Sithole, Sicelo Vincent.
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.
