Heteroleptic [n]chromoarenophanes: ansa complexes derived from [Cr(η(5)-C5H5)(η(6)-C6H6)]

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.