Synthetic, Structural, NMR, and Computational Study of a Geminally Bis(<i>peri</i>-substituted) Tridentate Phosphine and Its Chalcogenides and Transition-Metal Complexes

Coupling of two acenaphthene backbones through a phosphorus atom in a geminal fashion gives the first geminally bis­(<i>peri</i>-substituted) tridentate phosphine <b>1</b>. The rigid nature of the aromatic backbone and overall crowding of the molecule result in a rather inflexible ligand, with the three phosphorus atoms forming a relatively compact triangular cluster. Phosphine <b>1</b> displays restricted dynamics on an NMR time scale, which leads to the anisochronicity of all three phosphorus nuclei at low temperatures. Strained bis- and tris­(sulfides) <b>2</b> and <b>3</b> and the bis­(selenide) <b>4</b> have been isolated from the reaction of <b>1</b> with sulfur and selenium, respectively. These chalcogeno derivatives display pronounced in-plane and out-of-plane distortions of the aromatic backbones, indicating the limits of their angular distortions. In addition, we report metal complexes with tetrahedral [(<b>1</b>)­Cu­(MeCN)]­[BF₄] (<b>5</b>), square planar [(<b>1</b>)­PtCl]­[Cl] (<b>6</b>), trigonal bipyramidal [(<b>1</b>)­FeCl₂] (<b>7</b>), and octahedral <i>fac</i>-[(<b>1</b>)­Mo­(CO)₃] (<b>8</b>) geometries. In all of these complexes the tris­(phosphine) backbone is distorted, however to a significantly smaller extent than that in the mentioned chalcogenides <b>2</b>–<b>4</b>. Complexes <b>5</b> and <b>8</b> show fluxionality in ³¹P and ¹H NMR. All new compounds <b>1</b>–<b>8</b> were fully characterized, and their crystal structures are reported. Conclusions from dynamic NMR observations were augmented by DFT calculations