Dedicated to Professor Maurice Brookhart on the occasion of his 60th birthdayThe presence of electron-releasing main-group-metal substituents on the nitrogen atom increases the reactivity of imines A towards dipolar reagents such as isocyanates [1] and ketenes. [2] We speculated that, in addition to this inductive effect, a low-oxidation transition-metal substituent would contribute a destabilizing interaction between the lone pair on the nitrogen atom and the filled metal d orbitals. [3] However, all structurally characterized M(N¼CR 2 ) complexes have essentially linear M-N-C geometries [4] as a result of p donation of the lone pair on the nitrogen atom to empty metal orbitals. Thus, these azavinylidene [5] complexes B are more related to alkylideneammonium cations than to imines. [6] Herein we report the synthesis, structure, and a preliminary account of the reactivity of an N-metalloimine (type A) which contains a transition-metal fragment.The reaction of (1), which was characterized spectroscopically and by X-ray diffraction (Figure 1 a). For comparison, the structure of the imine complex [Re(HN¼CPh 2 )(CO) 3 (bpy)] þ (2), synthesized as its triflate salt by reaction of 1 with HOTf, was also determined (Figure 1 b). The Re-N-C angle (133.9(4)8) for the alkylideneamido group of 1, even smaller than the Re-N-C angle (138.9(2)8) of 2, indicates the absence of N-to-Re p donation. The larger deviations from linearity in previously known azavinylidene complexes (152.9(4)8 and 157.2(4)8 for [OsCl(¼N¼CMe 2 )(CCH 3 )(PiPr 3 ) 2 ][OTf] [7] and [OsCl(¼N¼CMe 2 )(¼CHPh)(PiPr 3 ) 2 ], [8] respectively) can be related to the presence of bulky ancillary ligands, whereas such effects are absent in 1. The ReÀNCPh 2 distance (2.113(4) ä) in 1 is comparable to the ReÀN(H)CPh 2 distance (2.192(3) ä) in 2, which is in agreement with the lack of multiple-bond character of the ReÀN bond. [9] Despite the structural similarity, the spectroscopic data of 1 and 2 are very different. Values of n CO even lower than those found for the related alkoxo [10] and amido [11] complexes reflect the strongly donor character of the alkylideneamido ligand in the neutral complex 1, whereas the higher wavenumbers of 2 are consistent with its cationic nature. 13 C NMR spectroscopy data indicate that the two phenyl groups of 1 are equivalent. Given the angular geometry of the alkylideneamido group, this should result from a fast exchange of the position of the metal atom between the two electron pairs at the alkylideneamido nitrogen atom. [12] Complex 1 acts as a nucleophile towards isocyanates. Thus, its reactions with RNCO (R ¼ Ph, pTol; Scheme 1) afford the products (3 and 4, respectively) of formal isocyanate insertion ZUSCHRIFTEN 4014