2 ]Li in toluene at 65°C. The complexes were isolated after recrystallization from hexane in 66, 64, and 68 % yield, respectively. X-ray diffraction studies revealed that compounds 1-3 are heterodimetallic complexes that have two borohydride li-

The synthetic pathway to a new bis(amidine) ligand with a conformationally rigid naphthalene linker, 1,8‐C10H6[NHC(tBu)=N(2,6‐Me2–C6H3)][N=C(tBu)NH(2,6‐Me2–C6H3)] (3) was elaborated. Deprotonation of this bis(amidine) ligand with two equivalents of nBuLi and subsequent reaction with anhydrous LnCl3 (Ln = Y, Nd, Sm) allowed the synthesisof the chlorido complexes [1,8‐C10H6{NC(tBu)N‐2,6‐Me2–C6H3}2]YCl(dme) (4), [1,8‐C10H6{NC(tBu)N‐2,6‐Me2–C6H3}2]Nd(dme)(μ‐Cl)2Li(dme) (5), and [1,8‐C10H6{NC(tBu)N‐2,6‐Me2–C6H3}2]Sm(thf)(μ‐Cl)2Li(thf)2 (6), which are coordinated by the linked dianionic bis(amidinate) ligand. The structures of complexes 4–6 were established by X‐ray diffraction studies, which reveal that the new ligand framework can coordinate to the lanthanide atoms in different fashions depending on the central atom ion size. Alkylation of complex 6 with equimolar amounts of LiCH2SiMe3 afforded the unexpected amido–amidinate complex [{1,8‐C10H6(NC(tBu)N‐2,6‐Me2–C6H3)2}{1,8‐C10H6(NC(tBu)N‐2,6‐Me2–C6H3)(NH)}Sm][Li(dme)3] (7), which obviously results from the cleavage of one amidinate group during decomposition of the transient alkyl species and ligand redistribution.

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The reactions of lanthanide tris(borohydrides) Ln(BH 4 ) 3 (thf) 3 (Ln = Sm or Nd) with 2 equiv. of lithium N,N´ diisopropyl N´ bis(trimethylsilyl)guanidinate in toluene produced the [(Me 3 Si) 2 NC(NPr i ) 2 ]Ln(BH 4 ) 2 Li(thf) 2 complexes (Ln = Sm or Nd), which were isolated in 57 and 42% yields, respectively, by recrystallization from hexane. X ray diffraction experi ments and NMR and IR spectroscopic studies demonstrated that the reactions afford mono meric ate complexes, in which the lanthanide and lithium atoms are linked to each other by two bridging borohydride groups. The complexes exhibit catalytic activity in polymerization of methyl methacrylate.Lanthanide borohydride complexes of the metallocene series have been known for more than three decades. 1 Nevertheless, this class of compounds continues to at tract considerable interest because of the structural diver sity and high catalytic activity. 2 The borohydride groups can serve as both bridging and terminal ligands having different dentation. 3,4 Depending on the ionic radius of the central atom and its coordination environment, boro hydride groups can serve as bi , 1,3-8 tri , 1,9 or tetradentate ligands. 3,4 A renewed interest in lanthanide borohydride complexes has been stimulated by reports on their high catalytic activity in polymerization of lactones, 10,11 me thyl methacrylate, 12 and isoprene. 13 The reactivity of or ganic derivatives of lanthanides depends primarily on the high polarity of the metal-ligand bond and large ionic radii of Ln. Due to this, combined with a large positive charge on the metal center, these compounds are very sensitive to the degree of steric saturation of their coordi nation sphere. Hence, a search for new types of the coor dination environment, which can stabilize lanthanide complexes and modify their reactivity and catalytic activ ity, is an important problem. Until recently, the range of known rare earth metal borohydride complexes has been limited primarily to derivatives of the metallocene se ries. 2 The yttrium bis(amidinate) borohydride complex [PhC(NSiMe 3 ) 2 ] 2 YBH 4 (thf) 14 and lanthanide derivatives containing the polydentate diphenoxide O,O,N,N li gands 11,12 are the only exception. In the synthesis of new lanthanide borohydride complexes, we used tetrasub stituted guanidinate ligands, whose steric and electronic properties can easily be modified by varying substituents at the N atoms. The aim of the present study was to synthesize lanthanide bis(guanidinate) borohydride de rivatives {(Me 3 Si) 2 NC(NPr i ) 2 } 2 Ln(BH 4 ) 2 Li(thf) 2 (Ln = Sm (1) or Nd(2)) and investigate their structures and catalytic activity. Results and DiscussionInitially, we intended to prepare borohydride complexes by the reactions of NaBH 4 with the cor responding bis(guanidinate) chloride derivatives [{(Me 3 Si) 2 NC(NPr i ) 2 } 2 LnCl] 2 (Ln = Nd or Sm). 15,16 The latter are easily produced in the reaction of anhydrous halides LnCl 3 with 2 equiv. of {(Me 3 Si) 2 NC(NPr i ) 2 }Li, which is generated in situ from [(Me 3 Si...

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