Template controlled self-assembly of bidentate phosphine complexes with hemilabile coordination behaviour

Abstract

Template-assisted self-assembly of ditopic catechol phosphines creates complexes containing a chelating diphosphine ligand, which display hemilabile coordination properties with prospects for applications in catalysis.

Template‐Controlled Assembly of Ditopic Catechol Phosphines: A Strategy for the Generation of Complexes of Bidentate Phosphines with Different Bite Angles

“…The product, which was isolated in 60 % yield after precipitation from a ternary DMF/CH 2 Cl 2 /diethyl ether mixture, was identified by its analytical and spectroscopic data and a single-crystal X-ray diffraction study as the trinuclear complex 9 (Scheme 2), in which the zirconium atom acts as a double template spanning two bisphosphine moieties. Interestingly, this species was likewise obtained as the only isolable product during attempts to prepare a monopalladium template complex with a structure similar to those of 6-8 from the starting bis(cyclopentadienyl)zirconium dichlor- [12] and indicates that the p-bonded Cp ligand is more vulnerable to electrophilic attack than a methyl substituent. The reactions involving aluminium and silicon chlorides as templates were messy and did not yield isolable products; these reactions were therefore not pursued further.…”

“…The reaction involving tin tetrachloride was less selective, and after 24 h had produced a mixture of several products from which complex 6 was isolated in 40 % yield after a similar workup procedure. [12] In attempts to optimize the reaction conditions it was found that the highest level of conversion to the desired template complex was obtained when the reaction temperature was raised to 60 8C; performing the reaction under these conditions allowed 6 to be isolated in 60 % yield after the same workup procedure.…”

“…The available results show that the assembled ligand entities are sufficiently rigid to display specific bite angles [11] and exhibit interesting features such as hemilabile coordination behavior. [12] Correspondingly, it might be expected that self-assembly of the same ligand building block on templates of different size and coordination geometry should be utilizable to construct a series of bisphosphine chelates with variable geometric predispositions of the donor moieties, thus allowing fine-tuning of the steric bulk and, in particular, the bite angle of the chelating ligand by directed adjustment of the shape of the supramolecular backbone. In order to validate this hypothesis, we have explored in some detail the synthesis of complexes through self-assembly of 1, a palladium precursor, and different templates derived from tri-or tetravalent main group elements or transition metals, respectively.…”

“…[11] In a preliminary account, it was further reported that the construction of a template-based bidentate ligand and its complexation to yield 6 can be accomplished in one-step manner in a self-assembling process (Scheme 1ii). [12] Because this aggregation relies heavily on the reversibility and kinetic lability of the formed tin-A C H T U N G T R E N N U N G (template) À oxygen bonds, the template-based bisphosphine moiety may be considered a supramolecular ligand. The available results show that the assembled ligand entities are sufficiently rigid to display specific bite angles [11] and exhibit interesting features such as hemilabile coordination behavior.…”

“…Figure 5. Correlation between covalent radius of the main group element template and P-Pd-P bite angle in 6-8. the results of DFT calculations [12] that the molecular structure of this species is most likely represented by a macrocyclic complex as shown in Scheme 3, in which the m 2 -bridging oxygen atoms at palladium have been displaced by two newly incorporated solvent molecules. The observed temperature dependence of the equilibrium [6 ' ]/ [6] indicates that the solvent adduct is energetically more favorable than the solvent-free complex but that its formation is disfavored by entropy.…”