Access to Metal Complexes of the Elusive Imidobis(phosphaalkene) Anion by N–Si Bond Cleavage of a N‐Silylimino‐Bridged Bis(phosphaalkene)

Metalation of the aminophosphaalkene (iPrMe 2 Si) 2 C=PN(H)-SiMe 3 (2) with lithium diisopropylamide (LDA) in THF solution, followed by the reaction of the lithium salt 3 with the P-chlorophosphaalkenes (RMe 2 Si) 2 C=PCl (1a, R = Me; 1b, R = iPr; 1c, R = Ph), furnishes the first N-silylimino-bridged bis(phosphaalkenes) [(iPrMe 2 Si) 2 C=P] 2 NSiMe 3 (4a) and [(iPrMe 2 Si) 2 C=P][(RMe 2 Si) 2 C=P]NSiMe 3 (4b, R = Me; 4c, R = Ph). The N―Si bond cleavage of 4a under very mild conditions with AuCl(THT) and with [RhCl(COD)] 2 provides binuclear Au I and Rh I complexes 5, 6 of the P,P'-coordinated imidobis(phosphaalkene) anion [(iPrMe 2 Si) 2 C=P] 2 N ― , the first case of elusive P=C-unsaturated congeners of the "classic" bis(phosphanyl)amide ligands. Solid 4a exists in a helically distorted S-shaped structure with two inequivalent P=C groups, but 31 P-NMR reveals the equivalence of both P=C groups in solution at the NMR time scale. The P=C and P―N bonds distances in 4a do not indicate significant conjugation within the C=P―N―P=C moieties whereas in complexes 5 and 6 the W-shaped CPNPC heteropentadienide anion exhibits strong 5-center-6-π conjugation according to DFT calculations and to the experimental P=C and P=N bond lengths.