Tetraborane 8 Adducts

Figure 15 Trisaminophosphorus derivative of 2-aminopyridine and its tetraborane adduct...

The concept of using an excess of the alkyne to enhance vinylborane formation is not workable for an a,co-diyne if both alkyne moieties are to be hydrobo-rated. However, for example with 4 1 9-BBN l,8-nonadiyne stoichiometry, the l,l,9,9-tetra-9-BBN adduct is cleanly formed. The treatment of tetraborane adduct with 2 equiv of PhCHO results in the clean formation of trans,tram-, 9-di-9-BBN-l,8-nonadiene which on deuterolysis with AcOD affords the pure tranSytrans-didevLterated diene in 64% overall yield (Scheme 24.8) [27]. 

The dimethyl ether adduct of triborane(7) 124> has been prepared by the cleavage of tetraborane(lO) at room temperature according to the equation ... 

Removal of diborane(6), unreacted tetraborane(lO) and excess dimethyl ether at —45° left the adduct as a white solid (melting point 10.5 to 11.1°). 

The question of the molecular structure of the adducts of tetraborane(8) has now been resolved 144>. The boron-11 nmr spectra of the carbon monoxide and trifluorophosphine adducts have been analyzed 140> in terms of the 2112 topological geometry 141> proposed by Dupont and Schaeffer 142>. The dimethylaminodifluorophosphine adduct of tetra-borane(8) 143> which was prepared by the following reaction is stable at room temperature. 

The reaction of the carbon monoxide adduct of tetraborane(8) with deuterium gas gives only dideuterotetraborane(lO) which has one bridging deuterium and a terminal deuterium at the 1 position 140> ... 

Although tetraborane(8) has not been isolated, it is known from its trifiuorophosphine and dimethylaminodifluorophosphine adducts. The former complex can be made directly from pentaborane(ll) and the... 

---