Dimethylphenylphosphine
# Dimethylphenylphosphine

Dimethylphenylphosphine is an organophosphorus compound with a formula $P(C_6H_5)(CH_3)_2.$ 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 $(CH_3)_{3-n}(C_6H_5)_2P$ that also includes n = 0, n = 2, and n = 3 that are often employed as ligands in metal phosphine complexes.

## Preparation

Dimethylphenylphosphine is prepared by the reaction of methylmagnesium halide with dichlorophenylphosphine.

    $(C_6H_5)Cl_2P$ + $2CH_3MgBr$ → $(C_6H_5)(CH_3)_2P$ + 2MgBrCl

The phosphine is purified by distillation under reduced pressure. A solution of $(C_6H_5)(CH_3)_2P$ in $CDCl_3$ shows proton NMR signals at δ 7.0-7.5 and a doublet at δ 1.2. The phosphorus-31 NMR spectrum shows a singlet at -45.9 ppm in $CDCl_3.$

## Structure and properties

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: $P-C_{Me}:$ 1.844, $P-C_{Ph}:$ 1.845 Å, C-C: 1.401 Å, $C-H_{Me}:$ 1.090 Å, $C-H_{Ph}:$ 1.067 Å, C-P-C: 96.9°, C-P-C (ring): 103.4°, P-C-H: 115.2°.

When attached to chiral metal centers, the P-methyl groups are diastereotopic, appearing as separate doublets in the $^1H$ NMR spectrum.

## Comparisons with related phosphine ligands

The $ν_{CO}$ of $IrCl(CO)(PPh_3)_2$ and $IrCl(CO)(PMe_2Ph)_2$ are both at 1960 $cm^{−1},$ whereas $ν_{CO}$ for $IrCl(CO)(PMe_3)_2$ is at 1938 $cm^{−1}.$

In terms of basicity, dimethylphenylphosphine is intermediate between that of trialkyl- and triphenylphosphine:

* $[HPEt_3]^+$ = 8.7
* $[HPMe_2Ph]^+$ = 6.8
* $[HPPh_3]^+$ = 2.7

The ligand cone angle (θ) is the apex angle of a cylindrical cone, which is centered 2.28 Å from 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 $PX_1X_2X_3,$ the following equation is used:

    $\theta ={\frac {2}{3}}\sum _{i=1}^{3}{\frac {\theta _{i}}{2}}$

Where $θ_i$ represent the half angle.

The resulting angles for $PMe_3,$ $PMe_2Ph,$ $PPh_3$ are: $PMe_3$ = 118°, $PMe_2Ph$ = 122°, $PPh_3$ = 145°. Thus, $PMe_2Ph$ is intermediate in size relative to $PMe_3$ and $PPh_3.$

