Sterically Tuned P‐Phosphanylamino Phosphaalkenes (Me₃Si)₂C=PN(R)PPh₂ and (iPrMe₂Si)₂C=PN(R)PPh₂

Abstract

Deprotonation of the aminophosphanes Ph2PN(H)R 1a–1h [R = tBu (1a), 1‐adamantyl (1b), iPr (1c), CPh3 (1d), Ph (1e), 2,4,6‐Me3C6H2 (Mes) (1f), 2,4,6‐tBu3C6H2 (Mes*) (1g), 2,6‐iPr2C6H3 (DIPP) (1h)], followed by reactions of the phosphanylamide salts Li[Ph2PNR] 2a, 2b, 2g, and 2h with the P‐chlorophosphaalkene (Me3Si)2C=PCl, and of 2a–2g with (iPrMe2Si)2C=PCl, gave the isolable P‐phosphanylamino phosphaalkenes (Me3Si)2C=PN(R)PPh2 3a, 3b, 3g, and (iPrMe2Si)2C=PN(R)PPh2 4a–4g. 31P NMR spectra, supported by X‐ray structure determinations, reveal that in compounds 2a, 2b, 3a, and 3b, with bulky N‐alkyl groups the Si2C=P–N–P skeleton is non‐planar (orthogonal conformation), whereas 3g, 3h, and 4g with bulky N‐aryl groups exhibit planar conformations of the Si2C=P–N–P skeleton. Solid 3g and 4g exhibit cisoid orientation of the planar C=P–N–C units (planar I) but in solid 3h the transoid rotamer is present (planar II). From 3g, 4d, and 4g mixtures of rotamers were detected in solution by pairs of 31P NMR patterns (3h: line broadening).

P‐Aminophosphaalkenes with C‐Isopropyldimethylsilyl Groups

“…After 3 weeks, the P ‐phosphanylamino phosphaalkene 19 was the main product according to 31 P NMR, accompanied by small amounts of 18 , 13 , and tetraphenyldiphosphane. Usually, P ‐phosphanylamino phosphaalkenes are available from reactions of metallated aminophosphanes with P‐chlorophosphaalkenes ,…”

“…The structures of aminophosphaalkenes can be assigned on the basis of the relative orientations of the PNCP and Si 2 C=PN planes to the idealized cases of planar I or II or orthogonal (Scheme 3). [4,5,10] Compounds 7, 10, and 12 contain only one bulky substituent at the nitrogen atom, allowing the PNCP and Si 2 C=PN planes to adopt planar structures that involve favorable n(N)Ǟπ(P=C) conjugation, as suggested from their NMR spectroscopic data (see above). In the phosphanylphosphoranes 15 and 17, the P=C distances are similar to those in the aminophosphaalkenes (1.66-1.67 Å), but the (polar) P=N distances are significantly shorter in the phos-Z.…”

“…[9,11d] To prepare the N-bis[dimethyl(phenyl)silyl]amino phosphaalkene (iPrMe 2 Si) 2 C=PN(SiMe 2 Ph) 2 (14), the metallation route with with n-butyllithium was chosen. [4,5,10]…”

“…(Scheme 3). [4,5,10] When one of the bulky substituents is an aryl group, such as 2,4,6-tBu 3 C 6 H 2 -(Mes*), the aromatic ring plane can rotate into a position orthogonal to the nitrogen plane, causing a conformation with nearly coplanar phosphaalkene and nitrogen planes (planar I, RЈ = Mes*, in Scheme 3); in the related compound (Me 3 Si) 2 C=PN(Mes*)SiMe 3 the dihedral angle between the amino group and the nodal plane Si 2 C=P of the double bond is 11.2°. [4] The new C-isopropyldimethylsilyl aminophosphaalkenes (iPrMe 2 Si) 2 C=PN(H)R (3-8 and 10-13) exhibit 31 P-NMR shifts between δ = 310 and 326 ppm and 13 C-NMR shifts between 70 and 77 ppm, indicating undisturbed n(N)Ǟπ(P=C) conjugation, as known for the C-trimethylsilyl congeners.…”

“…Usually, P-phosphanylamino phosphaalkenes are available from reactions of metallated aminophosphanes with P-chlorophosphaalkenes. [10,13]…”