Insertion Reactions into the Boron–Boron Bonds of Barrelene-Type 1,2-Diaminodiboranes(4)

Double lithiation of 9,10-dihydroanthracene
(DHA) or 6,13-dihydropentacene
(DHP) with nBuLi, followed by the addition of B2(NMe2)2Cl2, affords 9,10-DHA-9,10-diyl-
(1a) or 6,13-DHP-6,13-diyl-bridged B2(NMe2)2 (1p) in good yields. Upon treatment
with Pt­(PEt3)3 in C6H6 at 60 °C, both compounds cleanly insert a Pt­(PEt3)2 moiety into their B–B bonds to furnish the corresponding
diboryl Pt­(II) complexes 2a and 2p. Compound 2a reacts with excess tBuCCH to give an equimolar
mixture of the B–(tBu)­CC­(H)–B-bridged
9,10-DHA 3 and Pt­(η2-tBuCCH)­(PEt3)2 (4). The addition
of isocyanides to either the Pt­(II) complex 2a or the
Pt-free species 1a yields bicyclic products, in which
a 9,10-DHA-9,10-diyl fragment is spanned by a B–C­(NR)–B
linker (R = tBu (5), iPr (6)). Both 5 and 6 are
extremely prone to hydrolysis. In the case of 6, a water-induced
rearrangement reaction leading to a B–C-bridged 9,10-DHA 8 was observed.