Synthetic,
Structural, NMR, and Computational Study of a Geminally Bis(<i>peri</i>-substituted) Tridentate Phosphine and Its Chalcogenides and Transition-Metal Complexes
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Abstract
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)][BF<sub>4</sub>] (<b>5</b>), square planar [(<b>1</b>)PtCl][Cl] (<b>6</b>), trigonal bipyramidal [(<b>1</b>)FeCl<sub>2</sub>] (<b>7</b>), and octahedral <i>fac</i>-[(<b>1</b>)Mo(CO)<sub>3</sub>] (<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 <sup>31</sup>P and <sup>1</sup>H 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