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.

Ethylene polymerizations were conducted using β-diketimine complexes of Zr [LZrX 3 (1) and L 2 ZrX 2 (2) with L ) MeC(NAr)CHC(NAr)Me and X ) Cl, R (R ) Me, Bn)] as well as Cp(L)ZrX 2 (3) in the presence of MAO. Complexes 1 possess low polymerization activities (ca. 10 5 g PE/(mol Zr h)) and provide PEs with a trimodal, molecular weight distribution. Both 2 and 3 behave as single-site catalysts under these conditions, with the activity of the latter being considerably higher than the former (ca. 10 6 -10 7 vs 10 5 g PE/(mol Zr h)). Induction periods of 10-20 min at 70 °C were observed in polymerizations involving 3 (Ar ) Ph, X ) Cl, Me) when activated by MAO. The use of [Ph 3 C][B(C 6 F 5 ) 4 ] and 3b (Ar ) Ph, X ) Me) in the presence of small amounts of MAO (ca. 100:1 Al:Zr) led to rapid monomer uptake and an increase in catalytic activity by about a factor of 4. Lower activities were observed in the presence of Me 3 Al or i Bu 3 Al. Little or no polymerization activity was observed when excess 3b was used as a scrubbing agent (in the presence of [Ph 3 C][B(C 6 F 5 ) 4 ]), and rapid loss of activity was observed when excess 3b was added to a catalyst system already producing PE. Complex 3b reacts withwhich was characterized by X-ray crystallography. Complex 4 forms dinuclear complexes with 3b or Me 3 Al in solution at room temperature. These complexes, [Cp(L)Zr(µ-Me) 2 AlMe 2 ][B(C 6 F 5 ) 4 ] (6) or [(Cp(L)ZrMe) 2 -(µ-Me)][B(C 6 F 5 ) 4 ] (7), are fluxional in solution; at lower temperature, the solution NMR spectra are consistent with the structures shown. Complex 3b is a potent inhibitor of ethylene polymerization by 4, forming 7, which is resistant to dissociation. The presence of AlMe 3 (or MAO) appears to reversibly displace 3b from 7, allowing the reaction of 3b with [Ph 3 C]-[B(C 6 F 5 ) 4 ] to proceed to completion.

The clusters Ru 4 (CO) 13 (PNPr i 2 ) (1) and Os 4 (CO) 13 (PNPr i 2 ) (4) have been prepared via the reactions of Cl 2 PNPr i 2 with respectively [Ru 4 (CO) 13 ] 2and the reaction product of Na 2 [Os-(CO) 4 ] and Os 3 (CO) 12 . The successful synthesis of 4 suggests that the reaction of Na 2 [Os-(CO) 4 ] with Os 3 (CO) 12 generates [Os 4 (CO) 13 ] 2-, thus providing a relatively easy route for the preparation of this dianion. Thermal decarbonylation of 1 and 4 affords the tetranuclear clusters M 4 (CO) 12 (PNPr i 2 ) (M ) Ru, 2, and Os, 5), which upon chromatography and subsequent metathesis with Et 4 N[Cl] afford the [H 2 NPr i 2 ] + and [Et 4 N] + salts of [M 4 (CO) 12 (PO)] -(M ) Ru, 3, and Os, 6), respectively. The structures of 1, 2, 3[H 2 NPr i 2 ], 4, and 6[Et 4 N] were determined by X-ray crystallography. The M 4 P frameworks in 1 and 4 form a square pyramidal arrangement with the P atom occupying a basal position. The molecular structure of 2 reveals a five-vertex polyhedron with the PNPr i 2 ligand capping one face of a Ru 4 tetrahedron. The arrangement of metal and phosphorus atoms in 3[H 2 NPr i 2 ] and 6[Et 4 N] remains similar to that in 2. The phosphorus monoxide ligand, in each case, triply bridges a M 3 face of the tetrahedral M 4 skeleton with the P-O vector essentially perpendicular to this face. The interatomic P-O distances in 3[H 2 NPr i 2 ] and 6[Et 4 N] suggest double-bond character for the P-O moiety. Cleavage of the PN bond of an aminophosphinidene ligand followed by P-O bond formation may have general applicability for the preparation of metal clusters containing a PO ligand.