Xiaolai Zheng

Synthesis and structure of aminobis(η1-cyclopentadienyl)boranes and related compounds

Abstract Amino(diorganyl)boranes of the type R2NB(η1-CxHy)2 R=various ligands, CxHy=C5H5 (cyclopentadienyl), C9H7 (indenyl), C13H9 (fluorenyl) were recently reported as ligands in corresponding [1]borametallocenophanes of the Group IV metals Ti, Zr, and Hf. Several of those ligands including bis(cyclopentadienyl)boranes, cyclopentadienyl(indenyl)boranes, and difluorenylboranes such as iPr2NB(η1-C5H5)2 (7), iPr2NB(η1-C5H5)(η1-C9H7) (12), and Me2NB(η1-C13H9)2 (13), were obtained in very high yields and fully characterised. All compounds besides 13 show the expected presence of different constitutional isomers. Compound 7 was chosen as a representative example to assign all isomers by NMR methods. The structures of 12 (one isomer) and 13 in the solid state were determined by X-ray diffraction methods.

1‐Aminoboratabenzene Complexes of Scandium Group Metals

The syntheses of the new lithium boratabenzenes Li(3,5-Me2C5H3BNiPr2), Li(3), and Li2[(3,5-Me2C5H3BNMe)2(CH2)2], Li2(5), via the dicarbanion route are described. Lithium 1-aminoboratabenzenes react with metal trihalides in toluene (110 °C, 3 d) to give the stepped ladder dimers [(3,5-Me2C5H3BNMe2)2Y(μ-Cl)2Li]2, (12), [(3,5-Me2C5H3BNMe2)2Lu(μ-Cl)2Li]2 (13), and the mononuclear complexes YCl[3,5-Me2C5H3BN(SiMe3)2]2 (18), LuCl[3,5-Me2C5H3BN(SiMe3)2]2 (19), and ScCl(3,5-Me2C5H3BNiPr2)2 (20). When donor solvents such as THF or THP are used, analogous reactions take place at ambient temperature, giving solvates such as (3,5-Me2C5H3BNMe2)2Sm(μ-Cl)2Li(THF) (15), (3,5-Me2C5H3BNMe2)2Y(μ-Cl)2Li(THP) (16), (3,5-Me2C5H3BNiPr2)2Y(μ-Cl)2Li(THF)2 (21), (3,5-Me2C5H3BNiPr2)2Sm(μ-Cl)2Li(THF)2 (22), and the ansa complexes [(3,5-Me2C5H3BNMeCH2)2]Lu(μ-Cl)2Li(THF)2 (23) and [(3,5-Me2C5H3BNMeCH2)2]Lu(μ-Cl)2Li(THP)2 (24). The bridge cleavage product Y(acac)(3,5-Me2C5H3BNMe2)2 (14) is obtained from 12 and Na(acac) in toluene at ambient temperature. The complexes 12, 14, 16, 18·PhMe, 19·PhMe, 20 (as two polymorphs α-20 and β-20), 21, and 24 (as the rac-stereomer) are characterized by single-crystal structure determinations. In all structures except those of the mononuclear complexes 18 and 19, the ring-ring rotational positions are close to 180°, cf. e.g. 14, or to 60°, cf. e.g. 20; these conformations minimize transannular ligand-ligand repulsions. The internal coordination of a B-NMe2 sidearm, which is unprecedented, is found in the structures of the stepped ladder dimers 12 and 13, and in the mononuclear complexes 15 and 16. According to solution NMR spectroscopy, all complexes are dynamic with respect to ring-ring rotation and, in the cases with internal coordination, they are dynamic with respect to the interchange between free and coordinated B-NMe2 sidearms.

Bent Metallocenes of Germanium, Tin, and Lead with Aminoboratabenzene Ligands − Crystal Structures of E[3,5-Me2C5H3BN(SiMe3)2]2 (E = Ge, Sn, and Pb)

The reaction of GeI2, SnCl2, or PbCl2 with two equivalents of lithium aminoboratabenzenes in diethyl ether affords the new sandwich compounds Pb(3,5-Me2C5H3BNMe2)2 (4) and E[3,5-Me2C5H3BN(SiMe3)2]2 (5: E = Ge, 6: E = Sn, 7: E = Pb). While compound 4 undergoes a redox ligand coupling reaction at ambient temperature to give lead black and ligand dimers, the bis(trimethylsilyl)amino compounds 5−7 are thermally stable, and coupling products are only detected under the conditions of mass spectrometry. This difference in stability can be attributed to the different perturbation effects which the B-amino groups exert on the electronic properties of the boratabenzene rings. Crystal structure determinations reveal that the compounds 5−7 possess a monomeric bent-sandwich geometry in the solid state with facially bonded boratabenzenes. The E−C distances span rather large ranges [5: 2.320−2.939(4) A; 6: 2.519−3.033(9) A; 7: 2.632−3.054(7) A]; the central element E is always particularly close to one of the two α-C atoms and displays intermediate E−B distances.