11-Vertex arachno-clusters with an NB10, SNB9, and SeNB9 skeleton

One of the two bridging protons of the aza-nido-decaboranes RNB9H10X can be removed by certain bases to give nido-anions [RNB9H9X](-) [R/X = H/H (1a), Ph/H (1b), p-MeC6H4/H (1c), Bzl/H (1d), H/N-3 (1'a)]; the stericly demandi ng base 1,8-bis(dimethylamino)naphthalene ("proton sponge", ps) is ideal. I n the case of tBu anion, the deprotonation (--> C4H10) may be accompanied b y a hydridation (--> C4H8), yielding the arachno-anions [RNB9H11X](-) (2a, b, d, 2'a); these are the main products, when stericly non-demanding bases like H- are applied. The Lewis acid BH3 is added to 1a and 1'a to give the aza-arachno-undecaborates HNB10H12X [X = H (3a), N-3 (in position 2) (3'a)] . Thia- and selenaaza-arachno-undecaborates, [S(RN)B9H10](-) (4b, c) and [S e(RN)B9H10](-) (4'b, c), are obtained from 1b, c by the addition of sulfur or selenium, respectively. The methylation of the anions 4c and 4'c gives t he thia- and selenaaza-arachno-undecaboranes (MeS)(RN)B9H10 (5c) and (MeSe) -(RN)B9H10 (5'c), respectively. The action of HBF4 on the arachno-borates [ HNB10H12X](-) (3a, 3'a) leads to a mixture of nido-HNB9H10X and nido-HNB10H 11X by the elimination of BH3 or H-2, respectively; the aza-nido-decaborane predominates in the case of 3'a and the aza-nido-undecaborane in the case of 3a. The action of HBF4 on the anion 4c yields the hypho-undecaborate [S( RN)B9H10F2](-) (6c). The structures of the products are elucidated on the b asis of H-1 and B-11 NMR spectra, supported by 2D COSY and HMQC techniques. Two types of 11-vertex-arachno structures and an 11-vertex-hypho structure are found for the products. The crystal structures of 5c and [Hps] 6c . CH 2Cl2 are reported.