Reactions of the diazonium derivative of closo-decaborate anion with oxygen nucleophiles were studied. The reaction of [1-B10H9N2](-) with hydroxide ion gives the corresponding hydroxy derivative [1-B10H9OH](2-) in high yield. The reactions with OR (R = Me, Et, i-Pr, Ph) result in mixture of [I-B10H9OR](2)- and [a(2) -B20H18](4-). (c) 2005 Elsevier B.V. All rights reserved.