Planar-chiral ferrocenylphosphine-borane complexes featuring agostic-type B-HE (E = Hg, Sn) interactions.

The synthesis of ferrocenylphosphine-borane adducts 1,2-fc(E)(PPh2·BH3) (E = SnR2R', HgX; 1,2-fc = 1,2-ferrocenediyl) that are substituted with organotin or organomercury Lewis acid moieties in ortho-position is presented. Several compounds that feature two ferrocenylphosphine-borane moieties bridged by Sn or Hg are also introduced. The products are fully characterized by multinuclear NMR spectroscopy, high-resolution MALDI-TOF mass spectrometry and elemental analysis. The attachment of the Lewis acid substituent to the same Cp ring of the ferrocene results in planar-chirality and the close proximity between the boron hydride group and the Lewis acid is expected to allow for agostic-type B-HE (E = Sn, Hg) interactions. Structural investigations by X-ray diffraction reveal a short B-HSn contact of 2.755(4) Å for 1,2-fc(SnMe2Cl)(PPh2·BH3), which is only the second reported example of such a short agostic-type contact involving a coordinatively saturated tin(iv) center. In contrast, for the tetraorganotin derivatives 1,2-fc(SnMe3)(PPh2·BH3) and [1,2-fc(PPh2)](µ-SnMe2)[1,2-fc(PPh2·BH3)], in which the Lewis acidity of the tin atom is weaker than in 1,2-fc(SnMe2Cl)(PPh2·BH3), the B-HSn distances are much longer but still within the sum of the van der Waals radii of Sn and H (∑vdW = 3.27 Å). The chloromercury-substituted ferrocenylphosphine-borane 1,2-fc(HgCl)(PPh2·BH3) shows a similarly short B-HHg contact of 2.615(5) Å (∑vdW = 3.15 Å). Inspection of the extended structure of 1,2-fc(HgCl)(PPh2·BH3) reveals that the Lewis acidic mercury atom is also involved in intermolecular HgCl interactions with a neighboring molecule. An analysis of 31P and 11B NMR data reveals a correlation between the chemical shifts and the Lewis acidity of the adjacent organotin/mercury substituent. Structure optimization of 1,2-fc(SnMe3)(PPh2·BH3) and 1,2-fc(SnMe2Cl)(PPh2·BH3) by density functional theory (DFT) indicates B-HSn contacts respectively of 3.129 and 2.631 Å that are close to the experimental values. Natural bond orbitals (NBO) and atom in molecules (AIM) analyses reveals a B-H→Sn donor-acceptor interaction energy of 5.46 kcal mol-1 and a B-HSn bond path for the chlorodimethyltin-substituted derivative with a modest electron density ρ(r) of 0.0082 a.u. and a positive Laplacian at the bond critical point.

Tuning the strain and polymerizability of organometallic rings: the synthesis, structure, and ring-opening polymerization behavior of [2]ferrocenophanes with C-SI, C-P, and C-S bridges.

A series of novel [2]ferrocenophanes with unsymmetrical C-E bridges has been prepared in which the covalent radius of the second-row element, E, and hence the ring strain present is varied. Species [Fe(eta-C(5)Me(4))(eta-C(5)H(4))CH(2)ER(x)] (7, ER(x) = SiMe(2); 8a, ER(x) = PPh; 8b, ER(x) = PMes; 9, ER(x) = S) were synthesized via reaction of the PMDETA (N,N,N',N' ',N' '-pentamethyldiethylenetriamine) adduct of [(eta-C(5)H(4)Li)Fe(eta-C(5)Me(4))CH(2)Li] with Cl(2)ER(x) (E = Si or P) or S(SO(2)Ph)(2). Studies of 7-9 by single-crystal X-ray diffraction confirmed the presence of ring-tilted structures: for 7, alpha (angle between the planes of the Cp rings) = 11.8(1) degrees; for 8a, alpha(average) = 14.9(3) degrees; for 8b, alpha(average) = 18.2(2) degrees; and for 9, alpha = 18.5(1) degrees. The least tilted compound, 7, was found to be resistant to thermal, anionic, and transition metal catalyzed ROP. In contrast, the significantly more tilted compounds 8a, 8b, and 9 were all found to polymerize thermally with small negative values of DeltaH(ROP) of ca. 10-20 kJ.mol(-1) determined by DSC. Whereas thermal ROP of 8a yielded the soluble high molecular weight polycarbophosphaferrocene [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)PPh](n) (11), species 9 formed the insoluble polycarbothiaferrocene [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)S](n) (14). Attempted anionic ROP of 8a and 9 with (n)BuLi was unsuccessful and treatment of 8a with CF(3)SO(3)Me resulted in the formation of the novel phosphonium salt [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)PMePh][CF(3)SO(3)] (13), which was found to be resistant to thermal ROP as a result of its less strained structure (for 13, alpha = 11.4(7) degrees ). Treatment of 9 with CF(3)SO(3)Me or BF(3).Et(2)O resulted in the first example of cationic ROP for a transition metal-containing heterocycle to yield polycarbothiaferrocene 14. In the presence of excess 2,6-di-tert-butylpyridine as a selective proton trap, ROP of 9 was only observed with CF(3)SO(3)Me, and not BF(3).Et(2)O, which indicated that Me(+) and H(+) are the probable cationic initiators, respectively. Thermal copolymerization of 9 with trimethylene sulfide resulted in the isolation of the soluble, high molecular weight, random copolymer [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)S](n)[(CH(2))(3)S](m), 15.

Selective ring-opening reactions of

The reactivity of strained [1]ferrocenophanes, [Fe(eta-C5H4)2ERx] (ERx = SiMe2, 1a: SiMePh, 1b; SnR2, 1c), towards boron halides has been investigated and has been shown to provide a facile pathway to ferrocene derivatives functionalized with Lewis acidic boron centers. The boron halides RBX2 (R = Cl, Ph, fc; X = Cl, Br) (fc = Fe(eta-C5H4)2) lead to selective cleavage of the Si-Cp bonds in 1a and 1b to give, depending on the reaction stoichiometry, functionalized mono- or diferrocenylboranes RnB [(eta-C5H4)Fe(eta-C5H4SiMe2Cl)](3-n) (2a: R = Cl, n = 2; 2b: R = Cl, n = 1; 2c: R = Ph, n = 1) and RnB[(eta-C5H4)Fe(eta-C5H4SiMePhCl)](3-n) (2d: R = Cl, n = 2) in high yields. Compounds 2a-d were characterized by multinuclear NMR spectroscopy, mass spectrometry, and by single-crystal X-ray diffraction (for 2b). Most likely due to steric constraints, a triferrocenylborane was not obtained even from the reaction of BCl3 with an excess of 1a, whereas facile formation of the diferrocenylphenylborane 2c from PhBCl2 and two equivalents of 1a was observed. Selective hydrolysis of the B-Cl bonds of chlorodiferrocenylborane 2b in the presence of trace amounts of water led to the silylated tetranuclear ferrocene complex [(ClMe2Sifc)2B-O-B(fcSiMe2Cl)2] (3) without cleavage of the Si-Cl bonds. The structure of 3 was confirmed by an X-ray diffraction study. Studies of the reactivity of the higher Group 14 homologue of 1a and 1b, the tin-bridged [1]ferrocenophane 1c, revealed that facile addition of B-Cl bonds occurs across the Sn-Cp bonds to yield the 1-stannyl-1'-borylferrocenes [(ClMes2Sn)fc(BClR)] (4a: R = Cl; 4b: R = Ph; Mes = 2,4,6-Me3C6H2). The new synthetic methodology can be extended to bifunctional Lewis acids such as the bis(boryl)ferrocene 1,1'-fc(BBr2)2, which affords the linear boron-bridged ferrocene trimer 1,1'-[fc[B(Br)fcSiMe2Br]2] 5 in 54% isolated yield. In order to incorporate the functionalized ferrocenylboranes into polymer structures, compound 2c was reduced with Li[BEt3H] to give the silicon-hydride functionalized species [PhB[(eta-C5H4)Fe(eta-C5H4SiMe2H)]2] (6), which was then used as a capping reagent in the transition metal catalyzed polymerization of 1a. This process leads to the incorporation of the ferrocenylborane unit into the main chain of a poly(ferrocenylsilane) to afford [PhB-[(fcSiMe2)(n-1)fcSiMe2H]2] (7).