Bis-- dimethylamino -diborane

The compound bis-/i-(dimethylamino)-diborane(6), [(CH3)2NBH2]2, has been prepared by the pyrolysis of dimethylamine-borane, (CH3)2NH BH3,1-3 and by a novel iodination-deprotonation of (CH3)2NH BH3,4 The gas-phase pyrolysis described here is the simplest and most convenient method for the preparation of small samples, since no solvent is involved and separation problems are thus minimized. The basic vacuum-line techniques necessary for this synthesis are outlined in reference 7. 

A dry pyrolysis bulb (Fig. 5), constructed from a 500-mL round-bottomed flask and previously checked for leaks, is charged with 1.18 g (20 mmol) of dimethylamine-borane.J The vessel is quickly evacuated to less than 1 torr, 

I Available from Research Organic/lnorganic Chemical Corp., 11686 Sheldon St., Sun Valley, CA 91352. A convenient synthesis is detailed in reference 6. 

A magnetic breaker is inserted in the side arm B, and the vessel is attached to the vacuum line and evacuated. The lower portion of the apparatus is cooled with liquid nitrogen and the break seal is opened. Because the sudden release of hydrogen pressure into the vacuum line can sometimes propel the breaker upward with considerable speed, it is advisable to cushion the upper surface of the inlet port with glass wool to avoid possible breakage. 

For purification and isolation, the volatile products are pumped through U traps maintained at —30.8° (bromobenzene) and —63.5° (chloroform). Pure crystals of [(CH3)2NBH2]2 (yield ca. 90%), having the properties given below, slowly condense in the trap held at —63.5°. 

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Reaction of l,2-dichloro-l,2-bis(dimethylamino)diborane(4) with N-dilithio bis- or tris(amino)borane derivatives resulted in several derivatives of the system named in the heading, according to the following equation ... 

Organoboron heterocycles containing the boron-boron bond have also been prepared by the reaction of A -lithio derivatives of alkylbis(alkylamino)-boranes with l,2-dichloro-l,2-bis (dimethylamino)diborane(4) 74) ... 

Thermal decomposition of l,2-dibutyl-l,2-bis (dimethylamino)diborane-(4) at 200°-230°C was found by Noth and Fritz to yield 1-butene and butyl-(dimethylamino)borane, the reaction postulated being... 

C4HioLiN, Lithium, tcrt-butylamide, 34 43 C4H12B2CI2N2, Diborane(4), l,2-dichloro-l,2-bis(dimethylamino)-, 34 3 C4Hi2Br2Mo04S2, Molybdenum(Vl),... 

ClNa60i9P2RhS6C37H24, Rhodate(6-), trans-carbonylchlorobis(tris(3-sulfonatophenyl)-phosphine)-, sodium, 34 124 CI2B2N2C4H12, Diborane(4), 1,2-dichloro-1,2-bis(dimethylamino)-, 34 3 CI2CUN4O9C18H20, Copper(II), aquatris(2-pyri-dylmethyl)amine-, perchlorate, 34 135 Cl2Fe7N24Oi2Ci32Hi50 6H2O, Iron(II), hexa-kis cyanobis(3-salicylidenoaminopropyl)-methylamineiron(lll) -, chloride, hexahy-drate, 34 143... 

Bis(dimethylamino)borane may be prepared by the reduction of CIB[N(CH3)2]21 or by gas-phase exchange of hydride and dimethylamino groups on boron.2,3 The latter method, using diborane(6) and excess B[N(CH3)2]3 and described here, is the most convenient for the synthesis of a few millimoles of product. The basic vacuum-line techniques necessary to carry out this synthesis are detailed in reference 4. 

The reaction of diborane(6) with bis or tris(dimethylamino)borane has recently been shown to be synthetically useful in the stepwise buildup of a boron-nitrogen chain leading to bis( -dimethylamino)triborane(9).7... 

Reactions of this type are somewhat less satisfactory for preparation of mixed diboron derivatives containing boron-carbon bonds. Thus, while tetrakis(dimethylamino)diborane(4) is readily hydrolyzed to tetrahydroxy-diborane(4) in aqueous acid, l,2-bis(dimethylamino)-l,2-diethylborane(4) reacts with formation of hydrogen and cleavage of the boron-boron bond 14). Reaction of the dibutyl analog with a twofold excess of water gave the dimethylamine adduct of the boroxole... 

At the other extreme, the most stable derivatives of the B2X4 type appear to be the tetrakis(dialkylamino) compounds. Thus, tetrakis(dimethylamino)-diborane(4) is stable at its boiling point of 206° C 17). The compound decomposes at 300° C to form bis(dimethylamino)borane and involatile residues containing B—C bonds. It is reported that tetra(A -methylanilino)-borane(4) is pyrolyzed at 300° C by a different mechanism to yield N-methylaniline 18). 

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