Insertion and Cycloaddition Reactivity of a Transition-Metal N-Metalloimine** Eva Hevia, Julio Pÿrez,* VÌctor Riera, and Daniel Miguel Dedicated to Professor Maurice Brookhart on the occasion of his 60th birthday The presence of electron-releasing main-group-metal sub- stituents 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 substitu- ent 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 alkylide- neammonium 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 KN¼CPh 2 with [Re(OTf)(CO) 3 (bpy)] (bpy ¼ 2,2’-bipyridine) afforded the complex [Re(N ¼ CPh 2 )- (CO) 3 (bpy)] (1), which was characterized spectroscopically and by X-ray diffraction (Figure 1a). For comparison, the structure of the imine complex [Re(HN ¼CPh 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 Re NCPh 2 distance (2.113(4) ä) in 1 is comparable to the Re N(H)CPh 2 distance (2.192(3) ä) in 2, which is in agreement with the lack of multiple-bond character of the Re N 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 alkylide- neamido 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 ¹ 2002 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim 0044-8249/02/11420-4014 $ 20.00+.50/0 Angew. Chem. 2002, 114, Nr. 20 [*] Dr. J. Pÿrez, E. Hevia, Prof. Dr. V. Riera Departamento de QuÌmica Orgμnica e Inorgμnica-IUQOEM Facultad de QuÌmica-CSIC, Universidad de Oviedo 33071 Oviedo (Spain) Fax: (þ 34) 98-510-3446 E-mail: japm@sauron.quimica.uniovi.es Dr. D. Miguel Departamento de QuÌmica Inorgμnica Facultad de Ciencias, Universidad de Valladolid 47071 Valladolid (Spain) [**] We thank Dr. Luis A. LÛpez for helpful comments and the Ministerio de Ciencia y TecnologÌa and the Ministerio de EducaciÛn for support of this work (Projects MCT-00-BQU-0220 and PB97-0470-C02-01) and a predoctoral fellowship (to E.H.). Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Figure 1. Thermal ellipsoid (30%) plots of 1 (a) and 2 (b). See Supporting Information for further details. M N C M N C A B