New Class of Phosphine Oxide Donor-Based Supramolecular Coordination Complexes from an in Situ Phosphine Oxidation Reaction or Phosphine Oxide Ligands Bhaskaran Shankar, Palani Elumalai, Ramasamy Shanmugam, Virender Singh, Dhanraj T. Masram, and Malaichamy Sathiyendiran* Department of Chemistry, University of Delhi, Delhi 110 007, India * S Supporting Information ABSTRACT: A one-pot, multicomponent, coordination- driven self-assembly approach was used to synthesize the first examples of neutral bridging phosphine oxide donor- based supramolecular coordination complexes. The complexes were self-assembled from a fac-Re(CO) 3 acceptor, an anionic bridging O donor, and a neutral soft phosphine or hard phosphine oxide donor. O ver the past 3 decades, significant research interest has been shown for discrete supramolecular coordination complexes (SCCs) because of their properties and potential applications in sensors, catalysts, flasks, anticancer agents, light harvesters, and nanomaterials. 1,2 The synthesis of SCCs by coordination-driven self-assembly, using predesigned transition- metal-based acceptors and organic donor precursors, is well- established. Because of their high importance in many fields, efforts are being directed toward making complex SCCs and SCCs with functional units and finding a one-pot strategy for multicomponent assembly. As a continuation of the research on the development of rhenium(I)-based SCCs, 2 which exhibit rich photophysical properties and potential applications in many fields, 1b,j-l,2 we envision that substituting the commonly used neutral N donors with phosphine oxide (PO) donors would result in a SCC with different photophysical properties because of the electronic di fferences that exist between these coordinating units. 3 Although bis(PO) ligands have been utilized as bridging ligands between the metal centers in supramolecular architecture including coordination polymers, metal-organic frameworks, and discrete lanthanide-based SCCs, 4-6 rhenium-based SCCs with a bis(PO)-donor building unit are scarce. 7 Herein, we report the first examples of neutral hard PO-donor-bridged neutral and heteroleptic rhenium(I)-based SCCs (1-3). The multicomponent assembly of 1 and 2 was achieved by a combination of the fac-Re(CO) 3 acceptor, anionic O donors, and a neutral ditopic phosphine donor ligand, whereas 3 was assembled from fac-Re(CO) 3 , anionic O donors, and a neutral tetratopic PO donor. This report is also the first example of SCCs constructed via transforming a soft ditopic P donor to a hard ditopic OP donor during the self-assembly process (Scheme 1). In this study, 1,4-bis(diphenylphosphino)butane (P-P), 1,2,4,5-tetrakis(dimethylphosphoryl)benzene (tpbO), chlora- nilic acid (H 2 -CA), and tetrahydroxy-1,4-quinone hydrate (H 4 - thq·xH 2 O) were explored as basic building units. In the synthetic route to 1 and 2, a neutral P donor is used as the starting material, which is transformed into a PO donor through in situ oxidation; the PO group coordinates to the metal via the neutral O-donor atom. This approach is different from the known fac-Re(CO) 3 -directed orthogonal bonding approach, in which the neutral ligand is limited to N donors, which coordinate to the metal without any change in the donor properties. Compounds 1 and 2 were prepared by treating Re 2 (CO) 10 ,P- P, and anionic O donors (H 2 -CA for 1 and H 4 -thq·xH 2 O for 2) in a one-pot procedure (Scheme 2). The products are air- and moisture-stable. Complex 1 is soluble in polar organic solvents, whereas 2 is sparingly soluble. The Fourier transform infrared (FT-IR) spectrum of 1 exhibits strong bands at 2014, 1919, and 1878 cm -1 , characteristic of fac-Re(CO) 3 . 2a The band at 1522 cm -1 indicates the presence of a bis-chelating CA 2- unit in 1.A strong band at 1149 cm -1 was assigned to the ν(PO) Received: May 18, 2013 Published: August 28, 2013 Scheme 1. Neutral Ditopic Donors Scheme 2. Synthesis of 1 and 2 Communication pubs.acs.org/IC © 2013 American Chemical Society 10217 dx.doi.org/10.1021/ic401257w | Inorg. Chem. 2013, 52, 10217-10219