Synthesis and characterization of gold (I) complexes of bis(diphenylphosphino)-acetonitrile.

Abstract

This study comprised the synthesis and characterization of select phosphine ligands and their complexation to gold(I). An initial approach was the reaction between Ph2PCl in "wet" organic solvent and [ClAu(tht)] (tht = tetrahydrothiophene) which led to the complex [ClAu{Ph2P(OH)}], 1, which was the second polymorph of this complex based on solid state Xray crystallographic studies. Related to the Ph2PCl precursor, the study refocused on the preparation of the ligand bis(diphenylphosphino)acetonitrile, (PPh2)2CHCN, ("dppm-CN"), 2, obtained from a modified literature method. Ligand 2 underwent a facile reaction with either [ClAu(tht)] or [(C6F5)Au(tht)] (molar ratio 1:2) to yield new open-ended dinuclear gold(I) complexes [(ClAu)2(dppm-CN)], 3, and [(C6F5Au)2(dppm-CN)], 4, respectively, both in satisfactory yield. Ligand 2 can also be deprotonated to form the anion [(PPh2)2CCN]¯ which reacted with [AuCl(tht)] (molar ratio 1:1) to form the neutral cyclic dinuclear gold(I) complex [Au2{(PPh2)2CCN}2], 5. The anion [(PPh2)2CCN··· showed unexpected reactivity behaviour toward mono- or bis(phosphine) gold(I) chloride complexes that led to the cleavage and formation of new Au-P bonds. Complexes 1, 3, 4, 5 were all subjected to a single crystal X-ray studies. Complex 1 has a central intermolecular Au···Au interaction of 3.0375(2) Å, and peripheral hydrogen bonding (O-H···Cl) within the structure. Complex 3 displays an intramolecular Au···Au interaction of 3.1669(4) Å, but no other intermolecular interactions. The structure of complex 4 reveals a side-by-side "dimer of dimers" structural motif in the solid state and represents a new type of system. Complex 4 contains intramolecular Au· · ·Au interactions alternating between 3.0902(7) Å and 3.0809(6) Å, and an intermolecular Au· · ·Au interaction of 3.592 Å. The next dimeric unit along the virtual 1D chain is more than 6 Å away. Complex 5 has an intramolecular Au···Au separation of 2.8650(4) Å and no intermolecular interactions. The C≡N bond in 5 is 1.160(7)° and is longer relative to the C≡N bond in complexes 3 and 4. The new complexes were further investigated by elemental analyses, mass spectrometry, 1H and 31P solution NMR, and FT-IR. The luminescence properties of the complexes was investigated in the solid state. Results showed 3 to be non- or very weakly emissive at room-temperature, the emission of 4 seems to be quenched by the C6F5 group at room temperature and qualitative results for 5 showed luminescence both at room temperature and at 77K.