Syntheses and structures of calcium and ytterbium bis(diphosphanylamido) complexes Tarun K. Panda, Michael T. Gamer, Peter W. Roesky * Institut fu ¨ r Chemie und Biochemie, Freie Universita ¨ t Berlin, Fabeckstraße 34-36, 14195 Berlin, Germany Received 31 January 2006; accepted 16 March 2006 Available online 24 March 2006 Dedicated to Professor Dr. Dr. h.c. Mult. Wolfgang A. Herrmann. Abstract Bis(diphosphanylamido) complexes of calcium and ytterbium, [{(Ph 2 P) 2 N} 2 M(THF) 3 ] (M =Ca (1), Yb (2)), have been prepared by reaction of [K(THF) n N(PPh 2 ) 2 ](n = 1.25, 1.5) and MI 2 . The single crystal X-ray structures of compounds 1 and 2 always show a g 2 - coordination of the ligand via the nitrogen and one phosphorus atom. In solution a dynamic behavior of the ligand is observed, which is caused by the rapid exchange of the two different phosphorus atoms. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Calcium; Chelates; Coordination chemistry; Ytterbium; N,P ligands 1. Introduction Recently, there has been a significant research effort in d- and f-transition metal chemistry to find an alternative to the well established cyclopentadienyl ligand [1] for stabilizing high reactive metal centers. In these regards, one approach among others is the use of phosphines with P–N bonds [2]. In this context, we have introduced the well known mono- phosphanylamide, (Ph 2 PNPh) À [3], and diphosphanyla- mide, {(Ph 2 P) 2 N} À [4–6], as ligands in trivalent lanthanide chemistry. In dependence of the steric demand of the ligand, either metallate complexes of composition [Li(THF) 4 ][(Ph 2 - PNPh) 4 Ln] (Ln = Y, Yb, Lu) [3] or the homoleptic com- pounds [Ln{N(PPh 2 ) 2 } 3 ] (Ln = Y, La, Nd, Er) [4] can be obtained. The later complexes were used as catalysts for the polymerization of e-caprolactone. Significant differ- ences in terms of correlation of theoretical and experimental molecular weights, as well as polydispersities, were observed depending on the nature of Ln. The single crystal X-ray structures of these complexes solely show a g 2 -coor- dination of the ligand via the nitrogen and one phosphorus atom. In solution a dynamic behavior of the ligand is observed, which is caused by the rapid exchange of the two different phosphorus atoms. Thus, the coordination of phosphorus atom to the metal center is weak and the corresponding bond length is rather long. Recently, we also introduced the {(Ph 2 P) 2 N} À ligand into divalent lanthanide and heavy alkaline earth metal chemistry [7,8]. Whereas to the best of our knowledge, the {(Ph 2 P) 2 N} À ligand was not previously used in group 2 chemistry, the oxidized version, {(Ph 2 PO) 2 N} À , was taken very recently to synthesize complexes of composition [M{(OPPh 2 ) 2 N] 2 (M = Sr, Ba) [9]. It is well established that the reactivity and coordination behavior of the divalent lanthanide metals and the heavier alkaline earth metals are somewhat related [10]. This similarity in coordination chemistry originates from the similar ion radii (for CN 6 (pm): Ca 2+ 100, Yb 2+ 102, Sr 2+ 118, Eu 2+ 117, Ba 2+ 135) [11]. Bis(diphosphanylamido) complexes of strontium and europium, [{(Ph 2 P) 2 N} 2 M(THF) 3 ] (M = Sr, Eu), were obtained by reaction of [K(THF) n N(PPh 2 ) 2 ] (n = 1.25, 1.5) and MI 2 . The single crystal X-ray structures of these compounds again show a g 2 -coordination of the ligand 0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.03.016 * Corresponding author. Tel.: +49 83854004; fax: +49 3083852440. E-mail address: roesky@chemie.fu-berlin.de (P.W. Roesky). www.elsevier.com/locate/ica Inorganica Chimica Acta 359 (2006) 4765–4768