Boron Compounds - American Chemical Society

25

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Boron Compounds

Structures containing at least one organic group attached to a boron atom through carbon are called organoboron compounds; the broader class name organic boron compounds also includes structures not containing carbon-to-boron bonds. Except when functional groups are present that take precedence, organic boron compounds are preferably named as derivatives of inorganic parent structures in accordance with official rules adopted by the American Chemical Society (1). The A C S Rules are comprehensive and explicit; since they are readily available, only a few principles enabling one to name the more common types of organic derivatives are included in this chapter.

Recommended Nomenclature Practice The compound B H is called borane; this term is also used to designate boron hydrides, B X H y , as a class. Hydrides containing more than one boron atom are named by using the customary multiplying prefixes and adding an Arabic numeral within parentheses as a suffix to denote the number of hydrogen atoms present. 3

B H 5

Pentaborane (9)

9

B Hii

Pentaborane (11)

s

Organic derivatives are named substitutively in the usual manner, highest-ranking function being expressed as a suffix. CH BH BH CH3 3

2

3

1,2-Dimethyldiborane (6)

2

CH CH B(OCH ) 2

3

Ethyldimethoxyborane

2

(CH ) NBHCH CH CH 3

2

2

C H CH BC1 6

5

2

2

the

2

3

JV,AT-Dimethyl-l-propylboranamine Dichloro(phenylmethyl)borane

Compounds having the structures ( R O ) B , ( R O ) B O H , and R O B ( O H ) are named as esters of boric acid, B(OH) . 3

2

3

196 In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2

25.

Boron Compounds

197 Triphenyl borate

(C H O) B 6

s

3

Dipropyl hydrogen borate

(CH CH CH 0) BOH 3

2

2

2


Organic ring systems containing one or more boron atoms are preferably named by replacement nomenclature as described for hetero cyclic systems in Chapter 6.

H—B

W

B—H

1,4-Diboracyclohexane

For three particularly stable inorganic ring systems containing boron, A C S Rules recommend retention of well established trivial names. Numbering is fixed as shown.

H l 2

HB6

BH Borazine

HN 5

3NH

H

2

HB6

BH Boroxin

OS

\0 B^ H

2

HB6

BH Borthiin

S5

3

S

B H

In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

198

NOMENCLATURE OF ORGANIC COMPOUNDS

The class of compounds in which one or more carbon atoms replace boron in polyboron hydrides (polyboranes) is called carbaboranes. Individual members are named by using the replacement prefixes carba, dicarba, etc.


B

i

Dicarbadodecaborane (12)

0C2H12

Structures in which a nucleophilic group has combined with boron by completing the latter's octet of electrons are regarded as addition compounds and are named by citing the two component molecules and joining their names with a dash. The nucleophilic compound is listed first. CH NH -BH CH CH 3

2

2

2

Methanamine-ethylborane

3

Boron-containing ions are named as coordination compounds by applying the regular inorganic rules. [BC

KOW.NI

T W

K[B(C H ) ] 6

5

"Z32=J"

Potassium tetraphenylborate

4

When a group containing boron must be named as a substituent, prefix names based o n boryl for H B — , borylene for H B < , borylidyne for B < , diboran(4)yl for B H - , diboran(6)yl for B H - , etc. are formed in the regular manner. 2

2

3

(C H ) BCH CH COOCH 6

5

2

2

2

2

3

S

Methyl 3-(diphenylboryl)propanoate

Discussion The unusual types o f bonding encountered in many boron compounds require that specialized methods be used in forming systematic names for these structures. With this i n mind, committees of both organic and inorganic chemists have developed what are now the official A C S Rules for the Nomenclature of Boron Compounds ( i ) . In general the Rules adhere to principles previously established and approved by the I U P A C Commissions on Organic and Inorganic Nomenclature; they also take note of practices employed by Chemical Abstracts. However, a few comments are in order. In naming boron hydrides containing 20 boron atoms, the multiplying prefix icosa (to emphasize the spatial geometry of the molecule) is preferred to the form eicosa used in hydrocarbon nomenclature. 'JThe A C S Rules state that in naming boranes it is permissible to omit the Numerical designation of hydrogen atoms i n certain cases where no I In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

25.

199

Boron Compounds

ambiguity would result. However, since this practice requires careful judgement and tends to produce apparent inconsistencies throughout the published literature, it is not recommended here, except for the simple and very common hydride B H . 3

Systematic names for the inorganic heterocyclic structures ( B H N H ) , ( B H O ) , and ( B H S ) formed by replacement nomenclature—i.e., 1,3,5-triazacyclohexaborane, 1,3,5-trioxacyclohexaborane, and 1,3,5-trithiacyclohexaborane—can be formed, but these have not yet received official recognition. Thus, although systematic names are generally preferred, the three trivial names recommended by the A C S Rules are here regarded as currently preferable. The older name "borazole" for borazine should no longer be used. 3


3

3

There has been considerable use of "carborane," a shortened form of carbaborane, both as a class name and as a trivial name for the hydride B C H . Neither practice is recommended. 1 0

2

1 2

In recognition of significant usage among organic chemists, Chemical Abstracts has named structures of the types R B ( O H ) and R B O H as "boronic acids" and "borinic acids," respectively. A s with the corres ponding organophosphorus compounds (see Chapter 36), this treatment may be extended to include not only the esters R B ( O R ) and R B O R ' but other formal acid derivatives, such as halides,'anhydrides, and amides, as well. However, in naming organoboron compounds containing function al groups attached to boron, the application of principles used in naming organosilicon compounds (see Chapter 38) is more appropriate because of the close chemical analogy of boron to silicon; this method leads to the functional parent names boranol for H B O H and boranediol for H B ( O H ) , boranamine for H B N H and boranediamine f o r H B ( N H ) , but it does not affect the naming of the corresponding halogen or O R derivatives. Except for their use by Chemical Abstracts, the aforemention ed phosphorus-type names for organoboron compounds have not received official sanction. 2

2

2

2

2

2

2

2

2

2

For the compound B ( O H ) , the 1970 I U P A C Inorganic Rules recognize both the names orthoboric acid and boric acid. Usage has heavily favored the latter. Structures i n which halogen or nitrogen have replaced one or more O H groups in boric acid should be named as borane derivatives—e.g., aminoboranediol for H N B ( O H ) , not amidoboric acid. 3

2

2

The prefix names for boron-containing groups recommended in the A C S Rules are logically formed by analogy with their carbon counter parts. The prefix borono for ( H O ) B—, although used by Chemical Abstracts, should be abandoned in favor of dihydroxyboryl 2


NOMENCLATURE OF ORGANIC COMPOUNDS

Table 25.1. Examples of Acceptable Usage

CH CH B(CH ) 3

2

3

CH

Ethyldimethylborane

2

3

C H CH CH BOCH2CH Downloaded by STANFORD UNIV GREEN LIBR on June 21, 2012 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0126.ch025

6

s

2

2

C1 BCH CH BC1 2

2

H

2

Ethoxy(methyl)(2-phenylethyl)borane 3

E thy lenebis( dichloroborane)

2

,,CH CH

H

2

V

3

2-Ethyl-3-methylpentaborane (9) (for structures and numbering of other polyboranes, see the ACS Rules) CH,

C H NHBCH CH 6

$

2

1-Ethyl-l-methyl-N-phenylboranamine Ethylmethyl(phenylamino)borane

3

CH B(OH) 2

2

(1,4-Dichloro-2-naphthy lmethyl)boranediol (1,4-Dichloro-2-naphthy lmethyl)dihy droxyborane

CI

CH CH CH B(OCH ) 3

2

2

3

Dimethoxypropylborane

2

Triethyl borate not Ethyl borate

(CH CH 0) B 3

2

3

CH CH=CHCH OB(OH) 3

2

2

C H CH CH OBCl 6

5

2

2

(CH COO) B 3

3

2

2-Butenyl dihydrogen borate Dichloro( 2-pheny lethoxy )borane Boric ethanoic trianhydride Boric acetic trianhydride


25. 12.

Boron Compounds (CH 0)2BB(OCH CH3)2 3

2

13.

l,l-Diethoxy-2,2-dimethoxydiborane(4)

N

N

14. Downloaded by STANFORD UNIV GREEN LIBR on June 21, 2012 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0126.ch025

201

/

2H-1,3-Diaza-2-boraindene 2H-Benzo[

Boron Compounds - American Chemical Society

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