Synthesis and Structural Characterization of Main Group 15 Organometallics R3M and R(Ph)2P(=N-Ar)(M = P, Sb, Bi; R = phenanthrenyl; Ar = 2,6-iPr2-C6H3)

Abstract

New group 15 organometallic compounds, M<TEX>$(phenanthrenyl)_3$</TEX> (M = P (1), Sb (2), Bi (3)) have been prepared from the reactions of 9-phenanthrenyllithium with <TEX>$MCl_3$</TEX>. A reaction of 9-(diphenylphosphino)phenanthrene with 2,6-diisopropylphenyl azide led to the formation of (phenanthrenyl)<TEX>${(Ph)}_2P$</TEX>=N-(2,6-<TEX>$^iPr_2C_6H_3$</TEX>) (4). The crystal structures of 2 and 4 have been determined by single-crystal X-ray diffractions, both of which crystallize with two independent molecules in the asymmetric unit. Compound 2 shows a trigonal pyramidal geometry around the Sb atom with three phenanthrenyl groups being located in a screw-like fashion with an approximately <TEX>$C_3$</TEX> symmetry. A significant amount of CH- -<TEX>$\pi$</TEX> interaction exists between two independent molecules of 4. The phosphorus center possesses a distorted tetrahedral environment with P-N bond lengths of 1.557(3)<TEX>$\AA$</TEX> (P(1) N) and 1.532(3)<TEX>$\AA$</TEX> (P(2)-N), respectively, which are short enough to support a double bond character. One of the most intriguing structural features of 4 is an unusually diminished bond angle of C-N-P, attributable to the hydrogen bonding of N(1)-H(5A) [ca. 2.49<TEX>$\AA$</TEX> between two adjacent molecules in crystal packing. The compounds 1-3 show purple emission both in solution and as films at room temperature with emission maxima (<TEX>$\lambda_{max}$</TEX>) at 349, 366, and 386 nm, respectively, attributable to the ligand centered <TEX>$\pi$</TEX> <TEX>$\rightarrow$</TEX> <TEX>$\pi^\ast$</TEX> transition in phenanthrene contributed by the lone pair electrons of the Gp 15 elements. Yet the nature of luminescence observed with 4 differs in that it originates from <TEX>$\pi$</TEX> (diisopropylbenzene)-<TEX>$\pi^\ast$</TEX> (phenanthrene) transitions with the <TEX>$\rho\pi$</TEX>contribution from the nitrogen atom. The emission maximum of 4 is red-shifted ranging 350-450 nm due to the internal charge transfer from the phenanthrenyl ring to the N-arylamine group as deduced from the ab initio calculations.