Macromolecules derived from 1,3-dienes, such as polyisoprene (or natural rubber), are of considerable importance in polymer science. Given the parallels between P=C and C=C bonds, the prospect of polymerizing P-containing 1,3-dienes, such as 1-phosphaisoprene, is intriguing due to the unique chemical functionality imparted by the heavier element combined with their structural relationship to natural rubber. Herein, we report the synthesis, characterization and coordination chemistry of the first polymers derived from Mes*P=CR-CH=CH (Mes*=2,4,6-t-Bu C H ; R=H, Me). In the case of 1-phosphaisoprene (R=Me), the monomer is isolable and its anionic polymerization affords a polymer that retains P=C bonds in its microstructure. The chemical functionality of these novel materials is demonstrated by forming the macromolecular gold(I) complex where the P=C bond is retained for further chemical elaboration.

The synthesis of the first tin-bridged bis(benzene) vanadium and trovacene sandwich compounds and the investigation of their oxidative addition and insertion behavior are reported. The vanadoarenophanes and the corresponding platinum insertion products were fully characterized including electrochemical and electron paramagnetic resonance (EPR) measurements. Controllable ring-opening polymerization of the heteroleptic tin-bridged [1]trovacenophane using Karstedt's catalyst yields a high molecular weight polymer (up to M(n) = 89 200 g·mol(-1)) composed of d(5)-vanadium metal centers in the main chain, making it a rare example of a spin-carrying macromolecule. Magnetic susceptibility measurements (SQUID) confirm the paramagnetic scaffold with repeating S = 1/2 centers in the main chain and suggest antiferromagnetic interactions between adjacent spin sites (Weiss constant Θ = -2.9 K).

Taking advantage of an improved synthesis of [Ti(η(6) -C6 H6 )2 ], we report here the first examples of ansa-bridged bis(benzene) titanium complexes. Deprotonation of [Ti(η(6) -C6 H6 )2 ] with nBuLi in the presence of N,N,N',N'',N''-pentamethyldiethylenetriamine (pmdta) leads to the corresponding 1,1'-dilithio salt [Ti(η(6) -C6 H5 Li)2 ]⋅pmdta that enables the preparation of the first one- and two-atom-bridged complexes by simple salt metathesis. The ansa complexes were fully characterized (NMR spectroscopy, UV/Vis spectroscopy, elemental analysis, and X-ray crystallography) and further studied electrochemically and computationally. Moreover, [Ti(η(6) -C6 H6 )2 ] is found to react with the Lewis base 1,3-dimethylimidazole-2-ylidene (IMe) to give the bent sandwich complex [Ti(η(6) -C6 H6 )2 (IMe)].

The synthesis of ansa complexes has been studied intensively owing to their importance as homogeneous catalysts and as precursors of metal-containing polymers. However, paramagnetic non-metallocene derivatives are rare and have been limited to examples with vanadium and titanium. Herein, we report an efficient procedure for the selective dilithiation of paramagnetic sandwich complex [Cr(η(5)-C(5)H(5))(η(6)-C(6)H(6))], which allows the preparation of a series of [n]chromoarenophanes (n = 1, 2, 3) that feature silicon, germanium, and tin atoms at the bridging positions. The electronic and structural properties of these complexes were probed by X-ray diffraction analysis, cyclic voltammetry, and by UV/Vis and EPR spectroscopy. The spectroscopic parameters for the strained and less strained complexes (i.e., with multiple-atom linkers) indicate that the unpaired electron resides primarily in a d(z)2 orbital on chromium(I); this result was also supported by density functional theory (DFT) calculations. We did not observe a correlation between the experimental UV/Vis and EPR data and the degree of molecular distortion in these ansa complexes. The treatment of tin-bridged complex [Cr(η(5)-C(5)H(4))(η(6)-C(6)H(5))SntBu(2)] with [Pt(PEt(3))(3)] results in the non-regioselective insertion of the low-valent Pt(0) fragment into the C(ipso)-Sn bonds in both the five- and six-membered rings, thereby furnishing a bimetallic complex. This observed reactivity suggests that ansa complexes of this type are promising starting materials for the synthesis of bimetallic complexes in general and also underline their potential to undergo ring-opening processes to yield new metal-containing polymers.

The preparation of [3]thoro- and [3]uranocenophanes, the first structurally authenticated ansa-bridged complexes of actinocenes, is reported. Following a flytrap route, 1,2-bis(cyclooctatetraenyldimethylsilyl)methane was synthesized, reduced to its tetraanion, and subsequently converted into bridged uranocene and thorocene complexes by salt metathesis with the corresponding actinide tetrachlorides. In addition, their electronic structures have been investigated by experimental (UV/Vis spectroscopy, cyclic voltammetry) and theoretical (DFT) methods.