P,P-Bis[4-(dimethyl­amino)­phen­yl]-N,N-bis­(propan-2-yl)phosphinic amide

Stephen J Evans; C Alicia Renison; D Bradley G Williams; Alfred Muller

doi:10.1107/S1600536812050398

. 2013 Jan 9;69(Pt 2):o195. doi: 10.1107/S1600536812050398

P,P-Bis[4-(dimethylamino)phenyl]-N,N-bis(propan-2-yl)phosphinic amide

Stephen J Evans ^a, C Alicia Renison ^a, D Bradley G Williams ^a,^*,^‡, Alfred Muller ^a

PMCID: PMC3569256 PMID: 23424479

Abstract

The molecular structure of the title compound, C₂₂H₃₄N₃OP, adopts a distorted tetrahedral geometry at the P atom, with the most noticeable distortion being for the O—P—N angle [117.53 (10)°]. An effective cone angle of 187° was calculated for the compound. In the crystal, weak C—H⋯O interactions create infinite chains along [100], whereas C—H⋯π interactions propagating in [001] generate a herringbone motif.

Related literature

For the synthesis of ligands derived from phosphinic amides, see: Williams et al. (2009 ▶). For background to DoM technology, see: Snieckus (1990 ▶). For cone angles, see: Tolman (1977 ▶); Otto (2001 ▶).

Experimental

Crystal data

C₂₂H₃₄N₃OP
M _r = 387.49
Orthorhombic,
a = 6.2960 (4) Å
b = 16.6389 (8) Å
c = 19.9475 (11) Å
V = 2089.7 (2) Å³
Z = 4
Mo Kα radiation
μ = 0.15 mm⁻¹
T = 100 K
0.13 × 0.11 × 0.1 mm

Data collection

Bruker X8 APEXII 4K KappaCCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2004 ▶) T _min = 0.981, T _max = 0.985
18896 measured reflections
5212 independent reflections
3840 reflections with I > 2σ(I)
R _int = 0.074

Refinement

R[F ² > 2σ(F ²)] = 0.050
wR(F ²) = 0.110
S = 1.04
5212 reflections
252 parameters
H-atom parameters constrained
Δρ_max = 0.30 e Å⁻³
Δρ_min = −0.35 e Å⁻³
Absolute structure: Flack (1983 ▶), 2224 Friedel pairs
Flack parameter: 0.11 (10)

Data collection: APEX2 (Bruker, 2005 ▶); cell refinement: SAINT-Plus (Bruker, 2004 ▶); data reduction: SAINT-Plus and XPREP (Bruker, 2004 ▶); program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg & Putz, 2005 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶) and WinGX (Farrugia, 2012 ▶).

Supplementary Material

Click here for additional data file.^{(30KB, cif)}

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536812050398/bt6869sup1.cif

e-69-0o195-sup1.cif^{(30KB, cif)}

Click here for additional data file.^{(250.1KB, hkl)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812050398/bt6869Isup2.hkl

e-69-0o195-Isup2.hkl^{(250.1KB, hkl)}

Click here for additional data file.^{(8.4KB, cml)}

Supplementary material file. DOI: 10.1107/S1600536812050398/bt6869Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

Cg1 and Cg2 are the centroids of the C11—C16 and C21—C26 rings, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C12—H12⋯O1ⁱ	0.95	2.59	3.493 (3)	159
C33—H33A⋯O1ⁱ	0.98	2.58	3.501 (3)	158
C18—H18A⋯Cg1ⁱⁱ	0.98	2.96	3.821 (2)	148
C18—H18C⋯Cg2ⁱⁱ	0.98	2.97	3.915 (3)	162
C27—H27C⋯Cg1ⁱⁱⁱ	0.98	2.69	3.468 (3)	137

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

The University of the Free State is thanked for the use of their diffractometer. Financial assistance from Sasol, THRIP and the Research Fund of the University of Johannesburg is gratefully acknowledged.

supplementary crystallographic information

Comment

An expedient rapid synthesis of ligands derived from phosphinic amides that were found to be suitable for the Suzuki-Miyaura reactions at low palladium catalyst loadings was developed (Williams et al., 2009). The brief practical synthesis affords arylphosphine ligands resistant to oxidation and hydrolysis while maintaining high catalyst activity. The synthesis rests strongly on DoM technology (Snieckus, 1990) making use of a directing group that is highly underrepresented in this type of chemistry. We envisioned that the use of phosphinic amides as directing groups, together with phosphinous chloride (Cy₂PCl) electrophiles would allow the synthesis of sterically hindered phosphines that are stable to hydrolysis and oxidation. Manipulating the phosphinic amide functionality has been shown to influence the catalytic performance of the resulting alkyl phosphine ligands and the structure reported here is one of the substrates for further ligand studies.

The title compound (see Fig. 1) crystallizes in the orthorhombic space group P2₁2₁2₁ (Z=4) with its molecules adopting a distorted tetrahedral arrangement about the phosphorus atom. The O3—P1—N3 angle of 117.53 (10)° shows this distorted arrangement the most prominent, and it is further exemplified by the twisted orientation of the bulky amide substituent to fit into the coordination sphere of the phosphorus atom (seen from the torsion angles C34—N3—P1—O1 = -63.71 (19)° and C31—N3—P1—O1 = 87.2 (2)° respectively). The most common method used for determining the steric behaviour of a phosphane ligand is the Tolman cone angle (Tolman, 1977). We used the geometry from the title compound and adjusted the P═O distance to 2.28 Å (the average Ni—P distance used in the original Tolman model) to cancel the bias this may have on the calculated cone angle value. In this way we obtain the effective cone angle (Otto, 2001) value of 187°. Several weak C—H···O interactions are observed in the crystal lattice creating infinitely long chains along the [100] direction (Fig. 2). Additional C—H···π interactions are also observed which propagates along the [001] direction in the crystal lattice (Fig. 3). These interactions (summarized in Table 1) generate a herring-bone packing motif (Fig. 4).

Experimental

Diisopropyl amine (1.55 ml, 5.53 mmol) was added to a solution of PCl₃ (241 µL, 2.77 mmol) in toluene (250 ml) at 0 °C. The mixture was allowed to stir for 2 h at room temperature. In a separate flask p-bromo-N,N-dimethylaniline (1.728 g, 8.63 mmol) in THF (5 ml) was added to magnesium turnings (200 mg, 8.22 mmol) in THF (5 ml) and heated to 65 °C. The reaction was initiated with a crystal of iodine and the suspension allowed to stir for 3 h at that temperature. Once the magnesium had fully reacted the two solutions were combined and the salts were removed by filtration through a pad of celite under argon.

The solution was cooled to 0 °C and hydrogen peroxide (30%, 15 ml) was added over 20 minutes. The mixture was allowed to stir for a further 1 h. The product was extracted with EtOAc and H₂O and the solvent removed in vacuo. The product was isolated by flash column chromatography (EtOAc).

Crystals were grown by dissolving in a minimal amount of DCM and layering an excess of hexane on top and allowing to stand in a refrigerator until the crystals were formed.

Yield: 60% (yellow solid). ¹H NMR: (300 MHz, CDCl₃) δH 7.58 (t, 4H, H2, H2`, H6 and H6`, J = 9.9 Hz), 6.61 (d, 4H, H3, H3`, H5 and H5`, J = 7.2 Hz), 3.41 (sept, 2H, NCH(CH₃)₂, J = 6.9 Hz), 2.90 (s, 12H, NCH(CH₃)₂), 1.12 (d, 12H, NCH(CH₃)₂, J = 6.9 Hz). ¹³C NMR: (75 MHz, CDCl₃) δC 151.6 (d, 2 C, C4 and C4`, J = 2.3 Hz), 133.4 (d, 4 C, C2, C2`, C6 and C6`, J = 10.6 Hz), 120.3 (d, 2 C, C1 and C1`, J = 135.3 Hz), 110.7 (d, 4 C, C3, C3`, C5 and C5`, J = 13.0 Hz), 46.5 (d, 2 C. NCH(CH₃), J = 4.3 Hz), 398 (s, 4 C, NCH(CH₃)₂, 32.1 (d, 4 C, NCH(CH₃)₂, J = 2.6 Hz). ³¹P NMR: (121 MHz, CDCl₃) δP 31.1(S,1P). ElMS: m/z 387 [(M), 10%], 344 [(M—C₃H₇), 12%], 287 [(M—C₆H₁₄N), 100%]. IR: ν (CHCl₃) 2980, 1262, 1172. HRMS: Calculated: 387.2440 C₂₂H₃₄N₃OP Obtained: 387.2445