SHORT COMMUNICATION DOI: 10.1002/ejic.200900282 Templated Synthesis and Site-Selective Conversion of Completely Nonsymmetrical Bis-Metallosalphen Complexes Ana M. Castilla, [a] Simona Curreli, [a] Nina M. Carretero, [a] Eduardo C. Escudero-Adán, [a] Jordi Benet-Buchholz, [a] and Arjan W. Kleij* [a,b] Keywords: Nonsymmetrical complexes / N,O ligands / Diastereoselectivity / Templated synthesis / Zinc A metal-templated, stepwise approach toward fully nonsym- metrical bis-metallosalphen complexes is described. The synthesis comprises the selective monometalation of diimine precursors and subsequent introduction of the second metal ion by using various salicylaldehyde reagents. In the case of a bis-Zn(salen) derivative, the presence of different periph- eral substituents on the two metallosalen units gave rise to a Introduction Salen ligands are generally considered privileged, be- cause many stereoselective transformations can be carried out with these versatile structures. [1] Recently, the use of (multimetallic) metallosalen complexes in material chemis- try has emerged as a powerful approach towards functional (supramolecular) systems with wide-ranging properties. [2,3] Although synthetic salen chemistry has matured signifi- cantly over the last decade, [4] the development of pro- cedures for multinuclear salen complexes that allow particu- lar control over the properties of each individual complexed metal ion still represents a great challenge, [5] as a conse- quence of the labile nature of the imine bond during synthe- sis. The presence of different metallosalen units within the multinuclear complex can provide a means for site-selective functionalization that is potentially interesting for the devel- opment of heteromultimetallic systems [6] useful in cascade or orthogonal tandem catalysis. We recently reported on the preparation of a small library of diimine precursors derived from 3,3'-diaminobenzidine (see Scheme 1 for an example) and their conversion into symmetrical bimetallic salphen complexes with a nonsymmetry within each salen unit. [7,8] We anticipated that a selective introduction of one metallo- salen module onto the diaminobenzidene backbone could lead to an interesting monometallic triimine precursor, whose unreacted half-salen unit [7] subsequently tolerates the [a] Institute of Chemical Research of Catalonia (ICIQ), Av. Paisos Catalans 16, 43007 Tarragona, Spain Fax: +34-977-920-224 E-mail: akleij@iciq.es [b] Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.200900282. Eur. J. Inorg. Chem. 2009, 2467–2471 © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2467 large difference in kinetic stability, which was used to selec- tively demetalate the more labile site. This result shows promise for the preparation of heterobimetallic structures. The first X-ray molecular structure of a completely nonsym- metrical bis-salphen complex is also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) introduction of different aryl substituents in the second salen unit. Here we report the Zn-templated synthesis of a unique monometallic precursor and its conversion into fully nonsymmetrical bis-metallosalphen complexes [salphen = N,N'-1,2-phenylenebis(salicylideneimine)]. The presence of different peripheral substituents on both Zn(salphen) mod- ules creates a significant difference in the kinetic stability of the Zn ions, which is demonstrated by a site-selective demetalation of one of the Zn(salphen) units. Scheme 1. Synthesis of monometallic triimine precursors 1 and 2. Results and Discussion We recently reported the preparation of a series of di- imines, including A and B (Scheme 1), derived from 3,3'- diaminobenzidine. [7,8] These diimines can be prepared on a larger scale and serve as valuable intermediates for symmet- rical homobimetallic salphen complexes. We anticipated that, under appropriate conditions, these diimines could