Trends in ortho-carboranes 1-X-2-R-1,2-C 2B 10H 10 (R = Ph, Me) bearing an exo-CN-bonded substituent group (X = NO, N [dbnd]NR′ or NHR′′)

Abstract

The preparation and crystal structures of four ortho-carboranyl-nitrogen compounds, PhCb o N N(C 6H 4Me-4) ( 1), PhCb o NHNH(C 6H 4Me-4) ( 2), MeCb o NHNHPh ( 3) and PhCb o NHOH ( 4) (Cb o = 1,2-C 2B 10H 10; nitrogen groups at cage carbon C1, Ph or Me at C2), the last as a 1,4-dioxane solvate, are reported. Comparisons of their structures with those of other ortho-carboranyl-nitrogen systems studied earlier reveal further correlations between their cage C–C and exo-C–N bond distances and bond orders. Substituent orientations and bond distances (cage C1–C2, exo-C1–N) in RCb o NHR′′ systems (R = Ph or Me at C2) are consistent with dative π-bonding from a nitrogen lone pair into the cage carbon p-AO otherwise responsible for cage C1–C2 σ bonding. Their C1–C2 bond distances are remarkably sensitive to the planar ( sp 2) or pyramidal ( sp 3) nature of the NHR′′ group. The N O and N NR′ residues in RCb o X prefer to be orientated in plane with the cage C1–C2 in contrast to the RCb o NHR′′ systems. Correlations between their cage C–C and exo-C–N bond distances and the 11B NMR chemical shifts of their antipodal boron atoms reflect the π-bonding characteristics of the nitrogen substituent.