A novel non-facial mode of azulene cluster co-ordination. Crystal and molecular structure of the dicarbenoid Os-3(mu-H)(2)(CO)(9)(mu(3)-eta(1):eta(1):eta(1)-C10H6)

Azulene oxidatively added to Os-3(CO)(11)(NCCH3) to afford the triosmium cluster Os-3(mu-H)(2)(CO)(9)(mu(3)-eta(1):eta(1):eta(1)-C10H6) 1 in high yield. The organic moiety is bound perpendicularly to the trimetallic plane and acts as a 4e(-) donor forming one terminal and one bridging carbene-metal bond. An X-ray diffraction study of 1 was made and full spectroscopic assignment has been made using 1- and 2-D homo- and hetero-nuclear NMR; 2-D C-13 EXSY experiments have also allowed the elucidation of the CO exchange process.