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22 Cyclic Boron Compounds VII. Cyclic Boroureas and Borocarbamates RICHARD H. C R A G G and MICHAEL F. LAPPERT

Downloaded by HARVARD UNIV on May 27, 2014 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch022

Department Manchester,

of Chemistry, England

Faculty

of Τechnology,

University

of

Manchester,

Cyclic boroureas have been prepared by reaction of phenyl isocyanate with either B, B',B"-tris (diethylamino)borazine, (Et Ν· Β· NEt) , or tert -butylamino bis(diisopropylamino)borane, (Pri2 N) Β· NHBu . Similarly, from tris (tert-butylamino) borane, B(NHBu ) , and carbon dioxide, a cyclic borocarbamate has been obtained. Analogous ex amples of aminoboration of phenyl isocyanate and phenyl isothiocyanate using tris(tert-butylamino) borane, affording acyclic derivatives, B[N(Ph)· C(:X)· NHBu ] , (X = Ο or S), have been demonstrated. Structures have been confirmed by alcoholic degradations and infrared spectra. It is suggested that the mechanism of the reactions from aminoboranes involves successive addition and elimination steps. 2

3

2

t

t

t

3

3

VU hile this work was in progress (6), we became aware of the experiments of others, which also involve aminoboration of organic isocyanates and/or isothiocyanates. Thus, -trimethylborazine, (MeB-NH) , with isocyanates gave (Equation 1) cyclic boroureas (4). This has been confirmed, although the possibility of various alternative and structurally isomeric species was recognized (3). Other examples —e.g., Equation 2 (6) — of aminoboration of isocya nates and isothiocyanates have been described (3, 6, 7, 8). 1 1

Me (Me* Β· Ν· H)

Q

+ 6RNCO

•

HEr

^NR

I

(1)

ι

OC

CO R

l l T "

V N H B ^ + PhNCO ^ l l T "

V-N

- eft

220

In Boron-Nitrogen Chemistry; Niedenzu, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1964.

(2)

22

CRAGG

AND

LAPPERT

Cyclic

Boroureas

221

The present work also forms part of a program on the boration re actions of unsaturated compounds. Thus, initially it was shown that chloroboration and phenylboration of certain olefins could be effected (10); and later, that this could be extended (Equation 3) to phenyl isoand isothiocyanates (12). Relevant to aminoborations are observations that aminostannanes, such asMe Sn-NMe , and other metal- or metal loid-amino derivatives react—e.g., Equation 4—with many unsaturated compounds, including phenyl iso- and isothiocyanates, in an analogous fashion (5, 9). 3

2

BXYZ + 2ArNCO

-* Ar - Ν

ι Downloaded by HARVARD UNIV on May 27, 2014 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch022

Ζ - Β

ι

\X

Ar - Ν Me Sn- NMe 3

2

+ U = Q -»

(3)

ο

Me Sn - U - Q - NMe^

() 4

3

Acyclic boroureas (13) and borourethanes (14) have been made i n dependently by other methods, the former from isocyanatoboranes and amines, and the latter from aminoboranes and organic urethanes. Discussion Reactions leading to cyclic boroureas and borocarbamates, and the alcoholic degradation of these species, are outlined in reaction schemes A to C ; no attempt was made to isolate those compounds indicated in italics in scheme A. A.

(Et N.B-N.Et) 2

3

-r 6PhNCO

Ph ^

-

N

y=Ο

Et N-B 2

^NEt

I Et^NH

+ B(OR)

3

+

PhNH- C(: O)-N(Et) · C (:0)

\

2

r

o

-NHPh

h

2PhNH- C(:0)» OR + EtNH^

B.

(Pr^N^B-NHBu*

+ 2PhNCO

3ROH Pr*NH + B(OR) + PhNH- C(: O).N(Bu> C(i Ο)· NHPh 3


222

A D V A N C E S IN CHEMISTRY SERIES

Table \ . Compound

M.P.,

N-H Str.,

°c.

Cm. ~

1

Characterization of Boroureas,

a

C-HAromatic Str.,

C-HAliphatic Str.,

Cm.'

1


Cm. " I

65-68

II

142-45

III

118-20

3413 sh 3367 s

IV, x=o

125-30

3387 s

v, x=s

130-33

3289 s 3257 s

C=0

Str.,

Cm. ~

1

1

3040 sh

2976 vs 2933 sh

1704 sh 1626 vs

2941 s

2899 sh

1706 s 1667 vs

2950 vs

1686 sh 1675 vs

3030 sh

2967 vs

1695 sh 1653 s

2967 s

2899 sh

bend.=bending mode, str. = stretching mode, sh = shoulder, s = strong, vs = very strong, w = weak.

C.

B (NHBu*) g + 2 C 0

2

III

B(OR) + 2Β^ΝΗ·0(:Ο).ΟΗ 3

By contrast to scheme C, the aminoboration of phenyl iso- andisothiocyanate (scheme D), using tris(ter£-butylamino)-borane, did not give cyclic boroureas or thioureas, but gave acyclic derivatives, which failed to cyclize (by elimination of tert- buty lamine) upon pyrolysis. Even with a deficiency of phenyl isocyanate, all three tert- buty lamino groups were replaced. Structure IV (X=0) was confirmed by alcoholysis of IV to afford teri-butylcarbanilide and orthoborate. D.

Β (NHBu*)

3

+ 3PhNCX -

B[N(Ph) · C (: X) · NHBu*] , IV

X = Ο or S

The contrasting results in (B) and (D) are attributed to the greater steric hindrance of replacement of P r g N - compared with B u ^ N H - , when either is attached to boron. Further examples of steric effects are our failure to observe any reaction between phenyl isocyanate and 5-chloroborazines, e.g., with ( C l - B - N - R ) , R = B u , Pr , or Ph; reflux after 48 hours. Similarly, it was noted (15) that ( M e N - B - N H ) and phenyl isocyanate not only formed a ring compound analogous to I, but also gave V; while with phenyl isothiocyanate, the sulfur analog of V was the only product isolated. ITiese results indicate that insertion res

n

1

2

3


22

CRAGG

AND

LAPPERT

Cyclic

Boroureas

223

Borocarbamates, and a Dithioborocarbamate C - C Ring Str., -I

Cm.

B-N Cm.

Str.,

Bu

t

Bend,

Cm. ~

M

N-C

Str.,

Cm. "

1

1

C-H Outof Plane Bending, Cm. ~


1

1595 vs

1439 vs

1590 vs 1575 s

1437 s

1250 w

752. 7 vs 691. 4 vs

1370 s

1224 s

749. 7 vs 689. 7 vs

1389 vs

1205 s 1214 s

1597 s

1449 s 1437 s

1389 s

1618 s 1600 s

1431 s

1389 s

actions into the > B - N M e homolog.

2

B O str. cm. 1359 s 749.2 vs 691.1 vs

C=S str? cm. 1198 s

716.7 vs 689.7 vs

bond are more facile than into the diethyl H

Me N(0:)C. (Ph)N-B^

Ί3-Ν(Ρη)· C(: 0 ) » N M e

2

I

2

I

ν

N(Ph).C(:0).NMe

= Ο

Me

2

VI

NH

RN ^B^ tf

Ο

Some characteristics of the new boron compounds are indicated in Table I.

We regard the mechanism of these aminoboration reactions as in volving successive addition and elimination steps. This is illustrated in two instances in schemes (E) and (F); in (F), traces of free amine were required for reaction to proceed. For this reason, we prefer, in absence of further experimental data, to formulate the product of Re action 1 as VI, and not as indicated in Equation 1. In Boron-Nitrogen Chemistry; Niedenzu, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1964.

224

A D V A N C E S I N C H E M I S T R Y SERIES

N(Ph)-C(:0)-NHBu t E.

(Pr^N^B-NHBu* + 2PhNCO -

Pr*N-B N(Ph).C(:0).NPT2 -Pr^NF Π

F.

2C0 + 2Bu NH - 2H0-C(:0)- NHBu L

2

t

Β(ΝΗΒυ ) 1

3

Βιι*ΝΗ· Β[θ. C(:0). NHBu*]

2

-Bu NH Downloaded by HARVARD UNIV on May 27, 2014 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch022

t

Experimental

2

2

m

Scheme A. Phenyl isocyanate (5-58 grams) was heated under re flux with the borazine (2-95 grams) (2) in light petroleum (30 ml.) (b. p. 60 - 80°) for 3 hours. On removal of solvent, the crude borourea (I) (8 20 grams), (m.p. 60- 65°), was obtained. After recrystalliza tion from benzene it had a melting point of 65 - 68° (Found: C, 68-3; H, 6·9; N, 15-1; B, 3-3%; MW. 352. H N 0 Β requires C, 68-7; H, 7-0; N, 15· 2 ; B, 3· 2%; MW. 363). 1-Octanol (in excess) was added to I (1.95 grams). The mixture was refluxed for 1 hour. Distillation afforded tri-w-octoxyborane (2.05 grams, 95%), (b.p. 176°/0.4 mm., n ^ 1.4384 (Found: B, 2.69. Calculated for C H 0 B : B , 2.72%) [Lappert (11) gives b.p. 174°/0.4 mm. , η β 1.4377]. From the solid residue, there was obtained w-octyl AT-phenylcarbamate (2.40 grams, 90%) (m.p. 72 - 74° ) (Found: N, 6.1. C H N 0 requires N, 5. 9%); this appears to be a new compound. Scheme B. Two experiments were carried out, using an equimolar or a 1 to 2 molar ratio of borane to isocyanate. In both instances, the latter stoichiometry was established; only the former experiment is described. tert- Buty lamino- bis (diisopropylamino)borane (4-40 grams) (2) was heated under reflux with phenyl isocyanate (1-80 grams) in light petro leum (ca. 30 ml.) (b.p. 40-60°) for 4 hours. Only a small amount of product appeared to have beenformed and solvent was therefore re moved. Benzene (ca. 30 ml.) was then added, in order to enable a high er reflux temperature to be employed. After 3 hours'further reflux ing, the mixture was cooled, and addition of light petroleum (ca. 15 ml.) (b.p. 40 - 60°) precipitated the cyclic borourea (Π) (2-8 grams, 90%) (m.p. 142- 45°) (Found: C, 68-5; Η, 7-5; N, 13-4; B, 2-72%;MW. 403. C H N 0 B requires C, 69-0; Η, 7-9; N, 13-3; B, 2-75%; MW. 420). Removal of volatiles from the filtrate led to recovery of the starting borane (2 · 30 grams). A mixture of II (2-00 grams) and w-butanol (1-06 grams) was heated under reflux for 0.5 hour. Diisopropylamine (0-45gram, 93%) (authen tic infrared spectrum) was condensed at -78°/760 mm. A white solid crystallized, when the residue was cooled, and complete precipitation was effected by addition of light petroleum (ca. 5 ml. ) (b.p. 40 - 60°). The solid was identified as N, ΛΓ'-di- ter£-butyl-biuret (1-40 grams, 88%) 25

4

2

2

2 4

5 1

3

2

4

2 4

2 3

3 3

2

4

2


22

CRAGG

AND

LAPPERT

Cyclic

Boroureas

225

(m.p. 137 - 40°) (Found: N, 13-7; C H N 02 requires N, 13-5%); this appears to be a new compound. The filtrate afforded t r i - w-butoxyborane (1-0 gram, 95%) (b.p. 95°/5 m m . , r$ 1-4094) (Found: B, 4-68. Calculated for C H 0 B : B, 4-72%) [Lappert (11) gives b.p. 115°/15 m m . , n™ 1-4085] . 18

1 2

2 7

21

3

3

Scheme C . Solid carbon dioxide (in excess) was washed with light petroleum and added to tris- (tert-butylamino) borane (4· 00 grams) at 20°. Initially there appeared to be no reaction, but addition of a trace of tert- buty lamine resulted in the exothermal formation of a white solid. The mixture was shakenfor 0.5 hours with light petroleum and the cyclic borocarbamate (ΙΠ) (4-15 grams, 96%) (m.p. 118-20°) (Found: C, 49-8; H, 7-4; N, 11-6; B, 4-45. C H N O B requires C, 49-6; H, 7- 9; N, 11-6; B, 4-50%) was thus obtained. Downloaded by HARVARD UNIV on May 27, 2014 | http://pubs.acs.org Publication Date: January 1, 1964 | doi: 10.1021/ba-1964-0042.ch022

10

19

2

4

To compoundΙΠ (5-40grams), 1-butanol (4-80grams) was added and the mixture was refluxed for 1 hour, while volatile material was col lected in a trap at -78° . There was thus obtained tri-n-butoxyborane 4-90 grams, 95%) (b.p. 110°/10mm., ng 1-4081) (Found: B, 4-72%), while in the trap was isolated the white solidN-teri-butylcarbamic acid, identical to a specimen produced from fer£-buty lamine and carbondioxide. Scheme D (X=0). Two experiments were carried out, using 1 to 2 and 1 to 3 molar ratios of borane to isocyanate. In both instances, the latter stoichiometry was established ; only the former experiment is described. The borane (3·00 grams) was dissolved in light petroleum (ca. 40 ml.) (b.p. 40 - 60°). Addition of phenyl isocyanate was exothermal; the mixture was heated under reflux for 3 hours. The acyclic borourea (IV; X = 0 ) (4-4 grams, 85%) (m.p. 125 - 30°) (Found: C, 67-9; H, 8- 4; N, 14-3; B, 1-95%; MW. 541. C H N 0 B requires C, 68-0; H, 7-7; N, 14-4; B, 1-88%; MW. 584) was obtained by filtration and re crystallization from benzene. From the filtrate, t r i s - (tert-buty lamino) borane (1-00 gram) (authentic infrared spectrum) was obtained. Compound IV (X = O) (3-20 grams) was heated under reflux with 1butanol (1-20 grams) for 1 hour. Precipitation was completed, after cooling the mixture, by addition of light petroleum. N-tert-butyl-N'phenylurea (2-7 grams, 86%) (m.p. 148 - 50°) (Found: N, 14.4. C H N 0 requires N, 14-7%) was thus obtained; it appears to be a new compound. From the filtrate, tri-n-butoxyborane (1-00 gram, 80%) (wf) 1-4096) (Found: B, 4-70%) was recovered. Compound IV (X = O) was recovered substantially unchanged after being heated at 120°/0·02 m m . , for 2 hours. Scheme D (X = S). A mixture of the borane (2-60 grams) and phenyl isothiocyanate (3-10 grams) in light petroleum (ca. 40 ml.) (b.p. 40 60°) was heated under reflux for 3 hours. No reaction appeared to have taken place, so the solvent was removed and the residue was heated under reflux for a further 2 hours. After the resulting solid had been cooled and recrystallized from benzene, there was obtained the acyclic borothiourea (IV; X = S) (4-40 grams, 77%) (m.p. 130 - 33°) (Found: C, 62-5; Η, 8-4; N, 12-9; S, 14-9. C N S B requires C, 62· 5; H, 7-2; N, 13-1; S, 15-1%). 33

11

14

45

e

3

2

3 3

e

3


226 Physical

A D V A N C E S I N C H E M I S T R Y SERIES

Measurements

Molecular weights were determined using a Mechrolab molecular weight bridge, Model 310A (based on the lowering of the vapor pressure). Infrared spectra were takenona Perkin-Elmer PE 21 instrument, using sodium chloride optics. Acknowledgment


Most of the work described in this paper was carried out with gen erous support which we gratefully acknowledge, from the Office of Aero space Research, U.S. Air Force, through its European Office. Literature

Cited

1. Aubrey, D. W., Lappert, M . F., J. Chem. Soc. 1959, 2927. 2. Aubrey, D. W., Lappert, M . F., Majumdar, M . K. Ibid., 1962, 4088. 3. Beyer, H . , Niedenzu, K . , Dawson, J. W., Southeastern Regional Meeting, ACS, Gatlinburg, Tenn., November 1962. 4. Boone, J. L., Willcockson, G. W., Abstracts of Papers, 142nd Meeting ACS, Atlantic City, N. J., 1962, p. 6N. 5. Breederveld, H . , Rec. Trav. Chem. 61, 276 (1962). 6. Cragg, R. H . , Lappert, M . F., Tilley, B. P., Technical (Final) Summary Report, Contract No. A F 61(052)-419, October 1962. 7. Heying, T . L . , personal communication, December 1962. 8. Heying, T . L., Smith, H. D., Advan. Chem. Ser. No.42, 201(1963). 9. Jones, K . , Lappert, M . F., Proc. Chem. Soc. 1962, 358. 10. Joy, F., Lappert, M . F., Ibid., 1960, 353. 11. Lappert, M . F., Chem. Revs. 56, 959 (1956). 12. Lappert, M . F., Prokai, B . , J. Chem. Soc., 1963, 4223. 14. Lappert, M . F., Pyszora, H . , Rieber, M . , unpublished observa tions. 15. Niedenzu, Κ., written comments on present paper, communicated at Symposium on Boron-Nitrogen Chemistry, Durham, N. C . , April 1963. Received June 6, 1963.


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