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A series of neutral pyridyl adducts involving the strong Lewis acids BF 3 and B(C 6 F 5 ) 3 has been prepared, and their second-order nonlinear optical coefficients (EFISH method) have been examined. The formation of the pyridyl-boron bond leads to enhancement of the dipole moments and second-order NLO coefficients (β and β(0)). Reactions of DMAP (4-Me 2 N-C 5 H 4 N) with BH 3 , BF 3 , and B(C 6 F 5 ) 3 give the corresponding neutral pyridine adducts DMAP‚-BH 3 (orthorhombic, Pbca, a ) 9.6914(7) Å; b ) 11.7173(9) Å; c ) 22.718(2) Å; V ) 1622.4(5) Å 3 ; Z ) 8; p ) 1.114 g cm -3 ), DMAP‚BF 3 (orthorhombic, Pbca, a ) 10.430(3) Å; b ) 8.111(2) Å; c ) 20.295(7) Å; V ) 1717.0(9) Å 3 ; Z ) 8; p ) 1.470 g cm -3 ), and DMAP‚B(C 6 F 5 ) 3 (orthorhombic, Pbca, a ) 12.322(1) Å; b ) 20.556(2) Å; c ) 28.455(3) Å; V ) 7207.4(14) Å 3 ; Z ) 8; p ) 1.508 g cm -3 ). Reactions of Me 2 N-4-C 6 H 4 -CHdCH-C 5 H 4 N, MeO-4-C 6 H 4 -CHdCH-C 5 H 4 N, and Me 2 N-4-C 6 H 4 -CtC-C 5 H 4 N with BF 3 and B(C 6 F 5 ) 3 result in materials that are highly luminescent and incorporate structural features that are known to give rise to large second-order NLO effects. X-ray diffraction analysis for the compound Me 2 N-4-C 6 H 4 -CtC-C 5 H 4 N‚B(C 6 F 5 ) 3 (monclinic, P2 1 /c, a ) 9.883(2) Å; b ) 10.717(1) Å; c ) 28.421-(4) Å; β ) 91.96(1)°; V ) 2993.4(8) Å 3 ; Z ) 4; p ) 1.629 g cm -3 ) is also described.

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There is considerable interest in the use of metallocene or lanthanocene complexes as initiators of polymerization of acrylate-based monomers. 1 We and others have demonstrated that C 2 -symmetric, dialkyl zirconocene initiatorsse.g. rac-en(H 4 Ind) 2 ZrX 2 (1, X ) Me)spolymerize methyl methacrylate to isotactic poly-(methyl methacrylate) (i-PMMA) by an enantiomorphic, site-control mechanism. 2 While syndiotactic PMMA can be prepared using sterically encumbered, lanthanocene initiators at low temperatures, 1a,c,d,g attempts to use C ssymmetric, dialkyl zirconocene initiatorssi.e., Me 2 C-(Cp)(Flu)ZrX 2 (2, X ) Me)sfor this purpose have been unsuccessful. 2b,cAs we have shown elsewhere, either cationic enolate or neutral enolate complexes of zirconium (the latter in concert with metallocenium activators) may serve as initiators of acrylate polymerization. 1h Mechanistic studies can be simplified using such compounds, as formation of these species in situ (from, e.g., metallocene dialkyls, ionic activators, and acrylates) can be slow and/ or inefficient.We have attempted to prepare bis(enolate) complexes of 1 or 2 in the hope of studying isospecific or syndiospecific MMA polymerization using cationic enolates derived from such species. These synthetic studies have met with very limited success; in one case the bis-(enolate) complex 1 could be prepared [X ) OC(Me)d CH 2 ] but this compound failed to effect polymerization of MMA in the presence of B(C 6 F 5 ) 3 , [Ph 3 C][B(C 6 F 5 ) 4 ], or [PhNHMe 2 ][B(C 6 F 5 ) 4 ]. 3 More recently, we have focused our attention on linked, Cp-amido complexes of zirconium, as these compounds are less sterically encumbered than their metallocene "analogues", a feature which facilitates the synthesis of bis(enolate) complexes. We report here our observations using this class of initiators for MMA polymerization.The prototypical complex 4 4 reacts cleanly with 2 equiv of stable, lithium enolate 5 (R ) O t Bu) 5 to provide bis(enolate) complex 3 as a crystalline, white solid (eq 1). 6