Dimethylphenylphosphine is an organophosphorus compound with a formula P(C<sub>6</sub>H<sub>5</sub>)(CH<sub>3</sub>)<sub>2</sub>. The phosphorus is connected to a phenyl group and two methyl groups, making it the simplest aromatic alkylphosphine. It is colorless air sensitive liquid. It is a member of series (CH<sub>3</sub>)<sub>3-n</sub>(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>P that also includes n = 0, n = 2, and n = 3 that are often employed as ligands in metal phosphine complexes.
Dimethylphenylphosphine is prepared by the reaction of methylmagnesium halide with dichlorophenylphosphine.
The phosphine is purified by distillation under reduced pressure. A solution of (C<sub>6</sub>H<sub>5</sub>)(CH<sub>3</sub>)<sub>2</sub>P in CDCl<sub>3</sub> shows proton NMR signals at ô 7.0-7.5 and a doublet at ô 1.2. The phosphorus-31 NMR spectrum shows a singlet at -45.9 ppm in CDCl<sub>3</sub>.
Dimethylphenylphosphine is a pyramidal molecule where the phenyl group and two methyl groups are connected to the phosphorus. The bond length and angles are the following: P-C<sub>Me</sub>: 1.844, P-C<sub>Ph</sub>: 1.845 à, C-C: 1.401 à, C-H<sub>Me</sub>: 1.090 à, C-H<sub>Ph</sub>: 1.067 à, C-P-C: 96.9ð, C-P-C (ring): 103.4ð, P-C-H: 115.2ð.
When attached to chiral metal centers, the P-methyl groups are diastereotopic, appearing as separate doublets in the <sup>1</sup>H NMR spectrum.
The ý<sub>CO</sub> of IrCl(CO)(PPh<sub>3</sub>)<sub>2</sub> and IrCl(CO)(PMe<sub>2</sub>Ph)<sub>2</sub> are both at 1960 cm<sup>âÂÂ1</sup>, whereas ý<sub>CO</sub> for IrCl(CO)(PMe<sub>3</sub>)<sub>2</sub> is at 1938 cm<sup>âÂÂ1</sup>.
In terms of basicity, dimethylphenylphosphine is intermediate between that of trialkyl- and triphenylphosphine:
The ligand cone angle (ø) is the apex angle of a cylindrical cone, which is centered 2.28 àfrom the center of the P atom. However, the cone angle of an unsymmetrical ligand cannot be determined in the same. In order to determine an effective cone angle for an unsymmetrical ligand PX<sub>1</sub>X<sub>2</sub>X<sub>3</sub>, the following equation is used:
Where ø<sub>i</sub> represent the half angle.
The resulting angles for PMe<sub>3</sub>, PMe<sub>2</sub>Ph, PPh<sub>3</sub> are: PMe<sub>3</sub> = 118ð, PMe<sub>2</sub>Ph = 122ð, PPh<sub>3</sub> = 145ð. Thus, PMe<sub>2</sub>Ph is intermediate in size relative to PMe<sub>3</sub> and PPh<sub>3</sub>.