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A series of high molecular weight, symmetrically substituted poly(ferrocenylsilanes) [Fe(ij-C5H4)2(SiR2)]n (2a-e: a, R = Me; b, R = Et; c, R = Bu; d, R = Hex; e, R = Ph) have been prepared via the thermal ring-opening polymerization of the corresponding strained cyclic ferrocenylsilane monomers Fe(ij-C6H4)2(SiR2) (la-e). The latter species were prepared via the reaction of dilithioferrocene/TMEDA (TMEDA = tetramethylethylenediamine) with the appropriate symmetrically substituted dichloroorganosilane R2-SiCl2. Polymers 2a-d were structurally characterized by , 13C, and 29Si NMR, UV/visible spectroscopy, and elemental analysis. The molecular weights of polymers 2a-d were estimated by gel permeation chromatography using polystyrene standards. Polymer 2e was found to be insoluble in common organic solvents and was characterized by solid-state NMR. In addition, the solution behavior of [Fe(j)-C5H4)2-(SiBu2)]n (2c) was investigated by low-angle laser light scattering which yielded an absolute value of = 2.29 X 105 and a second virial coefficient, A2 = 1.3 X 10-4 mol cm2 g~2 in THF at 20 °C. The glass transition behavior of the poly (ferrocenylsilanes) 2a-d was investigated by differential scanning calorimetry and dynamic mechanical analysis. Glass transition temperatures varied with the substituents present and were found in the range of -26 °C (for polymer 2d) to +33 °C (for polymer 2a). No evidence for melting transitions was detected for the polymer samples studied. UV/visible spectra of polymers 2a-d were measured in THF in the 200-800-nm range and were found to be consistent with an essentially localized electronic structure for the polymer backbone.

The strained cyclic ferrocenylsilane Fe(tpC5H4)2(SiMe2) (11, containing a single silicon atom in the bridge, undergoes thermal ring-opening polymerization a t 130 OC to yield the highmolecular-weight poly(ferrocenylsi1ane) [Fe(?-C5H4)2(SiMez)I. (2). In contrast, the analogous cyclic ferrocenyldisilane Fe(tpC5H&(SiMe2)2 (31, with two silicon atoms in the bridge structure, is resistant to polymerization under the same conditions. In order to probe the reasons for the dramatic difference in polymerization behavior between 1 and 3, the molecular structures of these species have been determined by single-crystal X-ray diffraction. This has allowed the first structural comparison of [ 11-and [2]ferrocenophanes with the same bridging atoms (silicon) and substituents (methyl). The cyclic ferrocenylsilane 1 was found to possess a strained, ringtilted structure with an angle between the planes of the cyclopentadienyl rings of 20.8(5)". In addition, considerable distortion from planarity was detected for the cyclopentadienyl carbon atom bonded to the bridging silicon moiety. In contrast, the cyclic ferrocenyldisilane 3 possesses a much less distorted structure and the corresponding tilt angle between the cyclopentadien 1 ligands is only 4.19 (2)O. Crystals of 1 are monoclinic, space group P21/a, with a = 7.438(3) x , b = 10.322(4) A, c = 15.575(6) A, @ = 99.04(3)O, V = 1180.9(8) A3, and 2 = 4. Crystals of 3 are monoclinic, space group P21/n, with a = 10.433(2) A, b = 8.703(1) A, c = 17.243(2) A, @ = 107.32(1)O, V = 1494.6(12) A3, and 2 = 4.

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The addition of Lewis bases L to the methyl(methylidene)boranes MeBϭCA 2 (A ϭ SiMe 3 ) and MeBϭCAAЈ (AЈ ϭ SiMe 2 Cl) gives the adducts MeB(L)ϭCA 2 (1a, b; L ϭ trimethylpyridine, PMe 3 ) and MeB(L)ϭCAAЈ (1c, d; L ϭ di-and trimethylpyridine), respectively. Alcohols and amines HX are added to the BC double bond to give boranes MeB(X)ϪCHA 2 (8aϪc; X ϭ OiPr, OtBu, NiPr 2 ); MeBϭCAAЈ and HNMe 2 react in the ratio 1:2, yielding MeB(X)ϪCHA(SiMe 2 X) (2d; X ϭ NMe 2 ). From MeBϭCA 2 and BH 3 , the five-membered ring [ϪCA 2 ϪBHϪCA 2 ϪBMe(Hm) 2 BMeϪ] (2e; 2:1) or the six-membered ring [ϪCA 2 ϪBH(H µ ) 2 BMeϪCA 2 ϪBH(H µ ) 2 BMeϪ] (2f; 1:1) are formed, both containing double hydrogen bridges; the product 2f crystallizes in the space group P1. The metallocene trihydrides [Cp 2 MH 3 ] add to the BC double bond under formation of a double hydrogen bridge to give [Me(A 2 CH)B(H µ ) 2 MCp 2 ] (2g, h; M ϭ Nb, Ta). MeBϭCA 2 can be chloroborated, -stannated, and -phosphated with EϪCl to yield the boryldisilylmethanes MeB(Cl)ϪCA 2 ϪE (2iϪl; E ϭ EtClB, tBuClB, Me 2 ClSn, Cl 2 P). The alkyloboration and -alumination with EϪR leads to the boryldisilylmethanes MeBRϪSiA 2 ϪE (2mϪo; EϪR ϭ Me 2 BϪMe, Et 2 BϪEt, Cl 2 AlϪEt) and the bromination to MeB(Br)ϪCA 2 Br. (2ϩ2) Cycloadditions are achieved, when MeBϭCA 2 is reacted with unsaturated molecules aϭb, yielding four-membered rings [ϪBMeϪCA 2 ϪbϪaϪ] [4aϪd; aϭb ϭ fluorenone, bis(methoxycarbonyl)ethyne (reacting at both of the CϭO bonds), phenylisocyan-Reaktionen an der Bor-Kohlenstoff-Doppelbindung von Methyl(methyliden)boranen Inhaltsübersicht. Die Addition von Lewisbasen L an die Methyl-(methyliden)borane MeBϭCA 2 (A ϭ SiMe 3 ) und MeBϭCAAЈ (AЈ ϭ SiMe 2 Cl) führt zu den Addukten MeB(L)ϭCA 2 (1a, b; L ϭ Trimethylpyridin, PMe 3 ) bzw. MeB(L)ϭCAAЈ (1c,d; L ϭ Di-und Trimethylpyridin). Alkohole und Amine HX addieren sich an die BC-Doppelbindung unter Bildung von MeB(X)ϪCHA 2 (2a-c; X ϭ OiPr, OtBu, NiPr 2 ); MeBϭCAAЈ und HNMe 2 reagieren im Verhältnis 1:2 zu MeB(X)ϪCHA(SiMe 2 X) (2d; X ϭ NMe 2 ). Aus MeBϭCA 2 und BH 3 bilden sich der fünfgliedrige Ring [ϪCA 2 ϪBHϪCA 2 ϪBMe(H µ ) 2 BMeϪ] (2e; 1:2) oder der sechsgliedrige Ring [ϪCA 2 ϪBH(H µ ) 2 BMeϪCA 2 ϪBH(H µ ) 2 BMeϪ] (2f; 1:1), die beide Wasserstoff-Doppelbrücken enthalten; der Sechsring 2f kristallisiert in der Raumgruppe P1. Die Metallocentrihydride [Cp 2 MH 3 ] addieren sich an die BC-Doppelbindung unter Bildung einer Wasserstoff-Doppelbrücke zu [Me(A 2 CH)B(H µ ) 2 MCp 2 ] (2g, h; M ϭ Hf, Ta). MeBϭCA 2 kann mit EϪCl zu Boryldisilylmethanen MeB(Cl)ϪCA 2 ϪE chloroboriert, -stanniert und -phosphaniert werden (2iϪl; E ϭ EtClB, tBuClB, Me 2 ClSn, Cl 2 P). Die Alkyloborierung und -aluminierung mit EϪR ergibt die Boryldisilylmethane MeB(R)ϪCA 2 ϪE (2mϪo; EϪR ϭ Me 2 BϪMe, Et 2 BϪEt, Cl 2 AlϪEt) und die Bromierung MeB(Br)ϪCA 2 Br (2p). (2ϩ2)-Cycloadditionen beobachtet man, wenn MeBϭCA 2 mit ungesättigten Molekülen aϭb zu Vierringen [ϪBMeϪCA 2 ϪbϪaϪ] [4aϪd;508 MeBϭCAAЈ und AN 3 . Schließlich entstehen aus MeBϭCA 2 bzw.MeBBϭCAAЈ und dem Nitron OϪNMeϭC...

The structural characterization of the boratophosphazene N-(PCl 2 NMe) 2 BCl 2 (1) is reported and reveals a distorted structure in which the boron atom is bent out of the plane of the other ring atoms (0.39 (1) show the presence of planar rings with B ± N bond lengths (ca.

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