RING-OPENING POLYMERIZATION OF STRAINED, RING-TILTED [1]FERROCENOPHANES WITH GERMANIUM IN THE BRIDGE - STRUCTURES OF THE [1]GERMAFERROCENOPHANE FE(ETA-C5H4)(2)GEME(2) AND THE FERROCENYLGERMANE FE(ETA-C(5)H(4)ET(2)CL)(ETA-C5H5)

The germanium-bridged [1]ferrocenophanes Fe(eta-C5H4)(2)GeR(2) (3a-c: a, R = Me, b, R = Et, and c, R = Ph) have been prepared via the reaction of Fe(eta-C5H4Li)(2).TMEDA (TMEDA = tetramethylethylenediamine) with the appropriate dichloroorganogermane R(2)GeCl(2). The monosubstituted ferrocenylgermane Fe(eta-C(5)H(4)GeEt(2)Cl)(eta-C5H5) (5) was isolated as a byproduct from the synthesis of 3b. An X-ray diffraction study of 3a revealed that this molecule possesses a highly strained, ring-tilted structure with an angle between the planes of the cyclopentadienyl rings of 19.0(9)degrees. The Fe-Ge distance (2.804(2) Angstrom) in 3a is ca. 18% longer than the sum of the covalent radii (2.38 Angstrom) and is consistent with a weak dative interaction. This conclusion was also supported by Fe-57 Mossbauer spectroscopic data for this species. The monosubstituted ferrocenylgermane 5 was also studied by single crystal X-ray diffraction. In this species the two cyclopentadienyl rings are modestly inclined toward each other in an opposite sense to those in 3a by 4.5(9)degrees. However, interestingly, the GeEt(2)Cl fragment is tilted significantly toward the iron center with an angle between the plane of the cyclopentadienyl ligand to which it is attached and the C(ipso)-Ge bond of 7.5(7)degrees. The Fe-Ge distance (3.412(5) Angstrom), although ca. 42% longer than the sum of the covalent radii, is consistent with a very weak dative interaction similar to that in ferrocene-stabilized carbocations such as [Fe(eta-C(5)H(4)CPh(2))(eta-C5H5)](+) (6). Compounds 3a-c were found to undergo facile ring-opening polymerization when heated in the melt to yield high molecular weight (M(w) = (1.0 x 10(6))-(2.0 x 10(6)) and M(n) = (2.3 x 10(5))-(8.5 x 10(5))) poly(ferrocenylgermanes) [Fe(eta-C5H4)(2)GeR(2)](n) 7a-c. Compounds 3a and 3b were found to be sensitive to moisture and afforded the ferrocenylgermoxanes 8a and 8b when exposed to the atmosphere. Crystals of 3a are triclinic, space group P $($) over bar$$ 1, with a = 7.269(3) Angstrom, b = 8.426(4) Angstrom, c = 9.273(4) Angstrom, alpha 82.96(4)degrees, beta = 78.78(4)degrees, gamma = 80.07(3)degrees, V = 546.4(3) Angstrom(3), and Z = 2. Crystals of 5 are tetragonal, space group I4(1)/a, with a 12.307(4) Angstrom, c = 38.690(10) Angstrom, V = 5860(2) Angstrom(3), and 2=16.