No abstract

The synthesis and characterization of 4,4′-dinonyl-2,2′-bisoxazole (NBO) and its oligomers are described. The optical, electronic, and structural properties of these oligomers, NBO, NBO 2 , and NBO 3 , are compared to their sulfur analogues (NBT, NBT 2 , and NBT 3 ). In the series (NBO) n and (NBT) n , there is a red shift in the λ max as "n" increases. This effect is observed in both the solid and solution states. The bithiazole oligomers have longer wavelength absorbances than those of the bisoxazole oligomers; however, the observed red shift is greater as "n" increases for the bisoxazole oligomers leading to a merging of the absorption maxima between the two systems. The larger red shift for the bisoxazole series is explained by the larger atomic orbital coefficients at the coupling sites of the bisoxazole oligomers versus those of the bithiazole derivatives. Both systems exhibit thermochromic behavior corresponding to a transition from an ordered to disordered state. Upon heating, the bisoxazole system shows a gradual conformational change indicated by continual blue shifts of the absorption maximum. Conversely, the less rigid bithiazole system exhibits an immediate order-disorder transition upon heating evidenced by the appearance of an isosbestic point in the absorption spectrum. The solid-state packing of the n ) 2 and 3 oligomers is very similar; however, the solid-state structures of NBO and NBT are different as determined by single-crystal X-ray diffraction. NBO packs in a two-layered "ribbonlike" structure, whereas NBT forms molecular stacks. The reduction potentials of (NBO) n increase (become more positive) from -2.97 to -2.60 to -2.46 V for n ) 1, 2, and 3, respectively, and the number of reductions observed corresponds to the number of NBO units.

The (phosphinosilyl)cyclopentadiene 1-SiMe 2 PHMes-2,3,4,5-Me 4 C 5 H, prepared from 1-SiMe 2 -Cl-2,3,4,5-Me 4 C 5 H and LiPHMes (Mes ) 2,4,6-Me 3 C 6 H 2 ), reacts with MeLi to yield Li 2 [(C 5 -Me 4 )SiMe 2 PMes] (2). The (phosphinomethyl)cyclopentadienide Li[(C 5 H 4 )CMe 2 PH t Bu] (4) is obtained by the reaction of LiPH t Bu with 6,6-dimethylfulvene. Li 2 [(C 5 Me 4 )SiMe 2 PR] (R ) cyclohexyl (Cy; 1), Mes (2)) reacts in situ with ZrCl 4 at -30°C to give [{(η-C 5 Me 4 ) 2 SiMe 2 }-ZrCl 2 ] (5). The formation of (PCy) 4 and (PHMes) 2 , respectively, in these reactions was shown by 31 P NMR spectroscopy. In the reaction of Li[(C 5 H 4 )CMe 2 PHR] (R ) Ph (3), t Bu (4)) with ZrCl 4 or [TiCl 3 (thf) 3 ], [{(η-C 5 H 4 )CMe 2 PHR} 2 ZrCl 2 ] (R ) Ph (6), t Bu (7)) and [{(η-C 5 H 4 )CMe 2 -PHR} 2 TiCl] (R ) Ph (9), t Bu (10)) are formed. 6, 7, 9, and 10 slowly decompose on recrystallization from thf, Et 2 O, or toluene with formation of [{(η-C 5 H 4 ) 2 CMe 2 }MCl 2 ] (M ) Zr (8), Ti (11)). The formation of (PR) n (R ) Ph, n ) 4-6; R ) t Bu, n ) 4) and PH 2 R was shown by 31 P NMR spectroscopy. 2, 4, 5-8, and 11 were characterized by NMR spectroscopy ( 1 H, 13 C, 31 P) and the paramagnetic Ti(III) complexes 9 and 10 by EPR spectroscopy and mass spectrometry. 5, 8, and 11 were also characterized by crystal structure determinations.

No abstract

No abstract