Planar tetracoordinate carbon in tungstenacyclobutadiene from alkyne metathesis and expanded structures

Abstract

The planar tetracoordinate (_ptC) character of C_β in the tungstenacyclobutadiene (WCBD) from alkyne metathesis is analyzed with the support of structural, electronic, molecular orbital and electron density data obtained from density functional theory calculations. The _ptC character of C_β is due to 1,3-WC bonding, which is established on the basis of the single bond-like WC_β distance in X-ray structures and calculated structures, a catastrophe ring critical point for the WCBD ring in quantum theory of atoms-in-molecule analysis (QTAIM) and a large difference in the ¹³C-NMR data of C_α and C_β atoms. The metalloaromatic character of WCBD is revealed by nuclear independent chemical shift (NICS) values and diatropic ring current observed in the anisotropy of the induced current density (AICD) plot. These WCBD structural motifs provide a new strategy to build 1-, 2- and 3-dimensional organometallic polymeric structures containing multiple _ptC centers. Several such structures are reported, and their 3-dimensional extensions provide access to novel _ptC-incorporated metal–organic frameworks.