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

Deprotonation of the aminophosphanes Ph2PN(H)R1a-1h [R = tBu (1a), 1-adamantyl (1b), iPr (1c), CPh3 (1d), Ph (1e), 2,4,6-Me3C6H2 (Mes) (1f), 2,4,6-tBu(3)C(6)H(2) (Mes*) (1g), 2,6-iPr(2)C(6)H(3) (DIPP) (1h)], followed by reactions of the phosphanylamide salts Li[Ph2PNR] 2a, 2b, 2g, and 2h with the P-chlorophosphaalkene (Me3Si)(2)C=PCl, and of 2a-2g with (iPrMe(2)Si)(2)C=PCl, gave the isolable P-phosphanylamino phosphaalkenes (Me3Si)(2)C=PN(R)PPh2 3a, 3b, 3g, and (iPrMe(2)Si)(2)C=PN(R)PPh2 4a-4g. P-31 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 P-31 NMR patterns (3h: line broadening).