Synthesis and reactivity of 7,9-diphenyl-nido-carbaundecaboranes: rearrangement processes in carbaplatinaboranes revisited

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Abstract
A number of synthetic routes towards diphenyl nido-carbaborane [7,9-Ph 2 -7,9-nido-C 2 B 9 H 10 ] - have been elucidated. Base-induced degradation of 1,7-Ph 2 -1,7-closo-C 2 B 10 H 10 afforded two isolable products [NEt 3 H][7,9-Ph 2 -x-OEt-7,9-nido -C 2 B 9 H 9 ] (x = 3 1a or 2 1b), both of which contain an ethoxide-substituted cage. The structural identity of 1a was established by a single-crystal X-ray diffraction study. Fluoride-induced degradation gave a product assigned as [NBu 4 ][7,9-Ph 2 -10-OH-7,9-nido-C 2 B 9 H 9 ] 2, also studied crystallographically. Heating a solid sample of Cs[7,8-Ph 2 -7,8-nido-C 2 B 9 H 10 ] in a sealed tube under vacuum for 4 h at 300 °C afforded the target species [NEt 3 H][7,9-Ph 2 -7,9-nido-C 2 B 9 H 10 ] 3, after cation metathesis. Deprotonation of 3 and reaction with [PtCl 2 (PMe 2 Ph) 2 ] afforded the new compound 1,1-(PMe 2 Ph) 2 -2,4-Ph 2 -1,2,4-closo -PtC 2 B 9 H 9 4. Compound 4 has been characterised by multinuclear ( 1 H, 11 B and 31 P-{ 1 H}) NMR spectroscopy as well as a single-crystal X-ray diffraction study. The isolation of this stable (in refluxing toluene) compound having a 1,2,4-MC 2 B 9 cage architecture indicates that a hextuple-concerted diamond–square–diamond mechanism cannot be operating in the spontaneous isomerisation of 1,2-Ph 2 -3,3-(PMe 2 Ph) 2 -3,1,2-closo -PtC 2 B 9 H 9 below ambient temperature to afford 1,1-(PMe 2 Ph) 2 -2,8-Ph 2 -1,2,8-closo -PtC 2 B 9 H 9 . The new compounds 1,1-(PR 3 ) 2 -2,4-Ph 2 -7-OEt-closo -1,2,4-PtC 2 B 9 H 8 (R 3 = Me 2 Ph 5a or Et 3 5b), both fully characterised by multinuclear NMR spectroscopy, have also been synthesized.

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