10H10 with excess nitrous acid is immediate and exothermic, with the accompanying separation of a brown solid. This solid is very hazardous because it detonates extremely readily when dry. However, it is readily reduced by zinc and hydrochloric acid, or preferably by sodium borohydride in alcoholic solution to give the nonexplosive 1,lOBloHs(Nz)~. Reaction of zinc and hydrochloric acid with the aqueous filtrate from separation of the explosive intermediate gives additional amounts of l,lo-BloHs(N~)~ for a total yield of 15-25 %. Although the exact course of this reaction is not known, it may be related to that of the direct preparation of organic diazonium salts by reaction of organic aromatic species, preferably activated ones, with excess nitrous acid.6 This relationship is probable in view of the general similarity between BloHlo2- chemistry2r7-9 (1) Part XXV: H. C. Miller, W. R. Hertler, E. L. Muetterties, W. H. Knoth, and N. E. Miller, Inorg. Chem., 4, 1216 (1965). (2) W. H. Knoth, J. C. Sauer, H. C. Miller, and E. L. Muetterties, J . Am. Chem. SOC.,86, 115 (1964). (3) W. R. Hertler, W. H. Knoth, and E. L. Muetterties, ibid., 86, 5434 (1964). (4) W. H. Knoth, W. R. Hertler, and E. L. Muetterties, Inorg. Chem., 4, 280 (1965). ( 5 ) W. R. Hertler, W. H. Knoth, and E. L. Muetterties, ibid., 4, 288 (1965). (6) J. M. Tedder and G. Theaker, Tetrahedron, 5 , 288 (1959). (7) W. H. Knoth, H. C. Miller, D. C. England, J. C. Sauer, G. W. Parshall, and E. L. Muetterties, J . Am. Chem. SOC.,84, 1056 (1962). (8) W. R. Hertler and M. S. Raasch, ibid.,86, 3661 (1964). (9) W. H. Knoth, J. C. Sauer, D. C. England, W. R. Hertler, and E. L. Muetterties, ibid., 86, 3973 (1964).
and organic aromatic chemistry. Tedder and Theaker6 have hypothesized possible reaction schemes such as the following for the direct formation of organic diazonium salts. ArH
+
HONO
- ArNO
NO
Ar-N-N=O
NO -+
I
0. Ar-N-N=O
%
GO\. /
+. Ar-N=NON02
+
ArNzi,N03-
*
N=O
A scheme such as this may be applicable, in part, to the present case. The obvious differences are that, while the organic system spontaneously proceeds to completion, the formation of 1,10-B10Hs(Nz)~ requires a reduction step, and that it is readily demonstratable that at least two intermediates (water-insoluble and water-soluble) are involved in the latter preparation. At most, therefore, only the initial stages of Tedder's reaction scheme can be applied to our system, the Blo intermediates apparently being more stable than those in the organic system. It would be expected that any intermediate similar to those above would be explosive, as is observed, and that any of the intermediateslO after the first would be readily reducible to a diazonium compound. A second preparation of l,lO-BloHs(Nz)zconsists of diazotization of 1,10-BloHa(NHz)22-. Unfortunately this is of no present synthetic value since the diamine is prepared from the diazonium compound. It is of interest, however, as additional evidence for the structure of the diazonium compound and because of the contrast in the conditions required for this diazotization and those of the corresponding halogenated diamines, 1,10-BloCls(NH2)22- and 1,10-BloI~(NHz)22-. Aqueous diazotization does not succeed with 1,lOBloHs(NH2)22-,possibly because the concentration of these anions in aqueous acidic solution is negligible because of the extremely weak character of the conjugate acid l,lO-BloH~(NH&([~KJcH~cx = 12.211). (lo) The only direct evidence as to the nature of the explosive, waterinsoluble intermediate is a strong band in the infrared at 2380 cm-1. It has been suggested by Professor R. C. Lord that this may be due to an NOZ+cation. A strong absorption band at 2360 cm-' for NOS+ in NOZBF~, NOZPF~, and NOzSbF6 has been reported: D. Cook, S. J. Kuhn, and G. A. Olah, J . Chem. Phys., 33, 1669 (1960). (11) We are indebted to Dr. J. S. Fok, who has determined the pK values for a number of BioHloZ- amine derivatives, for allowing us to use these results prior to publication.
936
rT
T
-
T
,
,
,
,
,
,
,
nucleophiles. Derivatives of BloHlo2- have been prepared which bear dimethyl sulfide,j amines,* or acetonitrile as ligands, but although it might be expected that these would be readily displaceable by stronger nucleophiles, such is not the case. A pertinent example is the previously reported4 reaction of 1,lON ~ B ~ o H ~ S ( Cwith H ~ ) ~pyridine to give 1, 10-C:HjNBloHsS(CH&. The dimethyl sulfide is not displaced by pyridine in this system, although such a displacement readily occurs in the reaction of B10H12.2(CH3)2S with pyridine.': The facile displacement of nitrogen Figure 1. Infrared spectrum (KBr wafer) of l,10-BloHs(N2)2. by nucleophiles is common to all the BloHlo2- diazonium derivatives studied thus far.?-j In this work, the reactions of 1, lO-BloHs(N& with ammonia, hydrazine, Diazotization can be achieved by the reaction of acetonitrile, pyridine, and carbon monoxide have given Na2B10H8(NH?)2 with nitrosyl chloride in glyme. The the corresponding 1, 10-BloHs(ligand)s species. l G Simyield is low, presumably because the by-product water ilarly reaction of the chlorinated diazonium salt with hydrolyzes unreacted anion to l,10-BloH8(NH3)2, thereby carbon monoxide and with hydrogen sulfide gave 1,iOrendering it inert. The electron-withdrawing effect l 2 Bl0Cls(C0)2'~ and 1, 10-BloCls(SH2)2, respectively. Disof the halogen substituents in 1,10-BloC18(NH3)22 and placement reactions were also observed with azide ion 1,10-Blo18(NH3)P13 make these more acidic ([pKalCHaCN and hydroxide ion as described below. for 1,10-BloCls(NH3)2= 10.911)than 1,10-BloH8(NHa)2. In studies of the displacement products, ionization of The concentration of the corresponding halogenated 1, 1O-BloH8(NH3)2la was demonstrated by precipitation of diamine anions in aqueous solution is appreciable, and the nearly insoluble thallium salt of l,10-BloHe(NH2)s2reaction with nitrous acid in conventional fashion from basic solution. Ionization of 1, 10-BloC18(SH2)2 proceeds readily to give good yields of l,10-BlaClg(N2)s was demonstrated by preparation of the cesium salt of and 1, 10-BloIs(Nz)z. The hemidiazotized product 1,lOl,10-B&1~(SH)22-. In addition, 1,10-BloH8(NCCH3)2 H3NBloClsN2has also been isolated. was found to hydrate readily to form l,10-BloH8In common with other derivatives of BlOHl0?-, (NH2COCH&, similar to the previously reported l,lO-BloHa(N& has unusual hydrolytic and oxidative facile hydration of BI2Hl1NCCH3-. A very diverse stability for a boron hydride derivative. It is a colorchemistry was found for l,10-BloH8(C0)21i and for the less, crystalline solid, stable toward air, water, dilute chlorinated carbonyl; this was outlined earlier2 and will acid or base and is not oxidized by alcoholic silver be reported in detail in a subsequent article.I3 nitrate. It sublimes readily at 100" in V U C K O and is The reactions of 1,10-BloHa(N2)zwith molecular soluble in common organic solvents including benzene ; nucleophiles were run at 125-140" with no solvent other it is insoluble in water. It begins to decompose at than excess reagent. This is advantageous where about 125" in a sealed tube. The perhalogenated feasible because additional solvents can lead to undiazonium compounds, 1,10-BloC1s(N2)2 and 1,lOexpected products in these reactions. For example, if B1018(N&,have greater thermal stability ; they begin to cyclohexane is present in the carbonylation reaction, decompose at about 180 and 160°, respectively. As in the major products obtained are C6HllBl0H7(C0)2and other halogen derivatives of B10H102-,14 the boronI , 10-BloHg(CO)2 with minor amounts of (C6H11)ehalogen bonds in these compounds are quite resistant to BloHG(CO)a also being formed. The stereochemistry of hydrolysis, and no cleavage of these bonds has been obthe cyclohexylated products is unknown as is the mechserved. anism of their formation. However, certain speculaThin layer chromatography has indicated that the tions can be made. They are almost certainly formed B,oHs(N2)2species under consideration consists essenin a radical reaction. The radical initiator may be tially of only one isomer, and the stereochemical NPBIOHg or BloHs existing in the triplet state as finiteassignment of this as the 1,lO-(bis-apical) isomer follows lived intermediates. This possibility is suggested by the readily from its B" nuclear magnetic resonance specobservation that nitrogen is evolved when 1,lQ-Biotrum. The infrared spectrum (Figure 1) has a strong HY(N& is heated alcne at 125-150", coupled with the band at 2530 cm-I for the B-H stretching and one at fact that carbon monoxide is a notoriously poor nucleo2250 cm-' for the -N=N stretching mode. The latter phile which would not be expected to participate in absorption is shifted to 2280 cm-1 in 1,10-BloC18(N2)2 nucleophilic attack. Furthermore, although the reand l,10-Blo18(N2)2,possibly as a result of inductive action of l,10-BloH~(N2)2 with carbon monoxide proelectron withdrawal by the halogen substituents. ceeds readily at 140", the reaction of the chlorinated Reactions. The nitrogen group is a valuable ligand diazonium salt with carbon monoxide does not proin BloHlo2-chemistry because it is the only ligand yet ceed at this temperature but does occur at 200". This is found that is readily displaceable by a variety of (12) Inductive electron withdrawal by halogen substituents on BloHla*- derivatives has also been demonstrated by infrared comparison9 of BloH~cOcsH5~with BIOC~SCOCOHF,and by comparison of nucleophilic cleavage of boron-sulfur bonds in BIOH~[S(CH~)& with cleavage of those in BloH~Cls[S(CH3)21?.~ (13) W. H. Knoth, J. C. Sauer, J. H. Balthis, H. C. Miller, and E. L. Muetterties, to be published. The preparation parallels that of 1,lOBloCIs(NH3)z. (14) W. H. Knoth, H. C. Miller, J. C. Sauer, J. H. Balthis, Y . T. Chia, and E. L. Muetterties, Znorg. Chem., 3, 159 (1964).
Jourrial of the American Chemical Society
88:s
(15) W. H. Knoth, unpublished. This reaction has been explicitly predicted (R. J. Pace, J. W. Williams, and R. E. Williams, J . Chem. Soc., 2196 (1961)) based on work on related displacement reactions (Pace, et al., above; also M. F. Hawthorne and A. R. Pitochelli, J. A m . C h m . Soc., 80, 6685 (1958)). (16) Except that the hydrazine reaction rather surprisillglg gave HaNBioHsNsH4. (17) W. H. I
