The divalent lanthanide borohydrides [Ln(BH(4))(2)(THF)(2)] (Ln = Eu, Yb) have been prepared in a straightforward approach. The europium compound shows blue luminescence in the solid state, having a quantum yield of 75%. Nonradiative deactivation of C-H and B-H oscillator groups could be excluded in the perdeuterated complex [Eu(BD(4))(2)(d(8)-THF)(2)], which showed a quantum yield of 93%. The monocationic species [Ln(BH(4))(THF)(5)][BPh(4)] and the bis(phosphinimino)methanides [{(Me(3)SiNPPh(2))(2)CH}Ln(BH(4))(THF)(2)] have been prepared from [Ln(BH(4))(2)(THF)(2)]. They show significantly lower or no luminescence. Using the diamagnetic compound [{(Me(3)SiNPPh(2))(2)CH}Yb(BH(4))(THF)(2)], we performed a 2D (31)P/(171)Yb HMQC experiment.

In the last few years a number of research groups started significant activity in the exploration of the coordination and organometallic chemistry of the heavier alkaline-earth metals. [1] Most of this work is focused on calcium, [2] an inexpensive and non-toxic element present in significant amounts in the human body. Indeed, synthetic access to such large alkalineearth metal complexes is often limited by their kinetic lability with detrimental Schlenk-type equilibria. [3] Within this reserach not only the synthesis of new compounds but also the structures, [4] the reactivity, [5] and some catalytic applications were investigated. [6] Among these latter the ring-opening polymerization (ROP) of cyclic esters such as e-caprolactone (e-CL) and lactide (LA), allows access to polymers with controlled molar mass and molar mass distribution and especially, in some cases, controlled stereochemistry. [2a, 7] In contrast to this well-established chemistry, the application of structurally characterized strontium compounds as initiators in ROP remains very rare. Besides ill-defined amino isopropoxyl strontium, [8] phenoxide ligated cationic strontium complexes [9] and some phenoxide strontium amides [10] were only very recently used for the ROP of LA.Whereas in related rare-earth chemistry, borohydrides such as [Ln(BH 4 ) 3 (thf) 3 ] [11] or its derivatives have become well-established initiators for the ROP of cyclic esters and carbonates, [12] comparable chemistry of alkaline-earth elements was only first published recently by Cushion and Mountford (e.g. on calcium). [13] This is rather surprising because [Ca(BH 4 ) 2 (thf) 2 ] is commercially available for applications in materials science. [14] In contrast, such borohydride chemistry involving strontium is even less developed. Although, the synthesis and the solidstate structure of [Sr(BH 4 ) 2 (thf) 2 ] (1) were already reported in 1995, [15] there is to date, to the best of our knowledge, no structurally characterized coordination or organometallic strontium borohydride compound known.Herein, we describe the synthesis and structural characterization of the half-sandwich [Cp*Sr(BH 4 )(thf) 2 ] 2 (Cp* = h 5 -C 5 Me 5 ; 2) and the bis(phosphinimino)methanide [{(Me 3 SiNPPh 2 ) 2 CH}Sr-(BH 4 )(thf) 2 ] (3) complexes, as well as their application as initiators for the ROP of e-CL. The starting material 1 was prepared according to a literature procedure from [Sr(OEt) 2 ] and a solution of BH 3 in THF. [15] Reaction of 1 with KCp* and K[(Me 3 SiNPPh 2 ) 2 CH] [16] resulted in the corresponding heteroleptic monoborohydride derivatives 2 and 3, respectively (Scheme 1).The new complexes 2 and 3 have been characterized by standard analytical/spectroscopic techniques and the solidstate structures were established by single-crystal X-ray analysis. The 1 H NMR spectra show the expected resonance for the Cp* ligand of 2 at d = 1.98 ppm and a broad signal for the methine group of the bis(phosphinimino)methanide ligand of 3 at d = 1.72 ppm. The BH 4 À groups are observed as...

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Reactions of the bis(phosphinimino)methane {CH2(Ph2PNSiMe3)2} with the zinc dihalides ZnCl2 and ZnI2 afforded the corresponding bis(phosphinimino)methane complexes [{(Me3SiNPPh2)2CH2}ZnCl2] (1) and [{(Me3SiNPPh2)2CH2}ZnI2] (2). In contrast, treatment of {CH2(Ph2PNSiMe3)2} with ZnPh2 in toluene gave the bis(phosphinimino)methanide complex of [{(Me3SiNPPh2)2CH}ZnPh] (3). Further reaction of 3 with the heterocumulenes di(p-tolyl)carbodiimine and diphenyl ketene resulted via a nucleophilic addition of the methine carbon atom of the {CH(Ph2PNSiMe3)2}- ligand to the heterocumulenes in a C-C bond formation. New tripodal phenyl zinc complexes of composition [{(Me3SiNPPh2)2CH)(p-Tol)NC-N(p-Tol)}ZnPh] (4) and [{(Me3SiNPPh2)2CH)(Ph2CC-O)}ZnPh] (5) were obtained.

[Ca(BH4)2(THF)2] (1a), a known compound, was easily prepared following a convenient new procedure from [Ca(OMe)2] and BH3·THF in THF. Reaction of 1a with KCp* (Cp* = (η(5)-C5Me5)) and K{(Me3SiNPPh2)2CH} in a 1 : 1 ratio in THF resulted in the corresponding dimeric heteroleptic mono-borohydride derivatives [Cp*Ca(BH4)(THF)n]2 (2a) and [{(Me3SiNPPh2)2CH}Ca(BH4)(THF)2] (3a), respectively. Both compounds were fully characterized and the solid-state structure of 3a was established by single crystal X-ray diffraction. Compounds 1a, 2a, and 3a, together with the earlier reported compounds [Sr(BH4)2(THF)2] (1b), [Cp*Sr(BH4)(THF)2]2 (2b), and [{(Me3SiNPPh2)2CH}Sr(BH4)(THF)2] (3b), were used as initiators for the ROP of polar monomers. The general performances of the complexes in the ROP of ε-caprolactone and l-lactide demonstrate a relatively good control of the polymerization under the operating conditions established. α,ω-Dihydroxytelechelic poly(ε-caprolactone)s (PCLs) and poly(lactide)s (PLAs) were thus synthesized. DFT calculations on the initiation step of the ROP of ε-CL were carried out. Gibbs free energy profiles were determined for the three calcium complexes highlighting slightly more active calcium complexes as compared to strontium analogues, in agreement with experimental findings.