Amidinate bisborohydride complexes of rare-earth metals [6-Me-C5H3N-2-CH2C(NPri)2]Ln(BH4)2THF2 (Ln = Y, Nd): synthesis, structure, and catalytic activity in isoprene polymerization

Reactions of equimolar amounts of RN=C=NR (R = Pr i , Cy) and 6-Me-C 5 H 3 N-2-CH 2 Li prepared in situ by metallation of 2,6-dimethylpyridine with n -butyllithium afforded corresponding lithium amidinates [Li{6-Me-C 5 H 3 N-2-CH 2 C(NPr i ) 2 }]•1/3THF ( 1 ) and [Li{6-MeC 5 H 3 N-2-CH 2 C(NCy) 2 }] 4 ( 2 ) containing new tridentate amidinate ligands. The salt metathesis reactions of Ln(BH 4 ) 3 (THF) 3 (Ln = Y, Nd) with 1 (1: 1 molar ratio, THF) result in neutral amidinate bisborohydride complexes [Ln{6-Me-C 5 H 3 N-2-CH 2 C(NPr i ) 2 }(BH 4 ) 2 (THF) 2 } (Ln = Y ( 3 ), Nd ( 4 )). According to X-ray data, both compounds are monomeric, terminal borohydride ligands being coordinated to the rare earth metal atom in η 3 -fashion. Nitrogen atoms of the pyridine fragments of amidinate ligands are not involved in complexation with metal cations. Complexes 3 and 4 in combination with [Ph 3 C][B(C 6 F 5 ) 4 ] and AlBu 3 i (1: 1: 10 molar ratio) exhibit catalytic activity in isoprene polymerization.