“…34.58 8.Whereas the analogous reaction with adialumene precursor yields the 1,2-dihydro-1,2-dialumete IV (Figure 1), [13] the 1,3-isomer is obtained in this case.A lthough this reaction involves formal cleavage of CCa nd B=Bb onds,p revious synthetic and theoretical studies have shown that 1,2-dihydro-1,2-diboretes spontaneously rearrange to the thermodynamically more stable 1,3-isomer. [21] It is thus likely that diborene VI first undergoes the expected [2+ +2] cycloaddition to form the kinetic 1,2-dihydro-1,2-diborete,w hich immediately rearranges to the thermodynamic product, 1.T he short BÀC bond lengths to the sp 2 -hybridized C1 atom [1.486(4), 1.465-(4) ] are indicative of a2p-homoaromatic system delocalized over B1C1B2, whereas the B À Cb onds to the sp 3hybridized C3 atom [1.630(4), 1.666(4) ] are within the upper range of BÀCs ingle bonds.C ompound 1 is thus structurally similar to the allenyl-bridged 1,3-dihydro-1,3diborete reported by Berndt and co-workers. [22] TheP 1-C3 distance [1.759 (2) ] is typical for aP !Cd onor-acceptor bond;t he PMe 3 donor moiety thus stabilizes the build-up of positive charge on C3 (mesoionic resonance structure in Figure 2).…”