Alkylideneamido-derivatives of metals and metalloids. Part VI. The synthesis of alkylideneamido(carbene)rhodium(I) complexes and related chemistry; the crystal and molecular structure of trans-Rh[N:C(CF3)2][C(NMeCH2)2](PPh3)2

Abstract

Two rhodium(I) complexes, trans-Rh[N:C(CF₃)₂][C(NRCH₂)₂](PPh₃)₂, (I; R =p-MeC₆H₄) and (II; R = Me), containing both alkylideneamido- and substituted carbene ligands have been prepared. Variable temperature ¹⁹F n.m.r. spectra suggest a low barrier to planar inversion at N. It did not prove possible to rearrange these to aza-allyl/allene isomers. As a contribution to the mechanism of formation of the latter, the synthesis of a C-alkylideneamidocarbene complex (V) is reported. A Pt^II imidoyl complex Pt–C(R)NR′, prepared by an oxidative addition reaction, did not isomerise to the alkylideneamide Pt–NCRR′; but with HCI the former gave a 1 : 1 adduct, presumed to be the carbene complex Pt–C(R)NHR′. A single crystal X-ray analysis of (II) has been carried out to R 0·067 for 2853 independent terms : the complex has an approximately square planar Rh environment with disorder about N:C and Rh–N, 2·02(3); NC, l·27(3); Rh–P, 2·290(4) and 2·291(4); and Rh–C_carb, 2·006(15)Å, and RhNC = 152°. Noteworthy are the significant departure from linearity at N and the exceptionally short mutually trans-Rh–P bond lengths; the M–NO/M–N:NR analogy is extended to M–N:CR₂.