Low-Dimensional Architectures in Isomeric cis-PtCl2{Ph2PCH2N(Ar)CH2PPh2} Complexes Using Regioselective-N(Aryl)-Group Manipulation

Abstract

The solid-state behaviour of two series of isomeric, phenol-substituted, aminomethylphosphines, as the free ligands and bound to Pt^II, have been extensively studied using single crystal X-ray crystallography. In the first library, isomeric diphosphines of the type Ph₂PCH₂N(Ar)CH₂PPh₂ [1a-e; Ar = C₆H₃(Me)(OH)] and, in the second library, amide-functionalised, isomeric ligands Ph₂PCH₂N{CH₂C(O)NH(Ar)}CH₂PPh₂ [2a-e; Ar = C₆H₃(Me)(OH)], were synthesised by reaction of Ph₂PCH₂OH and the appropriate amine in CH₃OH, and isolated as colourless solids or oils in good yield. The non-methyl, substituted diphosphines Ph₂PCH₂N{CH₂C(O)NH(Ar)}CH₂PPh₂ [2f, Ar = 3-C₆H₄(OH); 2g, Ar = 4-C₆H₄(OH)] and Ph₂PCH₂N(Ar)CH₂PPh₂ [3, Ar = 3-C₆H₄(OH)] were also prepared for comparative purposes. Reactions of 1a-e, 2a-g, or 3 with PtCl₂(η⁴-cod) afforded the corresponding square-planar complexes 4a-e, 5a-g, and 6 in good to high isolated yields. All new compounds were characterised using a range of spectroscopic (¹H, ³¹P{¹H}, FT-IR) and analytical techniques. Single crystal X-ray structures have been determined for 1a, 1b∙CH₃OH, 2f∙CH₃OH, 2g, 3, 4b∙(CH₃)₂SO, 4c∙CHCl₃, 4d∙½Et₂O, 4e∙½CHCl₃∙½CH₃OH, 5a∙½Et₂O, 5b, 5c∙¼H₂O, 5d∙Et₂O, and 6∙(CH₃)₂SO. The free phenolic group in 1b∙CH₃OH, 2f∙CH₃OH_,2g, 4b∙(CH₃)₂SO, 5a∙½Et₂O, 5c∙¼H₂O, and 6∙(CH₃)₂SO exhibits various intra- or intermolecular O-H∙∙∙X (X = O, N, P, Cl) hydrogen contacts leading to different packing arrangements.

Keywords: P-ligands; amide groups; isomers; late-transition metals; phenols; secondary interactions; single crystal X-ray crystallography.

Chart 1

Potential modification sites of a Ph₂P–C–N(Ar)–C–PPh₂ backbone.

Scheme 1

Synthesis of 1a–e, 2a–g, and 3.

Figure 1

Molecular structure of 1a. All hydrogens, except on C(1), C(2) and O(1), have been omitted for clarity.

Figure 2

Molecular structure of 3 showing a dimer pair. All hydrogens, except on C(1), C(2) and O(1), have been omitted for clarity. Symmetry code: A = 1 − x, 1 − y, 1 − z.

Figure 3

Crystal structure packing plot for 1b∙CH₃OH. Most H atoms, two Ph groups per P atom have been omitted for clarity. Symmetry code: A = x, −y + ½, z + ½.

Figure 4

Dimers of 2f forming R²₂(16) graph set motifs. Most H atoms omitted for clarity. The second unique molecule which adopts a similar, centrosymmetric motif, is not shown.

Figure 5

Intra- and intermolecular interactions in the crystal structure of 2g. Most H atoms omitted for clarity. Symmetry operator A = x, −y + ³/₂, z − ½.

Chart 2

Structures of compounds 4a–e, 5a–g, and 6.

Figure 6

H-bonded packing arrangement in the crystal structure of 4c∙CHCl₃. Most H atoms omitted for clarity. Symmetry operator A = x+½, –y+½, z+½.

Figure 7

Crystal structure of 6∙(CH₃)₂SO showing the hydroxyl group H-bonding to the (CH₃)₂SO molecule of crystallisation. Most H-atoms omitted for clarity.

Figure 8

Crystal structure of 4d∙½Et₂O. Most H atoms and the disordered OEt₂ molecule omitted for clarity.

Figure 9

(a) Crystal structure of 4b∙(CH₃)₂SO showing the hydroxyl group H-bonding to the DMSO molecule of crystallisation. Most H-atoms removed for clarity. (b) Packing interactions in the crystal structure of 4b∙(CH₃)₂SO. Most H atoms omitted for clarity. Symmetry operator A = y − 1, 1 − x, ¼ + z.

Figure 10

H-bonded packing motifs in the crystal structure of 4e∙½CHCl₃∙½CH₃OH. Most H atoms, two Ph groups per P atom, and the disordered chloroform of crystallisation which is not involved in any significant intermolecular interactions, are omitted for clarity. Symmetry operators are x, y − 1, z and x, y + 1, z.

Figure 11

Most H atoms and 2 Ph groups per P atom have been omitted for clarity. (a) Packing motif 1 in the crystal structure of 5c. Symmetry operator A = x + 1, y, z. (b) Packing motif 2 in the crystal structure of 5c. The true structure is most likely an alternation of motifs 1 and 2. Symmetry operator A = x + 1, y, z.

Figure 12

Packing motif in the crystal structure of 5a∙½Et₂O. Most H atoms, two Ph groups per P atom and the two, half-occupied, Et₂O molecules have been omitted for clarity.

Figure 13

Packing plot of 5d∙Et₂O. Most H atoms, two Ph groups per P atom, and a diordered Et₂O molecule modelled by the Platon Squeeze procedure, are omitted for clarity. Symmetry operators: (i) for the mirror x, y, −z + ½, (ii) for the chain direction x + 1, y, z.

Figure 14

Packing plot in the crystal structure of 5b. Phenyl groups and hydrogen atoms not involved in hydrogen bonding have been omitted for clarity.