Dimethylphenylphosphine is an
organophosphorus compound
Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbo ...
with a formula P(C
6H
5)(CH
3)
2. The
phosphorus
Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
is connected to a
phenyl
In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula , and is often represented by the symbol Ph (archaically φ) or Ø. The phenyl group is closely related to benzene and can be viewed as a benzene ...
group and two
methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated as ...
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
ligand
In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...
s 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
Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
is purified by distillation under reduced pressure.
A solution of (C
6H
5)(CH
3)
2P in CDCl
3 shows
proton NMR
Proton nuclear magnetic resonance (proton NMR, hydrogen-1 NMR, or 1H NMR) is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the stru ...
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
In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula , and is often represented by the symbol Ph (archaically φ) or Ø. The phenyl group is closely related to benzene and can be viewed as a benzene ...
group and two
methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated as ...
groups are connected to the phosphorus. The
bond length
In molecular geometry, bond length or bond distance is defined as the average distance between Atomic nucleus, nuclei of two chemical bond, bonded atoms in a molecule. It is a Transferability (chemistry), transferable property of a bond between at ...
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 In stereochemistry, topicity is the stereochemical relationship between substituents and the structure to which they are attached. Depending on the relationship, such groups can be ''heterotopic'', ''homotopic'', ''enantiotopic'', or ''diastereotopi ...
, 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:
*
PEt3sup>+ = 8.7
*
PMe2Phsup>+ = 6.8
*
PPh3sup>+ = 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:
:
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.
[C. A. Tolman, ''Chem. Rev.'', Steric effects of Phosphorus Ligands in Organometallic Chemistry and Homogeneous Catalysis., 1977, volume 77, pages 313-348. ]
References
{{Reflist
Tertiary phosphines
Phenyl compounds
Methyl compounds