Silica-induced elimination of dimethylamide from [(CO)5M(C⋮C)3C(NMe2)3]- [M = Cr (4a), W (4b)] affords the first isolated and characterized heptahexaenylidene complexes [(CO)5MCCCCCCC(NMe2)2] (5a,b). Complexes 4a,b were generated by sequential reaction of Me3Si(C⋮C)3SiMe3 with LiMe·LiBr, [(Me2N)3C]+Cl-, LiBu, and [(CO)5M(thf)]. Complex 5b is inert in methanol, but adds dimethylamine across the C5C6 bond to give [(CO)5WCCCCC{CHC(NMe2)2}NMe2]. The reaction of 5a,b with LiMe·LiBr and SiO2 generates the heptahexaenylidene complexes [(CO)5MCCCCCCC(Me)NMe2] (8a,b). Trapping of 8b with HNMe2 yields pentatetraenylidene complex [(CO)5WCCCCC{CHC(Me)NMe2}NMe2].

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The sequential reaction of the (dimethylamino)ethynylcarbene complexes [(CO)5MC(NMe2)C⋮CH] (1a−c:  M = W (a), Mo (b), Cr (c)) with BuLi, [M(CO)6], and CF3SO3CH3 affords homobinuclear complexes with an aminocarbene−cyclopropenylidene bridging ligand, (3a−c). Two isomeric heterobinuclear complexes (4xy and 4yx) are formed in the reaction of [(CO)5MC(NMe2)C⋮CH] (1) with BuLi, [M‘(CO)6] (M ≠ M‘:  W, Mo, Cr), and CF3SO3CH3. 4xy and 4yx differ in the relative distribution of the metals M and M‘:  (4xy) and (4yx). The 4xy/4yx ratios obtained by the two different possible reaction sequences are similar. Complexes 4xy and 4yx do not interconvert. The reaction of cis-[(CO)4(Me3P)WC(NMe2)C⋮CH] with BuLi, [W(CO)6], and CF3SO3CH3 likewise gives two isomers, (7) and (8). These results demonstrate the facile migration of carbonylmetal fragments along a carbon chain. The structures of the complexes 3b,c and 7 have been established by X-ray structural analyses.

To elucidate the dependence of the nonlinear optical (NLO) response on the conformation of triply branched derivatives, a new series of D-pi-A dendrimers has been synthesized. A combined approach of experiments (UV-vis and EOA measurements) and computational predictions (semiempirical and ab initio) was applied both on the dendrimers and on the corresponding single-strand chromophores. It has been shown that depending on the surrounding media the NLO activity of a flexible dendrimer can be very different. Two limiting cases are proposed: (i) the dendrimer resembles a solution of the corresponding single-strand chromophores with about 3-fold concentration, where the hyperpolarizability is the sum of the effect of three noninteracting single-strand subunits ("independent chromophores" limit); (ii) the dendrimers show nearly parallel or helical alignments of the single-strand subunits. Because of this change of conformation the NLO activity can be enhanced up to nine times the value of the "independent chromophores" limit and, thus, are more than a single strand chromophore. Conformers of dendrimers with interacting single-strand chromophores have been identified experimentally in nonpolar solutions by the EOA spectroscopy and possible structures have been revealed by numerical calculations, which could moreover show the tendency of the effects on the hyperpolarizability due to structural changes of the flexible dendritic architecture. Implications for future research developments are given to implement the "more than three times" concept.