Synthesis and Structural Studies of peri -Substituted Acenaphthenes with Tertiary Phosphine and Stibine Groups.

Two mixed peri -substituted phosphine-chlorostibines, Acenap(P i Pr 2 )(SbPhCl) and Acenap(P i Pr 2 )(SbCl 2 ) (Acenap = acenaphthene-5,6-diyl) reacted cleanly with Grignard reagents or n BuLi to give the corresponding tertiary phosphine-stibines Acenap(P i Pr 2 )(SbRR') (R, R' = Me, i Pr, n Bu, Ph). In addition, the Pt(II) complex of the tertiary phosphine-stibine Acenap(P i Pr 2 )(SbPh 2 ) as well as the Mo(0) complex of Acenap(P i Pr 2 )(SbMePh) were synthesised and characterised. Two of the phosphine-stibines and the two metal complexes were characterised by single-crystal X-ray diffraction. The peri -substituted species act as bidentate ligands through both P and Sb atoms, forming rather short Sb-metal bonds. The tertiary phosphine-stibines display through-space J (CP) couplings between the phosphorus atom and carbon atoms bonded directly to the Sb atom of up to 40 Hz. The sequestration of the P and Sb lone pairs results in much smaller corresponding J (CP) being observed in the metal complexes. QTAIM (Quantum Theory of Atoms in Molecules) and EDA-NOCV (Energy Decomposition Analysis employing Naturalised Orbitals for Chemical Valence) computational techniques were used to provide additional insight into a weak n(P)→σ*(Sb-C) intramolecular bonding interaction (pnictogen bond) in the phosphine-stibines.